CN102571120B - Timing demodulation method of Loran-C signals under condition of low signal to noise ratio - Google Patents
Timing demodulation method of Loran-C signals under condition of low signal to noise ratio Download PDFInfo
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Abstract
The invention discloses a timing demodulation method of Loran-C signals under the condition of low signal to noise ratio. The timing demodulation method comprises the steps of: sampling the Loran-C signal by adopting an acquirer, then searching and tracking a station signal; tracking a point position and a weight value according to a first pulse of a pulse train, and reconstructing a first pulse waveform, wherein in the single pulse train, an interval between every two adjacent pulses is 1ms and only 6 pulses carry time-code information; reconstructing possible existential states of other pulses according to the first pulse reconstructing method; in order to overcome the defect of insufficient time-code information carried by the waveform under the condition of low signal to noise ratio, carrying out decoding operation by using a full-waveform relevant algorithm, obtaining actual demodulation information through comparing relevant values, and then obtaining time information included by the pulse train according to a time-code demodulation mapping table; and finally, circularly implementing the steps according to the quantity of the pulse trains to obtain the time information carried by all tracking signals. The timing demodulation method overcomes the problem of failed receiving signal demodulation caused by the low signal to noise ratio, more accurately obtains the time information of the Loran-C signals, and is superior to the conventional time-code demodulation algorithm.
Description
Technical field
The present invention relates to radio timing technology, particularly the Loran-C signal timing demodulation method under a kind of Low SNR.
Background technology
Rowland C is a kind of radio navigation system of remote high-precision, belongs to continental rise, low frequency, impulse phase radionavigation system.Rowland C timing receiver is installed on naval vessel, aircraft and moving vehicle conventionally, by follow the tracks of three above station signals simultaneously, or the in the situation that of known carrier particular location, follows the tracks of the signal of a station, obtains the normative reference time.At present, domestic rowland C timing receiver often uses whip antenna to receive the electric field signal of station transmitting, from the transmitting station close to time, the signal amplitude receiving is stronger.But, the relation that square is inversely proportional to of signal strength signal intensity and distance, apart from the station compared with territory, far field, can only receive faint signal.Simultaneously, magnetic antenna is the inexorable trend of following rowland C reception antenna development, but according to electromagnetic wave propagation theory, the field signal that derives from same emission source a bit receiving at free space is 1/120 π of electric field signal, the field signal receiving in same position a little less than than electric field signal many.
At present, rowland C time signal PPM demodulation is mainly to adopt phase place correlation demodulation algorithm.This algorithm, in the good situation of signal conditioning, can be realized data demodulates function, but along with user improves constantly the requirement in timing accuracy and use region, its shortcoming shows gradually.In the time that the acceptance point range transmission station is far away or use magnetic antenna to collect mail under water, the useful signal receiving a little less than, and timing signal can not by accumulation method improve signal to noise ratio, now, phase place correlation demodulation algorithm to be demodulated to power lower, can not successfully obtain the time service information in signal.
Summary of the invention
The object of the invention is to provide the timing demodulation method of the Loran-C signal under a kind of Low SNR, the method is take low signal-to-noise ratio Loran-C signal as object, the various reasons that may cause low signal-to-noise ratio situation are taken into full account, expand the use region of rowland C timing receiver, and improved its timing accuracy.
Object of the present invention is realized by following technical scheme:
The present invention includes following steps:
The first step: adopt collecting device, with 1M sample rate, Loran-C signal is carried out to line sampling, search is also correctly followed the tracks of the signal of a station, obtains the pulse tracking point sequence position of m impulse train;
Second step: carry out parameter initialization, parameter comprises group repetition period GRI, odd cycle pulse code m1, even cycle pulse code m2 and the time service mapping table map of Loran-C signal;
The 3rd step: extract each pulse cluster pulse tracking point sequence A_1 from position, obtain new sequence A _ 2 after being accurate to 0.1 μ s, each trace point decimal place sequence is designated as to a;
The 4th step: take pulse tracking point A_2 (i) as starting point, trace point decimal place a (i) is as weighted value, on the basis of collection signal, resolution of reconstruct is that 1 μ s, length are the impulse waveform sequence B (i) of 300 μ s, is each pulse cluster impulse reconstruction wave sequence;
The 5th step: the concrete steps of signal waveform correlation demodulation are as follows:
(5.1) consider that pulse spacing in each impulse train is that 1ms and the pulse that caused by modulation are moved, from A_2 (i) pusher 1999 μ s, 2000 μ s, 2001 μ s respectively, 6999 μ s, 7000 μ s, 7001 μ s, repeat the 4th step take these as starting point, obtain each impulse train the 3rd to reconfiguration waveform sequence C _ 1, C_2 and C_3 under three kinds of modulation case of the 8th pulse;
(5.2) take individual pulse group as unit, under the condition of parity of considering its coding, B (i) is carried out to Full wave shape related operation with C_1 (i), C_2 (i) and C_3 (i) respectively, correlation maximum be true modulation positions, after demodulation, obtain individual pulse group modulation code sequence mold;
(5.3) according to mapping table map, demodulating data mold is carried out to time service information decoding, obtain the time service data of this impulse train;
(5.4), according to impulse train number m, repeating step (5.1)-(5.3), obtain the time service data of all impulse trains.
The described pulse being caused by modulation of step (5.1) move refer to reach 1 μ s, after move 1 μ s or do not move.
Step (5.2) described take individual pulse group as unit, refer to odd cycle pulse code m1 and even cycle pulse code m2 in the parity condition of considering its coding.
Beneficial effect of the present invention:
The present invention, take Loran-C system timing demodulation method under Low SNR as object, has proposed a kind of high, practical demodulating algorithm of power that is demodulated to.Solve dexterously because low signal-to-noise ratio causes the problem that traditional demodulation algorithm can not acquisition time information.This algorithm is easily realized, and reliability is high.Particularly, the present invention has following features:
1. totally digitilized high-precision linear sampling.Adopt the A/D collector of 16 precision to carry out line sampling to Loran-C signal, the high accuracy that is conducive to signal is obtained.
2. the method for Waveform Reconstructing application.The prerequisite of the correct demodulation of time service data energy is that the significance bit of pulse tracking point is at least 0.1 μ s, so just needs acquisition system to possess 10M sample rate.The present invention only need to gather signal by 1M sample rate, then by the mode of Waveform Reconstructing, Wave data is accurate to 0.1 μ s, has reduced data capacity to be stored and that process, has effectively improved system handling property.
3. design is ingenious.The present invention, in time signal demodulating process, does not extract according to a conventional method the part phase information in impulse waveform, but whole modulated impulse waveform is carried out to correlation computations as useful information.This is that due to the impact of noise, signal waveform is disturbed excessive, the shape information of considerable part occurs most probably by noise jamming because under Low SNR, and traditional phase place related algorithm was lost efficacy.
Accompanying drawing explanation
Fig. 1 is overall process flow figure of the present invention;
Fig. 2 is the 5th step process chart of the present invention;
Fig. 3 is Waveform Reconstructing schematic diagram;
Fig. 4 is the Loran-C signal oscillogram that actual acquisition obtains 8390 chain of stations under Low SNR;
Fig. 5 is slave station 2 pulse tracking schematic diagrames in Fig. 4;
Fig. 6 is the partial enlarged drawing of Fig. 5.
Embodiment
Below in conjunction with embodiment, the invention will be further described:
The invention solves Loran-C signal time service information under Low SNR and be demodulated to the problem that power is low.Adopt the A/D collector of 16 precision to carry out line sampling to Loran-C signal, and utilize the method for Waveform Reconstructing, under the condition of 1M sample rate, just can meet the precision of 0.1 required μ s of signal demodulation.According to the pulse spacing in an impulse train be three kinds of modulation systems that 1ms and each pulse may exist, the in the situation that of known first pulse tracking point, can reconstruct impulse train the 3rd waveform to the 8th pulse.Take an impulse train as unit, considering after the parity of impulse train, carry out correlation computations with the reconfiguration waveform of other pulse respectively with first impulse reconstruction waveform, obtain the modulating data of this impulse train.Finally, demodulate timing data according to the corresponding relation of time service mapping table.
Specific implementation step of the present invention comprises:
The first step: adopt collecting device, with 1M sample rate, Loran-C signal is carried out to line sampling, obtain sampled data channel; Search is also correctly followed the tracks of the signal of a station, obtains all pulse tracking point sequence position of m impulse train of this station;
Second step: carry out parameter initialization, parameter comprises after group repetition period GRI, the odd cycle of Loran-C signal after 6 pulse code m1, even cycle that 6 pulse code m2 and time service mapping table map are (if follow the tracks of master signal, m1=[--+-+-], m2=[-+++++]; Otherwise, if tracking is slave signal, m1=[+++--+], m2=[+-++--]);
The 3rd step: extract each pulse cluster pulse tracking point sequence A_1 from position, be accurate to 0.1 μ s after rounding up, and obtain new sequence A _ 2.Each trace point decimal place sequence is designated as to a, for the weighted value of this burst waveform reconstruct simultaneously;
The 4th step: take first pulse tracking point A_2 (i) as starting point, trace point decimal place a (i) is as weighted value, on the basis of collection signal channel, resolution of reconstruct is that 1 μ s, length are the impulse waveform sequence B (i) of 300 μ s, is each pulse cluster impulse reconstruction wave sequence;
The 5th step: the concrete steps of signal waveform correlation demodulation are as follows:
(5.1) in individual pulse group, consider that the pulse that is spaced apart 1ms and is caused by modulation between pulse moves (reach 1 μ s, then move 1 μ s or do not move), from A_2 (i) pusher 1999 μ s, 2000 μ s, 2001 μ s respectively, 6999 μ s, 7000 μ s, 7001 μ s, repeat the 4th step take above-mentioned point as starting point, obtain individual pulse group the 3rd to reconfiguration waveform sequence C _ 1, C_2 and C_3 under three kinds of modulation case of the 8th pulse;
(5.2) take individual pulse group as unit, B (i) is carried out to Full wave shape related operation with C_1 (i), C_2 (i) and C_3 (i) respectively, also to consider the parity (correlation that is first impulse reconstruction waveform and i impulse reconstruction waveform must be multiplied by respective pulses coding) of impulse train simultaneously, correlation maximum be the true modulation positions of pulse, after demodulation, obtain individual pulse group modulation code sequence mold;
(5.3) according to mapping table map, demodulating data mold is carried out to time service information decoding, obtain the time service data of this impulse train;
(5.4), according to impulse train number m, repeating step (5.1)-(5.3), obtain the time service data of all impulse trains.
Embodiment:
The 1st step: utilize certain type rowland C timing receiver to receive Loran-C signal, the high accuracy 16 collector PXI-5922 that utilize NI company to produce, amplifying output acquisition length from the automatic gain of timing receiver is that 6M, resolution are the Loran-C signal of 1 μ s.Then search for and follow the tracks of 60 pulse-burst signals of main, obtain all pulse tracking sequence position.Collection signal and main tracking schematic diagram are respectively as shown in Figure 4, Figure 5.
The 2nd step: parameter initialization.Set the group repetition period GRI=83900 of Loran-C signal, after slave station odd number, even cycle 6 pulse codes be respectively m1=[+++--+], m2=[+-++--], time-code demodulation mapping table map is in table 1.
Table 1 is modulated pattern and data corresponding relation
| The decimal system | Modulation pattern | The decimal system | Modulation pattern | The decimal | Modulation pattern | |
| 0 | --00++ | 43 | 00-+-+ | 86 | ++-00- | |
| 1 | --0+0+ | 44 | 00-++- | 87 | ++0--0 | |
| 2 | --0++0 | 45 | 00+--+ | 88 | ++0-0- | |
| 3 | --+00+ | 46 | 00+-+- | 89 | ++00-- | |
| 4 | --+0+0 | 47 | 00++-- | 90 | -0000+ | |
| 5 | --++00 | 48 | 0+--0+ | 91 | -000+0 | |
| 6 | -0-0++ | 49 | 0+--+0 | 92 | -00+00 | |
| 7 | -0-+0+ | 50 | 0+-0-+ | 93 | -0+000 | |
| 8 | -0-++0 | 51 | 0+-0+- | 94 | -+0000 | |
| 9 | -00-++ | 52 | 0+-+-0 | 95 | 0-000+ | |
| 10 | -00+-+ | 53 | 0+-+0- | 96 | 0-00+0 | |
| 11 | -00++- | 54 | 0+0--+ | 97 | 0-0+00 | |
| 12 | -0+-0+ | 55 | 0+0-+- | 98 | 0-+000 | |
| 13 | -0+-+0 | 56 | 0+0+-- | 99 | 00-00+ | |
| 14 | -0+0-+ | 57 | 0++--0 | 100 | 00-0+0 | |
| 15 | -0+0+- | 58 | 0++-0- | 101 | 00-+00 | |
| 16 | -0++-0 | 59 | 0++0-- | 102 | 000-0+ | |
| 17 | -0++0- | 60 | +--00+ | 103 | 000-+0 | |
| 18 | -+-00+ | 61 | +--0+0 | 104 | 0000-+ | |
| 19 | -+-0+0 | 62 | +--+00 | 105 | 0000+- | |
| 20 | -+-+00 | 63 | +-0-0+ | 106 | 000+-0 | |
| 21 | -+0-0+ | 64 | +-0-+0 | 107 | 000+0- | |
| 22 | -+0-+0 | 65 | +-00-+ | 108 | 00+-00 | |
| 23 | -+00-+ | 66 | +-00+- | 109 | 00+0-0 | |
| 24 | -+00+- | 67 | +-0+-0 | 110 | 00+00- | |
| 25 | -+0+-0 | 68 | +-0+0- | 111 | 0+-000 | |
| 26 | -+0+0- | 69 | +-+-00 | 112 | 0+0-00 | |
| 27 | -++-00 | 70 | +-+0-0 | 113 | 0+00-0 | |
| 28 | -++0-0 | 71 | +-+00- | 114 | 0+000- | |
| 29 | -++00- | 72 | +0--0+ | 115 | +-0000 |
| 30 | 0--0++ | 73 | +0--+0 | 116 | +0-000 |
| 31 | 0--+0+ | 74 | +0-0-+ | 117 | +00-00 |
| 32 | 0--++0 | 75 | +0-0+- | 118 | +000-0 |
| 33 | 0-0-++ | 76 | +0-+-0 | 119 | +-+-+- |
| 34 | 0-0+-+ | 77 | +0-+0- | 120 | -+-+-+ |
| 35 | 0-0++- | 78 | +00--+ | 121 | +-+--+ |
| 36 | 0-+-0+ | 79 | +00-+- | 122 | -+-++- |
| 37 | 0-+-+0 | 80 | +00+-- | 123 | +--+-+ |
| 38 | 0-+0-+ | 81 | +0+--0 | 124 | -++-+- |
| 39 | 0-+0+- | 82 | +0+-0- | 125 | +--++- |
| 40 | 0-++-0 | 83 | +0+0-- | 126 | -++--+ |
| 41 | 0-++0- | 84 | ++--00 | 127 | +0000- |
| 42 | 00--++ | 85 | ++-0-0 |
Note: in modulation pattern, " 0 "--pulse is uncomfortable; 1us is adjusted forward in "-"--pulse; 1us is adjusted in "+"--pulse backward.
The 3rd step: extract each pulse cluster pulse tracking point sequence A_1 from position, be accurate to 0.1 μ s after rounding up, and obtain new sequence A _ 2.Each trace point decimal place sequence is designated as to a, for the weighted value of this burst waveform reconstruct simultaneously.
The 4th step: take A_2 (i) as starting point, trace point decimal place a (i) is as weighted value, on the basis of collection signal channel, resolution of reconstruct is that 1 μ s, length are the impulse waveform sequence B (i) of 300 μ s, is each pulse cluster impulse reconstruction wave sequence.
The 5th step: carry out the time-code demodulation of Loran-C signal according to (5.1) of step 5 of the present invention to (5.4).Meanwhile, for comparative analysis, table 2 has shown phase place correlation demodulation method and the comparison of the present invention to 7430 chain of stations slave station 2 time-code data demodulates results.
The comparison of table 2 conventional method and the inventive method time-code demodulation result
| Phase place correlation demodulation accuracy | Demodulation accuracy of the present invention |
| 66.7％ | 83.3％ |
From table 2, decoded the preferably signal of main of 8390 chain of stations of time-code data demodulates algorithm of the present invention.Known according to Fig. 5, because main of distance is far away, the signal to noise ratio of this collecting Loran-C signal is lower, and signal quality is poor.The time-code data demodulates result being obtained from the traditional demodulation method in table 2 and waveform correlation demodulation algorithm of the present invention, demodulating algorithm of the present invention is better than traditional demodulation algorithm far away, illustrates that its reliability is high.And the decoded result of conventional method does not reach the requirement of regulation, cannot realize the object of carrying out timing with Loran-C signal.Therefore, Loran-C signal time-code demodulating algorithm of the present invention has more practicality.
The present invention is not limited to above-mentioned embodiment; persons skilled in the art are according to content disclosed by the invention; can adopt other multiple embodiment to implement the present invention; in every case be to adopt project organization of the present invention and thinking; do some simple designs that change or change, all will fall into the scope of protection of the invention.
If there is the content not being described in detail in this specification, belong to the known technology of professional and technical personnel in the field, repeat no more herein.
Claims (2)
1. the Loran-C signal timing demodulation method under Low SNR, is characterized in that: the method comprises the following steps:
The first step: adopt collecting device, with 1M sample rate, Loran-C signal is carried out to line sampling, search is also correctly followed the tracks of the signal of a station, obtains the pulse tracking point sequence position of m impulse train;
Second step: carry out parameter initialization, parameter comprises group repetition period GRI, odd cycle pulse code m1, even cycle pulse code m2 and the time service mapping table map of Loran-C signal;
The 3rd step: extract each pulse cluster pulse tracking point sequence A_1 from position, obtain new sequence A _ 2 after being accurate to 0.1 μ s, each trace point decimal place sequence is designated as to a;
The 4th step: take pulse tracking point A_2 (i) as starting point, trace point decimal place a (i) is as weighted value, on the basis of collection signal, resolution of reconstruct is that 1 μ s, length are the impulse waveform sequence B (i) of 300 μ s, is each pulse cluster impulse reconstruction wave sequence;
The 5th step: the concrete steps of signal waveform correlation demodulation are as follows:
(5.1) consider that pulse spacing in each impulse train is that 1ms and the pulse that caused by modulation are moved, from A_2 (i) pusher 1999 μ s, 2000 μ s, 2001 μ s respectively, 6999 μ s, 7000 μ s, 7001 μ s, repeat the 4th step take these moment as starting point, the each pulse that obtains the 3rd to the 8th pulse of each impulse train move forward 1 μ s, after move reconfiguration waveform sequence C _ 1, C_2 and the C_3 under 1 μ s or mobile three kinds of modulation case;
(5.2) take individual pulse group as unit, under the condition of parity of considering its coding, B (i) is carried out to Full wave shape related operation with C_1 (i), C_2 (i) and C_3 (i) respectively, correlation maximum be true modulation positions, after all pulses are demodulated, obtain individual pulse group modulation code sequence mold;
(5.3) according to mapping table map, demodulating data mold is carried out to time service information decoding, obtain the time service data of this impulse train;
(5.4), according to impulse train number m, repeating step (5.1)-(5.3), obtain the time service data of all impulse trains.
2. the Loran-C signal timing demodulation method under Low SNR as claimed in claim 1, it is characterized in that: step (5.2) described take individual pulse group as unit, refer to odd cycle pulse code m1 and even cycle pulse code m2 in the parity condition of considering its coding.
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| CN105259411B (en) * | 2015-11-04 | 2018-03-06 | 陕西科技大学 | The method of the underwater propagation characteristic of high-precision forecast Loran-C pulse |
| CN107332574A (en) * | 2017-08-11 | 2017-11-07 | 北京北广科技股份有限公司 | A kind of high-power Loran-C pulse emitter and its waveform modulated method |
| CN111323014B (en) * | 2018-12-14 | 2023-06-23 | 天津光电通信技术有限公司 | Method for rapidly capturing and locking Roland C signal |
| CN111726317B (en) * | 2020-05-25 | 2021-06-01 | 中山大学 | Rowland C signal modulation method, device, equipment and storage medium |
| CN112198539B (en) * | 2020-09-23 | 2022-08-30 | 中国科学院精密测量科学与技术创新研究院 | Rowland-C high-power half-cycle pulse peak and trough sampling implementation method |
| CN114785425B (en) * | 2022-04-07 | 2023-11-17 | 中国科学院国家授时中心 | Enhanced Rowland system data demodulation method based on log likelihood ratio |
| CN115296967B (en) * | 2022-07-19 | 2023-09-08 | 中国人民解放军国防科技大学 | Enhanced Roland signal waveform and modulation method based on linear frequency modulation |
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