14 November 2017

by Angazu & Rapidbit

SIGFOX [1] is a signal for Internet of Things (IoT) with some features that predict a great future. The use of the spectrum, adapted to its purposes, does not waste resources as other systems do. Its advantages in terms of cost and efficiency have made its develop quickly and its main usage being the internet of things.
Its data capacity is very low (100 bps), allowing up to 140 messages per day, but enough for its uses. It is cheap and has good coverage. The signal is robust and not easy to interfere with. To this we must add that the battery consumption is minimal, and may last several years. It also uses the free band of 868 MHz  and does not require any type of SIM. The standard is the ETSI GS LTN 003 V1.1.1 (2014-09) [1]

The signal was received at home, probably from a near home alarm  system carrying out installation tests.
Spectrogram (edited) in Fig. 1 shows three segments (three "telegrams") in different frequencies. Each segment lasts about 2.1 sec and is separated by a dead time of about 42 msec. Each emission uses a different frequency within its allowed range. In what has been observed so far, it always transmits the  message 3 times using  a different frequency in every Tx.

Fig.1 - spectrogram
The spectral occupation (Fig. 2)  is about 200 Hz. In this case, there are quite a few lateral lobes  due to the proximity of the transmitter-receiver. The measurement was made about 30 dB below the peak.

Fig. 2 - spectrum
Estimated modulation speed is Differential BPSK at a rate of about 100bps, the overview of 3 frames (Fig. 4) is aligned  to 210 bits. (ID has been removed once demodulated).

Fig. 3
Fig. 4
Frame as per  etsi standard:


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