“…Since the licensed spectrum (radio resource) is limited and costly, the co-channel assignment is more preferred by wireless network operators, but interference must be coordinated to fully enjoy its benefits. There are two types of co-channel interference, these are cross-tier interference (interference between macrocells and femtocells) and co-tier interference (interference between neighbouring femtocells) [17][18][19]. Moreover, the unplanned and ultra-dense deployment of femtocells that adopt cochannel resource assignment will lead to interference and throughput degradation considering different users with heterogeneous services, if radio resources are not efficiently allocated.…”