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Wireless CommunicationsPrinciples and Practice

T.S. Rappaport2nd Edition

Chapter 2: Modern Wireless Communication Systems

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Figure 2.1 Growth of cellular telephone subscribers throughout the world.

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Figure 2.2 Worldwide subscriber base as a function of cellular technology in late 2001.

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• 1st Generation cellular systems relied on FDMA / FDD and Analog FM.

• 2nd Generation standards use digital modulation formats and TDMA / FDD

and CDMA / FDD.

• Global System Mobile (GSM) supports 8 time slotted users for each 200 kHz

each, radio channel.

• Interim Standard 136 (IS-136) supports three time slotted users each of 30 kHz

each. Pacific Digital Cellular (PDC) is similar to IS-136.

• Interim Standard 95 Code Division Multiple Access (IS-95), also known as

cdmaOne supports up to 64 users that are orthogonally coded and

simultaneously transmitted on each 1.25 MHz channel.

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Figure 2.3 Various upgrade paths for 2G technologies.

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EVOLUTION TO 2.5G MOBILE RADIO NETWORKS

• 2 G technologies use circuit-switched data modems that limit data users to a

single circuit-switched voice channel.

• Data through put of an individual user is limited.

• Data rates of the order of 10kbps supported which is slow for rapid e-mail and

internet browsing.

• Data-centric 2.5 standards were introduced for increased throughput data rates

to support modern Internet applications.

• 2.5G technologies support a popular web browsing format language called

Wireless Applications Protocol (WAP) that allows standard webpages to be

viewed in a compressed format designed for small, portable hand held devices.

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EVOLUTION FOR 2.5G TDMA STANDARDS

HSCSD for 2.5G GSM

• High Speed Circuit Switched Data is a circuit switched technique that allows a

single mobile subscriber to use consecutive time slots in the GSM standard.

• Instead of limiting each user to a particular time slot, HSCSD allows individual

data users to use consecutive user time slots in the GSM standard to obtain high

speed data access.

• Data rate increases to 14,400 bps as compared to 9,600 bps in GSM.

• Using 4 consecutive time slots, HSCSD provides transmission rate of upto 57.6

kbps to individual users.

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EVOLUTION FOR 2.5G TDMA STANDARDS

GPRS for 2.5G GSM and IS-136

• General Packet Radio Service is a packet-based data network which is well-

suited for non-real time internet usage, including retrieval of e-mail, faxes and

web browsing.

• GPRS supports multi-user network sharing of individual radio channels and

time slots.

• Can support many more users as compared to HSCSD but in a bursty

manner !!

• When all eight time slots of a GSM radio channel are dedicated to a GPRS, an

individual user is able to achieve as much as 171.2 kbps data throughput.

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EVOLUTION FOR 2.5G TDMA STANDARDS

EDGE for 2.5G GSM and IS-136

• Enhanced Data rates for GSM Evolution is an enhanced version of GSM

standard and requires addition of new hardware and software to existing BS.

• EDGE introduces a new modulation format 8-PSK (Octal Phase Shift Keying)

which is used in addition to GMSK.

• Provides practical data rate of about 384 kbps for a single dedicated user on a

single GSM channel.

• By combining the capacity of different radio channels (Multiple Carrier

Transmission), EDGE can provide up to several megabits per second

throughput.

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3G WIRELESS NETWORKS

3 G W-CDMA (UMTS)

• Universal Mobile Telecommunications System (UMTS) or Wide-band CDMA

(W-CDMA) assures backward compatibility with 2.5G TDMA standards.

• Designed for “Always-ON” packet-based wireless service so that computers,

mobiles and laptops etc. may all share the same wireless network to be

connected to the Internet anytime, anywhere.

• W-CDMA supports data rates upto 2.408 Mbps per user to allow high quality

data, multimedia and streaming video broadcasting services.

• Requires a minimum spectrum allocation of 5 MHz where a channel (5 MHz)

will be able to support 100 to 350 simultaneous voice calls at once.

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3G WIRELESS NETWORKS

3 G cdma2000

• Channel bandwidth of 1.25 MHz per radio channel

• The first CDMA interface cdma2000 1xRTT means that a single 1.25 MHz

radio channel is used.

• cdma2000 1X supports an instantaneous data rate upto 307 kbps with typical

throughput rate of 144kbps.

• cdma2000 1xEV : Evolutionary advancement for CDMA• cdma2000 1xEV-DO: CDMA carriers with the option of Data Only radio

channels• cdma2000 1xEV-DV: carriers with Data and Voice.

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3G WIRELESS NETWORKS

3 G TD-SCDMA

• Time Division Synchronous Code Division Multiple Access

• TD-SCDMA combines TDMA and TDD techniques to provide a data-only

overlay in existing GSM network.

• Up to 384 kbps of packet data is provided to data users in TD-SCDMA.

• Radio channels are 1.6 MHz in bandwidth

• A 5ms frame is used which is divided into 7 time slots which are flexibly

assigned to a single high data rate user or several slower users.

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Figure 2.4 Example of the emerging applications and markets for broadband services. (Courtesy of Harris Corporation, ©1999, all rights reserved.)

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WIRELESS LOCAL LOOP (WLL)

• Wireless local loop (WLL), is a term for the use of a wireless communications

link as the "last mile " connection that resides between the Central Office (CO)

and the individual homes and businesses in close proximity of the CO.

LOCAL MULTIPOINT DISTRIBUTION SERVICE (LMDS)

• LMDS is a broadband wireless access technology originally designed for

digital television transmission (DTV). It was conceived as a fixed wireless,

point-to-multipoint technology for utilization in the last mile. LMDS commonly

operates on microwave frequencies across the 26 GHz and 29 GHz bands. In the

United States, frequencies from 31.0 through 31.3 GHz are also considered

LMDS frequencies.

• LMDS has been allocated a spectrum of 1300 MHz which can support over 200

broadcast quality channels or 65,000 full duplex voice channels.

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Figure 2.5 Allocation of broadband wireless spectrum throughout the work. (Courtesy of Ray W. Nettleton and reproduced by permission of Formus Communications.)

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Figure 2.7 A wireless Competitive Local Exchange Carrier (CLEC) using Asynchronous Transfer Mode (ATM) distribution.

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Local Exchange Carrier (LEC)

• LEC owns a very wide bandwidth Asynchronous Transfer Mode (ATM) or

Synchronous Optical NETwork (SONET) backbone switch, capable of

connecting hundreds of megabits per second of traffic with the Internet, the

PSTN or some private network.

• As long as LOS path exists, LMDS allows LECs to install wireless equipment

on the premises of customers for rapid broadband connectivity without having to

lease or install its own cables to the customers.

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Figure 2.8 Measured received power levels over a 605 m 38 GHz fixed wireless link in clear sky, rain, and hail [from [Xu00], ©IEEE].

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Figure 2.9 Measured received power during rain storm at 38 GHz [from [Xu00], ©IEEE].

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Figure 2.10 Overview of the IEEE 802.11 Wireless LAN standard.

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IEEE 802.11

• IEEE 802.11 is a set of standards for implementing wireless local area network

(WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands.

• Provides 11 Mcps DS-SS spreading and 2Mbps user data rates.

• IEEE 802.11a provides upto 54 Mbps throughput in 5GHz band.

• DS-SS IEEE 802.11b standard has been named Wi-Fi by WECA (Wireless

Ethernet Compatibility Alliance).

• IEEE 802.11g is developing Complementary Code Keying Orthogonal

Frequency Division Multiplexing (CCK-OFDM) standards in both the 2.4 GHz

(IEEE 802.11b) and 5 GHz (IEEE 802.11a)

• FH-SS : Frequency Hopping - Spread Spectrum• DSSS : Direct-Sequence Spread Spectrum

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Figure 2.11 Photographs of popular 802.11b WLAN equipment. Access points and a client card are shown on left, and PCMCIA Client card is shown on right. (Courtesy of Cisco Systems, Inc.)

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Figure 2.12 Channelization scheme for IEEE 802.11b throughout the world.

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Figure 2.13 A predicted coverage plot for three access points in a modern large lecture hall. (Courtesy of Wireless Valley Communications, Inc., ©2000, all rights reserved.)

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Figure 2.14 Schematic of an experiment to determine how received interference impacts end user performance on a WLAN network [Hen01] demonstrated that a CAD prediction and measurement environment can be used to accurately and rapidly predict true end user throughput in a multi-node network using blind prediction. Such capabilities will be vital as user densities increase in WLAN networks within buildings or campuses.

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Figure 2.15 A typical neighborhood where high speed license free WLAN service from the street might be contemplated [Dur98b].

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Figure 2.16 Measured values of path loss using a street-mounted lamp-post transmitter at 5.8 GHz, for various types of customer premise antenna [from [Dur98], ©IEEE].

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Figure 2.17 Example of a Personal Area Network (PAN) as provided by the Bluetooth standard.