# Experimental Evaluation of the Packet Reception Performance of LoRa
## 5 Results and Analysis
### Parameter Setting of the Transmission Scheme
Therefore, we need to find the optimal parameter configuration to balance these variables, so as to obtain the minimum time \(t\) required for the packet to be successfully received. We use examples to illustrate how to adjust these parameters to obtain the minimum \(t\). In order to make our proposed scheme easy to understand, we first clarify how to optimize  
Figure 11: The number of packet retransmissions for different Signal to Noise Ratio (SNR) and SF settings. the SF to reduce the \(t\). Then, multiple parameters are comprehensively considered to obtain the minimum transmission time \(t\), thereby reducing the energy consumption of successful communication, and finally achieving a balance of reliability, delay, and energy consumption. We assume that the SNR is \(-9\) dB, the BW is \(125\) kHz, the CR is \(4/8\), and the packet length is \(32\) bytes, and then adjust the SF to reduce \(t\). Meanwhile, in order to ensure that the receiver has a sufficient receiving time window without being interfered with by other data packets, we restrict the interval time of data packets so that it is not less than \(3\) times of the packet transmission time. We substitute the previous experimental results under this condition into Equation (12), and obtain the \(t\) at different SFs, as shown in Table 2. The result shows that \(t\) is the smallest when SF is \(8\). Although SF = \(8\) has a longer transmission time \(t_{0}\) than SF = \(7\), the Packet Error Ratio of SF = \(8\) is much smaller than SF = \(7\). In other words, SF = \(8\) will also have fewer retransmissions, thus shortening the time \(t\) required for the packet to be successfully received. Moreover, although the Packet Error Ratios for SF = \(9\), \(10\), \(11\), and \(12\) are small, the number of retransmissions required will be small. However, their Packet Error Ratio is not that different from SF = \(8\), and their transmission time \(t_{0}\) is much greater than SF = \(8\), so it takes more time for the packet to be successfully received. Imagine that if we still use SF7 without adjusting the SF, the time \(t\) for successful communication will be three times as long as the SF adjusted. If the most sensitive parameter configuration (SF12) is adopted directly, the time required is \(11\) times that after adjustment. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**SF** & **PER** & \(t_{0}\) **(ms)** & \(t_{r}\) **(ms)** & \(t\) \\ \hline
7 & 0.5380 & 96.51 & 386.04 & 546.05 \\
8 & 0.0050 & 176.64 & 706.56 & 180.19 \\
9 & 0.0019 & 320.51 & 1282.04 & 322.95 \\
10 & 0.0011 & 575.49 & 2301.96 & 578.02 \\
11 & 0.0003 & 1150.98 & 4603.92 & 1152.36 \\
12 & 0.0000 & 2039.81 & 8159.24 & 2039.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Given some parameters, the result of the transmission time t with different SF values. Figure 12: Transmission time t for different SNR and SF settings. The lower the (t), the better. In order to test the effectiveness of this method, we first set the required initial conditions, then used the USRP transmitter to continuously send 1000 packets, and repeated the experiment five times. The interval between packets is the time of three packets. Therefore, the result of the average time required for each packet to be successfully transmitted is shown in Figure 13a. As expected, the time required for SF8 is the smallest value, which is the same as the result we obtained through theoretical calculations. The comprehensive consideration of multiple parameters is the same as the previous method. The PER of all parameters corresponding to the SNR is substituted into Equation (12) to obtain the shortest successful transmission time \(t\). For example, when the SNR is \(-3\) dB, we optimized the configuration of SF, CR, BW, and the packet length to reduce the communication time, thereby reducing the energy consumption of the node. Since short packets will send more headers than long packets, there is no need to divide long packets into short packets.