Streaming data over BLE without any ACK

[Rytis]

Hello,

I'm trying to stream data at ~ 30KB/s rate. I use nRF52840 development board with S140 as peripherial and smartphone with "nRF Connect" app as central. UART example works fine and I can send mentioned data in short range, but data rate decrease after distance between phone and nRF board increases. As far as I understant UART example uses notifications to send data and notifications has ACK in Link Layer. So increasing range lower my data transfer speed.

In my case packet loss is tolerable and i'm even curious how distance between devices affect packet loss. Every packet has index so after streaming i want to calculate how many packets were lost.

So I wand to ask if there any way to stream data without any ACK?

Thanks.

[Simonr]

Hi

At what range is your connection starting to break up? I suggest you take a look at our BLE throughput demo, which shows how to maximize your throughput based on your range and necessary bit rate.

Best regards,

Simon

[Rytis]

At ~140m. I'm more interesed about the whole idea to have data stream without any ACK. Maybe this is corner case and not many people use sending data without ACK.

So is there any easy or not necessarily easy way to do that?

Thank you

[Simonr]

Hi Rytis

I think you've misunderstood here. Notifications do not need acknowledgments for each packet sent. A notification allows you to queue a certain number of packets before sending, and once the buffer is full, you get a NO_TX_BUFFERS error back from sd_ble_gatts_hvx(). When a packet has been sent you'll get a BLE_EVT_TX_COMPLETE event and should be able to queue further packets.

Indications, however, must do an application layer ACK when sending data, making it slower than notifications.

You can check out this great guide to see how to maximize throughput in your application.

Best regards,

Simon

[Rytis]

Hello,

Thank you for your answer.

I have one more question: So if my nRF52840 development board send data using notifications to mobile phone there is no guarantee that smartphone received every packet?

I've done some test based on UART example and noticed that in longer range between devices transfer speed decreases but zero packets are lost, i used notifications. So in my theory smartphone as data receiver send some ACK in lower BLE layer to my development board which is peripheral.

Best regards,

Rytis

[Simonr]

Hi

Yes, apparently there is some two-way communication between the two devices, can you provide a sniffer trace of the connection so we might see what exactly is happening between the two devices. 

Best regards,

Simon