Real-Time Upstream Services Demonstration in Orthogonal Frequency Division Multiplexing- Passive Optical Network System

In recent years,dual-homed topologies have appeared in data centers in order to offer higher aggregate bandwidth by using multiple paths simultaneously.Multipath TCP(MPTCP) has been proposed as a replacement for TCP in those topologies as it can efficiently offer improved throughput and better fairness.However,we have found that MPTCP has a problem in terms of incast collapse where the receiver suffers a drastic goodput drop when it simultaneously requests data over multiple servers.In this paper,we investigate why the goodput collapses even if MPTCP is able to actively relieve hot spots.In order to address the problem,we propose an equally-weighted congestion control algorithm for MPTCP,namely EW-MPTCP,without need for centralized control,additional infrastructure and a hardware upgrade.In our scheme,in addition to the coupled congestion control performed on each subflow of an MPTCP connection,we allow each subflow to perform an additional congestion control operation by weighting the congestion window in reverse proportion to the number of servers.The goal is to mitigate incast collapse by allowing multiple MPTCP subflows to compete fairly with a single-TCP flow at the shared bottleneck.The simulation results show that our solution mitigates the incast problem and noticeably improves goodput in data centers.

Joint nonlinearity and chromatic dispersion pre-compensation for coherent optical orthogonal frequency-division multiplexing systems

This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems.The research results show that this method can reduce the walk-off effect and can therefore equalize the nonlinear impairments effectively.Compared with the only other existing nonlinearity pre-compensation method,the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system,but also effective for high-dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation.The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method.For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20×80 km standard single-mode fibre system,the suggested method can improve the nonlinear threshold(for Q > 10 dB) about 2.7,1.2 and 1.0 dB,and the maximum Q factor about 1.2,0.4 and 0.3 dB,for 2,8 and 16 ps/(nm·km) dispersion coefficients.

The Effect and Compensation of Phase Noise on Orthogonal Frequency Division Multiplexing (OFDM) System

Orthogonal Frequency Division Multiplexing (OFDM) is characterized by its high data rate. However, the modulation method used in the system is subject to the influence of phase noise due to the need of time synchronization. In this paper, an algorithm based on MMSE (minimum mean square error) is developed to compensate the influence of both the common phase error (CPE) and inter carrier interference (ICI), which are two aspects of phase noise, under common Gaussian white noise. The result of noise cancellation is presented in signal-to-noise ratio (SNR) and symbol error rate (SER). Like digital signal in general, SNR can reduce SER with or without phase noise compensation. The compensation of phase noise significantly reduces the SER of the decoded signal. However, the bandwidth of phase noise still determines the signal accuracy. Under high bandwidth of phase noise, increasing SNR will only slightly increase SER, which is not efficient.

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.

Security in Multicast Over α-μ Fading Channels with Orthogonal Frequency Division Multiplexing

The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.

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 802.11 a WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.

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. .

Implementation of Synchronization Technology in Orthogonal Frequency Division Multiplex System Based on Field Programming Gate Array

In this paper,analyzed is the symbol synchronization algorithm in orthogonal frequency division multiplex(OFDM)system,and accomplished are the hardware circuit design of coarse and elaborate synchronization algorithms.Based on the analysis of coarse and elaborate synchronization algorithms,multiplexed are,the module accumulator,division and output judgement,which can evidently save the hardware resource cost.The analysis of circuit sequence and wave form simulation of the design scheme shows that the proposed method efficiently reduce system resources and power consumption.

A Non-orthogonal STFC-OFDM on Frequency-Selective Fading Channels

A new non-orthogonal space-time-frequency code (STFC) was proposed. In conjunction with orthogonal frequency-division multiplexing (OFDM), it is appropriate for the application on frequency-selective fading channels. On the basis of the existing non-orthogonal STC, frequency diversity is studied and a new non-orthogonal STFC is further designed. Monte-Carlo simulations show that the non-orthogonal STFC-OFDM has the advantage of large diversity order, high bandwidth efficiency and better BER performance when compared with the orthogonal STC/STFC-OFDM and non-orthogonal STC-OFDM systems.

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。

高速置换索引差分混沌移位键控通信系统

为了提高置换索引差分混沌移位键控系统的数据传输速率和能量效率,提出了高速置换索引差分混沌移位键控通信系统。该系统采用置换矩阵索引多元信息,并携带一个调制位。发射端将参考信号复制P次作为信息承载信号,通过希尔伯特变换,每个信息时隙中多传输N个用户的信息,将信号级联到正交频分复用系统进行正交载波调制,大大提高了系统的数据传输速率;同时推导了该系统在高斯白噪声信道和多径瑞利衰落信道下的误码率表达式。理论分析及仿真结果证明,该系统相比其他置换索引类系统具有高速率、低误码率的良好特性,有更好的应用前景。

注意力去噪与复数LSTM的时变信道预测算法

随着无线通信技术的发展,高速场景下通信技术的研究也越来越广泛,其中获取到准确的信道状态信息对提升无线通信系统的性能具有重要的意义。针对正交频分复用系统在高速场景下,现有信道预测算法未考虑噪声影响及预测精度低的问题,提出了一种注意力去噪与复数卷积LSTM的时变信道预测算法。首先,设计了一种通道注意力信道去噪网络对信道状态信息进行去噪处理,降低了噪声对信道状态信息的影响。然后,提出了基于复数卷积层和长短期记忆网络的信道预测模型,对去噪后历史时刻的信道状态信息进行特征提取,并且对未来时刻的信道状态信息进行预测;改进后的LSTM预测模型增强了对信道时序特征的提取能力,提高了信道预测的精度。最后,结合Adam优化器对未来时刻信道状态信息进行预测输出。仿真结果表明:与对比算法相比,所提基于注意力去噪与复数卷积LSTM的时变信道预测算法对信道状态信息的预测精度更高,能够适用于高速移动场景下的时变信道预测。

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。

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。

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。

LDPC编码辅助的判决反馈信道估计与均衡方法

信道频率选择性衰落较强的环境下,传统正交频分复用非盲信道估计与均衡方法的系统误码性能较差,且需要在信号中增加导频符号的插入,降低系统吞吐量。针对上述问题,提出一种低密度奇偶校验(Low-Density Parity-Check,LDPC)编码辅助的判决反馈信道估计与均衡方法。将LDPC编码增益引入判决反馈回路中,以提升收敛性,在插入极少导频符号的条件下达到渐进非盲信道估计与均衡方法的性能。另外提出一种基于条件最大似然原则的信道估计改进算法,以恒虚警原则检测有效抽头信号以提高信道估计精度,并且能够与判决反馈信道估计与均衡方法相结合,进一步提升算法性能。仿真结果表明,在仿真所选用的信道环境下,LDPC编码辅助的判决反馈信道估计与均衡方法相比传统判决反馈方法具有11~13 dB的误码性能提升,具有优秀的系统误码性能和鲁棒性。

基于LWT的可见光OFDM-IM系统研究

针对索引调制正交频分复用(OFDM-IM)技术峰均比过高,对相位噪声和载波频偏敏感,系统复杂度高等问题,提出基于小波提升变换(LWT)的可见光OFDM-IM系统。首先选择正交小波基作为子载波,通过对信号的分裂、预测和更新,将信号分为高频信号和低频信号,再结合可见光信道构成LWT-OFDM-IM系统,最后通过理论分析和蒙特卡罗方法对系统的可靠性、峰均比特性和最佳小波分解层数进行了仿真验证,结果表明:当子载波N=256,子块中子载波数量L=4,激活子载波数量k=2,系统误码率为10~(-4)时,LWT-OFDM-IM比FFT-OFDM-IM改善约8 dB,相较于DWT-OFDM-IM提高约4 dB。当系统互补累计分布函数(CCDF)为10^(-1)数量级时,LWT-OFDM-IM的峰均比较FFT-OFDM-IM改善约2.3 dB。随着小波层数的递增,系统的误码性能越好,当小波层数为3层时,大约在10 dB附近,误码率可到10^(-5)量级。

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。

基于改进子载波预留算法的正交频分复用信号峰均比抑制方法研究

由于系统对线性元器件的要求非常严格,导致目前正交频分复用(OFDM)系统产生峰值平均功率比(PAPR)过高的问题,引起OFDM和基于OFDM的雷达一体化系统的信号失真,影响系统性能。针对该问题,该文提出了基于加权最小二乘法的子载波预留法(TR)。该算法首先将OFDM设计方案中的子载波分为数据子载波和预留的空白子载波,数据子载波调制数据子载波,空白子载波调制空白数据。然后利用原始数据通过加权最小二乘法得到最佳削峰系数和削峰数据,并将削峰数据调制在空白子载波上面。最后将削峰数据叠加到原始数据上,完成PAPR的抑制。仿真表明,基于加权最小二乘法的TR算法能够在1~3次迭代下实现良好的PAPR抑制效果,并且它的收敛速度相比于传统算法有了明显的提高。

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。