A High Spectral Efficient Frequency-Domain Channel-Estimation Method for the Polarization-Division-Multiplexed CO-OFDM-OQAM System

Contrary to the other multi-carrier modulation systems, the coherent optical orthogonal frequency division multiplexing communication system with an offset quadrature amplitude modulation (CO-OFDM-OQAM) possesses inherent imaginary interference (IMI). This has an important impact on the channel estimation process. Currently, a variety of frequency-domain channel estimation methods have been proposed. However, there are various problems that still exist. For instance, in order to reduce the influence of IMI, it is necessary to insert more guard intervals between the training sequence and the payload, leading to the occupation of excessive spectrum resources. In order to address this problem, this work designs a high spectral efficient frequency-domain channel estimation method for the polarization-division-multiplexing CO-OFDM-OQAM systems. First, the working principle of the proposed method is described in detail. Then, its spectral efficiency, power peak-to-average ratio, and channel estimation performance are studied based on simulations. The simulation results show that the proposed method improves the spectral efficiency without worsening the power peak-to-average ratio. The channel estimation capability of this method is verified in three scenarios of long-distance transmissions, including back-to-back, 100 km, and 200 km transmissions. .

A frame synchronization solution for orthogonal frequency division multiplexing system

To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.

Performance of multi-band orthogonal frequency division multiplexing ultra wide-band system on IEEE UWB channels

Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.

Coarse-fine joint target parameter estimation method based on AN-RSC in OFDM passive radar

In this paper,we study the accuracy of delay-Doppler parameter estimation of targets in a passive radar using orthogonal frequency division multiplexing(OFDM)signal.A coarse-fine joint estimation method is proposed to achieve better estimation accuracy of target parameters without excessive computational burden.Firstly,the modulation symbol domain(MSD)method is used to roughly estimate the delay and Doppler of targets.Then,to obtain high-precision Doppler estimation,the atomic norm(AN)based on the multiple measurement vectors(MMV)model(MMV-AN)is used to manifest the signal sparsity in the continuous Doppler domain.At the same time,a reference signal compensation(RSC)method is presented to obtain highprecision delay estimation.Simulation results based on the OFDM signal show that the coarse-fine joint estimation method based on AN-RSC can obtain a more accurate estimation of target parameters compared with other algorithms.In addition,the proposed method also possesses computational advantages compared with the joint parameter estimation.

SIGNAL CONSTELLATIONS DESIGN FOR DIFFERENTIAL UNITARY SPACE-TIME IN MIMO-OFDM SYSTEM OVER FREQUENCY-SELECTIVE FADING CHANNELS

In this paper, the design of signal constellations parameters is studied for Differential Unitary Space-Time Modulation (DUSTM) based on the design criterion of maximizing the diversity product. Further, noninteger searching method for the signal constellation parameters design is proposed in order to get better codes. Experimental results show that under the different Doppler spread and data transmission rate, the proposed design performs better than the previous design using integer parameters in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over frequency-selective fading channels.

智能反射面辅助的OFDM系统稀疏信道估计研究

针对智能反射面(IRS)辅助的宽带正交频分复用(OFDM)系统的信道估计,当前大多数研究都是基于单符号全导频设置,且级联信道系数过多会导致导频开销较大。为此,提出了一种基于时域-角域块稀疏的两阶段信道估计方案。首先,通过分析信道在时域和角域上存在的共同稀疏特性,将级联信道矩阵转换为时域-角域上的块稀疏表示,并将信道估计问题转换为块稀疏矩阵恢复问题。其次,考虑传输导频限制和时域-角域块稀疏特性,提出了一种两阶段稀疏信道估计方案对级联信道进行稀疏恢复。仿真结果表明,相比另外三种基准方案,该方案可以使用较少的导频获得更优的信道估计性能,有效减少了导频开销,且估计准确度更高。

DRFM干扰在OFDM新体制雷达中的研究

新体制雷达以正交频分复用(OFDM)数字调制方式作为雷达信号源,具有高频谱效率、高分辨能力等优点。本文首先介绍了新体制雷达系统的基本组成部分,主要包括OFDM信号源、发射模块、环境模块、接收模块和信号处理模块。其次介绍了数字射频存储器(DRFM)干扰的主要组成部分以及工作原理,其中主要包括假目标干扰。最后将DRFM干扰与新体制雷达结合,在加干扰和不加干扰两种情况下对仿真目标进行测距和测速,结果验证了新体制雷达测量目标的准确性以及DRFM干扰的可行性。对新体制雷达及DRFM干扰研究具有参考意义。

NC-OFDM雷达通信一体化设计

雷达通信一体化有利于提高设备硬件资源利用率和频谱利用率,已成为近年来的研究热点。针对目前频谱资源稀缺的情况,结合认知无线电的概念,提出了基于非连续正交频分复用(NC-OFDM)的雷达通信一体化设计,对NC-OFDM雷达通信一体化信号测量目标特征进行了距离及速度的估计,并对基于NC-OFDM雷达通信一体化信号模糊函数、雷达成像的距离分辨率和方位分辨率、自相关性及误码率进行了分析,同时,选取互信息作为指标,利用优化算法进行波形设计。仿真结果表明,NC-OFDM雷达通信一体化信号具有较好的雷达探测性能和更为优良的无线通信性能。

PSO算法下GP-周期随机共振的微弱OFDM信号检测

为了解决传统随机共振系统在微弱正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号解调应用中存在的人工选择参数困难、解调效果差的问题,提出一种基于粒子群优化(Particle Swarm Optimization,PWO)算法的GP(Gaussian Potential)-周期随机共振系统的微弱OFDM信号检测方法。该方法利用GP-周期随机系统对OFDM信号经正交变换后的两路高频信号分别进行随机共振,同时运用阻尼参数与信号频率之间的关系对两路信号进行降频处理,使得上下两路信号都能够发生随机共振;然后使用PWO算法对随机共振的系统参数进行优化处理,以使得上下两路信号达到最优的共振效果;最后,将上下两路共振之后的信号合成完成OFDM信号解调,得到最终的数字序列。本文探讨了优化前后GP-周期随机共振系统的共振效果,研究了优化前后GP-周期随机共振诱导下的OFDM系统星座图的聚集程度以及误码率情况,对比分析了经典双稳随机共振、经典三稳随机共振和所提模型对OFDM信号检测的影响。仿真结果表明:相比常用的传统随机共振模型,该方法用于OFDM信号检测的星座图中信号点的聚集程度更高,同时OFDM系统误码率在同样的信噪比下降低50%左右。

基于数据失真的雷达通信一体化OFDM波形设计方法

正交频分复用(OFDM)波形设计是实现雷达通信一体化的物理层关键技术之一。OFDM波形通常存在峰均功率比(PAPR)高,以及波形自相关旁瓣电平高的问题。该文针对现有联合降低PAPR和自相关旁瓣方法存在的通信速率下降问题,提出了一种基于数据失真的一体化波形设计方法。该文还将通信数据的误差矢量幅度作为优化目标之一,降低了数据失真引起的通信误码率。首先,构建了PAPR约束下最小化积分旁瓣比和误差矢量幅度的优化模型。其次,根据调制星座图特点,通过外围星座调制的数据失真和所有调制数据失真,将多目标高维非凸优化问题转化为两个单目标优化子问题,分别采取凸松弛操作和交替方向乘子法(ADMM)求解简化后的子问题,得到低积分旁瓣比波形和PAPR约束下的低误差矢量幅度波形。仿真结果表明该方法设计的一体化波形可满足PAPR要求,同时具有良好的感知和通信性能。

GDS-MIMO-OFDM雷达通信一体化波形设计

针对正交频分复用(OFDM)雷达通信一体化波形存在的通信速率较低、自相关旁瓣较高的问题,提出了一种基于Gold码扩频的多输入多输出-正交频分复用(MIMO-OFDM)雷达通信一体化波形。将MIMO-OFDM与扩频序列相结合,利用相关性较好的Gold码对通信信息进行扩频,再与OFDM脉冲符号进行调制,进而设计出一种既能提高通信速率又能改善雷达性能的一体化波形。仿真实验证明,较相同仿真条件下的Gold-OFDM、脉冲压缩-正交频分复用(PC-OFDM)一体化波形而言,所设计的一体化波形的通信速率能够倍数提高且可以在不影响通信性能的前提下降低信号模糊函数的旁瓣,从而改善一体化系统的雷达性能。

OFDM水声通信多普勒估计与跟踪方法

水声通信中传统宽带多普勒估计方法难以准确跟踪时变多普勒因子,从而导致正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)在变速运动通信场景中补偿性能不佳。针对该问题,文章提出了一种基于空载波的多普勒估计与跟踪算法。首先对三频信号做线性调频Z变换(Chirp-Z Transform,CZT)得到多普勒先验值,然后利用OFDM符号中的空载波结合载波频偏(Carrier Frequency Offset,CFO)搜索补偿技术,把估计的最优CFO值转换为宽带多普勒因子,进而计算当前符号的加速度并预测下一符号的速度。通过更新加速度对预测值进行修正,实现每个OFDM符号的多普勒估计。数值仿真和湖试结果表明,文中算法不仅能有效跟踪多普勒的变化,在匀速和变速条件下都有较好的补偿性能,而且对帧结构设计要求低,对先验误差不敏感,有利于水声通信系统的工程实现。

深度学习辅助的5G OFDM系统的信道估计

传统的信道估计算法难以满足5G系统中的高速率低时延的需求。针对该问题,将通信信道的时频响应视为二维图像,提出了一种基于图像恢复技术的信道估计方法。首先,设定参数产生基于5G新空口(New Radio,NR)标准的物理下行链路共享信道(Physical Downlink Shared Channel,PDSCH)的信道数据信息数据集,将所产生的信道矩阵看作二维图像;然后,构建基于卷积神经网络的图像恢复网络,并融入残差连接来提高网络的性能;最后,利用训练好的网络模型进行信道估计。仿真结果表明,与最小二乘算法(Least Square,LS)、实际信道估计(Practical Channel Estimation,PCE)和基于图像超分辨率ChannelNet网络相比,所提出的信道估计算法性能提升明显。

基于多特征融合的MIMO-OFDM系统单-混信号调制识别算法

为解决非协作通信中多输入多输出正交频分复用(multiple-input multiple-output orthogonal frequency division multiplexing, MIMO-OFDM)系统的单-混信号调制识别问题,提出一种基于多特征融合和决策融合的调制识别方法。首先,利用特征矩阵的联合近似对角化(joint approximate diagonalization of eigenvalue matrix, JADE)算法从接收端恢复发送信号;然后,提取恢复后信号的四次方谱、循环谱和高阶累积量作为输入样本,利用多特征融合网络对输入样本进行训练;最后,使用决策融合策略根据每条支路输出得到最终判决结果。仿真实验结果表明,所提方法可以对MIMO-OFDM系统中的7种信号进行有效识别,在信噪比为10 dB时识别精度可达99.4%。

基于排序码本的水声自适应OFDM通信中信道状态信息反馈研究

水声(UWA)信道时延扩展大等特点导致信道频响(CFR)快衰落,水声通信(UWAC)技术发展受到挑战。发射端获取有效可靠的信道状态信息(CSI)是自适应通信的前提,针对水声自适应正交频分复用(OFDM)通信的需求,该文提出基于排序码本的信道状态信息分组排序拟合反馈算法(CSI-GSFF),包括分组、排序、数据拟合3个步骤。该算法首先将相邻导频子载波分组,以组为反馈单元;然后对各组内的导频子载波按照信道增益值进行排序,以减轻水声信道频响快衰落造成的反馈开销大等不利影响;最后进行多项式拟合,排序操作有效地降低了拟合阶数。通过实测海试时变信道数据仿真,结果表明,该文提出的信道状态信息反馈算法能够基本达到完美信道状态信息情形下的水声自适应OFDM通信系统误码率性能,同时可以有效地减少反馈开销。

基于深度学习的下行大规模MIMO OFDM系统的1比特预编码算法

大规模多输入多输出(MIMO)系统中通过在基站端配备数百根天线,在提高频谱利用效率的同时,也带来了系统成本的增加。本课题组之前提出了一种适用于下行大规模MIMO正交频分复用(OFDM)系统的收敛保证的多载波1比特预编码算法(CG-MC1bit),能够获得较优的系统性能,但相应的计算复杂度较高,阻碍了其在实时系统中的应用。为进一步解决大规模MIMO系统中的成本和功耗问题,该文提出了一个模型驱动的神经网络,在CG-MC1bit算法的基础上迭代展开(Unfolding)得到了一种更加高效的CG-MC1bit-Net算法。具体而言,将迭代算法展开为一个神经网络,并引入可训练的参数来替代前向传播中的高复杂性操作。实验结果表明,该方法能够自动更新参数,与传统的预编码算法相比,收敛速度更快,计算复杂度更低。

Frequency Diversity for OFDM Mobile Communication via Underwater Acoustic Channels

The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.

基于深度学习的OFDM半相干水声通信方法

针对正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)水声通信中常用的相干和非相干通信分别面临的对多普勒敏感和频谱效率低的问题,提出一种高阶幅度键控调制的半相干通信技术,将OFDM符号时频帧结构中全部频点采用高阶幅度键控调制方式,并利用信号幅度信息完成半相干信道估计。通过两种基于深度学习的算法优化半相干信道估计这一非线性过程,较非相干通信有效提高了频谱效率,较一定信噪比下的相干通信提高了鲁棒性,降低了误比特率和系统复杂度,并利用元学习算法降低深度学习算法对训练数据的依赖。最后,提取海试信道数据,完成OFDM半相干水声通信系统仿真,验证了所提方法在频谱效率和系统误比特率性能方面较非相干和相干通信的优势,当信道长度改变时,基于元学习的算法依然可以获得较好的性能。

Joint frequency offset tracking and PAPR reduction algorithm in OFDM systems

This paper presents an algorithm that aims to reduce the peak-to-average power ratio（PAPR） of orthogonal frequency division multiplexing（OFDM） communication systems while maintaining frequency tracking.The algorithm achieves PAPR reduction by applying the complex conjugates of the data symbol obtained from the frequency domain to cancel the phase of the data symbol.A likelihood estimator is used to obtain the sub-carrier phase error due to the residual carrier frequency offset（RCFO） using the same complex conjugates as a pilot signal.Furthermore,a joint time and frequency domain multicarrier phase locked loop（MPLL） is developed to compensate additional frequency offset.Simulation results show that this algorithm is capable of reducing PAPR without impacting the frequency tracking performance.

OFDM叠加导频联合信道估计和检测方法

针对现有正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统信道估计和迭代检测算法中频谱效率低和鲁棒性差等问题,提出了一种基于酉近似消息传递和叠加导频的信道估计与联合检测方法。首先,在软调制/解调中叠加导频对正交幅度调制的星座点进行预处理,检测时将叠加的导频作为频域符号的先验分布,利用置信传播算法进行调制和解调,实现检测模型的简化。然后,应用因子图-消息传递算法对OFDM传输系统和信道进行建模和全局优化,引入酉变换加强信道估计算法的鲁棒性。最后,建立OFDM仿真环境对现有方法进行仿真分析。仿真结果表明,相对于现有的独立导频类算法,所提算法能够以相同复杂度显著提升OFDM系统的频谱效率和鲁棒性。