What Is an ATSC Receiver?

8VSB is a modulation method used for broadcasting in the ATSC digital television standard. ATSC and 8VSB modulation are mainly used in North America; instead, the DVB-T standard uses COFDM.

8VSB is an 8-level residual sideband modulation. Essentially, it converts a binary stream to an octal representation by shifting the sine carrier amplitude to one of eight levels. 8VSB is capable of transmitting three bits per symbol (2 ^ 3 = 8); in ATSC, each symbol includes two bits from the MPEG transport stream, which are trellis modulated to produce a three-bit number. The resulting signal is then band-pass filtered with a Nyquist filter to remove redundancy in the side lobes and then moved up to the broadcast frequency.

Vestigial sideband modulation (VSB) is a modulation method that attempts to eliminate the spectral redundancy of pulse amplitude modulation (PAM) signals. Modulating a carrier by a real-valued data sequence results in a sum frequency and a difference frequency, thereby generating two symmetrical carrier sidebands. Symmetry means that one of the sidebands is redundant, so removing one sideband still allows demodulation. Because the filter with zero conversion bandwidth cannot be realized, the implemented filtering leaves traces of redundant sidebands, so it is called "VSB" ^[1]

In a 6MHz (megahertz) channel used to broadcast ATSC, 8VSB carries a symbol rate of 10.76 megabytes, a total bit rate of 32Mbit / s, and a net bit rate of 19.39Mbit / s of available data. The net bit rate is lower due to the addition of forward error correction codes. Use a trellis encoder to select eight signal levels. There are similar modulations 2VSB, 4VSB and 16VSB. 16VSB is specifically used for ATSC digital cables, but quadrature amplitude modulation (QAM) has become the de facto industry standard because it is cheap and readily available.

A significant advantage of 8VSB to broadcasters is that it requires much less power to cover an area comparable to earlier NTSC systems, and it is reported to be better than the most common alternative system, COFDM. Part of the advantage is the lower peak-to-average power ratio required compared to COFDM. The peak power requirement of an 8VSB transmitter is 6 decibels (four times) its average power. 8VSB is also more resistant to impulse noise. Some stations can cover the same area while transmitting at an effective radiated power of approximately 25% of the analog broadcast power. Although NTSC and most other analog TV systems also use vestigial sideband technology, unwanted sidebands are more effectively filtered in ATSC 8VSB transmissions. 8VSB use

For some time, people have been working to change the modulation of ATSC to COFDM, the transmission mode of DVB-T in Europe and ISDB-T in Japan. However, the FCC has always considered 8VSB to be a better modulation for digital TV broadcasting in the United States. In a 1999 report, the Commission found that 8VSB has better threshold or carrier-to-noise ratio (C / N) performance, higher data rate capabilities, requires less transmitter power for equivalent coverage, and Impulse and phase noise are more robust [2]. As a result, it rejected Sinclair Broadcasting's rulemaking application in 2000, asking for broadcasters to be allowed to choose between 8VSB or COFDM to best suit their coverage. The FCC report also acknowledges that COFDM "is usually expected to perform better with dynamic multipath," such as mobile operations or trees with strong winds. However, with the introduction of the 5th generation demodulator in 2005 and subsequent improvements to the 6th and 7th generation, the equalization range is now approximately -60 to +75 microseconds (135 microsecond extension), and static is almost eliminated And dynamic multipathing. 8-VSB reception. In contrast, the equalization span in COFDM is -100 to +100 microseconds (200 microsecond extensions), but applying so much guardband space for COFDM greatly reduces its useful payload. In fact, 1280 × 720p has been adopted as the high-definition standard for DVB-T1 in most parts of Europe, because its payload capacity has been reduced [citation needed]. The introduction of DVT-T2 aims to improve the ability of terrestrial transmission to carry 1920 × 1080p content. 1920 × 1080i has been part of the 8-VSB scheme since its establishment, and its improved demodulator has no effect on its innate payload capacity.

As the United States continues to adopt the 8VSB-based ATSC standard, and the ATSC receiver population continues to grow, it is now basically impossible to switch to COFDM. Most analog terrestrial transmissions in the United States were shut down in June 2009, and 8VSB tuners are common in all new TVs, which will complicate the future transition to COFDM.