JP2011029698A - Code converter, optical transmitter for optical code division multiplexing, and optical code division multiplexing transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a code converter for keeping light power that a transceiver transmits and receives, enlarging the minimum step of coding by reducing a multi-value number, and performing multi-value modulation of chips having the same optical frequency with a plurality of codes in a lump while the minimum step of coding has been enlarged, and to provide an optical transmitter for optical code division multiplexing and an optical code division multiplexing transmission system. <P>SOLUTION: The code converter uses orthogonality between codes, where the total of chips added by chips of codes not to be received and the total of chips to be subtracted are nearly balanced in a receiver, performs an equivalent subtraction for chips to be added and chips to be subtracted by a decoder at a reception side from a multicode, where coding data coded for each code has been multiplexed, and reduces a multi-value number while maintaining a balanced state between the total of chips to be subtracted and the total of chips to be subtracted, thus enlarging the minimum step. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a code converter used for optical code division multiplexing communication, an optical transmitter for optical code division multiplexing, and an optical code division multiplexing transmission system.

  Optical code division multiplexing, in which a propagation medium and an optical frequency band are shared by a plurality of signals by code identification, is being studied as a future optical communication. In addition, optical code division multiplexing using a spectral domain code capable of blocking interference light due to erroneous connection has been studied.

  However, since the same optical frequency is used for a plurality of code lights in optical code division multiplexing communication, there is a problem of sensitivity deterioration due to beat noise between code lights (see, for example, Non-Patent Document 1). In particular, it is a spectral domain code, and light (chips) having different optical frequencies constituting the code light is coherent light, and if the optical frequency difference between chips constituting different codes is less than or equal to the transmission band, the influence is greatly multiplexed. Transmission becomes difficult.

  As a method of reducing sensitivity deterioration due to beat noise, there is a method of performing multi-level modulation on a plurality of codes of chips having the same optical frequency (see, for example, Patent Document 1). This method essentially does not generate inter-code beat noise, and can be directly detected, so that the receiver can be simplified.

WO2005 / 008923

“Beat Noise Mitigation of Spectral Amplitude Coding OCDMA Using Heterodyne Detection”, Yoshino, M .; et al. , Journal of Lightwave Technology, Volume: 26, Issue: 8, April 15, 2008, Page (s): 962-970

FIG. 1 is a diagram for explaining a signal-to-noise ratio (SNR) after decoding with respect to the total input light intensity of a signal transmitted when 32 spectral domain intensity codes are multiplexed using a conventional method. The curve in FIG. 1 is the SNR of the transmitted signal. The straight line in FIG. 1 means an SNR corresponding to a code error rate of ^10-12 . The conventional method has two problems. First, the first problem will be described. As shown in FIG. 1, the minimum light receiving sensitivity at a code error rate of 10 ⁻¹² does not reach −27 dBm or less defined by IEEE 802.3ah. In addition, as shown in FIG. 1, the light receiving area with a code error rate of 10 ⁻¹² or more is −10 dBm or more, while the overload corresponding to the breakdown threshold of the optical detector on the receiver side is ⁻⁶ dBm or less, It is also difficult to satisfy the required light receiving dynamic range of 21 dB. For this reason, in the conventional method, it is difficult to obtain the minimum light receiving sensitivity that maintains the code error rate of ^10-12 , and there is a problem that it is difficult to satisfy the light receiving dynamic range necessary for the PON. However, there is a possibility that this problem can be improved by increasing the destruction threshold of the optical detector or improving the sensitivity of the receiver.

  In the conventional method, the number of multi-values increases as the number of codes increases. For this reason, the conventional method has a second problem that the minimum step of encoding becomes smaller as the multi-value number increases, assuming that the optical power is kept constant. If the minimum step of encoding is reduced, the SNR is lowered, so that the number of codes that can be modulated together is limited. Further, since the increase in the multi-value number has a narrow output linear region with respect to the input of the modulator or the direct modulation laser, the step is further reduced when modulation is performed in the linear region. If the nonlinear region is to be linearly modulated, there is a problem that the nonlinear modulation must be performed. Here, the relationship in which the SNR deteriorates due to the increase in the maximum number of codes when the transmission power is constant will be described. If the optical power transmitted by the transmitter is P and the number of codes to be multiplexed is F, the signal light power S for a single signal can be expressed as S = P / F. When beat noise between spectrum chips constituting the same code can be ignored, receiver noise and shot noise are dominant as noise, and noise is constant when transmission power is constant. Accordingly, the SNR deteriorates in inverse proportion to the maximum number of codes. It should be noted that the “multi-value number” and the “step” have a relationship that the step width decreases as the multi-value number increases, and the step width increases as the multi-value number decreases.

  Therefore, the present invention reduces the number of multi-values and expands the minimum encoding step while maintaining the optical power transmitted and received by the transceiver, and the same optical frequency chip is expanded with the minimum encoding step expanded. It is an object of the present invention to provide a code converter, an optical code division multiplexing optical transmitter, and an optical code division multiplexing transmission system that collectively modulate a plurality of codes.

  In this specification, the code is composed of a combination of “0” and “1” coding chips, and the number of “0” and “1” coding chips constituting the code is described as a code length. Also, encoded transmission data is referred to as encoded data. Furthermore, since the code of the encoded data is also multiplexed when the encoded data is multiplexed, the multiplexed code is described as a multiplexed code, and each chip constituting the multiplexed code is described as a multiplexed chip.

  In order to achieve the above object, the code converter according to the present invention uses orthogonality between codes in which the sum of the chips to be added by the chips of the codes not to be received and the sum of the chips to be subtracted are approximately balanced in the receiver. Then, from the multiplex code obtained by multiplexing the encoded data encoded for each code, the receiving side decoder subtracts an equal amount of the chip to be added and the chip to be subtracted, and the sum of the chips to be subtracted and the sum of the chips to be subtracted The number of multi-values was reduced while maintaining the equilibrium state between them, and the minimum step was expanded.

  Specifically, the code converter according to the present invention multiplexes encoded data obtained by encoding transmission data of a plurality of channels with a different code for each channel. The code converter includes an arithmetic circuit having a reference unit and a comparison arithmetic unit. The reference unit multiplexes the coding chips constituting the multiplexed signal obtained by multiplexing the coded data at the same time among the possible combinations of the transmission data of the respective channels at the same time as multiplexed chips for each coded chip. It has the maximum value difference as a reference. The comparison operation unit combines the transmission data of each channel at the same time, and sets the encoded chip constituting the multiplexed signal obtained by multiplexing the encoded data at the same time as a multiplexed chip, and the minimum value of the values multiplexed for each encoded chip A comparison operation unit that detects a chip minimum value and subtracts the smaller of the reference and the chip minimum value in the multiplex code from the multiplex chip in the multiplex code.

  The code converter according to the present invention is a code converter that multiplexes encoded data obtained by encoding transmission data of a plurality of channels with a different code for each channel, and the transmission data of each channel at the same time Among the possible combinations, the encoding chip constituting the multiplexed signal in which the encoded data at the same time is multiplexed is a multiplexed chip, and the reference unit having the maximum difference between the non-zero multiplexed chips as a reference, A chip minimum value that is a minimum value of a non-zero multi-chip value among multiple chips constituting a multiplexed code of the multiplexed encoded data is detected, and the reference and the reference value are detected from the non-zero multiplexed chip in the multiplexed code. A comparison operation unit that subtracts the smaller value of the chip minimum value in the multiplex code may be provided.

  The code converter according to the present invention subtracts an equal amount of a chip to be added and a chip to be subtracted from a multiplexed code obtained by multiplexing encoded data encoded for each code, and subtracts the sum and subtraction of the chips to be subtracted. The number of multi-values is reduced while maintaining an equilibrium state between the sums of chips to be played. Therefore, the present invention reduces the number of multi-values while maintaining the optical power transmitted and received by the transceiver, expands the minimum encoding step, and expands the minimum encoding step to a plurality of chips of the same optical frequency. It is possible to provide a code converter that performs multi-level modulation of the codes.

  An optical transmitter for optical code division multiplexing according to the present invention receives the multiplex code multiplexed from the code converter and the code converter, and transmits light having different optical frequencies and / or delay times from the multiplex code. A modulator that outputs a chip modulated by the value of the multiplexed chip; and a multiplexer that combines the chips output from the modulator and outputs an optical code division multiplexed signal.

  Light is modulated with a signal from a code converter according to the present invention. Therefore, the present invention can provide an optical transmitter for optical code division multiplexing capable of reducing the number of multi-values while increasing the optical power, expanding the minimum encoding step, and improving the SNR.

  The optical code division multiplexing transmission system according to the present invention receives the optical code division multiplexed signal output from the optical code division multiplexing optical transmitter, demultiplexes the optical code division multiplexed signal for each chip, and A receiver that detects each of the demultiplexed light as a reception target and adds / subtracts the detection output according to the code of the channel.

  The optical code division multiplex transmission system according to the present invention uses the orthogonality between codes in which the sum of chips to be added by the chips of codes that are not to be received and the sum of chips to be subtracted are balanced in the receiver, for each code. The reception side decoder subtracts an equal amount of chips to be added and a chip to be subtracted from the multiplex code obtained by multiplexing the encoded data encoded in the above, and the balance state between the sum of the chips to be subtracted and the sum of the chips to be subtracted is determined. While maintaining, reduce the number of multi-values and expand the minimum step. Therefore, the present invention can provide an optical code division multiplex transmission system capable of reducing the number of multi-values while maintaining optical power, expanding the minimum encoding step, and improving the SNR.

  The present invention reduces the multi-value number and expands the minimum encoding step while maintaining the optical power transmitted and received by the transceiver, and a plurality of chips having the same optical frequency are expanded in the state where the minimum encoding step is expanded. It is possible to provide a code converter, an optical code division multiplexing optical transmitter, and an optical code division multiplexing transmission system that perform multi-level modulation of codes. Since the code converter, the optical code division multiplexing optical transmitter, and the optical code division multiplexing transmission system according to the present invention reduce the multi-value number from the multi-value code and expand the minimum step, the SNR is improved.

It is a figure explaining SNR of the optical code division multiplexing communication by the conventional method. It is a block diagram explaining the optical code division multiplexing transmission system which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this invention. It is a figure explaining operation | movement of the code converter which concerns on this 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.

(Embodiment 1)
FIG. 2 is a block diagram for explaining the optical code division multiplexing transmission system of this embodiment. The optical code division multiplexing transmission system includes an optical code division multiplexing optical transmitter 10, a receiver 20-n (n is an integer of 1 to N), and an optical distribution network 30 connecting them.

  The optical code division multiplexing optical transmitter 10 includes a multi-wavelength light source 11, a demultiplexer 12, a modulator group 13, a multiplexer 14, and a code converter 15. The multi-wavelength light source 11 outputs light of J optical frequencies different from each other. The demultiplexer 12 demultiplexes the light output from the multi-wavelength light source 11 for each optical frequency. The duplexer 12 is, for example, a combination of an optical coupler and a filter, or an AWG (Array Waveguide Gratings). The modulator group 13 includes J modulators 13-j. The modulator 13-j modulates the intensity of the demultiplexed light according to the multiplexed code output from the code converter 15 and outputs it as a spectrum chip. The multiplexer 14 multiplexes the spectrum chip output from the modulator 13-j and outputs an optical code division multiplexed signal. The multiplexer 14 is, for example, an AWG or an optical coupler. The multiplexer 14 is preferably an AWG when the number of chips to be multiplexed increases (approximately 4 or more) from the viewpoint of reducing insertion loss.

  The code converter 15 multiplexes encoded data obtained by encoding transmission data of a plurality of channels with different codes for each channel. The code converter 15 has a code composed of a plurality of coding chips for each channel. The code converter 15 generates encoded data for each channel according to the mark / space value of the transmission data input for each channel and the code encoding chip for each channel. Further, the code converter 15 multiplexes these encoded data. By multiplexing the encoded data, the encoded chips of the encoded data are also multiplexed to form a multiplexed chip. That is, transmission data which is binary of 0 and 1 is converted into multi-value data. The code converter 15 outputs a multiplex code composed of multiplex chips to the modulator 13-j. At this time, the code converter 15 outputs multiple chips for each modulator 13-j. The detailed operation of the code converter 15 will be described later.

  As described above, the optical code division multiplexing optical transmitter 10 modulates the light separated for each optical frequency, thereby performing encoding and modulation according to the value of the signal. FIG. 2 shows an optical code division multiplex transmission system when the code length (number of encoded chips) of the code converter 15 is four. The code converter 15 converts the transmission data into a multiplex code having a multiplex chip number of 4 and outputs it. The demultiplexer 12 demultiplexes the light from the multi-wavelength light source 11 into four lights having optical frequencies f1, f2, f3, and f4. There are four modulators 13-j. The modulator 13-1 modulates the light of the optical frequency f1 with the first multiplex chip of the multiplex code. Similarly, the modulators (13-2, 13-3, 13-4) modulate light of optical frequencies (f2, f3, f4) with the second, third, and fourth multiplexed chips of the multiplexed code, respectively.

  The multi-wavelength light source 11, the duplexer 12, and the modulator 13-j may be replaced with light sources that can be directly modulated for each optical frequency. The modulated spectrum chip is multiplexed by the multiplexer 14 and output as an optical code division multiplexed signal.

  The receiver 20-n outputs the optical outputs of the duplexer 21, multiplexers (22-n-1, 22-n-2), and multiplexers (22-n-1, 22-n-2), respectively. A differential optical detector 23 is provided for optical detection and adding / subtracting the output. The duplexer 21, the multiplexer (22-n-1, 22-n-2) and the differential optical detector 23 constitute a decoder. The demultiplexer 21 receives the optical code division multiplexed signal and demultiplexes it for each optical frequency. The duplexer 21 is, for example, a combination of an optical coupler and a filter or an AWG. The multiplexers (22-n-1, 22-n-2) combine the lights demultiplexed by the demultiplexer 21 into two groups and multiplex them. The multiplexers (22-n-1, 22-n-2) are, for example, AWGs or optical couplers. The demultiplexer 21 and the multiplexers (22-n-1, 22-n-2) branch the spectrum chip to be received according to the values of “1” and “0” of the code of the decoder.

  The multiplexers (22-n-1, 22-n-2) are preferably AWGs when the number of chips to be multiplexed increases (approximately 4 or more) from the viewpoint of reducing insertion loss. When using components with optical frequency dependency such as AWG, the spectrum chips to be aggregated by the multiplexers (22-n-1, 22-n-2) are different for each code to be received. AWG is different for each code. The demultiplexer 21 and the multiplexers (22-n-1, 22-n-2) branch the optical code division multiplexed signal according to the values “1” and “0” of the spectrum chip of the code light. Can do. When the multiplexer (22-n-1, 22-n-2) has an optical frequency selection function, the duplexer 21 may be an optical coupler. The differential optical detector 23 optically detects the branched spectrum chip, and adds or subtracts the output according to the values of “1” and “0” of the spectrum chip of the code to be received. The differential optical detector 23 connects, for example, two photodiodes in series. Since the positive and negative sides of the two photodiodes are connected and a signal is taken from the connection point, the difference between the two detection outputs is output. The differential photodetector 23 may combine a photodiode or a photodetector other than a photodiode and an operational amplifier.

  The receiver 20-n demultiplexes the optical code division multiplexed signal for each optical frequency by the demultiplexer 21. Furthermore, the receiver 20-n distributes the demultiplexed light to the addition side and the subtraction side of the differential photodetector 23 in accordance with the code for receiving.

  In the receiver 20-n, the spectrum chip whose value of the coding chip constituting the code is “1” is either one of the adding side photodiode or the subtracting side photodiode of the differential optical detector 23. And the other photodiode is configured not to arrive. When using orthogonal codes, due to the orthogonality of the codes, the chips constituting the codes that are not to be received arrive at both the adding side and the subtracting side with an intensity that is effectively equalized during the addition / subtraction process. Therefore, it is canceled out by addition / subtraction, and ideally there is no multiple access interference.

For example, the receiver 20-1 receives the transmission data of the channel encoded by the code [1100] by the code converter 15, and therefore the optical frequencies f1, f2, f3 demultiplexed by the demultiplexer 21. The light of f4 is distributed to the addition side multiplexer 22-1-1, the addition side multiplexer 22-1-1, the subtraction side multiplexer 22-2-2, and the subtraction side multiplexer 22-2-2. . Further, the receiver 20-2 receives the transmission data of the channel encoded by the code [1010] by the code converter 15, so that the optical frequencies f1, f2, f3, demultiplexed by the demultiplexer 21 are received. The light of f4 is distributed to the addition side multiplexer 22-2-1, the subtraction side multiplexer 22-2-2, the addition side multiplexer 22-2-1, and the subtraction side multiplexer 22-2-2. .

  Note that the distribution of the demultiplexed light may be reversed from the above. That is, the receiver 20-1 subtracts the light having the optical frequencies f 1, f 2, f 3, and f 4 demultiplexed by the demultiplexer 21, respectively, as a subtraction side multiplexer 22-1-2 and a subtraction side multiplexer 22-1. -2, addition side multiplexer 22-1-1 and addition side multiplexer 22-1-1. Similarly, the receiver 20-2 subtracts the light of the optical frequencies f1, f2, f3, and f4 demultiplexed by the demultiplexer 21, respectively, and the adder-side multiplexer 22-2-2 and the adder-side multiplexer 22-. 2-1, the subtraction side multiplexer 22-2-2, and the addition side multiplexer 22-2-1 may be distributed.

(Operation of code converter)
Here, the operation of the code converter 15 will be described in detail. The code converter 15 can perform two operations. The first operation is to subtract an equal amount of the chip to be added and the chip to be subtracted from the multiplexed code obtained by multiplexing the encoded data encoded for each code, and to subtract the sum of the subtracted chips. This is an operation of reducing the number of multi-values while maintaining an equilibrium state between the sums of the values. The second operation is an operation to reduce the multi-value number other than the multiple chips having a value of “0” that is not counted on the addition side or the subtraction side on the receiver side when reducing the multi-value number. Here, the equal amount means an equal amount in the intensity after addition / subtraction. Therefore, in the case of a code in which one strength of addition / subtraction is 1 / K (K is a natural number), K times the other strength is subtracted.

  First, the first operation will be described. The code converter 15 includes a reference unit 51 and a comparison calculation unit 52. The reference unit 51 sets, for each coding chip, a coding chip constituting a multiplexed signal obtained by multiplexing the coded data at a single time among the possible combinations of the transmission data of each channel at the same time as a multiplexed chip. The maximum difference between the multiplexed values is used as a reference. The comparison operation unit 52 detects a chip minimum value, which is the minimum value of the multiple chips constituting the multiplexed code of the encoded data that has been multiplexed, and detects the reference and the multiple codes from the multiple chips in the multiplexed code. The smaller value of the chip minimum value is subtracted.

  The code used by the code converter 15 is such that, for example, the multiple access interference is suppressed by the duplexer 21, the multiplexer (22-n-1, 22-n-2), and the differential optical detector 23 on the receiving side. An orthogonal code is desirable. In the ON / OFF intensity codes of “1” and “0”, as such orthogonal codes, for example, Hadamard codes or cyclically shifted M-sequence codes are transmitted, and a spectrum chip corresponding to either 1 or 0 is transmitted. An example of the optical code is as follows.

  Description will be made in the case of using a unipolar code that uses only such a code and sends out only a chip having a value of 1.

  Hereinafter, description will be made using equations. The transmission data at time t of the nth code n (n = 1 to N, n; integer, N; number of codes) is Dn, and the value of the coding chip j constituting the code n is Cnj (j = 1 to J, j: integer, J: code length), the value of each channel of the encoded data combining the transmission data Dn and the code of each channel at time t is DnCnj, Σ is the sum of values from 1 to J, The value of the multiplex chip constituting the multiplex code obtained by multiplexing the encoded data is assumed to be ΣDnCnj. Further, min (A, B) is set to the smaller value of A and B, the value of the maximum multiplexed chip among the multiplexed codes in transmission data Dn at time t is set to Max (ΣDnCnj), and transmission data Dn at time t. The minimum multiplex chip value among the multiplex codes in is defined as min (ΣDnCnj).

  The type of encoded data is limited to a finite number due to the relationship between the value of transmission data Dn input for each channel and the value of encoded chip j. Then, for all types of encoded data that can be taken by the transmission data Dn and the encoded chip j, the difference between the maximum value and the minimum value of the chip value DnCnj is obtained for each encoded data. However, in the second operation, the chip value where DnCnj = 0 is not set to the minimum value. Further, the value having the maximum difference among all types of encoded data is determined as the reference S.

The code converter 15 adjusts the multiplex code so that the maximum of the multiplex chip value ΣDnCnj is equal to or less than the reference S. Specifically, the following equation is applied to the multiple chip 'ΣDnCnj' of the multiple code to be output.
(Formula 1)
'ΣDnCnj' = ΣDnCnj−min {min (ΣDnCnj), S}
In addition, although it demonstrates by Numerical formula 1 here, the formula (for example, Numerical formula 2) which subtracts the chip | tip which adds at the time of decoding and the chip | tip which subtracts equally is employable.
(Formula 2)
'ΣDnCnj' =
ΣDnCnj−IF {Max (ΣDnCnj)> S, min (ΣDnCnj), S}
Here, IF (A, B, C) takes a value of B when A is true, and takes a value of C when A is false.

  FIG. 4 is a diagram for explaining ΣDnCnj, min (ΣDnCnj), reference S, and multiple chip ‘ΣDnCnj’ of the multiplex code to be output in the case of a Walsh Hadamard sequence having a code length of 4 and a code number of 3.

  The value of the reference S is 2. The left column of FIG. 4 means the code number n (code for each channel), and the value in each row on the right side means the value of the coding chip of each code. There may be a case where a numerical value is written in the column of the coding chip and a case where it is blank. This means that the transmission data value Dn is 1 (mark) when a numerical value is written in the encoding chip column, and the transmission data value Dn is 0 (space) when the value is blank. .

  As shown in columns 2 to 5 of FIG. 4, the value of the multiplex code is the addition of the codes of each channel, and the number of codes that can transmit data becomes the upper limit of the values that can be multi-valued. In this case, in the case where the number of codes that can be transmitted is equal to the code length, the code length becomes the upper limit of a multivalued value. In general, the maximum value of the number of times chips that constitute different codes do not overlap each other is the upper limit of a multivalued value. As shown in columns 1 to 5 of FIG. 4, in the conventional technology, when transmission data is three-code multiplexed with three channels, a multi-value number (number of steps) of 3 or more is required.

  On the other hand, the code converter 15 according to the present embodiment performs a calculation such as Equation 1 and converts the multiplex chip of the multiplex code to be output into values as described in columns 6 to 9 in FIG. As shown in FIG. 4, the code converter 15 can set the number of steps to two. This number of steps is half the code length and is equivalent to the reference S.

Specifically, the calculation of Expression 1 performs the following conversion. The values of the multiplex chip in FIG. 4 are “3, 1” (“3, 1, 1, 1” of pattern 1), “2, 1, 0” (patterns 2 to 4), “1,0” (pattern 5-7) or “0” (pattern 8). That is, there are 2, 2, 1, and 0 intensity differences between patterns 1-8. Therefore, the reference S which is the maximum intensity difference is 2. Here, in order to make the maximum intensity of all the patterns smaller than the reference S, it is only necessary to reduce the intensity by one equal amount from each of the multiple chips of the pattern 1. That is, the multiplex code of each pattern is converted as follows.
Pattern 1 is obtained by subtracting 1 from “3, 1” to “2, 0”.
Patterns 2 to 4 are “2, 1, 0” and are not converted.
Patterns 5 to 7 are “1,0” and are not converted.
Pattern 8 is “0” and is not converted.

  FIG. 5 shows an example of a modified Hadamard sequence in which 0 and 1 of the code of FIG. 4 are inverted and chips whose spectrum chips of all codes are 0 are deleted. The effect of this embodiment is the same as in the case of FIG. 4, and the number of steps is approximately halved and can be set to 1 which is the same value as the reference S which is approximately ¼ of the code length. In the example of FIG. 5, when the optical power transmitted and received by the transceiver is the same as in the conventional example, the eye opening is the same as in the conventional example.

  6 to 21 are diagrams for explaining the ΣDnCnj, min (ΣDnCnj), the reference S, and the multiplex chip ‘ΣDnCnj’ of the multiplex code to be output in the case of the Walsh Hadamard sequence having the code length of 8 and the code number of 7. FIGS. 22 to 37 are examples of modified Hadamard sequences in which the codes 0 and 1 of FIGS. 6 to 21 are inverted and the chips whose spectrum chips of all codes are 0 are deleted.

  In the case of FIGS. 6 to 21, the value of the reference S is 4. The detailed description of the figure is the same as in FIG. In the case where ΣDnCnj, min (ΣDnCnj), reference S, and ‘ΣDnCnj’ are the same as the pattern with a smaller number, the description is omitted. In the conventional example shown in columns 1 to 8 of FIGS. 6 to 21, when transmission data is 7-code multiplexed with 7 channels, a multi-value number (step) of 7 or more is required.

  On the other hand, the code converter 15 according to the present embodiment performs a calculation such as Equation 1 and converts the multiplex chip of the multiplex code to be output into values as described in columns 9 to 16 in FIGS. As shown in FIGS. 6 to 21, the code converter 15 can set the number of steps to four. This number of steps is half the code length and is equivalent to the reference S.

  The same applies to the modified Hadamard sequences described with reference to FIGS. 22 to 37, and the number of steps can be approximately halved and can be set to 2 which is the same as the reference S which is approximately 1/4 of the code length.

  FIGS. 38 to 42 are diagrams illustrating ΣDnCnj, min (ΣDnCnj), reference S, and multiple chip ‘ΣDnCnj’ of the multiplex code to be output in the case of a Walsh Hadamard sequence having a code length of 16 and a code number of 15. In the case of a Walsh Hadamard sequence having a code length of 16 and a code number of 15, the number of combinations is large, so a part of all patterns is displayed. 43 to 47 are examples of modified Hadamard sequences in which the codes 0 and 1 in FIGS. 38 to 42 are inverted and the chips whose spectrum chips of all codes are 0 are deleted.

  In the conventional example shown in columns 1 to 16 in FIGS. 38 to 42, when transmission data is 15-code multiplexed with 15 channels, a multi-value number (step) of 15 or more is required. On the other hand, the code converter 15 according to the present embodiment performs a calculation such as Equation 1, and converts the multiplex chip of the multiplex code to be output into values as described in columns 17 to 32 of FIGS. As shown in FIGS. 38 to 42, the code converter 15 can set the number of steps to eight. This number of steps is half the code length and is equivalent to the reference S.

  The same applies to the modified Hadamard sequences described with reference to FIGS. 43 to 47, and the number of steps can be reduced to approximately half and can be set to 4 which is the same value as the reference S which is approximately 1/4 of the code length.

  As described above, in this embodiment, the number of multi-level modulation can be reduced and the modulation step can be increased.

(Embodiment 2)
FIG. 3 is a diagram showing an example applied to a (pseudo) bipolar signal in which the presence / absence of light in a spectrum chip is inverted in the case of 2 codes.
In the present embodiment, the second operation among the two operations that the code converter 15 can take will be described. In other words, this is an operation that can be used when the encoding chip before multiplexing at the transmitter is an encoding chip composed of “1” and “0”. This is an operation for reducing the number of multi-values other than multiple chips having a value of “0” that is not counted on the addition side or the subtraction side.

  As shown in FIG. 3, the encoding chip of code 1 is assumed to be (1, 1, 0, 0) when the transmission data is a mark and (0, 0, 1, 1) when the transmission data is a space. The coding chip of code 2 is assumed to be (1, 0, 1, 0) when the transmission data is a mark and (0, 1, 0, 1) when the transmission data is a space.

  Here, the number in parentheses is the value of each coding chip. In the conventional example, when optical modulation is performed with an encoding chip having a value of 1, the spectrum chip outputs only unit intensity corresponding to the value 1 corresponding to the encoding chip, and the value 0 is optically modulated by the encoding chip. When performing the above, no spectrum chip is output corresponding to the coding chip. The unit intensity is the intensity of the spectrum chip corresponding to one encoding chip of one code, and may be different for each signal light corresponding to the code. In addition, if the code is not a code that is encoded by ON / OFF of the light of the spectrum chip but is a code that is encoded by changing the intensity of the spectrum chip in an analog or multi-value, each signal light that corresponds to the same code is configured As long as the ratio of the spectrum chip is maintained, it may be different for each signal light.

Here, when the code converter 15 multiplexes the encoded data of each channel, in the conventional example, as shown in FIG.
When code 1 is encoded with a mark and code 2 is encoded with a mark (2, 1, 1, 0),
When code 1 is encoded with a mark and code 2 is encoded with a space (1, 2, 0, 1),
When code 1 is encoded with a space and code 2 is encoded with a mark (1,0,2,1),
When code 1 is encoded with a space and code 2 is encoded with a space (0, 1, 1, 2)
It becomes.

  In the case of the present embodiment, the maximum intensity difference when the zero chip value is excluded is 2-1 = 1, so the reference S is 1. Further, when the code converter 15 extracts only non-zero multiplex chips from the multiplex chip and applies Equation 1, the equal intensity (min (min (ΣDnCnj), S) from each multiplex chip having a non-zero light intensity is applied. ) Are subtracted, the multiple codes are (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) and Become.

When the intensity is doubled to obtain the same optical power as that of the conventional example, the multiplexed codes are (2, 0, 0, 0), (0, 2, 0, 0), (0, 0, 2, 0), respectively. , (0, 0, 0, 2). The receiver 20-1 with code 1 adds, adds, subtracts, and subtracts the spectrum chips in the order of the optical frequencies f1 to f4. The receiver 20-2 with code 2 adds, subtracts, adds and subtracts the spectrum chips in the order of the optical frequencies f1 to f4. For this reason, the outputs of the receivers (20-1, 20-2) are as follows.
(1) For multiple codes (2, 0, 0, 0),
Output of receiver 20-1 +2 (mark), output of receiver 20-2 +2 (mark),
(2) For multiple codes (0, 2, 0, 0),
Output of receiver 20-1 +2 (mark), output of receiver 20-2 -2 (space),
(3) For multiple codes (0, 0, 2, 0),
Output-2 of receiver 20-1 (space), output of receiver 20-2 +2 (mark),
(4) For multiple codes (0, 0, 0, 2),
Output-2 of receiver 20-1 (space), output-2 of receiver 20-2 (space).
Therefore, the optical code division multiplexing transmission system can correctly transmit the transmission data to the receiver.

  In this embodiment, the equal intensity (min (min (ΣDnCnj), S)) is not subtracted from the multiplex chip whose multiplex code value of the multiplex code is zero. In the case of a spectrum intensity code that is encoded based on the presence or absence of the intensity of a spectrum chip, the spectrum chip that constitutes a signal of a certain code has the balance of addition and subtraction only for the spectrum chip that is emitting light for receivers that receive other codes. It will be taken. For this reason, a chip that does not emit light is not processed in the chip intensity, and only a non-zero chip is processed (in this embodiment, 1 is subtracted and doubled).

  In the present embodiment, the spectral domain intensity code has been described as an example. However, a spectral domain phase code, a time domain code, or a multidimensional code such as a time-spectral domain may be used. May be. For example, in the case of a phase code, the increment on the addition side multi-level J and the increment on the subtraction side multi-level J may be replaced with the increment on the addition side π / (2J) and the increment on the subtraction side −π / (2J). The modulator 13-j is not an intensity modulator but a phase modulator. However, the value of the transmitting chip is positive and negative. In the case of a time domain code, the spectrum chip may be replaced with a time chip. In the encoding, instead of the demultiplexer 12, the modulator 13-j, and the multiplexer 14 that demultiplexes for each optical frequency, a modulator that divides the light and adds different delay times and modulates each delay time, Alternatively, it may be replaced by a device that multiplexes the modulated light, or may be realized by a high-speed modulator that modulates each time chip. The same applies to decoding. In the case of a multidimensional code in the time-spectral domain, it can be realized by a combination of both codes.

10: Optical transmitter for optical code division multiplexing 11: Multi-wavelength light source 12, 21: Demultiplexer 13: Modulator groups 13-1, 13-2, ..., 13-j, ..., 13-J : Modulator 14, 22-n-1, 22-n-2: multiplexer 15: code converters 20-1, 20-2, ..., 20-n, ..., 20-N: reception Machine 23: Differential optical detector 30: Optical distribution network 51: Reference unit 52: Comparison operation unit

Claims (5)

  A chip that multiplexes encoded data obtained by encoding transmission data of a plurality of channels with a different code for each channel and is added by a decoder on the receiving side from a multiplexed chip in the multiplexed code in which the encoded data is multiplexed And a code converter comprising an arithmetic circuit for subtracting equal amounts of chips to be subtracted. The arithmetic circuit is:
Among possible combinations of the transmission data of each channel at the same time,
A reference unit having, as a reference, the maximum difference in values multiplexed for each of the encoding chips, which constitutes a multiplexed chip that constitutes a multiplexed signal obtained by multiplexing encoded data at the same time;
A chip minimum value, which is a minimum value of multiple chips constituting the multiplexed code of the encoded data that has been multiplexed, is detected, and the reference and the minimum chip value in the multiplexed code are detected from the multiple chips in the multiple code. A comparison operation unit that subtracts the smaller value;
The code converter according to claim 1, further comprising: The arithmetic circuit is:
Among possible combinations of the transmission data of each channel at the same time,
A reference chip having, as a reference, a maximum of a difference between non-zero multiple chips, a coding chip constituting a multiplexed signal obtained by multiplexing encoded data at the same time as a multiplexed chip;
A chip minimum value which is a minimum value of a non-zero multi-chip value among multiple chips constituting a multiplexed code of the multiplexed encoded data is detected, and the reference is detected from the non-zero multiplexed chip in the multiplexed code. And a comparison operation unit for subtracting the smaller value of the chip minimum values in the multiplex code,
The code converter according to claim 1, further comprising: A code converter according to any one of claims 1 to 3;
A modulator that receives the multiplexed code multiplexed from the code converter, and outputs a chip obtained by modulating light having different optical frequencies or / and delay times from each other by the value of the multiplexed chip of the multiplexed code;
A multiplexer that multiplexes the chips output by the modulator and outputs an optical code division multiplexed signal;
An optical transmitter for optical code division multiplexing. An optical transmitter for optical code division multiplexing according to claim 4,
The optical code division multiplexing signal output from the optical code division multiplexing optical transmitter is received, the optical code division multiplexing signal is demultiplexed for each spectrum chip, and the demultiplexed light is optically detected. A receiver to receive and add / subtract the detection output according to the sign of the channel;
An optical code division multiplexing transmission system.

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