Wireless infrared indoor communications: Wireless infrared indoor communications: how to combat the multi-path distortionhow to combat the multi-path distortion

S. Jivkova and M.KavehradS. Jivkova and M.KavehradCenter for Information & Communications Technology Research (CICTR)Center for Information & Communications Technology Research (CICTR)

Department of Electrical EngineeringDepartment of Electrical EngineeringThe Pennsylvania State UniversityThe Pennsylvania State University

Photonic EAST 2000Photonic EAST 2000

OutlineOutline

• Multi-Spot Diffusing Configuration (MSDC): characteristic features

• Multi-path distortion

• Receiver geometrical configuration

• Channel parameters

• Novel receiver optical front-end design

• Conclusions

Photonic East 2000Photonic East 2000

Characteristic features

• One-to-many and many-to-one communications

• Lack of alignment requirement

• Roaming possible

• Can be virtually free from multipath induced temporal distortion

• Relatively large cell size

• Tolerance to shadowing and blockage

Quasi non-directed non-LOS configuration

Element

0

)( )()(k

k thth

T

R

Multipath distortion

Multi-spot diffusing configurationMulti-spot diffusing configuration

At least one diffusing spot lies

within each branch field-of-view

At most one diffusing spot lies within each branch

field-of-view

FOV1 FOV2

Multi-spot diffusing configurationMulti-spot diffusing configuration

FOV1

FOV2

6m

6m

Multi-spot diffusing configurationMulti-spot diffusing configuration

Circle areas on the ceiling covered by the central receiver branch for a receiver position (0.3m, 05m) measured from the room corner

Room size: 6m x 6m x 3mReflectivity of room surfaces: 0.7 (walls and ceiling),

0.3 (floor)Number of reflections considered: 3Transmitter position: center of the room,

0.9m above the floor

time [ns]

0 20 40 60 80

impu

lse

resp

onse

[s-1

]

0

1

2

3

300

400

500

three bounces

0 20 40 600123

0 20 40 600123

0 20 40 600

200

400

6001st bounce (88.8%)

2nd bounce (1.7%)

3rd bounce (9.5%)

frequency [MHz]

0 50 100 150 200 250

mag

nitu

de r

espo

nse

[dB

]

-144

-142

-140

-138

one bounce (f3dB=236.6MHz)

two bounces (f3dB=232MHz)

three bounces (f3dB=191MHz)

FOV1 (two diffusing spots within receiver branch FOV)

time [ns]

0 20 40 60 80

impu

lse

resp

onse

[s-1

]

0

1

2

3

300

400

500

three bounces

0 20 40 600123

0 20 40 600123

0 20 40 600

200

400

6001st bounce (92%)

2nd bounce (0%)

3rd bounce (8%)

frequency [MHz]

0 50 100 150 200 250m

agni

tude

res

pons

e [d

B]

-148

-146

-144one bounce (f3dB=2.82GHz)

three bounces (f3dB=2.47GHz)

FOV2 (one diffusing spot within receiver branch FOV)

Multi-spot diffusing configuration:Multi-spot diffusing configuration:Channel characteristics

Field-of-view of a 7-branch

composite receiver

r

1H2

ΔS)FOVtan(

r22 H

ΔDΔS)tan(FOV)tan(3FOV

Number of spots covered by each branch:

- At least one:

- At most one:

S

2ΔS/

D

FOV2

FOV1

ΔD-ΔS

central side

central

Multi-spot diffusing configurationMulti-spot diffusing configuration

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

Major factors in receiver optical subsystem design:Major factors in receiver optical subsystem design:

• Signal gain

• Ambient light rejection

• Physical weight, size and cost

wave 1,

wave 2,

hologram

two plane waves,plane substrate

(plane holographic mirror)

wave 2,

wave 1,

hologram

two spherical waves,curved substrate

(spherical holographic mirror)

two spherical waves,plane substrate

(spherical holographic mirror)

wave 2,

wave 1,

hologram

Recording of Reflection Holograms

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

Holographic curved mirror as a receiver optical front-end

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

photodetector

holographic curved mirror

2

dielectricfilling

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

Angular and spectral selectivity of a reflection hologram

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

0.0

0.5

1.0

-10

0

10

20 820830

840850

860

diff

r. e

ffic

ienc

y

angle of incidence

[deg]

wavelength [nm]

=0, =, =850nm, n=1.5, n=0.01, d=60m

angle of incidence [deg]

-15 -10 -5 0 5 10 15

diff

ract

ion

effi

cien

cy

0.0

0.2

0.4

0.6

0.8

1.0

844nm

846nm

848nm

850nm

angle of incidence [deg]

0 2 4 6 8 10 12 14

effective area

[cm

2 ]

0

2

4

6

8

=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8

effective area

[cm

2 ]

0

2

4

6

8=1mm=2mm=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8 10 12 14

effective area

[cm

2 ]

0

2

4

6

8

=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8

effective area

[cm

2 ]

0

2

4

6

8

=1mm=2mm=3mm=4mm=5mm

HSM

HPM

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

angle of incidence [deg]

0 2 4 6 8 10 12 14

figu

re of merit gain [dB]

-10

-5

0

5

10

15

20

=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8

figu

re of merit gain [d

B]

-10

-5

0

5

10

15

20

25

=1mm=2mm=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8 10 12 14

figu

re of merit ga

in [dB

]

-10

-5

0

5

10

15

20

=3mm=4mm=5mm

angle of incidence [deg]

0 2 4 6 8

figu

re of merit gain [dB]

-10

-5

0

5

10

15

20

25

=1mm=2mm=3mm=4mm=5mm

HSM

HPM

Multi-spot diffusing configurationMulti-spot diffusing configurationReceiver optical subsystem

Diffuse configuration:Diffuse configuration:Channel characteristics

time [ns]

0 20 40 60 80

impu

lse

resp

onse

[s-1

]

0

20

40

60

80

100

120

1st bounce (53.7%)

2nd bounce (26.5%)

3rd bounce (19.8%)

frequency [MHz]

0 50 100 150 200 250

mag

nitu

de r

espo

nse

[dB

]

-145

-140

-135

-130

-125

-120

one bounce (f3dB=49.9MHz)

two bounces (f3dB=35.5MHz)

three bounces (f3dB=19.2MHz)

time [ns]

0 20 40 60 80

impu

lse

resp

onse

[s-1

]

0

2

41st bounce (45.7%)

2nd bounce (25.6%)

3rd bounce (28.7%)

frequency [MHz]

0 50 100 150 200 250

mag

nitu

de r

espo

nse

[dB

]

-175

-170

-165

-160

-155

-150

one bounce (f3dB=188MHz)

two bounces (f3dB=91MHz)three bounces (f3dB=23MHz)

FOV=70deg

FOV=10deg

Diffuse configuration:Diffuse configuration:Channel characteristics

emitter to receiver distance [m]

0 1 2 3 4 5

3dB

ban

dwid

th [

MH

z]

1

10

100

100010deg 30deg 50deg 70deg 90deg

Room size: 8m x 8m x 4mReflectivity of room surfaces: 0.7Number of reflections considered: 5Transmitter position: center of the room, 1m above the floor

Lomba, Valadas and Duarte, 6th IEEE Intl. Symp. On Personal, Indoor and Mobile Radio Communications, Sept. 27-29, 1995, Toronto, Canada, Proc., pp.321-325

Comparison between Pure-Diffuse and Multi-Spot Diffuse (MIMO) in terms of 3-dB Optical Channel Bandwidth for a Sample Receiver Position 3.7m away

from Transmitter

3-dB BandwidthArchitecture Type Field-of-View

Diffuse

Multi-Spot-Diffuse

70 deg

10 deg

FOV1

FOV2

19MHz

23MHz

190MHz

2.4GHz

Photonic East 2000Photonic East 2000

Conclusions

• Major factors causing channel distortion- Higher order reflections- Number of diffusing spots- Diffusing spot size

• Virtually ideal channel: conditions- FOV1 (3dB < 200MHz)- FOV2 (3dB > 2GHz)

• Holographic curved mirror as a receiver optical front-end- Multi-functionality- Insignificant physical weight

Photonic East 2000Photonic East 2000