ISDB-T technical seminar(7) in Brazil Section 3 Transmission system June, 7 Digital Broadcasting Epert Group () Japan Yasuo TAKAHASHI (Toshiba) Preface Transmission system of ISDB-T is most feature of ISDB-T. Different from another DTTB standard, ATSC and DVB-T. For eamples, (1)One segment service within same bandwidth, ()High performances for mobile/portable reception, (3)Robustness against multipath and impulse noise, etc. These features re mainly led from ISDB-T transmission system. So, it is very important to study the structure of ISDB-T transmission system for understanding the background of the features of ISDB-T. This seminar document is prepared according ARIB STD-B31. But,as described in seminar #, SBTVD-T 1 is almost same as B31. Therefore, it is useful for Brazilian engineer to know this section. In this section, mainly the principle of channel coding and OFDM Modulation technology are presented. 1 Contents 1. Outline of ISDB-T transmission system 1.1 Features of ISDB-T and technical baseline 1. Block diagrams of transmission system 1.3 transmission parameter. Principle of segment construction and hierarchical transmission 3. Transmission coding 3.1 Channel coding 3. Mapping and Interleaving 4. OFDM modulation 4.1 OFDM modulation and Guard interval adding 4. Quadrature modulation 5. Outline of ISDB-T SB 5.1 outline of ISDB-T SB transmission system 5. Consecutive transmission system 5.3 eample of consecutive transmission station 1. Outline of ISDB-T transmission system 1.1 Features of ISDB-T and technical baseline 1. Block diagrams of transmission system 1.3 transmission parameter 3 4
Requirement for transmission system Solutions Features of ISDB-T transmission system High-Quality, Multi-Channels -HDTV 1CH or SDTV 3CH within 6MHz band. -Robustness against multi-path Multimedia-Service -Integrated Service(Video/Audio/Data) Technical Specification Japanese Requirements for DTTB Fleible/Versatile -High quality Data Service -Bi-directional Service OFDM Robustness, SFN Efficient Spectrum utilization Single Frequency Network(SFN) Segment Structure Etensible, Partial Reception Mobile and handheld service -Robustness against mobile/portable reception -fied/mobile/portable service within same band --- Layer Transmission Technology Time Interleaving TMCC Mobile Reception, Indoor Reception Fleible, Versatile Commonality of receiver - Commonality for BS/Cable/Terrestrial Broadcasting. 5 6 ISDB-T system Segmented Structure and Partial Reception Band Segmented OFDM : Orthogonal Frequency Division Multipleing 1 segment 49KHz 6MHz 13 Segments Features Modulation: DQPSK, QPSK, 16QAM, 64QAM 1HDTV or N SDTV/channel (Eample; 1seg + 1 seg) Layer A (LDTV,Audio,Data) 13segments (6MHz bandwidth) Layer B (HDTV or Multi- SDTV with Data)) frequency Frequency Net data rate: 3.4Mbps (6MHz) Single Frequency Network Mobile reception (time interleaving) 7 QPSK constellation Difference of required C/N Between 64QAM and QPSK is about 1 db 64QAM constellation *13 segments are divided into layers, maimum number of layers is 3. *Any number of segment for each layers can be selected (totally 13 segment) *Transmission parameter sets of each layer can be set independently (In above eample, modulation inde of each layer are different) 8
Feature of ISDB-T transmission system 1. Efficient frequency utilization (1)Adopt OFDM transmission system; SFN operation ()Adopt hierarchical transmission; service for different type of reception in one frequency channel MPEG- multipleer TS TS re-multiple er Outer code (4,188) Division of TS into hierarchical levels Byte -> Bits MSB first Byte -> Bits MSB first Energy dispersal Energy dispersal Delay adjustment Delay adjustment Bits -> Byte MSB first Bits -> Byte MSB first Byte interleaving Byte interleaving Byte -> Bits MSB first Byte -> Bits MSB first Convolutional coding Convolutional coding. Mobile/ handheld service in one transmission standard (1)Time interleave; Improve mobile reception quality ()Partial reception; handheld service in same channel 3. Robustness against interference (1) Adopt concatenated error correction with plural interleave ()Time interleave; very effective for impulse noise (urban noise) 4. Fleibility for several type of service/ reception style Carrier modulation Bit interleaving Mapping Carrier modulation Bit interleaving Mapping Carrier modulation Bit interleaving Mapping Byte -> Bits MSB first Combining of hierarchical levels Time interleaving Energy dispersal Delay adjustment Frequency interleaving Bits -> Byte MSB first OFDM-frame structure Byte interleaving IFFT Byte -> Bits MSB first Guardinterval addition Convolutional coding 5. Commonality of TV/audio transmission standard 6. Auiliary (AC) channel can be used for transmission network management Pilot signals TMCC signal Transmission system blockdiagram( B31 Fig.3-) 9 1 Parameters of ISDB-T (6MHz Bandwidth) ISDB-T mode Number of OFDM segment Useful bandwidth Carrier spacing Total carriers Modulation Number of symbols / frame Active symbol duration Guard interval duration Inner code Outer code Time interleave Useful bit rate Mode 1 (k) Mode (4k) Mode 3 (8k) 13 5.575MHz 5.573MHz 5.57MHz 3.968kHz 1.984kHz.99kHz 145 89 499 QPSK, 16QAM, 64QAM, DQPSK 4 5μ s 54μ s 1.8ms 1/4, 1/8, 1/16, 1/3 of active symbol duration Convolutional code (1/, /3, 3/4, 5/6, 7/8) RS (4,188) ~.5s 3.651Mbps ~ 3.34Mbps 11 Equation for calculating bit rate STEP 1: calculate the bit rate of one(1) segment ISDB-T is composed 13 segments, so, to calculate transmission bit rate, at first, calculate the bit rate of one(1) segment, and multiply number of Segment of each layer. Then lead total bit rate of each layer (1) reed-solomon coding rate; (188/4), fied value () r: convolutional coding rate( depends on coding rate) (3) M: modulation inde(bit/ symbol); QPSK=, 16QAM=4, 64QAM=6 (4) Ts/(Ts+Tg); ratio of total symbol length and effective symbol length (5) (effective data carrier)/(total carrier) =96/18 fied value for mode 1,, 3 (note) total carrier; including pilot carrier, TMCC, and scattered pilot symbol (6)Nf : Number of carrier in one segment; mode 1=18,mode =16, mode 3=43 (7) fd: carrier spacing = effective symbol transmission speed mode 1=(6/14)/18*1 3 khz=3.96854khz, mode = (1/) of mode 1 mode 3=(1/4) of mode 1 (note) (6/14)*1 3 khz = bandwidth of one(1) segment 1
Eample Mode 3, guard interval ratio=1/16, modulation=qpsk, coding rate(r)=/3 Bit rate of 1 segment=.99635 *43 * (16/17) * * (/3) * (188/4) =44.56 kbps fd Nf Ts/(Ts+Tg) M r RS coding rate. Segment construction and Hierarchical Transmission STEP : multiply number of segment (Nseg) Eample 1 : 1 layer fied reception, mode 3, guard interval ratio=1/16, Modulation =64QAM, coding rate(r)=3/4 Number of segment Bit rate of 1 segment=.99635 *43 * (16/17) * 6 * (3/4) * (188/4) * 13 =19.39 Mbps Eample : layer,1 segment for portable, 1 segment for fied Layer A: Nseg=1, mode 3, Tg/Ts=1/16, M=(QPSK), r=/3 Bit rate of A layer=.99635 *43 * (16/17) * * (/3) * (188/4) * 1 =44.56 kbps Layer B: Nseg=1, mode 3, Tg/Ts=1/16, M=6(64QAM), r=3/4 Bit rate of A layer=.99635 *43 * (16/17) * 6 * (3/4) * (188/4) * 1 =17.84 Mbps.1 Concept and feature of hierarchical transmission system. The rules of hierarchical transmission.3 Segment construction and hierarchical transmission Relating clause of ARIB standard; B31 clause 3. 13 14 Blockdiagram of ISDB-T Transmission coding.1 Concept and feature of hierarchical transmission system TS TS RE-MUX RS Coding Divide To Hierarchy Energy Dispersal Delay Adjust Byte Convolutional Coding Hierarchical transmission is the feature of ISDB-T, this concept is not in DVB-T system. The concept of hierarchical transmission system is shown in figure.-1after. The transmission parameters can be assigned as each service ID. This transmission system is called hierarchical transmission For eample, the service which should be strong against interference such as noise should be assigned to QPSK layer, other service is assigned to 64QAM layer. Bit Mapping Combine Hierarchy Frequency Time OFDM Framing In this case, service of QPSK layer could be received under serious receiving condition such as handheld reception. Pilot/TMCC/AC In case of DVB-T system, for handheld reception service, another frequency should be prepared separately. But, in ISDB-T system, different reception service can be achieved within one frequency channel by making use of this transmission system., IFFT Add Guard interval Quad. MOD D/A Conv. OFDM signal TSP s are divided into plural layers at Re-multipleer, and re-arranged in each layer. After re-arranged, these TSP s are combined to 1 transport stream and feed to OFDM modulator. (see figure. -) These functions are presented in this section 15-16- 16
Divide TSP s into each hierarchy Fig.-1 Image of hierarchical transmission Transmission capacity is not high, but interference level is low Combine each hierarchy, and re-arrange TSP s Fig. - Blockdiagram of TS re-multipleer TS input PID etract A layer buffer A layer MUX buffer Path of QPSK layer Path of 64 QAM layer DE- MUX INF1 B layer buffer C layer buffer B layer MUX C layer MUX buffer buffer MUX TS re-multiple output Packet which path through the QPSK layer Packet which path through the 64 QAM layer Transmission capacity is high, but interference level is high TS input TS input TS input INF INF3 INF4 PCR select PSI-SI buffer Interference such as noise 17 18 TV program #1 TV program # Fig. -3 Image of multiple layer transmission #1-V #1-A #1-D #-V #-A #-D Eample of programs into 3 layers ISDB-T Re multipleer #1-A Layer A #1-D Layer B #1-V #-A #-D #-V Layer C M U X MUX. The rules of hierarchical transmission (a) The strongest hierarchy layer should be able to be demodulated and decoded alone. Reason; to be able to demodulate and decode, PCR and minimum required PSI should be transmitted by strongest layer. (see Fig.-4) (b) Transmission delay difference between hierarchy should be compensated at the transmission side. The compensated transport stream is called Multi-frame pattern Image of Multi-frame pattern is shown in Fig. -5 later (c) Multi-frame pattern should be completed within 1 OFDM frame. (d) The number of packet in 1 segment should be integer in any combination of transmission parameter and coding rate. Reason; minimum unit of hierarchical transmission is the segment. (e) Even though the information transmission speed is different because of its transmission parameters, the clock rate of TS at the output of receiver RS decoder should be constant( for TV, clock rate is 4fs). To adjust the clock rate, Null packets are inserted. See details in fig. -6 later. 19 --
Transmit TSP(RS input) Received TSP (RS output) Fig. -4 Concept of hierarchical transmission (strongest layer should be recovered alone) A-1 B-1 B- A- B-3 B-4 A-3 B-5 B-6 A-4 B-7 The B layer packets are interfered and broken A-1 B-1 B- A- B-3 B-4 A-3 B-5 B-6 A-4 B-7 Transmit TS Transmission in layer A Received layer A TS Transmission in layer B Fig. -5 Concept of hierarchical transmission(1/) (delay adjustment of each layers) A-1 B-1 B- B-1 B- B-3 Time ais A- B-3 B-4 A-3 B-5 B-6 A-4 B-7 A-1 A- A-3 A-4 A-1 A- A-3 B-4 B-5 B-6 B-7 Recovered TSP s Received layer B TS B-1 B- B-3 B-4 B-5 B-6 A-1 A- A-3 A-4 TSP s of layer A should include PCR and minimum required PSI which are necessary to recover TSP 1 Layer A + layer B(order is different from transmission side (operation of S1 in Fig.-7) B-1 A-1 B- B-3 A- B-4 B-5 A-3 B-6 As shown above, Transmission delay of each layer is different according to each layer transmission parameter set. As a result, because of its transmission parameter set. Therefore, order of TSPof receiver side is different from transmitter side Fig. -5 Concept of hierarchical transmission(/) (delay adjustment of each layers) Time ais Fig. -6 Concept of hierarchical transmission (How to adjust constant clock rate) Transmit TS Transmission in layer A Received layer A TS Transmission in layer B A-1 B-1 B- A- B-3 B-4 A-3 B-5 B-6 A-4 B-7 A-1 A- A-3 A-4 A-1 A- A-3 B-1 B- B-3 B-4 B-5 B-6 Transmit TS (RS coder input) transmission A-1 null null A- null null A-3 null null A-4 null null Null packets are not transmitted A-1 A- A-3 A-4 Received layer Delay B TS adjustment Layer A + layer (operation of S1 in Fig.-7) B-1 B- B-3 B-4 B-5 B-6 A-1 B-1 B- A- B-3 B-4 A-3 B-5 B-6 As shown above, delay adjustment is inserted at transmitter side. As a result, same order of TSP is recovered in receiver side. 3 Received TS (RS decoder output) A-1 null null A- null null A-3 null null Packet output timing (operation of S in Fig.-7) At the output portion of receiver RS decoder, TS is read by same clock rate of transmit TS (for TV, clock rate is 4fs). At the timing of head packet, packet does Not decoded yet, in this case, RS decoder feeds null packet. If decoded, RS decoder feeds decoded packet. 4
FFT Division into hierarchical levels Figure -7 Model receiver for multi-frame reproducing Differential demodulation Synchronous demodulation Depuncturing Depuncturing Hierarchical level A Hierarchical level C Hierarchical buffer Hierarchical buffer Frequency/time de-interleaving S1 Combining of hierarchical levels S3 TS reproduction section TS buffer Null TSP TS buffer Null TSP S S TS reproduction TS reproduction S4 Viterbi decoding.3 Segment construction and hierarchical transmission Segment of ISDB-T is the concept for hierarchical transmission. The segment is decided as follows considering the rule shown in clause. (1) Number of TSP in one OFDM frame is integer for all cases of transmission parameter set. Number of TSP is shown in Table -1. () For easy tuning operation of receiver, bandwidth of 1 segment is set to 6/14 MHz. (3) Number of multi-frame pattern is proportional to number of set of hierarchy. For this reason, number of hierarchy is limited as many as 3. S1; select the layer. If all data of 1 packet has been input to buffer, S1 select the buffer and send data to net stage S; select TS/Null packet, according to TS buffer status 5-6- 6 Table -1 Number of TSP in one OFDM frame (mode 1) coding rate 1/ /3 3/4 5/6 7/8 modulation DQPSK/QPSK 1 16 18 1 16QAM 4 3 36 4 4 64QAM 36 48 54 6 63 3. Channel coding (note1) number of TSP/segment (note ) in case of mode, number of TSP is twice, and in case of mode 3, four times Relating clause of ARIB standard; B31 clause 3.3 clause 3.11 7 8
Blockdiagram of ISDB-T Transmission coding Outer coder (Reed-Solomon coding) TS TS RE-MUX Bit RS Coding Mapping Divide To Hierarchy Combine Hierarchy Energy Dispersal Frequency Delay Adjust Time Pilot/TMCC/AC Byte Convolutional Coding OFDM Framing A shortened Reed-Solomon code (4,188) is used in every TSP as an outer code. The shortened Reed-Solomon (4,188) code is generated by adding 51-byte HEX at the beginning of the input of the data bytes of Reed-Solomon (55,39) code, and then removing these 51 bytes. The GF (8) element is used as the Reed-Solomon code element. The following primitive polynomial p () is used to define GF (8): p () = 8 + 4 + 3 + + 1 Note also that the following polynomial g () is used to generate (4,188) shortened Reed-Solomon code: g () = ( - λ) ( - λ1) ( - λ) ---- ( - λ15) provided that λ = HEX Sync. 1 byte Data (187 bytes) (a) MPEG- TSP IFFT Add Guard interval Quad. MOD D/A Conv. OFDM signal Sync. 1 byte Data (187 bytes) Parity 16 byte (b) TSP error-protected by RS code (transmission TSP) These functions are presented in this section 9 MPEG TSP and Transmission TSP(B31, Fig. 3-6) 3 Inner coding Energy Dispersal G 1 = 171 Octal Output X Energy dispersal is conducted at each hierarchical layer using a circuit, shown in Fig. 3-8, that is generated by a PRBS (Pseudo Random Bit Sequence). All signals other than the synchronization byte in each of the transmission TSPs at different hierarchical layers are EXCLUSIVE ORed using PRBSs, on a bit-by-bit basis. Data input D D D D D D D output g() = X 15 + X 14 + 1 D D D D D D D D D D D D D D 1 3 4 5 6 7 8 9 1 11 1 13 14 15 PRBS-Generating Polynomial and Circuit (B31,Fig. 3-8) + G = 133 Octal Fig. 3-1: Coding Circuit of a Convolutional Code with Constraint Length k of 7 and a Coding Rate of 1/ Coding rate 1/ /3 3/4 5/6 7/8 Puncturing pattern X : 1 Y : 1 X : 1 Y : 1 1 X : 1 1 Y : 1 1 X : 1 1 1 Y : 1 1 1 X : 1 1 1 Y : 1 1 1 1 1 Transmission-signal sequence X1, Y1 X1, Y1, Y X1, Y1, Y, X3 X1, Y1, Y, X3 Y4, X5 X1, Y1, Y, Y3, Y4, X5, Y6, X7 Output Y 31 Table 3-8: Inner-Code Coding Rates and Transmission-Signal Sequence 3
Puncturing Pattern Eample of input C/N vs BER characteristics data input(1 bit) Convolutional Coding (K=7) X out(1 bit) Y out(1 bit) Puncture output( bits) 1.E+ 1.E-1 Mode;1 GI=1/8, 64QAM, I=, RS;OFF coding rate Number of input bits Number of output bits Puncturing pattern Output of puncturing 1/ 1 X:1 X1, Y1 Y:1 () /3 4 X: 1 X1, Y1, Y Y: 11 (3) 3/4 3 6 X: 11 X1, Y1, Y,Y3 Y: 11 (4) BER 1.E- 1.E-3 1.E-4 no correction FEC=7/8 FEC=5/6 FEC=3/4 FEC= FEC= FEC= FEC= 5/6 5 1 X: 111 X1, Y1, Y,Y3,Y4, Y5 Y: 111 (6) 7/8 7 14 X: 111 X1, Y1, Y,Y3,Y4, Y5,Y6,Y7 Y: 11111 (8) 33 1.E-5 1.E-6 5 1 15 5 3 35 4 C/N[dB] 34 Effect of interleave Kind of interleave and these effect is one of important technology in transmission system. Error correction system is most effective when the characteristics of noise is random. The purpose of interleave is to randomize the burst error occurred in transmission path Burst error; FEC does not work well Random error; FEC works well RS coder Byte interleave Convolutional coding Bit interleave Mapping Time interleave Byte interleave Byte interleave is located between outer coder and inner coder. Randomize the burst error of Viterbi decoder output Frequency interleave transmitter before interleave receiver after de-interleave interleave transmitter after interleave Burst error occurs at transmission path receiver before de-interleave de-interleave 35 Bit interleave Bit interleave is located between convolutional coding and mapping. Randomize the symbol error before Viterbi decoding Time interleave Time interleave is located at the output of maping(modulation). And randomize the burst error of time domain which is mainly caused by impulse noise, fading of mobile reception, etc. Frequency interleave Frequency interleave is located at the output of time interleave. Randomize the burst error of frequency domain which is mainly caused by multi-path, carrier interference, etc. 36
Switching between paths every byte 1 Byte interleave The 4-byte transmission TSP, which is error-protected by means of RS code and energy-dispersed, undergoes convolutional byte interleaving. Interleaving must be 1 bytes in depth. Note, however, that the byte net to the synchronization byte must pass through a reference path that causes no delay. 3 17 bytes 17 bytes 17 3 bytes b,b1,b,b3,b11 S/ P b* b*1 b* b*3 bc b8 b4 b bc1 b81 b41 b1 bc b8 b4 b bc3 b83 b43 b3 Bit interleave (B31, clause 3.9.3) Bit interleave circuit is different according to carrier modulation. Following diagram is a eample of 16QAM. 4 bits delay 8bits delay 1 bits delay 16QAM Mapping b bx by bz b41 b1 bx1 by1 b8 b4 b bx bc3 b83 b43 b3 I Q 11 17 3 bytes FIFO shift register 37 4 carriers Without bit interleave; burst error 4 carriers With bit interleave; errors are randomized 38 Relation between OFDM frame and interleave Effect of time interleave Time interleave time 3N 3N 3N 3N 3N 3N +1 + +3 +4 +5 +N N+1 N+ N+3 N+4 N+5 N 1 3 4 5 N frequency no time interleave frequency Error symbol Transmitter side time Transmitting delay field strength varied receiver side (After de-interleave) With time interleave Receiving delay time Frequency interleave N=144(mode 1) 88(mode ) 5616(mode 3) 39 Burst error Error randomized 4
C/Neq [db] (Carrie to Equivalent Gaussian 3-. What is the merit of Time-? (/) How much improved by using Time- 16 14 1 1 8 6 4 - -4-6 -8-1 -1 Following graph shows degradation by impulse noise, which is dedicated by Mackenzie Presbyterian University measured in Autumn, 5 5 1 15 5 3 35 4 45 5 DVB-T (7dB improved!) ISDB-T ATSC Pulse Width [µs] ATSC Latest Generation - 19.39Mbps-8 VSB /3 ATSC Previous Generation - 19.39Mbps-8 VSB /3 DVB Latest Generation - 19.3Mbps-64QAM 8k 3/4 1/16 DVB Previous Generation - 19.3Mbps-64QAM 8k 3/4 1/16 ISDB Latest Generation - 19.3Mbps - 64QAM 8k 3/4 1/16,s ISDB Previous Generation - 19.3Mbps - 64QAM 8k 3/4 1/16,s Switched every IFFT sample clock Intradata-segment time 1 interleaving section 1 No. : : n c -1 c -1 Intradata-segment time interleaving section : n c -1 No. 1 c -1 Intradata-segment time interleaving section : n c -1 No. c -1 Intradata-segment time interleaving section : : n -1 c No. 1 c -1 Time interleaver blockdiagram(b31, 3.11.1) Switched every IFFT sample clock 7dB improved Transmitter power reduced to 1/5!! 41 4 Table 3-1: Time Interleaving Lengths and Delay Adjustment Values Im symbol buffer Mode 1 Mode Mode 3 1 nc-1 Im1 symbol buffer Im symbol buffer Im nc-1 symbol buffer Provided that mi = (i 5) mod 96 nc is 96, 19, and 384 in modes 1,, and 3, respectively. Length (I) 4 Numbe r of delayadjust ment symbol s 8 Number of delayed frames in transmiss ion and reception Length (I) Numbe r of delayadjust ment symbol s 14 Number of delayed frames in transmiss ion and reception 1 Length (I) 1 Numbe r of delayadjust ment symbol s 19 Number of delayed frames in transmiss ion and reception 1 8 56 4 4 8 14 1 Fig. 3-3: Configuration of the Intra-segment Time Interleaving Section 16 11 8 8 56 4 4 8 (Notification) 43 44
Frequency characteristics distortion caused by multi-path This drawing shows the effect of multi-path. As shown, received signal level is varied in frequency domain. Effect of frequency interleave Frequency interleave Envelope of combined wave Reciprocal of delay time Multi-path Multipath Direct path Vector diagram Received signal In-band frequency Frequency characteristics Frequency de-interleave ; error As shown above, function of frequency interleave is to disperse the error caused by multi-path 45 46 Segment division Partial-reception portion Differentially modulated portion Intersegment interleaving Synchronously modulated portion Intersegment interleaving Intrasegment carrier rotation Intrasegment carrier rotation Intrasegment carrier rotation Configuration of frequency interleaving section Intrasegment carrier randomizing Intrasegment carrier randomizing Intrasegment carrier randomizing OFDMframe formation The input signal must be bits per symbol and QPSK-mapped to output multi-bit I- and Q-aes data. To conduct mapping, the 1-bit delay element shown in Fig. 3-14 is inserted into the mapping input for bit interleaving. Figs. 3-14 and 3-15 show the system diagram and mapping constellation, respectively. T b,b1, b S/P b1 1-bit retardation element QPSK mapping 1-bit delay Fig. 3-14: QPSK Modulation element System Diagram Q (level corresponding to b1) (1,) (b,b1)=(,) +1-1 +1 (1,1) -1 (,1) I Q I (level corresponding to b) Fig. 3-15: QPSK Constellation 47 Mapping. 48
The input signal must be 4 bits per symbol and 16QAM-mapped to output multi-bit I- and Q- aes data. To conduct mapping, the delay elements shown in Fig. 3-16 are inserted into b1 to b3 for bit interleaving. Figs. 3-16 and 3-17 show the system diagram and mapping constellation, respectively. t b b1 4-bit retardation element 16QAM I S/P b 8-bit retardation mapping b,b1,b,b3 element b3 Q 1-bit retardation 4-bit element delay element Fig. 3-16: 16QAM Modulation 8-bit delay System Diagram element 1-bit delay Q (Level corresponding element to b1, b3) (1,,,) (1,,1,) (,,1,) (b,b1,b,b3) = (,,,) +3 (1,,,1) (1,,1,1) (,,1,1) (,,,1) +1 I (Level corresponding -3-1 +1 +3 to b, b) -1 (1,1,,1) (1,1,1,1) (,1,1,1) (,1,,1) -3 (1,1,,) (1,1,1,) (,1,1,) (,1,,) Required C/N (db) (note) Coding rate Modulation 1/ /3 3/4 5/6 7/8 QPSK 4.9 6.6 7.5 8.5 9.1 DQPSK 6. 7.7 8.7 9.6 1.4 16QAM 11.5 13.5 14.6 15.6 16. 64QAM 16.5 18.7.1 1.3. (note) after Viterbi decoding, BER is as much as *1-4 Fig. 3-17: 16QAM Constellation Mapping. 49 Note: these data are simulation data at early stage, but recently, receiver LSI shows more good data. 5 1.E+ Input C/N vs BER characteristics Mode; 1, GI=1/8 FEC=3/4, RS=OFF 4. OFDM modulation 1.E-1 BER 1.E- 1.E-3 1.E-4 64QAM 16QAM QPSK DQPSK 16QAM 64QAM (1) IFFT () Pilot signal (3) AC (4) TMCC (5) Guard interval 1.E-5DQPSK (6) Quad. Modulation and RF format 1.E-6 QPSK 5 1 15 5 3 35 4 C/N[dB] 51 Relating clause of ARIB standard; B31 clause 3.1 clause 3.15 5
Blockdiagram of ISDB-T Transmission coding Nyquist separation and orthogonal FDM TS TS RE-MUX RS Coding Divide To Hierarchy Energy Dispersal Delay Adjust Byte Convolutional Coding Fourier transform and inverse FFT amplitude T frequency Bit Mapping Combine Hierarchy Frequency Time OFDM Framing time 1/T Nyquist bandwidth IFFT Add Guard interval Quad. MOD D/A Conv. Pilot/TMCC/AC OFDM signal Orthogonal division multiple These functions are presented in this section 53 At the adjacent carrier position,all other 54 carrier energy is zero. OFDM signal generation by IFFT IFFT output and frequency allocation Q ais I ais Sample point Symbol length = T f=/t f=1/t f=3/t f=/t f=1/t f= ; Sample point to generate sine wave of f=1/t cycle Symbol length=t Sample point to generate sine wave of f=/t cycle IFFT output 55 Freq. separation=1/t 56
Time ais carrier #1 Frequency ais TV signal spectrum + carrier # + + + + carrier #k + analog Digital; OFDM + + = = OFDM signal Frequency GI Effective symbol OFDM symbol Eample of OFDM signal waveform 57 58 OFDM frame structure (DQPSK, mode 1) OFDM frame structure (QPSK, 16QAM, 64QAM, mode 1) Carrier number 1 17 Carrier number 1 3 4 5 6 7 8 9 1 11 1 17 OFDM-symbol number 3 7 6 5 4 3 1 CP S, S,1 S, S,3 S,4 S,5 S,6 S,7 S,3 S 1, S 1,1 S 1, S 1,3 S 1,4 S 1,5 S 1,6 S 1,7 S 1,3 TMCC AC (AC1, AC) S 95, S 95,1 S 95, S 95,3 S 95,4 S 95,5 S 95,6 S 95,7 S 95,3 59 OFDM-symbol number 1 3 4 1 3 SP S, S 1, S, S 3, S 4, S 5, S 6, S 7, S 8, S 9, S 1, SP S 95, S,1 S 1,1 S,1 SP S 3,1 S 4,1 S 5,1 S 6,1 S 7,1 S 8,1 S 9,1 S 1,1 S 11,1 S 95,1 S, S 1, S, S 3, S 4, S 5, SP S 6, S 7, S 9, S 9, S 1, S 11, S,3 S 1,3 S,3 S 3,3 S 4,3 S 5,3 S 5,3 S 6,3 S 7,3 SP S 9,3 S 1,3 S 11,3 SP S,4 S,4 S,4 SP S 3,4 S 4,4 S 5,4 S 6,4 S 7,4 S 8,4 S 9,4 S 1,4 SP SP TMCC AC (AC1) S,1 S 1,1 S,1 SP S 3,1 S 4,1 S 5,1 S 6,1 S 7,1 S 8,1 S 95,1 S, S 1, S, S 3, S 5,1 S 5, SP S 6, S 7, S 8, S 95, S,3 S 1,3 S,3 S 3,3 S 4,3 S 5,3 S 6,3 S 7,3 S 8,3 SP S 95,3 S 95, S 95,3 S 95,4 S 95,5 S 95,6 S 95,7 6
Effect of scattered pilot (SP) signal Frequency characteristics distortion caused by multi-path This drawing shows the effect of multi-path. As shown, received signal level is varied in frequency domain. Envelope of combined wave Reciprocal of delay time Scattered pilot (SP) is used to Compensate the frequency distortion caused by multi-path frequency Estimation of transmission characteristics by SP frequency Multipath Direct path Vector diagram Received signal In-band frequency Frequency characteristics time 61 Scattered pilot (SP) AC(Auiary Channel) TMCC 6 Segment No. AC1_ 1 AC1_ TMCC 1 Eample of AC, TMCC (mode 1, QPSK,16QAM, 64QAM) (a) AC and TMCC Carrier Arrangements in Mode 1 11 1 8 7 9 53 83 5 7 61 1 17 5 11 11 86 3 4 44 1 74 1 47 35 79 49 76 97 31 4 4 89 83 6 4 89 61 8 8 64 85 1 7 89 11 1 98 11 3 What is AC? AC; (Auiliary Channel) AC is a channel designed to convey additional information on modulating signaltransmission control. AC s additional information is transmitted by modulating the pilot carrier of a type similar to CP through DBPSK. The reference for differential modulation is provided at the first frame symbol, and takes the signal point that corresponds to the Wi value stipulated in Section 3.13.1. Details of AC is specified in ARIB STD-B31 reference Recently, new utilization of AC has been proposed, that is, the transmission network management information can be carried to relay station by using AC. Details will be eplained in seminar #9 In DVB-T system, CP is inserted for carrier synchronization instead of AC, but CP cannot carry any information. This is the feature of AC 63 64
TMCC; transmission management and configuration control signal The TMCC signal is used to convey information on how the receiver is to perform demodulation of information such as the hierarchical configuration and the OFDMsegment transmission parameters. Guard interval A guard interval, the latter part of the IFFT (Inverse Fast Fourier Transform) data output for the specified duration, is added without any modification to the beginning of the effective symbol. This operation is shown in Fig. 3-33. IFFT output data IFFT output data Table 3-: Bit Assignment Guard interval Effective symbol Guard interval Effective symbol t B B 1 B 16 B 17 B 19 Segment type identification (differential: 111;synchronous: ) B B 11 TMCC information (1 bits) B 1 B 3 Reference for differential demodulation Synchronizing signal (w = 1111111111, w1 = 111111) Parity bit I ais 1 effective Symbol delay switch I ais See details of TMCC information in 3.15.6 of ARIB STD-B31 IFFT Q ais Q ais 65 66 (a) Effect of guard interval Time Ais Transmitted OFDM symbol GI Effective Symbol GI Effective Symbol Performances under multi-path condition Performances of each DTTB systems Following graph shows degradation by single multi-path, which is dedicated by Mackenzie Presbyterian University measured in Autumn, 5 - -3-5 - -15-1 -5 5 1 15 5 3 (b) GI Effective Symbol GI Effective Symbol td (c) FFT Window (a) : Direct wave from transmitter, (b) : reflected wave (multi-path wave) GI: Guard Interval, td: delay time of multi-path, (c) FFT window of receiver Desired to Undesired (D/U) [db] 4 6 8 1 1 14 16 18 ATSC ISDB-T DVB-T FFT window of receiver cuts a signal with Ts (effective symbol ) length, this signal is fed to FFT to demodulate OFDM signal. If FFT window can be set within the interval of transmitted OFDM symbol, Inter Symbol Interference (ICI) is not occurred. As a result, if multi-path delay time is no longer than GI, multi-path interference is almost compensated. 67 4 D e la y S p re a d (µ s ) A TS C Latest G eneration - 19.39M bps - 8V S B /3 ATSC Previous Generation - 19.39M bps - 8VSB /3 DVB -T Latest G eneration - 19.76M bps - 64QAM 8k 3/4 1/16 DVB-T Previous Generation - 19.76M bps - 64QAM 8k 3/4 1/16 ISDB-T Latest Generation - 19.3M bps - 64QAM 8k 3/4 1/16,s ISDB-T Previous Generation - 19.3M bps - 64QAM 8k 3/4 1/16,s As shown above, within guard interval length (+/- 63 us), ISDB-T work well almost db D/U ratio. In addition, newest ISDB-T demodulator LSI adopt adaptive compensation technology, so, widen the low D/U area up to 5us 68
Quad. modulation I signal Interpolation FIR multiplyer ADD D/A 8 MHz IF X SAW filter 37.15MHz IF output 5. ISDB-T SB transmission system Q signal 8 MHz digital processing Interpolation FIR multiplyer sin/cos gen. 3MHz digital processing Lo. OSC Analog processing 1. Outline of ISDB-T SB transmission system. Consecutive transmission system 3. Eample of consecutive transmitter station (1) interpolation/fir; convert from 8MHz sampling to 3 MHz sampling () Quad. Mod.; multiply I and Q data and add, 3 MHz digital signal process. The output is 8MHz OFDM signal with 3MHz sampling Relating clause of ARIB standard; B31 clause 3.1 clause 3.15 (3) Analog circuit; up convert to 37.15 MHz IF and SAW filter. 69 7 1. ISDB-T SB transmission system ISDB-T SB transmission and partial reception (1) What is ISDB-T SB ISDB-TSB transmission system is unique in ISDB-T family. This transmission system has been standardized for narrow band ISDB-T transmission system, which is focused to audio and data service, therefore, called ISDB-TSB. () Commonality with ISDB-T (a) Same segment transmission construction. But,considering narrow band reception, only 1 segment and 3 segment transmission systems are standardized (b) Adopt same transmission parameters as ISDB-T. (c) Commonality of 1 segment receiver with ISDB-T partial reception (3) Efficient use of frequency resource (a) Consecutive transmission system. This system is unique for ISDB-TSB, this transmission system is to transmit plural channel without guard band (b) To achieve consecutive transmission, phase compensation technology at transmitter side is adopted Layer A Layer B ISDB-T SB Partial reception Data segment Layer A Channel coding & Segmented OFDM framing Spectrum 43kHz ISDB-T Eample of DTTB spectrum 43kHz Partial reception 71 3-Segment receiver 819 FFT [mode 3]) 1-Segment receiver (14 FFT [mode3]) 7
Transmission parameters Mode 1 3 Segment(s) 1 or 3 Bandwidth 43kHz or 1.3MHz Carrier spacing 3.97kHz 1.98kHz.99kHz Total carriers 19 / 35 17 / 649 433 / 197 Data carriers 96 / 88 19 / 576 384 / 115 TMCC,AC,CP, SP carriers Modulation 13 / 37 5 / 73 49 / 145 QPSK, 16QAM, 64QAM, DQPSK Transmission parameters (continued) Mode 1 3 Symbol duration 5μs 54μs 1.8ms Guard interval 1/4 ~ 1/3 of symbol duration Symbols/frame 4 Frame duration 53~64ms 16~19ms 1~57ms Inner code Outer code Interleaving Convolutional code (1/, /3, 3/4, 5/6, 7/8) (4,188) RS code Time and Frequency 73 74 Eample of information bit-rate(ts rate) 1segment 3segment note QPSK, r=1/,tg=1/4 8kbps.84Mbps Minimum rate QPSK, r=1/,tg=1/16 33kbps.99Mbps QPSK, r=/3,tg=1/16 44kbps 1.3Mbps 16QAM, r=1/.tg=1/16 66kbps 1.98Mbps 64QAM,r=7/8,Tg=1/3 1.87Mbps 5.Mbps Maimum rate Bandwidth 43kbps 1.3Mbps The information bit rates do not depend on transmission mode1, or 3, They depend on modulation,coding rate and guard interval 75 Spectrum utilization (1) Broadcasting frequency bands are looked upon as a sequence of segments,which have a bandwidth of one fourteenth of a TV channel. BST-OFDM scheme provides followings. -DTV uses 13 segments, remaining one ; guard band, -DSB uses 1 or 3 segments -1-segment reception of 13 segment-tv signal by DSB receiver -Consecutive-segment transmission without guard bands -systematic frequency re-packing towards total digital age 76
Frequency allocation of consecutive transmission Concept of sub-channel 1/7 MHz Sub-channel- bandwidth=1/7 MHz Allocation of sub-channel Spectrum utilization () Consecutive-segment Transmission of DSB channels Transmission from single transmitter keeping OFDM -condition Conventional allocation 3/7MHz ISDB-T SB allocation with guard band Eample of allocation Guard bands guard band guard band ISDB-T SB allocation for consecutive transmission 77 43kHz 1.3MHz 43kHz 1.3MHz Frequency utilization efficiency will be improved up to 15%. 78 Image of consecutive transmission and reception Why is the phase compensation of segment necessary for consecutive transmission? A studio B studio C studio D studio Segment MUX Consecutive Transmission MOD/PA A B C D Frequency spectrum transmitter A B C D E Center of IFFT receiver D f Frequency allocation for 5 one segment channel consecutive transmission Select channel D at receiver side Select required channel Audio/dada decoder OFDM DEM A B C D tuner/ filter Center of FFT The center of IFFT and FFT is different, as a result, each carrier of received OFDM signal rotate during Guard interval period. (see net page) This phase rotation is compensated at the transmitter side. (digital terrestrial audio receiver) channel select 79 8
F =4/Ts F =3/Ts F =/Ts F =1/Ts Tg Phase rotation in every symbol Ts During guard interval (Tg) period, phase rotation (=*N*pai*Tg/TS) occurs. Consequently, each carrier seems to rotate in every symbol period. Tg=1/4*TS Rotate *pai in every symbol Rotate 3*pai/ in every symbol Rotate pai in every symbol Rotate pai/ in every symbol 81 IFFT carrier Relationship between IFFT and FFT for consecutive transmission F=(4N+)/Ts F=(4N+1)/Ts F=/Ts F=1/Ts F= F=-1/Ts F=-/Ts F=-(4N+1)/Ts F=(4N+1)/Ts Center of FFT Center of IFFT F=/Ts F=1/Ts F= F=-1/Ts F=-/Ts (note) F= means the frequency which is the center of FFT and IFFT FFT carrier 8 Phase compensation at transmitter side Center frequency of IFFT Transmitter side Phase of Each carrier in consecutive transmission Frequency slot No. After phase compensation Phase of each carrier at the front end of guard interval Frequency slot No. Center frequency of FFT Receiver side Without phase compensation With phase compensation Tg Eample of phase compensation Ts Pai rotate at the net symbol F =(4N+)/Ts Tg=(1/4)*Ts In every symbol, phase rotate pai No phase rotation In case of consecutive transmission, center frequency of IFFT and FFT is different. Therefore, during guard interval, each carrier phase rotate according to above figure. To avoid such phase rotation at receiver FFT, phase compensation is done at transmitter side. 83 In this eample, center frequency of FFT is equal to F=(4N+)/Ts of IFFT. Therefore, if Tg is equal to (1/4)*Ts, at the front end of every symbol rotate pai. 84
Phase compensation in every symbol Upper adjusent channel format ISDB-TSB studio & transmitter system for consecutive transmission system 1 3 1 segment 3 segment GI mode 1 mode mode 3 mode 1 mode mode 3 1/3-3/8-3/4-1/ -6/8 -/4 1/16-3/4-1/ -/4 1/8-1/ 1/4 1/3-6/8 -/4-1/8-1/4-1/ 1/16 -/4-1/4-1/ 1/8-1/ 1/4 Audio MTX Authoring terminal Audio MTX Authoring terminal Audio ENC Data server (broadcaster studio) Audio ENC Data server (broadcaster studio) Service MUX Service MUX (Consecutive transmitter station) RE- MUX RE- MUX TS interface FEC ENC FEC ENCsegment combine U/C & PA OFDM MOD Number of segment pf received channel 85 86 Details of ISDB-T SB transmitter block diagram System controller (SCS) Broadcaster studio Broadcaster studio Test signal SW SW RE- MUX RE- MUX Sync. signal GEN. FEC ENC FEC ENC Monitor GEN.segment combine OFDM MOD (OFDM MOD) PA U/C IF signal END of Seminar #3 Thank you for your attention After RE-MUX, frame and clock of each channel are synchronized 87 88