3,383 research outputs found
Capacity and Modulations with Peak Power Constraint
A practical communication channel often suffers from constraints on input
other than the average power, such as the peak power constraint. In order to
compare achievable rates with different constellations as well as the channel
capacity under such constraints, it is crucial to take these constraints into
consideration properly. In this paper, we propose a direct approach to compare
the achievable rates of practical input constellations and the capacity under
such constraints. As an example, we study the discrete-time complex-valued
additive white Gaussian noise (AWGN) channel and compare the capacity under the
peak power constraint with the achievable rates of phase shift keying (PSK) and
quadrature amplitude modulation (QAM) input constellations.Comment: 9 pages with 12 figures. Preparing for submissio
On Low Complexity Detection for QAM Isomorphic Constellations
Despite of the known gap from the Shannon's capacity, several standards are
still employing QAM or star shape constellations, mainly due to the existing
low complexity detectors. In this paper, we investigate the low complexity
detection for a family of QAM isomorphic constellations. These constellations
are known to perform very close to the peak-power limited capacity,
outperforming the DVB-S2X standard constellations. The proposed strategy is to
first remap the received signals to the QAM constellation using the existing
isomorphism and then break the log likelihood ratio computations to two one
dimensional PAM constellations. Gains larger than 0.6 dB with respect to QAM
can be obtained over the peak power limited channels without any increase in
detection complexity. Our scheme also provides a systematic way to design
constellations with low complexity one dimensional detectors. Several open
problems are discussed at the end of the paper.Comment: Submitted to IEEE GLOBECOM 201
Time-Frequency Packing for High Capacity Coherent Optical Links
We consider realistic long-haul optical links, with linear and nonlinear
impairments, and investigate the application of time-frequency packing with
low-order constellations as a possible solution to increase the spectral
efficiency. A detailed comparison with available techniques from the literature
will be also performed. We will see that this technique represents a feasible
solution to overcome the relevant theoretical and technological issues related
to this spectral efficiency increase and could be more effective than the
simple adoption of high-order modulation formats.Comment: 10 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1406.5685 by other author
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Unified Capacity Limit of Non-coherent Wideband Fading Channels
In non-coherent wideband fading channels where energy rather than spectrum is
the limiting resource, peaky and non-peaky signaling schemes have long been
considered species apart, as the first approaches asymptotically the capacity
of a wideband AWGN channel with the same average SNR, whereas the second
reaches a peak rate at some finite critical bandwidth and then falls to zero as
bandwidth grows to infinity. In this paper it is shown that this distinction is
in fact an artifact of the limited attention paid in the past to the product
between the bandwidth and the fraction of time it is in use. This fundamental
quantity, called bandwidth occupancy, measures average bandwidth usage over
time. For all signaling schemes with the same bandwidth occupancy, achievable
rates approach to the wideband AWGN capacity within the same gap as the
bandwidth occupancy approaches its critical value, and decrease to zero as the
occupancy goes to infinity. This unified analysis produces quantitative
closed-form expressions for the ideal bandwidth occupancy, recovers the
existing capacity results for (non-)peaky signaling schemes, and unveils a
trade-off between the accuracy of approximating capacity with a generalized
Taylor polynomial and the accuracy with which the optimal bandwidth occupancy
can be bounded.Comment: Accepted for publication in IEEE Transactions on Wireless
Communications. Copyright may be transferred without notic
On the use of multiple satellites to improve the spectral efficiency of broadcast transmissions
We consider the use of multiple co-located satellites to improve the spectral efficiency of broadcast transmissions. In particular, we assume that two satellites transmit on overlapping
geographical coverage areas, with overlapping frequencies. We first describe the theoretical framework based on network information theory and, in particular, on the theory for multiple access channels. The application to different scenarios will be then considered, including the bandlimited additive white Gaussian noise channel with average power constraint and different models for the nonlinear satellite channel. The comparison with the adoption of frequency division multiplexing (FDM) is also provided. The main conclusion is that a strategy based on overlapped signals is convenient with respect to FDM, although it requires the adoption of a multiuser detection strategy at the receiver
Frequency-domain transmit processing for MIMO SC-FDMA in wideband propagation channels
This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available
- âŠ