How does DS CDMA Work?

แชร์
ฝัง
  • เผยแพร่เมื่อ 23 ธ.ค. 2024

ความคิดเห็น • 37

  • @blistergeist
    @blistergeist 2 ปีที่แล้ว +4

    I work tangentially with wireless communications signals in my day job and although I have a good innate understanding of FDMA and TDMA, I was having a hard time grasping the concept of CDMA. This video gave me the clear explanation I was looking for, thank you!

    • @iain_explains
      @iain_explains  2 ปีที่แล้ว

      That's great to hear. I'm so glad it was helpful.

  • @fifaham
    @fifaham 3 ปีที่แล้ว

    Now the challenge of synchronizing between the symbol signals and the sequence codes is real challenge. Also what makes it more challenging is having long sequence and knowing when to switch to the next sequence code, syncing is vital or else we lose the received data. It would be greatly appreciated if you could explain how to perform this syncing between code sequence and the correlated original symbol signal data.

    • @iain_explains
      @iain_explains  3 ปีที่แล้ว +3

      Thanks for the suggestion. It's on my "to do" list (but it's a long list).

    • @fifaham
      @fifaham 3 ปีที่แล้ว

      @@iain_explains I understand your very busy schedule ... Thank you for all of your great efforts you have done so far. I am one of your fans and am always watching your great videos.

  • @smaaack
    @smaaack หลายเดือนก่อน

    Very clear explanation, thank you! I was struggling with the one given in my textbook

  • @alalolol9949
    @alalolol9949 2 ปีที่แล้ว

    Thanks for this wonderful video. Could you further explain how DSSS makes Inter-Symbol Interference negligible in the multi-path scenario?

    • @iain_explains
      @iain_explains  2 ปีที่แล้ว +1

      Thanks for the suggestion, I'll put it on my "to do" list. In summary, each delayed path in the channel (ie. the ISI paths) will arrive at the receiver with a different time offset, and can be correlated with the spreading code at that respective time offset, in order to detect the data on each path separately. If the spreading code is orthogonal to time-shifted versions of itself, then they won't interfere with each other.

  • @RisteardB2007
    @RisteardB2007 2 ปีที่แล้ว +1

    Really grateful for your videos, you do a great job!

  • @jamesgordan5549
    @jamesgordan5549 ปีที่แล้ว

    Would this be able to work with chirps? So for instance using Generalized-Chirp like (GCL) Polyphase codes/sequences. In order to closely resemble LoRa..

    • @iain_explains
      @iain_explains  ปีที่แล้ว

      It'll work for any waveform that spreads the bandwidth and is orthogonal to the waveforms being employed by other users.

  • @gorovskybrankovic9144
    @gorovskybrankovic9144 11 หลายเดือนก่อน

    Hello are we mixing the spread sequence with the bits together? I am wondering how this mixing would result in the frequency domain... I have read from books (what you have also mentioned in the video) that the the resultant spectrum is wider and makes the signal more resistant to interference. But how does that work mathematically I am wondering.
    Last but not least, this is a great video 👍

    • @iain_explains
      @iain_explains  11 หลายเดือนก่อน +1

      I'm not sure what you're asking, exactly. Multiplication in the time domain is the same as convolution in the frequency domain. That's the mathematical relationship. Perhaps these videos will help: "Convolution in the Time Domain is Equivalent to Multiplication in the Frequency Domain" th-cam.com/video/Ex318cCXSBM/w-d-xo.html and "Amplitude Modulation AM Radio Signal Transmission Explained" th-cam.com/video/-PWg-0k2oks/w-d-xo.html

    • @gorovskybrankovic9144
      @gorovskybrankovic9144 11 หลายเดือนก่อน +1

      @@iain_explains "Multiplication in the time domain is the same as convolution in the frequency domain." yea that's what I mean exactly.

  • @georgepalafox5967
    @georgepalafox5967 2 ปีที่แล้ว

    Hi Sir! Great video and thanks for uploading! Just for my clarification, the psd of the spread signal would be for one chip not for the entire 6 chips, correct?

    • @iain_explains
      @iain_explains  2 ปีที่แล้ว

      I think what you're trying to ask is whether the wide frequency width of the PSD is a result of the short time period of the chip waveform. If so, then the answer is Yes.

    • @georgepalafox5967
      @georgepalafox5967 2 ปีที่แล้ว

      @@iain_explains thanks Sir! For further clarification. When u say 1 chip waveform do u mean 1 chip and not 6 chip, correct?

    • @iain_explains
      @iain_explains  2 ปีที่แล้ว +1

      A 6-chip waveform is just a 1-chip waveform added to 5 other 1-chip waveforms each offset by an increasing number of chip intervals. Time offsets are just phase changes in the frequency domain, and so the bandwidth of the 6-chip waveform is the same as the bandwidth of the 1-chip waveform.

  • @jaypatel3233
    @jaypatel3233 3 ปีที่แล้ว

    This is wonderful. Thanks for uploading this on my previous request. Had few questions in mind, I was referring "Wireless Communication" book by Rappaport and found out that we need to use the equalizer at Receiver for the time varying channel. How those would affect in this DS-CDMA case ? And i think RAKE receiver would be a way to go as receiver for most of the CDMA system. Is there any simple way for designing a receiver ? Simply let's say we have ADALM PlutoSDR, can we use that as receiver, which i believe is not RAKE receiver. If you can comment on these questions, would be helpful. Thanks for your great work.

    • @iain_explains
      @iain_explains  3 ปีที่แล้ว +1

      Sorry, I'm not familiar with the particular SDR you mentioned. In general though, yes, you're right, typically DS-CDMA is received with a rake receiver. I've got it on my "to do" list.

  • @ananthakrishnank3208
    @ananthakrishnank3208 7 หลายเดือนก่อน

    This is how teaching should be!

    • @iain_explains
      @iain_explains  7 หลายเดือนก่อน

      I'm glad you liked it.

  • @佐助宇志波-p5g
    @佐助宇志波-p5g 8 หลายเดือนก่อน

    very well explained, thank u !

    • @iain_explains
      @iain_explains  8 หลายเดือนก่อน

      Glad it was helpful!

  • @tuongnguyen9391
    @tuongnguyen9391 3 ปีที่แล้ว

    CDMA seems to be a great idea (theoretically) but what make people abandoned CDMA and move on to OFDMA ?

    • @iain_explains
      @iain_explains  3 ปีที่แล้ว +2

      Did you see my video comparing them? "Mobile Standards Evolution: FDMA, TDMA, CDMA, OFDMA" th-cam.com/video/bm53RpK-S2k/w-d-xo.html

    • @tuongnguyen9391
      @tuongnguyen9391 3 ปีที่แล้ว

      @@iain_explains thank you so much !

  • @jeffi.8074
    @jeffi.8074 หลายเดือนก่อน

    Thanks! 😁

  • @fifaham
    @fifaham 3 ปีที่แล้ว

    Oh man ... I am now feeling I am 30 years younger LOL

    • @iain_explains
      @iain_explains  3 ปีที่แล้ว +1

      I didn't expect my videos would help to reverse the ageing process, but I'm glad they are 😀

  • @senantiasa
    @senantiasa 2 ปีที่แล้ว

    3 pluses + 3 minuses = 0 (I understand this)
    6 pluses = 1 (What? How? Shouldn't that equal 6 instead?)

    • @iain_explains
      @iain_explains  2 ปีที่แล้ว +1

      Sorry, I probably didn't make it clear that I'm assuming a scaling here. Technically, we should be writing down the value of the output of a matched filter in each case. So, the non-spread pulse would be received as (+1)(+1)(T) = T. Each chip in the spread pulse would be received as (+1)(+/-1)(T/6) = +/-(T/6), and then they get summed up. So it's all OK in the video, just called by T.

  • @deepakdavid8355
    @deepakdavid8355 3 ปีที่แล้ว

    I never understood CDMA in its core principle, not I got a clear idea thanks