Nasiri Khormuji, Majid (Huawei Technologies Sweden AB, Stockholm)
We propose two time–frequency alignment schemes for multi-user uplink transmission when the receiver is equipped with abundant numbers of antennas. The proposed solutions are constructed using the long-term characterization given by coherence time and coherence bandwidth of radio channels. The schemes align pilot and data symbols of multiple users to simultaneously avoid pilot contamination and provide good channel estimations. We develop analytical rate-expressions and study the scheme in multi-cell scenarios as well. The analytical and simulation results show that the proposed solutions can encouragingly enhance the aggregate rate at virtually the same receiver complexity as that of the conventional massive MIMO uplink transmission. The basic solution with two aligned groups of users in the time–frequency plane can increase the aggregate rate up to 33 % as compared to those of conventional solutions.