36 research outputs found
Random Beamforming over Correlated Fading Channels
We study a multiple-input multiple-output (MIMO) multiple access channel
(MAC) from several multi-antenna transmitters to a multi-antenna receiver. The
fading channels between the transmitters and the receiver are modeled by random
matrices, composed of independent column vectors with zero mean and different
covariance matrices. Each transmitter is assumed to send multiple data streams
with a random precoding matrix extracted from a Haar-distributed matrix. For
this general channel model, we derive deterministic approximations of the
normalized mutual information, the normalized sum-rate with
minimum-mean-square-error (MMSE) detection and the
signal-to-interference-plus-noise-ratio (SINR) of the MMSE decoder, which
become arbitrarily tight as all system parameters grow infinitely large at the
same speed. In addition, we derive the asymptotically optimal power allocation
under individual or sum-power constraints. Our results allow us to tackle the
problem of optimal stream control in interference channels which would be
intractable in any finite setting. Numerical results corroborate our analysis
and verify its accuracy for realistic system dimensions. Moreover, the
techniques applied in this paper constitute a novel contribution to the field
of large random matrix theory and could be used to study even more involved
channel models.Comment: 35 pages, 5 figure
Random Beamforming over Quasi-Static and Fading Channels: A Deterministic Equivalent Approach
In this work, we study the performance of random isometric precoders over
quasi-static and correlated fading channels. We derive deterministic
approximations of the mutual information and the
signal-to-interference-plus-noise ratio (SINR) at the output of the
minimum-mean-square-error (MMSE) receiver and provide simple provably
converging fixed-point algorithms for their computation. Although these
approximations are only proven exact in the asymptotic regime with infinitely
many antennas at the transmitters and receivers, simulations suggest that they
closely match the performance of small-dimensional systems. We exemplarily
apply our results to the performance analysis of multi-cellular communication
systems, multiple-input multiple-output multiple-access channels (MIMO-MAC),
and MIMO interference channels. The mathematical analysis is based on the
Stieltjes transform method. This enables the derivation of deterministic
equivalents of functionals of large-dimensional random matrices. In contrast to
previous works, our analysis does not rely on arguments from free probability
theory which enables the consideration of random matrix models for which
asymptotic freeness does not hold. Thus, the results of this work are also a
novel contribution to the field of random matrix theory and applicable to a
wide spectrum of practical systems.Comment: to appear in IEEE Transactions on Information Theory, 201
Performance of MMSE MIMO Receivers: A Large N Analysis for Correlated Channels
Linear receivers are considered as an attractive low-complexity alternative
to optimal processing for multi-antenna MIMO communications. In this paper we
characterize the performance of MMSE MIMO receivers in the limit of large
antenna numbers in the presence of channel correlations. Using the replica
method, we generalize our results obtained in arXiv:0810.0883 to
Kronecker-product correlated channels and calculate the asymptotic mean and
variance of the mutual information of a MIMO system of parallel MMSE
subchannels. The replica method allows us to use the ties between the optimal
receiver mutual information and the MMSE SIR of Gaussian inputs to calculate
the joint moments of the SIRs of the MMSE subchannels. Using the methodology
discussed in arXiv:0810.0883 it can be shown that the mutual information
converges in distribution to a Gaussian random variable. Our results agree very
well with simulations even with a moderate number of antennas.Comment: Invited article at the IEEE Vehicular Technology Conference,
Barcelona 200
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
Performance Analysis of Massive MIMO Networks with Random Unitary Pilot Matrices
A common approach to obtain channel state information for massive MIMO
networks is to use the same orthogonal training sequences in each cell. We call
this the full-pilot reuse (FPR) scheme. In this paper, we study an alternative
approach where each cell uses different sets of orthogonal pilot (DOP)
sequences. Considering uplink communications with matched filter (MF)
receivers, we first derive the SINR in the large system regime where the number
of antennas at the base station, the number of users in each cell, and training
duration grow large with fixed ratios. For tractability in the analysis, the
orthogonal pilots are drawn from Haar distributed random unitary matrices. The
resulting expression is simple and easy to compute. As shown by the numerical
simulations, the asymptotic SINR approximates the finite-size systems
accurately. Secondly, we derive the user capacity of the DOP scheme under a
simple power control and show that it is generally better than that of the FPR
scheme.Comment: Draf
The effect of clock frequency offset on OFDM-CDMA systems
6 pagesRecently, Orthogonal Frequency and Code Division Multiplexing (OFCDM) access technology has been investigated for the next generation of mobile communication systems. A known drawback of these multi carrier systems is their sensitivity to synchronization errors, particularly to clock frequency offset. The contribution of this article is twofold. First, a generalized framework is proposed for modelling the effect of clock frequency offset on 2 dimensional spreading OFDM-CDMA systems. Then, exploiting some results from the random matrix theory, an analytic expression of the Signal to Interference and Noise Ratio (SINR), modeling the impact of clock frequency offset, is derived. This formula is independent from the actual values of the spreading codes while taking into account their orthogonality. This is the novelty of this article. This model works for frequency selective channels and any single user detector
Sensitivity of OFDM-CDMA systems to carrier frequency offset
6 pages;This paper presents the impact of a carrier frequency offset on the performance of 2 dimensional spreading OFDM-CDMA systems. This is measured by the degradation of the Signal to Interference plus Noise Ratio (SINR) obtained after despreading and equalization. Using some properties of random matrix and free probability theories, a new expression of the SINR is derived. It is independent of the actual value of the spreading codes while still accounting for the orthogonality between codes. This model is validated by means of Monte-Carlo simulations. . It is also exploited to compare the sensitivities of MC-CDMA and MC-DS-CDMA systems to carrier offset in a frequency selective channel. This work is carried out for zero forcing (ZF) and minimum mean square error (MMSE) equalizers
SINR evaluation of OFDM-CDMA systems with constant timing offset: asymptotic analysis
5 pagesThis article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the Signal to Interference plus Noise Ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users' spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss the validity of this model