Real Time GPS Data Transmission Using VSAT Technology
Michael E. Jackson1*, Chuck Meertens1, Oivind Ruud1,
Spencer Reeder1, Warren Gallaher1, and Chris Rocken2
1University NAVSTAR Consortium (UNAVCO),
University Corporation for Atmospheric Research (UCAR) Office of Programs 2GPS Science & Technology (GST) Program,
University Corporation for Atmospheric Research (UCAR) Office of Programs
* Corresponding author address: Submitted to: GPS Solutions
Michael E. Jackson, UNAVCO Boulder CO Date: May 8, 2001
e-mail: mikej@unavco.ucar.edu
Abstract
The University NAVSTAR Consortium (UNAVCO)
Boulder Facility is assessing Very Small Aperture
Terminal (VSAT) technology for near real-time
transmission of GPS data from a remote receiver to
a central processing facility. The study is motivated
by the need for a robust, cost effective data
communications solution to transfer GPS data from
remote sites where no other communication
alternatives exist. Future large-scale plate
boundary deformation initiatives using spatially
dense networks of GPS will require receivers to be
located where the science dictates and not the
power or communications infrastructure. For other
applications, such as determining rapid GPS orbits
and time transfer, there is a push towards reducing
the latency in GPS data used to produce GPS data
products and differential corrections (Talaya &
Bosch, 1999; Jackson, Meertens & Rocken, 2000,
Muellerschoen, Bar-Sever, Bertiger & Stowers,
2001), and to support upcoming Low Earth Orbiting
(LEO) missions requiring low latency, 1 s GPS
data.
In this paper we evaluate two Ku-band systems, the
Nanometrics Libra VSAT and the StarBand 2-way
satellite Internet VSAT. The Nanometrics system
test results show that continuous, 1 s GPS data can
be streamed from multiple remote stations within
the VSAT footprint, quality checked, and delivered
for processing with a <2.5 s latency (mean 1.2 s)
and a 99.8% reliability. Benefits of the
Nanometrics system include global coverage,
control of bandwidth allocation and data hub and
the low power draw of the system. Negatives
include the cost of hub and remote infrastructure
and the need to negotiate landing rights issues on a
country-by-country basis. The facility currently
operates a Nanometrics hub and 3 remote VSAT
systems.
The StarBand system showed 98.9% reliability with
a maximum latency of 10.2 s (mean latency 1.7 s)
for 1 Hz GPS data and an average uplink speed of
31.7 kbps. Benefits of the StarBand system
include the cost and small profile of the remote
antenna. Negatives include coverage limited to
coterminous United States and high power draw of
remote systems.
[See attached .pdf file for more.]
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