Channel Equalization
Keith Q.T. Zhang · 2015
The influence of inter-symbol interference (ISI) can be minimized based on different criteria, resulting in different types of channel equalizers, which are studied in this chapter. A simple methodology is to remove the overlapped portion causing ISI, leading to the technique of zero-forcing equalizer (ZFE). The drawback of ZFE is that its output signal-to-noise ratio (SNR) can be very small if the overall channel response has singularities or near-singularities in its Fourier spectrum. A remedy is the use of an MMSE channel equalizer. The output SNR of ZFE and MMSE equalizers is uniquely determined by the harmonic mean of the channel power spectrum, while its decision feedback equalizer (DFE) counterpart is determined by its geometric mean, revealing an elegant picture of channel equalization. The chapter factorizes a power spectrum for the construction of an equalizer, and shows that spectrum factorization was feasible through some particular examples.