Send a single beacon with extended size

[Kaveh.M]

Hi, 

I am sending 20 bytes of data in a beacon format. These are fit into m_beacon_info[2] to m_beacon_info[21] defined in ble_app_uart code from nordic SDK: 

I send beacon using this code:   

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manuf_specific_data.data.p_data = (uint8_t *) m_beacon_info;
advdata.p_manuf_specific_data = &manuf_specific_data;

err_code = ble_advdata_encode(&advdata, m_adv_data.adv_data.p_data, &m_adv_data.adv_data.len);
APP_ERROR_CHECK(err_code);

err_code = sd_ble_gap_adv_set_configure(&m_adv_handle, &m_adv_data, &m_adv_params);
APP_ERROR_CHECK(err_code);

advertising_start();
nrf_delay_ms(20);
advertising_stop();

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Is it possible to extend the size of the beacon, so that instead of sending 20 bytes, I send 30 or 40 bytes in one single beacon without sending multiple beacons that contain 20 bytes of data?

Thanks

[Sigurd]

Hi!

Kaveh.M said:

Is it possible to extend the size of the beacon, so that instead of sending 20 bytes, I send 30 or 40 bytes in one single beacon without sending multiple beacons that contain 20 bytes of data?

An ADV_IND/ADV_NONCONN_IND advertising packet can be up to 31 bytes of data. Each field (i.e. appearance, name, service UUID or similar) have a header of 2 bytes (length and type), meaning that the maximum user payload is 29 bytes. 

But with Bluetooth 5, we have something called Extended Advertising, that allows you to have up to 255 bytes of advertising data.

These posts here shows you how to modify the beacon code to acheive that:

 Changing advertising maximum size with BLE extended advertisin 

 RE: Extended advertising fails configuration 

PS: For new projects we recommend nRF Connect SDK.

[Kaveh.M]

Thanks. That was helpful. 

Compared with the case of 31 bytes beacon, how much more time the central receiver has to spend to read and extended beacon if we send a 60 bytes beacon instead instead of 31 bytes? 

I need to know how extending the size of the beacon is going to impact my traffic as my central device receiver has to connect with multiple devices. 

[Sigurd]

60-31= 29 more bytes. 

29*8 / 1 Megabits per second  = 232 microseconds. So at least 232 microseconds extra .Might be some extra header byte as well with Extended Advertising. 

[Kaveh.M]

It seems that the extended beacon is sent in another channel. So there should be also some time associated with switching between channels. 

[Kaveh.M]

So the time that it takes the central device switch from one channel to the other is a fixed number or has a variable value? What does it depend on and what are the min-max values in time that it takes a central device to switch between channels?