JPH0671278B2 - Demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention is directed to Quadrature Amplitude Modulation.
Modulation: hereinafter referred to as QAM), relates to a demodulator of a digital wireless communication system, and in particular, an automatic DC level (DC offset) for two demodulated signals that are orthogonal to each other and are obtained by synchronously detecting a received signal. ) A demodulator having improved control means.

(Prior Art) Conventionally, in a digital radio communication system, amplitude and phase demodulation (Amplitude and Ph
ase Shift Keying (hereinafter referred to as APSK) system has been proposed, and multilevel QAM system is generally used as a practical digital wireless communication system among APSK systems.

The sinusoidal carrier in the multi-valued QAM system changes its amplitude and phase in proportion to two baseband signals that are independent of each other, and is a polar coordinate representation of the sinusoidal carrier in a signal space diagram (hereinafter referred to as a signal point arrangement diagram). The arrangement of the respective signal points in is a rectangular arrangement.

Fig. 4 shows the constellation diagram of the 256-value QAM system. The 256 signal points are the intersections of 16 columns related to the horizontal axis (hereinafter, I axis) and 16 columns related to the vertical axis (hereinafter, Q axis), that is,
It is arranged at 16 × 16 grid points. In this specification, the QAM system modulated to have the signal point constellation as shown in FIG. 4 is referred to as a Conventional QAM (hereinafter, referred to as C-QAM) system.

In recent years, there is a case where a multi-valued QAM system in which the code error rate of a signal is improved by modulating the signal point arrangement as shown in FIG. 3 to the C-QAM system. In this specification, this QAM method is referred to as Stepped Squa
It is called a re QAM (hereinafter referred to as SS-QAM) method.

The signal point arrangement of the 256-value SS-QAM system is different from the signal point arrangement of the 256-value C-QAM system as follows. That is,
Of the 256-value C-QAM system signal point constellation shown in FIG. 4, six signal points disposed near the first corner and a second
A total of 24 signal points (six signal points arranged near the corner, six signal points arranged near the third corner, and six signal points arranged near the fourth corner ( That is, the fourth
The signal points with black circles in the figure) are the 256-value SS-QAM in Figure 3.
As indicated by the black circles in the signal point arrangement diagram of the method, the I-axis 0'column outside the I-axis 0 column,
It is arranged on the I axis 15 'row outside the I15 row, the Q axis 0'row outside the Q axis 0 row, and the Q axis 15' row outside the Q15 row. , 6 signal points are arranged in each column.

A conventional demodulator in a digital radio signal system using a 256-value SS-QAM system that is modulated to have a signal point arrangement as shown in FIG. SS-QA shown in Fig. 3
The DC level control signal is converted from the data signal and the error signal after once converting the M system signal point constellation to the C-QAM system signal point constellation shown in FIG. 4 and converting it to the C-QAM system signal point constellation. I was getting. Hereinafter, a conventional technique will be described with reference to the drawings.

FIG. 5 is a block diagram of a conventional demodulator, where 1 is a QAM demodulator, 2, 2'is a DC level controller, 3 and 3'is an A / D converter, 4,
4'is a signal point arrangement converter, 5,5 'is a control signal generator, 6 is an input terminal, 7,7', 8,8 'are output terminals, 9 is an I channel system, 10 is a Q channel system, 101 Is the received signal, 102 is I
Channel demodulation signal, 102 'is Q channel demodulation signal, 1
03 is the I channel first data signal, 103 'is the Q channel first data signal, 104 is the I channel second data signal, 104' is the Q channel second data signal, 105 is the I channel error signal, and 106 is the I channel DC. This is a level control signal. The received signal 101 from the input terminal 6 of the demodulator is Q
Input to the AM demodulator 1. The QAM demodulator 1 synchronously detects the received signal 101 and two demodulated signals having an orthogonal relationship with each other, that is, a bipolar I channel demodulated signal 102 and an orthogonal component signal which are in-phase component signals. (Q
and a bipolar Q channel demodulation signal 102 'which is a uadrature component signal.

The I channel demodulated signal 102 is input to the DC level controller 2 of the I channel system 9, and the Q channel demodulated signal 10 is input.
2'is input to the DC level controller 2'of the Q channel system 10. For subsequent operations, refer to I channel system 9
Since the operation of and the operation of the Q channel system 10 are similar,
The operation of the I channel system 9 will be described, and the operation of the Q channel system 10 will be omitted.

The DC level controller 2 controls the I channel DC level control signal so that the DC level of the input I channel demodulated signal 102 is matched with the center of the predetermined discrimination level of the A / D converter 3.
The DC level is automatically controlled based on 106. The analog signal output from the DC level controller 2 is input to the A / D converter 3, and the A / D converter 3 quantizes the amplitude of the input analog signal at predetermined intervals and indicates a predetermined amplitude level value. Convert to digital signal. If the DC level of the I-channel demodulated signal 102 is controlled by the DC level controller 2 so that the DC level of the I-channel demodulated signal 102 matches the center of a predetermined discrimination level of the A / D converter 3, the A / D converter 3 The output digital signal is a digital signal that optimally matches the amplitude of the I channel demodulated signal 102. The digital signal output from the A / D converter 3 and the digital signal output from the A / D converter 3'of the Q channel system 10 are input to the signal point arrangement converter 4.

The digital signal output from the A / D converter 3 that is input to the signal point arrangement converter 4 is a signal that indicates the amplitude level value of the I channel of the signals related to the 256 signal points in FIG.
The digital signal output from the D converter 3'is a signal indicating the amplitude level value of the Q channel of the signal relating to the 256 signal points in FIG. The signal point arrangement converter 4 is the A / D converter 3
Based on the digital signal of the output of A and the digital signal of the output of the A / D converter 3 ', the signal point arrangement of the SS-QAM system shown in FIG. 3 is changed to the signal point of the C-QAM system shown in FIG. Convert to placement.

If the signal point arrangement position of the SS-QAM system is represented by SS (I axis column number, Q axis column number) and the signal point arrangement position of the C-QAM system is represented by C (I axis column number, Q axis column number), for example, Convert as follows.

SS (15 ', 8) → C (15,13), SS (15', 9) → C (15,1)
4), SS (15 ', 10) → C (15,15), SS (10,15') → C
(14,14), SS (9,15 ') → C (14,15), SS (8,15')
→ C (13,15), SS (7,15 ') → C (2,15), SS (6,1)
5 ')-> C (1,15), SS (5,15')-> C (0,15), SS
(0 ′, 10) → C (1,14), SS (0,9 ′) → C (0,14),
SS (0 ', 8) → C (1,13), SS (0', 7) → C (0,
2), SS (0 ', 6) → C (0,1), SS (0', 5) → C (0,
0), SS (5,0 ′) → C (1,1), SS (6,0 ′) → C (1,
0), SS (7,0 ′) → C (2,0), SS (8,0 ′) → C (13,
0), SS (9,0 ′) → C (14,0), SS (10,0 ′) → C (1
5,0), SS (15 ', 5) → C (14,1), SS (15', 6) → C
(15,1), SS (15 ', 7) → C (15,2).

The signal point constellation converter 4 converts the signal constellation of the SS-QAM system into C
-I channel first data signal 103 which is a projection signal to the I axis after conversion to the signal point arrangement of the QAM system and which shows an amplitude level value of 16 and I channel first data signal 103 are C-QA
Whether or not the signal exists outside the M-system signal point constellation, that is, the I-axis 0'of the SS-QAM system signal point constellation
An I-channel second data signal 104 indicating a binary value indicating whether it is a signal of the I-th column or the I-axis 15'-th column, and an I-channel error signal 105 which is an error signal with respect to the I-channel first data signal are output. . The I channel error signal 105 is
It is a signal indicating two values quantized at about half the quantization level for each of the 16 values indicated by the I-channel first data signal 103, and each of the 16 values is divided into about two. One step below that, that is, the amplitude level of the I channel of each signal corresponding to each of the 16 values deviates to the negative side from the normal amplitude level defined for each signal, or to the positive side. It is an error signal indicating whether or not there is a deviation.
For example, the I-channel first data signal 103 of the 0-th column of the I-axis
On the other hand, when the I channel error signal 105 is at a low level, the I channel first data signal on the 0th column of the I axis
103 shows a state of being offset to the outside from the predetermined signal point arrangement position and displaced to the negative side from the normal amplitude level,
When the I-channel error signal 105 is at a high level, the I-channel first data signal 103 on the 0th row of the I-axis deviates inward from the predetermined signal point arrangement position and deviates to the plus side from the normal amplitude level. It shows the state of being closed.

The I channel first data signal 103 and the I channel error signal 105 output from the signal point arrangement converter 4 are input to the control signal generator 5. The control signal generator 5 determines the I-axis based on the I-channel first data signal 103 and the I-channel error signal 105.
A signal existing outside the predetermined signal point arrangement position of the 15th column, that is, a signal existing in the positive maximum level error region (I) shown in FIG. 4 is detected.

Further, a signal existing outside the predetermined signal point arrangement position on the 0th column of the I-axis, that is, a signal existing in the negative maximum level error region (I) shown in FIG. 4 is detected. The signal existing in the maximum positive level error region (I) is I axis 15
It is considered that the amplitude of the signal in the column is shifted to the plus side from the predetermined normal amplitude level, and the signal existing in the negative maximum level error region (I) is in the column 0 of the I-axis. It is considered that the amplitude of the signal is a signal deviated to the negative side from a predetermined normal amplitude level.

Therefore, the control signal generator 5 compares the number of signals in the positive maximum level error region (I) detected within a predetermined time with the number of signals in the negative maximum level error region (I), If the number of signals in the positive polarity maximum level error region (I) is larger than the number of signals in the negative polarity maximum level error region (I) by a predetermined value or more, control is performed to lower the DC level, and the negative polarity maximum level error region (I) is controlled. When the number of signals in (I) is larger than the number of signals in the positive maximum level error region (I) by a predetermined value or more, an I channel DC level control signal 106 for controlling to increase the DC level is generated to generate a DC level controller. Output to 2. By this I channel DC level control signal 106, the DC level controller 2 always controls the DC level of the output signal.
The DC level is automatically controlled so as to match the center of the predetermined discrimination level of the A / D converter 3.

By the above operation, the I channel first signal which is a digital signal optimally adapted to the amplitude of the I channel demodulated signal 102
The data signal 103 and the I-channel second data signal 104 are output from the output terminals 7 and 8 of the demodulator. In the Q channel system 10, the same operation as that of the I channel system 9 described above is performed, and the Q channel demodulated signal 10
A Q channel first data signal 103 'and a Q channel second data signal 104' which are digital signals optimally adapted to the amplitude of 2'are output from the output terminals 7'and 8'of the demodulator.

Incidentally, in this conventional example, the signal point arrangement positions SS (10,15 '), SS (0', 10), SS (5,0 ') and SS (15', 0) of the SS-QAM system are present. The four signals with the maximum level
C (14,14) when converted to the C-QAM signal constellation,
The signals are present in C (1,14), C (1,1 ') and C (14,1) and do not contribute to the generation of the DC level control signal because they are not the maximum level signals.

(Problems to be Solved by the Invention) However, the above-described conventional demodulator converts the SS-QAM system signal point constellation into the C-QAM system signal point constellation in order to obtain a DC level control signal. There must be. Therefore, a signal point arrangement conversion means that requires a signal of the Q channel system to process a signal of the I channel system and a signal of the I channel system to process a signal of the Q channel system is required. Is large and complicated.

Also, by converting the SS-QAM system signal point constellation to the C-QAM system signal point constellation, the signal has the maximum level in the SS-QAM system signal point constellation and is used to generate a DC level control signal. Some of the signals to be played are C
-There is a problem in that the signal level of the QAM system is not used to generate the DC level control signal because it does not become the maximum level signal, and the amount of information for generating the DC level control signal decreases.

In order to solve the above-mentioned problems of the conventional technique, the object of the present invention is not to have the signal point arrangement conversion means of the complicated circuit required by the conventional technique, and only the I-channel system signal is used for the I-channel first data signal. And I channel second data signal and I
I-channel system signal converting means for generating a channel error signal, and Q-channel system signal converting means for generating a Q-channel first data signal, a Q-channel second data signal, and a Q-channel system error signal only by the Q-channel system signal. It is to provide a demodulation device capable of performing automatic DC level control on a demodulation signal with a simple circuit configuration.

(Means for Solving Problems) The present invention has the following means configuration in order to achieve the above object. That is, the demodulator of the present invention is a multi-valued stepped square quadrature A
mplitude Modulation (SS-QAM) system is used as an input, and two demodulated signals that are synchronously detected and have a quadrature relationship, that is, an I-channel demodulated signal of the in-phase component signal and a Q of the quadrature component signal. QAM demodulation means for outputting a channel demodulation signal; I channel DC level control means for controlling the DC level of the I channel demodulation signal; Amplitude of the analog signal output from the I channel DC level control means to a predetermined quantization I-channel A / D conversion means for quantizing at a level and outputting a digital signal showing a predetermined amplitude level value; the digital signal output from the I-channel A / D conversion means is subjected to signal conversion processing, and SS-QAM system Except for the outermost signal point in the signal constellation of, simple rectangular quadrature amplitude modulation (Conven
(Traditional Quadrature Amplitude Modulation: C-QAM) signal point arrangement, there is a corresponding signal point. The amplitude level value of the I channel of the signal related to the SS-QAM signal point corresponds to the C-QAM signal point. Signal having the same amplitude level value as the I-channel amplitude level value of the signal relating to the above-mentioned signal and being arranged at the outermost side in the SS-QAM signal point arrangement and corresponding to the C-QAM signal point arrangement The amplitude level value of the I channel of the signal related to the signal point of the SS-QAM system where there is no point is C
I indicating an amplitude level value corresponding to the outermost signal point in the QAM signal point arrangement and having the same amplitude level value as that of the I channel of the signal relating to the corresponding C-QAM signal point Channel first data signal,
An I channel second data signal indicating whether or not the I channel first data signal is a signal relating to an outermost signal point in the SS-QAM system signal point arrangement;
The amplitude level of the I channel of each signal corresponding to each amplitude level value indicated by the I channel first data signal is shifted to the plus side from the normal amplitude level defined for each signal, or is minus. I channel signal conversion means for outputting an I channel error signal indicating whether the I channel error signal is in the state of being shifted to the side; and the I channel first data signal and the I channel error signal as input, A signal in which the amplitude level of the positive polarity maximum amplitude level is shifted to the plus side from the normal amplitude level is detected from the inside, and the amplitude level of the negative polarity maximum amplitude level signal is normal. Of the I-channel demodulated signal is detected based on the detection result. I-channel control signal generation for generating an I-channel DC level control signal for controlling a DC level so as to match the center of a predetermined discrimination level of the channel A / D conversion means and outputting it to the I-channel DC level control means Q channel DC level control means for controlling the DC level of the Q channel demodulated signal; Quantizing the amplitude of the analog signal output from the Q channel DC level control means with a predetermined quantization level, and a predetermined amplitude level Q channel A / D conversion means for outputting a digital signal indicating a value; the digital signal output from the Q channel A / D conversion means as an input, and the I channel first data signal and the I channel second data signal And the above I channel error signals respectively, and are related to the Q channel in the same manner as the contents of each signal. The contents signal Q-channel first data signal and the Q-channel second
Q-channel signal converting means for outputting a data signal and a Q-channel error signal; inputting the Q-channel first data signal and the Q-channel error signal and performing the same operation as the I-channel control signal generating means for the Q-channel signal converting means. The Q channel DC level control means is generated to generate a Q channel DC level control signal for controlling the DC level so that the DC level of the channel demodulation signal matches the center of a predetermined discrimination level of the channel A / D conversion means. And a I channel control signal generating means for outputting to the demodulator.

(Operation) The operation of the demodulating device having the above-mentioned means will be described below. The demodulator receives the signal which is modulated based on the multi-level SS-QAM system.

The received signal is also input to the QAM demodulating means, and the QAM demodulating means synchronously detects the received signal and outputs two demodulated signals having an orthogonal relationship with each other, that is, an I channel demodulated signal of the in-phase component signal and a Q channel demodulated signal of the quadrature component signal. Output.

The I channel demodulated signal is input to the I channel DC level control means, and the I channel DC level control means controls the DC level of the I channel demodulated signal. The analog signal whose DC level of the output of the I-channel DC level control means is controlled is input to the I-channel A / D conversion means, and the I-channel A / D conversion means quantizes the amplitude of the input analog signal by a predetermined quantization. It quantizes with a level and outputs a digital signal showing a predetermined amplitude level.

The output digital signal of the I channel A / D conversion means is input to the I channel signal conversion means, and the I channel signal conversion means performs signal conversion processing on the input digital signal and outputs the following three types of digital signals. That is, SS-QA
Amplitude level of the I channel of the signal relating to the SS-QAM system signal point where there is a corresponding signal point in the C-QAM system signal point layout, except for the outermost signal point in the M system signal point layout A value of the amplitude level whose value is the same as the amplitude level value of the I channel of the signal relating to the corresponding signal point of the C-QAM system is shown, and C- which is arranged at the outermost side in the SS-QAM system signal point arrangement SS-QA with no corresponding signal point in QAM system signal point constellation
The amplitude level value of the I channel of the signal relating to the M-system signal point is made to correspond to the outermost signal point arranged in the C-QAM system signal point arrangement, and is related to the corresponding C-QAM system signal point. An I-channel first data signal showing a side-level difference value that is the same as the amplitude level value of the I-channel of the signal, and a signal point at which the I-channel first data signal is arranged on the outermost side in the SS-QAM system signal point arrangement. The I-channel second data signal indicating whether or not the I-channel second data signal and the I-channel amplitude level of each signal corresponding to each I-level first data signal are determined for each signal. The I-channel error signal and three kinds of digital signals, which indicate whether the amplitude level is shifted to the plus side or the minus side from the normal amplitude level, are output. I of the output of the I channel signal conversion means
The channel first data signal and the I channel error signal are I
A state in which the I-channel control signal generating unit is input to the I-channel control signal generating unit and the amplitude level of the signal related to the maximum positive amplitude level of the I-channel first data signal is deviated to the plus side from the normal amplitude level. And a signal in which the amplitude level of the signal relating to the maximum negative polarity amplitude level is deviated to the negative side from the normal amplitude level.

Based on the detection result, it is determined whether the DC level of the output signal of the I-channel DC level control means is shifted to the plus side or the minus side, and the state is shifted to the plus side. In this case, the DC level is lowered, and in the case of a state of being shifted to the negative side, an I channel DC level control signal for controlling the DC level is generated and output to the I channel DC level control means.

The I-channel DC level control means automatically controls the DC level based on the I-channel DC level control signal so that the amplitude of the I-channel demodulation signal always matches the predetermined identification level of the I-channel A / D conversion means. To do. The Q channel demodulation signal output from the QAM demodulation means is input to the Q channel DC level control means, and the Q channel DC level control means controls the DC level of the Q channel demodulation signal, and the DC level is controlled. To Q channel A / D conversion means. Q channel A
The / D conversion means quantizes the amplitude of the input analog signal with a predetermined quantization level and outputs a digital signal showing a predetermined amplitude level value to the Q channel signal conversion means. The Q-channel signal conversion means performs the same operation as the I-channel signal conversion means to perform signal conversion processing on the digital signal output from the Q-channel A / D conversion means, and outputs the Q-channel first data signal and the Q-channel second data signal. And 3 kinds of digital signals of Q channel error signal are output. The Q channel first data signal and the Q channel error signal are input to the Q channel control signal generating means, and the Q channel control signal generating means performs the same operation as the I channel control signal generating means to generate the Q channel DC level control signal. Then Q
Output to the channel DC level control means.

The Q-channel DC level control means automatically controls the DC level based on the Q-channel DC level control signal so that the amplitude of the Q-channel demodulated signal always matches the predetermined identification level of the Q-channel A / D conversion means. To do. With the above operation, the I channel first data signal, the I channel second data signal, the Q channel first data signal, and the Q channel second data signal are output from the demodulator.

In order to output the same signal as in the C-QAM system, the I-channel first data, the I-channel second data, the Q-channel first data, and the Q-channel which are the output signals of the demodulator are provided at the subsequent stage of the demodulator. A logic conversion circuit for performing logic conversion from SS-QAM to C-QAM described on page 11 of the specification using the second data (prior art) is required. This logic conversion circuit can be easily realized by a ROM (Read Only Memory) or the like.

(Example) Next, the Example of this invention is described with reference to drawings.

FIG. 1 is a block diagram of a demodulator according to an embodiment of the present invention.
11, 11 'is a signal converter, 12, 12' is a signal conversion processing circuit, 1
3, 13 'is a selection circuit, 107 is an I channel first error signal, 1
08 is an I channel second error signal.

The signal converter 11 is composed of a signal conversion processing circuit 12 and a selection circuit 13, and the signal converter 11 'is composed of a signal conversion processing circuit 12' and a selection circuit 13 '. The components and signals to which other numbers are assigned are the same as the components and signals to which the same numbers are assigned in the configuration diagram of the conventional demodulation device in FIG. Details of the components and signals of are omitted.

2 shows the output signal of the A / D converter 3, the I-channel first data signal 103, the I-channel second data signal 104, and the I-channel first error signal 10 in the embodiment of the present invention.
7 is a diagram showing the relationship between the I channel second error signal 108 and the I channel error signal 105. FIG.

In Fig. 1, the SS input to the input terminal 6 of the demodulator
-Received signal 101 modulated based on the QAM method is QAM
It is input to the demodulator 1 and is synchronously detected, and an I channel demodulation signal 102 and a Q channel demodulation signal 102 'which are orthogonal to each other are output. The I channel demodulated signal 102 is input to the DC level controller 2 of the I channel system 9,
The Q channel demodulated signal 102 'is input to the DC level controller 2'of the Q channel system 10. I channel system 9
The operation of the I-channel system 10 is the same as that of the Q-channel system 10, and the operation of the I-channel system 9 will be described below, and the description of the operation of the Q-channel system 10 will be omitted.

The DC level controller 2 receives the input I signal based on the I channel DC level control signal 106 from the control signal generator 5.
It controls the DC level of the channel demodulation signal 102 and outputs an analog signal to the A / D converter 3. The A / D converter 3 quantizes the auxiliary signal of the input analog signal with a predetermined quantization level, converts it into a digital signal showing a predetermined amplitude level value, and outputs it to the signal converter 11. I channel demodulation signal 102
When the DC level of the A / D converter 3 is controlled by the DC level controller 2 so as to match the center of the predetermined discrimination level of the A / D converter 3, the digital signal output from the A / D converter 3 is It is a digital signal that optimally matches the amplitude of the I channel demodulated signal 102.

The digital signal output from the A / D converter 3 that is input to the signal converter 11 is subjected to signal conversion processing by the signal conversion processing circuit 12, which is a component of the signal converter 11. The signal conversion processing circuit 12 sets the amplitude level values related to the I-axis 0th column to the I-axis 15th column of the SS-QAM system of FIG. 3 to the corresponding I-level of the C-QAM system of FIG.
Signal conversion processing is performed from the 0th column of the axis to the same amplitude level value as the 15th column of the I-axis, and the SS-QA of FIG.
The amplitude level values for the I-axis 0's and I-axis 15's of the M system are shown in FIG. 4 as the amplitude levels for the C-QAM system I-axis 0s and I-axis 15s. The signal is converted into the same amplitude level value as the value and the I channel first data signal 103 as shown in FIG. 2 is output.

For example, a 6-bit digital signal indicating a 36-level value in a straight binary code as shown in FIG.
When the signal from MSB to 5SB is output as the signal of the amplitude level value when output from the D converter 3, the I-axis 0'th column,
I-axis No. 0 column, I-axis No. 1 column, ... I-axis No. 14 column, I-axis No. 15 column, and I-axis No. 15 'column, 18 corresponding amplitude level values "0" and "1" , The same “2”, the same “15”, the same “16” and the same “17”, which are 18-value data signals, and the amplitude level value “1” corresponding to the 0th column of the I-axis to the 15th column of the I-axis. For each of the data signals from "" to "16", 1 from each amplitude level value
The same amplitude level value as the amplitude level value of the C-QAM method (amplitude level value “0” to “15”) by subtracting the MSB signal to generate a 4-bit data signal of 2SB to 5SB. 16-value I channel first data signal 10 indicating
3 is easily obtained. Further, the data signal having the amplitude level value "0" corresponding to the 0th column of the I axis is not subjected to the subtraction process and is left as it is, and the data signal having the amplitude level value "17" corresponding to the 15th column of the I axis is left. 2 is subtracted, the amplitude level values “0” and “15” corresponding to the I-axis No. 0 column and the I-axis No. 15 column of the C-QAM system, respectively.
The I-channel first data signal 103 having the same QAM value as the above can be easily obtained.

The signal conversion processing circuit 12 performs signal conversion processing on the input digital signal and outputs an I channel second data signal 104 as shown in FIG.

The I-channel second data signal 104 is the I-channel first data signal.
When the data signal 103 is a signal relating to the I-axis No. 0 column to the I-axis No. 15 column of the SS-QAM system in FIG. 3, a high level signal of the I-axis No. 0'column and the I-axis column No. 15 ' In this case, the I-channel first data signal 103 is SS
-A signal indicating whether or not the signal is related to the outermost signal point in the QAM system signal point arrangement. Based on the LSB signal of the digital signal output from the signal conversion processing circuit 12 and the A / D converter, the I channel first error signal 107 and the I channel of the error signal for the I channel second data signal 103 as shown in FIG. An I-channel second error signal 108 of the error signal for the second data signal 104 is generated and output to the selection circuit 13. The selection circuit 13 selects the I channel second error signal 107 when the I channel second data signal 104 is at a high level, and selects the I channel second error signal 108 when the I channel second data signal 104 is at a low level to select the I channel error signal 105.
Is generated and output to the control signal generator 5. In the above-mentioned configuration, the signal points in every two columns outside the SS-QAM system are involved in the generation of the error signal. In terms of the reliability of the error signal, it is better to generate the error signal only from the signal points arranged in the outermost one column of the SS-QAM method.

However, in that method, the number of signal points involved in the generation of the error signal is very small (in the case of 256SS-QAM, 12 channels are combined in the upper and lower sides in one channel), the probability that the error equation is obtained is low and the accuracy of the control signal is low. Lost. Therefore, in order to improve the accuracy of the overall control signal, the error signal is generated by using the signal points of every two columns from the outside of the SS-QAM method. As described above, the I-channel first data signal 103 and the I-channel second data signal 104 output from the signal converter 11
Each of the I-channel error signal 105 and the I-channel error signal 105 is sent to the SS-QAM by the signal point arrangement converter 4 in the conventional demodulator.
Signals having the same properties as the I-channel first data signal 103, the I-channel second data signal 104, and the I-channel error signal 105, which are obtained by converting the signal point arrangement of the C-QAM method into the signal point arrangement of the C-QAM method. Has become. Therefore, the control signal generator 5 performs the same operation as the control signal generator 5 in the conventional demodulator to generate the I channel DC level control signal 106 and outputs it to the DC level controller 2. Regarding the I-channel first data signal 103 input to the control signal generator 5, the amplitude level values of the signals relating to the I-axis 0'th row and the I-axis 15'th row of the SS-QAM system of FIG. However, as shown in FIG.
The same amplitude level value as the amplitude level value of the signal relating to each of the 15th row of the axis (that is, the same as the amplitude level value “0” and “1”).
5 ”), the signal whose amplitude level related to the maximum positive amplitude level detected by the control signal generator 5 is deviated to the plus side from the normal amplitude level is the third signal. The signal has the maximum level error amount (I) of positive polarity shown in the figure. Further, a signal in which the amplitude level of the signal related to the negative polarity maximum amplitude level is deviated to the minus side from the normal amplitude level exists in the negative polarity maximum level error region (I) shown in FIG. It is a signal.

Therefore, SS in the SS-QAM system signal point arrangement in FIG.
All I channel maximum level signals, including the signals present at (0 ', 10) and SS (15', 5), are used to generate the 1 channel DC level control signal. Based on the I channel DC level control signal 106 output from the control signal generator 5, the DC level controller 2 always adjusts the DC level of the output signal to the center of the predetermined discrimination level of the A / D converter 3. To automatically control the DC level. Further, in the Q channel system 10, the same operation as the operation of the I channel system 9 described above is performed. By the above operation, the I channel first data signal 103 and the I channel second data signal 104, which are digital signals optimally adapted to the amplitude of the I channel demodulated signal 102, are output from the output terminals 7 and 8 of the demodulator, Q channel demodulation signal 10
A Q channel first data signal 103 'and a Q channel second data signal 104' which are digital signals optimally adapted to the amplitude of 2'are output from the output terminals 7'and 8'of the demodulator.

The demodulator according to the embodiment of the present invention forcibly sets the I-channel second data signal 104 and the Q-channel second data signal 104 'to a high level so that the reception is performed based on the C-QAM system. It can also be used for signals.

(Effects of the Invention) As described above, in the demodulation device according to the present invention, it is possible to cope with the signal point constellation of the C-QAM system.
Signal conversion processing is performed so that the amplitude level value of the signal related to the signal point of the S-QAM system becomes the same as the amplitude level value of the signal related to the signal point of the corresponding C-QAM system, and the signal of the C-QAM system The amplitude level value of the signal related to the outermost signal point of the SS-QAM system that cannot correspond to the point allocation is defined as the amplitude level value of the signal related to the outermost signal point of the C-QAM system. By having the signal conversion means that performs the signal conversion processing so as to be the same, demodulation is performed with a simple circuit configuration by using all the signals related to the outermost signal points in the SS-QAM system signal point arrangement. The effect is that automatic DC level control for signals can be performed. Furthermore, there is an effect that it can also be used as a demodulator of a digital wireless communication system using the C-QAM system.

[Brief description of drawings]

FIG. 1 is a block diagram of a demodulator of an embodiment of the present invention, FIG. 2 is a signal relation diagram of an I channel system of an embodiment of the present invention, and FIG.
Signal value constellation diagram of 256-value SS-QAM system, Fig. 4 shows 256-value C-Q
FIG. 5 is a configuration diagram of a conventional demodulation device, which is an AM signal point arrangement diagram. 1 ... QAM demodulator, 2,2 '... DC level controller, 3,3'
... A / D converter, 4,4 '... Signal point arrangement converter, 5,5' ...
... Control signal generator, 6 ... Input terminal, 7,7'8,8 '... Output terminal, 9 ... I channel system, 10 ... Q channel system, 11,11' ... Signal converter, 12 , 12 '... Signal conversion processing circuit, 13, 13' ... Selection circuit, 101 ... Received signal, 102
... I channel demodulated signal, 102 '... Q channel demodulated signal, 103 ... I channel first data signal, 103' ...
... Q channel first data signal, 104 ... I channel second data signal, 104 '... Q channel second data signal, 105 ... I channel error signal, 106 ... I channel DC level control signal, 107 ... I channel first error signal, 108 ... I channel second error signal.

Claims (1)

[Claims] 1. Multilevel stepped quadrature amplitude modulation (multilevel stepped
Square Quadrature Amplitude Modulation (referred to as SS-QAM) method is used as an input, and two demodulated signals that are synchronously detected and have a quadrature relationship with each other, that is, an I channel demodulated signal and a quadrature component of the in-phase component signal. QAM demodulation means for outputting a Q channel demodulation signal of the signal; DC level (DC
I channel DC level control means for controlling the offset); I for quantizing the amplitude of the analog signal output from the I channel DC level control means by a predetermined quantization level, and outputting a digital signal indicating a predetermined amplitude level value. Channel A / D conversion means; signal conversion processing of the digital signal output from the I channel A / D conversion means, and SS-QAM
With the exception of the outermost signal points in the signal constellation of the method, simple quadrature quadrature amplitude modulation (Conventional Quadrat
ure Amplitude Modulation (referred to as C-QAM) method, the amplitude level value of the I channel of the signal related to the SS-QAM method signal point corresponding to the signal point arrangement is set to the corresponding signal point of the C-QAM method. Showing the amplitude level value which is the same as the amplitude level value of the I channel of the related signal,
Also, the amplitude level of the I channel of the signal relating to the SS-QAM system signal point which is arranged at the outermost side in the SS-QAM system signal point arrangement and has no corresponding signal point in the C-QAM system signal point arrangement. An amplitude level corresponding to a signal point arranged on the outermost side in the C-QAM system signal point arrangement and having the same value as the amplitude level value of the I channel of the signal relating to the corresponding C-QAM system signal point I-channel first data signal indicating a value and I-channel second data indicating whether the I-channel first data signal is a signal related to an outermost signal point in the SS-QAM system signal point arrangement The amplitude level of the data signal and the I channel of each signal corresponding to each amplitude level value indicated by the I channel first data signal is higher than the normal amplitude level determined for each signal. I-channel signal converting means for outputting an I-channel error signal indicating whether the state is shifted to the side or the negative side; and the I-channel first data signal and the I-channel error signal are input. And detecting a signal in which the amplitude level of the signal relating to the maximum amplitude level of the positive polarity is deviated to the plus side from the normal amplitude level from the I-channel first data signal, and the maximum negative polarity level is detected. A signal in which the amplitude level of the signal related to the amplitude level is deviated to the negative side from the normal amplitude level is detected, and the DC level of the I channel demodulated signal is determined based on the detection result. The I channel DC level control signal for controlling the DC level so as to match the center of the predetermined identification level of the converting means is generated to generate the I channel. I-channel control signal generation means for outputting to the flow level control means; Q-channel DC level control means for controlling the DC level of the Q-channel demodulated signal; Amplitude of the analog signal output from the Q-channel DC level control means is predetermined. Q-channel A / D conversion means for quantizing at a quantization level of, and outputting a digital signal showing a predetermined amplitude level value; the digital signal output from the Q-channel A / D conversion means is subjected to signal conversion processing, A Q-channel first data signal corresponding to the I-channel first data signal, the I-channel second data signal, and the I-channel error signal and having the same contents as those of the signals and related to the Q-channel; Q channel signal converting means for outputting a Q channel second data signal and a Q channel error signal; By inputting the channel first data signal and the Q channel error signal, the DC level of the Q channel demodulated signal is a predetermined discrimination level of the Q channel A / D conversion means by the same operation as the I channel control signal generation means. I channel control signal generating means for generating a Q channel DC level control signal for controlling a DC level so as to match the center of the I channel control signal and outputting the Q channel DC level control signal to the Q channel DC level control means. Demodulator.