Demodulation device and demodulation method

Abstract

[Problem] To achieve demodulation for a multilevel PSK signal with higher reliability. [Solution] A tracking processing unit 45 comprises a phase rotation unit 452, a phase adjustment unit 453, a phase comparison unit 454, and a VCO 451. The phase rotation unit 452 rotates the phases of an I signal and a Q signal in the received signal of a multilevel PSK signal by using a reference signal. The phase adjustment unit 453 makes a phase adjustment by multiplying the phase of the I signal and the phase of the Q signal by an integer, the I signal and the Q signal being outputted from the phase rotation unit 452. The phase comparison unit 454 compares the adjusted phase of the I signal and the adjusted phase of the Q signal. The VCO 451 generates the reference signal by using the comparison result of the phases.

Description

[Technical Field]

[0001] The present invention relates to a technique for demodulating a multi-level PSK modulated signal. [Background technology]

[0002] Patent Document 1 describes a demodulation circuit for a π / 4 shift QPSK signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-132996 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is difficult for the demodulation circuit described in Patent Document 1 to demodulate a multi-level PSK signal such as 8PSK.

[0005] Therefore, an object of the present invention is to more reliably achieve demodulation of a multi-level PSK signal. [Means for solving the problem]

[0006] The demodulation device of the present invention includes a phase rotation unit, a phase adjustment unit, a phase comparison unit, and a reference signal generation unit. The phase rotation unit rotates the phases of the I signal and the Q signal in a received multi-level PSK signal using a reference signal. The phase adjustment unit adjusts the phases of the I signal and the Q signal output from the phase rotation unit by an integer multiple. The phase comparison unit compares the phase of the phase-adjusted I signal with the phase of the phase-adjusted Q signal. The reference signal generation unit generates a reference signal using the phase comparison result.

[0007] In multi-level PSK, the phase difference (angle difference) between adjacent symbols in the phase rotation direction is constant. In this configuration, the phase adjustment amount is set to a predetermined integer multiple, so that the phase difference (angle difference) between adjacent symbols in the phase rotation direction after phase adjustment is adjusted to 45°. Therefore, even with multi-level PSK such as 8PSK, the frequency adjustment of the reference signal can be achieved in the same way as with QPSK. [Effects of the Invention]

[0008] According to the present invention, demodulation of a multi-level PSK signal can be more reliably achieved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram of a tracking processing unit according to an embodiment of the present invention. [Figure 2] FIG. 2 is a functional block diagram of the automatic identification system of a vessel according to the embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing an example of the data structure of an automatic identification signal for vessels. [Figure 4] FIG. 4 is a diagram showing a concept of transition of the phase adjusted by the phase adjustment unit. [Figure 5] FIG. 5(A) shows a constellation before tracking according to the first embodiment, and FIG. 5(B) shows a constellation after tracking according to the first embodiment. [Figure 6] FIG. 6 is a flowchart showing an example of a demodulation method according to an embodiment of the present invention. [Figure 7] FIG. 7 is a functional block diagram of a tracking processing unit according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a functional block diagram of a tracking processing unit according to the third embodiment of the present invention. [Figure 9] FIG. 9(A) shows a constellation before tracking for a 16PSK signal according to the third embodiment, and FIG. 9(B) shows a constellation after tracking for a 16PSK signal according to the third embodiment. [Figure 10]FIG. 10(A) shows a constellation before tracking for a 32PSK signal according to the third embodiment, and FIG. 10(B) shows a constellation after tracking for a 32PSK signal according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] A demodulation technique according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a functional block diagram of a tracking processing unit according to a first embodiment of the present invention. Fig. 2 is a functional block diagram of an automatic identification system according to an embodiment of the present invention. Fig. 3 is a diagram showing an example of the data structure of an automatic identification signal.

[0011] (Configuration of Automatic Identification System) 2, the automatic identification system 10 comprises an antenna 20, a downconverter 30, a rough frequency control unit 41, a symbol timing detection unit 42, a downconverter 43, a phase control unit, a tracking processing unit 45, a signal detection unit 51, a correlation unit 52, and a decoding unit 60. Note that the components of the automatic identification system 10 other than the antenna 20 can be realized by analog circuits, digital circuits, a processing unit such as a computer, or the like.

[0012] The antenna 20 receives the automatic vessel identification signal and outputs the received signal to the downconverter 30. The downconverter 30 downconverts the received signal to a frequency that is a predetermined multiple (for example, 10 times) of the baseband signal. The downconverter 30 outputs the downconverted received signal to the coarse frequency control unit 41 and the signal detection unit 51.

[0013] As shown in Figure 3, the Automatic Identification Signal consists of RU (Ramp-up) data, SW (Syncword) data, LCID (Link Config ID) data, DS (Data Symbol) data, RD (Ramp-down) data, and GD (Guard time) data.

[0014] The RU data, SW data, LCID data, DS data, RD data, and GD section are arranged in this order. The RU data, SW data, LCID data, DS data, and RD data each have a predetermined number of bits and a predetermined bit arrangement. The RU data, SW data, and LCID data are, for example, π / 4QPSK modulated signals. The DS data is an 8PSK modulated or 16QAM modulated signal.

[0015] RU data is data that indicates the start of the data for the Automatic Identification Signal. SW data is data for timing detection and frequency control. LCID data is data that indicates the modulation method of the DS data. DS data is data that contains various information for Automatic Identification Signal, such as the ship identification ID. RD data is data for the Automatic Identification Signal, more specifically, data that indicates the end of the DS data. The GD section is a non-signal section and does not contain any data.

[0016] The frequency coarse control section 41 estimates and calculates the amount of frequency deviation from the received signal and performs coarse frequency control. For example, the processing of the frequency coarse control section 41 narrows the frequency of the reference signal from a range of ±500 Hz to a range of ±30 Hz with respect to the frequency of the received signal.

[0017] The symbol timing detector 42 detects the symbol timing of the received signal after the coarse control output from the frequency coarse controller 41. The downconverter 43 downconverts the output signal of the symbol timing detector 42 to a baseband frequency.

[0018] The phase control unit 44 performs automatic phase control on the signal down-converted to baseband (baseband signal).

[0019] The tracking processing unit 45 performs more accurate automatic phase control and automatic frequency control on the baseband signal output from the phase control unit 44. As a result, the frequency of the reference signal is narrowed from a range of ±500 Hz to a range of ±30 Hz relative to the frequency of the received signal. This makes it possible to achieve convergence to a desired symbol point with high accuracy. The tracking processing unit 45 outputs the signal (demodulated signal) after automatic phase control and automatic frequency control to the decoding unit 60. The specific contents of the automatic phase control and automatic frequency control performed by the tracking processing unit 45 will be described later. The tracking processing unit 45 corresponds to the "demodulation device" of the present invention.

[0020] The signal detector 51 detects RU data in the received signal. The correlator 52 uses the timing of the RU data to perform correlation processing between the received signal and the reference code. The correlator 52 outputs the correlation processing result to the decoder 60.

[0021] The decoding unit 60 uses the demodulated signal and the timing of detection of the main lobe (peak detection timing) of the correlation processing result to decode data including various information for automatic ship identification, such as a ship identification ID, from the DS (Data Symbol) data.

[0022] (Configuration and processing of tracking processing unit) 1, tracking processing section 45 includes VCO 451, phase rotation section 452, phase adjustment section 453, phase comparison section 454, and integration section 455. VCO 451 corresponds to the "reference signal generation section" of the present invention.

[0023] VCO 451 adjusts the frequency using the integral value of the phase comparison result output from integrator 455. VCO 451 generates a frequency-adjusted reference signal. VCO 451 generates an I-phase reference signal and a Q-phase reference signal from the reference signal and outputs them to phase rotation unit 452.

[0024] The I-phase signal and Q-phase signal of the received signal are input to the phase rotation unit 452, along with the I-phase reference signal and Q-phase reference signal from the VCO 451. The I-phase signal and Q-phase signal of the received signal are generated, for example, by quadrature detection of the received signal.

[0025] The phase rotation unit 452 rotates the phases of the I-phase signal and the Q-phase signal using the I-phase reference signal and the Q-phase reference signal. The phase-rotation-controlled I-signal and Q-signal are output to the decoding unit 60 and also to the phase adjustment unit 453.

[0026] Phase adjustment section 453 adjusts the phase of the I signal and the phase of the Q signal. More specifically, phase adjustment section 453 adjusts the phase of the I signal and the phase of the Q signal using the double angle theorem.

[0027] 4 is a diagram showing the concept of transition of the phase adjusted by the phase adjustment unit, in which θ represents the amount of phase shift.

[0028] 4 shows the case of an 8PSK modulated signal. In 8PSK, the phase difference (angular difference) between adjacent symbol points in the phase rotation direction is π / 4 [rad], or 45 [°].

[0029] 4, when phase adjustment is performed by phase adjustment unit 453, the point at 0+θ[°] is adjusted to 0+2θ[°]. The point at 45+θ[°] is adjusted to 90+2θ[°], the point at 90+θ[°] is adjusted to 180+2θ[°], and the point at 135+θ[°] is adjusted to 270+2θ[°]. The point at 180+θ[°] is adjusted to 360+2θ[°], and the point at 225+θ[°] is adjusted to 450+2θ[°]. The point at 270+θ[°] is adjusted to 540+2θ[°], and the point at 315+θ[°] is adjusted to 630+2θ[°].

[0030] Here, 360+2θ[°] is 0+2θ(+360)[°], 450+2θ[°] is 90+2θ(+360)[°], 540+2θ[°] is 180+2θ(+360)[°], and 630+2θ[°] is 270+2θ(+360)[°].

[0031] Therefore, the phase difference between adjacent symbol points in the phase rotation direction after phase adjustment is 90°. That is, even with 8PSK, the phase difference between adjacent symbol points on the IQ coordinate is the same as with QPSK.

[0032] This allows a known QPSK processing circuit with a simple configuration to be used for processing subsequent to the phase comparator 454. As a result, the tracking processor 45 can achieve highly accurate phase control and frequency control, similar to QPSK tracking processing.

[0033] Phase adjustment section 453 outputs the phase-adjusted I signal and the phase-adjusted Q signal to phase comparison section 454.

[0034] Phase comparison unit 454 compares the phase of the phase-adjusted I signal with the phase of the phase-adjusted Q signal. More specifically, phase comparison unit 454 calculates the phase difference between the phase-adjusted I signal and the phase-adjusted Q signal as the comparison result. Phase comparison unit 454 outputs the comparison result to integrator 455.

[0035] The integrating section 455 integrates (accumulates) the comparison result (the phase difference between the phase-adjusted I signal and the phase-adjusted Q signal) over a predetermined time period, and outputs the integrated value to the VCO 451.

[0036] As described above, VCO 451 adjusts the phase and frequency of the reference signal using the integrated value, and outputs the adjusted signal to phase rotation section 452 .

[0037] By repeating the above-described process, the phases and frequencies of the I and Q signals output from phase rotation section 452 are driven to high precision, thereby enabling convergence to a desired symbol point with high precision.

[0038] Fig. 5(A) shows the constellation before tracking according to the first embodiment, and Fig. 5(B) shows the constellation after tracking according to the first embodiment. Fig. 5(A) and Fig. 5(B) show the case where the frequency deviation is 30 [Hz].

[0039] As shown in FIGS. 5(A) and 5(B), by executing the processing of the tracking processing unit 45, it is possible to detect symbol points with high accuracy.

[0040] This allows the tracking processing unit 45 to demodulate the 8PSK signal more reliably. Also, the tracking processing unit 45 can demodulate the 8PSK signal with high accuracy.

[0041] (Demodulation method) Fig. 6 is a flowchart showing an example of a demodulation method according to an embodiment of the present invention. Note that, in the specific content of each process in the flowchart shown in Fig. 6, the parts explained in the explanation of the above configuration will not be explained below.

[0042] The tracking processing unit 45 performs phase rotation processing of the I-phase signal and the Q-phase signal of the received signal using the reference signals (I-phase reference signal and Q-phase reference signal) (S11). Note that, at the beginning of the phase adjustment processing, the reference signals (I-phase reference signal and Q-phase reference signal) are set to, for example, predetermined values ​​that do not cause frequency deviation.

[0043] The tracking processing unit 45 performs a phase adjustment process on the phases of the I signal and the Q signal after the rotation process (S12). The phase adjustment process is a process of doubling the phase, for example, using the double angle theorem.

[0044] The tracking processing unit 45 performs a phase comparison process between the phase-adjusted I signal and the phase-adjusted Q signal (S13). The phase comparison process is, for example, a process of calculating a phase difference.

[0045] The tracking processing unit 45 integrates the comparison result (S14). The integration of the comparison result is, for example, the integration (accumulation) of the phase difference.

[0046] The tracking processing unit 45 uses the integral value of the comparison result to perform phase adjustment and frequency adjustment of the reference signal (S15).

[0047] Thereafter, the tracking processing unit 45 repeatedly executes the processes from step S11 to step S15.

[0048] [Second embodiment] A demodulation technique according to a second embodiment of the present invention will be described with reference to the drawing. Fig. 7 is a functional block diagram of a tracking processing unit according to the second embodiment of the present invention.

[0049] The demodulation technique according to the second embodiment differs from the demodulation technique according to the first embodiment in that it includes a tracking processing unit 45A. Other details of the demodulation technique according to the second embodiment are the same as those of the demodulation technique according to the first embodiment, and therefore, a description of the same parts will be omitted.

[0050] The tracking processing unit 45A differs from the tracking processing unit 45 according to the first embodiment in that it includes a gain adjustment unit 456. Other configurations of the tracking processing unit 45A are the same as those of the tracking processing unit 45, and a description of similar parts will be omitted.

[0051] The comparison result is input to gain adjustment section 456 from phase comparison section 454. Gain adjustment section 456 adjusts the gain of the comparison result and outputs it to integrating section 455. Integrating section 455 integrates the gain-adjusted comparison result.

[0052] In this configuration, the tracking processing unit 45A can detect symbol points with high accuracy. Furthermore, the gain adjustment unit 456 performs gain adjustment, so that the comparison result (phase difference) is corrected to a value appropriate for tracking. This allows the tracking processing unit 45A to detect symbol points more reliably and with even higher accuracy.

[0053] [Third embodiment] A demodulation technique according to a third embodiment of the present invention will be described with reference to the drawing. Fig. 8 is a functional block diagram of a tracking processing unit according to the third embodiment of the present invention.

[0054] The demodulation technique according to the third embodiment differs from the demodulation technique according to the second embodiment in that it includes a tracking processing unit 45B. Other details of the demodulation technique according to the third embodiment are the same as those of the demodulation technique according to the third embodiment, and therefore, a description of the same parts will be omitted.

[0055] Tracking processing unit 45B differs from tracking processing unit 45A according to the second embodiment in that it includes adjustment amount control unit 457. Other configurations of tracking processing unit 45B are the same as those of tracking processing unit 45A, and a description of similar parts will be omitted.

[0056] Adjustment amount control unit 457 sets the amount of phase adjustment for phase adjustment unit 453. More specifically, adjustment amount control unit 457 sets, for example, the number of times to repeat phase adjustment using the double angle theorem. For example, if the received signal is 8PSK, adjustment amount control unit 457 sets phase adjustment unit 453 to perform phase adjustment using the double angle theorem once. If the received signal is 16PSK, adjustment amount control unit 457 sets phase adjustment unit 453 to perform phase adjustment using the double angle theorem twice. If the received signal is 32PSK, adjustment amount control unit 457 sets phase adjustment unit 453 to perform phase adjustment using the double angle theorem three times.

[0057] The phase adjustment unit 453 performs the phase adjustment according to the number of times set by the adjustment amount control unit 457 .

[0058] In this configuration, the tracking processor 45B can detect symbol points with high accuracy. Furthermore, by using this configuration and processing, the tracking processor 45B can detect symbol points with high accuracy not only of 8PSK but also of other multi-level PSK signals such as 16PSK and 32PSK.

[0059] Fig. 9(A) shows the constellation before tracking for the 16PSK signal according to the third embodiment, and Fig. 9(B) shows the constellation after tracking for the 16PSK signal according to the third embodiment. Fig. 9(A) and Fig. 9(B) show the case where the frequency deviation is 30 [Hz].

[0060] As shown in FIGS. 9A and 9B, by executing the processing of the tracking processing unit 45B, the symbol points can be detected with high accuracy.

[0061] Fig. 10(A) shows the constellation before tracking for the 32PSK signal according to the third embodiment, and Fig. 10(B) shows the constellation after tracking for the 32PSK signal according to the third embodiment. Fig. 10(A) and Fig. 10(B) show the case where the frequency deviation is 30 [Hz].

[0062] As shown in FIGS. 10(A) and 10(B), by executing the processing of the tracking processing unit 45B, it is possible to detect symbol points with high accuracy.

[0063] It should be noted that adjustment amount control section 457 may not perform phase adjustment by phase adjustment section 453, that is, may set the number of phase adjustments to 0, thereby enabling demodulation of QPSK signals.

[0064] This allows the tracking processor 45B to demodulate a plurality of types of multi-level PSK signals more reliably.Furthermore, the tracking processor 45B can demodulate a plurality of types of multi-level PSK signals with high accuracy. [Explanation of symbols]

[0065] 10: Automatic Identification System 20: Antenna 30: Down converter 41: Coarse frequency control section 42: Symbol timing detector 43: Down converter 44: Phase control section 45, 45A, 45B: Tracking processing section 51: Signal detection unit 52: Correlation section 60: Decryption unit 451:VCO 452: Phase rotation section 453: Phase adjustment unit 454: Phase comparison section 455: Integral part 456: Gain control unit 457: Adjustment amount control section

Claims

1. a phase rotation unit that rotates the phases of a pair of I and Q signals generated from a received multi-level PSK signal using a reference signal; a phase adjustment unit that adjusts the phases of the pair of I and Q signals output from the phase rotation unit by integrally multiplying the I and Q signals by the same multiplication factor; a phase comparator that compares the phase of the phase-adjusted I signal with the phase of the phase-adjusted Q signal in the pair; a reference signal generation unit that generates the reference signal using the phase comparison result; A demodulation device comprising:

2. 2. The demodulation device according to claim 1, an integration unit that integrates the phase comparison result, The reference signal generation unit generating the reference signal using an integral value of the phase comparison result; Demodulator.

3. 3. The demodulation device according to claim 2, a gain adjustment unit that adjusts the gain of the phase comparison result; The integration unit integrating the comparison result of the gain-adjusted phase; Demodulator.

4. 4. A demodulation device according to claim 1, The phase adjustment unit varies the integer multiple. Demodulator.

5. A demodulation device according to any one of claims 1 to 4, the phase comparator is a phase comparator for QPSK, The multi-level PSK signal is any one of 8PSK, 16PSK, and 32PSK signals. Demodulator.

6. The phases of a pair of I and Q signals generated from a received multi-level PSK signal are rotated using a reference signal; phase-rotated pair of I signal and Q signal are phase-adjusted by integrally multiplying the I signal and the Q signal by the same multiplication factor; comparing the phase of the phase-adjusted I signal with the phase of the phase-adjusted Q signal in the pair; generating the reference signal using the phase comparison result; Demodulation method.

7. The demodulation method according to claim 6, comprising: Integrating the phase comparison result; generating the reference signal using an integral value of the phase comparison result; Demodulation method.

8. The demodulation method according to claim 7, comprising: performing gain adjustment on the phase comparison result; integrating the comparison result of the gain-adjusted phase; Demodulation method.

9. A demodulation method according to claim 6, further comprising: Making the integer multiple variable; Demodulation method.

10. A demodulation method according to any one of claims 6 to 9, comprising: the phase comparison is for QPSK; The multi-level PSK signal is any one of 8PSK, 16PSK, and 32PSK signals. Demodulation method.

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