Dynamic spectrum access to the unused licensed spectrum has been proposed as a solution to the spectrum scarcity problem. However, efficient spectrum sensing techniques are crucial on the way towards systems, which use idle spectrum bands opportunistically and increase the overall spectral efficiency. The spectrum occupancy measurement is very important for the efficient spectrum sensing. Current spectrum occupancy was evaluated in few measurement campaigns. This paper describes spectrum occupancy measurement about TV spectrum source performed in Chengdu. Through analysis measurement result, we can find the idle spectrum band which can be used by the Cognitive Radio.I.

SUMMARY In an opportunistic spectrum sharing system, secondary users (SUs) opportunistically access the white space spectrum that is not occupied by the primary user (PU). Some analytical performance models have been available based on Markov chain modeling. In these models, SUs and PUs access the spectrum by randomly selecting the available channels with equal probability. However, how SUs and PUs use the spectrum are controlled by the access strategy designed in their MAC layer in an ad‐hoc network or centralized radio resource management layer in an infrastructure‐based network. To analyze the grade of service (GoS) of the secondary system under consideration for the access strategy, we propose an access rule transition matrix to model the access behavior of radio resource management, and apply it into the continuous‐time Markov chain model. It was proved that the proposed model is equivalent to the original models assuming the random access strategy by simulation. Moreover, we analyzed the GoS performance of the secondary system by assuming an ordered hunt access strategy. The results showed that the GoS performance of secondary systems can be improved greatly if it knows the spectrum access strategy of the primary system. Copyright © 2011 John Wiley & Sons, Ltd.

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We analyze the performance of an opportunistic spectrum sharing systems. The secondary users detect channels that are unused by the primary users and hence use the idle channels. If all channels are not idle, the secondary user can wait in a buffer until either one channel becomes available or a maximum waiting time is reached. Which can reduce obviously the blocking probability of secondary users.If an active secondary user detects the arrival of a primary user on a given channel, it releases the channel and switches to another idle channel. If no channel is available, the call also comes into a buffer. At the same time, We take the errors of spectrum sensing into consideration, which can potentially degrade the quality-of-service experienced by primary users.Our results suggest that opportunistic spectrum sharing can significantly improve spectrum efficiency and system capacity, even under unreliable spectrum detection, but doesn't breakdown the quality-of-service experienced by secondary users.

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