packet sending rate drastically changed depending on distance

[LeeJW]

Hi i am developing application that utilize SAADC and send it to pc by ble_nus service

my goal is to acheive 250Hz sampling frequency which means i have to send data packet  every 4ms.

i used nrf52840dk as adc role and nrf52840 dongle as interface to PC

when DK and dongle are in close distance, they are able to send packet every 4ms quite well

but when i put dk at a distance, sending rate decreases to about 200Hz,

worst case was 170Hz for ~3m distance

depending on surroundings, even dongle and dk are close , data sending rate was very low.

i need application that can send packet as constant as i can robust to surroundings.

nrf sniffer when they are close

when distance increased, some empty pdu arise, 

also i observe l2cap 

 

also i observed above packet i can't figure out it's source

some arrived packet is followed by unknown strings

is there are any good approach to establish robust connection?

due to my lack of knowledge to ble, i could miss  a lot but 

any advise would be a big help 

conn interval = 50ms

MTU_size = 247

phy = 1m

tx power= 8dbm

i used ble_nus_send function 

in nrfSDK v17

thank you very much

[Sigurd]

Hi,

Could you upload the sniffer files here?

[LeeJW]

hi i attached both project and sniffer

for project , send g to activate adc and send s to stop adc 

thanks 

[LeeJW]

wireshark_240113.pcapng

ble_uart_adc_dk_use_this 250hz_0112.zip

[Sigurd]

Hi,

There is a lot of retransmits and bad CRC in the trace, so that explains why the throughput goes down.

If you replace the dongle with e.g. a nRF52840-DK instead, do you still see the same behavior ?

[LeeJW]

i tried ble uart central to dk to replace dongle but doesn't seem to be better

even worse, they got disconnected after receving for packets about 10seconds

is this case of packet loss is mainly due to physical antenna limit on pcb?

or is there any approach can be done on code?

we will implement it on moblie phone eventually,

so would phone's antenna would be expected to have less packet loss?

[Sigurd]

Hi,

Are you in a noisy RF environment? If yes, could you try in a less noisy RF environment?

[LeeJW]

Hi 

i have done it in my home , interference candidates are 

wifi router and my phone i think no significant packet loss emerges( although some packet indeed  got dropped)

definitely when i do same thing in my office with 10 people in room ( many bluetooth device )

dongle is not capable of pick every packet from dongle , less then 200Hz

i have few knowledge of how noisy environment leads to performance degradation.

is 52840 should have no problem with sending packet at 250Hz theoreticaly?

[Sigurd]

Ok, so you saw big improvement when testing at home?

[LeeJW]

Hi sorry for my late reply

Yeah it seems perform well at home

so you suspect environment noise caused 

those bad crc errors and retransmission?

[Sigurd]

LeeJW said:

Yeah it seems perform well at home

so you suspect environment noise caused 

those bad crc errors and retransmission?

Yes, correct.

[LeeJW]

i see,

thanks for your reply!