Link Adaptation Algorithm in Wireless Networks

近年來，IEEE 802.11無線網路被廣泛的應用在許多地方，如居家、辦公室、與機場等等，已經成為目前最熱門的技術。IEEE 802.11的實體層以不同的調變方式提供了不同的傳輸速度去達到較多的傳輸量，而以不同的演算法去選擇速率會對系統效能造成重大的影響。在本篇論文中我們提出了一個新的想法去調整速率，也和現存的演算法去做了方析比較。我們演算法的基本概念是去選擇某個調變方式能以最短時間送出目前的封包。除此之外，大部分的演算法並沒有將短時間通道狀況的改變情形考慮在內，它們只針對封包碰撞或封包毀損去做設計，這樣一來，它們不能真實反應現實生活中的情形也就無法在現實生活中達到較好的效能。對於它們的演算法我們提出了不同的見解，也提供了將來要設計新的演算法應該考量的準則。我們以電腦模擬來評估我們的演算法與別人的做比較，從模擬結果中可以很明顯的看出我們的確實表現的比其他的演算法好。此外，由於我們的設計只單純使用了傳送端可得到的資訊像ACKs、和連續錯誤的次數去選擇適當的速率，因此我們的演算法能夠很容易的實現在所有802.11相容的產品上。In recent years, IEEE 802.11 Wireless local area networks (WLANs) have become the most popular technology due to the wide deployment in many areas, such as home, office, airport, and so on. IEEE 802.11 PHY supports multiple transmission rates by using different Modulation and Coding Schemes (MCS) to achieve better performance. Different rate adaptation algorithms affect the performance significantly in all wireless networks. In this paper, we propose a novel algorithm, and compare it with several other algorithms. The basic idea of our algorithm is to choose the MCS with the shortest time to transmit a frame successfully. In addition, most algorithms don’t take the effect of small-scale fading into account, and they only focus on collisions or corruptions. In this way, those algorithms may not attain the best performance in real life. We make some comments on all other algorithms and provide more complete guidelines to design an algorithm. We evaluate the performance of the proposed algorithm via computer simulation. From simulation results, we can obviously see that our algorithm really performs better than the other algorithms. In addition, our algorithm only uses the available information locally like ACK, consecutive failure times, to choose suitable rate. Therefore our algorithm can easily implement in all 802.11-based devices.致謝 i要 iibstract iiiist of Figures viist of Tables viihapter 1 Introduction 1hapter 2 Related Work 11.1 ARF & AARF 11.2 CARA 13.3 RRAA 14.4 SampleRate 15.5 RBAR 16.6 Summary 16hapter 3 Algorithm 18.1 Background 18.2 Proposed algorithm 20.2.1. Fast transmission rate controller 22.2.2. Burst error detector 24.2.3. Collisions avoider 25hapter 4 Simulation 29.1 Simulation setup 29.2 Test scenarios 29.2.1. Different distances 30.2.2. Mobility 32.2.3. Multiple stations 38.2.4. Mixed 41.3 Discussion 43hapter 5 Conclusion 46eferences 4