How does 5G NOMA compare to 4G OFDMA and 3G CDMA?

[@tuongnguyen9391]

Why do sometime people use the term bit per channel use when comparing between OMA and NOMA

[@iain_explains]

It's a bit hard to explain in a short comment. I'll add it to my "to do" list.

[@amahbubul85]

Hi Lain, thanks for this video. I did not understand the part where you said that the rates become half in CDMA as the rate is given in b/s/Hz and thé users use two times bandwidth. Are not they using the same bandwidth as TDMA?

[@iain_explains]

Ah, good question. Instead of just saying "twice the bandwidth" at 4:45, what I should have said was "twice the bandwidth, all the time". You don't get a choice about varying the rates between the two users. They both do the same/equal amount of spreading. You're right, TDMA also sends the data symbols over a shorter time period (in order to leave time for the other user), and if you halve the data symbol duration for each user (in the 2-user case - in order to fit them both in to a given TDMA time period), then this does use twice the bandwidth (as with CDMA), but each user only uses a proportion of the symbol times (not necessarily half each).

[@tuongnguyen9391]

1/ For math people we have math stack exchange, but for telecommunication people =)) it seems there arent any stack exchange available to discuss great idea like this =)) what a pitty. 2/ When you said this have been selected for 5G mobile are there any related document or proposal for us to read ?

[@lephong8947]

Actually, there is DSP StackExchange

[@raedal-moussawy4737]

Thanks for your clear explanation! I think your capacity diagrams in this video belong to uplink transmission, right?

[@iain_explains]

Yes, I described the capacity region from the point of view of the uplink, however there is a duality between the uplink and the downlink, and the shape of the region is the same for both. Differences in the actual numerical values will come from potentially having different noise powers at the different users in the downlink case. Also, it would be necessary for all users to know the error correction codes of all the other users, in order for this to work in the downlink (since the high rate users will need to decode the low rate users first, in order to subtract them, and be able to decode their own message).

[@aldogannon763]

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[@leonardocayson3456]

@Aldo Gannon instablaster ;)

[@jimmybuffet4970]

EXCELLENT! Thank you! I still think CDMA2000 had the potential to evolve past EVDO. It has many inherent benefits over OFDM, especially in regards to efficiency & privacy. Obviously it has some limitations which were somewhat handled with LTE, but have oddly returned with the implementation of NR (primarily line-of-sight).

[@iain_explains]

Yes, it's very interesting to explore the relative benefits of spread spectrum (eg. CDMA) and orthogonal spectrum (eg. OFDM). Much of it comes down to practicalities of handling inter-symbol interference (eg. via equalisation/precoding) and multi-user interference (eg. via MU detection/precoding).

[@oggamer2244]

Very useful, thank you good sir.

[@iain_explains]

Glad it helped

[@saijaya694]

Thanks for the detailed explanation.Can you please post on SCMA. Can you post your email id for sending queries ?

[@iain_explains]

I will add SCMA to my "to do" list, but I'm sorry to say it will be a long way down the priority list. Did you mean SC-FDMA? If so, then that's already on my list, and getting closer to the top.