Joint blind equalization, carrier recovery, and timing recovery for 64-QAM and 128-QAM signal constellations

Two existing blind equalization tap update recursions suitable for 64-point and greater QAM signal constellations are studied, along with existing carrier and timing recovery techniques. The superior tap update recursion is determined to be the constant modulus algorithm. Carrier recovery requires a modified second-order decision-directed digital phase-locked loop. An all-digital implementation of band-edge timing recovery is used. With 14.4-kb/s outbound transmission using CCITT V.33 trellis-coded 128-QAM signals having 12.5% excess bandwidth, a prototype blind retrain procedure is developed to demonstrate feasibility of the new techniques for high-speed multipoint modems. A WE DSP32-based real-time digital signal processor was employed to successfully test the retrain over a set of severely impaired channels.<
>