  This paper presents a decentralized relay selection protocol for a dense
wireless network and describes channel feedback strategies that improve its
performance. The proposed selection protocol supports hybrid
automatic-repeat-request transmission where relays forward parity information
to the destination in the event of a decoding error. Channel feedback is
employed for refining the relay selection process and for selecting an
appropriate transmission mode in a proposed adaptive modulation transmission
framework. An approximation of the throughput of the proposed adaptive
modulation strategy is presented, and the dependence of the throughput on
system parameters such as the relay contention probability and the adaptive
modulation switching point is illustrated via maximization of this
approximation. Simulations show that the throughput of the proposed selection
strategy is comparable to that yielded by a centralized selection approach that
relies on geographic information.
