Description
Detect And Avoid (DAA) is a critical feature for New Radio in Unlicensed spectrum (NR-U) operation, mandated to ensure harmonious coexistence with incumbent systems like Wi-Fi (IEEE 802.11) and radar in shared frequency bands such as 5 GHz and 6 GHz. The mechanism operates through a continuous two-phase process: detection and subsequent avoidance. In the detection phase, the gNB (Next Generation NodeB) or UE (User Equipment) performs energy detection or specific waveform sensing (e.g., for radar pulses) on the target channel before and during transmission opportunities. This sensing is defined by regulatory requirements (e.g., FCC, ETSI) and involves listening for signals above a predefined threshold over a minimum channel occupancy time. The gNB coordinates this sensing, potentially using UE-assisted measurements, to build a comprehensive view of the channel environment.
Upon detecting an incumbent signal, the system enters the avoidance phase. The core principle is that the NR-U transmission must immediately vacate the channel or significantly reduce its interference potential. This is achieved through mechanisms like channel switching, where the gNB schedules transmissions on an alternative clear channel identified during prior sensing. Alternatively, the gNB can employ dynamic power control, reducing its transmission power below the interference threshold for the incumbent. For radar avoidance, a more stringent 'move away' protocol is often required, where the system must not use the channel for a specified quiet period. The gNB manages these procedures via RRC (Radio Resource Control) signaling, configuring UEs with measurement gaps for sensing and updating scheduling decisions based on sensing results.
Architecturally, DAA functionality is integrated within the gNB's MAC (Medium Access Control) and PHY (Physical Layer), with support from higher-layer RRM (Radio Resource Management). The gNB acts as the central controller, instructing UEs when to perform Listen-Before-Talk (LBT) and DAA measurements. These measurements are reported back to the gNB, which consolidates the data to make channel occupancy decisions. The system supports both wideband and narrowband sensing to accommodate different incumbent signal characteristics. DAA's role is foundational for NR-U, transforming unlicensed spectrum from a 'best-effort' arena into a managed resource where 5G can operate predictably while respecting legal mandates and promoting spectral efficiency through intelligent, reactive sharing.
Purpose & Motivation
DAA was created to address the fundamental challenge of deploying 5G New Radio in globally available unlicensed and shared spectrum bands. The primary motivation was to expand cellular network capacity and support high-throughput, low-latency services without exclusive reliance on licensed spectrum, which is scarce and expensive. However, bands like 5 GHz and 6 GHz are already populated by entrenched technologies, primarily Wi-Fi for consumer and enterprise use, and by radar systems for weather, military, and satellite applications. Regulatory bodies worldwide impose strict 'coexistence' or 'incumbent protection' rules on new entrants to these bands. Without DAA, NR-U transmissions could cause harmful interference, degrading Wi-Fi performance or disrupting critical radar operations, leading to regulatory non-compliance and service failure.
The technology solves the problem of how a scheduled, synchronous cellular system like 5G NR can fairly share spectrum with contention-based, asynchronous systems like Wi-Fi and protected radar services. Previous approaches in LTE-LAA (License Assisted Access) introduced basic Listen-Before-Talk (LBT), but this was primarily designed for coexistence with other LBT-based systems. DAA extends this concept with more sophisticated detection capabilities tailored to specific incumbent signatures (e.g., radar pulse patterns) and more deterministic avoidance protocols mandated by regulators. It addresses the limitation of simple LBT, which might not reliably detect non-LBT signals like certain radar types, by incorporating feature detection and longer measurement periods. The creation of DAA in 3GPP Release-18 was driven by the need to standardize a unified, globally applicable framework that enables NR-U equipment to meet diverse regional regulatory requirements, thereby ensuring device interoperability and successful market deployment of 5G in shared spectrum.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (66 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the DAA (Detect And Avoid) function was newly introduced to enable network-assisted detection of airborne UEs, specifically for UAVs, by allowing the RAN (eNB/gNB) to detect UEs above certain altitude thresholds. This provided a foundational ground-assisted component for DAA, complementing direct UAV-to-UAV methods, by gathering information such as UE altitude for the network to support tactical deconfliction.
- Avoiding FGI20 limitation TS 36.331CR3407
- SI message scheduling enhancement to avoid conflicts between legacy and positioning System Information TS 36.331CR3596
- Beam management, failure detection and recovery TS 38.300CR0070
- Correction to beam failure detection in Stage-2 TS 38.300CR0103
- CR to avoid unnecessary L3 filtered beam measurements TS 38.331CR0282
- Avoiding security risk for RLC UM bearers during termination point change TS 38.331CR0570
+ 2 more changes
In Release 16, the DAA (Detect And Avoid) function was enhanced through the introduction of NR-U (NR in Unlicensed spectrum) operations, with specific technical procedures defined for its support. Key additions included new mechanisms for Radio Resource Management (RRM) measurements, Energy Detection Threshold configuration, and RSSI measurement procedures specifically for NR-U. The release also provided clarifications and corrections for prioritization of HARQ retransmissions, RRC procedures, and RLF (Radio Link Failure) detection to ensure robust operation in unlicensed bands.
- Introduction of NR-U in 38.321 TS 38.321CR0694
- Clarification on RLF detection of source PCell TS 36.300CR1339
- Inter-RAT RRM measurement on NR-U TS 36.331CR4654
- Correction of CAPC for NR-U TS 38.300CR0294
- Clarification on RLF detection of source PCell TS 38.300CR0368
- Clarification on prioritization of retransmission over initial transmission for HARQ PID selection in NR-U TS 38.321CR1115
+ 13 more changes
In Release 17, the enhancements for the Detect and Avoid (DAA) function focused on improving network-assisted detection and reporting for UAVs. Specifically, corrections were made to the measurement reporting procedure for interference detection in UAV operations. Furthermore, the release introduced the capability for the 5G system to detect that a connected UE is airborne even when the UE's subscription does not include an aerial flag, enabling more reliable identification for DAA services.
- Addition of NR-U RSSI/CO measurement UE capability TS 36.331CR4729
- Minimization of data loss and duplication avoidance during mobility from MBS non upporting gNB to supporting gNB TS 38.300CR0605
- Correction on measurement reporting for interference detection in UAV TS 36.300CR1373
- Correction on PDCCH blind detection capability in CA TS 38.331CR3430
- Correction to time domain resource assignment in NR-U TS 38.331CR4142
In Release 18, the DAA (Detect And Avoid) function was enhanced to introduce a ground-assisted component, enabling the 5G system to detect that a connected UE is airborne even without an aerial subscription or UE-provided identification. This release added architectural enhancements and configuration procedures to support UTM (UAS Traffic Management) by allowing the network to gather information from sources like RAN awareness of UE altitude and wireless sensing, and to subsequently alert the UTM or enable it to take over UAV control. It also expanded DAA support to cover scenarios involving UAVs both with and without U2X (UAV-to-Everything) communication capabilities.
- Requirements for support for DAA TS 23.255CR0036
- Additions to functional entities on support for DAA deployments TS 23.255CR0037
- Addition of DAA assist capability to UAE layer registration TS 23.255CR0038
- Addition of procedures for DAA configuration TS 23.255CR0039
- Addition of API for DAA TS 23.255CR0040
- Enhancements to Realtime UAVs status for DAA support TS 23.255CR0042
+ 16 more changes
In Release 19, the key enhancement for the Detect And Avoid (DAA) function was the formal introduction and procedural support for **ground-based** and **network-assisted** mechanisms. This expanded the system's capability beyond direct UAV-to-UAV (PC5) detection by enabling the 5G network to use sources like RAN altitude detection and wireless sensing to gather information for UTM-controlled DAA operations. The updates specifically defined procedures for UAV-triggered network-assisted DAA and refined the data semantics and triggering thresholds to support this ground-assisted functionality.
- pCR on updating use case 5.4 network-assisted UAV DAA TS 22.843CR0004
- Support for DAA ground-based UAE layer assistance TS 23.255CR0055
- Adding support of network-assisted/ground-based mechanism for Detect And Avoid with 5GS information TS 23.256CR0135
- Update DAA procedure to support ground based DAA TS 24.257CR0040
- Update XML coding to support ground based DAA TS 24.257CR0045
- Update structure and data semantics to support ground based DAA TS 24.257CR0044
+ 6 more changes
Explore further
Broader topics and technologies where DAA plays a role.
Defining Specifications
3GPP specifications that define or reference DAA, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 22.843 vj20 | Study on Uncrewed Aerial Vehicle (UAV) Phase 3 | Rel-19 |
| TS 23.255 vj50 | UAS Application Layer Support | Rel-19 |
| TS 23.256 vj50 | UAS Support Architecture Enhancements | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 24.257 vj40 | UAS Application Enabler (UAE) Layer | Rel-19 |
| TS 29.257 vj40 | Application layer support for Uncrewed Aerial System (UAS) | Rel-19 |
| TS 33.256 vj10 | Security for Uncrewed Aerial Systems (UAS) | Rel-19 |
| TS 33.759 vj00 | UAS Security Enhancements Phase 3 Study | Rel-19 |
| TR 33.891 vi00 | Security and Privacy Threats for UAVs and UAM | Rel-18 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |