Multiuser linear precoding for cooperating base stations with asynchronous interference

This paper addresses multiuser linear precoding using multiple cooperating base stations (BSs). All BSs, and potentially the users, are equipped with multiple antennas. Prior work in multiuser precoding with a single BS extensively uses a downlink/uplink duality that significantly reduces the computation load. Here we show that the presence of asynchronous interference, unfortunately always present due to multiple BSs, precludes a simple duality. This in turn complicates deriving the needed precoding matrices. Even when duality is assumed to exist, asynchronous interference has its implications on the convexity of the power allocation problem. An optimization formulation and several related simulations for the asynchronous case are presented, including one where duality is assumed and another wherein orthogonal frequency division multiplexing (OFDM) is used for transmission and its cyclic prefix is used to mitigate asynchronous reception for edge users.