Method for operating an OFDM radar system

Abstract

The present invention relates to a method for operating an OFDM radar system (100), the method having the following steps: generating an analog transmit signal in the baseband; mixing the analog transmit signal with a first mixing signal at a first frequency (fLO), wherein the first frequency (fLO) of the first mixing signal is centered between two sidebands (SB1, SB2) of the transmit band; receiving a received signal; and mixing the received signal with a second mixing signal at a second frequency (fLO2) into the baseband, wherein the second frequency (fLO2) of the second mixing signal is located beside the total bandwidth (2B) of the received signal in a defined manner.

Description

Technical Field

[0001] The present invention relates to a method for operating an OFDM radar system. Furthermore, the present invention relates to a transmitting device of an OFDM radar system. Furthermore, the present invention relates to a receiving device of an OFDM radar system. Furthermore, the present invention relates to an OFDM radar system. Furthermore, the present invention relates to a computer product. Background Art

[0002] A radar system transmits a signal, which is reflected by an object in the radar channel. The reflected signal is received and analyzed to detect the distance, speed, and angle relative to the vehicle's sensor. The signals used and modulated can also be generated by means of OFDM (orthogonal frequency division multiplexing).

[0003] DE 10 2015 210 454A1 discloses a method for operating an OFDM radar device in which the ability to separate distances is obtained without reduction compared to a conventional combination of OFDM and MIMO, where the clearly uniquely estimable distance range is not reduced. Summary of the Invention

[0004] The object of the present invention is to provide an improved method for operating an OFDM radar system.

[0005] According to a first aspect, this object is solved by a method for operating an OFDM radar system, the method having the following steps:

[0006] Generate an analog transmission signal in the baseband;

[0007] Mix the analog transmission signal with a first mixing signal of a first frequency, where the first frequency of the first mixing signal is located in the center between the two sidebands of the transmission band;

[0008] Receive a received signal; and

[0009] Mix the received signal with a second mixing signal of a second frequency into the baseband, where the second frequency of the second mixing signal is located beside the total bandwidth of the received signal in a defined manner.

[0010] In this way, a method is provided by which an improved range resolution for an OFDM radar system is provided based on an increased bandwidth of the received signal, or less technical effort is required in the case of a lower range resolution.

[0011] According to a second aspect, the task is solved by means of a transmitting device for an OFDM radar system, the transmitting device having:

[0012] a memory device for storing a digital transmission signal;

[0013] a first D / A converter for generating an analog transmission signal, the first D / A converter being functionally connected to the memory device;

[0014] a first mixer device, the first mixer device being functionally connected to the first D / A converter; and

[0015] a first oscillator device, the first oscillator device being functionally connected to the first mixer device, wherein the analog transmission signal is mixed into a transmission spectrum having two sidebands by means of the first oscillator device and the first mixer device, wherein a first frequency of the first oscillator device is located in the center between the two sidebands, and wherein the analog transmission signal is transmitted by means of a transmitting antenna.

[0016] Advantageously, in this way a transmitting device is provided which, compared to a conventional transmitting device of an OFDM radar system, has only half the number of paths. As a result, the range resolution of the OFDM radar system can advantageously also be doubled thereby.

[0017] According to another aspect, the task is solved by means of a receiving device for an OFDM radar system, the receiving device having:

[0018] a receiving antenna for receiving a received signal;

[0019] a second mixer device for mixing the received signal into the baseband, the second mixer device being functionally connected to the receiving antenna;

[0020] a third mixer device for generating a second mixing signal having a second frequency, the third mixer device being functionally connected to the second mixer device;

[0021] an A / D converter, the A / D converter being functionally connected to the second mixer device; wherein,

[0022] the second frequency of the second mixing signal is offset with respect to the bandwidth of the received signal in a defined manner.

[0023] Advantageously, compared to the prior art, the overhead of the receiving device for an OFDM radar system increases only in an insignificant manner.

[0024] Preferred embodiments of the proposed method and of the proposed receiving device are the subject of the dependent claims.

[0025] A preferred and advantageous expansion of this method provides that the second frequency of the second mixing signal is generated from the first frequency of the first mixing signal. Advantageously, the cost for generating the mixing signals can thus be minimized, since only a single oscillator is provided therefor.

[0026] Another preferred expansion of this method provides that the second frequency of the second mixing signal is generated in a manner independent of the first frequency of the first mixing signal, wherein a defined correlation of the phase noise of the two frequencies is provided. Advantageously, this enables the physical distance between the transmitting device and the receiving device to be configured to be greater, since independent oscillators are used to generate the mixing signals.

[0027] An advantageous expansion of this receiving device provides that the second frequency of the second mixing signal is higher than or lower than the bandwidth of the received signal. Thus, depending on the design of the OFDM radar system, different frequencies can be selected for the mixing signals.

[0028] Another advantageous expansion of this receiving device provides that a frequency offset between the second frequency and the first frequency of the first mixing signal is generated by means of a digital module. Advantageously, this enables a simple generation of the frequency offset between the mixing signals.

[0029] Another advantageous expansion of this receiving device provides that a frequency offset between the frequencies of the mixing signals is generated by means of a voltage-controlled module in combination with a PLL module. Advantageously, this provides an alternative way of generating the frequency offset of the mixing signals.

[0030] Another advantageous expansion of this receiving device provides that the second frequency is generated from the first frequency, or alternatively, the second frequency is generated separately. Advantageously, this provides different possibilities for providing the second mixing signal.

[0031] Another advantageous expansion of this receiving device provides that the spacing between the second frequency and the bandwidth of the received signal is an integer multiple of the spacing of the frequency lines of the sidebands of the received signal. Thus, the entire OFDM radar system is advantageously matched to the structure of the OFDM signal, whereby the range resolution of the entire OFDM radar system is optimized. Description of the Drawings

[0032] Hereinafter, the present invention will be described in detail with reference to several drawings in connection with other features and advantages. Herein, all features described or shown, either individually or in any combination, form the subject matter of the present invention, regardless of their generalization in the claims or their citation relationship, and regardless of their representation or illustration in the specification or in the drawings. Identical or functionally identical elements have the same reference numerals.

[0033] The disclosed method features are derived in a similar manner from the corresponding disclosed device features, and vice versa. This particularly means that the features, technical advantages, and embodiments related to the method are derived in a similar manner from the corresponding embodiments, features, and advantages of the transmitting device and the receiving device, and vice versa.

[0034] Shown in the figures:

[0035] FIG. 1 shows a schematic block circuit diagram of the principle of a conventional OFDM radar system;

[0036] Figure 2 Shows a schematic block circuit diagram of an embodiment of the transmitting device of the proposed OFDM radar system;

[0037] Figure 3 Shows a schematic diagram of the receiving spectrum of the receiving device of the proposed OFDM radar system;

[0038] Figure 4 Shows a schematic block circuit diagram of an embodiment of the receiving device of the proposed OFDM radar system;

[0039] Figure 5 Shows a schematic block circuit diagram of another embodiment of the receiving device of the proposed OFDM radar system;

[0040] Figure 6 Shown with a higher level of refinement Figure 4 of the receiving device;

[0041] Figure 7 Shows the principle flow of the proposed method for operating an OFDM radar system; and

[0042] Figure 8 Shows a block circuit diagram of the proposed OFDM radar system. Detailed Description

[0043] The OFDM signal is up-converted in the transmitter in sideband mode and down-converted with an intermediate frequency in the receiver in order to analyze and process both sidebands. The resolution twice as high is also generated by the resulting doubled bandwidth.

[0044] FIG. 1 shows a simplified overview circuit diagram of a conventional radar system based on the orthogonal frequency division multiplexing method OFMD. The digital information of the transmitted signal, for example a sequence of discrete, equally spaced transmitted frequencies or OFDM subcarriers to be transmitted, is stored in an electronic memory device 1a (for example a RAM). For example, the complex sampled values of the baseband transmitted signal are generated by an inverse fast Fourier transform iFFT, where these values are stored in the electronic memory device 1a and can be cyclically read out from this electronic memory device.

[0045] The D / A converter 2a generates a cyclic, complex analog baseband signal from a sequence read out periodically from the memory device 1a.

[0046] The baseband transmission signal is transferred into a desired frequency range (e.g., 77...78 GHz) by means of a first mixer device 3 and an oscillator device 4 and then transmitted via a transmission antenna 5, for example, at a carrier frequency of 77 GHz in the automotive field.

[0047] If a simple mixer is used, two sidebands SB1, SB2 are thereby generated. If the receiver mixes at the baseband (approx. f = 0 Hz) with the same carrier frequency, the bands are convolved with each other and cause unwanted interference, especially in the case of dynamic scenarios. Therefore, an IQ mixer can be used in the transmitter, which suppresses the second sideband. However, the hardware cost in the transmitter thereby becomes twice as high because the I signal and the Q signal must be generated separately and independently via D / A converters and pre-stored. An intermediate frequency system can also be used, which uses filters either in the transmitter or in the receiver to suppress unwanted sidebands.

[0048] The second path of the transmission device 10 can be seen, which has a second memory device 1b and a second D / A converter 2a, which is used to largely eliminate the first sideband SB1. This is used so that the baseband can be processed in the receiving channel.

[0049] Figure 2 A first embodiment of the transmission device 10 for an OFDM radar system 100 is shown. It can be seen that there is now only a single path, which has a memory device 1a and a D / A converter 2a, which are used to up-convert an analog transmission signal with the aid of a first oscillator device 4. The OFDM-modulated transmission signal is generated by means of a first mixing device 3 (double-sideband mixer). Thus, when the modulation bandwidth of the baseband signal is B, the OFDM-modulated transmission signal has a transmission bandwidth of 2xB. As a result, the transmission spectrum of the transmission signal as Figure 2 shown is produced, which has two sidebands SB1, SB2, where the frequency fLO of the mixed signal is located in the center between the two sidebands SB1, SB2. However, in this form, the receiving device cannot process the transmission spectrum because an image effect occurs during down-conversion, whereby the sidebands are superimposed on each other.

[0050] Since the transmitting device 10 operates in the double-sideband mode, the transmitting device does not require an IQ mixer as in the prior art. Therefore, the second D / A converter 2a of the conventional transmitting device 10 and the digital memory device 1b required therefor are advantageously eliminated. In addition, with the same sampling rate in the transmitting device 10, the bandwidth of the generated analog signal of the transmitting device 10 becomes twice as large, which advantageously doubles the possible range resolution of the OFDM radar system.

[0051] In order to process the transmitted signal emitted by the transmitting device 10, a receiving device 20 for an OFDM radar system is further proposed, by means of which the received spectrum as shown in Figure 3 is obtained. When an oscillator signal having a frequency fLO2 and offset by a bandwidth B is provided, a second mixer 22 in the form of a double-sideband mixer can be used for the proposed receiving device 20. This enables the use of only a single A / D converter 25 for sampling the received signal. In this case, the frequency fLO2 of the oscillator signal is located beside the total bandwidth of the received signal, as can be seen in Figure 3 . In the case of Figure 3 , the frequency fLO2 is lower than the first sideband SB1, however, this frequency can also be higher than the second sideband SB2 (not shown).

[0052] Different from the application in communication technology, in the case of radar applications, the coded information on the subcarriers is not used, but is eliminated in the receiving device 20 by spectrum splitting, so that only the channel information on the carrier is retained. Since the second sideband SB2 is a complex conjugate and mirror copy of the first sideband SB1 in this case, the two sidebands SB1, SB2 contain the same code, but traverse different frequency points in the channel and thus have non-redundant channel information.

[0053] In the proposed receiving device 20, mixing is performed with an intermediate frequency in such a way that the two sidebands SB1, SB2 can be analyzed and processed. Here, the sampling rate of the A / D converter 25 must be adjusted in such a way that the two sidebands SB1, SB2 are sampled clearly, uniquely and completely. Then, the bandwidth (range resolution) analyzed and processed in this way is twice the bandwidth generated by the transmitting device 10 for the transmitted signal.

[0054] The oscillator frequency for mixing the signals can be between 57 GHz and 300 GHz, and is preferably between 76 GHz and 81 GHz for automotive radar. The spacing between the frequencies fLO and fLO2 of the mixed signals is calculated as:

[0055] fLO2 ≈ fLO ± B (1)

[0056] where

[0057] The modulation bandwidth of the B OFDM signal (e.g., between 1 MHz and 2 GHz).

[0058] Figure 4 A schematic block circuit diagram showing a first variant of the proposed receiving device 20 is shown. To ensure the relevant phase noise between the proposed transmitting device 10 and the proposed receiving device 20, the same oscillator signal can be used for the transmitting device 10 and the receiving device 20. The intermediate frequencies required for the transmitting device 10 and the receiving device 20 can be generated by means of a ZF device 23, a third mixer device 24 in the form of an IQ mixer, and a second frequency source (e.g., a DDS (Direct Digital Synthesis, not shown) or a VCO (Voltage Controlled Oscillator, not shown)). Since the intermediate frequency can be generated at a low frequency (e.g., at 1 GHz), the added phase noise is smaller. Since the carrier frequency and the intermediate frequency are usually mixed at fixed frequencies, the third mixer device 24 can be accurately coordinated with this frequency characteristic.

[0059] This is achieved by Figure 4 the receiving device 20. In the receiving device 20, the received signal is mixed with an oscillator signal offset by the bandwidth B and sampled. Thus, the two transmitted sidebands SB1, SB2 can be recovered, and for this purpose, an IQ receiving mixer is not required.

[0060] The first oscillator device 4 can be seen, which is functionally connected to the third mixer device 24 together with the intermediate frequency device 23. Thus, the received signal received by the receiving antenna 21 can be mixed into the baseband by means of the second mixer device 22 and then can be analyzed and processed by means of the A / D converter 25. Thus, a complex digital time signal in the baseband is provided at the output of the A / D converter 25. For this purpose, the A / D converter 25 must be constructed such that it can sample the complete received spectrum. In this way, a bandwidth 2B is obtained for the received signal, which can significantly improve the range resolution of the proposed OFDM radar system 100.

[0061] Figure 5Shows a second variant of the proposed receiving device 20. In this case, the frequency of the mixed signal for receiving the signal is generated independently of the transmitting device 10. For this purpose, independent oscillator means 4, 26 of the transmitting device 10 and the receiving device 20 are used respectively. Then, although in this configuration the phase noises of the two oscillator means 4, 26 are no longer correlated, this can be improved by coupling the two oscillator means 4, 26 (for example, through the same reference (Referenz), not shown).

[0062] Figure 6 Shows Figure 4 Details of the receiving device, wherein a way of generating the frequency offset between the oscillator frequency fLO of the transmitting device 10 and the oscillator frequency fLO2 of the receiving device 20 is shown in more detail. Here, the difference between the mentioned oscillator frequencies fLO, fLO2 is provided to the third mixer means 24, and the difference is up-converted to the receiving band according to Figure 3 by means of the first oscillator means 4.

[0063] The following table shows a comparison of some technical parameters between a conventional OFDM radar system and the proposed OFDM radar system.

[0064]

[0065] Table

[0066] It can be seen that the important technical parameters of the OFDM radar system 100 according to the present invention are halved in terms of numerical values, so only basically half of the technical overhead is required to achieve the technical parameters.

[0067] Figure 7 Shows the principle flow of the proposed method for operating the OFDM radar system 100.

[0068] In step 200, an analog transmission signal is generated in the baseband.

[0069] In step 210, the analog transmission signal is mixed with a first mixed signal at a first frequency fLO, wherein the first frequency fLO of the first mixed signal is located in the center between the two sidebands SB1, SB2 of the transmission band.

[0070] In step 220, the received signal is received.

[0071] Finally, in step 230, the received signal is mixed with a second mixed signal at a second frequency fLO2 into the baseband, wherein the second frequency fLO2 of the second mixed signal is located beside the total bandwidth 2B of the received signal in a defined manner.

[0072] Alternatively, it is also possible that some of the signal processing steps are performed in an order different from the order shown.

[0073] The proposed method supports an optimized utilization of the existing resources of an OFDM radar system.

[0074] Although the described method is described only in the context of an OFDM radar system, applications to other systems with digital multicarrier modulation can also be envisaged, especially in the radar field.

[0075] Figure 8 A block circuit diagram of the proposed OFDM radar system 100 with the proposed transmitting device 10 and the proposed receiving device 20 is shown.

[0076] Advantageously, the proposed method can also be implemented as a software program that runs on the electronic OFDM radar system 100, thereby advantageously supporting the adaptability of the method.

[0077] Those skilled in the art can make appropriate modifications and combinations of the described features of the present invention without departing from the core of the present invention.

Claims

1. A method for operating an OFDM radar system (100), the method having the following steps: Generate an analog transmit signal in the baseband; Mix the analog transmission signal with a first mixing signal at a first frequency (fLO), wherein, The first frequency (fLO) of the first mixing signal is located in the center between the two sidebands (SB1, SB2) of the transmit band; Receive a received signal; And Mix the received signal with a second mixing signal at a second frequency (fLO2) into the baseband, wherein the second frequency (fLO2) of the second mixing signal is located beside the total bandwidth (2B) of the received signal in a defined manner.

2. The method according to claim 1, wherein, Generate the second frequency (fLO2) of the second mixing signal from the first frequency (fLO) of the first mixing signal.

3. The method according to claim 1, wherein Generate the second frequency (fLO2) of the second mixing signal in a manner independent of the first frequency (fLO) of the first mixing signal, wherein the correlation of the phase noise of the two frequencies (fLO, fLO2) is improved.

4. A transmitting device (10) of an OFDM radar system (100), the transmitting device having: A memory device (1a) for storing a digital transmit signal; A first D / A converter (2a) for generating an analog transmit signal, the first D / A converter being functionally connected to the memory device (1a); A first mixer device (3), the first mixer device being functionally connected to the first D / A converter (2a); and A first oscillator device (4), which is functionally connected to the first mixer device (3), wherein, Mix the analog transmit signal into a transmit spectrum having two sidebands (SB1, SB2) by means of the first oscillator device (4) and the first mixer device (3), wherein the first frequency (fLO) of the first oscillator device (4) is located in the center between the two sidebands (SB1, SB2), and wherein the analog transmit signal is transmitted by means of a transmit antenna (5).

5. A receiving device (20) of an OFDM radar system (100), the receiving device having: A receiving antenna (21) for receiving a received signal; A second mixer device (22) for mixing the received signal into the baseband, the second mixer device being functionally connected to the receiving antenna (21); A third mixer device (24) for generating a second mixing signal having a second frequency (fLO2), the third mixer device being functionally connected to the second mixer device (22); An A / D converter (25), the A / D converter being functionally connected to the second mixer device (22); wherein The second frequency (fLO2) of the second mixing signal is offset relative to the bandwidth of the received signal in a defined manner.

6. The receiving device (20) according to claim 5, characterized in that, The second frequency (fLO2) of the second mixing signal is higher or lower than the bandwidth of the received signal.

7. The receiving device (20) according to claim 5, wherein, Generate a frequency offset between the second frequency (fLO2) and the first frequency (fLO) of the first mixing signal by means of a digital module.

8. The receiving device (20) according to claim 6, wherein, Generate a frequency offset between the frequencies (fLO, fLO2) of the mixing signals by means of a voltage-controlled module in combination with a PLL module.

9. The receiving device (20) according to any one of claims 5 to 8, wherein, The second frequency (fLO2) is generated from the first frequency (fLO), or alternatively, the second frequency (fLO2) is generated separately.

10. The receiving device (20) according to any one of claims 5 to 9, wherein, The spacing between the second frequency (fLO2) and the bandwidth of the received signal is an integer multiple of the spacing of the frequency lines of the sidebands (SB1, SB2) of the received signal.

11. An OFDM radar system (100) having a transmitting device (10) according to claim 4 and a receiving device (20) according to any one of claims 5 to 10.

12. A computer program product having program code means for performing the method according to any one of claims 1 to 3 when the computer program product is run on an OFDM radar system (100) or stored on a computer-readable data carrier.

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