Connectionless Bluetooth Channel Sounding via PAwR for Scalable and Energy-Efficient Ranging
Bluetooth Core Specification v6.0 introduces Channel Sounding (CS) as a high-accuracy ranging primitive for Bluetooth Low Energy. However, the standard procedure requires per-pair connections. This binds ranging to a multi-stage initiation procedure, limits concurrent partners per radio, and forces result transfer over the connection. We present a connectionless CS architecture combining the LE CS Test command with Periodic Advertising with Responses (PAwR). A Central Orchestrator, a gateway, and synchronized CS devices handle coordination, configuration alignment, and result aggregation at the application layer. Each device derives its role, deterministic random bit generator initialization state, channel sequence, and response slot assignment from its device index and a Peer-to-Peer Assignment Matrix. The deterministic channel sequence prevents same-step collisions across parallel CS procedures, and the matrix can be updated per cycle to reconfigure arbitrary device-to-device pairings within a PAwR subevent group. A compact data plane omits fields recoverable from the shared measurement configuration and reduces the ranging-data payload by approximately 69%, so complete results are reported through PAwR response slots. A proof-of-concept evaluation on the nRF54L15 platform shows that deterministic channel management eliminates the collision-induced outliers observed under simulated dense-deployment channel overlaps. At a 1 s update cycle, the architecture reduces steady-state active charge by 40-48% relative to a fair connected baseline, cuts per-switch initiation overhead by approximately 98%, and, under per-cycle partner switching, achieves up to 88% lower total charge over 24 h. An empirical timing model projects up to 14,080 active devices per PAwR train for a four-measurement workload.