JP2825890B2 - Voice communication system for CATV system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a voice communication system of a CATV system for simultaneously transmitting data and voice signals between a center and a terminal in two directions.

[Prior Art] Conventionally, the one shown in FIG. 5 is known as a voice communication system of a two-way CATV system.

In FIG. 5, a data modem 14-
1 and a voice modem 16-1, and the terminal device 12 is also provided with a data modem 14-2 and a voice modem 16-2, which are connected via a coaxial transmission line 20 having a bidirectional amplifier 18. You. The center device 10 is controlled by the CPU 40 as shown in FIG.
As shown in, the terminal device 12 is sequentially polled,
This polling is determined by the terminal CPU 80, and FIG. 6 (b)
Response data is returned from the terminal device 12 as shown in FIG.

As shown in FIG. 7, a dedicated channel band is assigned to the frequency band of the transmission channel, for example, downlink data 71 MHz downlink voice 74 MHz uplink data 42 MHz uplink voice 44 MHz.

[Means for Solving the Problems] However, in such a system in which the voice communication function is added to the data transmission of the bidirectional CATV system, a total of four channels of two voices are required in addition to two channels of data. Therefore, there is a problem that the utilization efficiency of the available transmission band is low, and that the data modem and the voice modem need to be provided in the center and the terminal, respectively, so that the equipment cost increases.

The present invention has been made in view of such a conventional problem, and provides a voice communication system of a CATV system capable of performing voice communication in addition to two-way data transmission with a small number of channels and a simple device. Aim.

[Means for Solving the Problems] First, the present invention connects a center modem 22 and a terminal modem 24 via a coaxial transmission line 20 capable of bidirectional transmission, and transmits data between the center modem 22 and the terminal modem 24. It is intended for CATV systems that perform FM modulation after FSK modulation and FM modulation of audio signals to perform bidirectional communication.

In such a CATV system, in the voice communication system of the present invention, the center modem 22 transmits a downlink transmission band (70%) to a frequency multiplexed signal with an FSK modulated data signal voice signal.
Up to 450MHz) predetermined channel frequency f1 signal (f1 = 71MHz)
And a first modulator for demodulating an FSK-modulated data signal from a signal transmitted from a terminal at a first channel frequency f10 (= 42 MHz) of an upstream transmission band (10 to 50 MHz). The upstream demodulation unit 28 and the upstream transmission band (10 to 50 MHz)
a) a second uplink demodulation unit 30 that demodulates a signal sent from the terminal side at the second channel frequency f20 (= 44 MHz) in z), and separates and outputs the FSK data signal and the audio signal having different frequency bands. On the other hand, on the terminal device 12 side, a downlink demodulation unit 32 that demodulates a signal transmitted from the downlink modulation unit 26 of the center modem 22 and then separates and outputs the FSK modulated data signal and the audio signal having different frequency bands from each other. When transmitting only data, the upstream transmission band (10-5
0 MHz) of the first channel frequency signal f10 (= 42 MHz) is transmitted after FM modulation, and when transmitting only data and voice signals or voice signals, the upstream transmission band (FSK modulated data signal and voice signal is frequency-multiplexed). 10 ~ 50MHz) second
An up-modulation unit 34 for FM-modulating and transmitting the channel frequency signal f20 (= 44 MHz) is provided.

[Operation] According to the voice communication system of the CATV system of the present invention having such a configuration, for downlink transmission from the center to the terminal, data and voice are frequency-multiplexed and transmitted through the same channel. For uplink transmission from the terminal to the center, transmission is performed using an uplink channel different from when only data is added and when voice is added, and voice is sent to the center without being disturbed by response data from other terminals, can do.

In addition, the number of channels is three in total, and the utilization efficiency of the transmission band can be increased.

Further, by modulating the data and the voice by frequency multiplexing, the modem modulation / demodulation circuit can be shared, so that the apparatus configuration can be simplified and the cost can be reduced.

[Embodiment] FIG. 1 is an embodiment configuration diagram showing one embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a center device, which is a center device.
A bidirectional amplifier 18 is connected to the coaxial transmission line 20 drawn out from 10, and a tap-off 36 connected to the coaxial transmission line 20.
Is connected to the terminal device 12. A television signal from a head end is added to the coaxial transmission line 20 by a mixer 38.

The center device 10 includes a CPU 40, a display device 42, and a communication unit 4
4. It comprises a modem 22 and a communication device 46.

The CPU 40 sequentially increments the terminal address and repeats the terminal polling sequentially. At each polling, the CPU 40 receives and determines response data from the terminal and performs a process such as displaying an error. The communication unit 44 receives the polling data from the CPU 40, and receives the terminal address, command data, BCC
A transmission format consisting of 3 bytes (block check code) is created and output to the modem 22 as transmission data SD. Further, the parity check is performed from the BCC of the received data RD from the modem 22, and if correct, the terminal address and the command data are output to the CPU 40 as the received data RD.

The communication device 46 includes a transmitter / receiver 48, which outputs a voice signal from the transmitter circuit 50 to the modem 22 in a call state and receives a voice signal from a terminal demodulated by the modem 22 from the receiver circuit 52.

The modem 22 provided in the center device 10, a so-called center modem, includes a down-modulation unit 26, a first up-demodulation unit 28, and a second up-demodulation unit 30.

The downstream modulation unit 26 includes the FSK modulation circuit 54 and the bandpass filter 5
6. It is composed of a band-pass filter 58 for passing the audio signal from the transmission circuit 50 and an FM modulation circuit 60. That is, FSK
The modulation circuit 54 has a carrier band of 10 KHz to 20 KHz shown in FIG.
To convert the data bits of the transmission data SD into two different frequencies f1 and f2,
Input to M modulation circuit 60. Also, the voice signal (0.3 to 3.4 KHz) from the transmission circuit 50 is
The signal is input to the M modulation circuit 60. The FM modulation circuit 60 outputs the FSK modulated data signal (10 to 2
A signal of a specific channel frequency f0 in the downstream transmission band is FM-modulated by a frequency multiplexed signal of 0 KHz) and an audio signal (0.3 to 3.4 KHz) obtained from the band-pass filter 58 and transmitted.
Specifically, the channel frequency within the downlink transmission band of 70 to 450 MHz
f ₀ = 71 MHz is used.

Next, the first uplink demodulation unit 28 includes an FM demodulation circuit 62 and an FSK demodulation circuit 64. A transmission signal from a terminal is input to the FM demodulation circuit 62 from the coaxial transmission line 20 via a mixer 66 and a distributor 68.

Here, the terminal device 12 transmits a signal using the channel frequency of the uplink transmission band shown in FIG.

FIG. 4 (a) shows frequency allocation when the terminal device 12 transmits only data, and a first channel frequency signal f10 in an uplink band of 10 to 50 MHz, for example, f10, using FSK modulated data of 10 to 20 KHz. = 42MHz signal is FM-modulated and transmitted.

FIG. 4 (b) shows a frequency assignment when transmitting a voice signal and a data signal from the terminal device 12, and a second channel frequency f20 different from the first channel frequency f10 when only data is used, for example, f20 = 44 MHz. The signal is FM-modulated by the frequency multiplexed signal of the audio signal and the FSK modulated data signal and transmitted.

Such a channel frequency f10 or f10 shown in FIG.
FM modulation circuit of the first uplink demodulation unit 28 for 20 transmission signals
Reference numeral 62 demodulates the channel frequency f10 = 42 MHz and outputs an FSK modulated signal to the FSK demodulation circuit 64. The FSK demodulation circuit 64 converts the data into reception data SD of data bits 0 and 1, and outputs the data to the communication unit 44.

Further, the second uplink demodulation unit 30 provided in the modem 22
A demodulation circuit 70, band-pass filters 72 and 74, and an FSK demodulation circuit 64 provided in the first uplink demodulation unit 28 are also used.

The FM demodulation circuit 70 converts the audio signal shown in FIG.
The transmission signal of the second channel frequency f20, which is FM-modulated by the frequency multiplex signal with the modulation data signal, is demodulated. Bandpass filter 72 has a passband of 10-20 KHz, and
Only the FSK modulated signal included in the demodulated signal demodulated by the M demodulation circuit 70 passes through and is output to the FSK demodulation circuit 64. The band pass filter 74 has a pass band of 0.3 to 3.4 KHz, passes the audio signal demodulated by the FM demodulation circuit 70, and outputs the signal to the reception circuit 52.

FIG. 2 is a block diagram of an embodiment of the terminal device 12 shown in FIG.

In FIG. 2, the terminal device 12 includes a modem 24, a CPU 80, and a communication device 82.

Appropriate sensor data and the like are input to the CPU 80 via the I / O 84, and the sensor data obtained via the I / O 84 is returned as response data to polling from the center device 10.

The communication device 82 is provided with a transmitter / receiver 86, and the transmitter / receiver 86 is provided with a transmission circuit 88 and a reception circuit 90. A call button 92 for using the communication device 82 is connected to the CPU 80 via the I / O 84.

The modem 24 provided in the terminal device 12 includes a downlink demodulation unit 32 and an uplink modulation unit 34. The downstream demodulation unit 32 is connected to the coaxial transmission line 20 via an input terminal 96 from a channel filter 94 for separating the downstream transmission band (H channel) and the upstream transmission band (L channel).

Bandpass filter 98, FM demodulation circuit
100, a bandpass filter 102, an FSK demodulation circuit 104, and a bandpass filter 106 on the communication device 82 side are provided. The band-pass filter 98 has a pass band of 70 to 450 MHz in the downstream transmission band, and the FM demodulation circuit 100 uses the frequency multiplexed signal of the audio signal and the FSK-modulated data signal as shown in FIG.
The M-modulated signal of channel frequency f0 = 71 MHz is demodulated. The band-pass filter 102 has a pass band of 10 to 20 KHz, and converts the FSK modulated data signal demodulated by the FM demodulation circuit 100
The signal is output to the K demodulation circuit 104, demodulated into reception data RD including data bits 0 and 1, and output to the CPU 80. The band pass filter 106 has a pass band of 0.3 to 3.4 KHz, and the FM demodulation circuit 100
The signal passes through the demodulated audio signal and is output to the receiving circuit 90.

Next, the upstream modulation unit 34 includes an FSK modulation circuit 108, a band-pass filter 110, a band-pass filter 112, and a PLL-FM modulation circuit 11.
4. It includes a high-frequency switch 116, a band-pass filter 118, a transmission switching circuit 120, and a channel switching circuit 122.

The FSK modulation circuit 108 FSK modulates the data bits 0 and 1 of the transmission data SD for reply to the polling from the CPU 80 with different frequencies f1 and f2 of the carrier band of 10 to 20 KHz and outputs the result. Bandpass filter 110 has a pass band of 10-20 KHz. The FSK modulated data signal from the band-pass filter 110 is added to the voice signal from the communication circuit 88 that has passed through the band-pass filter 112, and the PLL is used as a frequency multiplexed signal.
-Given to the FM modulation circuit 114. The PLL-FM modulation circuit 114 controls the first channel frequency f10 =
The frequency is switched to 42 MHz and the second channel frequency f20 = 44 MHz. That is, at the time of non-call without operating the call button 92,
The channel switching circuit 112 instructs the PLL-FM conversion circuit 114 to switch to the first channel frequency f10 = 42 MHz. In this case, since only the FSK data modulation signal is input, FIG. The first by the FSK data modulation signal
The channel frequency f10 = 42 MHz is FM-modulated and output. On the other hand, when the call button 92 is turned on for a call, the channel switching circuit 122 instructs the PLL-FM modulation circuit 114 to switch to the second channel frequency f20 = 44 MHz. As shown in FIG. 4 (b), at least the second channel frequency f20 = 44 MHz is FM-modulated and output by the audio signal. Of course, if the FSK modulation data signal based on the transmission data SD of the polling response is obtained from the band-pass filter 110 at the same time as the voice signal, the second channel frequency signal f20 which is switched by the frequency multiplexed signal with the voice signal.
= 44MHz is FM modulated and output.

The high-frequency switch 116 is turned on by the output of the transmission switching circuit 120 when the mode is switched to the transmission mode by the CPU 80, and outputs the FM modulation signal via the band-pass filter 118.

 Next, the operation of the above embodiment will be described.

First, in the bidirectional data transmission between the center device 10 and the terminal device 12, the polling from the center device 10 is performed according to the channel frequency by the FSK data modulation signal of 10 to 20 KHz shown in FIG.
The response data from the terminal device 12 in response to this polling is obtained by FM-modulating the first channel frequency f10 with an FSK modulation data signal of 10 to 20 KHz as shown in FIG. 4 (a). This is done by sending.

Next, in the call communication between the center device 10 and the terminal device 12, the transmission from the center device 10 to the terminal device 12 is performed as shown in FIG.
The channel frequency f0 = 71 MHz is FM-modulated by the frequency multiplexed signal of the FSK modulation data signal of Hz and transmitted.

On the other hand, in the terminal device 12, the PLL-FM
The modulation circuit 114 has a second channel frequency f shown in FIG.
The frequency is switched to 20 = 44 MHz, and the second channel frequency f20 is changed to FM by the frequency multiplexed signal of the audio signal and the FSK modulation data signal.
Modulate and transmit. The transmission signal including voice and data from the terminal is demodulated by the FM demodulation circuit 70 of the second uplink demodulation unit 30 of the center device 10, and is separated into a voice signal and an FSK modulation signal by band-pass filters 72 and 74. From receiver circuit 52 to transmitter 4
The received data SD is demodulated by the FSK demodulation circuit 54 into the received data SD and supplied to the CPU 40 via the communication unit 44.

In the above embodiment, the downlink channel frequency f0 = 71 MHz,
First and second uplink channel frequencies f10 = 42 MHz, f20 =
The channel assignment of 44MHz was taken as an example,
Of course, an appropriate channel frequency may be used as needed.

[Effects of the Invention] As described above, according to the present invention, for downlink transmission from a center to a terminal, data and voice are frequency-multiplexed and transmitted on the same channel, while uplink transmission from a terminal to the center is performed. Is transmitted using a different uplink channel when only data is added and when voice is added, so that continuous voice communication can be performed between the center and the terminal device without being affected by intermittent bidirectional data transmission. Since the number of channels used is three in total, the efficiency of use of the transmission band can be increased, and furthermore, the frequency and frequency division multiplexing of data and voice can share the modem circuit of the modem. And the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention; FIG. 2 is a block diagram of an embodiment of a terminal device of the present invention; FIG. 3 is an explanatory diagram of frequency allocation for downlink transmission of the present invention; FIG. 5 is an explanatory diagram of a conventional system; FIG. 6 is an explanatory diagram of a conventional bidirectional data transmission; FIG. 7 is an explanatory diagram of a conventional data and voice transmission channel allocation frequency. In the figure, 10: center device 12: terminal device 18: bidirectional amplifier 12: transmission line 22: modem (center modem) 24: modem (terminal modem) 26: downlink modulator 28: first uplink demodulator 30: 2 uplink demodulation section 32: downlink demodulation section 34: uplink modulation section 36: tap-off 38,66: mixer 40,80: CPU 42: display unit 44: communication unit 46,82: communication device 48,86: handset 50 , 88: Transmission circuit 52,90: Reception circuit 54,108: FSK modulation circuit 56,58,72,74,102,106,110,112,116,118: Band pass filter 60: FM modulation circuit 62,70,100: FM demodulation circuit 64,104: FSK demodulation circuit 68: Distributor 84 : I / O 92: Call button 94: Filter 96: Input terminal 114: PLL-FM modulation circuit 116: High frequency switch 120: Transmission switching circuit 122: Channel switching circuit

Claims (1)

(57) [Claims] 1. A center modem and a terminal modem are connected via a coaxial transmission line capable of bidirectional transmission, data is FSK-modulated between the center modem and the terminal modem, FM-modulated, and a voice signal is FM-modulated. In a CATV system that performs two-way communication, a downlink modulator that FM-modulates and transmits a predetermined channel frequency signal in a downlink transmission band to the center modem using a frequency multiplexed signal of an FSK modulated data signal and a voice signal; A first uplink demodulation unit for demodulating an FSK modulated data signal from a signal transmitted from a terminal at a first channel frequency of a transmission band;
A second upstream demodulation unit is provided, which demodulates a signal sent from the terminal side at the second channel frequency of the upstream transmission band and then separates and outputs an FSK modulated data signal and an audio signal. A downlink demodulation unit for demodulating a signal transmitted from a downlink modulation unit of the center modem and then separating the signal into an FSK data signal and a voice signal and outputting the FSK data signal and a voice signal; Uplink modulation for transmitting a channel frequency signal by FM modulating, and transmitting a data and voice signal by FM-modulating the second channel frequency signal of the upstream transmission band using a frequency multiplexed signal of an FSK modulation data signal and a voice signal. The voice communication system of the CATV system, characterized by having a unit.