ATSC 3.0: Features, Protocol, Physical Layer & Frame Structure

This tutorial provides a comprehensive overview of ATSC 3.0 TV technology, covering its key features, protocol stack, physical layer, frame structure, and advantages. ATSC 3.0 is the successor to ATSC 1.0 and ATSC 2.0, designed for digital television broadcasting across various transmission networks like terrestrial, satellite, and cable. These standards are developed and managed by the Advanced Television Systems Committee (ATSC).

Features of ATSC 3.0 TV Technology

ATSC 3.0 aims to deliver a next-generation television experience with several enhancements:

• 4K UHD TV: The primary goal of ATSC 3.0 is to support 4K Ultra High Definition television. Future iterations may even support 8K resolution.
• High Resolution: Supports a resolution of 3840x2160 at a frame rate of 60 Hz.
• High Dynamic Range (HDR): Provides a wider range of colors and contrast for a more realistic picture.
• Color Depth: Employs 10 bits per pixel for transmission, resulting in a broader color palette.
• Mobile Device Support: Enables HDTV delivery to mobile devices like smartphones and tablets.

ATSC 3.0 Protocol Stack

Figure 1: ATSC 3.0 Protocol Stack

The ATSC 3.0 protocol stack (Figure 1) is structured as follows:

• System Discovery and Signaling: This layer uses unique sequences to identify the beginning of a frame or signal, allowing the receiver to synchronize.
• Physical Layer: The physical layer employs Orthogonal Frequency Division Multiplexing (OFDM) to transmit data within a 6 MHz bandwidth.
• Protocols: This layer utilizes internet protocols, organizing data into streams or files for transmission.
• Presentation: This layer manages compression by using different coding schemes for video and audio, supporting UHD, HD, and SD multicast, along with immersive audio.
• Applications: This is the software layer where the screen is treated as a web page, enabling interactive features and applications.

ATSC 3.0 Frame Structure

Figure 2: ATSC 3.0 Frame Structure

The ATSC 3.0 frame structure (Figure 2) consists of three main parts:

• Bootstrap: Configures the receiver to decode the preamble.
• Preamble: Contains two parts:
  • L1-Basic: Aids in decoding L1-Detail and the first subframe. It uses 200 bits per coded block at a fixed code rate of 3/15, employing 3 QPSK and 4 NUC types (NUC_16_8/15, NUC_64_9/15, NUC_256_9/15, NUC_256_13/15).
  • L1-Detail: Carries essential information such as FFT size, modulation type, and FEC code rate, assisting in decoding the remaining subframes. L1-detail uses a code rate of 6/15 for modes 3 to 7, and QPSK at a code rate of 3/15 for modes 1 and 2.
• Payload: The remainder of the ATSC 3.0 frame comprises the payload, formatted as defined by L1 signaling.

A frame is composed of one or more subframes.

ATSC 3.0 Physical Layer

Figure 3: ATSC 3.0 Physical Layer

The ATSC 3.0 physical layer (Figure 3) illustrates the downlink and uplink components. The downlink encompasses the modules within a digital TV transmitter at the broadcasting station. The ATSC tuner in the TV set receives and demodulates this signal. The uplink processing, shown in the figure, occurs at the transmitter end of subscribers with ATSC 3.0-enabled devices, facilitating broadband connectivity with the main station.

The ATSC 3.0 physical layer incorporates these generic modules:

• Scrambler
• FEC (Forward Error Correction)
• Bit Interleaver
• Mapper
• Time Interleaver
• OFDM Framer
• Frequency Interleaver
• Pilots
• Reserved Tones
• Guard Interval functions

Figure 3 highlights the Bit Interleaved and Coded Modulation (BICM) module, consisting of FEC, Bit Interleaver (BIL), and Mapper (MAP).

ATSC 3.0 employs Layered Division Multiplexing (LDM), a spectrum overlay technique that superimposes physical layer streams with different power levels, modulations, and code rates. This enables data decoding in varied environments and applications. LDM receiver uses signal cancellation to decode the signal. Due to different power levels for different layers, the technique is also called as Power Division Multiplexing.

Advantages of ATSC 3.0

ATSC 3.0 offers a wide range of benefits:

• Convergence of Broadcast and Broadband: Integrates over-the-air TV with internet broadband, including Wi-Fi.
• Emergency Alerts: Supports weather and emergency alerts.
• Efficient Compression: Utilizes advanced compression techniques to deliver diverse audio and video content within a 6 MHz bandwidth.
• Robust Modulation: Supports modulation schemes up to 4096QAM.
• Targeted Advertising: Enables advertisers to display customized advertisements on TV.
• Interactive Features: Offers interactive functionalities, including multichannel immersive audio.
• Backward Compatibility: Maintains compatibility with previous TV technologies.
• LTE Mobile Offload: Can be used for LTE mobile offload, relieving bandwidth demands on LTE networks by delivering content via TV transmission networks.
• Spectrum Efficiency: Channel bonding enables efficient use of available spectrum.
• Higher Data Capacity: The use of OFDM and advanced modulation techniques (e.g., 256 QAM or 4096QAM) in the physical layer allows for significantly higher data throughput.