LTE: Why SC-FDMA has PAPR lower than OFDMA?

Question

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

Answer 1

I read this question as why OFDMA has higher PAPR, if we are clear then other is easy to understand -

In case of OFDMA, a multicarrier signal (OFDMA has many subcarriers which are orthogonal to each other) is the sum of many narrowband signals. At some time instances, this sum is large and at other times is small, which means that the peak value of the signal is substantially larger than the average value.

Now if we see SC-FDMA which is single carrier so this situation does not arise.

Comments

thank you, actually I know why OFDMA has high PAPR, But I want to know what makes SC-FDMA different, you know that SC-FDMA symbol consists also from multiple orthogonal 15KHz sub-carrier and a short duration compared to OFDMA Symbol which is 15KHz * 66.7us

Answer 2

Source: http://en.wikipedia.org/wiki/Single-carrier_FDMA

The distinguishing feature of SC-FDMA is that it leads to a single-carrier transmit signal, in contrast to OFDMA which is a multi-carrier transmission scheme. Subcarrier mapping can be classified into two types: localized mapping and distributed mapping.

Owing to its inherent single carrier structure, a prominent advantage of SC-FDMA over OFDM and OFDMA is that its transmit signal has a lower peak-to-average power ratio (PAPR), resulting in relaxed design parameters in the transmit path of a subscriber unit. Intuitively, the reason lies in the fact that where OFDM transmit symbols directly modulate multiple sub-carriers, SC-FDMA transmit symbols are first processed by an N-point DFT block