Signal processing for interference suppression in direct-sequence CDMA systems

The major limitation on the performance and capacity of direct-sequence code division multiple access (CDMA) is the multiple-access interference due to simultaneous transmissions. The signal processing for near-far resistant multiuser detectors typically follows a bank of matched filters or correlators (sampled at the symbol rate to produce sufficient statistics for demodulation) corresponding to all simultaneous transmissions. Due to the asynchronism among the transmissions, implementation of any near-far resistant demodulator using such a front end requires an infinite memory. However, an alternative front end which consists of a chip matched filter sampled at a multiple of the chip rate, coupled with the use of a finite observation interval for the demodulation of each symbol, can be used to obtain finite memory, near-far resistant, methods for demodulation and timing acquisition for asynchronous CDMA systems. We discuss the design of interference suppression schemes based on this front end