New nonlinear detector for interference cancellation in spread spectrum overlay systems

Abstract

Overlaying spread spectrum systems on narrowband services has been proposed as a way to obtain greater bandwidth efficiencies with respect to sparsely narrowband systems. It is shown that, in overlay situation, the performances of both narrowband and spread spectrum systems are significantly degraded by each other. This paper presents a new nonlinear detector which enhances the performance of the narrowband system considerably. In our approach we use maximum likelihood (ML) and maximum entropy, which are two optimal criteria. Computer simulation results show that the proposed detector has much better performance than the conventional matched filter. The estimated narrowband signal can be subtracted from the received signal in the spread spectrum receiver to enhance its performance.