Evaluation of Joint Sleep and Idle Mode in IEEE 802.16e WIMAX

As energy availability limits usage time for mobile devices, modern wireless systems implement Power Saving Mechanisms (PSMs). Determining optimal PSM parameters and switch points when applying all PSM mechanisms jointly in the same scenario is a trade-off between power savings and system performance degradation. This work presents an unpublished performance study of the joint operation of Sleep Mode and Idle Mode on an accurate 802.16e PSM NS-2 simulation implementation, with the MS experiencing two different classes of Internet traffic, namely HTTP Web Browsing and Always-On traffic. We first determine which set of PSM parameters influence the most on power savings and performance degradation (in terms of TCP retransmissions) via a 2k.r factorial analysis. Then, we explore those PSM parameters via full factorial analysis in order to determine optimal transition points between Sleep Mode and Idle Mode, such that we achieve power savings without high performance degradation. Results showed that although we managed to obtain good power saving results for a wide range of PSM parameters, performance degradation can be substantial if the Sleep Mode Inactivity Timer is such that PSM is activated within TCP RTT or the timers for Sleep Mode and Idle Mode are such that there is a “competition” between which PSM mechanism should be activated. Under established conditions, we observe a significant power saving gains followed by a surprising system performance enhancement.