Abstract: This paper analyzes the probability of error of QPSK OFDM systems with sampling frequency offset in additive white gauss noise，rayleigh flat fading and rayleigh frequency selective fading channels respectively.The analysis results show that the inter-channel-interference（ICI） of OFDM subcarrier brought by sampling frequency offset is not only have relation to the space of each subcarrier，but also have relation to the index of the analyzed subcarrier，so it can not be equivalent to the ICI brought by carrier frequency offset.The characteristic function（CHF） of the received signals in different channels is obtained with analysis of the ICI，the exact probability of error formula of QPSK OFDM systems is gotten in such three kinds of channel.The validity of the exact probability of error formula is proved by computer simulation results.

Key words: Orthogonal Frequency Division Multiplexing（OFDM）, Sampling Frequency Offset（SFO）, Characteristic Function（CHF）, Symbol Error Ratio（SER）

摘要： 研究了采样频率偏差在加性高斯白噪声信道、瑞利平坦衰落信道和瑞利频率选择衰落信道下对QPSK OFDM系统误码率的影响。通过分析发现，采样频率偏差引起的OFDM系统子载波间的邻道干扰（ICI）不仅与子载波间的间隔有关，而且还与子载波的位置有关，其不能等效为载波频率偏差引起的ICI。通过对OFDM系统子载波间的ICI进行分析，求得上述三种信道条件下接收信号的特征函数;在基带调制方式为QPSK调制时得到了OFDM系统误码率的理论解析解。计算机仿真结果验证了该误码率理论解的正确性。

关键词: 正交频分复用, 采样频率偏差, 特征函数, 误符号率