936 research outputs found
Performance Analysis of the Decentralized Eigendecomposition and ESPRIT Algorithm
In this paper, we consider performance analysis of the decentralized power
method for the eigendecomposition of the sample covariance matrix based on the
averaging consensus protocol. An analytical expression of the second order
statistics of the eigenvectors obtained from the decentralized power method
which is required for computing the mean square error (MSE) of subspace-based
estimators is presented. We show that the decentralized power method is not an
asymptotically consistent estimator of the eigenvectors of the true measurement
covariance matrix unless the averaging consensus protocol is carried out over
an infinitely large number of iterations. Moreover, we introduce the
decentralized ESPRIT algorithm which yields fully decentralized
direction-of-arrival (DOA) estimates. Based on the performance analysis of the
decentralized power method, we derive an analytical expression of the MSE of
DOA estimators using the decentralized ESPRIT algorithm. The validity of our
asymptotic results is demonstrated by simulations.Comment: 18 pages, 5 figures, submitted for publication in IEEE Transactions
on Signal Processin
Joint Antenna Selection and Phase-Only Beamforming Using Mixed-Integer Nonlinear Programming
In this paper, we consider the problem of joint antenna selection and analog
beamformer design in downlink single-group multicast networks. Our objective is
to reduce the hardware costs by minimizing the number of required phase
shifters at the transmitter while fulfilling given distortion limits at the
receivers. We formulate the problem as an L0 minimization problem and devise a
novel branch-and-cut based algorithm to solve the resulting mixed-integer
nonlinear program to optimality. We also propose a suboptimal heuristic
algorithm to solve the above problem approximately with a low computational
complexity. Computational results illustrate that the solutions produced by the
proposed heuristic algorithm are optimal in most cases. The results also
indicate that the performance of the optimal methods can be significantly
improved by initializing with the result of the suboptimal method.Comment: to be presented at WSA 201
Transmit Precoding for Interference Exploitation in the Underlay Cognitive Radio Z-channel
This paper introduces novel transmit beamforming approaches for the cognitive radio (CR) Z-channel. The proposed transmission schemes exploit non-causal information about the interference at the SBS to re-design the CR beamforming optimization problem. This is done with the objective to improve the quality of service (QoS) of secondary users by taking advantage of constructive interference in the secondary link. The beamformers are designed to minimize the worst secondary user's symbol error probability (SEP) under constraints on the instantaneous total transmit power, and the power of the instantaneous interference in the primary link. The problem is formulated as a bivariate probabilistic constrained programming (BPCP) problem. We show that the BPCP problem can be transformed for practical SEPs into a convex optimization problem that can be solved, e.g., by the barrier method. A computationally efficient tight approximate approach is also developed to compute the near-optimal solutions. Simulation results and analysis show that the average computational complexity per downlink frame of the proposed approximate problem is comparable to that of the conventional CR downlink beamforming problem. In addition, both the proposed methods offer significant performance improvements as compared to the conventional CR downlink beamforming, while guaranteeing the QoS of primary users on an instantaneous basis, in contrast to the average QoS guarantees of conventional beamformers
Robust Hybrid Precoding for Interference Exploitation in Massive Mimo Systems
In this paper, we consider a multiuser massive MIMO system with hybrid analog-digital precoding architecture. The phase shifters in the hybrid precoding architecture are assumed to be imperfect, where the true values of both phase and magnitude of the phase shifters are different from their nominal values. For a given analog precoding matrix, we develop an iterative algorithm to compute robust digital precoders based on the interference exploitation approach to eliminate any potential symbol errors due to the phase shifter impairments. Numerical experiments demonstrate the performance of the proposed algorithm and show its advantage over a conventional robust precoding technique
Interference Exploitation-Based Hybrid Precoding With Robustness Against Channel Errors
The extremely high cost associated with massive multiple-input multiple-output (MIMO) systems when it is employed with fully digital precoding can be reduced by applying hybrid precoding at an expense of increased transmit power. In such a hybrid precoding system, the transmit power required to achieve a certain quality-of-service (QoS) can be significantly reduced by employing the constructive interference (CI) precoding technique. However, as illustrated in the paper, the symbol error rate (SER) performance of CI-based precoding is very sensitive to channel errors. To address this challenge we propose a hybrid precoding approach with robustness against channel quantization error and channel estimation error. Simulation results demonstrate the superior energy efficiency of the proposed robust hybrid precoding when compared to that of a conventional non-robust precoding scheme in achieving a required QoS target
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Characterization of a continuous feline mammary epithelial cell line susceptible to feline epitheliotropic viruses.
Mucosal epithelial cells are the primary targets for many common viral pathogens of cats. Viral infection of epithelia can damage or disrupt the epithelial barrier that protects underlying tissues. In vitro cell culture systems are an effective means to study how viruses infect and disrupt epithelial barriers, however no true continuous or immortalized feline epithelial cell culture lines are available. A continuous cell culture of feline mammary epithelial cells (FMEC UCD-04-2) that forms tight junctions with high transepithelial electrical resistance (>2000Omegacm(-1)) 3-4 days after reaching confluence was characterized. In addition, it was shown that FMECs are susceptible to infection with feline calicivirus (FCV), feline herpesvirus (FHV-1), feline coronavirus (FeCoV), and feline panleukopenia virus (FPV). These cells will be useful for studies of feline viral disease and for in vitro studies of feline epithelia
Simple solid-phase spectrophotometric method for free iron(III) determination
A simple and rapid solid-phase spectrophotometric procedure to determine free Fe(III) in environmental and biological samples is proposed. In particular, a deferoxamine (DFO) self assembled monolayer on mesoporous silica (DFO SAMMS) is developed and here applied as a sensor for iron(III). The solid product became brownish when put in contact with iron(III) solutions; so an immediate application as colorimetric sensor is considered. In order to optimize the DFO SAMMS synthesis and to obtain the best product for iron(III) sensing, a factorial experimental design is performed selecting the maximum absorption at 425 nm as response. The robustness of the spectrophotometric method is also proved
Extended Successive Convex Approximation for Phase Retrieval with Dictionary Learning
Phase retrieval aims at reconstructing unknown signals from magnitude
measurements of linear mixtures. In this paper, we consider the phase retrieval
with dictionary learning problem, which includes an additional prior
information that the measured signal admits a sparse representation over an
unknown dictionary. The task is to jointly estimate the dictionary and the
sparse representation from magnitude-only measurements. To this end, we study
two complementary formulations and develop efficient parallel algorithms by
extending the successive convex approximation framework using a smooth
majorization. The first algorithm is termed compact-SCAphase and is preferable
in the case of less diverse mixture models. It employs a compact formulation
that avoids the use of auxiliary variables. The proposed algorithm is highly
scalable and has reduced parameter tuning cost. The second algorithm, referred
to as SCAphase, uses auxiliary variables and is favorable in the case of highly
diverse mixture models. It also renders simple incorporation of additional side
constraints. The performance of both methods is evaluated when applied to blind
sparse channel estimation from subband magnitude measurements in a
multi-antenna random access network. Simulation results demonstrate the
efficiency of the proposed techniques compared to state-of-the-art methods.Comment: This work has been submitted to the IEEE Transactions on Signal
Processing for possible publication. Copyright may be transferred without
notice, after which this version may no longer be accessibl
Towards the development of cascaded surface plasmon resonance POF sensors exploiting gold films and synthetic recognition elements for detection of contaminants in transformer oil
The possibility of developing a multichannel optical chemical sensor, based on molecularly imprinted polymers (MIPs) and surface plasmon resonance (SPR) in a D-shaped multimode plastic optical fiber (POF), is presented by two cascaded SPR-POF-MIP sensors with different thicknesses of the gold layer. The low cost, the high selectivity and sensitivity of the SPR-POF-MIP platforms and the simple and modular scheme of the optical interrogation layout make this system a potentially suitable on-line multi-diagnostic tool. As a proof of principle, the possibility of simultaneous determination of two important analytes, dibenzyl disulfide (DBDS) and furfural (2-FAL), in power transformer oil was investigated. Their presence gives useful indication of underway corrosive or ageing processes in power transformers, respectively. Preliminarily, the dependence of the performance of the D-shaped optical platform on the gold film thickness has been studied, comparing two platforms with 30 nm and 60 nm thick gold layers. It has been found that the resonance wavelengths are different on platforms with gold layer of different thickness, furthermore when MIPs are present on the gold as receptors, the performances of the platforms are similar in the two considered sensors. Keywords: Cascaded multianalyte detection, Surface plasmon resonance, Dibenzyl disulfide, Furfural (furan-2-carbaldehyde), Molecularly imprinted polymers, Plastic optical fiber
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