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4.2.1 Intersatellite LinksAs indicated earlier in Chap. 2, satellite networks often require communicationsbetween two satellites via an intersatellite link (ISL) as in Fig. 4.6. AnISL is also called a cross-link. As a communication link, an ISL has thedisadvantage that both transmitter and receiver are spaceborne, thereby limitingoperation to both low transmitter power P t and low figure-of-merit ðG=TÞvalues. For long cross-links, it would be necessary to increase the satelliteEIRP. This means resorting to transmitting with narrow beams to achieve ahigher power concentration. We are constrained by the size of the antenna onthe satellite as such narrow beams can be achieved by transmitting at higherfrequencies. What are the other tradeoffs? The answer will become obvious bymodelling cross-linked satellites as seen in Fig. 4.7.The two satellites (A and B) in Fig. 4.7 are assumed to know the exactlocation of one another, use identical antenna of diameter D and beamwidth f cpointing at each other, in the same orbit of altitude h, and are not influenced byany aerodynamic drag.If the satellites are separated by propagation distance d c and angle g s ,and satellite A transmits signal of power P t to satellite B of equivalent noisetemperature T e , then, by geometry,d c ¼ 2ðR e þ hÞ sin g s =2 ð4:29ÞFIGURE 4.7A model of an intersatellite link.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
Page 262: FIGURE 3.21 A representation of mut
Page 266: In practice, Eqs. (3.78) and (3.76)
Page 270: This condition is always satisfied
Page 274: Copyright © 2002 by Marcel Dekker,
Page 278: epeaters overshooting into subseque
Page 282: 6. Conventional BPSK modulation all
Page 286: 4Satellite LinksA satellite link co
Page 290: FIGURE 4.2 Basic antenna parameters
Page 294: For unity efficiency, and substitut
Page 298: This expression neglects losses oth
Page 302: This expression is equally valid fo
Page 306: and Lin [5]:whereL ¼L o1 þ L oðr
Page 310: 3. Calculate attenuation A r in dB
Page 316: FIGURE 4.8Satellite separation dist
Page 320: inability of satellite A to accurat
Page 324: FIGURE 4.10 Cross-link E b =N 0 vs.
Page 328: Then using (4.41), the overall C=N
Page 332: (iv)(v)(vi)(vii)Calculate the recei
Page 336: 5Communication Networks andSystemsC
Page 340: discriminate among carriers by temp
Page 344: FIGURE 5.2 Principle of FDMA system
Page 348: FIGURE 5.3 Operational concept of T
Page 352: FIGURE 5.5TDMA: bit rate r b for 1
Page 356: Copyright © 2002 by Marcel Dekker,
Page 360: 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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