CR-OFDM系统中最优导频序列设计的研究

发布时间：2018-05-23 23:11

本文选题：认知无线电 + 正交频分复用　；参考：《东北大学》2014年硕士论文

【摘要】：随着无线通信技术的飞速发展,频谱资源短缺、频谱利用率低等缺陷越来越凸显,Cognitive Radio OFDM(CR-OFDM)作为一种适用于离散频谱环境的高效的频谱调制技术,不仅具备传统OFDM的抗多径衰落和高速传输的优势,在频谱聚合、功率控制以及频谱分配方面也具有很强的灵活性,因此,成为未来移动通信系统中最具竞争力的一个关键的传输技术。由于CR-OFDM系统可用频谱的非连续和动态变化特性,随之产生的关键技术和科学课题已成为相关领域的研究热点。其中,导频序列设计因其可以保证无线信道估计的准确性以及通信系统的高性能品质而成为研究的热点。本文详细介绍了CR-OFDM系统导频序列设计的基础理论,详细地分析了最优导频序列设计的经典算法,针对CR-OFDM系统下授权用户和认知用户之间存在干扰的情况,提出了基于信道估计的最优导频序列设计算法,包括对导频位置、导频功率以及位置与功率的联合优化设计,在保证系统性能的前提下,可有效提高信道估计精度。考虑CR-OFDM系统子载波非连续且动态变化的特殊性质,传统等功率、等间隔分布的导频序列存在计算复杂度高、频谱利用率低、处理时延大和干扰影响明显等缺点。针对上述问题,首先,提出了基于交叉熵算法的导频位置的优化设计方法,该方法以最小化系统均方误差为准则,采用交叉熵优化算法在所有可用子载波中求解目标函数的最优解,有效解决了穷举搜索算法计算复杂度高等问题；其次,对导频功率的设计,以最大化系统容量为准则,在认知用户与授权用户之间的干扰温度限制下,对优化问题进行建模,采用差分进化搜索算法进行目标函数的求解,提高了频谱利用率,解决了由于功率分配不合理造成的资源浪费；最后,考虑等功率分配导频会使信道估计不能有效地进行,提出了一种对导频功率和位置联合优化的设计算法,该算法以最小化系统均方误差为准则,对导频功率进行归一化操作,并将交叉熵优化算法应用于对优化问题的求解中。与传统算法相比,所提算法提高了数据传输利用率,保证了信道的估计精度,降低了系统均方误差(Mean Square Error, MSE)和误码率(Bit Error Rate, BER),从而从整体上提高了系统性能。
[Abstract]:With the rapid development of wireless communication technology, the shortage of spectrum resources and the low spectral efficiency are more and more obvious Cognitive Radio OFDM CR-OFDM) as an efficient spectrum modulation technology suitable for discrete spectrum environment. It not only has the advantages of anti-multipath fading and high-speed transmission of traditional OFDM, but also has strong flexibility in spectrum polymerization, power control and spectrum allocation. To become the most competitive mobile communication system in the future a key transmission technology. Due to the discontinuous and dynamic characteristics of available spectrum of CR-OFDM system, the key technologies and scientific topics have become the focus of research in related fields. Among them, pilot sequence design has become a hot research area because it can guarantee the accuracy of wireless channel estimation and the high performance of communication system. In this paper, the basic theory of pilot sequence design in CR-OFDM system is introduced in detail, and the classical algorithm of optimal pilot sequence design is analyzed in detail, aiming at the interference between authorized and cognitive users in CR-OFDM system. An optimal pilot sequence design algorithm based on channel estimation is proposed, including the joint optimization of pilot position, pilot power and position and power, which can effectively improve the accuracy of channel estimation on the premise of ensuring the system performance. Considering the special property of discontinuous and dynamic variation of subcarriers in CR-OFDM systems, the traditional equal-power and equal-interval pilot sequences have the disadvantages of high computational complexity, low spectral efficiency, large processing delay and obvious interference. In order to solve the above problems, a pilot position optimization method based on cross-entropy algorithm is proposed, which is based on minimizing the mean square error (MSE) of the system. The cross-entropy optimization algorithm is used to solve the optimal solution of the objective function in all available subcarriers, which effectively solves the problem of high computational complexity of exhaustive search algorithm. Secondly, the design of pilot power is based on maximization of system capacity. Under the restriction of interference temperature between cognitive user and authorized user, the optimization problem is modeled, and the objective function is solved by differential evolution search algorithm, which improves the spectrum efficiency. The waste of resources caused by unreasonable power allocation is solved. Finally, considering the pilot of equal power allocation, channel estimation can not be carried out effectively, and a joint design algorithm of pilot power and position is proposed. Based on the criterion of minimizing the mean square error of the system, the pilot power is normalized and the cross-entropy optimization algorithm is applied to solve the optimization problem. Compared with the traditional algorithm, the proposed algorithm improves the data transmission efficiency, ensures the channel estimation accuracy, reduces the mean square error (Mean Square Error, MSE) and bit Error rate (bit Error rate), and thus improves the performance of the system as a whole.
【学位授予单位】：东北大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

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