1,667 research outputs found
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
Regularity of quasi-stationary measures for simple exclusion in dimension d >= 5
We consider the symmetric simple exclusion process on Z^d, for d>= 5, and
study the regularity of the quasi-stationary measures of the dynamics
conditionned on not occupying the origin. For each \rho\in ]0,1[, we establish
uniqueness of the density of quasi-stationary measures in L^2(d\nur), where
\nur is the stationary measure of density \rho. This, in turn, permits us to
obtain sharp estimates for P_{\nur}(\tau>t), where \tau is the first time the
origin is occupied.Comment: 18 pages. Corrections after referee report. To be published in Ann
Proba
Hitting times for independent random walks on
We consider a system of asymmetric independent random walks on
, denoted by , stationary under the
product Poisson measure of marginal density . We fix a
pattern , an increasing local event, and denote by the
hitting time of . By using a loss network representation of our
system, at small density, we obtain a coupling between the laws of
conditioned on for all times . When , this provides
bounds on the rate of convergence of the law of conditioned on
toward its limiting probability measure as tends to infinity.
We also treat the case where the initial measure is close to
without being product.Comment: Published at http://dx.doi.org/10.1214/009117906000000106 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
On the Supersymplectic Homogeneous Superspace Underlying the OSp(1/2) Coherent States
In this work we extend Onofri and Perelomov's coherent states methods to the
recently introduced coherent states. These latter are shown to be
parametrized by points of a supersymplectic supermanifold, namely the
homogeneous superspace , which is clearly identified with a
supercoadjoint orbit of by exhibiting the corresponding equivariant
supermoment map. Moreover, this supermanifold is shown to be a nontrivial
example of Rothstein's supersymplectic supermanifolds. More precisely, we show
that its supersymplectic structure is completely determined in terms of
-invariant (but unrelated) K\"ahler -form and K\"ahler metric on
the unit disc. This result allows us to define the notions of a superK\"ahler
supermanifold and a superK\"ahler superpotential, the geometric structure of
the former being encoded into the latter.Comment: 19 pgs, PlainTeX, Preprint CRM-185
Minimum BER Precoding in 1-Bit Massive MIMO Systems
1-bit digital-to-analog (DACs) and analog-to-digital converters (ADCs) are
gaining more interest in massive MIMO systems for economical and computational
efficiency. We present a new precoding technique to mitigate the
inter-user-interference (IUI) and the channel distortions in a 1-bit downlink
MUMISO system with QPSK symbols. The transmit signal vector is optimized taking
into account the 1-bit quantization. We develop a sort of mapping based on a
look-up table (LUT) between the input signal and the transmit signal. The LUT
is updated for each channel realization. Simulation results show a significant
gain in terms of the uncoded bit-error-ratio (BER) compared to the existing
linear precoding techniques.Comment: Presented in IEEE SAM 2016, 10th-13th July 2016, Rio De Janeiro,
Brazi
Multiple Parameter Estimation With Quantized Channel Output
We present a general problem formulation for optimal parameter estimation
based on quantized observations, with application to antenna array
communication and processing (channel estimation, time-of-arrival (TOA) and
direction-of-arrival (DOA) estimation). The work is of interest in the case
when low resolution A/D-converters (ADCs) have to be used to enable higher
sampling rate and to simplify the hardware. An Expectation-Maximization (EM)
based algorithm is proposed for solving this problem in a general setting.
Besides, we derive the Cramer-Rao Bound (CRB) and discuss the effects of
quantization and the optimal choice of the ADC characteristic. Numerical and
analytical analysis reveals that reliable estimation may still be possible even
when the quantization is very coarse.Comment: 9 pages, 9 figures, International ITG Workshop on Smart Antennas -
WSA 2010, Bremen, German
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