Diffuse Optical Channels Research Articles

Artificial neural-network-based visible light positioning algorithm with a diffuse optical channel

Visible light positioning becomes popular recently. However, its performance is degraded by the indoor diffuse optical channel. An artificial neural-network-based visible light positioning algorithm is proposed in this Letter, and a trained neural network is used to achieve positioning with a diffuse channel. Simulations are made to evaluate the proposed positioning algorithm. Results show that the average positioning error is reduced about 13 times, and the positioning time is reduced about two magnitudes. Moreover, the proposed algorithm is robust with a different field-of-view of the receiver and the reflectivity of the wall, which is suitable for various positioning applications.

Optical impulse modulation for indoor diffuse wireless communications

Current lasers and LEDs have far higher pulse rates than can be supported by the lowpass indoor diffuse optical wireless channel. Although high-frequency emissions are attenuated by the channel and are not detected by the receiver, a key insight of this paper is that these bands can be used to satisfy the channel non-negativity constraint. We define optical impulse modulation (OIM) in which data are confined to the lowpass region while the highpass region, which is attenuated by the channel, is used to satisfy the channel amplitude constraints. A mathematical framework for OIM is presented, and a simple suboptimal receiver filter is designed which is channel independent. Using a well-known exponential model for indoor diffuse optical channels, at a normalized delay spread of 0.2, the gain in optical average power of OIM with a simple lowpass receiver is shown to be 4.9 dBo which exceeds the gain of rectangular on-off keying (Rect-OOK) with a complex decision feedback equalizer. From an information theory point of view, at the same normalized delay spread of 0.2, the information rate of OIM with a lowpass receiver is shown to be 11.5% higher than that of Rect-OOK with a more complex whitened matched filter receiver.

Adaptive OFDM system for communications over the indoor wireless optical channel

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 have chosen OFDM systems because of their capability of supporting high data rates without channel equalisation. They also mitigate the quality of service fluctuations induced when space distribution of emitters and receivers varies. The performance of the new proposed scheme is compared with that of an adaptive system described in a previous work. The obtained results show that a significant increase of the system throughput is attained over noisy wireless optical channels.

Combined emitter and receiver diversity to achieve data rates > 100 Mbit/s on diffuse optical channels

The use of combined emitter and receiver angular diversity to effectively combat the multipath dispersion of the indoor diffuse optical channel is studied. A system allowing transmission at baud rates > 100 Mbit/s with low inter-symbol interference and negligible power penalty is proposed.

Monte Carlo calculation of impulse response on diffuse IR wireless indoor channels

A method to calculate multipath dispersion owing to wall reflections on indoor wireless diffuse optical channels using Monte Carlo simulation is presented. It allows evaluation of not only Lambertian but also specular reflections, and can be used to validate previous simulation schemes. It can be extended for Lambertian (with modal number 1 or higher) or non-Lambertian light sources.

Modified Monte Carlo scheme for high-efficiency simulation of the impulse response on diffuse IR wireless indoor channels

A modified Monte Carlo method to calculate multipath dispersion due to wall reflections on indoor wireless diffuse optical channels is presented. As with other Monte Carlo methods, it allows evaluation of not only the Lambertian but also specular reflections and can be used to validate previous simulation schemes. The main difference is that for each ray traced and for each rebound, a contribution to the receiver is calculated. This leads to a faster and more accurate simulation.

Wireless in-house data communication via diffuse infrared radiation

A novel wireless broadcast/multi-access channel is described for flexibly interconnecting a cluster of data terminals located within the same room. The transmission medium is diffusively scattered infrared radiation at 950-nm wavelength. Transmission is low-to-medium speed and the range up to 50 m. Theoretical analysis indicates that the time dispersion limits the transmission bandwidth of the system to 260 Mbit ċ m/s, but background noise produced by ambient daylight reduces the transmission speed below 1 Mbit/s. The transmission properties of the diffuse optical channel are analyzed, and experimental digital links for baseband PCM at 125 kbit/s and PSK 64 kbit/s are demonstrated.