Mobile Standards Evolution: FDMA, TDMA, CDMA, OFDMA
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- เผยแพร่เมื่อ 6 ส.ค. 2020
- Summarises the main fundamental elements in the evolution of the physical layer of mobile communications standards from 2G to 5G from a signals perspective.
* Note a small "typo"/error: I wrote 3G under OFDMA, but actually 3G used a version of CDMA called Wideband CDMA. Originally, the OFDMA system was part of the 3G standard, called Long Term Evolution (LTE), but ultimately that part of the standard ended up being called 4G. Also, note that the 5G standard is also based on OFDMA (although I forgot to mention that in the video).
Related Videos: (see: iaincollings.com)
• What is NOMA in 5G Mobile Communications? • What is NOMA in 5G Mob...
• How does 5G NOMA compare to 4G OFDMA and 3G CDMA? • How does 5G NOMA compa...
• What is SC-FDMA? And why is it used for the Uplink of 4G/5G Mobile? • What is SC-FDMA? And w...
• Why is SC-FDMA called "Single Carrier"? • Why is SC-FDMA called ...
• What is Pulse Shaping and the Square Root Raised Cosine? • Pulse Shaping and Squa...
• OFDM Waveforms • OFDM Waveforms
• OFDM and the DFT • OFDM and the DFT
• What is a Cyclic Prefix in OFDM? • What is a Cyclic Prefi...
• How does OFDM Overcome ISI? • How does OFDM Overcome...
For a full categorised list of videos: www.iaincollings.com
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Excellent videos！！ Much much better than others ：D
Glad you like them!
Thank you for your tutorial
You're welcome 😊
nice video on this topic.
I will be very thankful to you if you make video on the difference , features of TDMA versus TDM and FDMA versus FDM . I have searched a lot on this two confusing topics on internet but could not able to clear my doubts properly.
Thanks in advance
Thanks for the suggestion. I've added it to my "to do" list.
great video !
Thanks!
Excellent explanation
Glad you liked it
thanks a lot man :)
You're welcome!
thank you sir for considering my request to make this video.
No worries. Thanks for the suggestion. I hope you found it useful.
Very good
Thanks
Great video, Iain. Love your content. I have three questions though. Why is it beneficial to spread the spectrum like that? Does it offer more resiliency to interference, or does it just allow more users to be served on the same transmission? Also, the "multiply" operation you mentioned for CDMA is actually an XOR operation, correct? Finally, when an individual user is receiving a CDMA signal I am assuming they would multiply by the carrier frequency, then LPF the upper mixing term away, then XOR with their pseudo-noise sequence to extract their data. Is that correct? Thanks again! --Jacob
Answers: 1) both. 2) No, it's not XOR. When sending binary +1/-1 you use a multiply operation. 3) Yes.
Hi Iain, thanks again for the video. The pdf of this video points to the SNR Eb/No video's pdf. Do you mind fixing it, please? Thank you!
Updated. Thanks for letting me know.
Nice, but you forgot to mention MUST and NOMA which are also mutiple accessing schemes with non orthogonal characteristics.
I didn't forget them, I just decided to focus on the schemes that are actually being used in the 2G/3G/4G standards in this video. I've got videos on NOMA, if you're interested, including: "How does 5G NOMA compare to 4G OFDMA and 3G CDMA?" th-cam.com/video/1P3Si23OsC8/w-d-xo.html
is there a difference between multiple acces and multiplexing? for example, frequency division multiplexing and frequency division multiple access?
The term Multiplexing is mainly used to refer to the situation where a device (a multiplexer) takes multiple input data streams (eg. from end users in an access network), and combines them into a single data stream that is then sent over a wide bandwidth channel (eg. a backhaul link to the core network).
However, the term is also used in the acronym OFDM, which is a modulation scheme. This is because, in OFDM, a single data stream is split (demultiplexed) into multiple data streams, that are then "multiplexed" onto a wide bandwidth channel (with each data stream sent on a different subcarrier). Note that all of this happens in a single transmitting device (ie. not multiple access).
The term Multiple Access refers to the situation where multiple (seperate) users are all accessing the same channel either in a coordinated way (eg. 2G/3G/4G/5G) or in an uncoordinated way (eg. WiFi).
Dear Ian, can we use the concept of cyclic prefix in order to avoid ISI for single carrier modulation schemes too?
Well it's not really a cyclic prefix if you've only got one carrier. It would just mean sending the symbol for longer.
Hey man, i am fairly familiar with the EM spectrum and how it works, I clicked this to see another way of explaining it to my students.
One critique, there are so many ads randomly sparsed through your video it is extremely distracting.
Hey man, I don’t control the ads.
Thanks for the video. So, CDMA is better than OFDMA because the user can use all the time slots and all the frequency band. However, the orthogonality of the codes is the problem. Right??
Yes, exactly. Plus it's much easier to implement a receiver detector for OFDMA (just need an FFT and then decode the frequency bands for your own user). For more insights from an information theory perspective, check out: th-cam.com/video/1P3Si23OsC8/w-d-xo.html
Hi Iain, Thanks for the explains. Is there any video for PSD and PDP？
Also, a suggestion of the topics: "coherence time, time correlation, coherence bandwidth, and frequency correlation."
Thanks for those suggestions. They're on my list, but unfortunately I haven't had time to get to them yet.
Ow nice explanation.
It will be a great help if you made videos on the topic DAMA(Demand Assigned Multiple Access)
DA-TDMA, DA- FDMA.
Thanks for the suggestion. I'm not familiar with it, but I'll look into it.
@@iain_explains
Oh I'm really sorry i wrote wrong words.
Now i have corrected it. It is
DAMA - Demand Assigned Multiple Access.
Hi, in OFDMA how can the reciever detect which codes are assigned to which user ?
The receiver knows which code it's using... if not another transmission affects the codes
In OFDMA, all receivers are allocated the specific bands (subcarriers) in the frequency domain by the network manager.
Professor for 4g we got ofdma, what technology do they use for 5G ?
5G also uses OFDMA. Sorry I should have said that in the video!
NOMA for 5G ban a =))
At 13:06 I was expecting to see CDMA for IS-95 and 3G (UTRAN) and then OFDM for 4G. Not OFDM credited to 3G (UTRAN). Were there OFDM UTRAN?
Yes, there's a note about this in the description under the video (it was at the bottom, but I've now moved it up to the top). It says: "Note a small "typo"/error: I wrote 3G under OFDMA, but actually 3G used a version of CDMA called Wideband CDMA. Originally, the OFDMA system was part of the 3G standard, called Long Term Evolution (LTE), but ultimately that part of the standard ended up being called 4G. Also, note that the 5G standard is also based on OFDMA (although I forgot to mention that in the video)."
@@iain_explains OK. Sorry. I skimmed though the comments but there were too many and I overlooked the notes. Many Thanks for all your videos. Much easier to digest than and a good introduction to the literature.
I'm glad you're finding them useful.
How to know which users when communicate on tdma?
I'm not exactly sure what you're asking, sorry. There are always other control channels where information is shared between the base station and the user terminals. This is how they all agree on which time slots each user will send in. Also, there are synchronisation signals so that the users can have accurate timing information about when the time slots start and end.
In what situation do you use a particular communication strategy. Not considering cost ?
Basically it's about interleaving more identifying communications into the existing allocation of the frequency spectrum. Since the Frequency spectrum is basically allocated it means the approach is to invent a method of increasing communications throughput. Which means that the semiconductor devices are required at higher clock frequencies. In terms of mass communications who is inventing these strategies....who are the inventors and where do there ideas come from ? We should know who is leading the forefront of the digital communications not by equipment but by the theory and invention.
I'd like to point out that when quantum communications becomes practical it will displace the entire volume of digital communications and leave it's inadequacy behind.
With Ai it may be possible to have it process to invent the next advance of digital communications while also using robotics to make the equipment. Up until quantum communications become available.