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6.1 CHANNEL CODINGNoise within a transmission channel inevitably causes discrepancies or errorsbetween the channel input and channel output. A channel is a specific portionof the information-carrying capacity of a network interface specified by acertain transmission rate. In Chap. 3, Sec. 3.2.5, and Chap. 5, Sec. 5.2, theconcepts of bit error rate and channel capacity using Shannon’s theorem wererespectively discussed in some detail [2].Coding enables the receiver to decode the incoming coded signals notonly to detect errors but also to correct them. Effectively encoding signalsfrom discrete sources and approximating a specified Shannon limit areachievable by symbol combination in large blocks and by the application ofspecial coding methods such as Huffman [3] codes and Fano 1 [4] codes. Forclarification, the terms ‘‘data compression’’ and ‘‘effective encoding’’ aretreated as synonyms: meaning that redundancy is eliminated from the originalsignal, and it is then encoded as economically as possible with a minimumnumber of binary symbols [5]. An encoder performs redundancy elimination.The application of the effective encoding methods essentially reduces therequired channel transmission rate.In general, if k binary digits enter the channel encoder, and the channelencoder outputs n binary digits, then the code rate can be defined asR c ¼ k nð6:1ÞThe channel-coding theorem specifies the capacity C c as a fundamental limiton the rate at which the transmission of reliable errorfree message can takeplace over a discrete memoryless channel (DMC). The concept of DMC hasbeen discussed in Chap. 3. For example, let a discrete memoryless source withan alphabet X have entropy HðX Þ and produce one symbol every T s sec.Supposing that a DMC with capacity C c (bit=symbol) is used once every T csec; then ifHðX ÞT s C cT cð6:2Þthere exists a coding scheme for which the source output can be transmittedover the channel and be retrieved and reconstructed with an arbitrarily smallprobability of error. Conversely, it is impossible to transfer information over1 Also called Shannon–Fado codes.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
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2.7 ANTENNASBased on function, sate
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Two kinds of horns in common use ar
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FIGURE 2.13Geometry of a parabolic
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FIGURE 2.14 Axisymmetric reflector
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A transceiver antenna is a single a
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The gain, in the axial mode, of a h
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angles, spacecraft may shadow the s
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3. The probability of both parallel
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the baseband signal (more details a
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matrix in the communications subsys
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FIGURE 2.24Typical transfer charact
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4. Iridium LCC (1997). Iridium Syst
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3Earth StationsIn Chap. 2 we discus
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The most popular forms of modulatio
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Small earth stations are antennas w
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FIGURE 3.2BPSK space diagram.Instea
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OQPSKOffset QPSK (OQPSK) is a modif
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FIGURE 3.7An 8-PSK space diagram.an
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aud. The word ‘‘baud’’ hono
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Noise power density N 0bandwidth:N
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We observe in (3.11) that E b =N 0
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to (3.23) shows that a margin of 11
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FIGURE 3.12 Principle of scrambling
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Equalization FilterAn equalization
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that is, N zeros at the top and bot
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Example 3.2: Consider a transmissio
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which can be written as89>=R xy ðt
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ecause a voice signal is usually hi
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systems is discussed in Sec. 4.2. O
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where T e is the equivalent tempera
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operating principle of all directio
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performance of the satellite commun
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3. For two independent sources, wit
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FIGURE 3.21 A representation of mut
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In practice, Eqs. (3.78) and (3.76)
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This condition is always satisfied
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Copyright © 2002 by Marcel Dekker,
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epeaters overshooting into subseque
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6. Conventional BPSK modulation all
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4Satellite LinksA satellite link co
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FIGURE 4.2 Basic antenna parameters
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For unity efficiency, and substitut
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This expression neglects losses oth
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This expression is equally valid fo
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and Lin [5]:whereL ¼L o1 þ L oðr
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3. Calculate attenuation A r in dB
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4.2.1 Intersatellite LinksAs indica
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We know from (4.4b) that f c is dep
Page 322: FIGURE 4.9 Cross-link transmission
Page 326: Follow the uplink procedure for the
Page 330: Satellite:Frequencies:14.75 GHz up
Page 334: 6. For link to be maintained betwee
Page 338: 5.1 PRINCIPLES OF MULTIPLE ACCESSAs
Page 342: neously, their transmissions collid
Page 346: technique and would remain the most
Page 350: FIGURE 5.4 Typical TDMA frame struc
Page 354: FIGURE 5.6TDMA throughput for an IN
Page 358: and transmits through the satellite
Page 362: FIGURE 5.8FDMA total capacity respo
Page 366: tion; that is, log e ð1 þ xÞ x t
Page 370: REFERENCES1. Spilker, J.J. (1977).
Page 376: the channel and reconstruct the sou
Page 380: message sequence X . Thus, a system
Page 384: If we consider a message X ¼ð1010
Page 388: can be seen in Table 6.1 that the m
Page 392: FIGURE 6.1A (7, 4) cyclic code gene
Page 396: FIGURE 6.2Convolutional codes encod
Page 400: Alternative methods of describing a
Page 404: FIGURE 6.5 Code tree diagram of Fig
Page 408: FIGURE 6.8 Code tree diagram of rat
Page 412: consistent with the constraint leng
Page 416: trellis depth is approximated to 5L
Page 420: 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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