Receiving the L2C Signal with “Namuru” GPS L1 Receiver

L2C is the first modernised GPS signal for civilians, broadcast by the new generation of satellites, designated Block IIR-M. Currently three of these satellites (PRN-17, PRN-31 and PRN-12) have been declared operational by the Air Force Space Command at Schriever Air Force Base, Colorado. The structure of the L2C signal is designed such that it achieves a number of advantages over the GPS L1 signal alone. This includes weak signal acquisition, ionospheric error elimination when both L1 and L2C are used, quicker operations and improved tracking performance. It was suggested that it would be interesting as well as challenging to acquire and track the L2C signal with a standard GPS L1 receiver. “Namuru” is an FPGA-based GPS L1 receiver, developed at School of Surveying & Spatial Information Systems, UNSW. In this work, the RF front end of “Namuru” has been modified by hardware augmentation, to process real L2C signals from Block IIR-M satellites. The modified RF front end provides real time samples of the L2C signal. These samples are recorded in a memory module on “Namuru” board and further processed in Matlab environment to perform the acquisition of L2C signal. The new structure of the L2C signal requires novel approaches for its acquisition. The L2C signal consists of two codes, L2C CM and L2C CL. The L2C CM-code is modulo-2 added to data and the resultant sequence is time-multiplexed with the L2C CL-code on a chip by chip basis. In this work, the replica code used for acquisition primarily contains CM chips while CL chips being replaced by zeros. This replica code is referred to as return to zero (RZ) CM code and can be used for signal search across any 20 milliseconds segment of an L2C signal record. The L2C signal is successfully acquired from all the three operational satellites and “Namuru” is now equipped with L2C acquisition capability.