Wireless Comparison

8/14/2019 Wireless Comparison

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Copyright Ekahau Inc. 2000-2005

Comparison of Wireless Indoor Positioning Technologies

- An Ekahau Whitepaper


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Copyright Ekahau, Inc. 2000-2006 Page 2 of 11

1 POSITIONING DEFINED................................................................................................. 3

2 RADIO FREQUENCY IDENTIFICATION (RFID)............................................................ 4

3 INFRARED (IR) ............................................................................................................... 5 4 SENSOR NETWORKS.................................................................................................... 5

5 ULTRA-WIDEBAND (UWB)............................................................................................ 6

6 GLOBAL POSITIONING SYSTEM (GPS) ...................................................................... 6

7 STANDARD WI-FI-BASED POSITIONING .................................................................... 7

8 CONCLUSION............................................................................................................... 10


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This paper discusses the various types of positioning technologies as the basis for realizing mobile, location-aware system solutions.

1 Positioning DefinedA positioning system determines the location of an object (client) in a particular space, suchas an enterprise facility or warehouse. Ideally, the positioning is done in real time, with theability to track the location of the object as it move through a space. By offering thecoordinates of an object, positioning technologies realize a vast number of beneficial,location-aware solutions:

Local information pushing . In this case, apositioning system sends valuable information to aclient based on the clients location. For example, aprocessing plant may push workflow information toemployees regarding operating and safety procedures

relevant to their locations in the plant. The positioningsystem tracks each employee and has knowledge of the floor plan of the facility as well as the procedures.When an employee steps within a defined perimeter of a particular area, such as a packaging department,the positioning system displays on a persons PDA thesteps on for the work needing to be done in that area.This significantly increases efficiency and safety byensuring that employees follow carefully designedguidelines.

Centralized tracking . Insome cases, itsadvantageous to keep tabs

on the location of objects.With centralized tracking, apositioning systemcontinuously stores anddisplays the positioninformation to an operator.This leads to more effectivemanagement of assets. Asan example, a hospital cantrack patients in an

operating room to analyze and remove bottlenecks in the flow of work to increasethroughput and ultimately the quality of care. Historical workflow data and asset usageper location can provide

invaluable information inoptimizing a variety of processes.

Decentralized tracking . Thisgoes a step further thancentralized tracking by having thecentralized station broadcastclient positions to all clients. As aresult, each client knows the


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position of other clients in relation to themselves. With this capability, its possible toexploit the location of other users to make better decisions, such as in emergencyresponse to natural disasters and terrorist attacks. In these situations firefighters, for example, can better spread out and make decisions when responding to a massive fire

when they can know the position of each of the other firefighters. Navigating . Positioning systems make navigation simple by supplying the x-y

coordinates of a client superimposed onto a map of a particular area. When knowing their location, a user discovers how to proceed to a specific location in a timely manner.Libraries, for example, have found this form of positioning very useful for patrons. Aperson looking for a book carries a PDA that offers an electronic map of the library andthe persons location. After entering book information, the PDA clearly illustrates theplace of the book on the map. After following some simple directions that the PDA offers,the patron finds the book much faster, without the help of library staff.

2 Active Radio Frequency Identification (RFID)An Active RFID location system includes proprietary RFID scanners installed throughout a

facility that interrogate either active (radio transceivers) or passive tags that attach to objects.Active tags use batteries and allow up to a twenty foot range between the scanner and thetags. Passive tags dont use batteries, and they receive energy when being scanned. Theradio waves emitted by an RFID scanner energize a passive tag long enough for the tag totransmit its code to the scanner. Passive tags, however, must be relatively close (withininches or a few feet ) to the scanner. As a result, radio transceivers are the most commontype of RFID tag ( Active RFID Tag ) found in positioning systems.

Active RFID tags contain electronic codes that identify one tag from another. A centralizedstation stores the tag codes that the scanners collect. Because the scanners are placed inknown positions throughout a facility, the centralized station is able to identify and display thelocation of each tag (and of course the client device that the tag corresponds with).

Active RFID systems determine position based merely on the presence of the object in a

particular area, within range of a RFID scanner. When a person wearing an Active RFID tagenters a room, for instance, the system indicates the existence of that person as soon as itdetects the tags signal. As a result, the accuracy of an Active RFID system is highlydependent on the positioning of the scanners. One scanner per room only provides locationaccuracy to the size of the room.

The cost of installing additional RFID scanners for finer tracking is cost-prohibitive for mostapplications because of the relatively high cost for multiple scanners per room or area. As aresult, its not practical to use RFID to provide real-time tracking of objects. In addition, thedeployment of an RFID system over a large campus or enterprise area is very expensivebecause of the need for installing a multitude of scanners completely separate from thecorporate network. Also, changing the layout of a manufacturing plant or moving walls in anoffice requires remounting and rewiring of the RFID readers. This is a major problem infrequently changing environments or in complex indoor environments.

An issue with the proprietary hardware used with RFID systems is that the resultingdeployments are difficult and costly to scale up to support a larger numbers of users.Proprietary hardware is usually only available from a single vendor, making equipment priceshigher than standards-based solutions. In some instances, vendors may even go out of business, making the hardware obsolete. Standards-based solutions are certainly preferablein order to reduce these costs and operational support risks.

In addition, some RFID systems operate in the same frequency band as wireless LANs,which poses RF interference issues for companies needing wireless LAN connectivity for


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mobile data applications. Its nearly impossible to ensure that the RFID system and thewireless LAN are operating on different, non-interfering channels throughout the facility. Thecontinual transmissions taking place in a RFID system causes a decrease in throughput inthe nearby wireless data network.

3 Infrared (IR)Similar to using RFID, an IR location system determines position of an object based on thepresence of an object, which as mentioned before makes real-time tracking not practical toimplement. Each object being tracked includes a proprietary emitter that periodicallytransmits an IR beacon containing a unique code. Infrared light is invisible to the human eyeunder most conditions, so people cant see the beacons. Specialized IR receivers placedthroughout the facility detect the beacons and determine the approximate position of theobject because of the known location of the IR receiver.

An IR system is practically immune to interference, largely because most other wirelesscommunications systems operate in the RF spectrum far below the frequencies of light.Because IR signals dont penetrate opaque materials, such as walls and ceilings, an IR

tracking system must often have several receivers in each room to avoid losing trackedobjects as they go around corners and behind office partitions. The orientation of the IR Tagto the IR reader can also cause problems if for instance the tracked asset itself is blockingthe line of sight view from the IR Tag to the reader. In addition to the proprietary nature of IRsystems, this adds to the cost and complexity of the overall solutions and as with ActiveRFID systems, scaling these proprietary solutions can become very costly endeavors.

4 Sensor NetworksIn a sensor network solution, clients include a battery-powered radio module that transmits aRF beacon containing a unique identification number from every five seconds once eachhour. Other types of proprietary sensor networks include those that operate by measuringthe time is takes for a signal to travel between the sensor and the trackec object, commonlyreferred to as Time Difference of Arrival ( TDOA ). These systems makes use of modifiedWi-Fi access points or separate sensors installed throughout a facility that receive thebeacons, which are proprietary data packets containing the identity of the client in the caseof TDOA timing information of the packets transmitted. Centralized software then interpretsthe position of a particular client using a triangulation method based on differences in signalstrength measurements retrieved from three or more access points or by using a serried of calculations to interpret the timing information obtained by the proprietary sensors.

Triangulation based methods do not usually produce very accurate positioning results andare very susceptible to errors caused by walls, furniture and other elements in theenvironment This has generally lead to the failure and disappearance of many such systemsoff the market.

TDOA systems also rely on having a relatively clear line of sight between the sensor and thetag. In complex environments such as factories and hospitals, TDOA systems would requirean exceptionally high number of sensors to achieve decent positional accuracy which in turnmay completely destroy the business case for a location tracking system. TDOA systems onthe other hand perform better in outdoor spaces where there are fewer obstructions blockingthe signal path between the sensors and the tags. In this type of environment combiningGPS with WiFi may however be a more cost-effective alternative.

Most of the sensor network tracking solutions allow the access points to carry typical datatraffic associated with Wi-Fi users. This is a strong benefit over the other positioning


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systems, such as RFID and IR that make use of only proprietary equipment. Because thesensor network access points include proprietary enhancements that enable the trackingmechanisms, however, users must purchase and support sole source hardware for wirelessLAN applications. This severely limits scalability and increases costs for support.

Most sensor network solutions allow the setting of beacon rate for each tag in order to tradeoff battery life with accuracy. Higher beacon rates are best for fast moving objects; whereas,lower beacon rates are better for slower moving objects. The beacon rate should be set justfast enough to capture position at a rate acceptable to the application but slow enough toconserve battery power within practical values.

The problem, though, is that its not trivial to predict the speed at which objects will move. Ina hospital, for example, a doctor will not move much as they work in a patients room, butwithin minutes the doctor may be running to assist an ailing patient in a different wing of ahospital. The balance of beacon rate and battery conservation is difficult to achieve whenplanning and supporting most sensor network positioning systems. Most users guess atthese values, leading to inefficient operation.

In practice, sensor network beacon rates must be kept low in order to achieve acceptablebattery conservation, with a beacon rate of once every minute or so. This diminishes thereal-time aspect of the system because position update will be relatively infrequent. A personcan go pretty far within a minute in between beacons. Thus, good accuracy is obtained byhaving frequent beacons with reduced battery life.

Another issue with some sensor networks is that tags are relatively large, with eachmeasuring roughly two by four inches and weighing a couple ounces. The addition of thissize of device for tracking purposes can be unacceptable in some cases. Its cumbersome toplace the tags on common client devices, such as PDAs, bar code scanners, and evenlaptops.

5 Ultra-Wideband (UWB)Similar to most other positioning solutions, UWB positioning systems have proprietaryscanners installed throughout the facility that continuously monitor UWB radio transceiversattached to clients. UWB systems, however, operate using radio signals having very widebandwidth, and position calculations are made based on time-of-arrival techniques instead of signal strength. This leads to fairly good location accuracy. By reading the time of arrival of abeacon signal from a specific UWB radio transceiver from three or more scanners, for instance, the position of the tag and applicable object can be found.

The use of UWB signalling considerably reduces signal impairments, such as RFinterference and multipath propagation, which makes the coexistence with Wi-Fi networksacceptable. The issue, however, is that UWB makes use of technologies that are notconsistent with standards in use by most companies. Thus, UWB hardware is expensive topurchase and scale. Furthermore the public use of UWB is still under consideration with theFCC, which makes the future of this technology unclear.

UWB tags generally transmit several beacons each second, which makes batteries lastapproximately one year. Beacon rates are usually adjustable, but, as with a sensor networksolution, the optimum rate is difficult to determine and battery replacement can be costly.

6 Global Positioning System (GPS)GPS is commonly deployed in a variety of devices, such as handheld GPS receivers thatprovide latitude and longitude as well as moving maps for navigating airplanes andautomobiles. The GPS consists of satellites in located geostationary orbit around the Earth.These satellites remain in a fixed position relative to the ground and continuously transmit


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coded beacon signals. A GPS receiver located on a client receives simultaneous signalsfrom multiple GPS satellites and uses a time-based approach for calculating position. Thesuccessful reception of at least three satellite signals is enough to calculate x-y coordinates.With a greater number of satellite signals, however, accuracy is better, and its even possible

to determine elevation.GPS solutions calculate range between satellites and receivers based on propagation timeand the fact that signals travel at the speed of light. With knowledge of range between itself and several satellites, a particular GPS receiver can calculate its position. The range is greatenough for this approach to work fairly well with available clock accuracies. With positioningsystems installed indoors, except for UWB technologies, propagation delay is so small thatits difficult for most clocks to measure to determine range within accuracies consistent withthe actual ranges.

An issue is that GPS signals are relatively weak, making it only usable in areas with anunobstructed path between the GPS receiver and the sky. In fact, GPS is not usable at allinside buildings. Tree foliage also significantly limits GPS signals. Even narrow areassurrounded by tall buildings, such as within large cities, will impair signal reception. In order

to enhance coverage of GPS, the Assisted GPS (A-GPS) systems are available. A-GPS useground-based GPS servers to extend range in large cities and in some cases inside facilities.A-GPS solutions, however, are very costly to deploy.

As with the positioning technologies discussed so far, GPS requires a dedicated chipset inthe client device. This entails the installation of GPS circuitry, which adds to the expense andcomplexity of the user device.

7 Standard WiFi-based PositioningThe critical issues of the positioning technologies discussed so far include the proprietary nature of the scanners and tags, needs for an infrastructure that is completely separate from a companysdata network, and limited real-time operation. These common

attributes make the systems costly to deploy, scale, and support.In some cases, the negative characteristics make the systemsunsuitable for highly mobile, location-aware or trackingapplications found in hospitals, warehouses, manufacturingplants, universities, and enterprises.

Over the past few years, WiFi has been proliferating as the primary standard for wirelessLANs in company facilities and homes worldwide. Based on the IEEE 802.11 standards, Wi-Fi addresses needs for secure, high performance mobile data networking. With thewidespread adoption of wireless LANs, Wi-Fi is an ideal technology as the basis for positioning technologies.

As mentioned before, sensor network solutions make use of Wi-Fi access points. However,the proprietary modification that traditional sensor solutions demand in access points is amajor drawback due to the need for sole source acquisitions of the products. In addition,sensor solutions generally require the installation of specialized, proprietary transmitters onthe devices being tracked.

A standard WiFi-based positioning system, such as the one offered byEkahau, is completely software-based and utilizes existing Wi-Fi accesspoints installed in a facility and radio cards already present in the user devices. Ekahau also offers a WiFi-based radio tag that uses industrystandard components that adhere to the 802.11 standards. This approachallows for the use of commercial off-the-shelf hardware and drivers to


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produce a standards-based radio tag that can communicate bi-directionally over the 802.11network.

Ekahaus standard WiFi-based solution is completely vendor-agnostic in terms of hardware.Wi-Fi cards come in many different form factors, such as PC Card and Compact Flash aswell as built into newer PDAs, laptops, tablet computers and a variety of other purpose builtdevices. Thus, a standard WiFi-based positioning system can realize any type of location-aware application that involves PDAs, laptops, bar code scanners, voice-over-IP phones andother 802.11 enabled devices. For embedded solutions,there is no need for the client to include a specialized tag,transmitter, or receiver.

Because of the entire use of standards-based hardware,such as 802.11b, 802.11g, and 802.11a, a standard WiFi-based solution rides the installed based and economies of

scale of the networks and end user devices that areproliferating today. Without the need for additionalhardware, a company can install the system much faster

and significantly reduce initial and long-term support costs. A commoninfrastructure supports both the data network and the positioning system,something companies strive for. The positioning system works wherever there is Wi-Fi coverage. If the clients are outside of the Wi-Fi coverage area,the system will know the last known location and when the clients comeback the tracking continues.

In addition to cost savings in hardware, a standards WiFi-based positioning systemsignificantly reduces the potential for RF interference. The total Wi-Fi positioning systemshares the same network along with other network clients, so there is no additionalinstallation of a separate wireless network (as RFID requires) that may cause RFinterference with the existing wireless network. Most wireless LANs are underutilized, leavingplenty of capacity available for location-aware applications. Thus, WiFi is an idealinfrastructure for positioning systems.

The Ekahau Wi-Fi positioning solution includes the following components:

Ekahau Client: Software client program that runstransparently in the background of a client device,such as a laptop computer, PDA or embedded Wi-Fidevice. The Ekahau client is available in Windows2K/XP, Win CE/PPC, Palm and Linux OS versions.The Ekahau Client can also provide end-users apowerful opt-in function to turn tracking on of off.

Ekahau Positioning Engine: Software thatruns on a desktop or rack-mounted server andcalculates the client devices position attributes,such as x-y coordinates, heading, and speed.The Positioning Engine is a Java-based systemthat can be run on Windows XP, Linux, Solaris


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and a number of Unix variants.

Ekahau Manager: Application software for system administrators for creating andmaintaining the positioning model, tracking client devices on a map and analyzing thepositioning accuracy.

Ekahau Application Framework and SDK: A setof ready-made applications, tools and aprogramming interface for applicationdevelopers creating location-aware solutions aswell as End-Users requiring an out-of-the-boxtracking application suite.

Ekahau uses the received signal strength indicator (RSSI) as the basis for positioning and aprobabilistic framework for estimating the location of the tracked item. The frameworkcompares the received RSSI values with the values stored in the Positioning Model todetermine the location of the device.

A strong advantage of the Ekahau positioning and tracking system is that it doesnt requireany changes to an existing Wi-Fi network infrastructure. The Ekahau system is fullysoftware-based. Another benefit is that the signal strength values change relatively smoothlywith respect to changes in location, which means that the RSSI approach is not as sensitiveto measuring errors as other solutions encounter.

In a typical officeenvironment, the Ekahausolution can achieve

down to one meter average accuracy andtwo to three meter accuracy 99% of the timeAccuracy may varydepending on theenvironment type, accesspoint density, antennatypes and site calibrationdensity. Unlike other positioning systems inthe market, thepositioning algorithm of the Ekahau PositioningEngine continues tooperate effectively in thepresence of multi-pathissues, complex RFunfriendly environmentswhere one may have RFinterference, and accesspoint break-downs.


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8 ConclusionStandard WiFi-based positioning, which Ekahau implements, is the most effective method for deploying location-aware applications. The following provides a summary of the

corresponding advantages: Covers both indoor and outdoor areas accurately Fewer limitations as compared to

other positioning technologies.

Quick installation Install the system in days or weeks rather than months or years for proprietary networks, which allows users to begin generating a return on their investmentmuch quicker.

Cost effective scalability Start with a small deployment and easily enlarge thepositioning system as the number of access points increases.

No disruption to existing operations Installation rides over the existing Wi-Fiinfrastructure, resulting in no interruptions to operations during the installation phase.

Standards-based and not dependent on any single proprietary infrastructure Thewireless infrastructure is completely vendor agnostic.

Can track using soft tags (client software) or hardware (Wi-Fi tags) More cost effectivethan alternatives.

By relying on industry standard infrastructure, Ekahau is future-proof supporting 802.11A/B/G today and new 802.11 variants in the future.

A software-based solution is easier and more cost-effective to maintain over time.


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Copyright Ekahau Inc. 2000-2005

Contact InformationWest Coast

Ekahau, Inc.12930 Saratoga Avenue, Suite B-9Saratoga, CA 95070Tel: 1-866-4EKAHAUFax: 1-408-725 8405Email: [email protected]

East Coast

Ekahau, Inc.1851 Alexander Bell Drive Suite 150Reston VA 20191Tel: 1-866-4EKAHAU

Tel: 1 703 860 2850Fax:1 703 860 2028Email: [email protected]

Europe

Ekahau, Inc.Tammasaarenlaituri 300180 Helsinki, FinlandPhone: +358 20 743 5910Fax: +358 20 743 5919Email: [email protected]

Asia

Ekahau, Inc.Suite 1002Chuangs Tower 30-32 Connaught Road CentralHong KongTel: +852 3426 4770Fax: +852 3426 4061Email: [email protected]

www.ekahau.com [email protected] [email protected]

Copyright Ekahau, Inc. 2000-2004. All rights reserved. Ekahau, Ekahau Positioning Engine, Ekahau Manager, Ekahau SiteCalibration, Ekahau Rail Tracking and the Ekahau logo are trademarks or registered trademarks of Ekahau Corporation.Other product and company names mentioned herein may be trademarks or trade names of their respective owners.

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