Editorial

The world has been facing the problems of unprecedented urbanization, especially in developing countries. At the time of writing, 54% of the world population lives in cities due to multiple economic advantages in a very efficient form of social organization, and this number is expected to reach 66% by 2050. The centralized proliferation of job opportunities and skilled citizens on a relatively small geographical area (i.e., 2% of the earth’s surface), which enables scale economies on infrastructure and service provision, reducing costs in transportation, energy, communications and social interactions; poses an obvious emerging challenge of resource access and supply management that obstructs their growth and development in the context of smart cities. Smart cities have become emerging innovation of institutions, entrepreneurs, technology enterprises, and governments. A Bsmart city^ is established relying on both the outstanding infrastructures (e.g., buildings, transportation, and health and education systems) and modern information and communication technologies (ICT) where wireless communications and networks play an important intermediate role to connect smart things (e.g., objects, people, and sensors) together and to the Internet. Wireless communications and networks based smart cities can provide advanced services such as e-services (e.g., health, earning, commerce, and government), security and safety, real-time traffic monitoring, and resource and environment management, etc. Considering the significance of wireless communications and networks for realizing the vision of smart cities, it is still complex and farreaching development with many challenges in terms of design, optimization, standardization, and sustainability. And thus, there is a need for conducting research on further solutions to smart cities assisted wireless communications and networks. This special issue focuses on overcoming the aforementioned challenges of wireless communications and networks for smart cities. The special issue includes seven selected papers with high quality. In the first paper entitled BCognitive Heterogeneous Networks with Unreliable Backhaul Connections^, the authors studied the impact of cognitive spectrum sharing over multiple small-cell transmitters. Many important system performance metrics, i.e., outage probability, ergodic capacity, symbol error rate, and related asymptotic expressions, have been derived exactly to evaluate the considered system. Numerical results provide a proper framework for network designers to clearly understand the effects of unreliable backhaul links and how to enable the cognitive radio networks for those cooperative transmitters in order to efficiently utilize the spectrum. The second paper is abo ut BA Mobility Solution for Hazardous Areas Based on 6LoWPAN^. In particular, a decentralized approach for mobility management of mobile nodes in hazardous areas has been proposed to organize static nodes as a tree for an efficient routing, automatic addressing, and handling the movement of mobile nodes. The objective is to gain high coverage of monitoring area at high number mobile nodes by handling multiple failures of static nodes that disconnect a mobile node from the network. This novel decentralized scheme for monitoring safety critical environment can be applied to health care applications in many factories in smart cities. Because the proliferation of mobile devices and base stations in wireless communication systems causes the problems of energy consumption and security capacity, the authors of the third paper BSecure Energy Harvesting Communications with Relay Selection over Nakagami-m Fading Channels^ investigated an energy harvesting relay system over Nakagami-m fading.