# Performance Comparison of NB-Fi, Sigfox, and LoRaWAN
## 3 An Overview of NB-Fi, Sigfox, and LoRaWAN
### Channel Access and Operation Modes  
#### 3.3.1 Nb-Fi  
In NB-Fi, the operating frequency band can be configured by the operator and is at least 51.2 kHz in the uplink and 102.4 kHz in the downlink. The uplink and downlink frequency bands do not intersect.  
For uplink transmissions, sensors calculate the central frequency as a function of bitrate, Modem_ID, and MIC0_7. MIC0_7 with high probability changes for each transmission; therefore, central frequency in uplink is different for each transmission, including retransmission and block transmission. For downlink transmissions, the server uses a central frequency which is a function of bitrate and Modem_ID. Therefore, the server always transmits frames intended for one sensor at the same central frequency.  
NB-Fi sensors can operate in three modes. By default, the sensors operate in the discontinuous RX mode (DRX). In this mode, the sensors transmit data if needed and listen to the downlink channel for a short period of time after the end of their transmission. The server buffers all data that have to be transmitted to each sensor and transmits the data during the time interval, when the appropriate sensor is listening to the channel.  
Let us consider the transmission procedure of an NB-Fi sensor working in the DRX mode, illustrated in Figure 7. \(T_{B}\) seconds after the start of the frame transmission, the sensor listens to the downlink channel for \(T_{L}\) seconds. If the sensor does not receive an acknowledgment, intended for it, it makes a retry after a random backoff time uniformly distributed within the retry window \(T_{md}\). The sensor retransmits the frame until it receives an acknowledgment or exceeds a configurable retry limit. Table 3 lists \(T_{B}\), \(T_{L}\), and \(T_{md}\) values.  
The second mode, called No RX, supports only one-way communications from sensors to BS. In this mode, the sensors transmit data if needed. Otherwise, they stay in the \"sleep\" state with their radio switched off.  
In the last mode, called continuous RX mode (CRX), the sensors always listen to the channel and can transmit and receive data at any time. Most of the devices in sensor networks are battery-powered and, therefore, do not use this mode. Thus, we do not consider the CRX mode in this paper.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**SF** & \(T_{up}^{max}\)**, **s** & \(T_{up}^{min}\)**, **s** & \(T_{down}^{max}\)** & **s** & \(T_{down}^{min}\)**s** & **PL, Bytes** \\ \hline
12 & 3.121 & 1.155 & 3.072 & 1.057 & 51 \\
11 & 1.708 & 0.602 & 1.683 & 0.553 & 51 \\
10 & 0.688 & 0.268 & 0.678 & 0.258 & 51 \\
9 & 0.667 & 0.144 & 0.656 & 0.134 & 115 \\
8 & 0.697 & 0.077 & 0.692 & 0.072 & 242 \\
7 & 0.396 & 0.0425 & 0.393 & 0.039 & 242 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Frame parameters in LoRaWAN.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bitrate, bps** & \(T_{f}\)**, ms** & \(T_{B}\)**, ms** & \(T_{L}\)**, ms** & \(T_{md}\)**, ms** \\ \hline
50 & 5760 & 5900 & 60,000 & 5000 \\
400 & 720 & 740 & 30,000 & 1000 \\
3200 & 90 & 95 & 6000 & 100 \\
25,600 & 11.25 & 15 & 6000 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Time interval values in NB-Fi.