1seg

1seg, also known as One Seg or ワンセグ, is a mobile-oriented terrestrial digital broadcasting service associated with Japan's ISDB-T digital television system. It is not a conventional consumer-goods brand or a single broadcaster; rather, it is a technical and service layer that enables television, audio and supplementary data to be transmitted to portable receivers. The service was designed for mobile phones and other compact devices while using the same terrestrial broadcast infrastructure as fixed digital television. The name refers to the structure of an ISDB-T channel. Each channel is divided into 13 segments. A high-definition television service normally uses 12 of those segments, leaving one segment available for a lower-bandwidth transmission intended for mobile reception. That single-segment arrangement gives the service its name. The design allows broadcasters to provide a mobile stream without requiring a separate frequency allocation, while receivers can operate with comparatively small antennas and modest processing requirements. Experimental transmissions began in Japan during 2005, and regular commercial service started on April 1, 2006. The first consumer mobile phone identified as supporting 1seg was the Sanyo W33SA, sold through au by KDDI in autumn 2005. During the following decade, 1seg became a common feature of Japanese feature phones, carrier-branded Android devices and a variety of portable electronics. Compatible products included mobile phones, car-navigation systems, portable televisions, electronic dictionaries, personal-computer receivers, set-top boxes, handheld-game accessories and media players. The service carried television pictures and sound, but its value also came from associated data services. Broadcast Markup Language, or BML, could deliver text-based news, sports information, weather forecasts, emergency notices and links to broadcaster-operated online content. Earthquake early-warning information was among the types of public-safety information that could be distributed through the system. Electronic program information was transmitted separately through the broadcast data structure. Copy-control information could also be included, allowing devices to restrict copying or encrypt stored recordings. Technically, 1seg uses one 428 kHz segment of an ISDB-T channel. The reference implementation uses QPSK modulation, forward-error correction and a guard interval suited to mobile reception. Video is encoded using H.264/MPEG-4 AVC and audio using HE-AAC, with a maximum video resolution of 320 by 240 pixels. The available transport capacity is limited compared with a fixed high-definition broadcast, but the reduced data requirement supports reception on mobile and portable hardware. Japan remained the principal market and the service became especially visible through its integration into feature phones. A 2007 industry survey reported that roughly 63.5 percent of mobile phones shipped in Japan during November of that year could receive 1seg; for fiscal 2007 as a whole, the average was approximately 45 percent. Regulatory rules initially required mobile programs to be substantially the same as those on the corresponding high-definition channel. A revision effective April 1, 2008 permitted more experimental and independently designed mobile programming. The service also spread internationally through adaptations of ISDB-T. Brazil adopted a related ISDB-Tb implementation and began using 1seg commercially in late 2007, initially in a limited number of cities. The Brazilian implementation used a 30-frame-per-second transmission setting, compared with the 15-frame-per-second setting used in Japan. Brazil subsequently became an important regional reference point, and other Latin American countries and the Philippines adopted ISDB-T variants that supported comparable mobile broadcasting. 1seg's importance has declined as smartphones, high-speed mobile networks, streaming video and unlimited data pl…

1seg emerged from the architecture of Japan's Integrated Services Digital Broadcasting–Terrestrial system, or ISDB-T. Unlike systems that require a separate mobile television network, ISDB-T divides each terrestrial television channel into 13 segments. A typical high-definition transmission occupies 12 segments, leaving one segment that can carry a lower-capacity stream intended for portable receivers. This design made it possible to add mobile television and related data services within the terrestrial broadcast channel plan. Experimental 1seg transmissions began in Japan in 2005. The first widely identified compatible mobile phone was the Sanyo W33SA, released through au by KDDI in autumn of that year. Commercial service began nationally on April 1, 2006. Japanese broadcasters used the service to reach mobile phones, portable televisions, car-navigation units, electronic dictionaries, personal-computer accessories and other compact devices. Reception was free at the point of use because the service was delivered over the broadcast network rather than through a mobile-data subscription. The service combined compressed video and audio with supplementary data. Its mobile stream used H.264/MPEG-4 AVC video and HE-AAC audio, with a maximum resolution of 320 by 240 pixels. Broadcast Markup Language enabled text and interactive information such as news, sports, weather, emergency messages and links to related web pages. Program-guide information was carried separately. Broadcast copy-control descriptors could instruct compatible devices to protect stored recordings and prevent unauthorized duplication. During its early growth, 1seg was closely tied to Japan's feature-phone market. A Japanese electronics-industry shipment survey reported that about 3.054 million of 4.806 million mobile phones shipped in November 2007 supported 1seg. Across fiscal 2007, approximately 45 percent of sold mobile phones had reception capability, with the proportion rising considerably during the year. These figures reflected the service's role as a standard premium feature in Japan's carrier-led handset market. Japanese regulation initially required 1seg programs to be essentially the same as those carried on the corresponding high-definition service. That restriction was relaxed from April 1, 2008, enabling more experimental and independently produced mobile programming. On June 23, 2008, Tokyo MX introduced multiple-program broadcasting, later referred to as 1seg2, allowing two programs to be transmitted through a divided mobile segment. NHK Educational TV and Nara Television subsequently used the capability for selected programming. International expansion followed the adoption of ISDB-T variants. Brazil began commercial 1seg deployment in late 2007, initially in a limited group of cities. Its ISDB-Tb implementation differed from Japan's in using a 30-frame-per-second setting rather than Japan's 15-frame-per-second setting. By 2014, digital television signals carrying 1seg were reported to cover approximately 62 percent of Brazil's population, while the government had targeted nationwide coverage by 2016. Brazil's adoption helped encourage use of related ISDB-T implementations in Argentina, Peru, Chile, Ecuador, Venezuela, Bolivia and Paraguay. The Philippines also adopted a closely related international version of the standard. The market context changed with the spread of smartphones, 4G and 5G networks, on-demand video and inexpensive or unlimited data plans. Dedicated 1seg reception was increasingly omitted from newer mobile devices, although it remained common in Japanese feature phones and many carrier-branded Android models into the 2020s. iPhone users historically needed a separate third-party antenna accessory to receive the service. In Brazil, the emergence of newer digital television initiatives is expected to create a long transition in which ISDB-T and its mobile component continue operating alongside newer technologies.

1. 2014Brazilian 1seg coverage reaches reported national scale

   Approximately 62 percent of Brazil's population is reported to be covered by digital television signals carrying 1seg.

   Source
2. 2009Additional Japanese broadcasters adopt 1seg2

   NHK Educational TV and Nara Television begin using multiple-program transmission for selected programming.

   Source
3. 2008Japanese programming rules are relaxed

   Regulatory changes allow more experimental and independently produced 1seg programming from April 1.

   Source
4. 20081seg2 multiple-program operation begins

   Tokyo MX begins transmitting two programs through a multiple-program 1seg arrangement on June 23.

   Source
5. 2007Brazil begins commercial deployment

   Brazil launches 1seg through its ISDB-Tb digital television system, initially in selected cities.

   Source
6. 2006Commercial service starts in Japan

   Regular commercial 1seg broadcasting begins on April 1.

   Source
7. 2005Experimental 1seg transmissions begin

   Japan conducts experimental transmissions of the mobile ISDB-T service.

   Source
8. 2005First 1seg-compatible mobile phone reaches consumers

   The Sanyo W33SA, sold through au by KDDI, becomes the first identified consumer mobile phone with 1seg reception.

   Source

A low-bandwidth, broadcast-based mobile extension of ISDB-T that provides free television, audio and data services to portable receivers.

• 1seg mobile televisionMobile terrestrial television2006

  The core service transmits a compact television stream through one segment of an ISDB-T terrestrial channel. It is optimized for mobile and portable reception, using low-resolution H.264 video and HE-AAC audio alongside error-correction techniques intended to improve reception while devices are moving.

• BML data broadcastingBroadcast data service

  Broadcast Markup Language supports text and interactive information delivered with 1seg programming. Typical uses include news, weather, sports information, emergency warnings and links to broadcaster websites. The data layer adds public-information and interactive functions without requiring a separate internet connection for the initial broadcast.

• 1seg2Multiple-program broadcasting2008

  1seg2 is the name used for multiple-program operation on the mobile service. It allows a broadcaster to transmit two programs using a divided segment arrangement. Tokyo MX introduced the capability in 2008, and later receivers manufactured in Japan were increasingly designed to support it.

• 2008Japan permits differentiated 1seg programmingStrategy

  The original regulatory framework generally required mobile programs to match the equivalent HDTV service, limiting the scope for mobile-specific content.

  What changed. From April 1, Japan revised the rules to permit experimental and third-party 1seg programming.

  Aftermath. The change expanded the editorial and programming possibilities for broadcasters using the mobile service.

  Source
• 2008Introduction of 1seg2 multiple-program broadcastingProduct launch

  Broadcasters sought to use the mobile segment more flexibly while continuing to operate within the ISDB-T channel structure.

  What changed. Tokyo MX launched simultaneous multiple-program transmission on June 23, using the format later called 1seg2.

  Aftermath. Compatible receivers could access two programs transmitted through the divided mobile allocation; NHK Educational TV and Nara Television later adopted the capability for selected programs.

  Source

• 2008Tokyo MX introduces 1seg2 multiple-program broadcasting

  Tokyo MX began using multiple-program transmission on June 23, allowing two programs to be carried through a divided 1seg arrangement.

  Product generation
  Source
• 2008Japanese rules permit more independent 1seg programming

  A regulatory revision taking effect April 1 allowed experimental and third-party programming to move beyond the previous requirement that 1seg content fundamentally mirror the associated HDTV broadcast.

  Regulation
  Source
• 20071seg expands through Brazil's digital television rollout

  Brazil began commercial use of 1seg in late 2007, initially in selected cities, using the country's ISDB-Tb digital television implementation.

  Product launch
  Source
• 20061seg commercial broadcasting begins in Japan

  Regular commercial 1seg broadcasting began in Japan on April 1, following experimental transmissions in 2005.

  Product launch
  Source

1. 1seg