Connection parameter optimize: nRF52840(central) multilink with 8x52832 peripherals

[Avadacadabara]

Hi all,

I'm developing a multilink system with 52840 dongle as central and 8 52832 devices as peripherals, which is similar to previous project in thread part I & Part II.

8 peripherals are exactly the same and generates 172Bytes/each device every 100ms, so total data rate would be 13.76kB/s. 

↑According to power profiler, I foud that data packets generated every 100ms, which is 8(peripheral devices) * 251(PDU size) * 1(packet per device) could be transmited within 25ms.  So I set central connection parameters as follows：

But here is my problem: the throughput could reach the requirement, but the connection stability seems very sensitive to distance. When peripheral devices are placed closely to central, the connection is very stable. Then I move peripherals 1 meter away from the central, the devices start to disconnect & reconnect frequently which cause severe packet loss.

I've tried different parameters in previous thread, for instance, 100ms connection interval or 80ms interval. I also tried 52840 module with PA/LNA to raise TX/RX sensitivity. Seems no help. So I think there might be some faults in parameter setting?

Thnaks.

Ava

[Avadacadabara]

Hi,

I tried to set Central GAP_EVENT_LENGTH to 3 but seems like the disconnection is getting worse. Then I set both Central and Peripheral GAP_EVENT_LENGTH to 24 and it could hold connection quite a long time in range of 2 meters. But when I try to move further (3m), they could still hold for several minutes. Then first come the throughput unstablization, followed with massive disconnection and reconnection. 

 

I've already turn on DLE for all Central and peripherals.

Sigurd said:

PS: Connection Event Length Extension could also be helpful for the throughput:

[Avadacadabara]

Plus following snippet is current scan parameters on my Central, is there any conflicts between connection event and scanning event?

[Sigurd]

With NRF_SDH_BLE_GAP_EVENT_LENGTH=3 (in 1.25ms units), you have 8*3,75 = 30ms, then you have the scanner on top of that.

NRF_BLE_SCAN_SCAN_WINDOW = 16 (in 0.625 ms units) -> 10ms , with tScanReserved ~1ms, you should have a connection interval of at least 41ms when you have 8 connections running + the scanner running.