SigFox Protocol Stack | LTN | SigFox Protocol Layers
This page describes SigFox protocol stack. It mentions functions of each of the protocol layers used in Sigfox which is a LTN (Low Throughput Network).
The figure-1 depicts simple protocol stack of sigfox wireless system.
It consists of following layers.
• Radio Frequency layer (i.e. RF Layer)
• PHY (Physical) Layer
• MAC layer
• Application layer
RF Layer
Following are the functions of RF layer:
• There are two implementations of the radio layer in sigfox system viz.
UNB (Ultra Narrow Band) and OSSS (Orthogonal Sequence Spread Spectrum).
• There are different frequency spectrum allocated in USA (915 MHz), Europe (868 MHz),
China (433 MHz) and Japan.
• The max. transmit power of 25 mW is specified for UNB uplink transmissions for 868 MHz Band.
• The Sigfox receiver sensitivity should be better than
-135 dBm.
PHY Layer
Following are the functions of PHY layer:
• It handles MAC frame during transmission and during reception.
• It uses BPSK modulation in the uplink and GFSK in the downlink
(in UNB implementation). DSSS with orthogonal signaling is used in OSSS implementations.
• The sigfox end device adds preamble during transmit (i.e. in uplink
from end device to Gateway) and removes it during receive operation (at Gateway receiver part).
The process is followed in Gateway transmit and end device receive link i.e. in the
downlink direction. Preamble is used for synchronization purpose.
MAC Layer
Following are the functions of MAC layer:
• It handles assembly of MAC frame (during transmit) and disassembly of MAC frame
(during receive) as per uplink and downlink structure defined.
• UNB implementation is carried out for uplink transmission of messages.
The downlink transmission of messages can be implemented either using piggy backing or broadcast.
• It takes care of authentication of end users.
• It takes care of error detection using FCS.
• Piggy backing: The LEP (LTN end device) wanting to receive any downlink
messages from LAPs will open fixed window for the purpose.
LAPs utilize this window to send the messages to the LEP.
Application Layer
Following are the functions of Application layer:
• The layer defines different applications as per user requirements viz. web, message etc.
References: ETSI GS LTN 001, 002, 003 (Low Throughput Networks) documents.
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