【作者】 高红梅；

【导师】 唐小虎；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2007， 硕士

【摘要】 在当今和未来的移动通信系统中，都需要高速的数据传输。而当数据在移动信道中以高速传输时，由于时延扩展现象会引起符号间干扰。多载波扩展频谱码分多址系统(MC／CDMA)是一种消除符号间干扰的有效技术，它是利用正交频分复用(OFDM)与码分多址(CDMA)技术相结合的一种调制方法。在准同步CDMA(QS-CDMA)系统中，LS码通过零相关区(ZCZ)，可以消除码间干扰(ISI)和多址接入干扰(MAI)。广义LS(GLS)码是对LS码的广义描述，它可以降低QS-CDMA系统的小区间干扰(ACI)。本文首先提出了一种改进的多载波码分多址(MC／CDMA)系统。与传统的MC-CDMA系统相比，其主要区别是该方案同时在时域和频域进行扩频。这种系统能更有效地利用传输带宽，实现频率分集。由于该系统降低了每个子载波上的数据速率，扩频序列更容易同步。最后给出了在瑞利衰落信道下的性能分析。其次本文用高斯近似的方法得出了应用GLS码的多小区QS-CDMA的系统的误码性能。并且与基于LS码的QS-CDMA系统，进行了仿真分析与比较。分析结果表明，与LS码相比，GLS码显著地改善了系统的性能。最后本文把GLS码应用在MC-DS-CDMA中，并得出了系统的误码性能。该系统利用GLS所具有的零相关区特性克服了OFDM系统存在频偏时的多用户接入干扰(MAI)。结果表明，该系统比之使用Walsh序列的MC-DS-CDMA系统有更好的误码性能，并且有更高的频谱利用率。更多还原

【Abstract】 High-rate data transmission becomes indispensable for nowadays and future mobile communication system. However, when the data is being transferred in mobile channel, there will be inter-symbol interference (ISI) because of delay spreading. Multi-carrier CDMA is one of effective techniques to mitigate the ISI. It is an integrated modulation method of Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA) technologies. In a quasi-synchronous code-division multiple-access (QS-CDMA) system, loosely synchronous (LS) code can eliminate inter symbol interference (ISI) and multiple access interference (MAI) by using zero correlation zone (ZCZ). Generalized LS (GLS) code is a general description of LS code. Adjacent cell interference (ACI) can be minimized by applying GLS in QS-CDMA system.First of all, an improved Multi-carrier CDMA system is proposed in this thesis. Compared with conventional MC-CDMA system, the main difference is that this scheme performs the spreading in the time and frequency domain simultaneously. This system can utilize the transmission bandwidth more efficiently and achieve frequency diversity. Furthermore, this system lowers the data rate of each carrier branch, so it is easier to make spreading sequence synchronized than the conventional system. Then the performance of the system is analyzed in a Rayleigh fading channel in this thesis.Next, based on the Gaussian approximation method, the bit error rate of multiple cellular QS-CDMA system using a GLS code family and scrambled LS codes is estimated and their simulations and performance comparison are presented. It is shown that the GLS code improve the system performance greatly, much better than the LS code.Finally, generalized loosely synchronous (GLS) codes are applied to the MC-DS-CDMA system and the bit error rate of the new system is obtained. The system overcomes MAI of OFDM when there is frequency offset because of the ZCZ characteristic of GLS code. The simulation result shows that the system using GLS code performs better than the MC-DS-CDMA using Walsh sequence, and has high frequency utilizing rate.更多还原