Performance analysis for pilot decontamination of Massive MIMO using alternating projection

Pilot contamination problem mainly comes from the linearity of channel estimation algorithms, e.g. zero forcing, and MMSE, which can be overcame by applying nonlinear channel estimation algorithms. Therefore, the alternating projection (AP) algorithm is back to our sights. Since an AP based channel estimation uses the unknown data symbols (blind) for channel estimation, the concern of pilot contamination is vanished. This paper deals with AP for Massive multi-input multi- output (MIMO) system with focus on the channel estimation mean square error (MSE) analysis. Through analytical results, we will show that an AP based blind channel estimation is biased at high signal to interference ratio (SIR) and tends to be unbiased at low SIR. The reason of biasing is that it estimates the channel and detects data for both the target user and the interfering users simultaneously, so the higher interfering power can benefit the detection performance. Simulation results further confirm the results.