17 research outputs found
Asymptotic Analysis of Double-Scattering Channels
We consider a multiple-input multiple-output (MIMO) multiple access channel
(MAC), where the channel between each transmitter and the receiver is modeled
by the doubly-scattering channel model. Based on novel techniques from random
matrix theory, we derive deterministic approximations of the mutual
information, the signal-to-noise-plus-interference-ratio (SINR) at the output
of the minimum-mean-square-error (MMSE) detector and the sum-rate with MMSE
detection which are almost surely tight in the large system limit. Moreover, we
derive the asymptotically optimal transmit covariance matrices. Our simulation
results show that the asymptotic analysis provides very close approximations
for realistic system dimensions.Comment: 5 pages, 2 figures, submitted to the Annual Asilomar Conference on
Signals, Systems, and Computers, Pacific Grove, CA, USA, 201
On Outage Probability and Diversity-Multiplexing Tradeoff in MIMO Relay Channels
Fading MIMO relay channels are studied analytically, when the source and
destination are equipped with multiple antennas and the relays have a single
one. Compact closed-form expressions are obtained for the outage probability
under i.i.d. and correlated Rayleigh-fading links. Low-outage approximations
are derived, which reveal a number of insights, including the impact of
correlation, of the number of antennas, of relay noise and of relaying
protocol. The effect of correlation is shown to be negligible, unless the
channel becomes almost fully correlated. The SNR loss of relay fading channels
compared to the AWGN channel is quantified. The SNR-asymptotic
diversity-multiplexing tradeoff (DMT) is obtained for a broad class of fading
distributions, including, as special cases, Rayleigh, Rice, Nakagami, Weibull,
which may be non-identical, spatially correlated and/or non-zero mean. The DMT
is shown to depend not on a particular fading distribution, but rather on its
polynomial behavior near zero, and is the same for the simple
"amplify-and-forward" protocol and more complicated "decode-and-forward" one
with capacity achieving codes, i.e. the full processing capability at the relay
does not help to improve the DMT. There is however a significant difference
between the SNR-asymptotic DMT and the finite-SNR outage performance: while the
former is not improved by using an extra antenna on either side, the latter can
be significantly improved and, in particular, an extra antenna can be
traded-off for a full processing capability at the relay. The results are
extended to the multi-relay channels with selection relaying and typical outage
events are identified.Comment: accepted by IEEE Trans. on Comm., 201
Optimal space-time codes for the MIMO amplify-and-forward cooperative channel
In this work, we extend the non-orthogonal amplify-and-forward (NAF)
cooperative diversity scheme to the MIMO channel. A family of space-time block
codes for a half-duplex MIMO NAF fading cooperative channel with N relays is
constructed. The code construction is based on the non-vanishing determinant
criterion (NVD) and is shown to achieve the optimal diversity-multiplexing
tradeoff (DMT) of the channel. We provide a general explicit algebraic
construction, followed by some examples. In particular, in the single relay
case, it is proved that the Golden code and the 4x4 Perfect code are optimal
for the single-antenna and two-antenna case, respectively. Simulation results
reveal that a significant gain (up to 10dB) can be obtained with the proposed
codes, especially in the single-antenna case.Comment: submitted to IEEE Transactions on Information Theory, revised versio
Iterative Deterministic Equivalents for the Performance Analysis of Communication Systems
In this article, we introduce iterative deterministic equivalents as a novel
technique for the performance analysis of communication systems whose channels
are modeled by complex combinations of independent random matrices. This
technique extends the deterministic equivalent approach for the study of
functionals of large random matrices to a broader class of random matrix models
which naturally arise as channel models in wireless communications. We present
two specific applications: First, we consider a multi-hop amplify-and-forward
(AF) MIMO relay channel with noise at each stage and derive deterministic
approximations of the mutual information after the Kth hop. Second, we study a
MIMO multiple access channel (MAC) where the channel between each transmitter
and the receiver is represented by the double-scattering channel model. We
provide deterministic approximations of the mutual information, the
signal-to-interference-plus-noise ratio (SINR) and sum-rate with
minimum-mean-square-error (MMSE) detection and derive the asymptotically
optimal precoding matrices. In both scenarios, the approximations can be
computed by simple and provably converging fixed-point algorithms and are shown
to be almost surely tight in the limit when the number of antennas at each node
grows infinitely large. Simulations suggest that the approximations are
accurate for realistic system dimensions. The technique of iterative
deterministic equivalents can be easily extended to other channel models of
interest and is, therefore, also a new contribution to the field of random
matrix theory.Comment: submitted to the IEEE Transactions on Information Theory, 43 pages, 4
figure
Second-Order Coding Rate of Quasi-Static Rayleigh-Product MIMO Channels
With the development of innovative applications that require high reliability
and low latency, ultra-reliable and low latency communications become critical
for wireless networks. In this paper, the second-order coding rate of the
coherent quasi-static Rayleigh-product MIMO channel is investigated. We
consider the coding rate within O(1/\sqrt(Mn)) of the capacity, where M and n
denote the number of transmit antennas and the blocklength, respectively, and
derive the closed-form upper and lower bounds for the optimal average error
probability. This analysis is achieved by setting up a central limit theorem
(CLT) for the mutual information density (MID) with the assumption that the
block-length, the number of the scatterers, and the number of the antennas go
to infinity with the same pace. To obtain more physical insights, the high and
low SNR approximations for the upper and lower bounds are also given. One
interesting observation is that rank-deficiency degrades the performance of
MIMO systems with FBL and the fundamental limits of the Rayleigh-product
channel approaches those of the single Rayleigh case when the number of
scatterers approaches infinity. Finally, the fitness of the CLT and the gap
between the derived bounds and the performance of practical LDPC coding are
illustrated by simulations