Research On Spectrum Sensing And Dynamic Spectrum Accessing Technology In Cognitive Radio Systems

The problem of spectrum resource scarcity is becoming more and more serious as the number of wireless communication devices developing rapidly. Cognitive Radio (CR) technology can solve the problem effectively. CR is a revolutionary technology of the wireless mobile communication area; users can detect all the opportunities of utilizing spectrum in the wireless network environment, and access the idle spectrum dynamically, thus the capacity of the network and the spectrum utilization ratio can both be enhanced.Cognitive Radio Users (CRUs) opportunistically access the spectrum band that is licensed to but is currently not being used by other systems. The basic requirement of the opportunistic accessing is that it can not cause interference to the Licensed Users (LUs), thus the precondition of dynamic spectrum accessing is detecting the idle spectrum resource; only when the idle spectrum resource is found, can the CRUs opportunistically access the spectrum.In this paper, firstly we briefly introduce the concept, development, and the key technologies of CR. In the following we investigate the current research about spectrum sensing technology in CR network, and propose a confidence-based collaborative sensor selection algorithm which can select the CRUs having the highest signal detection performance to participate in cooperative spectrum sensing. The simulation results show the signal detection performance can be significantly promoted when our algorithm is used.CRUs need to access the idle spectrum after detecting it. In the next we investigate the current work about dynamic spectrum sensing protocol in CR network. Specifically we introduce the channel hopping-based spectrum accessing protocol and the hidden terminal problem in the CR network, and propose a channel hopping-based MAC protocol which can solve the hidden terminal problem by using two transceivers and a control channel, and enable CRUs to reserve spectrum resource by extending the 802.11 RTS/CTS handshake to a three-way handshake. In addition, by flexibly adjusting the channel sensing sequence according to the channel usage, CR users could choose data channels having the highest transmission opportunity to sense and access to improve their throughput. We develop a mathematic model to analysis the network throughput and use Matlab to verify it.Besides, noticing the fact that in the current MAC protocols CRUs have to spend much time on spectrum sensing, we develop a two-stage sensing-based MAC protocol which can shorten the spectrum sensing time significantly by reducing the number of channels that the sender and receiver have to sense in order to find a channel available to both of them, and design an accessing protocol enabling users to exchange control messages effectively to start data transmissions quickly. We use NS-2 to simulate the network throughput under varying parameters.