8,289 research outputs found
Statistics of the MLE and Approximate Upper and Lower Bounds - Part 2: Threshold Computation and Optimal Signal Design
Threshold and ambiguity phenomena are studied in Part 1 of this work where
approximations for the mean-squared-error (MSE) of the maximum likelihood
estimator are proposed using the method of interval estimation (MIE), and where
approximate upper and lower bounds are derived. In this part we consider
time-of-arrival estimation and we employ the MIE to derive closed-form
expressions of the begin-ambiguity, end-ambiguity and asymptotic
signal-to-noise ratio (SNR) thresholds with respect to some features of the
transmitted signal. Both baseband and passband pulses are considered. We prove
that the begin-ambiguity threshold depends only on the shape of the envelope of
the ACR, whereas the end-ambiguity and asymptotic thresholds only on the shape
of the ACR. We exploit the results on the begin-ambiguity and asymptotic
thresholds to optimize, with respect to the available SNR, the pulse that
achieves the minimum attainable MSE. The results of this paper are valid for
various estimation problems
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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Millimeter wave wearable communication networks : analytic modeling and MIMO support
Future high-end wearable electronic devices including virtual reality goggles and augmented reality glasses require rates of the order of gigabits-per-second and potentially very low latency. Supporting high data rate wireless connectivity for applications such as uncompressed video streaming among wearable devices in a densely crowded environment is challenging. This is primarily due to bandwidth scarcity when many users operate multiple devices simultaneously. The millimeter wave (mmWave) band has the potential to address this bottleneck, thanks to more spectrum and less interference because of signal blockage at these frequencies. This dissertation addresses key questions that need to be answered before realizing mmWave-based wearables in practice: (i) what are the expected achievable rates in a crowded user environment, with mmWave devices using a given hardware configuration? (ii) how is the wireless connectivity affected in an indoor operation, which is prone to surface reflections? (iii) can multi-stream data transmission, involving large bandwidth communication under hardware constraints be realized? To answer these, tools from stochastic geometry and compressive sensing, and architectures involving hybrid analog/digital multiple-input multiple-output (MIMO) are leveraged. The main contributions of this dissertation are 1) analytical modeling to compute average achievable rates in mmWave wearable networks consisting of finite number of user devices and human blockages, 2) characterizing the impact of reflections and non-isotropic performance of mmWave wearable networks in crowded indoor environments, 3) channel estimation to support MIMO for wideband mmWave wearable devices using hybrid architecture, and 4) designing optimal, but easy-to-implement, precoding/combining strategies in frequency-selective mmWave systems. Both analysis and numerical simulations show how the proposed evaluation methodology and solutions serve to enable mmWave based communication among next generation wearable electronic devices.Electrical and Computer Engineerin
Quantum noise in second generation, signal-recycled laser interferometric gravitational-wave detectors
It has long been thought that the sensitivity of laser interferometric
gravitational-wave detectors is limited by the free-mass standard quantum
limit, unless radical redesigns of the interferometers or modifications of
their input/output optics are introduced. Within a fully quantum-mechanical
approach we show that in a second-generation interferometer composed of arm
cavities and a signal recycling cavity, e.g., the LIGO-II configuration, (i)
quantum shot noise and quantum radiation-pressure-fluctuation noise are
dynamically correlated, (ii) the noise curve exhibits two resonant dips, (iii)
the Standard Quantum Limit can be beaten by a factor of 2, over a frequency
range \Delta f/f \sim 1, but at the price of increasing noise at lower
frequencies.Comment: 35 pages, 9 figures; few misprints corrected and some references
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