2.4 - OFDMA/SC-FDMA IN 4G LTE - PART 2
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- Опубліковано 26 сер 2024
- OFDMA/SC-FDMA in 4G LTE - Part 2
Streams of data, in the form of bits, reaches network gateway from various sources. The Gateway forwards it to the eNodeB. But how does the eNodeB converts them into radio signals and transmit them to the user over the air interface? How does the user equipment communicate back with e Node B?
We have shown, how data is transmitted and mapped on resource element using different modulation scheme, serial to parallel converter and Resource mapping technique.
Further how it is inefficient to transmit data using 1200 Oscillator, so to overcome this we have introduce IFFT in OFDMA block diagram, which convert frequency domain to Time domain sample signal.
We have also describe, number of sample required for 1 subcarrier and 1200 subcarrier for 1 second and for 1 symbol with period of 66.7Microseconds. How Backward compatibility used in OFDMA for sampling rate.
How OFDMA is not suitable for UPLINK Direction due to Large PAPR, and how it is overcome by using SCFDMA and introduction of FFT block.
Enjoy the video.
HAPPY LEARNING
Reference:
Images - Google images, Openclipart,
Video - Norway (Rusted Media)
Music - Bensound, Google youtube audio library
Content - 1. LTE - The UMTS Long Term Evolution (From Theory to Practice - book)
2. LTE Advanced by Wiley Publication - Book
3. Wikipedia
4. LTE in Bullets
5. Other Internet Resource
I think a human voice-over would be better than the automated read-out voice. Lacks emotion and stress. !!
+Shouvik Das human voice will be always better choice, but our intention was more towards material we provide rather then spending time in human voice processing and editing.
May be in future we will come with human voice.
We have finally migrated to human voice. Do help us with a feedback. :P
@@LTE4G i like it automated way ..and this animated way is nice
Wow.... no fake no free energy just useful & creative knowledge
I'll use this video to test & analyze LTE signals during the field test in Ulaanbaatar city urban areas
Update: I will make a video about it, stay tuned!
this video is reallllly helpful!!!! i'm so lucky to watch it before my final exam XD
I really appreciate your work. I've been reading 3GPP and IEEE docs. The videos are much more effective for learning these concepts.
Thanks a lot Raymond. The videos are just a gateway. The docs are the real thing. We are proud of our technical team. They worked really hard to tone down the docs. Hope you will enjoy our upcoming videos as well.
Happy Learning!
Really good job, this 3 dimensional view of teaching will take viewers to exact imagination how communication is happening that what human can not see, please do videos on 5G NR also......
hats off to the simplicity in explaination ...all was possible bcz of animation ...tnx I had hard time unerstanding these concept...but this video made it easy to understand
Thanks a lot for the nice words. We are glad that the video was helpful. Happy Learning
Thanks for making concise and easy to absorb content!
It makes learning LTE so much more fun!
There is a typo error in the table "Transmission BW vs Sampling frequency .." @ time 3:36 for 15 MHz BW --> Sampling Freq is 23.04 MHz instead of 20.34 MHz... bcoz 3.84*6=23.04 matched the position!
Thanks again!
Great visualization of OFDMA/SC-FDMA. Thanks a lot.
This is excellent!! Thank you for this very informative video series. Finally I understod OFDMA and FFT
Great to hear! Don't forget to share it among your peers. happy learning
Great visualization of the physical layer aspects
Really helpful in understanding SC-FDMA as compared to OFDMA.
Thanks Tim. Your support keeps us motivated.
The best channel for LTE videos. THANK YOU :)
Thanks Lalitha. Happy Learning. :)
The best educational videos ever made!
+Cy Zimmer - Thanks a lot. Harpy learning
I really like this video. Easy to understand
glad to hear that. Happy Learning.
There is an error at 3:29 when presented the LTE specifications. For a transmission BW equals to 15MHz, the sampling value has to be 23.04MHz, doesn't it?
anyway great job! thanks!
luv the future-like vocal. Very inspiring videos. Thank you
Nice animation to clear the concepts. Keep it up
+Bodapally Kedarnath - Thanks a lot.
Respect!!!
WOW, thanks a lot, these are crazy. I recommend to any communication engineer.
Thanks a lot. This is what inspires us to strive for excellence.
Excellent
Best presentation ever. Thank you very much.
+Mohammed Al-Haddad - You are welcome buddy
I have a question if you don't mind. I didn't quite understand the part about SCFDMA from 6:30-7:20, it seems to me it is a MC technique to reduce PAPR but why calling it a (SC)-FDMA?
excellent work guys, keep it up :)
+Manhal Moussa Thanks.
Excellent video! Not understand why the max frequency for 20MHz channel is 9MHz? Could someone please explain
veryyy nice explanation
very use full videos -good clarity
Thanks Rajesh. Happy Learning.
you guys are fucking awesome
Thanks Ahmed.
Very very good apresentation about LTE. How I can see the video about Channels Physical-Transport-Logical?
+Luiz Carlos, we are working on the same.. stay tuned ☺
+Luiz Carlos - the video on logical and transport channels have been uploaded
thank you very much!
You are welcome. Happy Learning
VERY VERY VERY GOOD, THANES
+M ali - you are welcome
I dont get it as to why dac is used after ifft. Basically the output of ifft is discrete time domain signals but its representaion in frequency domain is a continuous sinusoid signal right and can be used to transmit over channel? Could u please help me out. Thanks in advance.
Super bro... thnku somuchh...:)
SO GOOD!
Can OFDMA or SC-FDMA be used for broadcasting video without an infrastructure? Like, say low latency video for piloting drones?
Hi, at 1:50, since we re using QPSK, each RE (duration of 66.7x10^-6 sec) should consist of 2 bits instead of 1 bit as shown in your video, am I right?
right
Really great videos. I'm currently looking at SC-FDMA and determining how it would be possible to improve the power consumption, and then simulating the hypothesis. It's been a bit difficult so far to setup. Are there any resources you would recommend for LTE simulations related to power consumption?
+WashedSun sorry mate, but we don't have any adequate resources on that.. however if you look at the equation for PAPR, in a n-channel OFDM system with ideal conditions, PAPR will be 'n'. So PAPR increases with the increase in number of subcarriers. since multiple subcarriers are clubbed together in OFDMA during FFT, what it basically does is to reduce the effective no. Of carriers in the system to decrease PAPR. For a simple simulation to compare OFDMA and SCFDMA , you can use a MATLAB simulation for OFDMA to calculate PAPR using certain IFFT size say 256, now for SCFDMA of equivalent bandwidth, which uses 4 point FFT, you can simply replace the IFFT size by 64(256/4).
Hope this helps
Excellent!
+Raul Silva - Gracias
i am referring fundamentals of lte textbook to study the subject, i want to know the downlink and uplink transport channel processing how they work in simple words, in textbook i am unable to understand the practical aspects
Hey, How do I get 1200 subcarriers for 20 MHz Bandwidhth by calculatation if subcarrier spacing is 15KHz?
Could someone explain to me how many users fit in an LTE frame?
Question, Why do we need IFFT ? Videos says the reason is 1200 oscillators is too hard, then why this IFFT is the solution? Why set the symbols from freq to time domain is solution? I always want to ask this question, why do we need ifft, but most of tutorials never say the reason. hope someone master could help. thank you so much.
+SunSon29 , here in OFDMA, IFFT is nothing but a summation operation that sums all the individual subcarriers so that all the subcarriers can be processed together. If not for IFFT, we could have used any other technique that does the same task. Conversion from frequency to time domain is not the aim here, it happens as a consequence of IFFT...Said that, time and frequency domain representations are a mathematical way of representing signals..A signal will always remain the same...However when FFT operation is applied over a signal, it will break it into sinusoids and IFFT reverses this.
thank you so much for your reply, may I ask this? If IFFT just for summation, why not just sum together, why we still to do bother IFFT? simply sum is easier, right? Because in the video, it says that IFFT will solve the problem to complexity for 1200 oscillators, but why IFFT is easier ? Thank you!
Simply summing the signals together is not the same as modulation - you must be able to get back the original signals on the other side. Similar in concept to 4+4 and 1+7 -- if you just send 8 the receiving side will not know the original signals used to create the signal it received. IFFT is an alternative to individually modulation 1200 signals with individual oscillators, essentially it is creating the modulation, not the simple sum such that the output can be demodulated into the original 1200 components.
thank you.
It's been more than a year, but I had the same question until recently I got the answer to this question:
Sub-carrier assignment using oscillators simply means multiplying each (modulation) symbol X[k] with one of the frequency components of oscillator i.e X[k] multiplication by exp(jkwn).
Now if you look at the IFFT operation formula, it's exactly the same !
very good
Sir, I need how to Rf Singals are varied while change of E-tilt and M-tilt in Antenna or how to split the waves from Enode B Antenna for 2g Calls.....
Perfectly staged, please keep up...
Bohot baaap video
it is good , but very fast ..........difficult to grasp and understand some times
question why not scfdm in downlink??
+nba fun, why make it complex when a simpler alternative (OFDMA) is available..SC-FDMA tackles power limitation in handheld devices which is not an issue with the ENBs
thx for the reply and thx for your channel
+nba fun - We are glad that you found our channel useful.
Happy Learning.
we can send more data with SCFDM as we can map 1 symbol per subcarrier, also in SCFDMA the symbol is transmitted over a short duration unlike OFDMA hence more data transmission in DL than UL
can u do video on matlab implementation of OFDMA!!!!
I'm sorry but right now we can't.
РТФ, привет
Human voice will be more effective. Animations are good
at 6.20 you say 1 symbol= 1 subcarrier
but bellow link
rfmw.em.keysight.com/wireless/helpfiles/89600b/webhelp/subsystems/wlan-ofdm/content/ofdm_basicprinciplesoverview.htm
1 symbol= Multiple carriers (subcarriers) ????
You are confusing it. OFDM uses multiple carriers which are called subcarriers.
The information is sent using symbols.
1 Symbol can have multiple bits. Depends on the modulation scheme used.
1 Symbol is mapped against 1 Subcarrier.
Is it clear now?
thanks
I don't understand English well :(
The robot voice over is dreadful same as those special effects swooshing in the background grrrrrrr.....
You've got to loose the annoying folk guitar, ticking and robot voice. They make it nearly impossible to concentrate and learn.