Abstract
Integrating the ultra-high capacity millimeter wave (mmWave) band into the existing cellular network is one of the main challenges towards a unified multi-Gbps 5G network. In this paper, a novel hierarchical multi-band heterogeneous network (HetNet) is proposed to efficiently overlay mmWave small cells (SCs) over the legacy LTE eNB. By which, a medium coverage band is used to precisely control the access over the small coverage mmWave band via the proposed concept of sub-clouds; while, the large coverage LTE eNB only controls the access over the distributed sub-clouds. Without loss of generality, Wi-Fi band is used as the medium coverage band in this paper. Consequently, a novel concept of 2C/U plane splitting is introduced. The Cl plane carried by the LTE eNB controls the access between the LTE eNB and the sub-clouds. Whereas, the C2 plane carried by the medium coverage (Wi-Fi) band controls the access among the mmWave SCs inside each sub-cloud. By this distributed control, associated signaling/processing load on both core network (CN) and LTE eNB can be highly relaxed. Analytical and numerical analysis confirm performance superiority of the proposed LTE/WiFi/mmWave HetNet over the conventional LTE/mmWave HetNet in terms of handover (HO) signaling delays and mmWave band usability.