J. Rufo

Experimental evaluation of video transmission through LED illumination devices

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 eye and security against undesired network access. These conditions make this system suitable for co-existing with commercial RF networks -WiFi, Bluetooth, etc.-, especially for in-house applications. For the uplink channel we have also included in the prototype an infrared 115 kbps transceiver. This VLC system could be used for supporting data transmission applied to low-speed sensor network connections as well. The electronic structure of a low-cost VLC transceiver, based on commercial off-the-shelf components and LED lamps is presented too. The modulation process and the Ethernet interface implemented in each access point are also described. Finally, some conclusions and application scenarios are drawn.

Reading lamp-based visible light communication system for in-flight entertainment

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 Monte Carlo Ray-Tracing algorithm. The hardware implementation and testing results are also presented.

Design and Implementation of an Ethernet-VLC Interface for Broadcast Transmissions

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 using a 2Mbps VLC Link, obtaining distances of, at least, 3 meters in an interfering environment. The PPM characteristics allow transmission without severe signal degradation on this environment. This Ethernet-VLC interface is intended to demonstrate the capability of IP broadcast applications of this kind of devices. This interface performs packing functions and flow control.

Time-hopping spread-spectrum system for wireless optical communications

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 interference rejection capability and the number of simultaneous users supported, compared with other wireless optical standards. Moreover, a wide analysis is carried out about the mutual interference between time-hopping spread-spectrum systems and other infrared ones. Finally, some conclusions are drawn about some design parameters of the time-hopping system in order to allow its compatibility with preexisting optical devices.

Visible light communication systems for passenger in-flight data networking

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.

Considerations on modulations and protocols suitable for visible light communications (VLC) channels: Low and medium baud rate indoor visible ligth communications links

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 this work, we present the Ethernet interface that has been implemented in each AP (access point), the light modulation used and the sensor network developed for demonstration. The main advantages of VLC technology are the robustness against electromagnetic (EM) interference, safety for human eye, and security against undesired network access.

Wireless optical communications for intra-spacecraft networks based on OCDMA with random optical codes

In recent years, spacial agencies have shown a growing interest in optical wireless as an alternative to wired and radio-frequency communications [1,2]. The use of these techniques for intra-spacecraft communications reduces the effect of take-off acceleration and vibrations on the systems by avoiding the need for rugged connectors and provides a significant mass reduction. Diffuse transmission also eases the design process as terminals can be placed almost anywhere without a tight planification to ensure the proper system behaviour. Previous studies [3,4] have compared the performance of radio-frequency and infrared optical communications. In an intra-satellite environment optical techniques help reduce EMI related problems, and their main disadvantages - multipath dispersion and the need for line-of-sight - can be neglected due to the reduced cavity size. Channel studies [5] demonstrate that the effect of the channel can be neglected in small environments if data bandwidth is lower than some hundreds of MHz.

Hybrid Visible Light and Ultrasound-Based Sensor for Distance Estimation

Distance estimation plays an important role in location-based services, which has become very popular in recent years. In this paper, a new short range cricket sensor-based approach is proposed for indoor location applications. This solution uses Time Difference of Arrival (TDoA) between an optical and an ultrasound signal which are transmitted simultaneously, to estimate the distance from the base station to the mobile receiver. The measurement of the TDoA at the mobile receiver endpoint is proportional to the distance. The use of optical and ultrasound signals instead of the conventional radio wave signal makes the proposed approach suitable for environments with high levels of electromagnetic interference or where the propagation of radio frequencies is entirely restricted. Furthermore, unlike classical cricket systems, a double-way measurement procedure is introduced, allowing both the base station and mobile node to perform distance estimation simultaneously.

QoS in optical underwater-to-air links

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 received power estimations. After defining the mathematical formulation, a Monte Carlo Ray Tracing algorithm has been used to obtain simulation results at different scenarios.