4,845 research outputs found
On the Impact of Hardware Impairments on Massive MIMO
Massive multi-user (MU) multiple-input multiple-output (MIMO) systems are one
possible key technology for next generation wireless communication systems.
Claims have been made that massive MU-MIMO will increase both the radiated
energy efficiency as well as the sum-rate capacity by orders of magnitude,
because of the high transmit directivity. However, due to the very large number
of transceivers needed at each base-station (BS), a successful implementation
of massive MU-MIMO will be contingent on of the availability of very cheap,
compact and power-efficient radio and digital-processing hardware. This may in
turn impair the quality of the modulated radio frequency (RF) signal due to an
increased amount of power-amplifier distortion, phase-noise, and quantization
noise.
In this paper, we examine the effects of hardware impairments on a massive
MU-MIMO single-cell system by means of theory and simulation. The simulations
are performed using simplified, well-established statistical hardware
impairment models as well as more sophisticated and realistic models based upon
measurements and electromagnetic antenna array simulations.Comment: 7 pages, 9 figures, Accepted for presentation at Globe-Com workshop
on Massive MIM
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
Massive MIMO with Non-Ideal Arbitrary Arrays: Hardware Scaling Laws and Circuit-Aware Design
Massive multiple-input multiple-output (MIMO) systems are cellular networks
where the base stations (BSs) are equipped with unconventionally many antennas,
deployed on co-located or distributed arrays. Huge spatial degrees-of-freedom
are achieved by coherent processing over these massive arrays, which provide
strong signal gains, resilience to imperfect channel knowledge, and low
interference. This comes at the price of more infrastructure; the hardware cost
and circuit power consumption scale linearly/affinely with the number of BS
antennas . Hence, the key to cost-efficient deployment of large arrays is
low-cost antenna branches with low circuit power, in contrast to today's
conventional expensive and power-hungry BS antenna branches. Such low-cost
transceivers are prone to hardware imperfections, but it has been conjectured
that the huge degrees-of-freedom would bring robustness to such imperfections.
We prove this claim for a generalized uplink system with multiplicative
phase-drifts, additive distortion noise, and noise amplification. Specifically,
we derive closed-form expressions for the user rates and a scaling law that
shows how fast the hardware imperfections can increase with while
maintaining high rates. The connection between this scaling law and the power
consumption of different transceiver circuits is rigorously exemplified. This
reveals that one can make the circuit power increase as , instead of
linearly, by careful circuit-aware system design.Comment: Accepted for publication in IEEE Transactions on Wireless
Communications, 16 pages, 8 figures. The results can be reproduced using the
following Matlab code: https://github.com/emilbjornson/hardware-scaling-law
MIMO Channel Correlation in General Scattering Environments
This paper presents an analytical model for the fading channel correlation in
general scattering environments. In contrast to the existing correlation
models, our new approach treats the scattering environment as non-separable and
it is modeled using a bi-angular power distribution. The bi-angular power
distribution is parameterized by the mean departure and arrival angles, angular
spreads of the univariate angular power distributions at the transmitter and
receiver apertures, and a third parameter, the covariance between transmit and
receive angles which captures the statistical interdependency between angular
power distributions at the transmitter and receiver apertures. When this third
parameter is zero, this new model reduces to the well known "Kronecker" model.
Using the proposed model, we show that Kronecker model is a good approximation
to the actual channel when the scattering channel consists of a single
scattering cluster. In the presence of multiple remote scattering clusters we
show that Kronecker model over estimates the performance by artificially
increasing the number of multipaths in the channel.Comment: Australian Communication Theory Workshop Proceedings 2006, Perth
Western Australia. (accepted
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