20 channel coherent FSK system using subcarrier multiplexing

A 20-channel multioctave coherent frequency shift keying (FSK) system using subcarrier multiplexing techniques is described. The microwave subcarriers range from 2.1 to 5.9 GHz with a 200-MHz channel spacing. The receiver consists of a p-i-n photodiode, electrical isolator, low-noise amplifier, and bandpass filter to provide channel selection. The channels are modulated at 100 Mb/s, corresponding to one digitized video channel. Results for the optimal phase modulation index and degradation due to second- and third-order intermodulation distortion are discussed. For the worst-case channel, a receiver sensitivity of -27 dBm was achieved     

光纤SCM通信系统中的噪声分析

本文首先分析了光纤SCM通信系统中存在的噪声,然后深入讨论了光检测器的散粒噪声及其与光器件工作参数的关系和对载噪比C/N的影响,结论可作为实际系统设计时的依据。     

Performance evaluation of digital and analogue video distribution systems using coherent subcarrier multiplexing

Compares digital and analogue approaches for broadband distribution of video signals using a coherent subcarrier multiplexed architecture. The analysis shows that FM is most attractive for near-term applications because it offers very good receiver sensitivity and high channel capacity.<>     

本振相位噪声对接收机性能的影响

针对工程中本振相位噪声对接收机的影响常难以估量的问题,提出利用等效相位白噪声谱密度进行评估的方法.通过分析相位噪声的产生及其对剩余误码率和动态范围的影响机理,仿真了不同相位噪声对误码率的影响程度.通过仿真结果可知:相位噪声对接收机性能具有重要的影响,工程中应针对不同的应用场合要求合理的相位噪声指标.     

Theoretical investigation of local oscillator intensity noise inoptical homodyne systems

The degradation of system performance due to the intensity noise from a semiconductor local oscillator laser is theoretically investigated. A statistical model for the optical receiver is presented to calculate the bit error rate and the power penalty resulting from the local oscillator intensity noise. The power penalty depends critically on the noise power, data rate, and spectral characteristics of the noise. Simulation results are given for homodyne systems and compared to the results of Gaussian approximation     

Performance comparison of subcarrier multiplexed coherent systems using optical intensity and phase modulators

The performance of subcarrier multiplexed coherent systems is compared theoretically using optical intensity and phase modulators. The results show that a subcarrier multiplexed coherent system with a symmetrical optical intensity modulator can offer a receiver sensitivity improvement as high as 9.1 dB over that with an optical phase modulator.<>     

空间相干光通信中本振光功率对信噪比的影响

为研究空间相干光通信的信噪比受本振光功率、探测器特性和光波偏振态的影响,对探测器在不同工作状态下以及光波偏振态变化时的信噪比进行了研究,讨论了在不同工作状态下探测器特性参数和本振光功率对信噪比的影响,并通过实验验证了本振光功率和光波偏振态对信噪比的影响。结果证明空间相干光通信中探测器特性参数限制了本振光功率的取值,实际最大信噪比小于理论值,最佳本振光功率大于理论值,且两光束的偏振方向越接近,输出信噪比越大,最佳本振光功率越小。     

Performance improvement of hybrid subcarrier multiplexing optical spectrum code division multiplexing system using spectral direct decoding detection technique

This paper proposes a hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system for the purpose of combining the advantages of both techniques. Optical spectrum code division multiple-access (OSCDMA) is one of the multiplexing techniques that is becoming popular because of the flexibility in the allocation of channels, ability to operate asynchronously, enhanced privacy and increased capacity in bursty nature networks. On the other hand, subcarrier multiplexing (SCM) technique is able to enhance the channel data rate of OSCDMA systems. In this paper, a newly developed detection technique for the OSCDM called spectral direct decoding (SDD) detection technique is compared mathematically with the AND subtraction detection technique. The system utilizes a new unified code construction named KS (Khazani–Syed) code. The results characterizing the bit-error-rate (BER) show that SDD offers a significant improved performance at BER of 10^?9.     

Influence of noise intensity on the spectrum of an oscillator

This paper investigates the influence of high-intensity noise on the correlation spectrum of a two-dimensional (2-D) nonlinear oscillator. An exact analytical solution for the correlation spectrum of this 2-D oscillator is provided. The analytical derivations are well suited for oscillators with white noise of any intensity, but computational constraints on the solution of the partial differential equation may make it impractical for cases where the number of state variables exceeds three. The spectral results predicted by our analytical method are verified by numerical simulations of the noisy oscillator in the time domain. We find that the peak of the oscillator spectrum shifts toward higher frequencies as the noise intensity is increased, as opposed to the fixed oscillation frequency predicted in the existing literature. This phenomenon does not appear to have been reported previously in the context of phase noise in oscillators.     

基于多载波复用多模光纤通信系统的设计与分析

分析了多模光纤高频带通区域的传输特性,提出一种基于多载波复用的多模光纤通信系统.对该系统的传输特性进行了分析和仿真,结果表明:系统所用载波数是影响系统性能的重要因素;选取合适载波数,该系统可将10.2Gb/s的数据传输1km、将2.5Gb/s的数据传输4.2km;增大激光器的发送功率可以显著增加系统的传输距离.     

Effects of phase noise on subcarrier modulation performance over Malaga turbulence channel

The performance of wireless optical system employing subcarrier phase-shift keying modulation was researched,which was influenced by phase noise of system demodulator under on Malaga atmospheric turbulence channel.Combined Fourier series and MeijerG function properties,the probability density function of instantaneous signal to noise ratio in the Malaga turbulence model was got.The Fourier series of receiving signal phase and the closed form expression of symbol error probability were derived,which were in the wireless optical subcarrier shift keying modulation system.Under different modulation order and light intensity fluctuation variance,the influence of phase noise on the system symbol error rate was analyzed.The numeric results present that the system symbol error rate increases with the light intensity fluctuation variance when the phase noise is lower.When the phase noise is larger,the influence of modulation order is greater than of turbulence intensity to the error-rate floor appearing.And with the increasing of modulation order,the corresponding average signal to noise is lower when symbol error-rate floor appears.     

Impact of local oscillator intensity noise and the threshold levelon the performance of a {2×2} and {3×3} phase-diversity ASKreceiver

The impact of local oscillator intensity noise and the threshold level on the performance of the {2×2} and the {3×3} phase-diversity amplitude-shift keying (ASK) receiver has been investigated for the first time for non-Gaussian statistics. Exact equations are derived for the bit-error-rate (BER), taking into account the non-Gaussian statistics and the statistical dependency of the relative intensity noise (RIN) in the receiver branches. The results differ substantially from the case in which a priori Gaussian statistics were assumed. The sensitivity penalty of the receivers is calculated with respect to the performance of an ideal heterodyne ASK receiver for a BER of 10^-9. It is shown that for a minimum sensitivity penalty the threshold level should be chosen in relation to the local oscillator power and the intensity noise level     

Research on the system error performance of coherent orthogonal frequency division multiplexing system with M-distribution in satellite-to-ground laser communication

In order to alleviate the influence of atmospheric turbulence on the performance of satellite-to-ground laser communication system,based on the M-distribution atmospheric channel model,a multi-carrier coherent orthogonal frequency division multiplexing (OFDM) modulation system was proposed for uplink and downlink in the satellite-to-ground laser communication.The closed-form expression of bit error rate (BER) of coherent OFDM modulation system was derived.The relationship between the zenith angle,receiving aperture,signal-to-noise ratio (SNR),optimal beam divergence angle,and optimal transmission radius and the BER were studied under weak,and strong atmosphere turbulence,and compared with binary coherent differential phase shift keying (DPSK) modulation.Both the theory and the simulation results show that compared with coherent DPSK modulation,the bit error performance of the coherent OFDM modulation system in the satellite-to-ground laser communication system is better.     

DSRC系统中微波信号源相位噪声分析

在专用短程通信系统中采用M-PSK调制通信方式,以适应多种速率要求.给出了射频信道模型和微波数字锁相本振信号源的相位噪声模型,分析了微波本振信号源相位噪声的影响,仿真给出了相位噪声功率谱密度与系统误码率之间的关系.利用该结果,有助于无线通信系统的设计.     

The performance of coherent BPSK in the presence of oscillator phase noise for ka-band pico-terminal inbound links

In microwave systems, the phase noise is well known to be a significant source of degradation especially for low data rate transmission, giving rise to a significant irreducible error rate. In an earlier study [1,2] based on the European Space Agency's Olympus Satellite 30/20 GHz payload parameters, it was found that several thousands of simultaneous transmissions of 50 to 200 bits/sec each could be supported from hand-held pico-terminal earth stations. It is important to use the most appropriate modulation scheme in the presence of oscillator phase noise for such low data rate systems. It is generally assumed that noncoherent or differentially coherent modulation schemes will perform best in applications where the coherence time of the oscillators is short compared to the bit period. However, our analysis of these schemes has shown that they are subject to irreducible error rates and minimum useable data rates. This has led us to reconsider coherent BPSK (CPSK). It is shown that the choice of the optimum noise bandwidth of the phase locked loop (PLL) in the carrier recovery circuit is very important when considering the coherent schemes. The PLL bandwidth must be wide enough to track the oscillator phase noise at its input, but, on the other hand, it must be as narrow as possible to exclude the thermal noise. Results show that coherent BPSK in the phase noise contaminated channel is also subject to an irreducible error rate, which increases as the noise bandwidth is reduced. For the optimum loop bandwidth, however, this appears to be lower than the corresponding figure for DPSK [3]. There is a minimum useable data rate for any given bit error rate (BER) requirement. Results of a complete analysis are presented in the form of BER versusE _b/N _o plots.     

Analysis of relative intensity noise in semiconductor lasers andits effect on subcarrier multiplexed lightwave systems

It is found that the presence of the asymmetric nonlinear gain causes the longitudinal modes of a Fabry-Perot laser as well as a nearly single-mode laser to couple such that the low-frequency relative intensity noise is greatly enhanced. For the first time we have included this asymmetric mode coupling to adequately model the translation of the enhanced low-frequency noise to the signal band of a subcarrier multiplexed transmission system in the presence of both modulation and fiber dispersion. This effect, which is crucial in determining the system's signal-to-noise ratio, is also verified experimentally. Theoretical and experimental investigations of system impairment caused by noise translation and fiber dispersion are also performed. Excellent agreement between the theoretical predictions and the experimental results is obtained     

Impact of additive noise on system performance of a digital X-ray imaging system

The impact of additive noise on the performance of a digital X-ray imaging system was investigated. The X-ray system is uniquely designed for small animal studies with a focal spot of 20 microm and an adjustable source-to-object distance for radiography. The noise power spectrum and the detective quantum efficiency of this system were measured. The additive noise increased rapidly when the exposure time exceeded a certain range, since the charge-coupled devices of the detector had no cooling system. The noise power spectrum for the additive noise and the noise of the entire imaging system were studied and compared at different exposure times. The detective quantum efficiency was also measured at different exposure times. It was observed that for exposure times less than 10 s, the detective quantum efficiency ((DQE)(0)) is approximately 0.26, dropping to 0.13 at 4 lp/mm and to 0.026 at 8 lp/mm. However, when the exposure exceeds a certain limit (10 s in this study), the rapidly increased additive noise caused the system to be no longer quantum noise limited, resulting in a decreased detective quantum efficiency and a degraded system performance. For example, at an exposure of 20 s, the DQE(O) is approximately 0.22, dropping to 0.11 at 3 lp/mm and to 0.022 at 8 lp/mm.     

基于ADF4106的低相噪本振设计

为了实现低相噪的本振信号输出,本文设计出一种基于锁相环芯片ADF4106的低相噪本振源.通过实际调试,测试结果满足设计要求,并作为第二点频本振应用于一款通信测试仪器的中.     

Impact of 1/f-type FM noise on coherent optical communications

When a semiconductor laser operates in a high power state, the l/f-type FM noise is a dominant cause of spectral broadening. The degradation of the bit error rate performance of the heterodyne DPSK optical communication system due to such 1/f noise is calculated. The result shows that the 1/f noise is much less harmful than the white noise originated from spontaneous emission events.     

GSM现网底噪对网络性能的影响

随着GSM网络的大力发展,数据业务突飞猛进,网络干扰也越来越复杂,网络质量问题逐渐成了最迫切的问题.本文基于提升网络质量问题为目的,提出了改善无线底噪的若干方案和建议.