DISTANCE MEASURING DEVICE

Abstract

According to various embodiments, a distance measuring device is described, comprising: a receiver designed to receive first pulses of a first pulse train sent by a transmitter with a first interval between the pulses, and to receive second pulses of a second pulse train sent by the transmitter with a second interval between the pulses, wherein the first interval is different from the second interval;and a processor designed to produce a first processing result by analyzing the timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses, to produce a second processing result by analyzing the timing of one or more peaks in a second received signal received by the receiver upon receiving the second pulses, and to determine a distance between the transmitter and the distance measuring device as a function of a comparison of the first processing result and the second processing result.

Description

The present disclosure relates to distance measuring devices. Current ultra-wideband (UWB) distance measurement technology relies on the transmission of a pulse train. These pulses are typically exchanged between devices to enable accurate distance measurement. Due to environmental reflections and the limited time interval between pulses, reflected pulses (corresponding to a particular transmission slot) can interfere with the next transmission slot(s) in the respective receiving (RX) device, leading to inaccurate distance estimates. This error can occur, in particular, whenever sufficiently reflected pulses fall within a defined backward search window (BSW, a time interval at which UWB transceivers search for an earlier peak preceding the stronger peak in the accumulator).Accordingly, approaches are desirable to avoid distance estimation errors in environments where there is strong reflection of UWB radar pulses. According to various embodiments, a distance measuring device is provided comprising: a receiver designed to receive first pulses of a first pulse train sent by a transmitter with a first interval between the pulses, and to receive second pulses of a second pulse train sent by the transmitter with a second interval between the pulses, wherein the first interval is different from the second interval;and a processor designed to produce a first processing result by analyzing the timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses, to produce a second processing result by analyzing the timing of one or more peaks in a second received signal received by the receiver upon receiving the second pulses, and to determine a distance between the transmitter and the distance measuring device as a function of a comparison of the first processing result and the second processing result. In the drawings, similar reference numerals generally refer to the same parts across different views. The drawings are not necessarily to scale; instead, they generally emphasize an illustration of the principles of the invention. The following description describes various aspects with reference to the following drawings, in which: Fig. 1 shows a UWB (ultra-wideband) radar system. Fig. 2 shows signal diagrams illustrating the relationship between transmitted pulses and received signal peaks for two different PRFs (pulse repetition frequencies) in a first scenario. Fig. 3 shows signal diagrams illustrating the relationship between transmitted pulses and received signal peaks for two different PRFs in a second scenario.Figure 4 shows signal diagrams illustrating the relationship between transmitted pulses and received signal peaks for two different PRFs in a third scenario. Figure 5 shows a flowchart illustrating the performance of a distance measurement using two PRFs. Figure 6 shows two diagrams illustrating received signals. The following detailed description refers to the accompanying drawings, which illustrate specific details and aspects of this disclosure in which the invention can be implemented. Other aspects may be used, and structural, logical, and electrical modifications may be made without departing from the scope of the invention. The various aspects of this disclosure are not necessarily mutually exclusive, as some aspects of this disclosure may be combined with one or more other aspects of this disclosure to form new aspects. Fig. 1 shows a UWB radar system (ultra-wideband radar system) 100. The UWB radar system 100 comprises a first UWB device 101 and a second UWB device 102. The first UWB device 101 comprises a pulse generator 103, a controller 104, a receiver 107, and a processor 108. The pulse generator 103 produces pulses under the control of the controller 104, specifically with a time interval between successive pulses defined by the controller 104; that is, it generates a pulse for each transmission time slot of a sequence of transmission time slots separated by a predetermined time interval. This time interval, also called the pulse period, corresponds to a pulse repetition frequency (PRF); that is, the reciprocal of the PRF is the time interval between successive pulses, e.g., time interval = 256 ns, PRF ≈ 4 MHz. A (UWB) transmitting antenna 105 of the first UWB device 101 emits the pulse signals generated by the pulse generator 103. The second UWB device 102 includes a (UWB) receiving antenna 106, a receiver 107 (which includes, for example, an amplifier, a filter, and a pulse accumulator), and a processor 108. It also includes a pulse generator 103 and a control unit 104. The processor 108 of the second UWB device 102 analyzes signals received by the receiver 107 via the receiving antenna 106. The receiver 107 can receive pulses emitted by the UWB transmitter 101 on a direct path 111 (“first path”) to the second UWB device 102 (resulting in a “first path” peak in the receiver 107) as well as on a second path 112 with pulses emitted by the first UWB device 101, which are reflected in the environment by surrounding objects and then reach the second UWB device 102 as reflected pulses. One method for calculating propagation time is two-way distance measurement. A first anchor sends a data frame, a second device receives the data frame and waits a fixed time T. The second device then sends an acknowledgment frame. The first device receives the acknowledgment frame and estimates the delay t that has elapsed since the transmission of the original data frame. The fixed time is subtracted, and the result is the propagation time, which is a measure of the distance r between the first UWB device 101 and the second UWB device 102: r = 1 / 2 · c · (tT). The confirmation frame can be transmitted via the first path 111 and / or via a further, reflected path 113. Strong reflections can lead to errors in the distance measurement, i.e., the estimation between the first UWB device 101 and the second UWB device 102, which is performed by the processor 108 as illustrated in Fig. 2. Likewise, the confirmation signal can be transmitted via the first path and / or via a further path 113. If the signal received via path 113 is used to calculate the propagation time, the measured distance will be significantly greater than the actual distance between the devices. Fig. 2 shows signal diagrams 201-204 illustrating the relationship between transmitted pulses (diagrams 201, 203) and received signal peaks (diagrams 202, 204) for two different sets of repeated pulses (first set: diagrams 201, 202; second set: diagrams 203, 204). In Fig. 2 and the other similar diagrams described below, the time scale is assumed to be the same for all diagrams; time passes from left to right. In the case of the first set of repeated pulses, the pulse period is 256 ns, as shown in diagram 201 and diagram 202. The first transmitted pulse, 205, is received by the receiver immediately afterward because the signal of this peak was transmitted along a direct path. However, due to strong reflection, a second peak, 206, is later received by the receiver, with a lower amplitude than the first received peak. When a high peak is received, the smaller signals just before the high peak are examined to find the first indication of a UWB signal. The time frame in which the signal is searched is called the reverse search window (RSW). In this case of signal 201, shown in Fig. 2, the pulse 206 of a first transmitted pulse 205 appears in the reverse search window (RSW) of a second transmitted pulse 207. The corresponding highest received signal peak 208 indicates the end of the reverse search window, in which the reflection 206 is received by the receiver 107 shortly before the peak 208. Because the reflection 206 is strong, the processor 108 may mistakenly interpret the reflection 206 as the first path peak of the second transmitted pulse 207 and misjudge the distance between the first UWB device 101 and the second UWB device 102. Therefore, according to various embodiments, the first UWB device 101 (in particular the controller 104) varies the PRF parameter to shift the one or more reflected pulses to different times with respect to the signals received by the respective receiving device, in this case the second UWB device 102. In the example of Fig. 2, a second PRF has a second pulse period of 200 ns, i.e., the second PRF is higher than the first PRF, see the lower diagram 204. The reflection 206 of the first transmitted pulse 205 is shifted behind the highest received signal peak 208. Therefore, it can no longer be considered the first-path peak within the reverse search window. An incorrect distance estimation for the distance between the first UWB device 101 and the second UWB device 102 by the processor 108 can be avoided, since the reflection 206 does not interfere with the distance estimation. As illustrated in Fig. 2, the same can be achieved for a reflection of the second transmitted pulse 207. Accordingly, according to different embodiments, different PRFs are used to detect and possibly correct distance measurements that are disturbed by reflected pulses falling within the reverse search windows of successive slits, also referred to as "gealiast" pulses, such as the reflection 206 in the example of Fig. 2 for the first PRF. While in the example of Fig. 2 a reflection for the lower PRF falls into a backward search window (BSW) but not for the higher PRF, it is also possible that the reflected pulse appears in front of the BSW for a certain lower PRF 1, while for a higher PRF 2 it appears inside the BSW, as illustrated in Fig. 3. Fig. 3 shows signal diagrams 301-304, which illustrate the relationship between transmitted pulses (diagrams 301, 303) and received signal peaks (diagrams 302, 304) for two different PRFs. The first PRF is illustrated in diagrams 301, 302, while a second PRF determines diagrams 303, 304. In the case of the first PRF, see the first diagram 301 and the second diagram 302, the reception of a strong reflection (and therefore a spike caused by it) 306 of a first transmitted pulse 305 appears before the reverse search window (BSW) for a second transmitted pulse 307. Accordingly, it does not affect the distance measurement based on pulses transmitted with the first PRF. In the case of the second PRF, see diagrams 303 and 304 (third and fourth), the reflection 306 of the first transmitted pulse 305 appears in the reverse search window for the second transmitted pulse 307, which has a corresponding peak received signal 308. Because the reflection 306 is strong, the processor 108 may mistakenly interpret it as the first-path peak of the second transmitted pulse 307 and incorrectly estimate the distance between the first UWB device 101 and the second UWB device 102. Therefore, the distance estimation based on pulses transmitted by the second PRF can be affected by the reflection. In both scenarios of Figures 2 and 3, since the measurement is only affected for one of the PRFs, distance measurement errors can be detected by comparing distance measurement results obtained for the two PRFs. The correct of the two can be selected, for example, based on historical estimates. If the distance was measured as approximately 3 m for the last 10 estimates, and it is now 20 m for one of the PRFs while remaining approximately 3 m for the other, the 3 m estimate can be assumed to be the correct one, as such a large change is unlikely. For this approach, a threshold for whether a change is unlikely or not can be set based on an expected speed of movement of the UWB devices 101 and 102. However, it can indeed happen that the distance estimates for both PRFs are incorrect, as illustrated in Fig. 4. Fig. 4 shows signal diagrams 401-404 illustrating the relationship between transmitted pulses (diagrams 401, 403) and received signal peaks (diagrams 402, 404) for two different PRFs (first PRF: diagrams 401, 402; second PRF: diagrams 403, 404). In the case of the first PRF (PRF1), see the second diagram 402, a strong reflection (and thus a spike caused by it) 406 of a first transmitted pulse 405 is received within the reverse search window for a second transmitted pulse 407, which has a corresponding highest received signal spike 408. The reflection 406 is received by the receiver 107 shortly before this spike. Because the reflection 406 is strong, the processor 108 may mistakenly interpret the reflection 406 as the first-path spike of the second transmitted pulse 407 and misjudge the distance between the first UWB device 101 and the second UWB device 102. In the case of the second PRF (PRF2), which is smaller than PRF1 (see diagrams 403 and 404, the reflection 406 of the first transmitted pulse 405 is shifted to the right relative to the peak 408, but is still within the reverse search window for the second transmitted pulse 407. Because the reflection 406 is strong, the processor 108 may again mistakenly interpret the reflection 406 as the first-path peak of the second transmitted pulse 407 and misjudge the distance between the first UWB device 101 and the second UWB device 102. Accordingly, in such a scenario, both distance estimates may be incorrect. However, the processor 108 can detect this by comparing the two distance estimates, as they are most likely to be different. Furthermore, the processor 108 can distinguish the misleading reflected pulse 106 from a legitimate attenuated first-path (FP) peak—for example—by measuring the distance on the timescale between the strongest peak 408 and the previous peak, which is the reflected pulse 406 in the example of Fig. 4, but which could also be the FP peak. A legitimate attenuated FP is expected to have the same distance, on the timescale, from the strongest peak 408, whereas a reflected peak 406 has different distances, as is the case in Fig. 4, since the difference should not depend on the PRF. One approach for the processor to recognize 108 scenarios, as illustrated in Figures 2, 3 to 4, is to compare distance estimates made based on pulses sent with different PRFs and discard both if they do not match. Discarding distance estimates or other processing results can be understood as determining the distance and arriving at a final distance (distance estimate) without considering those distance estimates (i.e., those being discarded), or omitting the distance estimates (or other processing results) that are discarded by further processing. In other words, alternating PRFs (two or more) are used for successive measurements to check whether the measurements obtained for the different PRFs agree and to filter out results that do not agree, accepting small differences below a predetermined threshold to ensure a given level of accuracy. This approach is illustrated in Fig. 5. Fig. 5 shows a flowchart 500 illustrating the performance of a distance measurement using two different PRFs, PRF1 and PRF2. In step 501, the processor 108 of the second UWB device 102 determines a first distance estimate d1 for the distance between the second UWB device 102 and the first UWB device 101. This estimate is based on the reception of pulses sent by the first UWB device 101 with the first PRF (PRF1). In step 502, the processor 108 of the second UWB device 102 determines a second distance estimate d2 (the distance between the second UWB device 102 and the first UWB device 101) based on the reception of pulses sent by the first UWB device 101 with the second PRF (PRF2). At step 503, the processor 108 determines whether the difference between the two distance estimates is below a predefined threshold (e.g., several percent, e.g., 5%, depending on the typically expected accuracy). If the difference is not below the threshold, the processor 108 discards the estimates at step 504 and waits for new signals from the receiver 107 to perform another distance measurement. If the difference is below the threshold, processor 108 uses the estimates at 505 to create a distance estimate (e.g., using both of them or averaging them to generate a final estimate). It can then wait for new signals from receiver 107 to perform another distance measurement. In another embodiment, the processor 108 can proceed as described with reference to Fig. 5 and, after detecting a significant discrepancy in nearby measurements (i.e., the difference is not below the threshold 503), check after a PRF (e.g., after each of the two PRFs) – e.g., via channel impulse responses (CIRs) – whether there is an impulse within the BSW, and discard the measurement obtained for the given PRF if so. In this way, the processor 108 can not only detect distance measurement errors but also correct them, assuming a scenario such as in Fig. 2 or Fig. 3, where the reflection 206, 306 for at least one of the PRFs occurs after the peak 208, 308, such that one of the estimates is correct. Fig. 6 shows two diagrams 601, 602, illustrating a scenario in which the processor 108 can safely discard the measurement obtained at the pulse period 256 ns (upper diagram 601) because the reflected peak was shifted behind the BSW with pulse period 200 ns (lower diagram 602). In one embodiment, a significantly lower PRF (e.g., two or four times lower) can be used if there is doubt regarding a particular distance estimate. For example, if the second UWB device 102 determines a distance estimate for a first PRF that is suspicious because it deviates more than reasonably from a previous distance estimate, the second UWB device 102 instructs the first UWB device 101 (e.g., by sending a corresponding control message) to switch to a second PRF that is substantially lower than the first PRF, i.e., to send pulses with the second PRF. While using a low PRF might not be desirable, it only occurs in the case of estimation errors, and therefore this approach is more efficient than an approach of constantly using low PRFs to avoid errors. According to one embodiment, the first UWB device 101 sends pulses on a single PRF and – after detection of a suspicious distance measurement by a higher-level application (e.g., a filter or other component that detects that a distance estimate deviates more than reasonably from a previous distance estimate) – uses (upon notification or instruction from the second UWB device 102) a different PRF to enable the second UWB device 102 to determine whether the error is due to a reflection and to take action, such as discarding the measurement or correcting it, as explained above. It is also possible that a first UWB device 101, if it (or the second UWB device 102) detects that reflections are to be expected, uses a predefined PRF or a predefined set of PRFs to avoid one or more reflected peaks falling within the BSW. In summary, according to various embodiments, a range-measuring device (or radar device) is provided (corresponding, for example, to the second UWB device 102 of the radar system 100 of Fig. 1) comprising a receiver designed to receive first pulses of a first pulse train transmitted by a transmitter with a first interval between the pulses, and to receive second pulses of a second pulse train transmitted by the transmitter with a second interval between the pulses. According to one embodiment, the transmitter sends the sequences sequentially, but, for example, immediately one after the other, so that the distance of the range-measuring device to the transmitter can be expected to be nearly constant. In other words, the first pulses of the first pulse train are pulses that are sent with a given pulse repetition frequency (PRF) (which are received sequentially at the receiver), and the second pulses of the second pulse train are pulses that are sent with a different PRF (which are also received sequentially at the receiver, e.g., after the first pulses). Sending and receiving pulses can be a sending and receiving of packets, with each packet containing multiple pulses. The first interval differs from the second interval, e.g. by several percent, e.g. by at least 5%, 10% or 15%. The distance measuring device further comprises a processor designed to produce a first processing result by analyzing the timing of one or more peaks in a signal received by the receiver upon receiving the first pulses, and a second processing result by analyzing the timing of one or more peaks in a signal received by the receiver upon receiving the second pulses. The processing results may be distance estimates and / or distances between the earliest and highest peaks in the received signals, as explained with reference to Fig. 4. The processor is designed to determine a distance (i.e., the geographical distance) between the transmitter and the distance measuring device based on the result of a comparison of the first processing result and the second processing result. In other words, different PRFs (or pulse periods) are used in different embodiments to achieve versatility in UWB radar range measurement. The following are various examples described: Example 1 is a distance measuring device comprising: a receiver designed to receive first pulses of a first pulse train transmitted by a transmitter with a first interval between the pulses, and to receive second pulses of a second pulse train transmitted by the transmitter with a second interval between the pulses, the first interval being different from the second interval; and a processor designed to produce a first processing result by analyzing a timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses, and to produce a second processing result by analyzing a timing of one or more peaks in a second received signal received by the receiver upon receiving the second pulses.and determine a distance between the transmitter and the distance measuring device as a function of the result of a comparison of the first processing result and the second processing result. Example 2 is the distance measuring device of Example 1, wherein the processor is designed to perform the comparison of the first processing result and the second processing result by comparing a difference between the first processing result and the second processing result with a threshold value. Example 3 is the distance measuring device of Example 2, wherein the processor is designed to discard the first processing result and / or the second processing result in response to the difference between the first processing result and the second processing result exceeding the threshold value. Example 4 is the distance measuring device of Example 3,wherein the processor is designed, in response to the difference between the first processing result and the second processing result exceeding the threshold, to check whether a reverse search window before a highest peak in the first received signal contains a peak, and to discard the first processing result in response to the reverse search window before the highest peak in the first received signal containing a peak, and to check whether a reverse search window before a highest peak in the second received signal contains a peak, and to discard the second processing result in response to the reverse search window before the highest peak in the second received signal containing a peak. Example 5 is the distance measuring device of Example 3 or 4, wherein the processor is designed to discard one of the first processing result or the second processing result.that is less close to a processing result that the processor generated from earlier pulses of a previous pulse sequence that were sent by the transmitter before the first and second pulse sequences. Example 6 is the distance-measuring device of Example 5, wherein the processor is designed to determine the distance between the transmitter and the distance-measuring device from either the first processing result or the second processing result that is closer to the processing result generated by the processor from the earlier pulses of the previous pulse sequence that were sent by the transmitter before the first and second pulse sequences. Example 7 is the distance-measuring device of any of Examples 2 to 6, wherein the processor is designed to determine the distance between the transmitter and the distance-measuring device from one or more processing results.which are generated from analyzing a timing of one or more peaks in a further received signal, which is received by the receiver upon receiving further pulses of one or more further pulse sequences, excluding the first pulse sequence and the second pulse sequence, in response to the difference between the first processing result and the second processing result exceeding the threshold. Example 8 is the range-measuring device of one of Examples 1 to 7, wherein the first radar processing result is a first estimate of the distance between the transmitter and the range-measuring device, and the second radar processing result is a second estimate of the distance between the transmitter and the range-measuring device. Example 9 is the range-measuring device of one of Examples 1 to 3 or 5 to 7.wherein the first processing result is a first time interval between an earliest peak in a reverse search window prior to the highest peak in the first received signal, and the second processing result is a second time interval between an earliest peak in a reverse search window prior to a highest peak in the second received signal. Example 10 is the distance-measuring device of Examples 2 and 9, wherein the processor is configured to determine the distance between the transmitter and the distance-measuring device from the earliest peak in the reverse search window prior to the highest peak in the first received signal and / or from the earliest peak in the reverse search window prior to the highest peak in the second received signal in response thereto,that the difference between the first time interval and the second time interval does not exceed the threshold. Example 11 is a method for performing a radar range estimation between a transmitter and a receiver, comprising: receiving at the receiver first pulses of a first pulse train transmitted by a transmitter with a first interval between the pulses, receiving at the receiver second pulses of a second pulse train transmitted by the transmitter with a second interval between the pulses, wherein the first interval is different from the second interval, and generating a first processing result by analyzing a timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses, generating a second processing result by analyzing a timing of one or more peaks in a second received signal,that is received by the receiver upon receiving the second pulses, and determining a distance between the transmitter and the distance measuring device depending on a result of a comparison of the first processing result and the second processing result. Examples described in the context of the distance measuring device apply analogously to the procedure. Although specific embodiments have been illustrated and described herein, it will be clear to those skilled in the art that a variety of alternative and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover all adaptations or variations of the specific embodiments discussed herein. Therefore, this invention is to be limited only by the claims and their equivalents. Reference sign 101 First UWB Device 102 Second UWB Device 103 Pulse Generator 104 Control Unit 105 First Antenna 106 Antenna 107 Receiver 108 Processor 201-204 Diagrams 205 First Transmitted Pulse 206 Reflected Pulse 207 Second Transmitted Pulse 208 Highest Peak (in Received Signal) 301-304 Diagrams 305 First Transmitted Pulse 306 Reflected Pulse 307 Second Transmitted Pulse 308 Highest Peak (in Received Signal) 401-404 Diagrams 405 First Transmitted Pulse 406 Reflected Pulse 407 Second Transmitted Pulse 408 Highest Peak (in Received Signal) 500 Flowchart 501-505 Processing 601,602 Diagrams

Claims

Distance measuring device comprising: a receiver designed to receive first pulses of a first pulse train transmitted by a transmitter with a first interval between the pulses, and to receive second pulses of a second pulse train transmitted by the transmitter with a second interval between the pulses, wherein the first interval is different from the second interval; and a processor designed to produce a first processing result by analyzing the timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses; and to produce a second processing result by analyzing the timing of one or more peaks in a second received signal received by the receiver upon receiving the second pulses.and to determine a distance between the transmitter and the distance measuring device depending on the result of a comparison of the first processing result and the second processing result. Distance measuring device according to claim 1, wherein the processor is designed to perform the comparison of the first processing result and the second processing result by comparing a difference between the first processing result and the second processing result with a threshold value. Distance measuring device according to claim 2, wherein the processor is designed to discard the first processing result and / or the second processing result in response to the fact that the difference between the first processing result and the second processing result exceeds the threshold. Distance measuring device according to claim 3, wherein the processor is configured to check, in response to the difference between the first processing result and the second processing result exceeding the threshold, whether a reverse search window before a highest peak in the first received signal includes a peak, and to discard the first processing result in response to the fact that the reverse search window before the highest peak in the first received signal includes a peak, and to check whether a reverse search window before a highest peak in the second received signal includes a peak, and to discard the second processing result in response to the fact that the reverse search window before the highest peak in the second received signal includes a peak. Distance measuring device according to claim 3 or 4, wherein the processor is configured to discard one of the first processing result or of the second processing result which is less close to a processing result which the processor has generated from earlier pulses of an earlier pulse sequence which were sent by the transmitter prior to the first pulse sequence and the second pulse sequence. Distance measuring device according to claim 5, wherein the processor is designed to determine the distance between the transmitter and the distance measuring device from one of the first processing results or the second processing result which is closer to the processing result which the processor generated from the earlier pulses of the earlier pulse sequence which were sent by the transmitter before the first pulse sequence and the second pulse sequence. Distance measuring device according to one of claims 2 to 6, wherein the processor is designed to determine the distance between the transmitter and the distance measuring device from one or more processing results generated by analyzing a timing of one or more peaks in a further received signal received by the receiver upon receiving further pulses of one or more further pulse sequences, with the exception of the first pulse sequence and the second pulse sequence, in response to the difference between the first processing result and the second processing result exceeding the threshold. Distance measuring device according to one of claims 1 to 7, wherein the first processing result is a first estimate of the distance between the transmitter and the distance measuring device and the second processing result is a second estimate of the distance between the transmitter and the distance measuring device. Distance measuring device according to one of claims 1 to 3 or 5 to 7, wherein the first processing result is a first time interval between an earliest peak in a backward search window before the highest peak in the first received signal and the second processing result is a second time interval between an earliest peak in a backward search window before a highest peak in the second received signal. Distance measuring device according to claims 2 and 9, wherein the processor is designed to determine the distance between the transmitter and the distance measuring device from the earliest peak in the reverse search window before the highest peak in the first received signal and / or from the earliest peak in the reverse search window before the highest peak in the second received signal in response to the fact that the difference between the first time interval and the second time interval does not exceed the threshold. A method for performing a distance estimation between a transmitter and a receiver, comprising: receiving at the receiver the first pulses of a first pulse train transmitted by a transmitter with a first interval between the pulses; receiving at the receiver the second pulses of a second pulse train transmitted by the transmitter with a second interval between the pulses, wherein the first interval is different from the second interval; and generating a first processing result by analyzing the timing of one or more peaks in a first received signal received by the receiver upon receiving the first pulses; generating a second processing result by analyzing the timing of one or more peaks in a second received signal received by the receiver upon receiving the second pulses;and determining a distance between the transmitter and the distance measuring device depending on the result of a comparison of the first processing result and the second processing result.

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