Pep Canyelles-Pericas

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370-780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

Chaos synchronization on Visible Light Communication with application for secure data communications

This paper studies the possibility of implementing a chaos synchronization scheme in the context of Visible Light Communication (VLC) with potential application to message encryption. For this, a unidirectional transmitter-receiver configuration is employed whereby the encrypted data is sent over a VLC optical wireless channel. More precisely, the classical chaotic masking, with the use of a Rossler oscillator and a corresponding nonlinear observer, and the inverse system approach with Lorenz oscillators, have been employed to demonstrate the proof of concept of chaos synchronization in VLC. By employing a pseudo random binary data sequence as a message it is shown that acceptable message recovery is obtained despite the presence of delay, attenuation and noise in the channel. Simulations results using Matlab Simulink are provided to show the performance and the level of the synchronization achieved for both methods.

Chaotic bidirectional communication using high gain observers with modified inclusion method

This work is concerned with the design of a chaotic communication system based on a modified inclusion method. For this, we propose a bidirectional transmitter-receiver communication scheme whereby the transmitter is a Rossler oscillator and the receiver is a corresponding nonlinear high gain observer. The main motivation to employ a bidirectional communication scheme is exclusively to eliminate the nonlinearities in the error dynamics of the observer. We propose an approach where a message is embedded with a proportional and integrated form in the state variables, proving that if amplification factors are correctly calculated the transfer function is equal to unity and message recovery is possible with simple error dynamics subtraction. Consequently the proposed technique does not require a left inversion message recovery block, contrary to traditional inclusion methodology.

Output observer for chaos synchronization applications

This article introduces the concept of output observer to chaos synchronisation applications. Here output observer is understood as a low order system designed to estimate a single measured variable of a higher order system only. In this work we show how this notion can be used to evaluate nonlinear systems with single output, being a chaotic state variable used as an example. Following this point a Duffing oscillator is used as a model. We show how a lower order observer can be employed to accurately estimate nonlinear time series dynamics.

Output observer design for fault detection

In this paper, we propose an output observer design methodology for linear single output systems for fault detection purposes. Unlike traditional observers that are based on the the state-space representation of the system, the proposed observer design is based on the input output representation of the system. The main advantage of the proposed observer is its simplicity of design and it has a lower order that the original system.

Data encryption with chaotic Colpitts oscillators via power supply modulation

In this work we present numerical investigations for a simple data modulating technique employing Colpitts electronic oscillator models operating in the chaotic regime. The procedure includes a low amplitude half-wave rectified sinusoidal function on top of power supply terms, which acts as a message embedded data. We show how the suggested method does not take away the transmitters chaotic dynamics or the unidirectional complete chaotic synchronisation achieved. Advantages are in form of straightforward implementation that does not require hardware modifications as well as information recovery based on a simple subtraction. The proposed methodology can be applied to either positive or negative power supply. Traces of embedded data in the transmitted chaotic carrier cannot be spotted in time or frequency domain. In consequence the proposed method falls in the category of chaotic inclusion or embedding techniques but without requiring complex and computationally expensive left inversion protocols.

High gain observer with algorithm transformation to extended Jordan observable form for chaos synchronization applications

This work is concerned with the high gain observer design for a class of a third order ordinary differential equation chaotic nonlinear system for chaos communications applications. For this, we consider mainly the Rossler model as drive oscillator. We start by transforming the Rossler equations into the so-called Extended Jordan Controllable Form in order to facilitate the construction of the observers gain. It is shown that synchronization is achieved under a typical unidirectional master-slave configuration by using the receiver as the observer. The designed observer is tested against initial conditions mismatch, delay and noise presence via Matlab Simulink simulation in sight of potential application to real communication systems. The proposed observer shows good quality convergence performance. A chaotic masking scheme making use of the transformed Rossler observer is implemented in order to provide a descriptive example of a chaos communication system with the presented methodology.

Bimorph material/structure designs for high sensitivity flexible surface acoustic wave temperature sensors.

A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.

Temporal solution-based output observer design for single output LTI systems

In this paper, we present an output observer for single output linear time invariant (LTI) systems based on the temporal state solution of the system. The aim of an output estimator/observer is to reconstruct the output of the system for various purposes, namely fault detection, filtering and output stabilisation among others. A distinctive feature of this observer is that time variable is used as input in the observer equation. Proper transformations are employed to avoid the inversion of large matrices involved in the systems solution computation. Numerical simulations are presented with and without noise presence.

Chaotic cryptography with modified inclusion method and indirect coupled chaotic synchronisation

This work proposes a chaotic cryptographic system based on a modified inclusion method in combination with indirect coupled synchronisation to create a chaotic private key. A Rossler type chaotic oscillator is used to embed an encrypted message in its dynamics as well as to drive the piece-wise linear function of a Chua type system, used to create a chaotic key to encrypt the embedded message. In the receiver side a Rossler high gain observer is used to synchronise with the transmitter as well as to drive a second Chua oscillator to decrypt the message. A bidirectional link is applied to remove the nonlinear term in transmitter-receiver error dynamics analysis. Information retrieval is achieved when encrypted message amplification factors and gain matrix values are correctly tuned; leading to a transfer function between error dynamics and encrypted message equal to unity. In this way encrypted message is retrieved with straight forward error dynamics subtraction, avoiding left invertibility problem. Message is finally obtained with key chaotic decryption from a second receiver-driven Chua oscillator. All results presented are based on software simulation in an ideal communication channel.