Adaptive optimization of receiver chip waveform for DS/SSMA with random spreading sequences

We consider the receiver optimization problem in asynchronous direct-sequence spread-spectrum multiple-access (DS/SSMA) communications with random spreading sequences. It is shown that the minimum average bit error rate of a correlation receiver is achieved by adaptively optimizing the receiver chip waveform depending on the energy and delay profiles of interfering users. Instead of directly solving an integral equation which gives the optimum chip waveform, we discretize the receiver chip waveform and develop a simple adaptive algorithm to find an approximate solution. Analytical predictions, as well as numerical results, show that the proposed receiver achieves a significant performance improvement over the conventional correlation receiver by effectively suppressing the multiple-access interference.