Investigation of dual-polarization antenna scheme in TD-LTE systems

Abstract

Downlink beamforming technology has been adopted in time division long term evolution (TD-LTE) systems as a promising scheme to exploit array gains and diversity gains by the development of uplink-downlink reciprocity at the base station (BS). Downlink beamforming is typically utilized with closely spaced uniform linear array (ULA) at BS where high channel correlation is achieved between antennas. Significant promotion of spectrum efficiency and transmission reliability is provided by this scheme; however, the large span of eight-element antenna array will take tremendous cost on the deployment of BS, which is not encouraged to be applied in the future LTE architectures. In comparison with ULA (also called co-polarization), dual-polarization scheme has two groups of antenna arrays which are configured on different polarization planes, and each group owns one half of antenna elements compared with ULA antenna array. It could not only reduce the installation cost and the size of BS equipment, but also provide multiplexing gains. The authors in [1] and [2] analyzed the performance of dual-polarization in TD-SCDMA and TD-HSPA+ systems, respectively. To our best knowledge, however, there is no literature emphasizing on the impact of dual-polarization scheme on the cellular performance in TD-LTE systems. In this paper, we first investigate the downlink beamforming technology in TD-LTE, which includes single-layer and dual-layer transmission. Then the channel model for dual-polarization antenna is developed to derive the expression of downlink channel response. The performance of single-layer and dual-layer beamforming is evaluated by the system level simulation for dual-polarization and ULA in various scenarios. According to the simulation results, the performance of dual polarization array is worse than that of ULA in single-layer transmission, while the former outperforms the latter in dual-layer and rank adaptation transmission modes in the scenario of small cell radius. The performance of dual-polarization declines drastically when the cell radius increases, and therefore it is not preferable to be applied to serve the users at the cell edge.