Design And Simulation Of Spectrum Sensing Mechanisms In Cognitive Radio Networks

Today's wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used disproportionately in space and time. The contradiction between limited available spectrum and the inefficient spectrum usage makes an intelligent spectrum allocation mechanism imperatively. This new networking paradigm is referred to as cognitive radio networks. Cognitive radio is a promising technology for solving the spectrum scarcity problem by opportunistically identifying spectrum holes and using them for transmission, while ensuring that primary users are not affected. One of the key enabling functions in cognitive radio networks is spectrum sensing that is used to explore spectrum holes and to avoid interference with primary users. In the paper, we focus on the spectrum sensing mechanism which can increase achievable throughput by the optimization of sensing parameter, selection of sensing strategies and partly cooperative spectrum sensing.Four scenarios are considered in our research, namely:single secondary user and single channel, single secondary user and multiple channels, multiple secondary users and single channel, multiple secondary users and multiple channels. In scenario one, we study the design of an optimal sensing period and sensing time to maximize the throughput under the constraint that the primary users are sufficiently protected. In addition, we introduce the interference temperature into the traditional dynamic spectrum access. In that case, not only can secondary users access spectrum holes, but also they can transmit with a low transmitting power while keeping the interference temperature under a threshold. In scenario two, the channels are arranged in a descending order of the probability that the channel would be idle at a certain time based on previous samples. Then secondary users sense the channels sequentially to minimize the searching time of confirming an idle channel. In scenario three, we change the frame structure of one sensing period and select some particular secondary users according to certain rules to only sense the spectrum without transmission. Compared with the traditional cooperative spectrum sensing, partial cooperative spectrum sensing brings fewer sensing overheads for the same performance. In the final scenario, we combine the methods used in the above three scenarios. Moreover, we set a spectrum pool in the fusion center to record the states of the channels. The ranking of the channels is based on both channel availability and channel occupation by secondary users. The secondary users, who are close to the secondary user occupying a certain channel, are selected to sense the channel cooperatively. Finally, the simulation results show that cognitive radio network can increase the spectrum efficiency to some degree, especially in the situation that the spectrums are used inadequately.