Maximum likelihood estimation based algorithm for tracking cooperative target

The scheme which is based on the Digital Delay Locked Loop (DDLL), Frequency Locked Loop (FLL), and Phase Locked Loop (PLL) is implemented in the microwave radar for spatial rendezvous and docking, and the delay, frequency and Direction Of Arrival (DOA) estimations of the incident direct-sequence spread spectrum signal transmitted by cooperative target are obtained. Yet the DDLL, FLL, and PLL (DFP) based scheme has not made full use of the received signal. For this reason, a novel Maximum Likelihood Estimation (MLE) Based Tracking (MLBT) algorithm with a low computational burden is proposed. The feature that the gradients of cost function are proportional to parameter errors is employed to design discriminators of parameter errors. Then three tracking loops are set up to provide the parameter estimations. In the following section, the variance characteristics of discriminators are investigated, and the low bounds of Root Mean Square Errors (RMSEs) of parameter estimations are given for the MLBT algorithm. Finally, the simulations and computational efficiency analysis are provided. The low bounds of Root Mean Square Errors (RMSEs) of parameter estimations are verified. Additionally, it is also shown that the MLBT algorithm achieves better performances in terms of estimators accuracy than those of the DFP based scheme with a limited increase in computational burden.