LTE隨機存取訊號於可能具有宏大都卜勒位移之多徑通道中之檢測

Abstract

本篇論文研究了在於LTE-A的環境下隨機存取偵測的系統，在隨機存取偵測 的過程，基地台必須決定是否使用者傳送了隨機存取前置符元(preamble)。 在論文中，我們建立了傳送系統模型，而當中我們考慮了符元時間偏移、載 波偏移、多徑通道。然後我們把問題制定成多重假說試驗和二元假說試驗，基於 多重假說試驗的實行計算複雜度太高，我們著眼於二元假說試驗。我們使用了普 遍化相似度比率檢驗(generalized ratio likelihood testing, GLRT)當成偵測的準據來 解決問題，而當中我們需要去解出符元時間偏移、載波偏移、多徑通道的最大可 能性估計(maximum likelihood estimate, MLE)。在推導中，我們也提出了一個減 低普遍化相似度比率檢驗的計算複雜度的近似。 在模擬中，在不同載波偏移和多徑通道下，我們驗證了我們提出的普遍化相 似度比率檢驗檢測器的效能。對於多徑通道模型，我們考慮了可加性白色高斯雜 訊(additive white Gaussian noise, AWGN)和史丹佛大學暫定(Standford University Interim, SUI)的模型。

The thesis studies the random access detection schemes in LTE-A system. In random access detection procedure, the base station needs to determine whether random access preambles are transmitted by the users. In this thesis, we first develop transmission system model, in which we consider the symbol timing offset (STO), carrier frequency offset (CFO), and multipath channels. Then we formulate the problem by the multiple hypothesis and binary hypothesis testing. Due to high computational complexity for implementation of multiple hypothesis testing, we focus on the binary hypothesis testing formulation. We use the generalized likelihood testing technique (GLRT) as a detection criterion to solve the problem, in which we need to get the maximum likelihood estimate (MLE) of the STO, CFO, and channel. In the derivation, we also propose an approximation of the GLRT to further reduce the computational complexity. In the simulation we verify our proposed GLRT detector performance with difference values of CFO and different kind of channel model including AWGN and Standford University Interim (SUI).