Cellular modem interface using SPI

[MichaelS]

Hi

I am wanting to interface an ESP32 to a cellular modem 4G LTE / 5G (later) using SPI bus instead of serial. 4G / 5G seems a bit academic if interface is serial only and limited to 15200 Baud. I have not seen any dev boards which support SPI so an IC solution on my own board would seem to be required as the modem ICs do support SPI as well as serial with full hardware handshaking, I2C etc...

Does anyone know of a 4G 5G dev board which does support SPI?

If I use SPI on a modem IC direct, how usable would the modem libraries be. eg Is it feasible to expect once I change the low level interface from asynch serial to SPI, the interface would remain the same with AT command and PPP once a connection is established?

Thanks

[aitech]

Hi,

You are correct that achieving 4G/5G speeds using the UART interface is not feasible due to its inherent communication speed limitations. However, by utilising alternative interfaces such as SPI, we can attain respectable speeds in the range of 10-20 Mbps, with USB interfaces offering even higher potential speeds. In my current project, we encountered similar speed limitations with the UART interface. We are employing the SIM7672G module from Simcom. Given that the ESP32-S3 supports dedicated USB OTG, it seems viable to interface it with the Simcom module. I have successfully established an internet connection (PPP) using the ESP_Modem library over UART.

I am yet to validate the connection over the USB interface. Hope by next week I can validate the connection over USB.

Thanks,
Karan S. Sisodia
(Alfa Intellitech, India)

[MichaelS]

Hi Karan
Thanks for the reply.
Are you just using the SIM7672G IC on your own board?
I can't find a SIM7672G development board which support SPI or USB
If you have found one, could you please let me know where from?
I would really appreciate it if you keep me posted on your progress.
Good Luck!
Michael

[aitech]

Hi,
Yes I am using SIM7672G on my custom board.
Past few days I am working on upload speed optimisation on UART communication the maximum baud rate that I have achieved is 1842000 beyond this speed module just not respond. I have tested with 10Mb single file which took 10 min. So it is 1Mb per minute, which is quite not good yet.
I still have to test it over USB. I will let you know once I got some new results.

Thanks,
Karan S. Sisodia
(Alfa Intellitech, India)

[MichaelS]

Thanks for the update.
1,842,000 Baud (bits / second) divide by 10 bits = 184,200 Bytes per second.
Ignoring overheads of file transfer protocol, this should take about 55 seconds theoretically to transfer 10MB
Does the transfer time for your 10MB file increase heaps (double) if you halve the baud rate. This would prove the baud rate is the limitation. If not there could be something else at play?

[aliarifat794]

All existing modems support I2C communication. No SPI.

[MichaelS]

What sort of equivalent baud rate can you get out of i2c?