Decoupled UL/DL User Association in Wireless-Powered HetNets With Full-Duplex Small Cells

In this article, we propose two downlink (DL)-uplink (UL) decoupled (DUDe) user association schemes in wireless-powered full-duplex (FD) heterogeneous networks (HetNets). We consider a two-tier HetNet comprising of half-duplex (HD) massive multi-antenna macrocell base stations (MBSs) and dual-antenna FD small cell base stations (SBSs) to support UL and DL transmissions of FD user equipments (UEs). Each FD UE is first associated to one MBS/SBS, based on the mean maximum received power (MMP) scheme or maximum received power (MRP) to harvest energy. During the consecutive data transmission phase, UEs choose to receive DL traffic from the same MBSs/SBSs as that associated with during energy harvesting phase, and send UL traffic through the same/another SBS. Leveraging tools from the stochastic geometry, we develop an analytical framework to analyze the average harvested energy and derive expressions for the UL and DL coverage probabilities of the proposed DUDe user association schemes. Our results show that there is an optimal value for the SBS density in the wireless-powered FD HetNets, at which both DL and UL coverage probabilities are maximized. Moreover, by applying MMPA and MRPA scheme, wireless-powered FD HetNets with DUDe achieves up to 138.78% and 83.37% energy efficiency gain over the FD HetNets with DL/UL coupled user association scheme and without wireless power transfer, respectively.