JP6231438B2 - Relay transmission system and relay transmission method - Google Patents

Description

  The present invention relates to a technique for realizing relay transmission capable of maintaining a link even when a relay link is momentarily interrupted, particularly in a CPRI and ORI relay transmission system.

  In mobile communication systems such as LTE (Long Term Evolution), a base station configuration using a remote antenna is adopted in order to improve connectivity in a radio cell. In this basic configuration, the radio base station function is divided into a radio controller (REC) 91 that performs radio modulation / demodulation and a radio device (RE) 92 that performs radio transmission / reception, as in the radio base station system shown in FIG. Are connected by a transmission line 93. As a transmission method, CPRI (Common Public Radio Interface) or ORI (Open Radio equipment Interface) technology for transmitting a digital radio signal using an optical fiber is widely used (for example, see Non-Patent Documents 1 and 2). .)

  In CPRI and ORI, as shown in FIG. 2, since not only digitized radio signals but also control / maintenance signals of REC 91 and RE 92 are multiplexed and transferred, maintenance monitoring of REC 91 and RE 92 becomes easy. In addition, an inexpensive line such as a dark fiber can be used as the transmission line 93. For this reason, a configuration such as a C-RAN (Centralized RAN) that realizes a highly functional radio access network by connecting a large number of REs 92 to the REC 91 installed in one place is also possible.

  In LTE-advanced, which is an evolution of LTE, the radio transmission capacity is expanded, so that more frequency bands and MIMO multiplicity can be increased. For this reason, the line capacity of CPRI also increases, and multiplex transmission by time division or wavelength division is required. Also, as shown in FIG. 3, a configuration is adopted in which a plurality of small cells 94 are accommodated to improve the throughput of the entire cell, and a small cell base station (RRH (Remote Radio Head)) can be efficiently accommodated. It becomes important. Further, since the small cell 94 is installed at a location where traffic is concentrated, the cell density at the installation location is high. For this reason, it has been studied to adopt a passive optical network (PON) configuration used for optical access and efficiently accommodate the small cell 94, and further to implement a device by a time division multiplexing (TDM) -PON configuration. A method for reducing the cost by sharing is studied (for example, see Non-Patent Document 3). In TDM-PON, a normal dynamic bandwidth allocation (DBA) technique is used for bandwidth allocation in upstream TDMA from an optical subscriber line network unit (ONU) to an optical subscriber line termination unit (OLT). Does not satisfy the requirements of MFH. For this reason, a bandwidth allocation method with low delay has been studied, and performance that satisfies the required conditions has been obtained (see, for example, Non-Patent Document 4).

CPRI Specification V6.0, 2013. Open Radio equipment Interface (ORI); ORI Interface Specification; Part 1: Low Layers (Release 3), Jan. 2014. Taniguchi et al., "Technical Requirements for Optical Access Systems that will Support Wireless Access and Mobile Optical Networks in the Future", IEICE Technical Report, MWP 2013-88, January 2014 Kuwano et al., "Low latency DBA for TDM-PON application to mobile optical networks", IEICE General Conference, B-8-54, March 2014 “Technology Basic Course“ GE-PON Technology ”2nd IEEE 802.3ah Standard”, NTT Technical Journal, pp. 91-94, September 2005

In order to avoid unnecessary radio signal radiation, the CPRI line detects signal disconnection due to a plurality of codeword errors. In the case of signal disconnection, the transmission and reception of the radio signal is stopped and the link is established again. take time. For this reason, a very high communication quality with a bit error rate of 10 ⁻¹² or less is required, and in the case of multiplex transmission, it is assumed that the conditions will become more severe, and measures against instantaneous interruptions in a short time of 1 ms or less Necessary.

  On the other hand, in TDM-PON, in order to recognize newly connected or reconnected ONU by OLT, discovery processing is executed as shown in FIG. Communication interruption occurs (for example, see Non-Patent Document 5).

  FIG. 4 is a diagram for explaining the operation of the discovery process. The OLT 34 periodically broadcasts a signal called a discovery gate to all of the subordinate ONUs 35. The unregistered ONU 35 transmits a response signal in the discovery window based on information in the discovery gate. At this time, in order to avoid collision of response signals from a plurality of ONUs 35, transmission times from the registered ONUs 35 are set at random. The size of the discovery window is set according to the delay in the optical distribution network and the number of ONUs.

  At the network initialization stage, registration of a plurality of ONUs 35 is required. However, since most of the registration and re-registration of a single ONU 35 is in operation, the discovery window can be set small. In the case of normal data transmission, even if there is a time during which communication is impossible in the discovery window, it is possible to transfer data without any problem by storing the data of that time in the ONU and transmitting it after discovery is completed. In CPRI, it is necessary to transmit data with a low delay and a fixed rate. This discovery window is about several hundred us to ms, and when a discovery operation occurs, it takes a long time to establish a link again. For this reason, the channel quality of the wireless system transmitted by CPRI is greatly affected.

  As described above, if repeat optical transmission is to be realized between the radio network controller (REC) and the radio equipment (RE) using the optical transmission technology, it takes time to establish a relink due to a link disconnection. There was a problem of having a big impact on

  An object of the present invention is to maintain a link even in the event of a momentary disconnection of a relay link in a relay transmission system using optical transmission technology.

  In the present invention, when a signal interruption occurs in the optical transmission between the relay apparatuses, a signal simulating a signal to be transmitted is transmitted to maintain the link, so that the time required for establishing the relink can be relayed. Realize transmission.

Specifically, the relay transmission system according to the present invention is:
A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission system,
A first relay device that converts the signal of the predetermined format from the first communication device into a predetermined transmission frame and transfers it;
A second relay device that converts the transmission frame transferred by the first relay device into a signal of the predetermined format and transfers the signal to the second communication device;
With
When a link break occurs between the first relay device and the second relay device,
The first relay device generates a simulated frame that simulates a transmission frame from the second relay device, converts the simulated frame into the signal of the predetermined format, and transmits the signal to the first communication device.
The second relay device generates a simulated frame that simulates the transmission frame from the first relay device, converts the simulated frame into a signal of the predetermined format, and transmits the signal to the second communication device.

In the relay transmission system according to the present invention,
The transmission line includes a passive optical network that transmits an optical signal using time division multiplexing,
The first relay device, which is connected with the passive optical optical network device provided in the network, if the link break due di Sukabari processing occurred, and the first relay device of the second switching device Link break information indicating that a link break has occurred between the second relay devices,
The second repeater is connected to an optical subscriber line network device provided in the passive optical network, and when the link disconnection information is received, transfer of a transmission frame to the optical subscriber line network device is stopped. Good.

Specifically, the relay transmission device according to the present invention is:
A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay device,
A signal transmission / reception unit for transmitting / receiving a signal in a predetermined format to / from the first communication device;
A frame transmission / reception unit for transmitting / receiving a predetermined transmission frame to / from another relay device arranged in a transmission path with the second communication device;
The signal of the predetermined format received by the signal transmission / reception unit is converted into the transmission frame and output to the frame transmission / reception unit, and the transmission frame received by the frame transmission / reception unit is converted to the signal of the predetermined format. A conversion unit for outputting to the transmission / reception unit;
When it is detected that a frame loss has occurred in the transmission frame received by the frame transmission / reception unit, a simulated frame simulating the transmission frame from the other relay device is generated, and a signal interruption to be output to the conversion unit as the transmission frame is generated. A processing unit;
Is provided.

  In the relay transmission device according to the present invention, when the signal disconnection processing unit detects that the frame loss of the transmission frame received by the frame transmission / reception unit is eliminated and the transmission frame received by the frame transmission / reception unit is normal, The transmission frame including link recovery information may be generated and transmitted from the frame transmitting / receiving unit to the other relay device.

  In the relay transmission device according to the present invention, the signal disconnection processing unit is configured such that a sequence number of a transmission frame received by the frame transmission / reception unit is discontinuous or a transmission frame received by the frame transmission / reception unit has not arrived. It may be detected that a frame loss has occurred based on a predetermined time or more.

  In the relay transmission device according to the present invention, the signal in the predetermined format may be CPRI (Common Public Radio Interface) or ORI (Open Radio equipment Interface).

Specifically, the relay transmission method of the relay transmission system according to the present invention is:
A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission method for a relay transmission system,
The first relay device converts the predetermined format signal from the first communication device into a predetermined transmission frame and transfers it, and the second relay device transmits the transmission frame transferred by the first relay device. A relay procedure for converting the signal into a signal of the predetermined format and transferring it to the second communication device,
In the relay procedure, a signal disconnection detection procedure for detecting that a link disconnection has occurred between the first relay device and the second relay device;
When a link break occurs, the first relay device generates a simulated frame that simulates a transmission frame from the second relay device, converts the simulated frame into the signal of the predetermined format, and And the second relay device generates a simulated frame that simulates the transmission frame from the first relay device, converts the simulated frame into the signal of the predetermined format, and the second relay device. A simulated frame transmission procedure to be transmitted to the communication device of
In order.

Specifically, the relay transmission method of the relay device according to the present invention is:
A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission method for the relay device,
A signal interruption detection procedure for detecting that a frame loss has occurred in a predetermined transmission frame received from another relay apparatus arranged in a transmission path with the second communication apparatus;
When a frame loss occurs, a simulated frame simulating a transmission frame from the other relay device is generated instead of a signal of a predetermined format transmitted to the first communication device, and the simulated frame is A simulated frame transmission procedure for converting the signal into a predetermined signal and transmitting the signal to the first communication device;
In order.

  The above inventions can be combined as much as possible.

  According to the present invention, in a relay transmission system, a link can be maintained even when a relay link is momentarily interrupted.

An example of a remote antenna structure is shown. An example of a structure of CPRI is shown. An example of a small cell structure is shown. An example of a discovery process is shown. The structural example of the radio base station system which concerns on 1st Embodiment is shown. An example of a signal disconnection processing circuit configuration is shown. An example of a header structure of a CPRI hyperframe is shown. An example of the header configuration of the ORI hyperframe is shown. An example of the structure of the radio base station system which concerns on 2nd Embodiment is shown. An example of the process at the time of discovery is shown.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
FIG. 5 shows an example of the configuration of the radio base station system according to the present embodiment. The radio base station system according to the present embodiment configures a link between the radio control device 91 and the radio device 92 via the transmission path 93 and transmits / receives signals in a predetermined format. The wireless control device 91 functions as a first communication device, and the wireless device 92 functions as a second communication device. The predetermined format signal is a digitized radio signal used in a base station configuration using a remote antenna, for example, a CPRI signal or an ORI signal. In the present embodiment, as an example, a case where the digitized radio signal is CPRI will be described.

  A first relay device 31, a transmission path 93, and a second relay device 32 are arranged on the transmission path between the wireless control device 91 and the wireless device 92. The first relay device 31, the transmission path 93, and the second relay device 32 constitute a relay transmission system according to the present embodiment.

  The first relay device 31 includes a CPRI interface 311, a format conversion circuit 312, a transmission path interface 313, and a signal disconnection processing circuit 314. Similar to the first relay device 31, the second relay device 32 includes a CPRI interface 321, a format conversion circuit 322, a transmission path interface 323, and a signal disconnection processing circuit 324. The CPRI interfaces 311 and 321 function as signal transmission / reception units for the wireless control device 91 and the wireless device 92, the transmission path interfaces 313 and 323 function as signal transmission / reception units between relay devices, and the format conversion circuits 312 and 322 are between the relay devices. The signal disconnection processing circuits 314 and 324 function as processing circuits when signal disconnection occurs.

  The relay transmission system according to the present embodiment executes the relay transmission method according to the present embodiment. The relay transmission method according to the present embodiment has a relay procedure. In the relay procedure, the first relay device 31 and the second relay device 32 relay signals as follows.

  The first relay device 31 relays a signal from the wireless control device 91 to the wireless device 92. At this time, the CPRI interface 311 receives the CPRI signal from the radio control apparatus 91. The format conversion circuit 312 converts the CPRI signal into a transmission line format. The transmission path interface 313 transfers the transmission frame whose format has been converted by the format conversion circuit 312 to the second relay device 32.

  The first relay device 31 relays a signal from the wireless device 92 to the wireless control device 91. At this time, the transmission path interface 313 receives the transmission frame from the second relay device 32. The format conversion circuit 312 converts the transmission line format into a CPRI signal. The format-converted CPRI signal is subjected to processing related to signal disconnection by a signal disconnection processing circuit 314. The CPRI interface 311 transfers the CPRI signal processed by the signal disconnection processing circuit 314 to the wireless control device 91.

  The second relay device 32 relays a signal from the wireless device 92 to the wireless control device 91. At this time, the CPRI interface 321 receives the CPRI signal from the wireless device 92. The format conversion circuit 322 converts to a transmission line format. The transmission path interface 323 transfers the transmission frame whose format has been converted by the format conversion circuit 322 to the first relay device 31.

  The second relay device 32 relays a signal from the wireless control device 91 to the wireless device 92. At this time, the transmission path interface 323 receives the transmission frame from the first relay device 31. The format conversion circuit 322 converts the transmission path format into a CPRI signal. The format-converted CPRI signal is subjected to processing related to signal disconnection by a signal disconnection processing circuit 324. The CPRI interface 321 transfers the CPRI signal processed by the signal disconnection processing conversion circuit 324 to the wireless device 92.

  Here, the transmission path format between the first relay device 31 and the second relay device 32 uses a frame in which a basic frame of a CPRI signal is multiplexed / encapsulated and a header for transmission is added. This format may be an original format, but a low-cost system can be constructed by using a general-purpose format. Examples of general-purpose formats include Ethernet (registered trademark) frames and OTN frames.

  The signal disconnection processing circuit 314 detects a signal disconnection from the second relay device 32 and controls transfer information to the wireless control device 91. The signal disconnection processing circuit 324 detects signal disconnection from the first relay device 31 and controls transfer information to the wireless device 92. The signal disconnection processing circuits 314 and 324 function as a signal disconnection processing unit.

  The relay transmission method according to the present embodiment sequentially executes a signal loss detection procedure and a simulated frame transmission procedure in the relay procedure. The signal disconnection processing circuits 314 and 324 execute a signal disconnection detection procedure and a simulated frame transmission procedure.

  FIG. 6 shows an example of the signal break processing circuits 314 and 324. The signal disconnection processing circuit includes a frame loss detection circuit 41, a simulated frame generation circuit 42, a frame monitor circuit 43, and a frame switching circuit 44.

  The frame loss detection circuit 41 receives information necessary for detecting that a link break has occurred between the first relay device 31 and the second relay device 32. For example, time stamp information including the time at which the transmission path interfaces 313 and 323 received the transmission frame is input to the frame loss detection circuit 41.

  The frame loss detection circuit 41 executes a signal disconnection detection procedure and detects that a link disconnection has occurred between the first relay device 31 and the second relay device 32. For detecting the link break, for example, transmission frame loss in the transmission path 93 is detected using time stamp information of the transmission frame received by the transmission path interfaces 313 and 323. Details of the transmission frame loss detection method will be described later.

  When the frame loss detection circuit 41 does not detect a link break, the frame switching circuit 44 transfers the CPRI signal converted by the format conversion circuits 312 and 322 to the CPRI interfaces 311 and 321. As a result, the signal whose format has been converted from the transmission frame to the CPRI signal is transmitted to the wireless control device 91 and the wireless device 92.

  When the frame loss detection circuit 41 detects a link break, the simulated frame generation circuit 42 and the frame switching circuit 44 execute a simulated frame transmission procedure. Specifically, the simulated frame generation circuit 42 generates a simulated frame that simulates a transmission frame. For example, a frame simulating the CPRI frame generated when the CPRI signal is converted into the transmission path format is generated as a simulated frame and output to the frame switching circuit 44. The frame switching circuit 44 switches the transmission frame from the CPRI frame to the simulated frame and transfers it to the CPRI interfaces 311 and 321. As a result, a CPRI signal including a simulated frame is transmitted to the radio control device 91 and the radio device 92.

  As described above, since the relay transmission system according to the present embodiment executes the signal interruption detection procedure and the simulated frame transmission procedure, the first relay device 31 and the second relay device 32 are wirelessly connected even in the signal interruption state. The simulation frame simulated by the control device 91 and the wireless device 92 is continuously transferred.

  When the link of the transmission path 93 is restored and a normal transmission frame is received by the first relay device 31 and the second relay device 32, the frame loss detection circuit 41 of the signal disconnection processing circuits 314 and 324 Release the state. Then, the frame switching circuit 44 provided in the first relay device 32 switches the transmission frame transferred to the radio control device 91 from the simulated frame to the CPRI frame. The frame switching circuit 44 provided in the second relay device 32 switches the transmission frame transferred to the wireless device 92 from the simulated frame to the CPRI frame.

  When the transmission frame loss continues for a certain time or longer, the simulated frame generation circuit 42 may stop generating the simulated frame. In this case, it is preferable that the CPRI interface 311 of the first relay device 31 and the CPRI interface 321 of the second relay device 32 make the CPRI link disconnected. This fixed time is a time longer than the period in which the transmission frame arrives at the first relay apparatus 31 or the second relay apparatus 32, and is preferably after a plurality of periods have been exceeded.

  In this way, when the link from the first relay device 31 to the second relay device 32 is broken and when the link from the second relay device 32 to the first relay device 31 is broken. In both cases, since the CPRI link using the simulated frame between the wireless device 92 and the wireless control device 91 is maintained, the link between the wireless control device 91 and the wireless device 92 is not broken. Therefore, when the links from the first relay device 31 to the second relay device 32 and from the second relay device 32 to the first relay device 31 are restored, the transfer of the CPRI frame can be resumed at high speed.

  The determination of the link break between the first relay device 31 and the second relay device 32 in the present embodiment is made by, for example, discontinuity of sequence numbers given to transmission frames and non-arrival of frames for a fixed time. The determination of frame non-arrival is performed, for example, based on CPRI signal reception time information (time stamp) written in the header of the transmission frame.

  Since the CPRI is fixed rate transmission, the time stamp value written by the second relay device 32 is a constant interval. The first relay device 31 outputs a CPRI signal to the radio control device 91 at a time obtained by adding a certain time to the received time stamp value. By doing so, it is possible to transmit the CPRI frame at a fixed rate without fluctuation of delay.

  When there is a frame loss, there is no CPRI signal transmitted at that time, so the first relay device 31 and the second relay device 32 can detect a disconnection state. Further, even when the time obtained by adding a certain time to the time stamp value of the transmission frame is in the past, or when it is far in the future, the first relay device 31 and the second relay device 32 are normal. It can be detected as a state that is not. Here, the fixed time used when determining the non-arrival of the frame is a time longer than the period in which the transmission frame arrives at the first relay apparatus 31 or the second relay apparatus 32, and after a plurality of periods have been exceeded. It is preferable.

  About the normality of the frame transmission at the time of link restoration, the frame loss detection circuit 41 can determine using the time stamp value written in the header of the simulated frame. For example, the determination is made based on the arrival of a frame having normal time information. The normal time information is determined to be normal when, for example, the time obtained by adding the transmission delay between the first relay device 31 and the second relay device 32 to the reception time and the time stamp value of the simulated frame matches. To do.

  In order to perform processing using a time stamp in the present embodiment, it is necessary to accurately synchronize the time between the first relay device 31 and the second relay device 32. A synchronous Ethernet (registered trademark) or IEEE 1588 synchronous protocol can be used, or GPS can be used.

  Regarding the configuration of the simulated frame in the present embodiment, the header of the CPRI frame during normal transmission is monitored by the frame monitor circuit 43, and the simulated frame generation circuit 42 simulates the next frame of the current CPRI frame. Is always created. Since the simulated frame generation circuit 42 always creates a simulated frame, when the frame monitor circuit 43 detects that the signal is interrupted, the simulated frame generation circuit 42 can instantaneously switch to the simulated frame, so that the CPRI signal is wirelessly controlled without interruption. Can be transmitted to the device.

  FIG. 7 shows an example of the header configuration of the CPRI hyperframe. The header of the CPRI hyperframe includes a Comma Byte portion, which is a special code for frame synchronization, a synchronization portion, a low-speed device control monitoring interface portion, an L1 in-band protocol portion, an AxC control signal portion, a reserved word, a vendor-specified area, and a high-speed Including a device control monitoring interface portion.

  In FIG. 7, as an example, the case where Ns = 0 to 63 and Xs = 0 to 3 in which 256 blocks are arranged in four columns is shown. Ns = 0 and Xs = 0 are Comma Byte parts, Ns = 0 and Xs = 1 to 3 are synchronous parts, Ns = 1 is a low-speed control monitoring interface part, and Ns = 2 is an L1 in-band protocol. Ns = 4-7 are AxC control signal portions, and Ns = 3, 8-15 are reserved words for fixed data. A pointer p indicating the head of the high-speed device control monitoring interface portion is described in the L1 in-band protocol portion. Ns = 16 to p−1 is a vendor designation area, and Ns = p to 63 is a high-speed device control monitoring interface part.

  The synchronization part with Ns = 0 can be completely simulated, and the L1 in-band protocol part with Ns = 2 can be simulated in a normal transmission state. The AxC control signal of Ns = 4 to 7 can be simulated if it is a normal operation. The low-speed and high-speed device control monitoring interfaces of Ns = 1, p to 63 are simulated as no signals. In addition, the vendor-specified area of Ns = 16 to p−1 can be simulated when information from the vendor can be obtained, but when it cannot be obtained, it is simulated by a monitored signal.

  The IQ data area is assumed to be no signal or IQ data of a noise signal of a small level so that the processing in the radio physical layer L1 of the radio control device 91 does not malfunction. Particularly in the down direction, since it is actually radiated as radio waves, it is necessary to use a low-level signal. By doing this, a rapid level change equivalent to fading occurs in the wireless section and affects the wireless quality, but frame loss due to bit errors etc. is restored in a short time, so the influence on the total system is ignored it can.

In this embodiment, it is assumed that the wireless signal is disconnected and the apparatus control monitoring signal is disconnected, which affects the scheduling of the subsequent wireless section. In the case of LTE, since 10 ms is handled as a frame, a signal loss of about ms is considered to affect the subsequent LTE frame. However, since the radio signal disconnection when the CPRI signal is interrupted reaches several hundred ms, the influence of the link disconnection in this embodiment can be suppressed to a very small level. For example, even if a 1 ms link disconnection occurs once an hour, the influence (ratio of signal disconnection time) is about 2.8 × 10 ⁻⁷ and has almost no effect on the radio channel quality.

  In the present embodiment, the case where the digitized radio signal is CPRI has been described, but the present invention is not limited to this. For example, an ORI signal can be used instead of CPRI.

  FIG. 8 shows an example of the header configuration of the ORI hyperframe. The header of the ORI hyperframe includes CPRI L1 control words, CPRI reserved area, vendor specified area, ORI reserved area, and ORI C & M.

  FIG. 8 shows an example where Ns = 0 to 63 and Xs = 0 to 3 in which 256 blocks are arranged in four columns. Ns = 0 to 2 are CPRI L1 control words, Ns = 3 to 15 are CPRI reserved areas, Ns = 16 to 40 are vendor-specified areas, Ns = 41 to 52 are ORI reserved areas, and Ns = 53 to 63 are ORI C & M.

  In the case of ORI, since a part of the CPRI header is changed and a high-speed device control monitoring interface is redefined and used for monitoring control signal transmission, transmission of the monitoring control signal is interrupted in this embodiment. For this reason, it is necessary to link with an operation system for controlling the transmission apparatus as necessary.

  As described above, by applying the present invention, it is possible to maintain a link even when a short-time signal interruption occurs in a transmission line, particularly in a CPRI and ORI relay transmission system.

(Second Embodiment)
FIG. 9 shows an example of the configuration of the radio base station system according to the present embodiment. In the present embodiment, a TDM-PON system is used as the transmission path 93 between the first relay device 31 and the second relay device 32. The TDM-PON system includes an OLT 34 that functions as an optical subscriber line network device, an ONU 35 that functions as an optical subscriber line termination device, and an optical distribution network 36 that connects the OLT 34 and the ONU 35. The optical signal from the first repeater 31 is transmitted on the optical distribution network 36 via the OLT 34 and is transmitted to the ONU 35.

  Since delay fluctuation occurs in the section of the optical distribution network 36, a time stamp is added as header information of signals transmitted by the first relay device 31 and the second relay device 32, and a fixed delay time is added to the time stamp. At this time, a signal is transferred to the wireless control device 91 and the wireless device 92. By doing so, even if delay fluctuation occurs in the TDM-PON, it is absorbed and the signal is transferred between the first relay device 31 and the second relay device 32 with a fixed delay time. Is possible.

FIG. 10 shows an example of the operation of the radio base station system according to this embodiment.
A normal CPRI signal is transmitted from the wireless device 92 to the wireless control device 91 (S101). Then, the OLT 34 sends a discovery gate signal to the ONU 35 (S102), and the discovery process starts (S103). Also during this discovery process, the second relay device 32 receives data from the wireless device 92 (S104).

  In the discovery window of the discovery process described with reference to FIG. 4, when the first relay device 31 detects a signal disconnection due to discovery (S111), a simulated frame is inserted into the CPRI signal to the radio control device 91 (S112). The link break information detected by the frame loss detection circuit 41 is inserted into the header of the transmission frame to the second relay device 32 (S113). When detecting the link disconnection information, the second relay device 32 stops and discards the transfer data to the ONU 35 side in the format conversion circuit 322 (S114).

  At this time, data from the start of the discovery window (S103) to the data transfer stop (S114) remains in the buffer of the ONU 35. When the discovery process is completed, the data stored in the ONU 35 is transferred to the first relay device 31 via the OLT 34 (S115), and the frame loss detection circuit 41 detects the restart of the link (S116). .

  When detecting the recovery of the link, the first relay device 31 transfers the staying data received from the OLT 34 to the wireless control device 91. However, in this case, since the staying data transferred in S115 is past data, the first relay device 31 transfers a simulated frame to the radio control device 91 (S117).

  When detecting the recovery of the link, the first relay device 31 transmits link recovery information indicating link resumption to the second relay device 32 (S118). Link recovery information is inserted into the header of the transmission frame. The second relay device 32 resumes data transfer to the ONU 35 based on the link recovery information (S119). After confirming that the time stamp of the transmission frame whose transfer has been resumed is in a normal state, the first relay device 31 switches the signal to be transferred to the radio control device 91 from the simulated frame to the CPRI frame.

  In the present embodiment, the criterion for signal interruption in the signal interruption processing circuit 314 is a continuous loss state of a plurality of frames. By doing so, it is possible to distinguish between a frame loss due to a code error or the like in the transmission path 93 and a frame loss due to discovery, and it is possible to prevent unnecessary CPRI signal transmission from being stopped.

  In the present embodiment, it is estimated that the time until the link disconnection and recovery due to discovery is about 1 ms, so that the link disconnection continues longer than that time due to the failure between the OLT 34 and the ONU 35. Whether it is done or not.

  Note that the processing at the time of frame loss in the downlink direction in the present embodiment is the same as that in the first embodiment.

  In this way, even when TDM-PON is used as a relay line, it is possible to transmit without interrupting the CPRI link.

  The present invention can be applied to the information communication industry.

11: Radio modulation / demodulation circuit 12, 22: Network interface 21: Radio transmission / reception circuit 31: First relay device 32: Second relay device 34: OLT
35: ONU
311, 321: CPRI interface 312, 322: format conversion circuit 313, 323: transmission line interface 314 and 324: signal disconnection processing circuit 41: frame loss detection circuit 42: simulated frame generation circuit 43: frame monitor circuit 44: frame switching circuit 91: Radio control unit (REC)
92: Radio equipment (RE)
93: Transmission path 94: Small cell

Claims (8)

A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission system,
A first relay device that converts the signal of the predetermined format from the first communication device into a predetermined transmission frame and transfers it;
A second relay device that converts the transmission frame transferred by the first relay device into a signal of the predetermined format and transfers the signal to the second communication device;
With
When a link break occurs between the first relay device and the second relay device,
The first relay device generates a simulated frame that simulates a transmission frame from the second relay device, converts the simulated frame into the signal of the predetermined format, and transmits the signal to the first communication device.
The second relay device generates a simulated frame that simulates a transmission frame from the first relay device, converts the simulated frame into the signal of the predetermined format, and transmits the signal to the second communication device.
Relay transmission system. The transmission line includes a passive optical network that transmits an optical signal using time division multiplexing,
The first relay device, which is connected with the passive optical optical network device provided in the network, if the link break due di Sukabari processing occurred, and the first relay device of the second switching device Link break information indicating that a link break has occurred between the second relay devices,
The second repeater is connected to an optical subscriber line network device provided in the passive optical network, and stops receiving a transmission frame to the optical subscriber line network device when receiving the link disconnection information.
The relay transmission system according to claim 1. A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay device,
A signal transmission / reception unit for transmitting / receiving a signal in a predetermined format to / from the first communication device;
A frame transmission / reception unit for transmitting / receiving a predetermined transmission frame to / from another relay device arranged in a transmission path with the second communication device;
The signal of the predetermined format received by the signal transmission / reception unit is converted into the transmission frame and output to the frame transmission / reception unit, and the transmission frame received by the frame transmission / reception unit is converted to the signal of the predetermined format. A conversion unit for outputting to the transmission / reception unit;
When it is detected that a frame loss has occurred in the transmission frame received by the frame transmission / reception unit, a simulated frame simulating the transmission frame from the other relay device is generated, and a signal interruption to be output to the conversion unit as the transmission frame is generated. A processing unit;
A relay device comprising: When the signal loss processing unit detects that the frame loss of the transmission frame received by the frame transmission / reception unit is eliminated and the transmission frame received by the frame transmission / reception unit is normal, the signal disconnection processing unit detects the transmission frame including link recovery information. Generate and transmit from the frame transmission / reception unit to the other relay device,
The relay device according to claim 3. In the signal disconnection processing unit, the sequence number of the transmission frame received by the frame transmission / reception unit is discontinuous, or the arrival of the transmission frame received by the frame transmission / reception unit is longer than a predetermined time. To detect that a frame loss has occurred,
The relay device according to claim 3 or 4. The signal of the predetermined format is CPRI (Common Public Radio Interface) or ORI (Open Radio equipment Interface).
The relay device according to any one of claims 3 to 5. A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission method for a relay transmission system,
The first relay device converts the predetermined format signal from the first communication device into a predetermined transmission frame and transfers it, and the second relay device transmits the transmission frame transferred by the first relay device. A relay procedure for converting the signal into a signal of the predetermined format and transferring it to the second communication device,
In the relay procedure, a signal disconnection detection procedure for detecting that a link disconnection has occurred between the first relay device and the second relay device;
When a link break occurs, the first relay device generates a simulated frame that simulates a transmission frame from the second relay device, converts the simulated frame into the signal of the predetermined format, and And the second relay device generates a simulated frame that simulates the transmission frame from the first relay device, converts the simulated frame into the signal of the predetermined format, and the second relay device. A simulated frame transmission procedure to be transmitted to the communication device of
The relay transmission method which has in order. A link is formed between the first communication device and the second communication device via the transmission line, and is arranged on the transmission line in the wireless base station system that transmits and receives a signal of a predetermined format, and relays communication. A relay transmission method for the relay device,
A signal interruption detection procedure for detecting that a frame loss has occurred in a predetermined transmission frame received from another relay apparatus arranged in a transmission path with the second communication apparatus;
When a frame loss occurs, a simulated frame simulating a transmission frame from the other relay device is generated instead of a signal of a predetermined format transmitted to the first communication device, and the simulated frame is A simulated frame transmission procedure for converting the signal into a predetermined signal and transmitting the signal to the first communication device;
The relay transmission method which has in order.

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