Recursive stream selection for CF MU-MIMO BC precoders design

A lot of work has been done in the MU-MIMO BC to maximize sum rate (SR). Some of the solutions, especially the iterative ones, are capable of achieving very high performance. Nevertheless, they suffer from convergence problems. Closed form (CF) solutions on the other hand offer poor performances. This paper proposes a novel CF precoder design algorithm for the MU-MIMO BC, facilitated by stream selection. The proposed algorithm constructs the precoders per stream in a recursive manner. It contains two complementary steps: The first step consists in a recursive selection of the best available streams to minimize interference between users. This selection procedure is based on a null space criterion combined with the eigenvalues for each available stream. In the second step, the precoders are calculated according to the chosen precoding technique with eventually a power distribution optimization. Several precoding techniques can be applied, namely ZF (Zero Forcing) or MMSE (Minimum Mean Squared Error) linear beamforming (BF) and DPC (Dirty Paper Coding).