OFDM explained well. Multiplexing is about sharing single channel to many users. OFDM is used in wireless communication and utilize radio resources well. OFDM uses multiple small subcarriers (15kHz) so there is no much need for guard bands. Subcarriers are orthogonally placed so there is no interference. They are also overlapped in freq domain so resources are used efficiently. For 20MHz bandwidth, we have 1200 subcarriers which take 18MHz and the rest 2MHz are for guardband. So, the subcarriers value ranging from -9MHz to 9MHz travel with different sinusoids. In order to transmit symbols in these subcarriers, modulation schemes are used.
Sorry the strong reverb killed it for me. Just use normal voice, I couldnt watch the video to the end because it annoyed so hard. Which is a pitty because the animation and information seems to be quite decent. sry this is a downvote
Hi Josch. Thanks for the valuable feedback. We have tried using natural voice. But it seems weirder. That is why we are using Text to Speech converter. Hope in some near future you will hear human voice. We are trying our best. Till then stay with us. Happy Learning
Then just put some kind of filter to your natural voice signal that makes it less weird. The point is: A speech converter doesnt understand the concept of flow, the way humans pronounce words and adjust breaks between words to create a flowing sound that appears natural and smooth. The speech converter just puts words after each other and sounds terrible.
+Josch K we agreed and we already in process of preparing next video on Carrier Aggregation using our voice. Hope this will be less weird than today's voice. Thanks for valuable feedback. 😊
Sure! I just watched the video featured by the indian accent speaker and I think its great! The overall video quality improved tremendously in my eyes I enjoyed watching a lot. Take that and the high informational density of these clips and you just got yourself another fan of your channel! Thats a like and a subscription, very well done.
a very good and informative video is reined by background music.. it is very much easy to understand when there is male voice in video but it is opposite when there is female voice.
Hi guys. your videos are excellent. Nice job! I will wait for the next ones. By the way, I wish I could see an explanation so clear for the carrier aggregation part.
hello Luis! Thanks for the nice words. We will be making a video on Carrier aggregation but it will take some time. You can check the video- channel roadmap where we have mentioned the topics that we are going to cover. happy learning
Excellent work! Just a small question, are each sub carriers assigned to each user (handheld devices like mobile phones) or is each user is assigned all the sub carriers? I am not able to comprehend how each user, among millions, get the network service. Thanks in advance.
Subcarrier along with time formed a resource element and further resource block. This group of resource block are given to user on demand as they requested. For example 1 subcarrier (15Khz) with 1 symbol (0.5second/6 or 7 symbol) make one resource element. Further 12 subcarrier (15x12=180Khz) with (6 or 7 Symbol = 0.5 Second) make one resource Block. This combination always there and assiged to user. Initially 1.6Mhz bandwidth assiged by default to handset which means around 6 resource block, which carries required data to be used by handset to make decisions and request further resource to start using service. I hope this is clear. Any doubt you can ask ? Happy Learning...!
LTE Thank you very much for answering. But if that is the case, then what about other users sharing same bandwidth? If I am not mistaken, at 20MHz downlink we get only 20/1.6=12 users only! If for example some video is sent to a particular user continuosuly, doesn't other users who are sharing the same bandwidth of 1.6MHz experience interference? Let me know if I have made mistake somewhere.
Yes indeed.....12 Users only....but that for only 0.5second time slot... But users can get chance in next 0.5 second and so on.... Apart from this one more things to be cleared, there are fixed resources and there are on dedicated resources which mapped on control channels and shared channel accordingly. User will always get resource, except network is fully congested and everyone is using it heavily. In that case some users have to be in queued and they will fill like buffering that is nothing but congestion in radio or in other word high physical resource utilization.
Basics of OFDM are explained here well, but how to address the disadvantages of OFDM like high peak to average power ratio (PAPR), OOBE, synchronization sensitivity, and security issues are not mentioned in this video.
We thought that it would be easier as we are not native speakers, I guess that was stupid of us. But we have now moved on to human voice in our latest videos. Do share your review about it.
I understand. I just want to emphasize the good job you guys do with the videos. The robotic voice was really holding you back. Good you decided to change!
great use of animation, but still the volume of sound is high, and sometimes annoying... that would be great if you turn it down when the narrative is talking. Thank you
Yeah, all of them, i study Communications Engineering at TU Munich, your videos are perfectly matching to subjects like "System Aspects in Communications" and some other sujects. I will share your channel with my friends 100% 😉
+Alireza Mokhtari Doust - Aw that's so sweet of you. You can follow us on Facebook. The details is mentioned in the about section. For technical queries you can ask us on Quora as well. We use the same name for Quora i.e LTE. Thanks again for your support. Happy learning.
Hi! Rohit we have tried to keep a tempo so that people don't get bored. if you are having difficulty in understanding you can pause the video while watching. You can also switch on the subtitles. happy learning
Hello Aashwini. We will come to it eventually. But before that we need to explain the basics. You can check the video channel roadmap, where we have shown, what are the topics that we are going to cover.
Hi, @2:33 min you tell symbol time=1/bandwidth & for single carrier signal in time domain delay spread occupy 66% of the signal. so @3.16 min how symbol duration of 1 subcarrier(10kHz) became 100 microsec AND delay spread become 2 microsec.
Why is the center frequency more important, Does the data modulation have any impact on this or? . Also what is a dc frquency ahy is it important. Thanks/
The centre frequencies actually represent the OFDM subcarriers. As a single monochromatic frequency cannot carry any data(as bandwidth is required for that), OFDM subcarriers occupy a portion of bandwidth in a form of sinc wave which in turn is centred around the centre frequency..Data modulation(psk, qam) will neither impact the centre frequency nor the shape of the sinc function.. it just changes the amplitude and phase of sinc function. Again DC frequency is actually the centre point(zero) of a frequency graph(on x axis). Since it has no frequency or alternating component, it is also called DC(direct current). Also since the LTE spectrum consists of both positive and negative frequencies(frequencies with 180 degrees phase shift) it is basically centred around the DC.
Orthogonal means that they don't interfere. That's what the word means; independentness. In LTE OFDM, orthogonality is provided by FFT transform. That's a key property of FFT. You take a bunch of numbers, make FFT to them, it makes a waveform. Make FFT again to the waveform, you get back the same numbers. Now change one of the numbers. The waveform changes and again you get numbers back from the other end. *Only the one number that you changed, changes.* That's orthogonality, that is what it means.
Question, since in OFDM, all carriers are overlap each other @7:31, then where is the guard band? Because in FDMA, I can tell that. in this video @3:43, all carriers are not overlap at all. But where is the band in OFDM???
+SunSon29 - The guard bands are at the begining and at the end. See the part 2 of OFDMA. At 5:12 there is an image. Hopefully that image will help you understand.
@@43SunSon There are no guard bands required in OFDM since all the subcarriers are orthogonal to each other. This is the beauty of OFDM that guards buands are not required between the sub carriers and hence the Bandwidth efficiency is highly improved.
Time period is the reciprocal of frequency i.e T=1/f, Where T=Time Period f= Frequency. So, when frequency is 10khz the Time period =1/f=10^-4 sec or 100x10^-6 sec or 100 microsec
+BlackLeg199 every time there is a service request from the UE, An ENB scheduler will allocate some PRBs. The number of PRBs depend on their availability, QoS demands of the radio bearer as well as on the radio parameters like RSRP and the LTE radio band, the user is latched upon. The number of subcarriers will be 12 times the Allocated PRBs.
let's say that i saw a signal at the oscilloscope, and recognize that it uses multi-carrier modulation. Is there a mathematical tool or any other way to find the number of modulated tones and their frequencies? Thank you for your help.
+BlackLeg199 I suppose you're asking about radio frequencies assigned to a particular user when it receives user plane data.. so first of all, the user data is sent over the downlink shared channel but before that, the ENB will inform the user about the Allocated resources I.e PRBs and the corresponding modulation scheme in the DCI(downlink control information) over PDCCH channel. Using the DCI, a UE is able to decode the frequencies which are carrying information specific to that user. So if you somehow convert the RF signal of a particular band from an ENB and feed it to an oscilloscope, you will get a composite signal ranging the whole Spectrum having data for all the users.. moreover this signal would be a analog wave which would require to be converted to digital discrete signal and once you do the FFT operation, you will see all the frequency components, now in order to find out frequency components for a particular user, you will have to read it's DCI.....this is done by every LTE receiver... Hope this helps and do see our next videos.. :)
+Mohammadhussain Hussaini - Yes! You don't need any guard band between subcarriers. If you see carefully the guard bands are located somewhere else. Hope we could clarify your doubt. Happy Learning.
The process is to choose sub carrier frequencies that are harmonics of the base frequency.In LTE the base frequency starts with 15khz.To this base frequency, values of 2,3,4 and so on are multiplied to get subsequent subcarrier frequency. The modulating signal which is going to modulate these sub carriers must have a 1/15khz symbol duration. The above two steps ensure orthogonality.
![BLACK BAG - Official Trailer [HD] - Only in Theaters March 14](http://i.ytimg.com/vi/Du0Xp8WX_7I/mqdefault.jpg)
OFDM explained well. Multiplexing is about sharing single channel to many users. OFDM is used in wireless communication and utilize radio resources well. OFDM uses multiple small subcarriers (15kHz) so there is no much need for guard bands. Subcarriers are orthogonally placed so there is no interference. They are also overlapped in freq domain so resources are used efficiently. For 20MHz bandwidth, we have 1200 subcarriers which take 18MHz and the rest 2MHz are for guardband. So, the subcarriers value ranging from -9MHz to 9MHz travel with different sinusoids. In order to transmit symbols in these subcarriers, modulation schemes are used.
Amazing introduction, somehow it may represent the essence of a 1 year university courses on wireless communications.
Wow! Thanks Petrut. That's a lot of nice words.
Happy Learning.
Best way to explain the subject of OFDM. Thanks for the effort.
The credits goes to our research team. We hope that we will be able to make even better videos in coming future.
Happy Learning.
Highly useful series of short lectures. Thank you for sharing!
+Barış Volkan Yıldırım - Thanks a lot man. The series is not complete yet, it's just the beginning. Stay tuned for our upcoming videos.
Happy Learning
1hr of clases = 8min of video. Perfect. Also, nobody on internet nor university ever explains ortogonality this way and is just so simple. Congrats
Best explanation of OFDM on the net!
Sorry the strong reverb killed it for me. Just use normal voice, I couldnt watch the video to the end because it annoyed so hard. Which is a pitty because the animation and information seems to be quite decent. sry this is a downvote
Hi Josch. Thanks for the valuable feedback. We have tried using natural voice. But it seems weirder. That is why we are using Text to Speech converter. Hope in some near future you will hear human voice. We are trying our best. Till then stay with us.
Happy Learning
Then just put some kind of filter to your natural voice signal that makes it less weird. The point is: A speech converter doesnt understand the concept of flow, the way humans pronounce words and adjust breaks between words to create a flowing sound that appears natural and smooth. The speech converter just puts words after each other and sounds terrible.
+Josch K we agreed and we already in process of preparing next video on Carrier Aggregation using our voice. Hope this will be less weird than today's voice.
Thanks for valuable feedback. 😊
Hi Josch. We have finally started using human voice. Would you mind giving us your valuable feedback?
Sure! I just watched the video featured by the indian accent speaker and I think its great! The overall video quality improved tremendously in my eyes I enjoyed watching a lot. Take that and the high informational density of these clips and you just got yourself another fan of your channel! Thats a like and a subscription, very well done.
Great, great video - and I've watched a fair few during the course of my studies.
This is the best tutorial and nicely explained about the FDMA & OFMDA.
Thanks Pragyan. Happy Learning.
a very good and informative video is reined by background music.. it is very much easy to understand when there is male voice in video but it is opposite when there is female voice.
+Sukhpreet Singh - Ok! We have moved on from text to speech convertor to real voice. We will keep the music low from next video.
Good job explaining the concept of OFDMA in this video!
Happy Learning.
GLaDOS just gave me a radiofrequency lecture!
Excellent! very clear. succinct graphics too..
Fun to watch for us DSP fans!
High quality content...thanks for the great video!
Hi guys. your videos are excellent. Nice job! I will wait for the next ones. By the way, I wish I could see an explanation so clear for the carrier aggregation part.
hello Luis! Thanks for the nice words. We will be making a video on Carrier aggregation but it will take some time. You can check the video- channel roadmap where we have mentioned the topics that we are going to cover.
happy learning
Wow, great introduction. Thank you.
+Chuan Huang - Thanks buddy. We try our best. Watch the other videos and share your feedback.
Happy learning
Nice and wonderful technology,it worth pay any price due to high quality service for customers
Excellent presentation, thanks for sharing!!
Thanks Victor.
Thanks for sharing, very short, informative and useful lectures.
9ICE ONE...
+Omidiji Rasheed A. - Thanks Omidiji. Don't forget to share it among your friends.
Happy Learning.
Impeccably Explained, thanks a lot....
Thanks for your support. Happy Learning.
Thank you for your efforts. Very nice.
very simple and comprehensive
You video is excellent.
hey great work guys.
btw what is the text to speech program you guys use when making these videos?
Excellent work! Just a small question, are each sub carriers assigned to each user (handheld devices like mobile phones) or is each user is assigned all the sub carriers? I am not able to comprehend how each user, among millions, get the network service. Thanks in advance.
Subcarrier along with time formed a resource element and further resource block. This group of resource block are given to user on demand as they requested.
For example 1 subcarrier (15Khz) with 1 symbol (0.5second/6 or 7 symbol) make one resource element.
Further 12 subcarrier (15x12=180Khz) with (6 or 7 Symbol = 0.5 Second) make one resource Block.
This combination always there and assiged to user.
Initially 1.6Mhz bandwidth assiged by default to handset which means around 6 resource block, which carries required data to be used by handset to make decisions and request further resource to start using service.
I hope this is clear. Any doubt you can ask ?
Happy Learning...!
LTE Thank you very much for answering. But if that is the case, then what about other users sharing same bandwidth? If I am not mistaken, at 20MHz downlink we get only 20/1.6=12 users only! If for example some video is sent to a particular user continuosuly, doesn't other users who are sharing the same bandwidth of 1.6MHz experience interference? Let me know if I have made mistake somewhere.
Yes indeed.....12 Users only....but that for only 0.5second time slot... But users can get chance in next 0.5 second and so on....
Apart from this one more things to be cleared, there are fixed resources and there are on dedicated resources which mapped on control channels and shared channel accordingly.
User will always get resource, except network is fully congested and everyone is using it heavily. In that case some users have to be in queued and they will fill like buffering that is nothing but congestion in radio or in other word high physical resource utilization.
You should check our video on Throughput Calculation.
May ve you can get better picture.
ruclips.net/video/uIPtLr8R1-U/видео.html
LTE Perfect! Thanks a lot!
Basics of OFDM are explained here well, but how to address the disadvantages of OFDM like high peak to average power ratio (PAPR), OOBE, synchronization sensitivity, and security issues are not mentioned in this video.
How to make the robot voice less robot-like? hmmm......... "I know! Lets add reverb!"
Please check #dwdmotnc#discreteoptical #Norteltn #Ciena32slot
@@nicholasroos3627 ok
That and background music... :-/
Thank you for sharing
Good 🙏🙏🙏
Great Video. But please use less audio effects. They distract from the actual information.
you people are amazing! keep up the good work! :D
Thanks Mohamed.
Hi! It's very informative but the background noise is too loud. Makes things that are being spoken very unclear.
Please check #dwdmotnc#discreteoptical #Norteltn #Ciena32slot
Superb explanation
+All Rounder - Thanks a lot.
Happy Learning
great video love it and thanks
You are welcome Robert. Happy Learning.
Great video, awesome!
Thankyou very much for that precise explanation. I was wondering if you could please share a blocks diagram to show the process of OFDMA.
+José Ricardo Moyeda - you are welcome Jose. Send us your email id; we will mail it to you.
This video has very good information but it is so hard to follow with that mechanic voice. What did you choose to have it instead of your real voice?
We thought that it would be easier as we are not native speakers, I guess that was stupid of us. But we have now moved on to human voice in our latest videos. Do share your review about it.
I understand. I just want to emphasize the good job you guys do with the videos. The robotic voice was really holding you back. Good you decided to change!
great use of animation, but still the volume of sound is high, and sometimes annoying... that would be great if you turn it down when the narrative is talking. Thank you
+Alireza Mokhtari Doust - Do You mean to say the background sounds and the soothing track?
yeah, the background sound
+Alireza Mokhtari Doust - Ok we will keep that in mind. By the way, have you seen our other videos?
Yeah, all of them, i study Communications Engineering at TU Munich, your videos are perfectly matching to subjects like "System Aspects in Communications" and some other sujects.
I will share your channel with my friends 100% 😉
+Alireza Mokhtari Doust - Aw that's so sweet of you. You can follow us on Facebook. The details is mentioned in the about section. For technical queries you can ask us on Quora as well. We use the same name for Quora i.e LTE.
Thanks again for your support.
Happy learning.
Hello, Thank you for your contributions to us. I will be very appreciate if you prepare a li-fi training video
Very nice information but the explanation was very quick please explain a bit slow :)
Hi! Rohit we have tried to keep a tempo so that people don't get bored. if you are having difficulty in understanding you can pause the video while watching. You can also switch on the subtitles.
happy learning
Could make a video for physical resource blocks of OFDMA, resources allocation, supported MIMO modes... Plz sir
Excellent videos. plz make video on LTE call flow
Hello Aashwini. We will come to it eventually. But before that we need to explain the basics. You can check the video channel roadmap, where we have shown, what are the topics that we are going to cover.
this is perfect
thanks for your efforts 😍
You are welcome Zeinab. Did you see our other videos?
thanks this has been very helpful.
You are welcome Buddy. Don't forget to share it with your friends. Happy Learning.
Nice lecture ... #HariKrishnaSahu
This class was amazing! But can you please share the slides? It will help me a lot! and congratulations again!
Please check #dwdmotnc#discreteoptical #Norteltn #Ciena32slot
Hi, @2:33 min you tell symbol time=1/bandwidth & for single carrier signal in time domain delay spread occupy 66% of the signal. so @3.16 min how symbol duration of 1 subcarrier(10kHz) became 100 microsec AND delay spread become 2 microsec.
Thank you very much
Thank you so much!!!!
awesome video
Nycc
very well explained
+Aqeel Ahmed - Thanks. Don't forget to share it with your friends.
Why is the center frequency more important, Does the data modulation have any impact on this or? . Also what is a dc frquency ahy is it important. Thanks/
The centre frequencies actually represent the OFDM subcarriers. As a single monochromatic frequency cannot carry any data(as bandwidth is required for that), OFDM subcarriers occupy a portion of bandwidth in a form of sinc wave which in turn is centred around the centre frequency..Data modulation(psk, qam) will neither impact the centre frequency nor the shape of the sinc function.. it just changes the amplitude and phase of sinc function.
Again DC frequency is actually the centre point(zero) of a frequency graph(on x axis). Since it has no frequency or alternating component, it is also called DC(direct current).
Also since the LTE spectrum consists of both positive and negative frequencies(frequencies with 180 degrees phase shift) it is basically centred around the DC.
Im a beginner in wireless communication,in ofdm if two signals overlap why won't they interfere?and what do mean by they are orthogonal?
Orthogonal means that they don't interfere. That's what the word means; independentness. In LTE OFDM, orthogonality is provided by FFT transform. That's a key property of FFT. You take a bunch of numbers, make FFT to them, it makes a waveform. Make FFT again to the waveform, you get back the same numbers. Now change one of the numbers. The waveform changes and again you get numbers back from the other end. *Only the one number that you changed, changes.* That's orthogonality, that is what it means.
Can someone explain where rectangle function comes into play? Is it just the 66.7us time slot?
Question, since in OFDM, all carriers are overlap each other @7:31, then where is the guard band? Because in FDMA, I can tell that. in this video @3:43, all carriers are not overlap at all. But where is the band in OFDM???
+SunSon29 guard bands in OFDMA are not between the subcarriers rather they are at the both ends of the OFDMA spectra.
+SunSon29 - The guard bands are at the begining and at the end. See the part 2 of OFDMA. At 5:12 there is an image. Hopefully that image will help you understand.
LTE thank you. Btw, in OFDM, the guard bands are between each channel, not each subcarriers, am I right on this ?? Thank you again.
please please share the slides
@@43SunSon There are no guard bands required in OFDM since all the subcarriers are orthogonal to each other. This is the beauty of OFDM that guards buands are not required between the sub carriers and hence the Bandwidth efficiency is highly improved.
Could you also do video for 5G? I know that it uses some sort of "enhanced OFDM"....
This is so freaky o_O I am legit scared
Please tell me that after dividing wideband of 1MHz into 100 sub carriers of 10khz, how you set time period of each sub carrier 100 microseconds?
Time period is the reciprocal of frequency i.e T=1/f, Where T=Time Period f= Frequency.
So, when frequency is 10khz the Time period =1/f=10^-4 sec or 100x10^-6 sec or 100 microsec
The overall slides are excellent, but the speed of the slides are way too fast..
Great content, but the audio is not good.
Great content, but the artificial voice is not the best choice.
vous navez pas de videos en francais sur ofdm/ofdma?
Nice #dwdmotnc#discreteoptical #Norteltn #Ciena32slot
4:52 What is x what is y ? I don't have a clue
thank you so muchhh
Sir/Ma'am, can you upload some videos on Modulation,modulation techniques used in LTE ?
how can i find out the number of sub-carriers of an OFDM modulated signal?
thank you
+BlackLeg199 every time there is a service request from the UE, An ENB scheduler will allocate some PRBs. The number of PRBs depend on their availability, QoS demands of the radio bearer as well as on the radio parameters like RSRP and the LTE radio band, the user is latched upon.
The number of subcarriers will be 12 times the Allocated PRBs.
let's say that i saw a signal at the oscilloscope, and recognize that it uses multi-carrier modulation. Is there a mathematical tool or any other way to find the number of modulated tones and their frequencies?
Thank you for your help.
+BlackLeg199 I suppose you're asking about radio frequencies assigned to a particular user when it receives user plane data.. so first of all, the user data is sent over the downlink shared channel but before that, the ENB will inform the user about the Allocated resources I.e PRBs and the corresponding modulation scheme in the DCI(downlink control information) over PDCCH channel. Using the DCI, a UE is able to decode the frequencies which are carrying information specific to that user. So if you somehow convert the RF signal of a particular band from an ENB and feed it to an oscilloscope, you will get a composite signal ranging the whole Spectrum having data for all the users.. moreover this signal would be a analog wave which would require to be converted to digital discrete signal and once you do the FFT operation, you will see all the frequency components, now in order to find out frequency components for a particular user, you will have to read it's DCI.....this is done by every LTE receiver... Hope this helps and do see our next videos.. :)
Thank you
Thank you.
Background sound is too high. please reduce it and re-upload it if possible.
That sound that is similar to the sound of something moving fast was totally disturbing for me. Unfortunately its volume is also quite high :(
will u please please provide ber and snr lecture.
Please, next time reduce the background music.
Brilliant videos!
That was smart
+J.D. Kouam - Thanks a lot. Happy Learning.
in OFDMA there is no need of guard band.
+Mohammadhussain Hussaini - Yes! You don't need any guard band between subcarriers. If you see carefully the guard bands are located somewhere else.
Hope we could clarify your doubt.
Happy Learning.
Hi friends, send me any link which is best for preparing dct mtech exam.
Wow! :D
The max delay spread is 66% ??? or 88%
66% is used for example. It can vary.
Too bad they don't even explain what the acronyms OFDM, QPSK, etc, actually mean. I wonder if the author really knows, WITHOUT HAVING TO LOOK IT UP ?
there is no traduction? ??😔
I'm sorry what do you mean?
Would be perfect if you just used normal voice
How do we achieve orthogonality between subcarriers? What is the process?
The process is to choose sub carrier frequencies that are harmonics of the base frequency.In LTE the base frequency starts with 15khz.To this base frequency, values of 2,3,4 and so on are multiplied to get subsequent subcarrier frequency. The modulating signal which is going to modulate these sub carriers must have a 1/15khz symbol duration. The above two steps ensure orthogonality.
FFT. You need a transform function that is orthogonal. For LTE, FFT is used. For fibre, DCT is used.
Try to slow down.
Friends
Everything is good except this Machine generated voice using Text to Speech.
Do they really pretend for tutoring video using such format? Dislike.
voice hurting my ears
"Hello Friends" so annoying in every video
РТФ, привет
Voice too annoying. Cant watch
Cos'è il tratto? | Cause della malattia del colpo ruclips.net/video/eNXJDUMxM_U/видео.html
Isn't bad
I doesn't sound like a human voice.
Because it isn't. But we will be uploading the same with human voice shortly.
Happy Learning.
USE a real human voice
Poor narration.