JPH047851B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to the control of SSB communication systems, and in particular to high-quality signal transmission even in environments where fading exists such as in land mobile communications. This relates to an SSB communication method that allows

[Conventional technology]

Communication methods using SSB signals enable narrowband transmission and are excellent in terms of effective frequency utilization, but they are used under conditions where the signal propagation environment between transmitters and receivers varies greatly, such as in land mobile communications. In this case, fading causes amplitude distortion and degrades transmission quality.

Conventionally, in land mobile communications, narrowband communication has been used to eliminate the effects of amplitude distortion caused by fading.
As an SSB communication method, there is a method using an all-carrier SSB signal and an amplitude limiter as shown in Japanese Patent Application No. 59-259354 and Japanese Patent Application No. 60-12618. It is shown in the document “Daikoku and Ogoshi, “REAL
ZERO SSB Transmitter/Receiver Experiment”, Proceedings of the 1985 National Conference of the Institute of Electronics and Communication Engineers, No. 2394.

Among these conventional methods, the former patent application filed in 1983
-259354, the transmitting side uses an SSB signal with a carrier wave added as the transmitting signal, and the receiving side amplitude-limits the received signal and then generates a signal with an amplitude proportional to the time interval of the amplitude-limited output. After restoring the amplitude information, demodulation is performed by performing multiplicative detection using a recovered carrier wave.
The latter, according to Japanese Patent Application No. 12618/1980, modulates SSB (Single Sideband) with an audio signal on the transmitting side, adds a carrier wave to this to create a transmitted signal, and receives this on the receiving side, and then The audio signal is demodulated by making the amplitude constant using an amplitude limiter and then performing frequency detection.

[Problem that the invention seeks to solve]

In the conventional method described above, in which the transmitting side sends out an SSB signal with a carrier wave added as a transmitted signal, the receiving side limits the amplitude of the received signal, and then detects it to obtain a demodulated signal. There was a problem in that noise was generated when receiving signals.

In other words, when fading occurs during signal transmission, a sudden change in the phase of the received signal occurs due to a sudden drop in the reception level, but this phase change cannot be corrected by an amplitude limiter. , audible noise occurs in the demodulated signal when the reception level drops.

This is a problem that needs to be improved in order to achieve high quality signal transmission.

The present invention is an SSB that reduces the audible noise that occurs when the reception level drops due to such fading and enables high-quality signal transmission.
The purpose is to provide a communication method.

[Means for solving problems]

According to the present invention, the above-mentioned objects include a level compression means for level compressing a modulated input signal, an SSB modulation means for SSB modulating the level compressed signal, and a carrier wave signal for modulating the modulated signal. amplitude limiting means for forming a transmission signal by an additional addition means, receiving the transmission signal, and limiting the amplitude;
An SSB characterized in that the signal is restored by a detection means for detecting an amplitude-limited signal, a distortion compensation means for compensating for distortion of the detected signal, and a level expansion means for level-expanding the output signal of the distortion compensation means. This is achieved through communication methods.

〔Example〕

FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is a modulation signal input terminal, 2 is a level compressor, 3 is a carrier wave oscillator, 4 is an SSB modulator, 5 is an adder circuit, and 6 is a transmitter. 7 is a transmitting antenna, 8 is a transmitting section, 9 is a receiving antenna, 10 is a receiver, 11 is an amplitude limiter, 12 is a detector, 13 is a level expander, 14 is a demodulated signal output terminal, 15 is a receiving section It represents.

The operation of the embodiment shown in FIG. 1 will be explained according to the signal flow. In the transmitter 8, an information signal such as a band-limited audio signal input to the modulation signal input terminal 1 or a modulation signal using a subcarrier is transmitted. is input to the level compressor 2.

This level compressor 2 has the function of compressing the level of an input that is larger than a certain reference level, and amplifying the level of an input that is smaller than a certain reference level, and is also called a compressor.

Depending on the level compressor output, the output of the carrier wave oscillator 3 is converted into a lower sideband SSB or an upper sideband by the SSB modulator 4.
Generate SSB modulated wave. To generate the SSB modulated wave,
Well-known methods such as a filter method and a phase shift method may be used.

The SSB modulator output and carrier wave oscillator output are added by an adder circuit 5, and an SSB signal to which a carrier wave is added is obtained as the output. The adder circuit output is up-converted and power amplified by the transmitter 6, and then radiated from the transmitting antenna 6 at a desired frequency and power. In the receiving section 15 , the signal received by the receiving antenna 9 is down-converted and amplified by the receiver 10 and then input to the amplitude limiter 11 .

The amplitude limiter 11 suppresses fluctuations in the reception level due to fading and maintains a constant amplitude. After the amplitude limiter output is detected by a wave detector 12, the detected output is input to a level expander 13, and its output is guided to a demodulated signal output terminal 14.

As the detector, commonly used envelope detectors, product detectors, and frequency detectors can be used.

A level expander is also called an expander and has the function of compressing the level of an input that is smaller than a certain reference level and amplifying the level of an input that is larger.

FIG. 2 shows a first example of the detection means.

In FIG. 2, 16 is a detector input terminal, 17
18 is a band pass filter, 19 is an envelope detector, and 20 is a detector output terminal.

In FIG. 2, the output of the amplitude limiter led to the detector input terminal 16 is led to the sawtooth signal generator 17, which generates a sawtooth wave signal having an amplitude proportional to the time interval between zero points on the time axis. do.

After unnecessary components are removed from the sawtooth wave by a bandpass filter 18 , the wave is detected by an envelope detector, and a detected output is outputted to a detector output terminal 20 .

FIG. 3 shows a second example of the detection means. In FIG. 3, the output of the amplitude limiter led to the detector input terminal 16 is divided into two parts, one of which is led to the sawtooth signal generator 17 and has an amplitude proportional to the time interval between zero points on the time axis. The other signal is guided to a carrier wave regeneration circuit 21 to perform carrier wave regeneration. After unnecessary components are removed from the sawtooth wave by a band pass filter 18, the output thereof and the output of the carrier wave regeneration circuit are sent to a product detector 22.
The wave is detected by the detector and the detected output is output to the detector output terminal 20.

FIG. 4 shows a third example of the detection means.

In FIG. 4, the output of the amplitude limiter led to the detector input terminal 16 is detected by the frequency detector 23, and then input to the integrator 24 whose frequency vs. amplitude characteristic is -6 dB/octave. is output to the detector output terminal 20.

FIG. 5 shows an example of distortion compensating means corresponding to the embodiment of claim 2.

In FIG. 5, the detector output signal input to the distortion compensation circuit input terminal 25 is divided into two parts and input to a squarer 26 and a delay circuit 27, respectively. The squarer output signal and the delay circuit output signal are sent to the subtracter 28
and output to the distortion compensation circuit output terminal 29 (the squarer has a level adjustment function in addition to squaring operation).

FIG. 6 shows another example of the distortion compensation means.

In FIG. 6, the multiplicative detection output input to the distortion compensation circuit input terminal 25 is divided into three parts, one of which is input to a Hilbert transformer 30, and the output is squared by a squarer 31. Further, one of the three divided parts is squared by a squarer 32. squarer 31
The output of the squarer 32 is given a proportionality constant using amplifiers 33 and 34, respectively, and then the adder 3
5 and input to a -6 dB/octave equalizer 36. On the other hand, one output of the squarer 32 is passed through an amplifier 37 to provide a proportionality constant. The remaining one of the signals previously divided into three is input to the delay circuit 27.
By adding the outputs of 27, 31, 36, and 37 in an adder 38, 2 is output to the distortion compensation circuit output terminal 29.
A demodulated signal output without next-order distortion can be obtained.

FIG. 7 shows an example of distortion compensating means corresponding to the embodiment of claim 3.

In FIG. 7, the signal input to the distortion compensation circuit input terminal 25 (the frequency detection output integrated by an integrator with a frequency-to-amplitude characteristic of -6 dB/octave) is divided into three parts, and is divided into three parts, a Hilbert transformer 30 and a multiplier 39. , and delay circuit 27, respectively. The Hilbert transformer output is multiplied together with the frequency detection output in a multiplier 39. The multiplier output is input to amplifier 40. The delay circuit output is subtracted together with the amplifier output by a subtracter 41 and output to the distortion compensation circuit output terminal 29. Figure 2 above
In FIG. 7, parts common to each embodiment are omitted, and only the detection means or distortion compensation means is shown as a block diagram. Next, the operating principle of the present invention will be explained. As shown in Japanese Patent Application No. 59-259354, the band-limited information signal
For example, a transmission signal obtained by adding a carrier signal to an SSB signal obtained by lower sideband SSB modulation can be transmitted without distortion by transmitting only the zero point on the real time axis, so an amplitude limiter is required on the receiving side. Application of this makes it possible to remove amplitude distortion caused by fading.

Note that as long as the highest frequency of the band-limited information signal is lower than the carrier wave frequency, the distortion-free transmission described above is possible using either lower sideband SSB modulation or upper sideband SSB modulation.

The operating principle of the level compressor and level expander is as follows.

FIG. 8 is a diagram showing a level diagram explaining the operation of the level compressor and level expander.

As shown in FIG. 8, when the reference input level is 0 dB, the level compressor suppresses the level for inputs larger than 0 dB, and expands the levels for inputs smaller than 0 dB. Therefore, the overall dynamic range of the level of information components included in the transmitted signal is reduced.

Furthermore, the level expander inserted on the receiving side has the opposite characteristics to the level compressor, suppressing the level for inputs smaller than 0 dB, and expanding the level for inputs larger than 0 dB. Therefore, if a level compressor is provided on the transmitting side and a level expander is provided on the receiving side, the level expander output signal level will be equal to the level compressor input signal level. On the other hand, in the propagation path, noise generated due to a drop in the reception level, etc. is suppressed by the level expander on the receiving side, so the noise component included in the level expander output signal is reduced.

The operating principle of the main embodiments of the present invention will be explained below using mathematical formulas.

Here, for ease of explanation, the information signal m
(t) is a tone signal with an angular frequency ωm, and an example will be explained in which a carrier signal is added to a lower sideband SSB signal. At this time, the transmission signal S(t) is expressed by the following equation.

S(t)=Ccos(ωct)+Acos(ωc−ωm)t(C>A,ωc
>>ωm)=A(t)cos{ωct−φ(t)}…(1) A(t)=√[+()] ² +
() ² φ(t)=arctan〔Asin(ωmt)〕/〔C+Acos(ωmt
)〕≒(A/C)sin(ωmt) Here, C and ωc are the lower sideband waves, respectively.
These are the level and angular frequency of the carrier signal added to the SSB signal. Further, A is the level of the lower sideband SSB signal.

Furthermore, A(t) and φ(t) are the amplitude and phase of S(t).

When S(t) passes through the amplitude limiter, its output signal E(t) becomes E(t)=sgn[cos(ωct−φ(t))] (2).

When performing envelope detection or product detection as shown in FIG. 2 or 3, the amplitude term lost from the time interval of the zero point of E(t) is recovered. In other words, finding the period T(t) of the zero point, T(t)=2π/[d(ωct-φ(t))/dt]≒(1/fc)[1-(fc/fm) (A/C )cos(ωmt)] …(3) Here, fc=ωc/2π.

The part in [ ] in the above equation is the restored amplitude term. In order to extract this term, a sawtooth wave generation circuit is used that generates a sawtooth wave by integrating a constant voltage over a period of time equal to the time interval between zero points.

Since sawtooth waves contain many harmonic components,
A bandpass filter is used to extract only the component of ωc and to equalize the coefficient fm in equation (3).

As a result, the signal S ₀ (t) with restored amplitude information
is S ₀ (t)∝[1+(1/fc)(A/C) cos(ωmt)]·cos(ωct−φ(t)) (4).

By performing envelope detection on S ₀ (t), the following is obtained as the detection output V(t): V(t)∝1+(1/fc)(A/C)cos(ωmt) (5). A demodulated signal can be obtained by removing the direct current in equation (5).

On the other hand, in order to perform multiplicative detection, it is necessary to input E(t) to a carrier wave recovery circuit and extract the carrier wave component, but the carrier wave recovery circuit is a circuit using a general PLL (Phase Locked Loop). etc. can be used.

On the other hand, by performing product detection on the carrier wave regeneration circuit output and So(t), the detected output V(t) is V(t)≒K[1+(1/fc)(A/C)cos
(ωmt)]・[cosφ(t)]≒[1+(1/fc)
(A/C) cos (ωmt)]・cos [(A/C) sin
(ωmt)]≒K[1+(1/fc)(A/C) cos
(ωmt)]・[1-(1/2)(A/C) ² sin ²
(ωmt)]≒K[1+(1/fc)(A/C) cos
(ωmt)] ...(6) (K: proportionality constant), and a demodulated signal can be obtained by removing the DC component.

When performing frequency detection shown in Figure 4, the formula
Since the detection output is obtained as the time derivative of the phase term given in (1), the detection output V(t) is V(t)≒K{d[ωct−φ(t)]/dt}≒K{ωc
−
ωm (A/C) [cos (ωmt) + (A/C)]/
[1+2(A/C)cos(ωmt)]}≒K{ωc−
ωm(A/C) [cos(ωmt)+(A/C)]・[1
−2(A/C)cos(ωmt)〕}≒K{ωc−ωm
(A/C) [(A/C)+cos(ωmt)-2(A/
C) ² cos(ωmt)〕}≒K{ωc−ωm(A/C)
[(A/C)+cos(ωt)]} ...(7) (K: constant of proportionality). After removing the DC component of the detection output given by equation (7), it is passed through an integrator with a frequency vs. amplitude characteristic of -6 dB/octave to obtain V(t)≒K(A/C) sin(ωmt)...( 8) (K: proportionality constant) A demodulated signal is obtained.

The demodulated signals given by equations (5), (6), and (8) each have ωm
The harmonic components of are included as minute terms. That is, the detection output V(t) is given by V(t)= _∞ 〓 ⁿ⁼¹ Vn cos(nωmt) (9). Also, the coefficient Vn is usually Vi>Vj(i
<j). If the second harmonic among the harmonic components is audible, it becomes a problem, and by removing it, the transmission quality is improved. Therefore, the detection output V
The second Harmonic components can be removed and good transmission quality can be obtained. In an actual circuit configuration, it is necessary to perform the subtraction in equation (10) after giving V(t) a delay equivalent to the time required for the square operation, and when setting the delay time, use a spectrum analyzer, etc. Adjust so that the second harmonic component is minimized. Further, similar adjustment is required for the proportionality constant h so that the second harmonic component is minimized.

On the other hand, the frequency detection output V(t) given by equation (7)
is V(t)≒K{ωc−ωm(A/C)[cosωmt(1+
(A/C) cosωmt + (A/C) sinωmt
sinωmt〕｝≒Kωc−Kωm(A/C) cosωmt
−K(A/C) ² cosωmt [d(sinωmt)/dt]+
K(A/C) ² sinωmt [d(cosωmt)/dt]≒
Kωc−K(A/C) [d(sinωmt)/dt]−K
(A/C) ² [d(cosωmt・cos^ωmt)/dt]
…(11) can also be expressed.

cos^(ωmt) is the Hilbert transform of cos(ωmt). When the DC component in equation (11) is removed and integrated with a -6 dB/octave integrator, the output is V(t)≒l{sin(ωmt)−(A/C)cos (ωmt)sin(ωmt) } ...(12) (l: constant of proportionality).

Hilbert transform output V of V(t) in equation (12)
The product of (t) and V^(t) is V(t)V(t)≒l ² sin(ωmt)cos(ωmt) considering A/C<1.
......(13) becomes. Therefore, from equations (12) and (13), V(t)-1/l・A/C・V(t) ・V^(t)∝sin(ωmt) …(14) is obtained, and 2 It can be seen that since the first-order distortion components can be removed, the transmission quality can be improved by the embodiment of claim 3.

Note that in an actual circuit configuration, it is necessary to perform the subtraction in equation (14) after delaying V(t) in equation (12) by a time corresponding to the time required for various calculations.
The delay time is adjusted using a spectrum analyzer or the like so that the 2ωmt component is minimized.

According to the circuit configuration shown in FIG.
As shown in No. 23647, second-order distortion can be removed as follows. If the information signal m(t) is expressed by the analytical signals f(t) and f^(t), the detection output after multiplicative detection and equalization of -6 dB/octave is V(t) = 1 + f (t)/C - [f(t)/C] ² + [f^(t)/C] ² - (-6dB/octave) [(3/2) (f(t)/C) ² + ( 1/2) (f^(t)/C) ² +O(C ^-3 ) ...(15).

The second term f(t)/C represents the principal component. Based on this, (3/2)(f(t)/C) ² and (1/
2) (f(t)/C) ² can be generated, so -
6dB/octave equalization and further (f(t)/C)
² and -(f(t)/C) ² using an adder circuit, V(t)=1+f(t)/C+O(C ^-3 )...(16) is obtained, and the second-order distortion can be removed.

〔Effect of the invention〕

As explained above, according to the SSB communication system of the present invention, it is possible to insert an amplitude limiter to remove amplitude distortion received in the propagation path, and also to improve reception by using a level compressor and a level expander. It greatly reduces audible noise caused by drop in level, and the distortion compensation means makes it possible to remove the second harmonic of the detected signal, resulting in a narrow band with good transmission quality. It has the advantage of being able to implement a wireless communication line.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
4 to 4 are block diagrams showing an embodiment of the detection means, FIGS. 5 to 7 are block diagrams showing an embodiment of the distortion compensation means, and FIG. 8 explains the operation of the level compressor and level expander. It is a diagram showing a level diagram. 1...Modulation signal input terminal, 2...Level compressor, 3...Carrier wave oscillator, 4...SSB modulator, 5
...Addition circuit, 6...Transmitter, 7...Transmission antenna, 8...Transmission unit, 9...Reception antenna, 10...
... Receiver, 11 ... Amplitude limiter, 12 ... Detector, 13 ... Level expander, 14 ... Demodulated signal output terminal, 15 ... Receiver section, 16 ... Detector input terminal, 17 ... Sawtooth wave signal generator, 18...bandpass filter, 19...envelope detector, 20...
Detector output terminal, 21...Carrier regeneration circuit, 22
...Multiplicative detector, 23...Frequency detector, 24...
...Integrator, 25...Distortion compensation circuit input terminal, 26,
31, 32... Squarer, 27... Delay circuit, 2
8, 41...Subtractor, 29...Distortion compensation circuit output terminal, 30...Hilbert transformer, 33, 34, 3
7, 40...Amplifier, 35, 38...Adder, 3
6... Equalizer, 39... Multiplier.

Claims (1)

[Claims] 1. Level compression means for level compressing a modulated input signal, and SSB for SSB modulating the level compressed signal.
A modulation means, an addition means for adding a carrier signal to the modulated signal to form a transmission signal, an amplitude limiting means for receiving the transmission signal and limiting the amplitude, a detection means for detecting the amplitude limited signal, and a detection means for detecting the amplitude limited signal. 1. An SSB communication system characterized in that a signal is restored by a distortion compensating means for compensating for the distortion of a signal that has been transmitted, and a level expanding means for level expanding the output signal of the distortion compensating means. 2. The SSB communication system according to claim 1, wherein the distortion compensation means comprises a circuit that subtracts a signal obtained by squaring the detection output signal and a signal obtained by temporally delaying the detection output signal. . 3. The detection means is composed of a frequency detector and an integrator having a characteristic of -6 dB/octave which receives the output of the frequency detector as input, and uses the output of the integrator as the detection output, and is configured to perform distortion compensation. The means is configured to subtract a signal obtained by multiplying the detection output by a signal obtained by Hilbert transformation of the detection output signal and a signal obtained by temporally delaying the detection output. Range of SSB communication method described in item 1.