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) including a correction processing unit (110) and a correction signal generation unit (130); and a reception-side digital signal processing device (600) that includes a digital separation processing unit (610) that generates a correction signal (Scal (t)), the digital separation processing unit (610) performs a demultiplexing process and separates the correction signal (Scal (t)) into a plurality of baseband signals (SOUT1 (t), SOUT2 (t),..., SOUTn (t)), and a weight correction value calculation unit (620) that calculates parameter coefficients (a1, a2,..., an) from the baseband signals (SOUT1 (t), SOUT2 (t),..., SOUTn (t)), and calculates a weight correction value (a1, a2,..., an) on the basis of the calculated parameter coefficients (a1, a2,..., an). A correction processing unit (110) uses the parameter coefficients (a1, a2,..., an) to correct the amplitude of each of a plurality of input wireless signal strings that are input.

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. Generally speaking, an optical transmission system uses optical fiber as a medium for propagating light. Therefore, the method of 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 the optical transmission system, a light intensity modulation method of transmitting a signal corresponding to the on-off of a laser or a coherent optical communication method of modulating the frequency or phase shift of a laser in combination with a signal is adopted.

[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 an A-RoF solution, as the number of signal channels increases, a wider frequency band must be used. When the number of signal channels is increased by using the Nyquist band of the ADC and DAC as much as possible, the signal channel level may vary depending on the frequency characteristics of the components that constitute the transmission system. For example, the optical modulation device, photodiode, analog circuit elements in the ADC and DAC, optical fiber, etc. that constitute the optical transmission system based on an A-RoF solution may affect the frequency characteristics of the entire transmission system (see Figure 1 ).

[0013] The purpose of the disclosed technology is to provide an optical transmission system based on an A-RoF solution that improves the deviation of the signal channel level caused by the comprehensive frequency characteristics of the transmission system.

[0014] Means for solving problems

[0015] The IFoF optical transmission system of the disclosed technology comprises: a sending-side digital signal processing device, which includes a correction processing unit and a correction signal generating unit; and a receiving-side digital signal processing device, which includes a digital separation processing unit and a weight correction value calculation unit, wherein the correction signal generating unit generates a correction signal, the digital separation processing unit performs demultiplexing processing to separate the correction signal into a plurality of baseband signals, the weight correction value calculation unit calculates parameter coefficients based on the baseband signals, and the correction processing unit uses the parameter coefficients to correct the respective amplitudes of a plurality of input wireless signal strings.

[0016] Effects of the Invention

[0017] The optical transmission system of the disclosed technology has the above-mentioned structure, and therefore improves the deviation of the signal channel level caused by the comprehensive frequency characteristics of the transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a reference diagram for explaining the problem to be solved by the disclosed technology.

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

[0020] Figure 3 This is a block diagram showing the functional structure of the receiving side of the optical transmission system according to Embodiment 1.

[0021] Figure 4 This is a block diagram showing a functional configuration (an example) of the digital separation processing unit 610 constituting the optical transmission system according to Embodiment 1.

[0022] Figure 5 It is a graph obtained by Fourier transforming the baseband signal.

[0023] Figure 6 It is a hardware configuration diagram of the transmitting-side digital signal processing device 100 according to the second embodiment.

[0024] Figure 7 This is a hardware configuration diagram of a receiving-side digital signal processing device 600 according to the second embodiment. DETAILED DESCRIPTION

[0025] Figure 1 This is a reference diagram that illustrates how the power level of a signal channel in an optical transmission system based on an A-RoF solution may deviate due to the integrated frequency characteristics of the transmission system.

[0026] Figure 1 In Figure 1 A shows a data signal sampled by a DAC (Digital-to-Analog Converter) on the BBU side (or base station side) when the number of signal channels is set to 5 in the frequency domain. Figure 1 The horizontal axis of A shows frequency, Figure 1 The vertical axis of A shows the power of the signal. Figure 1 "#1", "#2", ..., "#5" in the graph of A are signal channel numbers for identifying signal channels. Figure 1 The stage shown in A shows that all signal channels are at the same power level. Figure 1Each signal channel in the graph of A has a certain width in the horizontal axis direction, that is, in the frequency direction. This is because each data is quadrature amplitude modulated (QAM: Quadrature Amplitude Modulation) in each intermediate frequency (IF) sub-band.

[0027] Figure 1 In Figure 1 B shows Figure 1 Each data signal shown in A is an analog signal converted by a DAC. Figure 1 The horizontal and vertical axes of the graph shown in B are Figure 1 The horizontal and vertical axes shown in A are the same. Figure 1 In the stage shown in B, the power level of the signal channel is deviated due to the influence of analog circuit elements in the DAC. Figure 1 B also shows that noise is generated regardless of the frequency.

[0028] Figure 1 In Figure 1 C is shown by Figure 1 The analog signal generated by the DAC shown in B is optically transmitted and sampled by an ADC (Analog-to-Digital Converter) on the RRH side (or antenna station side). Figure 1 The horizontal and vertical axes of the graph shown in C are Figure 1 A or Figure 1 The horizontal and vertical axes shown in B are the same. Figure 1 In the stage shown in C, due to the comprehensive frequency characteristics of the transmission system, the power level of the signal channel is Figure 1 B has a large deviation in stage. In addition, Figure 1 C also shows that noise is generated regardless of the frequency. Figure 1 C shows a signal channel having a low SNR, that is, poor quality, which may be caused by noise generated in the transmission system and the comprehensive frequency characteristics of the transmission system.

[0029] The optical transmission system of the disclosed technology improves the deviation of the signal channel level caused by the comprehensive frequency characteristics of the transmission system by means shown in the following embodiments. The details of the means adopted by the optical transmission system of the disclosed technology are clarified by the following description based on the drawings of each embodiment.

[0030] Implementation Method 1

[0031] Figure 2 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 2As 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 2 As shown, the transmitting side digital signal processing device 100 includes a correction processing unit 110, a multiplexing processing unit 120, a correction signal generating unit 130, and a data switching unit 140. The transmitting side of the optical transmission system can also be considered as an A-RoF optical subscriber line terminal device, for example.

[0032] <Correction Processing Unit 110 Constituting Transmitting-Side Digital Signal Processing Device 100>

[0033] The correction processing unit 110 constituting the transmitting-side digital signal processing device 100 is a component that corrects the amplitude of each input wireless signal sequence arranged in each IF channel. Figure 2 In the record, it is s 1 (t), s 2 (t), …, s n The arrows in (t) represent the signals that configure the input wireless signal train to each IF channel or the digital data streams for the signals. n is the number of digital data streams. It can also be said that n is the number of signal channels.

[0034] Although the signal processed by the transmitting-side digital signal processing device 100 is a digital signal, the input wireless signal string is recorded as s 1 (t), s 2 (t), …, s n (t). The signal processed by the correction processing unit 110 is recorded as a function of time t as if it were an analog signal. There is a reason for this. 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.

[0035] The processing performed by the correction processing unit 110 can be expressed by the following mathematical formula.

[0036]

[0037] Here, the bold letter u is the input wireless signal string input to the correction processing unit 110, specifically, s 1 (t), s 2 (t), …, s n (t) is the longitudinal quantity of the element. In addition, the bold y is the corrected signal string output by the correction processing unit 110. The bold W represents the weight matrix. The processing of the correction processing unit 110 shown in formula (1) is a processing that changes the ratio of input to output when observing the correction processing unit 110 as a reference, so it can be said to be a processing that changes the gain. The a as a component of the weight matrix (W)1 、a 2 , …, a n It is calculated by the weight correction value calculation unit 620 described later. 1 、a 2 , …, a n is a parameter, also s 1 (t), s 2 (t), …, s n (t) involves coefficients, and therefore, are sometimes referred to as "parameter coefficients". 1 、a 2 , …, a n The details of the calculation of ) will be clarified by the following description.

[0038] like Figure 1 As shown, the correction processing unit 110 in principle performs the following function: amplifying the gain of the signal channel with a low power level to match the power level. Therefore, a, which is the parameter coefficient shown in equation (1), 1 、a 2 , …, a n In principle, each is a real number greater than 1.

[0039] However, when the gain of the signal channel is excessively amplified, the signal level exceeds the upper limit assumed by the transmitting digital signal processor 100, that is, the upper limit of the DAC 200 located in the subsequent stage of the transmitting digital signal processor 100, and so-called saturation may occur.

[0040] The correction processing unit 110 constituting the transmitting-side digital signal processing device 100 can function as a gain balancer that dynamically increases / decreases the parameter coefficient (a 1 、a 2 , …, a n ) so that the signal level does not exceed the upper limit of DAC200. When the overall gain is reduced, the parameter coefficient (a 1 、a 2 , …, a n ) are sometimes real numbers less than 1.

[0041] The corrected signal string (bold character y) output by the correction processing unit 110 is sent to the multiplexing processing unit 120 .

[0042] <Multiplexing Processing Unit 120 Constituting Transmitting-Side Digital Signal Processing Device 100>

[0043] The multiplexing processing unit 120 constituting the digital signal processing device 100 on the transmitting side is a structural element for multiplexing the corrected signal string (y in bold) sent from the correction processing unit 110. Multiplexing is sometimes referred to as multiplexing processing, Multiplexing, or more simply as Muxing. The device that multiplexes (Muxing) to the 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 multiplexing processing unit 120 collects the digital data streams related to the corrected signal string (y in bold) and sends them to the optical receiving side (hereinafter simply referred to as the "receiving side") using a shared analog optical transmission path (AOTL: Analog Optical Transmission Line). The analog optical transmission path (AOTL) is composed of, for example, optical fibers.

[0044] The signal multiplexed by the multiplexing processing unit 120 is sent to the data switching unit 140 .

[0045] <Correction signal generating unit 130 constituting the transmitting-side digital signal processing device 100>

[0046] The correction signal generating unit 130 constituting the transmitting-side digital signal processing device 100 generates a for determining a component of the weight matrix (W). 1 、a 2 , …, a n The correction signal (S cal (t)) structural elements. Correction signal (S cal (t)) is designed to Figure 1 The frequency characteristic is flat in the use frequency band indicated by A.

[0047] The correction signal (S) generated by the correction signal generating unit 130 cal (t)) is sent to the data switching unit 140.

[0048] <Data Switching Unit 140 Constituting Transmitting-Side Digital Signal Processing Device 100>

[0049] The data switching unit 140 constituting the transmission-side digital signal processing device 100 is a structural element for switching the data to be used depending on whether the optical transmission system is in the operation mode or the calibration mode. Figure 2As shown, the data switching unit 140 has two input systems and one output system. One of the two input systems is an input system from the multiplexing processing unit 120, and the other is an input system from the correction signal generating unit 130. When the optical transmission system is in the operation mode, the data switching unit 140 outputs the signal from the multiplexing processing unit 120 to the DAC 200. When the optical transmission system is in the correction mode, the data switching unit 140 outputs the signal from the correction signal generating unit 130 to the DAC 200.

[0050] The timing for calibrating the optical transmission system, i.e., entering the calibration mode, includes the test run for starting the optical transmission system, the periodic inspection, the test run after replacing consumable parts, or the test run after repair work.

[0051] 《DAC200》

[0052] DAC200 is a component that converts a digital signal into an analog signal. As mentioned above, the DAC in the name of DAC200 is the first letter of Digital-to-Analog Converter. The signal converted into an analog signal by DAC200 is sent to the analog optical transmitter 300.

[0053] 《Analog Optical Transmitter 300》

[0054] 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 an optical intensity modulator that applies the principle of the Mach-Zehnder interferometer to the laser, or it can also be implemented by direct modulation of the laser.

[0055] 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).

[0056] Figure 3 1 is a block diagram showing the functional structure of the receiving side of the optical transmission system of Embodiment 1. Figure 3As 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 3 As shown, the receiving-side digital signal processing device 600 includes a digital separation processing unit 610 and a weight correction value calculation unit 620. The receiving side of the optical transmission system can also be considered as an optical line terminal device of A-RoF, for example.

[0057] 《Analog Optical Receiver 400》

[0058] 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.

[0059] 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.

[0060] The analog electrical signal output from the analog optical receiver 400 is sent to the ADC 500 .

[0061] 《ADC500》

[0062] ADC500 is a component that converts analog signals into digital signals. As mentioned above, the ADC in ADC500 stands for Analog-to-Digital Converter. The signal converted into a digital signal by ADC500 is sent to the receiving-side digital signal processing device 600.

[0063] 《Receiving-side digital signal processing device 600》

[0064] 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 digital separation processing 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.

[0065] <Digital separation processing unit 610 constituting the receiving-side digital signal processing device 600>

[0066] The digital separation processing unit 610 constituting the receiving-side digital signal processing device 600 is a structural element that separates the signal multiplexed (multiplexed) to the intermediate frequency (IF) into each signal channel again. The processing performed by the digital separation processing unit 610 is sometimes called demultiplexing, or more simply called demuxing. In particular, the demultiplexer related to the intermediate frequency (IF) is sometimes referred to as IF-DeMUX. In addition, the processing performed by the IF-DeMUX is sometimes referred to as IF-DeMUX processing.

[0067] The signal sent from the ADC 500 is separated into each signal channel through the demultiplexing process of the digital separation processing unit 610 . Figure 3 The description "(baseband conversion)" in hereinafter indicates the processing contents of the digital separation processing unit 610 such as separation into baseband signals.

[0068] Figure 4 1 is a block diagram showing a functional structure (one example) of the digital separation processing unit 610 constituting the optical transmission system of Embodiment 1. Figure 4 As shown in FIG. 1 , the digital separation processing unit 610 is a 1-input n-output structural element having n systems. The n systems in the digital separation processing unit 610 include a frequency shift processing unit 612, a digital filter 614, and a decimation processing unit 616. Figure 4 As shown, the functional blocks in the first system are represented as the frequency shift processing unit 612-1, the extraction processing unit 616-1 and the extraction processing unit 616-1. Thus, the functional blocks marked with "-1" after the reference number are functional blocks in the first system. Similarly, the functional blocks marked with "-2" after the reference number are functional blocks in the second system. In this specification, i is set as a variable taking a natural number from 1 to n, and by marking "-i" after the reference number, the functional block is represented as a general functional block of the i-th system.

[0069] 《Frequency shift processing unit 612-i in digital separation processing unit 610》

[0070] The frequency shift processing unit 612-i of the i-th system in the digital separation processing unit 610 processes the i-th signal channel. Specifically, the frequency shift processing unit 612-i shifts the frequency of the frequency band involved in the i-th signal channel to, for example, 0 [Hz] or other easily processable frequencies.

[0071] <<Digital filter 614-i in digital separation processing unit 610>>

[0072] The digital filter 614 - i of the i-th system in the digital separation processing unit 610 performs filtering processing to extract only the frequency band related to the i-th signal channel.

[0073] 《Extraction processing unit 616-i in digital separation processing unit 610》

[0074] The decimation processing unit 616-i of the i-th system in the digital separation processing unit 610 performs decimation processing on the frequency band related to the extracted i-th signal channel. Decimation is a process of digitally sampling and thinning out the output after the filtering process.

[0075] Figure 4 The functional configuration of the digital separation processing unit 610 shown is only an example, and any other unit may be used as long as it can realize IF-DeMUX processing, that is, channel separation processing.

[0076] like Figure 4 As shown, the signal obtained by IF-DeMUX processing is called the baseband signal, denoted by S OUT_1 (t), S OUT_2 (t),…,S OUT_n (t).

[0077] in addition, Figure 4 It is shown that m baseband signals (S) are output by parallel processing. OUT_1 (t), S OUT_2 (t),…,S OUT_n (t)) structure, but the disclosed technology is not limited to this. The digital separation processing unit 610 can also implement signal processing in series, that is, in multiple stages, instead of in parallel. In addition, the digital separation processing unit 610 can also adopt a competition structure to select frequency bands and rates in multiple stages.

[0078] Depending on whether the optical transmission system is in the operation mode or the calibration mode, the destination to which the output signal of the digital separation processing unit 610 is sent and the purpose of the output signal differ.

[0079] When the optical transmission system is in the operating mode, that is, when the data switching unit 140 on the transmission side selects the signal from the multiplexing processing unit 120 , the output signal of the digital separation processing unit 610 is output to the outside.

[0080] When the optical transmission system is in the calibration mode, that is, the data switching unit 140 on the transmission side selects the calibration signal (S) from the calibration signal generating unit 130. cal (t)), the output signal of the digital separation processing unit 610 is sent to the weight correction value calculation unit 620.

[0081] <Weight correction value calculation unit 620 constituting the receiving-side digital signal processing device 600>

[0082] The weight correction value calculation unit 620 constituting the receiving-side digital signal processing device 600 is a structural element that determines the weight matrix (W) used by the correction processing unit 110 on the transmitting side. The weight correction value calculation unit 620 is a component that selects the correction signal (S) from the correction signal generation unit 130 only when the optical transmission system is in the correction mode, that is, only when the data switching unit 140 on the transmitting side selects the correction signal (S) from the correction signal generation unit 130. cal Structural element that performs an action at (t)).

[0083] The first processing performed by the weight correction value calculation unit 620 is to calculate the baseband signal (S OUT_1 (t), S OUT_2 (t),…,S OUT_n (t)) is subjected to Fourier transform processing.

[0084] Figure 5 It is a curve graph obtained by Fourier transforming the baseband signal. Figure 5 In the graph shown in FIG. 1 , the horizontal axis shows the angular frequency (ω), and the vertical axis shows the spectrum (complex number, S i (jw)) related to the size (the distance from the origin in the complex plane, |S i (jw)|). Figure 5 k=1, 2, ..., m appearing in the graph shown may be, for example, an interval of angular frequency (ω) or an identification number marked on a spectrum peak.

[0085] Figure 5 The shaded rectangles in the graph shown correspond to Figure 1 One of the five rectangles #1 to #5 (i=1, 2, ..., 5) shown. Figure 5 The Fourier transform result related to the i-th baseband signal is shown, but the weight correction value calculation unit 620 performs Fourier transform on all baseband signals (i=1, 2, ..., n). In the Fourier transform performed by the weight correction value calculation unit 620, the number of Fourier transform points (the number of sampling points or the number of FFT points) can be appropriately determined according to the specifications of the optical transmission system.

[0086] The second process performed by the weight correction value calculation unit 620 is as follows: based on the Fourier transform result, the baseband signal (S OUT_1 (t), S OUT_2 (t),…,S OUT_n (t)) Calculate a representative value representing the power level.

[0087] The representative value indicating the power level may be, for example, an average value given by the following equation.

[0088]

[0089] The baseband signal (S OUT_1 (t), S OUT_2 (t),…,S OUT_n (t)), in addition to the average value, the representative value representing the power level can also be the most frequent value or the central value. In addition, formula (2) gives the representative value representing the power level by arithmetic mean, but other average values ​​such as geometric mean and harmonic mean can also be used.

[0090] The third process performed by the weight correction value calculation unit 620 is to calculate the baseband signal (S OUT_1 (t), S OUT_2 (t),…,S OUT_n (t)) The representative value calculated determines the weight matrix (W) used by the correction processing unit 110 on the transmission side.

[0091] Specifically, as shown in formula (1), the weight matrix (W) can be a diagonal matrix. In addition, the diagonal components of the weight matrix (W), i.e., the parameter coefficients a 1 、a 2 , …, a n For example, it can be calculated as follows.

[0092]

[0093] As shown in formula (3), it can be said that the diagonal components of the weight matrix (W), that is, the parameter coefficients a 1 、a 2 , …, a n The baseband signal (S OUT_1 (t), S OUT_2 (t),…,S OUT_n The representative value calculated by (t)) is normalized by the maximum value (M) of the representative value and then the inverse thereof is taken. The normalization by the maximum value (M) of the representative value is intended to prevent the above-mentioned saturation from occurring.

[0094] The weight matrix (W) or parameter coefficient (a) calculated by the weight correction value calculation unit 620 1 、a 2 , …, a n ) is sent to the correction processing unit 110 on the sending side. Figure 2 and Figure 3 , the output of the weight correction value calculation unit 620 is sent to the correction processing unit 110 via "data communication", but the disclosed technology is not limited to this. The weight matrix (W) or parameter coefficient (a) calculated by the weight correction value calculation unit 620 1 、a 2 , …, a n) may also be transmitted by a person, such as a user of the optical transmission system, so that the correction processing unit 110 on the sending side can use it.

[0095] The optical transmission system of the disclosed technology has a technical feature of monitoring the deviation of the signal channel level in the frequency domain through the first to third processes implemented by the weight correction value calculation unit 620. Comparing the signal channel levels in the frequency domain means comparing the energy amount of each signal channel. The first to third processes implemented by the weight correction value calculation unit 620 are referred to as "FFT monitoring" in this specification.

[0096] As described above, the optical transmission system according to Embodiment 1 has the above-mentioned configuration, and therefore, it is possible to improve the deviation of the signal channel level caused by the comprehensive frequency characteristics of the transmission system.

[0097] Implementation Method 2

[0098] The optical transmission system of Embodiment 2 is a modified example of the optical transmission system of the present disclosure technology. Specifically, the optical transmission system of Embodiment 2 shows that the present disclosure technology can also be realized by software.

[0099] In Embodiment 2, the same reference numerals as those used in Embodiment 1 are used except for cases where they are clearly stated. In Embodiment 2, descriptions overlapping with those in Embodiment 1 are omitted as appropriate.

[0100] Figure 6 It is a hardware configuration diagram of the transmitting-side digital signal processing device 100 according to the second embodiment. Figure 6 As shown in the above paragraph Figure 6 A shows a case where the functions of the optical transmission system (transmission side) of the disclosed technology are realized by hardware. Figure 6 As shown in the following paragraph Figure 6 B shows a case where the functions of the optical transmission system (transmission side) of the disclosed technology are realized by software.

[0101] exist Figure 6 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 .

[0102] exist Figure 6 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 .

[0103] The functions of the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130 and the data switching unit 140 in the transmitting side digital signal processing device 100 are implemented by a processing circuit. The processing circuit may be dedicated hardware (see Figure 6 A), 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 Figure 6 B) Either one is fine.

[0104] like Figure 6 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 correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140 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.

[0105] like Figure 6 As shown in FIG. 1B, when the processing circuit is a CPU, the functions of the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140 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 transmission side memory 724. The processing circuit reads out and executes the program stored in the transmission side memory 724, thereby realizing the functions of each unit. That is, the transmission side digital signal processing device 100 has a transmission side memory 724, which is used to store programs that, when executed by the processing circuit, result in the execution of the processing contents performed by the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140 described in Embodiment 1. In addition, it can also be said that these programs cause the computer to execute the steps and methods of the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140. Here, the transmission side memory 724 may be, for example, a non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, EEPROM, etc. The transmission side memory 724 may 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 may also be in the form of a HDD or SSD.

[0106] The transmission side memory 724 may also store the correction signal (S cal(t)) the information required.

[0107] 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 .

[0108] In addition, each function of the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140 may be partially implemented by dedicated hardware and the other part may be implemented by software or firmware. In this way, the processing circuit can implement each function of the correction processing unit 110, the multiplexing processing unit 120, the correction signal generating unit 130, and the data switching unit 140 by hardware, software, firmware, or a combination thereof.

[0109] Figure 7 This is a hardware configuration diagram of a receiving-side digital signal processing device 600 according to the second embodiment. Figure 7 As shown in the above paragraph Figure 7 A shows a case where the functions of the optical transmission system (receiving side) of the disclosed technology are realized by hardware. Figure 7 As shown in the following paragraph Figure 7 B shows a case where the functions of the optical transmission system (receiving side) of the disclosed technology are realized by software.

[0110] exist Figure 7 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 .

[0111] exist Figure 7 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 .

[0112] The functions of the digital separation processing unit 610 and the weight correction value calculation unit 620 in the receiving side digital signal processing device 600 are implemented by a processing circuit. The processing circuit may be dedicated hardware (see Figure 7 A), or a CPU that executes a program stored in a memory (see Figure 7 B) Either one is fine.

[0113] like Figure 7As 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 can 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 digital separation processing unit 610 and the weight correction value calculation unit 620 can be implemented by multiple independent receiving side processing circuits 820, or the functions of each unit can be uniformly implemented by one receiving side processing circuit 820.

[0114] like Figure 7 As shown in FIG. 1B, when the processing circuit is a CPU, the functions of the digital separation processing unit 610 and the weight correction value calculation unit 620 can be implemented by software, firmware, or a combination of software and firmware. Software and firmware are described as programs and are stored in the receiving side memory 824. The processing circuit reads out and executes the program stored in the receiving side memory 824, thereby realizing the functions of each unit. That is, the receiving side digital signal processing device 600 has a receiving side memory 824, which is used to store a program that, when executed by the processing circuit, results in the execution of the processing content performed by the digital separation processing unit 610 and the weight correction value calculation unit 620 described in Implementation Example 1. In addition, it can also be said that these programs cause the computer to execute the steps and methods of the digital separation processing unit 610 and the weight correction value calculation unit 620. Here, the receiving side memory 824 can also be 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 may be in the form of a HDD or a SSD.

[0115] The receiving-side memory 824 may store the weight matrix (W) calculated by the weight correction value calculation unit 620 together with information such as the calculated date and time as history.

[0116] 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 .

[0117] In addition, the functions of the digital separation processing unit 610 and the weight correction value calculation unit 620 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 digital separation processing unit 610 and the weight correction value calculation unit 620 by hardware, software, firmware, or a combination thereof.

[0118] As described above, the optical transmission system of embodiment 2 has the above-mentioned structure and can therefore be implemented by hardware, software, firmware or a combination thereof, thereby achieving the effect of improving the deviation of the signal channel level caused by the comprehensive frequency characteristics of the transmission system.

[0119] Implementation 3

[0120] The optical transmission system of Embodiment 3 is a modified example of the optical transmission system of the presently disclosed technology.

[0121] In Embodiment 3, the same reference numerals as those used in the above embodiments are used except for cases where they are clearly stated. In Embodiment 3, descriptions overlapping with those in the above embodiments are appropriately omitted.

[0122] As described above, the disclosed technology sets the deviation of the signal channel level that may occur when the signal channels are increased by using the Nyquist band of the ADC and DAC as much as possible as a problem to be solved. In order to solve this problem, for example, the following method can be considered: compressing the information on the transmitting side and restoring it on the receiving side, thereby suppressing the number of signal channels. However, the disclosed technology does not change the premise of using the Nyquist band of the ADC and DAC as much as possible to increase the signal channels, and solves the problem through pre-emphasis.

[0123] In particular, deviations in the signal channel levels that may occur when increasing the number of signal channels by using the Nyquist bands of the ADC and DAC as much as possible appear as attenuation on the high-frequency side.

[0124] In Embodiment 1, FFT monitoring is performed on all signal channels, but the disclosed technology is not limited thereto. The optical transmission system of the disclosed technology may be configured to perform FFT monitoring only on specific signal channels, for example, only on a few high-frequency side signal channels.

[0125] The correction processing unit 110 constituting the transmitting-side digital signal processing device 100 of the third embodiment may perform correction processing only on specific signal channels, for example, only on a few high-frequency-side signal channels. 1 、a 2 , …, a n ), all parameter coefficients corresponding to signal channels other than a specific signal channel are substituted with a value of 1.

[0126] The correction signal generating unit 130 constituting the transmitting-side digital signal processing device 100 of the third embodiment may generate a correction signal for only a specific signal channel, for example, only a few high-frequency-side signal channels.

[0127] The weight correction value calculation unit 620 of the receiving-side digital signal processing device 600 of Embodiment 3 only needs to calculate the weight correction value based on the specific signal channel amount included in the correction signal sent from the transmitting side. 1 、a 2 , …, a n ), all parameter coefficients corresponding to signal channels other than the specific signal channel are substituted with the value 1.

[0128] As described above, the optical transmission system according to the third embodiment has the above-mentioned configuration, and therefore can perform pre-emphasis on a specific signal channel where attenuation occurs, thereby improving the variation in the signal channel level.

[0129] Implementation 4

[0130] The optical transmission system of Embodiment 4 is a modified example of the optical transmission system of the presently disclosed technology.

[0131] In Embodiment 4, the same reference numerals as those used in the above embodiments are used except for cases where they are clearly stated. In Embodiment 4, descriptions overlapping with those in the above embodiments are appropriately omitted.

[0132] As described in Embodiment 3, the deviation of the signal channel level is particularly expressed as attenuation on the high frequency side. Moreover, the characteristics of the high frequency attenuation can be approximated by a simple mathematical model. Specifically, a polynomial can be considered as the mathematical model that approximates the characteristics of the high frequency attenuation.

[0133] The disclosed technology is not limited to this, but for simplicity, the case where the high frequency attenuation characteristics are linearly approximated is considered. In the case of linear approximation, the correction signal generation unit 130 of the transmitting side digital signal processing device 100 constituting the fourth embodiment only needs to generate the correction signal for at least two signal channels among the signal channels of the high frequency attenuation.

[0134] First, the weight correction value calculation unit 620 of the receiving-side digital signal processing device 600 constituting the fourth embodiment calculates the weight correction value only based on the specific signal channel amount included in the correction signal sent from the transmitting side, that is, the weight correction value is calculated only based on the amount of at least two signal channels. Second, the weight correction value calculation unit 620 sets the characteristics of high-frequency attenuation to be linearly approximated, that is, interpolation or extrapolation is performed to obtain the weight correction value related to the remaining signal channels of high-frequency attenuation.

[0135] As described above, the optical transmission system of Embodiment 4 has the above-mentioned structure, and therefore can mathematically model the characteristics of high-frequency attenuation, perform pre-emphasis on a specific signal channel where attenuation occurs, and improve the deviation of the signal channel level.

[0136] Industrial Applicability

[0137] 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.

[0138] Description of symbols

[0139] 100: a digital signal processing device on the transmitting side; 110: a correction processing unit; 120: a multiplexing processing unit; 130: a correction signal generating unit; 140: a data switching 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 digital separation processing unit; 620: a weight correction value calculation unit; 710: an input interface on the transmitting side; 720: a processing circuit on the transmitting side; 722: a processor on the transmitting side; 724: a memory on the transmitting side; 730: an output interface on the transmitting side; 810: an input interface on the receiving side; 820: a processing circuit on the receiving side; 822: a processor on the receiving side; 824: a memory on the receiving side; 830: an output interface on the receiving side.

Claims

1. An IFoF optical transmission system, the IFoF optical transmission system comprising: A digital signal processing device on the transmitting side, comprising a correction processing unit and a correction signal generating unit; and The receiving-side digital signal processing device comprises a digital separation processing unit and a weight correction value calculation unit. The correction signal generating unit generates a correction signal, The digital separation processing unit performs demultiplexing processing to separate the correction signal into a plurality of baseband signals. The weight correction value calculation unit calculates parameter coefficients according to the baseband signal. The correction processing unit corrects the amplitude of each of the plurality of input wireless signal sequences using the parameter coefficient.

2. The IFoF optical transmission system according to claim 1, wherein: The parameter coefficient is obtained by normalizing the representative value calculated for the baseband signal with the maximum value of the representative value and then taking the inverse thereof.

3. The IFoF optical transmission system according to claim 1, wherein: The 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.

4. The IFoF optical transmission system according to claim 1, wherein: The 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.

5. The IFoF optical transmission system according to claim 1, wherein: The correction signal is a signal related to the signal channel on the high frequency side.

6. The IFoF optical transmission system according to claim 1, wherein: The receiving-side digital signal processing device has a mathematical model that approximates the characteristics of high-frequency attenuation. The receiving-side digital signal processing device obtains a weight correction value related to a signal channel with high-frequency attenuation based on the mathematical model.

Images