7. Conclusions

In the previous chapter, the ideas of centralized and distributed baseband precoding in the hybrid RF-baseband architecture were explored for the purpose of suppressing the inter-cell interference (ICI) and improving the system error performance at the cell edge. In the distributed implementation, it is seen that by partitioning the high-dimensional multiple-input multiple-output (MIMO) channel into multiple near-orthogonal, low-dimensional subspaces as dictated by block diagonalization in the RF domain, cell-wise spatial multiplexing can be carried out at baseband without causing severe ICI. Although this obviates the need of channel state information (CSI) and user data exchange between base stations (BSs), the lack of cell coordination unfortunately prevents balancing intra-cell spatial multiplexing and ICI suppression in a resource efficient manner. On the contrary, by allowing inter-BS collaboration as in the centralized approach to baseband spatial multiplexing, the error performance enjoys a significant enhancement.