LTE Advanced: 3GPP Solution for IMT-Advanced

8.1 Introduction

The traffic volumes in mobile broadband networks have increased considerably during recent years and this growth is expected to continue. While network capacity can be increased through transmission schemes achieving higher spectral efficiency or by using more spectrum, as addressed in previous chapters, the most straightforward approach is to deploy more base stations. With more base stations, radio resources can be reused more often per area, effectively increasing the spectral efficiency per area. Naturally, a mobile network operator will gradually deploy additional base stations where the traffic demand is highest, and choose antenna configurations and transmit powers in order to optimally complement the existing cell infrastructure at minimized cost. This typically leads to network configurations with a co-existence of large base stations and new smaller base stations. In addition, the evolution of networks will lead to a co-existence of different Radio Access Technologies (RATs), such as GSM, WCDMA/HSPA and LTE/LTE-Advanced. Constellations of multiple kinds of base station sizes (so-called layers) and multiple RATs are often referred to as heterogeneous networks (HetNets), which are to be addressed in this chapter.

What makes small cells particularly attractive is that their cost of hardware is lower than that of large cells, which are typically referred to as macro cells, and technology evolution further pronounces this trend. The reason is that digital ...