Search

The digital correlator is one of the most crucial data processing components of a radio telescope array. With the scale of radio interferometeric array growing, many efforts have been devoted to developing a cost-effective and scalable correlator in the field of radio astronomy. In this paper, a 192-input digital correlator with six CASPER ROACH2 boards and seven GPU servers has been deployed as the digital signal processing system for Tianlai cylinder pathfinder located in Hongliuxia observatory. The correlator consists of 192 input signals (96 dual-polarization), 125-MHz bandwidth, and full-Stokes output. The correlator inherits the advantages of the CASPER system, for example, low cost, high performance, modular scalability, and a heterogeneous computing architecture. With a rapidly deployable ROACH2 digital sampling system, a commercially expandable 10 Gigabit switching network system, and a flexible upgradable GPU computing system, the correlator forms a low-cost and easilyupgradable system, poised to support scalable large-scale interferometeric array in the future. [ABSTRACT FROM AUTHOR]

Large scale Radio Telescopes for Radio Astronomy highly depend on the availability of large (digital) processing capacities for imaging. Estimates concerning power efficiency for future Radio Telescopes lead to anticipated power consumption numbers beyond feasibility. To reduce the power budget, the use of approximate multipliers within the correlator is explored. A baseband equivalent executable model of a radio synthesis telescope is constructed to assess the effects of approximate multipliers. Besides ideal multipliers with floating point accuracy, the use of accurate 8-bit multipliers and 4 different types of approximate multipliers is explored. For each of these multipliers, the energy efficiency of an individual multiplier is known and used to determine the energy efficiency improvement of a correlator when using approximate multipliers. The effects of approximation are quantified by 3 metrics (Signal-to-Noise-Ratio (SNR), Spurious-Free-Dynamic-Range (SFDR) and Root-Mean-Square (RMS) level) derived from maps constructed by the executable model based on an empty sky with only a single point source. This is considered to be the worst case scenario. For illustration purposes, a more realistic input is processed by the model as well. The metrics have been determined based on different SNR levels at the input of each antenna element. For input SNR levels up to 10 dB, all types of approximate multipliers used in this paper can be exploited to improve energy efficiency of correlators, leading to a maximum energy reduction of 19 %. For input SNR values up to 30 dB an energy improvement up to 12 % can be achieved. These percentages are based on implementations in a 40nm low power IC technology at 1 GHz. [ABSTRACT FROM AUTHOR]

Modern and upcoming radio telescopes at low frequencies are often characterized by hundreds or thousands of antenna elements operating at wide bandwidths up to about 0.5 GHz. A spectral correlator for such an array is required to estimate the cross-power spectrum of the response of each element with that of every other element with a high spectral resolution. The resulting all-to-all connectivity between signals from the entire array poses a serious bottleneck. In this paper, we propose a simple digital receiver architecture that interfaces the digitized time series from a large number of antenna elements to a High-Performance Computing (HPC) cluster through a communication switch to overcome the data ingest bottleneck. Each HPC node can then perform wideband processing in steps of finite but significant time-slices for the entire array. We explain in detail the implementation of our architecture for the proposed expansion of the Ooty Wide Field Array (OWFA) into a 1056 element array. Since the proposed digital receiver is based on Field Programmable Gate Array (FPGA), it can be reconfigured for different applications. This is illustrated by considering the case of Phased Array Feeds (PAF) for the proposed expanded Giant Metrewave Radio Telescope (eGMRT). [ABSTRACT FROM AUTHOR]

We present an overview of the Graphics Processing Unit (GPU)-based spatial processing system created for the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The design employs AMD S9300x2 GPUs and readily available commercial hardware in its processing nodes to provide a cost- and power-efficient processing substrate. These nodes are supported by a liquid-cooling system which allows continuous operation with modest power consumption and in all but the most adverse conditions. Capable of continuously correlating 2048 receiver-polarizations across 400 MHz of bandwidth, the CHIME X-engine constitutes the most powerful radio correlator currently in existence. It receives 6.6 Tb/s of channelized data from CHIME's FPGA-based F-engine, and the primary correlation task requires 8. 3 9 × 1 0 1 4 complex multiply-and-accumulate operations per second. The same system also provides formed-beam data products to commensal FRB and Pulsar experiments; it constitutes a general spatial-processing system of unprecedented scale and capability, with correspondingly great challenges in computation, data transport, heat dissipation, and interference shielding. [ABSTRACT FROM AUTHOR]

One of the main technologies to open up a wider field of view for today's radio telescopes are phased arrays. This is especially the case for radio astronomy instruments operating below 2 GHz. Nowadays, the existing dish-type instruments are being upgraded with phased array feeds (PAF) in the focal plane. This increases the field of view at the expense of needing more analog electronics and digital signal processing. One of the digital signal processing functionalities used to combine the digitized signals from the PAF is a beam-former which creates multiple high sensitivity beams within the field of view of the dish. Before beams can be formed, the signals from the PAF need to be calibrated using a correlator. In this paper, we present a solution where these two operations are combined by using the beam-former also as a correlator. The statistics unit used as part of the beam-former implementation, can be used as well for calculating correlation products. With the proper settings of the beam-former weight of each beamlet, a frequency sub-band with a direction, can be used as a single cross correlation product. By implementing the correlator on the beam-former, the digital resources and development time can be reduced. To validate the idea, two versions of the algorithm are implemented in the Apertif PAF system on the Westerbork Synthesis Radio Telescope (WSRT). Results show that two full-bandwidth correlation matrices per beam, needed to determine the static beam weights for the calibration, and a single column of the correlation matrix, used to compensate for any drift between the receiver chains, can be performed. [ABSTRACT FROM AUTHOR]

Purpose Sensor networks have found wide applications in the monitoring of environmental events such as temperature, earthquakes, fire and pollution. A major challenge with sensor network hardware is their limited available energy resource, which makes the low power design of these sensors important. This paper aims to present a low power sensor which can detect sound waveform signatures.Design/methodology/approach A novel mixed signal hardware is presented to correlate the received sound signal with a specific sound signal template. The architecture uses pulse width modulation and a single bit digital delay line to propagate the input signal over time and analog current multiplier units to perform template matching with low power usage.Findings The proposed method is evaluated for a chainsaw signature detection application in forest environments, under different supply voltage values, input signal quantization levels and also different template sample points. It is observed that an appropriate combination of these parameters can optimize the power and accuracy of the presented method.Originality/value The proposed mixed signal architecture allows voltage and power reduction compared with conventional methods. A network of these sensors can be used to detect sound signatures in energy limited environments. Such applications can be found in the detection of chainsaw and gunshot sounds in forests to prevent illegal logging and hunting activities. [ABSTRACT FROM AUTHOR]

Modern global navigation satellite system (GNSS) front ends sample the received radio-frequency signal at an intermediate frequency (IF) and, then, downconvert it to baseband in the digital domain. A locally generated spreading code is subsequently correlated with the baseband signal at the sampling frequency. This can mean that the receiver correlates at an unnecessarily high frequency (sometimes more than four times the chipping rate). The power consumption is, thus, high. If the baseband signal is downsampled after appropriate filtering, the correlator can process at a fraction of the sampling frequency. The power dissipation is considerably reduced as a result. Furthermore, by resampling at an integer submultiple of the sampling frequency, not only is downsampling jitter eliminated, but also architectural configurability in the correlator is possible, allowing further reductions in power and resource consumption. In this paper, a dynamically configurable decimator for a matched filter correlator is presented. The mathematical model of the signal processing is analyzed for various downsample rates. The effective postcorrelator signal-to-noise-plus interference ratio is estimated in theory and measured by experiment, illustrating that the proposed decimator correlator outperforms the resample IF correlator. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the performance of code acquisition system in atmospheric optical code division multiple access (OCDMA) communications using optical orthogonal codes. Memory introduced by temporal correlation of optical fading process precludes us from using the Markov chain model for a code acquisition analysis. By considering this issue, we discuss how to extend the applicability of the Markov chain model to the atmospheric OCDMA communications. We analyze and compare the performance of correlator and chip level detector (CLD) structures in the acquisition system. In our analysis, we consider the effects of free space optical channel impairments, multiple access interference, and receiver thermal noise in the context of semi-classical photon-counting approach. Furthermore, we evaluate the performance of various two stage schemes that utilize different combinations of active correlator, matched filter, and CLD in search and verification stages, and we find the optimum acquisition scheme among them. Numerical results show significant improvement in reducing the acquisition time and required power for synchronization using our optimum scheme in the wireless OCDMA communications. [ABSTRACT FROM AUTHOR]

The Global Positioning System (GPS) has become widespread in many civilian applications. GPS signals are vulnerable to interference and even low-power interference can easily spoof GPS receivers. In this paper, two techniques are proposed based on correlators and adaptive filtering to diminish the effect of spoofing on GPS-based positioning. The suggested algorithms are implemented in the tracking loop of the receiver. As a first method, a high-resolution correlator is utilised to avoid big parts of the influence of interference. To improve the results, a multicorrelator technique is also employed. In the second method, an adaptive filter is used for estimating the parameters of authentic plus spoof signals. Interference elimination is performed by subtracting the estimated conflict effects from the measured correlation function. These techniques provide easy-to-implement quality assurance tools for anti-spoofing. As a primary step, in this article, the proposed algorithms have been implemented in a Software Receiver (SR) to prove the concept of idea in multipath-free environments. [ABSTRACT FROM AUTHOR]

According to the characteristics of the 21CMA correlator algorithm, we propose a novel high-efficient method to implement this specific algorithm on the Hadoop+CUDA platform, and it out-­performs the MPI alone and MPI+CUDA solutions. The proposed method improves the parallel model of the correlator. Compared to the earlier MPI solution, it greatly enhances the running performance by utilizing the advantages of GPU for FFT processing, vector multiplication and vector addition. The Hadoop software architecture, a big-data platform, is employed in the method by using Hadoop Streaming tool to realize parallel execution of non-Java programs running on distributed systems, and linear speed-ups on clusters are easily obtained. In addition, the resutt data and procedure logs can be flexibly managed in the parallel file system of the Hadoop HDFS, which provides a well precondition for future big-data analysis. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a technique of frequency domain correlation for illumination tolerant face recognition. A pair of correlation filters are generated from input image projected onto class specific subspace, called optimum projecting image correlation filter and from reconstructed image, called reconstructed correlation filter. As the test face image dynamically configures the nature of these two filters, illumination tolerance is achieved. A sharp peak at the correlation plane measured by peak to sidelobe ratio indicates the detection of test face image. The performance of the proposed strategy is evaluated on YaleB and PIE database. The proposed technique outperforms the other existing correlation filters. A hybrid optical system is used for the hardware implementation of the proposed system. [Copyright &y& Elsevier]

This paper presents a pulse-compression radar baseband analog signal processing integrated in a silicon process for low cost and power dissipation. The analog signal-processing circuitry exhibits the autocorrelation properties of the polyphase codes, maximizes the sensitivity and resolution of a pulse radar system, and alleviates speed and resolution requirements of the analog-to-digital converter (ADC) via an analog correlator. The circuitry includes a two-stage variable gain amplifier (VGA) for high dynamic range, a correlator/integrator circuit, a comparator, and offset calibration circuits. The differential 6-bit VGA is designed to adaptively track the Friis path loss through rapid change of the VGA gain and offset calibration, relaxing the dynamic range requirements of the correlator. The measured performance shows a VGA gain variation of 52 dB and a VGA group-delay imbalance of 50 ps over 64 states. The high-speed pulse compression/correlation is performed in analog current domain and the speed requirement on the ADC is reduced by a factor equal to the duty cycle lowering the ADC power consumption. The chip is fabricated in a 90-nm process, wire bonded on the FR4 printed circuit board, and tested with a Stratix IV field-programmable gate-array board to evaluate the system performance for different radar polyphase codes. [ABSTRACT FROM AUTHOR]

The proposed next-generation radio-telescope, the Square Kilometre Array (SKA), has ~3000 parabolic dish antennas and operates over many gigahertz of bandwidth. This results in a telescope with correlator requirements ~10 000 times more than any current telescope. This will be a challenge using traditional approaches. A method is proposed that will reduce the computational requirements for that part of the SKA where the antenna separation is not too great. This is done by deliberately introducing redundancy so that many of the outputs of the correlator measure the same data. We then show that the sum of these redundant correlations can be obtained efficiently by the use of fast convolution. The degree to which computational requirements are reduced is selectable. This translates directly into a power saving in the correlator and image processing. [ABSTRACT FROM AUTHOR]

Carrierless impulse radio ultra-wideband (IR-UWB) radios have attracted significant research interest due to their low system complexity and power consumption. Unfortunately, IR-UWB systems suffer from the difficulty in controlling the transmitted spectral mask because of process, voltage, and temperature variations. In this paper, a monolithic 3–5-GHz IR-UWB transceiver is presented that integrates both amplitude and spectrum tunability, thereby providing adaptable spectral characteristics for different data rate transmission. The noncoherent receiver employs a simplified low-power merged correlator, eliminating the need for a conventional sample-and-hold circuit. After self-correlation, the demodulated data is digitally synchronized with the baseband clock. The 4 \ mm^2 0.13 \mu\ m CMOS transmitter and receiver consume 2.2 and 13.2 mW, respectively at the data rate of 100 Mb/s. The measured peak-to-peak transmitted pulse amplitudes are 240, 170, and 115 mV, with a tunable frequency range of 3.2–4.1 GHz. The receiver exhibits a maximum gain of 70 dB, noise figure of 8.6 dB, and the input 1-dB compression point of -\28 dBm. With off-chip antennas, the transceiver achieves a bit error rate of \10^-3 at a sensitivity of -\50 dBm. [ABSTRACT FROM AUTHOR]

This paper presents a carrierless RF-correlation-based impulse radio ultra-wideband transceiver (TRX) front-end in a 130-nm CMOS process. Timing synchronization and coherent demodulation are implemented directly in the RF domain, targeting applications such as short-range energy-efficient wireless communication at gigabit/second data rates. The 6–10-GHz band is exploited to achieve higher data rate. Binary phase-shift keying modulated impulse is generated by edge combining the delayed clock signal at a lower frequency of 2 GHz to avoid a more power-hungry phase-locked loop at higher frequency (e.g., 8 GHz). An on-chip pulse shaper inside the pulse generator is designed to provide filtering for an edge-combined signal to comply with the Federal Communications Commission spectrum emission mask. In order to achieve 25-ps delay accuracy and 500-ps delay range for the proposed two-step RF synchronization, a template-based digital delay generation scheme is proposed, which delays the locally generated trigger pulse instead of the wideband pulse itself. Occupying \ 6.4 mm^2 of chip area, the TRX achieves a maximum data rate of 2 Gb/s and a receiver (RX) sensitivity of -\64 dBm with a bit error rate of \10^-5, while requiring only 51.5 pJ/pulse in the transmitter mode and 72.9 pJ/pulse in the RX mode. [ABSTRACT FROM AUTHOR]

recent development in radio astronomy is to replace traditional dishes with many small antennas. The signals are combined to form one large, virtual telescope. The enormous data streams are cross-correlated to filter out noise. This is especially challenging, since the computational demands grow quadratically with the number of data streams. Moreover, the correlator is not only computationally intensive, but also very I/O intensive. The LOFAR telescope, for instance, will produce over 100 terabytes per day. The future SKA telescope will even require in the order of exaflops, and petabits/s of I/O. A recent trend is to correlate in software instead of dedicated hardware, to increase flexibility and to reduce development efforts. We evaluate the correlator algorithm on multi-core CPUs and many-core architectures, such as NVIDIA and ATI GPUs, and the Cell/B.E. The correlator is a streaming, real-time application, and is much more I/O intensive than applications that are typically implemented on many-core hardware today. We compare with the LOFAR production correlator on an IBM Blue Gene/P supercomputer. We investigate performance, power efficiency, and programmability. We identify several important architectural problems which cause architectures to perform suboptimally. Our findings are applicable to data-intensive applications in general. The processing power and memory bandwidth of current GPUs are highly imbalanced for correlation purposes. While the production correlator on the Blue Gene/P achieves a superb 96% of the theoretical peak performance, this is only 16% on ATI GPUs, and 32% on NVIDIA GPUs. The Cell/B.E. processor, in contrast, achieves an excellent 92%. We found that the Cell/B.E. and NVIDIA GPUs are the most energy-efficient solutions, they run the correlator at least 4 times more energy efficiently than the Blue Gene/P. The research presented is an important pathfinder for next-generation telescopes. [ABSTRACT FROM AUTHOR]

Abstract: The Search for ExtraTerrestrial Intelligence (SETI) finally has its own full-time telescope. The Allen telescope array (ATA) in Northern California was dedicated on October 11, 2007. This array, which will eventually be composed of 350 small radio antennas, each 6.1m in diameter, is being built as a partnership between the SETI Institute and the University of California Radio Astronomy Laboratory. Last October, Paul G. Allen (who provided the funds for the technology development and the first phase of array construction) pushed a silver button and all 42 antennas of the current ATA-42 slewed to point in the direction of the distant galaxy M81. Specialized electronic backend detectors attached to the ATA began making a radio map of that galaxy and simultaneously began SETI observations of HIP48573, a G5V star near M81 on the sky and a distance of 264 light years from Earth. The Allen telescope array will greatly improve the speed of conducting SETI searches over the next few decades, and it will allow a suite of different search strategies to be undertaken. This paper summarizes some of the earliest SETI observations from the array, and describes the search strategies currently being planned. [Copyright &y& Elsevier]

A wideband correlator, with 45% relative bandwidth is proposed at the frequency range of 3.0–5.1 GHz. The structures of the correlator components such as the delay line and the Wilkinson power divider are designed to be realized in transmission line using the Agilent's Advanced Design System. The correlator made by using three unique wideband 3-dB couplers, rat-race coupler, and one 3-dB Wilkinson power divider to reach the required bandwidth. The insertion loss, amplitude imbalance, and phase imbalance between ports are presented. The proposed correlator makes compact size better than correlator of conventional structure. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1771–1774, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25305 [ABSTRACT FROM AUTHOR]

The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT. [ABSTRACT FROM AUTHOR]

Correlators play key roles in impulse radio ultrawideband (IR-UWB) transceivers. Multiplier-based correlator performs correlation-type demodulation in addition to select desired UWB signals by correlating incoming pulses with templates. This paper reports design and implementation of a fully integrated low-power broadband multiplier-based correlator for a 3.1-10.6-GHz fullband IR-UWB receiver in 0.18 μm CMOS that consists of a UWB multiplier core, two UWB pulse generators, single-ended-to-differential-ended converter, a first-order RC integrator with a 200-MHz bandwidth, and a buffer. Measurement results confirm desired correlation-type demodulation and correlation functions with a conversion gain of 11.03 dB, noise figure of 15.7 dB, very low power consumption of 52mWand a 1-dB compression point of better than-0.8 dBm over a 7.5-GHz bandwidth. [ABSTRACT FROM AUTHOR]

A single-chip broadband CMOS receiver front-end, integrating a low-noise amplifier (LNA), a correlator, and a template pulse generator, was investigated in nonsinusoidal time-domain environment for possible use as an impulse-type ultra-wideband (UWB) receiver front-end. Particularly, the CMOS LNA and the multiplier making up the core component of the correlator were designed, fabricated, and tested to verify operation in the UWB range. Time-domain results of the integrated CMOS receiver front-end demonstrate its workability as a receiver for nonsinusoidal UWB applications. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2590–2595, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24682 [ABSTRACT FROM AUTHOR]

Abstract: The ground wire on top of a H.V. transmission line poses a unique problem when measuring the resistance of pole footings. With a multimeter most of the current is diverted away from the footing and a simple clamp-on type current meter is impractical for poles ranging in diameter from 8 to 32in. In addition, clamp-on meters typically fail below a few milliamperes but sub-milliampere measurements are required for accurate monitoring of pole footing resistance. A correlator-based sub-milliampere current measurement system using giant magneto-resistive (GMR) magnetic field sensors is reported in this paper. A correlator-based phase insensitive algorithm was used with injected currents at 94Hz. Experiments conducted on a pole in the laboratory indicate measurement of current values exceeding 1mA with a standard deviation of less than 2%. Measurements were also performed with current values as low as 0.2mA with a standard deviation of 16%. Details of the system, correlator algorithm, and results are presented in this paper. [Copyright &y& Elsevier]

Abstract: An encrypted holographic scheme with a compact alignment system for a phase key is proposed. Alignment for a phase key is performed by a holographic correlator. A filter in the correlator system contains the phase information used for encryption. Thus, it can be used to check the authorization of the phase key. Owing to the shift-invariant property of the holographic correlator, the location of the correlation peak is highly related to the alignment of the phase key. Therefore, the phase key can be repositioned on the desired location by searching for the specific position of the correlation peak. With the help of the correlator, alignment of the phase key can be done in 1min. Experimental results using a correlator system in support of our proposed idea are demonstrated as well. [Copyright &y& Elsevier]

This paper studies a frequency offset estimation and compensation technique taking advantage of Complementary Code Keying (CCK) in a baseband architecture. The proposed technique can switch between coarse and fine frequency offset estimation subsystems in order to achieve lower estimation errors and lower bit-error rates (BERs). The architecture mainly exploits the specific characteristics of the CCK code set; thus it blindly extracts the frequency offset without any assistance from a training sequence. The proposed technique is very suitable to be employed in a CCK-based WLAN system for the purpose of increasing data transmission rate. Extensive computer simulations show that the proposed technique and its architecture realization exhibit superiority in overall system performance. [ABSTRACT FROM AUTHOR]

Sea surface salinity can be remotely measured by means of L-band microwave radiometry. However, the brightness temperature also depends on the sea surface temperature and on the sea state, which is probably today one of the driving factors in the salinity retrieval error budgets of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission and the NASA—Comisión Nacional de Actividades Espaciales Aquarius/SAC-D mission. This paper describes the Passive Advanced Unit (PAU) for ocean monitoring. PAU combines in a single instrument three different sensors: an L-band radiometer with digital beamforming (DBF) (PAU-RAD) to measure the brightness temperature of the sea at different incidence angles simultaneously, a global positioning system (GPS) reflectometer [PAU-reflectometer of Global Navigation Satellite Signals (GNSS-R)] also with DBF to measure the sea state from the delay-Doppler maps, and two infrared radiometers to provide sea surface temperature estimates. The key characteristic of this instrument is that both PAU-RAD and the PAU-GNSSIR share completely the RFIIF front-end, and analog-to-digital converters. Since in order to track the GPS-reflected signal, it is not possible to chop the antenna signal as in a Dicke radiometer, a new radiometer topology has been devised which makes uses of two receiving chains and a correlator, which has the additional advantage that both PAU-RAD and PAU-GNSSIR can be operated continuously and simultaneously to perform the sea-state corrections of the brightness temperature. This paper presents the main characteristics of the different PAU subsystems, and analyzes in detail the PAU-radiometer concept. [ABSTRACT FROM AUTHOR]

Whereas boson coherent states with complex parametrization provide an elegant, and intuitive representation, there is no counterpart for fermions using complex parametrization. However, a complex parametrization provides a valuable way to describe amplitude and phase of a coherent beam. Thus we pose the question of whether a fermionic beam can be described, even approximately, by a complex-parametrized coherent state and define, in a natural way, approximate complex-parametrized fermion coherent states. Then we identify four appealing properties of boson coherent states (eigenstate of annihilation operator, displaced vacuum state, preservation of product states under linear coupling, and factorization of correlators) and show that these approximate complex fermion coherent states fail all four criteria. The inapplicability of complex parametrization supports the use of Grassman algebras as an appropriate alternative. [ABSTRACT FROM AUTHOR]

In an attempt to measure and correct the surface profile of the Sheshan 25-m radio telescope, the author carried out a phase coherent holographic experiment at 12.26 GHz with a geostationary communication satellite SINO-1 in the far field. To improve the spatial resolution, the author took the drift of the communication satellite into consideration. For the backend, a digital cross correlator was used to measure the complex beam pattern of the antenna under test. According to the data collected in the experiments, the holography software can give the energy distribution map, error map, and a suggested adjustment for every junction of the panels, after four iterations of measurement and adjustment in a week, the surface accuracy of the antenna is improved from 0.948 mm to better than 0.5 mm. The experiment shows that the microwave holography is much faster and more convenient than traditional method. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 467–470, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22171 [ABSTRACT FROM AUTHOR]

ABSTRACT: The majority of published experimental evaluations of the performance of the IBIS™ system are based on very specific conditions, mainly considering IBIS™ as a tool to create a "ballistic database." No recent reports were found covering the performance of the IBIS™ system to search an open case file of realistic structure. In this paper, the performance of the IBIS™ correlator will be evaluated, based on four different data sources that predominantly concern the operation of the central collection of evidence ammunition of the Federal Criminal Police Office (BKA), Germany. The results allow a conclusion on the success and error rates to be expected of the IBIS™ correlator in a realistic OCFDB ("open case file database") environment, given certain conditions. It was found that success rates of 75–95% for cartridge case comparisons and 50–75% for bullet comparisons can be achieved in practice. Recommendations for a most efficient way to operate the IBIS™ electronic comparison system will be presented based on the results of the evaluations. The terms and definitions in this report completely correspond with the definitions in an earlier article. Familiarity with this article is therefore absolutely necessary to fully understand many of the statements presented here. [ABSTRACT FROM AUTHOR]

ABSTRACT: The electronic system IBIS™ has been used by numerous agencies worldwide as the standard tool to compare firearm markings on bullets and fired cartridges. There is a general interest among users concerning the likelihood with which the IBIS™ correlator may locate hits in its databases. Test results of the performance under different test conditions have been published in various papers. Experience has also been gained with the IBIS™ system from years of practical usage. All of these findings are difficult to compare with each other. No systematic presentation exists that actually shows the parameters upon which the success rate of the IBIS™ correlator depends. There has also been no mention of what values these parameters take on during each test. This paper first generally defines the success and error rates of the IBIS™ correlator. The parameters used will be discussed. Results of previously published tests will be re‐examined based on this methodology. An illustrative form of presentation for the success rate of an electronic comparison system will also be suggested. It will be shown that the success rate of the IBIS™ correlator highly depends on the quality of the firearms‐generated markings. It increases with the number of considered mark types, the number of available signatures per firearm, and the number of items inspected in the hit list. The success rate decreases with the database size. The paper will conclude with a series of practical recommendations for the setting up and successful operation of an electronic collection of ballistic evidence. [ABSTRACT FROM AUTHOR]

The article discusses the spatial position detection of a three-dimensional (3D) object by a correlator based on Fourier transform profilometry (FTP). It implies that if 3D object in the input scene is shifted spatially, the correlation output is shifted to the corresponding position in the output plane and the phase of the correlation output is shifted correspondingly. The squared value of the correlation output of the translated 3D object is equal to the squared autocorrelation value.

Due to its high-performance broadcast capability, M-ary phase-shift-keying (MPSK) direct sequence code division multiple access (DS/CDMA) technique is widely used in terrestrial and satellite communications to provide wired/wireless services such as audio broadcasting, video broadcasting and high-speed data transmission. However, both coherent and noncoherent MPSK modulation schemes are sensitive to the carrier frequency offset (CFO) incurred by transceiver oscillator instability and/or Doppler shift. In this paper, a nondata-aided and nonphase-based automatic frequency control (AFC) method for MPSK DS/CDMA transceivers is proposed. Different from phase-based AFC approaches, which utilize the frequency-offset-induced phase rotation and suffer from the modulo- 2π phase ambiguity, the proposed method exploits the frequency-offset-induced power degradation and has a wide tracking range of twice the symbol rate, which is independent of the phase keying number as well as the spreading code length. To shorten the tracking time of AFC, the improved steepest descent algorithm and the reshaped S curve are employed. Due to its wide tracking range, short tracking time and low implementation complexity, the proposed AFC method is attractive for terrestrial and satellite-based digital broadcasting. [ABSTRACT FROM AUTHOR]

The low-frequency very-long-baseline interferometry network (LFVN) project was started in 1996, having the purpose to arrange the international very-long-baseline interferometry (VLBI) cooperation with participation of former Soviet Union radio telescopes. Currently there are three directions of LFVN development: a Mk 2 subsystem at 92 cm wavelength for solar research, an international S2 ad hoc array at 18 cm for active Galactic nuclei and OH-maser survey, and VLBI radar at 6 cm for investigation of Solar System bodies. 14 VLBI experiments were carried out using various combinations of radio telescopes in Canada, China, England, India, Italy, Japan, Latvia, Poland, Russia, South Africa, Ukraine and USA. The five sessions were processed by the Jet Propulsion Laboratory (California Institute of Technology) Block II and Dominion Radio Astrophysics Laboratory Penticton correlators. The Russian Mk 2 correlator in Nizhny Novgorod is under development. The paper describes the main project milestones, results obtained so far and further plans. [ABSTRACT FROM AUTHOR]

When several moving targets are detected by two two-dimensional angle sensors (elevation and azimuth angles) separately spaced, three-dimensional tracking of each target is possible if the range to each target is computed by triangulation. What is important in such a step is correlation processing to find out which pairs of sensor information are obtained from the same target. Especially, if several targets enter a region that can be considered within the same plane seen from the two angle sensors, a false intersection with no actual target, namely, a ghost, is generated among the intersections of the line of sight from the sensor to the target so that the correlation process becomes difficult. In this paper, the angle and angular velocity of the target with respect to each sensor are tracked by an angle tracking filter. The proposed system for the correlation process carries out discrimination of the same target by using the angle tracking results. By means of simulation, the performance of the proposed system is investigated. It is made clear that the proposed system can effectively eliminate the ghosting when several targets enter temporarily the same plane. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 30–38, 1999 [ABSTRACT FROM AUTHOR]