what is main Difference between DL and UL in LTE ?
OFDMA
  • Advantages
  • Robust against narrow-band co-channel interference
  • Robust against Intersymbol interference (ISI) and fading
  • High spectral efficiency
  • Efficient implementation using FFT
  • Drawbacks
  • High Peak-to-Average Power Ratio
The power limitation is more problematic in UL than in DL Signal with high PAPR will limit the Tx power in UL and reduce coverage.
LTE uses in UL a modified form of OFDMA process, called SC-FDMA
SC-FDMA = Single Carrier – Frequency Division Multiple Access
SC-FDMA improves the peak-to-average power ratio (PAPR) compared to
OFDM
Reduced power amplifier cost for mobile
Reduced power amplifier back-off -> improved coverage
In DL, use OFDM together with some PAPR reduction techniques (“clipping and filtering”, “tones reservation”, etc…)
In UL, find an alternative to OFDM combining some of OFDM’s advantages, but with a PAPR equivalent to single carrier’s one: DFT-Spread OFDM (DFT-SOFDM), also known as Single-Carrier FDMA (SC-FDMA)
.