基于逼近噪声子空间的求根时延估计算法

多重信号分类(MUSIC)时延估计算法需要多径数估计,且其特征分解和谱峰搜索的计算复杂度较高。针对此问题,给出了一种基于逼近噪声子空间的求根时延估计算法。该算法利用协方差矩阵逆的高次幂逼近噪声子空间与其自身共轭转置的积,并构造多项式等式,以多项式求根的方式避免谱峰搜索,从而降低了计算复杂度。仿真结果表明,在无需多径数估计和复杂度低于MUSIC算法的条件下,所提算法的性能与MUSIC算法的性能相当,并且逼近克拉美罗界。     

Efficient sidelobe suppression by source power apodisation in fibreoptic microwave filters composed of linearly chirped fibre grating bylaser array

First results are provided on efficiently apodised RF filters based on linearly chirped fibre gratings fed by laser arrays yielding sidelobe reductions of 10-20 dB as compared to uniform (unapodised) filters     

线性啁啾光纤光栅使色散补偿超过100km

报告了用简单的应力方法使均匀光栅成为线性啁啾光纤光栅的技术,并推导出了相应理论。在常规单模光纤Ｇ．６５２、１０Ｇｂ／ｓ系统中实现超过１００ｋｍ的色散补偿。     

强双折射光纤中三阶色散对DGD的影响

依据强双折射光纤中两垂直偏振分量所满足的非线性耦合模方程,研究了三阶色散对偏振分量间的时延差的影响。结果表明,当二阶色散、三阶色散同时存在时,三阶色散可以减小时延差;当只有三阶色散时,除了产生较大时延差外,还会在两个偏振脉冲的前后沿产生较大的色散波。     

Power penalty analysis for realistic weight functions using differential time delay with higher-order dispersion

In this paper, the power penalty analysis for approximate and realistic weight functions has been presented for combating the pulse broadening effects of group-velocity dispersion in a fiber-optic communication link using differential time delay method including higher-order dispersion terms. The expressions for root mean square (RMS) phase deviation, optimum chirp factor and figure of merit have been evaluated for approximate and realistic systems. We show that the optimum value of chirp factor corresponds to dispersion compensation. The power penalty graphs for second-, third-, and fourth-order dispersion and their combinations have been presented for distance up to 300 km for this chirp factor for different weight functions. It is observed that the power penalty for realistic weight functions is less in comparison with the approximated weight function. It has also been shown that it is possible for a short pulse to propagate without significant broadening over the lengths many times longer than the usual dispersion length of fiber.     

Convergence of the chirped return-to-zero and dispersion managedsoliton modulation formats in WDM systems

We investigated chirped return-to-zero (CRZ) and dispersion-managed soliton (DMS) formats that have been employed in experimental demonstration systems at Tyco, CNET, and KDD. We find that the DMS format and the CRZ pulse format used in these systems have been converging. By careful study of noise effects, single-channel nonlinear effects, and multichannel nonlinear effects, we provide evidence that these systems all operate in a quasi-linear region. In this regime, the pulse shape evolution is dominated by linear dispersion and the spread in the eye diagrams is dominated by signal-spontaneous beat noise, much as would be the case in a linear system. However, it is necessary to carefully manage the nonlinearity in these systems to minimize timing jitter due to interpulse interactions in a single channel, as well as interchannel interactions. Thus, nonlinearity plays an important role in system design     

A perturbation and iterative perturbation analysis of linearly chirped grating lenses of medium Q in dielectric waveguides

A perturbation and iterative perturbation analysis of linearly chirped quasi-periodic structures of mediumQfactor in planar dielectric waveguides has been formulated. This analysis can be used to calculate the diffraction efficiency and the angular field of view of a given linearly chirped grating structure, for a specific incident beam including the effect of higher orders of diffractions. The numerical example of aF = 10 , f = 10m.m,Lambda_{min} = 2.06, Lambda_{max} = 4.25and grating groove length = 15 μm is presented.     

Determination of the dispersion relation in tunnel structures: Influence of the barrier shape and validity of the WKB approximation

A simulation study has been made of the way in which the shape of the barrier influences the determination of the energy-momentum relationship in the insulator forbidden band of M-I-M tunnel junctions. It is shown that the method which analyses current-voltage data for different insulator thicknesses (Stratton, Lewicki, Mead) is rather insensitive to the barrier shape. Analysis of current-voltage data for only a single insulator thickness (Korneffel, Ludwig) is found to be less appropriate because the dispersion relationship is strongly affected by the barrier shape. Some consequences are discussed. Application of an exact expression for the transmission probability indicates that the error involved by the use of the WKB approximation is small.     

色散缓变光纤中皮秒啁啾脉冲的孤子效应压缩

文章从描述皮秒光脉冲在色散缓变光纤（FSDD）中所满足的非线性Schroedinger(NLS)方程出发，数值模拟了高阶皮秒光孤子在不同的FSDD中的孤子效应压缩，并讨论了初始啁啾对其的影响，结果表明，利用FSDD和孤子效应压缩来压缩带有初始啁啾的高阶皮秒光孤子，可以得到更高的压缩比和品质因子，压缩后的脉冲的峰值功率明显提高，而且脉冲被压缩到最窄所需的光纤长度也大大缩短，最后讨论了初始脉宽的影响。     

On wavelet denoising and its applications to time delay estimation

The application of dyadic wavelet decomposition in the context of time delay estimation is investigated. We consider a model in which the source signal is deterministic and the received sensor outputs are corrupted by additive noises. Wavelet denoising is exploited to provide an effective solution for the problem. Denoising is first applied to preprocess the received signals from two spatially separated sensors with an attempt to remove the contamination, and the peak of their cross correlation function is then located from which the time delay between the two signals can be derived. A novel wavelet shrinkage/thresholding technique for denoising is introduced, and the performance of the algorithm is analyzed rigorously. It is proved that the proposed method achieves global convergence with a high probability. Simulation results also corroborate that the technique is efficient and performs significantly better than both the generalized cross correlator (GCC) and the direct cross correlator (CC)     

时间色散导致网络掉话的分析处理

在隧道等特殊网络环境中,光纤直放站或分布式基站往往导致多径传播,带来时间色散问题。分析时间色散产生原理及对网络的影响,并通过实际案例指出,解决此类问题:一要从规划源头避免,二可以通过变更施主小区解决。     

DDF色散值的阶梯曲线近似在色散管理系统中的应用

针对色散管理系统中色散渐减光纤(DDF)制造工艺复杂的缺点,设计一种色散渐减光纤的替代色散管理链路.利用两种正负色散光纤,通过设计正负色散光纤的长度来调整各个色散管理周期的平均色散值,使相邻放大器中光纤链路的色散值呈阶梯曲线状递减,从而近似代替色散渐减光纤平衡减弱的非线性效应.数值模拟结果表明色散渐减光纤的阶梯曲线近似对40Gbit/s的光传输系统性能有很大的提高作用.     

Multiple stage dispersion compensation in long haul optical fibresystems using chirped fibre Bragg gratings

Modelling is used to assess the performance of an optical fibre link which has fibre grating dispersion compensators spaced at intervals along its length. A 10 Gbit/s electroabsorption modulator with high positive chirp is shown to transmit in excess of 158 km in normal dispersion fibre using two 2 cm long compensators, incurring a dispersion penalty of only 1.0 dB. Thus the transmission range is improved by a factor of 6.6 over the uncompensated case     

子空间算法在OFDM信道时延估计中的应用

到达时延(TOA)和到达时延差(TDOA)定位算法是无线定位中应用最广泛的2种方法,TOA测量值的准确获取将影响定位的精确度。正交频分复用(OFDM)是实现无线多媒体通信的关键技术,利用OFDM信号的导频子载波所携带的信息,参考均匀线列阵的DOA估计过程,提出将MUSIC子空间法应用到OFDM信道的时延估计上。给出了OFDM符号内导频子载波分布的相关条件,对提出算法进行仿真实验,可以看出,导频子载波个数的增加和导频子载波间隔的扩大都可以提高估计精确度。     

A 3-D impedance method to calculate power deposition in biologicalbodies subjected to time varying magnetic fields

A previously described two-dimensional impedance method (ibid., vol.31, p.644-51, 1984) for modeling the response of biological bodies exposed to time-varying electromagnetic fields has been extended to three dimensions. This method is useful at those frequencies where the quasistatic approximation is valid and calculates the fields, current densities, and power depositions in the bodies. Solutions using this method for homogeneous spheres in plane waves are presented and compared to the analytic solutions for the same configuration. Solutions for a man exposed to a uniform radio-frequency magnetic field at 30 MHz, are presented, as well as for a man exposed to either circularly or linearly polarized magnetic fields at 63 MHz, uniform within a portion of his body and linearly decreasing outside of that portion, which approximates the exposure in some nuclear-magnetic-resonance imaging devices     

Investigation of fiber grating-based performance limits in pulse stretching and recompression schemes using bidirectional reflection from a linearly chirped fiber grating

We demonstrate the controlled stretching and recompression of ultrashort optical pulses using bidirectional reflection from both ends of a single linearly chirped fiber grating. We identify operating regimes for minimal pulse distortion due to the phase and filtering responses of a simple linear grating and experimentally demonstrate complete pulse reconstruction.     

On application of MUSIC algorithm to time delay estimation in OFDM channels

The time delays of the OFDM paths delimit the size of guard interval in OFDM symbols-important factor for system throughput. In order to apply guard interval as an adaptive parameter like in DRM system, time delays should have been evaluated in real time and in a simple way. Presented software method takes advantage of the information carried out by pilot subcarriers of the OFDM signal. It is shown that pilot subcarriers of OFDM signal in multipath channel are described by equations formally equivalent to equations of Direction-Of-Arrival (DOA) problem in antenna array processing. This analogy leads to application of the MUSIC algorithm of DOA problem to time delay estimation of the individual OFDM paths. Related condition for distribution of pilots within OFDM symbol is given. In case of time delays outside the guard interval the MUSIC algorithm is shown to produce 'shadow' and 'ghost' paths.     

Power penalty due to the amplitude and phase response ripple of a dispersion compensating fiber Bragg grating for chirped optical signals

A concise method is presented for rigorously calculating the power penalty due to the combined implications of the amplitude and phase response ripples of a dispersion compensating fiber Bragg grating and the chirp of the transmitted optical signal. By using trigonometric series to represent the ripples, the calculated penalty can be positive or negative, as obtained in numerical simulations and measurements, depending on the signal chirp and ripple within the modulated signal bandwidth. An approximate upper bound on the power penalty is also presented as an extension of earlier results that always yield positive penalties. Calculated and measured results are compared for two 10-Gb/s return-to-zero (RZ) signals with distinct chirp properties.     

Joint estimation of time delay and frequency delay in impulsivenoise using fractional lower order statistics

New methods for time delay estimation and joint estimation of time delay and frequency delay in the presence of impulsive noise are introduced. First, degradation of the conventional approaches based on second-order statistics is shown both theoretically and experimentally. Then, a new class of robust algorithms are developed using the theory of alpha-stable distributions, including the fractional lower order covariance (FLOC) method, which is formulated for the time delay estimation problem and the fractional lower order ambiguity function (FLOAF), which is defined for the joint estimation of time delay and frequency delay. It is shown that these new methods are robust for both Gaussian and non-Gaussian impulsive noise environments. The improved performance is clearly demonstrated through detailed analysis and comprehensive simulations with computer-generated data as well as actual radar and sonar clutter data     

Electronically variable time delay in a LiNbO3SAW delay line

The time delay of surface acoustic waves (SAW's) in 128° rotated Y-cut, X-propagating LiNbO3is found to vary linearly with a biasing electric field. Fractional changes in time delay greater than 9 × 10^-4have been obtained in a delay line fabricated using this material.