Implementation of the Inverted GPS Range for Modernized GPS Testing

By Fall 2003, an Inverted GPS Range (IGR), similar to the Inverted Range developed at Yuma in the 1970s prior to launch of the GPS Block I satellites, will be imple- mented at White Sands Missile Range (WSMR), NM. Its purpose is to broadcast both legacy and modernized GPS signals to enable testing of user equipment (UE) in a field environment, validate the compatibility between current and modernized user equipment, and evaluate perform- ance with new concepts of operation. Along with the legacy GPS signals (L1-C/A & L1/L2-P/Y) the IGR will broadcast new military signals (L1/L2-M) and a civilian L2C signal (at L2), and possibly in the future the new civilian signal at L5. The IGR will employ a centralized architecture consisting of an Inverted Range Control Center (IRCC) and a net- work of 8 ground transmitters (GTs) deployed to support testing in an area up to 20 miles x 20 miles at WSMR. This implementation will enable centralized generation and control of all broadcast signals including closed-loop tracking at the IRCC even when significant intentional jamming is introduced in the IGR test environment. This paper reviews the IGR implementation requirements and describes major elements of the IGR design includ- ing: the IRCC and GT configurations; the frequency plan; signal power control for delivering required levels along a user trajectory; time synchronization to GPS and between individual GTs; GT siting considerations for adequate GDOP and signal availability; IRCC monitor receiver requirements; and the IGR Nav message designed to minimize UE software changes for operations in the IGR alone or in a mixed mode with both GPS and IGR signals.