Optimizing Energy Consumption with Transmission Pushbacks in Sensor Networks

Failed transmission attempts lead to significant wastage of energy in sensor networks. CSMA attempts to address this issue by sensing the carrier before transmissions and by backing off in case of failed transmissions. However, in many scenarios packet losses are caused by interfering nodes, that are not directly contending with a given transmission. We propose a new technique to reduce such losses by delayed transmissions, called transmission pushbacks, to overcome periods of poor channel quality due to high interference, while ensuring a high throughput. In order to determine the optimum pushback period, we devise an adaptive channel prediction technique. Our technique is based on estimating the parameters of a simple hidden Markov model (HMM), which represents the channel. We dynamically update the parameters of the HMM based solely on the ACK sequence for the previous packet transmissions. We choose the appropriate pushback period by considering the throughput requirement measured by the incoming data rate, and the predicted quality of the channel. We implement this approach over CSMA in the ns2 simulator, and show that the pushback algorithm can improve the packet success rate by up to 71% and reduce the number of transmissions needed by up to 38% with the throughput maintained.