A pilot contamination avoidance based on pilot pattern design for ultra-dense network

With the ever-growing number of base stations (BSs) and user equipments (UEs) in ultra-dense networks (UDN), reusing the same pilot sequences among the cells is inevitable. With pilot reuse scheme, the channel estimation obtained at a BS contains not only the desired channel-state information (CSI) but also interference from neighboring cells, which can severely degrade CSI estimation performance and adversely affect communication performance. In this paper we consider a pilot contamination avoidance based on pilot pattern design for UDN where the pilot reuse employed and the interfering users from neighboring cells may be not at lower power levels at the BS compared to the in-cell users. We present a novel statistical interference model of sub-carriers to describe the non-deterministic interference from neighboring cells. Then, we provide a pilot pattern design model with non-uniform pilot distribution. Based on this, a pilot contamination avoidance based on pilot pattern design is proposed where pilot reuse scheme and the non-deterministic interference from neighboring cells are taken into consideration. Unlike existing interference mitigation approaches, the proposed method eliminates interference through the method of interference avoidance and can be applied to different kinds of channel estimation algorithms. Simulation results showed that the proposed approach can effectively avoid the interference and ensure the accuracy of channel estimation.