Improving CSMA for WLANs via Piggybacking and Scheduled Backoff Mechanisms

In this work, we propose a novel medium access scheme named Smart-CSMA with piggybacking that can effectively solve the collision problem and enhance the throughput and access delay performance as well as the quality-of-service support for a high-speed WLAN in the infrastructure topology. Smart-CSMA with piggybacking combines the advantages of the standard PCF and DCF modes. It can efficiently supports the quality-of-service requirements like in the PCF access mode while relying on the simple on- demand CSMA channel access mechanism like in the DCF mode. In the proposed scheme, every station employs the standard CSMA mechanism with a slightly modified backoff procedure. A master station is responsible for scheduling backoff timers for all client stations. It shall send the backoff timer information together with the frames destined to each client station. The client station then uses the received backoff timer value to start the backoff procedure associated with the current transmission in the queue. If the client station has not obtained the backoff schedule from the master station due to any reason, it then uses a random backoff value to start the backoff procedure. A generic algorithm is provided for the master station to allocate arbitrary slots for each client station. Furthermore, a piggybacking frame exchange mechanism is proposed to enhance capacity of the system. Numerical results show that the proposed scheme significantly outperforms the standard IEEE 802.11 DCF and PCF schemes, and the superior performance is not sensitive to the number of active and inactive client stations in the network.