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Why it wasn't possible to use OFDMA for uplink in LTE? How SC-FDMA working is different from OFDMA BPSK ?

+1 vote
Why it wasn't possible to use OFDMA for uplink in LTE? How SC-FDMA working is different from OFDMA BPSK ?
posted May 19, 2014 by Puneet Batra

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3 Answers

+3 votes
Best answer

Adding some more points in above answer.

One of the major drawbacks of an OFDMA system is that the transformation of a complex symbol mapped sequence (e.g. BPSK, QPSK, etc.) onto a small set of sub-carriers produces time sequences that have high PAPR (Peak-to-Average Power Ratio).

PAPR is the ratio between the maximum power and the average power This results in requirements for expensive transmission amplifiers and furthermore lead to high power consumption. Both effects are -particularly on terminal side unwanted.

It is thus a major design goal to limit this effect for the UL direction.

In order to reduce the PAPR a variant of OFDMA is used. It is called SC-FDMA (Single Carrier Frequency Division Multiple Access). SC-FDMA works according to the following mechanism, described for the associated transmitter structure. SC-FDMA is the method of choice for EUTRAN in the uplink direction.

answer May 20, 2014 by Hiteshwar Thakur
+2 votes

I am not a PHY expert but let me try to explain based on what i know.

OFDM has a disadvantage that it has a high PAPR Peak to Avg Power Ratio, which makes the receiver design complex and is prone to ISI in sub carriers in case of multi path propagation. This makes it impractical to be used for the UE radio design.

In OFDM the data symbols modulate the sub carriers independently whereas in SC FDMA the modulated signal is a linear combination of all data symbols transmitted one after the other within the time instant.

answer May 19, 2014 by Shyam Purkayastha
Thank you...
0 votes

OFDMA requires more power for transmission whereas SC-FDMA requires lesser power. There is a limitation at UE to send more power due to limitation of battery size. Hence SC-FDMA is used for UL by UEs.

answer Sep 20, 2016 by Shivananda Gavalkar S
Similar Questions
+1 vote

PAPR is the major disadventage of OFDMA which require high resolution D/A and A/D or increasing Transmission Power.
I know that SC-FDMA used on Uplink becuase it has lower PAPR than OFDMA. On downlink direction, the high PAPR Problem of OFDMA solved by increasing eNB transmission power. This solution cannot be implemented on Uplink direction because UL is power limited link. so SC-FDMA used on UL instead of OFDMA, but why? why SC-FDMA has LOWER PAPR

+1 vote

I know the reason why OFMDA cannot be used for the uplink but I wonder why SC-FDMA is not used for the downlink. It is still a form of OFDMA technology.

+1 vote

Are the demodulation reference symbols modulated using SC-FDMA like other PUSCH symbols or using OFDM. I have seen in a couple of places that OFDM is used for the DRMS, but I cannot find anything about it in 3GPP TS 36.211.

Any pointer would be appreciated?

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