Performance investigation of the modified costas carrier recovery loop for a QPSK modulated signal in the presence of co-channel interference

One of the important challenges in communication systems is drift in the carrier frequency of received signal due to the clock skew and Doppler effect. Every communication receiver requires an automatic frequency control (AFC) loop to estimate the carrier drift in the received signal. One of the well-known AFC loops in communication systems is the Costas loop. In this paper a modified version of Costas loop for binary phase-shift keying (BPSK) modulation is presented which is capable to estimate the carrier frequency of the quadrature phase-shift keying (QPSK) modulation, and therefore significantly simplifies practical implementation. The performance of the modified Costas loop is investigated for the carrier recovery of a QPSK signal in the presence of a co-channel interference. Both simulations and analytical results illustrate that the modified Costas loop may estimate the carrier frequency drift of received signal when the desired signal is stronger than interference.