IEEE 802.16 鏈結調整演算法之研究

Abstract

在過去幾年來，由於無線寬頻接取技術如: IEEE 802.11已經發展成熟並且提供高速上網的服務。加上行動個人裝置如: 個人數位助理(PDA)、筆記型電腦和智慧型手機等已經發展出功能強大、省電和便宜的產品，有越來越多的企業和個人使用者轉而在行動個人裝置上使用多媒體的服務如: 視訊會議、隨選視訊、語音服務、線上遊戲及點對點的線上服務。但，IEEE 802.11 並不適合移動性和長距離的使用，因此有另一個無線寬頻接取技術 IEEE 802.16被發展出來，因為它具有移動性和長距離使用的特性，所以它是最適合使用在戶外的無線寬頻接取技術。在無線網路中，接收到的訊號品質常常會因為雜訊、干擾、多重路徑、移動等因素所影響。而這些無線網路的特性常會引發接收資料的錯誤。一個好的鏈結調整機置可以處理這樣的狀況。在這篇論文裡，我們提出一個有效率的鏈結調整演算法並且在有長時間和短時間通道改變的環境中實驗。我們演算法的機本概念是去選擇某個調變方式和良好的封包傳送率以最短時間傳送現在的封包，並且在選擇適當的傳送速率後我們還配置一個防止封包傳送連續錯誤的機置。藉以防止在選擇適當的傳送速率後因無線頻道環境突然快速劇烈改變而造成封包傳送的連續錯誤。我們的演算法使用到ACKs、封包成功傳送率、傳送時間、封包大小和連續訊框損失率等當作參數計算。我們以Qualnet 4.0 模擬器來評估我們演算法和其他演算法的效能，從實驗模擬結果中可以很清楚得知我們的演算法確實表現得比其他的演算法好。

During the last pass years, the broadband wireless access technologies, such as IEEE 802.11a/g/n have developed to become mature and provide high speed Internet services. At the same time, the mobile personal devices, such as personal digital assistant (PDA), laptops, and mobile phones have developed to cheaply, powerful functions, compactness, mobility, and less battery consumption. People can easily use mobile personal devices to access Internet services via broadband wireless access technologies. So, many of commercial and residential consumers have rapid grow on multimedia applications demand, such as Video conference, Video on Demand (VoD), Voice over IP (VoIP), online game, and peer to peer applications running on mobile personal devices. But IEEE 802.11 is not suitable for mobility and the radio coverage area is not too far. Therefore, another broadband wireless access technology that IEEE 802.16 is proposed. Due to it has mobility and long distance transmission characteristic. IEEE 802.16 is good for outside use. In any wireless network, the quality of the received signal may change over a short period of time due to noise, interference, multipath, and mobility effect. These characteristics of wireless can lead to occurring bit errors at the receiver. A good link adaptation scheme can take care of these conditions. In this paper, we proposed an efficient link adaptation algorithm, and compare it with several other algorithms in large and small scale fading environment. The idea of our algorithm is choice small transmission time with good protocol data unit (PDU) success rate to transmit a frame successfully. And the proposed link adaptation algorithm is also implemented burst error detector to prevent the burst errors condition after the rate is selected. The burst errors detector can fast reflect the wireless channel is changed violent. The proposed link adaptation algorithm uses ACKs, PDU success rate, transmission time, PDU size, and consecutive frame loss times as the parameters. We evaluate the performance of the proposed algorithm via Qualnet 4.0 emulator. According to the simulation results, we can clearly see that our proposed algorithm has better performance than other algorithms.