LTE下行链路立方度量抑制技术研究

发布时间：2018-03-13 17:15

本文选题：LTE　切入点：OFDM　出处：《电子科技大学》2014年硕士论文　论文类型：学位论文

【摘要】：作为被ITU所接受的第四代通信标准之一,LTE采用了OFDM和高阶QAM调制等技术。与第三代移动通信标准相比,LTE可以提供更高的传输带宽和更高的频谱效率。但是,采用OFDM和高阶QAM调制的主要缺点之一是LTE信号的包络波动性高。高包络波动性对系统的影响主要包括:(1)引起射频功放效率下降;(2)输入射频功放的信号会产生严重的非线性失真,造成信号带内失真以及频谱扩展;(3)要求A/D具有较高的动态范围,造成A/D转换效率下降。为了避免这些问题,需要对LTE信号进行输入功率回退。峰均功率比是一种广泛应用的预测功率回退量的度量。但是,最近的研究表明,峰均功率比不能准确预测功率回退量,而立方度量是一种更加有效的衡量信号波动性的度量。因此,通过抑制立方度量来降低信号的功率回退量,能够提升功放的效率。通过研究立方度量的度量方式,提出了两种应用于LTE下行链路的抑制立方度量的方法。第一,提出了一种下降式限幅滤波算法,该法是通过对传统限幅滤波算法改进得到的。结合立方度量的表达式,理论推导发现:在限幅阶段,如果对高于门限电平的信号限幅后,再进一步乘以下降因子,可以降低迭代次数,提高收敛速度。仿真结果表明:所提的算法可以将迭代次数由原来的8次降低到了1次。第二,提出了一种凸优化技术抑制立方度量的方法。LTE信号的子载波可以分成数据子载波、带内空闲子载波和带外空闲子载波部分。在设计算法抑制立方度量的时候,信号的失真程度需要满足EVM、ACLR的约束。利用最优化理论,建立了立方度量和EVM、ACLR之间的最优化模型。然后,理论分析并完成了该模型的凸化变换。最后,详细设计了定制内点法数值求解该模型的实现流程。仿真表明,该方法具有收敛性好、时间复杂度较低的优点。本文提出的两种算法并不需要改变现有的通信协议,具有方便、实用的特点。
[Abstract]:As one of the 4th generation communication standards accepted by ITU, OFDM and high order QAM modulation technology are adopted. Compared with the third generation mobile communication standard, LTE can provide higher transmission bandwidth and higher spectrum efficiency. One of the main disadvantages of using OFDM and high order QAM modulation is the high envelope volatility of LTE signal. The influence of high envelope volatility on the system mainly includes: 1) causing a decrease in RF power amplifier efficiency and 2) serious nonlinear distortion of the input RF power amplifier signal. In order to avoid these problems, it is required that A / D has a high dynamic range, resulting in a decrease in the conversion efficiency of A / D. The peak-to-average power ratio (PAPR) is a widely used measure of predictive power fallback. However, recent studies have shown that PAPR can not accurately predict the power fallback. The cubic metric is a more effective measure of signal volatility. Therefore, by suppressing the cubic metric to reduce the power fallback of the signal, the efficiency of the power amplifier can be improved. In this paper, two methods of suppressing cubic metric for LTE downlink are proposed. First, a descending amplitude limiting filtering algorithm is proposed, which is obtained by improving the traditional amplitude limiting filtering algorithm and combining the expression of cubic metric. The theoretical derivation shows that in the limiting stage, if the signal above the threshold level is limited, the number of iterations can be reduced by multiplying it further by the descent factor. The simulation results show that the proposed algorithm can reduce the number of iterations from 8 to 1. Second, In this paper, a convex optimization technique to suppress cubic metric is proposed. The subcarriers of LTE signal can be divided into data subcarriers, in-band free subcarriers and out-of-band free subcarriers. The distortion degree of the signal needs to satisfy the constraints of EVMN ACLR. By using the optimization theory, the optimization model between cubic metric and EVMN ACLR is established. Then, the convexity transformation of the model is analyzed and completed theoretically. The simulation results show that this method has the advantages of good convergence and low time complexity. The two algorithms presented in this paper do not need to change the existing communication protocols and are convenient. A practical feature.
【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】：TN929.5

【共引文献】