Research On Load Balance And Enhanced Inter-Cell Interference Coordination In LTE-Advanced Heterogeneous Networks

The traditional cellular networks consist of homogeneous macro base station, and mainly provide the macroscopic coverage and outdoor coverage. This network structure may cause some problems such as signal blind area, poor indoor signal, and overload at the hotspots. Hence, LTE-Advanced introduces heterogeneous networks as a solution to these problems which employ low power nodes, such as pico-cells, femtos, relays, and remote radio heads(RRHs) along with macros.In heterogeneous networks, because of the much higher transmit power of macros than the pico-cells’, the majority of UEs will access to the macros if the traditional maximum Reference Signal Received Power(RSRP) cell selection strategy is applied. LTE-A introduces Cell Range Expansion(CRE) to extend the coverage of the pico-cells by adding an positive bias on the RSRP of pico-cells before UEs choose their serving cells. CRE can reduce the huge load gap between the macros and the pico-cells by offloading more UEs to the pico-cells.However, the UEs in the extend areas will suffer strong interference from macros. Thus LTE-A introduces enhanced Inter-Cell Interference Coordination(e ICIC), which includes three solution schemes, i.e., time-domain e ICIC, frequency-domain e ICIC, and power-setting. Time-domain e ICIC sets some of the macros subframes to be Almost Blank Subframe(ABS) in which the macros stop data transmission, while the pico-cells schedule UEs suffering serious interference in corresponding subframes to improve their performances.In order to balance the load and manage the interference in heterogeneous networks, we jointly optimize the UEs’ cell selections and the ratio of ABS to maximize the sum logarithmic throughputs of the UEs. We propose an effective algorithm and compare it with Low Power ABS through simulations. Finally, we provide a solution for jointly optimizing load balance and time-domain e ICIC in heterogeneous networks.