Galileo GIOVE-A Broadcast E5 Codes and their Application to Acquisition and Tracking

In this paper, we decode the PRN codes of the E5a and E5b signals broadcast by the Galileo GIOVE-A test satellite. The Galileo E5 band overlaps with Distance Measuring Equipment (DME) and Tactical Air Navigation (TACAN) bands. These navigation systems emit high-power pulses, causing severe interference to E5 signals and thus challenging the decoding process. We apply the 1.8 meter dish of the Stanford GNSS Monitor System to receive the satellite signals. The received data are processed in a chain of signal conditioning, Doppler wipeoff, secondary code wipeoff, code sequence demodulation, and code generator derivation. Two primary code sequences are revealed in each frequency band, E5a-I, E5a-Q, E5b-I, and E5b-Q. The E5 signals have a chip rate of 10.23 Mbps. All four primary codes have a period of 1msec with 10230 bits and are modulated by secondary codes. The secondary code of E5a-I has 20 bits and that of E5b-I has 4 bits. The secondary codes of E5a-Q and E5b-Q are both 100 bits. In addition to obtaining the code sequences, we also deduce the code generators. This reduces the required receiver memory size from thousands of bits to 56 bits per code sequence, a potentially important consideration of a multiplicity of codes are made available. As a result, the receiver cost can be dramatically decreased. All broadcast E5 primary codes are proven to be truncated 14-order Gold Codes. They can be generated by Linear Feedback Shift Registers, which are completely specified by tap weights and initial states. We then apply the codes for acquisition and tracking. By using our own software receiver, we are able to successfully acquire and track the GIOVE-A satellite. This is useful for evaluating the performance of the selected codes. We intend to use the above technique to further evaluate the GIOVE-B and other Galileo signals as they become available.