摘要
随着移动通信业务的发展,用户对网络的质量和覆盖要求越来越高。在国内3G网络建设伊始、尚未成熟、成规模覆盖的情况下,运营商仍然需要投入大量的人力与财力致力于GSM移动通信网络的扩容建设与优化。在实际建设优化工作中,直放站以其性价比高、建设周期短等优点而被大量应用于网络建设中。目前,架设直放站已成为运营商优化网络质量、增强网络覆盖的主要手段之一。近两年在国内,传统模拟直放站因种种性能上的不足,而逐渐被数字化直放站所代替。本文认为数字直放站不应该仅仅只是数字化模拟直放站中的一些主要模拟部件,而应该充分利用数字信号处理提供更多的功能,提高工作性能。
本文正是以设计新型GSM跳频数字化直放站为目标,以实现数字中频系统、直放站的跳频功能为研究重心,围绕数字中频、GSM信号基带处理的相关技术而展开研究。文章介绍了数字直放站的研究背景和国内外的研究现状;比较分析了直放站对GSM无线网络的几种干扰的成因以及各种类型的传统直放站的设计架构上的优缺点,从而提出在数字直放站中引入基带处理模块,实现与基站同步跳频;简述了GSM系统中跳频的类型及性能,分析了引入跳频功能后数字直放站性能的改善情况,并给出跳频功能模块的实现方案;说明了GSM跳频数字直放站系统的设计思想及总体实现框图,并对数字直放站的数字中频部分以及基带处理部分进行了详细地模块划分。针对数字上下变频模块、GMSK解调以及信道译码模块设计所涉及到的相关技术作了详细介绍,涉及到的理论主要有信号采样理论、整数倍内插和抽取理论、维特比解调、维特比译码等,并给出各模块在FPGA上的实现方案。最后根据国家规定的直放站设备测试准则,对GSM跳频数字直放站系统进行实物测试。
GSM跳频数字直放站在时隙同步时钟的控制下实现净噪功能,避免在无有用信号时输出噪声信号;提取小区跳频信息,在时隙同步时钟下准确变换选频模块频率,实现与基站的同步跳频,在射频跳频下可避免或减少数字直放站对GSM网络的负面影响。
With the development of mobile communication business, the demand for network quality and network coverage is rising. Nowadays, 3G is in her immature phase, operator still has to pay much effort to capacity expansion and optimization of GSM in order to achieve large-scale coverage. Repeater is adopted in actual construction due to its advantages such as high cost performance and short construction cycle. At present, building repeaters is one of the main means to improve network quality and enhance network coverage. In recent years, traditional analog repeater was gradually replaced by digital repeater due to its inadequate performances. This paper points out that the main task of constructing digital repeater is making full use of digital signal processing functions to improve working performance rather than just digitizing the major analog processing unit of analog repeater.
This article aim at designing a new GSM frequency-hopping repeater, it focus on realizing DIF system and frequency-hopping function, so the research is according to technologies of DIF and GSM signal baseband process. Firstly, the article introduces the research background of the digital repeater and current status. Secondly, interference factors to GSM radio network caused by digital repeater are analyzed as well as merit and demerit of several types of traditional repeater. Then this paper put forward a scheme to bring baseband processing module into digital repeater to achieve frequency-hopping synchronizd with base station. Thirdly, types and performances of frequency-hopping in GSM are described, analysis about performance improvements after bring frequency-hopping into digital repeater ,and the blue Print of frequency-hopping module is also given. Fourthly, it introduces the design philosophy and system framework, then the detail module division is also given. Fifthly, technologies involved in DDC/DUC, GMSK demodulation and channel decoder module are describes in detail, which are signal sampling theory, interpolation and decimation theory, Viterbi demodulate and Veterbi decode, etc. Then FPGA implementation about each module is presented. Finally, testing about GSM frequency-hopping digital repeater system are given according to the national test criteria.
GSM frequency-hopping digital repeater is noise free under the control of Slot synchronous clock, it means that it don't output noise when there is no useful signal. The system abstracts frequency-hopping information, switches the working frequency accurately to achieve the Frequency Hop Synchronization with base station. The Adverse Impact to GSM network which is caused by digital repeater can be avoid or reduced in under the RF frequency-hopping working condition.
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