Fine tuning connection and scanning parameters in a BLE Network

RE: Fine tuning connection and scanning parameters in a BLE Network

Hieu — Thu, 25 May 2023 08:36:50 GMT

[quote user="Karim_Os"]First of all, I hope you enjoy your holiday,[/quote]

Thank you. I had a good time.

[quote user="Karim_Os"]1- Yes, we can reconnect, but we can have two times disconnection per hour[/quote]

Depends on how electromagnetically noisy your environment is, and what range your device is operating at, this might be normal.

If your devices are very far from each other, try bumping up the TX Power of the devices. You can find the method discussed several times on DevZone via the search function or an internet search engine.

[quote user="Karim_Os"]2- We use both ways, from central to peripheral and vice versa, so slave latency actually delays some of the messages if SL is large[/quote]

You don't need to use a large SL. Just a small amount is already very helpful for the central to schedule events.

Larger values are mostly used for peripheral power saving purpose.

What is your requirement regarding latency? At 30ms connection interval, even with large peripheral latency (like 100), the delay will only be 3s.

RE: Fine tuning connection and scanning parameters in a BLE Network

Karim_Os — Wed, 17 May 2023 17:41:53 GMT

First of all, I hope you enjoy your holiday,
second things:
1- Yes, we can reconnect, but we can have two times disconnection per hour
2- We use both ways, from central to peripheral and vice versa, so slave latency actually delays some of the messages if SL is large

RE: Fine tuning connection and scanning parameters in a BLE Network

Hieu — Tue, 16 May 2023 19:51:17 GMT

I understand your requirement as followed:

- Up to two type-C devices shall be connected to one type-B device
- Up to two type-B devices shall be connected to one type-A device
- Each type-C device shall transmit 100 bytes of data every 1 minute
- Each type-B device shall transmit all date received from type-C devices to the type-A device it is connected to

This requirement is not extreme, and achieving stability and reliability should not be an issue. How often are you having the connection timeout issue? Is the reconnection also not working well?

[quote user="Karim_Os"]I tried to increase slave latency, but it affected the data sent back from A to C.[/quote]

What is the concern regarding this? Must the latency be very low?

[quote user="Karim_Os"]nRF52 SDK16.0.0[/quote]

If you are in the early stage of your project, please try to use our newest SDK. We are actively developing the nRF Connect SDK, and the latest version is v2.3.0 as of time of writing. If you have to use the nRF5 SDK, we recommend using the latest version, v17.1.0.

Please be informed that I will have a holiday and days off from tomorrow. I will return later next week and continue to support you if you have any further questions. My apology for the inconvenience.

RE: Fine tuning connection and scanning parameters in a BLE Network

Karim_Os — Tue, 16 May 2023 10:18:31 GMT

Thank you for your quick response,

[quote userid="9456" url="~/f/nordic-q-a/99733/fine-tuning-connection-and-scanning-parameters-in-a-ble-network/425722"]

What SDK are you using? nRF Connect SDK or nRF5 SDK? And which version?

[/quote]

nRF52 SDK16.0.0

[quote userid="9456" url="~/f/nordic-q-a/99733/fine-tuning-connection-and-scanning-parameters-in-a-ble-network/425722"]By 100 bytes, do you mean that each Device C will send 100 byte at a time? [/quote]

Yes, for each device

[quote userid="9456" url="~/f/nordic-q-a/99733/fine-tuning-connection-and-scanning-parameters-in-a-ble-network/425722"]you can try looking into the Supervision Timeout and Peripheral Latency connection parameters. [/quote]

[quote userid="9456" url="~/f/nordic-q-a/99733/fine-tuning-connection-and-scanning-parameters-in-a-ble-network/425722"]could you give some estimation on how many type-C is connected to a type-B, and how often each type-C will transmit data?[/quote]

We have C devices double the count of others; each sends 100 bytes of data every 1 minute.

I tried to increase slave latency, but it affected the data sent back from A to C.

RE: Fine tuning connection and scanning parameters in a BLE Network

Hieu — Mon, 15 May 2023 20:37:42 GMT

By the way, there are a few things I would like to recommend you to:

Search for previous DevZone questions, for example, I can find two relevant ones fairly quickly: BLE Connection parameters choice for multiple connection
BLE Multi-link high throughput / lowest latency
Even if you are using a different SDK from the one in discussion, the numbers should still relevant be and can be referred.

Checkout this NovelBits blog post on maximizing throughput: https://novelbits.io/bluetooth-5-speed-maximum-throughput/

RE: Fine tuning connection and scanning parameters in a BLE Network

Hieu — Mon, 15 May 2023 20:33:02 GMT

Hi Karim_Os,

What SDK are you using? nRF Connect SDK or nRF5 SDK? And which version?

[quote user=""]1- How to know the packets per connection interval as we have ~ 100 bytes of sensor data, so we need to ensure it is transmitted in a single connection interval - hopefully, that is the right decision for throughput- [/quote]

By 100 bytes, do you mean that each Device C will send 100 byte at a time? Or all Devices C will send a total of 100? How often is this sent?

Sending all 100 bytes in one connection interval is possible, as a link layer packet can be 251 bytes maximum. Subtracting some overhead of other layers, you are still left with maximum 244 bytes of application data for each packet, which you can have multiple in a connection interval.

[quote user=""]2- What is the best connection interval to be chosen? The smaller, the better, or it has other calculations?[/quote]

It depends on both your data rate requirement and how likely devices are transmitting within the (relatively) same time.

In addition to the questions I asked previously, could you give some estimation on how many type-C is connected to a type-B, and how often each type-C will transmit data?

[quote user=""]3- How to perform scanning while connecting (as devices A and B are connected together to forward the sensor data) and at the same time always scan for new C-devices without affecting the throughput?[/quote]

Scanning can be enabled the same way that is done when there is no connection established yet.

[quote user=""]

4- for instance, if we have the following:
a- Device A connected to device B and receiving data

b- device A connected to 2 devices B and receiving data from only one, and the other is idle

c- device A connected to 2 devices B and receiving from both of them simultaneously,

what is the effect of the throughput and connection stability in these cases, I think case (a) is the best, but for b and c, would it differ? Why? And most importantly, how to manage throughput in a multilink like this while maintaining connection stability and reliability
as sometimes I face a connection timeout for the current configurations of all devices (30 ms connection intervals)

[/quote]

It quite depends on the details I have asked for above. As some general tips, you can try looking into the Supervision Timeout and Peripheral Latency connection parameters.

If you feel like you could use some review of the fundamentals of a BLE connection, Nordic provides a free online course on BLE Fundamentals, where the basics of a connection is covered in Lesson 3.

Hieu