Convergence time improvement in the carrier recovery circuits for digital QAM radio link

The performance of a particular baseband circuit for carrier recovery (CR) in QAM (quadrature amplitude modulation) digital radio links is analyzed. An increase of convergence speed is made possible by adopting conventional phase detectors through the use not only of the diagonal QAM signal states, but also of the all-QAM signal states. Use of this technique makes blind convergence possible. S-curves are plotted for the analysis of algorithm performances. A differential modulation method should also be implemented in order to recover the phase errors greater than pi /2. It is suggested that an optimum subset of QAM signal states be investigated to find an optimum compromise between convergence speed and performance.<>