The ISDB-TSB system uses OFDM modulation, two-dimensional frequency-time interleaving and concatenated error correction codes. OFDM is a multi-carrier modulation method, and it is a multipathproof modulation method, especially adding a guard interval in the time domain. The transmitted information is spread in both the frequency and time domains by interleaving, and then the information is corrected by the Viterbi and Reed-Solomon (RS) decoder. Therefore a high quality signal is obtained in the receiver, even when working in conditions of severe multipath propagation, whether stationary or mobile.
126.96.36.199 Wide variety of transmission
The ISDB-TSB system adopts BST-OFDM, and consists of one or three OFDM-segments. That is single-segment transmission and triple-segment transmission. A bandwidth of OFDM-segment is defined in one of three ways depending on the reference channel raster of 6, 7 or 8 MHz. The bandwidth is a fourteenth of the reference channel bandwidth (6, 7 or 8 MHz), that is, 429 kHz (6/14 MHz), 500 kHz (7/14 MHz), 571 kHz (8/14 MHz). The bandwidth of OFDM-segment should be selected in compliance with the frequency situation in each country.
The bandwidth of single-segment is around 500 kHz, therefore the bandwidth of single-segment transmission and triple-segment transmission is approximately 500 kHz and 1.5 MHz.
The ISDB-TSB system has three alternative transmission modes which allow the use of a wide range of transmitting frequencies, and four alternative guard interval lengths for the design of the distance between SFN transmitters. These transmission modes have been designed to cope with Doppler spread and delay spread, for mobile reception in presence of multipath echoes.
A multiplex structure of the ISDB-TSB system is fully compliant with MPEG-2 systems architecture. Therefore various digital contents such as sound, text, still picture and data can be transmitted simultaneously.
In addition, according to the broadcaster’s purpose, they can select the carrier modulation method, error correction coding rate, length of time interleaving, etc. of the system. There are four kinds of carrier modulation method of DQPSK, QPSK, 16-QAM and 64-QAM, five kinds of coding rate of 1/2, 2/3, 3/4, 5/6 and 7/8, and five kinds of time interleaving length from 0 to approximately 1 s. The TMCC carrier transmits the information to the receiver indicating the kind of modulation method and coding rate that are used in the system.
188.8.131.52 Flexibility Commonality and interoperability
The ISDB-TSB system uses BST-OFDM modulation and adopts MPEG-2 systems. Therefore the system has commonality with the ISDB-T system for digital terrestrial television broadcasting (DTTB) in the physical layer, and has commonality with the systems such as ISDB-T, ISDB-S, DVB-T and DVBS which adopt MPEG2 Systems in the transport layer.
184.108.40.206 Efficient transmission and source coding
The ISDB-TSB system uses a highly-spectrum efficient modulation method of OFDM. Also, it permits frequency reuse broadcasting networks to be extended using additional transmitters all operating on the same radiated frequency.
In addition, the channels of independent broadcasters can be transmitted together without guardbands from the same transmitter as long as the frequency and bit synchronization are kept the same between the channels.
The ISDB-TSB system can adopt MPEG-2 AAC. Near CD quality can be realized at a bit rate of 144 kbit/s for stereo.
220.127.116.11 Independency of broadcasters
The ISDB-TSB system is a narrow-band system for transmission of one sound programme at least. Therefore broadcasters can have their own RF channel in which they can select transmission parameters independently.
18.104.22.168 Low-power consumption
Almost all devices can be made small and light weight by developing LSI chips. The most important aspect of efforts to reduce battery size is that the power consumption of a device must be low. The slower the system clock, the lower the power consumption. Therefore, a narrow-band, low bit rate system like single-segment transmission can allow for the receiver to be both portable and lightweight.
In the triple-segment transmission, both one layer transmission and hierarchical transmission can be achieved. There are two layers of A and B in the hierarchical transmission. The transmission parameters of carrier modulation scheme, coding rates of the inner code and a length of the time interleaving can be changed in the different layers.
The centre segment of hierarchical transmission is able to be received by single-segment receiver. Owing to the common structure of an OFDM segment, a single-segment receiver can partially receive a centre segment of full-band ISDB-T signal whenever an independent program is transmitted in the centre segment.
Figure 10 shows an example of hierarchical transmission and partial reception.
Example diagram of hierarchical transmission and partial reception
OFDM frame structure
1.4.2 Transmission parameters
The ISDB-TSB system can be assigned to 6 MHz, 7 MHz or 8 MHz channel raster. Segment bandwidth is defined to be a fourteenth of channel bandwidth, therefore that is 429 kHz (6/14 MHz), 500 kHz (7/14 MHz) or 571 kHz (8/14 MHz). However, the segment bandwidth should be selected in compliance with the frequency situation in each country.
The transmission parameters for the ISDB-TSB system are shown in Table 1.
(1) The ISDB-TSB system uses 1 or 3 segments for sound services, while any number of segments may be used for other services such as television services. (Compare with System C of Recommendation ITU-R BT.1306.)
(2) SP (scattered pilot), and CP (continual pilot) can be used for frequency synchronization and channel estimation. The number of CP includes CPs on all segments and a CP for higher edge of whole bandwidth.
(3) TMCC carries information on transmission parameters.
(4) AC (auxiliary channel) carries ancillary information for network operation.
1.4.3 Source coding
The multiplex structure of the ISDB-TSB system is fully compliant with MPEG-2 systems architecture, therefore MPEG2 transport stream packets (TSPs) containing compressed digital audio signal can be transmitted. Digital audio compression methods such as MPEG-2 Layer II audio specified in ISO/IEC 13818-3, AC3 (Digital Audio Compression Standard specified in ATSC Document A/52) and MPEG2 AAC specified in ISO/IEC 138187 can be applied to the ISDB-TSB system.
The multiplex of the ISDB-TSB system is compatible with MPEG-2 TS ISO/IEC 13818-1. In addition, multiplex frame and TMCC descriptors are defined for hierarchical transmission with single TS.
Considering maximum interoperation among a number of digital broadcasting systems, e.g. ISDBS recommended in Recommendation ITU-R BO.1408, ISDB-T recommended in Recommendation ITU-R BT.1306 (System C) and broadcasting-satellite service (sound) system using the 2.6 GHz band recommended in Recommendation ITU-R BO.1130 (System E), these systems can exchange broadcasting data streams with other broadcasting systems through this interface.
22.214.171.124 Multiplex frame
To achieve hierarchical transmission using the BST-OFDM scheme, the ISDB-TSB system defines a multiplex frame of TS within the scope of MPEG-2 systems. In the multiplex frame, the TS is a continual stream of 204-byte RS-TSP composed of 188-byte TSP and 16 bytes of null data or RS parity.
The duration of the multiplex frame is adjusted to that of the OFDM frame by counting RSTSPs using a clock that is two times faster than the inverse FFT (IFFT) sampling clock in the case of single-segment transmission. In the case of the triple-segment transmission the duration of the multiple frame is adjusted to that of the OFDM frame by counting RSTSPs using a clock that is four times faster than the IFFT sampling clock.
1.4.5 Channel coding
This section describes the channel coding block, which receives the packets arranged in the multiplex frame and passes the channel-coded blocks forward to the OFDM modulation block.
126.96.36.199 Functional block diagram of channel coding
Figure 11 shows the functional block diagram of channel coding of the ISDB-TSB system.
The duration of the multiplex frame coincides with the OFDM frame by counting the bytes in the multiplex frame using a faster clock than IFFT-sampling rate described in the previous section.
At the interface between the multiplex block and the outer coding block, the head byte of the multiplex frame (corresponding to the sync-byte of TSP) is regarded as the head byte of the OFDM frame. In bit-wise description, the most significant bit of the head byte is regarded as the synchronization bit of OFDM frame.
For the triple-segment layered transmission, the RS-TSP stream is divided into two layers in accordance with the transmission-control information. In each layer, coding rate of the inner error correction code, carrier-modulation scheme, and time-interleaving length can be specified independently.
Channel coding diagram
188.8.131.52 Outer coding
RS (204,188) shortened code is applied to each MPEG-2 TSP to generate an error protected TSP that is
RS-TSP. The RS (208,188) code can correct up to eight random erroneous bytes in a received 204-byte word.
b) RS-TSP (transmission TSP), RS (204,188) error protected TSP
MPEG-2 transport multiplexed data
184.108.40.206 Energy dispersal
In order to ensure adequate binary transitions, the data from the splitter is randomized with pseudorandom binary sequence (PRBS).
The polynomial for the PRBS generator shall be:
g(x) x15 x14 1
1.4.6 Delay adjustment
In the byte-wise interleaving, the delay caused in the interleaving process differs from stream to stream of different layer depending on its properties (i.e. modulation and channel coding). In order to compensate for the delay difference including de-interleaving in the receiver, the delay adjustment is carried out prior to the byte-wise interleaving on the transmission side.
Convolutional byte-wise interleaving with length of I 12 is applied to the 204-byte error protected and randomized packets. The interleaving may be composed of I 12 branches, cyclically connected to the input byte-stream by the input switch. Each branch j shall be a first-in first-out (FIFO) shift register, with length of j 17 bytes. The cells of the FIFO shall contain 1 byte, and the input and output switches shall be synchronized.
The de-interleaving is similar, in principle, to the interleaving, but the branch indices are reversed. Total delay caused by interleaving and de-interleaving is 17 11 12 bytes (corresponding to 11 TSPs).
220.127.116.11 Inner coding (convolutional codes)
The ISDB-TSB system shall allow for a range of punctured convolutional codes, based on a mother convolutional code of rate 1/2 with 64 states. Coding rates of the codes are 1/2, 2/3, 3/4, 5/6 and 7/8. This will allow selection of the most appropriate property of error correction for a given service or data rate in the ISDB-TSB services including mobile services. The generator polynomials of the mother code are G1 171oct for X output and G2 133oct for Y output.
Configuration of the modulation block is shown in Figs. 13 and 14. After bit-wise interleaving, data of each layer are mapped to the complex domain.
Modulation block diagram
Configuration of carrier modulation block
18.104.22.168 Delay adjustment for bit interleave
Bit interleave causes the delay of 120 complex data (I jQ) as described in the next section. By adding proper delay, total delay in transmitter and receiver is adjusted to the amount of two OFDM symbols.
One of the carrier modulation schemes among DQPSK, QPSK, 16-QAM and 64-QAM is selectable for this System. The serial bit-sequence at the output of the inner coder is converted into a 2bit parallel sequence to undergo /4-shift DQPSK mapping or QPSK mapping, by which n bits of Iaxis and Q-axis data are delivered. The number n may depend on the hardware implementation. In the case of 16-QAM, the sequence is converted into a 4-bit parallel sequence. In 64-QAM, it is converted into a 6-bit parallel sequence. After the serial-to-parallel conversion, bit-interleaving is carried out by inserting maximum 120-bit delay.
22.214.171.124 Data segment
Data segment is defined as a table of addresses for complex data, on which rate conversion, time interleaving, and frequency interleaving shall be executed. The data segment corresponds to the data portion of OFDM segment.
126.96.36.199 Synthesis of layer-data streams
After being channel-coded and mapped, complex data of each layer are inputted every one symbol to pre-assigned data-segments.
The data stored in all data segments are cyclically read with the IFFT-sample clock; then rate conversions and synthesis of layer data streams are carried out.
188.8.131.52 Time interleaving
After synthesis, symbol-wise time interleaving is carried out. The length of time-interleaving is changeable from 0 to approximately 1 s, and shall be specified for each layer.
Frequency interleaving consists of inter-segment frequency interleaving, intra-segment carrier rotation, and intra-segment carrier randomization. Inter-segment frequency interleaving is taken among the segments having the same modulation scheme. Inter-segment frequency interleaving can be carried out only for triple-segment transmission. After carrier rotation, carrier randomization is performed depending on the randomization table.
184.108.40.206 OFDM segment-frame structure
Data segments are arranged into OFDM segment-frame every 204 symbols by adding pilots such as CP, SP, TMCC and AC. The modulation phase of CP is fixed at every OFDM symbol. SP is inserted in every
12 carriers and in every 4 OFDM symbols in the case of coherent modulation method. The TMCC carrier carries transmission parameters such as carrier modulation, coding rate and time interleaving for the receiver control. The AC carrier carries the ancillary information.