Research and Implementation of the Early-late Gate Bit Synchronization Algorithm in the Non-coherent Spread Spectrum System

The data clock and the pseudocode clock of the non-coherent spread spectrum system are not homologous, and the phase relationship between them is not fixed, which may have the problem of random data flipping during coherent integration and affect the bit decision. Thus, the bit synchronization loop becomes a key technology for bit timing recovery. In this paper, an improved bit synchronization algorithm based on the Early-Late Gate is proposed. A bit-synchronous loop is constructed to identify the phase using the Early-Late integration results of two adjacent data codes, which can effectively improve the communication performance under random data flipping conditions. The bit clock can be dynamically adjusted according to the loop tracking result so that the integration start moment is aligned with the data bit start edge. This enables full bit coherent integration to improve the signal-to-noise ratio and thus reduce the demodulation bit error rate. The effectiveness and correctness of this method is validated by MATLAB simulations and board tests. For highly dynamic signals, the loop can be bit-synchronized within 30ms. In addition, for a signal with an Eb/N0 of 10.97dB, the bit error rate is 0 (better than 10-6) when running at a rate of 8ksps for 125s, which is in general agreement with the theoretical value.