Method, computer program, electronic storage medium and device for analyzing a processed optical reception signal

Abstract

The invention relates to a method (900) for analyzing an optical received signal (401): - emitting (901) a plurality of optical transmission signals, which are used for being received as optical received signals (401), wherein the respective transmission signals are emitted in an equidistantly varying manner; - receiving (902) the optical received signals (401); - assigning the respective received optical received signals (401) to the plurality of optical transmission signals; - analyzing (904) the received optical received signals (401) depending on the respective maximum values (402) of the assigned optical received signals (401).

Description

Background Technology

[0001] In the coming years, lidar sensors will be crucial for enabling highly automated driving functions. Currently, only mechanical laser scanners are known to cover large horizontal detection angles between 150° and 360°. In the first configuration, a rotating mirror laser scanner with a maximum detection range limited to approximately 120°, only a motor-driven deflector mirror rotates. For even larger detection ranges up to 360°, all electro-optical components are located on a motor-driven rotating disk or rotor.

[0002] Multi-pulse lidar systems are known. The literature primarily describes systems that utilize multiple pulses within a single measurement. Here, a measurement is understood as emitting a predetermined number of laser pulses. This number ranges from 3 to 6 pulses, sometimes up to 20 pulses, and especially 12 pulses. This approach has several drawbacks.

[0003] If multiple pulses are used within a single measurement, it is necessary to ensure that the laser pulses are emitted at very small intervals, typically in the nanosecond range, and especially up to tens of nanoseconds. This necessitates significantly more complex charging circuitry for the laser, as the time between pulses is insufficient to recharge the next emission (Schuss). While this problem can be circumvented using a DC power supply, such a source has the drawback of generating very high laser power in the event of a functional failure, thereby raising eye safety concerns. This necessitates very expensive safety mechanisms.

[0004] Additionally, such systems have the following problem: due to the typically low number of pulses (typically 3 to 6, sometimes up to 20, especially 12), very poor statistical data is produced for measurements. This leads to the problem of being able to skip the desired distance under very low signal conditions.

[0005] One final drawback to mention is that signal analysis and processing in such a system is very expensive. Filters covering the entire time range of the multi-pulse signal are required.

[0006] This results in a very long filter, and the computational work involved in such analysis and processing is therefore enormous.

[0007] Another possibility for achieving such a multi-pulse system is to use pulses spaced out within the measurement range. For example, if you want to measure distances up to 300 meters, the time interval would be 2 microseconds. This time is sufficient to recharge the current charging circuit for the next laser pulse. This allows for the use of simple charging circuits and reliably meets eye safety requirements with simple means.

[0008] Furthermore, it is known that the signals received after emitting a laser pulse are aggregated into a histogram. After emitting all the laser pulses for a measurement, the aggregated histogram can be analyzed using a simple method. For example, all the received signals can be summed into a single signal, and this signal can be analyzed using a simple filter.

[0009] The fundamental problem of such a system is given by a finite range of single-valuedness. This range of single-valuedness is determined by the time interval of the pulses.

[0010] The finite range of single-valuedness leads to the appearance of ghost echoes. Ghost echoes are unwanted detection artifacts.

[0011] Ghost echoes should be understood as received signals that are outside the system's single-valued range. This can occur, for example, when a laser beam emitted in a lidar system is reflected off an object farther than the system's detection range. When the reflected signal is received, it may be misattributed to the correct emitted signal. This can lead to incorrect calculations of signal propagation time and, consequently, incorrect estimations of the distance to the object.

[0012] Furthermore, signals from external sensors can be unwanted detection artifacts. Summary of the Invention

[0013] In this context, the present invention should help eliminate detection artifacts, such as the aforementioned ghost echoes or signals from foreign sensors.

[0014] Therefore, the present invention proposes a method for analyzing and processing optical received signals. This method comprises the following steps.

[0015] Multiple optical transmission signals are transmitted, and these signals are received as optical reception signals. The key feature of the method of this invention is that the corresponding transmission signals are transmitted in a manner of equidistant variation.

[0016] Receives optical signals.

[0017] The corresponding received optical receiving signals are assigned to the plurality of optical transmitting signals.

[0018] In the current context, "transmitting optical signals in a manner of equidistant variation" should be understood as each pulse (optical signal) being transmitted with a time interval between them, which depends on the predetermined single-valued range of the system and is therefore equidistant. To more easily distinguish ghost echoes and signals from external sensors, the equidistant spacing varies in such a way that, on the one hand, it does not significantly affect the size of the single-valued range, and on the other hand, it makes ghost echoes easier to identify. This means that the variation appears small compared to the time interval. For example, if the time interval is 2 microseconds in the case of a given single-valued range of 300 meters, then the variation can be in the range of up to 100 nanoseconds, especially in the range between 10 and 40 nanoseconds.

[0019] In the current context, the optical transmission signal can be understood as the laser pulse of a multi-pulse lidar system.

[0020] In the current context, the optical received signal can be understood as the signal detected by the lidar system's detector due to the reflection of the optical transmitted signal. Furthermore, the optical received signal should also be understood as signals from external sensors that are accidentally detected by the lidar system's detector. Additionally, the optical received signal can be understood as the signal that contributes to background noise in the lidar system's detector. This primarily includes background light and thermal noise. In principle, this should be understood as every signal detected by the lidar system's detector.

[0021] The key feature of this method is the analysis and processing step, which involves analyzing and processing the received optical signal based on the corresponding maximum value of the assigned optical received signal.

[0022] In the current context, analysis and processing can be understood in two ways: firstly, as extracting signals from received signals; and secondly, as processing the received signals in a way that makes information extraction easier or more reliable. This includes, for example, removing unwanted detection artifacts. Here, the signal to be extracted generally refers to the presence of an object, and more specifically, the distance to that object.

[0023] According to one implementation, in the analysis and processing step, analysis and processing are performed based on a threshold for the corresponding maximum value.

[0024] According to this embodiment, when analyzing and processing optical received signals, the received signals can be analyzed and processed based on the maximum value exceeding a threshold. This results in that, even when excluding the corresponding maximum value from the analysis and processing, only the maximum value generated by an unwanted detection artifact with an approximately certain probability is still excluded. Thus, overall, fewer or only interfering information components are excluded from the analysis and processing. This leads to more accurate analysis and processing results.

[0025] According to one embodiment of the method of the present invention, the method has an additional pre-filtering step after the step of receiving the optical signal.

[0026] Another aspect of the present invention is a computer program that sets up all the steps of one embodiment of the method of the present invention for carrying out the implementation of the method of the present invention.

[0027] Another aspect of the present invention is an electronic storage medium on which a computer program according to an aspect of the present invention is stored.

[0028] Another aspect of the invention is an apparatus that provides all the steps of one embodiment of the method of the invention. Such an apparatus can be constructed as a so-called application-specific integrated circuit (ASIC). Attached Figure Description

[0029] In the following sections, embodiments of the invention are described in more detail with reference to the drawings.

[0030] The attached diagram shows:

[0031] Figure 1 An exemplary time-varying curve of a measurement is shown;

[0032] Figure 2 An exemplary time-varying curve of one measurement in the detector is shown;

[0033] Figure 3 The histogram shows the analysis and processing of the optically received signal;

[0034] Figure 4 A block diagram illustrating one embodiment of the present invention is shown;

[0035] Figure 5 A block diagram illustrating another embodiment of the present invention is shown;

[0036] Figure 6 A block diagram illustrating another embodiment of the present invention is shown;

[0037] Figure 7 A block diagram illustrating another embodiment of the present invention is shown;

[0038] Figure 8 A block diagram illustrating another embodiment of the present invention is shown;

[0039] Figure 9 A flowchart illustrating one embodiment of the method of the present invention is shown. Detailed Implementation

[0040] Figure 1 An example is shown showing the time variation curve of a measurement.

[0041] In the left figure, a timeline is plotted for six measured laser pulses, which reproduces the distance in meters based on the propagation time of the laser beam.

[0042] The time interval of the laser pulses indicates that the single-valued range is 300 meters. This is evident from the fact that the laser pulses are emitted with time intervals between them, which correspond to the 300-meter propagation time of the laser beam.

[0043] In the right figure, measurements in the detector are illustrated exemplarily during the same time period. The swing first appears after a propagation time corresponding to 180 meters, and then the swing appears periodically after a propagation time corresponding to 300 meters, and thus precisely after the time when another laser pulse is emitted, after which the swing indicates that an object located at a distance of approximately 180 meters has been identified.

[0044] Figure 2 The measurement in the detector is shown as an example, which is generated when an object outside the single-value range is detected.

[0045] In the measurement shown, an object located at approximately 350 meters was identified. Within a single-valued range of only 300 meters, without corresponding countermeasures, the distance to that object would be calculated to be only 50 meters due to, for example, the detection of ghost echoes.

[0046] This type of incorrect measurement can cause huge problems.

[0047] Therefore, the present invention proposes corresponding countermeasures.

[0048] Figure 3 Measurement data generated when using the present invention are shown exemplarily.

[0049] The first histogram shows the aggregation of the amplitude of the detected signal in a time region corresponding to the single-valued range. This aggregation essentially corresponds to the summation of the detected signal (including noise components).

[0050] The second histogram shows the maximum emission amplitude for each time unit (Max.Hold Histogramm, the maximum value hold histogram), which corresponds to the corresponding distance due to the propagation time of the laser beam.

[0051] Now, the first histogram can be analyzed based on the second histogram. This analysis can, for example, involve subtracting the value of the second histogram from the value of the first histogram. This eliminates all signals generated solely by a single transmission. Therefore, ghost echoes or signals from external sensors can be reliably eliminated. This avoids erroneous analysis caused by these detection artifacts.

[0052] Figure 3 The third histogram in the figure shows the result of one embodiment of the invention, according to which analysis is performed in the analysis processing step based on a threshold for the corresponding maximum value.

[0053] This specifically means that, when analyzing and processing the received signal, only the following signals with maximum value preservation histograms are considered: signals that are above a predetermined threshold. In the second histogram, these are the various strong swings.

[0054] As shown in the third histogram, this allows for the reliable elimination of detection artifacts, such as ghost echoes and signals from foreign sensors, without eliminating other information, such as low-threshold background noise. Consequently, the analysis and processing of the received signal can be more accurate and detailed.

[0055] In particular, this implementation method effectively prevents the subtraction of the "true signal component" and thus avoids compromising the system's operating range.

[0056] Figure 4 A block diagram is shown according to one embodiment of the present invention.

[0057] This implementation is based on the following: providing a received signal 401 and a corresponding maximum value 402 of the assigned optical received signal for analysis and processing. Furthermore, providing a threshold 403 for the corresponding maximum value 402 for analysis and processing.

[0058] The received signal 401 and the maximum value 402 are presented in the form of a histogram. In the histogram, the received signal 401 and the maximum value assigned to said received signal are plotted within a single-valued range. The received signal 401 is here assigned to a transmitted signal. Here, the duration begins after each transmitted signal. Therefore, the received signals can be plotted superimposed (see...). Figure 3 (First histogram). Furthermore, for each time unit, the maximum value for that time unit is plotted after the assigned transmission signal (see [reference]). Figure 3 (Second histogram).

[0059] Then, in block 400, the received signal is analyzed and processed according to the corresponding maximum value of the assigned optical received signal and according to the threshold for the corresponding maximum value of the maximum value preservation histogram 402.

[0060] This means that the corresponding maximum value 402 for the corresponding time unit is subtracted from the received signal. This effectively and efficiently eliminates detection artifacts. To eliminate as little information as possible, according to this embodiment, the corresponding maximum value 402 is only subtracted when the corresponding maximum value 402 for the time unit is higher than a provided threshold 403 for the corresponding maximum value. Therefore, the eliminated information can be reduced to the point that it can be attributed to detection artifacts with a high probability.

[0061] It can calculate the distance to detected objects as the result of analysis and processing.

[0062] Figure 5 Another block diagram is shown according to another embodiment of the present invention.

[0063] In this embodiment, the received signal 401 is also analyzed and processed according to the corresponding maximum value 402 of the assigned optical received signal 401 and according to the threshold 403 for the corresponding maximum value 402.

[0064] Additionally, according to the illustrated embodiment, the maximum value 402 is pre-filtered for smoothing. This filtering can be applied, for example, to the histogram of the maximum value (see...). Figure 3 (Second histogram). Here, methods known to those skilled in the art can be considered as filtering methods, mainly matched filtering or top-head filtering.

[0065] According to this embodiment, when the corresponding filtered maximum value is higher than the threshold 403, the corresponding maximum value 402 is subtracted from the received signal 401.

[0066] The advantage of this implementation is that this type of pre-filtering can reduce or avoid undesirable effects when analyzing downstream filtering processes.

[0067] Figure 6 A block diagram is shown according to another embodiment of the present invention.

[0068] According to this embodiment, the received signal 401 is analyzed and processed 400 based on a corresponding maximum value 402 for the received signal. Here, in block 605, it is checked whether the received signal 401 is less than the corresponding maximum value 402.

[0069] The corresponding maximum value of 402 can be adjusted using a predetermined factor. This factor is generally an application factor, determined when the system is built, taking into account relevant known conditions. It is usually determined by considering the use of a heuristic method.

[0070] If the conditions checked in block 605 apply, the received signal 401 is analyzed in block 400 based on the maximum value 402. One aspect of this analysis is subtracting the maximum value 402 from the received signal 401. Furthermore, this consideration is performed within a predetermined number of time units. This is represented by block 606, which, if the conditions in block 605 apply, provides an enable signal to block 400 within a predetermined number of time units.

[0071] This implementation achieves the analysis and processing of the received signal 401 in a simple manner by eliminating interfering detection artifacts (such as ghost echoes and signals from foreign sensors).

[0072] The simple implementation may result in the removal of information-containing signal components from the received signal 401. However, this has no significant impact on overall performance, i.e., the ability to determine the distance to the detected object.

[0073] This implementation is particularly well-suited for use in low-resource environments, such as for embedded applications.

[0074] Figure 7 A block diagram is shown according to another embodiment of the present invention.

[0075] According to this embodiment, the received signal 401 is further analyzed and processed 400 based on the average value of the background noise 701 and the average value of the maximum value 702.

[0076] According to this embodiment, this dependency of the analysis process is reflected in the following part of the analysis process: this part leads to a decision on whether it is necessary to subtract the corresponding maximum value 402 from the received signal 401 during the analysis process 400.

[0077] To make this decision, the average value 701 of the received signal 401 is calculated. This value essentially characterizes the effect of background noise on the received signal 401.

[0078] In addition, the average value of the corresponding maximum value 402 is calculated as 702.

[0079] In block 605, the received signal, after the background noise has been removed, serves as the basis for decision 605: whether to subtract the corresponding maximum value 402 from the received signal 401 during analysis processing 400.

[0080] In this box, a comparison is made with the value 705, which is the average value 702 after the maximum value 402 was cleared.

[0081] According to this implementation, in order to clear the maximum value 402, the maximum value 402 and the average value 702 are adjusted not only by means of factors 703 and 704 respectively.

[0082] This implementation is based on the understanding that the maximum value 402 at the corresponding position is subtracted from the received signal 401 only when the received signal 401 at the corresponding position is generated solely by a laser pulse. In other words, the maximum value 402 at the corresponding position is subtracted from the received signal 401 only when the signal level in the histogram of the received signal 401 (see...) Figure 3 The first histogram (where the signal is from another laser pulse) indicates the location at which there is an additional signal. The maximum value of 402 at the corresponding location is subtracted only if this is not the case.

[0083] This approach results in the first received signal being subtracted when a strong signal is received, i.e., when a high-amplitude received signal 401 is received, because the signal is incorrectly processed as a ghost echo or a signal from an external sensor, i.e., as if detecting an artifact.

[0084] Figure 8 A block diagram is shown according to another embodiment of the present invention.

[0085] From the basis Figure 7 Starting from the implementation method. Additionally, in order to determine whether 605 needs to subtract the maximum value 402 from the received signal 401, a threshold 403 is considered and based on... Figure 5 The implementation method pre-filters the maximum value 402 by 504.

[0086] According to this embodiment, signal peaks in background noise can be eliminated. The elimination of these signal peaks is not necessary. Furthermore, the elimination of these signal peaks has no significant impact on the performance of this embodiment, i.e., on the determination of the distance to the detected object.

[0087] Figure 9 A flowchart illustrating one embodiment of the method of the present invention is shown.

[0088] In step 901, a plurality of optical transmission signals are transmitted, which are then received as optical reception signals 401. A key feature of step 901, according to the invention, is that the optical transmission signals are transmitted in a manner of equidistant variation.

[0089] In step 902, an optical receiving signal 401 is received. The optical receiving signal 401 can be received in response to the emission of an optical transmitting signal. This is, for example, when an optical transmitting signal strikes an object and is reflected by that object. The optical receiving signal is then a reflection of the previously emitted optical transmitting signal. Furthermore, the optical receiving signal can be so-called optical background noise. This is typically present and generated by reflections from natural or artificial electromagnetic sources (e.g., natural or artificial light sources). Additionally, optical background noise can be generated by thermal noise from components used in or in the case of the detector.

[0090] In step 903, the optical receiving signal is assigned to the optical transmitting signal. Based on this assignment, for example, the propagation time of the optical transmitting signal can be determined, and the distance to the detected object can be calculated using this propagation time.

[0091] One possible allocation scheme is to allocate all received signals received after the transmission of one transmission signal and before the transmission of another transmission signal to the transmission signal.

[0092] In step 904, the received optical signal is analyzed and processed according to the corresponding maximum value of the assigned received signal.

[0093] This analytical processing can be achieved, for example, by analyzing and processing histograms. Here, the received signals within the single-valued range over the duration in the first histogram are summed. In the second histogram, the corresponding maximum values ​​are held over the same duration (Max.Hold Histogram).

[0094] By analyzing and processing the received signal according to the corresponding maximum value 904, unwanted detection artifacts, such as ghost echoes and signals from foreign sensors, can be eliminated by means of the present invention.

[0095] This elimination can be achieved, for example, by subtracting the maximum value at the corresponding position from the received value.

[0096] Other embodiments of the present invention can provide partially more accurate signal analysis and processing in a simpler manner within the scope of the analysis and processing of the received signal 904 steps.

Claims

1. A method (900) for analyzing and processing an optical received signal (401): - transmitting (901) a plurality of optical transmitted signals, said plurality of optical transmitted signals being received as an optical received signal (401), wherein, Transmit corresponding optical signals in a manner of equidistant variation, wherein each optical signal is transmitted with a time interval between it and the other, the time interval depending on a predetermined single-value range and being equidistant, wherein the equidistant interval varies such that the variation appears small compared to the time interval; - Receive (902) optical received signals (401); - Distribute (903) the corresponding received optical received signals (401) to the plurality of optical transmitted signals; The received optical received signal (401) is analyzed and processed (904) according to the corresponding maximum value (402) of the assigned optical received signal (401), wherein, in the step of the analysis and processing, the analysis and processing is performed according to a threshold (403) for the corresponding maximum value (402) and the analysis and processing is implemented by analyzing and processing a histogram, wherein, in the first histogram, the received signals are summed over a duration of a single value range, and in the second histogram, the corresponding maximum value is maintained over the same duration, wherein, when the corresponding maximum value (402) is higher than the provided threshold (403) for the corresponding maximum value, the corresponding maximum value (402) is subtracted from the received optical received signal (401), wherein the value of the second histogram is subtracted from the value of the first histogram.

2. The method (900) according to claim 1, wherein the method has an additional step of pre-filtering the corresponding maximum value (402).

3. The method (900) according to claim 2, wherein, The analysis process is performed based on the corresponding maximum value (402) and by applying the threshold (403) to the filtered maximum value (402).

4. The method (900) according to any one of the preceding claims, wherein, In the analysis process step, the analysis process is performed based on the factor used for the corresponding maximum value (402).

5. A computer program product configured to implement all steps of the method (900) according to any one of the preceding claims.

6. An electronic storage medium on which a computer program product according to claim 5 is stored.

7. An apparatus configured to perform all steps of the method (900) according to any one of claims 1 to 4.

8. The device according to claim 7, wherein, The device is a dedicated integrated circuit.

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