arXiv subjects

Qinghua Guo

Publications and source records attributed to Qinghua Guo.

81 records · Page 5Linked to original sources

arXiv2016

Low-Complexity and Basis-Free Channel Estimation for Switch-Based mmWave MIMO Systems via Matrix Completion

Recently, a switch-based hybrid massive MIMO structure that aims to reduce the hardware complexity and power consumption has been proposed as a potential candidate for millimeter wave (mmWave) communications. Exploiting the sparse nature of the mmWave channel, compressive sensing (CS)-based channel estimators have been proposed. When applied to real mmWave channels, the CS-based channel estimators may encounter heavy computational burden due to the high dimensionality of the basis. Meanwhile, knowledge about the response of the antenna array, which is needed for constructing the basis of the CS estimators, may not be perfect due to array uncertainties such as phase mismatch among array elements. This can result in the loss of sparse representation and hence the degraded performance of the CS estimator. In this paper, we propose a novel matrix completion (MC)-based low-complexity channel estimator. The proposed scheme is compatible with switch-based hybrid structures, does not need to specify a basis, and can avoid the basis mismatch issue. Compared with the existing CS-based estimator, the proposed basis-free scheme is immune to array response mismatch and exhibits a significantly lower complexity.

cs.IT↗

arXiv2016

Controlling plasmonic orbital angular momentum by combining geometric and dynamic phases

Tunable orbit angular momentum (OAM) of surface plasmon polaritons (SPPs) is theoretically studied with appropriately designed metasurfaces. By controlling both the orientation angle and spatial position of nano aperture array on an ultrathin gold film, the field distributions of the surface waves can be engineered to contain both spin dependent and independent OAM components. Simultaneous control over the geometric phase and optical path difference induced phase (dynamic phase) provides extra degrees of freedom for manipulating OAM of SPPs. We show that arbitrary combination of OAM numbers can be realized for the SPPs excited by incident light of different circular polarizations. The results provides powerful control over the OAM of SPPs, which will have potential applications on optical trapping, imaging, communications and quantum information processing.

physics.optics↗

arXiv2016

Turbo-Equalization Using Partial Gaussian Approximation

This paper deals with turbo-equalization for coded data transmission over intersymbol interference (ISI) channels. We propose a message-passing algorithm that uses the expectation-propagation rule to convert messages passed from the demodulator-decoder to the equalizer and computes messages returned by the equalizer by using a partial Gaussian approximation (PGA). Results from Monte Carlo simulations show that this approach leads to a significant performance improvement compared to state-of-the-art turbo-equalizers and allows for trading performance with complexity. We exploit the specific structure of the ISI channel model to significantly reduce the complexity of the PGA compared to that considered in the initial paper proposing the method.

cs.IT↗

arXiv2016

A BP-MF-EP Based Iterative Receiver for Joint Phase Noise Estimation, Equalization and Decoding

In this work, with combined belief propagation (BP), mean field (MF) and expectation propagation (EP), an iterative receiver is designed for joint phase noise (PN) estimation, equalization and decoding in a coded communication system. The presence of the PN results in a nonlinear observation model. Conventionally, the nonlinear model is directly linearized by using the first-order Taylor approximation, e.g., in the state-of-the-art soft-input extended Kalman smoothing approach (soft-in EKS). In this work, MF is used to handle the factor due to the nonlinear model, and a second-order Taylor approximation is used to achieve Gaussian approximation to the MF messages, which is crucial to the low-complexity implementation of the receiver with BP and EP. It turns out that our approximation is more effective than the direct linearization in the soft-in EKS with similar complexity, leading to significant performance improvement as demonstrated by simulation results.

cs.IT↗

arXiv2016

Low Complexity Sparse Bayesian Learning Using Combined BP and MF with a Stretched Factor Graph

This paper concerns message passing based approaches to sparse Bayesian learning (SBL) with a linear model corrupted by additive white Gaussian noise with unknown variance. With the conventional factor graph, mean field (MF) message passing based algorithms have been proposed in the literature. In this work, instead of using the conventional factor graph, we modify the factor graph by adding some extra hard constraints (the graph looks like being `stretched'), which enables the use of combined belief propagation (BP) and MF message passing. We then propose a low complexity BP-MF SBL algorithm based on which an approximate BP-MF SBL algorithm is also developed to further reduce the complexity. Thanks to the use of BP, the BP-MF SBL algorithms show their merits compared with state-of-the-art MF SBL algorithms: they deliver even better performance with much lower complexity compared with the vector-form MF SBL algorithm and they significantly outperform the scalar-form MF SBL algorithm with similar complexity.

cs.IT↗

arXiv2016

Message-Passing Receiver for Joint Channel Estimation and Decoding in 3D Massive MIMO-OFDM Systems

In this paper, we address the message-passing receiver design for the 3D massive MIMO-OFDM systems. With the aid of the central limit argument and Taylor-series approximation, a computationally efficient receiver that performs joint channel estimation and decoding is devised by the framework of expectation propagation. Specially, the local belief defined at the channel transition function is expanded up to the second order with Wirtinger calculus, to transform the messages sent by the channel transition function to a tractable form. As a result, the channel impulse response (CIR) between each pair of antennas is estimated by Gaussian message passing. In addition, a variational expectation-maximization (EM)-based method is derived to learn the channel power-delay-profile (PDP). The proposed joint algorithm is assessed in 3D massive MIMO systems with spatially correlated channels, and the empirical results corroborate its superiority in terms of performance and complexity.

cs.IT↗

arXiv2015

Phenomenological modeling of Geometric Metasurfaces

Metasurfaces, with their superior capability in manipulating the optical wavefront at the subwavelength scale and low manufacturing complexity, have shown great potential for planar photonics and novel optical devices. However, vector field simulation of metasurfaces is so far limited to periodic-structured metasurfaces containing a small number of meta-atoms in the unit cell by using full-wave numerical methods. Here, we propose a general phenomenological method to analytically model metasurfaces made up of arbitrarily distributed meta-atoms based on the assumption that the meta-atoms possess localized resonances with Lorentz-Drude forms, whose exact form can be retrieved from the full wave simulation of a single element. Applied to phase modulated geometric metasurfaces, our analytical results show good agreement with full-wave numerical simulations. The proposed theory provides an efficient method to model and design optical devices based on metasurfaces.

physics.optics↗

arXiv2015

Approximate Message Passing with Unitary Transformation

Approximate message passing (AMP) and its variants, developed based on loopy belief propagation, are attractive for estimating a vector x from a noisy version of z = Ax, which arises in many applications. For a large A with i. i. d. elements, AMP can be characterized by the state evolution and exhibits fast convergence. However, it has been shown that, AMP mayeasily diverge for a generic A. In this work, we develop a new variant of AMP based on a unitary transformation of the original model (hence the variant is called UT-AMP), where the unitary matrix is available for any matrix A, e.g., the conjugate transpose of the left singular matrix of A, or a normalized DFT (discrete Fourier transform) matrix for any circulant A. We prove that, in the case of Gaussian priors, UT-AMP always converges for any matrix A. It is observed that UT-AMP is much more robust than the original AMP for difficult A and exhibits fast convergence. A special form of UT-AMP with a circulant A was used in our previous work [13] for turbo equalization. This work extends it to a generic A, and provides a theoretical investigation on the convergence.

cs.IT↗

arXiv2014

One-way helical electromagnetic wave propagation supported by magnetized plasma

In this paper we reveal the presence of photonic one-way helical surface states in a simple natural system - magnetized plasma. The application of an external magnetic field to a bulk plasma body not only breaks time-reversal-symmetry but also leads to separation of Equi-Frequency Contour surfaces (EFCs) to form topologically nontrivial gaps in k space. Interestingly, these EFCs support topologically protected surface states. We numerically investigate an interface between magnetized plasma, using a realistic model for parameter dispersion, and vacuum, to confirm the existence of one-way scatter-immune helical surface states. Unlike previous proposals for achieving photonic one-way propagation, our scheme does not require the use of artificial structures and should therefore be simple to implement experimentally.

physics.optics↗