A Novel Carrier Frequency Offset Tracking Scheme in MQAM-OFDM Systems

A novel carrier frequency offset tracking scheme for multilevel quadrature amplitude modulation-orthogonal frequency division multiplexing (MQAM-OFDM) systems is proposed using a designed conjugate code composed of MQAM mapping values and their complex conjugates which can also reduce peak-to-average power ratio (PAPR). The peak power is reduced by phase cancellation in the conjugate pairs avoiding accumulation of too much same phase subcarriers. A likelihood function is deduced from the conjugate code to estimate the phase offset caused by carrier frequency offset (CFO). A novel multicarrier phase locked loop (MPLL) is described tracking the frequency offset in time and frequency domain. The algorithm performance was investigated in a designed system showing that the proposed scheme can reduce the PAPR of the system effectively and track the frequency offset in high precision.