| Summary: | 碩士 === 國立中正大學 === 資訊工程研究所 === 103 === In Wireless Sensor Network, medium access control (MAC) layer standard design is more important due to the constraint on wireless sensor. IEEE 802.15.4 standard, proposed in 2004, has been widely used as the underlying transport protocol on wireless sensors. The Zigbee Alliance has also adopted this protocol as the underlying transport protocol. There are two major problems in IEEE 802.15.4 under the low-power and multi-hop networks. First, the sensors which are responsible for relaying data need to stay in 100% duty cycle status, which means sensors are transmitting constantly. For limited power sensors, the power consumption of constantly transmitting becomes a huge problem. On the other hand, IEEE 802.15.4 transmit data packets on single frequency, which causes high transmission interference. The data rate reduces and the retransmission becomes more frequent when transmission interference happens. Moreover, the sensors consumes more unnecessary power. These two problems shows that IEEE 802.15.4 is not suitable for wireless sensor network environment. Therefore, the IEEE release a revised version, IEEE 802.15.4e, in 2012. They revise the MAC layer of IEEE 802.15.4 and define the Slotted Channel Hopping (TSCH) mechanism. TSCH features the slotframe structure. The time synchronization could be accomplished among sensor nodes. A time slotframe is compose of several time slots. The time slot scheduling is planned based on routing topology. Each sensor node knows the time when data transmission/reception would happen from the schedule. Another feature in IEEE 802.15.4e standard is frequency hopping for packet transmission. With frequency hopping, reliability of data transmission could be better than that with single frequency. However, the IEEE 802.15.4e TSCH standard does not specify the approach to plan time slot scheduling. This thesis proposes a distributed scheduling strategy to improve the performance of wireless sensor networks. Each sensor node knows the time to transmit packets, this thesis that achieve real time distributed scheduling method.
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