23 research outputs found
Kronecker Product Correlation Model and Limited Feedback Codebook Design in a 3D Channel Model
A 2D antenna array introduces a new level of control and additional degrees
of freedom in multiple-input-multiple-output (MIMO) systems particularly for
the so-called "massive MIMO" systems. To accurately assess the performance
gains of these large arrays, existing azimuth-only channel models have been
extended to handle 3D channels by modeling both the elevation and azimuth
dimensions. In this paper, we study the channel correlation matrix of a generic
ray-based 3D channel model, and our analysis and simulation results demonstrate
that the 3D correlation matrix can be well approximated by a Kronecker
production of azimuth and elevation correlations. This finding lays the
theoretical support for the usage of a product codebook for reduced complexity
feedback from the receiver to the transmitter. We also present the design of a
product codebook based on Grassmannian line packing.Comment: 6 pages, 5 figures, to appear at IEEE ICC 201
On the Impact of Antenna Topologies for Massive MIMO Systems
Approximate expressions for the spatial correlation of cylindrical and
uniform rectangular arrays (URA) are derived using measured distributions of
angles of departure (AOD) for both the azimuth and zenith domains. We examine
massive multiple-input-multiple-output (MIMO) convergence properties of the
correlated channels by considering a number of convergence metrics. The
per-user matched filter (MF) signal-to-interference-plus-noise ratio (SINR)
performance and convergence rate, to respective limiting values, of the two
antenna topologies is also explored.Comment: 6 pages, 6 figure
Rayleigh Fading Modeling and Channel Hardening for Reconfigurable Intelligent Surfaces
A realistic performance assessment of any wireless technology requires the
use of a channel model that reflects its main characteristics. The independent
and identically distributed Rayleigh fading channel model has been (and still
is) the basis of most theoretical research on multiple antenna technologies in
scattering environments. This letter shows that such a model is not physically
appearing when using a reconfigurable intelligent surface (RIS) with
rectangular geometry and provides an alternative physically feasible Rayleigh
fading model that can be used as a baseline when evaluating RIS-aided
communications. The model is used to revisit the basic RIS properties, e.g.,
the rank of spatial correlation matrices and channel hardening.Comment: Published in IEEE Wireless Communications Letters, 6 pages, 4 figure
Optimization of Massive Full-Dimensional MIMO for Positioning and Communication
Massive Full-Dimensional multiple-input multiple-output (FD-MIMO) base
stations (BSs) have the potential to bring multiplexing and coverage gains by
means of three-dimensional (3D) beamforming. Key technical challenges for their
deployment include the presence of limited-resolution front ends and the
acquisition of channel state information (CSI) at the BSs. This paper
investigates the use of FD-MIMO BSs to provide simultaneously high-rate data
communication and mobile 3D positioning in the downlink. The analysis
concentrates on the problem of beamforming design by accounting for imperfect
CSI acquisition via Time Division Duplex (TDD)-based training and for the
finite resolution of analog-to-digital converter (ADC) and digital-to-analog
converter (DAC) at the BSs. Both \textit{unstructured beamforming} and a
low-complexity \textit{Kronecker beamforming} solution are considered, where
for the latter the beamforming vectors are decomposed into separate azimuth and
elevation components. The proposed algorithmic solutions are based on Bussgang
theorem, rank-relaxation and successive convex approximation (SCA) methods.
Comprehensive numerical results demonstrate that the proposed schemes can
effectively cater to both data communication and positioning services,
providing only minor performance degradations as compared to the more
conventional cases in which either function is implemented. Moreover, the
proposed low-complexity Kronecker beamforming solutions are seen to guarantee a
limited performance loss in the presence of a large number of BS antennas.Comment: 30 pages, 6 figure