Factor Graph based Equalizer for Two Way Relaying Channels with General Waveforms

Multi-carrier schemes with general waveforms are flexible bandwidth efficient transmission schemes offering a robust design regarding practical impacts like carrier frequency offset and timing offsets. Especially for two phase two way relaying channels (TWRC) where two users simultaneously transmit data on the same resources, a robust design in presence of practical constraints is important. This paper focuses on the equalization at the relay with factor graph based techniques reducing the impact of the physical channels and offsets. The combination of general waveforms and factor graph based equalizers offers a flexible structure giving control of the complexity and FER performance at the relay. Hence, we fully describe a TWRC transmission by factor graphs for general multi-carrier transmissions, which gives us a framework on iterative detection of the relay message based on the sum-product algorithm. It turns out that well localized waveforms applying a factor graph based equalizer outperforms OFDM w.r.t. FER performance under practical constraints.