779 research outputs found
A Generalized Spatial Correlation Model for 3D MIMO Channels based on the Fourier Coefficients of Power Spectrums
Previous studies have confirmed the adverse impact of fading correlation on
the mutual information (MI) of two-dimensional (2D) multiple-input
multiple-output (MIMO) systems. More recently, the trend is to enhance the
system performance by exploiting the channel's degrees of freedom in the
elevation, which necessitates the derivation and characterization of
three-dimensional (3D) channels in the presence of spatial correlation. In this
paper, an exact closed-form expression for the Spatial Correlation Function
(SCF) is derived for 3D MIMO channels. This novel SCF is developed for a
uniform linear array of antennas with nonisotropic antenna patterns. The
proposed method resorts to the spherical harmonic expansion (SHE) of plane
waves and the trigonometric expansion of Legendre and associated Legendre
polynomials. The resulting expression depends on the underlying arbitrary
angular distributions and antenna patterns through the Fourier Series (FS)
coefficients of power azimuth and elevation spectrums. The novelty of the
proposed method lies in the SCF being valid for any 3D propagation environment.
The developed SCF determines the covariance matrices at the transmitter and the
receiver that form the Kronecker channel model. In order to quantify the
effects of correlation on the system performance, the information-theoretic
deterministic equivalents of the MI for the Kronecker model are utilized in
both mono-user and multi-user cases. Numerical results validate the proposed
analytical expressions and elucidate the dependence of the system performance
on azimuth and elevation angular spreads and antenna patterns. Some useful
insights into the behaviour of MI as a function of downtilt angles are
provided. The derived model will help evaluate the performance of correlated 3D
MIMO channels in the future.Comment: Accepted in IEEE Transactions on signal processin
Does Massive MIMO Fail in Ricean Channels?
Massive multiple-input multiple-output (MIMO) is now making its way to the
standardization exercise of future 5G networks. Yet, there are still
fundamental questions pertaining to the robustness of massive MIMO against
physically detrimental propagation conditions. On these grounds, we identify
scenarios under which massive MIMO can potentially fail in Ricean channels, and
characterize them physically, as well as, mathematically. Our analysis extends
and generalizes a stream of recent papers on this topic and articulates
emphatically that such harmful scenarios in Ricean fading conditions are
unlikely and can be compensated using any standard scheduling scheme. This
implies that massive MIMO is intrinsically effective at combating interuser
interference and, if needed, can avail of the base-station scheduler for
further robustness.Comment: IEEE Wireless Communications Letters, accepte
Massive MIMO performance evaluation based on measured propagation data
Massive MIMO, also known as very-large MIMO or large-scale antenna systems,
is a new technique that potentially can offer large network capacities in
multi-user scenarios. With a massive MIMO system, we consider the case where a
base station equipped with a large number of antenna elements simultaneously
serves multiple single-antenna users in the same time-frequency resource. So
far, investigations are mostly based on theoretical channels with independent
and identically distributed (i.i.d.) complex Gaussian coefficients, i.e.,
i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in
channels measured in real propagation environments. Channel measurements were
performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a
physically large aperture, and a practical uniform cylindrical array (UCA)
which is more compact in size, both having 128 antenna ports. Based on
measurement data, we illustrate channel behavior of massive MIMO in three
representative propagation conditions, and evaluate the corresponding
performance. The investigation shows that the measured channels, for both array
types, allow us to achieve performance close to that in i.i.d. Rayleigh
channels. It is concluded that in real propagation environments we have
characteristics that can allow for efficient use of massive MIMO, i.e., the
theoretical advantages of this new technology can also be harvested in real
channels.Comment: IEEE Transactions on Wireless Communications, 201
Uplink Analysis of Large MU-MIMO Systems With Space-Constrained Arrays in Ricean Fading
Closed-form approximations to the expected per-terminal
signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral
efficiency of a large multiuser multiple-input multiple-output system are
presented. Our analysis assumes correlated Ricean fading with maximum ratio
combining on the uplink, where the base station (BS) is equipped with a uniform
linear array (ULA) with physical size restrictions. Unlike previous studies,
our model caters for the presence of unequal correlation matrices and unequal
Rice factors for each terminal. As the number of BS antennas grows without
bound, with a finite number of terminals, we derive the limiting expected
per-terminal SINR and ergodic sum spectral efficiency of the system. Our
findings suggest that with restrictions on the size of the ULA, the expected
SINR saturates with increasing operating signal-to-noise-ratio (SNR) and BS
antennas. Whilst unequal correlation matrices result in higher performance, the
presence of strong line-of-sight (LoS) has an opposite effect. Our analysis
accommodates changes in system dimensions, SNR, LoS levels, spatial correlation
levels and variations in fixed physical spacings of the BS array.Comment: 7 pages, 3 figures, accepted for publication in the proceedings of
IEEE ICC, to be held in Paris, France, May 201
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