No single best connection
Every wireless link balances four things: how far it reaches, how much data it carries, how much power it uses, and what it costs. Improving one usually worsens another. A link that carries video uses far more energy than one that sends a few bytes a day, and a link that reaches many kilometers carries data slowly. That is why IoT uses several kinds of wireless protocols, and why the right one depends on the job instead of on which is newest.
The figures below are general rules of thumb. Actual range and speed vary widely with buildings, interference, antennas, settings and local conditions.
At a glance
| Type | Typical range | Data rate | Power use | Typical uses |
|---|---|---|---|---|
| Wi-Fi | Within a home or building | High | Relatively high | Cameras, speakers, appliances on mains power |
| Bluetooth (low energy) | Short, about a room or so | Low to moderate | Low | Wearables, phone-connected sensors, locks |
| Mesh short-range radio | Short hops, extended by relaying | Low | Low | Lighting, sensors and switches in a home or building |
| Cellular | Wide, wherever coverage exists | Low to high, depending on type | Moderate to high | Vehicles, trackers, remote equipment |
| Low-power wide-area | Long, up to several kilometers in good conditions | Very low | Very low | Meters, agricultural and environmental sensors |
Wi-Fi
Wi-Fi is familiar, fast and already present in most homes and offices. It can carry video and large updates, and devices connect to a router that most people already own. Its drawbacks are higher power use, which makes it a poor fit for small battery sensors expected to last years, and a limit on range. Crowded networks can also slow down when many devices compete, and setup often means typing a password into a device with no screen. The strengths and weak spots are covered in more detail under Wi-Fi connectivity.
Bluetooth
Bluetooth was built for short-range links between nearby devices, most often a phone and an accessory. The low-energy variant is designed to run for long periods on a small battery by sending short bursts of data and sleeping in between. It suits wearables, medical accessories and simple sensors that talk to a phone, and it is explained under Bluetooth Low Energy. Its range is short, so a device usually needs a phone or gateway nearby to reach the internet.
Mesh networks
In a mesh, devices relay messages for one another, so a signal can hop across a house or building even if no single device reaches the hub. This helps coverage and resilience: if one node fails, traffic can often find another path. It is common in lighting and home sensors. Each relaying device must stay awake enough to pass messages along, which can limit battery use for those nodes. See mesh networking for more.
Cellular
Cellular IoT uses the same kind of network as mobile phones, through a subscription or a data plan. It shines where there is no local network to join: vehicles, shipping containers, remote pumps and anything that moves around. Coverage is broad and the connection is managed by an operator. The costs are the ongoing subscription fees, higher power use than the lowest-power options, and dependence on a provider. Different cellular offerings trade speed for lower power and cost; the basics appear in cellular IoT.
Low-power wide-area networks
These links are designed for tiny messages sent infrequently over long distances using very little energy. A sensor might report a handful of readings a day and run on a small battery for years, though real lifetimes depend on how often it transmits and on conditions. The tradeoff is very low data rates and often limited ability to send data back to the device, so large downloads, such as firmware, may be impractical. They suit meters, soil and water sensors and similar slow, spread-out devices, and are covered in low-power networks.
Matching a link to a job
Work through a few questions.
- How much data and how often? A video stream needs a fast link. A temperature value once an hour does not.
- How far must it reach? Within a room, within a building, across a farm, or across a country?
- What powers the device? A mains-powered camera can afford Wi-Fi. A coin-cell sensor generally cannot. This links directly to battery life, and techniques such as duty cycling reduce the radio’s on-time.
- Does it move? Moving assets favor cellular. Fixed ones have more choices.
- What infrastructure exists? Using an existing Wi-Fi network is cheaper than building a new one, while remote sites may have none at all.
- What does it cost over time? Count subscriptions, gateways and maintenance, not just the hardware.
- How secure and reliable must it be? Safety-related functions deserve extra thought about what happens when the link fails.
Mixed setups and gateways
Real deployments often combine several. Short-range sensors may talk to a nearby gateway, which then uses Wi-Fi, a wired connection or cellular to reach the internet. This approach lets cheap, low-power radios do the local work while one better-connected device handles the backhaul. The role is described under IoT gateways.
A radio link is also only the bottom of the stack. Higher layers decide how messages are addressed, formatted and secured, as laid out in the guide to communication layers. And because manufacturers use different standards, mixing brands can be awkward, a problem explored under device interoperability.
Practical advice
Choose the simplest link that does the job with margin to spare. Test range in the actual location, not on a bench, since walls, metal and distance can change results sharply. Plan for what the device does when it loses connection. And remember that the connection should be chosen early, since it affects battery size, enclosure, cost and maintenance for the whole life of the deployment.