Power management is an important part of the emerging standard of IEEE 802.16e (mobile WiMAX). The sleep-mode operation in power management helps to increase the life of a station by saving energy consumed, but at the same time it increases the response delay of awakening medium access control (MAC) service data units (SDUs). Its performance metrics, energy consumption and the average response delay of awakening MAC SDUs, are affected by correlations among the initial sleep window (Tmin)(Tmin), the final sleep window (Tmax)(Tmax), and the average interarrival time of awakening MAC SDUs (TI)(TI) during sleep-mode operation. There is a trade-off relationship between the performance metrics, so it is imperative to determine the most effective size for the two windows, TminTmin and TmaxTmax, in order to reduce energy consumption and still maintain a reasonable response delay time. To reach a fuller understanding of this problem, this paper first models sleep-mode operation in an IEEE 802.16e system and analyzes the effects of the size of the windows on the performance. Based on this analysis, the authors then present a decision making process for leveraging the two performance metrics by manipulating the size of the windows. The decision making process aims to provide some guidelines for determining the most advantageous size of each window to achieve the targeting performance goals.
The explosive growth of the Internet over recent decades has led to increasing demands for high speed and ubiquitous Internet access. To address these requirements, a lot of attention has been given to broadband wireless access (BWA). This technology aims to provide low cost and high performance BWA to residential and small business applications. Worldwide interoperability for microwave access (WiMAX) [2] and [3] is a standard technology enabling fixed and mobile convergence through BWA technology and flexible network architecture. IEEE 802.16e (mobile WiMAX) [1] is an extension of this technology, targeting for service provisioning to mobile subscriber stations (MSSs). It is optimized to deliver a high data rate to mobile subscribers, and the advanced MAC architecture can simultaneously support real-time applications such as voice over IP (VoIP) in mobile environments. Since an MSS is powered by a limited battery, the energy conservation of an MSS in IEEE 802.16e is a key factor in WiMAX application.
For efficiently managing energy in IEEE 802.16e, an MSS repeatedly goes from wake-mode to sleep-mode whenever it does not communicate with a base station (BS), and vice-versa. Sleep-mode operation is generally controlled by the initial sleep window (Tmin)(Tmin) and the final sleep window (Tmax)(Tmax). The main performance metric varies depending on which station (MSS or BS) initiates the MSS to transition into wake-mode. When an MSS wants to initiate self-awakening (MSS initiating awakening ), energy consumption will be the key performance metric, because it can awaken without the response delay of awakening medium access control (MAC) service data units (SDUs). On the other hand, when a BS initiates an MSS to awaken (BS initiating awakening ), both energy consumption and the response delay of awakening MAC SDUs will be given attention because an MSS should wait to transition in waking mode until the listening state arrives. Since the size of two windows, TminTmin and TmaxTmax, affects the power management performance, it is necessary to examine their effects and decide the size of the windows based upon performance.
Due to its importance, power management has been paid attention by many researchers. Sleep-mode operation is specified in MAC protocol [1] and [2]. In [5] and [6], sleep-mode operation and its analytical model are studied in consideration of uplink and downlink traffic. In [7] and [10], sleep-mode is analytically evaluated in terms of average energy consumption and the average response delay of awakening MAC SDUs. In [8] and [9], several energy efficient mechanisms are proposed by trading off energy and other costs associated with overhead. Since energy consumption and the response delay have a tradeoff relationship in power management, it is imperative to study and determine the optimal power management condition where the target performance is well satisfied. However, as far as the authors are aware, there has been minimal research regarding this trade-off relationship between energy consumption and the response delay, and how to decide the size of the windows based on reasonable criteria. Therefore, the main purpose of this paper is to explore how to leverage the two windows for satisfying the target performance metrics.
To achieve this end, this paper is organized as follows. Section 2 introduces sleep-mode operation in IEEE 802.16e and the effects of TminTmin and TmaxTmax on the power management performance. In Section 3, an analytical model for sleep-mode operation and a decision making process for supplying the trade-off guidelines are depicted. Section 4 shows how the two windows affect sleep-mode operation, utilizing both simulation results and numerical analysis. The proposed decision maker also presents suitable operation conditions in power management, depending on its applications. Finally, Section 5 concludes this paper.
For sleep-mode operation, it is difficult to decide the optimal values of TminTmin and TmaxTmax, because the two windows affect both energy consumption and the response delay of awakening MAC SDUs, which have a trade-off relation between each other. In order to determine the most advantageous values of the windows in a specific environment, this paper suggested a trade-off guideline for sleep-mode operation to support both required performance and a differentiated service based on the decision making process. The process can help decide the values of TminTmin and TmaxTmax in consideration of both the energy consumption and the response delay of awakening MAC SDUs. The decision methodology for the window value is expected to be widely applied in a IEEE 802.16e systems for better power management operation.
