The big idea: Embedded systems communicate over Bluetooth, Wi-Fi or cellular (5G), and the three differ on two axes that decide everything else: range and power.
Reaching further means transmitting harder, and transmitting harder costs energy — so a battery product cannot have long range, whatever else a designer wants.
The three protocols plotted on range against power, which is the trade that decides between them.
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| Bluetooth | Wi-Fi | 5G | |
|---|---|---|---|
| Range | About 10 m — a room | Tens of metres — a building | Kilometres, wherever there is coverage |
| Power | Very low; Bluetooth Low Energy runs for months on a coin cell | Moderate to high; it flattens a small battery in days | High, and it needs a subscription as well as a supply |
| Data rate | Enough for audio, sensor readings and control | High — video, software updates, continuous streams | Very high, with very low latency |
| What it needs | Nothing but the other device; the two pair directly | A router and a network to join | A network operator, a subscription and a SIM |
| Typical products | Wearables, headphones, a sensor talking to a phone | Thermostats, cameras, printers, smart speakers | Vehicles, trackers, remote sensors, field monitors |
Three questions decide it: Is the product battery-powered and must it last? Bluetooth.
Is it mains-powered, inside a building with a network? Wi-Fi.
Does it move, or is there no local network to join? Cellular — and somebody has to pay a subscription for the life of the product.
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| What it adds | What it costs |
|---|---|
| Remote monitoring, alerts and control from a phone | Standby power for the radio, for the whole life of the product |
| Software updates and new features after sale | A dependence on the manufacturer still publishing them, and an update that can break a working product |
| Data that improves the product and the next one | Privacy obligations, and a security surface that has to be maintained for years |
| Systems working together rather than alone | A product that loses its main feature when a router, a server or a contract goes away |
The design rule that follows: Keep the core function working without the network.
A connected doorbell should still ring from its button. A smart thermostat should still hold a temperature. If it cannot, the manufacturer's server has become a part of the product — and one the user cannot replace.
How this is tested — comparing protocols embedded systems use to communicate. It comes up two ways:
Paper 1 — multiple choice
- Choose the protocol suited to a stated product.
- Identify what a named protocol requires.
Paper 2 — analysing a product
- Justify a communication protocol for a named product.
- Explain what adding communication costs a product.
The trap: Choosing by data rate. Range and power decide almost every real case, and a battery product cannot afford long range whatever its data needs.
A soil-moisture sensor is to be buried in a field and report daily to a farm office 800 m away. Justify the communication protocol.
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