基于列正交变换实现串行干扰消除的MIMO检测算法

针对用于多输入多输出（MIMO）通信系统检测的按序QR分解（SQRD）算法在多径瑞利慢衰落信道中检测误码率较高的不足,提出了一种基于列正交（CO）变换的串行干扰消除（SIC）算法——COSIC。该算法对信道矩阵按列正交变换,避免了求上三角矩阵的运算,并且在判决信号过程中,将先判决出的信号通过信道后的输出向量作为干扰进行消除,在略微增加系统时间复杂度的基础上,使系统检测性能得到了明显改善。在多散射物的无线通信环境下进行的仿真实验证实,与传统的SQRD算法相比,所提算法误码率显著下降．系统检测性能明显改善。     

自由空间光通信系统天线阵接收的误码率分析

为了提高通信链路接收端的接收性能,降低系统的误码率,提出了分布式天线阵接收技术.采用开关键控(OOK)强度调制直接检测(ID/DD),研究了对数大气湍流信道下自由空间光通信的性能.在接收端我们采用最大比合并(OC)和等增益合并(EGC)技术,推导出分布式天线阵接收的平均误码率表达式.仿真结果表明,等增益合并下,误码率的性能受天线阵子天线个数的影响比较大;选取最佳的分布式天线阵子天线的个数和减小子天线的间距可以降低信道误码率,提高空间光通信的接收性能.     

FSO中分层空时编码的串行干扰消除算法

自由空间光通信(FSO)中的分层空时编码(LST),能极大地提高系统的传榆速率,但误码率较大,严重影响光通信系统的可靠性.在分析了光强起伏的特性之后,建立了湍流信道中多输入多输出(MIMO)信道的模型;提出了采用串行干扰消除算法来完成FSO中分层空时编码译码的方法,并和线性译码算法的性能进行了对比.最后,利用仿真实验进一步验证了该方法的可行性.结果表明:在FSO中,采用串行干扰消除译码算法时的误码性能明显优于线性译码算法的误码性能.     

基于OSSK调制的MIMO星地激光通信上行链路系统

目的:研究光学空间移位键控(OSSK)调制的多输入多输出(MIMO)星地激光通信上行链路系统。方法:利用Malaga(M)分布表征近地面湍流光强闪烁、光束漂移、到达角起伏的联合影响。推导OSSK调制的MIMO星地激光通信上行链路误码率的闭合表达式。仿真分析信噪比、天顶角对系统误码率的影响,并且与差分相移键控、最小位移键控等传统调制进行对比,最后采用蒙特卡洛方法对仿真结果进行验证。结果:OSSK调制相较于传统调制可以在同等条件下降低约2个数量级误码率,增加接收天线可以进一步提高系统性能。为满足最低通信需求,OSSK调制可以获得更大的最大天顶角。结论:OSSK调制可以有效地优化通信性能,降低星地激光通信的成本,从而为星地激光通信系统的研究提供了有效方案。     

一种兼顾照明与通信的环形光源布局模型

传统基于阵列的光源布局方式在室内难免存在光照度及系统误码率不均匀现象,为提高系统照度均匀性及通信可靠性,需合理对光源进行优化布局。本文以4 m×4 m×3 m的房间为模型,设计了单LED阵列+灯带的环形光源布局模型。模型中间采用6×6 LED阵列,阵列内部灯珠之间的距离为0.3 m;四周采用环形灯带形式,灯珠个数为316个,灯珠之间的距离为0.05 m。仿真结果表明,该模式下系统光照度均值为437.08 lx,光照度均匀性为93.9%,同时,系统误码率均值为2.8716×10-7。因此,本文所设计的环形光源布局模型兼顾了室内光照度分布的均匀性和通信的可靠性,可同时满足室内照明和通信,为室内可见光通信光源布局提供了一种优化方法。     

基于距离加权的室内可见光定位算法

针对室内可见光定位采用的三边定位算法普适性不高、定位区域较小的问题,提出了一种四LED加权定位算法。该算法结合室内照明LED布局实际情况,从可见光传输距离短定位精度高的特点出发,将传输距离信息作为加权因子引入定位算法中,提高了定位精度及扩大了定位区域。仿真实验结果表明：提出的定位算法在5 m×5 m×3 m的空间区域中可以获得约为18 cm的平均定位误差性能,有效地提高了室内定位精度和系统应用的普适性及鲁棒性。     

一种稳健的水声MIMO通信系统调制技术

作为一种极具潜力的高速水下通信技术,基于VBLAST（贝尔实验室垂直分层空时）编码调制的水声MIMO通信技术,借助于空间复用,可在不增加系统带宽的条件下成倍提高数据传输速率。但由于同时受到同频干扰及多径干扰的影响,当信道多径扩展严重时,基于VBLAST调制的水声MIMO通信系统性能下降严重。为此,提出一种新的调制技术,该技术通过将各层信号调制到彼此正交的子载波上,可完全消除同频干扰,从而有效改善系统误码性能,显著提高系统的稳健性。仿真结果证明了所提调制技术的良好性能。     

5G通信中基于混合波束成型的多用户MIMO调度算法研究

大规模多输入多输出(MIMO)技术是5G通信的核心技术之一,信号多入多出可以有效提高通信传输中的频谱效率与用户的通信质量。本文从用户下行信道与通信向量函数2个维度阐述了信道有效传输原理,并基于此设计了一种毫米波MIMO混合波束成型模型。文章分析了毫米波混合波束成型模型设计原理、实现步骤及算法复杂度情况,并利用混合波束成型模型设计了多用户MIMO调度的具体实现方法;基于模型确定出双向交替优化MIMO系统的发射端和接收端子阵列的天线加权矢量,给出数字模拟混合波束成型的算法方案,最终实现多用户MIMO的均衡调度。仿真结果表明,所提出的调度算法具有收敛速度快、计算复杂度低、基带传输效率高等优势。     

基于VBLAST的水声MIMO高速通信技术研究

为实现高速水下通信,提出了一种基于VBLAST（贝尔实验室垂直分层空时）编码的水声MIMO（多输入多输出）通信技术。该技术通过在发射端和接收端同时采用多个阵元进行多发多收,借助空间复用,可有效解决水下通信系统带宽资源缺乏的难题,使系统在不增加带宽的条件下成倍提高数据传输速率。在水声MIMO通信系统的接收端,提出采用带有二阶数字锁相环、基于自适应空时判决反馈均衡的相干解调技术。该技术可有效克服水声MIMO信道中的多径干扰及同频干扰,且能自适应跟踪信道变化。仿真及湖试结果证明了所提水声MIMO高速通信技术的良好性能。     

基于OFDM技术电力通信系统的仿真研究

<正>交频分复用(OFDM)技术是常用的电力通信调制技术。本文在深入研究OFDM基本原理和电力线信道特性的基础上,建立电力通信系统模型,对该模型采用4QAM、16QAM、BPSK三种调制方式以及DTF、LS、MMSE三种信道估计算法进行了MATLAB性能仿真,得出结论在一定条件下运用QAM调制方式及LS算法更能体现了OFDM技术应用于电力线通信的优越性。同时,也为我们在不同环境下为提高通信系统整体性能,信道估计算法的选择提供了有力依据。     

Performance of zero-forcing detectors over MIMO flat-correlated Ricean fading channels

The bit error rate (BER) performance of the zero-forcing (ZF) receiver over transmit-correlated flat Ricean fading channels is investigated. In particular, for a multiple-input multiple-output (MIMO) channel with M transmit and N receive antennas, an approximation for the average BER of each substream is derived. Then the system performance in receive-correlated flat Ricean fading channels is addressed. In this case, it is shown that the performance, when N ? M, is the same as that of transmit-correlated flat Ricean fading channels. A closed-form expression for the optimum transmit correlation coefficient, which achieves the maximum capacity (i.e. uncorrelated case), is also derived. As a result, a significant capacity gain is achieved by exploiting the knowledge of the Ricean channel. Extensive simulations are presented to validate and demonstrate the performance gain with different system parameters.     

Spot diffusing angle diversity MC-CDMA optical wireless system

Multi-carrier code division multiple access (MC-CDMA) combines some of the desirable features of orthogonal frequency-division multiplexing (OFDM) and CDMA in that it offers multi-user capabilities at a reduced channel rate. The authors report the analysis of a MC-CDMA system over the bandlimited optical wireless (OW) channel. Furthermore, the authors evaluate the performance when a line strip multibeam system (LSMS) is used in conjunction with an angle diversity receiver in the OW MC-CDMA system. The results indicate that at a bit error rate of 10^-4 a 7 and 10 dB signal-to-noise ratio (SNR) improvements are obtained through the use of MC-CDMA in a 4-user system when compared to a single-user OW on?off keying system and a 4-user OW CDMA system, respectively. This improvement is obtained by enabling multi-user communication. The performance degrades gradually with increase in the number of users. The use of LSMS and angle diversity offers a more uniform SNR over a given indoor geometry compared to a conventional diffuse OW system (CDS). Results are reported for an angle diversity LSMS MC-CDMA system and are compared to the CDS MC-CDMA system.     

Simple correlated channel model for ultrawideband multiple-input multiple-output systems

A simple correlated channel model for ultrawideband (UWB) multiple-antenna systems is proposed. The authors show that a single numerical value of the spatial correlation coefficient is sufficient to accurately model the performance of UWB spatial multiplexing systems in an indoor environment. The appropriate value of the correlation coefficient is selected by ensuring a close match between the bit error rate results achieved on the proposed correlated channel and those on the measured indoor channel. The authors also experimentally confirm that the performance substantially degrades in the presence of high values of spatial correlation for a range of spatial multiplexing receivers, and quantify the relationship between this degradation and the value of the spatial correlation coefficient. Thus, a route for the development of the existing standards for single- antenna UWB channels to the multiple-antenna regime is provided here.     

Joint Channel and Multi-User Detection Empowered with Machine Learning

The numbers of multimedia applications and their users increase with each passing day. Different multi-carrier systems have been developed along with varying techniques of space-time coding to address the demand of the future generation of network systems. In this article, a fuzzy logic empowered adaptive backpropagation neural network (FLeABPNN) algorithm is proposed for joint channel and multi-user detection (CMD). FLeABPNN has two stages. The first stage estimates the channel parameters, and the second performs multi-user detection. The proposed approach capitalizes on a neuro-fuzzy hybrid system that combines the competencies of both fuzzy logic and neural networks. This study analyzes the results of using FLeABPNN based on a multiple-input and multiple-output (MIMO) receiver with conventional partial opposite mutant particle swarm optimization (POMPSO), total-OMPSO (TOMPSO), fuzzy logic empowered POMPSO (FL-POMPSO), and FL-TOMPSO-based MIMO receivers. The FLeABPNN-based receiver renders better results than other techniques in terms of minimum mean square error, minimum mean channel error, and bit error rate.     

一种新的水声MIMO空时频编码技术

基于贝尔实验室垂直分层空时编码（Vertical Bell Labs Layered Space-Time,VBLAST）的水声多输入多输出（Multiple-Input Multiple-Output,MIMO）通信技术,通过充分开发空间资源,可在不增加系统带宽的条件下成倍提高数据传输速率,是一种极具潜力的高速水下通信技术。但由于其接收信号中同时含有同频干扰及多径干扰,当信道多径扩展严重时,其性能下降严重。为此,提出一种新的空时频编码技术,该技术通过将各层信号调制到彼此正交的子载波上,不但可在接收端完全消除同频干扰,同时还能获得频率分集增益,从而使水声MIMO通信系统的性能获得极大改善。仿真及湖试结果证明了其有效性。     

Chaos-based multi-user time division multiplexing communication system

A chaos-based multi-user time division multiplexing (TDM) communication system has been proposed and its benchmark performance compared to that of the chaos-based direct sequence code division multiple access (DS-CDMA) system in the noisy and Rayleigh fading channels. The benchmark performance of the systems is investigated in terms of the bit error rate (BER) under the assumption of perfect synchronisation. The chaotic spreading signals, used to encrypt the binary messages, are generated using the logistic map. The degradation in performance of the systems in the Rayleigh fading channel when compared with the noisy channel is demonstrated. Furthermore, it is shown that in both noisy and Rayleigh fading channels, the chaos-based multi-user TDM system outperforms the chaos-based DS-CDMA system for a large number of users in the system, whereas the chaos-based DS-CDMA system yields better performance for low user numbers. The overall BER performance degradation for the chaos-based DS-CDMA multi-user system in noisy and Rayleigh fading channels is characterised by the flattening of the BER curves at low levels of noise due to the prevailing effects of the interuser interferences.     

Optimization of Channel Estimation Using ELMx-based in Massive MIMO

In communication channel estimation, the Least Square (LS) technique has long been a widely accepted and commonly used principle. This is because the simple calculation method is compared with other channel estimation methods. The Minimum Mean Squares Error (MMSE), which is developed later, is devised as the next step because the goal is to reduce the error rate in the communication system from the conventional LS technique which still has a higher error rate. These channel estimations are very important to modern communication systems, especially massive MIMO. Evaluating the massive MIMO channel is one of the most researched and debated topics today. This is essential in technology to overcome traditional performance barriers. The better the channel estimation, the more accurate it is. This paper investigated machine learning (ML) for channel estimation. ML channel estimations based on the Extreme Learning Machine (ELMx) group are also implemented. These estimations, known as the ELMx group, include Regularized Extreme Learning Machine (RELM) and Outlier Robust Extreme Learning Machine (ORELM). Then, it was compared with LS and MMSE. The simulation results reveal that the ELMx group outperforms LS and MMSE in channel capacity and bit error rate. Additionally, this paper has proven complexity for verified computational times. The RELM method is less time consuming and has low complexity which is suitable for future use in large MIMO systems.     

Improved Hybrid Beamforming for mmWave Multi-User Massive MIMO

Massive multiple input multiple output (MIMO) has become essential for the increase of capacity as the millimeter-wave (mmWave) communication is considered. Also, hybrid beamforming systems have been studied since full-digital beamforming is impractical due to high cost and power consumption of the radio frequency (RF) chains. This paper proposes a hybrid beamforming scheme to improve the spectral efficiency for multi-user MIMO (MU-MIMO) systems. In a frequency selective fading environment, hybrid beamforming schemes suffer from performance degradation since the analog precoder performs the same precoding for all subcarriers. To mitigate performance degradation, this paper uses the average channel covariance matrix for all subcarriers and considers an iterative algorithm to design analog precoder using approximation techniques. The analog precoder is iteratively updated for each column until it converges. The proposed scheme can reduce errors in the approximating process of the overall spectral efficiency. This scheme can be applied to fully-connected and partially-connected structures. The simulation results show that spectral efficiency performance for the proposed scheme is better than the conventional schemes. The proposed scheme can achieve similar performance with full-digital beamforming by using a sufficiently large number of RF chains. Also, this paper shows that the proposed scheme outperforms other schemes in the frequency selective fading environment. This performance improvement can be achieved in both structures.