Model-Based Opportunistic Channel Access in Cognitive Radio Enabled 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 refer to primary network as the network which carry the main traffic in a designated spectrum band. 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. When the secondary sender node has one or more frames to send, this model is used by the the sender and receiver pair to estimate residual idle time duration after the channel is sensed as idle. The secondary sender then opportunistically transmits frames in that duration without significantly degrading performance of the primary WLAN applications. 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.