Optimal Channel Shortener Design for Reduced Reduced- State Soft-Output Output Viterbi Equalizer in Single Single-Carrier Systems
Abstract: We consider optimal channel shortener design for a reduced reduced-state state soft-output soft Viterbi equalizer (RS-SOVE) SOVE) in single single-carrier carrier systems. To use RS-SOVE, RS three receiver filters need to be designed: a prefilter, a target response, and a feedback filter. The collection of these three filters are commonly referred to as the “channel shortener.� Conventionally, nventionally, the channel shortener is designed to transform an intersymbol interference (ISI) channel into an equivalent minimumminimum phase equivalent form. In this paper, we design the channel shortener to maximize a mutual information lower bound based on a mismatched detection model. By taking the decision decision-feedback quality in the RS-SOVE SOVE into consideration, the prefilter and feedback filter are found in closed forms, while the target response is optimized via a gradient gradient-ascending ascending approach with the gradient explicitly xplicitly derived. The information theoretical properties of the proposed channel shortener are analyzed. Moreover, we show through numerical results that the proposed channel shortener design achieves superior detection performance compared with previous channel shortener designs at medium and high code rates.