Ble mesh radio mode

[luciom]

In order to change the bitrate of the nRF52840 I tried to change the following code on advertiser.c :

static inline void set_default_broadcast_configuration(broadcast_t * p_broadcast)
{
p_broadcast->params.access_address = BEARER_ACCESS_ADDR_DEFAULT;
p_broadcast->params.radio_config.payload_maxlen = RADIO_CONFIG_ADV_MAX_PAYLOAD_SIZE;
p_broadcast->params.radio_config.radio_mode = RADIO_MODE_BLE_1MBIT;
//p_broadcast->params.radio_config.tx_power = RADIO_POWER_NRF_0DBM;
#if NRF52840_XXAA
p_broadcast->params.radio_config.tx_power = RADIO_POWER_NRF_POS8DBM;
#else
p_broadcast->params.radio_config.tx_power = RADIO_POWER_NRF_POS4DBM;
#endif
}

I tried to change the radio_mode to RADIO_MODE_NRF_62K5BIT in order to gain more receiver sensitivity.

After the change the nodes stop communicating.

Can you help?

[AndreasF]

Hi Lucio.

I've tried to set up nrf5_SDK_for_Mesh_v2.2.0_src\examples\light_switch client, server, and provisioner using the radio_mode RADIO_MODE_NRF_62K5BIT (62.5 kbit), but I haven't been successful in the implementation yet. I will have to look at this more thorough, and I hope I can give you a better answer on Monday.

However, the bitrate you try to implement is not in the Bluetooth specification, and any successful implementation with that bitrate would therefore not be able to qualify the Bluetooth qualification. And even if you get this to work between two devices, it will not work in Mesh, as Mesh required a different bitrate in order to operate. You can read more about this on Bluetooth SIG's official website.

- Andreas

[luciom]

Hi Andreas,

thank you for your clarification.

I'm looking to the BLE Mesh docs and specifications but I cannot find any reference to a particular bitrate.

I simply referenced to the nRF52840 product specifications where I read:

-95 dBm sensitivity in 1 Mbps Bluetooth® low energy (BLE) mode

-103 dBm sensitivity in 125 kbps BLE mode (long range)

Since we work in Long Range mode with TX power set to +8dBm as you can see on the code snippet above (modified by me) we also would maximize the rx sensitivity but 125 kbps BLE mode is not listed in the enumeration (only 62.5kbps mode that I know is not Bluetooth specified).

You think that also +8dBm TX power is not compliant with BLE Mesh specifications?

[AndreasF]

Hi Lucio.

The BLE Mesh SDK uses the Bluetooth 4.0 specification, that bitrate is 1 Mbit/s.

The sensitivity you read in the product specification for the nRF52840 is for the hardware, it's not valid for all the different SDK's. The -103 dBm sensitivity is not related to Mesh, as the bitrate in the BLE Mesh SDK is 1 Mbit, not 125 kbps. This means that the long range mode is not compliable with BLE Mesh.

An increase in TX power affects your energy consumption only. So that is something you have to see if you can accept, based on how much energy you have available.

In short, if you want to have long range I suggest you do not try to implement Mesh, as Mesh is neither specified or meant to be a long range solution.

- Andreas