CN100483977C - Time-frequency matrix two-dimensional channel dynamic allocation method in multimedia information transmission - Google Patents
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Abstract
It is a multimedia information transmission time frequency matrix two-dimensional sub-channel dynamic alignment method, which belongs to digit information transmission technique field and comprises the following steps: to generate two-dimensional time zone and frequency zone matrix TFM channel alignment pattern according to certain rules; to align the multimedia program code flow input to the relative TDS-OFDM signal frame and OFDM sub-carrier wave according to the alignment pattern; to insert TFMp matrix information into the head frame group of TDS-OFDM; finally to send the complete signal of TDS-OFDM.
Description
Technical field
The invention belongs to digital information transmission technical field, specially refer to time-frequency matrix (Time-Frequency Matrx, TFM) two dimensional channel dynamic allocation method in the multimedia messages transmission of using OFDM (OFDM) multi-carrier modulation technology.
Background technology
The world today has gone on foot people's information age, and the marked change of rapid increase of the information requirement of society and information-intensive society function makes multimedia research and development become the certainty in epoch, and obtained application more and more widely.
Multimedia is that multiple medium such as data, literal, sound, music, animation, video, image are incorporated into one, by digitized processing, realizes the novel information technology of man-machine interaction's formula information interchange and propagation.People obtain, when processing and exchange of information, the most natural form is carried out with multimedia mode, it is sensory and use often to show as vision, the sense of hearing, sense of smell etc.The red Rui Tela of experimental psychology man (Treicher) did a famous experiment of obtaining information source about the mankind: the information 83% that the mankind obtain is from vision, 11% from the sense of hearing, and adding up for these two just has 94%, also has 3.5% from sense of smell, 1.5% from sense of touch, and 1% from the sense of taste.This shows, multimedia can with people exchange naturally and the mode of process information reaches best coupling.
Multimedia is a system engineering that relates to multi-door subject and multiple technologies field, comprises computer technology, artificial intelligence technology, electronic technology, the communication technology, broadcast television technique and some other technology.Become better and approaching perfection day by day as video technique, Audiotechnica, Information Compression and the decompression technique of multimedia technology core, image technique, high-density memory technology etc.; Multimedia hardware system, operating system platform, window system, authoring tool etc. just reach its maturity.
Multimedia application is along with the research and development of multimedia technology develop, round the multimedia service type with at different network environments, constantly researching and developing various multimedia application, to society and economic various aspects such as animation, audio frequency and video making, stunt, virtual world, digital art creation, all deep change has taken place in the extensive employing owing to multimedia technology from administration office, military security, traffic environment-friendly, education and medical care, banking and insurance business, information retrieval, amusement and recreation, publication and printing.
One of multimedia main target is to satisfy the demand of people to multiple information processing and propagation.The multimedia technology that does not have information to propagate also will not have to be used so rapidly and develops.
People are to the high request of the sense of reality of medium, presence, the property participated in directly proposition, and the varying of external conditions such as application purpose, object and environment, and an urgent demand information transmission system has characteristics such as quick, flexible, efficient.But no matter be in television broadcasting, communication and network system, the propagation of multimedia messages still has many specific questions to need to solve, and for example the real-time of the dynamically adapting of different terminals and front-end server, multimedia messages requires, processing, network spectrum and channel allocation, high-performance and high reliability, the compression performance etc. of variable video data stream.
For example for the transmission code rate of video, different application (high definition TV HDTV, standard definition television SDTV and DVD, VCD and palmtop PC PDA, mobile phone etc.) has different demands.
For example according to the ITU-R601 standard, use the sample format of 4:2:2, remove capable field flyback after, the SDTV transfer rate is 165Mb/s, and HDTV is more up to 829Mb/s.And for the handheld device (as mobile phone) of the small screen, CIF and QCIF are just with satisfying the picture quality requirement.CIF is 352 * 288 pixels, 8bit/ pixel, 25 frames/s, light tone 4:2:0, then unpressed image signal transmission code check is 30Mb/s, present compress technique, as MPEG-2/4, MS WM9, H264 etc., conservative calculating can be accomplished compression ratio R=40 doubly, and then the code check after the compression is 760kb/s.If QCIF (166x144), then transmission code rate is further reduced to 190kb/s.Therefore, for the small screen, the advanced video compress technique makes the video flowing code check have only hundreds of kbps magnitude.And the transmittability of channel may be greater than 10Mbps, is exactly so in ground digital television broadcast, like this, how to optimize and utilizes transfer resource just to become a major issue neatly.
For short message, amount of information is smaller, may have only several bits or several thousand bit, how in big volume transport passage, to transmit so little amount of information efficiently? and for instant message, how apace how response transfers out apace, also is a key issue.
Different demands in the above-mentioned application, embodied quick, flexible, the effective forthright requirement of multimedia messages transmission, for an information transmission system, can physical layer, link once or different ISO protocol layer such as application layer satisfy quick, the flexible and efficient requirement of multimedia messages transmission.
The present invention is primarily aimed at and propagates the multimedia television program in the ground system of digital television broadcast, propose a kind of transmission channel dynamic allocation method that on physical layer, adopts time domain-frequency domain two-dimensional matrix mode, satisfied quick, the flexible and efficient requirement of multimedia messages transmission.
(Digital TV terrestrial broadcasting is DTTB) just at high speed development for ground digital television broadcast both at home and abroad.Digital Television has only time of short more than ten years till now from end of the eighties development, but development speed make us surprised soon.Through insistent research and development these years, DTTB has obtained a lot of achievements, and having reached can implementation phase.From in November, 1998 North America and the Europe DTTB program that started broadcasting, many countries have announced that their DTTB standard selects and realize a plan.At present, mainly contain three kinds of DTTB transmission standards in the world:
1) United States advanced television systems committee (Advanced Television Systems Committee, ATSC) eight level vestigial side bands of Yan Fa lattice code (Trellis-Coded 8-Level Vestigial Side-Band, 8-VSB) modulating system.
The ATSC digital television standard is the ATSC of Advanced Television Systems Committee exploitation.Modulation scheme has adopted the single-carrier modulated with pilot signal, i.e. eight level vestigial side bands modulation (8-VSB), and (multiple frequency network, MFN Multi-FrequencyNetwork MFN) realizes to be used for the single transmit machine.U.S. VSB system has added the pilot signal of 0.3dB, is used for subcarrier and recovers.Transmission signals adopts section, field structure, and framing sends, and data frame structure as shown in Figure 1.The segment sync signal that adds is used for system synchronization and clock recovery; And length reaches 511 two level field sync signals, is used for system synchronization and equalizer training, eliminates the echo interference that multipath fading causes by adopting well-designed adaptive decision feedback equalizer.
In U.S. ATSC digital television standard, transmission stream (the TransportStream that multiple medium such as video, audio frequency and data constitute, TS) by above-mentioned composition data frame structure shown in Figure 1, a TS stream is to be placed on fixing data segment position continuously, there is not the dynamics of channels assignment problem, but can not satisfy multimedia messages transmission fast, requirement flexibly, and data are just placed (distribution) in time domain.
2) European digital video broadcast-terrestrial (Digital Video Terrestrial Broadcasting-Terrestrial, DVB-T) Coded Orthogonal Frequency Division Multiplexing (COFDM) of standard employing (Coded Orthogonal Frequency Division Multiplexing, COFDM) modulation.
The DVB-T system is European digital video broadcasting (Digital Video Broadcasting, DVB) organization development.Aspect terrestrial transmission, it adopts the modulation technique COFDM different with U.S. 8-VSB, and OFDM belongs to multi-carrier modulation technology (being called the DMT modulation in the similar technology of ADSL).The effectively clean bit code check of transmission depends on chnnel coding parameter, modulation type and protection selection at interval in the 8MHz channel in 4.98～31.67Mbit/s scope.DVB-T has used 1705 (2k patterns) or the individual subcarrier of 6817 (8k patterns) in each television channel.The frame structure of DVB-T as shown in Figure 2.The basic principle of OFDM is divided into a broad frequency band-a little channel (Sub Channel or Subcarrier) exactly.If the shared bandwidth of each subchannel is enough narrow, they will experience flat fading respectively.In this case, the equalizer of receiver is easy to realize.And in order to improve system spectral efficiency, the frequency spectrum of each subchannel is overlapping in the ofdm system, but is quadrature again between them, the origin of its OFDM (OFDM) title that Here it is.Under the multipath channel situation, in order to keep the orthogonality between its each subchannel, must add protection at interval (Guard Interval, GI).DVB-T uses Cyclic Prefix, and (Cycle Padding, CP) protection copies to each code element front end with OFDM code element last part at interval exactly.
For the auxiliary synchronous task of finishing, DVB-T has placed a large amount of pilot signals at frequency domain, intert among data subcarrier, and to be higher than the power transmission of data 3dB, as shown in Figure 3, be divided into the continuous pilot of signal frame original position and the scattered pilot of offset, four signal frames constitute a superframe, also have a limited number of channel to be used for transmission system parameters information in addition, be called transmission parameter signaling (Transmission Parameter Signaling, TPS), at present in the DVB-T system, TPS only is left valuable several bits also at leisure, and the function that is used for system's indication is so just received considerable restraint.
Each pilot tone numerical value is calculated by PRBS (pseudo-random binary sequence) modulation, so its autocorrelation is better, most COFDM system regularly, scheduling algorithm is based on all that these pilot signals carry out at frequency domain synchronously.But pilot tone is inserted before in discrete Fourier transform (DFT), and carrying out DFT calculating needs (just can carry out correct demodulation afterwards) at first synchronously again.Therefore, the synchronous needs of COFDM system used the iterative approach algorithm, so just has convergence error and convergence time problem.Be that receiver receives a needed time from unlatching, locking signal to the beginning section lock in time.In current DVB-T realized, this time was estimated in the 200-250ms magnitude.Just be not suitable for the application of multimedia messages this lock in time, do not satisfy quick, the flexible and efficient requirement of multimedia messages transmission, for example transmission of short message and instant message.
The same with U.S.'s ATSC digital television standard, European DVB-T also is a continuous fixed data position of placing as shown in Figure 3 of TS stream, does not have the dynamics of channels assignment problem, and just place at frequency domain.
3) Japanese floor synthetic service digital broadcasting (Integrated Service Digital Broadcasting-Terrestrial, ISDB-T) the frequency band segment transmissions of Cai Yonging (Bandwidth Segmented Transmission, BST) orthogonal frequency division multiplex OFDM.
The ISDB-T system is that (Association of Radio Industries and Businesses ARIB) develops Japanese association of radio industrie and business.The modulator approach that system adopts is called frequency band segment transmissions (BST) OFDM, is made up of one group of common fundamental frequency piece that is called the BST section.Except that the OFDM characteristic, BST-OFDM adopts different carrier modulation scheme and ISN encoder bit rate to different BST sections, and the hierarchical transmission characteristic is provided according to this.Each data segment has its oneself error protection scheme (ISN encoder bit rate, the time-interleaved degree of depth) and modulation type (QPSK, DQPSK, 16-QAM or 64QAM), and every section can be satisfied different business demands like this.This system is derived from European system, and main change is at multimedia broadcasting and moves the demand that receives, and frequency band has been carried out segmentation, and the interleave depth (reaching 0.5 second most) that extended greatly, to improve mobile reception.Though Japanese system shows certain superiority (the also corresponding European system that proved needs improvement) in mobile test, it does not solve the question of substance among the COFDM.
Since these three DTTB systems had been arranged, many countries and regions were all in the DTTB system of selecting oneself.From the foregoing background introduction, these three DTTB systems, all be to design at traditional continuous bit stream transmission, the main problem of considering is the efficient and highly reliable of transmission, forward error correction coding (FEC) and high-order orthogonal frequency division multiplexing (mQAM-OFDM) multi-carrier modulation technology have been adopted, and just in single time domain or frequency domain, realize, and when not considering transmitting multimedia information needed fast, flexibility.When needs transmitting multimedia information, these DTTB systems can not satisfy the demand on physical layer, and can only take certain technical measures on link layer or application layer, satisfy application demand.European hand-held digital video broadcast (DVB-H) system of for example telling about below.
Europe ground digital television broadcast (DVB-T) standard is in order to adapt to different requirements, be provided with variable parameter, these parameters mainly still receive and outdoor reception at indoor and outdoor is fixing, but anti-impulse disturbances is indifferent, and do not consider electricity-saving function, for portable handheld mobile device and inapplicable, also there is the inflexible problem of the network planning.Therefore, European DVB organizes the terrestrial DTV standard of formulating at handheld mobile device, is referred to as DVB-H.
In order to satisfy the business demand of DVB-H, DVB-H system definition is the combination of physical layer, link layer and business information completely, wherein in order to increase the service time of battery, must reduce power consumption.Therefore, the program distribution of DVB-H has adopted above-mentioned Time Division Multiplexing technology at link layer, in DVB-H, be called timeslice (Time-Slicing), the burst form transmission television broadcast data of multimedia messages with high code check (about 12Mbs), between two bursts, do not transmit this business code flow data, this makes receiver only just keep state of activation when receiving the business burst of being asked.
For the time of informing that the receiving terminal next one happens suddenly,, the time that next one burst begins is described in current burst.Between two bursts, there are not the transmission code stream data, can transmit other program stream this moment.Timeslice makes receiving terminal only when the business burst of the request of receiving, and just starts working.Notice that transmitter is being worked (being the not interruption of transmission that TS transmits stream) always, as shown in Figure 4.
Fig. 5 has described the conceptual configuration of DVB-H system, comprises DVB-H modulator/demodulator and DVB-H terminal, wherein free sheet and modules such as MPE-FEC, 4K.
In European DVB-T system, be 250ms lock in time, burst length will with analogy property lock in time, can not be much smaller than the system synchronization time, otherwise the expense that accounts for lock in time is just too big.Therefore, according to the characteristic of European ground digital television broadcast standard DVB-T, the burst length of DVB-H is elected 200ms as, and burst bandwidth is 15Mbps, and free time is 4s, and burst sizes is 2Mb.Europe DVB-H needs the buffer of a 2Mb, with the output that is constant code rate of level and smooth burst code stream.The problem of bringing thus is that the transmission delay of system increases, and the memory of 2Mb capacity can increase the cost of handheld device significantly.
In addition, from the communication angle, information transmitted unit is more little, and it is flexible more to commence business.In the DVB-H system, the burst length minimum is 200ms, and the data volume of each burst transfer is 2Mbits, is unfavorable for transmitting little information and instant messages, for example short message, paging, alarm etc.
Need especially explanation be that the timeslice technology among the DVB-H must realize at link layer, does not relate to the DVB-T physical layer anywhere.And DVB-H has selected that (Multi-ProtocolEncapsulation MPE) goes up transmission IP bag data, implements timeslice on the MPE of link layer in the encapsulation of existing multi-protocols.The timeslice technology of DVB-H has increased the flexibility of program distribution to a certain extent, has arrived purpose of power saving, but just in time-domain, realize.
Sum up the above, existing three ground digital television broadcast international standards, these three DTTB systems, all be at transmission of traditional continuous bit stream and design, can't satisfy the desired transmission of a plurality of multimedia programmings fast and reliable, program distribution flexibly and efficient, power saving and requirement such as maintain secrecy.
Summary of the invention
The Hierarchichal frame structure characteristic synchronous that the present invention adopts according to time-domain synchronization OFDM (TDS-OFDM) multi-carrier modulation with natural time, at the multimedia messages transmission requirements, a kind of T/F matrix (Time-Frequency Matrix, TFM) channel dynamic allocation method of two dimension have been proposed.
Bright being characterised in that of we:
Time-frequency matrix two dimensional channel dynamic allocation method in the multimedia messages transmission, it is characterized in that: it is to be under the condition of transmitting multimedia information in the time domain synchronous orthogonal frequency-division multiplexing system at TDS-OFDM, utilize the two-dimensional time frequency matrix according to what propose in physical layer with the synchronous Hierarchichal frame structure characteristic of natural time, be TFM, come the method for dynamic assignment channel randomly, it is at transmitting terminal, when input code flow is carried out the channel error correction coding successively, the modulation symbol mapping, after the IDFT conversion, by to utilize field programmable gate array be FPGA the output code flow of IDFT is carried out following processing successively and realizes:
The 1st step:
The distribution pattern of the multimedia messages of multi-user's broadcast channel is described with time one frequency matrix of a following two dimension:
The element S C in the TFM matrix wherein
M * nN OFDM subcarrier among the expression TDS-OFDM in m signal frame;
In the TFM matrix, horizontal direction is represented frequency vector, uses symbol
Expression, vector
In element represented the position of certain multimedia programming on the OFDM subcarrier; Vertical direction is represented time vector, uses symbol
Expression, vector
In element represent the index of certain multimedia programming signal frame in the frame group; Thereby with the distribution of the multimedia programming of assign representation of element in the TFM matrix at the TDS-OFDM used physical transmission channel;
When p program of transmission, represent this p that will transmit program with a three-dimensional matrice that constitutes by the T/F matrix of each program, described three-dimensional matrice is used symbol with a program vector representation
Or TFMp representative:
TFM
p＝[TF
1，TF
2，…TF
m，…，TF
p]
TF wherein
mRepresent m program channel allocation information in time-frequency two-dimensional matrix T FM;
The 2nd step:
Multi-user's broadcast channel assigned scheme according to the described TFM defined matrix of step 1, multimedia programming code stream from above-mentioned IDFT input is assigned to the relevant position of TFM matrix, represent that with 1 the subcarrier of this element representative transmits this program data, represent that with 0 this subcarrier does not transmit this program data, receiver is in idle condition, close corresponding part receiving circuit, but transmitter continues to send other TV programme at this moment;
The 3rd step:
Respectively each user's broadcast message is protected processing with forward error correction, the data behind the forward error correction are done the symbol constellation mapping through ovennodulation;
The 4th step:
Multi-user's data are carried out multiple connection at frequency domain, form length in pre-determined data block, adopting IDFT then is the time domain discrete sample value frame that discrete Fourier transform is for conversion into formed block of frequency domain data respective length, obtain OFDM multicarrier baseband modulation signal, constitute the frame of TDS-ofdm signal frame;
The 5th step:
Press the channel frame structure of TDS-OFDM, the PN sequence of inserting certain-length in OFDM protection is at interval formed signal frame to frame head and frame as frame head;
The 6th step:
In TDS-OFDM frame group's frame group head, insert the TFM matrix information;
The 7th step:
The frame group is further formed superframe and day frame, constitute a complete signal that meets the TDS-OFDM transmission frame-form;
Transmitting terminal forms Filtering Processing to the complete TDS-OFDM signal that step 7 forms at last, passes through frequency up-converted and power amplifier again, launches in predetermined channel bandwidth.
According to time-frequency matrix two dimensional channel dynamic allocation method in the above-mentioned TDS-OFDM system, it specifically is characterised in that: described TFM matrix is a sparse matrix.
According to time-frequency matrix two dimensional channel dynamic allocation method in the above-mentioned TDS-OFDM system, it specifically is characterised in that: described TFM matrix transmits with compression method.
According to time-frequency matrix two dimensional channel dynamic allocation method in the above-mentioned TDS-OFDM system, it specifically is characterised in that: the arrangement of elements pattern is at random in the described TFM matrix.
According to time-frequency matrix two dimensional channel dynamic allocation method in the above-mentioned TDS-OFDM system, it specifically is characterised in that: the arrangement of elements pattern has unalterable rules in the described TFM matrix.
TDS-OFDM and the synchronous multi-layer channel frame structure of natural time that the present invention invents according to Tsing-Hua University, proposed a kind ofly to utilize two-dimensional time-frequency matrix (TFM) to come the method for dynamic assignment channel randomly, satisfied the demand of transmitting a plurality of multimedia programmings in the TDS-OFDM physical layer.Because the TFM matrix has sparse property, embody the burst transfer characteristic, by closed portion circuit between the program burst, thereby arrive power saving effect; Because the frequency hopping of TFM matrix, at random with discontinuous characteristic, characterized time-frequency two-dimensional and united and interweave, strengthened the ability of opposing error burst, increased confidentiality simultaneously; Because the TFM matrix can predefined, special signaling channel (control frame) in, transmit the flexible allocation of realization program; Because the burst interval of each element representative is very short among the TFM, the performance practical requirement that the power consumption that can arrive reduces, the length of required memory size and burst packets is far smaller than existing other digital television transmission system, make the realization cost and the signal delay of receiver reduce greatly, be beneficial to the transmission of short message and instant messages simultaneously, and compatible with present TDS-OFDM system maintenance.
Description of drawings
Fig. 1 is the ATSC frame structure.
Fig. 2 is the DVB-T frame structure.
Fig. 3 is the DVB-T pilot signal.
Fig. 4 is the distribution method of program among the European DVB-H.
Fig. 5 is the conceptual configuration of DVB-H system.
Fig. 6 is TDS-OFDM and the synchronous hierarchical frame structure of natural time.
Fig. 7 distributes giving an example of pattern for the physical channel that adopts a multimedia programming of the present invention.
Fig. 8 is three-dimensional TFM schematic diagram.
Fig. 9 is for adopting the ground digital television broadcast emission system signal processing flow block diagram of the method for the invention.
Figure 10 is for adopting the ground digital television broadcast receiving system signal processing flow block diagram of the method for the invention.
Embodiment
The invention provides a kind of time-frequency matrix (Time-Frequency Matrix, TFM) two dimensional channel dynamic allocation method, at time-domain synchronization OFDM, be TDS-OFDM, adopt the time domain-frequency domain channel distribution method of two dimension in the system, with satisfy multimedia programming flexibly, efficient, low-power consumption and demand such as instant.
Below in conjunction with accompanying drawing specific embodiments of the invention are described in detail.
China also began the research work of high definition TV from 1994.And succeeded in developing Chinese first generation functional prototype of high definition TV in 1998.Organized the expert of China that Digital Television and digital high-definition television standard are formulated by radio and television responsible institution, SARFT(The State Administration of Radio and Television), (Digital MultimediaBroadcasting for Terrestrial, DMB-T) host-host protocol is one of testing scheme to Tsing-Hua University's T-DMB.
The time-domain synchronization OFDM that adopts among the DMB-T of Tsing-Hua University (Time Domain Synchronous OFDM, TDS-OFDM) modulation belongs to multi-transceiver technology, but it is different with the COFDM in Europe, in TDS-OFDM, do not insert the pilot tone signal, but inserted the PN sequence, time domain carry out frame synchronization, Frequency Synchronization, regularly synchronously, channel transfer characteristic is estimated and follow the tracks of phase noise etc.System uses more optimal forward error correction coding FEC to resist error burst, for example Reed-Solomon (Reed-Solomon, RS) or Turbo code, convolution code and their cascade etc.
Seeing grant number for details about the correlation circumstance of DMB-T, TDS-OFDM is that 00123597.4 " ground digital multimedia TV broad cast system " by name, grant number are 01115520.5 " time-domain synchronous orthogonal frequency division multiplex modulation method " by name, and grant number is the Chinese invention patent that 01124144.6 " protection fill method at interval in the orthogonal FDM modulation system " by name waits Tsing-Hua University to apply for.
For realize quick and stable synchronously, the DMB-T transmission system has adopted the hierarchical frame structure synchronous with natural time.It has periodically, and can be synchronous with natural time.The elementary cell of frame structure is called signal frame, as shown in Figure 6.The frame group of DMB-T transmission system is made of a control frame and 225 signal frames subsequently.Each frame group's duration is 125ms.First signal frame among the frame group is defined as frame group head (control frame), is used to transmit this frame of control group's signaling.Each signal frame among the frame group has unique frame number, and it is coded in the PN sequence of frame head.Each frame group is by the frame group number sign of a 9bit.The frame group number is coded in the transmission parameter signaling (TPS) of signal frame.TPS repeats in each signal frame in the frame group, only could change when new frame group begins.The superframe of DMB-T transmission system comprises 480 frame groups.Each frame group in the superframe is by its frame group number unique identification.First frame group number of superframe is 0, and last frame group number is 479.The duration of each superframe is 60s.The day frame of DMB-T transmission system is made up of 1440 superframes, and is to carry out periodicity repetition the cycle with a consecutive days.In Beijing time 0:0:0AM or other selected reference time, the frame structure of DMB-T transmission system is reset and begins a new day frame.Each day, last superframe of frame was incomplete.
A kind of like this and the synchronous Hierarchichal frame structure of natural time, signal frame and frame group are unique addressable, and can provide second synchronised clock corresponding with TS stream for single frequency network in physical layer, are convenient to single frequency network; Also can match, be convenient to carry out timing and receive with the across-the-board that by the calendar day is the cycle; Also help the function expansion of system in future, as two-way interactive and positioning function etc.For the hand-portable receiver, be beneficial to power-saving control, this is an important characteristic.
The signal frame of DMB-T transmission system uses the OFDM modulation of Domain Synchronous, and perhaps being called with the PN sequence is protection OFDM modulation at interval.A signal frame is made up of frame synchronization and frame two parts, and they have identical baseband signalling rate 7.56MS/s (1/T).Consider the time selectivity (Doppler distributes and is about 100Hz) of channel, the length of each signal frame is defined as＜600 μ s.A signal frame can be used as an OFDM (OFDM) piece.An OFDM piece further is divided into a protection interval and an inverse discrete Fourier transform (IDFT) piece.For TDS-OFDM, frame synchronization sequence is as the protection interval of OFDM, and frame is as the IDFT piece; the frame of signal frame adopts multi-carrier modulation; the frequency domain sub-carrier number of frame is 3780, adjacent sub-carrier be spaced apart 2kHz, each sub-carrier adopts 64QAM planisphere.In TDS-OFDM, the length of frame is fixing 500us, and is separated with 1/4 and 1/9 two kind of pattern between protection, promptly protects gap length to be respectively 1/4 (625us) or 1/9 (555.6us) of frame length.
Frame synchronization in the signal frame is made of preamble, synchronous three parts of 8 rank PN sequences and back.The PN preamble and after be defined as the cyclic extensions of PN sequence synchronously, 8 rank PN sequence definitions are proper polynomial x
8+ x
6+ x
5The m sequence of+x+1, its initial condition will be determined the phase place of the m sequence that generated.The frame number of each signal frame determines the initial condition of its m sequence.Each signal frame among the signal frame group is assigned unique frame synchronizing signal, with the recognition feature as signal frame.
Another explanation of TDS-OFDM is the OTDM of PN sequence and IDFT piece.Because the PN sequence is a known array for receiving terminal, PN sequence and IDFT piece are can be separated at receiving terminal.
The PN sequence is except as the protection of OFDM piece at interval, can also be used as the purposes such as frame synchronization, carrier wave recovery and automatic frequency tracking, symbol clock recovery, channel estimating of signal frame at receiving terminal.
TDS-OFDM is undertaken synchronous by the PN sequence, only carry out in time domain, and the synchronization acquistion of TDS-OFDM system is about about 1ms in theory, is equivalent to the time interval of adjacent PN sequence.In the national digital ground digital television broadcast laboratory and place test of national departments concerned tissue, be 2ms the lock in time of TDS-OFDM.And the simultaneous techniques of European DVB-T realizes complexity, and be about about 250ms lock in time.
As previously mentioned, for a kind of like this and synchronous TDS-OFDM Hierarchichal frame structure of natural time, signal frame and frame group are addressable, embodied the temporal characteristics of TDS-OFDM, and each of 3780 subcarriers also is unique in the signal frame, and be addressable, this has embodied the frequecy characteristic of TDS-OFDM.Owing to adopted the Domain Synchronous technology of PN sequence, that can realize is synchronous fast, and the system that makes can be addressed to needed subcarrier, signal frame and frame group position soon.
The time and the frequecy characteristic that embody based on the synchronous Hierarchichal frame structure of TDS-OFDM and natural time, and system can immediate addressing arrive subcarrier, signal frame and frame group, can be distributed in a plurality of multimedia programmings dispersedly on unlike signal frame, the different sub carrier and transmit, we can describe this distribution locations with matrix, promptly can constitute the subcarrier, signal frame or the frame group that distribute certain multimedia programming the T/F matrix (TFM) of a two dimension:
The element S C in the TFM matrix wherein
M * nN OFDM subcarrier (Sub-Carrier) among the expression TDS-OFDM in m signal frame.
In the TFM matrix, horizontal direction is represented frequency vector (Frequency Vector), uses symbol
Expression, vector in the present embodiment
Length N elect the sub-carrier number 3780 of TDS-OFDM, vector as
In element represented the position of certain multimedia programming on the OFDM subcarrier; Vertical direction is represented time vector (TimeVector) in the TFM matrix, uses symbol
Expression, vector in the present embodiment
Length M elect the number 224 of signal frame among frame group of TDS-OFDM as, can certainly select other numerical value, vector
In element represent the index of certain multimedia programming signal frame in the frame group.
In the present invention, we are with the distribution at the TDS-OFDM used physical transmission channel of the multimedia programming of assign representation of element in the TFM matrix, and this distribution can be done according to factors such as application demand, programme content, urgency and importance and on-the-fly modifies.
The present invention utilize the Time Division Multiplexing technology in the time-frequency two-dimensional territory with burst time slot form transmission data, thereby reach power saving, encryption, purpose such as reliable and flexible.In order to realize the burst transfer of data, on the basis of TDS-OFDM channel frame structure, the physical channel of a multimedia programming distributes pattern for example as shown in Figure 7.
Fig. 7 can represent that also the element of relevant position is 1 among the grey vertical bar representing matrix TFM among Fig. 7 with matrix T FM, and this subcarrier transmits this program data; Vertical white band represents 0, and then this subcarrier does not transmit this program data, and receiver is in idle condition, just can the closed portion receiving circuit, but transmitter can continue to send other TV programme this moment.With the above-mentioned channel allocation of time-domain matrix (TFM) expression be:
At frequency vector
In the channel allocation pattern can be original that arrange, fixing regular, the perhaps distribution that produces at random.
In time vector
Between the channel allocation pattern can be identical, or certain rule, or at random.
When p program of transmission, can be further by three-dimensional matrice of T/F matrix (TFM) formation of each program, as shown in Figure 8, this three-dimensional matrice can be used symbol with a program vector (Program Vector) expression
Or TFM
pExpression:
TFM
p＝[TF
1，TF
2，…TF
m，…，TF
p]
TF wherein
mRepresented program m channel allocation information in time-frequency two-dimensional matrix T FM.
Generally speaking, TFM matrix of the present invention is a sparse matrix.If matrix T FM
M * NIn s nonzero element arranged, if s be far smaller than matrix element sum (be s＜＜M * N), claim that then TFM is a sparse matrix.
When the transmission number of programs is a lot, TFM
pIt is very big that the data volume of matrix will become, and so how compresses this sparse TFM effectively
pMatrix? for sparse matrix, generally only store its nonzero element according to certain algorithm.Because the distribution of nonzero element generally is random, therefore in the storage nonzero element, row that also must storage nonzero element place number, row number, could determine rapidly that a nonzero element is which element in the matrix, promptly wherein the row at each nonzero element place number, row number and numerical value are formed a tlv triple (m, n, V), and tlv triple is only definite thus.The compression method that sparse matrix is commonly used has two kinds: sequential storage and chain type storage, and can be with reference to relevant data.Certainly, also can further study more effective sparse matrix compression algorithm.
From the above, TFM
pCarry the dynamic assignment information of program in channel, so how to have informed this TFM of receiver
pInformation? in TDS-OFDM frame group, the 1st signal frame is control frame (frame group head), TFM above-mentioned compression or unpressed
pMatrix information can carry in control frame, and sends receiver to, and receiver just can come the needed program of process user according to the TFMp matrix information of receiving.
The ground digital television broadcast emission system principle composition frame chart of an employing the method for the invention as shown in Figure 9.In the present embodiment transmitting terminal, the step of signal processing is as follows:
(1) produces the channel allocation pattern according to certain rule, obtain the time domain-frequency domain matrix T FM multi-user broadcast channel of a two dimension;
(2), multimedia programming code streams such as the video of input, audio frequency, figure, text, data are assigned to the relevant position of the time domain-frequency domain matrix of two dimension according to multi-user's broadcast channel assigned pattern of above-mentioned TFM defined matrix;
(3) in order to resist the error code that produces in the transmission course; broadcast message to each user has adopted forward error correction (LDPC sign indicating number or RS sign indicating number and serially concatenated systematic convolutional code are as inside and outside error correcting code) to protect respectively, and the data behind the forward error correction are after the symbol constellation mapping of ovennodulation.
(4) multi-user's data are carried out multiple connection at frequency domain, form the data block of determining length, (for example, employing length is 3780 data block), adopt inverse discrete fourier transform (IDFT) formed block of frequency domain data to be for conversion into the time domain discrete sample value frame of respective length then, obtain 0FDM multicarrier baseband modulation signal, constitute the frame of TDS-0FDM signal frame;
(5) by the time domain synchronous OFDM, i.e. TDS-OFDM, the channel frame structure, the PN sequence of inserting certain-length in OFDM protection at interval is as frame head, with frame head and frame composition signal frame;
(6) in TDS-OFDM frame group's frame group head (frame group control frame), insert the TFM matrix information, be used to transmit the channel allocation information of program;
(7) the frame group is further formed superframe and day frame, constitute a complete signal that meets the TDS-OFDM transmission frame-form;
(8) above-mentioned complete TDS-OFDM signal is formed Filtering Processing, pass through frequency up-converted and power amplifier then, in predetermined channel bandwidth, launch.
The ground digital television broadcast receiving system principle composition frame chart of an employing the method for the invention mainly comprises following some parts as shown in figure 10:
(1) AFE (analog front end)
AFE (analog front end) is a high-frequency tuner, and it amplifies the RF signal that receives, and finishes channel selection, and the signal of selecting is transformed to a fixing medium-frequency IF 1 (36.25Mhz) from RF band.The voltage of control tuner automatic gain control AGC is provided by intermediate-frequency section.Channel selection realizes by the divide ratio that changes PLL.The IF1 signal is through the filtering of 8MHz bandwidth filter.A local oscillator in intermediate frequency unit transforms to little medium-frequency IF 2 (4.5MHz) with IF1, and the signal of this moment is a bandpass signal near base band.
(2) AD conversion and hilbert filter
Through after the AFE (analog front end), the filtering of analog signal process is through four sampling T
s(being 30.40MHz) becomes digital little intermediate-freuqncy signal, and the sampling clock of AD converter does not pass through phase-locked, is free-running.Therefore, digital little intermediate-freuqncy signal will be recovered through the carrier wave of back just can obtain accurate carrier frequency after the processing module.Become complex signal behind the little intermediate-freuqncy signal process hilbert filter of numeral (Hilbert Filter), promptly be demultiplexed back into two paths of data: I road (in-phase component) and Q road (quadrature component).
(3) carrier wave recovers and down-conversion
The frequency of receiver oscillator can not be very stable, so always there is a quantitative frequency shift (FS), regularly digital and other synchronized algorithms only could be normal under the situation of little frequency difference, is necessary so carry out the carrier wave recovery.A coarse frequency estimation that scope is bigger to be arranged when receiver powers up, need more high-precision Frequency Estimation AFC that frequency error is reduced to below the 1Hz afterwards.It is that sampled data by with time domain is multiplied by that carrier frequency shift is proofreaied and correct
(one has the complex exponential that increases progressively phase place, and wherein the phase place recruitment is
Variable k is a data sequence number,
For with the normalized frequency offset estimating value of Ts).
After the carrier signal that is restored, digital little intermediate-freuqncy signal realizes down-conversion by multiplier, obtains digital baseband signal.
(4) clock recovery
The TDS-OFDM clock recovery comprise the PN sign indicating number catch (Code Acquisition, CA) and symbol timing recovery (Symbol Timing Recovery, STR) two parts.During beginning, receiver is not known the phase place of PN sign indicating number in the received signal frame, catch by sign indicating number and obtain this phase place, thereby the PN sequence becomes known signal, can be used for other synchronization modules.The sign indicating number acquisition algorithm is that received signal is relevant with the local PN sequence slip that produces, because the local PN sequence that produces and the PN sequence of reception only are that a time migration is arranged, so very strong peak value will occur in the correlated results.
After sign indicating number was caught, only in ± Ts/2 scope, we needed more accurate timing synchronous to timing error, and STR estimates remaining timing error ε 0, obtains estimated value
, by linear interpolation, with sampled signal { r
f(kT
s) convert the synchrodata consistent to sending symbol rate 1/T.Because sampling clock has drift, STR adopts the second order feedback control loop to come the departure signal, finishes the tracking to sampling clock simultaneously.
Simultaneously, after the PN sign indicating number is caught, just can from digital baseband stream, separate PN sign indicating number (frame head) part and data division (frame), give different processing modules then.
(5)DFT
At receiver end, suppose that correct timing is synchronous, carry out the demodulation that DFT finishes OFDM by the time domain second mining sampling point after N is proofreaied and correct.
(6) channel estimating and equilibrium
Receiver channel estimates that (Channel Estimation) part is mainly each OFDM piece the estimation of channel response is provided, so that proofread and correct each data sampling that receives (coherent detection).After finishing Frequency Estimation, stationary phase error that signal is also residual has also comprised this error in the channel estimating.After obtaining channel estimating, the channel equalization part realizes channel equalization (Channel Equalization) at frequency domain by simple division arithmetic.
(7) phase noise is removed
Use is based on transmission parameter signaling (Transmission Parameter Signals, TPS) removal phase noise (PhaseNoise Correction) method, its TPS signal behind the DFT obtains the frequency domain baseband signal of phase noise, through IDFT the frequency-region signal that obtains is converted into the time domain phase noise then and estimates, then use to obtain the time domain phase noise and estimate the data before the DFT are carried out phase compensation.
(8) the catching and analyzing of control frame among the frame group
In the frame group of the transmission frame-form of TDS-OFDM system, comprising a frame group head (control frame), receiver can obtain the information of the TFM matrix of transmitting terminal defined from control frame, thereby obtain the assignment information of program time domain-frequency domain in channel, obtain system parameterss such as signal frame frame number and OFDM sub-carrier positions, these parameters can every frame group/or a plurality of frame group detect once.Can obtain the formation of business (program) by these parameters, the business of selecting according to the user provides an activations/resting state index signal, work partly such as deexcitation channel demodulation and error correction in the residing position of transmission frame, receive the burst code stream, deposit in the buffer.And between two bursts, then quit work, save power consumption, sense data is given source coding and demonstration etc. from buffer simultaneously.
Therefore, as can be seen from Figure 10, adopt the signal processing sequence of embodiments of the invention receiving terminal as follows:
Becoming digital signal after a high frequency analog signals is passed through tuner and AD conversion, is I road (in-phase component) and Q road (quadrature component) data-signal by Variational Solution Used behind the hilbert filter.
The IQ signal is divided into two-way: the one tunnel gives AGC control module, and the IQ signal and the frame synchronization PN sequence of catching later produce an AGC control voltage together in AGC, removes to control the gain amplifier of high-frequency tuner; Another road IQ signal is given low-converter, multiplies each other with the local carrier that recovers, then through obtaining digital baseband signal behind sample value interpolation and the SRRC low pass filter.
One way word baseband signal is through being used to control carrier wave to the AFC signal and recovering after the Frequency Estimation, obtain one relatively accurately local carrier be used for above-mentioned low-converter; Another way word baseband signal makes PN sign indicating number in the signal frame that receiver obtains to receive after through PN sign indicating number trapping module, after the PN sign indicating number is caught, it is synchronous to obtain more accurate timing through clock recovery module, being used for above-mentioned sample value interpolation handles, after the PN sign indicating number is caught simultaneously, just can be decomposed into PN sign indicating number (frame head) and DFT data-signal (frame) two parts to the signal frame that receives.
The PN signal section is given channel estimation module, the channel response that obtains each OFDM piece is estimated, then the data behind the phasing are carried out channel equalization, so that proofread and correct each data sampling that receives (coherent detection), balanced data feeds back to channel estimating more then, so that the next frame channel estimating is more accurate.Simultaneously, the PN signal section is also given above-mentioned AGC control circuit.
Behind data division process frame group's head (frame group control frame) capture circuit, obtain frame group head, frame group head by analysis, obtain the TFM matrix parameter of transmitting terminal regulation, as matrix size M * N, program (business) quantity, error correcting system, program length, have or not encryption etc., thereby obtain the required program data of user, and provide circuit activation/resting state index signal.
Circuit activation/resting state index signal is given modulation and circuit such as error correction decoding, the work of controlling these circuit whether, arrival power saving purpose.Simultaneously, this signal is also given data buffer, the reading writing working of indication buffer.
Frame sheet data division is through the phase noise correction module, after data process DFT conversion behind the phasing and the above-mentioned channel estimating and equilibrium, give forward error correction coding FEC module, depositing in the buffer behind the fec decoder, give source coding sense data from buffer, the final transmission sequence of recovering.
Adopt the system of time-frequency matrix T FM two dimensional channel dynamic allocation method of the present invention to have tangible performance advantage:
(1) the sparse property of TFM matrix has reduced the power consumption of receiving equipment, is beneficial to the transmission of short message and instant message.
After a program (business) input, at first according to the channel allocation pattern shown in the TFM matrix the many bursts of program, be distributed on the different OFDM subcarrier of unlike signal frame among the frame group.To a program, this has embodied the time division multiplexing and the frequency division multiplexing burst transfer pattern of information, receiving equipment only just activates parts such as channel demodulation and error correction when receiving the program (business) of being asked, carry out work, receive the burst code stream, deposit in the buffer, and between two bursts, equipment stops the work of foregoing circuit, saves power consumption, and sense data is given source coding and demonstration etc. from buffer simultaneously.In order to obtain suitable energy-saving effect, burst bandwidth (code check) should be the certain multiple of constant bandwidth (code check).For example, as long as the burst code check is 2 times of constant code rate, so just can save 50% energy.
Because the TFM matrix is a sparse matrix, utilize short, the synchronous fast characteristics of TDS-OFDM system signal frame, the burst length of institute of the present invention extracting method is shorter, free time is long, and the capacity register that needs is little, realizes that cost is low, and be beneficial to the transmission of short message, improve the efficiency of transmission of short message.Simultaneously, program (business) postpones little, even be convenient to transmission of Information.Therefore, behind employing the present invention, can significantly reduce the power consumption of receiving equipment, and be beneficial to the transmission of short message and instant message.
(2) randomness of TFM matrix and discontinuity, the confidentiality of enhanced system, opposing error burst and multipath disturb.
The randomness of TFM matrix and discontinuity show as dynamics of channels and distribute pattern to carry out time division multiplexing and frequency division multiplexing by certain pattern (sequence) in time-domain signal frame and subcarrier in frequency domain.
If there is not other specific (special) requirements, wish that generally the TFM matrix pattern presents randomness.The randomness of TFM matrix pattern itself is good more, and antijamming capability is also strong more, and the probability that requires each multiplexing program of participation to occur is preferably identical; It is big that the size of key of TFM matrix pattern is wanted, and requires the number of pattern abundant, and the anti-ability of decoding is strong.Therefore, anti-interference noise of TFM matrix and confidential nature mainly are the character that depends on pseudo random sequence.
Pseudo random sequence commonly used has m sequence, M sequence and R-S sequence.The m sequence is called the maximum length linear shift register sequence.The advantage of m sequence is to be easy to generate, and autocorrelation performance is good, and is pseudorandom.But operational pattern is few, and their cross correlation is undesirable, and what adopt because of its again is the linear feedback logic, is just decoded the sequence of sign indicating number easily by the enemy, and promptly confidentiality, the anti-property intercepted and captured are poor.The M sequence is a non-linear sequence, and available pattern is a lot, and the size of key of pattern is also big, and auto-correlation and their cross correlation are preferably arranged, so it is comparatively ideal frequency hopping command code.Equipment was complicated when its shortcoming was the hardware generation.The hardware of R-S sequence produces fairly simple, can produce a large amount of useful pattern, is suitable for doing the formation sequence of TFM matrix pattern.
In the present invention, the TFM Matrix Technology can improve anti-fading, antijamming capability.The randomness of TFM matrix has good anti-fading effect for mobile reception static or that move at a slow speed, and for the mobile reception of fast moving because its alternate position spike of burst sequence of two connections of same channel has been enough to make them uncorrelated with the Rayleigh variation, the variation that time and frequency are being stopped for a short time during according to the TFM matrix allocation, the interference of frequency is instantaneous, Here it is, and the TFM matrix has regular hour and frequency diversity effect, has improved system's opposing pulse and multipath interference capability.
(3) flexibility
From the above, the channel allocation of a program in TDS-OFDM is by the decision of TFMp matrix, and the TFMp matrix is carried to receiver by frame group control frame.And the pattern of TFMp matrix is determined according to factors such as programme content, urgency, importance, flow size, reception complexity by operator, thereby has very big flexibility, adapts to different application demands.
(4) compatibility
Because in original DMB-T visual broadcast service, code stream is continuous, mainly utilized this one deck of signal frame of TDS-OFDM channel frame structure.The present invention utilizes the TFM matrix of time division multiplexing and frequency multiplexing technique to realize in physical layer, combines closely with the TDS-OFDM transmission frame-form.Therefore, the method that proposes of the present invention can keep compatible with existing DMB-T system.
Used field programmable device (FPGA) to realize adopting the function model machine of the described method of present embodiment.
In conjunction with the accompanying drawings specific embodiments of the invention are had been described in detail above, but the present invention is not restricted to the foregoing description, under the spirit and scope situation of the claim that does not break away from the application, those skilled in the art can make various modifications or remodeling.
Claims (5)
1, time-frequency matrix two dimensional channel dynamic allocation method in the multimedia messages transmission, it is characterized in that: it is under the condition of transmitting multimedia information in time-domain synchronous orthogonal frequency-division multiplexing system TDS-OFDM, utilize two-dimensional time frequency matrix TFM according to what propose in physical layer with the synchronous Hierarchichal frame structure characteristic of natural time, come the method for dynamic assignment channel randomly, it is at transmitting terminal, when input code flow is carried out the channel error correction coding successively, the modulation symbol mapping, after the IDFT conversion, by to utilize field programmable gate array be FPGA the output code flow of IDFT is carried out following processing successively and realizes:
The 1st step:
The distribution pattern of the multimedia messages of multi-user's broadcast channel is described with the time-frequency matrix of a following two dimension:
The element S C in the TFM matrix wherein
M * nN OFDM subcarrier among the expression TDS-OFDM in m signal frame;
In the TFM matrix, horizontal direction is represented frequency vector, uses symbol
Expression, vector
In element represented the position of certain multimedia programming on the OFDM subcarrier; Vertical direction is represented time vector, uses symbol
Expression, vector
In element represent the index of certain multimedia programming signal frame in the frame group; Thereby with the distribution of the multimedia programming of assign representation of element in the TFM matrix at the TDS-OFDM used physical transmission channel;
When p program of transmission, represent this p that will transmit program with a three-dimensional matrice that constitutes by the T/F matrix of each program, described three-dimensional matrice is used symbol with a program vector representation
Or TFM
pRepresentative:
TFM
p＝[TF
1，TF
2，…TF
m，…，TF
p]
TF wherein
mRepresent m program channel allocation information in time-frequency two-dimensional matrix T FM;
The 2nd step:
Multi-user's broadcast channel assigned scheme according to the described TFM defined matrix of step 1, multimedia programming code stream from above-mentioned IDFT input is assigned to the relevant position of TFM matrix, represent that with 1 the subcarrier of this element representative transmits this program data, represent that with 0 this subcarrier does not transmit this program data, receiver is in idle condition, close corresponding part receiving circuit, but transmitter continues to send other TV programme at this moment;
The 3rd step:
Respectively each user's broadcast message is protected processing with forward error correction, the data behind the forward error correction are done the symbol constellation mapping through ovennodulation;
The 4th step:
Multi-user's data are carried out multiple connection at frequency domain, form length in pre-determined data block, adopting IDFT then is the time domain discrete sample value frame that discrete Fourier transform is for conversion into formed block of frequency domain data respective length, obtain OFDM multicarrier baseband modulation signal, constitute the frame of TDS-ofdm signal frame;
The 5th step:
Press the channel frame structure of TDS-OFDM, the PN sequence of inserting certain-length in OFDM protection is at interval formed signal frame to frame head and frame as frame head;
The 6th step:
In TDS-OFDM frame group's frame group head, insert the TFM matrix information;
The 7th step:
The frame group is further formed superframe and day frame, constitute a complete signal that meets the TDS-OFDM transmission frame-form;
Transmitting terminal forms Filtering Processing to the complete TDS-OFDM signal that step 7 forms at last, passes through frequency up-converted and power amplifier again, launches in predetermined channel bandwidth.
2. time-frequency matrix two dimensional channel dynamic allocation method in the TDS-OFDM according to claim 1 system, it specifically is characterised in that: described TFM matrix is a sparse matrix.
3. time-frequency matrix two dimensional channel dynamic allocation method in the TDS-OFDM according to claim 1 system, it specifically is characterised in that: described TFM matrix transmits with compression method.
4. time-frequency matrix two dimensional channel dynamic allocation method in the TDS-OFDM according to claim 1 system, it specifically is characterised in that: the arrangement of elements pattern is at random in the described TFM matrix.
5. time-frequency matrix two dimensional channel dynamic allocation method in the TDS-OFDM according to claim 1 system, it specifically is characterised in that: the arrangement of elements pattern has unalterable rules in the described TFM matrix.
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