IoT Low-Power Wearable Device Design

The device is a low-power wearable IoT unit designed around the Nordic nRF91 series (preferably nRF9151) with NB-IoT cellular connectivity and optional GNSS positioning for secure cloud communication and remote management. It must be 3GPP Release 13 (or later) compliant and support NB-IoT deployment modes including standalone, in-band, and guard-band operation, with regional band configuration (for example B3, B5, B8, B20, B28 depending on target markets) and support for NB-IoT power classes such as 20 dBm (Class 5) and 23 dBm (Class 3). The design shall include nano-SIM or MFF2 eSIM (1.8 V/3 V) with proper ESD protection, and RF implementation must follow best practices for wearable products: a minimum 4-layer PCB with controlled-impedance 50 Ω RF traces, solid ground reference, provision for RF shielding, and a tunable cellular antenna matching network (Pi network recommended) accounting for on-body detuning; if GNSS is included, a dedicated GNSS RF path and antenna solution (passive or active) must be supported. Power is provided by a single-cell Li-Po battery (typically 200–500 mAh) with integrated protection and charging via USB-C or pogo pins, targeting ultra-low sleep currents (single-digit microamps where feasible) while tolerating NB-IoT transmit bursts with peak current that can reach hundreds of milliamps. The system shall provide the necessary interfaces for sensors and debugging (UART, I2C, optional SPI, GPIO, ADC for battery measurement) and firmware must support NB-IoT attach, secure data transport over MQTT/HTTPS using TLS, low-power features such as PSM/eDRX, and firmware-over-the-air updates, leveraging hardware security features (secure boot, secure key storage, and root-of-trust capabilities). Mechanically, the PCB should be compact (targeting under ~40 × 30 mm where possible), suitable for wrist-wearable enclosures, and designed toward future compliance goals such as CE/FCC and carrier certification expectations (e.g., PTCRB), including robust ESD protection on external interfaces.

Project ID: 40255673