Coordinated multi-cell multi-user pilot allocation in massive MIMO systems with time-shifted pilots

In this paper we consider the problem of pilot contamination reduction in time division duplexing (TDD) cellular networks with large antenna arrays at each base station. Shifting pilot locations in time is an effective way to obtain better channel estimation and therefore reduce inter-cell interference. We study the method further, and propose a low-complexity time-shifted pilot allocation algorithm performing joint cell and user allocation. We show that the algorithm achieves a coordination gain over the original frequency-reuse-like pattern in terms of spectrum efficiency, and greatly reduces computational complexity compared with the exhaustive method used to obtain the optimal solution.