B. R. Mendoza

Error analysis of the simulated impulse response on indoor wireless optical channels using a Monte Carlo-based ray-tracing algorithm

This work describes a method to determine the error in a Monte Carlo-based ray-tracing algorithm used to compute the impulse response on indoor wireless optical channels. The algorithm, which accounts for multiple reflections of any order on irregularly shaped furnished rooms with diffuse and specular reflectors, allows for their analysis. Equations that estimate algorithm-produced error are given. We also report several simulation results concerning the error estimation which verify the reliability of the equations.

Simulation of impulse response for indoor visible light communications using 3D CAD models

In this article, a tool for simulating the channel impulse response for indoor visible light communications using 3D computer-aided design (CAD) models is presented. The simulation tool is based on a previous Monte Carlo ray-tracing algorithm for indoor infrared channel estimation, but including wavelength response evaluation. The 3D scene, or the simulation environment, can be defined using any CAD software in which the user specifies, in addition to the setting geometry, the reflection characteristics of the surface materials as well as the structures of the emitters and receivers involved in the simulation. Also, in an effort to improve the computational efficiency, two optimizations are proposed. The first one consists of dividing the setting into cubic regions of equal size, which offers a calculation improvement of approximately 50% compared to not dividing the 3D scene into sub-regions. The second one involves the parallelization of the simulation algorithm, which provides a computational speed-up proportional to the number of processors used.

Comparison of Monte Carlo ray-tracing and photon-tracing methods for calculation of the impulse response on indoor wireless optical channels

We present a comparison between the modified Monte Carlo algorithm (MMCA) and a recently proposed ray-tracing algorithm named as photon-tracing algorithm. Both methods are compared exhaustively according to error analysis and computational costs. We show that the new photon-tracing method offers a solution with a slightly greater error but requiring from considerable less computing time. Moreover, from a practical point of view, the solutions obtained with both algorithms are approximately equivalent, demonstrating the goodness of the new photon-tracing method.

Comparison of Three Non-Imaging Angle-Diversity Receivers as Input Sensors of Nodes for Indoor Infrared Wireless Sensor Networks: Theory and Simulation

In general, the use of angle-diversity receivers makes it possible to reduce the impact of ambient light noise, path loss and multipath distortion, in part by exploiting the fact that they often receive the desired signal from different directions. Angle-diversity detection can be performed using a composite receiver with multiple detector elements looking in different directions. These are called non-imaging angle-diversity receivers. In this paper, a comparison of three non-imaging angle-diversity receivers as input sensors of nodes for an indoor infrared (IR) wireless sensor network is presented. The receivers considered are the conventional angle-diversity receiver (CDR), the sectored angle-diversity receiver (SDR), and the self-orienting receiver (SOR), which have been proposed or studied by research groups in Spain. To this end, the effective signal-collection area of the three receivers is modelled and a Monte-Carlo-based ray-tracing algorithm is implemented which allows us to investigate the effect on the signal to noise ratio and main IR channel parameters, such as path loss and rms delay spread, of using the three receivers in conjunction with different combination techniques in IR links operating at low bit rates. Based on the results of the simulations, we show that the use of a conventional angle-diversity receiver in conjunction with the equal-gain combining technique provides the solution with the best signal to noise ratio, the lowest computational capacity and the lowest transmitted power requirements, which comprise the main limitations for sensor nodes in an indoor infrared wireless sensor network.

Adaptive OFDM system for multi-user communications over the indoor wireless optical channel

In this paper, an adaptive Orthogonal Frequency Division Multiplexing (OFDM) system is proposed for multiuser communications over indoor wireless optical channels. The designed system uses multi-user least-squares (LS) detection techniques applied to SDMA-OFDM schemes, in conjunction with angle diversity reception. The system, which does not present an excessive complexity, supports high bit rates for multiple users, beyond one hundred megabits per second. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with an adaptive single-user system described in previous works. The obtained results show a significant improvement with respect to previous adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment.

Design considerations of conventional angle diversity receivers for indoor optical wireless communications

A conventional angle diversity receiver uses multiple receiving elements that are oriented in different directions, where each element employs its own filter and nonimaging concentrator, such as a compound parabolic concentrator (CPC) or hemispheric lens. In this paper, a study of the design of a conventional receiver structure using angle diversity that offers improved performance with respect to the infrared channel characteristics is presented. To this end, a recently proposed model for the effective signal collection area of a conventional angle diversity receiver that more closely approximates real behaviour than the ideal model is used. The inclusion of this model in a Monte Carlo ray-tracing algorithm allows us to investigate the effects of conventional receiver parameters on the main infrared channel parameters, such as path loss and rms delay spread. Furthermore, in order to determine the number of receiver elements, the outage probability and the average error probability are also considered. Based on the results, a conventional angle diversity receiver composed of seven elements is proposed, with one of them oriented towards the ceiling, and six angled at a 56° elevation with a 60° separation in azimuth. For each element, a CPC with a 50° field of view must be used.A conventional angle diversity receiver uses multiple receiving elements that are oriented in different directions, where each element employs its own filter and nonimaging concentrator, such as a compound parabolic concentrator (CPC) or hemispheric lens. In this paper, a study of the design of a conventional receiver structure using angle diversity that offers improved performance with respect to the infrared channel characteristics is presented. To this end, a recently proposed model for the effective signal collection area of a conventional angle diversity receiver that more closely approximates real behaviour than the ideal model is used. The inclusion of this model in a Monte Carlo ray-tracing algorithm allows us to investigate the effects of conventional receiver parameters on the main infrared channel parameters, such as path loss and rms delay spread. Furthermore, in order to determine the number of receiver elements, the outage probability and the average error probability are also considered. Based on the results, a conventional angle diversity receiver composed of seven elements is proposed, with one of them oriented towards the ceiling, and six angled at a 56° elevation with a 60° separation in azimuth. For each element, a CPC with a 50° field of view must be used.

Models and algorithm for the calculation of the impulse response on IR-wireless indoor channels

Recently there has been growing interest in using infrared (IR) light for broadband indoor wireless communications. There are two major limitations for establishing a wideband infrared communications link. The first and most important limit is the power requirements of such a link. The second important impairment is the intersymbol interference caused by multipath dispersion. The use of angle-diversity receiver allows to achieve high optical gain and a wide field of view simultaneously, it can reduce the impact of ambient light noise, path loss and multipath distortion, in part by exploiting the fact that they are often received from different directions than the desired signal. The advantages achieved depend on how signal received in the different elements are detect and processed. For this reason, we have developed a fast simulation tool that allows to study the influence of the IR channel and to propose new techniques and receiver structures for those systems. The indoor optical channel simulation can significantly benefit the design of high performance IR systems, but requires models that fit correctly the channel characteristics. In contrast to previous works, we define new models for the emitter, lenses, receiver, nonimaging concentrators and reflectors upon which a Monte Carlo ray-tracing algorithm allows to study different links. The inclusion of these models benefit the design of IR links since the are nearer to real behavior than the ideals models. The use of this simulation tool allowed us to analyze the behavior of several links and suggest a configuration of a receiver using angle diversity.

Laboratory experiment on the use of pulse code modulation to transmit audio digitally

In this paper we present a practical laboratory experiment intended for undergraduate and graduate Electronic Engineering courses on Digital Communications Systems. The main objective of the experiment is to design and implement the electronics of a baseband system that uses pulse code modulation (PCM) to transmit audio signals digitally.

Using a PIC18F4550 microcontroller to conduct an educational experiment intended for a general physics laboratory course

This paper presents the design and implementation of a laboratory experiment for first year undergraduates of Bachelor of Science or Engineering degrees. The aim of the experiment is to consolidate concepts related to the subject of Physics. The laboratory experiment involves measuring the period and frequency of oscillation of a simple pendulum by means of an electronic device based on the PIC 18F4550 microcontroller, which handles the data acquisition and processing. The student will discover that for small angles, the period for a simple pendulum does not depend on the mass or on the initial angular displacement, but only on its length and on the value of the gravitational field strength (g), the latter being one of the parameters to be indirectly determined with this experiment.

Multi-user THSS system for visible light links

In this paper, a system based on time-hopping spread spectrum techniques for indoor visible light communications is studied via simulation. A 2-PPM modulation scheme is selected because it yields good results in wireless optical communications. Furthermore, the system allows for selecting the number of pulses per symbol to be transmitted and makes use of an optimum maximum-likelihood receiver for A WGN channels with the ability to choose between hard- or soft-decision decoding. The system designed allows for comparing the performance based on the computation of the bit error rate as a function of the pulse energy to noise power spectral density ratio, for different configurations in single-user and multi-user environments.