1. Problem Formulation
During monsoon flash floods in mountainous regions of Northern and Southern Thailand, commercial fiber lines and cellular base stations frequently lose mains power or suffer physical severed lines. Communities are left without communication precisely when river water levels surge.
This architecture establishes an autonomous, decentralized LoRaWAN & Packet Mesh Network capable of transmitting hydrological telemetry and emergency SMS alerts across mountain ridges without dependence on utility grids or telecommunication carriers.
2. Multi-Hop Mesh Topology
[Remote River Sensor Node] (Level: 4.8m / CRITICAL)
|
| LoRa (923 MHz, SF10) - 4.2 km Line of Sight
v
[Ridge Repeater #1 (Solar)] (Wat Tham Mountaintop)
|
| LoRa (923 MHz, SF10) - 8.5 km Line of Sight
v
[Ridge Repeater #2 (Solar)] (Village Water Tower)
|
+--------------------------+--------------------------+
| |
v v
[Village Alert Siren Controller] [Community Clinic Hub]
(Activates 110dB Audio Horn) (Displays River Metrics)3. Repeater Power Sizing & Energy Balance
To achieve true indefinite operation in tropical rainforest canopies with up to 4 consecutive days of heavy cloud cover, node power budgets must adhere to the following balance equation:
E_{\text{storage}} \ge I_{\text{quiescent}} \times 24\,\text{h} \times 4\,\text{days} + E_{\text{tx}} \times N_{\text{packets}}| Operational State | Current Draw @ 3.7V | Duty Cycle | Daily Energy Consumption |
|---|---|---|---|
| Deep Sleep / CAD Rx | 18\,\mu\text{A} | 98.2% | 0.0016\,\text{Wh} |
| Active Listening (Rx) | 4.6\,\text{mA} | 1.5% | 0.061\,\text{Wh} |
| Packet Forwarding (Tx 22dBm) | 110\,\text{mA} | 0.3% | 0.029\,\text{Wh} |
| Total Daily Budget | — | — | 0.0916\,\text{Wh/day} |
A dual 18650 pack (6.8\,\text{Ah} \times 3.7\,\text{V} = 25.16\,\text{Wh}) provides over 270 days of total autonomy without solar harvesting, ensuring zero blackout risk.
4. Node Assembly & Deployment Checklist
- Configure radio bandwidth to 125 kHz with Coding Rate 4/5 adhering to NBTC AS923 channel frequency plans.
- Coat all PCB solder joints with silicone conformal coating (MG Chemicals 422B) against tropical humidity.
- Mount fiberglass omnidirectional 5.8 dBi antenna using stainless steel U-bolts grounded to copper earth rod.
- Test end-to-end packet transmission from lowest riverbed sensor to central clinic console.
- Confirm audio horn siren relay triggers within 4 seconds of emergency threshold receipt.