Signal monitoring on the downlink of cellular CDMA communications with interference cancellation

We develop and evaluate receiver algorithms for the detection of signals transmitted via the downlink of a cellular system modeled after the IS-95 standard for code-division multiple-access (CDMA) communications. Multiuser detectors on board airborne and terrestrial mobile signal monitors attempt the simultaneous detection, in a single receiver, of all communication signals transmitted by the base station of interest. Due to the detrimental effects of transmitter, receiver and channel nonlinearities, very fast multipath fading, Doppler spread, additive white Gaussian noise, and intercell multiple-access interference, the user signals are de-orthogonalized. This leads to performance degradation in conventional receivers that is too severe, especially when the powers of some of the interfering users are dominant. In order to improve upon the performance of conventional matched filter receivers, this article focuses on the development and evaluation of relatively simple successive interference canceling (SIC) algorithms. The techniques we have developed can be used to enable successful interception of CDMA signals; to relax the strict requirements on power control; and to improve the capacity of CDMA systems.