Editing Orthogonal frequency-division multiplexing (section)

=== Terrestrial digital radio and television broadcasting ===
Much of Europe and Asia has adopted OFDM for terrestrial broadcasting of digital television ([[DVB-T]], [[DVB-H]] and [[T-DMB]]) and radio ([[EUREKA 147]] [[Digital Audio Broadcasting|DAB]], [[Digital Radio Mondiale]], [[HD Radio]] and [[T-DMB]]).

==== DVB-T ====
By Directive of the European Commission, all television services transmitted to viewers in the European Community must use a transmission system that has been standardized by a recognized European standardization body,<ref>{{cite web|url=http://ec.europa.eu/archives/ISPO/infosoc/legreg/docs/dir95-47en.html|title=DIRECTIVE 95/47/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on the use of standards for the transmission of television signals|website=ec.europa.eu}}</ref> and such a standard has been developed and codified by the DVB Project, ''Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television''.<ref>ETSI Standard: EN 300 744 V1.5.1 (2004-11).</ref> Customarily referred to as DVB-T, the standard calls for the exclusive use of COFDM for modulation. DVB-T is now widely used in Europe and elsewhere for terrestrial digital TV.

==== SDARS ====
The ground segments of the [[Digital Audio Radio Service]] (SDARS) systems used by [[XM Satellite Radio]] and [[Sirius Satellite Radio]] are transmitted using Coded OFDM (COFDM).<ref>{{cite web |website=EE Times |author=Junko Yoshida |date=June 28, 2001 |url=https://www.eetimes.com/agere-gets-sirius-about-satellite-radio-design/ |title=Agere gets Sirius about satellite radio design}}</ref> The word "coded" comes from the use of [[forward error correction]] (FEC).<ref name=cobas />

==== COFDM vs VSB ====

The question of the relative technical merits of COFDM versus [[8VSB]] for terrestrial [[digital television]] has been a subject of some controversy, especially between European and North American technologists and regulators. The [[United States]] has rejected several proposals to adopt the COFDM-based [[DVB-T]] system for its digital television services, and for many years has opted to use [[8VSB]] ([[vestigial sideband modulation]]) exclusively for terrestrial digital television.<ref>{{Cite web|last=Lung|first=Doug|date=2001-01-01|title=8-VSB vs. COFDM: The Debate Continues|url=https://www.tvtechnology.com/opinions/8vsb-vs-cofdm-the-debate-continues|access-date=2021-11-18|website=TVTechnology|language=en}}</ref> However, in November 2017, the [[Federal Communications Commission|FCC]] approved a voluntary transition to [[ATSC 3.0]], a new broadcast standard which is based on COFDM. Unlike the first digital television transition in America, TV stations will not be assigned separate frequencies to transmit ATSC 3.0 and are not required to switch to ATSC 3.0 by any deadline. Televisions sold in the U.S. are also not required to include ATSC 3.0 tuning capabilities. Full-powered television stations are permitted to make the switch to ATSC 3.0, as long as they continue to make their main channel available through a simulcast agreement with another in-market station (with a similar coverage area) through at least November 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>

One of the major benefits provided by COFDM is in rendering radio broadcasts relatively immune to [[multipath interference|multipath]] distortion and signal [[fading]] due to atmospheric conditions or passing aircraft. Proponents of COFDM argue it resists multipath far better than 8VSB. Early 8VSB [[digital television|DTV]] (digital television) receivers often had difficulty receiving a signal. Also, COFDM allows [[single-frequency network]]s, which is not possible with 8VSB.

However, newer 8VSB receivers are far better at dealing with multipath, hence the difference in performance may diminish with advances in equalizer design.<ref>{{Cite web|last=TVTechnology|date=2008-04-11|title=Distortions and 8-VSB|url=https://www.tvtechnology.com/news/distortions-and-8vsb|access-date=2021-11-18|website=TVTechnology|language=en}}</ref>

====Digital radio====
<!-- This section is linked from [[Digital Audio Broadcasting]] -->
COFDM is also used for other radio standards, for [[Digital Audio Broadcasting]] (DAB), the standard for digital audio broadcasting at [[VHF]] frequencies, for [[Digital Radio Mondiale]] (DRM), the standard for digital broadcasting at [[shortwave]] and [[medium wave]] frequencies (below 30&nbsp;MHz) and for [[Digital Radio Mondiale#DRM Plus|DRM+]] a more recently introduced standard for digital audio broadcasting at [[VHF]] frequencies. (30 to 174&nbsp;MHz)

The United States again uses an alternate standard, a proprietary system developed by [[iBiquity]] dubbed ''[[HD Radio]]''. However, it uses COFDM as the underlying broadcast technology to add digital audio to AM (medium wave) and FM broadcasts.

Both Digital Radio Mondiale and HD Radio are classified as [[in-band on-channel]] systems, unlike Eureka 147 (DAB: [[Digital Audio Broadcasting]]) which uses separate VHF or [[Ultra high frequency|UHF]] frequency bands instead.

====BST-OFDM used in ISDB====
The ''band-segmented transmission orthogonal frequency-division multiplexing'' (''BST-OFDM'') system proposed for Japan (in the [[ISDB-T]], [[ISDB-TSB]], and [[ISDB-C]] broadcasting systems) improves upon COFDM by exploiting the fact that some OFDM carriers may be modulated differently from others within the same multiplex. Some forms of COFDM already offer this kind of [[hierarchical modulation]], though BST-OFDM is intended to make it more flexible. The 6&nbsp;MHz television channel may therefore be "segmented", with different segments being modulated differently and used for different services.

It is possible, for example, to send an audio service on a segment that includes a segment composed of a number of carriers, a data service on another segment and a television service on yet another segment—all within the same 6&nbsp;MHz television channel. Furthermore, these may be modulated with different parameters so that, for example, the audio and data services could be optimized for mobile reception, while the television service is optimized for stationary reception in a high-multipath environment.