15,272 research outputs found
Conditions for a Monotonic Channel Capacity
Motivated by results in optical communications, where the performance can
degrade dramatically if the transmit power is sufficiently increased, the
channel capacity is characterized for various kinds of memoryless vector
channels. It is proved that for all static point-to-point channels, the channel
capacity is a nondecreasing function of power. As a consequence, maximizing the
mutual information over all input distributions with a certain power is for
such channels equivalent to maximizing it over the larger set of input
distributions with upperbounded power. For interference channels such as
optical wavelength-division multiplexing systems, the primary channel capacity
is always nondecreasing with power if all interferers transmit with identical
distributions as the primary user. Also, if all input distributions in an
interference channel are optimized jointly, then the achievable sum-rate
capacity is again nondecreasing. The results generalizes to the channel
capacity as a function of a wide class of costs, not only power.Comment: This is an updated and expanded version of arXiv:1108.039
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.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Capacity of optical reading, Part 1: Reading boundless error-free bits using a single photon
We show that nature imposes no fundamental upper limit to the number of
information bits per expended photon that can, in principle, be read reliably
when classical data is encoded in a medium that can only passively modulate the
amplitude and phase of the probe light. We show that with a coherent-state
(laser) source, an on-off (amplitude-modulation) pixel encoding, and
shot-noise-limited direct detection (an overly-optimistic model for commercial
CD/DVD drives), the highest photon information efficiency achievable in
principle is about 0.5 bit per transmitted photon. We then show that a
coherent-state probe can read unlimited bits per photon when the receiver is
allowed to make joint (inseparable) measurements on the reflected light from a
large block of phase-modulated memory pixels. Finally, we show an example of a
spatially-entangled non-classical light probe and a receiver
design---constructable using a single-photon source, beam splitters, and
single-photon detectors---that can in principle read any number of error-free
bits of information. The probe is a single photon prepared in a uniform
coherent superposition of multiple orthogonal spatial modes, i.e., a W-state.
The code, target, and joint-detection receiver complexity required by a
coherent-state transmitter to achieve comparable photon efficiency performance
is shown to be much higher in comparison to that required by the W-state
transceiver.Comment: 11 pages, 12 figures, v3 includes a new plot characterizing the
photon efficiency vs. encoding efficiency tradeoff for optical reading. The
main technical body of the paper remains unaltere
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