Abstract: The analysis of OFDM system over time-variant channel is often performed under the assumption that the channel remains constant within one symbol period, however this is not always true for any situations. With the higher carrier frequency, faster movement speed and longer symbol duration, the Inter-Carrier Interference (ICI) caused by Doppler spread will be increased. The authors analyze the Maximum Achievable Data Rate (MADR) and SINR (Signal to Interference and Noise Ration) for time-frequency selective fading channels when the orthogonality of sub-carriers is destroyed by the Doppler spread. The authors also find out the optimal symbol durations to maximize the MADR and SINR. Numerical results corroborate the theoretical findings.

Key words: Doppler spread, capacity, ICI, Rayleigh channel, OFDM

摘要： 针对时变信道下的OFDM系统的性能分析，通常采用信道在一个符号持续时间内保持不变的假设为前提。然而，这种假设在某些情况下并不合理。随着载波频率的提高，终端移动速度的加快以及符号长度的增加，由多普勒效应导致的载波间的串扰变得更加严重。本文分析了多普勒效应对最大可传送速率和信干比的影响，并且分别设计了使信干比和最大可传送速率最大化的符号长度。数值仿真结果进一步证实了作者的理论结果。

关键词: 多普勒效应, 容量, 载波间串扰, Rayleigh信道, OFDM