Efficient Channel Estimation for Iterative MIMO SC-FDE Systems

SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) are promising candidates for future broadband MIMO (Multiple Input, Multiple Output) wireless systems. These modulations allow excellent performances in severely time-dispersive channels, provided that accurate channel estimates and performing decoding algorithms are available at the receiver. For this purpose, pilot symbols and/or training sequences are usually multiplexed with data symbols. However, since this leads to overhead and some spectral degradation, the use of implicit pilots (i.e., pilots superimposed to data) should be considered. In this paper we consider MIMO SC-FDE systems where the channel estimation is based on either explicit or implicit pilots. Since the interference levels between data and pilots might be very high (for the implicit bits), we propose an iterative receiver with joint equalization, turbo decoding and channel estimation. Our performance results show that the use of implicit pilots, combined with the proposed receiver, allows performances close to the case with perfect channel estimation, even for severely time-dispersive channels.