# Development of a Digital System for Monitoring Emergency Conditions in 20 kV Distribution Networks
## 3 Results  
### Development of a Simulation Model for a Wireless Transmission Channel  
In wireless technologies, various types of modulation are used, and the properties of these determine their resistance to industrial and other types of interference. We will simulate signal transmission under conditions of intense interference from measurement nodes to the server for the following basic types of modulation:  
QAM--Quadrature Amplitude Modulation  
PSK--Phase Shift Keying  
FSK--Frequency Shift Keying  
PAM--Pulse Amplitude Modulation  
LoRa--Combined Modulation  
The goal of the simulation is to determine the status of each type of modulation in terms of its resistance to interference and to identify the most reliable type of modulation based on this criterion. During the simulation, the oscilloscope monitors the shape of the input and output signals, detects errors, and generates a signal scatter plot, which displays the state of the code combinations (CC) transmitted over the communication channel. When the level of interference affecting the signals during transmission changes, the signal-to-noise ratio (SNR) changes. When the threshold value is reached, the noise damages the signal, and the signal reception stops. It should be noted that in digital transmission systems, the bit error rate (BER) or the probability of a bit error P(e) is used as a quantitative measure of reliability. The noise coefficient characterizes the system's performance, while the BER indicates whether the system is operational or nonfunctional. Using this bit error rate, we will simulate noise impact on transmission channels with different types of modulation to compare the threshold values of the signal-to-noise ratio Eb/N\({}_{0}\), expressed in dB, at which the system becomes nonoperational at BER = \(10^{-8}\). For the development of the models, we use the educational and practical guide MATLAB 6.5 SP1/7 + Simulink 5/6 in Mathematics and Modeling, as well as methodological guidelines for independent work \"Mathematical Modeling of Radio Engineering Devices and Systems\" and the manual [7; 8]. The simulation of noise impact on the transmission channel for each type of modulation is performed in the range from low to intense noise impact and is recorded for two cases:  
1. The threshold value of the signal-to-noise ratio Eb/N\({}_{0}\), expressed in dB, at which the system becomes nonoperational at BER = \(10^{-8}\). 2. The signal-to-noise ratio at which there is significant interference, but the transmission channel remains operational. Figure 8: Structural diagram of the transmission system model. The model of the channel with FSK modulation, shown in Figure 9, is universal and is used for all types of modulation with the necessary replacement of the modulator and demodulator types, taking into account the provisions of Section 4. In Figure 10, the results of simulating transmission modes in a channel with FSK modulation are presented for two cases: operational (A) and nonoperational (B). In the first case, the signal-to-noise ratio (SNR) is 10 dB, and the oscilloscope does not display any signals in the error channel, indicating error-free signal transmission (Figure 10A). In the second case, shown in the oscillogram in Figure 10B, the SNR is 9 dB, and the oscilloscope displays a distorted signal at the receiver and signals in the error channel, which demonstrate the difference between the signals at the transmission and  
Figure 10: Simulation Results of a Channel with FSK Modulation. T1—Original signal, T2—Carrier frequency with FM modulation, T3—Original signal delayed by the signal propagation time in the wireless channel, R—Signal at the output of the receiving path, error—error signal (distortions) representing the difference between the transmitted and received signals. In Figure 10, the results of simulating transmission modes in a channel with FSK modulation are presented for two cases: operational (**A**) and nonoperational (**B**).