Minimisation of carrier frequency acquisition time in QAM systems

Two recent carrier recovery loops for high-order quadrature amplitude modulation (QAM) and optimisation of their parameters for minimum frequency acquisition times are analysed. All variations on the parameters were analysed and optimised to obtain optimal loop bandwidths and damping factors, for given signal-to-noise ratios. Simulation results show that after optimisation, the average acquisition time for 64-QAM is kept below 1000 symbols over the entire range of initial frequency offsets from 0 to 1/8 the symbol rate. This number increases to 3200 symbols for 256-QAM.