JPS6024621B2 - Pseudo pull-in detection method for carrier wave regeneration circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulation device that detects a multi-phase multi-level modulated signal using two mutually orthogonal reference carrier waves to reproduce a data signal in a wireless communication system or a waveguide communication system.

In particular, it relates to a pseudo pull-in detection method for a reference carrier regeneration circuit connected to a demodulator. BACKGROUND ART In an information transmission system using a multi-phase multi-level signal, a known demodulation system is one in which a received signal is synchronously detected using two orthogonal reference carrier waves and a data signal is regenerated from each detected signal. For example, as shown in the signal vector diagram in Figure 1, 16
For a multi-phase, multi-value modulated signal in which vectors are arranged in a lattice pattern, the signal is synchronously detected using a reference carrier wave having phases corresponding to the x-axis and y-axis in the figure. Here the first
The conventional demodulation method will be explained using the modulated signal shown in the figure as an example.
State what drawbacks there are.

FIG. 2 shows a circuit diagram of a conventional demodulator. In the figure, 1 is an input terminal for modulated waves, 2 to 5 are output terminals for reproduced data signals, 6 and 7 are phase detectors, 8 is a data signal regeneration circuit, 9 is a reference carrier wave regeneration circuit, and 10 is a scale/2 It is a phase shifter. The modulated wave 101 is input to phase detectors 6 and 7, and is synchronously detected by orthogonal reference carrier waves 102 and 103, respectively. The phase detection signals 104 and 105 are input to a data signal reproducing circuit 8, where they are each encoded into a 2-bit binary code and output as data signals 106-109. The reference carrier regeneration circuit 9 is a phase synchronization circuit having a phase comparison characteristic of 2 m/4 period, and as is well known, various systems have been put into practical use. The example in this figure shows a configuration using an inverse modulation method or a remodulation method, and the branched input modulated wave 101 and reproduction data signals 106 and 108 are inputted to reproduce the reference carrier wave 106 and 108, respectively. This is the output obtained by determining the magnetic properties of two detected signals. Regarding the specific configuration of this conventional circuit, see the following documents [1] and [2].
], so detailed descriptions are omitted here.

The description in this specification can be understood by recognizing that this circuit 9 has a phase comparison characteristic of 2m/4 period. [1] Koyariyama et al. “Transmitter/receiver for 2-eaves-40mM system” Telecommunications Research Institute Research and Application Report No. 24 No. 1 (1975) p.
p. 2193-2195 [2] Ishio et al. “A method of multi-phase multi-value carrier digital communication” Institute of Electronics and Communication Engineers communication system research group material CS74-158, 1973 Wang January Added a 4-phase Ou K signal to this reference wave regeneration circuit 9. 2 if
It is well known that a mirror-tooth phase comparison characteristic with m/4 period can be obtained, but when the multi-phase multi-level modulation signal shown in Fig. 1 is added, this input signal has four types of phases or amplitudes. Since it can be regarded as a combination of different four-phase PSK waves, it no longer exhibits an accurate mirror-tooth phase comparison characteristic, resulting in a characteristic as shown in FIG. 3.

In FIG. 3, the horizontal axis is the phase difference between the reference carrier wave and the input modulated wave, and is indicated by e as a quantity measured with reference to the x-axis and y-axis in FIG. 1. The vertical axis is an amount indicating the amplitude of a control signal applied to a voltage controlled oscillator (hereinafter abbreviated as VCO) inside the reference carrier regeneration circuit, and is indicated by . As is well known in the theory of phase-locked loops, V
Assuming that there is no frequency difference between the CO and the input signal, the CO will come to a standstill and be in a retracted state at the point where it crosses the machine axis in FIG. In other words, as can be seen from the characteristics in Figure 3, in this loop -45
There are three retraction states in the range of 0<e×450, one being 8=0 and the other being e...±240. Now, since the purpose of this device is to pull in e=0, the other two pull-in points become pseudo pull-in points. If the loop is pulled into these two pull-in points, it becomes impossible to reproduce the data signal.
This can be understood by rotating the axis and y-axis by 24 degrees. The object of the present invention is to improve this and to provide a method for realizing a loop free of pseudo-pulling phenomena and controlling a circuit that is always in a normal pulling state.

That is, the present invention provides a detection circuit that reliably determines whether the phase-locked loop of the reference carrier regeneration circuit is in a normal pull-in state or a pseudo pull-in state, and provides a sweep signal to the control terminal of the VCO using the output of the detection circuit. It is possible to configure the device so that it does not stand still in a pseudo-retracted state. FIG. 4 shows a configuration diagram of an apparatus according to an embodiment of the present invention.

This circuit corresponds to the conventional device described above and is designated by the same reference numeral. The invention is characterized by a control circuit for applying a control voltage to the voltage controlled oscillator VCO, which is a part of the reference carrier regeneration circuit 9, and the configuration of this part will be explained in more detail with reference to FIG. FIG. 5 is a circuit diagram of the main part of the embodiment of the present invention, including a pseudo-retraction state detection circuit and a sweep circuit.

In Figure 5, 11 is an AM detector, 12 is a threshold circuit, 13 is a signal comparator, 14 is a sign discrimination circuit, 15 is an integration circuit, 1
6 is a threshold circuit, and 17 is a sweep signal generator. The AM detector 11 receives the multiphase multilevel modulated wave 101 as an input and detects its amplitude modulation component. This detected signal is applied to a threshold value circuit 12 and is selected according to a predetermined threshold value. That is, if the detected signal exceeds the threshold value, a digital signal corresponding to "1" is transmitted, and if it does not exceed the threshold value, a digital signal corresponding to "0" is transmitted. In this embodiment, the threshold values are the signal vectors Soo, S, . , S2 and S pin are set to distinguish them from the others. In other words, if the signal vector group shown in Fig. 1 is layered into groups with the same amplitude, {SI}(
S's, SI・, S22, S33) {S ro} ko (S.

,,S. 3.S.

,S. There are three groups: 2, Sa, S Lake S30, S32) and {Sm}2 (S SI3, S31 of S2).

If the amplitude component of the vector S is expressed by ISI, the darkness value described above is set near {ISII+ISl}/2, and a detected signal higher than this level is determined to belong to {SI}.

On the other hand, the code discrimination circuit 14 inputs the output signals 106 to 109 of the data signal reproducing circuit 8 in FIG. Determine. In other words, the operation of encoding each of the two detected signals synchronously detected by one orthogonal reference carrier wave in Fig. 2 into IT creates a two-dimensional space constituted by the two reference carrier waves as shown in Fig. 6. This is equivalent to dividing into 16 sub-areas and determining which of these sub-areas the input signal vector is included in. In FIG. 5, each of the output signals 106 to 109 of the data signal reproducing circuit is a, . ，
a. 2, a2,, a22 (aij = +1 or -1, the detected signals 104, 105 are each s,, s2, and these quantized signals are [s,] [s2], then [s
,]={zo×a,. 〆〆×a,2}[s2]={zo×. The relationship is 10〆×a22}.

The codes written in each area in Fig. 6 correspond to aii, 11 corresponds to 1, and 11 corresponds to 0 (a, ., aa, a, 2, a22).
), and shows the correspondence between the area to which the signal vector belongs and the output code string of the data signal reproducing circuit. The code discrimination circuit 1 4 is a code string (
0000), (0101), (1111) or (10
10) When any of the code strings ``1'' and other code strings are input, a digital signal corresponding to ``0'' is generated. The signal comparator 13 includes a function value circuit 12 and a sign discrimination circuit 1.
4 is input, and when the two match, it outputs a signal corresponding to "1" and "0" when they do not match. That is, the signal comparison circuit 13 is equivalent to a normal AND circuit. The output of the signal comparison circuit 13 is averaged by an integrating circuit 15, and a threshold value circuit 16 determines whether or not it exceeds a certain threshold value, thereby determining whether or not the parent is in a positive pull-in state. If it is determined that the normal pull-in state is not present, the sweep signal generation circuit is activated to generate sweep signals 1 to 10. This sweep signal is applied to the control terminal of the VCO. When determining the normal retraction state,
Controls the sweep signal generation circuit to stop striping. The signal vector group {SI} is the code string (00
00), (0101), (1111) or (1010
), but in the pseudo-retraction state, it is encoded as (0001), (0100), (0111), (110
1), . . . , etc., so in the former case the two inputs of the signal comparator 13 match, but in the latter case they do not match. Based on this principle, the above-described synchronous pull-in state determination can be performed reliably. On the other hand, the input modulated wave contains noise in the communication system, which may cause the above-mentioned vector amplitude discrimination or data signal reproduction operation to malfunction. For this purpose, the output of the signal comparator 13 is averaged for a certain period of time by an integrating circuit 15, and then a threshold circuit 16 finally determines the synchronization state. This operation requires a certain amount of time for the loop pull-in process, and by the time the loop pull-in is completed, the phase difference between the input modulated wave and the VCO output sometimes fluctuates, so it is necessary to determine the normal pull-in state. This is also required because a certain amount of observation time is required. In the above embodiment, the vectors selected by the selection means are those with maximum amplitudes Soo, S, . , S22, and S33, and the code groups that the selected vector can take during regular pull-in are (0000), (0101), and (1111) in FIG.
, (1010), the above vectors Soo,S, . , S22, the demodulated signal sequence of the input modulated wave signal with S illusion is (0000), (010
1), (1111), and (1010), but since the phase of the reference carrier wave is rotated during pseudo pull-in, the demodulated signal sequence is different from this.

Therefore, by sorting the input modulated wave signal according to the amplitude of its vector, performing the above-described determination on the demodulated signal sequence, and comparing these with each other, it is possible to compare whether the input modulation wave signal is a regular pull-in or a pseudo pull-in. In the above embodiment, the vector with the largest amplitude is selected, but the present invention can be similarly implemented by selecting the vector with the second largest amplitude.

As is clear from the above description, according to the present invention, in a reference carrier regeneration circuit that regenerates a reference carrier wave from a multi-phase multilevel modulated wave, a vector group having a specific amplitude among a signal vector group, and a vector group regenerated from them. To make it possible to determine the retraction state of a loop and control the loop so that it always remains stationary in a normal retraction state by utilizing the fact that the correlation between the data signal code string and the data signal code string changes depending on the retraction state. I can do it.

This allows extremely reliable carrier wave recovery. Note that the means for detecting the amplitude of the signal vector group is not limited to the present embodiment; for example, the means for detecting the amplitude of the signal vector group is
104), s2 (105) to perform the calculation of NoSuteijuSkoto.

Further, as described above, the specific configuration of the reference carrier regeneration circuit does not limit the scope of the present invention, and it may be any circuit that has a phase comparison characteristic of 2 phases/4 cycles with respect to an unmodulated wave. Furthermore, although the above explanation has been made for a signal in which single-phase signal vectors are arranged in a grid pattern as shown in FIG. 1, the present invention can be implemented in the same way for other multi-phase multi-billion modulated waves. I can do it.

[Brief explanation of drawings]

FIG. 1 is a vector diagram of a multiphase multilevel modulation signal. FIG. 2 is a circuit configuration diagram showing a conventional demodulation circuit, and FIG. 3 is a diagram showing an example of carrier recovery phase-locked loop phase comparison characteristics of the demodulation circuit shown in FIG. 2. FIG. 4 is a configuration diagram of an embodiment of the present invention. FIG. 5 is a circuit configuration diagram of the main part. FIG. 6 is a signal space diagram showing the relationship between a reference carrier wave and a reproduced data signal. 1...
...Modulated wave signal terminal, 2 to 5...Regenerated data signal output terminal, 6,7...Phase detector, 8...
Data signal regeneration circuit, 9...Reference carrier wave regeneration circuit,
1 0...Medium/2 phase shifter, 1 1...AM detector, 12
... Dark value circuit, 13 ... Signal comparator,
14...Sign discrimination circuit, 15...Integrator circuit, 16...Block value circuit, 17...Sweep signal generator. Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, new figure.

Claims (1)

[Claims] 1. Contains means for performing phase detection on an input modulated wave signal subjected to polyphase multi-value modulation using two reference carrier waves whose phases are orthogonal to the carrier wave of the signal, and a data reproduction output as the output of the means. In the reference carrier regeneration circuit of the demodulation circuit for obtaining a reference carrier wave, a means for detecting the amplitude of the vector of the input modulated wave signal, and a means for selecting the vector by sorting the amplitude detected by the means according to a certain reference value. amplitude selection means; and code determination means that inputs the data reproduction output and determines whether the data reproduction output matches any of the code groups that the vector selected by the selection means can take during normal pull-in. and,
a comparison means for inputting the output of the sign discrimination means and the output of the amplitude selection means and detecting a match between the two outputs;
A pseudo pull-in detection method for a carrier wave regeneration circuit, comprising: an integrating means for integrating the output of the comparing means; and a threshold circuit for determining whether the output of the integrating means exceeds a predetermined threshold.