Revert back to Coded PHY connection when 2M is not possible because of distance.

[JasonGeo]

Hi,

I have 2 nrf52840 DK boards advertising on coded PHY mode. Once connected the connection is updated (using sd_ble_gap_phy_update()) to use 2M mode. No problem in doing so.

However, I have a situation or use case where after the successful update to 2M mode, but because of the distance between the 2 boards is too far for 2M mode to continue, I would like the connection to revert back down to coded PHY. Is that even possible in the first place? If it is possible, what are steps required to revert back to coded PHY.

In my testing,

I tried walking around to find the distance that is too far for 2M communication but still possible with Coded PHY. 

What I find is that they always connect on coded and then updated to 2M. When the distance is too far apart, there is no connection at all even on coded PHY. 

I can't find a distance/case where they connect on coded PHY but fail to update to 2M because of distance.

Some may say why not just connect on coded PHY and forget about 2M. My case is we want to use 2M whenever possilbe and auto revert down to coded PHY when physical distance does not allow 2M mode.

Your help is very much appreciated.

[Simonr]

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This other DK or 52 device (on top of the 840 DK) also doing BLE transmissions is indeed likely to affect the range you'll be able to achieve over Coded PHY, as they transmit on similar frequencies they're bound to affect each others performance I'm afraid. I don't think the data length will affect your range, just the transmission time between each event, since Coded PHY transmissions take ~8 times longer than transmissions on the other PHYs.

Best regards,

Simon

[JasonGeo]

Thank you Simon, at least now we have more understanding why we don't see the extended range possible with Coded PHY.

One more thing, in our setup, we have this nRF52840 DK siting in between 2 other DKs communicating back and forth between them. This middle DK establishes 2M connection with one DK and Coded PHY with the other DK.

Do you think as a result of this setup/configuration, we get reduced range as well with the Coded PHY link since the radio on the middle DK is shared/multiplexed between talking on 2M to one and Coded PHY to the other?

[Simonr]

No, I don't think the Coded PHY should have reduced range because you switch between 2MBPS and Coded PHY. You will need to make sure that the Coded PHY side have enough time to transmit its data between every time it switches between 2MBPS and Coded PHY, but as soon as it is in Coded PHY, it shouldn't be hindered by its own radio.

Best regards,

Simon