CP-OFDM vs DFT-S-OFDM: Waveform Differences in 5G

This article delves into the comparison between CP-OFDM (Cyclic Prefix Orthogonal Frequency Division Multiplexing) and DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) waveforms, both crucial components in 5G New Radio (NR) technology. We’ll explore their differences and understand why they are used in specific scenarios within the 5G NR downlink and uplink chains.

CP-OFDM

• Usage: CP-OFDM is used in both the downlink and uplink chains within the physical layer of the 5G NR system.
• Scenario: Designed primarily for scenarios demanding high throughput.
• MIMO: Well-suited for MIMO (Multiple Input Multiple Output) configurations, enabling increased data rates through spatial multiplexing.
• Sequences: Utilizes sequences similar to Gold sequences, as employed in PDSCH (Physical Downlink Shared Channel).
• Spectral Efficiency: CP-OFDM offers very high spectral packing efficiency within RBs (Resource Blocks). This makes it ideal for network operators seeking to maximize network capacity, particularly in dense urban environments where spectrum is a precious commodity.

DFT-S-OFDM

• Usage: DFT-S-OFDM is employed in the uplink chain within the physical layer of 5G NR, mirroring its use in LTE uplink.
• Scenario: Primarily intended for power-limited scenarios. This means it’s beneficial for devices that need to conserve battery power while still maintaining a reliable connection.
• Single Layer Transmission: Exclusively used in single-layer transmission.
• Sequences: Employs sequences analogous to Zadoff-Chu sequences, commonly used in uplink transmissions.
• Range: While offering less efficient spectral packing compared to CP-OFDM, DFT-S-OFDM is favored to address greater range requirements. This makes it a good choice for scenarios where coverage is more important than maximizing data throughput.