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trellis depth is approximated to 5L c nodes. This allows decoding of only theoldest received sequence within the trellis and selecting the path with thefewest errors, while deleting the remaining paths.6.3 SUMMARYThe transmission of data over a communication link is highly likely to result insome errors occurring in the received data, for at least a small proportion oftime, because of noise added by the transmission medium and system. Sometechniques on how the errors can be detected and correction effected havebeen explored in this chapter. These techniques are forward error correcting,broadly classified under two headings: block codes and convolutional codes.In the block coding techniques, the encoder splits up incoming datastream into blocks of finite-number digits and processes each block by addingextra bits (called redundancy) according to a predefined algorithm. The outputof the encoder is a codeword with another finite number of digits. A fewsubsets of linear block codes, such as Hamming, cyclic, and BCH, have alsobeen discussed. Their importance is the existence of practical decodingtechniques.In the convolutional coding techniques, the encoder processes theincoming data stream continuously while its decoder employs the Viterbialgorithm among others. Convolutional codes are very popular because theyare simple in concept and in practice to utilize.Examples were sparingly used as illustrative tools to explain theseforward error correction techniques.BIBLIOGRAPHY1. Berlekamp, E.R. (1968). Algebraic Coding Theory. McGraw-Hill: New York.2. Hagenauer, J. and Hoeher, P. (1989). AViterbi algorithm with soft-decision outputsand its applications, GLOBECOM’89 Dallas, Texas Conference Proc., 1680–1686.REFERENCES1. Feher, K. (1984) Digital Communications: Satellite=Earth Station Engineering.Prentice-Hall.2. Shannon, C.E. (1948). A mathematical theory of communication, Bell System TechJ., vol. 26.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
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FIGURE 4.9 Cross-link transmission
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Follow the uplink procedure for the
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Satellite:Frequencies:14.75 GHz up
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6. For link to be maintained betwee
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5.1 PRINCIPLES OF MULTIPLE ACCESSAs
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neously, their transmissions collid
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technique and would remain the most
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FIGURE 5.4 Typical TDMA frame struc
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FIGURE 5.6TDMA throughput for an IN
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and transmits through the satellite
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FIGURE 5.8FDMA total capacity respo
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Page 370: REFERENCES1. Spilker, J.J. (1977).
Page 374: 6.1 CHANNEL CODINGNoise within a tr
Page 378: where G is a generator matrix that
Page 382: The syndrome is a single word of le
Page 386: SolutionComparing (i) and (ii) with
Page 390: Cyclic CodesCyclic codes are a subs
Page 394: When errors occur in bursts, the nu
Page 398: FIGURE 6.3Rate 1/2 convolutional en
Page 402: us to a particular node in the tree
Page 406: FIGURE 6.6 Trellis diagram of Fig.
Page 410: FIGURE 6.9 Trellis diagram of Fig.
Page 414: A generalized Viterbi algorithm is
Page 420: FIGURE P.1A convolutional coder.the
Page 424: 7Regulatory Agencies andProceduresT
Page 428: of the radiofrequency spectrum, and
Page 432: The CCIR works through the medium o
Page 436: 7.1.3 IFRBThe International Frequen
Page 440: The national or regional spectrum m
Page 444: 3. The need to expand or enhance th
Page 448: The DSP will be responsible for res
Page 452: 2. Provide a convenient framework w
Page 456: FIGURE 8.3Types of user-to-network
Page 460: H1-channels are designed to carry v
Page 464: 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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