Research Of Cooperative Sensing Technology Based On Cognitive Radio

With the development of cognitive radio, dynamic spectrum accessing has been coming into reality increasingly which provides new research direction of solving the problems of shortage of spectrum. There are many primary users’authorized spectra which is unused in surrounding wireless communication environment. The basic thought of cognitive radio is that after detecting these spectrum holes by spectrum sensing, cognitive users access them dynamically to make their own communication. Cognitive radio technology can improve spectrum efficiency. At present, the main research directions of cognitive radio include spectrum sensing, spectrum analysis, spectrum decision, spectrum sharing, spectrum mobility management, route designing, transport layer protocol, network security problem and so on. From them, spectrum sensing is concerned widely as precondition of making use of unauthorized spectrum. There are two purposes of spectrum sensing. The one is that cognitive users detect of spectrum holes to utilize them effectively. The anther is when primary users are back to their authorized spectra, cognitive users need to detect it precisely and hand over these spectra to primary users in time.This thesis pays attention on cooperative spectrum sensing technology. Single cognitive user’s spectrum sensing is affected by multi-path effect and Hidden terminal effect easily. Cooperative spectrum sensing can solve these problems. This paper discusses cooperative energy detection with different data fusion methods under fading channels. The main works are as follows.1. A scheme of double-threshold cooperative energy detection with square-law combining was proposed. The expressions of detection probability over AWGN, Rayleigh and Nakagami channels were derived. And error detection probability was defined to quantize system’s error detection. Double-threshold energy detection algorithm can settle the problem of noise uncertainty to decrease error detection probability. But in the other hand, it also reduces the detection probability. Square-law combining technology was presented because it can solve the problem of low detection probability caused by double-threshold energy detection scheme. Simulation results show that error detection probability can be reduced by using double-threshold energy detection algorithm, and it becomes lower after square-law combining. Further more, square-law combining technology can greatly decrease high miss probability caused by double-threshold energy detection algorithm.2. Cooperative energy detection with hard fusion technology was discussed. The expressions of detection probability and the normalized average number of sensing bits are derived in AND-rule and OR-rule cooperative energy detection method with double-threshold. A scheme of cluster-based cooperative spectrum sensing was proposed. In this scheme within each cluster the channels between cognitive users and cluster head are Nakagami channels and fusion method of cluster head and fusion centre is under AND-rule. The normalized average number of sensing bits under AND-rule, OR-rule and cluster-based method were compared through Matlab simulation. Simulation results show that cluster-based cooperative spectrum sensing algorithm has preferable sensing performance by expending more sensing bits. 3. A method of cooperative energy detection with K-out-of-N rule data fusion which is better than AND-rule and OR-rule was presented. The expressions of optimal voting number of single-threshold and double-threshold cooperative energy detection were derived as minimizing error function. The simulation results prove that the error function of K-out-of-N rule cooperative energy detection is greatly decreased under optimal voting number.To sum up, this thesis analyzed cooperative sensing schemes of soft and hard fusion rules in order to increase system’s detection performance. Article’s research provides new thinking of devising more effective project of spectrum sensing. And it contributes to development of cooperative sensing technology of cognitive radio.