On the Sub-Terahertz 6G+ Cellular System Requirements for Near-Field Operation

Abstract

Seeking higher data rates at the air interface, prospective wireless communications systems will eventually occupy the sub-terahertz (0.1-0.3 THz) band. Due to the use of large antenna arrays, a part of the Base Station (BS) coverage will be located in the Near-Field (NF) region, where traditional beamforming is no longer optimal. Beamfocusing is considered a viable solution for NF communications; however, it requires highly accurate positioning techniques and timely feedback. The aim of this poster is to assess the system-level requirements for cellular systems in terms of positioning accuracy and feedback delay for beamforming and beamfocusing in the NF region. Using mean spectral efficiency as the metric of interest, we characterize the gains as a function of carrier frequency, positioning accuracy, and feedback delay. Our results show that efficient use of beamfocusing in the NF region requires positioning accuracy below 1mm and feedback delay below 0.1ms, which impose very stringent constraints on its support in future cellular systems and question its practicality. Instead, beamforming, although originally designed for Far-Field (FF) conditions, may be well-suited for NF due to its reduced sensitivity to positioning errors.