Method and device for compensating for phase noise

Abstract

Phase noise compensation can be performed in a primary radar system, such as in transceiver hardware. A first reflected reception signal can be received, corresponding to a reflection of a first transmission signal from an object, and a first measurement signal can be generated using mixing or correlation of the first reflected reception signal and the first transmission signal. A second measurement signal can be similarly generated from a second transmission signal and a second reflected reception signal. The first and second measurement signals include respective components including complex conjugate representations of each other. The components correspond to interfering components associated with phase noise, and such respective components can cancel each other to suppress phase noise.

Claims

1. A method for compensating for noise in a primary radar system, the method comprising: using a transceiver, transmitting a first transmission signal containing a first interfering component, caused by the noise; using the transceiver, transmitting at least one second transmission signal containing a second interfering component, caused by the noise, in a temporally overlapping manner with the first transmission signal, the first transmission signal comprising at least one frequency ramp with a first slope and the at least one second transmission signal comprising at least one frequency ramp with a second slope having a sign opposite the first slope; and compensating for at least one of phase shifts or frequency shifts resulting from the first and second interfering components by evaluation of the transmission signals, the compensating comprising: receiving a first reflected reception signal corresponding to a reflection of the first transmission signal from an object; generating a first measurement signal using mixing or correlation of the first reflected reception signal and the first transmission signal; receiving a second reflected reception signal corresponding to a reflection of the second transmission signal from an object; and generating a second measurement signal using mixing or correlation of the second reflected reception signal and the second transmission signal; wherein the first measurement signal and the second measurement signal comprise respective components including complex conjugate representations of each other, the respective components corresponding to the first and second interfering components.

2. The method according to claim 1, wherein a first interfering component, resulting from the noise, of the first measurement signal and a second interfering component, resulting from the noise, of the second measurement signal represent complex conjugates of each other.

3. The method according to claim 1, wherein the first transmission signal has a first factor which represents a complex conjugate to a second factor of the second transmission signal.

4. The method according to claim 1, wherein a value of the first slope and a value of the second slope are substantially equal.

5. The method according to claim 1, wherein a base signal used for generation of the first and second measurement signals, or the first and second transmission signals is generated by a shared generator.

6. The method according to claim 1, wherein the first transmission signal or the first measurement signal is based on an output of a first modulation generator; and wherein the second transmission signal or the second measurement signal is based on an output of a second modulation generator.

7. The method according to claim 1, wherein a fundamental signal for at least one of the first or second transmission signals is generated and then the respective transmission signal is modulated using a vector modulator; and wherein at least one of the first or second transmission signals is generated by applying a modulation signal to a real signal input or complex signal input of the vector modulator, to contemporaneously generate the first transmission signal and a mirror representation of the first transmission signal defining the second transmission signal.

8. The method according to claim 1, wherein a frequency corresponding to propagation time information, is derived from at least one of the first or second measurement signals.

9. The method according to claim 1, wherein the first measurement signal is generated by a first mixer and the second measurement signal is generated by a second mixer.

10. The method according to claim 1, wherein the first and second measurement signals comprise mixer outputs representing products of FMCW ramps.

11. The method of claim 1, wherein a beat frequency corresponding to propagation time information, is derived from at least one of the first or second measurement signals.

12. A device for compensating for noise in a primary radar system, the device comprising: a transceiver configured to: generate and transmit a first transmission signal containing a first interfering component, caused by the noise, the first transmission signal comprising at least one frequency ramp with a first slope; and generate and transmit, in a temporally overlapping manner, a second transmission signal containing a second interfering component, caused by the noise, the second transmission signal comprising at least one frequency ramp with a second slope having a sign opposite the first slope; and compensate for at least one of phase shifts or frequency shifts resulting from the first and second interfering components using the first and second transmission signals, the compensating comprising: receiving a first reflected reception signal corresponding to a reflection of the first transmission signal from an object; generating a first measurement signal using mixing or correlation of the first reflected reception signal and the first transmission signal; receiving a second reflected reception signal corresponding to a reflection of the second transmission signal from an object; generating a second measurement signal using mixing or correlation of the second reflected reception signal and the second transmission signal; wherein the first measurement signal and the second measurement signal comprise respective components including complex conjugate representations of each other.

13. The device according to claim 12, wherein a first interfering component, resulting from the noise, of the first measurement signal and a second interfering component, resulting from the noise, of the second measurement signal represent complex conjugates of each other.

14. The device according to claim 12, wherein the first transmission signal has a first factor which represents a complex conjugate to a second factor of the second transmission signal.

15. The device according to claim 12, wherein the transceiver comprises a transmitting antenna (TX) and a receiving antenna (RX); and wherein the transmitting antenna (TX) transmits the first and second transmission signals and the receiving antenna (RX) receives the first and second reflected reception signals.

16. The device according to claim 12, comprising one or more mixers configured to generate at least one of the first measurement signal from the first transmission signal and the first reception signal by mixing or the second measurement signal from the second transmission signal and the second reception signal by mixing.

17. The device according to claim 12, comprising a joint mixer configured to generate the first measurement signal and the second measurement signal by mixing.

18. The device according to claim 12, comprising: a shared generator for generating a base signal for the first and second transmission signals or for the first and second measurement signals.

19. The device according to claim 12, comprising a vector modulator including an output configured to provide the first transmission signal and the second transmission signal.

20. The device of claim 12, wherein the transceiver comprises a joint transmitting/receiving antenna (TX/RX) configured to transmit the first transmission signal and to receive the first reflected reception signal, and to transmit the second transmission signal and to receive the second reflected reception signal.

21. The device of claim 12, comprising a vector modulator including an output configured to provide the first measurement signal and the second measurement signal.

22. The device of claim 12, wherein a beat frequency corresponding to propagation time information, is derived from at least one of the first or second measurement signals.

Description

(1) In the figures:

(2) FIG. 1 shows a schematic representation of a device according to the invention for compensating for phase noise;

(3) FIG. 2 shows a frequency diagram;

(4) FIG. 3 shows an alternative embodiment of a device according to the invention; and

(5) FIG. 4 shows a further embodiment of the device according to the invention.

(6) In the following description, the same reference numerals are used for identical and equivalent parts.

(7) FIG. 1 shows a primary radar system. This comprises a transceiving unit SEE having at least one local oscillator LO, two mixers M1 and M2 and two modulation generators G1 and G2. The primary radar system shown in FIG. 1 is intended to be used in particular to determine a distance to one or more objects which may be separated from the transceiving unit SEE by a reciprocal transmission channel (usually an air transmission channel). To do this, a modulated signal is transmitted over the transmission channel by means of a transmitting antenna TX, is received by a receiving antenna RX, and then is mixed into a baseband by the mixers M1, M2. A frequency shift (caused by a defined propagation time) of the mixed signal can then be (digitally) processed. The distance information can then be obtained therefrom.

(8) The matter of interest here is in particular that of (completely) compensating for correlated phase noise by means of a specifically configured signal form. The intention is thus for it to be possible on the one hand to place lower demands on the quality (for example frequency stability) of components which are used to generate a high-frequency (carrier) signal. On the other hand, the phase noise level preferably does not (any longer) represent a lower limit for the accuracy of the distance measurement.

(9) In the embodiment shown in FIG. 1, a first measurement signal s.sub.m1(t) (mixed signal) is generated. This can then be received and further processed (as described in detail below) by a further component (which may optionally be a constituent part of the transceiving unit SEE). Simultaneously (or at least in a temporally overlapping manner), a second measurement signal s.sub.m2(t) (in particular mixed signal) is generated and is received and further processed by the further component. The second measurement signal (mixed signal) is characterized in that a frequency shift caused by phase noise is (exactly) opposite to the first measurement signal (first mixed signal), which is transmitted and received simultaneously (or at least in a temporally overlapping manner).

(10) FIG. 1 shows a (relatively simple) structure, in which the first and second signal are generated from the same clock source LO by way of the modulation generators G1 and G2. Alternatively, it is also possible for just one modulation generator to be provided; by way of example, a modulation generator which operates by means of direct digital synthesis (DDS) may be used. This may have the result that the two measurement signals (the first and the second measurement signal) are oppositely influenced by noise components (in particular by phase noise or uniformly occurring non-linearities of FMCW ramps). The mixing process by way of the one or both mixers may in principle generate four signal components, of which one component, which is relevant for the measurement, has a relatively low beat frequency and can be separated from the high-frequency components, for example by way of a low-pass filter configured as hardware and/or software.

(11) FIG. 2 shows a characteristic of transmitted and received signals over time. Here, s12(t) is the transmission signal, known from the above description of a conventional FMCW radar, in the form of a rising (linear) frequency ramp, and s22(t) is the reception signal that has been reflected at an object. The signal s12(t) will hereinafter be referred to as the first transmitted signal. The signal s22(t) will hereinafter be referred to as the first reflected signal. In addition, a second signal s11(t) is simultaneously transmitted, reflected, and received after a propagation time in the transmission channel (this being referred to as the reflected second signal s21(t)). It is important here that a (ramp) slope of this second transmitted signal s22(t) is selected to be negative (or with a different sign than the first transmitted signal s12(t)).

(12) In general, the characteristic in FIG. 2 is to be regarded only as one possible embodiment. By way of example, it is alternatively also possible for just a portion of the signal characteristic shown therein to be selected and/or used. In particular, a time-shifted (for example starting at Ts/2) portion may also be selected. One possible alternative would also be the (simultaneous) use of multiple frequency ramps, for example multiple second transmitted signals or second measurement signals (mixed signals). In principle, other radar signal forms may also be used, such as for example SFCW (Stepped Frequency Continuous Wave) or orthogonal frequency division multiplexing (OFDM), preferably at least as long as the second measurement signal (mixed signal) is complex conjugate to the first measurement signal (mixed signal).

(13) The transmitted signals shown in FIG. 1 can be described by

(14) $s_{11}\left(t\right)=e^{j2\pi \left(\left(f_c+\frac{B}{2}\right)t-\frac{\mu }{2}{t}^2\right)}{e}^{j{\phi }_n\left(t\right)}\mathrm{and}{s}_{12}\left(t\right)=e^{j2\pi \left(\left(f_c-\frac{B}{2}\right)t+\frac{\mu }{2}{t}^2\right)}{e}^{j{\phi }_n\left(t\right)}$

(15) where B is the bandwidth used by the radar system and μ=B/T.sub.s is the sweep rate (that is to say the increase in frequency per unit of time). The received signals s.sub.21(t)=As.sub.11(t−τ) and s.sub.22(t)=As.sub.12(t−τ) are also considered here as an attenuated and time-shifted version of the transmitted signal. After the process of mixing the transmitted signals with the received signals and low-pass filtering (preferably carried out by the hardware of the measuring system in order to reduce thermal noise and interference with other radio applications), the mixed products

(16) $s_{m1}\left(t\right)=s_{11}^{*}\left(t\right)s_{21}\left(t\right)={\mathrm{Ae}}^{j2\pi \left(-\left(f_c+\frac{B}{2}\right)\tau +\mathrm{\mu \tau }t-\frac{\mu }{2}{\tau }^2\right)}{e}^{j\left(-{\phi }_n\left(t\right)+{\phi }_n\left(t-\tau \right)\right)}={\mathrm{Ae}}^{j{\Phi }_{m1}\left(t\right)}\mathrm{and}{s}_{m2}\left(t\right)=s_{22}\left(t\right)s_{12}^{*}\left(t\right)={\mathrm{Ae}}^{j2\pi \left(\left(f_c-\frac{B}{2}\right)\tau +\mathrm{\mu \tau }t-\frac{\mu }{2}{\tau }^2\right)}{e}^{j\left({\phi }_n\left(t\right)-{\phi }_n\left(t-\tau \right)\right)}={\mathrm{Ae}}^{j{\Phi }_{m2}\left(t\right)}$

(17) are obtained.

(18) It will be assumed here that the measuring system can only process positive frequencies, which corresponds to a basic structure according to FIG. 1. A description for a system according to FIGS. 3 and 4 can be found analogously by a person skilled in the art. By way of these mixed products, the two beat frequencies

(19) $f_{b1}\left(t\right)=\frac{1}{2\pi }\frac{d{\Phi }_{m1}\left(t\right)}{\mathrm{dt}}=\mathrm{\mu \tau }-\frac{1}{2\pi }\frac{d}{\mathrm{dt}}\left({\phi }_n\left(t\right)-{\phi }_n\left(t-\tau \right)\right)=\mathrm{\mu \tau }+\delta f\left(t\right)\mathrm{and}{f}_{b2}\left(t\right)=\frac{1}{2\pi }\frac{d{\Phi }_{m2}\left(t\right)}{\mathrm{dt}}=\mathrm{\mu \tau }+\frac{1}{2\pi }\frac{d}{\mathrm{dt}}\left({\phi }_n\left(t\right)-{\phi }_n\left(t-\tau \right)\right)=\mathrm{\mu \tau }-\delta f\left(t\right)$

(20) can be calculated by differentiation, said beat frequencies being subject, as in the case shown above, to a statistical deviation caused by the correlated noise component δf(t). Due to the complex conjugate phase characteristic of the mixed signals, the signal f.sub.b1(t) shifts towards the higher frequencies and the signal f.sub.b2(t) shifts towards the lower frequencies if δf(t) is positive.

(21) Summing then gives the (synthetic) measurement frequency
f.sub.b(t)=f.sub.b1(t)+f.sub.b2(t)=2μτ,

(22) which no longer has any dependence on the correlated phase noise δf(t). This result can be solved for τ, and the distance to an object can be estimated via the relationship τ=2x/c.sub.0 using the propagation speed c.sub.0 of the electromagnetic wave.

(23) Due to the linear relationship, it is possible to detect multiple objects, that is to say to receive multiple time-shifted and attenuated copies (superposition, or linear combination of target responses) of the transmitted signal.

(24) The embodiment shown in FIG. 1 comprises two (real-value) mixers, which can be used in particular for separating upsweep and downsweep. These may optionally be replaced by just one (complex) mixer (in particular the mixer M.sub.RX in FIG. 3). In this case, one measurement signal (mixed signal) can be generated with a positive frequency and a second measurement signal (mixed signal) can be generated with a negative frequency. As an alternative or in addition, the two modulation generators G1 and G2 in FIG. 1 may also be replaced by one modulation generator G (see FIG. 3). The signal thereof may then optionally be mixed by a transmitting mixer M.sub.TX, wherein the two transmitted signals (shown in FIG. 3) may optionally represent an upper and a lower sideband.

(25) In the embodiment shown in FIG. 4, a single antenna is provided instead of two (separate) transmitting and receiving antennas, which single antenna is used (jointly) for transmitting and receiving. In this case, a transmission mixer (TM) may be used, which in particular may have advantageous transmission properties in the case of FMCW systems.

(26) The method described above and the system described above can be used to suppress phase noise, in particular also to reduce for example hardware requirements (such as, for example, in terms of the quality of a phase-locked loop) so as to generate a high-frequency carrier signal with little phase noise. Any error resulting therefrom can (subsequently) be compensated for by the method described above.

(27) It should be noted at this point that all the parts and functions described above are claimed as essential to the invention individually and in any combination, particularly the details shown in the drawings. Modifications thereof are familiar to a person skilled in the art.

LIST OF REFERENCE SIGNS

(28) G modulation generator G1 modulation generator G2 modulation generator LO local oscillator M mixer M1 mixer M2 mixer M.sub.RX (receiving) mixer M.sub.TX (transmitting) mixer RX receiving antenna s.sub.1(t) first signal s.sub.2(t) second signal s.sub.1(t−τ) first reflected and received signal s.sub.2(t−τ) second reflected and received signal s.sub.m1(t) first measurement signal (mixed signal) S.sub.m2(t) second measurement signal (mixed signal) SEE transceiving unit TM (transmission) mixer TX transmitting antenna