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Design of an Multi-Gbp Optical Wireless Transmission Link

This project focuses on optimizing a wireless transmission link using 1550nm wavelength. It covers system structure, alignment, assumptions, calculations, and upcoming design challenges. The chosen wavelength offers advantages in power and sensitivity. The system utilizes a unique five-beam design with alignment and tracking mechanisms. Detailed calculations ensure performance and safety standards are met. Future steps involve finalizing optic designs and adjustment systems. References provide valuable insights in optical wireless communication.

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Design of an Multi-Gbp Optical Wireless Transmission Link

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  1. Design of an Multi-GbpOptical Wireless Transmission Link EE8114 Student Name: Wen Zu

  2. Content: • Selection of wavelength • System Structure • Alignment and tracking, Adjustment • Assumptionsand Calculation • Problems in the next step • References

  3. 1. Selection of wavelength:1550nm • Options of wavelength:780 nm to ~ 850nm, 1300nm~1550nm 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 @800nm • Receivers have nearly 3 dB better receiver sensitivity at 1550nm than 850nm due to the lower energy per photon.

  4. 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.

  5. 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.

  6. Figure 1. The function parts of this design

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

  8. Figure 3.The working of transmitters and receivers.

  9. 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 system’s use in CANON Optical Wireless Communication designs .

  10. Figure 5. Use of Tracking system. Figure 6. Performance of Tracking system

  11. 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.

  12. 4. Assumptions and Calculation Assumptions: • 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

  13. BER: 1.00E-12 • Transmit Optics Degradation: -1dB • Receive Optics Attenuation: -1dB Calculation • 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

  14. Maximum Rangeat -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.

  15. Figure 4. Mie scattering attenuation in dB/km for the various fog distribution models

  16. 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

  17. 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”

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