應用於超高速傳輸多天線系統(MIMO-OFDM)頻域上之高時脈誤差容忍時間同步器

Abstract

隨著無線通訊技術的快速發展，超高速傳輸系統已成為新一代無線通訊系統的發展核心，然而高速傳輸需要更快的取樣頻率，這將使得「大量取樣頻率偏移」此問題發生的機率增加，這將造成訊號嚴重的衰減。因此，本論文致力於研究在2048-FFT下超高速多天線正交分頻多工系統中(MIMO OFDM)，頻率域上的時間同步器，並以調節取樣相位的方式補償取樣頻脈誤差，達到同步取樣的目的。 本論文所提出的演算法，主要應用在 IEEE 所制定的無線區域網路標準 IEEE 802.11n，藉由利用封包前端格式固定的preambles，針對其彼此間的相關性對取樣頻率誤差作估計以及補償。此演算法中，總共使用六個preambles。在高斯雜訊及多路徑衰減的情形下，以封包錯誤率(PER)小於8%為標準，效能可以達到容忍-30000~40000-ppm的時脈偏移影響。

Due to the explosive growth demand for wireless communication, the next-generation wireless communication systems are expected to provide high-speed and high-throughput. However, high-speed transmission needs high sampling rate, which would cause wide sam-pling clock offset. Based on phase adjustment, this work investigates a frequency-domain timing synchronizer to perform coherent sampling for 2048-FFT Multiple-Input Mul-tiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) timing recov-ery. In the proposed algorithm, we use a multiphase all-digital clock management (ADCM) which can generate more than 32 phases over GHz without phase-locked or delay-locked loops to adjust sampling phases and utilize the correlation between short preambles to es-timation the sampling phase error. It can perform the sampling clock synchronization effi-ciently and quickly. Performance evaluation indicates that the proposed timing synchronizer can tolerate -30000 ~ 40000ppm sampling clock offsets with 0.2db SNR losses at 8% PER in frequency-selective fading. Hence, this scheme involves a little overhead to ensure fast recovery and wide offset tolerance for OFDM packet transmissions.