WO2023186851A1

WO2023186851A1 - Receiving system for a global satellite navigation system

Info

Publication number: WO2023186851A1
Application number: PCT/EP2023/057908
Authority: WO
Inventors: Götz Caspar Kappen; Markus Biermann
Original assignee: Fh Münster
Priority date: 2022-03-28
Filing date: 2023-03-28
Publication date: 2023-10-05

Abstract

The invention relates to a receiving system for a global satellite navigation system, comprising: • an antenna array (ANT); • a receiving device (RX); • an interference suppression unit (ISU); • an upconversion unit (TX); and • a real-time kinematic receiving unit (RTK-RX), • wherein the real-time kinematic receiving unit (RTK-RX) feeds data relating to a signal or a plurality of signals back to the interference suppression unit (ISU) so that the interference suppression and propagation time correction parameters are adjusted on the basis of these data.

Description

Receiving system for a global satellite navigation system

The invention relates to a reception system for a global satellite navigation system.

background

In many areas of today's technology there is a desire for precise local knowledge.

Satellite-based navigation systems are known for the general tasks of location coordinates. These systems require that a receiver can receive signals from multiple satellites at the same time. Using known properties, a position can then be determined from transit time differences and/or received signal strengths by means of triangulation, or a speed and direction can also be determined from the determination of temporally successive positions.

However, the signals are very weak, so disruptive signals, so-called interferers, can hinder or, in the worst case, even prevent the reception of one or more signals.

The accuracy of these systems is also comparatively low.

This is because conceptually different sources of error can lead to an error in the location determination in the range of several meters.

With the introduction of so-called Assisted GNSS reception systems, the location determination time in the range of seconds was possible with a spatial resolution of less than 1.5 m and signal levels of up to -148 dBm. Although it is possible to further improve the accuracy with differential GPS approaches, such differential systems are comparatively expensive and generally require an additional receiving device.

However, in agriculture, for example, there is an increasing need for centimeter-precise location determination, so that, for example, modern machines can be used to apply fertilizers and/or other additives to agricultural areas with precise location. On the one hand, this would allow resources to be conserved, but on the other hand, it would also be possible to react to very different local conditions, for example, so that pests and/or vegetation can be addressed more specifically.

Other areas where more precise location determination would be necessary include drones and/or the monitoring of moving objects.

In the scientific literature, the issues of interference suppression and achieving better accuracies have been considered separately. This results in essentially disjoint approaches being provided.

Task

It is therefore the object of the invention to provide a solution that is cost-effective, allows good suppression of interference radiation and the achievement of position determinations in the cm range.

Brief description of the invention The task is solved by a receiving system for a global satellite navigation system having a multiple antenna device, a receiver device for processing signals from the multiple antenna device, an interference suppression unit for processing signals from the receiver device, an up-conversion unit for processing signals from the interference suppression unit, and a real-time kinematic receiver unit, wherein the real-time kinematic receiver unit returns data relating to one or more signals to the interference suppression unit, so that the interference suppression and transit time correction parameters are set based on this data.

Further advantageous refinements are the subject of the respective dependent claims, the figures and the description.

Short description of the characters

The invention is explained in more detail below using a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

Show it:

Fig. 1 is a schematic representation of embodiments of the invention

aspects of the invention,

2 shows a schematic representation of a detail of embodiments of the invention,

Fig. 3 is a schematic representation of a further detail of embodiments

Invention,

Fig. 4 shows a schematic representation of embodiments of the invention according to further

Aspects of the invention, and

Fig. 5 is a schematic representation of a further detail of embodiments of the

Invention.

Detailed description of the invention The invention will be presented in more detail below with reference to the figures. It should be noted that different aspects are described, which can be used individually or in combination. This means that any aspect can be used with different embodiments of the invention unless explicitly presented as a pure alternative.

Furthermore, for the sake of simplicity, reference will generally only be made to one entity. Unless explicitly stated, the invention can also have several of the affected entities. In this respect, the use of the words “a”, “an” and “an” should only be understood as an indication that at least one entity is used in a simple embodiment.

As far as procedures are described below, the individual steps of a procedure can be arranged and/or combined in any order, unless the context explicitly states otherwise. Furthermore, unless expressly stated otherwise, the methods can be combined with each other.

Information with numerical values is generally not to be understood as exact values, but also includes a tolerance of +/- 1% up to +/- 10%.

To the extent that standards, specifications or the like are named in this application, reference is always made to at least the standards, specifications or the like that are applicable on the filing date. This means that if a standard/specification etc. is updated or replaced by a successor, the invention can also be applied to this.

Various embodiments are shown in the figures.

In particular, the figures show different aspects of embodiments of a reception system according to the invention for a global satellite navigation system. This receiving system according to the invention initially has, as shown in Figure 1 and Figure 3, a multiple antenna device ANT. Different types of multiple antenna devices can be provided, which, on the one hand, ensure that correspondingly (circularly) polarized signals can be received on more than one path.

3 also shows optional (adjustably variable) preamplifiers which can amplify a corresponding signal from an antenna (four exemplary antennas of a multiple antenna device ANT are shown in FIG. 3). Although shown as part of the multiple antenna device ANT, this is not mandatory, but in the same way the optional (adjustably variable) preamplifiers could also be arranged in a receiver device RX. The preamplifier values set here and changeable during runtime are known to the following signal processing (ECU) (Figure 4). From this, runtime correction parameters are determined.

The multiple antenna device ANT can be, for example, a rectangular 2*2. Using such multiple antenna devices ANT, spatial scanning/processing can be made possible. The corresponding antenna parameters (determine the so-called beam pattern) can be taken into account in appropriate processing and, for example, stored in a memory.

The antennas of the multiple antenna device ANT are designed, for example, to receive different bands, in particular LI, L2/E5b, B2I. In particular, the antennas of the multiple antenna device ANT can have a phase center variation for LI of less than 5 mm horizontally or less than 5 mm in all azimuth angles. In initial tests, it was sufficient for the L2 band to have a phase center variation of less than 5 mm horizontally or less than 10 mm in all azimuth angles.

Furthermore, the reception system according to the invention has a receiver device RX as shown in FIG. 1 and FIG. 3. Although referred to as a receiving device, this receiving device RX can convert the high-frequency antenna signal into an intermediate band/to one for one or more antennas of a multiple antenna device ANT Provide intermediate frequency or baseband - together or in separate receiving units.

In embodiments it can be provided that the receiver device RX mixes down incoming signals into the baseband or to an intermediate frequency of less than 100 MHz, preferably less than 20 MHz, in particular 15.42 MHz.

The receiver device RX can, for example, be a (programmable) multi-channel (e.g. 4-channel) mixer including an analog-digital converter (e.g. a GNSS receiver). As part of test patterns, the conversion to an intermediate frequency (for example fiF = 15.42 MHz) was carried out without, however, excluding the use of the baseband.

Logically following the receiver device RX, an interference suppression unit ISU is arranged in the reception systems according to the invention, as shown in Figure 1.

Furthermore, the receiving system according to the invention, as shown in Figure 1, has an upconversion unit TX and a real-time kinematic receiver unit RTK-RX.

The up-conversion unit TX converts the signal, which has been cleared of interference, back to a higher frequency - generally corresponding to the frequencies received on the side of the receiver device RX - which is then made available to a real-time kinematic receiver unit.

In one embodiment of the invention it can be provided that the upconversion unit TX generates interference-suppressed signals, ie signals after processing by the interference suppression unit ISU, at frequencies compatible with a conventional GNSS receiver, in particular in one of the L-bands. mixes up. The renewed conversion and transfer to a recipient unit may seem absurd at first glance. However, data relating to one or more signals can be determined using the real-time kinematic receiver unit and fed back to the interference suppression unit ISU, so that the interference suppression is set based on this data.

This means that, unlike the classic solution of sub-problems, interaction is made possible here, so that findings that arise when determining the position using one of the real-time kinematic receiver units RTK-RX, but which are not required for the actual position determination, are now used for the setting the interference suppression unit ISU can be used, which means that they can be adjusted more specifically

Using the invention presented, it is possible to determine the position with an accuracy of 1-5 cm in the range of seconds to fractions of a second, although there is still room for improvement here.

In one embodiment of the invention - as shown in Figure 4 - it is provided that the real-time kinematic receiver unit RTK-RX receives data relating to a signal or several signals for setting and / or selecting one or more antennas of the multiple antenna device ANT (and / or the Preamplifier) returns so that the multiple antenna device ANT and / or the interference suppression ISU can be adjusted based on this data

In one embodiment of the invention, the interference suppression unit ISU has an FPGA logic or an ASIC. Using such implementations, it is possible to keep the processing speed high so that this processing can take place within a short period of time.

Without limiting the generality, additional elements can also be provided/integrated on the FPGA/ASIC - see Figure 5. Likewise, the FPGA can be provided with a daughter board - if the provision is more cost-effective or effective - which, for example, has certain functions such as that of an analog-digital converter ADC on the input side and/or a digital-analog converter DAC on the output side.

In particular, it can be provided that the analog-digital converter ADC samples analog signals with an (adjustable) sampling frequency and quantizes them with a (eg hardware-dependent) word length. In a test setup, f _s = 62.5 MSamp and a quantizer with 14 bits were used as the sampling frequency.

In one embodiment of the invention, the interference suppression unit ISU has a Hilbert filter.

In particular, the Hilbert filter is provided as a forward linear digital filter.

The interference suppression unit ISU can - as shown in Fig. 2 - be constructed from a NIOS softcore and an FPGA. In order to achieve particularly good performance, the VHDL coding can be optimized by hand. The complete feature set, i.e. cache memory and floating point unit, was used in a test setup.

In Figure 5, for example, the beam shaping weighting factor calculation BF-WT can be implemented in the NIOS softcore, while the other elements such as the Hilbert filter Hilbert, a phase locked loop PLL, the covariance matrix determination covariance, a low pass LP, an interpolator IP and a beam shaper BF and also a high-mixing upconversion unit TX can be coded in the FPGA.

The Hilbert filter can in particular be designed in such a way that it removes negative frequency components in the spectral domain, which in turn leads to a non-symmetrical spectrum and therefore complex data samples. The weights for the complex beam shaper BF can be estimated based on the covariance matrix covariance of the incoming signal data streams of the (four) antennas of the multiple antenna device ANT.

This input signal in the time domain at each of the NANT antennas (e.g. 4) can be used as

being represented. The length of the vector x _n (t) is the observation time used to calculate the expected value. The notation of the matrix with the vector x _n (t) in the row dimension and the antenna vectors in the spade dimension is X. An estimate of the covariance matrix can now be given as R _xx = E[ ^H ]. This result can also be achieved in the digital domain. The observation time for calculating the covariance matrix can preferably be set to the order of a few 100 ms. The observation time essentially depends on the dynamics of the observed objects and directly influences the interference suppression capabilities.

The beam shaper BF can be implemented, for example, by complex multipliers. As a rule, a complex multiplier instance (e.g. 4) will be provided for each antenna. These multipliers can be provided as a VHDL macro. As with the calculation of the inverse covariance matrix, attention should be paid to ensuring that the scaling, rounding and signal limitation of the digital values are selected appropriately.

The interpolator IP and the low-pass filter LP preprocess signal streams for upconversion in the upconversion unit TX. In a test setup, an intermediate frequency with a center frequency of f| _F 2 = 40.41 MHz and a sampling frequency of f _D Ac = 125 MHz.

In a further upconversion unit TX (see FIGS. 1 and 4), the signal streams (located at an intermediate frequency fj _F 2 ) are now increased to the target band - in this case, for example, at least one of the L bands. Without limiting the generality, further components, such as a surface filter or the like, can of course be provided to suppress disturbing signals/mixed products.

An exemplary interference suppression unit ISU can suppress/remove interference signals based on spatial signal processing. An example processing operation may be based on estimating the phase and covariance matrix of the incoming interferer signal. Based on this, a set of complex coefficients can then be calculated and applied to an incoming full-rate data stream.

In order to receive an interference-free signal y the antenna input vector

with the inverse of the covariance matrix

R _xx = E[XX"] multiplied, where ^H denotes the Hermitian operator and E [] the expectation operator.

Accordingly, the output signal can be described as y=w ^H X.

The required weights can then be calculated as follows

, where R _xx is the dimension N _ANT XN _ANT , X is the dimension N _ANT X 1, W is the dimension

^x 1 and the control vector d also has the dimension N _ANT X 1. The control vector d is a freely selectable parameter in the test setup, which is set to the zenith if no further information is available, ie the beam shaping weights are set to (0.25,0.25,0.25,0.25). The calculation of the inverse of the covariance matrix R _xx places the highest demands on the calculation. This is implemented in a test setup using eigenvalue decomposition.

For this purpose, the covariance matrix is broken down into the corresponding eigenvalues A and eigenvectors U.

R _xx = UAU ^H

Based on A and U, the calculation of the inverse of R _xx can be simplified.

In a simple implementation, the interference suppression unit ISU is based on a simple multiplication of the incoming (4-channel) signal (at the down-converted intermediate frequency), the inverse covariance matrix ß^l and the control vector d to the zenith.

An external processing unit ECU is also shown in FIG. This provides exemplary signal processing of the control signals so that the individual units of the receiving system can exchange both configuration data and data to be configured. This data includes, but is not limited to: An antenna pattern, a covariance matrix, weighting factors, eigenvalues, carrier phases, code phases, visible satellites, etc.

The external processing unit ECU can, for example, use the data from the multiple antenna device ANT, which is available, for example, from a measurement or a simulation of the arrangement of the individual antennas of the multiple antenna device ANT, in order to take phase and amplitude corrections (time of flight correction parameters) into account.

The input data for the receiver device RX represents configuration data; among other things, amplification factors and characteristic curve parameters that can be adjusted adaptively to the input signal. The adaptation should be carried out via the ECU for better results, as all the information is bundled here. The interference suppression unit ISU can, for example, return information about the type and characteristics of the interference to the ECU for further processing.

Likewise, the upconversion unit TX can receive parameters from the ECU and return status signals to the external processing unit ECU.

Furthermore, the real-time kinematic receiver unit RTK-RX can send a calculated position to the external processing unit ECU. RTK receiver settings and/or receiver measurements (e.g. range measurements, amplifier settings) can also be sent to the external processing unit ECU. The real-time kinematic receiver unit RTK-RX can receive runtime correction parameters from the ECU's external processing unit to improve, for example, accuracy and stability.

Output data of the entire system can be the improved receiver measurements and optional additional information ZI, which, among other things, indicates the internal state of the system.

That is, the external control unit (ECU) can enable positioning based on a carrier phase estimate, but in particular a carrier phase measurement, based on data that was collected by one or more other units of the signal path and made available to the external control unit (ECU). . This means that with information from the processing chain, e.g. antenna characteristics, front end settings, information from the interference suppression and the information from the RTK reception, together RTK position accuracy can be achieved again despite the interference suppression, which leads to phase errors in conventional processing.

The invention also relates to the use of a receiving system according to the invention for position determination, whereby the position can be determined precisely in a range of less than 1 dm. The invention further relates to the use of a receiving system according to the invention for position determination in agriculture.

Claims

Claims receiving system for a global satellite navigation system comprising:

• a multiple antenna device (ANT),

• a receiver device (RX) for processing signals from the multiple antenna device (ANT),

• an interference suppression unit (ISU) for processing signals from the receiver device (RX),

• an upconversion unit (TX) for processing signals from the interference suppression unit (ISU), as well as

• a real-time kinematic receiver unit (RTK-RX) for processing signals from the upconversion unit (TX),

• whereby the real-time kinematic receiver unit (RTK-RX) returns data relating to one or more signals to the interference suppression unit (ISU), so that the interference suppression and transit time correction parameters are set based on this data. Reception system according to claim 1, characterized in that the real-time kinematic receiver unit (RTK-RX) returns data relating to a signal or several signals for setting and / or selecting one or more antennas of the multiple antenna device (ANT), so that based on this data Multiple antenna device (ANT) and interference suppression (ISU) can be set. Receiving system according to claim 1 or 2, characterized in that the interference suppression unit (ISU) has an FPGA logic or an ASIC. Reception system according to one of the preceding claims, characterized in that the receiver device (RX) mixes down an incoming signal into the baseband or to an intermediate frequency smaller than 100 MHz, preferably smaller than 20 MHz, in particular 15.42 MHz. Reception system according to one of the preceding claims 1 to 3, characterized in that the receiver device (RX) downmixes an incoming signal to an intermediate frequency of 15.42 MHz.

6. Receiving system according to one of the preceding claims, characterized in that the interference suppression unit (ISU) has a Hilbert filter.

7. Receiving system according to claim 6, characterized in that the Hilbert filter is provided as a forward, linear digital filter.

8. Receiving system according to one of the preceding claims, characterized in that the upconversion unit (TX) upconverts interference-suppressed signals to frequencies compatible with a conventional GNSS receiver.

9. Receiving system according to one of the preceding claims. , characterized in that an external processing unit (ECU) provides signal processing of control signals so that the individual units of the receiving system can exchange both configuration data and data to be configured.

10. Use of a receiving system according to one of the preceding claims for position determination, wherein the position can be determined precisely in a range of less than 1 dm.

11. Use of a receiving system according to one of the preceding claims 1 to 9 for position determination in agriculture.