5G • Spectrum
SDL
Supplementary Downlink
Downlink-only carrier paired with standard FDD/TDD carriers to inject additional downlink capacity.
Technical Explanation
Supplementary Downlink (SDL) utilizes dedicated spectrum bands (such as 1.4 GHz L-Band n75/n76) exclusively for downlink transmission. It has no associated uplink carrier, and is aggregated with existing FDD or TDD anchors to accommodate highly asymmetric mobile broadband download traffic.
Key Functions
- Provides downlink-only spectrum boost for asymmetric broadband traffic
- Aggregated with standard FDD/TDD primary carriers
- Commonly deployed in L-Band (n75, n76) and 700 MHz European SDL
Specifications
3GPP TS 38.101-1, TS 38.300
Interfaces
Uu
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