A fine synchronization method for coherent fast frequency hopping

Coherent fast frequency hopping (CFFH) is attracting growing attention owing to its good antijamming performance and the coherent combining ability. However, compared with the conventional non-coherent fast frequency hopping, CFFH requires a more precise system synchronization. In this paper, we propose a new fine synchronization algorithm for CFFH. This algorithm consists two stages, namely, open-loop stage and closed-loop stage. In the open-loop stage, a grid-based search parameter estimation method is proposed. In the closed-loop stage, we construct a fully coherent phase-locked loop (PLL) and a delay-locked loop (DLL) with decoding feedback structure to perform further fine estimation of the system clock skew and time delay, respectively. Moreover, we analyze the effect of the search parameter settings on the estimation error and derive the root mean squared error (RMSE) of estimates in the steady state of the closed-loop stage. Finally, through simulation, the RMSE performance are compared with the corresponding Cramer-Rao low bound (CRLB) and conventional code loop estimation to show the effectiveness of proposed algorithm.