On SC/FDE Block Transmission with Reduced Cyclic Prefix Assistance

For conventional CP-assisted (Cyclic Prefix) SC/FDE implementations (Single- Carrier/Frequency-Domain Equalization), as well as for OFDM implementations (Orthogonal Frequency Division Multiplexing), the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long FFT block for FDE purposes and keeping good performances through a moderate increase of the FDE receiver complexity. Firstly, we present an algorithm for a Decision-Directed Correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. The resulting FDE performance is then evaluated in worst-case (CP-free) conditions, and the impact of previous decisions which are not error-free is shown to be rather small. In the following, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of the DDC algorithm for replacing "useless" CP redundancy by fully useful channel coding redundancy: highly power/bandwidth efficient block transmission schemes, especially recommendable for both strongly time-dispersive and time-varying channel conditions, are then achieved.