Packet loss when multiple Cyton working in the same lab
Hello,
I’m teaching a lab course in a university, and we are using up to 7 or more sets of Cyton+dongle working in the lab at the same time. The radio channels of Cyton+dongle had been set different from one another, but we still found when devices with near channel numbers interfere each other sometimes. For example, when devices in radio channel of 7 and 10 working at the same time in the same room (in the distance about 4 meters), one might work well but the other has packet loss and totally incorrect signal, with an huge impulse at the beginning. When the former stopped session, the latter then work back to normal.
My questions are:
1. How could we avoid this kind of interference, since the channels have been set different?
2. If we need to separate these devices to a larger distance to avoid interference, what distance do you recommend?
Thanks!
Comments
Hi,
You are going to have to experiment to see what channel interval works best in your situation. If '3' is not working, try '5' etc. Unfortunately as is the case with all wifi and Bluetooth radio channels, there is a small amount of crosstalk because these are almost the same radio frequency.
https://www.electronics-notes.com/articles/connectivity/bluetooth/bluetooth-low-energy-le-frequency-channels.php
The physical distance also seems correlated as you have found. So you may need both wider channel spacing and more physical distance between channels that are near.
One other possible 'workaround' you could employ, is to place the dongle on a usb extension cord, and position the dongle closer to paired Cyton board. Then that channel's signal strength will be stronger.
William
Thank you for responding. I plan on trying the USB extension cord as you suggested.
However, I have a new question regarding the BLE channels. The webpage you provided states that there are 40 channels for BLE. However, when I attempt to change channels using OpenBCI GUI, the options only range from 1-25. How could I set the devices on channels larger than 25? Thanks again.
It's seems likely that the older RFduino (~2014) radio modules only support the smaller number of channels. BLE specs changed over time and RFduino was early generation of BLE.
https://cdn.sparkfun.com/datasheets/Dev/RFduino/rfduino.datasheet.pdf
https://www.rfwireless-world.com/Terminology/BLE-Advertising-channels-and-Data-channels-list.html
Thank you for your prompt response.
According to the datasheet, RFduino is a Bluetooth 4.0 low energy BLE module. Compared with classic Bluetooth, BLE has fewer channels, 40 vs. 80. But all the BLT versions, 4.0 through 5.0, have 40 channels.
https://ieeexplore.ieee.org/document/8528458, TABLE 4 Comparison of Bluetooth Standards
Do you mean RFduino does not support all 40 channels and only 1-25 channels?
The RFduino specs you are reading are for the STANDARD model of RFduino firmware. Which uses pseudo-random channel hopping, so no fixed radio channel. The Cyton RFduino's have special firmware that increases the data transmission capability, by using more channel bandwidth. This may account for the 25 limit.
Please try different rooms or using the usb extension as suggested.
Thanks for your help