A new adaptive carrier synchronization applying the extended Kalman filtering algorithm is proposed. The state model in the new algorithm uses only phase rather than both phase and frequency in the conventional method. The frequency is used as an input term to the state equation and estimated by a phase error detector. A reduced observation model is also considered to reduce complexity by only calculating scalar instead of matrix in the Kalman recursions. The simulations show that the one-state Kalman algorithm has better performance and lower complexity than the two-state Kalman algorithm. The proposed algorithm is applied to the cable modem downstream system to demonstrate its effectiveness.