Loran-C skywave delay estimation using eigen-decompositiontechniques

A novel eigen-decomposition technique for estimating the delays of Loran-C skywave components is presented. This provides the basis for a new generation of receivers which implement adaptive skywave interference monitoring, enhancing reliability and positioning accuracy. Performance of the new technique is demonstrated using off-air data     

Loran-C skywave delay detection using ARMA algorithm

The autoregressive moving average technique (ARMA) is applied to the problem of estimating the delay of Loran-C skywaves. The performance of this technique is evaluated and compared with Fourier-based methods. The simulation results show that the ARMA algorithm yields a significantly greater estimation accuracy and that it can also operate successfully with very noisy signals     

Discrete time techniques for time delay estimation

Basic aspects of time delay estimation (TDE) based on sampled signals are investigated. The direct cross-correlation method is analyzed and compared to the average square difference function (ASDF) and the (addition only based) average magnitude difference function (AMDF) estimators, Their relative accuracy is theoretically evaluated, and previous empirical results are explained. It is shown that both the ASDF- and the AMDF-based estimators outperform the direct cross-correlation based estimator for medium-high signal-to-noise ratios. Moreover, the AMDF-based estimator, which avoids any multiplications, significantly reduces the computational complexity of the estimation procedure while offering only a moderate performance loss with respect to the ASDF based estimator     

Active high resolution time delay estimation for large BT signals

Two different high-resolution time-delay estimation (HRTDE) methods, a temporal method and a frequency method, specially adapted to large bandwidth duration (BT) product time-resolvent signals, are described. The performance gain of these methods is shown to be about four times better in comparison with the classical time-delay resolution methods. The frequency HRTDE method is applied to real data obtained from an ocean acoustic experiment. Although classic methods cannot distinguish close signal components, the method presented yields estimates of the delay differences and the attenuation associated with each propagation path     

High resolution 20 GHz wideband delay generator

A digitally-programmable method for linearly controlling signal delay over a wide frequency and delay range has been developed. Circuits were fabricated in the HRL's G2+ InP HBT technology. Test results at 20 GHz confirm simulation results, showing a 5 ps range in delay, ramped in 16 steps to provide a 0.3 ps resolution step. Larger delay ranges are possible by combining several of the delay cells in series.     

Joint angle and delay estimation using shift-invariance techniques

In a multipath communication scenario, it is often relevant to estimate the directions and relative delays of each multipath ray. We derive a closed-form subspace-based method for the simultaneous estimation of these parameters from an estimated channel impulse response, using knowledge of the transmitted pulse shape function. The algorithm uses a two-dimensional (2-D) ESPRIT-like shift-invariance technique to separate and estimate the phase shifts due to delay and direction of incidence with automatic pairing of the two parameter sets. Improved resolution is obtained by enlarging the data matrix with shifted and conjugated copies of itself     

High resolution two-dimensional ARMA spectral estimation

The authors present a practical algorithm for estimating the power spectrum of a 2-D homogeneous random field based on 2-D autoregressive moving average (ARMA) modeling. This algorithm is a two-step approach: first, the AR parameters are estimated by solving a version of the 2-D modified Yule-Walker equation, for which some existing efficient algorithms are available; then the MA spectrum parameters are obtained by simple computations. The potential capability and the high-resolution performance of the algorithm are demonstrated by using some numerical examples     

应用超分辨率方向估计实现通信卫星干扰源定位

利用卫星天线多波束特性来获取干扰信号波达方向（DOA）信息,是实现通信卫星干扰源定位的一条新思路。本文研究了在结合卫星多波束天线模型时,利用超分辨率方向估计方法实现通信卫星干扰源精确定位的可毛生,研究表明MN和LP两种算法在用于多波束天线的DOA估计时存在着方向估计模糊,而MV和MUSIC可应用于多波束天线的二维测向;文中还讨论MV、MUSIC应用于卫星干扰源定位的性能情况,并得到一些有益的结论。     

Highly efficient techniques for mitigating the effects of multipath propagation in DS-CDMA delay estimation

Delay estimation in direct-sequence code-division multiple-access (DS-CDMA) systems is necessary for accurate code synchronization and for applications such as mobile phone positioning. Multipath propagation is among the main sources of error in the DS-CDMA delay estimation process, together with multiple access interference and non-line-of-sight (NLOS) propagation. This paper provides a review of main delay estimation techniques, existing in the literature so far, which are able to cope with multipath propagation, together with our novel delay estimation techniques proposed in the context of DS-CDMA systems. The performance of all these techniques is compared through analysis and simulations, considering also their relative computational complexity and required prior information. Starting from the traditional delay locked loops (DLL) and their improved variants, we discuss several recently introduced delay estimation techniques able to cope with multipath propagation. The characterization of these methods is given in a unified framework, suited for both rectangular and root raised cosine pulse shapes. The main focus in the performance comparison of the algorithms is on the closely-spaced multipath scenario, since this situation is the most challenging for achieving diversity gain with low delay spreads and for estimating LOS component with high accuracy in positioning applications.     

High resolution two-dimensional minimum free energy AR spectral estimation

We extend the minimum free energy (MFE) parameter estimation method to 2-D fields. This 2-D MFE method may be used to determine autoregressive (AR) model parameters for spectral estimation of 2-D fields. It may also be used to provide AR models for texture synthesis. The performance of the technique for closely spaced sinusoids in white noise is demonstrated by numerical example. Better results can be achieved than with the multidimensional Levinson algorithm.     

High resolution estimation for sub-gaussian stable signals in a linear array model

The authors describe a high resolution subspace fitting (HRE) algorithm for robust estimation of direction of arrival (DOA) in the uniform linear array model with heavy-tailed signals and noise. Electromagnetic disturbances on telephone lines, atmospheric noise and underwater acoustic noise often exhibit heavy-tailed behaviour with differing characteristics. Although statistical models under Gaussian assumptions of signals and noise have been extensively investigated in the literature, there is limited research on robust methods in the non-Gaussian setting. A general model with sub-Gaussian alpha-stable signals is described, which includes the isotropic alpha-stable, and independent and dependent Gaussian models as special cases. It is shown that the HRE algorithm provides strongly consistent estimates of the DOAs. In addition, Monte Carlo simulation studies show that the proposed algorithm works extremely well for closely spaced targets, and outperforms the multiple signal classification-type algorithms for strongly dependent signals, both in the stable and the Gaussian cases     

High resolution techniques for the fabrication of small area Josephson tunnel junctions

Superconducting tunnel junction devices as small as 10^-10cm²have been made using novel self-aligning techniques in conjunction with optical or e-beam lithography. This process has been used to fabricate complete circuits and multijunction arrays under well controlled conditions, using a single resist patterning step.     

Fast algorithm for nonstationary delay estimation

A computationally efficient algorithm for estimating time delay between signals received at two spatially separated sensors is proposed. The delay estimate is adapted directly to maximise the mean product of the first sensor output and the filtered output of the second received signal. The convergence behaviour and variance of the delay estimate are derived. It is shown that the proposed algorithm outperforms the explicit time delay estimator at a low signal-to-noise ratio     

High resolution ultrasonic backscatter coefficient estimation based on autoregressive spectral estimation using Burg's algorithm

An autoregressive (AR) method for spectral estimation was applied toward the task of estimating ultrasonic backscatter coefficients from small volumes of tissue. High spatial resolution is desirable for generating images of backscatter coefficient. Data was acquired from a homogeneous tissue-mimicking phantom and from a normal human liver in vivo. The AR method was much more resistant to gating artifacts than the traditional DFT (discrete Fourier transform) approach. The DFT method consistently underestimated backscatter coefficients at small gate lengths. Therefore backscatter coefficient image formation will be quantitatively more meaningful if based on AR spectral estimation rather than the DFT. The autoregressive method offers promise for enhanced spatial resolution and accuracy in ultrasonic tissue characterization and nondestructive evaluation of materials.     

Realizable lower bounds for time delay estimation

The accuracy of time delay estimates obtainable in active localization systems is studied, focusing on the effect of ambiguities in the time delay estimates. Such ambiguities occur when the transmitted signal has small relative bandwidth. Then, for signal to noise ratios below a certain threshold, the commonly used Cramer-Rao lower bound is not realizable. The study concentrates on the region of intermediate SNR values, where the Cramer-Rao bound is no longer achievable, but useful information on time delays can still be obtained from the measurement. Realizable bounds for the single and two echo cases are obtained by deriving a new form of the Barankin (1949) bound for active time delay estimation. This form maintains the realizability property of the most general form, but is of reasonable complexity. New bounds are derived for the multiple echo case. Examples are presented to illustrate the dependence of the bound on parameters such as SNR, relative bandwidth, and echo separation     

An efficient algorithm for time delay estimation

We present a conceptually simple and computationally efficient algorithm, which is referred to as WRELAX for the well-known time delay estimation problem. The method is a relaxation-based minimizer of a complicated nonlinear least squares criterion, WRELAX can be applied to detecting and classifying roadway subsurface anomalies by using an ultra-wideband ground-penetrating radar. Numerical and experimental examples are provided to demonstrate the performance of the new algorithm     

Power estimation techniques for FPGAs

The dynamic power consumed by a digital CMOS circuit is directly proportional to both switching activity and interconnect capacitance. In this paper, we consider early prediction of net activity and interconnect capacitance in field-programmable gate array (FPGA) designs. We develop empirical prediction models for these parameters, suitable for use in power-aware layout synthesis, early power estimation/planning, and other applications. We examine how switching activity on a net changes when delays are zero (zero delay activity) versus when logic delays are considered (logic delay activity) versus when both logic and routing delays are considered (routed delay activity). We then describe a novel approach for prelayout activity prediction that estimates a net's routed delay activity using only zero or logic delay activity values, along with structural and functional circuit properties. For capacitance prediction, we show that prediction accuracy is improved by considering aspects of the FPGA interconnect architecture in addition to generic parameters, such as net fanout and bounding box perimeter length. We also demonstrate that there is an inherent variability (noise) in the switching activity and capacitance of nets that limits the accuracy attainable in prediction. Experimental results show the proposed prediction models work well given the noise limitations.     

Adaptive delay estimation for partitioning-driven PLD placement

This paper describes the application of weighted partitioning techniques to timing-driven placement on a hierarchical programmable logic device. We discuss the nature of placement on these architectures, the details of applying weighted techniques specifically to the programmable logic device (PLD) CAD flow, and introduce the new concept of adaptive delay estimation using phase local to increase performance. Empirical results show that these techniques, in a fully complete system with large industrial designs, give an average 38.5% improvement over the unimproved partitioning-based placement tool. Approximately two-thirds of this benefit is due to our improvements over a straightforward weighted partitioning approach.     

High power broadcasting skywave transmitters interference analysisfor navigation and communication systems

The operation of high-power broadcasting transmitters (Tx) can strongly interfere with collocated and even remote radio communication and navigation systems on broad frequency ranges. In these cases, extensive analysis and computation method developments are essential in order to assess the feasibility of reliable operation of indispensable radio communication links. The magnitudes of the interference effects are computed, based on specifications of 500 kW skywave Tx parameters and the important airborne VHF radio navigation and communication systems. The critical interference (i.e. desensitization or blocking of the victim airborne receivers) and other interference modes are analyzed using semiempirical state-of-the-art computation methods. Limits for victim receiver distances and frequency intervals for no-interference situations and optimal reception conditions are obtained     

Average interconnection delay estimation for on-FPGA communication links

A new method is presented and an analytical expression is derived for average interconnection delay estimation. This method is directly applicable to predicting the average delay for high-bandwidth communication links implemented on FPGAs. The theoretical results are compared with the measured data from the actual circuits and an average error of 4.6% is reported.