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 videoto

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: www.broadcast.harris.com/customer-service/8-vsb.html

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