以偵測循環字首類型為重點之LTE初始下行同步

Abstract

本篇論文介紹LTE-A系統裡關於初始下行同步的問題，包括問題陳述、演算 法推導、以及程式模擬。在初始下行同步中，我們發展了一套同步估測演算法， 包括了符元時間偏移、載波偏移和訊號傳輸所使用的循環字首類型。首先，我們 建立了LTE-A系統下的傳送端和接收端的訊號模型，然後基於最大可能性估測 (maximum likelihood)法推導其解。此解不僅於可加性白色高斯雜訊(additive white Gaussian noise, AWGN)、單一路徑瑞利衰減(single-path Rayleigh fading)通 道下在具有普遍正確性，且也適用於多路徑衰減(multipath fading)通道。為了大 幅減低計算複雜度，我們在處理載波偏移過程中做一近似，雖然在多路徑衰減通 道下此解為次優解，但因為此近似在可加性白色高斯雜訊和單一路徑瑞利衰減通 道下不影響估測程序，所以在這些通道下亦為最佳解。 在模擬部分，我們設計出一個合理的LTE-A系統接收訊號模型，在可加性白 色高斯雜訊通道下得到的數據驗證此演算法，然後在多路徑衰減通道傳輸中使用 數種不同多路徑通道、相對移動車速以及雜訊比來測試此演算法對這些環境下所 產生的結果。

This thesis introduces the topic about initial downlink synchronization, including problem formulation, algorithm derivation and program simulation, in LTE-A system. We develop an algorithm about the joint estimation of symbol timing offset (STO), carrier frequency offset (CFO), and detection of the cyclic prefix (CP) type used in signal transmission. We first establish the transmitted and received signal models of LTE-A system and then derive the solution based on the maximum likelihood (ML) criterion. It is a general solution over not only additive white Gaussian noise (AWGN) and single-path Rayleigh fading channels but also multipath fading channels. In estimating CFO, we consider an approximation so as to reduce computational complexity largely. Though it is the suboptimal solution under multipath fading channels, it is an optimal solution under AWGN and single-path Rayleigh fading channels because the approximate term has no effect on estimation process. In simulation, we establish a reasonable received signal model in LTE-A system, and then simulate our proposed estimator under AWGN channel to verify its performance. Moreover, we test it under single-path Rayleigh fading and different multipath fading channels, including Standford University Interim (SUI) and Pedestrian B (PB), at different mobility and different signal to noise ratio (SNR).