JPH08111663A - Optical coaxial hybrid transmission system - Google Patents

Abstract

PURPOSE: To obtain an optical coaxial hybrid transmission system which is capable of effectively utilizing the wide transmission band of an optical fiber, providing much video information and being inexpensively and quickly formed. CONSTITUTION: A node 21 is connected to coaxial cables 41a to 41c of three series. A center station 11 outputs each of frequency division multiplex signals to be outputted from signal sources 111 to 113 to each series of the coaxial cables 41a to 41c. By a multiplex part 131 and an optical transmission part 121, the multiplexed signals which are possible to pass within the transmission band of an optical fiber 31 and obtd. by further subjecting plural frequency division multiplex signals to multiplex processing are outputted. The separation part 221 of the node 21 separates the multiplexed signal via the optical fiber 31 into plural frequency division multiplex signals and outputs each frequency division multiplex signal to each of the coaxial cables 41a to 41c of the corresponding series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coaxial hybrid transmission system, and more particularly to transmitting information of a plurality of channels output from a center station to a subscriber via an optical fiber, a node and a coaxial cable. The present invention relates to an optical coaxial hybrid transmission system.

[0002]

2. Description of the Related Art Conventionally, in a CATV or the like, a coaxial cable has been arranged between a center station and a subscriber in consideration of easiness of connection with equipment such as a television tuner of a subscriber. However, the transmission loss of the coaxial cable is high. For this reason,
In recent years, an optical coaxial hybrid transmission system has been considered in which a part of the coaxial cable is replaced with an optical fiber. Such an optical coaxial hybrid transmission system is described in, for example, Maeda et al., "Development of 150ch AM / 16QAM hybrid optical transmission system", IEICE Technical Report OCS93-97, pp.
23-31 (1994).

FIG. 7 is a block diagram showing the configuration of a conventional optical coaxial hybrid transmission system. In FIG.
The optical coaxial hybrid transmission system uses a center station 100
0, the node 2000, and the optical fiber 3 for transmitting the optical signal output from the center station 1000 to the node 2000.
000 and a coaxial cable 4000 for transmitting the signal output from the node 2000 to the subscriber. The coaxial cable 4000 has a transmission bandwidth of 1 GHz, for example. The optical fiber 3000 is, for example, 4 GHz.
It has a transmission bandwidth of.

The signal source 1100 of the center station 1000 is
A frequency division multiplexed signal FDM having a bandwidth of 1 GHz in the frequency band 0 to 1 GHz is output. Signal source 110
The frequency division multiplexed signal FDM output from 0 is composed of mutually different video information of 166ch frequency-multiplexed by 6 MHz, for example, and is converted into an optical signal by the optical transmission unit 1200. Therefore, the optical fiber 300
0 is a frequency division multiplexed signal FD with a transmission band of 1 GHz.
M is transmitted by light. The node 2000 converts the optical signal from the optical fiber transmission line 3000 into an electric signal, sends the electric signal to the coaxial cable 4000, and distributes the frequency division multiplexed signal FDM to the subscribers.

[0005]

However, in the conventional optical coaxial hybrid transmission system, the number of video information that can be provided to the subscriber, that is, the number of channels, is determined by the coaxial cable having a narrow transmission band, and the transmission of a wide optical fiber is performed. There is a first problem that the band is not effectively used.

Further, in recent years, a service for providing more video information is required due to the diversification of social life and hobbies / preferences, but only the number of channels determined by the transmission band of the coaxial cable is used. There is a second problem that the information providing service cannot be provided.

In this case, the center station 1000, the node 2000, the optical fiber 3000, and the coaxial cable 40
It is conceivable to provide a plurality of sets of optical coaxial hybrid transmission systems, one set of which is 00, and to provide various video information providing services from each set. However, providing a plurality of sets of optical coaxial hybrid transmission systems causes another problem that it takes a lot of cost and time.

The present invention solves the above technical problems and provides an optical coaxial hybrid transmission system which can effectively use a wide transmission band of an optical fiber, can provide a lot of video information, and can be formed inexpensively and quickly. The purpose is to

[0009]

The invention according to claim 1 is
An optical coaxial hybrid transmission system for transmitting information of a plurality of channels output from a center station to a subscriber via an optical fiber, a node and a coaxial cable, wherein the coaxial cable is prepared in a plurality of series, and the center station is A means for further multiplexing a plurality of frequency division multiplexed signals each having information of a plurality of channels and having a bandwidth not wider than the transmission bandwidth of the coaxial cable of the corresponding series, and outputting it to the optical fiber in the form of an optical signal. Prepare, the node is
The optical signal received via the optical fiber is separated into a plurality of frequency division multiplexed signals, and each frequency division multiplexed signal is output to the corresponding series of coaxial cables.

According to a second aspect of the present invention, in the first aspect, the center station further multiplexes a plurality of frequency division multiplexed signals by frequency division multiplexing, and the nodes have different frequency bands of the optical signals. The optical signal is demultiplexed into a plurality of frequency division multiplexed signals.

According to a third aspect of the present invention, in the first aspect, the center station uses wavelength division multiplexing to
The plurality of frequency division multiplexed signals are further multiplexed, and the node separates the optical signal into a plurality of frequency division multiplexed signals according to the difference in wavelength of the optical signals.

According to a fourth aspect of the present invention, in the second aspect, when the center station further multiplexes a plurality of frequency division multiplex signals by frequency division multiplex, the frequency division multiplex signals are mutually multiplexed. It is multiplexed including a guard band that has no information to be transmitted.

The invention according to claim 5 relates to claims 1 to 4.
In any of the above items, the node adjusts the frequency band of each frequency division multiplexed signal output to the coaxial cable of the corresponding series to the same band.

The invention according to claim 6 relates to claims 1 to 5.
The node has jurisdiction over a plurality of regions, and at least one system of the coaxial cable is
Wired across multiple regions, the remaining lines of coaxial cable are each routed to a corresponding specific region of the multiple regions.

[0015]

In the invention according to claim 1, a plurality of series of coaxial cables are prepared. The center station further multiplexes a plurality of frequency division multiplexed signals, each of which contains information of multiple channels and has a bandwidth not wider than the transmission bandwidth of the coaxial cable of the corresponding series, to form an optical fiber in the form of an optical signal. A means for outputting is provided. The node includes means for separating an optical signal received through an optical fiber into a plurality of frequency division multiplexed signals and outputting each frequency division multiplexed signal to a coaxial cable of a corresponding series. As a result, the wide band characteristic of the optical fiber can be effectively used without being limited to the band characteristic of the coaxial cable. Further, since the wide band characteristic of the optical fiber can be effectively used, it is not necessary to prepare a plurality of sets of optical fibers, and an optical coaxial hybrid transmission system capable of providing a lot of video information can be inexpensively and quickly formed.

In a second aspect of the present invention, the center station further multiplexes a plurality of frequency division multiplexed signals by frequency division multiplexing, and the node outputs a plurality of the optical signals according to the difference in the frequency band of the optical signals. Of frequency division multiplexed signals. As a result, it is possible to facilitate multiplexing / demultiplexing that matches the transmission band of the optical fiber and the coaxial cable.

In the invention according to claim 3, the center station further multiplexes a plurality of frequency division multiplexed signals by wavelength division multiplexing, and the node outputs a plurality of the optical signals according to the difference in the wavelengths of the optical signals. Separated into frequency division multiplexed signals. As a result, it is possible to facilitate multiplexing / demultiplexing that matches the transmission band of the optical fiber and the coaxial cable.

In the invention according to claim 4, when the center station further multiplexes a plurality of frequency division multiplexed signals by frequency division multiplexing, the center station does not have information to be transmitted between the frequency division multiplexed signals. Multiplex including bands. As a result, it is possible to easily prevent signals in other bands from being mixed into the separated frequency division multiplexed signals, and it is possible to prevent the reproduction of the video information from being adversely affected.

In the invention according to claim 5, the node adjusts the frequency band of each frequency division multiplexed signal output to the coaxial cable of the corresponding series to the same band. As a result, the subscriber does not need to prepare a special device such as a TV tuner capable of receiving 400 to 500 channels, and the existing device can be used more without changing the reception band of the high band. It becomes possible to receive the information of.

In the invention according to claim 6, the node has jurisdiction over a plurality of regions, at least one system of the coaxial cable is wired throughout the plurality of regions, and the remaining system of the coaxial cable is in each of the plurality of regions. Wired to the corresponding specific area. Therefore, it is possible to provide more video information services that match the regional characteristics of the target region, that is, the subscriber's social life, hobbies, and tastes.

[0021]

1 is a block diagram showing the configuration of an optical coaxial hybrid transmission system according to a first embodiment of the present invention.
In FIG. 1, the optical coaxial hybrid transmission system includes a center station 11 that outputs a plurality of video information as optical signals, a node 21 that outputs a plurality of video information as electrical signals, and a plurality of videos output from the center station 11. An optical fiber 31 for transmitting information to the node 21 by an optical signal, and a three-system coaxial cable 4 for transmitting a plurality of video information to a subscriber by an electric signal 4
1a, 41b, 41c. Coaxial cable 41
The a, 41b, 41c have a transmission bandwidth of 1 GHz, for example. The optical fiber 31 is, for example, 4 GHz.
It has a transmission bandwidth of.

The center station 11 is connected to each coaxial cable 41.
a, 41b, 41c corresponding to three signal sources 111, 1
12, 113, a multiplexing unit 131, and an optical transmission unit 121. The node 21 includes an optical receiving unit 211 and a separating unit 22.
1 is provided. In addition, FIG. 2 shows a frequency spectrum of a signal output from each unit of the optical coaxial hybrid transmission system of FIG.

Each signal source 111, 11 of the center station 11
2 and 113 are 1 GHz of the same frequency band 0 to 1 GHz
Frequency division multiplexed signals FDM1, FD having a bandwidth of z
M2 and FDM3 (see FIGS. 2A to 2C) are output. Each frequency division multiplexed signal FDM1, FD
The M2 and the FDM3 are composed of mutually different image information of 166 channels, which are frequency-multiplexed for every 6 MHz, for example.

The multiplexing unit 131 shifts the frequency division multiplexed signal FDM2 to the 1.5 to 2.5 GHz band (not shown) and the shifter (not shown) to shift the frequency division multiplexed signal FDM3 to the 3 to 4 MHz band, for example. (Not shown),
The frequency division multiplex signal FDM1 and the frequency division multiplex signals FDM2 and FDM3 shifted by the shifter are respectively added, and an adder (not shown) is provided to output the frequency division multiplex signal FDM4 (see FIG. 2).
See (d). ). The optical transmitter 121 includes, for example, a light emitting element that emits light with a predetermined wavelength λ0 (for example, 1.500 μm), converts the frequency division multiplexed signal FDM4 output from the multiplexer 131 into an optical signal as it is, and outputs the optical signal as an optical signal. Output to the fiber 31. Therefore, the optical signal transmitted through the optical fiber 31 has the same frequency spectrum as the frequency division multiplexed signal FDM4 output from the multiplexing unit 131 shown in FIG.

The optical receiver 211 of the node 21 is provided with a light receiving element for receiving light of a predetermined wavelength λ0 (for example, 1.500 μm), and converts an optical signal through the optical fiber 31 into an electric signal as it is. , And outputs the frequency division multiplexed signal FDM4. The separating unit 221 may be, for example, 0 to
A bandpass filter (not shown) that passes 1 GHz,
A band filter (not shown) that passes 1.5 to 2.5 GHz, a band filter (not shown) that passes 3 to 4 GHz, and a band of 1.5 to 2.5 GHz are shifted to a band of 0 to 1 GHz. A shifter (not shown) and a shifter (not shown) for shifting the 3 to 4 GHz band to the 0 to 1 GHz band are provided, and the division multiplexed signal FDM4 is separated into the original three frequency division multiplexed signals FDM1, FDM2, and FDM3. And separated frequency division multiplexed signals FDM1, FDM2, FDM3
Are output to the coaxial cables 41a, 41b, 41c, respectively.

By the way, the multiplexing unit 131 of the center station 11
Shifts the frequency division multiplexed signal FDM2 to the 1 to 2 GHz band, and shifts the frequency division multiplexed signal FDM3 to 2 to 2 GHz.
It shifts to the 3 MHz band, and the separation unit 22 of the node 21
It is conceivable to shift the 1 to 2 GHz band to the 0 to 1 GHz band and shift the 2 to 3 GHz band to the 0 to 1 GHz band at 1. In this case, the bandwidth of the frequency division multiplexed signal FDM4 output from the multiplexing unit 131 is 3
GHz.

However, when the bands of the frequency division multiplexed signals FDM1, FDM2 and FDM3 are attached to each other in this way, it is difficult to make the cutoff characteristic of the bandpass filter of the separation unit 221 steep, and therefore each frequency division is performed. Signals in other bands are mixed in the multiplexed signals FDM1, FDM2, and FDM3, which adversely affects reproduction of video information (for example, crosstalk).

Therefore, the multiplexing unit 131, as shown in FIG. 2D, the frequency division multiplexed signals FDM1, FDM2.
Signal-free guard bands α1 and α2 are provided between the FDM3s. As a result, even if the cutoff characteristic of the bandpass filter of the separation unit 221 is not steep, signals in other bands are not mixed in the frequency division multiplexed signals FDM1, FDM2, FDM3, which adversely affects reproduction of video information. It has no effect.

The guard band α1, based on the cutoff characteristic of the filter of the separation unit 221 of the node 21 and the like.
The necessity of α2 and the amounts of guard bands α1 and α2 may be determined. Generally, considering band division and frequency conversion in the demultiplexing unit 221, it is sufficient to widen the guard bands α1 and α2. However, if the guard bands α1 and α2 are widened, high performance is required for the optical transmission system and the amplifier. It may be decided based on the balance of.

Next, the operation of the optical coaxial hybrid transmission system of FIG. 1 will be described. Multiplex section 13 of center station 11
1 is 3 output from the signal sources 111, 112, 113
Two frequency division multiplexed signals FDM1, FDM2, FDM3
(See FIGS. 2A to 2C) is further frequency division multiplexed. Therefore, the frequency spectrum of the frequency division multiplexed signal FDM4 output from the multiplexing unit 131 is as shown in FIG. The optical transmitter 121 directly converts the frequency division multiplexed signal FDM4 output from the multiplexer 131 into an optical signal and outputs the optical signal to the optical fiber 31. Therefore, the frequency spectrum of the optical signal transmitted through the optical fiber 31 is shown in FIG.
(D).

The optical receiving section 211 of the node 21 converts the optical signal from the optical fiber 31 into an electrical signal, and the demultiplexing section 221.
Output to. Therefore, the optical receiver 211 outputs the same frequency division multiplexed signal FDM4 as the input of the optical transmitter 121, that is, the multiplexer 131. Therefore, its frequency spectrum becomes equal to that of FIG. Separation part 22
1 is 0 to 1 for the 4 GHz frequency division multiplexed signal FDM4
GHz, 1.5 to 2.5 GHz, and 3 to 4 GHz are band-divided into three bands, two signals of which are frequency-converted to the low frequency side, and three frequency-division multiplexed signals FDM1 and FD
It outputs M2 and FDM3 (see FIGS. 2 (e) to 2 (g)). The three frequency division multiplexed signals FDM1, FDM2 and FDM3 output from the demultiplexing unit 221 are shown in FIG.
It has the same frequency spectrum as (a) to (c) and is sent to the coaxial cables 41a, 41b, 41c, respectively.
Distributed to subscribers.

Each coaxial cable 41a, 41b, 41c
Transmits the frequency division multiplexed signals FDM1, FDM2, FDM3 output from the signal sources 111, 112, 113. That is, they provide different video information services. Therefore, the subscriber may connect the coaxial cables 41a, 41b, 4 depending on the service he / she wants to receive.
1c is different. For example, a subscriber who wants to receive all services is connected to all three coaxial cables 41a, 41b, 41c. In this subscriber, the coaxial cables 41a, 41b, 41c are respectively connected to three TV tuners, or the coaxial cables 41a, 41b
By connecting b and 41c to one tuner via the changeover switch, it is possible to receive the service of the video information of three systems.

Here, as shown in the frequency spectrum of FIG. 2 (d), the frequency division multiplexed signals FDM1, FDM2, FDM having a bandwidth of 1 GHz are provided in the optical fiber 31.
The frequency division multiplexed signal FDM4 including 3 is transmitted. Therefore, the bandwidth of the optical fiber 31 can be effectively used. Further, since only the signal in the band of 4 GHz is transmitted to the optical fiber 31, the existing optical fiber can be used. Further, as shown in the frequency spectra of FIGS. 2E to 2G, the coaxial cables 41a and 41a
Since only signals having a bandwidth of 1 GHz are transmitted to b and 41c, the existing coaxial cable can be used. Therefore, only the center station 11 and the node 21 need to be exchanged, and an optical coaxial hybrid transmission system in which the amount of video information provided is dramatically expanded can be inexpensively and quickly formed.

FIG. 3 is a block diagram showing the configuration of the optical coaxial hybrid transmission system according to the second embodiment of the present invention. The parts corresponding to those of the optical coaxial hybrid transmission system in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the optical coaxial hybrid transmission system of FIG.
In place of the signal sources 111, 112, 113, the multiplexer 131 and the optical transmitter 121 of
6, optical transmitters 122, 123, 124 and optical multiplexer 1
41 is used. In addition, FIG. 4 shows a frequency spectrum of a signal output from each unit of the optical coaxial hybrid transmission system of FIG.

Each signal source 114, 11 of the center station 12
5,116 are different frequency bands 0 to 1 GHz, 1.5
Frequency division multiplexed signals FDM5, FDM6, FDM having bandwidths of 1 GHz each of 2.5 GHz and 3 to 4 GHz
7 (see FIGS. 4A to 4C) are output. Frequency division multiplexed signals FDM5, FDM6, FDM
7 is, for example, 166c that is frequency-multiplexed every 6 MHz.
It is composed of image information of h different from each other.

Each of the optical transmitters 122, 123, and 124 includes a light emitting element that emits light at a predetermined wavelength λ0 (for example, 1.500 μm), and has signal sources 114, 115, and 1, respectively.
16 frequency division multiplexed signals FDM5, FD
M6 and FDM7 are directly converted into optical signals.
The optical multiplexer 141 includes, for example, an adder (not shown),
The optical signals output from the optical transmitters 122, 123, and 124 are further frequency-division-multiplexed by adding the optical signals by the light emitting elements, and the optical signals are output to the optical fiber 31. Therefore,
The optical signal transmitted through the optical fiber 31 is the frequency division multiplexed signal FDM output from the optical transmitter 121 shown in FIG.
It has the same frequency spectrum as 4. The addition of the optical signals can be performed more easily than the addition of the electric signals.

Next, the operation of the optical coaxial hybrid transmission system of FIG. 3 will be described. Signal source 11 of the center station 12
The frequency division multiplexed signals FDM5, FDM6 and FDM7 output from the optical transmission units 122, 1
It is converted into an optical signal by 23 and 124. Therefore,
The frequency spectrums of the optical signals output by the optical transmitters 122 to 124 are equal to those in FIGS. 4A to 4C, respectively. The optical multiplexer 141 multiplexes the three optical signals output from the optical transmitters 122, 123, and 124, and sends the frequency division multiplexed signal FDM4 to the optical fiber 31.

Here, each signal source 114, 115, 116
Are different frequency bands 0-1GHz, 1.5-2.5G
Frequency division multiplexed signals FDM5, FDM6, FDM7 having a bandwidth of 1 GHz of 3 Hz to 4 GHz (see FIG. 4).
See (a)-(c). ) Are output respectively. That is, since the frequency bands of the signal sources 114, 115, and 116 are appropriately shifted in advance, the frequency division multiplexed signal FD
Guard bands α1 and α2 are formed in M4.

The optical receiving section 211 of the node 21 converts the optical signal from the optical fiber 31 into an electric signal, and the demultiplexing section 221.
Output to. Therefore, the optical receiver 211 outputs the same frequency division multiplexed signal FDM4 as the input of the optical transmitter 121, that is, the multiplexer 131. Therefore, its frequency spectrum is equal to that of FIG. Separation part 22
1 is 0 to 1 for the 4 GHz frequency division multiplexed signal FDM4
GHz, 1.5 to 2.5 GHz, and 3 to 4 GHz are band-divided into three bands, two signals of which are frequency-converted to the low frequency side, and three frequency-division multiplexed signals FDM1 and FD
It outputs M2 and FDM3 (see FIGS. 4 (e) to 4 (g)). The three frequency division multiplexed signals FDM1, FDM2 and FDM3 output from the demultiplexing unit 221 are shown in FIG.
It has the same frequency spectrum as (a) to (c) and is sent to the coaxial cables 41a, 41b, 41c, respectively.
Distributed to subscribers.

Each coaxial cable 41a, 41b, 41c
Transmits the frequency division multiplexed signals FDM1, FDM2, FDM3 output from the signal sources 111, 112, 113. That is, they provide different video information services. Therefore, the subscriber may connect the coaxial cables 41a, 41b, 4 depending on the service he / she wants to receive.
1c is different. For example, a subscriber who wants to receive all services is connected to all three coaxial cables 41a, 41b, 41c. In this subscriber, the coaxial cables 41a, 41b, 41c are respectively connected to three TV tuners, or the coaxial cables 41a, 41b
By connecting b and 41c to one tuner via the changeover switch, it is possible to receive the service of the video information of three systems.

Here, as shown in the frequency spectrum of FIG. 4 (d), the frequency division multiplexed signals FDM5, FDM6 and FDM having a bandwidth of 1 GHz are provided in the optical fiber 31.
The frequency division multiplexed signal FDM4 including 7 is transmitted. Therefore, the bandwidth of the optical fiber 31 can be effectively used. Further, since only the signal in the band of 4 GHz is transmitted to the optical fiber 31, the existing optical fiber can be used. In addition, as shown in the frequency spectra of FIGS. 4E to 4G, the coaxial cables 41a and 41a
Since only signals having a bandwidth of 1 GHz are transmitted to b and 41c, the existing coaxial cable can be used. Therefore, only the center station 12 and the node 21 need to be exchanged, so that an optical coaxial hybrid transmission system in which the amount of video information provided is dramatically expanded can be formed inexpensively and quickly.

FIG. 5 is a block diagram showing the configuration of the optical coaxial hybrid transmission system of the third embodiment of the present invention. The parts corresponding to those of the optical coaxial hybrid transmission system in FIGS. 1 and 3 are designated by the same reference numerals, and the description thereof will be omitted. In the optical coaxial hybrid transmission system of FIG. 5, the center station 13 includes the optical transmitters 125, 126, 12
7, the node 23 is an optical demultiplexer 23.
1, optical receivers 213, 214, 215 and converter 24
1, 242, 243.

In FIG. 5, the optical transmitters 125, 126, 127 of the center station 13 have predetermined wavelengths λ1, λ2, λ3 (eg 1.300, 1.32) which are different from each other.
Each of the frequency division multiplexed signals FDM5, FDM6, and FDM7 output from the signal sources 114, 115, and 116 is directly combined at the respective wavelengths λ1, λ2, and λ3, and combined. The waved optical signal is output to the optical fiber 31.

The optical demultiplexer 231 of the node 23 has a demultiplexer for demultiplexing the optical signals multiplexed with the wavelengths λ1, λ2, and λ3, for example, into wavelengths, and the optical signal passing through the optical fiber 31 has a wavelength of λ1. , Λ2, λ3 are separated. Optical receiver 2
Reference numerals 13, 214, 215 each have a light receiving element for receiving the optical signals of the respective wavelengths λ1, λ2, λ3, and convert the optical signals of the respective wavelengths λ1, λ2, λ3 output from the optical demultiplexing section 231 into electric signals. To do. The conversion units 241, 242, 243
A shifter (not shown) for shifting the 1.5 to 2.5 GHz band to the 0 to 1 GHz band, and the 0 to 1 GHz for the 3 to 4 GHz band.
and a shifter (not shown) for shifting to the z band, and the frequency division multiplexed signals FDM1, FDM2, and FDM3 are separated and separated.
2, FDM3 is output to the coaxial cables 41a, 41b, 41c, respectively.

Next, the operation of the optical coaxial hybrid transmission system of FIG. 5 will be described. The frequency spectrum of each part of the optical coaxial hybrid transmission system of FIG.
Since this is basically the same as the case of the optical coaxial hybrid transmission system, the description will be made with reference to FIG.

Frequency division multiplexed signals FDM5, FDM6 and FDM output from the respective signal sources 117, 118 and 119.
7 is converted into an optical signal by the optical transmitters 125, 126, 127. Therefore, the optical transmitters 125, 126, 12
The frequency spectrums of the optical signals output from 7 are equal to those in FIGS. The optical multiplexer 141 is
The three optical signals output from the optical transmitters 125, 126, 127 are multiplexed and sent to the optical fiber 33. Therefore, the frequency spectrum of the optical signal output by the optical multiplexer 141 is as shown in FIG. The optical transmitter 125,
Since the wavelengths of the optical signals of 126 and 127 are different from each other, low loss multiplexing can be realized by using a demultiplexer / multiplexer having wavelength characteristics adapted for the optical multiplexer 141. In addition, even when using a branching combiner with an addition function that does not have wavelength characteristics,
There is no problem in terms of functionality, only the loss increases when multiplexing.

The optical demultiplexer 231 of the node 23 has the wavelength λ
The optical signals corresponding to 1, λ2 and λ3 are divided into three and output to the optical receiving units 213, 214 and 215, respectively. Here, the optical multiplexer 141 multiplexes the optical signals of wavelengths λ1, λ2, and λ3, and the optical demultiplexer 231 demultiplexes the optical signals of wavelengths λ1, λ2, and λ3. Therefore, the frequency-division multiplexed signals FDM5, FDM6, and FDM7 have a wavelength λ
That is, wavelength division multiplexing is performed with 1, λ2 and λ3.

The wavelengths λ1, λ2 and
Since it is separated for each λ3, the frequency spectrum of the optical signal output by the optical receiving unit 213 is equal to that in FIG. Similarly, the frequency spectrum of the optical signal output by the optical receiver 214 is equal to that in FIG. 4B, and the frequency spectrum of the optical signal output by the optical receiver 215 is equal to that in FIG. 4C. Since the frequency spectrum of FIG. 4E is equal to that of FIG. 4A, it is not necessary to convert the frequency in the conversion unit 241, and in this case, the signal may be passed as it is. As a result, the conversion unit 241 outputs the frequency division multiplexed signal FDM1.

On the other hand, the conversion unit 242 has the frequency spectrum of the input signal as shown in FIG. 4B, and performs the frequency conversion to the low frequency side as shown in FIG. 4F, and the conversion unit 243 has the frequency spectrum of the input signal. It is FIG.4 (c) and frequency-converts to a low frequency side so that it may become FIG.4 (g). Therefore, the frequency division multiplexed signals FDM1, FDM2, FDM3 output from the respective conversion units 241, 242, 243 are as shown in FIG.
(E), (f), (g) frequency spectrum,
It is distributed to the subscribers via the coaxial cables 41a, 41b, 41c.

Here, as shown in the frequency spectrum of FIG. 4 (d), the frequency division multiplexed signals FDM5, FDM6 and FDM having a bandwidth of 1 GHz are provided in the optical fiber 31.
The frequency division multiplexed signal FDM4 including 7 is transmitted. Therefore, the bandwidth of the optical fiber 31 can be effectively used. Further, since only the signal in the band of 4 GHz is transmitted to the optical fiber 31, the existing optical fiber can be used. In addition, as shown in the frequency spectra of FIGS. 4E to 4G, the coaxial cables 41a and 41a
Since only signals having a bandwidth of 1 GHz are transmitted to b and 41c, the existing coaxial cable can be used. Therefore, since it is only necessary to exchange the center station 13 and the node 23, it is possible to quickly and inexpensively form an optical coaxial hybrid transmission system that dramatically expands the amount of video information provided.

FIG. 6 is a block diagram showing the configuration of the optical coaxial hybrid transmission system according to the fourth embodiment of the present invention. The parts corresponding to those of the optical coaxial hybrid transmission system in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the optical coaxial hybrid transmission system of FIG. 6, the coaxial cable 41a is wired in the first area β1 and the second area β2 that provide a service of providing video information.
On the other hand, the coaxial cable 41b is wired only in the first area β1, and the coaxial cable 41c is wired only in the second area β2.

The optical signal output from the center station 11 is
It is transmitted to the node 24 via the optical fiber 31. The service target area of the node 21 is the first area β1 and the second area β2. The frequency division multiplex signal FDM1 from the signal source 111 of FIG. 1 is output to the coaxial cable 41a, and the frequency division multiplex signal FDM1 is used for a basic service commonly provided to all subscribers, for example, a broadcast television program. Has been assigned to the offer. Further, the frequency division multiplexed signal FDM2 from the signal source 112 of FIG. 1 is output to the coaxial cable 41b, and the first area β
It is dedicated to the provision of unique services to only one subscriber, eg Yamanote information. The coaxial cable 41c is
Frequency division multiplexed signal FDM3 from signal source 113 of FIG.
Is output, and the service is assigned to a specific service only to the subscribers in the second area β2, for example, the provision of downtown information.

With this structure, for example, a subscriber in the first area β1 can receive the basic service by the coaxial cable 41a and another service by the coaxial cable 41b. Moreover, since the coaxial cable 41b is dedicated to the first area α1, only the first area α1
A more limited and dedicated service is available to subscribers in the area α1. Further, when considering video-on-demand as one of services, the serviceability is improved as the number of signal channels with high utility value per subscriber is increased. Therefore, it is advantageous to have a dedicated coaxial cable for each area.

In the embodiments shown in FIGS. 1, 3, 5, and 6, the coaxial cable has been described as having three systems.
You may make it implement | achieve by the number of systems of 2 systems or 4 systems or more. In this case, the number of signal sources of the center station may be adjusted according to the number of systems.

Further, in the optical coaxial hybrid transmission system of FIG. 1, the signal sources 111, 112 and 113 which output the frequency division multiplexed signals of the same frequency band are used, but the signals which output the frequency division multiplexed signals of different frequency bands are used. Source 114,
You may make it comprise the center station 11 using 115,116. In this case, the multiplexing unit 131 only needs to add the three frequency division multiplexed signals FDM5, FDM6, and FDM7, and the configuration is simplified.

Although the wavelengths of the optical signals of the optical transmitters 122, 123 and 124 of the optical coaxial hybrid transmission system of FIG. 3 are the same, they may be different. In this case, if a demultiplexer / multiplexer having a wavelength characteristic adapted to the optical multiplexer 141 is used, lower loss multiplexing can be realized.

Further, like the optical coaxial hybrid transmission system shown in FIG. 5, if optical transmission is performed by a multiplexing method that combines frequency division multiplexing and wavelength division multiplexing, the node 21 shown in FIGS. 1 and 3 also separates. It is possible to select a method that is advantageous in terms of cost and the like.

Further, in the optical coaxial hybrid transmission system of FIG. 6, although there are two areas and three coaxial cables, the area may be three or more and the coaxial cables may be two or four or more. Good. Further, instead of the center station 11 and the node 21, the center stations 12 and 13 and the node 23 shown in FIGS. 3 and 5 may be used.

[0059]

According to the first aspect of the present invention, a plurality of series of coaxial cables are prepared, the center station includes information of a plurality of channels, and is not wider than the transmission bandwidth of the corresponding series of coaxial cables. A plurality of frequency division multiplexed signals having a bandwidth are further multiplexed and output to an optical fiber in the form of an optical signal, and a node separates the optical signal received through the optical fiber into a plurality of frequency division multiplexed signals, Since the frequency division multiplexed signal is output to the corresponding series of coaxial cables, the wide band characteristic of the optical fiber can be effectively used without being limited by the band characteristic of the coaxial cable.
Further, since the wide band characteristic of the optical fiber can be effectively utilized, it is not necessary to prepare a plurality of sets of optical fibers, and an optical coaxial hybrid transmission system capable of providing a large amount of video information can be inexpensively and quickly formed.

According to the second aspect of the present invention, the center station further multiplexes a plurality of frequency division multiplexed signals by frequency division multiplexing, and the node transmits the optical signals according to the difference in the frequency band of the optical signals. Since the signals are separated into a plurality of frequency division multiplexed signals, it is possible to facilitate the multiplexing and separation matching the transmission bands of the optical fiber and the coaxial cable.

According to the third aspect of the present invention, the center station further multiplexes a plurality of frequency division multiplexed signals by wavelength division multiplexing, and the node outputs a plurality of the optical signals according to the difference in the wavelengths of the optical signals. Since it is separated into the frequency-division multiplexed signals of, it is possible to facilitate the multiplexing and separation matching the transmission bands of the optical fiber and the coaxial cable.

According to the invention of claim 4, when the center station further multiplexes a plurality of frequency division multiplexed signals by frequency division multiplexing, there is no information to be transmitted between the respective frequency division multiplexed signals. Since the signals including the guard band are multiplexed, it is possible to easily prevent signals in other bands from being mixed into each of the separated frequency division multiplexed signals, and to prevent the reproduction of the video information from being adversely affected.

According to the invention of claim 5, the node is
Since the frequency band of each frequency division multiplexed signal output to the coaxial cable of the corresponding series is adjusted to the same band, it is not necessary for the subscriber to prepare a special device such as a television tuner capable of receiving 400 to 500 ch. Moreover, it becomes possible to use the existing device and receive more information without changing the reception band of the high band.

According to the invention of claim 6, the node administers a plurality of regions, at least one system of the coaxial cable is wired throughout the plurality of regions, and the remaining system of the coaxial cable is in each of the plurality of regions. Since it is wired to the corresponding specific area, it is possible to provide a service of providing more video information that matches the regional characteristics of the target area, that is, the subscriber's social life, hobbies and tastes.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical coaxial hybrid transmission system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum of a signal output by each unit of the optical coaxial hybrid transmission system of FIG.

FIG. 3 is a block diagram showing a configuration of an optical coaxial hybrid transmission system according to a second embodiment of the present invention.

4 is a diagram showing a frequency spectrum of a signal output by each unit of the optical coaxial hybrid transmission system of FIG.

FIG. 5 is a block diagram showing a configuration of an optical coaxial hybrid transmission system according to a third exemplary embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an optical coaxial hybrid transmission system according to a fourth exemplary embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a conventional optical coaxial hybrid transmission system.

[Explanation of symbols]

 11, 12, 13 ... Center station 21, 23 ... Node 31 ... Optical fiber 41a, 41b, 41c ... Coaxial cable 111-116 ... Signal source 121-127 ... Optical transmission part 131 ... Multiplexing part 141 ... Optical multiplexing part 211, 213 -215 ... Optical receiving part 221, Separation part 231, ... Optical separation part 241, 242, 243 ... Conversion part α1, α2 ... Guard band β1 ... First area β2 ... Second area

Claims (6)

[Claims] 1. An optical coaxial hybrid transmission system for transmitting information of a plurality of channels output from a center station to a subscriber via an optical fiber, a node and a coaxial cable, wherein the coaxial cable is prepared in a plurality of series. The center station further multiplexes a plurality of frequency division multiplexed signals each including information of a plurality of channels and having a bandwidth that is not wider than the transmission bandwidth of the coaxial cable of the corresponding series to form an optical signal. At the node, the node separates the optical signal received via the optical fiber into a plurality of frequency division multiplexed signals, and each frequency division multiplexed signal to the coaxial cable of a corresponding series. An optical coaxial hybrid transmission system including means for outputting. 2. The center station further multiplexes the plurality of frequency division multiplexed signals by frequency division multiplexing, and the node transmits the optical signals to the plurality of frequencies according to a difference in frequency band of the optical signals. The optical coaxial hybrid transmission system according to claim 1, wherein the optical coaxial hybrid transmission system separates into a division multiplexed signal. 3. The center station further multiplexes the plurality of frequency division multiplexed signals by wavelength division multiplexing, and the node divides the optical signal into the plurality of frequency division signals according to a difference in wavelength of the optical signal. The optical coaxial hybrid transmission system according to claim 1, wherein the optical coaxial hybrid transmission system separates into multiple signals. 4. The center station, when further multiplexing the plurality of frequency division multiplexed signals by frequency division multiplexing, multiplexes including guard bands having no information to be transmitted between the respective frequency division multiplexed signals. Claim 2
The optical coaxial hybrid transmission system described in. 5. The optical coaxial hybrid transmission according to claim 1, wherein the node adjusts the frequency bands of the respective frequency division multiplexed signals output to the coaxial cables of the corresponding series to the same band. system. 6. The node has jurisdiction over a plurality of regions, at least one system of the coaxial cable is wired throughout the plurality of regions, and the remaining systems of the coaxial cable are respectively in the plurality of regions. The optical coaxial hybrid transmission system according to any one of claims 1 to 5, wherein the optical coaxial hybrid transmission system is wired in a corresponding specific area.