S o n o m a U s e r M a n u a l
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C H A P T E R O N E
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S o n o m a U s e r M a n u a l
sions are monitored from ground stations located around the world and carefully measured relative to
GPS time. The results of these measurements for each satellite are then uploaded to that satellite so
that they may be incorporated into the data contained in its transmissions. The receiver can use this
data to relate the time-of-arrival of the received transmissions from that satellite to GPS time.
All of this means that during normal operation, the source of the timing information being transmitted
from each of the satellites is directly traceable to UTC. Due to the nature of the GPS spread-spec-
trum modulation scheme, this timing information may be extracted by a well-designed receiver with a
precision of a few nanoseconds. The GPS Subsystem in the Sonoma does just that.
GPS Receivers
GPS-based timing systems supporting critical infrastructure could be vulnerable to malfunction due
to weak signals, jamming, spoofing or accidental GPS control system errors. Proprietary algorithms
in Sonoma perform advanced integrity checks to filter random and persistent errors to the GPS sub-
frame data.
EndRun developed a timing optimized GPS receiver for additional resilency, accuracy, and reliability.
The EndRun GPS Receiver strictly complies to the IS-GPS-200 specification. and began shipping in
Sonoma in June 2017. GPS receiver specifications are listed in
Appendix H - Specifications
.
Time Synchronization
Components
The Sonoma is composed of a Global Positioning System (GPS) Subsystem containing the EndRun
GPS Receiver and system oscillator. The GPS Subsystem is integrated with a fanless, convection-
cooled 1.2 GHz CPU with two integrated Ethernet ports that provide NTP (and optionally PTP).
This is called the Linux/NTP Subsystem. The drawing below shows Sonoma’s time synchronization
components.
System
Oscillator
Receiver
Subsystem
Processor
Receiver
Oscillator
PLL
GPS Receiver Module
Receiver
Processor
1PPS
EFC
10MHz
Linux NTP/PTP Subsystem
1PPS
10MHz
GPS Receiver Subsystem
10MHz
SONOMA GPS SUBSYSTEM
Summary of Contents for Sonoma N12
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