ABSTRACT
This chapter begins with the overview and key features of relay in LTE standardization, which can be considered as a predecessor technology of the RIS in 4G. Basic categories of LTE relay, such as a Type 1 relay and a Type 2 relay, are described with a certain level of detail. Then, another predecessor technology of the RIS – full-dimensional MIMO in LTE – is briefly discussed. The middle part of the chapter is spent on recent field trials of the RIS in commercial 5G networks are carried out in two cities of China, Nanjing and Shenzhen, respectively, where slightly different techniques of RIS beamforming were tested. Significant performance improvements in the RSRP, SINR, and data throughput were observed. In the end, the standardization road map for the RIS is outlined where lessons from the LTE era are considered, so that the multi-stage approach is suggested in a relay study and standardization in 3GPP.
