# On Vulnerability of Selected IoT Systems to Radio Jamming--A Proposal of Deployment Practices
## 5 Presentation of the Selected IoT Systems: The Weightless and the Sigfox
### SigFox  
SigFox is a representative of the UNB systems class (see Figure 2), wherein a matter of the highest priority is the service coverage, leaving the transmission rate and on-time delivery as less significant matters. The consortium that created it [27] authorizes specific companies by providing them with BS modules and conferring on them an operator's right for using the system. End-customers, wishing to base their own networks on SigFox, become clients to these authorized entities [28]. The remarkable energetic efficiency required from SigFox system devices finds its expression in the Random Frequency Time Division Multiple Access (RFTDMA) scheme, wherein the transmit channel is randomly picked in both time and frequency without any prior mechanisms for detecting the possible channel occupancy. Although similar to the pure ALOHA protocol, where only the time domain is unslotted, in RFTDMA also the carrier frequencies are chosen from a continuous range (192 kHz wide in SigFox) instead of being picked from a discrete set of channels as in ALOHA. A transmit spectrum of a sequence of several SigFox transmissions is shown in Figure 3. This random channel selection, beside relieving transmitting devices from any efforts associated with energy-consuming channel sensing, also allows for the use of lower quality transmitters in end-devices, even such whose local oscillator frequencies uncertainty is greater than the channel bandwidth (BW) itself, i.e., 100 Hz in uplink. Each UL packet (i.e., a single message) is retransmitted three times, as stated above, on different, randomly selected channels, prolonging the effective single packet transmission up to 6.24 s and providing 4.8 dB of extra processing gain \(G_{p}\) to the link budget. A list of SigFox key operational features includes:  
* the frequency range 868.034 MHz-868.226 (yielding 192 kHz of the total band);
* uplink (UL) bandwidth, _BW_: 100 Hz;
* downlink (DL) bandwidth, _BW_: 600 Hz;
* network topology: star;
* maximum EIRP: 14 dBm (25 mW);
* modulations: Differential Binary Phase Shift Keying (DBPSK) in UL, GFSK in DL;
* maximum transmission rate \(R_{b}\) in UL: 100 b/s;
* maximum transmission rate \(R_{b}\) in DL: 600 b/s;
* sensitivity \(P_{min}\) equal to \(-144\) dBm in UL and \(-134\) dBm in DL (assuming the Signal-to-Noise Ratio, _SNR_ =7 dB, \(G_{p}\) = 4.8 dB and a noise factor (NF) equal to 5 dB and 3 dB in DL and UL, respectively).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Channel Bandwidth** & **Modulation** & **Coding Rate** & **Spreading Factor,** & **Data Rate [kb/s]** \\ _BW_ & _MOD_ & \(R\) & _SF_ & _R\({}_{b}\)_ \\ \hline \multirow{3}{*}{12.5 kHz (narrowband, NB)} & OQPSK & 0.5 & 8 & 0.625 \\  & & 0.5 & 4 & 1.25 \\  & GMSK & 0.5 & 1 & 5 \\  & OQPSK & 1 & 1 & 10 \\  & OQPSK & 0.5 & 8 & 6.25 \\  & GMSK & 0.5 & 4 & 12.5 \\  & GMSK & 0.5 & 1 & 50 \\  & & 1 & 1 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Relationship between the modulation, data rate and bandwidth in Weightless.