Ambient IoT — Battery-Free Devices Explained

Ambient IoT (A-IoT), sometimes called zero-energy IoT, is one of the most striking ideas feeding into 6G: tiny devices that run with no battery at all, powered entirely by energy harvested from their surroundings. This page explains what they are, how they work, the network architecture 3GPP has defined, and where they fit.

Status: Ambient IoT reached its first normative release in 5G-Advanced (Release 19), building on a Release 18 study. Release 20 continues the work, and the concept is a central design goal carried toward 6G.

What an ambient IoT device is

An ambient IoT device is an IoT device powered by energy harvesting — either completely battery-less or with only a small store such as a capacitor. The energy comes from radio waves, light, motion, heat, or similar ambient sources. Compared with earlier low-power IoT devices, an ambient IoT device is simpler, smaller, cheaper, and lower-power, carries only small amounts of data, and is designed for maintenance-free operation at massive scale.

The defining constraint: the network cannot assume the device is powered at any given moment. It communicates only when it has harvested enough energy. That single fact reshapes how the protocols are designed.

How it is powered

3GPP describes two harvesting modes:

Continuous harvesting — the device regularly receives enough ambient energy (for example, a light-powered sensor in daylight).
Incidental harvesting — energy is available only when the event the device must report occurs (for example, a vibration sensor that harvests from the vibration it detects).

Some devices can also be powered on demand, energised by radio waves beamed from the network, which makes passive tags predictable to interact with.

How it communicates: backscatter

The zero-energy trick is on the uplink. Instead of generating its own signal (which costs power), the device reflects and modulates an incoming carrier wave — a technique called backscatter. This device-to-reader path needs almost no energy. In the other direction, the reader-to-device path uses a simple on-off-keying waveform aligned with the normal NR structure, so a device only has to detect the presence or absence of energy — again, cheap to do.

Devices range from fully passive (backscatter only, no storage) through semi-passive (a small capacitor buffers energy for more reliable reception) to more capable variants aimed at sensor and actuator tasks.

The network architecture

The key innovation is turning the base station into a reader:

The reader (in this release, a gNB-reader) is the active network-side transceiver. It sends the reader-to-device waveform — which also energises passive devices — and receives the backscattered responses.
A gNB can serve one or more readers; each reader belongs to one gNB. Readers map to A-IoT Areas, so operations can be scoped geographically.
A new core function, the Ambient IoT Function (AIOTF), orchestrates the service. The base station connects to it either directly or indirectly via the access-and-mobility function (AMF), which forwards the ambient-IoT information transparently.

What it does: the two main procedures

Inventory — the network discovers which devices are present in an area. It triggers a broadcast, and devices in range respond with their identifier and optional status, measurement, or location data.
Command — the network sends a targeted instruction to one or more devices (for example, trigger an actuator or change a setting).

Where it is used

Typical use cases span logistics, retail, industry, agriculture, healthcare, and smart cities:

Inventory taking — discovering boxes, containers, tools, or packages in an area.
Sensor data collection — reporting readings such as temperature or pressure.
Asset tracking — locating goods, sometimes with a capable handset acting as a local reader.
Actuator control — network-initiated commands to simple actuators.

Reference points (3GPP)

TR 38.848 — the ambient power-enabled IoT study.
TS 22.369 / TS 22.261 — service requirements for ambient IoT.
TS 23.369 — the system architecture (the AIOTF and procedures).
TS 38.300 §16.23 — the radio interface and RAN architecture.

In short

Ambient IoT removes the battery — the biggest barrier to deploying sensors at enormous scale — by harvesting energy and using backscatter to communicate. First standardised in 5G-Advanced, it is a foundational building block for the extreme device density that 6G targets.