All-digital implementation of the carrier recovery loop in digital radio systems

The authors address the issue of complete digitization of the carrier recovery loop in digital microwave radio systems. First, they present digital equivalents of conventional carrier recovery loops employing either a passive filter or an active filter with a high gain. Next, they address the issue of extending the acquisition range of these loops, which is a critical problem in digital radio receiver design. For carrier recovery loops with the digital equivalent of an active loop filter, the loop acquisition range was investigated using two previously proposed PFDs (phase and frequency detectors). With the best of these two detectors, it was shown that the acquisition range can be very close to 1/8 T, which constitutes a fundamental limit for decision-feedback carrier recovery loops with symbol-rate phase error measurements