Adaptive Cooperative Multi-hop Transmission in Ad Hoc Networks

Cooperative communication techniques have been proposed in order to improve the quality of the received signals at the receivers by using the diversity added by du plication of signals sent by relay terminals situating between e ach transmission pair. This paper proposes an adaptive cooperation technique for frame transmissions in Ad Hoc networks that is compatible to both of the basic ac cess mode and the optional access mode of IEEE 802.11 Medium Access Control (MAC) protocol. The transmission mode for each data frame is adaptively switched between a cooperative mode and a non-cooperative mode based on the absence of ackn owledge (ACK) frame. Simulations show that transmission performance is improved by decreasing the number of retransmissions due to frame errors; thus, chances of multi-hop mode transitions that are costly in time and bandwi dth are alleviated. The analysis of the proposition performance indicates the interest of the adaptation paradigm. It puts forward that, in addition to the channel quality parameter, the channel availability parameter must be concerned in the adaptation process. Keywords-adaptive cooperation; cooperative transmissions; IEEE 802.11