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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.

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Digital TV Standard

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  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)

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