Ambient IoT (A-IoT), aiming to connect hundreds of billions of ultra-low-power and battery-free devices, has been included in the agenda for 5G-A and 6G standardization by 3GPP 1-2. Ultra-low-power means the capability of maintenance-free operation for years. 3GPP technical report provides A-IoT's application scenarios such as automated warehousing, electronic shelf labels, forest fire monitoring, and smart farms. These crucial applications require key performance indicators (KPIs) including: (1) The power consumption shall be less than 1μW for passive devices (battery-free) and 1~100μW for semi-passive devices (no battery replenishment) to minimize maintenance cost. (2) The communication range of both downlink and uplink will be tens to hundreds of meters to cover most indoor and outdoor applications. (3) The network will support node density ranging from 1 to 15 per square meter which translates to hundreds to thousands of devices within a cell's coverage area.
Zhu et al. (Thu,) studied this question.