Improved Wideband Precoding with Arbitrary Subcarrier Grouping in MIMO‐OFDM Systems

Precoding in the multiple‐input multiple‐output orthogonal frequency division multiplexing system is investigated. In conventional wideband precoding (WBP), only one precoder, obtained from the decomposition of the subcarrier independent channel matrix, is used for all subcarriers. With an investigation of the relationship between the subcarrier independent channel matrix and the temporal/frequency channels, an improved WBP scheme is proposed for practical scenarios in which a part of subcarriers are allocated to a user. The improved WBP scheme is a generalized scheme of which narrow‐band precoding and conventional WBP schemes are special modes. Simulation results demonstrate that the improved WBP scheme almost achieves the optimum performance of a single precoder and outperforms the conventional WBP scheme in terms of the bit error ratio and ergodic capacity with slight complexity increase. The largest advantage of the improved WBP scheme on signal‐to‐noise ratio in simulation results is over 2.1 dB.     

Improved Design Criterion for Space‐Frequency Trellis Codes over MIMO‐OFDM Systems

In this paper, we discuss the design problem and the robustness of space‐frequency trellis codes (SFTCs) for multiple input multiple output, orthogonal frequency division multiplexing (MIMO‐OFDM) systems. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with the regular correlation function of the number and time delay of the multipaths. By introducing the first‐order auto‐regressive model, we decompose the correlated fading channel into two independent components: a slow fading channel and a fast fading channel. Therefore, the design problem of SFTCs is converted into the joint design in both slow fading and fast fading channels. We present an improved design criterion for SFTCs. We also show that the SFTCs designed according to our criterion are robust against the multipath time delays. Simulation results are provided to confirm our theoretic analysis.     

MIMO-OFDM系统基于线性预编码的自适应加载方案

在MIMO-OFDM无线通信系统中,采用基于子载波线性预编码设计和变步长加载算法得到一种优化的自适应加载算法,在完全已知信道状态前提下,能在满足固定速率和给定误比特率约束下使系统总发射功率达到最小。仿真结果表明,该算法复杂度比Capello算法低,并且性能与之近似,都远远优于非自适应MIMIO系统的性能。     

Deepen spectrum notch and reduce PAPR in OFDM systems via combining subcarriers precoding with tone reservation

In orthogonal frequency division multiplexing (OFDM) systems,spectrum notch can be generated to mitigate interference to other narrow-band services by turning off corresponding subcarriers.However,the inter-carrier interference may limit considerably the produced notch depth.Another problem in OFDM is the high peak-to-average power ratio (PAPR).In this paper,a technique combining subcarriers precoding with tone reservation is proposed to deepen spectrum notch and simultaneously reduce peak-to-average power ratio.Simulation results show that this presented joint algorithm can produce satisfied results to solve these problems at the expense of a moderate loss in bit error rate (BER) performance.     

Precoder Distribution and Adaptive Codebook in Wideband Precoding

Based on wideband precoding (WBP) in the multiple‐input multiple‐output orthogonal frequency division multiplexing system, an adaptive nonuniform codebook is presented in this paper. The relationship between the precoder distribution and spatial correlation is analyzed at first. A closed‐form expression based on overlapped isosceles triangles is proposed as an approximation of the precoder distribution. Then, the adaptive codebook design is derived with the approximate distribution to minimize quantization errors. The capacity and bit error rate performance demonstrate that the adaptive codebook with WBP outperforms the conventional fixed uniform codebook.     

一种改善OFDM信号峰平比的新方法

提出了一种基于星座映射选择改善正交频分复用(OFDM)信号峰值平均功率比(PAPR)的方案,并针对这种映射方案提出了一种基于格栅搜索的简化算法。仿真表明,该方法不仅能够有效降低OFDM系统的峰均功率比,并具有较低的复杂度和较好的实用价值。     

一种采用压扩算法来降低OFDM信号PAPR的新方法

OFDM技术具有很高峰平功率比（PAPR），这是其实用化的一个瓶颈。针对这一问题，构造了一个新的压扩函数来降低OFDM信号的峰平功率比，通过计算机仿真表明，它不但可以大幅度降低OFDM信号的PAPR，而且，还可以通过适当的选择压扩系数得到一定的系统增益。     

大规模MIMO系统的预编码算法综述

相比于传统多输入多输出（MIMO）系统,大规模MIMO的天线数量大幅增加,使得系统的容量提升、误比特率下降,但也造成预编码矩阵维度升高,算法复杂度、系统成本及实现难度增大。将大规模MIMO系统主要采用的预编码技术分为线性和非线性两个部分,对两者进行了归纳和对比,并着重介绍了几种经过简化的线性预编码算法和几种比较典型的非线性预编码算法,指出因为非线性算法的复杂度很高,故未来大规模MIMO系统的预编码应当以线性算法为主。     

抑制OFDM信号峰均比的PTS算法分析与优化

部分传输序列（PTS）方法作为降低高峰均功率比（PAPR）信号的有效方法,因具有较高的计算复杂度而限制了其应用,也因此演化出许多的改进PTS算法。文中对包括IPTS、滑动窗搜索PTS、子块联合分割PTS、Had-amard-PTS、m序列-PTS和pso-PTS等在内的多种PTS演化算法作了研究与仿真,分析比较各种方法...     

基于分数阶Fourier变换减小OFDM系统PAPR的研究

介绍了基于分数阶Fourier变换的OFDM系统,给出了这种系统中经过变换后的信号的表达形式,探讨了该系统在不同的调制方式下（QAM调制和QPSK调制）使用Clipping算法降低系统PAPR的情况,并使用Matlab对不同阶数的CCDF进行了仿真。仿真结果表明,QAM调制下基于分数阶Fourier变换的Clipping算法性能不如基于傅立叶变换的Clipping算法好,而在QPSK调制方式下基于分数阶Fourier变换的OFDM系统PAPR性能比基于傅立叶变换的OFDM系统性能有了显著的提高。     

移动通信下行链路中的非线性预处理技术

首先介绍了经典的汤姆林森预编码技术,然后分别介绍了在其基础上发展起来的两种预处理技术——网格预编码和传输非线性迫零,并分析了其特点,指出非线性的预处理技术是性能和复杂度的折中,是很具潜力的一种下行链路技术。最后文中给出了一种新的预处理技术,同样具有较好的性能。     

一种简单PTS旋转因子优选方法降低OFDM数字广播系统的PAPR

OFDM技术已经广泛应用于数字广播系统，首先对OFDM技术中用PAPR（peak-to-average power ratio）的基本定义和PTS方法作简要的介绍，之后提出一种简单的PTS旋转因子优选方法来降低以朋，仿真表明，提出的方法能够有效地降低OFDM系统的PAPR，运算复杂度与基本PTS相当。     

多用户MIMO系统广播信道的连续块对角化预编码算法

针对块对角化(BD)算法无法满足各个用户的需要、串行优化(SO)算法排序复杂、容量较低的问题,提出了一种连续块对角化(SBD)算法.该算法按照各用户的信道条件、服务质量(QoS)需求给用户定义不同的优先级,并按优先级次序进行块对角化,后续用户在对高优先级用户及同优先级用户不干扰的条件下采用块对角化法抵消共信道干扰(CC...     

多输入多输出系统中的预编码技术研究

MIMO系统中的预编码技术,利用信道信息,使发射信号和空间信道相匹配,有效的对抗信道衰落,提高系统误码率和频谱利用效率,已成为无线通信技术的研究热点。本文首先对MIMO系统模型和容量进行了简单的介绍,然后分析了基于不同角度的预编码技术,其中主要针对基于信道预测的预编码技术的预测算法进行了研究。