Benefits and Limitations of LPWAN
There are many organizations competing to make the most out of the Internet of Things using LPWAN technology. At this point, there is so much being said about the technology that I thought it would be best to write a guide establishing exactly what LPWAN is, what it can do, and how a few companies are actively pushing those limits.
First, what is ‘LPWAN’ anyway?
LPWAN stands for ‘Low Power, Wide Area Network’. (LPWA and LPN mean exactly the same thing, by the way.) It is a type of wide area network that allows radio-equipped devices to communicate. WANs are simply telecommunications networks. The system of cell phone towers and 5G you rely on every day is a WAN. So is the internet, if you want to get technical. You could form an Internet of things WAN using 5G technology, or even landline broadband. However, unless your device has a mains plug, you’re going to run out of battery power very very fast that way. Instead, the future of large scale, low maintenance, widely dispersed IoT applications will be found in LOW POWER wireless WANS – LPWANs.
LPWANs use wireless communications to link devices together over very long ranges using very low power signals. Their chief drawback is that they have a painfully slow bit rate compared to Wi-Fi or mobile data networks. Few LPWANs can manage even 1 Mbit per second per channel, and the slowest operate at around 100 bits per second. This drawback is acceptable because they really are low-power applications. Many LPWANS connect battery-operated sensors that are miles apart and have to run for years between battery changes to be practical.
LPWANs can be developed and fielded on a private level, but that requires setting up your own gateway, something we’ll talk about later. One of the technologies, MXProtocol, encourages third parties to set up gateways, and allow sensor owners or operators to use their networks on a commercial basis. This is one place where we’re seeing most of the really fascinating innovations.
So, there is a convenient, universal LPWAN protocol, right?
Heh. Have you ever met an electronics engineer? Alas, no. There are a number of competing protocols. That can cause confusion and a bit of unnecessary duplication, but it also allows for the technology to differentiate, doing different things very well.
There are two broad categories of LPWAN protocols: Cellular and Non-Cellular. Cellular LPWAN systems use licensed cellular frequencies – the same signal range our phones use – and Non-Cellular systems do not. Instead, they use the ISM radio bands set aside for ‘industrial, scientific and medical’ use, which are not licensed at all.
Popular Cellular LPWAN protocols include:
- LTE-M (also called LTE Cat-M1 and Cat-M1)
- NB-IoT (also called Cat-M2)
Of these, perhaps the most popular is LTE-M, which uses smartphone infrastructure, making it a very wide network indeed. The ‘M’ is standing in for MTC (Machine Type Communication) over the LTE standard cell phone infrastructure. LTE-M networks operate at the high end in terms of bitrate at up to 1 Mbps.
Telecoms providers can make LTE-M LPWAN gateways out of their cellular towers by adding a bit of software – no new hardware needed. Verizon, AT&T and Bell have already started rolling out gateways.
NB-IoT stands for Narrowband Internet of Things, and it does just what it sounds like. It has perhaps a quarter the maximum bitrate of the LTE-M systems at around 250 kbps, and it does not use the LTE in the same way mobile devices do. It relies on DSSS modulation instead. It can be used on LTE bands, or on GSM bands at around 180 kHz.
NB-IoT, interestingly, does not require a gateway. Devices can send data directly to the server, if the other physical and data infrastructure is in place. It is also considered a very reliable protocol, so it is preferred for high priority monitoring applications. It also requires dramatically less power to operate than LTE-M.
This standard is more popular in Europe than in the US, and is held back perhaps by a lack of investment. There are not a great many Narrowband chipsets manufactured, and that keeps the cost per unit fairly high. Rumor has it that more are on the horizon, though, so this may change.
Last but not least, let’s look at EC-GSM-IoT. This mouthful of alphabet soup stands for Extended Coverage Global System for Mobile IoT. It works over the GPRS (General packet Radio Service) band. Any GSM network can run the protocol, so long as it is running the software.
Compared to the other 2 ‘big’ standards, EC-GSM-IoT is not very popular with users or developers. I’m not saying that’s BECAUSE it has a lousy name, but come on… that name is awful.
Non-cellular LPWAN protocols include:
- LoRa (including both LoRaWAN and Symphony Link)
- Ingenu (also called RPMA)
- Weightless (including Nwave and Weightless-p)
Of these, LoRaWAN is the best known. It is put out by the LoRa Alliance, a collection of more than 500 companies including real influencers like IBM, Cisco, and Alibaba. Note that the LoRaWAN specification is publicly available to developers, but the core LoRa technology is proprietary, and royalties are paid on every chip sold.
To use LoRaWAN, you’ll need the whole kit – servers, switches, access points, and gateways. The good news in that many of those 500 companies sells individual items such as gateways and servers. On one level this can be a hassle, but it ensures that you have complete control over your network and can configure it any way you like.
LoRa systems can support up to 222 bytes which are not huge but does offer some flexibility. It can even carry over the air updates if you’re patient enough. It runs at 915 MHz in the US and 869 in Europe.
LoRAWAN with MXProtocol the MXProtocol uses an advanced anti-collision coordinator to allow really massive IoT networks with thousands or even tens of thousands of devices using 2-way communication over many square miles of geographical territory. It does this by making it possible for gateways with overlapping areas to coordinate transmissions.
MXProtocol has 4 major features that it adds to LoRaWAN networks:
It minimizes packet collisions across multiple networks:
- It can reallocate resources on the fly between different networks
- It allows the use of extra-network resources to be magnetized – essentially allowing ‘network roaming’ for LoRaWAN sensors
- It creates a monetization system using cryptocurrency (the Machine eXchange Coin)
They have a white paper online that covers all of the details.
Symphony Link uses the LoRa PHY layer but does everything else itself. It never really took off, not because there was anything wrong with it but because the LoRa Alliance juggernaut was too much to compete with. These days Link Labs is focusing on developing IoT apps.
Sigfox is the oldest standard on the ISM band, and also runs at 915 and 869 MHz. It essentially created the category. It is widespread, having networks in nearly 5 countries already and plans to expand to 60 before the end of 2018.
Sigfox is unique that they own and operate the infrastructure, and charge users/owners to send data. It is inexpensive, in general. If your devices only send a handful of messages a day, you’ll end up paying just a few dollars a year for the service. Sigfox does not charge royalties to chip vendors and makes much of their IP freely available. After all, they want you to design devices that use their system.
On the downside, each Sigfox message is limited to a minuscule 12 bytes. You also have to wait for them to set up a network for you. However, if you can pare your signals down to a dozen 1s and 0s and you can work to their schedule, it is an infrastructure-free option with good security and low power needs.
Ingenu (RPMA) runs on the same band that carries Bluetooth and Wi-Fi – 2.4 GHz. This band is available all over the world, which is a significant advantage. It is also a wider band overall.
Ingenu’s Random Phase Multiple Access (RPMA) system is both a PHY and MAC layer. It allows Ingenu networks to do some very interesting things, like deliver half a million messages per hour across 176 square miles with a single gateway. Their transmitters can go 10 to 20 years (estimated, of course) on a single battery, and some of the first ones installed are still chirping away happily today.
The system offers features that Ingenu would like to see made LPWA standards – broadcast capability, authentication, a responsive network, flexible packet size, delivery acknowledgment and even full 2-way communication with IoT devices.
Ingenu’s Machine Network currently covers more than 100,000 square miles of territory in 30 countries (as well as 30 cities within the US). They are making moves to offer the RPMA on a platform as a service (PaaS) basis as well.
Then we have the Weightless LPWAN standard. Weightless operates on potentially any sub-GHz ISM band from 163 MHz to 923 MHz. These are all unlicensed, of course.
Weightless-N, Weightless-W, and Weightless-P were all offered by the Weightless Special Interest Group, but N and W have been all but abandoned, and P has been rebranded as simply ‘Weightless’.
The Weightless SIG is a non-profit, interestingly enough. They have made Weightless and open standard, ideally to increase uptake and innovation. However, it isn’t very popular, and there is not a lot of hardware available. The one exception is the Nwave smart parking company, they use a proprietary version of the old Weightless N standard which is very widespread.