Blind Channel Estimation and Signal Detection for Direct Sequence(DS) Code Division Multiple Access (CDMA) Systems Employing Long Spreading Codes

摘要徐正元，美国加州河滨大学的研究员全球信息社会的快速发展是由对无缝宽带综合服务日益增长的需求所推动的。为了满足这种需求，发展先进的通信技术变得势在必行。未来所需的服务范围将从传统的话音和寻呼服务到包括高速数据通信在内的交互式多媒体。 为了支持多比特率传输，直接序列（DS）码分多址（CDMA）技术由于其固有的优点而成为一种有吸引力的解决方案。在DS扩频中，下一代无线系统将采用的扩频序列将是非周期的，其周期远大于比特持续时间。长码的使用给通信系统带来了几个好处。首先，由于来自不同用户的不同比特的特征波形的相关性较小，因此平均而言，它增加了系统对多用户干扰（MUI）的抗扰性。这导致改进的系统性能。其次，长码扩频可以在可用频谱上均匀分配信号带宽，从而提高带宽利用率。此外，长扩频码为终端用户提供更安全的通信，并防止窃听者的窃听。

ABSTRACT0207931Xu, Zhengyuan U of California - RiversideThe rapid evolution of the global information society has been fostered by the increasing demand for seamless wideband integrated services. The development of advanced communication technologies is becoming imperative to meet such a demand. Future desired services will range from the traditional voice and paging services to interactive multimedia, including high speed data communications. To support multiple bit-rate transmissions, direct sequence (DS) code division multiple access (CDMA) technology appears as an appealing solution due to the inherent merits of CDMA modulation. In DS spreading, the spreading sequence which will be adopted for next generation wireless systems will be aperiodic with period much longer than the bit duration. Employment of long codes bestows several benefits on the communication system. First, it increases the immunity of the system to multiuser interference (MUI) on the average because of less correlation of signature waveforms of different bits from different users. This leads to improved system performance. Secondly, spreading by long codes can uniformly distribute the signal bandwidth over the available spectrum, thus improving the bandwidth efficiency. In addition, longspreading codes provide end-users more secure communication and prevents interception by eavesdroppers.