BLE arm — is a BLE anchor a second counting modality, or a calibration aid?
Campaign: c-mall-archcad · Session: 01KY0CYKXEV4XXZ3RCSYRHBAKJ · Runs: 5 coupled walk→ray-traced seeds with the BLE modality enabled, on mall-archcad-floor-0 (14-candidate grid)
Executive summary
The thesis is about BLE-calibrated CSI crowd counting, so the natural question is: does a BLE signal actually help you count — could you place access points by BLE, or fuse BLE with CSI? We enabled a BLE link alongside the Wi-Fi CSI on the same five simulated crowds and asked which ceiling mounts each modality says are informative about the crowd. The answer: BLE does carry counting information — on average about as much as CSI — but it is blurry. Every mount looks about equally (un)informative to BLE, and BLE's verdict wobbles a lot from one crowd to the next, whereas CSI sharply and stably separates the good mounting spots from the bad ones. So BLE is not a stand-in for CSI when deciding where to put sensors; it behaves like a coarse presence/calibration signal, with CSI doing the fine-grained counting — exactly the division of labour the thesis assumes. (Caveat up front: the simulator models BLE at the Wi-Fi carrier, not the real 2.4 GHz BLE band, so treat the specific BLE numbers as a proxy.)
Why this ran
Every prior mall result placed APs by CSI mutual information. If a BLE anchor were an equally good — or complementary — counting modality, the counting-optimal placement should look similar under BLE, or a fused CSI+BLE signal should beat CSI alone. Testing that is the on-thesis step: it tells us whether BLE earns a counting role or a calibration role.
What we measured
On the identical five runs we computed, per candidate mount, the mutual information I(C;Φ) between occupancy count C and (a) the CSI mean amplitude and (b) the BLE RSSI — each a single scalar per mount per frame-window, multi-seed mean + t-CI. We then compared the counting-optimal AP set under each modality (Jaccard overlap) and the agreement of their per-mount informativeness rankings (Spearman).
Results
BLE carries counting signal, but a blurry one. Mean per-mount BLE MI is 0.212 nats — marginally above CSI's 0.172 — so BLE is not uninformative. But the spread across mounts is 0.103 nats for BLE versus 0.251 for CSI: BLE assigns nearly every mount a similar value, while CSI strongly distinguishes hubs (top CSI mount 0.344 nats) from dead spots. And BLE's ranking is unstable across crowds — seed-rank Spearman ρ = 0.186 for BLE versus 0.593 for CSI. A modality that can't reproduce its own ranking across seeds can't be trusted to choose mounting points.
The two modalities pick different placements. BLE-optimal {0, 5, 7, 10, 11} vs CSI-optimal {3, 4, 5, 6, 7} share only {5, 7} — Jaccard 0.25 — and their per-mount informativeness rankings barely agree (Spearman 0.248). BLE would send you to different mounts than CSI, but because BLE's own ranking is noise-dominated (ρ=0.186), that divergence is not a better placement, just an unreliable one.
What it means
BLE, as a single-scalar RSSI anchor, is a poor instrument for where to place counting sensors: it is spatially blurry and seed-noisy compared with CSI. This is consistent with — and empirically motivates — the thesis's architecture, where BLE serves calibration and presence (a coarse, cheap "someone is here" / drift reference) and CSI does the fine-grained counting and placement. It argues against treating BLE as a co-equal counting modality, and for using it the way the thesis proposes: to periodically re-anchor the CSI counter, not to replace it. A CSI+BLE fusion for counting is still worth testing, but on this evidence BLE's contribution to placement is small.
Confidence & caveats
Not real BLE. The simulator models the BLE link at the 5.2 GHz CSI carrier, not the 2.4 GHz BLE band — different propagation and wall/body interaction — so the specific BLE magnitudes are a proxy, not a BLE measurement. Both features compared are scalars, which understates CSI's true advantage (its full 52-subcarrier vector carries more than the mean). Single floor, seed is the unit (n=5), sim-only. The clean next step is a real 2.4 GHz BLE beacon + AX210/Pi5 CSI floor (IP-106/IP-112) to confirm the calibration-vs-counting division of labour on hardware.
Figure: fig_placement_oracle_mall-archcad-floor-0_ble (BLE-informativeness panel), with rec_ble.json + rec_csi.json at the session artefacts prefix for the full A/B.