摘要
OFDM(Orthogonal Frequency Division Multiplexing)是一种高效并行多载波传输技术,它将高速串行数据流调制到多个低速并行数据信道中,从而使信道的码元宽度大于信道时延扩展;同时通过加入循环前缀来避免ISI。它可以有效对抗频率选择性衰落。
分集(Diversity)是一种在独立的衰落路径上多次发送或接收相同的数据,将各次发送或接收的数据进行合并,从而有效改善系统信噪比,提高数据速率和无线系统容量的技术。它可以有效对抗多径衰落。
分集技术是提高系统链路性能的有效措施。本文主要运用C语言完成了一个加入最大比合并分集技术的OFDM系统的设计,并在Visual C++环境下进行仿真研究。最后比较了在AWGN和Rayleigh衰落信道下加入分集技术前后OFDM系统的性能(误码率)。结果表明:分集技术有利于改善系统性能,并且系统性能在AWGN信道中较Rayleigh信道中好。
关键词:正交频分复用,信道编码,交织,最大比合并分集,通信系统仿真,C语言
ABSTRACT
OFDM(Orthogonal Frequency Division Multiplexing) is a highly efficient parallel multi-carrier transmission technology. It will decompose a high-speed serial data and modulate it to multiple parallel sub-channels, so that the width of each sub-channels symbol is larger than the channel delay expansion .Meanwhile adds cycle of expansion to ensure that systems from multi-path interference ,which will cause the interference between the Symbol (ISI) impact. It can be effective against Frequency selective fading.
Diversity is a technology than it sends or receives the same data in independent fading channel for several times, then merge the data above for improving system’s SNR, raising data rate and system capacity. It can be effective against multi-path transmission.
Diversity is a effective measure to improve system performance. This paper has designed and simulated an OFDM system with maximal-ratio combining Diversity technology, using C-language under Visual C++. Finally, I compare the error rate of OFDM with or without Diversity technology in the conditions of AWGN channel or Rayleigh fading channel. The results show that: Diversity technology is in favor for improving system performance, and the system performance is better in AWGN channel than that in Rayleigh fading channel.
Keywords: Orthogonal Frequency Division Multiplexing, channel coding, interleaving, maximal-ratio combining diversity, Communication System Simulation, C language