【作者】 孙鹏；

【导师】 吴玉成；

【作者基本信息】 重庆大学 ， 通信与信息系统， 2011， 硕士

【摘要】 无线通信信号在传输中的多径效应以及无线信道的带宽有限性和非理想性,都会造成码间干扰(ISI),ISI会造成接收端误码的增加从而降低通信系统的传输效率甚至使通信系统无法正常工作。为了克服ISI通常在接收端使用均衡器来校正或补偿系统特性,以减小ISI的影响。使用了训练序列的自适应均衡技术结构简单、性能可靠、在现有通信系统中普遍应用,另外,不需要训练序列的盲自适应均衡技术近年来也得到了广泛的研究和应用。论文在研究了无线通信信道特性的基础上,研究了多种均衡器结构以及均衡算法,提出了一种盲自适应均衡的改进方案,并根据实际需要设计实现了一种T/2分数间隔的判决反馈均衡器。论文的研究内容包括:1)从电磁波的传播特点出发,研究无线通信信道的特性,对无线信道中的选择性衰落、平坦衰落、多普勒扩展以及时延扩展进行了研究和仿真分析,通过数学模型重点研究了码间干扰的形成原理。2)对均衡器结构原理进行了详细阐述并分析了各自的优缺点,对基本的自适应均衡算法进行了研究和分析,着重研究了盲自适应均衡的原理和对常用的盲均衡算法进行了研究,分析了算法存在的优点和不足。3)针对修正恒模算法(MCMA)收敛速度慢、判决反馈结构均衡器对采样时间敏感的问题,论文提出了一种基于分数间隔判决反馈(FS-DFE)结构的可变步长MCMA的改进均衡方案,设计方案利用了MCMA在恢复星座图的同时纠正载波的频偏和相偏的优点,利用了可变步长控制在均衡的捕获阶段使用较大的步长以便快速收敛而在进入跟踪阶段使用较小的步长以获得较低的均方误差的特点,利用了FS-DFE中分数间隔结构对采样时间不敏感和判决反馈结构抵抗多径的良好性能,实现了算法的快速收敛,获得较小的稳态误差。通过仿真结果,设计方案在调制方式为16QAM、信号通过具有高斯白噪声和多普勒频移的多径信道的情况下,相对于固定步长的MCMA在收敛速度和稳态误差上均有提高。4)根据实际需要设计了一种T/2分数间隔的判决反馈均衡器,通过理论分析和实验仿真推导和验证了设计方案的正确性,并详细阐述了均衡器各部件的设计,在FPGA上加以实现,在实际通信环境的仿真模型下进行了时序仿真并能够在FPGA上正常运行。更多还原

【Abstract】 The multipath effect of the wireless communication signal in transmission as well as the wireless channel’s band width finiteness and the non-ideal, can create the intersymbol interference (ISI). The ISI will cause the increase of receiver error and reducing transmission efficiency of the communication system even makes communication system doesn’t work. In order to overcome the ISI, the equalizer is used usually at the receiving end to correct or compensate system characteristics, to reduce the influence of the ISI. The adaptive equalization technology using the training sequences is simple in structure, reliable in performance, and used widely in existing communication systems. In addition, the blind adaptive equalization technique that needs no training sequence in recent years has also been extensively researched and applied.Based on the study of the wireless communication channel characteristic, this thesis has studied many kinds of equalizer structures as well as the equalization algorithms, proposed an improved program of the blind adaptive equalization, and has realized one kind of T/2 fractional interval decision feedback equalizer according to the actual need design. This thesis research content includes:1) The characteristics of the wireless communication channel and the selective fading, flat fading, Doppler spread and delay spread in the wireless channel are studied and simulation analyzed in terms of the feature of electromagnetic wave propagation. The forming principle of the intersymbol interference is studied through the mathematical model.2) The principle of the equalizer structures is fully described and their merits and shortcomings are analyzed. And the basic adaptive equalization algorithm has been studied and analyzed. The principle of the blind adaptive equalization is centrally studied. And the usual blind equalization algorithm is studied and analyzed the algorithm’s merits and shortcomings.3) With respect to the problem of the slow convergence speed of MCMA and the sensitivity to the sampling time of the decision feedback equalizer, an improved equalization scheme--the variable step size MCMA, which is based on the FS-DFE structure--is proposed. The scheme exploit the merit of the MCMA in correcting the carrier’s frequency and phase deviation while restoring the constellation diagram, the character of the variable step control of using the longer step size in equalization capturing period in order to converge quickly and using the smaller step size in tracking period in order to gain lower deviation, the low sensitivity to the sampling time of the fractional interval structure in FS-DFE, and the good nature of countering multipath in decision feedback structure, to realize the quick convergence of algorithm and decrease steady state error. By simulating the result, the scheme, under the circumstance of 16QAM modulation method, with the signal passing through the multipath channel having Gaussian White noise and Doppler shifting, serves good in raising convergence speed and decreasing steady state error in contrast with the fixed-step MCMA.4) According to the actual need, a T/2 fractional interval decision feedback equalizer is designed. Through theoretical analysis and experimental simulating deduction, the validity of the scheme is proved. The design of all parts of the equalizer is fully presented. And the scheme is implemented in FPGA. By stimulating actual communication circumstances, the timing stimulation has been carried out, and it can operate normally in FPGA.更多还原