Introduction

The fourth generation (4G) standardization and the ongoing worldwide deployment of 4G cellular network is maturing. However, with an explosion of wireless mobile devices and services, there are still some challenges that the 4G physical layer technologies cannot be accommodated. Technologists worldwide, thereby, have begun searching the 5G physical layer technologies to meet the anticipated demands in the 2020 era. The recently emerging index modulation appears as a promising candidate. In this chapter, first, we briefly address the 5G demand and identify key challenges. Then, we introduce the history of index modulation, mainly focusing on the space, space-time, and frequency domains realizations. Finally, the organization of this monograph is given at the end of this chapter.