Research On Cooperate Specturm Sencing In Cognitive Radio

With the decrease of spectrum resource and the growth of demand for high speed communication, cognitive radio has attracted broad attention for its potential to increase the spectrum efficiency. The most important job of cognitive radio is to find out spectrum hole and utilize them, and quit to use them when detecting primary users. Considering the limits of mobile end, spectrum detection techniques for single user can not satisfy the growing requirement for spectrum sensing, collaborative and cooperative spectrum sensing schemes have been proposed and studied by researches these years.In this article, we first introduce the concept of spectrum hole and how to conduct spectrum sensing. Based on the theoretical analysis of spectrum sensing for single user, we analysis the performance of collaborative spectrum sensing. Simulation shows that collaboration would gain more if only the parts of good performance are chosen.At the mean time, the probability of detection for cognitive radio network can be improved through amplify-and-forward based cooperative communication among cognitive radio users. However the previous model suffers from the unpractical assumption that perfect channel estimation for relay channel could be gained. So we analysis and deduce the probability of false alarm and probability of detection for cooperative spectrum sensing system. And we point out that the probability of detection would decrease with the increase of estimation error. And if the users fail to realize the existence of estimation error, the probability of false alarm would also grow, thus lower the spectrum efficiency.Then, we analyze the channel estimation problem for cooperative communication. First, through analysis of the PDF of the channel gain and level cross rate, we point out that it's much easier for AF channel to fall in deep fading, and the fluctuation is heavier. Then we analyze the common estimation algorithm, including ZF, MMSE and LMMSE. And we point out that due to the non-Gaussian property of noise; it's hard to calculate the MMSE algorithm.Finally, we choose the frequency domain processing for single carrier DS-CDMA communication mode as system mode, to conduct our research on the performance of cooperative spectrum sensing system. First, we introduce the system's payoff for the AF cooperative scheme. And we introduce the delay time-domain windowing technique and decision feedback technique for cooperative channel estimation. Our simulations show that delay time-domain windowing technique can improve the channel estimation for AF. And we analyze the application problem of decision feedback for AF. At last, through comparing the theoretical BER performance and simulation BER performance, we verify the accuracy of our system and present the performance for cooperative spectrum sensing. Simulation shows that cooperative spectrum sensing could outperform non-cooperative scheme under some circumstance.