JP4549730B2 - Code modulation pulse compression method and code modulation pulse compression method - Google Patents

Description

  The present invention relates to a code modulation pulse compression method and a code modulation pulse compression method for transmitting a code modulation pulse and performing pulse compression.

  In a code modulation pulse compression method in various sensors such as radars and ultrasonic sensors using a pulse compression method, for example, in a pulse radar having a spectrum-spread transmission wave, when trying to detect a target by radiating radio waves, The phase of the received signal rotates due to the Doppler frequency due to the relative speed between the target and the radar-mounted platform (hereinafter referred to as Doppler shift), and the performance of pulse compression (referred to as spectrum despreading in communications) deteriorates and the target is detected. It becomes an obstacle.

  Considering practical use, in a situation where the Doppler frequency is unknown or there is a correction error in the Doppler frequency, the distance error after pulse compression is small and the distance side lobe (hereinafter simply referred to as side lobe) increases. It is important that the modulation pulse is small and the degradation of resolution is small. For example, the linear FM modulation method is relatively less susceptible to Doppler shift, but it is known that a bias error occurs at the pulse peak position (that is, distance) after pulse compression. As a code modulation pulse compression method, a P4 code in which a linear FM modulated wave is four-phase encoded has been reported. However, as with a linear FM modulation code, there is a problem that a bias error occurs at a pulse position after pulse compression. is there.

  On the other hand, as a code modulation pulse of a two-phase code in which the side lobe level is 0 or 1 even with a relatively short code length, and there is no error in the pulse position after pulse compression even in the presence of Doppler shift, for example, As shown in Non-Patent Documents 1 and 2, there is a Barker series. This Barker sequence has good sidelobe characteristics and anti-Doppler characteristics despite its short code length, and is used in many radars and wireless LANs. However, the relative speed with the target increases and the Doppler shift is large. It is known that the peak width increases and the resolution decreases.

  Furthermore, as shown in Non-Patent Document 1, by using two code sequences, a complementary sequence (Complementary sequence) consisting of a set of sequences in which the side lobe value other than the peak of each pulse compression output has an inverse code amplitude is used. ) This complementary series has an ideal characteristic in which the side lobe is zero when there is no Doppler shift. However, when the Doppler shift is present, the resolution is greatly reduced, the side lobe is increased, and the characteristic is deteriorated.

M.M. Skolnik, “Radar Handbook, 2nd edition” McGraw-Hill, New York, USA, 1990. p10.17, p10.21 G. V. Morris, “Airborne Pulsed Doppler Radar” Arttech House, MA, USA, 1988. p134-p135

  Since the conventional code modulation pulse compression method is configured as described above, an error occurs in the pulse position after pulse compression in a situation where Doppler shift exists, the peak pulse width becomes thicker, and the resolution decreases. There was a problem that the side lobe also rose.

  The present invention has been made to solve the above-described problems, and even in the presence of Doppler shift, there is no error in the pulse position after pulse compression, and the resolution is lowered without increasing the peak pulse width. It is another object of the present invention to obtain a code modulation pulse compression method and code modulation pulse compression method in which side lobes do not increase.

The code modulation pulse compression method according to the present invention includes a forward sequence generator that generates a forward sequence, a backward sequence generator that generates a backward sequence that is a time reversal sequence of the forward sequence, and the forward sequence that has a first frequency. A first transmission frequency converter for converting the signal into a signal; a second transmission frequency converter for converting the Backward sequence into a second frequency signal orthogonal to the first frequency signal; and the first frequency signal; A synthesizer that synthesizes the second frequency signal and simultaneously outputs it as a transmission signal to the target; a first reception frequency converter that converts the first frequency signal in the received signal from the target into a forward sequence; and a target The second received frequency for converting the second frequency signal in the received signal from the signal into a Backward sequence A converter, a forward sequence pulse compressor that outputs a first pulse compression signal by a cross-correlation function of the forward sequence from the first reception frequency converter and the forward sequence from the forward sequence generator, and the second A Backward sequence pulse compressor that outputs a second pulse compression signal using a Backward sequence from the Backward sequence generator and a Backward sequence from the Backward sequence generator, a Forward sequence cross-correlation function, and the Backward An addition / subtraction processor that adds and subtracts the first and second pulse compression signals by adding and subtracting with the cross-correlation function of the sequence, and an addition / subtraction processor when the time lag in the cross-correlation function is an even number other than 0. Select the subtraction result and the time lag Or with an odd number of the window processor for selecting the addition result by the adder processor when said Forward sequence generator and the Backward sequence generator, the cross-correlation function at odd time lag in the Forward sequence pulse compressor Then, a Forward sequence and a Backward sequence are generated such that the cross-correlation function at an odd time lag in the Backward sequence pulse compressor is in reverse phase.

According to the present invention, there is no error in the pulse position after pulse compression even in a situation where the influence of Doppler shift exists in the received signal, and the level of the side lobe at all time lags other than the peak becomes 0 and the resolution. effect that the deterioration of Ru can be suppressed is obtained.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a code modulation pulse compression system according to Embodiment 1 of the present invention. This code modulation pulse compression method includes an F-Barker sequence generator 1, a B-Barker sequence generator 2, a transmission frequency converter (first transmission frequency converter) 3, a transmission frequency converter (second transmission frequency conversion). 4), synthesizer 5, frequency converter 6, transmission antenna 7, reception antenna 8, frequency converter 9, reception frequency converter (first reception frequency converter) 10, reception frequency converter (second reception) Frequency converter) 11, an F-Barker sequence pulse compressor 12, a B-Barker sequence pulse compressor 13, and a synthesis processor 14.

In FIG. 1, an F-Barker sequence generator 1 generates a Forward-Barker (referred to as F-Barker) sequence, and a B-Barker sequence generator 2 generates a Backward-Barker (B-Barker) that is a time-reversed sequence of the F-Barker sequence. Generate a sequence (called -Barker). The transmission frequency converter 3 converts the F-Barker sequence into a first frequency signal having a frequency f _1. The transmission frequency converter 4 converts the B-Barker sequence into a _second frequency f _{2 that} is orthogonal to the first frequency signal. Convert to frequency signal. The synthesizer 5 synthesizes the first frequency signal and the second frequency signal and outputs them simultaneously as a transmission signal to the target, the frequency converter 6 converts the frequency of the transmission signal into an RF signal, and the transmission antenna 7 has F -An RF signal including the Barker sequence and the B-Barker sequence is emitted toward the target.

  In FIG. 1, the receiving antenna 8 receives the RF signal reflected from the target, and the frequency converter 9 converts the received RF signal into a received signal. The reception frequency converter 10 converts the first frequency signal in the reception signal into an F-Barker sequence, and the reception frequency converter 11 converts the second frequency signal in the reception signal into a B-Barker sequence. The F-Barker sequence pulse compressor 12 outputs a first pulse compression signal based on the cross-correlation function of the F-Barker sequence from the reception frequency converter 10 and the F-Barker sequence from the F-Barker sequence generator 1. The B-Barker sequence pulse compressor 13 outputs a second pulse compression signal by the cross-correlation function between the B-Barker sequence from the reception frequency converter 11 and the B-Barker sequence from the B-Barker sequence generator 2. The synthesis processor 14 calculates the average of the first pulse compression signal and the second pulse compression signal and outputs the synthesized pulse compression signal.

Here, the basic principle of the present invention will be described.
Two code sequences of code length M are φ _{n, m} (n = 1, 2; m = 1, 2,..., M), and the code modulation pulse uφ _{n, m} is expressed by the following equation (1). To express.
u _{n, m} = exp (jφ _{n, m} π) (n = 1, 2; m = 1, 2,..., M) (1)
Note that n represents a code sequence number, m represents an element number, and M represents a code length.

Here, for the sake of simplicity, ignoring the amplitude attenuation due to the propagation path length of the received wave or the like, the received signal x _{n, m} is _expressed by the following equation (2) when the Doppler frequency f _d is present.
x _{n, m} = exp (jφ _{n, m} π) exp (j2πf _d t) (2)
The Doppler frequency f _d is expressed by the following equation (3) with the relative velocity v and the wavelength λ.
f _d = 2v / λ (3)

The pulse compression process is a cross-correlation process expressed by the following equation (4), where s is a time lag and Z _{n, s} is a pulse compression signal.

In the present invention, two Barker sequences that do not generate a distance error even under the influence of Doppler shift and are excellent in sidelobe characteristics are used as the code sequences. That is, the F-Barker sequence φ _{1, m} and the B-Barker sequence φ _{2, m} represented by the following equation (5), which is a time reversal sequence of the F-Barker sequence _, are used.
φ _{2, m} = φ _{1, Mm} (5)
For example, a 13-bit F-Barker sequence φ _{1, m} is
φ _{1, m} = {1 1 1 1 1 0 0 1 1 1 0 1 0 1} (6)
When, 13 B-Barker sequence phi _{2, m} bits inverts the 13-bit F-Barker sequence phi _{1, m} times,
φ _{2, m} = {1 0 1 0 1 1 0 0 1 1 1 1 1} (7)
It becomes.

  The Barker sequence having the code length M is a code sequence in which the cross correlation function has a peak level of time lag 0 and the level at other time lags, that is, the side lobe level is 0 or 1. That is, the Barker sequence having a code length of 13 bits has a peak level of 13 and a side lobe level of 0 or 1.

上記式（８）から、ピーク位置の隣（タイムラグ１）を含み、タイムラグｓが奇数の場合には、ドップラシフトが存在しても出力は０である。このことは、１タイムラグだけ離れた複数目標の分離を可能とすることが期待できる。タイムラグｓが偶数の場合には、ドップラシフトの影響を受けて利得が低下するが、ドップラシフトがないときの本来のサイドローブレベルからの劣化は少ない。 Furthermore, in the present invention, as shown in the following equation (8), the average of the pulse compression processing of these two code sequences is used as the final pulse compression processing output.

From the above equation (8), when the time lag s is an odd number including the peak position (time lag 1), the output is 0 even if there is a Doppler shift. This can be expected to enable separation of multiple targets separated by one time lag. When the time lag s is an even number, the gain decreases due to the influence of the Doppler shift, but there is little deterioration from the original sidelobe level when there is no Doppler shift.

すなわち、相互相関関数の２つの要素ｕ_1,m ｕ^* _1,m+s，ｕ_2,m ｕ^* _2,m+sが、タイムラグｓが偶数のときは同相となり、タイムラグｓが奇数のときは逆相となることが必要である。各タイムラグｓの和である相互相関関数（式（４））が二つの符号系列で、逆符号となるものが相補系列であるが、ここでは各タイムラグｓの偶奇により同符号（同相）か逆符号（逆相）となっている。 Thus, when the F-Barker sequence and the B-Barker sequence that is the time reversal sequence are used, the reason why the above equation (8) is satisfied is that the time lag s is even and odd, and the following equation (9) This is because.

That is, the two elements u1 _, mu ^* _{1, m + s} , u2 _, mu ^* _{2, m + s of} the cross-correlation function are in phase when the time lag s is even, and when the time lag s is odd. Must be in reverse phase. The cross-correlation function (Equation (4)), which is the sum of each time lag s, is two code sequences, and the one with the opposite sign is a complementary sequence, but here the same sign (in-phase) or opposite depending on the even / odd of each time lag s. It has a sign (reverse phase).

Note that the characteristic of the above equation (9) is the Barker sequence with the sign inverted,
φ _{1, m} = {0 0 0 0 0 0 1 1 0 0 1 0 1 0} (10)
It is the same even if is used.

As described above, according to the present invention, the F-Barker sequence φ _{1, m} and the B-Barker sequence φ _{2, m} that is the time-reversed sequence are such that the cross-correlation function at an odd time lag in pulse compression is in reverse phase. By using it, the pulse compression signal at an odd time lag after synthesis can be set to 0, and the side lobe of the time lag 1 next to the peak is fixed at 0 even in the presence of Doppler shift, and the resolution is lowered. Can be suppressed.

Next, the operation will be described.
The F-Barker sequence generator 1 generates, for example, the F-Barker sequence φ _{1, m in} which the side lobe level shown in the above equation (6) is 0 or 1, and the B-Barker sequence generator 2 A B-Barker sequence φ _{2, m in} which the level of the side lobe shown in the above formula (7), which is a time inversion sequence of the Barker sequence φ _{1, m} , is 0 or 1 is generated.

  Here, in the pulse compression processing according to the above equation (8), it is assumed that there is no phase difference between two F-Barker sequences and B-Barker sequences that are received signals. However, when two F-Barker sequences and B-Barker sequences are transmitted in a time-sharing manner for each pulse, a phase difference depending on the pulse interval is generated by the Doppler frequency. An object of the present invention is to provide a code modulation pulse compression method in which the decrease in resolution is small under the condition that the Doppler frequency is unknown. Therefore, the embodiment does not correct the Doppler frequency between pulses by any means. 1 adopts the following method.

That is, the F-Barker sequence and the B-Barker sequence are converted into a first frequency signal having a frequency f _{1 and} a second frequency signal having a frequency f ₂ that are orthogonal to each other in the baseband, combined, and transmitted simultaneously. And Here, the reason why the first frequency signal and the second frequency signal that are orthogonal to each other is converted is to enable the reception side to separate the synthesized F-Barker sequence and B-Barker sequence.

The frequencies f ₁ and f ₂ that are orthogonal to each other are frequencies separated by the reciprocal of the sub-pulse width Tc (or the chip width) of the code modulation pulse, as shown in the following equations (11) and (12). It becomes.
f ₁ = 1 / Tc (11)
f ₂ = f ₁ + 1 / Tc = 2 / Tc (12)

The transmission frequency converter 3 converts the F-Barker sequence φ _{1, m} into a first frequency signal having the frequency f _1. Similarly, the transmission frequency converter 4 converts the B-Barker sequence φ _{2, m} into the frequency f ₂ . Convert to a second frequency signal. The synthesizer 5 synthesizes the first frequency signal and the second frequency signal and outputs them simultaneously as a transmission signal to the target.
FIG. 2 shows that a F-Barker sequence and a B-Barker sequence having a code length of 13 bits are converted into a first frequency signal having a frequency f _{1 and} a second frequency signal having a frequency f ₂ and synthesized to generate a transmission signal. It is a figure which shows the example to produce | generate.

  The frequency converter 6 frequency-converts the synthesized transmission signal into an RF signal, and the transmission antenna 7 radiates the frequency-converted RF signal toward the target toward the space.

The RF signal radiated to the space hits the target, the receiving antenna 8 receives the RF signal reflected by the target, and the frequency converter 9 converts the received RF signal into a received signal. The reception frequency converter 10 converts the first frequency signal having the frequency f ₁ in the reception signal into an F-Barker sequence and converts a phase term in the baseband into a complex amplitude sequence. The reception frequency converter 11 converts the second frequency signal having the frequency f ₂ in the reception signal into a B-Barker sequence, and converts the phase term in the baseband into a complex amplitude sequence. Here, in general, the frequency conversion by the reception frequency converter 10 and the reception frequency converter 11 can use Fourier transform.

  The F-Barker sequence pulse compressor 12 has an F-Barker sequence based on the cross-correlation function of the F-Barker sequence complex amplitude sequence and the F-Barker sequence from the F-Barker sequence generator 1 as shown in Equation (4). The first pulse compression signal is output. The B-Barker sequence pulse compressor 13 uses the B-Barker sequence cross-correlation function from the complex amplitude sequence of the B-Barker sequence and the B-Barker sequence from the B-Barker sequence generator 2 as shown in Equation (4). The second pulse compression signal is output.

  The synthesis processor 14 obtains an average of the first pulse compressed signal of the F-Barker sequence and the second pulse compressed signal of the B-Barker sequence as shown in Expression (8), and the absolute value thereof is synthesized. Output as a pulse compression signal.

FIG. 3 is a diagram for explaining the timing of the code modulation pulse compression method according to the first embodiment. Here, a transmission signal obtained by synthesizing an F-Barker sequence converted to a first frequency signal of frequency f ₁ and a B-Barker sequence converted to a second frequency signal of frequency f ₂ is transmitted at the same time. The reflected received signal is subjected to frequency conversion processing, and F-Barker sequence and B-Barker sequence pulse compression processing and their synthesis processing are continuously performed in the time direction, and the level of the side lobe at an odd time lag s is 0. Thus, a post-synthesis pulse waveform with a small side lobe level at another even time lag s is obtained.

In this way, by transmitting and receiving two code sequences simultaneously with one transmission signal pulse, there is no phase shift as seen between pulses, and the amplitude value fluctuates between transmission signal pulses. In FIG. 4, pulse compression having an ideal characteristic of the equation (8) is possible. Here, although the phase difference between the first and second frequency signals of the two orthogonal frequencies f ₁ and f ₂ is set to 0, the two orthogonal frequencies are actually increased so that the Peak to average level is increased. The phase difference between the first and second frequency signals to be selected is selected.

  FIG. 4 is a diagram showing an example of the waveform of the pulse compression signal. FIG. 4A shows the waveform of the pulse compression signal when only the F-Barker sequence having a code length of 13 bits is transmitted, and FIG. The waveform of the pulse compression signal when the F-Barker sequence having a code length of 13 bits and the B-Barker sequence having a code length of 13 bits are simultaneously transmitted as in the first embodiment is shown. In FIG. 4, the bird's-eye view on the left is the amount of time shift centered on time lag s = 0 on the horizontal axis, the Doppler frequency (0 Hz to 40 kHz) in the depth direction, and the relative amplitude value after pulse compression in the height direction. The right diagram shows the relationship between the amount of time shift and the relative amplitude value for Doppler frequencies of 0, 20, and 40 kHz in the left diagram.

  In the example of FIG. 4, when the Doppler frequency is 40 kHz, the side lobe level of the time lag 1 next to the peak increases as shown in the right diagram of FIG. 4A in the case of only the F-Barker sequence. However, the resolution is reduced and the level of the side lobes of other time lags s is also increased. However, when the F-Barker sequence and the B-Barker sequence are transmitted simultaneously as in the first embodiment, FIG. As shown in the right diagram of b), even in a situation where the influence of Doppler shift exists in the received signal, the level of the side lobe of the time lag 1 next to the peak is fixed to 0, and the decrease in resolution is suppressed. The side lobe level in the odd time lag s is 0, and the side lobe level in the other even time lag s is approximately the same size as when there is no Doppler shift. Level of lobes can be obtained.

  As described above, according to the first embodiment, an F-Barker sequence in which the side lobe level is 0 or 1, and a side lobe level that is a time reversal sequence of this F-Barker sequence is 0 or 1. The B-Barker sequence is converted into two orthogonal frequency signals, combined and transmitted simultaneously, and the F-Barker sequence and B-Barker sequence reflected at the target are separated, and the transmitted F-Barker sequence and Pulse compression is performed using a cross-correlation function with the B-Barker sequence, and an average of the first pulse compressed signal of the F-Barker sequence and the second pulse compressed signal of the B-Barker sequence is obtained and output as a combined pulse compressed signal In addition, the cross-correlation function with an odd time lag in the F-Barker sequence and the odd-number in the B-Barker sequence By using an F-Barker sequence and a B-Barker sequence in which the cross-correlation function at the time lag of the signal is in reverse phase, the pulse after pulse compression is obtained even under a situation where the influence of the Doppler shift exists on the received signal. When there is no error in position, the level of the side lobe of the odd time lag s including next to the peak position is 0 and the degradation of the resolution can be suppressed, and there is almost no Doppler shift even at the position of the even time lag s. As a result, the side lobe level can be suppressed to the same level.

Embodiment 2. FIG.
FIG. 5 is a block diagram showing a configuration of a code modulation pulse compression system according to the second embodiment of the present invention. This code modulation pulse compression system includes a forward sequence generator 21, a backward sequence generator 22, a transmission frequency converter (first transmission frequency converter) 3, a transmission frequency converter (second transmission frequency converter) 4, Synthesizer 5, frequency converter 6, transmission antenna 7, reception antenna 8, frequency converter 9, reception frequency converter (first reception frequency converter) ) 10, a reception frequency converter (second reception frequency converter) 11, a Forward series pulse compressor 23, a Backward series pulse compressor 24, and a synthesis processor 14, which are shown in FIG. An F-Barker sequence generator 1, a B-Barker sequence generator 2, an F-Barker sequence pulse compressor 12 and a B-Barker sequence pulse compressor 13 shown in FIG. 5 are respectively shown as a Forward sequence generator 21 and a Backward sequence generator. 22, the Forward sequence pulse compressor 23 and the Backward sequence pulse compressor 24.

  In the first embodiment, as two code sequences, an F-Barker sequence in which the side lobe level is 0 or 1 and a B-Barker sequence in which the side lobe level is 0 or 1 are the time inversion sequences. However, in the second embodiment, the code sequence is not limited to the Barker sequence in which the side lobe is 0 or 1, and the above equation (2) is used in a certain Forward sequence and a Backward sequence that is a time reversal sequence. The Forward sequence and the Backward sequence satisfying the relational expression 9) are used as a set of code sequences.

Next, the operation will be described.
The operation of the second embodiment is the same as that of the first embodiment in which the F-Barker sequence is replaced with a Forward sequence and the B-Barker sequence is replaced with a Backward sequence.

As a result of searching for a code sequence that satisfies the above formula (9) using a computer, for example, for a code length of 13 bits, a two-phase code that satisfies the above formula (9) is all code sequence patterns 2 ^ ( 13) Among 8192 types, there are 128 types (64 sets) including the Barker sequence. There are 40 (20 sets) of which the side lobe level is 3 or less.
FIG. 6 shows a code sequence having a code length of 13 bits, which satisfies the above equation (9), and the two elements u1 _, mu ^* _{1, m + s} and u2 _, mu ^* _{2, m + s} of the cross-correlation function are FIG. 5 is a diagram showing a code sequence in which the side lobe level is 3 or less when the time lag s is an even number and in phase, and when the time lag s is odd, the phase is opposite. In this way, even with another code length, the code sequence can be searched for by the computer program under the condition that the above expression (9) is satisfied.

As in the second embodiment, the waveform of the pulse compression signal when the Forward sequence and the Backward sequence are converted to the first and second frequency signals of the frequencies f ₁ and f ₂ and transmitted simultaneously is the received signal Even in a situation where the influence of Doppler shift exists, the side lobe level of the time lag 1 next to the peak is fixed to 0 to suppress the degradation of the resolution, and the side lobe levels in the other odd time lags s are also 0. However, the level of the side lobe in other even time lags s becomes higher than that when the F-Barker sequence and the B-Barker sequence are used, and the noise level increases, but the Barker sequence has a code length of 13 bits at the maximum. However, the number of code sequences that can be used can be increased.

  As described above, according to the second embodiment, a certain forward sequence and a backward sequence that is a time reversal sequence of the forward sequence are converted into two orthogonal frequency signals, combined, and transmitted at the same time. The Forward sequence and the Backward sequence reflected at step S are separated and pulse-compressed by the cross-correlation function between the forward and Backward sequences respectively transmitted, and the first pulse compression signal of the Forward sequence and the second pulse compression signal of the Backward sequence are The forward sequence and backward system in which the average is obtained and output as a combined pulse compressed signal, and the cross-correlation function at the odd time lag in the forward sequence and the cross-correlation function at the odd time lag in the backward are in reverse phase Is used, there is no error in the pulse position after pulse compression even in a situation where the influence of the Doppler shift exists in the received signal, and the level of the side lobe in the odd time lag s including the next to the peak position is 0. Thus, the effect of suppressing the reduction in resolution can be obtained.

  In the second embodiment, the level of the side lobe at an even time lag s increases as compared with the first embodiment, but the effect that the number of usable code sequences can be increased is obtained.

Embodiment 3 FIG.
FIG. 7 is a block diagram showing a configuration of a code modulation pulse compression system according to Embodiment 3 of the present invention. This code modulation pulse system includes a forward sequence generator 21, a backward sequence generator 22, a transmission frequency converter (first transmission frequency converter) 3, a transmission frequency converter (second transmission frequency converter) 4, a synthesis 5, frequency converter 6, transmission antenna 7, reception antenna 8, frequency converter 9, reception frequency converter (first reception frequency converter) 10, reception frequency converter (second transmission frequency converter) 11 , Forward series pulse compressor 23, Backward series pulse compressor 24, addition / subtraction processor 31 and window processor 32. The synthesis processor 14 shown in FIG. And the window processor 32.

Next, the operation will be described.
In the first embodiment and the second embodiment, when the time lag s is an odd number, 0 is satisfied, and when the time lag s is an even number, the above equation (9) is satisfied, that is, the two elements u 1,2 of the cross correlation function are satisfied _{. The} basic principle is that mu ^* _{1, m + s} , u2 _, mu ^* _{2, m + s} are in phase when the time lag s is even, and are out of phase when the time lag s is odd. In the third embodiment, paying attention to this, the synthesis processor 14 in the first embodiment and the second embodiment is changed to the addition / subtraction processor 31 and the window processor 32.

  The process from the transmission / reception of the Forward sequence and the Backward sequence to the respective pulse compression processing by the Forward sequence pulse compressor 23 and the Backward sequence pulse compressor 24 is the same as that of the second embodiment. The addition / subtraction processor 31 adds and subtracts the two first and second pulse compression signals from the Forward series pulse compressor 23 and the Backward series pulse compressor 24. The window processor 32 selects the subtraction result by the addition / subtraction processor 31 when the time lag s is an even number other than 0, and selects and outputs the subtraction result by the addition / subtraction processor 31 when the time lag s is 0 or odd.

すなわち、タイムラグｓが０でない偶数のときは、Ｆｏｗａｒｄ系列パルス圧縮器２３及びＢａｃｋｗａｒｄ系列パルス圧縮器２４からの二つの第１及び第２のパルス圧縮信号の減算を行い、タイムラグｓが０又は奇数のときは、Ｆｏｗａｒｄ系列パルス圧縮器２３及びＢａｃｋｗａｒｄ系列パルス圧縮器２４からの二つの第１及び第２のパルス圧縮信号の加算を行っている。 As described above, the adder / subtractor 31 and the window processor 32 are configured so that the first and second pulses from the Forward series pulse compressor 23 and the Backward series pulse compressor 24 are expressed by the following equation (13). This means that addition or subtraction is performed for each time lag s of the compressed signal.

That is, when the time lag s is an even number other than 0, the two first and second pulse compression signals from the Forward series pulse compressor 23 and the Backward series pulse compressor 24 are subtracted, and the time lag s is 0 or an odd number. In some cases, the two first and second pulse compression signals from the Forward series pulse compressor 23 and the Backward series pulse compressor 24 are added.

As shown in the above equation (9), the two elements of cross-correlation u1 _, mu ^* _{1, m + s} , u2 _, mu ^* _{2, m + s} are in phase when the time lag s is even. When the time lag s is an odd number, the phase is reversed, so that the two first and second pulse compression signals from the Forward series pulse compressor 23 and the Backward series pulse compressor 24 are when the time lag s is an even number. Are in phase, and when the time lag s is odd, the phase is reversed. Therefore, when the time lag s is an even number other than 0, the subtraction result by the addition / subtraction processor 31 is selected, and when the time lag s is 0 or odd Since the addition result by the adder / subtractor 31 is selected, the pulse compression signal output from the window processor 32 becomes 0 in all time lags s where the time lag s is not 0. That is, even in the presence of Doppler shift, the side lobe is completely zero except for the peak, and the actual radar can obtain signal samples of only internal noise.

FIG. 8 is a diagram for explaining the timing of the code modulation pulse compression method according to the third embodiment. Here, a transmission signal obtained by synthesizing a forward sequence converted to a first frequency signal of frequency f ₁ and a backward sequence converted to a second frequency signal of frequency f ₂ is simultaneously transmitted, and the reception signal reflected by the target After the window processing in which the forward sequence and Backward sequence pulse compression processing, addition processing, subtraction processing, and window processing are continuously performed in the time direction, and the side lobes other than the peak are completely zero. A pulse waveform is obtained.

  As described above, according to the third embodiment, a certain forward sequence and a backward sequence that is a time reversal sequence of the forward sequence are converted into two orthogonal frequency signals, combined, and transmitted at the same time. The Forward sequence and the Backward sequence reflected in step 1 are separated and pulse-compressed by the cross-correlation function of the forward and Backward sequences transmitted, respectively. When the time lag s is an even number other than 0, the two first and second pulse compressions When the time lag s is 0 or odd, the two first and second pulse compression signals are added, and the cross-correlation function at the odd time lag in the Forward sequence and the odd number in the Backward are calculated. Forwa where the cross-correlation function in the time lag is out of phase By using the d-sequence and the Backward sequence, there is no error in the pulse position after pulse compression and the sidelobe levels in all time lags other than the peak even under the situation where the influence of Doppler shift exists in the received signal As a result, the effect of reducing the resolution can be obtained.

Embodiment 4 FIG.
FIG. 9 is a block diagram showing a configuration of a code modulation pulse compression system according to Embodiment 4 of the present invention. This code modulation pulse compression method includes a forward sequence generator 21, a backward sequence generator 22, a transmission switch 41, a frequency converter 6, a transmission antenna 7, a reception antenna 8, a frequency converter 9, a reception switch 42, and a forward sequence. A pulse compressor 23, a Backward series pulse compressor 24, and a synthesis processor 14 are provided. The transmission frequency converter 3, the transmission frequency converter 4 and the synthesizer 5 shown in FIG. Is replaced with a transmission switch 41, and the reception frequency converter 10 and the reception frequency converter 11 of FIG. 5 are replaced with a reception switch 42 in FIG.

Next, the operation will be described.
In the first embodiment, the second embodiment, and the third embodiment, two code sequences are converted into two orthogonal frequency signals and transmitted at the same time. The code sequence is transmitted in a time division manner.

  The transmission switcher 41 switches the Forward sequence from the Forward sequence generator 21 and the Backward sequence from the Backward sequence generator 22 at predetermined time intervals, and outputs them to the frequency converter 6 as a transmission signal to the target. The frequency converter 6 is output in a time-sharing manner, but converts the Forward signal and the Backward sequence transmission signal into an RF signal, and then outputs the same to the transmission antenna 7 with the phase of transmission start in each RF signal pulse.

  The frequency converter 9 converts the received RF signal reflected by the target into a forward signal and a backward signal, which are received signals, and the reception switcher 42 switches the output in synchronization with the switching timing of the transmission switcher 41. The sequence is output to the Forward sequence pulse compressor 23, and the Backward sequence is output to the Backward sequence pulse compressor 24. The operations of the forward series pulse compressor 23 and the backward series pulse compressor 24 are the same as those in the second embodiment.

  The synthesizing processor 14 holds the F-Barker sequence pulse compression signal and the B-Barker sequence pulse compression signal input in time division in an internal memory (not shown), and matches the timing to the F-Barker sequence pulse compression signal. An average of the first pulse compression signal and the second pulse compression signal of the B-Barker series is obtained, and the combined pulse compression signal is output.

  FIG. 10 is a diagram for explaining the timing of the code modulation pulse compression method according to the fourth embodiment. Here, the Forward sequence and Backward sequence transmission signals are transmitted in a time division manner, the Forward sequence and Backward sequence pulse compression processing of the received signal reflected by the target is performed in a time division manner, and the synthesizing processing is performed in accordance with the timing. A combined pulse waveform with small side lobes other than the peak is obtained.

  As described above, according to the fourth embodiment, a certain Forward sequence and a Backward sequence that is a time reversal sequence of the Forward sequence are transmitted in a time division manner, and the Forward sequence and the Backward sequence reflected by the target are in a time division manner. Received and pulse-compressed by the cross-correlation function between the forward and backward sequences respectively transmitted, and the average of the first pulse-compressed signal of the forward sequence and the second pulse-compressed signal of the backward sequence is obtained at the same time and synthesized In addition to outputting as a pulse compression signal later, a forward sequence and a backward sequence are used such that the cross-correlation function at an odd time lag in the forward sequence and the cross-correlation function at an odd time lag in the backward are in reverse phase. Yo Even in a situation where the influence of Doppler shift exists in the received signal, there is no error in the pulse position after pulse compression, and the level of the side lobe in the odd time lag s including the next to the peak position becomes 0, and the resolution is The effect that a fall can be suppressed is acquired.

In the fourth embodiment, the forward sequence and the backward sequence to be transmitted are converted into first and second frequency signals of two orthogonal frequencies f ₁ and f ₂ , respectively, as in the second embodiment. As a result, the sampling rate can be reduced as compared with the second embodiment.

  Further, although the fourth embodiment is based on the configuration of the second embodiment, the same processing can be performed based on the configuration of the first embodiment or the third embodiment. The effect is obtained.

It is a block diagram which shows the structure of the code modulation pulse compression system by Embodiment 1 of this invention. In the code modulation pulse system according to Embodiment 1 of the present invention, an F-Barker sequence and a B-Barker sequence having a code length of 13 bits are converted into a first frequency signal having a frequency f _{1 and} a second frequency signal having a frequency f ₂ . It is a figure which shows the example which produces | generates a transmission signal by carrying out combining. It is a figure explaining the timing of the code modulation pulse compression system by Embodiment 1 of this invention. It is a figure which shows the example of the waveform of a pulse compression signal. It is a block diagram which shows the structure of the code modulation pulse compression system by Embodiment 2 of this invention. In the code modulation pulse system according to the second embodiment of the present invention, in a code sequence having a code length of 13 bits, two elements of the cross-correlation function are in phase when the time lag is an even number, and are opposite in phase when the time lag is an odd number. It is a figure which shows the code sequence whose lobe level is 3 or less. It is a block diagram which shows the structure of the code modulation pulse compression system by Embodiment 3 of this invention. It is a figure explaining the timing of the code modulation pulse compression system by Embodiment 3 of this invention. It is a block diagram which shows the structure of the code modulation pulse compression system by Embodiment 4 of this invention. It is a figure explaining the timing of the code modulation pulse compression system by Embodiment 4 of this invention.

Explanation of symbols

  1 F-Barker sequence generator, 2 B-Barker sequence generator, 3 Transmit frequency converter, 4 Transmit frequency converter, 5 Synthesizer, 6 Frequency converter, 7 Transmit antenna, 8 Receive antenna, 9 Frequency converter, DESCRIPTION OF SYMBOLS 10 Reception frequency converter, 11 Reception frequency converter, 12 F-Barker series pulse compressor, 13 B-Barker series pulse compressor, 14 Compositing processor, 21 Forward series generator, 22 Backward series generator, 23 Forward series Pulse compressor, 24 Backward series pulse compressor, 31 addition / subtraction processor, 32 window processor, 41 transmission switcher, 42 reception switcher.

Claims (2)

A forward sequence generator for generating a forward sequence;
A Backward sequence generator for generating a Backward sequence that is a time reversal sequence of the Forward sequence;
A first transmission frequency converter for converting the Forward sequence into a first frequency signal;
A second transmission frequency converter for converting the Backward sequence into a second frequency signal orthogonal to the first frequency signal;
A combiner that combines the first frequency signal and the second frequency signal and simultaneously outputs the combined signal as a transmission signal to a target;
A first reception frequency converter for converting a first frequency signal in a reception signal from a target into a forward sequence;
A second reception frequency converter for converting a second frequency signal in the reception signal from the target into a Backward sequence;
A forward sequence pulse compressor that outputs a first pulse compression signal by a cross-correlation function of the forward sequence from the first reception frequency converter and the forward sequence from the forward sequence generator;
A Backward sequence pulse compressor that outputs a second pulse compression signal by a cross-correlation function of the Backward sequence from the second reception frequency converter and the Backward sequence generator from the Backward sequence generator;
An addition / subtraction processor for adding and subtracting the forward correlation cross-correlation function and the backward cross-correlation function to add and subtract the first and second pulse compression signals;
A window processor for selecting a subtraction result by the addition / subtraction processor when the time lag in the cross-correlation function is an even number other than 0, and selecting an addition result by the addition / subtraction processor when the time lag is 0 or an odd number,
In the forward sequence generator and the backward sequence generator, the cross-correlation function at an odd time lag in the forward sequence pulse compressor and the cross-correlation function at an odd time lag in the backward sequence pulse compressor are in reverse phase. A coded modulation pulse compression system characterized by generating a forward sequence and a backward sequence. The Forward sequence and the Backward sequence that is the time-reversed sequence are respectively converted into the first and second frequency signals, combined and transmitted simultaneously as the transmission signal to the target, and the first and second in the received signal from the target. Are respectively converted into a Forward sequence and a Backward sequence, and a cross-correlation function between the received Forward sequence and the transmitted Forward sequence is added to and subtracted from a cross-correlation function between the received Backward sequence and the transmitted Backward sequence, and When selecting the subtraction result when the time lag in the cross-correlation function is an even number other than 0, and selecting the addition result when the time lag is 0 or an odd number, a cross-correlation function with an odd time lag in the Forward sequence; Odd number in the above Backward sequence Coded modulation pulse compression method is the cross-correlation function at time lag using the Forward sequence and Backward sequence such that reverse phase.

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