On The Hybrid Channel Access Strategy In Cognitive Radion Networks

Along with the emergence of wireless communication technology such as the mobileinternet and networking, the limit of traditional static spectrum access is more obvious.Cognitive radio networks is an important technical means for solving the shortage ofspectrum resources in wireless network communications and receives widespreadattention. Considering two different network environments, the corresponding channelaccess strategies are proposed. System performance analysis and optimization are alsoinvestigated.Firstly, considering the strategy of centralized channel access can be optimizedglobally, the strategy of distributed channel access has better flexibility, aiming at thenon-real-time traffic in cognitive radio networks, a coordination schedule between thestochastic back-off and the central control is established; A hybrid channel access strategyis then proposed named HCAS. Assuming that there exists only one primary user and agroup of authorized channel in the primary network, based on the numbers of channelsoccupied by primary users and cognitive users respectively, a discrete-timetwo-dimensional Markov model is constructed. Given that the cognitive user has a perfectspectrum sensing, the transition probability matrix is built, and the system model isanalyzed in steady-state. Some important performance measures for the hybrid channelaccess strategy are derived accordingly, such as the channel utility, the interruption ratioand the blocking ratio of the cognitive users.Secondly, on the basis of HCAS strategy, considering the primary network containswith different business communication characteristics of the two authorized users and thecorresponding two groups of authorized channels, given that cognitive user can switchbetween the two groups, a novel channel access strategy with channel group switchingwas proposed named GS-HCAS. Based on the numbers of the primary packets on eachgroup channels and the total number of the cognitive packets on both of the two groups ofchannels in a slot, a three-dimensional Markov model was constructed. The model isanalyzed in steady-state; some important measures of cognitive users are derivedaccordingly, such as the channel utility, the packet loss rate, the blocking ratio and the average delay.Finally, Numerical results of analysis and simulation are provided to investigate theinfluence of cognitive users’ capacity and average back-off time on the systemperformance of HCAS and GS-HCAS. For the HCAS strategy, The results show that, withthe change of cognitive users capacity, there is a trade-off between different performancemeasures. So a maximum system income will be received by optimizing the averagecognitive user’s capacity. For the GS-HCAS strategy, The results show that, with thechange of the average back-off time, there is a tradeoff between different performancemeasures. So a minimum system cost will be received by optimizing the average back-offtime.