Radio efficiency enhancement schemes in heterogeneous networks

Abstract

With the increase in data traffic by a new generation of wireless devices, mobile users expect high data rate similar to a wired broadband network regardless of indoor or outdoor environments. Although wireless communication technologies have been evolved rapidly in order to meet high data rate with high level of service quality via MIMO (Multiple-Input Multiple-Output), carrier aggregation, multi-cell coordination, etc, it is expected that the demand of mobile users has surpassed it and is continuing to grow more rapidly. In addition, increasing data rate by increasing bandwidth and/or improving radio access technology (RAT) has a natural limitation due to limited radio resources. Therefore, improving reuse of radio resources is an attractive evolution for increasing spectral efficiency. The most promising way to increase reuse of radio resource is densifying the network with low-power small cells. In addition to a well-planned high-power macrocell, low power nodes such as picocell, femtocell, and relay are implemented throughout a macrocell area. These types of deployment are called heterogeneous networks (HetNet). Heterogeneous network can offer substantial increase in data rate by offloading traffic from the macrocell to the small cell with fully reused frequence resources, which results in improving spectral efficiency per unit area (bps/Hz/$m^2$). However, a transmit power difference between high-power and low-power cells is large enough to suffer severe interference between different cells. In addition, since the cell with the strongest received signal strength is generally selected as a serving cell, the number of users connected to the low-power cells is much smaller than that for the high-power cells due to large transmit power difference, which reduces cell splitting gain in heterogeneous network. In this dissertation, therefore, radio efficiency enhancement schemes for the heterogeneous network are investigated. Firstly, a cell selection scheme fo...