Mid-term questions Here are four essay questions for your consideration. On Wednesday, we will select two and ask you to write responding essays in your blue book. 1) Walter Ong's essay "Orality, Literacy and Modern Media" raises the point that amon
428 CHAPTER 6 PASSBAND DATA TRANSMISSION
0 5 10
t/TJ
FIGURE 6.52 A digital modem's waveforms of the standard pulses 901:0), k = 1, 2, . . . , 7.
incoming data stream across the PSTN every 1,000 us. Moreover, they deliver the data to
the receiver wit
542 CHAPTER 8 l MULTIUSER RADIO COMMUNICATIONS
Bandwidth
Time«flat Non—flat in both
time and frequency
Flat-flat Frequency-flat
O 71' Time duration
FIGURE 8.21 Illustrating the four classes of multipath channels: Tc = coherence time,
B6 = coherenc
548
CHAPTER 8 MULTIUSER RADIO COMMUNICATIONS
TABLE 8.3 Summary of two widely used
wireless communication systems
Item GSM“ IS-95Jr Comments
Number of duplex 125 20 CDMA assumes 12.5 MHz in each direction-
channels see the next line ’
Channel bandwidth 2
554
CHAPTER 8 MULTIUSER RADIO COMMUNICATIONS
User of
interest
"rim 0
Array Army
MZU) o chaff”?! signa[ _> Pl’OCessar
ma "X processor Output
c yizl
Interfering
u5ers
WING) '
vMit)
Multipath Sources of
channel AWGN Receiver
FIGURE 8.29 Block d
8.9 Source Coding of Speech ﬁn’ Wireless Communications 5 5 I
of the natural redundancy in speech, while maintaining a high—quality speech on decoding.
The common approach is to use source coding, which, in one form or another, exploits
the linear predict
734 APPENDIX 2 E REPRESENTATION 0F SIGNALS AND SYSTEMS
IN) I110)
2y1(t)
ZyQ (1‘)
A59 (1) h, (t)
FIGURE A2.8 Block diagram illustrating the relationships between the in-phase and quadrature
components of the response of a band-pass filter
A33 Modiﬁed Bessel Function 737
Interchanging the order of integration and summation:
m
E ]n(x)exp(in¢)=%l_7d06XP(ixsin0) E expnn(¢— 6)] (A314)
n=7m "=7w
m
We now invoke the following relation from Fourier transform theory:
6(4) ~ 1
277' n=wm
exp[in(¢)],
CONFLUENT
HYPERGEOMETRIC
FUNCTIONS
g A4.l Kummer’s Equation
The conﬂuent hypergeometric function1 is a solution of Kummer’s differential equation;
dzy dy _ r
x dxz + (b x) a — ay — 0 (A4.1)
where, in general, the parameters a and b are complex numbers. Fo
8.6 Statistical Characterization ofMultipath Channels 5 39
The function S(T;1/) is called the scattering function of the channel. For a physical
interpretation of it, consider the transmission of a single tone of frequency f’ (relative to
the carrier). Th
536
CHAPTER 8 E MULTIUSER RADIO COMMUNICATIONS
compared to the reciprocal of the spread in propagation path delays. Multipath in such
an environment results in two effects: rapid fading of the received signal envelope and a
spread in Doppler shifts in the
6. 12 Multichannel Modulation 43 l
V.90 Modem
The V.90 modem standard embodies digital and analog modems. The digital modem
at the ISP end is based on the second realization described earlier; it sends data downstream
at the rate of 5 6 kb/s. The analog m
434
CHAPTER 6 PASSBAND DATA TRANSMISSION
Maximum likelihood
Modulators detectors
Symbols
cos (21173;) 42(t) sin (Zflflt) 505 (211730 45") sin (211m
Linear wideband
a2 noisy channel A
A2 Modulator ; ———————— “—| 7 Detector
518
CHAPTER 8 MULTIUSER RADIO COMMUNICATIONS
energy-to-noise spectral density ratio, Eb/NO. Once a modulation scheme has been chosen
the ﬁrst design task is to specify two particular values of Eb/NO as described here; ’
1. Required Eb/No.
Suppose for exam
8.4 Radio Link Analysis 52 1
if any losses are present in the antenna (i.e., nmdiadm < 1). Henceforth, we assume that the
antenna is 100 percent efﬁcient and therefore refer only to the power gain of the antenna.
The concept of power gain, which is based
524
CHAPTER 8 MULT‘IUSER RADIO COMMUNICATIONS
with open—circuit voltage V0 cos(277ft), the available signal power is obtained when the
load connected to the source is
Z*(f) = R(f) - iX(f)
where the asterisk denotes complex conjugation. Under this conditio
8.4 Radio Link Analysis 527
Signal from
Wile
. _ r Frequency Intermediate
Zara? amt: —>
converter amplifier
Local
oscillator
FIGURE 8.10 Block diagram of earth terminal receiver.
ampliﬁer. The equivalent noise temperatures of these compon
530
CHAPTER 8 MULTIUSER RADIO COMMUNICATIONS
a radio transmitter or receiver is capable of being moved, regardless of whether it actually
moves or not. Due to the stochastic nature of the mobile radio channel, its CharacteriZatjoIl
mandates the use of pra
8.5 Wireless Communications 533
Direct-path signal f\/\/\/
Reflected signal W
Composite signal W;
Direct-path signal
Reflected signal
Composite signal
E5?
4>
Time Time
(a) (17)
FIGURE 8.14 (a) Constructive and (b) destructive forms of the multipath phenom
A5. 1 Secret-Key Cryptography 743
Enemy
Messa e X Y
EHCWPtEI’ Decrypter Message x
2
Secure
Key channel
FIGURE A5.l Block diagram of secret-key cryptographic system.
its security is inadequate for the needs of its users. It is assumed that
746 APPENDIX5 E Cnmocmm
graphic system can be subjected, and any system that succumbs to it is therefore considered
totally insecure. Thus, for a cryptographic system to provide secrecy, at the minimum it
should be immune to ciphertext—only attacks; ideal
Books 779
N.S. Jayant and P. Noll, Digital Coding of Waveforms: Principles and Applications to Speech and
Video (Englewood Cliffs, N.J.: Prentice-Hall, 1984).
N.S. Jayant (editor), Waveform Quantization and Coding (New York: IEEE Press, 1976).
H. Jeffreys
782
BIBLIOGRAPHY
RM. Woodward, Probability and Information Theory, with Applications to Radar, 2nd ed. (Elms-
ford, N.Y.: Pergamon Press, 1964).
I.M. Wozencraft and I.M. Jacobs, Principles of Communication Engineering (New York: Wiley,
1965).
W.W. Wu, Ele
Papers, Reports, Patents 785
G.D. Forney, ]r., and M.V. Eyuboglu, “Combined equalization and coding using precoding,” IEEE
Communications Magazine, vol. 29, no. 12, pp. 25—34, 1991.
GD. Forney, IL, L. Brown, M.V. Eyuboglu, and LL. Moran III, “The V.34 hig
788
BIBLIOGRAPHY
P. Noll, “MPEG digital audio coding standards.” In V.K. Madisetti and DB. Williams (editors),
The Digital Signal Processing Handbook, Piscataway, N.].: IEEE Press, pp. 40-1—40—28, 1998_
DO. North, “An analysis of the factors which determi
I NOTES
Notes 79 l
N. Zervos and I. Kalet, “Optimized decision feedback equalization versus optjm'ued orthogonal
frequency division multiplexing for high-speed data transmission over the local cable net-
work,” International Conference on Communications,