A Novel FLL-Assisted PLL With Fuzzy Control for TC-OFDM Carrier Signal Tracking

The time and code division-orthogonal frequency-division multiplexing (TC-OFDM) signal is a promising wireless positioning signal, which multiplexes the China mobile multimedia broadcasting signal and pseudorandom noise codes in the same frequency band. The drastic change of carrier-to-noise ratio can increase carrier tracking error of the TC-OFDM receiver and may lead to the loss of lock. To address this problem, a novel frequency-lock loop (FLL)-assisted phase-lock loop (PLL) with fuzzy control is proposed, and the effect of signal strength on the carrier tracking loop is analyzed. The proposed algorithm uses the outputs of the phase and frequency discriminator as measured residuals of the Kalman filter (KF), and a KF-based second-order FLL-assisted three-order PLL carrier tracking loop is designed. Moreover, fuzzy control is applied to the designed loop. It can automatically switch between pure KF-based PLL, pure KF-based FLL, and KF-based FLL-assisted PLL, and automatically adjust the noise bandwidth. Simulation and experimental results show that, compared with the existing carrier tracking algorithms, the proposed algorithm can effectively avoid the divergence of the tracking loop and improve the robustness of the TC-OFDM receiver.