Hi,
we're developing BLE sensor platforms with 10+ sensors on a device. We have some bandwidth issues if we connecting more than one BLE device to a BLE host:
For Example: If connect one sensor to a host, the throughput is limited by the theroetical maximum of ~700kB/s (we're using 1M PHY and max. MTU, see Bluetooth Low Energy data throughput), here is an example:
It shows ~12000 data samples per second; One Data sample are 6 Bytes (48 Bit), so the bitrate is ~600 kBit/s which is close to the maximum. The sample rate is 12800 Hz, so the data throughput is fine and close the the desired data rate.
Now, If we connect 2 devices with the half frame rate (6400 Hz) which is in summary also 12800 Hz, it should also fit to the maximum throughput , but it's not:
The second device never reaches the full bandwidth of 6400 Hz.
It's getting even worse with more device, in example 200 Hz and 4 devices which is far from the limit:
200 Hz Acc + Gyro are 12 Bytes per sample which is ~20 kBit/s. There should be no problem at all, but it is. One of the nodes is always below the designed frame rate.
So, how can BLE be tweaked to handle more than one device to push the bandwidth limits?
Is there a reason why more than one node decreasing the theoretical bandwith so dramatical?
