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. .

Ground roll wave suppression based on wavelet frequency division and radial trace transform

Ground roll waves interfere with seismic data. The suppression of ground roll waves based on the division of wavelet frequencies considers the low-frequency characteristics of ground roll waves. However, this method will not be effective when the ground roll wave and the effective signal have the same frequency bands because of overlapping. The radial trace transform （RTT） considers the apparent velocity difference between the effective signal and the ground roll wave to suppress the latter, but affects the low-frequency components of the former. This study proposes a ground roll wave suppression method by combining the wavelet frequency division and the RTT based on the difference between the ground roll wave velocity and the effective signal and their energy difference in the wavelet domain, thus making full use of the advantages of both methods. First, we decompose the seismic data into different frequency bands through wavelet transform. Second, the RTT and low-cut filtering are applied to the low-frequency band, where the ground roll waves are appearing. Third, we reconstruct the seismic record without ground roll waves by using the inverse RTT and the remaining frequency bands. The proposed method not only improves the ground roll wave suppression, but also protects the signal integrity. The numerical simulation and real seismic data processing results suggest that the proposed method has a strong ability to denoise while preserving the amplitude.

MOTION COMPENSATION FOR WIDE BEAM SAR BASED ON FREQUENCY DIVISION

Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.

A VERIFICATION ON DIVISION OF HYDROCLIMATIC AREA IN CHINA SEAS USING DIGITAL CHARACTERISTIC OF FREQUENCY DISTRIBUTION

oceanographic data files on the China Seas prepared by the National Marine Data and Information Service, SOA, China and the '30-year (1953-1982) Reports of Sea Surface Monthly Mean Temperature in the East China Sea by the Meteorological Agency, Japan,' were used to calculate the digital characteristics of frequency distribution of sea and air temperature in 153 areas in the China Seas. Principal factor analysis and fuzzy cluster ISODATA were used to divide the China hydroclimatic area into three climatic zones including ten climatic regions. It is concluded that the characteristic values derived by this method may completely show the characteristics of frequency distribution of sea and air temperature in the studied area and the final division of hydroclimatic area is fully coincident with the author's former result [2].

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

Abstract： Real-time digital service and mul- timedia service upstream transmission in Dig- ital Signal Processing （DSP）-based Orthogo- nal Frequency Division Multiplexing-Passive Optical Network （OFDM-PON） is experimen- tally demonstrated with Centralised Light Sou- rce （CLS） configuration in this paper. After transmitted over 25 km Standard Single Mode Fibre （SSMF） with -16.5 dBm optical power at receiver, the Bit Error Rate （BER） is 9.5 ×10^-11. The implementations of digital domain up-conversion and down-conversion based on Field Programmable Gate Array （FPGA） are int- roduced, which can reduce the cost of In-ph- ase and Quadrature （IQ） radio frequency mix- ers utilised at transmitter and receiver. A car- rier synchronization algorithm is implemented for compensating carrier offset. A channel eq- ualization algorithm is adopted for compen- sating the damage of channel. A new structure of Frequency Synchronization Unit （FSU） des- igned in FPGA is also proposed to cope with the frequency shifting at receiver.

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.

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 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.

Application of frequency division inversion in the prediction of heterogeneous natural gas hydrates reservoirs in the Shenhu Area,South China Sea

Drilling results suggest that the thickness of natural gas hydrates(NGHs)in the Shenhu Area,South China Sea(SCS)are spatially heterogenous,making it difficult to accurately assess the NGHs resources in this area.In the case that free gas exists beneath hydrate deposits,the frequency of the hydrate deposits will be noticeably attenuated,with the attenuation degree mainly affected by pore development and free gas content.Therefore,the frequency can be used as an important attribute to identify hydrate reservoirs.Based on the time-frequency characteristics of deposits,this study predicted the spatial distribution of hydrates in this area using the frequency division inversion method as follows.Firstly,the support vector machine(SVM)method was employed to study the amplitude versus frequency(AVF)response based on seismic and well logging data.Afterward,the AVF response was introduced as independent information to establish the nonlinear relationship between logging data and seismic waveform.Then,the full frequency band information of the seismic data was fully utilized to obtain the results of frequency division inversion.The inversion results can effectively broaden the frequency band,reflect the NGHs distribution,and reveal the NGHs reservoirs of two types,namely the fluid migration pathway type and the in situ self-generation self-storage diffusion type.Moreover,the inversion results well coincide with the drilling results.Therefore,it is feasible to use the frequency division inversion to predict the spatial distribution of heterogeneous NGHs reservoirs,which facilitates the optimization of favorable drilling targets and is crucial to the resource potential assessment of NGHs.

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.

Design of Simulation for Time-Division Multiplexing Digital Optimal Frequency Band Transmission System

This paper designs a simulation experiment model of the overall structure of time-division multiplexing digital optimal frequency band transmission system based on MATLAB simulation platform. The parameters of each module in the simulation model are set. The working process and performance of the time-division multiplexing digital optimal band transmission system are simulated. The simulation results show that the digital optimal band transmission system achieves the best transmission receiving conditions and performance, and the designed time-division multiplexing optimal digital band transmission simulation system achieves its functions. The research in this paper will help to improve the level of digital communication technology and to understand the structure of time-division multiplexing digital optimal band transmission system.

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.

面向外辐射源雷达目标探测的非时变稀疏模型和深度展开网络实现方法

近年来,基于稀疏特征提取的目标探测方法成为了雷达领域的研究热点。基于正交频分复用调制的外辐射源雷达(简称“外源雷达”)由于发射波形不受控,一方面构建的稀疏模型会随未知发射波形时变,导致相应的目标探测方法计算量大;另一方面目标回波常常因被直达波等强杂波掩盖而面临探测困难。在此背景下,利用外源雷达的正交频分复用波形特点,使用导频位置处频域信道响应提出一种非时变稀疏模型。通过将稀疏模型求解的每一次迭代过程替代为一层神经网络,首次研究了基于深度展开网络的智能化外源雷达目标探测实现方法。仿真和实测数据结果表明:所提方法与传统杂波抑制方法在目标探测上性能相近,但有着更低的计算复杂度,且无需人工设计稀疏矩阵等稀疏模型求解参数。

时间反转OFDM系统中增强安全性能的功率分配与人工噪声设计

时间反转技术特有的时空聚焦特性使其具有抗窃听能力.本文对提高时间反转正交频分复用系统安全性能的优化方案进行研究.首先,通过应用时间反转预滤波的时空聚焦特性来提高合法接收端相对于窃听端的信号强度;然后,以最大化保密速率为目标对子载波的功率分配进行优化.为进一步提升系统保密传输能力,利用循环前缀提供的自由度实现零空间人工噪声,在对窃听端形成有效干扰的同时,不对合法接收端造成影响.通过对子载波功率分配和人工噪声协方差阵进行联合优化,最大化系统的保密传输速率.仿真结果表明,所提优化方案能显著提高系统的保密速率.

OFDM-UAV中继广播通信系统航迹优化方法

为了提高无人机中继广播通信系统的性能,针对频率选择性衰落信道,考虑基站到无人机以及无人机到用户的全通信链路,提出了基于正交频分复用(OFDM)技术的无人机中继广播通信系统航迹优化方法。首先提出了基于OFDM的无人机中继广播通信传输模型,对单用户节点中断概率和系统平均中断概率进行理论分析并给出近似计算公式;然后以平均中断概率最小化和最大用户中断概率最小化为优化准则,提出无人机的航迹优化方法并分析了各因素对系统中断性能的影响;最后通过计算机仿真,证明了所提航迹优化方法正确有效。研究表明:在多径信道下,基于OFDM的无人机中继广播通信系统能有效克服频率选择性衰落,且译码转发方式下的连通性优于放大转发方式;基于平均中断概率最小化准则得到的系统中断性能优于最大用户中断概率最小化准则。

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STM32H7A3的频分复用型TDLAS激光驱动系统研制

随着气候变化问题日渐凸显,习近平主席作出了碳达峰、碳中和的重要指示,因此对二氧化碳检测的研究具有重要的意义。针对二氧化碳和水汽同时检测的需要,本文设计了一种频分复用型TDLAS激光驱动系统。系统采用STM32H7A3作为主控器,利用其内部高级定时器和多通道DAC产生多路幅值频率可调的电压信号,搭配外部V-I转换电路和光纤合束器研制出频分复用型TDLAS激光驱动系统。系统配备FLASH存储芯片和对应的上位机软件,具有灵活设置系统参数、存储加载控制数据并且在断电时保护数据不丢失的功能。经过测试,该系统输出的电流信号波形稳定,频率误差小,可应用于TDLAS系统进行多个激光器的同时驱动。

基于稀疏贝叶斯学习的GFDM系统联合迭代信道估计与符号检测

针对当前广义频分复用(Generalized Frequency Division Multiplexing,GFDM)系统时变信道估计精度低的问题,提出基于稀疏贝叶斯学习的GFDM系统联合信道估计与符号检测算法.具体地,采用无干扰导频插入的GFDM多重响应信号模型,在稀疏贝叶斯学习框架下,结合期望最大化算法(Expectation-Maximization,EM)和卡尔曼滤波与平滑算法实现块时变信道的最大似然估计;基于信道状态信息的估计值进行GFDM符号检测,并通过信道估计与符号检测的迭代处理逐步提高信道估计与符号检测的精度.仿真结果表明,所提算法能够获得接近完美信道状态信息条件下的误码率性能,且具有收敛速度快、对多普勒频移鲁棒性高等优点.

准噶尔盆地白家海凸起侏罗系西山窑组煤岩气“甜点”储层智能综合预测技术

为了解决准噶尔盆地白家海凸起侏罗系西山窑组煤岩厚度小、气源断裂垂向断距小导致的地震资料信噪比低及煤岩气“甜点”储层预测难度大的问题,提出了“五步法”逐级控制的测井-地质-地震一体化智能综合预测方法。研究结果表明:①“五步法”是利用构造保边去噪和谐波高频恢复处理技术提高叠前CRP道集的信噪比和分辨率;通过调谐厚度法和分频智能反演法相结合定量预测煤岩厚度分布;利用深度学习智能断裂检测技术预测气源断裂展布特征;基于煤岩流体替换对不同含气饱和度时的AVO特征进行分析,通过含气饱和度预测含气分布范围;采用叠合分析法预测“甜点”储层,即位于断鼻(或断块)、煤岩厚度大,存在气源断裂及含气饱和度高于50%的叠合部位。②研究区“甜点”主要分布在北部走滑断裂的南北两侧断鼻或断块圈闭中,共发育31个煤岩气“甜点”区,累计面积达231.9 km^(2),其中走滑断裂北侧的5个“甜点”储层勘探潜力更大。③依据“五步法”部署的预探井与实钻井考核指标的吻合率达92%;对部署的水平井井轨迹进行了优化设计和动态监控,提高了单井产能。