JP2016039589A - Station-side device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light-receiving sensitivity of OLT without erroneously detecting noise in a non-signal interval.SOLUTION: The time required for a communication between a first subscriber device and a second subscriber device is measured during a first period. During the first period, a request signal instructing the transmission of a response signal for measuring the time required for the communication is transmitted to the first subscriber device and the second subscriber device, and an offset value stored in a memory is updated so as to be decreased with the lapse of time from start to end of the first period. A threshold for discriminating whether a signal received within the first period is the response signal is calculated so as to be decreased with the lapse of time while using the offset value in the case where the signal is received. A signal received within the first period with an optical level equal to or higher than the calculated threshold is discriminated as the response signal and within the first period, the response signal is received from the first subscriber device ahead of the second subscriber device.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a station side device.

  In order to cope with the increase in speed and bandwidth of communication networks, the introduction of optical networks is being attempted. In a passive optical network (hereinafter referred to as PON) system, one station side optical transmission line termination device (hereinafter referred to as OLT) is connected via an optical splitter and an optical fiber that branch the optical fiber. And a plurality of in-home optical transmission line termination units (hereinafter referred to as ONUs) via a star type point-to-multipoint network.

  Typical PON standards include EPON (Ethernet PON (Ethernet is a registered trademark, the same shall apply hereinafter)) standardized by IEEE 802.3, and ITU-T G.264. There is GPON (Gigabit Capable PON) standardized in 984.

  The upstream signal transmitted from the ONU to the OLT in the PON and the downstream signal transmitted from the OLT to the ONU are multiplexed by wavelength division multiplexing (hereinafter referred to as WDM). The downstream signal transmits the same data from the OLT to all ONUs connected by optical fiber. The ONU that has received the data refers to the destination information included in the signal, discards the signals other than the signal addressed to itself, and transfers only the data addressed to itself to the user side.

  On the other hand, the upstream signal is multiplexed and communicated by time division multiplexing (hereinafter referred to as TDMA) in which the ONU outputs data at a specified time in accordance with transmission permission from the OLT.

  The communication speed of PON begins with a system that handles low-speed signals such as 64 kbit / s, BPON (Broadband PON) that transmits and receives fixed-length ATM cells at a maximum of about 600 Mbit / s, and variable-length packets of Ethernet at a maximum of about 1 Gbit. The introduction of EPON that transmits / receives at a rate of G / sec or GPON that handles higher-speed signals of about 2.4 Gbit / sec is underway. Furthermore, in the future, it is required to realize a high-speed PON capable of handling signals of 10 Gbit / second to 40 Gbit / second and to extend the distance of the current system at a maximum distance of 20 km or more.

  The upstream signal of the ONU is a TDMA system, and the OLT side needs to receive an optical signal transmitted from the ONU that is a burst signal. That is, the OLT needs to receive burst signals having different input levels (power and strength) at different timings.

  Since the ONUs have different distances, the input level to the OLT is different for each signal, and it is necessary for the OLT to receive a signal from the ONU. The OLT receiving unit detects a peak value for each ONU burst signal, compares the peak value with a predetermined threshold value, sets “0” when the threshold value is lower than the threshold value, and sets “1” when the threshold value is higher than the threshold value.

  The OLT receiving unit minimizes the threshold value for discriminating “0” or “1” in order to prepare for the reception of the next ONU burst signal by the reset signal from the OLT control unit every time reception of the burst signal is completed. Reset to threshold.

  However, this method has a problem in that noise is erroneously detected in a non-signal section where no burst signal is received. In particular, the ranging for measuring the delay time for transmitting a signal to the ONU is a process on the assumption that the time for receiving the uplink signal is not fixed. For this reason, the OLT cannot identify whether the signal received in the ranging window is noise or a burst signal. As a result, the OLT misdetects noise as a burst signal, or misdetects a burst signal as noise.

  Accordingly, the burst signal receiving unit in the OLT uses a constant offset with respect to the threshold value for determining “0” or “1” in order to guard the noise in the non-signal section in the ranging window.

  For example, in the PON system and the optical concentrator, a technique has been proposed in which a threshold using the first offset is used in the ranging window and a second offset lower than the first offset is used in a period in which other data is received ( For example, see Patent Document 1).

JP 2009-38753 A

  By providing an offset as in Patent Document 1, the threshold for discriminating between “0” and “1” is increased by the amount of setting the offset, and output pulse width distortion near the minimum light receiving level occurs. Therefore, the sensitivity in the post-stage CDR is reduced. For this reason, the PON burst reception characteristic becomes steep, and the effect of FEC cannot be obtained sufficiently.

  In the ranging window, a signal transmitted from an ONU that is close to the OLT reaches the OLT at a high input level, and a signal transmitted from an ONU that is far away reaches the OLT at a lower input level. In the prior art, since the first offset in the ranging window is a fixed value, the signal received by the OLT is less than or equal to the first offset, and the ONT signal that has a long distance and a low input level is correctly detected in the ranging window. It cannot be detected.

  An object of the present invention is to improve the first offset of the ranging window, thereby reducing erroneous detection of signals, and improving the light receiving sensitivity of the OLT and extending the distance.

  In order to solve the above-mentioned problems, the present invention is a station-side device, which has a processor and a memory, and is located farther from the station-side device than the first subscriber device and the first subscriber device. And a second subscriber device installed in the first communication device via an optical communication path, and a time required for communication with each of the first subscriber device and the second subscriber device is set to the first subscriber device. A request signal instructing transmission of a response signal for measuring the time required for the communication in the first period to the first subscriber unit and the second subscriber unit. Whether the offset value transmitted and updated so that the offset value stored in the memory decreases with time from the start to the end of the first period, and the signal received in the first period is the response signal When the signal is received, the threshold for determining whether or not The offset value is calculated so as to decrease with the passage of time, and a signal in which the optical level of the signal received in the first period is equal to or greater than the calculated threshold is determined as the response signal. In the first period, the response signal is received from the first subscriber device before the second subscriber device.

  According to the present invention, by updating the offset value in ranging, signal misdetection can be reduced and the light receiving sensitivity of the OLT can be improved.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a block diagram which shows the structure of the communication system to which a present Example is applied. It is a block diagram which shows the structure of OLT of a present Example. It is a block diagram which shows the structure of the optical receiver which the electric / optical conversion part in OLT of a present Example has. It is a sequence diagram which shows the process in PON of a present Example. It is a flowchart which shows the process which sets the offset of a present Example. It is explanatory drawing which shows the optical input level of the upstream message input into OLT in the grant period of a present Example, the voltage level of a reset signal, and an offset value. It is explanatory drawing which shows the optical input level of a ranging transmission, a threshold value, the voltage level of a reset signal, the voltage level of a ranging signal, and an offset value in the ranging window of a present Example. It is explanatory drawing which shows the optical input level of a ranging transmission, a threshold value, the voltage level of a reset signal, the voltage level of a ranging signal, and an offset value in the ranging window of a present Example. It is a flowchart which shows the process which sets an offset value using the noise detection part of a present Example.

  The embodiment described below relates to a passive optical network (PON) system in which a plurality of subscriber connection devices share an optical transmission line.

  The OLT in the PON system of this embodiment measures a delay time in communication with the ONU within a predetermined period. This period is hereinafter referred to as a ranging window. When this ranging window starts, the OLT does not hold information regarding the timing of receiving the burst signal and the ONU that is the transmission source of the received burst signal.

  On the other hand, when the physical distance between the OLT and the ONU is short, the burst signal transmitted from the ONU has a high optical input level to the OLT. Further, when the physical distance between the OLT and the ONU is long, the burst signal transmitted from the ONU has a low optical input level to the OLT.

  Focusing on this point, the OLT of this embodiment holds an offset value used only for the ranging window. And even if the optical input level is extremely low, the offset value is updated by the following two methods in order to receive the ONU burst signal without erroneously detecting noise. As a result, the burst signal of the ONU below the conventional offset value can be received on the OLT side, and the communicable distance can be extended.

  In the first method, the offset value is linearly decreased in the ranging from the first offset to the second offset, and the offset value becomes the second offset at the end of the ranging period. Thereby, the burst signal of the ONU at the farthest end can be received without erroneously detecting it as noise, and the communication distance can be extended.

  In the second method, the optical input level of noise is detected in the no-signal section in the grant period, and the second offset is set to the optical input level of noise. As a result, a PON burst signal near the minimum light reception can be received, and a burst signal from an extremely far ONU can also be received, so that the communication distance can be extended.

  By executing at least one of the first method and the second method, or both the first method and the second method, it becomes possible to detect the ONU at the farthest end during ranging, and to detect near the minimum light reception. A PON burst signal can be received, and the communication distance can be extended.

  FIG. 1 is a block diagram showing a configuration of a communication system 1 to which the present embodiment is applied.

  The communication system 1 includes a PON 10, an upper network 20, and a subscriber terminal. For example, the PON 10 transfers data between the upper level network 20 which is an upper level public communication network and the subscriber terminal. The host network 20 is, for example, PSTN / Internet. Subscriber terminals include, for example, telephone (TEL) 180 (180-1 to 180-l: 1 is an arbitrary positive number), PC 190 (190-1 to 190-m: m is an arbitrary positive number), etc. It is.

  The PON 10 includes an optical splitter 120, a trunk optical fiber 130, a branch optical fiber 140 (140-1 to 140-n: n is an arbitrary positive number), an OLT 100, and an ONU 110 (110-1 to 110-n). The ONU 110 accommodates subscriber terminals (telephone 180, PC 190, etc.). The OLT 100 is connected to the upper network 20.

  The OLT 100 and each ONU 110 are connected by the trunk optical fiber 130, the optical splitter 120, and the plurality of branch optical fibers 140. Then, the PON 10 relays communication between the upper network 20 and the subscriber terminals or communication between the subscriber terminals. A plurality of (n, for example, 32, etc.) ONUs 110 can be connected to the OLT 100 via a single trunk optical fiber 130, an optical splitter 120, and a branch optical fiber 140.

  FIG. 1 shows five (n = 5) ONUs 110 as an example. Each of the five ONUs 110 has a different fiber length from the OLT 100. In the illustrated example, the ONU 110-1 has a fiber length from the OLT 100 of 1 km, the ONU 110-2 has a fiber length from the OLT 100 of 10 km, the ONU 110-3 has a fiber length from the OLT 100 of 20 km, and the ONU 110- 4, the fiber length from the OLT 100 is 20 km or more, and the ONU 110-n has a fiber length from the OLT 100 of 15 km.

  The OLT 100 transmits a downstream signal 150, which is a broadcast signal, to all of the ONUs 110. The upstream signal 170 (170-1 to 170-n) is transmitted from the ONU 110 to the OLT 100. The upstream signal 160 includes an upstream signal 170 multiplexed by time in the optical splitter 120. The OLT 100 receives the upstream signal 160. The uplink signal included in the uplink signal 160 and transmitted from each of the ONUs 110 is a burst signal.

  FIG. 2 is a block diagram illustrating the configuration of the OLT 100 according to the present embodiment.

  The OLT 100 includes an electrical transmission / reception unit 200, a reception buffer unit 270, a medium access control unit 220, a noise detection unit 280, an electrical / optical conversion unit 210, and a control unit 230. The electric-side transmitting / receiving unit 200 communicates with the relay device included in the higher-level network 20 using electric signals.

  The electrical / optical converter 210 communicates with the ONU 110 using optical signals. The medium access control unit 220 controls data communication of the ONU 110. The reception buffer unit 270 temporarily stores the received upstream signal 160. The noise detector 280 detects the optical input level of noise in the no-signal section used for the offset value.

  The control unit 230 controls functional blocks in the OLT 100. The control unit 230 includes a grant processing unit 240, a reset control unit 250, and a ranging processing unit 260.

  The grant processing unit 240 determines the transmission permission time of the upstream signal 170 transmitted by each ONU 110. The reset control unit 250 resets the peak held by the electrical / optical conversion unit 210 between the burst signal transmitted from each ONU 110 to 0 (or a value close to 0 as much as possible). Is sent to the electrical / optical converter 210. The ranging processing unit 260 controls the ranging window by continuously transmitting a signal to the electrical / optical conversion unit 210.

  When the electrical / optical conversion unit 210 receives the upstream signal 160, the medium access control unit 220 transmits the transmission source MAC address of the upstream signal 160 and the ONU 110 information of the transmission source given to the preamble part (for example, LLID: Logical). Link ID, etc.) are stored in association with each other as route information, and the upstream signal 160 is transmitted from the electrical transmission / reception unit 200 to the OLT 200.

  When the electrical transmission / reception unit 200 receives a downlink signal, the medium access control unit 220 refers to the destination MAC address of the downlink signal and gives the destination ONU identification information to the preamble part of the downlink signal from the route information held in advance. Then, the data is transmitted from the electrical / optical converter 210. The medium access control unit 220 has such a switching function.

  The sending of the reset signal 290 will be described below. The grant processing unit 240 extracts notification information (queue information) indicating transmission data accumulation status in the ONU 110 from the medium access control unit 220.

  This queue information is transmitted from the ONU 110 to the OLT 100 as one piece of information included in the control signal. The control signal in this embodiment is a ranging transmission in the ranging window and an upstream message in the grant period (described later in FIG. 4). The grant processing unit 240 determines the transmission timing of the reset signal 290 during the ranging window based on the queue information included in the ranging transmission.

  Further, the grant processing unit 240 calculates an uplink time slot to be allocated to the ONU 110 in the grant period based on the bandwidth control information designated in advance by the administrator and the extracted queue information. The grant processing unit 240 holds the upstream bandwidth as bandwidth control information, and periodically updates the content of this bandwidth control information.

  Further, the reset control unit 250 determines the break (at the end) of the burst signal transmitted from each subscriber apparatus based on the uplink time slot calculated by the grant processing unit 240, and the peak hold circuit 320 (FIG. 3). Reset signal 290.

  As a result, the peak hold circuit 320 resets the threshold value. Specifically, the reset is to update the threshold value to 0, or to update the threshold value to a value as close to 0 as possible.

  FIG. 3 is a block diagram illustrating the configuration of the optical receiver 211 included in the electrical / optical converter 210 in the OLT 100 according to the present embodiment.

  The electrical / optical converter 210 includes an optical receiver 211 for receiving an optical signal transmitted from the ONU 110 and an optical transmitter for transmitting an optical signal to the ONU 110. FIG. 3 shows only the optical receiver 211.

  The optical receiving unit 211 includes a photodetector (hereinafter referred to as PD) 300, a transimpedance amplifier (hereinafter referred to as TIA) 310, a peak hold circuit 320, a threshold setting unit 330, a minimum threshold setting unit 340, and a comparator 350. Is provided.

  The PD 300 of the optical receiver 211 receives the optical signal from the ONU 110 sent from the trunk optical fiber 130. The PD 300 converts an optical signal into an electric signal (current).

  The TIA 310 converts an electric signal (current) into a voltage. The TIA 310 outputs an electric signal (voltage) to the comparator 350 and the peak hold circuit 320.

  The peak hold circuit 320 holds the peak value of the signal from the TIA 310 until the reset signal 290 is received from the reset control unit 250 of the OLT 100. The threshold setting unit 330 calculates a threshold based on the minimum threshold acquired from the minimum threshold setting unit 340 and the peak value transmitted from the peak hold circuit 320.

  The minimum threshold setting unit 340 sets a minimum threshold in the threshold setting unit 330. The minimum threshold value setting unit 340 of the present embodiment has a memory and holds an offset value in the memory. In addition, the minimum threshold setting unit 340 receives, as a minimum threshold, the threshold value setting unit 330 using an offset value that is valid only during ranging while receiving the ranging signal 370 from the ranging processing unit 260 of the OLT 100. Send.

  The minimum threshold value setting unit 340 according to the present embodiment may receive the noise peak value in the no-signal section in the grant period from the noise detection unit 280 and set the minimum threshold value based on this value.

  The comparator 350 compares the optical level of the signal transmitted from the TIA 310 with the threshold transmitted from the threshold setting unit 330, and determines that a burst signal has been received from the ONU 110 if the optical level is equal to or greater than the threshold. In this embodiment, when it is determined that an uplink signal has been received, the comparator 350 transmits “1” to the medium access control unit 220 via the noise detection unit 280.

  Further, when the light level is smaller than the threshold value, the comparator 350 determines that the burst signal is not received, and sends “0” to the medium access control unit 220.

  FIG. 4 is a sequence diagram showing processing in the PON 10 of this embodiment.

  FIG. 4 shows a relationship between a ranging and ranging window 420 in which DBA (Dynamic Bandwidth Allocation) is performed, and a grant operation and a grant period 421 based on the result of each DBA.

  The ranging window 420 is a ranging period during which ranging by DBA is executed, and the grant period 421 is a period for receiving the upstream signal 160 including user data. The length of the ranging window 420 may be determined in advance based on the number of ONUs 110, the maximum fiber length from the OLT 100 to the ONU 110, and the like.

  The OLT 100 executes DBA in the ranging window 420 in order to allocate the transmission band of the upstream message 410 to the ONU 110. When the ranging window 420 starts, the OLT 100 first transmits a ranging request 411 as a broadcast signal 150 to all ONUs 110.

  When receiving the ranging request 411, the ONU 110 transmits the ranging transmission 412 to the OLT 100. The OLT 100 calculates a delay time for communicating with the ONU 110 based on the transmission time of the ranging request 411, the reception time of the ranging transmission 412, and the waiting time until the ranging transmission 412 specified by the ranging request 411 is transmitted. To do.

  Thereby, the OLT 100 can calculate the distance from the OLT 100 to the ONU 110 based on the calculated delay time and the characteristics of the trunk optical fiber 130 and the branch optical fiber 140. Further, by calculating the delay time, the OLT 100 can appropriately allocate a time for transmitting the upstream message 410 to the ONU 110 in the subsequent grant processing.

  The period from when the ranging request 411 is transmitted until the first ranging transmission 412 is received is described as a no-signal section 430 in the ranging window 420 in this embodiment. When receiving the first ranging transmission 412, the OLT 100 does not maintain a delay time for communicating with each ONU 110. For this reason, it is difficult to identify whether the received signal is the signal of the ranging transmission 412 or the noise in the no-signal section 430 in the ranging window 420.

  After the ranging window 420 ends, the OLT 100 transmits a transmission permission message 400 including a grant instruction to each ONU 110-1 to 110-3, for example, every grant period 421 having a period of 125 μsec. This transmission permission message 400 includes a transmission permission time ST and a transmission available time L. The transmission permission message 400 also includes information (Request report) for requesting a report of the amount of data waiting for transmission accumulated in the transmission queue of each ONU 110.

  Each ONU 110-1 to 3 transmits data accumulated in the transmission queue in the time slot designated by the grant instruction Start and End, and uses the queue length included in the upstream message 410 to determine the amount of data waiting for transmission. Report to OLT100.

  Further, the OLT 100 calculates in advance a section in which a no-signal section 430 for transmitting a grant instruction to the ONU 110 is generated based on a delay time calculated in the ranging window 420. For this reason, the noise detection unit 280 of the OLT 100 may detect the noise peak value in the no-signal section 430 and transmit it to the medium access control unit 220.

  FIG. 5 is a flowchart showing processing for setting an offset value according to the present embodiment.

  When the ranging window 420 starts after the OLT 100 is activated, the minimum threshold setting unit 340 first sets the first offset in the threshold setting unit 330 as an initial value of the minimum threshold (500). After step 500, the ranging processing unit 260 of the OLT 100 starts the ranging window 420 and sends a broadcast signal 150 (ranging request 411 shown in FIG. 4) to all ONUs 110 (510).

  When the ranging request 411 is received, the ONU 110 waits for the waiting time specified by the ranging request 411 and then sends a response signal (ranging transmission 412 shown in FIG. 4) to the OLT 100 (520).

  The OLT 100 ends the ranging window 420 (530). Specifically, the ranging processing unit 260 stops transmission of the ranging signal 370 based on the period of the ranging window 420 that is held in advance. Accordingly, the minimum threshold setting unit 340 determines that the ranging window 420 has ended, and sets the second offset lower than the first offset in the threshold setting unit 330 as the minimum threshold (540).

  After step 530, the OLT 100 starts a grant process for receiving data transmitted from a subscriber terminal connected to each ONU 110. Specifically, the electrical / optical converter 210 transmits a transmission permission message 400 to the ONU 110, and each ONU 110 transmits a burst signal (upstream message 410) to the OLT 100 according to the grant period 421 (550).

  After step 550, the electrical / optical converter 210 of the OLT 100 performs data processing on the received burst signal (uplink message 410) and ends the grant processing (560). After step 560, the minimum threshold value setting unit 340 sets the first offset as the minimum threshold value in the threshold value setting unit 330, and starts the ranging window 420 (570). Thereafter, step 520 to step 570 are repeated.

  FIG. 6 is an explanatory diagram illustrating the optical input level of the upstream message 410, the voltage level of the reset signal 290, and the offset value 640 input to the OLT 100 in the grant period 421 of the present embodiment.

  FIG. 6A to FIG. 6C show the level of each signal in the grant period 421, and the horizontal axis is time. FIG. 6A is an explanatory diagram showing an optical input level 600 and a threshold value 620 that are input to the OLT 100 during the grant period 421 of this embodiment.

  FIG. 6B shows the voltage level of the reset signal 290 during the grant period 421 of this embodiment. FIG. 6C shows the offset value 640 of the present embodiment.

  When the optical signal that is the upstream message 410 is received from the ONU 110, the threshold setting unit 330 of the optical receiving unit 211 calculates the threshold 620 using the peak value and the minimum threshold of the optical input level 600. For example, the threshold setting unit 330 calculates the addition result of the half value of the peak value (received from the peak hold circuit 320) of the optical input level 600 and the minimum threshold as the threshold 620.

  In addition, since a predetermined time for reflecting the setting of the threshold value 620 is required to change the threshold value 620, the minimum threshold value setting unit 340 receives the upstream message 410 for the first time, The threshold 620 is changed while receiving the preamble.

  Then, the comparator 350 compares “0” or “1” of the upstream message 410 from the ONU 110 by comparing the threshold 620 set by the threshold setting unit 330 with the optical input level of the signal transmitted from the TIA 310. judge.

  A reset signal 290 is transmitted to the peak hold circuit 320 via the reset control unit 250. When the peak hold circuit 320 receives the reset signal 290, the peak hold circuit 320 sets the held peak value to zero. As a result, the threshold setting unit 330 sets the threshold 920 to the minimum threshold 630.

  The offset value 640 is a value held by the minimum threshold setting unit 340. In the grant cycle 421, the minimum threshold setting unit 340 sets the offset value 640 as the minimum threshold in the threshold setting unit 330.

  The offset value 640 of the threshold value 620 in the grant period 421 is the same value throughout the period. That is, the minimum threshold value 630 and the offset value 640 in the grant period 421 are the same value.

  FIG. 7 shows an example of the optical input level 600 of the ranging transmission 412, the threshold 620, the voltage level of the reset signal 290, the voltage level of the ranging signal 370, and the offset value 640 in the ranging window 420 of this embodiment. It is explanatory drawing shown.

  7A to 7D show the level of each signal in the ranging window 420, and the horizontal axis is time. FIG. 7A is an explanatory diagram showing an optical input level 600 and a threshold 620 input to the OLT 100 in the ranging window 420 of the present embodiment.

  FIG. 7B shows the voltage level of the reset signal 290 in the ranging window 420 of this embodiment. FIG. 7C shows the voltage level of the ranging signal 370 in the ranging window 420 of this embodiment. FIG. 7D shows an offset value 640 in the ranging window 420 of this embodiment.

  As shown in FIG. 7, in the ranging window 420, the ranging transmission 412 transmitted from the ONU 110-1 having a short distance is transmitted to the OLT 100 by a higher optical input level 600 than the ranging transmission 412 transmitted from the ONU 110-4 having a long distance. To reach.

  Further, it is highly likely that the ranging transmission 412 transmitted from the ONUs 110-2 to 4-4 having a long distance will reach the OLT 100 after the ranging transmission 412 transmitted from the ONU 110-1 having a short distance.

  Since the ranging transmission 412 is received in ascending order of the distance between the OLT 100 and the ONU 110, the medium access control unit 220 of the OLT 100 according to the present embodiment waits until the ranging transmission 412 indicated by the ranging request 411 is transmitted. May be adjusted. For example, when the medium access control unit 220 holds the rough positional relationship of the ONUs 110 and holds information that the distances to the ONUs 110 are clearly different among the ONUs 110, the medium access control unit 220 adjusts the waiting times of all the ONUs 110 to the same value. Also good.

  Further, when holding information indicating a plurality of ONUs 110 (hereinafter referred to as ONU group A) determined that the distance from the OLT 100 to the ONU 110 is relatively close, the medium access control unit 220 determines the waiting time of the ONUs 110 in the ONU group A. , Each may be adjusted to a different time. Then, the waiting time of the ONU 110 closer to the ONU group A is adjusted to the same value as the lowest waiting time assigned to the ONU group A, and the waiting time of the ONU 110 farther than the ONU group A is assigned to the ONU group A It may be adjusted to the same value as the maximum value of the waiting time.

  When the minimum threshold setting unit 340 receives the ranging signal 370 from the ranging processing unit 260, the minimum threshold setting unit 340 sets the first offset 700 that is held in advance in the threshold setting unit 330. For this reason, the threshold value 620 is set to the first offset. The first offset 700 is a value larger than the second offset 710, and the second offset 710 is the same value as the offset value 640 in the grant period 421.

  When the ranging transmission 412 is received, the threshold setting unit 330 calculates the threshold 620 using the peak value of the optical input level 600 of the ranging transmission 412 and the first offset 700 set as the minimum threshold. Then, the calculated threshold value 620 is transmitted to the comparator 350. The threshold setting unit 330 calculates, for example, a result obtained by adding ½ of the peak value of the optical input level 600 of the ranging transmission 412 and the first offset 700 as the threshold 620.

  The comparator 350 compares the threshold 620 transmitted from the threshold setting unit 330 with the optical input level 600 of the received signal. If the optical input level 600 of the received signal is equal to or higher than the threshold 620, the received signal is a burst signal. And “1” is transmitted to the noise detection unit 280. If the optical input level 600 of the received signal is lower than the threshold 620, the comparator 350 determines that the received signal is noise and transmits “0” to the noise detection unit 280.

  Accordingly, the optical receiving unit 211 can accurately distinguish between noise in the no-signal section 430 in the ranging window 420 (for example, white noise) and a burst signal of the ranging transmission 412. And since it can distinguish correctly, the optical receiving part 211 can make the inclination of a PON burst receiving characteristic gentle, and can improve the FEC effect.

  When the peak hold circuit 320 receives the reset signal 290 from the reset control unit 250, the peak hold circuit 320 resets the peak value to be transmitted to the threshold setting unit 330 to 0 or a value close to zero. The threshold value setting unit 330 transmits the first offset 700 to the comparator 350 as the threshold value 620 because the peak value has been reset.

  By doing so, the threshold setting unit 330 differs between the threshold 620 for distinguishing the ranging transmission 412 of the ONU 110-1 from the noise and the threshold 620 for distinguishing the ranging transmission 412 of the ONU 110-3 from the noise. Can be set to a value. Then, the comparator 350 can distinguish the ranging transmission 412 of the ONU 110-3 from noise.

  However, in the above method, the comparator 350 cannot detect a signal of the ONU 110 (for example, the ONU 110-4 shown in FIG. 7) smaller than the first offset 700.

  FIG. 8 shows other values of the optical input level 600 of the ranging transmission 412, the threshold 620, the voltage level of the reset signal 290, the voltage level of the ranging signal 370, and the offset value 640 in the ranging window 420 of this embodiment. It is explanatory drawing which shows an example.

  8A to 8D show the level of each signal in the ranging window 420, and the horizontal axis is time. FIG. 8A is an explanatory diagram showing an optical input level 600 and a threshold value 620 that are input to the OLT 100 in the ranging window 420 of this embodiment.

  FIG. 8B shows the voltage level of the reset signal 290 in the ranging window 420 of this embodiment. FIG. 8C shows the voltage level of the ranging signal 370 in the ranging window 420 of this embodiment. FIG. 8D shows the offset value 640 of the present embodiment.

  The optical input level 600 of the ranging transmission 412 in FIG. 8A is the same as the optical input level 600 of the ranging transmission 412 in FIG. Further, the ranging signal 370 in FIG. 8C and the ranging signal 370 in FIG. 7C are the same.

  The threshold value 620 shown in FIG. 8A is different from the threshold value 620 shown in FIG. Also, the reset signal 290 shown in FIG. 8B and the reset signal 290 shown in FIG. 7B are reset signals at the end of reception of the ranging transmission 412 transmitted from the ONU 110-4 in FIG. 8B. The difference is that 290 is output.

  Further, the offset value 640 shown in FIG. 8D is different from the offset value 640 shown in FIG. Below, the difference of the offset value 640 of FIG. 8 and FIG. 7 is demonstrated.

  According to FIG. 8D, the minimum threshold setting unit 340 linearly decreases the offset value 640 in the ranging window 420 from the first offset 700 to the second offset 710. Specifically, the offset value 640 at the start of the ranging window 420 is set to the first offset 700, the offset value 640 is decreased by a predetermined value given every predetermined time, and the ranging value is further reduced. The offset value 640 at the end of the window 420 is set to the second offset 710.

  The minimum threshold value setting unit 340 updates the offset value 640 to a lower value as time elapses from step 510 to step 530 shown in FIG. As a result, the threshold value 620 can be reduced according to the distance between the OLT 100 and the ONU 110, so that false detection can be reduced.

  Here, as a method of linearly decreasing the offset value 640, for example, there is a method of decreasing the offset value 640 from the first offset 700 to the second offset 710 using optical fiber loss. In IEEE 802.3, the optical fiber loss is defined as 0.4 dB / km @ 1310 nm.

  As described above, the greater the distance between the OLT 100 and the ONU 110, the smaller the optical input level 600 at which the OLT 100 receives an optical signal transmitted from the ONU 110. For example, the delay time of a general optical fiber is 5 ns / m as a value. From this, the delay time per 1 km (one way 2 km) is 10 μs.

  For this reason, the minimum threshold setting unit 340 maintains the slope 910 of the loss amount per hour for the optical fiber loss, so that the minimum threshold setting unit 340 has an appropriate offset according to the distance from the OLT 100 to the ONU 110. The value 640 is calculated, and the offset value 640 is attenuated with a slope of 0.4 dB / 10 μs = 0.04 dB / μs. In FIG. 8D, the slope 910 of the offset value 640 is 0.04 dB / μs.

  Note that the minimum threshold setting unit 340 may smoothly decrease the first offset 700 to the second offset 710, but decrease the plurality of values from the first offset 700 to the second offset 710 in a stepwise manner. Also good. For example, the minimum threshold setting unit 340 may decrease the offset value 640 step by step for each time necessary for the comparator 350 and the threshold setting unit 330 to update the threshold 620.

  In addition, when the distance from the OLT 100 to the furthest ONU 110 is 40 km, the minimum threshold setting unit 340 sets the first offset 700 as an offset value until 200 μs (that is, up to a distance of 20 km) after the ranging window 420 starts. The offset value 640 after 200 μs may be set to a value obtained by lowering the first offset 700 by 8 dB. This 200 μs is because the transmission path delay of 20 km is 200 μs, and is the time until the ranging transmission 412 is received from the ONU 110 that is 20 km away.

  As described above, when the minimum threshold setting unit 340 changes the offset value 640, the threshold setting unit 330 sets the minimum threshold while the ranging transmission 412 is not being received to a low value as time passes. Therefore, even when the comparator 350 receives the ranging transmission 412 transmitted from the ONU 110 (for example, the ONU 110-4) installed far from the OLT 100 and having the optical input level 600 lower than the first offset 700, The received signal is not erroneously detected as noise. As a result, the ranging transmission 412 can be correctly received.

  As described above, by setting the offset value 640 according to the distance from the OLT 100 to the ONU 110, the PON burst signal transmitted by the farthest end ONU 110 and near the minimum light input level that can be received. Can be accurately received by the optical receiver 211 of this embodiment. As a result, the distance between the OLT 100 and the ONU 110 can be extended regardless of the value of the first offset 700.

  Further, in the following, the noise detection unit 280 detects a noise (for example, white noise) in the no-signal section 430 of the grant period 421, and obtains a peak value of the noise so that a minimum signal equal to or higher than the noise can be received. Processing for setting the offset value 640 to 620 will be described.

  FIG. 9 is a flowchart illustrating processing for setting the offset value 640 using the noise detection unit 280 of the present embodiment.

  Step 1000, step 1010 and step 1020 are the same as step 500, step 510 and step 520 shown in FIG. On the other hand, the optical receiver 211 of the OLT 100 shown in FIG. 9 decreases the offset value 640 from the first offset 700 to the second offset 710 in the ranging window 420 after step 1010 (1015). In step 1015, the minimum threshold setting unit 340 may decrease the offset value 640 at a predetermined time interval.

  After step 1020 and step 1015, when the ranging window 420 ends and the OLT 100 ends the ranging process, the OLT 100 starts a grant process for receiving subscriber terminal data from each ONU 110 (1030). Specifically, the OLT 100 transmits a transmission permission message 400 to the ONU 110.

  The OLT 100 holds the arrival timing of the burst signal transmitted from the ONU 110 in the grant period 421 based on the delay time of each ONU 110 acquired in ranging and the uplink time slot information managed by the grant processing unit 240. . That is, the noise detection unit 280 holds information indicating the timing of the no-signal section 430 in the grant period 421.

  For this reason, the noise detection unit 280 detects the peak value of the received noise during the no-signal section 430 in the grant period 421 (1040).

  After step 1040, the noise detection unit 280 sets the detected peak value in the minimum threshold setting unit 340 as the second offset 710 (1050). After the setting in step 1050, the optical receiver 211 of the OLT 100 receives the burst signal (upstream message 410) transmitted by each ONU 110. Then, the processing unit of the OLT 100 such as the medium access control unit 220 grants the received upstream message 410 (1060).

  When the grant process in Step 1060 is completed, the ranging processing unit 260 and the electrical / optical conversion unit 210 start the ranging process using the threshold 620 set in Step 1050 (1070). After step 1070, the processing from step 1020 is repeated.

  After setting the noise peak value as the second offset 710 in the minimum threshold setting unit 340, the comparator 350 can accurately distinguish between the noise and the ranging transmission 412. Then, the comparator 350 detects a signal equal to or higher than the noise peak value as a burst signal.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. For example, the noise detection unit 280 of the present embodiment may not notify the minimum threshold setting unit 340 of the noise peak value, and the minimum threshold setting unit 340 may use the second offset 710 determined in advance.

  Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In addition, each of the above-described configurations, functions, processing units, processing procedures, and the like may be realized in hardware by designing some or all of them, for example, with an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as a program, a table, or a file that realizes each function can be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  Further, the control lines or information lines indicate what is considered necessary for the explanation, and not all the control lines or information lines on the product are necessarily shown. In practice, almost all the components are connected to each other.

10 PON
100 OLT
110 ONU
120 Splitter 130, 140 Optical fiber 150 Downstream signal 160, 170 Upstream signal 180, 190 Terminal 200 Electrical side transceiver 210 Electrical / optical converter 220 Medium access controller 230 Controller 280 Noise detector 300 Photodetector (PD)
310 Transimpedance Amplifier (TIA)
320 Peak hold circuit 330 Threshold setting unit 340 Minimum threshold setting unit 350 Comparator

Claims (4)

A station side device,
A processor and a memory;
Communicating with a first subscriber device and a second subscriber device installed at a position farther from the station side device than the first subscriber device via an optical communication path,
Measuring a time required for communication with each of the first subscriber unit and the second subscriber unit in a first period;
Transmitting a request signal instructing transmission of a response signal for measuring the time required for the communication to the first subscriber unit and the second subscriber unit in the first period;
Update from the start to the end of the first period so that the offset value stored in the memory decreases as time passes,
A threshold for determining whether or not a signal received in the first period is the response signal is calculated so as to decrease with the passage of time using the offset value when the signal is received. And
A signal having an optical level of a signal received during the first period equal to or greater than the calculated threshold is determined to be the response signal;
In the first period, the response signal is received from the first subscriber device prior to the second subscriber device. The station side device according to claim 1,
When starting the first period, the highest offset value that is the highest value of the offset value is stored in the memory as the offset value,
After the start of the first period, the offset value acquired from the memory, and an offset stored in the memory by a result of subtracting a predetermined value less than the maximum offset value from the acquired offset value The station-side apparatus, wherein the value is updated every predetermined period shorter than the first period. The station side device according to claim 2,
When the optical signal passes through the optical communication path, the loss per unit time of the optical level of the optical signal is held in the memory,
The station-side apparatus, wherein the predetermined period and the predetermined value are determined so that the offset value decreases according to the loss per unit time from the start to the end of the first period. The station side device according to claim 1,
Connected to a subscriber terminal via at least one of the first subscriber unit and the second subscriber unit;
In a period in which data transmitted from the subscriber terminal is not received from the start to the end of the second period, an optical level of a signal to be received is acquired as an optical level of noise;
From the start to the end of the first period after the end of the second period, the offset value is updated so that the offset value decreases until the offset value stored in the memory is less than or equal to the light level of the acquired noise. A station side device characterized by:

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