| Wireless spectrum is a very precious and limited resource, with the rapid development of wireless communication theory and technology, wireless service is constantly expanding, then resulting in the current radio spectrum resource becoming increasingly strained. At the same time the unreasonable static spectrum allocation causes an extremely low resource utilization rate. How to solve this problem has become the key to keep a sustainable development of communication technology in the future.CR(Cognitive Radio) can radically solve the issue about relative shortage of wireless spectrum resource. Through spectrum hole detecting and give a reasonable allocation, CR can effectively improve the spectrum efficiency. On the other hand, multi-antenna technology added space dimension on the time and spectrum dimension. By using spatial multiplexing, in theory, MIMO can exponentially increase link capacity without taking up additional spectrum resources. In recent years, MIMO has been a hot research point in the field of wireless communication and also become one key technology of next generation mobile communication system. Above all, CR and MIMO are both effective ways to improve spectrum efficiency, it is naturally imaged that if applying the multi-antenna to cognitive radio system, besides the flexibility of traditional time and spectrum domain brings, it will reach a higher spectrum efficiency by using additional space domain, and it also bring with the improvement in capacity and flexibility of system.This paper mainly gives a system performance analysis and designs a cooperative spectrum sensing algorithm based on the cognitive MIMO radio system. The system performance analysis part focuses on system capacity and outage probability. First, through establishing a simple analysis model which consists of one primary and one secondary communication system and each system just contains a pair of a transmitter and a receiver, give a quantitative analysis of system capacity and outage probability based on some common spectrum access technology, then give an assessment of the performance through a simulation of several scenarios by matlab. The results show that, system capacity reaches the maximum under overlay access technology, then followed by underlay and interweave. Through the comparison with non-cognitive scenario, it’s clear that cognitive technology improve capacity largely. About outage probability, because underlay and underlay both use authorized spectrum when primary users are busy, then the QoS of primary users are affected, and the algorithm complexity of these two are higher than interweave algorithm, so the choose of optimal access method should be based on the actual needs in practical system.Secondly, based on the study of system performance analysis, this paper analyzes spectrum sensing algorithm of cognitive MIMO system. In consideration of the advantages of cooperative spectrum sensing and features of MIMO system, it supposes a cooperative spectrum sensing algorithm based on user selection. The algorithm firstly through local multi-antenna’s combined detection to get a result of each user, then just apply partial results of some specific users who has a high SNR to give a final detection result. Through user selection, it not only keep a high sensing performance and the signaling and power overhead of network can be greatly reduced, thereby improving detection efficiency. At last, this paper through simulation and analysis of detection probability and false alarm probability, proves that after the application of multi-antenna in cognitive radio system, the total system performance and detection strategy flexibility improves significantly. |
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