## 2 Proposed Simulation Environment
### Modeling of Emitter, Sensor and Radio Assign  
In the beginning, we need to define the radio and select the type of signal, which could be GNSS Upper L-band, GSSN Lower L-Band, or Interference. After that, starting with Instance-1, we can specify the trajectory of the dynamic emitter from the Interference section. In the study, we consider the UAV as an RF emitter. After that, we can specify the trajectory of the UAV(as a dynamic emitter) from the interference section. Next, we can specify the reference power level (that we considered \(-90\) dBm). From the transmitter section, we can select signal and trajectory. We can observe the power level at the receiver side (LEO satellite) specified at the transmitter side. Additionally, in the transmitter section, we can ignore propagation loss. In the trajectory, we can choose a fixed position of service that we can put as a circle shape or import the trajectory of the dynamic emitter as Keyhole Markup Language (KML) or Comma-Separated Values (CSV) file format with timestamps.  
Moreover, the information of transmitter and receiver can also be downloaded using logging files for each epoch as a reference file, which will be useful to fix the parameters of UAV and LEO satellites coordinates and velocity etc. From the Settings-Interference-Transmitter 1, and Signal section, we can select the type of signal we want to transmit. It could be Continuous-Wave (CW), Chirp, Pulse, or Binary Phase-Shift Keying (BPSK) signal, see Figure 3.  
Figure 2: A general diagram of emitter estimation using multi-LEO satellites based on TDOA and FDOA Measurement.  
As well, the central frequency of the BBSK signal, which was considered in this study as 1575.42 MHz with 2.046 MHz bandwidth as shown in Figure 4.  
From the antenna section, we can import the antenna pattern of the emitter, or we can select None to avoid interfering with the power of the signal, see Figure 5.  
Figure 4: Creating central frequency of BPSK signal.  
Figure 3: Selection of interference signal.  
After configuring the transmitter, we need to configure the receiver. To configure the LEO satellite as a receiver, we can click on the Settings-Vehicle tab and specify the Keplerian Elements. For example, we can change reference time that will change satellite position and adjust the best line of sight (LOS) between the LEO satellite and the emitter; see Figure 6. Regarding antenna pattern, it is the same situation as the transmitter; we import the antenna pattern or select it None to avoid interfering with the signal's power.  
We can repeat the same steps in the next instances, and put the first instance as master and others as slave. From the Settings-Global-Synchronize Simulators section, we can select the instance if it is master or slave, see Figure 7. Eventually, we can save all changes at each instance, and click on start at instance-1 to run the scenario configured. All configurations are saved in the Skydel-SDX/Configurations folder, and the configuration files use the (sdx) filename. After passing the selected time, we can stop the running simulation and save the simulation scenario at I/Q files (CSV format) [44].  
Figure 5: Specifying antenna pattern.  
Figure 6: Screenshot of LEO satellite orbital parameters setup.