When we think about IoT, we often forget that we are usually also talking about wireless communication. Even though we are protected with legislation, which controls the power and frequencies of communication between devices, problems may arise. Our message in short is:
The more there are devices sharing frequency channel, the more disturbed the channel is.
In the old era of computing and communication studies, Shannon and Hartley studied and defined “the maximum rate at which information can be transmitted over a communications channel” (nice sentence from Wikipedia).
IoT is about wireless – is it?
If I start talking you about new IoT application (or device), first visualization which comes to your mind, is most likely wireless device. Even though IoT (Internet of Things) actually stands for devices connected to internet. As term connected implies, some networking is involved. However, it does not imply wired nor wireless networking. We have just been so often talked about wireless IoT, that we always assume that everybody else is talking too.
Most important challenges in IoT are power and communication. If we are using wired communication, it is very convenient to use parallel wires to power the device. When wireless communication is used, batteries are used most often. This can change very quickly, when solar powered and wireless powered devices become more common.
Every open wire, which transmits alternating current, usually called signal, is a sending antenna. And every open wire is receiver antenna, whether it is sending or not. If the open wire has a a signal, and there are powerful enough RF around it, the resulting signal (measured from the wire) is the sum of signals (original signal and received signal from antenna).
Wireless is Shared Channel
When we are talking of wireless IoT, we are talking about shared channel. All wireless devices which are communicating wireless using same bandwidth can be heard by other devices. In this I refer to radio signal, not the data, which should be encrypted anyway. Radio signal is the media and data is the payload.
Like in football game; the more there are viewers shouting at the same time, more difficult it is to hear the actual message, unless the message is same. In IoT it usually is not. With a number of sensors, a number of different measurements should be received.
When we wish to overcome the disturbance of signal “next door”, we usually just turn “up the knob”. In IoT, this is impractical solution, since using more power to radio means bigger power consumption. And since most IoT devices don’t have external power sources with infinite capacity, that would mean running out of batteries sooner.
How we can protect our wireless IoT devices? The normal way:
- Choose radio protocol and frequency with care
- Design IoT device with care
- Shield the electronics from RF with casing
- Only antenna(s) should be outside of the shielding/case
- Use shielded cables when transmitting data from PCB to PCB, if there is any possibility that the open wire would act as antenna
Updated Jan 16th 2018; I re-wrote some of the article, to emphasize more that IoT is not totally only about wireless.