Digital tracking loops for a programmable digital modem

An analysis and hardware emulation of the tracking loops for a very flexible programmable digital modem are presented. The modem can be programmed for 2, 4, 8, 16 PSK (phase shift keying), 16-QAM (quadrature amplitude modulation), MSK (minimum shift keying), and offset-QPSK modulation schemes over a range of data rates from 2.34 to 300 Mb/s with programmable spectral occupancy from 1.2 to 1.8 times the symbol rate. The demodulator architecture has been adapted from a joint estimator-detector (JED) mathematical analysis. The JED realization uses interdependent, mutually aiding tracking loops with postdetection data feedback. The emulation results confirmed tracking loop operation over the entire range of operational parameters listed above, as well as the ability to achieve and maintain synchronization at bit error rates in excess of 10^-1