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.

Multi-cell massive MIMO transmission with coordinated pilot reuse

In this paper, we propose a coordinated pilot reuse(CPR) approach to reduce the pilot overhead for multi-cell massive multi-input multi-output transmission. Unlike the conventional multi-cell pilot reuse approach in which pilots can only be reused among different cells, the proposed CPR approach allows pilots to be reused among both inter-cell and intra-cell user equipments, and thus, pilot overhead can be efficiently reduced. For spatially correlated Rayleigh fading channels, we first present a CPR-based channel estimation method and a low complexity pilot allocation algorithm. Because CPR might lead to additional pilot interference, we develop a statistically robust uplink receiver and downlink precoder that takes channel estimation errors into account. The proposed uplink receiver and downlink precoder are robust to channel state information inaccuracy, and thus, can guarantee a certain transmission performance. Monte-Carlo simulations illustrate the significant performance improvement in net spectral efficiency offered by the proposed CPR approach.