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Slow BLE throughput with Nexus 5X

Hi,

I am trying to transfer large amounts of data over BLE, to a large amount of devices so speed is critical.

So far, i am able to send the nRF51422 (S110 V8.0.0) a 48Kbyte chunk of data in 12.6 seconds which is roughly 32kBits a second if i am right, which is far from the value of 125kbits i have seen in another thread.

Writes in the app are queued, so whenever onCharacteristicWrite is called, another 20 byte packet is sent to the device. Also i use the BluetoothGatt#requestConnectionPriority to get a better connection interval prior to the transfer.

To my understanding, via this method of transferring, the nexus 5 should transfer 6 packets per interval, which should be around 10mS, resulting in much faster speed than i have now.

At the minute packets seem to be going to the device at a rate of around 5mS which would indicate that there are multiple packets being sent during the interval, as i think it cannot be lower than 7.5mS (if it was sending 6, then the interval would be 32mS).

The nRF51 is configured to accept a connection interval between 7.5 and 100mS.

Is there a different method i should be using in the app, or some missed config on the nRF51?

Parents Reply
  • Hi Emil, hope you had a good new year. I have just gotten around to looking in the HCI logs at the connection interval commands and i am not sure if i am understanding them correctly. I have been following this document from ST about how to look at the raw numbers, what i have in my logs is not lining up with what they have, although i realise this is for a different stack, i thought that would have been standard.

    www.st.com/.../en.DM00162667.pdf

    I have found some interesting things in this log however, i will post a snippet of a connection parameter update in another comment along with another possible issue i found. also here is the log if it is of any use to you drive.google.com/open

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