DoF Analysis in a Two-Layered Heterogeneous Wireless Interference Network

TL;DR

This paper analyzes the degrees of freedom in a two-layered heterogeneous wireless network, showing how interference management strategies affect the maximum achievable data rates under different connectivity and antenna configurations.

Contribution

It introduces new interference management schemes that optimize per user degrees of freedom in complex two-layered wireless networks with varying connectivity.

Findings

Optimal puDoF of 1/2 achieved with simple schemes for L_T=1,2

Increased connectivity beyond L_T=2 limits zero-forcing schemes, but optimal puDoF can be restored with message sharing

Maximum per user DoF of 1/2 achievable with sufficient antennas using interference avoidance

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 (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.