# Modeling the Energy Performance of LoRaWAN
## 3 LoRaWAN Overview
### LoRaWAN Physical Layer  
#### 3.2.1 Physical Layer Main Features  
LoRa modulation and Gaussian Frequency Shift Keying (GFSK) provide the physical transmission support for communication between the end-device and the gateway. LoRa modulation is based on chirp spread spectrum mechanism [38]. Each LoRa symbol is composed of 2\({}^{\text{SF}}\) chirps, where SF represents the corresponding spreading factor [7]. The use of six orthogonal SFs in the range of 7 to 12, which provide different Data Rates (DRs), results in a better spectral efficiency and an increased network capacity. LoRa modems also use forward error correction, adding a small overhead to the transmitted message, which provides recovery features against bit corruption. This is implemented through different Coding Rates (CRs), from 4/5 to 4/8 (denoted CR = 1 to CR = 4, respectively). On the other hand, to avoid issues regarding drift of the crystal reference oscillator, a low data rate optimization mechanism is applied, which adds a small overhead to increase robustness to frequency variation over the timescale of the LoRa message [38]. This is done for SF = 11 and SF = 12.  
The Radio Frequency (RF) band to be used depends on the country where LoRaWAN is deployed. Our study considers operation in the European region, in the EU863-870 Industrial Scientific Medical (ISM) band, where three default channels are defined: 868.10, 868.30, 868.50 MHz. Each one of these channels has a bandwidth of 125 kHz, uses the LoRa modulation, and must allow data rates from 0.3 kbps to 5 kbps (DR0 to DR5, see Table 3). These channels must be implemented in every end-device within the European region. LoRaWAN also enforces duty-cycle limitations stated by ETSI regulations. For the sub-band comprising between 868.0 MHz to 868.6 MHz, the duty-cycle must be \(<\)1%. Then, this duty cycle has to be distributed in the three channels of this sub-band [18]. Note, however, that ETSI regulations limit the duty-cycle over one-hour intervals, whereas LoRaWAN enforces compliance with such limitation over the interval between transmission of a message and the next one. The reference indices for each data rate (DR), and the corresponding spreading factor (SF), bandwidth and modulation configuration, and resulting physical bit rate are shown in Table 3, which also includes the details for optional DR6 and DR7.  
As mentioned earlier, Class A LoRaWAN functionality focuses on the end-device, which has the main role in message exchanges: all transactions are started by the end-device, whereas the network server can only transmit in one of two downlink slots, called receive windows (RX1 and RX2, in Figure 2), opened by the end-device, following a previous uplink transmission. Therefore, any message the network server has to transmit after RX2 must wait until the next receive window to be sent.  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Data Rate (DR)** & **Configuration** & & & **Physical Bit Rate (bit/s)** \\ \hline  & **Modulation** & **Spreading Factor (SF)** & **Bandwidth** & \\ \hline
0 & LoRa & SF12 & 125 kHz & 250 \\
1 & LoRa & SF11 & 125 kHz & 440 \\
2 & LoRa & SF10 & 125 kHz & 980 \\
3 & LoRa & SP9 & 125 kHz & 1760 \\
4 & LoRa & SF8 & 125 kHz & 3125 \\
5 & LoRa & SF7 & 125 kHz & 5470 \\
6 & LoRa & SF7 & 250 kHz & 11,000 \\
7 & FSK & 50 kbit/s & & 50,000 \\
8–15 & Reserved for Future Use & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Data rates and related configuration for EU863-870 band channels.  
An end-device uses a different frequency channel for each message transmission, by following a pseudo-random channel sequence. This procedure makes communication robust against interference or other radio propagation impairments (e.g., multipath, etc.).