Cell Identification Performance Optimization in Co-Channel Heterogeneous Cellular Networks Employing CRE Based on a Hierarchical Synchronization Signal Structure

摘要

Recently, data traffic has been explosively increasing in mobile communication due to the prevalence of smart phones. A co-channel heterogeneous cellular network (HetNet), in which small-cell base stations (S-BSs) with low transmission power are placed at the hot spot area of a macro-cell base station (M-BS) with a high transmission power and S-BSs use the same carrier frequency as M-BS, has been receiving attention in order to deal with the increasing traffic. In general cellular systems, synchronization signal (SS) symbols for the cell identification at user equipments (UEs) are periodically transmitted from each base station (BS). For HetNet, Cell Range Expansion (CRE), in which a bias value is added to the reference signal received power from S-BSs, has been investigated as a promising approach to offload the traffic into small cells from macro-cells. However, there is an issue that the cell identification performance at small-cell area degrades with the CRE bias value, since larger CRE bias value suffers from larger interference from M-BSs at the received SS symbols transmitted from S-BSs in the small-cell area expanded by CRE. In our previous work, we proposed a performance improvement scheme on small-cell identification possible with synchronization signal power boosting (called SSPB) at S-BSs for HetNet employing CRE. Unfortunately, the proposed SSPB suffers from a trade-off issue of improving the cell identification performance between macro-cell area and small-cell area. Then, this paper investigates a transmission power optimization of the SS symbols in co-channel HetNet employing CRE based on a hierarchical SS structure. The authors evaluate the cell identification performance when applying SSPB. And then, they evaluate its quality with a parameter of the power boosting value of SS symbols for various CRE bias values, and clarify that the optimal transmission power boosting value of the SS symbols at S-BSs is almost the same as the CRE bias value.