Complex signal transmission for multi-user multiple-input multiple-output relay

A full-duplex wireless communications system is considered where K user wants to exchange common messages and private messages via a relay with multiple antennas simultaneously. The proposed scheme combines signal space alignment with zero forcing during multiple access channel phase and broadcast channel phase to cancel self-interference. The authors can achieve high degree of freedom by using successive network coding and aligning multiple interfering signals. The result is extended to a more generalised Y channel circumstance where they can transfer each message with different interference-free streams.