LPWA stands for Low-Power Wide-Area. It does not refer to any one specific technology, but rather serves as a generic term for any network designed to communicate wirelessly with lower power than other networks such as cellular, satellite, or WiFi.
Moreover, LPWANs communicate over greater distances than other low-power networks that use Bluetooth or NFC, for example.
LPWA is also referred to as LPWAN, where the N stands for network. LPWA is similar to the terms LAN or WAN in that it does not have an official, specific definition.
Typically, communicating over long distances with low power allows only small amounts of data to be transmitted at a time. Whereas modern cellular networks are pushing into gigabit per second territory with LTE Advanced and the forthcoming 5G networks, LPWA networks transmit much less—often just a few kilobits per channel. On the other hand, many LPWA technologies can communicate over greater distances, sometimes up to 500 miles or more.
The very limited bandwidth of LPWA networks are not suitable for most consumer and commercial applications such as voice, video, audio, or even text messaging. As such, LPWA networks are used almost exclusively by devices on the Internet of Things (IoT), and M2M (machine-to-machine) communications.
While home-based or business-based devices such as refrigerators, lightbulbs, or Nest thermometers can all easily piggyback on a home or office WiFi connection, some devices cannot rely on such connectivity.
Consider an irrigation ditch that stretches over miles in America’s farm country. Along this chain of streams and ditches are hundreds or even thousands of pumps and gates. Much of the irrigation channel runs through private land, between crop fields, and across several miles. As such, following the path even once per day to ensure that the pumps are running properly is impractical, not to mention of limited value. If a pump near the far end fails, it might be hours until you get to it. If one fails behind you, you might not know until the next day.
In cases like these, there is no local network to access. Standard cellular networks out on the plains are spotty, or non-existent in many areas. A satellite connection might work, but would be very pricy, and such a connection takes a lot of power. In this case, an LPWA network is exactly what is necessary.
With a range of up to dozens of miles, the network of pumps can all connect easily and inexpensively. Although the amount of data transmitted is limited, it takes surprisingly little data to do something like provide the status of a water pump. A single number can convey an overall status: one number for normal operation, a series of others for various error conditions, and another number could signify the number of gallons pumped per day. This system would allow farmers to monitor every pump on the line from a central console. An error condition for overheating, plus a drop in the number of gallons pumped, might signal a failing pump. Early warnings like this allow for technician to be notified in advance. All from a tiny, periodic, data transmission.
From devices located in mountaintop weather stations and lights in a multiple-acre greenhouse complex, to traffic lights, train crossing signals, and more can all be monitored, and in some cases even managed, with the limited data and low-power requirements of LPWA.
LoRaWAN stands for Low-Power Long Range Wide Area Network. The LoRa Alliance is a non-profit association that defines and implements the LoRaWAN protocol. Currently, there is no dominant or standardized protocol for LPWA networks, and this alliance seeks to change that. Some big names in technology serve as members of the LoRa Alliance including Alibaba, Cisco, IBM, Charter Communications, and SoftBank.
The LoRaWAN protocol is an open standard, although currently only one company makes chips that use the protocol. It is designed to use a star-of-stars topology. Devices connect to gateways, and the gateways connect in a more traditional manner over regularly connected IP networks.
The protocol defines three types of classes. Class A uses the lowest power and must be supported on all LoRaWAN devices. Class A devices are asynchronous, and communication always originates with the end device. After sending the uplink, a short window opens in which replies can be sent, creating the possibility for bi-directional communications. In addition to endpoint-initiated connections, Class B devices sync with periodic signals or beacons. These syncs create listening windows during which the device can receive signals or commands, creating real bidirectional communication. Class C moves toward keeping a receiver open at all times on the end device. This offers a low-latency, bidirectional communication channel. However, this significantly increases power usage, such that this class is only suitable where a continuous power supply is available.
Sigfox, a proprietary LPWA network offered by a French company, is currently one of the larger LPWA networks. It uses an unlicensed frequency in the 868 MHz or 902 MHz bands. Characterized as an ultra-narrowband radio transmission, it offers long distance coverage, but with a low data transfer rate. Each message is 100 Hz wide with transfer rates of 100 or 600 bits per second depending upon region. Communication back to the device is limited, making it a poor choice for applications requiring bidirectional communications. Each uplink message has a maximum payload of 12-bytes.
In rural areas, it can theoretically communicate over distances up to 30+ miles using a star network style architecture where any broadcast can be received by any base station in range. Unlike open protocols, the only way to get and use Sigfox is through the company.
With a range of 3-6.5 miles (non-line-of-sight), Ingenu offers a technology it calls Random Phase Multiple Access (RPMA). This large range of coverage allows the company to cover the Dallas/Fort Worth area with just 17 network towers. According to the company RPMA can penetrate concrete and even connect with devices underground.
This technology runs in the 2.4 GHz spectrum, which can subject it to interference from other devices using the same spectrum such as WiFi, Bluetooth, and older wireless phones. However, the upside is that the 2.4 GHz spectrum is open for usage in many different countries, making a single signal radio type usable all over the world.
A 2017 press release claims coverage across 29 countries on six different continents.
LTE-M is a 4G cellular-based technology. This standard is published by the 3rd Generation Partnership Project (3GPP) in its Release 13 specification. Typically, cellular devices are not low-power, as anyone who has to constantly charge their cell phone knows. To create the “low power” part of the LPWA promise, these specialized 4G wireless chips are designed with a Power Saving Mode. The chip is essentially turned off most of the time, waking up only at predetermined intervals. In addition, the chips are half-duplex, so they use less power even when on, but are much slower than a traditional 4G connection. The maximum data rate is approximately 100 kbits/s. This version of LPWA offers low-power connectivity, but only where you can get an LTE connection. The concern about cellular technologies like these is the tendency of such technologies to get sunsetted by carriers faster than the devices leave the field. For example, any devices relying on a 2G connection are unlikely to work almost anywhere in the U.S. where such networks have been turned off and upgraded.
Companies like IBM are noticeably missing from the LTE-M Task Force working on this standard. However, the LTE-M Task Force does include many of the world’s cellular carriers, including the four major U.S. carriers—Verizon, AT&T, Sprint, and T-Mobile—as well as several chip manufacturers like Qualcomm.
NB-IoT stands for Narrowband Internet of Things. NB-IoT also comes from the 3GPP Release 13 specification and is sometimes known as CAT M2. It uses DSSS modulation for communications. NB-IoT offers a peak download rate of 250 kbit/s, and an uplink rate of 250 kbit/s with multi-tone or 20 kbit/s with single tone. NB-IoT devices can have battery life of 10 years.
NB-IoT uses a new physical layer and signals. As a result, it can coexist with equipment on 2G, 3G and 4G networks. Operators currently deploying NB-IoT networks include China Mobile, China Telecom, Deutsche Telekom, and others.
A recent article suggests that this standard might pick up some momentum when Ericsson launches an NB-IoT network in India.
Outside of the United States, many cellular networks use the GSM protocol. Similar to how the LTE-M protocol uses the existing LTE network in a low power way, the Extended Coverage-GSM-IoT (EC-GSM-IoT) Protocol aims to piggyback on existing GSM networks around the world. Many use cases can support battery life up to 10 years.
As a GSM-based protocol, it can coexist with 2G, 3G and 4G networks.
Weightless is an open standard that operates in the unlicensed spectrum. This makes it both carrier and hardware-vendor independent, but also less commercial. There are three kinds of Weightless. Weightless-W uses the unlicensed frequencies between TV station frequencies. Weightless-N uses unlicensed narrowband protocol. Weightless-P uses the 12.5 kHz narrowband range and offers bidirectional communications.
An interesting offering from Haystack Technologies, DASH7 is designed to connect things that move. DASH7 uses the 433 MHz frequency. This allows ranges between 200 meters and 2 km, depending upon location and other interference. While DASH7 battery life is measured in years for most use cases, the company notes that it can even harvest energy from solar cells.
For security, DASH7 supports device cloaking to hide them from scanners, as well as AES 128 cryptography with public key encryption.
Additional LPWA technologies are in various stages of development or rollout. It is likely that more technologies will continue to develop until a handful of dominant player emerge, or standard specifications are merged. Some of the other technologies include:
- GreeOFDM from GreenWaves Technologies
- Symphony Link from Link Labs
- ThingPark Wireless
Recent IoT security issues have made headlines. For example, the Mirai attack worked to gain access to end devices. Such attacks may be less useful on many IoT devices using LPWA due to lower bandwidth, and the fact that the connected devices may not be “smart” enough to be useful to a hacker. However, man-in-the-middle attacks are possible on many LPWA networks. The potential for abuse is less spectacular, but just as important. Spying on competitors by receiving their device reports is one possibility, and unlike traditional hacking, because these signals are broadcast out into the air, there wouldn’t be any way to know the communications have been compromised.
One problem is that the end devices themselves are often not capable of providing their own encryption. A shared hash might be a good solution, except that many networks require packet sizes too small to implement a hash that is long enough for ongoing security. For example, the Sigfox LPWA technology only offers a 16-bit digital signature, which is far below the 128-bit industry standard. LoRaWAN, however, offers AES 128-bit encryption and authentication.
Cellular-based technologies, like LTE-M, NB-IOT, as well as EC-GSM-IoT piggyback on the authentication of the existing network.
While there are many possibilities for LPWA networks, some concepts are more established than others.
There are a lot of applications in the area of parking management. A sensor in or near a parking spot can report whether the spot is occupied or not. The data can then be used to feed numerous applications including signs that show how many open parking spots are available on a parking garage level. Or in apps that show where there are open meters as well as interfaces that tell a city where a car has been parked at a meter for too long. In this application, the low power matters more than the long distance for LPWA networks. No one wants to take on the burden of changing the batteries in hundreds or even thousands of parking spot monitors.
Water meters and pipelines
A simple pressure meter communicating its current reading can help pinpoint a leak even before it is reported. For pipelines that stretch over miles the ability to communicate over long distances without an existing network is critical, and battery life needs to be measured in years. In a city, the same signal that provides long-distance communication in a rural environment can provide underground communication instead, allowing monitoring of pipelines buried beneath the city.
Tracking shipments typically require that cargo is scanned at every point in which it changes hands. Between these changes, it is simply assumed that the cargo is still in the same building, or when on the move, in the same truck or train. With a smart pallet, a ping can continuously update not only the location, but also whether the container has been opened, dropped, or otherwise mishandled. LPWA is needed both for long distance communication while the shipment is on the move between cities, and for the long battery life, because no one wants to find and change the batteries on frequently moved pallets.
Street lighting and highway lighting
There are tens of thousands of lights out there shining on neighborhood sidewalks, busy intersections, and lonely stretches of highway. These days, monitoring often consists of nothing more than someone noticing and making a phone call. With LPWA, these lights can let a central command center know if the bulb is working, or if the light is currently on, potentially allowing for better energy usage and increased safety.
Other uses include smart meters (home and commercial), as well as smart agriculture, and factory and warehouse sensors.
The market for LPWA networks offers several choices. Some see this as fragmentation, while others see it as a market where the offerings can be chosen based on what is best for each particular project. For now, while LPWA demand is growing, there isn’t a one-size-fits-all solution available.