Time-shifted pilots multiplexed with uplink data and unequal power allocation

Abstract

Pilot contamination has been identified as one of the main limitations for massive MIMO. In this work, we consider to reduce pilot contamination by having time-shifted non-overlapping uplink pilot transmissions in neighboring cells, which are time-multiplexed with the uplink data transmission. As simply shifting the pilots will not avoid the pilot contamination, we propose an unequal power allocation between the pilot and the uplink data transmission. We show that the proposed approach with an optimum power allocation between the pilot and uplink data transmission is able to mitigate pilot contamination and achieve significant gains compared to related schemes. Furthermore, lower bounds of the uplink and downlink sum rate with the proposed scheme are provided, which can be employed for obtaining the optimum power allocation.