Sigfox Pros and Cons

logo510f703a4647f

Internet of Things Wireless Connectivity Option Analysis: Sigfox

PROS and CONS

Sigfox intends to deploy a managed network, much like a cellular network, dedicated to the IoT. Sigfox uses sub-GHz frequency bands and claims that it achieves long-range communication by relying on a very low data rate of 100 bps, approximately 100 to 1,000 times less than the other IoT technologies discussed so far. Such a low data rate results in great sensitivity, which allows for long-range communication of multiple kilometers, provided there is no interference at all. Like LORA, Sigfox faces constant criticism regarding its theoretical vs actual range performance. Its actual performance substantially worse than the theoretical marketing numbers use to attract LPWAN  enthusiasts. Although a managed IoT network is a viable approach to a number of IoT applications, the current Sigfox technology has several shortcomings that make it not suitable for the widespread IoT applications.

Sigfox does not employ any collision-avoidance techniques. Consequently, Sigfox technology is put under stringent transmit power, and in Europe duty cycle, limitations by not being able to transmit more than 1% of the time. Stricter regulation in Japan enforces power spectral density limitations, essentially making ultra-narrowband inapplicable.

Sigfox’s 100 bps data rate is not practical for regular GMSK modulation. This translates into a 2 seconds transmission time for a mere 12 bytes of payload. Because of the ultra-narrowband requirement, it also mandates the use of a very precise crystal, like Temperature-Compensated TCXOs, which are more expensive than regular 20ppm crystals. Besides, such narrowband transmission is the worst type of interferer for other systems. A single Sigfox device could already interfere with any wideband system. If you consider thousands of Sigfox devices, which do not implement any fair use, collision avoidance and Listen Before Talk mechanisms.

The narrow band also makes it difficult to recover the data from the base station as the result of frequency error. Current Sigfox deployments are only one-way. Enabling two-way communication is quite challenging if possible at all. One-way communication means no acknowledgement. This means that an application can only achieve reliability by retransmitting the same data many times in case the applications did not receive it in the first place. Always transmitting 3 times, for instance, directly translates in a 3x power consumption increase, which is very inefficient for resource-constrained devices.

Relying on high sensitivity, i.e., low received power, to achieve communication in a shared frequency band is most likely bound to cause reliability issues. Although Sigfox system can theoretically achieve km range, in practice any legal and regulation-compliant system using the same spectrum and that are deployed nearby a Sigfox device, or even worse a Sigfox base station, may be enough to jam the Sigfox network.

Sigfox’s data rate is so low that even sending the smallest of data, for instance 10 bytes of information, requires a transmission time of about 10 seconds. This means the probability of collision with other devices is increased. In addition, the power consumption is high as the transmitter consumes roughly the same whether it operates at 10 bps or 100 kbps, but it has to be on for 1,000x longer, resulting in 1,000x higher energy consumed.

Such a low data rate and long packet duration, several seconds compared to typically milliseconds, make Sigfox extremely sensitive to frequency inaccuracy and interference. In particular, mobility is almost impossible, and experiments have shown that communication is unreliable over 6 km/h pedestrian speed, and may have issues with the speeds of cycling or running.

In short, Sigfox would not be a feasible IoT protocol for fast-moving and resource-constrained IoT devices that need to communicate at high data rates.

3 thoughts on “Sigfox Pros and Cons

  1. A TCXO is expensive but the transceiver is cheap (compared to a LoRa transceiver).

    Someone criticizes that ultra-narrowband transmission is the worst type of interferer because high power concentrated in small spectrum. Others criticize that spread spectrum is the worst type of interferer because it affects a wide band.

    Sigfox is bidirectional and is already enabled. Base stations perform Software-Defined-Radio to receive data from modems and learn the frequency error of each modem to transmit data to them with the right frequency displacement.

    My tests tell me that it is very hard to jam sigfox, even near base stations. Sigfox base stations are often placed is GSM 900MHz cell towers or UHF broadcasting TV towers.

    Halving datarate, potentially improves SNR by 3dB and comunication range by x1.4. So, lowering datarate 1000x results in 1000x higher energy consumed but also in 28x higher range.

    Sigfox recomends in mobility less than 40km/h. I tested by car at 100km/h and works fine. I tested by airplane (800km/h, free air, 10000 feet distance) and works fine, even the extreme doppler effects.

    Like

    • Hi Nestor, I enjoy the site you curate: The French (wireless) Connection. Thanks for your comments. One thing I must point out is Sigfox is NOT bidirectional. I have some very close friends who are actually vendors of their modules. 100% not bidirectional . 100% unable to use indoors. You should know that if you have done tests. There is no doubt the base stations have good coverage. The main question is: what application is this technology good for? The module vendors don’t even have a good answer for a solid use-case. Outdoor parking and lighting maybe? Every indoor application is out of the question.

      A good way to jam sigfox? Easy…with LoRa . These two technologies cannot co-exist. Try deploying a LoRa network near a Sigfox network and you will understand what I mean.

      And as for your Sigfox mobility tests, how are you conducting your tests? and what are you envisioning for a use-case for your test results?

      Like

      • Sigfox is bidirectional for customers since Nov-2014. The use cases for Sigfox are very few because of the limitation on the network (mainly uplink only with no more than 140messages/day and up to 4 downlink dessages/day). In the use cases that Sigfox is viable, Sigfox beats LoRaWAN.
        In the US and other use cases, of course, LoRa is better and adapts better to customer needs. Sigfox has better link budget and coverage, particularly indoor, is better.

        My tests comparing interference impacts and mobility was not rigorous, but my feeling is that Sigfox is more immune to interferences and hardest to jam.

        Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s