Performance analysis of CSMA/CA protocol during white space identification in cognitive radio networks

In this paper, we analyze the delay performance of distributed and centralized cooperative sensing approaches to find out which one is suitable for sensing inter packet white space. For simultaneous sharing of channels by primary users (PUs) and secondary users (SUs), the white space has duration of approximately 50 ms. In distributed cooperative sensing, the SUs perform carrier sense multiple access with collision avoidance (CSMA/CA) with distributed coordination function (DCF) for accessing common control channel to share sensing information among each other. In centralized cooperative sensing, SUs access common control channel to send sensing result to a fusion centre (FC) using CSMA/CA point coordination function (PCF) mechanism. Total delay of these two sensing approaches is given as the sum of total channel access delay and queuing delay. We find that for a particular number of SUs, the delay of sensing in centralized environment is within the permissible limit (i.e. within 50 ms). Although distributed cooperative sensing is much more reliable and scalable than centralized cooperative sensing, it has higher sensing delay than centralized sensing approach.