JPH0732375B2 - 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]

The structure of the present invention detects whether or not a carrier having a predetermined frequency exists in a transmission medium, and if there is no carrier having a predetermined frequency, the first carrier having the predetermined frequency is detected. Generate and amplitude-modulate the first carrier wave with the first information signal wave including the transmission information to generate the both sidebands, attach the generated both sidebands to the transmission medium, and transmit When a carrier with a predetermined frequency is present in the medium, it is about π with respect to the first carrier that has the same frequency as that of the carrier and is locked to the phase of the carrier at the receiving point.
A search carrier having a phase difference of / 2 (or -π / 2) is generated, both sidebands propagating in the transmission medium are synchronously detected by the search carrier, it is determined whether or not the detection output is zero, and detection is performed. When the output is zero, the second carrier having a predetermined phase angle with respect to the first carrier is generated, and the second carrier is amplitude-modulated by the second information signal wave including the transmission information to generate the double-sided band. A wave is generated, the generated double sideband waves are suppressed to a carrier wave and transmitted to a transmission medium, the first carrier wave is received from the transmission medium, and the frequency is the same as the frequency of the first carrier wave at the reception point. Of the first carrier and the second carrier having a predetermined phase difference with respect to the first carrier, respectively, has a phase difference of about π / 2 (or −π / 2). Second
When the demodulated carrier wave and the first demodulated carrier wave are generated and the first information signal wave is detected, the both sideband waves received by the first demodulated carrier wave are synchronously detected, and the second information signal wave is detected. , Both sideband waves received by the second demodulation carrier wave are synchronously detected.

[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)
However, E _1U (t), E _1L (t) are the upper sideband (USB) and the lower sideband (LSB) of the first channel, and 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 and the lower sideband.
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 This holds 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, if two channels of the same frequency are vacant, the oscillating station that exclusively occupies the first channel of the two channels transmits the modulated signal as a double sideband with a carrier. If one of the two channels of the same frequency is vacant, the first carrier of the first channel is received, and the first carrier having the phase delayed by a predetermined phase angle α with respect to the phase of the first carrier at the reception point is received. 2 carriers first
It is generated by phase-locking with a carrier wave, and the second carrier wave is amplitude-modulated with a second signal wave and transmitted as a double-sided wave of carrier wave suppression. Further, upon reception, the first modulated demodulated wave and the second modulated demodulated wave receive the first carrier wave propagating through the transmission medium and are phase locked to the first carrier wave with reference to the phase of the first carrier wave at the reception point. Is generated.
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, if a carrier having a predetermined frequency does not exist in the transmission medium, the first carrier is amplitude-modulated by the first information signal wave and the double sideband with the first carrier is transmitted to the transmission medium. , If there is a carrier of a predetermined frequency, it is approximately π / 2 (or -π / 2) with respect to the phase of that carrier at the receiving point.
A search carrier wave locked to the phase difference of is generated and synchronously detected with the search carrier wave. When the detection output is zero, the second carrier wave having a predetermined phase angle with respect to the first carrier wave at the receiving point is detected. The first carrier wave and the first carrier wave, which are amplitude-modulated by the second information signal wave and transmit the both-sideband waves of carrier suppression to the transmission medium, receive the first carrier wave from the transmission medium, and lock the phase of the carrier wave at the receiving point. A second demodulation carrier and a first demodulation carrier having a phase difference of about π / 2 (or −π / 2) with respect to a second carrier having a predetermined phase difference with respect to one carrier are generated, Both side bands are synchronously detected by the demodulated carrier.

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. 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 first carrier wave is extracted from the coaxial cable A by the crystal filter 11. The signal waveform at the reception point of this first carrier is (12)
In the equation, it is represented by an equation with β = 0.

This first carrier wave is input to the phase comparator 12 and compared in phase with the output signal of the voltage controlled oscillator 13. The phase difference is input to the voltage controlled oscillator 13, and the frequency of the signal output from the voltage controlled oscillator 13 is controlled.
Eventually, a signal in which the signal output from the voltage controlled oscillator 13 and the first carrier wave are phase locked is generated. The signal is split into two by the splitter 40 and input to the π / 2 phase shifter 16 and the π / 2-α phase shifter 15. This gives π
/ 2-α From the phase shifter 15, β = π /
A first demodulation carrier of the formula expressed by 2-α is generated. or,
From the π / 2 phase shifter 16, β = π / 2 in the equation (12)
A second demodulated carrier of the above equation is generated.

The first demodulated carrier wave is the synchronous detection circuit 1
I am typing in 7. Further, the signal wave received from the coaxial cable A is input to the band pass filters 19L and 19U, only the both side bands are extracted and input to the synchronous detection circuit 17. Then, by being synchronously detected by the synchronous detection circuit 17, the detection signal waveforms D ₁ (t) and D ₂ (t) represented by the equations (19) and (20) can be generated. However, β = π / 2−
Since α, only D ₁ (t) of the equation (19) (represented by the equation similar to the equation (22) for the first information signal) is detected, and D ₂ (t) = 0. Therefore, only the first information signal wave is detected.

On the other hand, the second demodulated carrier wave output from the π / 2 phase shifter 16 is input to the synchronous detection circuit 18.
Further, the signal wave received from the coaxial cable A is input to the band pass filters 19L and 19U, only the both side bands are extracted and input to the synchronous detection circuit 18. Then, by being synchronously detected by the synchronous detection circuit 17, the detection signal waveforms D ₁ (t) and D ₂ (t) represented by the equations (19) and (20) can be generated. However, since D ₁ (t) and D ₂ (t) are β = π / 2, they are represented by the equations (21) and (22). Therefore, only the second information signal wave is detected.

A channel can be selected by switching and transmitting one of the first information signal wave or the second information signal wave according to the channel setter. If there is no carrier having a predetermined frequency on the coaxial cable A, neither the first demodulated carrier nor the second demodulated carrier is generated, so both the first information signal wave and the second information signal wave become zero.

The transmitter S is constructed as shown in FIG. In the transmitter S, the first modulated carrier wave whose frequency and phase are locked to the oscillation waveform of the crystal oscillator 50 is generated by the phase comparator 51 and the voltage controlled oscillator 52. The first modulated carrier wave is input to the -α phase shifter 54 and the phase thereof is shifted to generate the second modulated carrier wave represented by the equation (4). The first modulated carrier wave and the second modulated carrier wave are input to the switch 53.

On the other hand, the first information signal wave output from the synchronous detection circuit 17 of the receiver R and the synchronous detection circuit 18 of the receiver R.
The second information signal waves output from the are input to the zero determination circuit 24 and the zero determination circuit 25, respectively. Then, it is determined whether the detected signal wave is zero. If the detected signal wave is zero, it means that the channel is not used and is empty. The switch 53 allows the first modulated carrier wave to pass if both the first channel and the second channel are vacant, and allows only the second modulated carrier wave to pass if only the second channel is vacant, and both channels are vacant. If not, both modulated carriers are operated so as not to pass.

As a result, only the modulated carrier wave corresponding to the vacant channel is output to the modulator circuit 55, and the carrier wave is amplitude-modulated in the modulator circuit 55 based on the information signal wave. Then, the band pass filters 58L and 58U
A carrier-suppressed double-sided band is sent to the coaxial cable A via. At this time, only when the modulated carrier used for amplitude modulation is the first modulated carrier, the first modulated carrier is output to the coaxial cable A. That is, the first channel is a double sideband with a first modulated carrier, and the second channel is a double sideband with carrier suppression.

In this way, if both of the two channels are empty, the information signal wave is transmitted by the double sideband with the first modulated carrier wave, and the first channel is used. Therefore, the first channel is used. If the modulated carrier exists in the coaxial cable A and the second channel is empty, the information signal wave amplitude-modulated from the second modulated carrier is transmitted as the carrier suppressed double sideband. That is, the second modulated carrier wave is not transmitted to the coaxial cable A.

On the other hand, if both channels are not empty, the pass band of the crystal BPF 11 is set to the frequency band of another carrier, and the carrier of another frequency is extracted. 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, at the time of reception, it is possible to select one channel in an arbitrary band by frequency scanning.

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 ... π / 2-α phase shifter 16 ... π / 2 phase shifter 17, 18 ... Synchronous detection circuit 1 ... Head end

Claims (2)

[Claims] 1. A first information including a transfer information is detected by detecting whether or not a carrier of a predetermined frequency is present in a transmission medium, and if the carrier of the predetermined frequency is not present, a first carrier of the predetermined frequency is generated. A first carrier is amplitude-modulated by a signal wave to generate a double sideband, and the generated double sideband is attached to the first carrier and transmitted to the transmission medium, and the transmission medium has a carrier of a predetermined frequency. In this case, at the same frequency as that of the carrier, about π with respect to the first carrier locked to the phase of the carrier at the receiving point.
A search carrier having a phase difference of / 2 (or -π / 2) is generated, both sidebands propagating through the transmission medium are synchronously detected by the search carrier, and it is determined whether the detection output is zero, When the detection output is zero, a second carrier having a predetermined phase angle with respect to the first carrier is generated, and the second carrier is amplitude-modulated by a second information signal wave including transfer information. A double sideband is generated, the generated double sideband is suppressed to a carrier wave and transmitted to the transmission medium, the first carrier wave is received from the transmission medium, and
For a first carrier wave that has the same frequency as that of the carrier wave and is locked to the phase of the carrier wave at the reception point and a second carrier wave that has a predetermined phase difference with respect to the first carrier wave, about π / 2 ( Alternatively, when the second demodulation carrier wave and the first demodulation carrier wave having a phase difference of −π / 2) are generated and the first information signal wave is detected, both sideband waves received by the first demodulation carrier wave are detected. Is detected synchronously and the second information signal wave is detected, the double sideband waves received by the second demodulation carrier wave are synchronously detected. 2. When the detection output is not zero when synchronous detection is performed with the search carrier wave of the predetermined frequency, an empty channel of the transmission path is detected for another predetermined frequency,
2. The amplitude modulation phase double transmission system according to claim 1, wherein both sidebands are transmitted to the vacant channel.