JP5697518B2 - Station-side terminator, subscriber-side terminator, and optical transmission system - Google Patents

Description

  The present invention relates to an optical transmitter that performs multilevel / high-order modulation in the form of hierarchical coding, and an optical transmission system including the same.

  In the PON system currently popular as an optical access network, research and development for speeding up are widely performed. Studies have also been made to apply a multilevel modulation system or a higher-order modulation system as a means of speeding up.

  1 to 3 are schematic diagrams of a conventional PON system 101 using OOK (on-off-keying) as a modulation method, and its optical transmitter 11 and optical receiver 21. FIG. An optical transmitter 11 that transmits a downstream signal modulates and transmits a pulsed frame sequence (direct modulation or external modulation) with a single light source and modulator 15, and a plurality of optical receivers 21 under the splitter 30 All the same signals are received / reproduced by the reception / signal reproduction unit 22 to perform frame restoration. After restoring the frame, the destination address in the frame is determined. If it is addressed to itself, it is acquired, and the other frames are discarded. Here, the OLT 10 is a station side terminal device (Optical Line Terminal). The ONU 20 is a subscriber-side terminal device (Optical Network Unit).

  In order to increase the communication capacity on the same transmission path, the frame may be subjected to multilevel modulation or higher-order modulation. At least one of multi-level modulation and higher-order modulation (hereinafter, “at least one of multi-level modulation and higher-order modulation” may be referred to as “multi-level / high-order modulation” may be described as “multi-level / high-order modulation”). Examples of schematic diagrams of the PON system 102 and its optical transmitter 11 ′ and optical receiver 21 ′ when applied are shown in FIGS. First, as the entire system (FIG. 4), it is necessary to replace all the OLT 10 'and ONU 20' with ones for multi-level / high-order modulation schemes. Regarding the configurations of the optical transmitter 11 ′ and the optical receiver 21 ′, there are various multi-level / high-order modulation schemes, and the optical transmitter 11 ′ and the optical receiver 21 for one modulation scheme. There are various configurations of '(for example, see Non-Patent Document 1). As a typical modulation example, FIG. 5 shows the configuration of an optical transmitter 11′-a when the light of one light source is modulated in multiple stages and multilevel / high-order modulation is performed, and the configuration of the optical receiver 21′-a. Is shown in FIG. As another modulation example, FIG. 6 shows the configuration of an optical transmitter 11′-b that performs encoding and upconversion in the electrical stage, and an optical receiver that performs decoding and downconversion in the electrical stage. The configuration of 21′-b is shown in FIG.

  The optical transmitter 11′-a of FIG. 5 uses n modulators 15 having different modulation axes or dynamic ranges, and multi-stage modulates the output light from one light source 14 with encoded n-parallel signals and transmits them. . The optical receiver 21′-a in FIG. 7 includes a plurality of light receiving / signal reproducing units 22, and the received light is divided by the splitter 24 and decoded by the decoding unit 25 in the optical stage to receive the light and reproduce the signals, respectively. Do.

  The optical transmitter 11′-b in FIG. 6 generates a multi-level / high-order modulated signal in the digital signal processing unit 16 and uses the signal converted into an analog signal by the digital-analog converter 17, and uses the light from the light source 14. The signal is modulated by the modulator 15 and transmitted. The optical receiver 21 ′ -b in FIG. 8 performs processing reverse to that on the transmission side, converts the received analog signal into a digital signal by the analog-digital conversion unit 27, and performs decoding processing by the digital signal processing unit 28.

High-Order Modulation for Optical Fiber Transmission, Matthias Seimetz, 2009, pp. 26-53, 66-73, 79-81, 84-93, 100-101

  Generally, when the modulation multi-level or the modulation order is increased from a low level to a high level, both the transmitter and the receiver increase in price and power consumption. For example, when FIGS. 2 and 3 are compared with FIGS. 5 and 7 or FIGS. 6 and 8, the number of modulators 15 and light receiving / signal reproducing units 22 that are one for FIGS. 6 and 8, the modulator 15 and the light receiving / signal reproducing unit 22 are one, but the ADC 27, the DAC 17, the upconversion and the downconversion, the digital signal processing unit (16, 28) which is a functional part such as encoding and decoding, and the like. ) Is increasing.

  Regarding configurations other than those shown in FIGS. 5 to 8 for increasing the communication capacity, for example, a high power output laser, an amplifier, a highly sensitive APD may be used in order to ensure an S / N ratio according to the inter-symbol distance, or encoding may be performed. In addition, since the calculation amount for decoding increases, a large-scale signal processing unit may be used at a higher speed. In any case, there is a high possibility of increasing the price and power consumption of the device. In particular, the number of optical receivers is larger than that of transmitters in downlink communication of the PON system. For example, in GE-PON, optical transmitter: optical receiver = 1: 32. Therefore, when the multi-level / high-order modulation signal optical receiver 21 ′ shown in FIGS. 7 and 8 is uniformly mounted on all ONUs 20 ′ as shown in FIG. 4, the cost of the entire network is increased and the power consumption is increased. The impact of computerization is expected to increase. That is, when the communication capacity is increased in the PON system, the effects of high price and high power consumption become problems.

  Therefore, in order to solve the above problems, an object of the present invention is to provide an optical transmitter and an optical transmission system capable of increasing communication capacity while suppressing an increase in cost and power consumption.

  In order to achieve the above object, the optical transmitter according to the present invention performs transmission by performing multi-level / high-order modulation using a code that can be received in a plurality of layers having different capacities for downlink signals. At this time, the optical transmitter refers to the correspondence table in which the destination address of the optical receiver included in each ONU and the receivable layer are stored in association with each other, and determines the modulation layer of each frame according to the destination address. Thus, user multiplexing by hierarchy can be performed.

  Specifically, the optical transmitter according to the present invention refers to a correspondence table that associates a hierarchy of modulation schemes that can be received for each of a plurality of optical receivers that are the destinations of a frame, and refers to the correspondence table. Hierarchical distribution means for assigning each frame to a hierarchy based on a destination, and modulation means for modulating the light of the light source by a modulation method according to the hierarchy of the frames assigned by the hierarchical distribution means.

  This optical transmitter performs multi-level / high-order modulation in the form of hierarchical coding, and uses the hierarchy for user multiplexing. Here, the hierarchical encoding is a scheme in which a hierarchy is divided and encoded so that a signal modulated in advance by a single code can be received as a signal of a plurality of patterns. In one PON system, by using a hierarchical code, a plurality of patterns of optical receivers can be mixed so that the ONU side which is the receiving side can also receive signals in a plurality of layers. For this reason, with this optical communication device, not only ONUs that can receive high-price, high-power-consumption, large-capacity tiers but also ONUs that can only receive low-price, low-power-consumption tiers with low-capacity It can be included in one PON system. That is, the present optical communication device can reduce the price and power consumption without reducing the frequency utilization efficiency of the entire PON system.

  Therefore, the present invention can provide an optical transmitter capable of increasing communication capacity while suppressing increase in price and power consumption.

  At least one of the layers of the optical transmitter according to the present invention is a layer of a modulation scheme that can be received by at least two or more of the optical receivers. This optical transmitter can multicast and broadcast frames.

  The modulation means of the optical transmitter according to the present invention is characterized in that the light of the light source is intensity-modulated by a multistage intensity modulator, and the correspondence table associates a frame destination with the intensity modulator. And

  The modulation means of the optical transmitter according to the present invention encodes the frame to perform phase amplitude modulation of the light of the light source, and the correspondence table associates the destination of the frame with the bit position of encoding. It is characterized by.

  The modulation means of the optical transmitter according to the present invention encodes the frame to perform quadrature amplitude modulation of the light of the light source, and the correspondence table associates the destination of the frame with the bit position of the encoding. It is characterized by that.

  An optical transmission system according to the present invention includes the optical transmitter, a plurality of optical receivers, and an optical transmission path that branches an optical signal from the optical transmitter and couples the optical signal to the optical receiver.

  Since this optical transmission system includes the optical communication device according to the present invention, it is not only an ONU that can receive a high-price, high-power-consumption, large-capacity communication layer, but also a low-priced, low-power-consumption layer with small communication capacity ONUs that cannot be received can also be connected. That is, the present optical transmission system can reduce the price and power consumption without reducing the frequency utilization efficiency of the entire PON system.

  Therefore, the present invention can provide the present optical transmission system capable of increasing the communication capacity while suppressing the increase in price and power consumption.

  The optical transmission system according to the present invention is characterized in that the optical receivers of encoding systems having different reception capacities are mixed.

  The present invention can provide an optical transmitter and an optical transmission system capable of increasing the communication capacity while suppressing an increase in price and power consumption.

It is a figure explaining the structure of PON (OOK). It is a figure explaining the structure of an optical transmitter (OOK). It is a figure explaining the structure of an optical receiver (OOK). It is a figure explaining the structure of PON (multi-value / high-order modulation). It is a figure explaining the structure of an optical transmitter (multi-value / high-order modulation). It is a figure explaining the structure of an optical transmitter (multi-value / high-order modulation). It is a figure explaining the structure of an optical receiver (multi-value / high-order modulation). It is a figure explaining the structure of an optical receiver (multi-value / high-order modulation). It is a figure explaining the optical transmission system concerning the present invention. It is a figure explaining the optical transmitter which concerns on this invention. It is a figure explaining the correspondence table which the optical transmitter concerning the present invention has. It is a figure explaining the optical transmitter which concerns on this invention. It is a figure explaining the optical transmitter which concerns on this invention. It is a figure explaining the correspondence table which the optical transmitter concerning the present invention has. It is a figure explaining the optical transmitter which concerns on this invention. It is a figure explaining the case where the hierarchy of multi-level modulation is divided according to multi-level in the optical transmitter according to the present invention. It is a figure explaining the case where a hierarchy is divided in the optical transmitter which concerns on this invention. It is a figure explaining the case where a hierarchy is divided in the optical transmitter which concerns on this invention. It is a figure explaining the case where a hierarchy is divided in the optical transmitter which concerns on this invention. It is a figure explaining the example of the symbol mapping which is not suitable for hierarchical modulation. It is a figure explaining the optical receiver of the optical transmission system concerning the present invention. It is a figure explaining the optical receiver of the optical transmission system concerning the present invention. It is a figure explaining the optical receiver of the optical transmission system concerning the present invention.

  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. Moreover, when it demonstrates without attaching a branch number, it is description common to all the branch numbers of the said code | symbol.

(Constitution)
FIG. 9 shows the configuration of an optical transmission system 103 that is a PON of this embodiment. The OLT 50 transmits the multilevel / higher order modulation signal in a hierarchical coding format. The ONU 60 includes a receiver capable of receiving a large capacity and a receiver capable of receiving only a small capacity under the splitter 30. The optical transmission system 103 is characterized in that at least one ONU 60 for large capacity reception and one ONU 60 for small capacity reception exist and are mixed.

  A configuration example of the optical transmitter 51 for downstream signals of the OLT 50 will be described with reference to FIGS. FIG. 10 shows an example in which hierarchical modulation is applied to a system that performs multi-level / high-order modulation by modulating light from the light source 14 described in FIG. 5 in multiple stages. FIG. 13 is an example in the case where the encoding / decoding described in FIG. 6 is performed by the digital signal processing unit and hierarchical modulation is applied to the analog transmission scheme.

  The difference in configuration between the optical transmitter of the present embodiment and the optical transmitter of the multilevel / higher order modulation system of FIGS. 5 and 6 is that hierarchical encoding processing is performed before the frame sequence is modulated. is there. This hierarchical encoding process is a process for modulating a corresponding frame in a hierarchy that can be received by the ONU 60 that is the destination of the frame. The hierarchical encoding processing unit 52 has a correspondence table 53. 11 and 14 are examples of the correspondence table 53-a and the correspondence table 53-b, respectively. The correspondence table 53 describes in advance information necessary for modulation in the corresponding layer in each configuration based on information indicating which destination ONU can receive which layer. In addition, instead of the correspondence table as shown in FIG. 11 or FIG. 14, another form of means for obtaining information such as the correspondence table 53 may be used.

  FIG. 12 shows a flow in which hierarchical encoding processing is performed after a frame arrives. The modulator determining unit 54 of the hierarchical encoding processing unit 52-a refers to the destination address stored in the header of the arrived frame. Then, information necessary for modulating the frame in a layer that can be received by the destination ONU 60 is obtained from the correspondence table 53-a. The modulator determination unit 54 distributes the frames in consideration of the order of the modulator 15 so that the destination ONU 60 is modulated in a layer that can be received according to the information in the correspondence table 53-a.

  FIG. 15 shows a flow in which another hierarchical encoding process is performed after a frame arrives. The bit position determination unit 55 of the hierarchical encoding processing unit 52-b refers to the destination address stored in the header of the arrived frame. Then, information necessary for modulating the frame in a layer that can be received by the destination ONU 60 is obtained from the correspondence table 53-b. The bit position determining unit 55 distributes the frames in consideration of the order of the bit strings of the codes so that the destination ONU 60 is modulated in a layer that can be received according to the information in the correspondence table 53-b.

  The operation of the hierarchical encoding processing unit 52 is not limited to the examples of FIGS. The hierarchical coding processing unit 52 only needs to perform an operation that can modulate a frame in a specific hierarchy. Further, in this example, the hierarchical modulation processing is explicitly expressed as a functional block, but this operation may be incorporated into the layer 2 processing and may not be an explicit functional block.

  When the hierarchical encoding processing unit 52 distributes a unicast frame (an ONU individual frame), the frame is modulated in any one of the layers that can be received by the ONU that is the destination of the address of the corresponding frame. Sort out. When allocating multicast or broadcast frames, the hierarchical encoding processing unit 52 distributes the frames so that the destination ONUs are modulated in a hierarchy that can be received in common. For example, in the examples of FIG. 11 and FIG. 14, there is no hierarchy that all ONUs can receive in common. In such a case, the hierarchical encoding processing unit 52 needs to transmit the broadcast signal in two layers. In the case of FIG. 11, the number of the modulator 15 is two layers of 1 and 2. In the case of FIG. 14, the bit positions are two layers of 1 and 2. In consideration of broadcasting, it is possible to configure at least one layer so that all ONUs can receive in common.

  The correspondence table in FIG. 11 and FIG. 14 is updated when a change occurs in the ONU or a receivable hierarchy, such as when the user applies for a service with a higher transmission rate.

  With respect to an allocation method for which address of an ONU to receive a modulation signal of which address, an allocation method of providing services with different communication capacities as an added value is possible. Specifically, the configuration of the optical receiver is intentionally changed for each user, such as using an ONU equipped with an optical receiver capable of receiving a large-capacity hierarchical signal for the desired user, and the charge is differentiated. Service is possible.

  Here, an example of how to divide a symbol hierarchy of a multi-level / higher order modulation signal and a symbol mapping for associating a bit position with a hierarchy will be shown separately in the following three cases.

(1) When dividing a multi-level modulation layer according to multi-levels A layer is divided based only on multi-levels for one modulation axis. An example in which the amplitude modulation is divided into two layers is shown in FIG. In FIG. 16, a four-level ASK signal is divided into two layers by four-value reception using three threshold values and binary reception using one threshold value.

    In FIG. 16, a, b, and c represent inter-symbol distances, and all of them can be set equal with a = b = c. As in the example of FIG. 17, the symbols to be used may be switched depending on whether the hierarchy is divided or not.

  In the example of FIG. 17, the transmission side first modulates the signal with 8-value ASK. If the destination of a frame is an ONU that can receive a large-capacity layer in a certain time slot, it is not necessary to divide the layer, and therefore all eight symbols are used. When a frame addressed to an ONU that can only receive a small-capacity layer is included, information is not included in symbols 2 to 5 in decimal numbers, and only four-value symbols 0, 1, 6, and 7 are used. .

  In either case, the symbol mapping as shown in FIGS. 16 and 17 allows the MSB (most significant bit) and the LSB (least significant bit) to be received at the time of binary reception. Only the MSB can be received. It should be noted that the number of layers can be increased to three or more by changing the axis other than the amplitude of the multi-level modulation (phase or the like) or increasing the multi-level.

(2) When the higher-order modulation layer is divided according to the dimension Modulation is performed with the order of the second or higher order, and the layer is divided according to the modulation axis. An example of phase amplitude modulation is shown in FIG. In this example, it is divided into a layer that receives all 4 bits by amplitude and phase, a layer that receives 3 bits other than the MSB only by phase, and a layer that receives 1 bit of MSB only by amplitude.

  Although phase amplitude modulation is shown here, it is also possible to use another axis such as polarization as the modulation axis, increase the number of modulation multi-values, and increase the number of layers.

(3) Case of Dividing Multi-Level / High-Order Modulation Hierarchy Based on Multi-Value / Order An example in which a multi-level / high-order modulation signal is divided into multi-level / high-order modulation having a smaller multi-level is shown in FIG. Show. In this example, a signal modulated by 64QAM is received in three layers of 64QAM, 16QAM, and QPSK.

  The inter-symbol distance can be set to be equal to all of a = b = c, or is inclined so that a> b> c, or when hierarchical modulation is performed as in FIG. There are cases where symbols that are not used are specified and the symbol mapping method is switched.

  As shown in FIGS. 16 to 19, the hierarchical encoding processing unit 52 in FIGS. 12 and 15 needs to distribute frames so that the bit position corresponding to the destination address can be received in the bit string corresponding to each symbol. There is.

  Further, the symbol mapping is not limited to the examples of FIGS. 16 to 19, but it must be taken into consideration so that data of a specific layer can be extracted by the receiving unit. FIG. 20 is an example of symbol mapping by 16APSK gray code. When performing encoding by digital signal processing or the like, if it is desired to perform mapping as shown in FIG. 20, it is necessary to add a function for converting mapping.

  FIG. 21 and FIG. 22 show a configuration example of an ONU optical receiver capable of receiving a layer with a large communication capacity in the configuration of the present embodiment. FIG. 21 and FIG. 22 show a configuration example of an ONU optical receiver capable of receiving only a layer with a small communication capacity. It shows in FIG. An optical receiver 61-a in FIG. 21 is a configuration example when hierarchical modulation is applied to the optical receiver 21'-a in FIG. An optical receiver 61-b in FIG. 22 is a configuration example when hierarchical modulation is applied to the optical receiver 21'-b in FIG.

  The difference between the optical receiver 61 and the optical transmitter 21 ′ of FIGS. 7 and 8 is configured so that the frames that are modulated and transmitted by the optical transmitter 61 for each layer can be restored for each allocated frame. Is a point. An ONU that can receive a layer with a large communication capacity receives a signal including a layer with a small communication capacity, but determines whether the frame is addressed to itself after being restored to a frame.

  FIG. 23 is a diagram for explaining an optical receiver 71 possessed by an ONU that can receive only a modulated signal of a layer having a small communication capacity. The optical receiver 71 has the same configuration as that of the optical receiver 21 in FIG. 3, or a change is made to the threshold determination portion or the like so that only a signal having a low capacity can be determined in symbol mapping as shown in FIGS. Is. The price and power consumption of the optical receiver 71 are lower than those of the optical receiver 61 shown in FIGS.

  The configuration of the optical receiver is not limited to the configurations of FIGS. The light receiving / signal reproducing unit 22 has a function of restoring all signals in the receivable layer set in itself. For example, the light receiving / signal reproducing unit 22 needs to have a function of receiving phase information if the optical transmitter is transmitting by phase modulation in a receivable hierarchy, and if it is encoded and transmitted by digital signal processing. DAC / ADC is required.

(Operation)
When transmitting a PON downstream signal, a time-multiplexed frame sequence is input to an optical transmitter 51 having a structure that performs FIG. 10 to 12, FIG. 13 to 15, or other hierarchical modulation. First, the hierarchical encoding processing unit 52 reads the destination of the ONU 60 stored in the header of the frame, and refers to the correspondence table 53 and allocates each frame to the hierarchy so that the destination ONU 60 can receive the frame.

  In the case of the optical transmitter 51-a in FIGS. 10 to 12, the allocated frame is modulated by a different modulator for each layer. This transmission signal is restored to a frame by the ONU optical receiver 61-a that can receive the large-capacity layer described in FIG. The optical receiver 61-a branches the transmission signal by the optical splitter 24, decodes it by the decoding unit 25 of the optical stage, and restores the transmission signal by the plurality of light receiving / signal reproducing units 22. Therefore, the optical receiver 61-a can restore a frame for each allocated frame.

  In the case of the optical transmitter 51-b in FIGS. 13 to 15, the hierarchical encoding processing unit 52-b allocates a frame to an appropriate bit position using the correspondence table 53-b, and performs parallel / serial conversion on the allocated frame. I do. The digital signal processing unit 16 performs encoding on a bit string arranged at a desired bit position. This transmission signal is restored to a frame by the ONU optical receiver 61-b that can receive the large-capacity layer described in FIG. In the optical receiver 61-b, the transmission signal is AD converted by the analog / digital conversion unit 27 and decoded by the digital signal processing unit 28. Then, the optical receiver 61-b can restore the frame for each distributed frame by serial-parallel conversion of the decoded signal.

  In this example, parallel serial conversion is explicitly shown as a functional block, but there is no parallel serial conversion functional block, and the digital signal processing unit 28 performs an operation that can obtain the same result. Sometimes it is done.

  On the other hand, the optical receiver 71 of FIG. 23 can receive only a signal of a small capacity layer when transmitted by any of the optical transmitters 51 of FIG. 10 and FIG. Only.

  After the frame is restored, both the optical receiver 71 and the optical receiver 61 receive or discard the frame depending on whether it is addressed to itself according to the destination address stored in the header of the frame, as in the TDM-PON system. Decide what to do.

(effect)
The optical transmitter 51 and the optical transmission system 103 have the following effects.
The optical transmission system 103 in FIG. 9 arranges ONUs including high-priced and high-power-consumption optical receivers necessary for receiving multilevel / high-order modulation signals only at necessary locations under the splitter. On the other hand, the PON system 102 of FIG. 4 arranges ONUs including optical receivers with high cost and high power consumption under all of the splitters. However, the optical transmission system 103 can configure a PON system with the same frequency utilization efficiency as the PON system 102. Here, the same frequency utilization efficiency represents that a downlink signal can be transmitted at the highest bit / symbol that can be transmitted by the OLT in all time zones.

A comparison of the optical receiver of the PON system 102 and the optical receiver of the optical transmission system 103 reveals the following points. Although there are some differences depending on the components, FIGS. 7, 821, and 22 are high-priced and high-power-consumption optical receivers, and FIG. 23 is a low-priced and low-power-consumption optical receiver. For example, when a PON of 1:32 is configured, the multilevel / modulation method of the PON system 102 is an OLT × 1 including the optical transmitter 11′-a in FIG.
ONU × 32 including the optical receiver 21′-a in FIG.
Or OLT × 1 including the optical transmitter 11′-b of FIG.
ONU × 32 including the optical receiver 21′-b of FIG.
Thus, all 32 ONUs become high-priced and high-power optical receivers.
On the other hand, the optical transmission system 103 is
OLT × 1 including the optical transmitter 51-a of FIG.
ONU × 16 including the optical receiver 61-a of FIG.
ONU × 16 including the optical receiver 71 of FIG.
Or OLT × 1 including the optical transmitter 51-b of FIG.
ONU × 16 including the optical receiver 61-b of FIG.
ONU × 16 including the optical receiver 71 of FIG.
With this configuration, it is possible to achieve the same frequency use efficiency as that of the PON system 102.

  The ONU 60 including the optical receiver 61 of FIGS. 21 and 22 and the ONU 60 including the optical receiver 71 of FIG. 23 are not limited to the same number, but all of the ONUs 60 under the splitter 30 have high prices and high power consumption. The optical receiver 61 is not configured, and the optical receiver 71 of FIG. 23 having a low price and low power consumption can be included.

  For this reason, the optical transmission system 103 can realize multi-level / high-order modulation PON with lower cost and lower power consumption without lowering the frequency utilization efficiency as compared with the PON system 102.

  The configuration and operation of the transmitter / receiver in the present embodiment are described as for one-channel transmission for ease of explanation, but are not limited to one-channel transmission. For example, the optical transmitter and the optical transmission system according to the present invention can also transmit signals to be transmitted in multiple channels in parallel by using a part of the configuration in plural and adding a function for multiplexing channels. It is.

10, 10 ': OLT
11, 11 ′, 11′-a, 11′-b: optical transmitter 14: light source 15: modulator 16: digital signal processing unit 17: digital / analog converters 20, 20-1, 20-2,. , 20-m (m is an arbitrary integer): ONU
20 ′, 20′-1, 20′-2,..., 20′-m (m is an arbitrary integer): ONU
21, 21 ′, 21 ′ -a, 21 ′ -b: optical receiver 22: light reception / signal reproduction section (“/” here means that both light reception and signal reproduction are performed)
24: splitter 25: decoding unit 27: analog-digital conversion unit 28: digital signal processing unit 30: splitter 40: optical fiber 50: OLT
51, 51-a, 51-b: Optical transmitters 52, 52-a, 52-b: Hierarchical encoding processing unit 53, 53-a, 53-b: Correspondence table 54: Modulator determination unit 55: Bit position Determination unit 60, 60-1, 60-2, ..., 60-m (m is an arbitrary integer): ONU
61, 61-a, 61-b: optical receiver 71: optical receiver 101, 102: PON system 103: optical transmission system

Claims (3)

A station-side terminator connected to one or more subscriber-side terminators via an optical transmission line and an optical power splitter,
By encoding a downlink frame addressed to the subscriber-side terminating device with a single set encoding method, a combination of one of a predetermined binary amplitude value and a predetermined multi-value phase value An optical transmitter that uses a plurality of symbols having the represented bit positions and modulates an optical multilevel phase amplitude modulation signal in which a code of 2 bits or more is associated with one symbol;
The optical transmitter in accordance with the hierarchy defined in a range of bit position or bit position of the subscriber-side termination apparatus can receive the optical multilevel amplitude modulation signal, the subscriber-side terminations of the destination of the downlink frame have a hierarchical coding processing unit for performing hierarchical coding process for coding by the single encoding scheme in accordance with the hierarchy of the device,
The hierarchical encoding processing unit
The downstream frame addressed to the subscriber-side terminal device of the first layer is distributed to predetermined one bit of the code of 2 bits or more, and the value represented by the predetermined one bit and the binary amplitude value in the symbol And correspondingly,
The downstream frame addressed to the subscriber terminal on the second layer is allocated to bits other than the predetermined 1 bit of the code of 2 bits or more, and the value and the symbol represented by the bits other than the predetermined 1 bit The station-side termination device characterized in that the multilevel phase value in the encoding is associated with each other . The station-side termination device according to claim 1 , wherein the optical transmitter further includes a correspondence table in which the subscriber-side termination device is associated with a hierarchy. An optical transmission system for connecting the station-side terminator according to claim 1 or 2 and a plurality of subscriber-side terminators via an optical transmission line and an optical power splitter,
The subscriber side terminating device of one or more of the first hierarchy of the plurality of subscriber-side termination apparatus, the symbols of the optical multilevel amplitude modulation signal the station side terminating transmits, one amplitude threshold To receive the predetermined 1 bit of the code of 2 bits or more corresponding to the symbol ,
The other subscriber side terminating device of the second hierarchy among the plurality of subscriber terminating device, the symbols of the optical multilevel amplitude modulation signal the station side terminating transmits, the using phase threshold value An optical transmission system for receiving a bit other than the predetermined one bit of the code of 2 bits or more corresponding to a symbol .

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