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causes signal fading. Of course, the crossover effect precludes the use of twodifferent orthogonally polarized waves to increase channel capacity.A diversity scheme is needed to combat fading. Several diversityschemes have been employed, including space diversity, frequency diversity,micro- and macrodiversity, and time diversity. The mode of operation in whichtwo or more base stations serve the same area is called macrodiversity.Microdiversity refers to the condition in which two or more signals arereceived at one base site or mobile site. Microspace diversity is routinelyused in cellular base sites.Space diversity can be used to combat short-term fading, whereaspositioning satellites at different locations, not necessarily in the same orbitalplane, can be used to reduce long-term fading. Space-diversity systemsemploy two or more antennas spaced a certain distance apart. For example,a separation of only 30 cm wavelength, which is suitable for implementationon the mobile side, is sufficient to provide a notable improvement in somemobile radio channel environments. Macrodiversity is also a form of spacediversity.Frequency-diversity systems employ two or more different carrierfrequencies to transmit the same information. Statistically, the same informationsignal may or may not fade at the same time at the different carrierfrequencies. An example of a frequency-diversity scheme includes frequencyhopping and very wide band signalling. Time-diversity systems are usedprimarily for data transmission. The same data are sent through the radiochannel as many times as necessary until the required quality of transmissionis achieved. An example of this type of scheme is the well-known automaticrepeat request (ARQ).The improvement of any diversity scheme strongly depends on thecombining techniques employed: the switched combining, feed-forward orfeedback combining, majority vote, and so forth.8.3 THE INTERNET AND SATELLITESSatellites have offered broadband services like television or video-on-demandbroadcast, wireless telephone, and electronic mail for years. Developers nowplace more emphasis on the speed of delivery of electronic commerce via theInternet and other telecommunication applications, which makes multimediainteractivity via the satellite very attractive. This section examines how theInternet works via the existing land-based integrated digital networks and viathe satellite as well as the technical difficulties that currently prevent rapidexpansion and delivery of these services via the Internet.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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tion; that is, log e ð1 þ xÞ x t
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REFERENCES1. Spilker, J.J. (1977).
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6.1 CHANNEL CODINGNoise within a tr
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where G is a generator matrix that
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The syndrome is a single word of le
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SolutionComparing (i) and (ii) with
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Cyclic CodesCyclic codes are a subs
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When errors occur in bursts, the nu
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FIGURE 6.3Rate 1/2 convolutional en
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us to a particular node in the tree
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FIGURE 6.6 Trellis diagram of Fig.
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FIGURE 6.9 Trellis diagram of Fig.
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A generalized Viterbi algorithm is
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3. Huffman, D.A. (1952). A method f
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4. Draw a block diagram for a convo
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1. The first essential requirement
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use. The ITU Radio Regulations gove
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Within the CCITT structure exist a
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7.2 NATIONAL AND REGIONAL REGULATIO
Page 442: 8Mobile Satellite System Services8.
Page 446: Copyright © 2002 by Marcel Dekker,
Page 450: may reside within a single LDSN. Th
Page 454: destination through the intermediat
Page 458: can be used at separate user-to-net
Page 462: where0 n 40 m 246n þ m 24ð8:
Page 466: elationship between OSI and ISDN: t
Page 470: network and for networks to communi
Page 474: Copyright © 2002 by Marcel Dekker,
Page 478: shown in Fig. 8.1. Some of the attr
Page 482: It is possible to formulate a metho
Page 486: transmitting power. The smaller the
Page 490: FIGURE 8.12Tessellated clusters of
Page 496: FIGURE 8.14TCP=IP suite and its rel
Page 500: access to an Internet point of pres
Page 504: message security via satellite is d
Page 508: REFERENCES1. Wu, W.W. (1989). Eleme
Page 512: Appendix ANotationsThe symbols have
Page 516: N sPP rP sP TRRðtÞR cR eR rR vSS
Page 520: g Central anglez Channel gainZ Ante
Page 524: AttenuationBandwidthBearer serviceB
Page 528: Frequency divisionmultiple accessFr
Page 532: MultiplexingNetworkOmnidirectionala
Page 536: UplinkUser-to-networkinterfaceThe e
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