With the advancement of information technology, the requirement for enabling wireless communication has become an important factor in realizing modern applications. Connected networks of machines and devices communicating with each other in Internet of Things (IoT) and Machine-to-Machine (M2M) applications require wireless communication techniques as these devices are widely spread over a large geographical area. Furthermore, these devices would be battery powered meaning they require low power-consuming communication technologies which are also capable of communicating over a large range of distances. As a result of these requirements, we see increasingly communication technologies competing such as LoRa, Sigfox and NB-IoT etc. This article will discuss what is Sigfox and its applications and significance.
What is Sigfox?
Sigfox is a narrowband LPWAN (Low Power Wide Area Network) protocol developed in 2009 in France. This protocol is widely used in IoT when the volume data is low and the operating range is large (more than tens of km). Sigfox uses unlicensed ISM bands and is a proprietary protocol meaning its patented technology. However, Sigfox hardware is open while the network should be subscribed.
Originally, Sigfox was unidirectional, meaning only facilitating communication via the uplink was supported. However, a downlink was introduced later, enabling it to be more competitive among LPWAN communication protocols. Now we will look deeper into some of the key technological principles behind Sigfox:
- Ultra-Narrow Band (UNB)
Sigfox uses D-BPSK (Differential Binary Phase-Shift Keying) modulation for uplink communication in which the message has a fixed bandwidth of 600 Hz (for U.S.) which is sent with lower bit rates of 600bps (for U.S.). This modulation technique is known as Ultra-Narrow Band (UNB) modulation, because of this, Sigfox base stations can communicate across long distances without being affected by noise. The channel bandwidth is 192 KHz (for U.S.) and has a central frequency which is below 1 GHz depends on the region. The U.S. has a central frequency of 915 MHz whereas in Europe this is 868 MHz and in Asia its 433 MHz. For the downlink signal, Sigfox uses GFSK (Gaussian Frequency Shift Keying) modulation. A lower bit rate enables the use of low-cost components at the transceiver end.
- Time, Frequency and Spatial Diversity
Another interesting underlying technology behind Sigfox is the use of random access. This ensures a high Quality of Service (QoS). The network and the device cannot transmit the Sigfox messages synchronously, meaning there is no need of pairing the device or need for channel allocation for uplink communication. This is achieved by the technique known as time and frequency diversity, where two copies of the same frame are sent over a different time and frequency, which allows more than one Sigfox base station to listen to a single message. In the case of downlink communication, the device needs to incur a delay of 20s after sending the first uplink message and the downlink receive window is only open for 25s.
Moreover, as said before, unlike cellular protocols, a Sigfox device is not connected to a dedicated base station. This enables spatial diversity, where an emitted message is received by at least three nearby base stations. This principle is known as cooperative reception. Spatial diversity coupled with time and frequency diversity are the key factors in ensuring high QoS of the Sigfox network.
- Short messages
Sigfox has designed a small message communication protocol to solve the cost and autonomy limitations of remote items. The range of uplink communication message size is 0 to 12 bytes. Sensor data, status data, application data and GPS coordinates can all be transmitted with a 12-byte payload. The size of the downlink message is static and 8 bytes long. This is enough for triggering an action, managing a device or setting application parameters remotely.
How Sigfox works?
Sigfox has a thin and flat, two-layer architecture composing of Network Equipment layer and Sigfox Support System. The Network Equipment layer consists of end-devices and base stations. This layer is responsible for transferring messages and data from these devices to the Sigfox Support System. To reduce the total cost of operation (TCO), Sigfox base stations use Software Defined Radio (SDR) where a software algorithm will handle demodulation instead of dedicated hardware. Network Equipment layer is connected to the Sigfox Support System through backhaul which uses public internet via Digital Subscriber Line (DSL) connectivity with 4G/3G backup. Satellite connectivity is used as a backup where there is no DSL connectivity or cellular (4G/3G) connectivity is present. This connection is secured by a VPN connection.
Sigfox Support System consists of a core network which is in charge of processing the messages and forwarding them to customer systems through callbacks which is collectively known as Operation Support System (OSS). It also provides the capability to interact with the system through web interfaces and APIs. Moreover, this layer includes features such as monitoring of the system; for example, Business Support System (BSS) for ordering and billing, and supervising operations. It is also responsible for handling message processing, where only one replica of the message is stored and also manages the base stations globally.
Features of Sigfox
Now let us briefly look at some performance features of Sigfox, which makes it competitive among other communication protocols and an ideal candidate for your IoT application.
High Network Capacity and High QoS
Sigfox provides high network capacity and high QoS and is able to connect billions of objects. This is enabled by previously discussed technological principles where UNB mitigates the interference due to noise, time, and frequency diversity providing random access and cooperative reception which increases the consistency of the radio link and QoS.
The main competitive advantage of Sigfox technology over other communication technologies is the coverage of a large distance with a minimum number of base stations. This largely reduces the OPEX and CAPEX of implementing a Sigfox network. This is enabled by the following features:
- The range of the radio frequency (RF) link is determined by the bit rate for a given output. When the data rate is lower, the range is higher.
- Another factor is the link budget, where the sum of the base station sensitivity and the output power of the object are the major concern. Lowering the link budget will facilitate a wider range with low power.
- However, the range also depends on the topography and would have good indoor coverage due to the use of sub-GHz band.
High energy efficiency
The reason behind the high energy efficiency in Sigfox technology is the efficiency of semiconductor chips enabled by Sigfox semiconductor partners such as NXP, Texas Instruments, etc. These semiconductors would operate around 10 mA – 50 mA of current in transmission. There are two more factors that explain the long battery life with Sigfox:
- To establish a connection, there is no need for pairing, as no synchronization is required before transmitting data from the device to the base station.
- Moreover, in the idle state the current consumption is in the range of nanoamperes, which makes it almost negligible.
Resilience to interferers
With the use of UNB coupled with spatial diversity of the base stations of +20dB, Sigfox is capable of unique anti-jamming capabilities. This enables Sigfox an ideal candidate to operate in the public Industrial, Scientific, and Medical (ISM) band, a spread spectrum that is affected by the UNB. The UNB modulation has some intrinsic ruggedness because the overlap with the noise is very low. To receive a message, the signal should be at least 8 dB above the noise floor. When compared to Sigfox, competing technologies built on spread spectrum modulation are highly impacted by noise because the surface they have in common is much bigger.
Network based geolocation
With Sigfox Atlas service you can locate your assets (Sigfox device) regardless of its components up to km precision and can locate the device even if they have no GPS service. This is very much favorable for tracking your mobile assets.
The Sigfox integrates following security features by-default:
- Provides authentication, integrity, and anti-replay on messages transmitted on the network
- Advanced Encryption Standard (AES) with no key OTA transmission
- Provide payload encryption as an option
- Parts of the network can be isolated into sections in case of an emergency
- Ensures that the device ID is not duplicated. In the case of a corrupted device, it will be prevented from communication via a blacklist list mechanism
- Has an inbuilt firewall
Service Coverage tools
There are different features provided to channel partners to evaluate the service coverage, which are briefly mentioned below:
- A link to the service coverage map can be access via http://www.sigfox.com/coverage
- A new global coverage API is being developed which is aiming to provide the coverage quality of all Sigfox public operators worldwide
When to consider Sigfox?
Now we have gone through into technical details of Sigfox and its competitive features, how will you know when to consider Sigfox for your IoT application? Here are some important tips to look into:
- When the volume of data sent is low (ranging from few bytes to kilobytes)
- When the operating range is on the order of kilometers
- When the required current consumption is low (in the order of milliampere or tens of milliampere per transmission)
Applications of Sigfox:
Sigfox is an ideal candidate for low-power and low-cost long-range applications in areas such as:
- Fleet management
- Security applications
- Asset tracking for goods and even people
- In transport and logistics sector
- mHealth applications, where remote monitoring and control are required
Sigfox vs Other LPWANs
As mentioned previously, there exits other LPWANs which are competitors of Sigfox technology. LPWAN are created to enable machine-to-machine (M2M) and Internet of Things (IoT) networks with low power over a wide area of network. We have introduced the difference between lora and sigfox before, now let’s have a brief comparison of various LPWAN technologies based on their performance criteria with a score out of 5.
|Sigfox||LoRa / LoRaWAN||NB-IoT|
Also let’s look into a more detailed comparison of the technologies based on their technical features.
|Standards||Proprietary||Open network standard||Open standard from 3GPP||Open standard|
|Spectrum||Unlicensed ISM band||Unlicensed ISM band||LTE In-band, Guard band, Standalone||LTE In-band|
|Distance||15-17 km||12-14 km||20-22 km||As per LTE|
|Traffic Direction||Mostly Uni-directional as its device to base station link has a good bandwidth||Symmetrically bi-directional||Bi-directional||Bi-directional|
|Hardware||Proprietary standards with few suppliers||Open Standard, many suppliers||Open Standard, many suppliers||Open Standard, many suppliers|
|Data rate||100bps (for Europe)||10kbps||200kbps||1mbps|
|Security||Limited security||Limited security||Good security||Best security|
Sigfox is a competitive candidate in LPWAN applications which is currently deployed in many industrial applications. Sigfox have already established partnerships with module makers such as InnoComm, Murata, WiSOL, LITEON and TD Next to realize hardware modules enabling Sigfox. In conclusion, we can say that watch out for Sigfox when you need low-power and high-range IoT applications.