Carrier Recovery for Data Communication Systems with Adaptive Equalization

This paper describes the problem of carrier recovery for adaptively equalized data communication receivers. A conventional receiver structure that employs baseband equalizers is considered first, and a practical method for jointly adjusting the demodulating carrier and the equalizer is briefly described. The reader is then introduced to an equalizer time delay problem critical to the system's performance. The first remedy for this problem involves the use of dual-mode carrier control loops. A method for designing such loops is presented and its use is illustrated by a conceptual design and a numerical example. The second remedy is to adopt a passband equalizer receiver structure. A tutorial introduction to this concept and a summary of the basic principles involved are presented. This paper concludes by reviewing related timing recovery problems. Joint design approaches such as the maximum likelihood estimate approach and the minimum mean-square error approach will be described and compared.