Densely deployed wireless networks provide one of the most important and sustainable solutions to improve the area spectral efficiency, and to handle the spectrum crunch expected by 2020. They are expected to have a huge economic impact, contributing to 5G small-cell technology, wireless sensor networks (WSN), machine-to-machine (M2M) communications, vehicular-to-vehicular (V2V) communications, and to public safety networks (PSN). However there are many serious technical issues identified in the implementation of these networks:

• Dense wireless networks are inherently interference limited environments, and for conventional network approaches the overall system throughput does not increase linearly with the size of the network. This effect has also been observed for the energy efficiency of conventional dense wireless networks.
• In some dense wireless networks such as M2M, V2V, and PSN, it is not always feasible to have accurate network planning and/or accurate link budget allocation due to their high demand to signalling overhead. In such cases reliable communications over unplanned dense networks becomes a significant technical issue to investigate.
• Increased density provides increased opportunities for user cooperation and networking. Advanced concept of opportunistic networking in heterogeneous networks becomes an interesting issue. On the other hand, security is an increasingly important issue in this new context.

One of potential solutions to these problems is low-complexity opportunistic node cooperation, which reduce the load of devices meanwhile utilising the advantages of route diversity in densely populated wireless networks. Moreover distributed self-organization algorithms have been intensively investigated to support robust and flexible distributed network optimisation. These concepts open a broad spectrum of research directions, standardisation paths and market opportunities, which will involve the relevant communities in both academia and industry arenas in the next decade.