JPS6025936B2 - code conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a code conversion circuit using a multilevel superposition modulation method.

One of the modulation methods is a multi-level superimposition modulation method in which a four-phase modulated signal for the first path is added with a four-phase modulated signal having, for example, half the amplitude of the first path, called a second path, and transmitted simultaneously. Already proposed.

A modulation and demodulation device using this modulation method has the configuration shown in FIG. 1, for example. That is, the input signals IN1 and IN2 of the first path PI are input to the four-phase modulator MODI, and
The force signals INI', M2' of bus P2 are applied to the four-phase modulator MOD.
2, respectively, and the carrier wave from RG is subjected to four-phase phase modulation to the carrier wave generator. Output 4 of this four-phase modulator MODI
The modulated signal and a signal obtained by attenuating the amplitude of the four-phase modulated signal output from the four-phase modulator MOD2 to half by an attenuator AN are combined in a sum circuit AD and then transmitted. The vector of this transmitted modulated signal is shown in Figure 2, and o
One stitch will be straight as shown by the mark.

Note that the numbers in [ ] are the input signals IN1 and IN2 of the first path PI.
The combination of () is the input signal INI' of the second path P2.
, shows the combination of melon 2'. On the receiving side, the modulated signal is applied to a four-phase demodulator DEM1, a phase comparator FD, and a difference circuit SB, and the output signals OUT1 and OUT2 of the first path PI are demodulated by the four-phase demodulator OEM1.

The carrier wave is regenerated by the voltage controlled oscillator VC○, the low frequency wave generator LPF, the phase comparator PD, the 4-phase demodulator OEM1, and the 4-phase modulator MOD, and this regenerated carrier wave is transmitted to the 4-phase demodulator DEM1.
, DEM2 as carrier waves for demodulation. Also, the demodulated output signal of the first path PI becomes a four-phase modulation signal again in the four-phase modulator MOD, and the four-phase modulation signal is added to the phase comparator PO and the difference circuit SB, and then in the multiplex circuit SB. , 4 of the output of the 4-phase modulator MOD from the received modulated signal
By subtracting the phase modulation signal, a 4-phase modulation signal of the second bus P2 is obtained, and by demodulating the 4-phase modulation signal of the second path P2 in the 4-phase demodulator OEM2, the 4-phase modulation signal of the second bus P2 is obtained. demodulated output signals OUTI' and OUT2' are obtained.

Figure 3 shows the demodulation eye pattern of the first pass. The same is true for the case of .0.

The above-mentioned multi-billion superimposed modulation method is disclosed in the Electronic Bookkeeping Society of Japan's Communication Method Research Group, Material No. CS74-1, "A Method of Multiphase Multilevel Carrier Digital Transmission" (January 29, 1973). , for example, in the modulation of one haikudo, the conventional four
This has the advantage that it can be easily realized by applying phase PSK modulation/demodulation technology.

However, if the above method is used, if an error occurs in the demodulated data of the first pass, the remodulated signal by the four-phase modulator MOD of the first pass will also be incorrect, so that error will be transmitted to the second pass. A defect that propagates occurs.

The point where the probability of an error occurring outside the demodulated data of the first pass is highest is in the demodulated eye pattern of the first pass shown in Fig. 3.
Among the sampling points A to D, these are points B and C. That is, since the level difference between point 8 and point C is small, the threshold value at the time of demodulation of the first pass, that is, the level of 0 during relative vibration in Fig. 3,
On the other hand, there may be cases where point B is misjudged as point C or point C is misjudged as point B. However, the codes of the second pass associated with each level of A, B, C, and 0 are as follows. In other words, in the vector diagram of FIG. 2, when the reference carrier phase is set on the Y axis, the coarse code, for example (0, 1 ) (1, 1
), etc., the former is projected onto the Y axis and correlated.
In other words, the second pass code associated with A is “
0". Similarly, B, C, and 0 are associated with 1, 0, and 1, respectively. Similarly, in the case of the X axis, 0
, 1, 0, 1 are associated with A, B, C, 0.

Therefore, if B is mistaken for C or C is mistaken for B, the second pass number will always be incorrect because different things are associated with B and C. This means that in the vector diagram in Figure 2, the four signals closest to the origin all have different second
It is also clear that the path signals are associated.

The present invention improves the momme point in the multilevel convolution modulation method as described above, and its purpose is to provide a simple structure that can prevent errors in demodulated data in the second pass from occurring in the demodulated data in the second pass. The goal is to prevent errors from propagating.

Examples will be described in detail below. FIG. 4 is a block diagram of main parts of an embodiment of the present invention, and shows MMOD and MD.
EM is a multilevel modulator on the transmitting side and a multilevel demodulator on the receiving side shown in FIG. 1, and EXRI to EXR4 are exclusive OR circuits.

The input signals IN1 and 2 of the first path PI are directly applied to the multilevel modulator MMOD, and the input signals IN1 and 2 of the second path P2 are applied as they are to the multilevel modulator MMOD.
', IN2' are applied to the multilevel modulator MMOD via exclusive OR circuits EXR1, EXR2. The exclusive OR circuits EXR1 and EXR2 receive the input signal I of the first path PI.
N1 and IN2 are added, so the input signals INI' and IN2' of the second path P2 are the input signal IN1 of the first path PI.
, it will be converted to a code according to State 2. FIG. 5 shows the vector of the transmitted modulated signal obtained by code conversion, and the modulated signal of the second path P2 has a symmetrical vector relationship with respect to the x-axis and the y-axis.

Therefore, during demodulation, when the x-axis or y-axis is set to the demodulation threshold level of the first path PI, the demodulation data of the first path PI is "1".
” to “0” or “0” to “1”, the data on the second pass P2 will remain in the correct state, so the error in the demodulated data on the first pass PI will be avoided. The demodulated output signals OUT1 and OUT2 of the first path PI demodulated by the multilevel demodulator MDEM are output as they are, and are not propagated to the second path P2.
The temporary demodulated output signal of No. 2 is sent to the exclusive OR circuit EXR3,E
Inversely converted by XR4 and demodulated output signals OUT1', O
It becomes UT2'.

As explained above, the present invention provides a multilevel weighted modulation method in which a modulated signal of the first path and a modulated signal of the second path are superimposed at a predetermined level ratio. On the other hand, so that the content of the modulated signal of the second path is symmetrical,
A gate circuit such as an exclusive OR circuit converts the sign of the input signal of the second path in accordance with the input signal of the first path, thereby performing multilevel superposition modulation.
Even if the demodulated data of the path is erroneous, it will not affect the demodulated data of the second path.

Further, the configuration for code conversion can be easily realized using a gate circuit such as an exclusive OR circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a transmission modulation device and a receiving side demodulation device of a multi-level superposition modulation system, Fig. 2 is a vector explanatory diagram of a multi-level superposition modulation signal, and Fig. 3 is a demodulation eye pattern of the first path.
FIG. 4 is a block diagram of a main part of an embodiment of the present invention, and FIG. 5 is a vector explanatory diagram of a multilevel superimposed modulation signal of an embodiment of the present invention. PI is the first path, P2 is the second path, MMOD is a multi-level modulator, MDEM is a multi-level demodulator, MDEM is a multi-level demodulator, E
XRI to EXR4 are exclusive OR circuits. 1 goods is 3 figures, 2 figures are 4, 4 soups, 5 figures

Claims (1)

[Claims] 1 A vector of a multi-level superimposed modulation signal obtained by superimposing the phase modulation signal of the first path and the phase modulation signal of the second path is
Demodulating the received modulated signal in a demodulation circuit that performs code conversion to obtain the multilevel superimposed modulated signal so that the content of the phase modulated signal of the second path is symmetrical with respect to the demodulation threshold level of the path. to obtain the demodulated output signal of the first path, and demodulate the signal obtained by subtracting the signal obtained by modulating the carrier wave regenerated from the received demodulated signal with the demodulated output signal of the first path from the received modulated signal, and then demodulate the signal of the second path. multilevel demodulation means for obtaining a temporary demodulated output signal, and obtains a demodulated output signal for the second path by performing an exclusive OR of the temporary demodulated output signal of the second path and the demodulated output signal of the first path; A code conversion circuit characterized by comprising a gate circuit.