BPSK‒QPSK和QPSK‒16QAM的光调制格式转换

信号在调制方式不同的系统之间传输时,需要对信号调制格式进行转换,而调制格式转换通常在电信号上进行,要将光信号恢复成电信号。在电信号上进行调制格式转换后,再经电光调制器变换成光信号发射。频繁的光电或电光转换通常会增加系统成本,针对该问题,提出了利用相干叠加在光域上实现二进制相移键控(BPSK)到正交相移键控(QPSK)以及QPSK到正交幅度调制(16QAM)的调制格式转换的方法。实验通过Optisystem软件对转换模型进行仿真,采用10 Gpbs伪随机信号作为测试信源,通过星座图观测出信号成功转换为QPSK和16QAM;并在不同光信噪比、光源线宽和信号功率下对转换模型与直接QPSK、16QAM传输模型进行误码分析对比,在相同条件下转换模型和直接传输的误码率高度保持一致,表明这种调制格式转换方法具有较高的稳定性和准确性,能够适用于不同系统间的信号传输。     

用于APSK和QAM信号信噪比估计的改进分段数据拟合算法

为提高幅相键控( APSK)信号和正交调幅( QAM)信号信噪比估计范围和精度,提出了一种改进的信号信噪比估计算法。算法首先计算接收信号平方的均值和绝对值的均值之比,然后根据星座图特征,利用多项式拟合该比值与信噪比的关系。在拟合过程中,对信噪比区间进行分段拟合来提高各段拟合精度,并用蒙特卡洛仿真经验值修正算法的固有偏差,从而得到信噪比的近似无偏估计。仿真结果表明,当信噪比估计区间为-5~20 dB且数据长度合适时,16 APSK和32 APSK信号信噪比估计偏差均值小于0.5 dB,标准差小于2 dB;该算法对16QAM和32QAM信号信噪比估计的标准差小于传统数据拟合算法。该算法运算复杂度较低,便于实时应用和硬件实现,对恒模和非恒模信号均能实现信噪比宽范围精确盲估计。     

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。     

16QAM相干光检测OFDM系统性能研究

利用Optisystem软件结合Matlab,搭建相干检测光正交频分复用(Coherent Optical Orthogonal Frequency Division Multiplexing)系统仿真平台.通过加入训练序列学习出不同频率信号的相位噪声规律并进行补偿,结合传输距离、光源线宽,研究了基于16QAM调制的相干光检测OFDM系统的传输性能.结果表明,16QAM调制下的相干光检测OFDM系统做简单的基于训练的信道估计与均衡处理下,系统误码性能提高了近两个数量级.预示了在高速长距离光纤通信中相干光检测OFDM系统的良好前景.     

基于Systemview的移动通信系统仿真分析

移动通信系统实验设备成本高．结构复杂．受客观环境条件影响大,通过软件仿真可以在理想环境下设计通信系统．且成本低。本文分析了在移动通信系统设计与教学中引入Systemview仿真软件的必要性．通过分析MQAM正交幅度调制的原理．得出MQAM调制与解调的原理框图．并给出基于Systemview平台的仿真电路图及16QAM的仿真结果,并对16QAM仿真星座图进行了分析。     

APSK在基于OFDM的水声通信系统中的应用研究

信道带宽窄,强多途,强噪声干扰一直是水下信息高速、可靠传输的主要障碍,提出了一种适合水声信道的用幅度-相移联合键控调制技术APSK与正交频分复用技术OFDM相结合的高阶调制的传输体制,可有效解决水下无线高速数据传输的带宽效率、功率效率和可靠性问题;介绍了APSK的原理及在基于OFDM的水声通信系统中的应用。计算机仿真结果证明,使用该方案的水声通信系统在高阶调制情况下综合性能优越。     

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。     

一种新的非2的整数幂阶的QAM调制设计

 本文提出了一种新的具有普遍适用性的调制阶数非2的整数幂的正交幅度调制(Quadrature Amplitude Modulation,QAM)设计方法,通过建立特定个连续星座点与特定长度比特序列的映射关系,实现了码速率分辨率更高的QAM调制解调,丰富了自适应调制中QAM的选择,缩小待选QAM调制的性能间隔.本文以28QAM为例说明其设计方法.     

一种抗频偏的卫星幅相调制信号识别算法

该文针对卫星中的常用调制QPSK, 16QAM和新型调制16APSK, 32APSK,提出一种自适应构造幅度分布模板,并通过计算实际信号幅度分布向量与幅度分布模板间的匹配误差来进行调制识别的算法。该方法不需要知晓载噪比,不需要人为确定阈值,且对频偏误差的容忍能力强,适合实际工程应用。仿真表明,在载噪比为9 dB,符号个数为4000时,该算法对4种调制信号的识别率能达到98%以上,证明了其有效性。     

数字电视传输中的关键技术：第四讲旋转不变QAM星座的获得和Offset-QAM

为了进行数字电视传输，必须解决数字调制和数字解调技术。到目前为止，已提出四种数字调制和数字解调技术：①多电平正交幅度调制(QAM)；②多电平残留边带调制(VSB)；③正交频分复用调制(OFDM)；④直接扩频调制。在这里我们就QAM调制进行讨论。     

Performance evaluation of (D)APSK modulated coherent optical OFDM system

Performance of amplitude and phase shift keying (APSK) modulated coherent optical orthogonal frequency division multiplexing (CO-OFDM) with and without differential encoding is investigated. Numerical simulations based on 40 Gbit/s single-channel and 5 ^* 40 Gbit/s wavelength division multiplexing transmission are performed, and the impacts of amplified spontaneous emission noise, laser linewidth, chromatic dispersion, and fiber nonlinearity on the system performance are analyzed. The results show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, although 16(D)APSK modulated optical OFDM signal has a lower tolerance towards amplified spontaneous emission (ASE) noise, it has a higher tolerance towards fiber nonlinearity such as self-phase modulation (SPM) and cross-phase modulation (XPM): the optimal launch power and the corresponding Q² factor of 16(D)APSK modulated OFDM signal are respectively 2 dB and 0.5 dB higher than 16QAM modulated optical OFDM signal after 640 km transmission, both in single-channel and WDM CO-OFDM systems. Although the accumulated CD decreases the peak-to-average power ratio (PAPR) during transmission, 16(D)APSK modulated OFDM signal will still remain an advantage compared with 16QAM modulated OFDM signal up to 1000 km single-channel transmission, meanwhile relaxing the needs for training symbols and pilot subcarriers and consequently increase the spectral efficiency.     

光OFDM在接入网中的应用及仿真分析

正交频分复用(OFDM)频谱利用率高、抗干扰性强、能够有效对抗单模光纤偏振模色散,在高速光通信系统中有很好的应用前景.利用Matlab和Optisystem,对强度调制(IM)/直接检测(DD)的单模光纤系统进行了性能仿真,结果显示在不进行色散补偿和光放大的前提下能够传输40km,满足接入网的要求.     

Study of 16 Tbit/s WDM transmission system derived from the CO-OFDM with PDM 16-QAM

In this paper,a wavelength division multiplexing (WDM) transmission system derived from the coherent optical orthogonal frequency division multiplexing (CO-OFDM) with polarization division multiplexing (PDM) and 16-order quadrature amplitude modulation (QAM) is studied. A simulation of 80-channel WDM transmission system with data rate of 200 Gbit/s is built, and the transmission performance of the system is analyzed. The simulation results show that the system Q value of the WDM channels at 16 Tbit/s with a spectral efficiency of 7.14 bit/s/Hz is potentially over 10.0 dB for a long haul transmission up to 1800 km in a standard single-mode fiber.     

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.     

基于雪崩二极管的光正交频分复用系统接收机

提出了一个完整的高灵敏度光正交频分复用(OOFDM)系统,以实现高速长距离传输。实验中,将10Gbit/s的4QAM调制OOFDM信号在光纤中传输了50km,直接探测后得到的星座图和误码率都达到了良好的效果。在此基础上,对比了采用雪崩二极管(APD)和传统的光电二极管(PIN)两种不同的探测方式,结果发现,使用APD探测使得OOFDM系统接收的灵敏度提升了5.2dB。     

Comparison of Laguerre-Gaussian and Donut modes for MDM-WDM in OFDM-Ro-FSO transmission system

Radio-over-free-space-optics (Ro-FSO) technology may pave the way towards a ubiquitous platform for seamless integration of radio and optical networks without expensive optical fiber cabling. In this paper, to increase the capacity of Ro-FSO, mode division multiplexing (MDM) of two modes has been capitalized in a three-channel WDM system spaced by 1 nm over a FSO link of 80 km, resulting in a 120 Gbps six-channel Ro-FSO system. The SNR and received power of MDM of two Laguerre-Gaussian modes LG00 and LG01 is compared with respect to MDM of two transverse donut modes. The performance of four-level quadrature amplitude modulation (QAM) for orthogonal frequency division multiplexing (OFDM) of radio subcarriers in the WDM-MDMs system is investigated for mitigation of frequency-selective fading under strong atmospheric turbulence.     

Colorless ONU implementation for WDM-PON using direct-detection optical OFDM

A novel architecture for the colorless optical network unit (ONU) is proposed and experimentally demonstrated with direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM). In this architecture, polarization-division multiplexing is used to reduce the cost at ONU. In optical line terminal (OLT), quadrature amplitude modulation (QAM) intensity-modulated OFDM signal with x-polarization at 10 Gbit/s is transmitted as downstream. At each ONU, the optical OFDM signal is demodulated with direct detection, and y-polarization signal is modulated for upstream on-off keying (OOK) data at 5 Gbit/s. Simulation results show that the power penalty is negligible for both optical OFDM downstream and the on-off keying upstream signals after over 50 km single-mode fiber (SMF) transmission.     

Corona Based Optimal Node Deployment Distribution in Wireless Sensor Networks

This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.     

2.5Gb/s FSO-OFDM系统调制方式研究

OFDM是一种能有效抵御大气散射效应的调制技术,提出了一种实现FSO-OFDM传输的系统方案。对速率为2.5Gb/s的FSO-OFDM系统在不同的天气条件下进行了仿真研究。仿真分析了不同的调制方式和不同的子载波数时FSO-OFDM系统的误码率和光信噪比。仿真结果表明,与采用16PSK调制方式相比,采用16QAM方式系统将具有更低的误码率和更高的Q值。     

A full-duplex optical access system with hybrid 64/16/ 4QAM-OFDM downlink

A full-duplex optical passive access scheme is proposed and verified by simulation, in which hybrid 64/16/4-quadrature amplitude modulation (64/16/4QAM) orthogonal frequency division multiplexing (OFDM) optical signal is for downstream transmission and non-return-to-zero (NRZ) optical signal is for upstream transmission. In view of the transmitting and receiving process for downlink optical signal, in-phase/quadrature-phase (I/Q) modulation based on Mach-Zehnder modulator (MZM) and homodyne coherent detection technology are employed, respectively. The simulation results show that the bit error ratio (BER) less than hardware decision forward error correction (HD-FEC) threshold is successfully obtained over transmission path with 20-km-long standard single mode fiber (SSMF) for hybrid downlink modulation OFDM optical signal. In addition, by dividing the system bandwidth into several sub-channels consisting of some continuous subcarriers, it is convenient for users to select different channels depending on requirements of communication.