Evaluation of Wireless Techniques for Short-Range Communication19373/FULLTEXT01.pdf · 2006. 3....

Evaluation of Wireless Techniques for

Short-Range Communication

Master’s thesisperformed in Data Transmission

byJonas Soderkvist

Reg nr: LiTH-ISY-EX-3411-2003

30th September 2003

Evaluation of Wireless Techniques forShort-Range Communication

Master’s thesis

performed in Data Transmission,Dept. of Electrical Engineering

at Linkopings universitet

by Jonas Soderkvist

Reg nr: LiTH-ISY-EX-3411-2003

Supervisor: Kennet AdolfssonSaab Rosemount

Examiner: Associate Professor Lasse AlfredssonLinkopings Universitet

Linkoping, 30th September 2003

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� Engelska/English

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� Licentiatavhandling

� Examensarbete

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� D-uppsats

� Ovrig rapport

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URL for elektronisk version

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Abstract

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Keywords

On radar level gauges currently shipped by Saab Rosemount, someadjustments of the unit’s parameters has to be performed in the field.Presently, this is a cumbersome procedure; the operator has to be veryclose to the gauge and he either has to carry with him a bulky configu-ration unit or use a basic control unit on the gauge. A wireless solution,where a portable device and a receiver replace the control unit, wouldboth allow the operator to work from a distance and eliminate the needfor the bulky device.

The most conspicuous restraint for such a solution is a very low al-lowed power dissipation. The reason for this is that some gauges donot have a separate power supply, but are fed directly off the commu-nication bus. A viable solution should also be commercially availableand robust enough to operate in an industrial environment.

To meet these requirements both a theoretical and a practical assess-ment was conducted, where the two techniques for wireless communi-cation, IrDA, and Bluetooth, was given special consideration. As forthe portable device, the market for hand-held computers was investi-gated and ultimately a PDA from Palm was selected for this project.Together with this PDA, a prototype for each of the two wireless tech-niques was tested to ascertain their performance with respect to powerdissipation, communication range, and communication robustness.

This investigation revealed that Bluetooth could be used over a muchgreater distance than IrDA and it did also provide a more robust so-lution overall. IrDA is nonetheless also a competent technique, andhas its primary advantage in terms of much lower power dissipationcompared to Bluetooth.

Data Transmission,Dept. of Electrical Engineering581 83 Linkoping

30th September 2003

—

LITH-ISY-EX-3411-2003

—

http://www.ep.liu.se/exjobb/isy/2003/3411/

30th September 2003

Evaluation of Wireless Techniques for Short-Range Communication

Utvardering av tradlosa tekniker for kommunikation over korta avstand

Jonas Soderkvist

××

IrDA, infrared, Bluetooth, wireless, short-range, communication, PDA

Abstract

On radar level gauges currently shipped by Saab Rosemount, some ad-justments of the unit’s parameters has to be performed in the field.Presently, this is a cumbersome procedure; the operator has to be veryclose to the gauge and he either has to carry with him a bulky configu-ration unit or use a basic control unit on the gauge. A wireless solution,where a portable device and a receiver replace the control unit, wouldboth allow the operator to work from a distance and eliminate the needfor the bulky device.

The most conspicuous restraint for such a solution is a very lowallowed power dissipation. The reason for this is that some gauges donot have a separate power supply, but are fed directly off the commu-nication bus. A viable solution should also be commercially availableand robust enough to operate in an industrial environment.

To meet these requirements both a theoretical and a practical as-sessment was conducted, where the two techniques for wireless commu-nication, IrDA, and Bluetooth, was given special consideration. As forthe portable device, the market for hand-held computers was investi-gated and ultimately a PDA from Palm was selected for this project.Together with this PDA, a prototype for each of the two wireless tech-niques was tested to ascertain their performance with respect to powerdissipation, communication range, and communication robustness.

This investigation revealed that Bluetooth could be used over amuch greater distance than IrDA and it did also provide a more robustsolution overall. IrDA is nonetheless also a competent technique, andhas its primary advantage in terms of much lower power dissipationcompared to Bluetooth.

Keywords: IrDA, infrared, Bluetooth, wireless, short-range, commu-nication, PDA

v

Preface

The work presented in this thesis was carried out between Februaryand June 2003 and is the culmination of my master’s degree in AppliedPhysics and Electrotechnology.

For this concluding work, my aim was to locate a subject and aproject close to the public. Instead of digging deep into one very spe-cialized and obscure matter, I wanted to work with something recog-nizable to other than my peer students and the academic world. In thetechnical domain, Bluetooth may be one of the best examples of sucha subject, as it is being very much popularized and marketed.

Also IrDA is a well-known technology and wireless techniques ofdata transfer overall are highly interesting, as everything points in thedirection of replacing wiring with its counterpart. Nowadays, mobiledevices are by default equipped with infrared capabilities and Bluetoothproducts are emerging more rapidly than ever. I am therefore verysatisfied with the field of this study.

By this thesis, I am adding the finishing touch to a period of studyat Linkopings Universitet—a period that has been very stimulating andalso very memorable. An especially pleasant memory is my fourth yearwhen I was given the opportunity to study abroad at Monash Universityin Melbourne, Australia.

Acknowledgment

This project was initiated by Saab Rosemount in Linkoping and wasalso conducted on their premises. I would therefore like to use thisopportunity to thank my supervisor Kennet Adolfsson and the rest ofthe staff at Saab Rosemount. I would also like to express thanks to myexaminer Lasse Alfredsson at Linkopings Universitet.

Linkoping, 30th September 2003

Jonas Soderkvist

vii

Abbreviations

List of Acronyms and Abbreviations

4PPM 4-Pulse Position ModulationACL Asynchronous ConnectionlessBER Bit Error RatioCRC Cyclic Redundancy CheckCTP Cordless Telephony ProfileCTS Clear To SendDCF Distributed Coordination FunctionDNP Dial-up Networking ProfileDSR Data Set ReadyDSSS Direct Sequence Spread SpectrumDTR Data Terminal ReadyFMCW Frequency Modulated Continuous WaveFP Fax ProfileFTP File Transfer ProfileGAP Generic Access ProfileGOEP Generic Object Exchange ProfileHART Industrial Communications ProtocolHDLC High Level Data Link ControlHP Headset ProfileIAS Information Access ServiceIEEE Institute of Electrical and Electronic EngineersIP Intercom ProfileIR InfraredIrCOMM IR Serial Data Transfer ProtocolIrDA Infrared Data AssociationIrLAN IR Local Area Network ProtocolIrLAP IR Link Access ProtocolIrLMP IR Link Management ProtocolISM Industrial, Scientific and MedicalL2CAP Logical Link Control and Adaptation ProtocolLAN Local Area Network

ix

LAP Lower Address PartLAP LAN Access ProfileLMP Link Manager ProtocolMAC Medium Access ControlNAP Non-significant Address PartNDM Normal Disconnect ModeNRM Normal Response ModeNRZ Non Return to ZeroOBEX Object Exchange ProtocolOEM Original Equipment ManufacturerOFDM Orthogonal Frequency Division MultiplexingOPP Object Push ProfileOS Operating SystemPAN Private Area NetworkPCF Point Coordination FunctionPCM Pulse Code ModulationPDA Personal Digital AssistantRAM Random Access MemoryRF Radio FrequencyRFCOMM Bluetooth Serial Data Transfer ProtocolRS-232 Standard for Serial TransmissionRTS Request To SendRZI Return to Zero, InvertedSCO Synchronous Connection-OrientedSDAP Service Discovery Application ProfileSDK Software Developer’s KitSDLC Synchronous Data Link ControlSDP Service Discovery ProtocolSNR Signal to Noise RatioSP Synchronization ProfileSPP Serial Port ProfileTFT Thin Film TransistorTiny TP Tiny Transport ProtocolTRL TankRadar LandTRM TankRadar MarineTTP Tiny TPUAP Upper Address PartUART Universal Asynchronous Receiver TransmitterUSB Universal Serial BusWECA Wireless Ethernet Compatibility AllianceWEP Wireless Equivalent PrivacyWi-Fi Wireless FidelityWLAN Wireless Local Area NetworkXOFF Transmitter OffXON Transmitter On

x

Contents

Abstract v

Preface and Acknowledgment vii

Abbreviations ix

1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Saab Rosemount . . . . . . . . . . . . . . . . . . 11.1.2 Radar Technology . . . . . . . . . . . . . . . . . 21.1.3 Radar Level Gauging Units . . . . . . . . . . . . 3

1.2 Problem Description . . . . . . . . . . . . . . . . . . . . 41.3 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4 Document Outline . . . . . . . . . . . . . . . . . . . . . 5

2 Hand-held Computers 72.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Operating Systems . . . . . . . . . . . . . . . . . . . . . 7

2.2.1 Windows CE and Pocket PC . . . . . . . . . . . 82.2.2 Palm OS . . . . . . . . . . . . . . . . . . . . . . 9

2.3 Market Share . . . . . . . . . . . . . . . . . . . . . . . . 10

3 Wireless Techniques 113.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 113.2 IrDA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.3 Bluetooth . . . . . . . . . . . . . . . . . . . . . . . . . . 123.4 Other Wireless Techniques . . . . . . . . . . . . . . . . . 12

3.4.1 Wi-Fi . . . . . . . . . . . . . . . . . . . . . . . . 123.4.2 Magnetic Induction . . . . . . . . . . . . . . . . 13

4 IrDA 154.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 154.2 IrDA Stack . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.2.1 Required IrDA Protocols . . . . . . . . . . . . . 16

xi

4.2.2 Optional Protocols . . . . . . . . . . . . . . . . . 164.2.3 Physical Layer . . . . . . . . . . . . . . . . . . . 174.2.4 Link Access Protocol . . . . . . . . . . . . . . . . 194.2.5 IrLMP & IAS . . . . . . . . . . . . . . . . . . . . 224.2.6 Tiny TP . . . . . . . . . . . . . . . . . . . . . . . 234.2.7 IrCOMM . . . . . . . . . . . . . . . . . . . . . . 23

4.3 Connection Procedure . . . . . . . . . . . . . . . . . . . 23

5 Bluetooth 275.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 275.2 Bluetooth Stack . . . . . . . . . . . . . . . . . . . . . . . 28

5.2.1 Radio . . . . . . . . . . . . . . . . . . . . . . . . 285.2.2 Baseband . . . . . . . . . . . . . . . . . . . . . . 295.2.3 Link Manager Protocol . . . . . . . . . . . . . . 325.2.4 Logical Link Control and Adaptation Protocol . 335.2.5 Service Discovery Protocol . . . . . . . . . . . . 335.2.6 RFCOMM . . . . . . . . . . . . . . . . . . . . . 34

5.3 Connection Procedure . . . . . . . . . . . . . . . . . . . 355.4 Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.4.1 Serial Port Profile . . . . . . . . . . . . . . . . . 37

6 Other Wireless Techniques 416.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 416.2 Wi-Fi . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

6.2.1 Specification . . . . . . . . . . . . . . . . . . . . 426.2.2 Security . . . . . . . . . . . . . . . . . . . . . . . 436.2.3 Power Management . . . . . . . . . . . . . . . . 43

6.3 Magnetic Induction . . . . . . . . . . . . . . . . . . . . . 436.3.1 Effective Range . . . . . . . . . . . . . . . . . . . 446.3.2 Security . . . . . . . . . . . . . . . . . . . . . . . 446.3.3 Interference . . . . . . . . . . . . . . . . . . . . . 44

7 Theoretical Evaluation 457.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 457.2 Infrared vs. Radio . . . . . . . . . . . . . . . . . . . . . 467.3 Special Environment . . . . . . . . . . . . . . . . . . . . 477.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 48

8 Implementation 518.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 518.2 Hand-held Computer . . . . . . . . . . . . . . . . . . . . 51

8.2.1 Palm Tungsten T . . . . . . . . . . . . . . . . . . 538.3 IrDA Hardware . . . . . . . . . . . . . . . . . . . . . . . 53

8.3.1 Agilent HSDL-7000 . . . . . . . . . . . . . . . . . 548.3.2 Everlight TM1001/TR1 . . . . . . . . . . . . . . 55

xii

8.3.3 Microchip MCP2150 . . . . . . . . . . . . . . . . 558.3.4 IrDA Prototype . . . . . . . . . . . . . . . . . . . 56

8.4 Bluetooth Hardware . . . . . . . . . . . . . . . . . . . . 568.4.1 connectBlue OEMSPA13 . . . . . . . . . . . . . 578.4.2 Free2Move F2M03-C2 . . . . . . . . . . . . . . . 578.4.3 Bluetooth Prototype . . . . . . . . . . . . . . . . 59

8.5 Software Implementation . . . . . . . . . . . . . . . . . . 598.5.1 Palm OS Wireless Support . . . . . . . . . . . . 598.5.2 Configuration Utility . . . . . . . . . . . . . . . . 618.5.3 Program Execution . . . . . . . . . . . . . . . . . 628.5.4 Further Development . . . . . . . . . . . . . . . . 66

9 Experiments 699.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 699.2 Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 69

9.2.1 Software . . . . . . . . . . . . . . . . . . . . . . . 709.2.2 Hardware . . . . . . . . . . . . . . . . . . . . . . 70

9.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729.3.1 IrDA . . . . . . . . . . . . . . . . . . . . . . . . . 729.3.2 Bluetooth . . . . . . . . . . . . . . . . . . . . . . 75

10 Conclusion 8110.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 8110.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 8110.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 83

10.3.1 Power Dissipation . . . . . . . . . . . . . . . . . 8310.3.2 Connection Robustness . . . . . . . . . . . . . . 84

10.4 Further Work . . . . . . . . . . . . . . . . . . . . . . . . 84

References 87

A IrDA Prototype Layout 91

B Bluetooth Prototype Layout 93

xiii

Chapter 1

Introduction

This chapter presents Saab Rosemount as a company and puts thismaster’s thesis into context.1 Moreover it defines the purpose of thisreport and gives an outline how the report is organized textually.

1.1 Background

This section is intended to give the reader a background to the workperformed in this thesis.

1.1.1 Saab Rosemount

Saab Rosemount is today a market leader in the area of level measure-ments using radar techniques. About 50 per cent of all new tankersare equipped with a gauge from Saab. Tankers are only one side of themarket though. The high-accuracy tank gauging systems are also usedin both the inventory and process industry. Saab Rosemount operateson the international market and exports account for about 96 per centof the sales.

To maintain its market leadership, Saab Rosemount has focused onresearch and development. A majority of the engineers at the R&Ddepartment holds a Master’s degree or higher. Saab Rosemount hasalso been granted a number of important patents, and a number oftechniques are also licensed to other companies.

In the year 2002 Saab Rosemount had about 370 employees sharedamong a head office in Gothenburg, Sweden and twelve subsidiariesaround the world. The R&D department is split between the cities of

1The first two sections are based on publicly available information from SaabRosemount. For further information—see www.saabrosemount.com.

1

2 Chapter 1. Introduction

Gothenburg and Linkoping; both in Sweden. The head office is locatedin Gothenburg.

1.1.2 Radar Technology

Radio technology came into use at the end of the 19th century and asearly as 1904, a patent was filed for a unit detecting reflected radiowaves from objects. The technology was not much developed in thisstage, so the break-through for radar equipment had to wait a few moreyears. With the Second World War, a lot of research and funding wereput into radar technologies, and in the late forties radar altimeters forsensing the height of an aircraft emerged. At this time, radar equipmentwere bulky units needing kilovolts to operate.

As the semiconductor industry became more developed in the midsixties, smaller units could be built. This was rapidly exploited by thedefense industry, and radar altimeters were, for example, installed onairplanes. Engineers at Saab now also started to think about exploitingthis technology in another area; radar level gauges for liquids tanks.

In comparison with aircraft altitude meters, the far higher accuracyrequirement, the far lower cost target, and especially the mandatoryrequirement of electrical intrinsic safety (i.e. not being able to causeexplosions) constituted a formidable task. An idea came as a spin-offfrom the radar and signal processing used in missiles and in 1973 apatent was filed on a construction fulfilling these requirements. SaabRosemount supplied the first production unit in 1975 and has sincethen been setting the industry standard in the radar gauging field.

In the years to come, the number of installed units would grow ata rate of at least 100 per cent per year. In 1985 two new systemswere launched by Saab, each of them optimized for the two importantmarkets of that time. The TRM-system (TankRadar Marine) was opti-mized for ships, while the other TRL (TankRadar Land), was adaptedfor measurements on oil refineries, with increased accuracy and a num-ber of other features. Figure 1.1 shows a typical setup with a gauge, inthe upper left, fitted on a tank.

Safety has been a major theme in radar development from the verybeginning. One safety issue sometimes asked about, is whether theradar can have any effect on someone entering the tank. Even right infront of the antenna, the power level is about one ten thousandth ofwhat the authorities in most countries consider to be the safe limit forcontinuous exposure. Another comparison can be made with a mobilephone, which has ten thousand times higher microwave power. Onesimple reason for this is that the intrinsically safe feeding only allowstransmission at a very low power.

1.1. Background 3

Figure 1.1: A Radar Level Gauge Unit Fitted on a Tank. Source: SaabRosemount.

1.1.3 Radar Level Gauging Units

A radar unit consists of transmitter, antenna, receiver and an electronicunit responsible for signal processing, power supply and communica-tion (see Figure 1.2). The electronic unit is sometimes equipped with alocal display showing the current measured value. The gauge could alsoperform auxiliary measuring, such as measuring the temperature. Theconstruction of transmitter and receiver are important for the sensitiv-ity of the system, for allowing high accuracy in measurements, and forhaving a low power dissipation. A larger antenna increases sensitivityand lets the antenna pick up faint echoes. However, a smaller antennaincreases the maneuverability and makes the installation easier. A lowenergy consumption is important for allowing use in a hazardous en-vironment (e.g. petroleum products) and for allowing connections tovarious bus systems.

There is a shortage of power in certain environments where radargauges are installed. This scarcity comes from the fact that, occa-sionally, no separate wiring exist for voltage supply—so the gauge hasto draw its current from the communication bus itself. The primarypurpose of the bus is to provide a communication link and not to pro-vide electricity. Hence, the amount of energy available for adding extraequipment is very modest.

Traditionally, short pulses (where the power is spread over a certainbandwidth) are used for measuring the distance with a radar. Thepulses are sent and then echoed back to the gauge by the liquid in thetank. Since the frequency of the echo is related to the distance betweenthe transmitter and the reflecting surface, the received spectrum can bemapped to corresponding tank levels. For a resolution of a few tenths


Figure 1.2: A Radar Level Gauge Unit (Rosemount 5600). Source:Saab Rosemount.

of a meter, 1 ns long low-power pulses are sufficient. Componentsdelivering such pulses are obtainable at a low cost, thus this method isused in a number of radar level gauging systems.

Other constructions utilize a DC-pulse of 1 ns. In this case a wireis often needed to keep the radar beam together. More advanced unitsinstead use a pulse formed by a carrier at, for instance, 5.8 GHz. Low-power pulse systems can have very low power dissipation, but thiscomes at the expense of low sensitivity and low accuracy.

In many cases, the sensitivity of the gauge is the most importantparameter, as it sets the boundaries for under what circumstances mea-surements can be conducted. The most used system is called FMCW(Frequency Modulated Continuous Wave). This technique is based ona linear frequency sweep of a signal having constant amplitude andprovides a high level of both accuracy and sensitivity.

1.2 Problem Description

Regardless of the technology used, some configuration of the gaugeshas to be done in the field, for example setting up device parametersand adjusting for the internal geometry of the tank. This is tradition-ally done with a PC or a specialized configuration unit over a serialconnection, or by using a local control unit.

Presently, this is a cumbersome procedure; the operator has to bevery close to the gauge and he either has to carry with him a bulkyconfiguration unit or use the basic control unit fitted on the gauge. Asa result of the hazardous environment where these sensors reside (i.e.in refineries, crude oil tankers etc.) there is also a need to keep thenumber of cable lead-throughs to a minimum.

A wireless solution, where a portable device replaces the control

1.3. Purpose 5

unit, would both allow the operator to work from a distance and elimi-nate the need for the bulky device. This would also reduce the numberof apertures needed in the gauge housing.

The wireless solution should preferably involve a commercial andalready available tool such as a hand-held computer. Such a devicewould allow more advanced configuration, e.g. downloading and up-grading the software of the gauge. Another possibility would be tocollect data for later processing, or to forward it to someone else us-ing a mobile phone connected to the Palm. This may well be used forremote trouble shooting.

In order to complete the wireless circuit, a receiver also has to bedesigned and built. This receiver should connect easily to the gaugewithout modifications. The most important issue is to keep the energyconsumption on this side as low as possible.

Other issues also exist, such as the robustness of the technique andits operational range. Communication speed is of lesser concern, as theamount of data to be transferred is fairly small. Low computationalpower of a gauge also imposes a limit on the connection speed.

1.3 Purpose

The purpose of this master’s thesis is to investigate what wireless so-lution is feasible for the above stated configuration needs. This inves-tigation will be based on both a theoretic study and a practical testassessment, and a prototype will therefore have to be built. Focus isput on the wireless techniques IrDA and Bluetooth; other techniquesare investigated for comparison reasons only.

1.4 Document Outline

This thesis is divided into three parts:

Chapters 2–7: This part contains a theoretical discussion of exist-ing technologies; both in terms of hardware and in terms of tech-niques for wireless communication. For wireless techniques, mainemphasis is put on IrDA and Bluetooth.

Chapters 8–9: In this part a prototype is constructed for both IrDAand Bluetooth, by using standard components. A software ap-plication is also built, to show how a link is established, and todemonstrate how communication with the gauge is performed.Experiments are also conducted to evaluate each prototype withrespect to communication range, robustness, and power dissipa-tion.


Chapter 10: In the last part, conclusions are presented and dis-cussed, and finally some thoughts on future work are offered.

Chapter 2

Hand-held Computers

This chapter gives an introduction to hand-held computers and oper-ating systems used on these devices. Moreover, market shares of theleading brands are indicated.

2.1 Introduction

PDA stands for Personal Digital Assistant and refers to a small hand-held device. These devices, sometimes called handhelds, are usuallycapable of acting as address books, phone books, calendars and more.[5]

As development progresses PDAs are predicted to be even morecapable. The trend is that handhelds will be interacting and connect-ing increasingly with other devices. The higher-end models are nowshipped with integrated support for both Bluetooth and Wi-Fi, lettingthe user connect to her private network or even Internet, either throughwireless LAN or through a Bluetooth-enabled mobile phone.[5]

A PDA either has a small keyboard or a small pen for the user togive her input. The pen is used by either tapping on a touch sensitivescreen or by writing on a specific area that uses a character recognitionalgorithm to understand what the user wants.

2.2 Operating Systems

Some PDA manufacturers use the Microsoft Windows CE as the op-erating system. Other companies like Palm, have developed their ownOS. Other operating systems exist and are used for handhelds e.g. Epocand Linux, but as their share of the market is limited, these will notbe treated further.

7

8 Chapter 2. Hand-held Computers

Figure 2.1: HP iPaq 5950. Source: Hewlett Packard (www.hp.com).

2.2.1 Windows CE and Pocket PC

Windows CE is developed by Microsoft1 and created for the embeddedmarket: The 32-bit operating system could be found in a variety ofareas; from hand-held PDA’s to cash registers and home entertainmentdevices. Windows CE is meant to be used whenever there is a need foran embedded operating system using little system resources.

There is a fair share of confusion regarding Windows CE and PocketPC and their relation. Windows CE is a set of components that lets amanufacturer to build a custom-made OS of its choice. Consequently,the manufacturer takes a subset of Windows CE and adds some customcomponents and custom device drivers to create her own operatingsystem image. The OS image is then programmed into the read-onlymemory of a microprocessor chipset.

Pocket PC OS is one of those custom built images, targeting thehand-held market. Bundled with applications like Microsoft PocketInternet Explorer, Microsoft Pocket Word, Microsoft Pocket Excel, andMicrosoft Pocket Outlook it is called a Pocket PC.

Along with Dell and Toshiba, Hewlett Packard, Casio Computerand NEC are the major Pocket PC licensees.[23]

Microsoft offers eMbedded Visual Tools2 for free, which includes asoftware development kit for the Pocket PC. It includes all the toolsnecessary to design, compile, link, debug, and install a Pocket PC ap-

1This section is derived from information found on www.microsoft.com, exceptwhen stated otherwise.

2See www.microsoft.com.

2.2. Operating Systems 9

Figure 2.2: Palm Tungsten T. Source: Palm (www.palm.com).

plication.

2.2.2 Palm OS

Palm OS is developed by Palm Inc.3 for their series of hand-held com-puters. This operating system was even from the beginning specificallydesigned for a palm-size device with a fixed display size.

Although the OS uses multitasking, only one task is for applications.This means that only one application can be run at a time. When theuser switches from one application to another, the former is shut down.This limitation improves the performance, because all resources areavailable to the application.

The space needed by the system for any application that is run-ning, is kept in a dynamic and reusable random access memory. Theapplication and its related database are kept in a so called permanentstorage. However, in this case, permanent storage is nothing more thana portion of the RAM, separated from that used as dynamic memory.Some applications are also built-in and shipped with the device.

Palm supports Metrowerks’ CodeWarrior4 as the official softwaredevelopment kit. There is also some non-commercial alternatives likeGCC on the Unix platform. The recently released Palm OS 5 is a 32-bitoperating system running on new hardware.

Major players in the Palm OS camp include Palm, Handspring,Sony, Acer, Kyocera, and Samsung Electronics.[23]

3Information in this section is taken from www.palm.com, except when notedotherwise.

4See www.metrowerks.com.

10 Chapter 2. Hand-held Computers

Company 2002 Shipments 2002 Mar-ket Share(%)

GrowthSince 2001(%)

Palm 4,438,730 36.8 -12.2Hewlett-Packard 1,628,729 13.5 -27.2Sony 1,332,666 11.0 163.2Handspring 698,228 5.8 -49.1Toshiba 450,298 3.7 3,652.5Casio 396,890 3.3 -22.9RIM 272,450 2.3 -30.5Nokia 267,310 2.2 -16.5Hi-Tech Wealth 257,378 2.1 26.7Sharp 226,300 1.9 -14.7Others 2,097,396 17.4 -12.3Total 12,066,375 100.0 -9.1

Table 2.1: Preliminary Worldwide PDA Vendor Unit Shipment Esti-mates for 2002. Note: Does not include smart phones such as Hand-spring Treo 300. Source: Gartner Dataquest (January 2003).

2.3 Market Share

The lion’s share of all PDAs is sold to private consumers. The morelucrative enterprise market only stands for about 30 per cent. Analystsbelieve that the enterprise market is, as of 2003, still another year awayfrom embracing PDAs.[23]

As can be seen in Table 2.1, Palm’s worldwide PDA shipmentsdeclined 12.2 percent in 2002. Nevertheless, Palm keeps its grip on itsnearest competitors by delivering more than twice as many units.[23]

When considering the PDA operating system market, devices shippedwith Palm OS totaled 6.7 million units, compared to 3.1 million Win-dows CE units. Thus, Palm OS equipped devices accounted for 55.2per cent of all PDA shipments, while Windows CE devices had 25.7per cent of the worldwide PDA market.[23]

Chapter 3

Wireless Techniques

This chapter discusses existing wireless techniques and gives a shortintroduction to them. The purpose of this chapter is to provide a basefor the next three chapters going into depth with wireless techniques.

3.1 Introduction

The main purpose of this thesis is to determine the most suitable wire-less technique in this specific application. The technique has to meet alldemands raised because of the environment, where radar level gaugesusually are installed. For that reason, each method will be evaluatedon the basis of power dissipation, effective operating range, and robust-ness.

Most attention is given IrDA and Bluetooth and each will be coveredin-depth in a chapter of its own (Chapter 4 and Chapter 5 respectively).Both these techniques are commercially available and marketed as low-power consumers and provide short-range connectivity. Hence, bothtechniques are potentially practicable in this particular application.

In chapter 6, two other wireless techniques, Wi-Fi, and magneticinduction, are presented and compared with Bluetooth and IrDA.

The present chapter gives a short introduction to each one of thesewireless techniques found in the subsequent three chapters.

3.2 IrDA

IrDA is short for Infrared Data Association and is a standard createdfor transmitting data wirelessly by using infrared light. The key mo-tivation when designing the IrDA standard was to develop a low-costcable replacement technology. In addition, it should consume as littlepower as possible, because an anticipated application was to be used in

11

12 Chapter 3. Wireless Techniques

portable devices. IrDA was for example intended to let a user connecther laptop to a printer.[22]

As IrDA uses an optical link, no obstacles can be placed betweentransmitter and receiver. The infrared receiver could also be affected byother light sources, such as an incandescent light or even the sun. To beable to deliver speeds from 9600 bps up to 4 Mbps, the distance betweencommunicating devices should be no more than 1 meter, according tothe standard.[29]

3.3 Bluetooth

Bluetooth was developed in 1994 by Ericsson who had the same ob-jectives in view as the people behind IrDA. The aim was to create aproduct that would enable users to connect mobile phones with theiraccessories. This product should of course operate without cables andconsume as little energy as possible. Another objective was to reducethe cost of implementing this capability in end-user products.[20]

Bluetooth is a short-range radio, operating in the free 2.4 GHz bandand comes in 13 different “profiles”. Each Bluetooth equipped devicecan support all of them, but most common is that a device only supporta few profiles. A Bluetooth unit does, however, need to support at leastone: the Generic Access Profile (GAP). GAP defines how two Bluetoothunits discover and establish a connection with each other. The SerialPort Profile is another profile, focusing on how Bluetooth can be usedto replace serial cables.[28]

3.4 Other Wireless Techniques

Other wireless techniques were examined to provide more input whencomparing IrDA and Bluetooth. To find comparable techniques themarket of wireless solutions providing short-range communication wereexamined. Two technologies that were found having points in commonwith Bluetooth and IrDA were Wi-Fi and magnetic induction.

3.4.1 Wi-Fi

Wi-Fi, which is a shortened form of Wireless Fidelity, is another tech-nology for wireless connectivity. It is based on the family of 802.11 stan-dards for WLAN, issued by Institute of Electrical and Electronic En-gineers (IEEE). A WLAN is working as a Local Area Network (LAN),with the distinction that it is based on a wireless interface. Thus theneed for cables is eliminated. The Wi-Fi label is issued for productsproduct conforming to this standard.[17]

3.4. Other Wireless Techniques 13

3.4.2 Magnetic Induction

Magnetic induction is also a way of providing short-range communica-tion. Traditionally, magnetic induction been used to power or rechargedevices, such as electronic toothbrushes. With the growing popular-ity of Private Area Networks (PANs) however, a new use has beendiscovered.[6]

A company called Aura Communications has patented a way ofexploiting magnetic induction to transfer data. Many characteristicsare shared with radio systems, but usage of frequency bands and powerlevels differs.[7]

Chapter 4

IrDA

This chapter aims to give a summary of the IrDA standard specificationand to discuss certain aspects of the IrDA protocol in depth.

4.1 Introduction

IrDA is short for Infrared Data Association, an industry-based group ofdevice manufacturers that developed a standard for transmitting datavia infrared light waves. The standard is, according to the association,especially suited for low-cost, short-range and point-to-point commu-nication and is used for providing wireless connectivity for devices thatnormally would use a cable-oriented solution.[27]

Increasingly, computers, cell phones, and other devices come withIrDA ports, which let the user transfer data from one device to anotherwithout using any cables. For example, if both your laptop computerand printer have IrDA ports, you can simply put your computer in frontof the printer and output a document, without needing to connect thetwo devices physically.[5]

IrDA technology is today employed in about 40 million new prod-ucts each year.[29]

IrDA ports support transmission rates of 9600 bps to 4 Mbps, whichare roughly the same as traditional parallel ports. The only restrictionson their use are that the two devices must be close to each other, andthere must be a clear line of sight between them. The standard isdesigned to operate over a distance of 0 to 1 meter at a narrow angle.[27]

4.2 IrDA Stack

The IrDA standard is broken up in several layers, each layer handlinga specific need. All layers have their set of responsibilities, and they all

15

16 Chapter 4. IrDA

IrLMP

IrLAP

Physical

Tiny TP

IrLAN OBEX IrCOMM

IAS

Figure 4.1: IrDA Stack.[22]

supply different capabilities for adjacent levels. These layers on top ofeach other are said to comprise the stack. This stack architecture canbe depicted as in Figure 4.1.[22]

The layers within this stack can be divided into two groups—requiredand optional protocols.

4.2.1 Required IrDA Protocols

The required layers an IrDA protocol stack needs in order to conformto the standard, are shown in shaded boxes in Figure 4.1. The followingare included:[22]

Physical Layer: Specifies optical properties, encoding of data, andframing for different speeds.

IrLAP: Link Access Protocol. Provides the basic reliable connection.

IrLMP: Link Management Protocol. Multiplexes services and appli-cations on top of the LAP connection.

IAS: Information Access Service. Enables services supported by thedevice to be advertised.

4.2.2 Optional Protocols

The optional protocols are displayed in Figure 4.1 as unshaded boxes.The use of the optional layers depends upon the particular application.The optional protocols are:[22]

TinyTP: Tiny Transport Protocol. Adds flow control for each chan-nel.

IrOBEX: Object Exchange Protocol. Enables transfer of files andother data objects.

4.2. IrDA Stack 17

IrCOMM: Serial port emulation. Enables legacy applications thatuse serial and communications to benefit from IR without changes.

IrLAN: Local Area Network access. Enables LAN access for infraredcapable devices, such as notebooks.

4.2.3 Physical Layer

The physical layer is at least partially implemented in the hardwareof the device. This layer is responsible for how the infrared signalsare shaped in the optical transceiver. Another responsibilities includeencoding data bits into light pulses, framing of the data, and cyclicredundancy checks.[22]

The physical layer is also responsible for presenting a common in-terface to the rest of the stack. Because of the ever-changing nature ofthe hardware layer, a so-called framer is used. The framer is responsi-ble for receiving frames and forward them to the Link Access Protocollayer (IrLAP). The framer is also accountable for accepting outgoingframes from the IrLAP layer and send them to the other device. Athird responsibility is to allow and act if the IrLAP layer wishes tochange hardware speeds.[22]

Optical Link

The optical link itself is a point-to-point link, meaning that only twodevices could communicate with each other simultaneously. The opticallink supports link lengths from 0 to at least 1 meter. Furthermore, twopower classes are defined. Devices in the standard power class have tosupport up to 1 meter and devices in the low power class can sufficethemselves with supporting only 20 cm.

An infrared device has to overcome interference from other devices,sunlight, and other interfering light sources. It also has to functionover a certain temperature range. The Bit Error Ratio (BER), or theprobability of a bit error, should be no greater than 10−8. The linkshall operate and meet the BER specification over its full operationalrange.[4]

Modulation Schemes

A simple way of sending data is to use a fixed level for a binary one andanother fixed level for a binary zero. The Non Return to Zero (NRZ)method uses this modulation scheme, where a binary one is representedby a low level, and a binary zero is represented by a high level.

This encoding scheme is, however, not a good option for IR datatransfer, since a continuous string of bits could turn on the IR diode for

18 Chapter 4. IrDA

0 1 0 1 0 0 1 1 0 1

RZI

NRZ

Bit

Period

Data Bits

Start

Bit

Stop

Bit

Figure 4.2: NRZ and RZI Modulation.

00

01

10

11

500 ns

Bit Pattern Signal

Figure 4.3: 4PPM Modulation.

4.2. IrDA Stack 19

an arbitrarily long time. Thus, the powering of the diode would haveto be limited and by that, working distance would be reduced.[22]

For IR transmission, different modulation schemes are used depend-ing on the speed of the link. The Return to Zero Inverted (RZI) mod-ulation scheme (Figure 4.2) is used for data rates up to and including1.152 Mbit/s. In this scheme, a binary zero is transmitted as a lightpulse as long as 3/16 of a bit duration. Binary ones are represented asno light pulse during a bit period.

Only certain data rates are defined in the IrDA standard. Above1.152 Mbit/s, only 4.0 Mbit/s is supported. For this data rate, an-other modulation scheme called 4-Pulse Position Modulation (4PPM)is used. In the 4PPM scheme, two data bits are encoded together andthe position of the pulse is the determinant (Figure 4.3).[4]

In addition to the encoding, data is organized in frames for datarates up to and including 115.2 kbit/s. Each byte is sent asynchronouswith a start bit, 8 data bits, and a stop bit.[4]

4.2.4 Link Access Protocol

The Link Access Protocol (IrLAP) resides directly above the physicallayer in the protocol stack. It is based on the High Level Data LinkControl (HDLC) and the Synchronous Data Link Control (SDLC) pro-tocols, and is responsible for a dependable connection. IrLAP usesthe following methods for providing a reliable data transfer for layersabove:

• Low-level flow control

• Error detection

• Retransmission

This means that higher levels can go on about their business, withouthaving to be concerned with the delivery of data. If the optical pathis obstructed, IrLAP notifies the upper layer, which is responsible forinforming the user, and have her to remedy the problem.[22]

IrLAP was designed with the specific needs of an infrared connectionin mind. To begin with, the connection will always be only one-to-one,and because of the nature of the link, the connection will be half-duplex. To simulate a full-duplex connection, the direction is changedfrequently, giving both devices a possibility to transmit.

Moreover IrLAP has to deal with hidden nodes, where other IRdevices are placed behind the current transmitter. Such units will beblocked, and therefore impossible to detect, until the link is turnedaround. The infrared device also has to overcome interference fromother devices, sunlight, and other interfering light sources. Finally,there is also no collision detection because of the hardware.[22]

20 Chapter 4. IrDA

A transmitting device will turn off its receiver, as to not blind itself,thus making it impossible to know if the other device was transmittingconcurrently. This has to be dealt with in software, by methods suchas random back off. In this scheme, devices stop sending for a randomperiod of time, before trying to retransmit.[22]

Roles

When a connection is set up between IR devices, there is an unequalrelationship. Only one can be a primary station (master) and theothers have to be secondary stations (slaves). Not all devices mustbe able to be primary stations, but only those who are, will be able tocommunicate with secondary devices. It is preferred by the standard,that all devices are able to play both roles.[3]

The two communicating devices have different responsibilities. Atypical primary device could be a computer or a PDA, or a camera,whereas the secondary devices often are printers and devices with theneed to keep a low level of complexity.[22]

The primary device sends command frames (i.e. initiates connec-tions and transfers), is responsible for data flow control and deals withunrecoverable data link errors. The secondary device, on the otherhand, only sends response frames, i.e. responding to the master. Thismaster/slave relationship is only in effect on the IrLAP level. When alink is set up, upper levels in the stack perception of the link is that itconsists of two peer entities.[22]

After the two communicating devices are connected, they take turnstalking. The maximum amount of time a device could be transmittingis 500 ms. After that, the link must be turned around.[22]

This implies that a primary must poll a secondary within 500 msand a secondary must return control within 500 ms. If a primary istalking to two or more secondary stations it is allowed to give eachsecondary 500 ms.[3]

Modes

IrLAP operates in two modes:

1. Normal Disconnect Mode (NDM)

2. Normal Response Mode (NRM)

NDM is used whenever a device is not taking part of a conversation,and NRM is used when a connection is established.[22]

NDM is the default state for a device not engaged in a conversation.In this mode the device has to detect other infrared activity. If no ac-tivity is detected for more than 500 ms, the media is assumed available

4.2. IrDA Stack 21

Address Control Information

8 bits 8 bits 8xM bits

Figure 4.4: IrLAP Frame Structure.

for transmission and link establishment. To reduce user involvement,all communication in NDM uses the following link parameters: 9600bps, 8 data bits, and no parity. During the connection process thebest parameters supported by both devices are negotiated. All of thishappens automatically; therefore making it easier for the end user.[22]

When devices are connected, they are considered to be in NRM.In this state, higher layers in the stack can use normal command andresponse frames to communicate.[22]

Each device knows if it plays the role of the primary or secondarystation. A secondary station in NRM can only transmit on the ex-plicit permission of the primary station. When permission is given,the secondary station can transmit a number of response frames untilit indicates that it has sent its last frame. Following the last framethe secondary station, once again, has to wait for permission from theprimary station to start transmitting.[3]

IrLAP Frame Structure

Messages exchanged by the IrLAP peer layers are sent in a specific for-mat called frames (Figure 4.4). This format carries data and controlinformation from a transmitting station to the receiving station. Theframe is, among other things, needed for determining where the mes-sage begins and stops, to whom the information is intended, and fordetecting errors during transmission.[3]

Every IrLAP frame consists of three parts: address, control, andinformation. The address field contains the address of the secondarystation. If the primary device is transmitting, this field tells the ad-dress of the designated recipient. Conversely, if the secondary deviceis transmitting, the address field indicates from whom the messageoriginates.[3]

The control field defines the function of the frame. If the fieldspecifies that information follows, data is added in the informationfield. This field carries the actual information bits and has to be amultiple of 8 bits.[3] The address and control field only add two bytesoverhead to the information data.[22]

22 Chapter 4. IrDA

IrLAP Frame Wrappers

Apart from the IrLAP frame, some extra information is added to themessage called wrapping. The wrapper precedes and succeeds the Ir-LAP frame, in order to let the frame be transmitted reliably. For datarates up to and including 115.2 kbps asynchronous framing is used. Theframing layer adds a start and a stop flag, and also a Cyclic RedundancyCheck (CRC) sequence for the frame. The CRC is used for detectingerrors in transmission, and it is computed from the Address, Controland Information fields by using the X16 +X12 +X5 +1 polynomial.[3]

Device Address

Each IrDA capable device has a 32-bit device address that uniquelyidentifies the IrLAP layer. This address is randomly generated eachtime the IrLAP layer is initialized. If an address conflict occurs (i.e.another device is already using the specific address) the IrLAP layer willbe requested to change its address. This request will only be honored,if the device is in NDM state. The 0xFFFFFFFF address is used forbroadcasting messages to all devices.[3]

When a device is connected and in NRM state, the IrLAP layerwill use a short 7-bit connection address to uniquely identify secondarydevices. The primary station selects this address randomly from ad-dresses currently not in use, and assigns it to the secondary station.[3]

4.2.5 IrLMP & IAS

To meet the demand from an increasing population of multi-threadedcomputers, the Infrared Link Management Protocol (IrLMP) was de-fined. This protocol provides the means for several applications touse one physical infrared connection by introducing a multiplexingmodel.[29]

Another responsibility for IrLMP is to resolve IrLAP address con-flicts. When two devices are found to have an identical address duringthe discovery phase, IrLMP forces them to generate new addresses.[22]

IrLMP also comes with a look-up service, letting an applicationclaim a port above the multiplexer and advertise its service over theinfrared link.[29]

This look-up service is called the Information Access Service (IAS),and all services available for incoming connections to the device hasto be advertised through this protocol. By using the IAS, it is alsopossible to query for further information about a specific service.[22]

4.3. Connection Procedure 23

4.2.6 Tiny TP

The Tiny Transport Protocol (TTP) was introduced to give indepen-dent flow control per IrLMP connection.[29] This flow control is workingat a higher level compared to the IrLAP flow control. In contrast to thelatter, which works on a connection basis, the former is needed whenthe multiplexing capability of IrLMP is utilized. If IrLAP flow controlis turned on and one multiplexed channel has to halt, all channels arestalled as well. If on the other hand TTP flow control is used, therest of the channels could go on about their business, without beingnegatively affected.[22]

4.2.7 IrCOMM

IrCOMM was developed to provide an infrared cable replacement forexisting products. To fully take on the role as a serial cable, the half-duplex property of the IR medium had to be hidden from the user.IrCOMM is typically used as an serial port driver interacting with apeer IrCOMM entity; thus, providing a way to transfer serial databetween devices.[29]

A serial connection does not only provide data transmission, how-ever. There is also certain control signals that has to be handled tofully implement a virtual serial connection. IrCOMM can be used inboth 3-wire and 9-wire mode. In the first mode, only the data signals(receive and transmit) and the ground signal are implemented. In ad-dition to this, modem control lines are implemented in 9-wire mode.These control lines could for example be used to indicate if a carrier ispresent or if it possible to transmit or not.[29]

4.3 Connection Procedure

When two IrDA compatible devices come into range, they must firstrecognize each other. The basis of this process is that one device hassome task to accomplish, and the other device has a resource neededto accomplish this task. One device is referred to as a primary station,and the other is referred to as a secondary station.[22]

In the IrDA standard, a connection process has been defined toidentify other IrDA compatible devices and establish a communicationlink. There are certain steps that devices need to go through to makethis connection. These steps are shown in Figure 4.5 and describedbelow.

Sniff-Open: The sniff-open procedure is designed for letting a devicebe connectable, but consuming a small amount of energy. In thismode, the device is sleeping most of the time, only to wake up

24 Chapter 4. IrDA

Information

Transfer

Address

Conflict

Resolution

Address

Discovery

Sniff-Open

DisconnectConnect

Reset

Figure 4.5: IrDA Connection Procedure.

periodically, listening for traffic. If traffic is detected, it goes backto sleep. Otherwise, it transmits a response frame, indicating itsdesire to be connected as secondary station. If a reply is givenfrom another device, willing to connect, the discovery process isinitiated. If no reply is sent during a specific amount of time, thedevice goes back into sleep and the process is repeated.

Address Discovery: The main purpose of the discovery procedureis to determine the device address and key attributes of all nearbyIrDA capable devices. The station initiating the discovery pro-cedure broadcasts a discovery command frame. All stations thatare active may then respond with information about itself. Thisinformation is then passed on to upper levels in the stack. If anydiscovered device has the same address as the initiating station oras any other discovered device, the address resolution procedurecan be used to resolve those address conflicts.

Address Conflict Resolution: If two or more stations have cho-sen the same address, they may not be able communicate witheach other. Address conflicts can be detected, either if a stationmakes a connection attempt in an environment were another de-vice already has selected the same address, or when a device hascompleted the address discovery process. When this happens theaddress conflict resolution assists in the process of selecting newaddresses.

Connection Establishment: This procedure involves two stations—one station wanting to connect to a second station. The addressof the second station has to be known beforehand via the addressdiscovery procedure. Establishment of a connection starts witha connection request sent by the first station. Piggy-backed withthis request from the initiating station, are supported communi-cation parameters, such as baud rates and number of data bits.If the receiving device accedes, a negotiation process takes place


where parameters supported by both stations are chosen. Theseparameters are then returned to the initiating station. By that,a link is established for information transfer.

Information Transfer: The information transfer procedure admin-istrates how information is transferred when a link is established.It is specified, what frame types that can be used, and in whatorder.

Reset: The reset procedure dictates how and when an establishedconnection could be reset.

Disconnect: To terminate an established connection gracefully, thedisconnect procedure is used.

Chapter 5

Bluetooth

This chapter illustrates how Bluetooth technology works and summa-rizes certain aspects of the set standard. A short history of Bluetoothis also provided.

5.1 Introduction

Bluetooth was developed in 1994 by the Swedish telecommunicationscompany Ericsson. The technology sprung from an idea to connectmobile phones and their accessories via a low-power and low-cost tech-nology. There was also a need to eliminate cables between such devices(e.g. between a mobile phone and a headset). The result of this investi-gation was a short-range radio link, capable of point-to-multipoint datatransfer. It was named after the Danish Viking king Harald Blatandwho united the Danes under one religion. Bluetooth is also aboutunification—specifically enabling users to connect their products wire-lessly using a global standard.[21]

Bluetooth enables portable electronic devices to connect and com-municate wirelessly via short-range, ad hoc networks. It is a universalradio interface in the 2.4 GHz frequency band that has gained the sup-port of Ericsson, Nokia, IBM, Toshiba, Intel, and many other manufac-turers. In order to function on a worldwide basis, Bluetooth requiresa radio frequency that is license-free and open to any radio. The 2.4GHz ISM band satisfies these requirements, although it must cope withinterference from baby monitors, garage door openers, cordless phonesand microwave ovens, which also are using this frequency.[20]

27

28 Chapter 5. Bluetooth

RFCOMM SDP

Baseband

Radio

LMP

L2CAP

Figure 5.1: Bluetooth Protocol Stack.

5.2 Bluetooth Stack

The Bluetooth standard can be viewed as a number of protocols stackedon each other, known as a protocol stack. This stack can be describedschematically as in Figure 5.1. It should be noted that, for a singleapplication, all layers may not be used, but rather a vertical slice ofthe stack.[24]

The basis of the Bluetooth protocol stack is formed by four coreprotocols.

• Baseband

• Link Manager Protocol (LMP)

• Logical Link Control and Adaptation Protocol (L2CAP)

• Service Discovery Protocol (SDP)

For a Bluetooth device, the core protocols and the radio layer are es-sential, whereas the rest are used when needed. The top-most layersare even re-used existing protocols, incorporated into the Bluetoothspecification, as to not reinvent the wheel.[24]

5.2.1 Radio

Bluetooth operates in the 2.4 GHz ISM band. The ISM (Industrial, Sci-entific and Medical) band is globally available and free to use withouta license, a fact that vouches for a wide acceptance for the technol-ogy. To mitigate the effects of interference and fading Bluetooth usesfrequency hopping. The frequency band is divided into a number ofhop channels by using a spread spectrum coding scheme. During aconnection, instead of staying on one frequency, radio transceivers hopfrom one channel to another 1600 times a second in a pseudo-randomfashion.[21]

5.2. Bluetooth Stack 29

PowerClass

Max OutputPower

Range(Theoreti-cal)

Range(RealWorld)

Class 1 100 mW (20 dBm) 300 m 42 mClass 2 2.5 mW (4 dBm) 50 m 16 mClass 3 1 mW (0 dBm) 30 m 10 m

Table 5.1: Bluetooth Power Classes. Source: Palmsource[15].

According to the specification, Bluetooth has a nominal link rangefrom .1 to 10 meters.[25] However, other sources mention ranges from10 to 40 meters (Table 5.1).[15] This range could be extended up to a100 meters by using more transmission power and/or repeaters.[20]

Due to Bluetooth’s wireless nature, it is possible to connect devicesirrespective of blocking objects. Thus, it is possible to leave the mobilephone in the briefcase, while connecting your PDA through it to theInternet.[21]

Power Classes

Three power classes are defined in the Bluetooth specification. Thepower class defines the outputted power from the radio transmitter,thus governing the effective communication range.

Class 1 devices are typically AC-powered devices such as desktopcomputers, network access points, and printers. Small battery-drivendevices, such as hand-held computers on the other hand, adheres toClass 3.[25]

When two devices are communicating, the unit with the lowestpower class determines the actual communication range. Other pa-rameters, such as the sensitivity of the receivers, the amount of metalin the surroundings, and the amount of interference with other 2.4 Ghzproducts, also determines the real world range.[24]

5.2.2 Baseband

When a physical link is set up between two or more Bluetooth units,they are said to constitute a piconet. In accordance with the Bluetoothspecification, this link is handled by the Baseband protocol togetherwith the Link Manager Protocol (LMP). Another responsibility of thislayer is to provide synchronization of units participating in the piconet.It is imperative that all devices keep the same pace, as Bluetooth relieson a frequency-hopping scheme.[24]

Two types of physical links can be used: Synchronous Connection-Oriented (SCO) and Asynchronous Connectionless (ACL). Both of these


link types can coexist on the same RF link by using multiplexing. ASCO link is utilized for transmitting voice and/or data, while ACLpackets are used for data transmission only. Different levels of errorcorrection can be provided, and it is also possible to encrypt packets.[24]

Piconets

A piconet is a collection of devices connected via Bluetooth technologyin an ad hoc fashion. The piconet comprises the shared communicationchannel, letting the participating devices connect and communicate.When a Bluetooth device is communicating with other devices, all ofthem need to be hop synchronized. In this context, synchronizationmeans that all communicating devices share the same hop sequence.This sharing of hop sequence is the actual definition for units being ina piconet. These piconets are created when needed and will exist for aslong as there are devices left communicating. A piconet is sometimesalso called a PAN (Private Area Network).[20]

Although all Bluetooth devices have identical implementations, apiconet has one master and one or more slaves for the duration ofthe piconet. The master and slave roles are only temporary and arevalid only for the currently formed piconet. Because Bluetooth utilizesfrequency-hopping, piconets can co-exist both in place and time with-out interfering with each other. A device could for example act as amaster in one piconet and a slave in another. When piconets overlapin this way, they are said to form a scatternet.[21]

A master is the coordinator of the piconet, and it has four majorresponsibilities:[20]

• Managing the frequency-hopping sequence used in the piconet.

• Defining when hops should occur.

• Stating the currently used frequency.

• Polling slaves, in order to give them a possibility to transmit.

To form a piconet, there has to be at least one and at the mostseven slaves. More slaves could take part, but only seven can be activeat the same time. The other devices has to be in one of the definedlow-power modes.[21]

Physical Links

Two link types can be established between the master and its slaves:[25]

• Synchronous Connection-Oriented (SCO) link

• Asynchronous Connection-Less (ACL) link


The SCO link is a point-to-point link between a master and a singleslave. The link is symmetric, and the master maintains the link in acircuit-switched manner, by reserving slots at regular intervals. Thistype of link is mainly used for voice connections, and the packets aretherefore never retransmitted. A single device can be connected to upto three units using SCO links.[20]

The ACL link, on the other hand, uses packet-switching, and sup-ports either a point-to-point or a point-to-multipoint link between themaster and all the slaves participating in the piconet. Also, in thismode, both asynchronous and isochronous services are provided.[21]

The asynchronous service is for traditional load-and-store applica-tions where data transfer can be initiated, and the application is inter-rupted, as a given length of data has arrived in a buffer. Conversely,isochronous data transfer ensures that data flows at a pre-set rate, sothat an application can handle it in a timed way.[21]

Because ACL links are on a per-slot basis, a link could be establishedsimultaneously as an SCO link is under-way. Only slots not reservedfor the SCO link are used in that case. In contrast to SCO links, onlyone ACL link can be established at a time. ACL links are typicallyused for sending data, and retransmission schemes are therefore usedto ensure data integrity.[21]

ACL packets not addressed to a specific slave are considered asbroadcast packets and received by every slave. If there is no data tobe sent over the ACL link and no polling is required, no transmissiontakes place.[21]

A maximum bit rate of 723.2 kb/s can be achieved for an ACLconnection. For an SCO link, the maximum rate is 64 kb/s.[28]

Bluetooth Device Address

Every Bluetooth device comes with a single static 48-bit address, whichis globally unique. This address is assigned by a numbering authorityto ensure its uniqueness. The address consist of three parts: lower ad-dress part (LAP), upper address part (UAP), and the non-significantaddress part (NAP). UAP and NAP together make up the organizationunique identifier, which is assigned by the numbering authority to dif-ferent organizations. LAP is distributed internally at the organization’sdiscretion.[20]

Besides uniquely identifying the Bluetooth unit, the device addressalso has other uses. The device address of the master in the piconetis, for example, an input to the pseudo-random algorithm determiningthe frequency hopping sequence.[20]


Power Management

A Bluetooth device offers multiple energy-conserving features. Thebaseband can be in two states: standby and connected. In the standbystate, the device typically only has its internal clock running in a low-power mode. In the connected state there are four modes.[21]

Active: The active mode is used when the device is fully operational.The slaves are always ready for transmission and are always lis-tening for packets from the master. An active slave also regularlyreceives packets from the master, in order to stay synchronized.

Sniff: In sniff mode, the master and slave negotiates a sniff interval.At the beginning of every interval, the slave goes into active mode.If a packet is received, the device stays in active mode; otherwiseit goes back to sleep until next interval.

Hold: The hold mode is entered when there is no need to transmitor receive data for a period of time. The master and slave agreeson a hold time. During this period of time, it is up to the slaveto decide what to do. Typically, the device turns off the radio inorder to save energy, but this mode could also be used if the slavewants to enter discovery mode and detect other devices.

Park: When a slave device enters park mode, it is no longer consid-ered active. In this context, being active means taking part inthe piconet. Because a piconet only supports up to seven slavesat once, this mode can be used to park certain devices, thus mak-ing it possible for other units to join the piconet. A parked slavestays synchronized with the master, though, so it has to listen tothe master periodically to maintain synchronization.

These modes applies for a single Bluetooth connection only—not forthe device as a whole. Park mode is typically the least responsivemode, because the slave needs to rejoin the piconet before it is possibleto take part in the conversation again. Generally the least responsivemode consumes the least energy. How low the power dissipation canbe, is dependent on many factors, such as how long the hold and sniffintervals are, and the amount of traffic in the piconet.[20]

5.2.3 Link Manager Protocol

The Link Manager Protocol (LMP) is used for setting up and control-ling the link on a low level. Hence, a LMP command is trapped at a lowLink Manager level and is not propagated further up in the protocolstack.[25]


Link Manager packets enjoy higher priority than user data, butcould still be affected by retransmissions at baseband level. As theunderlying level provides a reliable link explicit acknowledgement issuperfluous.[25]

LMP is also involved in the authentication and pairing processesbetween communicating devices. This includes generating, exchanging,and checking of link and encryption keys. The size of a basebandpacket is also negotiated via the LMP. Moreover, LMP determines thepower modes of the Bluetooth radio device and a unit’s connectionstate within a piconet.[24]

5.2.4 Logical Link Control and Adaptation Proto-col

The Logical Link Control and Adaptation Protocol (L2CAP) operatesin parallel with the Link Management Protocol. The distinction isthat L2CAP adapts upper layer protocols over the baseband, whereasno data is sent with LMP messages.[24]

L2CAP resides in the data link layer, and provides both connection-oriented and connectionless data services to upper layers in the protocolstack. L2CAP adds multiplexing capability, segmentation and reassem-bly operations, and group abstractions to the other protocols, such asthe Service Discovery Protocol and RFCOMM.[25]

The protocol complexity of L2CAP was adapted to what personalcomputers, PDAs, and other wireless devices could accept. Anotherobjective, when designing L2CAP, was to develop a protocol that wouldachieve a reasonably high bandwidth efficiency.[25]

5.2.5 Service Discovery Protocol

The Service Discovery Protocol (SDP) makes it possible for a Blue-tooth equipped device to advertise what services that are available toother units. A device can query other devices on their device-specificinformation, their services, and the characteristics of those services.This querying is the first step that has to be taken when establishing aconnection between two devices, thus making SDP an integral part ofthe Bluetooth specification.[24]

Communication at the SDP level takes place between an SDP serverand an SDP client. The client is the side that desires to retrieve in-formation about another unit—the server. This information, or servicerecord, is maintained by the SDP server and retrieved by issuing anSDP request from the client side. Each service record contains infor-mation about one service only, but if multiple services are available ona device, SDP acts on behalf of them all. Thus, only one SDP server


is needed for a single device. If a device is only intended to serve as aBluetooth client, it could even manage without an SDP server.[25]

SDP is only intended for service discovery—not for providing amechanism for using discovered services. If an application that hasdiscovered a service through SDP aspires to utilize the service, anotherseparate connection has to be opened.[25]

5.2.6 RFCOMM

The RFCOMM protocol provides serial line emulation over the L2CAPProtocol. As RFCOMM replaces serial cables, it supports full emula-tion of both RS-232 control signals and data signals (data transmit anddata receive). This means that even the state of the non-data signalssuch as carrier detect (CD), request to send (RTS), and clear to send(CTS) is transferred.[20]

Generally, serial cables are used for connecting a peripheral de-vice to a computer, but sometimes the need to connect two computersarises—this is when a null modem is employed. Null modem emulationcapability is also part of the RFCOMM specification, which makes itpossible to connect two primary devices, such as computers, to eachother directly.[25]

Although a serial connection is emulated, the transport level is usingpacket data structures. The actual emulation is done in a level above—at the RFCOMM layer. RF indicates that it is a wireless technology,and a COM port is a name often used for a serial interface on a PC.[20]

RFCOMM looks very much as a real COM port, complete with RS-232 control signaling, and it supports data rates up to 128 kbps.[21]

A peculiarity with Bluetooth is that if the baud rate is set, forthe serial link RFCOMM acts as a substitute for, the actual packettransfer speed is not affected. This means that the data packets maybe delivered much faster than the set baud rate.[25]

RS-232 Signaling

Because of the wide use of the RS-232 standard for serial interfaces,Bluetooth has to conform to the control signaling prescribed by thisstandard. Typically, a serial cable is composed of nine wires, althoughall of them are not necessarily used. These wires are used for flowcontrol, synchronizing the two devices, and of course for sending andreceiving data.[20]

Being a wireless solution, Bluetooth obviously lacks these wires.But in order to fully implement a virtual serial interface, all of thesewires have to be emulated. The data channel is of course used for dataexchange, but the other signals also need a replacement. Bluetooth usesthe following solution: instead of monitoring and setting signal levels,


a control channel is opened. On this channel, commands are exchangedand thus communicating the state of the serial connection.[20]

In an ordinary serial connection, flow control can be implementedin two ways. It can be done through software by using special char-acters as Transmitter On/Transmitter Off (XON/XOFF) or throughhardware. The hardware method uses signals such as Data TerminalReady/Data Set Ready (DTR/DSR) or Request to Send/Clear to Send(RTS/CTS). Emulating hardware signals such as these makes it pos-sible for RFCOMM to act as a real serial port as far as its users areconcerned.[21]

Some signals are not merely used to convey information in itself.The baud rate is, for instance, conveyed over the connection by lettingthe signal wire pulse at a specified frequency. For Bluetooth, this isnot an option. RFCOMM relies on the underlying transport protocol,which uses packets. So, it is those packets’ type and structure thatdetermines the baud rate—not the data rate. The actual data rate isspecified by the baseband and could therefore be higher than the baudrate set by the user.[20]

5.3 Connection Procedure

Before a specific link can be established between two Bluetooth devices,they must first detect and synchronize with one another. This proce-dure is performed transparent to the user—no involvement is requiredin the set-up process.[28]

A Bluetooth device could be in a number of different states.[25]

• Standby

• Inquiry/Inquiry Scan

• Page/Page Scan

• Connected

When a master wants to set up a piconet by connecting to a slave,there are certain steps that need to be completed. If a device is notassociated with any piconet, it is in the standby operational mode.[20]

To move to the connected state, the master has to find a potentialslave to connect to. This is done by entering the inquiry state, wherethe master tries to discover other devices in the vicinity. In order fora slave to be able to respond to an inquiry, it has to be in the inquiryscan state, i.e. listening for inquiries.[20]

When a slave is discovered, the master could try to invite it to thepiconet by paging the slave explicitly. To receive this invitation, the


slave has to be in the page scan state. If the slave gives its consent,both devices are then moved to the connected state.[20]

Before the two devices can begin to actually transfer data, vital in-formation has to be shared. This includes the device address and clockof the paging device, both of which that are used to establish the fre-quency hop sequence for the newly created piconet. At the completionof this process, information can be exchanged.[28]

5.4 Profiles

There are 13 “profiles” described in version 1.1 of the Bluetooth speci-fication. These profiles are general behaviors through which units com-municate with each other. The profiles defined so far are also meant toprovide the foundation for future profiles.[26]

Generic Access Profile (GAP): GAP defines how two Bluetoothunits discover and establish a connection to each other. Thisprofile defines generic operations and can be used as a basis forother profiles. Thus, support for GAP is mandatory and ensuresbasic interoperability between Bluetooth devices, regardless ofmanufacturer.

Service Discovery Application Profile(SDAP): SDAP defines thediscovery of services available to a Bluetooth unit. This profileis based on the GAP and involves an application, the ServiceDiscovery User Application. This application interfaces the Ser-vice Discovery Protocol and provides the end-user with a tool tosearch for specific services, as well as a general service search.

Cordless Telephony Profile (CTP): CTP defines how a Bluetoothdevice can be used as wireless phone. This profile also dictateshow a Bluetooth equipped cellular phone should switch to wire-less phone mode, when it is placed in reach of a Bluetooth basestation.

Intercom Profile (IP): IP is related to the CTP and defines howtwo Bluetooth enabled cellular phones can connect directly toeach other without using the public telephone network. A usagescenario for this profile is within an office.

Serial Port Profile (SPP): SPP is based on GAP and provides away of replacing serial cables, by emulating RS-232 signalling andproviding virtual serial ports. SPP defines how these virtual portsare set up on two Bluetooth devices and how they are connected.

5.4. Profiles 37

Headset Profile (HS): HS is dependent of SPP and defines how aBluetooth-equipped headset should connect and communicate tocellular phones or computers.

Dial-up Networking Profile (DNP): DNP is dependent on SPPand defines how a Bluetooth-equipped device could link to a mo-dem connection. This enables a laptop to use a dial-up connectionthrough a Bluetooth enabled cellular phone.

Fax Profile (FP): FP is similar to DNP, except that is provides ac-cess to a fax instead of a modem.

LAN Access Profile (LAP): LAP is also similar to DNP, exceptthat it defines interconnections between Bluetooth-equipped de-vices and local area networks (LANs). The Bluetooth base stationis in this scenario, connected to the LAN and uses the Point-to-Point protocol for data transmission.

Generic Object Exchange Profile (GOEP): GOEP is built uponSPP and defines the set of protocols and procedures to be used byapplications handling object exchanges. Applications using thisprofile assume that a link between the Bluetooth units already isestablished.

Object Push Profile (OPP): OPP is used in conjunction with GOEPto transfer and receive small objects. This could, for example, in-clude electronic business cards.

File Transfer Profile (FTP): FTP is also used in conjunction withGOEP to transfer files between two Bluetooth devices.

Synchronization Profile (SP): SP is another profile used in con-junction with GOEP. This profile enables synchronization of in-formation such as calendar notations between Bluetooth devices.

5.4.1 Serial Port Profile

As the Serial Port Profile is the most interesting profile from thisproject’s point of view, this profile will be covered in greater detail.

Many devices uses a serial interface to send and receive data (e.g.notebook computers, digital cameras, PDAs). As Bluetooth aims toreplace cables, implementing a serial interface over Bluetooth was anatural thing. Because of this need, the serial port profile (SPP) wascreated.[20]

The SPP is built upon the Generic Access Profile and emulates aserial cable connection. The virtual serial port lets any legacy applica-tion run on the device without being aware of the underlying Bluetoothtechnology.[21]


The SPP supports only a point-to-point connection between twodevices, although it is possible to have multiple instances of the profilerunning simultaneously. Furthermore, there are no fixed master/slaveroles in this profile, as both devices are assumed to be peers.[21]

Supporting security features as authorization, authentication, andencryption is not mandatory, but they have to be supported on thepeer unit’s request.[20]

To be able to reach all services and applications accessible throughRFCOMM, an SDP service record is required. This record is part ofthe Service Database that includes parameters needed to connect toa certain service or application. A helper application is provided toassist the user in setting up the virtual port and to register a device’sservices.[21]

SPP Connection Process

When two Bluetooth-equipped devices are connecting to each otherusing the RFCOMM, it involves both an initiator and an acceptor.The initiator initiates the forming of a connection, and the acceptor isthe recipient of the connection request.[21]

The procedure followed when setting up a virtual serial connectioncomprises the following steps.[20]

1. The initiator queries the remote device, by using the Service Dis-covery Protocol (SDP), to determine the RFCOMM server chan-nel number. The Service Class ID associated with the RFCOMMservice is used to retrieve this information.

2. As an optional step, the device may have to authenticate itself.As another optional step, encryption could be negotiated andturned on if requested.

3. The initiator requests a new L2CAP channel to the remote RF-COMM entity.

4. The RFCOMM session is initiated on the L2CAP channel.

5. The initiator can now start a new data-link connection on theRFCOMM session, using the server channel number from thefirst step.

From the acceptor’s point of view there are also certain steps thatare needed to be performed.

1. Provide authentication if requested, and upon further request,turn on encryption.

2. Accept a new channel establishment indication from L2CAP.

5.4. Profiles 39

3. Accept an RFCOMM session establishment on that channel.

4. Accept a new data-link connection on the RFCOMM session.

The last step may trigger a local request to authenticate and turnon encryption for the link, if this level of security is required by theuser. On the completion of the connection process, a serial connectionis enabled and ready to be used by applications on both devices. Step3 and 4 are superfluous if a connection is already active. In that case,the connection is created on the existing RFCOMM session.[20]

Chapter 6

Other WirelessTechniques

This chapter presents two additional wireless techniques comparable toIrDA and Bluetooth: Wi-Fi and magnetic induction.

6.1 Introduction

A number of wireless techniques exist—all with a common goal of de-livering wireless connectivity. However, not all of these technologieshave reached a mature state and could be viewed as standards. Inter-operability has been a grave issue, but as more standardization organsare formed, the picture gets clearer and the end user will have an easiertask.

This is especially true with the IEEE 802.11 standards, which Wire-less Ethernet Compatibility Alliance (WECA) has started a certifica-tion programme for. To ensure interoperability between devices of dif-ferent manufacturers, tests are performed. If a device passes the test,a Wi-Fi (Wireless Fidelity) certification is issued.[11]

HomeRF is another standard that, like the 802.11 standard, usesradio waves to transfer data and voice. HomeRF is developed for thehome market by the International Telecommunication Union to providean inexpensive alternative for voice and data communication. Version1.0 of the standard supports speeds up to 1 Mbps and can communicateover a range of 50 meters.[11]

There also exist more proprietary technologies, of which magneticinduction is one. This technique of transferring data wirelessly uses amagnetic field and induction instead of a radio waves.

As magnetic induction is an interesting concept this will be furtherexamined. HomeRF is also a potential candidate for further treatment,

41

42 Chapter 6. Other Wireless Techniques

but as many characteristics are shared with the IEEE 802.11 standardsand these are more well-spread, this report will suffice itself with onlyinvestigating IEEE 802.11 further.

This is but a small selection of available techniques, but as the mainfocus is put on Bluetooth and IrDA, only Wi-Fi and magnetic inductionare examined, and only for comparison purposes.

6.2 Wi-Fi

Wireless Fidelity (Wi-Fi) is a term used for techniques that, like Blue-tooth, also use radio waves to transmit data over the air. Wi-Fi isnot a standard in itself, but rather a certification programme for IEEE802.11-based technologies. This includes IEEE 802.11a, 802.11b, orproducts that contain both these technologies.[11]

Both 802.11a and 802.11b are developed by the Institute of Electri-cal and Electronic Engineers as standards for wireless local area net-works (WLANs). WLANs typically covers distances of 10 to a fewhundred meters with a speed of 11 Mbps or more, depending on thestandard. 802.11a uses the 5 GHz frequency range, whereas 802.11bshares the 2.4 GHz band with Bluetooth.[11]

A typical wireless LAN (or Wi-Fi) configuration consists of an accesspoint which acts like a bridge to the wired network at a company.The access points are transceivers that relay information between thewireless and the wired network. Multiple users can share one of theseaccess points.[11]

Using air as transmission medium means that data transmitted iseasily eavesdropped on. To prevent that, a technique called wiredequivalent privacy was developed, giving the WLAN the same privacyas a wired LAN.[13]

As the standard is intended to be used over a distance up to 100meters, the energy consumption is high. In order to let mobile usersbenefit from the technology, power saving techniques are used.[13]

6.2.1 Specification

In the IEEE 802.11 definition, a single Medium Access Control (MAC)layer is specified together with several physical layers. The MAC layeris responsible for the sharing of the air medium and the physical layersare concerned with different ways of sending data.

Medium Access Control Layer

The MAC layer can take two forms: Distributed Coordination Function(DCF) and Point Coordination Function (PCF). The DCF is manda-tory for designers of an IEEE 802.11 compliant device to implement.

6.3. Magnetic Induction 43

The DCF only supports asynchronous connections and is therefore notsuitable for real-time applications, such as streaming video. The PCF,in contrast, supports synchronous communication. However, it doesnot enjoy the mandatory status as DCF.[1]

Physical Layers

Originally, two forms of spread spectrum modulation were used in the802.11 standard. These were both using the 2.4 GHz band and operat-ing at speeds up to 2 Mbps. Later, two more physical layers were addedto the standard: 802.11a and 802.11b. The former used an OrthogonalFrequency Division Multiplexing (OFDM) and had moved up to the5.8 GHz frequency band, allowing for data rates up to 54 Mbps. Thelatter was more of an extension to the original standard with additionaldata rates of 5.5 and 11 Mbps. It also kept the 2.4 GHz frequency bandand used Direct Sequence Spread Spectrum (DSSS) modulation.[1]

6.2.2 Security

The IEEE 802.11 standards use an optional security scheme known asWireless Equivalent Privacy (WEP). WEP is designed to provide thesame level of security as with a wired LAN. Because 802.11 operatesover the air, it is inherently less secure than a wired network and moresusceptible to tampering. The WEP seeks to provide security by offer-ing encryption of frames sent between source and destination. Only thepayload of the MAC layer frames is encrypted, which means that theframe headers are left with no encryption. Due to the fact that WEPis implemented in the MAC layer and not in the application level, noprotection is given against man-in-the-middle attacks.[11]

6.2.3 Power Management

Power management is employed by the 802.11 standards, for extendingthe life of mobile devices equipped with a WLAN interface. In orderto save batteries, it is possible to switch into a standby-mode when thedevice is not actively transmitting. The radio is put to sleep after agiven time, and only awakens periodically to check if another devicewants to connect.[13]

6.3 Magnetic Induction

Magnetic induction provides an alternative for short-range communi-cation. This technology has been used for many years in other applica-tions, but not so much in data and voice communication. This mostlyhas to do with the limited range this technique can operate over. With

44 Chapter 6. Other Wireless Techniques

the emerging of private-area networks, this can however appear to itsadvantage.[6]

Magnetic communication shares some of the properties of RF com-munication systems. Both systems establish a wireless link, but usageof frequency bands and power levels separates the two. Instead of rely-ing on a plane wave propagating in free space, the magnetic system setsup a quasi-static magnetic field around the transmitting coil. When thereceiving coil is introduced in the magnetic field, a modulated currentis induced in that antenna. This current can be processed and decodedinto to data or sound, at the user’s discretion.[7]

6.3.1 Effective Range

Because the electric field component is small, the signal will not prop-agate far. As for the magnetic field component, the effective radius isdictated by the diminishing field strength which drops off at a 1/R3,which means that the power dissipation is proportional to 1/R6 (Rbeing the radius). This results in an effective range of 0–3 meters formagnetic systems. In contrast to RF systems, magnetic systems arelimited to the orthogonal properties of the magnetic field. Thus, bothreceiving and transmitting coil has to be aligned in the same plane anddirection to benefit from maximum field strength. This can be reme-died by employing an antenna with three coils, each orthogonal to eachother.[7]

6.3.2 Security

As magnetic system operates over only a few meters, security is not ascritical as with wireless solutions that cover a larger range. In order tobe able to eavesdrop on a user communicating over a magnetic inductivelink, the perpetrator has to come very close to the victim. Even so, thesame security techniques as used in RF systems could also be added toa magnetic system.[7]

6.3.3 Interference

With the use of magnetic induction, interference is a much lesser prob-lem than with RF systems. A radio system is subject to both interfer-ence from intentionally and unintentionally transmitting devices. Theunderlying problem is that radio devices often has to coexist with otherwireless technologies and therefore share the same spectrum.

Magnetic induction on the other hand, does not have to use a car-rier frequency picked from an overcrowded band. The close-proximityproperty would also alleviate the problem of interference among likedevices.[7]

Chapter 7

Theoretical Evaluation

This chapter aims to discuss the wireless techniques covered in the lastthree chapters and to compare them and reveal their advantages anddisadvantages.

7.1 Introduction

One of the primary objectives in this project was that commercial prod-ucts should be taken advantage of as much as possible. This boundarycondition implies, among other things, that a highly standardised tech-nology were to be used or at least be ranked higher than solutions notbacked by a standard.

In the light of this, IrDA, Bluetooth and Wi-Fi take the lead becauseeach of them is supported by a standard and a certification programme.Magnetic induction on the other hand is a propriety technology of onesingle company and therefore short of such a support.

On regards of power dissipation, the other limitation, the tables areturned. Magnetic induction seems to be the best choice of the groupof four in this respect. As Wi-Fi targets longer distance and higher bitrate connections, it also consumes more energy. For example, typicalWi-Fi CompactFlash and PC Cards use 110–140 mA during idle modeand 200–300 mA during transmission, which is twice the power used byBluetooth cards.[17] IrDA looks even more promising than Bluetoothin this respect, but both of these technologies target close-range low-power communication.

The main drawback with a magnetic induction system is that it isonly applicable where only short-range communication is needed. An-other negative aspect is that the antenna construction, with its threeorthogonal antennas, impedes small packaging. High data rate appli-cations are better off with 802.11 or Bluetooth.[17]

45

46 Chapter 7. Theoretical Evaluation

Wi-Fi is also an infelicitous technique in that sense that an accesspoint is needed. As mobile devices, such as a PDA, normally only arebeing able to act as clients, this would imply that the access point hasto be connected to the gauge itself. Such a solution would probably beovershooting the mark.

As a result of this, both magnetic induction and Wi-Fi will notbe further examined. It should, however, be noted that each of thesetechnologies has its pros and cons. Hence, one of the technologiesruled out might very well outperform IrDA or Bluetooth in anotherapplication with other objectives.

Implementing IrDA in consumer products is simple, and a completesolution may cost ten times less than a Bluetooth. Future Bluetoothdevices are targeted, though, for around $5, a number that would fa-cilitate the advance of the technology.[27]

Another important aspect for this project is how well a Bluetooth orIrDA device would operate in an industrial environment. As the targetplatform is a radar gauge typically located in a hazardous environment,this is also an important factor to consider.

Bluetooth and IrDA can also be seen as two representatives fordifferent transmission media. The next section will therefore discussinfrared and radio transmission in more general terms.

7.2 Infrared vs. Radio

For short-distance wireless communication, infrared technology offerssome advantages over radio technology. By the close relationship withvisible light, infrared light shares some of its properties. Infrared com-munication does, for example, enjoy the fact that the signal will notpass opaque objects, thus both making eavesdropping harder and re-ducing interference. This simplifies the design of infrared links, as itdoes not require transmissions in different rooms to be taken into ac-count. Also, direct infrared links are not as susceptible to multi-pathfading as radio links, because of the short carrier wavelength. Radiolinks, on the contrary, has the handle different magnitudes and phaseshifts in the received signal.[16]

There is, however, also certain drawbacks involved when using lightinstead of radio. For one thing, light beams need an unobstructedpath from sender to receiver. Infrared links are also subject of inducednoise from ambient light arising from sunlight, incandescent lighting,and fluorescent lighting. Because the signal to noise ratio (SNR) isproportional to the square of the received optical power, this can bedetrimental for infrared links. This necessitates the use of relativelyhigh transmission effect and communication over relatively short dis-tances. Even though it is fairly easy to increase output effect, energy

7.3. Special Environment 47

Property ofMedium

Radio Infrared Implication forIR

Bandwidth Regulated? Yes No Approval not re-quired. Worldwidecompatibility.

Passes Through Walls? Yes No Less coverage.More easily se-cured. Independentlinks in differentrooms.

Multipath Fading? Yes No Simple link design.Multipath Distorsion? Yes YesPath Loss High HighDominant Noise Other

UsersBackgroundLight

Limited range.

Input X(t) Represents Amplitude Power Difficult to operateoutdoors.

SNR Proportional to∫|X(t)|2dt

∫|X(t)|2dt High transmitter

power requirement.Average Power Pro-portional to

∫|X(t)|2dt

∫X(t)dt Choose waveform

X(t) with highpeak-to-averageratio.

Table 7.1: Comparison between Radio and Infrared Systems. Source:Kahn, Wireless Infrared Communications.

consumption and concerns for eye safety can impose a limit for howmuch it can be increased.[16]

Some of the properties of IR and radio are compared in Table 7.1.

7.3 Special Environment

Electrical equipment have to operate in hazardous atmospheres in cer-tain industries. An hazardous atmosphere means that it exists a risk ofexplosion on the premises due to gas mixtures or other flammable com-binations. In such an environment, precaution has to be taken againstthis risk and sources of ignition, such as sparks or static electricity,have to be eliminated. Electrical equipment specifically, has to be pro-tected against over-currents, internal short circuits, and other electricalfaults.[8]

Protection can be obtained in a variety of ways. Two accepted ap-proaches are either to insert the apparatus in a flameproof enclosure,or by designing the equipment as to be intrinsically safe. In an intrinsi-

48 Chapter 7. Theoretical Evaluation

cally safe product, electrical energy is limited such that any generatedspark would be insufficient to ignite the atmosphere.[18]

An electrical device has to pass a test in order to be permitted tooperate in certain environments. A product that has passed the testis rewarded with a classification marking. This marking follows thepattern class, division and group. The class denotes the category ofthe atmosphere, and the group specifies it more closely. Class 1 would,for example, indicate gas, and group A would be the most explosivegases. The process plant itself is divided geographically into divisionsaccording to the likelihood of a potentially explosive atmosphere beingpresent. A division 2 classification would reveal that the device couldonly be used in an area in which explosive gas mixtures are not likelyto be present during normal circumstances.[18]

7.4 Discussion

Both IrDA and Bluetooth are designed for short-range, low-power com-munications. Infrared light and radio are nevertheless two transmis-sion media having different characteristics. Each has its qualities, andhence, one technique could not be proclaimed superior to the other.

It depends on the application, which one of the two technologiesthat is preferred. Radio provides most mobility and transmission range.Infrared, on the other hand, excels when cost has to be minimized andthe amount of signal processing in the receiver has to be kept to aminimum.

Both techniques can be used as an replacement for a serial cable,though—a property that would simplify the development process ofthis work. The reason for this is that communication currently takesplace over a serial interface, and it would therefore be advantageous toutilize this access point directly.

There is also other ways of transmitting information using light ascarrier. Ordinary remote controls would be one example. Differentvendors seem to have different protocols, however. Also, the availableprotocols are not as advanced as IrDA with, for example, handshakingand retransmission schemes.

Some PDAs do have the opportunity to access the IR hardwaredirectly (raw IR) and hence let the programmer take control and useany protocol. This method is, for example, used for having a PDA tosimulate a remote control. This is not officially supported though, andtests show that the Palm Tungsten does not allow raw IR. All of thismakes this solution impracticable.

Concerning the requirements of hazardous environments, it is un-certain whereas equipping a unit with IrDA or Bluetooth capabilitieswill affect its property of intrinsic safety. As both techniques consume

7.4. Discussion 49

little power and hence does not produce strong currents, it is, however,plausible that these requirements will not be impeding.

Chapter 8

Implementation

This chapter details the process of developing prototypes and equippinga gauge with a wireless access point. It also gives details about whycertain hardware was selected and used in this project.

8.1 Introduction

Two hardware prototypes were built for evaluation purposes; one unitthat uses IrDA and one unit that uses Bluetooth technology. A softwareapplication was also developed for the PDA, to conclude if any of thesetwo technologies would actually work in an existent gauging system.In other words, the focus of this chapter lies on the construction of amodule that would let a user connect to and communicate with a radarlevel gauge by using a hand-held computer.

This module would connect to the gauge and replace the local con-trol unit with a wireless access point. This control unit is connectedto the processor via a serial interface. Thus, the prototype must alsooperate over such an interface.

Another purpose of this chapter is to elucidate why certain hard-ware was chosen for further treatment, and why other hardware wasconsidered as not as good.

8.2 Hand-held Computer

When choosing the hand-held device, it essentially boils down into mak-ing a choice between a Palm OS powered device and a Pocket PC. Thisis clear when studying Table 2.1 in Chapter 2. As can be seen, thereare in essence only two major players on the market.

To decide on which platform to go with, some criteria were set. Thedevice should be: a commercially available product, be equipped with

51

52 Chapter 8. Implementation

General Dimensions (Heightx Width x Depthcm)

10.1 / 12.1 x 7.5 x1.5

Weight 158 gTouch-sensitivescreen

Yes, Stylus pro-vided

Processor, memoryand operating sys-tem

Processor 144 MHz TexasInstrument OMAP1510

RAM (Mb) 16Original OperatingSystem

Palm OS 5.0

Upgradeable OS YesConnectivity Physical:

Serial cable/cradle Accessory/NoUSB cable/cradle Yes/YesWireless:Bluetooth/802.11b Yes/NoInfrared Yes, IrDA

Screen Resolution (Pixels) 320 x 320 pixelsColor or Mono-chrome

Color, 16-bit reflec-tive TFT

Table 8.1: Palm Tungsten T Characteristics. Source: Palm Inc.

both IrDA and Bluetooth, and be available in an intrinsically safe ver-sion. The first criterion was stated in the assignment, whereas supportfor both IrDA and Bluetooth was a consequence of the former choiceof what wireless techniques to further pursue. Because both IrDA andBluetooth were to be tested, a device capable of communicating us-ing both techniques would facilitate the implementation and testingprocess.

The last demand is due to the environment were this product ismeant to operate. As gauges often are installed where petroleum prod-ucts are present, safety measurements are called for. Intrinsic safety isa protection concept employed in potentially explosive environments.A product being intrinsically safe is designed in a way that it is un-able to produce sufficient energy for igniting a flammable gas, eitherelectrically or thermally.

As mentioned above both devices using Palm OS and Pocket PC’sare widely offered on the market, so the first demand is met readily.Some newer devices of each camp also boast built-in support for both

8.3. IrDA Hardware 53

Bluetooth and IrDA.1 Intrinsically safe industrial PDAs, also, do existon the market, but these are of an older generation supporting onlyIrDA. Both Palm OS devices and Pocket PCs can be found.2

One last point when deciding on what PDA to use was the availablesoftware development tools. Also, in this aspect, both platforms are ona par. Microsoft offers a free development suit for Pocket PC. Palm,on the contrary, does not give away such a tool, but instead workclosely with Metrowerks and their product Codewarrior. Codewarrioris a commercial product, but an evaluation version can be downloadedfrom their internet site. What tipped the balance to Palm’s favour wastheir release of a Bluetooth SDK, delivering an easy interface for theprogrammer to work with Bluetooth and some sample applications.

Ultimately, a Palm Tungsten T (see Table 8.1 for key features) waschosen for this project. It should, however, be noted that choosingone platform is not a strong restriction. Some development tools evenexist were source code could be compiled for both platforms, at theprogrammer’s discretion.

8.2.1 Palm Tungsten T

The Palm Tungsten T is one of the newest hand-held computers fromPalm Inc. and comes with a built-in support for both Bluetooth andIrDA. Among the Bluetooth profiles supported are the Generic AccessProfile and the Serial Port Profile.[14]

Currently, all Bluetooth hardware for Palm OS devices belong toClass 3. Expected communication range is therefore about 10 meters,between two devices. This range is, however, affected by the surround-ings and the amount of interfering traffic in the 2.4 GHz frequencyband.[15]

According to the specification, the Palm Tungsten T is cleared tooperate in some hazardous locations. It is classed as a Class 1, Div 2,Group A,B,C,D device, which means that it can be brought to locationswhere there is a low probability of ignitable gas being present.

8.3 IrDA Hardware

IrDA support can be found in a variety of products, such as notebooks,PDAs, digital cameras, and so forth. Some companies3 also manufac-ture dongles and adapters to add IrDA capability to products alreadyon the market.

1For example HP iPaq 5950 (Pocket PC) and Palm Tungsten T (Palm OS)2Visit for example: www.ecom-ex.com3See for example Actisys (www.actisys.com), Extended Systems

(www.extendedsystems.com)


Parameter Min. Max. UnitsMaximum Operating Temperature -40 +85 ◦CRecommended Supply Voltage 2.7 5.5 VMaximum Output Current - 10 mAMaximum Power Dissipation - 0.22 W

Table 8.2: HSDL-7000 Characteristics. Source: Agilent TechnologiesInc.

Adding IrDA capability to existing products can also be done inother ways. One possibility is to assemble the hardware from groundup, either by choosing pre-made IrDA transceivers, or by building a re-ceiver and a transmitter oneself. In conjunction with the transceiver, anIrDA controller has to be used for decoding the light pulses. However,just having a hardware layer makes no connection.

On top of the hardware, at least the basic levels of the IrDA soft-ware stack have to be added. The software incorporates the intelligenceneeded for complying with the IrDA standard, hence making a connec-tion possible. The software stack could either be bought4 or developedin-house.

There is also a possibility to purchase a complete IrDA controllerequipped with a full stack, which together with an infrared transceivermakes up a stand-alone IrDA module. Such a module will take care ofeverything regarding the receiving and transmitting of infrared signalsand other activities prescribed by the IrDA specification.

Below, examples of products for implementing the latter two ofthese approaches are given and examined.

8.3.1 Agilent HSDL-7000

The HSDL-7000 from Agilent is an IrDA controller performing modula-tion and demodulation of electrical pulses to and from an IR transceiver.By handling the encoding and decoding of data and relieving the hostsystem from this, the HSDL-7000 can be connected to the host systemvia an ordinary UART. There is, however, no IrDA stack available onthis chip. This implies the use of an additional microcontroller, wherean IrDA software stack could be implemented.[2]

Technical data for the HSDL-7000 chip can be found in Table 8.2.

4See for example Extended Systems (www.extendedsystems.com) on their Em-bedded Irda Protocol Stack

8.3. IrDA Hardware 55

Parameter Min. Typ. Max. UnitsMaximum Operating Temperature -10 - +70 ◦CRecommended Supply Voltage 2.7 - 5.5 VReceiverSupply Current (9.6kbps) 110 170 220 µA (5 V)Average IrLED Current (9.6kbps) - 0 0 µA (5 V)TransmitterSupply Current (9.6kbps) 2.8 3 3.2 mA (5 V)Average IrLED Current (9.6kbps) 28 30 32 mA (5 V)Angle of Half Intensity 30 degreesPeak Wavelength of Emission 830 860 900 nm

Table 8.3: TM1001/TR1 Characteristics. Source: Everlight.

8.3.2 Everlight TM1001/TR1

The TM1001 is an integrated IrDA module containing both transmitterand receiver. The module is used to communicate wirelessly, usinginfrared light, and has to be connected to an IrDA controller (e.g.HSDL-7000) to do the actual shaping of the signal. TM1001 supportsdata rates up to 115.2 kbps over a distance of 1 meter.[10]

For some characteristics of the Everlight TM1001, see Table 8.3.

8.3.3 Microchip MCP2150

The MCP2150 from Microchip is a device containing both an IrDAcontroller and an IrDA stack. In addition to this chip, only an IrDAtransceiver (e.g. Everlight TM1001) has to be added for the actualtransmitting and receiving of the light pulses. Apart from this, thischip handles everything else. This makes it a fast way for implementingIrDA standard functionality into existing products. The chip offersbuilt-in support for the following IrDA protocols: IrLAP, IrLMP, IAS,TinyTP and 9-wire IrCOMM.[19]

MCP2150 also provides a serial interface, with a user selectablebaud rate, for communication with the host system. Supported baudrates ranges from 9.6 kbaud to 115.2 kbaud. The same range of baudrates are available for the infrared communication, and these two mustmatch in order for the device to operate properly. Only point-to-pointapplications are supported though. This means that only two devicescan be communicating when the MCP2150 is involved.[19]

Some of the key parameters for MCP2150 are listed in Table 8.4.


Parameters Min. Typ. Max. UnitsMaximum Operating Temperature -40 - 125 ◦CMaximum Power Dissipation 800 mWRecommended Supply Voltage 3.0 - 5.5 VSupply Current - - 2.2 mA (3.0 V)Supply Current - 4.0 7.0 mA (5.5 V)Device Disabled Current - - 2.2 µA (3.0 V)Device Disabled Current - - 9.0 µA (5.5 V)

Table 8.4: MCP2150 Characteristics. Source: Microchip.

8.3.4 IrDA Prototype

To build a prototype around the MCP2150 was an attractive solution,because everything needed came with the chip. So, for the prototype,an Everlight TM1001 transceiver was combined with the MCP2150IrDA controller and some peripheral components to form a completeIrDA capable communication device. A layout of the IrDA prototypecould be found in Appendix A.

The implementation follows reference designs found in documenta-tion for the two modules, as to be certain to have proper values on theadded external components. This was essential, as power dissipationwas very important and wrong components could give an inaccurate re-sult. There would, however, be possible to reduce energy consumptionby tuning the prototype some more.

A peculiarity of the MCP2150 is that it does not support a paritybit. This appears as a disadvantage as the application it is intendedfor uses odd parity. This could either be solved in software by usingthe last data bit as a parity bit or by modifying the host. For thisapplication, the software for the host was readily available, so it wasdecided to modify the software in the gauge.

8.4 Bluetooth Hardware

There are plenty of companies5 delivering Bluetooth products addingwireless capabilities to systems. In particular, many solutions are in-tended for eliminating serial cables using the Bluetooth Serial PortProfile (SPP). These solutions often aim for simple connection to their

5See for example:Code Blue Communications Inc (www.codebluecommunications.com),Bluenext Technology Pte Ltd (www.bluenext-tech.com.sg),Brain Boxes (www.brainboxes.com),Inventel (www.inventel.com),Stollmann E+V GmbH (www.stollmann.de),Wireless Futures (www.wirelessfutures.co.uk)

8.4. Bluetooth Hardware 57

host environment, by using an RS-232 interface. By using this standardinterface, the host itself does not have to be adapted to the Bluetoothmodule, thus eliminating the need of hardware or software modifica-tion of the existing system. These modules typically come with its ownhousing and are meant for external use.

The number of available modules narrows down, however, if there isneed for an OEM (Original Equipment Manufacturer) solution. In suchan application, the Bluetooth module is preferably added internally tothe existing product, thus being more incorporated into the product.Some companies do deliver modules like this with a fully operatingBluetooth stack and communication interface. The fact that it comeswith a full stack, eliminates the need of developing, implementing, andtesting it by oneself. This greatly reduces the time-to-market for com-panies wanting to integrate Bluetooth wireless connectivity into theirexisting products.

An OEM device would be the best in this case, and two deviceswith this quality are discussed further below.

8.4.1 connectBlue OEMSPA13

The OEMSPA13 from the Swedish company, connectBlue6, is a serialport adapter replacing serial cables with a Bluetooth link. As thename indicates, the unit can be used in OEM applications. Accordingto connectBlue, the module is well tested with PDAs, PCs, and mobilephones. It is also designed to consume as little energy as possible, thusaiming for the embedded or portable device market.[9]

connectBlue also offer a development kit, allowing the Bluetoothmodule to be connected to a PC. When connected to a PC, a configu-ration utility can be run, letting the user set up some parameters suchas baud rate, parity bits, and flow control of the module. It is alsopossible to set if the unit should operate as a server or client.

Technical data for the OEMSPA13 unit is displayed in Table 8.5.

8.4.2 Free2Move F2M03-C2

Another Swedish company, Free2Move7, also markets a Bluetooth mod-ule (F2M03-C2) for OEM applications. Their module could either beused as a stand-alone fully functional Bluetooth unit or together withan external Bluetooth stack. The module can utilize four low powermodes in order to preserve energy. It is also equipped with a PCM in-terface for up to 3 simultaneous voice channels. Key features are listedin Table 8.6.[12]

6For more information, see: www.connectblue.se7For more information, see: www.free2move.se


Supported BluetoothProfiles

Serial Port Profile, Dial-up NetworkingProfile, LAN Access Profile

Recommended Oper-ating Temperatures

−20◦ to +75◦C

Output Power 0 dBmPower Supply 3–6 VSerial Interface Logic-level UART, RS-232Baud Rate 300–912.6kControl Signals CTS/RTS or NoneAntenna Internal or External

Table 8.5: OEMSPA13 Characteristics. Source: connectBlue AB.

Supported Bluetoothprofiles

Generic Access Profile, Serial Port Pro-file, Headset Profile

Recommended Oper-ating Temperatures

−40–85◦C

Output Power Up to +4 dBmPower Supply 2.7–3.3 VSerial Interface UART, USB, PCMBaud Rate 2400(488 through software)–723.2kControl Signals CTS/RTS (Others can be made avail-

able on demand)Antenna Depends on Host Device

Table 8.6: F2M03-C2 Characteristics. Source: Free2Move AB.

8.5. Software Implementation 59

8.4.3 Bluetooth Prototype

The OEMSPA13 from connectBlue was selected, because it satisfied allrequirements set for this project. It supported the Serial Port Profileand had a logic-level UART for communication—all of this in one pack-age. The device from Free2Move would also have been a conceivablechoice, as it too supports the Serial Port Profile. This profile providesa natural way of providing a wireless connection point to a radar gaugeby interfacing its serial port.

The prototype consists of the OEMSPA13 and a few pull-up andpull-down resistors needed for setting the state of certain pins. As mostelectronics are integrated on the board, possibilities of modifying thedevice are limited. The layout of the prototype is enclosed in AppendixB.

Before the OEMSPA13 module can be used, it has to be configuredusing a PC software, where the correct serial parameters need to be set.It is also important to configure the device to use logic-level UARTmode, instead of RS-232 mode. The device is capable of deliveringboth signal levels but not simultaneously, and in this case, the logic-level signals are used because the device is connected directly to thegauge.

8.5 Software Implementation

The prototypes make it possible to set up a communication link to agauge, but no means of actually communicating with it. In order totry out the prototypes, a software application had to be programmedon the Palm Tungsten to be able to utilize this link.

For this reason, a small software application called ’Config’ was de-signed using the Metrowerks’ Codewarrior development environmentand programmed in C. (see Figure 8.1). The software applicationdemonstrates how the master side could be implemented. Further-more, it illustrates how a configuration utility could look like—a utilitythat the operator can use to configure the gauge.

8.5.1 Palm OS Wireless Support

The Palm device provides a similar interface for both IrDA and Blue-tooth; a virtual serial port. To the programmer, a virtual port can beused almost as a normal serial communication port. There are a fewinitialization routines that have to be carried out, but once the port isset up, it can be used as any other serial port.

The advantage is twofold; firstly, it provides a quick an easy solutionfor the programmer, and secondly, it reduces the need for building twoseparate applications. Only the part involving the initialization of the


Figure 8.1: Config Graphical Interface.


Figure 8.2: Config Connection Menu.

virtual port differs; the rest of the application can be used for bothBluetooth and IrDA. Once the connection is established, data could betransferred in the same way, no matter if the link consists of a wiredor wireless connection.

By using the IrDA or Bluetooth connection as a serial port, normalsettings are available such as baud rate, parity, and the number of databits. This is, however, only supported if the peer device offers the sameservice, because the serial parameters are negotiated when the link isinitialized.

8.5.2 Configuration Utility

The ’Config’ software provides a graphical interface for handling a wire-less connection to a radar level gauge. Both Bluetooth and IrDA aresupported as wireless connection methods. Conveniently, as describedabove, the Palm OS supports both RfCOMM and IrCOMM (see Figure8.2) and is able to treat both of these methods as ordinary serial con-nections. Once the connection is established, commands can be sent tothe gauge.


HART Protocol

The software application uses the HART industry standard protocol toexchange messages with the gauge. This protocol prescribes a masterand slave relationship between communicating devices, and commu-nication takes place by sending specific commands and receiving anddecoding the responses. Every device is given a unique address com-posed of a manufacturer code and their serial number for the device.

The initial master procedure is to ask a potential slave for thisaddress. This is possible, since a HART device also has a short addressthat distinguishes it from other devices attached to the system bus. So,before any other commands are sent, the long address is retrieved fromthe slave by transmitting a specific command, using the short address.Once the address is revealed, commands can be sent to acquire moreinformation about the gauge, for instance its currently measured value.

Features

Currently, a basic selection of available HART commands is imple-mented. This selection allows the operator to retrieve the long addressand read a number of variables such as tank level, level rate, ullage, andsignal strength. The operator could also set the short address of thelevel gauge. These commands are given as examples of what could bedone—a full implementation of the HART standard consists of severalcommands letting the user perform various operations on the device.

This software application is to be seen as a proof-of-concept. Thus,it is only intended to show that it is possible to connect to a gauge andgive a hint of what could be achieved with this technology.

The software application could be extended to allow more complexconfiguration such as downloading and upgrading of the software in thegauge. Another possibility would be to collect data for later processing,or to forward it to someone else, using a mobile phone connected to thePalm. Such a possibility would, for example, allow remote troubleshooting.

A monitor feature is also included in the software application. Inthis mode, the primary variable (e.g. tank level) is read periodically.The value of this variable is then plotted in a graph against time.

8.5.3 Program Execution

During the execution, a number of states could be reached. Thesestates, depicted in Figure 8.3, will be further described in this section.


Disconnected state Disconnected state Open RfCOMM Open RfCOMM

Open Previous (RfCOMM)

Open IrCOMM Open IrCOMM

Connected? Connected?

Connected state Connected state Get long address Get long

Has long address? Has long address?

Long Address state

Close connection Close connection

Close connection Close connection

Disconnected? Disconnected?

Disconnected? Disconnected?

Send message Send message

Monitor mode Monitor mode

No

Yes

No

No

Yes

Yes

Yes

No

Start: Initialize HART command database

Figure 8.3: Config Program Execution Flowchart.


Disconnected state

In the Disconnected state, no connection is active. To move from thisstate, the operator has to choose to open a connection to a gauge.Both to connect by using Bluetooth (RfCOMM) and by using IrDA(IrCOMM) are available in the menu (see Figure 8.2). To speed up theconnection to a Bluetooth device, an option exists to connect to thesame Bluetooth address as last time. This will bypass the discoveryprocess.

These procedures are available in this state.

• The ’Open RfCOMM’ procedure is used to establish a Bluetoothconnection and consists of five steps.

1. Setup Bluetooth to play the client role and use a serial ser-vice connection.

2. Try to locate a near-by device.

3. Establish a connection.

4. Flush the serial port to remove any lingering data.

5. Set up serial port parameters such as number of data bits,number of stop bits, and parity.

If no error did occur, a connection is here-by established andready to be used.

• The ’Open Previous’ procedure is used to re-connect to the lastBluetooth device connected to. This procedure consists of 4 steps.

1. Setup Bluetooth to play the client role and use a serial ser-vice connection.

2. Establish a connection to the last Bluetooth device con-nected to.



If no error did occur, the Bluetooth connection can now be used.

• The ’Open IrCOMM’ procedure is used to establish a connectionto an infrared device using the IrDA protocol. This procedureconsists of three steps.

1. Open the IR port and establish a connection.



Figure 8.4: Config With a Long Address Successfully Retrieved.


If no error did occur, a connection is at this point established andready for transmitting data.

Connected State

If a connection is established the Connected state becomes active. Inthis state, it is possible to retrieve the long HART address from theradar level gauge, by pushing the Get long address button seen inFigure 8.4. The ’Get Long Address’ procedure (see Figure 8.3) is usedto retrieve the long address of the remote HART device. There are foursteps needed for this.

1. Get command structure from HART command database and buildmessage.

2. Send message to the slave.

3. If a response was received, extract long address from response.


4. Output the long address to screen.

When this procedure is completed successfully, the long addressof the gauge is written to the screen, as can be seen in Figure 8.4.The operator could now use any of the available HART commands forinteraction with the gauge. This state is called Long address state.

Long Address State

The ’Send Message’ procedure is used to send a command of the oper-ator’s choice to the remote HART device. The command to transmitis picked from a list of available commands (see upper left corner inFigure 8.4). When a command is chosen in the list, its parametersare retrieved from the HART command database and displayed in the’Data in command’ and ’Data in reply’ tables. When the button ’SendMessage’ is pressed, the following five steps are taken.

1. If a response was received, extract long address from response.

2. The message is built, as the structure in the HART commanddatabase dictates.

3. The message is sent over the serial connection.

4. If a reply was successfully received, it is decoded.

5. The decoded response is outputted to the ’Data in reply’ table.

The special monitor mode could also be reached from this state. Inthis state, a new window is opened, and the primary variable is fetchedperiodically and plotted in a graph.

8.5.4 Further Development

It should be possible to share data when synchronizing the Palm witha PC. This should work both ways.

PC → Palm would make it possible to update the database contain-ing known HART commands. This would give the opportunity toadd more HART commands from a text file on the PC, instead ofhaving them hard-coded into the software. Another user scenariowould be to download new software for later transferring to theradar level gauge. This would also be possible to implement as asynchronization task.

Palm → PC would make it possible to transfer data, read from thegauge, to the PC for analysis. This would also make it possibleto do remote trouble-shooting, where the entire memory contentsof a gauge could be downloaded to the PDA and then forwardedto a service engineer.


Only a small subset of the available HART commands were imple-mented. To be fully compliant with the standard, more commandsshould be added. This should however be a straightforward task, asthe structure already exists.

Chapter 9

Experiments

This chapter explains how empirical data has been gathered and answersthe question how well the IrDA and Bluetooth implementations behavein certain circumstances. Acquired empirical data are also presented.

9.1 Introduction

This chapter is dedicated to comparisons between Bluetooth and IrDA.More specifically, the two prototypes designed in the previous chapterare tested. This testing is not meant to give an exhaustive answer, onwhich one of the two technologies is best in a general sense. Never-theless, an ambition is to be able to produce relevant results for thisparticular application. Hence, the main focus for the testing lies on en-ergy consumption, and how well the two systems operate in industrialenvironments.

9.2 Test Setup

In order to perform this assessment, a simple software application wascreated both for a Palm device and a PC. This software was then usedfor establishing a wireless connection between the PDA and the PCfitted with either the IrDA or the Bluetooth prototype module.

Two types of tests were conducted: A maximum distance test andan energy consumption test. The former test was carried out to as-certain how well the modules performed, when exposed to differenttypes of contamination. The latter test was aimed to reveal the powerdissipation of the unit.

69

70 Chapter 9. Experiments

Figure 9.1: Test Software on the PC Side.

9.2.1 Software

As mentioned above, a small software application was built for botha PC and a PDA, for testing purposes. On the PC side, the testsoftware (Figure 9.1) consisted of a plug-in for an existing Visual Basicterminal program, developed at Saab Rosemount. This program wasused as a base, because the serial connection was already implemented,and because it provided an already working graphical interface. Thus,only the specific functionality for the experiments had to be added.The plug-in provided a simple echo utility, which echoed a transmittedcharacter back to the sender.

On the PDA side, another utility was built (see display contents ofFigure 9.2). The purpose of this software was to open a serial connec-tion with another device, and to send characters one at a time, at auser-defined interval. The application also displays the number of sentand received characters. This function was added in order to give theuser an indication of whether the communication is up and runningand whether characters were lost during transmission.

The two aforementioned software applications were used to test bothIrDA and Bluetooth.

9.2.2 Hardware

The main hardware used in these experiments are the same hardwarediscussed in Chapter 8. When assessing the IrDA and Bluetooth mod-ules, they had to be connected to a PC via a serial cable. Hence, inaddition to the modules, an RS-232 converter had to be connected totheir serial interfaces. This RS-232 converter was essential to convert

9.2. Test Setup 71

Figure 9.2: Test Software on the PDA Side.

from the low-level signals available on the modules, to a signal thatcould be interpreted by a PC. The converter had a separate voltagesupply, to avoid influencing the tested prototype and by that, affectingthe result.

The other side of the link consisted of the Palm Tungsten T dis-cussed earlier. The PDA was capable of both IrDA and Bluetoothcommunication and was, thus, used for the testing of both modules.

In order to make the experiments more in accordance with how themodules would be implemented and operated in the field, the proto-types were enclosed in a housing from an existing radar gauge. Thishousing consisted of a metal case with a small glass window in front(see Figure 9.3).

Furthermore, the communication speed were set to 9.6 kbit/s in alltests, for both IrDA and Bluetooth. This is the lowest baud rate avail-able in the IrDA standard, and was chosen because of the assumptionthat lower communication speed implies lower energy consumption. Alower data rate could be impairing when large amount of data has tobe transferred, but this is, however, not the case in this thesis.

As for Bluetooth, the user has little control over the data rate. Thelink speed is set by the devices themselves, and the baud rate overthe virtual serial connection is thereafter emulated. To be consistent,though, the same baud rate was used when communicating over Blue-


Figure 9.3: Housing Used in the Tests.

tooth as well.

9.3 Results

Results from tests, using the test setup in the previous section, willnow be presented. Firstly, IrDA is assessed and thereafter Bluetooth isexamined.

9.3.1 IrDA

IrDA was tested both to determine its maximum operable range andto decide the energy consumption.

Maximum Distance

The purpose of the maximum distance test was to determine how farfrom each other two IrDA devices could be, while still being able tooperate. The supply voltage level for the IrDA module was varied from2.7 to 4.9 volts. The PDA was then placed as far away from the moduleas possible while still being able to connect. When the connection waslost, the distance was recorded.

It was assumed that infrared light from the PDA was transmittedstraight forward and from the middle of the glass window in its front.In order to aim as good as possible, the PDA rested on a laser pointingdevice. The laser beam was used as an aiming aid and showed wherethe PDA was pointing. Therefore, it is likely that the devices werebetter aligned than during normal usage. The laser device was shut offduring the actual test. The test setup is shown in Figure 9.4.

9.3. Results 73

Distance

Height

PDAIrDA Prototype

Laser Device

Figure 9.4: IrDA Maximum Distance Test Setup.

Four tests were conducted with different types of contamination.

Clear Path: No interfering objects between devices.

Glass: The IR module was placed inside the housing, behind a cleanglass window.

Water: Water was richly sprayed on the glass window, giving it acoating of small water drops.

Grease: A thin layer of flowing edible fat was smeared on the glass.

Apart from this, the path between the communicating devices was un-obstructed. Each test was performed in a dim room, devoid of any lightsources such as fluorescent and incandescent lights.

The results are given in Figure 9.5. As can be seen in the figure,water does not seem to interfere much with the infrared light, whereasgrease seems to be a bit more impeding to the transmission.

Power Dissipation

To be able to control the environment, the power dissipation test wasconducted in a climate chamber. The temperature in the chamber wasvaried from −20◦C to +50◦C. In this test the IrDA module was nolonger in its housing, but it was still connected to a PC via an RS-232adapter, as discussed above. Figure 9.6 depicts the test setup.

By using the test software on the PDA, an infrared link was set upthrough the glass of the climate chamber. 100 characters were thensent to the PC and echoed back with a 1 ms interval. During thisprocess the current was monitored, and the highest value shown on theampere meter was taken as a maximum. Current was also measuredwith no infrared activity; this value was taken as a minimum. This


2.5 3 3.5 4 4.5 5100

150

200

250

300

350

Voltage (V)

Dis

tan

ce

(c

m)

Maximum Distance

Clear Path

Glass

Water

Grease

Figure 9.5: IrDA Maximum Distance Results.

PDAIrDA

Prototype

Climate chamber

Glass

Window

Figure 9.6: IrDA Power Dissipation Test Setup.

9.3. Results 75

20 10 0 10 20 30 40 5015

20

25

30

35

40

45

50

55

Temperature °C

mW

Power Dissipation, Communicating Mode

Power Dissipation @ 2.7 VPower Dissipation @ 3.3 VPower Dissipation @ 3.9 VPower Dissipation @ 4.5 V

Figure 9.7: IrDA Power Dissipation in Communicating Mode.

procedure was repeated for four different supply voltage levels over thetemperature range. For comparison purposes, power dissipation wascalculated from the measured current and voltage levels. The resultsof this test are shown in Figures 9.7 and 9.8.

An odd behaviour is seen when the circuit is powered with 4.5 volts.This anomaly may be caused by temperature dependencies of individualcomponents in the circuit.

9.3.2 Bluetooth

Bluetooth was tested both to examine its maximum range and to de-termine the energy consumption.

Maximum Distance

The Bluetooth module was tested to discover over what distance it wasstill possible establish a connection and using it for communication.The module was inserted into a metal housing with a glass window inthe front. To keep the radio energy from escaping by any other meansthan through the glass window, holes such as cable lead-throughs weresealed and shielded with metal foil. The module itself was attached tothe window, with the antenna facing the glass. All of this was intendedto mimic a real installation of the Bluetooth module, where it is likely


20 10 0 10 20 30 40 5015

20

25

30

35

40

45

50

Temperature °C

mW

Power Dissipation, Disconnected Mode


Figure 9.8: IrDA Power Dissipation in Disconnected Mode.

to be put inside a gauge system, with only a small window throughwhere the radio waves can be transmitted.

Four test scenarios were set up, to see how the Bluetooth modulewould react exposed to different environments likely to be encounteredon the field.

Free path: Nothing was placed between transmitter and receiver ex-cept the glass window of the housing.

Water: Water was richly sprayed on the housing, leaving a film ofwater on the glass window.

Grease: A thick layer of edible grease was smeared on the glass win-dow.

Grease and Charcoal: The greased glass window was sprinkled withpulverized charcoal, giving the window a coating impervious tolight.

All tests were conducted outdoors, with nothing blocking the pathbetween sender and receiver. Supply voltage was also kept constantat 2.7 V throughout all four tests. This voltage level was chosen a bitunder the lowest recommended level of 3.0 volts, as to determine whatwould happen in a case with a minimum of energy consumption. ThePDA and the glass window were kept aligned pointing at each otherand on the same height.

9.3. Results 77

Free Path Water Grease Grease + Charcoal45 m 42 m 43 m 42 m

Table 9.1: Bluetooth Maximum Operating Distance.

PDABluetooth

Prototype

Climate chamber

Glass

Window

Figure 9.9: Bluetooth Power Dissipation Test Setup.

However, no soiling of the glass window did severely affect the per-formance of the Bluetooth module. In every scenario, it was possibleto connect to and communicate with the prototype at a distance justover 40 meters. The results can be seen in Table 9.1.

The Bluetooth prototype was also tested in an office environment toget a feel how the technology is affected by blocking obstacles, such asinterior walls. The same housing as before was used in this experiment.The housing with the Bluetooth module inside was placed 50 cm offthe floor facing an interior wall. No soiling was done this time.

In this experiment, it was possible to connect to and communicatewith the prototype using the PDA up to 15 meters away, even thoughthe radio waves had to pass through a wall.

Power Dissipation

In order to measure power dissipation of the Bluetooth prototype, aclimate chamber was used. The climate chamber could provide bothhigh and low temperatures in a controlled atmosphere. The set-up isshown in Figure 9.9.

For the test, the prototype and the RS-232 converter were placedinside the chamber while connected to a computer outside the chamberacting as a host. The temperature was varied from −20◦C to +50◦C,and the supply voltage was varied between 2.7 V to 4.9 V. At a giventemperature and a given voltage level, tests were conducted in threedifferent modes.


20 10 0 10 20 30 40 5080

90

100

110

120

130

140

150

160

Temperature °C

mW

Power Dissipation, Disconnected Mode


Figure 9.10: Bluetooth Power Dissipation in Disconnected Mode.

• Disconnected Mode

• Connected Mode

• Communicating Mode

In disconnected mode, no connection was established between theBluetooth module and the PDA. In connected mode, a connection wasestablished, but no data was transferred, whereas in communicatingmode 100 characters were sent one at a time with a 1 ms gap. Eachcharacter was also echoed back to the PDA, resulting in high link ac-tivity.

In Figures 9.10–9.12 it can be seen how temperature and voltagelevel affected energy consumption. Values in this figure were calculatedfrom the measured current in the circuit and the voltage supplied.

Probably as a consequence of the low power supply, it was impos-sible to connect to the prototype at +50◦C and 2.7 volts. Otherwise,everything was working and it was found that power dissipation didnot vary with the temperature, only with the variation in voltage.

9.3. Results 79

20 10 0 10 20 30 40 50100

120

140

160

180

200

220

Temperature °C

mW

Power Dissipation, Connected Mode


Figure 9.11: Bluetooth Power Dissipation in Connected Mode.

20 10 0 10 20 30 40 50100

120

140

160

180

200

220

240

Temperature °C

mW

Power Dissipation, Communicating Mode

Power Dissipation @ 2.7 V Power Dissipation @ 3.3 VPower Dissipation @ 3.9 VPower Dissipation @ 4.5 V

Figure 9.12: Bluetooth Power Dissipation in Communicating Mode.

Chapter 10

Conclusion

This chapter provides an analysis of the test results from last sectionand discusses what conclusions can be drawn from this study. Thoughtsare given on what can be done to remedy some of the problems foundduring this research, as well as what steps that can be taken in thefuture.

10.1 Introduction

Both Bluetooth and IrDA have been covered in detail in this report.Each of the two standards has been presented and summarized, andeach technology has been evaluated on theoretical grounds. Both wereset on each other as well as compared to other potential techniques inChapters 3–7.

This was however done theoretically. In Chapter 8 and Chapter 9,two prototypes were built and tested, to ascertain what can be expectedfrom each technique in an authentic application. This practical testassessment together with the theoretical evaluation forms the basis forthis chapter.

Now, time has come to analyze results found in previous chaptersand to deliver some thoughts on what technology would be best inthis particular implementation, namely radar level gauging. The firstsection is concerned with the analysis, while the second section bringsup a discussion about the results, and the third provides thoughts onhow this study can be extended.

10.2 Analysis

From the testing of the prototypes in the last chapter, it was found thatboth IrDA and Bluetooth were robust technologies. When the proto-

81

82 Chapter 10. Conclusion

types were exposed to soiling such as grease and water, communicationwas still possible. IrDA was, however, found to be more sensible tosoiling compared to Bluetooth, which was virtually unaffected of thedirt.

The Bluetooth module was also little affected by operating tem-perature. The power dissipation was close to constant for Bluetooth,whereas it varied some in the IrDA case.

Each also delivered more than the standard promised in terms ofrange. There is, however, a large discrepancy between the two; IrDAconnects at about 1–3 meters, whereas Bluetooth covers a distance offully 40 meters. This range was measured outside in open air, but testsalso showed that Bluetooth could cover 15 meters indoors through aninterior wall.

The Bluetooth module used for the prototype was also more tech-nically advanced than its adversary. There were, for instance, no lim-itations in terms of serial parameters. Support was provided for stan-dard baud rates from 300 baud to 921.6 kbaud. It also supported anyparity bit setting and any flow control setting. This contrasts withthe IrDA controller that only supported baud rates from 9.6 kbaud to115.2 kbaud. This module did also not allow the use of parity bitsand depended on flow control to operate properly. This would makethe Bluetooth solution the better candidate as this gives more freedomfor the serial interface, and it also renders it possible to implement theHART protocol, which uses odd parity, according to the specification.

The IrDA prototype was however much more affordable than itscompetitor, notwithstanding the fact that it has a greater componentcount than the Bluetooth prototype. IrDA has been available for alonger period of time and must from that perspective be recognized asa more mature technology.

The overall feeling is nevertheless that Bluetooth is easier to workwith and much more stable. There is no necessity to align the twocommunicating devices geometrically, and it is possible to connect at agreater distance. It does, however, consume more energy than IrDA.

Because of this fact and as energy consumption being of prime im-portance for the specific application of Saab Rosemount, IrDA is se-lected as the best candidate for adding wireless connectivity to a radarlevel gauge unit.

Some issues remain, though, and the next section is dedicated tothose.

10.3. Discussion 83

10.3 Discussion

Two points have surfaced during this study to be of principal impor-tance.

1. Power Dissipation

2. Connection Robustness

Each of these aspects has been investigated in detail in this reportalready, but some thoughts will be delivered in this section on whatcan be done to alleviate some of the problems this entails.

10.3.1 Power Dissipation

In this particular application, power consumption is of great importanceas radar gauges sometimes are used in locations where the only powersource available is the communication bus it is attached to. About 20mW is necessary for the IrDA prototype and the Bluetooth consumesalmost ten times as much. Although these figures are quite low, theremight still be a problem. Yet, there are a couple of techniques thatmay provide a remedy.

The communicating part could be forced into a low power or sleepmode. The Bluetooth module for example can be controlled via a signalto enter a stop mode, which is the most energy saving mode. In thismode the unit may accept incoming connections, but is not able to senddata over the serial interface before the stop mode is left.

In the IrDA case, such a mode is not supported internally, but it ispossible to do a work-around solution. Applying voltage to a specificpin can disable both the infrared transceiver and the controller. Thiscould be exploited for simulating a sleep mode, where the device willbe disabled when no infrared activity is occurring and only awaken forshort periods of time. This window in time does only have to be longenough for a user to be able to connect to the device. A pin could bemonitored on the MCP2150 to discover when it moves to a connectedstate. If this happens, the sleep mode could be abandoned, until theconnection is terminated.

A power saving mode does, however, not provide a solution for whenthe device is communicating, but a low power mode makes it possibleto store energy during periods with no communication. This energycould for example be used to charge a capacitor or a battery.

Still another possibility is to reduce the effective communicationrange, by modifying the output power. The integrated structure of theBluetooth device may pose a problem for such a solution, but with theIrDA prototype, tuning of the transceiver might provide a workablesolution.

84 Chapter 10. Conclusion

10.3.2 Connection Robustness

Robustness is another important factor to consider when comparingtechniques for this application. Both IrDA and Bluetooth standardsare built on a protocol with a guaranteed delivery of data. This isapparent when testing the two; either there is a connection, or it isnot. The downside of this is that a connection establishment processhas to be run through before any communication can take place.

This can be avoided when using infrared communication, by bypass-ing the IrDA protocol and using what is called raw IR. Raw IR could beused in some PDA models, letting the PDA act like a remote control.This is, however, not officially supported, so a solution built on thisfunction could be obsolete by the next generation. Another possibility,would be to just use an ordinary remote control. Remote controls tendto speak different dialects though, so this would imply a custom-madesolution. A step in this direction does violate the objective to use acommercially available product. It would also jeopardize the robustnessof the communication link, as, for example, no retransmission schemesare present.

On the radar gauge side, tests have shown that both techniques arefairly resistant to dirt and soiling. The IrDA solution is a bit weaker inthis point, but as infrared communication has a limited range anywayand is performed close to the gauge, this is easily remedied by wipingthe glass window of the gauge housing.

10.4 Further Work

This report has solely been concentrating on hand-held devices, andmore specifically PDAs. A solution does not, however, have to limititself to PDAs. One possibility that immediately suggests itself is touse a cellular phone instead. The use of a notebook computer wouldalso be an obvious alternative. The possibility to use the same sourcecode and development tools for all platforms would therefore be worthinvestigating.

From what is shown earlier in this report, it comes down to a tiebetween the Palm OS and the Pocket PC camp, regarding what plat-form to use for the hand-held computer. Both sides have a great pieceof the market and have about the same field of application. There arealso devices available of both kinds that can be brought into hazardousenvironments. Both operating systems are also available on cellularphones (“smart phones”) implying that an application created for aPDA, also could be used on a cellular phone, giving the user morefreedom of choice.

Another incentive to test more PDAs and the like, is to determine

10.4. Further Work 85

how well the Palm Tungsten T performs in terms of communication.As performance is dependent on both sides and all experiments in thisreport have involved the Tungsten, an interesting test would be to findout whether this PDA is better or worse than other products in the mar-ket. The PDA used may also be responsible for the lost connections inthe maximum distance test. Such testing could also be combined witha field test, performed in an actual installation to see how performanceis affected in a real industrial environment.

Yet another point worth examining, is whether Bluetooth could beused to connect auxiliary sensors such as temperature and pressure sen-sors to the radar gauge. This would of course imply that the auxiliarysensors are powered from another source than the communication linefrom the main gauge. If this is possible, Bluetooth would facilitate theconnection of such devices, especially in hard-to-reach places, and alsoreduce the need for wiring.

Regarding the software developed for this project, more commandsneed to be added in order to fully support the industry standard HARTprotocol. For instance, a function could be added to support the down-loading of new software to the radar gauge. Such a function wouldmake it possible to update the software in the field.

To make this process easier, software could be designed to run on aPC that is capable of synchronizing with the PDA. This synchroniza-tion could be used to transfer data, such as software upgrades and tankparameters, between the PC and the PDA, thus making it possible toload up the portable device with data in the office and later just carrythe data over to the gauge. This implies, for example, that softwareupgrades for the gauge could be distributed over the Internet.

References

[1] IEEE Std 802-1999. IEEE standards for local and metropolitanarea networks: Part 11: Wireless LAN medium access control(MAC) and physical layer (PHY) specifications. www.ieee.org,1999.

[2] Agilent Technologies Inc. HSDL-7000 IR 3/16 Encode/Decode ICDatasheet (5988-4569EN), November 2001. www.agilent.com.

[3] Infrared Data Association. Serial infrared link access protocol(Ir LAP). www.irda.org, June 1996. Version 1.1.

[4] Infrared Data Association. Serial infrared physical layer specifica-tion. www.irda.org, May 2001. Version 1.4.

[5] Glenn Bachmann. Palm programming. Sams, Indianapolis, 1999.

[6] Ashok Bindra. Gmsk-modulated magnetic link spurs pans. Elec-tronic Design, 49(15):15–16, July 2001.

[7] Chris Bunszel. Magnetic Induction and RF. Aura Communica-tions, Wilmington, Massachusetts. www.auracomm.com.

[8] International Electrotechnical Commission. IEC standard: Electri-cal apparatus for explosive gas atmospheres, 1983. Part 0: Generalrequirements.

[9] connectBlue AB, Stora Varvsgatan 11 N:1, SE-211 19 Malmo, Swe-den. Serial Port Adapter and OEM Serial Port Adapter: Productdatasheet, February 2003. www.connectblue.se.

[10] Everlight. TM1001/TR1 Infrared Data Receiver ModuleDatasheet. www.everlight.com.

[11] P. Fowler. 5 ghz goes the distance for home networking. IEEEMicrowave Magazine, 3(3):49–55, September 2002.

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88 References

[12] Free2move AB, Pilefeltsgatan 77, SE-302 50 Halmstad, Sweden.Class 2 Bluetooth module - F2M03-C2 Datasheet, April 2002.www.free2move.se.

[13] Jim Geier. Wireless LANs. Sams, Indianapolis, July 2001.

[14] PalmSource Inc. Developer knowledge base: What bluetooth pro-files does the Palm OS support? kb.palmsource.com, March 2003.Answer ID:382.

[15] PalmSource Inc. Developer knowledge base: What is the range ofBluetooth? kb.palmsource.com, March 2003. Answer ID:383.

[16] J.M. Kahn and J.R. Barry. Wireless infrared communications.Proceedings of the IEEE, 85(2):265–298, February 1997.

[17] Michelle Man. Bluetooth and Wi-Fi: Understanding these twotechnologies and how they can benefit you. www.socketcom.com,March 2002. Socket Communications, Inc.

[18] Medc Ltd., Colliery Road, Nottingham, UK. A guide to theuse of electrical equipment in potentially explosive atmospheres.www.medc.com.

[19] Microchip Technology Inc. MCP2150 Data Sheet 21655b, 2002.www.microchip.com.

[20] Brent A. Miller. Bluetooth revealed. Prentice Hall, Upper SaddleRiver, N.J., 2001.

[21] Nathan J. Muller. Bluetooth demystified. McGraw-Hill, New York,2001.

[22] Patrick J. Megowan, David W. Suvak, Charles D. Knutson. IrDAinfrared communications: An overview. www.irda.org, May 1998.Counterpoint Systems Foundry, Inc.

[23] Gartner Dataquest Press Release. Gartner dataquest saysworldwide PDA market suffers through a dismal year in 2002.www.gartner.com, January 2003.

[24] Bluetooth SIG. Bluetooth protocol architecture.www.bluetooth.org, August 1999. Version 1.0.

[25] Bluetooth SIG. Specification of the Bluetooth system v1.1.www.bluetooth.org, February 2001. Volume 1: Core.

[26] Bluetooth SIG. Specification of the Bluetooth system v1.1.www.bluetooth.org, February 2001. Volume 2: Profiles.

References 89

[27] David W. Suvak. IrDA and Bluetooth: A complementary com-parison. www.extendedsystems.com, 2000. Counterpoint SystemsFoundry, Inc.

[28] W.-S. Wang. Bluetooth: A new era of connectivity. IEEE Mi-crowave Magazine, 3(3):38–42, September 2002.

[29] S. Williams. IrDA: Past, present and future. IEEE Personal Com-munications, 7(1):11–19, February 2000.

Appendix A

IrDA Prototype Layout

Figure is found on next page.

91

92A

ppen

dix

A.

IrDA

Prototy

pe

Layou

t

Txd6

Rxd4

Vcc3

Gnd5

PD1

BC2

LEDC7

LEDA8

TX7

EN6

BAUD118

BAUD01

RX8

RTS13

CTS12

DSR10

DTR11

CD17

RI9

TXIR2

RXIR3

OSC116

OSC215

/Reset4

Vss5

Vdd14

R2

10k

C5

18pFY1

11.0592MHz C6

18pF

U2

TM1001

C4

1uF

C3

0.1uF

C1

0.1uF

C2

10uF

R1

4.7

U1

MCP2150

5V

5V

CTS

RX

TX

Appendix B

Bluetooth PrototypeLayout

Figure is found on next page.

93

94A

ppen

dix

B.

Blu

etooth

Prototy

pe

Layou

t

Vss1

Vss2

Vcc3

Vcc4

RS232-CTS5

RS232-TxD6

RS232-RTS7

RS232-RxD8

RS232-DTR9

RS232-DSR10

RED/Mode11

Switch-012

GREEN/Switch-113

BLUE14

UART1-CTS15

UART1-TxD16

UART1-RTS17

UART1-RxD18

UART1-DTR19

UART1-DSR20

J1

CON20

R8

10k

R7

10k

R4 100

R5 100

R9

10k

R6

10k

3V

RX

TX

Copyright

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