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1 Sychroizatio Schee ad Iterferece Cacellatio for DVB Syste Hsi-Piao Li Istitute of Coputer, Couicatio atioal Taipei Uiversity of Techology 9.5. Wireless Co. Lab.

2 Outlie Overview of DVB-T/H Syste Sychroizatio ad Chael Estiatio Typical OFDM syste & ICI Effect Literature review ICI Reductio of OFDM Receiver Widowig ethod Liear tie-varyig chael approxiatio & a ICI selfcacellatio algorith Further research Equivalet liear chael tie-variatio itigatio Equivalet low-coplex receiver widowig ethod Siulatio results Coclusio

3 數位電視的優點對雜訊有較高的容忍力可加入錯誤更正碼, 修正錯誤可對信號作壓縮, 降低資料量, 減少所需傳送頻寬較能對抗訊號衰落問題所需發射功率較低容易將信號鎖碼可提供影像聲音資料的整合性數位服務內容積體電路化 3

4 現有的數位電視廣播系統 Europe: Europea Telecouicatios Stadards Istitute (ETSI) Digital Video Broadcastig (DVB) Aerica: Advaced Televisio Systes Coittee (ATSC) ATSC DTV Japa: Associatio of Radio Idustries ad Busiess (ARIB). itegrated services digital broadcastig (ISDB). Korea: Digital ultiedia broadcastig (DMB) Chia 4

5 數位電視廣播系統比較規格歐規 (DVB-T) 美規 (ATSC) 日規 (ISDB-T) 頻寬 6/7/8 MHz 6 MHz 6 MHz 調變方式 COFDM QPSK,6QAM,64QAM Guard iterval : /3,/6,/8,/4 of OFDM Sybol odes; ad 8 FFT 5 8VSB BST-OFDM DQPSK,QPSK,6QAM ad 64QAM 3 ode :,4 ad 8 FFT 視訊壓縮 MPEG- MPEG- MPEG- 音訊壓縮 MPEG-(or AC3) Dolby AC-3 MPEG-(or AC3) 訊息碼率 (Mbps) 4.35~ MHz : 3.68~ KHz : 83~.65K 移動接收可差可抗鬼影可尚可可單頻網路可否可外部編碼 RS(4,88,t8) RS(7,87,t) RS(4,88,t8) 外部交錯 RS bloc iterleaver 5 RS bloc iterleaver RS bloc iterleaver 內部編碼迴旋碼 Rate /3 trellis code 迴旋碼內部交錯資料擾亂器 Bit-wise iterleavig ad frequecy iterleavig to trellis code iterleaver 6-bit PRBS Bit-wise iterleavig ad frequecy iterleavig,ad selectable tie iterleavig

6 傳輸技術特點比較 8-VSB 系統的特點 : 可在一個 6MHz 的通道傳送最高解析度的 HDTV 信號在相同廣播大小範圍, 所需的發射功率較小處理短脈衝噪聲源的能力強 COFDM 系統的特點 : 可行動接收, 在車速達到 3 公里時仍可收看電視抗多路徑干擾能力強, 室內接收能力較佳適用於單頻網路 (Sigle Frequecy etwor, SF), 所謂單頻網是指相鄰的發射站台使用相同的頻率來傳送資料, 進而提升頻譜使用效率更多更靈活的選擇, 能適應未來廣播不斷變化的需求分層模式可解決臨界接收性能問題 6

7 歐規 DVB 系列 Satellite DVB-S DVB-S Terrestrial DVB-T Cable DVB-C Mobility DVB-H 7

8 DVB 系列傳輸技術 DVB-H eploys additioal FEC ecodig for ehaced robustess. DVB-S eploys LDPC cocateated with BCH code 8

9 DVB-T S C 調變技術 DVB-C: the odulatio chose is QAM (with 6, 3, 64, 8, or 56 poits i the costellatio diagra) DVB-S: QPSK or BPSK DVB-T: OFDM was selected where each idividual carrier ca be odulated with QPSK, 6 QAM, or 64 QAM. 9

10 DVB 規格特性 Coded OFDM (COFDM) Sigle-Frequecy etwor (SF) Multipath receptio perforace better tha ATSC. Flexible (K 8 ode, variable code rate) Digital Video Broadcastig-Hadheld was published as (ETSI) Stadard E 3 34 i oveber 4. Based o DVB-T for fixed ad i-car receptio of digital TV. DVB-H is desiged for hadheld device ad obile receptio. DVB-H is bacward copatible to DVB-T

11 Carriers Type DVB-T cotais the followig types of carrier : Payload carriers with fixed positio. Iactive carriers with fixed positio. Cotiual pilots with fixed positio. Scattered pilots with chagig positio i the spectru. TPS carriers with fixed positio.

12 Carriers Positio

13 TPS Carriers The TPS carriers are located at fixed frequecy positios. TPS stads for Trasissio Paraeter Sigalig. These carriers represet virtually a fast iforatio chael via which the trasitter ifors the receiver about the curret trasissio paraeters. All the TPS carriers i oe sybol carry the sae iforatio, i.e. they are all either at degrees or all at 8 degrees o the I axis. The coplete TPS iforatio is broadcast over 68 sybols ad coprises 68 bits. 3

14 TPS Purpose & Cotet 4

15 TPS Carry Iforatio Thus, the TPS carriers eep the receiver ifored about: The ode (, 8). The legth of the guard iterval (/4, /8, /6, /3). The type of odulatio (QPSK, 6QAM, 64QAM). The code rate (/, /3, 3/4, 5/6, 7/8). The use of hierarchical codig. 5

16 DVB-T Costellatio Diagra DVB-T Costellatio Diagras for QPSK,6-QAM ad 64-QAM 6

17 Carrier Type Value 7

18 DVB-T 可選擇之傳輸參數 OFDM 模式 K 8K 載波數 K 75(.74) 687(.686) RF 通道頻寬 6 MHz 7 MHz 8 MHz 6 MHz 7 MHz 8 MHz 區間 K ad K ax 5.7 MHz 6.66 MHz 7.6 MHz 5.7 MHz 6.66 MHz 7.6 MHz 載波區間 3348 Hz 396 Hz 4464 Hz 837 Hz 977 Hz 6 Hz 期間 T wat 99μs 56μs 4μs 95μs 4μs 896μs /4 75μs 64μs 56μs 99μs 56μs 4μs 保護區間 /8 37μs 3μs 8μs 49μs 8μs μs /6 9μs 6μs 4μs 75μs 64μs 56μs /3 9μs 8μs 7μs 37μs 3μs 8μs 載波調變方式 QPSK,6-QAM,64-QAM 內部編碼率 /,/3,3/4,5/6,7/8 8

19 6MHz 通道下的網路資料傳輸率 (Mbps) 調變方式編碼率 Guard /4 Guard /8 Guard /6 Guard /3 / / QPSK 3/ / / / / QAM 3/ / / / / QAM 3/ / /

20 DVB-T Trasitter

21 DVB-T Receiver

22 Set-Top Box The trasport strea coig out of the DVB-T deodulator is fed ito the MPEG- decoder where it is decoded bac ito video ad audio. All these odules are cotrolled by a icroprocessor via a IC bus.

23 Coceptual Structure of DVB-H Receiver Fig. Coceptual structure of a DVB-H receiver. The tie-slicig odule cotrols the receiver to decode the wated service ad shut off durig the other service bits. (reduce power cosuptio) 3

24 Coceptual Descriptio of DVB-H Syste Fig. A coceptual descriptio of usig a DVB-H syste (sharig a MUX with MPEG- 4services).

25 Tie Slicig The receiver power off copletely durig off-tie ad will power o agai to receive the ext burst. Fig. Priciple of tie slicig. 5

26 6 MPE-FEC Method

27 Sharig with DVB-T Fig. Sharig a etwor with DVB-T by ultiplexig. 7

28 Dedicated DVB-H etwors Fig. A dedicated DVB-H etwor. 8

29 Mobile Receptio () The chael is ot characterized by just oe direct ad doiat sigal path, but by ultiple fast chagig echo sigals. These ultipath sigals ca atheatically be described as a tie-varyig Rayleigh chael ad require a higher carrier-to-oise ratio tha eeded for statioary receptio. A specialty of obile receptio is the Doppler effect which is a frequecy shift i the sigals arrivig at the receiver. 9

30 Mobile Receptio () Doppler effect ( frequecy chage ) f d f c v cosα c f d,ax f c v c α 3

31 Mobile Receptio (3) Doppler effect ( frequecy shift ) f c Classical Doppler Spectru fc f f + d c f 3

32 Mobile Receptio (4) To achieve successful obile DVB-T receptio, a uber of factors eed to be cosidered: 3 eed to trac chael variatios i tie ad frequecy. Correct chael estiatio eeds to be provided. To be able to copesate for oise-lie distortios called FFT leaage due to the tie varyig chael. (oorthogoality of the DVB-T subcarriers)

33 Diversity Techiques for Mobile Receivers Utilize two or ore receptio ateas. (space diversity) Two approaches:. Selectio Cobiig: Select the highest carrier-to-oise-ratio.. Maxiu Ratio cobiig: Cobie the sigals of L diversity braches. More cost. 33

34 Selectio Cobiig Practical used. 34 Fig. Selectio Cobiig structure

35 Maxiu Ratio Cobiig Sychroized i phase ad ultiply weight coefficiets. 35 Fig. Maxiu Ratio Cobiig structure

36 OFDM 時間與頻率偏移歐規數位電視系統所使用的傳輸架構為正交分頻多工,OFDM 系統可以支援大量的資料傳輸, 但在無線的傳輸上會造成時間偏移相位偏移以及頻率偏移, 這些問題對於接收訊號會有很大的影響, 受到這些影響 OFDM 系統效能將明顯地降低, 因此接收機對於符元同步和頻率同步的要求更加嚴格 36

37 時間偏移保護區間 OFDM 符元 FFT 訊窗 (a) 保護區間 OFDM 符元保護區間 OFDM 符元 FFT 訊窗 37 (b)

38 頻率偏移頻譜中心點 (a) 頻譜中心點 (b) ( ) + α Hz 38

39 Sychroizatio Sychroizatio Tie syc. Frequecy syc. 39 Fig. Receiver Basebad

40 部分相似估測法 Delay Delay Sybol Sybol Sybol 3 s s s CP CP CP s CP s CP s CP Sybol 6 s CP s CP 4

41 部分相似估測法 3 最大相似估測法表示式 : ( θ ) ΛC t * ( + ( + L) ) y ( + + ( + L) ) θ + s [ ( ( )) ( ( )) ] y + + L + y L t θ + s θ θ y 時間取樣點估測值 ˆ θ arg ax θ { ( θ )} Λ C 4 ˆ ε Λ π C ( ˆ θ )

42 Why eed Chael Estiatio 在無線通訊環境中, 由於通道環境的不確定性, 也就是通會受到地形地物和地貌影響, 造成接收機在接收信號的同時會因為干擾, 造成接收信號和發射信號不同而造成失真, 失真就是信號經過通道後其信號的大小 (aplitude) 和相位 (phase) 不同通道估測 (chael estiatio) 就是利用各種演算法 (algorith) 解決通道的影響, 求出通道響應 (chael respose) 使接收端可以還原出發射端的訊號以台灣的現況而言, 其數位電視信號是使用 6-QAM 的調變 6MHz 的頻寬, 因此如果信號振幅變得太小, 則經過 6-QAM 的解調變後, 可能會得到錯誤的結果此外, 由於通道及其他因素 ( 例如時間或取樣頻率有小幅偏差 ) 的影響, 進入 6-QAM 解調變器的符元, 有一些會有相位偏差, 而這些相位偏差, 則又會造成解調變錯誤 4

43 Chael Estiatio To copesate chael effect ( gai ad phase) The ow sigal, Pilot sigal, iserted i the trasitted sigal. The receiver utilize the pilot sigal to fid the ipairet of chael ad copesate the whole received sigal. 43

44 44 FPTC

45 FPTC 一般而言一個在時域中有點的 OFDM 符元可表示如下式 : x( ) X e π j,,,, - 其中代表通過 IFFT 後時域上的信號, 為原始輸入的頻域信號 x() X 45

46 46 Oe Path Detectio

47 47 Six Path Detectio

48 部分相似估測法結合 FPTC 同步演算法連續性導引信號之檢測 I (real) 時間同步頻率細同步 FFT 頻率粗同步 Q (iage) 頻率響應補償分散式導引信號之檢測通道估測 48 信號同步與通道估測流程圖

49 49 Oe-Tap Equalizer Costellatio

50 5 FPTC Costellatio

51 ICI Effects The OFDM systes suffers ICI durig tie-varyig chael or trasceiver oscillator frequecy isatch. The typical OFDM systes usig cyclic prefix (CP) as guard iterval to prevet ISI. However, the ISI-free part of guard iterval ca be also utilized to suppress ICI. 5

52 Typical OFDM Bloc Diagra Tx. Mappig Serial to Parallel poit IFFT Parallel to Serial Cyclic Prefix Rx. Deappig Parallel to Serial poit FFT Serial to Parallel Reove CP r 5

53 OFDM Deodulatio (o-widowig) (/) Without Frequecy Offset r : g Reove CP : Aplitude Widow legth, -FFT t 53 f

54 Oscillator Frequecy Misatch Tx. Mappig Serial to Parallel poit IFFT Parallel to Serial Cyclic Prefix Rx. Deappig Parallel to Serial poit FFT Serial to Parallel Reove CP r e jπ Δft+ θ 54

55 OFDM Deodulatio (o-widowig) (/) With Frequecy Offset (ICI) r : g Reove CP : Aplitude Widow legth, -FFT t 55 f

56 56 ICI Iduced by Costat Frequecy Offset ) ( ) ( j ΔfT π j j j ΔfT π j j X C e e X e e e X e r Y θ θ π θ π where ΔfT j ΔfT j e ΔfT ΔfT e C ) )( ( ) ( ) ( si ) ( si π π π π

57 Leaage Coefficiets Fig. Leaage coefficiets for 6 ad ΔfT. [] Aalysis of ew ad existig ethods of reducig itercarrier iterferece due to carrier frequecy offset i OFDM, IEEE Tras. Cou.,

58 ICI Reductio of OFDM Receiver Widowig [] proposed the receiver widowig ethod by applyig Raised-cosie widow i tie doai to suppress ICI effect. The widowig ethod utilizig the guard iterval of ISI-free part to suppress the ICI effect. The Raised-cosie (yquist) widow ca preserve the orthogoality betwee subcarriers whe there is o frequecy offset. [] Iprovig a OFDM receptio usig a adaptive yquist widowig, IEEE Tras. Cosuer Electro., vol. 4, pp , Aug

59 Covetioal Receiver Widowig (/) Tx. X() Serial to Parallel poit IFFT Parallel to Serial Cyclic Prefix Rx. r - - g Serial to Parallel poit FFT Parallel to Serial X () DSP Widow adjust Echo legth detectio (Chael Estiatio) ' g g 59

60 Double Legth FFT ad Square Widwoig CP Iforatio r widow legth -FFT Fig. Filter ba of double-legth DFT... X X X X 4 X 3 X -4 X - X -5 X -3 X - f 6

61 Adaptive yquist Widowig GI Iforatio r g-'g ' g +'g -FFT α Fig. Raised cosie widow fuctio g... X X X X 4 X 3 X -4 X - X -5 X -3 X - f Fig. Frequecy respose of Raised cosie 6

62 Side Lobe Copariso Raised-cosie for differet 6, ' g 6 α tie doai frequecy doai 6

63 Sigal to Iterferece Ratio The desired sigal power σ E The ICI power σ ICI { } X W(Δf ), p, p The average sigal to Iterferece ratio E { * } - * p- X X W( + Δf )W ( + Δf ) p T u T u SIR, W(Δf W( - T u ) + Δf ) 63

64 SIR Copariso of Differet Widow Fig. The SIR i 64-subcarrier OFDM receiver widowig with the eployet of differet widow fuctios (α.3). Receiver widowig for reductio of ICI i OFDM systes with carrier frequecy offset, i Proc. IEEE GLOBECOM Cof., vol. 5, pp , ov

65 I Tie-varyig Chael Tx. Mappig Serial to Parallel poit IFFT Parallel to Serial Cyclic Prefix Multipath Tie-varyig chael Rx. Deappig Parallel to Serial poit FFT Serial to Parallel Reove CP r 65

66 66 ICI Iduced by Tie-varyig Chael ) ( ) ( Z X H X H Z e h e X e z e e X h e z x h e r Y ICI ters,, desired sigal, ) ( π j (l) L l τ π j π j L l π j τ π j (l) j L l l j (l) (l) l π τ π

67 Slow Tie-varyig Chael.7% (a) Tie variatio of the CIR for differet Doppler frequecies withi a bloc period (b) Correspodig agitude resposes for differet Doppler frequecies. A Equalizatio Techique for Orthogoal Frequecy-Divisio Multiplexig Systes i Tie-Variat Multipath Chaels, IEEE Tras. Cou.,999 67

68 68 Pilot-Aided Chael Estiatio Pilot extractio The estiate of the l th tap Liear chael tie-variatio approxiatio, ˆ Q q Q q, P W I H P Y H q q q q q q q q + + ˆ ˆ L- l, e H Q h l L πq j Q q (l) ave q ) ( ) ( l l h ave h E To iiize ICI Mitigatio for Pilot-Aided OFDM Mobile Systes, IEEE Tras. Wireless Cou.,5 ) ( ˆ l (l) ave h h

69 Piece-wise Liear Tie-variatio Approxiatio (Ⅰ) Liear tie-varyig chael approxiatioⅠ: h ( + ) T, ( l) ( l) h + αl s The sigal odel of piece-wise liear approxiatio i tie doai 69

70 Piece-wise Liear Tie-variatio Approxiatio (Ⅰ) The sigal odel of piece-wise liear approxiatio i frequecy doai where H H r Y id slope r H X + C diag id H slope r X { ( ) } ( ) ( ) ( ) FFT h h Lh L] [ L { FFT ( α α L L] ) } diag α L [ C B, B FFT( ( - ) Ts ) Ts e. 5 π j 7

71 Piece-wise Liear Tie-variatio Approxiatio (Ⅱ) Liear tie-varyig chael approxiatioⅡ: ˆ r α l h ( ), ext ( h T ) l l l L 7

72 Piece-wise Liear Tie-variatio Approxiatio (Ⅱ) The sigal odel i tie doai The sigal odel i frequecy doai 7

73 A ICI Self-cacellatio Algorith Periodic exted to duratio x jπ X,,, 3 e K Perfors -poit FFT o shiftig d saples X (d) X e d jπ,, L,- x x x x x x x (- ) () ( 3 ) X X - X (d) X ca provide a diversity of by ultiplyig. A ovel Algorith of Iter-Subchael Iterferece Cacellatio i OFDM Systes, i Proc. IEEE Vehicular Techology Cof., vol., pp , Sept. 4. X j e π d 73

74 74 Cobies to Estiate Y ad (d ) Y ( ) + + ) ( ' ' ' ' ' ' ) )( ' ( ) ( ' ) ' ( '], [ ICI l d j l d j j d d d l T d e h X e X e H π τ π π

75 75 Self-Cacellatio of the ICI Assue vary liearly withi oe sybol iterval. Let, where are costat coefficiet. Thus, (l) h ( ) ICI ) ( ) ( ) ( ) ( ) ' ( ) ' ( ) )( ' ( d d d j j l l l d j l d e e c d c c e h π π π ) ( ) ( ) ( ) ( ) ( l l l l d c d c c h + + +

76 Further Extesio fro Chag s Method : Periodic exted to - duratio: x X e jπ ),..., If 4 for exteded OFDM sybol : ~ x, ( ~ x 3 x x x ~ x x 3 4 ad assue liear tie varyig chael. 76

77 ICI self cacel tie doai cobie (l) h () () () (3) ~ x ~ x x 3 Circular shift & Cobie () () () (3) ~ x 3 x x x 4 4 x x x 3 x ~ x x x x 3 ~ x x x ~ x 3 ~ ~ x x x ~ x () : () : () : (3) : - - ( l ) h (l) h : x x x x3-3 77

78 Widowig & Cobiig (l) h For 4: : ~ x ~ x x ~ x x 3 x x w: x x x x Triagular widow shape w (l) h : 78

79 Widow coefficiets calculatio (/) Assue liear tie varyig chael CP c l c l c l h ( l ) c l + a l itigatio h ( ) ' l c l c l ( + α ) ( α ) ( α ) ( +α ) α ( ) α ( + ) ( α ) ( +α ) h w h + h w h w h + w h c l 79

80 8 Widow coefficiets calculatio (/) For liear tie varyig chael : Cobiig, a c h l l l + ) ( ( ) [ ] [ ] l l l l l l a w w w w a w a c w h w h w < + + ) ( c ) ( ) ( c, ) ( ) ( α α + + () ) ( () Let L L w w w w c l CP ) ( ) ( ) (, w w w α α + < The coefficiets are siilar to Fras widow

81 The Fras widow Defiitio of Fras widow : p For 64 : f Tu (, t < t Tu (α ) Tu ( ( t) T, t < u, otherwise α ) + α ) CP CP CP Useful CP 5 poits Useful CP 3 poits Useful CP 63 poits L.E. Fras, Further results o yquist s proble i pulse trasissio, IEEE Tras. Cou. Techol., vol. 6, pp , Apr

82 Mitigatio for differet widow (/) Assue liear tie varyig chael : ad α.5 h CP 8

83 Mitigatio for differet widow (/) 83

84 84 Covetioal Receiver Widowig Widowig & Zero paddig Reove ISI-part of GI - FFT Choose eve bis Equalizer r y Y Y ~,, < g g w r y -, e y Y j π ~ -, Y Y

85 Low-coplex Receiver Widowig Method The coplexity of covetioal receiver widowig ethod (-FFT) is twice as typical OFDM receiver. However, the -FFT ca be reduced to -FFT by cobig the useful GI to the correspodig iforatio part. r Reove ISI-part of GI Widowig y Y ~ Cobiig -FFT Equalizer 85

86 86 Low-coplex Receiver Widowig Method [ ] [ ], y ~ e )e w r r (w e w r e w r r w e y e y e y Y Y π j π j π j π j π j π j - π j g g,, + < g g w r r w w r y,, < g g w r y

87 Low-coplex Receiver Widowig Method g r ' w ( α ) y wr w r, + w r g, g < r S/P w(+ α ) y Y ~ g w(+ α ) -FFT Oe-tap Equalizer w( α ) 87

88 Siulatio Paraeter DVB-T syste paraeters Tie-varyig ultipath chael TU6 chael odel Jae s odel with Doppler Rayleigh fadig Oe-tap equalizer 88

89 Siulatio Results (/) 7.5 /Hr (DVB-T 8Kode 6Mhz) 89

90 Siulatio Results (/) 9

91 Coclusio The coplexity of covetioal receiver widowig was reduced fro -FFT to -FFT ad receivig perforace ca be aitaied. The Fras widow ca itigate the chael tie variatio of correspodig part ito costat i the assuptio of liear tie-varyig chael. The perforace of Fras widow outperfors tha raised-cosie widow ad Chag s ethod. Whe α icreased, the receivig perforace ca be ore iproved. 9

92 Tha you for your listeig. 9

MAN- Metropolitan Area Network Resilient Packet Ring a : 5GHz 54Mbps b : 2.4GHz 11Mbps c : MAC Bridge 802.1D 80

MAN- Metropolitan Area Network Resilient Packet Ring a : 5GHz 54Mbps b : 2.4GHz 11Mbps c : MAC Bridge 802.1D 80 IEEE 802.11a s0323516@ncnu.edu.tw 1 (WLAN) [1] 1963 IEEE Institute Of Electrical and Electronics Engineers LAN MAN-Metropolitan Area Network IEEE 802 IEEE 802 Working Group 802.11 IEEE 802 802.1 LAN MAN