Sigfox

It’s a patented technology of the same-named French company, which also operates the main “hub”, cloud, where all the messages from all the endpoints end. If the previous sentence sounds weird to you, it is because the Sigfox network(s) works in a really unique way. Namely, in every country, only one operator can operate the Sigfox network, and subsequently, he forward all the received messages from all operated BTS’s, through the secured VPN connection, to the main Sigfox cloud, called Sigfox Backend, which process them and forward them to their recipients. Thanks to this, Sigfox can be considered as the one global network without geographical borders. Also from the technical point of view, things are designed in a way that devices can seamlessly move between more networks (countries borders), without the need to deal with roaming or changing radio configurations¹.

When it comes to availability, today Sigfox operates in 77 countries of the world and covers 1,3 billion people. The highest density of coverage is in Europe, where most of the countries have, or will have practically full coverage, except some mountainous areas, etc.

The principle of operation

It is quite simple. The message is modulated into the bandwidth of only 100Hz² using the DBPSK (for uplink) or GFSK modulation (for downlink), and is blindly broadcasted into the ether, without any previous negotiation with the “network”, or even detecting it. One or more base stations in the surrounding can receive the signal, and after a successful CRC check, they send the message to Sigfox cloud, as explained above.

BTS’s do not provide any acknowledgment of reception back to the endpoint by default (downlink message can be used for it, but must be initiated by cloud, not BTS itself). In addition, each message from the endpoint is broadcasted 3 times (default setting), with random time and frequency offsets, to increase the probability that at least one broadcast will be received by some BTS (different signal propagation depending on the frequency in the freq. domain, and collisions with any other broadcasts, in the time domain).

The tech details

The maximum payload of one message is just 12 bytes. The transmission speed of Sigfox is strictly set to 100bits/s. While it looks enormously small and slow, it is enough to transfer the small amount of information between machines, once in a while. After all, this is the goal of this technology. Sigfox is mainly focused on upstream communication (from endpoints to server), but it supports also downstream messages (in smaller amounts). The whole transmission chain is secured by end-to-end AES128 encryption, the payload is not decrypted until the cloud.

Thanks to the fact, that energy is radiated in a narrow band, the reach of the signal is much higher, compared to conventional technologies which use the bandwidth of hundreds of kHz. Actually, the whole small country can be covered by several base stations. Also, it brings very low power requirements, so Sigfox is great for small battery-powered devices, which can last to work for up to 10 years without the battery change. The cons of Sigfox are the tight payload limit, a limited amount of messages per day (it results from regulations of ISM bands and touches all the technologies working in unlicensed bands), and no acknowledgment of receipt.

Overall, Sigfox, along with its main competitor (LoRa technology) are considered as the leading LPWAN technologies in the unlicensed (ISM) frequency bands.

Why we chose it

The reason why we chose Sigfox as the used technology for our project is its simplicity, cheapness, reliability, available global network operated by trustworthy authority, and the seamless roaming possible around the whole globe. It means that the user can travel with his vehicle between the countries, and its functionality will be always available, without the need to set or configure something.

The topic of Sigfox is widely covered in my diploma thesis (Slovak only).