闕斯合併及增量冗餘混合式自動重傳機制之性能分析

Abstract

對於使用封包交換的無線網路來說，利用增量冗餘(Incremental redundancy)或闕斯合併(Chase-combining)的混合式重傳機制在控制錯誤的系統中是非常有效率的。相較於傳統的自動重傳機制，他們通常能提供較好的錯誤比率效果並且有較高的吞吐量。 在本文中，我們針對這幾種協定衍伸出的一些適應性調變系統分析了他們的吞吐量和延遲效能。在我們的系統裡面，編碼和調變機制主要都是根據IEEE 802.16e的規格，採用的分別是迴旋渦輪碼(convolutional turbo code)以及四相位移鍵訊號(QPSK)、16正交振幅調變(16QAM)和64正交振幅調變(64QAM)。我們考慮了加法性白色高斯雜訊(AWGN)和平坦瑞利衰落(flat Rayleigh fading)的環境。而在分析中，我們需要利用計算多維生成函數(generating function)來描繪轉換域(transform domain)的隱馬爾可夫程序(hidden Markov process)。我們提供了一些數值例子來展現並比較這兩種機制的效果，一般而言，增量冗餘的方式在兩種通道中都有較佳的性能比現。

Incremental redundancy (IR) or Chase-combining (CC) based hybrid ARQ (HARQ) protocols are very efficient error-control schemes for packet-switching wireless networks. With proper design, they outperform other ARQ protocols in both latency and throughput. In this thesis we analyze the throughput and delay performance of several variations of these protocols with adaptive modulation. The coding and modulation schemes used in our system are primarily based on the IEEE 802.16e standard, i.e., convolutional turbo code (CTC), QPSK, 16QAM, and 64QAM, respectively. Both AWGN and flat Rayleigh fading environments are considered. Our analysis calls for the evaluation of the multi-dimensional generating function that characterizes the transform domain behavior of the underlying hidden Markov process. Numerical examples are provided for assessing the two classes of protocols. It is shown that, as far as performance is concerned, IR is a better choice although CC is easier to implement.