Abstract — 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.
Index Terms — Visible Light Communications, In-flight communications.
Offering data access during flight has recently become an area of interest for many plane building companies and airlines. Moreover, the availability of wireless bandwidth opens the door for new entertainment services such as video selection and collaborative games. While some networking companies are offering solutions for the plane- to-earth data link, others are providing Wi-Fi-based solutions to deal with compatibility problems with the flight instrumentation. However, the available baud rate for each user is limited and the EM compatibility problems are still present (not with the plane systems, but among other users when the amount of them increases). Other proposals are devoted to multimedia delivery inside the aircraft so as to provide seatback entertainment . Wireless optical communications is a way of reducing the overall system weight induced by wiring each passenger seat.
Wireless optical connectivity offers some advantages on a typical plane cabin as it has no EM concerns. The position of the passenger during flight is well defined: s/he is usually placed on a seat with a reading lamp pointing to her/his position at a distance of about 1.5 m, and having a data device
1 This research has been funded in part by the Spanish Science & Innovation Ministry (Project COLIBRI TEC2009-14059 -C03-01) and the Canary Islands Regional Government Project ICARO ProID20100117). C. Quintana has been awarded a PhD. grant of the Canary Islands Research Administration (ACIISI).
C. Quintana is with the Institute for Technological Development and Innovation in Communications (IDeTIC), Spain (e-mail: [email protected]).
V. Guerra is with the Institute for Technological Development and Innovation in Communications (IDeTIC), Spain (e-mail: [email protected]).
J. Rufo is with the Institute for Technological Development and Innovation in Communications (IDeTIC), Spain (e-mail: [email protected]).
J. Rabadan is with the Institute for Technological Development and Innovation in Communications (IDeTIC), Spain (e-mail: [email protected]). R. Perez-Jimenez is with the Institute for Technological Development and Innovation in Communications (IDeTIC) Spain, (e-mail: [email protected]).
(laptop, tablet or phone) over the table. The coverage area of a typical infrared emitter pointing upwards has a diameter of about 50 cm, so focusing the uplink channel should be easy.
Furthermore, we shall employ an existing resource as the illumination lamp is always present. As the use of LEDs instead of other illumination sources does not present major regulation concerns, many plane providers appreciate their lifetime, low power consumption and chromaticity properties.
There are several research groups working in this area. M. Kavehrad has also studied theoretically the use of on-board power line networks for providing both electricity and communications by modulating LED lamps, while Elgala et al have proposed creating infrared communications cells to implement the user link . In previous works, we have presented how to solve the connection of the lamp with the Ethernet link and a first approach based on an USB connection . In this paper we propose a full optical wireless strategy for passenger connectivity in planes during flight. It uses a VLC system as a downlink, while an infrared link provides the uplink channel. Modulations and circuit implementations for a system prototype are also studied. Moreover, we introduce a new network adapter architecture, an exhaustive description of the system performance and an analysis of the power budget on the passenger seat.
This paper is organized as follows: a system description is presented in section II, while sections III and IV are devoted to the downlink VLC simulation and the HW system implementation. Section V shows results and different performed measurements. Finally, some conclusions are provided.
Fig. 1: Block diagram of the proposed system.
II. SYSTEM DESCRIPTION
An internet in-flight system can be divided into three main subsystems:
• Ground to aircraft link: It provides the connection between the aircraft and the Internet Service Provider (ISP). It can be implemented by satellite or a direct ground RF link. This block can be removed if only entertainment services like video and audio broadcasting are to be offered by a company.
• Network distribution: Shielded twisted pair cables are the most commonly used inside the aircraft, however optical fiber is expected to be used in the future.
• User link: With the aim of reducing the amount of needed cable, a wireless link seems to be an optimal solution. This work focuses on this subsystem.
Let us consider a line-of-sight VLC data link from the reading lamp and an uplink channel based on a line-of-sight infrared channel from the computer (or data device) to a photodiode on the plane ceiling (close to the reading lamp, see Fig. 1). Two communication devices working as adapters have been developed: the first one, known as “lamp adapter”, gets the packets from the regular distribution network (Ethernet or PLC) and behaves as a bridge, replicating the information at the optical interface. The second one, known as “passenger data adapter”, is characterized by having a similar behavior, using the Ethernet or USB port of the mobile devices instead of the aircraft distribution network as data source or sink. Therefore, the only difference between the adapters is the working wavelength of the optical link (VLC from distribution network to user, and IR in the other direction).
III. VLC DOWNLINK CHANNEL ANALYSIS
In the proposed system topology, each passenger is considered to be inside a microcell. However, it could be possible that nearby users or cabin illumination lamps generate harmful interference due to a wide lamp emission pattern or a high photodiode FOV. In addition, reflections on different objects could dramatically reduce the system performance. Here we opt for the use of optical lenses for collimating the light beam in the passenger’s table. A simulation based on a Monte Carlo-Ray tracing algorithm has been performed in order to calculate the Signal Noise Ratio (SNR) at different points of the user’s table. We have considered 3 emitters, corresponding to the three reading lights, and 740 receivers distributed over the passenger’s table.
The following table shows the parameters used in all the performed simulations.
Photodiode Area 66 mm2
Photodiode FOV 120º
Photodiode responsivity 0.63 A/W
Photodiode darkness current 2 nA
Transimpedance BW 5 MHz
Amplifier NEP 750 W/?Hz
Number of rays 100.000
Number of reflections 10
Objects reflection coefficients 0.6-0.7
Fig. 2 shows the cabin model developed, which has been used by the simulator to determine the environment under study.