A rate adaptive multicast protocol for providing MAC layer reliability in WLANs

IEEE802.11b standard provides 1, 2, 5.5, 11 Mbps data rates. These data rates can be made possible by using different modulation techniques: DBPSK, DQPSK, CCK5.5 and CCK11 respectively. Rate adaptation is the process of dynamically selecting a proper modulation scheme depending on channel conditions in order to improve total throughput. Current rate adaptation protocols deal with unicast links rather than multicast. Measuring the received Signal Strength (RSS) of a feedback message (CTS, ACK) to estimate the receiver's link condition, can be one way to do this. A receiver may send its channel condition information to the sender allowing it to adapt its data rate for the following transmission. IEEE802.11 standard however, does not provide feedback messages for MAC layer recovery on multicast frames. This is due to collisions occurring if multicast group members simultaneously initiate a feedback message. Therefore, in order to link adapt multicast, a reliable multicast MAC protocol has to be introduced. In this paper, we propose a Rate Adaptive Multicast (RAM) protocol which provides reliability to WLANs and enhances its throughput by using Rate Adaptation. Further, we evaluate our protocol by throughput analysis and computer simulation. Simulation results suggest that our protocol performs better than related/existing protocols in both throughput as well as reliability.