Narrow-band Interference Suppression For DSSS/DS-CDMA Systems Based On Code-Aided Techniques

Spread spectrum communication is widely used in the mobile communication and personal communication systems. The large narrow band interference (NBI) can make spread spectrum communication invalid, although the system can suppress NBI in the common degree. So the work on the suppression of NBI in the spread spectrum communication is significative.The valid NBI suppression methods used in spread spectrum communications can be effectively grouped into linear predictive (LP), nonlinear predictive (NLP), and code-aided techniques. Code-aided technique is a major advance in the development of NBI suppression of techniques which has made by exploiting the spreading codes and NBI codes. Code-aided technique can not only reject the NBI in the presence of a single spread spectrum signal but also reject the NBI and multi-access interference (MAI) in overlay spread spectrum systems. And this paper pays the attention to the code-aided techniques.To begin with, this paper analyzes the NBI rejection in the direct-sequence spread spectrum systems based on code-aided techniques. The performance of decoding is badly affected based on general code-aided techniques because of the phase of complex gain accounting for channel effects. The system based on modified code-aided techniques can cancel or relieve the effects but attend by high computational complexity. So this paper designs a new optimal restrictive code-aided technique to solve this trouble without increase of the computational complexity.Then, this paper analyzes the NBI rejection in the code division multiple access of synchronous direct-sequence spread spectrum communication (DS-CDMA) based on code-aided techniques. Although the general code-aided techniques have the ability of joint suppression of MAI and NBI, the system based on it is similarly affected by phase of complex gain accounting for channel effects. In addition, the system based on modified code-aided techniques can cancel or relieve the effects but attend by high computational complexity. This paper uses the idea of optimal restrictive condition to solve this problem without increase of the computational complexity in synchronous DS-CDMA systems.At last, this paper investigates the adaptive least-mean squares (LMS) code-aided technique and adaptive recursive-least-squares (RLS) code-aided technique and analyzes the effect of different parameter in the NBI suppression of spread spectrum systems.