Model-based opportunistic channel access in Dynamic spectrum access networks

We propose a model-based channel access mechanism for cognitive radio-enabled secondary network, which opportunistically uses the channel of an unslotted primary network when the channel is sensed idle. We have considered IEEE 802.11 WLAN as a de facto primary network operating in ISM band. Our study focuses on a single WLAN channel that is used by WLAN clients and a WLAN server for a mix of Email, FTP, and HTTP-based web browsing applications. We model the occupancy of the channel by primary WLAN nodes as an alternating renewal process. The secondary node uses the model to estimate residual idle time duration after the channel is sensed idle, and opportunistically transmits frames in that duration. Our simulation results show that the performance of secondary network is sensitive to the channel sensing duration and that high secondary throughput can be achieved without affecting the primary network significantly by choosing appropriate value of channel sensing duration