Design of an Optical Wireless Transmission Link

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Design of an Optical Wireless Transmission Link

• Student Name Wen Zu
• Instructor Dr.Xavier N. Fernando

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Content

• Selection of wavelength
• System Structure
• Alignment and tracking, Adjustment
• Assumptions and Calculation
• Problems in the next step
• References

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1. Selection of wavelength1550nm

• Options of wavelength780 nm to 850nm,
  1300nm1550nm and 9 micron.
• Advantages of using 1550nm
• 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 _at_800nm
• Receivers have nearly 3 dB better receiver
  sensitivity at 1550nm than 850nm due to the lower
  energy per photon.

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• 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.

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2. Structure

• 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.

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• Figure 1. The function parts of this design

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• Figure 2. The function parts of this design(2)

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• Figure 3.The working of transmitters and
  receivers.

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3. Alignment and tracking, Adjustment

• Alignment and tracking system is designed to
  co-align 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 systems use in CANON
  Optical Wireless Communication designs .

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• Figure 5. Auto-Tracking System

Figure 6. Effect of Beam Diameter on Receiver
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• Adjustment system operates transmit optics to
  fulfill the function showing in figure 3
  depending on the real BER in different weathers,
  and to maintain an acceptable system performance.

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4. Assumptions and Calculation

• Assumptions
• Transmitter Laser (1550nm) x 5
• Average Laser Power 1000mw/30dBm
• Transmit Divergence 0.5 mrad(1/e2 )
• Transmit aperture 4cm
• Receiver InGaAs APD (1550nm) x 5
• Receiver Sensitivity -37 dBm
• Receive Aperture 15cm
• Max. Data Rate 1000Mbps x 4

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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 _at_ 1550nm is
  -220dB/km, and atmospheric loss is 62dB
• Max. Range 281m.

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• BER 1.00E-12
• Transmit Optics Degradation -1dB
• Receive Optics Attenuation -1dB
• Calculation
• Eye safety
• Transmit power/Transmit area 79.6mw/cm² lt
  100 mW/cm² (Eye safety limit _at_1550nm)
• Beam spread _at_500m7.9cm lt Receive Aperture 15cm
• Max. link power margin Transmit Power x 4
  (36dBm)-Receiver Sensitivit (-30dBm)-Geometric
  Range Loss(1)-Transmit Optics Degradation(1)-Recei
  ve Optics Attenuation(1)-Filter Loss(1) 62dB

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Figure 4. Mie scattering attenuation in dB/km
for the various fog distribution models
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5.Problems in the next step

• Design of transmit optic and receive optic.
• Completing design of alignment and tracking
  system
• Completing design of adjustment system

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References

• 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