Channel estimation using time-shifted pilot sequences in non-cooperative cellular TDD networks with large antenna arrays

Inter-cell interference is a challenging issue in noncooperative time-division duplex (TDD) cellular systems with large antenna arrays. Such a problem arises when pilot sequences received by a base station (BTS) are contaminated by users in adjacent cells transmitting the same training sequences. In [7], Fernandes, Ashikhmin and Marzetta proposed a time-shifted scheme in which the transmission of pilots is shifted in time from one cell to the next, avoiding overlap, thus completely cancelling interference from inter-cell users in their asymptotic analysis. However, a specific question was raised by the authors: Can a BTS obtain an accurate estimate of the channel vector in the presence of strong downlink signals from adjacent cells? In this paper we answer positively to this inquiry. In order to do this, firstly, we propose a modification to the proposed scheme in [7] in order to implement a robust estimation technique which uses both the pilot sequence as well as the uplink information to obtain the desired channel coefficients. Secondly, we assess the sensitivity of the system to the received downlink signals of the interferers and to the length of the training sequence.