CN103364802A - TDDM spread spectrum navigation signal capturing method based on two-channel combined utilization - Google Patents

Abstract

The invention discloses a TDDM spread spectrum navigation signal capturing method based on two-channel combined utilization. According to the method, a local spread spectrum code sequence without data modulation is used for generating two-way local spread spectrum sequences acquired after being modulated through +1 navigation messages and -1 navigation messages respectively. According to a first scheme, subsection correlation is conducted on the two-way spread spectrum sequences and base-band signals, N groups of relevant data are completely collected to conduct FFT calculation, and after the module of a calculation result is worked out, maximum peaks of the two ways are overlaid to acquire the combined judgment amount; according to a second scheme, I-way integral values and Q-way integral values of the two ways are respectively added, N groups of data are completely collected to conduct FFT calculation, and after the module of a calculation result is worked out, the capturing judgment amount is acquired. Whether the phase of a received signal is searched out or not is judged according to the detection judgment amount and a capturing threshold value; if the judgment amount is smaller than the capturing threshold value, the signal is not searched out yet, a numerically-controlled oscillator is regulated by a capturing control unit according to a set searching step length regulation code, and signal phase searching and detecting are continuously conducted on the next searching unit; if the signal is searched out, a receiver judges that the signal is successfully captured.

Description

A kind of TDDM spread spectrum navigation signal catching method of uniting utilization based on binary channels

Technical field

The invention belongs to technical field of navigation and positioning, be specifically related to a kind of catching method of TDDM navigation signal.

Background technology

Perfect along with new generation satellite navigation system signal system, the spread spectrum mode of navigation signal has had new development.TDDM (TimeDivisionDataModulation) technology becomes the focus of concern as a kind of new modulation system.It no longer defers to traditional routine data modulation treatment, allows in the navigation signal existence without data message component (being weight of pilot frequency).The appearance of this new modulation system correctly recovers navigation message to receiving end and has proposed new challenge, and original catching method no longer adapts to new signal modulation system.Therefore, the research of TDDM signal acquisition methods has certain perspective and important realistic meaning.

The modulation mechanism of TDDM signal as shown in Figure 1.Wherein, PN (t) is for the spread spectrum code sequence of input, by odd bits chip PN _o(t) and even bit chip PN _e(t) consist of; D (t) is the navigation message data message, PN _TDDM(t) be the spread spectrum code sequence through output after the TDDM modulation.As seen, the odd bits in the spread spectrum code sequence is carried out mould two by spreading code and base band data information and is added computing and obtain, and the even bit chip is without data message.

Take the navigation message data rate as 50bps, spread-spectrum pseudo code speed is example as the spread-spectrum signal of 10.23MHz, TDDM signal spread-spectrum result is as shown in Figure 2.When navigation message was+1, no matter spreading code was odd bits or even bit, and the spreading code output after the modulation equals spreading code itself; When navigation message was-1, if spreading code is odd bits, then the spreading code output equivalent after the modulation was in spreading code phase overturn 180 degree, if spreading code is even bit, then the output of the spreading code after the modulation equals spreading code itself, i.e. PN _TDDM(t) can be equivalent for to have modulated a square-wave signal in PN (t) sequence, the code check of PN (t) is 2 times of square-wave signal frequency.

At present, TDDM code acquisition method commonly used is straight laws on arrests.The local two-way spread spectrum code sequence that produces is respectively navigation message and is+1 and-1 o'clock spread spectrum code sequence after the TDDM modulation, is referred to as+1 spread spectrum code sequence and-1 spread spectrum code sequence.Receive signal and carry out pre-correlation with this two-way spread spectrum code sequence respectively, obtain the prize judgment amount, serial search code phase successively if the prize judgment amount surpasses thresholding, is then thought acquisition success, and the spread spectrum code sequence that captures is current spread spectrum code sequence.But there is the risk of striding symbolic integration in straight laws on arrests, in the worst case, in the post detection integration+1 and each lasting half the time of-1 spread spectrum code sequence, then prize judgment amount will be decreased to half of when striding symbolic integration prize judgment amount, snr loss 3dB affects court verdict.Therefore need research for the insensitive TDDM signal acquisition methods of Data Modulation.

Summary of the invention

The present invention is directed to the prior art above shortcomings, a kind of catching method of TDDM spread spectrum navigation signal is provided.The method is insensitive to the data modulation, can effectively process the symbolic integration problem of striding that exists in the acquisition procedure.The binary channels that utilization of the present invention+1 frequency expansion sequence and-1 frequency expansion sequence consist of is carried out joint acquisition, has provided two kinds of implementations of joint acquisition method, as shown in Figure 3 and Figure 4.

The present invention proposes a kind of TDDM spread spectrum navigation signal catching method of uniting utilization based on binary channels, comprises two kinds of implementations, and concrete steps are as follows:

Step-: the spread spectrum navigation signal is sent into radio-frequency front-end through antenna reception and is processed, quantize to obtain digital medium-frequency signal through ADC, itself and inner homophase carrier wave and the quadrature carrier that generates of receiver are multiplied each other, remove intermediate frequency, obtain in-phase base band signal i (k) and digital orthogonal baseband signal q (k), as follows.Wherein a is signal amplitude, and D (k) is navigation message, and pn (k) is spreading code, T _sFor adopting interval, f _eAnd φ _eBe respectively Doppler frequency deviation and residual phase.

i(k)＝aD(k)pn(k)cos(2πf _ekT _s+φ _e)

q(k)＝aD(k)pn(k)sin(2πf _ekT _s+φ _e)

Step 2: based on the countless spread spectrum code sequences according to modulation in this locality, generate by+1 and the two-way local frequency expansion sequence of-1 navigation message after modulating respectively, be designated as pn _{+ 1 (}K) and pn _-1(k).

Step 3: respectively+1 ,-1 two-way spread spectrum code sequence and baseband signal are carried out related operation, peel off the spreading code that carries in the signal, obtain twin-channel homophase and Orthogonal correlation value, be designated as respectively I _{+ 1}(n), Q _{+ 1}(n) and I _-1(n), Q _-1(n), as follows.T wherein _Coh=mT _sBe post detection integration,

$R_{+1}\left(\mathrm{\τ}\right)=\frac{1}{\mathrm{mTs}}\underset{\mathrm{nm}{T}_s}{\overset{(n+1)\mathrm{mTs}}{\mathrm{\Σ}}}\mathrm{pn}\left(k\right)\·{\mathrm{pn}}_{+1}(k+\mathrm{\τ})\mathrm{Ts},R_{-1}\left(\mathrm{\τ}\right)=\frac{1}{\mathrm{mTs}}\underset{\mathrm{nm}{T}_s}{\overset{(n+1)\mathrm{mTs}}{\mathrm{\Σ}}}\mathrm{pn}\left(k\right)\·{\mathrm{pn}}_{-1}(k+\mathrm{\τ})\mathrm{Ts}.$

I ₊₁(n)＝aD(n)R ₊₁(τ)sinc(f _eT _coh)cosφ _e

Q ₊₁(n)＝aD(n)R ₊₁(τ)sinc(f _eT _coh)sinφ _e

I _-1(n)＝aD(n)R _-1(τ)sinc(f _eT _coh)cosφ _e

Q _-1(n)＝aD(n)R _-1(τ)sinc(f _eT _coh)sinφ _e

Step 4: if adopt implementation one, collect respectively neat N group related data for two passages and carry out the FFT computing, with the operation result delivery, select peak-peak to obtain+1 ,-1 passage prize judgment amount A _{+ 1}=max (| FFT (I _{+ 1}+ jQ _{+ 1}) |) and A _-1=max (| FFT (I _-1+ jQ _-1) |).Associating+1 ,-1 passage prize judgment amount A _{+ 1}And A _-1Obtain conclusive judgement value A=A _{+ 1}+ A _-1Striding in the symbolic integration situation single channel prize judgment amount A _{+ 1}, A _-1With joint acquisition judgement amount A with shared integral time of-1 navigation message duration number percent change curve as shown in Figure 5.As seen from the figure, only get single pass prize judgment amount A _{+ 1}Or A _-1, when symbolic integration is striden in existence, have the snr loss of 3dB under the worst case; And adopt the joint acquisition decision rule can effectively reduce the snr loss, and eliminate and stride the impact that symbolic integration brings, promote and catch robustness.

If adopt implementation two, first with in-phase data component and the respectively addition of orthogonal data component of two passages, collect neat N group related data and carry out the FFT computing, with the operation result delivery, select maximal value obtain prize judgment amount A=max (| FFT ((I _{+ 1}+ I _-1)+j (Q _{+ 1}+ Q _-1)) |).Compared to implementation one, the twin-channel I/Q component coherence stack of the advanced row of this scheme is sent into delivery behind the FFT, is better than the first scheme (single channel prize judgment amount A in the squelch performance like this _{+ 1}And A _-1All introduced the noisiness of non-zero, thus obtained cascading judgement amount contains the non-zero noisiness twice, and can't offset), simulation result is as shown in Figure 6.The essence of this scheme is, utilizes the stack of binary channels I/Q two-way correlated results, thereby eliminates+1 ,-1 data component, only retains weight of pilot frequency, has therefore also avoided striding symbolic integration, has promoted equally acquisition performance.

Above-mentioned two kinds of implementations all can be eliminated and stride the impact that symbolic integration brings, and wherein scheme two is better than scheme one at the squelch aspect of performance.In addition, adopt the relevant benefit in conjunction with the FFT method of segmentation to be to realize disposable whole search of all frequency intervals of a code phase, the frequency of navigation signal, code phase two-dimensional search are reduced to linear search, greatly improve phase search speed, shorten capture time.

Step 5: judge whether searched arriving of received signal code phase place by the size that detects A: if decision value A is less than detection threshold value Thr, then signal not yet is retrieved, so receiver catch control module according to set step-size in search adjustment code digital controlled oscillator, continue to carry out signal search and detection at next search unit; Otherwise if A surpasses Thr, then signal is searched arrives, and receiver confirmation signal acquisition success begins to start and follows the tracks of.

Under the condition of given decision threshold Thr, the acquisition probability of the straight method for catching of tradition and the pass of false-alarm probability are:

In binary channels joint acquisition method of the present invention, catching with false-alarm probability of scheme one is: $P_{\mathrm{fa}}=[1+\frac{\mathrm{Thr}}{{2\mathrm{\σ}}^2}]e^{-\frac{\mathrm{Thr}}{{2\mathrm{\σ}}^2}},$ $P_d=Q_2(\sqrt{2\mathrm{SNR}},\frac{\sqrt{\mathrm{Thr}}}{\mathrm{\σ}}),$ Catching with false-alarm probability of scheme two is: $P_{\mathrm{fa}}=e^{-\frac{\mathrm{Thr}}{2{\mathrm{\σ}}^2}},$ $P_d=Q_1(\sqrt{2\mathrm{SNR}},\frac{\sqrt{\mathrm{Thr}}}{\mathrm{\σ}}).$ Be 10 in false-alarm probability ^-3, the coherent integration time is under the simulated conditions of 2ms, obtains the acquisition performance of binary channels joint acquisition method as shown in Figure 7.As can be seen from the figure, scheme one is compared with traditional directly scheme of catching, and has larger signal to noise ratio (S/N ratio) to promote, and scheme two is compared with scheme one, and acquisition performance is further promoted.

The invention has the advantages that: scheme one has been inherited the basic thought of straight laws on arrests, and carried out certain improvement, under the prerequisite that does not increase the hardware resource expense, the method by the binary channels joint acquisition has overcome the existing symbolic integration problem of striding of straight laws on arrests, and acquisition performance is highly improved; Scheme two has been done further improvement on the basis of scheme one, its characteristics be to obtain first the binary channels coherence stack the I/Q component, have better squelch performance, resource overhead reduces and is about half simultaneously.

Description of drawings

Fig. 1 is the modulation mechanism schematic diagram of TDDM signal.

Fig. 2 is TDDM signal spread-spectrum result schematic diagram.

Fig. 3 is binary channels joint acquisition method implementation one.

Fig. 4 is binary channels joint acquisition method implementation two.

Fig. 5 is binary channels prize judgment amount schematic diagram.

Fig. 6 is the contrast of binary channels joint acquisition method implementation.

Fig. 7 is binary channels joint acquisition method performance simulation.

Fig. 8 is binary channels joint acquisition method judgement amount distribution plan.

Embodiment

The present invention proposes a kind of TDDM spread spectrum navigation signal catching method of uniting utilization based on binary channels, and take TDDM-QPSK (10) signal as example, the below will be described in detail the present invention.

Spread spectrum navigation signal signal is produced by Agilent E4438C vector signal generator, intermediate frequency is 46.45MHz, and adds the maximum Doppler frequency deviation that is no more than 12kHz, and the spreading code cycle is 10230 chips, spread-spectrum code rate is 10.23MHz, and bit rate is 50bps.This invention comprises following step:

Step 1: analog if signal obtains digital medium-frequency signal through the ADC sample quantization of 62MHz, homophase carrier wave and the quadrature carrier of the inner 15.55MHz that generates of itself and receiver are multiplied each other, and be the FIR filter filtering of 12MHz through 128 rank three dB bandwidths, obtain in-phase base band signal i (k) and digital orthogonal baseband signal q (k), as follows.Wherein a is signal amplitude, and D (k) is navigation message, and pn (k) is spreading code, T _sFor adopting interval, f _eAnd φ _eBe respectively Doppler frequency deviation and residual phase.

i(k)＝aD(k)pn(k)cos(2πf _ekT _s+φ _e)

q(k)＝aD(k)pn(k)sin(2πf _ekT _s+φ _e)

Step 2: based on the countless spread spectrum code sequences according to modulation in this locality, generate by+1 and the two-way local frequency expansion sequence of-1 navigation message after modulating respectively, be designated as pn _{+ 1}(k) and pn _-1(k).Wherein, local spread spectrum code sequence is that Cycle Length is the code stream of 10230 chips.

Step 3: respectively+1 ,-1 two-way spread spectrum code sequence and baseband signal are carried out related operation, peel off the spreading code that carries in the signal, obtain+1, homophase and the Orthogonal correlation data of-1 spread spectrum passage, be designated as respectively I _{+ 1}(n), Q _{+ 1}(n) and I _-1(n), Q _-1(n), as follows.Wherein integration is counted and is taken as the m=256 point, $T_s=\frac{1}{62\mathrm{MHz}},$ Therefore $T_{\mathrm{coh}}=\frac{256}{62\mathrm{MHz}}=4.13\mathrm{\μs},$

$R_{+1}\left(\mathrm{\τ}\right)=\frac{1}{\mathrm{mTs}}\underset{\mathrm{nm}{T}_s}{\overset{(n+1)\mathrm{mTs}}{\mathrm{\Σ}}}\mathrm{pn}\left(k\right)\·{\mathrm{pn}}_{+1}(k+\mathrm{\τ})\mathrm{Ts},R_{-1}\left(\mathrm{\τ}\right)=\frac{1}{\mathrm{mTs}}\underset{\mathrm{nm}{T}_s}{\overset{(n+1)\mathrm{mTs}}{\mathrm{\Σ}}}\mathrm{pn}\left(k\right)\·{\mathrm{pn}}_{-1}(k+\mathrm{\τ})\mathrm{Ts}.$

I ₊₁(n)＝aD(n)R ₊₁(τ)sinc(f _eT _coh)cosφ _e

Q ₊₁(n)＝aD(n)R ₊₁(τ)sinc(f _eT _coh)sinφ _e

I _-1(n)＝aD(n)R _-1(τ)sinc(f _eT _coh)cosφ _e

Q _-1(n)＝aD(n)R _-1(τ)sinc(f _eT _coh)sinφ _e

Step 4: if adopt implementation one, collect respectively neat 512 groups of related datas for two passages and carry out 512 FFT computings, therefore total coherent integration time is T _Coh=4.13 μ s * 512=2.12ms.With FFT operation result delivery, select the prize judgment amount of peak-peak conduct+1 ,-1 passage, be respectively A _{+ 1}=max (| FFT (I _{+ 1}+ jQ _{+ 1}) |) and A _-1=max (| FFT (I _-1+ jQ _-1) |).Associating+1 ,-1 passage prize judgment amount A _{+ 1}And A _-1Obtain conclusive judgement value A=A _{+ 1}+ A _-1

If adopt implementation two, with I road integrated value and the respectively addition of Q road integrated value of two passages, collect neat 512 groups of related datas and carry out the FFT computing first, the total mark time is similarly 2.12ms.With the operation result delivery, select maximal value as prize judgment amount A=max (| FFT ((I _{+ 1}+ I _-1)+j (Q _{+ 1}+ Q _-1)) |).

Step 5: judge whether searched arriving of received signal code phase place by the size that detects A: if decision value A is less than detection threshold value A _Threshold, signal searched arriving not yet then, so receiver catch control module according to set step-size in search adjustment code digital controlled oscillator, continue to carry out signal search and detection at next search unit; Otherwise, if A surpasses A _Threshold, then signal is searched arrives, and receiver confirmation signal acquisition success passes to track loop with code phase and the doppler values that captures, the settling signal demodulation.

In this example, according to above-mentioned parameter setting and step, can obtain the prize judgment amount distribution plan of binary channels joint acquisition method used in the present invention as shown in Figure 8.As seen, the present invention can finish catching for the TDDM signal smoothly.

Claims (6)

1. TDDM spread spectrum navigation signal catching method of uniting utilization based on binary channels, its feature comprises following five steps:

Steps A: spread spectrum navigation signal digital sample;

Step B: based on the countless spread spectrum code sequences according to modulation in this locality, generate by+1 and the two-way local frequency expansion sequence of-1 navigation message after modulating respectively;

Step C: respectively+1 ,-1 two-way spread spectrum code sequence and baseband signal are carried out related operation, peel off the spreading code that carries in the signal, obtain+1, homophase and the Orthogonal correlation value of-1 spread spectrum passage;

Step D: one, two passage of employing scheme collects respectively neat N group related data and carries out the FFT computing, with the operation result delivery, selects peak-peak to obtain+1 ,-1 passage prize judgment amount, and parallel connection is should the binary channels prize judgment measures the conclusive judgement value; Employing scheme two with the respectively addition of correlation of two passages, then collects neat N group related data and carries out the FFT computing, and delivery is therefrom chosen peak-peak as the prize judgment amount as a result;

Step e: the prize judgment amount is adjudicated.

2. binary channels according to claim 1 is united the TDDM spread spectrum navigation signal catching method of utilization, and it is characterized in that: the baseband signal of extracting in the steps A is Wherein D (k) is binary modulated information, and pn (k) is spread spectrum code sequence, f _eBe Doppler frequency deviation, T _sBe the sampling period, φ _eBe carrier phase.

3. binary channels according to claim 1 is united the TDDM spread spectrum navigation signal catching method of utilization, it is characterized in that: the local frequency expansion sequence stream of two-way that generates+1 and-1 modulation among the step B.

4. binary channels according to claim 1 is united the TDDM spread spectrum navigation signal catching method of utilization, it is characterized in that: among the step C two-way spread spectrum code sequence stream and baseband signal are carried out related operation, peel off the spreading code that signal carries, obtain twin-channel homophase and Orthogonal correlation value.

5. binary channels according to claim 1 is united the TDDM spread spectrum navigation signal catching method of utilization, it is characterized in that: scheme one obtains+1 ,-1 passage prize judgment amount among the step D

A _{+ 1}=max (| FFT (I _{+ 1}+ jQ _{+ 1}) |) and A _-1=max (| FFT (I _-1+ jQ _-1) |), associating+1 ,-1 passage prize judgment amount A _{+ 1}And A _-1Obtain conclusive judgement value A=A _{+ 1}+ A _-1Scheme two acquisition binary channels joint acquisition judgement amount A=max (| FFT ((I _{+ 1}+ I _-1)+j (Q _{+ 1}+ Q _-1)) |).

6. binary channels according to claim 1 is united the TDDM spread spectrum navigation signal catching method of utilization, it is characterized in that: compare prize judgment amount and judging threshold in the step e, if less than threshold value, then re-execute step B.

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