Analysis and Architecture Design of a Downlink $M$ -Modification MC-CDMA System Using the Tomlinson–Harashima Precoding Technique

This paper investigates the feasibility of applying Tomlinson-Harashima precoding (THP) to multicarrier code-division multiple-access (MC-CDMA) system downlinks, in which multiple-access interference and possible complexity in the mobile terminal (MT) are major burdens. A THP based on the minimum mean-square error (MMSE) criterion is also presented, making it possible to realize a low-complexity receiver at the MT. The hardware architecture of the MMSE THP with modified QR decomposition at the transmitter is presented, along with the required word length analyzed. Pipeline and parallel schemes are adopted to reduce the execution time. For a generic square matrix of order for RQ decomposition, the required latency is time units, which is based on the modified Gram-Schmidt algorithm.