14,963 research outputs found
Distortion Analysis for the Assessment of LTI and non-LTI Transmitters
Bounds on the frequency domain behavior of electrically small antennas are
adapted to assess the time domain distortion or fidelity achievable by simple
linear time-invariant (LTI) systems. Rigorous expressions for a TM
spherical shell are used as a direct analog to the well known Chu limit on an
antenna's bandwidth-efficiency product. These expressions are shown to agree
with results obtained using narrowband single resonance approximations,
allowing for the analysis of arbitrary small dipole-like structures through
bounds on their single frequency Q-factor and efficiency. The resulting
expressions are used as a basis for assessing the performance gains of
electrically small non-LTI (e.g., direct antenna modulation) transmitters for
which Q-factor and impedance bandwidth are not defined but which can be
analyzed directly in the time domain via distortion.Comment: 8 pages, 8 figure
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.
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On Detection Issues in the SC-based Uplink of a MU-MIMO System with a Large Number of BS Antennas
This paper deals with SC/FDE within a MU-MIMO system where a large number of
BS antennas is adopted. In this context, either linear or reduced-complexity
iterative DF detection techniques are considered. Regarding performance
evaluation by simulation, appropriate semi-analytical methods are proposed.
This paper includes a detailed evaluation of BER performances for uncoded
4-Quadrature Amplitude Modulation (4-QAM) schemes and a MU-MIMO channel with
uncorrelated Rayleigh fading. The accuracy of performance results obtained
through the semi-analytical simulation methods is assessed by means of parallel
conventional Monte Carlo simulations, under the assumptions of perfect power
control and perfect channel estimation. The performance results are discussed
in detail, with the help of selected performance bounds. We emphasize that a
moderately large number of BS antennas is enough to closely approximate the
SIMO MFB performance, especially when using the suggested low-complexity
iterative DF technique, which does not require matrix inversion operations. We
also emphasize the achievable "massive MIMO" effects, even for strongly
reduced-complexity linear detection techniques, provided that the number of BS
antennas is much higher than the number of antennas which are jointly employed
in the terminals of the multiple autonomous users.Comment: 7 pages, 4 figure
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