Method for determining the direction to an object

Abstract

The invention relates to a method for determining the direction to an object, wherein a transmission data sequence is transmitted by way of at least one transmission antenna and reflected by the object, whereupon a reflection data sequence is received by means of a receiving antenna and the direction of the object is determined therefrom. In order to make possible a method for determining the direction to an object which can be used in a large frequency range, requires low signal levels and is nevertheless largely insusceptible to interference, it is proposed that at least two different transmission data sequences are generated and transmitted, each by means of a respective isotropic transmission antenna, wherein reference data sequences are generated for a plurality of reference directions by superimposing the transmission data sequences with a time offset corresponding to the respective reference direction, and that the reference direction of that reference data sequence which has the greatest correlation with a test data sequence generated from the reflection data sequence is output as the direction to the object.

Description

[0001] Method for determining the direction to a

[0002] Technical field

[0003] The invention relates to a method for determining the direction to an object, wherein a transmission data sequence is sent via at least one transmission antenna and reflected by the object, after which a reflection data sequence is received by means of a receiving antenna and the direction of the object is determined from it.

[0004] State of the art

[0005] From US20060114146A1, a sensor system is known in which each sensor transmits a data sequence, for example, the modulated base signal of an FMCW radar, simple pulses, or pseudonoise, via a transmitting antenna. This data sequence is reflected by a surrounding object and received as a reflection data sequence by at least two receiving antennas assigned to the same sensor to determine the direction to the object. A disadvantage of this system is that the transmitted data sequence signal is susceptible to interference and multipath propagation in space, leading to interference signals that disrupt the detection of genuine targets and, conversely, detect false targets. To achieve a sufficiently high signal-to-noise ratio in this case, correspondingly high signal levels are required, which entails corresponding regulatory restrictions. Nevertheless, such sensor systems remain vulnerable to interference from other systems. [Description of the invention.]

[0006] The invention is therefore based on the objective of proposing a method for determining the direction to an object which can be used in a large frequency range, requires low signal levels and yet is largely immune to interference.

[0007] The invention solves the stated problem by generating at least two different transmission data sequences and transmitting them via separate isotropic transmitting antennas. For multiple reference directions, reference data sequences are generated by superimposing the transmission data sequences with a time offset corresponding to the respective reference direction. The reference direction output to the object is that of the reference data sequence exhibiting the highest correlation with a test data sequence generated from the reflection data sequence. As a result of these measures, crosstalk between the transmitting and receiving antennas, as well as the influence of any external systems, is effectively prevented. This is because individual transmission data sequences and their reflections are perceived as noise by the receiver due to their low correlation with the reference data sequences, and only the reflection data sequence reflected from the object correlates with one of the reference data sequences.This means that, in a preferred embodiment, the reflection data sequence in the measurement space is unique and is generated exclusively by reflection from an object. To nevertheless determine a direction to the object from this reflection data sequence, reference data sequences assigned to reference directions are generated from the transmitted data sequences. For this purpose, the transmitted data sequences are superimposed with a time offset corresponding to the distance between the transmitting antennas and the resulting relative differences in signal propagation times for each reference direction. Thus, the test data sequence, which in the simplest case can correspond to the reflection data sequence, exhibits the highest correlation with the reference data sequence whose time offset, and therefore whose reference direction, shows the highest agreement with the test data sequence.For the purpose of determining direction, the temporal course of the correlation, in the sense of a channel impulse response, can initially be disregarded, as only the local maxima within this temporal course are relevant. For clarification, it should be noted that, within the meaning of the invention, a data sequence is understood to be both a sequence of individual characters and a signal modulated accordingly, in particular a carrier signal. In principle, various modulation methods known from the prior art can be used for transmitting the data sequences via a carrier signal. For example, in the case of amplitude modulation of the data sequences, both constructive and destructive interference occur at the surface of the object, leading to the superposition of the transmitted data sequences to form the reflected data sequence. Electromagnetic or mechanical waves, for example, can be used as the carrier signal.For example, electromagnetic waves in the range of 30 MHz to 300 GHz or optical waves can be used. It is understood by experts that the transmitted data sequences must be time-synchronized via the transmitting antennas. This can be achieved with simple design means by ensuring that the transmitters are identical in construction and that the signal paths to the transmitting antennas are of equal length. If this is not the case, time synchronization between the transmitters, which may be located at different locations, can be implemented. For example, the transmitted data sequences can also be pre-delayed to compensate for any differences in transit time to the transmitting antennas. The receiving antenna can be spatially separated from the transmitting antennas. In particular, the receiving antenna can be positioned between two adjacent transmitting antennas.Although several receiving antennas can be used in accordance with the invention, one receiving antenna is sufficient for the implementation of the invention.

[0008] To reliably determine the highest correlation regardless of the transmitted data sequences used, it is proposed that the test data sequence be generated from the difference between the reflected data sequence and at least one transmitted data sequence. This allows the test data sequence to be normalized with respect to the transmitted data sequences, thus enabling differential measurement. With suitable implementation, this can also minimize the influence of the transmitting and receiving equipment on the measurement if the transmitted data sequence is tapped after the transmitting equipment.

[0009] Although the transmission data sequences can, in principle, be based on any binary or ternary strings, particularly advantageous conditions arise when the transmission data sequences are generated by decomposing a base sequence with high autocorrelation. A base sequence with optimal or very high autocorrelation could, for example, be an Ipatov sequence.

[0010] In a preferred embodiment, the base sequence can be generated by encryption according to the Advanced Encryption Standard (AES). The subsequent decomposition, for example, code spreading of the base sequence to generate the transmitted data sequences, can be performed such that the cross-correlation of the transmitted data sequences is lower than the autocorrelation of the base sequence.

[0011] The decomposition of the basic sequence into the transmitted data sequences can be carried out particularly efficiently if an odd number of at least three transmitted data sequences are provided for at least three transmitting antennas, wherein the basic sequence is assigned to the individual transmitted data sequences alternately in sections, with the remaining transmitted data sequences in the respective section being provided with characters that cancel each other out upon superposition. As a result of these measures, the cross-correlation of the transmitted data sequences is lower than the autocorrelation of the basic sequence. Furthermore, if the transmitting antennas are arranged outside a straight line, the use of at least three transmitting antennas allows the determination of two spatial directions, i.e., the solid angle to the object.

[0012] Object localization beyond simple directional determination can be achieved by calculating a channel impulse response from the reflection data sequence and the test data sequence with the highest correlation. The distance to the object is then determined from the local maxima of the channel impulse response that exceed a predefined reference threshold. The reference threshold must be chosen such that any local maxima resulting from multipath propagation or other disturbances lie below the reference threshold, while the local maxima of the objects being measured lie above it. For example, the reference threshold could be set at one-third of the maximum value of the channel impulse response. Based on the time interval of each local maximum in the channel impulse response, the distance to the corresponding object, and thus its position, can be determined in conjunction with its direction.

[0013] To reduce susceptibility to interference while simultaneously increasing spatial resolution, it is proposed that the character duration of the transmitted data sequences be less than 5 ns, preferably less than 4 ns, and even more preferably less than 2 ns. The resulting signals can therefore have a bandwidth of more than 500 MHz to enable error-free signal reconstruction according to the Nyquist-Shannon sampling theorem. A correspondingly broadband signal also has the advantage of reduced susceptibility to narrowband interference.

[0014] Particularly in combination with broadband, preferably ultra-broadband, signals with a bandwidth of at least 500 MHz, the method according to the invention can be carried out with minimal regulatory restrictions and simultaneously low energy consumption if the signals of the transmitted data sequences have a spectral power density of less than -45 dBm / MHz. In a preferred embodiment, the signals of the transmitted data sequences have a spectral power density of less than -41.3 dBm / MHz. Due to the long, known transmitted data sequences or the generally known expected reflection data sequence, a correspondingly low signal-to-noise ratio is sufficient to enable correct direction determination by correlating the test data sequence with the reference data sequences. Increased interference immunity of the method can be achieved by using pseudorandom transmitted data sequences.The low correlation of the individual values ​​in such a data transmission sequence ensures that the time offset of this sequence can be reliably detected, because such a sequence only exhibits high autocorrelation when there is no time offset, while the autocorrelation is negligibly small for any other time offset. Similarly, for multiple pseudorandom data transmission sequences of correspondingly high quality, their cross-correlation is also negligibly small, thus ensuring that the data transmission sequences do not influence each other.

[0015] To reduce storage requirements despite detection over a wide angular range, while simultaneously enabling the synchronization of multiple systems, it is proposed that at least one transmitted data sequence be generated from a source data sequence using a predefined algorithm. This eliminates the need for long-term storage of transmitted data sequences, while maintaining low susceptibility to interference, as these are generated from significantly less memory-intensive source data sequences during the process. Encryption algorithms, particularly symmetric encryption algorithms, can be employed. An example of this is the Advanced Encryption Standard (AES). The source data sequence can then serve as the key for the encryption algorithm.This results in the further advantage that the process can be carried out very securely, because manipulation of the reflection data sequence is only possible if the source data sequence is known. Conversely, the source data sequence can be transmitted correspondingly easily in distributed systems, so that not only high security but also great flexibility in the system architecture is achieved.

[0016] The invention also relates to a device for carrying out a method according to the invention, wherein a control unit is connected to at least two transmit data sequence generators via a transmitter with a transmitting antenna on one side and via several correlators, each assigned to a reference data sequence, and a receiver with a receiving antenna on the other. The control unit can additionally include a basic sequence generator for generating a basic sequence, which is decomposed into transmit data sequences by the transmit data sequence generators. The generation of reference data sequences can take place in a reference data sequence generator by superimposing the transmit data sequences with a time offset. Depending on the time offset, a reference direction can be assigned to the resulting reference data sequences, according to which the reference data sequences are each assigned to a correlator.The receiver can transmit the reflection data sequence from the receiving antenna to a test data generator. The test data generator creates a test data sequence from the reflection data sequence and preferably at least one transmitted data sequence. The test data sequence is then transmitted to the correlators, after which the reference direction of the reference data sequence with the highest correlation to the test data sequence can be output as the direction of the object to be located in an output unit of the control unit.

[0017] Brief description of the invention

[0018] The invention is illustrated in the drawing as an example. It shows

[0019] Fig. 1 a schematic representation of a device according to the invention, Fig. 2 a schematic representation of a decomposition of a basic sequence with high autocorrelation into three transmitted data sequences with low cross-correlation, Fig. 3 a schematic representation of the device according to the invention during the exemplary detection of two objects and

[0020] Fig. 4 shows a schematic representation of the correlation of the test data sequence with reference data sequences of different reference directions, in the form of graphs depicting the magnitude over individual time intervals. Ways to implement the invention

[0021] A device for carrying out a method for determining the direction to an object 1 comprises data sequence generators 2 for generating data sequences 3. The data sequences 3 are transmitted via transmitters 4 to isotropic transmitting antennas 5, which radiate the data sequences 3. At the object 1, the data sequences 3 superimpose and are received as a reflection data sequence 6 by a receiving antenna 7. A receiver

[0022] Receiver 8 then processes the reflection data sequence 6, whereby the difference between the reflection data sequence 6 and a transmission data sequence 3 can be calculated in the receiver 8. From this difference, a test data sequence 9 can be generated and compared with reference data sequences 11 using various correlators 10. The reference data sequences 11 are previously generated in a reference data sequence generator 12 from the transmission data sequences 3 with different time offsets, whereby reference directions are assigned to the reference data sequences 11 depending on the time offset.

[0023] An output unit 13 determines, based on the output values ​​14 of the correlators 10, the reference data sequence 11 that has the highest correlation with the test data sequence.

[0024] 9. The reference direction assigned to this reference data sequence 11 with the highest correlation is output in the output unit 13 as direction 15 to object 1.

[0025] The transmission data sequences 3 can be generated by decomposing a base sequence 16 with high autocorrelation, which was generated by a base sequence generator 17, into the respective transmission data sequence generators 2. The generated transmission data sequences 3 are transmitted on the one hand to the transmitters 4 for subsequent transmission and on the other hand to the reference data sequence generator 12 for determining the reference data sequences 1. The transmission data sequence generators 2, the reference data sequence generator 12, the output unit 13, and the base sequence generator 17 can be arranged in a common control unit 18. As shown in Fig. 2, the base sequence 16 with high autocorrelation can be decomposed into three different transmission data sequences 3 with low cross-correlation.The various basic sequence sections 19 are assigned alternately to the three transmission data sequences 3, with the remaining transmission data sequences in the respective section being provided with filler characters 20a, 20b that cancel each other out when superimposed. For the sake of clarity, not all basic sequence sections 19 and filler characters 20a, 20b are provided with reference marks.

[0026] Fig. 3 schematically shows the use of the device according to the invention in the detection of two objects 1 using two transmitting antennas 5 and a receiving antenna 7.

[0027] Figure 4 shows the corresponding correlations of a correlator 10a with a time offset of a first reference direction 21 of Figure 3 and of a correlator 10b with a time offset of a second reference direction 22 of Figure 3. According to the arrangement of the objects 1 in the second reference direction 22, the test data sequence 9 shows no correlation in the graph 23 of correlator 10a, since it has a time offset corresponding to the first reference direction 21. In contrast, the graph 24 of correlator 10b shows two sharp local maxima 25, which correspond to the objects 1 in reference direction 22. The distance of the local maxima 25 from the ordinate allows conclusions to be drawn about the distance to the objects 1.

Claims

Patent claims 1. A method for determining the direction to an object, wherein a transmission data sequence is sent via at least one transmitting antenna and reflected by the object, after which a reflection data sequence is received by means of a receiving antenna and the direction of the object is determined from it, characterized in that at least two different transmission data sequences are generated and each is sent via an isotropic transmitting antenna, wherein reference data sequences are generated for several reference directions by superimposing the transmission data sequences with a time offset corresponding to the respective reference direction, and that the reference direction of that reference data sequence which has the greatest correlation with a test data sequence generated from the reflection data sequence is output as the direction to the object.

2. Method according to claim 1, characterized in that the test data sequence is generated from the difference between the reflection data sequence and at least one transmission data sequence.

3. Method according to one of claims 1 or 2, characterized in that a channel impulse response is determined from the reference data sequence with the greatest correlation and the test data sequence, and the distance to the object is determined from the local maxima of the channel impulse response that lie above a predetermined reference threshold.

4. Method according to one of claims 1 to 3, characterized in that the character duration of the transmitted data sequences is less than 5 ns.

5. Method according to one of claims 1 to 4, characterized in that the signals of the transmitted data sequences each have a signal level of less than -45 dBm / MHz.

6. Method according to one of claims 1 to 5, characterized in that the transmission data sequences are pseudorandom.

7. Method according to one of claims 1 to 6, characterized in that at least one transmission data sequence is generated from a generator data sequence using a predetermined algorithm.

8. Device for carrying out a method according to one of claims 1 to 7, characterized in that a control unit with at least two transmit data sequence generators is connected on the one hand via a transmitter with a transmitting antenna each and on the other hand via several correlators, each assigned to a reference data sequence, and a receiver with a receiving antenna.

Images