Optical transmission system, transmitter, and control method

Abstract

An aspect of the present invention provides an optical transmission system including a transmission device connected to a transmission line including M spatial channels and a reception device that receives a signal transmitted from the transmission device via the transmission line. The transmission device includes: a separating unit that separates a transmission bit sequence to be transmitted to the transmission line into a bit sequence used for a base signal and a bit sequence used for spatial channel information; a generation unit that generates N (M > N) signals from the bit sequence separated by the separating unit and used for the base signal; and a selection unit that, on the basis of the bit sequence separated by the separating unit and used for the spatial channel information, selects N spatial channels for transmitting the N signals generated by the generation unit from M spatial channels.

Description

[Technical Field]

[0001] The present invention relates to techniques for an optical transmission system, a transmitting device, and a control method. [Background technology]

[0002] With the development of information technology, the demand for communications continues to expand. Optical fiber communications is often used for fixed lines, which require particularly high capacity, due to its wide available frequency band and low signal attenuation. To continue supporting the expanding demand for communications, continuous capacity increases are required for optical fiber communications.

[0003] Currently, the optical fiber mainly used for high-capacity communications is called single-mode fiber, which has one spatial propagation mode within the optical fiber. The capacity of this single-mode fiber is said to be approaching a theoretical limit called the nonlinear Shannon limit. Therefore, a technology called spatial multiplexing transmission, which can increase capacity by using optical fiber with multiple spatial channels, has attracted attention and is being actively researched.

[0004] In spatial multiplexing transmission, by modulating each spatial channel with an independent signal, it is possible to achieve a capacity per optical fiber that exceeds the nonlinear Shannon limit of single-mode fiber.

[0005] To realize multiple spatial propagation modes within a single optical fiber, multicore fibers, multimode fibers, and multicore-multimode fibers have been proposed. The realization of multiple spatial propagation modes has been demonstrated in these optical fibers (see, for example, Non-Patent Document 1).

[0006] Multicore fibers have multiple cores (the parts of the optical fiber through which light propagates) within a single optical fiber. Multimode fibers realize multiple propagation modes within a single core. Multicore multimode fibers are a combination of multicore fibers and multimode fibers. In the following explanation, the above multicore fibers, multimode fibers, and multicore multimode fibers will be collectively referred to as spatial multiplexing fibers.

[0007] In optical transmission using multimode fiber or multicore fiber with strong coupling between cores (coupled-core fiber), signal crosstalk occurs between modes or cores. When this crosstalk occurs, it is possible to separate and restore the signals from each channel by using digital signal processing based on the MIMO (multiple-input and multiple-output) method using adaptive filter technology.

[0008] Typically, independent signals are sent to all propagation channels of each optical fiber (modes in the case of multimode fiber, or cores in the case of coupled-core fiber), and MIMO digital signal processing is performed on the receiving side using signals from all channels (Full MIMO).

[0009] In spatial multiplexing transmission, particularly when the transmission distance is long, such as across the ocean, noise from amplifier repeaters and signal distortion due to nonlinear optical effects in optical fibers can have a significant impact on transmission, making it possible for signals to be received in full MIMO (see, for example, Non-Patent Document 2).

[0010] When signal reception becomes impossible, there are two main ways to deal with this. One is to use a more powerful error-correcting code. The other is to use diversity reception, which transmits the same signal on multiple channels and combines them at the receiving end.

[0011] The method using correction codes increases the coding rate, making it possible to correct errors even if the signal error rate increases due to signal distortion. The method using diversity reception effectively increases the signal strength, thereby reducing the signal error rate. These two methods are techniques used in low SNR (signal to noise ratio) environments. [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] Mizuno, T., Takara, H., Shibahara, K., Sano, A., & Miyamoto, Y. (2016). Dense space division multiplexed transmission over multicore and multimode fiber for long-haul transport systems. Journal of Lightwave Technology, 34(6), 1484-1493. [Non-patent document 2] Shibahara, K., Mizuno, T., Ono, H., Nakajima, K., & Miyamoto, Y. (2020, March). Long-haul DMD-unmanaged 6-mode-multiplexed transmission employing cyclic mode-group permutation. In Optical Fiber Communication Conference (pp. Th3H-3). Optical Society of America. Summary of the Invention [Problem to be solved by the invention]

[0013] The method using correction codes requires a dedicated circuit design that corresponds to the correction codes when manufacturing the integrated circuits used for communication. Also, the method using diversity reception reduces the amount of information that can be transmitted in inverse proportion to the number of signals transmitted together.

[0014] As such, conventional technologies for dealing with low SNR environments have had issues such as the need for dedicated circuit design and a reduction in the amount of information that can be transmitted.

[0015] In view of the above circumstances, an object of the present invention is to provide a technique that can realize suitable optical transmission in a low SNR environment. [Means for solving the problem]

[0016] One aspect of the present invention is an optical transmission system including a transmitting device connected to a transmission path having M spatial channels, and a receiving device receiving a signal transmitted from the transmitting device via the transmission path, wherein the transmitting device has a distribution unit that distributes a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information, a generation unit that generates N (M>N) signals from the bit sequence serving as the basic signal distributed by the distribution unit, and a selection unit that selects, from the M spatial channels, N spatial channels that will transmit the N signals generated by the generation unit, based on the bit sequence serving as the spatial channel information distributed by the distribution unit.

[0017] One aspect of the present invention is a transmitting device connected to a transmission path having M spatial channels, the transmitting device having: a distributing unit that distributes a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information; a generating unit that generates N (M>N) signals from the bit sequence serving as the basic signal distributed by the distributing unit; and a selecting unit that selects, from the M spatial channels, N spatial channels that will transmit the N signals generated by the generating unit, based on the bit sequence serving as the spatial channel information distributed by the distributing unit.

[0018] One aspect of the present invention is a control method for a transmitting device connected to a transmission path having M spatial channels, the control method comprising: an allocation step of allocating a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information; a generation step of generating N (M>N) signals from the bit sequence serving as the basic signal allocated in the allocation step; and a selection step of selecting, from the M spatial channels, N spatial channels for transmitting the N signals generated in the generation step, based on the bit sequence serving as the spatial channel information allocated in the allocation step. [Effects of the Invention]

[0019] The present invention makes it possible to realize optical transmission suitable for a low SNR environment. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a block diagram showing a configuration of an optical transmission system. [Figure 2] FIG. 10 is a diagram illustrating a configuration example when N=1 and M=2. [Figure 3] 10 is a diagram illustrating an example of a configuration in which a fundamental signal generating unit outputs an electrical signal to a selecting unit. FIG. [Figure 4] FIG. 10 is a diagram illustrating an example of a configuration using a DSP unit. [Figure 5]10 is a diagram illustrating a configuration example in which a fundamental signal generating unit modulates an electrical signal into an optical signal. FIG. [Figure 6] 1 is a graph showing an example of evaluation of GMI. [Figure 7] FIG. 10 is a block diagram showing the configuration of Modification 1. [Figure 8] FIG. 10 is a block diagram showing the configuration of Modification 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. 1 is a block diagram showing the configuration of an optical transmission system 1 according to an embodiment. The optical transmission system 1 includes a transmitting device 100, a transmission path 200, and a receiving device 300. The transmitting device 100 and the receiving device 300 are connected via the transmission path 200. The transmission path 200 is a spatial multiplexing fiber (a multicore fiber, a multimode fiber, or a multicore-multimode fiber). The transmission path 200 has M spatial channels (M is an integer equal to or greater than 2).

[0022] A transmission bit sequence to be transmitted to the receiving device 300 is input to the transmitting device 100. The transmitting device 100 is composed of a distribution unit 110, a selection signal generation unit 120, a basic signal generation unit 130, and a selection unit 140. The distribution unit 110 distributes the transmission bit sequence to be transmitted to the transmission path 200 into a bit sequence to be used as a basic signal and a bit sequence to be used as spatial channel information. In the following description, the bit sequence to be used as a basic signal may be referred to as a basic bit sequence, and the bit sequence to be used as spatial channel information may be referred to as a channel bit sequence.

[0023] The allocating unit 110 outputs the channel bit sequence to the selection signal generating unit 120. The allocating unit 110 outputs the basic bit sequence to the basic signal generating unit 130. The selection signal generating unit 120 generates the channel bit sequence as a selection signal that drives the selecting unit 140 and outputs it to the selecting unit 140. The basic signal generating unit 130 generates N (M>N) independent electrical or optical signals from the basic bit sequence and outputs them to the selecting unit 140. Note that the signal generating method used by the basic signal generating unit 130 is based on conventional techniques such as mapping to symbols such as QAM, inserting a training signal, and waveform shaping. Note also that the basic signal generating unit 130 is an example of a generating unit.

[0024] Based on the channel bit sequence, the selection unit 140 selects, from the M spatial channels, N spatial channels for transmitting the N signals generated by the basic signal generation unit 130. The basic signals are transmitted to the receiving device 300 via the selected spatial channels in the transmission path 200. In the following description, the "nth channel" refers to the channel corresponding to the order counted from the top of the M channels shown in FIG. 1. For example, the top channel is the first channel, and the bottom channel is the Mth channel.

[0025] Before describing the processing of each unit of the transmitting device 100 described above, it will be explained that information can be transmitted from the transmitting device 100 to the receiving device using a combination of channels used for transmission. First, when a signal is transmitted using N channels out of M channels, there are M! / ((MN)!×N!) (expressed as =C(M, N)) combinations of channels to be used for transmission.

[0026] Using C(M, N), it is possible to express a bit string of up to [log(C(M, N))] (= k). Here, [a] indicates the largest integer less than a. The logarithm is base 2. In the following explanation, the logarithm is base 2 unless otherwise specified.

[0027] A part of C(M, N) can be in one-to-one correspondence with a value that can be expressed by k bits. Therefore, by associating a combination of channels to be used with each k-bit value between the transmitting device 100 and the receiving device 300, the receiving device 300 can obtain k-bit information from the combination of channels that received the signal. In other words, a k-bit signal can be transmitted to the receiving device 300 using the combination of channels to be used, without actually transmitting the k bits as a signal.

[0028] For example, there are three combinations of using two channels out of three, since C(3, 2) is 3. Specifically, there are three combinations: using the first and second channels, using the first and third channels, and using the second and third channels.

[0029] Furthermore, in the case of C(3, 2), k=1. For example, the combination of using the first and second channels is associated with "0," and the combination of using the first and third channels is associated with "1." By sharing this correspondence in advance between transmitting device 100 and receiving device 300, it is possible to convey "0" or "1" from transmitting device 100 to receiving device using the combination of channels used for transmission.

[0030] Based on this, a specific example will be described using the above-mentioned case where M=3 and N=2. Suppose the transmission bit string is 10111. In this case, the allocating unit 110 allocates the most significant 4 bits "1011" of 10111 as the basic bit string and the least significant bit "1" as the channel bit string.

[0031] The four most significant bits "1011" are output to the basic signal generating section 130. The least significant bit "1" is output to the selection signal generating section 120.

[0032] The basic signal generating unit 130 generates a signal indicating two (=N) bit strings, the most significant two bits "10" and the least significant two bits "11" of the four bits "1011." In addition, since the channel bit string is "1," which is a combination that uses the first and third channels, the selection signal generating unit 120 outputs a drive signal that uses the first and third channels to the selecting unit 140.

[0033] The selector 140 transmits a signal indicating the most significant two bits "10" of the four bits "1011" on the first channel, and transmits a signal indicating the least significant two bits "11" on the third channel.

[0034] Receiving device 300 receives "10" on the first channel and "11" on the third channel. As a result, receiving device 300 acquires a bit string "1011". Furthermore, since the first channel and the third channel have been used, receiving device 300 acquires "1". As a result, receiving device 300 acquires a bit string "10111".

[0035] In this way, the signal actually transmitted is "1011," and the least significant bit is obtained using channel combination information shared between the transmitting device 100 and the receiving device 300. In contrast, conventional diversity reception does not use channel combination information, and therefore, if the noise level after reception is the same, only the bit string "1011" can be transmitted. Therefore, according to this embodiment, if the basic signal can be received with the same error rate, it can be seen that more information can be transmitted compared to conventional diversity reception.

[0036] For example, when the transmission bit string is A-valued, a maximum of N × logA + [log(C(M, N))] bits can be transmitted per symbol, which increases the transmission capacity compared to logA bits when there is only one spatial channel.

[0037] It should be noted that the allocation method of the allocation unit 110 is preferably such that the number of bits of the channel bit string determined by the allocation is as close to [log(C(M, N))] as possible. For example, possible allocation methods may be listed, the number of bits of the channel bit string resulting from each allocation method may be calculated, and the obtained value may be selected as close to [log(C(M, N))].

[0038] For example, let's say we have a multimode fiber with M=6 and N=2, with each mode represented as mode 1, 2, ..., 6. Consider an allocation method in which fundamental signal 1 is selected from the four modes 1 to 4, and fundamental signal 2 is selected from the two modes 5-6. In this case, the number of bits in the resulting channel bit string is log4 + log2 = 3. On the other hand, since [log(C(6, 2))] = 3, we can see that this is the optimal allocation method, and so we can see that this allocation method should be adopted.

[0039] Fig. 2 is a diagram showing a configuration example when N=1 and M=2. Receiving device 300 is omitted in Fig. 2. Since [log(C(2, 1))]=1, the number of bits in the channel bit string is 1. Then, for example, the combination using the first channel is made to correspond to "0", and the combination using the second channel is made to correspond to "1".

[0040] By sharing this correspondence between the transmitting device 100 and the receiving device 300 in advance, the receiving device 300 can obtain the least significant bit of the received signal according to the channel used. For example, as shown in Fig. 2, when the transmission bit string is "010" and the transmitting device 100 transmits a signal "01" from the first channel, the receiving device 300 obtains "010". On the other hand, when the transmitting device 100 transmits a signal "01" from the second channel, the receiving device 300 obtains "011".

[0041] Next, a description will be given of a configuration example in which the basic signal generating section 130 outputs an electrical signal to the selecting section 140. Fig. 3 is a diagram showing a configuration example in which the basic signal generating section 130 outputs an electrical signal to the selecting section 140. Explanations of the symbols already mentioned in Fig. 3 will be omitted.

[0042] The configuration example shown in Fig. 3 is a configuration in which processing is performed in the electrical domain using a dedicated electronic circuit (electrical signal switch) before the signal is input to the optical modulator. The basic signal generation unit 130 includes a digital signal processing unit 131. The selection unit 140 is an electrical signal switch. Furthermore, light sources 401 and 402 and optical modulators 411 and 412 are provided to generate optical signals. The light source 401 is a light source for modulation by the optical modulator 411. The light source 402 is a light source for modulation by the optical modulator 412.

[0043] The electrical signal generated by the digital signal processing unit 131 is output to the first or second channel by the selection unit 140. In Fig. 3, it is output to the first channel. The electrical signal output to the channel selected by the selection unit 140 is modulated into an optical signal by the optical modulator 411 or the optical modulator 412 and output to the transmission path 200. In Fig. 3, it is modulated into an optical signal by the optical modulator 411 and the optical signal is transmitted on the first channel.

[0044] Fig. 4 is a diagram showing an example of a configuration using a digital signal processing (DSP) unit. Explanations of the reference symbols already mentioned in Fig. 4 will be omitted. In the configuration shown in Fig. 4, a digital signal processing unit 150 performs the functions of the selection signal generation unit 120, the basic signal generation unit 130, and the selection unit 140.

[0045] As shown in the configuration in Fig. 4, instead of using a dedicated electronic-optical circuit, optical transmitters are prepared in the same number as the spatial channels to be used. Then, the digital signal processing unit may virtually switch in the digital signal processing during encoding, generating signals such that the optical power of unused channels is 0.

[0046] Next, a description will be given of a configuration example in which the fundamental signal generating unit 130 modulates an electrical signal into an optical signal and outputs the signal to the selecting unit 140. Fig. 5 is a diagram showing a configuration example in which the fundamental signal generating unit 130 modulates an electrical signal into an optical signal. Explanation of the symbols already mentioned in Fig. 5 will be omitted.

[0047] 5, the basic signal generation unit 130 includes a digital signal processing unit 131, a light source 132, and an optical modulator 133. The selection unit 140 is an optical circuit (optical switch). The electrical signal generated by the digital signal processing unit 131 is modulated into an optical signal by the optical modulator 133 and output to the selection unit 140. The selection unit 140 outputs the input optical signal to the first or second channel. In FIG. 5, the signal is output to the first channel. The signal output by the selection unit 140 is output to the transmission path 200.

[0048] 1 to 5, the transmission path 200 may include an amplifier repeater configured with a fiber optical amplifier, a ROADM (Reconfigurable optical add / drop multiplexer), etc. Furthermore, the receiving device 300 may use maximum likelihood estimation or the like as a demodulation method.

[0049] According to the present embodiment described above, the signal power per channel can be increased compared to Full MIMO. Generally, in long-distance optical transmission, there exists a maximum input power beyond which increasing the optical power would conversely reduce the transmittable information capacity due to noise caused by nonlinear optical effects in the transmission line.

[0050] In this embodiment, in which only N of M spatial channels are used on the transmitting side, the power per channel decreases, particularly in multimode fibers or coupled-core fibers where crosstalk between spatial channels is significant. As a result, when considering inputting power up to the maximum input power of the transmission path, this embodiment can ideally increase the signal power per channel by M / N times compared to Full MIMO. This is the same signal power as diversity transmission, which transmits the same signal using M / N channels.

[0051] Furthermore, according to this embodiment, it is possible to reduce inter-channel interference due to non-orthogonality between channels. Specifically, when the transmission signal of the i-th spatial channel is denoted by x i , the received signal of the i-th spatial channel is expressed as y i (defined in the frequency domain).

[0052] The transmitted signal and the received signal are respectively represented by vectors as follows: x = [x1, x2, …, x M ] T y=[y1, y2, …, y M ] T

[0053] The channel transfer function is defined as the matrix H below. H=[h1h2…h M ]

[0054] If the noise generated during transmission is n, the relationship between these can be expressed by the following equation. y=Hx+n

[0055] The receiver 300 calculates the appropriate filter matrix W=[w1 w2 ... w M ] is estimated and W H The transmitted signal is restored by calculating y. H is the adjoint matrix of W. For example, in the MMSE (minimum mean square error) filter often used in spatial multiplexing optical transmission, the estimated transmitted signal of the i-th channel (x i)^ is given by (1) below.

number

[0056] The second term on the right side of the above equation (1) represents the interference from other channel signals. In general spatial multiplexing transmission, there are differences in loss between spatial channels and in gain due to repeater amplification. Therefore, the orthogonality between each channel is lost, and (w j h j )≠0, which causes inter-channel interference and reduces transmission capacity. For more information, please refer to the following literature.

[0057] Shibahara, K., Takayuki M., and Yutaka M. (2020). Long-Haul Mode Multiplexing Transmission Enhanced by Interference Cancellation Techniques Based on Fast MIMO Affine Projection."Journal of Lightwave Technology 38(18), 4969-4977.

[0058] As mentioned above, in general, (w j h j )≠0, but in this embodiment, there are unused channels. In unused channels, x j = 0. Therefore, no inter-channel interference occurs due to unused channels, and it is possible to reduce the influence of inter-channel interference.

[0059] As described above, according to this embodiment, when the SNR is low and Full MIMO demodulation is impossible, but the SNR is high enough to demodulate the channel selection signal, the amount of transmittable information can be increased by [log(C(M, N))] compared to diversity reception using the same number of signals, and therefore optical transmission suitable for a low SNR environment can be realized.

[0060] Fig. 6 is a graph showing an evaluation example of GMI (Generalized Mutual Information). In the graph shown in Fig. 6, the horizontal axis represents SNR and the vertical axis represents GMI. The graph shown in Fig. 6 is a graph in which GMI was evaluated by performing a Monte Carlo simulation using maximum likelihood estimation in the case of a six-mode fiber.

[0061] Graph A shows the GMI of a configuration in which 6x6 MIMO is applied to a 6-mode fiber. Dashed line a shows the spectral efficiency of 6x6 MIMO when a code rate of 0.826 is assumed. Graph B shows the GMI of a configuration in which this embodiment is applied to a 6-mode fiber. Dashed line b shows the spectral efficiency of this embodiment when applied to a 6-mode fiber when a code rate of 0.826 is assumed. Graph C shows the GMI of a configuration in which 6x3 MIMO is applied to a 6-mode fiber. Dashed line c shows the spectral efficiency of 6x3 MIMO when a code rate of 0.826 is assumed. Graph D shows the GMI of a configuration in which 6x2 MIMO is applied to a 6-mode fiber. Dashed line d shows the spectral efficiency of 6x2 MIMO when a code rate of 0.826 is assumed.

[0062] Section 700 shows the optimal configuration and the section at that time. As shown in section 700, there is a section where the configuration to which this embodiment is applied has the largest capacity between the sections where the configuration to which 6×6 MIMO is applied and the configuration to which 6×3 MIMO is applied are optimal.

[0063] (Variation 1) 7 is a diagram showing an example of the configuration of a receiving device in a wavelength multiplexing configuration in which light of different wavelengths is independently modulated, multiplexed, and transmitted. The configuration differs from that shown in FIG. 1 in that WDMs 160-1, ..., 160-N are provided between the fundamental signal generating unit 130 and the selecting unit 140. Another difference from the configuration shown in FIG. 1 is that B2 transmitting devices 100 are provided, and a WDM 500 is also provided between these transmitting devices 100-1, ..., 100-B2 and the transmission path 200. When the WDMs 160-1, ..., 160-N are not distinguished from one another, they are simply referred to as WDMs 160. When the transmitting devices 100-1, ..., 100-B2 are not distinguished from one another, they are simply referred to as transmitting devices 100.

[0064] As shown in FIG. 7 , the basic signal generating unit 130 outputs a B1×N basic signal to the WDM 160. The WDM 160 wavelength-multiplexes the B1 basic signal input from the basic signal generating unit 130 and outputs the multiplexed signal to the selecting unit 140. The WDM 160 is an example of a multiplexing unit. The selecting unit 140 selects, from the M channels, N spatial channels for transmitting the N signals generated by the basic signal generating unit 130 based on the channel bit sequence, and outputs the multiplexed signal to the WDM 500. The WDM 500 wavelength-multiplexes the signals output to the spatial channels selected by the selecting unit 140 and outputs the multiplexed signal to the receiving device 300. That is, the WDM 500 wavelength-multiplexes the B1 signal input from the transmitting device 100 and outputs the multiplexed signal to the transmission path 200. The WDM 500 is another example of multiplexing.

[0065] In this way, by combining wavelength multiplexing, it is possible to improve the amount of information per time slot for all multiplexing methods combined. Specifically, when B1 wavelength channels are multiplexed before allocation to spatial channels and B2 wavelength channels are multiplexed after allocation, and the transmission bit string is A, the number of bits per time slot is B2 × (B1 × N × logA + [log(C(M, N))]). Since the number of bits without wavelength multiplexing is N × logA + [log(C(M, N))]), wavelength multiplexing can increase the transmission capacity compared to the number of bits without wavelength multiplexing. Note that wavelength multiplexing may be performed either before or after allocation to spatial channels. Furthermore, although wavelength multiplexing is performed by both WDM 160 and WDM 500 in the example of FIG. 7, wavelength multiplexing may be performed by only one of them.

[0066] (Variation 2) Fig. 8 is a diagram showing a configuration example in which the total number of channels received by receiving device 300 is m (m is less than the number of spatial channels M). As shown in Fig. 8, the number of channels input to receiving device 300 is m, which is less than the number of spatial channels M. In this way, reception is possible even if the total number of channels received by receiving device 300 is less than the number of spatial channels M.

[0067] In normal Full MIMO transmission and reception, all spatial degrees of freedom are used, so signals from all M channels must be received independently to decode the signals. However, in this embodiment, the channels used for transmission are only a portion of the total, and a condition is imposed that signals passing through unused channels are zero, so the effective degrees of freedom are smaller than Full MIMO (sparseness).

[0068] Similar work in wireless communications has shown that it is mathematically possible to decode a signal from a partial channel signal, see the following references: Wen, M., Zheng, B., Kim, KJ, Di Renzo, M., Tsiftsis, TA, Chen, KC, & Al-Dhahir, N. (2019). A survey on spatial modulation in emerging wireless systems: Research progresses and applications. IEEE Journal on Selected Areas in Communications, 37(

[0069] 8, it is possible to simplify the hardware configuration and reduce power consumption by reducing the scale of calculations. Note that the receiving device 300 may utilize regularization using the L1 norm or the L0 norm, obtain an unknown signal using a convex optimization algorithm, and use the obtained signal to decode the signal.

[0070] The allocating unit 110, the selection signal generating unit 120, the basic signal generating unit 130, and the selecting unit 140 may be configured using a processor such as a CPU (Central Processing Unit) and a memory. In this case, the allocating unit 110, the selection signal generating unit 120, the basic signal generating unit 130, and the selecting unit 140 function as the allocating unit 110, the selection signal generating unit 120, the basic signal generating unit 130, and the selecting unit 140 by the processor executing a program. Note that all or part of the functions of the allocating unit 110, the selection signal generating unit 120, the basic signal generating unit 130, and the selecting unit 140 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. The computer-readable recording medium may be, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a semiconductor storage device (e.g., an SSD (Solid State Drive)), or a storage device such as a hard disk or semiconductor storage device built into a computer system. The above program may be transmitted via a telecommunications line.

[0071] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0072] The present invention is applicable to an optical transmission system that performs transmission over an optical fiber transmission line. [Explanation of symbols]

[0073] 1...optical transmission system, 100...transmitting device, 110...distributing section, 120...selected signal generating section, 120...selected signal generating section, 130...basic signal generating section, 131...digital signal processing unit, 132...light source, 133...optical modulator, 140...selecting section, 150...digital signal processing unit, 200...transmission path, 300...receiving device, 401, 402...light source, 411, 412...optical modulator, 700...section

Claims

1. An optical transmission system including a transmitter connected to a transmission path having M spatial channels, and a receiver receiving a signal transmitted from the transmitter via the transmission path, The transmitting device a distribution unit that distributes a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information; a generator for generating N (M>N) signals from the bit strings to be the basic signals allocated by the allocation unit; a selector that selects, from the M spatial channels, N spatial channels that transmit the N signals generated by the generator, based on the bit sequence that is the spatial channel information allocated by the allocator; An optical transmission system having:

2. The optical transmission system according to claim 1 , wherein the receiving device acquires the fundamental signal from signals received from the N spatial channels selected by the selector.

3. 3. The optical transmission system according to claim 1, wherein the receiving device acquires the spatial channel information corresponding to the N spatial channels from the N spatial channels through which the signals are received.

4. 3. The optical transmission system according to claim 1, further comprising a multiplexing unit that wavelength-multiplexes the fundamental signal output from the generating unit and outputs the multiplexed signal to the selecting unit.

5. a plurality of the transmitting devices; 3. The optical transmission system according to claim 1, further comprising another multiplexing unit that wavelength-multiplexes signals output to the spatial channels selected by the selectors of the plurality of transmitting devices and outputs the multiplexed signals to the receiving device.

6. 3. The optical transmission system according to claim 1, wherein the receiving device determines an unknown signal from signals received from less than M spatial channels out of M spatial channels, and decodes the signal transmitted from the transmitting device via the transmission path using the unknown signal.

7. A transmitting device connected to a transmission path having M spatial channels, a distribution unit that distributes a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information; a generator for generating N (M>N) signals from the bit strings to be the basic signals allocated by the allocation unit; a selector that selects, from the M spatial channels, N spatial channels that transmit the N signals generated by the generator, based on the bit sequence that is the spatial channel information allocated by the allocator; A transmitting device having:

8. A method for controlling a transmitting device connected to a transmission path having M spatial channels, comprising: a dividing step of dividing a transmission bit sequence to be transmitted to the transmission path into a bit sequence serving as a basic signal and a bit sequence serving as spatial channel information; a generating step of generating N (M>N) signals from the bit strings to be used as the basic signals allocated in the allocating step; a selection step of selecting, from the M spatial channels, N spatial channels for transmitting the N signals generated in the generation step, based on the bit string that serves as the spatial channel information allocated in the allocation step; A control method comprising:

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