Your smartphone uses a ton of power to send lots of data over medium distances. It’s not really a problem when your phone dies because you can recharge it in your car or at home. On the other hand, many Internet of Things (“IoT”) applications—e.g. agricultural soil monitoring or climate monitoring in remote areas—require sensors to transmit small packets of information periodically for years or even a decade on a single battery charge.
LPWAN: Innovating Within Physical LimitsBut those remote, long-term, spread-out IoT applications face a problem of simple physics: if you want to transmit information wirelessly over long distances, you have to either increase signal power or decrease signal bandwidth. Consider this: if water is flowing through a pipeline, and you want to send it further away from the source, you either have to increase the pressure (power) behind the water or use a narrower pipe (bandwidth)—or both. The latter physical problem inspired a certain class of wireless networks: the “Low Power Wide Area Network” or “LPWAN” (sometimes “LPWA”). You may have heard the terms LPWAN and LoRaWAN before without knowing what they are. You might be wondering, what is LPWAN? What is LoRaWAN? Why do they matter? In this article, I’ll introduce LPWAN before focusing on one particular LPWAN protocol: the LoRaWAN open standard.
A Brief History of the LPWAN LandscapeSigfox popularized LPWANs in the 2000s as a highly-effective alternative to the power requirements and licensing costs of cellular networks. French startup, Cycleo, developed some compelling low-power RF semiconductor IP and Semtech acquired them in 2012 to consolidate their low-power RF portfolio. Semtech now controls some of the core IP underneath the LoRa protocol, which has become the de facto non-cellular LPWAN protocol, although Sigfox recently announced a new global (re)expansion. The major cellular carriers and 3GPP, the global cellular standards body, weren’t happy with the way Sigfox and Cycleo (Semtech) had created IoT-specific LPWANs, isolating cellular players from the LPWAN market—a market that had started to attract a lot of industrial clients. 3GPP started standardizing and popularizing LTE-Cat M1 and NB-IoT (Narrowband IoT) as cellular LPWANs that operate mostly within licensed bands. Cellular IoT is becoming increasingly popular for IoT systems that for almost a decade would’ve been designed as non-cellular LPWANs, however, LoRaWAN is still going strong. Semtech—with obvious potential bias—predicts that by 2019 as much as 40 percent of LPWANs will run on LoRa (we’ll dive into LoRa later). 5G is poised to shake up the entire LPWAN landscape. It promises low-latency, low-power, and high data transfer rates—a previously unattainable combination. 3GPP is also considering allowing 5G technologies to operate in the unlicensed bands—specifically, 3.5 GHz, 5 GHz, and 60 GHz—further encroaching upon non-cellular LPWANs. However, since 3GPP is only now finalizing the standards, and Verizon and AT&T are just starting to pilot the first 5G networks, much remains to be seen.
LPWAN as a SolutionBasically, LPWANs allow solutions providers to design IoT systems for use cases that require devices to send small amounts of data periodically over often-remote networks that span many miles and use battery-powered devices that need to last many years. LPWANs achieve that feat by having their IoT devices send only small packets of information periodically or even infrequently—status updates, reports, etc.—upon waking from an external trigger or at a preprogrammed interval. However, with the advent of the cellular LPWAN, there is now more flexibility in the definition of “low-power” and “wide-area,” as the below chart demonstrates.
Some Core Strengths of LPWANsTracy Hopkins describes in the following video that LPWAN designs are popular because they’re low-cost, they have a long battery life, and they operate at long ranges. That’s a great combination for many use cases. LPWANs are great solutions for certain kinds of use cases requiring periodic or inconsistent data transfer over long distances for a significant amount of time. Think smart garbage disposal meters, smart parking meters, or soil and water quality sensors. Given the range and relative simplicity of LPWAN data packets, sensors can even report from underground, in difficult climates, and far away from gateways or towers. Many LPWANs also have simple architectures and established protocols—more on that below—making them relatively easy, cheap, reliable, and effective to deploy at scale. LPWANs are great solutions for certain kinds of use cases requiring periodic or inconsistent data transfer over long distances for a long time. Think smart garbage disposal meters, smart parking meters, or soil and water quality sensors. Click To Tweet
Some Basic Limitations of LPWANsEvery technology has limitations. More precisely, no technology is use case agnostic. LPWANs are great for the scenarios described above, however, they’re unfit for use cases requiring data to be transferred frequently and/or in large volumes. LPWANs generally carry packets ranging from 300 bit/s to 50 kbit/s. Remember 56 kbit/s or “dialup” internet? More data is transferred over dial-up than most data-intensive LPWANs, so you won’t be sending cat pictures, puppy videos, or rambling voicemails over most LPWANs. That’s not their purpose. LPWANs can also run into problems because they often operate in unlicensed bands: the Industrial, Scientific, and Medical (“ISM”) bands that governments leave open. Common US ISM bands include 915 MHz, 2.4 GHz, and 5 GHz. LPWAN solutions often operate in the 902-928 Mhz ISM bands—just below the GHz threshold. Open-air LPWAN devices—e.g. on top of a building or tower—sending faint signals in those sub-GHz bands can encounter interference from high-energy signals operating just above the GHz boundary. Often, such interferences won’t matter. If you miss a few soil testing intervals, it’s not life or death, but for many mission-critical IoT applications (“MC-IoT”), e.g. medical applications and self-driving cars, such interferences can be catastrophic. It all comes down to knowing the intricacies of your use case and how the network will interact with the limitations of the local radio and physical environment.
The LoRaWAN Open StandardThe LoRa Alliance is a non-profit organization composed of 500 member companies dedicated to utilizing the “LoRaWAN open standard” as a way of keeping LPWAN deployments integrated, coherent, and interoperable at scale. The alliance creates standards and protocols to which LPWAN device manufacturers and solutions providers adhere. LoRa Alliance is similar to 3GPP, which standardizes cellular technologies, except that LoRa is a body of companies while 3GPP is a group of standard bodies. LoRa maintains the “LoRaWAN open standard” and certifies new IoT devices to work within its specifications. LoRaWAN-certified devices use a proprietary radio frequency modulation scheme that spreads the signal out to increase receiver sensitivity while lowering the data transfer rate. Think of how hard it is to be heard at a loud party. Now imagine you’re at a massive outdoor festival, trying to pass whispers across hundreds of meters. LoRa solves this kind of problem by sending simple messages (LoRa CHIRP signals) that are structured to avoid noise pollution. LoRaWAN receivers are sensitive enough to pick up these modulated CHIRPs at great distance amid noisy environments. The spreading factor (modulation), payload size (quantity of data), and data rate (speed of transmission), all diminish gradually as the end-node devices transmit information to gateway RF receivers from greater and greater distances. This short video explains some key features of LoRaWAN transmissions:
Core Features of LoRaWAN Systems
- Long range (>5 km urban, >10 km suburban, >80 km line of sight)
- Long battery life (>10 years)
- Low cost (<$5/module)
- Low data rate (0.3 bps – 50 kbps, often around ~10 kB/day)
- Localization support
- Operates in unlicensed spectra