I was hoping to get an explanation of how the LTE Sensor Gateway sample app works. The SDK documents the sample app here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/0.3.0/nrf/samples/nrf9160/lte_ble_gateway/README.html#nrf9160-lte-sensor-gateway
I understand that this sample app makes use of the lte_ble_gateway sample app for the nRT91 on the development kit, and the Bluetooth: HCI UART sample for the nRF52 board controller. My understanding is that this makes use of the Host Controller Interface H:4 to allow the lower levels of the BLE stack to run on the nRF52 while the higher levels are run on the nRF91.
I think that in a real application, there is a need for only either the BT radio or the LTE radio to transmit at any particular time; they should never both transmit at once. Does this LTE Sensor Gateway sample make use of some mechanism to make sure that the transmit of the two radios is mutually exclusive, and, if so, where is that handled in the code? I wasn't sure if the BT radio in the sample app would ever transmit once the BT connection was made, or if it just received data from the Thingy.
If this is not handled in the code, do you have a suggestion as to how the code could ensure that the radios would never transmit at the same time? Any sample code?
What is a design approach that could be taken where the situation was reversed, where the BT MCU was the host and the LTE MCU the host controller, so that the BT MCU would decide when something should get sent out on LTE?
Maybe a better way to frame my final question would be to ask what could you suggest for a design to coordinate BLE/LTE where the entire BLE stack is implemented on one MCU and LTE on another.
The LTE Sensor Gateway sample does nothing for coexistence, which means you may get the occasional packet loss. However it has minimal impact due to so little time spent in TX, leading to very few collisions.
On the LTE side there is the LTE modem coexistence interface, but we do not offer any corresponding software for the BLE side yet.
You can also improve coexistence in hardware, e.g. by adding filters to the RF lines.
Do you have any samples or can give any examples how the coexistence interface is used?
Can you please provide more of a description of the BLE Coexistence interface than is in the spec?
Is it handled by modem firmware?
How is the COEX0 pin handled in the nRF91?
Does the interface have an enable/disable?
Please explain use of the COEX1 pin.
Can you provide an example or description of a design that uses the interface?
Correction: LTE Modem coesistence interface, not BLE...