Pilot hopping in massive MIMO systems with MMSE channel estimation

Next generation wireless promises high data rate using advanced MIMO techniques. Large-Scale antenna system, or massive MIMO, has been proposed as a strong candidate for broadband next generation wireless applications. However, pilot contamination is one of the major challenges that limits the promised massive gains. In this paper, a new pilot assignment procedure is proposed to mitigate the pilot contamination problem. The assignment algorithm performs pilot reuse strategy and pilot hopping across multiple time slots during the channel coherence time. The goal is to randomize the contaminating users experienced by each user so that the interferences (and noise) are averaged out and thus increase the cell throughput. We show that this randomization can be made in a structured manner and that pilot reuse strategy has to be carefully designed in order to achieve high throughput. The covariance matrix of the channel estimation error using MMSE channel estimation is obtained.