The full specification
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Note: This document describes the Sigfox protocol on the device side. The server side (base stations and Sigfox Cloud) is not part of the public offering.
A few highlights
The Sigfox radio protocol is designed to operate in license-free frequency bands. In each country, these frequency bands are under control of local regulations, that define technical constraints for using the spectrum (…) Sigfox has defined "Radio Configurations" that define radio parameter values that comply with local regulations.
Sigfox radio protocol is named 3D-UNB in the present document. UNB stands for Ultra Narrow Band. 3D stands for triple diversity, i.e. diversity in time, in frequency and in space.
Receiver characteristics: 3D-UNB protocol is designed to operate even if some objects are uplink only. When reception is implemented, radio engineers are strongly encouraged to pay close attention to receiver design, because their characteristics have a direct impact on the overall performance of downlink communication.
The uplink protocol stack aggregates 10 different field for building a radio burst. In downlink mode, the protocol stack aggregates 7 different fields only.
For an uplink message, 3D-UNB protocol allows to transmit one or three radio burst(s). The transmission of one radio burst only results in the lowest energy consumption. The transmission of three radio bursts provides increased resiliency.
Over-the-air security in uplink implements several mechanisms: message counter for replay attack protection, AES128 in mode CBC for authentication and integrity check, CRC-16 for error detection.
Frequency selection in bi-directional procedure: in B-procedure, carrier center frequency of the radio burst sent back by the Sigfox network is shifted by DeltaFGAP from the carrier center frequency of the corresponding uplink radio burst.
Content length of an uplink message is between 0 bit (empty) and 12 bytes (…) Content format of applicative message is freely defined by the application user.
Over-the-air security in downlink implements the following mechanisms: AES128 for authentication and integrity check, BCH for error correction, CRC-8 for error detection.
Payload encryption is a procedure than encrypts payload of applicative messages over the air, in both uplink and downlink communication. It uses AES128 algorithm in mode CTR with encryption key, unique per device.
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