Two-Stage Time-Domain Pilot Contamination Elimination in Large-Scale Multiple-Antenna Aided and TDD Based OFDM Systems

Pilot contamination (PC) is a major impediment of large-scale multi-cell multiple-input multiple-output systems. Hence, we propose an optimal pilot design for time-domain channel estimation, which is capable of completely eliminating PC. More specifically, a sophisticated combination of downlink training and “scheduled”uplink training is designed with the aid of the optimal pilot set. Given the optimal pilot set, every user acquires its unique downlink time-domain channel state information (CSI) through downlink training. The estimated downlink CSIs are then embedded in the uplink training. As a result, PC can be completely eliminated, at the cost of a slight increase in training computational complexity. Our simulation results demonstrate the power of the proposed scheme. Most significantly, our scheme imposes a modest training overhead of (L + 3), training-phase durations corresponding to the number of orthogonal frequency division multiplexing symbols, where L is the number of cells, which is substantially lower than that imposed by some of the existing PC elimination schemes. Therefore, it imposes a less stringent requirement on the channel's coherence time. Finally, our scheme does not need any information exchange between base stations.