On 5G radio access architecture and technology [Industry Perspectives]

In early 2012, the International Telecommunication Union (ITU) under the United Nations initiated a program to develop an International Mobile Telecommunication (IMT) system for 2020 and beyond (IMT-2020), thereby officially kicking off the global race toward a yet to be defined fifth generation (5G) mobile network. Fast forward three years, the vision of this next-generation system is beginning to take shape. A recent ITU-Radiocommunication Standardization Sector (ITU-R) Draft Recommendation [1] on IMT-2020 identifies three key usage scenarios in 5G as enhanced mobile broadband, massive machine-type communications, and ultra-reliable and low-latency communications. The same report also issues guidance on the requirements for these scenarios in terms of performance index such as spectrum efficiency, latency, connection density, and area traffic capacity, as shown in Fig. 1. In order to meet these requirements and bring this visionary system to reality, we believe that the future 5G network will be one that is built on a small cell backbone. As spectrum suitable for mobile communication becomes more and more scarce, densification is the only way to meet the area traffic capacity demand. Even for millimeter-wave band, where spectrum is abundant, the channel's propagation characteristics will likely limit its range for mobile access to that of a small cell, at least in the early phase of 5G before device technology matures. The small cell also brings the radio access point closer to the end device, thereby shortening the last and most challenging segment of an end-to-end communication link, consequently reducing latency and increasing reliability. Many of the massive number of machine-type communications can also benefit from the extended battery life resulting from shorter uplink distance. To facilitate the deployment of a future mobile network that has the small cell as its primary traffic bearing workhorse,the current radio access architecture needs to undergo some major revamping, and new technologies need to be introduced.