Energy efficiency of cooperative ARQ strategies in low power networks

It has been shown in the literature that Cooperative Automatic Repeat Request (C-ARQ) strategies can improve the throughput and delay in wireless networks by jointly exploiting cooperative diversity gains with the adaptive rate capabilities of wireless communications technologies. In this paper, the suitability of using C-ARQ strategies in low-power networks using constant transmission rates is analyzed. Under these conditions, cooperation can help combat shadow fading in the direct link between a source and a destination. In order to quantify the performance gain achieved with C-ARQ in low power networks, we use an energy efficiency metric based on the average number of packet transmissions considering a realistic wireless channel. Because of the shadowing effect, an upper-bound on the allowed number of transmissions is imposed to characterize the outage probability. Results obtained through computer simulations confirm the validity of the analysis and show the improvement in energy efficiency achieved with cooperation as well as the conditions under which the cooperation yields better results than traditional non-cooperative ARQ strategies.