LTE 平台下頻域SCO 與CFO 協同估測與補償

Abstract

本論文致力研究於1024-FFT 下高速傳輸正交多工分頻系統(OFDM)中，頻率 域上的時間同步與載波頻率偏移評估，以角度旋轉偏量進行載波頻率偏移與取 樣振盪器偏移等同步問題的評估。 本論文所提出的演算法，利用收到LTE 封包的固定索引的參考訊號 (reference signal)與理想參考訊號的角度差異對頻率偏移與取樣時脈偏移進 行評估與補償。殘餘的頻率偏移與取樣時脈偏移以參考訊號在極座標上的靠近 理想參考訊號的落點數目進行進一步評估補償。 本論文所提出的演算法，主要應用在無線網路標Long term evolution (LTE) 4G 上，所提出頻率域上的載波頻率偏移與時間同步演算法可在高斯白雜訊與多 通到效應進行並且在達到位元錯誤率0.01 以下只損失SNR 0.3~1.5 db。可容 忍載波頻率偏移高達25ppm 與 頻率偏移達 300ppm。

This thesis is dedicated to design of frequency-domain frequency and timing synchronizer for 1024-point FFT Orthogonal Frequency Division Multiplexing (OFDM) communication system. The proposed algorithm takes advantage of rotation phase and the changing speed of phase. This thesis uses the known reference signal (pilot) to do both carrier frequency offset and sampling clock offset estimation. It compares the difference of phase between received signal and ideal reference signal and uses these information to design the algorithm. The residual CFO and SCO estimation uses the falling number of received signal close to ideal reference signal on constellation to do further compensation. This proposed algorithm is based on 3GPP Long Term Evolution. It works in the environment with AWGN, Multipath, CFO and SCO effects. It only loss 0.3~1.5dB compared to optimal solution when BER is below 1%. It can tolerate CFO up to 25ppm and SCO up to 300ppm.