CN103487815A - Satellite navigation signal enhancement method based on orthogonal domain interference optimization overlapped reusing - Google Patents

Abstract

The invention discloses a satellite navigation signal enhancement method based on orthogonal domain interference optimization overlapped reusing. The satellite navigation signal enhancement method based on the orthogonal domain interference optimization overlapped reusing is a mode for enhancing satellite navigation signals. Spread spectrum communication is carried out through Walsh domain orthogonal transformation on C/A code modulated satellite navigation signals and by preferably selecting Walsh codes with small interference in the Walsh domain, the overlapped emission of satellite navigation enhanced signals and spread spectrum communication signals is achieved, and the covert enhancement of the satellite navigation signals of different frequency bands and the double-signal frequency spectrum overlapped reusing problems are solved. According to the satellite navigation signal enhancement method based on the orthogonal domain interference optimization overlapped reusing, a double-signal overlapped reusing spread spectrum transmitter and a double-signal spread spectrum processing receiver are designed to complete the Walsh domain orthogonal transformation of the satellite navigation enhanced signals, the Walsh domain interference optimization of the communication signals, the reconstruction and counteraction of the communication signals and the functions of separating, capturing, tracking and ranging of the satellite navigation signals.

Description

A kind of satellite navigation signals Enhancement Method based on orthogonal domain interference optimization overlapping multiplexing

One, technical field

The invention belongs to the Satellite Navigation Technique field, related in particular to and adopted communications band to carry out to satellite navigation signals the method that alien frequencies strengthens emission, be that a kind of new satellite navigation signals strengthens and Anti-Jamming Technique, be also a kind of new technology that realizes navigation safe and out of sight simultaneously.

Two, background technology

Satellite navigation system is due to the high rail characteristic of satellite and CDMA (CDMA) the spread spectrum system of signal, makes the signal power that arrives ground very low, and interference free performance is poor, is easy to be subject to variously have a mind to or disturb unintentionally.Another kind of even more serious situation is, needs due to some special circumstances, the satellite controlling party also can be carried out scrambling or counter taking advantage of (AS) to system sometimes, and this can make originally just more fragile system make the matter worse especially, and causing positioning precision greatly to reduce even can't directly use.Therefore, strengthen availability and the anti-interference of satellite navigation signals, for the Modern Satellite navigation neceiver, just have very important significance.On the other hand, in the spread spectrum mobile communication, with many signal overlaps of standard communication system comparative maturity after deliberation and deep, the purpose of these researchs is to eliminate the interference of other system signal of same system to native system, to improve the performance of system, and many signal overlaps of different systems communication technology is also studied less.The many signal overlaps of different systems can further improve the availability of frequency spectrum, realize the hidden transmission of weak signal, reach the purpose of secure communication.

The thought of patent of the present invention based on the interference optimization overlapping multiplexing by the conversion of orthogonal domain, is superimposed with a weak satellite navigation signals with carrier modulation on signal of communication, thereby realizes the purpose that satellite navigation system strengthens.Specifically, at first from communication spread spectrum Walsh code, extraction portion demal sequence is carried out linear transformation to weak satellite navigation signals, to guarantee the mutually orthogonal property of figure signal and former signal of communication, then signal and signal of communication after conversion are superposeed, and realized carrier modulation and the emission to signal after synthetic on the respective communication frequency range.Utilize the difference of two kinds of superposed signal powers at receiving end, at first reconstruct strong signal of communication, and from receive signal, it is suppressed and is offset, strengthen signal to obtain weak satellite navigation, the despread-and-demodulation method of navigation neceiver routinely again, complete tracking and demodulation to signal, thereby realize the enhancing of alien frequencies section satellite navigation signals.

Three, summary of the invention

1, goal of the invention: the purpose of this invention is to provide a kind of navigation satellite signal Enhancement Method, for weak signal environment or navigation frequency range, availability and the integrity of enhanced navigation receiver while being subject to strong jamming provide a kind of new safeguard.

2, technical scheme: in order to reach the foregoing invention purpose, the present invention includes the following step:

(1) provided a kind of approximate representation method of C/A coded signal: according to selected Walsh code, according to the FWHT mapping mode, produced GPS C/A coded signal is converted, the requirement simultaneously recovered according to signal is carried out Threshold to the coefficient after converting, make all to become 0 lower than all coefficients of this threshold value, and the coefficient that is greater than this threshold value remains unchanged, can complete like this to the LS-SVM sparseness of conversion coefficient and to inputting the linear transformation of C/A coded signal, complete the purpose that means the C/A code with part Walsh code.And the C/A coded signal after this LS-SVM sparseness, as long as it is suitable that the threshold value of compressibility coefficient is chosen, with it, C/A approximately linear is meaned and impact is very little on the signal performance of rear end, Fig. 1 has just provided this after FWHT conversion and coefficient LS-SVM sparseness, and C/A code approximately linear is meaned to 128 rank Walsh code sequence numbers used (wherein coefficient become 0 expression do not select).

(2) will convert rear C/A coded signal and signal of communication is superposeed: make the linear expression of C/A code part Walsh code be

$g=a_1{W_g}^{\left(1\right)}+a_2{W}_g^{\left(2\right)}+\·\·\·a_m{W}_g^{\left(m\right)}---\left(1\right)$

{ a wherein ₁, a ₂..., a _m) in step (1) not being 0 conversion coefficient,

for Walsh sequence sets used closes.G in above formula is carried out to pseudo-code reconstruct, to g carry out the decoding judgement with recover 0,1 or ± 1 sequence, be that available its strengthens data to the navigation that will send and carry out spread spectrum like this.Ream weight structure pseudo-code is

, send navigation data signal D (t), the GPS of stack enhancing baseband signal can be expressed as

$g^{\′}\left(t\right)=\tilde{g}D\left(t\right)=\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{\tilde{c}}_{k}D\left(t\right)---\left(2\right)$

In formula, N is the gain of reconstruct Pseudo Code Spread Spectrum.For signal of communication, have

$C\left(t\right)=q_1{W}_c^{\left(I_1\right)}P{N}_1\left(t\right)+q_2{W}_c^{\left(l_2\right)}{\mathrm{PN}}_2\left(t\right)\·\·\·+q_r{W}_c^{\left(I_r\right)}{\mathrm{PN}}_r\left(t\right)---\left(3\right)$

Wherein $W_c^{\left(I_r\right)}\&Element;W_c=\{W_c^{\left(1\right)},W_c^{\left(2\right)},\&CenterDot;\&CenterDot;\&CenterDot;,W_c^{\left(n\right)}\}$ For signal post's spread spectrum code sequence, and $<W_g^{\left(i\right)},W_c^{\left(j\right)}>=0,$ 1≤i≤m, 1≤j≤n,

for the Walsh spreading code.Carrier transmit signal after the signal stack is like this

$s\left(t\right)=[\sqrt{P_g}{g}^{\&prime;}\left(t\right)+\sqrt{P_c}C\left(t\right)]\exp (-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA0000095897860000032.png,HSA0000095897860000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{c}t)---\left(4\right)$

P wherein _g, P _cbe respectively gps signal and the signal of communication power of emission, f _cfor the communications band carrier frequency.For the signal of communication frequency-domain waveform before and after the stack gps signal as shown in Figure 2.As seen from the figure,, will on its signal of communication that is added to, only be equivalent to increase the substrate Background Noise Power, and can not change waveform and the spectrum structure of original signal when its power is relatively lower with respect to signal of communication for the satellite navigation signals superposeed.According to above-mentioned signal superposition principle, the design of corresponding transmitting terminal as shown in Figure 3.

(3) according to the stack structure that transmits, receiving end is designed: receiving end is down-converted to baseband signal y (t) at first to received signal,

$y\left(t\right)=\underset{i=1}{\overset{2}{\mathrm{\&Sigma;}}}{A}_i{D}_i\left(t\right)C_i(t-{\mathrm{\&tau;}}_{\mathrm{ci}})\cos [({\mathrm{\&omega;}}_{\mathrm{IF}}-{\mathrm{\&omega;}}_d)t+\mathrm{\&phi;}]+n\left(t\right)---\left(5\right)$

I=1 in formula, 2 mean respectively the gps signal after signal of communication and conversion, A _i, D _iand C _ifor corresponding signal amplitude, information data and spreading code used, and ω _iF, ω _diand φ _imean respectively the down coversion intermediate frequency, carrier doppler and corresponding carrier phase, n (t) is noise signal.

Then strong signal of communication is reconstructed and offsets, as shown in Figure 4, its mathematical notation is

${\hat{s}}_1\left(t\right)=\hat{A}\hat{s}\left(t\right)---\left(6\right)$

$\hat{s}\left(t\right)=D\left(t\right)C(t-{\widehat{\mathrm{\&tau;}}}_c)\cos [({\mathrm{\&omega;}}_{\mathrm{IF}}-{\widehat{\mathrm{\&omega;}}}_d)+\widehat{\mathrm{\&phi;}}---\left(7\right)$

Wherein for through phaselocked loop and code ring, estimating the strong signal of communication produced,

for it estimates amplitude,

$\hat{A}={\&Integral;}_0^T\hat{s}\left(t\right)y\left(t\right)\mathrm{dt}/{\&Integral;}_0^T{\hat{s}}^2\left(t\right)\mathrm{dt}---\left(8\right)$

Finally the mode by signal cancellation obtains the C/A coded signal that part Walsh code approximately linear means

$v\left(t\right)=y\left(t\right)-{\hat{s}}_1\left(t\right)---\left(9\right)$

It is carried out to tracking range finding and the corresponding navigation locating function that despread-and-demodulation can realize strengthening signal.According to this signal processing, the design of corresponding receiving end as shown in Figure 5.

(4) power of stack navigation signal is controlled: for this signal enhancement system, the satellite navigation of stack strengthens signal can not affect the performance of former signal of communication, or its performance is caused to appreciable impact, by power, controls and can realize this point.For the gps signal superposeed, under different signal to noise ratio (S/N ratio) conditions, the demodulation bit error rate of signal of communication as shown in Figure 6.As can be seen from the figure, when gps signal is weak, during as be less than-15dB of GPS signal to noise ratio (S/N ratio) (SNRgps), its signal of communication that is added to is not caused to the loss on performance to former signal of communication basically, and when gps signal becomes large gradually, it will become significantly gradually to the performance impact of signal of communication, therefore for guaranteeing that this strengthens security and the disguise of system, must strengthen signal to the GPS of stack and carry out power control.

3, the beneficial effect that the present invention has: the alien frequencies satellite navigation signals that utilizes the present invention to realize strengthens system, can make navigation neceiver be subject to the unavailable or signal attenuation of severe jamming when more serious, be added in through the stack reception and the utilization of the satellite navigation enhancing signal on signal of communication, recover or improve the navigation performance of receiver, thereby improve reliability and the antijamming capability of system.In addition, the present invention is also a kind of important method that realizes navigation safe and out of sight.

Four, accompanying drawing explanation

Fig. 1 is C/A code 128 rank Walsh code FWHT conversion coefficient and rarefaction schematic diagram thereof

Fig. 2 is spectral change schematic diagram before and after the signal of communication stack

Fig. 3 is system transmitting terminal design concept block diagram

Fig. 4 is signal of communication reconstruct and offsets schematic diagram

Fig. 5 is system receiving terminal design concept block diagram

Fig. 6 is the signal of communication demodulation BER performance chart under different gps signal intensity

Fig. 7 is the acquiring satellite performance map of signal of communication while not offsetting

Acquiring satellite performance map when Fig. 8 is the signal of communication counteracting

Fig. 9 is the navigation signal Acquisition Detection probability curve diagram under unlike signal intensity

Figure 10 is the code ring tracking performance curve map of different correlator spacings

Figure 11 is the GPS demodulation performance figure under the different communication signal intensity

Five, embodiment

Embodiment mono-: the satellite navigation acquisition performance that strengthens signal

Strengthen signal for the weak satellite navigation be superimposed upon on strong signal of communication, receiver depends on the signal to noise ratio (S/N ratio) of signal self on the one hand to its acquisition performance, can be subject to again on the other hand the cancelling capabilities impact of strong signal of communication.Fig. 7 and Fig. 8 have just provided respectively and have not offset signal of communication and the signal of communication signal capture result in two kinds of situations while obtaining better offsetting.

Catching result and can find out in two kinds of situations of comparison diagram 7 and Fig. 8, the existence of strong signal of communication has very important impact for the acquisition performance of weak navigation signal.This is mainly due to the gps signal of strong signal of communication for stack, can regard cochannel as and disturb, and this interference meeting increases along with the enhancing of signal of communication power.On the contrary, if we can effectively estimate and offset it, can make weak satellite navigation signals effectively be strengthened, thereby improve it, catch and the performance of following the tracks of.

Embodiment bis-: strengthen the analysis of signal capture detection probability

For satellite navigation receiver, another physical quantity that characterizes the performance enhancing is the signal capture detection probability.Acquisition probability and threshold value thresholding and the false alarm rate of setting in advance are closely related, detection threshold thresholding and false alarm rate P _fabetween pass be:

σ wherein _nfor navigation signal detection background noise.Under the signal to noise ratio (S/N ratio) condition different, the input ground unrest is not identical, therefore adopts a kind of detection method of adaptive threshold thresholding here.Its specific implementation is: adopt the method for parallel capture, this locality is produced to C/A coded signal and input signal and carry out relevantly, correlated results is

wherein M is the maximum Doppler frequency offset segments, and N counts for C/A code in each Doppler frequency deviation segmentation is relevant, gets relevant peaks $l(i_0,j_0)=\underset{1\&le;j\&le;N}{\max }\left\{\underset{1\&le;i\&le;M}{\max }\right\{\mathrm{\&xi;}\left(i\right)\left\}\right\},$ Have like this ${\mathrm{\&sigma;}}_n\&ap;\frac{1}{\mathrm{MN}}\sqrt{\left[\underset{i=1,i\&NotEqual;i_0}{\overset{M}{\mathrm{\&Sigma;}}}\left(\underset{j=1,j\&NotEqual;j_0}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{\&xi;}}^2\left(i\right)\right)\right]-l^2(i_0,j_0)}.$

Utilize said method gained testing result as shown in Figure 9.As seen from the figure, when the signal of communication signal to noise ratio (S/N ratio) is very low, the Acquisition Detection probability of GPS enhancing signal depends primarily on the power of signal itself, signal is stronger, capture ability is also stronger, but, when the intensity of signal of communication increases gradually so that strengthen the signal to noise ratio (S/N ratio) of signal considerably beyond GPS, at this moment the acquisition probability of gps signal is not only relevant with the signal power of self, but also will be subject to the impact of signal of communication.Equally, signal of communication is stronger, even when the signal of GPS itself is also stronger, and the receiver satellite navigation signals that also defies capture, this explanation strengthens signal for the alien frequencies satellite navigation of stack, and effective counteracting of strong signal of communication is vital for the performance raising of satellite navigation system.On the other hand, the power of the satellite navigation signals that we also just can add is through the stack controlled, and makes the method that adopts conventional decorrelation be difficult to realize that navigation is strengthened to signal effectively to be followed the tracks of and catch, thereby improves the disguise transmitted.

Embodiment tri-: satellite code ring tracking performance and data demodulates performance

In the situation that capture satellite-signal with certain probability, the GPS receiver can be transferred to the signal trace stage.The signal trace of GPS receiver is to cooperatively interact by phaselocked loop and code ring.Suppose effectively estimated and offset at the front end communication signal, this time-code ring is followed the tracks of simulation result as shown in figure 10.

For the code ring, different correlator spacing (i.e. early correlator E and the spacing between correlator L late) can cause different code tracking precision.What in emulation, code ring Discr. adopted is the incoherent hysteresis envelope Discr. that subtracts in advance of normalization,

i wherein _eS, I _lSbe respectively the result of code ring I road E, L correlator correlation integral after removing the interfere with communications signal, correspondingly, Q _eS, Q _lSbe respectively code ring Q road E, L correlator correlation integral result.

As shown in Figure 10, along with the increase of GPS signal to noise ratio (S/N ratio), code ring tracking accuracy also can be along with increase.Simultaneously, in identical sampling rate situation, the correlator spacing is less sooner or later, and code ring Discr. tracking error also can correspondingly reduce, and the tracking accuracy of receiver is also just higher.In addition, from figure, it can also be seen that, in the situation that identical signal to noise ratio (S/N ratio) and correlator spacing, sampling rate is higher, and the tracking accuracy of code ring is also higher.

After the code ring is correctly followed the tracks of the input signal code phase, lock frequency input signal by phaselocked loop, can demodulate the satellite navigation information data.Suppose that reception has obtained bit synchronization, utilize the method for symbol judgement can obtain final navigation data information, specifically, its demodulation implementation method is: ${\hat{b}}_i=\mathrm{sgn}\left\{\mathrm{Re}\left(\underset{k=1}{\overset{N_p}{\mathrm{\&Sigma;}}}{s}_{i,k}{A}_i\exp (-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA0000095897860000032.png,HSA0000095897860000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;k}/f_s){\tilde{r}}_k\right)\right\},$

wherein

t in formula _cfor the C/A code chip time interval, f _sfor sampling rate, A _ifor the carrier amplitude corresponding to i data bit, N _cbe a C/A code sequence period length, L=T _b/ (N _ct _c) number of contained C/A code sequence period in Bit data, s _i(t) be the C/A code frequency expansion sequence corresponding to i data bit, c _mfor spreading code, and s _{i, k}be frequency expansion sequence s in the bit time _i(t) expansion sampling,

for being input to the signal of GPS receiver after the counteracting signal of communication.

Certainly, if strong signal of communication is not offset, and directly the input data are carried out to data demodulates, at this moment the data demodulates performance with the front signal of communication is the same, the data demodulates bit error rate of navigation signal can change along with the difference of communication signal strength, Communication Jamming is stronger, and demodulation bit error rate will be higher, and simulation result as shown in figure 11.As shown in Figure 11, in the situation that strong communication interference is arranged, while as signal to noise ratio (S/N ratio), being 5dB, at this moment directly adopt relevant method demodulation navigation data out basically unavailable, and when signal of communication is effectively offset, as the signal of communication remnants after offsetting during lower than-15dB, performance limit when at this moment GPS enhancing signal demodulation error performance just is in close proximity to without Communication Jamming, this illustrates the inhibition of strong signal of communication and offsets for the demodulation performance that improves satellite navigation enhancing signal is also very important.

Claims (1)

1. the satellite navigation signals Enhancement Method based on orthogonal domain interference optimization overlapping multiplexing.It is characterized in that adopting the interference optimization measure of Walsh territory, GPS C/A coded signal, with after a plurality of Walsh code approximate representations modulation, with alien frequencies section signal of communication stack emission, is realized to the dual-use function that the spread spectrum communication of Walsh code and satellite navigation signals strengthen.Concrete methods of realizing is that GPS C/A coded signal is converted through FWHT, and the Walsh numeral collection that is greater than a certain threshold value with conversion coefficient comes approximately linear to mean the C/A code, then carries out spread spectrum communication from the concentrated less code of interference of choosing of residue Walsh numeral; The first reconstruct of receiving end is also offset signal of communication, extracts faint satellite navigation signals, by catching, following the tracks of, realizes the enhancing of satellite navigation signals with finding range.

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