License bands

All the buzz about the standardization of mobile communication is probably one of the most complex phenomena in the entire universe. We talked about the license-free band 868 MHz (alternatively, 433 MHz and 915 MHz). When talking about the guaranteed NB-IoT bands, we’ll mention at least thirteen bands that are being used around the world.

For common users, band 20 is the most interesting one because it’s used by Vodafone for its NB-IoT network. This is closely followed by band 8, used for indoor coverage in, for example, shopping malls and office buildings. So far, Vodafone is the only provider in the Czech Republic that has a stable network commercially available to everyone.

Here, the frequencies get very close to the license-free band. So, from a physics point of view, the networks are quite similar in terms of their reach and throughput.

Even more complications

It all sounds quite simple, if we’re talking about the Czech Republic. The situation around the world is quite diverse; you can easily encounter a different band from one global provider in each country. In Australia, Vodafone uses band 8 for its NB-IoT network. Other providers plan to run NB-IoT in the Czech Republic, but so far, Vodafone is the only one worth considering. And that’s true not only for the Czech Republic, but also for most of Europe and other parts of the developed world.

What does this mean for you, should you decide to produce a device? First, you must choose your provider very carefully, one that uses as few bands in as many countries as possible where you want to sell your device. Your antenna must be calibrated for all those bands, and you also need a modem (or an NB-IoT module) that supports all the bands you plan to use. The choice is not always simple, and the modules are not always accessible.

Here is a simple overview:

Right now, you’re thinking, “Wait a second! What band 71? We didn’t talk about that one.” Well, we sort of did. Band 71 was established by the 3GPP Release 15 standard, together with six other bands.

“What? Release 15? What’s that about? Where is Release 14?”, you might ask. No worries, the 3GPP Release 14 standard also exists, and it introduced four new bands. So, we get 25 bands all together. From 450 MHz up to 2.2 GHz, that makes a wavelength range of 13–66 cm.

Modems, modules, antennas, hardware support

Because NB-IoT is quite a new standard in the business world (even though Vodafone has been operating its commercial network for about three years now), the development of communication modules lacks far behind the actual needs and requirements. There is still no producer that makes a module supporting all bands. There are rumors about such modules, but so far, we have been able to find only pre-manufacture samples that support several bands (usually 6+). But, when it comes to modems (modules), the future is bright. Manufacturers like μBlox, Nordic, and Quectel are all trying hard to get their company logos on the billions of modules that will be sold in the future.

Antennas are another interesting topic. As we’ve already shown, the NB-IoT wavelength has quite a large range, and the most suitable antennas seem to be the ceramic chip ones (for several reasons). The smallest that we are  happy with has an area of 35 × 5 mm2 with a height of 6 mm. But, for DPS, it needs an area about 40 mm2 larger. Moreover, it ignores bands around 450 MHz, and supports only 698–960 MHz and 1710–2690 Mhz. That is because no other bands are being used around the world yet. Most of you can probably deduce that a bigger antenna would be better to support longer waves. But, having a device that supports all bands is still a thing of the future. We recommend researching what bands are supported by providers in markets you want to conquer, and focus only on those.

There are a lot of modules to choose from, and their production and further development is still booming. Looking at the LPWAN module market, it’s clear that the manufacturers see future profits. And, this vision is also supported by the fact that the standards are open.

How does it work?

Why is NB-IoT so awesome that everyone is talking about it? The word narrowband in the name suggests that the width of the broadcast band is not so amazing. The main reason behind this is the effort to service as many IoT clients as possible from one base station. 180 kHz is quite suitable for this. And, while Sigfox has a bit rate of around 100 bits per second and LoRaWAN has 300 bits to 50 kb/s, NB-IoT reaches up to 200 kb/s. And what’s amazing about a license band? You can do as many transmissions as you want! And, as opposed to license-free bands, you also get a long-term guarantee of stable service. Well, at least as long as your battery and wallet hold out.

The size of the modules is very similar to LoRaWAN and Sigfox. Just remember to account for a SIM card. If you glanced at the referred standard at the beginning of this article, you already know that the NB-IoT is basically an extension of LTE, so it won’t work without a SIM card. Most commonly, you can get 4FF or the mini MFF2 (eSIM). At least these are the cards that Vodafone offers for NB-IoT.

Because providers pay licensing fees for all active SIM cards on their networks, you’ll usually get an inactive SIM card that you have to activate yourself. Most providers have a simple API for this task, and some of them also have a nice clickable interface.

The exceptions are various test kits, where you get e.g. 20 SIM cards that are all already activated. You can try it here if you’d like (and you’ll also get a development kit as a bonus for €225). Sending and receiving is a breeze with the test kit. You connect to a network using a few AT commands, you automatically get an IP address, and you can start sending UDP packets.

Security is taken care of within the LTE standard. Connection between your device and the provider is encrypted via a key that is stored on the SIM card. The chance of your packet being heard and decrypted is like that of a phone call using a modern cell phone. Because there is an IPSec or TLS encrypted connection between your provider and your server, there’s nothing to worry about here either. The same applies when it comes to the packet being forged.

As we are talking about telecom providers, it’s clear that you will need money. Fortunately, the NB-IoT data tariffs are reasonable. If you’d like to transmit a lot of data, it’ll cost you around 1 € (or 1 $) a month in most countries. Based on the provider, you’ll get the REST API and callbacks, or your communication will take place on the UDP layer. We prefer the second option, securing it using IPSec. A more down-to-earth alternative is, for example, Twilio.

Energy efficiency

When it comes to energy efficiency, NB-IoT is superior to all other technologies we discussed. But, you’ll need a few tricks from the network’s side. Most NB-IoT modules use a few microamperes; newer modules use 1–2 µA.

Power Saving Mode (PSM) is today supported (probably) by all LTE networks. It’s a mode when a device does not transmit, but still has a network connection configured. The so-called Random Access CHannel procedure (RACH) is performed during connection. That, basically, agrees on a transmission channel with the base station, and then a Radio Resource Control (RRC) is established. This increases the energy consumption of most modules to a few dozen mA.

The module can’t discard the RRC; only the base station can do that after it receives an expiry confirmation from the network. This usually takes 20 seconds, but can take less, depending on the network. Still, every second that you are connected drains energy unnecessarily. But, if the provider has implemented the Release Assistance Indication (RAI), you’re lucky. Because, during the transmission, you can say how long you want to wait before disconnecting. As when it comes to energy consumption, it might be worth waiting a second or two for a reply from the other side. If you are not expecting a reply, you can set this time to zero.

There is also so-called paging. This, simply put, is a mechanism that the network can use to tell the end device that it has a message for it. Paging interval is then another feature that you don’t need for applications where you send only data. If the network supports the eDRX mechanism, you can also modify the paging interval (or set it to zero if it’s allowed by the network). So, for networks that have implemented eDRX and RAI, most modules will use a few dozen mA while transmitting, and 1–2 µA the rest of the time. Also, remember to account for energy loss, depending on the quality and tuning of the antenna.

Roaming and portability

There is a looming question concerning any license band: What’s the situation abroad? Well, we’re sorry to tell you this, but there is no roaming. At least not for now. But there are rumors and promises, and we’re eager to see what happens in the near future. We’ll hopefully hear more by the end of 2019.

It’s true to say that providers would happily collect profits from roaming. The technology is there, but the business agreements are still non-existent, as there is no critical mass of customers yet. There are some virtual providers available, but so far, we haven’t tried any.

If you’re using a global provider, it’s possible to use one NB-IoT service (for one fee) in all countries in which that provider has a network set up.

Prices

Let’s look at the modules. These are, for now, a bit more expensive than Sigfox modules, and the prices are getting on par with LoRaWAN devices. They’ll go for 2–3 dollars, potentially, as the produced volume will surpass the combined produced volume for all LPWAN technologies we mentioned in this series. They either have an integrated antenna, or you’ll buy it for a few bucks. Wonderful.

There are no specific certifications that you’ll have to pass, unless you start developing your own communication module.

And the tariffs are quite affordable. The situation in the Czech Republic is full-on production! If you have thousands of modules and tariffs around 150 kB a month, you can easily offer lower prices than Sigfox (while the amount of data transmitted will be at least three times as much). Yes, you sacrifice the REST API comfort and will have to settle for a UDP connection, but if you are really into all of this, that won’t be a problem. On the contrary.

Conclusion

All LPWAN technologies we presented have their uses. IQRF is very local, even though there are already real-life applications outside of the EU.

LoRaWAN is much more widespread and useful for industrial applications where there is no reliable LTE (or NB-IoT) coverage, and when you can let the customer manage a part of the infrastructure and setup (as the setup is not very user friendly).

Sigfox is a good fit, mainly for simple metering devices (because of the pricing) that transmit once a day, or even longer intervals. Devices like flood or smoke detectors are perfect examples, because you don’t expect them to transmit more than once during its lifetime. Or maybe an open window sensor or that new post in your mailbox reminder device. It’s true that manufacturers who have adopted Sigfox will argue and present their awesome devices, but the truth is that there is a lot of competition out there.

NB-IoT and other technologies like LTE Cat M1 allow the production of tiny, affordable, low-power devices that can be self-installed and work anywhere in the world. And the monthly fees are hilariously cheap, compared to all other LPWAN technologies mentioned. Have a look at our device here.

Previous articles:

IoT Technology: IQRF, LoRa, Sigfox, NB-IoT, and other weird words (1/5)

IoT Technology: IQRF (2/5)

IoT Technology: LoRa and LoRaWAN (3/5)

IoT Technology: Sigfox (4/5)