EMC/RF testing of the GPy LTE Cat M1 modem

[E W]

My company is conducting electromagnetic compatibility (EMC) and radio frequency (RF) testing with the GPy module and we were wondering how we could generate/transmit LTE Cat M1 signals inside the testing room? (a faraday cage where no network connection is available).
We are trying to simulate normal IP data traffic and pinging of an IP address such as 8.8.8.8.

I have been looking at the Sequans LTE Modem PDF containing AT commands (see here) to try and find an AT command that might transmit something without a network connection but have had no luck so far.

Note: Pycom's certification of the GPy, see Radio section (here)

Any information would be great, thanks

[kjm]

The sequans runs RF in an attachment loop. It's not a good simulation for IP traffic I guess but at least you get to characterise carrier?

[jcaron]

@kjm I'm not familiar with the details of LTE, but I was under the impression that cellular devices never transmitted anything before hearing something from the network. They normally need to know what network is there, on which band (so they don't start transmitting on a band which is not usable in the country the device is in), and for all xxDMA (TDMA, CDMA, OFDMA...) they need to get a slot/channel assigned (so there's no collision with other devices), so they first scan passively (listen for broadcasts from the network on various bands) before transmitting anything.

Am I wrong?

[jcaron]

@E-W There are a lot of other proprietary AT commands that are not in the doc (starting with AT!=). See https://forum.pycom.io/topic/6724/gsm-scanning/8 for a list.

Maybe there's one in there for a test mode of some sort? The list is quite long so I haven't really checked if there's anything relevant.

I would believe testing usually involves a base station of some sort, though I have no idea how the test equipment/procedure would then differentiate the RF emission of the device v. the base station.

You may try to find test reports of similar equipment to see how they do it. Some test reports can be found on the web and some can be quite detailed, though I haven't looked at any of that recently.

[kjm]

@jcaron Probably not, what you say makes sense & anytime I've seen RF from the sequans on an SDR there has been a tower within range.

[E W]

Result: The testing facility had equipment to simulate a base station inside the testing room and provided us with a special SIM which connected to it (on LTE band 20 - 800MHz). We could then use our normal MicroPython code to send a ping lte.send_at_cmd('AT!="IP::ping 8.8.8.8"') or send data over a socket connection.