1seg

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Official 1seg logo

1seg (Katakana: ワンセグ) is a mobile terrestrial digital audio/video and data broadcasting service in Japan. Service began experimentally during 2005 and officially on April 1, 2006. First mobile phone handsets for 1seg were sold by KDDI to consumers in autumn 2005.

Terrestrial digital broadcast in Japan (ISDB-T) is designed so that each channel is divided into 13 segments (plus one segment for separating channels). HDTV broadcast occupies 12 segments, and the remaining (13th) one segment is used for mobile receivers. Thus the name, '1seg'.

1 Technical information
2 Criticism
3 Receivers
4 See also
5 External links

[edit] Technical information

1seg broadcasting uses H.264 video and AAC+SBR audio encapsulated in MPEG2 Transport Stream. 1seg, like ISDB-T also uses QPSK for modulation, 2/3 FEC and 1/4 guard ratio. Total bit-rate is 416kbps. Maximum video resolution is 320x240 pixels, video bitrate is 220-320 kbit/s. Audio conforms to AAC+SBR profile, with bitrate of 48-64 kbit/s. Additional data broadcasting using BML (EPG, interactive services, etc) occupies the remaining 10-100 kbit/s.

Conditonal access and copy control is not implemented in 1seg broadcast, however each receiver device manufacturer can limit recording function. For example, W33SA receiver only allows recording 1seg broadcasts to internal memory, and disallows copy or move to external miniSD card.

[edit] Criticism

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Almost a year after the 1seg trial started, the purpose of the service is still unclear. Mobile reception is difficult, especially in a moving vehicle/train, as the signal quality deteriorates quickly even at speeds around 20km/h (12 MPH). This leaves the majority of the target audience for this service unable to receive it. In-car reception requires use of diversity antenna and increases receiver complexity and price.

Handheld 1seg receivers generally do not work well at all in moving cars or trains, even when held by a window because the signal drops out every few seconds. There is minimal or no reception in trains that are underground, or go inside buildings, such as most of the commuter trains in Tokyo. In addition, long distance trains, especially the shinkansen, move from one service area to another in a matter of minutes, making it impossible to view a program to completion before having to scan for a new set of channels and find whatever local channel may be broadcasting the program in question.

Handheld 1seg receivers work well inside homes, although it may be necessary to be near a window and/or adjust the antenna for reception. However, a home user can watch HDTV on a large screen TV instead of a 320x180 small screen 1seg.

Even though 1seg signal is not encrypted, every receiver manufacturer chose to apply DRM, preventing users from archiving or editing 1seg contents.