OFDM vs. DFT-s-OFDM Simulator
Analyze Peak-to-Average Power Ratio (PAPR) for 5G/LTE Uplink Design
| Metric | Standard OFDM | DFT-s-OFDM |
|---|---|---|
| Waveform | Multi-carrier | Single-carrier-like |
| 5G Context | Downlink (gNB to Phone) | Uplink (Phone to gNB) |
How This Simulator Works
The Signal Processing Chain
This simulator generates random M-QAM symbols and processes them through two different paths:
- OFDM Path: Maps data directly to subcarriers and applies an
IFFT. This creates a multi-carrier signal where the sum of many independent sinusoids can align to create massive power spikes. - DFT-s-OFDM Path: First applies a
DFT(spreading) to the data before theIFFT. Mathematically, the DFT and IFFT partially "cancel" each other's multi-carrier characteristics, resulting in a Single-Carrier behavior.
What to Observe
1. The Envelope: Notice the Blue line (OFDM) has "jagged" peaks. The Green line (DFT-s-OFDM) is much flatter and more compressed.
2. Scaling N: As you increase the number of subcarriers, the OFDM peaks typically become more extreme. This is because the probability of $N$ carriers adding up constructively increases.
3. PAPR Value: A PAPR of 10dB (OFDM) means the peak power is 10x higher than the average. A PAPR of 3dB (DFT-s-OFDM) means the peak is only 2x the average.
Engineering Impact: The "Power Amplifier" Problem
In a real smartphone, the Power Amplifier (PA) must be linear enough to handle these peaks. If the signal has high PAPR (OFDM), we must turn down the average volume (Input Back-Off) to prevent the peaks from clipping. This wastes energy and generates heat. By using DFT-s-OFDM, we can run the amplifier "hotter" and more efficiently, which is why 5G uses it for the Uplink to save your phone's battery.