Eigenstructure methods for direction finding with sensor gain and phase uncertainties

An eigenstructure-based method for direction finding in the presence of sensor gain and phase uncertainties is presented. The method provides estimates of the Directions of Arrival (DOA) of all the radiating sources as well as calibration of the gain and phase of each sensor in the observing array. The technique is not limited to a specific array configuration and can be implemented in a'ny eigenstructure-based DOA system to improve its performance.This work was supported by the Army Research Office under Contract No. DAAL03-89-C-0007.     

Estimation of sensor gain and phase

The problem of estimating the direction-independent gain and phase characteristics of an array of sensors, using knowledge of the true field covariance at the sensor locations, is considered. A concise expression for the log-likelihood function is derived and several mathematical properties of this objective function are given. The Cramer-Rao (C-R) lower bounds on the variances of gain and phase estimates are derived, with the plane wave in isotropic noise considered as a special case. The maximum-likelihood estimates are shown to be consistent, asymptotically efficient and asymptotically normal. A simple estimator is proposed which is consistent and which gives good initial estimates for a Newton algorithm for finding the maximum-likelihood solution. Comparison of the maximum-likelihood estimates and the C-R bounds is given for the plane-wave-in-isotropic-noise example     

Performance of phase noisy optical systems with frequencystabilization

Laser phase noise causes a significant performance degradation of coherent optical communication systems. The effect of noise is analyzed using a model more general than usually considered. Bounds and approximations for the probability of error of binary orthogonal modulation, such as wide deviation frequency-shift keying (FSK), are evaluated, paying particular attention to the effects of frequency feedback stabilization on system robustness     

Robust Direct position determination against sensor gain and phase errors with the use of calibration sources

Multidimensional Systems and Signal Processing - The direct position determination (DPD) method can provide high localization performance than conventional two-step localization methods. However,...     

内场干涉仪测向误差分析及相位误差校正方法

根据干涉仪测向的基本原理,分析了干涉仪测向误差产生原因,提出了近场试验条件下的相位误差校正方法,可消除试验条件对测向误差的影响,提高试验结果可信度。仿真结果说明,本文提出的内场干涉仪测向误差校正方法可显著减少内场测试的影响。     

Cascadable CMOS current gain cell with gain insensitive phase shift

By using a complementary circuit topology, electronically variable gain in combination with a gain insensitive phase shift can be achieved. A cascadable CMOS current gain cell based on this concept is proposed, together with a linearisation technique for this circuit.<>     

Performance comparison of high-order IFLF and LF linear phase lowpass OTA-C filters with and without gain boost

Design and performance comparison of high-order operational transconductance amplifier and capacitor (OTA-C) filters using leapfrog (LF) and inverse-follow-the-leader-feedback (IFLF) structures are investigated. The filters are designed for a 125 MHz seventh-order equiripple group delay lowpass characteristic with and without gain boost and simulated in 0.25 μm 2-V CMOS. A fully differential highly linear OTA with cross-coupled input pairs and regulated cascode output is used for the simulation. Simulated results show that while the IFLF OTA-C filter can achieve a higher gain boost, the LF OTA-C filter has better other performances.     

New hybrid controller for systems with deterministic uncertainties

In this paper, a new hybrid controller for systems with deterministic uncertainties is developed. The proposed controller identifies and compensates deterministic uncertainties simultaneously. It is the combination of a time-domain feedback controller and a frequency-domain iterative learning controller. The feedback controller decreases system variability and reduces the effect of random disturbances. The iterative learning controller shapes the system input to suppress the error caused by deterministic uncertainties such as friction and backlash. The control scheme use only local input and output information, no system model is required. The uncertainties can be structured or unstructured. The effectiveness of the proposed controller is experimentally verified on a servo system with gearbox     

Robust steady-state filtering for systems with deterministic and stochastic uncertainties

For uncertain systems containing both deterministic and stochastic uncertainties, we consider two problems of optimal filtering. The first is the design of a linear time-invariant filter that minimizes an upper bound on the mean energy gain between the noise affecting the system and the estimation error. The second is the design of a linear time-invariant filter that minimizes an upper bound on the asymptotic mean square estimation error when the plant is driven by a white noise. We present filtering algorithms that solve each of these problems, with the filter parameters determined via convex optimization based on linear matrix inequalities. We demonstrate the performance of these robust algorithms on a numerical example consisting of the design of equalizers for a communication channel.     

VXI总线结构下的多信道无线电监测测向系统应用

随着无线电通信事业的飞速发展,对无线电监测、测向系统也提出了越来越高的技术和性能方面的要求.世界上少数发达国家抓住时机,正不断研制和推出新的无线电监测、测向系统,其目的不仅在于满足本国无线电监测和国防等领域的需求,还企图在技术上和市场上对其他国家形成长期的垄断之势并不断谋取高额利润.我国作为世界上最大的发展中国家和社会主义市场经济国家,不可能在这个涉及到国家安全和有较大利润空间的高科技领域长期受制于人,而应该与时俱进,从我国现有的电子工业基础和实际出发,走一条有中国自己特色的、跨越式的发展无线电监测产业的道路.本文从VXI总线结构下的多信道无线电监测、测向系统的应用入手,希望对我国无线电监测产业如何与时俱进起到抛砖引玉的作用.     

Microwave phase shifting with gain using IMPATT diodes

The use of an IMPATT reflection amplifier to produce phase modulation at microwave frequencies has been demonstrated. By operating the IMPATT diode near to avalanche resonance frequency, phase-switching through 180° can be obtained, and the drive current can be set to give equal gain in the two phase states so that no amplitude modulation is produced. Possible application to high-frequency data-transmission systems is envisaged.     

Performance analysis of low processing gain DS/CDMA systems withrandom spreading sequences

The performance analysis of a RAKE receiver for low processing gain direct sequence code-division multiple access (DS/CDMA) systems is presented. The multipath interference effects, that have typically been assumed negligible or approximated as Gaussian noise, become significant for low processing gain systems. A scheme to accurately evaluate the multipath interference effects is proposed     

Performance analysis of asynchronous time-spreading phase coding and wavelength-time OCDMA systems

We compare the theoretical bit-error-rate (BER) and throughput performance of asynchronous time-spreading (TS) phase coding and two-dimensional (2D) wavelength-time (WT) optical code division multiple access (OCDMA) communication systems. Particular consideration is given, however, to both beat noise (BN) and multiple access interference (MAI) effects. BER performance of the TS OCDMA scheme is much superior to that of the WT scheme in the MAI limited case, while the WT scheme has better tolerance to beat noise. Improvement of BER performance and throughput can be obtained by utilization of optimum threshold detection. The two OCDMA schemes have comparable bit-error probability, and the WT scheme achieves a higher throughput for a heavy load when the optimum threshold is employed.     

Robust filtering for 2-D state-delayed systems with NFT uncertainties

This paper is concerned with the robust filtering problem for two-dimensional (2-D) state-delayed systems with uncertainties represented by nonlinear fraction transformation. The authors first establish the stability H/sub /spl infin// performance and generalized H/sub 2/ performance criteria for the system. Based on the results, the authors propose efficient methods to solve the robust H/sub /spl infin// filtering, generalized H/sub 2/ filtering, and mixed generalized H/sub 2//H/sub /spl infin// filtering problems by using a parameter-dependent Lyapunov function approach. The methods involve solving linear matrix inequalities. Two examples are given to show the effectiveness of the proposed approach.     

Wavefront curvature sensor with phase defocus grating

The proposed optimum phase defocus grating for wavefront curvature sensing features an equidistantly quantized two-phase-step and a phase step height of π. The optimum phase defocus grating suppresses the influence of zero-order diffraction. The high diffractive efficiencies of the ±1 diffraction orders are verified experimentally, showing average values of 38.08% and 40.36% respectively. The phase plate introduces the wavefront deformation, which are measured by wavefront curvature sensing and reconstructed via the Green's Function algorithm. The reconstructed wavefront is compared with the measurement result of a Veeco interferometer. It is verified that the measurement of the self-designed curvature sensor is correct. The error percent of peak-valley value (PV) is 10%, and the error percent of root mean square (RMS) is 2%.     

Performance degradation of phase-modulated systems due to nonlinear phase noise

The error probability is calculated for phase-modulated systems with nonlinear phase noise. Using the assumption that the phase of amplifier noise and nonlinear phase noise are independent of each other, the error probability and penalty are calculated for both phase-shift keying (PSK) and differential phase-shift keying (DPSK) systems. The mean nonlinear phase shift must be less than about 1.00 and 0.63 rad for a penalty less than 1 dB for PSK and DPSK systems, respectively.     

A new "active" predistorter with high gain and programmable gain and phase characteristics using cascode-FET structures

A MMIC-compatible miniaturized "active" predistorter using cascode FET structures is presented. The predistorter has added functionality of gain, as well as programmable gain and phase variation characteristics, which are required to compensate or the nonlinear distortion of a wide range of power amplifiers (PAs). Thanks to the inherent gain of the predistorter, a need for an additional buffer amplifier is eliminated. Furthermore, it can eventually replace the first-stage amplifier in the multistage PAs, making this approach well suited to MMIC implementation. A simple analysis is performed to understand the phase variation mechanisms in the proposed predistorter and to identify the dominant sources of phase variation. To demonstrate the general usefulness of this predistorter, the cascode predistorter was applied to linearize watt-level MMIC amplifiers for CDMA handset applications, as well as 30 W high power amplifiers for base-station applications. Adjacent channel power ratio (ACPR) improvement of 3-5 dB was achieved with off-chip predistorter when applied to 0.9 W monolithic amplifiers. The predistorter was also integrated with a 1.6 W MMIC PA on a single chip, replacing the first-stage transistor of the amplifier.     

Amplifier gain insensitive SC integrators with 'sample-sample correction' of both gain and phase errors for singlepath and multipath circuits

Amplifier gain insensitive integrator building-blocks are described that use a 'same-sample correction' technique. By adding a parallel signal path to a conventional circuit, then using one path to generate an error-correction signal for the other, extremely high accuracy output is obtained. In particular, both gain and phase errors are reduced together, whereas previous, similarly intentioned, circuits traded gain accuracy for accuracy in phase. Both single and pseudo-N-path circuits are described, with the latter showing dramatically improved performance over the previously proposed last cycle correction pseudo-N-path circuit.<>     

Potential direction-finding accuracy of systems with antenna arrays configured as a set of an arbitrary number of rings

Configurations of antenna arrays for direction-finding systems in the form of a set of concentric circumferences are considered. An estimate of the potential accuracy of the measured bearing, which was obtained using the Cramer-Rao lower bound, is proposed. It is shown that in the case of antenna-feeder systems with antennas distributed uniformly over each circle, the potential accuracy is independent of the direction from which the received signal arrives.