Channel modeling for reflective phased array type RISs in mmWave networks
This paper presents and overview, challenges and some recent results on channel modeling of the phased array type reconfigurable intelligent surfaces (RISs) in the millimeter Wave band (mmWave, 30‐300 GHz) networks. The RISs have been under intense investigation lately for their ability to provide control on the mmWave sparse channels. This has been shown to improve the coverage and signal power levels in environments where line-of-sight (LoS) paths cannot be guaranteed. The gain properties of RISs in LoS channels are analyzed with respect to carrier frequency and the size of the RIS. It is shown that the RISs provide the best gain compared to LoS links at lower frequencies due to the larger RIS sizes for a fixed number of antenna elements. On the other hand, high gain RISs tend to push the near field far away from the array in the low frequencies. These observations mean that different parts of the mmWave band have advantages and disadvantages when utilizing RIS assisted channels.