Method for secure time of arrival measurement

Abstract

A method for UWB secure ToA: receiving, at a receiving device, a secure distance message from a transmitting device, the secure distance message comprising a UWB signal, the UWB signal comprising a secret distance pulse sequence; determining, at the receiving device, a ToA of a path of the secure distance message; determining, in the UWB signal, an instant of a pulse of an expected secret distance pulse sequence of the path based on the determined time of arrival of the path of the secure distance message; decoding its respective bit value from the UWB signal at the determined time of the respective UWB pulse to determine a bit sequence received over the path of the secure distance message; the received bit sequence decoded from the UWB signal is compared to the provided secret distance bit sequence to verify the authenticity of the transmitting device and the integrity of the time of arrival measurement.

Description

Technical Field

[0001] The invention relates to the field of ultra-wideband (UWB) safe arrival time measurement and UWB safe distance measurement. Background Art

[0002] UWB distance measurement is well known. The verifier V sends a challenge message C1 with a distance pulse sequence N to the prover P in the UWB channel, and the prover P sends a response message R1 with the distance pulse sequence N back to the verifier V in the UWB channel, as shown in Figure 1. The distance pulse sequence N is used to detect the exact arrival time of the challenge message C1 and the response message R1. Due to the verifier time difference DTv between the arrival time of the sent challenge message C1 and the response message R1, the flight time of the two messages C1 and R1 can be determined, and thus the distance between the verifier V and the prover P can be determined. Due to the use of the UWB channel, the pulses of the distance pulse sequence N can be sent with a very short duration of 1ns to 2ns in length, so that the arrival time of the distance pulse sequence N can be determined with a small error, and thus the arrival time of the messages C1 and R1 can be determined. The distance between the prover and the verifier can be determined based on the verifier time difference DTv and the response time of the prover P. The reply time of the prover P may be sent from the prover P to the verifier V (bilateral two-way ranging) or may be fixed (unilateral two-way ranging). Thus, the quality of the distance measurement depends on the quality of the arrival time measurement of the message R1 at the verifier V and, for bilateral two-way ranging, also on the quality of the arrival time measurement of the message C1 at the prover P.

[0003] The arrival time of the range pulse sequence N at the receiver is usually determined by the cross-correlation between the theoretical / expected signal of the (transmitted) range pulse sequence N and the UWB signal received at the receiver. When the expected range pulse sequence N corresponds to the range pulse sequence N received at the receiver, the correct arrival time is indicated by the peak of the cross-correlation. However, for a random range pulse sequence N, the cross-correlation function will result in a high peak for the correct arrival time and multiple small peaks (false peaks) corresponding to some cross-correlation positions shifted by a multiple of the inter-pulse distance of the range pulse sequence, which happen not to be averaged. The false peaks may have amplitudes well above the noise level and create false early paths (as discussed later with respect to FIG. 1 ). Fig.11). This is why for distance measurement, a distance pulse sequence N with special properties is always used, which theoretically removes false peaks. The distance pulse sequence N usually uses Ipatov codes or Gold codes that show these properties. For such a special distance pulse sequence N, the cross correlation does not show any false peaks, so that each peak of the cross correlation corresponds to a different real path of the message or distance pulse sequence N. The same problem arises for determining the CIR based on the preamble in the header of the message. This is also the reason why the preamble (also called SYNC mode in UWB) uses such special properties with, for example, Ipatov codes. Therefore, the preamble of a UWB message is usually used to measure the arrival time of the message. This is why the distance pulse sequence used for arrival time measurement is also often called a preamble or a preamble fragment.

[0004] In order to prevent someone from falsifying the distance by sending a known distance pulse sequence N from an unauthenticated device, the messages C1 and R1 include security pulse sequences SECv and SECp, which are usually sent in a fixed time relationship with the distance pulse sequence N. The security pulse sequence SEC, sometimes also called the ranging integrity fragment, is usually a pulse sequence that is randomly modulated (i.e., carries random bits). In order to authenticate the transmitter V or P, the receiver P or V again creates a cross-correlation of the expected security pulse sequence SECv or SECp with the received UWB signal. In the prior art, the authenticity of the transmitter P or V or the integrity of the messages C1, R1 are verified by two methods. The arrival time determined by the cross-correlation of the security pulse sequence is compared with the arrival time determined using the preamble N, and if they are consistent, the transmitter V or P is recognized. Alternatively, the arrival time can also be determined using only the security pulse sequence SECv or SECp. Since the attacker does not know the security pulse sequence SECv or SECp, it is generally considered safe to perform distance measurements using such a security pulse sequence SECv or SECp.

[0005] However, Singh et al., in their article “Security Analysis of IEEE802.15.4z / HRP UWB Time-of-Flight” published at ACM WiSec 2021, show an attack that can actually compromise the security distance measurement and create a false shorter distance. Since the security pulse sequence SECv or SECp is based on the cross-correlation of the complete security pulse sequence SECv or SECp, an attack corrects the power of the wrong guess of the security pulse sequence by using twice the power of the next guess until the guess is correct.

[0006] Even if the security pulse sequence SECp or SECv is decoded, standard data decoding techniques are used, which usually do not use the earliest path but the strongest path or the complete channel impulse response (CIR) to decode the data. This also compromises the security of the distance measurement.

[0007] Another problem with the separate transmission of the distance pulse sequence N for arrival time measurement and the security pulse sequence SECp or SECv for authentication is that the UWB messages that need to be transmitted become longer, while the energy or TX budget that can be transmitted in a UWB message is limited for regulatory reasons. TX budget. This means that the transmission energy of a UWB channel is limited within a certain time. The energy corresponds to the average power of the UWB channel multiplied by the time or integrated over time. More precisely, the energy of each UWB channel cannot exceed a maximum energy (also called TX budget or transmission budget) every 1ms. During this 1ms period, the energy can be freely allocated as long as it does not exceed the maximum energy. Shorter UWB messages that require fewer UWB pulses can use pulses transmitted with higher energy, while longer UWB messages that usually have a larger number of pulses can only be transmitted with lower energy of the individual pulses. This makes it more difficult to receive such longer UWB messages because their pulses are hidden in the noise. Therefore, UWB messages with more pulses sent at lower power using the same TX budget usually make the reception of UWB messages more difficult for longer distances and noisy environments. A part of the TX budget is already occupied by the header of the UWB message (usually including the preamble or the range pulse sequence N for the arrival time measurement). The remaining TX budget can be used for the security pulse sequence SEC. The longer the range pulse sequence N is chosen, the more accurately and robustly the arrival time of the UWB message can be determined. The longer the safety range pulse sequence SEC is chosen, the higher the security of the distance measurement. Therefore, the length of these two pulse sequences in a UWB message is therefore always a compromise between robustness / time accuracy and security.

[0008] US2018 / 138993A1 discloses a secure arrival time measurement, wherein the arrival time is measured using correlation with a synchronization pattern and verified by correlation with a secret verification pattern. In one embodiment, the arrival time is directly measured using correlation with a secret verification pattern without the need for a synchronization pattern. In one embodiment, a bit sequence transmitted in a secret verification pattern is demodulated to authenticate a transmitter device.

[0009] US2018 / 254925A1 also discloses safe arrival time measurement.

[0010] The LAN / MAN Standards Committee of the IEEE Computer Society has published the standard "Draft P802.15.4z(TM) / D07 Low-Rate Wireless Network Amendment: Enhanced Ultra-Wideband (UWB) Physical Layer (PHY) and Related Ranging Techniques" along with information on the error resilience of decoded bit sequences used for transmitter authentication. Summary of the invention

[0011] It is an object of the present invention to provide a protocol for UWB secure time of arrival measurement which avoids the problems of the prior art and in particular is secure against attacks.

[0012] According to the invention, this object is solved by the independent claims.

[0013] The object is achieved by a method for UWB secure arrival time measurement of a secure distance message, wherein the secure distance message transmits a distance pulse sequence corresponding to a secret distance bit sequence from a transmitting device to a receiving device in a UWB channel, the method comprising the following steps: providing a secret distance bit sequence at a receiving device; determining an expected secret distance pulse sequence corresponding to a secret distance bit sequence expected to be received in the UWB channel at the receiving device when receiving the secure distance message; receiving a secure distance message from the transmitting device at the receiving device, wherein the received secure distance message comprises a UWB signal, and the UWB signal comprises a secret distance pulse sequence corresponding to the secret distance bit sequence; based on The invention relates to a method for determining an arrival time of a path of a safe distance message at a receiving device based on an expected distance pulse sequence and a UWB signal containing a secret distance pulse sequence in a received safe distance message; determining the moment of a pulse of an expected secret distance pulse sequence of the path in the UWB signal based on the determined arrival time of the path of the safe distance message; decoding a corresponding bit value of the corresponding UWB pulse value from the UWB signal at the moment of the determined corresponding UWB pulse value to determine a bit sequence received through the path of the safe distance message; comparing the received bit sequence decoded from the UWB signal with the provided secret distance bit sequence to verify the authenticity of the transmitting device and the integrity of the arrival time measurement.

[0014] The object is solved by a method for transmitting a secure range message, the method comprising the following steps: transmitting a secure range message to a receiving device, wherein the secure range message comprises a secret range pulse sequence for distance measurement and authenticity verification, wherein at least the secret range pulse sequence of the secure range message is sent in a UWB channel.

[0015] This object is solved by a computer program comprising instructions configured to perform one of the methods described above when executed on a processor.

[0016] The object is solved by a receiving device for receiving a safe distance message from a transmitting device, the safe distance message comprising a range pulse sequence corresponding to a secret distance bit sequence, the receiving device comprising a receiving device and a processing device; wherein the receiving device is configured to receive the safe distance message from the transmitting device, wherein the received safe distance message comprises a UWB signal, and the UWB signal comprises a secret distance pulse sequence corresponding to the secret distance bit sequence; wherein the processing device is configured to: provide the secret distance bit sequence; when receiving the safe distance message, determine an expected secret distance pulse sequence corresponding to the secret distance bit sequence expected to be received in the UWB channel; based on the expected distance pulse sequence The method comprises: determining an arrival time of a path of the safety distance message at a receiving device based on a pulse sequence of the safety distance message and a UWB signal containing a secret distance pulse sequence in the received safety distance message; determining the moment of a pulse of an expected secret distance pulse sequence for the path in the UWB signal based on the determined arrival time of the path of the safety distance message; decoding a corresponding bit value of the corresponding UWB pulse value from the UWB signal at the moment of the determined corresponding UWB pulse value to determine a bit sequence received through the path of the safety distance message; and comparing the received bit sequence decoded from the UWB signal with the provided secret distance bit sequence to verify the authenticity of the transmitting device and the integrity of the arrival time measurement.

[0017] The object is solved by a transmitting device for transmitting a secure range message to a receiving device, wherein the secure range message comprises a secret range pulse sequence for distance measurement and authenticity verification, wherein at least the secret range pulse sequence of the secure range message is sent in a UWB channel.

[0018] The object is also solved by a method for distance measurement between a verifier and a prover, the method comprising the following steps: sending a challenge message having a challenge pulse sequence from the verifier to the prover; sending a response message having a response pulse sequence from the prover to the verifier; securely determining an arrival time of the response message at the verifier based on a method for secure arrival time measurement; determining the distance between the verifier and the prover based on a verifier time difference between a challenge message sent from the verifier and a determined arrival time of the response message.

[0019] The object is also solved by a system for distance measurement, the system comprising a verifier and a prover, wherein the verifier is configured to send a challenge message with a challenge pulse sequence to the prover; wherein the prover is configured to send a response message with a response pulse sequence to the verifier; wherein the verifier is configured to securely determine the arrival time of the response message at the verifier based on a method for secure arrival time measurement, or wherein the verifier is a receiving device that determines the secure arrival time of the response message as described above; and the distance between the verifier and the prover is determined based on the verifier time difference between the challenge message sent from the verifier and the determined arrival time of the response message.

[0020] The idea of ​​the present invention is to use the same secret distance pulse sequence to perform arrival time measurement and verify the authenticity of the transmitting device, and decode the bit sequence at the moment corresponding to the path determined as the arrival time of the safe distance message to verify the integrity of the arrival time measurement. In this way, high security is achieved against any known attack. Instead of simply considering the cross-correlation of the secret distance pulse sequence to verify the authenticity of the transmitting device, the actual transmitted bit sequence is decoded from the UWB signal. However, the decoding of the UWB signal is only performed at the moment defined by the path corresponding to the determined arrival time. This guarantees a high level of security relative to any method that attempts to guess the secret distance pulse sequence and manipulate the power of individual pulses (based on previous guesses). Therefore, the method is also used to verify the integrity of the arrival time measurement, and any manipulation of the arrival time measurement can be detected when decoding the bit sequence at the corresponding moment on the path. Since the same secret distance pulse sequence is used for arrival time measurement and authenticity verification, the pulse sequence can be selected to be longer, so that the influence of false paths can be reduced. In addition, in the case where the bit decoding associated with a path is based on the same pulse sequence that is also used to determine the arrival time (i.e., the path selected for decoding), the robustness of the bit decoding is increased. This decoding technique is also different from most known classical UWB decoding techniques, which usually use the strongest path or the full CIR for decoding, and are therefore independent of the path of the determined arrival time. This opens up the possibility of security attacks against secure arrival time measurements.

[0021] The dependent claims relate to advantageous embodiments of the invention.

[0022] In one embodiment, the step of comparing the received bit sequence decoded from the UWB signal with the provided secret distance bit sequence includes determining the number of errors in the received bit sequence relative to the secret distance bit sequence, and if the determined number of errors is below a threshold, the transmitter is considered authenticated. Decoding the bit sequence at a moment in the path associated with the determined arrival time may increase the error rate of the decoded bit sequence. By accepting a certain error rate in the bit sequence decoded to verify the authenticity of the transmitting device and the integrity of the arrival time, secure arrival time measurements can also be performed in noisy environments.

[0023] In one embodiment, at each determined time instant of the UWB signal, bits of the time instant are decoded from a time window of the UWB signal surrounding the time instant, wherein the time window is less than or equal to sixteen nanoseconds.

[0024] In one embodiment, at the receiver, the same pulse of the secret range pulse sequence is used once to detect the arrival time and once to decode the bit value of the pulse.

[0025] In one embodiment, the secret range pulse sequence is transmitted in the UWB channel using a time hopping method using two or more different inter-pulse distances, preferably more than two different inter-pulse distances.

[0026] The different inter-pulse distances reduce the magnitude of false paths when determining the arrival time based on a combination (e.g., cross-correlation) of the expected range pulse sequence and the received UWB signal containing the secret range pulse sequence in the safe range message, and improve the quality of the arrival time measurement to find the correct true earliest path of the safe range message.

[0027] In one embodiment, the arrival time of the secure range message at the receiving device is determined based on the cross-correlation between the expected secret range pulse sequence and the received UWB signal.

[0028] In one embodiment, an early path time window prior to a maximum value of the cross-correlation is determined, wherein a weak early path is detected in this early path time window.

[0029] In one embodiment, a mismatched range pulse sequence is calculated, which changes some pulse values ​​of the secret pulse sequence to minimize false peaks in the cross-correlation in the early path time window, wherein the weak early path is determined based on the cross-correlation between the mismatched range pulse sequence and the received UWB signal in the early path time window. This embodiment enables the reduction of false paths when determining the arrival time based on the cross-correlation of the expected range pulse sequence and the UWB signal containing the secret range pulse sequence in the received safe range message, and enables the improvement of the quality of the arrival time measurement to find the correct true earliest path of the safe range message.

[0030] In one embodiment, the secret distance pulse sequence includes a combination of a known part and a secret part, wherein the known part corresponds to a special code that reduces or removes false peaks. Due to the effect of the known special code pulse, the false paths generated by the secret part are reduced.

[0031] In one embodiment, each pulse of the secret distance pulse sequence has a first pulse value or a second pulse value, wherein the secret distance pulse sequence includes known pulses and secret pulses, wherein the known pulses are pulses whose pulse values ​​are known, wherein the secret pulses are pulses whose pulse values ​​are secret, wherein the known pulses follow a special code that reduces or removes false peaks, wherein the special code includes a first code value corresponding to the first pulse value, a second code value corresponding to the second pulse value, and a third code value corresponding to a non-transmitted pulse, wherein the secret pulses are transmitted at positions of at least some of the third code values ​​in the special code. Preferably, the special code is an IPATOV code. Due to the effect of the known special code pulses, the false paths generated by the interleaved secret pulses are reduced.

[0032] Subsequent embodiments enable increasing the TX budget available for secret range pulse sequences. The increased TX budget enables sending longer secret range pulse sequences with more pulses, which reduces the magnitude of false paths as they are averaged over larger numbers.

[0033] In one embodiment, the safety distance message includes a first information portion and a subsequent second information portion, wherein the second information portion contains a safety distance bit sequence, and wherein the first information portion is used to detect the safety distance message in the received signal and / or to determine a clock offset between a system clock of the receiving device and a system clock of the transmitting device.

[0034] In one embodiment, the safety distance message includes a message frame in the physical layer, wherein a first information portion is transmitted in a narrowband channel, and a second information portion is transmitted in a UWB channel after the second information portion, and a time relationship between the first information portion and the second information portion is defined by the message frame in the physical layer.

[0035] In one embodiment, the safe distance message includes a message frame in a physical layer, wherein a first information portion is transmitted in a first UWB frequency-time portion and a second information portion is transmitted in at least one second UWB frequency-time portion, wherein each UWB frequency-time portion is defined as a portion of the UWB frequency-time domain limited by a TX budget of the UWB channel, wherein the first UWB frequency-time portion is different from the second UWB frequency-time portion.

[0036] In one embodiment, the second information portion is sent after a minimum time after the start of the first information portion that is required to have the full UWB TX budget in the UWB channel again.

[0037] In one embodiment, an expected arrival time of an expected range pulse sequence in a UWB channel relative to an arrival time of the first information portion is determined based on a message protocol of the safety range message and based on a determined clock offset, wherein an arrival time of the safety range message at a receiving device is determined based on the expected range pulse sequence and a UWB signal received at the expected arrival time.

[0038] In one embodiment, the second information portion is transmitted in the UWB channel without a message portion including a preamble, a frame start delimiter, and a packet header.

[0039] In one embodiment, the second information portion includes a plurality of second information sub-portions transmitted in different UWB frequency-time portions, wherein each different UWB frequency-time portion is defined as a portion of the UWB frequency-time domain limited by a TX budget of the UWB channel, and wherein the secret range pulse sequence includes a plurality of different secret range pulse sub-sequences transmitted in different second information sub-portions.

[0040] In one embodiment, the secret range pulse sequence comprises a plurality of different secret range pulse sub-sequences transmitted in different UWB frequency-time portions of the UWB channel.Other embodiments according to the invention are mentioned in the attached claims and in the subsequent description of the drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a schematic diagram showing an implementation of the prior art of safety distance measurement.

[0042] FIG. 2 is a diagram of a frame in a physical layer for a UWB message or a NB message according to the prior art.

[0043] FIG. 3 shows an exemplary time sequence of a pulse sequence with equally spaced pulses.

[0044] FIG. 4 shows an exemplary time sequence of a pulse sequence with burst pulses.

[0045] Figure 5A is a diagram of a first example of a message frame in a physical layer for a safety distance message according to the present invention.

[0046] Figure 5B is a diagram of a second example of a message frame in a physical layer for a safety distance message according to the present invention.

[0047] Figure 6 is a diagram of the transmission of an exemplary message frame and its communication channel between a transmitter and a receiver.

[0048] Figure 7 is a diagram of a third example of a message frame in a physical layer for a safety distance message according to the present invention.

[0049] Figure 8 is a diagram of a fourth example of a message frame in a physical layer for a safety distance message according to the present invention.

[0050] Fig. 9 is a diagram of a fifth example of a message frame in a physical layer for a safety distance message according to the present invention.

[0051] Fig.10 An example of a method of measuring the safe arrival time of a message is described.

[0052] Fig.11 Embodiments of a system, method, verifier, and prover for secure distance measurement according to the present invention are shown.

[0053] FIG. 12 illustrates the problem of determining the cross-correlation of a sequence of short random pulses in a multipath environment.

[0054] Fig.13 An improved implementation for reducing the false path problem is shown. DETAILED DESCRIPTION

[0055] Other characteristics and advantages of the invention will emerge from the following non-limiting description with reference to the accompanying drawings.

[0056] In the following, some terms used herein are defined.

[0057] A message is a data unit in the physical layer of the OSI model. In other words, a message is a data unit transmitted through a communication channel, in the present invention, via a radio communication channel, wherein the data unit has a common organizational structure. This organizational structure of a message is called a message frame or a message protocol. A message usually includes some information at the beginning that enables detection of a message, determination of a clock offset, and / or determination of a frequency offset, etc. A message usually contains other information about a transmitting device (source point) and a receiving device (end point) so that the receiver RX knows whether the message is indeed addressed to the receiver RX. Otherwise, it can ignore the message. Depending on the message protocol, the management information is simpler or more complex. The management information applies to the complete data transmitted in the message. The new message includes the management information again and is therefore completely independent of the previous message. The two messages are independent of each other in terms of the data transmitted, as well as in terms of transmission timing. The new message requires a new synchronization of the new message. Traditionally, messages are transmitted in the same communication channel. In the present invention, there are some such embodiments in which messages are transmitted in two subsequent different communication channels, as will be explained in more detail below.

[0058] A message frame is a definition of the arrangement of data transmitted in a message (also called a message protocol). The message protocol or frame is known. This means that the message protocol is fixed (always the same) or defined by parameters sent within the message itself. Figure 2 shows an example definition of a message frame for a message in the physical layer. A message frame in the physical layer includes a synchronization header SHR, a packet header PHR, and a physical payload P. The synchronization header includes a synchronization pattern, which is generally referred to as PREAMBLE in NB and SYNC in UWB. The terms PREAMBLE and SYNC are used interchangeably here. After the synchronization pattern, the synchronization header SHR generally includes a frame start delimiter SFD. PHR generally includes the length of the message so that the receiver RX will know when the message / frame ends. The physical payload includes the transmitted data. SHR and PHR are used for the physical layer, i.e., for the receiving chip to identify the message in the received signal of the communication channel. The physical payload generally includes other frames of the next higher OSI model layer (data link layer), generally referred to as MAC frames. The MAC frame comprises a MAC header MHR with communication management information about the transmitter, the receiver RX, the network connection, etc. The MAC payload comprises the data that should be transmitted. Even though this is the preferred organization of the transmitted frames, other organizations are possible.

[0059] Messages and / or frames are physically transmitted through a communication channel (short channel), and in the present invention, they are transmitted via a radio communication channel. The radio communication channel includes a radio signal that transmits a message. The wireless communication channel or wireless signal has a bandwidth. The bandwidth in the present invention can be ultra-wideband (UWB) or narrowband (NB). UWB preferably has a bandwidth of more than 50MHz, more preferably a bandwidth of more than 100MHz, more preferably a bandwidth of more than 200MHz, more preferably a bandwidth of more than 300MHz, more preferably a bandwidth of more than 400MHz, and most preferably a bandwidth of more than 500MHz. NB has a bandwidth that does not significantly exceed the coherent bandwidth of the channel, that is, less than the coherent bandwidth of the channel. NB has a bandwidth that is preferably less than 50MHz, preferably less than 20MHz, preferably less than 10MHz, preferably less than 5MHz, preferably less than 1MHz, and preferably less than 500Hz. The bandwidth of the NB defined here refers to the bandwidth used in a single NB communication channel. The data or bits of the message frame are transmitted by symbols. Depending on the modulation scheme, a symbol usually transmits one or more bits. It is also possible that a symbol including multiple pulses transmits one bit. While NB symbols (symbols of the NB channel) can be transmitted in an infinite time but preferably long enough for high symbol energy, UWB symbols are transmitted in short time periods with high instantaneous power. UWB symbols can be, for example, hundreds of ns long or even a few microseconds, but each of the at least one UWB pulses that constitute the UWB symbol is in the nanosecond range or less. A radio signal has a carrier frequency at which the message is transmitted. Traditionally, the NB carrier frequency for oob messages is in the ultra-high frequency (UHF) band (below 3 GHz), and the UWB carrier frequency is in the extremely high frequency (SHF) band (above 3 GHz). Preferably, in the present invention, if a NB channel is used, its carrier frequency is greater than 2.4 GHz, preferably greater than 2.5 GHz, preferably greater than 3 GHz, preferably greater than 5 GHz. Preferably, the carrier frequency of the NB channel is selected near the carrier frequency of the UWB channel so that the same antenna and the same transceiver components can be used for NB and UWB channels. Preferably, the carrier frequency of the NB channel is closer to the carrier frequency of the UWB channel than 2 GHz, preferably than 1 GHz, preferably than 500 MHz. In theory, the same carrier frequency can also be used for NB and UWB channels. However, for regulatory purposes and bandwidth sharing (e.g., multi-user), different carrier frequencies are preferably used. The UWB channel may include different UWB sub-channels.

[0060] like Figure 6As shown, a message M is transmitted from a transmitting device TX to a receiving device RX. The transmitting device is also referred to as a transmitter TX and / or the receiving device is also referred to as a receiver RX. The transmitter TX is described as a device having all the functions required to transmit the message M, and the receiver RX is described as a device having all the functions required to receive the message M. However, in a preferred embodiment, the transmitting device TX can act as a receiver RX and a transmitter TX, i.e. as a transceiver. In a preferred embodiment, the receiving device RX can act as a receiver RX and a transmitter TX, i.e. as a transceiver. In such a case, the transceiver has the functions of a transmitting device and a receiving device.

[0061] The range pulse sequence is a sequence of UWB pulses used at the receiver RX to measure the arrival time of the received message M. The arrival time of the received message M can be used to calculate the flight time, for example, the time between sending the previous message M and the measured arrival time (for example, the verifier time difference) or the time between the measured arrival time and the time of sending the subsequent message (for example, the prover time difference). The range pulse sequence according to the present invention is always transmitted in the UWB channel. The arrival time measurement is sometimes also referred to as the timestamp of the received message M. Therefore, other UWB pulses or NB symbols that are not directly used to measure the arrival time transmitted before or after the range pulse sequence are not considered to be range pulse sequences. The range pulse sequence corresponds to the range bit sequence. Therefore, the range bit sequence refers to the bit sequence after the transmitted range pulse sequence. The number of pulses of the range pulse sequence is generally equal to the number of bits of the range bit sequence, but it can also be higher or lower than the number of bits of the range bit sequence. In some embodiments, one bit of the range bit sequence corresponds to one UWB pulse of the range pulse sequence, resulting in the same number of bits of the range bit sequence as the number of pulses in the range pulse sequence. UWB symbols generally have one or more UWB pulses. Multiple bits may also correspond to a certain UWB symbol. It is also possible that one bit of the distance bit sequence corresponds to a UWB symbol with multiple UWB pulses, just as when a spread spectrum code is used. Moreover, the order of the bits or spread spectrum codes generally corresponds to the order of the pulses of the distance pulse sequence. However, the order of the bits in the distance pulse sequence (or the chips of the spread spectrum code) may also be rearranged, for example as in WO2017 / 121452. Therefore, the term distance pulse sequence refers to a complete sequence of UWB pulses for arrival time measurement, i.e., preferably, for the cross-correlation between the expected distance pulse sequence and the UWB signal transmitting the distance pulse sequence. The distance pulse sequence is a conversion of the distance bit sequence in the physical layer of the OSI model, i.e., what is sent from the device. The term distance bit sequence refers to the data behind the distance pulse sequence. These data or distance bit sequences may have been transmitted before the actual distance pulse sequence (but transmitted in encrypted form to maintain the confidentiality of the distance bit sequence). The distance bit sequence refers to the data carried by the distance pulse sequence on the physical layer of the OSI model. The abbreviation "range pulse / bit sequence" shall mean a range pulse sequence and / or a range bit sequence.

[0062] In the prior art, the distance pulse / bit sequence used is known to a third party, usually a periodic bit sequence that facilitates arrival time detection, usually a preamble or SYNC pattern of a UWB message. In the present invention, the distance bit / pulse sequence is secret and / or varies with the message. Therefore, a secret distance bit / pulse sequence will mean that a third-party device cannot know the distance pulse sequence used in advance, for example, by predicting the last part of the distance pulse sequence, thereby compromising the distance measurement. The secret distance bit sequence is usually a random number (nonce) generated by a cryptographic method. It is also feasible that only a part of the distance bit / pulse sequence is secret. In this case, the secret distance bit / pulse sequence includes at least one secret part and at least one known part. The secret distance bit / pulse can theoretically include a secret part and a known part, and the two parts are connected to each other. Unlike the prior art, the secret part is also used to determine the arrival time. However, preferably, the secret part is interleaved with the known part. Therefore, the secret distance pulse sequence includes known pulses and secret pulses, and the secret pulses are distributed between the known pulses. In one embodiment, more than 20%, preferably more than 30%, preferably more than 50%, preferably more than 70%, preferably more than 80%, preferably more than 90%, preferably more than 95% of the pulses / bits of the distance pulse / bit sequence are secret, i.e. unknown to an attacker. For example, the initial part of the distance pulse / bit sequence can be periodic, while the subsequent secret part is, for example, random. However, in such a case, both the non-secret part and the secret part of the distance pulse sequence are always used completely for the arrival time and completely for the verification step (see below). Most preferably, the entire distance bit / pulse sequence is secret. For the sake of brevity, the secret distance pulse / bit sequence is referred to as the distance pulse / bit sequence without the adjective "secret", but should always be intended (if not otherwise mentioned) to be a secret distance pulse / bit sequence.

[0063] In most cases, the range pulse sequence is transmitted by an equidistant pulse sequence 41, which is transmitted in an equidistant manner, i.e. with the same time difference between all pulses of the range pulse sequence, as shown in the example of FIG3. However, the range pulse sequence can also be transmitted in a time sequence different from that of FIG3. For example, an alternative is to transmit the pulses 41 of the range pulse sequence in a pulse group 42 as shown in FIG4, i.e. as a group pulse sequence. The pulse group 42 comprises at least two pulses 41. The group pulse sequence comprises a sequence of at least two groups (multiple groups). The time difference between two consecutive pulses 41 of the same group 42 is less than the time difference T between two consecutive groups 42. G. The pulses 41 of the same group 42 are usually sent one after another in a short time. Preferably, the time difference between consecutive pulses 41 of the same group 42 is less than 10 times, preferably less than 8 times, preferably less than 6 times, preferably less than 5 times, preferably less than 4 times, preferably less than 3 times, of the duration of the pulse 41. The time difference between two consecutive pulses 41 of the same group 42 is preferably less than or equal to ten times the pulse duration, preferably less than or equal to five times the pulse duration, preferably less than or equal to three times the pulse duration, preferably less than or equal to two times the pulse duration, preferably less than or equal to one times the pulse duration. The time difference between consecutive pulses should be the time difference between the same characteristic points (e.g., the peaks of the pulses 41) of the corresponding pulses 41. The pulse duration is, for example, 2ns, and the pulses in the group 42 of pulses 41 are sent every 4ns or 2ns. Usually the group 42 of pulses 41 is a symbol of a bit, also called a burst or a spread spectrum code. The symbol or the pulse 41 of the group 42 is also usually called a chip. Such a spreading code or burst 42 facilitates the reception of the transmitted bit sequence, since the transmission energy per bit is increased by a factor of the number of chips per symbol. However, the longer the symbol length becomes, the higher the risk of manipulation of the arrival times by a malicious third party. It is therefore preferred that the pulses 41 are sent as close together as possible to make manipulation of the arrival times as difficult as possible. Group pulse sequences have the additional advantage that the pulses 41 are grouped so that large time differences are produced between the groups 42, which avoids the generation of noise by the first group 42 with respect to the second group in an environment with a long channel impulse response. This greatly facilitates the reception of the signal and avoids complex and power-consuming post-processing of the received signal in order to filter out the channel impulse response.

[0064] The term distance bit information shall indicate any information that enables the determination of a (secret) distance bit sequence from the distance bit information. The distance bit information may be the distance bit sequence itself. In other embodiments, the distance bit information may be shorter than the distance bit sequence. For example, the distance bit information may be seed information that allows the determination of the distance bit information by a (cryptographic) function. When the distance bit information must be (secretly) exchanged between a transmitting device and a receiving device, the latter embodiment enables the amount of data to be exchanged to be reduced.

[0065] The above explanations of the message M also apply to the safety distance message M according to the invention.

[0066] Figure 5AA first example of a message frame of a safety distance message M according to the present invention is shown. The safety distance message M is a standard UWB message including a synchronization header SHR and optionally a MAC header PHR. The (MAC) payload of the message M contains a safety distance bit sequence transmitted together with a safety distance pulse sequence. The complete message M is transmitted in the UWB channel and in the same UWB time slot and in the same UWB subchannel.

[0067] Figure 5B A preferred embodiment of a message frame or protocol of a safety distance message M is shown. The message M contains a first information part A and a second information part B in a common message frame. The second information part is always transmitted in the UWB channel.

[0068] In one embodiment, the first information part is transmitted in the same UWB channel as the second information part, but preferably in a different UWB frequency-time part than the second information part. A UWB frequency-time part is defined as a part of the UWB frequency-time domain that is limited by the TX budget LB. Therefore, two different UWB frequency-time parts each have an independent TX budget LB, so that the two different UWB frequency-time parts allow twice the energy of the TX budget LB to be transmitted together in the UWB spectrum. The two different UWB frequency-time parts can be two different UWB subchannels or two different TX budget (time) slots. Two different UWB subchannels mean that the first information part A and the second information part B are sent in different UWB subchannels of the UWB channel, that is, at different carrier frequencies. Two different TX budget (time) slots mean that the first information part A and the second information part B are sent in different UWB TX budget (time) slots, that is, usually 1ms after the start of the first information part A, so that the second information part B has an available TX budget again. Such an embodiment is Figure 7 In this embodiment, the first information portion A is intended to be the complete information of the message M transmitted in the first UWB frequency-time portion (before the second information portion B), and the second information portion B is intended to be the complete information of the message M transmitted in at least one second UWB frequency-time portion (different from the first frequency-time portion).

[0069] In another embodiment, Figure 8As shown, the first information part is transmitted in the NB channel. In this embodiment, the first information part A is intended to be the complete information of the message M transmitted in the NB channel (before the second information part), and the second information part B is intended to be the complete information of the message M transmitted in the UWB channel. In a preferred embodiment, the message M does not include other parts except the first information part A and the second information part B, so that the message consists of the first information part A and the second information part B. However, in another embodiment, the third information part can also be transmitted in the NB channel after the second information part. Preferably, the first information part A and the second information part are sent using the same oscillator / clock in the transmitter and received using the same oscillator / clock in the receiver RX. This enables the clock offset in the UWB channel to be determined by the recovered clock offset in the NB channel.

[0070] The first information part A is transmitted before the second information part B (in a NB or UWB channel). Preferably, the second information part B is transmitted after the first information part A has been completely transmitted, i.e. the second information part B is transmitted only after the end of the first information part A has been transmitted. Preferably, the second information part B has a well-defined time relationship with respect to the first information part A. This well-defined time relationship enables a receiver RX receiving a message M with a common frame to know based on the arrival time of the first information part and to know / calculate the expected arrival of the second information part B based on the well-defined time relationship. In case the first information part A is transmitted in a UWB channel, the second information part B may be sent at least one TX budget time period after the start of the first information part A, so that the second information part B has the full TX budget available again. The TX budget time period is a regulatory time defined in the UWB radio standard, after which the UWB channel again provides a full TX budget. Currently, the TX budget time period is 1 ms. In case the first information part A is transmitted in a NB channel, the well-defined time relationship may for example be a fixed time period between the end of the first information part A and the start of the second information part B. In one embodiment, the symbol length of the NB channel of the first information portion A and the symbol length of the second information portion B may be equal, so that the UWB symbols of the second information portion may be arranged after the NB symbols of the first information portion A by a multiple of the symbol length. However, many other well-defined time relationships may be implemented.

[0071] The first information part A preferably comprises synchronization information, preferably a synchronization header SHR in a classic frame as shown in FIG2 . The synchronization header or synchronization information preferably comprises a preamble SYNC and an SFD. As described above, the SHR or the preamble SYNC can be used at the receiver RX to detect the message M in the radio channel and determine the clock offset. The receiver RX can detect the message M in the radio channel, for example, by correlating the received signal of the radio channel with a reference signal corresponding to the radio signal containing the synchronization information, the SHR and / or the preamble SYNC. When the correlation becomes high, the receiver RX knows that the message M is received. Due to the longer symbols in the time domain and the clearer frequency shape of these symbols and due to the higher transmission amplitude (without the energy per millisecond limit in UWB), it is easier, less power-consuming and less error-prone to detect the message M in the NB channel than to detect the message or SHR in the UWB channel.

[0072] The transmitter TX, the receiver RX or the transceiver usually has an oscillator that defines the clock of the transmitter TX, the receiver RX or the transceiver. The clock or oscillator is used to generate a carrier frequency and determine the transmission or reception time of a bit, pulse or symbol of a signal. The receiver RX determines the clock offset based on the first information part A. In contrast to the arrival time of the NB message, the clock offset between the receiver RX and the transmitter TX can be determined more accurately than from the UWB part of the message M. The receiver RX preferably determines the clock offset based on synchronization information, SHR and / or preamble. The clock offset defines the offset of the system clock of the receiver RX relative to the system clock of the transmitter TX. When the transmitter TX has a different system clock (compared to the receiver RX), between the transmitter TX and the receiver RX, the symbol can be different in length (time drift) and carrier phase (phase rotation), thereby reducing the TX budget and the maximum range of communication. Therefore, if the clock offset is not taken into account at the receiver RX, this will result in the symbols of the message M transmitted at the transmitter TX and the symbols of the message M expected at the receiver RX. Different length and / or carrier phase. Therefore, it is important to make the receiver RX aware of the clock offset so that when symbols are expected to be received at the receiver RX based on the above synchronization, the time reference of the receiver RX does not drift due to different system clocks. It is also important to synchronize the phase of the receiver RX with the transmitter TX so that the demodulation performance is not degraded in the coherent signaling scheme. Therefore, the receiver RX detects the second information part B of the message M using the system clock of the receiver RX and the clock offset determined based on the first information part A. The receiver RX adapts the system clock of the receiver RX based on the clock offset and detects the second information part B based on the adapted system clock. Alternatively, the receiver RX post-processes the UWB signal using the second information part B based on the determined clock offset.

[0073] The receiver RX may also determine a frequency offset for the frequency of the carrier signal. The frequency offset may be determined based on the determined clock offset, or vice versa. The receiver RX may then adjust the frequency of its oscillator to generate the carrier signal according to the determined frequency offset.

[0074] The first information part A preferably also comprises a PHR. The PHR preferably comprises information about the length of the message M so that the receiver RX will know when the last symbol of the message M and / or the last symbol of the first information part A has been received. In one embodiment, the PHR may comprise only the length of the complete message M or any other information enabling the complete length of the message M to be determined. In a preferred embodiment, the PHR may comprise information about the length of the first information part A (or any other information enabling the length of the first information part A to be determined) and information about the length of the second information part B (or the length of a sub-part thereof). Thus, the physical layer in the receiver RX may determine from the PHR when the first information part A ends, and thus when the second information part B begins, and therefore when the receiving mode of the UWB receiver RX must be switched on. However, the information about the length of the first information part A may also be included in the remaining first information part A, for example in the physical or MAC payload P.

[0075] The rest of the message M contains a physical payload P. The physical payload is divided into a first information part physical payload P1 defining the remaining data of the first information part A, and a second information part B. In another embodiment, the first information part physical payload P1 can also be omitted, and the complete physical payload P can be transmitted in the second information part or in the UWB channel.

[0076] The first information part A (physical payload P1) preferably comprises (at least a portion of) a media access control (MAC) frame. A MAC frame typically comprises a MAC header (MHR) at the beginning of the MAC frame, a MAC payload, and a MAC trailer at the end of the MAC frame. Preferably, the MHR is the first information transmitted in the first information part physical payload. The MHR typically contains communication management information such as a frame control counter, a sequence number, a source address, a destination address, and / or other communication management information. The MAC trailer can be transmitted as the last information of the first information part A or as the last information of the second information part B. Depending on how the frame of the message M is defined, whether the MAC frame is extended on both the first information part and the second information part or only on the first information part A.

[0077] The first information part A (physical payload P1), preferably a MAC payload, comprises the information that should be exchanged with the message M, preferably also non-time related distance measurement information, such as one or more of the SSID, the distance bit information and the prover time difference. The distance bit information is preferably transmitted in encrypted form, or such that a third party cannot retrieve the secret distance bit sequence from the distance bit information. However, this information is optional and can also be transmitted in an out-of-bounds message.

[0078] The second information part B includes Figure 5B The distance pulse sequence SEC shown. Since the same secret distance pulse sequence SEC is used for distance measurement and for authenticating the transmitter, the entire available UWB TX budget of the second information part B can be used for distance measurement and for security at the same time. In a preferred embodiment, the second information part B does not include a separate / complete UWB message header with one or more of a preamble (equivalent to SYNC), SFD, PHR, MHR and SSID. This is possible when the header information is transmitted in the first information part A. This makes it possible to increase the TX budget of the distance pulse sequence SEC of the message M or the second information part B, so as to achieve a more robust / secure distance measurement. The TX budget of the distance pulse sequence SEC can be increased by dedicating the entire TX budget to the sequence, that is, using a distance pulse sequence with a higher number of pulses, and / or by using higher power / amplitude to send the pulses of the distance pulse sequence. In one embodiment, the second information part B includes only the distance pulse sequence SEC, which makes it possible, for example, to use the entire available TX budget for the distance pulse sequence. In another embodiment, other information other than the pure distance pulse sequence can be transmitted in the second information part B. For example, a reduced UWB message header may also be sent within the second information part B. The reduced UWB message header may include only a SYNC pattern or even a reduced SYNC pattern. In one embodiment, the second information part B is transmitted in the UWB channel without a message part including a preamble, a frame start delimiter SFD, and a packet header PHR. The message part including the preamble, SFD, and PHR placed at the beginning of each UWB message according to the standard is missing in the second information part B because it has been transmitted in the first information part A. This embodiment without the message part should not exclude the second information part B including a reduced UWB message header that does not include at least one of the preamble, SFD, and PHR. For example, the second information part may have only a preamble. In another embodiment, the second information part B does not include at least one of the preamble, SFD, and PHR, preferably does not include at least two of the preamble, SFD, and PHR, and preferably does not include all three of the preamble SFD and PHR.

[0079] Using a different first information part A has the advantage that the header information including the synchronization pattern can be transmitted outside the TX budget of the second information part B. This increases the TX budget available for the secret distance pulse sequence SEC and allows the pulse sequence to have a higher energy. This reduces the problem of false paths. This implementation is particularly advantageous because the SYNC pattern of the header information is no longer used for the distance measurement according to the invention and can therefore be moved out of the TX budget of the second information part B without having to repeat such a SYNC pattern in the second information part B for the distance measurement. Even if it is preferred that the security distance message M comprises a first information part A (transmitted in the NB channel or in a separate UWB frequency-time part) and the second information part B can have the removed or reduced header information of the message M, it is also possible to send the message M without such a first information part A so that in the second information part B in the same manner as the first information part A, the message M is transmitted. Figure 5A The necessary header information is transmitted in the same UWB frequency-time part as the SEC shown. However, this reduces the available length / power / TX budget of the range pulse sequence SEC. The embodiment in which the first information part A is transmitted in the NB has the additional advantage that the clock offset between the transmitter TX and the receiver RX can be determined with higher accuracy in the NB than in the UWB, so that in this embodiment the estimated arrival time of the second information (sub)part B and / or the moment of the pulse of the expected range pulse sequence SEC in the UWB signal can be determined with higher accuracy.

[0080] Figure 7 , Figure 8 and Fig. 9A preferred embodiment of the present invention is shown, in which the second information part B includes a plurality of second information sub-parts B1, B2, ..., BY. Each second information sub-part B1, ..., BY corresponds to a different UWB frequency-time part. The different UWB frequency-time parts may be Y different UWB frequency parts transmitted in Y different sub-channels, may be Y different UWB time parts each corresponding to Y different UWB TX budget (time) time slots, or a combination of the two, that is, the second information sub-parts B1, ..., BY are transmitted in different UWB frequency parts and in different UWB time parts. In the latter case, for example, each UWB TX budget time slot may include two or more different UWB frequency parts, each UWB frequency part being transmitted in a different UWB sub-channel. In a preferred embodiment, each second information sub-part B1, ..., BY corresponds to a different different TX budget (time) time slot. That is, Y second information sub-parts B1, ..., BY are transmitted in Y different UWB TX budget time slots. The number Y is the number of the sub-portion Bi, where i=1, ..., Y. In this embodiment, the range pulse sequence SEC includes Y range pulse sub-sequences SEC1, ..., SECY. Different range pulse sub-sequences SECi are each transmitted in a different second information sub-portion Bi, where i=1, ..., Y. In other words, the first range pulse sub-sequence SEC1 is transmitted in the first second information sub-portion B1, the second range pulse sub-sequence SEC2 is transmitted in the second second information sub-portion B2, ..., and the Y-th range pulse sub-sequence SECY is transmitted in the Y-th second information sub-portion BY. The different range pulse sub-sequences SEC1, ..., SECY are preferably different from each other, making it more difficult for a malicious third party to damage the message M. However, the different range pulse sub-sequences SEC1, ..., SECY may also be the same. Y is preferably 2, 4, 6 or 8. Obviously, other numbers Y are also possible. In the case where Y is selected to be 1, as described in the above embodiment, only one second information (sub)portion B(1) is sent.

[0081] The present invention is particularly advantageous for very secure and robust UWB distance measurements, which typically require 2X second information sub-parts Bi (where i=1, ..., 2X), of which X second information sub-parts convey the periodic distance pulse sequence N of the prior art, and the other X second information sub-parts convey the secure distance information SEC1, ..., SECX (not used for distance measurement). Therefore, for the same robustness and security, twice the number of second information sub-parts Bi is required in the prior art. However, if the number 2X of second information sub-parts Bi becomes too high, such as 16, the drift of the clock offset may cause serious problems for the last second information sub-part Bi. Since the present invention reduces the number of required second information sub-parts Bi by two at the same level of security and robustness, the present invention is particularly meaningful for inventions with multiple second information sub-parts Bi. In addition, because the TX budget of the secure distance message M is increased, the use of the first information part A, the use of multiple second information sub-parts B1, ..., BY enables the use of longer secret distance pulse sequences SEC. This reduces the size of false peaks.

[0082] Fig. 9 An embodiment is shown in which the first information portion A is absent, but message header information and a first secret range pulse subsequence SEC1 are transmitted in the first second information portion B1, while the remaining second information subsequences B2, ..., BY transmit the remaining secret range pulse subsequences SEC1, ..., SECY. As in the previous embodiment, multiple UWB frequency-time portions enable the available TX budget to be increased above the regulatory limit to transmit even longer secret range pulse sequences, which further reduces false peaks in the cross-correlation.

[0083] Fig.10 A method for measuring the arrival time of a safety distance message M according to the present invention is shown. A transmitter TX transmits a safety distance message M comprising a distance pulse sequence SEC. The distance pulse sequence corresponds to a secret distance bit sequence. As previously mentioned, at least the distance pulse sequence SEC is transmitted in a UWB channel. The following steps correspond to an embodiment of the method for determining the arrival time of a safety distance message M at a receiver.

[0084] In step S1, a secret distance bit sequence is provided at the receiver RX. The secret distance bit sequence can be determined based on the secret distance bit information. The secret distance bit information can be received from the transmitter TX. Preferably, the secret distance bit information is transmitted in a manner that a third party cannot determine the secret distance bit sequence based on the transmission form of the distance bit information. For example, the distance bit information can be encrypted (by a shared key of the transmitter TX and the receiver RX or by a public key of the receiver RX). The transmitter TX can, for example, transmit the secret distance bit information in the secure distance message M itself, for example in the first information part A, preferably in the first information part payload P1. However, the transmitter TX can also transmit the distance bit information in other messages, for example in an out-of-band channel / message, before or after sending the secure distance message M. The distance bit information can also be received by another party other than the transmitter TX, which, for example, sends the distance bit information (secretly) to a device of the transmitter TX and the receiver RX.

[0085] In step S2, the receiver RX determines an expected distance pulse sequence corresponding to the secret distance bit sequence provided in S1. When receiving the security distance message M, the expected distance pulse sequence corresponds to the UWB radio signal expected to be received in the UWB channel. For example, the expected distance pulse sequence can be determined based on the secret distance bit sequence provided in S1 and the message protocol of the physical layer, that is, the expected distance pulse sequence will correspond to the UWB signal of the secret distance pulse sequence transmitted from the transmitter TX. In a more complex solution, for example, the expected distance pulse sequence can be determined based on the secret distance bit sequence provided in S1 and the message protocol of the physical layer and the channel impulse response (CIR) of the UWB channel used, that is, the expected distance pulse sequence will also include multiple paths of the CIR. In this case, the CIR is obviously not determined based on the distance pulse sequence. In the case of transmitting the first information part A in the UWB channel, the CIR can be determined based on the first information part A, preferably based on the synchronization information, preferably based on the SYNC pattern. In the case of transmitting the first information part A in the NB channel, the CIR can be determined based on the known message part / pattern transmitted in the UWB channel used to transmit the second information part B. For example, in this case the second information part B may contain only a small SYNC pattern for determining the CIR of the UWB channel. Or the CIR may be retrieved from a separate UWB message. In a simple embodiment, each bit of the secret range bit sequence corresponds to a pulse of the secret range pulse sequence, wherein the pulse value corresponds to the bit value. However, it is also possible that a first number of bits of the secret range bit sequence corresponds to a second number (different from the first number) of pulses of the secret range pulse sequence. In case the secret range pulse sequence is transmitted via time hopping (see the embodiment described in more detail below), the positions of the pulses of the secret range pulse sequence have to be arranged as transmitted from the transmitter TX.

[0086] In step S3, a safe distance message M is received at the receiver RX from the transmitter TX.

[0087] If the safety distance message M has a first information part A, the receiver RX receives the first information part A in the NB or UWB channel. The receiver RX preferably determines the (rough) arrival time of the first information part A and / or the clock offset between the receiver RX and the transmitter TX. Based on the determined arrival time and / or clock offset, the receiver RX determines the rough arrival time of the second information part B, and in the case of Y>1, the arrival time of all Y second information sub-parts B1, ..., BY. This makes it possible, for example, to receive the UWB signal in the UWB channel only for the estimated time window of the expected second information (sub) part B. Since the UWB receiver is quite energy-consuming, this will save some energy of the receiver RX. Since the receiver RX is much more power-efficient when operating in the NB channel, the embodiment of sending the first information part A in the NB greatly reduces the power consumption of the receiver RX, because the receiver RX does not have to be forced to turn on for a long time before finally receiving the safety distance message M. The UWB signal of the second information (sub) part is preferably digitized by an analog-to-digital converter and then digitally processed. However, the subsequent processing steps of analog processing can also be performed. In the case of multiple second information sub-parts B1, ..., BY, the UWB signal containing different range pulse sub-sequences SEC1, ..., SECY can be a signal with a signal "island" Bi every millisecond. The signal "island" corresponds to the UWB signal portion carrying the second information sub-part B1, ..., BY. However, if the same operation is performed in the expected range pulse sequence, the time between the second information sub-parts B1, ... BY can be reduced by removing some or all of these (information-free) signal parts. Preferably, the safe distance message with the previous first information part A is sent so that all or at least the increased TX budget can be used for the range pulse sequence SEC, but it is also possible to send the safe distance message M without such a first information part A. The first information part A is particularly advantageous because the preamble of the second information (sub) part in the UWB channel is no longer needed for the arrival time measurement and can therefore be transmitted in the first information part A (in the NB or UWB channel). Therefore, the TX budget of the second information (sub) part can be maximized for the secret range pulse sequence SEC.

[0088] In step S4, the arrival time of the safety distance message M at the receiver RX is determined based on the expected distance pulse sequence and the UWB signal containing the distance pulse sequence SEC in the safety distance message M. Preferably, at the receiver RX, the arrival time of the safety distance message M is determined based on the cross-correlation between the expected distance pulse sequence and the received UWB signal. The cross-correlation moves the expected distance pulse sequence on the UWB signal corresponding to the safety distance message M (more precisely, the second information (sub) part B). When the expected distance pulse sequence corresponds to the UWB signal, the cross-correlation will show a peak. Due to noise, suboptimal matching and different paths of the safety distance message M, the cross-correlation will show several peaks. The arrival time of the shortest or earliest path may not necessarily correspond to the highest peak. Some smaller earlier peaks may correspond to weaker earlier paths, which will be the true arrival time of the shortest path of the safety distance message M. Therefore, the estimation of the arrival time can include the step of detecting a weaker earlier path before the maximum peak of the cross-correlation. Preferably, the early path time window 7 is defined before the arrival time of the maximum peak (strongest path) of the cross-correlation. The end of the early path detection window is preferably the time of the maximum path, and the start of the early path detection window may be defined by a time before the time of the maximum path. Fig.13 Such an early path time window 7 is exemplarily shown in FIG. However, some smaller (false) peaks may be due to the suboptimal match of the expected range pulse sequence on the UWB signal and the offset of one or more pulses as described before and after, or simply due to the noise level. Therefore, the arrival time of the earliest peak greater than a certain threshold is usually regarded as the arrival time of the safe distance message M. If such a weaker early path is detected in the early path time window 7, the time of the early path is defined as the arrival time of the safe distance message M. If the range pulse sequence includes Y range pulse subsequences, the cross-correlation is based on the signal including all range pulse subsequences one by one. This can be achieved by utilizing all real-time signal interruptions between the second information part B1, ..., BY, utilizing the signal interruption reduced between them, or by connecting Y range pulse subsequences SEC1, ..., SECY one by one without any signal interruption.

[0089] In step S5, based on the determined arrival time of the UWB safety distance message M, the moment of the pulse of the expected distance pulse sequence SEC is determined in the UWB signal. In other words, the moment determined in this step corresponds to the arrival time of the pulse of the secret distance pulse sequence of the message path associated with the determined arrival time. Since the message protocol / frame of the safety distance message M is known, the moment of each pulse of the distance pulse sequence within the safety distance message M is known. Once the arrival time of the safety distance message M is determined, the moment of the corresponding pulse can be calculated. Preferably, the moment of each pulse is determined based on the arrival time of the safety distance message M and based on the clock offset. This also includes the case where the moment is calculated using only the clock of the receiver RX, but the receiver clock has been adapted by the clock offset before. In the embodiment using time hopping described below, the time position of each pulse of the secret distance pulse sequence must be considered to determine the moment of the pulse of the secret distance pulse sequence. If the secret distance pulse sequence has a known part and a secret part, this will be sufficient to determine the moment of the secret pulse.

[0090] In step S6, the received bit sequence is decoded from the UWB signal at the determined moment. The modulation parameters of the UWB signal at each moment are determined to determine the corresponding bit value of the corresponding pulse (or, in the case where several pulses correspond to one bit, multiple pulses). Based on the modulation parameters of the UWB signal at the corresponding moment, the bit value of the pulse at that moment is determined. For example, for binary amplitude modulation, a positive amplitude can mean a first bit value (e.g., 1), and a negative or zero amplitude can mean a second bit value (e.g., 0). For example, for binary phase shift keying, a first phase can mean a first bit value (e.g., 1), and a second phase can mean a second bit value (e.g., 0). For example, for binary frequency shift keying, a first frequency can mean a first bit value (e.g., 1), and a second frequency can mean a second bit value (e.g., 0). Preferably, (only) a small time window around each moment is used to decode the transmitted bit of the corresponding pulse received at that moment. In other words, the secret distance bit sequence following the secret distance pulse sequence is decoded using only the pulses of the path associated with the determined arrival time, rather than using the other or strongest paths or all CIRs of the pulses as is the case in normal UWB data decoding. The decoding time window around each moment of the bit value for detecting the pulse is preferably less than 20 nanoseconds (ns), preferably less than 17ns, preferably less than 9ns, preferably less than 5ns, preferably less than 3ns. The decoding time window may also depend on the security level, for example, the time window is 2ns for very secure applications and 16ns for less secure applications. A time window of 16ns may result in potential distance spoofing of 3 to 5 meters. Another difference from the distance measurement of the prior art is that the security segment (here the secret distance pulse sequence) is decoded bit by bit and is not checked by some statistical methods that may be subject to a large number of attacks. In the prior art, this is usually done by cross-correlation of the received UWB signal with the expected security segment, which is not done here to verify the authenticity of the transmitter. If the secret distance pulse sequence has a known part and a secret part, it is sufficient to decode the bit sequence only from the secret pulses. But it is also possible to use the complete sequence with known pulses and secret pulses for authentication.

[0091] It is important for the invention that the same secret range pulse sequence SEC is used for decoding the received bit sequence (S6) and for determining the arrival time (step S4). Preferably, using the same secret range pulse sequence SEC means that each pulse of the secret range pulse sequence SEC is used once for the arrival time measurement (S4) and once for the bit decoding (S6). However, in a less preferred embodiment, this may also mean that a majority (greater than 50%), preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, preferably greater than 95% of the pulses of the secret range pulse sequence SEC are used for the arrival time measurement (S4) and for the bit decoding (S6).

[0092] By actually decoding the bit sequence transmitted via the path associated with the determined arrival time, the arrival time measurement cannot be corrupted by a third party as in the prior art. Since each bit is counted only once and is independent of the energy of the pulse, the attack described at the beginning of the patent cannot be used to guess the secret distance pulse sequence. Since the same sequence is used for arrival time measurement and bit decoding, potential drifts between the distance pulse sequence and the security pulse sequence are avoided, and the entire TX budget of the UWB message can be used for the secret distance pulse sequence.

[0093] In step S7, the received bit sequence decoded from the UWB signal is compared with the secret distance bit sequence. The comparison result is used to verify the authenticity of the transmitter TX. In a first embodiment, the transmitter TX is verified / authenticated by the receiver RX in the case that the received bit sequence is completely equal to the secret bit sequence. In a second preferred embodiment, the transmitter TX is verified / authenticated by the receiver RX in the case that the received bit sequence shows a number of errors below a threshold. The threshold depends on the number of bits of the secret distance bit sequence and the desired security level. The threshold or allowed error rate k can be calculated based on the following formula:

[0094]

[0095] Wherein L is the length, i.e. the number of bits of the secret distance bit sequence, and the security level is the cryptographic security level (corresponding to the number of bits of the secret distance bit sequence with zero error rate). In the case of L=4096 (bits) and k<1848 (errors), the security level is better than 32 bits. This embodiment with an allowed error rate has the advantage that the verification is secure and robust since some errors are allowed. This is particularly advantageous for the present embodiment, in which the bit decoding is limited to the transmission energy of the path related to the determined arrival time. Thus, the reduced energy used may lead to a higher error rate, which is however compensated by the longer secret distance pulse sequence SEC, which also reduces the pseudo lobes. In particular, the solution is highly secure (since the decoding is strictly related to the selected path) and robust (since the long distance pulse sequence SEC allows a certain error rate corresponding to the desired security level).

[0096] As mentioned previously, the use of a secret distance pulse sequence for both determining the arrival time of a message and verifying the authenticity of the transmitter TX doubles the length / power / TX budget of the pulse sequence for the arrival time measurement and the pulse sequence for verification, compared to the prior art using two different pulse sequences. In particular, this reduces the length of the message at the same security and robustness when using longer messages with multiple UWB frequency-time parts, and avoids drift problems due to errors in the detection of clock offsets. The embodiment of the first information part A transmitted in the NB is particularly advantageous for the present invention, since it enables the clock offset to be determined with higher accuracy, and therefore enables the moment for decoding the received distance pulse sequence to be determined with higher accuracy.

[0097] The use of secret range pulse sequences for arrival time measurements introduces the problem of false peaks in the cross-correlation and may result in false early paths. This problem has been reduced by longer secret range pulse sequences, which can benefit from the full TX budget available in the UWB message without reducing the TX budget with a separate specific range pulse sequence. The problem of false paths can be further reduced by the following two improved implementations. Before describing the two improved implementations, the problem of false peaks is better described using the noise-free simulation in Figure 12 for a random range pulse sequence.

[0098] The first row shows the case with only one path (free space line of sight with no reflections). The first column (of the first row) shows the received range pulse sequence, which in this case is equal to the transmitted pulse sequence. The second column of the first row shows the cross-correlation between the transmitted pulse sequence and the received pulse sequence, where the correlation value is shown as positive or negative. The third column shows the absolute value of the received cross-correlation function at the receiver. The correlation shows the highest peak 1 at delay zero (range zero), which corresponds to the true peak of the only path.

[0099] In an environment where a message is received only once using the shortest direct path, false peaks will not be a problem. But in many cases, a message or range pulse sequence N is received at the receiver via multiple paths, so that the cross-correlation shows multiple "real" peaks. False peaks may be confused with weaker real paths, or even worse, reduce the power of the real peaks. This can be a problem when the shortest, earliest "real" path is not the strongest path, for example due to some shielding of an object (non-line-of-sight, NLOS). The second and third rows will show the phenomenon in a simulation of receiving the same random range pulse sequence via two or three paths, where the first column shows a random pulse sequence for multiple paths, the second column shows the cross-correlation value for a single path, and the third column shows the absolute cumulative cross-correlation value for all paths.

[0100] In the second row, a random distance pulse sequence is received via a weak early path (small dot) and a strong late path (large circle), and the strong late path is received one pulse interval distance later than the early path. The true late path 1 is clearly distinguishable. However, the weak true early path 2 at position-1 is visible in the second column in a single cross-correlation, but as seen in the third column, it is weakened by the negative false path in this simulation. On the other hand, two negative false paths as two paths at position-6 accumulate into a strong false path 3 in the third column. This shows that the false path may obtain a stronger peak than the true early path. The third row shows a similar situation with a strong early path (large circle), a first late path (small dot) delayed by two pulse intervals relative to the earliest path, and a third late path (cross) delayed by three pulse intervals. As can be seen in the second and third columns, the false path as the three paths of the delayed position-3 produces a strong false peak 4, and may cause a false "early path" that does not actually exist. Therefore, even the false peak of the late path will result in the detection of a false early peak.

[0101] In a first improved embodiment, false peaks in the cross-correlation are reduced by applying time hopping to the pulses of the transmitted secret distance pulse sequence SEC. Instead of transmitting the pulses of the secret distance pulse sequence SEC with always the same inter-pulse sequence or always the same two inter-pulse distances as shown in FIG3, time hopping is applied, i.e. there are more than two inter-pulse distances in the secret distance pulse sequence. Therefore, the power of the cross-correlation of the false peaks is divided into different time delays of the cross-correlation, and the power of the false peaks is reduced on average. The security pulse sequence of the prior art is transmitted using the STS scheme, i.e. one pulse / bit is transmitted at every 8th position of the normal UWB pulse. The position of each pulse can now be randomly changed around the 8th position, for example between the 7th position and the 10th position (+ / -2 positions) or between the 5th position and the 12th position (+ / -4 positions), resulting in many different inter-pulse distances, and the power of the false peaks in the cross-correlation is divided into different false peaks, thereby reducing their average energy / height. The periodicity of applying time hopping around 8 positions is due to historical reasons and can be further increased so that time hopping can be applied even at more positions. However, this is only one implementation and other implementations where there are multiple different inter-pulse distances in the transmitted secret range pulse sequence may also be used. Fig.13The results of the cross-correlation 6 (shown with small dots) of a secret distance pulse sequence SEC transmitted with time hopping (changing the position by + / - 4 positions) and the cross-correlation 5 (shown with large circles) of a standard secret distance pulse sequence SEC with always the same pulse-to-pulse distance are shown. The x-axis shows the time delay between the correlation functions and the y-axis shows the amplitude of the cross-correlation relative to the maximum peak in decibels (dB). The results of the cross-correlation are mainly shown in the early path time window 7, which is used to determine potential weaker early paths. It can be clearly seen that the number of false peaks 6 increases with time hopping, but their average peak value decreases, while the number of false peaks 5 is less and the value is higher. This is also shown by the maximum value 8 of the false peaks that appear in the simulation without time hopping, which is 6db or 7db higher than the maximum value 9 of the false peaks that appear in the simulation with time hopping. By increasing the number of pulse-to-pulse distances in time hopping, the attenuation can be further increased. This 6dB to 7dB attenuation is very important because it increases the ability to detect real paths above the floor of false paths. In the case of not performing time hopping, there are several false peaks (also false peaks in the early path time window) above the -30dB noise level, which may lead to erroneous early path detection. The receiver RX obviously must know the time hopping position used to determine the correct expected secret distance pulse sequence in step S2 and / or to determine the moment of the pulse in step S5. In a preferred embodiment, the time hopping position of each pulse is randomly selected, i.e., different in each security distance message M. The random time hopping position used can be transmitted from the transmitter TX to the receiver RX. Preferably, the random time hopping position used is determined based on the distance bit information. Therefore, the receiver RX can use the distance bit information to determine the position of each pulse of the secret distance bit sequence (and the corresponding secret distance pulse sequence) and the secret distance pulse sequence. The distance bit information can be, for example, the seed information of the position bit sequence used to determine the secret distance bit sequence and the position of the pulse indicating the secret distance pulse sequence (corresponding to the secret distance bit sequence).

[0102] In a second improved implementation, after the strongest peak in the cross-correlation is detected in step S4, a mismatch pulse sequence is generated that reduces the false peaks in the early path time window. The mismatch pulse sequence corresponds to a secret distance pulse sequence having one or more pulses flipped to opposite values. A plurality of mismatch pulses are tried, and their cross-correlations with the received UWB signal or with the theoretically expected secret distance pulse sequence are calculated in the early path time window. The mismatch pulses that reduce the false paths in the early path time window are selected from the plurality of tried mismatch pulses. Several flipped pulses can significantly change the false paths, but will not have a large impact on the true early paths. Therefore, the selected mismatch pulse sequence is used to calculate the cross-correlation of the UWB signal in the early path time window, and the early path is detected in the newly calculated cross-correlation.

[0103] In a third improved embodiment, the secret distance pulse sequence has a known part and a secret part, wherein the known part has a special code that reduces or removes false peaks, preferably an IPATOV code. The special code preferably includes a series of code values, and the code value can be a first value, a second value, and a third value. The first value corresponds to a first bit value (e.g., 1) or a first pulse value, and the second value corresponds to a second bit value (e.g., 0) or a second pulse value. When such a special code is issued, subsequent code values ​​are transmitted at periodic times or positions, that is, two subsequent code values ​​are issued, and the time distance between them is the same. All positions of the special code with the third value mean that no pulse is issued at this position. In a preferred embodiment, now, pulses of the secret part are sent at some or all positions of the special code corresponding to the third value. The (third value) position of the special code that transmits the secret pulse can be fixed, but only their values ​​change each time. In another embodiment, the (third value) position selected for sending the secret pulse can change with the message. This embodiment has the advantage that, relative to a completely random sequence, false peaks are reduced by the nature of the special code.

[0104] Any (sub)combination of the first improved embodiment, the second improved embodiment and the third improved embodiment is possible. For example, the time-hopping secret pulse sequence can be mismatched to reduce false peaks. Time hopping can also be applied to the position of the secret pulse in the special code (without changing the time position of the known pulse). This summarizes the effect of different improved embodiments on reducing false paths.

[0105] Fig.11 The use of the above-mentioned safe distance message M for UWB distance measurement is shown. It shows a system and method for safe distance measurement using the above-mentioned safe arrival time measurement method.

[0106] The system and / or method includes a verifier V and a prover P.

[0107] The verifier V sends a challenge message C with a challenge distance pulse sequence SECv to the prover P. The challenge message C is a safe distance message as described above. The challenge distance pulse sequence SECv is a distance pulse sequence as defined above. For the safe distance message C, the verifier V acts as a transmitter TX and the prover P acts as a receiver RX. The prover P receives the challenge message C, determines the arrival time of the challenge message C based on the challenge distance pulse sequence SECv, and verifies the authenticity of the verifier V or the challenge message C based on the same challenge distance pulse sequence SECv, as described above in Fig.10 As described in more detail in the method shown. Preferably, the challenge distance pulse sequence SECv is transmitted in the second information (sub) part B. The challenge distance bit information (corresponding to the challenge distance pulse sequence SECv) can be transmitted in the first information part, preferably encrypted. The encryption is based on a public key known to both the verifier V and the prover P, preferably based on a symmetric key. However, the first distance bit information can also be transmitted in another message before or after the first message C. The first information part A (payload P1) of the challenge message C preferably includes an identifier (SSID) of the verifier V / transmitter TX, an identifier (SSID) of the prover P / receiver RX, an SHR and / or a PHR.

[0108] The prover P determines the prover time difference DTp based on the arrival time of the challenge message C and the time to transmit the response message R back to the verifier V.

[0109] The prover P sends a response message R back to the verifier V. Therefore, the prover P is now a transmitter TX, the response message R is a safety distance message M, and the verifier V is a receiver RX. The verifier V receives the response message R, determines the arrival time of the response message R based on the response distance pulse sequence SECp, and verifies the authenticity of the prover P or the response message V based on the same response distance pulse sequence SECp, as described above in Fig.10 The method shown in more detail in the response message R is described in more detail in the method shown in the figure. The response message R, preferably, the second information (sub) part B includes the response pulse sequence SECp. The response pulse sequence SECp is a distance pulse sequence as defined above. The prover P preferably transmits the prover time difference DTp and / or the response distance bit information corresponding to the response distance pulse sequence SECp in the first information part A of the response message R. The first information part A (payload P1) of the response message R preferably includes the identifier (SSID) of the verifier V / receiver RX, the identifier (SSID) of the prover P / transmitter TX, the SHR and / or the PHR.

[0110] The verifier V determines the verifier time difference DTv between sending out the challenge message C (in particular, the challenge pulse sequence SECv) and receiving the response message R (in particular, the response pulse sequence SECp) at the verifier V. The verifier V then calculates the flight time ToF as the difference between the verifier time difference DTv and the prover time difference DTp. Preferably, the prover time difference DTP is received from the prover P. However, the prover time difference may also be fixed to a specific time difference that the prover P waits before sending back the response message R each time.

[0111] If the time of flight ToF or the corresponding distance is less than a threshold, and if the authenticity of the prover P and the verifier V is authenticated at the corresponding receiver RX, a specific request, such as opening the door of a car, can be approved. If the prover P cannot verify the authenticity of the verifier V or the verifier V cannot verify the authenticity of the prover P, the processing can be stopped or the specific request can be rejected.

[0112] A wake-up message may be sent from the verifier V to the prover P to switch on the receiver RX of the prover P, in particular in case the first information part A is sent in a very power-hungry UWB channel.

[0113] It will be understood that the invention is not limited to the embodiments described and that variations may be applied without departing from the scope of the claims.

Claims

1. A method for measuring UWB secure arrival time of a secure distance message, wherein the secure distance message transmits a range pulse sequence corresponding to a secret distance bit sequence from a transmitting device to a receiving device in a UWB channel, the method comprising the following steps: providing (S1) the secret distance bit sequence at the receiving device, upon receiving the secure range message (M), determining (S2) at the receiving device an expected secret range pulse sequence (SEC) corresponding to the secret range bit sequence expected to be received in the UWB channel, receiving (S3) a safety distance message (M) from the transmitting device (TX) at the receiving device (RX), wherein the received safety distance message (M) comprises a UWB signal, and the UWB signal comprises a secret distance pulse sequence (SEC) corresponding to the secret distance bit sequence, determining (S4) an arrival time of a path of the safety range message (M) at the receiving device (RX) based on the expected secret range pulse sequence (SEC) and the UWB signal containing the secret range pulse sequence (SEC) in the received safety range message (M), determining (S5) in the UWB signal the instants of pulses of the expected secret range pulse sequence (SEC) for the path based on the determined arrival time of the path of the security range message (M), decoding (S6) the corresponding bit value of the corresponding UWB pulse value from the UWB signal at the time of the determined corresponding UWB pulse value to determine the bit sequence received via the path of the safety distance message (M), The received bit sequence decoded from the UWB signal is compared (S7) with the provided secret range bit sequence to verify the authenticity of the transmitting device (TX) and the integrity of the arrival time measurement.

2. The method according to claim 1, wherein: The step of comparing the received bit sequence decoded from the UWB signal with the provided secret range bit sequence comprises determining the number of errors in the received bit sequence relative to the secret range bit sequence and considering the transmitter as authenticated if the determined number of errors is below a threshold.

3. The method according to claim 1 or 2, wherein: At each determined time instant of the UWB signal, bits of the time instant are decoded from a time window of the UWB signal surrounding the time instant, wherein the time window is less than or equal to sixteen nanoseconds.

4. A method according to any one of the preceding claims, wherein: At the receiver, the same pulses of the secret range pulse sequence (SEC) are used once to detect the arrival times and once to decode the bit values ​​of these pulses.

5. A method according to any one of the preceding claims, wherein: The secret range pulse sequence (SEC) is transmitted in the UWB channel using a time hopping method utilizing two or more different inter-pulse distances, preferably the time hopping method utilizing more than two different inter-pulse distances.

6. The method according to any one of claims 1 to 5, wherein: An arrival time of the safety range message at the receiving device (RX) is determined based on a cross-correlation between the expected secret range pulse sequence (SEC) and the received UWB signal.

7. A method according to the preceding claim, wherein: An early path time window (7) prior to a maximum value of the cross-correlation is determined, wherein a weak early path is detected in the early path time window (7).

8. A method according to the preceding claim, wherein: A mismatch range pulse sequence is calculated, the mismatch range pulse sequence changing some pulse values ​​of the secret pulse sequence to minimize false peaks in the cross correlation in the early path time window (7), wherein the weak early path is determined based on the cross correlation between the mismatch range pulse sequence and the received UWB signal in the early path time window (7).

9. A method according to any one of the preceding claims, wherein: Each pulse of the secret distance pulse sequence has a first pulse value or a second pulse value, wherein the secret distance pulse sequence includes known pulses and secret pulses, wherein the known pulses are pulses whose pulse values ​​are known, wherein the secret pulses are pulses whose pulse values ​​are secret, wherein the known pulses follow a special code for reducing or removing false peaks, wherein the special code includes a first code value corresponding to the first pulse value, a second code value corresponding to the second pulse value, and a third code value corresponding to not emitting a pulse, wherein the secret pulse is sent at the position of some of the third code values ​​in the special code.

10. A method according to any one of the preceding claims, wherein: The safety distance message (M) comprises a first information part (A; B1) and a subsequent second information part (B; B1, B2, ..., BY), wherein the second information part (B; B1, B2, ..., BY) contains the safety distance bit sequence, wherein the first information part (A; B1) is used to detect the safety distance message (M) in the received signal and / or to determine the clock offset between the system clock of the receiving device (RX) and the system clock of the transmitting device (TX).

11. The method according to the preceding claim, wherein: The safety distance message (M) comprises a message frame in a physical layer, wherein the first information part (A) is transmitted in a narrowband channel, and the second information part (B; B1, B2, ..., BY) is transmitted in the UWB channel after the second information part, and the time relationship between the first information part (A) and the second information part (B; B1, B2, ..., BY) is defined by the message frame in the physical layer; or The safety distance message (M) comprises a message frame in the physical layer, wherein the first information part (B1) is transmitted in a first UWB frequency-time part, and the second information part (B2, B3, ..., BY) is transmitted in at least one second UWB frequency-time part, wherein each UWB frequency-time part is defined as a part of the UWB frequency-time domain that is limited by the TX budget of the UWB channel, wherein the first UWB frequency-time part is different from the second UWB frequency-time part.

12. The method according to claim 11, wherein: The second information part (B1, B2, ..., BY) includes a plurality of second information sub-parts (B1, B2, ..., BY) transmitted in different UWB frequency-time parts, wherein each different UWB frequency-time part is defined as a part in the UWB frequency-time domain that is limited by the TX budget of the UWB channel, and wherein the secret range pulse sequence (SEC) includes a plurality of different secret range pulse sub-sequences (SEC1, SEC2, ..., SECY) transmitted in different second information sub-parts (B1, B2, ..., BY).

13. The method according to any one of claims 1 to 12, wherein: The secret range pulse sequence (SEC) comprises a plurality of different secret range pulse sub-sequences (SEC1, SEC2, ..., SECY) transmitted in different UWB frequency-time portions of the UWB channel.

14. A method for measuring the distance between a verifier (V) and a prover (P), the method comprising the following steps: sending a challenge message (C) with a challenge pulse sequence (SECv) from the verifier (V) to the prover (P); sending a response message (R) with a response pulse sequence (SECp) from the prover (P) to the verifier (V); securely determining the arrival time of the response message (R) at the verifier (V) based on the method according to any one of the preceding claims; The distance (ToF) between the verifier (V) and the prover (P) is measured based on a verifier time difference (DTv) between the challenge message (C) sent from the verifier (V) and the determined arrival time of the response message (R).

15. The method according to the preceding claim, wherein: The prover (P) securely determines the arrival time of the challenge message (C) at the prover (P) based on the method described in any one of claims 1 to 13, and determines the prover time difference (DTp) between the determined arrival time of the challenge message (C) and the response message (R) sent from the prover (P), wherein the first information part (A) of the response message (R) includes the prover time information (DTp), and wherein the distance between the verifier (V) and the prover (P) is determined based on the verifier time difference (DTv) and the prover time difference (DTp).

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