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 audio encapsulated in MPEG2 Transport Stream. 1seg, like ISDB-T also uses 64QAM for modulation, 1/2 FEC and 1/8 guard ratio. Maximum video resolution is 320x240 pixels, and maximum video bitrate is 128 kbit/s. Audio conforms to AAC-LC profile, with max bitrate of 64 kbit/s. Additional data broadcasting using BML (EPG, interactive services, etc) occupies the remaining 60 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

Almost a year after 1seg trial started, the purpose of 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. This leaves majority of the target audience for this service unable to receive it. In-car reception requires use of diversity antenna and increases receiver compexity and price. Even though 1seg signal is not encrypted, every receiver manufacturer chose to apply DRM, preventing users from archiving or editing 1seg contents, which is quite an unfortunate decision, considering the quality of received video is similar to that available nearly 10 years ago from VIVO.