As an independent NTN communication module, how is nRF9151 connected to an external MCU on the circuit?

[Baoxiang]

Hello, I am currently using the nRF9151 LACA A1A SIP module for the development of NTN communication application terminals.

In my hardware design scheme, the nRF9151 module is used as a standalone NTN module. The module communicates with the external application MCU through a serial port, and the external MCU controls the working state, data transmission and reception, etc. of the nRF9151 module through AT commands.

Without secondary development, the nRF9151 module will be programmed with two Nordic-provided firmware: one for NTN communication and the other for serial modem functionality, enabling the nRF9151 module to possess comprehensive NTN communication and serial AT command capabilities.

The hardware design has referenced the reference design of the development board nRF9151_SMA_DK, but there are still some issues. Please help me answer them. Thank you!

The current problem encountered is:
1. The nRF9151 module has two serial ports for external communication, which are respectively used for NTN AT commands and Modem trace and debug. Could you please help me identify which serial port is used for AT commands and which one is used for trace and debug, and provide the corresponding pin numbers for the nRF9151 module? According to the reference design of the development board nRF9151_SMA_DK, my current understanding is that UART1's Tx and Rx are P0.27 and P0.26, while UART2's Tx and Rx are P0.29 and P0.28. Is this correct?

2. For the aforementioned UART1 and UART2 types, besides using Tx and Rx, are the corresponding RTS and CTS also required to be wired out and controlled? If they are not wired out, what would be the impact?

3. Can the NTN firmware of the nRF9151 module officially released operate stably for a long time? Can it be used for commercial applications?

4. In my application, which firmware should I program into the APP MCU firmware inside the nRF9151 module? I noticed that the official website provides many firmware options, but I'm not sure which one is suitable for my application. Could you please provide me with the name of the APP MCU firmware that should be programmed into the module.

[Simon D-M]

Hi,

4. In my application, which firmware should I program into the APP MCU firmware inside the nRF9151 module? I noticed that the official website provides many firmware options, but I'm not sure which one is suitable for my application. Could you please provide me with the name of the APP MCU firmware that should be programmed into the module.

I'm addressing that question first as it will influence some of the other questions.

If I understood your needs correctly, you want to use the nRF9151 as a "modem-only" solution for your device. To do that you need to program the "Serial Modem Add-On" application (link). This application is handling the link between the host MCU and the actual modem in the nRF9151. It also has some more feature, like some custom AT commands, FOTA/DFU capabilities, ...

(if your schedule allows you to wait a bit, I would like to recommend you waiting for the v2.0.0 as it will have quite a lot of new features. You can find some key new features and the scheduled release date on here.)

1. The nRF9151 module has two serial ports for external communication, which are respectively used for NTN AT commands and Modem trace and debug. Could you please help me identify which serial port is used for AT commands and which one is used for trace and debug, and provide the corresponding pin numbers for the nRF9151 module? According to the reference design of the development board nRF9151_SMA_DK, my current understanding is that UART1's Tx and Rx are P0.27 and P0.26, while UART2's Tx and Rx are P0.29 and P0.28. Is this correct?

The UART pins are mostly software defined. For the Serial Modem Add-On application you can find the documentation for UART configuration here.

And about the usage of the two UARTs, one of them is indeed used for logging and debugging. And the other is used to actually communicate with the modem.

2. For the aforementioned UART1 and UART2 types, besides using Tx and Rx, are the corresponding RTS and CTS also required to be wired out and controlled? If they are not wired out, what would be the impact?

For the Logging/Debugging UART, hardware flow control is disabled by default, so no problem not having it.

However, for the UART connecting the host MCU and nRF9151, it is highly recommended to use hardware flow control. As you can see here it is possible to use it without hardware flow control, but it is still experimental. So I would advise you to treat hardware flow controlled as required for this UART.

3. Can the NTN firmware of the nRF9151 module officially released operate stably for a long time? Can it be used for commercial applications?

I think the NTN modem firmware v1.0.0 is stable enough to be in commercial applications. But still, I would recommend you to have some kind of FOTA/DFU capabilities in order to update the NTN modem firmware to a newer version as more feature and bug fix will probably be added in the future.

I hope I was able to answer your questions. If you want more details on an answer, or still have more questions on the same topic, feel free to ask them here.

Best regards,

Simon D-M

[Achim Kraus]

Baoxiang said:

3. Can the NTN firmware of the nRF9151 module officially released operate stably for a long time? Can it be used for commercial applications?

In my expperience (last 8 months) the "stability" (of the communication) seems more to depend on the antenna ;-).

As also for other modes, e.g. LTE-M or NB-IoT, you will need to use a "reconnect strategy", when the network gets deregistered. In many case the modem is able to register to the network again automatically. in some cases, it may require to restart the modem with a cfun=0/cfun1 cycle, if the modem doesn't get reconnected within a timeout (e.g. 1h). And, unfortunately, in my experience it requires in rare cases to reboot the device, if it can't reconnect for longer (e.g. 6 h).

But with that, my experience is pretty well. 

Simon D-M said:

But still, I would recommend you to have some kind of FOTA/DFU capabilities in order to update the NTN modem firmware to a newer version as more feature and bug fix will probably be added in the future.

Let me recommend to consider also the costs for a FOTA over NTN ... I guess you will do this only if it's really, really required.

[Baoxiang]

Hello, Simon !

Thank you very much for your detailed and professional response. Regarding the following point, I still have some questions. Please help me with a further reply. Thank you!

If I understood your needs correctly, you want to use the nRF9151 as a "modem-only" solution for your device. To do that you need to program the "Serial Modem Add-On" application (link). This application is handling the link between the host MCU and the actual modem in the nRF9151. It also has some more feature, like some custom AT commands, FOTA/DFU capabilities, ...

Here is mentioned the " need to program the 'Serial Modem Add-On' application (link). This application is handling the link between the host MCU and the actual modem in the nRF9151. It also has some more features, like some custom AT commands, FOTA/DFU capabilities, ..."
How to understand this sentence? Does my application development require further programming on the nRF9151 module?

At the current stage, our goal is to quickly develop a functional prototype. Initially, we are not inclined to spend a lot of time on programming and development for nRF9151, and familiarizing ourselves with nRF9151 programming also requires some time for research and study.

At the current stage, ideally, we should only program the relatively stable firmware (NTN firmware + Serial modem firmware) officially provided by Nordic into the nRF9151, and then operate the corresponding AT commands through the serial port to achieve the application.

After we have completed product verification and become familiar with the use of nRF9151, we will proceed with further programming and development for nRF9151.

So some of the problems I am currently facing are also raised based on this idea. Could you please give us some more guidance and suggestions? Is there any more detailed and directly operable information? It would be even better if there is.

Thank you very much again!

[Baoxiang]

Thank you very much for sharing your application experience and suggestions. I can sense that you have rich application experience. We hope to have the opportunity to consult you more in the future regarding issues that may arise during our development process.
The antenna is indeed a crucial component. Our prototype utilizes the development board antenna provided by Taoglas, and we may later engage a professional antenna team to design a built-in antenna (FPC antenna). I'm wondering if you have experience with built-in FPC antennas, and how their communication performance is when connected to Skylo's satellite network?
Thank you！

[Achim Kraus]

Baoxiang said:

I'm wondering if you have experience with built-in FPC antennas

Unfortunately, no. I just bought an external antenna to run the device in my office and put the antenna outside.