220,471 research outputs found
Combined trellis coding with asymmetric MPSK modulation: An MSAT-X report
Traditionally symmetric, multiple phase-shift-keyed (MPSK) signal constellations, i.e., those with uniformly spaced signal points around the circle, have been used for both uncoded and coded systems. Although symmetric MPSK signal constellations are optimum for systems with no coding, the same is not necessarily true for coded systems. This appears to show that by designing the signal constellations to be asymmetric, one can, in many instances, obtain a significant performance improvement over the traditional symmetric MPSK constellations combined with trellis coding. The joint design of n/(n + 1) trellis codes and asymmetric 2 sup n + 1 - point MPSK is considered, which has a unity bandwidth expansion relative to uncoded 2 sup n-point symmetric MPSK. The asymptotic performance gains due to coding and asymmetry are evaluated in terms of the minimum free Euclidean distance free of the trellis. A comparison of the maximum value of this performance measure with the minimum distance d sub min of the uncoded system is an indication of the maximum reduction in required E sub b/N sub O that can be achieved for arbitrarily small system bit-error rates. It is to be emphasized that the introduction of asymmetry into the signal set does not effect the bandwidth of power requirements of the system; hence, the above-mentioned improvements in performance come at little or no cost. MPSK signal sets in coded systems appear in the work of Divsalar
Optimal modeling for complex system design
The article begins with a brief introduction to the theory describing optimal data compression systems and their performance. A brief outline is then given of a representative algorithm that employs these lessons for optimal data compression system design. The implications of rate-distortion theory for practical data compression system design is then described, followed by a description of the tensions between theoretical optimality and system practicality and a discussion of common tools used in current algorithms to resolve these tensions. Next, the generalization of rate-distortion principles to the design of optimal collections of models is presented. The discussion focuses initially on data compression systems, but later widens to describe how rate-distortion theory principles generalize to model design for a wide variety of modeling applications. The article ends with a discussion of the performance benefits to be achieved using the multiple-model design algorithms
A Multistage Method for SCMA Codebook Design Based on MDS Codes
Sparse Code Multiple Access (SCMA) has been recently proposed for the future
generation of wireless communication standards. SCMA system design involves
specifying several parameters. In order to simplify the procedure, most works
consider a multistage design approach. Two main stages are usually emphasized
in these methods: sparse signatures design (equivalently, resource allocation)
and codebook design. In this paper, we present a novel SCMA codebook design
method. The proposed method considers SCMA codebooks structured with an
underlying vector space obtained from classical block codes. In particular,
when using maximum distance separable (MDS) codes, our proposed design provides
maximum signal-space diversity with a relatively small alphabet. The use of
small alphabets also helps to maintain desired properties in the codebooks,
such as low peak-to-average power ratio and low-complexity detection.Comment: Submitted to IEEE Wireless Communication Letter
Polar Codes over Fading Channels with Power and Delay Constraints
The inherent nature of polar codes being channel specific makes it difficult
to use them in a setting where the communication channel changes with time. In
particular, to be able to use polar codes in a wireless scenario, varying
attenuation due to fading needs to be mitigated. To the best of our knowledge,
there has been no comprehensive work in this direction thus far. In this work,
a practical scheme involving channel inversion with the knowledge of the
channel state at the transmitter, is proposed. An additional practical
constraint on the permissible average and peak power is imposed, which in turn
makes the channel equivalent to an additive white Gaussian noise (AWGN) channel
cascaded with an erasure channel. It is shown that the constructed polar code
could be made to achieve the symmetric capacity of this channel. Further, a
means to compute the optimal design rate of the polar code for a given power
constraint is also discussed.Comment: 6 pages, 6 figure
A 2.0 Gb/s Throughput Decoder for QC-LDPC Convolutional Codes
This paper propose a decoder architecture for low-density parity-check
convolutional code (LDPCCC). Specifically, the LDPCCC is derived from a
quasi-cyclic (QC) LDPC block code. By making use of the quasi-cyclic structure,
the proposed LDPCCC decoder adopts a dynamic message storage in the memory and
uses a simple address controller. The decoder efficiently combines the memories
in the pipelining processors into a large memory block so as to take advantage
of the data-width of the embedded memory in a modern field-programmable gate
array (FPGA). A rate-5/6 QC-LDPCCC has been implemented on an Altera Stratix
FPGA. It achieves up to 2.0 Gb/s throughput with a clock frequency of 100 MHz.
Moreover, the decoder displays an excellent error performance of lower than
at a bit-energy-to-noise-power-spectral-density ratio () of
3.55 dB.Comment: accepted to IEEE Transactions on Circuits and Systems
Designing Power-Efficient Modulation Formats for Noncoherent Optical Systems
We optimize modulation formats for the additive white Gaussian noise channel
with a nonnegative input constraint, also known as the intensity-modulated
direct detection channel, with and without confining them to a lattice
structure. Our optimization criteria are the average electrical and optical
power. The nonnegativity input signal constraint is translated into a conical
constraint in signal space, and modulation formats are designed by sphere
packing inside this cone. Some remarkably dense packings are found, which yield
more power-efficient modulation formats than previously known. For example, at
a spectral efficiency of 1 bit/s/Hz, the obtained modulation format offers a
0.86 dB average electrical power gain and 0.43 dB average optical power gain
over the previously best known modulation formats to achieve a symbol error
rate of 10^-6. This modulation turns out to have a lattice-based structure. At
a spectral efficiency of 3/2 bits/s/Hz and to achieve a symbol error rate of
10^-6, the modulation format obtained for optimizing the average electrical
power offers a 0.58 dB average electrical power gain over the best
lattice-based modulation and 2.55 dB gain over the best previously known
format. However, the modulation format optimized for average optical power
offers a 0.46 dB average optical power gain over the best lattice-based
modulation and 1.35 dB gain over the best previously known format.Comment: Submitted to Globecom 201
Designing low carbon buildings : a framework to reduce energy consumption and embed the use of renewables
EU policies to mitigate climate change set ambitious goals for energy and carbon reduction for the built environment. In order meet and even exceed the EU targets the UK Government's Climate Change Act 2008 sets a target to reduce greenhouse gas emissions in the UK by at least 80% from 1990 levels by 2050. To support these targets the UK government also aims to ensure that 20% of the UK's electricity is supplied from renewable sources by 2020. This article presents a design framework and a set of integrated IT tools to enable an analysis of the energy performance of building designs, including consideration of active and passive renewable energy technologies, when the opportunity to substantially improve the whole life-cycle energy performance of those designs is still open. To ensure a good fit with current architectural practices the design framework is integrated with the Royal Institute of British Architects (RIBA) key stages, which is the most widely used framework for the delivery of construction projects. The main aims of this article are to illustrate the need for new approaches to support low carbon building design that can be integrated into current architectural practice, to present the design framework developed in this research and illustrate its application in a case study
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