Spread Spectrum Modulation and Demodulation

[@AllElectronicsChannel]

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[@camodudeA51]

I've always wondered how correlation worked in DSSS, with your great explanation I now know how they work...a major thank you. Now its on to the Costas Loop.🙂

[@AllElectronicsChannel]

Thank you!!

[@johnaweiss]

Outstanding explanation and presentation!

[@dominikgs]

Very nice explanation! Especially the recovery of the phases which is often left out on literature. Thanks for explaining the concept of phase recovery 👍 Perhaps you should make another video orthogonality of the spreading sequences. Multiplexing in Frequency only works if your spreading codes are orthogonal to each other. In the end it is the same principle of mixing one signal with sine and one with cosine of the same frequency. The signals can only be recovered out of the sumsignal because sine and cosine are orthogonal to each other. Nevertheless a brilliant video 👍👍👍 Learned something.

[@AllElectronicsChannel]

Thanks!! A video about orthogonality and how the LFSR works is a good idea!

[@asharnajid1957]

I wish that my College lecturer would have taught like this...... Hat's off to you Sir

[@AllElectronicsChannel]

Thanks!

[@CallistoPili]

fantastic explanation, well done. I always loved to understand this such topics in deep. Even if I studied this stuff I've never find the way to use as practical daily basis. I want to make from scratch one on these intricated spread spectrum systems!!!!

[@AllElectronicsChannel]

Excellent!

[@laurentcadet6523]

Your videos are mindblowing !!! The way you explain things is absolutely marvelous !! Moreover, I would like to know in which case the SSM is used, based on its complexity, it should be somewhat interesting (or it would not exists....). But why is it used ? If the PRBS signal is acting like a noise, what happens if you add real white noise on top of it ? will it be still recoverable ?

[@AllElectronicsChannel]

Thanks!! The spread Spectrum modulation has some magical aspects. Think with me: what happens if we have an interfering signal close to our signal? The process of despreading in the receiver will transform this signal into noise!!! And our desired signal will come from noise and appear clear! So, non linear distortion, IP3, spurious, all affect the receiver equal no thermal noise! Over all that, we can have multiple transmitter with different code sequences, transmitting at the same frequency. The receiver will despread only the signal of interest. GPS uses spread Spectrum. All satelites transmits at the same frequency, each one with a different code! And it even more fun, it connects to multiple satellites using paralel receivers, despreading each one with the correct code. The phase different of the codes relative to each other is the difference distance between you and the satelites!! This is what is used to decode your position!

[@laurentcadet6523]

@@AllElectronicsChannel very interesting ! Thank you for your reply ! And I like this format, don't change it (simulation and signal path explanation) !!!

[@Confucij]

Great video! Unfortunately for me, I'm still missing the point at which the spreading sequence applies. Will it matter if we apply the spreading sequence to the data stream - as what was shown on a slide at 6:26 - first and then mix it with the carrier or we should first get the modulated data stream signal and then apply the spreading sequence? As I see it it should produce the same result, shouldn't it?

[@AllElectronicsChannel]

Yes, absolutely!

[@BalticLab]

Great video, Gregory!

[@AllElectronicsChannel]

Let's thing in a topic to make a colab! 😄😄 I follow you since your beginning

[@BalticLab]

@@AllElectronicsChannel I sent you an eMail ;)

[@johnwiley542]

Perfect, thanks for sharing this video 🙏

[@AllElectronicsChannel]

Glad it helped!

[@varjagg]

Thanks for the educating video. What's the advantage of re-mixing a BPSK with spreading sequence instead of doing that earlier in digital domain?

[@AllElectronicsChannel]

Today all the topology is commonly implemented in the digital domain! I have a video where I design a DSSS beacon, take a look. All the steps are done inside the AVR uC.

[@varjagg]

@@AllElectronicsChannel Fantastic, thanks!

[@johnaweiss]

How does the rcvr generate the identical spreading code as the xmtr? Is it pre-programmed into both?

[@AllElectronicsChannel]

Pre programmed !

[@johnaweiss]

The spreading code is a much higher frequency than the bit stream. But, is it a much higher frequency than the carrier?

[@AllElectronicsChannel]

No!! Think about that.. what happens if you" modulate" a signal with a much higher frequency? It alias.. The data becomes the carirer, the carrier becomes the data...

[@johnaweiss]

I would say the Acquisition stage is a closed loop, but the feedback only senses Correct or Incorrect. The feedback doesn't give Magnitude. In the Tracking phase, feedback gives Magnitude (so locks faster than Acquisition stage), but there may still be some "searching", as the feedback is affected by resolution, speed, error, and maybe tolerances in the Correlator.

[@southpark5555]

Nice vid! The incoming pn sequence in the spread spectrum signal is running at chip rate. For your correlation procedure with the local pn sequence, what sampling frequency do you use? eg. 10 times the chip rate? Thanks!!

[@AllElectronicsChannel]

Hey! For this example, I don't remember. I think anything higher than 5x should work fine. Probably the first systems used 2x...

[@southpark5555]

@@AllElectronicsChannel Thanks very much for your reply, and for mentioning higher than 5X should work. Best regards.

[@mhmtsrml]

Which is the program it to you use, how can i do it

[@AllElectronicsChannel]

I used octave !

[@mhmtsrml]

@AllElectronicsChannel do you have a link program Octave

[@joeyglasser2574]

Great video!

[@AllElectronicsChannel]

THanks!

[@mjs825]

Let's assume that the receiver PRBS generator is not the same as the transmitter's, how would you change the receiver's PRBS in real time?

[@AllElectronicsChannel]

You only need to change the PRBS generator. If it is a table you change it, if it is a LFSR you change the taps

[@mancio92M]

what are the advantages in a spread spectrum system?

[@AllElectronicsChannel]

The spread Spectrum modulation has some magical aspects. Think with me: what happens if we have an interfering signal close to our signal? The process of despreading in the receiver will transform this signal into noise!!! And our desired signal will come from noise and appear clear! So, non linear distortion, IP3, spurious, all affect the receiver equal no thermal noise! Over all that, we can have multiple transmitter with different code sequences, transmitting at the same frequency. The receiver will despread only the signal of interest. GPS uses spread Spectrum. All satelites transmits at the same frequency, each one with a different code! And it even more fun, it connects to multiple satellites using paralel receivers, despreading each one with the correct code. The phase different of the codes relative to each other is the difference distance between you and the satelites!! This is what is used to decode your position!

[@Sebas_Cba_82]

Excelente explicación, (debo traducirlo), sobre temas poco difundidos. Que libro recomienda que hable de estos temas? Ya que algunos son muy generales como el de Wayne Tomassi. Saludos desde Córdoba, Argentina

[@AllElectronicsChannel]

Thank you!

[@Mr_ASIC]

thank you very much

[@AllElectronicsChannel]

🤓🤓🤓

[@Electrnick]

Could you do it in GNU Radio?

[@AllElectronicsChannel]

Hey man, I personally don't use GNU radio, but certainly you could do it

[@Electrnick]

@@AllElectronicsChannel I need a guide, I don't know how to do it. 😭

[@AllElectronicsChannel]

Aren't good videos about it here on YT?

[@RickLizotte]

I have subscribed, but did not find simulation files. Explanation is very good but have the simulation files would make this great.

[@AllElectronicsChannel]

Hi man, I attached in the post about this video on Patreon. Did you search there ?

[@RickLizotte]

Yes, I subscribed and searched that area. I could not locate the video posted here or simulation files. @@AllElectronicsChannel

[@AllElectronicsChannel]

Send a message to me on Patron

[@RickLizotte]

The message interface does not appear to be active on Patreon. Maybe a firewall issue on my end.(??) @@AllElectronicsChannel

[@AllElectronicsChannel]

I replied there 🙂