Interference hunting in TDD networks

Polychrome display method with the R&S®MNT100, R&S®PR100 and R&S®DDF007

Interference hunting in TDD networks

Your task

In time division duplex (TDD) networks, the downlink (DL) and uplink (UL) use the same frequency band in different time slots. When viewing such TDD signals on a conventional spectrum display, it is impossible to differentiate between the two and any other unwanted signals present in the same spectrum. This makes interference hunting extremely difficult.

10 MHz realtime spectrum and waterfall display of partial TDD-LTE signal
10 MHz realtime spectrum and waterfall display of partial TDD-LTE signal with a relatively persistent interferer at 2602 MHz.
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Rohde & Schwarz solution

The R&S®PR100 portable receiver, the R&S®MNT100 RF interference locator and the R&S®DDF007 portable direction finder provide a polychrome display that enables users to visually separate two or more pulsing signals that occupy the same frequency spectrum. This method enables simultaneous monitoring of both TDD signals as well as interferers. The user can hunt for interference and at the same time remain aware of the signal environment. When using the polychrome display to home in on the interferer, it is recommended to sweep the handheld directional antenna slowly to allow sufficient time for updating the signal level on the display.

Simple and quick setup steps

The polychrome display is available only in FFM mode.
Make the following settings:

In FFM mode, tune the center frequency to TDD frequency. Press [DISP] button followed by [F1] Display Mode, select “Spectrum” or “RX + Spectrum” display.

Press [F4] Polychrome Param button and turn on Polychrome IF Panorama. Adjust 100 % Time to obtain a good display contrast between interferers and TDD signals, e.g. 15 ms.

With a polychrome FFT speed of 4X, both DL and UL TDD signals as well as the relatively persistent interferer at 2602 MHz can be observed in the spectrum display.

The constant interferer that is continuously emitting at 2602 MHz will appear in red and become obvious in the spectrum display.

Polychrome display

In polychrome display mode, the frequency of occurrence of a signal is presented as a histogram. In the example below, a histogram is produced for each FFT bin of the signals at locations A, B and C. The histogram shows the distribution of signal level values and is mapped to a color scale with following limits:

  • Upper limit: 100 % = red
  • Lower limit: 0 % = black

i.e. signals that appear very frequently, such as noise, will appear red, allowing the user to visually differentiate pulsing signals that occupy the same frequency spectrum.

Left side: Example of signal at locations A, B and C of the spectrum display with their respective histogram on the left. Red indicates high frequency of occurrence while blue shows lower frequency of occurrence.

Right side: The 100 % time limit can be adjusted to give better visualization of signals that occur less frequently.