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The most popular forms of modulation used in digital communications arebinary phase shift keying (BPSK), quadrature phase shift keying (QPSK),offset-quadrature phase shift keying (OQPSK), and 8-PSK. These modulationformats can be described in a general form as M-PSK modulation, whereM ¼ 2 b bits, each symbol represents b bits, and b is an integer, 1, 2, or 3. Thegeneralized M-PSK is discussed in Sec. 3.2.A modem converts a digital signal to an analog tone (modulation) andreconverts the analog tone (demodulation) into its original digital signal at theother side of connection (modems are described in Sec. 3.3.1). Both amplitude-modulation(AM) and frequency-modulation (FM) techniques are examplesof analog-type or uncoded signal-transmission systems with one-to-onecorrespondence between the input signal and the modulated carrier eventuallytransmitted.The reader might ask, why code? A coded system makes much moreefficient use of bandwidth widening to increase the output signal-to-noise ratiothan does an uncoded system. Coded systems are inherently capable of bettertransmission efficiency than the uncoded types.A general division may be made to classify frequency division multiplexing(FDM) voice and video signals to use FM while classifying digitallymultiplexed voice and data to use some form of phase modulation.In the receiving chain, the received signals pass through a sequence ofprocessing steps that are essentially the reverse of those followed to preparethe outgoing signals. The RF received signals are passed through a low-noisewideband RF front end, followed by a translator to IF. It is at the IF stage thatthe specific uplink carriers hoping to be received are separated and grouped bydestination, then demodulated to their original baseband signals followed byan FEC decoder (in the case of digital satellite communications). Those notspecifically destined to the earth station are retransmitted, thereby acting like atransponder. The demodulated baseband signals may then be demultiplexed, ifnecessary, and thereby transferred to the users.The antenna in Fig. 3.1 is used for transmitting and receiving: this typeis called a transceiver. The basic principles and characteristics of antennashave been discussed in Chap. 2, Sec. 2.7; they also apply to the earth stationantennas. However, in addition to the antenna characteristics discussed in Sec.2.7, the antenna subsystem requires separate tracking equipment, whichensures precise pointing of the antenna at the satellite. With small earthstations where the antenna’s bandwidth is large, precision-tracking equipmentis not necessary. The antenna tracking system can be programmed to point topreassigned direction(s) automatically and can also be directed manually. Wediscuss more on antenna tracking systems in Sec. 3.4.2.Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.
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SatelliteCommunicationEngineeringMi
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This book is dedicated to my famili
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Because of the immense importance o
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means of a combination of applicati
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about my promise to my students, an
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2.3 Coverage Area and Satellite Net
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1Basic Principles of SatelliteCommu
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and voice (telephone) communication
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FIGURE 1.2Communication between two
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interpreting or uncovering the deci
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cryptographic keys K ti (where i ¼
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FIGURE 1.6Block ciphering technique
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FIGURE 1.7Part of block ciphering w
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Based on the ordering sequence of (
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TABLE 1.1 (continued )S612 1 10 15
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For an uncoded message x and the fe
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2. Your task is to develop a commun
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FIGURE 2.1Geometry of a satellite.
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Future trends in satellite antennas
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In the United States, the three sat
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TABLE 2.3Typical Links Frequency Ba
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FIGURE 2.4Satellite period and orbi
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FIGURE 2.6An illustration of covera
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FIGURE 2.7constellation.A sketch of
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width of 1:73 with reduced coverag
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y ¼ elevation angle of satellite f
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We can conclude that the antenna mu
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FIGURE 2.9Design flowchart of a sat
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Risk control and monitoring measure
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TABLE 2.4Antenna Selection Criteria
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Then the system availability can be
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In fact, MTBF is the reciprocal of
Page 130: 2.7 ANTENNASBased on function, sate
Page 134: Two kinds of horns in common use ar
Page 138: FIGURE 2.13Geometry of a parabolic
Page 142: FIGURE 2.14 Axisymmetric reflector
Page 146: A transceiver antenna is a single a
Page 150: The gain, in the axial mode, of a h
Page 154: angles, spacecraft may shadow the s
Page 158: 3. The probability of both parallel
Page 162: the baseband signal (more details a
Page 166: matrix in the communications subsys
Page 170: FIGURE 2.24Typical transfer charact
Page 174: 4. Iridium LCC (1997). Iridium Syst
Page 178: 3Earth StationsIn Chap. 2 we discus
Page 184: 3.1.1 Technical and Operational Req
Page 188: excellent protection against noise
Page 192: FIGURE 3.3QPSK modulator.FIGURE 3.4
Page 196: TABLE 3.28-PSK Truth TableInput bit
Page 200: FIGURE 3.8An M-ary PSK demodulator
Page 204: where B is the allocated channel ba
Page 208: A frequently used function is the Q
Page 212: In view of (3.11), Eq. (3.18) can b
Page 216: Encoder and DecoderAn encoder is an
Page 220: Modulator and DemodulatorA modulato
Page 224: Zero Forcing Technique. Suppose the
Page 228: The adjoint of matrix A is obtained
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FIGURE 3.14The three-tap equalizer
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First, in the case of digital signa
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than 1=A. Whichever law is used, th
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FIGURE 3.16Block diagram for estima
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3.4.2 Antenna TrackingAn earth stat
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controlling antenna pointing. The m
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FIGURE 3.19A generalized model of a
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FIGURE 3.20Entropy of a binary sour
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whereHðYÞ¼output entropy, the av
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To have a feel for this expression,
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2. The system’s overall condition
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transmitted down the fiber as digit
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10. Kantor, L. Y. (ed). (1987). Han
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142. Simulate the probability of bi
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FIGURE 4.1A simplex link.baseband c
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Chapter 2, Sec. 2.7, discusses that
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From (4.6), the received power P r
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FIGURE 4.3A model of the combined-l
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4.1.2 Rain AttenuationRain attenuat
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FIGURE 4.5rates.Average rainstorm p
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FIGURE 4.6Adjacent satellite interf
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FIGURE 4.8Satellite separation dist
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inability of satellite A to accurat
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FIGURE 4.10 Cross-link E b =N 0 vs.
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Then using (4.41), the overall C=N
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(iv)(v)(vi)(vii)Calculate the recei
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5Communication Networks andSystemsC
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discriminate among carriers by temp
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FIGURE 5.2 Principle of FDMA system
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FIGURE 5.3 Operational concept of T
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FIGURE 5.5TDMA: bit rate r b for 1
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Copyright © 2002 by Marcel Dekker,
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5.2 CAPACITY COMPARISON OFMULTIPLE-
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Rearranging (5.11) in terms of ener
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The transmission bit rate isR r ¼
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6Error Detection and CorrectionCodi
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the channel and reconstruct the sou
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message sequence X . Thus, a system
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If we consider a message X ¼ð1010
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can be seen in Table 6.1 that the m
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FIGURE 6.1A (7, 4) cyclic code gene
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FIGURE 6.2Convolutional codes encod
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Alternative methods of describing a
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FIGURE 6.5 Code tree diagram of Fig
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FIGURE 6.8 Code tree diagram of rat
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consistent with the constraint leng
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trellis depth is approximated to 5L
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FIGURE P.1A convolutional coder.the
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7Regulatory Agencies andProceduresT
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of the radiofrequency spectrum, and
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The CCIR works through the medium o
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7.1.3 IFRBThe International Frequen
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The national or regional spectrum m
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3. The need to expand or enhance th
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The DSP will be responsible for res
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2. Provide a convenient framework w
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FIGURE 8.3Types of user-to-network
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H1-channels are designed to carry v
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information. The transfer cell prov
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The OSI layers are divided into two
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plane is denoted by U, the control
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interfacing, maintenance, and conne
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adjoining base station to scan the
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FIGURE 8.9Geometry of a polygon.The
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FIGURE 8.11Splitting cells into sma
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causes signal fading. Of course, th
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FIGURE 8.14TCP=IP suite and its rel
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access to an Internet point of pres
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message security via satellite is d
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REFERENCES1. Wu, W.W. (1989). Eleme
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Appendix ANotationsThe symbols have
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N sPP rP sP TRRðtÞR cR eR rR vSS
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g Central anglez Channel gainZ Ante
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AttenuationBandwidthBearer serviceB
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Frequency divisionmultiple accessFr
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MultiplexingNetworkOmnidirectionala
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UplinkUser-to-networkinterfaceThe e
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