burst notifications with Bluetooth Low Energy on Android

Question

I'm developing a Bluetooth low energy application to connect with a device which will be sending 20 byte long transmissions in notification mode in intervals of 6 milliseconds or more.

So far the application is working fine. It can scan, discover and then subscribe to the characteristic to receive data notifications. The issue is that for the first 2-4 seconds the data will be read nicely in a sequential order but after that the notification data starts to appear in bursts or as in chunks of data but not in consistent intervals between each transmission.

This doesn't happen when i check the data transmission with the Texas Instruments BLE evaluation kit, there my reader shows a perfect transfer with not bursts appearing. Only on android it's become visible. Could this be an issue that can be configured to fix in android side? Could this be a problem with the high transmission rate (~milliseconds intervals)?

Thank you..

So it sums up to that optimal throughput can be achieved with the proper configuration of connection parameters for the BLE connection. It is usually done at the peripherals end and may have to differ for the platform connecting to (i.e. IOS , Android may have different connection requirements..)

P.S. : Since i was looking at android found this method documented here https://developer.android.com/reference/android/bluetooth/BluetoothGatt.html#requestConnectionPriority(int) which is calling for a connection priority( CONNECTION_PRIORITY_BALANCED, CONNECTION_PRIORITY_HIGH or CONNECTION_PRIORITY_LOW_POWER) But I didn't test it.

Answer 1

You could try to enable Bluetooth HCI Snoop Log in Developer Options and then view the log file in WireShark. Look for connection update commands, these can be issued by either side of communication. This command change the transmission settings and slow down the transfer. Also look for GAPROLE_PARAM_UPDATE_ENABLE in your TI BLE app.

Answer 2

Yes Michael we use CC2650 and for our requirement BLE is sufficient bur I'm not sure if it really supports bluetooth classic (http://www.ti.com/product/CC2650/description) .

You can try playing around the BLE connection parameters to get the setup tuned, that's what we did other than trying to build the app giving priority to BLE operations.Take a look at this for more information on connection parameters. https://devzone.nordicsemi.com/question/60/what-is-connection-parameters/

You can't configure the connection parameters on the phone but the peripheral(i.e. SensorTag) even so there's not guarantee that the given parameters will actually be accepted by the central device in case will settle with a set of parameters accepted by the central device. (Android and IOS have different policies in terms of these..)

In our case we are transmitting in intervals of 15ms and seems quite stable. But all these high frequent transfers at the cost of the low power consumption capabilities of BLE which is really what it is intended for. We could go even below that close to 7.5ms which is the minimum connection interval supported by Android. Our initial tests were stable but reliability of such a low latency is questionable.