Ambient IoT (A-IoT) is an emerging paradigm that enables connectivity for IoT devices powered by ambient energy harvesting or radio frequency wireless power transfer (WPT). This survey provides a holistic and detailed overview of the technology landscape, starting with device classification and environmental impact, and moving on to use cases and ongoing standardization efforts in 3GPP, IEEE, and ETSI. It reviews the technological building blocks of A-IoT devices, including energy harvesting and power management circuits, low-power wake-up and backscatter radios, and approaches for on-device and edge intelligence. At the network level, the paper explores architectures and protocols for WPT, low-power protocols for both backscatter and active communication, solutions for resource management, and A-IoT security protocols. Practical insights are drawn from experimental testbeds and real-world deployments. Finally, the survey outlines major research directions, from scalable WPT and interoperable protocols to context-aware scheduling, lightweight security, and reproducible field trials. This work provides a roadmap for researchers and industry to advance A-IoT as an integral part of future 6G networks.
Security of data transmitted over wireless links is typically dependent on bit-level encryption performed by higher layers of the network stack. This typically involves encryption keys exchanged between the communicating entities as part of an authentication process. The authentication process in a cellular network starts with the transmission of the international mobile subscriber identity (IMSI), which is not encrypted. This is followed by an authentication request and authentication response based on a mutually known secret code associated with the IMSI. An advancement in 5G NR is that the IMSI is replaced with SUCI (Subscriber concealed Identity) which is the encrypted version of the IMSI. With recent advancements in computing power and resources, the probabilities of breaching the authentication process and the consequent vulnerabilities to interception, denial of service and breach of data security have increased multi-fold. Proliferation of IMSI/SUCI catchers and man-in-the-middle interceptors devices enable spoofing and denial of service capabilities to even novice hackers. One of the ways to enhance the security of data over in the presence of adverse nodes is to tighten the authentication process based on logs of past events in encrypted formats, similar to multi-factor authentication used by financial institutions. One of the aspects in wireless communications that cannot be cloned with ease is the physical air interface, whose parameters are exchanged between the network and the user equipment. In this paper, we propose a novel enhancement to the authentication scheme by complementing the exchange of existing authentication parameters with cryptographic hashes of PHY parameters from previous connections. The exchange of hashes does not expose the hidden history owing to their irreversibility but verifies the authenticity of the peer node hereby increasing resilience to spoofing and man-in-the-middle interception.
Ambient Internet of Things (A-IoT) targets energy harvesting (EH), battery-less devices as a simple connectivity solution for extensive ultra-low-power deployments. These devices typically face intermittent energy availability, making uplink reports increasingly susceptible to access collisions and energy outages. In this paper, we build upon the cellular standardization of A-IoT and examine the paging-triggered contention-based random access (CBRA) framework for uplink reporting. We analyze the effects of energy availability and collisions on these systems and introduce an EH-aware access control mechanism. In this mechanism, the reader broadcasts an access probability in the paging message, which helps regulate the number of devices attempting random access. Results show that, unlike the baselines, the proposed method scales well under dense deployments by keeping collisions nearly constant, improving access efficiency, and substantially reducing the number of paging rounds required for successful reporting. These results highlight the importance of lightweight reader-side access control for reliable and resource-efficient reporting in A-IoT environments.
This paper presents a technique to implement a wideband Doherty Power Amplifier using stacked patch antenna as the combiner cum radiator. A Schiffman phase shifter is employed to accomplish the quadrature phase relationship between the peaking and carrier amplifiers at the antenna's feeding ports. This approach enables the co-design of the antenna and amplifier, allowing both to be integrated on the same substrate. The proposed structure reduces system complexity and footprint. This compact and high-performance solution is suited for next-generation wireless communication systems.
