Low-power WAN (LPWAN) is a wireless wide area network technology that interconnects low-bandwidth, battery-powered devices with low bit rates over long ranges.
Created for machine-to-machine (M2M) and internet of things (IoT) networks, LPWANs operate at a lower cost with greater power efficiency than traditional mobile networks. They are also able to support a greater number of connected devices over a larger area.
LPWANs can accommodate packet sizes from 10 to 1,000 bytes at uplink speeds up to 200 Kbps. LPWAN's long range varies from 2 km to 1,000 km, depending on the technology.
Most LPWANs have a star topology where, similar to Wi-Fi, each endpoint connects directly to common central access points.
Types of LPWANs
LPWAN is not a single technology, but a group of various low-power, wide area network technologies that take many shapes and forms. LPWANs can use licensed or unlicensed frequencies and include proprietary or open standard options.
The proprietary, unlicensed Sigfox is one of the most widely deployed LPWANs today. Running over a public network in the 868 MHz or 902 MHz bands, the ultra-narrowband technology only allows a single operator per country. While it can deliver messages over distances of 30-50 km in rural areas, 3-10 km in urban settings and up to 1,000 km in line-of-site applications, its packet size is limited to 150 messages of 12 bytes per day. Downlink packets are smaller, limited to four messages of 8 bytes per day. Sending data back to endpoints can also be prone to interference.
Random phase multiple access, or RPMA, is a proprietary LPWAN from Ingenu Inc. Though it has a shorter range (up to 50 km line of sight and with 5-10 km nonline of sight), it offers better bidirectional communication than Sigfox. However, because it runs in the 2.4 GHz spectrum, it is prone to interference from Wi-Fi, Bluetooth and physical structures. It also typically has higher power consumption than other LPWAN options.
The unlicensed LoRa, specified and backed by the LoRa Alliance, transmits in several sub-gigahertz frequencies, making it less prone to interference. A derivative of chirp spread spectrum (CSS) modulation, LoRa allows users to define packet size. While open source, the underlying transceiver chip used to implement LoRa is only available from Semtech Corporation, the company behind the technology. LoRaWAN is the media access control (MAC) layer protocol that manages communication between LPWAN devices and gateways.
Weightless SIG has developed three LPWAN standards: The unidirectional Weightless-N, bidirectional Weightless-P and Weightless-W, which is also bidirectional and runs off of unused TV spectrum. Weightless-N and Weightless-P are often more popular options due to Weightless-W's shorter battery life. Weightless-N and Weightless-P run in the sub-1 GHz unlicensed spectrum but also support licensed spectrum operation using 12.5 kHz narrowband technology.
Narrowband-IoT (NB-IoT) and LTE-M are both 3rd Generation Partnership Project (3GPP) standards that operate on the licensed spectrum. While they have similar performance to other standards, they operate on existing cellular infrastructure, allowing service providers to quickly add cellular IoT connectivity to their service portfolios.
NB-IoT, also known as CAT-NB1, operates on existing LTE and Global System for Mobile (GSM) infrastructure. It offers uplink and downlink rates of around 200 Kbps, using only 200 kHz of available bandwidth.
LTE-M, also known as CAT-M1, offers higher bandwidth than NB-IoT, and the highest bandwidth of any LPWAN technology.
Some vendors, including Orange and SK Telecom, are deploying both licensed and unlicensed technologies to capture both markets.
Other LPWAN technologies include:
- GreenOFDM from GreenWaves Technologies
- DASH7 from Haystack Technologies Inc.
- Symphony Link from Link Labs Inc.
- ThingPark Wireless from Actility
- Ultra Narrow Band from various companies including Telensa, Nwave and Sigfox
LPWAN vs. cellular, RF, mesh
While Bluetooth, Zigbee and Wi-Fi are adequate for consumer-level IoT connectivity, many IoT applications -- particularly in industrial, civic and commercial deployments -- benefit from an LPWAN where large numbers of low-power devices in a wide area range can be supported cost-effectively.
Unlike prior wireless technologies, LPWAN provides battery-efficient, ubiquitous wide-area connectivity, enabling more M2M and IoT applications that were previously prohibitive due to cost. However, a major tradeoff is the amount of data that can be transmitted. Yet, according to James Brehm & Associates, 86% of all IoT devices use less than 3 MB of data per month, and 3GPP estimates that 99.9% of LPWAN devices will use less than 150 KB of data per month.
Cellular networks often suffer from poor battery life and may have gaps in coverage. Cellular technologies are also frequently sunset. As many IoT devices are deployed for 10 years or longer, sunsetting cellular coverage isn't a feasible option.
Radio frequency (RF) technologies, such as Bluetooth and near-field communications (NFC), don't have the range many IoT applications require.
Mesh technologies, such as Zigbee, are better suited for medium-distance IoT applications such as smart homes or smart buildings. They have high data rates and are far less battery-efficient than LPWAN.
With decreased power requirements, longer ranges and lower costs than traditional mobile networks, LPWANs enable a number of M2M and IoT applications, many of which were previously constrained by budgets and power issues.
Choosing an LPWAN depends on the specific application, namely the desired speed, data amounts and area covered. LPWANs are best suited for applications requiring infrequent uplink message delivery of smaller messages. Most LPWAN technologies also have downlink capabilities.
LPWANs are commonly used in applications including smart metering, smart lighting, asset monitoring and tracking, smart cities, precision agriculture, livestock monitoring, energy management, manufacturing, and industrial IoT deployments.
Different LPWAN technologies offer varying levels of security. Most include device or subscriber authentication, network authentication, identity protection, advanced standard encryption (AES), message confidentiality and key provisioning.
The future of LPWAN
As a fairly new technology, the LPWAN landscape is constantly changing and far from mature. With many players in the market, it is unclear who the winner(s) will be, especially as the speed of market expansion is also unknown. Long-term performance of each LPWAN variation is also uncertain, as many are still in their initial rollouts and real-world testing at scale has not yet been completed.