LPWAN technology can be critical in building distributed IoT systems. In this article we evaluate SIGFOX as one such LPWAN technology and discuss how it can be leveraged using ubiworx™ from Emutex to rapidly develop and manage remote sensor nodes.

SIGFOX is one of a group of emerging Low-Power Wide-Area Network (LPWAN) technologies which is seeing rapid adoption and application in IoT solutions. It has many unique selling points which make it attractive as a communication technology for a wide range of IoT applications; for example:

• Its use of Ultra-Narrow Band wireless technology enables it to reach long distances with relatively little power. Transmission ranges of several kilometres are typical, even in urban areas, and 100’s of kilometres are sometimes achieved in ideal conditions.
• It is designed to facilitate very low power consumption for battery-powered applications, ideally suited to devices which may “sleep” normally to conserve energy and “wake-up” occasionally to send short messages. Devices can run for years on a single small battery.
• The SIGFOX network is built around a managed global infrastructure which simplifies deployment. Adding a new SIGFOX device to a network can be as simple as adding the device ID to a SIGFOX account, and powering it up anywhere that there is network coverage. The user is not burdened with network infrastructure design or configuration.
• Seamless roaming between countries (subject to network coverage) is possible, with no configuration or additional charges. Several countries in Europe have already achieved full national coverage, and roll-out in other countries is progressing well. Dual-band radio chipsets are now available which can enable roaming between 868MHz (e.g. EU) and 915MHz (e.g. US) frequency bands.
• Operating costs for SIGFOX nodes are relatively low. Typically, a small one-off registration fee is paid per device, and subscription costs thereafter vary between approximately €0.77-€10 per year per device, depending on volume of messages required and total number of devices. This is offset by savings realised from using an established managed network infrastructure.

At Emutex, we have recently been evaluating SIGFOX technology and adding it to our portfolio of IoT communication technologies supported by our ubiworx™ IoT Software Framework. Our initial impressions have been very positive so far. We are based in the mid-west of Ireland, and the network coverage and support provided by the Irish SIGFOX network operator, VT Networks, has been excellent. We’ve used a variety of SIGFOX radios, and all have been trivial to set up but worked without a hitch on the local SIGFOX network.

Of course, the network connectivity is just one piece of the puzzle. For us, the more interesting part is the IoT applications which can be built on top. There are many, many examples. Here are just a few:
• Remote monitoring
• Smart metering
• Security
• Fleet/asset tracking

With low-power long-range communication, SIGFOX devices can be placed literally anywhere.

With a message payload of 12 bytes, and a maximum rate of 140 messages per day, one crucial aspect is the need to optimise the use of those messages carefully. SIGFOX devices are implicitly limited in the data that they can send, and this also limits what they can do with that data.

ubiworx™ offers significant advantages in this regard. It defines a compact ubiworx™ Sensor Protocol (USP) which is ideal for optimising the use of SIGFOX messages. It achieves tiny message sizes without sacrificing functionality or flexibility. The message protocol supports automatic device and sensor discovery, and provides flexible data types to suit almost any kind of sensor.

The ubiworx™ USP implementation does the hard work of encoding and decoding these messages, so the end user can simply deal with the real data values from their sensors through a simple API.

The sensor announcement feature offers tremendous flexibility, as it means that the device nodes can use any combination of sensors and the ubiworx™ gateway will automatically discover them and start collecting and processing the data from those sensors.

In fact, we’ve designed our SIGFOX support in ubiworx™ to make deploying sensor nodes a trivial matter. Once the customer has registered their devices on the SIGFOX network with a specific Group ID, ubiworx™ can automatically discover all of those devices associated with that group, and each of the sensors attached to them, and will immediately proceed to start retrieving/storing/processing any data sent from those sensors. Registering multiple devices on the network is a simple process which involves uploading a single file containing the unique Device IDs and Porting Authorization Codes.

When a sensor node device implementing USP starts up, it announces and describes itself (i.e. its set of sensors) to a ubiworx™ gateway server. The USP protocol for SIGFOX allows for as many as 256 sensors to be announced by a single node, and can be a wide variety of types such as simple digital or analog inputs, temperature/humidity sensors, motion sensors, GPS location sensors, and much more. A data format is specified by the device node for each of its sensors, specifying the number of bits required to transport data samples from the sensor in subsequent messages. For example, a digital input requires just a single bit, while a high-accuracy temperature sensor can use 12-bits, for example.

Sensor data readings from multiple sensors can be combined, and packed with bit-level granularity, into a single SIGFOX message. In practical terms, this means that a single USP sensor update message could, for example, transport data from:
• 72 GPIO sensors, or
• 6 ADC sensors with <1mV granularity, or
• 6 temperature sensors with 0.0625 degree granularity, or
• 9 temperature sensors with 1 degree granularity, or
• various combinations of the above, or other types of sensors

The sensors on those remote SIGFOX nodes are treated just like any other sensors on the ubiworx™ gateway. Details of interfacing with the SIGFOX network are managed implicitly by ubiworx™, such that the fact that the sensors are connected remotely is virtually transparent to the end user.

ubiworx™ offers many features to control how the sensor data is stored and processed. At the most basic level, all data samples will automatically be time-stamped and stored on the ubiworx™ cloud server, allowing the user to inspect the current values and historical trends via the ubiworx™ server web interface. Via an intuitive drag-and-drop interface, the user can also configure rules logic to analyse the data values and perform a variety of actions on those. For example, if a temperature sensor reading exceeds a specified threshold, an alarm notification could be sent to relevant parties, or a cooling device could be activated. Other options include filtering and condensing the data, forwarding data to 3rd party cloud services, and of course a RESTful API is provided to allow all kinds of custom applications to access the data for further processing or presentation to provide a fully bespoke solution.

In addition to sensor node connectivity, ubiworx™ gateways can also leverage SIGFOX as a primary or back-up communication path to a central server. In scenarios where a higher-bandwidth uplink is typically needed between the gateway and the server, a traditional high-bandwidth communication option (e.g. ethernet/Wi-Fi/cellular) may be used as the primary communication path, with SIGFOX as a back-up solution to ensure redundancy for sending critical alert messages. And, for scenarios where a low-bandwidth uplink is entirely sufficient, SIGFOX offers unique advantages in terms of power consumption, running costs, and coverage in some geographical areas or environments where other communication technologies may not be viable.

Thinking about using ubiworx™ or SIGFOX for your next IoT project? At Emutex, we design, develop and deliver end-to-end IoT solutions. Check out our website, http://www.ubiworx.com/, for further information and contact details. We look forward to working with you.