The effect of carrier phase jitter on MC-CDMA performance

We investigate the influence of the carrier phase jitter of a phase-locked local oscillator on the performance of a multicarrier code-division multiple-access (MC-CDMA) system in a nondispersive channel. This carrier phase jitter degrades the signal-to-noise ratio at the input of the decision device. When all users have the same power level and phase jitter spectrum, it is shown that for the highest load, the degradation only depends on the jitter variance but not on the specific shape of the jitter spectrum nor on the number of carriers     

The effect of timing jitter on MC-DS-CDMA

In this paper, we consider the effect of timing jitter on the performance of a multicarrier direct-sequence code-division multiple-access system for both uplink and downlink transmission, assuming orthogonal spreading sequences. Theoretical expressions are derived for the performance degradation caused by the timing jitter, in the presence of a multipath channel. Assuming an additive white Gaussian noise channel, perfect power control, and full load, it is shown that the performance degradation for the downlink transmission is independent of the number of subcarriers, of the spreading factor, and of the spectral contents of the jitter at the receiving mobile station, but only depends on the jitter variance. Under the same assumptions, we point out that, if the jitter spectra of all transmitting mobile stations are the same, the degradation on the uplink is the same as the degradation on the downlink.     

Measurement of ultralow Gordon-Haus timing jitter in dispersion-managed soliton systems

We measure, for the first time, the growth of the Gordon-Haus timing jitter in dispersion-managed soliton communication systems without inline soliton control. After 650-km transmission with a relatively high average dispersion of 0.87 ps/nm/km and a pulsewidth of 14 ps, compatible with 20 Gb/s, we measure a very low timing jitter of 45 fs. Hence, medium range dispersion-managed soliton transmission systems have, in general, a good margin toward Gordon-Haus timing jitter.     

Effect of distributed Raman amplification on timing jitter indispersion-managed lightwave systems

It is shown that the timing jitter of dispersion-managed soliton systems can be reduced by up to 40% by using a hybrid amplification scheme in which fiber losses are compensated by using erbium-doped fiber amplifiers in combination with backward pumped Raman gain. The jitter is smallest in the case of 100% Raman amplification, but considerable reduction occurs even for partial distributed amplification     

一种改进的MC-CDMA系统ORC技术

基于对频率非选择性Rayleigh衰落信道中采用ORC(orthogonality restoring combining)技术的MC-CDMA系统误码率下边界的分析,提出了忽略最弱子载波(信道衰减系数最小的子载波)的改进ORC检测方案。仿真结果表明,该方案比传统ORC在性能上有很大提高,比较接近MMSEC技术;如果忽略过多的弱子载波反而会影响用户间扩频码的正交性,引起系统性能恶化。改进方案具有随子载波数线性增长的运算复杂度,是一种比较实用的MC-CDMA系统检测技术。     

The effect of timing jitter on the performance of a discretemultitone system

The transmission of high-speed data over severely band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation, a modulation technique that has been proposed for a number of new applications. While the performance of a DMT system has been analyzed by a number of authors, these analyses ignore the effect of timing jitter on system performance. Timing jitter becomes an increasingly important concern as higher data rates are supported and larger constellations are allowed on the DMT subchannels. Hence, in this paper, we assume that synchronization is maintained by using a digital phase-locked loop to track a pilot carrier, Given this model, we derive error rate expressions for an uncoded DMT system operating in the presence of timing jitter, and we derive an expression for the interchannel distortion that results from a varying timing offset across the DMT symbol. In addition, we investigate the performance of trellis-coded DMT modulation in the presence of timing jitter. Practical examples from the asymmetric digital subscriber line (ADSL) service are used to illustrate various results     

Efficient approach for modeling collision-induced timing jitter inWDM return-to-zero dispersion-managed systems

A semi-analytical approach that allows us to create an efficient numerical algorithm to accurately evaluate collision-induced timing jitter in wavelength-division-multiplexing (WDM) systems with return-to-zero (RZ) modulation format is developed. The approach agrees well with full numerical simulations. The computational time is reduced by two orders of magnitude compared to full numerical simulations     

Theoretical analysis of timing jitter in monolithic multisectionmode-locked DBR laser diodes

We present a theoretical analysis of the timing jitter in monolithic multisection mode-locked DBR lasers which is shown to agree well with experimental measurements. The analysis uses a traveling-wave equation model with Langevin spontaneous emission noise and includes the important physical effects of gain nonlinearities, self-phase modulation, and the presence of DBR filtering. It is found that spontaneous noise limits low-jitter operation. The impact of frequency detuning on the timing jitter is studied and the effects of laser parameters, such as linewidth enhancement factor and gain section length, are discussed for achieving low-jitter pulses     

MC-CDMA系统存在频偏时的性能分析

多载波码分多址(MC-CDMA)是把正交频分复用(OFDM)和码分多址(CDMA) 结合起来的新一代移动通信系统.详细构建了一个MC-CDMA 系统的数学模型,并给出了载频偏移和多径信道存在时的矩阵-向量表示模型.在此系统模型的基础上,分析了频偏对MC-CDMA系统多用户检测器性能的影响.MATLAB仿真显示了MC-CDMA系统对频偏极为敏感,当经历多径Rayleigh信道时,系统只能忍受较小的频偏.     

Quantum-limited timing jitter in actively modelocked lasers

Expressions for the quantum-limited timing jitter in an actively modelocked fiber laser are derived. We identify a set of characteristic constants that govern the timing jitter for the cases using amplitude modulation (AM) and phase modulation (PM) as the active modelocking elements. We find that when using AM, the Gordon-Haus jitter is proportional to the square of the group-velocity dispersion and reaches a minimum value for the case of low dispersion. Using PM, the Gordon-Haus jitter increases only linearly proportional to group-velocity dispersion, and there exists an optimum group-velocity dispersion that minimizes the jitter. We compare the theory to recent experiments of the timing jitter for an active harmonically modelocked fiber laser.     

Gordon-Haus timing jitter reduction in dispersion-managed solitoncommunications

An analytic theory is presented which demonstrates that the noise induced Gordon-Haus timing jitter in arbitrary dispersion-managed transmission systems is reduced by the power-enhancement factor required to support a dispersion-managed solitons provided the path-average soliton period is much greater than the dispersion-map period. The analysis further predicts the behaviour of the amplitude, width, and quadratic chirp fluctuations due to the amplified spontaneous emission (ASE) noise     

The effect of external optical feedback on timing jitter in modulated laser diodes

Laser diodes with optical feedback are numerically modeled using single-mode rate equations. The effects of the optical feedback on the pulse turn-on delay and timing jitter are examined, for gain-switching, periodic and pseudorandom modulation formats. It is shown that there is a change in turn-on delay and a considerable increase in the timing jitter due to the changes in the output power distributions as optical feedback increases. The cause of the increased jitter is found to be the additional intensity noise introduced by the optical feedback.<>     

Theory of timing jitter in actively mode-locked lasers

An analysis of the pulse-to-pulse timing jitter in an actively mode-locked laser is presented. The model includes spontaneous emission noise, mode-locker driver phase noise, and cavity length detuning. Analytical expressions for the laser pulse train phase noise spectrum, the intensity power spectrum, and the RMS timing jitter are given. The timing fluctuations are characterized by a time constant proportional to the cavity round-trip time times the number of locked modes squared divided by the modulation depth. The contribution from the mode-locker driver phase noise will dominate unless high-stability RF sources are used. The residual timing jitter due to spontaneous emission noise is very sensitive to cavity detuning     

Minimisation of timing jitter in CDMA code tracking

A method for chip waveform design that minimises the tracking jitter in code division multiple access (CDMA) synchronisation is presented. The method is based on the use of prolate spheroidal wave functions. Examples of optimised waveforms are given and their performance compared to other conventional pulse shapes in terms of timing error variance and bandwidth occupancy.     

Correlated and uncorrelated timing jitter in gain-switched laserdiodes

The author describes correlated and uncorrelated timing jitter of gain-switched pulses generated from sinusoidally modulated laser diodes measured from photocurrent power spectra. It is found that if dc bias is decreased to obtain shorter pulses, then the root-mean-square (rms) value of uncorrelated timing jitter drastically increases to more than 2 ps, while correlated jitter remains constant at the drive circuit level of ~0.2 ps. By optimizing the bias condition and compression fiber length, total timing jitter of gain-switched pulses can be reduced to as low as ~0.5 ps, as their pulse width is kept less than 10 ps     

Effect of soliton interaction on timing jitter in communicationsystems

Timing jitter in soliton communication systems is studied, taking into account both soliton interaction and amplifier noise. Deviations from Gordon-Haus jitter for closely spaced solitons are observed. A new analytical model for the timing jitter is proposed. The model presented considers interaction in a random sequence of solitons and the effect of the amplified spontaneous emission noise added in each amplification stage. We obtain a good agreement between the new analytical model and simulation results for practical communication systems     

BER analysis of the optimum multiuser detection with channel mismatch in MC-CDMA systems

In this paper, we analyze the bit-error-rate (BER) performance of the optimum multiuser detection (MUD) with channel mismatch in multicarrier code-division-multiple-access (MC-CDMA) systems. The BER performance of the optimum MUD without channel mismatch in MC-CDMA systems has been recently derived using the replica method. However, it is left unjustified, since the replica method is not a rigorous approach. In addition, it is NP-hard to implement an optimum MUD algorithm. To justify the BER performance and to make the optimum MUD feasible, based on Pearl's belief propagation (BP) scheme, we put together a low-complexity iterative MUD algorithm for MC-CDMA systems. Furthermore, channel mismatch is introduced into the BP-based MUD algorithm to make the scenario general. With channel mismatch, the analytical results of the BP-based MUD algorithm conform perfectly to, and the simulation results of the BP-based MUD algorithm conform very closely to the BER performance of the optimum MUD derived using the replica method, which is a nontrivial extension of the existing replica approach mentioned above. Without channel mismatch, the problem becomes a special case of our contribution.     

锁模Cr4+:YAG固体激光器脉冲的时间抖动理论性分析

固体激光器的脉冲稳定性限制了激光器在很多方面的应用.从被动锁模Cr4 :YAG激光器腔内脉冲的传播方程出发,得到了带噪声的非线性Schr(o)dinger方程,进一步分析了脉冲在激光器腔内的时间传播形式,建立了锁模Cr4 :YAG固体激光器振荡脉冲参数的线性扰动方程,推导出了脉冲参数波动的动力学方程以及时间和相位的均方根波动关系式.提出了一个减少锁模Cr4 :YAG固体激光器脉冲时间抖动的实验方案,旨为锁模Cr4 :YAG固体激光器能够用作光纤通信和量子通信中的光源提供理论上的帮助.