provide dynamic aiding data to the receiver that can be used to propa gate the GPS solution

during satellite outages and to aid in reacquisition of lost satellite signals.  B asically, the

marriage is between a short term, precise aiding source and the very long term, stable GPS

reference.

8.2  MISSION REQUIREMENTS

The level of integration will largely depend on the particular mission requirements for

navigation data accuracy and availability. Navigation system designers therefore need to

clearly examine the mission requirements before deciding on the level of GPS integration

necessary to adequately support military operations.  Sample considerations that drive an

integration design are listed below.

a.  Navigation accuracy   What position, velocity and/or time accuracy are

required from the navigation solution supported by GPS?  GPS accuracy can

be improved through the use of DGPS if proper host and support equipment

is in place (see Chapter 10).

b.  Availability of navigation solution   What are the maximum HV dynamics for

which the GPS set must navigate continuously with the highest level of

accuracy? Is the user required to navigate accurately in a high interference or

jamming environment?  Sensor aiding data can greatly improve GPS

availability under adverse conditions.

c.  Reacquisition of GPS signal   How soon after any satellite signal inter ruption

must GPS regain full navigation accuracy?  How long can GPS interruption

be accepted without measurable degradation of system per formance? 

Reacquisition can be improved by other sensors as a rough initial ization for

initial GPS signal acquisition as well as for rapid reacquisi tion should signals

temporarily be lost.

d.  Sensor calibration   Is calibration of other navigation sensors by GPS

required in order to maintain a high quality navigation during GPS outages?

Does GPS have to provide INS platform misalignment error estimates to a

quality that could support inflight INS alignment?  Is management of multiple

sensor output required for fault tolerance?  GPS and other navigation

sensors provide dissimilar redundancy for detecting hard and soft failures in

either system.

e.  Output rate of navigation solutions    The GPS receiver navigation solution

output rate may be limited. If a higher output rate is required, the

integration may require the GPS receiver to aid the INS, or for the GPS

and navigation system data to be combined in an external navigation

processor instead of GPS being used as the primary navigation source.