Optical transmission system of IFOF mode

Abstract

An IFoF optical transmission system according to the present disclosure is provided with a transmission-side digital signal processing device (100) that includes: a system number compression unit (150) that compresses n digital data streams into m less than n digital data streams; the parameter update unit (160) updates the parameter used in the system number compression unit (150) on the basis of the value of an evaluation function that uses the signal string processed by the transmission-side digital signal processing device (100) as an independent variable.

Description

Technical Field

[0001] The disclosed technology relates to an IFoF optical transmission system. Background Art

[0002] An optical transmission system is a transmission system that uses light as a signal transmission unit instead of electromagnetic waves used in televisions and radios. In an optical transmission system, optical fibers are generally used as a medium for propagating light. Therefore, the optical transmission system is distinguished from a method of irradiating light toward the atmosphere and propagating it in the air. The light source in the optical transmission system uses, for example, a semiconductor laser or a light emitting diode. In an optical transmission system, a light intensity modulation method is used to send a signal corresponding to the on-off of a laser, or a coherent optical communication method is used to modulate the frequency or phase of a laser in combination with a signal.

[0003] Optical transmission systems are expected to be the transmission systems for the next generation mobile networks.

[0004] As methods of realizing mobile fronthaul (MFH) of a centralized radio access network (C-RAN) that is expected to be a next-generation mobile network, there are digital radio-over-fiber (D-RoF) and analog radio-over-fiber (A-RoF).

[0005] A-RoF has the following advantages: By directly transmitting the analog waveform of the wireless signal, it requires significantly less optical transmission bandwidth than D-RoF, maintaining signal quality in MFH operation. On the other hand, by using a high-performance DSP (Digital Signal Processor), it is possible to multiplex and separate the intermediate frequency (IF) through digital signal processing. Digital signal processing based on high-performance DSP enables efficient and flexible transmission based on dense frequency configuration. In addition, digital signal processing based on high-performance DSP enables multiple channels to be clustered, and multiple clusters to be multiplexed and separated.

[0006] By combining these DSP-based multiplexing and separation with A-RoF, multiple wireless signals are frequency-multiplexed in the intermediate frequency band (IF band), and through analog optical modulation, they can be uniformly transmitted to the antenna using one optical fiber and one wavelength. This optical fiber wireless technology is sometimes also called IFoF (Intermediate Frequency over-Fiber: intermediate frequency optical fiber) method.

[0007] For example, Patent Document 1 discloses the following A-RoF solution: In wireless signal transmission between a BBU (Base Band Unit) and an RRH (Remote Radio Head), a plurality of different IF signals are frequency-multiplexed and transmitted via A-RoF (see

[0004] to

[0005] , Patent Document 1). Figure 2 A. Figure 2 B) In Patent Document 1, the A-RoF solution is referred to as "A-RoF solution with ADC / DAC and IF multiplexer / demultiplexer". Figure 2 B shows its schematic structure.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2020-5303 Summary of the invention

[0011] Problems to be solved by the invention

[0012] In an optical transmission system based on the A-RoF solution, the number of signal channels is expected to be increased as much as possible. However, there is a limit to this number.

[0013] The disclosed technology aims to effectively use the limited number of signal channels in a transmission system.

[0014] Means for solving problems

[0015] The IFoF optical transmission system of the disclosed technology has a sending-side digital signal processing device, which includes a system number compression unit and a parameter updating unit. The system number compression unit compresses n digital data streams into m which are less than n, and the parameter updating unit updates the parameters used in the system number compression unit according to the value of an evaluation function that takes the signal string processed by the sending-side digital signal processing device as an independent variable.

[0016] Effects of the Invention

[0017] The optical transmission system of the disclosed technology has the above-mentioned structure, and therefore can effectively use the limited number of signal channels that the transmission system has. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a block diagram showing the functional structure of the transmission side of the optical transmission system according to Embodiment 1.

[0019] Figure 2 This is a block diagram showing the functional structure of the receiving side of the optical transmission system according to Embodiment 1.

[0020] Figure 3 This is a block diagram illustrating detailed functions of the frequency division multiplexing unit 120 constituting the transmitting-side digital signal processing device 100 according to the first embodiment.

[0021] Figure 4 This is a block diagram illustrating detailed functions of the frequency division multiplexing unit 610 constituting the receiving-side digital signal processing device 600 according to the first embodiment.

[0022] Figure 5 This is a block diagram showing the functional structure of the transmission side of the optical transmission system according to the second embodiment.

[0023] Figure 6 This is a block diagram showing the functional structure of the transmission side of the optical transmission system according to the third embodiment.

[0024] Figure 7 This is a block diagram showing the functional structure of the receiving side of the optical transmission system according to the third embodiment.

[0025] Figure 8 This is a block diagram showing the functional structure of the transmission side of the optical transmission system according to the fourth embodiment.

[0026] Fig. 9 This is a block diagram showing the functional structure of the receiving side of the optical transmission system according to the fourth embodiment.

[0027] Fig.10 It is a hardware configuration diagram of the transmitting-side digital signal processing device 100 according to the fifth embodiment.

[0028] Fig.11 This is a hardware configuration diagram of a receiving-side digital signal processing device 600 according to the fifth embodiment. DETAILED DESCRIPTION

[0029] Implementation Method 1

[0030] Figure 1 1 is a block diagram showing the functional structure of the optical transmission side (hereinafter simply referred to as the "transmission side") of the optical transmission system of Embodiment 1. Figure 1 As shown in FIG. 1 , the optical transmission system of Embodiment 1 includes a transmitting side digital signal processing device 100, a DAC 200, and an analog optical transmitter 300 on the transmitting side. Figure 1 As shown, the transmitting side digital signal processing device 100 includes a frequency division multiplexing unit 120, a system number compression unit 150, and a parameter updating unit 160. The transmitting side of the optical transmission system can also be considered as an A-RoF optical subscriber line terminal device, for example.

[0031] <Frequency Division Multiplexing Unit 120 Constituting Transmitting-Side Digital Signal Processing Device 100>

[0032] The frequency division multiplexing unit 120 constituting the transmitting-side digital signal processing device 100 multiplexes the m signal sequences (y1(t), y2(t), . . . , y m (t)). Multiplexing is sometimes referred to as multiplexing processing, multiplexing, or simply referred to as muxing. The device that multiplexes (muxing) into an intermediate frequency (IF) is sometimes referred to as IF-MUX. In addition, the processing performed by the IF-MUX is sometimes referred to as IF-MUX processing. More specifically, the frequency division multiplexing unit 120 multiplexes the m signal strings (y1(t), y2(t), ..., y m The digital data streams involved in (t)) are collected into one and sent to the optical receiving side (hereinafter simply referred to as "receiving side") via one shared analog optical transmission line (AOTL). The analog optical transmission line (AOTL) is composed of, for example, optical fibers.

[0033] Although the signal processed by the transmitting-side digital signal processing device 100 is a digital signal, the m signal sequences are recorded as y1(t), y2(t), ..., y m (t). The signal processed by the frequency division multiplexing unit 120 is recorded as a function of time t as if it were an analog signal. There is a reason for this recording. This is because the sending side digital signal processing device 100 is implemented by a high-performance DSP, which means that the sending side digital signal processing device 100 can process the input signal as if it were an analog signal.

[0034] The signal multiplexed by the frequency division multiplexing unit 120 is sent to the DAC 200 .

[0035] Figure 3 1 is a block diagram illustrating detailed functions of the frequency division multiplexing unit 120 constituting the transmitting-side digital signal processing device 100 according to Embodiment 1. Figure 3 As shown, the frequency division multiplexing unit 120 has m signal strings (y1(t), y2(t), ..., y m (t)) involves a digital data stream. Figure 3 As shown, each digital data stream includes, for example, an upsampler 121, a digital filter 122, an NCO 123, and a multiplier 124. The functional blocks involved in the first digital data stream are distinguished by marking "-1" after the reference numerals, just like the upsampler 121-1, the digital filter 122-1, the NCO 123-1, and the multiplier 124-1. In this specification, the functional blocks involved in other digital data streams are also distinguished by the same reference numeral marking method.

[0036] The upsampler 121 in the digital data stream performs sampling according to the rate of the DAC 200. Specifically, the upsampler 121 performs, for example, 0 (zero) interpolation to increase the sampling rate and implement sampling corresponding to the rate of the DAC 200.

[0037] In addition, the upsampler 121 samples the signal sequence (y1(t), y2(t), ..., y m (t)) can be a complex signal with the input frequency centered at 0 (zero) [Hz] or a real signal.

[0038] The digital filter 122 in the digital data stream removes the unnecessary image signals generated in the upsampler 121 .

[0039] The NCO 123 in the digital data stream generates a data string of a predetermined frequency according to each digital data stream. For example, NCO 123-1 generates a data string with a frequency of f1, and NCO 123-2 generates a data string with a frequency of f2. The name of NCO 123 is derived from the first letter of Numerically Controlled Oscillator, which means numerically controlled oscillator.

[0040] Let i be a variable with a natural number between 1 and n, and let the frequency of the data string generated by NCO123-i in the i-th digital data stream be f i This manual will i It is referred to as the "i-th NCO frequency".

[0041] In addition, the data string generated by NCO123-i can be a complex number or a real number. That is, the processing performed by the frequency division multiplexing unit 120 can be a complex area or a real area. When the processing performed by the frequency division multiplexing unit 120 is a complex area, with respect to the output of DAC200, either the real part or the imaginary part of the obtained complex number is selected for use.

[0042] The multiplier 124 in the digital data stream multiplies the output from the digital filter 122 by the output from the NCO 123. More specifically, the multiplier 124-i in the i-th digital data stream multiplies the output from the digital filter 122-i by the output from the NCO 123-i. i ) means shifting the NCO frequency (f i ).

[0043] The adder 125 in the frequency division multiplexing unit 120 adds the signals of the frequency-shifted digital data streams. The signal obtained by the addition in the adder 125 is called a multiplexed signal.

[0044] In addition, Figure 3In FIG. 1 , m signal strings (y1(t), y2(t), ..., y m (t)) structure, but the disclosed technology is not limited thereto. The frequency division multiplexing unit 120 may perform signal processing in series, that is, in multiple stages, instead of in parallel.

[0045] <<System number compression unit 150 constituting the transmitting-side digital signal processing device 100>>

[0046] The system number compression unit 150 constituting the transmitting-side digital signal processing device 100 is a component that compresses n (n>m) digital data streams into m digital data streams. Specifically, the system number compression unit 150 performs processing given by the following mathematical formula.

[0047]

[0048] Among them, the matrix W in formula (1) H is a matrix of size m×n, which is given by the parameter updating unit 160. The matrix W H The superscript H in stands for the Hermitian transpose. The matrix W H The details will be clarified by the following description.

[0049] <<Parameter updating unit 160 constituting the transmitting-side digital signal processing device 100>>

[0050] The parameter updating unit 160 constituting the transmitting-side digital signal processing device 100 is a component that updates the parameters used by the system number compression unit 150. Specifically, the parameter updating unit 160 updates the matrix W that appears in the equation (1).

[0051] The matrix W that maps the compressed system number H It is determined so that the evaluation function (V) given by the following mathematical formula is minimized.

[0052]

[0053] Here, the function E in equation (2) represents the expected value. In addition, the symbol "||||" in equation (2) represents a norm such as the Euclidean norm. The matrix W is given by the following mathematical formula.

[0054]

[0055] As mentioned above, the matrix W H is a matrix of size m×n, and performs mapping of compressed system numbers. On the other hand, the matrix W appearing in equations (2) and (3) is a matrix of size n×m. The matrix W is a matrix used in the system number restoration unit 650 described later, and plays a role in restoring the system number from m to n.

[0056] The evaluation function (V) appearing in Equation (2) is an evaluation function of the matrix W that compares x(t), which is the original signal string, and the compressed and restored signal string WW H x(t) and is designed to obtain the matrix W with the smallest difference therebetween.

[0057] x(t), which is the original signal string, is n-dimensional. However, if the space in which x(t) expands when the time t changes is m-dimensional (m < n), the matrix W H is given as a mapping from the n-dimensional space to the m-dimensional subspace in which x(t) expands.

[0058] Even if the space in which x(t) expands when the time t changes is a dimension higher than m-dimensional, the matrix W H also reduces the dimensions with less influence and performs mapping to the m-dimensional subspace so that the difference between x(t), which is the original signal string, and the compressed and restored signal string WW H x(t) does not increase.

[0059] Thus, the matrix W H performs mapping from the n-dimensional space to the m-dimensional subspace. On the contrary, the matrix W performs mapping from the m-dimensional subspace to the n-dimensional space. As shown in Equations (2) and (3), the optical transmission system of the present disclosure technology updates the matrix W so that the matrix W becomes the H demapping of.

[0060] The optical transmission system of the present disclosure technology thus updates the matrix W and the matrix W according to x(t), which is the original signal string, and can thus be said to be an adaptive optical transmission system. H

[0061] The parameter update unit 160 may also update the matrix W using an intermediate operation vector (h k ) given by the following mathematical formula.

[0062]

[0063] Here, the subscript k used in Equation (4) indicates the k-th sampling time. y k appearing in Equation (4) represents the same signal as y(t) appearing in Equation (1). In addition, the matrix P k appearing in Equation (4) is called an estimation matrix and is updated according to the update rule shown by the following mathematical formula.

[0064]

[0065] ​The matrix operation Tri in formula (5) represents the operation of first performing the operation on the lower triangular part and then copying the Hermitian transpose of the lower triangular part to the upper triangular part. In addition, β in formula (5) is a forgetting parameter that determines the degree of update (update speed), and takes a value greater than 0 and less than 1.

[0066] Finally, the matrix W is updated according to the update rule shown in the following mathematical formula.

[0067]

[0068] Here, the e in formula (6) k is the error vector.

[0069] The parameter updating unit 160 may update the matrix W not every sampling but at regular intervals. When the parameter updating unit 160 updates the matrix W once every L samplings, for example, the update matrix (P) and the update rule of the matrix W are given by the following mathematical formula.

[0070]

[0071] The purpose of updating the matrix W by thinning out at regular intervals is to update the matrix (P) and the matrix W according to the total latency, taking into account the processing capability of the digital signal processing device 100 on the transmitting side.

[0072] 《DAC200》

[0073] DAC200 is a component that converts a digital signal into an analog signal. The DAC in the name of DAC200 stands for Digital-to-Analog Converter. The analog signal converted by DAC200 is sent to the analog optical transmitter 300.

[0074] 《Analog Optical Transmitter 300》

[0075] The analog optical transmitter 300 is a structural element that converts the electrical analog signal sent from the DAC 200 into an optical signal and sends it to the analog optical transmission path (AOTL). That is, the analog optical transmitter 300 is an EOC (Electrical-to-Optical Converter). The analog optical transmitter 300 is implemented, for example, by an EML (Electro-absorption Modulator Laser). The EML is a semiconductor laser that integrates an electric field absorption type optical modulator for converting an electrical signal into an optical signal. In addition to the EML, the analog optical transmitter 300 can also be implemented by a combination of a laser and a Mach-Zehnder optical modulator or by directly modulating the laser.

[0076] The optical signal output from the analog optical transmitter 300 (hereinafter referred to as an "IFoF signal") is sent to the receiving side of the optical transmission system via the analog optical transmission path (AOTL).

[0077] Figure 2 1 is a block diagram showing the functional structure of the receiving side of the optical transmission system of Embodiment 1. Figure 2 As shown in FIG. 1 , the optical transmission system of Embodiment 1 includes an analog optical receiver 400, an ADC 500, and a receiving-side digital signal processing device 600 on the receiving side. Figure 2 As shown, the receiving-side digital signal processing device 600 includes a frequency division multiplexing unit 610 and a system data restoration unit 650. The receiving side of the optical transmission system can also be considered as an optical line terminal device of A-RoF, for example.

[0078] About Data Communications

[0079] like Figure 1 and Figure 2 As shown, information related to the matrix W is communicated from the transmitting side to the receiving side of the optical transmission system. The data communication can be realized by a digital optical transceiver such as a SFP (Small Form-Factor Pluggable).

[0080] If the SFP involved in data communication has a wavelength different from that of the EML involved in analog optical communication, the communication of information related to the matrix W can use the optical transmission path involved in the frequency division multiplexing unit 120 and the frequency division multiplexing unit 610 without using a separate data communication path.

[0081] Data communication is not limited to SFP, and can also be achieved through other digital transceivers. In addition, data communication for the purpose of data transmission and reception, connecting the sending side and the receiving side is not limited to optical transmission, but can also be wireless transmission. That is, the optical transmission system of the disclosed technology can also combine both optical fiber wireless transmission and wireless transmission using the IFoF method.

[0082] 《Analog Optical Receiver 400》

[0083] The analog optical receiver 400 is a component that converts an IFoF signal sent from an analog optical transmission line (AOTL) into an analog electrical signal. In other words, the analog optical receiver 400 is an OEC (Optical-to-Electrical Converter). The analog optical receiver 400 is implemented by, for example, a photo diode.

[0084] The analog optical receiver 400 corresponds to the analog optical transmitter 300 on the transmission side. The analog optical receiver 400 on the reception side plays a role opposite to that of the analog optical transmitter 300 on the transmission side.

[0085] The analog electrical signal output from the analog optical receiver 400 is sent to the ADC 500 .

[0086] 《ADC500》

[0087] The ADC 500 is a component that converts an analog signal into a digital signal. The ADC in the name of the ADC 500 stands for Analog-to-Digital Converter. The signal converted into a digital signal by the ADC 500 is sent to the receiving-side digital signal processing device 600 .

[0088] 《Receiving-side digital signal processing device 600》

[0089] The receiving-side digital signal processing device 600 is a structural element that realizes IF channel separation on the receiving side by a digital signal processing method in an optical transmission system of the IFoF method. The details of IF channel separation are clarified in the description related to the frequency division multiplexing unit 610 described later. In addition, generally speaking, as a method for realizing IF channel separation, in addition to the digital signal processing method, a method based on an analog circuit can also be considered. The advantages of digital signal processing, compared with the method based on an analog circuit, can be listed as the ability to reduce circuit scale, excellent flexibility, and excellent separation capability.

[0090] 《Frequency Demultiplexing Unit 610 Constituting Receiving-Side Digital Signal Processing Device 600》

[0091] The frequency division multiplexing unit 610 constituting the receiving side digital signal processing device 600 is a structural element that separates the signal multiplexed (muxing) into the intermediate frequency (IF) into each signal channel again. The processing performed by the frequency division multiplexing unit 610 is sometimes called demultiplexing processing, Demultiplexing, or Demuxing for short. In particular, the demultiplexer related to the intermediate frequency (IF) is sometimes recorded as IF-DeMUX. In addition, the processing performed by the IF-DeMUX is sometimes recorded as IF-DeMUX processing.

[0092] <<System number restoration unit 650 constituting the receiving-side digital signal processing device 600>>

[0093] The system number restoration unit 650 constituting the receiving-side digital signal processing device 600 is a structural element that restores the system number from m to n. The system number restoration unit 650 uses the matrix W obtained by the parameter updating unit 160 to restore the system number from m to n. The matrix W used by the system number restoration unit 650 for restoration becomes the matrix W used by the system number compression unit 150 on the transmitting side for compression. H The Hermitian transposition of , that is, obtaining synchronization (simultaneity) is important. The disclosed technology has the matrix W on the sending side H The matrix W on the receiving side is synchronized, so the timestamp can also be used. H An example of a method of achieving synchronization with the matrix W on the receiving side is shown in Embodiment 3.

[0094] Figure 4 1 is a block diagram illustrating detailed functions of the frequency division multiplexing unit 610 constituting the receiving-side digital signal processing device 600 according to Embodiment 1. Figure 4 As shown, the frequency division multiplexing unit 610 has the function of outputting m signal strings (z1(t), z2(t), . . . , z m (t)) digital data stream. Figure 4 As shown, each digital data stream has, for example, a downsampler 611, a digital filter 612, an NCO 613, and a multiplier 614. This structure is similar to Figure 3 The structure of the receiving side frequency division multiplexing unit 120 is paired. Similar to the receiving side frequency division multiplexing unit 120, the functional blocks involved in the first digital data stream are distinguished by marking "-1" after the reference numerals, such as the sampler 611-1, the digital filter 612-1, the NCO 613-1 and the multiplier 614-1. In this specification, the functional blocks involved in other digital data streams are also distinguished by the same reference numeral marking method.

[0095] The multiplier 614-i in the i-th digital stream multiplies the digital signal sampled by the ADC 500 by the output from the NCO 613-i.i ) means a shift in the frequency domain, i.e., a frequency shift of the NCO frequency (-f i ).

[0096] The NCO613-i in the i-th digital stream generates an NCO frequency (-f i ) opposite to that of the i-th NCO123-i on the transmission side. More specifically, the NCO613-i in the i-th digital stream generates a data string of complex numbers (handwritten z) given by the following mathematical formula.

[0097]

[0098] where the angular frequency ω appearing in Equation (8) is equal to 2πf i . In addition, T appearing in Equation (8) represents the sampling period.

[0099] The digital filter 612 in the digital data stream can be a band-pass filter that extracts signals in a necessary frequency band.

[0100] The downsampler 611 in the digital data stream samples according to the output rate. Specifically, the downsampler 611 performs, for example, decimation processing to reduce the sampling rate and achieve sampling corresponding to the output rate.

[0101] In addition, the signal string (z1(t), z2(t), …, z m (t)) obtained by the downsampler 611 can be a baseband of 0 (zero) [Hz] or can have other intermediate frequencies (IF). However, the intermediate frequency (IF) of the signal output by the frequency demultiplexing unit 610 is a frequency corresponding to the frequency division multiplexing unit 120 on the transmission side.

[0102] In addition, Figure 4 shows a structure for outputting m signal strings (z1(t), z2(t), …, z m (t)) through parallel processing. However, the disclosed technology is not limited to this. The frequency demultiplexing unit 610 can also perform signal processing in series (serially) rather than in parallel (parallel), i.e., in multiple stages.

[0103] Generally speaking, as a method of compressing the number of signal channels of a transmission system to m (m < n) when the original signal string x(t) is n-dimensional, a method of mechanically reducing the number of bits in the quantization of the original signal string x(t) can also be considered. However, this method does not depend on the nature of the original signal string x(t) and always reduces the number of bits of the original signal string x(t). Therefore, it is neither adaptive nor intelligent.

[0104] As described above, the optical transmission system of Embodiment 1 has the above structure. Therefore, it has the function of adaptively compressing the number of signal channels of the transmission system to m (m < n) when the original signal string x(t) is n-dimensional. Through this function, the optical transmission system of Embodiment 1 can effectively use the limited number (m) of signal channels of the transmission system.

[0105] Embodiment 2

[0106] The optical transmission system of Embodiment 2 is a modified example of the optical transmission system of the present disclosure technology. Unless otherwise specifically stated, in Embodiment 2, the same reference numerals as those used in Embodiment 1 are used. In addition, in Embodiment 2, the description repeated with Embodiment 1 is appropriately omitted.

[0107] Figure 5 is a block diagram showing the functional structure of the transmission side of the optical transmission system of Embodiment 2. As Figure 5 shown, the optical transmission system of Embodiment 2 has a parameter convergence determination unit 170 in the transmission-side digital signal processing device 100 on the transmission side, based on the structure shown in Embodiment 1.

[0108] 《Parameter Convergence Determination Unit 170 Constituting Transmission-Side Digital Signal Processing Device 100》

[0109] The parameter convergence determination unit 170 constituting the transmission-side digital signal processing device 100 is a structural element that determines whether the matrix W to be updated converges in the update process of the matrix W as a parameter. The parameter convergence determination unit 170, for example, uses the error vector (e k ) that appears in Equation (6), and calculates the value of the following evaluation function (V k ) every time it is updated.

[0110]

[0111] Here, the superscript T that appears in Equation (9) represents transpose. In addition, the evaluation function (V k ) is a scalar function. The evaluation function (V k ) given by Equation (9) is essentially the same as the evaluation function (V) given by Equation (2) that appears in Embodiment 1.

[0112] The parameter convergence determination unit 170 calculates the difference between the evaluation function (V k-1 ) of the previous time (sampling is k - 1) and the evaluation function (V k ) of the current time (sampling is k), and compares it with the threshold value (ε). As shown in the following mathematical formula, between the evaluation function (V k-1 ) of the previous time (sampling is k - 1) and the evaluation function (V k) is sufficiently small to be smaller than the threshold value (ε), the parameter convergence determination unit 170 determines that the matrix W to be updated has converged.

[0113]

[0114] The information obtained by the parameter convergence determination unit 170 (specifically, the evaluation function (V k ) and the difference value (V k-1 -V k )) Various uses can be considered.

[0115] The simplest method is to use the evaluation function (V k ) as an evaluation index of the optical transmission system. The optical transmission system of the disclosed technology may also display the evaluation function (V) using a curve graph or the like on a display at the receiving side, for example. k ) value. As shown in formula (9), the evaluation function (V k ) represents the error vector (e) in quadratic form k ), therefore, the evaluation function (V k ) is an indicator of the extent to which information is lost in the system number compression unit 150. k ) is 0 (zero), then the error vector (e k ) is a 0 vector (zero vector), which means that there is no lost information about the sampling time in the system number compression unit 150.

[0116] The parameter updating unit 160 may also perform data communication of the information of the matrix W to the receiving side only when the parameter convergence determination unit 170 determines that the update of the matrix W has converged. The reason for limiting the transmission of the information of the matrix W to the receiving side in this way is based on the following inferred principle: even if the matrix W when the update has not fully converged is used, the quality of data restoration in the system number restoration unit 650 on the receiving side of the optical transmission system cannot be ensured.

[0117] The update of the matrix W implemented by the parameter updating unit 160 may not necessarily converge within a certain number of times. The parameter convergence determination unit 170 may also count the number of updates of the matrix W in the parameter updating unit 160, and even if the convergence condition shown in the upper part of equation (10) is not satisfied, when the number of updates reaches a predetermined certain number (U max ), data communication of the information of the matrix W is also performed to the receiving side.

[0118] The threshold (ε) and the upper limit of the number of updates (U max) can be set as parameter values ​​that the user can appropriately set according to the use purpose of the optical transmission system. In addition, these parameter values ​​can be stored in a memory or the like of the optical transmission system, and the optical transmission system can access the memory and use it.

[0119] Regarding the optical transmission system of Embodiment 2, in the parameter convergence determination unit 170, even after the convergence condition shown in the upper part of equation (10) is satisfied, the parameter update in the parameter update unit 160 may not be stopped. By continuing the parameter update in the parameter update unit 160 even after the convergence condition is satisfied, the optical transmission system of Embodiment 2 can continue to function adaptively.

[0120] As described above, in the optical transmission system of the second embodiment, the parameter convergence determination unit 170 focuses on the evaluation function (V k-1 ) and the evaluation function (V k ), but the disclosed technology is not limited to this. The optical transmission system of the disclosed technology can also focus on the evaluation function (V k ) value itself, to determine whether the parameters have converged. In addition, the optical transmission system of the disclosed technology can also focus on updating the matrix (P), the error vector (e k ) or the updated intermediate generated vector (g k 、h k ) to determine whether the parameters have converged. Furthermore, the optical transmission system of the disclosed technology may also prepare two or more thresholds and use the algorithm used in the chattering eliminator to determine whether the parameters have converged.

[0121] In special situations where real-time communication is not required, the optical transmission system of embodiment 2 may also be used as follows: in the parameter convergence determination unit 170, before the convergence condition shown in the upper part of equation (10) is met, the communication data is reserved and not allowed to flow to the simulated optical transmission path (AOTL).

[0122] As described above, the optical transmission system of embodiment 2 has the above-mentioned structure. Therefore, on the basis of the effect shown in embodiment 1, since the matrix W judged to be updated and converged is used, the effect of being able to maintain the quality of data recovery in the system number recovery unit 650 on the receiving side of the optical transmission system is exerted.

[0123] Implementation 3

[0124] The optical transmission system of Embodiment 3 is a modified example of the optical transmission system of the disclosed technology. In Embodiment 3, the same reference numerals as those used in the above embodiments are used except for cases where they are specifically stated. In addition, in Embodiment 3, descriptions that overlap with those in the above embodiments are appropriately omitted.

[0125] Figure 6 1 is a block diagram showing the functional structure of the transmission side of the optical transmission system of Embodiment 3. Figure 6 As shown, in the optical transmission system of the third embodiment, in the digital signal processing device 100 on the transmitting side, the structure shown in the first embodiment (see Figure 1 ) has a modulation signal generating unit 180.

[0126] In addition, Figure 6 The transmission system for data communication is not shown.

[0127] <<Modulation signal generation unit 180 constituting the transmitting-side digital signal processing device 100>>

[0128] The modulation signal generating unit 180 constituting the transmitting side digital signal processing device 100 converts the parameter information sent from the parameter updating unit 160 into a modulation signal so as to make it correspond to y1(t), y2(t), ..., y m (t) is similarly sent to the structural elements of the analog optical transmission path (AOTL).

[0129] The conversion performed by the modulation signal generation unit 180 may be, for example, phase shift keying (PSK) such as quadrature phase shift keying (QPSK), quadrature phase-shift keying, or quadriphase phase-shift keying.

[0130] Furthermore, the signal generated by the modulation signal generating unit 180 may be a multi-subcarrier signal using an orthogonal frequency division multiplexing (OFDM) method or the like.

[0131] The signal generated by the modulation signal generating unit 180 is distributed to y1(t), y2(t), ..., y m (t) different intermediate frequencies (IF). The signal generated by the modulation signal generating unit 180 is sent to the frequency division multiplexing unit 120. Figure 6 In the example shown, m+1 signal sequences are multiplexed in the frequency division multiplexing unit 120 in the transmitting-side digital signal processing device 100 .

[0132] Figure 7 1 is a block diagram showing the functional structure of the receiving side of the optical transmission system of Embodiment 3. Figure 7 As shown, in the optical transmission system of Embodiment 3, in the receiving-side digital signal processing device 600, the structure shown in Embodiment 1 (see Figure 2 ) has a demodulation processing unit 680. The demodulation processing unit 680 is a component corresponding to the modulation signal generating unit 180 in the transmitting-side digital signal processing device 100.

[0133] exist Figure 7 In, with Figure 6 Likewise, a transmission system for data communications is not shown.

[0134] exist Figure 7 In the example shown, Figure 6 Correspondingly, in the frequency division multiplexing unit 610 in the receiving-side digital signal processing device 600, the signal sent from the ADC 500 is demultiplexed into m+1 signal strings. The m+1 signal strings generated by demultiplexing are y1(t), y2(t), ..., y m (t) corresponds to the m signal strings (z1(t), z2(t), ..., z m (t)) is sent to the system number restoration unit 650. The signal sequence corresponding to the signal generated in the modulation signal generation unit 180 among the m+1 signal sequences generated by demultiplexing is sent to the demodulation processing unit 680.

[0135] 《Demodulation Processing Unit 680 Constituting the Receiving-Side Digital Signal Processing Device 600》

[0136] The demodulation processing unit 680 constituting the receiving-side digital signal processing device 600 is a structural element that performs a demodulation process on the parameter information converted into a modulation signal by the modulation signal generating unit 180 constituting the transmitting-side digital signal processing device 100. When the parameter information converted into a modulation signal by the modulation signal generating unit 180 constituting the transmitting-side digital signal processing device 100 is a matrix W, the demodulation processing unit 680 constituting the receiving-side digital signal processing device 600 demodulates the modulation signal and extracts the matrix W. In this way, the modulation signal generating unit 180 and the demodulation processing unit 680 together constitute a set.

[0137] As described above, the optical transmission system of the third embodiment has the above-mentioned structure, and therefore, a transmission system that does not use data communication can also send parameter information to the receiving side, thereby achieving the same effect as that shown in the first embodiment.

[0138] Implementation 4

[0139] The optical transmission system of Embodiment 4 is a modified example of the optical transmission system of the disclosed technology. In Embodiment 4, the same reference numerals as those used in the above embodiments are used except for cases where they are specifically stated. In addition, in Embodiment 4, descriptions that overlap with those in the above embodiments are appropriately omitted.

[0140] Figure 84 is a block diagram showing the functional structure of the transmission side of the optical transmission system of Embodiment 4. Figure 8 As shown, in the optical transmission system of the fourth embodiment, in the digital signal processing device 100 on the transmitting side, the structure shown in the first embodiment (see Figure 1 ) has a PILOT signal generating unit 190.

[0141] <<PILOT signal generating unit 190 constituting the transmitting-side digital signal processing device 100>>

[0142] The PILOT signal generating unit 190 constituting the transmitting-side digital signal processing device 100 is a component that generates a PILOT signal that serves as a basis for calculating a phase correction value for phase correction performed in the receiving-side digital signal processing device 600 described later.

[0143] The details of the phase correction performed in the receiving-side digital signal processing device 600 will be clarified by the following description.

[0144] The PILOT signal generated in the PILOT signal generating section 190 is sent to the frequency division multiplexing section 120 .

[0145] The PILOT signal generated by the PILOT signal generating unit 190 is, for example, a sin wave of two different frequencies (hereinafter referred to as a "dual-tone sin wave"). a 、f b ), choose the same as in y1(t), y2(t), …, y m In addition, in this specification, it is assumed that two different frequencies (f a 、f b ) b -f a ) is shown as Δf. In addition, in this specification, it is assumed that f a Ratio b Small, Δf is a positive value. The two-tone sin wave is generated, for example, in the following manner: it is output in a pulsed form, and at the moment of output, the phase is 0 (zero) [rad]. In any case, the following two-tone sin wave is used: when DFT (Digital Fourier Transform) is performed, the frequency is f a The phase and frequency when b The phases at the time of output are known. For example, DFT can be set to take the instant of output as the reference and start sampling from the instant of output. For easy understanding of the description, in this specification, it is assumed that the PILOT signal is sampled from the frequency f when the above DFT is implemented. a The sin wave is observed with a frequency of fb The phase delay of the sin wave is 0 (zero) [rad].

[0146] In this specification, it is assumed that y1(t), y2(t), ..., y m The intermediate frequencies (IF) used in (t) are f1, f2, …, f m For convenience, in this specification, f1, f2, ..., f m and f a 、f b The size relationship of is shown in the following formula.

[0147]

[0148] The frequency division multiplexing unit 120 of the fourth embodiment multiplexes the m signal sequences (y1(t), y2(t), . . . , y m The signal multiplexed in the frequency division multiplexing unit 120 is sent to the analog optical transmission line (AOTL) via the DAC 200 and the analog optical transmitter 300.

[0149] Fig. 9 4 is a block diagram showing the functional structure of the receiving side of the optical transmission system of Embodiment 4. Fig. 9 As shown, in the optical transmission system of Embodiment 4, in the receiving-side digital signal processing device 600, the structure shown in Embodiment 1 (see Figure 2 ) has a phase adjustment value calculation unit 692 and a phase adjustment unit 694.

[0150] exist Fig. 9 In the example shown, Figure 8 Correspondingly, in the frequency division multiplexing unit 610 in the receiving-side digital signal processing device 600, the signal sent from the ADC 500 is demultiplexed into m+2 signal strings. The m+2 signal strings generated by demultiplexing are y1(t), y2(t), ..., y m (t) corresponds to the m signal strings (z1(t), z2(t), ..., z m (t)) is sent to the phase adjustment unit 694. The signal sequence corresponding to the two-tone sinusoidal wave among the m+2 signal sequences generated by demultiplexing is sent to the phase adjustment value calculation unit 692.

[0151] <Phase adjustment value calculation unit 692 constituting the receiving-side digital signal processing device 600>

[0152] The phase adjustment value calculation unit 692 constituting the receiving-side digital signal processing device 600 calculates the m signal sequences (z1(t), z2(t), . . . , z m(t)) is a structural element of the phase adjustment value used in the phase adjustment of FIG.

[0153] The phase adjustment value calculation unit 692 performs DFT processing on the demultiplexed and transmitted dual-tone sin wave. The DFT performed by the phase adjustment value calculation unit 692 may be based on the instant when the dual-tone sin wave is received and may start sampling from the instant when the dual-tone sin wave is received.

[0154] In this specification, it is assumed that when the phase adjustment value calculation unit 692 performs the above-mentioned DFT, from the frequency f a The sin wave is observed with a frequency of f b The phase delay of the sin wave is Δθ [rad]. The phase adjustment value calculated by the phase adjustment value calculation unit 692 is Δθ [rad] related to the phase delay. The optical transmission system of embodiment 4 attempts phase adjustment based on the following premise: for two signals, when the frequency difference between them is Δf, a new phase difference of Δθ [rad] is generated by passing through an analog optical transmission path (AOTL). However, strictly speaking, the phase difference (Δθ) is not actually determined only by the relative frequency difference (Δf), and the phase difference (Δθ) also varies depending on the absolute intermediate frequency (IF) value.

[0155] The phase adjustment value Δθ [rad] calculated by the phase adjustment value calculation unit 692 is sent to the phase adjustment unit 694 .

[0156] <<Phase adjustment unit 694 constituting the receiving-side digital signal processing device 600>>

[0157] The phase adjustment unit 694 constituting the receiving-side digital signal processing device 600 performs frequency division multiplexing on the m signal sequences (z1(t), z2(t), . . . , z3(t)) generated by the frequency division multiplexing unit 610 using the phase adjustment value calculated by the phase adjustment value calculation unit 692. m (t))'s phase adjustment structural elements.

[0158] Specifically, the phase adjustment unit 694 adjusts the m signal sequences (z1(t), z2(t), . . . , z m (t)), calculate the complex number (α i , i=1, 2, …, m) and multiply them.

[0159]

[0160] Here, in this specification, a given in the lower part of formula (12) is i It is called the "correction factor". i) and equation (12) concretize the following premise, perform linear interpolation and expand it, and the premise is: for certain two signals, when their frequency difference is Δf, a new phase difference of Δθ [rad] is generated by passing through the analog optical transmission path (AOTL).

[0161] In the optical transmission system of the fourth embodiment, the phase adjustment unit 694 adjusts the phase of the m signal sequences (z1(t), z2(t), . . . , z m (t)), respectively calculate the complex number (α i , i = 1, 2, ..., m) and multiply them, thus, we expect m signal strings (z1(t), z2(t), ..., z m The phase difference of each of the m signal sequences (y1(t), y2(t), ..., y m (t)) their respective phase differences.

[0162] Strictly speaking, the complex number (α i Therefore, more precisely, the phase adjustment unit 694 converts the signal string sent from the frequency division multiplexing unit 610 into the frequency domain and multiplies it by the complex number (α) given by equation (12) i , i=1, 2, ..., m), and converted into the time domain again. The details will be clarified by the description in the sixth embodiment.

[0163] The m signal strings (z1(t), z2(t), ..., z m (t)) is sent to the system number recovery unit 650.

[0164] As described above, even if the space in which x(t) is extended is higher than m dimensions when the time t is changed, the matrix W H The dimension with less influence is also reduced, and the mapping to the m-dimensional subspace is performed so that the original signal string x(t) and the compressed and restored signal string WW H Here, the signals mapped to the m-dimensional subspace are y1(t), y2(t), ..., y m (t).

[0165] As described above, the optical transmission system of Embodiment 4 can adjust the m signal strings (z1(t), z2(t), . . . , z m The phase difference of each of the m signal sequences (y1(t), y2(t), ..., y m (t)) their respective phase differences. This effect makes z1(t), z2(t), …, zm The trajectory of (t) is close to y1(t), y2(t), ..., y in the m-dimensional subspace. m That is, this effect improves the restoration accuracy in the systematic number restoration process based on the multiplication operation of the matrix W in the systematic number restoration unit 650.

[0166] As described above, the optical transmission system of embodiment 4 has the above-mentioned structure, and therefore, in addition to the effect shown in embodiment 1, the effect of improving the restoration accuracy in the system number restoration processing based on the multiplication operation of the matrix W in the system number restoration unit 650 is exerted.

[0167] Implementation method 5

[0168] The optical transmission system of Embodiment 5 is a modified example of the optical transmission system of the present disclosure technology. Specifically, the optical transmission system of Embodiment 5 shows that the present disclosure technology can also be realized by software.

[0169] In Embodiment 5, the same reference numerals as those used in the above embodiments are used except for cases where they are clearly stated. In Embodiment 5, descriptions overlapping with those in the above embodiments are appropriately omitted.

[0170] Fig.10 It is a hardware configuration diagram of the transmitting-side digital signal processing device 100 according to the fifth embodiment. Fig.10 As shown in the above paragraph Fig.10 A shows a case where the functions of the optical transmission system (transmission side) of the disclosed technology are realized by hardware. Fig.10 As shown in the following paragraph Fig.10 B shows a case where the functions of the optical transmission system (transmission side) of the disclosed technology are realized by software.

[0171] exist Fig.10 In the structure shown in example A, the transmitting-side digital signal processing device 100 includes a transmitting-side input interface 710 , a transmitting-side processing circuit 720 , and a transmitting-side output interface 730 .

[0172] exist Fig.10 In the structure shown in Example B, the transmitting-side digital signal processing device 100 includes a transmitting-side input interface 710 , a transmitting-side processor 722 , a transmitting-side memory 724 , and a transmitting-side output interface 730 .

[0173] The functions of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generating unit 180 and the PILOT signal generating unit 190 in the transmitting side digital signal processing device 100 are implemented by a processing circuit. The processing circuit may be dedicated hardware (see Fig.10A), or a CPU (Central Processing Unit, also called central processing unit, processing unit, computing unit, microprocessor, microcomputer, processor, DSP) that executes programs stored in a memory (see Fig.10 B) Either one is fine.

[0174] like Fig.10 As shown in FIG. 1A , when the processing circuit is dedicated hardware, that is, when it is implemented by the transmitting side processing circuit 720, the transmitting side processing circuit 720 may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a component formed by combining them. The functions of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generating unit 180, and the PILOT signal generating unit 190 may be implemented by multiple independent transmitting side processing circuits 720, or the functions of each unit may be uniformly implemented by one transmitting side processing circuit 720.

[0175] like Fig.10 As shown in FIG. 1B, when the processing circuit is a CPU, more specifically, when the processing circuit is a transmitting side processor 722, each function of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generation unit 180, and the PILOT signal generation unit 190 can be implemented by software, firmware, or a combination of software and firmware. Software and firmware are described as programs, which are stored in the transmitting side memory 724. The transmitting side processor 722 reads out and executes the program stored in the transmitting side memory 724, thereby realizing the functions of each unit. That is, the transmitting side digital signal processing device 100 has a transmitting side memory 724, which is used to store a program that, when executed by the transmitting side processor 722, results in the execution of the processing content performed by the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generation unit 180, and the PILOT signal generation unit 190 described in the embodiment. In addition, it can also be said that these programs cause the computer to execute the steps and methods of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generation unit 180, and the PILOT signal generation unit 190. Here, the transmission side memory 724 can be, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, etc. The transmission side memory 724 can also have a disk such as a magnetic disk, a floppy disk, an optical disk, a high-density disk, a mini disk, or a DVD. Furthermore, the transmission side memory 724 can also be in the form of a HDD or SSD.

[0176] The transmission side memory 724 may store parameters updated by the parameter updating unit 160, in particular, parameters determined to be converged by the parameter convergence determining unit 170. In addition, the transmission side memory 724 may store information required for the PILOT signal generating unit 190 to generate a PILOT signal.

[0177] The transmission-side output interface 730 may also include the function of the DAC 200 , or include the functions of the DAC 200 and the analog optical transmitter 300 .

[0178] In addition, the functions of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generating unit 180, and the PILOT signal generating unit 190 may be partially implemented by dedicated hardware and partially implemented by software or firmware. In this way, the processing circuit can implement the functions of the frequency division multiplexing unit 120, the system number compression unit 150, the parameter updating unit 160, the parameter convergence determination unit 170, the modulation signal generating unit 180, and the PILOT signal generating unit 190 by hardware, software, firmware, or a combination thereof.

[0179] Fig.11 This is a hardware configuration diagram of a receiving-side digital signal processing device 600 according to the fifth embodiment. Fig.11 As shown in the above paragraph Fig.11 A shows a case where the functions of the optical transmission system (receiving side) of the disclosed technology are realized by hardware. Fig.11 As shown in the following paragraph Fig.11 B shows a case where the functions of the optical transmission system (receiving side) of the disclosed technology are realized by software.

[0180] exist Fig.11 In the structure shown in example A, the receiving-side digital signal processing device 600 includes a receiving-side input interface 810 , a receiving-side processing circuit 820 , and a receiving-side output interface 830 .

[0181] exist Fig.11 In the structure shown in example B, the receiving-side digital signal processing device 600 includes a receiving-side input interface 810 , a receiving-side processor 822 , a receiving-side memory 824 , and a receiving-side output interface 830 .

[0182] The functions of the frequency division multiplexing unit 610, the system number restoration unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694 in the receiving side digital signal processing device 600 are implemented by a processing circuit. The processing circuit may be dedicated hardware (see Fig.11 A), or a CPU that executes a program stored in a memory (see Fig.11 B) Either one is fine.

[0183] like Fig.11 As shown in FIG. 1A , when the processing circuit is dedicated hardware, that is, when it is implemented by the receiving side processing circuit 820, the receiving side processing circuit 820 may be a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a component formed by combining them. The functions of the frequency division multiplexing unit 610, the system number recovery unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694 may be implemented by multiple independent receiving side processing circuits 820, or the functions of each unit may be uniformly implemented by one receiving side processing circuit 820.

[0184] like Fig.11 As shown in FIG. 2B , when the processing circuit is a CPU, more specifically, when the processing circuit is a receiving-side processor 822, the functions of the frequency division multiplexing unit 610, the system number restoration unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694 can be implemented by software, firmware, or a combination of software and firmware. Software and firmware are described as programs, which are stored in the receiving-side memory 824. The receiving-side processor 822 reads out and executes the program stored in the receiving-side memory 824, thereby implementing the functions of each unit. That is, the receiving-side digital signal processing device 600 has a receiving-side memory 824 for storing a program that, when executed by the receiving-side processor 822, results in the execution of the processing contents performed by the frequency division multiplexing unit 610, the system number restoration unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694 described in the embodiment. In addition, it can also be said that these programs cause the computer to execute the steps and methods of the frequency division multiplexing unit 610, the system number recovery unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694. Here, the receiving side memory 824 can be, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, etc. The receiving side memory 824 can also have a disk such as a magnetic disk, a floppy disk, an optical disk, a high-density disk, a mini disk, or a DVD. Furthermore, the receiving side memory 824 can also be in the form of an HDD or an SSD.

[0185] The reception-side memory 824 may store the phase adjustment value (Δθ related to the phase delay) calculated by the phase adjustment value calculation unit 692 together with information such as the date and time of the calculation as a history.

[0186] The receiving-side input interface 810 may also include the function of the ADC 500 , or include the functions of the ADC 500 and the analog optical receiver 400 .

[0187] In addition, regarding the respective functions of the frequency-division multiplexing unit 610, the system number restoration unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694, part of them can also be implemented by dedicated hardware, and the other part can be implemented by software or firmware. In this way, the processing circuit can implement the respective functions of the frequency-division multiplexing unit 610, the system number restoration unit 650, the demodulation processing unit 680, the phase adjustment value calculation unit 692, and the phase adjustment unit 694 through hardware, software, firmware, or a combination thereof.

[0188] As described above, the optical transmission system of Embodiment 5 has the above structure. Therefore, it can be implemented through hardware, software, firmware, or a combination thereof, and has the effect of adaptively compressing the number of signal channels of the transmission system to m (m < n) when the original signal string x(t) is n-dimensional. Through this effect, the optical transmission system of Embodiment 5, like the optical transmission systems of the above embodiments, can effectively use the limited number (m) of signal channels possessed by the transmission system.

[0189] Embodiment 6

[0190] The optical transmission system of Embodiment 6 is a modified example of the optical transmission system of the present disclosure technology. Specifically, the optical transmission system of Embodiment 6 is a modified example of the optical transmission system of Embodiment 4.

[0191] Unless otherwise specifically stated, in Embodiment 6, the same reference numerals as those used in the above embodiments are used. In addition, in Embodiment 6, the descriptions that overlap with the above embodiments are appropriately omitted.

[0192] As Fig. 9 shown, the optical transmission system of Embodiment 4 has a phase adjustment value calculation unit 692 and a phase adjustment unit 694 in the receiving-side digital signal processing device 600. Here, when considering what phase is, phase is a periodic motion represented by vibration or fluctuation, and is a quantity representing the progress stage within one period. Generally, the phase (θ(t)) in a certain periodic motion is given by the following formula.

[0193] θ(t) = θ(0) + ωt...(13)

[0194] Here, ω is the angular frequency, and t is the time. In addition, θ(0) is the initial value at time 0.

[0195] In this way, it can be said that phase is a value initially obtained for a periodic motion by giving the initial value (θ(0)), the angular frequency (ω), or the frequency (f = ω / (2π)) and the time (t).

[0196] In the Laplace transform that realizes conversion from the time domain to the frequency domain, the time shift in the time domain is given by the following equation in the frequency domain.

[0197]

[0198] Here, the handwritten L on the left side of equation (14) means that the Laplace transform is performed on the brackets. s in equation (14) is the Laplace operator. x(t) is an arbitrary function in the time domain (time signal, etc.).

[0199] By substituting jω into s of the Laplace operator, the behavior in the angular frequency region can be understood. In addition, by setting s = jω, the Laplace transform is equivalent to the Fourier transform. It can be seen that when s = jω, the right side of the lower part of equation (14) is -τs is the complex number (α i , i = 1, 2, ..., m) has the same structure and is a complex number on the unit circle.

[0200] As shown by comparison between equation (12) and equation (14), the optical transmission system of embodiment 4 is intended to ultimately correct the deviation of the time delay caused by the difference in the intermediate frequency (IF).

[0201] If we consider this, it can be seen that the PILOT signal generation unit 190 in the transmitting-side digital signal processing device 100 generates the intermediate frequencies (f1, f2, ..., f m ) can be used as the PILOT signal. The receiving-side digital signal processing device 600 observes the intermediate frequencies (f1, f2, ..., f m ) at what timing the sin wave arrives. Furthermore, the phase adjustment unit 694 of the receiving-side digital signal processing device 600 may perform the following time shift correction in the time domain.

[0202]

[0203] Among them, τ1, τ2, ..., τ appearing on the right side of formula (15) m is the time lapse correction amount in each signal channel. In addition, the time lapse correction amount is determined by the relative relationship between each signal channel. Therefore, the time lapse correction amount of the remaining signal channels (τ2, τ3, ..., τ4) can be determined based on the first signal channel, that is, τ1 = 0. m ).

[0204] It can be said that the optical transmission system of Embodiment 6 causes the m signal strings (z1(t+τ1), z2(t+τ2), . . . , z m (t+τ m)) is close to the m signal strings (y1(t), y2(t), ..., y m (t)). In other words, this action makes z1(t+τ1), z2(t+τ2), …, z m (t+τ m ) is close to y1(t), y2(t), …, y in the m-dimensional subspace. m That is, this effect improves the restoration accuracy in the systematic number restoration process based on the multiplication operation of the matrix W in the systematic number restoration unit 650.

[0205] As described above, the optical transmission system of embodiment 6 functions as described above, and therefore, in addition to the effects shown in embodiment 1, an effect of improving the restoration accuracy in the system number restoration processing based on the multiplication operation of the matrix W in the system number restoration unit 650 is achieved.

[0206] In addition, the optical transmission system of the disclosed technology is not limited to the forms illustrated in the embodiments, and the embodiments can be combined, arbitrary components of the embodiments can be modified, or arbitrary components can be omitted in the embodiments.

[0207] Industrial Applicability

[0208] The disclosed technology can be applied to, for example, the mobile fronthaul (MFH) of a centralized radio access network (C-RAN) that is expected to be a next-generation mobile network, and has industrial applicability.

[0209] Description of symbols

[0210] 100: a digital signal processing device on the transmitting side; 120: a frequency division multiplexing unit; 121: an upsampler; 122: a digital filter; 123: an NCO; 124: a multiplier; 125: an adder; 150: a system number compression unit; 160: a parameter updating unit; 170: a parameter convergence determination unit; 180: a modulation signal generation unit; 190: a PILOT signal generation unit; 200: a DAC; 300: an analog optical transmitter; 400: an analog optical receiver; 500: an ADC; 600: a digital signal processing device on the receiving side; 610: a frequency division multiplexing unit; 611: downsampler; 612: digital filter; 613: NCO; 614: multiplier; 650: system number recovery unit; 680: demodulation processing unit; 692: phase adjustment value calculation unit; 694: phase adjustment unit; 710: transmitting side input interface; 720: transmitting side processing circuit; 722: transmitting side processor; 724: transmitting side memory; 730: transmitting side output interface; 810: receiving side input interface; 820: receiving side processing circuit; 822: receiving side processor; 824: receiving side memory; 830: receiving side output interface.

Claims

1. An IFoF optical transmission system, wherein: The IFoF optical transmission system includes a transmitting-side digital signal processing device, the transmitting-side digital signal processing device includes a system data compression unit and a parameter updating unit. The system digital compression unit compresses n digital data streams into m which are less than n. The parameter updating unit updates the parameters used in the system number compression unit according to the value of an evaluation function having as an argument the signal sequence processed by the transmitting-side digital signal processing device.

2. The IFoF optical transmission system according to claim 1, wherein: The IFoF optical transmission system further comprises a receiving-side digital signal processing device including a system digital restoration unit. The system number restoration unit restores the digital data stream compressed into m pieces into n pieces based on the parameter updated by the system number restoration unit.

3. The IFoF optical transmission system according to claim 2, wherein: The parameter updated by the parameter updating unit is a matrix (W H ) and the matrix obtained by taking the Hermitian transpose of the matrix (W).

4. The IFoF optical transmission system according to claim 1, wherein: The transmitting-side digital signal processing device further includes a parameter convergence determination unit, The parameter convergence determination unit determines whether the parameter has converged based on a difference in the value of the evaluation function.

5. The IFoF optical transmission system according to claim 2, wherein: The transmitting-side digital signal processing device further comprises a modulation signal generating unit, The modulation signal generating unit converts the parameters into a modulation signal, The receiving-side digital signal processing device further includes a demodulation processing unit, The demodulation processing unit demodulates the modulated signal into the parameter.

6. The IFoF optical transmission system according to claim 2, wherein: The transmitting-side digital signal processing device further comprises a PILOT signal generating unit, The PILOT signal generating unit generates a polyphonic sin wave as a PILOT signal. The receiving-side digital signal processing device further comprises a phase adjustment unit, The phase adjustment unit performs time shift correction of the signal sequence based on the PILOT signal.

7. The IFoF optical transmission system according to claim 1, wherein: The IFoF optical transmission system is composed of a sending side input interface, a sending side processor, a sending side memory and a sending side output interface. Each function of the transmitting-side digital signal processing device is implemented by software, firmware or a combination thereof and is described as a program. storing the program in the sending side memory, The program is executed by the transmission-side processor, thereby executing each function of the transmission-side digital signal processing device.

8. The IFoF optical transmission system according to claim 2, wherein: The IFoF optical transmission system is composed of a receiving side input interface, a receiving side processor, a receiving side memory and a receiving side output interface. Each function of the receiving-side digital signal processing device is implemented by software, firmware or a combination thereof and is described as a program. storing the program in the receiving side memory, The program is executed by the receiving-side processor, thereby executing each function of the receiving-side digital signal processing device.

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