LoRa, Wi-Fi or 4G: choosing how your field sensors connect

The sensor is the easy part. Getting its reading back to you, every time, from the far end of a field or a remote pump house, is where many IoT projects succeed or fail. The choice usually comes down to three options: Wi-Fi, 4G or LoRa.

Our Viva platform supports all three, so we make this decision on almost every project. There's no single best answer. Each radio is excellent in some situations and a poor fit in others. Here's how we think it through.

Start with three questions

Before comparing technologies, we answer three questions about the site and the data.

1. How far does the signal need to travel? Ten metres to a router, a kilometre across a farm, or from anywhere with mobile coverage?
2. How much data, and how often? A soil reading every 15 minutes is a few bytes. A camera image or continuous vibration data is thousands of times more.
3. How is the device powered? Mains power, a battery that should last years, or a small solar panel?

Cost and who owns the network come next, but these three questions usually narrow the choice to one or two options straight away.

Wi-Fi: great indoors, limited outdoors

Wi-Fi is familiar, cheap and fast. If a greenhouse, warehouse or office already has good coverage, a Wi-Fi sensor can be the quickest thing to deploy, and it can easily handle larger data such as images.

The limits show up outdoors and on batteries:

• Range. Outdoors, a standard access point typically reaches tens of metres, perhaps around a hundred with a clear line of sight. Covering a farm needs extenders, and every extender needs power.
• Power. Wi-Fi radios draw much more current than low-power alternatives, and reconnecting to a network after sleeping takes time and energy. Battery-powered Wi-Fi sensors need careful design to last more than a few months.
• Reliability. Home and office routers aren't built for dust, heat and monsoon humidity, and a router restart can take every sensor offline.

Choose Wi-Fi when devices are indoors or close to existing infrastructure, mains power is available, or you need to send larger amounts of data.

4G: coverage almost anywhere

A cellular connection lets a device report from anywhere with mobile coverage, with no network of your own to install. That makes it ideal for things that move, like vehicles and containers, and for single devices at remote sites.

The trade-offs:

• Running costs. Every device needs a SIM and a data plan. That's fine for ten devices, but it adds up across hundreds.
• Power. Standard 4G modems use a lot of energy. The low-power cellular versions designed for IoT, LTE-M and NB-IoT, use far less, but check that they're supported by operators in the area before relying on them.
• Coverage gaps. Rural sites, basements and areas with thick walls can have weak signal. Test on site, at the actual installation height, before committing.

Choose 4G when devices are mobile or spread across many separate locations, when there's no practical place for a gateway, or when you need a reliable link from a single remote site.

LoRa: long range on very little power

LoRa is a radio technology designed for exactly the kind of data most sensors produce: small readings sent occasionally over long distances. A LoRa sensor can typically reach a few kilometres in built-up areas and often much further across open countryside with a clear line of sight. Because it sends so little and sleeps most of the time, a LoRa device can run for years on a battery.

Sensors talk to a gateway, which forwards their data to the internet over Wi-Fi, Ethernet or 4G. One gateway can serve many sensors across a whole farm or campus. You own the network, so there's no per-device monthly fee. LoRaWAN is the widely used standard protocol built on LoRa; in India it uses the licence-free 865 to 867 MHz band.

The limits:

• Small messages. LoRa carries tens to a couple of hundred bytes per message at low data rates. That's ideal for readings and alarms, but not for images or audio.
• Not instant. Devices send occasionally and are mostly asleep. Sending commands back to a device usually waits until it next checks in, which matters if you need to switch something on immediately.
• A gateway to install. You need a good spot for it, ideally high up, with power and an internet connection.

Choose LoRa when you have many battery or solar-powered sensors spread over a large area, each sending small readings every few minutes.

Side by side

Often the answer is a mix

On many sites the best design uses more than one. A common pattern on farms looks like this:

• LoRa sensors in the field measure soil moisture, temperature and humidity, running on small batteries or solar panels.
• A solar-powered gateway on a pole collects their readings.
• The gateway sends everything to the cloud over 4G, so only one SIM is needed for the whole site.
• Wi-Fi is used inside the packhouse or office, where power and coverage already exist, for devices like cameras.

This combines the reach and battery life of LoRa with the convenience of cellular backhaul, and keeps monthly costs to a single data plan.

A quick way to decide

• Indoors with power and good coverage? Wi-Fi.
• Moving, or a handful of devices far apart? 4G, ideally LTE-M or NB-IoT if available.
• Lots of low-power sensors across one large site? LoRa, with a gateway that uses Wi-Fi or 4G to reach the internet.
• Not sure? Mix them, and test on site first.