What is Low-Power Wide Area Network technology?
Low-Power Wide Area Network Technology is a wireless wide area network technology that provides low cost, low power, and wide-area coverage. It is geared for periodically transitioning small amounts of data. These features are the reason why LPWAN is used in IoT.
But how low power, low cost, and long-range is defined in IoT?
In IoT, low power means that it is optimized for power consumption – LPWAN transceivers run on small batteries with 10 to 15 years of battery life which means reducing maintenance costs. This is one way of achieving a low cost. Other ways are simplified protocols that reduce complexity in hardware design and thus lower device costs and reduced infrastructure requirements using star topology.
There are 4 LPWAN technologies on the market today, which we can divide into two groups based on their operating spectre: licensed (Cellular LPWAN) and licensed-free (Ultra-Narrowband LPWAN, Spread Spectrum, Telegram Splitting).
According to research from 2020, four technologies account for over 96% of the global installed base of LPWAN-enabled active devices are LoRa, Sigfox, NB-IoT, and LTE-M, where NB-IoT leads with 47% and LoRaWAN follows him with 36%.
Narrowband Internet of Things (NB-IoT) definition and overview
Narrowband Internet of Things or NB-IoT is Cellular LPWAN which means that it uses a licensed spectrum (700-900 MHz) in existing cellular infrastructure for data transmission. Since there is little co-channel interference, this ensures reliable data transmission. But this operation requires more complex protocols because nodes must first get permission from the base station to send a message. This can take several attempts to get approval which can significantly increase power consumption. Despite this, NB-IoT offers a battery life of more than 10 years for a wide range of use cases.
NB-IoT occupies a frequency bandwidth of 200 kHz, which corresponds to one resource block in GSM and LTE transmission. It allows connectivity for more than 100 000 devices per cell and that number can be increased by exploiting multiple NB-IoT carriers. NB-IoT is using FDMA (Frequency Division Multiple Access) in the uplink and OFDMA (Orthogonal FDMA) in the downlink. The maximum data rate is 200 kbps. This LPWAN has an unlimited number of messages which can be sent per day with a payload length of a maximum of 1600 bytes. NB-IoT disadvantage compared to other LPWANs is range: it is 1km in urban areas and 10km in rural areas, but NB-IoT has better indoor coverage (in basements, tunnels, etc.) than others.
LoRaWAN definition and overview
LoRa, from “Long Range”, defines the physical layer, while LoRaWAN defines protocol and system architecture. LoRaWAN provides an easy way to connect and monitor assets using unlicenced sub-GHz ISM band – 868 MHz in Europe, 915 MHz in North America, and 433 MHz in Asia. It is developed for large-scale IoT communication: running on low power and ensuring long battery life, vast distances with a range greater than 16 km in rural and greater than 5 km in urban environments, transmit signals through physical barriers. LoRaWAN ensures robustness, thus it can operate without issues in harsh weather conditions and noisy communication environments.
LoRaWAN is unique in its flexibility to accommodate different business models and the ability to use public or private networks. Provides in protocols written security, open and interoperable standard with low cost of ownership. LoRaWAN can cover thousands of devices from a single gateway, that can send unlimited number of messages for day with maximum data rate of 50 kbps and a maximum payload length of 243 bytes. Messages sent from end-devices travel through all gateways within range. Network Server receives all messages, and in this case, the server has received multiple copies of the same message, it keeps a single copy and discards others. This system is used to increase the reliability ratio.
LoRaWAN defines multiple communication classes for addressing the different latency in IoT applications:
- Class A is the default class and every end device must support this. Communication is synchronous, bidirectional, initiated by the end-device using ALOHA protocol: each end-device’s uplink transmission is followed by two short windows for receiving downlink messages. End-device is in low power mode as long as it is defined in its application, which makes this class a class with minimal power needed while enabling communication at any moment.
- Class B has bidirectional end-devices with scheduled receive slots: receive window is open at scheduled times. End-device receives a time synchronized Beacon from the base station, which allows the server to know when the end device is listening.
- Class C has bidirectional end-devices with maximal receive slots: receive window is continuously open. The window is closed only while sending data. This class consumes more energy thus it is used in IoT applications with continuous energy power resources.
Sigfox definition and overview
Sigfox is a network operator founded in 2010 with a vision to connect every object in the physical world to the digital universe. It is built as a global network dedicated to the IoT, with its own based station deployed in various countries around the world, pioneering the next Internet revolution.
Sigfox is using Ultra Narrow Band on unlicenced ISM bands – the same ones as LoRaWAN. The end devices connect to base stations using BPSK (Binary Phase-shift keying) modulation with a bandwidth of 100 Hz at a maximum data rate of 100 bps. As Sigfox uses a sub-GHz spectrum, it leads to very low power consumption, higher receiver sensitivity, and low-cost antenna design.
Sigfox was intended to be a sensor network, so it has limited half-duplex communication. The maximum number of uplink messages is 140 per day with a payload of 12 bytes and only 4 download 8 bytes messages per day, from which it follows that all messages cannot receive an acknowledgment. Reliability is ensured by sending messages three times through different frequency channels (there are 333 different channels). Base stations can simultaneously receive messages over all channels, so the end-device can transmit messages in a randomly chosen channel which reduces the end-device complexity and cost.
Sigfox has the best range of these three with range of 10 km in urban and 40 km in rural areas.
NB-IoT, LoRaWAN and Sigfox technologies comparison
Every IoT application needs specific requirements. To choose the best LPWAN technology for project, you need to take the following factors into consideration:
- Quality of service – NB-IoT uses licensed spectrum and synchronous protocol which provide a better quality of service than asynchronous protocol in the license-free spectrum that Sigfox and LoRaWAN use. But the better quality of service implies more cost and that is the reason why it is better to use Sigfox and LoRaWAN in applications that don’t need to guarantee the quality of service.
- Scalability – All LPWAN technologies provide high scalability features. However, in the lead position is NB-IoT with the possibility to connect more than 100 000 devices per base station, which is twice more than Sigfox and LoRaWAN.
- Coverage & Range – Best range has Sigfox with coverage of more than 40 km. In second place is LoRaWAN, and the lowest range and coverage capability has NB-IoT. But NB-IoT is deployed only within LTE infrastructure, thus it is not adapted for regions without LTE coverage like rural areas.
- Cost Efficiency – Various factors should be considered while cost calculation. In the last position here is NB-IoT with a spectrum cost of more than 500 M€/MHz, a deployment cost of 15000 € for the base station, and more than 20€ for end-device cost.
- Battery life – Although all three technologies are made with the intention to be in sleep mode as much as the application allows them, NB-IoT consumes additional energy due to synchronous communication, QoS handling, and OFDMA/FDMA access model.
- Latency – For latency, insensitive applications best choices are Sigfox and LoRaWAN Class A, but for applications with low latency connectivity, NB-IoT and LoRaWAN Class C is a better choice.
- Payload length – With a payload length of 1600 bytes, NB-IoT is the best. In second place is LoRaWAN with a maximum of 243 bytes, and the last one is Sigfox with only 12 bytes in length.
