IEEE 802.11無線區域網路與IEEE 802.16e無線都會網路上省電協定之設計

Abstract

隨著無線網路的蓬勃發展，越來越多無線存取技術在不同的應用層面與需求下被提出來。在眾多的無線技術當中，IEEE 802.11無線區域網路與IEEE 802.16無線都會網路是兩個最直接影響到使用者存取網際網路的技術。前者提供一個簡單、廉價的方案讓使用者建構自己的無線區域網路。後者提供一個無線存取方案來替代目前有線網路中以電纜或ADSL存取網際網路的方式。由於在無線網路中大部份的行動裝置都是由電池供應電力，節省電源以延長的運作時間是一個非常重要的議題。因此，在此篇論文當中，我們分別針對IEEE 802.11無線區域網路的基礎建置模式(infrastructure mode)、隨意網路模式(ad hoc mode)、與IEEE 802.16e無線都會網路設計相應的省電機制。 對於IEEE 802.11無線區域網路的基礎建置模式，我們提出一個新方法來安排休眠主機(sleep stations)醒來的時間，所提出的方法企圖讓每一個信標區間(beacon interval)中醒來的主機數量得以更加平均。藉由這個方法來降低封包相撞的機率，讓主機避免重傳資料來節省電力。此外，我們也考慮控制所要通知之醒來主機的數量以及他們之間的存取順序，藉以避免過多醒來的主機在發現擷取點(Access Point)上有暫存的資料之時，同時發送PS-Poll訊框存取網路而造成嚴重的封包衝撞。在設計上我們提供三種不同的選取機制來控制所要通知的主機數，通知機制為分別為只選一台主機、或是根據聯結識別碼(AID)、或預存資料長度來選取主機數。模擬的結果證實我們提的方法能有效的節省電力。 對於IEEE 802.11無線區域網路的隨意網路模式，我們提出一個能自我組態的省電方法，稱為SCPS。每一台主機如同基礎建置模式一樣，可以選取自己的休眠時間長度。當有一台主機進入或離開省電模式時，SCPS會讓其他在省電模式下的主機去調整它們醒來的排程，這樣的調整可以平衡在每一個信標區間裡醒來的主機數量，使得能源因傳輸媒介的競爭與衝撞而耗損的問題可以進一步的改善。模擬的結果顯示SCPS成功的平衡了每一個信標區間裡醒來的主機數量、增加休眠時間的百分比、同時也降低主機彼此之間封包衝撞的機率。 對於IEEE 802.16e無線寬頻網路，我們提出幾個能源效率高的排程方法，這些排程方法考慮的是多台行動主機(MSS)，而非像目前大多數的研究僅考量單一行動主機的排程方式，所考量的資料流都是有服務品質延遲限制的常數速率資料流，所提出的方法同時考量能源使用的效益與頻寬利用率。我們提出的方法分為兩類，一是定期的自主休眠週期(PASC)，另一則為定期的相同休眠週期(PUSC)。在PASC中，所有行動主機的資料流所限定的服務品質限制直到它們加入前都未知，每一個行動主機都使用自己的休眠週期來節省電力。若是每一個行動主機的服務品質限制可以事先得知，則可以用PUSC方式讓行動主機的排程更有效率，因為在PUSC中所有的行動主機都使用相同的休眠週期，基地台可以很簡單的安排行動主機醒來的時間。模擬結果顯示PUSC 與PASC皆有不錯的省電效能，特別是在VOIP的應用下，PUSC還能讓頻寬利用率展現出更好的結果。

Recently, wireless networks have widely developed. Many different wireless technologies have been proposed for different network aspects. Among all of the wireless technologies, the IEEE 802.11 WLANs and the IEEE 802.16 WMAN directly influence the internet access of end users. The former provides easy and low cost solution for people to build their own local area networks and the latter provides a wireless internet access solution to substitute the last-mile internet accessing in the wired networks. Because most of the mobile devices in the wireless networks are powered by battery, saving power to extend the operation time is a critical issue. Therefore, we design several power saving protocols for the infrastructure and ad hoc mode of IEEE 802.11 WLANs and for the IEEE 802.16e WMANs. For the infrastructure mode of IEEE 802.11 WLANs, a novel method is presented to schedule the listening duration of sleeping stations and to balance the amount of wakeup stations in each beacon interval. This method saves stations’ power by reducing the probability of collision. We also control the amount of wakeup stations which can send the PS-Poll frames to get back their buffered data to avoid contention. Three different mechanisms, single wakeup stations, the smallest association ID, and the smallest queue length, are proposed for to control the access order of wakeup stations. Our simulation results show that the proposed methods are effective in the power-saving. For the ad hoc mode of IEEE 802.11 WLANs, a novel self-configuring power-saving protocol, called as SCPS, is proposed. Stations choose their listening intervals as the infrastructure mode. Besides, all stations in the PS mode can adjust their wakeup schedules whenever a station enters or exits the PS mode. The adjustment can balance the amount of wakeup stations in each beacon interval so that both the contention for transmission medium and the collisions in transmission can be ameliorated, which results in more efficient energy usage. Simulation results show that SCPS successfully balances the amount of wakeup stations in each beacon interval, increases the sleep ratio, and reduces the collision probability. For the IEEE 802.16e broadband wireless networks, we proposed several energy efficient scheduling approaches. Instead of considering a single Mobile Subscriber Station (MSS) as most of the current researchers do, multiple MSSs are considered in our work. We consider constant bit rate traffic with QoS delay constraint. The proposed approaches address both energy efficiency and bandwidth utilization. Two classes of scheduling approaches are proposed, the periodical autonomic sleeping cycle (PASC) and the periodical uniform sleeping cycle (PUSC) approaches. In the PASC, the QoS information of all MSSs needs not to know beforehand. Each MSS uses its own sleeping cycle for power saving. While the possible QoS requirement of the MSSs can be known beforehand, the efficiency of the scheduling can be improved further. Thus, the PUSC approaches let all MSSs use the same length of sleeping cycle for their wakeup schedule. BS simply schedules the MSSs’ wakeup time. Simulation results show that both PUSC and PASC can have higher power efficiency. Besides, the PUSC approaches are superior to the PASC approach on the bandwidth utilization under the application of VoIP.