Share Email Print

Proceedings Paper

Demonstration of free-space optical communication for long-range data links between balloons on Project Loon
Author(s): Bruce Moision; Baris Erkmen; Edward Keyes; Todd Belt; Oliver Bowen; Devin Brinkley; Paul Csonka; Michael Eglington; Andrei Kazmierski; Nam-hyong Kim; John Moody; Thanh Tu; William Vermeer
Format Member Price Non-Member Price
PDF $17.00 $21.00

Paper Abstract

Internet connectivity is limited and in some cases non-existent for a significant part of the world's population. Project Loon aims to address this with a network of high-altitude balloons traveling in the stratosphere, at an altitude of approximately 20 km. The balloons navigate by using the stratified wind layers at different altitudes, adjusting the balloon's altitude to catch winds in a desired direction. Data transfer is achieved by 1) uplinking a signal from an Internet-connected ground station to a balloon terminal, 2) crosslinking the signal through the balloon network to reach the geographic area of the users, and 3) downlinking the signal directly to the end-users' phones or other LTE-enabled devices. We describe Loon's progress on utilizing free-space optical communications (FSOC) for the inter-balloon crosslinks. FSOC, offering high data rates and long communication ranges, is well-suited for communication between high-altitude platforms. A stratospheric link is sufficiently high to be above weather events (clouds, fog, rain, etc.), and the impact of atmospheric turbulence is significantly weaker than at ground level. In addition, being in the stratosphere as opposed to space helps avoid the typical challenges faced by space-based systems, namely operation in a vacuum environment with significant radiation. Finally, the angular pointing disturbances introduced by a floating balloon-based platform are notably less than any propelled platform, which simplifies the disturbance rejection requirements on the FSOC system. We summarize results from Project Loon's early-phase experimental inter-balloon links at 20 km altitude, demonstrating full duplex 130 Mbps throughput at distances in excess of 100 km over the course of several-day flights. The terminals utilize a monostatic design, with dual wavelengths for communication and a dedicated wide-angle beacon for pointing, acquisition, and tracking. We summarize the constraints on the terminal design, and the key design trades that led to our initial system. We illustrate measured performance during flight tests: received signal power variations with range, pointing system performance, and data throughput.

Paper Details

Date Published: 24 February 2017
PDF: 14 pages
Proc. SPIE 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX, 100960Z (24 February 2017);
Show Author Affiliations
Bruce Moision, X (United States)
Baris Erkmen, X (United States)
Edward Keyes, X (United States)
Todd Belt, X (United States)
Oliver Bowen, X (United States)
Devin Brinkley, X (United States)
Paul Csonka, X (United States)
Michael Eglington, X (United States)
Andrei Kazmierski, X (United States)
Nam-hyong Kim, X (United States)
John Moody, X (United States)
Thanh Tu, X (United States)
William Vermeer, X (United States)

Published in SPIE Proceedings Vol. 10096:
Free-Space Laser Communication and Atmospheric Propagation XXIX
Hamid Hemmati; Don M. Boroson, Editor(s)

© SPIE. Terms of Use
Back to Top
Sign in to read the full article
Create a free SPIE account to get access to
premium articles and original research
Forgot your username?