nRF 52 Throughput with different phones

[Rytis]

Hello,

I'm using BT840XE module and ATT_MTU Throughput Example with S140. My goal is to measure maximum data transfer speed between module and different phones. Module acts as peripheral and phone as master. For phones, I use nRF Connect app. 

Problem is that i get different data transfer speed with different phones. I measure how many data packets are send per connection interval. Every time BLE_GATTS_EVT_HVN_TX_COMPLETE arrives GPIO pin is toggled. And i see that some phones accept more packets per connection interval than others. Please see attached pictures. Samsung J7 accepts only 5 packets per connection interval and Google pixel a3 accepts packets in whole connection interval.

Settings:

Connection interval: 100ms

NRF_SDH_BLE_GATT_MAX_MTU_SIZE 247

NRF_SDH_BLE_GAP_EVENT_LENGTH 300

My question is what could cause that huge differences in delivering data packets to phone? Maybe phones has some kind of limitation?

Best regards,

Rytis

[Rytis]

Hi Edvin,

Thank you for fast response.

Is there some function in SoftDevice API to request increasing Event Length?

If phone accept larger MTU this means DLE is enabled?

My goal is to deal with phones with at least Bluetooth 4.2 (My Samsung has 4.2). I tested iPhoneX also and it behaved similar to Samsung J7.

Have a nice day,

Rytis

[Edvin]

    ret_code_t err_code;
    ble_opt_t  opt;

    memset(&opt, 0x00, sizeof(opt));
    opt.common_opt.conn_evt_ext.enable = 1;

    err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);
    APP_ERROR_CHECK(err_code);

I copied this from the ble_app_att_mtu_throughput example. I normally don't recommend this example as a starting point, because it is quite complex, and can act as both a peripheral and central during runtime. However, you can see how the different settings are being set based on the incoming CLI commands. 

when you write a command, you typically get a response on the CLI. search for this response in the project, and you will find the function that will set the configuration.

Best regards,

Edvin

[Rytis]

Last question.

So there is also a function to enbale DLE? Or MTU size just need to be increased?

Best regards,

Rytis

[Edvin]

Test the ble_app_mtu throughput example. If you write config print, you should have these settings, which gives the maximum throughput:

Note that this is between two nRFs. You will not get the same throughput to a phone. And by the way. The Samsung J7 looks like it has Bluetooth 4.1, not 4.2.

Look at the test description for how to test the throughput example to see how to use putty to run the commands. You want to set both the MTU and Data length to maximum. 

If you test the ble_app_uart example, this already requests these parameters, but as I mentioned, I don't think the Samsung J7 supports these features. And even if it is 4.2, many of the features that are added in Bluetooth are optional, so it still may not support increased data length.