Cell-Free IoT With Non-Orthogonal Random Pilots: Key Research and Future Directions

With the proliferation of Internet of things (IoT) applications, the massive machine-type connections (MTCs) bring great challenges to traditional cellular networks, wherein cell-boundary devices with severe path-loss and inter-cell interference normally suffer from poor performance. By contrast, cell- free massive MIMO is a promising technique to support massive MTCs, since its user-centric architecture can shorten the distance between devices and access points, and boost the network coverage performance significantly. In this article, we first introduce the benefits and the main challenges of cell-free IoT with non-orthogonal random pilots. Then, we present the key research topics and several promising solutions for two typical IoT application scenarios: grant-based cell- free IoT and grant-free cell- free IoT. Some future research directions of cell-free IoT are also highlighted.