For junior- to senior-level introductory communication systems courses for undergraduates, or an introductory graduate course. A useful resource for electrical engineers.

This revision of Couch’s authoritative text provides the latest treatment of digital communication systems. The author balances coverage of both digital and analog communication systems, with an emphasis on design. Readers will gain a working knowledge of both classical mathematical and personal computer methods to analyze, design, and simulate modern communication systems. MATLAB is integrated throughout.

ALLOCATIONS Wireless communication systems often use the atmosphere for the transmission channel. Here, interference and propagation conditions are strongly dependent on the transmission frequency. Theoretically, any type of modulation (e.g., amplitude modulation, frequency modulation, single sideband, phase-shift keying, frequency-shift keying, etc.) could be used at any transmission frequency. However, to provide some semblance of order and to minimize interference, government regulations

use Eq. (2–83) to generate w(t) from the w j(t) functions and the coefficients aj. In this case, w(t) is approximated by using a reasonable number of the w j(t) functions. As shown in Fig. 2–10, for the case of real values for aj and real functions for w j(t), w(t) can be synthesized by adding up weighted versions of w j(t), where the weighting factors are given by {aj}. The summing-and-gain weighting operation may be conveniently realized by using an operational amplifier with multiple inputs.

when evaluated. The equivalence between the Fourier series coefficients is demonstrated geometrically in Fig. 2–11. It is seen that, in general, when a physical (real) waveform w(t) is represented by a Fourier series, cn is a complex number with a real part xn and an imaginary part yn (which are both real numbers), and consequently, an, bn, Dn, and wn are real numbers. In addition, Dn is a nonnegative number for n Ú 1. Furthermore, all of these coefficients describe the amount of frequency

117 b. Given the RC low-pass filter transfer function 1 1 + j(f/f0) H(f) = where f0 = 1 Hz, use the inverse fast Fourier transform (IFFT) of MATLAB to calculate the impulse response h(t). Solution. (a) From Eq. (2–30), the ICFT is q w(t) = L-q W(f)ej2pft df Referring to the discussion leading up to Eq. (2–184), the ICFT is approximated by w(k¢t) L ©W(n¢f)ej2pn¢fk¢t ¢f But ¢t = T/N,¢f = 1/T, and fs = 1/¢t, so w(k¢t) L Nc 1 ©W(n¢f)ej(2p/N)nk d ¢f N Using the definition of the IDFT as

generator is continuously compared to the sample value; when the value of the ramp becomes equal to the sample value, the binary value of the counter is read. This count is taken to be the PCM word. The binary counter and the ramp generator are then reset to zero and are ready to be reenergized at the next sampling time. This technique requires only a few components, but the speed of this type of ADC is usually limited by the speed of the counter. The Maxim ICL7106 LCD output ADC integrated