Design of co-phasing allpass filters for full-duplex OFDM relays

This paper studies amplify-and-forward relaying of OFDM signals. In the considered cellular hotspot scenario, a destination node receives superposition of single-hop transmission from a source node and two-hop transmissions via full-duplex relays. We propose a novel co-phasing scheme that results in significant coherent combining gain in the destination due to subcarrier phase rotation in the relays. In full-duplex relays, the phase rotation is achievable by time-domain baseband filtering. Taking into account the properties of this particular application, we propose to use a complex FIR eigenfilter method for designing approximately allpass filters with desired phase response.