A common response when discussing cellular site surveys is:
“I use a multi-network IoT SIM, so the SIM will just choose whichever network is best.”
Multi-network IoT SIMs can provide an important resilience advantage because they may allow a device to connect to several mobile network operators rather than being permanently restricted to one.
However, multi-network does not automatically mean best network.
There are several reasons for this.
Some roaming and IoT SIM services use network steering.
This allows the connectivity provider or home network to influence which visited mobile network the device attempts to use.
The preferred network may be selected for reasons including:
This means that the network preferred by the SIM provider is not necessarily the network with the strongest or highest-quality RF signal at the installation location.
Other IoT SIM services are deliberately supplied as non-steered services, giving the device more freedom to select from the available networks.
The important point is that the behaviour depends on the SIM provider and connectivity service.
Even when a SIM is not being actively steered towards a preferred operator, a cellular device does not necessarily continuously scan every available network and move to whichever one currently has the strongest signal.
The modem may remain registered on an acceptable network that it has already successfully used.
For an IoT application this can be desirable.
Constantly leaving one functioning network to search for another would:
Therefore:
Available network ≠ selected network
and:
Selected network ≠ necessarily strongest network
More importantly:
Strongest network ≠ necessarily best network
because signal quality, technology, available cells, frequency band and application requirements also matter.
| IoT SIM / Modem Behaviour | Installation Engineering Question |
|---|---|
| Can I register on this network? | Which available network provides the best RF conditions at this site? |
| Which networks am I permitted or encouraged to use? | Which operators actually have usable cells at this location? |
| Is my current network acceptable? | Is another network significantly stronger or better quality? |
| Can I maintain a connection? | How much RF margin does the installation have? |
| Which network should I attach to according to my selection rules? | Which network would we choose if RF performance were the deciding factor? |
| Can I roam onto another operator if this network fails? | Is that alternative operator actually available with useful signal at this exact location? |
These are related questions, but they are not the same.
Suppose an IoT SIM can use four mobile networks.
The installer may assume that this automatically provides excellent resilience.
A cellular survey might instead reveal:
| Network | Available Cells | Signal | Signal Quality | Practical Observation |
|---|---|---|---|---|
| Operator A | 1 | Moderate | Poor | Device currently registered here. |
| Operator B | 4 | Strong | Good | Potentially much better RF environment. |
| Operator C | 3 | Good | Good | Useful alternative network. |
| Operator D | 1 | Weak | Poor | Technically available but provides limited resilience. |
The IoT SIM may be capable of registering on all four networks.
That fact alone does not tell the installer which of those networks provides the best RF environment.
Nor does it tell them that two of the four available networks may provide very little useful backup coverage.
A multi-network IoT SIM primarily addresses connectivity choice and resilience.
A cellular network analyser addresses visibility and measurement.
Multi-Network SIM's and SNYPER's actually complement each other rather than replace each other.
| Multi-Network IoT SIM | Cellular Network Analyser |
|---|---|
| Provides access to multiple cellular networks. | Shows which cellular networks and cells are actually available. |
| Allows the modem to register with permitted roaming partners. | Measures the RF performance of those networks. |
| Can provide network resilience. | Shows whether meaningful alternative coverage actually exists. |
| Controls or influences network access. | Provides visibility of signal strength, signal quality, technology and cell information. |
| Operates after the equipment has been deployed. | Can be used before deployment to optimise the installation. |
A SIM can decide which networks the device is allowed or encouraged to use.
A survey helps the engineer understand which networks they would want it to use.
A multi-network SIM cannot compensate for a badly positioned antenna.
If an antenna is:
then every available mobile network may perform worse than necessary.
A SNYPER survey can help identify a better antenna location before the installation is finalised.
This means that even if the final product uses a multi-network IoT SIM, the installation can still benefit from:
This is perhaps the most important distinction.
An IoT connectivity provider may legitimately state that its SIM can access several UK mobile networks.
That describes the commercial and technical network access available to the SIM.
It does not guarantee that all of those networks provide good RF coverage at a particular:
Coverage is local.
Sometimes extremely local.
Moving an antenna only a relatively small distance can materially change the cellular environment.
The only way to understand the actual RF conditions at the installation is to measure them.
Instead of asking:
“My IoT SIM supports multiple networks, so why would I survey them?”
a more useful question is:
“If my IoT SIM gives me access to several networks, wouldn't it be useful to know how good each of those networks actually is?”
That is where a cellular network analyser provides additional information.
A multi-network SIM gives the application options.
A SNYPER shows the engineer what those options look like at the installation site.