叢集樹網路是一個特殊的點對點網路類型，其中大部分設備是全功能設備（FFD）。全功能裝置可作為網路的協調者與其他設備或其他協調者實施同步服務。在IEEE 802.15.4的叢集樹網路拓撲結構，個人區域網絡（PAN）的協調者週期性地發送訊標框至其他協調者以及其中幾個協調者節點週期性的發送訊標框至裝置，以形成叢集網路。叢集樹網絡中所面臨的挑戰是訊標碰撞以及訊標和資料封包之間的碰撞。

如果協調節點在不正確的時間發送訊標框，訊標將會相互碰撞，並妨礙子節點裝置與其協調者進行同步。此外，如果沒有正確地配置活動周期的長度，訊標框將有可能與其他資料框碰撞，進而降低網路效能。

為了改良碰撞避免，本論文提出超碼框調整和訊標傳輸機制（SABTS），其藉由指定準確的訊標級數（BO）和超碼框級數（SO）給個人區域網路協調者，叢集協調者和設備節點，並決定個人區域網路和協調節點間訊標傳輸的時間。本論文並提出一個以馬可夫鏈的叢集樹網路分析的數學模型，此模型考慮到封包重傳、確認封包以及延遲傳輸。分析與模擬結果顯示，就傳輸成功的機率、網路的有效資料傳送量、訊標丟棄率、封包傳輸率、網路能源消費總量以及能源利用率（能源消費量/有效產能）來看，本論文提出的超碼框調整和訊標傳輸機制（SABTS）有較好的表現。

此外，個人區域網路協調者可以分配保證時槽（GTS），其分配一個特定時間給有需求的設備。 而保證時槽機制所面臨的挑戰是個人區域網路協調者如何分配時槽給需要保證時槽時間的設備。然而，如果分配的設備使用保證時槽的部分插槽或流量形態不適合，則浪費的頻寬將會增加，而降低網路效能。

為了克服上述問題，本論文提出一個分區GTS的分配計劃（PEGAS）用於IEEE 802.15.4網路下。 PEGAS旨在決定保證時槽的開始時間（GTSstart）和保證時槽的結束時間（GTSend）的確切時間分配給有需求的設備，其中考慮了超碼框級數（SO）、資料封包的長度和抵達的資料封包速率值。模擬的結果呈現出本論文所提出的機制效能不論在總傳輸的資料封包，產能，能量效率，延遲，頻寬利用率等各方面均超越了IEEE 802.15.4規格。

The cluster tree network is a distinctive type of a peer-to-peer network in which most devices are full function devices (FFDs). An FFD may serves as a coordinator and implements synchronization services to other devices or other coordinators. In cluster tree topology of IEEE 802.15.4, the personal area network (PAN) coordinator transmits periodically beacon frames to coordinator nodes as well as the several coordinator nodes transmit periodically beacon frames to device nodes in order to form a cluster network. The challenge in cluster tree network is the beacon collisions as well as collision between beacon and data packets transmission.
If the coordinator nodes send regular beacon frames at improper time, the beacon transmission will collide each other and prevent children device nodes to synchronize to their coordinator. Moreover, if the length of active period is not configured appropriately, the beacon frame can collide with other data frames, which make degrade the performance of network.
In order to improve the collision avoidance, this thesis proposes the superframe adjustment and beacon transmission scheme (SABTS) by assigning the accurately value of Beacon Order (BO) and SuperFrame Order (SO) for PAN coordinator, cluster coordinator and device nodes, and deciding the precise time for beacon transmission of PAN and coordinator nodes. An analytical model for cluster tree network based on Markov chain is developed taking into account packet retransmission, acknowledgment, and defer transmission. Both analytical and simulation results present that the SABTS performs better in terms of the probability of successful transmission, the network goodput, beacon drop ratio, packet delivery ratio, the total of network energy consumption, and energy efficiency (ratio of energy consumption/goodput).
Furthermore, PAN coordinator can assign guaranteed time slot (GTS) to allocate a particular duration for requested devices. The challenge in GTS mechanism is how the PAN coordinator allocates time slot duration for the devices which request GTS. However, if the allocated devices use GTS slot partially or the traffic pattern is not suitable, the wasted bandwidth will increase which make degrade the performance of network.
In order to overcome the above mentioned problem, this thesis proposes a partitioned GTS allocation scheme (PEGAS) for IEEE 802.15.4 networks. PEGAS aims to decide the precise time for the starting time (GTSstart) and the end of GTS (GTSend) allocation for requested devices taking into the value of superframe order (SO), length of data packet and arrival data packet rate. The simulation results show that the proposed mechanisms outperform the IEEE 802.15.4 standard in terms of total of transmitted packet, goodput, energy efficiency, latency, and bandwidth utilization.

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