解决OFDM系统频偏的正交序列设计

针对OFDM对多普勒效应非常敏感的问题,研究了采用设计特定的正交序列来消除干扰,提高系统性能.根据OFDM系统的原理,建立了OFDM基础模型,推导出多普勒对系统传输过程的影响.针对应用设计的正交序列自相关、互相关性好和可选码序列比传统码多的特点,对传输信息进行信道编码.将该码序列变换置于IFFT之前,接收端采用软判决,提高了系统信噪比.Matlab仿真显示系统的误码率相对于标准BPSK调制的OFDM系统大幅度下降.

Orthogonal Sequence Design for Metigating Offset of OFDM System

Targeting at the sensitivity of OFDM system to frequency shift,mutually orthogonal sets of complementary sequences arc designed to mitigate the ICI, improving the overall system performance. According to the principle of OFDM system ,we construct a basic OFDM model, simulating the negative effect brought by the Doppler Effect. Then we demonstrate that orthogonal sequence has excellent self-correlation and cross-correlation properties together with a long sequence length. We apply orthogonal sequence to the coding of the message. By converting code sequence before IFFT manipulation and adopting soft-decision in receiver, we enhance the SNR of the system. The Matlab simulation results show that the BER of the modified OFDM system drops down critically compared with the standard OFDM system.