Performance of decoder-based algorithms for signal synchronization for DSSS waveforms

This paper presents results on the implementation of pilotless carrier synchronization algorithms at low SNRs using joint decoding and decision-directed tracking. A software test bed was designed to simulate the effects of decision-directed carrier synchronization (DDCS) techniques. These techniques are compared to non-decision directed algorithms used in phase-locked loops (PLLs) or Costas loops. In previous work by the authors, results for direct M-ARY modulation constellations, with no code spreading were introduced. This paper focuses on the application of the proposed family of decision directed algorithms to direct sequence spread spectrum (DSSS) waveforms, typical of GPS signals. The current algorithm can utilize feedback from turbo codes in addition to the prior support of LDPC codes.