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OFDMA with different numbers of users

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cruiser_sun

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Hi everyone, I have a problem with my project.

Recently I'm working on a OFDMA system. I run some simulations, which assume there are 1024 subcarriers and 64/32/16/8 users. Now I get the BER vs SNR curves of the results and see that the curve for 8 users is the best, and then 16/32/64 users. I'm confused that the performance of the OFDMA system is supposed to be better with more users, isn't it? Is there a certain rule between the performance and the number of users?

PS: the subcarrier allocation scheme I use is very simple. It allows each user to choose the best subcarrier one by one until all subcarriers are distributed.

TQ!
 

Dear friend
i sent to u a file help u in this issue ok
 

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  • Synchronization in Interleaved OFDMA Systems.pdf
    166.1 KB · Views: 182

I do not think that you have any problem. OFDMA is OFDM with multiple users. The fewer user the less interference you have, thus the better results you get. So I think that it is expexted to have the best perfromance results with the fewer users. Furthermore I do not think that your perfromance results are associated with the synchronization as I think that you assume perfect syncronization.
 
Hi eng_ana1982,
Thank you very much for the file.
Actually in this simulations I assumed a perfect synchronization between the transmitter and receiver, so I guess maybe that's not the point. Anyway, thanks for your reply :)

---------- Post added at 19:21 ---------- Previous post was at 19:13 ----------

Hi Tom Duke,
Thank you for your answer.
I think I've confused the performance of BER and capacity and your reply is very reasonable. But I also saw some different results in papers that the BER performance is better with more users. So I'm wondering that is this BER performance associated with the subcarrier allocation scheme or some other aspects?
Thank you for your time:)
 

BER performance is directly connected with the way of the subcarrier allocation. There are very simple to very complex allocation algorithms. A clever one that for example exludes some subcarriers with low SNR is preferrable from one that assigns these subcarriers to users. This is just a very quick example. Furthermore, as in every communication problem all the aspects that impact the BER performance of a system also have an impact, smaller or bigger. Depending on the case that you examine they have a different weight factor. Every paper tells its considerations and acts accordingly. I know that my answer is very general, but unless that you suggest a bad point such as interefernece for exmple, the answer can not be more specific.
 
hello, dear cruiser_sun can you send me your model of OFDMA system, I really need it, because I just started my year-end project about LTE, help me please, here is my email address: mrd9991@hotmail.fr ; thank you in advance.
 

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