Limited feedback for multi-antenna multi-user communications with Generalized Multi-Unitary Decomposition

In this paper, we propose a decomposition method called Generalized Multi-Unitary Decomposition (GMUD) which is useful in multi-user MIMO precoding. This decomposition transforms a complex matrix H isin C^mtimesn into H = P_iRQ_i ^H, where R is a special matrix whose first row contains only a non-zero user defined value at the left-most position, P_i and Q_i are a pair of unitary matrices. The major attraction of our proposed GMUD is we can obtain multiple solutions of P_i and Q_i. With GMUD, we propose a precoding method for a MIMO multi-user system that does not require full channel state information (CSI) at the transmitter. The proposed precoding method uses the multiple unitary matrices property to compensate the inaccurate feedback information as the transmitter can steer the transmission beams of individual users such that the inter-user interference is kept minimum.