正交分頻多工系統中載波頻率位移、取樣頻率位移與通道響應之同估測

Abstract

正交分頻多工系統已成功應用在許多通訊系統，但是此系統很容易受到傳送器和接收器參數的非同步影響而破壞其正交性，降低成效。此篇論文主要討論如何估測兩個參數的非同步:載波頻率位移和取樣頻率位移與通道響應估測。

Orthogonal frequency division multiplexing (OFDM) systems have been widely used and standardized for broadband wireless and wired communication systems. Due to cost, package size and power consumption, direct-conversion radio frequency (RF) receivers are popularly adopted to demodulate OFDM signals recently. For silicon implementation, The devices can suffer from various mismatches between transmitters and receivers. Unfortunately, OFDM systems are very sensitive to these distortions or synchronization errors such as Carrier frequency offset (CFO) and sampling frequency offset (SFO). These synchronization errors at the receiver lead to intolerable inter-carrier interference (ICI). Hence we must get an accurate estimation of the CFO and SFO and compensate them properly at the receiver. In this thesis, the effects of CFO and SFO on OFDM systems are first studied. We discussed that joint influence of SFO and CFO in frequency domain. Then several estimation methods of these parameters are proposed. Firstly we propose a time domain method based on Taylor expansion for joint estimation of CFO, SFO and channel response by using a repeated training sequences. Secondly we introduce a frequency-domain method that can jointly estimate these parameters by using pilots (instead of training sequences). A low cost iterative algorithm is proposed to solve the joint estimation of SFO and CFO in the frequency domain. Simulation results show that the performance of the proposed methods is good.