Author: Mark Patrick, Mouser Electronics
These days, we have multiple options for connecting with other people almost anywhere on the planet. Some are almost instant (landline telephone, cell phone, VoIP phone, video conferencing), while others allow us to meet in person or send goods (rail, airplane, road transport). Much of this is being driven by the Internet of Things (IoT), which not only enables people to communicate globally, but also facilitates machine-to-machine (M2M) communication. In fact, there are already billions of deployed IoT devices around the world that communicate without borders, whether to send data or to receive and execute an instruction.
To facilitate this unprecedented level of connectivity, multiple network technologies will be required to connect the IoT nodes, depending on their function and where they are located.
Given the variety of IoT nodes deployed, it comes as no surprise that their needs in terms of connectivity are quite diverse. However, there are a few key requirements that apply to almost every device in use today:
- Wireless is the preferred medium
- The connection should have a fairly long range – several kilometers in urban environments and up to 40km when deployed rurally
- Power consumption must be minuscule to allow a small battery to last several years, or to allow the node to be powered by energy harvesting
- The deployment and maintenance of the device (including its wireless connection) must be simple and low cost
The numbers involved with the IoT are staggering. Active global IoT connections will more than double from the 2018 level of 7 billion to 15.8 billion by 2023, according to a report by research firm IoT Analytics. Its report goes on to estimate that low-power wide-area networks (LPWANs) will be used by 1.15 billion devices to connect to the wider world. Looking farther into the future, IDTechEx Research has produced a forecast that there will be around 2.7 billion IoT connections via LPWAN by the end of this decade.
LPWAN Protocol Overview
Short-range wireless connections (Bluetooth, Wi-Fi and Zigbee) are not well suited to IoT applications where the node is placed remotely, and cellular networks (2G, 3G and 4G) are generally too power-hungry to meet the battery life requirements of the IoT.
LPWAN technologies such as Sigfox, LoRa and Weightless have longer range than the wireless connections and use less power than cellular, making them an ideal “sweet spot” for IoT. There is also narrowband IoT (NB-IoT), which uses the cellular LTE protocol over either GSM or LTE networks. However, NB-IoT is able to transmit small packets of data bi-directionally while consuming low levels of power.
In 2009, Sigfox (a French company) developed this proprietary technology with a 100Hz bandwidth that takes advantage of the unlicensed industrial, scientific and medical (ISM) band (Europe: 868MHz; North America: 915MHz; Asia: 433MHz). Sigfox was deployed in France in 2014 and has subsequently been used in around 60 countries.
Intended for messages where the size is limited, Sigfox runs at 100bps or 600bps, depending on the region it is deployed in. Based on binary phase shift keying (BPSK), Sigfox provides bi-directional communication subject to a daily restriction of sending up to 140 12-byte messages and receiving four 8-byte messages.
Microchip Technology offers 868MHz ATA8520 single-chip RF transceivers for European Sigfox that are flexible and are able to be paired with any microcontroller (MCU) to form a Sigfox solution. The single-chip solution incorporates controller technology and an RF front end that consumes just 5nA in off-mode and 32.7mA when transmitting at 14.5dBm.
Another French invention, LoRa (long range) was developed and patented by Cycleo in 2009 before its 2012 acquisition by Semtech. It supports end-to-end AES-128 encryption and also uses the public ISM band, albeit at an increased bandwidth of 125kHz and 250kHz. The use of chirp spread spectrum (CSS) allows for a 50kbps bi-directional data transmission rate that supports 243-byte messages.
The LoRa Alliance defined LoRaWAN as the default LoRa protocol in 2015. So far, LoRaWAN is in use in 100 countries.
All of the available LoRa ICs are supplied by Semtech, including the SX1301 digital baseband chip that creates outdoor LoRaWAN macro gateways for applications such as smart metering, security sensors and agricultural monitoring. The SX1301 includes a multichannel high-performance transceiver (LoRa concentrator IP) that is able to receive several LoRa packets simultaneously using random spreading factors on random channels.
The Semtech solution delivers a good connection from a central wireless data concentrator to multiple wireless end points distributed over many different distances. The device also features dual-band operation, dynamic data rate (DDR) adaptation and a total of 10 programmable parallel demodulation paths.
Murata, an influential member of the LoRa Alliance, recently released several small, energy-efficient ABZ LoRa wireless modules that are intended for applications such as smart metering, wearables and asset tracking. Housed in fully shielded packages, these devices measure just 12.5mm x 11.6mm x 1.76mm and incorporate a Semtech SX1276 ultra-long-range spread-spectrum wireless transceiver as well as an STM32L0 series ARM Cortex M0+ 32-bit MCU with 192kB of Flash memory and 20kB of RAM from STMicroelectronics.
Every LoRa network requires a gateway, one or more nodes and a local server for monitoring the connected devices. Seeed Studio’s LoRa/LoRaWAN 868MHz and 915MHz gateways are ideally suited to developing LPWAN solutions as the kits include several building blocks that speed up the process. Included are a Raspberry Pi 3, a Seeeduino LoRaWAN with GPS, and a 10-channel gateway/local server for receiving and distributing data to each LoRa node. It takes just minutes for engineers to build a working prototype by connecting the gateway with Seeeduino LoRaWAN and Grove modules.
The Weightless Special Interest Group (SIG), a non-profit organization based in Cambridge, UK, developed the Weightless open standard. Operating in the unlicensed sub-1GHz area, the standard has three versions – Weightless-W, Weightless-N and Weightless-P – that make use of different available spectra. Weightless-W occupies the unused local spectrum in the licensed TV band – known as the “whitespace” – while Weightless-N uses the unlicensed ultra-narrowband protocol based on NWave’s unidirectional technology.
Weightless-P operates in the full range of unlicensed sub-1GHz ISM/SRD bands, uses FDMA + TDMA modulation in the 12.5kHz narrowband and has an adaptive data rate (going from 200bps to 100kbps). Weightless supports AES-128/256 encryption and authentication of both the terminal and the network.
Narrowband IoT (NB-IoT)
Standardized in 2016 by the 3rd Generation Partnership Project (3GPP), NB-IoT is a low-power standard that uses licensed GSM and LTE cellular networks. It offers a data rate up to 50kbps with a 180kHz bandwidth. Message size is 1.6kB. The service is expanding rapidly with both T-Mobile and AT&T rolling out networks across North America. Vodafone have a European network that covers 10 countries: Netherlands, UK, Czech Republic, Ireland, Germany, Greece, Italy, Spain, Hungary and Romania.
The Right Protocol for an Application
There are several factors to consider when selecting the best LPWAN technology for a given application. These include the network coverage and range, latency, energy efficiency and quality of service (QoS) along with scalability and cost.
Remotely located sensors, such as those in farming/agriculture, will have minimal transmissions but will require long battery life or the ability to energy harvest. As LTE coverage is likely to be patchy at best, Sigfox and LoRa are the most likely to be selected here.
In a factory or other indoor facility, monitoring of equipment will require multiple sensor types that may have different communication needs. Wi-Fi and Ethernet are able to be used, but where they are not available, NB-IoT has the capacity to deliver a high QoS, even with frequent transmissions.
Similarly, when monitoring slow-moving environmental parameters in smart buildings such as workplaces or residences where high QoS or significant data are not required, then LoRa or Sigfox could well be the best choice (depending on coverage and indoor penetration).
Tracking or monitoring the status of mobile assets needs a long battery life and a low-cost solution, meaning that LoRa or Sigfox are likely to be the best solutions. If the assets are constantly mobile (trucks, pallets, etc.) then LoRa will most likely be the most reliable solution.
Quite a few IoT deployments will benefit from some form of hybrid LPWAN solution based on STMicroelectronics’ STEVAL-FKI001V1 development/prototyping platform that facilitates system designs based on Sigfox, Bluetooth Low Energy (BLE) and sub-1GHz technologies. The kit includes a programmable Jorjin Technologies WS2118 module, which embeds the BlueNRG-1 system-on-chip (SoC) for BLE functionality and the S2-LP transceiver for sub-1GHz functionality. The minuscule active RF and MCU currents, as well as a low-power mode for reduced current consumption, enable extended battery life, permitting long-term operation with coin cell batteries or from energy harvesting. The STEVAL kit is compatible with Arduino shield boards, including those that contain MEMS motion sensors, environmental sensors and time-of-flight (ToF) ranging sensors.
Alternatively, designers can utilize STMicroelectronics’ B-L072Z-LRWAN1 STM32 LoRaWAN discovery board (which incorporates Murata’s integrated open-module LoRaWAN solution) to develop IoT solutions based on LoRa and/or FSK/OOK technologies. Certified I-CUBE-LRWAN embedded software is included, enabling the setup of a comprehensive LoRaWAN node.