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The LTE specification specifies SC-FDMA as the encoding scheme for the reverse link (mobile to base station) when the forward link uses OFDMA.

What is the reason for the difference?

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SC-FDMA is encoded and transmitted from the handset where there are power tradeoffs. This encoding is better than OFDMA for the handset for the following related reasons:

  • Reduces peak to average power ratio
  • Increases efficiency of the power amplifier
  • Increases battery life

So at the base station they can employ transmitters that can handle a higher peak transmit power, with lower efficiency as it has a significant amount of power available. But on a mobile handset, this requires more expensive components, more space, and, probably most importantly, more power since peak transmissions are not as efficient as transmitting at a lower level but for a longer period of time (ie, higher peak to average ratio means lower energy efficiency, more heat, more power). The tradeoff is a little lower spectrum efficiency, but it's worth it for increased battery life, and particularly since most high speed data is going to the handset, not coming from it.

This short video explains further.

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