JP2815853B2 - Signal selection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal selection system in a system for providing a subscriber with a video signal, an audio signal, or a data signal as required. [Technical Background of the Invention and Problems Thereof] Recently, a system capable of providing a subscriber with a multi-channel video signal and an audio signal has been receiving attention for an advanced information society. In the system, a video signal, an audio signal such as Hi-Fi music, or a data signal is transmitted to a subscriber as needed. Each signal is selected according to a request from the subscriber, but a system in which the signal selection device is centrally located at a place called a sub-center is preferable from the viewpoint of eavesdropping prevention, system maintenance, a charging system, and the like. Signals provided to the subscriber from the sub-center include signals supplied from the center to the sub-center, signals obtained by receiving radio waves from broadcasting satellites at the sub-center, and signals reproduced from package media at the sub-center. , Sub-centers, etc., but most of the signals are supplied from the center to the sub-center from the viewpoint of common use of equipment. When transmitting a video signal, an audio signal, or a data signal as needed from the center to the sub-center, an optical fiber may be used. In this case, the video signal, the audio signal, or, if necessary, the data signal are frequency-division multiplexed in a frequency arrangement as shown in FIG. 5 from the viewpoint of reducing the transmission path, broadening the optical fiber, and preventing cross modulation. Often.
Here, (51) is a video signal, (52) and (53) are frequency-modulated audio signals, and (54) is a data signal, for example, FSK that is added as necessary. The signal (50). The audio signals (52) and (53) are often audio signals accompanying the video signal (51).
The selection signal from the subscriber is input to the control circuit (62) shown in FIG. 6, and the control circuit (62) outputs the multiplexed signal (60-
1), (61-2), --- (60-n), the corresponding (60-k) (1≤k≤n) is the calling name (61-l) (1 ≦ l ≦ m) to control the wideband analog switch (63). The selected voice, data and video signals are converted to light without pre-modulation or pre-modulation and distributed to subscribers. It is assumed that the subscriber side has a device for separating the multiplexed signal after performing optical-to-electric conversion and pre-modulation demodulation as necessary, for example, an LC filter. Conventionally, for video and audio transmission services using light, in addition to the above, the same signal as in the VHF band multiplexing method currently used in radio waves is transmitted by light, and signal selection is directly performed on the final receiving side Methods have been considered and experiments have been performed. Compared with this method, in the above-described conventional example, it is technically easy to increase the number of basic channels composed of video, audio, and data. In addition, it has a feature that an emergency signal or the like can be simultaneously transmitted to all subscribers by a switch in the sub-center. However, in the conventional system, as shown in FIG. 5, since four video signals, two audio signals, and four data signals are frequency division multiplexed, the difference between the respective signals is caused by the nonlinear distortion of the wideband analog matrix switch. There is a problem that the frequency leaks into the video signal. The influence of the difference frequency leakage increases as the number of frequency division multiplexing increases. In addition, this effect depends on the power levels of the audio signal and data. In order to transmit voice and data with high quality, it is necessary to increase the power to about a few dB compared to the video signal power level, and the tolerance for nonlinear distortion is small. In addition, there is a problem that the frequency band of the audio signal cannot be set to 15 KHz or more because the video horizontal synchronization signal leaks into the audio due to the nonlinear distortion. [Object of the Invention] The present invention eliminates the above drawbacks, and can transmit high-quality video signals, audio and data transmitted as necessary even when using a wideband analog matrix switch having nonlinearity. It is to provide a signal selection method. SUMMARY OF THE INVENTION The present invention provides at least one pulse-coded audio signal and time-division multiplexed digital information of a data signal to be added as needed, performs angular modulation, and frequency-multiplexes with a video signal. The multiplexed signal is selected by a wideband analog matrix switch, pre-modulated, converted to an optical signal, and transmitted. [Effects of the Invention] According to the present invention, a signal selected by the wideband analog matrix switch is obtained by frequency-division multiplexing only a video signal and an angle-modulated signal. So that it is possible to switch in a region where the nonlinear distortion of the wideband analog matrix switch is small. Since the number of multiplexing is two, leakage of the difference frequency into the video signal due to the nonlinear distortion is reduced. In addition, since the voice is coded and transmitted, error correction, error detection, and the like can be performed. The level of the angle-modulated signal can be reduced as compared with the conventional FM and analog voice, and the influence of nonlinear distortion can be reduced. Further, there is no leakage of the video horizontal synchronizing signal into the audio, and a large audio frequency band can be obtained.
In addition, since speech is pulse-encoded, a sufficiently large dynamic range and signal-to-noise ratio can be obtained. Further, when the sound is interrupted on the transmitting side and the silent state continues, the conventional method is expressed as noise on the final receiving side due to leakage of the video signal and the difference frequency, but in the method of the present invention, the silent state is present. Even in, digital information including voice is not cut off,
The spectrum of angle modulation is broadening. Therefore, even if the above-mentioned leakage occurs, it does not appear as noise. Further, when an electric signal is converted into an optical signal, pre-modulation is performed and then converted into an optical signal, so that non-linear distortion, which is a problem in the electric-optical converter, does not occur. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Control circuit (10
4) controls a wideband analog matrix switch (103) consisting of n (n is a natural number) input signal lines and m (m is a natural number) output signal lines, and among the n input signals,
Select one signal and connect it to one of the output signal lines. Here, the input signal (101) is, as shown in FIG.
This is a signal (203) obtained by multiplexing the video signal (201) and the digital information (202) on the frequency axis. Digital information (202)
Is composed of at least one pulse-encoded audio signal and data signal. These signals are multiplexed, that is, time-division multiplexed on the time axis, and are assumed to be four-phase modulated. The feature of four-phase phase modulation, that is, QPSK, is that the spectrum width is small, and even when frequency-division multiplexing is performed with a video signal, the entire occupied frequency band is reduced. However, since the amount of digital information is voice and low-speed data, two-phase modulation (PSK) or frequency modulation (FSK) may be used instead of four-phase modulation.
Broadband analog matrix switch (103) in FIG.
(102) is pre-modulated by a pulsed FM modulator (105) having a pulse duty cycle of 50% and a pulse frequency that changes according to the input signal.
The light is converted into a light pulse in the light conversion unit (106) and transmitted. Here, the pulsed FM modulator (105) is a PFM in which the pulse width is constant and the pulse frequency changes according to the input signal.
It may be a modulator or an analog amplifier that directly modulates the intensity of light according to an input signal, and is not limited to the embodiment. Here, the wideband analog matrix switch shown in FIG. 1 is, for example, a MOS-FET (30
It can be configured in 1). This is a switch in which the resistance between the source and the drain is changed according to the potential of the gate to form a switch, which can be integrated, and can be integrated. However, when the signal passing through the switch is in a wide band, that is, about 10 MHz, non-linear distortion tends to increase particularly in a high band. Therefore, it is desirable that the input signal has as narrow a bandwidth as possible, and further, on the low frequency side. In this regard, in the system of the present invention, two signals, namely, a video signal and a QP
Since only the SK signal is used, the band is up to about 7 MHz, and the nonlinear distortion of the analog switch is small. Further, the FDM signal obtained by multiplexing the video signal and the QPSK signal has two multiplexes, and causes little difference frequency due to non-linear distortion generated by the analog switch. Further, in the method of the present invention, even if the frequency of the video horizontal synchronizing signal leaks into the QPSK signal, it is not necessary to limit the audio band in order to avoid this effect, and a large dynamic range and signal-to-noise ratio can be obtained. Next, a second embodiment of the present invention will be described. This is an application of the first embodiment, and is an embodiment of a video, audio and data service system using light. FIG. 4 is a diagram showing a second embodiment of the present invention. In this embodiment, one video channel, four audio channels, and one data channel are set as basic service channels. It is assumed that the service receiving side, that is, the subscriber side, can select from a plurality of service channels. First, in the center in Fig. 4,
The pulse-encoded four audio channels are time-division multiplexed together with the data in the multiplexer (401) to form one digital information. Here, the data signal is a facsimile signal, a control signal of a subscriber device, a control signal to a sub-center, or the like. Digital information is subjected to QPSK by a four-phase phase modulator (402) having a center frequency of about 6 MHz and multiplexed with a video signal. This multiplexed signal (403) is the same as that shown in FIG. In optical communication, as a method of transmitting a video signal with high quality, a method of converting a video signal into a pulsed analog signal in advance and transmitting the signal is generally used. In this case as well, the signal is pulsed by a PFM modulator (404). This output signal is electro-optically converted to an optical signal. In the center, the above-described transmission devices are provided by the number of service channels. In order to increase the use efficiency of the optical fiber between the center and the sub-center, wavelength multiplexing is performed and a plurality of service channels are transmitted by one fiber. Therefore, the center and the sub-center are connected by the number of optical fibers (407) obtained by dividing the number of service channels by the number of multiplexed wavelengths. On the other hand, in the sub-center, the light from the center is demultiplexed by the demultiplexer (408), converted into an electric signal by the optical-electrical conversion unit (409), and further demodulated by the demodulator (410).
This signal has the spectral distribution of FIG. Further, in the sub-center, a signal having the same spectral distribution as that shown in FIG. 2 produced by another method, that is, by radio waves or reproduced from package media, is also added. The aforementioned signals are selected and output by the analog matrix switch (411). This output signal is pre-modulated by a pre-modulation modulator (412) as necessary, and further converted to light by an electro-optical converter (413) and distributed to subscribers. The above-mentioned premodulation modulator is a PFM or a pulsed FM modulator. Further, on the subscriber side, optical-electrical conversion and pre-modulation demodulation are performed, and the video signal and the QPSK signal are separated by a filter.
The QPSK signal is further demodulated and demultiplexed by a PC.
M audio and data are separated, and the audio is further analogized by a PCM decoder. Here, the service channel selection signal is transmitted from the subscriber side to the sub center in the opposite direction on the same fiber. In the video, audio, and data service system described above, the pre-modulation between the center and the sub-center is PFM, but it can also be configured with pulsed FM. Here, if the center frequency of the PFM is 50 MHz and the maximum frequency deviation is 30 MHz, QP
The power level of the center side QPSK signal for setting the SK error rate to 1 × 10 ⁻⁵ may be about −10 dB as compared with the video signal level. Therefore, leakage of the difference frequency into the video signal caused by the nonlinear distortion of the wideband analog matrix switch in the sub-center is reduced. Furthermore, even if the voice is interrupted at the center, the subscriber QPSK demodulator demodulates the signal that has been scrambled and, if necessary, BSI-converted for the purpose of establishing synchronization on the receiving side of the digital information. The effect of the embedding does not increase. Here, the digital information is modulated by QPSK, but may be two-phase modulated PSK or FSK.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a spectrum distribution of an input signal shown in FIG. 1,
FIG. 3 is a diagram showing a configuration example of the wideband analog matrix switch shown in FIG. 1, and FIG.
FIG. 5 is a diagram showing a spectrum distribution of a signal input to a conventional signal selection device, and FIG. 6 is a diagram for explaining a conventional signal selection method. 103 …… Broadband analog matrix switch, 201 ……
Video signal, 202: angle modulation signal, 401: multiplexer, 402: QPSK modulator, 406: multiplexer.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Takeshi Koseki               1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi Toshiba Corporation               Within the Research Institute (72) Inventor Yoichi Hirayama               1 Stock Association of 3-1-1 Asahigaoka, Hino City               Inside the Toshiba Hino Plant                (56) References JP-A-56-94865 (JP, A)                 JP-A-49-46812 (JP, A)

Claims (1)

(57) [Claims] A multiplexed signal obtained by multiplexing at least an audio signal and a video signal is selectively connected and transmitted through a wideband analog switch, and the multiplexed signal selected by the wideband analog switch is converted into an optical signal. In the signal selection method for converting and transmitting, the multiplexed signal is a time-division multiplex of a plurality of pulse-coded audio signals or one or a plurality of pulse-coded audio signals and a data signal. The multiplexed signal is a multiplexed signal that is angle-modulated and further multiplexed with a video signal, and the conversion into the optical signal is performed by pre-modulating the signal selected by the switching unit into a pulse signal. After that, a signal selection method in which an electric-optical conversion is performed. 2. 2. The signal selection method according to claim 1, wherein the angle modulation is a modulation of the time-division multiplexed signal by a phase shift keying method. 3. 2. The signal selection method according to claim 1, wherein the angle modulation is a modulation of the time-division multiplexed signal by a frequency shift keying method. 4. 2. The signal selection method according to claim 1, wherein said premodulation is a pulse frequency modulation in which a pulse width is constant and a frequency changes according to an input signal. 5. 2. The signal selection method according to claim 1, wherein the premodulation is a pulsed FM modulation in which a pulse duty cycle is 50% and a frequency changes according to an input signal.