JPH07118684B2 - Double sideband amplitude modulation phase double transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new transmission system in which amplitude modulated signals in wired and wireless are multiplexed by phase doubling.

[0002]

2. Description of the Related Art Conventionally, there are an amplitude modulation transmission system and a frequency division multiplexing transmission system. These methods involve an operation of amplitude-modulating a carrier wave of a certain frequency with a signal containing information. In this operation, the lower sideband and the upper sideband are generated centering on the carrier wave in the frequency space. Even in the case of frequency division multiplexing, the frequency transition of the modulation signal is necessary, but this operation also involves amplitude modulation of the carrier in a broad sense. Therefore, by amplitude-modulating the carrier with the amplitude-modulated modulation signal and the frequency-modulated modulation signal, the amplitude-modulated wave is frequency-division multiplexed, and the frequency-modulated wave is frequency-division multiplexed. Hereinafter, in the present specification, the amplitude modulation is not limited to the meaning of the amplitude modulation of the original signal, and also includes the modulation of the carrier wave that is performed when the frequency of the modulated signal is changed when the various modulated signals are frequency division multiplexed. .

In the above amplitude modulation, only one carrier is used at the same frequency. Therefore,
If all the cosine waves used for modulation in the process of frequency division multiplexing are used as carriers, not only the waves that are modulated when they are transmitted to the transmission line, but one channel is assigned to each carrier.

[0004]

[Problems to be Solved by the Invention]
No transmission method for channel transmission has been proposed. The present invention proposes a transmission method capable of transmitting two channels per carrier.

[0005]

According to a first aspect of the present invention, a pilot signal having a predetermined frequency is transmitted through a transmission medium, the pilot signal is received, and the phase of the pilot signal is locked at the receiving point. Predetermined pilot signal
A carrier wave of a predetermined frequency that has a predetermined relationship with the frequency is generated, the sidebands received from the transmission medium are synchronously detected while the phase of the carrier wave is changed, and the detection output is zero regardless of the phase of the carrier wave. In this case, the first carrier having the same frequency as the carrier and having an arbitrary phase is amplitude-modulated by the first information signal wave containing the transmission information to generate the both sidebands, and the both sidebands are transmitted to the transmission medium, If the detection output becomes zero in one phase, ± π / 2 phase with respect to that phase
A second carrier wave having a phase having no difference is generated, the second carrier wave is amplitude-modulated with a second information signal wave containing transmission information to generate a double sideband wave, and the double sideband wave is transmitted. To the carrier, receive the pilot signal from the transmission medium, lock the phase of the pilot signal at the receiving point, and
It is characterized in that both sidebands received from the transmission medium are synchronously detected while generating and shifting the phase of the carrier wave.

[0006]

In order to facilitate the explanation, the first information signal wave is

## EQU1 ## S ₁ (t) = F ₁ (ω) cos (ωt + φ ₁ (ω)) (1) The second information signal wave is

## EQU00002 ## Consider a single frequency as S ₂ (t) = F ₂ (ω) cos (ωt + φ ₂ (ω)) (2). When the signal wave is an arbitrary waveform, the above equation may be considered by Fourier integration. Therefore,
When the signal wave is an arbitrary waveform, it can be regarded as the synthesis of the single spectrum in the above equation, and therefore the principle can be understood by analyzing the single spectrum.

A first carrier wave and a second carrier wave used at the time of modulation (hereinafter, referred to as "first modulated carrier wave" and "second modulated carrier wave", and both are collectively referred to as "modulated carrier wave").
Is defined as follows.

[Number 3] _{C 1 (t) = A 1} cos (ω c t + θ) ... (3)

[Number 4] _{C 2 (t) = A 2} cos (ω c t + θ-α) ... (4)

Here, α is a phase angle of the first modulated carrier wave with respect to the second modulated carrier wave. The amplitude-modulated wave at the transmission point (hereinafter referred to as the “modulated wave”) is as follows.

[Number 5] _{E 1 (t) = S 1} (t) C 1 (t) = F 1 (ω) A 1 cos (ωt + φ 1 (ω)) cos (ω c t + θ) ... (5)

[6] _{E 2 (t) = S 2} (t) C 2 (t) = F 2 (ω) A 2 cos (ωt + φ 2 (ω)) cos (ω c t + θ-α) ... ( 6) Hereinafter, the transmission division by the first modulated carrier wave and the second modulated carrier wave will be referred to as the first channel and the second channel.

[0009]

[Equation 7] E ₁ (t) = E _1U (t) + E _1L (t) = F ₁ (ω) A ₁ cos ((ω _c + ω) t + θ + φ ₁ (ω)) + F ₁ (ω) A ₁ cos ((ω _c -ω) t + θ-φ ₁ (ω))… (7)

[Equation 8] E ₂ (t) = E _2U (t) + E _2L (t) = F ₂ (ω) A ₂ cos ((ω _c + ω) t + θ + φ ₂ (ω) -α) + F ₂ (ω) A ₂ cos ((ω _c -ω) t + θ-φ ₂ (ω) -α) (8) where E _1U (t) and E _1L (t) are Upper sideband (USB), lower sideband (LSB), E _2U (t), E
_2L (t) is the upper sideband (USB) and lower sideband (LSB) of the second channel. The transfer function of the transmission line

[0010]

## EQU9 ## Let G (ω) exp (jψ (ω)) (9). Then, both sidebands of the first channel at the receiving point
R ₁ (t) and the double sideband R ₂ (t) of the second channel are as follows.

[Formula 10] R ₁ (t) = R _1U (t) + R _1L (t) = F ₁ (ω) G (ω _C + ω) A ₁ cos ((ω _c + ω) t + θ + φ ₁ (ω) + ψ (ω _c + ω)) + F ₁ (ω) G (ω _C -ω) A ₁ cos ((ω _c -ω) t + θ-φ ₁ (ω) + ψ (ω _c- ω))… (10)

[Equation 11] R ₂ (t) = R _2U (t) + R _2L (t) = F ₂ (ω) G (ω _C + ω) A ₂ cos ((ω _c + ω) t + θ + φ ₂ (ω) + ψ (ω _c + ω) -α) + F ₂ (ω) G (ω _C -ω) A ₂ cos ((ω _c -ω) t + θ-φ ₂ (ω) + ψ (ω _c- ω) -α)… (11)

However, R _1U (t) and R _1L (t) are the upper sideband (USB) and the lower sideband (L) of the first channel at the receiving point.
SB) and R _2U (t) and R _2L (t) are the upper sideband (USB) and the lower sideband (LS) of the second channel at the receiving point.
B). Next, the carrier used for synchronous detection at the receiving point (hereinafter referred to as “demodulated carrier”) is defined by the following equation.

[0012]

[Equation 12] H (t) = Bcos (ω _C t + θ + ψ (ω _C ) + β) (12) where θ + ψ (ω _C ) is the phase angle at the receiving point of the first modulated carrier. is there. β is a deviation phase angle with respect to the phase angle. With the demodulated carrier of formula (12), the following formula is established for the synchronous detection of the reception double sideband R ₁ (t) of the first channel.

[0013]

[Equation 13] D ₁ `(t) = R ₁ (t) H (t) = F ₁ (ω) G (ω _C + ω) A ₁ cos ((ω _c + ω) t + θ + φ ₁ ( ω) + ψ (ω _c + ω)) × B cos (ω _C t + θ + ψ (ω _C ) + β) + F ₁ (ω) G (ω _C -ω) A ₁ cos ((ω _c -ω ) t + θ-φ ₁ (ω) + ψ (ω _c -ω)) × Bcos (ω _C t + θ + ψ (ω _C ) + β)… (13) Frequency of D ₁ ｀ (t) ω _C Letting D ₁ (t) be the detected signal wave with the above components removed, D ₁ (t) is expressed by the following equation.

[0014]

[Equation 14] D ₁ (t) = 1/2 × F ₁ (ω) G (ω _C + ω) A ₁ B × cos (ωt + φ ₁ (ω) + ψ (ω _c + ω) -ψ ( ω _C ) -β) +1/2 × F ₁ (ω) G (ω _C -ω) A ₁ B × cos (ωt + φ ₁ (ω) -ψ (ω _c -ω) + ψ (ω _C ) + β) (14) Similarly, with the demodulated carrier of formula (12), the following formula is established for synchronous detection of the reception double sideband R ₂ (t) of the second channel.

[0015]

[Equation 15] D ₂ `(t) = R ₂ (t) H (t) = F ₂ (ω) G (ω _C + ω) A ₂ cos ((ω _c + ω) t + θ + φ ₂ ( ω) + ψ (ω _c + ω) -α) × B cos (ω _C t + θ + ψ (ω _C ) + β) + F ₂ (ω) G (ω _C -ω) A ₂ cos ((ω _c -ω) t + θ-φ ₂ (ω) + ψ (ω _c -ω) -α) × Bcos (ω _C t + θ + ψ (ω _C ) + β)… (15)

[0016] D ₂ `a detection signal waves ingredients remove frequency omega _C or more components of a (t) and D ₂ (t), D ₂ (t) is expressed by the following equation.

## EQU16 ## D ₂ (t) = 1/2 × F ₂ (ω) G (ω _C + ω) A ₂ B × cos (ωt + φ ₂ (ω) + ψ (ω _c + ω) -ψ ( ω _C ) -α-β) +1/2 × F ₂ (ω) G (ω _C -ω) A ₂ B × cos (ωt + φ ₂ (ω) -ψ (ω _c -ω) + ψ (ω _C ) + α + β) (16) Here, the following assumption is introduced.

(17) G (ω _C + ω) = G (ω _C -ω) (17)

(18) ψ (ω _c + ω) -ψ (ω _C ) = ψ (ω _C ) -ψ (ω _c -ω) ≡ψ (ω) (18)

Assuming that Eq. (17) is such that the magnitude of the transfer function in the transmission line is the frequency ω _C between the upper sideband band and the lower sideband band.
Means to be a subject. Applies to space and coaxial cables. The assumption in Eq. (18) is that the phase difference with respect to the phase at the frequency ω _C of the transfer function in the transmission line is the target for the frequency ω _C between the upper sideband band and the lower sideband band. Means It is established if the phase characteristic of the transfer function in the transmission line is linear with respect to the frequency ω, that is, if there is no dispersion. Usually, space and coaxial cables have no dispersion, that is, can be regarded as non-phase distortion transmission lines.

When the assumptions of the above equations (16) and (17) are introduced, (1
Equations 4) and (16) can be transformed as follows.

## EQU19 ## D ₁ (t) = F ₁ (ω) G (ω _C + ω) A ₁ B cos (ωt + φ ₁ (ω) + Ψ (ω)) cos β (19)

[Equation 20] D ₂ (t) = F ₂ (ω) G (ω _C + ω) A ₂ B cos (ωt + φ ₂ (ω) + Ψ (ω)) cos (α + β) (20) ( What can be said from equations (19) and (20) is that if β = π / 2,

[Equation 21] D ₁ (t) = 0 ... (21)

[Equation 22] D ₂ (t) =-F ₂ (ω) G (ω _C + ω) A ₂ B cos (ωt + φ ₂ (ω) + Ψ (ω)) sin (α) (22) .

What can be said from the above equation is that if the DSB received wave is synchronously detected with the demodulated carrier wave having the same frequency ω _C , which has a π / 2 phase difference with respect to the phase angle of the first modulated carrier wave at the receiving point, This means that the detection signal wave of the first channel can be set to zero and the second information signal wave of the second channel can be detected.

On the contrary, if the DSB received wave is synchronously detected with the demodulated carrier wave having the same frequency ω _C , which has a phase difference of π / 2 with respect to the phase angle of the second modulated carrier wave at the receiving point, The first information signal wave of the first channel can be detected by setting the detection signal wave of the channel to zero.

Further, by setting the phase difference α between the first modulated carrier wave and the second modulated carrier wave to π / 2, the detection output of the detection channel can be maximized. In this way, it is possible to transmit and detect the amplitude-modulated signal waves of the both sideband waves in which the information signal waves of the two channels are multiplexed with the phase double.
In this transmission method, it is necessary to generate a second demodulation carrier and a first demodulation carrier of the same frequency, which are phase-locked with a phase difference of approximately π / 2 with respect to the phase of the reception point of the first modulation carrier and the second modulation carrier. There is.

Therefore, in the present invention, the pilot signal is transmitted to the transmission medium, the pilot signal is phase-locked to generate the first modulated carrier wave and the second modulated carrier wave of a predetermined frequency, and the first phase is changed by the phase shift. A demodulation carrier wave and a second demodulation carrier wave are generated. If two channels of the same frequency are vacant, the transmitter that exclusively occupies the first channel of the two channels uses the first information carrier wave as the first modulated carrier wave of an arbitrary phase of a predetermined frequency generated from the pilot signal. Amplitude-modulate and output as both sidebands. When the first channel is used and only the second channel is vacant, the first channel having a phase difference of π / 2 with respect to the phase of the carrier wave at which the detection output of the signal of the first channel becomes zero. Preferably non-zero for one modulated carrier
A second modulated carrier wave having a phase having a π / 2 phase difference is generated, the second carrier wave is amplitude-modulated by the second information signal wave, and the second carrier wave is transmitted to the transmission medium as a double-sided wave. Also, for reception,
When a pilot signal is received from a transmission medium, the pilot signal is phase-locked to generate a carrier wave of a predetermined frequency, and synchronous detection is performed while sequentially shifting the phase of the carrier wave, there is a phase in which the other information signal wave disappears. . When the time when the other information signal wave disappears is confirmed by the human ear and the carrier wave is fixed to the phase and synchronous detection is performed, only the desired information signal wave can be detected. Therefore, it becomes possible to select a desired one channel out of two channels by the phase shift of the carrier wave. In this way, it becomes possible to transmit the amplitude modulation signals of two channels in the same frequency band.

[0023]

According to the present invention, a pilot signal having a predetermined frequency is transmitted through a transmission medium, and in the case of transmission, the pilot signal is locked to the phase at the receiving point and the pilot signal is transmitted.
A carrier wave of a predetermined frequency that has a predetermined relationship with a predetermined frequency of the signal is generated, and while the phase of the carrier wave is shifted, both sideband waves received from the transmission medium are synchronously detected, and the detection output is independent of the phase of the carrier wave. When it is zero, the first carrier having the same frequency as the carrier and having an arbitrary phase is amplitude-modulated by the first information signal wave including the transmission information to generate the both sidebands, and the both sidebands are transmitted to the transmission medium. , In one phase of the carrier,
When the detection output becomes zero, it is ± π with respect to the phase.
/ 2 generates a second carrier having a phase having no phase difference , amplitude-modulates the second carrier with a second information signal wave containing transmission information, and generates a double-sided band Is transmitted to the transmission medium, and in the case of reception, the carrier wave is generated by locking the phase at the receiving point of the pilot signal, and the double sideband waves received from the transmission medium are synchronously detected while shifting the phase of the carrier wave. I am trying to do it.

Therefore, one DSB can transmit and receive the information signal waves of two channels. Each transmitter can send an information signal wave to an empty channel.

[0025]

EXAMPLES The present invention will be described below based on a specific example. The present embodiment is an application of this system to a local area network. The coaxial cable A has an upstream band (low group) in which a signal is transmitted to the headend 1 and a downstream band (high group) in which a signal is transmitted back from the headend 1 and transmitted from the headend 1 to a terminal. Exists. A pilot signal transmission station 2 is provided at the final end of the coaxial cable A, and the pilot signal is transmitted in the lower limit frequency band of the upstream channel. The pilot signal is frequency-converted into a high-group downlink channel at the head end and transmitted to the coaxial cable A.
The receiver R of each terminal connected to the coaxial cable (transmission medium) A is configured as shown in FIG.

In the present embodiment, the phase angle of the second modulated carrier wave is delayed by α with respect to the phase of the first modulated carrier wave. Therefore, the phase of the first demodulation carrier wave is delayed from the phase of the second demodulation carrier wave by α.

In such a system, as shown in FIG. 1, a large number of receivers R are provided at each position of the coaxial cable A. In each receiver R, the crystal filter 11 extracts a pilot signal of a predetermined frequency from the coaxial cable A. The pilot signal is phase-locked, and the phase comparator 12, the voltage-controlled oscillator, and the frequency divider 40 generate a carrier wave having a predetermined frequency with respect to the pilot signal.

This carrier wave is input to the phase shifter 15 to shift its phase at a predetermined speed. This phase shifter 1
The carrier wave output from 5 is expressed by equation (12). However, θ + ψ (ω _C ) + β is the phase term of the generated carrier wave. β is the phase difference with respect to the phase of the carrier wave at the receiving point. The phase shift is achieved by changing β.

The carrier wave whose phase shifts sequentially is the synchronous detection circuit 1
7, the signal wave received from the coaxial cable A is also input to the band pass filters 19L and 19U, and only the both side band waves are extracted and input to the synchronous detection circuit 17. Then, by being synchronously detected by the synchronous detection circuit 17, a detection signal waveform represented by the equations (19) and (20)
D ₁ (t) and D ₂ (t) can be generated.

When β becomes equal to π / 2, the detection signal waveform D ₁ (t) of the equation (19) is zero, and only the detection signal waveform D ₂ (t) can be detected. That is, the second of the second channel
It becomes possible to detect only the information signal wave. When β becomes (π / 2-α), the detected signal waveform D ₂ (t) is zero, and only the detected signal waveform D ₁ (t) can be detected. That is, it becomes possible to detect only the first information signal wave of the first channel.

The phase of the carrier wave is sequentially changed, and when only the first information signal wave or the second information signal wave is detected, the channel selection switch 16 is operated to stop the phase change and the carrier wave is changed. The phase of can be fixed to the tuning phase.

The transmitter S is constructed as shown in FIG. The detection output output from the synchronous detection circuit 17 of the receiver R is input to the zero determination circuit 24. Then, it is determined whether the detected signal wave is zero. All phases of carrier wave (-π /
In 2 <β ≦ π / 2), if the detected signal wave is zero,
This means that both channels are empty. In that case, the phase shift stop signal indicates that the phase shifter 1
5, the phase shifter 15 stops the phase shift, and the first modulated carrier wave whose phase is fixed is output to the modulation circuit 55.

As a result, in the modulation circuit 55,
The first modulated carrier is amplitude-modulated based on the first information signal wave input at that time. Then, the carrier suppressed double sideband waves are sent to the coaxial cable A through the bandpass filters 58L and 58U.

On the other hand, the zero discrimination circuit 24 causes all phases (-
In the case of π / 2 <β ≦ π / 2), when the detection output becomes zero in only one phase, the phase shift stop signal is output to the phase shifter 15 in the phase in which it becomes zero. And
The carrier wave whose phase shift has stopped and which is output from the phase shifter 15 is output to the modulation circuit 55 as the second modulated carrier wave.
The second modulated carrier is a carrier having a π / 2 phase difference from the first modulated carrier at the receiving point. That is, α =
π / 2.

Then, in the modulation circuit 55, the second modulated carrier wave is amplitude-modulated by the second information signal wave inputted at that time, and is passed through the band-pass filters 58L and 58U as a carrier-suppressed double-sided wave to the coaxial cable. Sent to A.

On the other hand, if both channels are not empty, the above-mentioned signal processing is executed for the channel of another frequency band by automatically changing the set value of the frequency divider 40. In this way, an empty channel is searched for along with the frequency scan, and the information signal wave is amplitude-modulated and transmitted to the empty channel.

Also during reception, the channel of the arbitrary frequency band can be detected by detecting the information signal wave of the channel of the predetermined band according to the set value by the channel setter 18.

Although the wire communication system has been described in the above embodiments, the present invention can be applied to a wireless communication system as well.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a receiver of a transmission system according to a specific example of the present invention.

FIG. 2 is a block diagram showing a configuration of a transmitter in the transmission system according to the embodiment.

[Explanation of symbols]

 A ... Coaxial cable 15 ... Phase shifter 17 ... Synchronous detection circuit 1 ... Head end

Claims (2)

[Claims] 1. A pilot signal having a predetermined frequency is transmitted through a transmission medium, the pilot signal is received, and the phase of the pilot signal is locked at a receiving point.
It has a predetermined relationship with the predetermined frequency of the pilot signal.
Generates a carrier wave having a predetermined frequency that, while changes the phase of the carrier wave, and coherent detection of both sidebands are received from the transmission medium, when the detection output is zero regardless of the phase of the carrier, the 1st with the same frequency as the carrier wave and arbitrary phase
A carrier wave is amplitude-modulated with a first information signal wave including transmission information to generate a double sideband wave, and the double sideband wave is transmitted to a transmission medium, and the detection output becomes zero in one phase of the carrier wave. In that case, there is a ± π / 2 phase difference with respect to that phase.
Generate a second carrier with a phase that is not
A carrier wave is amplitude-modulated with a second information signal wave containing transmission information to generate a double sideband wave, the double sideband wave is transmitted to a transmission medium, the pilot signal is received from the transmission medium, and the pilot signal the transportable by locking the phase at the receiving point
A double-sided wave amplitude modulation phase double transmission method characterized in that a double-sided wave received from a transmission medium is synchronously detected while generating a wave and shifting the phase of the carrier wave. 2. When synchronous detection is performed while shifting the phase of the carrier wave, if there is no phase where the detection output becomes zero, another carrier wave of a predetermined frequency locked to the pilot signal is generated. 2. The amplitude modulation phase double transmission system according to claim 1, wherein the carrier wave is phase-shifted and synchronous detection is performed to search for a vacant channel.