Code Generation Scheme And Property Analysis Of Broadcast Galileo L1 And E6 Signals

In this paper, we decode the PRN codes of the L1 and E6 signals broadcast by the Galileo GIOVE-A test satellite. We apply the 45.7 m Stanford SRI Dish and the 1.8m dish of the Stanford GNSS Monitor System to receive the satellite signal. The received data are processed in a chain of wiping off carrier, Doppler offset, Binary Offset Carrier (BOC) and navigation bits.Two code sequences are revealed in each frequency band, L1-B, L1-C, E6-B and E6-C. The L1 signals have the chip rate of 1.023 Mbps. The L1-B primary code has a period of 4 msec with 4092 bits. The L1-C primary code lasts 8 msec, and has 8184 bits. L1-B has navigation data modulated on its primary code, while L1-C has 25 bits of secondary code, which extends the whole L1-C code period to 200 msec. The E6 signals' chipping rate is 5.115 Mbps. The E6-B code is 5115 bits long and carries navigation data. The E6-C code contains a 10230-bit primary code and 50-bit secondary code. It lasts 100 msec in total.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 around 50 bits. As a result, the receiver cost can be dramatically decreased. All L1 and E6 broadcast codes are proven to be truncated Gold Codes. Among them, E6-C is a 14-order Gold Code, and the others are 13-order. They can be generated by Linear Feedback Shift Registers (LFSR), which are completely specified by tap weights and initial states.We then analyze the code properties such as balancing, run-length distribution and correlation to evaluate the pseudorandomness. These properties determine the code processing gain, the robustness to noise or interference, and the lowest tolerable signal to noise ratio (SNR). We calculate the correlation performance at different frequency offsets to take account of the Doppler residual in the current satellite signal and Doppler frequency shifting in other potential satellite signals.By investigating this code we make it possible to track the GIOVE-A signal with our own software receiver and evaluate the performance of the selected code. We intend to use this technique to further evaluate the GIOVE-B and other Galileo signals as they become available.