Oversampled M-sequences for joint data and bit epoch estimation in DSSS transmissions

The maximum likelihood (ML) estimator for the bit synchronization epoch and data bit values in direct-sequence spread-spectrum (DSSS) transmission consists of determining the binary sequence that maximizes the correlation with the recovered data samples. This requires the exhaustive test of all sequences generated by the different bit combinations and alignments, resulting in a computationally intensive process. In this letter, the properties of maximum length sequences (m-sequences) are exploited for testing all the bit combinations and alignments in parallel, leading to a computationally efficient implementation of the ML estimator. The case where the data bits are modulated by an overlay or secondary code is also considered and the proposed algorithm is generalized to include the effect of this additional modulation.