JPL real-time analysis software:

Ron Muellerschoen 

The open Internet  is shown to provide reliable 
delivery of real-time GPS data. High quality dual-
frequency  receivers at pre-existing world-wide 
JPL/NASA sites have been augmented with laptops 
running network software that 1.) Compresses the 
real-time GPS observable stream and 2.) Transmits 
the compressed stream as UDP (User Datagram 
Protocol) packets to JPL.  TCP reliability is 
achieved by requesting retransmission of missed 
packets, and backup processes automatically take 
over should the primary data stream fail.  The 
global network currently consists of 18 receivers, 
a mixture  of Ashtech Z-12s, AOA ACT Benchmarks, 
and AOA TurboRogues.

The global data streams are merged, unpacked, and 
sorted at JPL, where global orbits and dual-
frequency clocks are computed using JPL's Real-
Time Gipsy (RTG) software. These solutions are 
converted to a 560-bit/sec-correction message to 
the broadcast GPS ephemeredes and clocks.  The 
message will also be made available over the 
Internet.

Global  real-time orbit  products are shown to be 
30-40 CMS (3D RSS) compared to IGS orbits, and 20 
CMS over the North Western Hemisphere where most 
of the ground reference stations are concentrated.

Results of real-time  kinematic point  positioning  
of a dual-frequency  user will be presented.  The 
accuracy is better  than  20 cm RMS vertical and 
10-cm RMS horizontal.