A new cooperative access protocol is presented in the context of IEEE 802.11-based fixed ad hoc networks. The protocol achieves optimal diversity-multiplexing tradeoff thanks to two known functionalities: on-demand cooperation and selection of the best relay. The on-demand approach allows maximization of the spatial multiplexing gain. The selection of the best relay allows maximization of the spatial diversity order. The main contribution of this paper consists in the design of a proactive mechanism in order to select the best relay. The mechanism is centralized at the destination terminal. Destination terminals maintain lists of relays for all possible source terminals by overhearing ongoing transmissions. So when cooperation is needed, a destination terminal just picks the best relay for a specific source terminal in the corresponding table. Hence, collision among relay candidates is now avoided. Moreover, only terminals that can improve the direct transmission are selected. This guarantees the usefulness of relaying. This study focusses on Nakagami-m wireless channel models in order to encompass a wide variety of fading models.
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