Originally Posted by
njkayaker
"Pairing" is a bit of a confusing term.
The sensors send out packets of data. Each packet includes a number that uniquely identifies the sensor.
The sensor doesn't care what is listening to it or that it's being listend to at all.
That is, there's nothing special that the sensor needs to do when paring.
It's the head unit that does all the work.
Basically, "pairing" is the process by which the head unit knows which sensors (by their identification number) to pay attention to.
The only type of sensor that would need to have a button is one where the communication was two-way. (The fact that the bicycle sensors don't have a button is an indication that the communication is one way.)
Note that Bluetooth devices are often two way. For two-way communication, both devices need to be put into a "pairing" mode so that both can determine which other devices to pay attention to.
The ANT devices are not usually two-way but, since two-way is possible, the same "pairing" term is used.
So in general terms (for the typical Ant+ implementation that a cyclist would run into)
1) When the sensor is alive it is sending both ID (and other if it is required) information that allows the head unit to distinguish it from the other devices on your bike, devices on other bikes near you, noise/crap that exists in the 2.4 GHz range, etc
2) A head unit has a 'list' of devices that it should pay attention to. In a noisy or possibly crowded situation it might well be getting all kinds of 'input' and it is ignoring this unless it can see that it is coming from 'somebody on the list'
3) Ant+ dramatically narrows the range of data for a given/valid connection (part of the device profile for a given sensor)
4) "Pairing" is the process that puts a device 'on the list' (see
#2 )
5) Anytime an Ant+ sensor is active (for the typical implementation of Ant+) it is sending the data required to authenticate itself to the head in the system
6) The 'special steps' that happen when pairing happen at the head. In this case it is critical that ONLY valid devices be in range of the head. Once you put the head in pairing mode, unless the Ant+ implementation in question has additional steps for pairing, anything 'in range' at that time is now paired.
Is that how things typically work?
Thanks.
dave