# Study and Analysis of Interference Signals of the LTE System of the GNSS Receiver
## 4 Simulation Studies
### Noise in the GNSS Receiver--Identification  
In the literature [36; 44], various approaches are proposed to solve the problem of detecting interference signals from radio systems. The selection of the appropriate method is dictated by the computational capabilities of the GNSS receiver. The least computationally complex are methods based on the analysis of parameters related to the power or time  
Figure 6: The radiation characteristics of the antenna used in the research for the 1554 MHz frequency. dependencies of the received signals. However, the efficiency of such solutions is relatively low, as such parameters can most often be defined so that their values do not differ from the values observed in the case of receiving signals from satellites. Another suggestion is to compare the indications of the designated position with the position determined using another navigation system; however, in this case, territorial limitations (ground-based radio navigation systems) or problematic calibration (inertial systems) should be taken into account. Moreover, it was postulated to introduce cryptographic safeguards to navigation messages contained in civil GPS signals. This would involve designating a digitally signed hash of the navigation message to be transmitted to verify that it is genuine. The hash would be sent in message fields that are not currently in use, thus maintaining backward compatibility with all receivers produced so far. The inconvenience of this solution is the necessity to introduce changes on the broadcasting side, which requires actions on the part of the authorities supervising the operation of the satellite system. One of the most effective methods of detecting radio interference signals is the analysis of the direction of the incoming signals. When signals are received from GNSS satellites in direct visibility conditions, their arrival directions to the receiving antenna are different. It is different in the case of interference where all the signals produced are transmitted using the same transmitting antenna, hence their directions of arrival being the same. To determine the direction of the signal arrival, it is important to use a system of several antennas (antenna array) and measure the relative phase delays of the signals reaching the individual antennas. The receiver needs to receive at least four GNSS signals for the position to be determined by the receiver. Thus, it can be concluded that spoofing is present when the phase delay values associated with at least four GPS signals are close to each other. The Dependence of \(C/N\) on \(E_{b}/N_{0}\)  
The key issue in modeling the GNSS receiver in the situation of receiving LTE system interference signals is the determining the element dependence of the error rate BER (Bit Error Rate) at the output of the GNSS receiver as a function of the signal-to-noise ratio (\(C/N_{0}\)) and the signal-to-interference ratio (\(C/I\)) at the input of this decoder in the channel with additive white Gaussian noise AWGN (Additive White Gaussian Noise) as the basic one in the determination of protection factors for different LTE transmission modes (different carrier modulations and different convolutional code efficiencies). Knowledge of these functions enables computer simulations of the element error rate depending on the parameters of the useful GNSS signal, noise parameters of the transmission path, and the level of interfering signals. The detection threshold, i.e., the value of the signal phase delay difference below which a positive interference detection decision is made, depends on the number of false signals received and their quality, as expressed by the parameter \(C/N_{0}\). The values of this parameter measured in real conditions range from 35 to 60 dBHz. The most sensitive receivers can detect signals \(C/N_{0}\) as low as 30 dBHz, but after demodulation, their waveform is close to noise.