Power Management Strategy For IEEE 802.11 Based Wireless Local Area Networks

IEEE 802.11 WLANs are widely used due to deployment flexibility, scalability, its supporting users’ mobility, and low maintenance cost. Due to the use of license-free spectrum, IEEE 802.11 wireless local area networks(WLANs) interfaces are increasingly incorporated in portable electronic devices to provide Internet access capabilities. Portability and mobility of these devices require that they are powered by batteries. Due to limited energy of battery, energy saving has become a research hotspot of WLANs.IEEE 802.11 standard defines basic power management strategy which permits mobile station to turn off the radio to prolong the run-time of power resource. However, the basic power management strategy has many deficiencies, and is unable to support energy saving in WLANs under unreliable and delay intolerable wireless link. This dissertation studies power management strategy which is suitable for the unreliable link and uplink delay intolerable traffic. Based on vector Markov theory, this dissertation derives the steady-state probability of mobile station in doze state, idle state and active state. To achieve optimal energy conversation, delay, and number of buffered frames of the STA under unreliable WLANs, we can adjust the MAC layer parameters to optimize the power consumption of the STA, number of frames buffered, and average delay per frame. The main work and achievements are as follows:1) Efficient power management strategy supporting the applications with Delay-Intolerant Uplink Traffic(DIUT) in IEEE 802.11 WLANs is proposed and the enhanced timer-based power management(E-TPM) scheme is presented. With E-TPM, the radio transceiver of the dozing STA is woken up right away when an outgoing frame is generated by the STA so that DIUT is transmitted in a timely manner. By optimizing the idle timer and doze duration at the STA, the doze mode does not result in extra delay in DIUT and the delay of downlink traffic is controlled within a given bound. Numerical results show that the proposed E-TPM is able to considerably reduce delay with the limited available memory space at the AP.2) Efficient power management strategy considering Unreliable Wireless Links(UWLs) in IEEE 802.11 WLANs is investigated. The existing Timer-based Power Management(TPM) is able to balance energy-saving and Quality of Service(QoS) requirements by tuning the values of its idle and doze timers. In fact, the wireless links connecting itself to its neighboring nodes have different successful packet delivery probabilities so that the number of transmission trials for a node to transmit a given packet varies. Thus, power management should take account into unreliability of wireless link. However, the TPM is difficult to apply in energy saving under unreliable WLANs. The TPM qualified for the WLANs with Unreliable Wireless Links(UWLs), referred to as TPM-UWL, is presented, in which the Maximum Number of Retransmission(MNR) in the MAC layer and the probability of successful transmitting a packet over a link are taken into account.3) Efficient power management strategy considering DIUT and UWLs is studies. A hybrid power management model is presented in this paper. The power consumption of the STA, number of frames buffered, and average delay per frame are derived in this model. To optimize power-save of STA, we can adjust MAC layer parameters and balance the above indicators. Moreover, the improved E-TPM is presented in this paper. Considering DIUT constraints, the power consumption of STA is further reduced by setting the STA in active or doze state and canceling the idle state. We also compare the power consumption of the STA and number of frames buffered with those of the E-TPM.4) On the model assumptions in this paper, the process of transmit/receive a frame obeys the general probability distribution, while the arrivals of the streams are modeled by Poisson processes. The operations of the STA are classified as active, free and doze states. Based on vector Markov process theory, we in great detail derive the steady-state probability of the STA in each state, the power consumption of the STA, number of frames buffered, and average delay per frame, etc. The mobile stations are able to save energy economically while keep packet delay within a preset limit and the number of buffered frames within a preset bound by setting the optimal MNR and the optimal values of the idle and doze timers through solving the optimization problem.E-TPM and its improvement strategy together with TPM-UWL are suitable for unreliable WLANs, and reduce energy consumption of the STA under delay and buffer constraints.