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.     

时钟抖动对射频脉宽调制性能的影响分析

在全数字发信机系统中,射频脉宽调制(RF-PWM)将基带调制信号的幅度与相位信息编码为输出脉冲的宽度和位置。由于数字信号处理器件的非理想特性,其时钟信号的上升沿和下降沿存在抖动误差,影响RF-PWM的输出信号质量。基于3种RF-PWM实现方案,本文通过公式推导确定了时钟抖动引入的非线性失真项,并给出了时钟抖动影响下不同方案输出脉冲信号底噪的数学解析式。最后利用Matlab软件,对不同方案在时钟抖动条件下的基波、奇次谐波和底噪进行仿真验证,结果证明理论推导正确;同时对信号的矢量幅度误差(EVM)和邻信道功率比(ACPR)进行仿真,分析出时钟抖动对信号带内外性能的影响。结果表明,时钟抖动引入的非线性失真主要体现为底噪的抬高;不同RF-PWM实现方案时钟抖动的影响特性各有不同,其中五电平方案对时钟抖动影响具有抑制效果,且随时间分辨力的增大而增大。     

带有时偏的MC-CDMA上行链路的盲信道估计

为了能在带有时偏的MC-CDMA上行链路中估计信道，提出了一种新的信道估计方法。该方法能消除时偏对信道估计产生的影响，从而无需系统同步就能准确估计出信道。另外，由于扩频序列的信息对接收端是已知的，因此该信道估计方法可以利用扩频码的信息来完成盲估计。最后的仿真结果显示，该信道估计方法有良好的性能。     

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.     

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.<>     

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     

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.     

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.     

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     

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     

快速片上互连缓冲器插入时序优化分析

互连线延时已成为制约大规模集成电路性能的瓶颈,而缓冲器插入能很好解决互连线延时。Van GinnekenfvGl算法是缓冲器插入互连时序优化的经典算法,针对此算法的3个主要操作过程进行改进,利用红黑树数据结构存储路由拓扑数据结构,缩短数据结构的更新访问时间;利用快速冗余判别和排序方法减小解方案数量和求解最优的复杂度。通过标准测试电路集ISCAS89中的电路对本文方法进行测试,测试结果表明,虽然随着电路规模增加,改进方法和传统方法运行时间都相应增加,但改进方法的优势更加明显;且随着缓冲器库规模的增加,其优势也越发明显,如只有一种缓冲器的缓冲器库,改进算法耗时为VG算法的73．28％,当有8种和20种缓冲器的缓冲器库时,耗时分别为VG算法的67．34％和63．05％。采用本文中的快速缓冲器插入算法,能有效缩短基于缓冲器插入的大规模互连时序优化时间。