Question regarding the transfer speed of the BLE on nrf52832 using nordic uart service

[Rajat]

Hi Everyone

I have been trying to send a text file(reading from SD card) , The size of the file is 2MB. 
I am using softdevice s132 for nrf52832 to transfer the text file via the Bluetooth to the Android application(nrf Connect). 
I am able to transmit the file to the nrf connect app , but the problem is that the transfer is too slow , it gives me an average speed of around 20KBPS , which is very less for our application.

What  i would like to know is 
1. Is there any specification of the softdevice which i should enable to receive the maximum throughput(or atleast 3/4th of it). 
2. Is it related to the service that i am using , I am using Nordic Uart Service. 

Here are the settings that i have been using
PHY - LE 1M for both Tx and Rx
Here is a log file , i am attaching , if that helps.

5001.Log 2020-10-07 12_34_02.txt

[Sigurd]

Hi,

We have some throughput numbers here: https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/ble_data_throughput/ble_data_throughput.html

I assume you have NRF_SDH_BLE_GAP_DATA_LENGTH set to 251 in sdk_config.h

You might want to increase NRF_SDH_BLE_GAP_EVENT_LENGTH so that it matches the connection interval you are using.

It could be that the phone you are using does not support data length extension(DLE).

[Rajat]

Updates :

1. With the nrf Dongle connected to PC and data transfer via nrf Connect for PC gives me desirable result and following result are seen on connection

  Sending PHY Update, 2 Mbps.
  ATT MTU exchange completed. MTU set to 247 bytes.
  Data length updated to 251 bytes.
  PHY update accepted
  PHY set to 2 Mbps.


2. With any Android device and nrf Connect for android gives me the following results on connection(My android mobile is oneplus 7pro , it supports BLE5.0 with PHY-2M)

Sending PHY Update, 2 Mbps.
ATT MTU exchange completed. MTU set to 247 bytes.
Data length updated to 251 bytes.
PHY update rejected
PHY set to 1 Mbps.Connection interval updated: 0x6, 0x6.
ATT MTU exchange completed. MTU set to 247 bytes.
Connection interval updated: 0x24, 0x24.
Data length updated to 251 bytes.

Please help asap , it is very urgent for us to complete

[Sigurd]

Try increasing NRF_SDH_BLE_GAP_EVENT_LENGTH , e.g. to 50

[Rajat]

My connection interval is 7.5 ms by default , but when it connects to android nrf connect application , the PHY updates get rejected and the paramteres get modified 
But in the case of nrf dongle and pc nrf connect , no modifications in my original values occur and i get desirable results.

[Rajat]

It goes in a breakpoint if i change this value

[Rajat]

NRF_SDH_BLE_GAP_EVENT_LENGTH 50 , makes my software go to breakpoint