DoF analysis in a two-layered heterogeneous wireless interference network

Abstract Degrees of freedom (DoF) is studied in the downlink of a heterogenous wireless network modeled as a two-layered interference network. The first layer of the interference network is the backhaul layer between macro base stations (MBs) and small cell base stations (SBs), which is modeled as a Wyner type linear network. The second layer is the transmission layer between SBs and mobile terminals (MTs), which is modeled as a linear Wyner LT network. The SBs are assumed to be half-duplex, thus restricting the per user degrees of freedom (puDoF) in the system to 1/2. It is established that the optimal puDoF of 1/2 can be achieved in the linear network with sufficient number of antennas using only interference avoidance schemes. For the case of higher connectivity in the transmission layer, it is shown that the optimal puDoF is achieved by sending an appropriate linear combination to the SB to zero-force interference at the intended user. These results are also extended to a more realistic hexagonal cellular model