Adaptive waiting time threshold estimation algorithm for power saving in sleep mode of IEEE 802.16e

Sleep mode is a key feature introduced in IEEE 802.16e standard, which ensures power-efficient operation of battery operated mobile devices. The 802.16e standard does not define when to take decision to trigger sleep mode. However to the best of our knowledge some published works define waiting time threshold as a time for which mobile subscriber station (MSS) waits before entering into sleep mode, which is constant. In this paper, we propose an algorithm which optimizes waiting time threshold according to traffic arrival pattern (downlink + uplink), which leads to significant reduction in energy consumption. We have compared the performance of our algorithm with constant waiting time threshold scheme through simulations for different DL to UL ratios. The results show that our algorithm reduces the power consumption significantly by 47% with little increase in average waiting delay by 11% at arrival rate 0.05 per MSS, which is well accepted within end to end delay for non-real time traffic. Furthermore, the simulation results of the proposed algorithm are within tolerable limit of theoretical analysis discussed in the paper.