JPH0653937A - Hybrid modulated wave transmission system - Google Patents

Abstract

PURPOSE:To simultaneously attain a digital transmission and an analog transmission by superimposing a digital modulated signal transmitted in the same frequency band on an FM modulated signal of an arbitrary transmission level. CONSTITUTION:At a transmission side, inputs 1 and 2 are respectively FM- modulated and PSK-modulated by an FM modulator 101 and a PSK modulator 102 by sharing an intermediate frequency local oscillator 103. The PSK modulated signal is branched into 2, and fade is generated at the central frequency of the PSK modulated wave by using a delay element 106 and a subtracter 107. The FM modulated wave is synthesized with the PSK modulated wave by a synthesizer 104, and transmitted by a transmitter 105. At a reception side, the received wave is converted into an intermediate frequency by a receiver 108, the output is branched into 2, one received wave is transmitted through a band pass filter 109, the FM modulated wave is extracted, and demodulated by an FM demdoulator 110. The other received wave is transmitted through a discrimination feedback type equalizer 111, a waveform distortion due to the fade generated on the transmission side and the FM modulated wave multiplexed on the central frequency are removed, and the PSK demodulation is operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hybrid modulated wave transmission system, and in particular, by superimposing an analog signal on the same frequency band of an existing digital line, it can be added without changing the frame structure of the original digital transmission system. The present invention relates to a hybrid modulated wave transmission system that enables multiplex transmission of signals.

[0002]

2. Description of the Related Art A conventional hybrid modulated wave transmission system for performing digital transmission and analog transmission in the same frequency band, as shown in FIG. 5, 301 is a phase modulator (PSK modulator) and 302 is a frequency modulator ( FM modulator), 303 is an intermediate frequency local oscillator, 304 is a transmitter (TX), 3
Reference numeral 05 is a receiver (RX), 306 is a phase demodulator (PSK demodulator), and 307 is a phase-locked frequency demodulator (PLL-F).
M demodulator).

In the operation of this conventional example, the PSK modulator 301 performs phase modulation on the first transmission signal from the input 1.
On the other hand, the second transmission signal from the input 2 is the FM modulator 302.
Is frequency-modulated by. In this case, the FM modulator 302
The intermediate frequency local oscillator 303 is used as an intermediate frequency of, and modulation is performed with a very small capacity and a small modulation index. Therefore, since the frequency shift of the output of the FM modulator 302 is small, it is used as a local signal in the intermediate frequency band in the PSK modulator 301. A PSK modulated wave including FM modulation is converted into a carrier frequency band by the transmitter 304 and transmitted. On the receiving side, the receiver 305 converts the carrier reception wave into the intermediate frequency band. The converted intermediate frequency signal is branched into two, and one is input to the PLL-FM demodulator 307. This received wave contains a wideband phase modulation component, but PL
P is set by the band pass filter inside the L-FM demodulator 307.
The wideband signal of SK is removed. PLL-FM demodulator 3
07 performs FM demodulation while phase-synchronizing with the input intermediate frequency and outputs the second received signal. The intermediate frequency signal 307A reproduced by the PLL-FM demodulator 307 is PSK.
It is supplied to the demodulator 306. The other received wave branched at the output of the receiver 305 is input to the PSK demodulator 306.
The PSK demodulator 306 performs PSK demodulation and outputs the first received signal.

[0004]

The above-mentioned conventional technique is
The digital transmission system is modulated using the FM-modulated intermediate frequency signal as a carrier signal. Therefore, in order to suppress the influence on the digital system, the signal level of the FM transmission system cannot be increased so much that the quality of the FM transmission system deteriorates as compared with the digital system.

An object of the present invention is to provide a transmission system of a hybrid modulation signal capable of simultaneously transmitting the FM transmission system in the same frequency band as the digital system at an arbitrary level regardless of the level of the digital transmission system.

[0006]

The first means of the hybrid modulation signal transmission system of the present invention is a digital modulation means for performing PSK modulation by a first digital signal using an intermediate frequency local oscillator on the transmission side. A means for generating a fade at the center frequency of the digital modulation wave of the digital modulation means, an analog modulation means for performing FM modulation with a second analog signal using the intermediate frequency local oscillator, and a modulation wave by the analog modulation means. A receiving means for converting the received carrier wave signal into an intermediate frequency band at the receiving side, having a combining means for combining the faded digital modulated wave and a transmitting means for converting the output of the combining means into a carrier frequency band; , The output of the receiving means is branched into two, and one of them is passed through a band-pass filter and then frequency demodulated to obtain a second analog signal. Means for removing the waveform distortion by passing the other of the branched outputs through a decision feedback equalizer, and means for digitally demodulating the output of the equalizing means to obtain a first digital signal. Have and.

The second means is an analog modulating means for performing FM modulation with an analog signal by using a first intermediate frequency local oscillator which generates at least two different frequencies on the transmitting side, and the first intermediate means. Frequency modulating means for performing PSK modulation by a digital signal using an intermediate frequency local oscillator different from the frequency local oscillator, and positions corresponding to different frequencies of the first intermediate frequency local oscillator with respect to the output signal of the digital modulating means. Has a fade generating means for generating a fade and a transmitting means for synthesizing and transmitting the outputs of the analog modulating means and the fade generating means, and the receiving side demodulates each FM modulated signal of the analog modulating means. Means and a PSK modulated signal which is the output of the fade generating means. And force, and a digital demodulation means including a decision feedback equalizer for removing waveform distortion due to fading.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the first embodiment of the present invention, and FIG. 2 is an explanatory diagram for explaining the operation of the present embodiment. In FIG. 1, 1
01 is a frequency modulator (FM modulator), 102 is a phase modulator (PSK modulator), 103 is an intermediate frequency local oscillator, 104 is a combiner, 105 is a transmitter (TX), 106
Is a delay element of delay time τ, 107 is a subtractor, 108 is a receiver (RX), 109 is a band pass filter (BPF) 1
10 is a frequency demodulator (FM DEM), 111 is a decision feedback equalizer, 111A is a backward filter (BWD FI).
L).

In FIG. 2, 201 is the spectrum of the signal wave on the transmission side input from the transmission side, 202 is the output spectrum of the bandpass filter 109, 203 is the output spectrum of the front filter 111A, and 204 is the subtractor 111.
It is the output spectrum of B. The configuration of FIG. 2 has a bandpass filter 109, an FM demodulator 110, a delay element 207 having a delay time of a digital modulation symbol period T, and a complex multiplier 2.
08, adder 209, subtractor 111B, subtractor 211,
Judgment unit 212, delay element 213 having delay time of digital modulation symbol period T, complex multiplier 214, adder 215
And the components 207, 208 and 209 make up the front filter 111A and the components 213, 214 and 215
Constitutes a rear filter 111D and comprises components 211 and 2
12 is included in the PSK demodulator 111C.

Next, the operation of this embodiment will be described.

In FIG. 1, the FM modulator 101 has an input 1
And the PSK modulator 102 is PSK modulated by the input 2. Here, the intermediate frequency from the intermediate frequency local oscillator 103 is shared for FM modulation and PSK modulation. The PSK modulated wave is branched into two, and the other PSK modulated wave is input to the subtractor 107. Here, the delay element 10
The PSK modulated wave from 6 is subtracted. At this time, the subtractor 1
The PSK modulated wave of 07 output has a fade (also called a notch) at its center frequency. This phenomenon is equivalent to two-wave multipath propagation that occurs in wireless communication. The synthesizer 104 subtracts the intermediate frequency FM modulated wave and the subtractor 107.
And an intermediate frequency PSK modulated wave having a fade from Further, the composite wave is converted into a carrier frequency band by the transmitter 105 and transmitted.

Next, the receiving side will be described with reference to FIG. The received wave spectrum from the transmitting side becomes like 201. Here, the PSK wave is fading at the center frequency, and the purpose of the fading is that the interference of the PSK wave does not affect the FM wave. When the band of the FM modulated wave is narrow, the delay time τ of the delay element 106 is set to about T / 2 (T is a PSK wave symbol period) on the transmission side. In this case, a sharp and deep fade can be added. When the band of the FM modulated wave exceeds the fade band, τ is made smaller than T / 2 to widen the fade band width. In this case, it is not steep, but rather becomes a gentle fade and the fade band is widened, resulting in a wide band FM.
Impact on. The band pass filter 109 is F
The signal spectrum of the M-modulated wave is passed, and its output spectrum becomes a filter output waveform 202. F extracted
The M modulated wave 202A is demodulated by the FM modulator 110 and an output 1 corresponding to the input 1 on the transmission side is obtained. On the other hand, PS
As for the K-modulated signal, the waveform distortion due to the fade made on the transmission side and the FM-modulated wave 201 like the input waveform 201.
Both are interfered by A. Normally, such a received signal wave cannot be subjected to normal digital transmission even if PSK demodulation is performed. First, the fade (notch) created on the transmitting side is equivalent to multipath distortion as described above. The waveform distortion due to this can usually be removed by using a decision feedback equalizer (DFE). The FM interference wave has a narrower band than the PSK modulated wave and can be handled as a CW interference wave. DFE is CW
It is known to have the ability to remove interference waves. This document is based on "I E E Transactions on Communication Volcom 31 No. 4, 1983, published by Lee and Milstein.
Monthly “Rejection of CW Interference in QPSK Systems Using Judgment Feedback Filters”. According to this, in narrow-band interference removal using only a linear filter as a notch filter, a notch is created in the frequency of the interference wave to remove the interference wave, so that the spectrum of the desired wave itself is also affected. Therefore, the MMSE (minimum
Good interference removal cannot be performed as long as the Mean Square Error method is used. On the other hand, when DFE is used, the front filter 111A removes the interference wave by making a deep notch in the frequency of the narrow band interference wave. At this time, a notch is given to the spectrum of the desired wave signal to create waveform distortion. However, as described below, the rear filter 1
Since 10 compensates the desired wave signal component scraped by the notch, the narrow band interference wave can be sufficiently removed without affecting the desired wave.

Now, the frequency of the CW interference wave is Ω, the interference wave power is J, the desired wave symbol period is T, the desired wave signal power is S,
Assuming that the receiver noise power is σ ¹ and the number of taps of each of the front filter and the rear filter is N, the tap coefficient wi of the front filter and the tap coefficient fi of the rear filter are represented by equations (1) and (2).

[0014]

This tap coefficient is an ideal solution derived from the orthogonal condition between the error signal and the signal at each tap. In order to set the tap coefficient to the ideal solution, in order to minimize the root mean square value of the discriminator error signal ε, it is usual to use LMS (Least M
The tap coefficient is corrected by an ean square algorithm or the like. Equation (3) shows a tap correction equation by the LMS algorithm.

Wi ^{n + 1} = win ^n- με ⁿ ui ^{* n} (3) wi ⁿ is a value of the i-th tap coefficient at time n, u
i is the signal at the i-th tap, μ is the correction factor,
ε indicates a discriminator error signal, and * indicates a complex co-reduction. When the ideal solution of the tap coefficient is wopt, the Wiener-Hopf equation shown in the equation (4) holds.

Φ · wopt = v (4) Here, Φ is an N × N correlation matrix, where N is the number of taps of the front filter and the rear filter. v is a correlation vector between the signal component at each tap coefficient and the reference signal (here, the determination data signal when there is no error). That is, the expression (1) indicating the front filter tap coefficient means that the CW interference wave is canceled between the taps. Particularly noteworthy is that the tap coefficient of the rear filter corresponds to that of the front filter as shown in the equation (2). The physical meaning of this is CW by the front filter.
Although the interference wave could be removed, the received signal sequence is distributed in each tap. Since these are multiplied by the tap coefficient of equation (1) and combined, intersymbol interference occurs. However, as shown in the front filter of FIG. 2, the difference from the normal front filter is that the position of the reference tap 205 is directly input from the input side to the adder 209 without passing through the multiplier 208 and synthesized. It is a place. Therefore, the intersymbol interference due to the interference cancellation comes from the symbols transmitted at the time before the reference signal. In this case, these already transmitted past symbols are also distributed as decision symbols to each tap of the backward filter. Therefore, if there is no decision error, all the intersymbol interference due to the CW interference cancellation can be removed by the backward filter. Since this intersymbol interference is determined by the tap coefficient of the front filter, it can be removed if the tap coefficient of the rear filter corresponds to the tap coefficient of the front filter. This is the meaning of equation (2).

As described above, the decision feedback equalizer (DFE) has the ability to remove waveform distortion due to multipath propagation and the ability to remove CW interference waves. Then, regarding the operation of the DFE when multipath distortion and CW interference are simultaneously generated, Ichiro Tsujimoto, IEICE 1992 Spring National Convention B-418 "in the multipath propagation path" CW interference rejection characteristics by a decision feedback equalizer ”. That is, a fade (notch) due to multipath is given to the PSK desired wave, and a strong CW interference wave is added to input to the DFE. However, the simulation result shows that the DFE has the ability to remove both intersymbol interference and CW interference. It is reported that the D / U (desired wave to CW interference wave power ratio) has equalization capability up to about -5 dB. In FIG. 2, focusing on the PSK modulated wave, the input waveform 201 of the received wave spectrum
Is simultaneously receiving multipath distortion that causes a fade (notch) at the center frequency and a narrow band interference wave called an FM modulated wave, and the above-mentioned DFE can exert its effect. Further, even if D / U becomes negative, interference can be removed and waveform distortion can be equalized. Therefore, it is possible to raise the signal level of the FM modulated wave sufficiently to improve its quality.
Further, the fade created by the front filter removes the FM modulated wave by making a deep fade at the center frequency of the FM modulated wave regardless of the fade created on the transmitting side. That is, the front filter output waveform 203 is obtained. On the other hand, the rear filter removes all intersymbol interference associated with the CW interference removal of the front filter. Therefore, the subtractor 210 output waveform 204
It becomes a normal one. The determiner 212 makes a determination with respect to the PSK wave from which the interference due to the multipath distortion and the FM modulated wave is removed, and outputs determination data. DFE
The tap coefficient of is controlled so that the root mean square of the error signal output by the subtractor 211 is minimized. Both the front filter 111A and the rear filter 111B of the DFE are shown as an example in which they are operated by the processing of the intermediate frequency band (passband processing), so that the PSK modulator 111C is positioned in the loop of the rear filter. . If the front and rear filters are subjected to passband processing in this way, a circuit corresponding to the PSK demodulator 111C must be inserted between the subtractor 111B and the determiner 212.

Next, a second embodiment of the present invention will be described with reference to the configuration diagram of FIG. 3 and the operation explanatory diagram of FIG. FIG. 3 shows an embodiment in which two analog transmission systems are multiplexed on a digital transmission system. The FM modulators 151 and 152 perform analog modulation on the transmission signals of the input 1 and the input 2. Intermediate frequency local oscillators 156 and 15 used in this case
The center frequencies of 7 are f1 and f2 which are different from each other. PSK modulator 153 for the transmission signal of input 3
Is modulated by. The local frequency f0 of the intermediate frequency local oscillator 158 is used for this modulation. The PSK modulated signal is input to the notch filter 154, which creates a fade (notch) corresponding to the local frequency f1. Further, the output of the notch filter 154 is input to the notch filter 155 to create a fade corresponding to the local frequency f2. There is a two-wave multipath circuit as an example of the method of constructing the notch filter. In this method, an input signal is branched into two, one branch signal is delayed by a delay time τ, multiplied by a complex constant, and then combined into the other branch signal. This is equivalent to the two-wave multipath propagation model that often occurs in wireless communication. Here, the fade frequency can be determined by setting the complex coefficient by which the delayed wave is multiplied.
FM modulators 151 and 152 and notch filter 155
The synthesizer 159 synthesizes and multiplexes the PSK modulated waves that have received the fades of the outputs f1 and f2. The transmitter 160 converts the multiplexed intermediate frequency transmission signal into a carrier frequency band and transmits the carrier frequency band.

Next, the operation of each unit on the receiving side will be described with reference to FIG. The input signal sent from the transmitting side becomes like the received input spectrum 201. Here, the PSK wave is faded at f1 and f2, and it is shown that two independent FM modulated wave spectra are located around the fade frequency. The fades at f1 and f2 are intended to prevent the interference of the PSK wave from affecting the FM wave. Band pass filters 162, 16
The center frequencies of 3 are set to f1 and f2, respectively, and the FM modulated waves in the f1 and f2 bands are extracted, and have filter output waveforms 202 and 203, respectively. The extracted FM modulated wave 202A is generated by the FM demodulators 114 and 11
5 is demodulated to obtain output 1 and output 2 respectively corresponding to input 1 and input 2 on the transmitting side.

As described above, since the PSK-modulated signal is subjected to the waveform distortion due to the fade made on the transmitting side like the input spectrum waveform 201 and the interference due to the FM-modulated wave, such a received signal wave is usually PSK. Normal digital transmission is impossible even if demodulated. First, the fade (notch) created on the transmitting side is equivalent to the multipath distortion as described in the first embodiment. The waveform distortion due to this can be removed by using DFE. FM interference wave is PSK
Since it has a narrower band than the modulated wave and can be handled as a CW interference wave, it has the ability to remove CW interference.

[0022]

As described above, according to the present invention, a fade is generated at the center frequency of a digital modulated wave on the transmitting side,
The frequency modulated wave is combined with the fade frequency of the digital modulated wave and transmitted, and the received wave is branched on the receiving side, and only the frequency modulated wave is extracted from one received wave by the band pass filter,
This is frequency demodulated. The other received wave can be set to an arbitrary level by performing digital demodulation after removing the frequency modulation wave and the waveform distortion due to the fade on the transmission side by the decision feedback equalizer. Therefore, it is possible to superimpose and transmit a high-quality frequency-modulated wave on the same frequency of a digital signal. Also,
The present invention can be applied to the case where a plurality of fades are generated in the spectrum of a digital modulated wave on the transmission side and a plurality of analog modulated waves are combined and multiplexed corresponding to the plurality of fades, and the same effect can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the second embodiment.

FIG. 5 is a configuration diagram of a conventional hybrid modulation signal transmission system.

[Explanation of symbols]

 101, 151, 152 FM modulator 102, 153 PSK modulator 103, 156 to 158 Intermediate frequency local oscillator 104, 159 Combiner 105, 160 Transmitter 106 Delay element 107, 111B, 166B Subtractor 108, 161 Receiver 109, 162,163 band pass filter 110,164,165 FM demodulator 111,166 decision feedback equalizer 111A, 166A front filter 111C, 166C PSK demodulator 111D, 166D rear filter 154,155 notch filter

Claims (2)

[Claims] 1. A digital modulating means for performing PSK modulation by a first digital signal using an intermediate frequency local oscillator on a transmitting side, a means for generating a fade at a center frequency of a digital modulated wave of the digital modulating means, An analog modulation means for performing FM modulation by a second analog signal using an intermediate frequency local oscillator; a combining means for combining the modulated wave by the analog modulating means and the digitally modulated wave subjected to the fading; and an output of the combining means. And a receiving means for converting a received carrier signal into an intermediate frequency band on the receiving side, and an output of the receiving means is branched into two, and one of them is passed through a bandpass filter. Frequency demodulation second
Demodulation means for obtaining the analog signal of, the means for removing the waveform distortion by passing the other of the branched outputs through a decision feedback equalizer, and digital demodulation for the output of the equalization means to obtain the first digital signal. And a means for obtaining the hybrid modulated wave transmission method. 2. An analog modulating means for performing FM modulation by an analog signal on each of the first intermediate frequency local oscillators that generate at least two different frequencies on the transmitting side, and the first intermediate frequency local oscillator. Digital modulating means for performing PSK modulation by digital signals using different intermediate frequency local oscillators, and fades to the output signals of the digital modulating means at positions corresponding to different frequencies of the first intermediate frequency local oscillator. And a transmitting means for synthesizing and transmitting the outputs of the analog modulating means and the fade generating means, and at the receiving side, means for demodulating each FM modulated signal of the analog modulating means, and Input the PSK modulated signal which is the output of the fade generation means, and And a digital demodulating means including a decision feedback type equalizer for removing waveform distortion due to noise.