QP-CSMA-CA: A modified CSMA-CA-based cognitive channel access mechanism with testbed implementation

In this paper, a modified carrier sense multiple access-collision avoidance (CSMA-CA) mechanism, termed as quiet period-CSMA-CA (QP-CSMA-CA) is proposed, for the purposes of coexistence in a cognitive networking set-up with secondary clients that seek access using 802.11. In work to date, dedicated quiet periods have been defined for this purpose, as a synchronized duration wherein all clients are prohibited from uplink transmissions; this interval is intended for sensing channel status so as to detect out-of-network transmissions. However, such dedicated periods may adversely impact system throughput as the price for coexistence. In QP-CSMA-CA, the Wi-Fi nodes perform channel sensing during an extended back-off phase; thereby bypassing the need for separate dedicated sensing interval. The proposed QP-CSMA-CA protocol is implemented on the universal software radio peripheral (USRP)-based software defined radio platform and configured in a small network for measuring throughput and latency. Experimental and simulation results show the efficacy of the proposed algorithm over the dedicated sensing-based mechanism when compared in terms of system throughput and medium access latency.