Optimal training in continuous flat-fading massive MIMO systems

Comunicació presentada a la 20th European Wireless Conference celebrada del 14 al 16 de maig de 2014 a Barceloa, Espanya.Massive multiple-input multiple-output (MIMO) communication promises the full potential of MIMO communication realized through the deployment of hundreds of antennas at each base station. Accurate channel state information (CSI) is crucial for making the most of massive MIMO. In time-varying channels, however, if not periodically updated, CSI obtained at the base station becomes progressively outdated. In this paper, we formulate a training optimization problem for maximizing uplink sum-rates. The optimal training period and update interval are characterized as solutions to fixed-point equations, which depend on the normalized Doppler shift and large-scale channel coefficients. It is found that, for a sufficiently large number of antennas at each base station, the optimal training period is equal to the number of users per cell.This research is funded in part by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 102.02-2013.09 and by Huawei Technologies Inc. through MIMO Wireless Inc