OFDM（Orthogonal Frequency Division Multiplexing）是一种多载波数字调制技术, 它的基本原理是把高速的数据流通过串并转换，分配到传输速率较低的若干个子信道中进行传输。OFDM可以有效地克服多径传播中的衰落，消除符号间干扰，提高频谱利用率，已在宽带通信中获得了广泛的应用，是支持未来移动通信特别是移动多媒体通信的主要技术之一。
无线通信系统中随机时变信道的衰落特性会降低系统性能，为了对抗衰落，可以采用分集，均衡和信道编码等措施，分集接收技术被认为是明显有效而且经济的抗衰落技术。而在接收分集中，由于等增益合并分集易于实现，而且码率性能较高，所以本文采用了单天线发射和多天线接收的等增益合并分集，来降低整个系统的误码率。
本文介绍了OFDM的基本原理，并结合接受分集来提高系统的性能，在给出OFDM系统模型的基础上,用MATLAB语言实现了整个系统的计算机仿真并给出参考设计程序，分析整个系统的误码率。其仿真的结果与理论结果相吻合。
关键词 正交频分复用，无线信道，分集
ABSTRACT
Orthogonal Frequency Division Multiplexing is a kind of multiple carrier modulation technique,OFDM can resist the attenuation by the multi-path disturbance, eliminate the inter symbol interference,improve specturm utilization, It already obtained the widespread application in the wideband communication,is one of the major techniques which will be supports the mobile specially multimedia correspondence in the future.
The character of the random time-varying in the wireless communication system can reduce the performance of the system.To resist the attenuation,we can use the measures of diversity ,balance and channel coding.Because the diversity of equating gain merge is easy to implement and the perfomance of the bit error rate is good in the achieve diversity.So the paper focus on the diversity of equating gain merge with the single transmision and multiple achieve antenna to reduce the bit error rate of the whole system.
The paper introduces the basic principle of OFDM with the diversity to improve the system performance.On the basis of OFDM systematic mode,the simulation work has been done together with the designing procedures for reference through use of MATLAB tools.Analysis the bit error rate of the system.the result of the simulate is similar to the the theory result.
Keywords Orthogonal Frequency Division Multiplexing,Wireless channel, Diversity
