基于单边带调制的直接探测光OFDM-RoF系统研究

研究基于单边带调制(SSB)的直接探测光正交频分复用-光载射频(OFDM-RoF)系统的性能。10Gbit/s的二进制数据信号经过QAM符号映射和OFDM调制后,与10GHz射频信号混频并驱动双电极LiNbO3马赫-曾德尔调制器(LN-MZM)产生SSB-OFDM信号,调制信号通过光纤传输至基站,进行直接探测转换为毫米波电信号后再无线发送到用户端。仿真结果证实,OFDMRoF系统在4QAM和16QAM两种调制格式下的EVM都满足FEC的要求。同时,理论分析并仿真验证存在一个最佳调制指数可以使信号传输性能达到最佳,并且最佳调制指数与光纤长度无关。     

基于双平行MZM调制器的矢量毫米波信号传输性能分析北大核心CSCD

提出了一种基于双平行马赫-曾德尔调制器(dual parallel Mach-Zehnder modulators,DP-MZM)的单边带矢量毫米波信号产生和传输方案,在MATLAB和VPI联合仿真环境下分析了90 GHz波段不同调制格式信号的产生和传输性能。仿真中,DP-MZM工作在光载波抑制(optical carrier suppression,OCS)模式时,小信号驱动的两个子调制器输出的单边带信号相互叠加后,无需使用滤波器,可以实现完全抑制中心载波的效果。结果表明:经过该系统传输后,各调制信号的误码率(bit error rate,BER)均可达到硬判决前向纠错(hard judgment forward error currection,HD-FEC)阈值。概率整形后正交幅度调制信号的误码性能明显优于均匀正交幅度调制信号,其中,7 bit/symbol概率整形256阶正交幅度调制(probability shaping 256 quadrature amlitude modulation,PS-256QAM)信号经过系统传输后功率增益最为明显,经过50 km光纤传输后,提升了2.94 dB的功率增益。与目前存在的载波抑制毫米波产生方案相比,该系统结构相对简单,可调节度高,信号传输增益明显,因此具有一定的应用价值。     

基于窄带光纤光栅的单边带调制及其传输特性

利用自制的窄带光纤Bragg光栅(NFBG)获得了单边带(SSB)调制信号,并在标准单模光纤(G.652)上分别进行双边带(DSB)和SSB调制信号的传输,传输了155 km G.652后采用自制的啁啾光纤Bragg光栅(CFBG)进行色散补偿.结果表明,在同样的入纤光功率下获得相同的误码率(BER),SSB信号的功率代价比DSB信号的小,在BER为E-12数量级时,SSB信号的功率代价比DSB信号小0.8 dB.     

色散平坦光纤中的高速率PM-16QAM信号传输研究

提出了一种高速率、偏振复用、正交幅度调制信号的色散平坦光纤传输系统,传输速率分别为160 Gbps和256 Gbps,调制格式为PM-16QAM。实验研究了色散平坦光纤链路系统的传输特性,并分别与非零色散位移光纤和标准单模光纤链路传输特性做了比较。实验结果表明,较低输入光功率情况下,PM-16QAM信号在160 Gbps传输50 km时,经色散平坦光纤传输后的误差矢量幅度EVM优于经非零色散位移光纤传输情况0.5%,比特误码率BER优于非零色散位移光纤传输情况两个数量级;色散平坦光纤链路能更好地衰减旁瓣噪声;256 Gbps传输50 km和75 km时,仅在色散平坦光纤链路传输后可以较好地解调出信号;传输距离越长,保持较好特性时输入光功率范围越小。对比160 Gbps和256 Gbps情况,高速率PM-16QAM信号在色散平坦光纤链路的传输特性优于非零色散位移光纤和标准单模光纤链路的传输特性,传输速率越高、传输距离越长效果越明显。     

一种基于相位调制器的40 GHz OFDM-ROF系统实验研究

实验研究了一种基于相位调制器(PM)并级联强度调制器(IM)实现40 GHz毫米波传输正交频分复用(OFDM)信号的光纤无线通信(ROF)系统。在中心站,采用20 GHz的射频(RF)信号驱动PM,调节驱动信号的强度,使输出的信号经光纤布拉格光栅(FBG)滤除中心载波后再送入IM。2.5 Gbit/s的OFDM信号直接调制在光毫米波上,经过50 km标准的单模光纤(SSMF)传输到基站。在基站,光调制信号经光电转换器(PD)转换成电调制信号,再与RF信号混频,恢复出基带OFDM信号。实验结果表明,在无色散补偿、误码率(BER)为10-3的条件下,下行链路中2.5 Gbit/s的OFDM信号经光纤传输50 km后,其功率代价小于1 dB,而且信号的星座图依然较好。     

通过恒包络调制提高相干光OFDM系统的光纤非线性容限

相干光正交频分复用(CO-OFDM)对光纤链路中 的色度色散(CD)和偏振模色散(PMD)具有较强的容忍性,但 是OFDM信号高峰均功率比(PAPR)的特点使其对光纤非线性效应 非常敏感,严重影响了系统传输性能。 本文提出了基于恒包络(CE)调制的方法使得系统中光信号PAPR降低为0dB,从而提高了CO-OFDM系统的非 线性传输性能。仿真结果表明,子载波采用16QAM调制的40Gbit/s单信道CE调制CO -OFDM系统,在经800km无色散补偿、欠色散补偿和周期全色散补偿 标准单模光纤(SSMF)链 路传输后,虽然较传统CO-OFDM存在约1.8dB的代价,但是系统最大 发射光功率分别提高 了6.2、9.3dB。并且,将本文方案应 用 到CO-OFDM和10Gbit/s NRZ-OOK混合传输WDM系统中,信道最大发 射光功率仍获得了5.2dB的提高。因此,本文提出的CE调制方法能有 效地提高CO-OFDM系统在不同传输环境中的光纤非线性容限。     

Novel full-duplex SSB WDM-RoF system with SLM technique for decreasing PAPR

A novel full-duplex single-sideband (SSB) wavelength division multiplexing radio over fiber (WDM-RoF) system with selected mapping (SLM) technique for decreasing peak-to-average power ratio (PAPR) is proposed in this paper. At the central office (CO), the generated SSB signal carrying 10 Gbit/s 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) downstream signal with SLM technique is sent to the base station, and 60 GHz SSB optical signal carrying 10 Gbit/s 16QAM-OFDM upstream signal is sent back to CO utilizing the wavelength-reuse technology. Simulation results show the proposed method for PAPR reduction can effectively improve the sensitivity of receiver, and the power penalty of the 16QAM-OFDM downlink (uplink) signal is about 2 dB (3 dB) at BER of 1×10-3 after 42 km standard single-mode fiber (SSMF) transmission.     

偏振复用QPSK相干光数字通信系统实验研究

建立了偏振复用正交相移键控(QPSK)传输及相干检测的数字通信实验系统,并分析系统的性能。40Gbit/s的偏振复用QPSK信号在单模光纤(SMF)中传输了100km;信号光与本振光在接收端进行混频并下变频,最后用数字信号处理(DSP)算法对接收信号离线处理。比较了光纤传输前后不同的光信噪比(OSNR)下的误码率(BER),实验结果表明,所使用的DSP算法能克服光纤信道对信号的主要损伤,对高速的相干检测信号进行有效的恢复。     

基于微波光子六倍频的光载无线通信系统

构建了基于微波光子倍频的光载无线传输系统。基于偏振调制器实现了六倍频光毫米波产生,利用马赫增德尔调制器实现了QAM信号调制并进行光载无线传输,测试了41.5GHz QAM信号调制和10km光载无线传输光纤传输之后的QAM信号星座图。该系统实现了远距离音视频或高清数字信号传输。     

基于偏分复用技术的数字RoF系统研究

为有效缓解D-RoF系统高数字比特速率的不利影响,本文研究了偏振复用的D-RoF系 统,能有效 提高系统单波长的传输容量。分别在传统Stokes矢量检测和简化Stokes矢量检测下,采用一 路偏振态向量 追踪(OTV)与两路偏振态向量追踪(TTV)的DSP算法能够有效实现偏振解复用。仿真结果表明 ,两路偏振 态向量追踪方法能有效降低正交偏振复用D-RoF系统的功率预算,达到系统最终误码率时, TTV算法需要 的光功率要比OTV算法需要的光功率少2dBm。同时,可用TTV方法实现两路信号最小偏振复 用度为76° 的非正交偏振解复用,丰富了偏振复用的维度。该偏振复用D-RoF系统对其在未来5G无线传 输和有线数字电视传输具有重要意义。     

影响迭代译码器的QAM软值计算的实现

介绍了迭代译码器实现需要考虑的几个问题,以及在实际应用中迭代译码器需要的先决条件--软值计算的几种方法,给出相应算法的实现,并在最后对这几种实现方法进行了性能和资源上的比较.     

Compensation of quadrature imbalance in an optical coherent OQPSK receiver in presence of frequency offset

In this paper,we describe the impact of quadrature imbalance (QI) in the presence of frequency offset in an optical coherent offset quadrature phase shift keying (OQPSK) receiver.Arbitrary conjugate misalignment was realized in a 2×4 90° optical hybrid,and the ellipse correction (EC) method of quadrature imbalance was applied in our simulation.In the case of transmission,the EC method can significantly improve the system performance.     

基于FPGA实现的自适应OFDM VLC仿真系统

采用现场可编程门阵列(FPGA)技术搭建了一个自适应正交频分复用(OFDM)可见光通信(VLC)仿真系统。该系统实现了自适应高阶OFDM调制和高速数据速率传输,正交振幅调制(QAM)的调制阶数M有16、64、256、1024四种方式,数据传输速率为16.8~42.0Mb/s。     

Pointing error effects on performance of free-space optical communication systems using SC-QAM signals over atmospheric turbulence channels

In this paper, we theoretically analyze pointing error effects on performance of free-space optical (FSO) communication systems using subcarrier intensity quadrature amplitude modulation (SC-QAM) signals over atmospheric turbulence channels. Unlike previous studies, we take into account both atmospheric turbulence channels and the pointing error effect. In order to model atmospheric turbulence channels, we employ a log-normal distribution for weak-to-moderate turbulent condition and a gamma–gamma distribution for strong turbulent condition. Moreover, we study the pointing error effect by taking into account the influence of beamwidth, aperture size and jitter variance. In addition, we use a combination of these models to analyze the combined effect of atmospheric turbulence and pointing error to FSO/SC-QAM systems. Finally, we derive analytical expressions to evaluate the average symbol error rate (ASER) performance of such systems. Numerical results present the impact of pointing error on the performance of FSO/SC-QAM systems and how we use proper values of aperture size and beamwidth to improve the performance of such systems. In addition, simulation results of FSO/SC-QAM performance over strong atmospheric turbulence and pointing errors show that the closed-form expression can provide a precision for evaluating ASER of such systems.     

A Joint Scheme of AGC and Gain/Phase Mismatch Compensation for QPSK DCR

This paper presents a simple gain/phase blind compensation algorithm with an automatic gain control (AGC) function for the adoption of the AGC function and compensation for gain/phase imbalances in quadrature phase shift keying (QPSK) direct conversion receivers (DCRs). The AGC function is interactively operated with the compensation algorithm for gain/phase imbalances. By detecting the gain sum and difference values between the I‐channel and Q‐channel, the combined AGC and gain imbalance compensation algorithm provides a simpler DCR architecture.     

Si MEMS陀螺仪的正交耦合补偿技术

为了减小正交耦合误差对硅微电子机械系统(MEMS)陀螺仪性能的影响,提高陀螺仪零偏精度,对MEMS陀螺仪正交耦合补偿技术进行研究.建立MEMS陀螺仪动力学模型,分析正交耦合产生的原因,介绍了各类正交耦合补偿机理.设计了一款可实现静电刚度补偿的MEMS陀螺仪,并利用绝缘体上硅(SOI)工艺进行制备.利用现场可编程门阵列(...     

基于Nyquist脉冲副载波调制的短距离光纤传输技术研究

提出了一种适用于强度调制直接检测(IM/DD) 光系统的信号调制格式。这种基于Nyquist脉冲half cycle副载波调制(SCM)信号能有效提高频谱效率,为了减少传递函数引起的系统的性能 恶化,采 用了数字预均衡和后均衡实现对光纤损伤的补偿;建立了偏振复用(PDM)IM/DD系统 平台, 分析了Nyquist脉冲SCM信号在系统中的PAPR性能,实现了72Gbit/s 64-QAM N yquist脉冲SCM信号经过20km标准单模光纤(SMF)传输后其误码性能 小于前向纠错(FEC)阀值3．8×10－3。     

SQM-OTFT: A compact model of organic thin-film transistors based on the symmetric quadrature of the accumulation charge considering both deep and tail states

A physically-based compact model of organic thin-film transistors suitable for CAD simulators is proposed. It is worked out by means of a newly developed and particularly simple form of the charge-sheet model: the symmetric quadrature of the accumulation charge. The model is based on the variable-range hopping and accounts for both deep and tail states. It is simple, symmetric, accurately accounts for the below-threshold, linear, and saturation regimes via a unique formulation. The symmetric quadrature is accurate within 5% in all regions of operation and the resulting current model is suitable both for p- and n-type transistors. The model leads to a significant simplification of the drain current and of the quasi-static expressions of the terminal charges based on the Ward–Dutton partition. Finally, the symmetric quadrature leads to an explicit and analytically tractable solution for the surface potential as a function of position in the device channel that can be extremely useful to implement advanced physical effects.