There are many researches about Full-Duplex, and many of them mentioned that one of the merits of FD is that it could transmite and receive information with the same frequency, once the problem of SI is solved. But I think that the CDMA technology could also transmite and receive information with the same frequency without concerning about the SI. So what are the advantages of FD while comparing with CDMA? And if the CDMA is applied in a FD communication system, would there still be self-interference?. I am confused about that. Thanks for anyone who could answer my question. Best regard.
CDMA could be used to alleviate the self-interference, if orthogonal codes are used for uplink and downlink. But this is not a good solution to the problem!
You would need spreading codes of length two in CDMA, which means that you effectively only use half of the transmission resources for uplink and half of it for downlink. That means that you will get the same data rates as in half-duplex communication...
You can use also scrambling codes to make the two signals orthogonal and make the interference between them negligible.
The advantage of using orthogonal scrambling codes is to preserve the signal bandwidth the same as scrambling does not change the data rate. http://www.comlab.hut.fi/opetus/238/lecture6_ch6.pdf
Best wishes
Emil Björnson Thank you very much for your answer. They are very helpful.
I still have a question. If a communication system has already applied CDMA, like a satellite communication system that multiple transeceivers Exchange information through a satellite, do you think that there will still be SI and interference from different transeceivers when the satellite broadcasts the received signals to all the transeceivers?
Dear Ruiyang,
I would like to give a conceptual answer to your question that can be applied whenever it prevails. Interference occurs when the signals occupy the same space, have the same frequency, occur at the same time and have the same profile. If the signals are made strictly orthogonal they will not interfere. This is made by by space divisor, frequency division, time division and code division multiplexing.
So, if we have multiple signal with different codes they will not interfere and they can no be separated thank to their orthogonality. One point to be said still here, because there is no ideal orthogonality under real transmission conditions they will be interfere slightly. Interference may be acceptable if the S/(N+I) is sufficient to achieve the required bit error rate.
You can project my answer on your system.
Best wishes
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