CN101873288B - Method and device for code acquisition - Google Patents
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- CN101873288B CN101873288B CN 200910049866 CN200910049866A CN101873288B CN 101873288 B CN101873288 B CN 101873288B CN 200910049866 CN200910049866 CN 200910049866 CN 200910049866 A CN200910049866 A CN 200910049866A CN 101873288 B CN101873288 B CN 101873288B
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Abstract
The invention discloses a method and a device for code acquisition and relates to synchronization technology in the field of wireless digital communication. The method for code acquisition comprises steps of: associating PN local sequences with the same phase with a PN sequence of a received signal respectively, and acquiring a plurality of PN sequence related peak values; detecting the PN sequence related peak values, finding the maximum and the sub-maximum of the related peak values in each frame, and acquiring the position difference between the maximum and sub-maximum; if the absolute value of the position difference of the maximum and the sub-maximum is the same in continuous M frames, selecting the maximum peak value position and the small or big position of the sub-maximum in the M frames as code acquisition related peak value positions; performing difference on the code acquisition related peak value positions in the M frames, and acquiring the acquisition related peak value position difference, wherein the difference is realized through N-order difference operation; and processing the absolute value of the code acquisition related peak value position difference, and acquiring a phase index of the PN sequence. The invention also provides a receiver employing the method and device.
Description
Technical field
The present invention relates to the simultaneous techniques in wireless digital communication field, particularly a kind of method and apparatus of catching for code.
Background technology
In the practical application of many different digital informations such as sound, data and video communication etc., simultaneous techniques is a kind of very important technology, and synchronous losing can cause falling flat of receiver.In ground digital television receiver, simultaneous techniques mainly comprises Carrier Synchronization, Timing Synchronization technology, Phase Tracking technology, anti-with adjacent frequently perturbation technique and code capture technique." digital television ground broadcast transmission system frame structure, Channel Coding and Modulation " GB20600-2006 of issue on 08 18th, 2006 has described three kinds of data structures.The data segment of three kinds of data structures is identical, and frame head section difference is respectively: PN420, PN595, PN945.When adopting PN595 as frame head, the phase place of frame head PN sequence is constant, and when adopting PN420 and PN945, the phase place of frame head PN sequence can change.The cycle that frame head PN sequence phase changes is a superframe, and the PN sequence phase of the every frame in the superframe is not identical.Time domain frame head PN sequence has good autocorrelation, can be used as synchronous estimation and channel estimating.Yet, utilize the autocorrelation of PN sequence, at first to identify the phase position index of PN sequence, the process of obtaining PN sequence phase index is exactly a code capture technique.Whether the phase position index docking receipts machine that therefore, whether obtains exactly the PN sequence can demodulate exactly and receive signal and play key effect.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of code capture method and device of quick identification PN sequence phase.
In order to solve the problems of the technologies described above, the invention provides a kind of method of catching for code, it comprises the steps: to utilize the local sequence of the identical PN of phase place to make correlation step with the PN sequence that receives signal respectively, obtains several PN Serial relation peak values; PN Serial relation peak value is detected, find maximum and the second largest value of correlation peak in each frame, and obtain both alternate position spikes; If in the continuous N frame, maximum value position is identical with the absolute value of second largest value alternate position spike, then selects peak-peak position and the medium and small position of second largest peak value or large position in this M frame, catches correlation peak location as code; Code in the described M frame is caught correlation peak location carry out difference step, it is poor that the acquisition code is caught correlation peak location; Wherein difference step realizes by N difference computing, and N is the integer more than or equal to 1; The absolute value that it is poor that code is caught correlation peak location is processed, obtained the phase position index of PN sequence.
Further, selected correlation peak location in the M frame is carried out in the difference step, N=2 i.e. this step realizes by twice difference step.
In order to solve the problems of the technologies described above, the present invention also provides a kind of device of catching for code, and it comprises: the PN sequence generator, for generation of identical local PN sequence; Correlator utilizes local PN sequence that the PN sequence generator produces and reception signal to carry out relevant, exports several PN Serial relation peak values; And the code capturing unit, its yard capturing unit also comprises: the correlation peak location detection module, and the PN Serial relation peak value for detection of correlator output finds maximum and the second largest value of correlation peak in each frame, and obtains the absolute value of both alternate position spikes; Select module, select peak-peak position and the medium and small position of second largest peak value or large position in the frame that maximum value position is identical with the absolute value of second largest value alternate position spike in continuous at least M frame, output code is caught correlation peak location; Code is caught the poor acquisition module of correlation peak location, is used for the correlation peak location in the M frame is at least made difference, and it is poor that output code is caught correlation peak location; Wherein difference realizes by N difference computing, and N is the integer more than or equal to 1; The acquisition module of PN sequence phase index is used for the absolute value that it is poor that code is caught correlation peak location being processed the phase position index of output PN sequence.
Further, code is caught the difference computing of the poor acquisition module of correlation peak location by twice realization, i.e. N=2.
The present invention also provides a kind of receiver for received television signal, comprises analog-digital commutator, and the TV signal that is used for receiving is converted to digital signal; And the code acquisition equipment, for the phase position index of the PN sequence of identifying described digital signal; It is characterized in that, the code acquisition equipment comprises: the PN sequence generator, for generation of identical local PN sequence; Correlator utilizes local PN sequence that the PN sequence generator produces and reception signal to carry out relevant, exports several PN Serial relation peak values; And the code capturing unit, its yard capturing unit also comprises: the correlation peak location detection module, and the PN Serial relation peak value for detection of correlator output finds maximum and the second largest value of correlation peak in each frame, and obtains the absolute value of both alternate position spikes; Select module, select peak-peak position and the medium and small position of second largest peak value or large position in the frame that maximum value position is identical with the absolute value of second largest value alternate position spike in continuous at least M frame, output code is caught correlation peak location; Code is caught the poor acquisition module of correlation peak location, is used for the correlation peak location in the M frame is at least made difference, and it is poor that output code is caught correlation peak location; Wherein difference realizes by N difference computing, and N is the integer more than or equal to 1; The acquisition module of PN sequence phase index is used for the absolute value that it is poor that code is caught correlation peak location being processed the phase position index of output PN sequence.
Further, code is caught the difference computing of the poor acquisition module of correlation peak location by twice realization, i.e. N=2.
Adopt code capture method provided by the invention and device, can realize catching in the effective time; Further, exist when channel in the situation of timing frequency deviation or white noise, the present invention can also accurately identify the phase place of PN sequence by the mode of at least twice difference, thereby obtains strong robustness, anti-timing offset and the strong signal of dynamic channel ability.
Description of drawings
To the description of embodiments of the invention in conjunction with its accompanying drawing, can further understand purpose, specific structural features and the advantage of its invention by following.Wherein, accompanying drawing is:
Fig. 1 is that frame head is the PN sequence phase change curve of PN420;
Fig. 2 is that near the PN sequence phase of Fig. 1 A point changes schematic diagram;
Fig. 3 is that near the PN sequence phase of Fig. 2 B point changes schematic diagram;
Fig. 4 is the first embodiment ascent stage and the schematic diagram of decline stage that the present invention is used for code capture method;
Fig. 5 is the wherein maximum of the correlation peak of 3 frames and the schematic diagram of second largest value of a superframe;
Fig. 6 is the schematic diagram that the present invention is used for the second embodiment ascent stage of code capture method;
Fig. 7 is the schematic diagram that the present invention is used for the second embodiment decline stage of code capture method;
Fig. 8 exists in the timing frequency deviation situation, adopts the present invention to be used for the performance chart of the second embodiment of code capture method;
Fig. 9 is the structured flowchart of receiver of the present invention.
Embodiment
The present invention is applied in the digital tv ground broadcasting, and the signal of reception comprises frame head (PN sequence) and frame (data).The frame head of describing among " digital television ground broadcast transmission system frame structure, Channel Coding and Modulation " GB20600-2006 has three kinds of forms, and wherein frame head be PN420 (preamble, PN255 sequence, are synchronous afterwards) with the phase place of two kinds of structure PN sequences in a superframe of PN945 (preamble, PN511 sequence, are synchronous afterwards) is different.For PN420, a superframe comprises 255 signal frames; For PN945, a superframe comprises 200 signal frames.This place for convenience, take the various embodiments of PN420 as frame head code capture method of the present invention and device as example illustrates.What those having ordinary skill in the art will appreciate that is with the frame head that PN420 has identical or similar phase characteristic, can adopt method disclosed by the invention, device, receiver to carry out code and catch, and all belong to protection scope of the present invention.
See also Fig. 1 to Fig. 3, Fig. 1 has represented PN sequence phase change curve in the superframe, and phase place changes by correlation peak location embodiment, similar spindle shape.Numerical value among Fig. 2 is that PN255 carries out the correlation peak location that 2 samplings (2fs) obtain after relevant among the PN420.When selecting PN420 to be frame head, frame length is 4200,8400 samplings that obtain after relevant on the 2fs.The correlation peak location of first frame (signal frame) is " 0 "; The correlation peak location of the second frame is " 2 ", i.e. symbol in the relative first frame deflection left side (2 samplings); The position of the 3rd frame is 2, i.e. a symbol (2 samplings) on the right of relative the first frame deflection; So go down, along with frame number increases, the symbolic number of deflection is also increasing.Continue to consult Fig. 3, the correlation peak location of the 113rd frame is "+112 ", and subsequently, deflection is again gradually along with the increase of frame number reduces, until arrive the A point of next superframe.
According to the characteristic that above-mentioned PN sequence phase changes, method of catching for code of the present invention comprises the steps:
(1) adopt the PN sequence generator to produce the local sequence of the identical PN of phase place (the local sequence of the local sequence of same PN or several identical PN), the frame head (PN sequence) of the local sequence docking collection of letters of the PN that the phase place that utilization produces is identical number each frame is correlated with, and obtains several PN Serial relation peak values;
(2) PN Serial relation peak value is detected, find maximum and the second largest value of correlation peak in each frame, the maximum value position of the correlation peak of k frame is p
Max(k), the second largest value position of correlation peak is p
Sb-max(k);
(3) obtain maximum value position and the second largest value alternate position spike of each frame that step (2) detects, the absolute value of the maximum value position of k frame and second largest value alternate position spike is:
p
diff(k)＝abs[p
max(k)-p
sb-max(k)]
Abs[...] expression takes absolute value;
(4) if in the continuous N frame, described maximum value position is identical with the absolute value of second largest value alternate position spike, then selects peak-peak position and the medium and small position of second largest peak value or large position in this M frame, catches correlation peak location as code;
(5) selected code in the M frame is caught correlation peak location and carry out difference step, namely the code of present frame L frame is caught the code that correlation peak location deducts former frame L-1 frame and is caught correlation peak location, and to catch correlation peak location poor thereby obtain code; Wherein difference step realizes by N difference step; N is the integer more than or equal to 1;
(6) absolute value that it is poor that code is caught correlation peak location is processed, can be obtained the phase value (phase position index) of the PN sequence of L-N+1 frame.
The first embodiment of method of catching for code of the present invention is described in conjunction with Fig. 4 to Fig. 5.
Utilizing the PN sequence generator to generate phase place is 0 the local sequence of PN, and then the local sequence of this PN is carried out 2 sampling correlation step one by one with the PN sequence that receives the frame head (being PN420) in superframe of signal, obtains the correlation peak of several PN sequences.Then, the correlation peak of PN sequence is detected, find out maximum and the second largest value of correlation peak in each frame, Fig. 5 has illustrated maximum G1, G4, G5 and second largest value G2, G3, the G6 of correlation peak of 3 frame F1, F2, F3.Need to prove, the real maximum of a few frames of not faithful representation of Fig. 5 and second largest value only play the effect of explaining.Further, make maximum and the second largest value of correlation peak in each frame and make alternate position spike, for example, the alternate position spike of 3 frames is shown in Fig. 5: P2-P1, P4-P3, P6-P5.In continuous 9 frames (in actual applications, can select according to accuracy requirement, relatively good more than or equal to 5 frame range effect, but the present invention does not get rid of the situation less than 5 frames), if the absolute value of the alternate position spike of the correlation peak that obtains is identical, then select peak-peak in this 9 frame and the little position in the second largest peak value (such as P1, P3, P5) or large position (such as P2, P4, P6) as code catch correlation peak location 0 ,-2 ,+2 ,-4 ,+4 ,-6 ,+6 ,-8 ,+8.Code in 9 frames is caught correlation peak location and carried out difference step, and namely the code of present frame (k frame) code of catching correlation peak location and former frame (k-1 frame) is caught correlation peak location and is subtracted each other, and obtains yard to catch correlation peak location poor.
Code is caught correlation peak location, and increase is defined as ascent stage along with the frame number increase, code is caught correlation peak location along with the frame number increase and is reduced to be defined as the decline stage, such as Fig. 4, Fig. 6, Fig. 7.At method the first embodiment that catches for code of the present invention, when PN phase place during at ascent stage, the absolute value processing mode poor to correlation peak location is expressed as follows:
idx(k)＝abs[p(k)-p(k-1)]/2 (1)
Idx (k) represents the PN phase position index of k frame, and the code of p (k) expression k frame is caught correlation peak location, and the code of p (k-1) expression k-1 frame is caught correlation peak location, abs[...] represent to take absolute value.That is to say, when PN phase place during at ascent stage, by the code of present frame (k frame) catch correlation peak location and former frame (k-1 frame) yard to catch that correlation peak location subtracts each other (be difference step, N=1), doing an absolute value processes again divided by 2, can obtain fast the phase position index of the PN sequence of present frame k (k-N+1, N=1).
Equally, for when the decline stage, the phase position index of PN sequence obtains in the following way:
idx(k)＝224-abs[p(k)-p(k-1)]/2 (2)
Be understandable that, when the frame head that receives signal was PN945 (0-199 signal frame is a superframe), ascent stage was identical with PN420's; For when the decline stage, the PN sequence index obtains in the following way:
idx(k)＝199-abs[p(k)-p(k-1)]/2 (3)
In addition, the variation of PN sequence phase, timing frequency deviation, white noise or under the channel of abominable city different Doppler frequencies etc. all can cause the change in location of PN Serial relation peak value.Error occurs in order to reduce the identification of PN sequence phase, the invention provides method the second embodiment that catches for code, please refer to Fig. 6, this embodiment is in the situation that exist the timing frequency deviation to carry out.In Fig. 6, to compare shown in Fig. 4, the code of the frame in the dotted line frame is caught correlation peak location drift has been occured, and code is caught correlation peak location and odd number "+5 " and "+13 " have been occurred, and error can appear in the phase identification that do the PN sequence this moment.Along with the increase (perhaps channel situation is all the more abominable) of timing frequency deviation, code is caught and can be become more and more difficult.The second embodiment of method of catching for code provided by the invention can effectively reduce the error rate that above-mentioned code is caught, and specifically describes as follows:
At first, utilizing the PN sequence generator to generate phase place is 0 the local sequence of PN, then the local sequence of this PN is carried out 2 sampling correlation step one by one with the PN sequence that receives the frame head (being PN420) in superframe of signal, obtains the correlation peak of several PN sequences.Then, the correlation peak of PN sequence is detected, find out maximum and the second largest value of correlation peak in each frame, Fig. 5 has illustrated maximum G1, G4, G5 and second largest value G2, G3, the G6 of correlation peak of 3 frame F1, F2, F3.Need to prove, the real maximum of a few frames of not faithful representation of Fig. 5 and second largest value only play the effect of explaining.Further, make maximum and the second largest value of correlation peak in each frame and make alternate position spike, for example, the alternate position spike of 3 frames is shown in Fig. 5: P2-P1, P4-P3, P6-P5.In continuous 9 frames (in actual applications, can require to select according to preparation, relatively good more than or equal to 5 frame range effect, but the present invention does not get rid of the situation less than 5 frames), if the absolute value of the alternate position spike of the correlation peak that obtains is identical, then select peak-peak in this 9 frame and the little position in the second largest peak value (such as P1, P3, P5) or large position (such as P2, P4, P6) as code catch correlation peak location 0 ,-2 ,+3 ,-3 ,+5 ,-5 ,+8 ,-6 ,+10.
Then, code in 9 frames is caught correlation peak location carry out the difference step first time, be that the code of present frame (k frame) is caught yard catching correlation peak location and subtracting each other of correlation peak location and former frame (k-1 frame), obtaining the first subcategory number, to catch correlation peak location poor.Further, carry out the second difference step, namely the first subcategory number of present frame catches that correlation peak location is poor catches with the first subcategory number former frame that correlation peak location is poor subtracts each other, and obtains quadratic code and catches relative difference in position.That is to say in a second embodiment, carried out difference step twice, i.e. N=2.
When PN phase place during at ascent stage, the absolute value processing mode poor to correlation peak location is expressed as follows:
The PN phase position index of idx (k) expression k frame, the code of p (k) expression k frame is caught correlation peak location, and the code of p (k-1) expression k-1 frame is caught correlation peak location, and the code of p (k+1) expression k+1 frame is caught correlation peak location, abs[...] expression takes absolute value
Expression rounds.That is to say, when PN phase place during at ascent stage, to do twice front and back poor by code being caught correlation peak location, does an absolute value and process again divided by 4, then rounds the phase position index of the PN sequence that just can obtain former frame (k-1 frame).
Equally, for when the decline stage, the phase position index of PN sequence obtains in the following way:
Be understandable that, when the frame head that receives signal was PN945 (0-199 signal frame is a superframe), ascent stage was identical with PN420's; For when the decline stage, the PN sequence index obtains in the following way:
Passable from top description, in a second embodiment, to code catch correlation peak location poor process comprise two steps: at first the secondary difference is obtained code and catches the poor absolute value of correlation peak location and process 2N=4, then round the phase position index that step could obtain the PN sequence of former frame.
In the code capture method of secondary difference shown in Figure 6, " 1 " component that has more owing to timing offset in "+5 " (right value should be " 4 ") of alternate position spike is shared "+7 " and " 11 " after the poor difference, can eliminate easily this " 1 " component by rounding operation.Adopt the method can effectively eliminate the timing frequency deviation for the impact of PN Serial relation peak value, so the method shows robust having in the timing offset situation.
Be understandable that, the second embodiment is most preferred embodiment of the present invention, but protection scope of the present invention is not limited to this, and the present invention has also protected three times or the method for more times difference.
See also Fig. 8, this curve chart is the code capture technique performance simulation test under the 0dB white noise channel.The individual sub-carrier modulation modes of the parameter that this emulation relates to: C=3780, the mapping mode of 16QAM, LDPC0.8, symbol interleaving 720.
Because ground digital television broadcast is continuous transmission mode, and the PN phase position index that provides every frame that can continue after the in a single day realization of code capturing function of PN sequence phase identification, so receiver is just much of that as long as finish a subcategory number capturing function in the incipient stage.For receiver, if can't realize catching in the unit interval, must cause the host state machine of system to reset, so go down, until within the unit interval, finish a subcategory number capturing function.Mean acquisition time is shorter, illustrates that capture time is shorter.As can be known from Fig. 8, adopt the second embodiment of the present invention can resist the white noise of 0dB.Can find out from the simulation curve figure of Fig. 8, the present invention can resist the timing frequency deviation up to 1800H z, and mean acquisition time is 5.3 frames.Therefore, adopt method provided by the invention, in the situation that exist the timing frequency deviation to show robust.
Table 1 is the performance (mean acquisition time) of different white noises under the Brazilian e channel.
Table 1
| White noise (dB) | Mean acquisition time (frame) |
| 17 | 5.1871 |
| 18 | 5.0701 |
| 21 | 5.0316 |
| 22 | 5.0 |
Table 2 is the performance comparison of 8 times different timing frequency departures of typical static channel Brazil E and China.
Table 2
Above-mentioned emulation is based on the code acquisition algorithm performance of poor difference under the typical static channel, from data, can find out, static channel and white noise are little for the impact of code acquisition algorithm, and in the situation that the timing frequency deviation greater than 1800Hz, code acquisition algorithm performance descends to some extent, and this situation can solve by the number of times that increases difference.
The inventive method also can be applicable to abominable city channel (BU) commonly used in the ground digital television broadcast transmission system.Increase along with dynamic channel Doppler, because the quick variation of multipath, can't calculate accurately the autocorrelation peak change in location rule in certain separable footpath of root, the performance of comparing above-mentioned channel based on performance of the present invention descends to some extent, but still can satisfy the needs of practical application.
Fig. 9 is used for the structured flowchart of the receiver 100 of code capture method for using the present invention, be understandable that, this receiver 100 also can be the receiving system that is connected with television set, such as set-top box, also can be digital TV integrated machine.This receiver 100 includes but not limited to such as lower module: revolve filtration module 12, interpolater 13, synchronous error estimation module 17, code trapping module 16, down-sampler 14 and anti-single-frequency simulation co-channel interference module 15 more than A/D module 10, frequency mixing module 11, root rise.A/D module 10 is converted into digital signal by sampling with analog receiving signal (ground broadcast signal).The effect of frequency mixing module 11 is that the frequency departure of digital signal carrier wave is corrected, the effect of interpolater 13 is the correction that realize the timing frequency deviation, the digital signal of A/D module 10 output is undertaken after the correction of carrier deviation and interpolater 13 carry out the correction of timing offset by frequency mixing module 11, by down-sampler 14 and anti-single-frequency simulation co-channel interference module 15, carry out the elimination of single-frequency and simulation co-channel interference, then export to follow-up channel estimating and balance module.Correlator is correlated with for the signal after correcting, and catches the PN sequence phase value that provides according to code and is correlated with, and provide phase place and the change in location of autocorrelation peak.Synchronous error estimation module 17 is calculated by the detection of correlation peak being carried out frequency sweep control, the calculating of carrier wave error and timing error.Frequency sweep control and carrier wave error are calculated control frequency mixing module 11, and timing error calculates control interpolater 13.
The correlation peak location detection module is used for PN Serial relation peak value is detected, and finds maximum and the second largest value of correlation peak in each frame, and obtains the absolute value of both alternate position spikes;
Select module, (do not get rid of the situation that is less than 5 frames at continuous at least 5 frames, being at least 5 frames is preferred embodiments) select peak-peak position and the medium and small position of second largest peak value or large position in the interior maximum value position frame identical with the absolute value of second largest value alternate position spike, catch correlation peak location as code;
Code is caught the poor acquisition module of correlation peak location, be used for the correlation peak location at least 5 frames is made difference, be that the code of present frame L frame is caught the code that correlation peak location deducts former frame L-1 frame and caught correlation peak location, to catch correlation peak location poor thereby obtain code; Wherein difference realizes by N difference computing, and N is the integer more than or equal to 1;
The acquisition module of PN sequence phase index is used for the absolute value that it is poor that code is caught correlation peak location being processed the phase position index of output PN sequence.
Further, namely carry out the code of two steps difference computing for N 〉=2 and catch the poor acquisition module of correlation peak location, the acquisition module of this PN sequence phase index comprises divider and rounds device, wherein divider is caught the poor absolute value of correlation peak location divided by 2N to code, this rounds device the output of divider is rounded, and its output is the phase position index of PN sequence.
Need to prove, when N=1 namely adopted a difference computing, what round the output of device or divider was the phase position index of the PN phase place of present frame.When N=2 namely adopted twice difference computing, what round device output was the phase position index of the PN sequence of former frame; When N=3 namely adopted three difference computings, what round device output was the phase position index of the PN sequence of front cross frame, the like.
The description of above preferred embodiment makes those skilled in the art can make or use the present invention.The various modifications of these embodiment are apparent for a person skilled in the art, and the General Principle of definition can be applied among other embodiment and do not deviate from the spirit or scope of the present invention here.Therefore, the present invention is not limited to shown here embodiment, and will meet the most wide in range scope consistent with the principle that discloses and novel feature here.
Claims (15)
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| CN101262575A (en) * | 2008-04-01 | 2008-09-10 | 北京航空航天大学 | A frame header PN capture method and device for a terrestrial digital television system |
| CN101309251A (en) * | 2008-06-13 | 2008-11-19 | 高拓讯达（北京）科技有限公司 | PN sequence detection method and system of receiver based on DTTB standard |
| CN101317339A (en) * | 2005-10-31 | 2008-12-03 | 诺基亚公司 | Pilot Sequence Detection |
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| CN101317339A (en) * | 2005-10-31 | 2008-12-03 | 诺基亚公司 | Pilot Sequence Detection |
| CN101262575A (en) * | 2008-04-01 | 2008-09-10 | 北京航空航天大学 | A frame header PN capture method and device for a terrestrial digital television system |
| CN101309251A (en) * | 2008-06-13 | 2008-11-19 | 高拓讯达（北京）科技有限公司 | PN sequence detection method and system of receiver based on DTTB standard |
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