A/321, “System Discovery and Signaling”Approved: 11 June 2026

This document describes the system discovery and signaling architecture for the ATSC 3.0 physical layer. Broadcasters anticipate providing multiple wireless-based services, in addition to conventional broadcast television in the future. Such services may be time-multiplexed together within a single RF channel. The bootstrap provides a universal entry point into a broadcast waveform. The bootstrap employs a fixed configuration (e.g., sampling rate, signal bandwidth, subcarrier spacing, time-domain structure) known to all receiver devices and carries information to enable processing and decoding the wireless service associated with a detected bootstrap. This capability ensures that broadcast spectrum can be adapted to carry new services and/or waveforms for the public interest to continue to be served in the future.

Download current version: A/321:2026-06, “System Discovery and Signaling”, 11 June 2026.

Previous Versions

There are multiple versions of this document. Please be sure to download the desired version. For amendments, the text includes a list of changes, the rationale for the changes, and compatibility considerations. The following documents are listed by date, with the most recent first.

2026

Download A/321:2026-04, “System Discovery and Signaling”, 14 April 2026. This version of the Standard is normatively referenced in A/300:2026-04.

Download A/321:2026-04 Amendment No. 1, “Bootstrap Clarification”, approved 11 June 2026.

2025

Download A/321:2025-07, “System Discovery and Signaling”, 17 July 2025. This version of the Standard is normatively referenced in A/300:2025-07.

2024

Download A/321:2024-04, “System Discovery and Signaling”, 3 April 2024. This version of the Standard is normatively referenced in A/300:2024-04.

2023

Download A/321:2023-03, “System Discovery and Signaling”, 31 March 2022. This version of the Standard is normatively referenced in A/300:2023-03.

2022

Download A/321:2022-03, “System Discovery and Signaling”, 31 March 2022. This version of the Standard is normatively referenced in A/300:2022-04.

2016

Download A/321:2016, “System Discovery and Signaling”, approved 23 March 2016. This Standard is normatively referenced by A/300:2019, A/300:2020, and A/300:2021.

A/321:2016, dated 23 March 2016, was approved and adopted by reference into the U.S. FCC Rules 47 CFR § 73.682. In subsequent versions of A/321, normative and informative references to other ATSC standards and recommended practices have been updated to reference current version documents. The only other changes are described in A/321:2026-04 Amendment No. 1, Section 1 (see the link above.)