  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
(MB) and small cell base stations (SB), 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 $L_T$ network, i.e., each
MT is connected to $L_T+1$ SBs. The SBs are assumed to be half-duplex, thus
restricting the per user degrees of freedom (puDoF) in the system to $1/2$. The
puDoF can be further restricted by the number of antennas at the MB. For $L_T
\in \{1,2\}$, the optimal puDoF can be achieved by using simple interference
avoidance schemes. The increase in the connectivity of transmission layer
beyond $L_T=2$ limits the achievable puDoF using only zero-forcing schemes to
less than 1/2, even in the presence of large number of antennas at each MB but
the optimal puDoF can be achieved by making each message available at multiple
SBs. This is done by sending an appropriate linear combination to the SB to
zero-force interference at the intended user. The maximum per user DoF of 1/2
can be achieved in the linear network with sufficient number of antennas using
only interference avoidance schemes. These results are also extended to a more
realistic hexagonal cellular model as well.
