37 research outputs found
Uplink Analysis of Large MU-MIMO Systems With Space-Constrained Arrays in Ricean Fading
Closed-form approximations to the expected per-terminal
signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral
efficiency of a large multiuser multiple-input multiple-output system are
presented. Our analysis assumes correlated Ricean fading with maximum ratio
combining on the uplink, where the base station (BS) is equipped with a uniform
linear array (ULA) with physical size restrictions. Unlike previous studies,
our model caters for the presence of unequal correlation matrices and unequal
Rice factors for each terminal. As the number of BS antennas grows without
bound, with a finite number of terminals, we derive the limiting expected
per-terminal SINR and ergodic sum spectral efficiency of the system. Our
findings suggest that with restrictions on the size of the ULA, the expected
SINR saturates with increasing operating signal-to-noise-ratio (SNR) and BS
antennas. Whilst unequal correlation matrices result in higher performance, the
presence of strong line-of-sight (LoS) has an opposite effect. Our analysis
accommodates changes in system dimensions, SNR, LoS levels, spatial correlation
levels and variations in fixed physical spacings of the BS array.Comment: 7 pages, 3 figures, accepted for publication in the proceedings of
IEEE ICC, to be held in Paris, France, May 201
Interference and Deployment Issues for Cognitive Radio Systems in Shadowing Environments
In this paper we describe a model for calculating the aggregate interference
encountered by primary receivers in the presence of randomly placed cognitive
radios (CRs). We show that incorporating the impact of distance attenuation and
lognormal fading on each constituent interferer in the aggregate, leads to a
composite interference that cannot be satisfactorily modeled by a lognormal.
Using the interference statistics we determine a number of key parameters
needed for the deployment of CRs. Examples of these are the exclusion zone
radius, needed to protect the primary receiver under different types of fading
environments and acceptable interference levels, and the numbers of CRs that
can be deployed. We further show that if the CRs have apriori knowledge of the
radio environment map (REM), then a much larger number of CRs can be deployed
especially in a high density environment. Given REM information, we also look
at the CR numbers achieved by two different types of techniques to process the
scheduling information.Comment: to be presented at IEEE ICC 2009. This posting is the same as the
original one. Only author's list is updated that was unfortunately not
correctly mentioned in first versio
On the Convergence of Massive MIMO Systems
In this paper we examine convergence properties of massive MIMO systems with
the aim of determining the number of antennas required for massive MIMO gains.
We consider three characteristics of a channel matrix and study their
asymptotic behaviour. Furthermore, we derive ZF SNR and MF SINR for a scenario
of unequal receive powers. In our results we include the effects of spatial
correlation. We show that the rate of convergence of channel metrics is much
slower than that of the ZF/MF precoder properties.Comment: 6 pages, 6 figures, ICC 201
On the Impact of Antenna Topologies for Massive MIMO Systems
Approximate expressions for the spatial correlation of cylindrical and
uniform rectangular arrays (URA) are derived using measured distributions of
angles of departure (AOD) for both the azimuth and zenith domains. We examine
massive multiple-input-multiple-output (MIMO) convergence properties of the
correlated channels by considering a number of convergence metrics. The
per-user matched filter (MF) signal-to-interference-plus-noise ratio (SINR)
performance and convergence rate, to respective limiting values, of the two
antenna topologies is also explored.Comment: 6 pages, 6 figure
Impact of Line-of-Sight and Unequal Spatial Correlation on Uplink MU-MIMO Systems
Closed-form approximations of the expected per-terminal
signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral
efficiency of a multiuser multiple-input multiple-output system are presented.
Our analysis assumes spatially correlated Ricean fading channels with
maximum-ratio combining on the uplink. Unlike previous studies, our model
accounts for the presence of unequal correlation matrices, unequal Rice
factors, as well as unequal link gains to each terminal. The derived
approximations lend themselves to useful insights, special cases and
demonstrate the aggregate impact of line-of-sight (LoS) and unequal correlation
matrices. Numerical results show that while unequal correlation matrices
enhance the expected SINR and ergodic sum spectral efficiency, the presence of
strong LoS has an opposite effect. Our approximations are general and remain
insensitive to changes in the system dimensions, signal-to-noise-ratios, LoS
levels and unequal correlation levels.Comment: 4 pages, 2 figures, accepted for publication in the IEEE Wireless
Communications Letters, Vol. 6, 201
Favorable Propagation with User Cluster Sharing
We examine the favorable propagation (FP) behavior of a massive multi-user
multiple-input-multiple-output (MU-MIMO) system equipped with a uniform linear
array (ULA), horizontal uniform rectangular array (HURA) or uniform circular
array (UCA) using a ray-based channel model with user cluster sharing. We
demonstrate FP for these systems and provide analytical expressions for the
mean-squared distance (MSD) of the FP metric from its large-system limit for
each of the aforementioned topologies. We use these results to examine the
detrimental effects of user cluster sharing on FP behavior, and demonstrate the
superior performance of the ULA as compared to the UCA and the HURA with equal
inter-element spacing. Although cluster sharing has a negative impact on FP for
finite arrays, we additionally examine the asymptotic rate of convergence to FP
as a function of array size and show that this rate is unchanged with or
without user cluster sharing.Comment: 7 pages, 3 figures, Accepted for publication in IEEE PIMRC 202
3D Mobility Models and Analysis for UAVs
We present a flexible family of 3D mobility models suitable for unmanned
aerial vehicles (UAV). Based on stochastic differential equations, the models
offer a unique property of explicitly incorporating the mobility control
mechanism and environmental perturbation, while enabling tractable steady state
solutions for properties such as position and connectivity. Specifically,
motivated by UAV flight data, for a symmetric mobility model with an arbitrary
control mechanism, we derive the steady state distribution of the distance from
the target position. We provide closed form expressions for the special cases
of the Ornstein-Uhlenbeck (OU) process and on-off control (OC). We extend the
model to incorporate imperfect positioning and asymmetric control. For a
practically relevant scenario of partial symmetry (such as in the x-y plane),
we present steady state position results for the OU control. Building on these
results, we derive UAV connectivity probability results based on a SNR
criterion in a Rayleigh fading environment.Comment: 6 pages, 6 figures, accepted for publication at IEEE PIMRC 202