Energy efficiency of centrally controlled transmission of fixed size packets

Wireless network access protocols can assist nodes to conserve energy by identifying when they can enter a low energy doze state. The goal is to put all nodes not involved in a transmission into the doze state. However, in doing so, one must tradeoff the energy cost of coordinating dozing with the energy savings of putting nodes to sleep. In this paper, we define three alternative directory protocols that may be used by a central node to coordinate the transmission of data and the dozing of nodes. We attempt to optimize their performance by using scheduling and protocol parameter tuning. In addition, we consider the impact of errors and error recovery methods on energy consumption. Although one can argue that carefully scheduling transmissions will improve performance, ultimately, appropriately tuning protocols reduces scheduling significance. In most cases, scheduling transmissions between the same nodes continuously and ordering such transmissions shortest processing time first results in good performance. However, the ability of our protocols to conserve energy is highly dependent on 1) network size, 2) traffic type (e.g. down/uplink, and peer-to-peer) and 3) channel bit error rate. In particular, we show that when protocols are faced with packet errors, more elaborate schemes of coordinating the dozing of nodes can pay-off. Our simulations show that while energy savings can vary by a factor of 10 over the class of protocols we considered throughput varies by less than 20%.