Opportunistic multiuser MIMO for OFDM networks

This paper considers the application of opportunistic multiuser multiple-input multiple-output (MU-MIMO) techniques to multicarrier wireless networks based on orthogonal frequency division multiplexing (OFDM). Unlike related work where the design of the MU-MIMO component is jointly performed with the subcarrier allocation among the users (e.g. some form of OFDMA is present), here it is assumed that the selected users will have to share the utilization of all the subcarriers in the system. This scenario would be typical of deployments based on time multiplexing policies (e.g., WLANs) where the proposed MU-MIMO add-on would serve to increase the system capacity. A new algorithm is introduced to select the users taking into account their channel response over all subcarriers and performing a joint frequency-space power allocation. Numerical results demonstrate very significant improvements in terms of sum-rate capacity in comparison to a conventional (opportunistic) TDMA scheme.