JP2010107309A - On-vehicle radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress malfunction by reducing external noises without lowering radar performance, and to secure sufficient distance-measurement accuracy, even under an environment wherein an influence by the external noise is changed. <P>SOLUTION: Integration averaging processing for noise reduction following a vehicle speed signal is executed to frame data having a time correlation with a transmission pulse by a signal processing part 6a of a computing device 6, to thereby reduce noises of a distance-measuring signal, and a distance to an obstacle 10 is operated based on the distance-measuring signal by a distance measuring part 6b. The number of times of repetition of the integration averaging processing is restricted by a block period control part 6c so that a multiplication value between a transmission pulse generation period and the number of times of repetition satisfy a condition based on a distance resolution and vehicle speed, and even in an environment having many external noises, the noises are reduced without lowering the radar performance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an on-vehicle radar device that receives a reflected wave of a radar radio wave radiated to a target and performs distance measurement.

  Conventionally, wireless technology is used not only for radar but also for various purposes such as communication and broadcasting. In a radio device for each application, a signal other than necessary radio waves is treated as noise, and the influence of the noise may inhibit a desired operation or cause a malfunction. In addition, the intensity of each radio wave varies depending on the use and location of the radio wave, and the influence of noise is not constant depending on the location.

As a method of suppressing the influence of such noise, for example, in Patent Document 1, a predetermined number of times is sampled with respect to a noise signal and stored in a memory, a noise level is calculated using the value, and communication is performed. A wireless device that limits the application range (distance) of the device is disclosed, and malfunction due to noise can be prevented.
Japanese Patent Laid-Open No. 9-46247

  However, in the technology that limits the application range for preventing malfunction as disclosed in Patent Document 1, when applied to a radar apparatus, the ranging range changes depending on the environment in which the radar is used, There is a risk that the performance is greatly reduced.

  The present invention has been made in view of the above circumstances.In an environment in which the influence of external noise changes, the radar performance is appropriately ensured, and the external noise is reduced to suppress malfunction, thereby providing sufficient ranging accuracy. An object of the present invention is to provide an on-vehicle radar device that can be secured.

  In order to achieve the above object, an on-vehicle radar device according to the present invention is mounted on a vehicle and receives a reflected wave of a transmission pulse radiated to a target to measure a distance, and a predetermined period is a block period. A signal processing unit that statistically processes received data within the block period, removes a noise signal that does not have time correlation with the transmission pulse, and extracts a distance measurement signal that has time correlation; and the block period A block cycle control unit that controls the vehicle speed based on the vehicle speed and distance resolution at the time of distance measurement is provided.

  According to the present invention, it is possible to suppress malfunctions by reducing external noise while ensuring radar performance appropriately even in an environment where the influence of external noise changes, and to ensure sufficient ranging accuracy. it can.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 relate to an embodiment of the present invention, FIG. 1 is a configuration diagram of an on-vehicle radar device, FIG. 2 is a flowchart of signal processing, FIG. 3 is a flowchart of iteration count setting processing, and FIG. FIG. 5 is an explanatory diagram showing the frame data below, FIG. 5 is an explanatory diagram showing the block of the integration averaging process, and FIG. 6 is an explanatory diagram showing the frame data before and after the integration averaging process in a noisy environment.

  An on-vehicle radar device according to the present invention is mounted on a vehicle such as an automobile, and measures a distance from a target such as an obstacle by calculating a distance from a pulse echo method, that is, a time difference until a pulse signal is reflected from the target and received. Is what you do. In particular, when a weak wireless system that is easily affected by external noise, such as a 300 MHz band or a 3 GHz band, is adopted, a stable ranging accuracy can be ensured by avoiding a decrease in radar performance. As shown in FIG. 1, the radar apparatus 1 according to the present embodiment includes a transmission antenna 2 that radiates a pulsed radar wave and a reception antenna 3 that receives a reflected wave from an obstacle 10.

  The main functional units of the radar apparatus 1 mainly include a transmission circuit 4 that generates transmission pulses and outputs them to the transmission antenna 2, a reception circuit 5 that takes in signals from the reception antenna 3 and outputs them as digitized frame data, and transmission. A clock signal for generating a transmission pulse is output to the circuit 4, and an arithmetic unit 6 that performs distance measurement by processing frame data output from the receiving circuit 5 is configured. The arithmetic device 6 is constituted by a microcomputer or the like, and is connected to a vehicle control device (not shown) via an interface (I / F) circuit 7 to acquire vehicle speed data from the vehicle control device.

  The transmission circuit 4 generates a transmission pulse based on the clock signal from the arithmetic device 6, and periodically emits a radar radio wave from the transmission pulse from the transmission antenna 2. The receiving circuit 5 captures the reflected pulse and the external noise emitted from the transmitting antenna 2 and reflected by the target (obstacle) through the receiving antenna 3 as a received pulse. The reception pulse captured by the reception circuit 5 is processed by equivalent time sampling. In other words, the received pulse is sampled and held while delaying the timing little by little with respect to the transmitted pulse, and output to the arithmetic unit 6 as frame data having a time correlation with the transmitted pulse.

  The arithmetic unit 6 performs a signal processing unit 6a that performs statistical processing (accumulation averaging processing in the present embodiment) of noise reduction according to the vehicle speed signal on the frame data having time correlation with the transmission pulse, A distance measuring unit 6b that calculates the distance to the obstacle 10 based on the distance measurement signal that has been subjected to noise reduction processing by the unit 6a, and a block period control unit c that controls a later-described block period related to an integration averaging process in the signal processing unit 6a. It is configured with.

  In general, the external noise is a random signal that is uncorrelated with the transmission pulse, and is recognized on the signal regardless of a change that can be observed as a ranging response. Accordingly, the signal processing unit 6a performs the process of integrating and averaging the number of iterations according to the noise level, so that the external noise having no time correlation is repeated the number of times without affecting the reflected pulse having a temporal correlation with the transmission pulse period. As a result, the S / N ratio which is a signal-to-noise ratio can be improved.

  Note that the integration averaging process in the present embodiment is also referred to as a synchronous addition process. For a signal that repeats in time, the sample signal is measured in synchronism with the repetition period, and this is integrated and averaged. Specifically, a plurality of sampled reception pulses are added in synchronization with the timing of the transmission pulse, and an average process is performed.

Here, the traveling speed of the radio wave is 3.0 × 10 ⁸ m / sec, which is the speed of light, and the distance resolution normally required, for example, about 10 cm as the distance resolution, is taken as an example. The advance time is 0.33 nsec. Therefore, the time during which the radio wave travels the distance corresponding to the normally required resolution is sufficiently longer than the vehicle speed, and the distance between the vehicle and the target can be regarded as constant in the process of performing the averaging process.

In this case, the S / N ratio increases as the number of iterations in the averaging process is increased. However, if the number of iterations is increased too much, the influence of the vehicle speed increases, and the vehicle and the target in the process of performing the averaging process. The distance cannot be considered constant. For this reason, the number of iterations k in the integration averaging process of the signal processing unit 6a satisfies the condition of the following expression (1) based on the multiplication value Bf of the transmission pulse generation period Tp and the number of iterations k based on the distance resolution R and the vehicle speed V. It is limited by the block cycle control unit 6c to satisfy.
Bf ≦ R / V (1)

  In the present embodiment, one or more pieces of frame data are collectively handled as one block in order to speed up the averaging process. The multiplication value Bf of the transmission pulse generation period Tp and the number of repetitions k is used as a block period, and the block period control unit 6c variably controls the block period Bf so that the condition of the expression (1) is satisfied. Thereby, even in an environment with a lot of external noise, it is possible to reduce the noise while ensuring the radar performance appropriately.

That is, the number of iterations k is limited to a value obtained by dividing the distance resolution R by the product of the vehicle speed V and the transmission pulse generation period Tp, as shown in the following equation (1 ′).
k ≦ R / (V × Tp) (1 ′)

  That is, when the vehicle speed increases, the block cycle becomes smaller (shorter), and conversely, when the vehicle speed decreases, the block cycle becomes longer (longer). Therefore, in the process of performing the averaging process, the distance that the distance between the vehicle and the target moves during the block period can be kept within a certain range. Thereby, the influence of the vehicle speed can be reduced and sufficient distance measurement accuracy can be ensured.

  Further, if the distance resolution is improved, that is, it is possible to identify a smaller distance, the block cycle becomes smaller (shorter), and conversely, if the distance resolution is lowered, the block cycle becomes larger (longer). Therefore, in the process of performing the averaging process, the distance that the distance between the vehicle and the target moves during the block period can be kept within a certain range. Thereby, it can suppress that a vehicle moves exceeding the distance resolution excessively, and can ensure sufficient ranging accuracy.

  It should be noted that the transmission pulse generation period is constant for distance measurement with respect to a certain target, and changing the block period in this case means changing the number of iterations in the noise reduction integrated averaging process.

  Further, it is preferable that the number of iterations k is an integer because the processing becomes simple. However, it is not necessarily limited to integers. As long as the number of iterations k satisfies the condition of the expression (1), k is not an integer, and there is no problem even if it is processed with, for example, a decimal.

Further, the arithmetic unit 6 performs a moving average process when acquiring frame data for noise having a frequency component higher than the frequency of the desired signal, thereby reducing high frequency noise. The maximum number of moving averages is based on the distance resolution R and the vehicle speed V so that the integrated value of the moving average amount Dm of the frame data number Nf at the sampling time Ts satisfies the relationship shown in the following equation (2). Determined.
Dm × Ts × Nf ≦ R / V (2)

  Next, software processing related to the distance measuring function of the arithmetic device 6 will be described with reference to a flowchart of signal processing shown in FIG. 2 and a flowchart of iteration number setting processing shown in FIG.

  In the signal processing shown in FIG. 2, first, in the first step S1, frame data is acquired as an evaluation signal, and in step S2, this frame data is evaluated to determine the presence or absence of noise. Specifically, as shown in FIG. 4, a non-change portion is provided in the frame data by delay processing, and the presence or absence of noise is determined by evaluating the amount of change in the reaction intensity of this non-change portion.

  FIG. 4 shows frame data in a no-noise environment. In the figure, the horizontal axis indicates time corresponding to the distance, and the vertical axis indicates reaction intensity. When there is no noise, there is no change in the reaction intensity of the unchanged part of the frame data, and when there is noise, the reaction intensity of the unchanged part changes.

In step S2, if there is no change in the unchanged portion of the frame data, the process proceeds to step S3 to acquire a ranging signal following the unchanged portion of the frame data, and in step S4, the response intensity of the ranging signal Ranging is performed by evaluating. In this distance measurement process, the time (pulse travel time) from when the transmission pulse is reflected by the target to be received by the reception antenna 3 on the basis of the time when the transmission pulse is output from the transmission antenna 2 is determined as a distance measurement signal. Measured in the time until the reaction intensity exceeds a predetermined threshold, and the distance L is calculated according to the following equation (3).
L = c × Tr / 2 (3)
Where c: speed of light (3.0 × 10 ⁸ m / sec)
Tr: Pulse travel time from transmission pulse to reception pulse

  On the other hand, if there is a change in the reaction intensity in the unchanged part of the frame data in step S2, it is determined that there is noise and the process proceeds to step S5. In step S5, the number of iterations of the integration averaging process for noise level evaluation is set according to the preset level of the noise level by the iteration number setting process shown in the flowchart of FIG. Then, frame data corresponding to the number of iterations is obtained through the loop of the distance measurement signal acquisition in step S6 to the iteration number confirmation loop in step S7, and random noise having no time correlation is removed by integration averaging processing, and then measurement is performed in step S8. Calculate the distance response. The distance measurement process in step S8 is the same as step S4 described above.

  In the present embodiment, the frame is handled as a block for speeding up the integration averaging process. In the iteration count setting process of FIG. 3, within the limit of the iteration count according to the condition of the above-described equation (1), The number of times according to the noise level is set.

Specifically, in the iteration number setting process, first, the change amount Δ of the reaction intensity of the unchanged portion of the frame data is calculated in the first step S11, and then the threshold value Z1 of which the change amount Δ is the level 1 in step S12. Check whether or not. As a result, in the case of delta ≦ Z1 is set to 2 ^one iteration number of integration average processing in step S13.

On the other hand, if Δ> Z1 in step S12, the process proceeds from step S12 to step S14 to check whether or not the change amount Δ exceeds the level 2 threshold value Z2, and if Δ ≦ Z2, the number of iterations in step S15. Set to 2 ² times. In the case of Δ> Z2, the number of iterations corresponding to the noise level is set in the same process, and when the noise level n finally reaches the maximum (step S16_n), the number of iterations is set to 2 in step S16_n + 1. Set ⁿ times.

That is, as shown in FIG. 5, for example, when 8-bit frame data is set to one block, when the level of external noise is equal to or lower than level 1, one block of frame data is used without performing the averaging process. When the noise level is level 2, the frame data of 2 ² (= 4) blocks obtained by shifting the first frame data by 2 bits are added up and averaged. Further, when the noise level is level 4, the integration averaging process is performed with 2 ⁴ (= 16) blocks, and when the noise level is n, the integration averaging process is performed with 2 ⁿ blocks to reduce the noise. To reduce. In this case, the number of repetitions ²ⁿ of the averaging process is limited by the distance resolution R and the vehicle speed V of the radar apparatus 1. For example, the maximum integer value that satisfies the condition of the expression (1) or an integer value less than that is set as the number of iterations.

  As described above, as shown in FIG. 6, the integration averaging process is performed on the ranging signal S1 carrying the noise component Snz1 and the ranging signal S2 carrying the noise component Snz2, and random external noise components Snz1 and Snz2 are obtained. The offset / reduced ranging signal S3 can be obtained, and stable ranging accuracy can be ensured. In addition, since the influence of external noise is reduced by determining the level of noise superimposed on the distance measurement signal and optimizing the vehicle speed, it is possible to prevent malfunction of the radar reaction.

  In the above-described embodiment, the transmission antenna 2 and the reception antenna 3 are set separately. However, the present invention can also be applied to a radar apparatus using a transmission / reception antenna in which both are combined. In the above-described embodiment, a pulse echo radar (pulse radar) based on a weak radio system in the 300 MHz band or 3 GHz band is disclosed, but the present invention can also be applied to a radar apparatus using another frequency band. In addition to the pulse radar, the present invention can also be applied to a radar apparatus that transmits a signal that repeats in time. In the above-described embodiment, the equivalent time sampling is used for sampling the received pulse, but normal sampling can also be used.

Configuration diagram of in-vehicle radar system Signal processing flowchart Repetition count setting process flowchart Explanatory drawing showing frame data under no-noise environment Explanatory drawing showing blocking of integrated average processing Explanatory drawing showing frame data before and after the averaging process in a noisy environment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radar apparatus 4 Transmission circuit 5 Reception circuit 6 Arithmetic unit 6a Signal processing part 6b Distance measuring part 6c Block period control part Bf Block period R Distance resolution V Vehicle speed

Claims (7)

An on-vehicle radar device that is mounted on a vehicle and receives a reflected wave of a transmission pulse radiated to a target to perform distance measurement,
A signal processing unit that sets a predetermined period as a block period, statistically processes received data within the block period, and removes a noise signal that does not have time correlation with the transmission pulse to extract a distance measurement signal that has time correlation When,
An on-vehicle radar device comprising: a block cycle control unit that controls the block cycle based on a vehicle speed and distance resolution at the time of ranging.   The statistical process for the received data within the block period is an integration average process, and the number of repetitions of the integration average process is limited to a value obtained by dividing the distance resolution by the product of the vehicle speed and the transmission pulse generation period. The on-vehicle radar device according to claim 1.   3. The in-vehicle radar device according to claim 1, wherein the received data is subjected to a moving average process, and a processing amount of the moving average process is limited based on the vehicle speed and the distance resolution.   2. A delay process is performed on the received data to create an area that does not change due to a ranging response at the head part, and the noise signal is evaluated based on a signal intensity in the head part area. The on-vehicle radar device according to any one of?   The in-vehicle radar device according to any one of claims 2 to 4, wherein the number of repetitions of the integration averaging process is set according to a level of the noise signal.   6. The vehicle-mounted device according to claim 2, wherein reception data obtained for each generation period of the transmission pulse is handled as one block, and the integration averaging process is performed between the blocks over the number of repetitions. Radar device.   The on-vehicle radar device according to any one of claims 1 to 6, wherein the predetermined period is an integral multiple of a generation period of the transmission pulse.

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