DIFFERENTIAL

GPS

GPS DATA LINK

ANTENNA

ES

G

N

TES

A

A

R

N

IN

O

D

D

R

SITIO O

O

C

PSEU

DIFFERENTIAL

PO

GPS

DATA

DISPLAY

RECEIVER

PROCESSOR

CORRECTIONS

M

TA EA

DATA

A

D

STR

DATA

LINK

FORMATTER

RECEIVER

Figure 10 3.  Typical UE Block Diagram

10.6  DGPS INTEGRITY

DGPS does more than increase positioning accuracy, it also enhances GPS

integrity by compensating for anomalies in the satellite ranging signals and

navigation data message. The  range and range rate corrections provided in the

ranging code DGPS correction message  can compensate for ramp and step type

anomalies in the individual satellite signals, until the corrections exceed the

maximum values or rates allowed in the correction format. If  these limits are

exceeded, the user can be warned not to use a particular satellite by placing "do 

not use" bit patterns in the corrections for that satellite (as defined in or RTCM SC 

104 message formats) or by omitting the corrections for that satellite.  Step

anomalies will normally cause carrier phase DGPS receivers to lose lock on the

carrier phase, causing the reference and user receivers to reinitialize.  User

receiver noise, user processing anomalies, and multipath at the user GPS antenna

cannot be corrected by a DGPS system. These errors are normally small and

included in the overall DGPS error budget.

Errors in determining or transmitting the satellite corrections may be passed on to

the differential user if integrity checks are not provided within the reference station.

 These errors can include inaccuracies in the reference station antenna location(s)

that bias the corrections, systematic multipath due to poor antenna sighting (usually

in low elevation angle satellites), algorithmic errors, receiver interchannel bias

errors, receiver clock errors, and communication errors.  For these reasons, DGPS

reference station designs typically include integrity checking provisions to

guarantee the validity of the corrections before and after broadcast.

In a local area DGPS system that provides integrity checks on the corrections at the

reference station, Receiver Autonomous Integrity Monitoring (RAIM) may not be

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