4.8  GPS INTERFACE OPTIONS

4.8.1  Introduction

Choice of interfaces for a GPS receiver are dependent on the system to which a GPS

receiver shall be integrated, and are also dependent on the depth of the integration

required.  Alternative approaches to interfaces can be grouped as follows:

Implement a new interface in an existing GPS receiver

Redesign of HV systems to accommodate an existing GPS receiver

Development of an interface box to adapt an existing GPS receiver to an

existing HV system.

4.8.2  Implementing a New Interface in an Existing GPS Receiver

Good design of a GPS receiver allows the partitioning of the receiver portion and

the interface requirements.  Often this can be accom plished by using a separate

processor to manage interfaces, thus buffering the performance of the GPS

receiver portion from the individual demands of a platform interface.  This gives the

ability to add new interfaces with minimum impact on the majority of receiver

software design.  Given the flexibility of the software design, an existing GPS

receiver can have a new interface card inserted into a spare card slot, or if an

existing interface is not used, then the new interface card can be substituted for it. 

This choice is constrained by the hardware limitations of wiring, output pin

availability, etc.

4.8.3  Redesign of HV Interfaces to Accommodate an Existing GPS Receiver

Redesign of the HV interfaces to accommodate the GPS receiver with its current

interface is a possibility; however, it may not be considered practical unless major

components of the HV can be changed at the same time.  With GPS becoming

available as a sensor (rather than an LRU with interfaces), embedded GPS receiver

alternatives (e.g., embedded in an INS) should also be considered when systems are

being replaced.

4.8.4  Separate Development of an Interface Box

One approach that can have minimal impact on both an existing GPS receiver and

HV systems is the design of a separate "box" that performs the interface functions. 

This "box" would accept existing interface inputs and outputs of a GPS receiver and

convert them to the inputs and outputs normally used by the HV systems.  This

approach still requires the HV  system s software to be changed to accept another

navigation input, and the issues of space, weight, and power for the new "box" must

be addressed.  Of importance is the impact on the data senescence caused by the

additional time delay necessary for the "box" to convert  the data.

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