Spectral efficiency of CDMA with random spreading

The CDMA channel with randomly and independently chosen spreading sequences accurately models the situation where pseudonoise sequences span many symb ol periods, Furthermore, its analysis provides a comparison baseline for CD MA channels with deterministic signature waveforms spanning one symbol peri od, We analyze the spectral efficiency (total capacity per chip) as a funct ion of the number of users, spreading gain, and signal-to-noise ratio, and we quantify the loss in efficiency relative to an optimally chosen set of s ignature sequences and relative to multiaccess with no spreading. White Gau ssian background noise and equal-power synchronous users are assumed. The f ollowing receivers are analyzed: a) optimal joint processing, b) single-use r matched filtering, c) decorrelation, and d) MMSE linear processing.