Carrier recovery for 16 level QAM in mobile radio

Carrier recovery for quadrature amplitude modulation (QAM) has proved to be considerably more difficult than for binary modulation. One of the simplest effective solutions is the use of phase locked loops (PLLs) but with the phase detector replaced by a circuit capable of producing phase error signals from a received QAM phasor with varying phase and amplitude. Circuits to do this have been suggested but do not operate on all received signals. A circuit which can operate on all incoming signals thus increasing the stability of clock recovery is presented