JP2000046943A - Method and apparatus for synchronous qudrature modulation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a qudrature modulation even in a synthetic aperture sensor, by a method wherein the phase of a transmission signal in the start of a transmitting operation is made to agree with the phase of a qudrature carrier signal, which is used for the qudrature modulation of a reception signal. SOLUTION: A transmission synchronization circuit 13 in a synchronous qudrature modulation part 1 synchronizes a transmission start signal in a system control part 2 with a phase signal in a qudrature carrier-signal generation circuit 11 so as to generate a transmission start pulse signal. A transmission signal in a transmission-signal generation part 3 is inputted to a transmission part 4, and the echoed sound of its transmission sound is received by a reception part 5. A qudrature modulation computing circuit 12 to which its reception signal is inputted qudrature-modulates the reception signal by using the qudrature carrier signal in the qudrature carrier-signal generation circuit 11, and the signal is converted into a qudrature baseband signal so as to be then outputted to an A/D conversion part 6. At this time, the transmission synchronization circuit 13 synchronizes the signal so as to generate the transmission start pulse signal. As a result, the phase of the transmission signal in the start of a transmitting operation agrees with the phase of the qudrature carrier signal. Consequently, also a system which uses information on the phase of a certain target signal obtained by a plurality of transmitting operations can fetch a qudrature modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature modulation system for converting a received signal into a quadrature baseband signal performed by an active sonar, and more particularly to a target signal obtained by a plurality of transmissions such as a synthetic aperture sonar. The present invention relates to a quadrature modulation method using phase information of the above and its measures.

[0002]

2. Description of the Related Art In general, a reception frequency band in an active sonar generally uses a relatively narrow band with a center frequency of several KHz to several tens KHz. For example, this corresponds to a case where a signal in a frequency band of ± 100 Hz around a transmission frequency of 10 KHz is received.

As described above, when digitally processing a signal in which the ratio of the reception bandwidth to the transmission frequency, that is, the fractional band Q is one digit or two digits, the A / D conversion is performed as raw data.
When converted, the sampling frequency is determined by the transmission frequency, and the sampling rate becomes high. Therefore, the raw data is orthogonally modulated, converted to an orthogonal baseband signal having the center frequency of the reception band as a baseband, and then A / D converted. It is common practice to reduce the sampling rate to about the same as the reception bandwidth by treating it as complex sample data.

At this time, in a general active sonar,
Since the echoes of the signals transmitted from the transmitters are simultaneously received by the receiver array with multiple receivers and then directionally synthesized, the mutual phase of the signals received by each receiver is The relationship is important, and these phase relationships need to be maintained even after conversion to the orthogonal baseband signal by the above-described orthogonal modulation.

Therefore, in quadrature modulation of a received signal, the same orthogonal carrier signal equal to the center frequency of the reception band is used for all the received signals, and the phase relationship between the received signals due to the orthogonal modulation is used. I try not to change.

[0006]

However, in such a general active sonar, it suffices that the phase relationship between signals received by each receiver of the receiver array in each transmission be maintained. The phase relationship between transmissions was not usually taken into account.

[0007] However, like a synthetic aperture sonar, transmission / reception is repeated in a vertical direction at a constant interval while moving the transducer on a linear orbit at a constant speed, and at a position equivalent to a virtually arranged receiver. In a method of obtaining a directivity combined output equivalent to that of an actual receiver array by matching and combining the phases of received signals, the phase relationship of the received signals between transmissions is important, as described above. Like general active sonar,
There is a problem that quadrature modulation in which the phase relationship between transmissions is not guaranteed cannot be performed.

When the transmission signal and the quadrature carrier signal are not phase-synchronized, the received signal from the aforementioned fixed target retains phase information determined by the positional relationship before quadrature modulation. After the quadrature modulation, the phase information at the start of transmission of the quadrature carrier signal is not fixed every transmission, so that phase information cannot be maintained. For this reason, with the conventional synthetic aperture sonar, despite the sufficient fractional bandwidth,
Since the sampling rate cannot be reduced by the above-described quadrature modulation and raw data is handled without conversion to a quadrature baseband signal, the sampling rate of A / D conversion increases and the data rate becomes enormous. There are also problems.

A main object of the present invention is to provide a synchronous quadrature modulation method for solving the above-mentioned problem of the synthetic aperture sonar by maintaining the phase relationship of a received signal between transmissions even after quadrature modulation. It is to provide the device.

[0010]

SUMMARY OF THE INVENTION The present invention provides an orthogonal so-called orthogonal sonar having a center frequency of a reception band of zero when an A / D conversion of a received signal is performed by an active sonar or the like for digital processing. A /
In an orthogonal modulation method in which D-conversion is performed to generate complex sample data, in order to always make the relationship between the phase of the orthogonal carrier signal and the phase of the sonar transmission signal coincide between the orthogonal carrier signal generation circuit and the transmission signal generation circuit. It is characterized by adding a synchronization circuit for achieving synchronization.

FIG. 1 shows a synchronous quadrature modulation system according to the present invention. The transmission timing of a sonar is generated by a system control unit 2 which controls the operation of the whole sonar system. In the transmission synchronization circuit 13 of the quadrature modulation section 1, the orthogonal carrier signal generation circuit 11
The signal is synchronized with the phase signal sent from the transmitter, sent to the transmission signal generator 3 as a transmission start pulse signal, and the transmission signal generator 3 generates a transmission signal in accordance with the transmission start pulse signal. The signal is output to the transmitting unit 4 including an amplifier and the like.

The transmitted sound transmitted from the transmitting section 4 is resonated by a receiving section 5 comprising a receiver and a preamplifier and the like, and the received received signal is subjected to a synchronous orthogonal signal. After being sent to the orthogonal modulation operation circuit 12 of the modulation section 1, the orthogonal modulation operation circuit 12 orthogonally modulates the received signal with the orthogonal carrier signal sent from the orthogonal carrier signal generation circuit 11, and converts it into an orthogonal baseband signal. Output to A / D converter.

The quadrature carrier signal generation circuit 11 continuously generates two types of carrier signals corresponding to the center frequency of the reception band, that is, an in-phase component I and a quadrature component Q. Is generated, and this phase signal is output to the transmission synchronization circuit 13 described above.

The transmission synchronizing circuit 13 constantly monitors the phase signal to grasp the phase of the orthogonal carrier signal. In this state, when receiving the above-mentioned transmission start signal from the system control unit 2, the transmission synchronization circuit 13 receives the orthogonal carrier signal at the time of reception. Check the phase,
A transmission start pulse signal is generated in synchronization with a point in time when a predetermined phase is reached, and output to the transmission signal generation unit 3. This allows the transmission signal to always be generated at the same phase of the orthogonal carrier signal.

Therefore, the phase of the received signal due to the reverberation sound from a certain fixed target can be determined at any time of transmission if the relative positional relationship between the sonar transmitter and receiver and the fixed target remains unchanged. The same applies to the orthogonal baseband signal obtained by orthogonally modulating the received signal.
This means that the phase information of the received signal from a target obtained between a plurality of transmissions is accurately maintained, and applications using such phase information, for example, synthetic aperture sonar In such a case, conversion into orthogonal baseband signals becomes possible, and an effect that a data rate can be reduced by orthogonal modulation as in a conventional general active sonar can be obtained.

[0016]

Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of an apparatus to which a synchronous quadrature modulation method of the present invention is applied.

The synchronous quadrature modulator includes a system controller 2, a synchronous quadrature modulator 1, a transmission signal generator 3,
It comprises a transmitting unit 4, a receiving unit 5, and an A / D converting unit 6.
The system control unit 2 controls the entire sonar system,
It generates a transmission start signal that serves as a reference for distance measurement and the like. The transmission signal generator 3 generates a transmission signal to be actually transmitted, using the transmission start pulse signal synchronized by the synchronous quadrature modulation circuit 1 as a trigger. The transmitting unit 4 power-amplifies the transmission signal, converts the electric signal into an acoustic signal using a transmitter, and transmits the signal underwater. The receiving unit 5 amplifies a received signal obtained by acoustically-electrically converting underwater reverberation sound by a receiver with a preamplifier.

The synchronous quadrature modulator 1 has a quadrature carrier signal generation circuit 11, a quadrature modulation operation circuit 12, and a transmission synchronization circuit 13. The quadrature carrier signal generation circuit 11 has two carriers corresponding to the center frequency of the reception band. A signal and a phase signal indicating the phase of the carrier signal are generated. The two carrier signals are a Cos wave (cosine wave), which is an in-phase component I, and a Sin wave (sine wave), which is a quadrature component Q, and are continuously generated while maintaining the orthogonal relationship.

The orthogonal modulation operation circuit 12 orthogonally modulates the reception signal from the reception unit 5 with the orthogonal carrier signal generated by the orthogonal carrier signal generation circuit 11 and converts the signal into an orthogonal baseband signal. The transmission synchronizing circuit 13 performs the main function of the present invention. The transmission synchronizing circuit 13 synchronizes the transmission start signal output from the system control unit 2 with the phase signal output from the quadrature carrier signal generation circuit 11, and determines a certain phase signal. At this point, a transmission start pulse signal is generated and supplied to the transmission signal generator 3.

Hereinafter, the operation of the present embodiment will be described. FIG. 2 shows the synchronous quadrature modulation section 1 in further detail, FIG. 3 is a timing chart thereof, and FIG. 4 is a basic flowchart of the synchronous quadrature modulation method of the present invention.

In accordance with the synchronous quadrature modulation method of the present invention, the transmission start signal is converted into a transmission start pulse signal by a phase signal that maintains the phase of the in-phase and quadrature carrier signals when the transmission start signal is transmitted (step 21). Step 22), transmitting a transmission signal signal using the transmission start pulse signal as a trigger (Step 23). In order to realize this basic flow, the operations of the following devices are performed.

First, the operation of the orthogonal carrier signal generation circuit 11 will be described. Cos ωct generation circuit 111 and S
The inωct generation circuit 112 generates carrier signals of the in-phase component I and the quadrature component Q, respectively, and the two generation circuits are controlled so that a stable orthogonal relationship is always maintained.
Here, ωc is an angular frequency and is set to the center frequency of the normal reception band. In this example, the binarization circuit 113 is a signal in which the in-phase component I is represented by binary values of “1” and “0”, where “1” indicates a phase of 0 to 180 degrees and “0” indicates a phase of 0 to 180 degrees. It represents 180 degrees to 360 degrees.

Next, the operation of the quadrature modulation operation circuit 12 will be described. The in-phase component I is received by the multiplier 121 and the multiplier 123 with the received signal (in this case, represented by a real value of Cosωt).
And the quadrature component Q, respectively, and passing the results through low-pass filters (LPF) 122 and 124, respectively, to obtain an in-phase difference frequency component Cos (ω-ωc) t and a quadrature difference frequency component Sin (ω-ωc) t Is obtained. This is a quadrature baseband signal, which is obtained by converting the received signal Sinωt into complex data shifted to the positive and negative frequency regions where the carrier signal ωc is 0 Hz.

Finally, the operation of the transmission synchronization circuit 13 will be described. A D flip-flop circuit (hereinafter, referred to as DFF) 131 receives the transmission start signal output from the system control unit 2 as a D input, and outputs a signal from the quadrature carrier signal generation circuit 11.
This is for synchronizing the transmission start signal with the rise of the phase signal by using the phase signal output from the value conversion circuit 113 as a clock input.

The output of the DFF 131 is further synchronized with a phase signal by the DFF 132, and the inverted output of the DFF 132 and the positive output of the DFF 131 are logically negated (NAN).
D) 133, a transmission start pulse signal synchronized with the rising of the phase of the orthogonal carrier signal is generated.

The transmission start pulse signal generated by the transmission synchronization circuit 13 of the synchronous quadrature modulation section 1 is output to the transmission signal generation section 3, and the transmission signal generation section 3 always uses the transmission start pulse signal as a trigger to have the same phase. Generate a transmission signal.
Therefore, the transmission signal can always be generated from the same phase of the quadrature carrier signal, specifically, from the phase 0 degree of the in-phase component I.

[0027]

As described above, according to the present invention, an active sonar or the like converts a received signal into a quadrature baseband signal having a center frequency of a receiving band of 0 Hz, and performs A / D conversion. When performing processing such as reducing the sampling rate of the transmission signal, the generation timing of the transmission signal is not generated in synchronization with only the transmission start timing controlled by the system, but the orthogonal carrier used for quadrature modulation of the reception signal. Since the signal is generated in synchronization with the signal phase, the transmission signal phase at the start of transmission and the signal phase of the orthogonal carrier always coincide.

Therefore, at any time of transmission, the phase of the received signal returned from a certain fixed target after quadrature modulation depends on the relative positional relationship between the sonar transmitter and receiver and the above-mentioned fixed target. The phase of the received signal before quadrature modulation is not changed for each transmission by the phase of the quadrature carrier signal.

For this reason, based on the phase information from a certain target signal obtained by a plurality of transmissions, the quadrature modulation processing can be easily adopted even in a system using this phase information, for example, a synthetic aperture sonar. Thus, there is an effect that the sampling rate can be reduced.

The adoption of the synchronous quadrature modulation circuit system of the present invention makes it possible to reduce the sampling rate, adopt a low-speed A / D converter, and reduce the recording capacity of the data recorder by reducing the data rate. There is also a savings effect.

The present invention is not limited to the above embodiment,
It is obvious that each embodiment can be appropriately modified within the scope of the technical idea of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an embodiment of a synchronous quadrature modulation device according to the present invention.

FIG. 2 is a detailed configuration block diagram of a synchronous quadrature modulation unit 1 shown in FIG.

FIG. 3 is a timing chart of the synchronous quadrature modulator 1 shown in FIG.

FIG. 4 is a basic flowchart of the synchronous quadrature modulation method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synchronous orthogonal modulation part 2 System control part 3 Transmission signal generation part 4 Transmission part 5 Receive part 6 A / D conversion part 11 Quadrature carrier signal generation circuit 12 Quadrature modulation operation circuit 13 Transmission synchronization circuit 111 COSωct generation circuit 112 SINωct Generator 121 Multiplier 122 LPF 123 Multiplier 124 LPF 131, 132 D flip-flop 133 NAND gate

Claims (6)

[Claims] 1. A quadrature modulation method for converting a received signal into a quadrature baseband signal performed by an active sonar, wherein a phase of a transmission signal at the start of transmission and a phase of a quadrature carrier signal used for quadrature modulation of the received signal. A synchronous quadrature modulation method. 2. A quadrature modulation method for converting a received signal into a quadrature baseband signal performed by an active sonar, the method comprising: generating a transmission start signal indicating the start of transmission of the active sonar; and receiving the transmission start signal. Synchronizing with the phase of the quadrature carrier signal used for quadrature modulation of the wave signal, converting to a transmission start pulse signal, and having a step of generating a transmission signal with the transmission start pulse signal as a trigger, A synchronous quadrature modulation method, wherein the start of a transmission signal is synchronized with the phase of a quadrature carrier signal. 3. A quadrature modulation method for converting a received signal into a quadrature baseband signal performed by an active sonar, comprising: outputting a transmission start signal for instructing the start of transmission; and quadrature modulation used for quadrature modulation of the received signal. Outputting a phase signal indicating the phase information thereof together with the in-phase component I and the quadrature component Q of the carrier signal; and converting the transmission start signal into a transmission start pulse signal synchronized with the quadrature carrier signal based on the phase signal. And a step of generating a transmission signal by using the transmission start pulse signal as a trigger. 4. A quadrature modulation device for converting a received signal into an orthogonal baseband signal, which is performed by an active sonar, wherein a phase of a transmission signal at the start of transmission and a phase of an orthogonal carrier signal used for orthogonal modulation of the received signal. A synchronous quadrature modulation device characterized by having a synchronization circuit for matching 5. A quadrature modulator for converting a received signal into a quadrature baseband signal, the transmission being performed by an active sonar and being output by a system control unit for generating a transmission start signal indicating the start of transmission of the active sonar. A synchronous quadrature modulator that synchronizes a start signal with a phase of a quadrature carrier signal used for quadrature modulation of a received signal and converts the signal into a transmission start pulse; and a transmission that generates a transmission signal using the transmission start pulse signal as a trigger. A synchronous quadrature modulation device, comprising: a signal generation unit that always synchronizes a start of a transmission signal with a phase of a quadrature carrier signal. 6. A quadrature modulator for converting a received signal into a quadrature baseband signal, which is performed by an active sonar, comprising: a system control unit for outputting a transmission start signal for instructing a transmission start; A transmission signal generation unit that generates a transmission signal as a trigger; a quadrature carrier signal generation circuit; a quadrature modulation operation circuit; and a synchronous quadrature modulation unit including a quadrature synchronization circuit. A signal generation circuit outputs an in-phase component I, a quadrature component Q, and a phase signal indicating their phase information. A quadrature synchronization circuit converts a transmission start signal output from the system control unit based on the phase signal into a quadrature signal. The transmission signal is converted into a transmission start pulse signal synchronized with the phase of the carrier signal, and a transmission signal is generated by the transmission signal generation unit using the transmission start pulse signal as a trigger. Periodic quadrature modulator.