多载波CDMA频偏估计与多址干扰联合检测

【作者】 程晖；

【导师】 胡艳军；

【作者基本信息】 安徽大学 ， 电路与系统， 2004， 硕士

【摘要】 CDMA技术以其高抗干扰能力、高容量、高保密性等技术优势在第三代移动通信系统中被广泛应用，然而在高速数据业务中，严重的码间干扰和符号间干扰会导致系统性能明显下降。正交频分复用(OFDM)技术作为一种多载波传输的技术，在处理高速数据的系统中是非常有效的，该技术将系统带宽分成若干正交的子载波，每个子载波只传输相对低速率的数据。 CDMA技术和OFDM技术结合产生了多载波CDMA系统，它很好地解决了高速数据业务下传统CDMA系统性能下降等一系列问题。然而多载波CDMA系统也存在一些问题，多址干扰和频率偏移等问题会带来明显的性能下降。本文的研究是针对多载波CDMA系统的多址干扰和频率偏移两个问题进行的，希望通过我们的研究，能够进一步明确多载波CDMA系统内的干扰类型及其来源，综合考虑多载波CDMA系统中主要的干扰和性能下降因素，找到一种将频率偏移与多址干扰联合起来进行考虑和消除的方法，提高多载波CDMA系统的性能和抗干扰能力，并进而提高系统的容量。 论文的研究结合了中德(西门子)国际合作项目《面向后3G蜂窝移动通信的OFCDMA方案研究》及安徽省自然基金项目《CDMA自适应盲多用户检测方法的研究》(03042208)。 论文从移动通信的历史和发展出发，首先回顾了第一代、第二代通信系统的技术特点和发展历程，介绍了第三代通信系统的分类和发展态势，展望了超3G系统的研究领域和研究热点。然后对超3G系统研究的一个重要领域——多载波CDMA系统的类型和主要技术进行了介绍和分析，进而对多载波CDMA系统中的多址干扰和频率偏移进行了较为深入的分析，衡量了频率偏移对多载波CDMA系统性能的影响。随后，利用理论分析和实验仿真的方法比较了一些常规多用户检测器应用于存在频率偏移的多载波CDMA系统时的不同性能，指出了多址干扰和频率偏移对多载波CDMA系统性能的影响。最后，在各种分析结果和理论的基础上，我们提出了一种将基于保护间隔的最大似然频偏估计方法和改进的并行多址干扰消除方法联合起来进行处理的ML-MPIC方法，在一定程度上改善了频偏多载波CDMA系统的性能，计算安徽大学硕士论文机仿真的结果进一步验证了MLMPIC方法的有效性。更多还原

【Abstract】 For wireless communications, direct sequence code division multiple access (DS-CDMA) techniques have received a great deal of attention due to the expectation of capacity increase, interference rejection capability, security, and so on. In a high data rate application such as multimedia services, however, the capacity of DS-CDMA systems is limited by both the inter-chip, or inter-symbol interference. A demand for very high bit rates brought OFDM systems into focus. Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique, which divides the available spectrum into many carriers, each one being modulated by a low rate data stream.MC-CDMA system is a combination of direct-sequence CDMA and multicarrier modulation systems. Much attention has been paid to it, because the system can achieve better performance than conventional CDMA in high data applications and it is potentially robust to channel frequency selectivity. But MC-CDMA system still has some problems. Some of the most important sources for performance degradation of MC-CDMA systems are carrier frequency offset and the multiple access interference (MAI). In OFDM systems similar to MC-CDMA systems, many schemes have been proposed to estimate the frequency offset. These schemes, however, cannot be directly applied to MC-CDMA systems due to the MAI and the full correlation between the different subcarrier data. In DS-CDMA systems, many detection schemes have been proposed to eliminate the MAI. However, using these schemes for MC-CDMA systems, their performances get considerably worse even in the presence of the small frequency offset. Therefore, the frequency offset and the MAI should be jointly considered. Our research is focused on these two problems in MC-CDMA system. We hope to clarify the types and originations of interference and consider the main interference synthetically in MC-CDMA system. Our target is to find out a solution to estimate the frequency and eliminate the MAI jointly and also by this solution we can improve the performance and capacity in MC-CDMA system.The work in this thesis is part of the International Cooperate Project "Research on OFCDMA for beyond 3G mobile communications" and Nature Science Research Project of Anhui Education Department, "Research on the blind adaptive multiuser detection in CDMA systems".In this thesis we firstly analyze the MAI and frequency offset in multicarrier CDMA system respectively. Then we evaluate the effect of frequency offset in multicarrier CDMA systems by computer simulation and theoretical analysis. The performance analysis of some conventional multiuser detectors in multicarrier CDMA with frequency offset is performed. Based on the analysis of frequency offset and multiuser detectors in multicarrierCDMA system, we propose a method, named ML-MPIC method, to estimate the frequency offset for the desired user and to eliminate the MAI jointly .The performance analysis of the scheme is given, simulation results with different user number show its better performance than that of systems which deal with these two problems separately.更多还原