System design for DS/SSMA communications with negative chip excess bandwidth

Direct-sequence spread-spectrum multiple-access communications, strictly band-limited chip waveforms, random spreading sequences, an additive white Gaussian noise channel, and conventional matched filter receivers are considered. In this paper, system design with negative chip excess bandwidth is investigated. The effect of multiple-access interference (MAI) and interchip interference (ICI) on the system performance is analyzed. It is shown that the bit-error-rate can be reduced in near-far situations or in situations with unequal received powers by using chip waveforms with negative excess bandwidth. Other effects of using negative chip excess bandwidth are discussed. Numerical results are also provided.