為ZigBee無線感測網路所設計之一利用機率性隨播之兼具省電及耗電平衡之群播協定

Abstract

在無線感測網路中，由於感測節點的電力資源有限，因此省電的群播協定是一個重要的議題。而在ZigBee規範中，因為群播服務是由週期性的區域氾濫式傳播所達成，所以造成了非常高的成本消耗。另一方面，雖然有許多關於群播的轉傳節點選擇演算法被提出，但這些方法之中，資料傳輸路徑是固定的，導致耗電不平衡甚至單節點失效問題。除此之外，在網路拓樸會改變的情況下，必須要負擔額外的維護成本。在本篇研究中，我們提出一個利用機率性隨播之符合ZigBee規範的群播協定，目的是要減少電量消耗並且平衡耗電以延長網路壽命並且避免單節點失效問題。機率性隨播根據涵蓋率成本比例來選擇轉傳節點。涵蓋率成本比例為可到達之目的成員節點個數與電量消耗成本之折衷權衡，可幫助在最小化電量消耗的同時，最大化可到達之目的成員節點個數。我們更進一步利用在選擇轉傳節點時考量各節點之剩餘電量，而在我們的設計中引進耗電平衡的概念。當網路的拓樸改變且各節點之電量不斷消耗的同時，轉傳節點的集合會不斷隨之改變以適應這些情況。模擬的結果顯示，我們所設計之群播協定可比ZigBee規範提供更長的網路壽命，並且在電量消耗、延遲及可靠性上都更加出色。

In wireless sensor networks (WSNs), energy-efficient multicast is a critical issue due to the limited power resource of sensor nodes. In ZigBee, multicast is accomplished by periodical regional flooding, resulting in extremely high cost. On the other hand, although some works have proposed relay node selection algorithms for multicast, the data delivery paths are fixed, leading to unfair or even single-node-failure problem. Moreover, extra cost is required in the face of topology changes. In this paper, we propose a ZigBee multicast routing protocol with probabilistic anycast, which aims for less energy consumption and load balance in order to prolong the network lifetime and avoid single-node failure. The probabilistic anycast mechanism chooses relay nodes based on a coverage-over-cost ratio, which is a tradeoff between the number of destination nodes that can be reached and the energy cost to reach them. This helps maximize the number of reachable member nodes while minimize the energy consumption. We further introduce the idea of load balance to our design by considering each node’s residual energy when choosing relay nodes. As the network topology changes and the energy of the nodes deplete, the set of forwarders for multicast can adapt to such conditions. Simulation results show that our protocol provides longer network lifetime and outperforms ZigBee in energy consumption, latency, and reliability.