Direct Detect And Avoid

Description

Direct Detect And Avoid (DDAA) is a standardized feature introduced in 3GPP Release 18 to manage radio frequency interference in integrated terrestrial and non-terrestrial network (NTN) environments. It operates within the UE's radio access layer, enabling the device to perform autonomous spectrum sensing to identify potential interference from NTN signals, such as those from low Earth orbit (LEO) satellites or high-altitude platform stations (HAPS). Upon detection, the UE can initiate avoidance procedures, such as adjusting its transmission parameters or switching to alternative resources, to prevent harmful interference to the NTN receiver and maintain its own communication quality.

The architecture of DDAA involves enhancements to the UE's physical layer and medium access control (MAC) layer. The UE is equipped with sensing capabilities to monitor specific frequency bands for NTN signals, using predefined detection thresholds and patterns specified by the network. The gNodeB (gNB) configures the DDAA parameters via RRC signaling, including sensing occasions, measurement gaps, and reporting criteria. The UE reports detection events or measurement results to the gNB, which can then coordinate resource allocation or handover decisions to mitigate interference.

Key components include the DDAA sensing function, which utilizes advanced signal processing algorithms to distinguish NTN interference from other radio signals, and the avoidance mechanism, which may involve dynamic frequency selection, power control, or time-domain scheduling. The UE's radio resource management (RRM) is extended to support DDAA-related measurements and decisions. This functionality is critical for spectrum sharing regimes, such as those defined for the 3.5 GHz band or other shared bands, where terrestrial networks must protect NTN operations from harmful interference.

DDAA's role in the network is to enable efficient coexistence without requiring constant network coordination for every interference event. It reduces signaling overhead and latency compared to centralized interference management schemes. By empowering UEs with direct detection capabilities, the network can achieve more responsive and scalable interference mitigation, supporting the seamless integration of NTN services into the 5G ecosystem and beyond.

Purpose & Motivation

DDAA was created to address the growing need for spectrum sharing between terrestrial 5G networks and emerging non-terrestrial networks (NTN), such as satellite communication systems. As demand for wireless bandwidth increases, regulatory bodies are promoting shared use of frequency bands to maximize spectral efficiency. However, NTN receivers, particularly on satellites, are highly sensitive to interference from terrestrial transmissions. Traditional interference management relies on network-based coordination, which can be slow, inefficient, and inadequate for dynamic NTN environments where satellite positions change rapidly.

Previous approaches, such as geographic exclusion zones or static power limits, were overly conservative and reduced terrestrial network capacity. They also required extensive database coordination and could not adapt to real-time changes in NTN operations. DDAA solves these limitations by enabling UEs to directly sense NTN signals and autonomously avoid causing interference. This dynamic approach allows for more aggressive spectrum reuse while ensuring protection of NTN services, aligning with 3GPP's vision for integrated access and backhaul (IAB) and non-terrestrial networks in 5G-Advanced.

The motivation for DDAA stems from 3GPP's work on NTN standardization, where coexistence mechanisms are essential for commercial deployment. It supports regulatory requirements for interference mitigation in shared bands, such as those identified by the ITU and national authorities. By providing a standardized method for direct detection and avoidance, DDAA facilitates global interoperability and reduces deployment complexity for operators deploying both terrestrial and non-terrestrial networks.