| Summary: | 博士 === 國立交通大學 === 電信工程研究所 === 99 === In the past decade, IEEE 802.11 wireless LANs has gained large popularity in broadband wireless access. Users are demanding high performances while keeping respectable operation time for the mobile devices. Power management (PM) is an essential technique for energy saving by putting de-vices into low power state during appropriate interval. For a multi-user and shared medium wireless network, in addition to managing power state according to readiness of traffic, it is important to separate the usage time of different users to prevent energy-consuming overhearing. Hence, in this dissertation, considering variable-bit-rate traffic and unpredictable error recovery, we focus on the scheduling algorithms to reduce the chance of service period overlapping.
To support standardized power saving mechanism in IEEE 802.11e, we propose a feasible scheduling algorithm for the Scheduled Automatic Power Save Delivery. The goal is to maximize the minimum distance between the scheduled instants of new joining traffic stream (TS) and exist-ing scheduled events (SEs). By the proven periodicity of service schedules, the redundant check in the previous brute-force method can be avoided. Moreover, considering limited number of classes for TSs, we can pre-calculate and store necessary information to further reduce the implementation complexity. Extending the idea of finding the optimal service start time for new joining TS incre-mentally, we also study the rearrangement of existing SEs to further maximize the system minimum distance. We prove the upper bound of the system minimum distance and design efficient rearrang-ing algorithms to achieve satisfactory energy saving.
In order to achieve higher system bandwidth utilization (BU), multi-polling mechanisms are often employed to reduce protocol overhead. However, they may require wireless stations (STAs) to spend much time in overhearing. We propose an energy-efficient multi-polling mechanism which combines PM strategy with a low overhead Medium Access Control protocol. Given a desirable guarantee of BU, an energy optimized wake-up time schedule (WTS) is devised. Significant saving of energy can be obtained with only small loss of BU as trade-off. It is the consequence of alleviat-ing the overhearing problem by well scheduled WTSs for STAs. In the end, we also study the ener-gy saving issue induced from error recovery. A WTS and a renewal algorithm in correspondence with the delay caused by retransmissions are proposed for the TDMA-like multi-polling mechanism. Simulation results show that, compared with the original setting, significant improvement can be obtained by the proposed algorithms.
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