Satellite navigation simulator with settable frequency points

Abstract

The invention discloses a satellite navigation simulator with settable frequency points, which is used for function test in an automatic test process of a satellite navigation receiver and comprises a satellite navigation signal forwarding part and a time service part. The navigation signal simulation function is realized by adopting a same-frequency forwarding mode, in the same-frequency forwarding mode, satellite navigation signals of GPS, Beidou and GLONASS are received through a satellite receiving antenna, and after being filtered and amplified, the satellite navigation signals are radiated to a tested object through a transmitting antenna or transmitted to a satellite receiver of the tested object through a high-bandwidth interface. P code and C code satellite signal forwarding and satellite receiver P code and C code positioning function testing can be realized. Meanwhile, the built-in satellite navigation receiver resolves the navigation signal in real time and sends the resolved positioning data to the upper computer to judge the effectiveness of the simulated navigation signal. In the aspect of a time service function, the device has the functions of time service output, 1PPS output and ephemeris data output, and is used for assisting in completing a P code direct capturing function test of a P code receiver.

Description

Technical Field

[0001] The invention belongs to the field of satellite navigation simulation and timing, and relates to a satellite navigation simulator which can be set with frequency points and has navigation signal forwarding and timing functions. Background Art

[0002] Satellite navigation simulators play a very important role in various satellite navigation systems and various navigation terminal products, and have received widespread attention in the military and industrial sectors. Satellite navigation simulators are widely used in navigation positioning, precise timing, aerospace and other fields. At present, the mainstream indoor satellite navigation positioning technologies mainly include simulator simulation positioning, pseudo-satellite positioning, and forwarding positioning. Among them, the simulated signal simulated by the simulator simulation positioning is different from the real navigation signal, which will prolong the positioning time or even make it impossible to locate. Pseudo-satellite positioning uses pseudo-satellites to transmit similar navigation signals. The working principle of this method is the same as that of the real navigation positioning system, but new modules need to be added, which increases a lot of costs. Forwarding positioning receives outdoor satellite signals through a satellite signal receiving antenna. After noise reduction and amplification, the satellite signal is forwarded through a signal repeater installed indoors. Summary of the invention

[0003] In view of this, the present invention provides a satellite navigation simulator with an adjustable low-noise frequency, which solves the problems of co-frequency forwarding and precise timing of satellite navigation signals, thereby providing a solution for indoor equipment to navigate and obtain timing.

[0004] The specific technical solutions are as follows:

[0005] A satellite navigation simulator with adjustable frequency is used for function testing in the automatic testing process of a satellite navigation receiver, comprising a satellite signal forwarding module and a satellite timing module; the satellite signal forwarding module realizes the satellite navigation signal simulation function by adopting the same-frequency forwarding mode; the satellite timing module has a built-in satellite receiver, and solves the incoming navigation signal in real time, and the solved positioning data is sent to a host computer for judging the validity of the simulated navigation signal. In terms of the timing function, the module has the functions of timing output, 1PPS output and ephemeris data output, and is used to assist in completing the P-code direct capture function test of a P-code receiver.

[0006] Furthermore, the satellite signal forwarding module includes a satellite receiving antenna, a first low noise power amplifier LNA, a first radio frequency switch SP4T, four band pass filters BPF, a second radio frequency switch SP4T, a power divider, a conversion switch, a power amplifier PA, a second low noise power amplifier LNA, and a third low noise power amplifier LNA; the satellite receiving antenna receives satellite navigation signals of GPS, Beidou, and GLONASS, and the satellite navigation signal is divided into four paths by the first one-to-four radio frequency switch SP4T after passing through the first low noise power amplifier LNA, each path is filtered by a band pass filter BPF, and after filtering, it is outputted from four to one by the second radio frequency switch SP4T, and then divided into two paths by the power divider, and the first path of the power divider is divided into two branches by the radio frequency switch, the first branch is emitted by the transmitting antenna after passing through the power amplifier PA, and the other path is outputted through the second low noise power amplifier LNA to achieve high broadband output, and the second path of the power divider is output to the satellite timing module through the third low noise power amplifier LNA.

[0007] Furthermore, in the same-frequency forwarding mode, the satellite signal forwarding module receives the satellite navigation signals of GPS, Beidou and GLONASS through the satellite receiving antenna, filters the navigation signals, amplifies them, and radiates them to the object under test through the transmitting antenna or transmits them to the satellite receiver of the object under test through a high-bandwidth interface, thereby realizing P-code and C-code satellite signal forwarding and satellite receiver P-code and C-code positioning function testing; the satellite signal forwarding module selects filters and power dividers according to the frequency, supports three navigation systems, Beidou, GPS and GLONASS, and supports navigation signal forwarding of 12 frequency points in total.

[0008] Furthermore, for NTP network timing, the satellite receiver timestamps the NTP message, and timestamps the network data flow in and out at the lowest level.

[0009] Furthermore, for PTP network timing, the PTP timestamp working clock is 125MHz and the minimum measurement resolution is 8ns.

[0010] Beneficial Effects

[0011] 1. The present invention solves the problems of co-frequency forwarding and precise timing of satellite navigation signals, and provides a solution for indoor equipment to perform navigation and obtain timing.

[0012] 2. The present invention selects specific frequency forwarding through filters and switches, including a total of 12 forwarding frequency points, supporting the forwarding of three navigation signals: GPS, Beidou, and GLONASS.

[0013] 3. The present invention can obtain very high NTP timing accuracy. The present invention uses FPGA to time stamp NTP messages, and timestamps the network data from the lowest level of inflow and outflow, with high accuracy. After actual measurement, the delay error caused by the device itself is within 10μs.

[0014] 4. The present invention can obtain very high PTP timing accuracy. The PTP timestamp working clock of the present invention is 125MHz, the minimum measurement resolution is 8ns, the uncertainty of the back-to-back delay test is generally ±1, and the PTP back-to-back test accuracy can be less than 16ns.

[0015] 5. Using the design of the present invention, a very low noise coefficient can be obtained. Taking into account the noise, gain and compression point of the entire module, by selecting a suitable low-noise amplifier and reasonably allocating the gain of the entire module, the noise coefficient is calculated to be less than or equal to 1.7dB through the noise cascade formula and noise coefficient simulation software, and some margin is reserved during the calculation, so the actual test value will be better than 1.7dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 , the overall framework diagram of the present invention;

[0017] Figure 2 , a specific structural diagram of the simulator of the present invention;

[0018] Figure 3 , noise coefficient simulation schematic diagram;

[0019] Figure 4 , NTP delay error measured results diagram;

[0020] Figure 5 , PTP delay error measured results diagram; DETAILED DESCRIPTION

[0021] The present embodiment discloses a satellite navigation simulator with settable low-noise frequency, which specifically includes two parts: satellite navigation signal forwarding and timing, and is mainly used for functional testing in the automatic testing process of satellite navigation receivers. The satellite navigation signal simulation function is implemented by the same-frequency forwarding method. In the same-frequency forwarding mode, the satellite navigation module receives the satellite navigation signals of GPS, Beidou, and GLONASS through the satellite receiving antenna, filters, amplifies, and attenuates the navigation signals through the transmitting antenna, and then radiates them to the object under test or transmits them to the satellite receiver of the object under test through the high-bandwidth interface. It can realize the forwarding of P-code and C-code satellite signals and the P-code and C-code positioning function testing of the satellite receiver. At the same time, the built-in satellite navigation receiver in the satellite navigation module can solve the navigation signal entering the satellite navigation module in real time, send the solved positioning data to the host computer, and judge the validity of the simulated navigation signal. In terms of timing function, it has timing output, 1PPS output, and ephemeris data output functions, which are used to assist in completing the P-code direct capture function test of the P-code receiver.

[0022] The following is a further description with reference to the accompanying drawings.

[0023] A satellite navigation simulator with adjustable low noise frequency includes two parts: satellite signal forwarding and satellite timing;

[0024] Satellite signal forwarding is to receive the satellite navigation signals of GPS, Beidou, and GLONASS through the satellite receiving antenna, filter the navigation signals, amplify them, and radiate them to the object under test through the transmitting antenna or transmit them to the satellite receiver of the object under test through cables.

[0025] The present invention can realize P code and C code satellite signal forwarding and satellite receiver P code and C code positioning test. At the same time, the satellite navigation receiver built in the satellite navigation simulator can solve the navigation signal entering the satellite navigation simulator in real time, send the solved positioning data to the host computer, and judge the validity of the simulated navigation signal; it can be used to assist in the realization of the timing function.

[0026] The satellite navigation simulator can receive Beidou satellite signals, calibrate the internal high-temperature crystal oscillator, output B (DC) code, 1pps pulse signal, 10MHz frequency standard signal, and provide NTP and PTP timing signals. In the event of loss of the external reference source, high-precision timekeeping is achieved through the crystal oscillator, providing the timing system with high-precision time signals and high-accuracy frequency signals. The overall framework diagram is as attached. Figure 1 shown.

[0027] Satellite signal forwarding module: used to forward outdoor satellite signals, select a certain type of satellite signal output through power division and filter switch, and output satellite signals after combining, power division, low noise amplifier, etc. The design principle is as shown in the attached Figure 2The part circled by the dotted line. The satellite signal forwarding module includes a satellite receiving antenna, a first low noise power amplifier LNA, a first radio frequency switch SP4T, four band pass filters BPF, a second radio frequency switch SP4T, a power divider, a conversion switch, a power amplifier PA, a second low noise power amplifier LNA, and a third low noise power amplifier LNA; the satellite receiving antenna receives satellite navigation signals of GPS, Beidou, and GLONASS, and the satellite navigation signal is divided into four paths by the first one-to-four radio frequency switch SP4T after passing through the first low noise power amplifier LNA, each path is filtered by a band pass filter BPF, and after filtering, it is outputted by the second radio frequency switch SP4T from four to one, and then divided into two paths by the power divider, and the first path of the power divider is further divided into two branches by the radio frequency switch, the first branch is sent out by the transmitting antenna after passing through the power amplifier PA, and the other path is outputted by the second low noise power amplifier LNA to achieve high broadband output, and the second path of the power divider is output to the timing module through the third low noise power amplifier LNA.

[0028] The satellite signal forwarding module can select specific frequencies for forwarding through filters and switches. It can support three navigation systems: Beidou, GPS and GLONASS, and supports a total of 12 frequencies for navigation signal forwarding.

[0029] Optimization of noise factor: Noise factor is related to many aspects, such as RF input port connector matching, noise and gain of the previous low noise amplifier chip, bandpass filter, single-pole double-throw switch, loss of microstrip line in RF circuit, etc. Noise factor is defined as the ratio of the input signal-to-noise power ratio to the output signal-to-noise power ratio of the system, which represents the degree of deterioration of the signal-to-noise ratio caused by the internal noise of the system.

[0030] According to the working principle and the cascade system noise coefficient formula, the noise coefficient index of the satellite navigation simulator module is mainly determined by the cascade noise coefficient of the front-stage low-noise amplifier, switch, bandpass filter, etc. In order to reduce the noise coefficient, the entire module noise, gain, compression point and other indicators are comprehensively considered, and the appropriate low-noise amplifier is selected and the gain of the entire module is reasonably allocated.

[0031] The noise cascade formula and noise coefficient simulation software show that the noise coefficient is less than or equal to 1.7dB. Figure 3 As shown in the figure, some margin is reserved in the calculation, so the actual test value of the module will be better than 1.7dB, which has good noise performance.

[0032] The satellite timing module includes a satellite receiver, a crystal oscillator and a processor. The satellite timing module receives the timing and positioning signals of the satellite navigation receiver, parses and demodulates 1PPS and time information, tames the built-in constant temperature crystal oscillator, calibrates the local time, provides NTP, PTP network timing and monitoring functions, and generates B (DC) code, TOD and 1pps pulse signals. It can report the timing status, working mode, punctuality status and other information through the network port, configure the receiver working mode, switch satellite signal channel parameters, etc. The design principle is as follows. Figure 2 The part circled by the dotted line.

[0033] The satellite timing module realizes various time code generation, frequency taming and other functions, and outputs 1pps, B code and other time code signals; the satellite timing module not only completes the information exchange with external devices, but also realizes the satellite timing function. The main functions are as follows:

[0034] 1) Satellite data reception and analysis;

[0035] 2) Crystal oscillator taming and timekeeping compensation;

[0036] 3) Clock maintenance and calibration, generation of B(DC), TOD code, 1PPS and other signals;

[0037] 4) Realize NTP, PTP network timing and network monitoring functions;

[0038] 5) Interact with the system to complete command reception and response.

[0039] High-precision NTP timing: In this embodiment, FPGA is used to timestamp NTP messages, and timestamps are performed at the lowest level of network data inflow and outflow, with high accuracy. As for the error caused by device frequency offset, since the device itself has a certain time retention capability and the frequency source is always in a synchronized state, the error caused is generally in the nanosecond level, which has little effect on the accuracy of NTP timing. After actual measurement, the delay error caused by the device itself is within 10μs, with high accuracy. The actual measurement results are shown in the attached figure. Figure 4 shown.

[0040] High-precision PTP timing: The PTP timestamp working clock of the present invention is 125MHz, the minimum measurement resolution is 8ns, and the uncertainty of the back-to-back delay test is generally ±1. Therefore, the PTP back-to-back test accuracy is less than 16ns. Through long-term actual testing, the PTP back-to-back synchronization accuracy is better than 20ns, which has very high accuracy. The measured results are shown in the attached Figure 5 shown.

Claims

1. A satellite navigation simulator with adjustable frequency, used for functional testing in the automatic testing process of a satellite navigation receiver, characterized in that: Contains satellite signal forwarding module and satellite timing module; The satellite signal forwarding module adopts the same-frequency forwarding method to realize the satellite navigation signal simulation function; the satellite timing module has a built-in satellite receiver, which solves the incoming navigation signal in real time, and sends the solved positioning data to the host computer to judge the validity of the simulated navigation signal. In terms of timing function, it has timing output, 1PPS output and ephemeris data output functions, which are used to assist in completing the P-code direct capture function test of the P-code receiver.

2. A satellite navigation simulator with adjustable frequency according to claim 1, characterized in that: The satellite signal forwarding module includes a satellite receiving antenna, a first low noise power amplifier LNA, a first radio frequency switch SP4T, four band pass filters BPF, a second radio frequency switch SP4T, a power divider, a conversion switch, a power amplifier PA, a second low noise power amplifier LNA, and a third low noise power amplifier LNA; the satellite receiving antenna receives satellite navigation signals of GPS, Beidou, and GLONASS, and the satellite navigation signal is divided into four paths by the first one-to-four radio frequency switch SP4T after passing through the first low noise power amplifier LNA, each path is filtered by a band pass filter BPF, and after filtering, it is outputted from four to one by the second radio frequency switch SP4T, and then divided into two paths by the power divider, and the first path of the power divider is divided into two branches by the radio frequency switch, the first branch is emitted by the transmitting antenna after passing through the power amplifier PA, and the other path is outputted through the second low noise power amplifier LNA to achieve high broadband output, and the second path of the power divider is output to the satellite timing module through the third low noise power amplifier LNA.

3. A satellite navigation simulator with adjustable frequency according to any one of claims 1 to 2, characterized in that: In the same-frequency forwarding mode, the satellite signal forwarding module receives the satellite navigation signals of GPS, Beidou and GLONASS through the satellite receiving antenna, filters the navigation signals, amplifies them, and radiates them to the object under test through the transmitting antenna or transmits them to the satellite receiver of the object under test through a high-bandwidth interface, thereby realizing the P-code and C-code satellite signal forwarding and the P-code and C-code positioning function test of the satellite receiver; the satellite signal forwarding module selects filters and power dividers according to the frequency point, supports three navigation systems, Beidou, GPS and GLONASS, and supports the forwarding of navigation signals at a total of 12 frequency points.

4. The satellite navigation simulator with adjustable frequency according to claim 1, characterized in that: For NTP network timing, the satellite receiver timestamps the NTP message, and timestamps the network data flow in and out at the lowest level.

5. A satellite navigation simulator with adjustable frequency according to any one of claim 1, characterized in that: For PTP network timing, the PTP timestamp working clock is 125MHz and the minimum measurement resolution is 8ns.

Images