Study On Signal Detection In Wireless Broadband System

Broadband wireless communication systems offer high-speed data transmission services in wireless environment. By the employment of signal detection techniques, accurate acquisition of the received signal is obtained to provide subsequent communication signal analysis and processing. Effected by the multipath fading, frequency offset and narrow-band interference, the narrowband system based traditional signal detection scheme can not meet the requirement of the broadband system. Thus, it is an important issue to ensure the signal detection performance of wideband digital receiver in the complicated channel.This thesis focuses on signal detection techniques which use pseudo-random code sequences as preambles. The main content of the thesis is organized as follows:This thesis analyzes the signal detection technique of the communication system employing the pseudo-random code. By simulation results, it compares and analyzes detection performances of the delayed correlation method, the conjugate multiplication algorithm and the matched filtering method.Since the CFAR (constant false alarm ratio) adaptive threshold technique is sensitive to frequency offset, this thesis proposes an improved adaptive threshold detection scheme. By combining the delayed correlation technique and the adaptive threshold detection technique, the frequency offset is removed and the detection performance is guaranteed simultaneously. Meanwhile, the proposed scheme decreases the probability of false alarm detection when the signal to noise ratio increases by adding small offset. The simulation results show that the proposed scheme can maintain good detection performance in the large frequency offset environment where the frequency offset is 0.1 times as large as the symbol rate.As the multipath fading affects the correlation peak value, the precise acquisition can not be achieved. Therefore, this thesis proposes an improved scheme based on conjugate symmetry sequence detection algorithm to combat this problem. This improved scheme multiplies multiple short-time correlation peaks to enhance the correlation peak, thereby improving the signal detection performance. The simulation results show that the improved scheme obtains good detection performance in multipath environment. To eliminate the narrow-band interference which could lead to complete failure of signal detection in broadband wireless systems, this thesis designs two PN code acquisition schemes based on the amplitude processing in time domain and the frequency domain respectively to combat narrowband interference after analyzing the impact of narrowband interference on pseudo-random code sequences acquisition performance. Appling the design method to the traditional sum of squares detector, and combining with the adaptive threshold technology, this thesis achieves pseudo code acquisition in the strong interference environment. Simulation results show that the design can effectively suppress narrowband interference imposed on signal detection, and provide narrowband interference suppression gain with considerable additional spreading gain compared with detection without narrowband interference suppression scheme.