Stability-constrained optimization for energy efficiency in polling-based wireless networks

A wireless device's energy can be saved by putting it into the sleeping mode (power saving mode, PSM) or decreasing its transmission power (transmission power control, TPC) which prolongs the packet transmission time. However, decreasing one's transmission power would prevent others from transmitting their packets. Clearly, there are complex interactions when each tries to optimize its own energy efficiency. Therefore, in this paper we are considering the problem of optimizing the energy efficiency for all wireless devices in the network with the constraint that they are all stable. In particular, we consider the polling-based MAC protocols with phase grouping and mobile grouping schedules, and we employ both the PSM and TPC to save the energy. We have formulated stability-constrained optimization problems for them, and have proposed an iterative algorithm to compute the optimal power allocations for the wireless devices. We have conducted a lot of experiments to validate the accuracy of the algorithm and to evaluate the gains in the energy efficiency for the two schedules. The mobile grouping schedule is found to be much more energy efficient than the PG schedule, especially when the downlink traffic is higher than the uplink traffic. We have also studied the impact of the optimized schedules on the delay performance.