81 research outputs found
Trellis-Based Equalization for Sparse ISI Channels Revisited
Sparse intersymbol-interference (ISI) channels are encountered in a variety
of high-data-rate communication systems. Such channels have a large channel
memory length, but only a small number of significant channel coefficients. In
this paper, trellis-based equalization of sparse ISI channels is revisited. Due
to the large channel memory length, the complexity of maximum-likelihood
detection, e.g., by means of the Viterbi algorithm (VA), is normally
prohibitive. In the first part of the paper, a unified framework based on
factor graphs is presented for complexity reduction without loss of optimality.
In this new context, two known reduced-complexity algorithms for sparse ISI
channels are recapitulated: The multi-trellis VA (M-VA) and the
parallel-trellis VA (P-VA). It is shown that the M-VA, although claimed, does
not lead to a reduced computational complexity. The P-VA, on the other hand,
leads to a significant complexity reduction, but can only be applied for a
certain class of sparse channels. In the second part of the paper, a unified
approach is investigated to tackle general sparse channels: It is shown that
the use of a linear filter at the receiver renders the application of standard
reduced-state trellis-based equalizer algorithms feasible, without significant
loss of optimality. Numerical results verify the efficiency of the proposed
receiver structure.Comment: To be presented at the 2005 IEEE Int. Symp. Inform. Theory (ISIT
2005), September 4-9, 2005, Adelaide, Australi
Modelling Aspects of Planar Multi-Mode Antennas for Direction-of-Arrival Estimation
Multi-mode antennas are an alternative to classical antenna arrays, and hence
a promising emerging sensor technology for a vast variety of applications in
the areas of array signal processing and digital communications. An unsolved
problem is to describe the radiation pattern of multi-mode antennas in closed
analytic form based on calibration measurements or on electromagnetic field
(EMF) simulation data. As a solution, we investigate two modeling methods: One
is based on the array interpolation technique (AIT), the other one on wavefield
modeling (WM). Both methods are able to accurately interpolate quantized EMF
data of a given multi-mode antenna, in our case a planar four-port antenna
developed for the 6-8.5 GHz range. Since the modeling methods inherently depend
on parameter sets, we investigate the influence of the parameter choice on the
accuracy of both models. Furthermore, we evaluate the impact of modeling errors
for coherent maximum-likelihood direction-of-arrival (DoA) estimation given
different model parameters. Numerical results are presented for a single
polarization component. Simulations reveal that the estimation bias introduced
by model errors is subject to the chosen model parameters. Finally, we provide
optimized sets of AIT and WM parameters for the multi-mode antenna under
investigation. With these parameter sets, EMF data samples can be reproduced in
interpolated form with high angular resolution
Single-Element Beamforming using Multi-Mode Antenna Patterns
Recently, multi-mode antennas have been studied for communication as well as
localization purposes. In this work, the capabilities provided by a single
planar multi-mode radiator as a steerable multi-port antenna are explored. As
an original contribution, the radiation characteristics of individual groups of
modes of the single radiator are combined to optimize beamforming performance.
Three possible codebook realizations are studied and compared. A new
optimization criterion, gain by element factor, is introduced
Analytical derivation of EXIT charts for simple block codes and for LDPC codes using information combining
Publication in the conference proceedings of EUSIPCO, Viena, Austria, 200
Liquid Crystal Display Based Angle-of-Arrival Estimation of a Single Light Source
In this paper, a novel concept for visible light positioning is introduced, which employs a liquid crystal display as a dynamic optical filter in front of a photodetector. By electronically switching dedicated pixel areas in transparent or blocking mode, respectively, the angle of arrival is estimated. The measurement principle is supported by a mathematical model. Finally, an experimental setup is presented and measurement results are compared to the theoretical findings
Magnetic Communication Using High-Sensitivity Magnetic Field Detectors
In this article, an innovative approach for magnetic data communication is presented. For this purpose, the receiver coil of a conventional magneto-inductive communication system is replaced by a high-sensitivity wideband magnetic field sensor. The results show decisive advantages offered by sensitive magnetic field sensors, including a higher communication range for small receiver units. This approach supports numerous mobile applications where receiver size is limited, possibly in conjunction with multiple detectors. Numerical results are supported by a prototype implementation employing an anisotropic magneto-resistive sensor
Networking Aspects based on the Talkative Power Concept for DC Microgrid Systems
The talkative power concept is a simultaneous power-line communication and energy transfer technique which integrates data modulation into a power converter. The information sequence is deterministically represented by the ripple, which superimposes the output voltage. With a few exceptions, so far emphasis has been on scenarios where only a single node is actively transmitting data in a certain time slot in simplex mode. In microgrid applications, however, multiple active power sources are of interest as well. Examples include battery management systems, smart metering, electricity trading systems, and smart grids with several power sources, energy storage devices, loads, and data receivers. In this contribution, bus networking aspects based on the talkative power concept are presented for scenarios with several active nodes and for full-duplex communication. The paper addresses potential multiple access techniques as well as duplexing schemes for connected power converters supporting bidirectional power and information flow. In numerical results, a spread spectrum scheme based on orthogonal variable spreading factor codes in conjunction with frequency shift keying (FSK) is presented for four simultaneously active buck converters with a sum data rate of 500 kbps at a switching frequency of 1 MHz. In general, with 2-ary FSK, the maximum achievable sum data rate is half of the switching frequency in a synchronous setup
- …