CN1247026C - Mobile terminal oriented multimedia broadcasting system and implementing method thereof - Google Patents
Mobile terminal oriented multimedia broadcasting system and implementing method thereof Download PDFInfo
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- CN1247026C CN1247026C CN 200410037431 CN200410037431A CN1247026C CN 1247026 C CN1247026 C CN 1247026C CN 200410037431 CN200410037431 CN 200410037431 CN 200410037431 A CN200410037431 A CN 200410037431A CN 1247026 C CN1247026 C CN 1247026C
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Abstract
The present invention relates to a multimedia broadcasting system and a realizing method thereof which face a mobile terminal. The present invention is characterized in that the frequency band of the existing common television broadcasting system is used by the present invention based on an orthogonal frequency division multiplex multi-channel (OFDM-MC) system, and different channels are arranged on different sub-carrier groups in the form of large zone broadcasting to carry out the reverse rapid Fourier (IFFT) transformation of a transmission end and the rapid Fourier (FFT) transformation of a receiving end in order to provide multimedia broadcasting services to a mobile terminal. The multimedia broadcasting system can economically and efficiently provide scores of channel playing multimedia programs, and an utilization rate of a frequency band is high. The multimedia broadcasting system can realize individuation broadcasting to users having different quality requirements. Dynamical power control, modulation, forward error correction coding and frequency hopping can be realized to ensure transmission quality. The present invention is also favorable for the design simplification and the power consumption reduction of the receiving end.
Description
Technical field
The crossing domain that belongs to television broadcasting and wireless multimedia communication technology towards multi-media broadcasting system and its implementation of portable terminal, be particularly related to the multi-media broadcasting system that a kind of frequency range of utilizing existing Internet resources and television broadcasting is transmitted, be primarily aimed at portable terminal cheap MBMS service is provided.
Background technology
In modern wireless transmitting system, television broadcasting, mobile communication system and new generation of wireless local area network (LAN) (WLAN) can provide MMS (Multimedia Message Service) to a certain degree, but because the data volume of multimedia messages is very big, to the characteristics such as error code sensitivity of channel error, have some problems at the multi-media transmission system of portable terminal always.
The analog television broadcast system is a multi-media transmission system the earliest, but the vestigial sideband modulation technology is adopted in traditional analog television broadcasting, can't resist Doppler effect and multipath fading in moving, and data transfer rate is very low, the video transmission in can't supporting to move.Therefore, along with the development of digital technology, there has been the relevant criterion of many cover high definition digital televisions to come out now.Nineteen ninety-five, the U.S. took the lead in releasing digital television broadcasting standard A TSC, and 1996, European various countries also released digital television broadcasting standard DVB-T, and Japan proposed the digital television broadcasting standard I SDB-T of oneself in 1998.The standardization effort that China now also carries out digital television broadcasting.But these standards towards digital television broadcasting all do not have well to solve the problem how multimedia service is provided at portable terminal especially portable mobile termianl.
Second generation digital mobile communication system and 3-G (Generation Three mobile communication system) in the future can provide multimedia transmission to a certain degree, but it is because limited to the frequency resource of mobile communication system distribution, at the very big multimedia messages transmission of data volume, adopt the network of mobile communication to transmit the frequency spectrum resource that needs waste very big, and the technical scheme of ensuring the quality of products under the various low-power of needs is very uneconomic scheme.In addition, utilizing mobile communications network to carry out multimedia transmission needs complicated Network Management Function, and this network management for the mobile network is a very big challenge.
Therefore, with the advantages of digital television broadcasting and traditional mobile communication system, towards portable terminal, the multimedia service of big data quantity is provided is the only way of the communication technology and broadcast technology development.
Just be based on the promotion in above consideration and market, the multimedia broadcasting transmission standard at portable terminal has been formulated in Europe.2003, the portable terminal microwave digital television conversion regime DVB-H standard formulation work of the european microwave digital television standard DVB of group (digital video broadcasting project) was finished substantially.
Some main features of DVB-H standard are:
The target of ■ DVB-H standard is to make ground digital television broadcast (DVB-T) signal of portable mobile terminal receiving planes such as mobile phone to family expenses HD digital television set.
The architecture of ■ DVB-H needs " cooperation platform " (a Cooperate Platform), and this platform is considered network condition and determined to select to use ground digital television broadcast network or mobile network to transmit desired content to the DVB-H terminal.The DVB-H terminal can receive the content of multimedia based on the IP data broadcasting---by ground digital television broadcast network (DVB-T) or mobile network, as universal mobile telecommunications system (UMTS).
■ DVB-H is designed for to battery powered terminal and transmits the 10Mbps data.The DVB-H standard can be used part DVB-T receiving circuit, and receiving circuit some technological improvements have been carried out at portable terminal, so that reduce its power consumption, its target is that total power consumption such as antenna, TV tuner and OFDM decoding circuit are controlled at below the 100mW.
But also there are some problems in DVB-H:
■ DVB-H standard is being subjected to certain limitation in order to keep the compatibility with DVB-T aspect the design of architecture, be configured together with DVB-T.
■ just relays the TV programme of DVB-T based on the system of DVB-H standard, and this is greatly affected with regard to the scope that makes its service-user, is difficult to guarantee audience ratings.
■ DVB-H can cause the waste of resource, if adopt digital terrestrial television networks (DVB-T) transmission, then can cause the waste of frequency resource; If adopt mobile network such as UMTS, then can bring the very big challenge of resource management to the mobile network.
There is the incompatible digital television broadcasting standard of many covers in what is more important on the our times, China is releasing the digital television broadcasting standard of oneself, and DVB-H can't provide a kind of general service at all.
Based on above consideration, the present invention is directed to the development of Chinese TV broadcasting and communication network, the multi-media broadcasting system towards portable terminal of the suitable China's actual conditions of one cover has been proposed, this system adopts OFDM multichannel (OFDM-MC, Orthogonal Frequency Division Multiplexing-Multi-Channel) mechanism, distribution by subcarrier, a 8MHz frequency range of television broadcasting is divided into tens channels, can utilize limited band resource to greatest extent, and help adopting the simplified design of various adaptive optimisation strategy and receiving terminal.Compare with existing system, the present invention can more effectively utilize limited frequency resource, and the high quality multimedia service is provided.
Summary of the invention
The object of the present invention is to provide a kind of multi-media broadcasting system and its implementation towards portable mobile termianl.
An object of the present invention is to provide a kind of implementation of carrying out multimedia service towards portable terminal, the present invention uses the frequency range of existing public TV broadcasting, and the mode of broadcasting by Da Qu provides multi-media broadcasting service to portable terminal.OFDM multichannel (the OFDM-MC that the present invention proposes, Orthogonal Frequency Division Multiplexing-Multi-Channel) system is to realize by the fast Fourier transform (FFT) that different channels is configured in the contrary fast Fourier transform (FFT) that carries out transmitting terminal on the different sub carrier group and receiving terminal.Utilize this mechanism, can provide tens special channels that multimedia broadcasting program is provided economical and efficient, in moving, select to watch for the user.Made full use of limited frequency resource in the design of this system, the network architecture flexible configuration.Be to guarantee the quality of video transmission, adopted OFDM modulation technique and error correction coding efficiently, and adopt frequency hopping to guarantee with the needed QoS of multi-media broadcasting service in realizing moving at the broadcast node (BP) of transmitting terminal.
Another object of the present invention is to have proposed a kind of special multi-media broadcasting system at portable mobile termianl, and its system configuration is formed block diagram such as accompanying drawing 1.The physical structure of native system comprises a plurality of multimedia programmings source, multimedia coding unit, repeated link, distributed broadcast node and a plurality of portable mobile termianl.
For realizing purpose of the present invention, the work basic principle of the multi-media broadcasting system that the present invention proposes is:
1) make different multimedia programmings in program source, each road programme information all comprises video source, audio sources and additional information (as caption information, condition receiving control information etc.);
2) video source of each road program, audio sources and additional information through compressed encoding, multiple connection, packing encapsulation efficiently, form one tunnel multimedia code stream respectively;
3) coded data is multiplexed to one road code stream earlier, and repeated link is transferred to each broadcast node (BP) then, is divided into demultiplexing code stream more then; Repeated link in the native system can be metropolitan area network, proprietary microwave link and fiber optic network;
4) at broadcast node (BP), after the code stream in multi-channel program source is modulated through forward error correction coding, OFDM-MC, just can go out with the band transmit of multimedia broadcasting by transmitter module, cover certain zone, can guarantee the quality of multimedia transmission, can not impact existing broadcasting and communication system; In native system, the broadcast node of transmitting terminal (BP) can be formed multiple frequency network, MFN, also can form single frequency network;
5) at receiving terminal, travelling carriage receiving multimedia broadcast signal, demodulation then, decoding obtain multimedia messages.
For realizing purpose of the present invention, the employing of broadcast node (BP) OFDM-MC modulation and forward error correction coding scheme, can be used as an independent functional unit, also can with other module, the access point of WLAN (wireless local area network) (AP) for example, combining is configured; Broadcast node among the present invention (BP) can be according to the application scenario, its coverage of flexible design, realize the service (as a certain residential quarters, campus etc.) of different range, can farthest save resource and realize the covering (in subway station) in some special area.
For realizing purpose of the present invention, portable mobile receiving terminal adopts the OFDM-MC reception technique, and this receiving element can be independent travelling carriage, is configured in taxi, the bus etc. such as can be used as Vehicle mounted station, also can be configured in the personal car.This portable mobile termianl also can be used as a plug-in unit and other mobile device, fits together such as mobile terminal devices such as mobile phone, PDA(Personal Digital Assistant), notebooks, and the user can receive, watch multimedia broadcasting more easily in moving.
For realizing purpose of the present invention, repeated link can flexible configuration, can be the proprietary fiber optic network of metropolitan area network, operator, microwave relay link etc.; The transfer of data of repeated link can adopt general relay data host-host protocol, and interface adopts basic rate interface (BRI) and primary rate interface (PRI).
Multi-media broadcasting system towards portable terminal proposed by the invention is characterised in that it contains:
A plurality of multimedia programmings are made the source, and each road programme information of its output comprises video information, audio-frequency information and additional information, and additional information comprises caption information, condition receiving control information;
Multimedia coding unit, its input are the multi-channel program information of above-mentioned program making source output, and its output is the road multimedia messages code stream that above-mentioned multi-channel program information is formed through efficient compressed encoding, multiple connection, packing encapsulation back respectively;
Repeated link can be any in metropolitan area network, proprietary microwave link or the optical fiber link, and its input is the road multimedia messages code stream that above-mentioned multimedia coding unit forms;
The broadcast node of transmitting terminal, represent with BP, compose in series successively by forward error correction coding unit, OFDM-MC modulating unit, up-conversion and transmitter unit, a plurality of broadcast nodes can be formed multiple frequency network, MFN or single frequency network, their input is respectively established one road multimedia messages code stream that above-mentioned repeated link transmits, their output separately is the mode of broadcasting by multimedia broadcasting launching tower Yi Da district through forward error correction coding, OFDM multichannel modulation back, the multimedia broadcasting information of going out with the band transmit of multimedia broadcasting.
The implementation method of multi-media broadcasting system towards portable terminal proposed by the invention is characterised in that, it is a kind ofly to have based on the OFDM multichannel, it is the OFDM-MC system, utilize the frequency range of existing public TV broadcasting, mode by Da Qu broadcasting, different channels is configured on the different sub carrier group, carries out that the FFT conversion of the IFFT conversion of transmitting terminal and receiving terminal realizes, it is realized by following method in each following link:
The multimedia coding unit, according to the quality and the requirement of multi-media broadcasting service, adopt following two kinds of coding modes:
The low rate coding pattern: the data rate of each channel is 128Kbit/s, and coding is adopted international standards, and image adopts standardized picture format, i.e. QCIF or Sub-QCIF form;
High-rate coded pattern: and the coded format of Moving Picture Experts Group-2 compatibility, data rate is 352 * 288 standard C IF form for the 1.5Mbit/s picture format;
Repeated link adopts the I series of user network interface protocols of International Telecommunications Union's definition, comprises basic rate interface and primary rate interface, represents with BRI and PRI respectively;
The transmitting terminal broadcast node adopts OFDM-MC system and methods for forward error correction coding, and it is provided with following packet and form thereof:
(1) the control data packet format of transport layer:
The size of control data bag is 200, and its transmission intercal is 1s, because channel transmission rate is 130.358Kbit/s, the transmission time is approximately 1.53ms, and its data format is as follows:
40 of header informations are 1 all, represent that this packet is the control data bag;
Control data, every group is 32, repeats 5 times, has wherein adopted BCH (31,21), and parity check bit of back annex, constitutes 32, the data format in its 21 bit data is followed successively by:
The source encoding pattern field of data channel, is provided with the low bit rate mode of 128Kbit/s, the high bit rate mode of 1.5Mbit/s and other coding mode of reservation by 4;
Data channel modulating mode field, is provided with other modulating mode of BPSK, QPSK, 16QAM and reservation by 4;
The forward error correction pattern field of data channel is provided with the cascaded code, the code check that adopt code check to be respectively 1/2,2/3,3/4,7/8 four kinds of convolution codes and RS sign indicating number and is 1/2 the low density parity check code and the coding mode based on low density parity check code of other reservation;
The frequency hopping of user data/frequency-hopping mode field, 3/3, the pattern that be provided with and adopt frequency-hopping mode, adopts frequency hopping/frequency hopping pattern preference pattern and other reservation;
Reserved field, 4;
Bose-Chaudhuri-Hocquenghem Code and odd-even check field are respectively 10 BCH check bit and 1 bit parity check position, and this part adopts BCH (31,21) sign indicating number, and 21 Control Parameter is encoded, and its generator polynomial is:
S(x)＝x
10+x
9+x
8+x
6+x
5+x
3+1；
(2) the user data packet format of transport layer: it has 1504, and wherein header information is 7, and data are 1497; Header information is represented the numbering of the packet of transmission in the per second, from 0～84 numbering; 85 user data package are added 1 head information unit, transmission in 1 second; The header information element length is 1504;
(3) data frame format of air interface: it is made of continuous superframe, and each superframe comprises the superframe head, and it is one section synchronous training sequence; The superframe body, be to constitute by some radio frames, each radio frames also comprises two parts: channel estimating training sequence and wireless frame, wireless frame is the main part of data, constitute by some OFDM symbols, each OFDM symbol all is one and inserts protection IFFT data block at interval that before symbol the transmission and the standard time of described superframe are synchronous;
Described OFDM multichannel system is meant the influence according to translational speed and multipath transmission, the frequency resource of the 8MHz of one tunnel television broadcasting is divided into the use pattern of following two sub-carriers:
When and translational speed portable terminal comparatively serious in multipath effect is little, adopt the pattern of 2048 subcarriers; Otherwise adopt the pattern of 1024 subcarriers;
According to different source encoding patterns these subcarriers are divided into tens channels dynamically again, a channel in all channels is the control channel, it adopts above-mentioned frame format to send the control data bag with the power that promotes, and all the other are data channel, and two ends are the protection subcarrier; Described each channel that dynamically is meant occupies one group of subcarrier, and this group subcarrier distributes according to the frequency hopping pattern, continuous sub-carriers group or discontinuous sub carrier group can, these sub carrier group are dynamic assignment; Dynamically also comprise transmitting power, modulation system and the forward error correction coding scheme of coming the chooser carrier wave according to the dynamic change of channel;
After carrying out above-mentioned setting, method of the present invention contains following steps successively at transmitting terminal:
(1) program source deposits the multimedia programming of their number formats in the digital storage of this kind program special use at this mobile multimedia broadcast system design specialized program again;
(2) the multimedia source coding unit is for the low-quality multimedia service demand of user side, adopt the multi-media processing method of high compression ratio to obtain the encoding code stream that code check is 128Kbit/s, otherwise, obtain the encoding code stream that code check is 1.5Mbit/s with the high quality multimedia processing method, add a program source numbering and sign, multiple connection becomes the code stream of a unified multimedia broadcasting; Again they are distributed to each broadcast node by repeated link;
(3) broadcast node transforms into the multidiameter delay code stream to this unified code stream again according to following steps, makes the broadcast program of the corresponding channel of each road code stream:
(3.1) code stream to multi channel carries out forward error correction coding respectively;
For low-quality MBMS service demand, adopt the coding method of cascaded code, each road code stream waiting for transmission passes through successively respectively that scrambler, Reed-Suo Luomeng sign indicating number RS (204,188) are encoded, interweaved, carry out the position again after the convolutional encoding interweaves;
For high quality multimedia broadcast service demand, adopt the low density parity check code of non-rule or the low density parity check code of employing variable bit rate;
(3.2) the multi channel code stream behind the coding is carried out the OFDM-MC modulation, it contains following steps successively:
(3.2.1) at first according to predefined frequency hopping pattern, the code stream that makes every road channel is mapped to respectively on the subcarrier at control channel and data channel place through the constellation point mapping, becomes complex data flow;
Described frequency hopping pattern is to adopt pseudo random sequence to generate, and is stored in the memory of transmitting terminal and receiving terminal after generation respectively;
(3.2.2) all subcarriers after the mapping together with the parallel input of the pilot tone of protection subcarrier, insertion as IFFT, carry out the IFFT conversion;
(3.2.3) front end at the output block of IFFT inserts protection at interval, carries out and go here and there conversion output time domain data flowing;
(3.2.4) above-mentioned time domain data stream is carried out the branch frame according to the length of radio frames, add channel estimation sequence at frame head and form radio frames;
(3.2.5) above-mentioned radio frames is carried out the branch frame according to the length of superframe body, instruct the row sequence synchronously, form superframe in the frame head adding of superframe;
(3.2.6) above-mentioned data are carried out digital to analog conversion, form continuous analog signal, be modulated to radio-frequency head through up-conversion again;
(4) emission of OFDM-MC system is that the broadcast band of 8MHz sends modulation signal according to the mode of Da Qu broadcasting by the bandwidth of distributing to multimedia broadcasting promptly.The method that the multi-media broadcasting system towards portable terminal that the present invention proposes is realized, it is characterized in that: described protection is 1/8 of IFFT data block length N at interval, and wherein IFFT data block length N is 2048 or 1024.
The method that the multi-media broadcasting system towards portable terminal that the present invention proposes is realized, it is characterized in that: in the coding of described cascaded code, initial condition at the scrambler of the transmitting-receiving two-end that carries out scrambler is " 1 ", it is that 127 scrambler carries out scrambler that data field adopts length, and scrambler adopts following generator polynomial to generate: S (x)=x
7+ x
4+ 1.
The method that the multi-media broadcasting system towards portable terminal that the present invention proposes is realized, it is characterized in that: the concrete generation method of frequency hopping pattern has following steps:
(1) if the quantity of the subcarrier of dividing is N, then utilize the method for software program generate length for N 0～1 between obey equally distributed pseudorandom array
(2) this pseudorandom array is sorted, then can obtain an exchange sequence of this ordering, this exchange sequence is 1,2 ..., the arrangement of N;
(3), the exchange sequence of pseudorandom array is corresponded to the use subcarrier number of each data channel according to the situation of each data channel use different sub carrier;
Each radio frames adopts identical frequency hop sequence, generates 20 exchange sequences, uses for symbols different in the same radio frames of transmission.
The present invention combines some characteristics of existing television broadcasting system, mobile communication system and WLAN, has proposed a kind of economy and efficiently towards the multi-media broadcasting system scheme of portable terminal.The present invention is based on some key technologies of air interface and transport layer, make native system can realize high quality multimedia broadcasting, the translational speed of its coverage and support can satisfy the demand of real system.For further improving performance, the multi-media broadcasting system that the present invention proposes is provided with schemes such as Adaptive Modulation, coding, frequency hopping, and receiving terminal can further improve the quality of multimedia broadcasting by the improvement technology.
The multi-media broadcasting system that the present invention proposes has been brought into play the advantage that broadcast system can effectively utilize frequency spectrum resource, not need complicated Network Management Function, helps guaranteeing the quality of multimedia transmission; The present invention is directed to different users and made different programs, can loop play, be fit to move and receive, guaranteed audience ratings.The multi-media broadcasting system networking flexibility that the present invention proposes is convenient, can make full use of existing network resources, can maximum assurance benefits of operators.
Description of drawings
The composition frame chart of Fig. 1 multi-media broadcasting system.
The hierarchical chart of Fig. 2 multi-media broadcasting system.
The control data packet format of Fig. 3 transport layer.
The user data packet format of Fig. 4 transport layer.
The data frame format of Fig. 5 air interface.
The channel division of the OFDM-MC of Fig. 6 multimedia broadcasting.
Fig. 7 OFDM-MC modulating unit block diagram.
Orthogonality relation between Fig. 8 subcarrier.
Fig. 9 forward error correction coding scheme cascaded code.
Figure 10 scrambler unit.
Figure 11 block interleaved.
Figure 12 frequency hopping pattern.
The major function unit of Figure 13 transmitting terminal.
The bit error rate performance curve of Figure 14 multi-media broadcasting system.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described as follows.
The hierarchical chart of the multi-media broadcasting system that the present invention proposes comprises application layer, coding layer, link layer, transport layer and air interface as shown in Figure 2.Wherein, be air interface between the portable mobile termianl of broadcast node of transmitting terminal (BP) and receiving terminal.
In application layer, the invention is characterized in that the program making center can be at mobile multimedia broadcast system design specialized program.The program making of application layer can adopt high performance work station and some special interface circuits to finish according to the characteristics of program source.The general length of these programs is shorter, is generally a few minutes to dozens of minutes, and the reception in being fit to move is watched, and can loop play.These programs design at user different interest and requirement, to satisfy requirements of different users, for example can be some excellent physical culture segments, entertainment segment, then educational programs segment or the like.These programs comprise video, audio frequency, data and their combination.
Additional information is meant that some are used for the data of condition reception and other function.
Application layer of the present invention is not limited to the special special-purpose program of making, fully can be compatible at the multimedia programming that adopts the T-DMB design, that is to say that the present invention can compatible with DVB-T, the program of DVB-H and other T-DMB.
At the coding layer, the multimedia coding unit among the present invention, the technical finesses such as encapsulation, multiple connection of can encoding, pack the program source that the program making center provides, and add some control datas etc., form multimedia code stream.These multimedia code streams are stored in the local storage and can recycle.The multimedia coding unit can adopt different coding modes according to user's demand.The multimedia coding unit mainly is to realize that by the hardware description language programming multimedia coding unit also can be realized by the software on the work station in the programmable logic array (FPGA) at the scene.
Therefore, at coding layer, a most important characteristic of the present invention is: the selecting of coding mode, operator can select different coding modes for use according to program source situation and user's request.Provide two kinds of basic coding patterns among the present invention: low rate coding pattern and high-rate coded pattern.Describe respectively below:
◆ first kind of pattern: low rate coding pattern.Under this pattern, the data rate of each channel has only 128Kbit/s, can reach the quality of the Digital Television phone of family expenses level.The multimedia coding techniques of the low code check of this employing, can select existing international standard H261, H.263, H264 etc., the present invention can be compatible to these coding standards.This coding mode can provide the multi-media broadcasting service of relatively low quality.Image can adopt standardized picture format QCIF or Sub-QCIF form in this pattern, and resolution is relatively low.Adopt this coding mode, in the channel configuration, can utilize less OFDM subcarrier to transmit data, so just guaranteed effective utilization of channel resource.
◆ second kind of pattern: high-rate coded pattern.Multimedia source adopts traditional serial coding standard of Motion Picture Experts Group (MPEG), the invention provides the alternative mode with MPEG-2 coding standard compatibility.The pattern of employing and Moving Picture Experts Group-1 compatibility among the present invention, data rate is approximately 1.5Mbit/s, and picture format is 352 * 288 standard C IF pattern.Multimedia broadcasting under this high code check has adopted more subcarrier to transmit with the assurance transmission rate in transport layer, thereby high quality multimedia broadcasting can be provided, and is fit to the user's of some needs high-quality multimedia broadcastings demand.
Along with the development of multimedia coding techniques and the technical development of other increase transmission capacity, the present invention also can provide and other coding standard, for example the compatibility of MPEG-4 standard.
The advantage of the encoding scheme of the multi-media broadcasting system that the present invention proposes is: the operator of multimedia broadcasting can be according to existing program resource situation and user situation, select different service plans flexibly, provide high quality services to make full use of existing resources, obtain maximum economic interests simultaneously.
The task of link layer of the present invention is that encoding code stream is distributed to each broadcast node (BP), the I series of user network interface host-host protocol of International Telecommunication Union's definition is adopted in its transmission, and interface adopts basic rate interface (BRI) and primary rate interface (PRI).
Link layer interface of the present invention is not only limited to the User Network Interface host-host protocol that adopts the ITU-I definition, interface that yet can compatible other standard.
The advantage of data format of the present invention is: combine with forward error correction coding, OFDM-MC modulation and the dynamic channel configuration of transport layer, help the effectively dynamic of channel resource utilized, and can guarantee the quality of multimedia broadcasting.
The data owner of the multi-media broadcasting system that the present invention proposes will comprise:
● the control data bag of transport layer;
● the user data package of transport layer;
● the Frame of air interface layer.
Paired domination number describes according to the Frame of bag, user data package and air interface respectively below.
The control data bag of multi-media broadcasting system of the present invention is mainly used in transmission system running parameter data, and mobile receiving terminal need carry out the reception of data according to these Control Parameter.
The size of control data bag is 200, and its form as shown in Figure 3.The transmission intercal of control data bag is 1s, because channel transmission rate is 130.358Kbit/s, the transmission time is approximately 1.53ms.
Introduce the formation of transport layer control data bag below, the formation of control data bag as shown in Figure 3:
The implication of each field of control data is described as follows:
(1) coding mode field
The coding mode field, the pattern of description multimedia coding, the present invention can provide multiple multimedia coding pattern, and two kinds of fundamental modes wherein are: code check is the low bit rate mode of 128Kbit/s; Code check is the high bit rate mode of 1.5Mbit/s.This field specifies as shown in table 1:
Table 1 coding mode field
| Coding mode field (4) | Coding mode |
| 0101 | The low bit rate mode of 128Kbit/s |
| 1010 | 1.5Mbit/s high bit rate mode |
| Other | Be reserved as other coding mode |
Coding mode has adopted four bit representations, has following two advantages:
(2) modulating mode field
The modulating mode field, the modulating mode of data of description channel is used for the different modulating mode of receiving terminal identification.The advantage that this field is set is: the present invention can adopt adaptive modulation technique in transmitting user data information; These parameters are the control channel transmission by high reliability, have guaranteed the correct of parameter transmission.This field specifies as shown in table 2:
Table 2 modulating mode field
| Modulating mode field (4) | Modulating mode |
| 0010 | BPSK |
| 0101 | QPSK |
| 1100 | 16QAM |
| Other | Be reserved as other modulating mode |
Modulating mode has adopted four bit representations, has following two advantages:
(3) FEC coding mode field
FEC coding mode field, the FEC coding mode of data of description channel is used for the different coding mode of receiving terminal identification.
The advantage that this field is set is: the present invention can adopt adaptive coding techniques in transmitting user data information; These parameters are the control channel transmission by high reliability, have guaranteed the correct of parameter transmission.
This field specifies as shown in table 3:
Table 3FEC coding mode field
| Coding mode field (3) | Coding mode |
| 000 | Cascaded code, convolution code are 1/2 code check |
| 001 | Cascaded code, convolution code are 2/3 code check |
| 010 | Cascaded code, convolution code are 3/4 code check |
| 011 | Cascaded code, convolution code are 7/8 code check |
| 111 | The LDPC coding, code check is 1/2 |
| Other | Be reserved as other coding mode based on LDPC |
(4) frequency hopping/frequency-hopping mode field
Frequency hopping/frequency-hopping mode field, the frequency-hopping mode of data of description channel is in order to the different frequency-hopping mode of receiving terminal identification.The advantage that this field is set is: the present invention can adopt adaptive frequency hopping in transmitting data information; These parameters are the control channel transmission by high reliability, have guaranteed the correct of parameter transmission.This field specifies as shown in table 4:
Table 4 frequency hopping/frequency-hopping mode field
| Frequency hopping/frequency-hopping mode field (3/3) | Frequency hopping/frequency-hopping mode |
| 000/000 | Do not adopt frequency hopping |
| 111/abc | Adopt frequency hopping/frequency hopping pattern to select (the frequency hopping pattern can reach 8 kinds at most) |
| Other | Reserve |
(5) reserved field, Bose-Chaudhuri-Hocquenghem Code and odd-even check field
Reserved field, length is 4, expanded application after being mainly used in.
Bose-Chaudhuri-Hocquenghem Code and odd-even check field are mainly used in the transmission reliability that guarantees the Control Parameter data.
The advantage that this field is set is: the present invention can guarantee the correctness of transmitting in the transmission control parameters data message.If verification obtains error of transmission, then lose the data of this control data piece.
This part adopts BCH (31,21) sign indicating number, and 21 Control Parameter is encoded.Its generator polynomial is:
S(x)＝x
10+x
9+x
8+x
6+x
5+x
3+1
The generation method that this part is concrete is:
(1) utilizes the coding method of BCH code, carry out BCH (21,31) coding.
(2) add a parity check bit, constitute even parity check.
The user data package of transport layer comprises header information and user data.Its structure is seen accompanying drawing 4.
User data package comprises: header information is 7, and data are 1497, and the size of each bag is 1504 like this.The header information of packet is represented the numbering of the packet of transmission in the per second.From 0～84, use 7 bit representations.
Per 85 user data package are added a head information unit, and the header information element length also is 1504, and its data content is reserved, and can comprise information such as standard time;
Because source coding rate is 128Kbit/s, in 1 second, pass through to fill a spot of data like this, have 85 user data inclusions, add 1 header information then, transmission data rate reaches 129.344Kbit/s, and the actual transfer rate of channel is 130.358Kbit/s, can through-rate mates to realize.
The Frame of air interface is used for transmitting control data and user data, and its form as shown in Figure 5.
The Frame of air interface is made of continuous superframe, and each superframe comprises two parts: superframe head and superframe body.The superframe head is one section synchronous training sequence, and the duration is 576 μ s; The superframe body is made of 66 radio frames; each radio frames also comprises two parts: channel estimating training sequence and wireless frame; channel estimation sequence length is 288 μ s; wireless frame is the main part of data; constitute by 19 OFDM symbols; each OFDM symbol all is one and inserts protection IFFT data block at interval that before symbol the length of the data block of each OFDM is 288 μ s.The transmission and the standard time of superframe are synchronous.
Protection in the present invention can be got 1/8 of IFFT data block at interval.If the length of FFT data block is N like this, protection length at interval can be so:
Under the pattern of N=2048, the protection duration at interval is 32 μ s.
Emphasis of the present invention is the channel configuration, modulation, forward error correction (FEC) coding, frequency hopping of OFDM multichannel (OFDM-MC) system that adopts of transport layer and with the corresponding channel dynamic optimization of these technology technology etc.Its major advantage is and can realizes that dynamic optimization utilizes to channel resource.Implementation method to these key technologies is described in detail below.
The principal character of OFDM-MC channel allocation plan of the present invention is embodied in:
◆ transmit frequency band;
◆ the division of OFDM subcarrier and the configuration of channel;
Respectively two characteristics and the implementation method thereof of channel allocation plan described below:
(1) transmit frequency band
The working frequency range of the multi-media broadcasting system that the present invention proposes is a band limits of distributing to public TV broadcasting, comprises UHF, VHF, S-band etc., takies the one or several channels of television broadcasting according to user situation.
Maximum of the present invention is characterised in that having changed traditional multi-media broadcasting system adopts the method for frequency division multiplexing to divide channel, to distributing to a 8MHz frequency range of multimedia broadcasting, again the technical system (OFDM multichannel system just) according to native system carries out new division, and this is an important feature of the present invention.
These characteristics help receiving terminal and realize that all-channel receives, and have simplified the design of mobile receiving terminal, are fit to very much multi-media broadcasting system.
In the concrete explanation of implementing of native system, be the 800MHz explanation with the centre carrier frequency.
(2) OFDM-MC channel configuration
The principal character of OFDM-MC channel configuration:
◆ OFDM multichannel (OFDM-MC) system that the present invention proposes is that the bandwidth with the 8MHz of one tunnel television broadcasting is divided into the plurality of sub carrier wave, and the division of subcarrier can be divided into two kinds of patterns according to the influence of translational speed and multipath fading: 1024 subcarrier patterns and 2048 subcarrier patterns.Wherein:
The suitable translational speed of the scheme of 2048 subcarriers is little, multipath effect is comparatively used (for example urban district walking) under the serious situation;
Use (for example suburb speed of a motor vehicle) under the situation that the suitable translational speed of the scheme of 1024 subcarriers is big, multipath effect is less.
◆ the present invention distributes these subcarriers according to the source encoding pattern, and each user channel adopts the plurality of sub carrier wave, so just can dispose tens channels.The distribution of subcarrier in the present invention can be discontinuous one group of subcarrier, and this is that the ISDB-T standard that proposes with Japan provides the pattern of narrowband service inequality.Specifically with reference to the accompanying drawings 6, the division methods when accompanying drawing 6 is 2048 for number of subcarriers has just been expressed each channel here and has been adopted the situation of a subcarrier continuously.
◆ among the present invention these tens channels are divided into data channel and control channel.
◆ the present invention adopts different delivery plans for different channels; adopt special frame format (as previously described) and high quality transmission protection mechanism for the control channel; for example can adopt higher transmitting power, the control channel in the accompanying drawing 6 adopts 2 times power to send.
Adopt the pattern of 2048 subcarriers in this specific embodiment, the specific implementation method of its OFDM-MC channel configuration with reference to the accompanying drawings 6:
1) at first, use the bandwidth of 8MHz to be divided into 2048 subcarriers multi-media broadcasting system, the bandwidth of each subcarrier is approximately 3.90625KHz like this.
2) all data channels all are configured as the Low Bit-rate Coding pattern, it is the coding mode that data transfer rate is approximately 128Kbit/s, each data channel adopts QPSK modulation and RS (204,188), code check is the code cascading scheme of 1/2 convolution code, then transmission of one line multimedia broadcasting approximately need be distributed 43 subcarriers.Each channel is provided with 2 pilot sub-carriers in addition, 33,34 subcarriers is set as the protection subcarrier respectively on 2048 subcarrier both sides, and 1 zero-frequency subcarrier is set in addition.Therefore the bandwidth of 8MHz can be configured as 44 channels;
3) in concrete channel configuration, with wherein 1 channel as the control channel; Data channel has 43;
4) the control channel is adopted BPSK modulation, bring to power emission; And general data channel adopts QPSK or 16QAM modulation, not bring to power emission.
The great advantage of the OFDM-MC channel configuration that the present invention proposes is: can the most effectively utilize limited channel resource, the scheme of this channel division is the basis of OFDM multichannel (OFDM-MC) the adaptive optimization scheme that proposes with the present invention, is one of native system main innovate point.
OFDM (OFDM) technology is a kind of broad band multicarrier transmission technology, its outstanding feature just is high band efficiency, outstanding ability of anti-multipath and is convenient to adopt adaptive optimisation technique, be very suitable for high speed data transfer, especially go up the multi-medium data transmission.
In the present invention, we improve traditional OFDM modulation technique at the characteristics of multimedia broadcasting, OFDM multichannel (OFDM-MC) system has been proposed, the characteristics of the quadrature of each subcarrier of OFDM have been made full use of, proposed subcarrier allocation, power, modulation system are carried out the scheme of dynamic optimization design, also proposed the scheme of baseband hopping, can guarantee high-quality multimedia broadcasting towards portable terminal.The basic principle of OFDM-MC modulation of the present invention as shown in Figure 7.The OFDM-MC modulating unit is to realize by the hardware description language programming in the programmable logic array (FPGA) at the scene.
This OFDM-MC system is compared with traditional broadcasting system has following four notable features:
The band efficiency height;
Can realize the automatic dynamic configuration of channel;
Respectively these four characteristics are described below:
(1) do not protect at interval the band efficiency height
The channel division existing problems of traditional multimedia broadcasting: the different data channel of traditional digital broadcasting is to adopt the mode of frequency division to realize, certain protection must be set at interval between the different channels, to prevent the phase mutual interference of different channel program.The method of this division channel fails effectively to utilize limited frequency resource.
At the not high problem of the band efficiency of traditional multi-media broadcasting system, the present invention proposes a kind of new channel configuration mode: each broadcasting channel of multi-media broadcasting system occupies the subcarrier of some quadratures of OFDM modulation, because between the different subcarriers is mutually orthogonal, can there be certain overlapping region, sees accompanying drawing 8.The channel allocation plan based on the OFDM-MC of OFDM-MC modulation technique that adopts that the present invention proposes can farthest utilize limited frequency resource, so can utilize the bandwidth of a 8MHz that the multimedia broadcasting of tens channels is provided.
Therefore, band efficiency height of the present invention is a most important characteristics of native system.
(2) automatic dynamic that can realize channel disposes
The limitation that traditional broadcast system exists is: different channels adopts different transmission parameters, can't dynamically realize the podcast for the user of different quality demand.
Limitation based on traditional broadcast system the invention is characterized in:
Respectively these two aspects are described below:
The channel dynamic-configuration is characterised in that:
The dynamic-configuration of channel is carried out in base band, and therefore the sub carrier group that can adopt different channels easily is configured, and this sub carrier group can be one group of continuous subcarrier, also can be discontinuous plurality of sub carrier wave.
The automatic dynamic configuration is characterised in that:
The automatic dynamic configuration is meant that adopt this scheme, receiving terminal does not need to make the change of any hardware, and the user of mobile terminal device does not need to know the configuring condition of channel, and this configuration is to be undertaken by the control data of receiver according to the control channel transmission;
The present invention is for the major advantage of the dynamic auto configuration of channel:
(3) can realize dynamic power control and modulation, encoding mechanism
Because the scheme of the transmitting power of the subcarrier of OFDM modulation, modulation system, forward error correction coding all can freely be selected, therefore can do and adjust these parameters according to the dynamic change of broadcast channel, the transmission quality of multimedia broadcasting is guaranteed.Be primarily characterized in that:
The parameter of these dynamic assignment all sends to portable terminal by the control channel, and the strategy that the transmission of control channel adopts relatively large power and employing to repeat to send can effectively guarantee the transmission of these parameter control datas.
Portable terminal carries out corresponding demodulation, decoding to the data that receive dynamically according to the variation of the Control Parameter data that receive, and obtains the higher multi-medium data of quality.All-channel receives because receiving terminal adopts, the project organization of total digitalization, can handle data easily.
(4) all-channel that helps receiving terminal receives and condition decoder
Another one most important characteristic of the present invention is: help realizing receiver total digitalization design, and can realize that the all-channel of multimedia broadcasting receives condition decoder.
All-channel receives the data that are meant all subcarriers in whole reception 8MHz scopes, this OFDM-MC channel allocation plan is convenient to the design of receiver, owing in multi-media broadcasting system, need to adopt self-adaption frequency channel configuration, adaptive modulation and coding and frequency hopping, if the selection that utilizes filter to carry out channel at radio frequency is very complicated, so the OFDM-MC channel allocation plan of the present invention's proposition can reduce the complexity of receiver integral body effectively;
Condition decoder is meant by default, only control channel program advance notice code stream is carried out the multimedia source decoding; When the user selects to appreciate channel, only the employed subcarrier of user selected channel is carried out the multimedia source decoding, so just effectively reduced the power consumption of portable mobile termianl receiver.
The OFDM-MC system that the present invention proposes is that the advantage that mobile receiving terminal brings in this respect is:
All-channel receives, and can simplify the design of receiving terminal;
All-channel receives, and is convenient to broadcast system and adopts adaptive modulation and coding;
The condition decoder of receiving terminal can reduce the power consumption of receiver effectively.
The feature of forward error correction unit of the present invention is: adopt multiple coding mode, can select different coding modes according to the variation of channel situation.Two kinds of basic coding patterns are: cascaded code coding and low-density checksum (LDPC) coding.The FEC coding unit is to realize by the hardware description language programming in the programmable logic array (FPGA) at the scene.
Respectively these two kinds of encoding schemes are described in detail below.
1 cascaded code coding
Adopt the forward error correction coding unit of cascaded code to comprise: scrambler, RS encodes, interweave, convolutional encoding and interweave, as shown in Figure 9.The forward error correction coding unit that adopts cascaded code is to realize by the hardware description language programming in the programmable logic array (FPGA) at the scene.
Below various piece is described respectively.
(1) scrambler and descrambling
It is that 127 scrambler carries out scrambler that data field adopts length, and the data field byte is lined up transmitting data stream according to order from low to high.Scrambler adopts following generator polynomial to generate:
S(x)＝x
7+x
4+1
The scrambler that sends data adopts identical structure with the scrambler that receives data de-scrambling, as shown in Figure 10.
When carrying out scrambler, the initial condition of transmitting-receiving two-end scrambler should be made as equal state, and is not 0 entirely, and in native system, the transmitting-receiving two-end initial condition is " 1 " entirely.
(2) the outer sign indicating number of cascaded code
The outer sign indicating number of forward error correction (FEC) adopts Reed-Suo Luomeng (RS) sign indicating number, RS (204,188).
RS (204,188) is the Reed-Suo Luomeng sign indicating number RS (255,239) that shortens, and they have identical sign indicating number generator polynomial.
It is information byte that RS (204,188) sign indicating number has 188 bytes, and all the other 16 bytes are check byte, so RS (204,188) can correct the error of transmission of 8 bytes.
Its concrete cataloged procedure is:
Increase by 51 zero bytes as information byte 188 byte fronts, so just constituted 239 information bytes;
239 information bytes of encoding obtain 255 bytes behind the coding;
(3) ISN of cascaded code
The ISN of cascaded code has adopted convolution code.Convolution coder adopts generator polynomial g
0=1338, g
1=171
8With 1/2 code rate.Can obtain code check by the surplus technology of deleting of convolution code is 2/3,3/4 and 7/8 convolution code.
In this specific embodiment, adopting code check is 1/2 convolution code; 3 data blocks behind RS (204, the 188) coding have 1632 * 3 bits, be 1/2 convolutional encoding through code check earlier after, add 12 tail bits then in the back, therefore total bit number is: 1632 * 3 * 2+12=9804 bit.
(4) interweave and the position interweave
In the cascaded code of the present invention, interweaving between outer sign indicating number and the ISN, is-symbol interweaves, and adopts the block interleaved technology, also writes the interleaving technology of falling in lines and reading at once, and the size of grouping is: 12 * 17.Interweave pattern as shown in Figure 11.
Position of the present invention interweaves and also adopts the block interleaved technology, the interleaving technology that writing at once falls in lines reads, and the size of grouping is: 64 * 51.
Of the present invention interweave and deinterleaving be not limited to the block interleaved technology, also can adopt convolutional interleave and random interleaving etc.
2 LDPC code plans
Forward error correction unit of the present invention also can adopt low-density checksum (LDPC) coding.The LDPC coding unit is to realize by the hardware description language programming in the programmable logic array (FPGA) at the scene.
Adopt the LDPC coding can use scrambler identical and descrambling technology with cascaded code, because LDPC is the block code based on the random matrix of supersparsity, also can be without scrambler.
LDPC coding among the present invention adopts irregular LDPC codes, and the length of the information bit of irregular LDPC codes is 4512, and coding is 9024 later.
LDPC coding among the present invention also can adopt the LDPC coding of variable bit rate.
LDPC coding mode of the present invention is fit to the requirement of better quality multimedia broadcasting, and helps the joint decoding technology of receiving terminal realization based on the LDPC encoding scheme, further improves the quality of multimedia transmission.
Frequency hopping is meant that carrier frequency carrying out saltus step by certain pattern in the wide frequency ranges very much.Frequency hopping can effectively improve the transmission quality of wireless signal, is anti-bursty interference and the effective means that realizes frequency diversity.But adopt the system of traditional frequency hopping, complexity is bigger, is not suitable for using in the system at portable mobile termianl.Frequency hopping of the present invention is different from traditional frequency hopping, and is based on the OFDM-MC system, has designed a kind of hopping scheme of low complex degree, does not need frequency synthesizer, has overcome the defective of traditional frequency hopping.
Frequency hopping is a kind of pattern that adopts in order better to guarantee transmission quality.The frequency hopping unit is to realize by the hardware description language programming in the programmable logic array (FPGA) at the scene.
The frequency hopping that the present invention proposes has following feature: when sending different OFDM symbols, only need realize that in base band implementation complexity is low according to the subcarrier of each channel use of frequency hopping pattern dynamic-configuration.
The baseband hopping technology that the present invention proposes mainly comprises following two aspects: the overall plan design of (1) frequency hopping; (2) design of frequency hopping pattern.
The overall plan design of frequency hopping of the present invention:
Design for simplified system, the present invention adopts the technology of baseband hopping, be that transmitter and receiver all adopts fixing receive frequency and bandwidth, the frequency band of corresponding wave band 8MHz just, frequency hopping is exactly different channels to be carried out the configuration of subcarrier according to frequency hopping pattern.Adopt the scheme of this baseband hopping, do not need frequency synthesizer, can simplify the design of transmitter and receiver.
For the design of simplified system, can adopt fixing frequency hopping pattern, also be that frequency hopping pattern is stored in the memory of transmitter and receiver, realize frequency hopping by the method for tabling look-up; The present invention also can adopt the design of dynamic-configuration frequency hopping pattern, if adopt this scheme, then frequency hopping pattern arrives receiver by the control channel transmission that high-quality guarantees, is stored in then in the memory of receiver.
For the design of simplified system, the present invention adopts the scheme of circulation frequency hopping, adopts identical frequency hopping pattern when just transmitting each radio frames; Transmit each different OFDM symbol and just carry out frequency hopping, promptly change the sub-carrier frequencies of a certain channel correspondence.
The frequency hopping pattern of Cai Yonging can be according to the design of following method in the present invention, and frequency hopping pattern is to design in advance and be stored in to transmit and receive end in the native system.
The specific design method of frequency hopping pattern is as follows:
(1) if the quantity of the subcarrier of dividing is N, utilize software program generate length for N 0～1 between obey equally distributed pseudorandom array;
(2) this pseudorandom array is sorted, then can obtain an exchange sequence of this ordering, this exchange sequence is 1,2 ..., the arrangement of N;
(3), the exchange sequence of pseudorandom array is corresponded to the use subcarrier number of each data channel according to the situation of each data channel use different sub carrier;
(4) because each radio frames adopts identical frequency hopping pattern, only need to generate 20 exchange sequences, use for OFDM symbols different in the same radio frames;
For example, if the program channel division methods below adopting: whole frequency is divided into 10 subcarriers, is numbered subcarrier 1～10 respectively.Per 2 subcarriers are used to send the program of a channel, and 5 program channels 1～5 so just can be set.Each radio frames comprises 19 OFDM symbols and 1 channel estimation sequence, when therefore transmitting different OFDM symbols or channel estimation sequence, just changes the frequency of transmission according to frequency hopping pattern.When transmitting different radio frames, this frequency hopping pattern is adopted in circulation.Above-mentioned channel division method can adopt the frequency hopping pattern shown in the accompanying drawing 12.In real system, the quantity of subcarrier is N=2048, and frequency hopping pattern is one 2048 * 20 a matrix.
A specific embodiment of the present invention
The multi-media broadcasting system that the present invention proposes towards portable terminal, a 8MHz frequency range using existing public TV to broadcast, the mode that adopts Da Qu to broadcast can provide tens special channel broadcasting multimedia programmings by the OFDM-MC system.The user can use portable mobile termianl to select to watch multimedia broadcasting flexibly in moving.In conjunction with the course of work of present embodiment, can further understand purpose of the present invention, feature and advantage.
Describe the principle of each major function unit of the multi-media broadcasting system that the present invention proposes below in detail, the relation of each functional unit is seen accompanying drawing 13.
(1) the program making center needle is to mobile multimedia broadcast system design specialized program, and the general time of these programs is shorter, can loop play.These programs design at various interest of user and requirement, for example can be some excellent physical culture segments, entertainment segment, then educational programs segment or the like, to satisfy requirements of different users.
Concrete manufacture method is exactly:
Program editing excellent in the camera-shooting and recording device is become 5～10 minutes special-purpose program, comprise Voice ﹠ Video, sometimes also can add some data or pictorial information, then these programs are carried out the multimedia programming that analog-to-digital conversion becomes number format, and be stored in the special digital memory of this kind program.
(2) the multimedia coding unit provides the encoding scheme of different quality according to user's demand for services.At present embodiment, but therefore the broadcast service that the user need be abundant than the low quality program, adopts the coding mode of low code check, obtains the coded program code stream of 43 road 128Kbit/s;
(3) at the coding mode of low code check, the specific implementation method of OFDM-MC channel configuration of the present invention is:
1) at first, the employing number of subcarriers is 2048 pattern, is about to multi-media broadcasting system and uses the bandwidth of 8MHz to be divided into 2048 subcarriers, and the bandwidth of each subcarrier is 3.90625KHz.
2) subcarrier all is configured as the Low Bit-rate Coding pattern, it is the coding mode that data transfer rate is approximately 128Kbit/s, each subcarrier adopts QPSK modulation, RS (204,188) coding, code check are 1/2 convolutional encoding, then transmission of one line multimedia broadcasting approximately needs 43 subcarriers, adds 2 pilot sub-carriers, therefore, remove outside 67 protection subcarriers and 1 the zero-frequency subcarrier, the bandwidth of 8MHz can dispose 44 channels;
3) in concrete channel configuration, dispose a control channel, use 45 subcarriers, data transfer rate is 10Kbit/s, modulation system adopts BPSK or QPSK, forward error correction coding employing RS (204,188) coding and code check are 1/2 convolutional encoding, make the data rate unanimity by the method that repeats to transmit during transmission.The main effect of this channel is the control data that transmits some Adaptive Modulation, coding, makes receiver carry out demodulation, decoding according to the control word that receives to the information of user data channel.Therefore, actual data channel has 43, and 43 data channels provide abundant multimedia programming towards portable mobile termianl for the user simultaneously;
When 4) sending the control data bag, adopt BPSK modulation, 2 times of bring to power emissions; General user data adopts QPSK, 16QAM modulation, not bring to power emission.
(4) effect of relay transmission is to each broadcast node (BP) with 43 tunnel program distribution.
The concrete implementation step of this part is:
1) multiple connection of multichannel multimedia coding code stream just with the encoding code stream of 43 road multimedia broadcasting programs, is added a program source numbering and sign, is multiplexed to the code stream of a unified multimedia broadcasting.
2) after the multimedia coding unit is a unified code stream with the multi-channel program multiple connection, be distributed to each broadcast node (BP) through the relay transmission network.
3) at broadcast node, this unified code stream is converted into 43 tunnel parallel code streams again, the program of the corresponding channel of each road code stream.
(5) at broadcast node (BP) basis user's request and transmission environment at that time, generate one tunnel control channel data, formed the encoding code stream of 44 channels like this with 43 road next coded program streams of relay transmission;
The encoding code stream of 44 channels passes through forward error correction coding respectively.Forward error correction coding adopts the coding of cascaded code, and promptly the code stream of transmission is through scrambler, RS (204,188) coding, and class symbol interweaves, code check is that 1/2 convolutional encoding and packet bit interweave.
(6) bit stream of 44 channels of process forward error correction coding, carry out OFDM-MC modulation and emission:
1) 44 road later channel code streams of coding at first shine upon through constellation point, form complex data flow; According to the frequency hopping pattern that sets in advance, each channel adds 2 pilot sub-carriers, is mapped to respectively on 1980 subcarriers except that protection subcarrier and zero-frequency subcarrier;
2) through after the above-mentioned subcarrier mapping, 1980 circuit-switched data subcarriers, pilot tone and 68 protection subcarriers, zero-frequency subcarrier together as 2048 parallel inputs of IFFT, carry out 2048 IFFT conversion;
3) before the output block of above-mentioned IFFT, 1/8 the protection of inserting the IFFT data block length at interval; Carry out and go here and there conversion, output time domain data stream;
4) above-mentioned time domain data stream is carried out the branch frame according to the length of radio frames, add channel estimation sequence, form radio frames at frame head;
5) above-mentioned all radio frames are carried out the branch frame according to the length of superframe body, add synchronous training sequence, form superframe at frame head;
6) baseband OFDM-MC handles later data through digital-to-analogue (D/A) conversion, forms the continuous analog signal, passes through up-conversion then, is modulated to radio frequency;
7) be that the frequency range of 8MHz is launched modulation signal by the bandwidth of distributing to multimedia broadcasting.The special frequency range of television broadcasting is adopted in the transmission of these multimedia channels, can adopt bigger power emission to go out, and guarantees effectively to cover coverage and quality.
(7) be complete description specific implementation method of the present invention, below provide a kind of example of the possible basic realization flow of OFDM-MC system receiving terminal:
1) synchronous and channel estimating: the baseband signal of reception is carried out frame synchronization and carrier synchronization according to the synchronous instruction sequence of superframe frame head, after the carrier synchronization, can from the pilot tone of the channel estimation sequence of radio frames frame head and radio frames frame, extract channel situation, be used for channel compensation.
2) FFT conversion, extract control information: the data flow of reception is after removing Cyclic Prefix, carry out the FFT conversion, extract the subcarrier of control channel according to predefined frequency hopping pattern, carry out BPSK then and separate mapping, channel decoding, control informations such as the modulation system of extraction user data channel, encoder bit rate.After the control information verification is correct, just can be stored in control information in the register of receiving terminal, the separating of data message that is used for subsequently shone upon and decoding.
3) demodulation of user data channel, decoding: when not having the user to select information, the TV guide data message of controlling channel is carried out source coding according to the Control Parameter of above-mentioned storage.When having the user to select information, utilize the Control Parameter of above-mentioned storage and user to select the subcarrier of the channel that information selects the user to separate mapping, channel decoding and source decoding and obtain multi-medium data.In case the user has selected after the user data channel, stop the source coding of above-mentioned control channel program advance notice data message, the source coding of beginning user data channel.
Said system is carried out Computer Simulation and actual test, the result below having drawn.
Accompanying drawing 14 has been described employing OFDM-MC system of the present invention, towards the bit error rate performance of mobile multimedia broadcast system under the mobile broadcast channel of 800MHz centre frequency of portable terminal.The scheme that adopts is the pattern of 2048 subcarriers.Wherein, the multi-media broadcasting system that proposes for better explanation the present invention is for ambulant support, and channel model has adopted 3GPP (3-G (Generation Three mobile communication system) standardization body) to recommend the Rayleigh fading model in 6 footpaths of adopting.Receiving terminal does not compensate Doppler frequency shift.
Translational speed be 50 kms/hour situation under, the modulation system of subcarrier adopts the OFDM-MC mobile multi-medium system of QPSK mapping when all channels all come into operation, it receives required signal-to-noise ratio is 5dB@BER=10
-6When having only half channel to come into operation, it receives required signal-to-noise ratio less than 4dB@BER=10
-6Therefore, native system can be offered more channel according to the situation and the user's request of program source, does not need the transmitting power of system to have greatly increased, and the design that helps system realizes.
The OFDM-MC mobile multimedia broadcast system snr loss that the modulation system of subcarrier adopts the 16QAM mapping is big than the QPSK mapping, if receiving terminal does not compensate Doppler frequency shift, the multipotency of system support 20 kms/hour translational speed, but data transfer rate can double, the multimedia broadcasting of the high code check of receiving terminal broadcast high quality that can move low speed.
Further can obtain the coverage of multi-media broadcasting system of the present invention according to emulation and test result.
Assumed condition: maximum transmission power: 1000mW=30dBm
Antenna gain: 25dB
The level surplus of system: 30dB
Feeder line and antenna diplexer loss: 5dB
Demodulation loss: 1dB
Worsen and interference margin: 3dB
When the subcarrier-modulated mode was QPSK, the error rate was less than 1 * 10 before the decoding
-6, the input carrier-to-noise ratio of intermediate frequency inlet is: C/N=5dB.
Therefore, the loss when taking into account system is realized, the actual requirement of input carrier-to-noise ratio is: C/N=9dB
In this case, consider the noise of loss and receiver inlet, can calculate its coverage is 57.8 kms.
When the subcarrier-modulated mode was QAM, the error rate was less than 1 * 10 before the decoding
-6, intermediate frequency inlet input carrier-to-noise ratio is: C/N=16dB.
Loss when taking into account system is realized, the actual requirement of input carrier-to-noise ratio is: C/N=20dB
In this case, consider the noise of loss and receiver inlet, can obtain its coverage is 16.3 kms.
Claims (5)
1 multi-media broadcasting system towards portable terminal is characterized in that it contains:
A plurality of multimedia programmings are made the source, and each road programme information of its output comprises video information, audio-frequency information and additional information, and additional information comprises caption information, condition receiving control information;
Multimedia coding unit, its input are the multi-channel program information of above-mentioned program making source output, and its output is the road multimedia messages code stream that above-mentioned multi-channel program information is formed through efficient compressed encoding, multiple connection, packing encapsulation back respectively;
Repeated link can be any in metropolitan area network, proprietary microwave link or the optical fiber link, and its input is the road multimedia messages code stream that above-mentioned multimedia coding unit forms;
The broadcast node of transmitting terminal, represent with BP, compose in series successively by forward error correction coding unit, OFDM-MC modulating unit, up-conversion and transmitter unit, a plurality of broadcast nodes can be formed multiple frequency network, MFN or single frequency network, their input is respectively established one road multimedia messages code stream that above-mentioned repeated link transmits, their output separately is the mode of broadcasting by multimedia broadcasting launching tower Yi Da district through forward error correction coding, OFDM multichannel modulation back, the multimedia broadcasting information of going out with the band transmit of multimedia broadcasting.
2 methods that realize towards the multi-media broadcasting system of portable terminal, it is characterized in that: it is a kind ofly to have based on the OFDM multichannel, it is the OFDM-MC system, utilize the frequency range of existing public TV broadcasting, mode by Da Qu broadcasting, different channels is configured on the different sub carrier group, carries out that the FFT conversion of the IFFT conversion of transmitting terminal and receiving terminal realizes, it is realized by following method in each following link:
The multimedia coding unit, according to the quality and the requirement of multi-media broadcasting service, adopt following two kinds of coding modes respectively:
The low rate coding pattern: the data rate of each channel is 128Kbit/s, and coding is adopted international standards, and image adopts standardized picture format, i.e. QCIF or Sub-QCIF form;
High-rate coded pattern: and the coded format of Moving Picture Experts Group-2 compatibility, data rate is 352 * 288 standard C IF form for the 1.5Mbit/s picture format;
Repeated link adopts the I series of user network interface protocols of International Telecommunications Union's definition, comprises basic rate interface and primary rate interface, represents with BRI and PRI respectively;
The transmitting terminal broadcast node adopts OFDM-MC system and methods for forward error correction coding, and it is provided with following packet and form thereof:
(1) the control data packet format of transport layer:
The size of control data bag is 200, and its transmission intercal is 1s, because channel transmission rate is 130.358Kbit/s, the transmission time is approximately 1.53ms, and its data format is as follows:
40 of header informations are 1 all, represent that this packet is the control data bag;
Control data, every group is 32, repeats 5 times, has wherein adopted BCH (31,21), and parity check bit of back annex, constitutes 32, the data format in its 21 bit data is followed successively by:
The source encoding pattern field of data channel, is provided with the low bit rate mode of 128Kbit/s, the high bit rate mode of 1.5Mbit/s and other coding mode of reservation by 4;
Data channel modulating mode field, is provided with other modulating mode of BPSK, QPSK, 16QAM and reservation by 4;
The forward error correction pattern field of data channel is provided with the cascaded code, the code check that adopt code check to be respectively 1/2,2/3,3/4,7/8 four kinds of convolution codes and RS sign indicating number and is 1/2 the low density parity check code and the coding mode based on low density parity check code of other reservation;
The frequency hopping of user data/frequency-hopping mode field, 3/3, the pattern that be provided with and adopt frequency-hopping mode, adopts frequency hopping/frequency hopping pattern preference pattern and other reservation;
Reserved field, 4;
Bose-Chaudhuri-Hocquenghem Code and odd-even check field are respectively 10 BCH check bit and 1 bit parity check position, and this part adopts BCH (31,21) sign indicating number, and 21 Control Parameter is encoded, and its generator polynomial is:
S(x)＝x
10+x
9+x
8+x
6+x
5+x
3+1；
(2) the user data packet format of transport layer: it has 1504, and wherein header information is 7, and data are 1497; Header information is represented the numbering of the packet of transmission in the per second, from 0～84 numbering; 85 user data package are added 1 head information unit, transmission in 1 second; The header information element length is 1504;
(3) data frame format of air interface: it is made of continuous superframe, and each superframe comprises the superframe head, and it is one section synchronous training sequence; The superframe body, be to constitute by some radio frames, each radio frames also comprises two parts: channel estimating training sequence and wireless frame, wireless frame is the main part of data, constitute by some OFDM symbols, each OFDM symbol all is one and inserts protection IFFT data block at interval that before symbol the transmission and the standard time of described superframe are synchronous;
Described OFDM multichannel system is meant the influence according to translational speed and multipath transmission, the frequency resource of the 8MHz of one tunnel television broadcasting is divided into the use pattern of following two sub-carriers:
When and translational speed portable terminal comparatively serious in multipath effect is little, adopt the pattern of 2048 subcarriers; Otherwise adopt the pattern of 1024 subcarriers;
According to different source encoding patterns these subcarriers are divided into tens channels dynamically again, a channel in all channels is the control channel, it adopts above-mentioned frame format to send the control data bag with the power that promotes, and all the other are data channel, and two ends are the protection subcarrier; Described each channel that dynamically is meant occupies one group of subcarrier, and this group subcarrier distributes according to the frequency hopping pattern, continuous sub-carriers group or discontinuous sub carrier group can, these sub carrier group are dynamic assignment; Dynamically also comprise transmitting power, modulation system and the forward error correction coding scheme of coming the chooser carrier wave according to the dynamic change of channel;
After carrying out above-mentioned setting, method of the present invention contains following steps successively at transmitting terminal:
(1) program source deposits the multimedia programming of their number formats in the digital storage of this kind program special use at this mobile multimedia broadcast system design specialized program again;
(2) the multimedia source coding unit is for the low-quality multimedia service demand of user side, adopt the multi-media processing method of high compression ratio to obtain the encoding code stream that code check is 128Kbit/s, otherwise, obtain the encoding code stream that code check is 1.5Mbit/s with the high quality multimedia processing method, add a program source numbering and sign, multiple connection becomes the code stream of a unified multimedia broadcasting; Again they are distributed to each broadcast node by repeated link;
(3) broadcast node transforms into the multidiameter delay code stream to this unified code stream again according to following steps, makes the broadcast program of the corresponding channel of each road code stream:
(3.1) code stream to multi channel carries out forward error correction coding respectively;
For low-quality MBMS service demand, adopt the coding method of cascaded code, each road code stream waiting for transmission passes through successively respectively that scrambler, Reed-Suo Luomeng sign indicating number RS (204,188) are encoded, interweaved, carry out the position again after the convolutional encoding interweaves;
For high quality multimedia broadcast service demand, adopt the low density parity check code of non-rule or the low density parity check code of employing variable bit rate;
(3.2) the multi channel code stream behind the coding is carried out the OFDM-MC modulation, it contains following steps successively:
(3.2.1) at first according to predefined frequency hopping pattern, the code stream that makes every road channel is mapped to respectively on the subcarrier at control channel and data channel place through the constellation point mapping, becomes complex data flow;
Described frequency hopping pattern is to adopt pseudo random sequence to generate, and is stored in the memory of transmitting terminal and receiving terminal after generation respectively;
(3.2.2) all subcarriers after the mapping together with the parallel input of the pilot tone of protection subcarrier, insertion as IFFT, carry out the IFFT conversion;
(3.2.3) front end at the output block of IFFT inserts protection at interval, carries out and go here and there conversion output time domain data flowing;
(3.2.4) above-mentioned time domain data stream is carried out the branch frame according to the length of radio frames, add channel estimation sequence at frame head and form radio frames;
(3.2.5) above-mentioned radio frames is carried out the branch frame according to the length of superframe body, instruct the row sequence synchronously, form superframe in the frame head adding of superframe;
(3.2.6) above-mentioned data are carried out digital to analog conversion, form continuous analog signal, be modulated to radio-frequency head through up-conversion again;
(4) emission of OFDM-MC system is that the broadcast band of 8MHz sends modulation signal according to the mode of Da Qu broadcasting by the bandwidth of distributing to multimedia broadcasting promptly.
3 according to claims 2 described methods that realize towards the multi-media broadcasting system of portable terminal, and it is characterized in that: described protection is 1/8 of IFFT data block length N at interval, and wherein IFFT data block length N is 2048 or 1024.
4 according to claims 2 described methods that realize towards the multi-media broadcasting system of portable terminal, it is characterized in that: in the coding of described cascaded code, initial condition at the scrambler of the transmitting-receiving two-end that carries out scrambler is " 1 ", it is that 127 scrambler carries out scrambler that data field adopts length, and scrambler adopts following generator polynomial to generate: S (x)=x
7+ x
4+ 1.
5 according to claims 2 described methods that realize towards the multi-media broadcasting system of portable terminal, and it is characterized in that: the concrete generation method of frequency hopping pattern has following steps:
(1) if the quantity of the subcarrier of dividing is N, then utilize the method for software program generate length for N 0～1 between obey equally distributed pseudorandom array
(2) this pseudorandom array is sorted, then can obtain an exchange sequence of this ordering, this exchange sequence is 1,2 ..., the arrangement of N;
(3), the exchange sequence of pseudorandom array is corresponded to the use subcarrier number of each data channel according to the situation of each data channel use different sub carrier;
(4) each radio frames adopts identical frequency hop sequence, generates 20 exchange sequences, uses for symbols different in the same radio frames.
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