Pilot Reuse for Massive MIMO Transmission over Spatially Correlated Rayleigh Fading Channels

Abstract

We propose pilot reuse (PR) in single cell for massive multiuser\nmultiple-input multiple-output (MIMO) transmission to reduce the pilot\noverhead. For spatially correlated Rayleigh fading channels, we establish a\nrelationship between channel spatial correlations and channel power angle\nspectrum when the base station antenna number tends to infinity. With this\nchannel model, we show that sum mean square error (MSE) of channel estimation\ncan be minimized provided that channel angle of arrival intervals of the user\nterminals reusing the pilots are non-overlapping, which shows feasibility of PR\nover spatially correlated massive MIMO channels with constrained channel\nangular spreads. Regarding that channel estimation performance might degrade\ndue to PR, we also develop the closed-form robust multiuser uplink receiver and\ndownlink precoder that minimize sum MSE of signal detection, and reveal a\nduality between them. Subsequently, we investigate pilot scheduling, which\ndetermines the PR pattern, under two minimum MSE related criteria, and propose\na low complexity pilot scheduling algorithm which relies on the channel\nstatistics only. Simulation results show that the proposed PR scheme provides\nsignificant performance gains over the conventional orthogonal training scheme\nin terms of net spectral efficiency.\n