A spatial domain based method against pilot contamination for multi-cell massive MIMO systems

Massive multiple-input and multiple-output (MIMO) system has shown its outstanding performance in energy saving and spectrum efficiency, with channel state information (CSI) available at base-station (BS) side for downlink beam-forming [1]. Further study revealed that performance of massive-MIMO will be limited by so-called pilot contamination in multi-cell scenario [2], where the transmit CSI at one BS is a superposition of channel coefficient of its serving user and channel coefficients of users in adjacent cells using same pilot, which introduces inter-cell interference. The analysis in [2] ignored a fact that the spatial and/or temporal characters of channel coefficients of different users are different such that they are distinguishable in certain extends. However, the optimal method which can entirely isolate the user channels is extremely hard to achieve or even not feasible in certain cases. This paper presents a suboptimal spatial domain method which uses a pre-determined angular-tunable narrow beam pattern to match the desired user. Simulation results show that the majority of pilot contamination effect can be suppressed even with a not-so-well designed beam pattern.