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Publications (62)
In this paper, we introduce the Matrix‐MMC propagation model for indoor wireless optical channels. This proposed method is evolved from the modified Monte Carlo (MMC)–based ray tracing algorithm, but in addition to the properties of MMC, it has the capability of capturing reflection phenomena implying changes on wavelength (eg, fluorescence, phosph...
Nowadays, with the incursion of solid state lighting technology in our daily life, visible light communication (VLC) systems are becoming more important. This fact has generated a lot of attention on VLC to provide solutions on multiple applications where this technology can be exploited. At the same time, the growing of automation processes has cr...
In this paper, we present a new strategy to design the constellation symbols in a visible light communication (VLC) system by considering multiple LED transmitters at different wavelengths. For this purpose, the LED transmitters are modeled as fixed points in a color space, and the constellation symbols are obtained by convex combinations of these...
Indoor Wireless Optical Communications (IWOC) are highly conditioned by the communication channel, which depends on factors such as the endpoints’ positions and the reflective surfaces inside the room. Reflections have an important impact on the channel properties since both channel gain and multipath interference is directly affected by reflection...
Distance estimation is an important task in positioning systems, as it is needed for performing the triangulation process used by location algorithms. Different techniques, such as received signal strength indication (RSSI), time of arrival (ToA), and time difference of arrival (TDoA), can be used to estimate the distance between devices. Cricket i...
Distance estimation is an important task in positioning systems, as it is needed for performing the triangulation process used by location algorithms. Different techniques, such as received signal strength indication (RSSI), time of arrival (ToA), and time difference of arrival (TDoA), can be used to estimate the distance between devices. Cricket i...
The feasibility of using Visible Light Communications (VLC) technology is a reality nowadays. As this technology is being inserted into the mass market, deliberation about the security provided by this technology, which is one of their main selling points, should be taken into consideration. In this paper, different scenarios of VLC sniffing are st...
In this paper we present the use of visible light communications devices serving as data access point in a Smart City scenario, where the primary objective are tourism services (Following the proposal of the Smart Tourism Destination Spanish program). They use traffic or street lights for providing basic guidance information or even broadband acces...
Colour-shift keying (CSK) has emerged as a new modulation scheme for indoor visible light communication (VLC) systems, standardised in IEEE 802.15.7. This scheme transmits data by modulating the intensity of red-green-blue light-emitting diodes using a colour coding format. To support VLC, CSK requires the application of multiple light sources and...
In this paper, the PWM encoding of an optical OFDM transmission is studied and simulated. Traditional optical OFDM schemes make use of linear drivers, but the inherent nonlinear behavior of the optical emitters produce a harmful effect on the demodulated signal. PWM allows the use of nonlinear drivers, avoiding this harmful effects and increasing t...
Color Shift Keying (CSK) is a new modulation scheme for visible light communication systems using RGB LEDs which has been standardized in the PHY III level of the IEEE 802.15.7. This paper proposes some modifications so as to include multiuser capabilities provided by a time-based multiplexing, with the modulation constellation symbols being adapte...
In this work, we explore the use of digital communities as a way of providing data to the customer relationship management system inside a hospitality resource, even when no connectivity with internet is available. The case study will be a cruiser while sailing offshore where only a reduced data interchange can be achieved from satellite-based netw...
In this letter, a new synchronization scheme for color shift keying (CSK) modulation is presented. Proposed system uses pulse position modulation in combination with CSK to increase the bit rate and simultaneously control illumination intensity, avoiding flickering effects. Additionally, this modulation also provides synchronization for the color d...
In recent years, the rapid growth of visible light communications (VLC) is driven the interest into new applications of this technology. While single-user VLC systems are widely studied in the literature, less attention is given to multiuser scenarios which are likely to be deployed. Thus, this paper studies a new low-complexity multiuser structure...
In this work, a mathematical approach to the problem of modelling the underwater-to-air optical wireless channel is presented. The seawater interface has been considered as a plain monochromatic seawave where wind stress generates random variations on the surface. Furthermore, a quality of service (QoS) measurement is proposed, based on the receive...
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...
In this paper, an algorithm to calculate the underwater wireless optical impulse response is presented. It is based on a modified Monte Carlo Ray Tracing algorithm and takes into account the most significant phenomena of the underwater channel. In order to reduce the simulation time, two parallelization schemes are proposed, one based on a multipro...
This paper explores the use of a reading lamp as an access point for a Visible Light Communications (VLC) downlink channel. We have established an infrared uplink channel based on a network adapter, supporting both a VLC receiver and an infrared emitter. The optical signal power distribution over the passenger area has been also studied using a Mon...
An optical code-division multiple access system (OCDMA) for multi-user visible light communications is presented, which interfaces with the Ethernet network. The OCDMA scheme is based on the optical codes known as random optical codes, which do not present an optimal performance but are characterised by their ease of implementation. To combat the r...
This paper describes some applications under development for optical wireless systems based on visible light communications (VLC). The indoor scenario defines services which can be provided to users inside a room such as video broadcasting or home automation. For this purpose a 2Mbps visible downlink and a 125 kbps infrared uplink were used. In thi...
In this paper, the use of visible light communications (VLC) technologies for providing data networking for passengers during flight is explored. An uplink channel based on infrared is also studied. The potential capabilities of this optical access technique are examined. Nowadays, there are several proposals and solutions for providing high speed...
In this work, a complete interface between Ethernet and Visible Light Communications (VLC) networks is presented. It requires the use of previously proposed DPPM schemes for this kind of applications, but with some modifications so as to keep constant duty cycle in order to assure its use in illumination facilities. The prototype has been tested us...
In this paper we describe the implementation of a prototype of an optical wireless system based on visible white LED lamps, which allows a video broadcasting to reach a bit rate of 2 Mbps. This technology is usually called VLC or Visible Light Communications and presents several advantages as the robustness against EM interference, safety for human...
This article describes an optical wireless system based on visible light communication (VLC), which allows a video broadcasting to reach a bit rate of 1 Mbps, although this system can also be used for low-speed sensor interconnections. The main advantages of this technology are the robustness against EM interference, safety for human eye, and secur...
In this work, a new scheme for short-range distance measurement is presented. It reduces significantly the amount of signal processing needed for frequency-modulated continuous-wave radar or Lidar systems to obtain a good resolution in beat frequency measurement. In this article, a low cost and easy to implement technique is proposed. This resoluti...
This paper describes an optical wireless system based on time-hopping spread-spectrum techniques, as a first approach, at infrared wavelengths. It can be used either for low-speed sensor interconnections or as a return channel in a visible light communications system. The main advantage of this scheme is an improvement in the narrowband interferenc...
Modern solid-state lighting that uses light emitting diodes is increasingly used in a wide range of lighting applications. These sources are more efficient than incandescent lamps and can have very long lifetimes. As the efficiency of these sources increases and their cost decreases, they may become the predominant source in most lighting applicati...
In this work, an illumination interference reduction technique for visible light communications (VLC) is presented. In this kind of systems an optical wireless communication is established using visible light wavelength, therefore optical filtering for interference rejection can not be employed. Instead of the optical filtering a signal processing...
The authors propose an adaptive orthogonal frequency division multiplexing (OFDM) system for communications over the indoor wireless diffuse optical channel. This channel can be characterised as short-term stationary, with severe attenuation and multipath-induced penalty, and high dependence on the space distribution of emitters and receivers. We h...
This work presents the use of white LED (WLED) lamps as broadcast emitters in an optical wireless system. The proposed system allows the data transmission at medium data rate (500 kb/s). The level of illumination can be changed without any degradation of the transmission performances. If a pulse width modulation (PWM) driver is used to apply the el...
This paper introduces new techniques for improving the security level of the wireless optical systems. In this way, we are going to use modulation schemes based on spread spectrum theory. These techniques had been developed for military applications in order to obtain reliable and secure communications, so they seem to be a good candidate for our s...
In this paper, the application of orthogonal frequency division multiplexing (OFDM) over an indoor wireless optical channel is investigated. Previous studies have demonstrated that it can be characterised as almost stationary but with a severe penalty induced by multipath propagation. It is also highly dependent on the spatial distribution of emitt...
This paper describes both the design and implementation of an optical and guideless link based on IrDA technology and Direct Sequence Spread Spectrum techniques. The main objective of this work is to increase the environment interferences rejection and introduce the multichannel capability in IrDA standard. This system also reduces the multipath di...
In this paper, experimental results from the operation of a prototype of wireless indoor optical transceiver based on frequency hopping techniques are presented. The use of spread spectrum techniques allows multiple simultaneous access and increases the robustness of the system against multipath-induced distortion and narrowband interference (as co...
In this paper, the design and experimental testing of a direct-sequence spread spectrum (DSSS) system for wireless infrared LAN is presented. This method improves the wireless IR communications performances against multipath propagation and narrowband interference. We have implemented a IR-DSSS prototype with 100 MHz code frequency and 6 Mbps bit r...
In this paper, the design and experimental testing of a direct-sequence spread spectrum (DSSS) system for wireless indoor infrared network is presented. This method improves the wireless IR communications performances against multipath propagation and narrowband interference. We have implemented an IR-DSSS prototype with 100 MHz code frequency and...
In this paper, the design and experimental characterization of a wireless optical transceiver for indoor applications, based on Frequency-Hopping Spread-Spectrum techniques, is presented. Using these techniques reduce the narrowband interference produced by optical sources and the intersymbol interference induced by multipath propagation. It also m...
This paper presents concentrator and lens models for the detector and emitter, respectively, upon which a Monte Carlo ray-tracing algorithm allows the evaluation of impulse response on infrared (IR) wireless indoor channels. We also present computer simulation results that show the effects of concentrator FOV and reception direction on the impulse...
In this Letter the effect of using pulse conformation techniques over a DSSS wireless optical system is explored. The performances of both Gaussian and sinusoidal conformation over the spread and code signal are compared. As a pattern of comparison, the side-lobe elimination for adjacent-channel interference reduction, the process gain, and the BER...
The design and experimental characterization of a wireless
infrared fast frequency hopping spread spectrum (WIR-FFH-SS) system is
presented. The use of spread spectrum techniques on wireless infrared
indoor communications reduces the effect of interference present in the
infrared channel. It also improves the system performance versus
multipath pro...
The design and experimental characterisation of a wireless
infrared fast frequency-hopping spread-spectrum (WIR-FFHSS) system is
presented. The bit rate of this prototype is 512 kbit/s, but it can be
easily increased to 1 Mbit/s. It is suitable for different applications
at low and medium rates
This paper describes two modem prototypes based on spectrally
efficient filtered modulations for infrared wireless links. They are
fully compatible with commercial IrDA and IEEE 802.11 standards. These
links allow more channels, giving a more accurate use of the infrared
spectrum. We compare the performances of the two main alternatives:
phase (usi...
A low complexity system of optical links using indoor unguided infrared channels and direct-sequence code division multiple access is presented. Direct sequence spread spectrum techniques improve performance of optical unguided links with background illumination noise, and multipath propagation. It also allows several users to use code division mul...
A carrier-based modem for an IR Wireless LAN (IR-WLAN) design is presented. It is based on GMSK modulation schemes. This modem is capable of operating at 2 Mb/s, but it can easily modify to work up to 4.8 Mb/s. GMSK Schemes are filtered modulation schemes with higher spectral efficiency and robustness against jitter than basic FSK. The emitter uses...
The design and experimental characterization of a wireless infrared direct-sequence spread spectrum (WIR-DSSS) system is presented This prototype support low and medium data rates (up to 64 kbps) enough for most consumer appliances, but can be easily increased to rates of about 1-2 Mbps if required. This system is designed to be used in the control...
This article presents a modified PPM modulation technique for
infrared wireless LAN that improves the spectral efficiency of the
system significantly. The resulting signal (improved PPM or IPPM), which
is based on FQPSK IJF filters, is jitter- and ISI-free and can be
recovered with any standard PPM receiver. In order to reduce the
bandwidth a pulse...
A 2 Mbit/s FQPSK-2 modem design and its evaluation is presented.
Its main application is wireless infrared local area networks. The
design is fully digital, which enables the modem to be integrated on
only one chip. FQPSK-2 modulation was chosen for its high spectral
efficiency, robustness against jitter, and constant amplitude of its
complex envel...
RESUMEN En este trabajo se analizan los efectos de la aplicación de técnicas de conformación de pulsos a sistemas ópticos no guiados que utilizan una modulación de espectro ensanchado por secuencia directa. Las técnicas de conformación propuestas se basan en esquemas digitales sencillos y robustos y con un coste muy inferior al de otras soluciones...
In this paper, the design and experimental characterization of a Wireless Infrared Fast Frequency Hopping Spread Spectrum (WIR-FFHSS) system is presented. The use of spread spectrum techniques on wireless infrared indoor communications reduces the effect of interference present in the infrared channel and improves the system performance versus mult...
In this paper, the application of synchronous Fast Frequency-Hopping techniques to indoor wireless optical communications is presented. These techniques will be used for CDMA scenarios in order to simplify the receiver structure and the co-user interference. INTRODUCCIÓN El modelo empleado en este artículo sería el de una habitación con un emisor p...
