Power minimization in the multiuser MIMO-OFDM broadcast channel with imperfect CSI

This work addresses the design of linear precoders and receivers in multiuser Multiple-Input Multiple-Output (MIMO) downlink channels using Orthogonal Frequency Division Multiplexing (OFDM) modulation when only partial Channel State Information (CSI) is available at the transmitter. Our aim is to minimize the total transmit power subject to per-user Quality-of-Service (QoS) constraints expressed as per-user rates. We propose a gradient-projection algorithm to optimally distribute the per-user rates among the OFDM subcarriers. Then, another algorithm is used to obtain the per-subcarrier precoders and receivers that minimize the overall transmit power. Based on the Minimum Mean Square Error (MMSE) duality between the MIMO Broadcast Channel (BC) and the MIMO Multiple Access Channel (MAC), both algorithms perform an Alternating Optimization (AO).