Towards Green and Soft

Wireless communication systems have been developing from the first generation (1G) to the latest, fourth generation (4G) to satisfy ever increasing and more diverse mobile traffic demand. The thousand‐fold wireless traffic increase anticipated by 2020 and the global recognition of the importance of green communications, however, pose very tough challenges for fifth generation (5G) design. The design metric of spectrum efficiency (SE) maximization, which was highly emphasized in previous communication systems, will have to be jointly pursued with, amongst other metrics, energy efficiency (EE). In this chapter, we will describe green network design considerations from the perspective of network architecture, signaling and control, and high SE and EE transmission techniques. The motivations, requirements, and worldwide activities for green radio are introduced, and one particular EE and SE co‐design framework is presented for link‐level optimization. The impact of system parameters such as frequency bandwidth, total power, antenna number, and transceiver number on EE–SE performance is analyzed. Promising 5G technologies, such as large scale antenna systems and non‐orthogonal multiple access are investigated in terms of EE–SE co‐design. To satisfy user requirements, future networks should be user‐centric rather than cell‐centric, thus leading to 5G networks with “no more cells”. C‐RAN, a soft radio access architecture and an enabling element for 5G key technologies, is presented, describing how the baseband is centralized and virtualized to flexibly allocate resource and manage interference to save both radiated and circuit power. Since the future network will be more heterogeneous, with fluctuating traffic volumes and diversified services, a fundamental rethinking of signaling and control design in 5G is necessitated to facilitate energy saving. Finally, an aggregator‐based signaling optimization scheme that can accommodate trillions of wireless nodes in the Internet of Things is described. It is anticipated that 5G networks and beyond will be softer and greener.