CDMA Signal Spreading - The VERY basics of how it's done

[@SpazztechLLC]

It takes a smart person to explain a complicated thing in a complicated way, but it takes a real genius to explain a complicated thing in a simple way. Thanks for sharing, and great video!

[@mohammedriyadh5218]

i start with nothing ,ends with how signal spreading works.thank u again

[@Backflipmarine]

To everyone using 1 = +1V and 0 = -1V, use logical XNOR not XOR. Logical XNOR is: if bits are same output = 1, if not output = 0. Example of XNOR logic 1010 0000 0011 1101 =0110 0010

[@abhinavtripathi9678]

Thanks I was repeatedly making that mistake.

[@MasterTeeee]

So XOR, it... Then invert the result.

[@MonsieurBenLem]

What is the logic between using XNOR for a different line code representation?

[@hari-bhatta]

Thanks a lot mate👏 your comment is really helpful🙂

[@ItsMeTheUser]

now it makes sense for me , thanks a lot.

[@Duderantula]

This is brilliant, love the sounds effects. You can really tell you enjoy teaching people

[@RaviQi]

"tshuid, tshuid, tshuid.." waveforms

[@georgehowell2848]

"what's this guy on about?", gets half way through the video, "ahhhh!"

[@ChefMadAsHell]

Fascinating. Glad to finally get a basic understanding of this concept instead of being shoved a million acronyms to memorize. (Looking at you, CompTIA!)

[@farhanbadar1716]

Looking forward for more videos. It was so easy to understand, every step was crystal clear, superbly explained.

[@vimukthi.herath]

you forgot to mention that the codes of other users should be orthorgonal to each other, which is why they don't come up (=zero) at integration aka decoding.

[@purdysanchez]

Wouldn't all the codes need to be mutually orthogonal? Meaning it's not just my code against your code, its has to be every code in a user group can never be zero against any combination of data in the user group. How does that work?

[@madskillz1o1]

Thank you, I came here to find out what a "chip" was and you showed me. Cool exercise.

[@desmondtheredx]

same here!

[@phdrn]

me 2

[@stormbread5096]

This is such a good video! I didn't know what I was doing until I watched your video!!!

[@uzsa2100]

I don't know how often you check the comments but this was terrific! I needed to understand this for a blog I am writing and I can completely get it now. :-) Thank you so much!!

[@siddharthachatterjee9959]

+Chantuay McCoy Hi, did you get the excercise right for User#2 & 3 ? I did not get them right (see my post below). If you got, could you please help me on those. Thanks.

[@COMB0RICO]

Two codes are said to be orthogonal if when they are multiplied together the result is added over a period of time they sum to zero. For example a codes 1 -1 -1 1 and 1 -1 1 -1 when multiplied together give 1 1 -1 -1 which gives the sum zero. An example of an orthogonal code set is the Walsh codes

[@COMB0RICO]

Above was taken from radio-electronics.com

[@CallistoPili]

This kind of explanations are genuinely fantastic. CDMA, OFDM, and all digital modern signal processing are a sort of magic. the video is simple and effective straight to the point fot an initial understanding. Everyone aged remember the landline equipment to transfer data through a physical line up to 64kbps(if good cabling was fitted at home). At some point xDSL lines and clever modulation techniques arrived and now on the same cable you can transfer dozen of megabits, maybe 100mbit without to change the cabling at home. At some point the miniaturized electronics gone further and the WiFi in a similar manner skyrocketed the capability to provide network connections at cheap price.

[@BiscoBoi]

Comcast is rolling out a newish specification that allows 2Gbps up/download speeds on existing coax infrastructure.

[@anthonya910]

You have no idea how you just save my life!

[@manogyurka969]

Wow! That is what people need. This is called "explaining"! Thank you!

[@BazIrvine]

Thanks very much Carl you helped me unbend my mind. Watch it all the way through before you thumbs down folks.

[@jimmybuffet4970]

I used to work on a CDMA2000 Rev. A network. Nicely done!

[@1994ToyotaCamryEnjoyer]

I am going to pass my exam because of you. thank you so much

[@TekCroach]

An excellent video. I have seen very mathematical explanation of this simple beautiful theory that makes you go nuts. This is so wonderful an explanation. Good Luck.

[@goofypettiger]

Excellent! I would add some discussion on the need for codes to be "orthogonal" and the way to generate codes

[@hienphamthe90]

Thank you so much for the demonstration. I have struggled with CDM, but not anymore :D

[@patriotik]

Amazingly well explained. Thanks for your effort.

[@soorajsundaran3710]

VERY THANKS.for helped me to study cdma technology...for my university exams

[@09372556612]

Its explained in very simple manner !! I liked it !

[@FanMaoyi]

Amazing CDMA, amazing explanation, amazing video! Thanks!

[@adamhere238]

Very useful and clear explanation! Thanks a lot! Since the example you gave is synchronous, how to decode the asynchronous signals mixed up by different users?

[@purdysanchez]

This question bugs me as well. The phone tower output is an aggregate signal. But the cellphone output to the tower is a bunch of random devices concurrently broadcasting non synchronous signals. How the hell does the tower work out the time difference in radio waves?

[@ayoubmerzak1733]

To be more precise, the example you explained Sir concerns DS-CDMA. There still another version of CDMA used in Bluetooth for instance which is FH-CDMA.

[@profwork110]

loved it tomorrow is my midterm this helped me allot.

[@jorgedardon5487]

tomorrow is my midterm and it helped me a lot! life is funny!

[@carlosvazquez603]

Explaining it in such a simple way, absolutely useful. But just think about whoever came up with this idea the first in the last cubical at Qualcomm offices.

[@BenMatthewsMusic]

When working this out in google sheets, my user 2 comes out as "-0.25, 0", and my user3 data comes out as "-0.25, 0.25". Why is it +/- 0.25 instead of +/-1? Is it presumed in decoding that if it's a non-zero result, then it is a 1 result (there for -0.25 or +0.25 is converted to 1)?

[@DizzyVixen]

This helped me understand CDMA so much more! Thanks for posting!

[@siddharthachatterjee9959]

+DizzyVixen Hi, did you get the excercise right for User#2 & 3 ? I did not get them right (see my post below). If you got, could you please help me on those. Thanks.

[@dnwklin]

How does uplink works in CDMA? Does 3 transmitters of their chips naturally mixed over the air to the combined signal?

[@deepuvakkalagadda]

best explanation in the whole youtube and i love ur waveforms ishukk ishukk sounds

[@Anime_tamil_dub]

Super sir. Very good explanation

[@clubedohardware]

Finally understood this subject! Many thanks!

[@Njshanto89]

Nice explaination Sir Thank you very much

[@mohammed2noor]

such a great person you are,a follower from IRAQ

[@TomaszZarski]

+Carl Oliver when you are using -1V as 1 bit and +1V as 0 bit your spread massage sm = code XOR data, but when you are using -1V as 0 and +1V as 1 your spread massage should be sm = code XNOR data. That way all problems with switching bits voltage are gone. Am I right?

[@AkashAshky]

Best video out there for this topic! Thank you. Legendary.

[@AkashAshky]

cdma,networks

[@JDRBNFB]

Awesome explanation especially the last part which ties it together - that really demonstrates "orthogonality"... So now, can someone, anyone, add to this the Public Long Code Mask (Long PN Code) as well as the PN Offset (Short PN Code), and talk about how CDMA 2000 uses 3 codes simultaneous to achieve channel access? How do the PN Codes work, and how do they prevent them from interfering with the Walsh Code process?

[@Electosauce]

I like the color of your pen, makes me feel like i have wasted my life.

[@akmalinogamov8150]

Thanks for sharing very comprehensive explanation , Can we expect something like this for OFDMA ?

[@FoShizzle713]

Thank you this definitely cleared up confusion. I have some questions though. Does CDMA rely on the fact that the spreading codes do not interfere? I assume you can't just choose any spreading code for each user. How does CDMA account for power loss of an EM signal over the air? Amplitude decreases has the distance a signal travels increases. So +2V, +3V may look like +1V, +1.5V for someone far away. How do they account for that?

[@kimjong-un2001]

+FoShizzle713 The output power of every phone is adjusted so the signal strength of each one is the same at the receiver/tower

[@shivasukumarreddy1506]

good

[@purdysanchez]

I have been wondering about this too. The math makes sense in terms of a phone decoding the output of a cell tower, but surely it's more complicated for the cell tower to decode all the phone's concurrent output.

[@pavelberkovich1933]

Really well-explained and clear. Thanks a lot!

[@johnaweiss]

So... the combined signal has 4 x the bits of the original data. So your transceiver needs 4 x the data-rate that would be needed to transmit the original data. So that's extra cost in terms of data-rate. At what point does this extra cost pay off?

[@dikrahassen6592]

Thank you my teacher after now i give respect

[@miltontapia8839]

Very good explanation, great video

[@jizhongling]

If too many signals are combined together, does it mean the voltage would be very high or it should have a way to accurately measure the voltage?

[@purdysanchez]

There is obviously a hard limit in terms of how many users a local area can support with this type of system.

[@mzeishar]

Thanks For This. Been Really looking for a good detailed video!! Thumbs Up!!

[@GloryOrBust]

Still helpful 9 years later

[@aabdev]

Is that possible to predict the maximum and minimum magnitude of the composite signal?

[@manishyadav2704]

What are the different codes (other than Walsh codes) which can be used for this type of coding at transmitting end. The procedure of analysis(like the one which you have shown in your video), if we use a different coding scheme, will remain same or vary from code to code?

[@shunter2829]

FN brilliant explanation and presentation! Thank you so much

[@michaelshur2485]

Carl Oliver Im confused when do we use the XOR operation vs the AND( same bit output =1) operation.

[@jubrilak]

You nailed it man

[@dieterpelz1971]

Good stuff Carl. Easy to understand. thanks

[@MrMyutubechannel]

This is a very cool video. At the same time, if you just use -1 instead of 0, then you don't have to go through the awkward numerical manipulations of saying 0= +1 V and 1= -1 V. You can just say -1 = -1 V and 1 = +1 V. At least, it seems to work out that way if I haven't blundered in my calculations (always a possibility). Is there any particular reason to go through the artificial manipulations when it seems like there is a straight-forward way to do it?

[@shanti489]

I expect more videos regarding wireless communications n related technologies... I have subscribed to ur channel

[@sanjaytumati]

Genius lies is simplifying the concept without altering it's meaning. Take a Bow, Carl

[@deepseeker6245]

Thanks for the good video. Here is a question: Why do we use the MULTIPLICATION (and not another mathematical or logical operation) of the composite signal and the code of the n-th user?

[@xyanglui7795]

thank you, you saved me a lot of time. hope to complete the way for ofdma. thanks a lot

[@uvatham]

🎉 extremely good explanation

[@fiddlyphuk6414]

So a 4 bit spread code will let you multiplex a maximum of 16 users? A 5 bit spread code is good for a maximum of 32 users and so on? Is that the case here?

[@dsaltechnologies]

Man you are my hero.God Bless you!!!

[@tinti7947]

Very good example. Thanks.

[@tianrunguo2343]

very detailed and clear explanation

[@kritikashukla3830]

thnku so much......its very easy to understand the concept

[@icyzoneinfo]

I find the accent with which you transfer information very pleasing. For educational purposes: Where are you from? Otherwise, a very helpful video. Thanks!

[@amirsaid]

thankx man ur a legend

[@shaneyaw4542]

Great explanation. Thanks!

[@manishyadav2704]

Suppose User-1 wants to transmit his message to a user [say user-k]. Then to decode the transmitted message, user-k will be required the signature code i.e. pn-sequence or spreading code of user-1. How will he get that?

[@KhaledMohamed-is5pl]

Why we use spread code ? And how to choose the spread code ? For example : We used spread code 0101 for the 1st user While used spread code 0011 for the 2nd user While used spread code 0000 for the 3rd user

[@taoufikulislam]

nicely explained Oliver!

[@Karol-dw4xz]

Can user’s data be longer than the spreading code?

[@kavinashokan5692]

Awesome explanation

[@GharGrihasthi]

where were you all these year

[@JorgeMartinez-ve4jj]

oh tankyou, i dont unbderstabd the documets of eriksson but you make understand so easy

[@eshandawadi3111]

sir at last to check answer ..we must get 4/4=1in every 4 bit ?

[@michaelbrandt9164]

Little confused here...let the three codes equal C1 C2 C3 and sequence codes equal A B C respectively. Also, CC equal the resulting composite code. So CC = C1(A)+C2(B)+C3(C). How does ((C1(A)+C2(B)+C3(C))(A))/3=C1? Can someone please explain this to me in the simplest terms possible, keep in mind the furthest i've got in mathematics is calculus 1.

[@kiranmankame1365]

Thank you for making it so simple

[@oluwatobiodujobi1845]

Please how did you get the spreading code?

[@awat888]

I was trying to use this method for my assignment but it doesn't work for 0 bit =-1volt and bit 1 =+1 volt

[@manishyadav2704]

How does the interleaving of messages from different users in CDMA is done?

[@iagha]

Is there any mathematical relation between the number of users and the size of the spreading code or I can choose them randomly? I tried different example with 2 users using 4 bits spreading codes to form the composite signal but I wasn’t able to retrieve the data bits correctly after.

[@purdysanchez]

Very good question. In a perfect world I would thing you would have as many keys (unique users) as the max spreading number used. So in the case of 4 binary digits of spreading, it should work for 16 concurrent users without key collisions

[@purdysanchez]

I should add that a lot of people mentioning that codes need to be "orthogonal" to each other. I don't know what that means, but you will probably need to take that into account in your math. So my previous comment was an over simplification. The key space would not be the size of the binary number, but the size of the subset that meets the orthogonality constraints.

[@thegoonist]

why is it counterintuitively +1 = 0 and -1 = 1??? why not the other way around?

[@chandvirdi27]

can four users can send the data and receive the same waveforms at the end

[@yorlinblanco9688]

good video!! tanks for explain CDMA Signal Spreading

[@jamesmurinio5815]

These Walsh codes are even orthogonal?

[@ailakalp1624]

hey.is it work only with 3 users? can i increase/reduse the number of users/data?

[@eng360]

Yes ! You can !

[@farhanbadar1716]

Does the length of code depends on no.of bits going to be transmitted ? you have used 4 chips as a code against 2 bits. Is it like 2^2=4 ??

[@carloliver4402]

After spreading, each BIT of data will be represented by a number of chips that is equal to the length of the code. For example, if the code is 64 bits long, then 1 bit (after spreading) will be represented by 64 chips. For 1000 bits, 64*1000 = 64000 chips.

[@nischaltamrakar7702]

Can we use same technique for 3 bit data?

[@farhanbadar1716]

according to your way user no. 2 data is also 0 0 and user no. 1 data is also 0 0....what is this ??

[@MeLz3r0]

Very good explanation!

[@RedCurlyHead]

who defines the spreading code and how the opposite side knows the spreading code in order to decipher it

[@chinmaykeskar1988]

just wanted to make sure that this is Asynchronous CDMA. right?

[@seetaramsubedi5097]

Dear Carl Oliver, Thank you for nice tutorial. My small confusion is in your graph instead of +3, +2, +1, 0, -1, -2, -3 there should be +3, +2, +1 -1, -2.. I mean there should not be 0. If you could comment up on it, it would be great !

[@luis-aceituno]

In this specific example there are 3 users, which makes a 0 impossible. But imagine there are only 2 users (or any even number), then you could very well have +1 -1 = 0.

[@shanti489]

Wow excellent lecture

[@saifali-vx1bw]

What i do if i get 2 in user data after multiplying

[@cabeloDoPardal2]

I didn't know CDMA used amplitude modulation. That might be the cause weak signals are poor to be amplified well. The threshold for identifying to which user the data packed in the waveform belongs should not be distinguised well when a signal is not good enough

[@BazIrvine]

Oh the irony.

[@saranassiriane4749]

It is really great ! Thank you !