JPH059979B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention modulates a carrier microwave by an input digital signal, converts it into a modulated wave of a certain frequency band, and transmits the modulated wave to a receiving side. Among the digital communication methods that transmit the QAM wave to the receiving side, it particularly relates to the digital communication method that transmits the QAM wave to the receiving side using multilevel quadrature amplitude modulation QAM that modulates the amplitude and phase of the carrier wave at the same time. The present invention relates to a method that makes it easy to reproduce a carrier wave at a center frequency position required when demodulating a main signal from a wave. The QAM wave whose carrier wave is multilevel orthogonal amplitude modulated with the input digital main signal is spread by modulation with the digital signal whose input average is zero. Therefore, although the center frequency component exists momentarily, if the probability of occurrence of each phase is equal and averaged, it will not be biased toward any one phase, and the frequency component will not exist steadily. This makes it difficult to reproduce the carrier wave at the center frequency position of the QAM wave on the receiving side, making the carrier wave regeneration circuit complicated, but the carrier wave regeneration circuit on the receiving side is as simple as possible. things are desired.

(b) Prior art and problems Conventionally, multi-level quadrature amplitude modulation, such as 16-level QAM, which is obtained by converting two series of binary digital signals of the main signal and synthesizing four-level amplitude modulation signals in quadrature phase, has been used. For demodulation of the received QAM wave on the receiving side, the received QAM wave is synchronously detected using two reference carrier waves with a phase difference of 90 degrees, and then converted into a binary signal. The carrier wave must be regenerated from the received wave, but since the phase of the received wave changes every moment due to modulation, this modulation is canceled out and a constant control signal is fed back to the voltage controlled oscillator VCO. A method has been adopted in which the carrier wave having the center frequency of the received wave is regenerated by using a method such as using the output as a reference carrier wave. However, since the QAM wave is multi-level and multi-phase, it is greatly affected by phase distortion in the transmission path, making it difficult to reproduce a clean carrier wave on the receiving side. Therefore, on the transmitting side, the orthogonality of the two series of modulated input signals is intentionally broken to leak the carrier wave at the center carrier wave position of the QAM modulated wave, and then the carrier wave is transmitted. The receiving side then uses this leaky carrier wave to
Methods such as synchronous detection and demodulation of QAM modulated waves have been devised.

On the other hand, in normal wireless transmission methods, PCM
In addition to transmitting main signals such as multiplex signals, auxiliary signal SC is used for meeting calls and line monitoring in each relay section.
It is necessary to modulate and transmit. Therefore, as shown in Figure 1, for example, the main PCM signals (I) and (Q)
Frequency modulation (FM) is applied to a carrier wave oscillator 4 for QAM modulation using an auxiliary signal, which is combined with the QAM wave of the main signal in a synthesizer 8 and output as a modulated output to the receiving side. In this conventional method, the spectrum of the FM wave obtained by FM modulating the carrier wave oscillator 4 with the auxiliary signal on the transmitting side spreads widely, so it is distorted in the middle of the transmission path, and the auxiliary signal is extracted from the FM wave of the received auxiliary signal on the receiving side. Phase fluctuations remain in the central carrier wave, which adversely affects the demodulation operation of the QAM wave of the main signal.

(c) Object of the Invention The present invention solves the drawbacks of the conventional method, namely, that the main signal on the transmitting side is transmitted simultaneously with a QAM modulated wave. FM modulated target with auxiliary signal
The influence of phase distortion received in the transmission path remains on the carrier wave extracted and regenerated from the received wave on the receiving side of the FM wave, and when the QAM wave of the main signal is synchronously detected and QAM modulated,
When demodulating the QAM wave of the main signal on the receiving side in a communication system using multilevel quadrature amplitude modulation QAM, which eliminates the disadvantage of adversely affecting the modulation characteristics of the main signal and whose multilevel degree will increase in the future. A modulation communication method that simplifies the regeneration of the carrier wave at the center frequency position necessary for the transmission, and that is less affected by the transmission path because the spectrum of the modulated wave is less broadened by the auxiliary signal on the transmitting side. Our goal is to provide the following.

(d) Structure of the Invention The present invention is a so-called two-phase frequency shift keying (FSK) modulation, which is a type of FM modulation in which the phase changes continuously and the frequency is shifted by a certain amount as a result, in which the phase modulation index is 0.5. In other words, the MSK modulated wave that is transmitted after being modulated by what is commonly called MSK (Minimum Shift Keying) modulation is
The occupied bandwidth is narrow, so the influence of phase distortion (noise) on the transmission path is small, and the center frequency position of the MSK modulated wave received on the receiving side can be easily determined by doubling its frequency. Focusing on the fact that it has the feature of being able to reproduce carrier waves, it is constructed as follows. That is, sender 1
00 is a communication system in which the input main signals I _io , Q _io and the auxiliary signal SC _io are all digitally modulated on a carrier wave and transmitted, and the receiving side 200 regenerates, detects and demodulates the carrier wave, and the transmitting side 100 The carrier wave is divided into two with the same 101 waves, and one of the carrier waves is subjected to multilevel orthogonal amplitude modulation using two series of main PCM signal inputs I _io and Q _io
QAM, and the other carrier wave is subjected to MSK modulation of continuous phase frequency shift keying FSK with a phase modulation index of 0.5 using a binary auxiliary signal SC _io , and is simultaneously transmitted.
On the receiving side 200, the frequency of the received wave is doubled, the line spectrum is extracted, multiplied and frequency-divided, and the frequency is further divided to regenerate a carrier wave, and this regenerated carrier wave is used to perform QAM modulation of the main signal, which is multilevel orthogonal amplitude modulation. In addition to synchronously detecting the waves and demodulating and outputting the main signal,
The auxiliary signal is configured to be demodulated from the MSK modulated wave and output.

(e) Embodiments of the invention Examples of the invention will be described below with reference to the drawings.
FIG. 2 is a circuit diagram showing the configuration of a communication system according to an embodiment of the present invention. In FIG. 2, 100 is a transmitting side and 200 is a receiving side, which are connected by a transmission path 150. On the transmitting side 100, one carrier wave source 101 is divided into two by a branching hybrid 106, and one carrier wave CR is inputted into two main PCM signal inputs _Iio ,
Used for quadrature amplitude modulation QAM in quadrature amplitude modulators M102 and 103 by Q _io , and the other carrier wave is used as a binary auxiliary signal input SC _io for PLL oscillator 104
Used for MSK modulation in Then, the synthesizer 107 synthesizes the orthogonal amplitude modulation outputs of the two series of main signals I _{io and} Q _io to generate a QAM wave and a binary auxiliary signal.
Both modulated waves of the MSK modulated wave MSK modulated by the SC _io are combined by a combining hybrid 108 and sent to the transmission line 150 at the same time.

On the receiving side 200, the modulated wave received from the transmission line 150 is divided into two by a branching hybrid 208,
One received wave is further divided into two by a hybrid 207, multiplied by a carrier wave of orthogonal phase (described later), and synchronously detected by a QAM demodulator D 202, 203.
The QAM wave components are demodulated. and main signal PCM signal (I)
and outputs the main signal PCM signal (Q). The received wave of the other output of the branch hybrid 208 is FM
The demodulator 204 demodulates the MSK wave component to FM and outputs the auxiliary signal SC _put , and at the same time, the frequency multiplier 201 doubles the frequency of the received wave by 2 to set the center of the MSK wave component of the received wave. Regenerate the carrier wave at frequency position ₀ . And frequency multiplier 201
The regenerated carrier wave of frequency ₀ is directly supplied to the QAM demodulator D202, but the phase is changed by a phase shifter 205 to another QAM demodulator D203.
After changing only 2, supply QAM demodulator D20.
It is used for synchronous detection in No. 2, 203 and outputs demodulated main signal PCM signal (I) and main signal PCM signal (Q).

The frequency multiplier 201 on the receiving side 200 doubles the frequency of the input received wave to 2, thereby regenerating the carrier wave with center frequency ₀ of the MSK wave of the auxiliary signal and demodulating the QAM wave of the main signal. The operation of regenerating the carrier wave necessary to do this is the QAM wave of the main signal of the received wave in the signal spectrum diagram in Figure 3.
These are the QAM modulated wave and the MSK wave of the auxiliary signal.
From the received wave of the receiving system 200, which is a combination with the MSK modulated wave, the value of the phase modulation index m _p of the MSK modulated wave is 0.5
Then, the frequency shift amount is 1/2T, _H − _L = _CK /2, and the difference between the center frequency ₀ and _H and _L is _CK /4.
The MSK wave component of the auxiliary signal, which is an FSK modulated wave, is transferred from the distributor 208 on the receiving side 200 to the frequency multiplier 20.
1, the frequency is doubled, the center frequency of is ₂₀ , the value of the phase modulation index _m is 0.5 x 2 = 1, and the clock frequency is increased above and below the center frequency of ₂₀ .
Obtain the spectrum of an FSK modulated wave with m _p =1 having two line spectra separated by _CK /2.
Although not shown in the frequency multiplier 201, a filter first takes out the two line spectra of the FSK modulated wave of m _p =1 in FIG. 3, multiplies them, and divides the frequency by 2. Two line spectra are extracted above and below the center frequency ₀ of the MSK modulated wave at positions separated by half the clock _{frequency CK} /2, and the frequency is further divided by two. And the one in Figure 3
Generate a carrier wave with a center frequency of ₀ for the MSK modulated wave.
And the frequency ₀ of the output of this frequency multiplier 201
As described above, the carrier wave is supplied to the QAM demodulator 202 as it is, and is supplied to the other QAM demodulators 203 after shifting the phase by π/2 by the phase shifter 205. Analog main PCM signal (I) for QAM demodulation which synchronously detects the QAM modulated waves of the main signal from the distributor 207 in 203 and decodes them into baseband codes I and Q in the next stage.
and outputs the main PCM signal (Q).

(f) Effects of the Invention As detailed in the above embodiments, according to the present invention, the transmitting side QAM-modulates the carrier wave with the main signal.
The QAM wave and the MSK wave modulated by the auxiliary signal using the same carrier wave are combined and sent to the receiving side, so the receiving side regenerates the carrier wave with the center frequency necessary to demodulate the QAM wave of the main signal. The MSK modulated MSK wave of the auxiliary signal is used for this purpose. The MSK-modulated MSK wave of the auxiliary signal used has less spectrum spread, so it is less susceptible to distortion in the transmission path, and it is suitable for demodulating the QAM wave of the main signal on the receiving side. The required carrier wave reproduction can be achieved with a simple circuit such as simply doubling the frequency of the modulated wave of the received wave. Furthermore, due to the characteristic that the spectrum of the MSK wave of the auxiliary signal to be transmitted has little spread, it is less affected by the transmission path on the way and can be used for QAM demodulation of a clean main signal with good signal-to-noise ratio characteristics on the receiving side. The carrier wave can be regenerated, and the transmission characteristics of the main signal by multilevel QAM modulation can be significantly improved.

[Brief explanation of the drawing]

Figure 1 shows the modulation circuit on the transmitting side of a conventional communication system.
FIG. 2 is a circuit diagram showing the configuration of a modulation circuit on the transmitting side and a demodulating circuit on the receiving side of the communication system according to the embodiment of the present invention;
FIG. 3 is a signal spectrum diagram for explaining the operation of the embodiment of the present invention. In the figure, 100
is the transmitting side, 101 is the carrier wave source, 102 and 103 are the
QAM modulator, 104 is MSK modulator, 200 is receiving side, 201 is frequency multiplier, 202, 203
is a QAM demodulator, and 204 is an FM demodulator.

Claims (1)

[Claims] 1. The transmitting side 100 digitally modulates the carrier waves of the input main signals I _io , Q _io and the auxiliary signal SC _io and transmits them, and the receiving side 200 reproduces, detects, and demodulates the carrier waves. In this communication system, the transmitting side 100 divides the carrier wave into two with the same number of 100, performs multilevel quadrature amplitude modulation QAM on one carrier wave using the main signals I _io and Q _io , and uses the other carrier wave as a binary auxiliary signal SC _io MSK modulation is performed using frequency shift keying with a continuous phase shift modulation index of 0.5 and simultaneously transmitted. On the receiving side 200, the frequency of the received wave is doubled, the line spectrum is extracted, multiplied, frequency-divided, and then further frequency-divided. The regenerated carrier wave is used to synchronously detect the QAM modulated wave that has been subjected to multilevel orthogonal amplitude modulation of the main signal, and the main signal is demodulated and output, and the auxiliary signal is demodulated from the MSK modulated wave. A communication method characterized by output.