RU2784802C1 - Noise-immune rangefinder local radio navigation system providing high-precision positioning - Google Patents

Abstract

FIELD: radio navigation.

SUBSTANCE: invention relates to the field of radio navigation. The effect is achieved by the fact that the rangefinder local radio navigation system, which provides high-precision positioning, uses a navigation signal free from the influence of the ionosphere, troposphere and errors in determining the ephemeris of satellites, independent of global navigation satellite systems, solving both the problem of positioning and the problem of monitoring objects, contains transceivers at reference stations and user terminals, uses an interrogation mode and a rangefinder positioning method in the absence of synchronization of reference stations, provides centimeter positioning accuracy using a noise-immune method for signal code correlation processing, as well as resistance to generated imitation interference using dynamically changing according to a complex law pseudo-random sequences, resistance to retransmitted imitation interference using methods for combating re-reflected signals nalami, resistance to masking interference using high-power noise-like signals at the receiving point, for which the noise suppression at the output of the matched power filter is 2 V times, where B is the signal base.

EFFECT: ensuring high-precision positioning of subscribers in the interrogation mode using a rangefinding positioning method that provides centimeter positioning accuracy using a noise-resistant method for correlation processing of noise-like signals and high resistance to masking and imitation interference.

1 cl, 5 dwg, 2 tbl

Description

The invention relates to the field of radio navigation and allows the implementation of a noise-resistant rangefinder radio navigation system that provides high-precision positioning.

Currently known global navigation satellite systems (GNSS) such as GLONASS, GPS, Galileo, Beidou have a number of undeniable advantages, such as:

- full coverage of the earth and near-earth space;

- free use of systems;

- unification of equipment for all users, etc.

But GNSS also have a number of significant drawbacks:

- poor signal reception in wooded and mountainous areas, in urban areas;

- insufficient noise immunity - local interference of low power can make it difficult or impossible to navigate through GNSS signals.

Inertial systems (INS) alone cannot solve the problem of navigation in these conditions, since they need constant correction using GNSS.

Local navigation systems (LSN) complement GNSS systems in cases where the latter cannot be used due to powerful interference or the absence of a GNSS signal at the receiving point.

The prior art is known ground-based pulse-phase radio navigation system (IFRNS) "Seagull" (Loran) [1]. The system operates on ultra-long waves, includes powerful transmitters (more than 200 kW power) and operates over distances of more than 1000 km. The disadvantage of the system is the low positioning accuracy (tens of meters).

Known local radio navigation system "Krabik" [2]. The system uses rangefinder, difference-rangefinder and combined positioning method. A phase pseudorange measurement method is used to make accurate measurements based on carrier phase measurements.

The disadvantages of RNS "Krabik" are:

- low resistance to masking interference, since the phase of the signal is highly affected by such interference;

- low resistance to imitation interference, since the system does not provide for changing the signal code during operation, while there is a high probability of simulating a known signal code;

the ability of any unauthorized user with an appropriate navigation receiver to use the system for navigation.

Also known is the local radio navigation system of VedaProject LLC, which is a ground-based addition to the GLONASS system based on pseudosatellites (PS) [3]. The local radio navigation system (LRNS) is designed to provide high-precision navigation in conditions where it is difficult to receive GNSS GPS/GLONASS signals. The system can use a standard GNSS navigation receiver, with minimal software modifications, but with an external converter that allows you to change the range of carrier frequencies used.

The disadvantages of LRNS based on the PS of VedaProject LLC are:

- low electromagnetic compatibility with standard GNSS equipment;

- low resistance to imitation interference, since the system uses known GNSS signal codes, while there is a high probability of simulating a known signal code;

- the ability of any unauthorized user with an appropriate navigation receiver to use this system for navigation.

Known local navigation system LocataNet [4]. The Locata navigation system is a terrestrial network of transmitters that broadcast navigational radio signals that are generally very similar to the radio signals of satellite navigation systems. A navigation receiver capable of receiving and processing the signals of the Locata system transmitters is capable of independently navigating, in general, very similar to navigation (positioning) using radio signals from satellite navigation systems.

A distinctive feature of the Locata system from similar satellite navigation systems is the time division of channels (time division of the radio signals of transmitters); change during operation of the temporary location of the transmitter signal; different navigation message information in each transmitter; arbitrary allowable operating frequencies of subnets; different synchronization system for subnet transmitters and subnet groups.

The disadvantages of the Locata system are:

- the ability of any (unauthorized, unauthorized) user with an appropriate navigation receiver to use this system for navigation;

- lack of interaction (other than transmitter signals) between the navigation system and navigation receivers, in particular, making it difficult to change transmitter signals during its operation and change the structure and mode of operation of the navigation system;

- positioning and synchronization accuracy in the Locata system is ensured by accurate measurement of the carrier phase in the system. But the carrier phase is primarily affected by noise;

- low noise immunity, since everyone knows the signal used in the system.

The closest analogue of the described invention in the present patent is the local navigation system described in patent 2555860 (RU) [5].

The navigation system described in this patent 2555860 (RU) consists of several transmitters that transmit radio navigation signals, with the help of which a navigation receiver capable of processing these signals is able to navigate - determine its coordinates and, if possible, its other characteristics, for example, speed , motion vector, etc. The navigation system may include a control subsystem necessary to control the operation of the transmitters and/or to interact with the navigation receivers. The location may be used in the navigation receiver or sent by it to the control subsystem, or the control subsystem may receive it from the communication system.

The disadvantages of the proposed system are the following points:

- receivers are used separately in subscriber terminals and transmitters in reference stations, that is, only a non-request mode is implemented, in which precise synchronization of transmitters of reference stations is necessary in one way or another;

- at the same time, it is impossible to implement the request mode of solving the navigation problem in the system, which in a number of applications is the only possible one in cases where there is no synchronized network of reference stations;

- the method of synchronization of the transmitters is not separately given, which means that the same method is used to synchronize the transmitters as in the Locata system, based on the measurement of the phase of the carrier, which is affected in the first place;

- does not provide a way to provide high-precision navigation.

The essence of the invention

The purpose of the invention described in this patent is to create a navigation system with the absence of these disadvantages of the closest analogue, characterized by the following criteria:

- the radio navigation system provides high-precision positioning using a navigation signal free from the influence of the ionosphere, troposphere and the error in determining the satellite ephemeris;

- contains transceivers at reference stations and subscriber terminals, solves both the problem of positioning and the problem of monitoring objects;

- uses interrogation mode and rangefinder positioning method;

- provides increased positioning accuracy using a noise-resistant original method of signal code correlation processing;

- provides resistance to generated imitation noise (100%) using a large number of pseudo-random sequences (RRP), dynamically changing according to a complex law;

- provides resistance to retransmitted imitation interference using methods of combating re-reflected signals;

- resistance to masking interference is provided by the signal power at the receiving point 10,000 times higher than the GNSS signal power and the use of noise-like signals for which the noise suppression at the output of the matched power filter is 2 V times, where B is the signal base.

An example of the structure of a radio navigation rangefinder local navigation system is shown in FIG. one.

The radio navigation system is a local navigation system consisting of a network of transceivers that are part of radio navigation reference stations (1, 2, 3, 4), transceivers that are part of subscriber terminals (5, 6) and a hardware and software complex (7).

The system solves two tasks: monitoring and object navigation.

Query mode of operation and rangefinding method for determining coordinates are provided.

The technical result of the claimed invention is to provide high-precision positioning of subscribers in the interrogation mode using a rangefinder positioning method that provides centimeter positioning accuracy using a noise-resistant method of correlation processing of noise-like signals and high resistance to masking and imitation interference.

The system can solve both a navigation task, when subscriber terminals receive signals from reference stations and determine their coordinates, direction of movement and speed, and a monitoring task, when navigation data from subscriber terminals are transmitted to a hardware-software complex (7), where data is collected monitoring, the operation of the system is controlled, including the control of the change of the memory bandwidth in the reference stations (1,2,3,4) and subscriber terminals (5, 6) according to a complex law.

The system implements a request mode of positioning. The interrogation mode has an analogy with active radar with an active response, in which the interrogation and response signals are encoded so that the address of the object can be determined from the code and additional information can be obtained.

An important advantage of active response systems is the gain in range due to the significant power of the response signal.

As shown in FIG. 1, the user terminals provide a navigation signal in an interrogation mode. Reference stations receive such signals and issue response signals, which are received by subscriber terminals and solve the positioning problem using the ranging method. In this case, the double distance (pseudo-range) from the user terminals (5,6) to the reference stations (1, 2, 3, 4) and back is measured.

Advantages of the request mode:

- differs in the increased accuracy of the solution of the navigation problem;

- in some applications it is the only possible one when there is no synchronized network of reference stations;

- the mode can be implemented at two reference stations that receive signals from user terminals and send response signals asynchronously;

- request mode is used to synchronize reference stations in non-request mode;

- reference station transmitters do not work constantly, but only on request. This reduces the power consumption of the equipment.

In the interrogation mode, a ranging method of positioning is used, in which the user terminal emits a ranging code that modulates a carrier. In this case, there is no need to synchronize the reference stations. Several reference stations with known coordinates receive a signal and send response signals, which are received by the user terminal. Taking into account the speed of light in the atmosphere and the delays in the equipment when receiving and transmitting signals in the user terminal, the double distance between the user terminal and several reference stations is calculated. At the same time, the navigation task is solved in AT.

The ranging method for solving the navigation problem is shown in FIG. 2 and consists in determining the location of the user terminal (5) by measuring the distances between the user terminal (5) and reference stations (1,2).

Each position surface is a sphere centered at the reference station (1,2) with a radius equal to the range. Since points 5 (user terminal), reference stations (1,2) are in the same plane, the position surfaces pass into circles with radii R1 and R2 with the intersection point 5, as shown in FIG. 2. The second point of intersection of the spheres must be discarded based on additional data.

Calculation of the instrumental error of pseudorange measurement and positioning in the ranging mode in LSN.

1. Instrumental error in measuring pseudorange when sampling the input signal in an analog-to-digital converter (ADC).

When positioning in the request mode (ranging method), the user terminal (5) emits request signals, and the reference stations (1,2) receive them and re-emit them as response signals, which are received by the user terminal (5). Since the speed of propagation of radio waves in the air is constant, the response signals of the ROS reference stations (1,2) received in the subscriber terminal (5) are late in relation to the emitted signals for a certain time t ₃ :

where R is the distance between the reference station and the user terminal (m),

- время задержки обработки сигнала при приеме/передаче в опорных станциях и абонентских терминалах и определяется в процессе калибровки.

- signal processing delay time during reception/transmission in reference stations and subscriber terminals and is determined during the calibration process.

Since the instrumental positioning error in the LOS is determined by the accuracy of measuring the signal delay time, which depends on the sampling error of the input signal in the receiver in time, the following estimated calculation of the instrumental error in measuring the pseudorange in the LOS is Δinstr. (estimated calculation is given with numerical calculations for a better perception, naturally the values \u200b\u200bmay be different):

- инструментальная ошибка измерения псевдодальности при дискретизации входного сигнала в аналого-цифровом преобразователе (АЦП) приемника с точностью до одного символа псевдослучайной последовательности (ПСП);where

- instrumental pseudorange measurement error when sampling the input signal in the analog-to-digital converter (ADC) of the receiver with an accuracy of up to one symbol of a pseudo-random sequence (PRS);

- скорость света в вакууме (скорость распространения радиоволн)

- speed of light in vacuum (speed of propagation of radio waves)

- частота следования символов ПСП;

- frequency of repetition of PSP symbols;

- количество отсчетов выходного сигнала АЦП на каждый из символов ПСП.

- the number of samples of the ADC output signal for each of the PSP symbols.

2. Sampling frequency of the input signal.

The sampling frequency of the input signal in the receiver's ADC is selected on the basis of K1 samples per one PSS symbol.

Since double the distance between the reference station (1,2) and the user terminal is measured in the interrogation mode, and the measured delay is divided by 2, then the instrumental measurement error is also divided by 2.

при типовых числовых данных

в дальномерном методе:Thus, the instrumental error in measuring the pseudorange when sampling the input signal in the ADC of the receiver at the frequency

with typical numerical data

in the rangefinding method:

3. Upsampling of the input signal.

To reduce the instrumental error, the sampling frequency of the input signal is increased by K2 times without increasing the frequency of the ADC.

путем сдвига тактирующего сигнала на 1/10 такта на каждой из К2 посылок ПСП.To do this, K2 = 10 samples are taken for each symbol, following with a sampling frequency

by shifting the timing signal by 1/10 of the cycle on each of the K2 parcels of the PSP.

When processing K2=10 PSP messages, the instrumental error of pseudo-range measurement in the range-finding method is equal to:

4. Accurate determination of the position of the peak of the correlation function.

The correlation function (FC) at the subscriber's receiver is calculated using the statistics of the received samples.

The graph of the FC counts in the peak area looks like a triangle with a base of K 1=20 counts along the time axis, as shown in FIG. 3. In this case, the FK peak is not represented by one count, but is “stretched” by K1 cycles.

и обозначены точками, которые не лежат на одной прямой из-за ошибок распространения и обработки навигационного сигнала.FC counts follow frequency

and are indicated by points that do not lie on one straight line due to propagation and processing errors of the navigation signal.

от значения

полученного в случае, когда ФК вычисляется с точностью до отсчета с инструментальной ошибкой измерения псевдодальности Δдт=0,749 м.The position of the FC peak is calculated as the point of intersection of two straight lines constituting a triangle and drawn optimally among 10 samples (left) + 10 samples (right) using the least squares method. In this case, we obtain the point to, which determines a more accurate position of the FC peak and will differ by

from the value

obtained in the case when the FC is calculated up to a reading with an instrumental pseudo-range measurement error Δdt=0.749 m.

The determination of the exact value of the signal and the moment of the peak of the FK begins when the signal at the output of the matched filter exceeds a certain threshold.

At the same time, using the least squares method when calculating the moment of the FC peak, the instrumental pseudorange measurement error decreases by a factor of K3 and represents the root mean square deviation (RMS) taking into account the error in the propagation and processing of the navigation signal. According to available statistics - K3=2-3.

5. Increasing the number of pseudorange measurements.

According to the law of the theory of errors, if it is necessary to improve the accuracy of the result (with the systematic error excluded), it is necessary to increase the number of measurements.

If we increase the number of L1 measurements when measuring pseudorange by a factor of 25, i.e., process a frame of 25 PRS, then the RMS will be less in

The use of a frame of 25 PRs is necessary, since it contains the address of the subscriber and the reference station, as well as other necessary information.

при использовании метода наименьших квадратов при измерении псевдодальности учетом ошибки распространения и обработки навигационного сигнала:In this case, we obtain an instrumental error of RMS

when using the least squares method when measuring pseudo-range, taking into account the error of propagation and processing of the navigation signal:

(with a confidence level of 0.67).

The frame duration is 25 ms. In this case, the frequency of issuing the result is -10 Hz.

The obtained value of the instrumental error in determining the pseudorange is only a part of the real error.

The real error can only be determined by measuring on a signal simulator and conducting field tests.

6. Estimation of the real error of pseudorange measurement.

The potential pseudo-range measurement error characterizes the maximum achievable accuracy and is determined by the signal-to-noise ratio and the width of the navigation signal spectrum.

The potential error (RMS) of measuring the pseudorange for a radio pulse with a bell envelope is given in [9]. Since the interrogation mode measures twice the distance between POC and AT and the measured delay is divided by 2, the potential measurement error is also divided by 2:

where c \u003d 299796459.2 ± 1.1 m / s is the speed of light in vacuum (the speed of propagation of radio waves);

- эффективная ширина спектра навигационного сигнала на уровне 0,46;

- effective width of the spectrum of the navigation signal at the level of 0.46;

- частота следования символов ПСП;

- frequency of repetition of PSP symbols;

- количество отсчетов выходного сигнала АЦП на каждый из символов ПСП;

- the number of samples of the ADC output signal for each of the PSP symbols;

- отношение сигнал/шум по мощности на выходе согласованного фильтра, вычисляющего ФК. Расчетное отношение мощности сигнала к мощности шума

на выходе согласованного фильтра определяется пороговым устройством, стоящем на выходе согласованного фильтра и фиксирующем момент превышении порога на графике ФК (как показано на ФИГ. 3). Определение точного значения и момента пика ФК начинается при превышении сигналом на выходе согласованного фильтра некоторого порога.

- signal-to-noise ratio by power at the output of the matched filter that calculates the FK. Estimated Signal Power to Noise Power Ratio

at the output of the matched filter is determined by a threshold device that is located at the output of the matched filter and fixes the moment when the threshold is exceeded on the FK graph (as shown in FIG. 3). Determining the exact value and moment of the FC peak begins when the signal at the output of the matched filter exceeds a certain threshold.

Established experimentally

как при вычислении (7) потенциальная ошибка равна:Taking into account the increase in the sampling frequency (K1), the repetition of measurements (L1), the increase in the number of samples per symbol (K2), the refinement of the position of the peak of the correlation function (K3) for

as when calculating (7), the potential error is:

and is 10% of the actual pseudorange measurement error [9].

In this case, the estimate of the real error in measuring the pseudo-range in the range-finding method:

по двум опорным станциям, расположенным в точках 1 и 2, имеющим ошибки измерения псевдодальности до абонента7. Influence of the geometric factor on the positioning accuracy in the system. Instrumental positioning error RMS

for two reference stations located at points 1 and 2, having errors in measuring the pseudo-range to the subscriber

where n=2 (the number of position lines - LP).

Geometric factor (Dilution of Precision) DOP = 1/sinβ (β is the angle between the vectors R1 and R2 directed from the reference stations 1 and 2 to the subscriber terminal 5, as shown in FIG. 4.

The subscriber is at point 5 of the intersection of two circles with radii R1 and R2. The geometric factor DOP depending on the angle β is given in Table 1.

Positioning error (RMS) is proportional to DOP = 1/sin β because:

получаем СКО позиционирования (при β = 30°, DOP = 1/sin β=2,0, n = 2,

):Since in the RMS rangefinder method of measuring the pseudorange

we obtain the positioning RMS (at β = 30°, DOP = 1/sin β=2.0, n = 2,

):

In total, the frame contains 25 PSPs. Frame duration 25 ms.

This ensures the frequency of issuing the result up to -10 Hz.

8. Increasing the number of measurements in positioning.

If we increase the number of measurements when positioning in LSN by L2 = 16 times, that is, process 16 frames of 25 memory bands, then according to the error theory law, the RMS will be less in

With an ideal geometric factor DOP = 1 (angle β = 90°) we get

Duration 16 frames of 25 memory bandwidth - 400 ms. In this case, the frequency of issuing the result is 1 Hz.

The RMS value in the ranging method is only a part of the real positioning error, which can be determined using the LSN signal simulator and field tests.

8. The results of calculating instrumental errors in determining coordinates depending on the geometric factor and the frequency of issuing the result are shown in the Table. 2.

Calculations of instrumental positioning error showed the possibility of achieving centimeter accuracy (RMS) of a local radio navigation system with various geometric factors.

Immunity to masking interference is ensured by the fact that:

- the system uses noise-like signals, the level of which exceeds the level of GNSS signals at the receiver input by 10,000 times and for which the noise suppression at the output of the matched power filter is 2 V times, where B=1024 is the signal base [8];

- the solution of the problem in the navigation receiver is taken not by the phase of the carrier subject to interference, but by high-precision measurement of pseudorange based on the signal code resistant to interference, which is ensured by matched filtering of the signal with an accurate determination of the peak moment of the correlation function.

Resistance to imitation interference is ensured by the fact that:

- resistance to generated imitation noise (100%) is ensured by using a large number of pseudo-orthogonal PSPs (more than 1000 PSPs), dynamically changing according to a certain complex law under the control of the HSC, up to the use of cryptographic algorithms;

- resistance to retransmitted imitation interference is ensured by the fact that they are similar to re-reflected signals and are eliminated by methods of combating re-reflections.

In order to combat re-reflections, one should consider the working area of the LSN (spheres with radii R ₁ , R ₂ , R ₃ , R ₄ ) at the test site in the ranging method, shown in FIG. 5.

The centers of the spheres located at the locations of the four reference stations are shown by points (1,2,3,4). The subscriber is at the point of intersection of the spheres (5). The solution of the navigation problem is to find this point.

Re-reflected signals are not included in the solution of the navigation problem and are not taken into account, since they do not fall into the intersection points of circles (spheres), at the centers of which reference stations (1, 2, 3, 4) with known coordinates are located

Thus, the fight against the influence of imitation retransmitted interference is carried out by the same methods as the fight against re-reflected signals.

The task of monitoring in the rangefinding system is solved as follows.

After accurate positioning, the navigation information in the AT is superimposed on the error-correcting navigation signal (PSN) using the XOR function (modulo 2 addition) and transmitted to the APC (7). At the receiving end in the APC, the signal is overlaid with the same SRP using the XOR function, and the navigation information is extracted. This is how the monitoring problem is solved. This is possible because there are transmitters in the subscriber terminals (5,6).

Claims (1)

Range-finding local radio navigation system that provides high-precision positioning, using a navigation signal that is free from the effects of the ionosphere, troposphere and error in determining satellite ephemeris, independent of global navigation satellite systems, solving both the problem of positioning and the problem of monitoring objects, characterized in that it contains transceivers on reference stations and user terminals, uses an interrogation mode and a ranging method of positioning in the absence of synchronization of reference stations, provides centimeter positioning accuracy using a noise-resistant method of signal code correlation processing, as well as resistance to generated imitation noise using pseudo-random sequences dynamically changing according to a complex law, resistance to retransmitted imitation interference using methods of combating re-reflected signals, resistance to masking interference with them using high-power noise-like signals at the receiving point, for which the noise suppression at the output of the matched power filter is 2V times, where B is the signal base.

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