Pilot Decontamination Based on Superimposed Pilots in Massive MIMO Systems

Abstract

Massive multiple-input multiple-output (MIMO) has become a promising solution to provide unprecedented spectral efficiency (SE) to future cellular networks, based on the idea of equipping the base station (BS) with hundreds or thousands of antenna elements operating in a coherent fashion. At the doors of the future fifth generation mobile communication networks (5G), massive MIMO has been widely recognized as one of the cornerstones, given the ambitious key performance indicators of the future standard. The channel state information (CSI) acquisition is one of the core activities in massive MIMO, on which its entire performance depends to a great extent. Pilot contamination has been recognized as the main limiting factor to acquire an accurate CSI, becoming the focus of a large body of research. In this paper, we focus on the pilot contamination problem in massive MIMO systems. An approach is proposed to mitigate this problem based on the use of superimposed (SP) pilots in combination with time-multiplexed (TM) pilot sequences. Specifically, we use the contaminated channel estimates to reduce the amount of interference produced when SP pilots are used. Results show that the amount of interference caused by transmitting pilots alongside the data is substantially reduced when this method is put into place. In turn, the proposed method leads to mitigating the pilot contamination.