Evaluation of GPS receiver ranging accuracy

The GPS (Global Positioning System) Central Engineering Activity (CEA) of the Naval Air Development Center has developed facilities to support multiservice testing of Rockwell Collins GPS user equipment (UE). A capability has been developed within the CEA to evaluate the accuracy with which the GPS UE makes pseudorange measurement. CEA users are able to isolate and to examine receiver code tracking loop performance independently of GPS navigation performance. Pseudorange measurements consist of the true line-of-sight range and a number of error sources which include: tracking errors, satellite clock error, atmospheric delays, receiver clock error, and receiver channel delays. A range accuracy assessment process has been developed to isolate the tracking error from the other sources of error and the true line-of-sight range. Since the CEA provides a controllable test environment, some of the error sources can be zeroed (satellite clock error and ionospheric and tropospheric delay effects) while others can be quantified (receiver clock error and channel delays). The true line-of-sight range can be determined from the CEA trajectory generation function. The result is that the CEA provides for the direct determination of tracking error in UE receiver pseudorange values