Interference control and chip waveform design in multirate DS-CDMA communication systems

We study the interference effects in a multirate DS-code-division multiple-access (CDMA) system. Optimum chip waveform selection with arbitrary shapes is analyzed using a time domain approach. The problem is posed as an interference minimization problem under energy and time-bandwidth constraints and prolate spheroidal wave functions are used to arrive at a solution. Various factors affecting the interference are identified and the trade-off between competing factors is analyzed. The effect of the interchip interference on the optimum chip waveform design is also quantified under a practical bandwidth constraint. We study the benefits of employing two different chip waveforms for two classes of users. We compare the performance of systems employing two different chip waveforms with that of a single-chip waveform system such as IS-95. We show that when the power imbalance is large, it is advantageous to employ two different chip waveforms for different classes of users