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OFDM vs. DFT-s-OFDM Simulator


PAPR Simulator: OFDM vs. DFT-s-OFDM

OFDM vs. DFT-s-OFDM Simulator

Analyze Peak-to-Average Power Ratio (PAPR) for 5G/LTE Uplink Design

OFDM PAPR -- High (Inefficient PA)
DFT-s-OFDM PAPR -- Low (Battery Saver)
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 the IFFT. 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.

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