- 學位論文
On Distributed Scheduling over the TSCH mode of IEEE 802.15.4e Networks
On Distributed Scheduling over the TSCH mode of IEEE 802.15.4e Networks
摘要
在無線感測網路中，由於無線感測器硬體上的限制，MAC層標準的設計更顯得重要，目前普遍使用在無線感測器底層傳輸的協定為IEEE於2004年提出的IEEE 802.15.4標準，也被Zigbee聯盟採用為底層的傳輸協定。IEEE 802.15.4標準在low-power multi-hop networking會遭遇到兩項問題，一是扮演轉傳封包角色的無線感測器需要維持在100% duty cycle的狀態，這對無線感測器電源的消耗是非常大的，100% duty cycle狀態使得無線感測器無法進入休眠模式，對於需要低耗能的無線感測網路是非常嚴重的問題。另外IEEE 802.15.4標準使用單一頻率進行封包傳輸，在傳輸封包時容易受到干擾，導致傳送成功次數減少及重傳次數增加，直接影響的是對無線感測器不必要的電源消耗，上述兩項問題明確的顯示出IEEE 802.15.4並不是這麼適用於無線感測網路環境。因此，IEEE於2012年提出IEEE 802.15.4e協定，重新設計IEEE 802.15.4中的MAC層並定義了Time Slotted Channel Hopping(TSCH)機制，TSCH機制的特點是使用slotframe架構，可以使整個無線感測網路節點之間傳輸達到時間同步，一個time slotframe被切割成多個time slot，根節點根據整個無線感測網路路由情形進行time slot排程規劃，使得每個無線感測節點知道該在哪個time slot進行封包傳輸/接收，另一特點為重新設計的IEEE 802.15.4e使用跳頻率進行封包傳輸，相較於只使用單一頻率的傳輸方式，可增加資料在傳輸上的可靠性。然而IEEE 802.15.4e的TSCH機制並未明確指出該如何進行time slot排程規劃，本研究將設計出可提升無線感測網路效能的time slot分散式排程規劃方法，節點透過建置的RPL路由資訊，就可以知道在一個slotframe中需要在哪些slot進行封包傳輸，達成真正的分散式時間排程方法。
並列摘要
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.