RADAR SYSTEM AND A RADAR METHOD FOR COMPENSATING A CARRIER CHARACTERISTIC OFFSET

Abstract

It is described a radar system (100), comprising: i) a transmitter (110) having a transmitter carrier characteristic, configured to transmit a code signal (S); ii) a receiver (120) having a receiver carrier characteristic, configured to receive an echo (E) of the code signal (S); and iii) a control unit (130) configured to: a) identify a carrier characteristic tracking path (T) between the transmitter (110) and the receiver (120), b) estimate an offset between the transmitter carrier characteristic and the receiver carrier characteristic based on the identified tracking path (T), and c) compensate for the offset, in particular establish coherency, based on the estimation. iv) The tracking path (T) comprises hereby a communication path that is at least partially independent of the code signal (S) and the echo (E) of the code signal (S).

Claims

1. A radar system, comprising: a transmitter having a transmitter carrier characteristic, configured to transmit a code signal; a receiver having a receiver carrier characteristic, configured to receive an echo of the code signal; and a control unit configured to: identify a carrier characteristic tracking path between the transmitter and the receiver, estimate an offset between the transmitter carrier characteristic and the receiver carrier characteristic based on the identified tracking path, and compensate for the offset based on the estimation; wherein the tracking path comprises a communication path that is at least partially independent of the code signal and the echo of the code signal.

2. The radar system according to claim 1, wherein the communication path of the tracking path is a static path.

3. The radar system according to claim 2, wherein the static path comprises at least one of the following: the shortest distance between transmitter and receiver, the line-of-sight path, LoS, between transmitter and receiver, a path that is not the path of highest S/N ratio between transmitter and receiver.

4. The radar system according to claim 1, wherein the identification of the tracking path comprises communicate a communication signal between the transmitter and the receiver.

5. The radar system according to claim 1, wherein the tracking path comprises a combination of at least two paths.

6. The radar system according to claim 5, wherein the estimation of the offset further comprises at least one of the following: correlate the echo of the code signal to a code template; accumulate a plurality of symbols of the echo of the code signal.

7. The radar system according to claim 1, wherein the carrier characteristic comprises at least one of the carrier frequency and the carrier phase.

8. The radar system according to claim 1, wherein the control unit is further configured for at least one of the following: compensate for the effect of a movement of at least one of the transmitter and the receiver, not compensate for the effect of a Doppler shift caused by a movement of a target.

9. The radar system according to claim 1, wherein the control unit is further configured to: reconfigure the offset compensation for each transmitted code signal.

10. The radar system according to claim 1, wherein the control unit is further configured to: perform an optimization loop to optimize the compensation of the offset.

11. The radar system according to claim 10, wherein the optimization loop comprises a combiner, configured to combine at least two paths between the transmitter and the receiver to yield the tracking path.

12. The radar system according to claim 1, wherein the radar system is implemented as one of a monostatic radar application, a multi-static radar application, a statistical MIMO application, a coherent MIMO application.

13. The radar system according to claim 1, further comprising at least one of the following features: wherein the radar system is a pulse radar system; wherein the radar system is configured for transmitting and receiving ultra-wide band, UWB, signals, and echoes thereof; wherein a symbol of the code encodes a plurality of bits using a digital modulation scheme.

14. A method of operating a radar system, the method comprising: transmitting a code signal by a transmitter having a transmitter carrier characteristic; receiving an echo of the code signal by a receiver having a receiver carrier characteristic; identifying a carrier characteristic tracking path between the transmitter and the receiver, estimating an offset between the transmitter carrier characteristic and the receiver carrier characteristic based on the identified tracking path, and compensating the offset based on the estimation; wherein the tracking path comprises a communication path that is at least partially independent of the code signal and the echo of the code signal.

15. The method according of claim 14, wherein identifying is done before transmitting and receiving.

16. The radar system according to claim 2, wherein the identification of the tracking path comprises communicate a communication signal between the transmitter and the receiver.

17. The radar system according to claim 2, wherein the tracking path comprises a combination of at least two paths.

18. The radar system according to claim 2, wherein the carrier characteristic comprises at least one of the carrier frequency and the carrier phase.

19. The radar system according to claim 2, wherein the control unit is further configured for at least one of the following: compensate for the effect of a movement of at least one of the transmitter and the receiver, not compensate for the effect of a Doppler shift caused by a movement of a target.

20. The radar system according to claim 2, wherein the control unit is further configured to: reconfigure the offset compensation for each transmitted code signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 illustrates a radar system according to an exemplary embodiment of the present disclosure.

[0054] FIG. 2 illustrates a radar system according to a further exemplary embodiment of the present disclosure.

[0055] FIG. 3 illustrates a radar system according to a further exemplary embodiment of the present disclosure.

[0056] FIG. 4 illustrates a tracking path and a radar path according to a further exemplary embodiment of the present disclosure.

[0057] FIG. 5 illustrates a simulation of an FFT-CIR matrix for a line-of-sight path measurement after carrier characteristic offset compensation according to a further exemplary embodiment of the present disclosure.

[0058] FIG. 6 illustrates a simulation of a conventional FFT-CIR matrix for a line-of-sight path measurement without carrier characteristic offset compensation.

[0059] FIG. 7 illustrates a simulation of an FFT-CIR matrix for a distance measurement, which includes a movement, after carrier characteristic offset compensation according to a further exemplary embodiment of the present disclosure.

[0060] FIG. 8 illustrates a simulation of a conventional FFT-CIR matrix for distance measurement, which includes a movement, without carrier characteristic offset compensation.

[0061] The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs.

DETAILED DESCRIPTION OF THE DRAWINGS

[0062] Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the present disclosure have been developed.

[0063] According to exemplary embodiments of the present disclosure, the advantages of both areas, communication and radar, are combined. In particular an UWB device can be very suitable herefore. In the communication mode, a training sequence (preamble) is used to roughly estimate the carrier frequency/phase offset. After this rough estimation, an optimization loop takes over. For the tracking path, there should be no physical movement and the Doppler effect may only be caused by the carrier frequency offset. Well-suited for this condition may be the line-of-sight path.

[0064] According to exemplary embodiments of the present disclosure, it is desirable to identify a path which is used to track the carrier frequency offset and to measure a CIR with a high S/N ratio. A radar frame hereby differs from a ranging and a communication frame, since in a radar frame, a large number of symbols or pulses are coherently accumulated to gain S/N.

[0065] In this specification, embodiments have been presented in terms of a selected set of details. However, a person of ordinary skill in the art would understand that many other embodiments may be practiced which include a different selected set of these details. It is intended that the following claims cover all possible embodiments.

[0066] FIG. 1 is a schematic illustration of a radar system 100 according to an exemplary embodiment of the present disclosure. The radar system 100 comprises a transmitter 110 with a transmitter code generation unit 105, which is configured for generating a code C. It is schematically shown that the code C comprises a plurality of symbols. The transmitter 110 is configured for generating a signal S from the code C, and further configured for transmitting the signal S via an antenna 111. The transmitter 110 has a transmitter carrier characteristic which is different from a receiver carrier characteristic of an associated receiver 120, i.e. there is an offset in the carrier signal frequency and/or phase.

[0067] The radar system 100 further comprises a receiver 120, configured for receiving an echo E of the signal S via a further antenna 112. Hereby, the signal S is reflected from a target 150 (object of interest) as the echo E. The receiver 120 can be associated with a correlator 140, configured for correlating the code C′ of the received echo E with a code template.

[0068] The radar system 100 is further configured, as is exemplary shown in FIG. 1, to produce an output signal (in particular a correlator output O), which may, for example, be a visual output, or in general, any digital or analogue output for further processing. For example, once the echo E has been received, it may be demodulated, e.g. by a higher order digital modulation method according to exemplary embodiments.

[0069] The radar system 100 comprises a control unit 130 which is, in the shown Figure, implemented in the receiver 120. Nevertheless, the control unit 130 could also be implemented in the transmitter 110 or somewhere else in the radar system 100. The control unit 130 is configured to identify a carrier characteristic tracking path T between the transmitter 110 and the receiver 120. In the example shown, the tracking path T is a static communication path, in particular the line-of-sight path. Thus, in this embodiment, the tracking path T comprises a communication path that is independent of the code signal S and the echo E of the code signal S (i.e. the radar path).

[0070] The control unit 130 is further configured to estimate the offset between the transmitter carrier characteristic and the receiver carrier characteristic based on the identified tracking path T, and to compensate the offset based on the estimation. Thereby, a coherency between transmitter 110 and receiver 120 carrier frequency/phase can be established which leads to significantly improved radar measurements (see FIGS. 5 and 7 below).

[0071] FIG. 2 is an illustration of a radar system 100 according to a further exemplary embodiment of the present disclosure. The radar system 100 can be configured in a very similar manner as described for FIG. 1 above. In this example, the radar system 100 is arranged at the front of a car. While the transmitter device 110 is attached to the left side of the car front, the receiver device 120 is attached to the right side of the car front. The code signal S transmitted by the transmitter 110 is reflected at a target 150, being another car, and the echo E is received by the receiver 120. The path of S and E can be termed the radar path, while a line-of-sight path, along the front of the car, can be termed the communication path. In this example, there is a movement in the radar path (since the other car is driving), while the communication path is a static path. The diagram on the right side shows that the intensity (S/N ratio) of the radar path S, E is much higher than the intensity of the communication path T. Nevertheless, the distance of the radar path is much longer and there is a movement. As a consequence, the static communication path (which is in this example independent of the radar path S, E) is applied as the tracking path T (see also FIG. 4).

[0072] FIG. 3 illustrates a specific implementation of the radar system 100 according to a further exemplary embodiment of the present disclosure. FIG. 3 shows operation steps associated with the radar path S, E alone (radar operation) and steps associated only with the tracking path T (tracking operation). Signals received at the antenna 111, 112 are transferred via analog functionalities and an A/D converter to the carrier characteristic (frequency/phase) offset compensation performed by the control unit 130. Regarding the radar operation, the compensated carrier characteristic is time compensated, coherency integrated, and then further processed, e.g. stored in a memory.

[0073] The tracking operation comprises in this example a sophisticated estimation and compensation of the carrier characteristic offset operation. The tracking path T comprises a combination of at least two paths, including a static path (independent of the radar path) and an echo E of the code signal S (only partially independent of the radar path). Said echo E of the code signal is correlated (symbol-per-symbol) to a code template. The correlation can be done before or after a timing compensation step (in this example, after). Further, the control unit 130 is configured to perform an optimization loop 160 to optimize the compensation of the offset. In the example shown, a combiner is used (which is implemented here as a RAKE receiver 165) to combine the different path that yield the tracking path T.

[0074] In other words, this radar system 100 requires two receiving paths, wherein the first receive path being for radar mode with a phase/frequency compensation (mixer), a re-sampler for timing compensation, and a symbol accumulation, while the second receive path is used for searching and tracking the carrier frequency/phase offset, having in addition acquisition and tracking support. The acquisition is used to synchronize to a multipath component of the received signal. Contrary to a communication mode, where it would be used to find the strongest path, in this mode of operation, a distinctive path is defined of which a phase and frequency offset is estimated.

[0075] In this example, the tracking path itself (a complex number) is the result of the correlation of the input signal and the known symbol at the configured tracking path index. After the acquisition has found a rough carrier frequency and phase offset based on the tracking path, the tracking (optimization) loop 160 takes over. This loop 160 can be updated on a symbol basis. The tracking loop 160 keeps the phase of the tracking path to be zero in this example. Optionally, a combiner (e.g. a RAKE receiver) 165 can be used to combine multiple (static) paths to one tracking path. The output of the combiner 165 is then used as the tracking path T. The receive path in radar mode is only used for coherent integration of received data. The start time of the coherent integration is configurable such that the timing and carrier-phase tracking loop has settled to a stable carrier frequency offset estimation.

[0076] FIG. 4 illustrates a channel impulse response according to an exemplary embodiment of the present disclosure. In particular, FIG. 4 illustrates in detail the diagram shown on the right side of FIG. 2. The intensity (CIR amplitude) of the static communication path (one or more of the static paths can be identified as the tracking path T) is significantly lower than the intensity of the radar path S, E. At the same time, the tracking path T is much shorter (see distance) and does not comprise a movement (Doppler effect). The static path is obligatory and can employ a random phase and frequency offset, introduced by oscillator mismatches. The dynamic path faces the same phase and frequency offset but comprises on top also the Doppler shift. The solid line (curve) can be seen as the connection of individual paths. How close these paths are to each other can be defined by the sampling rate, for example around 15 cm.

[0077] FIG. 5 shows a simulation of an FFT-CIR matrix for line-of-sight path measurement with a carrier characteristic offset compensation. The line-of-sight path phase is in the range of +/−5 deg. The channel impulse responses can be added coherently.

[0078] FIG. 7 shows a simulation of an FFT-CIR matrix for distance measurement, which includes a movement (ranging measurement, Doppler map), after carrier characteristic offset compensation. A moving target and the line-of-sight path are clearly observable and identifiable.

[0079] The simulation set-up for FIGS. 5 to 8 is hereby as follows: the line-of-sight path between transmitter and receiver is used for synchronization (tracking path), the line-of-sight path is five times weaker than target reflection (radar path), target is moving with constant velocity (10 m/s) in front of the radar devices, the PLL is switched off between the frames and starts with a random start phase, the carrier frequency offset is 2 ppm of fc=6.4896 GHz.

REFERENCE NUMERALS

[0080] 100 Radar system [0081] 105 Transmitter code generation unit [0082] 110 Transmitter [0083] 111 Transmitter antenna [0084] 112 Receiver antenna [0085] 120 Receiver [0086] 130 Control unit [0087] 140 Receiver code correlator [0088] 150 Target [0089] 160 Optimization loop [0090] 165 Combiner, RAKE receiver [0091] C, C′ Code [0092] E Echo [0093] O Output [0094] S Code signal [0095] T Tracking path