摘要
OFDM(Orthogonal Frequency Division Multiplexing)是一種高效并行多載波傳輸技術，它將高速串行數(shù)據(jù)流調制到多個低速并行數(shù)據(jù)信道中，從而使信道的碼元寬度大于信道時延擴展；同時通過加入循環(huán)前綴來避免ISI。它可以有效對抗頻率選擇性衰落。
分集（Diversity）是一種在獨立的衰落路徑上多次發(fā)送或接收相同的數(shù)據(jù)，將各次發(fā)送或接收的數(shù)據(jù)進行合并，從而有效改善系統(tǒng)信噪比，提高數(shù)據(jù)速率和無線系統(tǒng)容量的技術。它可以有效對抗多徑衰落。
分集技術是提高系統(tǒng)鏈路性能的有效措施。本文主要運用C語言完成了一個加入最大比合并分集技術的OFDM系統(tǒng)的設計，并在Visual C++環(huán)境下進行仿真研究。最后比較了在AWGN和Rayleigh衰落信道下加入分集技術前后OFDM系統(tǒng)的性能（誤碼率）。結果表明：分集技術有利于改善系統(tǒng)性能，并且系統(tǒng)性能在AWGN信道中較Rayleigh信道中好。
關鍵詞：正交頻分復用，信道編碼，交織，最大比合并分集，通信系統(tǒng)仿真，C語言
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
