GPS L2 C signal survey and the development of the emergent MATLAB L2 C (EMAL2) receiver
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The United States Department of Defense has introduced two new GPS civilian signals on its “Link 2” (L2) and “Link 5” (L5) center frequencies. The first of these new civilian signals to reach full operational capability in the GPS constellation will be the L2 C signal. The L2 C signal boasts new signal structure features aimed at better tracking performance in comparison to the legacy L1 C/A signal. Amongst these are two new chip-by-chip interleaved spreading code sequences, Civilian Moderate (CM) and Civilian Long (CL), and a new, higher resolution navigation message, CNAV. The two new C codes are longer than the legacy C/A code and feature a data less pilot signal (CL) for improved tracking performance in weak signal environments. This work investigates L2 C acquisition and tracking considerations and implements algorithms for acquiring and tracking the signal in a software-defined receiver developed in MATLAB. The Emergent MATLAB L2 C (EMAL2) receiver was developed for the purpose of GPS signal simulator testing. This software-defined receiver differs from legacy receivers containing application specific integrated circuits (ASICs) in that all of EMAL2’s digital signal processing is done in software able to run on a general purpose processor. This approach offers greater flexibility and ease in configuration over ASICs for tracking a number of different types of signal structures in the receiver. The EMAL2 receiver’s design and implementation is described here-in. Initial testing of the EMAL2 receiver was conducted with live-sky signal data captured by antennas and front-ends at the University of Texas Radionavigation Laboratory (UT RNL). The data was processed by the GRID receiver (also at the UT RNL) to provide EMAL2 baseline received signal characteristics.