BLE and ANT data throughput

[goran]

Hi,

i am using three s210 master devices to broadcast ANT messages to a s310 central device. The central connnects to a PC through USB dongle and BLE.

When broadcasting with 4Hz message period, I can get all the data from ANT masters through the central on my PC. However, when I increase the ANT message period to 20Hz, the PC receives sometimes from all three sensors, but most of the time it gets only data from one or two ANT masters. I am using 10ms period to send BLE packets.

Does anybody know why this is happening? Is this data rate to much for S310 central device to handle?

Thank you

[Kenneth]

Hi,

Most likely what happens here is that the masters are transmitting at the same message period, and since they are transmitting independently of each other, they most likely will start to overlap in time. In such a scenario only one packet can be received, or in worst case none if they interfere with each other (collision on air). The ANT protocol do have some built in features to handle this situation, but if the masters are operating at different frequencies or using different network keys, this will not be handled. Also if there are multiple masters at short message periods, it most likely won't be able to handle it.

So how to solve it? I guess there are a few options:

1. For instance you can setup the central to be the master in the system, by configuring 3 master channels on the central, this way each slave can respond back using their own reverse data channel in ANT.

2. Setup each master to use different message period, for instance 19, 20 and 21 Hz. This will mean that the masters will from time to time collide, but they will also drift apart on next period.

3. Use auto-shared channel, this allow several slaves to communicate on a single master channel. For more information check out the ANT AN Auto Shared Channel Master Example (application note) on www.thisisant.com

Hope that helps, Kenneth

[goran]

Thank you for your answer. I tried with the second solution. Now I am able to receive from all three sensor nodes, however the receiving frequency is much lower than the one I set up. I noticed that whenever I open all three channels on my central device, the receiving frequency drops. If I open only one channel, the frequency is as expected. Do you maybe know what is causing this problems when all three channels are open at the same time?

[Kenneth]

Hi! It's only suggestion 1 and 3 that will allow it to work without any interference between the channels. With suggestion 2 there will be packets lost, if the packet loss is unacceptable you can try to increase the difference in message period between the master channels to for instance 18, 20 and 22 Hz. A better solution (if power consumption is not a limiting factor) on the receiver (slave), is to setup the receiver in continuous scanning mode with receive-only. Regard, Kenneth.