無線都會區域網路之效能分析

Performance Analysis of WiMAX

邱旭鋒(Hsu-Feng Chiu)

指導教授 ： 逄愛君

國立臺灣大學/電機資訊學院/資訊工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.10544

摘要

IEEE 802.16無線都會網路，在現今已經成為一種非常受歡迎的網路技術。不過，在這個新的網路協定裡，效能仍未被廣泛討論。本論文是針對效能及其潛在的問題進行研究。
在我們的研究過程中，使用具公信力的NS2網路模擬器，及其上的NIST(美國國家標準和技術研究院)模組以獲得公正的效能分析。我們在使用者不移動的情形下，使用PHY(物理層)和MAC(媒體存取控制層)的不同參數，研究無線都會區域網路的傳輸能力。首先，我們想了解調變技術是如何影響流量。當調變技術變好時，流量將變得更大。在使用最好的調變技術(64-QAM-cc-3/4)下，流量最高能達52Mbps。其次，我們改變不同的資料輸入量，用以測量資料流出量。在增加資料輸入量的過程中，我們將可得到更高的資料流出量。不過，若所要求的資料輸入量過大，反而會造成資料溢位。因此，實驗所得到的，會是異常的資料流出量。接著，我們配置不同數目的使用者以觀察延遲時間。結果顯示使用者數目越多，延遲時間也就越大。不過，若考慮封包的損失，將會發現封包的損失對延遲時間的減少，會有更顯著的影響。最後，我們測試在不同應用服務下的性能，包括網路電話，影像流和數據傳輸。很明顯的，在網路電話的應用服務裡，會有最小的延遲時間。
當我們在測試換手功能時，發現在DSDV(由目的節點的距離向量決定之路由方式)裡，存在三個問題。第一個涉及到網域限制。基地台必須在不同的網域裡，否則相鄰的基地台不能發現彼此。第二個問題是關於路徑選擇。由使用者傳出的封包，若不能找到正確的路徑時，將會造成數據傳輸的失敗。另外，使用DSDV會在換手程序完成之後，再多花十秒才成功地重新連結。為了解決上述的問題，我們利用NIST的移動式模組來支援換手功能。其模組包括MIHF (媒體獨立的換手功能)和ND(發現鄰居)的代理人，分別用來執行封包的傳遞和發現週遭的基地台。由我們的實驗結果顯示，即使時速高達每小時70公里的時候，換手延遲時間仍是少於50毫秒。
此研究分別用不同的調變技術、資料輸入量、使用者數目及應用服務，來討論其對效能的影響。另外，我們也發現在使用DSDV下，去處理的換手會有潛在的問題，然而我們可用MIHF和ND代理人取代DSDV，以成功地進行換手。總結來說，由我們的實驗指出，無線都會區域網路的確在資料輸出量和移動性上有優越的效能。而我們的實驗結果將可提供作為真實產品的設計和驗證之參考。

關鍵字

效能 ； 全球微波存取互通介面 ； 802.16e協定 ； 網路模擬器 ； 換手

並列摘要

IEEE 802.16 wireless metropolitan area networks have recently become an extremely popular network technique. However, within the new protocol, performance is still not broadly discussed. This research aims at the investigating of the performance and potential issues. In our study, the NIST modules upon NS2 are utilized to acquire a fair performance analysis.
We investigate the ability of WiMAX with immobile users under different parameters of PHY and MAC. First, we would like to figure out how modulation affects on throughput. As modulation is becoming better, throughput is getting higher. With the best modulation 64-QAM-cc-3/4, throughput is up to 52Mbps. Second, we measure throughput with different traffic loadings. In increasing traffic loading we will get higher throughput. However, a high traffic loading will cause the bandwidth request overflowed. Thus we will get abnormal throughput. Third, we allocate different numbers of SSs in our scenario to observe the time delay. The result shows that more SSs will cause larger delay. However, packet loss has a more significant effect on influencing decrease of delay. Finally, we test the performance of different applications including Voice over IP (VoIP), video stream and data. Obviously, VoIP traffic type has the least delay.
When testing the handoff function, we find that three problems exist in DSDV (Destination-Sequenced Distance-Vector Routing). The first one is concerned with the domain restriction. BSs have to be in different domains, or neighbor BSs can’t be found. The secondary issue is the path selection. Packets in MS can not find the right routing path, which will cause the failure of data transmission. In addition, using DSDV takes more than ten seconds to reconnect after handoff accomplishing. To overcome the above problems, we utilize the mobile module of NIST to support the handoff function in IEEE 802.16e. The module includes MIHF (Media Independent Handover Function) agent for performing packet delivering and ND (Neighbor Discovery) agent for neighbor discovering. Our result reveals that the handover latency is less than 50 ms even when velocity is up to 70 km/hr.
This research discovers the effects on performance with different modulation, traffic loading, numbers of SSs, and applications. We also find that using DSDV in processing handoff has potential problems and could be successfully carried out by MIHF and ND agents. In summary, our experiments indicate that WiMAX indeed has superior performance on throughput and mobility. Our results could be provided as references for designing and certifying real products.

並列關鍵字

Performance ； WiMax ； 802.16e ； NS2 ； handover

參考文獻

[1] IEEE 802.16-2004, “IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems”, IEEE, Oct. 2004.

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