LTE (Long Term Evolution) is the catch all term for the extention of the GSM/EDGE (2G) and UMTS/HSPA (3G) cellular technologies to increase capacity and throughput to meet current user requirements.
Commonly known as 4G, everyone is now used to 4G/LTE on their cell phones - so now everybody must have LTE based devices for their cellular application. But the term 'LTE' covers several different technologies - some of which are mutually exclusive and are unable to be implemented on the same piece of silicon.
So how do we select the correct device for our application?
Decoding LTE terminology
LTE covers a range of categories with different throughputs - and device selection depends on the data and power use cases for your particular application.
Rough guide to LTE Categories
The table below indicates the peak theoretical download and upload throughputs for each of the commonly available LTE categories.
| LTE Category | DL | UL |
|---|---|---|
| CAT-5 | 300 | 75 |
| CAT-3 | 102 | 51 |
| CAT-1 | 10 | 5 |
| CAT-M1 | 0.3 | 0.375 |
| CAT-NB1 | 0.023 | 0.058 |
Note:
- DL is Download speed in Mega Bits Per Second (Mbps)
- UL is Upload speed in Mega Bits Per Second (Mbps)
- not all categories are supported by all operators.
Selecting the correct device
Selection of LTE technology will depend on a few things:
- Data throughput
- Operator support
- Power supply
Here's a simple selection process to choose the appropriate LTE device for your application:
Step 1. How much data do you need to transmit and receive between your device and the 'cloud'?
If you have more than about 300kBytes/sec upload or download between your application and the cloud - or need voice services - then you're going to have to go with the heavyweight LTE category devices - CAT-1/CAT-3/CAT-5 etc. These categories are typically the same as is used in a cell-phone/smart-phone and don't allow allow the low-power modes/low power consumption that you might require.
If this is the case, you're stuck with using one of the heavyweight LTE devices.
Otherwise, if you have to move fewer than about 300kBytes/sec throughput, then you have the opportunity to use a device that supports the new low-power/low-bandwidth LTE categories - CAT-M1 or CAT-NB1 (also known as NB-IoT by some operators). These categories are specifically designed for Internet of Things (IoT) solutions.
Step 2. Is the device going to be moving around (eg a tracker) or mostly stationary (eg a smart meter)?
If you have a low bandwidth device that has to move about, then you need to use a CAT-M1 device to manage low power radio modes while moving around. CAT-M1 can put the cell radio into a 'low power' (sort of sleep) mode that can be woken up and immediately reconnect to the network, transfer data and then go back to sleep, no matter what cell the device is currently in.
NB-IoT has an even lower data throughput than CAT-M1 and can also put the cell radio into low-power mode and wake up immediately - but if the device has changed cells then the cell radio has to re-establish the cellular connection registration which uses time and power.
Step 3. Does your operator of choice support LTE CAT-M1 and/or LTE CAT-NB1?
Before getting excited about the possibility of using low power/low bandwidth CAT-M1 or CAT-NB1, you need to check that your operator actually supports one or both of these new categories. Just because the operator supports LTE (or 4G) services, doesn't mean that they support these new categories. In particular, European operators are still rolling out service upgrades to implement either of these categories. Additionally, not all operators are supporting both CAT-M1 and CAT-NB1 on their networks - some are only supporting one or the other.
If your operator does not support (or is not yet supporting) CAT-M1 or CAT-NB1 then you're out of luck - and will have to continue to use a heavy weight LTE category device. If this is the case, you're stuck with using one of the heavy weight LTE devices.
Conclusion
This note has provided a method that guides you through the complexities of selecting an appropriate LTE device to meet your communications needs. By following this method, it is hoped that you will be able to make the optimal choice the first time without making expensive mistakes.