Table 3 1.  GPS PPS System Range Error Budget

UERE Contribution

Segment

Error Source

(metres, 95%)

P Code

C/A Code

Space

Frequency Standard Stability

6.5

6.5

D Band Delay Variation

1.0

1.0

Space Vehicle Acceleration Uncertainty

2.0

2.0

Other

1.0

1.0

Ephemeris Prediction and Model

8.2

8.2

Control

Implementation

Other

1.8

1.8

User

Ionospheric Delay Compensation

4.5

9.8 19.6

Tropospheric Delay Compensation

3.9

3.9

Receiver Noise and Resolution

2.9

2.9

Multipath

2.4

2.4

Other

1.0

1.0

Total (RSS) System UERE (metres, 95%)

13.0

15.7 23.1

3.1.2.1  GPS UE Range Error Budget

The portion of the UERE allocated to the Space and Control segments is called the

user range error (URE) and is defined at the phase center of the satellite antenna. 

The portion of the UERE allocated to the user equipment is called the UE error

(UEE).  Specifically, the  UERE is the root sum square of the URE and UEE.  The

UEE includes residual errors after compensation for atmospheric delay, inherent

receiver errors of noise and resolution, and multipath.  Modern C/A code receivers

have demonstrated significant improvements in ionospheric delay compensation

over the budgeted values.  The values given for ionospheric  delay compensation

error are based on dual frequency delay measurements for P code and the single 

frequency ionospheric delay model for C/A code (as specified in "Technical

Characteristics of the Navstar GPS").  The budgeted values for C/A code can be

improved by use of a modified single frequency model or code less dual frequency

measurements on the L1 and L2 carriers.  Modern P code and C/A code receivers

have both demonstrated significant improvements over the budgeted values for

receiver noise, resolution, and multipath, using digital phase locking techniques

and variable or narrow code correlation techniques.

3 3