Outage Probability and Assignment Protocols in Cooperative Diversity

There has been widespread interest recently in cooperative relaying protocols for wireless networking, in which other terminals cooperate to send messages to an intended recipient node. Cooperation in the standard three-terminal model achieves diversity two in independently-faded channels, thus extending reach for a given outage probability, or allowing reduction in transmitter power relative to that necessary for direct transmission at the same outage probability. The performance of cooperating nodes in realistic wireless networks is the subject of this paper. We formulate a probabilistic model for outage probability in two relay-assignment scenarios for single-relay cooperative diversity. The model incorporates flexibility in choice of RF parameters, fading models, and network geometry. Illustrations are provided for square networks with varying number of nodes and path loss exponent to indicate impact of assignment protocol, and gains relative to direct transmission.