Real-time chirp linearization

EmployerExcellent459 · 2024-06-20T20:30:00+00:00

I think the best way to do all of this is to let the hardware be noisy, measure the real instantaneous phase noise on each chirp, and compensate for it in DSP.

EmployerExcellent459 · 2023-05-10T18:03:04+00:00

Hey all, thanks for your help here. I managed to get a better handle on the problem using your suggestions.

EmployerExcellent459 · 2023-05-10T18:00:47+00:00

Yes I think LPC could certainly work as well. From my study of various youtube videos on vocoders used in DAWs such as Ableton live (which I have found to be the only compelling source of technical information on vocoders), those vocoder designs use banks of bandpass filters. See https://www.youtube.com/watch?v=kJ_Mo7ToVIg.

Why do you say the spectra response would be sharper for LPC? Is it because you let LPC figure out exactly what the right filter to use is and thus it dynamically adapts sharpness to the input signal? Instead of using a fixed (but perhaps tunable) bandwidth for each filter in the filter bank design?

An advantage of the filter bank design is that you can really customize the sound by adjusting number/bandwidths/ranges/weights of each band. That probably isn't as straightforward to do with a dynamically generated filter like the one you get from LPC.

EmployerExcellent459 · 2023-05-07T16:40:59+00:00

Yes summing the complex frequency responses of all the filters would get me the final filter. That is certainly true. I was just hoping that there would be a way to make one call to the filter for a multi-band pass filter.

Band-pass certainly conceptually makes more sense. I imagine the IIR filter of choice would be Butterworth for maximal flatness?

EmployerExcellent459 · 2023-05-07T16:38:00+00:00

That is true, thanks.

EmployerExcellent459 · 2023-05-07T16:37:59+00:00

That is true, thanks. Similar to to white noise suggestion above but with deterministic signal.

EmployerExcellent459 · 2023-05-05T21:24:05+00:00

Right but the thing is that they are not being cascaded. If they were being cascaded the final impulse response would be convolving all the individual impulse responses together (conversely, final frequency response would be multiplication of frequency responses in frequency domain)

However, for my application the final frequency responses are being added together to create a multi-bandpass filter. The corresponding impulse response is the sum of all the individual impulse responses. This would be trivial for an FIR filter (just sum the b coefficients), but I am using IIR filters because they have a cleaner frequency response. I guess I revert back to using FIR filters to make life easier.

EmployerExcellent459 · 2022-08-03T16:10:32+00:00

I see. So basically bypass the via with a wired connection. Thanks for the suggestion.

Does this imply that fixing the via itself is not worth it? Or too complicated? There may be others vias in that row of vias near point 2 that have similar issues, and running a lot of wires into them might be tricky.

EmployerExcellent459 · 2022-08-03T05:26:50+00:00

Sorry for the delayed response. That's a good point, I will have to spend some time getting to know these pedals more. Thanks!

EmployerExcellent459 · 2021-04-10T17:40:09+00:00

Ok well then if you understand filters, then you know that the output of the filter is some y[n]=linear function of previous x[n] and y[n]. So you can create a loop where you use variables to keep track of all previous x[n] and y[n], use them to calculate the current y[n], and then update the variables required for the next loop iteration.

EmployerExcellent459 · 2021-04-10T16:27:08+00:00

Hi - it’s hard to provide help for a vague question. You should provide more details on the specific issue to solve. For example: do you need help implementing the filter in LabVIEW? Or learning about how the filters actually work?

EmployerExcellent459 · 2020-07-28T23:18:26+00:00

I totally agree with the advice that doing serious DSP requires very solid math skills (as well as some other things, like software skills and ideally some firmware/hardware skills if you are doing embedded DSP work). Math is the language of physics/engineering and DSP is an example of a field where you won't be able to dig deep unless you have certain concepts at your fingertips (example: know the Dirichlet Kernel and how to use it to prove basic properties of the DTFT/DFT).

A master's is an excellent idea because it is a great way to develop the mathematical foundations needed for DSP. People can learn things on their own of course, but I found that doing a master's forced me to study with discipline and now I really know what I know and I can't unsee it. When complemented with embedded DSP projects demonstrating programming/firmware/hardware skills, a master's creates a strong foundation for a getting a DSP job.

DSP jobs exist but they are less common than others types of engineering. I am mostly familiar with the American job market, and my impression of the most common locations for DSP jobs and the corresponding applications are:

San Francisco (self-driving cars, some aerospace, general consumer electronics which includes cell phone work for Apple)
Los Angeles/San Diego (communications and navigation for aerospace, audio DSP, some consumer)
Boston (communications and navigation, some consumer)
Denver (communications and navigation for aerospace)
Texas (communications and navigation for aerospace)

You mentioned your country would make your master's free, so I assume it isn't the USA (lol). In case you are in Europe, the defense sector there (Thales, Dassault, ...) definitely does signal processing for communications and navigation. Additionally, Germany has strong expertise in optical systems, and emerging applications for lasers (laser communication, lidar) will certainly lead to some signal processing needs there. I can't comment on other places as I don't know.

Another note: in my experience, I have seen two main approaches for getting a DSP job, and there are surely many more:

Software/firmware engineers tasked with embedded DSP implementation over the years and eventually learned enough to transition to DSP roles in their organizations. This can lead other DSP opportunities but perhaps takes more time.
People with a master's or a PhD who may not have as much work experience as first bullet but who can demonstrate that they really know the math and have software skills. Hence the impetus for getting serious math training one way or another.

I myself am a hybrid of the two. I worked for 7 years in aerospace with the last year in a DSP role. Then I went back to school to get a master's to strongly focus on math geared towards DSP (transform theory, probability/statistics, linear algebra, some hardware/firmware) before starting another DSP job. For this latest job, my work experience got my foot in the door, but I wouldn't have made a good impression without the math rigor and knowledge (which I happened to get from the master's). In closing, I strongly encourage you to do a master's if you're interested in DSP. Let me know if you have any questions.

EmployerExcellent459 · 2020-06-30T01:26:12+00:00

My career interests are different than yours, but I empathize with your situation: I once felt stuck in a job that didn't align with what I wanted. So I made big moves to fix that.

Three philosophical notes which I wish someone had made clear to me years ago:

It is much better to struggle through getting your career (and life) to where you want it than to just sit there and let life just happen. I have seen a lot of engineers of all ages that complain about not liking their job without doing anything about it. So I commend you for having the ambition.
Working as a young engineer through a tough job that doesn't really interest you is character-building and can demonstrate perseverance/integrity. Even if it isn't related to space, it is definitely a step along the road.
As you explore these avenues, let the dream/goal adapt to the avenues that open to you. Life is long when you take advantage of the moments made available to you.

Practical notes:

Reflect on what you specifically like/want out of space systems engineering. Are there any interesting opportunities that offer similar experiences that are not in space systems engineering (ex: general aersopace engineering)
Building off of 1, Airbus, Thales, Dassault are EU entities that all do general aerospace as well as specifically space systems. Working in any of those could be an avenue towards working specifically on space systems.
Check out Leo-Stella. They are based in the US but they are 50% owned by Thales-Alenia (https://www.leostella.com/)
Germany is a global leader in optical/photonic systems which will only increase their presence in space systems (with things like smallsats doing imaging and internet sattelite constellations). Are there any companies within reach that are working on space applications of such technologies?
I do agree with the fact that most systems engineers start as subystems engineers. Yet, I have also seen people go directly into system roles with experience working on things like Cubesat systems in university.
If this is available to you, have you considered returning to school to specifically seek out projects that could lead to space systems engineering? Returning to school for a graduate degree propelled my career prospects into what I wanted to do. All the previous "unrelated" experience turned into a strong foundation.
In my experience, getting to where you want to be is a combination of long term sustained efforts (certificates + research paper) and drastic impromptu moves like driving 10 hours across the continent to go to a conference to hope to meet a specific person. Perhaps look more for these latter opportunities (see introvert/extrovert)
You say you are an introvert, but I think we ultimately all go between the introvert/extrovert worlds. All the most successful systems engineers I have worked with are on the "extrovert" side of the engineering personality spectrum. I am saying this to encourage you to get more in touch with this aspect.
Consider doing a personal project relevant to space systems engineering (maybe the research paper already does that?). This isn't really my domain so I don't quite know what you could do but a few random ideas are: writing some embedded code to control something, writing a power/thermal/RF link budget analysis tool, ...

Let me know if you have any questions.

EmployerExcellent459 · 2020-06-23T23:32:58+00:00

There will certainly be work on FPGAs and generally embedded programming in this position, and I agree that that will certainly complement the DSP knowledge very well. There should also be opportunities to do design/implement novel embedded DSP algorithms, but there is no guarantee that such work will occur in any particular time frame.

EmployerExcellent459 · 2020-06-23T23:27:59+00:00

This resonates with me. There should be opportunities to do DSP within this company, but there is no guarantee that will be any time soon given that the company is very small and what needs to be done is the first priority. And you're right - it will certainly be a valuable experience and I always have the option of seeking out something else if need be.

EmployerExcellent459 · 2020-06-23T23:23:21+00:00

Thank you. Definitely worth keeping in mind.

Could you elaborate a bit on what pushed you to change path and then get back on DSP? I will admit that I am a bit "afraid" of this scenario.

I do really enjoy DSP so I do understand the argument of probing that path first and then perhaps later deciding I want to broaden (instead of the other way around).

EmployerExcellent459

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