648 research outputs found
Information-theoretic Characterization of MIMO Systems with Multiple Rayleigh Scattering
We present an information-theoretic analysis of a point-to-point Multiple-Input-Multiple-Output(MIMO) link affected by Rayleigh fading and multiple scattering, under perfect channel state informationat the receiver. Unlike previous work addressing this setting, we investigate the Random Coding ErrorExponent, its associated cutoff rate and the Expurgated Error Exponent, and derive closed-form expres-sions for them. Moreover, leveraging the average mutual information expression presented in [1], wederive another important metric, namely, the sum rate, under linear receive processing and independentstream decoding. In particular, we characterize the performance of the Minimum Mean Squared Errorreceiver in closed form, and that of the Zero Forcing receiver by resorting to bounding techniques. Thebulk of the work relies on results about finite-dimensional random matrix products, a number of whichare novel and detailed in the Appendices. The analysis, validated through numerical results, highlightsthe severe degradation in the performance of linear receivers due to multi-fold scattering. It also unveilsthe performance trend of multiple scattering MIMO channels as a function of the number of antennasand the number of scattering stages
From Multi-Keyholes to Measure of Correlation and Power Imbalance in MIMO Channels: Outage Capacity Analysis
An information-theoretic analysis of a multi-keyhole channel, which includes
a number of statistically independent keyholes with possibly different
correlation matrices, is given. When the number of keyholes or/and the number
of Tx/Rx antennas is large, there is an equivalent Rayleigh-fading channel such
that the outage capacities of both channels are asymptotically equal. In the
case of a large number of antennas and for a broad class of fading
distributions, the instantaneous capacity is shown to be asymptotically
Gaussian in distribution, and compact, closed-form expressions for the mean and
variance are given. Motivated by the asymptotic analysis, a simple,
full-ordering scalar measure of spatial correlation and power imbalance in MIMO
channels is introduced, which quantifies the negative impact of these two
factors on the outage capacity in a simple and well-tractable way. It does not
require the eigenvalue decomposition, and has the full-ordering property. The
size-asymptotic results are used to prove Telatar's conjecture for
semi-correlated multi-keyhole and Rayleigh channels. Since the keyhole channel
model approximates well the relay channel in the amplify-and-forward mode in
certain scenarios, these results also apply to the latterComment: accepted by IEEE IT Trans., 201
Information Theory of underspread WSSUS channels
The chapter focuses on the ultimate limit on the rate of reliable communication through Rayleigh-fading channels that satisfy the wide-sense stationary (WSS) and uncorrelated scattering (US) assumptions and are underspread. Therefore, the natural setting is an information-theoretic one, and the performance metric is channel capacity. The family of Rayleigh-fading underspread WSSUS channels constitutes a good model for real-world wireless channels: their stochastic properties, like amplitude and phase distributions match channel measurement results. The Rayleigh-fading and the WSSUS assumptions imply that the stochastic properties of the channel are fully described by a two-dimensional power spectral density (PSD) function, often referred to as scattering function. The underspread assumption implies that the scattering function is highly concentrated in the delay-Doppler plane. Two important aspects need to be accounted for by a model that aims at being realistic: neither the transmitter nor the receiver knows the realization of the channel; and the peak power of the transmit signal is limited. Based on these two aspects the chapter provides an information-theoretic analysis of Rayleigh-fading underspread WSSUS channels in the noncoherent setting, under the additional assumption that the transmit signal is peak-constrained
Why Does a Kronecker Model Result in Misleading Capacity Estimates?
Many recent works that study the performance of multi-input multi-output
(MIMO) systems in practice assume a Kronecker model where the variances of the
channel entries, upon decomposition on to the transmit and the receive
eigen-bases, admit a separable form. Measurement campaigns, however, show that
the Kronecker model results in poor estimates for capacity. Motivated by these
observations, a channel model that does not impose a separable structure has
been recently proposed and shown to fit the capacity of measured channels
better. In this work, we show that this recently proposed modeling framework
can be viewed as a natural consequence of channel decomposition on to its
canonical coordinates, the transmit and/or the receive eigen-bases. Using tools
from random matrix theory, we then establish the theoretical basis behind the
Kronecker mismatch at the low- and the high-SNR extremes: 1) Sparsity of the
dominant statistical degrees of freedom (DoF) in the true channel at the
low-SNR extreme, and 2) Non-regularity of the sparsity structure (disparities
in the distribution of the DoF across the rows and the columns) at the high-SNR
extreme.Comment: 39 pages, 5 figures, under review with IEEE Trans. Inform. Theor
Information-theoretic analysis of MIMO channel sounding
The large majority of commercially available multiple-input multiple-output
(MIMO) radio channel measurement devices (sounders) is based on time-division
multiplexed switching (TDMS) of a single transmit/receive radio-frequency chain
into the elements of a transmit/receive antenna array. While being
cost-effective, such a solution can cause significant measurement errors due to
phase noise and frequency offset in the local oscillators. In this paper, we
systematically analyze the resulting errors and show that, in practice,
overestimation of channel capacity by several hundred percent can occur.
Overestimation is caused by phase noise (and to a lesser extent frequency
offset) leading to an increase of the MIMO channel rank. Our analysis
furthermore reveals that the impact of phase errors is, in general, most
pronounced if the physical channel has low rank (typical for line-of-sight or
poor scattering scenarios). The extreme case of a rank-1 physical channel is
analyzed in detail. Finally, we present measurement results obtained from a
commercially employed TDMS-based MIMO channel sounder. In the light of the
findings of this paper, the results obtained through MIMO channel measurement
campaigns using TDMS-based channel sounders should be interpreted with great
care.Comment: 99 pages, 14 figures, submitted to IEEE Transactions on Information
Theor
Super-Wideband Massive MIMO
We present a unified model for connected antenna arrays with a massive (but
finite) number of tightly integrated (i.e., coupled) antennas in a compact
space within the context of massive multiple-input multiple-output (MIMO)
communication. We refer to this system as tightly-coupled massive MIMO. From an
information-theoretic perspective, scaling the design of tightly-coupled
massive MIMO systems in terms of the number of antennas, the operational
bandwidth, and form factor was not addressed in prior art and hence not clearly
understood. We investigate this open research problem using a physically
consistent modeling approach for far-field (FF) MIMO communication based on
multi-port circuit theory. In doing so, we turn mutual coupling (MC) from a foe
to a friend of MIMO systems design, thereby challenging a basic percept in
antenna systems engineering that promotes MC mitigation/compensation. We show
that tight MC widens the operational bandwidth of antenna arrays thereby
unleashing a missing MIMO gain that we coin "bandwidth gain". Furthermore, we
derive analytically the asymptotically optimum spacing-to-antenna-size ratio by
establishing a condition for tight coupling in the limit of large-size antenna
arrays with quasi-continuous apertures. We also optimize the antenna array size
while maximizing the achievable rate under fixed transmit power and
inter-element spacing. Then, we study the impact of MC on the achievable rate
of MIMO systems under light-of-sight (LoS) and Rayleigh fading channels. These
results reveal new insights into the design of tightly-coupled massive antenna
arrays as opposed to the widely-adopted "disconnected" designs that disregard
MC by putting faith in the half-wavelength spacing rule
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