JP5775105B2 - Transmitting apparatus / method and receiving apparatus / method in a passive optical communication network - Google Patents

Description

  The present invention relates to a technology for smoothly and economically transitioning from one generation system to the next generation system in an optical access system.

  At present, as an optical access system, as shown in FIG. 1, one station side apparatus (OLT: Optical Line Terminal) 1 and a plurality of subscriber premises apparatuses (ONU: Optical Network Unit) 2-1, 2. -1,..., 2-N are connected to each other via the power splitter 3, and a passive optical network (PON) is widely used.

  In general, it is difficult to replace all ONUs 2 at the same time due to the convenience of each subscriber, desired service, etc. when performing a transition that requires device replacement from one generation system to the next generation system. is there. Therefore, as shown in FIG. 2, some means is required to connect different generations of ONUs 2 (new ONU 2 and old ONU 2) to one next generation OLT 1 (new OLT 1) to provide different services. . This means is called a coexistence method.

  Up to now, a technique has been proposed in which a wavelength is divided into a service for a new ONU 2 and a service for an old ONU 2 by a wavelength division division multiplexing (WDM).

  On the other hand, it is possible to increase the speed of optical fiber communication without increasing the bandwidth by multi-level modulation using digital signal processing technology, and studies for applying this technology to optical access systems are also being conducted. . In order to newly introduce this technology to downlink communication of an optical access system, an old ONU 2 that cannot receive a multilevel modulation signal and can only receive an OOK signal, and a new ONU2 that can receive a multilevel modulation signal are simultaneously used. A coexistence method for connecting and providing services is required. The old ONU 2 includes only a direct detector as a receiver, and the new ONU 2 includes a coherent detector and a digital signal processing unit as a receiver.

  As a means of coexistence, the new OLT 1 uses a Star-QAM type multi-level modulation signal, and simultaneously transmits an OOK signal to the old ONU 2 and a multi-level modulation signal including phase modulation to the new ONU 2. A coexistence method has been proposed (see Non-Patent Document 1).

N. Iiyama, S-Y. Kim, T .; Shimada, S .; Kimura and N.K. Yoshimoto, "Co-existent Stream Scheme between OOK and QAM Signals in an Optical Access Network using Software-defined Technology Pro." OFC'12, paper JTh2A. 53, 2012.

  When the coexistence method for connecting the new ONU 2 and the old ONU 2 to the new OLT 1 is used, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 3 and 4, respectively. Here, as an example of the multi-level modulation method, Star 8-QAM is used in particular.

  First, as shown in FIG. 3, in the new OLT 1, the Star 8-QAM bit mapping unit 11 acquires each symbol obtained by connecting three bits by simultaneous input of one bit at each of three input ports. For each symbol in which three bits are connected, Star 8-QAM mapping is performed and the levels of the I and Q signals are output.

  On the other hand, as shown in FIG. 4, in the new ONU 2, the demapping unit 21 of the Star 8-QAM is input with the levels of the I signal and the Q signal, and the Star 8-- QAM demapping is performed, and each symbol in which three bits are connected is output by simultaneous output of one bit at each of three output ports.

  After the introduction of the coexistence method, as shown in Fig. 5, when all the replacement from the old ONU2 to the new ONU2 is completed under the new OLT1, a modulation method with high frequency utilization efficiency is aimed at further speeding up. It is desirable to adopt. In that case, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 6 and 7, respectively. Here, as an example of a modulation scheme with high frequency utilization efficiency, the Square 16-QAM scheme is particularly used.

  First, as shown in FIG. 6, in the new OLT 1, the square 16-QAM bit mapping unit 11 obtains each symbol obtained by connecting four bits by simultaneous input of one bit at each of four input ports. A Square 16-QAM mapping is performed on each symbol in which four bits are connected, and the levels of the I signal and the Q signal are output.

  On the other hand, as shown in FIG. 7, in the new ONU 2, the demapping unit 21 of the Square 16-QAM is input with the levels of the I signal and the Q signal, and the Square 16-QAM is compared with the level of the I signal and the Q signal. QAM demapping is performed, and each symbol in which the four bits are connected is output by simultaneous output of one bit at each of the four output ports.

  However, once the processing circuit as shown in FIGS. 3 and 4 is used at the time of introduction of the coexistence method, it is necessary to replace the processing circuit as shown in FIGS. 6 and 7 at the time of further speeding up. That is, it is necessary to change the number of input ports (FIGS. 3 and 6) and output ports (FIGS. 4 and 7), and a bit mapping unit (FIGS. 3 and 6) and a demapping unit (FIGS. 4 and 7). ) Needs to be changed. Therefore, economical and easy system migration is not possible.

  Therefore, in order to solve the above-mentioned problems, the present invention is economical and easy to switch to a modulation method with higher frequency use efficiency for each generation when introducing multi-level modulation technology by digital signal processing into an optical access system. The purpose is to do.

  In order to achieve the above object, in a passive optical communication network, a transmission device includes a modulation scheme execution unit corresponding to a switching target modulation scheme and a necessary number of input ports regardless of the current modulation scheme. At a stage where the switching target modulation scheme is not adopted, the symbol length of each symbol actually input to the input port is actually input to the input port where it is shorter than the symbol length of each symbol required for bit mapping. For each symbol, a specific bit is copied / inserted so as to eliminate the short symbol length, and then the current modulation scheme is executed. On the other hand, at the stage of switching to the switching target modulation scheme, the switching target modulation scheme is executed without copying / inserting the above-mentioned specific bits.

  The present invention relates to a transmission device in uplink communication or downlink communication in a passive optical communication network, and the adoption multi-level of the modulation scheme actually adopted by the transmission device is the maximum multi-value of the modulation scheme that can be adopted by the transmission device. A modulation multi-value degree comparison unit that determines whether the adopted multi-value degree is lower than the maximum multi-value degree, and the adopted multi-value degree and the maximum multi-value. A predetermined number of bits of each symbol input to the transmitting apparatus is copied by a number equal to the difference in degree, and the copied predetermined bit is predetermined for each symbol input to the transmitting apparatus. The symbol length is converted from the adopted multi-level to the maximum multi-level by inserting each symbol input to the transmitting device and the bit inserted at the predetermined bit position together and outputting it. , Taking the When it is determined that the multi-level is equal to the maximum multi-level, the modulation-side symbol length converter that maintains the symbol length at the maximum multi-level by directly outputting each symbol input to the transmission device And when the adopted multi-value is determined to be lower than the maximum multi-value, the maximum multi-value for each symbol whose symbol length is converted from the adopted multi-value to the maximum multi-value. When the modulation scheme having the adopted multilevel is executed by performing mapping of signal points on the IQ plane in the modulation scheme having the degree, and when the adopted multilevel is determined to be equal to the maximum multilevel Mapping the signal points on the IQ plane in the modulation scheme having the maximum multi-level to each symbol whose symbol length is maintained at the maximum multi-level. Modulation scheme execution unit for executing a modulation scheme that is a transmission apparatus in a passive optical network, characterized in that it comprises a.

  Further, the present invention is a transmission method in uplink communication or downlink communication in a passive optical communication network, and the adoption multi-level of the modulation scheme actually employed by the transmission method is the maximum of the modulation scheme that the transmission method can employ. When it is determined that the adopted multi-value is lower than the maximum multi-value after determining whether it is lower or equal compared to the multi-value, the difference between the adopted multi-value and the maximum multi-value A predetermined number of bits of each symbol input by the transmission method is copied by a number equal to the number, and the copied predetermined bit is copied to a predetermined bit position for each symbol input by the transmission method. The symbol length is converted from the adopted multi-value to the maximum multi-value, by combining and outputting each symbol inputted by the transmission method and the bit inserted at the predetermined bit position, symbol Mapping the signal points on the IQ plane in the modulation scheme having the maximum multi-level for each symbol converted from the multi-level to the maximum multi-level. When it is determined that the adopted multi-level is equal to the maximum multi-level, each symbol input to the transmission apparatus is output as it is, so that the symbol length is set to the maximum multi-level. By mapping the signal points on the IQ plane in the modulation scheme having the maximum multi-level, for each symbol that is maintained at the maximum level and the symbol length is maintained at the maximum multi-level, the maximum multi-level is obtained. A transmission method in a passive optical communication network characterized in that a modulation scheme having a degree of value is executed.

  According to this configuration, it is not necessary to change the number of input ports installed and the mapping configuration of the modulation method execution unit when switching from the current modulation method to the target modulation method, and the number of input ports used and specific bits Therefore, it is only necessary to switch whether or not the copy / insert function is necessary, so that the system can be migrated economically and easily.

  The transmission apparatus / method in the passive optical communication network described above can be implemented not only in the OLT but also in the ONU (see Embodiment 5). In addition, the switching process in the transmission apparatus / method described above can be applied not only in the switching from the introduction of the coexistence method to the further speeding up, but also in each downlink communication to each ONU receiving a different service from the OLT. (See Embodiment 6).

  In order to achieve the above object, in a passive optical communication network, a receiving apparatus includes a demodulation method execution unit corresponding to a switching target demodulation method and a required number of output ports regardless of the current demodulation method. At the stage where the switching target demodulation method is not adopted, the symbol length of each symbol generated by demapping is longer than the symbol length of each symbol output from the output port. Then, for each symbol generated by demapping, a specific bit copied / inserted is discarded so as to eliminate the length of the symbol length. On the other hand, at the stage of switching to the switching target demodulation method, the switching target demodulation method is executed, and the above-mentioned copy / inserted specific bits are not discarded.

  The present invention is a receiving apparatus for uplink communication or downlink communication in a passive optical communication network, and the adopted multilevel degree of the demodulation scheme actually adopted by the receiving apparatus is the maximum multilevel of the demodulation scheme that can be adopted by the receiving apparatus. A demodulating multi-level comparator that determines whether it is lower or equal to the degree, and a data signal transmitted from a transmitter in the passive optical communication network, in the demodulation system having the maximum multi-level When it is determined that the adopted multilevel is lower than the maximum multilevel by performing demapping of signal points on the IQ plane, a demodulation method having the adopted multilevel is executed, and the adopted multilevel When it is determined that the degree is equal to the maximum multi-value degree, a demodulation method execution unit that executes a demodulation method having the maximum multi-value value, and the adopted multi-value value is determined to be lower than the maximum multi-value value Sometimes the transmitter Of each transmitted symbol, the bit inserted at the predetermined bit position by the transmitter is discarded, and the bit inserted at the predetermined bit position by the transmitter is transmitted from the transmitter after being discarded. By outputting each symbol, the symbol length is converted from the maximum multilevel to the adopted multilevel, and when it is determined that the adopted multilevel is equal to the maximum multilevel, A receiver in a passive optical communication network, comprising: a demodulator-side symbol length conversion unit that maintains a symbol length at the maximum multilevel by outputting each transmitted symbol as it is.

  Further, the present invention is a reception method in uplink communication or downlink communication in a passive optical communication network, and the adoption multilevel of the demodulation method actually adopted by the reception method is the maximum of the demodulation methods that the reception method can adopt. On the IQ plane in the demodulation system having the maximum multi-level, for the data signal transmitted by the transmission method in the passive optical communication network after determining whether it is lower or equal to the multi-level When it is determined that the adopted multi-value is lower than the maximum multi-value, by performing demapping of the signal points, the demodulation method having the adopted multi-value is executed, and the adopted multi-value is When it is determined that the maximum multi-level is equal, the demodulation method having the maximum multi-level is executed, and when it is determined that the adopted multi-level is lower than the maximum multi-level, it is transmitted by the transmission method. Out of each symbol By discarding the bit inserted at the predetermined bit position by the transmission method and outputting each symbol transmitted by the transmission method after the bit inserted at the predetermined bit position by the transmission method is discarded. When the symbol length is converted from the maximum multi-level to the adopted multi-level, and it is determined that the adopted multi-level is equal to the maximum multi-level, each symbol transmitted by the transmission method is used as it is. The reception method in the passive optical communication network is characterized in that the symbol length is maintained at the maximum multi-level by outputting.

  According to this configuration, it is not necessary to change the number of output ports installed and the demapping configuration of the demodulation method execution unit when switching from the current demodulation method to the switching target demodulation method. It is only necessary to switch whether or not the bit discard function is necessary, so that the system can be migrated economically and easily.

  Note that the receiving apparatus / method in the above-described passive optical communication network can be implemented not only in the ONU but also in the OLT (see Embodiment 5). In addition, the switching process in the receiving apparatus / method described above can be applied not only when switching from the introduction of the coexistence method to the time of further speedup, but also for each upstream communication from each ONU that receives a different service to the OLT. (See Embodiment 6).

  Further, according to the present invention, the modulation scheme execution unit is configured such that a set of signal points on the IQ plane in the modulation scheme having the adopted multilevel degree is a set of signal points on the IQ plane in the modulation scheme having the maximum multilevel degree. The symbol length corresponding to each signal point on the IQ plane in the modulation scheme having the adopted multilevel is converted to the subset and from the adopted multilevel to the maximum multilevel. A signal point on the IQ plane in the modulation scheme having the adopted multi-level and the maximum multi-level is arranged so that the copied bit and the inserted bit of each symbol have the same value. In the passive optical communication network.

  Further, the present invention is such that the set of signal points on the IQ plane in the modulation scheme having the adopted multilevel is a subset of the signal points on the IQ plane in the modulation scheme having the maximum multilevel. The symbol length corresponding to each signal point on the IQ plane in the modulation scheme having the adopted multilevel is copied from among the symbols after the symbol length is converted from the adopted multilevel to the maximum multilevel. Passive optical communication network characterized in that signal points on the IQ plane in the modulation scheme having the adopted multi-level and the maximum multi-level are arranged so that the inserted bit and the inserted bit have the same value It is the transmission method in.

  According to this configuration, even when the switching target modulation scheme is not adopted, by applying the modulation scheme executing unit corresponding to the switching target modulation scheme, the current modulation scheme (on the IQ plane in the current modulation scheme) Are included in the signal points on the IQ plane in the switching target modulation scheme). Of course, at the stage of switching to the switching target modulation scheme, the switching target modulation scheme can be executed by applying a modulation scheme execution unit corresponding to the switching target modulation scheme.

  Further, according to the present invention, the demodulation scheme execution unit is configured such that a set of signal points on the IQ plane in the demodulation scheme having the adopted multilevel degree is a set of signal points on the IQ plane in the demodulation scheme having the maximum multilevel degree. The symbol length corresponding to each signal point on the IQ plane in the demodulation system having the adopted multilevel is converted into the subset and before the symbol length is converted from the maximum multilevel to the adopted multilevel. The signal points on the IQ plane in the demodulation scheme having the adopted multilevel and the maximum multilevel are arranged so that the copied bits and the inserted bits of the symbols have the same value. In the passive optical communication network.

  Further, the present invention is configured so that a set of signal points on the IQ plane in the demodulation scheme having the adopted multilevel is a subset of signal points on the IQ plane in the demodulation scheme having the maximum multilevel. The symbol length corresponding to each signal point on the IQ plane in the demodulation scheme having the employed multilevel is copied among the symbols before the symbol length is converted from the maximum multilevel to the employed multilevel. Passive optical communication network characterized in that signal points on the IQ plane in the demodulation system having the adopted multi-level and the maximum multi-level are arranged so that the obtained bit and the inserted bit have the same value It is the receiving method in.

  According to this configuration, even when the switching target demodulation method is not adopted, by applying the demodulation method execution unit corresponding to the switching target demodulation method, the current demodulation method (on the IQ plane in the current demodulation method) Is included in the signal points on the IQ plane in the switching target demodulation method). Of course, at the stage of switching to the switching target demodulation method, the switching target demodulation method can be executed by applying a demodulation method executing unit corresponding to the switching target demodulation method.

  The above inventions can be combined as much as possible.

  According to the present invention, when a multilevel modulation technique based on digital signal processing is introduced into an optical access system, it is possible to economically and easily switch to a modulation system with higher frequency use efficiency for each generation.

It is a figure which shows the structure of PON. It is a figure which shows the structure of PON at the time of employ | adopting a coexistence system. It is a figure which shows the signal generation process at the time of using Star 8-QAM of OLT of a prior art. It is a figure which shows the signal reception process at the time of using Star 8-QAM of ONU of a prior art. It is a figure which shows the structure of PON at the time of ONU exchange completion. It is a figure which shows the signal generation process at the time of using Square 16-QAM of OLT of a prior art. It is a figure which shows the signal reception process at the time of using Square 16-QAM of ONU of a prior art. It is a figure which shows the signal generation process at the time of using Star 8-QAM of OLT of Embodiment 1. FIG. It is a figure which shows the signal reception process at the time of using Star 8-QAM of ONU of Embodiment 1. FIG. It is a figure which shows the signal generation process at the time of using Square 16-QAM of OLT of Embodiment 1. FIG. It is a figure which shows the signal reception process at the time of using Square 16-QAM of ONU of Embodiment 1. FIG. It is a figure which shows the arrangement method of the signal point on IQ plane in the prior art and Square 16-QAM of Embodiment 1. FIG. It is a figure which shows the arrangement method of the signal point on IQ plane in Square 64-QAM of Embodiment 2. FIG. It is a figure which shows the signal generation process at the time of using Square 16-QAM of OLT of Embodiment 2. It is a figure which shows the signal reception process at the time of using Square 16-QAM of ONU of Embodiment 2. FIG. It is a figure which shows the signal production | generation process at the time of using OLT Square 64-QAM of Embodiment 2. FIG. It is a figure which shows the signal reception process at the time of using Square 64-QAM of ONU of Embodiment 2. FIG. 6 is a diagram illustrating a configuration of a TDM PON according to Embodiment 3. FIG. 6 is a diagram illustrating a configuration of a TDM / WDM PON according to Embodiment 3. FIG. It is a figure which shows the arrangement method of the signal point on the IQ plane in Star 8-QAM and Square 16-QAM of Embodiment 4.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
In the first embodiment, when the coexistence method is introduced, the new OLT1 and the new ONU2 use Star 8-QAM, and when further speeding up, the new OLT1 and the new ONU2 use Square 16-QAM. Such a case will be described.

When the coexistence method is introduced, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 8 and 9, respectively. The maximum multi-level of the modulation scheme and the demodulation scheme that the new OLT 1 and the new ONU 2 can respectively adopt is 4 (16 = 2 ⁴ ), and the modulation multi-level of the modulation scheme and the demodulation scheme that are actually adopted by the new OLT 1 and the new ONU 2 respectively. Is 3 (8 = 2 ³ ).

  First, the new OLT 1 shown in FIG. 8 will be described. The OLT switching unit 12 determines that the adopted multilevel (3 in FIG. 8) is lower than the maximum multilevel (4 in FIG. 8). Here, the OLT switching unit 12 corresponds to a modulation multilevel degree comparison unit of the solving means.

  In this case, the OLT switching unit 12 executes the following processing. First, of the four input ports, the first input port is switched to the unused state, and the remaining input ports are maintained in the used state. Then, a number equal to the difference between the adopted multi-level and the maximum multi-level (1 in FIG. 8) is a predetermined number (3 bits in FIG. 8) of each symbol (3 bits in FIG. 8) input to the new OLT 1. The upper first bit corresponding to the second input port is copied.

  Then, for each symbol input to the new OLT 1, the copied predetermined bit is inserted into a predetermined bit position (the upper first corresponding to the first input port in FIG. 8). Finally, each symbol input to the new OLT 1 and a bit inserted at a predetermined bit position are output together, thereby converting the symbol length from the adopted multi-level to the maximum multi-level. The OLT switching unit 12 here corresponds to the modulation-side symbol length conversion unit of the solving means.

  The square 16-QAM bit mapping unit 11 maps signal points on the IQ plane in the square 16-QAM modulation scheme for each symbol whose symbol length is converted from the adopted multilevel to the maximum multilevel. By performing the above, the Star 8-QAM modulation scheme is executed. The bit mapping unit 11 here corresponds to a modulation scheme execution unit.

  Here, the square 16-QAM bit mapping unit 11 arranges signal points on the IQ plane in the square 16-QAM modulation scheme as follows.

  First, a set of signal points on the IQ plane in the Star 8-QAM modulation scheme (black circles in FIG. 8) is a signal point on the IQ plane in the Square 16-QAM modulation scheme (black circles and white circles in FIG. 8). To be a subset of

  In addition, in each symbol after the symbol length is converted from the adopted multi-value to the maximum multi-value, corresponding to each signal point on the IQ plane in the Star 8-QAM modulation system, the copied bit ( In FIG. 8, the upper second bit) and the inserted bit (upper first bit in FIG. 8) have the same value (0 or 1 of the two values).

  Therefore, even when the Square 16-QAM modulation scheme is not adopted, it is guaranteed that the Star 8-QAM modulation scheme can be executed by applying the Square 16-QAM bit mapping unit 11.

  Next, the new ONU 2 shown in FIG. 9 will be described. The ONU switching unit 22 determines that the adopted multilevel (3 in FIG. 9) is lower than the maximum multilevel (4 in FIG. 9). Here, the ONU switching unit 22 corresponds to a demodulation multilevel comparison unit of the solving means.

  The Square 16-QAM demapping unit 21 performs demapping of signal points on the IQ plane in the Square 16-QAM demodulation method for the data signal transmitted from the new OLT 1, thereby performing the Star 8-QAM demapping. Perform a demodulation scheme. The demapping unit 21 here corresponds to a demodulation method execution unit.

  The Square 16-QAM demapping unit 21 arranges signal points on the IQ plane in the Square 16-QAM demodulation method as follows.

  First, a set of signal points on the IQ plane (in FIG. 9, black circles) in the Star 8-QAM demodulation method is a signal point on the IQ plane in the Square 16-QAM demodulation method (black circles and white circles in FIG. 9). To be a subset of

  In addition, in each symbol before the symbol length is converted from the maximum multilevel to the adopted multilevel corresponding to each signal point on the IQ plane in the Star 8-QAM demodulation method, the copied bit ( In FIG. 9, the upper second bit) and the inserted bit (upper first bit in FIG. 9) have the same value (0 or 1 of the two values).

  Therefore, even when the Square 16-QAM demodulation method is not adopted, it is guaranteed that the Star 8-QAM demodulation method can be executed by applying the Square 16-QAM demapping unit 21.

  When the adopted multilevel is lower than the maximum multilevel, the ONU switching unit 22 executes the following processing. First, among the four output ports, the first output port is switched to the unused state, and the remaining output ports are maintained in the used state. Of the symbols transmitted from the new OLT 1 (4 bits in FIG. 9), the bits inserted in the new OLT 1 at the predetermined bit position (upper first corresponding to the first output port in FIG. 9) Discard. Finally, each symbol transmitted from the new OLT 1 after discarding the bit inserted at the predetermined bit position in the new OLT 1 is converted to convert the symbol length from the maximum multi-level to the adopted multi-level. The ONU switching unit 22 here corresponds to the demodulation side symbol length conversion unit of the solving means.

When the speed is further increased, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 10 and 11, respectively. The maximum multi-level of the modulation scheme and the demodulation scheme that the new OLT 1 and the new ONU 2 can respectively adopt is 4 (16 = 2 ⁴ ), and the modulation multi-level of the modulation scheme and the demodulation scheme that are actually adopted by the new OLT 1 and the new ONU 2 respectively. Is 4 (16 = 2 ⁴ ).

  First, the new OLT 1 shown in FIG. 10 will be described. The OLT switching unit 12 determines that the adopted multi-level (4 in FIG. 10) is equal to the maximum multi-level (4 in FIG. 10). Here, the OLT switching unit 12 corresponds to a modulation multilevel degree comparison unit of the solving means.

  In this case, the OLT switching unit 12 executes the following processing. First, of the four input ports, the first input port is switched to the use state, and the remaining input ports are maintained in the use state. Then, each symbol input to the new OLT 1 is output as it is. The OLT switching unit 12 here corresponds to the modulation-side symbol length conversion unit of the solving means.

  The Square 16-QAM bit mapping unit 11 performs mapping of signal points on the IQ plane in the Square 16-QAM modulation scheme for each symbol whose symbol length is maintained at the maximum multilevel level. A 16-QAM modulation scheme is executed. The bit mapping unit 11 here corresponds to a modulation scheme execution unit.

  Next, the new ONU 2 shown in FIG. 11 will be described. The ONU switching unit 22 determines that the adopted multilevel (4 in FIG. 11) is equal to the maximum multilevel (4 in FIG. 11). Here, the ONU switching unit 22 corresponds to a demodulation multilevel comparison unit of the solving means.

  The square 16-QAM demapping unit 21 performs demapping of signal points on the IQ plane in the square 16-QAM demodulation method for the data signal transmitted from the new OLT 1, thereby performing the square 16-QAM demodulation. Perform a demodulation scheme. The demapping unit 21 here corresponds to a demodulation method execution unit.

  When the adopted multilevel is equal to the maximum multilevel, the ONU switching unit 22 executes the following process. First, of the four output ports, the first output port is switched to the use state, and the remaining output ports are maintained in the use state. Then, by outputting each symbol transmitted from the new OLT 1 as it is, the symbol length is maintained at the maximum multilevel. The ONU switching unit 22 here corresponds to the demodulation side symbol length conversion unit of the solving means.

  Here, the input port that is switched to the unused state in the new OLT 1 and the input port to which the input bits are copied, the output port that is switched to the unused state in the new ONU 2 and discards the output bits, and the Square 16-QAM The bit mapping unit 11 and the demapping unit 21 must be matched as described below.

  Bit mapping and demapping of Square 16-QAM of the prior art are shown in FIGS. 6 and 7, and are also shown on the left side of FIG. In this case, even if any two-bit combination is selected at a signal point on the IQ plane in the Star 8-QAM modulation / demodulation method, the values of these two bits are not necessarily equal. That is, even if any of the symbols before symbol length conversion is copied and inserted into any of the symbols after symbol length conversion, a Star 8-QAM modulation signal cannot be obtained. .

  The bit mapping and demapping of Square 16-QAM according to the first embodiment are shown in FIGS. 8 and 9, and are also shown on the right side of FIG. In this case, if a combination of the upper first two bits and the upper second two bits is selected at a signal point on the IQ plane in the Star 8-QAM modulation / demodulation method, the values of these two bits are necessarily equal. That is, if the upper first bit of each symbol before symbol length conversion is copied and inserted into the upper first bit of each symbol after symbol length conversion, the modulated signal of Star 8-QAM becomes can get. Correspondingly, the input port that is switched to the unused state in the new OLT 1 and the input port to which the input bits are copied, and the output port that is switched to the unused state in the new ONU 2 and discards the output bits are selected. That's fine.

  In the new OLT 1, there is no need to change the number of installed input ports and the mapping configuration of the modulation method execution unit when switching from the current modulation method to the target modulation method, and the number of input ports used and a copy of specific bits. -It is only necessary to switch whether or not the insertion function is necessary, so that an economical and easy system migration is possible.

  In the new ONU 2, there is no need to change the number of output ports installed and the demapping configuration of the demodulation method execution unit in switching from the current demodulation method to the target demodulation method, the number of output ports used and the number of specific bits It is only necessary to switch whether or not the disposal function is necessary, so that the system can be migrated economically and easily.

(Embodiment 2)
In the first embodiment, when the coexistence method is introduced, the new OLT 1 and the new ONU 2 use the Star 8-QAM, and when further speeding up, the new OLT 1 and the new ONU 2 use the Square 16-QAM. . In the second embodiment, the new OLT 1 and the new ONU 2 use Square 16-QAM before further speedup, and the new OLT 1 and the new ONU 2 use Square 64-QAM at the time of further speedup. ing.

  Here, Square 16-QAM cannot be used in the coexistence method with OOK. Therefore, the second embodiment can be applied for further speedup after all the ONUs 2 are switched from the old ONU 2 to the new ONU 2.

  In the square 64-QAM bit mapping and demapping, signal points on the IQ plane in the square 64-QAM modulation / demodulation method are arranged as shown in FIG.

  Signal points on the IQ plane in the Square 16-QAM modulation / demodulation system are indicated by black circles in FIG. Signal points on the IQ plane in the Square 64-QAM modulation / demodulation scheme are indicated by black and white circles in FIG.

  If a combination of the upper 1st bit and the upper 5th 2 bits is selected at a signal point on the IQ plane in the Square 16-QAM modulation / demodulation method, the values of these 2 bits are necessarily equal, and the upper 2nd and 6th If the 2nd bit combination is selected, the values of these 2 bits are always equal. Therefore, the modulation / demodulation method is as follows.

Before further speeding up, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 14 and 15, respectively. The maximum multilevel value of the modulation method and the demodulation method that the new OLT1 and the new ONU2 can respectively adopt is 6 (64 = 2 ⁶ ), and the modulation method and the demodulation method that are actually adopted by the new OLT1 and the new ONU2 respectively. Is 4 (16 = 2 ⁴ ).

  First, the new OLT 1 shown in FIG. 14 will be described. The OLT switching unit 12 determines that the adopted multilevel (4 in FIG. 14) is lower than the maximum multilevel (6 in FIG. 14).

  The OLT switching unit 12 executes the following processing. First, among the six input ports, the first and second input ports are switched to the unused state, and the remaining input ports are maintained in the used state. Then, among the symbols input to the new OLT 1, the upper third and upper fourth bits corresponding to the fifth and sixth input ports are copied. Then, for each symbol input to the new OLT 1, the upper third bit corresponding to the copied fifth input port is inserted into the upper first corresponding to the first input port. Then, for each symbol input to the new OLT 1, the upper fourth bit corresponding to the copied sixth input port is inserted into the upper second corresponding to the second input port. Finally, each symbol input to the new OLT 1 and a bit inserted at a predetermined bit position are output together, thereby converting the symbol length from the adopted multi-level to the maximum multi-level.

  The square 64-QAM bit mapping unit 11 maps signal points on the IQ plane in the square 64-QAM modulation scheme for each symbol whose symbol length is converted from the adopted multilevel to the maximum multilevel. By doing this, the modulation scheme of Square 16-QAM is executed (see the mapping shown in FIG. 13).

  Next, the new ONU 2 shown in FIG. 15 will be described. The ONU switching unit 22 determines that the adopted multilevel (4 in FIG. 15) is lower than the maximum multilevel (6 in FIG. 15).

  The Square 64-QAM demapping unit 21 performs demapping of the signal points on the IQ plane in the Square 64-QAM demodulation method on the data signal transmitted from the new OLT 1, thereby performing Square 16-QAM. The demodulation method is executed (see demapping shown in FIG. 13).

  The ONU switching unit 22 executes the following processing. First, among the six output ports, the first and second output ports are switched to the unused state, and the remaining output ports are maintained in the used state. Of the symbols transmitted from the new OLT 1, the first inserted bit corresponding to the first output port in the new OLT 1 is discarded. Then, among the symbols transmitted from the new OLT 1, the upper second inserted bit corresponding to the second output port in the new OLT 1 is discarded. Finally, each symbol transmitted from the new OLT 1 after discarding the bit inserted at the predetermined bit position in the new OLT 1 is converted to convert the symbol length from the maximum multi-level to the adopted multi-level.

When the speed is further increased, the signal generation part of the new OLT 1 and the signal reception part of the new ONU 2 are as shown in FIGS. 16 and 17, respectively. The maximum multilevel value of the modulation method and the demodulation method that the new OLT1 and the new ONU2 can respectively adopt is 6 (64 = 2 ⁶ ), and the modulation method and the demodulation method that are actually adopted by the new OLT1 and the new ONU2 respectively. Is 6 (64 = 2 ⁶ ).

  First, the new OLT 1 shown in FIG. 16 will be described. The OLT switching unit 12 determines that the adopted multilevel (6 in FIG. 16) is equal to the maximum multilevel (4 in FIG. 16). The OLT switching unit 12 switches the first and second input ports among the six input ports to the use state, and maintains the remaining input ports in the use state, and then the symbols input to the new OLT 1 as they are. Output. The square 64-QAM bit mapping unit 11 performs mapping of signal points on the IQ plane in the square 64-QAM modulation scheme for each symbol whose symbol length is maintained at the maximum multilevel. A 64-QAM modulation scheme is executed.

  Next, the new ONU 2 shown in FIG. 17 will be described. The ONU switching unit 22 determines that the adopted multi-level (6 in FIG. 17) is equal to the maximum multi-level (6 in FIG. 17). The Square 64-QAM demapping unit 21 performs demapping of the signal points on the IQ plane in the Square 64-QAM demodulation method for the data signal transmitted from the new OLT 1, thereby performing the Square 64-QAM. Perform a demodulation scheme. The ONU switching unit 22 switches the first and second output ports among the six output ports to the use state, maintains the remaining output ports in the use state, and directly uses each symbol transmitted from the new OLT 1. By outputting, the symbol length is maintained at the maximum multilevel.

(Embodiment 3)
In the third embodiment, the PON of the first embodiment is applied to one division of the WDM / TDM-PON in addition to applying the PON of the first embodiment to TDM (Time Division Multiplexing) -PON. Share.

  The configuration of the TDM PON of Embodiment 3 is shown in FIG. 18 includes an OLT 1, an ONU 2, a power splitter 3, and the like. The OLT 1 includes a transmission circuit, a reception circuit 16, and a wavelength multiplexing filter 15. The transmission circuit of the OLT 1 includes the processing circuit, the light source 13, and the IQ modulator 14 illustrated in FIGS. The ONU 2 includes a receiving circuit, a transmitting circuit 26, and a wavelength multiplexing filter 25. The ONU 2 receiving circuit includes the processing circuit, the local light source 23, and the coherent receiver 24 illustrated in FIGS. The wavelength of the downstream signal is λ1, and the wavelength of the upstream signal is λ1 '.

  In the TDM PON shown in FIG. 18, the PON having the old ONU 2 that is the premise of the coexistence method is standardized by, for example, G-PON, XG-PON, and IEEE standardized by ITU-T. 1G-EPON and 10G-EPON.

  The configuration of a WDM / TDM PON according to the third embodiment is shown in FIG. 19 are OLT1-1, 1-2, 1-3, 1-4, ONUs 2-1-1, 2-1-2, 2-2-1, 2-2-2, 2-3. 1, 2-3-2, 2-4-1, 2-4-2, power splitter 3, wavelength multiplexer / demultiplexer 4, and the like. OLT1-1, 1-2, 1-3, and 1-4 are the OLT1 shown in FIG. 18, and use wavelengths λ1, λ2, λ3, and λ4 of downstream signals, respectively. The ONUs 2-1-1, 2-2-1, 2-3-1, 2-4-1 are the ONUs 2 shown in FIG. 18, and use the wavelengths λ1, λ2, λ3, and λ4 of the downstream signals, respectively. . ONU 2-1-2, 2-2-2, 2-2-2, 2-4-2 are old ONUs 2 using OOK and use the wavelengths λ 1, λ 2, λ 3, and λ 4 of the downstream signals, respectively. .

  In the WDM / TDM PON shown in FIG. 19, the PON having the old ONU 2 that is the premise of the coexistence method is, for example, G. TWDM-PON is being prepared for standardization as the 989 series.

  In such a configuration, for standardized TDM-PON and WDM / TDM-PON, by introducing a coexistence method, the speed is improved for each wavelength of the downstream signal, and then further speed improvement is performed. Migration can be achieved with minimal processing circuit changes.

(Embodiment 4)
In the fourth embodiment, based on the arrangement interval of signal points on the IQ plane in the Star 8-QAM when the coexistence method is introduced, the arrangement interval of signal points on the IQ plane in the Square 16-QAM at the time of further speedup is set. Determine. FIG. 20 shows an arrangement method of signal points on the IQ plane in Star 8-QAM and Square 16-QAM according to the fourth embodiment.

  When Star 8-QAM is used, the extinction ratio ER of the included OOK signal is determined by the amplitude ratio a: b of the two QPSKs, as shown in the upper and middle stages of FIG. When using Square 16-QAM, as shown in the upper and lower stages of FIG. 15, the arrangement interval of signal points on the IQ plane is determined by the amplitude ratio a: b of the two QPSK.

  For example, as shown in FIG. 15A, if the amplitude ratio of two QPSK is 3: 1, the signal point arrangement interval on the IQ plane is equal. On the other hand, as shown in FIG. 15C, if the amplitude ratio of the two QPSK is 3: 2, the signal point arrangement interval on the IQ plane is not equal. The extinction ratio of 8.2 dB defined in XG-PON described later is satisfied by setting the amplitude ratio b / a of the two QPSKs to 0.23 or less at the stage of the electric signal input to the optical modulator. It is possible to replace the device and transfer the system.

  The old system is ITU-TG. A case where the XG-PON is defined by 987.2 will be described. When the coexistence method using the Star 8-QAM is introduced, the old ONU 2 receives the OOK signal and the new ONU 2 receives the Star 8-QAM signal as it is, or only the QPSK component in the Star 8-QAM signal. Receive. At the time of further speedup using Square 16-QAM, the old ONU 2 receiving the OOK signal receives the Square 16-QAM signal as it is, and the new ONU 2 receiving only the QPSK component is the Square 16-QAM. Only the QPSK component in the signal is received.

(Embodiment 5)
In the first and second embodiments, in PON, downlink transmission is performed by OLT 1 and downlink reception is performed by ONU 2. The OLT 1 includes the processing circuits of FIGS. 8 and 10 in the transmission circuit of FIG. 18, and the ONU 2 includes the processing circuits of FIGS. 9 and 11 in the reception circuit of FIG.

  In the fifth embodiment, as a modification of the first and second embodiments, in the PON, upstream transmission may be performed by the ONU 2 and upstream reception may be performed by the OLT 1. The OLT 1 may include the processing circuits of FIGS. 9 and 11 in the reception circuit 16 of FIG. 18, and the ONU 2 may include the processing circuits of FIGS. 8 and 10 in the transmission circuit 26 of FIG.

(Embodiment 6)
In the first and second embodiments, in the PON, the switching process on the transmission side is applied when switching from the introduction of the coexistence method to the further speedup, and the switching process on the reception side is further performed from the introduction of the coexistence method. Applicable when switching to high speed.

  In the sixth embodiment, as a modification of the first and second embodiments, in the PON, the switching process on the transmission side may be applied for each downlink communication to each ONU 2 that receives a different service from the OLT 1, and the switching process on the reception side. May be applied to each upstream communication from each ONU 2 that receives a different service to the OLT 1.

(Embodiment 7)
The first to sixth embodiments may be realized by software or hardware. Even when the first to sixth embodiments are implemented by software, it is possible to minimize resources such as memory required for software by minimizing changes in the processing circuit, and switching time and software update time when switching the modulation method Can be minimized.

  The present invention can be applied to a transition from one generation system to the next generation system smoothly and economically in an optical access system.

1: OLT
2: ONU
3: Power splitter 4: Wavelength multiplexer / demultiplexer 11: Bit mapping unit 12: OLT switching unit 13: Light source 14: IQ modulator 15: Wavelength multiplexing filter 16: Reception circuit 21: Demapping unit 22: ONU switching unit 23: Local light source 24: coherent receiver 25: wavelength multiplexing filter 26: transmission circuit

Claims (8)

A transmission device in uplink communication or downlink communication in a passive optical communication network,
A modulation multi-level comparison unit that determines whether the adopted multi-level of the modulation scheme that is actually adopted by the transmission device is lower or equal compared to the maximum multi-level of the modulation scheme that can be adopted by the transmission device;
When it is determined that the adopted multi-value is lower than the maximum multi-value, a predetermined number of symbols input to the transmission device are equal to the difference between the adopted multi-value and the maximum multi-value. The second bit is copied, and for each symbol input to the transmitting device, the copied predetermined bit is inserted into a predetermined bit position, and the symbol and the predetermined bit position input to the transmitting device are inserted. By combining and outputting the inserted bits, the symbol length is converted from the adopted multi-value to the maximum multi-value, and when it is determined that the adopted multi-value is equal to the maximum multi-value, A modulation-side symbol length conversion unit that maintains the symbol length at the maximum multi-level by directly outputting each symbol input to the transmission device;
When it is determined that the adopted multi-value is lower than the maximum multi-value, the maximum multi-value is calculated for each symbol whose symbol length is converted from the adopted multi-value to the maximum multi-value. When the modulation scheme having the adopted multilevel is executed by performing mapping of signal points on the IQ plane in the modulation scheme having, it is determined that the adopted multilevel is equal to the maximum multilevel. For each symbol whose length is maintained at the maximum multi-level, a modulation scheme having the maximum multi-level is obtained by mapping signal points on the IQ plane in the modulation scheme having the maximum multi-level. A modulation method execution unit to be executed;
A transmission apparatus in a passive optical communication network. The modulation scheme execution unit is configured such that a set of signal points on the IQ plane in the modulation scheme having the adopted multilevel is a subset of signal points on the IQ plane in the modulation scheme having the maximum multilevel. And among the symbols after the symbol length corresponding to each signal point on the IQ plane in the modulation scheme having the adopted multilevel is converted from the adopted multilevel to the maximum multilevel, a copy is made The signal point on the IQ plane in the modulation scheme having the adopted multi-level and the maximum multi-level is arranged so that the inserted bit and the inserted bit have the same value. A transmitter in the passive optical communication network described. A receiving device for uplink communication or downlink communication in a passive optical communication network,
A demodulating multi-level comparing unit that determines whether the adopted multi-level of the demodulation scheme that the receiving apparatus actually adopts is lower or equal compared to the maximum multi-level of the demodulating scheme that the receiving apparatus can adopt;
By performing demapping of signal points on the IQ plane in the demodulation method having the maximum multi-level, for the data signal transmitted from the transmission device in the passive optical communication network according to claim 1 or 2, When it is determined that the adopted multi-value is lower than the maximum multi-value, the demodulation method having the adopted multi-value is executed, and when it is determined that the adopted multi-value is equal to the maximum multi-value, A demodulation method execution unit for executing a demodulation method having the maximum multi-level,
When it is determined that the adopted multi-level is lower than the maximum multi-level, the bit inserted in the predetermined bit position by the transmitter in the symbols transmitted from the transmitter is discarded, and the transmission By converting each symbol transmitted from the transmitting device after discarding the bit inserted at the predetermined bit position in the device, the symbol length is converted from the maximum multilevel to the adopted multilevel, When it is determined that the adopted multi-level is equal to the maximum multi-level, the symbols on the demodulation side that maintain the symbol length at the maximum multi-level by outputting each symbol transmitted from the transmitter as it is A conversion unit;
A receiving apparatus in a passive optical communication network. The demodulation scheme execution unit is configured such that a set of signal points on the IQ plane in the demodulation scheme having the adopted multilevel is a subset of signal points on the IQ plane in the demodulation scheme having the maximum multilevel. In addition, among the symbols before the symbol length corresponding to each signal point on the IQ plane in the demodulation scheme having the employed multilevel is converted from the maximum multilevel to the employed multilevel, a copy is made. The signal point on the IQ plane in the demodulation system having the adopted multi-level and the maximum multi-level is arranged so that the inserted bit and the inserted bit have the same value. A receiver in the passive optical communication network described. A transmission method in uplink communication or downlink communication in a passive optical communication network,
After determining whether the adopted multi-level of the modulation scheme actually adopted by the transmission method is lower or equal compared to the maximum multi-level of the modulation scheme that can be taken by the transmission method,
When it is determined that the adopted multilevel is lower than the maximum multilevel,
Of the symbols input by the transmission method, a predetermined number of bits are copied by the number equal to the difference between the adopted multi-level and the maximum multi-level, and for each symbol input by the transmission method The copied predetermined bit is inserted at a predetermined bit position, and each symbol input by the transmission method and the bit inserted at the predetermined bit position are combined and output, whereby the symbol length is From the degree of value to the maximum multi-valued degree,
For each symbol whose symbol length is converted from the adopted multilevel to the maximum multilevel, mapping is performed on signal points on the IQ plane in the modulation scheme having the maximum multilevel. Perform a modulation scheme with multiple values,
When it is determined that the adopted multi-value is equal to the maximum multi-value,
By outputting each symbol input to the transmitter as it is, the symbol length is maintained at the maximum multi-level,
The modulation scheme having the maximum multi-level by performing mapping of signal points on the IQ plane in the modulation scheme having the maximum multi-level for each symbol whose symbol length is maintained at the maximum multi-level A transmission method in a passive optical communication network. The set of signal points on the IQ plane in the modulation scheme having the adopted multilevel is a subset of the signal points on the IQ plane in the modulation scheme having the maximum multilevel, and the adopted multilevel In each of the symbols after the symbol length is converted from the adopted multi-level to the maximum multi-level, corresponding to each signal point on the IQ plane in the modulation scheme having 6. The passive optical communication network according to claim 5, wherein signal points on an IQ plane in the modulation scheme having the adopted multi-level and the maximum multi-level are arranged so that bits take equal values. Sending method. A reception method in uplink communication or downlink communication in a passive optical communication network,
After determining whether the adopted multi-level of the demodulation method actually used by the reception method is lower or equal to the maximum multi-level of the demodulation method that can be taken by the reception method,
The data points transmitted by the transmission method in the passive optical communication network according to claim 5 or 6 are de-mapped by performing demapping of signal points on the IQ plane in the demodulation scheme having the maximum multi-level. When it is determined that the adopted multi-value is lower than the maximum multi-value, the demodulation method having the adopted multi-value is executed, and when it is determined that the adopted multi-value is equal to the maximum multi-value, Performing a demodulation scheme having the maximum multi-value degree;
When it is determined that the adopted multilevel is lower than the maximum multilevel,
Of each symbol transmitted by the transmission method, the bit inserted at the predetermined bit position by the transmission method is discarded, and the transmission after the bit inserted at the predetermined bit position by the transmission method is discarded A symbol length is converted from the maximum multi-level to the adopted multi-level by outputting each symbol transmitted by the method,
When it is determined that the adopted multi-value is equal to the maximum multi-value,
A reception method in a passive optical communication network characterized in that the symbol length is maintained at the maximum multi-level by outputting each symbol transmitted by the transmission method as it is. The set of signal points on the IQ plane in the demodulation scheme having the adopted multilevel is a subset of the signal points on the IQ plane in the demodulation scheme having the maximum multilevel, and the adopted multilevel Of the symbols corresponding to each signal point on the IQ plane in the demodulation system having the symbol length before being converted from the maximum multi-level to the adopted multi-level, the copied bits and inserted 8. The passive optical communication network according to claim 7, wherein signal points on an IQ plane in the demodulation scheme having the adopted multi-level and the maximum multi-level are arranged so that bits have the same value. Receiving method.

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