Will Low-Power Wide-Area Networks (LPWANs) form the backbone of IoT?

A low-power wide-area network (LPWAN) also known as a low-power wide-area (LPWA) network or low-power network (LPN) is a special type of telecommunication network specifically designed for long range communications at a low bit rate of about 0.3 kbit/s to 50 kbit/s per channel.

LPWAN is increasingly gaining popularity in industrial and research communities because of its low power, long range, and low-cost communication characteristics. It provides long range communication up to 10–40 km in rural zones and 1–5 km in urban zones. With up to 10+ years of battery lifetime and inexpensive chip-set and operating costs, LPWAN seems to be highly suitable for IoT applications that only need to transmit small amounts of data in long range. LPWAN technologies have arisen in the licensed as well as unlicensed frequency bandwidth.

Main Characteristic Specifics of a LPWAN network:

• Ultra low-power operation.
• Cheap deployment, easy network installation, and minimum maintenance.
• The network should not require the object to wake-up unless there is a need to send or receive data.
• Secure data transfer. Network operator should not be able to get access to meaningful data. The RF link should also be robust against jamming.
• In most applications, it is a valuable adder if the object can be easily localized, preferably without power-consuming GPS.
• Objects are generally not moving or slow-moving but may be positioned in environments having fast moving channel characteristics, like being next to a road. Modulation should be robust to some possible fading.
• From an application perspective, objects will provide data that will be used to build a large variety of services, either directly or through complex data fusion and machine learning processes.

Emergent LPWAN Technologies and Companies

1. Sigfox

Sigfox is a network operator that offers an end to-end IoT connectivity solutions that can be used in wide range of applications. It basically deploys its proprietary base stations equipped with cognitive software-defined radios and connect them to the back end servers using an IP-based network. The end devices connected to these base stations using binary phase-shift keying (BPSK) modulation in an ultra-narrow band (100 Hz) subGHZ ISM band carrier. Sigfox uses unlicensed ISM bands which are 868 MHz in Europe, 915 MHz in North America, and 433 MHz in Asia.

Some key features of Sigfox include-

• Employs the ultra-narrow band and uses the frequency bandwidth efficiently.
• Very low noise levels.
• Very low power consumption.
• High receiver sensitivity.
• Low-cost antenna design, however with a throughput of 100 bps at the most.
• Supports bidirectional communication with a significant link asymmetry. The downlink communication can only happen after an uplink communication.
• The number of messages over the uplink is limited to 140 messages per day.
• The maximum payload length for each uplink message is 12 bytes.
• The number of messages over the downlink is limited to four messages per day.
• The maximum payload length for each downlink message is eight bytes.
• The uplink communication reliability is ensured using time and frequency diversity as well as transmission duplication.

2. LoRa

LoRa is an emerging LPWAN technology that modulates the signals in sub-GHZ ISM band using a proprietary spread spectrum technique. Like Sigfox, LoRa also uses unlicensed ISM bands. Chirp spread spectrum (CSS) modulation implemented permits bidirectional communication that spreads a narrow-band signal over a wider channel bandwidth. This results in low noise levels, high interference resilience, and is difficult to detect or jam. There is longer range due to the high spreading factor but there is however a trade off with data rates.

Some key features of LoRa include-

• The data rate ranges from 300 bps and 50 kbps depending on spreading factor and channel bandwidth.
• Messages transmitted using different spreading factors can be received simultaneously by LoRa base stations.
• The maximum payload length for each message is 243 bytes.
• Using a standardized communication protocol called LoRaWAN, each message transmitted by an end device is received by all the base stations in the range. By exploiting this redundant reception, LoRaWAN improves the successfully received messages ratio.
• Network deployment cost may be more.
• The resulting duplicate receptions are filtered in the backend system (network server) that also has the required intelligence for checking security, sending acknowledgments to the end device, and sending the message to the corresponding application server.
• Multiple receptions of the same message by different base stations are exploited by LoRaWAN for localizing end devices. Time difference of arrival (TDOA)-based localization technique supported by very accurate time synchronization between multiple base stations is used.
• Multiple receptions of the same message at different base stations avoid the handover in LoRaWAN network.

LoRaWAN provides various classes of end devices to address the different requirements of a wide range of IoT applications as follows:

• Bidirectional end devices (class A): Class-A end devices allow bidirectional communications where by each end device’s uplink transmission is followed by two short downlink receive windows. Class-A operation is the lowest power end-device system for applications that only require short downlink communication after the end device has sent an uplink message. Downlink communications at any other time will have to wait until the next uplink message of the end device.
• Bidirectional end devices with scheduled receives lots (class B): In addition to the random receive windows of class A, class B devices open extra receive windows at scheduled times. To open receive windows at the scheduled time, end devices receive a time-synchronized beacon from the base station. This allows the network server to know when the end device is listening.
• Bidirectional end devices with maximal receive slots (class C): Class C end devices have almost continuously open receive windows, and only close when transmitting at the expense of excessive energy consumption.

3. NB-IoT

NB-IoT is a new narrow-band IoT system built from existing LTE functionalities. The technology standard was announced by the 3rd generation partnership project (3GPP) in 2016, which promises to provide improved coverage for a massive number of low-throughput low-cost devices with low device power consumption in delay tolerant applications.

NB-IoT network supports three deployment operation modes as follows:

• A standalone and dedicated carrier. In standalone operation, NB-IoT network can be used as a replacement for one or more GSM carriers. This allows the efficient re-farming of GSM infrastructure for IoT.
• Acting in-band within the reserved physical resource block (PRB) of a wideband LTE carrier. Here, all communication channels are shared between LTE and NB-IoT network, with the possibility of using power spectral density boosting on the NB-IoT PRB.
• A guard-band of an existing LTE carrier. In the guard-band mode of operation, NB-IoT network utilizes new resource blocks within the guard-band of an LTE carrier.

4. TELENSA

TELENSA is another provider for end-to-end solutions for LPWAN applications with fully designed vertical network stacks. They also support for integration with third party software. For a wireless connectivity between their end devices and the base stations, TELENSA uses its own proprietary UNB modulation technique, which operates in license-free SUBGHZ ISM band at low data rates.

Little is known about the implementation of their technology at this moment, TELENSA's goal is to standardize its technology using ETSI Low Throughput Networks (LTN) specifications for an easy integration within applications. It's current focus is on a few smart city applications which include intelligent lighting, smart parking, etc. To strengthen their LPWAN offerings in intelligent lighting business, TELENSA is involved with TALQ consortium in defining standards for monitoring and controlling outdoor lighting systems.

5. QOWISIO

QOWISIO deploys dual-mode LPWAN networks combining their own proprietary UNB technology with LORa. It provides LPWAN connectivity as a service to the end users: Apart from offering end devices, it also deploys network infrastructure, develops custom applications, and even hosts them at a backend cloud. Little is known about the technical specifications of their underlying technology and other system components at this moment.

Current Status:

The works for a successful implementation of LPWAN, such as NB-IoT and LoRa, has already started in several North American and European countries. Rise of these infrastructures in Asian countries is a testament to their practical applications. In Korea, the LoRa Alliance involves SK Telecom and Semtech and they along with over 300 companies, are dedicated to develop the LoRaWAN specification and the successful implementation and operation of LPWANs and IoT applications. "Under the “Partner Hub Program”, SK Telecom announced plans to provide 100,000 free LoRa modules as part of its effort to scale development and deployment of LoRa-based IoT solutions."

On the other hand, SoftBank in Japan is implementing IoT traffic by first deploying a LPWAN network using the LoRaWAN protocol. SoftBank is working towards building an NB-IoT network, which is a standardized cellular technology that is part of the 3rd Generation Partnership Project’s (3GPP) LTE Release.

Conclusions

1. Without a doubt, LPWAN is a better solution for low energy consumption and improved coverage. In comparison with the area IoT of ZigBee and WiFi, LPWAN enables massive connections covering long distances at the cost of minimum construction work and maintenance. The IoT/M2M market is humongous and is only expanding with every passing day. Commercial providers as explored before take advantage of different innovative techniques in their LPWAN connectivity solutions to tap profits from this upcoming lucrative market.
2. Sigfox and LoRa will be the best choice to use for lower-cost devices, long range (high coverage), infrequent communication rate, and very long battery lifetime. LoRa has an advantage over Sigfox in providing reliable communication even when devices move at high speeds.
3. NB-IoT will be prevalent in the higher-value IoT markets that are willing to pay for very low latency and high quality of service. Despite the cellular companies’ tests, the lack of NB-IoT commercial deployments currently leaves open questions on the actual battery lifetime and the performance attainable by this technology in real world conditions.
4. Finally, with the advent of the age of 5G, the number of devices connected to internet by 2020 will explode out of proportions. This could ultimately lead to a global LPWAN solution for IoT applications.

Note- This article is based on the literature survey of latest research in LPWANs carried out as a part of the coursework for ECPC 27, Wireless Communication.

References:

1. Mekki, K., Bajic, E., Chaxel, F., & Meyer, F. (2018). A comparative study of LPWAN technologies for large-scale IoT deployment. ICT Express.
2. Sinha, R. S., Wei, Y., & Hwang, S. H. (2017). A survey on LPWA technology: LoRa and NB-IoT. Ict Express, 3(1), 14-21.
3. Raza, U., Kulkarni, P., & Sooriyabandara, M. (2017). Low power wide area networks: An overview. IEEE Communications Surveys & Tutorials, 19(2), 855-873.
4. Bardyn, J. P., Melly, T., Seller, O., & Sornin, N. (2016, September). IoT: The era of LPWAN is starting now. In European Solid-State Circuits Conference, ESSCIRC Conference 2016: 42nd (pp. 25-30). IEEE.
5. Song, Y., Lin, J., Tang, M., & Dong, S. (2017). An Internet of energy things based on wireless LPWAN. Engineering, 3(4), 460-466.

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