4G Modems and Frequency Bands

4G Modems and Frequency Bands

When choosing a modem for your region, most people consider the obvious physical aspects of the device first – how rugged is it? what connections does it offer? How fast is it able to run and how much power does it consume?

What is not as often discussed is how good the reception is on the modem. This makes sense – the cellular network is something of a niche topic and is not something many SCADA or Embedded Systems engineers will have encountered before.

This document is intended to introduce the idea of Frequency Bands, the role of 4G and 3G modems in today’s cellular network and the role of these technologies going forward.

1. What are Frequency Bands Anyway?

Cellular networks operate on Radio Waves. Radio waves are broadcasted between base stations and cellular devices and the variation of these signals is used to determine what data is being sent. For this system to work, it is critical that different signals are kept separate so as not to interfere with each other – if two devices attempt to transmit a signal at the same frequency at the same time, they would shout over each-other and it would be difficult for the base station to understand either device.

To achieve this, the full frequency spectrum is divided into different frequency bands. Each band represents a range of frequencies, with a centre frequency and a given bandwidth. Frequency bands are then allocated for different uses by ACMA on the behalf of the Australian Government. Some bands are allocated for scientific or industrial use. Others are assigned as free for anyone to use providing they meet certain requirements, such as the 415MHz and 915MHz band used in remote controls or the 2.4Ghz and 5Ghz band used in Wi-Fi and other wireless communications standards.

For cellular applications, the band is auctioned off and sold to different Telcos such as Optus or Telstra. The telcoes then deploy equipment to their towers that are capable of operating on the frequencies they have rights to. The 3GPP standard specifies how remote devices should communicate with these towers in order to share a given frequency band between many customer devices.

There is a snag in this system. Around the world different governments regulate the usage of their own EM Spectrum differently, and they may auction off different frequency bands to those used in Australia. Additionally, as time goes on and older technologies are retired (such as Analog Television) spectrum previously allocated to those technologies is freed up to be used in new 4G cellular networks for greater speed or greater coverage.

The result is that each different carrier in each different nation of the world may use or not use whichever frequencies they are able to licence. If your device does not support a frequency offered in your area, your device may get no or substandard reception.

2. Coverage of a 4G moduleDesigning a 4G module capable of covering all frequency bands is an impossible undertaking. It simply makes the module too complex and too expensive. As a result, each manufacturer will offer their module in different variants to suit different markets. Sierra Wireless, for example, offer two different modules aimed at two different markets – the MC7455 aimed at the US market and the MC7430 aimed at the APAC market:

If you were to purchase the MC7455 and try to use it in Australia, you would have problems getting a signal in rural areas or the inside of buildings. This is because Band 28, which is now a crucial band for many on the Telstra network, is not supported in the US variant. If you were to take the Australian variant and try to use it in the US, you would encounter the same issue because it does cover bands 12 or 13. This issue is made worse when you consider that cheaper, slower modules typically cover fewer frequency bands and so will be even more specialised. A Cat 1 or Cat 4 module will typically not cover as many bands as a Cat 6 module. Some modules are even targeted to specific carriers (such as Telstra or Vodafone), not just specific regions.

3. The Australian Carriers

Let’s now talk specifically about the Australian Market.

The three largest carriers in Australia are Telstra, Optus and Vodafone. Of the three, Telstra offers the best reception in most areas.

Let’s look at the frequency bands covered by each:

4G Cellular Frequency Bands:

3G Cellular Frequency Bands:

There are two main points I want to make here:

1. Not all frequency bands are created equal.
   Some Frequency bands, like Band 28, are already widely deployed and offer a long range and excellent building penetration. Band 28 was made free when Analog TV was finally shut off and is a critical factor when choosing a modem. Band 40, on the other hand, is only offered in a few areas and is not used by most customers.
2. 3G fall-back is a good idea, but a pure 3G modem is not recommended.
   The 2G network is now shutdown in Australia. All 2G frequency bands are now either freed for other uses or transferred to 3G. The 3G network is not yet dead but is going to be less and less important in the future. As carriers deploy new towers, they will be focussed on 4G coverage and later 5G coverage rather than 3G and some will even ‘recycle’ their 3G spectrum into 4G spectrum.However – for the time being there are still some areas where 4G is not available and so 3G remains attractive as a backup option. Most of our 4G modems include 3G fall-back as a backup option in case the modem cannot get 4G reception.

4. Intercel’s 4G modems and their coverage

Intercel is an Australian company and our products are aimed at the Australian market. This means that coverage of Australian frequency bands is our top priority. For other markets, we make custom variants of our modems with different modules to suit different markets such as the European or American market, or entirely private network deployments.

Let’s compare all the Australian Frequency bands and which of our products support them;

1. Most important here is Band 28, which is covered by Telstra and Optus and Widely used.
2. Least important is Band 40, which is only offered by Optus in some areas.

Our SAM4QX, SAM4WX, SAM4Q and SAM4T provide excellent coverage. The SAM4QX and SAM4WX both cover every Australian Frequency Band while the SAM4Q and SAM4T cover the most significant Frequency Bands and offer a lower cost option.

The SAM4XQ and SAM4XT offer more limited coverage but are more forward looking technically. These modems offer support for Cat-M1 and NB-IoT 4G, which offer longer range and better penetration at a lower data rate. These are also our most cost-effective solution for Serial Metering and Serial Comms.

The SAM3T, offered here as a point of comparison, is a pure 3G meter that we no longer manufacture. It has been superseded by the SAM4Q and SAM4T, which offer much better coverage. It should be considered as an example of the limited coverage offered by a 3G product, and of the advantages of moving to a 4G solution.

When comparing modems, check which Frequency Bands they support and compare it to those listed in the above table. If they don’t offer coverage for all or most of the Bands used in your region, then you should look for a better option. For remote sites especially, greater frequency coverage can lead to better reception and better connection reliability.