Unlocking Ultralow-Power Bluetooth Low Energy Relays With Periodic Advertisements

This article demonstrates an unexplored relay operating mode in Bluetooth Low Energy (BLE)-based Wireless Sensor Networks, enabled by the link-layer synchronization inherent to BLE periodic advertisements. This synchronization allows relay nodes to avoid the power-hungry 100% duty primary-channel scanning that conventional passive BLE receivers rely on for reliable packet capture. To translate this insight into practice, we present the design and implementation of Dynamic Primary-Channel Scanning (DPCS), a practical strategy that disables primary-channel scanning after periodic synchronization and autonomously re-enables it upon synchronization loss, thereby allowing relay nodes to remain asleep for most of their lifetime while still forwarding data on scheduled secondary-channel receptions. We integrate DPCS into a multi-hop, chain-based data propagation framework for linear BLE-based WSNs, where sensor nodes themselves act as relays and forward concatenated data hop-by-hop toward a sink. Enabled by the innate properties of the periodic advertising mechanism, DPCS is directly deployable on commercial off-the-shelf (COTS) BLE 5.x devices as an application-level control logic using the provisions of the BLE stack. Experiments with nRF52832-based nodes in five-node chains demonstrate over 99% per-hop data reception reliability indoors across 50–60 m with modest retransmissions. In outdoor deployments, the per-hop reliability consistently remains above 99% without retransmissions across a 180–200 m span, with rapid automatic re-synchronization after interruptions. Power profiling shows consistently lower energy consumption than both continuous and duty-cycled primary-channel scanning baselines, with up to two to three orders of magnitude savings over continuous scanning at a sensing interval of 60 s. This chain-based analysis provides a baseline for extending the proposed periodic-advertising-based relay operation to more complex network topologies.