CN202110287U - Global positioning system (GPS) direct and multi-path signal simulator - Google Patents

Abstract

The utility model discloses a global positioning system (GPS) direct and multi-path signal simulator. A hardware platform of the simulator mainly comprises a digital signal processor (DSP) information processing module, a field programmable gate array (FPGA) signal processing module, a digital-to-analog (D/A) conversion module, an upper frequency conversion module and a transmitting antenna or an output cable, wherein a time delay unit and a signal synthesis unit are arranged in the FPGA signal processing module; the time delay unit is used for copying a generated GPS direct signal and performing corresponding delay on the GPS direct signal to obtain a multi-path signal component; and the signal synthesis unit is used for performing superposition digital synthesis on the GPS direct signal and the multi-path signal component and outputting to the rear-end D/A conversion module. By the utility model, the time quantum of a multi-path signal to the direct signal is relation to system work clock, so digital implementation is promoted; and a satellite signal output by simulation is realized in full digital mode, parameters of the direct signal and the multi-path signal are adjustable and controllable, and the simulator is accurate and convenient to use, and can be widely applied to the field of GPS.

Description

Through and the multipath signal simulator of a kind of GPS

Technical field

The utility model relates to the gps satellite navigation field, is specifically related to the through and multipath signal simulator of a kind of GPS.

Background technology

In the production of GPS receiver, debugging, research process; Needing to measure receiver receives and positioning performance satellite-signal; And the location availability of receiver under complex environments such as missile-borne, obtain such statistical property, can not carry out the practical flight checking of big quantity.For under the experimental ring static environment, realizing this class testing easily; According to relative motion principle, needn't be placed on receiver on the Space Facilities such as guided missile, star ship, only need simulator to simulate receiver received navigation satellite signal under these tracks; Indoor to static receiver test; The positioning result of receiver is exactly the predefined track of simulator, can make things convenient for test receiver locating effect under high-altitude, high-speed motion condition, has practiced thrift the testing cost of receiver like this.According to such application demand, the gps signal simulator just arises at the historic moment.The gps satellite signal simulator is simulated exactly and is produced the gps satellite navigation signal, for development, the test of GPS receiver provides simulated environment, and its critical equipment that to be satellite navigation system develop with receiver (especially high dynamic receiver).The simulated environment environment that the gps signal simulator is simulated is true to nature more, then gets over to accurate for the performance measurement of GPS receiver.

Under actual environment, the signal that receiving antenna is received not only includes the direct wave signal but also includes the mirror signal that after reflected by objects on every side, produced and reflection wave signal such as diffuse scattering signal.Reflection wave signal will produce direct signal (direct wave) from satellite and disturb, thereby make observed reading depart from true value, produce so-called " multipath error ".It is thus clear that the research multipath effect has great importance for the measuring accuracy of analyzing satellite navigation system and receiver.And to study multipath effect, and just require satellite signal simulator can not only simulate high-precision satellite direct wave signal, more main is simulates all the received satellite constellations emissions of the receiver of special time, locality or the signal of diffusion.

The utility model content

The utility model technical matters to be solved provides the through and multipath signal simulator of a kind of GPS; With the DSP+FPGA digital signal processing platform is core; According to parameters such as predefined satellite ephemeris and receiver tracks, calculate and produce high-accuracy digital signal, high fidelity simulation user sets the satellite direct signal and the multipath signal of scene; And connect high-speed digital-analog conversion and up-conversion module, accomplish the output of GPS radiofrequency signal.

For addressing the above problem, the utility model is realized through following proposal:

Through and the multipath signal simulator of a kind of GPS comprises DSP message processing module, FPGA signal processing module, D/A modular converter, up-conversion module and emitting antenna or output cable; The DSP message processing module links to each other with the FPGA signal processing module; The output of FPGA signal processing module connects the D/A modular converter; The D/A modular converter is connected with emitting antenna or output cable through the up-conversion module; Wherein be provided with time delay unit and signal synthesis unit in the FPGA signal processing module;

The DSP message processing module is set the GPS receiver movement locus of being simulated according to user's request; Ephemeris parameter is extracted and encoded as navigation message; Set emulation movement locus and satellite constellation constantly according to the user, whether the prediction gps satellite is visible; For visible star, calculate corresponding emulation phase retardation and signal frequency constantly, and issue the FPGA signal processing module to text, phase information and the frequency information of all visible stars;

The FPGA signal processing module is assigned to corresponding signal to visible star and generates passage according to the satellitosis of DSP message processing module transmission; Parameter according to the transmission of DSP message processing module; Set original carrier phase place, code phase, the navigation message of each satellite and select phase place; Generate corresponding text, sign indicating number, carrier signal according to frequency information again, and accomplish three's spread spectrum, modulation, obtain the GPS direct signal; Time delay unit duplicates the GPS direct signal that is produced, and obtains multi-path signal-component after it is postponed accordingly; GPS direct signal and multi-path signal-component carry out the synthetic D/A D/A converter module of rear end of exporting to of superposition numeral in signal synthesis unit;

After the digital intermediate frequency signal that the D/A modular converter transmits the FPGA signal processing module converts simulating signal into, deliver to the up-conversion module;

The up-conversion module is carried out mixing, filtering to the analog intermediate frequency signal of D/A modular converter input, and upconverts to the nominal radiofrequency frequency of GPS after by emitting antenna or output cable output.

In the such scheme, the time quantum that time delay unit postpones is the integral multiple in simulator work clock cycle.

In the such scheme, the DSP message processing module also is provided with the error model of all kinds of error sources, and the DSP message processing module generates corresponding Error Simulation signal according to all kinds of error sources by error model.

The nominal radiofrequency frequency of the direct wave of the said GPS of such scheme and multipath signal is 1575.42MHz.

The said emitting antenna of such scheme is a L-band right-handed circular polarization omnidirectional antenna.

Compared with prior art, the utility model has designed a kind of easy multipath signal analogy method, in the FPGA signal processing module, duplicates the direct signal of being produced, and it is postponed accordingly, has just obtained a multi-path signal-component.Because FPGA carries out work according to the sequential of work clock; The time that can postpone a clock to the direct signal that duplicates according to working clock frequency is in output; So just realized a multipath signal; And the like, multipath component also can postpone 2 to the arbitrarily individual clock period, can test multipath for receiver end and suppress algorithm effect.The utility model makes the time time quantum of the relative direct signal of multipath signal and system works clock connect; Be easier to Digital Implementation; And the satellite-signal of simulation output is digital realization, and direct signal and multipath signal parameter are adjustable controlled, very accurately; Instrument is easy to use, can be widely used in the GPS field.

Description of drawings

Fig. 1 is the through principle schematic with the multipath signal simulator of a kind of GPS of the utility model.

Embodiment

The through principle schematic with the multipath signal simulator of a kind of GPS of the utility model is as shown in Figure 1, and its hardware platform mainly is made up of DSP message processing module, FPGA signal processing module, D/A modular converter, up-conversion module and emitting antenna or output cable.The DSP message processing module links to each other with the FPGA signal processing module; The output of FPGA signal processing module connects the D/A modular converter; The D/A modular converter is connected with emitting antenna or output cable through the up-conversion module; Wherein be provided with time delay unit and signal synthesis unit in the FPGA signal processing module.The DSP message processing module is accomplished parameter setting and numerical evaluation such as signal frequency, phase place; FPGA given signal processing module in the control corresponding word, accomplishes simulation, the modulation of gps carrier signal, pseudo-random code signal and the navigation message of corresponding frequencies, and the multi-satellite signal carries out the numeral stack; Export to the D/A modular converter; Realize the conversion of digital quantity, deliver to the up-conversion module at last, become intermediate-freuqncy signal the rf frequency signal of GPS to analog quantity; And export to emitting antenna or output cable, for receiver test.According to test environment; Simulator provides accurate multipath signal, and according to the direct signal that has calculated, the time delay unit in the FPGA signal processing module postpones the corresponding work clock; Just can obtain multipath signal; And needn't recomputate signal, and saved computing time and circuit power consumption, time delay, weak point was a clock period.

1, DSP message processing module

The DSP message processing module is accomplished most of work such as parameter initialization and control, calculating in simulator, comprising: according to user's request, set the GPS receiver movement locus (time, position, speed, acceleration etc.) of being simulated; Ephemeris parameter is extracted and encoded as navigation message; Set emulation movement locus and satellite constellation constantly according to the user, whether the prediction gps satellite is visible; For visible star, calculate corresponding emulation phase retardation and signal frequency constantly, and issue the FPGA signal processing module to text, phase information and the frequency information of all visible stars.The DSP message processing module is also set up the error model of all kinds of error sources in this process, according to all kinds of error sources, generates corresponding Error Simulation signal by error model.

2, FPGA signal processing module

The FPGA signal processing module is assigned to corresponding signal to visible star and generates passage according to the satellitosis of DSP message processing module transmission; Parameter according to the transmission of DSP message processing module; Set original carrier phase place, code phase, the navigation message of each satellite and select phase place; Generate corresponding text, sign indicating number, carrier signal according to frequency information again, and accomplish three's spread spectrum, modulation, obtain the GPS direct signal; Time delay unit duplicates the GPS direct signal that is produced, and obtains multi-path signal-component after it is postponed accordingly; GPS direct signal and multi-path signal-component carry out the synthetic D/A D/A converter module of rear end of exporting to of superposition numeral in signal synthesis unit.The signal of the described certain frequency of the utility model generates, and all adopts high accuracy number frequency synthesis (NCO) technology to carry out signal frequency and accurately simulates, output high accuracy number intermediate frequency GPS simulating signal.

What the GPS receiver received is the composite signal of reflected by objects multipath signal around satellite direct signal and the receiver, therefore often need in simulator, produce multipath signal.

Gps signal is typical Direct Sequence Spread Spectrum Signal, and the direct signal that receiver antenna receives can be expressed as:

x(t)＝Ad(t)c(t)cos(ω ₀t) (1)

Multipath signal all lags behind direct signal and arrives receiver, and amplitude generally decay, and the multipath signal of therefore relative this direct signal can be expressed as:

m(t)＝α _iAd(t-τ _i)c(t-τ _i)cos[ω ₀(t-τ _i)] (2)

Phase delay generally still is expressed as phase place, so the expression formula of multipath signal can be expressed as:

m(t)＝α _iAd(t-τ _i)c(t-τ _i)cos[ω ₀t+φ _i(t)] (3)

A plurality of multipath signals and direct signal can be expressed as together:

$s\left(t\right)=\underset{i=0}{\overset{M}{\mathrm{\Σ}}}{\mathrm{\α}}_i\mathrm{Ad}(t-{\mathrm{\τ}}_i)c(t-{\mathrm{\τ}}_i)\cos [{\mathrm{\ω}}_{0}t+{\mathrm{\φ}}_i\left(t\right)]---\left(4\right)$

Wherein, i=0 representes that this signal is the satellite direct signal, and other is a M-1 multi-path signal; A representes carrier amplitude; α _iExpression signal amplitude fading coefficient, α ₀Corresponding direct signal; D (t) expression navigation data information; C (t-τ _i) the GPS pseudo-random code (because of civilian sign indicating number be the C/A sign indicating number, so representing with c (t)) of expression different delay; w ₀The IF-FRE (having supposed that here direct signal has identical frequency with multi-path signal) of expression satellite-signal; φ _i(t) phase place of i signal of expression.

In simulator, after having produced direct signal, often need produce multipath signal, so that receiver carries out the anti-multipath environmental testing.

The utility model is according to above formula, utility model a kind of easy multipath signal generation method.Because all being the main work clock according to simulator, each signal in simulator produces; Producing on the direct signal basis; If through a clock delay unit, export this signal again, just postponed the multipath signal of a clock easily on the generation time; And this signal amplitude decayed on request, can produce needed any multipath signal.Can export multipath signal and direct signal addition again through totalizer at last, just accomplish direct signal and the multipath signal output that postpones arbitrarily.

The clock delay unit can postpone a clock, also can postpone a plurality of clocks, and the time of delay is the integral multiple of clock period, and is very accurate, can conveniently contrast the anti-multipath test result of receiver like this.Because the FPGA signal processing module is to carry out work according to the sequential of work clock; The time that can postpone a clock to the direct signal that duplicates according to working clock frequency is in output; Promptly, so just realized a multipath signal through a time delay unit, and the like; Multipath component also can postpone 2 to the arbitrarily individual clock period, can test multipath for receiver end and suppress algorithm effect.The work clock of supposing simulator is 68MHz, and minimum resolution time delay of multipath signal just is 1/68000000 second, and is very accurate.

3, D/A modular converter

The D/A modular converter is carried out digital medium-frequency signal and is converted simulating signal into.Said utility model is used the DAC5687 chip, and this chip is the D/A conversion chip of 16 of American TI Company a high speed, high-performance, the binary channels released, and its highest sampling rate can reach 500MSPS.DAC5687 mainly contains 6 signal processing modules: fixedly interpolation filter FIR1, FIR2, FIR3 and have smart frequency mixer, orthogonal modulation correction module and the thick frequency mixer of 32 figure place controlled oscillators.DAC5687 can dispose through microcontroller flexibly, conveniently realizes digital signal to analog signal conversion, and has frequency conversion function.

4, up-conversion module

In the up-conversion module, the nominal analog intermediate frequency signal of importing is carried out mixing, filtering, upconvert to the nominal radiofrequency frequency 1575.42MHz of GPS, consistent with the signal that the gps satellite of actual environment is launched.Last radiofrequency signal is received transmission antennas transmit and is gone out, and supplies receiver test.

5, emitting antenna or output cable

In the utility model preferred embodiment, select for use L-band right-handed circular polarization omnidirectional antenna to be used as the output of simulator.

Claims (3)

1. the through and multipath signal simulator of GPS is characterized in that: comprise DSP message processing module, FPGA signal processing module, D/A modular converter, up-conversion module and emitting antenna or output cable; The DSP message processing module links to each other with the FPGA signal processing module; The output of FPGA signal processing module connects the D/A modular converter; The D/A modular converter is connected with emitting antenna or output cable through the up-conversion module; Wherein be provided with time delay unit and signal synthesis unit in the FPGA signal processing module; Said time delay unit duplicates the GPS direct signal that the DSP message processing module is produced, and obtains multi-path signal-component after it is postponed accordingly; GPS direct signal and multi-path signal-component carry out the synthetic D/A D/A converter module of rear end of exporting to of superposition numeral in signal synthesis unit.

2. the through and multipath signal simulator of a kind of GPS according to claim 1, it is characterized in that: the time quantum that time delay unit postpones is the integral multiple in simulator work clock cycle.

3. the through and multipath signal simulator of a kind of GPS according to claim 1, it is characterized in that: emitting antenna is a L-band right-handed circular polarization omnidirectional antenna.

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