JPH0123981B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field of the Invention The present invention relates to a variable phase method in a demodulator,
In particular, it relates to a variable phase method used in a data demodulation circuit of phase difference modulation method in quadrature phase modulation specified in CCITT Recommendation V26. Technology background, conventional technology, and problems In modems, the data transmission speed is 2400 bit/s.
Quadrature phase modulation is used in these cases. As shown in Fig. 1A, four points E ₁ to _{E 4,} which are out of phase by 90 degrees, are set as data point array points, and for example, E ₁ is set as "00", E ₂ is set as "01", Use E ₃ as a data point such as "11" and E ₄ as "10". And this is modulated at 1200bau with a carrier of 1800Hz.
Send at d/s. In the case of a modem, the concept of difference is incorporated into this, and a modulated signal is output so as to display data based on the phase difference between the previous signal and the previous signal. In this case, only the phase difference with the previous signal is considered without considering the absolute phase (for example, when "00", zero degrees,
90° for "01", 180° for "10", and 180° for "11"
270°). However, in such method A, when the same data "00" is continuously transmitted, it is not possible to obtain a reference timing component for determining the data, so a scrambler method must be used. Also, the B method is used for data transmission.
This B method generates a modulated signal wave so that there is always a phase difference even if the data is the same as the previous data. For example, when the data is "00", the modulation signal wave is 45 degrees,
A signal having a phase difference of 135° for "01", 225° for "10", and 315° for "11" is output. That is, as shown in Figure 1B, E ₁ , E ₂ , E ₃ ,
When E ₄ is used as the data points "00", "01", "10", and "11" as described above, E ₁ ' which is 45 degrees ahead of E ₁ is transmitted as the transmission data, E ₂ ′ for E ₂ , E ₃ ′ for E ₃ , E ₄
For , send E ₄ ′. When demodulating this B-format signal, if you move it back in 45° increments, it will return to the A-method, which is the original four-phase phase. In other words, in methods A and B, the second
As shown in the figure, the phase is shifted by 45 degrees for the same data, so if the B method signal is returned by 45 degrees, it will return to the A method signal. In other words, in method B, "00", "01", "10",
When transmitting the original data “11”, the transmitted data will be E ₁ ′, E ₂ ′, E ₃ ′, E ₄ ′, respectively, and this B
When demodulating the method, demodulated data E ₁ , E ₂ , E ₃ , and E ₄ of method A can be obtained by returning the signal by 45 degrees.
Note that waveform diagrams of the phase modulation states of the A method and the B method are shown in FIG. 1D. At this time, as shown in Figure 3, if the B-system signal has a phase of 90°, in order to return it to 45°, multiply the magnitude of the B-system signal by a value of sin45°. These are the X-axis and Y-axis values (x ₁ , y ₁ ) of the A-type signal. 〓=ae ^j 〓 (｜〓｜=｜〓｜=a) 〓=ae ^j 〓＊e ^-j 〓 =ae ^j( 〓 ^- 〓 ⁾ = acos (α-θ) + jasin (α-θ) where α =90° If θ=45°

[Formula] becomes. In this way, by multiplying the phase difference by a specific value, it is possible to convert the B-system signal to the A-system signal. Therefore, e.g. CCITT Recommendations
As shown in Figure 4, the demodulator of the V26 B modem
For conversion from B method to A method, a multiplier uniquely determined by the phase difference of B method is stored in ROM1 as a constant corresponding to the phase difference angle, and this is set at 45° increments for the input signal transmitted by a 1800 Hz carrier. By multiplying sequentially from 0℃ every sampling time of A
It is possible to obtain the values of the X-axis (Real) and Y-axis (Imag) of the signal of the system.
-56558)). Then, for the X-axis component of the A method signal obtained in this way, the phase angle θ of the sampling time with respect to the 1800 Hz carrier (as mentioned above, the signal by the V26 modulation method is modulated with the 1800 Hz carrier) is calculated. Multiply by cosθ, and the Y-axis component is also 1800
It is demodulated by multiplying by -sinθ having a phase angle θ of the sampling time with respect to the carrier of Hz, and after passing this through roll-off filters 2 and 3 to remove unnecessary components, the determination unit 4 converts the data of the received signal. can be determined. However, according to this conventional method, the ROM
1, the problem is that the amount of hardware becomes large. Purpose of the Invention The purpose of the present invention is to use a method to convert only method B to method A in order to improve such problems.
The object of the present invention is to provide a variable phase method in a demodulator that does not use ROM. Structure of the Invention In order to accomplish this purpose, the variable phase method in the demodulator of the present invention uses four
In a demodulation device that uses a point as a data point and transmits this data point as a quadrature phase difference modulated wave, and demodulates this signal by rotating the phase of this signal by 90 degrees on the receiving side, the received quadrature phase difference modulated wave is The present invention is characterized in that the carrier of this modulated wave is multiplied by a carrier signal having a 45° phase difference to obtain a real component and an image component, respectively, and these are determined by a determining section to obtain transmission data. Embodiment of the Invention An embodiment of the present invention will be described based on FIGS. 5, 6, and 7. FIG. 5 is a configuration diagram of an embodiment of the present invention, and FIG. 6 is an explanatory diagram of its operation. In the figure, 10 and 11 are multiplication units, 12 and 13 are roll-off filters, and 14 is a determination unit. Before describing the present invention in detail based on one embodiment, the operating principle of the present invention will be briefly explained. The B method demodulator of the modem shown in Figure 5 determines the transmitted data only when the 1200
Since it is performed for each baud rate of Hz, if a signal that is shifted by 45 degrees with respect to the 1800 Hz carrier can be applied at each baud rate, the result will be
It can be made so that they are offset by 45 degrees. In other words, it is possible to convert the B method to the A method. Therefore, it is sufficient to generate such a carrier. For this,
A carrier of 1650 Hz is generated as shown in Fig. 6 (c). Now, as shown in Figure 6 A, the baud rate is 1200Hz.
In this case, the modulation signal is 1800Hz as shown in the figure (b), so there are 1.5 cycles of the 1800Hz carrier during one cycle of the baud rate. For this 1800Hz carrier,
As shown in Figure C, there is a 1650Hz carrier that is delayed by 45 degrees for each baud rate. Therefore, in the state of point C in Figure 6, there is a 45° difference and lag from the modulation signal of 1800 Hz, but at the next baud rate (not shown) there is a 90° difference from the modulation signal, and at the next baud rate, there is a further 45° lag. There is a 135° difference, as if it were the fourth
It has the same effect as ROM1 in the figure. Furthermore, since the signals are multiplied by cos θ and -sin θ in the multipliers 10 and 11, demodulation is also performed at the same time. The multiplier 10 is multiplied by cosθ for 1650Hz, and the sampling clock for this cosθ is
It is 7.2KHz, which is the same as in Figure 4,
It is sampled every 90 degrees at a modulation carrier frequency of 1800 Hz. Similarly, the multiplier 11 also multiplies by -sin θ for 1650 Hz. In this way, the multiplier 10 outputs the real, ie, X coordinate value, and the multiplier 11 outputs the imaginary, ie, Y
Coordinate values are output. Each of these values passes through a roll-off filter to remove unnecessary components, and the determination unit 14 determines the data points for each baud rate. To easily illustrate this judgment state, E ₁ ′ and E ₂ ′ in Fig. 7A are the 7th
When input to the B-type demodulation section in Figure 2, the multiplication section 10
, x ₁ and x ₂ are output from the multiplier 11, and y ₁ and y ₁ are outputted from the multiplier 11 and determined as E ₁ and E ₂ by the determination unit 14, respectively. In the above embodiment, 1650 Hz was calculated as the carrier for demodulation based on the following calculation. As shown in Figure 6A, the baud rate is 1200Hz and one cycle is 1/1200. The angle to point B in Figure 6B is 540°, and the angle to point C in Figure 6C is 540°.
The angle to the point is 540°-45°. Therefore, if the frequency of FIG. 6C to be found is x, the following equation holds true. (1/1200)×(360°/540°−45°)=1/x From this, find x and obtain 1650Hz. In the above description, if cos θ and -sin θ applied to the multipliers 10 and 11 are prepared in a ROM table, the configuration can be much simplified. Effects of the Invention According to the present invention, it is possible to omit the table in ROM1 and its multiplication part as shown in FIG. Therefore, the demodulation section of the modem can be greatly simplified.

[Brief explanation of drawings]

Figure 1 is a diagram explaining data points and transmission signal states, Figure 2 is a diagram explaining the phase difference between A system and B system, Figure 3 is a diagram explaining the conversion state when converting B system to A system, and Figure 4 5 is a block diagram of an embodiment of the present invention, FIG. 6 is an explanatory diagram of its operation, and FIG. 7 is an explanatory diagram of the judgment state of the present invention. . In the figure, 1 is a ROM, 2 and 3 are roll-off filters, 4 is a determination unit, 10 and 11 are multiplication units, and 12 and 1
3 is a roll-off filter, and 14 is a determination section.

Claims (1)

[Claims] 1. In a demodulator, four points having a phase difference of 90 degrees from each other are taken as data points, and these data points are transmitted as a quadrature phase difference modulated wave, and the receiving side performs demodulation by rotating the phase of this signal by 90 degrees. For the quadrature phase difference modulated wave, the carrier of the modulated wave and
A real axis (X-axis) component and an imaginary axis (Y-axis) component are obtained by multiplying carrier signals having a 45° phase difference, respectively, and these are judged by a judgment unit to obtain transmission data. Variable phase method in demodulator.