Abstract: An Enhanced RIEMS rate-adaptive MAC protocol(RIEMS+) is proposed, which improves the NAV undate mechanism of the original RIEMS protocol. In the new mechanism, neighbors of transmission nodes update their NAV values depending not only on the information in the MAC header but also on the information in the PHY header. RIEMS+ can decrease the transmission failure probability and increase the channel utility factor, because it overcomes the drawback that nodes may have different cognitions on channel status, which arises from the differences in propagation ranges of frames with varying transmission rates. Simulation results prove that the proposed method can improve the ETE throughput and the average packet transmission delay obviously.

Key words: mobile Ad Hoc network, multi-rate transmission, routing protocol