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1seg (ワンセグ wansegu) is a mobile terrestrial digital audio/video and data broadcasting service in Japan and Brazil. Service began experimentally during 2005 and commercially on April 1, 2006. In Brazil the broadcast started in late 2007 in just a few cities, with a slight difference from Japanese 1seg: a 30 frame/s transmission, while in Japan they use a 15 frame/s transmission. The first mobile phone handsets for 1seg were sold by KDDI to consumers in autumn 2005. ISDB-T, the terrestrial digital broadcast system used in Japan and Brazil, is designed so that each channel is divided into 13 segments, with a further segment separating it from the next channel. An HDTV broadcast signal occupies 12 segments, leaving the remaining (13th) segment for mobile receivers. Thus the name, "1seg" or "One Seg".
[edit] Technical informationMain article: ISDB  The ISDB-T system uses the UHF band at frequencies between 470 and 770 MHz (806MHz in Brazil), giving a total bandwidth 300 MHz. The bandwidth is divided into fifty channels name channels 13 through 62. Each channel is 6 MHz wide consisting of a 5.57 MHz wide signalling band and a 430 kHz guard band to limit cross channel interference. Each of these channels is further divided into 13 segments, with each with 428 kHz of bandwidth. 1 seg uses a single of these segments to carry the 1seg transport stream. 1seg, like ISDB-T uses QPSK for modulation, with 2/3 forward error correction and 1/4 guard ratio. The total datarate is 416 kbit/s. The television system uses a H.264/MPEG-4 AVC video stream and a HE-AAC audio stream multiplexed into a MPEG-2 Transport Stream. The maximum video resolution is 320x240 pixels, with a video bitrate of between 220 and 320 kbit/s. Audio conforms to HE-AAC profile, with a bitrate of 48 to 64 kbit/s. Additional data (EPG, interactive services, etc) is transmitteed using BML and occupies the remaining 10 to 100 kbit/s of bandwidth. Conditional access and copy control are implemented in 1seg broadcasting by the use of Broadcast Flag-like structure contained in the "Copy Control Descriptor" within the broadcast. The broadcast contents themselves are not encrypted, but the Copy Control information forces the device to encrypt stored recordings and disallows making a copy of the recording. [edit] Broadcast Markup LanguageBroadcast Markup Language (BML), is a data-transmission service allowing text to be displayed on a 1seg TV screen. The text contains news, sports, weather forecasts, , "Earthquake Early Warning", etc. free of charge. Further information can be found through links to content on websites, frequently those belonging to the television station itself. EPG (program guides) is not included, but transmitted in separate stream(EIT). [edit] Multiple-program arrangementOn June 23, 2008, broadcaster Tokyo MX officially began using multiple-program arrangement (マルチ編成 Maruchi hensei) technology to simultaneously broadcast two programs on a single divided segment. Most 1seg receivers manufactured after September 2008 are compatible with this technology. [edit] Criticism
Mobile reception is difficult, especially in a moving vehicle/train, as the signal quality deteriorates quickly even at speeds around 20 km/h (12 mph). This leaves the majority of the target audience for this service unable to receive it. In-car or vehicles reception requires use of diversity antenna and increases the receiver's complexity and price. There is minimal to no reception in trains that are underground or go inside buildings, such as most of the commuter trains in Tokyo and other cities.[1] In addition, long distance trains, especially the shinkansen, can move between broadcast service areas in a matter of half an hour. Each broadcast region uses different frequencies for a particular channel, requiring the viewer to regularly re-scan or pick from a table of stored frequencies to find whatever local channel may be broadcasting the program in question. 1seg is a part of UHF band of approx. 429 MHz bandwidths and inherently susceptible by various atmospheric conditions as with UHF. Handheld 1seg receivers work well inside homes, although it may be necessary to be near a window and/or adjust the antenna for reception. 1seg was however developed as a mobile technology, and the relevance of watching it at home is reduced since the majority of viewers could watch the program on a larger high-definition screen TV instead. [edit] PopularityUntil end of March 2008, Japanese regulation enforced that the programs on 1seg are fundamentally the same as those broadcast on the equivalent HDTV channel, then regulation revised from April 1, 1seg own or independent program partially or experimentally started by several number of stations. On 2008-01-16, JEITA learned that the result of their monthly shipping out quantity survey showed approx. 4.806 million mobile phones were sold in Japan in November 2007. Of these, approx. 3.054 million phones, 63.5% of the total, can receive 1seg broadcasts. [2] In fiscal year 2007, total average 45.0% of mobile phone has 1seg reception capability out of 22.284 million units sold, the percent has been increased 26.8% in April 2007 to 64.2% at end of fiscal year March 2008.[3] [edit] Receivers 
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