CN1332556A - Channel transmission method for ground digital multimeldia television broadcast system - Google Patents
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Abstract
The present invention adopts hierarchical physical channel frame structure, and features that the signal frame consists of frame body with sync OFDM and frame sync comprising PN sequence codes. A frame group head and several signal frames constitute a frame group; several frame groups constitute a superframe; several superframe constitute a superframe group; and several superframe groups are transmitted circularly in the natural day period. The signal frame can be confirmed uniquely by the signal frame sync PN sequence and the superframe of the superframe group is defined uniquely by the frame group head. It is favorable to reliable and flexible information transmission.
Description
The present invention is dividing an application of the name of on August 25th, the 2000 application patent application that is called " ground digital multimedia TV broad cast system " (application number is 00123597.4).
The invention belongs to the digital TV Broadcasting Techniques field, relate more specifically to the channel transmission method in a kind of ground digital multimedia TV broad cast system.
For television transmission system, on the basis of simulated television, through insistent research and development of more than ten years, Digital Television Terrestrial Broadcasting (Digital Television Terrestrial Broadcasting, DTTB) obtained a lot of achievements, 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) ATSC of the U.S. (Advanced Television Systems Committee) digital television standard.
2) Ou Zhou DVB-T (Digital Video Terrestrial Broadcasting-Terrestrial) digital video broadcast-terrestrial standard.
3) Ri Ben ISDB-T (the floor synthetic service digital broadcast standard of Integrated Service Digital Broadcasting-Terrestrial).
Fig. 1 has shown the functional-block diagram of ground digital multimedia TV broad cast system.The digital television system signal structure is made up of compression layer, transport layer and transport layer three parts.The concrete formation of transport layer is determined by transmission channel (perhaps being transmission medium).The wireless medium of the wired media of transmission medium (comprising optical fiber, copper axle and both hybrid network), wireless medium (comprising satellite, microwave, MMDS etc.), surface wave transmission.
In transport layer one very important problem be exactly the physical frame structure of channel and its composition.For wireless medium, owing in transmission course, there are various noise jamming, for example impulse disturbances, multipath interference, white noise etc., in order in time to recover after transmission and the system break reliably, usually need break into Frame to the data that will transmit by certain form, frame length is generally fixed, and is layering.But according to different application and actual design, data frame structure may be different with forming.
U.S. ATSC 8-VSB payload user data code check in a NTSC 6MHz channel is 19.28Mb/s.What transport layer was exported to transport layer is that a serial data transmits code stream (TS stream), and it is made up of the 188byte data bit.Behind data randomization and error code correction coding FEC, after initial data, increase the redundancy check bit, the packet of each FEC all will be formatted as Frame, so that reliable transmission.In addition, for system synchronization and receiver equalization processing, also need to increase synchronization bit and training sequence.
Fig. 2 is the data transmission frame structure figure of ATSC 8-VSB system.Each Frame comprises 2 data fields, and each data fields has 313 data segments.Each data segment includes 832 symbols, preceding 4 symbols are to transmit with binary form, and provide data segment sync, payload data that all the other 828 symbols are 187byte and corresponding FEC error correction data, these 828 symbols are all with the transmission of 8 level symbols, thereby each symbol carries the 3bit data code flow.First data segment of each data fields is the synchronizing signal (data fields is synchronous) of a uniqueness and the training sequence that is used for receiver equalization.See that from figure can think that U.S. ATSC frame structure branch is for three layers: ground floor is a data segment; The second layer is a data fields; The 3rd layer is Frame, and therefore, row, field, frame notion in ATSC frame structure and the traditional tv scanning are closely similar.
Referring to Fig. 3, European DVB-T has adopted the COFDM technology, and its data also are to transmit or modulation after being organized into certain frame format again, and the lasting cycle of each frame is T in its data frame structure
F, and comprising 68 OFDM symbols, 4 frames constitute a superframe.The carrier number of each OFDM symbol is 1705 (2k patterns) or 6817 (8k patterns), and its transmission cycle is T
aTs is made up of two parts: term of validity Tu and protection interval D.Protection is a circulation of live part at interval, is inserted in the front of live part, and the protection gap length can be 1/4,1/8,1/16 and 1/32 of a data live part.
Except data carrier, European DVB-T also inserts additional informations such as pilot tone (dispersion with continuous) and TPS.Scattered pilot is as the estimation of the characteristic of channel; Continuous pilot is synchronous as frame, timing and carrier frequency.TPS is used for transmission system parameters.The continuous pilot that has just overlaps with scattered pilot in some position, and therefore, the active data number of carriers is for being 1512 (2k patterns) or 6048 (8k patterns) in the OFDM symbol, and DVB-T carrier number, pilot tone number see Table shown in 0.
European DVB-T number of carriers of table 0 and synchronizing pilot quantity
| The 2k pattern | The 8k pattern | |
| Total carrier number | 1705 | ?6817 |
| Data carrier | 1512 | ?6048 |
| Scattered pilot | 142 | ?568 |
| Continuous pilot | 45 | ?177 |
| The TPS pilot tone | 17 | ?68 |
This shows that European DVB-T has also adopted the channel frame structure of layering, similar with the U.S. also is to be divided into three layers of OFDM symbols, frame, superframe, but than the complexity of the U.S., inserted continuous and the pilot signal of disperseing therein according to certain rules.
Along with the development of technology and deepening continuously of research, people recognize at signal peak-average power ratio, C/N thresholding, move receive, indoor/outer reception, spectrum efficiency, HDTV transmittability, with frequency/adjacent channel disturb, aspect the flexibility of interference, single frequency network and co-channel forwarding, impulse disturbances and continuous wave interference to having simulated television now, phase noise, static state/dynamically multipath distortion, system or the like, respectively there are its pluses and minuses in above-mentioned three systems.
In signals transmission,, can between receiving symbol, produce intersymbol interference (ISI) because echo disturbs and the linear distortion of channel.The technology of effectively eliminating ISI at present has two kinds: time domain equalization and OFDM (OFDM).
Time domain equalization generally is to insert a transversal filter (also claiming transversal filter) behind matched filter, and it is made of the delay line of a band tap, and tap is the equal symbol cycle at interval.The time delayed signal of each tap is delivered to an adder circuit output after weighting, its form is identical with finite impulse response filter (FIR), and the signal after the addition is sent to decision circuit through sampling.The weight coefficient of each tap is adjustable, can eliminate ISI by adjusting weight coefficient.The portfolio effect of equalizer is mainly by the decision of tap number and equalization algorithm, and equalization algorithm is commonly used zero forcing algorithm and lowest mean square distortion algorithm etc.Equalizer divides two kinds of presetting system and self-adapting types.Also have noise jamming in actual channel, it can exert an influence to the convergence of equalizer.In order further to improve performance, often adopt decision-feedback formula equalizer in the practical application, the tap coefficient of feedback equalizer is determined by the channel impulse response hangover that forward equalizer caused.
The Digital Television of the U.S. has adopted DFF exactly, and modulation technique has adopted numeral 8-VSB mode.
The equalizer techniques comparative maturity is widely used in the various communications fields, but it has two shortcomings: the one, and complex structure, cost is higher; The 2nd, only relatively good to the short ISI effect of time delay, poor to the ISI effect that time delay is long.At this moment, adopt OFDM (OFDM) technology better.
Adopt the OFDM COFDM transmission of coding in the DVB-T system in Europe.In an OFDM Frame, use QPSK, 16QAM or the 64QAM modulation of the same Gray code mapping on all carrier waves.Each V bit symbol of exporting from interleaver is mapped to a constellation point in the modulation constellation.
One of the implication of " coding " among the Coded Orthogonal Frequency Division Multiplexing (COFDM) COFDM is meant has inserted some " pilot tone " signals at random in the OFDM frequency spectrum, here so-called " pilot tone " is meant the carrier wave of some OFDM like this, they are by the known data-modulated of receiver, what they transmitted is not modulating data itself, because it is known that these data receivers are systems, the purpose that pilot tone is set is that system transmits the parameter of some transmitter or the characteristic of test channel by the data on the pilot tone.
The effect of pilot tone in COFDM is very important, and its use comprises: frame synchronization, Frequency Synchronization, time synchronized, channel transfer characteristic are estimated, transmission mode is discerned and follow the tracks of phase noise etc.The data of modulated pilots are the pseudo random sequences that generates from a pseudo-random sequence generator of stipulating in advance.Distribution pilot tone and continuous pilot have been stipulated among the DVB-T.The position of continuous pilot in each COFDM symbol all fixed, and inserted 177 continuous pilot in the 8k pattern, inserted 45 continuous pilot in the 2k pattern.The position of scattering pilot tone is different in different COFDM symbols, but with four COFDM symbols is loop cycle, that is to say the 1st, 2,3, the position of the distribution pilot tone in 4 COFDM symbols has nothing in common with each other, but the 5th COFDM symbol is identical with pilot frequency locations in the 1st the OFDM symbol, the 6th COFDM symbol is identical with pilot frequency locations in the 2nd the COFDM symbol, the 7th COFDM symbol is identical with pilot frequency locations in the 3rd the COFDM symbol, the 8th COFDM symbol is identical with pilot frequency locations in the 4th the COFDM symbol, and the rest may be inferred for all the other COFDM symbols.
No matter how the position of pilot tone changes, the number that is used to transmit the carrier wave of effective programme information in each COFDM symbol all is constant, is 1512 in the 2k pattern, is 6048 in the k pattern.Because the effect of pilot tone in system is important, for guaranteeing the reliability of data on the pilot tone, prevent noise jamming, the average power of pilot signal is bigger 16/9 times than the average power of other carrier signal, and promptly pilot signal is launched on " lifting " power level.
But because FFT and pilot tone are mutual demands in COFDM, pilot tone is inserted after FFT, and FFT calculates and needs (pilot tone) at first synchronously, could calculate FFT then.Therefore, COFDM adopts the iterative approach algorithm, so convergence error is big, and convergence time is long.
The objective of the invention is provides the channel transmission method in a kind of ground digital multimedia TV broad cast system for overcoming the weak point of prior art.Method of the present invention adopts the frame of regular length, and is layered mode, is convenient to realize reliably, message transmission flexibly.
According to the channel transmission method in the ground digital multimedia TV broad cast system of the present invention, adopt the physical channel frame structure of layering; It is characterized in that:
Signal frame is made up of frame and frame synchronization, and frame adopts synchronized orthogonal frequency division multi-carrier modulation (OFDM), and frame synchronization is made of the PN sequence code;
A frame group head and a plurality of signal frame constitute a frame group;
A plurality of frame groups constitute a superframe;
A plurality of superframes constitute a superframe group;
A plurality of superframe groups are the transmission of loop cycle ground with natural order;
Described signal frame can be assert by its signal frame synchronic PN sequence uniquely;
Described superframe group's described superframe is defined uniquely by described frame group head.
Described frame synchronization is that the PN sequence code by spread spectrum constitutes; The described frame synchronizing signal that is made of the PN sequence code of spread spectrum is a signal of being modulated by the BPSK mode; The described frame synchronizing signal that is made of the PN sequence code of spread spectrum is the bpsk signal of a power ascension, and it is bigger than the data-signal power in the OFDM structure; In described frame group head, defined system parameters and Control Parameter, such as: transmission date (year, month, day), frame sign indicating number (frame group number, Hyper Frame Number, superframe group number) etc.; Described superframe group and certain Absolute Time Synchronization ground begin transmission; Described frame is made of at interval DFT piece and protection; Described signal frame body length is chosen as 4666 symbols;
Described signal frame body comprises the protection intervening sequence with 630 continuous symbols; Described signal frame synchronization length is chosen as 255 symbols; Frame group number in the described superframe is 512; Number of superframes among the described superframe group is 478.
Method of the present invention adopts the frame of regular length, and is layered mode, is convenient to realize reliably, message transmission flexibly.
The present invention not only can be used for ground, satellite, wired, microwave and other transmission medium, also can be used for data broadcasting, Internet and other wideband multimedia message transmission and integrated data business field.
Brief Description Of Drawings:
Fig. 1 is the functional-block diagram of ground digital multimedia TV broad cast system.
Fig. 2 is a U.S. ATSC system signal frame assumption diagram.
Fig. 3 is European DVB-T system signal frame assumption diagram.
Fig. 4 implements illustration according to the physical channel frame structure of the channel transmission method of ground digital multimedia TV broad cast system of the present invention.
Below in conjunction with accompanying drawing specific embodiments of the invention are described in detail.
In order to satisfy the demand of Digital Terrestrial Television Broadcast more reliably, neatly, the channel physical frame structure of the channel transmission method of ground digital multimedia TV broad cast system of the present invention.It can be used for 6MHz, 7MHz or 8MHz channel.
Physical channel structure of the present invention has following characteristic:
A. the frame structure of layering
B. synchronized orthogonal frequency division multi-carrier modulation (also claiming OFDM or DMT)
The C.PN sequence pilot frequency is synchronous
D. cyclical transmission scheme, be consecutive days circulation timei
E. unique frame address, the support time is shared multiple access
F. continuous and burst transfers of data is mixed application
Physical channel frame structure embodiment of the present invention as shown in Figure 4.Frame structure is classification, and a basic frame structure is called a signal frame.The frame group is defined as a group signal frame, and its first frame is defined as frame group head.Superframe is defined as a framing group.The top layer of frame structure is called the superframe group.As shown in the figure, for example, a superframe group is made up of 478 superframes, and a superframe comprises 512 frame groups, and a frame group comprises 255 signal frames.Physical channel is the cycle, and and Absolute Time Synchronization.
Signal frame is the elementary cell of down physical channel.A signal frame is made up of two parts: frame synchronization and frame.The baseband signalling rate of frame synchronization and frame is identical, is defined as 7.56MSps.Frame synchronization adopt the BPSK modulation with obtain stable synchronously.Frame synchronization comprises preamble buffering, PN sequence and back sync buffering.Symbolic number in the frame synchronization depends on the symbolic number in preamble buffering and the back sync buffering, and is as shown in table 1.
Symbolic number in table 1 frame synchronization
| Symbolic number in the frame synchronization | Symbolic number in the preamble buffering | Symbolic number in the PN sequence | Symbolic number in the back sync buffering |
| 256 | ?0 | ?255 | ?1 |
| 304 | ?24 | ?255 | ?25 |
| 384 | ?25 | ?255 | ?104 |
The OFDM modulator approach is used for frame.The DFT piece has 3780 symbols and continues 500us.Protection is chosen as 1/6,1/9,1/12,1/20 or 1/30 of DFT piece at interval, and is as shown in table 2.
Symbolic number in OFDM piece of table 2
| Symbolic number in the OFDM piece | The percentage of the at interval relative DFT piece of protection | Symbolic number in the protection at interval |
| 4410 | ?1/6 | ?630 |
| 4200 | ?1/9 | ?420 |
| 4095 | ?1/12 | ?315 |
| 3969 | ?1/20 | ?189 |
| 3906 | ?1/30 | ?126 |
A signal frame will have different symbolic numbers, depend on selected frame synchronization and OFDM protection at interval, and will be as shown in table 3.Table 3 has also been listed the time corresponding to a signal frame.
Symbolic number in signal frame of table 3
| The time of signal frame (μ S) | Symbolic number in the signal frame | Symbolic number in the frame synchronization | Symbolic number in the OFDM piece |
| 617.2 | ?4666 | ?256 | ?4410 |
| 623.5 | ?4714 | ?304 | ?4410 |
| 634.1 | ?4794 | ?384 | ?4410 |
| 589.4 | ?4456 | ?256 | ?4200 |
| 595.8 | ?4504 | ?304 | ?4200 |
| 606.3 | ?4584 | ?384 | ?4200 |
| 575.5 | ?4351 | ?256 | ?4095 |
| 581.9 | ?4399 | ?304 | ?4095 |
| 592.5 | ?4479 | ?384 | ?4095 |
| 558.9 | ?4225 | ?256 | ?3969 |
| 565.2 | ?4273 | ?304 | ?3969 |
| 575.8 | ?4353 | ?384 | ?3969 |
| 550.5 | ?4162 | ?256 | ?3906 |
| 556.9 | ?4210 | ?304 | ?3906 |
| 567.5 | ?4290 | ?384 | ?3906 |
A frame group contains 255 signal frames, and wherein first signal frame is defined as frame group head.Signal frame among frame group has unique frame number, label from 0 to 254, and signal frame number (FN) is encoded in the frame synchronization PN sequence of current demand signal frame.A frame group's duration depends on the sample number in its signal frame, at 140.4mS between the 161.7mS.
Superframe is numbered, from 0 to largest frames group number (511).Hyper Frame Number (SFN) (0-47) is encoded in first frame group head of superframe with superframe group number (SFGN).
Superframe group's transmission is to carry out periodicity the cycle to repeat with a consecutive days, and it is encoded as preceding two bytes in first frame group head of a superframe among the superframe group, coded format be month, day and year as metric MMDDYY, see Table 4.At (PST) 0:0:0AM Pacific standard time, physical channel frame structure is reset and begins a new superframe group.Last superframe of each superframe group can be incomplete resetting constantly.
As mentioned above, the low layer of the synchronous channel structure of layering is embedded in the signal frame.And the high level of the synchronous channel structure of layering, SFGN and SFN are encoded in first frame group head of superframe.SFGN and SFN packet are defined as the superframe-synchronized bag, and be as shown in table 4.
Table 4 downgoing line superframe-synchronized bag
[M3 ... M0]: the month on date, scope from 1 to 12[D4 ... D0]: the day on date, scope from 1 to 31[Y6 ... Y0]: the year on date, scope from 0 to 99[SFGN8 ... SFGN0]: superframe group number [SFN9 ... SFN0]: Hyper Frame Number [FGN7 ... FGN0]: frame group number [BS4 ... BS0]: Base Station Identification, default value are 0
| ?D3 | ?D2 | ?D1 | ?D0 | ?M3 | ?M2 | ?M1 | ?M0 |
| ?Y6 | ?Y5 | ?Y4 | ?Y3 | ?Y2 | ?Y1 | ?Y0 | ?D4 |
| ?SFGN7 | ?SFGN6 | ?SFGN5 | ?SFGN4 | ?SFGN3 | ?SFGN2 | ?SFGN1 | ?SFGN0 |
| ?SFN7 | ?SFN6 | ?SFN5 | ?SFN4 | ?SFN3 | ?SFN2 | ?SFN1 | ?SFN0 |
| ?SFGN8 | ?SFN8 | ?SFN9 | ?BS4 | ?BS3 | ?BS2 | ?BS1 | ?BS0 |
| ?FGN7 | ?FGN6 | ?FGN5 | ?FGN4 | ?FGN3 | ?FGN2 | ?FGN1 | ?FGN0 |
The base band frame synchronizing signal by a preamble cushion, sync buffering constitutes behind PN sequence and one.The preamble buffering may be defined as 0,24 and 25 symbol, and back sync buffering may be defined as 1,25 and 104 symbol, and the PN sequence has 255 symbols.Unlike signal frame among the signal frame group has different frame synchronizing signals.So frame synchronization can be made the frame synchronization feature of a distinctive signal frame and be used for identification.Preamble buffering and back sync buffering are defined as the cyclic extensions of PN sequence.Another file is seen in elaborating of relevant PN sequence.
The baseband signal of a frame is an OFDM (OFDM) piece.An OFDM piece can further be divided into protection interval and a DFT piece, as shown in Figure 8.Because the OFDM block protection is different at interval, has the OFDM piece of 3780 subcarriers that different number of samples (referring to table 2) is arranged corresponding to frequency domain in time domain.
The DFT piece has 3780 samplings in its time domain, they are contrary discrete fourier transforms of 3780 subcarriers in the frequency domain.DFT piece time-domain signal continues 500us, and it is equivalent in the frequency domain frequency interval of 2kHz between two adjacent sub-carriers.
5 kinds of optionally protection gap size are arranged, promptly 1/6 of the DFT block size, 1/9,1/12,1/20,1/30.Protection signal at interval is same as the final stage of DFT piece time-domain signal.The protection blanking time under different protection gap size about 83.3us between the 16.7us.Another file is seen in elaborating that the signal of relevant OFDM is formed.
Downlink transfer agreement of the present invention is a synchronous transmission structure.List the key property of this structure below.
All superframe groups start from PST (Pacific standard time) 0:0:0AM.
Superframe group's a superframe has frame group head to define uniquely.
A signal frame group of superframe is defined in its signal frame uniquely.
Frame group's a signal frame can be assert by its signal frame synchronic PN sequence uniquely.
Synchronizing signal is the bpsk signal of a power ascension, and it is more a lot of greatly than the data-signal power in the OFDM structure.
The frame address structure is based on the m sequence of one group of displacement, and it is a kind of specific type of pseudo random number (PN) sequence.
Arbitrary signal frame among frame group can be assert by its frame synchronization.Have 255 different m sequences synchronous as signal frame, they are to being applied to 255 signal frames among the frame group.Arbitrary frame group of a superframe is by label, and from 0 to 511, and can assert by signal frame DFT piece.
Arbitrary superframe of a superframe group is since 0 label, and it can be by the data identification of PST (Pacific standard time) time or frame.
It is synchronous that frame synchronization m sequence is used to signal frame.It is synchronous that frame synchronization m sequence in the frame group head is used to signal frame.The frame group energy of a superframe is assert by its frame group head.Frame synchronizing signal can be used for symbol timing recovery.Frame synchronization sequence is predictable behind the initial capture-process of process.
Claims (14)
1, the channel transmission method in a kind of ground digital multimedia TV broad cast system, the physical channel frame structure of employing layering; It is characterized in that:
Said signal frame is made up of frame and frame synchronization, and frame adopts synchronized orthogonal frequency division multi-carrier modulation, and frame synchronization is made of pseudo random sequence code;
A frame group head and a plurality of signal frame constitute a frame group;
A plurality of frame groups constitute a superframe;
A plurality of superframes constitute a superframe group;
A plurality of superframe groups are the transmission of loop cycle ground with the consecutive days;
Described signal frame can be assert by its signal frame synchronized pseudo-random sequences uniquely;
Described superframe group's described superframe is defined uniquely by described frame group head.
2, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: described frame synchronization is that the PN sequence code by spread spectrum constitutes.
3, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 2, it is characterized in that: the described frame synchronization that is made of the pseudo random sequence code of spread spectrum is a signal by the modulation of biphase phase shift keying modulation system.
4, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 3, it is characterized in that: the described frame synchronization that is made of the PN sequence code of spread spectrum is the bpsk signal of a power ascension.
5, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: in described frame group head, defined system parameters and Control Parameter.
6, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 5, it is characterized in that: in described frame group head, also defined broadcast parameter, paging parameters, clean culture parameter, multicast parameter.
7, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: described superframe group and Absolute Time Synchronization ground begin transmission.
8, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: described frame is made of at interval discrete Fourier transform (DFT) piece and protection.
9, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 7, it is characterized in that: the frame length of described signal frame is 3780.
10, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 7, it is characterized in that: described signal frame body length is chosen as 4666 symbols.
11, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 7, it is characterized in that: described signal frame body comprises the protection intervening sequence with 630 continuous symbols.
12, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: described signal frame synchronization length is chosen as 255 symbols.
13, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: frame group number is 512 in the described superframe.
14, according to the channel transmission method in the ground digital multimedia TV broad cast system of claim 1, it is characterized in that: the number of superframes among the described superframe group is 478.
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