Survey of Free Space
Optical (FSO)
Communications
Opportunities in Next
Generation Cellular
Networks
Frédéric Demers, Halim Yanikomeroglu &
Marc St-Hilaire
Presented at the
Communication Networks and Services Research
Conference
4 May 2011
Outline

Motivation & Key Characteristics of FSO systems

Channel model and path loss overview

Recent advances in FSO communications




Full Optical FSO systems
Hybrid RF/FSO systems
Mobile FSO systems
Indoor diffuse FSO systems

Applications within Next Generation Cellular Networks

Conclusions
2
Motivation & key characteristics





RF spectrum scarcity vs increasing throughput
requirements
A single FSO channel can offers Tb/s throughput
wirelessly
Free space optical spectrum is license free and
nearly unlimited (very dense reuse)
FSO systems are generally very difficult to
intercept
Effective range limited by weather and eyesafety considerations
3
Channel model

Factors affecting light propagation through
the atmosphere
 Physical
composition of atmosphere
Changes
in refractive indices
Aerosol
particles
4
Channel model
5
850 nm 1550 nm
Channel model

Channel effects:
 Absorption
 Diffraction
 Rayleigh
scattering (atmospheric
gases molecules)
 Mie scattering (aerosol particles)
 Atmospheric (refractive) turbulence:
Weather
Scintillation
 Beam wander

6
Channel model
7
Path loss, RF

Typical RF attenuation (e.g. 2 GHz, 15 dBi antenna gains)


Avg path loss in free space -> 68 dB @ 1km , 118 dB @ 10 km
Avg path loss in mobile radio (n=3.4, d0=100 m) -> 82 dB/km, 146
dB @ 10 km
 4 d 0   d 

  
    d0 
2
PL mobile-radio
n
8
Path loss, FSO
Intensity of light at point x and time t’
x
   N  x,t dx

0
I   , t, x   I  , t,0 e

Beer-Lambert Law
Space time distribution of species
Intensity of transmitter
      a     R     M  
Mie Scattering
Absorption
Raleigh Scattering
M. Bass, "Atmospheric optics," in Handbook of Optics ,Third
Edition ed., vol. 5, M. Bass, Ed. McGraw-Hill, pp. 3.3., 2010.
9
Pressure
Path loss, FSO
3
q  6
 p   7.53  10
Refractive index of air
n0  1  77    1 
 7733    10
2

T
T  
Temperature

Humidity

nT r  n0  n r
Point in space
Stochastic component
10
Path loss, RF vs FSO

Typical RF attenuation (e.g. 2 GHz, 15 dBi antenna gains)



Avg path loss in free space -> 68 dB @ 1km , 118 dB @ 10 km
Avg path loss in mobile radio (n=3.4, d0=100 m) -> 82 dB/km, 146
dB @ 10 km
Typical optical attenuation (e.g. 1550 nm or 194 THz)
 clear atmospheric conditions -> 0.2 dB/km
 urban (because of dust) -> 10 dB/km
 Rain -> 2-35 dB/km
 Snow -> 10-100 dB/km
 light fog -> 120 dB/km
 dense fog -> 300 dB/km
 maritime fog -> 480 dB/km
11
Full Optical FSO

No requirement for
electrical-optical
conversion

Easy extension of
RF-over-fibre links

Wavelength division
multiplexing
K. Kazaura, K. Wakamori, M. Matsumoto, T. Higashino, K. Tsukamoto
and S. Komaki, "RoFSO: A universal platform for convergence of fiber
and free-space optical communication networks," Communications
Magazine, IEEE, vol. 48, pp. 130-137, 2010.
12
Hybrid RF/FSO

FSO is most affected by fog, RF by
rain

RF links complements FSO to
achieve carrier class availability
(99.999%)

Lower throughput in adverse
weather
I. I. Kim and E. Korevaar, "Availability of free space optics (FSO) and
hybrid FSO/RF systems," Optical Wireless Communications IV, EJ
Korevaar, Eds. , Proc. SPIE, vol. 4530, pp. 84-95, 2001.
13
Mobile FSO Systems

Tightly packed LED
transceivers around
spherical device

Able to maintain optical
link in motion

Experiment rather
simplistic
J. Akella, C. Liu, D. Partyka, M. Yuksel, S. Kalyanaraman and P. Dutta,
"Building blocks for mobile free-space-optical networks," in Wireless
and Optical Communications Networks, 2005. WOCN 2005. Second
IFIP International Conference on, pp. 164-168, 2005.
14
Indoor Diffuse Optical Wireless

Non Line-of-Sight optical
communications

Multipath interference an
issue, limiting throughput

Hybrid narrow-beam
designs provide both
bandwidth and coverage
R. J. Green, H. Joshi, M. D. Higgins and M. S. Leeson,
"Recent developments in indoor optical wireless systems,"
IET Communications, vol. 2, pp. 3, 2008
15
Next Generation Cellular Networks

Densification of access points (eNodeB)
 Shorter
hops
 Suitability to mesh connectivity

Heterogeneous access points
 Relaying
 Distributed
antennas
 Coordinated Multi-Point Transmission &
Reception (CoMP)

Self-Organizing Networks
Next Generation Cellular Networks
Evolved UMTS Terrestrial Access Network (E-UTRAN)
Evolved Packet Core
aGW
eNB
UE
p-eNB
MME
p-eNB
SAE
GW
aGW
Indoor AP
relay
eNB
relay
UE
PDN
GW
17
Conclusions
Radio
Next
frequencies
generation
networks
alone
willwill
not
require
suffice
atodenser
provide
These
This
architectural
denser infrastructure
changes
will
open
shorten
the door
hops
to an
infrastructure
thebetween
required
throughput
to cater
toFSO
mobile
toand
the
end-users
userthe
needs
increased
reliance
base
upon
stations
communication
ease
PHY layer
not dead!
establishment
systems
ofismesh
connectivity
18
Main references
1.
J. Akella, C. Liu, D. Partyka, M. Yuksel, S. Kalyanaraman and P. Dutta, "Building blocks for
mobile free-space-optical networks," in Wireless and Optical Communications Networks, 2005.
WOCN 2005. Second IFIP International Conference on, 2005, pp. 164-168. Available:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.143.6352&rep=rep1&type=pdf
2.
M. Bass, "Atmospheric optics," in Handbook of Optics ,Third Edition ed., vol. 5, M. Bass, Ed.
McGraw-Hill, 2010, pp. 3.3.
3.
R. J. Green, H. Joshi, M. D. Higgins and M. S. Leeson, "Recent developments in indoor optical
wireless systems," IET Communications, vol. 2, pp. 3, 2008. Available:
http://www.ieeexplore.ieee.org.proxy.library.carleton.ca/stamp/stamp.jsp?tp=&arnumber=4446
618
4.
K. Kazaura, K. Wakamori, M. Matsumoto, T. Higashino, K. Tsukamoto and S. Komaki,
"RoFSO: A universal platform for convergence of fiber and free-space optical communication
networks," Communications Magazine, IEEE, vol. 48, pp. 130-137, 2010. Available:
http://www.ieeexplore.ieee.org.proxy.library.carleton.ca/stamp/stamp.jsp?tp=&arnumber=5402
676
5.
I. I. Kim and E. Korevaar, "Availability of free space optics (FSO) and hybrid FSO/RF
systems," Optical Wireless Communications IV, EJ Korevaar, Eds. , Proc. SPIE, vol. 4530,
pp. 84-95, 2001. Available:
http://www.ece.mcmaster.ca/~hranilovic/woc/resources/local/spie2001b.pdf
19