ATSC .0: Where We Stand

ALEXANDRIA, Va. Technology doesn't stand still; instead, it evolves at an ever-growing pace. This is especially true in the area of bringing media to viewers.

In the past, video entertainment in the home was relatively simple, consisting of sitting in front of the TV to watch broadcasts when they were scheduled. Today, people want the capability to watch nearly anything they want, on any device, wherever they are with content delivered over the air, over cable or satellite, via the Internet or locally stored. It is clear that the broadcast industry must evolve to accommodate this desire.

The current work on the ATSC 3.0 next-generation broadcast standard is meant to address this issue, using advanced transmission and video/audio coding techniques to bring new and creative services to viewers.

It has become clear that to adapt to consumers' changing habits and demands, a new system is needed by broadcasters to support new viewing behaviors. Such a system must include the capability to evolve with consumer demands, and thus provide extensibility that permits future adaptation.

Television is now viewed in a variety of ways, through a growing range of media sources and delivery platforms. Among these, the Internet has become a major source of television content for consumers. Developing a new DTV system that incorporates all these elements is now not only desirable, but has become essential.

Flexibility in service options is a keystone of the next-generation ATSC 3.0 DTV broadcast system, including the opportunity for terrestrial broadcasters to send hybrid content services to fixed and mobile receivers seamlessly combining both over-the-air transmission and broadband delivery. Options such as multiview and multiscreen are also important, as is the option of choosing among standard definition, HD and Ultra HD resolutions.

The ATSC 3.0 system also must adapt to future innovations. Scalable, interoperable and adaptable are some of the key words that describe the general principles behind ATSC 3.0.

Although work is already underway to enhance the existing ATSC TV system with Internet compatibility and caching capability for storing programs (a backwards-compatible suite of enhancements dubbed ATSC 2.0 ), the future needs of viewers and broadcasters is the focus of the ATSC 3.0 initiative. Technologies developed for ATSC 2.0 are expected to be supported in the new ATSC 3.0 system.

Because ATSC 3.0 is likely to be incompatible with current broadcast systems, it must provide improvements in performance, functionality, and efficiency significant enough to warrant implementation of a non-backwards-compatible system.

It is important to remember that the original A/53 DTV standard was launched in 1996. A number of significant developments have occurred since then, notably:

Spectrum is becoming increasingly scarce

Major improvements have been made in video coding efficiency

A strong desire exists for higher-resolution images

Audio has become more efficient and immersive

Interactivity has become expected on the part of consumers

Delivery paths other than broadcast have become commonplace

Mobile devices have proliferated

Tablets are in widespread use

These developments, taken collectively, have reshaped the television landscape, with the development of ATSC 3.0 as a response. The work on ATSC 3.0 has been broken up into a number of layers, as discussed below.

PHYSICAL LAYER

The physical layer is the core transmission system that is the basis for any over-the-air broadcast service. The physical layer is focused on modulation and coding, emission waveforms and other common system elements.

Multiple types of TV receivers, including fixed devices (such as traditional large-screen living room and bedroom TV sets), handheld devices, vehicular screens and portable receivers are being considered in the work on ATSC 3.0. A primary goal of the ATSC 3.0 physical layer is to provide TV service to both fixed and mobile devices.

Spectrum efficiency and robust service are some key focus areas. Increased data rates to support new services such as Ultra HD are a priority as well.

Furthermore, mechanisms for extensibility of the ATSC 3.0 system are being explored so that advancements and technologies that may be developed in the future can be accommodated without redefining the entire system. Determining mechanisms for graceful and agile evolution are an integral part of the ATSC 3.0 work.

In addition to traditional fixed services, ATSC 3.0 is intended to provide robust mobile services to devices that move, such as phones, tablets, laptops and personal televisions. Since these devices are likely to move across borders, it is highly desirable that the specification contains core technologies that will have broad international acceptance and enable global interoperability.

Figure 1: Physical layer skeleton architecture

The overall physical layer skeleton architecture is illustrated in Figure 1. Currently, the following baseline features are amongst those that have been tentatively agreed to:

OFDM-based modulation, with a wide range of guard intervals to mitigate multipath

LDPC based FEC, with a wide range of code rates in two code lengths (supporting mobile and fixed)

Wide range of constellation sizes

The ATSC 3.0 physical layer is expected to provide a large range of possible operating points for broadcasters, all of which are very close to the Shannon limit (the theoretical limit of how much information can be carried over a noisy channel) as illustrated in Figure 2, below. Basic operating tradeoffs include selecting a lower data capacity/more robust service and/or higher data capacity/less robust service, or points in-between.

Figure 2: Example capacity curve for ATSC 3.0 physical layer

Broadcasters have the opportunity to choose operating p

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