Study On Lapped Transform Of Narrow-Band Interference Rejection Techniques In DSSS

Spread spectrum technique has a number of internal advantages, such as anti-interference, low-probability-of-intercept, code division multiple access (CDMA) etc, which make it get broad applications in the third gerneration mobile communication systems, broadband wireless access systems and satellite communication systems, especially in military satellite communication systems. Despite of the fact that spread spectrum modulation techniques inherently offer some degree of protection against non-white interferences with its processing gain, it is often nessary to supplement the innate processing gain associate with the spreading code by using additional signal processing techniques.During the past twenty years, The study on the narrow-band interference(NBI) rejection techniques in spread spectrum system is active, a lot of research is focus on the exploitation of narrow-band interference rejection techniques of the spread spectrum system. It is still an important task of many researchers until now.The major work and achievement of this dissertation as follows.(l)Firstly, this thesis briefly introduces the spread spectrum communication systems, especially the direct sequence spread spectrum(DSSS) that the most typical spread spectrum communication system, and the developing NBI suppression techniques at present.(2)Secondly, this thesis deeply researchs NBI suppression technique based on lapped transform. Lapped transform principle, structure and basic type are analyzed. On the basis, a receiver model is developed, and an algorithm based on lapped transform domain is proposed, and simulate in computer. Simulation results show that the systems BER performance is improved greatly and NBI is suppressed greately.(3)Finally, a new adaptive algorithm is proposed to suppress unstable NBI in DSSS communication systems. Aim at the disadvantages of Wigner-Ville distribution(WVD), Lapped transform decomposes a multi-component signal into a number of single signals and the WVD isapplied to them. So the single-component interference is located and rejected by time-varying IIR filter. The IIR filter has ideal characteristic compared with FIR filter with linear angle. The results of computer simulation show the BER of IIR filter is lower than that of FIR filter.At last, we summarize all the working, and point out what we must do in the future.