CN105116424A - Beidou satellite navigation signal simulation source based on file generation and playback - Google Patents

Abstract

The invention discloses a Beidou satellite navigation signal simulation source design method based on file generation and playback. The Beidou satellite navigation signal simulation source design method comprises the steps that: a Beidou satellite navigation signal file is generated by using a universal computing platform, and a hardware system outputs a Beidou satellite navigation signal at a receiver end through loading and playing in an arbitrary wave pattern of a microwave vector signal source, so as to test receiving and positioning performances of the receiver. The hardware playback system is composed of an industrial control computer, a DDR2, an FPGA, a DAC, an RF modulation unit and a power amplification output unit. The generated Beidou satellite navigation signal file is transmitted to the industrial control computer through a network interface, and is stored in the DDR2 storage through a PCI bus under the control of the industrial control computer. The FPGA unit reads file data from the DDR2 and carries out digital signal processing such as up-sampling and filtering, a low-if signal is formed by the DAC, and the RF modulation unit outputs a simulated Beidou satellite navigation RF signal. The acceptance test of a Beidou receiver shows that the Beidou satellite navigation signal simulation source design method can simulate Beidou satellite navigation signals of the MEO/IGSO/GEO orbit, can simulate predetermined user geographical location and scene signals of tracks, and can test static and dynamic positioning performance of the receiver.

Description

Produce and the Beidou satellite navigation signal imitation source of playing based on file

Technical field

The present invention relates to a kind of Big Dipper satellite signal dummy source design and implementation methods, belong to satellite navigation and field tests.

Background technology

Signal source or title signal generator are the underlying instruments of modern electronic system design and exploitation, and along with the high speed development of technology and market, an urgent demand of modern signal source can produce the integrated signal of various system, complex environment.Compared with external integrated signal source, also there is certain gap in domestic integrated signal source, in order to cultivate the national industry in domestic integrated signal source, break external correlation technique monopolization, and the advantage of Beidou satellite navigation system in conjunction with China's autonomous Design, carry out the Beidou satellite navigation signal imitation technique study in conjunction with microwave vector signal source.

The present invention utilizes the signal file of universal computing platform to produce, and based on the instrument platform of any ripple play signal source, realizes a kind of Beidou satellite navigation signal imitation method being convenient to transplant to signal source instrument.The present invention is different from special satellite navigation signal simulator, the file of employing produce and broadcast mode low to System Hardware Requirement; Also be different from the signal source gathering playback formula simultaneously, producing signal by universal computer platform can user's scene environment of Simulation of Complex, the low-complexity of the diversity and system hardware that reach signal generation combines, and is the technical support that Beidou satellite navigation receiver Development and Production and application provide.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of Big Dipper satellite signal dummy source design and implementation methods, can with fairly simple system hardware, produce the stationary receivers simulating signal of single-point and complicated flight path scene dynamics receiver simulating signal, to solve the Beidou satellite navigation signal imitation problem of universal signal source platform.

Technical scheme of the present invention provides a kind of and produces and the Beidou satellite navigation signal imitation source method for designing play based on file, and comprise navigation data file generation and design with Play System, its designing points is summarised as following steps:

Step 1 relational model Time Created, the relative motion of analog satellite and receiver.Embody carrier doppler effect by carrier wave time delay, calculate the actual signal propagation delay of each signal sampling point, the propagation characteristic of simulating signal, realize the dynamic change of carrier doppler and code Doppler.

Step 2, by modular design method, in conjunction with any wave generator, designs and Implements dummy source Play System.Play System adopts FPGA as core processing unit, and DDR2, as data storage carrier, adopts the reading and writing data mode of FPGA+DDR2.Mainly comprise data memory module, time base module, intermediate-freuqncy signal generation module, D/A converter module and radio-frequency module.

Step 3 is controlled the read-write of data memory module by FPGA, is used for buffer memory to transmit from industrial computer the navigation data of coming by pci bus, and provides Data Source for each functional module follow-up.

Step 4 sets up time base module by means of DDS, for whole system provides element task clock.And avoided because of pci bus interface clock and DDR2SDRAM clock rate and the inconsistent and data corruption that causes of DDR2SDRAM and DAC clock rate by design cross clock domain processing capacity module.

Step 5 intermediate-freuqncy signal generation module carries out signals revivification according to navigation data unprocessed form to the data read from data-carrier store, comprises data-mapping, resampling and up-conversion.Data mapping module is used for 2bit quantized data being mapped to 16 symmetrical bit complement forms, thus avoids the introducing of DC component.Resampling module is then brought up to consistent with DAC work clock according to the sampling rate of original sampling data.Big Dipper signal data, by designing carrier wave NCO, is carried out frequency spectrum shift by up-converter module, thus reduces the impact between adjacent main lobe, improves locating effect.

Digital medium-frequency signal after reduction is converted to analog if signal by step 6 D/A converter module, after differential amplification and filtering, send into radio-frequency module; Radio-frequency module carries out mixing again to analog intermediate frequency signal, produces radiofrequency signal.

Step 7 satellite navigation data is transferred to industrial computer through Ethernet and deposits in memory disc, then via pci bus by data buffer storage in DDR2, and send into data processing module broadcasting the data that will be read by local data bus under pattern continuously, after carrying out the digital signal processing such as increasings sampling generation digital medium-frequency signal, carry out digital-to-analog conversion by DAC.The analog intermediate frequency signal that DAC exports is delivered to radio-frequency head and carries out mixing, radio-frequency carrier power and carrier frequency parameter are set according to Big Dipper satellite signal, be then sent to antenna and produce radiofrequency signal, realize the generation of Satellite Signal Source.

Beneficial effect

Beidou navigation signal imitation method based on microwave vector signal source, can provide real simulation environment for the development of Beidou receiver, test; Can simulate the Received signal strength such as One-Point Location, track model and height be dynamic, and signal parameter can be changed according to the motion state of carrier.In addition, this generation software is convenient to be transplanted on computer general-purpose platform, and signal file can be loaded in other similar surveying instruments.

Accompanying drawing explanation

Fig. 1 Play System Organization Chart of the present invention.

Fig. 2 data processing module structural drawing of the present invention.

Data rate schematic diagram between each module of Fig. 3 present system.

Fig. 4 intermediate-freuqncy signal generation module of the present invention schematic diagram

Fig. 5 median filter coefficient set of the present invention and difference coefficient set time domain response figure

Fig. 6 cordic algorithm realizes carrier wave NCO structural drawing

The Beidou satellite navigation signal receiver locating effect figure of Fig. 7 spiral flight path scene

Embodiment

In order to illustrate technical scheme of the present invention and technical purpose, below in conjunction with the drawings and the specific embodiments, the present invention is described further.

Relate to the foundation of big-dipper satellite intermediate-freuqncy signal model in the inventive method to realize with the design of dummy source Play System.

A kind of Beidou satellite navigation signal imitation source method for designing producing based on file and play of the present invention, comprises the following steps:

Step 1 when not considering multipath error and other signal disturbing, with for sampling rate, i-th satellite B1I branch road digital intermediate frequency signal can be expressed as:

Wherein, A is ranging code amplitude; D _ifor navigation data (for MEO, IGSO be through NH code modulation after navigation data); C _ifor ranging code; for carrier wave initial phase; R _noisefor noise signal.Formula (1) can convert following formula to and represent:

τ _code, τ _carribe the PN code delay of i-th Big Dipper satellite signal in communication process and carrier wave time delay, contain ionosphere time delay, troposphere time delay and clock correction, can be asked for by form below:

$\left\{\begin{array}{c}{\mathrm{\τ}}_1={\mathrm{\τ}}_0+{\mathrm{\υ}}_{\mathrm{\τ}}{N}_t+\frac{1}{2}{a}_{\mathrm{\τ}}{N_t}^2+\frac{1}{6}{a_{\mathrm{\τ}}}^{\′}{N_t}^3\\ {\mathrm{\τ}}_2={\mathrm{\τ}}_0+2{\mathrm{\υ}}_{\mathrm{\τ}}{N}_t+\frac{1}{2}{a}_{\mathrm{\τ}}{\left(2N_t\right)}^2+\frac{1}{6}{a_{\mathrm{\τ}}}^{\′}{\left(2N_t\right)}^3\\ {\mathrm{\τ}}_3={\mathrm{\τ}}_0+3{\mathrm{\υ}}_{\mathrm{\τ}}{N}_t+\frac{1}{2}{a}_{\mathrm{\τ}}{\left(3N_t\right)}^2+\frac{1}{6}{a_{\mathrm{\τ}}}^{\′}{\left({3N}_t\right)}^3\end{array}\right.---\left(3\right)$

Wherein τ ₀, τ ₁, τ ₂, τ ₃for four time point propagation delays of apart from one after another Δ t, its initial value can be calculated by the iterative algorithm of convergence.υ _τ, a _τ, a _τ' be single order rate of change and second order, three order derivatives of propagation delay, N _tthat Δ t is carried out the time series after uniform sampling.

Generating single the star signal containing sometimes becoming pseudo-code phase and carrier phase according to (2) formula, then all visible star superposition calculated being obtained the composite signal of many stars.Then many star composite signals are carried out 2bit quantification, finally obtain Big Dipper signal intermediate frequency data file.

Step 2, by modular design method, in conjunction with any wave generator, designs and Implements dummy source Play System, as shown in Figure 1.Satellite navigation signals generates the write type structure that scheme adopts FPGA+DDR2 herein, namely by FPGA, the read-write of navigation data in DDR2 is controlled, by navigation data according to certain form write DDR2, and then according to corresponding data form, navigation data is read, send after carrying out subsequent treatment.Dummy source Play System mainly comprises pci bus control module, data memory module, time base module, intermediate-freuqncy signal generation module, D/A converter module and radio-frequency module.

The present invention selects the PCI9054 chip of PLX company as the bridge be connected between pci bus with local bus, under the main transmission mode of operation of pci interface chip, directly the processor of system and memory read/write are controlled by pci bus, thus realize the configuration switching of system operating mode and dynamically updating of memory data.

The DDR2 that step 3 data memory module adopts FPGA to control realizes, and is mainly used to buffer memory and transmits from industrial computer the navigation data of coming by pci bus.Because relating to clock-domain crossing data transmission in the present invention, the clock reading data from DDR2 synchronously need process through clock synchronization module, to avoid causing confusion in data transmission procedure.Data need convert the sampling rate with raw data to and the form transmitted by single sampled point through data processing module, and data processing module as shown in Figure 2.The present invention adopts the FIFO1 that a bit wide is 256bit, the degree of depth is 1024 to carry out buffer memory to the data read.When the half-full state of FIFO1, stop the write of FIFO1 data.In Play System, data file is that 2bit quantizes, and in order to ensure the continuity of navigation data, need process by sampled point to data.So, by bit width conversion module, 256bit data stream is carried out serioparallel exchange, make navigation data send into subsequent module with the data of each 2bit under the triggering of sampling clock samp_in and process.

Step 4 time base module realizes by means of DDS chip, and DDS module is mainly used for synthesizing the clock signal of certain frequency, for whole system provides 200MHz reference clock.Adopt 40MHz, 50MHz and constant-temperature crystal oscillator to provide original work clock for each functional module, wherein the crystal oscillator of 50MHz is mainly used to as memory bar provides operate outside clock, and pci bus work clock is 40MHz.There is provided original frequency signal by constant-temperature crystal oscillator, after frequency synthesis, produce the clock of 200MHz as FPGA module system works clock.Between system modules, message transmission rate schematic diagram as shown in Figure 3, and DDR2 controller produces the data transfer clock of 160MHz after inner PLL frequency multiplication of phase locked loop.Because pci clock is different with DDR2 work clock, so must increase intermediate buffer unit to data caching process, the present invention adopts one-level asynchronous FIFO to complete the caching of data.

Step 5 intermediate-freuqncy signal generation module carries out signals revivification according to navigation data unprocessed form to the data read from data-carrier store, comprises data-mapping, resampling and up-conversion.Intermediate-freuqncy signal generation module as shown in Figure 4.Because the present invention's intermediate frequency data file used have employed 2bit quantitative relationship, namely a high position is 0 expression "+", and a high position is 1 expression "-", and low level is 0 expression " 1 ", and low level is 1 expression " 3 ".Direct current is there is because of the asymmetric of sampling number certificate, so need, by data mapping module, each sampled point of navigation data is mapped to symmetrical signed number in playing process.Mapping relations are as shown in table 1, because adopted DAC chip port is 16bit bit wide, so numerical value bit wide corresponding after mapping is 16bit.

Resampling module is then used for improving the sampling rate of data, makes it be consistent with the work clock of DAC, to ensure that navigation intermediate-freuqncy signal is with the continuous sampling dot generation of raw data.In the present invention, Big Dipper intermediate frequency data sampling rate is 16.369MHz, if sampling rate is brought up to 200MHz need fraction double interpolation, realizes arbitrary proportion interpolation with the multiphase filter of FARROW structure.Theoretical according to FARROW wave filter classical architecture, shown in (4), first calculate the FIR filter coefficient that 256 tap bandwidth are 6.5MHz, sampling rate is 200MHz, and calculate consecutive point coefficient differentials, coefficient time domain beamformer as shown in Figure 5.Then respectively filter coefficient and difference coefficient are formed the two-dimensional matrix that 32 row 8 arrange, an every a line i.e. sub-filter coefficient set of matrix.For the calculating of arbitrfary point sample value, by linearly calculating for Δ between adjoining sample point.

$H(z,p)=\underset{n=0}{\overset{N}{\mathrm{\Σ}}}\underset{m=0}{\overset{M}{\mathrm{\Σ}}}h(n,m)p^m{z}^{-n}=\underset{m=0}{\overset{M}{\mathrm{\Σ}}}{G}_m\left(z\right)p^m---\left(4\right)$

Wherein, p is fractional delay, and h (n, m) is subfilter impulse response.

Up-converter module is mainly used to carry out frequency spectrum shift to navigation data, to reduce influencing each other between two main lobes.For up-converter module, the generation of carrier wave NCO is key component.Usual carrier wave NCO has three kinds of implementation methods, i.e. ROM look-up table, cordic algorithm and Taylor series evaluation method.Because ROM loop up table carrier wave precision is by the restriction of storage space, ROM storage space must be increased to improve carrier wave resolution, larger for hardware resource consumption.And Taylor series evaluation method is because calculation of complex, comparatively difficult in realization.So the present invention adopts cordic algorithm to realize the generation of carrier wave NCO, structure as shown in Figure 6.Cordic algorithm iterative equation is such as formula shown in (5).

$\left\{\begin{array}{c}{X}_n=X_0\·{\cos Z}_0+Y_0\·{\sin Z}_0\\ Y_n=Y_0\·{\cos Z}_0-X_0\·{\sin Z}_0\\ Z_n\→0\end{array}\right.---\left(5\right)$

In NCO design, given Y ₀=K (N), X ₀=0, then can obtain sin cos functions value and export.

$\left\{\begin{array}{c}{X}_n=\sin Z_0\\ Y_n=\cos Z_0\end{array}\right.---\left(6\right)$

For the ease of hardware implementing, sampling n position binary representation 2 π, can be converted to binary number by floating number like this and calculate.Thus frequency control word can be drawn by (7) formula.

${\mathrm{\Φ}}_k=\frac{f_c\·2^n}{f_{\mathrm{clk}}}---\left(7\right)$

The scope of frequency control word is 0≤Φ _k≤ 2 ⁿ-1, any subcarrier frequency f can be calculated according to control word _c.From Nyquist sampling theorem, subcarrier frequency f _cscope be 0≤f _c≤ f _clk/ 2.The subcarrier frequency f adopted in the present invention _c=8.003125MHz, then frequency control word Φ _k=X " 0A3E76C8 ".

The Main Function of step 6 D/A converter module converts satellite digital intermediate-freuqncy signal to analog if signal, in order to carry out follow-up I/Q modulating circuit modulates and the mixing again of radio-frequency head.Radio-frequency module carries out mixing again to analog intermediate frequency signal, produces radiofrequency signal.Because the Big Dipper intermediate-freuqncy signal intermediate frequency produced in the present invention is 3.996875MHz, through subcarrier up-conversion rear center, frequency is 12MHz, and Big Dipper satellite signal carrier frequency is 1561.098MHz, so carrier frequency is set to 1573.098MHz in radio-frequency module, get its lower sideband as Big Dipper signal transmitted sideband.

Step 7 is for the whole processing procedure of Beidou satellite navigation data, first be transferred to industrial computer through Ethernet and deposit in memory disc, then the data transmitted from industrial computer by one-level FIFO buffer memory pci bus, then by local bus by data buffer storage in DDR2, structural drawing is as shown in fig. 1.Broadcast continuously under pattern by local data bus will read data send into data processing module, because the data read from DDR2SDRAM are 256bit and sampling rate is higher, the data of high-bit width high sampling rate are mainly converted to the sampled point quantized by original Big Dipper intermediate frequency data sampling rate and transmit by data processing module.Then carry out increasing sampling to improve raw data sampling rate, up-conversion to reduce the impact between satellite-signal two main lobes, then carry out digital-to-analog conversion by after generation digital medium-frequency signal by DAC chip AD9779.The analog intermediate frequency signal that DAC exports is delivered to radio-frequency head and carries out mixing, radio-frequency carrier power and carrier frequency parameter are set according to Big Dipper satellite signal, be then sent to antenna and produce radiofrequency signal, realize the generation of Satellite Signal Source.

In order to technical progress of the present invention and practicality are described, by receiver, dummy source dynamic trajectory scene signals is tested.Wherein Big Dipper dummy source track data coordinate is preset as somewhere, Wuxi coordinate, and spiral flight path as shown in Figure 7.

The Beidou satellite navigation signal imitation source method for designing producing based on file and play of the present invention, has following notable feature.

1) dummy source Play System is based on general any ripple playing platform, conveniently transplants to similar surveying instrument, realizes the simulation of Beidou satellite navigation signal;

2) file that adopts produces and broadcast mode, and producing signal by universal computer platform can user's scene environment of Simulation of Complex, realizes the diversity that signal produces.

More than show and describe ultimate principle of the present invention, principal character and advantage of the present invention.The technician of the industry should understand; the present invention is not restricted to the described embodiments; what describe in above-described embodiment and instructions just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications, and application claims protection domain is defined by appending claims, instructions and equivalent thereof.

Claims (1)

1. one kind produces and the Beidou satellite navigation signal imitation source of playing based on file, it is characterized in that: utilize universal computing platform to produce Beidou satellite navigation signal file, by the loading under any wave mode of microwave vector signal source and the Beidou satellite navigation signal playing hardware system output receiver end, hardware Play System is by industrial computer, DDR2, FPGA, DAC, rf modulations and power amplifier output unit composition, the Beidou satellite navigation signal file produced gives industrial computer by network interface, by pci bus, file is saved in DDR2 storer under industrial computer controls, FPGA unit is file reading data from DDR2, after carrying out the digital signal processing such as increasing sampling filter, low intermediate frequency signal is formed by DAC, the Beidou satellite navigation radiofrequency signal of simulation is exported again by rf modulations unit, produce predetermined static state fixed point and dynamic scene.