Immune is a strong phrase, suffers less from would be more accurate.- in the sense that LTE-M uses the same radio frequencies and is usually a firmware patch for the base-station- the signals have to co-exist and are sent from the same transmitter and receiver at the base-station end. In effect the other modulation schemes are seen as a rise in the noise floor of the one you want, and the UE has to be able to decode the cell information to know which base station to send to and when to send.

So while phones are not in direct competition in the sense of running out of phone lines in the traditional sense, a heavilty loaded cell will not be so easy to connect to. And the back-haul data rate (the base station to the rest of the wired network) is also possibly a limiting factor - in rural areas that is often a microwave link rather than a fibre to the back of beyond.

There is no free lunch...

Mike.

Thanks Mike, Yes agreed - immune was not best word to use.

Some of the benefits of LTE-M, compared to Cat 1 and higher, are low power usage, low cost of the receiver, and higher maximum coupling loss. If the application is not cost sensitive, signal strength is not an issue, and the application will be continuously transmitting, would it be fair to say that Cat-M does not have any advantages over Cat 1?

It all depends how much bandwidth you need and how much latency/ timing jitter you can withstand. They are really the solutions to slightly different problems. And LTE-M has been standardized more recently, and in many ways fills in the gaps for a very low data rate,  left in the earlier standards. But rather like singing Old McDonald s farm, the network has to be able to handle devices using all previous versions as well so the problem of adding new capability gets steadily harder.

Mike.

mapj1 said:

LTE-M has been standardized more recently

A Teltonika RUT240 (Cat 4) works fine most of the time, so the exploration of Cat-M was more about its resilience compared to other forms of LTE.

I'm transmitting 64 byte messages, once per second over MQTTS, and can tolerate up to 0.5 s of latency.

For the purposes of what you are trying to do, I would assume you will see similar network issues to other mobiles. Yes there is demand and traffic management etc but you will be  contended/congested etc.  Only so much BW transmitted to support all demands and users.  You have no priority access.   LTE-M/NB-IOT etc are all low BW applications. Have you considered a GSM modem as a fall back?  That is a different technology and broadcast with the LTE and 5G services.  Different resources   too.

Sound advice for now, but not so good for any product you intend to use for more than a few years.

By 2033 there will be no GSM or 3g serives to fall back to . In practice I rather suspect it will go before that. 2023 is the latest date in that Ofcom link.
Which considering the number of things using 2G (==GSM) will be quite a wrench I think.

3G oddly, will be less missed, and has already gone in some places.

Mike

Sound advice for now, but not so good for any product you intend to use for more than a few years.

By 2033 there will be no GSM or 3g serives to fall back to . In practice I rather suspect it will go before that. 2023 is the latest date in that Ofcom link.
Which considering the number of things using 2G (==GSM) will be quite a wrench I think.

3G oddly, will be less missed, and has already gone in some places.

Mike