The GMD-based precoding and antenna selection schemes for CoMP joint processing

In this paper, we discuss the precoding schemes for coordinated multi-point (CoMP) joint processing (JP) using geometric mean decomposition (GMD). Unlike JP singular value decomposition (JP-SVD) whose performance is dominated by the spatial pipe with weak channel gain, JP-GMD is proposed to derive the precoding matrix of all the cooperative cell sites and the decoding matrix of the user equipment (UE) so that equal spatial channel gains can be obtained. Sphere decoding (SD) is then employed to achieve the maximum likelihood (ML) solution. Besides, centralized Tomlinson Harashima precoding (THP) can be adopted at the base station to remove interference, called JP-GMD-THP. We show that the JP-GMD plus SD scheme has significant performance improvement over JP-SVD, JP-zero forcing (ZF) and JP-minimum mean square error (MMSE). JP-GMD-THP that allows simple one-tap equalization has performance loss only about 0.7 dB compared to the JP-GMD plus SD scheme. Furthermore, to reduce the joint processing efforts at all cell sites and to take advantage of the spatial domain, two antenna selection techniques, best antenna selection and grouping antenna selection, are also proposed. As opposed to the best antenna selection, the grouping antenna selection technique can reduce search efforts with about 0.5 dB SNR degradation, but is still better than the non-cooperative schemes.