12,486 research outputs found
Asymptotic Mutual Information Statistics of Separately-Correlated Rician Fading MIMO Channels
Precise characterization of the mutual information of MIMO systems is
required to assess the throughput of wireless communication channels in the
presence of Rician fading and spatial correlation. Here, we present an
asymptotic approach allowing to approximate the distribution of the mutual
information as a Gaussian distribution in order to provide both the average
achievable rate and the outage probability. More precisely, the mean and
variance of the mutual information of the separatelycorrelated Rician fading
MIMO channel are derived when the number of transmit and receive antennas grows
asymptotically large and their ratio approaches a finite constant. The
derivation is based on the replica method, an asymptotic technique widely used
in theoretical physics and, more recently, in the performance analysis of
communication (CDMA and MIMO) systems. The replica method allows to analyze
very difficult system cases in a comparatively simple way though some authors
pointed out that its assumptions are not always rigorous. Being aware of this,
we underline the key assumptions made in this setting, quite similar to the
assumptions made in the technical literature using the replica method in their
asymptotic analyses. As far as concerns the convergence of the mutual
information to the Gaussian distribution, it is shown that it holds under some
mild technical conditions, which are tantamount to assuming that the spatial
correlation structure has no asymptotically dominant eigenmodes. The accuracy
of the asymptotic approach is assessed by providing a sizeable number of
numerical results. It is shown that the approximation is very accurate in a
wide variety of system settings even when the number of transmit and receive
antennas is as small as a few units.Comment: - submitted to the IEEE Transactions on Information Theory on Nov.
19, 2006 - revised and submitted to the IEEE Transactions on Information
Theory on Dec. 19, 200
Delay Performance of MISO Wireless Communications
Ultra-reliable, low latency communications (URLLC) are currently attracting
significant attention due to the emergence of mission-critical applications and
device-centric communication. URLLC will entail a fundamental paradigm shift
from throughput-oriented system design towards holistic designs for guaranteed
and reliable end-to-end latency. A deep understanding of the delay performance
of wireless networks is essential for efficient URLLC systems. In this paper,
we investigate the network layer performance of multiple-input, single-output
(MISO) systems under statistical delay constraints. We provide closed-form
expressions for MISO diversity-oriented service process and derive
probabilistic delay bounds using tools from stochastic network calculus. In
particular, we analyze transmit beamforming with perfect and imperfect channel
knowledge and compare it with orthogonal space-time codes and antenna
selection. The effect of transmit power, number of antennas, and finite
blocklength channel coding on the delay distribution is also investigated. Our
higher layer performance results reveal key insights of MISO channels and
provide useful guidelines for the design of ultra-reliable communication
systems that can guarantee the stringent URLLC latency requirements.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Optimal Transmit Covariance for Ergodic MIMO Channels
In this paper we consider the computation of channel capacity for ergodic
multiple-input multiple-output channels with additive white Gaussian noise. Two
scenarios are considered. Firstly, a time-varying channel is considered in
which both the transmitter and the receiver have knowledge of the channel
realization. The optimal transmission strategy is water-filling over space and
time. It is shown that this may be achieved in a causal, indeed instantaneous
fashion. In the second scenario, only the receiver has perfect knowledge of the
channel realization, while the transmitter has knowledge of the channel gain
probability law. In this case we determine an optimality condition on the input
covariance for ergodic Gaussian vector channels with arbitrary channel
distribution under the condition that the channel gains are independent of the
transmit signal. Using this optimality condition, we find an iterative
algorithm for numerical computation of optimal input covariance matrices.
Applications to correlated Rayleigh and Ricean channels are given.Comment: 22 pages, 14 figures, Submitted to IEEE Transactions on Information
Theor
mmWave Massive MIMO with Simple RF and Appropriate DSP
There is considerable interest in the combined use of millimeter-wave
(mmwave) frequencies and arrays of massive numbers of antennas (massive MIMO)
for next-generation wireless communications systems. A symbiotic relationship
exists between these two factors: mmwave frequencies allow for densely packed
antenna arrays, and hence massive MIMO can be achieved with a small form
factor; low per-antenna SNR and shadowing can be overcome with a large array
gain; steering narrow beams or nulls with a large array is a good match for the
line-of-sight (LOS) or near-LOS mmwave propagation environments, etc.. However,
the cost and power consumption for standard implementations of massive MIMO
arrays at mmwave frequencies is a significant drawback to rapid adoption and
deployment. In this paper, we examine a number of possible approaches to reduce
cost and power at both the basestation and user terminal, making up for it with
signal processing and additional (cheap) antennas. These approaches include
lowresolution Analog-to-Digital Converters (ADCs), wireless local oscillator
distribution networks, spatial multiplexing and multistreaming instead of
higher-order modulation etc.. We will examine the potential of these approaches
in making mmwave massive MIMO a reality and discuss the requirements in terms
of digital signal processing (DSP).Comment: published in Asilomar 201
Communication Over MIMO Broadcast Channels Using Lattice-Basis Reduction
A simple scheme for communication over MIMO broadcast channels is introduced
which adopts the lattice reduction technique to improve the naive channel
inversion method. Lattice basis reduction helps us to reduce the average
transmitted energy by modifying the region which includes the constellation
points. Simulation results show that the proposed scheme performs well, and as
compared to the more complex methods (such as the perturbation method) has a
negligible loss. Moreover, the proposed method is extended to the case of
different rates for different users. The asymptotic behavior of the symbol
error rate of the proposed method and the perturbation technique, and also the
outage probability for the case of fixed-rate users is analyzed. It is shown
that the proposed method, based on LLL lattice reduction, achieves the optimum
asymptotic slope of symbol-error-rate (called the precoding diversity). Also,
the outage probability for the case of fixed sum-rate is analyzed.Comment: Submitted to IEEE Trans. on Info. Theory (Jan. 15, 2006), Revised
(Jun. 12, 2007
Achieving secrecy without knowing the number of eavesdropper antennas
The existing research on physical layer security commonly assumes the number
of eavesdropper antennas to be known. Although this assumption allows one to
easily compute the achievable secrecy rate, it can hardly be realized in
practice. In this paper, we provide an innovative approach to study secure
communication systems without knowing the number of eavesdropper antennas by
introducing the concept of spatial constraint into physical layer security.
Specifically, the eavesdropper is assumed to have a limited spatial region to
place (possibly an infinite number of) antennas. From a practical point of
view, knowing the spatial constraint of the eavesdropper is much easier than
knowing the number of eavesdropper antennas. We derive the achievable secrecy
rates of the spatially-constrained system with and without friendly jamming. We
show that a non-zero secrecy rate is achievable with the help of a friendly
jammer, even if the eavesdropper places an infinite number of antennas in its
spatial region. Furthermore, we find that the achievable secrecy rate does not
monotonically increase with the jamming power, and hence, we obtain the
closed-form solution of the optimal jamming power that maximizes the secrecy
rate.Comment: IEEE transactions on wireless communications, accepted to appea
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