12.7 Commercial Applications
12.7.1 Code-Division Multiple Access
Spread-spectrum multiple-access techniques allow multiple signals occupying the same RF bandwidth to be transmitted simultaneously without interfering with one another. The application of spread-spectrum techniques to the problem of multiple access was discussed in Chapter 11 for a frequency-hopped code-division multiple-access (FH/CDMA) scheme. Here we consider CDMA using direct sequence (DS/CDMA). In these schemes, each of N user groups is given its own code, gi(t) where i = 1, 2, … , N. The user codes are approximately orthogonal, so that the cross-correlation of two different codes is near zero. The main advantage of a CDMA system is that all the participants can share the ...
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