# Emergency Communication System Based on Wireless LPWAN and SD-WAN Technologies: A Hybrid Approach
## 5 Scenario and Simulation Report
### Scenario 2: SD-WAN Simulation  
To simulate the SD-WAN, we considered a scenario that requires the transmission of a photograph by a mobile UE. This one-base station case study is simulated on the  
Figure 7: LoRa Packets. MATLAB simulator using the LTE Toolbox and an ADALM PLUTO SDR device. Planning, constructing, and assessing the performance of radio communication networks (including cellular networks) depends on a thorough understanding of radio signal propagation Path Loss (PL). To organize, create, and assess the performance of wireless systems, PL models are created and tuned by the examined environment. Thus, we adopted the Log-Distance Path Loss (LDPL) model. LDPL is a radio propagation model that predicts the path loss a signal encounters inside a building or densely populated areas over a distance [51]. We consider a portable--private LTE/4G base station deployed in an off-grid small rural area without obstacles. Therefore, we examine a clear line-of-sight (LOS) scenario between the base station and a UE. The 4G/LTE technology uses Orthogonal Frequency Division Multiplexing (OFDM) a multicarrier modulation technique that uses the Discrete Fourier Transform (DFT) and the Inverse Discrete Fourier Transform (IDFT) to convert the frequency selective channel into the flat fading channel [52]. For simultaneous broadcast and reception on the ADALM PLUTO SDR platform, the simulation procedure outputs a single antenna LTE waveform. The algorithm packs and encodes the chosen image into radio frames during waveform synthesis. The application then extracts the received image from the LTE waveform after the reception. The simulator uses a baseband Reference Measurement Channel (RMC) waveform created by the LTE Toolbox to create numerous radio frames from an imported picture file. It produces a continuous RF LTE waveform by using the repeated transmission feature of the SDR. This feature transfers the baseband RMC waveform to the ADALM PLUTO SDR's hardware memory and transmits the waveform over the air continuously and without breaks. The first frame acquired by the receiver is not always the first transmitted because the LTE waveform is traveling over the air in a loop and the frames are decoded out of order. The frame number determination helps to recombine the received frames accurately. The current system frame number is revealed in the Master Information Block (MIB) and is also decoded. The simulator decodes the Physical Downlink Control Channel (PDSCH) and the Downlink Shared Channel (DL-SCH) after determining the frame number and showing the equalized PDSCH symbols. Subframe number 5 is not required for data transmission, so the subframe-captured data is not considered during decoding [53]. When the LTE frames are successfully decoded, the simulator shows the detected frame number for each frame (Table 6) and the equalized PDSCH symbol constellation for each subframe (Figure 8a). In LTE networks, the PDSCH is the upper data-carriage downlink channel. Based on the LTE standards, such as DCI format and bandwidth, the PDSCH provides Downlink Control Information (DCI) code words with varying lengths [54]. The simulation of the PDSCH transmission is vital, as it incorporates procedures of scrambling, modulation, layer mapping, precoding, and data mapping to resource elements. The simulator also computes the bit error rate (BER), error vector magnitude peak (EVM peak), and round mean square (EVM RMS) values for every frame, and analyzes an approximation of the channel magnitude frequency response between the cell reference point 0 and the receive antenna (Figure 8b). To determine the quality of the received data, we first initialize our SD-WAN variables to let the simulator calculate the BER between the transmitted and received data of our scenario. The BER is the ratio of the bit's error number and the number of bits transmitted, while a high BER causes a packet loss which increases delay and reduces throughput [55].