JP2021061575A - Relay system, transmission device, and reception device - Google Patents

Abstract

To achieve both high-speed communication and the use of long-distance fiber optic cables.SOLUTION: A relay system includes a transmission device that receives an original signal and transmits an optical signal, and a reception device that receives the optical signal and restores the original signal. The transmission device includes a first data rate conversion device that converts the original signal into a plurality of low-rate signals that are slower than the original signal, and a plurality of optical transmitters that convert the low-rate signal obtained by the first data rate conversion unit into a low-rate optical signal and transmit the signal. The reception device includes the same number of optical receivers as that of the optical transmitters, which convert the low-rate optical signal into the low-rate signal, and a second data rate conversion unit that restores the original signal on the basis of the plurality of low-rate signals obtained by the optical receivers.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a relay system, a transmitting device, and a receiving device.

Optical communication systems may be used in mobile fronthaul (MFH), mobile midhaul (MMH), and mobile backhaul (MBH) included in mobile communication networks. For example, Patent Document 1 discloses a relay transmission system in MFH using PON (Passive Optical Network).

International Publication No. 2017/073547 Japanese Unexamined Patent Publication No. 11-346191

In applying the optical communication system to the mobile communication network, it is conceivable that the existing dark fiber will be used. For example, the length of MFH is generally less than 20 km. However, when using dark fiber, it is conceivable to extend it to 30 km to 40 km. On the other hand, the communication speed in CPRI (Common Public Radio Interface) used in 4G (4th generation mobile communication system) was 2.4576 Gbps (option 2) to 9.8304 Gbps (option 5), but 5 G (fifth). The speed of eCPRI (enhanced CPRI) used in (generational mobile communication systems) will be increased to 25.78125 Gbps. As the communication speed increases, the reception sensitivity of the optical transceiver deteriorates and the dispersion penalty increases. Therefore, the power budget deteriorates, and it becomes difficult to use a long-distance optical fiber cable.

The relay system according to one aspect of the present disclosure is a relay system that relays communication between the first device and the second device, and receives the original signal transmitted from the first device and receives the original signal. A transmission device that transmits an optical signal corresponding to the original signal, and a transmission device that receives the optical signal transmitted from the transmission device and transmits the original signal that is restored based on the received optical signal to the second device. The transmitting device is obtained by a first data rate conversion unit that converts the original signal into a plurality of low-rate signals slower than the original signal, and the first data rate conversion unit. A plurality of optical transmitters that convert the low-rate signal into a low-rate optical signal and transmit the data, and a plurality of the low-rate optical signals transmitted from the plurality of optical transmitters are multiplexed and transmitted as a multiplexed optical signal. The first data rate conversion unit includes a multiplexer and generates a plurality of divided data by distributing the original signal in block units, and each of the generated divided data is used as a low rate signal, and the first data rate conversion unit is used. Output at a second speed slower than the speed, the receiving device receives the multiplexed optical signal transmitted by the multiplexer, and converts the received multiplexed optical signal into the plurality of low-rate optical signals. The demultiplexer, the same number of optical receivers as the optical transmitter that converts the low-rate optical signal generated by the demultiplexer into the low-rate signal, and the plurality of the optical receivers obtained by the plurality of the optical receivers. The second data rate converter includes a second data rate converter that restores the original signal based on the low rate signal, and the second data rate converter is the low output from each of the queue and the plurality of optical receivers. A writing unit that converts a rate signal into the divided data and sequentially writes the divided data to the queue at the second speed, and a writing unit that sequentially reads the divided data from the queue at the first speed and combines the divided data. It includes a reading unit that restores the original signal.

The transmission device according to one aspect of the present disclosure is a transmission device that receives an original signal transmitted from the first device and transmits an optical signal corresponding to the received original signal, and the original signal is transmitted to the original signal. A first data rate conversion unit that converts a plurality of low-rate signals slower than the original signal, and a plurality of optical transmissions that convert the low-rate signal obtained by the first data rate conversion unit into a low-rate optical signal and transmit the signal. The first data rate conversion unit includes a device and a multiplexer that multiplexes the plurality of low-rate optical signals transmitted from the plurality of optical transmitters and transmits them as a multiplexed optical signal, and the first data rate conversion unit converts the original signal. A plurality of divided data are generated by distributing the divided data in block units, and each of the generated divided data is output as a low rate signal at a second speed lower than the first speed.

The receiving device according to one aspect of the present disclosure receives the multiplexed optical signal generated based on the original signal, and transmits the original signal restored based on the received multiplexed optical signal to the second device. A demultiplexer that receives the multiplexed optical signal and converts the received multiplexed optical signal into a plurality of low-rate optical signals, and the low-rate light generated by the demultiplexer. It includes a plurality of optical receivers that convert a signal into a low-rate signal, and a second data rate converter that restores the original signal based on the plurality of the low-rate signals obtained by the plurality of optical receivers. The second data rate conversion unit converts the low rate signal output from each of the queue and the plurality of optical receivers into divided data, and converts the divided data into the queue at a speed lower than the first speed. It includes a writing unit that sequentially writes at two speeds, and a reading unit that sequentially reads the divided data from the queue at the first speed and restores the original signal by combining the divided data.

The present disclosure can be realized not only as a transmission device having a characteristic configuration as described above, but also as a transmission method in which a characteristic process in the transmission device is a step, or a computer is made to execute such a step. It can be realized as a computer program for. The present disclosure can be realized not only as a receiving device having a characteristic configuration as described above, but also as a receiving method in which characteristic processing in the receiving device is a step, or a computer is made to execute such a step. It can be realized as a computer program for. Further, a part or all of the transmitting device may be realized as a semiconductor integrated circuit, a part or all of the receiving device may be realized as a semiconductor integrated circuit, or a relay system including a transmitting device and a receiving device may be realized. it can.

According to the present disclosure, both high-speed communication and the use of long-distance optical fiber cables can be realized.

It is a schematic diagram which shows an example of the structure of the communication system which concerns on embodiment. It is a block diagram which shows the structure of the relay system which concerns on embodiment. It is a functional block diagram which shows an example of the function as a transmission device of the WDM concentrator according to an embodiment. It is a figure for demonstrating the outline of the half-rate conversion using a code word marker. It is a timing chart which shows an example of the signal processing by the function as the transmission device of the WDM concentrator according to the embodiment. It is a graph which shows an example of the relationship between a signal wavelength and a relative delay in an optical fiber. It is a graph which shows an example of the relative delay in two wavelengths of ± 10 nm with respect to a wavelength λ. It is a functional block diagram which shows an example of the function as a receiving device of the WDM line concentrator which concerns on embodiment. It is a timing chart which shows an example of the signal processing by the function as the receiving device of the WDM line concentrator which concerns on embodiment. It is a timing chart which shows the 2nd modification of the signal processing by the function as the receiving device of the WDM concentrator which concerns on embodiment. It is a timing chart which shows the 3rd modification of the signal processing by the function as the transmission device of the WDM transmission device which concerns on embodiment. It is a timing chart which shows the 3rd modification of the signal processing by the function as the receiving device of the WDM line concentrator which concerns on embodiment. It is a figure for demonstrating an example of the order check of a block.

<Outline of Embodiments of the present disclosure>
Hereinafter, the outlines of the embodiments of the present disclosure will be listed and described.

(1) The relay system according to the present embodiment is a relay system that relays communication between the first device and the second device, and receives the original signal transmitted from the first device and receives the original signal. A transmission device that transmits an optical signal corresponding to the original signal, and a transmission device that receives the optical signal transmitted from the transmission device and transmits the original signal that is restored based on the received optical signal to the second device. The transmitting device is obtained by a first data rate conversion unit that converts the original signal into a plurality of low-rate signals slower than the original signal, and the first data rate conversion unit. A plurality of optical transmitters that convert the low-rate signal into a low-rate optical signal and transmit the data, and a plurality of the low-rate optical signals transmitted from the plurality of optical transmitters are multiplexed and transmitted as a multiplexed optical signal. The first data rate conversion unit includes a multiplexer and generates a plurality of divided data by distributing the original signal in block units, and each of the generated divided data is used as a low rate signal, and the first data rate conversion unit is used. Output at a second speed slower than the speed, the receiving device receives the multiplexed optical signal transmitted by the multiplexer, and converts the received multiplexed optical signal into the plurality of low-rate optical signals. The demultiplexer, the same number of optical receivers as the optical transmitter that converts the low-rate optical signal generated by the demultiplexer into the low-rate signal, and the plurality of the optical receivers obtained by the plurality of the optical receivers. The second data rate converter includes a second data rate converter that restores the original signal based on the low rate signal, and the second data rate converter is the low output from each of the queue and the plurality of optical receivers. A writing unit that converts a rate signal into the divided data and sequentially writes the divided data to the queue at the second speed, and a writing unit that sequentially reads the divided data from the queue at the first speed and combines the divided data. It includes a reading unit that restores the original signal. With the above configuration, the transmitting device generates a plurality of low-speed low-rate optical signals from the original signal, and transmits a multiplexed optical signal obtained by multiplexing the plurality of low-rate optical signals. The receiving device receives the multiplexed optical signal, extracts a plurality of low-rate optical signals from the multiplexed optical signal, and restores a high-speed original signal from the plurality of low-rate optical signals. That is, low-speed optical communication is performed between the transmitting device and the receiving device. Therefore, deterioration of the power budget (increase in dispersion penalty and deterioration in reception sensitivity) is suppressed, and both high-speed communication and use of a long-distance optical fiber cable can be realized.

(2) In the relay system according to the present embodiment, the first data rate conversion unit divides the original signal into blocks of a predetermined number of bits to generate the divided data, and the second data rate conversion unit The writing unit further includes a boundary detecting unit for detecting the boundary of the block in the low rate signal, and the writing unit converts the low rate signal in which the boundary of the block is detected by the boundary detecting unit into the divided data. You may. By processing in block units, synchronization of divided data becomes easy.

(3) In the relay system according to the present embodiment, the original signal is a forward error correction-encoded signal including a plurality of code blocks having a predetermined number of bits, and the first data rate conversion unit converts the original signal into the original signal. The original signal may be divided into the blocks based on the included code blocks. Thereby, the boundary of the block can be easily detected by using the code block included in the forward error correction coded signal (hereinafter, referred to as “FEC signal”). In the FEC signal, since the DC balance is adjusted in the coding, an appropriate DC balance is maintained in the divided data.

(4) In the relay system according to the present embodiment, the original signal is a signal encoded by RS (528,514) FEC, and the first data rate conversion unit is a code word included in the original signal. The boundary of a plurality of blocks included in the original signal may be detected based on the marker, and the original signal may be divided into the block units. By using codeword markers, block boundaries can be quickly detected without decoding the FEC-encoded original signal.

(5) In the relay system according to the present embodiment, the boundary detection unit detects the code word marker included in the low rate signal, and detects the boundary of the block based on the detected code word marker. You may. By using codeword markers, block boundaries can be quickly detected without decoding FEC-encoded low-rate signals.

(6) In the relay system according to the present embodiment, the first data rate conversion unit is among N blocks or divided blocks in which the blocks are divided, which are arranged in order in the original signal and are multiples of 1024. The first low rate signal including a part of the block or the divided block, and the block or the divided block included in the first low rate signal among the N blocks or the divided blocks are excluded. A second low rate signal including the block or the divided block is generated according to an allocation rule that satisfies the first condition, the second condition, and the third condition, and the first condition is that the first low rate signal is the said. The block includes two consecutive blocks or the division block among the N blocks or the division block, and the second condition is that the first low rate signal and the second low rate signal are included in each of the first low rate signal and the second low rate signal. The order of the blocks or the divided blocks in the original signal is not changed, and the third condition is that the number of the blocks or the divided blocks included in the first low rate signal is N / 2 or N / 2 + 1. The number of the block or the divided block included in the second low rate signal is N / 2 or N / 2-1. The second data rate conversion unit is the first queue and the first queue. The writing unit includes two queues, the writing unit writes the block or the divided block included in the first low rate signal to the first queue, and the block or the divided block included in the second low rate signal. Is written to the second queue, and the reading unit reads the block or the divided block from each of the first queue and the second queue based on the allocation rule, and the read block or the divided block. The original signal may be restored by combining blocks in order. With the above configuration, codeword markers are alternately assigned to the two queues. Therefore, block boundaries can be quickly detected on any channel without decoding the FEC-encoded low-rate signal.

(7) In the relay system according to the present embodiment, the first data rate conversion unit divides a plurality of the blocks arranged in order in the original signal or a divided block obtained by dividing the blocks into one out of about 1024. And K low-rate signals other than 1024 are distributed according to the allocation rules satisfying the first condition, the second condition, and the third condition, and the first condition is each of the K low-rate signals. The second condition is that the order of the blocks or the divided blocks in the original signal is not changed, and the second condition is N in which the number of the blocks or the divided blocks included in the original signal is a multiple of 1024. In this case, the number of the blocks or the divided blocks included in each of the K low-rate signals is N / K or N / K ± 1, and the third condition is the code word marker. Is sequentially assigned to the K low-rate signals, the second data rate conversion unit includes K queues, and the writing unit receives each of the K low-rate signals. Corresponding to each of the K queues, the block or the divided block included in the low rate signal is sequentially written to the corresponding queue, and the reading unit assigns the block from each of the K queues. The block or the divided block may be read out according to a rule, and the read block or the divided block may be combined in order to restore the original signal. With the above configuration, CWMs are sequentially assigned to K queues. Therefore, by detecting the CWM in the receiving device, it is not necessary to FEC decode each of the K channels, and the FEC block can be quickly restored.

(8) In the relay system according to the present embodiment, each of the optical transmitters transmits the low-rate optical signal to which the initialization signal is added at the head, and the reading unit is based on the initialization signal. , The original signal may be restored by combining the blocks in the order of being read from the queue. As a result, the second reading unit can read the blocks in the correct order by using the initialization signal. Therefore, even when the transmission time of one block is equal to or shorter than the transmission delay difference between the transmission channels of the low-rate signal, the transmission delay difference is absorbed and the read timing of the divided data is synchronized between the low-rate signals. Can be taken.

(9) In the relay system according to the present embodiment, the original signal is a 64B / 66B encoded signal including a plurality of 66-bit blocks, and the first data rate conversion unit is included in the original signal. The original signal may be divided into the blocks based on the 66-bit block. Thereby, the boundary of the block can be easily detected by using the code block included in the 64B / 66B coded signal (hereinafter, referred to as “64B / 66B signal”). Further, since the error correction code is not included, low delay can be realized in the relay of the original signal.

(10) In the relay system according to the present embodiment, the first speed may be 25.78125 Gbps and the second speed may be 12.890625 Gbps. As a result, the transmission speed of the multiplexed optical signal between the transmitting device and the receiving device becomes 12.890625 Gbps. Therefore, the power budget can be secured even if a long-distance optical fiber cable exceeding 20 km is used.

(11) In the relay system according to the present embodiment, the transmission device receives n of the original signals, includes n of the first data rate conversion units, and combines the first data rate conversion unit with one. On the other hand, m of the optical transmitters are provided, and the multiplexer multiplexes n × m low-rate optical signals transmitted from the optical transmitter and transmits them as the multiplexed optical signals, and the receiving device. Includes n second data rate converters, m are provided for one second data rate converter, and the demultiplexer delivers the multiplexed optical signal. It may be converted into the n × m low-rate optical signals, and each of the low-rate optical signals may be input to each of the optical receivers. As a result, n × m low-rate optical signals can be multiplexed and transmitted while suppressing deterioration of the power budget. Further, since the dispersion penalty can be suppressed, it can be used even in a wavelength band having a large wavelength dispersion, and a wavelength can be selected with a high degree of freedom.

(12) The transmission device according to the present embodiment is a transmission device that receives the original signal transmitted from the first device and transmits an optical signal corresponding to the received original signal, and the original signal is transmitted. A first data rate conversion unit that converts a plurality of low-rate signals slower than the original signal, and a plurality of lights that convert the low-rate signal obtained by the first data rate conversion unit into a low-rate optical signal and transmit the signal. The first data rate conversion unit includes a transmitter and a multiplexer that multiplexes the plurality of low-rate optical signals transmitted from the plurality of optical transmitters and transmits them as a multiplexed optical signal. Is distributed in block units to generate a plurality of divided data, and each of the generated divided data is output as a low rate signal at a second speed lower than the first speed. With the above configuration, the transmitting device generates a plurality of low-speed low-rate optical signals from the original signal, and transmits a multiplexed optical signal obtained by multiplexing the plurality of low-rate optical signals. That is, a low-speed multiplexed optical signal is transmitted from the transmitting device. Therefore, the increase in the dispersion penalty is suppressed, and both high-speed communication and the use of a long-distance optical fiber cable can be realized.

(13) The receiving device according to the present embodiment receives the multiplexed optical signal generated based on the original signal, and transfers the original signal restored based on the received multiplexed optical signal to the second device. A receiving device for transmitting, which receives the multiplexed optical signal and converts the received multiplexed optical signal into a plurality of low-rate optical signals, and the low-rate generated by the demultiplexer. A plurality of optical receivers that convert an optical signal into a low-rate signal, and a second data rate converter that restores the original signal based on the plurality of the low-rate signals obtained by the plurality of optical receivers. The second data rate conversion unit converts the low rate signal output from each of the queue and the plurality of optical receivers into divided data, and converts the divided data into the queue at a speed lower than the first speed. It includes a writing unit that sequentially writes at a second speed, and a reading unit that sequentially reads the divided data from the queue at the first speed and restores the original signal by combining the divided data. With the above configuration, the receiving device receives the multiplexed optical signal, extracts a plurality of low-rate optical signals from the multiplexed optical signal, and restores a high-speed original signal from the plurality of low-rate optical signals. That is, the receiving device receives the low-speed multiplexed optical signal. Therefore, deterioration of reception sensitivity is suppressed, and both high-speed communication and use of a long-distance optical fiber cable can be realized.

<Details of Embodiments of the present disclosure>
Hereinafter, the details of the embodiments of the present disclosure will be described with reference to the drawings. In addition, at least a part of the embodiments described below may be arbitrarily combined.

[1. Relay system configuration]
FIG. 1 is a schematic diagram showing an example of the configuration of the communication system 10 according to the present embodiment. The communication system 10 shown in FIG. 1 is a mobile front hall. The communication system 10 includes a remote radio head (hereinafter referred to as “RRH”) 20 and a baseband device (hereinafter referred to as “BBU”) 30. The RRH20 is an antenna of a radio base station, and is installed so that, for example, three RRH20s having a radio wave transmission / reception range of 120 ° and a radio wave transmission / reception range of 360 ° are set. The BBU 30 is a signal processing unit of a radio base station, and for example, a plurality of RRH20s (three in the example of FIG. 1) are connected to one BBU30.

The communication system 10 includes a relay system 100 between the RRH 20 and the BBU 30. The relay system 100 relays the communication between the RRH 20 and the BBU 30. In this embodiment, the relay system 100 applied to the MFH will be described, but the present invention is not limited to this. The relay system 100 may be applied to MBH or MMH.

The relay system 100 includes WDM concentrators 200A and 200B. The WDM concentrator 200A is connected to each of the three RRH20s by an optical fiber cable 21. The WDM concentrator 200B is connected to the BBU 30 by three optical fiber cables 31. The WDM concentrators 200A and 200B are connected to each other via one optical fiber cable 201. The optical fiber cable 201 has a length of, for example, 20 km or more. For the optical fiber cable 201, for example, dark fiber is used.

FIG. 2 is a block diagram showing the configuration of the relay system 100 according to the present embodiment. As shown in FIG. 2, the WDM concentrator 200A includes three optical transceivers 210A, three data rate conversion circuits 220A, six optical transceivers 231A and 232A, and one multiplexer 240A. The WDM concentrator 200B includes three optical transceivers 210B, three data rate conversion circuits 220B, six optical transceivers 231B and 232B, and one multiplexer 240B.

The optical transceivers 210A, 231A, 232A, 210B, 231B, 232B mutually convert an optical signal and an electric signal. That is, each of the optical transceivers 210A, 231A, 232A, 210B, 231B, and 232B converts the input optical signal into an electric signal and outputs it, and converts the input electric signal into an optical signal and outputs it. Each of the optical transceivers 210A, 231A, 232A, 210B, 231B, and 232B is an optical transmitter and an optical receiver. The optical transmitter converts the input electric signal into an optical signal and outputs it. The optical receiver converts the input optical signal into an electric signal and outputs it.

The data rate conversion circuits 220A and 220B are signal processing circuits. The data rate conversion circuits 220A and 220B are made of, for example, logic circuit devices designed to enable specific information processing, and are, for example, among ASIC (Application Specific Integrated Circuit) and FPGA (Field Programmable Gate Array). Includes at least one.

The WDM concentrator 200A will be described. Each of the optical transceivers 210A is connected to the RRH 20 via an optical fiber cable 21 (see FIG. 1). One optical transceiver 210A, one data rate conversion circuit 220A, and two optical transceivers 231A and 232A correspond to one RRH20. That is, the original signal transmitted from one RRH20 is given to one data rate conversion circuit 220A through one optical transceiver 210A corresponding to this RRH20. In the data rate conversion circuit 220A, the original signal is separated into two low-rate signals at half the speed of the original signal and output to the two optical transceivers 231A and 232A, respectively. The optical transceivers 231A and 232A convert a low-rate signal, which is an electric signal, into a low-rate optical signal, and output two low-rate optical signals to the multiplexer 240A. The multiplexer 240A multiplexes a plurality of low-rate optical signals by wavelength division multiplexing (WDM) and outputs them as multiplexed optical signals. That is, the wavelengths of the six low-rate signals output from the three data rate conversion circuits 220A are different from each other. The multiplexer 240A is connected to the WDM concentrator 200B, which is an opposite device, via the optical fiber cable 201. The multiplexed optical signal output from the multiplexer 240A is transmitted through the optical fiber cable 201 at half the speed of the original signal and is given to the WDM concentrator 200B.

The multiplexer 240A also has a function as a demultiplexer. The multiplexed optical signal transmitted from the WDM concentrator 200B is separated into six low-rate optical signals by the multiplexer 240A and given to the optical transceivers 231A and 232A, respectively. The optical transceivers 231A and 232A corresponding to one data rate conversion circuit 220A convert a low rate optical signal which is an optical signal into a low rate signal which is an electric signal, and convert two low rate signals into a data rate conversion circuit 220A. Output. In the data rate conversion circuit 220A, two low-rate signals are combined to restore one original signal that is twice as fast as the low-rate signal, and output it to one optical transceiver 210A. The optical transceiver 210A converts the original signal, which is an electric signal, into an optical signal and transmits it to the RRH20.

Next, the WDM concentrator 200B will be described. Each of the optical transceivers 210B is connected to the BBU 30 via three optical fiber cables 31 (see FIG. 1). A different optical signal (original signal) is output from the BBU 30 to each of the three optical fiber cables 31. One optical transceiver 210B, one data rate conversion circuit 220B, and two optical transceivers 231B and 232B correspond to one optical fiber cable 31. That is, the original signal transmitted from one optical fiber cable 31 is given to one data rate conversion circuit 220B through one optical transceiver 210B corresponding to this optical fiber cable 31. In the data rate conversion circuit 220B, the original signal is separated into two low-rate signals at half the speed of the original signal and output to the two optical transceivers 231B and 232B, respectively. The optical transceivers 231B and 232B convert a low-rate signal, which is an electric signal, into a low-rate optical signal, and output two low-rate optical signals to the multiplexer 240B. The multiplexer 240A multiplexes a plurality of low-rate optical signals by wavelength division multiplexing (WDM) and outputs them as multiplexed optical signals. That is, the wavelengths of the six low-rate signals output from the three data rate conversion circuits 220B are different from each other. The multiplexer 240B is connected to the WDM concentrator 200A, which is an opposite device, via the optical fiber cable 201. The multiplexed optical signal output from the multiplexer 240B is transmitted through the optical fiber cable 201 at half the speed of the original signal and is given to the WDM concentrator 200A.

The multiplexer 240B also has a function as a demultiplexer. The multiplexed optical signal transmitted from the WDM concentrator 200A is separated into six low-rate optical signals by the multiplexer 240B and given to the optical transceivers 231B and 232B, respectively. The optical transceivers 231B and 232B corresponding to one data rate conversion circuit 220B convert a low rate optical signal which is an optical signal into a low rate signal which is an electric signal, and convert two low rate signals into a data rate conversion circuit 220B. Output. In the data rate conversion circuit 220B, two low-rate signals are combined to restore one original signal at twice the speed of the low-rate signal and output it to one optical transceiver 210A. The optical transceiver 210B converts the original signal, which is an electric signal, into an optical signal and transmits it to the BBU 30.

The WDM concentrators 200A and 200B have similar configurations to each other. That is, the configuration of the optical transceiver 210A is the same as the configuration of the optical transceiver 210B, and the configuration of the optical transceivers 231A and 232A is the same as the configuration of the optical transceivers 231B and 232B. The configuration of the data rate conversion circuit 220A is the same as the configuration of the data rate conversion circuit 220B. Further, the configuration of the multiplexer 240A is the same as the configuration of the multiplexer 240B. Hereinafter, the WDM concentrators 200A and 200B are collectively referred to as the WDM concentrator 200, the optical transceivers 210A and 210B are collectively referred to as the optical transceiver 210, the optical transceivers 231A and 231B are collectively referred to as the optical transceiver 231 and the optical transceivers 232A and 232B are collectively referred to as optical transceivers 232A and 232B. The transceivers 232 are collectively referred to, the data rate conversion circuits 220A and 220B are collectively referred to as a data rate conversion circuit 220, and the multiplexers 240A and 240B are collectively referred to as a multiplexer 240.
Different wavelengths are set for the low-rate optical signals transmitted from the optical transceivers 231A and 232A and 231B and 232B, and the low-rate optical signals are multiplexed by wavelength division multiplexing (WDM).

Here, for example, in a 5G mobile front hall, half-rate conversion (hereinafter, “HRC”) for multiplexing signals of a plurality of 25 Gigabit Ethernet (“Ethernet” is a registered trademark) channel (hereinafter, “25GE channel”) by WDM. The system will be explained. In each 25GE channel, the WDM concentrator 200A divides a single stream of 25.78125 Gbps (hereinafter abbreviated as "25.8 Gbps") into two streams of 12.890625 Gbps (hereinafter abbreviated as "12.9 Gbps"). Then, it is multiplexed by WDM and transmitted. When the WDM concentrator 200B receives the multiplexed signal, it combines the two 12.9 Gbps streams and reverses them into a single 25.8 Gbps stream. Due to such HRC, the baud rate of conversion is lowered, so that the dispersion penalty is reduced and the reception sensitivity is improved. In theory, the variance penalty for 12.9 Gbps NRZ (non-return-to-zero) modulation is proportional to the square of the baud rate, and the variance penalty for 10.3 Gbps NRZ modulation is 1.56 (= (12.9 / 12.9 /)). 10.3) ² ) times, a transmitter equivalent to 10GBASE-ZR can support a transmission distance of 50km if power budget is allowed.

[2. Transmitter]
The WDM concentrating device 200 has a function as a transmitting device that transmits an optical signal to a receiving device that is an opposite device. FIG. 3 is a functional block diagram showing an example of the function of the WDM concentrator 200 according to the present embodiment as a transmission device. The data rate conversion circuit 220 has functions of a parallel conversion unit 311, a boundary detection unit 312, a writing unit 313, cues 314a and 314b, a reading unit 315, and a serial conversion unit 316a and 316b.

Here, RS-FEC (Reed-Solomon Forward Error Correction) encoded data (hereinafter, also referred to as “eCPRI signal”) conforming to eCPRI is transmitted from RRH20 by 25GE, and the eCPRI signal is transmitted at 25.8 Gbps in BBU30. An example of receiving with will be described.

The optical transceiver 210 complies with the 25GBASE-LR specified in IEEE802.3. The optical transceiver 210 receives the eCPRI optical signal, which is a serial signal, converts it into a serial electric signal (eCPRI signal), and outputs the signal. The transmission speed of the eCPRI signal output from the optical transceiver 210 is 25.8 Gbps.

The eCPRI signal of the serial signal is given to the parallel conversion unit 311. The parallel conversion unit 311 extracts clock data from the eCPRI signal of the serial signal, performs timing reproduction, and converts the serial data into parallel data (hereinafter, referred to as “reproduction data”) at a clock rate of 25.8 Gbps. The clock rate of 25.8 Gbps means, for example, 25.8 / 66 GHz in the case of 66-bit parallel data.

In this embodiment, the two streams are combined using a codeword marker (CWM) as defined in 25GBASE-R. RS (528,514) FEC is used for 25GE. The block length of the RS (528,514) FEC is 5280 bits, and a CWM is arranged every 1024 blocks. The CWM is 257-bit fixed data, and in the present embodiment, the receiving side identifies the coded block (hereinafter, referred to as “FEC block”) by detecting the CWM. In the process of dividing one 25.8 Gbps stream into two 12.9 Gbps streams, the CWM is alternately distributed to both streams. In addition, it detects the boundaries of FEC blocks in the stream by detecting CWM from the 12.9 Gbps stream and correctly combines it into a single 25.8 Gbps stream. As a result, the boundary of the FEC block can be detected without decoding the FEC, so that low-delay processing becomes possible.

The reproduced data is given to the boundary detection unit 312. The boundary detection unit 312 detects the CWM included in the reproduced data. FIG. 4 is a diagram for explaining an outline of HRC using CWM. The eCPRI signal, which is RS-FEC RS (528,514) encoded data, has a configuration in which a plurality of FEC blocks are arranged side by side. In CWM, numbers # 1 to # 1024 are assigned to each of the 1024 FEC blocks. The FEC blocks # 1 to # 1023 do not contain CWM, and only the FEC blocks # 1024 contain CWM. The first 257 bits in the # 1024 FEC block is CWM.

The boundary detection unit 312 detects the CWM from the given reproduction data and detects the boundary of the FEC block. The boundary detection unit 312 divides the reproduced data into FEC blocks and generates the divided data. The boundary detection unit 312 outputs each divided data (FEC block) to the writing unit 313 so that the CWM is arranged at a predetermined position. That is, in the present embodiment, each divided data is adjusted so that the first bit of the CWM is arranged in the first bit of the parallel data. The writing unit 313 writes the given divided data to the two cues 314a and 314b at a clock rate of 25.8 Gbps. Each of the queues 314a and 314b has a data capacity of 2 blocks or more.

FIG. 5 is a timing chart showing an example of signal processing by the function of the WDM concentrator 200 according to the present embodiment as a transmission device. The boundary detection unit 312 divides the reproduced data into block units. The writing unit 313 alternately writes FEC blocks (divided data) of parallel data to the two cues 314a and 314b. However, the # 1024 FEC block and the next playback data # 1 FEC block are written to the same queue. By such a write operation, the FEC block of # 1024 containing the CWM is alternately assigned to the queues 314a and 314b.

It is not necessary to divide the reproduced data into FEC blocks and allocate each FEC block to the queues 314a and 314b alternately. The data obtained by further dividing the FEC block (divided block) may be distributed to the queues 314a and 314b. In a specific example, the reproduction data is divided into 2640-bit divided blocks (hereinafter referred to as "1 / 2FEC blocks") in which the FEC block is further divided into two, and the 1 / 2FEC blocks are alternately placed in the queues 314a and 314b. Can be sorted. In this case, the 1 / 2FEC block containing the CWM is written to the same queue as the immediately preceding 1 / 2FEC block. The number of divisions of the FEC block is not limited to 2. Since it is sufficient that the dividing block can include CWM, the size of the dividing block may be 257 bits or more. That is, the number of divisions of the FEC block may be 20 or less. Further, each of the queues 314a and 314b may have a data capacity of two or more divided blocks.

See FIG. 3 again. The reading unit 315 reads the FEC block or the divided block from each of the two cues 314a and 314b at a clock rate of 12.9 Gbps. The clock rate of 25.8 Gbps is an example of the first speed, and the clock rate of 12.9 Gbps is an example of the second speed. For the queues 314a and 314b, the writing and reading of the FEC block or the divided block is executed by the FIFO (First In, First Out). The queues 314a and 314b are temporary storage units that are read by the reading unit 315 in the order in which user data (blocks) are written from the writing unit 313, and may be, for example, a buffer that can hold data for two or more blocks. In this case, the data rate conversion circuit 220 includes two buffers (referred to as A and B), and the writing unit 313 alternately writes the block data to the buffers A and B at the first rate (however, the CWM of # 1024). The FEC block or division block containing the above is written in the same buffer as the immediately following block (in the case of the FEC block, the block # 1), and the reading unit 315 reads the block data written in the buffers A and B at the second rate. It may be a thing.

The reading unit 315 outputs the FEC block or the divided block read from each of the two cues 314a and 314b to the corresponding channels. That is, the FEC block or division block read from the queue 314a is output to the serial conversion unit 316a as one signal, and the FEC block or division block read from the queue 314b is output to the serial conversion unit 316b as another signal. It is output. As a result, two low-rate signals (parallel signals) are generated at a clock rate of 12.9 Gbps. The reading unit 315 gives two parallel signals of 12.9 Gbps to each of the serial conversion units 316a and 316b. Each of the serial conversion units 316a and 316b converts the parallel signal into a serial signal, and outputs the converted low-rate signal to each of the optical transceivers 231 and 232. It should be noted that instead of one reading unit 315, reading units may be provided individually for each of the two channels.

Each of the optical transceivers 231, 322 converts a low-rate signal of an electric signal into a low-rate optical signal and outputs the signal. That is, the optical transceivers 231 and 232 are part of two low-rate optical signal transmission channels, and the optical transceivers 231 and 232 output two data streams. The transmission speed of the low-rate optical signal output from the optical transceiver 210 is 12.9 Gbps. The low rate signal is generated by combining every other FEC block or division block (only the FEC block or division block containing the CWM of # 1024 is continuously combined with the immediately preceding block). Explaining with the example of FIG. 5, one low rate signal is generated by combining odd-numbered FEC blocks (FEC_1, FEC_3, FEC_5, FEC_7, ...), And even-numbered FEC blocks (FEC_2, FEC_4, FEC_6, FEC_8, ...) Is combined to generate another low rate signal. Although not shown, the 1024th FEC block FEC_1024 is combined with the following odd-numbered FEC blocks FEC_1, FEC_3, FEC_5, FEC_7, ... , FEC_6, FEC_8, ...

さらにＴ_ｄｉｆｆは式（３）で与えられる。

式（１）〜（３）により、式（４）が導かれる。

See FIG. 5 again. When the original signal is restored in the counter device, the write timing and read timing of the FEC block for the queues 314a and 314b are determined so that data shortage or omission does not occur due to data combination between channels. Delay _{T a} read start timing of the FEC blocks from the queue 314a from the writing start timing of the FEC block to the queue 314a, the write start timing of the FEC block to the queue 314b of the FEC blocks from the queue 314b read The delay of the start timing is T _b , the delay of the read start timing of the next FEC block from the queue 314b from the read start timing of the FEC block from the _{queue 314a is T diff} , and the delay of the read start timing from the queue 314a is the writing of one FEC block to the queues 314a and 314b. _{Let T block be} the time from the start timing to the end of writing, and α be the fluctuation component due to the transmission delay difference of T _diff. The condition that the order of the continuous FEC blocks is maintained is expressed by the equation (1), and the condition that no gap is generated between the continuous FEC blocks in the restored original signal is expressed by the equation (2).

Further, T _diff is given by the equation (3).

Equation (4) is derived from equations (1) to (3).

When the length of the optical fiber cable 201 is 40 km and the wavelength difference of the low-rate optical signal is 20 nm, α is less than 20 ns, and in RS-FEC RS (528,514), the block length of the FEC block is 5280 bits. There is, and the time required for transmission at _{25.8 Gbps T block} = 204.85 ns. This is sufficiently long with respect to α, _{and if Ta} = T _b is set, the equation (4) is satisfied.

In the relay system 100 according to the present embodiment, a multiplexed optical signal obtained by wavelength division multiplexing of a plurality of (six) low-rate signals is transmitted between the WDM concentrators 200A and 200B. For wavelength division multiplexing (WDM), CWDM (Coarse Wavelength Division Multiplexing), DWDM (Dense Wavelength Division Multiplexing) and the like are used.

ただし、Ｄｅｌａｙ_ｍａｘは最大遅延を、Ｄｅｌａｙ_ｍｉｎは最小遅延を、λは波長を示し、Ａは定数である。上記の最大遅延が図６において実線で示され、最小遅延が破線で示される。図６より、波長１３２０ｎｍ付近で相対遅延が０（ゼロ分散）となる。波長が１３２０ｎｍ付近から大きくなるにしたがって最大遅延及び最小遅延共に増加し、分散が増加することが分かる。 In WDM optical communication, signals having a plurality of wavelengths different from each other are multiplexed, but an optical fiber has a characteristic that the transmission speed of signals differs depending on the wavelength. That is, in WDM optical communication, a relative delay (delay difference) occurs between the two signals, and this relative delay may adversely affect the communication (incorrect block order, gap between blocks, etc.). FIG. 6 is a graph showing an example of the relationship between the signal wavelength and the relative delay in the optical fiber. In FIG. 6, the horizontal axis represents the wavelength and the vertical axis represents the relative delay. The relationship between the signal wavelength and the relative delay in the optical fiber is given by Eqs. (5) and (6).

However, Delay _max indicates the maximum delay, Delay _min indicates the minimum delay, λ indicates the wavelength, and A is a constant. The maximum delay is shown by a solid line in FIG. 6 and the minimum delay is shown by a broken line. From FIG. 6, the relative delay becomes 0 (zero dispersion) near the wavelength of 1320 nm. It can be seen that both the maximum delay and the minimum delay increase as the wavelength increases from around 1320 nm, and the dispersion increases.

FIG. 7 is a graph showing an example of relative delay at two wavelengths of ± 10 nm with respect to the wavelength λ. In FIG. 7, the horizontal axis represents the wavelength λ ± 10 nm, and the vertical axis represents the relative delay. In the case of CWDM, the wavelength difference is 20 nm, and FIG. 7 can be used for examining the transmission delay difference when CWDM is adopted. As shown in FIG. 7, it can be seen that a delay difference of 17.3 ns at the maximum occurs in the range of λ = 1260 to 1620 nm. That is, when CWDM is adopted, a delay difference of 17.3 ns occurs between the two signals in the worst case.

See FIG. 5 again. The block length of the FEC block is 5280 bits, and the time required for transmission at 25.8 Gbps is about 205 ns. _Therefore, T block = _204.8ns, When α = 17.3ns (worst value in CWMD), for example, be set to _T a = _{T b,} satisfying the equation (4).

[3. Receiver]
The WDM concentrator 200 has a function as a receiving device for receiving an optical signal transmitted from a transmitting device which is an opposite device. FIG. 8 is a functional block diagram showing an example of the function of the WDM concentrator 200 according to the present embodiment as a receiving device. The data rate conversion circuit 220 has functions of parallel conversion units 321a and 321b, boundary detection units 322a and 322b, writing units 323, queues 324a and 324b, reading units 325, and serial conversion units 325. ..

The optical transceivers 231,232 receive each of the low-rate optical signals transmitted from the transmitter. Optical transceivers 231,232 convert low-rate optical signals into low-rate signals, which are serial electrical signals. The transmission speed of the low-rate signal output from each of the optical transceivers 231 and 232 is 12.9 Gbps.

Each of the two low-rate signals of the serial signal is given to the parallel conversion units 321a and 321b. Each of the parallel converters 321a and 321b extracts clock data from the low-rate signal of the serial signal, reproduces the timing, and converts the serial data into parallel data (hereinafter, also referred to as "reproduced data") at a clock rate of 12.9 Gbps. Convert.

The reproduced data, which is parallel data, is given to the boundary detection units 322a and 322b. Each of the boundary detection units 322a and 322b detects the CWM included in the reproduced data, and in each of the two reproduced data (low rate signals), the boundary of the FEC block or the divided block (divided data) in the same division unit as the transmission device. Is detected. Further, the boundary detection unit 312 outputs each FEC block or division block to the writing unit 323. The boundary detection unit 312 adds a mark (information) to the FEC block or division block of # 1024 including the CWM. This mark is used by the reading unit 325 to identify the FEC block or the divided block containing the CWM. The writing unit 323 writes the two-channel FEC block or the divided block output from the boundary detection units 322a and 322b to the corresponding queues 324a and 324b at a clock rate of 12.9 Gbps, respectively.

The reading unit 325 reads the FEC block from each of the two queues 324a and 324b at a clock rate of 25.8 Gbps. Here, the reading unit 325 identifies the FEC block or the divided block containing the CWM of # 1024 by the mark added by the boundary detecting unit 312. The FEC block or division block containing the CWM of # 1024 and the block immediately after that are continuously read from the same queue. The reading unit 325 restores the eCPRI signal (original signal), which is a parallel signal, by combining the read FEC blocks.

FIG. 9 is a timing chart showing an example of signal processing by the function of the WDM concentrator 200 according to the present embodiment as a receiving device. In this example, the divided data is an FEC block. The receiving device receives a two-channel low-rate optical signal. The two-channel low-rate optical signal is received by each of the optical transceivers 231 and 232, converted into a low-rate signal which is a serial electric signal, and given to the parallel converters 321a and 321b.

Each of the parallel conversion units 321a and 321b converts a low-rate signal from a serial signal to a parallel signal.

The boundary detection units 322a and 322b detect the boundaries of adjacent FEC blocks. Since the block length of the FEC block is 5280 bits, if the boundary detection units 322a and 322b detect the CWM of # 1024 and detect the boundary of the FEC block, the boundary is bound every 5280 bits without decoding the FEC block. Can be detected.
The boundary detection units 322a and 322b may check the normality of the FEC block. For example, the boundary detection units 322a and 322b can determine that the boundary of the FEC block cannot be processed correctly when the FEC block is decoded and the state in which the FEC block cannot be correctly decoded continues.

Each of the boundary detection units 322a and 322b outputs the divided FEC block to the writing unit 323. That is, the boundary detection unit 322a outputs the FEC block of one channel to the writing unit 323, and the boundary detection unit 322b outputs the FEC block of the other channel to the writing unit 323. Each of the boundary detection units 322a and 322b adds a mark (information indicating that the block contains CWM) to the FEC block of # 1024 containing CWM. The writing unit 323 writes the FEC block (divided data) of the parallel data to each of the two queues 324a and 324b. That is, the FEC block output from the boundary detection unit 322a is written to the queue 324a, and the FEC block output from the boundary detection unit 322b is written to the queue 324b. The mark indicating that the block contains the CWM can be passed to the reading unit 325 using a queue (not shown) different from the queues 324a and 324b.

The reading unit 325 sequentially reads the FEC block from each of the two queues 324a and 324b at a clock rate of 25.8 Gbps. The reading unit 325 reads the FEC block of one channel in order from the queue 324a, and reads the FEC block of the other channel in order from the queue 324b. Further, the reading unit 325 reads the FEC block alternately from the two cues 324a and 324b. As a result, the FEC blocks are sequentially read out in the order of FEC_1, FEC_2, FEC_3, .... Since the block length of the FEC block is sufficiently large with respect to the delay fluctuation, the probability that the FEC block will overtake in the two channels is extremely low. Further, the reading unit 325 continuously reads the FEC block marked as a block containing the CWM, that is, the # 1024 FEC block and the next # 1 FEC block from the same queue.

The reading unit 325 restores the eCPRI signal (original signal), which is a parallel signal, at a clock rate of 25.8 Gbps by combining the read FEC blocks. Here, the FEC blocks # 2 to # 1024 are alternately read from the two queues 324a and 324b, but the FEC block # 1024 and the subsequent FEC block # 1 are continuously read from the same queue. In a specific example, the reading unit 325 identifies the FEC block of # 1024 by the above-mentioned mark, and reads the FEC block immediately after (# 1) from the same queue. The read FEC blocks are combined, and an eCPRI signal in which the FEC blocks # 1 to # 1024 are arranged in order is restored. The reading unit 325 gives the restored eCPRI signal to the serial conversion unit 326. The serial conversion unit 326 converts the parallel signal into a serial signal, and outputs the converted eCPRI signal to the optical transceiver 210. The optical transceiver 210 converts the eCPRI signal of the electric signal into an optical signal and outputs it.
The reading unit 325 may check the normality of the read block. For example, when the divided data is an FEC block, the reading unit 325 can determine that the boundary of the FEC block cannot be processed correctly when the FEC block is decoded and the state in which the FEC block cannot be correctly decoded continues.

[4. Modification example]
[4-1. First modification]
Not only the FEC block containing CWM and the block immediately after it are included in one low rate signal, but also the FEC block immediately after the FEC block containing CWM (# 1 FEC block) and the FEC block immediately after that (# 1 FEC block). # 2 FEC block) may be included in one low rate signal. In this case, when the reading unit 325 identifies the FEC block of # 1024, it continuously reads the FEC blocks of # 1 and # 2 from a queue different from the queue that read the FEC block of # 1024. Further, two consecutive FEC blocks included in one low rate signal may be arbitrarily set. For example, two consecutive FEC blocks out of 1024 FEC blocks (however, the two FEC blocks do not include CWM) and 1022 FEC blocks excluding the two FEC blocks are arranged every other 511. The FEC blocks are included in one low-rate signal (first low-rate signal), and the remaining 512 FEC blocks are included in a low-rate signal (second low-rate signal) different from the one low-rate signal. May be included. By including two consecutive FEC blocks in one low-rate signal in this way, CWM is alternately distributed to the two low-rate signals.

When the FEC block is divided into a plurality of divided blocks, the divided block immediately after the divided block including the CWM and the divided block immediately after that may be included in one low rate signal. Further, two consecutive divided blocks included in one low rate signal may be arbitrarily set. For example, two consecutive division blocks (however, the two division blocks do not include CWM) out of N consecutive division blocks (where N is a multiple of 1024) and the two division blocks are excluded. Include every other (N-2) / 2 division blocks in N-2 division blocks in one low rate signal (first low rate signal), and the remaining N / 2 division blocks. May be included in a low rate signal (second low rate signal) different from the one low rate signal. Generalized, N FEC blocks or division blocks, which are multiples of 1024, arranged in order in the original signal, are placed at the first low rate according to the allocation rules that satisfy the following conditions A, B, and C. It may be assigned to the signal and the second low rate signal. When the first data rate conversion unit and the second data rate conversion unit follow the same allocation rule, the order of N FEC blocks or division blocks is restored.
Condition A: The first low rate signal includes two consecutive blocks or split blocks out of N FEC blocks or split blocks.
Condition B: In each of the first low rate signal and the second low rate signal, the order of the FEC block or the divided block in the original signal is not changed.
Condition C: The number of FEC blocks or division blocks included in the first low-rate signal is N / 2 or N / 2 + 1, and the number of FEC blocks or division blocks included in the second low-rate signal is N / 2 or N. / 2-1.
In condition C, when the number of FEC blocks or division blocks included in the first low-rate signal is N / 2 + 1, and the number of FEC blocks or division blocks included in the second low-rate signal is N / 2-1. For example, in the following N FEC blocks or division blocks, the number of FEC blocks or division blocks included in the first low-rate signal is N / 2-1 and the FEC blocks or division blocks included in the second low-rate signal. By setting the number of to N / 2 + 1, the first low rate signal and the second low rate signal can be set to the same rate.

Further, the original signal may be divided into a number of low rate signals larger than 2. In this case, the transmission speed of the low-rate signal (and the low-rate optical signal) is a speed corresponding to the number of low-rate signals. For example, the number of low-rate signals can be a divisor of 1024, which is the spacing between FEC blocks containing adjacent CWMs. For example, when the number of low-rate signals is set to 4, the transmission speed of the low-rate signal can be 1/4 of the transmission speed of the original signal. N FEC blocks or division blocks are assigned to the four low rate signals (A to D) in the order of round robin from the low rate signal A, and the next N FEC blocks or division blocks are assigned to the next N FEC blocks or division blocks, for example, from the low rate signal B to the round. If the allocation is made in Robin order (then from C, and so on), the FEC block or division block containing the CWM can be assigned to the four low-rate signals (A to D).
Generalized, when generating K low-rate signals (where K is a divisor of 1024 excluding 1 and 1024), according to the allocation rules that satisfy the following conditions a, b, and c: An FEC block or a split block may be assigned to each low rate signal. When the first data rate conversion unit and the second data rate conversion unit follow the same allocation rule, the order of N FEC blocks or division blocks is restored.
Condition a: For each of the K low-rate signals, the order of the FEC block or the divided block in the original signal is not changed.
Condition b: When the number of FEC blocks or division blocks included in the original signal is N, which is a multiple of 1024, the number of FEC blocks or division blocks included in each of the K low-rate signals is N / K or N / K ± 1.
Condition c: CWM is allocated to K low rate signals.

In the above case, the number of channels is K. That is, K cues are provided in each of the WDM concentrators 200A and 200B, and K low-rate signals are assigned to each of the K cues. In the WDM concentrator 200A, the FEC block or the divided block divided from the original signal is written to each of the K queues, and the FEC block or the divided block is read from each queue to generate K low rate signals. To. In the WDM concentrator 200B, each of the K queues is associated with each of the K low-rate signals, and the FEC block or the division block included in the low-rate signal is sequentially written to the corresponding queue. The FEC block or the divided block is read from each queue, and the read FEC block or the divided block is combined in the original order to restore the original signal.

[4-2. Second variant]
CWM may not be used to detect FEC blocks. For example, it is possible to perform FEC decoding on the reproduced data and detect the boundary of the FEC block. Each of the boundary detection unit 312 and the boundary detection units 322a and 322b executes FEC decoding and detects the boundary of the FEC block.

[4-3. Third variant]
As described above, when a two-channel low-rate signal is transmitted for 40 km with a wavelength difference of 20 nm, a delay difference of 17.3 ns at the maximum occurs. On the other hand, the eCPRI signal cannot be accurately restored unless the FEC blocks are read from the queues 324a and 324b in the correct order and at the appropriate timing. Therefore, in this modification, for example, when an FEC code having a short code length is used, an initialization signal is used to absorb the delay difference between the low-rate signals and synchronize the read timing of the FEC block between the channels. Is used.

FIG. 10 is a timing chart showing a second modification of signal processing by the function of the WDM concentrator 200 according to the embodiment as a receiving device. The WDM concentrator 200, which is a transmission device (opposite device), adds an initialization block (initialization signal) to the head of a low-rate signal and transmits a low-rate optical signal. The initialization block is a block containing information that can be distinguished from an FEC block containing actual data. The block length of the initialization block is predetermined. The receiving device receives a two-channel low-rate optical signal to which an initialization block is added. The two-channel low-rate optical signal is received by each of the optical transceivers 231 and 232, converted into a low-rate signal which is a serial electric signal, and given to the parallel converters 321a and 321b.

Each of the parallel conversion units 321a and 321b converts the initialization block and the low rate signal from the serial signal to the parallel signal.

The boundary detection units 322a and 322b read the initialization block and execute the initialization process. In the initialization process, the end of the initialization block, that is, the boundary between the initialization block and the first FEC block is detected. The block length of the initialization block is used to detect this boundary. That is, when the boundary detection units 322a and 322b start data reception, they determine that the end of the initialization block is after the block length of the known initialization block. After the termination of the initialization block, the boundary of the FEC block is repeated every 5280 bits (block length of the FEC block). Therefore, the boundary of the subsequent FEC block is detected by detecting the termination of the initialization block. To.

The writing unit 323 does not write the initialization block to the queues 324a and 324b, but starts writing the first FEC block (FEC_1) to the queue 324a. The writing unit 323 notifies the reading unit 325 of the completion of initialization after the time when half of the FEC_1, that is, 2640 bits are written to the queue 324a. The writing unit 323 alternately writes FEC blocks (divided data) of parallel data to the two queues 324a and 324b in the order of FEC_1, FEC_2, FEC_3, FEC_4, ....

Upon receiving the notification of the completion of initialization, the reading unit 325 starts reading the FEC_1 from the queue 324a. The writing speed of the FEC block by the writing unit 323 to the queue 324a is 12.9 Gbps, and the reading speed of the FEC block by the reading unit 325 from the queue 324a is 25.8 Gbps. As described above, since the initialization completion is notified after half of the FEC_1, that is, after the time when the 2640 bits are written to the queue 324a, the reading of the FEC_1 by the reading unit 325 is the writing of the FEC_1 by the writing unit 323. Never overtake. The reading unit 325 sequentially reads the FEC block from each of the two queues 324a and 324b at a clock rate of 25.8 Gbps.

The reading unit 325 restores the eCPRI signal (original signal), which is a parallel signal, at a clock rate of 25.8 Gbps by combining the read FEC blocks. The reading unit 325 gives the restored eCPRI signal to the serial conversion unit 326. The serial conversion unit 326 converts the parallel signal into a serial signal, and outputs the converted eCPRI signal to the optical transceiver 210. The optical transceiver 210 converts the eCPRI signal of the electric signal into an optical signal and outputs it.

[4-4. Fourth modified example]
In the above embodiment, the eCPRI signal encoded by RS-FEC is relayed, but the present invention is not limited to this. Since low delay is required in 5G, communication of data without error correction coding is also assumed. Here, as an example, relay of 64B / 66B coded data without error correction coding will be described.

FIG. 11 is a timing chart showing a third modification example of signal processing by the function of the WDM concentrator 200 according to the embodiment as a transmission device. The eCPRI signal, which is 64B / 66B coded data, has a configuration in which a plurality of coded blocks (hereinafter, referred to as “66B blocks”) are arranged side by side. In 664 / 66B coding, a 2-bit synchronization header is added every 64 bits. The 66-bit bit string including the synchronization header at the beginning is the 66B block. The synchronization header takes alternating values of "01" or "10". Therefore, the synchronization header is the boundary of 66B blocks, and each 66B block can be separated by detecting the synchronization header.

The boundary detection unit 312 of the transmission device detects the boundary of the 66B block in the reproduced data, and the writing unit 313 divides the reproduced data in block units. The writing unit 313 alternately writes 66B blocks (divided data) of parallel data to the two cues 314a and 314b.

The reading unit 315 reads 66B blocks from each of the two cues 314a and 314b at a clock rate of 12.9 Gbps (see FIG. 3). The reading unit 315 generates two low-rate signals (parallel signals) at a clock rate of 12.9 Gbps by combining every other 66B block read. That is, one low-rate signal is generated by combining 66B blocks in the order of 66B_1, 66B_3, 66B_5, ..., And the other low-rate signal is generated by combining 66B blocks in the order of 66B_2, 66B_4, 66B_6, ... Is generated. This is to prevent the front and back of the 66B block of the two channels from being interchanged when the eCPRI signal is restored by combining the two low-rate signals in the receiving device which is the opposite device.

Here, the reading unit 315 can add an initialization block to the beginning of the low-rate signal. For example, the initialization block may be a / E / code with a 64B / 66B code.

The reading unit 315 gives two low-rate signals, which are 12.9 Gbps parallel signals, to the serial conversion units 316a and 316b, respectively. Each of the serial conversion units 316a and 316b converts the parallel signal into a serial signal, and outputs the converted low-rate signal to each of the optical transceivers 231 and 232.

Each of the optical transceivers 231, 322 converts a low-rate signal of an electric signal into a low-rate optical signal and outputs the signal. The transmission speed of the low-rate optical signal output from the optical transceiver 210 is 12.9 Gbps.

FIG. 12 is a timing chart showing a third modification of signal processing by the function of the WDM concentrator 200 according to the embodiment as a receiving device. In the case of 66B block, the time required for transmission at 25.8 Gbps is Tblock = 2.56 ns. This is shorter than the fluctuation α = 17.3 ns when a low-rate optical signal having a wavelength difference of 20 nm is transmitted during 40 km transmission. _{Therefore, there is no setting of Ta} and T _b that satisfy the equation (4), and the reception timing may be shifted by 3 to 4 blocks between the channels.
The WDM concentrator 200, which is a transmission device (opposite device), adds an initialization block (initialization signal) to the head of a low-rate signal and transmits a low-rate optical signal. The initialization block is a block containing information that can be distinguished from a 66B block containing actual data. The block length of the initialization block is predetermined. The receiving device receives a two-channel low-rate optical signal to which an initialization block is added. The two-channel low-rate optical signal is received by each of the optical transceivers 231 and 232, converted into a low-rate signal which is a serial electric signal, and given to the parallel converters 321a and 321b.

Each of the parallel conversion units 321a and 321b converts the initialization block and the low rate signal from the serial signal to the parallel signal.

The boundary detection units 322a and 322b read the initialization block and execute the initialization process. In the initialization process, the end of the initialization block, that is, the boundary between the initialization block and the first 66B block is detected. The block length of the initialization block is used to detect this boundary. That is, when the boundary detection units 322a and 322b start data reception, they determine that the end of the initialization block is after the block length of the known initialization block. After the termination of the initialization block, the boundary (synchronization header) of the 66B block is repeated every 66 bits (block length of the 66B block). Therefore, when the termination of the initialization block is detected, the subsequent 66B blocks Boundaries are detected.

The writing unit 323 does not write the initialization block to the queues 324a and 324b, but sequentially writes the 66B blocks (66B_1, 66B_3, 66B_5, ...) Following the initialization block to the queue 324a. The low-rate signal of the second channel may be delayed by about 3 to 4 blocks from the first channel (the one in which the reception start timing of the low-rate signal precedes). Therefore, the writing unit 323 notifies the reading unit 325 of the completion of the initialization after the time when the writing of the six 66B blocks is completed in the queue 324a in which the writing of the blocks precedes.

Upon receiving the notification of the completion of initialization, the reading unit 325 starts reading 66B_1 from the queue 324a. The writing speed of the 66B block by the writing unit 323 to the queue 324a is 12.9 Gbps, and the reading speed of the FEC block by the reading unit 325 from the queue 324a is 25.8 Gbps. As described above, since the initialization completion is notified after the time when six 66B blocks are written to the queue 324a of the preceding channel, the order of the blocks is changed in the restored eCPRI signal, or the blocks are interleaved. It is prevented that a gap is generated. The reading unit 325 sequentially reads 66B blocks from each of the two cues 324a and 324b at a clock rate of 25.8 Gbps.

The reading unit 325 restores the eCPRI signal (original signal), which is a parallel signal, at a clock rate of 25.8 Gbps by combining the read 66B blocks. The reading unit 325 gives the restored eCPRI signal to the serial conversion unit 326. The serial conversion unit 326 converts the parallel signal into a serial signal, and outputs the converted eCPRI signal to the optical transceiver 210. The optical transceiver 210 converts the eCPRI signal of the electric signal into an optical signal and outputs it.

The reading unit 325 may check the order of the read blocks. For example, the reading unit 325 includes a block including a / S / code indicating the beginning of an Ethernet frame (hereinafter referred to as “S block”), a block including a / T / code indicating the end (hereinafter referred to as “T block”), and the like. By checking the context of the blocks containing the / I / code (idle code) (hereinafter referred to as "I block"), the order of the blocks can be checked. FIG. 13 is a diagram for explaining an example of checking the order of the blocks. As shown in FIG. 13, in an Ethernet frame, one or a plurality of I blocks are followed by an S block, and then a block of actual data (hereinafter, referred to as “data block”). The last data block is followed by a T block, followed by an I block. In this way, the front of the S block is the I block (however, it may be the T block), and the S block is not the I block. For example, if the block immediately before the S block is a block other than the I block and the T block, or the block immediately after the S block is the I block, it can be determined that the order of the blocks is not appropriate.

[5. Other variants]
In the third modification, since the block length is short 64B / 66B coding, it is suppressed that the order of the blocks is changed by the initialization signal, but the initialization signal may not be used. For example, by replacing the 2-bit synchronization head with "00" (in the case of data) or "11" (in the case of including control information) at predetermined intervals, synchronization between channels can be performed without using an initialization signal. It is possible to prevent the order of blocks from being changed.

Instead of the RS-FEC and 64B / 66B coding blocks, a block having an independently specified number of bits N may be used. In a specific example, a 2-bit synchronization header (for example, "00" or "11") can be added for every N bits. However, for example, if N = 264, since N is a multiple of 66, it cannot be distinguished from the synchronization header of the 66B block. Therefore, N is set to a value other than a multiple of 66. For example, when N = 128, since N is not a multiple of 66, it is not confused with the synchronization header of the 66B block, and the block boundary can be detected correctly.

In the above embodiment, the data rate conversion circuit 220 is configured by a hardware logic circuit, but the present invention is not limited to this. For example, the data rate conversion circuit may be configured by a CPU (Central Processing Unit). That is, the function of the data rate conversion circuit may be realized by the CPU executing the computer program.

[6. effect]
As described above, the relay system 100 according to the embodiment is a relay system that relays the communication between the RRH 20 and the BBU 30. The relay system 100 includes a transmitting device and a receiving device. The transmitting device receives the original signal transmitted from the RRH20 (or BBU30), and transmits an optical signal corresponding to the received original signal. The receiving device receives the optical signal transmitted from the transmitting device, and transmits the original signal restored based on the received optical signal to the BBU30 (or RRH20). The transmitting device includes a data rate conversion circuit 220 (first data rate conversion unit), optical transceivers 231,232 (optical transmitter), and a multiplexer 240. The data rate conversion circuit 220 converts the original signal into a plurality of low rate signals slower than the original signal. The optical transceivers 231 and 232 convert the low-rate signal obtained by the data rate conversion circuit 220 into a low-rate optical signal and transmit the signal. The multiplexer 240 multiplexes a plurality of low-rate optical signals transmitted from the plurality of optical transceivers 231,232 and transmits them as a multiplexed optical signal. The data rate conversion circuit 220 generates a plurality of divided data by distributing the original signal in block units, and outputs each of the generated divided data as a low rate signal at a second speed lower than the first speed. The receiving device includes a multiplexer 240 (demultiplexer), optical transceivers 231 and 232 (optical receivers), and a data rate conversion circuit 220 (second data rate conversion unit). The multiplexer 240 receives the multiplexed optical signal transmitted by the multiplexer 240 of the transmitting device, and converts the received multiplexed optical signal into a plurality of low-rate optical signals. The optical transceivers 231 and 232 convert the low-rate optical signal generated by the multiplexer 240 into a low-rate signal. The number of optical transceivers 231 and 232 of the transmitting device and the number of optical transceivers 231 and 232 of the receiving device are the same. The data rate conversion circuit 220 restores the original signal based on a plurality of low rate signals obtained by the optical transceivers 231,232. The data rate conversion circuit 220 includes cues 324a and 324b, a writing unit 323, and a reading unit 325. The writing unit 323 converts the low-rate signals output from each of the optical transceivers 231 and 232 into divided data, and sequentially writes the divided data to the plurality of queues 324a and 324b at the second speed. The reading unit 325 sequentially reads the divided data from the cues 324a and 324b at the first speed, and restores the original signal by combining the divided data. With the above configuration, the transmitting device generates a plurality of low-speed low-rate optical signals from the original signal, and transmits a multiplexed optical signal in which a plurality of low-rate optical signals are multiplexed. The receiving device receives the multiplexed optical signal, extracts a plurality of low-rate optical signals from the multiplexed optical signal, and restores a high-speed original signal from the plurality of low-rate optical signals. That is, low-speed optical communication is performed between the transmitting device and the receiving device. Therefore, deterioration of the power budget (increase in dispersion penalty and deterioration in reception sensitivity) is suppressed, and both high-speed communication and use of a long-distance optical fiber cable can be realized.

The data rate conversion circuit 220A may divide the original signal into blocks having a predetermined number of bits to generate divided data. The data rate conversion circuit 220B may further include boundary detection units 322a and 322b for detecting the boundary of the block in the low rate signal. The writing unit 323 may convert the low-rate signal whose block boundary is detected by the boundary detecting units 322a and 322b into divided data. By processing in block units, synchronization of divided data becomes easy.

The original signal may be a forward error correction encoded signal including a plurality of code blocks having a predetermined number of bits. The data rate conversion circuit 220 may divide the original signal into blocks based on the code blocks included in the original signal. Thereby, the boundary of the block can be easily detected by using the code block included in the FEC signal. In the FEC signal, since the DC balance is adjusted in the coding, an appropriate DC balance is maintained in the divided data.

The original signal may be a signal encoded by RS (528,514) FEC. The data rate conversion circuit 220A may detect the boundary of a plurality of blocks included in the original signal based on the CWM included in the original signal, and divide the original signal into blocks. By using CWM, block boundaries can be quickly detected without decoding the FEC-encoded original signal.

The boundary detection units 322a and 322b may detect the CWM included in the low-rate signal and detect the boundary of the block based on the detected CWM. By using CWM, block boundaries can be quickly detected without decoding FEC-encoded low-rate signals.

The data rate conversion circuit 220A includes a first low-rate signal including a part of blocks or divided blocks in which N blocks or blocks which are multiples of 1024 are arranged in order in the original signal. Allocation rule that satisfies condition A, condition B, and condition C for the second low-rate signal including the block or division block other than the block included in the first low-rate signal or the division block among the N blocks or division blocks. It may be generated according to. Condition A is that the first low rate signal includes two consecutive blocks or divided blocks out of N blocks or divided blocks, and condition B is a condition B of the first low rate signal and the second low rate signal. In each case, the order of the blocks or divided blocks in the original signal is not changed, and the condition C is that the number of blocks or divided blocks included in the first low rate signal is N / 2 or N / 2 + 1, and the second The number of blocks or split blocks contained in the low rate signal may be N / 2 or N / 2-1. The data rate conversion circuit 220B may include two queues 324a and 324b. The writing unit 323 may write the block or the divided block included in the first low-rate signal to the queue 324a (or 324b), and write the block or the divided block included in the second low-rate signal to the queue 324b (or 324a). Good. The reading unit 325 may read a block or a divided block from each of the queues 324a and 324b based on an allocation rule, and may restore the original signal by combining the read blocks or the divided blocks in order. To read a block or split block based on an allocation rule, read N-2 blocks or split blocks excluding two consecutive blocks or split blocks from each of two queues 324a and 324b, and read two consecutive blocks or two blocks or split blocks. The split blocks can be continuously read from the queue 324a (or 324b). With the above configuration, CWMs are alternately assigned to the two cues 324a and 324b. Therefore, by detecting the CWM in the receiving device, it is not necessary to FEC decode each of the two channels, and the FEC block can be quickly restored.

The data rate conversion circuit 200A sets a plurality of blocks arranged in order in the original signal or a divided block in which the blocks are divided into K low-rate signals which are numbers other than 1 and 1024 out of divisors of 1024. Distribution may be performed according to the allocation rule satisfying the condition b and the condition c. Condition a is that the order of blocks or divided blocks in the original signal is not changed in each of the K low-rate signals, and condition b is that the number of blocks or divided blocks contained in the original signal is a multiple of 1024. When there is N, the number of blocks or division blocks included in each of the K low-rate signals is N / K or N / K ± 1, and the condition c is that the CWM is as low as K. It may be assigned to rate signals in order. The data rate conversion circuit 200B may include K queues. The writing unit 323 may associate each of the K low-rate signals with each of the K queues, and write the blocks or the divided blocks included in the low-rate signals to the corresponding queues in order. The reading unit 325 may read a block or a divided block from each of the K queues based on an allocation rule, and may combine the read blocks or the divided blocks in order to restore the original signal. As a result, CWMs are assigned to K queues in order. Therefore, by detecting the CWM in the receiving device, it is not necessary to FEC decode each of the K channels, and the FEC block can be quickly restored.

Each of the optical transceivers 231 and 232 may transmit a low-rate optical signal to which an initialization block (initialization signal) is added at the beginning. The reading unit 325 may restore the original signal by combining blocks in the order of reading from the queues 324a and 324b based on the initialization block. As a result, the reading unit 325 can read the blocks in the correct order by using the initialization signal. Therefore, even when the transmission delay difference between the transmission channels of the low-rate optical signal is large, the transmission delay difference can be absorbed and the read timing of the divided data can be synchronized between the low-rate signals.

The original signal may be a 64B / 66B encoded signal including a plurality of 66-bit blocks. The data rate conversion circuit 220 may divide the original signal into blocks based on the 66-bit block included in the original signal. Thereby, the boundary of the block can be easily detected by using the code block included in the 64B / 66B signal. Further, since the error correction code is not included, low delay can be realized in the relay of the original signal.

The first speed may be 25.78125 Gbps and the second speed may be 12.890625 Gbps. As a result, the transmission speed of the multiplexed optical signal between the transmitting device and the receiving device becomes 12.890625 Gbps. Therefore, the power budget can be secured even if a long-distance optical fiber cable exceeding 20 km is used.

The transmitting device receives n original signals, includes n data rate conversion circuits 220, and may be provided with m optical transceivers 231 and 232 for one data rate conversion circuit. The multiplexer 240 may multiplex n × m low-rate optical signals transmitted from the optical transceivers 231 and 232 and transmit them as one multiplexed optical signal. The receiving device may include n data rate conversion circuits 220, and m optical transceivers 231 and 232 may be provided for one data rate conversion circuit 220. The multiplexer 240 may convert the multiplexed optical signal into n × m low optical rate signals and input each of the low rate optical signals to each of the optical transceivers 231,232. As a result, n × m low-rate optical signals can be multiplexed and transmitted while suppressing deterioration of the power budget. Further, since the dispersion penalty can be suppressed, it can be used even in a wavelength band having a large wavelength dispersion, and a wavelength selection with a high degree of freedom can be performed.

[7. Supplement]
The embodiments disclosed this time are exemplary in all respects and are not restrictive. The scope of rights of the present invention is indicated by the scope of claims rather than the above-described embodiment, and includes meaning equivalent to the scope of claims and all modifications within the scope thereof.

10 Communication system 20 RRH
30 BBU
21,31,201 Optical fiber cable 100 Relay system 200,200A, 200B WDM concentrator (transmitter, receiver)
210, 210A, 210B Optical transceiver 220, 220A, 220B Data rate conversion circuit (first data rate conversion unit, second data rate conversion unit)
231,232,231A, 232A, 231B, 232B Optical transceiver (optical transmitter, optical receiver)
240, 240A, 240B multiplexer (demultiplexer)
311 Parallel conversion unit 312 Boundary detection unit 313 Writing unit 314a, 314b Queue 315 Reading unit 316a, 316b Serial conversion unit 321a, 321b Parallel conversion unit 322a, 322b Boundary detection unit 323 Writing unit 324a, 324b Queue 325 Reading unit 326 Conversion unit

Claims (13)

A relay system that relays communication between the first device and the second device.
A transmission device that receives the original signal transmitted from the first device and transmits an optical signal corresponding to the received original signal.
A receiving device that receives the optical signal transmitted from the transmitting device and transmits the original signal restored based on the received optical signal to the second device.
With
The transmitter is
A first data rate converter that converts the original signal into a plurality of low-rate signals that are slower than the original signal.
A plurality of optical transmitters that convert the low-rate signal obtained by the first data rate conversion unit into a low-rate optical signal and transmit the signal.
A multiplexer that multiplexes the plurality of the low-rate optical signals transmitted from the plurality of optical transmitters and transmits them as a multiplexed optical signal.
Including
The first data rate conversion unit generates a plurality of divided data by distributing the original signal in block units, and each of the generated divided data is used as a low rate signal, and the second speed is lower than the first speed. Output at speed,
The receiving device is
A demultiplexer that receives the multiplexed optical signal transmitted by the multiplexer and converts the received multiplexed optical signal into the plurality of low-rate optical signals.
An optical receiver having the same number as the optical transmitter, which converts the low-rate optical signal generated by the demultiplexer into the low-rate signal.
A second data rate converter that restores the original signal based on the plurality of low-rate signals obtained by the plurality of optical receivers.
Including
The second data rate conversion unit converts the low rate signal output from each of the plurality of optical receivers into the divided data.
The second data rate conversion unit is
Queue and
A writing unit that sequentially writes the divided data to the queue at the second speed,
A reading unit that sequentially reads the divided data from the queue at the first speed and combines the divided data to restore the original signal.
including,
Relay system. The first data rate conversion unit divides the original signal into blocks having a predetermined number of bits to generate the divided data.
The second data rate conversion unit further includes a boundary detection unit that detects the boundary of the block in the low rate signal.
The boundary detection unit converts the low-rate signal in which the boundary of the block is detected into the divided data.
The relay system according to claim 1. The original signal is a forward error correction coded signal including a plurality of code blocks having a predetermined number of bits.
The first data rate conversion unit divides the original signal into the blocks based on the code block included in the original signal.
The relay system according to claim 2. The original signal is a signal encoded by RS (528,514) FEC.
The first data rate conversion unit detects the boundaries of a plurality of blocks included in the original signal based on the code word marker included in the original signal, and divides the original signal into the block units.
The relay system according to claim 2. The boundary detection unit detects the codeword marker included in the low-rate signal, and detects the boundary of the block based on the detected codeword marker.
The relay system according to claim 4. The first data rate conversion unit includes the N blocks or the division blocks obtained by dividing the blocks, which are N multiples of 1024, which are arranged in order in the original signal, or the division blocks. A first low-rate signal and a second low-rate signal including the block or the divided block excluding the block included in the first low-rate signal or the divided block among the N blocks or the divided blocks. Is generated according to the allocation rules that satisfy the first condition, the second condition, and the third condition.
The first condition is that the first low-rate signal includes two consecutive blocks or the split blocks of the N blocks or the split blocks.
The second condition is that the order of the block or the divided block in the original signal is not changed in each of the first low rate signal and the second low rate signal.
The third condition is that the number of the block or the divided block included in the first low rate signal is N / 2 or N / 2 + 1, and the block or the divided block included in the second low rate signal. The number is N / 2 or N / 2-1
The second data rate conversion unit includes a first queue and a second queue.
The writing unit writes the block or the divided block included in the first low-rate signal to the first queue, and the block or the divided block included in the second low-rate signal is put into the second queue. writing,
The reading unit reads the block or the divided block from each of the first queue and the second queue based on the allocation rule, and sequentially combines the read blocks or the divided blocks to form the original. Restore the signal,
The relay system according to claim 5. The first data rate conversion unit divides a plurality of the blocks arranged in order in the original signal or a divided block obtained by dividing the blocks into K low rates, which is a number other than 1 and 1024 out of divisors of 1024. Distribute the signal according to the allocation rules that satisfy the first, second, and third conditions,
The first condition is that the order of the block or the divided block in the original signal is not changed in each of the K low-rate signals.
The second condition is that when the number of the block or the divided block included in the original signal is N, which is a multiple of 1024, the block or the divided block included in each of the K low-rate signals. The number of is N / K or N / K ± 1.
The third condition is that the codeword marker is assigned to the K low-rate signals.
The second data rate conversion unit includes K queues.
The writing unit associates each of the K low-rate signals with each of the K queues, and sequentially assigns the block or the divided block included in the low-rate signal to the corresponding queue. writing,
The reading unit reads the block or the divided block from each of the K queues based on the allocation rule, and restores the original signal by sequentially combining the read blocks or the divided blocks.
The relay system according to claim 5. Each of the optical transmitters transmits the low-rate optical signal prefixed with an initialization signal.
Based on the initialization signal, the reading unit restores the original signal by combining the blocks in the order of reading from the queue.
The relay system according to claim 2. The original signal is a 64B / 66B encoded signal including a plurality of 66-bit blocks.
The first data rate conversion unit divides the original signal into the blocks based on the 66-bit block included in the original signal.
The relay system according to claim 2. The first speed is 25.78125 Gbps.
The second speed is 12.890625 Gbps.
The relay system according to any one of claims 1 to 9. The transmitter receives n of the original signals and includes n of the first data rate converters.
The m optical transmitters are provided for one first data rate converter.
The multiplexer multiplexes n × m low-rate optical signals transmitted from the optical transmitter and transmits them as the multiplexed optical signals.
The receiving device includes n of the second data rate converters.
The m optical receivers are provided for one second data rate converter.
The demultiplexer converts the multiplexed optical signal into the n × m low optical rate signals, and inputs each of the low rate optical signals to each of the optical receivers.
The relay system according to any one of claims 1 to 10. A transmission device that receives an original signal transmitted from the first device and transmits an optical signal corresponding to the received original signal.
A first data rate converter that converts the original signal into a plurality of low-rate signals that are slower than the original signal.
A plurality of optical transmitters that convert the low-rate signal obtained by the first data rate conversion unit into a low-rate optical signal and transmit the signal.
A multiplexer that multiplexes the plurality of the low-rate optical signals transmitted from the plurality of optical transmitters and transmits them as a multiplexed optical signal.
With
The first data rate conversion unit generates a plurality of divided data by distributing the original signal in block units, and each of the generated divided data is used as a low rate signal, and the second speed is lower than the first speed. Output at speed,
Transmitter. A receiving device that receives a multiplexed optical signal generated based on the original signal and transmits the restored original signal based on the received multiplexed optical signal to the second device.
A demultiplexer that receives the multiplexed optical signal and converts the received multiplexed optical signal into a plurality of low-rate optical signals.
A plurality of optical receivers that convert the low-rate optical signal generated by the demultiplexer into a low-rate signal,
A second data rate converter that restores the original signal based on the plurality of low-rate signals obtained by the plurality of optical receivers.
With
The second data rate conversion unit converts the low rate signal output from each of the plurality of optical receivers into the divided data.
The second data rate conversion unit is
Queue and
A writing unit that sequentially writes the divided data to the queue at a second speed lower than the first speed,
A reading unit that sequentially reads the divided data from the queue at the first speed and combines the divided data to restore the original signal.
including,
Receiver.

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