ta signal as closely as possible. In the reverse direction, however, there is no pilot. There is, however, an expected PN code in the signal. The adaptive matched filter at the base station receiver attempts to combine the signals from different time delays to reassemble the PN code. The maximum signal level of the PN code is the optimal re- ceiver for the entire signal. This is an interesting tradeoff in CDMA design. The data rate in chips per second and the frequency bandwidth in hertz are typically very close. For example, a 1.25-MHz 8Triple amplitude is nine times the power because power is proportional to the square of amplitude. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The CDMA Principle Key Radio Concepts channel carries 1.2288 Mbps. If almost all the delay spread energy fits within one chip, then the rake filter and its time sidelobes have no damage to make up. However, if the delay spread energy is concentrated in a time that short, then the channel is narrow- band in terms of its resistance to multipath Rayleigh fading. The result is that if delay spread is in the nanoseconds range, the signal suffers from Rayleigh fading but not from delay-spread interference. However, if the delay spread is in microsecond range, then Rayleigh fading is not a problem, but delay-spread interference is. We have heard CDMA advocates tell us that one great advantage of CDMA is that "multipath is our friend." The idea seems to be that the adaptive matched filter creates a sort of processing gain of its own to discriminate between signal and interference. In actuality, the best possible rake filters achieve results almost as good as not having multipath at all. 9 As in the case of AMPS and GSM, more paths mean more power to combat receiver noise, but the advantage ends here for FDMA, TDMA, and CDMA. We see no particular advantage of having multip