Downlink exposure reduction in dual-hop OFDM decode-and-forward relay systems

Dual-hop OFDM based decode-and-forward (DF) relay system is adopted as a solution for extension of coverage area and performance improvement in LTE-Advanced systems. While the benefits of dividing the communication link between the base station (source - S) and end-user (destination - D) through implementation of relay (R) station are clear, there is still a certain public concern about the exposure to electromagnetic fields (EMF) originating from R, as it is located closer to end-users than base station. Thus, in this paper we propose implementation of multiple antennas at R station and transmit antenna selection (TAS) on subcarrier basis in downlink (DL) communication for reducing exposure from R. We have developed simulation model for the proposed system, with real-case simulation parameters given in LTE-Advanced relay reference scenario. The results obtained for the system with 3 antennas at R, show that the proposed solution provides reduction for more than 36% of the power transmitted from R, and thus reduction in EMF exposure originating from R, compared to OFDM DF relay system without TAS, while keeping the same level of ergodic capacity.