L-PHY

L-PHY (Leantegra PHY) is the 2.4 GHz radio layer for L-MESH and L-DCB protocols, which works on nRF52 chipsets by default.

L-PHY is not based on BLE stack — this is a custom implementation, which is highly optimized for the needs of L-MESH, L-DCB and Unified TDMA. It includes a separate radio configuration with its own addressing, packet format and channel map. BLE scanners will not see L-PHY traffic and BLE connection requests will not be answered by L-PHY devices.

One layer, several protocols

L-MESH and L-DCB are identical at the radio: the same modulation, the same packet structure, the same CRC, the same channel plan. What separates them is the access address — the four bytes a receiver matches before it will accept a frame at all. A receiver configured for one protocol does not merely hear the other poorly; it does not hear it.

That is the same mechanism BLE uses to keep connections apart, applied for the same reason: it costs nothing per frame, it is enforced by the radio rather than by software, and it makes adding a protocol a matter of choosing an address rather than changing a format.

It also sets a rule for the schedule. A node can be configured for one protocol at a time, so a slot belongs to one of them — see Unified TDMA for how the superframe divides between them.

The channel plan

Sixteen channels at 5 MHz spacing span 2402–2477 MHz. The spacing is chosen so that channels fade independently: a tunnel with 100–300 ns of delay spread has a coherence bandwidth of roughly 0.7–2 MHz, so 5 MHz apart is comfortably beyond it. Both protocols share the plan — L-MESH hops across it per slot, L-DCB steps through it inside one slot.

Wi-Fi occupies the same band. Sixteen channels spread across 75 MHz means an interferer sitting on one of them costs one channel out of sixteen rather than the link.

Where it sits

L-PHY carries L-MESH and L-DCB. It is not the only bearer under the schedule: Unified TDMA also drives UWB for ranging and BLE for configuration and telemetry, from one superframe. That is what unified names — one schedule over several radios, rather than one radio.

Applications   A-RTLS · A-GNSS · Sensors · Alarms
───────────────────────────────────────────────────────
Network        L-MESH        relay · hop gradient
───────────────────────────────────────────────────────
Scheduling     Unified TDMA  superframe · slot map · sync
───────────────────────────────────────────────────────
Bearers        L-PHY         BLE               UWB
               L-MESH        GATT config       TWR / TDoA
               L-DCB         ext advertising

Related

• L-MESH — the mesh network that runs on L-PHY
• L-DCB — positioning from signal strength across the channel plan
• Unified TDMA — the schedule above it
• BLE Ext Advertising — the separate BLE path