Degradation of bit-error rate in coherent optical communications due to spectral spread of the transmitter and the local oscillator

In coherent optical communication schemes, the FM noises of the transmitter and/or the local oscillator seriously deteriorate the receiver sensitivity. A theory is developed describing the effect of the FM noise on the bit-error rate (BER) performance of various heterodyne and homodyne schemes. To verify the theory, the BER of a phase-shift keying (PSK) heterodyne system is measured. The feasibility of the PSK scheme using semiconductor lasers is also discussed on the basis of analysis and experimentation.     

Impact of finite frequency deviation on the performance ofdual-filter heterodyne FSK lightwave systems

A detailed theoretical analysis is given of the impact of finite frequency deviation on the sensitivity of dual-filter heterodyne frequency-shift-keying (FSK) lightwave systems. The analysis provides closed-form signal-to-noise ratio (SNR) results for estimating the bit-error-ratio (BER) performance of the system. These closed-form results provide an insight into the impact of finite frequency deviation 2Δf_d, laser linewidth Δν, bit rate R_b, and IF filter bandwidths on the system performance. Simulation results indicate that the accuracy of the approximate theory presented is within 1 dB for linewidths up to 22% when BER=10^-9. It is shown that there is a well-defined relationship between the choice of frequency deviation and the tolerable amount of laser phase noise. The sensitivity degradation can be very severe for a fixed linewidth as the frequency deviation gets smaller     

Impact of spontaneous emission noise on the sensitivity of direct-detection lightwave receivers using optical amplifiers

A simple technique for analysing the sensitivity and bit-error rate performance of direct-detection lightwave receivers using optical amplifiers is presented. The analysis provides closed-form expressions for the system performance. For zero (negligible) linewidth, the theory predicts an average signal energy of 42.3 photon/bit at BER=10/sup -9/. In comparison, more accurate techniques predict an average signal energy of 38 photon/bit under the same conditions.<>     

Sensitivity of direct-detection lightwave receivers using opticalpreamplifiers

A simple technique for analyzing the sensitivity and bit-error-rate (BER) performance of direct-detection lightwave receivers using optical preamplifiers is presented. The analysis provides closed-form expressions for the system performance and includes the impact of phase noise. For a negligible linewidth, the theory predicts an average signal energy of 42.3 photons/bit at a BER of 10^-9. For comparison, a more accurate analysis predicts an average signal energy of 38 photons/bit under the same conditions     

Gradient estimation for stochastic optimization of opticalcode-division multiple-access systems .I. Generalized sensitivityanalysis

For optimizing the performance of optical code-division multiple-access (CDMA) systems, there is a need for determining the sensitivity of the bit-error rate (BER) of the system to various system parameters. Asymptotic approximations and bounds, used for system bit-error probabilities, seldom capture the sensitivities of the system performance. We develop single-run gradient estimation methods for such optical CDMA systems using a discrete-event dynamic systems (DEDS) approach. Specifically, computer-aided techniques such as infinitesimal perturbation analysis (IPA) and likelihood ratio (LR) methods are used for analyzing the sensitivity of the average BER to a wide class of system parameters. It is shown that the above formulation is equally applicable to time-encoded and frequency-encoded systems. Further, the estimates derived are unbiased, and also optimality of the variance of these estimates is shown via the theory of common random variates and importance sampling techniques     

Crosstalk degradation caused by optical amplification in amultichannel FSK heterodyne system

The crosstalk degradation caused by an optical amplifier in a four-channel FSK (frequency-shift-keyed) heterodyne communication system is measured. A bit error rate (BER) floor of 3×10^-4 is observed when the channels are spaced by 200 MHz, FSK modulation at 45 Mb/s, and when the optical input signal is large enough such that the gain is compressed by 2 dB relative to its small-signal value. The receiver is substantially improved by reducing the optical power amplifier input. However, the sensitivity increases only to a maximum value beyond which it degrades as the optical power of the demodulated channel becomes small relative to the noise of the optical amplifier. The combined effect of the crosstalk and the amplifier noise yields an optimum sensitivity of 250 photons/b for BER=10^-9. This result is 5 dB poorer than the sensitivity obtained in the absence of an optical amplifier     

Josephson latching driver with a low bit-error rate

A new Josephson latching driver with a current-injection device at an input port has been developed and tested. It has high input sensitivity and a wide bias margin. Under an optimal bias condition, the bit-error rate (BER) of this driver is below 10/sup -12/ at data rates of 5 and 10 Gb/s. The driver can be switched by superconducting single-flux quantum (SFQ) pulse input and can be used as an amplifier to test the BER of SFQ circuits. In such a test, the BER of an SFQ converter operating at 5 Gb/s was less than 10/sup -12/ with bias margin of /spl plusmn/20%.     

Estimation of the Bit Error Rate for Direct-Detected OFDM Signals With Optically Preamplified Receivers

In this paper, we provide a numerical bit error rate (BER) estimation approach for direct-detected orthogonal frequency division multiplexing (OFDM) signals in the presence of optical preamplified receivers. The individual BER of each subcarrier is first computed by considering their electrical signal-to-noise ratio (SNR), and then the ensemble BER is derived simply by taking the average of all the subcarriers' BERs. The calculated BER is verified by the conventional error-counting approach with high precision and is still accurate with higher quadratic-amplitude modulation (QAM) formats, even under the influences of the optical filtering and polarization mode dispersion (PMD) effects. Based on our simulation approach, the required extra power budget for 16- and 64-QAM relative to 4-QAM format are found to be ${sim}$3.8 and 8.2 dB, respectively, at a BER of 10$^{-9}$. Furthermore, we use this approach to compare the receiving sensitivities and PMD tolerances for the previous proposed gapped and interleaved radio-frequency (RF)-tone-assisted OFDM systems. The results show that the gapped OFDM has a better sensitivity while the interleaved OFDM has a more PMD-tolerable capability.      

1 Gb/s operation and bit-error rate studies of FET-SEEDdiode-clamped smart-pixel optical receivers

Experimental studies of the bit-error rate (BER) of diode-clamped optical receivers based on FET-SEED technology are described. 1 Gb/s operation of a receiver with optical input and electrical output is obtained. A strong dependence of the BER on clamping voltage is reported, confirming the digital nature of the receiver. The best receiver sensitivity measured at 1 Gb/s and an error rate of 1×10 ^-9 is roughly -11 dBm. At 622 Mb/s, it is -22 dBm     

Bit-error rate of PSK heterodyne optical communication system and its degradation due to spectral spread of transmitter and local oscillator

In a PSK heterodyne optical communication system, the FM noise of the transmitter and local oscillator degrades the bit-error rate (BER). A theory is presented giving the BER of such a system considering the FM-noise effect. To verify the theory, BER measurement is performed using a simulation model of the PSK heterodyne system.     

Noise Statistics in Fiber Optical Parametric Amplifiers

In this paper, we show both theoretically and experimentally that the probability density function of the intensity of an amplified signal by parametric amplifiers subject to a pump with excess noise is highly asymmetric. This is due to the nonlinear relationship between the optical pump power and the parametric gain. Because of this, the relationship between the noise figure (NF) and the bit error rate (BER) is modified, compared with that predicted by the chi² theory, which is an effect that is notable at large NFs and low BERs. The difference in predicted BER can be of several orders of magnitudes between the correct theory and the chi² approximation in single-stage parametric amplifiers. We also show that in the limit of many cascaded parametric amplifiers, the statistics of the noise of an amplified optical signal approaches chi². Furthermore, the BER of a parametric amplifier is generally lower compared with erbium-doped fiber amplifiers for the same NF values if we assume quantum-limited amplification     

Experimental evaluation of the BER performance in optical OFDM system based on discrete Hartley transform precoding

We experimentally assess the bit error rate （BER） performance of an intensity modulation/direct detection （IM/DD） optical orthogonal frequency division multiplexing （OFDM） system based on discrete Hartley transform （DHT） precoding in single-mode fiber （SMF） link for 2.5 Gbit/s quadrature phase shift keying （QPSK） OFDM symbol rate. The experimental results show that for the optical OFDM system based on DHT-precoding, the receiver sensitivity at the BER of 10-4 after 100 km SMF transmission is about 1.5 dBm better than that of the original QPSK OFDM signal, and the DHT-precoded OFDM QPSK signal can achieve approximately 1.3 dB of peak-to-average power ratio （PAPR） reduction.     

大气闪烁对无线激光通信效能的影响

由于大气湍流的存在,使激光信号在大气传输中产生振幅的随机起伏,称为大气闪烁。大气闪烁将引起激光通信误码率的增加。由光强起伏大小的统计规律和通信基本原理推导出了弱湍流条件下由光强闪烁引起的误码率计算公式,分别建立了地面水平链路和地-空斜向链路中的大气闪烁误码率模型,对模型进行了仿真,分析了湍流强弱、信号调制方式、链路距离、激光波长及地面发射仰角对闪烁误码率的影响,得到了闪烁误码率的变化规律。结果表明,通过合理选择信号调制方式、激光波长、站址位置及地面发射仰角等方式能够有效地降低大气闪烁误码率,提高通信可靠性。     

The Impact of Pulsed RFI on the Coded BER Performance of the Nonlinear Satellite Communication Channel

The coded bit error rate (BER) performance of a satellite communications system, wherein the satellite repeater contains an arbitrary nonlinearity and the system operates in the presence of pulsed radio frequency interference (RFI), is examined. A major result is an analytic method for determining soft decision statistics of the receiver demodulator output in which pulsed RFI effects are accounted for. It is further demonstrated how this result can be analytically applied to the approximate determination of the BER at the output of the Viterbi decoder when convolutional coding is employed. Computed results specialize the nonlinearity to either a hard limiter or clipper, in conjunction with an arbitrarily specified AM/PM characteristic. Performance curves examine BER sensitivity to RFI duty cycle, form of RFI (CW or noise), and various coding/decoding conditions.     

基于压扩变换的直接检测O-OFDM系统的实验研究

仿真研究并实验验证了直接检测光正交频分复用（O-OFDM）系统中引入压扩变换（CT）技术可降低OFDM信号峰值平均功率比（PAPR）和提高接收灵敏度。仿真结果表明,压扩系数μ越大,信号PAPR越低;随着μ的增大,系统误码率（BER）呈现先下降后上升的趋势。权衡PAPR的降低度和系统BER,选择μ=2时为最佳。实验研究表...     

码分多址系统误码性能仿真

通过对直扩系统处理增益分析,得到了直扩系统不比未扩频的匹配滤波器数字调制系统具有更强的抗白噪声功能的结论。利用Matlab软件中的Simulink对码分多址误码性能进行了仿真,得到不同用户数与不同PN码长度的误码率关系曲线和不同信噪比与不同PN码长度的误码率关系曲线。结果表明,在相同用户数和同样噪声的情况下,伪码长度越长,其系统误码率越低,证明了GPS军用导航采用长P码使系统具有抗干扰性能。     

A simplified non-Gaussian approach to digital optical receiverdesign with avalanche photodiodes: experimental

Detailed experimental measurements of various digital receiver parameters taken on a receiver using a low noise silicon avalanche photodiode are compared with simple theories that incorporate Gaussian and non-Gaussian models for the probability distribution functions for the avalanche gain. The authors analyze the salient aspects of the theories, particularly those parameters that give results different from the Gaussian approximation, and those parameters that are readily extracted from the theory (e.g., the influence of background current due either to dark current or to imperfectly extinguished light sources). Experiments were performed in which a receiver was characterized for bit error rate (BER) and optimum gain as the optical power at a modulation rate of 10 Mb/s (NRZ) was varied and as additional background light was allowed to fall on the detector. Excellent agreement with the author's newly developed simplified approximation to the non-Gaussian theory for receiver sensitivity (ibid., vol.9, p.1019-26, Aug. 1991) is obtained     

Performance bounds and cutoff rates of quantum limited OOK withoptical amplification

The bit error probability (BER) and the generalized cutoff rate (GCR) of optically amplified, direct-detection on-off keying (OOK) signaling are addressed utilizing the classical theory of Fredholm integral equations. The approach accounts for the impact of optical bandlimiting and upper bounds on the BER are found via Chernoff techniques, which address the resultant intersymbol interference (ISI) incurred by the linear pulse distortion. Simple rigorous upper bounds on the BER are derived in terms of basic system parameters relaxing the need for solving Fredholm related equations. Random coding is used to obtain the GCR of this channel. The theory is demonstrated for the Lorentzian and finite-duration bandpass optical filters and the optical bandwidth which optimally balances the ISI versus the amplified spontaneous emission noise is found     

2.5Gb/s/ch 0.18μm CMOS数据恢复电路

设计了一个应用于SFI-5接口的2.5Gb/s/ch数据恢复电路.应用一个延迟锁相环,将数据的眼图中心调整为与参考时钟的上升沿对准,因而同步了并行恢复数据,并降低了误码率.采用TSMC标准的0.18μm CMOS工艺制作了一个单通道的2.5Gb/s/ch数据恢复电路,其面积为0.46mm2.输入231-1伪随机序列,恢复出2.5Gb/s数据的均方抖动为3.3ps.在误码率为10-12的条件下,电路的灵敏度小于20mV.