Adaptive Equalization

Abstract

Chapter 8 derived a set of receiver structures that counter intersymbol interference under the assumptions of a known channel and unconstrained complexity. The resulting structures are impractical for most applications in the exact form we derived them for several reasons. First, assumption of a known received pulse shape is unrealistic, particularly for channels such as the digital subscriber loop (with bridged taps), radio channel (with selective fading), and voiceband data channel, where there are significant variations in the channel affecting the reception. Thus, the received pulse shape is not actually known in advance for these channels, and is sometimes varying during actual transmission. Second, the receiver structures we derived usually have an infinite number of coefficients, and cannot be realized. Third, our optimizations did not take into account significant impairments such as timing jitter and timing offset, which must be considered in the design of receive filtering.