JP3199149B2 - Passive point-multipoint optical transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a point-to-multipoint optical transmission method for performing communication between a center apparatus and a plurality of user apparatuses which face each other via an optical transmission line. In particular,
A passive point having a configuration in which light transmitted from a center device is modulated and turned back without disposing an active optical element in a user device.
The present invention relates to a multipoint optical transmission method .

[0002]

2. Description of the Related Art FIG. 16 is a block diagram showing a configuration of a conventional passive point-to-multipoint optical transmission system. Here, a case in which one-core optical fiber transmission using a reflection element is performed as a passive optical transmission technique will be described.

In FIG. 1, a center device 20 and N user devices 30-1 to 30-N are connected to a 1-to-N optical star coupler 1.
The optical fiber 11 is connected to the feeder optical fiber 11 and N branch optical fibers 12-1 to 12-N via the line 0. Center device 20
Is composed of a transmission unit 21, a reception unit 22, and a one-to-two optical coupler (or optical circulator) 23. Each user device 30 includes a receiving unit 31, a reflecting unit 32, and a one-to-two optical coupler 33.

Here, the operation of the conventional system will be described with reference to a transmission / reception diagram shown in FIG. The center device 20 time-division multiplexes the downstream optical signals D1 to DN to each of the user devices 30-1 to 30-N, and sends them out of the one-to-two optical coupler 23 to the feeder optical fiber 11. Each of the downlink optical signals D1 to DN multiplexes a signal light to each user device and a modulated light modulated by each user device in a time domain allocated to each user device. For example, a DC light is used as the modulated signal. Each of the downstream optical signals D1 to DN is 1
Each of the user devices 30-1 to 30-3 is divided into N branches by the N-star optical coupler 10, and the branch optical fibers 12-1 to 12-N.
0-N is transmitted in broadcast format.

[0005] In the user apparatus 30-1, the received signal is input to the receiving section 31 and the reflecting section 32 via the one-to-two optical coupler 33. The receiving unit 31 receives the signal light addressed to the own device from the downstream optical signal D1 in the allocated time domain. The reflection unit 32 modulates the modulated light addressed to the own device to transmit the upstream optical signal U.
1 is generated and transmitted to the branch optical fiber 12-1 via the one-to-two optical coupler 33. Note that the light other than the modulated light addressed to the own device is not modulated. The same applies to the other user devices 30-2 to 30-N.

The upstream optical signals U1 to UN transmitted from the respective user devices 30-1 to 30-N are combined by the 1: N optical star coupler 10, and transmitted to the center device 20 via the feeder optical fiber 11. You. In the center device 20, the upstream optical signals U1 to UN are transmitted to the receiving unit 22 via the one-to-two optical coupler 23.
Is received. For the sake of simplicity, in FIG. 17, a synchronization bit for synchronizing optical signals is omitted.

[0007]

By the way, in the passive point-multipoint optical transmission system, the transmission timing of the upstream optical signal of the user equipment is restricted by the reception timing of the downstream optical signal. On the other hand, since the round-trip propagation delay time varies depending on the distance between the center device and each user device, the upstream optical signals from each user device may overlap when arriving at the center device.

In the transmission / reception diagram shown in FIG. 17, the distance from the center device 20 to each of the user devices 30-1 to 30-N increases in order, and the arrangement of the downstream optical signals D1 to DN to each user device is changed. Since it corresponds to that, the center device 20 transmits the upstream optical signals U1 to U1 from each user device.
UNs are received in order.

However, when the distance from the center device 20 to the user device 30-1 and the distance from the user device 30-2 are reversed as shown in the transmission / reception diagram shown in FIG.
The upstream optical signal U2 from the user device 30-2 overlaps the upstream optical signal U1 from the user device 30-1. In such a case, the center device 20 cannot perform normal reception.

The present invention provides a passive point-to-multipoint optical transmission method capable of avoiding an overlap of upstream optical signals from a plurality of user equipments to a center equipment while minimizing a decrease in transmission efficiency. The purpose is to:

[0011]

According to the passive point-multipoint optical transmission method of the present invention , a center device is used for communication.
Measure the round-trip propagation delay time between each user equipment beforehand
Between downlink optical signals to each user device in a downlink frame.
Set the guard time between the center device and each user device.
Set a large round-trip propagation delay time.

[0012] Further, the center device is operated by each user prior to communication.
Measure the round-trip propagation delay time between the
Downlink optical signal to the i-th user equipment in the order of the frame
Between the downstream optical signal and the (i + 1) th user equipment
Time between the center device and the i-th user device.
Set the round-trip propagation delay time.

[0013] Further , before the communication, the center device transmits each user.
Measure the round-trip propagation delay time between the
The time width of the signal light to the device is determined by the center device and each user device.
Is set to the maximum round-trip propagation delay time.

[0014]

[0015]

[0016]

[0017]

[0018]

According to the passive point-to-multipoint optical transmission method of the present invention, a guard point between downstream optical signals to each user equipment is provided.
The maximum time between the center device and each user device
By setting the round-trip propagation delay time, each user equipment
Modulates the modulated light of the downstream frame with
Even if folded, each upstream optical signal does not overlap at the center device
May be so (claim 1).

[0019]

Further, as a guard time corresponding to each user equipment, by setting in accordance with the round-trip propagation delay time between the user apparatuses, the respective uplink optical signals with minimal guard time does not overlap with the center device ( Claim 2 ).

[0021]

[0022]

The signal light and the modulated light are time-division multiplexed to generate a downstream optical signal to each user equipment, and the time width of the signal light is set to the maximum round-trip propagation delay time between each user equipment. by setting the guard time between the downstream optical signal can be eliminated (claim 3).

[0024]

[0025]

[0026]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a transmission / reception diagram showing the first embodiment.

In the figure, a transmitting unit 21 is connected to a center device 20.
Is provided with a control unit 24 for controlling the transmission timing.
The rest is the same as the conventional configuration shown in FIG. The center device 20 communicates with each of the user devices 30-1 to 30-3 prior to communication.
The round trip propagation delay time τ _{1 to} τ N between 0 and _N is measured. For this measurement, for example, a method of transmitting an optical signal to each user device and observing the arrival time of the optical signal returned as a response is used. In the present embodiment, the maximum value τ of the round-trip propagation delay time with each user device in the downstream frame obtained by time-division multiplexing the downstream optical signals D1 to DN to each user device.
_MAX is used as the guard time T of each of the downstream optical signals D1 to DN. Thereby, each of the user devices 30-1 to 30-
The round-trip propagation delay time [tau] _{1 to} [tau] _N between N and _N is equal to or less than the guard time T (= [tau] _MAX ), and the upstream optical signals U1 to UN from each user device do not overlap. In the present embodiment, since the guard time between each downstream optical signal is constant,
Transmission timing control in the control unit 24 can be realized with a simple configuration.

FIG. 3 is a transmission / reception diagram showing a second embodiment of the present invention. The center device 20 similarly measures the round-trip propagation delay times τ _{1 to} τ _N between the user devices 30-1 to 30-N. This is applied to each of the downstream optical signals D1 to DN.
Are used as the guard times T _{1 to} T _N. For example,
Using the round-trip propagation delay time tau ₁ between the user device 30-1 as a guard time T ₁ of the between the downstream optical signal D1 and D2. Thus, the downstream optical signal D (i + 1) to the user device 30- (i + 1) is transmitted after the upstream optical signal Ui from the user device 30-i arrives, so that the upstream optical signal from each user device is transmitted. U1 to UN do not overlap. In addition, since the guard times T _{1 to} T _N are set in accordance with the round-trip propagation delay time between each user apparatus, transmission efficiency can be improved. Note that each guard time is τ ₁ −
τ ₂ , τ ₂ −τ ₃ ,…, τ _N −τ ₁ (0 if negative)
By doing so, it is possible to further increase the transmission efficiency.

FIG. 4 is a block diagram showing another embodiment of the present invention. The present embodiment is characterized in that the center device 20 and each of the user devices 30-1 to 30-N are connected in a time-division manner using the optical switch 25. As a result, only the downlink optical signal addressed to the user device is transmitted to each user device. Also, 1: N optical star coupler 1
Since there is no distribution loss occurring at 0, the output light intensity from the center device can be reduced.

In the transmission / reception diagram of this embodiment, a predetermined guard time is set between the downstream optical signals D1 to DN, and transmission / reception to / from each user device is individually performed, similarly to the transmission / reception diagrams shown in FIGS. The optical switch 25 is sequentially switched at the timing of the operation. Here, FIG. 5 shows a transmission / reception diagram when each guard time is appropriately set (corresponding to FIG. 3).

FIG. 6 is a block diagram showing a reference example .
FIG. 7 is a transmission / reception diagram of the reference example of FIG. In the figure, the center device 20 includes a control unit 24a for controlling the transmission timing of the transmission unit 21 and a control unit 24b for exchanging the signal sequence received by the reception unit 22. The rest is the same as the configuration of the embodiment shown in FIG.

In this embodiment, each of the user devices 30-1 to 30-3
0-N, the time widths of the downstream optical signals D1 to DN, and the upstream optical signals U1 to U from the respective user devices 30-1 to 30-N.
The time width of N is set to a value shorter than the maximum value τ _MAX of the round-trip propagation delay time between each user apparatus. Accordingly, when the upstream optical signal corresponding to the downstream optical signal to each user apparatus arrives at the center apparatus according to the round-trip propagation delay time between each user apparatus, there is a possibility that the optical signal may overlap or interchange. Become.

In the center device 20, each user device 30-
Using the round trip propagation delay τ ₁ ~τ _N between the 1 to 30-N, to calculate the reception timing of the uplink optical signal based on the timing of transmitting a downlink optical signal. Here, when it is expected that upstream optical signals from a plurality of user apparatuses are overlapped, the control unit 24a performs control to advance or delay the transmission timing of the downstream optical signal to the corresponding user apparatus. In the setting of the transmission timing, the control range of the transmission timing can be expanded by exchanging the arrangement of the downstream optical signals to each user apparatus. By performing such transmission timing setting for each user device, it is possible to prevent the upstream optical signals from each user device from overlapping each other. The transmitting unit 21 starts transmitting the downstream optical signal according to the transmission timing of each user device.

In the transmission / reception diagram shown in FIG. 7, it is assumed that the user devices 30-2, 30-3, and 30-1 are located farther in the order. Since the time width of the downstream optical signal and the upstream optical signal is sufficiently shorter than the maximum value τ _MAX of the round-trip propagation delay time between each user device, before the upstream optical signal U1 from the user device 30-1 arrives. , An upstream optical signal U2 from the user apparatus 30-2 located at a shorter distance therefrom arrives. Note that a necessary guard time is set so that the upstream optical signals U1 to UN from the respective user devices do not overlap each other and are normally received.

In this embodiment, the upstream optical signals U1 to UN received by the center device 20 from the respective user devices are changed according to the round-trip propagation delay time between the respective user devices regardless of the arrangement in the downstream frame. Therefore, the degree of freedom in the arrangement of upstream optical signals is increased, and more efficient transmission is possible. Note that the control unit 24b performs control to return the upstream optical signals U1 to UN received from the user devices to the receiving unit 22 to a predetermined arrangement.

The upstream optical signal U1 from each user equipment
The arrangement of the downstream optical signals D <b> 1 to DN may be exchanged and transmitted so that 〜UN does not overlap and further to a predetermined arrangement. FIG. 8 shows a transmission / reception diagram in this case.

In the above embodiment, the receiving unit 31 and the reflecting unit 32 of the user device are separate elements, but a reflection type light detection modulator in which these are integrated may be used. A reflection-type photodetector is a stack of a photodetector, a photomodulator, and a reflector. The photodetector receives incident light and reflects a part of the light to modulate the photodetector. This is a structure that emits light by turning it back.

In the above embodiment, a single optical fiber transmission structure using a reflection element is used. A transmission configuration can also be used. The transmission type light detection modulator is a structure in which a light detector and a light modulator are stacked, and has a structure in which incident light is received by the light detector, and transmitted light is modulated by the light modulator and emitted.

Here, in the reference example of FIG. 6, a two-core optical fiber transmission configuration using a transmission type photodetector modulator,
FIG. 9 shows the optical star coupler 10 replaced with an optical switch. Reference numeral 34 denotes a transmission-type light detection modulator,
12-Na is a branch optical fiber for transmitting a downstream optical signal, and 12-1b to 12-Nb are branch optical fibers for transmitting an upstream optical signal.

In the reference example shown in FIG . 6, since the downstream optical signal and the upstream optical signal are completely independent on the time axis, the optical switch 25a for switching the downstream optical signal and the optical switch 25a for switching the upstream optical signal are provided. The optical switch 25b is separately provided, and the switching operation is performed at an independent timing. FIG. 10 shows a transmission / reception diagram of this reference example .

The above is the basic configuration and transmission / reception diagram of the passive point-to-multipoint optical transmission system of the present invention. Next, the downstream optical signal Di to each user device
And a method of generating the upstream optical signal Ui from the downstream optical signal Di will be described.

FIG. 11 is a block diagram showing a reference example . In the present reference example , downstream optical signals D1 to
The phase modulation code is used as DN, and the upstream optical signals U1 to UN
RZ code obtained by amplitude-modulating the phase modulation code is used. The phase modulation code is, for example, a biphase code that causes two types of pulses, positive and negative, or negative and positive, to correspond to a signal of “1” or “0”.

In the center device 20, a phase modulation unit (PMO)
D) 26 drives the transmission unit 21 and generates downstream optical signals D1 to DN to each user device using the phase modulation code. In each of the user devices 30-1 to 30-N, the phase modulation code received by the reception unit 31 is demodulated by a phase demodulation unit (PDEM) 35. Further, the amplitude modulating unit (AMOD) 36 is
2 to generate the upstream optical signals U1 to UN to the center device by amplitude-modulating the received phase modulation code. In the center device 20, the amplitude modulation signal received by the reception unit 22 is demodulated by an amplitude demodulation unit (ADEM) 27.

FIG. 12 is a transmission / reception diagram showing the third embodiment. In the center device 20, signal light d1 to dN to each user device and modulated light m1 to mN modulated by each user device are time-division multiplexed, and downlink optical signals D1 to DN to each user device are obtained. Generate. Each of the user devices 30-1 to 30-N receives the signal light d1 to dN addressed to each user device from the downstream optical signal D1 to DN, and modulates the modulated light m1 to mN to transmit the upstream optical signal U1 to UN. Generate

Here, the time width of the signal lights d1 to dN is set to the maximum round-trip propagation delay time between the center device and each user device. Thereby, the time domain of the signal lights d1 to dN becomes a guard time between the upstream optical signals from the respective user devices in the center device. Therefore, in a downstream frame, it is not necessary to set a guard time between downstream optical signals to each user apparatus.

FIG. 13 is a block diagram showing a reference example . FIG. 14 is a transmission / reception diagram of the reference example of FIG. The transmission unit 21 of the center device 20
Downlink optical signals D1 to DN to 0-1 to 30-N are time-division multiplexed, and a DC superimposing unit 28 superimposes DC light in the entire time domain.

Each of the user devices 30-1 to 30-N receives the downstream optical signal addressed to the own device, and
The DC light component extracted through is input to the reflection unit 32,
A predetermined time domain is modulated to generate upstream optical signals U1 to UN. The time region (transmission timing) specified for each user device is notified from the center device 20 according to the round-trip propagation delay time between each user device. For example, a control channel specifying transmission timing of an upstream optical signal is multiplexed in downstream optical signals D1 to DN to each user apparatus. Each user device receives this control channel and drives the reflector 32 in a time domain corresponding to the designated transmission timing. Thereby, in each user device, the downstream optical signal D1
To the upstream optical signal U
Since the transmission timing of 1 to UN can be set, high transmission efficiency can be realized. For simplicity, FIG.
4, the control channel is omitted.

FIG. 15 is a transmission / reception diagram of another reference example . The center device 20 uses a phase modulation code as the downstream optical signals D1 to DN to each user device, and time-division multiplexes and transmits the signals.

Each of the user devices 30-1 to 30-N receives a downstream optical signal addressed to the own device, and performs amplitude modulation on a predetermined time domain with respect to the phase modulation code in the entire time domain of the received downstream optical signal. The signal is modulated to generate upstream optical signals U1 to UN. The time region (transmission timing) specified for each user device is notified from the center device 20 as described above. Thereby, in each user device, the downstream optical signals D1 to D1
Regardless of the reception timing of the DN, each upstream optical signal U1
To UN transmission timing can be set, so that high transmission efficiency can be realized. For simplicity, FIG.
In the figure, the control channel is omitted.

[0050]

As described above, in the passive point-to-multipoint optical transmission system according to the present invention, the transmission timing of the downstream optical signal is controlled by providing the guard time in the center device, whereby the transmission from each user device is controlled. Uplink optical signals can be prevented from overlapping in the center device. In addition, by appropriately setting the guard time according to the round-trip propagation delay time between each user apparatus, the guard time can be minimized and the transmission efficiency can be increased.

In a configuration in which the arrangement of downstream optical signals and the arrangement of upstream optical signals are irrelevant, by adjusting the transmission timing of downstream optical signals to each user apparatus, overlap of upstream optical signals can be prevented and the arrangement of upstream optical signals can be prevented. And the transmission efficiency can be increased.

In a configuration in which a downstream optical signal is generated using a phase modulation code, and the phase modulation code is amplitude-modulated to generate an upstream optical signal, a modulated signal for generating an upstream optical signal in each user apparatus is provided. There is no need to send light, and transmission efficiency can be increased.

Further, the signal light and the modulated light are time-division multiplexed to generate a downstream optical signal, and the time width of the signal light is set to the maximum round-trip propagation delay time, so that a guard between the downstream optical signals can be obtained. Time can be made unnecessary, and transmission efficiency can be improved.

Further, by superimposing and transmitting DC light as modulated light to each user apparatus over the entire time domain of the downstream frame, each user apparatus side can transmit the upstream light signal independently of the reception timing of the downstream optical signal. The transmission timing of the optical signal can be set. As a result, the upstream optical signals from each user apparatus can be prevented from overlapping in the center apparatus, and a guard time can be made unnecessary, and transmission efficiency can be improved.

Further, in the configuration in which each user apparatus generates an upstream optical signal by amplitude-modulating the phase modulation code, the phase modulation code over the entire time domain of the downstream frame can be handled in the same manner as DC light. That is, since the transmission timing of the upstream optical signal can be set independently of the reception timing of the downstream optical signal on each user device side, the upstream optical signals from each user device can be prevented from overlapping at the center device,
Guard time can be eliminated, and transmission efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of claim 1.

FIG. 2 is a transmission / reception diagram showing the embodiment of claim 1 ;

FIG. 3 is a transmission / reception diagram showing an embodiment according to claim 2 ;

FIG. 4 is a block diagram showing another embodiment of the present invention;

FIG. 5 is a transmission / reception diagram corresponding to the configuration of the embodiment in FIG. 4;

FIG. 6 is a block diagram showing a reference example .

FIG. 7 is a transmission / reception diagram of the reference example of FIG . 6 ;

FIG. 8 is another transmission / reception diagram of the reference example of FIG . 6 ;

FIG. 9 is a block diagram showing another configuration of the reference example of FIG . 6 ;

FIG. 10 is a transmission / reception diagram of the reference example of FIG. 9;

FIG. 11 is a block diagram showing a reference example .

FIG. 12 is a transmission / reception diagram showing the embodiment of claim 3 ;

FIG. 13 is a block diagram showing a reference example .

FIG. 14 is a transmission / reception diagram of the reference example of FIG . 13 ;

FIG. 15 is a transmission / reception diagram of another reference example .

FIG. 16 is a block diagram showing a configuration of a conventional passive point-multipoint optical transmission system.

FIG. 17 is a conventional transmission / reception diagram.

FIG. 18 is a transmission / reception diagram showing a conventional problem.

DESCRIPTION OF SYMBOLS 10 1: N optical star coupler 11 Feeding optical fiber 12 Branch optical fiber 20 Center device 21 Transmitting unit 22 Receiving unit 23 1: 2 optical coupler 24 Control unit 25 Optical switch 26 Phase modulation unit (PMOD) 27 Amplitude demodulation unit (ADEM) 28 DC superimposition unit 30 User device 31 Receiver unit 32 Reflection unit 33 One-to-two optical coupler 34 Transmission type photodetector modulator 35 Phase demodulation unit (PDEM) 36 Amplitude modulation unit (AMOD) 37 Filter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-235873 (JP, A) JP-A-2-1455043 (JP, A) JP-A-2-26425 (JP, A) JP-A-5-235 235867 (JP, A) JP 55-7736 (JP, B2) JP 55-5778 (JP, B2) JP 1-503107 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04J 14/00-14/08 H04B 10/00-10/28

Claims (3)

(57) [Claims] 1. An optical transmission system between a center device and a plurality of user devices.
Connected in a point-multipoint manner via a road, wherein the center device transmits a signal light to each of the user devices and the
Each of the units multiplexed with the modulated light modulated by each user device.
Assign the downstream optical signal to the user equipment to each user equipment
As time-division multiplexed downlink frames in the allocated time domain
Transmitting to the optical transmission line, wherein each of the user devices transmits the
The downlink from the time domain assigned to the device to the own device
Receives an optical signal and modulates the modulated light addressed to the own device.
The center device generates an optical signal and transmits the optical signal to the optical transmission line.
In the passive point-multipoint optical transmission method for receiving the upstream optical signal transmitted from the user device, the center device is configured to communicate with each of the user devices prior to communication.
Measure the round-trip propagation delay time between
Wherein the guard time between the downstream optical signals to each of the user equipments is set to the maximum round-trip propagation delay time between the center equipment and each of the user equipments. How . 2. Optical transmission between a center device and a plurality of user devices.
Connected in a point-multipoint manner via a road, wherein the center device transmits a signal light to each of the user devices and the
Each of the units multiplexed with the modulated light modulated by each user device.
Assign the downstream optical signal to the user equipment to each user equipment
As time-division multiplexed downlink frames in the allocated time domain
Transmitting to the optical transmission line, wherein each of the user devices transmits the
The downlink from the time domain assigned to the device to the own device
Receives an optical signal and modulates the modulated light addressed to the own device.
The center device generates an optical signal and transmits the optical signal to the optical transmission line.
In the passive point-multipoint optical transmission method for receiving the upstream optical signal transmitted from the user device, the center device is configured to communicate with each of the user devices prior to communication.
Measure the round-trip propagation delay time between
, And the downstream optical signal to the i-th user equipment and i +
A passive point-multipoint, wherein a guard time between a downstream optical signal to a first user equipment and a round-trip propagation delay time between the center equipment and the i-th user equipment is set. Optical transmission method . 3. An optical transmission system between a center device and a plurality of user devices.
Connected in a point-multipoint manner via a road, wherein the center device transmits a signal light to each of the user devices and the
Each of the units multiplexed with the modulated light modulated by each user device.
Assign the downstream optical signal to the user equipment to each user equipment
As time-division multiplexed downlink frames in the allocated time domain
Transmitting to the optical transmission path, wherein each of the user devices is
The downlink from the time domain assigned to the device to the own device
Receives an optical signal and modulates the modulated light addressed to the own device.
The center device generates an optical signal and transmits the optical signal to the optical transmission line.
In the passive point-multipoint optical transmission method for receiving the upstream optical signal transmitted from the user apparatus, the center apparatus, each of the user apparatuses before communication
Measuring the round-trip propagation delay time between the two, and setting the time width of the signal light to each of the user devices to the maximum round-trip propagation delay time between the center device and each of the user devices. Point-multipoint optical transmission method .