The mobile hotspot network (MHN) system is a system for high-speed railway communications capable of providing a gigabit-per-second backhaul capacity employing millimeter-wave. This paper provides an overview of MHN enhancement (MHN-E) system that's been developed so far, and also addresses some of the major technical challenges that need to be overcome and discuss several viable technical solutions for further enhancements. One of the most important goals in the development of the MHN-E is to further increase wireless backhaul capacity and improve its reliability compared with the first version of the MHN system, which will meet the high-speed-related requirements set by ITU for IMT-2020 or 5G.