Models of Radio Propagation in Indoor/Outdoor Environments: Past Efforts and Future Challenges

A fundamental approach in the optimal design of wireless communication systems is a proper comprehension of radio wave propagation through wireless channels. As wireless communications become more ubiquitous, new propagation environments emerge, and the propagation mechanisms therein are being constantly investigated. The objectives of this chapter are twofold. Firstly, to give a succinct review of new and emerging complex environments that require fine-tuning of the propagation models since traditional propagation models that simplify the propagation environment by ignoring the small and fine structures are no longer valid for such complex environments. Secondly, to explore the blossoming field of machine learning and probe its feasibility for propagation modeling. For this purpose, we have selected three cities for an initial study, namely, Munich, Paris, and Singapore. Field-measurement results and ray-tracing simulation were compared to our proposed machine-learning results for these cities. Very promising outcomes emerged. As a way forward, we foresee that machine learning and artificial intelligence will be incorporated a lot more in propagation modeling and prediction for the design of next-generation communication systems.