Coded modulation for noncoherent reception with application to OFDM

Abstract

Power- and bandwidth-efficient differentially encoded transmission over slowly time-varying fading channels with noncoherent reception and without channel state information is considered. For high bandwidth efficiencies, combined phase and amplitude modulation is used. For increased power efficiency, channel coding and multiple-symbol differential detection are applied, i.e., interleaving and detection are based on blocks of N>2 consecutive symbols. The presented concepts are directly applicable to transmission over flat fading channels. However, concentrating on the situation of frequency-selective channels, we consider their application to multicarrier transmission using orthogonal frequency-division multiplexing (OFDM). When coding across subcarriers, OFDM transforms the actual frequency-selective channel into a slowly time-varying frequency-nonselective fading channel. This paper presents a design for multilevel coding schemes to approach theoretical limits for power- and bandwidth-efficient noncoherent transmission over the equivalent fading channel. It is shown that bit-interleaved coded modulation, which relies on Gray labeling, is competitive only in the case of conventional differential detection with N=2. The theoretic considerations are well approved by simulation results, where turbo codes are applied as component codes.