View source for 8VSB

{{short description|Modulation method used by the American ATSC digital TV standard}}
{{about|the television modulation method|the SBE Certification|Certified 8-VSB Specialist}}

{{Citation style|date=July 2025}}
'''8VSB''' is the [[modulation]] method used for broadcast in the [[ATSC standards|ATSC digital television standard]]. ATSC and 8VSB modulation is used primarily in [[North America]]; in contrast, the [[COFDM#DVB-T|DVB-T standard uses COFDM]].

A modulation method specifies how the radio signal fluctuates to convey information. ATSC and DVB-T specify the modulation used for over-the-air digital television; by comparison, [[Quadrature amplitude modulation|QAM]] is the modulation method used for [[Cable television|cable]]. The specifications for a cable-ready television, then, might state that it supports 8VSB (for broadcast TV) and QAM (for cable TV).

8VSB is an 8-level [[vestigial sideband modulation]]. In essence, it converts a [[Binary number|binary]] stream into an [[octal]] representation by [[amplitude-shift keying]] a [[sine wave|sinusoidal]] carrier to one of eight levels. 8VSB is capable of transmitting three bits (2<sup>3</sup>=8) per [[symbol rate|symbol]]; in ATSC, each symbol includes two bits from the [[MPEG transport stream]] which are [[trellis modulation|trellis modulated]] to produce a three-bit figure. The resulting signal is then band-pass filtered with a [[Nyquist filter]] to remove redundancies in the side lobes, and then shifted up to the broadcast frequency.<ref>{{cite web|url=http://www.arrl.org/files/file/Technology/TV_Channels/8_Bit_VSB.pdf|title=WHAT EXACTLY IS 8-VSB ANYWAY?|last=Sparano|first=David|year=1997|access-date=8 Nov 2012}}</ref>

==Modulation technique==
Vestigial sideband modulation (VSB) is a modulation method which 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 and a difference frequency, resulting in two symmetrical carrier side-bands. The symmetry means that one of the sidebands is redundant, so removing one sideband still allows for demodulation. As filters with zero transition bandwidth cannot be realized, the filtering implemented leaves a vestige of the redundant sideband, hence the name "VSB".

==Throughput==
In the 6&nbsp;MHz ([[megahertz]]) channel used for broadcast ATSC, 8VSB carries a symbol rate of 10.76 [[megabaud]], a [[gross bit rate]] of 32 [[Mbit/s]], and a [[net bit rate]] of 19.39&nbsp;Mbit/s of usable data. The net bit rate is lower due to the addition of [[forward error correction]] codes. The eight signal levels are selected with the use of a [[trellis modulation|trellis encoder]]. There are also similar modulations [[2VSB]], [[4VSB]], and [[16VSB]]. 16VSB was notably intended to be used for ATSC [[digital cable]], but [[quadrature amplitude modulation]] (QAM) has become the ''de facto'' industry standard instead as it is cheap and readily available.

==Power saving advantages==
{{disputed section|reason=Power levels not lower|date=May 2025}}
A significant advantage of 8VSB for broadcasters is that it requires much less power to cover an area comparable to that of the earlier [[NTSC]] system, and it is reportedly better at this than the most common alternative system, [[Orthogonal frequency-division multiplexing|COFDM]].{{citation needed|date=March 2021}} Part of the advantage is the lower peak to average power ratio needed compared to COFDM.{{citation needed|date=March 2021}} An 8VSB transmitter needs to have a peak power capability of 6&nbsp;dB (four times) its average power.{{citation needed|date=March 2021}} 8VSB is also more resistant to impulse noise.{{citation needed|date=March 2021}} Some stations can cover the same area while transmitting at an [[effective radiated power]] of approximately 25% of analog broadcast power.{{citation needed|date=March 2021}} While NTSC and most other analog television systems also use a vestigial sideband technique, the unwanted sideband is filtered much more effectively in ATSC 8VSB transmissions. 8VSB uses a [[Low-pass filter|Nyquist filter]] to achieve this. [[Reed–Solomon error correction]] is the primary system used to retain data integrity.

In summer of 2005, the ATSC published standards for Enhanced VSB, or [[E-VSB]] [https://web.archive.org/web/20060214123607/http://www.tvtechnology.com/features/atsc/F_Whitaker.shtml]. Using [[forward error correction]], the E-VSB standard  will allow DTV reception on low power handheld receivers with smaller antennas in much the same way [[DVB-H]] does in Europe, but still using 8VSB transmission.

==Disputes over ATSC's use==
For some period of time, there had been a continuing lobby for changing the [[modulation]] for ATSC to [[COFDM]], the way [[DVB-T]] is transmitted in [[Europe]], and [[Integrated Services Digital Broadcasting#ISDB-T|ISDB-T]] in [[Japan]]. However, the [[Federal Communications Commission|FCC]] has always held that 8VSB is the better modulation for use in U.S. digital television broadcasting. In a 1999 report, the Commission found that 8VSB has better threshold or carrier-to-noise (C/N) performance, has a higher data rate capability, requires less transmitter power for equivalent coverage, and is more robust to impulse and phase noise.<ref>{{Citation
  | title = DTV REPORT ON COFDM AND 8-VSB PERFORMANCE
  | url = http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/reports/dtvreprt.pdf
  | publisher = FCC Office of Engineering and Technology
  | access-date = 2007-03-04
  | archive-url= https://web.archive.org/web/20070414182411/http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/reports/dtvreprt.pdf| archive-date= 14 April 2007 | url-status= live}}, September 30, 1999.
</ref> As a result, it denied in 2000 a petition for rulemaking from [[Sinclair Broadcast Group]] requesting that broadcasters be allowed to choose between 8VSB or COFDM as is most appropriate for their area of coverage.<ref>{{Citation
 |title=Sinclair Claims Wide Support For Dtv Petition 
 |url=http://findarticles.com/p/articles/mi_m3169/is_41_19/ai_56290133
 |archive-url=https://web.archive.org/web/20040902074405/http://www.findarticles.com/p/articles/mi_m3169/is_41_19/ai_56290133
 |url-status=dead
 |archive-date=2004-09-02
 |publisher=Television Digest with Consumer Electronics 
 |access-date=2008-06-06 
 |year=1999 
}}, Oct 11, 1999.
</ref>
The FCC report also acknowledged that COFDM would "generally be expected to perform better in situations where there is dynamic multipath," such as mobile operation or in the presence of trees that are moving in high winds. However, with the introduction of 5th Generation demodulators in 2005 and subsequent improvements in generations 6 and 7, the equalization span is now about −60 to +75 microseconds (a 135 microsecond spread) and has virtually eliminated multipath, both static and dynamic, in 8VSB reception. In comparison, the equalization span in COFDM is −100 to +100 microseconds (200 microsecond spread), but the application of this much guard band space for COFDM substantially reduces its useful payload. In fact, much of Europe has adopted 1280×720p as its HD standard for DVB-T1 because of its reduced payload capacity{{citation needed|date=August 2014}}. The introduction of DVB-T2 is meant to increase the ability of terrestrial transmissions to carry 1920×1080p content. 1920×1080i has always been part of the 8VSB scheme from its inception, and its improved demodulators have had no effect on its innate payload capacity{{citation needed|date=August 2014}}.

Because of continued adoption of the 8VSB-based ATSC standard in the U.S., and a large growing ATSC receiver population, a switch to COFDM will be challenging. Most analog terrestrial transmissions in the US were turned off in June 2009, and 8VSB tuners are common to all new TVs, further complicating a future transition to COFDM.

However, with the development of [[ATSC 3.0]], an updated version of the American digital television standard designed for mobile reception and better single frequency network performance, [[Advanced Television Systems Committee|the ATSC]] has decided to make the switch to OFDM with [[Low-density parity-check code|LDPC]] error correction (essentially COFDM).<ref>{{cite web|date=8 March 2021|title=ATSC 3.0 Technical overview|url=https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/ATSC_3_po_folded_en_3607-4093-82__v0100.pdf|url-status=live|archive-url=https://web.archive.org/web/20210308155634/https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/ATSC_3_po_folded_en_3607-4093-82__v0100.pdf|archive-date=8 March 2021|access-date=8 March 2021|website=Rohde & Schwarz}}</ref> As a result, ATSC 3.0 will be incompatible with all current ATSC 1.0 receivers, and viewers will need a new TV with a compatible tuner or a converter box.<ref>{{cite web |last1=Cohen |first1=Simon |title=ATSC 3.0: Everything you need to know about broadcast TV's next big thing |url=https://www.digitaltrends.com/home-theater/atsc-3-0-ota-broadcast-standard-4k-dolby-atmos/ |website=Digital Trends |date=9 January 2020 |publisher=Designtechnica Corporation |access-date=8 March 2021 |archive-url=https://web.archive.org/web/20201129055050/https://www.digitaltrends.com/home-theater/atsc-3-0-ota-broadcast-standard-4k-dolby-atmos/ |archive-date=29 November 2020}}</ref> Unlike the previous digital TV transition which was mandated by the FCC, the "transition" to ATSC 3.0 will be completely voluntary. Additionally, the FCC has required that broadcasters who decided to make the switch to ATSC 3.0 continue to make their main channel available through a simulcast agreement with another in-market station (with a similar coverage area) through at least 2022.<ref>{{cite web |title=Report and Order and Further Notice of Proposed Rulemaking |url=https://docs.fcc.gov/public/attachments/FCC-17-158A1.docx |website=Federal Communications Commission |access-date=8 March 2021 |archive-url=https://web.archive.org/web/20201018191123/https://docs.fcc.gov/public/attachments/FCC-17-158A1.docx |archive-date=18 October 2020 |date=20 November 2017}}</ref> Sinclair announced an intention to bring ATSC 3.0 to 40 cities by 2020.<ref>{{cite web |last1=Munson |first1=Ben |title=Sinclair announces 40 U.S. cities getting ATSC 3.0 by 2020 |url=https://www.fiercevideo.com/video/sinclair-announces-40-u-s-cities-getting-atsc-3-0-by-2020 |website=Fierce Video |access-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308162446/https://www.fiercevideo.com/video/sinclair-announces-40-u-s-cities-getting-atsc-3-0-by-2020 |archive-date=8 March 2021 |date=8 April 2019}}</ref>

== 8VSB vs COFDM ==
The previously cited FCC Report also found that COFDM has better performance in dynamic and high level static multipath situations, and offers advantages for single frequency networks and mobile reception. Nonetheless, in  2001, a technical report compiled by the COFDM Technical Group concluded that COFDM did not offer any significant advantages over 8VSB. The report recommended in conclusion that receivers be linked to outdoor antennas raised to roughly 30 feet (9 m) in height. Neither 8VSB nor COFDM performed acceptably in most indoor test installations.<ref name="comparison">[http://www.hdtvmagazine.com/archives/mstvtestsum.html 8VSB/COFDM Comparison Report] {{webarchive|url=https://web.archive.org/web/20051122132418/http://www.hdtvmagazine.com/archives/mstvtestsum.html |date=2005-11-22 }}</ref>

However, there were questions{{who|date=August 2014}} whether the COFDM receiver selected for these tests − a transmitter monitor [http://www.computermodules.com/pdf/dtvm2000t.pdf] {{Webarchive|url=https://web.archive.org/web/20070927234316/http://www.computermodules.com/pdf/dtvm2000t.pdf |date=2007-09-27 }} lacking normal front end filtering − colored these results. Retests that were performed using the same COFDM receivers with the addition of a front end band pass filter gave much improved results for the DVB-T receiver, but further testing was not pursued.[http://www.sbgi.net/dtv/newer/Receiver%20Anamoly%20Retest.pdf]{{dead link|date=June 2017 |bot=InternetArchiveBot |fix-attempted=yes }}

The debate over 8VSB versus COFDM modulation is still ongoing. Proponents of COFDM argue that it resists multipath far better than 8VSB. This is important property of the modulation for receiving HDTV in e.g. moving vehicles that is not possible with 8VSB. Early 8VSB [[Digital television|DTV]] (digital television) receivers often had difficulty receiving a signal in urban environments. Newer 8VSB receivers, however, are better at dealing with multipath, but a moving receiver can still not receive the signal. Moreover, 8VSB modulation requires less power to transmit a signal the same distance. In less populated areas, 8VSB may outperform COFDM because of this. However, in some urban areas, as well as for mobile use, COFDM may offer better reception than 8VSB. Several "enhanced" VSB systems were in development, most notably [[E-VSB]], [[A-VSB]], and [[MPH (ATSC)|MPH]]. The deficiencies in 8VSB in regards to multipath reception can be dealt with by using additional forward error-correcting codes which decreases the useful bit rate, such as that used by [[ATSC-M/H]] for Mobile/Handheld reception. [[ATSC 3.0]], the next major television standard in the United States, will use COFDM.

The vast majority of U.S. TV stations use COFDM for their studio to transmitter links and news gathering operations{{citation needed|date=August 2014}}. These are point-to-point communication links and not broadcast transmissions.

==See also==
*[[ATSC tuner]]
*[[ATSC-M/H]] for Mobile/Handheld receivers

==References==
<references />

== External links ==
* [http://www.arrl.org/files/file/Technology/TV_Channels/8_Bit_VSB.pdf What exactly is 8-VSB anyway?]

{{North American DTV}}
[[Category:ATSC]]
[[Category:Radio modulation modes]]
[[Category:Digital television]]