OOK (On-Off Keying)
OOK, in which information is carried by switching the carrier fully on and off, is the simplest member of the ASK family. For a one bit there is a carrier, for a zero bit there is none. It is common in simple garage and barrier remote controls; when the noise floor rises, the receiver cannot tell the gap from the signal and the link becomes unusable.
In an OOK transmitter the power stage runs only for the duration of a one bit, which lowers average consumption and gives long standby times on small batteries. On the receiver side, the problem is that a zero bit really is silence: during that interval the receiver listens to whatever is in the environment.
- Accidental interference makes a zero bit look like a one and corrupts the packet; the corrupted packet fails the checksum and is discarded.
- If there is a continuous noise source the receiver never sees a gap and the threshold slips; this is the behaviour closest to jamming.
- On receivers with automatic gain control, a strong nearby source can completely suppress a weak distant transmitter.
This is why, on industrial sites and especially in crane and hydraulic control, frequency-based modulations and frequency-hopping protocols are preferred over OOK. On the AXI side, the XRF protocol of the HCT400 and HCT402 sets is frequency hopping and bidirectional; a narrowband interference source affects only a few hops.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety