Pulse Modulation Types

Pulse modulation helps in achieving pulse compression, which facilitates high average transmit power and low peak power by making the pulse duration longer.

In pulse0 section, Modulation Type UI allows you to specify modulation with pulse envelope type. Selecting the modulation type is supported for all pulse envelope type except custom IQ.

The Pulse RFmx Waveform Creator supports the following modulation types.

All the modulation types are described in more detail in this section.

The 'None' modulation type does not apply any modulation on the pulse signal.

BPSK

A phase shift of 0 and 180 degrees is introduced after every specified step size during the pulse ON state (Width (100%-100%)).

Step Size: The step size is defined as time duration of the phase shift for each ON/OFF state. Valid values are from 0 to 1 second.

The following image shows BPSK phase changes from 0 to 180 and vice versa.

Phase shift of 90 degrees is introduced after every ‘Step Size’ duration during the pulse ON state (Width (100%-100%)).

Step Size: The step size is defined as time duration of the phase shift for each I/Q state. Valid values are from 0 to 1 second.

Valid values are from 0 to 50.

The QPSK sequence supported by the Pulse RFmx Waveform Creator application is Gray code ‘00’, ‘01’, ‘11’, and ‘10’.

The following image shows QPSK phase changes.

Frequency remains constant during rise time (0-100%) and fall time (100%-0) and modulated linearly over the pulse ON time (Width (100%-100%)) based on user-defined chirp deviation and chirp type parameter.

Chirp Deviation: Specifies the chirp deviation for FM Chirp modulation. The chirp deviation is defined as the maximum change in the modulation frequency that occurs over the time period of the pulse (Width (100%-100%)). Chirp deviation is represented in Hz. Valid values are from 0 to 5 GHz.

Chirp Type:Specifies the direction of chirp for FM chirp modulation.

The following image shows the UI selection for FM chirp modulation.

In the image, the chirp deviation is 10 MHz. Chirp frequency is held at -10 MHz below the carrier frequency during rise time (0-100%) and chirp frequency is held at 10 MHz above the carrier frequency during fall time (100%-0). During the width (100%-100%), the chirp frequency increases from 10 MHz below the carrier to 10 MHz above the carrier.

The following image shows the FM chirp deviation with the above settings.

For every user-defined step size, user-defined frequency is applied to the pulse signal during the pulse ON time (width (100%-100%)). The step size can be varied from step to step. If the sum of the step sizes is not equal to the pulse width, the FM steps will be padded (if there are insufficient steps) or truncated (if there are excessive steps).

Step Size: Step size for FM Step is defined as the time duration at each frequency step. Valid values are from 0 to 1 second.

Frequency: Specifies the frequency that is applied on the corresponding step size. Valid values are from -1 GHz to 1 GHz.

To create The FM Step table:

• Select FM Step from the Modulation Type drop-down list box.
• Click the Add button to enter step size and frequency values.
• Step size and Frequency values can be removed by clicking Remove button.

The following image shows UI selection for FM Step modulation.

The following image shows the frequency and time relationship for the table entries in UI details shown above.

For every user-defined step size, user-defined amplitude (dB) is applied to the pulse signal during the pulse ON time (width (100%-100%)). The step size can be varied from step to step. If the sum of step sizes is not equal to the pulse width, the AM steps will be padded (if there are insufficient steps) or truncated (if there are excessive steps).

Step Size: Step size for AM Step is defined as time duration at each AM step. Valid values are from 0 to 1 second.

Amplitude: Specifies the amplitude (dB) that is applied on the corresponding step size. Valid values are from -300 dB to 300 dB.

To create The AM Step table:

• Select AM Step from the Modulation Type drop-down list box.
• Click the Add button to enter step size and amplitude values.
• Step size and amplitude values can be removed by clicking Remove button.

The following image shows the UI selection for AM Step modulation.

The following images shows the amplitude and time relationship for the table entries in the UI details shown above.

Phase shift of 0 and 180 degrees is applied to the pulse based on the selected barker code length during pulse ON time (Width (100%-100%)).

The Pulse RFmx Waveform Creator application supports several barker codes which have unique auto correlation functions. When this modulation is selected, a drop-down list box, labelled Barker Code Length becomes available in the UI and displays the available barker code length.

The following table shows the barker code for specified barker code length.

The following image shows barker phase shift of 0 or 180 on barker-7 coded signal.