764 research outputs found
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
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 Outage Capacity of Correlated Multiple-Path MIMO Channels
The use of multi-antenna arrays in both transmission and reception has been
shown to dramatically increase the throughput of wireless communication
systems. As a result there has been considerable interest in characterizing the
ergodic average of the mutual information for realistic correlated channels.
Here, an approach is presented that provides analytic expressions not only for
the average, but also the higher cumulant moments of the distribution of the
mutual information for zero-mean Gaussian (multiple-input multiple-output) MIMO
channels with the most general multipath covariance matrices when the channel
is known at the receiver. These channels include multi-tap delay paths, as well
as general channels with covariance matrices that cannot be written as a
Kronecker product, such as dual-polarized antenna arrays with general
correlations at both transmitter and receiver ends. The mathematical methods
are formally valid for large antenna numbers, in which limit it is shown that
all higher cumulant moments of the distribution, other than the first two scale
to zero. Thus, it is confirmed that the distribution of the mutual information
tends to a Gaussian, which enables one to calculate the outage capacity. These
results are quite accurate even in the case of a few antennas, which makes this
approach applicable to realistic situations.Comment: submitted for publication IEEE Trans. Information Theory; IEEEtran
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Higher order nonclassicalities of finite dimensional coherent states: A comparative study
Conventional coherent states (CSs) are defined in various ways. For example,
CS is defined as an infinite Poissonian expansion in Fock states, as displaced
vacuum state, or as an eigenket of annihilation operator. In the infinite
dimensional Hilbert space, these definitions are equivalent. However, these
definitions are not equivalent for the finite dimensional systems. In this
work, we present a comparative description of the lower- and higher-order
nonclassical properties of the finite dimensional CSs which are also referred
to as qudit CSs (QCSs). For the comparison, nonclassical properties of two
types of QCSs are used: (i) nonlinear QCS produced by applying a truncated
displacement operator on the vacuum and (ii) linear QCS produced by the
Poissonian expansion in Fock states of the CS truncated at (d-1)-photon Fock
state. The comparison is performed using a set of nonclassicality witnesses
(e.g., higher order antiubunching, higher order sub-Poissonian statistics,
higher order squeezing, Agarwal-Tara parameter, Klyshko's criterion) and a set
of quantitative measures of nonclassicality (e.g., negativity potential,
concurrence potential and anticlassicality). The higher order nonclassicality
witness have found to reveal the existence of higher order nonclassical
properties of QCS for the first time.Comment: A comparative description of the higher-order nonclassical properties
of the finite dimensional coherent state
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