移动环境下OFDM系统的ICI抑制技术研究

发布时间：2018-03-09 13:07

本文选题：移动通信　切入点：正交频分复用　出处：《重庆大学》2014年硕士论文　论文类型：学位论文

【摘要】：正交频分复用技术具有抗多径衰落能力强、频谱利用率高、信道均衡简单、便于硬件实现等优点，是后3G时代通信系统物理层的核心技术。移动环境中多普勒频展产生的子载波间干扰会破坏OFDM子载波的正交性，影响系统性能，因此载波间干扰抑制是OFDM移动通信中的关键技术之一。本文结合实际OFDM系统项目，，从ICI抑制算法和系统FPGA实现两个方面展开研究，主要工作如下： ①分析了移动环境下OFDM系统ICI的成因和对系统的影响，对单个多普勒频移和多普勒频展的ICI影响分别做了分析和仿真。仿真结果表明，多普勒频展是移动信道时变性的主要因素。 ②ICI抑制算法需要综合考虑抑制效果、频谱利用率和实现复杂度。ICI自消除算法通过改变系统参数设计来抑制ICI，分别验证了编码和时域加窗抑制ICI的效果和仿真对比了系统性能，分析发现ICI自消除算法存在频谱利用率低和性能的地板效应等缺点。基于频域均衡的信道估计算法通过导频辅助准则估计的信道响应矩阵均衡接收信号以抑制ICI，对传统的LS和LMMSE算法做了理论分析、仿真和性能评估，并对比仿真了不同信道环境下常用导频图案的性能。仿真结果表明传统的信道估计算法存在性能上的极限。 ③为克服传统一维信道估计算法在移动环境下存在性能极限的问题，设计并研究了基于二维频域信道估计的简化G矩阵算法，该算法考虑了邻近子载波的影响，通过计算相邻两个符号的时域冲击响应斜率来对时变信道做线性近似，性能优于传统的信道估计算法且实现复杂度较低。针对简化G矩阵算法直接采用IFFT计算时域冲击响应会引入误差这一问题，本文提出了一种时频变换的修正方法，仿真表明算法修正后其MSE和BER性能均有一定程度的提升。 ④完成了简化G矩阵算法的FPGA实现，解决了实际通信中ICI影响系统性能的问题，设计中为减少硬件资源消耗提出了逻辑和存储资源流水线分时复用等优化方案。系统测试结果表明本文设计的模块功能正确，资源消耗较少，能够有效抑制ICI。
[Abstract]:Orthogonal Frequency Division Multiplexing (OFDM) has the advantages of strong anti-multipath fading ability, high spectral efficiency, simple channel equalization and easy hardware implementation. It is the core technology of the physical layer of communication system in the post-3G era. The inter-carrier interference generated by Doppler frequency expansion in mobile environment will destroy the orthogonality of OFDM subcarriers and affect the performance of the system. Therefore, inter-carrier interference suppression is one of the key technologies in OFDM mobile communication. Combined with the actual OFDM system project, this paper studies the ICI suppression algorithm and the system FPGA implementation. The main work is as follows:. The main contents are as follows: 1. The causes of ICI and its influence on OFDM system in mobile environment are analyzed, and the ICI effects of single Doppler frequency shift and Doppler frequency spread are analyzed and simulated respectively. The simulation results show that, Doppler frequency spread is the main factor of time variation of mobile channel. 2ICI suppression algorithm needs to consider the suppression effect synthetically. Spectrum efficiency and implementation complexity. ICI self-cancellation algorithm suppresses ICI by changing the system parameter design. The results of coding and time-domain windowed suppression of ICI are verified, and the system performance is compared by simulation. It is found that the frequency domain equalization based channel estimation algorithm equalizes the received signals by the channel response matrix estimation based on the pilot auxiliary criterion to suppress the frequency domain equalization of the received signals. The traditional LS and LMMSE algorithms are analyzed theoretically. The performance of common pilot patterns in different channel environments is compared and the simulation results show that the traditional channel estimation algorithms have performance limits. In order to overcome the performance limit problem of traditional one-dimensional channel estimation algorithm in mobile environment, a simplified G-matrix algorithm based on two-dimensional frequency-domain channel estimation is designed and studied. The influence of adjacent subcarriers is considered in this algorithm. Linear approximation of time-varying channels is made by calculating the time-domain impulse response slope of two adjacent symbols. The performance of channel estimation algorithm is better than that of traditional channel estimation algorithm and the complexity of implementation is low. To solve the problem that the error will be introduced to calculate the time-domain impulse response of the simplified G-matrix algorithm directly by using IFFT, a modified time-frequency transform method is proposed in this paper. The simulation results show that the MSE and BER performance of the modified algorithm are improved to some extent. (4) the FPGA implementation of simplified G-matrix algorithm is completed, and the problem that ICI affects the system performance in actual communication is solved. In order to reduce the consumption of hardware resources, an optimization scheme such as logic and pipeline time-sharing reuse of storage resources is put forward in the design. The system test results show that the module designed in this paper has correct function and less resource consumption, which can effectively suppress ICII.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.53

【相似文献】