Personal Optical Wireless Communications:LOS/WLOS/DIF

workablejeansMobile - Wireless

Nov 21, 2013 (3 years and 10 months ago)

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1


Personal Optical Wireless
Communications:

LOS/WLOS/DIF propagation model and
QOFI

CSNDSP 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


1.
Propagation types and definitions


2.
LOS/WLOS link margin analysis


3.
DIF link margin analysis


4.
QOFI


OW Modeling tool


5.
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

P
t

: transmitted power

Geometrical attenuation in dB:

Average optical received power
P
r
:

Link margin
M
l
:

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 : {r
s
, n
s
, m}

receiver : {r
R
, n
R
, A
R
, FOV}

r : position, n : orientation, A
R

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 QOFI

Impulse response from Barry and Kahn

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:


1.
Room creation in a 2D view associated to a 3D Ogre scene
maintaining its data structures (nodes) of models,


2.
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,


3.
Objects are divided into triangular 2D patches tracked down by
their position in 3D,


17

QOFI


Implementation
process (3/5)

4.
During the calculation, for each light source, for each iteration, we
determine patches that receive light according to the room and
elements geometry,


5.
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