Method for Providing Differential Code Bias (DCB) Corrections for Global Navigation Satellite Systems (GNSS)

Abstract

A method for providing differential code biases (DCBs), particularly a primary differential code bias (DCB1) and a secondary differential code bias (DCB2), in a Global Navigation Satellite System (GNSS) using a satellite (2) communicating by using at least a first signal (41) and an additional first signal (41'), both having a first carrier frequency (C1), and a second signal (42) and an additional second signal (42'), both having a second carrier frequency (C2), the method comprising determining a primary differential code bias (DCB1) for the first signal (41) and the second signal (42), and the primary differential code bias (DCB1) being used to determine, in particular to provide, a secondary differential code bias (DCB2) for the additional first signal (41') and the additional second signal (42').

Description

[Technical field]

[0001] The present invention relates to a method for providing differential code bias (DCB) correction, particularly primary and secondary differential code bias, for a global navigation satellite system (GNSS). [Background technology]

[0002] GNS systems are well known. Examples of GNS systems are GPS, GLONASS, BeiDou and Galileo. They provide functionality for determining the position of a static or mobile receiver, which can be integrated into many downstream market applications, such as geodesy or navigation systems and mobile phone receivers. DCBs are needed when processing signals or combinations of signals different from the clock reference signal. An integral part of a GNS system is the satellites that orbit the Earth and emit navigation signals. The navigation signals comprise several carrier signals, each with one or more ranging code modulations and, optionally, navigation data modulated onto the ranging codes.

[0003] DCB is the differential bias between two pseudorange signals on the same or different frequencies. Among the different origins of these biases are measurement instrument delays and imperfect signal synchronization in transmitting and receiving parts of the signal processing chain. DCB is evaluated based on empirical information collected by several reference stations consisting of reference receivers of the same or different types, all receiving the signals of the corresponding satellites. Reference stations provide the DCB estimator with pseudoranges and navigation messages, as well as other information. Proper knowledge of the biases is crucial for many navigation applications, but also for non-navigation applications, such as ionospheric analysis to extract the total electron content (TEC), and time transfer. DCB is required in particular for code-based positioning in GNSS receivers, as well as other applications.

[0004] Moreover, DCBs estimated for one signal combination cannot be transferred or applied to another signal combination, even on the same satellite. Rather, satellite- and receiver-dependent DCBs must be estimated for each signal combination of interest, because different components for signal generation and emission on board each satellite are affected by individual biases and synchronization errors that are also frequency- and signal-dependent. Similarly, different components in the receiver's signal processing chain are also affected by different frequency- and signal-dependent biases.

[0005] Furthermore, some signals are handled by reference stations and are not available to the public. Because the number of such reference stations is typically reduced compared to the number of reference stations available to the public, DCBs for signals assigned to non-public reference stations can only rely on a reduced amount of information to evaluate the corresponding DCBs.

[0006] In US Patent Application Publication No. 20170090038(A1), a correction data generating unit receives a value of an error used for satellite positioning at a first time interval, and receives a correction value of the error at a second time interval, which is a time interval that is 1 / n (n is an integer equal to or greater than 2) of the time interval of the first time interval. The correction data generating unit also corrects the value of the error at the second time interval by using the correction value.

[0007] US20160047917A1 relates to a method for generating receiver specific correction information for correcting pseudorange observations. The method includes receiving raw observations obtained by an NSS receiver observing multiple frequency signals from multiple NSS satellites over multiple epochs, obtaining precise satellite information with respect to (i) the orbital position of each of the satellites, (ii) the clock offset of each of the satellites, and (iii) a set of biases associated with each of the satellites, estimating a carrier phase ambiguity of the received raw observations using the precise satellite information or information derived therefrom, calculating a combination value based on the received raw observations together with the estimated ambiguity to offset geometric effects, as well as clock, troposphere, and ionosphere effects, and generating correction information for each satellite based on the calculated combination value. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 20170090038(A1) [Patent Document 2] US Patent Application Publication No. 20160047917(A1) [Patent Document 3] European Patent Application Publication No. 10194428(A2) [Patent Document 4] European Patent No. 2281210(B1) Summary of the Invention [Problem to be solved by the invention]

[0009] Starting from the prior art described above, it is the object of the present invention to realize a method that simplifies the steps of providing different code biases for signals that cannot be measured freely or when the number of reference stations is limited, in particular without reducing the reliability of the different code biases calculated or estimated for a number of signals emitted by a satellite. [Means for solving the problem]

[0010] This object is solved by a method for providing a differential code bias (DCB), in particular a primary differential code bias, in particular a primary differential code bias estimated with respect to measured GNSS signals, and a secondary differential code bias, in a Global Navigation Satellite System (GNSS) using satellites communicating by using at least a first signal, i.e. a first pilot channel signal and an additional first signal, both on the same first carrier frequency band or the same first carrier frequency, and a second signal, i.e. a second pilot channel signal and an additional second signal, both on the same second carrier frequency band or the same carrier frequency, wherein the primary differential code bias with respect to the first signal and the second signal is determined, in particular provided, for example for calculating a position, in particular a PPP position, of a receiver receiving the first signal and / or the second signal, and the primary differential code bias is used for determining a secondary differential code bias with respect to the additional first signal and the additional second signal, in particular used for providing the secondary differential code bias, for example for calculating a position of a receiver receiving the additional first signal and / or the additional second signal. 。

[0011] Contrary to the state of the art, according to the present invention, by using a first order differential code bias for the first signal and the second signal, , additional In one embodiment, a method is provided for determining a secondary differential code bias for the additional first signal and the additional second signal. As a result, it is advantageously possible to avoid calculating or evaluating the secondary differential code bias in a separate manner. Rather, the primary differential code bias is used to determine the secondary differential code bias. In particular, the present invention takes advantage of using a primary differential code bias that is based on the same carrier frequency as the secondary differential code bias. 。

[0012] Those skilled in the art know that preferably, besides the first signal and the first additional signal, there may be another additional first signal on the first frequency or the first frequency band, and besides the second signal and the second additional signal, there may be another additional second signal on the second frequency band of the second frequency band, and can determine the step of providing another secondary differential code bias by using the primary differential code and / or the secondary differential code, as described in detail with respect to the step of determining the secondary differential code. As a result, the method can be applied to the first and second carrier frequency bands and similarly behaving additional signals apart from their modulated channels.

[0013] Preferably, a global navigation satellite system is used to determine the position of a receiver, in particular the position of a mobile receiver such as a mobile phone or a vehicle. To that end, navigation signals emitted by satellites of the GNSS are used to measure pseudo-ranges, which are then used to determine the position of the receiver. Preferably, navigation signals of at least four satellites are used to estimate the position. In particular, a primary differential code bias and / or a secondary differential code bias is provided to the receiver for use in determining the exact position of the receiver, in particular for use in correcting the pseudo-ranges or a combination thereof. Moreover, the navigation signals comprise in particular a first signal, an additional first signal, a second signal, an additional second signal and / or a third signal having a constant carrier frequency. In particular, having a first carrier frequency or having a second carrier frequency means that the components of the first signal or the additional first signal on the one hand, or the components of the second signal or the additional second signal on the other hand, use the same carrier frequency. Thereby, the frequency bands or intervals allocated to the first carrier frequency and the second carrier frequency are spectrally separated from each other. Preferably, the differential code bias is related to a systematic error between two GNSS code observations of different carrier frequencies. Such a differential code bias is taken into account, for example, to remove such systematic errors from the code observations. Preferably, such a differential code bias is evaluated on information collected together by a number of reference stations. As a result, it is possible to estimate, for example, the time evolution of the differential code bias. Preferably, the differential code bias is empirically determined. To determine and / or provide the primary and / or secondary differential code bias, a calculation unit is used, which includes a microprocessor, in particular configured to perform at least one of the method steps according to the invention. Preferably, the primary differential code bias is provided via both a separate terrestrial and a separate satellite-based data channel. The DCB is preferably applied to provide clock correction data for the frequency combination applied by the end user.Moreover, it is preferably provided that the first signal and / or the second signal are not encrypted. In particular, the second differential code bias is provided for a non-public channel. In particular, a method is provided for estimating, shifting and providing a corrected differential code bias.

[0014] Preferably, the primary differential code bias is transferred to a secondary differential code bias. In other words, the correction of the additional first signal and the additional second signal by the secondary differential code bias is based mostly on the primary differential code bias without any further complicated calculation and / or transformation. In other words, the secondary differential code bias is assumed to be mostly consistent with the primary differential code bias, including the assumption that some additional offset may be used.

[0015] Moreover, those skilled in the art will understand in detail to approximate the term determining. Moreover, it is provided that the primary differential code relates to a relationship between the first signal and the second signal, respectively, to a common signal, and that the secondary differential code relates to a relationship between the first additional signal and the first signal, and / or between the second signal and the additional second signal.

[0016] In particular, it is provided that the common signal is used to approximate both the primary code bias and the secondary differential code bias. In particular, it is provided that the primary differential code bias is determined for the first signal and the second signal, respectively, and is provided to approximate the DCB of the additional first signal and the second additional signal in particular. As a result, the accuracy for determining the position based on the additional first signal and the additional second signal is at least comparable to or equal to the accuracy for determining the position based on the first signal and the second signal, in the example, since PPP requires the DCB to correct for, for example, clock corrections.

[0017] In particular, it is provided to determine at least two primary differential code biases, namely DCB1 (first signal-common signal) and DCB1 (second signal-common signal), using a common signal. In addition to DCB1 (first signal-common signal) and DCB1 (second signal-common signal), it is possible to determine / approximate another primary differential code bias DCB1 (first additional signal-common signal) and DCB1 (second additional signal-common signal). As a result, in the first stage, in particular by using at least five signals, four independent primary differential code biases DCB1 are provided.

[0018] Moreover, it is provided that the secondary differential code biases represent the differential code bias between the first signal and the further first signal and the differential code bias between the second signal and the further second signal, respectively. In particular, it is provided that two independent secondary differential code biases DCB2 are provided based on the four independent primary differential code biases DCB1. Knowing the second differential code bias, it is possible to apply to the further first signal and the further second signal a reduced amount of information, e.g. information required to perform PPP, is otherwise available to approximate the first and second additional signals, but the amount of information available and the reliability of the data with respect to the first and second signals.

[0019] For more details, DCB2(first signal-additional first signal)=DCB1(first signal-common signal)-DCB1(first additional signal-common signal) DCB2 (second signal - additional second signal) = DCB1 (second signal - common signal) - DCB1 (second additional signal - common signal) It is provided to transform the second difference code by:

[0020] To this end, the first signal and the additional first signal are tracked by the first receiver, the second signal and the additional signal are tracked by the second receiver, and the common signal is tracked by the first receiver and the second receiver. As a result, it is possible to provide the second receiver with highly accurate data that is well protected, even though the information about the differential code bias of the additional first signal and the additional second signal is limited, for example because the number of reference stations used to provide the data for calculating the required information is limited. As a result, it is also possible to provide sub-nanosecond and sub-decimeter resolution when determining the position of the second receiver that has access to the additional first signal and the additional second signal for which only a reduced amount of information is otherwise available.

[0021] Preferably, the first receiver and the second receiver are different types of receivers. In particular, the first receiver and the second receiver have different capabilities to observe and / or analyze distinctive signals. In other words, the first receiver can observe and / or analyze the first signal and the second signal, but cannot observe and / or analyze the additional first signal and the additional second signal. At the same time, the second receiver can observe and / or analyze the additional first signal and the additional second signal, while it cannot observe and / or analyze the first signal and the second signal. To establish the difference between the first receiver and the second receiver, the first receiver and the second receiver are distinguished from each other by hardware and / or software, such as a correlator implementation. In particular, the first receiver and the second receiver have different PRS authentication.

[0022] In a preferred embodiment of the invention, the second signal and / or the additional second signal comprise correction information for precise point positioning. Precise point positioning (PPP) methods have been developed to improve positioning accuracy without relying on a dense network of reference stations in the vicinity of the mobile receiver. In contrast to DGPS or RTK, the PPP approach does not rely on spatial error correlation of differential measurements, but rather removes individual error components caused by, for example, satellite orbits or clocks, biases, and atmospheric delays through accurate models in calculating the position relative to the mobile receiver. As a result, it is possible to calculate an accurate position to a decimeter or even less using dual-frequency measurements. Providing accurate correction information, in particular accurate orbit and clock correction information, is essential to achieve such accuracy. For this reason, navigation information for the "first or public" service is required as well as navigation information for the "additional or non-public" service to be corrected. Furthermore, PPP allows the position of the mobile receiver to be accurately determined even in areas without a dense network of reference stations. Examples for implementing a PPP approach can be found in EP 1 094 428 A2 and EP 2 281 210 B1, the contents of which relating to PPP are expressly incorporated herein by reference.

[0023] In a different preferred embodiment, it is provided that the additional first signal is available only to a subgroup of users. In particular, the additional first signal and / or the additional second signal contain information that is not required by the majority of users. For example, the additional first signal and the additional second signal are provided only to authorize users who can access the additional first signal and the additional second signal. For example, the additional first signal and / or the additional second signal are encrypted to make the information encoded in the additional first signal and / or the additional second signal available only to a certain subgroup of users. In particular, the additional first signal and the additional second signal are handled by a reference station, whereas the first signal and the second signal are handled by a different reference station that handles only the first signal and the second signal and / or the third signal, but not the additional first signal and / or the additional second signal. Since the number of reference stations handling the additional first signal and / or the additional second signal is reduced compared to the reference stations handling the first signal, the second signal, and the third signal, the step of calculating the secondary DCB depends only on the reduced number of information of the reference stations. Thus, by using or determining the secondary differential code bias by using the first differential code bias, the reliability of the secondary differential code bias for the additional first signal and the additional second signal is improved.

[0024] In particular, the determination of the corrections used for the positioning depends on the information assigned to the first signal and / or the second signal provided to the first receiver, in order to increase the accuracy of positioning the members of the sub-group, the members of the sub-group being represented by the second receiver.

[0025] Preferably, the first signal and the third signal having a third frequency are used for the two-frequency measurement. By using the two-frequency measurement, it is possible to determine the influence of the ionosphere. In particular, it was known by those skilled in the art to use the first signal and the third signal, which are used for the two-frequency measurement anyway, to calculate the differential code bias. However, since the additional second frequency does not have a third carrier frequency, the third-order differential code bias cannot be used to determine the second-order differential code bias.

[0026] Preferably, the first and / or second differential code biases are used to correct the ephemeris and / or are typically transmitted as part of satellite correction messages. DCB information obtained from these messages can then be used to use different signals or signal combinations as the clock reference signal.

[0027] Preferably, the primary differential code bias is determined from information encoded on the first and second signals, in particular by using pseudorange observations, so that it is possible to calculate and / or estimate the primary differential code bias which is subsequently used to determine the secondary differential code bias.

[0028] In particular, a time estimate of the primary differential code bias and / or the secondary differential code bias is determined. For example, the primary differential code bias, and thus the secondary differential code bias, may be estimated or estimated based on past recorded observations leading up to the correction period. Taking into account the past time estimates, it is possible to estimate the time estimate of the primary differential code bias, and thus the secondary differential code bias.

[0029] Preferably, the primary and / or secondary differential code biases are provided in near real time, in particular by using a time estimation or a time scale of the primary differential code bias, it is possible to provide the primary or secondary differential code biases, so that the primary and secondary differential code biases can be used, for example, to estimate the position of the receiver in real time.

[0030] Preferably, the method further comprises the steps of receiving raw data from the satellites at a number of reference stations, transferring the raw data received at the reference stations in a real-time data stream to a central computing unit, in particular to a single central computing unit, determining correction information at the computing unit based on the raw data received from the different reference stations, and transmitting the correction information to the receiver via at least one satellite or terrestrial link in order to determine the position of the mobile receiver. In particular, it is provided that the central computing unit collects all the raw data and determines the correction information, in particular the combined orbit error, clock offset, signal bias and additional correction information, after which the correction information message is transmitted to the mobile receiver implementing the means of authentication via at least one GNS (global navigation satellite), preferably via each GNS providing raw data to a certain mobile receiver. As a result, it is possible to take into account the raw data of a number of reference stations in order to determine the correction information for establishing the desired accuracy in one central computing unit. Furthermore, the invention allows a centralized distribution of correction information. As a result, no communication between different distribution centers is necessary. Another advantage of using a GNS to broadcast correction information is the possibility of using the infrastructure already available from existing satellites, without any additional terrestrial or satellite-borne transmitters being required.

[0031] Another aspect of the invention is a plurality of reference stations and a central computing unit, particularly a single central computing unit, configured to provide differential code biases, particularly a primary differential code bias and a secondary differential code bias, in a global navigation satellite system using satellites communicating by using at least a first signal and an additional first signal, both having a first carrier frequency, and a second signal and an additional second signal, both having a second carrier frequency, where a primary differential code bias for the first signal and the second signal is determined by the central computing unit, and the primary differential code bias is used to determine and provide, particularly a secondary differential code bias between the additional first signal and the additional second signal. Features and advantages described in relation to the method for providing differential code bias apply equally to the plurality of reference stations and the central computing unit, and vice versa.

[0032] Preferably, the central computing is configured to receive raw data from the satellites at said multiple reference stations, transfer the raw data received at the reference stations to said central computing unit, in particular to said single central computing unit, using a data stream, in particular a common data stream, determine correction information in the computing unit based on the raw data provided by the different reference stations, and transmit the correction information to the receiver via at least one satellite and / or terrestrial communication means or determine the position of the mobile receiver.

[0033] In particular, the plurality of reference stations includes a reference station handling an additional first signal and / or an additional second signal.

[0034] Another aspect of the invention is a software product and / or a network, the software product and / or the network comprising program code for implementing one of the methods according to the invention.

[0035] The features and benefits described in relation to the method for providing differential code bias apply equally to software products and / or networks, and vice versa.

[0036] Whenever not explicitly stated above, individual embodiments, or individual aspects and features of individual embodiments, can be so combined or exchanged with one another, whenever such combination or exchange makes sense from the perspective of the invention, without limiting or expanding the scope of the invention described. Advantages described with respect to one embodiment of the invention are also advantages of other embodiments of the invention, whenever applicable. [Brief description of the drawings]

[0037] [Figure 1] FIG. 2 is a schematic diagram illustrating a first portion of a method for providing differential code bias correction according to a first preferred embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic diagram illustrating a second portion of a method for providing a differential code bias according to a first preferred embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram illustrating the transmission of correction information from a central computing unit to a mobile receiver via at least one satellite. [Figure 4] FIG. 1 shows a satellite emitting a navigation signal for a method according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] In Fig. 1, a method for determining the position of a mobile receiver 5 by using a global navigation satellite system (GNS system) is illustrated. The global navigation satellite system comprises a satellite 2 orbiting the Earth 14 and emitting navigation signals 4 modulated at several carrier frequencies. A mobile receiver 5, such as a mobile navigation system that may be integrated into a mobile unit and / or a vehicle, receives the navigation signals 4 via an antenna 6. The received navigation signals 4 comprise raw data for determining the position, in particular the actual position, of the mobile receiver 5. The antenna 6 is connected to a bandpass filter and low noise amplifier 7 that amplifies the received navigation signals 4. A bandpass filter and low noise amplifier 7 and a subsequent downconverter 8 connected to a reference oscillator 9 convert the received navigation signal 4 to a lower frequency using an oscillation signal obtained from the reference oscillator 9. The downconverted navigation signal passes through a bandpass and sampling unit 10, which samples the analog navigation signal 4. The sampled navigation signal 4 is then passed to a tracking unit 11, which tracks the navigation signal 4, in particular the phase of the carrier signal and / or the delay of the code signal contained in the navigation signal 4. The tracking unit 11 is followed by a bias subtraction unit 12, which subtracts the phase and / or the code bias from the phase of the carrier signal and from the code signal. A subsequent position estimation unit 13 determines the actual position of the navigation device 5 based on the phase signal obtained by processing the carrier signal and based on the code signal. Finally, the position estimation result can be displayed on a monitoring device 14.

[0039] The mobile receiver 5 uses the received GNS signals 4 to generate pseudorange and carrier phase measurements and decodes navigation data encompassing coarse satellite positions, clock offsets, and signal biases. Additionally, the mobile receiver 5 decodes correction data information 20 distributed from a subset of the tracked satellites 2 for a subset of the GNS signals 4. The precise correction data is then used in combination with the coarse navigation data to accurately model the pseudorange and carrier phase measurements and possibly correct for atmospheric delays. The accurately modeled observations enable the mobile receiver to use PPP to compute an accurate estimate of its position, specifically its actual position.

[0040] 2 illustrates reference stations 15. These reference stations 15 are distributed around the Earth 14 and receive the navigation signals 4 by their antennas 6. The reference stations 15 generate observable raw data that is used to determine correction information 20 by using the fact that a large number of reference stations receive navigation signals from GNS satellites as well as the fact that their positions are known. Furthermore, the reference stations can be used to determine and / or estimate DCBs for the first and second signals, and in particular to determine and / or estimate time evaluations of the DCBs. Differential Code Bias (DCB) is the systematic error or bias between two GNSS code observations at the same or different frequencies. DCB is evaluated based on empirical information collected by several reference stations receiving the signals of the corresponding satellites. A good knowledge of DCB is crucial for many navigation applications, but also for non-navigation applications, such as ionospheric analysis, e.g., for extracting the ionospheric total electron content (TEC), and for time transfer. DCB is specifically required for code-based positioning and other applications of GNSS receivers.

[0041] In contrast to Real Time Kinematic (RTK) solutions, which require local base stations and links to mobile receivers several kilometers away to distribute correction data, Precise Point Positioning (PPP) techniques perform code-based positioning tasks globally, and therefore without local base stations and direct radio links to mobile receivers. In this case, correction information 20, which takes into account corrections for satellite orbits and clocks, offset errors, ionospheric delays, tropospheric delays, code biases, and / or phase biases, is transmitted via satellites 2 to mobile receivers 5.

[0042] To determine the correction information 20, provision is made for receiving raw data of a set of several satellites 2 by at least one reference station 15. Furthermore, there are additional reference stations 15 which receive raw data from another set of satellites 2 or from the same set of satellites 2. Moreover, provision is made for transferring the received raw data, preferably in the form of a data stream 18, to a central computing unit 30. In particular, the raw data contained in the data stream 18 are respectively assigned to certain reference stations 15.

[0043] Preferably, the raw data assigned to the corresponding reference station 15 is transferred together with other raw data obtained from the different reference stations 15 in a data stream 18, in particular in a common data stream, to a central computing unit 30. The central computing unit 30 in particular comprises a processor configured to determine correction information 20 for each satellite 2 individually.

[0044] As illustrated in Fig. 3, the determined, in particular calculated and authenticated, correction information 20 is transmitted from a central computing unit 30 to the mobile receiver 5 via at least one satellite 2. For example, the correction information is transmitted in an uplink at an uplink station 21 such that a correction signal 22 containing the correction information 20 is transmitted to the mobile receiver 5 via at least one satellite 2. Preferably, several satellites 2, in particular all satellites 2 available to the mobile receiver 5, provide the corresponding correction information 20 to the mobile receiver 5.

[0045] 4 shows a satellite 2 emitting a navigation signal 4 for a method according to a preferred embodiment of the present invention. The term "navigation signal 4" is used here as a general term for a signal being emitted by the satellite 2 for communication with a mobile receiver 5 and / or a reference station 15. In detail, the navigation signal 4 comprises at least a first signal 41 having a first carrier frequency C1 and a second signal 42 having a second carrier frequency C2. Moreover, the navigation signal 4 includes a third signal 43 having a third carrier frequency C3. In Galileo GNSS, the first carrier frequency C1, the second carrier frequency C2, and the third carrier frequency C3 are represented by frequency bands E1, E6, and E5, respectively. The first signal 41, the second signal 42, and / or the third signal 43 contain certain information by modulating the signals 41, 42, 43 with the corresponding carrier frequencies. In particular, the first signal 41 and the third signal 43 are used to perform a two-frequency method to eliminate or reduce effects such as those caused by the ionosphere, which otherwise result in a corresponding time delay with respect to the travel time of the signals 41, 42, and 43. In particular, it is provided to determine another third differential code bias DCB3 for the first signal 41 and the third signal 43.

[0046] Moreover, the second signal 42 includes the correction information 20 used for precise point positioning PPP. In other words, the second signal 42 mainly corresponds to the correction signal 22 presented or illustrated in the picture 3. It is also known that besides the first signal 41, the second signal 42 and the third signal 43, the navigation signal 4 can comprise an additional first signal 41' having a first carrier frequency C1 and an additional second signal 42' having a second carrier frequency C2. In detail, it is provided that the first signal 41 as well as the additional first signal 41' use the same carrier frequency C1, whereas the second signal 42 and the additional second signal 42' use the second carrier frequency C2. It will be clear to a person skilled in the art that the carrier frequency C1, the second carrier frequency C2 and the third carrier frequency C3 represent frequency intervals, such that using the same first carrier frequency C1 means that the first signal 41 and / or the additional first signal 41' use frequencies in the same frequency band.

[0047] The same is true with respect to the second signal 42 and the additional second signal 42' in the second carrier frequency interval or band. The additional first signal 41' and the additional second signal 42' may not be used by the majority of users, i.e. mobile receivers 5. For example, the additional first signal 41' and / or the additional second signal 42' contain information that was not needed during normal operation. For example, the receiver 5 cannot access the additional first signal 41' and / or the additional second signal 42'. For example, the additional first signal 41' and / or the additional second signal 42' are encrypted, so that the receiver 5 cannot access or has limited access to the additional first signal 41' and / or the additional second signal 42'. The additional first signal 41' and / or the additional second signal 42' are in particular handled by a reference station 15' different from the reference station 15 handling only the first signal 41 and the second signal 42 and / or the third signal 43. Thereby, the number of reference stations 15 handling the first signal 41, the second signal 42 and / or the third signal 43 is significantly greater than the number of reference stations 15' handling the additional first signal 41' and / or the additional second signal 42'. Preferably, the additional second signal 42' comprises correction information 20 used for precise point positioning PPP.

[0048] To take into account the secondary differential code bias DCB2 between the additional first signal 41' and the additional second signal 42', state of the art GNSS has to rely on reference stations 15' handling the additional first signal 41' and the additional second signal 42'. As the secondary code bias DCB2 is based on a reduced number of reference stations 15' handling the additional first signal 41' and the additional second signal 42', calculating or determining the secondary differential code bias DCB2 not only results in additional computational effort but also in differential code biases that may be less reliable.

[0049] In order to reduce the effort of calculating the secondary differential code bias DCB2 and to improve the reliability of the secondary differential code bias DCB2, it is provided to determine a first differential code bias DCB1 between the first signal 41 and the second signal 42. The primary differential code bias DCB1 can then be used to determine the secondary differential code bias DCB2, in particular by transferring the primary differential code bias DCB1 to the secondary differential code bias DCB2. This process has the advantage that the primary differential code bias DCB1 is transferred to the secondary differential code bias DCB2, and the first differential code bias DCB1 and the secondary differential code bias DCB2 are evaluated based on the same carrier frequency. [Explanation of symbols]

[0050] 2 satellites 4. Navigation Signals 5 Mobile receiver 6 Antennas 7 Bandpass filters and low noise amplifiers 8 Down Converter 9 Reference Oscillator 10 Bandpass and Sampling Units 11 Pursuit Knit 12 Subtraction Unit 13 Estimated Units 14 Earth 15, 15' reference station 18 Data Stream 20 Correction Information 21 Uplink Station 22 Correction Signal 30 Central Computing Unit 35 Reference Value 41 First Signal 41' Additional 1st signal 42 Second Signal 42' Additional second signal 43 Third Signal C1 First carrier frequency C2 Second carrier frequency C3 Third carrier frequency DCB1 Primary Differential Code Bias DCB2 Secondary Differential Code Bias DCB3 Third-Order Differential Code Bias

Claims

1. 1. A method for providing differential code bias (DCB) in a global navigation satellite system (GNSS) using a satellite (2) in communication using at least a first signal (41) and another first signal (41'), both on a first carrier frequency (C1), a second signal (42) and another second signal (42'), both on a second carrier frequency (C2), and a common signal tracked by both a first mobile receiver and a second mobile receiver, the method comprising: determining a primary differential code bias (DCB1) of said differential code biases (DCBs) for said first signal (41) and said second signal (42); said primary differential code bias (DCB1) being used to determine a secondary differential code bias (DCB2) of said differential code biases (DCB) for said further first signal (41') and said further second signal (42'); The primary differential code bias (DCB1) is related to the relationship of the first signal (41) to the common signal and the relationship of the second signal (42) to the common signal, The secondary differential code bias (DCB2) relates to the further first signal (41′) and the first signal (41), The primary differential code bias (DCB1) is are determined for the first signal (41) and for the second signal (42), provided for determining the secondary differential code bias (DCB2) for the further first signal (41') and the further second signal (42') using another primary differential code bias (DCB1) for the relationship of the further first signal (41') to the common signal and for the relationship of the further second signal (42') to the common signal; the primary differential code bias (DCB1) and the secondary differential code bias (DCB2) are provided to a second mobile receiver for use in determining a fine position of the second mobile receiver; the first signal (41) and the further first signal (41') are tracked by the first mobile receiver, the second signal (42) and the further second signal (42') are tracked by the second mobile receiver, and the common signal is tracked by the first mobile receiver and the second mobile receiver; the second signal (42) and / or the further second signal (42') comprises correction information (20) relating to satellite orbits and clock corrections for positioning based on the PPP (Precise Point Positioning) method, method.

2. 2. The method of claim 1, wherein the common signal is used to approximate both the primary differential code bias (DCB1) and the secondary differential code bias (DCB2).

3. 3. The method of claim 2, wherein the primary differential code bias (DCB1) and / or the secondary differential code bias (DCB2) are used to correct an ephemeris and / or are transmitted as part of a satellite correction message.

4. The method according to any one of claims 1 to 3, characterized in that the first signal (41) and a third signal (43) having a third frequency (C3) are used for a two-frequency measurement.

5. 5. The method according to claim 1, further comprising using information encoded in the first signal (41) and the second signal (42) to determine the primary differential code bias (DCB1).

6. Method according to any one of claims 1 to 5, characterized in that the time evolution of the primary differential code bias (41) and / or the secondary differential code bias (42) is estimated.

7. The method according to any one of claims 1 to 6, characterized in that the primary differential code bias (DCB1) and / or the secondary differential code bias (DCB2) are provided in near real time.

8. The method according to any one of claims 1 to 7, further comprising the steps of receiving raw data from satellites (2) at a plurality of reference stations (15), transferring the raw data received at the reference stations (15) in a real-time data stream to a central computing unit (30), in particular to a single central computing unit, determining the correction information (20) in the central computing unit (30) based on the raw data received from the different reference stations (15), and transmitting the correction information (20) to the second mobile receiver (5) via at least one of the satellites (2) in order to determine the position of the second mobile receiver (5).

9. 1. A system including a central computing unit (30) and a plurality of reference stations (15, 15') relaying between the central computing unit (30) and a satellite (2), the central computing unit (30) being configured to provide a Differential Code Bias (DCB) in a Global Navigation Satellite System (GNSS) using the satellite (2) in communication with the central computing unit (30) by using at least a first signal (41) and another first signal (41'), both having a first carrier frequency (C1), a second signal (42) and another second signal (42'), both having a second carrier frequency (C2), and a common signal tracked by both a first mobile receiver and a second mobile receiver, a primary differential code bias (DCB1) of said differential code biases (DCB) for said first signal (41) and for said second signal (42) is determined by said central computing unit, said primary differential code bias (DCB1) being used to determine a secondary differential code bias (DCB2) of said differential code biases (DCB) for said further first signal (41') and for said further second signal (42'); The primary differential code bias (DCB1) is related to the relationship of the first signal (41) to a common signal and the relationship of the second signal (42) to the common signal, The secondary differential code bias (DCB2) relates to the further first signal (41′) and the first signal (41), The primary differential code bias (DCB1) is are determined for the first signal (41) and for the second signal (42), provided for determining the secondary differential code bias (DCB2) for the further first signal (41') and the further second signal (42') using another primary differential code bias (DCB1) for the relationship of the further first signal (41') to the common signal and for the relationship of the further second signal (42') to the common signal; the primary differential code bias (DCB1) and the secondary differential code bias (DCB2) are provided to a second mobile receiver for use in determining a fine position of the second mobile receiver; the first signal (41) and the further first signal (41') are tracked by the first mobile receiver, the second signal (42) and the further second signal (42') are tracked by the second mobile receiver, and the common signal is tracked by the first mobile receiver and the second mobile receiver; the second signal (42) and / or the further second signal (42') comprises correction information (20) relating to satellite orbits and clock corrections for positioning based on the PPP (Precise Point Positioning) method, system.

10. 10. The system according to claim 9, further configured to receive raw data from satellites (2) at said plurality of reference stations (15), transfer said raw data received at said reference stations (15) to said central computing unit (30), in particular to a single central computing unit, using a data stream (18), determine correction information (20) in said central computing unit (30) based on the raw data provided by the different reference stations (15), and transmit said correction information (20) to said second mobile receiver (5) via at least one of said satellites (2) and / or terrestrial communication means in order to determine the position of said second mobile receiver (5).

11. The system according to claim 10, comprising a reference station (15') handling said further first signal (41) and / or said further second signal (42').

12. A program for causing a computer to execute the method according to any one of claims 1 to 8.

Images