一种自适应调制方案

阐述一种星座图可调的自适应调制方案，并在Beyond ITM-2000的相关参数下进行了性能仿真。该方案能克服移动无线信道时变衰落特性对传输性能的影响，在信道的传输质量满足一定误码率要求的前提下，根据无线信道衰落情况，使调制方式在四相移相键控调制（Quaternary Phase Shift Keying，QPSK）、正交幅度调制（Quadrature Amplitude Modulation，QAM）包括8QAM，16QAM，32QAM，64QAM，128QAM，256QAM之间自如切换。仿真结果表明，该系统方案可以有效地适应无线信道的时变衰落，不但能增加系统平均吞吐量，而且能提高频谱利用率。     

用于可见光通信的CAP-ADPPM混合调制系统设计

为提高可见光通信链路传输性能,提出一种无载波幅度相位(CAP)和幅度差分脉位调制(ADPPM)混合的调制系统.该系统通过将频谱高效的多维CAP调制与功率高效的ADPPM相结合,利用ADPPM的时隙脉冲搭载CAP信号进行信息传输;在高斯白噪声信道模型下,推导了 CAP-ADPPM混合调制系统的误帧率解析表达式并进行了仿真...     

RoFSO系统QAM调制解调仿真及其性能分析

由于自由空间光通信（FSO）具有速率高、功耗低、机动性强等特点,利用自由空间光信道传输射频信号（Radio Over FSO）,将其与正交幅度调制（QAM）相结合,可以使二者互相补充,发挥各自的优势。本文论述了自由空间光通信中正交幅度调制（QAM）的原理和特性,并进行了QAM调制和解调的matlab仿真。通过对得到的仿真结果进行比较和分析,研究了QAM信号的解调性能,分析计算了QAM信号相干解调的误比特率（BER）、误码率（SER）和信道容量。为Radio Over FSO系统的实现奠定了理论基础。     

一种频谱高效的可见光混合调制方案

为提高室内可见光通信系统传输性能，提出一种基于广义空间调制技术（GSM）的无载波幅度相位（CAP）-数字脉冲间隔调制（DPIM）混合方案。该方案基于空-时域联合思想，在信号域内将CAP信号加载到DPIM时隙脉冲上构建混合调制信号，在光空域内通过GSM技术同时激活多根天线进行信息传输。推导了可见光高斯信道下GSM-CAP-DPIM混合系统的误帧率理论表达式，仿真验证了解析式的准确性，探究了不同空时域参数选择对系统误帧性能的影响。实验结果表明：频谱效率相同时，GSM-CAP-DPIM混合系统的可靠性优于传统混合调制系统。     

可见光CAP-OFDM传输方案

针对室内高速可见光链路设计,提出了一种频谱高效的基于无载波幅度相位调制（CAP）的可见光正交频分复用（OFDM）传输方案,即CAP-OFDM。该方案首先采用一对相互正交的滤波器产生基带实信号,再利用哈特莱（Hartley）变换将其加载到频域正交的载波上,并通过添加直流偏置的方式实现信号单极化。基于朗伯(Lambert)辐射模型,推导了CAP-OFDM以及已有文献提出的基于脉冲振幅调制（PAM）的可见光正交频分复用（PAM-OFDM）、基于正交振幅调制（QAM）的可见光正交频分复用（QAM-OFDM）调制方案的误符号率理论解析式、频带利用率,并通过仿真实验验证了理论推导的正确性。仿真结果表明,调制阶数相同时,CAP-OFDM、QAM-OFDM误码性能相同,且优于PAM-OFDM;频带利用率相同时,CAP-OFDM误码性能最优,而QAM-OFDM最差。     

适用于高阶QAM解调的载波恢复算法及其实现验证

高阶正交幅度调制（QAM）系统中,随着QAM信号阶数的提高,频偏和相偏对系统解调性能的影响越敏感,其对同步性能的要求也越来越高。因此,必须在接收端对系统中的频偏和相偏进行更精确的补偿,使得接收端与发送端的载波信号达到同频同相,来提高解调系统的性能。本文首先简单介绍了两种常用两种面向判决的载波相位恢复算法,并利用MATLAB／Simulink为该算法搭建了系统仿真模型进行分析,然后给出了具体的实现方法并对其性能进行了分析。仿真结果表明,面向判决的载波恢复算法实现简单,稳态时抖动较小,非常适用于高阶QAM解调系统。     

CAP-DPIM可见光混合调制方案

针对可见光通信系统传输性能问题,文章提出了一种无载波幅度相位(CAP)调制与数字脉冲间隔调制(DPIM)结合的混合调制方案。该方案分别利用两者频谱效率和功率效率较高的特点,发送端在脉冲间隔调制的脉冲时隙加载直流偏置光CAP(DCO-CAP)信号,实现混合调制信号的并行生成,接收端通过门限检测和最大似然检测完成混合调制信号的串行解调。推导了室内可见光高斯信道下混合调制方案的误码率(BER)及误帧率(FER)解析表达式。此外,从频谱效率和FER两方面对比分析了该混合调制方案与传统DPIM及DCO-CAP方案的性能优劣。数值仿真结果表明:当频谱效率相同时,混合调制方案较单一调制有更高的可靠性。     

16APSK-OOFDM系统分析研究

基于Optisystem和Matlab软件构建相干解调光正交频分复用(CO-OFDM)系统仿真平台。从O-OFDM的调制出发,在Optisystem中用幅度相位键控(APSK)调制代替现在主流使用的方形正交振幅调制(QAM)。分析APSK调制在光通信中的优越性,并将得到的仿真星座图、误码率、线宽与QAM调制下的结果相互对比,从而区分APSK调制比QAM调制优越性并总结规律。     

VDSL线路编码技术-DMT还是CAP/QAM?

到底哪种线路编码技术-DMT（离散多音）还是CAP（无载波幅度和相位调制）/QAM（正交幅度调制）更适合于VDSL（甚高速率数字用户线路）呢?有关这一问题的争论已存在多年了。有些人认为虽然国际标准团体在ADSL（非对称DSL）技术中选择了DMT,但对VDSL而言,CAP/QAM更为合适。 确实,VDSL和ADSL面临不同的线路编码问题。然而,对实际线路状况和其他实际问题的工程分析却表明,DMT适用于VDSL的理由比在ADSL中还要充足。     

PDM-16QAM系统中几种相位估计算法的性能与复杂度比较以及改进

在偏分复用的高速相干光通信系统中,16进制正交幅度调制(PDM-16QAM)是最有前景的调制格式,且载波相位估计是补偿发射端与接收端激光器对信号造成的相位失真的重要技术。该领域最经常使用的算法为QPSK分区算法与盲相位搜索算法,但他们都有自己的缺点,如估计效果不够好,适用范围不够广,或者计算复杂度过高。本论文实验搭建了224Gb/s PDM-16QAM波分复用传输640km相干检测系统平台,首先利用几种基于前述两种算法的相位估计方法对接收到的信号进行了数据处理,分别给出了误码率曲线图、误差向量幅度曲线图、计算复杂度分析表。然后基于性能最优与计算复杂度的平衡,提出了针对16QAM信号星座图中间圈的点的省略两级处理算法。将该改进的算法用于实验系统相位估计单元进行数据处理,结果表明,改进的算法P1,3/ML其误码率性能和误差向量幅度性能基本保持不变,但是计算复杂度降低为原来的1/2。     

Coherent optical communication systems based on orthogonal frequency division multiplexing

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is considered as a key solution for long haul optical fiber communication systems thanks to its high spectral efficiency and robustness against chromatic dispersion. We have investigated a CO-OFDM based on quadrature phase shift keying (QPSK)-OFDM and 16 quadrature amplitude modulation (16QAM)-OFDM over 500 km uncompensated fiber links. The simulation results show that the proposed system is a promising solution to meet the aggregate data rate demands cost effectively in future high-speed optical communication systems.     

基于异步幅度抽样的高速光信号色散监测方法

针对目前异步幅度统计直方图（AAH）对色散监测范围小、灵敏度低的缺点,提出一种基于异步幅度抽样（AAS）的色散监测方法,定义无量纲色散监测参数G,将色散与其他损伤因子分离开。使用 OptiSystem9.0 软件搭建了200Gbps DP-16QAM 监测系统,在不同信噪比和占空比下进行色散监测仿真实验,探讨了信噪比和占空比对该方法的监测精度的影响,并对色散监测误差进行了分析。仿真结果表明基于该参数的色散监测方法受噪声因子影响小、精确度高,能实现在0~600 ps/nm 全范围内对色散的有效监测,为在更高阶调制信号的光纤通信系统中进行色散监测管理提供一定的参考。     

不同调制格式对400 Gb/s通信系统传输容量和距离的影响

单载波400 Gb/s传输是下一代通信系统的主要应用速率,为提高此速率通信在实际工程应用中的传输效率,理论分析了高速通信系统中不同调制方式与传输谱宽的关系,基于16阶正交幅度调制(16QAM)、16QAM/32QAM混传、32QAM、32QAM/64QAM混传和64QAM 5种不同调制格式,对400 Gb/s传输系统的单波入纤功率、传输容量和传输距离进行了实验研究,实验结果表明调制格式混传模式和单传模式对系统传输容量和传输距离存在着明显的差异。     

Recursive carrier phase tracking for synchronous multilevel 4QAMreceivers

Four-quadrature amplitude modulation (4QAM) allows high spectral efficiency in coherent optical data transmission by exploiting the two phases and the two polarizations of the propagating wave. In this paper the performance of 4QAM is analyzed in the presence of laser phase noise and photodetection noise. A decision feedback phase tracking scheme based on the Kalman filter and leading to a novel hybrid PLL structure is employed and its accuracy evaluated. The computational complexity of the proposed phase estimator is also discussed. The performance of the resulting 4QAM system is evaluated in terms of bit error probability versus the signal-to-noise ratio E_b/N₀, for different ratios of the symbol rate R_s over the laser linewidth B_L     

1-Gsymbol/s 64-QAM Coherent Optical Transmission Over 150 km

Quadrature amplitude modulation (QAM) is an excellent modulation format for realizing optical communication systems with a high spectral efficiency of much greater than 1bit/s/Hz. We describe QAM coherent optical communication that we achieved by using heterodyne detection with a frequency-stabilized fiber laser and an optical phase-locked loop (OPLL) technique. The phase error variance of the intermediate frequency signal of the OPLL was 6.1times10^-3 rad. A 1-Gsymbol/s 64-QAM coherent signal was successfully transmitted over 150km     

Blind equalization algorithms for dual-mode CAP-QAM reception

We propose a dual-mode receiver capable of blindly demodulating both carrierless amplitude modulation/phase modulation (CAP) and quadrature amplitude modulation (QAM) line codes. Our work is motivated by some emerging broad-band access standards which require a receiver that can first blindly start up, then blindly distinguish between CAP and QAM, and finally decode the signal. The “brute force” solution to this problem would be to implement CAP and QAM receivers in parallel. However, we propose a single novel receiver based on a single equalizer that accommodates both line codes, yielding significant computational savings. We describe the receiver architecture, blind start-up methods, and line code identification algorithms, as well as computer simulations and a laboratory experiment to verify the theoretical receiver behavior     

ADS在16QAM通信系统中的应用

介绍了16QAM通信系统的概念、工作原理以及利用ADS软件建立通信系统模型的方法,并进行了系统分析。在ADS中,对调制信号的表示方法、脉冲形成、通道滤波、频谱分析——数值频谱和频率频谱、客户化调制等技术进行了仿真,实现了通信系统的模拟。     

Phase Noise Effects on High Spectral Efficiency Coherent Optical OFDM Transmission

There are three major advantages for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) transmission using digital signal processing. First, coherent detection is realized by digital phase estimation without the need for optical phase-locked loop. Second, OFDM modulation and demodulation are realized by the well-established computation-efficient fast Fourier transform (FFT) and inverse FFT. Third, adaptive data rates can be supported as different quadrature amplitude modulation (QAM) constellations are software-defined, without any hardware change in transmitter and receiver. However, it is well-known that coherent detection, OFDM, and QAM are all susceptible to phase noise. In this paper, theoretical, numerical, and experimental investigations are carried out for phase noise effects on high spectral efficiency CO-OFDM transmission. A transmission model in the presence of phase noise is presented. By using simulation, the bit error rate floors from finite laser linewidth are presented for CO-OFDM systems with high-order QAM constellations. In the experiments, the phase noise effects from both laser linewidth and nonlinear fiber transmission are investigated. The fiber nonlinearity mitigation based on receiver digital signal processing is also discussed.     

Envelope-Derived Timing Recovery in QAM and SQAM Systems

The problem of continuously recovering timing phase and frequency in a high-rate carrier-modulated data communication device is addressed. The communication link is assumed narrowband with respect to the baud rate of the device, thus necessitating the use of some type of equalization in the receiver. The receiver demodulator is assumed coherent in nature. A timing recovery technique based on narrow-band filtering and squaring of the received demodulated waveform(s) is examined. Analysis of the first moment of the waveforms so generated reveals a convenient indicator of sampling instants. If the timing recovery filters are properly designed, then these sampling instants exactly satisfy a requirement previously derived, ensuring efficient operation of the equalizer. Design criteria for the filters are given. Two principal types of linear modulation techniques are considered. These are quardrature-carrier amplitude modulation (QAM) and staggered QAM (SQAM). A set of experimental waveforms observed in a QAM modem signaling at 2400 Bd is included for illustration. Several conclusions are drawn as a result of the study. First, the mean timing waveforms in QAM and SQAM systems bear fixed time relationships to suitable receiver sampling instants. Second, adequate timing filter design is attained with very narrowband filters centered on frequencies equal to half the baud rate and the full baud rate. Third, recovery circuits used in QAM systems may be designed so as to have negligible timing jitter. In SQAM systems and, consequently, in vestigial sideband-amplitude modulation (VSB-AM) systems, this advantage is generally not found.