Rate-Adaptive MAC Protocol for Wireless Multicast Over OFDMA-Based MANETs

Unlike in unicast transmissions, a feedback channel has not been implemented for multicast transmission over Mobile ad hoc networks (MANET), due to the increase in the overhead with increasing group member size. As a result, rate-adaptation for wireless multicast has not been considered either. In this paper, a novel rate-adaptive Medium Access Control protocol is proposed to allow dynamic rate-adaptation for wireless multicast transmission over MANETs by utilizing the orthogonality of the subcarriers in an Orthogonal Frequency-Division Multiplexing system. In the proposed rate-adaptation method, each member station is assigned a unique subcarrier and by using this subcarrier, its preferred data rate in the current channel condition is reported to the multicast source. Due to their orthogonality, the feedbacked packets simultaneously transmitted by the group members can be distinguished at the source. Therefore, the source chooses the most appropriate data rate for all member stations. By using this method, the data rate for wireless multicast is able to be adaptively changed, so that the overall network performance is improved.