NC-OFDM系统关键技术研究

发布时间：2018-04-06 03:33

本文选题：认知无线电　切入点：非连续OFDM　出处：《电子科技大学》2014年硕士论文

【摘要】：认知无线电的提出为解决静态频谱分配而导致的频谱利用效率低下的问题提供了一种有力的解决途径。NC-OFDM(Non-Contigous Orthogonal Frqeucny Divison Mutilplex)作为一种基于OFDM的底层传输技术是认知无线电环境下通信系统中底层传输技术方案的有效解决方案。本文工作的重点是NC-OFDM系统中关键技术的研究,主要分为信道估计算法、信噪比估计算法、自适应调制编码算法的研究。本文结构上共分为三个部分。第一、二章为本文的第一部分,其中首先介绍了本文研究内容的背景和意义以及NC-OFDM系统的研究发展现状,然后在OFDM系统的原理和系统模型基础上给出了NC-OFDM系统的模型,并对其中需要研究的关键技术进行了总结。第二部分为第三、四、五章,为本文的主要内容。第三章对NC-OFDM系统中的信道估计算法进行研究,主要研究了导频图案的设计、估计算法、内插算法。导频图案设计中根据传统OFDM系统中常用的导频图案进行了理论和性能上的分析,然后在NC-OFDM系统中对导频图案加以修正;估计算法分别针对LS估计算法研究了LS算法的降噪改进算法和基于MMSE算法的降低复杂度算法,经过改进后的算法性能要优于原算法;内插算法部分主要对比了常用的几种内插方法和IDFT内插方法的性能,仿真分析表明IDFT内插方法有较大的优势。第四章研究信噪比估计算法。首先对比分析了OFDM系统中AWGN信道下的信噪比估计算法,然后在瑞利衰落信道中研究了信噪比估计的算法,仿真分析了NC-OFDM系统在不同信道条件下各种信噪比估计算法的性能。仿真分析表明,在AWGN信道中MMSE估计和基于M2M4的估计放方法都具有较好的性能;在较强的频率选择性信道中,基于Ren估计算法比基于Boumard算法和时域估计算法有更好的性能。第五章主要研究了NC-OFDM系统自适应调制编码算法。本章首先得到了各种固定调制编码方式在衰落信道下的误码率性能,在此基础上对基于子带的固定门限自适应调制编码算法进行研究,仿真结果表明更多的子带划分使系统的误码率性能更接近系统目标误码率从而具有更高的系统容量,自适应门限算法中选取的门限随着信道的变化选择了更加合适的门限值,从而使系统有更好的性能。针对前面两种算法都需要进行信道估计和信噪比的估计从而导致复杂度较高,本文提出了一种基于双参数联合调整的自适应调制编码算法。该算法使用总PER和段PER两个参数来控制调制编码方式的切换,仿真结果表明在满足误码率要求时该算法能够逼近分子带自适应门限算法的性能。本文的第三部分是全文的总结,对本文的研究工作了做了概括性的总结,并指出了论文中工作不够完善的地方以及下一步研究的方向。
[Abstract]:The introduction of cognitive radio provides a powerful way to solve the problem of low spectral efficiency caused by static spectrum allocation. NC-OFDMN Non-Contigous Orthogonal Frqeucny Divison Mutilplex. as a kind of underlying transmission technology based on OFDM, cognitive radio ringThe effective solution of the underlying transmission technology scheme in the communication system.This paper focuses on the research of key technologies in NC-OFDM system, including channel estimation algorithm, SNR estimation algorithm and adaptive modulation coding algorithm.The structure of this paper is divided into three parts.The first and second chapters are the first part of this paper, which firstly introduces the background and significance of this research and the development of NC-OFDM system, then gives the model of NC-OFDM system based on the principle and system model of OFDM system.The key technologies that need to be studied are summarized.The second part is the third, fourth and fifth chapters, which is the main content of this paper.In the third chapter, the channel estimation algorithm in NC-OFDM system is studied, including the design of pilot pattern, estimation algorithm and interpolation algorithm.The pilot pattern design is analyzed in theory and performance according to the common pilot pattern in the traditional OFDM system, and then the pilot pattern is corrected in the NC-OFDM system.The improved algorithm of LS algorithm and the algorithm of reducing complexity based on MMSE algorithm are studied respectively. The performance of the improved algorithm is better than that of the original algorithm.In the part of interpolation algorithm, the performance of several commonly used interpolation methods and IDFT interpolation methods are compared. The simulation results show that IDFT interpolation method has great advantages.In chapter 4, the SNR estimation algorithm is studied.First, the SNR estimation algorithms in AWGN channel in OFDM system are compared and analyzed, then the SNR estimation algorithms in Rayleigh fading channel are studied. The performance of various SNR estimation algorithms in NC-OFDM system under different channel conditions is simulated and analyzed.Simulation results show that both MMSE estimation and M2M4 based estimation have better performance in AWGN channel, and Ren estimation algorithm has better performance than Boumard algorithm and time domain estimation algorithm in strong frequency selective channel.In chapter 5, the adaptive modulation coding algorithm of NC-OFDM system is studied.In this chapter, the BER performance of various fixed modulation and coding schemes in fading channel is obtained, and the adaptive modulation coding algorithm based on subband is studied.The simulation results show that more sub-band partitioning makes the BER performance of the system more close to the BER of the system target and thus has a higher system capacity. The threshold selected in the adaptive threshold algorithm is more appropriate with the change of the channel.So that the system has better performance.In view of the high complexity caused by the need of channel estimation and SNR estimation in the first two algorithms, an adaptive modulation coding algorithm based on the joint adjustment of two parameters is proposed in this paper.The algorithm uses two parameters, total PER and segment PER, to control the modulation coding switching. The simulation results show that the algorithm can approach the performance of the molecular band adaptive threshold algorithm when the BER requirement is satisfied.The third part of this paper is a summary of the full text, the research work of this paper has made a general summary, and pointed out that the work in the paper is not perfect and the next research direction.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN925

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