HDTV (High Definition Television)

HDTV History Early 1980’s: –Japan created analog HDTV Mid-1980s: –US, trying to stay competitive, decided to go digital –Congress gave stations a separate channel for transition to digital broadcast with the goal of all stations using digital broadcasts by 2006.

Currently... Less than 1% of US homes have HDTV capabilities Approximately 11% of stations have digital broadcasts

Digital Broadcasts Digital TV is not necessarily HDTV FCC only mandates transmission of digital television, not HDTV Several broadcasters use multicasting instead of transmitting HDTV

Multicasting By using lower-definition signals, one channel can be split into several channels Extra channels used for: –information services (datacasting) –music –Internet services

HDTV Standards 8-VSB (vestigial side band) –US, Canada, South Korea, Taiwan, Argentina DVB-T (digital video broadcasting- terrestrial) –Europe, Australia –Japan uses a system similar to DVB-T

HDTV Features Provides up to 60 frames/sec screen writing rate Uses MPEG-2 data compression –source info data rate is 1.2Gbps –broadcast data rate is 20Mbps Square pixels 1/4 the size of analog TV’s pixels

High definition studio video to Over-the-air broadcast form Two stages of processing needed: –MPEG-2 encoding –8-VSB modulation

MPEG-2 Encoding Discrete cosine transform Run length encoding Bi-directional motion prediction Multiplexes compressed video information together with pre-coded Dolby AC-3 audio

8-VSB Source:

HDTV Types HDTV or Digital-ready TV 16:9 aspect ratio (width:height) Displays: –720-line progressive scan signal OR –1080-line interlaced signal

Interlaced TV camera captures an image of 480 lines every 1/60th of a second Allocated broadcast spectrum isn’t wide enough, so signal is compressed by discarding 1/2 of the lines Transmits at 30 frames/sec with 2 fields/frame Fields alternate every other resolution line

Progressive Lines of picture transmitted consecutively one line after another rather than 2 overlapping fields Like computer monitor

Digital Cable Conventional cable broadcasts analog signal Digital cable broadcasts digital signal to provide higher quality picture/sound Digital cable is incompatible with digital signal used for HDTV HDTV signal received through satellite dish, conventional cable, or antenna

Future of Digital TV May 2002: All commercial stations must begin digital broadcasts May 2003: All stations (commercial & non- commercial) must begin digital broadcast May 2006: Analog TV signals completely eliminated