LEO Satellite Signal Simulation

Simulating low Earth orbit (LEO) satellite signals requires the ability to reproduce changes in signal frequency and amplitude as a satellite moves relative to a ground receiver. The Keysight M8190A AXIe arbitrary waveform generator uses digital upconversion (DUC) to simulate these changes while repeatedly playing the same digital waveform.

In this demonstration, see how the M8190A generates a quadrature phase-shift keying (QPSK) signal and applies Doppler frequency shifts and amplitude variations. A vector signal analyzer displays the resulting signal behavior, including changes in center frequency, signal power, and in-phase and quadrature (IQ) characteristics.

The demonstration illustrates how engineers can create controlled signal scenarios to explore key aspects of LEO satellite communications.

Why simulate LEO satellite signals?

LEO satellites move relative to ground-based receivers, creating changing signal conditions during a satellite pass. Two important effects are Doppler shift and amplitude variation.

Doppler shift is a change in received signal frequency caused by relative motion between the satellite and receiver. As the relative motion changes, the received frequency can shift over time.

Amplitude variation represents changes in received signal strength. During a satellite pass, signal power can vary as the distance and propagation conditions change.

Reproducing these effects in a laboratory helps engineers examine how receivers respond to changing frequency and signal levels. Controlled signal generation also supports repeatable observations during satellite communications development and testing.

How does the M8190A simulate satellite signals?

The Keysight M8190A arbitrary waveform generator uses its DUC mode to modify the frequency and amplitude of a repeating digital signal.

DUC shifts a digital waveform to a selected output frequency. In this demonstration, it also changes the signal frequency over time to represent Doppler behavior.

The demonstration uses a QPSK-modulated signal with a symbol rate of approximately 1 megasymbol per second. QPSK encodes digital information through changes in signal phase.

Rather than embedding each frequency and amplitude change into the stored waveform, the M8190A repeatedly plays the same digital data. DUC applies the changing signal conditions during playback.

This approach separates the underlying digital waveform from the frequency and amplitude adjustments used in the simulation.

Observing Doppler frequency shifts in real time

The demonstration shows how a simulated Doppler shift changes the center frequency of a QPSK signal.

The vector signal analyzer is configured with a center frequency of 1.7 GHz. The generated signal begins at approximately 1.6995 GHz and gradually moves toward 1.7 GHz as DUC changes its output frequency.

An occupied bandwidth measurement tracks the signal's frequency centroid as the Doppler shift progresses. The density diagram provides another view of the frequency movement.

When the generated signal reaches 1.7 GHz, it aligns with the analyzer's center frequency. The IQ display briefly shows the QPSK rotation stopping at this point.

The demonstration continues beyond the center frequency, showing how the applied Doppler shift can move the signal to higher frequencies.

For visibility, the presenter uses a faster and larger frequency variation than a representative satellite scenario requires. The settings illustrate the operating concept rather than reproduce a specific satellite orbit.

Simulating amplitude changes during a satellite pass

The M8190A DUC demonstration also shows how signal amplitude can change during waveform playback.

After the signal starts, its amplitude increases in visible steps. The presenter rapidly raises the signal power to its configured full-power level while the Doppler frequency shift continues.

The demonstration uses relatively coarse amplitude steps to make the changes easier to observe. The presenter explains that finer adjustments could produce a smoother amplitude transition.

These controlled variations illustrate how engineers can represent changing signal strength alongside frequency movement.

By combining amplitude stepping and Doppler shifting, the demonstration shows two signal characteristics relevant to satellite communications testing.

Analyzing satellite signal behavior with a vector signal analyzer

The vector signal analyzer provides multiple views of the generated waveform. Each view highlights a different aspect of signal behavior:

Occupied bandwidth measurement: Tracks changes in the signal's frequency centroid as DUC applies Doppler shifts.

Density diagram: Shows frequency movement over the course of the demonstration.

Spectrum display: Provides a view of the generated signal and its changing frequency position.

IQ display: Shows the QPSK signal behavior as the generated frequency moves relative to the analyzer's center frequency.

Together, these displays help engineers observe how the generated signal responds to changing frequency and amplitude settings.

The simultaneous measurements also make it easier to connect the waveform generator's programmed changes with the signal characteristics visible on the analyzer.

Why use digital upconversion for satellite signal simulation?

Digital upconversion allows engineers to change signal frequency and amplitude without embedding those changes directly into the stored digital waveform.

In the M8190A demonstration, the same QPSK data repeats while DUC controls frequency movement and amplitude stepping.

This separation provides a practical way to explore changing signal conditions while retaining the underlying modulation data.

For satellite communications engineers, the approach illustrates how a modular arbitrary waveform generator can support laboratory studies of Doppler effects, amplitude variation, and modulated signal behavior.

Watch the LEO satellite signal simulation demonstration

Watch the video to see the Keysight M8190A AXIe arbitrary waveform generator simulate a LEO satellite signal using DUC mode.

Follow the QPSK waveform as the signal amplitude increases, the center frequency shifts through 1.7 GHz, and the vector signal analyzer displays the resulting changes.

Explore how digital up conversion can help you create and observe dynamic signal conditions relevant to LEO satellite communications testing.