`WIRELESS COMMUNICATIONSWIRELESS COMMUNICATIONS
`
`AND NETWORKSAND NETWORKS
`
`SeCOND EDITIONSeCOND EDITION
`
`
`
`Williant StallingsWilliant Stallings
`
`
`
`•Upper Saddle River, NJ 07458•Upper Saddle River, NJ 07458
`
`Qualcomm Incorporated Ex. 1019
`Page 1 of 8
`
`

`

`-
`
`Library of Congress Cataloging-in-Publication Data on file
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`MarciaJ Horton
`Publisher: Alan Apt
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`• •
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`© 2005,2002 Pearson Education, Inc.
`Pearson Prentice Hall
`Pearson Education, Inc.
`Upper Saddle River, NJ 07458
`
`All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission
`in writing from the publisher.
`
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`development, research, and testing of the theories and programs to determine their effectiveness. The author and
`publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation
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`Printed in the United States ofAmerica
`10987654321
`
`ISBN: 0-13-191835-4
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`
`Qualcomm Incorporated Ex. 1019
`Page 2 of 8
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`

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`6.2 / DIGITAL DATA, ANALOG SIGNALS 131
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`• Cost and complexity: Although digital logic continues to drop in price, this
`factor should not be ignored. In particular, the higher the signaling rate to
`achieve a given data rate, the greater the cost. We will see that some codes
`require a signaling rate that is in fact greater than the actual data rate.
`
`We now turn to a discussion of various techniques.
`
`6.2 DIGITAL DATA, ANALOG SIGNALS
`
`:
`
`We start with the case of transmitting digital data using analog signals. The most
`familiar use of this transformation is for transmitting digital data through the public
`telephone network. The telephone network was designed to receive, switch, and
`transmit analog signals in the voice-frequency range of about 300 to 3400 Hz. It is
`not at present suitable for handling digital signals from the subscriber locations
`(although this is beginning to change). Thus digital devices are attached to the
`network via a modem (modulator-demodulator), which converts digital data to
`analog signals, and vice versa.
`For the telephone network, modems are used that produce signals in the
`voice-frequency range. The same basic techniques are used for modems that
`produce signals at higher frequencies (e.g., microwave). This section introduces
`these techniques and provides a brief discussion of the performance characteristics
`of the alternative approaches.
`We mentioned that modulation involves operation on one or more of the three
`characteristics of a carrier signal: amplitude, frequency, and phase. Accordingly, there
`are three basic encoding or modulation techniques for transforming digital data
`into analog signals, as illustrated in Figure 6.2: amplitude-shift keying (ASK),
`
`001 1 01 00 0 1
`
`0
`
`(a) ASK
`
`(b) BFSK
`
`(c) BPSK
`
`Figure 6.2 Modulation of Analog Signals for
`Digital Data
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`Qualcomm Incorporated Ex. 1019
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`132 CHAPTER 6 / SIGNAL ENCODING TECHNIQUES
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`frequency-shift keying (FSK), and phase-shift keying (PSK). In all these cases, the
`resulting signal occupies a bandwidth centered on the carrier frequency.
`
`All1plitude-Shift Keying
`In ASK, the two binary values are represented by two different amplitudes of the
`carrier frequency. Commonly, one of the amplitudes is zero; that is, one binary digit is
`represented by the presence, at constant amplitude, of the carrier, the other by the
`absence of the carrier (Figure 6.2a). The resulting transmitted signal for one bit time is
`
`ASK
`
`binary 1
`binary a
`
`(6.1)
`
`where the carrier signal is A COS(211fet). ASK is susceptible to sudden gain changes
`and is a rather inefficient modulation technique. On voice-grade lines, it is typically
`used only up to 1200 bps.
`The ASK technique is used to transmit digital data over optical fiber. For
`LED (light-emitting diode) transmitters, Equation (6.1) is valid. That is, one signal
`element is represented by a light pulse while the other signal element is represented
`by the absence of light. Laser transmitters normally have a fixed "bias" current that
`causes the device to emit a low light level. This low level represents one signal
`element, while a higher-amplitude lightwave represents another signal element.
`
`Frequency-Shift Keying
`
`The most common form of FSK is binary FSK (BFSK), in which the two binary
`values are represented by two different frequencies near the carrier frequency
`(Figure 6.2b). The resulting transmitted signal for one bit time is:
`
`BFSK
`
`set) = {A COS(211flt)
`
`A COS(211"ht)
`
`binary 1
`binary a
`
`(6.2)
`
`where 11 and 12 are typically offset from the carrier frequency Ie by equal but oppo(cid:173)
`site amounts.
`Figure 6.3 shows an example of the use of BFSK for full-duplex operation over
`a voice-grade line. The figure is a specification for the Bell System 108 series
`modems. A voice-grade line will pass frequencies in the approximate range 300 to
`3400 Hz. Full duplex means that signals are transmitted in both directions at the
`same time. To achieve full-duplex transmission, this bandwidth is split. In one direc(cid:173)
`tion (transmit or receive), the frequencies used to represent 1 and aare centered on
`1170 Hz, with a shift of 100 Hz on either side. The effect of alternating between
`those two frequencies is to produce a signal whose spectrum is indicated as the
`shaded area on the left in Figure 6.3. Similarly, for the other direction (receive or
`transmit) the modem uses frequencies shifted 100 Hz to each side of a center
`frequency of 2125 Hz. This signal is indicated by the shaded area on the right in
`Figure 6.3. Note that there is little overlap and thus little interference.
`BFSK is less susceptible to error than ASK. On voice-grade lines, it is typically
`used up to 1200 bps. It is also commonly used for high-frequency (3 to 30 MHz)
`
`Qualcomm Incorporated Ex. 1019
`Page 4 of 8
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`10.1 I PRINCIPLES OF CELLULAR NETWORKS 269
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`Table 10.1 Typical Parameters for Macrocells and Microcells [ANDE95]
`
`Macrocell
`
`Microcell
`
`Cell radius
`
`Example 10.1
`[HAASOO]. Assume a system of 32 cells with a cell radius of 1.6 km, a total
`of 32 cells, a total frequency bandwidth that supports 336 traffic channels, and a reuse fac(cid:173)
`tor of N = 7. If there are 32 total cells, what geographic area is covered, how many chan-
`.uyls. are there per cell, and what is the total number of concurrent calls that can be
`handled? Repeat for a cell radius of 0.8 km and 128 cells.
`Figure 10Aa shows an approximately square pattern. The area of a hexagon of radius
`R is 1.5R2v3. A hexagon of radius 1.6 km has an area of 6.65 km2
`, and the total area cov(cid:173)
`ered is 6.65 X 32 = 213 km2. For N = 7, the number of channels per cell is 336/7 = 48,
`for a total channel capacity of 48 X 32 = 1536 channels. For the layout of Figure"10Ab,
`the area covered is 1.66 X 128 = 213 km2. The number of channels per cell is 336/7 = 48,
`for a total channel capacity of 48 X 128 = 6144 channels.
`
`Operation of Cellular Systems
`
`Figure 10.5 shows the principal elements of a cellular system. In the approximate
`center of each cell is a base station (BS). The BS includes an antenna, a controller,
`and a number of transceivers, for communicating on the channels assigned to that
`cell. The controller is used to handle the call process between the mobile unit and
`the rest of the network. At any time, a number of mobile units may be active and
`moving about within a cell, communicating with the BS. Each BS is connected to
`a mobile telecommunications switching office (MTSO), with one MTSO serving
`
`00o
`
`x ~xo.
`
`.....
`
`II
`
`~ x ~x V
`
`)
`
`Width = 11 x 1.6 = 17.6 Ian
`(a) Cell radius = 1.6 km
`Figure 10.4 Frequency Reuse Example
`
`Width = 21 x 0.8 = 16.8 Ian
`(b) Cell radius = 0.8 km
`
`,L
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`Qualcomm Incorporated Ex. 1019
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`270 CHAPTER 10 / CELLULAR WIRELESS NETWORKS
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`Public
`telecommunications
`swib;hing
`network
`
`Mobile
`telecommun(cid:173)
`ications
`switching
`office
`
`Base
`transceiver
`station
`
`Base
`transceiver
`station
`
`Figure 10.5 Overview of Cellular System
`
`multiple BSs. Typically, the link between an MTSO and a BS is by a wire line,
`although a wireless link is also possible. The MTSO connects calls between mobile
`units. The MTSO is also connected to the public telephone or telecommunications
`network and can make a connection between a fixed subscriber to the public net(cid:173)
`work and a mobile subscriber to the cellular network. The MTSO assigns the voice
`channel to each call, performs handoffs (discussed subsequently), and monitors the
`call for billing information.
`The use of a cellular system is fully automated and requires no action on the
`part of the user other than placing or answering a call. Two types of channels are
`available between the mobile unit and the base station (BS): control channels and
`traffic channels. Control channels are used to exchange information having to do
`with setting up and maintaining calls and with establishing a relationship between a
`mobile unit and the nearest BS. Traffic channels carry a voice or data connection
`between users. Figure 10.6 illustrates the steps in a typical call between two mobile
`users within an area controlled by a single MTSO:
`
`• Mobile unit initialization: When the mobile unit is turned on, it scans and
`selects the strongest setup control channel used for this system (Figure 10.6a).
`Cells with different frequency bands repetitively broadcast on different setup
`channels. The receiver selects the strongest setup channel and monitors that
`channel. The effect of this procedure is that the mobile unit has automatically
`selected the BS antenna of the cell within which it will operate.2 Then a hand(cid:173)
`shake takes place between the mobile unit and the MTSO controlling this
`cell, through the BS in this cell. The handshake is used to identify the user and
`register its location. As long as the mobile unit is on, this scanning procedure
`is repeated periodically to account for the motion of the unit. If the unit
`
`2Usually, but not always, the antenna and therefore the base station selected is the closest one to the
`mobile unit. However, because of propagation anomalies, this is not always the case.
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`Qualcomm Incorporated Ex. 1019
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`10.1 / PRINCIPLES OF CELLULAR NETWORKS 271
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`(a) Monitor for strongest signal
`
`(b) Request for connection
`
`(c) Paging
`
`(d) Call accepted
`
`(e) Ongoing call
`
`(f) Handoff
`
`Figure 10.6 Example of Mobile Cellular Call
`
`enters a new cell, then a new BS is selected. In addition, the mobile unit is
`monitoring for pages, discussed subsequently.
`• Mobile-originated call: A mobile unit originates a call by sending the number
`of the called unit on the preselected setup channel (Figure lO.6b). The receiver
`at the mobile unit first checks that the setup channel is idle by examining
`information in the forward (from the BS) channel. When an idle is detected,
`the mobile unit may transmit on the corresponding reverse (to BS) channel.
`The BS sends the request to the MTSO.
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`Qualcomm Incorporated Ex. 1019
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`272 CHAPTER 10 / CELLULAR WIRELESS NETWORKS
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`• Paging: The MTSO then attempts to complete the connection to the called
`unit. The MTSO sends a paging message to certain BSs depending on the
`called mobile unit number (Figure 10.6c). Each BS transmits the paging signal
`on its own assigned setup channel.
`• Callaccepted: The called mobile unit recognizes its number on the setup chan(cid:173)
`nel being monitored and responds to that BS, which sends the response to the
`MTSO. The MTSO sets up a circuit between the calling and called BSs. At the
`same time, the MTSO selects an available traffic channel within each BS's cell
`and notifies each BS, which in turn notifies its mobile unit (Figure 10.6d). The
`two mobile units tune to their respective assigned channels.
`• Ongoing call: While the connection is maintained, the two mobile units
`exchange voice or data signals, going through their respective BSs and the
`MTSO (Figure 10.6e).
`• Handoff: If a mobile unit moves out of range of one cell and into the range of
`another during a connection, the traffic channel has to change to one assigned
`to the BS in the new cell (Figure 10.6f). The system makes this change without
`either interrupting the call or alerting the user.
`
`Other functions performed by the system but not illustrated in Figure 10.6
`include the following:
`
`.. Call blocking: During the mobile-initiated call stage, if all the traffic channels
`assigned to the nearest BS are busy, then the mobile unit makes a preconfig(cid:173)
`ured number of repeated attempts. After a certain number of failed tries, a
`busy tone is returned to the user.
`.. Can termination: When one of the two users hangs up, the MTSO is informed
`and the traffic channels at the two BSs are released.
`• Call drop: During a connection, because of interference or weak signal spots
`in certain areas, if the BS cannot maintain the minimum required signal
`strength for a certain period of time, the traffic channel to the user is dropped
`and the MTSO is informed.
`• Calls to/from fixed and remote mobile subscriber: The MTSO connects to the
`public switched telephone network. Thus, the MTSO can set up a connection
`between a mobile user in its area and a fixed subscriber via the telephone net(cid:173)
`work. Further, the MTSO can connect to a remote MTSO via the telephone
`network or via dedicated lines and set up a connection between a mobile user
`in its area and a remote mobile user.
`
`Mobile Radio Propagation Effects
`Mobile radio communication introduces complexities not found in wire communi(cid:173)
`cation or in fixed wireless communication. Two general areas of concern are signal
`strength and signal propagation effects.
`
`• Signal strength: The strength of the signal between the base station and the
`mobile unit must be strong enough to maintain signal quality at the receiver
`but not so strong as to create too much cochannel interference with channels
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`Qualcomm Incorporated Ex. 1019
`Page 8 of 8
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