between in the Multi-Gigabit Regime

Transcription

1 International Workshop on Aerial & Space Platforms: Research, Applications, Vision IEEE Globecom 2008, New Orleans, LA, USA 04. December 2008 Optical Backhaul Links between HAPs and Satellites in the Multi-Gigabit Regime Vienna University of Technology Institute of Communications and Radio-Frequency Engineering Gusshausstrasse 25/389, 1040 Vienna

2 Overview Introduction Scenario HAP to satellite communication Methodology Performance of optically preamplified receiver Influence of atmosphere on optical beam System performance Summary 2

3 Introduction Laser free space communication at data rates in the mutli-gigabit regime Application: broadband backhaul communication link HAP Advantages: no clouds less atmospheric turbulence larger power margins smaller outage probability higher data rates HAP High-Altitude Platform 3

4 Scenario Parameters: Satellite altitude: up to km (GEO) HAP altitude: 20 km Antenna diameter: 13.5 cm Wavelength: 1550 nm Zenith angle: 50 Aims: - Show feasibility of using optical communication terminals onboard HAPs - Design optical communication system - Assess influence of atmospheric turbulence on performance -.. HAP High-Altitude Platform LOS line-of-sight 4

5 Methodology Modulation Format Lasersource Atmospheric Turbulence Noise Sources Optically preamplified RX APD based RX Transmit Power Antenna Gain RX Receiver BEP bit error probability APD avalanche photodiode 5

6 Receiver (1) - Performance Optically preamplified receiver: Transmitter: Sensitivity ypenalty Return-to-zero (RZ) modulation relative to quantum limit: External modulation (20 db extinction) 16dB 1.6 G EDFA gain F noise figure S responsivity of photodiode R T transimpedance 6

7 Receiver (2) - Comparison Optically preamplified receiver 1.2 db APD-based receiver 1.6 db 9 db Bo optical filter bandwidth 14.4 db 7

8 Influence of Atmosphere on Laser Beam Absorption and scattering db power penalty Beam wander Beam spread Phasefront disturbance, scintillation power penalties and power fluctuations at the receiver Scintillation index σ² characterises temporal behaviour of intensity (I) fluctuations (normalized variance a of I(t)) 8

9 Coupling efficiency into EDFA (1) Mean coupling efficiency: E(r) () incident optical field F(r) backpropagated fiber mode Φ(r) phase function Fiber operated at single-mode cut-off Lens-to-fiber coupling geometry optimized Φ(r)=const. Exact field of fiber s eigenmode: η max = 78.6% EDFA Erbium doped fibre amplifier 9

10 Coupling efficiency into EDFA (2) efficienc cy Satellite HAP mean loss: 1.2 db coupling Phasefront distortions: Satellite Ground Station mean loss: 7 db phasefront disturbance Fried Parameter r 0 [m]: Aperture diameter with 1 rad rms-phasefront disturbance Phase function Φ(r) modeled as normal distribution with zero mean and standard d deviation σ φ D telescope diameter λ wavelength λ 2π = σ with D σ RMS ϕ λ σ ϕ r0 10

11 Power Budget Receiver Concept optically preamplified Link Distance [km] Modulation [db] external Modulation Format RZ Intensity Modulation Data Rate [Gbit/s] 1 10 Average Transmit Power [dbm] 40 Antenne gain, atmospheric loss, free space loss, implementation loss, coupling loss, pointing and tracking loss,... [db] RX Sensitivity [dbm] Power Margin [db] Fading Level (P F = 10-2 ) [db] 0.22 RZ return-to-zero P F fading probability / outage proability 11

12 Fading and forward error correction (FEC) Example: RS(255,239) code 10Gbit/s GEO-to-HAP link BEP... bit error probabiltiy BEP T... target bit error probability P... average receive power P t... target receive power p FEC... outage probability σ I ²... scintillation index 12

13 Summary (1) Impact of atmosphere Noise Channel model Transmitter Receiver Modulationformats System Model 13

14 Summary (2) System performance GEO-HAP communication feasible: at 1 Gbit/s using optically preamplified or APD-based RX at 10 Gbit/s using optically preamplified p RX in combination with FEC and Oswald Wallner, Application of Single-Mode Fiber-Coupled Receivers in Optical Satellite to High-Altitude Platform Communications, EURASIP Journal on Wireless Communications and Networking, Special Issue on Advanced Communication Techniques and Applications for High- Altitude Platforms, April 2008, Optical Backhaul Links between HAPs and Satellites in the Multi-Gigabit Regime, Workshop IWASP 2008 at Globecom 2008, New Orleans, USA, Dec FEC forward error correction 14