Spectrally Shaped DS–CDMA with Dual Sideband Combining for Increased Diversity on Dispersive Fading Channels

A new modulation scheme is proposed in this paper. This scheme uses sinusoidal chip waveforms to shape the spectrum of a direct sequence spread spectrum (DS-SS) signal such that the transmitted signal has two distinct spectral lobes, one from a lower sideband (LSB) and the other from an upper sideband (USB). By properly selecting the frequency of the sinusoidal chip waveforms, the two sideband signals can be made to undergo independent fading in a dispersive fading channel. These two independent sideband signals, when combined at the receiver, provide diversity gain. Our analysis and simulation results show that the bit error ratio (BER) performance of the proposed scheme is superior to that of the equivalent DS-SS system that uses conventional rectangular chip waveforms for severely faded channels.     

A novel scheme to implement duplex 60-GHz radio-over-fiber link with 20-GHz double-sideband optical millimeter-wave transmitted along the fiber

A duplex radio-over-fiber (RoF) link with a novel scheme to generate 60-GHz millimeter (mm)-wave using 20 GHz double sideband (DSB) optical mm-wave with signal carried only by its optical carrier is investigated. In the RoF downlink, the modulation frequency to generate the DSB optical mm-wave is reduced greatly. The theoretical analysis and numerical simulation show that this scheme cannot only eliminate the code form distortion caused by the time shifting of the sidebands, but also reduce the influence of the fading effect as the DSB optical mm-wave signal is transmitted along the fiber. Based on the scheme, the duplex RoF link with the frequency up- (down-) conversion of the down- (up-) link mm-wave signal is built and the uplink transmission performance is analyzed theoretically.     

基于两个平行马赫-增德尔调制器的光载无线传输系统

为提高光载无线(radio over fiber,RoF) 传输系统中的光波信号的利用率,本文提出了一种基于两个平行马赫-增德尔调制器 (Mach-Zehnder modulator,MZM) 的RoF传输系统。两个平行MZM经射频(radio frequency,RF) 信号调制后,产生5个光边带信号,分别是正负一阶光边带、正负二阶光边带和光载波。其中正负二阶光边带使用基带数据进行调制,经光电检测器(photodiode,PD) 拍频后产生已调数据的毫米波信号,再由天线发射出去。正二阶边带和光载波经PD拍频后产生未调制数据的毫米波,该毫米波用于接收端解调的本振信号(local oscillator,LO) 。负二阶边带信号用于上行链路的光载波。在本系统中,5个光边带信号都被充分利用,提高了光信号的利用效率。此外,还分析了该系统通过色散介质的传输特性,为RoF通信系统提供了一种实用化的解决方案。     

A novel scheme to generate multiband millimeter wave signals for 40 GHz full duplex radio-over-fiber system

This paper proposes a new scheme to generate frequency-diversity binary phase shift keying (BPSK) signals for radio-over-fiber (RoF) system. As is well known, the frequency diversity technology has the anti frequency selective fading characteristic and RoF system is a practical solution to increase the capacity and mobility of future-proof contents delivery and serve both fixed and mobile users. In this paper, our proposal can generate 20 GHz and 40 GHz millimeter-wave (mm-wave) signals simultaneously with the data rate of 1.25 Gbit/s employing only one electrical optical phase modulator (EOPM) and one Mach-Zehnder modulator (MZM) at the central station. With one additional MZM at the base station, the full duplex transmission can be accomplished. As the downstream data is phase modulated, the optical signal can be re-used to load the upstream data and no laser diode (LD) is needed at the base station, which simplify the structure of the base station. The 20 GHz electrical carrier is also generated which can be used to demodulate the BPSK signal. The whole scheme can be used in the future duplex RoF system.     

一种12倍频全双工RoF系统

为提高光载无线(RoF)通信系统倍频系数,提出了一种基于集成双平行马赫曾德尔调制器(MZM)和抑制载波光双边带调制的12倍频光生毫米波方案。理论分析了光生毫米波信号产生机理,讨论了相关参数对光生毫米波信号的影响,理论分析与仿真结果基本吻合。在此基础上设计了一种基于该方案的全双工RoF系统,通过调整基站(BS)线偏振器(Pol)偏振角度即可恢复出下行数据和上行载波。仿真结果表明,在误码率(BER)为10-9时,传输90km后上行链路功率代价为0.86dB,相同条件下下行链路功率代价仅为0.47dB。     

Effects of Direct Current Bias-Drifting on Radio on Fiber Link

The effects of direct current (dc) bias-drifting on radio on fiber (RoF) links are quantitative investigated and simulated. Single sideband (SSB) modulation and carrier suppressed double sideband (CS-DSB) modulation RoF links are considered, power variation of targeted signal and harmonic suppression on account for bias-drifting are calculated and evaluated. Our results suggest that power variation can be maintained within 1.1 dB with dc bias drift ε less than 5% in the SSB modulation RoF link and the degradation of harmonic suppression is evident with ε exceed 2% in the CS-DSB modulation RoF link.     

Full-Duplex 60-GHz RoF System With Optical Local Oscillating Carrier Distribution Scheme Based on FWM Effect in SOA

A full-duplex 60-GHz radio-over-fiber (RoF) system using novel optical local oscillating (LO) carrier distribution scheme to reduce the system cost and realize centralized management is proposed and experimentally demonstrated. In the proposed scheme, the optical LO carriers for producing remote electrical LO signals at the base stations (BSs) are generated together with the downlink RoF carriers at the central station (CS) via four-wave-mixing effect in semiconductor optical amplifier, and are then distributed to the BSs along with the downlink RoF signals. By down-converting the 60-GHz-band uplink signal with the remotely produced 60-GHz LO signal and reusing the optical LO carriers as the uplink optical source, only a cost-effective intermediate frequency modulator is required at each BS to transmit the uplink signal, which will dramatically reduce the whole system budget due to a large amount of BSs. Moreover, the operating frequency of each BS can be controlled remotely at the CS end to realize centralized management and convenient reconfiguration. Using the proposed scheme, 622-Mb/s signals for both directions are successfully transmitted over a 20-km single-mode fiber link and a 50-cm wireless channel with less than 0.1- and 0.2-dB power penalty for downlink and uplink, respectively.      

一种载边比可调单边带全双工光载无线系统

理论分析了一种基于双平行马赫曾德尔调制器(MZM)的2 倍频光单边带调制方案,仿真研究了基于 该方案的载波重用全双工光载无线(RoF)通信系统性能。合理设置射频驱动信号相移及双平行MZM 主调制器偏置 电压产生单边带信号,再调整调制指数以实现光载边比ROCS 的连续可调谐。讨论了射频信号相移、主调制器偏置电 压、双平行MZM 消光比RE 和调制指数对ROCS 的影响,理论分析与仿真结果较为一致。结果表明经20 km 光纤传输 后,在误码率BER 为10-9 时0 dB 和10. 33 dB 载边比系统的功率代价分别为2.5 dB 和3.4 dB,在背靠背(BtB)传输 中当载边比从10. 33 dB 降低至0 dB 后,接收机灵敏度提高了2.6 dB。     

基于偏振调制器并联产生16倍频毫米波的研究

针对高倍频毫米波的产生问题,文章提出了一种基于4个偏振调制器并联产生16倍频毫米波的方案,利用相关光边带极性的不同,使合成光信号中只保留载波和8n阶边带。经过适当选取调制指数值和光电探测器拍频后,获得16倍频毫米波信号。文章理论分析了产生16倍频毫米波信号的原理,推导出方案所产生的±8阶光边带信号的光边带抑制比为61.72 dB,16倍频毫米波信号的射频杂散抑制比为55.70 dB。仿真实验获得的光边带抑制比和射频杂散抑制比分别为60和53 dB。同时分析了射频信号相位偏移及调制指数对抑制比的影响。实验结果与理论分析吻合,验证了所提方案的可行性。     

基于FBG和偏振复用的8倍频全双工RoF系统

为简化光载无线通信系统(RoF)中心站(CS)和基站(BS)结构,提出了一种基于光纤布拉格光栅(FBG)和偏振复用技术的8倍频全双工RoF系统方案。通过设置马赫-曾德尔调制器(MZM)偏置电压和射频驱动信号幅度保留部分主载波与偶数阶边带,再利用FBG将主载波与偶数阶边带分离。结合偏振复用技术将主载波和偶数阶边带复用到X和Y两个偏振方向上,其中抑制载波偶数阶边带用于下行链路数据传输,而主载波在BS站作为上行链路载波使用。理论推导了实现机理并进行了实验验证,结果表明当使用10 GHz射频驱动时可实现稳定的80 GHz光载毫米波信号,传输20 km后下行链路和上行链路功率代价仅为0.1和0.07 dB,表现出了较好的系统性能。     

一种克服色度色散影响的四倍频光毫米波信号产生方法

提出一种克服色度色散影响的四倍频光毫米波信号产生方法。该方法使用一个双驱动马赫曾德尔调制器,通过调整上、下两路射频信号的相位差、直流偏置点、调制系数以及基带信号增益,将数据信号仅调制到四倍频光毫米波信号的一个2阶边带上传输,解决了色度色散引起的码元走离问题,有效增加了传输距离。理论分析和仿真实验结果表明,信号在光纤中传输120 km后眼图仍然十分清晰,经过60 km传输后的功率代价约为0.45 dB。另外,基于频率再用技术,没有调制数据的另一个2阶边带信号还可以作为全双工光纤无线通信(RoF)系统的上行链路光载波,简化了基站配置。仿真实验结果表明,双向2.5 Gbit/s数据信号在光纤中传输40 km后,功率代价小于0.6 dB。     

载波重用微波光纤矢量信号传输系统性能研究

提出了一种基于双边带(DSB)部分载波抑制调制(OCS)方式的微波光纤传输(ROF)系统结构,实现了矢量信号的传输以及调制方式由8PSK到QPSK的转换,并使用光纤Bragg光栅(FBG)实现了光载波的重新使用,降低了系统的成本。分析了实验原理并搭建了实验链路,在中心站,采用光OCS方案产生并倍频加载了携带有1 Mbps的8PSK矢量信号的5 GHz微波信号,实验结果表明,在基站,使用FBG实现光载波重用的同时,微波信号频率由5 GHz上转换为10 GHz,传输的矢量信号调制方式由8PSK变为QPSK。通过光谱可以看出,实验链路成功实现了50 GHz nm波矢量信号的产生和传输。     

基于啁啾光纤布拉格光栅的宽谱光单边带调制方法

提出一种基于啁啾光纤布拉格光栅(CFBG)的宽谱光单边带(OSSB)调制实现方法。光双边带(ODSB)调制信号经过同一CFBG两个相反方向的反射,利用偏振控制器(PC)实现两个方向偏振态的正交。这种双反射CFBG(DR-CFBG)结构可以滤出光载波与其中一个边带实现OSSB调制,同时消除了反射谱内的色散,避免了滤波引起的相位畸变。利用实验制作的线性CFBG搭建了DR-CFBG,实验数据仿真结果表明,本文方法可以实现宽谱基带信号与加载数据信息射频信号的OSSB调制,结果表明传输距离大于6km时,40Gb/s NRZ信号OSSB调制传输有明显优势;加载2.5Gb/s的NRZ信号,OSSB调制传输50km,误码率为10-9时,20GHz射频为载波的功率代价比10GHz低3dB,比40GHz低1.2dB。改进CFBG的边沿斜率可以更好地抑制边带残留,提高OSSB调制信号的传输性能。     

一种改进的载波抑制调制光毫米波信号的产生方案

为了克服光纤无线(ROF)系统中色散对光载波抑制(OCS)调制光毫米波信号传输的影响,提出一种改进的OCS调制方案。使用双驱动马赫-曾德尔调制器(MZM),通过调整两路输入射频信号相位、基带信号增益和直流偏置电压将2.5Gbit/s数据信号仅调制到(OCS)信号的一个边带上传输。理论分析表明,与传统OCS调制光毫米波信号产生方案相比,本文方案解决了色度色散引起的码元走离问题,大大增加了传输距离。仿真实验结果表明,经过110km光纤传输后信号的眼图仍然十分清晰,在BER=10-10条件下,信号经过20、40和60km光纤传输后的功率代价分别为0.78、1.7和1.9dB。     

基于多频相位调制的光学单边带调制器研究

提出了一种基于多频相位调制技术实现光学单边 带调制信号产生的新型方案。当含有基频和谐波成分的多频调制信号施加到Mach-Zehnder( MZ)电光调制器上时,若驱动信号波 形选取合适,可使调制后的光信号功率集中在边带谱的一个频率成分上,其它频率成分被抑 制, 从而获得光学单边带调制信号的输出。以十频相位调制为例,计算了与之对应的光学单边带 调 制信号的光谱结构,其中信号能量利用率近88%,载波抑制比大于24dB,边频抑制比大于18 d B, 从理论上证明了本文所述方案的可行性。进一步的仿真结果显示,随着驱动信号谐波数的增 加, 载波抑制比、边频抑制比和信号能量利用率均逐渐增大。可见,为了获得优质的光学单边带 调 制信号,应在实际条件允许的情况下使用尽可能多的调制频率。此方案能量利用率相对较高 , 仅用到了一级商用MZ相位调制器,方案结构简单,是一种产生光学单边带调制信号的有效途 径。     

光载射频信号在多模塑料光纤中的传输特性研究

实验研究了光载射频信号在多模塑料光纤(POF)中的传输特性,将24GHz的正弦波信号与1.5Gbt/s的数字信号进行混频后再通过光强度调制器产生双边带调制光信号,将双边带调制信号通过多模POF发送至接收机,在接收机转化为24GHz的射频信号。实验结果表明,这种双边带调制的光载波射频信号可以在多模POF中传输50m后而功率代价可以忽略不计。     

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。     

Optical Fiber Polarization Interferometer for Performance Improvement in Radio-Over-Fiber Systems

An extinction ratio tunable optical fiber polarization interferometer (OFPI) is proposed and implemented to increase the optical modulation depth in radio-over-fiber (RoF) systems by suppressing the optical carrier power. The extinction ratio of the OFPI can be simply tuned by adjusting the polarization state of the launched RoF signal. Experimental results illustrate that the receiver sensitivity and dynamic range of RoF systems are greatly improved using the proposed scheme.     

Multisideband Detection Radio-Over-Fiber Link With Phase Modulation and Fiber Demodulation for Vector Signal Transmission

We propose and demonstrate a multisideband detection (MSD) radio-over-fiber (RoF) link with optical phase modulation (PM) and fiber demodulation to transmit vector signals. In the scheme, the optical PM signal is demodulated by the fiber dispersion. The fading effect can be almost entirely overcome thanks to the MSD. In case of 50-Msymbols/s vector signal with frequencies of subcarrier ranging from 2 to 12 GHz over 25-, 50-, and 100-km single-mode fibers, respectively, the RoF-link's error vector magnitude of better than 4.5% and spurious-free dynamic range of more than 97 ${hbox {dB}}cdot hbox{Hz}^{2/3}$ are obtained experimentally.      

基于光偏振调制器产生亚毫米波的研究

亚毫米波源是亚毫米波应用的最重要的器件之一,电域中产生亚毫米波信号的成本十分昂贵.光生亚毫米波信号可极大地降低成本,是目前国内外研究的热点课题.提出了一种采用两组并行光偏振调制器级联产生32倍频亚毫米波的方案,首先用两个由4个偏振调制器并联构成的子系统级联产生主要保留载波和±16阶边带的光信号,同时利用光移相器和光分束器抑制载波,最后通过合成光信号在光电探测器上的拍频,获得32倍频亚毫米波信号.理论分析了产生32倍频亚毫米波信号的原理,推导出±16阶边带信号的光边带抑制比为55.7 dB,32倍频亚毫米波信号的射频杂散抑制比为43.7 dB.采用光子模拟软件,设计了一个基于上述原理产生32倍频亚毫米波的系统,获得了光边带抑制比为54 dB,射频杂散抑制比为43 dB,与理论分析吻合.同时分析了相移量、调制指数和分光比偏离对抑制比的影响.