ANT Forum

Dear All,

I have 8 ANT masters and 1 ANT slave. I need a net message rate of 8 Hz.

How do I calculate the optimal message periods to have minimum channel collision times?

How long is the messaging time slot?

Regards,
Peter      

Hi,

There isn't really a specific way to find an optimal message period for an ANT device with multiple channels open. However, the ANT protocol is designed in a way to prevent having channel collisions; therefore, you shouldn't see channel collision events generally with multi-channel ANT devices.

In your case, I would suggest setting the channel period to 1 Hz. Also, you can perform test scenarios of different channel periods using our software tool "ANTware II". You can find this tool in the "Downloads" section of the ANT website. ANTware II is used by ANT developers. Therefore, you can use this tool with an ANT device and open 8 slave channels. Then you can set different channel periods for each channel and accordingly check whether or not channel collision events are happening.

We are currently creating an application note about multi-channel ANT devices and design considerations. The note will be useful for ANT developers designing multi-channel devices.      

Hi muharram,

thanks for the reply.

It is not clear to me how ANT prevents channel collisions. Do the slaves cause the masters to eventually shift their time slot?

If masters keep sending at their configured periods unaware of any other masters or slaves then I don't see how ANT would manage channel collisions.

If ANT would really prevent channel collisions by some means then it would be the best procedure to set all masters to the same channel period so that only christal shift would have to be compensated for.

However, what I have found in the forums is the opposite, namely to set slightly differnt channel periods so that collisions would be of short duration.

Well, I'm puzzled -- what is really going on behind the scenes?

Best Regards,

Peter      

ANT channels achieve coexistence in the time domain, with an adaptive algorithm that allows master devices to detect and correct when other channels drift into their time slots.

This video from an ANT Basics presentation includes a nice animation that illustrates this.
http://www.youtube.com/watch?v=3BXnzBq70-U&feature=related

Note that there is no one optimal channel period to minimize collisions for a specific overall rate. In general, setting the channel period to the same value tends to perform well. We highly recommend using ANTware to mock up your setup and determine whether it is adequate for your application.

Some legacy products use a transmit only mode in which the coexistence features of ANT are not available - in this case, selecting periods that intentionally drift into each other ensures that the channels do not stay colliding for large periods of time.      

Hi Alejandra,

great, that's really a comprehensive answer, thanks a lot.

I this presentation available as a written document? My project is done in a medical environment, so I have to give some documentation on this and I rather have a reference to a printout than a link to YouTube...

Best Regards,

Peter      

A PDF with the complete presentation is available in the Support section of the website, under "ANT Technology Introduction". The animation is not included in that version.
http://www.thisisant.com/support