The Spreading and Overlay Codes for the L1C Signal

摘要

We describe the rationale and construction of the family of L1C spreading codes and the associated family of overlay codes. The length-10230 spreading codes comprise 210 pilot /data sequence pairs. The codes are perfectly balanced and exhibit good even and odd auto- and crosscorrelation. They are constructed using prime-length Weil codes: selected length-10223 Weil-codes were padded with a fixed 7-bit pad. A search over all Weil codes and insertion points yielded a set of 739 codes from which the final set of 420 codes was chosen. Two separate families of codes were optimized based on modulation scheme (BOC(1,1) and MBOC). The length-1800 overlay codes are truncated linear feedback shift register sequences of length 2047, including both m-sequences and Gold sequences. Besides full period even auto- and cross-correlation, the overlay code search considered the correlation when a small subsequence (100 or 200 symbols) is correlated against the full code.