Chapter 33: Beyond 5G / 6G Vision

Learning Objectives

• Describe the 6G spectrum vision from FR3 (7-24 GHz) through sub-THz (100-300 GHz) and articulate the propagation, regulatory, and hardware trade-offs at each frequency tier
• Explain the architectural pillars of 6G networks including Open RAN disaggregation, AI-native air interface design, and non-terrestrial network (NTN) integration with LEO/HAPS platforms
• Derive the Rayleigh distance $d_R = 2D^2/\lambda$ and analyse the transition from far-field beamsteering to near-field beamfocusing for XL-MIMO arrays, including spatial non-stationarity effects
• Analyse in-band full-duplex transceiver design by quantifying self-interference cancellation across propagation, analog, and digital domains and evaluating the resulting rate gain over half-duplex
• Formulate the over-the-air computation (AirComp) framework for function aggregation over a multiple-access channel and characterise the MSE under channel misalignment and noise
• Describe how site-specific digital twins combine ray tracing with machine learning to enable predictive network management, and connect this to integrated sensing and communication (ISAC)