| 摘要: | 行動隨意網路(mobile ad hoc network)與無線感應器網路(wireless sensor network)是近來最吸引研究者的兩種無線網路架構。對於所有由電池供電的無線裝置而言，最重要的課題便是省電。電池的電力是有限的資源，因此，如何延長電池的運作時間，對於這兩種完全由電池供電的網路而言，便成了一個重要的議題。雖然，行動隨意網路的省電協定也可套用在規則的無線網路上，但是比起針對規則無線網路設計的省電協定要來得複雜且沒效率。因此，我們也針對規則的無線感應器網路設計了電源管理協定。 讓閒置的無線裝置切換至省電模式是我們主要的省電策略。在行動隨意網路上，現存的的省電協定可分為同步與非同步兩類。同步的省電協定(如IEEE 802.11的省電協定)並不適用於multi-hop的行動隨意網路因為會造成同步、發現鄰居與網路分割的問題。為了解決這些問題，我們針對以IEEE 802.11為基礎的行動隨意網路提出了三種非同步的省電協定：分別為支配性醒來(dominating-awake-interval)、週期性完全醒來(periodically-fully-awake-interval)與以法定人數為基礎 (quorum-based)之協定。設計理念如下：首先我們強迫省電主機傳送更多的信標(beacon)，其次，我們很謹慎的安排省電主機的醒來與睡眠模式，使得兩個在睡眠模式且相鄰的主機保證能夠在限定的時間內偵測到彼此的存在。此外，針對我們的省電協定，我們提出了一對一傳送與廣播的通訊協定。模擬結果顯示，當交通量不高時，我們的省電協定可以節省許多的電源。 雖然非同步的解決方案很吸引人，但是相較於同步的省電協定，代價太高了。採用非同步協定的主機必須要醒來比較長的時間，以便發現其他非同步的省電主機。此外，當相鄰的行動主機醒來的時間不同步時，廣播的訊息必須要傳送好幾次才能被所有的鄰居收到。為了克服這個缺點，我們提出了以叢集架構為基礎的半非同步省電協定。基本的理念是將網路分成許多的叢集，在每個叢集內採用同步的省電協定，以便節省更多的電源。針對叢集間的偵測，我們提出了幾項方案：包括以機率、訊雜比與機率、輪流、鄰居覆蓋與位置為基礎的方案。模擬的結果顯示，我們提出的半非同步省電協定表現得比非同步省電協定好很多。 針對規則的無線感應器網路，我們提出新的電源管理協定，其目標是要讓網路維持連通，而又能讓最多的節點關閉無線天線進入省電模式。當偵測到緊急事件發生時，訊息可以藉由醒著的節點傳送至基地台而不必喚醒任何在省電模式的節點。此外，每個感應器節點應該輪流進入省電模式，這樣每個節點消耗的電量才能夠平衡。我們的協定運作方式如下：首先，依據網路拓樸選出好幾組連通的支配集合(connected dominating set)，這些連通的支配集合會輪流醒來去服務其他不屬於此集合的省電節點。即使有部分節點損壞，我們的協定仍能運作。分析與模擬的結果顯示，在合理的傳輸延遲下，我們的電源管理協定可以節省許多的電源並延長網路的運作的時間。 Among various types of network architectures, the mobile ad hoc network (MANET) and the wireless sensor network (WSN) are two of the most attractive wireless networks. One critical issue for almost all kinds of wireless devices supported by battery powers is power saving (PS). Without power, any wireless device will become useless. Battery power is a limited resource. Hence, how to lengthen the lifetime of batteries is an important issue, especially for MANETs and WSNs, those are supported by batteries only. The PS protocols design for MANETs can also be applied to irregular WSNs. However, when applied to regular WSNs, these protocols are more complicated and less efficient than the protocols design for regular WSNs. Therefore, besides the PS protocols of MANETs, we also design PS protocols for regular WSNs. For irregular wireless networks, several novel power saving protocols for multi-hop MANETs are proposed. The PS protocols for MANET can be categorized into synchronous, and asynchronous ones. The synchronous PS protocol (e.g. IEEE 802.11’s PS protocol) can not be applied to a multi-hop MANET, because it will cause three problems: namely clock synchronization, neighbor discovery, and network partitioning. To solve these problems, we propose three asynchronous PS protocols for IEEE 802.11-based multi-hop MANETs, namely dominating-awake-interval, periodically-fully-awake-interval, and quorum-based protocols. The basic idea is twofold. First, we enforce PS hosts sending more beacon packets than the original IEEE 802.11 standard does. Second and most importantly, we carefully arrange the wake-up and sleep patterns of PS hosts such that any two neighboring hosts are guaranteed to detect each other in finite time even under PS mode. Based on our powersaving protocols, we then show how to perform unicast and broadcast in an environment with PS hosts. Simulation results are presented, which show that our protocols can save lots of power when the traffic load is not high. Although asynchronous solutions are attractive, yet, the cost is high as opposed to synchronous protocols. Hosts in asynchronous protocols need to keep awake for longer time, so as to discover asynchronous PS neighbors. Besides, a broadcasting message has to be sent multiple times if a sending host’s neighbors wake up asynchronously. To conquer the deficiency of asynchronous PS protocols, we propose several cluster-based semiasynchronous PS protocols for multi-hop MANETs. The basic idea is to cluster neighboring hosts such that synchronous PS protocols can be adopted within each individual clusters, and thus conserves more power. Several schemes are provided in our inter-cluster strategy, including probability-based, SNR-probability-based, round-robin-based, neighbor coverage-based and location-based schemes. Simulation results show that, the proposed semi-asynchronous approaches outperform the asynchronous PS protocols when applied to a multi-hop MANET. As for regular wireless networks, since the PS protocols for regular WSNs have not been proposed before, we propose several novel power management protocols for regular WSNs. The goal of our protocols is to let as many sensor nodes as possible switch to PS mode while still maintaining the connectivity of the network so that if any emergency occurs, the sensor node, which senses the event, may transmit this information to the base stations through the active sensor nodes without need to wake up any node in PS mode. Besides, each sensor node should switch to PS mode in turn, so that the power consumption of each node can be balanced. Our protocols work as follows: first, choose several different connected dominating sets according to the network topology and assign an id to each of the connected dominating set, and then the nodes in each connected dominating set will switch to active mode to serve the other hosts in PS mode according to which dominating set they belong to in a round robin manner. Each node can decide which connected dominating set it belongs to according to its own id. In our power management protocols, each sensor node should belong to at least one connected dominating set and most of the sensor nodes should belong to the same number of connected dominating sets so that the power consumption can be balanced. Our protocol can still work properly even there are faulty nodes. Performance analysis shows that the ratios of active nodes of our protocols are near optimal and much lower than those of GAF and SPAN, those are designed for high density irregular networks. Simulation results show that our power management protocols can conserve lots of power and greatly extend the lifetime of the network with a reasonable extra transmission delay. |
