JPH08204650A - Point-multipoint optical transmission system - Google Patents

Abstract

PURPOSE: To realize the point-multipoint optical transmission system accommodating efficiently a user equipment in matching with a capability of a center equipment. CONSTITUTION: A center equipment 20 and plural user equipments 30-1-30-32 are connected in a point-multipoint form via an optical transmission line 11 and the optical signal is sent in two-way between the center equipment 20 and the plural user equipments 30-1-30-32 through time division multiplex processing. In the point-multipoint optical transmission system, the center equipment 20 is provided with plural transmission reception sections 25-1-25-8 sending an outgoing signal light to the user equipments 30-1-30-32 and receiving the incoming signal light from the user equipments 30-1-30-32 and applies time division multiplex transmission reception processing to a prescribed number of correspondent user equipments altogether via each transmission reception section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a point-multipoint optical transmission system for communicating between a center device and a plurality of user devices which are opposed to each other via an optical transmission line.

[0002]

2. Description of the Related Art FIG. 8 shows the configuration of a conventional point-multipoint optical transmission system. In the figure, the center device 20 and n user devices 30-1 to 30-n are connected via an optical fiber transmission line 11 and a 1-to-n optical star coupler 12. The center device 20 includes a one-to-two optical coupler (or optical circulator) 21, a transmitter 22 and a receiver 23, and an electric signal processing circuit 24.

In this point-to-multipoint optical transmission system, as shown in FIG. 9, the downlink signal light transmitted from the center device 20 to each of the user devices 30-1 to 30-n is time-division multiplexed, and an optical star coupler is used. It branches in 12 and is sent to each user apparatus 30-1 to 30-n. Each of the user equipments 30-1 to 30-n cuts out the signal light addressed to itself from the time-division multiplexed downlink signal light from the time axis and receives the signal light. On the other hand, each of the user equipments 30-1 to 30-n sends out signal light at a predetermined transmission timing by time division multiple access (TDMA). The upstream signal light from each user device is passively multiplexed by the optical star coupler 12 and received by the center device 20 side by side on the time axis. Center device 20
The electric signal processing circuit 24 performs the above-described time division multiplexing control for accommodating a plurality of user equipments, and interfaces with the higher-level equipment connected to the communication network.

In such a configuration, since it is possible to communicate with a plurality of user equipments by one set of transmitters / receivers of the center equipment, the center equipment cost per line can be kept low.

[0005]

In the point-multipoint optical transmission system, the number of user equipments that can be accommodated in one center equipment is limited by the loss in the optical fiber transmission line and the optical star coupler. For example, in a 32-branch optical star coupler, a loss of 15 dB occurs in principle, and in reality it is an excess loss added to it. In the optical fiber transmission line, loss occurs according to the distance. Here, for example, in the case where the center device has an ability to tolerate a loss of about 15 dB and the loss in the optical fiber transmission line can be ignored, a 32-branch optical star coupler as shown in FIG. 10 (1) is used. 32 user equipments can be accommodated.

However, if part of the user equipment is located at a long distance, the loss in the optical fiber transmission line cannot be ignored and 32 user equipment cannot be accommodated. For example, if the loss in the optical fiber transmission line is 9 dB, the branch loss allowed in the optical star coupler will be 6 dB, and therefore FIG.
As shown in (2), there is no choice but to use a 4-branch optical star coupler. In this case, the center device having the capacity of accommodating 32 user devices only accommodates 4 user devices, and the accommodating efficiency is significantly reduced.

Further, as shown in FIG. 10 (3), it can be seen that it cannot be effectively used even in the time domain. That is,
Since the upstream frame is composed of only the upstream signal light from the four user equipments, there is a sufficient margin for the center equipment capable of supporting 32 multiplexing. Here, the downlink frame has a fixed length with dummy areas other than four channels.

It is an object of the present invention to provide a point-multipoint optical transmission system capable of efficiently accommodating a user equipment that matches the capability of the center equipment.

[0009]

According to the present invention, a center device and a plurality of user devices are connected in a point-multipoint form via an optical transmission line, and an optical signal is transmitted between the center device and the plurality of user devices. In a point-multipoint optical transmission system for bidirectional transmission by division multiplexing, the center device includes a plurality of transmitting / receiving units that transmit downlink signal light to the user device and receive uplink signal light from the user device,
The configuration is such that time-division multiplex transmission / reception processing with a predetermined number of corresponding user devices is collectively performed via each transmission / reception unit.

A circuit for taking the logical sum of the received signals output from the plurality of transmitting / receiving sections is also provided.

[0011]

In the point-multipoint optical transmission system of the present invention, a predetermined number of user equipments are connected to a plurality of transmission / reception units provided in the center equipment. By collectively performing the time-division multiplex transmission / reception processing via the plurality of transmission / reception units, it is possible to accommodate a large number of user equipments while suppressing the branch loss, and to fully utilize the number of multiplexes that the center equipment can process. be able to.

Further, by providing a circuit for taking the logical sum of the received signals output from the plurality of transmitting / receiving sections, the interface between the transmitting / receiving section and the electric signal processing section can be ensured.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of a point-multipoint optical transmission system of the present invention. Here, 1 to 4
32 in one center device while using the optical star coupler of
An example of accommodating a single user device will be described. In the figure, a center device 20 and 32 user devices 30-1
˜30-32 are connected via the optical fiber transmission line 11 and eight optical star couplers 12-1 to 12-8 arranged in parallel. The center device 20 includes eight sets of transmission / reception units 25-1 to 25-25 connected in parallel to the electric signal processing circuit 24.
-8 is provided. Each transmitter / receiver includes a one-to-two optical coupler (or optical circulator) 21, a transmitter 22 and a receiver 23.
including. Regarding the function and configuration of the electric signal processing circuit 24, the conventional configuration shown in FIG. 10 can be used.

The operation of this system will be described below. FIG. 2 (1) shows a frame structure at the input / output points of the transmission / reception unit 25-1. FIG. 2 (2) shows transmitting / receiving units 25-1 to 25-25.
A composite frame configuration at each input / output point of -8 is shown. From the center device 20 to the user devices 30-1 to 30-4
The downlink signal transmitted to the optical signal processing circuit 24 is input from the electric signal processing circuit 24 to the transmission unit 22 of the transmission / reception unit 25-1 and converted into an optical signal. As shown in FIG. 2A, the downlink signal lights addressed to the user equipments 30-1 to 30-4 are time-division multiplexed in a predetermined time region in a fixed-length downlink frame, and the optical star coupler 12
It is branched at -1 and sent to the user devices 30-1 to 30-4. Each of the user equipments 30-1 to 30-4 cuts out the signal light addressed to itself from the time-division multiplexed downlink signal light from the time axis and receives the signal light. On the other hand, the user devices 30-1 to 30
-4 transmits signal light at a predetermined transmission timing by time division multiple access (TDMA). User device 30-
The upstream signal lights from 1 to 30-4 are optical star couplers 12-
1 is passively multiplexed, and the center device 2 is lined up on the time axis.
It is received by the receiving unit 23 of the transmitting / receiving unit 25-1 of 0.

Center device 20 and user devices 30-5 to 3
Also between 0 and 32, the transmitting / receiving unit 25-2
Similarly, transmission / reception of downlink signal light and uplink signal light is performed via 25 to 8-8. Therefore, the transceivers 25-1 to 25-1
At each input / output point of 25-8, the frame structure shown in FIG. 2 (2) is provided, and as a whole, one center device accommodates 32 user devices. However, in this system,
Since four user equipments are connected to each of the optical star couplers 12-1 to 12-8, it is possible to deal with a case where the loss in the optical fiber transmission line 11 becomes large, and to connect with 32 user equipments. It is possible to fully utilize the capability of the electric signal processing circuit 24 capable of transmitting and receiving.

FIG. 3 shows the structure of the transmitter 22 and the connection between the plurality of transmitters 22 and the electric signal processing circuit 24.
In the figure, the transmitter 22 has a configuration in which a drive circuit 42 is connected to a laser diode (LD) 41 as a light emitting element. The drive circuits 42 of the plurality of transmitters 22 are connected in parallel to the electric signal processing circuit 24. Here, since the electric signal processing circuit 24 is a logic circuit and has a section with a driver or a logic circuit having an interface of TTL or CMOS, as shown in the figure, a plurality of transmitters 22 are connected in parallel at the interface point. can do. In particular, C
In the case of the MOS interface, the fan-out (the number that can be connected) is large, so that parallel connection is easy.

FIG. 4 shows the configuration of the receiving section 23 and the connection modes (1) and (2) between the plurality of receiving sections 23 and the electric signal processing circuit 24.
Indicates. In the figure, the receiving unit 23 has a configuration in which a receiving circuit 52 is connected to a photodiode (PD) 51 as a light receiving element. The reception circuit 52 includes an amplifier 53, an automatic gain control circuit (AGC) 54, and a determination circuit (DEC) 55. An automatic threshold control circuit may be used instead of the automatic gain control circuit 54. The receiving circuits 52 of the plurality of receiving units 23 are connected in parallel to the electric signal processing circuit 24. Here, the electric signal processing circuit 24 is TTL or CMOS.
Since there is a cut-off with a driver or a logic circuit having an interface, the plurality of receiving units 23 can be connected in parallel at the interface point as shown in FIG. 4 (1). In addition, as shown in FIG.
The output of the receiving circuit 52 of is logically ANDed by the OR circuit 26,
You may make it input into the electric signal processing circuit 24.

In the transmitter / receiver 25 of the above-described embodiment, the transmitter 22 and the receiver 23 are independent because the light emitting element and the light receiving element are realized by dedicated elements. Therefore, it is necessary to arrange the one-to-two optical coupler 21 at the connection portion with the optical fiber transmission line 11. Here, by using a transmission / reception element (for example, a laser diode LD) that can be used as both a light emitting element and a light receiving element, the configuration of the transmission / reception unit 25 can be simplified.

FIG. 5 shows the configuration of the transmission / reception unit 25 and the connection between the plurality of transmission / reception units 25 and the electric signal processing circuit 24 when the transmission / reception element is used. In the figure, the transmitter / receiver 25 includes a laser diode (LD) 41, a drive circuit 42
And the receiving circuit 52 are connected in parallel. The receiving circuit 52 has the same configuration as that shown in FIG. Since the laser diode 41 has different operating conditions when used as a light emitting element and when used as a light receiving element, the operation mode of the transmission / reception unit 25 is switched by a transmission / reception switching control signal from the electric signal processing circuit 24. Transmitter / receiver 25
-1 to 25-8 and the electric signal processing circuit 24 are connected in parallel via a changeover switch 27 and a selection circuit 28 that change the transmission / reception direction by a transmission / reception switching control signal. The electric signal processing circuit 24 and each drive circuit 42 are bus-connected in the same manner as the connection of the transmitting unit 22 shown in FIG. 3, and the electric signal processing circuit 24 and each receiving circuit 52 are the receiving unit shown in FIG. 4 (2). Similar to the connection with 23, it is connected through the OR circuit 26.

Further, the embodiment described above is applied to the single-core bidirectional communication system in which bidirectional communication is performed by time division multiplexing (TCM) in one optical fiber transmission line. The present invention can be similarly applied to the two-core bidirectional communication system that is performed via the optical fiber transmission line. FIG. 6 shows an embodiment configuration of a point-multipoint optical transmission system of the present invention in a two-core bidirectional communication system.

In the figure, a center device 20 and 32 user devices 30-1 to 30-32 are a downstream optical fiber transmission line 11-1 and eight optical star couplers 12-1-1 to 12-1-1 arranged in parallel. 12-1-8 is connected to the upstream optical fiber transmission line 11-2 and eight optical star couplers 12-2-1 to 12-2-8 arranged in parallel. The center device 20 includes transmitting units 22-1 to 22-8 connected in parallel to the electric signal processing circuit 24-1 for transmission and a receiving unit connected in parallel to the electric signal processing circuit 24-2 for reception. Two
3-1 to 23-8. The connection form between the transmission unit and the reception unit and the electric signal processing circuit is the same as that shown in FIGS.

Further, as shown in FIG. 7 (1), the center device 2
In the case where the optical star coupler 12 is arranged in 0 and the passive double star (PDS) configuration is combined with the optical star coupler arranged between the user equipment and the user equipment, the point-multipoint optical transmission system of the present invention is also provided. It is valid. That is, as shown in FIG. 7 (2), the transmitting / receiving unit 25 is arranged at a plurality of input / output ports of the center device 20, so that the user device at a point with a large loss can be efficiently accommodated. it can.

[0023]

As described above, in the point-multipoint optical transmission system of the present invention, it is possible to accommodate a large number of user equipments in the center equipment while minimizing the number of branches in the optical transmission line. As a result, the characteristics of the electric signal processing circuit of the center device designed according to the transmission speed, the number of multiplexed signals, the service capacity, etc. can be fully utilized. Further, since the design of the electric signal processing part for performing the time division multiplexing processing and the design of the optical transmission line part can be separated to some extent, the design and facility operation of the system itself can be flexibly performed. Moreover, since the multiplex number at the time of design can be effectively utilized, an economical system can be constructed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a point-multipoint optical transmission system of the present invention.

FIG. 2 is a diagram showing an operation example of a point-multipoint optical transmission system of the present invention.

FIG. 3 is a diagram showing a configuration of a transmission unit 22 and a connection form between a plurality of transmission units 22 and an electric signal processing circuit 24.

FIG. 4 is a diagram showing a configuration of a receiving unit 23 and connection forms (1) and (2) of a plurality of receiving units 23 and an electric signal processing circuit 24.

FIG. 5 is a diagram showing a configuration of a transmission / reception unit 25 and a connection form between a plurality of transmission / reception units 25 and an electric signal processing circuit 24 when a transmission / reception element is used.

FIG. 6 is a diagram showing a configuration of an embodiment of a point-multipoint optical transmission system of the present invention in a two-core bidirectional communication system.

FIG. 7 is a diagram for explaining an application example of the point-multipoint optical transmission system of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional point-multipoint optical transmission system.

FIG. 9 is a diagram showing an operation example of a conventional point-multipoint optical transmission system.

FIG. 10 is an explanatory diagram of a problem of the conventional point-multipoint optical transmission system.

[Explanation of symbols]

 11 Optical Fiber Transmission Line 12 Optical Star Coupler 20 Center Device 21 1-2 Optical Coupler 22 Transmitter 23 Receiver 24 Electric Signal Processing Circuit 25 Transmitter / Receiver 26 OR Circuit 27 Changeover Switch 28 Selector Circuit 30 User Device 41 Laser Diode (LD) 42 Drive Circuit 51 Photodiode (PD) 52 Receiver Circuit 53 Amplifier 54 Automatic Gain Control Circuit (AGC) 55 Judgment Circuit (DEC)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area H04B 9/00 G

Claims (2)

[Claims] 1. A center device and a plurality of user devices are connected in a point-multipoint form via an optical transmission line,
In a point-multipoint optical transmission system for bidirectionally transmitting an optical signal by time division multiplexing between a center device and a plurality of user devices, the center device transmits downlink signal light to the user device, and the user device It is characterized in that it is provided with a plurality of transmitting / receiving sections for receiving the upstream signal light from the apparatus, and is configured to collectively perform time division multiplexing transmission / reception processing with a predetermined number of corresponding user apparatuses via the respective transmitting / receiving sections. Point-multipoint optical transmission system. 2. The point-multipoint optical transmission system according to claim 1, further comprising a circuit that ORs received signals output from a plurality of transmission / reception units. system.