【作者】 廖明；

【导师】 杨士中；

【作者基本信息】 重庆大学 ， 电路与系统， 2003， 博士

【摘要】 在恶劣的移动通信环境中可靠、高速地传输数据是未来蜂窝移动通信系统的目标和要求。正交频分复用(OFDM, Orthogonal Frequency Division Multiplex)多载波通信技术具有抗多径干扰和时延弥散的优异性能，能够提供非常高的数据吞吐率。由于系统采用离散傅立叶变换，因此大大降低了发射机和接收机的实现复杂度。多载波码分多址(MC-CDMA，Multicarrier CDMA)是最佳的 OFDM 和 CDMA(CodeDivision Multiple Access)多址接入技术融合方案，兼具 CDMA 和 OFDM 这两项技术的优点。而移动通信系统的容量和性能在很大程度上取决于多址方案的选择。在 MC-CDMA 系统中，用户的信息符号先经过频域扩谱，再进行 OFDM 调制，一个数据符号同时在所有并行子载波上传输，具有频率分集的优点。基于 OFDM 的蜂窝移动通信系统具有非常广阔的应用前景。 本文的分析表明，CDMA 技术是一种正交码分复用技术，而 OFDM 技术则是一种正交频分复用技术，OFDM 和 CDMA 发送信号都近似于高斯白噪声信号，是满足香农公式的高斯信道和多径衰落信道中传输的最佳信号形式。本文重点讨论了采用等增益合并(EGC, Equal Gain Combination)和最大比合并(MRC, MaximumRatio Combination)两种合并分集接收技术的 MC-CDMA 系统在瑞利信道和莱斯信道下的良好性能，并提出了一种系统的通用矩阵分析模型，给出了新颖的系统理论误码率分析公式。 针对 OFDM 系统实际应用中的两个关键问题—峰平功率比问题和同步问题，给出了两种等效的峰平比定义，重点研究了限幅、选择映射和基于部分传输序列三种降低峰平比的方法；同时针对 OFDM 系统符号同步的特点，讨论了频域和时域的符号同步方法，进一步介绍了一种基于统计的时域同步方法。而 MC-CDMA系统具有能够选择扩谱码来降低峰平比的独特性质，本文提出了在 MC-CDMA 系统中采用扩谱码的优选条件，即同时考虑扩谱码的峰值因子、相关特性、和谱相关特性。由于格雷互补序列具有峰值因子不大于 6dB 的优点和相关、谱相关特性差的缺点，本文采用 m 序列和 Gold 序列来改善格雷互补序列的相关和谱相关性能。基于优选扩谱码的 MC-CDMA 系统计算量小，实用性强。更多还原

【Abstract】 Data transmission reliably with high-speed rate in execrable wireless environmentis the goal of the future cellular mobile communication system. As a multicarriercommunication technology, Orthogonal Frequency Division Multiplex (OFDM) isprovided with excellent performance of antimultipath, and then can provide very highdata throughput. The complexity for realizing transmitter and receiver decreases greatlysince taking advantage of Discrete Fourier Transform (DFT). Multicarrier-CodeDivision Multiple Access (MC-CDMA) is the best combination of OFDM and CDMA(Code Division Multiple Access), thus advantages of both techniques are exploited, andthat capacity and performance of mobile communication system essentially depend onthe choice of the multiple access scheme. In MC-CDMA system, each data of thesubscriber is modulated by OFDM after spreading in domain, and then the data symbolis transmitted in parallel on all subcarriers, hence resulting in the advantage offrequency diversity. The cellular mobile communication system based on OFDM takeson well prospect for future business application. The significant research results from this dissertation manifest that CDMA isorthogonal code division multiplex technique, at the same time, OFDM is orthogonalfrequency division multiplex technique. Both of the transmitted radio waves areGaussian white noise approximately which is best signal meeting Shannon theorem inGaussian channel and multi-path fading channel. This thesis investigates theperformance of MC-CDMA system in Rayleigh and Rician channel respectivelyadopting Equal Gain Combination (EGC) technique and Maximum Ratio Combination(MRC) technique respectively, afterwards a general matrix analyzing model and noveltheoretical bit error rate (BER) formulas of MC-CDMA is proposed. For engineering application, OFDM system must solve two pivotal issues, thePeak-to-Average Power Ratio (PAPR) problem and the synchronization problem. Afterdefinition, three ways to reducing PAPR is studied, Amplitude Clipping, SelectedMapping, Partial Transmit Sequences. Subsequently, synchronization in time domainand in frequency domain is discussed due to the specialty of Cyclic Prefix (CP) addedinto system. And then a synchronous method in time domain based on statistics isintroduced. Another specialty of MC-CDMA system is selecting spread spectrum code to III<WP=8>重庆大学博士论文reducing PAPR. In this paper, a preferred method for selecting spread spectrumsequence is proposed, that is considering crest factor (CF), correlation function andspectrum correlation function all together. By reason of the characteristics of Golaysequence, CF less than 6dB, poor correlation and poor spectrum correlation, this thesiswill improve the Golay sequence making use of m sequence and Gold sequence.MC-CDMA system based on the rule put forward above have the advantage of lowcomputational complexity, therefore is suitable for practicality.更多还原