Pilot Decontamination with Directional Doppler PSD in Massive MIMO

Pilot contamination mitigation in the uplink (UL) is an important problem to tackle in massive multiple-input multiple-output (MIMO). Existing researches only relied on the angle of arrival knowledge at the base station (BS). In this paper, we propose an enhanced pilot decontamination strategy using the angle of departure information at the user side. Since this information is contained in the Doppler power spectrum density (PSD), we first analyze the directional Doppler PSD (D-PSD) at a particular angle impinging on the BS. A closed-form expression of the D-PSD for an arbitrary angle distribution at the user side is provided and the spatial-wideband effect caused by the large number of antennas is also considered. We then present a method to mitigate the pilot contamination by exploiting the D-PSD. We further verify its effectiveness in offering more orthogonal pilots and reducing channel estimation errors compared with our previous works. Simulations show the proposed scheme can serve as one additional decontamination mechanism for the UL pilots in massive MIMO.