Visible light communications: increasing data rates with polarization division multiplexing.

In this Letter, we propose a new configuration for visible light communication systems, which results in doubling of the data rate due to the use of polarization division multiplexing. As light-emitting diodes are unpolarized incoherent light sources, we isolate both the perpendicular s and parallel p modes for independent modulation. For the first time, to the best of our knowledge, we show that it is possible to transmit and successfully recover two separate orthogonal frequency division multiplexing (OFDM) signals on each polarization (pol-OFDM). Furthermore, we compare the performance of the pol-OFDM system with the transmission of a single conventional OFDM signal without a polarizer over the same physical link. We show that similar bit error rates can be achieved while obtaining ∼45% improvement in both the data rate and spectral efficiency due to polarization multiplexing.

Filter-less WDM for visible light communications using colored pulse amplitude modulation.

This Letter demonstrates, for the first time, to the best of our knowledge, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level colored pulse amplitude modulation. Unlike traditional WDM, no optical bandpass filters are required, and only a single optical detector is used. We show that, by transmitting n independent sets of weighted on-off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colors for multiple user access schemes. The system is empirically tested for M=4 and 8 using an off-the-shelf red, green, and blue (RGB) chip light-emitting diode (LED). We demonstrate that for M=4, using the R and B chips, a bit error rate (BER) of ≤10-6 can be achieved for each wavelength at bit rates up to 10 Mbps, limited by the LEDs under test. For M=8 using R, G, and B, a BER of ≤10-6 can be achieved for each wavelength at bit rates up to 5 Mbps.

Mobile User Connectivity in Relay-Assisted Visible Light Communications.

In this paper, we investigate relay-assisted visible light communications (VLC) where a mobile user acts as a relay and forwards data from a transmitter to the end mobile user. We analyse the utilization of the amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. The focus of the paper is on analysis of the behavior of the mobile user acting as a relay while considering a realistic locations of the receivers and transmitters on a standard mobile phone, more specifically with two photodetectors on both sides of a mobile phone and a transmitting LED array located upright. We also investigate dependency of the bit error rate (BER) performance on the azimuth and elevation angles of the mobile relay device within a typical office environment. We provide a new analytical description of BER for AF and DF-based relays in VLC. In addition we compare AF and DF-based systems and show that DF offers a marginal improvement in the coverage area with a BER < 10-3 and a data rate of 100 Mb/s. Numerical results also illustrate that relay-based systems offer a significant improvement in terms of the coverage compared to direct non-line of sight VLC links.