srx-10i GPS Interference Analysis

The srx-10i system includes a built-in analysis tool that allows the operator to plot the PSD vectors corresponding to the selected files, and obtain quantitative information for the detected interferences. This can be done either by using PSD files recorded in real time by the remote local monitors or by regenerating PSD files starting from raw-sample files.

For each processed file, the obtained results include:

  • PSD vector as a function of frequency (w.r.t. the GPS L1 carrier at 1575.42 MHz), in dBW-Hz.
  • Triangular marks indicating the estimated power for each interference (as identified by the estimation process), in [dBm]. 

For each file, PSD vector and power markers are plotted with the same color (one of: red, green, blue…) although with different tones: PSD are darker while power markers are lighter. In addition, both types share the same Y-axis (expressed in logarithmic scale), although they have in fact different units. Depending on the case, the Y values must be interpreted either as [dBW-Hz] (PSD) or [dBm] (power marks).

The following figure shows a real example of results obtained processing a PSD file: 

srx-10i analysis tool

Area 1 in the plot contains the check box buttons. The results for each file are associated to two check box buttons, one for PSD and another for the power markers (in the figure above, these boxes are contained within the rectangle labeled as “1”). The boxes have a twofold purpose:

  • Hide / show a plot (by checking or unchecking on the boxes)
  • Display the time bounds for the estimation period: Initial time in the PSD box and final time in the power-marker box

Area 2 contains a pop-up list: When the cursor is placed in front of the graph plots, a tooltip window pops up, indicating the list of plots being displayed together with the corresponding date and time.

Area 3 shows the interference values: A table is displayed below the plots area, with a column for each processed file, containing:

  • Power, frequency and bandwidth for the main interference peak of each plot
  • Total interference power for each plot

Area 4 is the time slider: When the tool is used in sample-file mode (i.e. not in the PSD mode), the piece of recorded signal contains several PSD estimation periods in configurable rates and the tool produces consecutive PSD vectors, spanning the recorded signal. These PSD vectors can be subsequently visualized by clicking at different points of the slider. Each point of the span represents a time shift multiple of 2 seconds from the origin of the sample file. The absolute time of the point can be visualized within the check boxes and the pop-up lists, as explained before.

Area 5 shows the PSD at one frequency: When the cursor is located within the plotted area, the PSD values (for all the plots) corresponding to the current cursor frequency can be visualized by single click of the left mouse button. PSD values then appear at Area 5 of the Window (left top corner).

When the plot is in its default view (not zoomed) and the cursor is placed within the plotted area, clicking the right button of the mouse will open a menu with as many options as plotted files (same color key). When one plot is selected from that menu, a table will appear showing all the interference peaks identified by the estimation process for that file with the following information:

  • Frequency of each peak [MHz].
  • Power of the peak [dBm].
  • Estimated bandwidth [KHz].

The analysis tool can also generate reports, which contain a set of files with the following extensions and contents:

  • .csv and .htm files (one per processed file) showing the list of interference peaks identified for the corresponding PSD vector, including for each peak frequency [MHz], peak power [dBm] and bandwidth [KHz]
  • .pdf and .png plots
  • PDF report: a single document in .pdf format, including the available information (tables and plot)

An example of report generated by the analysis tool is shown in the following figure:

srx-10i report