Cooperative multi‐cellular large MIMO over asynchronous channel training

Abstract

SummaryThis work analyzes multi‐cell MIMO systems equipped with a very large number of antennas in the base‐station (BS) side and with low‐complexity zero‐forcing and matched‐filter receivers. Cooperation between BSs in a multi‐cell scenarios is analyzed in order to avoid the well‐known pilot contamination effect on massive MIMO systems, while the effects of asynchronism between users and BSs in training phase using different pilot sequences, for example, Walsh–Hadamard, Gold, and Kasami sequence sets on the system performance are examined. As low‐complexity processing is deployed, the synchronism offset in training phase may introduce errors on the channel estimation process, adding its effect to the pilot contamination, resulting in an aggressive detection scenario. Numerical results using the BER as a performance figure of merit measure in downlink have corroborated our finding. It was also developed an analytical error formula for channel estimation subject to synchronization offset levels in terms of fractional unit of symbol time duration, which was validated through channel mean squared error and BER performance simulation results. Through these both performance figures and under practical scenarios, the use of pseudo‐random sequence sets may be preferable instead of orthogonal ones, mainly because of their out‐of‐phase cross‐correlation levels. Copyright © 2015 John Wiley & Sons, Ltd.