JPH04142847A - Carrier recovery circuit - Google Patents

Abstract

PURPOSE:To eliminate a steady-state phase error by obtaining a complex correlation between a complex signal subject to phase rotation and a reference signal corresponding to a complex signal waveform, detecting a phase from a peak level for a prescribed period and controlling a VCO circuit based on the phase. CONSTITUTION:A received modulation wave is fed to a phase rotation circuit 21 as a complex signal and subject to phase rotation by complex multiplication with an output of a VCO(voltage controlled oscillator) circuit 22, the result is fed to a complex correlation detection circuit 23, which generates a reference signal corresponding to the modulation signal waveform in its inside and outputs a complex correlation of both the signals. The complex correlation is fed to a peak detection circuit 24, which detects a complex peak for each symbol, a phase detection circuit 25 extracts a phase from the complex peak and uses a loop filter 26 to eliminate the noise component and the result is converted into a voltage control signal, which controls the VCO circuit 22. Thus, a steady- state phase error is eliminated regardless of the modulation system and an excellent carrier is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to a carrier regeneration circuit used for coherent detection by regenerating a carrier in a digital phase modulated wave receiver.

(Prior art) In a conventional receiver that receives digital phase modulated waves, a carrier regeneration circuit as shown in Fig. 4 is used to regenerate the gear carrier required for coherent detection from the received modulated wave. ing. That is, in the carrier regeneration circuit of FIG. 4, the received modulated wave is supplied to the phase rotation circuit 1j, where it undergoes phase rotation by complex multiplication with the output of the VCO (voltage controlled oscillation) circuit 12 as a complex signal, and the phase The signal is supplied to the detection circuit I3. This phase detection circuit 13 extracts the phase amount of the signal obtained by the above-mentioned complex multiplication. This phase amount corresponds to the phase difference between the output of the VCO circuit I2 and the received carrier. Therefore, the phase amount obtained by the phase detection circuit 13 is integrated by the loop filter 14 and converted into a voltage signal.
By controlling the VCO circuit 12 with this voltage signal,
It reproduces the carrier that follows the received modulated wave.

However, in the carrier regeneration circuit having the above configuration, a steady phase error occurs in the regenerated carrier, especially in the case of an offset QPSK modulated wave, resulting in deterioration of error rate characteristics. As a means to avoid such inconvenience,
It is conceivable that only the convergent part of the modulated waveform, that is, the phase error at the so-called center point of the eye pattern, is input to the carrier recovery loop. However, this requires that clock synchronization be established first, which is disadvantageous in that it takes a long time to establish synchronization for the entire receiver. Furthermore, there is a disadvantage that the application is limited to so-called cosine roll-off type modulation waveforms that have a convergence point as a modulation waveform.

(Problem to be solved by the invention) As described above, in the conventional carrier regeneration circuit, a steady phase error occurs in the regenerated carrier, and in order to improve this, it is required to establish clock synchronization, and furthermore, The method will be specified.

This invention was made to solve the above problem. Digital phase modulation eliminates the need to establish clock synchronization and eliminates steady phase errors regardless of the modulation method. It is an object of the present invention to provide a carrier regeneration circuit that can regenerate a good carrier without removing the carrier.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, a carrier regeneration circuit according to the present invention inputs a received modulated wave as a complex signal and also inputs a frequency signal. a phase rotation circuit that rotates the phase of the complex signal based on the input of the complex signal output from the phase rotation circuit, generates a reference signal corresponding to the complex signal waveform internally, and generates a complex correlation value with the complex signal. A complex peak detection circuit that detects the complex peak value of the output of this complex correlation detection circuit at fixed intervals, and extracts the phase amount of the complex peak value from the output of this peak detection circuit. and includes a loop filter that removes a noise component and converts it into a voltage control signal, and a voltage controlled oscillation circuit that generates a frequency signal to the phase rotation circuit in accordance with the voltage control signal obtained by the loop filter. It consists of

(Operation) In the carrier regeneration circuit having the above configuration, the complex correlation value of the phase-rotated complex signal with the reference signal corresponding to the complex signal waveform is obtained, the phase amount is detected from the peak value in a certain period, and the phase amount is Since the voltage controlled oscillator circuit is controlled based on It is possible to improve the deterioration of error rate characteristics caused by such nonlinear distortion.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 3 shows its overall configuration. The received modulated wave is supplied as a complex signal to the phase rotation circuit 21, and the VCO circuit 21 receives the modulated wave as a complex signal.
It undergoes phase rotation by complex multiplication with the output of 2, and is further sent to the complex correlation detection circuit 23.

This complex correlation detection circuit 23 internally generates a reference signal corresponding to the modulation signal waveform and outputs a complex correlation value of both signals. This complex correlation value shows a high absolute value for each symbol.

This complex correlation value is supplied to a peak detection circuit 2.4.

This peak detection circuit 24 detects the above-mentioned complex peak value for each symbol. The phase component of the complex peak value detected here indicates the phase difference between the output of the Vco circuit 22 and the received carrier. Therefore, the phase detection circuit 25 extracts the phase amount from this phase difference, that is, the complex peak value, and the loop filter 26 removes the miscellaneous components and converts it into a voltage control signal.
control.

In other words, in conventional carrier regeneration circuits, all instantaneous phase determination values are taken in and averaged by a loop filter, so depending on the type of band limiting, it may not be possible to obtain the correct phase error. The circuit detects the phase error over a period of one symbol (or several symbols) by correlation detection, so
The correct phase error can be obtained for any type of bandlimiting.

Therefore, since the carrier regeneration circuit based on the 1-1 configuration described above can obtain a correct phase error, a steady error will not appear in the reproduced carrier phase, and deterioration of the bit error rate can be prevented.Furthermore, the cycle slip characteristics can be improved. Furthermore, by adjusting the period of complex correlation detection, the initial phase pull-in characteristic can be changed, and the degree of freedom in design can be improved.

Taking the case of offset QPSK modulation method as an example,
This will be explained in more detail with reference to FIGS. 1 and 2.

In other words, offset (hereinafter O
There are many cases where QPSK modulation is adopted, and this is due to its advantages such as good frequency usage efficiency and less spectrum deterioration when passing through a class C amplifier with good power usage efficiency. . On the other hand, the OPSK modulation method has the disadvantage that the phase at the code point is not constant, and a reproduction phase error is likely to occur in a conventional carrier reproduction circuit.

In order to improve this, a method has been considered in which cosine roll-off filters are placed on both the transmitter and receiver. In other words, regarding the phase characteristics of OQ P S r<wave, assuming a cosine roll-off filter system, Q P S
In K, the phase at the time of sign determination is only 4 points every 90 degrees. From this, the ease of carrier phase detection can be understood, especially when sampling at a sign determination point. On the other hand, in the case of the 0PQSK wave, the only thing guaranteed at the time of sign determination is that one of the two orthogonal components will be a constant value, and the signal point will exist on the line "2".

However, in the above method of arranging filters, 0P
When an SK wave is transmitted through a class C amplifier, code amount interference occurs, leading to deterioration of the eye pattern, that is, deterioration of error rate characteristics. If the average phase error value when a steady phase rotation is applied to the 0PQSK wave is plotted, it will look like pattern A in FIG. 2.

This generates data of 4 samples per symbol on the computer, and the phase stability point of all samples (±45°, 1
35°) (instantaneous phase determination value) is calculated and averaged. It can be seen from the figure that unstable characteristics are exhibited near the amount of phase rotation of 0.

Therefore, the present invention uses the circuit configuration shown in FIG. 3 and configures the complex correlation circuit 23 as shown in FIG. 1, for example, to improve the phase comparison characteristics.

In Figure 1, 231 is 0Q in 8-bit serial format.
A complex analog shift register for sequentially outputting PSK wave input in 8-bit parallel, 232 is #1 (00,
00,00,00) to #256(1], 11.,
1.1. , 11. ), 233 is a storage device that stores the complex locus reference pattern of
This is a correlation detection unit that takes the correlation with all patterns #1 to #256 for PQSK input.

That is, the number of complex trajectory patterns of 0QPSK is finite, and the number is determined by the roll-off coefficient.

Therefore, in this correlation detection circuit 23, the 8-bit 0QPSK
256 complex locus reference patterns #1 for wave input
#256 is prepared, all of them are correlated with the 0QPSK wave input, and the phase of the correlation value with the maximum absolute value, that is, the complex correlation - F average, is output as the detected phase. The processing results are shown in Fig. 2 (pattern B in the figure).
). [P] O As is clear from comparing Turns A and B, an improvement in the phase comparison characteristics is recognized.

Therefore, according to the configuration shown in FIG. 1, it is possible to improve errors that were large near 0 in conventional instantaneous phase determination, eliminate steady phase errors, and improve the deterioration of error rate characteristics caused by nonlinear distortion. I can do it.

It should be noted that although the explanation has been made using the 0QPSK wave input as an example, it goes without saying that the same implementation is possible even with other digital phase modulation methods.

[Effects of the Invention] As described above, according to the present invention, if digital phase modulation is used, it is not necessary to establish clock synchronization, and regardless of the modulation method, steady phase errors can be eliminated, and a good carrier can be obtained. It is possible to provide a carrier regeneration circuit that can regenerate.

[Brief explanation of drawings]

1 to 3 show an embodiment of the carrier regeneration circuit according to the present invention, FIG. 1 is a block circuit diagram showing a specific configuration of the correlation detection circuit which is a feature of the invention, and FIG. The figure is a characteristic diagram showing a comparison of the phase characteristics of a conventional circuit and a circuit according to the present invention, Fig. 3 is a block circuit diagram showing the overall configuration of the carrier regeneration circuit according to the present invention, and Fig. 4 is a conventional carrier regeneration circuit. FIG. 2 is a block circuit diagram showing the configuration of a circuit. 11, 21-...phase rotation circuit, 12.22-=V
C0 circuit, 13, 25...phase detection circuit, 14.28
... Loop filter, 23 ... Complex (■Quantity detection circuit, 231 ... Complex analog shift register, 232 ・
-Storage device, 233...Correlation detection unit, #1~
#256...Complex locus reference pattern, 24...Peak detection circuit.

Claims (3)

[Claims] (1) A phase rotation circuit that inputs a received modulated wave as a complex signal and a frequency signal, rotates the phase of the complex signal based on the frequency signal, and inputs the complex signal output from this phase rotation circuit. a complex correlation detection circuit that internally generates a reference signal corresponding to a complex signal waveform and outputs a complex correlation value with the complex signal, and detects a complex peak value of the output of the complex correlation detection circuit every fixed period. A peak detection circuit, a loop filter that extracts the phase amount of the complex peak value from the output of this peak detection circuit, removes noise components, and converts it into a voltage control signal; and a voltage controlled oscillation circuit that generates a frequency signal to the phase rotation circuit. (2) The complex correlation detection circuit includes a complex analog shift register that converts an input complex signal from serial to parallel;
A storage device that stores complex locus reference patterns corresponding to the number of symbols of the input complex signal is correlated with all patterns stored in the storage device regarding the parallel complex input from the shift register, and a complex correlation average is calculated. 2. The carrier regeneration circuit according to claim 1, further comprising a correlation detection section that outputs a detected phase. (3) The received modulated wave has an amplitude limited offset Q
2. The carrier regeneration circuit according to claim 1, wherein the carrier regeneration circuit is a PSK modulated wave.