JPH09205408A - Optical burst signal reception system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct stable reception by comparing a reference signal level with a station side receiver output level for each time slot corresponding to a subscriber so as to control the gain of the receiver thereby absorbing signal level fluctuation caused by an environmental condition. SOLUTION: A received optical burst signal is converted into an electric signal by a photoelectric conversion circuit 1 and an output signal via a variable gain circuit 2 receiving the electric signal is given to a smoothing circuit 5, from which a voltage is obtained and it is given to a comparator circuit 4, in which the voltage is compared with the reference voltage of a reference signal level circuit 3. The comparator circuit 4 provides the output of a difference voltage as a control voltage and the control voltage is latched in plural control voltage storage circuits 8, the control voltage is used to control the variable gain circuit 2 to obtain a signal output at a desired level. In this case, a control circuit 10 controls changeover switches 6, 7 based on a switching order of subscribers and a time length to switches each subscriber based on each time slot, a corresponding control voltage is stored and the control voltage updated at any time is applied to the variable gain circuit 2. In the case of non-signal, the control voltage at the reception state is being stored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical burst signal receiving system, and in particular, it has a subscriber data in a predetermined time slot and a point-to-multipoint connection between stations and subscribers. Double Star (Passive Double Star; called "PDS")
The present invention relates to an optical burst signal receiving method for stably receiving a received burst signal having a level difference in a digital optical subscriber system according to the method.

[0002]

2. Description of the Related Art FIG. 2 shows the configuration of an optical subscriber system based on the PDS system.

Referring to FIG. 2, by connecting a star coupler 13 to the optical fiber transmission line 12 and branching the optical fiber transmission line on the subscriber side, a plurality (# 1, #) for one station device 14 can be obtained. 2, ..., #N) subscriber devices 11 are accommodated. In this configuration, one station device can be shared by a plurality of subscriber devices, and the optical fiber transmission line between the station and the star coupler can also be shared, so that a highly economical system can be provided. To have. In this way, PD
In the S system, an optical multiplexer / distributor (star coupler) including, for example, passive elements is provided between the master station (station device) and the subscriber terminal,
Connect the master station and the optical multiplexer / distributor with one optical fiber,
The optical multiplexer / distributor and each subscriber terminal are individually connected in a one-to-one manner with a dedicated optical fiber, and one master station is connected with a plurality of subscriber terminals in parallel and a communication network is provided. A plurality of similar master stations are connected in the entire system to be formed, and when such a connection configuration is viewed from the upstream side of the master station, there are a master station, an optical multiplexer / distributor, and two branches, which is called a "double star".

FIG. 3 shows the time position and the level of the signal received from each subscriber unit. In FIG. 3, 15 indicates a time slot allocated to each subscriber, and 16 indicates a guard time (guard t) for preventing data overlap between the subscribers.
ime) is shown. Each subscriber device 11 is included in the received signal.
From the star coupler to the star coupler 13, the optical signal level difference of the optical transmitter provided in the subscriber device 11, the star coupler 1
As shown in FIG. 3 (A), a large level difference was generated due to the loss variation of each output port of No. 3, the transmission line loss which varies depending on the environmental conditions, and the reflection on the transmission line.

FIG. 4 shows an example of a conventional technique for coping with this great level difference (referred to as "first conventional system"). FIG.
, 1 is a photoelectric conversion circuit, 2 is a variable gain circuit,
Reference numeral 3 is a reference signal level generation circuit, 4 is a comparison circuit, and 5 is a smoothing circuit. The received optical reception signal (input) is converted into an electric signal by the optical-electrical conversion circuit 1 and becomes a voltage value by the smoothing circuit 5. This voltage value is compared with the reference voltage value from the reference signal level generation circuit 3 in the comparison circuit 4 and output as a control voltage value. By controlling the variable gain circuit 2 with this control voltage to form a reception signal of a constant level, a large level difference as shown in FIG. 3A is absorbed (see FIG. 3B).

[0006] Further, in FIGS.
Prior art proposed in Japanese Patent Publication No. 30 (“second conventional method”)
). FIG. 6 shows a configuration of a variable gain circuit as a means for realizing the conventional technique shown in FIG. In FIGS. 5 and 6, 1 is an opto-electric conversion circuit, 2 is a variable gain circuit, 6 is a changeover switch, and 10 is a control circuit.
6, reference numeral 18 is a feedback resistance group of the amplifier 17, 6 is a high speed switch, and 10 is a control circuit for controlling the switching of the changeover switch 6, and the amplifier 17 is provided in accordance with the optical reception level obtained in advance. Of the feedback resistor group 18, each resistance value of the feedback resistor group 18 corresponds to the loss value of each subscriber, and the setting is electrically or automatically changed to each variable resistance, and the control circuit 10 Electrically controls the connection of the change-over switch 6 to one of the feedback resistor groups 18 for each subscriber based on the time division multiplexing scheduling obtained in advance, whereby the amplification degree (gain) of the amplifier 17 is increased. It changes rapidly and realizes stable reception at high speed even if the received light level changes significantly.

That is, in this conventional method, the optical transmission line loss for each subscriber is obtained by actual measurement or predetermined calculation in advance, and the gain value of the gain variable circuit 2 is created as a fixed value for each subscriber. Since the time slot for each subscriber is defined, the control circuit 10 sends a control signal by utilizing the fact that the subscriber switching order and the time length are known.
By changing the gain to a value corresponding to each subscriber by the change-over switch 6 and setting the received signal at a constant level, as shown in FIG.
By absorbing the large level difference as shown in FIG.
The uniform level as shown in (B) was obtained.

[0008]

However, the above-mentioned conventional method has the following problems.

That is, in the first conventional method, the level of the received signal is detected by the reset signal at the end of the guard time or the first few bits of each time slot, and the gain variable circuit 2 is controlled based on the detected value. Need time to do. For example, assuming that the transmission speed of the optical fiber transmission line is 52 Mbps, a variable gain circuit that responds at high speed to perform a variable gain of 20 dB or more in a short time of 20-40 nsec is required. It has been difficult to realize such a high-speed circuit.

Further, in the second conventional method, since the fixed gain value for each subscriber is determined, it is necessary to measure or calculate each optical transmission line in advance, and the fixed gain value is an environmental condition. However, there is a problem that it is not possible to deal with the received signal level variation caused by the above.

Therefore, the present invention solves the above problems,
The reference signal level and the output level of the receiver on the station side are compared and held for each time slot corresponding to the subscriber, and the receiver gain is controlled to automatically hold the control voltage according to the actual system installation conditions with high accuracy. Provide a method that absorbs variations in received signal level caused by environmental conditions, facilitates design of a comparison circuit and a variable gain circuit, and enables stable reception in a digital optical subscriber system based on the PDS method. The purpose is to do.

[0012]

According to the present invention, the above object is achieved by connecting one station apparatus and a plurality of subscriber apparatuses by point-to-multipoint connection with an optical fiber and a star coupler, and by time division multiplexing. In a digital optical subscriber system that transmits and receives signals in bursts, an optical burst signal reception that controls the receiver gain by comparing and holding the reference signal level and the station receiver output level for each time slot corresponding to each subscriber The scheme is achieved.

The optical burst signal receiving system according to the present invention is
In a preferred mode, a gain variable circuit for amplifying a signal obtained by converting a received optical signal into an electric signal by an optical-electrical conversion circuit in a variable gain and a control voltage supplied to the gain variable circuit are held corresponding to each subscriber. Control voltage holding circuit group for
Comparing means for comparing the output of the variable gain circuit with a reference voltage, the comparison result being set as a control voltage in the control voltage holding circuit corresponding to each subscriber via a first changeover switch, An output of the control voltage holding circuit group is supplied as a control voltage to the gain variable circuit via a second changeover switch, and further comprising control means for controlling the changeover of the first and second changeover switches. The feature is that it is possible to control and maintain the receiver gain by comparing and holding the reference signal level and the station receiver output level for each time slot corresponding to the subscriber, and the actual system installation conditions. The control voltage according to is automatically maintained with high accuracy, the received signal level variation caused by environmental conditions is absorbed, and the design of the comparison circuit and variable gain circuit is facilitated.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. Below, it is assumed that the time slot allocation for each subscriber is specified.

FIG. 1 is a diagram showing the configuration of an embodiment of the optical burst signal receiving system of the present invention, and shows the configuration of the receiving circuit of the station apparatus 14 shown in FIG. In FIG.
1 is an opto-electric conversion circuit, 2 is a variable gain circuit, 3 is a reference signal level generation circuit, 4 is a comparison circuit, 5 is a smoothing circuit, 6,
Reference numeral 7 denotes a changeover switch, 8 denotes N control voltage holding circuits prepared for N subscribers, 9 denotes a no-signal detection circuit, and 10 denotes a control circuit.

The received optical reception signal (input) is converted into an electric signal by the optical-electrical conversion circuit 1 and becomes an electric signal of a certain level by the gain variable circuit 2. This electric signal is converted into a voltage value by the smoothing circuit 5, and compared with the reference voltage value from the reference signal level generation circuit 3 by the comparison circuit 4.

The reference signal level generation circuit 3 outputs a reference voltage in which the output signal level of the variable gain circuit 2 is set to a voltage value that gives a desired signal level.

The comparison circuit 4 outputs the comparison result (difference voltage) between the voltage value from the smoothing circuit 5 and this reference voltage value as a control voltage, and the control voltage is passed via the changeover switch 6 to the control voltage holding circuit 8 Held in. At this time, the changeover switch 6 changes over the connection of the control voltage holding circuit 8 provided for each subscriber according to the control signal from the control circuit 10. Similarly, the changeover switch 7 also switches the connection of the control voltage from the control voltage holding circuit 8 held for each subscriber to the variable gain circuit 2 by the control signal from the control circuit 10.
Then, the variable gain circuit 2 is controlled and a desired level of signal output is obtained (for example, a level as shown in FIG. 3B is obtained).

Since the time slot for each subscriber is defined, the switching order and time length of the subscribers are known, so that the control circuit 10 switches the control signal according to the subscriber. 7 can be sent.

The no-signal detection circuit 9 which receives the voltage value of the smoothing circuit 5 controls the control voltage holding circuit 8 so that the control voltage is not updated and held when there is no signal. It is possible to continue to hold the control voltage of.

In the present embodiment, the initial setting of the control voltage holding circuit 8 is performed, for example, in a test call during system installation, and since the feedback loop configuration is adopted, the control voltage corresponding to the actual system installation condition is set. It is possible to automatically hold with high accuracy. Then, since the control voltage held in the control voltage holding circuit 8 is updated at any time, it is possible to absorb variations in the received signal level caused by environmental conditions.

Further, once the control voltage is held, the update amount of the control voltage performed for each subscriber's time slot is small, so that the signal level detection time is shortened as compared with the conventional method.

Furthermore, since the variable gain amount is also small,
The stabilization time of the variable gain circuit is also shortened. This facilitates the design of the comparison circuit and the variable gain circuit.

[0024]

As described above, the optical burst signal receiving system of the present invention controls the receiver gain by comparing and holding the reference signal level and the station receiver output level for each time slot corresponding to the subscriber. By doing so, the control voltage according to the actual system installation conditions can be automatically maintained with high accuracy, the received signal level variation caused by environmental conditions can be absorbed, and the design of the comparison circuit and variable gain circuit can be facilitated. All of the above can be achieved, and there is an effect that stable reception can be performed in the digital optical subscriber system based on the PDS method.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an optical burst signal receiving system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an optical subscriber system based on the PDS method.

FIG. 3 is a diagram showing a time position and an input / output signal level of a received signal from each subscriber.

FIG. 4 is a block diagram showing a conventional optical burst signal receiving system.

FIG. 5 is a block diagram showing another method of the conventional optical burst signal receiving method.

FIG. 6 is a diagram showing an example of a configuration of a conventional variable gain circuit.

[Explanation of symbols]

 1 Optical-electrical conversion circuit 2 Gain variable circuit 3 Reference signal level generation circuit 4 Comparison circuit 5 Smoothing circuit 6, 7 Changeover switch 8 Control voltage holding circuit 9 No signal detection circuit 10 Control circuit 11 Subscriber device 12 Optical fiber transmission line 13 Star coupler 14 Station device 15 Time slot 16 Guard time 17 Amplifier 18 Resistor

Claims (3)

[Claims] 1. A digital optical subscriber system in which one station apparatus and a plurality of subscriber apparatuses are point-to-multipoint connected by an optical fiber and a star coupler, and digital signals are transmitted and received in burst form by time division multiplexing. An optical burst signal receiving method characterized in that the reference signal level and the output level of the receiver on the station side are compared and held for each time slot corresponding to each subscriber, and the receiver gain is controlled. 2. A gain variable circuit that amplifies a signal obtained by converting a received optical signal into an electric signal by an optical-electrical conversion circuit, and a control voltage supplied to the gain variable circuit for each subscriber. A control voltage holding circuit group for holding, and a comparison means for comparing the output of the variable gain circuit with a reference voltage. The comparison result by the comparison means is stored as a control voltage in the control voltage holding circuit corresponding to each subscriber. The output of the control voltage holding circuit group is set as a control voltage to the gain variable circuit via a second changeover switch, and is set via a first changeover switch, and the first and second changeover switches are further provided. The optical burst signal receiving system according to claim 1, further comprising control means for controlling switching of the optical burst signal. 3. A no-signal detecting means for detecting a no-signal state from the output of the variable gain circuit is further provided, and at the time of no signal, the control voltage holding circuit group is controlled so that the control voltage is not updated and held. 3. The optical burst signal receiving system according to claim 2, wherein the control voltage of the above is maintained.