difference between OFDMA and SC-FDMA

Hello everybody...
please can I ask why ,in 4g LTE systems, beside of our using of scfdma as an uplink modulation technique, why we don't use it also for the downlink direction.. why we use ofdma in the downlink though scfdma is more power efficient than ofdma and carry almost the same other characteristics...

can anyone tells me what are the reasons behind that..."with a deep explanation plzz" !?!

SC-FDMA can be interpreted as a linearly precoded OFDMA scheme, in the sense that it has an additional DFT processing preceding the conventional OFDMA processing.

SC-FDMA has drawn great attention as an attractive alternative to OFDMA, especially in the uplink communications where lower peak-to-average power ratio (PAPR) greatly benefits the mobile terminal in terms of transmit power efficiency and terminal costs.

Although the performance gap is not much, SC-FDMA's additional advantage of low PAPR makes it a favorite especially for uplink wireless transmission in future mobile communication systems where transmitter power efficiency is of paramount importance.

- - - Updated - - -

What my understanding is that SC-FDMA is used where transmitter power efficiency is of paramount importance. In down-link this is not the case hence to avoid complexity the must have avoid using it.
Lower complexity at the transmitter which will benefit the mobile terminal in cellular uplink communications.
IN OFDMA the superposition of all the modulated subcarriers is a noise-like signal according to the central limit theorem. Thus the variation of the signal amplitude is quite high leading to a high Peak-to-Average-Ratio (PAPR). This requires expensive power amplifiers and high power transmission which is acceptable for the eNB but not desirable for the UL.

okey but I don't think that I full understand why we use ofdma in the downlink ,scfdma is just better isn't !!?!

MichelSa said:

okey but I don't think that I full understand why we use ofdma in the downlink ,scfdma is just better isn't !!?!

Click to expand...

OFDMA has better packet/audio transmit/handling capabilities. For base station this is important as it is necessary to handle/transmit large amount of packet/audio data to mobile terminal in individual cells. Also this capability is important to have a larger cell size.
However mobile terminal doesn't need to posses this capability. Here power requirement is main constraint.

Thanks a lot..
I would just like to get some papers about that so I can have a little more profound scientific knowledge about it ..
so can u provide me with some links please...

that's will be highly appreciated..
thanks again..

Now a lot of research in going on on scfdma.