A Practical Digital Signal Carrier Acquisition based on Kalman Filter Theory

Abstract

Traditionally Extended Kalman Filter has been proposed and studied for the acquisition of a digital carrier signal. However, this technique imposes a heavy load on the processor. And high performances cannot be expected for the poor linearity, in most cases. To overcome these problems, this paper shows that one can use a simple, purely linear Kalman Filter which consists of two states variables - phase and frequency. This new technique selects the carrier phase as the input to the filter, instead of a pair of orthogonal signal amplitudes. The filtering logic is made up of only 4 additions and 2 multiplications. The results of both simulations and experiments show that this filter can acquire the carrier signal within 10 symbols with a probability of 98 % during the initial phase, even when the frequency offset is as large as 20 % of the symbol rate frequency at C/N=6dB. In the steady state, the measured BER is close to the theoretical values. While delivering a similar performance mentioned above, this filter can operate even when the carrier frequency deviates from the expected figure.