Unit Tap Constrained Adaptive Channel Shortening Equalization

Abstract

Orthogonal frequency division multiplexing (OFDM) is a popular transmission format for emerging wireless communication systems. Single-carrier cyclic-prefixed (SCCP) modulation is similar to OFDM, but with all frequency-domain operations performed at the receiver. Systems employing OFDM and SCCP perform well in the presence of multipath provided that the channel delay spread is shorter than the guard interval between transmitted blocks. If this condition is not met, a channel shortening equalizer can be used. Existing adaptive channel shorteners require re-normalization to restrain the channel shortener away from zero. In this paper, we study the use of a unit-tap constraint rather than a unit-norm constraint. We use this constraint to manipulate existing algorithms into a framework analogous to the recursive least squares algorithm, and we develop adaptation rules for blind and semi-blind frequency domain equalizers for SCCP receivers. Simulations show an order of magnitude improvement in convergence speed and reduced asymptotic bit error rate.