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Technical Brief: Asynchronous Gossip (Trickle) Mesh over Zephyr RTOS

1. Objective

To implement a royalty-free, ultra-low-power, and mobility-resilient communication stack for mass-scale deployments. This protocol is the primary alternative to proprietary mesh stacks to meet the target node economics.

2. Core Algorithm: Trickle (RFC 6206)

The protocol follows the "Speak much when there are news, shut up when everything is the same" principle.

  • Consistency (Quiet): If a node hears the same data version from its neighbors, it exponentially increases its transmission interval (doubling each time).
  • Inconsistency (Active): If a node detects a new sensor reading or hears a neighbor with an older version, the interval resets to the minimum value ($I_{min}$) to disseminate the update rapidly.
  • Mobility Tolerance: Since there is no fixed topology (no parent-child trees), the network is immune to chaotic animal movement and "meat-shielding" effects.

3. Implementation Stack: Zephyr RTOS

The firmware must avoid heavy IPv6/6LoWPAN stacks and operate at the Raw MAC / L2 level.

3.1. Kernel Level

  • Utilize Zephyr's native Trickle logic: <net/trickle.h>.
  • Driver Interface: Direct control of the Sub-GHz radio (IEEE 802.15.4) or SPI driver for Semtech SX1262 / TI CC1312.

3.2. Energy Efficiency (Wake-on-Radio)

  • CAD (Channel Activity Detection): Radios must perform ultra-fast "sniffing" (2ms) of electromagnetic energy.
  • Deep Sleep: The MCU must remain in the lowest power state ($<2 \mu A$) between Trickle intervals.
  • Clock Sync: Synchronize radio wakeups only for critical "beacon" events if necessary, otherwise rely on asynchronous CAD.

4. Payload & Data Strategy

  • Compact Packet (Target: 30-64 bytes): Minimize on-air time to preserve battery and reduce collision probability.
  • Version Vectors: Every node maintains a sequence number/version for its own data and its neighbors.
  • Delta Compression: For GPS coordinates and sensor tracking signals, only transmit the delta (difference) from the last known state.

5. Network Roles

  • Member Node (Leaf): Harvests data, executes Trickle gossip, and sleeps 99.9% of the time.
  • Leader Node (Gateway): Aggregates gossiped packets and performs the long-range backhaul (Cellular / NB-NTN) to the cloud.

Status: Strategic Technical Requirement for Design House RFP (Early April).