Research On Dynamic Channel Access Strategy In Cognitive Radio Networks

Cognitive radio is an important technology in the field of wireless communications.Secondary users(SUs)in the system have cognitive capabilities but no licensed channels,they can use channel sensing to detect the surrounding wireless communication environment and dynamically adjust their own parameters to access licensed channels of primary users(PUs)opportunistically.On the basis of avoiding interference with PUs,channel sensing and dynamic channel access can realize channel sharing and maximize the channel efficiency.Since PUs access channels randomly,it will interrupt ongoing services of SUs,the quality of service(QoS)of SUs is often not guaranteed.Based on channel leasing and different modes of SUs access channels,two dynamic channel access strategies are proposed to improve the QoS of SUs and the channel efficiency of system.The main work of this paper is as follows:1.A dynamic channel assembling strategy based on channel leasing is proposed.In this case each SU can assemble as many channels as possible for signal transmission when idle channels are sufficient.The strategy with a smaller lower limit and a larger upper limit brings significant performance improvement to SUs in terms of capacity,blocking probability and forced termination probability.This strategy doesn't sacrifice the QoS for PUs,but instead makes capacity better and reduces blocking probability and forced termination probability.In addition,the channel efficiency of system has also been improved to some extent.2.A new underlay dynamic channel access strategy(UDCA)is proposed.Combining channel assembling,channel adaptation and limiting the occupied proportion of channels,in order to achieve better performance for SUs.We propose partial channel occupancy(PCO)mode and half channel occupancy(HCO)mode.According to the maximum allowable interference,system sets the appropriate value of ? for PCO to determine the proportion of channels that SUs can use.This parameter is monitored and configured by central base station.We use CTMC to model UDCA strategy and evaluate performance of capacity,blocking probability,forced termination probability,number of SUs in system,gain loss metrics,and compared with the strategy in interweave mode.The numerical results show that UDCA strategy is superior to the interweave mode in terms of SUs' capacity,blocking probability and forced termination probability.By analyzing the gain loss indicator,itis determined how to set the value of ? to maximize the overall performance of system when using UDCA strategy.