A MIMO Precoder Design for Downlink Coordinated Multipoint Communication

This study presents a multiple-input multiple-output (MIMO) precoder with a compensated QR-decomposition (CQRD) combination for coordinated multipoint (CoMP) downlink transmission. Unlike conventional QR-decomposition (QRD) combination, CQRD combination adopts compensated channel matrix orderings. This study first proposes CQRD combination for CoMP scenarios. The statistics for combined spatial subchannel gains with a CQRD combination of two coordinated base stations (BSs) are derived, and these statistics show that more balanced subchannel gains are generated with a CQRD combination than with a QRD combination. Furthermore, this study proposes a generalized CQRD combination scheme with a joint sorting strategy that can be applied to scenarios with more than two coordinated BSs. Unlike the unsorted strategy, the joint sorting strategy determines an enhanced compensated combination to further increase spatial subchannel gains; therefore, the performance can be upgraded. Because conventional Tomlinson–Harashima precoding (THP) cannot be used in the CQRD combination, interference presubtraction and vector precoding (VP) is adopted. Theoretical analysis and simulation results are both provided to demonstrate the advantages of higher spatial subchannel gains in the proposed CQRD-based schemes. Compared with existing QRD-based MIMO precoders in CoMP scenarios, the proposed CQRD-based schemes have substantial SNR improvements of 2–5 dB.