Design of robust adaptive equalizers for digital radio systems

The issue of adaptive equalizer behavior during the events of carrier synchronism loss in digital microwave radio systems is addressed. It is shown that, in the case of a QPSK system, conventional algorithms are very sensitive to carrier synchronism loss, and that a simple modification considerably improves their stability. Next, a 64-QAM system is considered, and the conventional zero-forcing algorithm (ZFA) and the maximum-level error algorithm (MLEA) are examined along with a new variant of the ZFA. A comparative study is made between the algorithms in terms of their self-noise, stability, and tracking speed. The results indicate that the proposed algorithm significantly improves the system robustness during loss of synchronism