1 / 18

Digital TV Standard

Digital TV Standard. NOV,26,2002 梁凱雯. Analog v.s. Digital TV. Introduction to Digital TV (1/3). What is Digital TV ? Access and display the TV programs with digital signals. Advantages: Higher resolution than the conventional analog TV. Why?. 格式. 水平掃描線數. 水平畫素數.

mayda
Download Presentation

Digital TV Standard

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Digital TV Standard NOV,26,2002 梁凱雯

  2. Analog v.s. Digital TV

  3. Introduction to Digital TV (1/3) • What is Digital TV ? Access and display the TV programs with digital signals. • Advantages: • Higher resolution than the conventional analog TV. Why?

  4. 格式 水平掃描線數 水平畫素數 寬高比 掃描方式 圖框速率(fps) HDTV 1080p 1080 1920 16:9 循序式 24 1080p 1080 1920 16:9 循序式 30 1080i 1080 1920 16:9 交錯式 30 720p 720 1280 16:9 循序式 24 720p 720 1280 16:9 循序式 30 720p 720 1280 16:9 循序式 60 EDTV 480p 480 704 16:9 循序式 24 480p 480 704 16:9 循序式 30 480p 480 704 16:9 循序式 60 480p 480 704 4:3 循序式 24 480p 480 704 4:3 循序式 30 480p 480 704 4:3 循序式 60 480p 480 640 4:3 循序式 24 480p 480 640 4:3 循序式 30 480p 480 640 4:3 循序式 60 SDTV 480i 480 704 16:9 交錯式 30 480i 480 704 4:3 交錯式 30 480i 480 640 4:3 交錯式 30 Introduction to Digital TV (2/3) • ATSC數位電視標準18種畫面格式 • 高畫質數位電視( HDTV : High definition television ) • 加強畫質數位電視( EDTV : Enhanced definition television ) • 標準畫質數位電視( SDTV : Standard definition television )

  5. Introduction to Digital TV (3/3) • Advantages: • Better performance in audio quality. How? • More efficient in bandwidth utilization. • Additional services with data broadcasting. • Special program coding. • Video on demand. • EPG ( electronic program guide ). • The advantages of digital TV broadcasting system come from the channel coding and digital modulation!

  6. Digital Terrestrial Television Broadcasting • Digital TV programs can be transmitted by cable ,satellite ,terrestrial ,and wireless cable. • Three terrestrial standard: • ATSC ( Advanced TV system committee ) 1996,USA • DVB-T ( Digital Video Broadcasting Terrestrial ) 1997,European Adopted in Australia,New Zealand,Latin America,Singapore, Taiwan ( 2001,6 ) • ISDBT-T( Integrated Service Digital Broadcasting Terrestrial) 1999,Japan

  7. DVB system scheme

  8. Channel coding (1/3) • Randomizer • To avoid the unexpected results in the time recovery process of the receiver. • Outer coder • Reed-Solomon code • With the error correcting capability to random noise. • Outer Interleaver • When burst error occurr.RS code becomes invalid in correcting. • Interleaver divided the data in the same MPEG2 packet into different packets.

  9. Channel coding (2/3) • Inner Coder • To protect the data from serious noise and disturbance transmitting media.

  10. Channel coding (3/3) • Inner Interleaver • 內交錯器共有兩種工作模式:非層次結構(non-hierarchical) 模式和層次結構(hierarchical) 模式 • 包括一個以位元為處理單位的位元交錯器(bit interleaver)與以符號(symbol)為處理單位的符號交錯器(symbol interleaver) • 資訊傳送之前將會編碼成QPSK (Quadrature Phase Shift Keying)、16-QAM (Quadrature Amplitude Modulation)或64-QAM等二維訊號。 • 符號交錯器則是將各個符號對應到(mapping) OFDM符號中不同的次載波(sub-carrier)。

  11. OFDM信號由多個載波構成,在2k模式是1705個,在8k模式是6817個。一般來說,載波信號之間的分隔必須保証載波信號適合6MHz、7MHz或8MHz信道的要求。上述載波信號包括: 1. 節目資訊數據:每個載波信號的位數可變(2、4或6位); 2.傳輸參數信令(TPS):傳輸與信道編碼和調制參數有關的資訊; 3.導頻信號:用於接收機同步。該信號在比其它載波信號高的功率電平上發射,它包括以下兩種類型:(a)連續導頻:8k模式為177個,2k模式為45個; (b)散佈導頻:8k模式為524個,2k模式為131個。 OFDM信號的頻譜由681 7個(8k模式)或1705個(2k模式)不同頻率的單頻離散載波組成,可見,這些頻率要藉由一定時間的傳輸才能到達接收機,其時域分佈如圖3所示,發送所有載波信號的這段特定時間,稱之為有用數據周期Tu。有用數據的一部份會重复傳輸,且在Tu之前發送,這段時間稱作保護間隔,其主要目的是消除回波和反射干擾。這些回波干擾是多徑信號,會在電視上造成重影。正是由於COFDM具備消除回波的功能,使其比8-VSB系統更具優勢,它可用於向移動電視接收機傳輸電視信號。目前,人們又把這一結構稱為OFDM符號,如圖3所示,OFDM幀由68個OFDM符號組成,4個OFDM幀構成一個OFDM超級幀。 MODULATION---OFDM • Multi-Carrier Modulation • Orthogonal sub-carriers with lower bit rate

  12. MODULATION---OFDM • OFDM信號由多個載波構成,在2k模式是1705個,在8k模式是6817個。一般來說,載波信號之間的分隔必須保証載波信號適合6MHz、7MHz或8MHz信道的要求。上述載波信號包括: • 1. 節目資訊數據:每個載波信號的位數可變(2、4或6位); • 2.傳輸參數信令(TPS):傳輸與信道編碼和調制參數有關的資訊; • 3.導頻信號:用於接收機同步。該信號在比其它載波信號高的功率電平上發射,它包括以下兩種類型: • (a)連續導頻:8k模式為177個,2k模式為45個; • (b)散佈導頻:8k模式為524個,2k模式為131個。

  13. MODULATION---OFDM (continue)

  14. ATSC v.s. DVB-T

  15. ATSC v.s. DVB-T • Frequency efficiency • OFDM ---multi carrier modulation has more frequency efficiency than the single carrier modulation , VSB. • For 6 MHZ channel • DVB-T effective bandwidth=5.7MHZ(5.7/6=95%) ATSC effective bandwidth=5.38MHZ(5.38/6=90%) • But the OFDM transmission system finally becomes the worse case in the frequency utilization. WHY?

  16. ATSC v.s. DVB-T • Multi-path interference • ATSC receiver contains an adaptive equalizer to reduced the effects of multipath interference. • DVB-T receiver contains a channel estimator which helps it reject interference such as multipath. • The pilot signals and the time interval preserved are the main concern of the DVB-T,it makes the DVB-T system has advantages than the ATSC 8-VSB system in the multipath interference.

  17. Conclusion • DTV將成為視訊廣播系統的主流是可預期的趨勢。 • 數位電視廣播提供了較佳的畫面品質與更好的音質,有更佳的頻譜使用效率,此外,能夠提供各種數據服務。 • 由於地面廣播的通道特性變化劇烈,系統容易不穩定,信號之振幅,相位容易受到多路徑延遲的影響,歐規之DVB-T系統對此的表現較美規ATSC來的好,台灣已決定採用 DVB-T 作為地面廣播的標準。

  18. References • 數位視訊多媒體月刊2002,8 • http//:www.dvb.com.tw • http//:www.wmr.com/html/Fact_about_DVB-T.htm • ATSC Implementation Subcommittee Informational Document. • Measurement guidelines for DVB system,ETSI TR 101 290 v1.2.1(2001,5)

More Related