Method for monitoring code-tracking loops of a GNSS signal receiver

Abstract

The invention relates to a method for monitoring a code-tracking loop (1) of a GNSS signal receiver (11) in order to detect erroneous jumps of the code-tracking loop from a main peak (8) to a side peak (9), comprising the following steps: a) tracking a first received GNSS signal (2) from a GNSS satellite on a first frequency band and determining a first signal increment of the first received GNSS signal (2); b) tracking a second received GNSS signal (2) from the same GNSS satellite on a second frequency band and determining a second signal increment of the second received GNSS signal (2); and c) comparing the first signal increment and the second signal increment in order to determine the jump from a main peak (8) to a side peak (9) if unexpected deviations between the first signal increment and the second signal increment have been ascertained.

Description

[0001] Description

[0002] title

[0003] Method for monitoring code-tracking loops of a GNSS signal receiver

[0004] State of the art

[0005] Disclosure of the invention

[0006] Modern GNSS receivers can work with various GNSS satellite systems, such as Galileo, GLONASS, or BeiDou. More complex GNSS receivers can also process signals in different frequency ranges. For example, common GNSS receivers can receive GNSS signals in both the E1 and E5 bands.

[0007] Receiving a GNSS signal from a GNSS satellite by a GNSS receiver involves determining the signal's travel time from the satellite to the receiver. This is done by comparing, or correlating, the received GNSS signal with a replicated signal generated internally within the receiver. The received signal and the internal replicated signal are synchronized. This allows the precise travel time of the received signal to be determined. In other words, by comparing the replicated signal with the received signal, the exact time at which a specific portion of the received signal arrives at the GNSS receiver is determined.

[0008] Synchronization of the replicated and received signals is typically achieved by maximizing a correlation function. The replicated signal is shifted by various time intervals, and the correlation function is calculated for different shifted versions of the replicated signal. The time-shifted version of the replicated signal whose correlation function yields the highest values ​​with the received signal represents the maximized autocorrelation function. This time-shifted version of the replicated signal best describes the received signal. The corresponding time shift can be used to determine the precise reception time, or the exact travel time of the received signal from the GNSS satellite to the GNSS receiver.The determined time shift is normally used as an input signal for a control loop, which then establishes the synchronization, and then the exact runtime can be determined with the correctly synchronized signal.

[0009] The reception and monitoring of received GNSS signals typically takes place continuously over an extended period in a GNSS receiver. The GNSS signals are tracked by the GNSS receiver. For each received GNSS signal, the signal's propagation time, and thus its path from the GNSS satellite to the receiver, is continuously monitored. This tracking involves regularly adjusting the replicated GNSS signals and comparing them with the received signals to determine the correlation function and thus the precise reception time and propagation time of the received GNSS signal.In a simple approach, two or three different time-shifted versions of the replicated signal are compared with the received GNSS signal using a correlation function, with each time shift determined based on the last recorded reception time. In commonly used GNSS receivers, however, significantly more complex algorithms are employed to determine reception times through correlation. For example, Fourier transforms can be used, which, in a common approach, compare several hundred time-shifted versions of the replicated signal with the received GNSS signal. The time-shifted replicated signal that best replicates the received GNSS signal, or yields the highest values ​​in the correlation function with the received GNSS signal, is used to determine the current reception time.The comparison of the replicated GNSS signals with the received GNSS signal thus functions in a loop. This loop is also known as a "code tracking loop." Each determination of a time shift or a reception time can also be referred to as an "epoch."

[0010] Comparing GNSS signals from the older GPS L1 system with those from Galileo (BOC), it becomes clear that the newer Galileo (BOC) signals are significantly more complex. While GPS L1 GNSS signals exhibit only a single maximum, Galileo (BOC) GNSS signals regularly display local minima in addition to the maximum, both before and after it. The maximum is often referred to as the "main peak," while the adjacent local minima are called "side peaks." These side peaks sharpen the definition of the main peak, resulting in a generally higher level of signal precision.

[0011] On the other hand, there is a risk that when comparing the received signal with the replicated signals, side peaks may be confused with the main peak, thus causing errors in determining the time of reception of the received GNSS signal.

[0012] Starting from this, the object of the present invention is to at least partially solve the problems described with reference to the prior art and in particular to present a method for monitoring a code-tracking loop with which unwanted and unexpected jumps in the GNSS signal can be detected, which may indicate a jump from a main peak to a side peak.

[0013] These problems are solved with an inspection device and a method according to the features of the independent claims. Further advantageous embodiments are specified in the dependent claims, as well as in the description and, in particular, in the description of the figures. It should be noted that a person skilled in the art can combine individual features in a technologically meaningful way and thereby arrive at further embodiments of the invention. Disclosure of the invention

[0014] This document describes a method for monitoring a code-tracking loop of a GNSS signal receiver in order to detect erroneous jumps of the code-tracking loop from a main peak to a side peak, comprising the following steps: a) tracking a first received GNSS signal from a GNSS satellite on a first frequency band and determining a first signal increment of the first received GNSS signal; b) tracking a second received GNSS signal from the same GNSS satellite on a second frequency band and determining a second signal increment of the second received GNSS signal; and c) comparing the first signal increment and the second signal increment to determine the jump from a main peak to a side peak if unexpected deviations between the first and second signal increments are detected.

[0015] The invention discussed here makes it possible to detect cases in which a side peak is mistakenly tracked instead of the main peak.

[0016] If a side peak is mistakenly tracked instead of the main peak, this leads to a systematic offset error in the travel time measurement and distance determination from the GNSS satellite to the GNSS signal receiver. This results in incorrect position determinations. Particularly in safety-critical applications (e.g., highly automated and / or even autonomous driving), this can lead to significant hazards.

[0017] The probability of a side peak being falsely tracked depends on the configuration of the so-called tracking loop. The tracking loop describes the configuration used to generate the various replicated signals for correlation and how the last recorded time of reception of the received signal is used. As described above, different numbers of shifted replicated signals can be generated and compared with the received signal. Many considerations and approaches exist for designing the tracking loop. Here, it is proposed to determine whether a side peak is being falsely observed by observing the tracking loop and its behavior. This is a different approach than trying to detect a false identification of a side peak as a main peak through the design of the tracking loop itself.It is not necessary to look inside the tracking loop when carrying out the procedure described here.

[0018] A prerequisite for using the method described here is that the GNSS signal receiver is fundamentally capable of receiving at least two different frequencies for a GNSS constellation. GNSS signal receivers for Galileo that are capable of receiving GNSS signals on the El band and the E5 band are generally suitable for carrying out the method described here. The same applies to GNSS signal receivers that can receive other signals on different frequencies.

[0019] When tracking GNSS signals from GNSS satellites on two different frequencies (where a single satellite transmits separate signals on different frequencies), it is possible to compare the tracked GNSS signals. Essentially, the tracked GNSS signals represent the distance from the GNSS signal receiver to the GNSS satellite. However, GNSS signals received on different frequencies cannot be directly compared because they contain different error terms.

[0020] The approach proposed here is to compare the differences or increments of the signals determined by tracking from epoch to epoch, and thus to identify unexpected deviations through differences of differences or differences of increments that indicate the change from a main peak to a side peak.

[0021] First, a measurement of the distance and / or signal propagation time of a GNSS signal received on a first frequency is compared to the distance and / or signal propagation time measured in the previous epoch based on this GNSS signal. In the following equation, the distance and / or signal propagation time determined using a signal on the E1 band is denoted as E1. E1(t) is the signal propagation time or distance determined for the current epoch. E1(t-1) is the signal propagation time or distance determined for the previous epoch. ΔE1 denotes the difference or increment between these two signal propagation times and / or distances.

[0022] E1 (t) - E1 (t-1) = deltaEI (1)

[0023] The same process is now applied to the measurement of the distance and / or signal propagation time of a GNSS signal received on the second frequency, but from the same GNSS satellite as the first GNSS signal. This is exemplified by the following equation for distances and / or signal propagation times determined on the E5 band. Here, E5a denotes the distance and / or signal propagation time. E5a(t) denotes the determined distance or signal propagation time for the current epoch. E5a(t-1) denotes the determined distance or signal propagation time for the previous epoch. ΔE0a denotes the difference or increment between these two signal propagation times and / or distances.

[0024] E5a(t) - E5a(t-1) = deltaEöa (2)

[0025] By comparing the signal increments deltaEI and delta E5a, it is possible in many cases to detect a jump from a main peak to a side peak.

[0026] Particularly advantageous is the additional comparison of the first received GNSS signal and the second received GNSS signal in order to detect unexpected deviations between the first received GNSS signal and the second received GNSS signal and to use this comparison to determine a jump from a main peak to a side peak.

[0027] This allows us to determine a delta between the two signal propagation times and / or distances, which were determined for the first received GNSS signal at the first frequency and for the second received GNSS signal at the second frequency. This is done, for example, according to the following equation: E1(t) - E5a(t) = delta E1 E5a (3)

[0028] Jumps that occur only in one of the two received GNSS signals can be detected using delteEI E5a and indicate that a side-peak was jumped when determining the time of reception from one of the two received GNSS signals.

[0029] The described method for detecting a false jump to a side peak can only detect such jumps if at least two different signals (at different frequencies) for a specific GNSS satellite are observed over a period of time. For example, the method can identify situations where a jump in the deltaEI value occurs, while no corresponding jump in the delta E5a value occurs. The magnitude of the jump resulting from the switch to a side peak will be on the order of the distance between a side peak and its corresponding main peak. This distance is shown, for example, in Fig. 1 and is approximately 0.5 chips. Comparing deltaEI and deltaE5a is necessary to detect jumps because, for example,Changes in distances and travel times caused by drifts, satellite movements or movements of the GNSS receiver can be of a similar order of magnitude to jumps occurring due to an unintentional switch from a main peak to a side peak.

[0030] The additional consideration of deltaEI E5a can further increase the robustness of the described method. Jumps in deltaEI E5a(t) compared to deltaEI E5a(t-1) also indicate an erroneous transition to a side peak.

[0031] The described method allows for the reliable detection of jumps from a main peak of a signal to a side peak that occur in the code-tracking loop.

[0032] In the event of a detected jump to a side peak, a code-tracking loop may need to be restarted. In this case, the procedure described here cannot be executed initially, as the historical data for E1, E5a, and detlaEI E5a, which are required for the described procedure, are missing. However, other approaches and methods exist for checking whether a jump from a main peak to a side peak has occurred, which can be implemented, for example, in a least-squares filter or a Kalman filter. These monitoring processes typically take place in parallel within the GNSS receiver. Therefore, the procedure described here is only intended as a cross-check to further increase the certainty that no erroneous tracking of a side peak occurs.

[0033] Because such methods based on least-squares filters and / or Kalman filters are typically executed in parallel, the greatest advantage of the method described here is increased availability. This method allows situations where a jump to a side peak may have occurred to be detected earlier. The GNSS signal receiver or the code-tracking loop can then be restarted more quickly to correct such errors.

[0034] Also described here is a GNSS signal receiver that is set up to carry out the described procedure.

[0035] The invention and its technical context are explained in more detail below with reference to the figures. The figures show a preferred embodiment, to which the invention is not limited. It should be noted that the figures and the size relationships depicted in the figures are only schematic. The following are shown by way of example and schematically:

[0036] Fig. 1: a code tracking loop as it is typically implemented in a GNSS signal receiver;

[0037] Figs. 2a and 2b: Signal evaluations as they usually take place in a code-tracking loop according to Fig. 1;

[0038] Fig. 3: a signal with main peak and side peak, in which a faulty jump from main peak to side peak can be detected using the method described here; and Fig. 4: a schematic representation of the described method.

[0039] Fig. 1 shows a code-tracking loop 1, as is commonly used to evaluate a received GNSS signal 2 in GNSS signal receivers 11. The received GNSS signal 2 is first duplicated by signal duplication 3. This can be done digitally, for example. Preferably, two or three duplicates of the received GNSS signal 2 are generated. In addition, replicated signals 5 corresponding to the received GNSS signal 2 are generated using a signal generator 43. Each replicated signal 5 corresponds to a specific reception time of the received GNSS signal 2. By comparing the replicated signals 5 with the received GNSS signal 2, the precise determination of the reception time of the received GNSS signal 2 is possible. Normally, an expected reception time of the received GNSS signal 2 exists, which was determined from previous measurements of the received GNSS signal 2.The replicated signals 5 are preferably generated by the signal generator 4 such that a replicated signal 5 IP (P = Peak) is produced, which corresponds to the expected reception time. In addition, a replicated signal 5 IE (E = Early) and a replicated signal 5 II (L = Late) are preferably generated. These are shifted forward (IE) and backward (II), respectively, in time. The correlation function 6 allows the received signal 2 and the replicated signals 5 to be compared. Signal evaluation 7 then determines which replicated signal 5 IE, IP, or IE best corresponds to the received GNSS signal 2. The corresponding reception time is then assigned to the received GNSS signal 2. Based on this, propagation time and distance measurements are performed.

[0040] Figures 2a and 2b illustrate this further. The upper section shows the received GNSS signal 2 and three replicated GNSS signals 5, IE, Ip, or II. Figure 2a shows that IE, IP, or II are shifted forward relative to the received GNSS signal 2, while Figure 2b shows IE, IP, or II symmetrically positioned relative to the received GNSS signal 2. The lower section of Figures 2a and 2b shows the correlation function 6. It is evident that the correlation in Figure 2a is best for II, and in Figure 2b for Ip. The reception time is determined by the code-tracking loop 1 according to the correlation function 6 and the replicated signals 5. According to Figure 2a, the reception time of the received GNSS signal 2 would be assumed to correspond to the time determined for II. According to Fig.2b would assume that the time of reception of the received GNSS signal 2 corresponds to the time that was set for IP.

[0041] Fig. 3 shows a received GNSS signal 2 with main peak 8 and side peaks 9. The peak spacing 10 between main peak 8 and side peaks 9 is shown in the diagram. A replicated signal 5 is also shown as an example. In the code-tracking loop 1, when correlating the received GNSS signal 2 and replicated GNSS signals 5, it is not possible to determine whether a signal value is positive or negative. For this reason, it is not possible to distinguish between the main peak 8 and the side peak 9 based on their sign. It is therefore understandable that the usual design of a code-tracking loop 1, which determines the reception time of a received GNSS signal 2 by correlating it with replicated signals 5, can lead to a side peak 9 being incorrectly tracked.This leads to errors in the determination of runtimes and distances, which correspond to the peak distance 10 between Main Peak 8 and Side Peaks 9 and which can be detected and avoided with the method described here.

[0042] Fig. 4 shows a schematic representation of the described method. Steps a) and b) are preferably each performed at least partially using a code-tracking loop 1 of a GNSS signal receiver 11. Step c) and the determination of the signal increments according to steps a) and b) can be performed subsequently without interfering with the code-tracking loop 1 of the GNSS signal receiver 11.

Claims

Claims 1. Method for monitoring a code-tracking loop (1) of a GNSS signal receiver (11) to detect erroneous jumps of the code-tracking loop (1) from a main peak (8) to a side peak (9), comprising the following steps: a) tracking a first received GNSS signal (2) from a GNSS satellite on a first frequency band and determining a first signal increment of the first received GNSS signal (2); b) tracking a second received GNSS signal (2) from the same GNSS satellite on a second frequency band and determining a second signal increment of the second received GNSS signal (2); and c) comparison of the first signal increment and the second signal increment to determine the jump from a main peak (8) to a side peak (9) if unexpected deviations between the first signal increment and the second signal increment were detected.

2. Method according to claim 1, wherein in step c) an additional comparison of the first received GNSS signal (2) and the second received GNSS signal (2) is carried out in order to detect unexpected deviations between the first received GNSS signal (2) and the second received GNSS signal (2) and to use them for determining a jump from a main peak (8) to a side peak (9).

3. Method according to one of the preceding claims, wherein tracking the first received GNSS signal (2) in step a) and the second received GNSS signal (2) in step b) comprises determining a time of reception, a transit time and / or a distance of the received GNSS signal (2) from the transmitting GNSS satellite to the GNSS signal receiver (11).

4. The method of claim 3, wherein first signal increments of the first received GNSS signal (2) and second signal increments of the second received GNSS signal (2) each represent differences between current reception times, propagation times and / or distances of the first received GNSS signal (2) and / or the second received GNSS signal (2) and previous reception times, transit times and / or distances of the first received GNSS signal (2) and / or the second received GNSS signal (2).

5. Method according to one of the preceding claims, wherein in the code tracking loop (1) several temporally shifted replicated signals (5) of the received first and / or second GNSS signal (2) are generated and each is correlated with the received first and / or second GNSS signals (2), wherein the temporal position and / or an assumed reception time of the replicated signal (5) with the highest correlation to the received first and / or second GNSS signal (2) is used to determine the reception time and / or propagation time of the received first and / or second GNSS signal (2).

6. Method according to one of the preceding claims, wherein the first received GNSS signal (2) is a signal on the E1 band of the Galileo GNSS system and the second received GNSS signal (2) is a signal on the E5 band of the Galileo GNSS system.

7. Method according to one of the preceding claims, wherein, following step c), the code tracking loop (1) is restarted if, in step c), an unexpected deviation is detected which indicates a jump from a main peak (8) to a side peak (9).

8. GNSS signal receiver (11) configured to perform the method according to any of the preceding claims.

Images