uency to a radio, assign a spread-spectrum carrier which is specified by a pseudorandom sequence. The pseudorandom sequence is in turn determined by a pseudo- random sequence generator key and its initial state. Thus, rather than assign a frequency to a radio we can assign a key to the radio that uses spread- spectrum signals. This is referred to as spread-spectrum multiple access (SSMA) [1]-[4], [58]-[62]. Multiple Access Assigning a key to a spread-spectrum radio is analogous to assigning a fre- quency to a conventional narrowband radio. The primary difference is that signals of different frequencies in an FDMA system are orthogonal functions of time, whereas spread-spectrum signals with different keys in an SSMA system have some time cross-correlation. When regarded as random processes, however, spread-spectrum signals with different keys are often designed to be statistically independent and are orthogonal in the statisti- cal sense of being uncorrelated random processes. This means that the expectation of the time cross-correlation is zero. It is possible for M signals of bandwidth of W Hz and T seconds to be orthogonal (zero time cross-correlation) for M < 2WT (coherent) and M < WT (non-coherent). These orthogonal signals can, in fact, be generated using the same waveforms as spread-spectrum signals discussed in previous chap- ters but with specific assigned chip sequences. For DS/BPSK waveforms, for example, using orthogonal binary sequences as the chip sequences will result in orthogonal signals. For FH/MFSK waveforms hopping sequences can be chosen SO that during a chip time (hop time) no two signals hop to the same part of the spread-spectrum frequency level. This is true as long as the chip sequences are time synchronized among all radios. If we relax the chip synchronization requirement, we can use chip sequence generators specifically designed to yield low time cross-correlations between signals for all relative time delays. Gold sequences and Bent sequences discussed in Chapter 5 of Part 1 result in