METHOD FOR OPERATING AN OFDM RADAR SYSTEM

Abstract

A method for operating an OFDM radar system. The method includes: generating an analog transmit signal in the baseband; mixing the analog transmit signal with a first mixed signal at a first frequency, the first frequency of the first mixed signal lying centrally between two sidebands of a transmission band; receiving a received signal; mixing the received signal with a second mixed signal at a second frequency into the baseband, the second frequency of the second mixed signal lying in a defined manner adjacent to a total bandwidth of the received signal.

Claims

1-12. (canceled)

13. A method for operating an OFDM radar system, comprising the following steps: generating an analog transmit signal in a baseband; mixing the analog transmit signal with a first mixed signal at a first frequency, the first frequency of the first mixed signal lying centrally between two sidebands of a transmission band; receiving a received signal; and mixing the received signal with a second mixed signal at a second frequency into the baseband, the second frequency of the second mixed signal lying in a defined manner adjacent to a total bandwidth of the received signal.

14. The method as recited in claim 13, wherein the second frequency of the second mixed signal is generated from the first frequency of the first mixed signal.

15. The method as recited in claim 13, wherein the second frequency of the second mixed signal is generated independently of the first frequency of the first mixed signal, a defined correlation of phase noise of the first and second frequencies being provided.

16. A transmitting device of an OFDM radar system, comprising: a storage unit configured to store a digital transmit signal; a first D/A converter functionally connected to the storage unit configured to generate an analog transmit signal; a first mixer unit functionally connected to the first D/A converter; and a first oscillator unit functionally connected to the first mixer unit, the analog transmit signal being mixed into a transmission spectrum including two sidebands using the first oscillator unit and the first mixer unit, the first frequency of the first oscillator unit lying centrally between the two sidebands, the analog transmit signal being emitted using a transmitting antenna.

17. A receiving device of an OFDM radar system, comprising: a receiving antenna configured to receive a received signal; a second mixer unit functionally connected to the receiving antenna and configured to mix the received signal into a baseband; a third mixer unit functionally connected to the second mixer unit and configured to generate a second mixed signal including a second frequency; and an A/D converter functionally connected to the second mixer unit; wherein the second frequency of the second mixed signal is offset in a defined manner to the bandwidth of the received signal.

18. The receiving device as recited in claim 17, wherein the second frequency of the second mixed signal is above or below the bandwidth of the received signal.

19. The receiving device as recited in claim 17, wherein a frequency offset between the second frequency and a first frequency of a first mixed signal is generated using a digital component.

20. The receiving device as recited in claim 19, wherein a frequency offset between the first and second frequencies of the first and second mixed signals is generated using a voltage-controlled component in combination with a PLL component.

21. The receiving device as recited in claim 19, wherein the second frequency is generated from the first frequency or the second frequency is generated separately.

22. The receiving device as recited in claim 17, wherein an interval of the second frequency to the bandwidth of the received signal is an integer multiple of an interval of frequency lines of the sidebands of the received signal.

23. An OFDM radar system, comprising: a transmitting device, including: a storage unit configured to store a digital transmit signal, a first D/A converter functionally connected to the storage unit configured to generate an analog transmit signal, a first mixer unit functionally connected to the first D/A converter, and a first oscillator unit functionally connected to the first mixer unit, the analog transmit signal being mixed into a transmission spectrum including two sidebands using the first oscillator unit and the first mixer unit, the first frequency of the first oscillator unit lying centrally between the two sidebands, the analog transmit signal being emitted using a transmitting antenna; and a receiving device, including: a receiving antenna configured to receive a received signal; a second mixer unit functionally connected to the receiving antenna and configured to mix the received signal into a baseband; a third mixer unit functionally connected to the second mixer unit and configured to generate a second mixed signal including a second frequency; and an A/D converter functionally connected to the second mixer unit; wherein the second frequency of the second mixed signal is offset in a defined manner to the bandwidth of the received signal.

24. A non-transitory computer-readable data carrier on which is stored a computer program including program code for operating an OFDM radar system, the program code, when executed by a computer, causing the computer to perform the following steps: generating an analog transmit signal in a baseband; mixing the analog transmit signal with a first mixed signal at a first frequency, the first frequency of the first mixed signal lying centrally between two sidebands of a transmission band; receiving a received signal; and mixing the received signal with a second mixed signal at a second frequency into the baseband, the second frequency of the second mixed signal lying in a defined manner adjacent to a total bandwidth of the received signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows a schematic block diagram of a conventional OFDM radar system.

[0035] FIG. 2 shows a schematic block diagram of an embodiment of a provided transmitting device of an OFDM radar system, in accordance with the present invention.

[0036] FIG. 3 shows a schematic view of a reception spectrum of a provided receiving device of an OFDM radar system, in accordance with the present invention.

[0037] FIG. 4 shows a schematic block diagram of a specific embodiment of a provided receiving device of an OFDM radar system, in accordance with the present invention.

[0038] FIG. 5 shows a schematic block diagram of another specific embodiment of a provided receiving device of an OFDM radar system, in accordance with the present invention.

[0039] FIG. 6 shows the receiving device of FIG. 4 in a higher degree of detail, in accordance with the present invention.

[0040] FIG. 7 shows a schematic sequence of a provided method for operating an OFDM radar system, in accordance with an example embodiment of the present invention.

[0041] FIG. 8 shows a block diagram of a provided OFDM radar system, in accordance with an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0042] OFDM signals are upmixed in the transmitter in the sideband mode and downmixed in the receiver with an intermediate frequency to evaluate both sidebands. Twice as high a resolution also results due to the doubled generated bandwidth.

[0043] FIG. 1 shows a simplified overview circuit diagram of a conventional radar system 100 based on the orthogonal frequency division multiplexing method OFDM. In an electronic storage unit 1a (for example a RAM), digital information of a transmit signal is stored, for example a sequence of discrete equidistant transmit frequencies or OFDM subcarriers to be emitted. For example, complex sampled values of a baseband transmit signal are generated by an inverse fast Fourier transform iFFT, these values being stored in electronic storage unit 1a, from which they may be read out cyclically.

[0044] A D/A converter 2a generates a cyclic complex analog baseband signal from the sequence read out periodically from storage unit 1a.

[0045] With the aid of a first mixer unit 3 and an oscillator unit 4, the baseband transmit signal is shifted into the desired frequency range (for example 77 . . . 78 GHz) and then emitted by a transmitting antenna 5, in the automotive field, for example using a carrier frequency of 77 GHz.

[0046] If a simple mixer is used, two sidebands SB1, SB2 thus result. If the receiver mixes using the same carrier frequency in the baseband (around f=0 Hz), the bands fold on one another and cause undesired interference, in particular in dynamic scenarios. Therefore, an IQ mixer may be used in the transmitter which suppresses the second sideband. However, a hardware complexity in the transmitter is thus increased by the factor of two, since I and Q signals each have to be generated separately via D/A converters and stored beforehand. An intermediate frequency system may also be used which uses a filter either in the transmitter and receiver to suppress the undesired sideband.

[0047] A second path is apparent of transmitting device 10 having a second storage unit 1b and a second D/A converter 2a, which is used to largely eliminate a first sideband SB1. This is used so that the baseband may be processed in the receiver channel.

[0048] FIG. 2 shows a first specific embodiment of a provided transmitting device 10 for an OFDM radar system 100. It is apparent that now only a single path having a storage unit 1a and a D/A converter 2a is provided, which is used to upmix the analog transmit signal using a first oscillator unit 4. The OFDM-modulated transmit signal is generated with the aid of first mixing unit 3 (double-sideband mixer) and thus has a transmission bandwidth of 2×B, if the modulation bandwidth of the baseband signal is B. As a result, a transmission spectrum of the transmit signal as shown in FIG. 2 thus results, which has two sidebands SB1, SB2, the frequency of mixed signal fLO lying centrally between the two sidebands SB1, SB2. In this form, however, the transmit signal could not be processed by a receiving device, because mirror effects occur upon downmixing, whereby the sidebands mutually overlap.

[0049] Because transmitting device 10 operates in the double-sideband mode, it does not require an IQ mixer as in the related art. Second D/A converter 2a and digital storage unit 1b required for this purpose of conventional transmitting device 10 are thus advantageously omitted. In addition, at equal sampling rate in transmitting device 10, the generated analog signal bandwidth of transmitting device 10 is increased by the factor of two, which advantageously doubles the possible distance resolution of the OFDM radar system.

[0050] Furthermore, a receiving device 20 for an OFDM radar system is provided for processing the transmit signal emitted by transmitting device 10, using which a reception spectrum as shown in FIG. 3 is obtained. For provided receiving device 20, a second mixer 22 in the form of a double-sideband mixer may be used, if an oscillator signal offset by bandwidth B is available at frequency fLO2. This enables only a single A/D converter 25 to be used for sampling the received signal. In this case, frequency fLO2 of the oscillator signal is adjacent to the entire bandwidth of the received signal, as may be seen in FIG. 3. In the case of FIG. 3, frequency fLO2 is above first sideband SB1, however, it could also be above second sideband SB2 (not shown).

[0051] In contrast to applications in communication technology, in radar applications the coding information on the subcarriers is not used, but is eliminated in receiving device 20 by spectral division, so that only the channel information remains on the carriers. Since second sideband SB2 is a complex-conjugated and mirrored copy of first sideband SB1 in this case, both sidebands SB1, SB2 contain the same code, but pass through different frequency points in the channel and thus have nonredundant channel information.

[0052] In provided receiving device 20, mixing is carried out with the aid of an intermediate frequency in such a way that both sidebands SB1, SB2 may be evaluated. The sampling rate of A/D converter 25 has to be set in such a way that both sidebands SB1, SB2 are sampled clearly and completely. The bandwidth thus evaluated (distance resolution) is then twice as high as the bandwidth of the transmit signal generated with the aid of transmitting device 10.

[0053] The oscillator frequencies for the mixed signals may be between 57 GHz and 300 GHz, for automobile radar preferably between 76 GHz and 81 GHz. The interval between frequencies fLO and fLO2 of the mixed signals is calculated as:

fLO2≈fLO±B  (1)

where:
B . . . modulation bandwidth of the OFDM signals (for example between 1 MHz and 2 GHz)

[0054] FIG. 4 shows a schematic block diagram of a first variant of provided receiving device 20. To ensure correlated phase noise between provided transmitting device 10 and provided receiving device 20, the same oscillator signal may be used for transmitting device 10 and receiving device 20. The required intermediate frequency for transmitting device 10 and receiving device 20 may be generated with the aid of a ZF unit 23, a third mixer unit 24 in the form of an IQ mixer, and a second frequency source (for example DDS (direct digital synthesis (not shown)) or VCO (voltage-controlled oscillator (not shown)). Since the intermediate frequency may be generated at low frequencies (for example at 1 GHz), the added phase noise is thus less. Since carrier frequency and intermediate frequency are generally mixed at a fixed frequency, third mixer unit 24 may be tuned precisely to this frequency behavior.

[0055] This is achieved using receiving device 20 of FIG. 4. In receiving device 20, the received signal is mixed and sampled using an oscillator signal offset by bandwidth B. The two emitted sidebands SB1, SB2 may thus be reproduced, without an IQ receiving mixer being required for this purpose.

[0056] First oscillator unit 4 is apparent, which is functionally connected together with an intermediate frequency unit 23 to a third mixer unit 24. The received signal received via a receiving antenna 21 may thus be mixed with the aid of second mixer unit 22 into the baseband and may subsequently be evaluated using an A/D converter 25. A digital, complex time signal is thus provided in the baseband at the output of A/D converter 25. For this purpose, A/D converter 25 has to be designed in such a way that it may sample the complete reception spectrum. In this way, a bandwidth 2B is obtained for the received signal, which may significantly improve the distance resolution of provided OFDM radar system 100.

[0057] FIG. 5 shows a second variant of provided receiving device 20. In this case, the frequency for the mixed signal of the received signal is generated separately by transmitting device 10, for which separate oscillator units 4, 26 of transmitting device 10 and receiving device 20 may be used in each case. The phase noise of the two oscillator units 4, 26 is no longer correlated in this configuration, this being able to be improved with the aid of a coupling (for example, via an identical reference (not shown)) of the two oscillator units 4, 26, however.

[0058] FIG. 6 shows a detail of the receiving device of FIG. 4, a way of generating the frequency offset between oscillator frequency fLO of transmitting device 10 and oscillator frequency fLO2 of receiving device 20 being shown in greater detail. A difference of mentioned oscillator frequencies fLO, fLO2 is supplied to third mixer unit 24 and upmixed with the aid of first oscillator unit 4 into the reception band according to FIG. 3.

[0059] The following table shows several technical parameters in the comparison between a conventional OFDM radar system and a provided OFDM radar system:

TABLE-US-00001 TABLE According to the Parameters Related art present invention Carrier frequency 79 GHz  OFDM useful bandwidth 2 GHz Measuring period 1 ms   Number of D/A 2 1 converters per transmission channel D/A sampling rate 4 GS/s 2 GS/s Total sampling rate 8 GS/s 2 GS/s per transmission channel Digital storage in 8 MS 2 MS the transmitter

[0060] It is apparent that significant technical parameters of OFDM radar system 100 according to the present invention are halved numerically and therefore essentially only require half of the technical expenditure for their implementation.

[0061] FIG. 7 shows a schematic sequence of a provided method for operating an OFDM radar system 100.

[0062] In a step 200, an analog transmit signal is generated in the baseband.

[0063] In a step 210, mixing of the analog transmit signal with a first mixed signal at a first frequency fLO is carried out, first frequency fLO of the first mixed signal lying centrally between two sidebands SB1, SB2 of a transmission band.

[0064] In a step 220, a received signal is received.

[0065] Finally, in a step 230, mixing of the received signal with a second mixed signal is carried out at a second frequency fLO2 in the baseband, second frequency fLO2 of the second mixed signal lying in a defined manner adjacent to a total bandwidth 2B of the received signal.

[0066] Alternatively, it is also possible to carry out some of the signal processing steps in other sequences than those shown.

[0067] Optimum utilization of existing resources of the OFDM radar system is assisted by the provided method.

[0068] Although the described method was described exclusively in conjunction with OFDM radar systems, an application for other systems including digital multicarrier modulation is also possible, in particular in the radar field.

[0069] FIG. 8 shows a block diagram of a provided OFDM radar system 100 including a provided transmitting device 10 and a provided receiving device 20.

[0070] The provided method may advantageously also be designed as a software program which runs on electronic OFDM radar system 100, whereby an adaptability of the method is advantageously assisted.

[0071] The person skilled in the art will suitably modify the described features of the present invention and combine them with one another without departing from the core of the present invention.