Sub-Band non-overlapping Full Duplex

Description

Sub-Band non-overlapping Full Duplex (SBFD) is an advanced duplexing scheme introduced in 3GPP Release 18 for NR (New Radio). It operates on a single carrier frequency but partitions the available bandwidth into distinct, non-overlapping sub-bands dedicated to uplink (UL) and downlink (DL) transmissions. This allows a base station (gNB) or user equipment (UE) to transmit and receive simultaneously within the same carrier, unlike Time Division Duplex (TDD) which alternates in time or Frequency Division Duplex (FDD) which requires paired spectrum with a guard band. The architecture involves sophisticated RF front-end design, digital signal processing, and interference cancellation algorithms to manage self-interference between the transmitter and receiver chains. Key components include SBFD-aware scheduling in the Medium Access Control (MAC) layer, physical layer procedures defined for channel state information (CSI) reporting and sounding reference signals (SRS) in SBFD slots, and resource allocation mechanisms that coordinate UL and DL resources within the sub-bands. Its role in the network is to significantly boost spectral efficiency, reduce latency for applications like XR and industrial IoT, and provide more flexible resource utilization compared to conventional duplexing, forming a foundational technology for 5G-Advanced evolution towards 6G.

Purpose & Motivation

SBFD was created to address the growing demand for higher spectral efficiency and lower latency in 5G-Advanced networks, overcoming limitations of existing duplexing methods. Traditional FDD requires paired spectrum, which is scarce and expensive, while TDD introduces latency due to switching gaps and requires strict synchronization across the network. SBFD solves these by enabling full-duplex operation on a single carrier, effectively doubling the utilization of available spectrum and enabling instantaneous bidirectional communication. The historical context stems from research in in-band full-duplex, which faced challenges with self-interference cancellation. SBFD's sub-band non-overlapping approach provides a more practical implementation by separating TX and RX frequencies, reducing interference complexity and making it feasible for commercial deployment. It addresses the need for enhanced capacity for dense urban deployments, ultra-reliable low-latency communication (URLLC), and support for asymmetric traffic patterns efficiently.