Low-Power Wide-Area Network (LPWAN) is a wireless network technology designed to allow long range communications at a low bit rate among objects. The term LPWAN by itself doesn’t refer to any particular protocol but encompasses various protocols, both proprietary and open-source. The most important advantages of LPWAN are power efficiency (the device can work up to 10 years without recharging), large area coverage and cost-effectiveness. The technology was specifically designed for the needs of M2M communication and the Internet of Things. But why is the new technology needed? What‘s wrong with GSM and LAN?
Actually, nothing. They do a great job in working with information in the way that suits humans (fast data transmission and heavy battery use). The thing is that tracking devices and measuring sensors use Internet quite differently than we do – they send small amounts of data and the recharging is more of a problem for them, so they need another kind of connection with different qualities. Nowadays tracking devices use all types of connection they can get – GSM, WiFi, Bluetooth, LPWAN, but what will they use in the future?
LPWAN: what is it and what’s in it for IoT ?
LPWAN interconnects low-bandwidth, battery-powered devices with low bit rates over long ranges. Its primary purpose is to diminish energy consumption and make the up-to-several-years-without-recharging use of devices possible thus making them cost-effective for a big variety of tasks. Devices operate on small, inexpensive batteries and have an operating range of more than 2 km in urban settings going up to 20-50 km and even more in the countryside.
LPWANs can accommodate packet sizes up to 1,000 bytes at uplink speeds up to 200 Kbps. LPWAN normally uses unlicensed spectrum (868 MHz in Europe and 915 MHz in US) and the cost of the chipset is very low – high ROI rate is always an attractive feature for any technology.
Key advantages of LPWAN:
- Communication range (up to 50 km and more)
- Low energy consumption (battery lifetime up to 10 years)
- Robustness to interference
- Network capacity (maximum number of nodes in a network), architecture (star topology) and security
- 5-10x fewer base stations required than 3G/4G
As we stated earlier, LPWAN is not a single technology or protocol. Various LPWANs use licensed or unlicensed frequencies and include proprietary or open standard options. We will focus on two players in the LPWAN field: Sigfox and LoRa to illustrate the possible business models and differences between LPWAN technologies.
SigFox is one of the most successful examples of LPWAN implementation and one of the most widely deployed as well. The company works with a range of partners, aiming to build a global IoT network outside the licensed spectrum. It successfully operates in the majority of the European countries and is also active in the USA, Latin America, Australia and South Africa.
Sigfox is a company and it owns all of its technology – from the backend data and cloud server to the end devices software. At the same time SigFox is essentially an open market for the end devices since it gives away its end device technology to manufacturers (like STMicroelectronics, Atmel, and Texas Instruments) to make the harwdware accessible. This is an important part of its strategy – minimizing hardware price to attract people.
SigFox sells the software as a service (in this case the network being the software) although in some cases the company actually deploys the network and acts as the network operator, e.g. in France and in the USA. But the primary goal is to get large network operators from all over to world to deploy their networks with Sigfox technology.
Sigfox technology uses a slow modulation rate to achieve longer range.Thanks to binary phase-shift keying (BPSK), the receiver only has to listen in a tiny slice of spectrum, thus reducing the effect of noise. Sigfox takes very narrow chunks of spectrum and encodes the data through the changes in the phase of the carrier radio wave (Ultra-Narrow Band technology). Inexpensive endpoint radio is quite enough (with a more sophisticated basestation to manage the data), its uplink is 12 bytes per message and 140 messages/day and its downlink capacity is severely limited: 8 bytes and only 4 messages a day (which is an obvious disadvantage in comparison with its competitors). It uses frequencies of public network in the 868 MHz or 902 MHz bands.
In short, this is a proprietary type technology with a great coverage. It allows you to minimize the use of battery and have your sensors reporting for years without recharging if you need a simple monitoring and metering. Downside: limited downlink capacity and vulnerability to interference.
LoRaWAN (Long Range Wide Area Network) is a LPWAN specification developed by Semtech and IBM with the following creation of the company LoRa Alliance that includes several other companies. The advantage of the physical layer LoRa is in its long range capability (a single base station can cover an entire city). While the range depends on the topography and density of the city, LoRa has the biggest link budget among the standardized communication technologies.
The LoRa Alliance has a different strategy than Sigfox. It is more open since every hardware or gateway manufacturer is free to build a module or gateway that conforms with the LoRa specifications. The LoRa Alliance is opened for anyone interested in building the hardware to support it, the openness is one of the key factors in its policy. The only problem is that the only company that makes the radio for LoRa is Semtech (although there are plans to change this in the future).
LoRa Alliance wants network operators to deploy the LoRa network (very similar to Sigfox model in this respect), and they also want private companies and startups to do so, thus making the deployment of the networks faster. This is hard to accomplish since the inevitable questions will arise between these companies (like what to do around roaming network to network).
How does LoRaWAN work?
LoRa chips transmit in unlicensed spectrum (109MHz, 433MHz, 866MHz, 915MHz), the network has a star-type architecture. Nodes are not associated with a specific gateway, they transmit data that is received by one or multiple gateways and sent to the server. The server manages the network and processes the data coming from the gateways, so all the hard computation is done by the server, the devices just send the data and that’s it.
The devices also only send the data when they need (or when scheduled) – without having to synchronize with the network by sending and receiving extra messages, thus consuming far less energy. Adaptive data rate allows LoRaWAN networks receive messages from a great number of devices without interference.
Not all the devices interact identically with the system. It all goes down to what is more important – battery lifetime or the possibility to constantly stay in touch with the device. There are three types of devices in LoRaWAn networks:
- bi-directional communication with each device’s uplink transmission followed by two short downlink receive windows (receive slots only open for short periods of time);
- bi-directional devices with scheduled receive slots;
- bi-directional devices with maximal receive slots (receive windows only closed when the device is transmitting).
In short, LoRa is a great option for the same goals that SigFox and they are similar in a lot of things, but LoRa is way more open and doesn’t have the downlink capacity issue.
Apart from Sigfox and Lora there is a number of other LPWAN solutions. Random phase multiple access, or RPMA, is a proprietary LPWAN from Ingenu Inc. It has a relatively short range (up to 50 km line of sight and with 5-10 km nonline of sight), and offers a better bidirectional communication than Sigfox. It is prone to interference from Wi-Fi, Bluetooth and physical structures because it runs in the 2.4 GHz spectrum and has a higher power consumption compared to other LPWAN options.
NarrowBand IoT (NB-IoT) uses cellular telecommunications bands. It is one of a range of Mobile IoT (MIoT) technologies standardized by the 3rd Generation Partnership Project (3GPP) alongside with LTE-M. Their advantage in comparison to other solutions is that they operate on existing cellular infrastructure. That allows service providers to quickly add cellular IoT connectivity to their service portfolios. This technology offers uplink and downlink rates of around 200 Kbps, using only 200 kHz of available bandwidth.
Apart from them there is a number of players that are also quite interesting and/or promising: Weightless SIG (the most independent option), GreenOFDM, DASH7, Symphony Link (based on LoRa), ThingPark Wireless and WAVIoT. They all aim at the same goal – to play an important role in the IoT evolution and they all have their pros and cons.
For the sake of this article we won’t go any deeper into their differences since it is not “what is the best LPWAN option” that is interesting but rather “what future awaits LPWAN technology”?
Projections for LPWAN
The potential of the LPWAN technology is quite promising. IoT market is growing and is estimated to reach $267 billion by 2020 according to Forbes. In the same time the demand for devices power efficiency is really high due to economical and environmental reasons. According to Machina Research, “11% of IoT connections in 2025 will use Low Power Wide Area (LPWA) connections such as Sigfox, LoRa and LTE-NB1”.
One technology just can’t satisfy all the different goals and projects of the IoT. WiFi and Bluetooth are widely spread and used standards that serve the personal devices applications. Cellular technology works for applications that need high data throughput and have a stable power source. And LPWAN is designed for sensors and applications that need to send small amounts of data over long distances a few times per hour from varying environments.
Each option has its pros and cons and none is ideal for the IoT in general, which is totally fine – the symbiosis of different technologies that work together but are designed for specific needs of IoT seems like a way to go for now.
The LPWAN technology offers some undeniable benefits, such as long battery lifetime, wide range and low cost. The Internet of Things market won’t lose such a possibility of making money while optimizing expenses and pushing the technology forward.