An asymmetric TDD distributed massive antenna system

To meet the increasing demand for high spectrum efficiency (SE), the distributed antenna system (DAS) is a promising approach. In DAS, multiple antenna ports (APs) are deployed at geographically separated locations but a central unit (CU) handles the signal processing. To further boost the SE, a massive antenna system (MAS) can be deployed at each AP. In this paper, we consider deploying MAS at each AP of a DAS. To effectively reduce the inter-AP interference, we further propose an asymmetric time division duplex (TDD) transmission scheme in which some APs are in downlink mode while the others are in uplink mode. This asymmetric TDD takes the advantage of centralized signal processing in DAS. Through computer simulation, we show the asymmetric TDD assignment provides higher SE than the symmetric TDD assignment. We also consider the deployment of massive antenna system (MAS) at each AP to boost the SE of DAS. The computer simulation shows that the asymmetric TDD-DAS increases 10% aggregate downlink (uplink) rate by around 50% (35%) compared to symmetric TDD-DAS when each AP is equipped with 16 antenna elements.