Why do I get complex signal after passing time domain signal to phased.MultipathChannel?

Dear all,

I am studying the problem of propagating acoustic signal in underwater environment. I am currently exploring the phased array toolbox. Specifically, I am studying the example "One-Way Signal Propagation in Multipath Underwater Sound Channel" in https://www.mathworks.com/help/phased/ref/phased.multipathchannel-system-object.html#:~:text=The%20phased.,you%20can%20use%20the%20phased.

I just wonder while the input sig is a time-domain signal, the output propsig is a complex signal after passing through the propagator object. What are the actual calculations/assumptions that lead to such result? Does it have anything to do with the narrowband signal assumption?

Best regards.

Answer 1

[Sudarsanan A K]

Hello Tran,

I understand that you are using MathWorks' example documentation "One-Way Signal Propagation in Multipath Underwater Sound Channel" for exploring the Phased Array System Toolbox. I also note that you are particularly curious about the complex nature of the output signal "propsig", after passing through the "propagator" object, and wanted to know the calculations and assumptions that lead to this result.

Here are some reasons for this transformation and its implications:

• The "propagator" object in the example simulates the propagation of sound waves through the underwater sound channel. The complex output signal "propsig" is obtained because the underwater environment is complex, with multipath propagation caused by reflections, scattering, and refraction.
• The complex values of "propsig" represent both the amplitude and phase information of the signal, capturing the strength and timing effects of the multipath components.
• This is not directly related to the narrowband signal assumption.

In order to know the functional implementation of the "propagatedSignal()" function in depth, I suggest you to open the MATLAB file "MultipathChannel.m" by typing the following command in the command window after running the example:

 open propagatedSignal 

This will open the definition of "MultipathChannel" class and will point to the "propagatedSignal()" method, where you can find the assumptions and calculation steps followed to simulate the multipath channel.

Additionally, you can refer to the MathWorks documentation on the "phased.MultipathChannel" System object to know more about its properties and use cases in the link:

https://mathworks.com/help/phased/ref/phased.multipathchannel-system-object.html

I hope this address your query.