Dsss Interference Suppression In Communication Systems Technology

Currently, Spread-Spectrum (SS) technique has been widely applied both in military and in civilian communications for its many advantages, which make it suitable for the environments of wireless communication. The best advantage is its outstanding ability to anti-jam if the processing gain is large enough. However, its ability of interference suppression is always limited. The system performance is dramatically degraded and its capacity is largely reduced if the processing gain is not sufficiently large and no other methods can be adopted to suppress strong interference.Therefore, interference suppression is a crucial issue in SS systems. It is necessary to apply the special suppression techniques in new detection structures. The suppression techniques to narrowband interference are very mature in DSSS systems. So, in this thesis we concentrate on wideband interference suppression. Secondly, since both interference and channel characteristics are dynamically changed in real environments, adaptive receiver construction must be applied.Recently the theory of cyclic Wiener filtering, based on the cyclostationarity assumption for the signals, developed greatly in signal reception program and can be applied to design single-channel adaptive frequency-shift (FRESH) filters. The FRESH filter exploits both temporal and spectral correlation properties to remove interferences and noises from the desired signal. As most digital communication signals are cyclostationary, FRESH filter can perform excellent of suppression interference in a communication receiver.This thesis firstly introduces the basic theories of both cyclostationarity and cyclic Wiener filtering. Then, it investigates how a FRESH filter removes interference by exploiting the cyclostationarity of signals including baud rate related and carrier related cyclostationarity. Finally an adaptive FRESH algorithm is programmed and a model of DSSS system is built and simulated, based on the principle and structure of FRESH filter. The results will prove that, in case ofstrong interference, FRESH filter can display good ability to wideband interference rejection.