28 research outputs found
Modeling the Random Orientation of Mobile Devices: Measurement, Analysis and LiFi Use Case
Light-fidelity (LiFi) is a networked optical wireless communication (OWC)
solution for high-speed indoor connectivity for fixed and mobile optical
communications. Unlike conventional radio frequency wireless systems, the OWC
channel is not isotropic, meaning that the device orientation affects the
channel gain significantly, particularly for mobile users. However, due to the
lack of a proper model for device orientation, many studies have assumed that
the receiver is vertically upward and fixed. In this paper, a novel model for
device orientation based on experimental measurements of forty participants has
been proposed. It is shown that the probability density function (PDF) of the
polar angle can be modeled either based on a Laplace (for static users) or a
Gaussian (for mobile users) distribution. In addition, a closed-form expression
is obtained for the PDF of the cosine of the incidence angle based on which
line-of-sight (LOS) channel gain is described in OWC channels. An approximation
of this PDF based on the truncated Laplace is proposed and the accuracy of this
approximation is confirmed by the Kolmogorov-Smirnov distance (KSD). Moreover,
the statistics of the LOS channel gain are calculated and the random
orientation of a user equipment (UE) is modeled as a random process. The
influence of the random orientation on signal-to-noise-ratio (SNR) performance
of OWC systems has been evaluated. Finally, an orientation-based random
waypoint (ORWP) mobility model is proposed by considering the random
orientation of the UE during the user's movement. The performance of ORWP is
assessed on the handover rate and it is shown that it is important to take the
random orientation into account.Comment: 14 pages, 7 figure
Low-mass dark matter search results from full exposure of PandaX-I experiment
We report the results of a weakly-interacting massive particle (WIMP) dark
matter search using the full 80.1\;live-day exposure of the first stage of the
PandaX experiment (PandaX-I) located in the China Jin-Ping Underground
Laboratory. The PandaX-I detector has been optimized for detecting low-mass
WIMPs, achieving a photon detection efficiency of 9.6\%. With a fiducial liquid
xenon target mass of 54.0\,kg, no significant excess event were found above the
expected background. A profile likelihood analysis confirms our earlier finding
that the PandaX-I data disfavor all positive low-mass WIMP signals reported in
the literature under standard assumptions. A stringent bound on the low mass
WIMP is set at WIMP mass below 10\,GeV/c, demonstrating that liquid xenon
detectors can be competitive for low-mass WIMP searches.Comment: v3 as accepted by PRD. Minor update in the text in response to
referee comments. Separating Fig. 11(a) and (b) into Fig. 11 and Fig. 12.
Legend tweak in Fig. 9(b) and 9(c) as suggested by referee, as well as a
missing legend for CRESST-II legend in Fig. 12 (now Fig. 13). Same version as
submitted to PR