IEEE 802.16j中繼網路之效能分析

Abstract

近年來無線區域網路蓬勃發展，造就了我們生活上的許多便利性，資訊變的隨手可得，但是這一切的便利僅侷限於100 公尺內的小範圍，提供寬頻無線接取服務(Broadband Wireless Access, BWA)變成了電信業者的一大挑戰。802.16 的出現解決了這個問題，因為它可以提供幾公里乃至幾十公里的涵蓋範圍，且最高傳輸速率可以到達75Mbps。但是他也遭受著傳統無線通訊技術所遭受的問題，如路徑衰減(path loss)和遮蔽衰減(shadow fading)等問題，這些問題會使得用戶端的傳輸速率下降，使得電信業者無法提供穩定品質的寬頻無線接取服務。為了解決這個問題，IEEE task group j 正在訂802.16j 的標準，就是希望透過多層次中繼網路(Multihop Relay, MR)來改善通訊的品質。透過適當的建置中繼站(relay station)來轉送基地台的訊號，可以避免路徑和遮蔽衰減等問題，在這篇論文中我們希望透過實驗，來分析多層次中繼網路如何可以改善網路傳輸速率以及是否會延伸出其他的問題等等，除此之外也希望可以找出布建中繼站的一些準則。

Wireless Local Networks (WLAN) have grown quickly in recent years, increasing the convenience of daily life by making information easy to obtain. However, WLANs work only within a radius of a hundred meters. Providing ubiquitous Broadband Wireless Access (BWA) service is a major challenge for telecommunication companies. IEEE 802.16 provides a solution to this issue, since it can provide radio coverage from several miles to dozens of miles with data rates up to 75Mbps. However, like other radio communication technologies, IEEE 802.16 suffers from normal radio propagation problems, including path loss and shadow fading. These problems degrade the data rate of Subscriber Station (SS), mean that the service providers cannot guarantee the Quality of Service (QoS) of the BWA service. To solve such issues, the IEEE task group j is defining the 802.16j specification to enhance the QoS through the Multihop Relay (MR) networks. IEEE 802.16j solves the radio propagation problems by placing the Relay Station (RS) into conventional 802.16 networks in order to relay the signal from Base Station (BS) to SS. This study analyzes how the MR network improves the system throughput, and the drawbacks and rules for RS placement through experiments.