MIMO relay channel signal transmission in transformed signal subspace

• Signal space alignment relies on more free antenna configuration condition.
• The unification of the signal processing method is proposed during MAC and BC.
• Improved signal space alignment fosters general transmission strategy knowledge.
• The transmission reliability of the relay system should be considered.

We design a new improved signal space alignment scheme in MIMO Y channel where one of K   source nodes sends K−1K−1 independent messages to the other nodes and each message achieves the degrees of freedom (DoF) of d  . The key is to let the messages to be exchanged by applying improved signal space alignment for network coding and interference cancellation when antennas configuration extends to N>2MN>2M, where N and M   denote the number of antennas at the relay and each source respectively. It is not feasible for the traditional signal space alignment to achieve the same DoF under this antenna number configuration. Moreover, we discuss the ill-conditioned channel to improve the system performance for Zero Forcing decoder. The simulations show that our proposed scheme achieves DoF of dK(K−1)dK(K−1) and improves system performance reliability.