Development of a Visible Light Communications System for Optical Wireless Local Area Networks P. A. Haigh † , T. T. Son † , E. Bentley † , Z. Ghassemlooy † , H. Le Minh † and L. Chao ‡ † Optical Communications Research Laboratory, NCRLab Northumbria University, Newcastle-upon-Tyne, United Kingdom ‡ Photonics Research Centre, Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hong Kong SAR, China e-mail: paul.haigh@northumbria.ac.uk Abstract—This paper presents the development of a Visible Light Communications (VLC) system for a local area network (LAN). The link is analyzed for all development stages and compared with a typical Ethernet system. The VLC system uses a Philips Luxeon Rebel as the transmitter and a Centronic OSD15- 5T as the receiver coupled with a blue filter to achieve the required 10 Mb/s bit rates. The distance in which the optical link was measured was up to 1 m, and the link was successful (BER 10-6) for distances up to 0.7 m. To achieve higher distances and therefore to make the system practical in the home or office environment, the number of LEDs used can be scaled. Index Terms—Visible Light Communications, Ethernet Net- works, Optical Link, Computer Networks I. I NTRODUCTION V ISIBLE light communications is rapidly gaining an atten- tion in the research community. Since solid state lights such as light emitting diodes (LEDs) can be switched faster than the human eye can respond, they can be modulated at high data rates; offering communications capabilities as well as general illumination. Additionally, the technology utilizes the licensed free spectrum, and generates no electromagnetic interference, thus making them very attractive for use in hospitals and aircraft. White light can be produced using two methods; the first is to use a four-chip LED that consists of a red, blue and green (RGB) LEDs and a control chip. This method offers high data rates by individually modulating the RGB colours and optical filters to recover the data at the receiver. However, it requires additional control and signal processing for balancing the RGB spectrum and producing the white light. The second method is far more simplistic; using a blue chip LED and a yellowish phosphor to produce the white light. A simple driving circuit can be used to directly modulate the blue LED. The yellowish phosphor is excited by the photons leaving the blue LED; therefore producing a white light. The disadvantage of this method is that the yellowish light is carried on a longer wavelength than the blue light. This can be overcome to an extent at the expense of signal power by using a blue filter at the receiver. Considerable research has been conducted into VLC using white phosphorous LEDs to overcome the small modulation bandwidth including equalizations [1] and complex modula- tion techniques such as orthogonal frequency division multiple access (OFDM) [2]. Combining these techniques and intro- ducing additional signal processing such as adaptive bit- and power-loading can increase data rates up to 513 Mb/s [3]. Since the increased data rates can carry the majority of non- optical fibre (up to 40 Gb/s in a single mode fibre (SMF)) IEEE 802.3 signals; we propose to transmit a standard LAN 10BASE-T (10 Mb/s) [4] Ethernet signal over a VLC link as a proof-of-concept for future homes, offices, hospitals as well as for providing an optical wireless LAN (VLC-LAN) for end users. Ethernet, developed between 1973-4 and standardized by the IEEE 802.3 in 1985, has since evolved from a coaxial cable based link (10 Mb/s), 100 Mb/s (100Base) in the mid 1990s, 1 Gb/s (1000Base) since 1998, and finally 10 Gb/s (10Gig Ethernet) from 2000 [5], to modern day optical fibre with 40 Gb/s or more data rates [6]. The Transmission Control Protocol/Internet Protocol (TCP/IP) was adopted to provide the nationwide communication services [7]. The standards for TCP/IP are published in a series of document by the Internet Engineering Task Force (IETF) [8]. There are four layers in this model. The first layer is described as the network access layer, which is comprised of the data link layer and physical layer in comparison with the OSI model. Due to the common use in LANs within the home and office environments, Ethernet has become the dominant LAN protocol for supporting TCP/IP traffic. In the second layer, the IP protocol, standardized by RFC 791 [9], supports the network nodes routing the packets from source to destination. Each node is assigned a unique IP address. The IP packet consists of two parts: the data and packet headers. The data part is a variable field holding up to a maximum of 65,535 bytes of data. The header has at least 20 bytes including the source IP address and destination IP address. Even though the data part in the IP packet can contain up to 65535 bytes, when it operates over Ethernet, it is limited by Ethernet frame maximum of 1500 bytes. So the Maximum Transmission Unit (MTU) for an IP packet over Ethernet should also be set at 1500 bytes to avoid the loss 978–1–4577–1719–2/12/ $26.00 c  2012 CROWN