Tutorial ATSC 3 0

Tutorial: ATSC 3.0 (NextGen TV)

What it is. ATSC 3.0, marketed as NextGen TV, is the IP-based successor to ATSC 1.0. It is on the air in parts of the United States and in South Korea. Instead of 8-VSB it uses OFDM with LDPC error correction, carries services as IP packets (ROUTE/DASH), and uses HEVC video. In OnAir you tune a 6 MHz channel, the receiver finds the bootstrap, reads the signalling, and lists the services; you watch them in the TV tab.

What you need

• A radio that samples at 6.5 Msps or faster (the mode asks for more). RTL-SDR is too slow. HackRF, Airspy, SDRplay, PlutoSDR, RX888 and similar work. See Supported radios.
• A UHF antenna with a clear view of the transmitter.
• A frequency. ATSC 3.0 broadcasts share the ATSC channel plan with ATSC 1.0 (6 MHz channels); the frequency database lists channel 2 at 57 MHz through channel 36 at 605 MHz. Use the Band plan list on the Scan tab for your country. If you do not know which channel carries NextGen TV, scan in this mode: only ATSC 3.0 channels lock.

Before you start

• Start the receiver with the mode set to ATSC 3.0; the receiver reports "Start the receiver with the ATSC 3.0 switch selected" otherwise.
• Gain: use Auto-tune or Optimise gain. The LDPC decoder is demanding, so give it the best SNR you can.
• ATSC 3.0 channels vary in FFT size (8k, 16k, 32k) and guard interval; OnAir reads them from the signalling, you do not set them.

Step by step

1. In the mode list open TV and choose ATSC 3.0 (second line NextGen TV).
2. Open the Scan tab, choose a Band plan and Start scan.
3. Press Start on a channel.
4. Watch the lamps in the status bar: Bootstrap, L1, PLP, Service, TS, Video, Audio.
5. Open the ATSC 3.0 panel on the left or the services list: it shows the Services table (channel number like 4.1, name, id, category, whether it is supported). Press Receive on a service.
6. Open the TV tab: picture and sound appear.

What you should see

• A flat, wide OFDM block, noticeably flatter than 8-VSB.
• Lamps lit in order: Bootstrap, L1, PLP, then Service. The service list arrives about once a second.
• On the status line: FFT size, guard interval (GI), carrier offset (CFO), frames, PLP ok counts, sample rate (fs), CPU load and dropped samples. Blocks lost should stay near zero.

Reading the screen

• Services: channel number, name, id, category and a state column. not supported yet appears for services that use MMTP instead of ROUTE.
• Level: the signal level meter.
• Receiver tab rows: synchronisation, carrier offset, bootstraps / frames, frame, bootstrap, PLP, baseband packets, link layer, decoder load.
• AC-4 sound (a column or note) appears for services whose audio is Dolby AC-4.

Options and settings

• Stream: record the remuxed transport stream, send it to UDP, or share it on the network.
• Optional AC-4 sound needs an FFmpeg with an AC-4 decoder you install yourself; see Voice codecs and docs/CODECS.md. Without it, AAC and AC-3 services still play, and AC-4 sound is left out.

Troubleshooting

• Bootstrap never locks. The channel is probably not ATSC 3.0, or the signal is too weak or overloaded. Try another channel, and check the sample rate.
• Locks, services listed, no picture. The service may use MMTP (not supported yet) or be encrypted. Pick another service.
• No sound but picture. The audio may be AC-4. Install an AC-4 capable FFmpeg (see above) or choose a service with AAC or AC-3.
• High decoder load or dropped samples. The LDPC decoding is heavy. Close other programs, use a faster machine, or reduce the rate if the channel still fits.
• Blocks lost keep growing. The signal is marginal; improve the antenna.

Tips

• Time interleaving and subframes are supported (release 0.2.4); long interleavers add a delay before the picture appears.
• Used and checked on real broadcasts.

Legal and privacy notes

Receiving free-to-air broadcasts is legal in most countries. NextGen TV services are often protected (DRM); OnAir does not decode encrypted services and does not try to.

Under the hood

ATSC A/321 (bootstrap), A/322 (physical layer: OFDM, LDPC with BCH, time and frequency interleaving, L1-Basic and L1-Detail), A/330 (link layer, ALP), A/331 (signalling and delivery: ROUTE, MMTP, LLS). OnAir finds the bootstrap with a carrier-offset search, reads the preamble and L1, decodes the PLPs, unpacks the link layer, reassembles ROUTE objects and remuxes the DASH segments (MP4) to a transport stream for playback.

Related

Mode page: ATSC 3.0 | ATSC 1.0 | DVB | Voice codecs | Supported radios | FAQ