Sensing of transmission opportunities at the Medium Access Control layer for cognitive radio networks

Detection of transmission opportunities is the critical part of establishing a cognitive radio network. Traditionally, it is achieved via spectrum sensing carried out at the physical layer to detect unused frequency bands. In this paper, we propose a novel approach to detect transmission opportunities at the Medium Access Control (MAC) layer based on the concept of interference temperature. In this approach, secondary transmissions are overlayed on top of primary transmissions as long as they do not affect the primary transmission. A Transmit Margin is defined and used to quantify the spare capacity in the primary network. We setup a system to estimate and track the Packet Error Rates (PER) and use it as a metric for transmit opportunity detection. A distributed estimation procedure to increase the robustness of the estimate is also proposed for cognitive radio networks. The scope of this hitherto unexplored area of cognitive radios is demonstrated and applied to IEEE 802.11 wireless networks through simulation studies.