共查询到19条相似文献,搜索用时 140 毫秒
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介绍了星形16-QAM高速光信号不同生成方案的结构和原理,并对几种方案的优缺点进行了对比分析.提出了一种基于双电极驱动马赫-曾德尔调制器(Dual electrical Mach-zehnder modulator,De-MZM)的星形16-QAM生成方案,详细阐述了其结构和工作原理,并对生成信号的星座图进行了仿真. 相似文献
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分析有线数字电视网络的各项指标对网络质量的影响,以及在幅度噪声、相位噪声、相位误差、带内干扰等情况下星座图的表现形式。 相似文献
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在相干光传输系统中,相位噪声是影响系统性能的一个重要因素,研究了16-QAM中基于QPSK分割的相位恢复算法原理,提出了一种加权重的QPSK分割相位估计改进算法。仿真结果表明,在BER=10-3,SNR灵敏度代价为1d B时,改进算法对激光器线宽的容忍度约有38.7%的提升。 相似文献
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研究了QPSK副载波调制下乘性噪声与加性噪声对接收端星座图影响。基于Gamma-Gamma信道模型,分析了乘性噪声和加性噪声影响下系统的接收星座图。通过仿真实验计算了混合噪声情况下的星座图分布以及接收端功率谱密度。讨论了混合噪声条件下,不同能见度、传输距离对系统误码率的影响。结果表明:随着湍流强度的增强,接收端功率谱存在明显的展宽迹象;不同加性噪声条件下,当能见度小于传输距离时,气溶胶粒子散射为影响通信的主要因素。不同乘性噪声条件下,当能见度处于0.5~1.5 km时,乘性噪声会影响接收光强,进一步增大系统误码率。文中工作对真实环境下降低无线激光通信的误码率和提高通信质量有重要意义。 相似文献
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为降低正交频分复用OFDM的峰均比(PAPR)提出了改进的蜂窝扩展星座图的方法。改进的算法采用音调注入技术(TI),在不增加信号功率的约束条件下,动态地向外扩展传输数据的星座点,从而降低OFDM信号的峰均功率比。该方法在接收机端不需要任何的处理过程,而且没有边带信息。改进的蜂窝星座图扩展方法经仿真能够取得的峰均功率比比64-QAM约低4dB,降低效果显著。 相似文献
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大气湍流引起的光强起伏是影响激光通信系统接收信噪比和误码率的主要因素。文中旨在研究大气湍流状态对无线通信系统性能的影响。首先利用对数正态分布和Gamma-Gamma分布分别对信道进行建模,分析表明前者不适用于中强湍流下的光强起伏行为,而后者具有更广的应用范围。在此基础上,研究相位噪声对系统接收信噪比和误码率的影响。文中最后在不同信道条件下进行仿真实验,观察光强起伏方差引起的星座图变化和误码率恶化情况。实验结果表明,当光强起伏方差逐渐增大时,星座图相位角度和误码率均随之变大。文中的分析与讨论对提高激光通信质量具有一定的参考价值。 相似文献
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The true Cramer-Rao lower bound (CRLB) is derived and evaluated for the estimation of carrier phase of Star 16-quadrature amplitude modulation (QAM) and can be simply applied to carrier frequency estimation. Different geometries are investigated by varying the ring ratio (RR). For signal-to-noise ratios (SNRs) between 6-15 dB, the CRLB with RR=3 is lower than that of Square 16-QAM. A modified phase estimator is presented, which closely follows the new CRLB. Investigation of symbol error performance in short packet length reveals Star 16-QAM to be superior to Square 16-QAM for SNR<13 dB, which is a reasonable operating range for a coded system. Although Square 16-QAM and Star RR=1.8 are optimum for a perfect receiver, when the effect of phase estimation is considered, we find Star RR=3 to be better for SNR below 10 dB. 相似文献
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《Lightwave Technology, Journal of》2005,23(12):4110-4124
We investigate carrier synchronization for coherent detection of optical signals encoding 3 and 4 bits/symbol. We consider the effects of laser phase noise and of additive white Gaussian noise (AWGN), which can arise from local oscillator (LO) shot noise or LO-spontaneous beat noise. We identify 8- and 16-ary quadrature amplitude modulation (QAM) schemes that perform well when the receiver phase-locked loop (PLL) tracks the instantaneous signal phase with moderate phase error. We propose implementations of 8- and 16-QAM transmitters using Mach-Zehnder (MZ) modulators. We outline a numerical method for computing the bit error rate (BER) of 8- and 16-QAM in the presence of AWGN and phase error. It is found that these schemes can tolerate phase-error standard deviations of 2.48/spl deg/ and 1.24/spl deg/, respectively, for a power penalty of 0.5 dB at a BER of 10/sup -9/. We propose a suitable PLL design and analyze its performance, taking account of laser phase noise, AWGN, and propagation delay within the PLL. Our analysis shows that the phase error depends on the constellation penalty, which is the mean power of constellation symbols times the mean inverse power. We establish a procedure for finding the optimal PLL natural frequency, and determine tolerable laser linewidths and PLL propagation delays. For zero propagation delay, 8- and 16-QAM can tolerate linewidth-to-bit-rate ratios of 1.8/spl times/10/sup -5/ and 1.4/spl times/10/sup -6/, respectively, assuming a total penalty of 1.0 dB. 相似文献
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By using a double-sideband suppressed carrier (DSB-SC) optical transmitter and a remote self-heterodyned (RSH) detection method, we experimentally and analytically proved the feasibility of a radio-over-fiber system using a 16-QAM signal at 5 Gb/s and 18 GHz, with a transmission distance of 100 km between a mobile service center and a base station. The transmission system performance was carefully analyzed by considering optical amplifier noise, fiber nonlinearity, phase noise, frequency response, and analog-to-digital converter (ADC) quantization noise. The 18-GHz, 16-QAM signal can be radiated from the base station to a remote antenna port without any upconverter, and the remote antenna port consists of a downconverter and high-speed digital signal processors (DSPs) to recover the 16-QAM signal. The high-speed DSP, which partially compensates the intersymbol-interference (ISI) and phase-noise-induced system penalties, was enabled by 20-Gs/s ADCs. The algorithms used in the DSP blocks were also described in details. 相似文献
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High spectral efficiency combined with power efficiency, is a requirement for high speed digital broadcast satellite systems. The effect of the recovered carrier phase noise and the nonlinearity on the performance of 16-QAM (quadrature amplitude modulation) and staggered 16-QAM is investigated and compared. It is found that for the phase noise, 16-QAM is more degraded for a roll-off factor of less than 0.4. For roll-off factor of more than 0.8, staggered 16-QAM has superior performance. For the nonlinearity staggered 16-QAM is more sensitive for a roll-off factor of less than 0.4. It is concluded that coincident 16-QAM is suitable for spectrally efficient digital broadcast systems 相似文献
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A millimetre-wave optical upconverter using a semiconductor laser diode and high-speed external optical modulator is described. Upconversion and transmission of 16-QAM and 64-QAM digital subcarriers over a 38 GHz optical fibre-wireless link are demonstrated 相似文献
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《Optical Fiber Technology》2014,20(5):453-460
Optical superchannel employing single-carrier (SC) and multi-carrier (MC) subband modulation techniques have been widely discussed for high-speed coherent optical transmission and networks. In this paper, we establish uniform system design based on frequency-domain equalization (FDE) and carry out a thorough study on orthogonal frequency division multiplexing (OFDM) superchannel versus SC frequency division multiplexing (SCFDM, also named as DFT-spread-OFDM) superchannel. The baseband signal characteristics of SCFDM and OFDM are analyzed. SCFDM and OFDM superchannel systems with 4-, 16-, 64- and 256-QAM formats and polarization division multiplexing (PDM) are numerically investigated against various impairments. The results show that SCFDM superchannel outperforms its MC counterpart against finite DAC&ADC resolution and fiber nonlinearities, while suffers more penalty when very large dispersion or laser phase noise exists. 相似文献
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Vivekanand Jha Shekhar Verma Nupur Prakash Garima Gupta 《Wireless Personal Communications》2018,101(1):325-337
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. 相似文献