Adding coded PHY to BLE mesh low power node (Mesh SDK v4.1.0)

[Sean Taylor]

I'm developing mesh nodes with serial interface, and have used the information in this thread to successfully modify the mesh firmware to support coded PHY

https://devzone.nordicsemi.com/f/nordic-q-a/29813/change-phy-in-mesh

I have been asked to add support for low power nodes and I'm finding that LPN-friend operation is very erratic with the coded PHY - I suspect that it's a timing issue, because sometimes friend requests and polls work, but mostly they do not.

I did have to make this change in core_tx_lpn.c

void core_tx_lpn_init(void)
{
    m_lpn_bearer.broadcast.params.access_address = BEARER_ACCESS_ADDR_DEFAULT;
 #if NRF_MESH_USE_CODED_PHY
    m_lpn_bearer.broadcast.params.radio_config.radio_mode = RADIO_MODE_NRF_62K5BIT;
 #else
    m_lpn_bearer.broadcast.params.radio_config.radio_mode = RADIO_MODE_BLE_1MBIT;
 #endif

and similarly in core_tx_friend_init() in the friend node.

I suspect there are some subtle timing changes that might be needed in the LPN and possibly in the friend - I'd really appreciate any help or pointers you could offer.   Thanks.

(You might be wondering why have a LPN with coded PHY - the answer is just so we can run all mesh nodes with coded PHY for range)

[Hung Bui]

Hi Sean, 

I suspect it was the MESH_FRIEND_RECEIVE_WINDOW_DEFAULT_MS that cause the issue. It's the receive window on the lpn's side (set by friend node). By default it's 5ms. Could you try changing it to something bigger ? Note that the bigger it is the longer the LPN node stay in scanning mode and draw more power.