Novatel SMART ANTENNA - Manual (Page 24)

24 SMART ANTENNA User Manual Rev 6
Chapter 3 Operation
3.6.2 Operational States
The receiver has 6 operating modes:
• Self-Test
• Initialization
• Acquisition
• Navigation
• Dead-Reckoning
• Fault
The receiver switches between modes automatically. The receiver reports the current operating and navigation
modes on its host port.
1. Self-Test Mode
The receiver enters Self-Test mode upon request from an external source (please refer to Message
ID# 51, Initiated BIT Request in the SUPERSTAR II Firmware Reference Manual). The time
duration spent in the Self-Test mode is no more than 15 seconds. On self-test completion, the
receiver reports the BIT results on its host port through Message ID# 51. Self-Test mode exits to
either Initialization or Fault mode.
2. Initialization Mode
Upon power-up, the receiver enters Initialization mode. During this mode hardware is initialized
prior to Acquisition mode entry. The Initialization mode is also initiated upon completion of the
Self-Test mode, but always exits to the Acquisition mode.
The SMART ANTENNA retrieves data from both NVM and SRAM (warm start). Integrity
checking is done on all data retrieved from the non-operating state.
During initialization, the receiver retrieves the last received valid almanac data and last user
position from NVM, the current time from the low-power time source, and predicts which
satellites are currently visible. This list of visible satellites is then used in Acquisition mode to
program the 12 parallel correlator channels.
3. Acquisition Mode
The receiver is in Acquisition mode when insufficient satellite data is available to produce an
initial navigation solution. Acquisition mode is entered from Initialization or Dead-Reckoning
mode and exits to Navigation or Fault mode.
To acquire signals from the GPS satellites, the receiver uses:
• Almanac data which describes the satellite orbits
• Time, which in conjunction with almanac data is used to estimate the present
position of satellites in their orbits
• The approximate location of the receiver so a prediction can be made as to which
satellites are visible
The receiver then collects ephemeris data by decoding the satellite down-link data message. After
each satellite in view is acquired, its measurement data set is produced. When a sufficient number
of satellites are being tracked, position, velocity and time can be computed and Navigation mode
entered.
If the receiver cannot perform an acquisition due to an absence of valid almanac data or user
position and/or time, it initiates a "Search the Sky" acquisition. The receiver attempts to acquire all
satellites in the GPS constellation. Once a satellite has been acquired, ephemeris data is decoded