【作者】 张炬；

【导师】 向敬成； 朱中梁；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2002， 博士

【摘要】 无线通信是目前和将来最重要的通信手段，其多址方式主要是采用时分多址TDMA和码分多址CDMA。实际上TDMA和CDMA都是与频分多址FDMA混合使用。在七十年代末TDMA通信体制就应用在数字卫星通信领域，并在九十年代的第二代数字移动通信系统中得到广泛应用，在第三代数字移动通信系统中也将占有一席之地。CDMA最早应用在军事领域，在第二代数字移动通信中窄带CDMA已成功地应用，而宽带CDMA将成为第三代数字移动通信系统的主流技术。本文针对这两种通信体制和其中一些关键技术进行研究，目的是解决工程中的实际问题。在某些应用场合会遇到较恶劣的接收条件。例如接收信噪比偏低，对于TDMA系统，会引起作为每帧开始标识的独特码检测错误概率增大。独特码检测错误将导致整个帧的数据丢失，为此研究了在低信噪比条件下旨在提高TDMA系统独特码检测概率的技术。在蜂窝CDMA系统中，由于接收位置不理想，会承受比在理想接收位置更大的多址干扰。在这种情况下，通常还不知道其它用户的扩频码和数据信息时，利用定向天线的空间分割方法是减小多址干扰的简单有效措施。针对这个情况，研究了工作在这种接收方式中的RAKE接收技术。由于TDMA通信系统信号规格繁多并且不断变化，研究设计了一种通用TDMA终端设备。最后，开发研制了一种新型低成本的，采用准同步直扩码分多址方式的无线本地环路（WLL）。它可提供常规的电话和数据业务，也可作为专用通信系统，并已进入实用阶段。本文的主要工作和创新在于：深入研究了TDMA系统中独特码的最大似然检测技术，提出了工作在低SNR下的解决方法。进行了计算机仿真模拟。结果表明在低信噪比，相干解调，UW码长为16时，3比特量化，检测窗为9和AGWN信道条件下，该方法较相关检测方法可获得1.5到<WP=6>1） 2dB的增益，比较常规的硬判决检测可获得2.5到3.5dB的增益。设计实现了一种通用高速独特码最大似然检测器并且应用于实际的工程系统，测试结果与理论分析相一致，解决了常规方法在低信噪比条件下丢帧率偏高的问题。提出了结合帧数据的编码方式，进一步提高帧定位正确率的方法。2） 设计研制了一种通用的TDMA终端设备，它的帧结构等参数可通过计算机串口设置。一些功能模块，如解调器，译码器则通过更换插件以实现不同的规格。这种设备已用于实际的TDMA通信系统中，效果良好。提出并着手研制一种基于计算机和局域网的TDMA接收终端设备。这种实现方案思路新颖，设计先进，通过更改配置和加载相应的处理软件以适应多种信号规格。3） 针对提出的CDMA系统空间分割的接收方案，研究设计了一种基于匹配滤波器的RAKE接收器。根据解扩信号在匹配滤波器顺序输出的特点，提出了相应的多径选择，信道参数估计，码片时钟定时等实用算法。对其性能进行了分析和仿真模拟。4） 研制了一种低成本准同步CDMA－WLL系统。它的工作频段为1.9GHz，每个基站的无线覆盖距离可达30公里。系统采用了时分复用/码分多址空中接口和上行信号闭环延迟控制两项关键技术，前者是为了减少端站数目以降低成本，后者是为了保持上行信道的准正交性以提高接收性能。分析了同步精度对比特误码率的影响。系统采用了基于误码率测量的闭环功率控制技术，效果良好。给出了仿真和现场实验的结果。更多还原

【Abstract】 New wireless communication methods have been enthusiastically adopted throughout the world. The majority of current and proposed wireless communication systems employ the multiple access method of TDMA or CDMA in combination with frequency reuse or FDMA. In late 1970s, the first TDMA system was used for satellite communication. In late 1991, a cellular system based on TDMA was adopted in second-generation mobile radio systems. TDMA will occupy a place in third generation mobile radio systems. The CDMA originated in spread spectrum communications for military purpose in 1960s. A cellular system based on CDMA (IS-95) had been developed and successfully deployed. In future third generation mobile radio systems, the dominant multiple access scheme is CDMA. This research concentrates on TDMA, CDMA systems and some key technologies. The value of the research resides in its practicable solutions to problems in engineering projects.Under severe receiving conditions, for example the lower SNR (Signal to Noise Rate), there is a high error rate of UW (Unique Words) detecting for TDMA system by conventional detecting methods. A missing or false UW detecting will result in the loss of all data in one frame because UW operates as a marker of a frame beginning. In order to improve detecting probability of UW, an UW detecting method working at low SNR is developed. Again, in cellular systems based on CDMA, a receiver that is located at another position in the vicinity of the base station will bear more MAI (Multiple Access Interference) than idealized position. Considering that spread sequences and data of other users cannot be also attained, the space division receiving could be a simple and effective method to reduce MAI. Then, a RAKE receiver that is fit for such cases is designed. There are many<WP=8>specifications of TDMA systems, and therefore a universal TDMA terminal is proposed to accommodate to wide variety of signal forms and rapid development. Finally, this dissertation describes a new low cost practical QS-CDMA-WLL (Quasi-Synchronous CDMA Wireless Local Loop), which is used to provide basic services of voice and data or is used as special wireless data network.The primary work and novelty in this dissertation resides in: 1) The UW detecting work at low SNR has been studied on the basis of maximum likelihood estimation techniques after analyzing and comparing various detecting methods of other’s progeny. The analysis and simulation results made evidence that the new method proposed attains gain by about 1.5 to 2dB as compared with correlation detecting by soft-decision, 2.5 to 3.5dB compared with hard-decision detecting, under conditions of coherent demodulation, UW length of 16bits, 3bits quantized input data, window width of 9bits and AGWN channel. The universal high speed UW detecting structure developed has been put to practice. It improves on UW detecting performance of traditional methods in which error rate of detecting is higher. The test results agree well with analyses and simulations. A new scheme combining with data structures in frames is proposed to improve further detecting performance. 2) The new universal TDMA receive terminal equipment has been developed. Its working parameters such as frame structures can be set or change by serial communication port of personal computer. Some modules of it such as demodulator, decoder and so on can be substituted with different parameters optional plug-in parts to be used for different signal specifications. This equipment worked well in actual communication systems. Another new advanced solution for implementing TDMA receive terminal is presented. This equipment is realized on the basis of preprocessor, PC and local area network. It could be set to rapidly adapt to wide variety of specifications by<WP=9>configuring corresponding parameters and downloading relevant processor software. It is under development.3) A RAKE receive structure based on match filter has been designed and implemented to be applied in the space division receive scheme.更多还原