| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 99 === Wireless sensor network (WSN) is a network system formed by many sensors. The sensors communicate with each other by wireless transmission. In contrast with wire transmission, wiring is needless. WSN has some special requirements such as low rate, low cost, and low power. IEEE 802.15.4 standard defines WSN operating at physical and MAC layer, so the standard is just fit for the properties.
In the IEEE 802.15.4, system can provide special time period for device with high quality of service (QoS) requirement. When a device is already decided to transmit data in this period, it will not have to content channel with others. The period is called contention-free period (CFP). CFP use the slot in superframe structure as transmission unit. These slots are called guaranteed time slots (GTSs). A GTSs can contain one or more slots to transmit data. The above transmission method brings that a portion of slot is unused, so it wastes space of slot and lowers transmission efficiency. When the value of superframe order (SO) increases, the situation becomes clearer.
To solve the above-mentioned problem about waste of unused slot, we propose Enhanced GTS Allocation Scheme(EGAS) to promote utilization of GTSs in CFP. Through simulating by program, we compare our proposed scheme, IEEE 802.15.4 standard, and some previous schemes. Our proposed scheme has improvement on the others about average bandwidth utilization of CFP, CFP goodput, ratio of CFP, and drop ratio of CFP.
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