Wireless Data Communications
`
`KAVEH PAHLAVAN, SENIOR MEMBER, IEEE, AND ALLEN H. LEVESQUE, SENIOR MEMBER, IEEE
`
`Invited Paper
`
`Wireless data services and systems represent a rapidly growing
`and increasingly important segment of the communications indus(cid:173)
`try./n this paper we present an overview of this field, emphasizing
`three major elements: 1) technologies utilized in existing and
`currently planned wireless data services, 2) issues related to the
`performance of these sytems, and 3) discernible trends in the con(cid:173)
`tinuing development of wireless data systems. While the wireless
`data industry is becoming increasingly diverse and fragmented,
`one can identify a few mainstreams which relate directly to users'
`requirement for data services. On one hand, there are requirements
`for relatively low-speed data services supporting mobile users over
`wide geographical areas, as provided by mobile data networks. On
`the other hand, there are requirements for high-speed data services
`in local areas, as provided by wireless LAN' s. The system-level
`issues are somewhat different for these two categories of services,
`and this has led to different technology choices in the two domains,
`which we discuss in the paper.
`
`I.
`
`INTRODUCTION
`We are all being exposed to a revolution in communica(cid:173)
`tions, a revolution that is taking us from a world where
`telephone subscribers were constrained to communicate
`over fixed telephone lines, to one where a tetherless and
`mobile communications environment has become a real(cid:173)
`ity. Wireless communications systems, of which cordless
`phones, pagers, and cellular telephones are some of the most
`familiar examples, have experienced enormous growth over
`the last decade. Recent market data indicate that there are
`currently about 13 million cellular subscribers in the United
`States, which compares with approximately 4.4 million in
`June 1990 and 90000 subscribers in 1984. It is clear that
`the convenience and efficiency afforded by wireless access
`to communications networks is fueling enormous growth
`in this segment of the communications industry, a growth
`which is likely to continue for many years. This growth
`has to date primarily served the ever-growing demands for
`voice service and message paging services. However, the
`increasing reliance on data communications in the business
`\
`Manuscript received October 15, 1993; revised May 13, 1994.
`K. Pahlavan is with Worcester Polytechnic Institute, Worcester, MA
`01609 USA.
`A. H. Levesque is with GTE Laboratories Inc., Waltham, MA 02254
`USA.
`IEEE Log Number 9403227.
`
`world provides the basis for a similar growth in demand
`for various forms of wireless data service. Just as the pager
`and the cellular telephone have become standard items in
`the business traveler's attache case, lap-top and notebook
`computers are becoming increasingly familiar elements
`of the "mobile office." The rapid proliferation of these
`small portable computers, spurred by miniaturization and
`improvements in wireless transmission methods, is certain
`to create an enormous demand for wireless data services.
`In the marketplace one already finds portable computers
`which can be connected directly to a cellular telephone.
`Some manufacturers have introduced modems with error(cid:173)
`correction capability implemented on a Personal Computer
`Memory Card International Association (PCMCIA) card,
`a small disk which is inserted into a PCMCIA slot on
`a notebook computer and also connected to the cellu(cid:173)
`lar telephone. These are examples of ways of providing
`data transmission over a network designed for wireless
`analog voice service, in effect the wireless equivalent of
`connecting a standard V -series data modem to the wired
`public switched telephone network (PSTN). However, just
`as terrestrial digital data networks have evolved to provide
`more efficient data communication than is provided by
`the use of modems, dedicated wireless data services and
`networks, including wireless LAN's, are being developed as
`well. It is the development of these wireless data networks
`which is the subject of this paper.
`In a digital network voice and data services have different
`and sometimes contradictory requirements. In order to
`understand the differences among service requirements, one
`must first examine the services from the user's point of
`view. At the outset, it is important to understand that
`users' expectations are based upon their experience with
`services provided in the public switched telephone network.
`Although digitized voice, imagery, and data are all "binary
`digits," there are different requirements for transmission of
`each service in a digital network. For example, because
`of the user's expectation of telephone-quality voice in the
`public wired network, voice service in a wireless network
`environment must be designed with careful attention to
`minimizing time delays. Delays in excess of 100 ms will be
`noticeable and annoying to the listener. In contrast, delay in
`
`PROCEEDINGS OF THE IEEE, VOL. 82, NO.9, SEPTEMBER 1994
`
`1398
`
`0018-9219/94$04.00 © 1994 IEEE
`
`Petitioners' Ex. 1007 - Page 1
`
`

`
`a data network, while not desirable, is generally acceptable
`to the data user. Packetized voice can tolerate packet loss
`rates of the order of w- 2, or bit-error rates of the same
`order, without a noticeable degradation in service quality.
`An error rate of w- 5 is ordinarily acceptable for uncoded
`data, but any loss of data packets is totally unacceptable.
`The lengths of telephone conversations are relatively uni(cid:173)
`form (approximately 3-20 min) and a few seconds of setup
`time is therefore acceptable. Each telephone conversation
`session generates megabytes of digitized information. On
`the other hand, a communication session for a data service
`can vary over a wide range from a short electronic mail
`message carrying only a few bytes of information up to a
`long file transfer such as the text of a book, which may be
`as large as several megabytes. On the average, the volume
`of information involved in a data communication session is
`much smaller than that of a digitized-voice communication
`session. The uncertainty in the amount of the information
`and the low average length of data communication sessions
`make long setup times undesirable.
`The difference between the requirements for voice and
`data packets have resulted in several major differences in
`the architecture of voice and data networks. The backbone
`of the voice networks is a circuit switch hierarchy while the
`data networks are implemented with packet swiches. The
`data packets access the network with a random wireless
`access technique while the access for the voice packets
`is assigned to users. The packet data networks generally
`use a retransmission strategy to ensure the accuracy of the
`transmission while voice packets are transmitted only one
`time. Packet data networks strive for higher data rates and
`as the data rate increases new applications evolve. The
`only application for the voice networks is transmission
`of the real-time voice and as the technology evolves the
`encoding rate is actually decreased. With all these different
`requirements the trend in wireline networks is to integrate
`because with one set of wiring and switching there are
`savings in the cost of the network. In the wireless arena
`this constraint does not hold and separation of frequency
`bands would be a reasonable alternative. The only time
`that we may intend to mix voice and data is to use the idle
`time among the voice spurts for data applications.
`While it is true that the major thrust of telecommunica(cid:173)
`tions is toward multimedia services, the existing infrastruc(cid:173)
`ture of communications networks is still very fragmented.
`Today we have wired PBX's for local voice communi(cid:173)
`cations within office complexes, the public switched tele(cid:173)
`phone network for wide-area voice communications, wired
`local-area networks for high-speed local data communica(cid:173)
`tions, packet-switched networks, voice-band modems for
`low-speed wide-area data communications, and a separate
`cable network for wide-area video distribution. The process
`of setting standards for various areas of communications
`has been similarly fragmented. The standards for voice
`transmission technology have evolved within the operating
`companies, while the standards for voice-band data modems
`have been developed by the CCI1T, and the standards for
`local-area networks by IEEE 802 and ISO. This separation
`
`has come about because each individual network was
`designed to meet the requirements of a particular type of
`service, be it voice, data, or imagery/video.
`The same pattern of separation exists in the wireless
`information industry as well. The new-generation wireless
`information networks are evolving around either voice(cid:173)
`oriented applications such as digital cellular, cordless tele(cid:173)
`phone, and wireless PBX; or around data-oriented networks
`such as wireless LAN's and mobile data networks. While
`it is true that all the major standards initiatives are focused
`on integration of services, one still sees a separation of
`the industrial communities that participate in the various
`standards bodies. That is, we see GSM, North American
`Digital Cellular, DECT, and other initiatives supported
`primarily by representatives of the voice-communications
`industry, while IEEE 802.11, WINForum, and HIPERLAN
`are supported primarily by those with interest in data
`communications.
`Although future personal communications devices may
`be designed as integrated units for personal computing as
`well as personal voice and data communications, the wire(cid:173)
`less access supporting different applications may use dif(cid:173)
`ferent frequency bands or even different transmission tech(cid:173)
`nologies. A personal communications service (PCS) may
`use wideband Code-Division Multiple Access (CDMA) in a
`shared spread-spectrum band. A digital cellular service may
`use Time-Division Multiple Access (TDMA) or CDMA in
`another band. Low-speed data may be transmitted in the
`gaps between bursts of voice activity. High-speed local(cid:173)
`area data may be transmitted in another shared wideband
`channel. At the same time, the various services may all
`be integrated in a metropolitan-area or wide-area net(cid:173)
`work structured with Asynchrnous Transfer Mode (ATM)
`switches.
`The future direction of this industry depends upon
`technological developments and a maturity in the spectrum(cid:173)
`administration organizations, who must understand the
`growing massive demand for bandwidth and must, in tum,
`develop strategies allowing a fair sharing of increasingly
`scarce bandwidth. Just as governmental agencies restrict
`abusive consumption of other limited natural resources
`such as water, appropriate agencies will have to protect
`the spectral resources needed for wireless information
`networks. After all, the electromagnetic spectrum is a
`modem natural resource supporting the ever-widening array
`of telecommunications services which are becoming an
`increasingly important part of the fabric of our personal
`and professional lives.
`This paper provides a summary of the rapidly expanding
`field of wireless data services, systems, and technologies.
`Section II provides an overview of the wireless data market,
`the user perspective of wireless data services, and the fre(cid:173)
`quency admistration issues that have an important influence
`on the evolution of new systems. Section III provides a brief
`description of mobile data networks and wireless local-area
`networks. Section IV reviews the major technical issues that
`bear upon the design of wireless data networks. Section V
`provides concluding remarks.
`
`PAHLAVAN AND LEVESQUE: WIRELESS DATA COMMUNICATIONS
`
`1399
`
`Petitioners' Ex. 1007 - Page 2
`
`

`
`II. OVERVIEW OF WIRELESS NETWORKS
`
`A. Evolving Wireless Information Networks
`The mid-1980's saw major initiatives in all sectors of the
`wireless information industry. To increase the capacity of
`cellular telephone systems, which have reached their techni(cid:173)
`callimits in some large market areas, the transition to digital
`cellular technology was begun. The Pan-European GSM
`standard [1] was followed by the EIA-TIA North American
`Digital Cellular Standards initiatives, and the Japanese
`Digital Cellular standard. The extraordinary success of
`the cordless-telephone market spurred new standardization
`efforts for digital cordless and CT-2 TelePoint in the UK
`[2], wireless PBX, DECT, in Sweden [3], [4], the advanced
`cordless phone in Japan [5], and the concept of a Universal
`Digital Portable Communicator in the US [6]-[9]. The
`success of the paging industry led to development of private
`wireless packet data networks for commercial applications
`requiring longer messages [10]-[12]. Motivated by the
`desire to provide portability and to avoid the high costs
`of installation and relocation of wired office information
`networks, wireless office information networks were sug(cid:173)
`gested as an alternative [13], [14]. Another major event in
`this period was the May 1985 FCC announcement on un(cid:173)
`licensed ISM bands [15]-[17]. This announcement cleared
`the way for development of a wide array of commercial
`devices from wireless PBX's [18] and wireless LAN's [19],
`[20] to wireless fire safety devices using spread-spectrum
`technology.
`Figure 1 distinguishes the various categories of wireless
`networks that we discuss in this paper. We first define
`two broad categories of networks as 1) voice-oriented or
`isochronous networks and 2) data-oriented or asynchronous
`networks. Under each main category of networks, we
`distinguish further between local-area networks and wide(cid:173)
`area networks. As will be seen subsequently in this paper,
`each of the resulting four subcategories of networks has
`a set of characteristics that leads to certain design choices
`specific to the subcategory.
`Figure 2, which is structured according to the categories
`and subcategories defined in Fig. 1, depicts various dimen(cid:173)
`sions of today's voice and data communications industries.
`The figure compares local cordless personal communication
`with wide-area cellular, and compares wireless LAN's
`with wide-area low-speed data services. Figure 2(a) [21]
`compares various dimensions related to the wireless voice
`industry and Fig. 2(b) provides an analogous comparison
`between wireless data systems. Although from the user's
`standpoint the service characteristics and the appearance
`of the handset will be very similar for digital cellular and
`PCS systems, there will in fact be a major difference in
`the operation of the networks supporting the two types of
`systems. The digital cellular system is designed to support
`mobile users roaming over wide geographic areas, and thus
`coverage is provided by an arrangement of cells with cell
`size typically more than 2 mi in diameter. The radio cell
`sites for this system are large and expensive, particularly
`in urban areas where the cost of property is very high.
`
`The handset requires an average power of around 1 W,
`which is reflected in limited battery life and the need for
`frequent recharging. The number of users per cell is large
`and to provide as many user channels as possible in the
`allocated bandwidth, complex speech coding techniques are
`used. The speech coding techniques minimize the digitized
`speech transmission rate, but consume a significant amount
`of electronic power, which in tum places a high demand
`on battery power. The PCS systems will be designed
`for small, low-power devices to be carried and used in
`and around office buildings, industrial complexes, and city
`streets. The size of each cell will be less than 0.25 mi and
`the relatively small base stations will be installed on utility
`poles or attached to city and suburban business buildings.
`The average radiated power will be 10-20 mW, leading
`to relatively long battery life. The PCS services are to
`replace cordless phones, and the quality of voice service
`is intended to be comparable to wireline phone service. As
`a result, simple but high-quality speech coding algorithms
`are to be used, and at this writing, the leading candidate
`for adoption is 32-kbit/s Adaptive Differential Pulse Code
`Moduation (ADPCM) [22]. While a high-quality voice
`coding algorithm of this type does not provide the spectral
`efficiency of the lower rate (4- to 8-kbit/s) vocoders used
`in the digital cellular standards, it is far less demanding
`of digital signal processing complexity, and thus permits
`the use of very low prime power in the portable units. It
`is expected that PCS service will distinguish itself from
`digital cellular service by higher voice quality, and smaller
`user terminal. Table 1 provides a summary of the wireless
`technologies employed in several worldwide standards for
`the wireless voice industry [23]. For more details on the
`digital cellular and PCS initiatives, the reader can refer to
`[24]-[29] and other references cited there.
`Mobile data networks operate at relatively low data rates
`over well-understood urban radio channels using familiar
`multiple-access methods. The technical challenge here is
`the development of a system which makes efficient use of
`the available bandwidth to serve large numbers of users
`distributed over wide geographical areas. The transmission
`technology used in mobile data networks is generally rather
`simple and similar from one network to another. We discuss
`the major existing and planned mobile data networks and
`services in Section III.
`Wireless local area networks (WLAN's) and mobile
`data networks serve somewhat different categories of user
`applications, and give rise to different system design and
`performance considerations. A WLAN typically supports
`a limited number of users in a well-defined indoor area,
`and system aspects such as overall bandwidth efficiency
`and product standardization are not crucial. The achievable
`data rate is generally an important consideration in the
`selection of a WLAN, and therefore the transmission chan(cid:173)
`nel characteristics and the application of signal processing
`techniques are important topics [30]-[32]. Access methods
`and network topologies used in WLAN's are much the same
`from one system to another, but the transmission technolo(cid:173)
`gies can be quite different. Efficient deign of these systems
`
`1400
`
`PROCEEDINGS OF THE IEEE, VOL. 82, NO.9, SEPTEMBER 1994
`
`Petitioners' Ex. 1007 - Page 3
`
`

`
`Table 1 Summary of the Wireless Technologies Employed in Several Worldwide Standards for
`the Wireless Voice Industry
`
`Digital Cellular
`
`Low-Power Systems
`
`System:
`
`IS-54
`
`GSM
`
`JDC
`
`IS-95
`
`DECT
`
`PHP
`
`CT-2
`
`CT-3
`
`Bell core
`UDPC
`
`Multiple Access:
`
`Frequency Band
`Base TX (MHz):
`Mobile TX (MHz):
`
`Duplexing:
`
`Ch. Spacing (kHz):
`
`Modulation:
`
`Portable Transmit
`Power, Max/Avg:
`
`TDMA/
`FDMA
`
`869-894
`824-849
`(U.S.)
`
`FDD
`
`30
`
`Tr/4-
`QDPSK
`
`TDMA/
`FDMA
`
`935-960
`890-915
`
`FDD
`
`200
`
`GMSK
`
`TDMAI
`FDMA
`
`FDMAI
`CDMA-SS
`
`TDMA/
`FDMA
`
`TDMAI
`FDMA
`
`810-826
`940-956
`1447-1489
`1429-1441
`1501-1513
`1453-1465
`
`FDD
`
`25
`
`TC/4-
`QDPSK
`
`869-894
`824-849
`(U.S.)
`
`FDD
`
`1250
`
`BPSK/
`QPSK
`
`200mW
`
`1800-1900
`(Europe)
`
`1895-1907
`(Japan)
`
`TDD
`
`1728
`
`GFSK
`
`TDD
`
`300
`
`!t/4-
`QDPSK
`
`FDMA
`
`864-868
`(Europe
`&Asia)
`
`TDD
`
`100
`
`GFSK
`
`TDMA/
`FDMA
`
`TDM!TDMAI
`FDMA
`
`862-866
`(Sweden)
`
`Emerging
`Technology
`(U.S.)
`
`TDD
`
`1000
`
`GFSK
`
`FDD
`
`350
`
`Tr/4-
`QDPSK
`
`200mW/
`20mW
`
`!OmW/
`5mW
`
`80mW/
`5mW
`
`600mW/
`200mW
`
`Fixed
`
`IW/
`125mW
`
`Dynantic
`
`Yes
`Yes
`
`VSELP
`8
`
`Yes
`Yes
`
`RPE-LTP
`13
`
`Fixed
`
`Yes
`Yes
`
`VSELP
`8
`
`Frequency
`Assignment:
`
`Power Control
`Handset
`Base:
`
`Speech Coding
`and Rate (kbits/s):
`
`Speech Channels per
`RF Channel:
`
`Channel Rate (kbits/s)
`
`48.6
`
`270.833
`
`42
`
`Channel Coding:
`
`Rate-1/2
`Conv.
`
`Rate-1/2
`Conv.
`
`1,228.8
`(ChipRate) ·
`
`R-112 fwd.
`R-1/3 rev.
`CRC
`
`Frame Duration (ms):
`
`40
`
`4.615
`
`20
`
`20
`
`Yes
`Yes
`
`QCELP
`1-8 (var.)
`
`No
`No
`
`ADPCM
`32
`
`ADPCM
`32
`
`4
`
`96
`
`CRC
`
`12
`
`1152
`
`CRC
`
`10
`
`250mW/
`IOmW
`
`Dynamic
`
`80mW/
`IOmW
`
`Dynamic
`
`Dynamic
`
`Dynantic
`
`Auto no-
`mous
`
`Yes
`No
`
`ADPCM
`32
`
`10
`
`500
`
`CRC
`
`No
`No
`
`ADPCM
`32
`
`72
`
`None
`
`No
`No
`
`ADPC
`32
`
`640
`
`CRC
`
`16
`
`Wireless Information Network
`
`Fig. 1. Categories of wireless information networks.
`
`requires evaluation of various transmission techniques, an
`understanding of the complexities of indoor radio propaga(cid:173)
`tion, and the analysis of the effects of interference. WLAN
`manufacturers currently offer a number of nonstandardized
`products based on conventional radio modem technology,
`
`spread-spectrum technology in the ISM bands, and infrared
`technology. We discuss the various WLAN technologies in
`Section Ill.
`The future of the wireless data communciation industry is
`toward multimedia, multirate, and multipower applications.
`
`PAHLAVAN AND LEVESQUE: WIRELESS DATA COMMUNICATIONS
`
`1401
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`Petitioners' Ex. 1007 - Page 4
`
`

`
`Tariff
`
`'\. Compalibility with LANa
`...... :\·············· .
`•,
`
`Data !We
`
`voice Services
`
`(a)
`
`(b)
`
`Fig. 2. Various dimensions of the voice and data services offered by the wireless information
`network industry. Mobile cellular is compared with cordless PCS, and WLAN's with mobile data.
`
`Multimedia developments will support the ever-growing
`demand for mixed data, voice, and imagery applications
`and will be used to connect the pen pad and lap-top de(cid:173)
`vices to backbone information resources and computational
`facilities. Multirate modems will support high-speed wide(cid:173)
`area as well as low-speed local applications with a single
`device. Multipower terminals will allow the selection of the
`power resources such as ac power lines, car battery, or small
`batteries, based on availability; and will adapt the quality
`of the service to the consumption of the power resource.
`
`B. Wireless Data: Market and User Perspectives
`From the data user's perspective, the minimum satisfac(cid:173)
`tory service requirement is low-speed access in wide areas
`and high-speed access in local areas. The low-speed wide(cid:173)
`area access will serve a variety of short-message applica(cid:173)
`tions such as notice of electronic or voice mail, while the
`local-area access will support high-speed local applications
`such as long file transfers or printing tasks. In the current
`literature, low-speed wide-area wireless data communica(cid:173)
`tion is referred to as mobile data, while local high-speed
`data communication systems are called wireless LAN' s. As
`we discussed in the last section, the relationship between
`WLAN and mobile data services is analogous to the rela(cid:173)
`tionship between PCS and digital cellular services. While
`PCS is intended to provide high-quality local voice commu(cid:173)
`nication, the digital cellular services are aimed at wider area
`coverage with less emphasis on the quality of the service.
`1) Low-Speed Wide-Area Systems (Mobile Data): Mobile
`radio data systems have grown out of the success of the
`paging-service industry and increasing customer demand
`for more advanced services. Today 100000 customers are
`using mobile data services and the industry expects 13
`million users by the year 2000. This could be equivalent to
`I 0% to 30% of the revenue of the cellular radio industry.
`Today, mobile data services provide length-limited wireless
`connections with in-building penetration to portable users
`
`terminals in metropolitan areas. The future direction is
`toward wider coverage, higher data rates, and capability
`for transmitting longer data files.
`The transmission rates of existing mobile data systems
`are comparable to voice-band modem rates (up to 19.2
`kbits/s). However, the service typically has a limitation
`on the size of the file that can be transmitted in each
`communication session. The coverage of the service is
`similar to standard land-mobile radio services with the
`difference that the mobile data service must provide in(cid:173)
`building penetration. Land-mobile radio users typically use
`a telephone unit inside a vehicle and usually while driving.
`Mobile data users typically use the portable unit inside a
`building and in a stationary location. Therefore, in-building
`penetration is an essential feature of mobile data services.
`Mobile data services are used for transaction processing
`and interactive, broadcast, and multicast services. Trans(cid:173)
`action processing has applications such as credit card
`verification, taxi calls, vehicle theft reporting, paging, and
`notice of voice or electronic mail. Interactive services
`include enterprise applications such as database access and
`remote LAN access. Broadcast services include general
`information services, weather and traffic advisory services,
`and advertising. Multicast services are similar to subscribed
`information services, law enforcement communications,
`and private bulletin boards.
`There are other low-speed data products using voice-band
`modems over radio systems originally designed for voice
`communications. Some of these products are used in the
`land-mobile radio bands around 100-200 MHz, for low(cid:173)
`speed local data communications in or around buildings.
`Other products, portable facsimile devices, and voice-band
`modems, are used over the analog cellular telephone net(cid:173)
`work to provide wide-area data communications for mobile
`users without any restrictions on the connection time. The
`term mobile office is sometimes used to describe these
`applications.
`
`1402
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`
`Petitioners' Ex. 1007 - Page 5
`
`

`
`2) High-Speed Local-Area Systems (Wireless LAN' s): To(cid:173)
`day, most large offices are already equipped with wiring
`for conventional LAN's, and the inclusion of LAN wiring
`in the planning of a new office building is done as a
`standard procedure, along with planning for telephone and
`electric-power wiring. The WLAN market will very likely
`develop on the basis of the appropriateness of the wireless
`solution to specific applications. The target markets for
`the wireless LAN industry include applications in manu(cid:173)
`facturing facilities, in offices with wiring difficulties, and
`in branch offices and temporary offices. In manufacturing
`facilities, ceilings are typically not designed to provide
`a space for distribution of wiring. Also, manufacturing
`floors are not usually configured with walls through which
`wiring might otherwise be run from the ceiling to outlets.
`Underground wiring is a solution that suffers from expen(cid:173)
`sive installation, relocation, and maintenance. As a result,
`the natural solution for networking on most manufacturing
`floors is wireless communications. Other wide indoor areas
`without partitioning, such as libraries or open-architecture
`offices, are also suitable for application of WLAN's. In
`addition, buildings of historical value, concrete buildings,
`and buildings with marble interiors all pose serious prob(cid:173)
`lems for wiring installation, leaving WLAN's as the logical
`solution. WLAN's are also well suited to unwired small
`offices such as real-estate agencies, where only a few
`terminals are needed and where there may be frequent
`relocations of equipment to accommodate reconfiguration
`or redecoration of the office space. Temporary offices
`such as political campaign offices, consultants' offices, and
`conference registration centers, define another set of logical
`applications for WLAN's. The WLAN industry expects to
`capture 5-15% of the LAN market in the near future.
`Although the market for personal computers (PC's) is
`not growing as it has in past years, the market for portable
`devices such as lap-top and pen-pad computers and personal
`digital assistants (PDA's) is growing rapidly. Of greater
`importance to the wireless data communication industry,
`the market for networked portables is growing much faster
`than the overall market for portable computing. Obvi(cid:173)
`ously, wireless is the communication method of choice
`for portable terminals. Mobile data communication services
`discussed earlier provide a low-speed solution for wide
`area coverage. For high-speed and local communications,
`a portable terminal with wireless access can bring the
`processing and database capabilities of a large computer
`directly to specific locations for short periods of time,
`thus opening a wide horizon for new applications. For
`example, one can take portable terminals into classrooms
`for instructional purposes, or to hospital beds or accident
`sites for medical diagnosis.
`
`C. Frequency Administration Issues
`The major long-standing problem facing the radio com(cid:173)
`munications industry is the fundamental limitation on avail(cid:173)
`ability of frequency spectrum. The history of the indus(cid:173)
`try has been characterized by a steady migration toward
`higher frequency bands as new systems and services have
`
`come into the market. When cellular telephone service was
`launched in the late 1970's, the FCC allocated 40 MHz of
`bandwidth in the 800-MHz band by moving prior occupants
`(educational TV channels) out of the bands. An additional
`allocation of 10 MHz was made in 1986 as the cellular
`industry grew. The current state of the cellular industry
`in many major market areas is that the analog cellular
`systems have reached capacity, and this is the primary
`motivation for the digital cellular initiatives, which will
`increase capacity by factors of about 3 to 10 over the
`analog systems. In the land-mobile radio (LMR) bands
`(150, 350, and 850 MHz), capacity limits are also being
`reached, though the market growth there is not as strong as
`in the cellular market. In the LMR industry, plans are being
`made to migrate from 25-kHz channels to 12.5 kHz, with
`plans for further migration in the future . All of this means
`that in these bands efficient spectrum utilization is of the
`utmost importance, and these systems must be designed to
`use the available bandwidth to serve the greatest number
`of users over wide service areas. Thus the emphasis here
`is on bandwidth-efficient modulation, efficient frequency
`management schemes, and in the case of data services,
`efficient multiuser access protocols.
`The principal technological problems for implementation
`of WLAN's are: 1) data-rate limitations caused by the mul(cid:173)
`tipath characteristics of radio propagation, 2) the difficulties
`associated with signal coverage within buildings, and 3)
`the need for low-power electronic implementations suitable
`for portable terminals. These technical difficulties can be
`resolved and effective solutions are being developed for all
`of them. The greatest obstacle to achieving wireless multi(cid:173)
`megabit data communication rates is the lack of a suitable
`frequency band for reliable high-speed communication. The
`existing ISM bands [ 15]-[ 17] assigned for multiple-user
`applications are suitable for WLAN's, but they are re(cid:173)
`stricted to spread-spectrum technology and can suffer from
`unnecessary interference caused by careless users. More
`widespread use of high-speed wireless data communication
`technology will depend upon cooperation from frequency
`administration organizations in providing wider bandwidth
`allocations without restriction on the adopted technology,
`and in administering rules and etiquette for cooperative use
`of these bands.
`At frequencies around several gigahertz the technology
`is available for wireless implementations having reason(cid:173)
`able size, power consumption, and cost. Moving to higher
`frequencies is the solution for the future. As frequency
`increases, the prospect for obtaining a wider bandwidth
`from spectrum regulatory agencies will improve. However,
`with today's technology, implementation at a few tens of
`gigahertz with reasonable product size and power consump(cid:173)
`tion is challenging, particularly when wideband portable
`communication is considered. At higher frequencies, signal
`transmission through walls is more difficult. This feature
`is advantageous in WLAN applications where confinement
`of the signal within a room or building is a desirable
`privacy feature. Also, at higher frequencies the relationship
`between cell boundaries and the physical layout of the
`
`PAHLAVAN AND LEVESQUE: WIRELESS DATA COMMUNICATIONS
`
`1403
`
`Petitioners' Ex. 1007 - Page 6
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`

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`building is more easily determined, facilita