6G presents new opportunities to enrich the cellular ecosystem by introducing battery-less Zero-energy Internet of Things (ZE-IoT) devices, thus unleashing an era of massive, sustainable, and smart connectivity. This explains the increased interest in ZE-IoT in academia and industry. The road to a 6G future empowered by ZE-IoT entails cohesive efforts in the realm of standardization, academic research, and industrial trials, which are synergistic with the anticipated market demand and the dominant technology direction. In this article, we provide a holistic view of a 6G ZE-IoT future informed by the ongoing standardization activities in the 3rd generation partnership project (3GPP) for ZE-IoT, the role of the emerging technology trends such as digital twins and artificial intelligence, and the technical challenges in integrating ZE-IoT into the cellular ecosystem. Finally, we present some recent research results to address some of the discussed challenges.  

Backscatter communications can enable the proliferation of Zero-energy (ZE) Internet of Things (IoT) services in 6G, ushering in a new era in green communications. To achieve a widescale adoption, backscatter communications needs to be integrated into the cellular ecosystem. This motivates the need to design a bistatic backscatter modulation technique which is not only compatible with the 3GPP New Radio (NR) physical layer but also robust to direct link interference. In this paper, a non-ambient bistatic backscatter communications system consisting of a cellular carrier emitter (CE), a backscatter device (BD) and a cellular reader (RD) is investigated. An analytical model is presented to explain the design rationale for an orthogonal frequency division multiplexing (OFDM) based physical layer for the considered system. Specifically, to achieve orthogonality between the CE and BD signals arriving concurrently at the RD, a comb-like OFDM subcarrier allocation is leveraged at the CE while a specially designed impedance switching sequence is applied at the BD to generate OFDM-compatible backscatter symbols with a binary or higher-order phase shift keying modulation. The link performance of the proposed system is evaluated in terms of the achievable bit error rate versus the signal-to-noise ratio at the RD for the CE-RD link and the BD-RD link under direct link interference. Simulation results confirm the viability of the proposed design for a cellular ZE-IoT system.