Heterogeneous ultra-dense network (HUDN) can significantly increase the
spectral efficiency of cellular networks and cater for the explosive growth of
data traffic in the fifth-generation (5G) communications. Due to the dense
deployment of small cells (SCs), interference among neighboring cells becomes
severe. As a result, the effective resource allocation and user association
algorithms are essential to minimize inter-cell interference and optimize
network performance. However, optimizing network resources in HUDN is extremely
complicated as resource allocation and user association are coupled. Therefore,
HUDN requires low-complexity but effective resource allocation schemes to
address these issues. Hypergraph theory has been recognized as a useful
mathematical tool to model the complex relations among multiple entities. In
this article, we show how the hypergraph models can be used to effectively
tackle resource allocation problems in HUDN. We also discuss several potential
research issues in this field