14,180 research outputs found
High-Speed Visible Light Indoor Networks Based on Optical Orthogonal Codes and Combinatorial Designs
Interconnecting devices in an indoor environment using the illumination
system and white light emitting diodes (LED) requires adaptive networking
techniques that can provide network access for multiple users. Two techniques
based on multilevel signaling and optical orthogonal codes (OOC) are explored
in this paper in order to provide simultaneous multiple access in an indoor
multiuser network. Balanced incomplete block designs (BIBD) are used to
construct multilevel symbols for M-ary signaling. Using these multilevel
symbols we are able to control the optical peak to average power ratio (PAPR)
in the system, and hereby control the dimming level. In the first technique,
the M-ary data of each user is first encoded using the OOC codeword that is
assigned to that user, and then it is fed into a BIBD encoder to generate a
multilevel signal. The second multiple access method uses sub-sets of a BIBD
code to apply multilevel expurgated pulse-position modulation (MEPPM) to the
data of each user. While the first approach has a larger Hamming distance
between the symbols of each user, the latter can provide higher bit-rates for
users in VLC systems with bandwidth-limited LEDs
Application of Expurgated PPM to Indoor Visible Light Communications - Part II: Access Networks
Providing network access for multiple users in a visible light communication
(VLC) system that utilizes white light emitting diodes (LED) as sources
requires new networking techniques adapted to the lighting features. In this
paper we introduce two multiple access techniques using expurgated PPM (EPPM)
that can be implemented using LEDs and support lighting features such as
dimming. Multilevel symbols are used to provide M-ary signaling for multiple
users using multilevel EPPM (MEPPM). Using these multiple-access schemes we are
able to control the optical peak to average power ratio (PAPR) in the system,
and hereby control the dimming level. In the first technique, the M-ary data of
each user is first encoded using an optical orthogonal code (OOC) assigned to
the user, and the result is fed into a EPPM encoder to generate a multilevel
signal. The second multiple access method uses sub-sets of the EPPM
constellation to apply MEPPM to the data of each user. While the first approach
has a larger Hamming distance between the symbols of each user, the latter can
provide higher bit-rates for users in VLC systems using bandwidth-limited LEDs.Comment: Journal of Lightwave Technology. arXiv admin note: substantial text
overlap with arXiv:1308.074
Development of a dc-ac power conditioner for wind generator by using neural network
This project present of development single phase DC-AC converter for wind
generator application. The mathematical model of the wind generator and Artificial
Neural Network control for DC-AC converter is derived. The controller is designed to
stabilize the output voltage of DC-AC converter. To verify the effectiveness of the
proposal controller, both simulation and experimental are developed. The simulation and
experimental result show that the amplitude of output voltage of the DC-AC converter
can be controlled
Hybrid Coding Technique for Pulse Detection in an Optical Time Domain Reflectometer
The paper introduces a novel hybrid coding technique for improved pulse detection in an optical time domain reflectometer. The hybrid schemes combines Simplex codes with signal averaging to articulate a very sophisticated coding technique that considerably reduces the processing time to extract specified coding gains in comparison to the existing techniques. The paper quantifies the coding gain of the hybrid scheme mathematically and provide simulative results in direct agreement with the theoretical performance. Furthermore, the hybrid scheme has been tested on our self-developed OTDR
Flexible digital modulation and coding synthesis for satellite communications
An architecture and a hardware prototype of a flexible trellis modem/codec (FTMC) transmitter are presented. The theory of operation is built upon a pragmatic approach to trellis-coded modulation that emphasizes power and spectral efficiency. The system incorporates programmable modulation formats, variations of trellis-coding, digital baseband pulse-shaping, and digital channel precompensation. The modulation formats examined include (uncoded and coded) binary phase shift keying (BPSK), quatenary phase shift keying (QPSK), octal phase shift keying (8PSK), 16-ary quadrature amplitude modulation (16-QAM), and quadrature quadrature phase shift keying (Q squared PSK) at programmable rates up to 20 megabits per second (Mbps). The FTMC is part of the developing test bed to quantify modulation and coding concepts
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