The Performance of Space-Time Processing for Suppressing Narrowband Interference in CDMA Communications

The requirement to suppress narrowband interferences in CDMA communications stems from the overlay concept, i.e., coexistence of different types of signals in the same frequency band. The conventional approach to rejecting the narrowband interferences has been to whiten the received signal containing the interference, prior to spread spectrum demodulation. In this paper, it is proposed to achieve the interference rejection through spatial processing. The main benefit of this approach is its robustness with respect to the interference bandwidth. Stepping up from single domain spatial processing to space-time processing provides degrees of freedom for both overlay interference cancellation and diversity combining. Two space-time architectures, cascade and joint-domain, are studied and compared to a Rake receiver preceded by a whitening filter. Main contributions of the paper are the development of analytical expressions of (1) the efficiency of each method, (2) the p.d.f.'s of the output SNR in a Rayleigh fading environment, and (3) the error probability associated with each method. The analysis therein demonstrates that the joint-domain architecture outperforms the cascade configuration, which in turn is superior to the whitening filter-Rake combination.