According to the International Telecommunication Union (ITU), the current 5G scenarios can be divided into three categories: enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Hotspots (indoor/outdoor), wide-area coverage, and high speed are typical use cases. Performance measures of human-centric communications such as the ultimate user experience are primary targets in the eMBB scenario. Use cases of mMTC include the monitoring and automation of buildings and infrastructure, smart agriculture, logistics, tracking, and fleet management. A high connection density, low complexity and cost, and long battery life are essential objectives in the mMTC scenario. There are many representative use cases related to URLLC, such as remote machinery and intelligent transportation systems. Low latency and high reliability are key points that need to be taken into account in the design of the radio technology in order to solve the problem of the specific requirements of URLLC scenarios.
Rethinking the Fundamentals for 5G Systems
The 5G network is anticipated to be soft, green, and superfast . To meet the critical requirements for various scenarios, it is simply not enough for 5G to evolve from current fourth generation (4G) systems. Rather, it requires a revolutionary path. In [2–4], it was proposed to rethink the fundamentals from seven perspectives, such as architectures, protocols, and functions, to revolutionarily redesign future 5G networks, including:
1. Rethinking Shannon, which is to take a green metric such as the energy efficiency as a key performance indicator of wireless systems.
2. Rethinking Ring and Young, which is to break the boundary of conventional cells. As we move toward the timeline of 2020 with the introduction of heterogeneous networks (HetNets) and ultra-dense networks (UDNs), multiple layers of radio networks have come into being.