Keynote talk #1: Wireless evolution and challenges for 5G wireless networks

Wireless networks have evolved from the 1st generation (1G) using analog technology to the 2nd generation (2G) using digital technology, the 3rd generation (3G) and then to the 4th generation (4G) called LTE-A via 3.9G LTE. Every 10 years, new generation networks appeared. LTE-A networks provide a very high speed transmission of several 100Mbps. The mobile data traffic has been increasing rapidly by about two times per year owing to increasing popularity of broadband data services such as high quality video. Because of limited available bandwidth, the spectrum-efficiency has been the most important concern for the last few decades. The available energy, in particular for battery operated user terminals, is also limited. Therefore, the energy-efficiency has become an important concern. To improve the spectrum-efficiency and energy-efficiency simultaneously, the wireless networks need to be significantly restructured. One promising solution is an introduction of small-cell structured network. However, a wide range of user mobility is problematic; frequent handover will be caused. Traffic density is not necessarily high everywhere. Therefore, it is wise to keep the cell size the same as macro-cell networks while exploiting more non-uniform spatial distribution of users. We are recently investigating a virtual macro-cell network, where a virtual macro-cell is consisted of a macro-cell and many small-cells. There are two approaches to implement the small-cell layer: distributed small base stations and distributed antennas. In this presentation, we will overview the wireless evolution over the last 30 years. Then, we will discuss the technical issues for the realization of 5G wireless networks. There is the spectrum-energy efficiency tradeoff when using the frequency reuse. The spectrum-efficiency and energy-efficiency can be improved by adopting the small-cell structure. We will introduce a virtual macro-cell network implemented by distributed antennas. Finally, we will present some simulation results of the communications quality achievable with the virtual macro-cell network.