Understanding the Wireless Medical Band and the Wireless Medical

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Understanding the Wireless Medical Band

and the Wireless Medical LAN

A Self-Study Activity

Understanding the Wireless Medical Band and Wireless Medical LAN

May 2001

TABLE OF CONTENTS

OVERVIEW.........................................................................................................................3

Objectives........................................................................................................................3

Intended Audience ..........................................................................................................3

INTRODUCTION ................................................................................................................3

CURRENT MEDICAL TELEMETRY SYSTEMS.................................................................4

WIRELESS MEDICAL TELEMETRY SERVICE .................................................................6

Strengths of the WMTS ...................................................................................................6

Limitations of WMTS .......................................................................................................7

THE INDUSTRIAL, SCIENTIFIC, AND MEDICAL (ISM) BAND..........................................7

Strengths of the ISM Band ..............................................................................................9

Limitations of the ISM Band...........................................................................................10

Spread Spectrum Modulation........................................................................................10

Frequency Hopping Spread Spectrum ..........................................................................11

Direct Sequence Spread Spectrum...............................................................................11

Advantages of using FHSS for Medical Monitoring .......................................................12

Potential Clinical Applications of ISM Band Wireless LANs ..........................................12

CHOOSING A NEW TELEMETRY SYSTEM....................................................................13

UNRESOLVED ISSUES ...................................................................................................14

2.4 GHz vs. 5 GHz ........................................................................................................14

Wireless LANs in Mixed Environments..........................................................................14

802.11 FHSS and DSSS..............................................................................................................................14Bluetooth .......................................................................................................................................................14

SUMMARY .......................................................................................................................15

GLOSSARY ......................................................................................................................15

REFERENCES .................................................................................................................18

REVIEW QUESTIONS......................................................................................................19

Answers to Review Questions.......................................................................................22


May 2001

OVERVIEW

More and more hospitals and healthcare facilities are using mobile monitoring andcomputing technologies based on wireless local area networks (WLANs) to improve thequality and reduce the cost of patient care. This study guide explains why medicaltelemetry systems currently in use are becoming obsolete, and describes alternativetechnologies that will make wireless communication more reliable. Limitations of systemsoperating as primary users in the Wireless Medical Telemetry Service (WMTS) banddesignated by the Federal Communications Commission (FCC) are discussed.Advantages of standards-based systems operating in the Industrial, Scientific, andMedical (ISM) band are outlined.

Objectives

After completing this educational program, the participant should be able to:

1. Explain why hospital telemetry systems need to move from their existing VHF & UHFbands to alternative bands, based on the Federal Communications Commission (FCC)ruling.

2. Differentiate between WMTS and ISM options.

3. Describe how information technology (IT) and biomedical engineering departments canwork together to find mutually satisfactory wireless telemetry solutions in the hospital.

4. Discuss unresolved issues for the future of wireless medical telemetry.

Intended Audience

This program is intended for use by IT professionals (including chief information officers orCIOs), hospital administrators, clinicians, and biomedical engineers involved in identifyingthe best wireless telemetry systems for their facilities.

INTRODUCTION

Recently released technologies now make it possible for hospital healthcare systemsaround the world to take advantage of the mobility, flexibility, and speed of mobilemonitoring and computing technologies based on WLANs to improve the quality andreduce the cost of patient care. Using integrated WLAN system solutions to support avariety of hospital-wide clinical and nonclinical patient-centered service applications allowshospitals to run more efficiently, effectively, and competitively.

State-of-the-art medical telemetry systems have a number of obvious advantages overhard-wired systems:


May 2001

• Using medical telemetry equipment to transmit and receive patient measurement data,such as heart rate, electrocardiogram (ECG), respiration rates, SpO2, and bloodpressure, permits patients wearing small monitors to ambulate throughout thehealthcare environment. The end result is greater mobility and increased comfort forthe patient.

• Displays on these new devices allow clinicians, for the first time, to view vital signsdata including waveforms at the patient location.

• Personnel can move freely from room to room, without having to return to a fixedstation to enter or check information. Hospital staff have real-time access to monitoringdata that are accurate and up-to-date at the bedside or other point of care, thusallowing them to make decisions and take actions accurately and efficiently.

• Because wireless LANs can be installed significantly faster and cheaper thantraditional telemetry systems, they allow unprecedented flexibility and responsivenessto organizational needs and changes. Wireless LAN-based, mobile computingtechnologies increase the reach of the institution's current information technology (IT)investment and infrastructure by bringing the power of computing to the point ofactivity.

In the past few years there has been a dramatic growth in the demand for telemetrysystems driven by rising patient acuity levels, as well as the need to ambulate patientsquickly after procedures. Along with excitement about the growing applications of medicaltelemetry systems has come legitimate concern about interference from otherradiofrequency (RF) applications. In February 1998, an incident occurred at BaylorMedical Center in Dallas, Texas, in which interference from a high-definition television(HDTV) test by a local television station knocked out 50% of a telemetry system on onefloor. This incident, along with other factors, highlighted the need for a medical telemetryband that would minimize the risk of such interference.

As the federal agency responsible for regulating the RF spectrum in the United States, theFederal Communications Commission (FCC) recently took action to address theseconcerns. On July 17, 2000, the FCC published a final rule that established a newWireless Medical Telemetry Service (WMTS).[1] This ruling and other recent FCC actionsthat affect frequencies currently used by medical telemetry systems will have far-reachingimplications for the operation of current and future medical telemetry systems. Let's take alook at how telemetry systems in your institution will be affected.

CURRENT MEDICAL TELEMETRY SYSTEMS

Each band of frequencies in the RF spectrum has primary users for whom the band wasset aside by the FCC. In some bands, these primary users share the band with secondaryusers who must not interfere with the licensed primary users. Before the FCC rule,unidirectional biomedical telemetry systems were implemented primarily as secondaryusers in the following RF bands:


May 2001

• VHF television channels 7 to 13 (174-216 MHz). To aid in the transition to digitaltelevision service, the FCC has assigned an additional HDTV channel for eachcurrently operating VHF TV station. Many HDTV stations are online and by May 1,2003 all stations will broadcast on both their existing signals, as well as the new HDTVsignal. (Monitoring the FCC web page for license allocations can assist the hospital inidentifying possible conflicts with HDTV stations that are initiating transmission in theirareas.) In addition, new low-power community TV station applications that have beenreceived by the FCC are now being approved. (Note, however, that the signalstransmitted by these "low-power" TV stations are 2500 times stronger than a medicaltelemetry signal.) New high-power and low-power primary users will consumespectrum that many hospitals are now using for medical telemetry, causing existingtelemetry systems in the VHF spectrum to become obsolete and unsupportable,including the costly antenna systems on which they operate.

• UHF television channels 14 to 46 (470-668 MHz). These channels suffer from thesame overcrowding as described above. Existing UHF systems will minimally need tobe re-tuned to operate on the WMTS. Unfortunately, mere re-tuning of analogsystems doesn’t allow the system to take advantage of bi-directional digitalcommunications that are now allowed in the WMTS. Existing UHF systems havelimited bandwidth and cannot support two-way communication. New designs for bothpatient-worn devices and the antenna system will be required to support two-waycommunication. Such changes will be costly to the hospital since existing transmittersand antenna infrastructures will need to be partially or entirely replaced.

• UHF Private Land Mobile Radio, or PLMR (450-470 MHz), such as that used bypolice, firemen, taxicabs, delivery trucks and the pervasive walkie-talkies. A freeze onnew applications for operation of high-power land mobile services in the 450-460 MHzband has been lifted and the freeze on applications for operation of these services inthe 460-470 MHz band will be lifted in 2003. The potential for interference of suchsystems with medical telemetry systems will make operation of medical telemetrysystems in these bands unfeasible.

Effective October 16, 2002, equipment approval may no longer be obtained for medicaltelemetry equipment operating in the UHF PLMR band, or in VHF or UHF televisionchannels, except for UHF channel 37 as allowed under the WMTS. Manufacturers maycontinue to support, and hospitals may continue to use, such equipment approved beforeOctober 16, 2002, but no new medical telemetry products will be approved for operation inthese bandwidths.

As HDTV and PLMR applications continue to crowd medical telemetry's traditionalspectrum of operation, the amount of telemetry dropout will potentially increase, makingtraditional biomedical telemetry bands very risky. Given that safer alternatives now exist,continuing to use a band that is recognized as risky could make the hospital liable fordamages if patient incidents should occur.[2] Fortunately, alternatives do exist, includingsystems that use either the Industrial, Scientific, and Medical (ISM) band or the WMTSfrequencies.


May 2001

WIRELESS MEDICAL TELEMETRY SERVICE

The main purpose of the FCC's July 2000 rule is to set aside the following three bands ofthe RF spectrum for primary use by biomedical applications:

608-614 MHz (UHF channel 37), which is not used for television stations and wasreserved for radio astronomy. Users of this band will be required to coordinate theiroperation with radio astronomy facilities, which will operate on a co-primary basis withmedical telemetry, and to design equipment to provide sufficient protection frominterference from adjacent televisions stations operating on channels 36 and 38. Toprevent users from monopolizing the 608-614 MHz band, wireless medical telemetrydevices utilizing broadband technologies such as spread spectrum must be capable ofoperating within one or more 1.5 MHz channels within this band (608.0-609.5, 609.5-611.0, 611.0-612.5, and/or 612.5-614.00 MHz), Note that the ability of spread spectrum toreject noise diminishes as the available bandwidth decreases.

1395-1400 MHz and 1429-1432 MHz are former government bands that were reallocatedfor non-government use. Military radar operations in those bands may continue at certainsites around the country for a number of years (until 2003 for 1395-1400 MHz and 2006for 1429-1432 MHz).

The FCC ruling states “physiological parameters and other patient-related information” areallowed. A WMTS station may transmit any biomedical emission appropriate forcommunications, except voice and video. Waveforms, such as ECGs, are not consideredvideo.

Prior to operation, health care providers who want to use the WMTS must register thefollowing information with a designated "frequency coordinator": specific frequencies orfrequency ranges; modulation scheme; effective radiated power; number of transmitters inuse, including manufacturer's name and model numbers; legal name of provider; location;and a point of contact. The frequency coordinator also must be notified of any changes inthese parameters.

The FCC will coordinate WMTS frequency allocations with the Canadian and Mexicangovernments, as appropriate; however, given the low power of this equipment, no inter-ference issues are anticipated at border areas.

Strengths of the WMTS

The WMTS provides medical telemetry with primary status in the three bands. For the firsttime, medical telemetry is not a secondary user and therefore should be relatively free ofintentional emissions from non-medical transmitters. Ultimately, the WMTS will allow two-way communication and higher data rates than are provided by current medical telemetry.


May 2001

Limitations of WMTS

Despite its advantages, WMTS has a number of limitations. For example:

The WMTS uses a restricted bandwidth with only 6 MHz of contiguous bandwidth and14 MHz total. The entire allocation is unlikely to be available in any individual market, andthe bandwidth provided is significantly less than the amount of RF spectrum currentlyavailable to medical telemetry on an unprotected basis.

Neither video nor voice transmission is permitted. Video is excluded because it couldoccupy a significant portion of the spectrum allocated to the WMTS. Voice transmission isexcluded because of concerns that allowing voice transmissions could encourage theequipment to be used as a form of wireless intercom.

Because the WMTS is broken up into three bands, a single facility will find it difficult to usethe entire spectrum. The options are either to use complicated and expensive trans-ceivers, or to bear the expense and trouble of installing multiple network transceivers tocover the various frequency bands.

Allocation of primary status precludes most intentional transmitters from creating inter-ference, but the possibility remains of "friendly" interference from conflicting or interferingsystems operating within the band. In addition, the FCC is not requiring television broad-casters to protect WMTS from adjacent band interference.

Because WMTS operation is authorized only within a health care facility, operation inambulances or other moving vehicles or in patients' homes is specifically excluded.

The FCC ruling forbids non-medical applications on the WMTS band, but does not preventvendors from implementing proprietary, incompatible, and potentially interfering systemswithin the band. It is up to hospitals and manufacturers to prevent interference amongincompatible devices from different vendors.

No standards of interoperability exist. Vendors will tend to develop their own propriet-ary communication infrastructure and protocols, making it challenging to coordinatemultiple vendors' equipment operating in the WMTS. For example, a monitor from onemanufacturer may not be able to communicate over the infrastructure installed by asecond manufacturer and could cause interference and dropouts. Using separate systemsfor each vendor will increase cost, system complexity and RF interference.

THE INDUSTRIAL, SCIENTIFIC, AND MEDICAL (ISM) BAND

The FCC ruling does not require that all medical devices use WMTS bands. An alternativespectrum for medical telemetry use is the 2.4 GHz Industrial, Scientific, and Medical (ISM)band. In fact, the FCC ruling specifically states that it will continue to allow medicaltelemetry equipment to operate in the ISM band.


May 2001

The 2.4 GHz ISM band is available worldwide on a secondary use basis as long asspread spectrum modulation techniques are used at relatively modest power levels. Theinternational standards bodies have identified this band for wireless local area networkapplications. The Institute of Electrical and Electronics Engineers (IEEE) has developedan open standard for two-way wireless communications (IEEE 802.11)[3]. Ratified in June1997, the original IEEE 802.11 specification is the wireless extension of the 802.3communications standard for hard-wired LANs that use physical cable and the Ethernetprotocol. Anyone who has worked in a networked office and used a file server is familiarwith 802.3-compliant technology, which allows hundreds of vendors to offer networkinterface cards, hubs and other products that all cooperate with each other withoutproblems due to interference.

Implementation of the IEEE 802.11 protocol is broken up into several layers:

• The physical layer describes how fast the data that go into and out of the computer aretransmitted and the method of communication (e.g., radio, infrared, or wired). IEEE802.11 defines three physical layers: frequency hopping spread spectrum (FHSS) inthe 2.4 GHz band, direct sequencing spread spectrum (DSSS) in 2.4 GHz andinfrared.

• Above the physical layer are the TCP/IP, MAC (medial access control), and link layers,which deal with things such as how many bytes to send at a time, how to determine ifa transmission fails, what to do if a transmission fails, and when to transmit. Theseprocesses are invisible to the user, but they affect the data rate, which the user cansee. The MAC layer is the same for all three 802.11 physical layers. The physical andMAC layers work together to determine if the channel is clear.

The 802.11 MAC is very similar to 802.3 (Ethernet standard) in that it is designed tosupport many users whose transmissions might experience interference without losingany data. One of the pieces of the Ethernet that supports this is called CSMA/CA (CarrierSense Multiple Access with Collision Avoidance). CSMA/CA works by having the senderlisten to the airways before attempting a transmission. The sender defers transmissionuntil later if the communication channel is busy. After transmission, the sender waits foran ACK (acknowledge) message from the recipient. If data are not received or arereceived with an invalid CRC (cyclic redundancy check), then the transmitter will notreceive an ACK from the receiver and automatically re-transmits the data.

Another feature of the 802.11 MAC layer is packet fragmentation. Packet fragmentationallows large packets to be broken into smaller units when sent over the air. This is usefulin very congested environments or when interference is a factor, since smaller packetshave a lower probability of being corrupted. This technique reduces the needs for re-transmission in many cases and thus improves overall wireless network performance. TheMAC layer is responsible for reassembling fragments received, rendering the processtransparent to higher-level protocols.


May 2001

Strengths of the ISM Band

Medical telemetry systems that utilize the ISM band have a number of advantages overWMTS:

• The ISM band occupies 83 MHz of bandwidth, including guard bands to protectagainst adjacent-channel interference. This is 14 times more than the 6 MHz currentlyoccupied by the WMTS, and WMTS has no guard bands to protect againstinterference from TV channels 36 and 38.

• Unlike the WMTS, the ISM band allows useful voice and/or video transmissions.

• 802.11-compliant medical telemetry devices can communicate with other wireless orhard-wired devices using bi-directional access points (APs). Thus, a single, open,802.11-compliant wireless network infrastructure can support a wide range of mobilecomputing and communications devices. Such devices may include ambulatorybiomedical telemetry and portable monitors, wireless laptop and desktop personalcomputers (PCs), wireless LAN pagers, wireless PDAs (personal digital assistantssuch as Palm Pilots™), and Internet protocol (IP) telephones. In addition, the wirelessmedical LAN can link to the institution's 802.3-compliant hard-wired network. Thelimitation on the number of connected devices is determined by the throughput of theaccess point infrastructure. Each access point is capable of supporting a givennumber of devices. Adding access points is simple, inexpensive, and allows moredevices to be supported as needs grow.

• The ISM band is available and compatible worldwide for wireless applications, andcompetition drives costs down while performance increases. Conformance to IEEE802.11 ensures that devices from different vendors can coexist on the same network.This allows the wireless network infrastructure to be utilized by multiple applicationsfrom multiple vendors.

• The propagation characteristics of the 2.4 GHz frequency make it ideal for in-buildinguse where structures attenuate the signal between floors. Low power, spread-spectrum technology, and attenuation characteristics within building structures allowreuse of the spectrum within large facilities.

• Conformance to 802.11 allows devices to be transportable between facilities with noneed to retune the device. Monitors are not tied to a particular receiver; rather, themonitor can associate with whichever AP it determines will provide the best commun-ication channel.

• Although spectrum management is necessary, no frequency management is required,even for large, multi-hospital applications.

• Widely used SNMP network management tools can be used to monitor traffic on thenetwork to determine loading and utilization factors and to warn when wireless networkloading exceeds a preset threshold.


May 2001

• Scalability permits flexible, cost-effective solutions to any wireless LAN needs, whetherthe installation is in a single laboratory, a multi-floor building, or a healthcare campuswith thousands of wireless devices.

• The IEEE 802.11 standard specifies a security mechanism that provides secure point-to-point access and communication. The wired equivalency privacy (WEP) algorithminhibits other stations from decrypting data sent over the wireless LAN. Under theWEP algorithm, both the access point and mobile unit share an encryption/decryptionkey. If an AP is set to only allow WEP communication (shared key authentication),then only mobile units (MUs) with the same key settings can associate with that AP.

• Unlike traditional telemetry, patient monitors are not tied to a particular receiver. If oneAP goes down or experiences immense amounts of interference, patient monitorsautomatically roam to a different AP and no clinical data are lost.

• Since all unlicensed transmitters in this band are required to use low-power spreadspectrum communications, there are no uncontrolled devices outside the hospital thatare of concern.

Limitations of the ISM Band

Networks that operate in the ISM band require careful site surveys before installation andwhenever new applications are added, in order to optimize the placement of APs so thatthe network has adequate capacity to serve the intended applications. Long-rangeplanning in anticipation of new applications, followed by good wireless network design, willensure that RF resources are reliable and dependable. Limiting or controlling patient andvisitor-owned wireless devices, in much the same way they are controlled today, willfurther ensure network reliability.

Other radiators in the ISM band such as other mobile devices, some wireless telephonenetworks, and microwave ovens can cause interference (but not necessarily a telemetrydropout, since 802.11 automatically re-sends the data). However, a proper site surveyidentifies these sources and places APs at locations to ensure continuous RF coverage.Also, with an 80 MHz band, spread spectrum modulation significantly enhances thedevice’s ability to successfully transmit in the presence of interference.

Spread Spectrum Modulation

Developed at the end of World War II, spread spectrum modulation "spreads" the RFsignal over a range of frequencies, which enhances the ability of the RF communicationsystem to reject interfering noise and provides security against eavesdropping. The IEEE802.11 Standard specifies two types of spread-spectrum modulation: Direct SequenceSpread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) at 1 and 2Mbps. IEEE 802.11b extended the DSSS definition to include 5.5 and 11 Mbpstransmission rates. The type of spread spectrum technology (FHSS or DSSS) utilized bya wireless LAN has implications for its reliability in medical telemetry.


May 2001

Frequency Hopping Spread Spectrum

FHSS accomplishes "spreading" by moving the center frequency of the broadcast. Todecode FHSS, the receiver must "hop" from frequency to frequency at the same time asthe transmitter.

The carrier frequency of the transmitter changes (or hops) in accordance with a pseudo-random hop pattern. The hop sequence dictates the frequency order used by the AP andits associated MUs. Stations in a cell using FHSS techniques hop or change the carrierfrequency at synchronized intervals. The AP transmits synchronization beacons to theMUs, which allows them to synchronize their hopping times to the AP’s. Each hop is atleast 6 MHz away from the previous frequency and has a 1 MHz bandwidth.

In the United States, there are 79 channels spaced 1 MHz apart. 802.11 devices hopthrough these channels in a pseudo-random order as defined by IEEE 802.11, whichallows up to 15 APs to be co-located without significant interference problems. Thisallows the wireless medical LAN designer to scale the system for higher net data rates.

Direct Sequence Spread Spectrum

DSSS multiplies the signal by a spreading function (an exclusive OR operation in thedigital world) and keeps the center frequency of the broadcast constant. For 1 and 2 MbpsDSSS, the data stream is exclusive OR'd with the Barker code to generate a series ofdata objects called chips. Each bit is "encoded" by the 11-bit Barker code or, in otherwords, each group of 11 chips encodes one bit of data. Since the chipping sequence has11 times the bandwidth of the original data, the resulting product has a higher bandwidththan the original data, i.e., it has been spread in frequency. The receiver recovers thedata using this same encoding pattern. For DSSS, IEEE 802.11 (and 802.11b) specify 14overlapping channels of 22-MHz bandwidth and 5-MHz spacing between centerfrequencies. In the United States, channels 1–11 are available, so there exist 3 non-overlapping channels (1, 6 and 11). The number of chips per bit of data is referred to asthe spreading ratio or the processing gain, and the FCC requires a minimum processinggain of 10. The higher the processing gain, the more immune the system is tointerference. To increase the processing gain, the bandwidth of the transmitted signalmust be increased or the data rate must be decreased. This means that the datatransmission rate can be traded off for noise immunity.

IEEE 802.11b defines the physical layer for the 11 Mbps DSSS communication and usesCCK (Complementary Code Keying) which uses an 8-bit code. The reason that CCKachieves a higher data rate with the same 22 MHz channel is that CCK’s 8-bit code wordcan represent 6 bits of data (as opposed to the single data bit represented by the Barkercode). The algorithm is more complex than the 1 and 2 Mbps DSSS algorithm and isbeyond the scope of this paper.


May 2001

Advantages of using FHSS for Medical Monitoring

Most implementations of wireless LANs on the market today use spread spectrum. FHSShas the following advantages for this purpose:

• Because vital signs monitors each require a relatively small bandwidth and manyFHSS systems can be co-located, FHSS implementations can be easily scaled tosupport more patient monitors than can a DSSS implementation.

• Potential for interference from other radio signals is less for FHSS than for DSSS. Theprobability of an interference source blocking all 79 channels is extremely low and theFHSS algorithm allows communication to continue even when a significant number ofthe channels are blocked. DSSS has only 3 non-overlapping channels.

• With DSSS, the time duration of each chip is quite short. Because of this, multipathsignals (those that bounce off reflective surfaces in route to the receiver) are moreproblematic than with FHSS. Fewer problems with interference means greaterreliability for FHSS systems.

• The advertised data rate for DSSS is only supported for very short distances. BothFHSS and DSSS use dynamic rate shifting, allowing data rates to be automaticallyadjusted to compensate for the changing nature of the radio channel or fortransmission to more distant mobile units. The lower the data rate, the better thesignal-to-noise ratio. Only about 20% of an 11 Mbps DSSS AP’s coverage area has11 Mbps coverage, and this number decreases in the presence of noise and/or multi-path propagation. This number decreases further if the MU is moving, or if there aremulti-path propagation effects.

Potential Clinical Applications of ISM Band Wireless LANs

Examples of potential clinical applications of wireless LAN technology utilizing the ISMband include[4]:

• Multi-parameter ambulatory medical telemetry

• Clinical documentation at bedside, with interactive range checking

• Immediate access to the hospital information system at the point of care

• Improved efficiency for respiratory care, physical therapy and other mobileprofessionals

• Bedside admitting, discharge and transfer

• Medication administration process improvements, including bedside drug useevaluation

• Laboratory and phlebotomy sampling control, through barcode scanning of thebiological containers and patient identification bands


May 2001

• Point-of-care documentation of diagnoses, interventions, and outcomes for ambulatorycare providers

CHOOSING A NEW TELEMETRY SYSTEM

To help you decide which medical telemetry system is right for your hospital, Table 1compares the features of systems operating in traditional bandwidths, WMTS frequencies,and the ISM band.

Table 1. Wireless Communications Options for Medical Telemetry

Characteristic Current Telemetry WMTS ISM

Frequencies VHF TV, UHF TV,UHF PLMR

UHF Channel 37 (608-614MHz);1395-1400 MHz and1429-1432 MHz

2.4-2.4835 GHz

Protection None; medical is asecondary user

Legal protection fromintentional non-medicaltransmissions. Not pro-tected from adjacentchannel interference nor“friendly fire” fromcompeting WMTS productvendors.

Unlicensed users usespread spectrum toreduce interference andincrease RFI immunity

Usable spectrum Adequate in ruralsettings,overcrowded in largeurban areas

Up to 14 MHz available, notall frequencies are availablein all areas.

83.5 MHz; shared by allusers in LAN

World wide use? No No YesSpectrum utilization Dedicated, fixed, 25-

kHz channelsNo restrictions within four1.5-MHz subchannels

Spread spectrumrequired

Two-waycommunication

No Allowed, but not used bymost WMTS systems.

Yes

Supportsnonmedical IT uses?

No No Yes

Standards-basedtransmissionetiquette?

No No Yes, IEEE 802.11

Network scalability Low Low/Moderate HighUsable in MD office? Yes, but improbable No YesLeverages hospitalIT infrastructure?

No; requires separateisolated antennasystem

No; requires isolatedantenna system; two-waycomms different fromcurrent telemetry

Yes; with appropriatenetwork design

Infrastructure cost High High/Moderate LowSupports voice andPDAs?

No No; specifically forbiddenby FCC rule

Yes

Management tools? No No standard networkmanagement toolsavailable.

Yes, management toolsavailable that use SNMPnetwork managementprotocol.


May 2001

UNRESOLVED ISSUES

A number of issues regarding wireless medical telemetry remain unresolved in the currentenvironment.

2.4 GHz vs. 5 GHz

In September 1999, the IEEE adopted 802.11a, which defines a high-speed (up to 54Mbps) standard in the 5 GHz ISM band that uses orthogonal frequency divisionmultiplexing (OFDM) technology. Some 802.11a radio modules were available in samplequantities in early 2001, but the technology is not yet available for deployment of WLANs.OFDM is superior to DSSS in term of resistance to multipath propagation effects, but onecan expect shorter range due to the higher frequency and higher data rate.

Wireless LANs in Mixed Environments

802.11 FHSS and DSSS

It is possible for FHSS and DSSS systems to coexist in a given facility. In fact, the IEEEstandards bodies anticipated this when the standards were developed. Careful RF infra-structure design, e.g., avoiding co-locating APs with different communication protocols, isrequired to minimize interference between the spread-spectrum technologies if they needto coexist in the same geographic area. Generally, a separation of 2 meters or moremakes interference issues inconsequential.[5]

The IEEE and the computer/communication industry are studying and developing ways tofurther enhance reliability and reduce the chance of interference of communication inmixed environments.

Facilities need to make a strategic deployment plan for WLANs that considers the applica-tions the WLAN is to support, and the placement of different WLAN devices with respectto each other.

Bluetooth

Bluetooth is a low-bandwidth, short-range wireless networking technology designedprimarily to replace cables for communication between small personal computing/communication devices, such as desktop computers, laptops, PDAs, and cell phones.This network is often called a Personal Area Network (PAN) or piconet., Each PAN islimited to 8 devices, usually with a maximum range of 30 feet. Piconets can be linkedwhen one device is a member of 2 piconets; however this type of networking has a largeoverhead cost and does not offer an adequate scale for enterprise installations. As with802.11 devices, Bluetooth devices have sleep modes and only transmit when there is aneed, so most of the time the transmitter is inactive.


May 2001

Bluetooth technology transmits both voice and data on the 2.4 GHz ISM band. It usesFHSS technology (1600 hops/second) to increase the reliability of the communicationchannel. The IEEE 802.15 working group for PANs has announced that it will adoptBluetooth as the IEEE 802.15 standard. Bluetooth and IEEE 802.11-based wireless LANsare complementary, rather than competing, technologies. Bluetooth is not primarilyintended for use in networking. Its low data rate and other limitations will probably prohibitits use for most networking purposes except home networking and small, ad hoc wirelessnetworks.[6]

SUMMARY

To avoid wasting money by prematurely replacing wireless infrastructure and telemetrysystems with newer systems that will quickly become obsolete, or upgrading to newersystems that are already obsolete (e.g. unidirectional systems), hospitals must work out along-term (i.e., 10-year) plan. Biomedical engineering and IT departments must worktogether to define, purchase, and maintain the most appropriate and cost-effectivewireless medical telemetry system for their facility. One approach is to define the facility's"musts" and "wants" with regard to medical telemetry, identify several possible vendors,make site visits to evaluate their systems in action, and define the roles of bothdepartments during both installation and operation. Throughout the whole process,communication is key!

Each wireless technology has certain advantages and limitations. The benefits and pitfallsof various options must be weighed against installation and performance requirements. Inpatient monitoring applications, the most important feature must be reliability: patientcontact must be maintained at all times. Bandwidth, flexibility, expandability, ease ofimplementation, and cost are important, but secondary considerations. With these criteriain mind, FHSS in the ISM band is an ideal candidate for wireless connectivity. Using thisband, a single open network can reliably support fixed, ambulatory, transport, andportable patient monitors, along with a variety of caregiver tools, such as IP telephones,PDAs, and laptop and desktop PCs.

GLOSSARY

AP (access point): A MAC-layer bridge that may be thought of as a wireless hub; manydevices can connect or "associate" with an AP, and the AP allows one device at a time toeither communicate with another device associated to the AP or to the hard-wired LAN.

Channel: A section of the radio spectrum, such as a television channel.

Chip: One bit of a sequence of bits used to increase the bandwidth of a signal for directsequence spread spectrum. Also, the process of applying a chipping sequence.

Chipping sequence: A sequence of bits (11 for 1 and 2 Mbps DSSS) used to encode asingle data bit. Used in Direct Sequence Spread Spectrum.


May 2001

DSSS (Direct Sequence Spread Spectrum): A modulation technique where a high-frequency chipping sequence is XOR’d with each bit of data to produce a wide-bandstream of encoded data that is then used to modulate an RF carrier. In 802.11 and802.11b implementations, direct sequence signaling technique divides the 2.4 GHz bandinto 14 twenty-two MHz-wide channels. The channel separation is 5 MHz, so most of thechannels overlap. Exclusive use of channels 1, 6, and 11 precludes frequency overlap.Data are sent across one of these 22 MHz channels without hopping to other channels.

FHSS (Frequency Hopping Spread Spectrum): A modulation technique that spreads thesignal by transmitting a short, narrowband burst on one frequency, then hopping to adifferent frequency for another short burst, and so forth.

GHz (gigahertz): A unit of frequency; 1 GHz = 1,000,000,000 cycles per second.

ISM Band: A set of frequency bands including 2.400 – 2.483 GHz set aside for industrial,scientific, and medical use. The 2.400 – 2.483 GHz band is available for use in almostevery country of the world.

IEEE (The Institute of Electrical and Electronics Engineers): As one of its functions, theIEEE acts as a standards body to define uniform ways for electronics and computers tocommunicate. The IEEE developed the standard (IEEE 802.3) that defines howcomputers communicate over the Ethernet.

IEEE 802.3: The Ethernet – the worldwide standard for computer networking.

IEEE 802.11: A standard for wireless networking in the 2.4 GHz ISM band – the wirelessextension of the Ethernet. IEEE 802.11 defines the PHY and MAC layers of thecommunication standard; all other aspects of wireless communication under 802.11 areidentical to the Ethernet. Three physical layers are defined: FHSS, DSSS, and Infrared.The FHSS and DSSS PHY layers have transmission rates of 1 or 2 Mbps.

IEEE 802.11a: A standard for wireless networking in the 5 GHz ISM band with data ratesof up to 54 Mbps.

IEEE 802.11b: A standard for wireless networking in the ISM band using DSSS at 5.5and 11 Mbps.

IEEE 802.15: A standard for wireless networking in the 2.4 GHz ISM band. IEEE 802.15and the Bluetooth standard are synonymous.

MAC Address (Media Access Control address or IEEE address): A unique hardwareencoded address that is available for all Ethernet devices to help determine the devicethat is sending or receiving data.

MHz (megahertz): A unit of frequency; 1 MHz = 1,000,000 cycles per second.


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Multi-path effect: Phenomenon that occurs when radio signal reach a destination viavarious paths, which can occur because of reflections. Radio waves that travel differentpaths and different distances arrive at the source at different times. They can addconstructively (e.g. when both paths result in the waves arriving in phase so the positivepeaks line up, resulting in a larger signal) or destructively (e.g. when the paths result inthe waves arriving 180 degrees out of phase so the positive and negative peaks align,resulting in a smaller signal).

PAN: Personal area network. A small network, often ad hoc, consisting of devices thatconnect to each other, but not to a larger network.

Piconet: Term used to describe a Bluetooth PAN.

PLMR (Private Land Mobile Radio): A broadcast band for radios that operate in the 450 –470 MHz band with 6.25 kHz channel spacing. Some traditional telemetry systemsoperate in this band. Previously, PLMR operated on 25 kHz channel spacing. With therefarming of this band to 6.25 kHz, there could be “interference to medical telemetryequipment, possibly making it to be unusable at times.”[1]

Receiver: A device that receives signals sent by a transmitter.

RF (radio frequency): The range of frequencies, between about 3 kHz and 300 GHz, overwhich electromagnetic radiation is used in radio broadcasts. It is subdivided into multiplebands, each whose maximum frequency is 10 times its lowest frequency: very lowfrequency (VLF, 3 kHz – 30 kHz), low frequency (LF, 30 kHz – 300 kHz), mediumfrequency (MF, 300 kHz – 3 MHz), high frequency (HF, 3 MHz – 30 MHz), very highfrequency (VHF, 30 MHz – 300 MHz), ultra high frequency (UHF, 300 MHz – 3 GHz),super high frequency (SHF, 3 GHz – 30 GHz), and extremely high frequency (EHF, 30GHz – 300 GHz).

Spread spectrum: A radio frequency modulation technique where the radio energy isspread over a wider bandwidth than required to transmit the data. The resultingtransmission is more resistant to interference and more difficult to intercept than is anarrowband transmission.

Telemetry: Transmitting measurements of physical phenomena (e.g., patient monitoringdata) to a distant recorder or observer.

Transceiver: A 2-way (bi-directional) device that can both transmit and receive signals.Medical telemetry is moving rapidly from using transmitter/receiver pairs to usingtransceivers.

Transmitter: A device that sends information to a receiver in one direction.

UHF (ultra high frequency): A radio frequency band in the range of 300 MHz to 3 GHz.

VHF (very high frequency): A radio frequency band in the range of 30 MHz to 300 MHz.


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WMTS (Wireless Medical Telemetry Service): The frequency bands 608-614, 1395-1400,and 1429-1432 MHz designated by the FCC for the transmission of physiologicalparameters and other patient-related information via radiated bi- or uni-directionalelectromagnetic signals.

WLAN (Wireless Local Area Network): Network that is connected by radio instead ofwires.

REFERENCES

[1.] Federal Communications Commission. Wireless Medical Telemetry Service. FederalRegister. July 17, 2000; 65(137): 43995-44010.

[2.] New Changes in FCC Rules Affects Everyone—Exploring Your Options. MSP IndustryAlert. Lincroft, NJ: Medical Strategic Planning; 2000: 1-12.

[3.] Available by subscription at http://standards.ieee.org. Accessed on January 4, 2001.

[4.] The Wireless Hospital: Extending the Reach of Your Information System Directly tothe Point of Activity. White Paper No. CJ0498. Holtsville, NY: Symbol Technologies Inc.;April 1998.

[5.] Bluetooth Central. Bluetooth FAQ. Available athttp://www.bluetoothcentral.com/faq_plain.html. Accessed on January 3, 2001.Shoemake, Matthew B., Wi-Fi (IEEE 802.11b) and Bluetooth Coexistence Issues andSolutions for the 2.4 GHz ISM Band, Texas Instruments White Paper, February 2001,Version 1.0.

[6.] Merritt, Rick, EE TIMES, Conflicts Between Bluetooth and Wireless LANs CalledMinor www.eetimes.com/story/OEG20010220S0040


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REVIEW QUESTIONS

Multiple choice. Please choose the word or phrase that best completes the followingstatements.

1. The federal agency responsible for regulating the radio frequency spectrum inthe United States is:

A. FTC.

B. NASA.

C. EPA.

D. FCC.

2. The VHF and UHF bands traditionally used by medical telemetry systems arebecoming risky for hospitals because of the potential for:

A. Increased interference from TV and PLMR signals.

B. Health effects of electromagnetic radiation.

C. Electrostatic shock.

D. Power failure.

3. WMTS will operate on UHF channel 37 on a co-primary basis with:

A. HDTV stations.

B. PLMR.

C. Radio astronomy.

D. Military radar.

4. A WMTS station may transmit:

A. Voice.

B. Patient Data.

C. Video.

D. All of the above.


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5. IEEE 802.11 is an international standard for:

A. Wide area networks.

B. Hard-wired local area networks.

C. Wireless local area networks.

D. Personal area networks.

6. Wireless devices that operate in the ISM band:

A. Are transportable between facilities without retuning.

B. Can co-exist and can be compatible, even if manufactured by different vendors.

C. Are bi-directional.


7. FHSS, DSSS and Bluetooth systems can co-exist with little interference as longas the devices are

A. Out of RF range of each other.

B. Spaced 2 feet apart

C. Spaced 2 meters apart

D. None of the above, spacing is not important

8. Medical telemetry has primary user status in:

A. Designated WMTS frequencies.

B. The ISM band.

C. VHF TV channels 7 to 13.



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9. Voice transmission and PDAs are supported by:

A. Conventional medical telemetry systems.

B. WLANs operating in the WMTS.

C. WLANs operating in the ISM band.


10. Bluetooth-based wireless technology can be expected to compete with 802.11-compliant LANs.

A. True.

B. False.


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Answers to Review Questions

1. D

2. A

3. C

4. B

5. C

6. D

7. C

8. A

9. C

10. B

Understanding the Wireless Medical Band and the Wireless Medical

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