On the sum DoF of the asymmetric four-user MIMO Y channel
Kangqi Liu, Meixia Tao · 2016
This work studies the sum degrees of freedom (DoF) of the asymmetric four-user MIMO Y channel, where each user i, for 1 ≤ i ≤ 4, is equipped with Mi antennas, and the relay is equipped with N antennas. By using the genie message approach, we derive that the sum DoF is upper bounded by min {Σi=14Mi, 2 Σi=24Mi, 2N, 2/7 Σ∀i,∀j>imax{N, Mi+ Mj} }, where M1≥ M2≥ M3≥ M4. Then, we show that the bound is tight under certain antenna constraints using signal alignment, generalized signal alignment, and antenna deactivation techniques.