Multi-user beamforming-aided AF relaying: A low-complexity adaptive design approach

The problem of cooperative multiple-input multiple- output (MIMO) amplify-and-forward (AF) relaying design for multi-user networks is studied, where each source transmits the data to its unique destination with the assistance of multiple relays equipped with antenna arrays. We aim for jointly optimizing the beamforming weights of different relays in order to minimize the total received power at all the destinations, subject to a global relays´ power constraint, while a set of linear constraints are imposed to preserve the desired signals at each destination. In contrast to prior contributions, which optimize the relaying weights in a batch processing mode, we propose a low-complexity adaptive update approach by designing a recursive algorithm for the relay beamforming weights. A relay power control method is also proposed, which can readily be incorporated into the proposed adaptive framework. The efficacy of the adaptive scheme is demonstrated by simulations in terms of its steady-state performance and tracking capability.