【作者】 张小艳；

【导师】 王彬；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2009， 硕士

【摘要】 移动通信频谱资源的有限性,决定了未来的移动通信,必须采用频谱利用率高的调制技术和信道抗衰落技术,来提高系统的性能,从而支持高速率数据和多媒体业务的传输。自适应传输技术是新一代移动通信和智能传输的核心技术之一,其中的自适应调制是根据信道的实时状态以及业务的不同特性动态调整传输参数,从而可以充分挖掘系统的传输潜力,提高频谱利用率,以获得最大的传输容量和最高的可靠性。本文首先概述了数字集群通信系统,以及TETRA标准特性,然后对自适应调制解调技术的起源和发展进行了归纳总结,并对国内外研究现状及前景进行了阐述。介绍了移动通信系统对调制技术的要求,分析了现代数字调制技术的特点,详细分析了QAM调制解调的原理、主要参数和调制信号星座图的分布结构。自适应调制解调系统依据信噪比实时选择调制方式,因此,信号的信噪比估计是自适应调制解调系统的关键技术之一。本文详细分析了最大似然(ML)估计算法和最大后验概率(MAP)估计算法的原理,并给出了信噪比估计的克拉米罗下限。针对自适应MQAM调制解调技术,详细分析了自适应调制解调系统的基本原理、判决准则及性能参数。最后,在MATALB平台下进行了仿真,并分析了QAM调制在高斯白噪声信道中的误码率,以及信噪比估计误差对自适应调制解调系统的影响。根据自适应调制解调技术的特点,进行了自适应变速率传输仿真系统的方案设计,包括:门限值的选择算法、信噪比区间的设定方法、系统功能的实现等,并对所提出的方案进行了仿真,给出仿真结果,并做了必要的分析。更多还原

【Abstract】 Future mobile communications have to support the transmission of high rate data and multimedia applications in the radio spectrum, which is already extremely scarce.As one of the key techniques of new generation mobile communication systems and broadband wireless communications systems, adaptive transmission technique can exploit potential channel transmission ability sufficiently so that it enables the systems to reach the maximum transmission capacity and reliability by dynamically adjusting transmission parameters according to channel estimation and traffic QoS requirement.Firstly, the digital trunking communication system and the characteristic of TETRA standard features are briefly introduced in this dissertation, and then summarize the origin and development of adaptive modulation technology, and describe the international actuality and tendency of adaptive modulation. Introduced the demand of modulation technologies for mobile communication system, and then analyze the modern digital modulation characteristics, the principle of QAM modulation and demodulation, the main parameters and the modulation signal constellation diagram of the distribution structure. Adaptive modulation and demodulation system choose the mode of modulation based on the signal-to-noise ratio of the signals.So,the estimation of signal-to-noise ratio is one of its key technologies.In this paper, analyze the principle of maximum likelihood (ML) estimation algorithm and maximum a posteriori probability (MAP) estimation algorithm, and give the lower limit of CRLB of the signal-to-noise ratio. For adaptive modulation and demodulation, analyze the basic principles, decision criteria and performance parameters.At last, simulate using MATLAB software, analyze the BER of QAM modulation based on AWGN channel, and the influence of SNR estimation error on adaptive modulation and demodulation system. Design the adaptive variable rate transmission simulation system based on the characteristics of adaptive modulation and demodulation techniques, including: the choice of threshold algorithms, methods of signal-to-noise ratio settings, the realization of system function, and the simulation results and analysis are given.更多还原