SBFD Guard Sub-Bands

Technical Explanation

Because digital filters cannot achieve brick-wall attenuation, simultaneous DL and UL sub-bands on the same carrier require a guard interval. 3GPP Rel-18 establishes guard sub-band sizing criteria (typically 5 to 10 MHz in a 100 MHz TDD carrier), balancing the trade-off between spectral efficiency loss and analog filter roll-off requirements.

Key Functions

• Provides spectral separation between high-power DL sub-bands and sensitive UL sub-bands
• Allows commercial RF filters to achieve required out-of-band rejection without massive insertion loss
• Optimizes the ratio between usable transmission resource blocks and guard sub-carriers
• Dynamically configures guard bandwidth based on active antenna isolation capabilities