The ATSC .0 Physical Layer-Bootstrap Basics

Why This Matters

ATSC 3.0 would allow the over-the-air television transmission methodology to be updated like software.

John Smith

THE BIG ISLAND-The ATSC 3.0 standard is nearing completion. Candidate standards have been released for system discovery, or bootstrap, and the physical layer. Broadcast engineers will have to understand how ATSC 3.0 works if they want to take advantage of the improved performance and flexibility it offers. This month, I'll describe the physical layer differences between ATSC 3.0 and other DTV standards in general and explain the unique ATSC 3.0 bootstrap signal in detail.

Most readers know that ATSC 3.0 uses OFDM (orthogonal frequency division multiplexing), which divides data among thousands of carriers (8K, 16K or 32K); versus the legacy ATSC standard that uses 8-VSB (eight-level vestigial sideband modulation), which puts all the data on a single carrier. All other DTV standards around the world, including DVBT, DVB-T2, ISDB-T, ISDB-Tb and DTMB use OFDM, although DTMB also supports a single-carrier mode.

ATSC 3.0 provides an improvement over existing OFDM-based DTV standards through use of the latest LDPC FEC (low-density parity-check forward error correction) codes and optimized constellations ranging from QPSK (quadrature phase shift keying) through 4096QAM (quadrature amplitude modulation).

Different combinations of codes, pilot patterns and constellations can be selected to allow data rates ranging from less than 1 Mbps in an extremely robust mode working at less than zero dB SNR (signal-to-noise ratio) to over 57 Mbps when a much higher SNR is available.

A key requirement for ATSC 3.0 is the ability to change the transmission format while continuing to support legacy receivers. This is accomplished through a framing structure that includes a System Discovery and Signaling signal, referred to as the bootstrap signal before each frame. This signal has a fixed physical configuration, but carries data identifying the version of the frame following it. This could be ATSC 3.0, a future ATSC 3.1 or some other variation; even one using a different waveform.

Frames carrying ATSC 3.0 data and those with different formats can be combined in the same RF channel. When it is time to transition to a new standard, the bootstrap will allow older receivers to ignore the new ATSC 3.1 frames, but continue to demodulate the ATSC 3.0 frames.

Fig. 7.10: ATSC 3.0 Frame Structure

LINK:	http://www.tvtechnology.com/expertise/0003/the-atsc-30-physical-layerb...
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