This paper introduces the general landscape of next?generation wireless communication systems (5G), including the impetus and requirements of 5G and the candidate technologies that might help 5G achieve its goals. The following areas, which the author considers particularly relevant, are discussed: detection of and access to free spectrum over bands of a heterogeneous nature, ex?treme densification of networks (massive base station deployments), extreme increase in the number of antennas in base station ar?rays and their interaction with a novel waveform, integration of both wireless and optical sides of telecom networks, and study of wireless networks from the perspective of complex systems science. The author discusses recent research conducted by his team in each of these research areas.