Accurate, least-squares based bias free direction-of-arrival (DOA) estimation from targets using a circular array is discussed. The proposed estimation method is based on a recently proposed decorrelation technique that uses regression sum of squares. The estimation meets Cramer-Rao bounds for any circular array geometry that uses either a large or a small number of sensors. The method is versatile as it can be used in accurate angle estimation even when sensors are placed sparsely and non-uniformly on the circle. The method is computationally efficient since matrix inversions can be avoided. Possibility of DOA estimation from extremely close-by targets with very small angles of separation is demonstrated.

A Photoplethysmographic (PPG) signal classification scheme for motion artefact detection is proposed. In the feature extraction, the PPG signal is modeled as a periodic signal with fundamental frequency and harmonics using a least-squares based algorithm. The extracted features correctly represent the morphological information of the PPG signal. A support vector machine (SVM) is used in the classification. A procedure is adopted to make the feature set scale and position independent, which improves the classification accuracy. Using 5 harmonics, a classification accuracy of 96.55% is achieved. As 26 different normal PPG morphologies are used in the classifier, the system would be able to identify any normal PPG signal among motion artefacts on a single beat basis.

An accurate frequency estimation method from a signal consisting of multiple complex sinusoids is presented. The method avoids inversion of data dependent matrices of large dimensions, and hence do not suffer from rank deficiency of the data covariance matrix. Using recursion, a procedure to reduce mw/t/-dimensional maximum likelihood estimation to a series of one-dimensional optimization while achieving Cramer-Rao bounds for estimation is proposed.

Photoplethysmographic signals are synthesized using a Fourier representation with a fundamental and 2 harmonic components, and an accurate method for parameter estimation using this synthesis model is discussed. The estimated parameters enable to determine physiologically meaningful features related to arterial stiffness, heart rate variability, blood pressure variations, etc. The method allows signal feature extraction in a uniformly sampled manner avoiding complicated signal interpolations. The modelling performances are evaluated using real signals collected in a laboratory environment.

Abstract The performance of decision‐directed approach for joint data detection and channel estimation for continuous phase modulation (CPM) signal is limited because of an inevitable decision delay, which results in a trade‐off between data detection and channel estimation. In this paper, a novel hard output demodulation that solves the conflict requirement on the decision delay by predicting the channel coefficients over a given observation interval through a Kalman filter is proposed for uncoded CPM signal. The prediction guarantees high channel tracking capability and meanwhile maintains the accuracy of data detection. The proposed hard output demodulator is further extended to design a soft‐input soft‐output demodulator for serially concatenated CPM signal, which allows iterative processing. The convergence behavior of the proposed iterative receiver is presented. Simulation results show that the proposed demodulators provide improved performance in terms of bit error rate over some existing algorithms. Copyright © 2014 John Wiley & Sons, Ltd.

This paper presents a robust design of the transmit beampattern for uniform linear antenna arrays. Existing designs are usually completed at the stage of achieving an optimal transmit covariance matrix from identifying a weighting matrix with the assumption of ideally orthogonal waveforms. However, we propose a compensation technique to achieve the optimal covariance matrix without the requirement of orthogonality. The corresponding solutions identify a set of weighting matrices that are robust against the imperfection of the waveforms. As a result, a set of easy-to-generate partially correlated linear frequency modulated (LFM) waveforms can be used to achieve identical transmit beampatterns which could be synthesized by ideally orthogonal multiple-input multiple-output (MIMO) radar waveforms. The proposed robust design is evaluated via numerical examples.

A Discrete Fourier transform (DFT) based method for estimating a sequence of frequencies is presented. The method is computationally efficient and also meets the Cramer-Rao bound. The method is then used for symbol detection in a Continuous Phase Modulation receiver. The performance of detection has been analyzed and simulation results are provided for comparison against other existing algorithms. It is shown that the proposed DFT based method is advantageous as its implementation is independent of the modulation index and the bit error performance can be predetermined.

The problem of iterative data detection and channel estimation for space‐time block coded continuous phase modulation (CPM) signals over quasi‐static flat fading channels is studied in this study. Firstly, the combination of space‐time block code with CPM is not as straightforward as with linear modulation schemes, because of the requirement of phase continuity and the associated inherent memory of CPM. Therefore a novel block construction method is proposed to insert a tail sequence into each block for ensuring the phase continuity. Secondly, at the receiver the expectation–maximisation algorithm is applied to channel estimation and the estimated channel information is used to evaluate a posteriori probability for data detection. The channel estimation and data detection work iteratively. Simulation results show that the spectral efficiency of transmission is improved by the proposed block construction method and that the proposed iterative receiver outperforms its non‐iterative counterpart significantly.

The design of the transmit beampattern of a radar system aims to focus the energy of the transmitted signals to the desired spatial section(s) in order to enhance the direction of arrival (DOA) estimation at the receiver. In this paper, we consider this problem for both multiple-input-multiple-output (MIMO) and phased-array radar from the perspective of finite impulse response (FIR) filter design. For MIMO radar, we formulate the design as a feasibility problem (FP) and show its advantages over the existing methods. For phased-array radar, we use the spectral factorization technique which has been considered to be better than conventional filter design methods. It is shown that the two systems can achieve similar transmit beampatterns for identical number of transmit antennas and waveform energy. This is contradictory to the existing argument that MIMO radar can achieve more flexible transmit beampattern design over its phased-array counterpart. Simulation results are provided and discussed.

In this paper, we propose a novel adaptive soft input soft output (SISO) demodulator that addresses the problem of joint data detection and channel estimation for serially concatenated continuous phase modulation (SCCPM) operating in a time-varying frequency-flat fading channel. Due to its ability of incorporating prior symbol probabilities and its soft output decisions, the proposed SISO demodulator is well suited for serially concatenated CPM systems in attaining better performance through iteration. The bit error rate (BER) results of the proposed iterative receiver and the BER comparison with SISO demodulators based on the per-survivor processing (PSP) and single estimation processing (SEP) methods are presented.

Multiple-input-multiple-output (MIMO) radar transmit beamforming mainly relies on designing transmitted signals with an appropriate covariance matrix. The signals can be designed using a two-step method which first optimizes the covariance matrix and then searches for the signals accordingly. A more efficient way is to synthesize transmitted signals by designing a weight matrix given a set of orthogonal waveforms, which makes use of both MIMO waveform diversity and phased-array transmit gain. In this paper, we propose a method to design the transmit beampattern by solving a semidefinite programming (SDP) problem. Then the eigen-decomposition of the optimal covariance matrix yields the weight matrix. Therefore it is called the SDP-EIG method. As a result, the overall transmitted waveforms are obtained more simply and efficiently, and the number of orthogonal signals required to form a desired beam reaches its minimum.

This paper addresses the problem of joint data detection and channel estimation on continuous phase modulation (CPM) operating under a frequency-flat time-varying Rayleigh fading channel. The proposed framework comprises of two parts working in a joint manner: a symbol by symbol MAP CPM receiver and a channel tracking scheme. We first illustrate the robustness of MSK over modulation schemes without memory such as BPSK in joint data and channel estimation scheme. In order to adopt coherent demodulation, channel tracking is commonly used in time-varying channels. The underlying channel model in conjunction with data based estimate enables the Kalman filter to produce LMMSE estimates of the channel coefficients. Most literature do not consider the channel estimation error covariance in data detection. Here, A MAP data detection combined with Kalman tracking of channel coefficients is proposed in which we consider the channel error covariance for every step of MAP data detection. The simulation results show that the proposed scheme offers good performance in moderate or even high fading rate environments.

Spectral efficiency is a major requirement in ultra-wideband (UWB) communication systems because of very low power spectral density (PSD) regulations imposed on the transmitted signals. Besides, large number of orthogonal waveforms is highly desirable in multiuser systems. In this study, the design of a set of spectrally efficient orthogonal waveforms is investigated. The design of UWB waveforms based on orthogonal Hermite–Rodriguez basis functions and linear frequency modulation (LFM) is proposed herein. The design is formulated as a quadratic semi-infinite programming problem with spectral and orthogonality constraints. Numerical examples are presented to illustrate the effectiveness of Hermite–Rodriguez-based waveforms with the proposed optimisation approach. Comparison with a recent result shows that the proposed approach compares favourably with those reported in the literatures in terms of the number of waveforms can be produced and the achievable spectral efficiency of the designed waveforms.

In this paper, a novel receiver for joint data detection and channel tracking on continuous phase modulation (CPM) operating under a frequency-flat time-varying Rayleigh fading channel is proposed. Due to the inherent memory of CPM, channel tracking on CPM is not as straightforward as on PSK and FSK, and therefore we first derive a phase estimation based CPM scheme to facilitate the phase tracking procedure. The most common method of channel tracking involves Kalman filter, which needs to know the channel model and environmental conditions. In here, we propose to use an alpha beta filter to realize a kind of 'blind' tracking independent of channel conditions. The results show that, in environments where a detailed channel model is unknown and channel variation is considerable, the proposed receiver can provide satisfactory BER performance.

In this paper, a new bidirectional decision feedback equalizer (BiDFE) is proposed. The novelty of the proposed structure is that the proposed equalizer design is based on channel zeros, which is different from traditional BiDFE designs. The proposed bidirectional zero-based decision feedback equalizer (BiZDFE) efficiently exploits the time reversal operation, which results in that zeros of the equivalent channel seen from equalizer are the reciprocals of the actual channel zeros. It is shown that BiZDFE is more efficient in fading channel equalization than traditional BiDFE and minimum mean square error-decision feedback equalizer (MMSE-DFE).

In active imaging, information such as range and velocity of a target can be obtained by transmitting a signal and processing the received signals. Signal processing of acoustic signals scattered from distributed targets has become an increasing attention to the researchers. The delay-scale wideband spreading function (WSF) is often used to characterize the distributed targets environment. This paper presents an efficient technique for estimating WSF using Hermite decomposition. In realistic sonar and radar, it may be necessary to detect more than one target simultaneously. Under this scenario, resolution is a major concern to be considered to separate multiple targets. This paper focuses on the applications of Hermite decomposition to efficiently compute WSF and the use of multiple transmissions to improve resolution

Sinusoidal models have long been used in the processing of audio signals. Many of these models are usually used to select significant frequencies in the amplitude spectrum for analysis and synthesis purposes. Therefore, when using these models, it is important to estimate the true frequency of the multiple sinusoids present in the signal. In this paper, the performance of frequency estimation using the phase vocoder is investigated. The performance of the frequency estimation under varying noise power and different window shapes and sizes is analyzed. The effect of the presence of multiple sinusoids in the signal on the frequency estimation is also discussed. In particular, the frequency bias resulting from the presence of multiple sinusoids, the selection of optimum window size and the impact of the frequency of the sinusoids on the estimates are comprehensively investigated

The pulse-pair (PP) method is an efficient time-domain-based technique of frequency estimation, which requires a very low number of multiplications, thus ideally suited for field-programmable gate array-type hardware implementations. The optimum frequency estimation using the PP method needs a lag value equal to two-thirds of the signal length, and requires phase unwrapping that usually makes the technique computationally unattractive. In this letter, we propose efficient techniques for estimating frequency using the optimum PP method and multiple correlation lags

A novel efficient technique, based on a Radon-ambiguity transform (RAT), for time delay and Doppler stretch estimation is presented. The proposed approach combines the narrowband ambiguity function (NAF), the wideband ambiguity function (WAF), and the Radon transform (RT) to estimate multiple targets in noisy environments. The main ridges of NAF represent straight lines whose slopes depend on the Doppler rates of the moving targets. These lines could be effectively detected by computing the RT of the NAF for all possible angles. However, the computation of RT for all possible angles is computationally exhaustive. It is shown that, without calculating the entire RAT, it is possible to estimate target parameters using only a single slice of RAT, i.e., using an appropriate projection of the NAF. The resolution issue and the effect of the integration length of RAT in complex white Gaussian noise are also discussed. It is demonstrated that the proposed method can successfully separate overlapping targets.

This paper provides a new frequency estimator based on the multiple lags of autocorrelations with discrete Fourier transform (DFT) phase unwrapping. It is proved that this estimator is efficient for short data length while maintaining a low signal noise ratio (SNR) threshold. It is also shown that this estimator is statistically similar to maximum likelihood estimator (MLE), but with lower computational load. Furthermore, the estimator can also be applied to frequency estimation in the presence of moving average (MA) colored noise. In this case, it is shown that the variance of the estimator achieves the Cramer-Rao bound (CRB) asymptotically.

The pulse-pair (PP) method is an efficient technique of frequency estimation, which requires a very low number of multiplications. Therefore, it is ideally suitable for FPGA type hardware implementations, especially in high frequency communication applications, as the multiplications are relatively expensive for silicon area optimization. The optimum frequency estimation using the PP method needs a lag value equal to the two-third of the signal length. In this paper, we use a new efficient technique for evaluating the optimum PP method without resorting to phase unwrapping. Detailed discussion of the performance of the optimum PP method is provided in the paper, for various fading environments.

In synchronous digital hierarchy and plesiochronous digital hierarchy networks, it is frequently necessary to recover a data clock from a gapped clock derived from stuff information present at the desynchronizer. In this paper, a comprehensive analysis of the timing jitter resulting from phase-locked loop-type desynchronizers is presented. This analysis is different from the conventional analysis where the jitter is represented using a phase-error sequence. It is shown that such a simplified approach cannot accurately describe the jitter at the output of the desynchronizer. From the detailed analysis, it is also shown how the use of threshold modulation at the synchronizer reduces the low-frequency jitter at the desynchronizer. It has been demonstrated in the paper that when threshold modulation is used at the synchronizer, the dominating low-frequency jitter terms cannot be explained by the conventional jitter analysis methods. Therefore, in future networks, where tighter jitter performances are to be imposed on the synchronizers, jitter characterization using the proposed true jitter analysis technique would be very useful.

Blind channel estimation using 2/sup nd/ order statistics of the over-sampled received signal with the exploitation of signal cyclo stationary properties, has gained much attention recently. A novel estimation procedure for a base-band communication channel parameters using a frequency domain model is proposed in this paper. The described method provides useful insight to the channel estimation problem. The frequency domain approach works by independently and blindly estimating the channel amplitude and phase spectra. This approach has also been extended for evaluating estimation bounds (CRB $Cramer-Rao bounds) of channel parameters. Furthermore, the proposed frequency domain technique does not depend on the noise probability density function and could be easily extended for evaluating the estimation performance in the presence of colored noise.

Digital watermarking for multimedia information has been widely adopted as a measure to detect copyright infringements. In many watermarking schemes, often only one watermarking signature is used in the embedding of hidden information. This paper introduces new multiple sequence families with good auto- and cross-correlation properties, which are ideal in the application of digital watermarking. It is also envisaged that the good cross-correlation property of these multiple families of sequences allows for the use of multiple signatures in a watermarking scheme. Multiple signatures increases the robustness of the watermarking scheme and also retrieving for independent signatures is straightforward due to the low cross-correlation property of the the member sequence.

Pulse stuffing and pointer adjustment are necessary for clock rate adaptation in synchronizers used in synchronous digital transmission networks (e.g.,, SDH/SONET). The method of adaptive threshold modulation (AT-Mod) may be used in the synchronizer to reduce the resulting waiting time jitter. This paper in detail addresses the performance of the method of AT-Mod technique. Using a nonlinear model to represent the thresholder, the paper provides mathematical expressions for the filtered jitter power resulting from AT-Mod in the synchronizer. The accuracy of using such a nonlinear technique is also demonstrated. Furthermore, the possibility of improving the AT-Mod circuit for further jitter reduction is discussed. Because the improved AT-Mod circuits are not always guaranteed to be stable, a stability analysis is presented. The impact of input noise on the filtered jitter is also investigated in the paper.

As an alternative to conventional FIR filters, IIR filter architecture based on orthonormal Laguerre functions is proposed for applications in narrow-band filtering. A Laguerre IIR filter design methodology is presented via a frequency transformation in the digital domain. The Laguerre filter can then be efficiently designed using a min-max criterion via a modified Parks-McClellan (1972) FIR filter design algorithm. The proposed Laguerre IIR filter architecture is easy to implement because it needs only a small number of components and therefore well suited for VLSI circuits. The impact of the selection of filter pole on the filter stability and phase linearity is discussed in the paper. The robustness issue of the narrow-band Laguerre IIR filter is also addressed.

Sigma-delta (/spl Sigma/-/spl Delta/) modulators have been widely used over the last few decades, and one of their many applications has been in the field of FIR filter design. In this paper, we investigate the performance of multiplier free FIR filter design using the Look Ahead Decision Feedback (LADF) /spl Sigma/-/spl Delta/ architecture. The LADF /spl Sigma/-/spl Delta/ architecture, which has not been used in FIR filter design before, is compared with other conventional /spl Sigma/-/spl Delta/ architectures. It is shown that the LADF architecture has relatively low noise power at low frequencies and is preferable over the other modulators in the design of multiplier free FIR filters. The selection of demodulator filters for reducing quantization noise due to the LADF /spl Sigma/-/spl Delta/ architecture is also addressed in the paper. Using low-pass FIR filter design examples, the appropriate filter design methodology is presented in the paper.

As an alternative to conventional FIR filters, an optimal IIR filter architecture based on orthonormal Laguerre functions is proposed for Sigma-Delta (/spl Sigma/-/spl Delta/) demodulators. A Laguerre IIR filter design methodology is presented via the optimization of a quadratic function subject to a linear and a quadratic constraint. An efficient procedure to perform the optimization is discussed. The proposed IIR filter is easy to implement because it needs only a small number of components and therefore well suited for VLSI implementations. The impact of the selection of filter pole on the filter stability and phase linearity is discussed. The robustness issue of the Laguerre IIR filter is also addressed.

By using the acoustic scattering form function, a method for classifying underwater spherical shell targets in an open ocean environment is proposed. The resulting backscatter signal from an incident wideband signal is used to illustrate some of the salient scattering features such as mid-frequency enhancement (MFE). A shell classification technique is then developed. An affine transformation of a template form function is used in the classification scheme. It is shown that the proposed scheme is robust against uncertainties in the material properties and noise.

Clock-rate adaptation circuits of network synchronizers work by controlling the output data rate by pulse stuffing. The technique of stuff threshold modulation (ST-Mod) is one method used to reduce the waiting time jitter produced by pulse stuffing. An expression for the filtered waiting time jitter in the presence of an ST-Mod sequence is present and the selection of a suitable ST-Mod dither sequence for a given set of data transmission conditions is investigated. It is shown that by using either a random ST-Mod sequence or a modified-wave ST-Mod sequence, it is possible to obtain minimal filtered jitter for given synchronizer-desynchronizer characteristics.

The use of wideband active sonar array processing to estimate the range, velocity and bearing of a target has received much interest in the literature recently. Although increased attention has been focused on wideband correlation processing for estimating range and velocity, array directivity patterns are almost always computed and interpreted under the narrowband signal assumption. This paper considers the target bearing estimation problem using the wideband correlation approach. Via this approach, it is shown how an optimum set of array weights can be selected for a known transmitted signal. The optimization procedure also provides robustness against errors in the array structure.

The method of 'stuff threshold modulation' (STM) is widely used with pulse stuffing in network synchronizers to obtain reduced jitter power at the output of desynchronizers. Of the various STM waveforms that appear in the published literature, none have been selected as an optimum for a given set of synchronizer-desynchronizer operating conditions. This paper formulates the problem of STM waveform optimization for arbitrary desynchronizer PLL characteristics and a specified range of synchronizer clock frequency offsets. By comparing three waveforms, i.e. a random sequence, a saw tooth sequence and a modified wave sequence, it has been shown that one particular type of STM waveform does not always produce optimum jitter performances under all conditions.>

The computation and characteristics of two new representations of single lead electrocardiogram data, both based upon the analytic signal corresponding to the waveform, are presented. The first method, employing a complex plane plot of the analytic signal, emphasizes waveform shape independently of time base; the second, a time-frequency representation using the Wigner-Ville distribution, appears to highlight instantaneous frequency variation within the waveform. Both are potentially useful when the patterns are displayed using contour plots, and a specific computerised pattern recognition technique is suggested and some results presented.