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Current Performance of DVB-T Demodulators

Explore the current performance of DVB-T demodulators through standardized testing and field analysis. Learn about OFDM parameters, signal spectra, multipath performance, immunity against interference, and the significance of field testing. Discover key insights for enhancing demodulator efficiency.

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Current Performance of DVB-T Demodulators

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  1. Current Performance of DVB-TDemodulators Min-Chen Ho ITE Tech, Inc.

  2. Outline • DVB-T Physical Layer – EN 300744 • Standardized DVB-T Testing • DVB-T Field Testing

  3. DVB-T Physical Layer – EN300744

  4. Block Diagram from EN 300 744 (204,188) Reed-Solomon 64-state R=1/2 convolutional code QPSK, 16QAM, 64QAM

  5. DVB Transmission Modes • There are many modes in DVB transmission • Bandwidth: 5MHz, 6MHz, 7MHz, 8MHz. • FFT Size: 2K, 4K, 8K • Modulation: QPSK, 16QAM, 64QAM, non-uniform 16QAM with =1 or =2, non-uniform 64QAM with =1, =2, or =4. • Code Rate: 1/2, 2/3, 3/4, 5/6, 7/8 • Guard Interval: 1/4, 1/8, 1/16, 1/32 • Different modes have different performance • It is very important to make sure that the correct mode is selected for testing.

  6. OFDM Parameters • Comments • Longer GI supports longer channel • For 2K, GI=1/32, the channel must be shorter than 7s • For 8K, GI=1/4, the channel can be as long as 256 s • With the same GI ratio, 8K mode can support longer channels than 2K mode. • Shorter Tu has better inter-carrier interference (ICI) tolerance • Sub-carriers are further apart when Tu is small. • 2K has better ICI tolerance than 8K. • Channel variation is a major cause of ICI, therefore 2K has better mobility support than 8K.

  7. Signal Spectra I 533 CTV 545 PTS 581 TTV 593 CTS 557 FTV 569 599

  8. Signal Spectra II

  9. Standardized DVB-T Testing

  10. Purpose of Standardized Testing • Purpose of standardized testing is to measure the performance of a DVB receiver under certain assumptions. • In practice • If these assumptions hold, then the performance of a DVB receiver can be predicted using standardized testing results. (Very rare) • If these assumptions do not hold, then standardized testing results only provides a reference. (Most of the time)

  11. Signal too strong Pmax (strong signal) Reception OK Input Signal Power C/N Bad Reception Input Signal Power Signal Power (dBm) Signal Power (dBm) Pmin (sensitivity) Reception OK Injected Noise Power Signal too weak System Noise Floor System Noise Floor Frequency Frequency AWGN Performance • AWGN assumptions • Injected noise power 和 [頻率或時間] 無關 • Signal power 和 [頻率或時間] 無關 • AWGN performance measures • C/N – 訊號強度應比雜訊強度高多少才能正常收訊 • Sensitivity (弱信號) – 訊號強度最弱可到多弱還能正常收訊 • Strong signal (強信號) – 訊號強度最強可到多少還能正常收訊

  12. P1X(t-T1) P2X(t-T2) X(t) P0X(t-T0) Receiver Transmitter Multipath Performance (Echo) • Multipath Assumptions • Injected noise power 和 [頻率或時間] 無關 • Signal power 隨 [頻率] 做某種規律之改變，但不隨時間改變 • Multipath specification • Number of echos (2-path, 3-path, etc) • Echo attenuation (P0, P1, …) and delay (T0, T1 …) • Echo channels • Inside Guard Interval ( < GI) • Outside Guard Interval ( > GI) • Performance measures • C/N • Sensitivity

  13. X(t) time P0X(t – T0) P1X(t – T1) time C/N Ave. Input Signal Power Reception OK Signal Power (dBm) Pmin (sensitivity) Input Signal Power Signal Power (dBm) Injected Noise Power Reception OK System Noise Floor System Noise Floor Frequency Frequency Multipath Performance (Echo) • Example: 2-path 0-dB echo 

  14. Desired Interferer CCI Immunity ACI Immunity Signal Power (dBm) Signal Power (dBm) Interferer Desired Channel No. Channel No. N N+1 N Immunity Against Interference – ACI and CCI • Adjacent Channel Interference (ACI) • 本身頻道符合 AWGN assumption，但其他頻道有極強之訊號 • 其他頻道之訊號如為類比電視訊號則稱為 Analog ACI • 其他頻道之訊號如為數位電視訊號則稱為 Digital ACI • Co-Channel Interference (CCI) • 本身頻道除收到符合 AWGN assumption之數位訊號外，也同時收到同頻道之類比電視訊號 • Immunity against interference – 干擾可以到多強還不會被蓋台

  15. Video Audio (FM) Color NICAM Immunity Against Interference – ACI and CCI • Example – CCI (可能發生在不同播放區的邊界) PAL BG spectrum DVB-T Signal with PAL BG

  16. DVB-T Field Testing

  17. Field Testing • Not part of standardized testing. • However, field testing is the most realistic way of performance evaluation. • Key difference between field testing and standardized lab testing • Standardized testing tests performance under certain assumptions. • Field testing tests performance in real situations. • Real situations are very different from standardized testing assumptions. Therefore: • Standardized tests 通過了並不代表在任何時間任何地點都能收訊 • Mobile performance predicted using standardized tests is very different from actual performance. • Lab 中得到的 mobile performance 數據僅能供參考用

  18. Transmitter @ London, UK • Location: Crystal Palace Park • Height: 219 m • Built: 1956 • Transmission • PAL-I Analog TV • DVB-T • FM • Measured Channel Power • p_inband ~ -40 dBm • p_total ~ -20 dBm 路測道具

  19. London Map

  20. London - Frequency Table

  21. London: UHF Spectra 506 530 538 562 578 482

  22. Transmitter @ Paris, France • Location: La Tour Eiffel • Height: 324 m • Built: 1889 • Transmission • SECAM-L Analog TV • DVB-T • FM • Measured Channel Power • p_inband ~ -40 dBm • p_total ~ -30 dBm 路測車

  23. Paris Map

  24. Paris: Frequency Table

  25. Paris: UHF Spectra (Star Hotel) 522 538 562 586 474 490 498

  26. Paris (474MHz)

  27. Transmitter @ Barcelona, Spain • Location: Torre de Collserola (on Tibidabo) • Height: 288.4 m • Built: 1992 • Transmission • PAL-B Analog TV • DVB-T • FM • Measured Channel Power • p_inband ~ -40 dBm • p_total ~ -20 dBm 路測車

  28. Barcelona Map

  29. Frequency Table (Bercelona)

  30. Barcelona: UHF Spectra 834~858 498 690 514 570 650 794 818 482

  31. Barcelona (858MHz)

  32. Transmitter @ Berlin, Germany • Location: Fernsehturm Berlin (near Alexanderplatz) • Height: 368 m • Built: 1969 • Transmission • DVB-T • FM • Measured Channel Power • p_inband ~ -40 dBm • p_total ~ -30 dBm

  33. Berlin Map

  34. Berlin: Frequency Table

  35. Berlin: VHF Spectra 177.5 N+2 DACI (191.5) 191.5: N-2 DACI (177.5) 177.5 191.5

  36. Berlin: UHF Spectra 506: N+2 DACI (522) 522: N-2 DACI (506) 570: N-6 DACI (522) 658: N-11 DACI (570) N+12 DACI (754) 506 522 570 658 754 778

  37. Berlin (506MHz)

  38. Summary – Signal Conditions

  39. Lessons Learned • Good sensitivity helps when input signal is weak. • Near ACI detection should be robust. • At some locations (fixed-point), signal changes quite fast. • All tuners need RF backed off significantly at Barcelona • [ACI] Field and Nordig/MBRAI conditions are very different • In the field, I/C ~ 10-30 dB; Nordig/MBRAI, I/C ~ 30-50 dB • In the field, many interference channels; Nordig/MBRAI, up to 2 channels.

  40. Thanks !

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