JP6381392B2 - PON system, OLT, ONU, and transmission method - Google Patents

Description

  The present invention relates to a PON (Passive Optical Network) system, an OLT (Optical Line Terminal), an ONU (Optical Network Unit), and a transmission method.

  In recent years, the area (cell) covered by a base station apparatus has become narrower as the speed of a radio access network provided by a mobile communication network has decreased, and as a result, the number of base station apparatuses to be installed to configure the mobile communication network Has increased. For this reason, a passive optical network (PON) system in which a single optical transmission line is shared by a plurality of subscribers has been studied as a network for accommodating a plurality of base station apparatuses.

  In the PON system, one optical transmission line terminal (OLT: Optical Line Terminal) installed at a telecommunications carrier's station connects to multiple subscriber-side terminals (ONU: Optical Network Unit) via an optical splitter. Has been. The OLT realizes high band utilization efficiency by dynamically allocating an upstream band to a plurality of ONUs, for example, 64 ONUs, by a time division multiplexing method.

  When accommodating a plurality of base station devices in the PON system, frequency and time synchronization between the base station devices is essential. Conventionally, it has been common to install a GPS antenna in each base station apparatus in order to receive reference time information. However, there are cases where the GPS antenna cannot be installed due to restrictions such as the installation environment in the base station apparatus. For this reason, for example, Non-Patent Documents 1 and 2 disclose techniques for distributing frequency and time information from an upper network device to a lower network device and synchronizing the frequency and time of the entire network. Non-Patent Document 3 and Patent Document 1 disclose a technology in which a GPS antenna is installed in an OLT, and frequency and time information received by the GPS antenna is distributed to each ONU via an optical access distribution network. .

JP 2011-040870 A

IEEE Std 1588-2008, IEEE Standard for a Precision Clock Synchronization Protocol for Network Measurement and Control Systems, 2008. K. Hann, “Synchtonous Ethernet (registered trademark) to Transport Frequency and Phase / Time,” IEEE Communication Magazine, vol.50, no.8, pp.152-160, August 2012. Takayoshi Tashiro et al., “10G-EPON system with frequency / time synchronization function for mobile backhaul applications,” IEICE Tech. (B), vol.J96-B, no.3, pp.321-329, March 2013.

  However, in the techniques described in Non-Patent Documents 1 and 2, all the upper and lower network devices must be replaced with devices dedicated to frequency and time synchronization. For example, in order to provide frequency and time information to each ONU from the OLT via the IP network by IEEE 1588, all devices on the IP network side must support IEEE 1588. For this reason, if there is at least one device on the IP network side that does not support IEEE 1588, a clock signal cannot be provided to each ONU.

  In the technology described in Non-Patent Document 3 and Patent Document 1, as shown in FIG. 9, a coaxial cable for transmitting a GPS signal to a station where an OLT is installed, or a GPS signal is received. However, it is difficult to apply when the equipment installation space of the station building is restricted.

  The present invention has been made in view of such circumstances, and a loopback method in which a GPS signal is received on the ONU side, frequency and time information is provided to the OLT, and the OLT distributes it to each ONU. An object of the present invention is to provide a PON system, an OLT, an ONU, and a transmission method that can be realized and improve the accuracy of frequency synchronization and time synchronization.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the PON system of the present invention is a PON (Passive Optical Network) system that realizes optical fiber transmission, and includes an OLT (Optical Line Terminal) and a plurality of ONUs connected to the OLT via an optical branching unit ( Optical Network Unit) and a GPS signal receiving device that is provided in any one ONU and receives a GPS (Global Positioning System) signal. The OLT is received by a master ONU that includes the GPS signal receiving device. Based on the GPS signal, the oscillation frequency of the local oscillator is corrected, and the corrected transmission frequency is used to establish a logical link with an ONU other than the master ONU.

  Thus, based on the GPS signal received by the master ONU equipped with the GPS signal receiver, the oscillation frequency of the local oscillator is corrected, and the logical link with the ONU other than the master ONU is established using the corrected transmission frequency. Therefore, it is possible to improve the accuracy of frequency synchronization and time synchronization in the loopback control via the OLT.

  (2) Further, in the PON system of the present invention, the OLT is indicated by a response time corresponding to a time stamp transmitted from the own apparatus to the master ONU and a time stamp based on a GPS signal received from the master ONU. The oscillation frequency of the local oscillator is corrected based on the difference from the time.

  Thus, based on the difference between the response time that should correspond to the time stamp transmitted from the own device to the master ONU and the time indicated in the time stamp based on the GPS signal received from the master ONU, the local oscillator Since the transmission frequency is corrected, the local oscillator can be controlled by grasping the difference on the OLT side.

  (3) In the PON system of the present invention, the master ONU transmits information indicating a difference between the time indicated in the time stamp received from the OLT and the time obtained from the GPS signal to the OLT. The OLT corrects the oscillation frequency of the local oscillator based on the difference indicated in the information received from the master ONU.

  In this way, the master ONU transmits information indicating the difference between the time indicated in the time stamp received from the OLT and the time obtained from the GPS signal to the OLT, so the master ONU side grasps the difference. The OLT can correct the oscillation frequency of the local oscillator.

  (4) In the PON system of the present invention, when the difference is larger than a predetermined threshold, the OLT transmits a time stamp to the master ONU again using the corrected transmission frequency. It is characterized by that.

  As described above, when the difference is larger than the predetermined threshold value, the time stamp is transmitted again to the master ONU using the corrected transmission frequency, so the difference is used until the difference becomes smaller than the threshold value. It is possible to control the local oscillator.

  (5) The OLT of the present invention is an OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and receives a GPS (Global Positioning System) signal. The master ONU including the receiving device corrects the oscillation frequency of the local oscillator based on the GPS signal received, and establishes a logical link with an ONU other than the master ONU using the corrected transmission frequency. To do.

  Thus, based on the GPS signal received by the master ONU equipped with the GPS signal receiver, the oscillation frequency of the local oscillator is corrected, and the logical link with the ONU other than the master ONU is established using the corrected transmission frequency. Therefore, it is possible to improve the accuracy of frequency synchronization and time synchronization in the loopback control via the OLT.

  (6) Further, the OLT of the present invention includes a response time that should correspond to a time stamp transmitted from the own device to the master ONU and a time indicated in the time stamp based on the GPS signal received from the master ONU. The transmission frequency of the local oscillator is corrected based on the difference.

  Thus, based on the difference between the response time that should correspond to the time stamp transmitted from the own device to the master ONU and the time indicated in the time stamp based on the GPS signal received from the master ONU, the local oscillator Since the transmission frequency is corrected, the local oscillator can be controlled by grasping the difference on the OLT side.

  (7) Further, the OLT of the present invention is characterized in that the oscillation frequency of the local oscillator is corrected based on the difference indicated in the information received from the master ONU.

  In this way, since the difference can be grasped on the master ONU side, it becomes possible to correct the oscillation frequency of the local oscillator by the OLT.

  (8) Further, the OLT according to the present invention is characterized in that when the difference is larger than a predetermined threshold, the time stamp is transmitted again to the master ONU using the corrected transmission frequency. .

  As described above, when the difference is larger than the predetermined threshold value, the time stamp is transmitted again to the master ONU using the corrected transmission frequency, so the difference is used until the difference becomes smaller than the threshold value. It is possible to control the local oscillator.

  (9) The ONU of the present invention is an ONU (Optical Network Unit) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission, and receives a GPS (Global Positioning System) signal. A receiving device is provided, and a time stamp based on a GPS signal is transmitted to an OLT (Optical Line Terminal), or a difference between a time indicated by the time stamp received from the OLT and a time obtained from the GPS signal is indicated. Information is transmitted to the OLT.

  As described above, the time stamp based on the GPS signal is transmitted to the OLT, or information indicating the difference between the time indicated by the time stamp received from the OLT and the time obtained from the GPS signal is transmitted to the OLT. It is possible to correct the oscillation frequency of the OLT local oscillator.

  (10) The transmission method of the present invention is a transmission method of a PON (Passive Optical Network) system that realizes optical fiber transmission, and receives a GPS (Global Positioning System) signal in an OLT (Optical Line Terminal). Correcting the oscillation frequency of the local oscillator based on the GPS signal received by the master ONU including the GPS signal receiving device, and establishing a logical link with the ONU other than the master ONU using the corrected transmission frequency. Features.

  Thus, based on the GPS signal received by the master ONU equipped with the GPS signal receiver, the oscillation frequency of the local oscillator is corrected, and the logical link with the ONU other than the master ONU is established using the corrected transmission frequency. Therefore, it is possible to improve the accuracy of frequency synchronization and time synchronization in the loopback control via the OLT.

  According to the present invention, it is possible to improve the accuracy of frequency synchronization and time synchronization in loopback control via OLT.

It is a figure showing a schematic structure of a PON system concerning an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of a master ONU according to Embodiment 1. FIG. It is a block diagram which shows schematic structure of OLT. It is a block diagram which shows schematic structure of a slave ONU. It is a figure which shows the example of a synchronous sequence of OLT and master ONU. It is a block diagram which shows schematic structure of the master ONU which concerns on Example 2. FIG. It is a figure which shows the example of a synchronous sequence of OLT and master ONU in Example 2. FIG. It is a flowchart which shows the outline | summary of operation | movement of the PON system which concerns on this embodiment. It is a figure which shows the outline | summary of the conventional PON system.

  The inventors pay attention to providing a GPS signal receiving device in any one of the plurality of ONUs, and transferring the frequency information and time information based on the GPS signals in a loopback manner via the OLT. By correcting the local oscillator of the OLT based on the GPS signal, it has been found that frequency and time synchronization between base station apparatuses can be easily realized, and the present invention has been achieved.

  That is, the PON system of the present invention is a PON system that realizes optical fiber transmission, and is provided in any one ONU, a plurality of ONUs connected to the OLT via an optical branching unit, A GPS signal receiving device that receives the GPS signal, and the OLT corrects the oscillation frequency of the local oscillator based on the GPS signal received by the master ONU including the GPS signal receiving device, and the corrected transmission frequency Is used to establish a logical link with ONUs other than the master ONU.

  With this configuration, the present inventors have made it possible to improve the accuracy of frequency synchronization and time synchronization in loopback control via OLT. Embodiments of the present invention will be specifically described below with reference to the drawings.

  In this embodiment, a GPS signal receiving device having a GPS antenna is installed in any one of a maximum of about 64 ONUs, and the ONU is set as a master ONU, and another ONU is transmitted from the master ONU via the OLT. And the structure which loops back a GPS signal to a base station is taken. As a result, it is possible to achieve frequency and time synchronization between base stations without requiring replacement of network equipment higher or lower than the PON system or pulling GPS into the station where the OLT is installed.

  Here, since the PON system normally operates based on the time of the local oscillator included in the OLT, when the GPS signal received by the ONU is used as a reference as described above, there is a frequency difference with the OLT. May occur and the frequency and time synchronization accuracy may deteriorate. This embodiment employs a configuration that improves the accuracy of frequency and time synchronization.

  FIG. 1 is a diagram showing a schematic configuration of a PON system according to the present embodiment. In this PON system, one OLT (station-side optical terminator) 10 and n (n is an arbitrary integer) ONUs (subscriber-side optical terminators) 50-1 to 50-n are connected to optical fibers and optical fibers. Connection is made via a splitter 40. Base stations 100-1 to 100-n are connected to the ONUs 50-1 to 50-n, and any one of the n ONUs (ONU50-1 in FIG. 1) has a GPS antenna 51. is set up. Although FIG. 1 shows a configuration in which base stations are connected to all ONUs, other services such as FTTH (Fiber-to-the-Home) may be connected.

  The frequency / time synchronization GPS signal received by the ONU 50-1 is distributed in a loopback manner to the other ONUs 50-2 to 50-n via the OLT 10, and the ONUs 50-2 to 50-n are transmitted to the ONU 50-1. Are synchronized with each other at the reference frequency / time. In this embodiment, an ONU to which a GPS antenna is connected is distinguished as a master ONU, and other ONUs are distinguished as slave ONUs.

  FIG. 2 is a block diagram illustrating a schematic configuration of the master ONU (ONU50-1) according to the first embodiment. The ONU 50-1 includes two interfaces, a UNI 52 that is a data transmission / reception interface with a base station, and a GPS receiver 62 that receives GPS signals. The GPS receiver 62 and the GPS antenna 51 constitute a GPS signal receiving device.

  The upstream data signal is transmitted from the E / O 56 after the CPU 54 grasps the transmission time and timing. The downstream data signal is received by the O / E 58 and then transferred from the UNI 52 to the base station via the CPU 54. The upper and lower optical signals are wavelength-multiplexed / demultiplexed by the WDM optical coupler 60.

  The GPS receiver 62 extracts a reference frequency (for example, 10 MHz), a reference pulse (for example, one pulse per second) and time information (ToD: Time of Day) from the received GPS signal, The time stamp (TS) generator 68 and the CPU 54 are supplied. The clock generator 64 generates clocks 1 (for example, 62.5 MHz used in the PON system) and 2 (for example, 1.25 GHz for a 1.25 Gbit / s transmission system) based on the reference frequency, respectively. Supply to timer 66 and E / O 56. The E / O 56 operates using the clock 2 as a reference frequency. A timer 66 that is an internal counter of the PON operates using the clock 1 as a reference frequency, and a time stamp (TS) generation unit 68 generates a TS described in the frame of the PON and supplies it to the CPU 54.

  The memory 70 stores the propagation delay time (a half value of RTT) between the OLT 10 and the ONU 50-1 notified from the OLT 10, and based on the propagation delay time, the ToD is received at the time when the ToD signal reaches the OLT. to correct. The ToD is, for example, text data or the like as an uplink control frame, time-multiplexed with the data signal, and transmitted to the OLT 10.

  FIG. 3 is a block diagram illustrating a schematic configuration of the OLT 10. The OLT 10 includes an NNI 20 that is a data transmission / reception interface with an upper network. The downstream data signal is transmitted from the E / O 16 after the CPU 18 grasps the transmission time and timing. The upstream data signal is received by the O / E 14 and then transferred from the NNI 20 to the upper network via the CPU 18. The upper and lower optical signals are wavelength-multiplexed / demultiplexed by the WDM optical coupler 12.

  Here, since the PON normally operates with the time of the OLT 10 as a reference, when the GPS signal received by the ONU 50-1 is used as a reference, a frequency difference occurs with the OLT, and the frequency and time synchronization accuracy deteriorates. Is concerned. In order to solve this problem, the CPU 18 of the OLT 10 is provided with a time stamp difference calculation function 22 for calculating the difference between the TS value generated by the ONU counter and the TS value of the OLT counter. A frequency difference (Δf) corresponding to Δt) is fed back to the local oscillator 24 inside the OLT 10 to control the oscillation frequency. This feedback control is repeated a plurality of times until the time stamp difference falls below a preset determination threshold.

  In the present embodiment, only the ONU 50-1 is first connected to the OLT 10, and the above feedback control is executed at the stage of initial registration of the ONU 50-1. After the time stamp difference is resolved, another slave ONU is connected and links with all ONUs are established.

  In FIG. 3, the clock generator 26 generates clocks 1 ′ and 2 ′ with reference to the oscillation frequency of the local oscillator 24 and supplies the clocks 1 ′ and 2 ′ to the timer 28 and the E / O 16, respectively. The TS generation unit 30 generates a TS based on the counter value of the timer 28 and supplies it to the CPU 18.

  FIG. 4 is a block diagram showing a schematic configuration of the slave ONU (ONU50-2). The configurations of the ONUs 50-2 to 50-n are the same. The ONU 50-2 includes a UNI 80 that is a data transmission / reception interface with the base station. The upstream data signal is transmitted from the E / O 74 after the CPU 78 grasps the transmission time and timing. The downlink data signal is received by the O / E 76 and then transferred from the UNI 80 to the base station via the CPU 78. The upper and lower optical signals are wavelength-multiplexed / demultiplexed by the WDM optical coupler 72.

  The CDR 82 regenerates the clock from the transmission rate of the downlink data signal and supplies it to the clock generation unit 84. The clock generation unit 84 generates clocks 1 (for example, 62.5 MHz used in the PON system) and 2 (for example, 1.25 GHz for a 1.25 Gbit / s transmission system), respectively. Supply to O74. The E / O 74 operates using the clock 2 as a reference frequency. The timer 86 operates in synchronization with the counter of the OLT 10 by operating with the clock 1 as a reference frequency.

  The clock 1 output from the clock generation unit 84 is converted into a reference frequency (for example, 10 MHz) of the original GPS signal by the frequency conversion unit 90 and supplied to the subordinate base station. The reference pulse generator 88 refers to the counter value of the timer 86 and the time stamp value supplied from the CPU 78, generates a reference pulse that is phase-synchronized with the original GPS signal, and supplies it to the subordinate base station. The ONU 50-2 extracts the ToD from the downlink control frame (text data) received from the OLT 10, corrects the amount of RTT (read from the memory 92) notified from the OLT 10, and supplies it to the subordinate base station. .

  FIG. 5 is a diagram illustrating an example of a synchronization sequence between the OLT and the master ONU. First, the OLT establishes a logical link with the master ONU and measures the round-trip propagation delay time (RTT = t2-t1). Next, the OLT notifies the master ONU of the RTT and instructs the master ONU to transmit an RTT reception completion message at time t4. Here, the master ONU transmits the upstream frame with the counter value (t4 ′) of the master ONU itself, not the instruction value of the OLT. The OLT measures the difference Δt between the predicted time (t5) at which the upstream signal from the master ONU is received and the time (t5 ′) at which the upstream signal is actually received from the master ONU, and calculates the frequency difference corresponding to the difference. , Feed back to the local oscillator of the OLT to correct. This is repeated N (N is an arbitrary integer) loop, and the OLT synchronization processing is terminated when the difference falls below a certain difference threshold value, and the processing shifts to logical link establishment processing with other slave ONUs.

  In the second embodiment, the difference Δt is calculated on the master ONU side. FIG. 6 is a block diagram illustrating a schematic configuration of the master ONU according to the second embodiment. The difference from the first embodiment shown in FIG. 2 is that the CPU 54 is provided with a difference calculation function. Other configurations are the same as those of the first embodiment. The OLT may have the same configuration as that of the first embodiment.

  FIG. 7 is a diagram illustrating an example of a synchronization sequence between the OLT and the master ONU in the second embodiment. The sequence from establishment of the logical link with the master ONU, RTT measurement, and RTT notification is the same as in the first embodiment. Next, the OLT requests the master ONU to notify the time difference between the OLT and the master ONU (Δt_Request). The master ONU measures the difference between the time t3 when the Δt_Request message is received and the counter value t3 'of the ONU, and transmits an uplink frame that conveys the difference at the time t4 instructed by the OLT (Δt_Response). The OLT feeds back and corrects the frequency difference corresponding to Δt notified from the master ONU to the local oscillator of the OLT. This is repeated N (N is an arbitrary integer) loop, and the OLT synchronization processing is terminated when the difference falls below a certain difference threshold value, and the processing shifts to logical link establishment processing with other slave ONUs.

FIG. 8 is a flowchart showing an outline of the operation of the PON system according to the present embodiment. When the OLT establishes a logical link with the master ONU (step S1), the OLT measures the RTT (step S2). Next, the difference Δt is calculated (step S3), and it is determined whether or not the difference is larger than the threshold value t _th (step S4). When the difference is larger than the threshold value t _th , the process proceeds to step S3 and step S3 is repeated. On the other hand, if the difference is not greater than the threshold value t _th in step S4, a logical link is established with another ONU (slave ONU) (step S5), and the process ends.

  As described above, according to the present embodiment, it is possible to improve the accuracy of frequency synchronization and time synchronization in loopback control via the OLT.

10 OLT
12 Optical coupler (WDM)
14 O / E
16 E / O
18 CPU
20 NNI
22 Time stamp difference calculation function (Δt calculation function)
24 Local oscillator 26 Clock generator (CLK generation)
28 Timer 30 TS Generation Unit 32 Memory 40 Optical Splitter 50-1 to 50-n ONU
51 GPS antenna 52 UNI
54 CPU
56 E / O
58 O / E
60 Optical coupler (WDM)
62 GPS receiver 64 Clock generator (CLK generation)
66 Timer 68 TS generator 70 Memory 72 Optical coupler (WDM)
74 E / O
76 O / E
78 CPU
80 UNI
82 CDR
84 Clock generator (CLK generation)
86 Timer 88 Reference pulse generator 90 Frequency converter 92 Memory 100-1 to 100-n Base station

Claims (11)

A PON (Passive Optical Network) system that realizes optical fiber transmission,
OLT (Optical Line Terminal),
A plurality of ONUs (Optical Network Units) connected to the OLT via optical splitters;
A GPS signal receiver provided in any one ONU and receiving a GPS (Global Positioning System) signal,
The OLT, on the basis of a GPS signal the master ONU receives with the GPS signal receiving apparatus corrects the oscillation frequency of the local oscillator, using the oscillation frequency after correction logic and ONU other than the master ONU A PON system characterized by establishing a link. The OLT based on the difference between the received estimated time of responses to time stamp transmitted to the master ONU from the own apparatus, and the reception time of the time stamp based on the GPS signal response received from the master ONU, the local oscillator to correct the oscillation frequency,
2. The PON according to claim 1 , wherein the time stamp transmitted to the master ONU includes a response transmission instruction time, and the time stamp transmitted to the master ONU and the response transmission instruction time are based on an oscillation frequency of a local oscillator. system. The master ONU transmits information indicating the difference between the time indicated in the time stamp received from the OLT and the time obtained from the GPS signal to the OLT,
The OLT, on the basis of the difference indicated in the received information from the master ONU, PON system according to claim 1, wherein the correcting the oscillation frequency of the local oscillator. The OLT, the difference is greater is than a predetermined threshold, using the oscillation frequency after correction, claim 2 or claim and transmits the timestamp to again the master ONU 3. The PON system according to 3. An OLT (Optical Line Terminal) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
Based on GPS (Global Positioning System) GPS signal master ONU receives with a GPS signal receiver for receiving signals, to correct the oscillation frequency of the local oscillator, using the oscillation frequency after correction, other than the master ONU An OLT characterized in that a logical link is established with the ONU. From its own device, wherein the reception estimated time of responses to time stamp transmitted to the master ONU, based on a difference between the reception time of the time stamp based on the GPS signal response received from the master ONU, originating local oscillator oscillation Correct the frequency ,
6. The OLT according to claim 5 , wherein the time stamp transmitted to the master ONU includes a response transmission instruction time, and the time stamp transmitted to the master ONU and the response transmission instruction time are based on an oscillation frequency of a local oscillator. . On the basis of the difference indicated in the received information from the master ONU, OLT of claim 5, wherein the correcting the oscillation frequency of the local oscillator. The difference is greater is than a predetermined threshold, using the oscillation frequency after correction, OLT of claim 6 or claim 7, wherein transmitting the time stamp to again the master ONU . An ONU (Optical Network Unit) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A GPS signal receiving device for receiving GPS (Global Positioning System) signals,
A time stamp based on the GPS signal is transmitted to an OLT (Optical Line Terminal) at a transmission instruction time included in the time stamp received from the OLT ,
An ONU characterized in that the time stamp and transmission instruction time received from the OLT are based on the oscillation frequency of a local oscillator . An ONU (Optical Network Unit) applied to a PON (Passive Optical Network) system that realizes optical fiber transmission,
A GPS signal receiving device for receiving GPS (Global Positioning System) signals,
To the OLT (Optical Line Terminal) , information indicating the difference between the time indicated by the time stamp received from the OLT and the time obtained from the GPS signal is transmitted .
The ONU, wherein the time stamp received from the OLT is based on an oscillation frequency of a local oscillator . A transmission method of a PON (Passive Optical Network) system that realizes optical fiber transmission,
In OLT (Optical Line Terminal), based on GPS (Global Positioning System) GPS signal master ONU receives with a GPS signal receiver for receiving signals, to correct the oscillation frequency of the local oscillator, the corrected oscillation frequency And establishing a logical link with an ONU other than the master ONU.

Images