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. 

[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? 

[Sigurd]

This guide seem to cover this topic in detail: https://cloud2gnd.com/foundations-of-le-audio-extended-advertising/ , you should also be able to find all the info in the Bluetooth core spec on the timing.

[Kaveh.M]

From this article, the time offset between sending AUXPtr on primary channel to send extended advertising beacon on secondary channel is variable and can be between 0-2.45 seconds. 

When using Softdevice BLE stack and Nordic SDK, is there a specific parameter or function that allows us to set this time offset for extended beacon advertisement? 

Thanks

[Sigurd]

Kaveh.M said:

When using Softdevice BLE stack and Nordic SDK, is there a specific parameter or function that allows us to set this time offset for extended beacon advertisement? 

No. It's static at 330 us. See this post: Possibility to configure "Aux Offset" in AUX Ptr in Extended advertising