Saman S. Abeysekera

Performance of pulse-pair method of Doppler estimation

Because of its simplicity, the pulse-pair method is usually used in the estimation of Doppler from backscattered acoustic signals. In the literature, various improvements to the basic pulse-pair estimate have been proposed. The statistics of these improved methods have also been derived using simplified assumptions for the signal and noise. By developing a multiplicative noise model for the backscatter signal, in this work, the variance of the Doppler estimate is derived under all signal scenarios. The dependency of the variance on the amplitude correlation length of the data is also discussed. It is demonstrated that the use of parabolic window in the estimate is the proper method of Doppler evaluation under all conditions.

MIMO Radar Transmit Beampattern Design With Ripple and Transition Band Control

The waveform diversity of multiple-input-multiple-output (MIMO) radar systems offers many advantages in comparison to the phased-array counterpart. One of the advantages is that it allows one to design MIMO radar with flexible transmit beampatterns, which has several useful applications. Many researchers have proposed solutions to this problem in the recent decade. However, these designs pay little attention to certain aspects of the performance such as the ripples within the energy focusing section, the attenuation of the sidelobes, the width of the transition band, the angle step-size, and the required number of transmit antennas. In this paper, we first propose several methods that can indirectly or directly control the ripple levels within the energy focusing section and the transition bandwidth. These methods are based on existing problem formulations. More importantly, we reformulate the design as a feasibility problem (FP). Such a formulation enables a more flexible and efficient design that achieves the most preferable beampatterns with the least system cost. Using this formulation, an empirical MIMO radar beampattern formula is obtained. This MIMO radar beampattern formula is similar to Kaisers formula in conventional finite-impulse-response (FIR) filter design. The performances of the proposed methods and formulations are evaluated via numerical examples.

Efficient frequency estimation using the pulse-pair method at various lags

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

Design of multiplier free FIR filters using a LADF sigma-delta (/spl Sigma/-/spl Delta/) modulator

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.

Receiver Design for Range and Doppler Sidelobe Suppression Using MIMO and Phased-Array Radar

This paper investigates the receiver instrumental variable (IV) filter design for sidelobe suppression using multiple-input-multiple-output (MIMO) and phased-array radar. First, we analyze the performance of existing integrated sidelobe level (ISL) and the zero sidelobe (ZS) methods for range sidelobe suppression, and show the latters superiority. The limitation of MIMO radar sidelobe suppression in a large number of range bins is discussed. It is shown that the phased-array radar avoids this limitation. Then we consider joint range and Doppler sidelobe suppression, and the solutions for both MIMO and phased-array radar are derived, classified, and analyzed. The conclusions are drawn through performance trade-off. The use of phased-array radar compromises the waveform diversity of MIMO radar. However, with the objective of range, and joint range and Doppler sidelobe suppression, phased-array radar has better performance in terms of computational complexity, sidelobe suppression level and signal-to-noise ratio (SNR) loss. This will relieve the design workload for large scale radar systems. In addition, we show via simulations that the bounds of clear area of matched filter output (ambiguity function) are inapplicable for the IV filter design.

Efficient wideband signal parameter estimation using a radon-ambiguity transform slice

A novel efficient technique based on a single slice Radon-ambiguity transform (RAT) for time-delay and time-scale estimation is proposed. The proposed approach combines the narrowband cross-ambiguity function (NBCAF), the wideband cross-ambiguity function (WBCAF), and a single slice RAT to estimate multiple target parameters in noisy environments. The square modulus of Gaussian-enveloped linear frequency modulated (GLFM) signals has high-energy centrality in the ambiguity plane. Its peaks in the NBCAF fall along nearly straight lines whose slopes depend on the Doppler rates of the moving targets. These lines could be effectively detected by computing the entire Radon transform of the NBCAF for all possible angles; however, it is a computationally intensive procedure. It is shown that without calculating the entire RAT, it is possible to estimate target parameters using only a single slice of the RAT, i.e., using an appropriate projection of the NBCAF. It is demonstrated that the proposed method can successfully separate overlapping targets efficiently. The efficiency is achieved due to fast Fourier transform (FFT)-bascd processing, use of a single slice of RAT, and the use of only one-dimensional (1-D) searches.

Performance of correlation-based frequency estimation methods in the presence of multiplicative noise

This paper provides a comprehensive performance evaluation of a correlation-based frequency estimator under different fading channel conditions. The efficiency of the estimator in terms of the Cramer-Rao lower bound (CRB) is investigated for different fading conditions, i.e., slow fading, fast fading, Rayleigh fading, and Ricean fading. The asymptotic CRB, which provides an insight to the frequency estimation in fading channels, has been evaluated via a frequency-domain approach. The optimal correlation lag value suitable for frequency estimation under different fading conditions is determined, and closed-form expressions for the variance of the estimates are provided. For proper implementation of the estimator, the Doppler spread of the signal is also estimated. It is shown that using the Doppler spread information, frequency estimation accuracy at low signal-to-noise ratios can be improved using multiple lags of correlations

A comparison of various low-pass filter architectures for sigma-delta demodulators

A comparison of various low-pass filter architectures that are commonly used in Sigma-Delta(/spl Sigma/-/spl Delta/) demodulators is presented in the paper. In this comparison the conventional demodulator filter architectures such as the optimal FIR filter, Sinc/sup k/ filter and non-linear Zoomer filter are considered. It is shown that the optimum FIR filter provides the most attractive properties among the conventional demodulator low-pass filters. As an alternative to the optimal FIR filter, optimal Laguerre IIR filter architecture is then proposed in the paper. A design scheme for the optimal IIR filter is presented via the use of orthonormal Laguerre functions. In comparison with the conventional FIR filter approach, this design offers several attractive features. The proposed IIR filter design problem is easy to solve and numerically robust. Furthermore, the optimal IIR filter is easy to implement because it needs only a small number of components and therefore well suited for VLSI implementations.

Design of optimal and narrow-band Laguerre filters for sigma-delta demodulators

Conventional sigma-delta (/spl Sigma/-/spl Delta/) decimation methods are not optimal because the downsampling operation following the noise-shaping filters enables some quantization noise to alias back into the baseband. This paper proposes a novel decimation method that simplifies the implementation of the decimation process. This method makes use of an optimal Laguerre filter as the noise-shaping filter followed by another Laguerre filter that acts as a narrow-band filter. Conventional finite-impulse response (FIR) low-pass filters such as the optimal FIR filter and Sinc/sup k/ filter are commonly used as noise-shaping filters in /spl Sigma/-/spl Delta/ demodulators. As an alternative, optimal infinite-impulse response (IIR) filter architecture based on orthonormal Laguerre functions is used in the proposed decimation scheme. An optimal Laguerre IIR filter design methodology is presented via the optimization of a quadratic function subject to a linear and quadratic constraint. An efficient procedure to perform the optimization is introduced. A Laguerre IIR filter can also be used as the narrow-band filter before the decimation process. In this paper, a narrow-band Laguerre filter design methodology is presented via a digital frequency transformation. The narrow-band Laguerre filter can then be efficiently designed using a min-max criterion via a modified Parks-McClellan FIR filter design algorithm.

Optimum Laguerre filter design technique for sigma-delta demodulators

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.