| 摘要: | 近來，行動式Ad Hoc 網路(Mobile Ad Hoc Network, MANET)吸引許多研究的注意。 MANET 是一個由沒有基地台(base station)設施支援的行動主機(mobile host)所構成的集合，而主機之間以多跳(multi-hop)的方式進行通訊。MANET 可應用在包括戰場上、急難救災現場及大型戶外活動等需要在無基地台支援情況下快速建立通訊網路的場合上。電力節省(power saving)在MANET 中是一個相當重要的問題，因為MANET 中的主機都是由有限電力之電池供電的可攜式設備。近來有許多相關於MANET 電力節省的研究被提出，我們大致可以將之歸納為三類：(1)電力察知繞徑(power-aware routing) (2)傳送功率控制(transmission power control) (3)低電力模式管理(low-power mode management)。本計畫預計探討以IEEE 802.11 無線通訊標準為基礎所建置的多跳通訊MANET網路的低電力模式管理。IEEE 802.11 支援二種電力模式；活躍(active)及省電(power-saving, PS)。在PS 模式中的主機只耗費相當低的電力，但是主機只有在活躍模式才可以傳遞、接收或監測封包。雖然IEEE 802.11 利用PS 主機週期性的進入活躍模式監測信標(beacon) 訊號之傳遞而達到單跳(single-hop)MANET 的省電模式管理，但是這個省電模式管理應用在多跳MANET 時卻會碰到如時脈同步(clock synchronization)及網路分割(network partition) 等問題。在參考文獻[88]中提出一個可以解決上述問題的非同步法定人數集合基礎省電模式通訊協定(asynchronous quorum-based power-saving protocol, AQPSP)，此通訊協定使用法定人數集合系統(quorum system: 一個由兩兩相交集合所構成的collection)以達到低信標(beacon)訊號傳送數的特性。而在參考文獻[62-63, 67]中，我們則已證明所有符合旋轉封閉(rotation closure)特性的法定人數集合系統都可以應用於AQPSP，我們更於參考文獻 [62-63, 67]中提出一個符合旋轉封閉(rotation closure)特性的法定人數集合系統的法定人數集合基數(cardinality)下限，並以此下限推導出達成最低活躍率(active ratio)的最佳 (optimal)AQPSP 通訊協定。然而，我們發現AQPSP 仍然可以由其他方向進行改進。本計畫預計以AQPSP 為基礎，推出HAT 省電通訊協定。HAT 通訊協定是一個利用忙線訊號及可調傳輸範圍之IEEE 802.11 ad hoc 網路虛擬骨幹混合式動態省電通訊協定，其具有以下特點： (1) 採用可調傳輸範圍技術，因此不需要選擇邊界節點即可連結叢集頭(cluster head)節點。 (2) 只需要依靠IEEE 802.11 信標(beacon)訊號即可以快速選擇出叢集頭節點。 (3) 叢集頭節點可以進入混合省電模式，而其他非叢集頭節點則可以進入更節省電力的同步省電模式。 (4) 虛擬骨幹可以因應節點的移動或節點能源的變化而快速調整，而且不會引起有重大變化的連鎖反應(chain effect)。而叢集頭節點可以根據本身的剩餘電源來決定是否要繼續擔任叢集頭節點，這可以達到負載平衡(load balance)，增長網路的壽命(prolong network lifetime)。 (5) 採用忙線訊號(busy tone)觀念解決隱藏終端機問題，並且讓不同cluster 之間，可以同時(concurrently)進行intra-cluster 資料傳輸。本計畫並預計針對HAT 通訊協定進行分析與模擬，並將之與其他相關省電通訊協定進行比較。 The mobile ad hoc network (MANET) has attracted a lot of attention recently. A MANET consists of a set of mobile hosts, and does not have the support of any base station. Hosts may communicate in a multi-hop manner. Applications of MANET include communications in battlefields, disaster rescue, and outdoor activities. Power saving is a critical issue for portable devices supported by battery powers. Battery power is a limited resource, and it is expected that battery technology is not likely to progress as fast as computing and communication technologies do. Hence, how to save the energy consumption in a MANET, of which hosts are all supported by batteries, is very important. There are three categories of the protocols for the power saving problem, namely the power control protocol, the power-aware routing protocol, and the low-power mode management protocol. This project planes to investigate the power mode management problem in an IEEE 802.11-based MANET, which is characterized by multi-hop communication, unpredictable mobility, and no plug-in power. IEEE 802.11 supports two power modes: active and power-saving (PS). Under the PS mode, a host can reduce its radio activity by only monitor some periodical signals (such as beacons) in the network. As can be seen, by tuning a host to the PS mode intelligently, a lot of energy can be saved. IEEE 802.11 has defined its power-saving (PS) mode management for single-hop MANET based on periodical transmissions of beacons. The protocol, when applied to a multi-hop MANET, may encounter several problems, including costly clock synchronization and even incorrect network partitioning. An asynchronous quorum-based power-saving protocol (called AQPSP hereafter) for solving such problems is proposed in [88]. An AQPSP utilizes the quorum system, which is a collection of pairwise-overlapping sets, to achieve very few number of beacons sent. In [62-63, 67], we have shown that every quorum system satisfying the 「rotation closure property」 can be translated to an AQPSP. We have also derived the lower bound of the quorum size for the quorum system satisfying the rotation closure property. In spite all the enhancements we』ve done with AQPSP, we have found that AQPSP can still be improved. In this project, we plan to design HAT power saving protocol based on the concept of AQPSP. HAT is a hybrid, dynamic power saving protocol on virtual backbones for IEEE 802.11 ad hoc networks using busy tones and adjustable transmission ranges. It has the following merits: (1) It does not need to choose border nodes since it adopts adjustable transmission ranges. (2) Only beacons are required for nodes to select cluster head nodes properly. (3) A cluster head node utilizes the hybrid (combination of synchronous and asynchronous) power saving mode, while a non-cluster head node utilizes the synchronous power saving mode. (4) It can achieve load balance based on the ratio of remaining energy, which can prolong the network lifetime. (5) It utilizes the busy tone technique to solve the hidden terminal problem, and allows concurrent intra-cluster data transmission. This project also plans to analyze and simulate HAT protocol, and compare it with related power-saving protocols. 研究期間：9308 ~ 9407 |
