Robust signal selection for the matched filter

A matched filter's performance is strongly related to the signal being detected and can be shown to be optimal when the signal is an eigenvector of the noise correlation matrix corresponding to a minimum eigenvalue. When fewer correlations are known than would be necessary to specify such an eigenvector, it is natural to choose a signal which is robust to the implied uncertainty in the noise dependency structure. This is shown to be tantamount to finding a tight upper bound on the minimum eigenvalue over all correlation matrices within the uncertainty class. Such a bound is achieved by the reduced correlation matrix of order equal to the number of available correlations, and hence the robust signal is shown to have this length. No matter how reasonable, any assumption used to extend the correlation matrix can degrade performance; a system designer should not try to use information that is not available     

A low-power digital matched filter for direct-sequencespread-spectrum signal acquisition

This paper presents a low-power 128-tap dual-channel direct-sequence spread-spectrum (DSSS) digital matched-filter chip. Design techniques used to reduce the power consumption of the system include latch-based register file filter structure, a high-rate compression scheme, optimized compressor cells, and semicustom layout design. To further reduce the power consumption and the hardware requirement of the clock tree, a double-edge-triggered clocking scheme is adopted. The proposed chip is fabricated using a 0.8-μm standard CMOS process. As the experimental results of the chip indicate, the matched filter can operate at 50 MHz and dissipates 184 mW at 5-V supply voltage. The supply voltage can be scaled down to 2 V for lower speed applications. As a consequence, the proposed design has low power consumption and can be used for code acquisition of DSSS signals in portable systems     

Correlation-based fiber sensor using a holographic matched filter

The principle of a fiber sensor based on an optical correlation technique is described and assessed for its feasibility. The device measures the correlation between the far-field radiation pattern of a multimode sensing fiber and a reference pattern stored in a holographic matched filter. The output is a monotonically decreasing function of the changes in the patterns caused by the perturbance applied to the fiber. The results of some preliminary experiments are discussed and some drawbacks of the technique are pointed out     

Acoustic-optical matched filter for LFM signals

The principle of building acoustic-optical matched filer for LFM signals is considered, its main parameters are analyzed and recommendations on their selection are elaborated.     

Mixed-signal matched filter for high-rate communication systems

A mixed-signal programmable filter suitable for high-rate communication systems is addressed. The proposed filter has analogue input and analogue-sampled outputs. The filter taps are stored in a digital memory and can be changed on the fly which is desirable in many practical applications such as adaptive filtering. The filter structure is based on a bank of digitally controlled transconductors along with small capacitors. The employed transconductors are based on simple Complementary Metal-Oxide Semiconductor (CMOS) transistors and thus can be integrated efficiently with the digital parts of systems. A cosine roll-off filter is designed and investigated by simulation in time and frequency domains. The results show that the proposed structure has a good speed-complexity-consumption trade-off.     

High-speed switched-current matched filter for WCDMA receivers

A matched filter (MF) based upon the cascoded class AB SI technique is presented for spread-spectrum communication receivers. Accomplished through both architectural and circuit developments, the filter's features include low power, high speed and compatibility with standard CMOS process inherent to SI signal processing. For performance assessment, a 31-tap 80 MS/s SI MF for despreading task in future high-speed WCDMA receivers is demonstrated.     

Sampling rate selection for a digital matched filter

The problem of selecting the sampling rate for the digital implementation of a matched filter for noncoherent digital communications is considered. The effects of bandwidth reduction and sampling are evaluated. A Nyquist rate of 8 samples per bit is found to be the critical value even with respect to the dependence on the carrier phase.     

Exact matched filter bound for two-beam Rayleigh fading

The matched filter bound (MFB) is exactly evaluated for a channel modeled by the sum of two delayed and independently Rayleigh-fading beams. It is shown that, if the two beams have comparable average powers, and if the delay spread is moderate or large, then considerable gain is obtained from a diversity-like effect. That is, it is as if the two beams could be detected separately and their results combined. This is true even though significant interference would seem to be present between the beams     

Differential matched filter architecture for spread spectrumcommunication systems

The authors present a new digital matched filter architecture: digital differential matched filter (DDMF), that employs novel schemes to reduce the number of multiplications and accumulations (M and A). Theoretical analysis shows that the DDMF saves half of the M and A hardware in comparison with the conventional filter, and maintains identical processing gain. This makes the proposed DDMF more suitable for direct sequence spread spectrum (DSSS) communication systems and low power VLSI implementations     

Simplified matched filter receiver designs for spread spectrumcommunications applications

The design of receiver architectures for use in direct sequence spread spectrum systems is reviewed. As it is difficult to construct the long matched filters for these systems, the authors propose a programmable receiver architecture which achieves the required high processing gain while, at the same time, simplifying the filter hardware requirements. Results are presented for a prototype receiver, based on digital signal processing (DSP) components, which can be reprogrammed for serial, serial-parallel or fully parallel operation while offering minimal degradation from theoretical performance     

A matched filter network for estimating pulse arrival times

Pulse arrival times are often close to the arrival times of pulses at nearby positions. A method that estimates arrival times from a series of closely related receptions has been developed. It combines the matched filter with the minimum path algorithm of network programming. In an environment where noise is present, the arrival time estimates using traditional matched filter processing degrade, owing to arrival time jumps equal to a period of the carrier. Results obtained from experimental and simulated pulses demonstrate that the method removes the jumps while retaining smaller-scale arrival time fluctuations that are of interest     

Chip-delay locked matched filter for DS-CDMA systems using longsequence spreading

This paper considers an improved single-user detection technique for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems using long sequence spreading (random-CDMA) Most of the known detection schemes for DS-CDMA suffer from either poor performance under power-imbalance (near-far like) conditions, excessive complexity, or incompatibility with systems employing long sequence spreading. To address these problems, this paper considers a signal-to-noise ratio maximizing linear time-invariant filter for one-shot bit symbol detection exploiting some information about the interferers. This filter, referred to as the chip-delay locked matched filter (CLMF), exploits the cyclostationarity in multiple-access interference, and it can offer good near-far resistance while remaining suitable for systems with long sequence spreading. The CLMF requires knowledge of interferers chip delays and signal powers; however, knowledge of their pseudonoise sequences is unnecessary. This paper also demonstrates the improvement in performances offered by the CLMF over other single-user receivers such as the conventional matched filter and noise-whitening matched filter performance is evaluated in terms of probability of outage for single-rate and dual-rate DS-CDMA systems using bandwidth-efficient chip pulses, over a single-path additive white Gaussian noise channel. Errors in the interferer chip delay estimates degrade the CLMF performance. However, if the root-mean-square value of these errors is less than 5% of the chip interval, then this degradation is small     

A matched filter using charge coupled device for pulse-code modulation

A matched filter using CCD for PCM is made. The experimental results of output waveform, transfer function and output signal-to-noise ratio are given and compared with the theoretical ones. The output signal-to-noise ratio for the non-return-to-zero codes is 1 dB below the theoretical value.     

A matched filter approximation for SC/MMSE iterative equalizers

This letter proposes a new iterative ISI equalization algorithm that offers low computational complexity: order L² with channel memory length L. The proposed algorithm is an extension of Reynolds and Wang's SC/MMSE (soft canceler followed by MMSE filter) equalizer: approximations are used properly to reduce the computational complexity. It is shown that the approximations used in the proposed algorithm do not cause any serious performance degradations from the trellis-based iterative equalization algorithms     

A new interpretation of the average matched filter for MSK-typereceivers

The minimum-mean-square-error approximation to a generalized minimum-shift-keying (MSK) signal using an offset quadrature phase-shift keying waveform with an elementary pulse, g(t), is considered. It is shown that the optimum shape of G(t), γ(t), coincides with the average pulse of the generalized MSK signal. Therefore, γ(-t) is the impulse response of the corresponding average matched fiber     

An adaptive Kalman filter for ECG signal enhancement

The ongoing trend of ECG monitoring techniques to become more ambulatory and less obtrusive generally comes at the expense of decreased signal quality. To enhance this quality, consecutive ECG complexes can be averaged triggered on the heartbeat, exploiting the quasi-periodicity of the ECG. However, this averaging constitutes a tradeoff between improvement of the SNR and loss of clinically relevant physiological signal dynamics. Using a bayesian framework, in this paper, a sequential averaging filter is developed that, in essence, adaptively varies the number of complexes included in the averaging based on the characteristics of the ECG signal. The filter has the form of an adaptive Kalman filter. The adaptive estimation of the process and measurement noise covariances is performed by maximizing the bayesian evidence function of the sequential ECG estimation and by exploiting the spatial correlation between several simultaneously recorded ECG signals, respectively. The noise covariance estimates thus obtained render the filter capable of ascribing more weight to newly arriving data when these data contain morphological variability, and of reducing this weight in cases of no morphological variability. The filter is evaluated by applying it to a variety of ECG signals. To gauge the relevance of the adaptive noise-covariance estimation, the performance of the filter is compared to that of a Kalman filter with fixed, (a posteriori) optimized noise covariance. This comparison demonstrates that, without using a priori knowledge on signal characteristics, the filter with adaptive noise estimation performs similar to the filter with optimized fixed noise covariance, favoring the adaptive filter in cases where no a priori information is available or where signal characteristics are expected to fluctuate.     

Vlsi programmable digital filter for video signal processing

High speed digital filtering is required in real time video signal processing, as well as high order filters are needed to match television studio signal quality. The hardware complexity involved by such system constraints may be faced by a two-fold approach, concerning both the architecture and the technological aspects of a specific electronics device devoted to the above task.This article deals with a processor especially developed for the purpose of fast digital video signal applications, such as filtering, equalization, interpolation and so on. The nonrecursive transposed F.I.R. (Finite Impulse Response) structure has been selected, which exhibits a linear phase behavior. A novel approach has been developed for the multipliers implementation, by optimizing an EPROM based look-up table storing the products between all video samples and the filter coefficients significant bits, resulting in a programmable system.TheProgrammable Filter Processor has been designed with a high level of parallelism and pipelining and a 1.2 µm CMOS EPROM, single metal technology has been employed for the integration process of the chip. This has been successfully production-tested for 40 Msamples/s throughput rate, thus both allowing to meet most video filtering applications and demonstrating the potentialities of nonvolatile memory technologies in embedded applications.Moreover multiple devices can be interconnected to yield multiprocessor structures for more demanding performances such as, cascaded or longer filters, input signal precision extension, computation improved accuracy, increased throughput rate, and two-dimensional signal processing.Work carried out in the framework of the agreement between the Italian P.T. Administration and the Fondazione UGO BORDONI.     

A BiCMOS continuous-time filter for video signal processingapplications

A fully integrated BiCMOS continuous-time filter for video signal processing applications is presented. It incorporates an input clamping circuit, a third-order equalizer, a fifth-order elliptic filter with sinx/x correction, and a 75-Ω driver. The architectures of the input and output amplifiers as well as the filter and the equalizer are chosen based on the extensive study of circuit structures and Monte Carlo simulation to meet the linearity requirement for the broadcast-quality video system. The complete chip achieves a low-pass filter response with a 5.5-MHz cutoff frequency (f_cc), 0.3-dB passband ripple, 20-ns group delay variation up to 0.9 f_c, and 43-dB attenuation at 1.45 f_c. With a nominal 2-Vpp signal at the output, measured results show 0.2% differential gain, 0.38° differential phase, and 1.7-mV rms noise demonstrating 10-bit linearity in a 1.5-μm 4-GHz BiCMOS process technology. The filter active area is 8 mm² and it dissipates 350 mW in a single 5-V power supply     

An adaptive matched filter that compensates for I,Q mismatch errors

An approach to adaptively match filter the I and Q components of complex-valued inputs consisting of a desired signal embedded in correlated external noise is presented. This approach is tolerant of I,Q mismatch errors, i.e., the external noise is effectively rejected and the desired signal enhanced in the presence of significant receiver I,Q errors. I,Q adaptive weighting removes many of the deleterious effects of I,Q quadrature detection imbalance, which can severely limit the adaptive matched filter (AMF) performance. However, for the I,Q AMF, the unknown desired signal's initial phase complicates the design procedure and even for a reasonable design criterion, the AMF performance can fluctuate significantly as a function of this phase. An I,Q AMF technique whose performance is almost phase invariant is developed, and example of its utility is shown     

Analysis of the adaptive matched filter algorithm for cases withmismatched clutter statistics

In the majority of adaptive radar detection algorithms, the covariance matrix for the clutter plus noise is estimated using samples taken from range cells surrounding the test cell. In a nonhomogeneous environment, this can lead to a mismatch between the mean of the estimated covariance matrix and the true covariance matrix for the test cell. Closed-form expressions are provided, which give the performance for such cases when the popular adaptive matched filter algorithm is used. The expressions are exact in some cases and provide useful approximations in others. To simplify the analysis, the samples from the surrounding range cells are assumed to be independent and identically distributed (i.i.d.), and these samples are assumed to be independent from the sample taken from the test cell. The performance depends on a small number of important parameters. These parameters describe which types of mismatches are important and which are not. Numerical examples are provided to illustrate how performance varies with each of the important parameters. Monte Carlo simulations are included that closely match the predictions of our equations. An airborne radar example is provided that demonstrates that covariance matrix mismatch can have a significant effect on performance in some practical cases