JP4843650B2 - Optical transmission equipment - Google Patents

Description

  The present invention relates to an optical transmission apparatus. In particular, the present invention relates to an optical transmission device using a trellis code.

  In recent years, the amount of light allocated to one symbol has decreased due to the increase in capacity of digital optical transmission systems. Due to the decrease in the amount of light, a transmitter / receiver having a high receiving sensitivity for ensuring a desired signal quality is required. As a result, the configuration of the transceiver is complicated, and the cost merit obtained by the increase in capacity is offset.

  By the way, in terms of cost, the same code sequence in data transmission is one of the cost factors of the transmitter. Since a sequence of the same code includes a low frequency component in a data string, an optical modulator for driving data onto carrier light and a driver amplifier (high-speed electric amplifier) for driving the data are several megahertz to several tens of modulation frequencies. This is because a low distortion and high output amplifier is required in a wide bandwidth up to gigahertz. As an example in which the same code continues, for example, in OTN transmission, which is a standard technology for optical transmission, the same code may continue for 60 symbols or more. Note that the use of the FEC of the Reed-Solomon code RS (255, 239) adopted in G.709 has no effect of removing the same code sequence.

  On the other hand, a measure for suppressing (limiting) the continuation of the same code has been devised. For example, in the SDH transmission system, a method of suppressing the continuation of the same code using a scrambler or the like has been devised. Further, in the case of Ethernet (registered trademark), continuation of the same code is suppressed to 5 bits or less by 8B / 10B encoding, but in 64B / 66B, 66 bits may be continuous.

  In radio technology, the power efficiency of the power amplifier is improved by using a modulation method called offset PSK or staggered PSK (π / 4 shift QPSK, etc.) so that the same code is not continuous. The sensitivity has not improved.

In wireless transmission, trellis-coded transmission has been studied as one of the measures for improving reception sensitivity, and has already been put into practical use in fields such as satellite broadcasting. Trellis-encoded transmission has been studied with an improvement in reception sensitivity, in other words, an increase in encoding gain, as a priority issue, and there are cases where many identical codes continue. In other words, at the present time, there is no effect of relaxing the above-described requirements for the driver amplifier. Trellis encoded transmission may be used together with OFDM transmission.
JP 2001-268039 A JGPROAKIS (translated by Yoshikazu Sakaiba) “Digital Communication” Science and Technology Publication 1999, P.223-227 BS digital broadcasting, [online], [search September 1, 2008], Internet <URL: http://www.nhk.or.jp/strl/open98/happyo/kl/index.html> E. Biglieri et al., Introduction to Trellis-Coded Modulation with Applications, Macmillian Publishing Company, 1991. Charan Langton, Trellis Coded Modulation, [online], [searched September 1, 2008], Internet <URL: http://www.complextoreal.com/chapters/tcw.pdf>

  From the above, there is a problem that there is no encoding transmission method that has high reception sensitivity and can narrow the bandwidth of the driver amplifier.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an encoded transmission system that has high reception sensitivity and can narrow the bandwidth of a driver amplifier.

In order to solve the above-described problem, an optical transmission device according to an aspect of the present invention uses a trellis encoding unit that outputs a code from an input value by trellis encoding, and an optical signal using the code output from the trellis encoding unit. An optical modulation unit that modulates a carrier wave, and a signal that is input to the optical modulation unit before the optical modulation unit, or a signal that is output from the optical modulation unit after the optical modulation unit is RZ (Return-to-to -Zero) RZ conversion unit , wherein the trellis encoding unit 2 ^ (2 (() so as not to continuously output the same code from the input value of 2 ^ n values ) The sign of the (n + 1) value is output, and the optical modulation unit performs phase modulation or quadrature amplitude modulation of the carrier wave using the sign of the 2 ^ (n + 1) value .

In order to solve the above problem, an optical transmission apparatus according to another aspect of the present invention uses a trellis encoding unit that outputs a code from an input value by trellis encoding, and a code output from the trellis encoding unit. Te a Bei obtain an optical transmission device and an optical modulator for modulating an optical carrier, the trellis encoding unit in the current 2 ^ m pieces of state to reflect the value of the code up to m th previous When one state is stored and one input value is acquired in one state, a code associated with the input value is output in the state, and another code that is not associated with the code is output. By storing the state as the current state, the code different from the previous code output from the previous input value is output from the current input value.

In order to solve the above problem, an optical transmission device according to another aspect of the present invention includes a trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value, and the trellis encoder An optical modulation unit that phase- modulates an optical carrier wave using the n + 1-bit code output from the signal, and a signal input to the optical modulation unit before the optical modulation unit, or RZ (Return-to-Zero) RZ converting unit that outputs a signal output from the optical modulation unit, wherein the trellis encoding unit outputs the previous output from the previous input value The code different from the code is output from the current input value, and the optical modulation unit calculates a phase of the carrier wave related to the previous input value and a phase of the carrier wave related to the current input value to 360 / (2 ^ (N + )), Wherein the varying degrees or more.

In order to solve the above problem, an optical transmission device according to another aspect of the present invention includes a trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value, and the trellis encoder And an optical modulation unit that phase-modulates an optical carrier wave using the n + 1-bit code output from the network , wherein the trellis encoding unit calculates the value of the code from the present to the previous m Storing one state in the reflected 2 ^ m states, and obtaining one input value in one state, outputting a code associated with the input value in the state; and The other state not associated with the code is stored as the current state, so that the code different from the previous code output from the previous input value is output from the current input value, and the light The modulator is And the phase of the carrier wave according to the input value, and wherein varying the phase 360 / (2 ^ (n + 1)) degrees or more carriers according to the current of the input value.

In order to solve the above problem, an optical transmission device according to another aspect of the present invention includes a trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value, and the trellis encoder An optical modulation unit that performs quadrature amplitude modulation of an optical carrier wave using the n + 1-bit code output from the signal, and a signal that is input to the optical modulation unit before the optical modulation unit, or a subsequent stage of the optical modulation unit RZ (Return-to-Zero) RZ converting unit that outputs a signal output from the optical modulation unit , wherein the trellis encoding unit outputs the previous output from the previous input value and outputs the code different from the code from the input value of the current times, the light modulating unit, at least one of the phase or amplitude of the carrier wave according to the input value of the current time, the carrier wave according to the input value of the previous And wherein to Rukoto to be different from the phase or amplitude.

In order to solve the above problem, an optical transmission device according to another aspect of the present invention includes a trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value, and the trellis encoder And an optical modulation unit that performs quadrature amplitude modulation on an optical carrier wave using the n + 1-bit code output from the optical transmission device, wherein the trellis encoding unit is configured to output the value of the code from the present to the previous m When one input value is acquired in one state, a code associated with the input value in the state is output, and outputs the other state not associated with the code I'll be stored as the current state, the previous the code different from the code which is output from the input value of the previous from the input value of the current times, The light modulator is At least one of the phase or amplitude of the carrier wave according to the present the input values, characterized in that the different from the phase or amplitude of the carrier wave according to the input value of the previous.

  According to the present invention, since the value of the modulation code input to the optical modulation / demodulation unit is not continuous, in other words, since the signal input to the optical modulator is not the same in consecutive symbols, the narrow band as a modulator driver is obtained. It becomes possible to use a simple electric amplifier. Therefore, a low cost amplifier can be provided. Further, since it is based on trellis coded transmission, the reception sensitivity can be maintained at a high level to some extent. Furthermore, since a narrow-band electrical amplifier is generally more efficient than a wide-band amplifier, power consumption can be reduced and the power supply circuit can be simplified.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram for explaining a transmission apparatus 1 which is an example of an optical transmission apparatus according to an embodiment of the present invention. A ^ B indicates A to the Bth power.

  As illustrated in FIG. 1A, the transmission device 1 includes a laser unit 11, a trellis encoding unit 12, a driver (driver amplifier) 13, and an optical modulation unit (optical modulator) 14. The laser unit 11 outputs carrier light (carrier wave). The trellis encoder 12 outputs a code (modulation code) from the data (input value) by trellis encoding. The driver 13 drives the optical modulation unit 14 in order to superimpose the code output from the trellis encoding unit 12 on the carrier light. The light modulation unit 14 modulates the carrier light with the code under the control of the driver 13. The modulated carrier light is transmitted to the optical fiber 9, and is relayed by the optical amplifier 3 or the like as necessary and transmitted to the receiving device 2. The optical modulation unit 14 may have a function of an optical demodulation unit 24 (described later), and the optical demodulation unit 24 may have a function of the optical modulation unit 14.

  The trellis encoding unit 12 outputs n + 1 bits from the n-bit data signal. That is, the trellis encoder 12 outputs a 2 ^ (n + 1) value code from 2 ^ n value data (input value). For example, when 2 bits (4 values) of data is input, the trellis encoder 12 stores 4 states reflecting values from the current symbol (code) to the value 2 symbols before, and based on that. 3 bits (8 values) are output.

  The trellis encoder 12 does not continuously output the same code regardless of the data (input value). Specifically, when the trellis encoding unit 12 stores a plurality of states in which data (input values) and codes are associated with each other and the current state, and acquires an input value in a certain state, the state Output the code associated with the input value and store the other state not associated with the code as the current state so that the same code is not continuously output. Yes.

  When the data (input value) is a 2 ^ n value, the optical modulation unit 14 outputs a 2 ^ (n + 1) value code by the trellis encoding unit 12, and thus performs a 2 ^ (n + 1) value multilevel modulation. Do. The Viterbi algorithm is mainly used for decoding by the driver 13 when performing modulation. Modulation / demodulation is not described in detail because it is described in textbooks, but as an optical modulation method, 8-phase phase modulation is used in the case of 8 values, and 16QAM modulation is used in the case of 16 values. That is, a known technique can be used for modulation / demodulation.

  The transmission device 1 may include an optical modulation unit 15 for RZ (Return-to-Zero) pulsing before or after the optical modulation unit 14 as illustrated in FIG. . This is to reduce the influence on the long-distance transmission characteristics. That is, in phase modulation, since there is a phase change between symbols (input values), an instantaneous frequency change (chirp) that hinders long-distance transmission occurs at the symbol change. In particular, when the bandwidth of the modulator driver amplifier is narrowed as in the present invention, since the switching time between symbols becomes long, the time during which chirp occurs is relatively increased. By making the RZ pulse, the electric field strength at the change of the symbol is reduced, and the influence of the chirp on the long-distance transmission characteristics can be reduced.

  As illustrated in FIG. 1A, the receiving device 2 includes a light receiving unit (light receiving unit) 21, a trellis decoding unit 22, a driver (driver amplifier) 23, and an optical demodulation unit (optical demodulator) 24. The light receiving unit 21 returns the modulated carrier light transmitted from the transmission device 1 to an electrical data signal. The driver 23 drives the optical demodulation unit 24 to demodulate the data signal output from the light receiving unit 21. The optical demodulator 24 demodulates the data signal under the control of the driver 23. The trellis decoding unit 22 outputs data (output value) from the code by trellis decoding.

  The trellis decoding unit 2 performs decoding using the Fano algorithm or the Viterbi algorithm in consideration of the trellis transition state from the continuously received M symbols (M> m). For example, when these algorithms follow the trellis shown in FIG. 3, if 0, 2, 4, and 6 are received at a certain time, they are transmitted from the state of S1 or S3, and the preceding symbol is S2 or S4. Therefore, it must be one of 1, 3, 5, and 7, and if it is not so, an error has occurred and it becomes a candidate for correction. In this way, a data string that can reproduce a series of symbols that change according to the trellis with the least inconsistency is determined to be a correct data string. Each symbol to be received is n bits per symbol, that is, 2 ^ n values, and what is decoded is (n-1) bits per symbol before trellis coding.

  Next, trellis encoding by the trellis encoding unit 12 will be described in comparison with a trellis encoding unit by conventional trellis encoding. A case where 2-bit (four-value) data (input value) is input (when eight values are subjected to 8-phase phase modulation) will be described as an example. FIG. 5 is a transition diagram (trellis diagram) of a conventional 2-bit, 4-state trellis code. FIG. 2 is a signal point arrangement diagram (Constellation diagram) when eight values are converted into eight phases. In FIG. 5, S1 to S4 are states (transition states) in which the conventional trellis coding unit can transition. For example, when the current state is the state S1, the conventional trellis encoding unit transitions to the state S1 or the state S3 according to the output code. Specifically, in the case where the current state is state S1, the conventional trellis encoding unit does not change the state S1 when the codes 0 and 4 are output, and the state when the codes 2 and 6 are output. Transition to S3. Similarly, in the case where the current state is state S2, the conventional trellis encoding unit transitions to state S1 when codes 1 and 3 are output, and to state S3 when codes 5 and 7 are output. Transition. The same applies when the current state is the state S3 or S4.

  FIG. 6 is an operation example of encoding according to the transition diagram shown in FIG. In the conventional coding shown in FIG. 6, 3-bit outputs y1, y2, and y3 (y1: most significant bit, y2: with respect to 2-bit inputs a1, a2 (a1: upper bits, a2: lower bits) The second bit, y3: the least significant bit) is obtained, and the four states that the encoding unit can take are stored by the two bits R1 and R2. Note that T in FIG. 6 represents a delay of one symbol. In the conventional encoding shown in FIG. 6, when the current state is the state S1 (R1 = 0, R2 = 0) or the state S3 (R1 = 1, R2 = 0), 1 bit having a value of 0 is assigned to the least significant bit. In addition, when the current state is the state S2 (R1 = 0, R2 = 1) or the state S4 (R1 = 1, R2 = 1), it operates so as to add 1 bit having a value of 1 to the lowest order. That is, the value of the least significant bit y3 of the output is the value of R2.

  Specifically, when the input value (0,0) is input when the state at a certain time T1 is the state S1, a bit (0) is added to the least significant bit and the code 0 (0,0,0) And the state at the next time T2 is the state S1.

  When the input value (1, 0) is input, the bit (0) is added to the least significant bit and the code 4 (1, 0, 0) is output, and the state at the next time T2 is the state S1. .

  When the input value (0, 1) is input, the bit (0) is added to the least significant bit and the code 2 (0, 1, 0) is output, and the state at the next time T2 is the state S2. .

  When the input value (1, 1) is input, the bit (0) is added to the least significant bit and the code 6 (1, 1, 0) is output, and the state at the next time T2 is the state S2. .

  That is, the codes that the trellis encoder can output in the state S1 at time T1 are 0 (0, 0, 0), 2 (0, 1, 0), 4 (1, 0, 0), 6 (1 , 1, 0), but when the state at the subsequent time T2 is the state S1, S3, 0 (0,0,0), 2 (0,1,0), 4 (1 , 0, 0), 6 (1, 1, 0) can be output, so that the same code may be output continuously. Specifically, when the input value (0, 0) is input in the state S1 at the time T1, the state S1 remains unchanged, so when the input value (0, 0) is input at the time T2. Outputs the code 0 continuously. When the input value (1, 0) is input, the state S1 remains unchanged. Therefore, the next time the input value (1, 0) is input, the code 4 is continuously output. The same applies when the state at the time T1 is the state S2 to S4. As described above, in the conventional trellis encoder, the same code may be output continuously. This is the same even when the number of states increases to 8 or more.

  As described above, since 2-bit (4-level) data (input value) is mapped to 3-bit (8-level) code by the conventional trellis encoder, optical modulation at the subsequent stage of the conventional trellis encoder is performed. For example, as shown in FIG. 2, the unit modulates the phase of the carrier light using an 8-level code having a phase difference of 45 degrees. That is, when the conventional trellis encoder outputs a 2 ^ (n + 1) -value code from 2 ^ n-value data (input value), the optical modulator at the subsequent stage of the conventional trellis encoder 2 ^ The carrier wave is phase-modulated or quadrature-amplitude modulated using the sign of the (n + 1) value. However, in the case of phase modulation, if the same code is continuously output from the conventional trellis encoder, continuous data (input value), that is, previous data (input value) and current data The phase of the carrier wave related to (input value) does not change, and the phase and amplitude of continuous data (input value) do not change even when quadrature amplitude modulation is performed.

  On the other hand, in the trellis encoding 12 according to the present invention, the same code is not continuously output. FIG. 3 is a transition diagram (trellis diagram) of a 2-bit, 4-state trellis code according to the present invention. In FIG. 3, S1 to S4 are states in which the trellis encoder 12 can make a transition. For example, when the current state is the state S1, the trellis encoding unit 12 transitions to the state S2 when the codes 0 and 4 are output, and transitions to the state S4 when the codes 2 and 6 are output. . Similarly, when the current state is the state S2, the trellis encoding unit 12 transitions to the state S1 when the codes 1 and 3 are output, and transitions to the state S3 when the codes 5 and 7 are output. To do. The same applies when the current state is the state S3 or S4. Similarly to the conventional trellis encoding unit, the trellis encoding unit 12 adds 1 bit having a value of 0 to the lowest order when the current state is the state S1 or the state S3, and the current state is the state S2 or In the case of state S4, 1 bit having a value of 1 is added to the lowest order.

  When the input value (0,0) is input when the state at a certain time T1 of the trellis encoder 12 is the state S1, the bit (0) is added to the least significant bit and the code 0 (0,0,0) is input. ) And the state at the next time T2 becomes the state S2.

  When the input value (1, 0) is input, the bit (0) is added to the least significant bit and the code 4 (1, 0, 0) is output, and the state at the next time T2 is the state S2. .

  When the input value (0, 1) is input, the bit (0) is added to the least significant bit and the code 2 (0, 1, 0) is output, and the state at the next time T2 is the state S4. .

  When the input value (1, 1) is input, the bit (0) is added to the least significant bit and the code 6 (1, 1, 0) is output, and the state at the next time T2 is the state S4. .

  That is, the codes that the trellis encoder 12 can output in the state S1 at the time T1 are 0 (0, 0, 0), 2 (0, 1, 0), 4 (1, 0, 0), 6 ( 1, 1, 0), but the states at the subsequent time T 2 are the states S 2 and S 4, and the codes that can be output in the states S 2 and S 4 are 1 (0, 0, 1), 3 (0 , 1, 1), 5 (1, 0, 1), or 7 (1, 1, 1), the trellis encoder 12 does not continuously output the same code. The same applies when the state at the time T1 is the state S2 to S4.

  As described above, since the 2-bit (4-value) data (input value) is mapped to the 3-bit (8-value) code by the trellis encoder 12, the optical modulator 14 at the subsequent stage of the trellis encoder 12. In the same way as the optical modulation unit at the subsequent stage of the conventional trellis encoding unit, for example, as shown in FIG. 2, the carrier light is phase-modulated using an 8-level code having a phase difference of 45 degrees. That is, when the trellis encoding unit 12 outputs a 2 ^ (n + 1) value code from the 2 ^ n value data (input value), the optical modulation unit 14 uses the 2 ^ (n + 1) value code. The carrier wave is phase modulated or quadrature amplitude modulated. Further, in the case of phase modulation, since the same code is not continuously output from the trellis encoder 12, the phase of the carrier wave related to continuous data (input value) changes by 360 / (2 ^ (n + 1)) degrees or more. Even in the case of quadrature amplitude modulation, at least one of the phase or amplitude of the carrier wave associated with continuous data (input value) changes.

  Since the trellis encoder 12 shown in FIG. 3 performs the same transition as the two-state trellis, the encoding gain is 1.1 dB, which is lower than that of the conventional 3 dB. However, by using a 2-bit, 8-state trellis code, a transition equivalent to that of a conventional 2-bit, 4-state trellis code can be performed, so that a gain of 3 dB can be ensured. Note that the gain when the state is set to 8 states using the conventional trellis code is 4.7 dB. That is, the continuation of the same code is avoided at the expense of some coding gain. Further, the sacrificed gain can be recovered by doubling the number of states. To double the number of states, the number of data registers should be increased by one. A method for calculating the gain is described in Non-Patent Document 3 (P74).

  Subsequently, the light modulation unit 14 will be briefly supplemented. FIG. 4 is a configuration example of the optical modulation unit 14 which is an optical 8PSK modulator. Since it is 8PSK, modulation is performed with 3 bits per symbol (input value). FIG. 4A shows an example in which the optical modulation unit 14 is mounted as one optical phase modulator 14a. The driver 13 is mounted as a driver 13a for the optical phase modulator 14a.

  In FIG. 4A, when the same code is not continuous (actually, the same code is not continuous because it is installed at the subsequent stage of the trellis encoder 12), at least ± 360 / (2 ^ 3) for each symbol. ) Degrees, that is, at least ± 45 degrees of phase change, the low frequency side band of the driver 13a only needs to be 1/8 of the baud rate. Further, since the band on the high frequency side of the driver 13a has a maximum phase change of ± 180 degrees, it becomes ½ of the baud rate as in the normal case.

  In FIG. 4B and FIG. 4C, the optical modulation unit 14 includes three optical phase modulators 14b, 14c, and 14d for each bit, or three optical phase modulators 14e, 14f, and 14g. It is an example to be implemented. The driver 13 is mounted as three drivers 13b, 13c, 13d for the phase modulators 14b, 14c, 14d, or three drivers 13e, 13f, 13g for the phase modulators 14e, 14f, 14g. .

  FIG. 4B is a cascade of phase modulators 14b, 14c, and 14d that perform π, π / 2, and π / 4 phase modulation. In FIG. 4C, π phase modulation is performed by each arm (phase modulators 14e and 14f) of the Mach-Zehnder interferometer, and the phase on the Q-axis side is shifted by π / 2 and combined to perform four-phase phase modulation. After that, 8PSK is generated by performing phase modulation of π / 4. In the case of trellis encoding by the trellis encoding unit 12 shown in FIG. 3, the bit “D” is always inverted for each symbol. That is, the D drivers 13d and 13g may be narrow band drivers having a peak in a half band of the baud rate. For I and Q, the same driver is used as usual. In many cases, the phase modulator (π) is used by inverting the intensity modulator.

  That is, when the optical modulator 14 is an optical 8PSK modulator, the driver 13 can be narrowed. Even when the optical modulation unit 14 is quadrature amplitude modulation such as 16QAM, the modulation code output from the trellis encoding 12 changes for each symbol as in the case of phase modulation such as 8PSK modulation. The band can be narrowed.

  As described above, according to the present invention, since the value of the modulation code input to the optical modulation / demodulation unit is not continuous, in other words, since the signal input to the optical modulator is not the same in consecutive symbols, Narrow band electrical amplifiers can be used. Therefore, a low cost amplifier can be provided. Further, since it is based on trellis coded transmission, the reception sensitivity can be maintained at a high level to some extent. Furthermore, since a narrow-band electrical amplifier is generally more efficient than a wide-band amplifier, power consumption can be reduced and the power supply circuit can be simplified.

  Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes a design and the like within a scope not departing from the gist of the present invention.

It is a figure for demonstrating the transmitter 1 which is an example of the optical transmission apparatus which concerns on embodiment of this invention. It is a signal point arrangement | positioning figure at the time of carrying out 8-phase phase conversion of 8 values. FIG. 6 is a transition diagram of a 2-bit, 4-state trellis code according to the present invention. It is an example of a structure of the optical modulation part 14 in the case of carrying out optical 8PSK modulation. It is a transition diagram of a conventional 2-bit, 4-state trellis code. 6 is an operation example of encoding according to the transition diagram shown in FIG. 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Transmission apparatus 2 Reception apparatus 3 Optical amplifier 9 Optical fiber 11 Laser part 12 Trellis encoding part 13 Driver 14 Optical modulation part 15 Optical modulation part (RZ conversion part) 21 Light receiving part 22 Trellis decoding part 23 Driver 24 Optical demodulation part

Claims (6)

A trellis encoder that outputs a code from an input value by trellis encoding ;
An optical modulation unit that modulates an optical carrier using a code output from the trellis encoding unit;
An RZ conversion unit that converts a signal input to the optical modulation unit before the optical modulation unit or a signal output from the optical modulation unit after the optical modulation unit into RZ (Return-to-Zero); An optical transmission device comprising:
The trellis encoder is
In order not to continuously output the same sign from the input value of 2 ^ n values, the sign of 2 ^ (n + 1) values is output,
The light modulator is
An optical transmission apparatus characterized in that a carrier wave is phase-modulated or quadrature-amplitude modulated using the sign of the 2 ^ (n + 1) value . A trellis encoder that outputs a code from an input value by trellis encoding;
An optical transmission apparatus to obtain Bei the <br/> a light modulation unit that modulates the optical carrier using the code outputted from the trellis encoder,
The trellis encoder is
When one state is stored in 2 ^ m states reflecting the value of the code from the present to the previous m and when one input value is acquired in one state, the input value in that state The code different from the previous code output from the previous input value is output by outputting the code associated with the current state and storing the other state not associated with the current code as the current state. the optical transmission apparatus and outputs from current said input value. A trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value;
A light modulator for phase modulating the optical carrier with the code of n + 1 bits output from the trellis encoder,
An RZ conversion unit that converts a signal input to the optical modulation unit before the optical modulation unit or a signal output from the optical modulation unit after the optical modulation unit into RZ (Return-to-Zero);
An optical transmission device comprising:
The trellis encoder is
The code different from the previous code output from the previous input value is output from the current input value,
The light modulator is
And the phase of the carrier wave according to the input value of the previous, the phase 360 / carrier according to the current of the input value (2 ^ (n + 1) ) optical transmission apparatus you wherein Rukoto varying degrees or more. A trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value;
An optical modulation unit for phase modulating an optical carrier wave using the n + 1-bit code output from the trellis encoding unit;
An optical transmission device comprising:
The trellis encoder is
When one state is stored in 2 ^ m states reflecting the value of the code from the present to the previous m and when one input value is acquired in one state, the input value in that state The code different from the previous code output from the previous input value is output by outputting the code associated with the current state and storing the other state not associated with the current code as the current state. Is output from the input value of this time ,
The light modulator is
And the phase of the carrier wave according to the input value of the previous, the phase 360 / carrier according to the current of the input value (2 ^ (n + 1) ) optical transmission apparatus you wherein Rukoto varying degrees or more. A trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value;
A light modulator for quadrature amplitude modulating an optical carrier by using the code of n + 1 bits output from the trellis encoder,
An RZ conversion unit that converts a signal input to the optical modulation unit before the optical modulation unit or a signal output from the optical modulation unit after the optical modulation unit into RZ (Return-to-Zero); An optical transmission device comprising:
The trellis encoder is
Outputs the last of the code different from the code which is output from the previous said input value from the input value of the current times,
The light modulator is
This time of at least one of the phase or amplitude of the carrier wave according to the input values, the optical transmission device according to claim to Rukoto to be different from the phase or amplitude of the carrier wave according to the input value of the previous. A trellis encoder that outputs an n + 1-bit code from an n-bit input value that is an arbitrary value;
An optical transmission device comprising a light modulator for quadrature amplitude modulating an optical carrier by using the code of n + 1 bits output from the trellis encoder,
The trellis encoder is
When one state is stored in 2 ^ m states reflecting the value of the code from the present to the previous m and when one input value is acquired in one state, the input value in that state and outputs a code associated with the, and I'm storing other conditions which are not associated with the sign as the current state, the code different from the previous of the code outputted from the input value of the previous the output from the input value of the now times,
The light modulator is
An optical transmission device characterized in that at least one of a phase or amplitude of a carrier wave related to the current input value is different from a phase or amplitude of a carrier wave related to the previous input value.

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