Methods for Reducing Interference caused to Licensed Systems by Overlay-CSMA/CA Cognitive Radios

Cognitive Radios (CR) have recently appeared as a solution to the spectrum scarcity problem, caused by static licensing policies. CRs can utilize spectral opportunities when and where Licensed Systems (LS) remain idle, operating in an overlay mode under the major restriction of not causing harmful interference to them. In this Paper, first, we investigate the IEEE 802.11 DCF behavior in the overlay network, in terms of interference caused to the LS. The importance of the three way hand shake mechanism in the overlay scenario is discovered. Then, we introduce a 3rd state to the carrier sensing mechanism of the CR stations and we extend the DCF functionality by exploiting the new state. Two new protocols that utilize the new mechanism are proposed, both of which achieve substantial reduction in the interference caused to the LS. The second protocol also improves the performance of the CR Network in terms of throughput.