In this paper, a multiple-input multiple-output (MIMO) technique for indoor optical wireless (OW) communication is proposed. The technique is referred to as \emph{optical spatial modulation (OSM)}. The key concept is based on spatial modulation (SM). At any given time instant, only one transmitter is active and the others are inactive. A transmitter in space is considered as a spatial constellation point which is assigned a unique bit sequence. Consequently, transmitters are turned on and off depending on the incoming data bits, similar to the activation of constellation points in traditional digital modulation schemes. Hence, a data rate of the base two logarithm of the number of transmit units is achieved. The active transmitter radiates a certain intensity level at a particular time instant. At the receiver side, the optimal SM detector is slightly modified and used to estimate the spatial constellation point. The estimated spatial constellation point is used to arrive at the original bit stream via de-mapping. The upper bound bit-error-ratio (BER) of OSM is analyzed for a MIMO configuration consisting of four transmit units (light emitting diodes (LEDs)) and four receive units (photo diodes (PDs)) in a room. The BER performance is determined for different transmitter and receiver separation distances and different transmitter half power semiangles. It is shown that the proposed OSM technique achieves twice and four times the data rate as compared to OOK (on-off keying) and PPM (pulse-position modulation), respectively.

Indoor MIMO Optical Wireless Communication Using Spatial Modulation

For future short-range applications, optical wireless communications present a viable and promising supplemental technology to radio wireless systems. This contribution presents a review of infrared and visible light optical wireless indoor communications, including basics, state of the art, challenges and prospects. Advanced approaches based on diversity techniques and adaptive signal processing show potential to achieve both high spatial coverage and high bit rates of more than 100 Mb/s.

Recent Developments in Optical Wireless Communications using Infrared and Visible Light

FSO is a line-of-sight technology that uses lasers to provide optical bandwidth connections or FSO is an optical communication technique that propagate the light in free space means air, outer space, vacuum, or something similar to wirelessly transmit data for telecommunication and computer networking. Currently, FSO is capable of up to 2.5 Gbps [1] of data, voice and video communications through the air, allowing optical connectivity without requiring fiberoptic cable or securing spectrum licenses. Operate between the 780 – 1600 nm wavelengths bands and use O/E and E/O converters. FSO requires light, which can be focused by using either light emitting diodes (LEDs) or lasers (light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiberoptic cables; the only difference is the transmission media. Light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of the light. FSO communication is considered as an alternative to radio relay link line-of sight (LOS) communication systems. This chapter is concentrate on ground-to-ground free-space laser communications. FSO components are contain three stages: transmitter to send of optical radiation through the atmosphere obeys the Beer-Lamberts`s law, free space transmission channel where exist the turbulent eddies (cloud, rain, smoke, gases, temperature variations, fog and aerosol) and receiver to process the received signal. Typical links are between 300 m and 5 km, although longer distances can be deployed such as 8–11 km are possible depending

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Free Space Optical Communications — Theory and Practices

In this paper, we present a high speed optical motion capture method that can measure three dimensional motion, orientation, and incident illumination at tagged points in a scene. We use tracking tags that work in natural lighting conditions and can be imperceptibly embedded in attire or other objects. Our system supports an unlimited number of tags in a scene, with each tag uniquely identified to eliminate marker reacquisition issues. Our tags also provide incident illumination data which can be used to match scene lighting when inserting synthetic elements. The technique is therefore ideal for on-set motion capture or real-time broadcasting of virtual sets. Unlike previous methods that employ high speed cameras or scanning lasers, we capture the scene appearance using the simplest possible optical devices - a light-emitting diode (LED) with a passive binary mask used as the transmitter and a photosensor used as the receiver. We strategically place a set of optical transmitters to spatio-temporally encode the volume of interest. Photosensors attached to scene points demultiplex the coded optical signals from multiple transmitters, allowing us to compute not only receiver location and orientation but also their incident illumination and the reflectance of the surfaces to which the photosensors are attached. We use our untethered tag system, called Prakash, to demonstrate methods of adding special effects to captured videos that cannot be accomplished using pure vision techniques that rely on camera images.

Prakash: lighting aware motion capture using photosensing markers and multiplexed illuminators

The multiple scattering effects of light propagation in rain and fog are investigated by means of numerical Monte Carlo photon propagation simulations. Rain and fog consisting of water droplets are described by realistic drop size distributions with parameters related to physical parameters of hydrometeors such as rain intensity, liquid water content, effective droplet radius of fog and atmospheric visibility. Simulations show that optical attenuation due to rain is about two times lower than predicted by single scattering approach. Fog attenuation is also reduced for the lowest visibilities. An impulse response of optical channel in rain and fog is obtained and the explicit models for the delay spread dependence are provided. Under realistic conditions, the RMS delay spread due to rain on 1 km long free space optics (FSO) path is limited below 10 ps. Moderate and dense fog can cause the delay spread about 50 ps or more. Frequency characteristics of the FSO channel impaired by rain and fog are given.

Frdrique de Fornel

Papers

Free-Space Optics