Patent Application
20110051825
The present invention relates to digital information transmission field, and more particularly, to a digital multimedia broadcast system and an information transmission method thereof.
Besides large coverage and large program capacity, wireless communication broadcasting has a most excellent characteristic of its broadcast capability which can be point-to-point and point-to-face, and it has high transmission bandwidth with low cost. Thus, as an important component of information communication industry, the wireless communication broadcasting plays an important role in the construction of national information infrastructure and realization of normal service and national information security strategy.
With years of research and development, the digital wireless broadcast has obtained many achievements which reaches practical use stage. Presently, there are 4 wireless digital television broadcast standards in the world:
1) Digital Video Broadcasting (DVB) Standards Series.
DVB is proposed by European Telecommunications Standards Institute (ETSI). After the Europe stopped development of Digital-to-Analog mixed television system in 1993, it began to undertake research on digital television broadcast system, and successively issued Digital Video Broadcasting-Satellite (DVB-S), Digital Video Broadcasting-Cable (DVB-C), Digital Video Broadcasting-Terrestrial (DVB-T) standards and Digital Video Broadcasting-Handheld (DVB-H) standard based on DVB-T.
The DVB-S standard in the above mentioned standards utilizes single carrier QPSK modulation, uses cascaded convolution code and RS code as channel encoding, scrambles with Pseudo-Random Bit Sequence (PRBS), uses wireless satellite links, which is only adaptable to fixed receiving system rather than mobile terminal devices. The DVB-T standard uses multi-carrier Orthogonal Frequency Division Multiplexing (OFDM) modulation technology and encoding technology of cascaded convolution code and RS code, which is adapted to open-ground transmission, however, the moving speed is low. Although the DVB-H system optimizes for mobilization and handheld purpose, the optimization is not sufficient due to the limitation of DVB-T coding and modulation technology.
2) American ATSC Standard
The American ATSC standard is a single-carrier digital television terrestrial transmission standard proposed by Advanced Television System committee (ATSC), which can support fixed receiving of digital television with standard definition and high-definition. However, the performance thereof is inferior under mobile reception condition and can not support satellite transmission.
3) Japanese ISDB-T Standard
ISDB-T is an Integrated Service Digital Broadcasting-Terrestrial standard revised by Japan digital broadcasting expert group which achieves terrestrial broadcasting of various digital services with OFDM technology, convolution code and RS code. However, the performance thereof is inferior under mobile reception condition and can not support satellite transmission.
4) Japan-Korean Digital Satellite Broadcasting Standard
In May, 1998, Toshiba Corp., SKTelecomm Corp., Sharp Corp., Toyota Motor Corp. etc. jointly invested and founded a Mobile Broadcasting Corporation. And it launched a broadcasting satellite in March, 2004, and now it is running into business, providing services for Japan and Korea. The system also uses PRBS, interleaving concatenated encoding, and it transmits in a manner of CDM frequency spreading. Although the Japan-Korean digital satellite broadcasting standard can support mobile reception, the performance thereof is not sound enough, which needs further improvement.
To overcome the shortcomings of the four kinds of transmission modes aforementioned, the present invention optimizes design and proposes an integrated wireless multi-service broadcast system architecture adapted for satellite transmission, terrestrial transmission etc., which can provide for mobile, portable and fixed receiving users with high-quality audio, video and multimedia data services.
The present invention provides a multi-carrier digital mobile multimedia broadcast system comprising a transmitter and portable, fixed or mobile receivers, the transmitter comprising:
a RS encoding and byte interleaving module for RS encoding and byte interleaving an upper layer data stream;
a LDPC encoder for LDPC encoding the data outputted from the byte interleaver to obtain bit data;
a bit interleaver for bit interleaving of the bit data outputted from the LDPC encoder;
a constellation mapping module, in which the data outputted from the bit interleaver is constellation mapped;
a frequency-domain symbol generator for multiplexing together discrete pilots, continuous pilots containing system information and data symbols being constellation mapped to form an OFDM frequency-domain symbol;
a scrambler for scrambling the OFDM frequency-domain symbol;
an OFDM modulator for performing IFFT transformation to the frequency-domain symbol outputted from the scrambler to generate an OFDM time-domain symbol;
a time-domain framing device for concatenating the time slots which are formed with the OFDM time-domain symbols to form a physical layer signal frame.
The system uses wireless channels such as satellite or terrestrial wireless channels etc. mainly for achieving mobile reception. The system supports single frequency network and multi-frequency network modes, and it can select corresponding transmission modes and parameters based on the transmitted data types and networking environments for transmitting video streams such as H.264, AVS, MPEG-2, MPEG-4 etc, and audio streams such as AC-3, AAC etc., and it supports mixed transmission modes with kinds of data types for transmitting broadcasting data including audio data, text and video data.
The present invention also provides a digital information transmission method for a multi-carrier digital mobile multimedia broadcast system, comprising the following steps:
RS encoding and byte interleaving an upper layer data stream with a RS encoding and byte interleaveing module, in which the row numbers of the byte interleaver is determined by a byte interleaving mode and a LDPC code rate;
LDPC encoding the byte interleaved data by a LDPC encoder to obtain bit data;
bit interleaving the LDPC encoded bit data by a bit interleaver;
constellation mapping the byte interleaved data by a constellation mapping module;
multiplexing discrete pilots, continuous pilots containing system information and data symbols being constellation mapped by a frequency-domain symbol generator to form an OFDM frequency-domain symbol;
scrambling the multiplexed OFDM frequency-domain symbol with a scrambler;
performing IFFT transformation to the scrambled frequency-domain symbol to generate an OFDM time-domain symbol by an IFFT transformer;
concatenating the time slots which are formed by inserting a frame head to the time-domain OFDM symbol with a time-domain framing device to form a physical signal frame;
transmitting the physical signal frame after low-pass filtering and orthogonal up-converting.
The digital information transmission method transmits multimedia broadcasting data including audio data, text and video data.
The system adopts an OFDM scheme of LDPC, and the receiver of the system uses the most advanced technologies of microwave and large scale digital integrated circuit which satisfies requirements of low cost and high performance.
The present invention is described but not limited in conjunction with the embodiments shown in the drawings throughout which the similar reference signs represent the similar elements, in which:
The present invention can provide multimedia programs including high quality digital audio broadcasting and digital video broadcasting.
The present invention defines functional modules of the physical layer which can perform adaptive processing to the broadcasting upper layer data stream of the mobile multimedia broadcast system within 8 MHz bandwidth, and it discloses frame structure, channel encoding and modulation technologies of the transmission signals in the physical layer of the mobile multimedia broadcast channel.
The physical layer is an under layer of OSI which is fundamental to the whole open system. The physical layer provides transmission media and interconnecting devices for data communication between devices and provides reliable environments for data transmission.
The physical layer of broadcast channel defined in the present invention meets different transmission rates for various applications of the upper layers by the physical logical channels. The physical logical channels support various encoding and modulating manners to satisfy different requirements of different applications, different transmission environments to signal quality.
The physical layer of the broadcast channel defined in the present invention supports two kinds of networking modes, i.e., a single frequency network and a multi-frequency network. And different transmission modes and parameters can be selected based on actually application characteristics and networking environments. And mixed mode of various applications is provided to match the application characteristics with the transmission mode, thus achieving flexibility and economy of applications.
The preferred embodiment of the invention will be described in detail with reference to accompanying figures.
As shown in the Figure, the physical layer provides a broadcast channel for upper layer application by a physical logical channel, i.e., PLCH, which includes a control logic channel (CLCH) and a service logic channel (SLCH). Each physical logical channel can use one or more of time slots in the 8MHz digital television bandwidth for transmission. The physical layer performs separate encoding and modulation for each physical logical channel. The physical logical channel can provide different transmission capacity with different encoding and modulating parameters.
As shown in the figure, the inputted, data stream of the physical logical channel undertakes OFDM modulation by multiplexing together with discrete pilot and continuous pilot after forward correction encoding, interleaving and constellation mapping. The modulated signal forms a physical signal frame after being inserted with a frame head. And the signal is transmitted after being transformed from baseband to RF (radio-frequency).
The physical logical channel is divided into the control logical channel (CLCH) and the service logical channel (SLCH). The control logical channel carries system configuration information, and uses a fixed channel encoding and modulation model to transmit at the 0th time slot of the system, in which: RS encoding uses RS(240, 240), the LDPC encoding uses LDPC encoding with ½ code rate, the constellation mapping uses BPSK mapping, the scramble mode adopts mode 0. The service logical channel can use one or more time slots except the 0th time slot for transition, and the encoding and modulation mode thereof are configured by the upper layers, the configuration information is broadcasted through the control logical channel.
The sub-modules in
As shown in the figure, each second represents 1 frame in the signal of the physical layer of the system, and each frame is divided into 40 time slots (TS), with each time slot having a length of 25 ms.
Each time slot comprises a beacon and 53 OFDM modulating data blocks.
As shown in the figure, the beacon has two same synchronous signals and a transmitter identification signal (ID).
The synchronous signal is a pseudo-random sequence with a limited frequency band, having a length of 204.8 us. The synchronous signal is generated as follows: firstly, the pseudo-random sequence is generated by a pseudo-random sequence generator for synchronous signal as shown in
The transmitter identification signal (ID) transmits a pseudo-random sequence with limited frequency-band having a length of 36 us for identifying different transmitter. The generating method of the transmitter identification signal is as follows:
Selecting a transmitter identification sequence; after BPSK mapping (0→1+0j, 1→−1+0j) of the 191-point transmitter identification sequence, they are putted into the 1th˜95th and 160th˜255th points in the 256-point (0˜255) sequence; after the 256 point being subjected to IFFT and extending the period to 360 points, thus obtaining the transmitter identification signal.
The transmitter identification sequence is a pseudo-random sequence with a length of 191 bits. The transmitter identification sequence includes 256 sequences in total in which the 0th˜127th sequence designates district identification for identifying location of the transmitter, and it is inserted and transmitted by the even time-slots in the signal frame (the 0th time slot, the second time slot, . . . ); the 128th˜255th sequence designates the identification of a transmitter for identifying different transmitters in a same district, which is inserted and transmitted by the odd time-slots in the signal frame (the first time-slot, the third time-slot, . . . ). The transmitter identification sequence is defined by a hex sequence which is mapped to a binary transmitter identification sequence in an order that the highest effective bit first to enter into the BPSK mapping step. The transmitter identification sequences are shown as in Table 1.
As shown in the figure, the OFDM symbol comprises a circular prefix (CP) and an OFDM symbol body, the length TCP of the circular prefix is 51.2 us, the length TS of the OFDM symbol is 409.6 us.
The transmitter identification signal, the synchronous signal and the neighboring OFDM symbol in
The expression of the window function is as follows:
The selection of the guard interval signals is as shown in
The sub-systems in
As shown in the figure, the byte interleaver is a block interleaver with M1 rows and 240 columns. The row number M1 of the byte interleaver is determined by the byte interleaving mode and the LDPC code rate as shown in Table 3:
The RS code adopts a RS(240, K) shortened code with a code length of 240 bytes. The code is generated by shortening the original RS(255, M) system code, in which M=K+15 where K is the byte number of information sequence in a code word while the check byte number is (240-K). The RS(240, K) code provides 4 kinds of modes with K values of K=240, K=224, K=192 and K=176 respectively.
Each code bit of the RS(240, K) code is picked from a domain GF(256) which has a generating polynomial p(x)=x8+x4+x3+x2+1.
The shortened code RS (240, K) is encoded as follows:
15 full “0” byte are added in front of K input information bytes (m0,m1, . . . ,mK-1), thus an input sequence (0, . . . 0,m0,m1, . . . ,mK-1) as the original RS (255, M) system code is constructed, after encoding the generated code word is (0, . . . , 0,m0,m1, . . . , mK-1,p0,p1, . . . ,p255-M-1), then the added bytes are removed from the code word, thus obtaining a code word (m0,m1, . . . , mK-1,p0,p1, . . . , p255-M-1) as a shortened RS code with 240 bytes.
The expression of the generating polynomial of the RS (240, K) code is as follows:
The expression of the inputted information sequence polynomial is as follows:
The expression of the outputted system code polynomial is as follows:
The coefficients gi of the generated polynomial expression of the RS (240, 224) are as follows:
The coefficients gi of the generated polynomial expression of the RS (240, 192) are as follows:
The coefficients gi of the generated polynomial expression of the RS (240, 176) are as follows:
The method of encoding and the byte interleaving is as follows: data block is transmitted by byte, and inputted into the block interleaver from left to right column by column until the Kth column with each column having MI bytes. The RS encoding is performed by row, and the verifying bytes are filled to the latter (240-K) columns. The encoded data is outputted from left to right column by column as the order of inputting until all 240 columns are finished.
The above RS encoding and the byte interleaving are undertaken based on physical logical channels. The upper layer packages of the same physical logical channel are inputted into the byte interleaver in turn for byte interleaving and RS encoding. The first byte of the 0th column in the byte interleaver is defined as a start byte of the byte interleaver. Each output of the byte interleaver (M1×240 bytes) are always mapped to a integer number of time slots to be transmitted, in which the start byte of the byte interleaver is mapped to a start point of a certain time slot to be transmitted.
After the RS encoding and byte interleaving, the transmission data is transmitted based on the rule of bit of higher order having higher priority for transmitting, and each byte is mapped to form a 8-bit stream to be transmitted into the LDPC encoder. The first byte of the 0th column in the byte interleaver is defined as the start byte of the byte interleaver with the bit of highest order being mapped to the first bit of the LDPC inputting bit block. The LDPC encoding configuration is shown in Table 4:
The LDPC encoding is given by a check matrix H, and the generating method of the matrix H is as follows:
The following is a circular program segment for generating the
LDPC code check matrix:
using the Ith row of the above table, and being designated as hexp;
for J=1:256;
column=[(└hexp(K)/36┘+J−1)% 256]*36+(hexp(K) % 36)+1.
The rowth row and the columnth column of the parity check matrix being non-zero elements;
2) a generating method of a
LDPC code check matrix
The following a is a circular program segment for generating the
LDPC code check matrix:
for I=1:9;
using the Ith row of the above table, and being designated as hexp;
for J=1:256;
column=[(└hexp(K)/36┘J−1)% 256]*36+(hexp(K) % 36)+1.
The rowth row and the columnth column of the parity check matrix being non-zero elements;
LDPC encoded.
As shown in the figure, the bit interleaver uses a 384×360 block interleaver. The LDPC encoded binary sequence is written into each row of the block interleaver in turn in the order from up to low until the whole interleaver is filled up, then it is read from left to right in turn based on column. The output of the bit interleaver is aligned with the time slot, i.e., the first bit transmitted in each time slot is always defined as the first bit outputted from the bit interleaver.
As shown in the figure, the part of oblique line is a continuous pilot signal, the black part is a discrete pilot signal, the white part is data obtained by constellation mapping. The pilot multiplexing procedure multiplexes the data symbol, the discrete pilot and the continuous pilot, forming an OFDM frequency-domain symbol. Each OFDM symbol comprises 3076 sub-carriers (0-3075), denoting as X(i), i=0,1, . . . 3075.
In
The 22th, 78th, 92th, 168th, 174th, 244th, 274th, 278th, 344th, 382th, 424th, 426th, 496th, 500th, 564th, 608th, 650th, 688th, 712th, 740th, 772th, 846th, 848th, 932th, 942th, 950th, 980th, 1012th, 1066th, 1126th, 1158th, 1214th, 1860th, 1916th, 1948th, 2008th, 2062th, 2094th, 2124th, 2132th, 2142th, 2226th, 2228th, 2302th, 2334th, 2362th, 2386th, 2424th, 2466th, 2510th, 2574th, 2578th, 2648th, 2650th, 2692th, 2730th, 2796th, 2800th, 2830th, 2900th, 2906th, 2982th, 2996th, 3052th carriers, 64 in total, carry 16 bit system information. The system information bits are transmitted by 4 times repeat encoding to be mapped to 4 continuous pilots. The mapping relationship is shown in Table 5, the detailed expression of the system information is shown in Table 6, with the remaining continuous pilots transmitting “0”.
Each bit in table 6 contains the following information:
1) bit.0˜bit 5 are the current time slot number ranging from 0 to 39;
2) bit 6 is the bit interleaver synchronous identification, when the bit is “1”, the current time slot is identified as the start time slot of the byte interleaver;
3) bit 7 is a control logical channel modify indication which indicates modification of the terminal's control logical channel configuration information by differential modulation. The differential modulation is as follows: supposing the bit 7 in the former frame transmitting a (zero or 1), and the system control channel configuration information will be modified in the next frame, the ā is transmitted in the current frame and remains until next modification.
4) bit 8˜bit 15 are reserved.
The continuous pilots are mapped to the sub-carriers in the manner of 0→√{square root over (2)}/2+√{square root over (2)}/2j, 1→−√{square root over (2)}/2−√{square root over (2)}/2j. The same continous sub-carrier points of different OFDM symbols in the same time slot transmit the same symbols.
The number OFDM symbol in each time slot is designated as n, 0≦n≦52; m is the sub-carrier number corresponding to the discrete pilot in each OFDM symbol, and m is:
All discrete pilots are set to 1+0j.
In
All symbols (effective sub-carriers) on the time-frequency grid of
in which Si(i) and Sq(i) are binary pseudo-random sequences (PRBS).
As shown in the Figure, the PRBS generating polynomial is: x12+x11+x8+x6+1 which is corresponding to the shift register structure shown in the figure. The initial value of the shift register is determined by scrambling mode with the corresponding relationships as follows:
1) scrambling mode 0: initial value 0000 0000 0001
2) scrambling mode 1: initial value 0000 1001 0011
3) scrambling mode 2: initial value 0000 0100 1100
4) scrambling mode 3: initial value 0010 1011 0011
5) scrambling mode 4: initial value 0111 0100 0100
6) scrambling mode 5: initial value 0100 0100 1100
7) scrambling mode 6: initial value 0001 0110 1101
8) scrambling mode 7: initial value 1010 1011 0011
PRBS is reset at the start of each time-slot, all time slots being scrambled by the same pattern of scrambling code.
The scrambling code is obtained by complex multiplication of the complex symbol on the effective sub-carriers with the complex pseudo-random sequence Pc(i), the expression of the scrambling code is as follows:
Y
n(i)=Xn(i)×Pc(n×3076+i), 0≦i≦3075, 0n≦52
in which the Xn(i) is the ith effective sub-carrier on the nth OFDM symbol in each time slot before scrambling and the Yn(i) is the effective sub-carrier after scrambling.
The OFDM sub-carriers X(i), i=0,1, . . . ,3075 after being inserted with pilot and scrambled generate an OFDM time-domain symbol after subjected to IFFT transformation. The IFFT transforming manner is as follows:
In which
The OFDM symbol after IFFT transformation is added with circular prefix (CP) to form a time-domain OFDM symbol as shown in
The modulated OFDM symbol is added with guard intervals, synchronous signal, and transmitter identification signal in turn according to the frame structure as shown in
The time-domain shaping filter used in the system is a FIR filter satisfying ripple attenuation <1 dB within the bandwidth of a signal and attenuation >40 dBc outside the bandwidth thereof. The frequency bandwidth is 8 MHz which is compatible with conventional analog television bandwidth. The system sampling rate is 10 MHz, and the signal bandwidth of each channel is 7.512 MHz.
The data stream of the upper layer of the system can adopt video streams including H.264, AVS, MPEG-2, MPEG-4 etc, audio streams such as AC-3, AAC etc and other various types of data formats. Encoding data can includes various types of broadcast data including single medium (such as video source encoding, text) and multimedia (mixture of audio, video, text and data).
Although the present invention is described in conjunction with the examples and embodiments, the present invention is not intended to be limited thereto. On the contrary, the present invention obviously covers the various modifications and may equivalences, which are all enclosed in the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200610113915.9 | Oct 2006 | CN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN2006/003070 | 11/15/2006 | WO | 00 | 11/8/2010 |
