In future networks, an operator may employ a wide range of access pointsusing diverse radio access technologies (RATs) over multiple licensed andunlicensed frequency bands. This paper studies centralized user association andspectrum allocation across many access points in such a heterogeneous network(HetNet). Such centralized control is on a relatively slow timescale to allowinformation exchange and joint optimization over multiple cells. This is incontrast and complementary to fast timescale distributed scheduling. A queueingmodel is introduced to capture the lower spectral efficiency, reliability, andadditional delays of data transmission over the unlicensed bands due tocontention and/or listen-before-talk requirements. Two optimization-basedspectrum allocation schemes are proposed along with efficient algorithms forcomputing the allocations. The proposed solutions are fully aware of trafficloads, network topology, as well as external interference levels in theunlicensed bands. Packet-level simulation results show that the proposedschemes significantly outperform orthogonal and full-frequency-reuseallocations under all traffic conditions.
展开▼