Phase tracking by fuzzy control loop

Fuzzy control, a control mechanism making use of fuzzy logic is implemented here for controlling a discrete phase locked loop (DPLL), and evaluating its performance by comparing the transient response with that of a similar uncontrolled DPLL. Even though other papers in the subject have been published, such as the one by D. Simon and H. El-Sherief (1995), this tutorial paper describes the essential components involved in the design of a fuzzy controlled DPLL or FDPLL. The FDPLL presented here contains a stage of fuzzification of the error signal and its time derivative. The two signals are used to control the FDPLL response by modifying the loop filter coefficients within predefined bounds, where a second order DPLL filter has been selected for the FDPLL vs. DPLL evaluation. Computer simulations of controlled and uncontrolled DPLL show that even with a small set of properly chosen fuzzy rules the transient response of the FDPLL to phase steps converges earlier and with smaller oscillatory peaks rewards the steady state than its conventional DPLL counterpart which produce faster signal acquisition and better tracking performance.