JP4608893B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus, and more particularly to a technique for stably extracting a composite signal of signals from each element of an array antenna even when fading occurs.

  In a multipath environment where radar waves radiated toward a target by an on-vehicle radar are reflected on the road surface and incident on the radar of the vehicle, the phase according to the difference in distance between multiple transmission paths A difference occurs, and the level of reception is increased or decreased. Such a phenomenon is called fading. As one of countermeasures against such fading, a method called frequency hopping is effective. However, the use of a plurality of frequencies complicates the apparatus, leading to an increase in cost, and in many cases, a plurality of frequencies cannot be used due to radio wave laws.

  On the other hand, as a fading countermeasure using a single frequency, there is a spatial diversity method including a plurality of antennas in the vertical direction (when a reflected wave from the road surface is taken into consideration). The spatial diversity includes a selection diversity method, an equal gain combining method, and a maximum ratio combining method (MRC: Maximum Ratio Combining). Among these, the maximum ratio combining method is a method that can maximize the S / N after combining by weighting and adding the signals received by the respective antennas and expecting the best performance. And the method of applying the maximum ratio synthetic | combination method with respect to road surface reflection fading supposing in-vehicle millimeter wave communication is also examined (for example, nonpatent literature 1 and 2).

Yoshio Karasawa, “Fundamental study on road surface reflection fading and space diversity in ITS millimeter-wave vehicle-to-vehicle communication,” IEICE Theory (B), vol.J83-B, no.4, pp.518-524, April 2000. Yukihiro Kamiya, Yoshio Karasawa, "Software Antenna [III]," IEICE Tech. Journal, AP-98-139, pp65-72, Jan. 1998.

  According to the conventional method, the eigenexpansion of the correlation matrix is performed, and the weight of the maximum ratio combining method is obtained as the eigenvector corresponding to the first eigenvalue. However, in order for the maximum ratio combining method to exhibit its original performance, highly accurate weight estimation is required. Therefore, when fading occurs in normal radar wave transmission / reception, the received signal S / N of each antenna is bad, so that the original maximum ratio combining effect is obtained from the estimation error of the eigenvector corresponding to the first eigenvalue of the correlation matrix. The problem that cannot be obtained arises.

  For example, in a radar apparatus having a configuration in which an array antenna interval cannot be sufficiently large, such as an in-vehicle radar in which a radar antenna is mounted on a bumper or the like, fading occurs simultaneously with almost all antennas of the array. In such a case, since the reception power is almost lost in all the antennas, the reception signal S / N at each antenna is generally lowered. For this reason, the estimation accuracy of the correlation matrix deteriorates, and the estimation error of the maximum ratio composite weight increases. As a result, the original maximum ratio synthesis has become difficult to achieve.

The radar apparatus according to the present invention transmits a reference signal as a plurality of transmission radar waves from a plurality of array elements as well as fading determination means for determining whether or not fading has occurred in the receiving antenna, and reflects the reference signal. When the fading determining means determines that fading has occurred in the receiving antenna that is receiving a wave, a plurality of orthogonal signals are switched from the plurality of array elements to a plurality of transmission radars by switching from the reference signal, respectively. A transmitting antenna for transmitting as a wave, the receiving antenna for receiving the reflected wave of the reference signal or the reflected wave of the plurality of orthogonal signals by a plurality of array elements, and the receiving antenna receiving the reflected wave of the reference signal or the plurality of whether the received signal data vector of the received signal obtained by receiving the reflected wave quadrature signals et before Symbol Maximum correlation matrix calculating unit, and eigenvectors estimating means for calculating an eigenvector from the correlation matrix of the received signal calculated by the correlation matrix calculating unit, to the received signal data vector, the eigenvector for calculating a correlation matrix of the signal signal A maximum ratio combining unit that multiplies as a ratio combining weight and calculates a combined signal of the received signal obtained from the reflected wave of the reference signal or the reflected wave of the plurality of orthogonal signals received by the receiving antenna; It is.

According to the radar apparatus of the present invention, when a fading occurs, a transmission radar wave based on a plurality of orthogonal signals is radiated, and a correlation matrix and a combined signal of each array element are calculated based on the reflected wave . Since the received power is obtained from each array element when the phase of the reflected wave of the orthogonal signal is different at the time of reception, the maximum ratio combined weight can be obtained from the correlation matrix, and the combined signal of each array element can be calculated stably. It has an extremely excellent effect that it can be performed.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. This radar apparatus is assumed to be composed of two antenna elements for the sake of simplicity. However, it goes without saying that the present invention can be applied even when more antenna elements are provided. In the figure, a transmission signal generator 1 is a part that generates a reference signal. In this description and the following description, the term “part” means an element or a circuit for realizing such a function. However, you may comprise the component of this invention so that an equivalent function may be implement | achieved combining a DSP (Degital Signal Processor), CPU (Central Processing Unit), and a computer program.

  The orthogonal PN code generator 2 is a part that generates an orthogonal PN (Pseudo Noise) code signal. The switch 3 is a switching element with two inputs and one output. If each terminal of the switch 3 is an input terminal A, an input terminal B, and an output terminal C, the movable terminal is connected to the output terminal C, and is connected to either the input terminal A or B as appropriate. Thus, one of the two inputs is output. In Embodiment 1 of the present invention, the transmission signal generator 1 is connected to the input terminal A, and the orthogonal PN code generator 2 is connected to the input terminal B. In the initial state, the movable terminal is connected to the input terminal A.

  The transmitter 4 is connected to the output terminal of the switch 3 and can radiate either the reference signal generated by the transmission signal generator 1 or the orthogonal PN code signal generated by the orthogonal PN code generator 2 to the space. This is the part that amplifies to the power level. Circulators 5-1 and 5-2, when a transmission signal is output from transmitter 4, outputs the transmission signal to antennas 6-1 and 6-2, which will be described later, and antennas 6-1 and 6- Reference numeral 2 denotes an element or a circuit that outputs a radar wave to receivers 7-1 and 7-2 described later when any radar wave is received. In the configuration of the first embodiment of the present invention, the antennas 6-1 and 6-2 are transmission / reception antennas, but a configuration in which the transmission / reception antennas are provided separately is also possible. In such a case, the circulator Sites like 5-1 and 5-2 are not required.

  Subsequently, the antennas 6-1 and 6-2 are array antenna elements, and radiate the transmission signal amplified by the transmitter 4 as a radar wave toward the target to be measured and reflected by the target. Radar waves are received. The receivers 7-1 and 7-2 are parts that output reception data vectors (hereinafter simply referred to as reception vectors) from the reception signals received by the antennas 6-1 and 6-2, respectively.

  The fading determination unit 8 is a part that monitors received power of the receivers 7-1 and 7-2 and determines whether fading has occurred in the antennas 6-1 and 6-2. Further, the fading determination unit 8 outputs a control signal for switching the movable terminal to the switch 3 and a switch 9 to be described later in accordance with the fading monitoring result.

  The switch 9 is a 1-input 2-output switch element. The switch 9 includes an input terminal D, an output terminal E, and an output terminal F, and a terminal that outputs when a movable terminal connected to the input terminal D is connected to one of the output terminals E and F. Is appropriately selected. In the initial state, the movable terminal is connected to the output terminal E. The input terminal D is wired so that the output signals of the receivers 7-1 and 7-2 are output.

  The correlation matrix estimator 10 is a part that performs processing for estimating a correlation matrix based on a baseband received signal, and is connected to an output terminal E of the switch 9. The correlation processor 11 is a part that calculates a correlation matrix from the received vector for the training pulse, and is connected to the output terminal F of the switch 9.

  The eigenvector estimator 12 is a part that performs eigenexpansion of the correlation matrix, obtains an eigenvalue, and calculates an eigenvector for the first eigenvalue. The maximum ratio synthesizer 13 is a part that synthesizes the output baseband signal of each array using the eigenvector for the first eigenvalue calculated by the eigenvector estimator 12 as the maximum ratio synthesis weight.

  The fading determination unit 8 is an example of the fading determination unit in the invention described in claim 1, the orthogonal PN code generator 2 is an example of the training pulse generation unit in the invention, and the correlation processor 11 is the same. The eigenvector estimator 12 is an example of the eigenvector estimator in the invention, and the maximum ratio synthesizer 13 is an example of the maximum ratio synthesizer in the invention.

  Next, the operation of the radar apparatus according to Embodiment 1 of the present invention will be described. The transmission signal generator 1 generates a reference signal S (t) such as the generated linear frequency modulation pulse or PN code modulation pulse and outputs it to the input terminal A of the switch 3. As described above, the switch 3 has a movable terminal connected to the input terminal A in the initial state, and as a result, the reference signal generated by the transmission signal generator 1 is output to the transmitter 4. The transmitter 4 converts the frequency of the reference signal, further amplifies the signal to a transmission wave level to obtain a transmission wave, and outputs the transmission wave to the antenna 6-1 and the antenna 6-2 via the circulators 5-1 and 5-2. The antennas 6-1 and 6-2 radiate the amplified transmission signal to space.

とする。すなわち送信レーダ波はアレー正面方向へビーム指向されるものとする。 Here, for the sake of simplicity, the weight w of the amplitude / phase given to the two antennas 6-1 and 6-2 is:

And That is, it is assumed that the transmission radar wave is beam-oriented in the front direction of the array.

と表される。 Furthermore, if the directivity of each antenna is simple and non-directional, the signal St (t) at the target position is

It is expressed.

ここでＲ_ｎは、アンテナ６−ｎ（ｎ＝１，２）から目標までの距離、φ_ｎはアンテナ６−ｎからの直接波と路面反射波の目標位置での位相差、ρ_ｎはアンテナ６−ｎからの路面反射波の路面での反射係数である。これらは、フレネル反射係数やスペキュラ反射係数（roughnessパラメータなどに依存）などの物理パラメータに依存している。 Here, it is assumed that the time delay and the time delay difference between the direct wave and the reflected wave are practically negligible, and the Doppler shift and attenuation due to the propagation path length are omitted for simplicity. A is a matrix that gives the amplitude and phase difference between the direct wave and the road surface reflected wave for each antenna, and is given by equation (3).

Here, R _n is the distance from the antenna 6-n (n = 1, 2) to the target, φ _n is the phase difference between the direct wave from the antenna 6-n and the road surface reflected wave at the target position, and ρ _n is the antenna. 6 is a reflection coefficient of the road surface reflected wave from 6-n on the road surface. These depend on physical parameters such as Fresnel reflection coefficient and specular reflection coefficient (depending on the roughness parameter).

となる。ここでＧは伝播行列である。式（４）から明らかなように、レーダにおいて路面反射が問題となるような状況において、伝播行列Ｇは、直接波と反射波に時間差やドップラ周波数差がない複素定数行列を用いて表すことができる。 The array antennas 6-1 and 6-2 receive the radar wave reflected by the target and output a received signal. This received signal is output to the receivers 7-1 and 7-2 via the circulators 5-1 and 5-2. The receivers 7-1 and 7-2 convert the received signal into baseband. If σ ₁ and σ ₂ are reflection coefficients in the target direct wave direction and road surface reflection direction, respectively, the received signal X (t) converted into baseband is

It becomes. Here, G is a propagation matrix. As is clear from Equation (4), in a situation where road surface reflection is a problem in radar, the propagation matrix G can be expressed using a complex constant matrix that has no time difference or Doppler frequency difference between the direct wave and the reflected wave. it can.

  The fading determination unit 9 monitors the amplitude (or power, etc.) of the reception signal X (t). More specifically, it is determined that fading has occurred when the signal amplitude becomes zero. When it is determined that fading has occurred, the fading generator 9 sends a control signal to the switch 3 and the switch 9 to switch the movable terminal. As a result, the movable terminal of the switch 3 is connected to the input terminal B, and the movable terminal of the switch 9 is connected to the output terminal E. Also, when fading that has occurred up to that point is stopped, that is, when the amplitude of the signal that was 0 becomes a non-zero value, the fading determination unit 9 sends a control signal to the switch 3 and the switch 9. As a result, the movable terminal of the switch 3 is connected to the input terminal A, and the movable terminal of the switch 9 is connected to the output terminal E.

なお、式（５）において、＜＊＞は平均操作を表す演算子である。 In the initial state, the movable terminal of the switch 9 is connected to the output terminal E. Therefore, the reception signal X (t) output from the receivers 7-1 and 7-2 is output to the correlation matrix estimator 10 via the switch 9. The correlation matrix estimator 10 calculates the correlation matrix R of the received signal X (t) using equation (5).

In formula (5), <*> is an operator representing an average operation.

式（６）において、Ｈは行列の複素共役転置を表している。ここまでは、フェージングが発生していない状態での、この発明の実施の形態１によるレーダ装置による信号処理の内容である。 Next, the eigenvector estimator 12 performs eigenexpansion of the correlation matrix R calculated by the correlation matrix estimator 10 to obtain an eigenvector W _M corresponding to the first eigenvalue. The maximum ratio synthesizer 13 uses the eigenvector W _M calculated by the eigenvector estimator 12 as the maximum ratio synthesis weight, and calculates the output Y (t) by Expression (6).

In equation (6), H represents the complex conjugate transpose of the matrix. Up to this point, the contents of the signal processing by the radar apparatus according to the first embodiment of the present invention in a state where no fading has occurred.

となった状態において、フェージング判定器８は、スイッチ３及びスイッチ９に制御信号を送る。その結果、スイッチ３は可動端子を入力端子Ｂに接続し、スイッチ９は可動端子を出力端子Ｆに接続する。 Next, signal processing in a state where fading occurs in the radar apparatus according to Embodiment 1 of the present invention will be described. Fading has occurred, i.e.

In this state, the fading determination unit 8 sends a control signal to the switch 3 and the switch 9. As a result, the switch 3 connects the movable terminal to the input terminal B, and the switch 9 connects the movable terminal to the output terminal F.

On the other hand, the orthogonal PN code generator 2 generates two orthogonal PN codes having the same number as the number of array antenna elements 6-1 and 6-2. As the orthogonal PN code, for example, a sequence such as an M sequence (Maximum Length Sequence) is generated. Let these two orthogonal PN codes be S _i (i = 1, 2).

The orthogonal PN code S _i generated by the orthogonal code generator 2 is output to the transmitter 4 via the switch 3. The transmitter 4 is amplified by the transmitter 4 in the same manner as the reference signal generated by the transmission signal generator 1, and is radiated to the space from the antennas 6-1 and 6-2 via the circulators 5-1 and 5-2. Reflected by the target and the road surface and the like, it arrives at the antennas 6-1 and 6-2 again. Radar waves arriving at the antennas 6-1 and 6-2 are output as reception signals to the receivers 7-1 and 7-2. The receivers 7-1 and 7-2 output the received signals as received signal data vectors (hereinafter referred to as received vectors) to the correlation processor 11 via the output terminal F of the switch 9. Reception vector X (t) is given by equation (8).

なお、ここで、δ_ijはクロネッカーのデルタであり、ｉ＝ｊで値を有し、ｉ≠ｊで０となる。この２つの直交ＰＮ符号の信号の位相が同じときは、フェージング状態となるが、異なるときは、各アンテナから受信電力が得られる。 In Expression (8), S ₁ (orthogonal PN code S _i when i = 1) and S ₂ (orthogonal PN code S _i when i = 2) are orthogonal PN codes, so Expression (9) S _i and S _j are satisfied.

Here, δ _ij is the Kronecker delta, has a value when i = j, and becomes 0 when i ≠ j. When the phases of the signals of the two orthogonal PN codes are the same, a fading state occurs, but when they are different, received power is obtained from each antenna.

を得る。ここで、Ｇ<k>は正方行列Ｇの第ｋ列ベクトルを表す。このように、各ｋに対して同様の相関処理を行うことで、伝播行列Ｇを求めることができる。ここで得られた伝播行列Ｇを用いて受信信号の相関行列Ｒは、

として算出される。なお、Ｐは受信信号電力値であるが、最大比合成ウエイトを求めるにあたり、無関係である。 Next, the correlation processor 11 multiplies the reception vector for the transmission training pulses S ₁ and S _{2 by} S _k ^H (k = 1, 2) from the right,

Get. Here, G <k> represents the k-th column vector of the square matrix G. In this way, the propagation matrix G can be obtained by performing the same correlation process on each k. Using the propagation matrix G obtained here, the correlation matrix R of the received signal is

Is calculated as Note that P is a received signal power value, but is irrelevant in obtaining the maximum ratio combined weight.

Eigenvector estimator 12 calculates the maximum ratio combining weight as the eigenvector corresponding to the first eigenvalue of GG ^H. The maximum ratio synthesizer 13 is the same as the process in the case where no fading has occurred, and thus the description thereof is omitted.

  As is apparent from the above, according to the radar apparatus of Embodiment 1 of the present invention, when it is determined that fading due to multipath has occurred, an orthogonal PN code is transmitted as a training pulse. This makes it possible to estimate the maximum ratio combined weight by estimating the propagation matrix from the received signal of the training pulse even in a fading environment, so that a highly accurate maximum ratio combined weight can be obtained, which is the most suitable for space diversity method. The original performance of the maximum ratio synthesis method that can be expected to have high performance can be expected.

Embodiment 2. FIG.
According to the radar apparatus of Embodiment 1 of the present invention, when a fading occurs, the orthogonal PN code signal is transmitted as a training pulse using a training pulse. And the propagation matrix was estimated from the received signal for the radar wave, and the maximum ratio combined weight was obtained. However, other than this, for example, a reference signal having a phase of 0 and π may be generated as a training pulse, and when a fading occurs, the training pulse may be radiated as a radar wave. For example, a radar wave based on a training pulse having a phase 0 is radiated from the antenna 6-1 and a radar wave based on a training pulse having a phase π is radiated from the antenna 6-2.

  FIG. 2 is a block diagram showing a configuration of a radar apparatus according to Embodiment 2 of the present invention having such characteristics. In the figure, a 0 / π signal generator 14 is a part that generates a training pulse having phases of 0 and π. The other components having the same reference numerals as those in FIG. 1 are the same as those in the first embodiment, and the description thereof is omitted.

  In this radar apparatus, when the fading determination unit 8 determines that fading has occurred, the switch 3 connects the movable terminal to the input terminal B, and transmits a training pulse generated by the 0 / π signal generator 14 to the transmitter. 4 is output. This training pulse is a signal as shown in FIG. In FIG. 3, 0 and π each represent the phase of the signal at each time.

  The training pulse is amplified by the transmitter 4 and radiated from the antennas 6-1 and 6-2 to the space via the circulators 5-1 and 5-2. The subsequent processing is the same as in the first embodiment.

  As is clear from the above, according to the radar apparatus of the second embodiment of the present invention, signals are obtained with all chips (1 chip width means the time width of one binary phase), and the propagation matrix The efficiency of estimation is improved.

  The phase is set to 0 and π, respectively, as an example, and any other two phases may be used. Further, when the number of array antenna elements is two, two phases are selected and configured. However, when N (N is a natural number of 2 or more), for example, 2π × (k−1) / N. A phase such as Further, it is not necessary that the phase differences are equally spaced in this way, and it is sufficient to select N phases from the range of 0 to 2π.

Embodiment 3 FIG.
Further, an orthogonal frequency signal may be used as the training pulse. The radar apparatus according to Embodiment 3 of the present invention has such features. FIG. 4 is a block diagram showing a configuration of a radar apparatus according to Embodiment 3 of the present invention. In the figure, an orthogonal frequency signal generator 15 is a part for generating a frequency signal having a frequency offset by f ₁ and a CW wave signal having an offset by f ₂ as a training pulse. In addition, since the component which attached | subjected the code | symbol same as FIG. 1 is the same as that of Embodiment 1, description is abbreviate | omitted.

という条件を設ける。こうすることで、すべての時間サンプルで信号が得られ、伝播行列の推定の効率が向上する。なお、スイッチ３以降の処理は、実施の形態１及び２と同様である。 Next, the operation of the radar apparatus according to Embodiment 3 of the present invention will be described. The orthogonal frequency signal generator 15 generates a frequency signal whose frequency is offset by f1 in the baseband and a CW wave signal offset by f2. Here, in order to satisfy the orthogonality shown in Equation 9, between the frequencies f ₁ and f ₂ ,

This condition is set. In this way, signals are obtained at all time samples, and the efficiency of propagation matrix estimation is improved. The processing after the switch 3 is the same as in the first and second embodiments.

Embodiment 4 FIG.
In Expression (12), the frequency f2 is an even multiple of the frequency f1, but may be a simple integer multiple as shown in Expression (13).

  The present invention can be applied to, for example, a radar device used in an environment where fading occurs, such as an in-vehicle radar device.

It is the block diagram which showed the structure of the radar apparatus of Embodiment 1 of this invention. It is the block diagram which showed the structure of the radar apparatus of Embodiment 2 of this invention. It is a figure which shows the example of the content of the training pulse which the radar apparatus of Embodiment 2 of this invention generate | occur | produces. It is the block diagram which showed the structure of the radar apparatus of Embodiment 3 of this invention.

Explanation of symbols

1 Transmit signal generator,
2 orthogonal PN code generator,
3,9 switches,
4 Transmitter,
5-1, 5-2 circulator,
6-1, 6-2 antenna,
7-1, 7-2 Receiver,
8 Fading discriminator,
10 correlation matrix estimator,
11 correlation processor,
12 eigenvector estimators,
13 Maximum ratio synthesizer,
14 0 / π signal generator,
15 Orthogonal frequency signal generator.

Claims (5)

Fading determination means for determining whether fading has occurred in the receiving antenna;
When the fading determining means determines that fading has occurred in the receiving antenna that receives the reference signal from a plurality of array elements as a plurality of transmission radar waves and receives the reflected wave of the reference signal, A transmission antenna that switches from the reference signal and transmits a plurality of orthogonal signals as a plurality of transmission radar waves from the plurality of array elements, respectively.
The receiving antenna for receiving the reflected wave of the reference signal or the reflected wave of the plurality of orthogonal signals by a plurality of array elements;
A correlation matrix calculating means for the reception antenna to calculate a correlation matrix of the received signal data vector or found before Symbol received signal of the reception signal obtained by receiving the reflected wave of the reflected wave or the plurality of orthogonal signals of the reference signal ,
Eigenvector estimation means for calculating an eigenvector from the correlation matrix of the received signal calculated by the correlation matrix calculation means;
Multiplying the received signal data vector by the eigenvector as a maximum ratio combining weight, and calculating a combined signal of the received signal obtained from the reflected wave of the reference signal or the reflected wave of the plurality of orthogonal signals received by the receiving antenna Maximum ratio combining means to
A radar apparatus comprising:   The radar apparatus according to claim 1, wherein the plurality of orthogonal signals are a plurality of orthogonal PN code signals.   The radar apparatus according to claim 1, wherein the plurality of orthogonal signals are a plurality of orthogonal frequency signals. Fading determination means for determining whether fading has occurred in the receiving antenna;
When the fading determining means determines that fading has occurred in the receiving antenna that receives the reference signal from a plurality of array elements as a plurality of transmission radar waves and receives the reflected wave of the reference signal, A transmission antenna that switches from the reference signal and transmits a plurality of reference signals of different phases from the plurality of array elements as a plurality of transmission radar waves, respectively.
A receiving antenna that receives a reflected wave of the reference signal or a reflected wave of a plurality of reference signals in different phases by a plurality of array elements;
Correlation the receiving antenna to calculate a correlation matrix of the received signal data vector or found before Symbol received signal of the reception signal obtained by receiving the reflected wave of the reflected wave or the different phases plurality of reference signals of the reference signal Matrix calculation means;
Eigenvector estimation means for calculating an eigenvector from the correlation matrix of the received signal calculated by the correlation matrix calculation means;
The received signal data vector is multiplied by the eigenvector as a maximum ratio combined weight, and the received signal obtained from the reflected wave of the reference signal received by the receiving antenna or the reflected waves of the plurality of reference signals having different phases from each other. Maximum ratio combining means for calculating a combined signal;
A radar apparatus comprising:   The transmission antenna uses, as a plurality of transmission radar waves, a plurality of reference signals having different phases with a phase of 2π × (k−1) / N (N is the number of phases, k is a natural number satisfying 1 ≦ k ≦ N). The radar apparatus according to claim 4, wherein the radar apparatus transmits the radar apparatus.

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