bus to meet its particular need. The only option is to program the 1553 bus controller to

convert message formats as required for GPS and other remote terminals to communicate

successfully.

MISSION

ANTENNA

COMPUTER

OTHER

INS

DATABUS

GPS

SYSTEMS

CONTROLLER

RECEIVER

MIL STD 1553

Figure 8 4.  GPS in 1553 Databus Configuration

8.3.5  Embedded GPS

The previous sections essentially address integrations of physically separate GPS

receivers and other sensors.  GPS may also be integrated into other systems by

embedding the receiver into the host system (eg., within an INS, DRNS, mission computer,

CDU, etc).  For these cases, the embedded system has the benefits of tight coupling as

described in paragraph 8.3.2. 

8.4  GPS AND TRANSIT/OMEGA/LORAN C

Some hybrid systems have been developed that use the best data available from each of

GPS, Transit and Omega.  Navigation system measure ments from all three systems can be

integrated to generate an optimum system solution.  If four GPS satellites are available and

PDOP is within limits, the Transit and Omega measurement data are not required. Some

manufacturers have produced hybrid GPS equipment and offered retrofit GPS kits for

installation in existing Transit/Omega receivers. This hybrid option has become significantly

less attractive since the GPS constellation has reached full capability and Omega has

begun phase out.

Another hybrid variation is to combine a GPS receiver with a Loran C receiver.  When

a GPS solution is available, the position information can be used to calibrate the Loran 

C receiver for daily and local effects.  When a GPS solution is not available, the

calibrated Loran C receiver can be used as a sta nd alone system. When GPS satellites

become visible again, the Loran  C can be used to initialize the GPS receiver and

therefore reduce acquisition time.  A combination of Loran  C and GPS data can also be

used to produce a position solution or provide an automated cross check for integrity

purposes.