4,825 research outputs found
Extension of Nested Arrays with the Fourth-Order Difference Co-Array Enhancement
To reach a higher number of degrees of freedom by exploiting the
fourth-order difference co-array concept, an effective structure extension
based on two-level nested arrays is proposed. It increases
the number of consecutive lags in the fourth-order difference coarray,
and a virtual uniform linear array (ULA) with more sensors
and a larger aperture is then generated from the proposed structure,
leading to a much higher number of distinguishable sources with
a higher accuracy. Compressive sensing based approach is applied
for direction-of-arrival (DOA) estimation by vectorizing the fourthorder
cumulant matrix of the array, assuming non-Gaussian impinging
signals
Simplified and enhanced multiple level nested arrays exploiting high order difference co-arrays
Based on the high order difference co-array concept, an enhanced four level nested array (E-FL-NA) is first proposed, which optimizes the consecutive lags at the fourth order difference co-array stage. To simplify the formulations for sensor locations for comprehensive illustration and also convenient structure construction, a simplified and enhanced four level nested array (SE-FL-NA) is then proposed, whose performance is compromised but still better than the four level nested array (FL-NA). This simplified structure is further extended to the higher order case with multiple sub-arrays, referred to as simplified and enhanced multiple level nested arrays (SE-ML-NAs), where significantly increased degrees of freedom (DOFs) can be provided and exploited for underdetermined DOA estimation. Simulation results are provided to verify the superior performance of the proposed E-FL-NA, while a higher number of detectable sources is achieved by the SE-ML-NA with a limited number of physical sensors
An Expanding and Shift Scheme for Constructing Fourth-Order Difference Co-Arrays
An expanding and shift (EAS) scheme for efficient fourth-order difference co-array construction is proposed. It consists of two sparse sub-arrays, where one of them is modified and shifted according to the analysis provided. The number of consecutive lags of the proposed structure at the fourth order is consistently larger than two previously proposed methods. Two effective construction examples are provided with the second sparse sub-array chosen to be a two-level nested array, as such a choice can increase the number of consecutive lags further. Simulations are performed to show the improved performance by the proposed method in comparison with existing structures
Extension of Co-Prime Arrays Based on the Fourth-Order Difference Co-Array Concept
An effective sparse array extension method for maximizing the number of consecutive lags in the fourth-order difference co-array is proposed, leading to a novel enhanced sparse array structure based on co-prime arrays (CPAs) with significantly increased number of degrees of freedom (DOFs). One method to exploit the increased DOFs based on nonstationary signals is also proposed, with simulation results provided to demonstrate the effectiveness of the proposed structure
Underdetermined DOA Estimation Under the Compressive Sensing Framework: A Review
Direction of arrival (DOA) estimation from the perspective of sparse signal representation has attracted tremendous attention in past years, where the underlying spatial sparsity reconstruction problem is linked to the compressive sensing (CS) framework. Although this is an area with ongoing intensive research and new methods and results are reported regularly, it is time to have a review about the basic approaches and methods for CS-based DOA estimation, in particular for the underdetermined case. We start from the basic time-domain CSbased formulation for narrowband arrays and then move to the case for recently developed methods for sparse arrays based on the co-array concept. After introducing two specifically designed structures (the two-level nested array and the co-prime array) for optimizing the virtual sensors corresponding to the difference coarray, this CS-based DOA estimation approach is extended to the wideband case by employing the group sparsity concept, where a much larger physical aperture can be achieved by allowing a larger unit inter-element spacing and therefore leading to further improved performance. Finally, a specifically designed ULA structure with associated CS-based underdetermined DOA estimation is presented to exploit the difference co-array concept in the spatio-spectral domain, leading to a significant increase in DOFs. Representative simulation results for typical narrowband and wideband scenarios are provided to demonstrate their performance
Wideband DOA Estimation with Frequency Decomposition via a Unified GS-WSpSF Framework
A unified group sparsity based framework for wideband sparse spectrum fitting (GS-WSpSF) is proposed for wideband direction-of-arrival (DOA) estimation, which is capable of handling both uncorrelated and correlated sources. Then, by making four different assumptions on a priori knowledge about the sources, four variants under the proposed framework are formulated as solutions to the underdetermined DOA estimation problem without the need of employing sparse arrays. As verified by simulations, improved estimation performance can be achieved by the wideband methods compared with narrowband ones, and adopting more a priori information leads to better performance in terms of resolution capacity and estimation accuracy
Recent developments in nucleic acid identification using solid-phase enzymatic assays
This review (containing 101 references) covers recent achievements in the development of new approaches for enzymatically assisted detection of nucleic acids on microarrays. We discuss molecular techniques including the polymerase chain reaction, reverse transcription, allele specific primer extension and a range of isothermal techniques for the amplification and discrimination of nucleic acids. This also includes their implementation into microfluidic systems. These techniques all show great promise for use in the life sciences by allowing for high throughput, cost effective and highly sensitive and specific analysis of nucleic acids. Importantly, they can be potentially integrated into personalized and point-of-care medicine
An improved expanding and shift scheme for the construction of fourth-order difference co-arrays
An improved expanding and shift (IEAS) scheme for efficient fourth-order difference co-array construction is proposed. Similar to the previously proposed expanding and shift (EAS) scheme, it consists of two sparse sub-arrays, but one of them is modified and shifted according to a new rule. Examples are provided with the second sub-array being a two-level nested array (IEAS-NA), as such a choice can generate more fourth-order difference lags (FODLs), although with the same number of consecutive lags. Furthermore, the array aperture of IEAS-NA is always greater than the corresponding EAS structure, which helps improving the DOA estimation result. Simulations results are provided to show the improved performance by the proposed new scheme
Nested Arrays: A Novel Approach to Array Processing With Enhanced Degrees of Freedom
A new array geometry, which is capable of significantly
increasing the degrees of freedom of linear arrays, is
proposed. This structure is obtained by systematically nesting two
or more uniform linear arrays and can provide O(N^2) degrees
of freedom using only physical sensors when the second-order
statistics of the received data is used. The concept of nesting is
shown to be easily extensible to multiple stages and the structure
of the optimally nested array is found analytically. It is possible to
provide closed form expressions for the sensor locations and the
exact degrees of freedom obtainable from the proposed array as a
function of the total number of sensors. This cannot be done for
existing classes of arrays like minimum redundancy arrays which
have been used earlier for detecting more sources than the number
of physical sensors. In minimum-input–minimum-output (MIMO)
radar, the degrees of freedom are increased by constructing a
longer virtual array through active sensing. The method proposed
here, however, does not require active sensing and is capable of
providing increased degrees of freedom in a completely passive
setting. To utilize the degrees of freedom of the nested co-array, a
novel spatial smoothing based approach to DOA estimation is also
proposed, which does not require the inherent assumptions of the
traditional techniques based on fourth-order cumulants or quasi
stationary signals. As another potential application of the nested
array, a new approach to beamforming based on a nonlinear
preprocessing is also introduced, which can effectively utilize the
degrees of freedom offered by the nested arrays. The usefulness of
all the proposed methods is verified through extensive computer
simulations
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