Introduction

1. Personal Optical Wireless Communications:LOS/WLOS/DIF propagation model and QOFICSNDSP 2008 - Paper 92894

2. Introduction Personal optical wireless communication POW • a solution for increasing the available communication bandwidth in an indoor environment • 3 typologies : line of sight (LOS), wide line of sight (WLOS) and diffuse (DIF) propagation model • compromise between distance and reliability -> analysis to be made • QOFI software simulates the QoS for a LOS/WLOS and/or DIF link in a given room

3. Summary • Propagation types and definitions • LOS/WLOS link margin analysis • DIF link margin analysis • QOFI – OW Modeling tool • QOFI – Implementation process

4. Propagation types and definitions (1/3) 3 typologies : • line of sight (LOS) (a) • wide line of sight (WLOS) (b) • diffuse (DIF) (c)

5. Propagation types and definitions (2/3) • LOS propagation : • simplest typology • the most used between point-to-point communications systems in indoor and outdoor environments • WLOS propagation • LOS • transmitters with larger divergence angle and receivers with larger field of view • DIF propagation • use multiple reflections of the optical beam on surrounding surfaces such as ceilings, walls, and furniture • transmitter and receiver not necessarily directed one towards the other

6. Propagation types and definitions (3/3) Definitions Input • Transmitter parameters • Average optical power transmitted (Pt) • Half power angle (HP) • Receiver parameters • Field Of View (FOV) • Receiver effective area (Aeff) • Receiver sensitivity (Se) Output • Average optical received power • Geometrical attenuation • Channel gain • Link Margin

7. LOS/WLOS link margin analysis (1/1) Considering a generalized Lambertian model, the equation of the channel gain (response at null frequency) is: d : distance transmitter/receiver φ: semi-angle of transmission ψ : semi-angle of reception Pt : transmitted power Geometrical attenuation in dB: Average optical received power Pr: Link margin Ml:

8. DIF link margin analysis (1/2) The main spatial discretization method • described by John BARRY's and J.M. KAHN • deals with a meshing of walls in a finished number of elementary reflecting surfaces(patches) • the optical energy resulting from the source can arrive directly on the receiver or by reflection on walls and objects

9. DIF link margin analysis (2/2) R: distance receiver/source ψ: angle between nR and (rS –rR) φ : angle between nS and (rS –rR) ρ: coefficient of reflectivity for the pixel. dA : receiver area dA receives a power dP. P : source power source S : {rs, ns, m} receiver : {rR, nR, AR, FOV} r : position, n : orientation, AR surface The light can undergo an infinite number of reflections. Each term h(k) represents the response when the light undergoes k reflections.

10. QOFI – OW Modeling tool (1/5) QOFI “Qualité de service Optique sans Fil Indoor” • a 3D modeling tool implemented to validate both LOS and DIF models • the user models a 3D interior creating a room and inserting 3D furniture and OW devices (base stations and modules) • in the edition mode, the user adds, moves, rotates, deletes objects in a 2D view and visualizes the scene in a 3D view • in the simulation mode, the user can simulate LOS and DIF models

11. QOFI – OW Modeling tool (2/5) The interface is based on a main window including • a 3D model library • a 2D view • a 3D view • a property window The OW simulation can be run • using a LOS, DIF or LOS & DIF model, • In the download or upload direction, • in COVER mode to view the reception areas according to a color code, • in LINK mode, to compute the average optical received power, the geometrical attenuation, the channel gain and link margin, and plot the impulse response.

12. QOFI – OW Modeling tool (3/5) Simulation use cases • COVER downlink: emission from all the base stations • COVER uplink: emission from a single module • LINK downlink: emission from all the base stations to a module • LINK uplink: emission from an end device to a base station

13. QOFI – OW Modeling tool (4/5)

14. QOFI – OW Modeling tool (5/5) Impulse response from Barry and Kahn Impulse response from QOFI

15. QOFI – Implementation process (1/5) The application is based on: • the Ogre 3D engine (www.ogre3d.org/) • uses the Qt framework (http://trolltech.com) • FSRAD (radiosity implementation from P. Nettle)

16. QOFI – Implementation process (2/5) Simulation process: • Room creation in a 2D view associated to a 3D Ogre scene maintaining its data structures (nodes) of models, • During a simulation, these data are transferred to the propagation module which gets back the Ogre 3D models and converts it into its own data structures, • Objects are divided into triangular 2D patches tracked down by their position in 3D,

17. QOFI – Implementation process (3/5) • During the calculation, for each light source, for each iteration, we determine patches that receive light according to the room and elements geometry, • As a result, Ogre nodes are deleted and new models are generated and attached to a new nodes arborescence. We generate one or several images files corresponding to lightmaps (textures of light). Ogre, handling these textures and new models, applies the texture to the models of the scene is rendered with colors.

18. QOFI – Implementation process (4/5) The OW calculation in 3D is made possible thanks to a propagation module allowing to divide the scene into patches and to calculate the route followed by a beam through the scene up to 3 iterations. The rendering mechanism is based on a radiosity technique: • a global illumination algorithm used in 3D computer graphics rendering • uses the physical formulae of the light radiative transfer between various elementary diffuse surfaces composing a 3D scene • a rendering method that simulates light reflections

19. QOFI – Implementation process (5/5) Each patch • receives energy from other patches • absorbes according to the material or sends back the rest towards the other patches The energy transmitted patch A to B is a function of: • the surface normal for the patches • a vector that represents the direction from the center of the transmission patch to the center of the receiving patch • the average distance between the two patches • the area of each patch • the amount of energy to be transmitted • the amount of visibility between the patches

20. Conclusion • a generic model of link margin analysis in LOS/WLOS and DIF configurations • a software tool which has integrated these models • improvements are possible changing the illumination model (currently a Lambert model), integrating new parameters