Transcript Design of an Optical Wireless Transmission Link

Design of an Multi-Gbp
Optical Wireless
Transmission Link
EE8114
Student Name: Wen Zu
Content:
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Selection of wavelength
System Structure
Alignment and tracking, Adjustment
Assumptions and Calculation
Problems in the next step
References
2
1. Selection of wavelength:1550nm
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Options of wavelength:780 nm to ~
850nm, 1300nm~1550nm and 9 micron.
Advantages of using 1550nm:
1. 50 times more transmitted power at 1550
nm than 800 nm considering the eye safety
limit. The eye safety limit of 1550 nm is 100
mW/cm², comparing to 20 mW/cm² @800nm
2. Receivers have nearly 3 dB better receiver
sensitivity at 1550nm than 850nm due to the
lower energy per photon.
3. 1550nm is the most commonly specified
wavelength range for fiber-based optical
communication. The supporting technical base for
this wavelength range is vast and growing rapidly
every year. Therefore, it will be easy to access
new cost-effective technologies to update this
design, and to keep this design on the top
performance.
2. Structure
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A five – beam system. Four beam are
used to transmit down. One beam is
used to transmit up, and used in
Alignment and tracking, Adjustment
systems.
Figure 1. The function parts of this design
Figure 2. The function parts of this design(2)
Figure 3.The working of transmitters and receivers.
3. Alignment and tracking,
Adjustment
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Alignment and tracking system is designed to coalign the transmit and receive optical axes when
settle these devices, and to keep the alignment
of transmitters and receivers in the future.
Buildings could bend, vibrate, or move slightly in
wind or uneven thermal loading, e.g. sunshine on
one side. This system receives dictations from a
micro processor system, and operate a 2D
mechanical structure- servo system. Figure 5,6
show tracking system’s use in CANON Optical
Wireless Communication designs .
Figure 5. Use of Tracking system.
Figure 6. Performance of Tracking system
• Adjustment system operates transmit optics to
fulfill the function showing in figure 3
depending on the real weather or BER, and to
maintain an acceptable system performance.
4. Assumptions and Calculation
Assumptions:
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Transmitter: Laser (1550nm) x 5
Average Laser Power: 1000mw/30dBm
Transmit Divergence: 0.1 mrad(1/e^2 )
Transmit aperture: 4cm
Receiver: InGaAs APD (1550nm) x 5
Receiver Sensitivity: -30 dBm
Receive Aperture: 15cm
Max. Data Rate: 1000Mbps x 4
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BER: 1.00E-12
Transmit Optics Degradation: -1dB
Receive Optics Attenuation: -1dB
Calculation
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Eye safety
Transmit power/Transmit area
=79.6mw/cm² < 100 mW/cm² (Eye safety
limit @1550nm)
Beam spread @280m=7.9cm < Receive
Aperture: 15cm
Max. link power margin= Transmit Power x
4 (36dBm)-Receiver Sensitivit (-30dBm)Geometric Range Loss(1)-Transmit Optics
Degradation(1)-Receive Optics
Attenuation(1)-Filter Loss(1)= 62dB
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Maximum Range at -220dB/km atmosphere
attenuation.
Figure 3 shows the main atmosphere
attenuation - Mie scattering, varies with
wavelengths. The max. atmosphere
attenuation @ 1550nm is -220dB/km, and
atmospheric loss is 62dB:
Max. Range = 281m.
Figure 4. Mie scattering attenuation in dB/km for
the various fog distribution models
5.Problems in the next step
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Design of transmit optic and receive optic.
Completing design of alignment and tracking
system
Completing design of adjustment system
References:
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Z.Ghassemlooy, “Optical Wireless Communications - Our
Contribution”
J.R. Barry, “Wireless Infrared Communication”, Kluwer
Academic Press, Boston, 1994, 1st edn.
Chaturi Singh, Y.N.Singh, J.John, K.K.Tripathi, “High-Speed
Power-Efficient Optical Wireless System”
Scott Bloom, Seth Hartley, “THE LAST-MILE SOLUTION :
HYBRID FSO RADIO”
Scott Bloom,” THE PHYSICS OF FREE-SPACE OPTICS”
Isaac I. Kim, Eric Korevaar,” Availability of Free Space
Optics (FSO) and hybrid FSO/RF systems”
Jim Alwan, “EYE SAFETY AND WIRELESS OPTICAL
NETWORKS”
fSONA Communications Corp. ‘WAVELENGTH SELECTION
FOROPTICAL WIRELESS COMMUNICATIONS SYSTEMS”