Choosing connectivity for remote monitoring in the Puna: LoRa, cellular or satellite
Before choosing sensors, a more basic question needs answering: how will data reach you from a site with no power grid and often no cellular signal? This article explains my approach to designing a remote monitoring station, with calculations you can check.
1. The three options at a glance
| LoRa (dedicated radio link) | Cellular 4G / LTE | Satellite | |
|---|---|---|---|
| Monthly fee | None for radio data transmission | Data plan or subscription | Subscription or per-message fee |
| Power consumption | Very low | Moderate, with connection peaks | High during transmission |
| Data volume | Small per message | Large | Very small |
| Site requirement | Line of sight to a gateway | Actual coverage, not just a coverage map | Clear view of the sky |
| Best suited to | Distributed stations without cellular coverage | Sites with stable coverage | Fallback or backup |
An often-overlooked detail: the LoRa gateway also needs internet access. At a field camp, this can often use the existing camp connection. Otherwise, cellular or satellite connectivity is still needed, but at a single point rather than at every station.
2. LoRa's practical limit: line of sight
At 915 MHz, free-space path loss between two antennas is calculated as follows:
At 915 MHz: FSPL ≈ 91.7 + 20·log₁₀(d)
At 30 km, the result is approximately 121 dB. Here is the link budget, using conservative example values:
Combined antenna gain (3+3) ....... +6 dBi
Cable and connector losses ....... −2 dB
Receiver sensitivity ............. −130 dBm (conservative example)
──────────────────────────────────
Total link budget ................ 154 dB
Path loss at 30 km (free space) ... 121 dB
Fade margin ...................... ≈ 33 dB
On paper, there is plenty of margin. Why, then, do links fail? At 915 MHz, the limiting factor is often that something obstructs the path: the Earth's curvature or a hill.
Radio horizon
Under standard atmospheric conditions, the approximate maximum line-of-sight distance between two antennas over flat terrain is:
- Two antennas at 3 m: approximately 14 km.
- One at 3 m and another at 30 m: approximately 30 km.
- One at 3 m and another at 100 m (on a hill): approximately 48 km.
The practical takeaway: good gateway placement can be more valuable than extra transmit power. Raising the gateway by a few tens of meters can greatly increase range, while increasing transmit power adds only a few dB.
The Fresnel zone
Seeing the other antenna is not enough: the first Fresnel zone, an ellipsoidal volume around the direct path, also needs clearance. Its radius at the midpoint is:
For a 30 km link at 0.915 GHz, the radius is approximately 50 m. A common design rule is to keep at least 60% of that radius clear: about 30 m around the direct path at midspan. This is why paths through a ravine or close to a hillside can be problematic even when there is visual line of sight.
3. Power: what changes at high altitude
- Plenty of sunshine, but also low temperatures. High-altitude solar irradiance is abundant, but nighttime temperatures can constrain the power system.
- Lithium iron phosphate (LiFePO₄) batteries should not be charged below 0 °C. Doing so can damage the cells. If temperatures fall below freezing, low-temperature charging protection or battery heating is needed and should be verified before installation.
- Transmission is a major power demand. Sampling every few minutes and sending short messages rather than large packets helps extend autonomy.
- Store records locally. If the link fails, the station should continue measuring and store records locally for forwarding when connectivity returns. Otherwise, each outage leaves a gap in the report.
4. Making the decision in practice
- Assess the site: identify possible station locations and an elevated gateway position.
- Check cellular coverage with an actual test at each point, rather than relying on the operator's map.
- Calculate the link budget using the terrain profile and an adequate design margin.
- Test in the field before permanent installation, using the actual equipment and antennas.
- Choose a backup for critical data, whether local storage or a second link.
A regulatory consideration: permitted transmit power and frequency bands depend on current Argentine regulations. Before finalizing a design, check the applicable limits with the relevant authority (ENACOM) and the equipment specifications.
Tell us what you need to measure and where. A site assessment helps identify the appropriate connectivity option.
Get in touch by emailRelated article: Environmental noise in the Puna: wind, low background levels and continuous monitoring.
