Beamspace Channel Estimation for Millimeter-Wave Massive MIMO with Lens Antenna Array Using Quasi-Orthogonal Pilots

For two major reasons, in multi input multi output (MIMO) systems, the use of orthogonal pilots for all users is not easy: firstly, the pilot length is limited by the time that channel is nearly constant and secondly, increasing the number of users and antennas increases the length of the pilot sequences that causes wasting of resources. In this paper, the practical beamspace channel estimation using lens antenna array (LAA) with quasi-orthogonal pilots is studied for millimeter-wave (mm-wave) massive MIMO systems. LAA acutely decreases the number of needed radio-frequency chains (RFCs). Based on comparing the average of sparse blocks, we propose a new channel estimation algorithm with reliable performance. Then the beamspace channel estimation in multi cell scenarios using quasi-orthogonal pilots is formulated. Theoretical analyses and simulation results show that the studied method lessens the channel estimation error, specifically in low signal to noise ratio (SNR).