Optimization of the hybrid asymmetric-FIR/analog square-root filters

This paper presents a method for designing asymmetric square-root (SR) FIR filters against the effects of jitter-induced interference at the receiver. The proposed method employs the linear programming to design the Nyquist filter coefficients for minimizing the power of the jitter-induced interference. The desired SR filter coefficients are obtained via the spectral factorization of the Nyquist filter polynomial. The proposed method takes the filter´s stopband attenuation, the system´s tolerable ISI, and the “roughness” of the analog/FIR-SR filter impulse response into account. Unlike previous publications, we show that the error-performance of a system employing a matched SR filter pair, in the presence of receiver timing jitter, is more strongly related to the roughness of the hybrid analog/FIR-SR filter´s impulse response, than it is to the eye width caused by the Nyquist pulse. The design example validates the proposition that the proposed method can lead to improved error performance of a high-order QAM communication system in the presence of receiver clock jitter.