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and transmits through the satellite whenever needed, with all active stationssuperimposing their waveforms on the downlink. As such, no time orfrequency separation is required. Carrier separation is achieved at each earthstation by identifying the carrier with the proper signature.The uplink station, as in Fig. 5.7(b), spreads the user’s spectrum of Fig.5.7(a). The spread spectrum might contain some noise and other interferencewhen it is retransmitted. The receiver recovers the useful information byreducing the spectrum of the carrier transmitted in its original bandwidth, as inFig. 5.7(c). The effect of noise and other interference has been suppressed inFig. 5.7(c) for brevity. This operation simultaneously spreads the spectrum ofother users in such a way that they appear as noise of low spectral density.It should be noted that one could not simply use codes of arbitrarydifferent phases to provide CDMA, because the codes have high-autocorrelationsidelobes at the subsequent periods. Furthermore, the power spectraldensity of the codes has line components at frequencies corresponding to eachof the code periods [8].The spreading ratio is determined primarily by the code ratio k c =r c andcan be achieved either with low-rate channel codes or long address codes,wherek c ¼ T s Bð5:5Þr c ¼ 1ð5:6ÞT s r bThus, the spreading ratio: k c =r c ¼ B=r b . This ratio is commonly referred to asthe spreading ratio of the code modulation or CDMA bandwidth expansionfactor. In some texts, this ratio is halved because the carrier bandwidth is takenas B=2.CDMA has some advantages:1. It is simple to operate.2. It does not require any transmission synchronization betweenstations. The only synchronization required is that of the receiverto the sequence of the received carrier.3. It offers sufficient protection against interference from other stationsand that due to multiple paths. This makes CDMA attractive fornetworks of small stations with large antenna beamwidths and forsatellite communication with mobiles.However, on the average, its main disadvantage is the low throughputdemonstrated in the next section.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
Page 306: and Lin [5]:whereL ¼L o1 þ L oðr
Page 310: 3. Calculate attenuation A r in dB
Page 314: 4.2.1 Intersatellite LinksAs indica
Page 318: 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 360: 5.2 CAPACITY COMPARISON OFMULTIPLE-
Page 364: Rearranging (5.11) in terms of ener
Page 368: The transmission bit rate isR r ¼
Page 372: 6Error Detection and CorrectionCodi
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
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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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