Multidimensional constellation map mapping enhanced orthogonal chirp multiplexing optical transmission sending method, receiving method and system

Abstract

The invention discloses a multi-dimensional constellation diagram mapping enhanced orthogonal chirp multiplexing optical transmission sending method, receiving method and system in the field of optical communication. The method comprises the following steps: a sending end converts data to be transmitted into an original signal bit stream; mapping through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point coordinate sequence, and dividing the four-dimensional constellation point coordinate sequence into two different branches; respectively carrying out OCDM modulation on the four-dimensional constellation point coordinate sequences on the two branches to generate two time domain sending signal sequences; performing power distribution and superposition on the time domain sending signal sequence to form a final sending signal; and a receiving end receives the sending signal from the channel, performs OCDM demodulation on the sending signal, recovers constellation point signals in the two branches by using a serial interference cancellation technology, and obtains an original signal bit stream through demapping of the four-dimensional constellation diagram model. According to the invention, the problems of selective fading of signal frequency and overlong CP in DD-OFDM can be solved.

Description

Technical Field

[0001] The invention relates to a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method, receiving method and system, belonging to the technical field of optical communication. Background Art

[0002] With the rapid development of technologies such as big data, the Internet of Things, and cloud computing, the surge in data traffic has posed a challenge to the expansion capacity of short-distance data center optical interconnection networks. In short-distance optical communication systems, in order to achieve low-cost, high-speed, and large-capacity data transmission, direct modulation-direct detection (IM-DD) technology is usually used. In order to improve the transmission rate and capacity, multi-level modulation technology is required, among which PAM (pulse amplitude modulation), DD-OFDM (direct detection-orthogonal frequency division multiplexing) modulation, and CAP (carrier-free amplitude phase) modulation are the mainstream solutions internationally. The DD-OFDM modulation scheme has attracted great attention from the industry and academia due to its high bandwidth utilization and strong channel fading resistance. However, there are also problems such as signal frequency selective fading caused by fiber dispersion and reduced spectrum efficiency caused by too long cyclic prefix (CP).

[0003] In order to solve these problems and improve transmission capacity, researchers began to explore high-order constellation mapping technology. High-order constellation mapping can increase the number of bits carried by each symbol, thereby increasing the amount of information transmitted. However, as the order of the constellation increases, the minimum Euclidean distance (MED) between constellation points decreases, and the constellation gain index (CFM) decreases, resulting in an increase in the decoding error rate.

[0004] As a new type of multi-carrier modulation scheme, orthogonal chirp multiplexing (OCDM) technology provides superior performance and similar complexity to OFDM. OCDM modulates the signal onto orthogonal chirped subcarriers and transmits them in a superimposed manner, using the pulse compression and spread spectrum capabilities of the chirped subcarriers to effectively combat frequency selective fading. Compared with OFDM, OCDM has better anti-interference ability and shorter CP while maintaining spectral efficiency. In order to further improve the transmission capacity of OCDM, researchers have expanded the dimension of the constellation diagram, using high-dimensional constellation points to carry more bit data and increase MED. However, this dimensional expansion may also lead to an increase in the transmission signal bandwidth and a decrease in spectral efficiency, which is a problem that needs to be solved in future research. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method, receiving method and system, which can use a higher dimensional signal space to represent data, thereby transmitting more information under the same spectrum conditions.

[0006] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions.

[0007] In a first aspect, the present invention provides a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method, comprising: Acquire data to be transmitted, and convert the data to be transmitted into an original signal bit stream; Mapping the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and dividing the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; Performing OCDM modulation on the first branch signal and the second branch signal respectively to generate a first time domain transmit signal sequence and a second time domain transmit signal sequence; The first time domain transmission signal sequence and the second time domain transmission signal sequence are power allocated and superimposed to form a final transmission signal.

[0008] In combination with the first aspect, further, the preset four-dimensional constellation diagram model includes: Selecting multiple points evenly distributed on a circle with a radius of r in a two-dimensional plane, and extending the multiple points to a three-dimensional spherical surface with a radius of r, to obtain a first three-dimensional constellation diagram; Rotate multiple points evenly distributed on a circle with a radius of r in the two-dimensional plane clockwise by a predetermined angle to form a new two-dimensional constellation diagram, and expand the new two-dimensional constellation diagram to a three-dimensional spherical surface with a radius of r to obtain a second three-dimensional constellation diagram; The first three-dimensional constellation diagram and the second three-dimensional constellation diagram are used as a basis, and a fourth dimension is added to the three-dimensional constellation diagram to obtain a four-dimensional constellation diagram model.

[0009] In combination with the first aspect, further, the expression of the four-dimensional constellation model is:

[0010] Constraints:

[0011] in, Indicates the minimum value of the gain index of the four-dimensional constellation diagram; represents the i-th constellation point; represents the nth constellation point; i represents the selected constellation point number; n represents the selected constellation point number; r represents the spherical radius of the three-dimensional spherical constellation diagram; Indicates the rotation angle of the 4D constellation point.

[0012] In combination with the first aspect, further, the four-dimensional constellation point signal sequence is divided, including: Arbitrarily combining four real numbers in the constellation point coordinates in the four-dimensional constellation point signal sequence into two complex numbers to form a new constellation point signal sequence with a sequence length of 2N; The new constellation point signal sequence is divided at a sequence length of N, the first half at N is the first branch signal, the second half at N is the second branch signal, and a training sequence TS1 and a zero sequence are added to the first branch signal, and a training sequence TS2 and a zero sequence are added to the second branch signal.

[0013] In combination with the first aspect, further, the expression of the OCDM modulation is:

[0014] in, represents a modulated first branch signal; represents a modulated second branch signal; represents the discrete inverse Fresnel transform matrix; Indicates the first branch signal; Indicates the second branch signal; Indicates that the first branch signal is serial-to-parallel converted according to the number of OCDM subcarriers and the number of symbols; Indicates that the second branch signal is serial-to-parallel converted according to the number of OCDM subcarriers and the number of symbols; represents the first additional phase matrix; represents the second additional phase matrix; F represents the fourth dimension.

[0015] In combination with the first aspect, further, power allocation and superposition of the first time domain transmit signal sequence and the second time domain transmit signal sequence include: The first time domain transmission signal sequence and the second time domain transmission signal sequence are respectively subjected to parallel-to-serial conversion and digital up-conversion operations in sequence, and the power allocation technology in NDMA is used to allocate power to the first time domain transmission signal sequence and the second time domain transmission signal sequence that have undergone parallel-to-serial conversion and digital up-conversion, so as to form a plurality of PDM signals, and the expression of the PDM signal is:

[0016] in, represents the weight assigned to the first branch; represents the weight assigned to the second branch; represents the first branch signal after parallel-to-serial conversion and digital up-conversion; represents the second branch signal after parallel-to-serial conversion and digital up-conversion; Indicates PDM signal; The multiple PDM signals are superimposed to form a final transmission signal.

[0017] In a second aspect, a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission receiving method is provided, characterized in that it includes: receiving a transmission signal from a channel, performing OCDM demodulation on the transmission signal, and recovering constellation point signals in two branches by using a serial interference cancellation technique; The constellation point signals in the two branches are demapped through the four-dimensional constellation model to obtain an original signal bit stream.

[0018] In combination with the second aspect, further, the recovering the constellation point signals in the two branches includes: The transmitted signal received from the channel is digitally down-converted and OCDM demodulated to obtain the frequency domain received signal ; The frequency domain received signal After parallel-to-serial conversion, the frequency domain signal is obtained ; The frequency domain signal is processed by serial interference cancellation technology Demodulate again to recover the constellation point signals in the two branches; The expression of the frequency domain signal is:

[0019] in, represents a frequency domain signal; represents the frequency domain channel relative to the first branch; represents the frequency domain channel relative to the second branch; represents the demodulated constellation point signal in the first branch; represents the demodulated constellation point signal in the second branch; represents additive white Gaussian noise in the time domain.

[0020] In combination with the second aspect, further, the frequency domain signal is Demodulate again, including: treating the constellation point signal in the second branch as noise, and demodulating the constellation point signal in the first branch; Performing channel equalization on the constellation point signal in the first branch by using the training sequence TS1, and demapping the constellation point signal by using the maximum likelihood criterion to restore the bit stream signal of the first branch; Mapping the bit stream signal of the first branch into the four-dimensional constellation model again to obtain a corresponding constellation point signal, and multiplying the constellation point signal by the channel response to restore the original constellation point signal in the first branch; Using the frequency domain signal Subtracting the constellation point signal in the first branch to obtain the constellation point signal of the second branch; The constellation point signal in the second branch is equalized by using the training sequence TS2, and the constellation point signal is demapped by using the maximum likelihood criterion to restore the bit stream signal of the second branch.

[0021] In a third aspect, a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission system includes: System sender: A data acquisition and conversion module, used to acquire data to be transmitted and convert the data to be transmitted into an original signal bit stream; A constellation mapping and allocation module, used to map the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and divide the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; An OCDM modulation module, configured to perform OCDM modulation on the first branch signal and the second branch signal to generate a first time domain transmission signal sequence and a second time domain transmission signal sequence; A power allocation and superposition module, used to allocate power to and superpose the first time domain transmission signal sequence and the second domain transmission signal sequence to form a final transmission signal; System receiving end: An OCDM demodulation and interference cancellation module, used to receive the transmission signal from the channel, perform OCDM demodulation on the transmission signal, and use serial interference cancellation technology to restore the constellation point signals in the two branches; The demapping module is used to demap the constellation point signals in the two branches through the four-dimensional constellation diagram model to obtain the original signal bit stream.

[0022] Compared with the prior art, the present invention has the following beneficial effects: Through the design of the communication system, the transmitting end of the present invention can efficiently process and transmit data. First, the system converts the data to be transmitted into the original signal bit stream, laying the foundation for subsequent signal processing. The use of the four-dimensional constellation model to map these bit streams not only increases the dimension of the signal and improves the density of data transmission, but also distributes the constellation point signal sequence to two different branches. The system can manage the signal more flexibly, reduce interference, and improve the reliability of the signal. The two branches are modulated separately by OCDM, which further enhances the anti-interference ability of the signal and optimizes the use of the spectrum.

[0023] In the process of power allocation and superposition, the system can adjust the power of each branch according to the needs of the signal to ensure the stability and efficiency of the signal during transmission. At the receiving end, through OCDM demodulation and serial interference elimination technology, the system can effectively recover the original constellation point signal from the complex signal, and maintain high signal quality even under unsatisfactory channel conditions. Finally, through the demapping of the four-dimensional constellation model, the system can accurately restore the original signal bit stream to ensure the integrity and accuracy of the data. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 1 is a schematic diagram of a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission method provided by an embodiment of the present invention; Figure 2 The figure shows a schematic diagram of a four-dimensional constellation diagram design provided by an embodiment of the present invention; Figure 3 Shown is a simulation diagram of a four-dimensional constellation gain index provided by an embodiment of the present invention; Figure 4 The figure is a schematic diagram of dividing four-dimensional constellation point signals provided by an embodiment of the present invention; Figure 5 The figure shows a demodulation principle diagram of a serial interference elimination technology provided by an embodiment of the present invention; Figure 6 FIG. 1 is a schematic diagram of a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission system provided by an embodiment of the present invention; Figure 7 The figure shows a bilateral power spectrum of a received signal under an ideal channel provided by an embodiment of the present invention; Figure 8 The figure shows a bilateral power spectrum of a received signal under a Gaussian white noise channel provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other unless there is a conflict.

[0026] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship. Example

[0027] See also Figure 1This embodiment introduces a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method, and steps S1 to S4 are the processing process of the sending end, which specifically includes the following steps: Step S1, obtaining data to be transmitted, and converting the data to be transmitted into an original signal bit stream; The data transmitted here can be diverse, including but not limited to high-definition video streams, audio streams, network data, etc. During the conversion process, necessary preprocessing operations may be required, such as frame synchronization to ensure the correct order of data, signal shaping to improve the transmission characteristics of the signal, and scrambling to increase the randomness of the signal and reduce inter-code interference.

[0028] Step S2, mapping the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and dividing the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; Here, a suitable constellation model is selected according to the actual transmission distance and the characteristics of the optical fiber. For example, the embodiment of the present invention selects a 16-point four-dimensional constellation model, which can provide better error performance while maintaining a high spectrum efficiency, and the allocation of the constellation can optimize the transmission quality of the signal according to the priority and type of the signal.

[0029] Step S3, performing OCDM modulation on the first branch signal and the second branch signal respectively to generate a first time domain transmission signal sequence and a second time domain transmission signal sequence; During the OCDM modulation process, each constellation point signal sequence is modulated onto a set of orthogonal chirped subcarriers. This step ensures the orthogonality of the signal in the frequency domain and reduces inter-symbol interference.

[0030] Step S4: power-allocate and superimpose the first time-domain transmission signal sequence and the second time-domain transmission signal sequence to form a final transmission signal; Here, the power allocation strategy can be dynamically adjusted according to the signal priority and channel conditions to ensure that important signals can be received with a higher signal-to-noise ratio. The linearity of the signal needs to be considered during superposition to avoid nonlinear effects affecting the signal quality.

[0031] See also Figure 1 This embodiment also introduces a multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission receiving method, steps S5-S6 are the receiving end processing process, specifically including the following steps: Step S5, receiving a transmission signal from the channel, performing OCDM demodulation on the transmission signal, and using serial interference cancellation technology to restore the constellation point signals in the two branches; First, the received transmission signal is demodulated by OCDM, which is the opposite of the modulation process at the transmitter. The purpose is to recover the time domain signal from the frequency domain. Then, the serial interference cancellation technology (SIC) is used to process and eliminate the interference in the signal in turn, and restore the clear constellation point signals in the first branch and the second branch.

[0032] Step S6: Demap the constellation point signals in the two branches through the four-dimensional constellation model to obtain an original signal bit stream.

[0033] The recovered constellation point signal is demapped through the four-dimensional constellation model and converted back to the original signal bit stream. This step marks the completion of the signal processing process and successfully recovers the original transmitted data from the received signal.

[0034] The above steps effectively improve the system's spectrum efficiency and transmission capacity through high-dimensional constellation mapping and OCDM technology, and at the same time achieve effective multiplexing and high-quality reception of signals through power multiplexing (PDM) technology and serial interference cancellation (SIC) technology. This makes this method particularly suitable for short-distance high-speed optical transmission scenarios such as data center optical interconnection networks. Example

[0035] The four-dimensional constellation model preset in step S2 is designed based on a specific optimization algorithm, aiming to maximize the performance indicators of the four-dimensional constellation, such as the constellation gain index CFM, the minimum Euclidean distance MED, and the average energy Eavg, and their expressions are: (1) in, Represents the average energy of the four-dimensional constellation diagram and is proportional to the signal transmission power; represents the i-th point in the constellation diagram A; i represents the i-th four-dimensional constellation point.

[0036] (2) in, Represents the minimum Euclidean distance of a four-dimensional constellation diagram; represents the nth point in the constellation diagram A; n represents the nth four-dimensional constellation point.

[0037] (3) in, Represents the constellation gain index.

[0038] Furthermore, the model starts with two 3D constellations with high CFM8, and forms a 4D constellation through 3D expansion and symmetry design. In the 4D space, each constellation point is represented by four coordinate values. The specific 4D constellation model design process includes: Step S21, selecting a plurality of points evenly distributed on a circle with a radius r in a two-dimensional plane, and extending the plurality of points to a three-dimensional spherical surface with a radius r, to obtain a first three-dimensional constellation diagram; Step S22: rotating multiple points evenly distributed on a circle with a radius of r in the two-dimensional plane clockwise by a predetermined angle to form a new two-dimensional constellation diagram, and extending the new two-dimensional constellation diagram to a three-dimensional spherical surface with a radius of r to obtain a second three-dimensional constellation diagram; Step S23: taking the first three-dimensional constellation diagram and the second three-dimensional constellation diagram as a basis, and adding a fourth dimension to the three-dimensional constellation diagram to obtain a four-dimensional constellation diagram model.

[0039] See also Figure 2 In the embodiment of the present invention, from Figure 2 In (a), eight points are evenly distributed on a circle with a radius of r in a two-dimensional plane. Each point corresponds to a bit combination. When the eight points are evenly distributed, the CFM is the largest. Without loss of generality, Taking the coordinates (0, r) as an example, The coordinates are expanded to Figure 2 (c) is a three-dimensional sphere with a radius of r. The coordinates are (0, , ); At the same time, Figure 2 The two-dimensional constellation diagram in (a) is rotated 45 degrees clockwise to form Figure 2 (b) shows the new two-dimensional constellation diagram, and The coordinates are expanded to Figure 2 (d) is a three-dimensional sphere with a radius of r. The coordinates of are ( , , ),Will Figure 2 (c) and Figure 2 The two three-dimensional constellation diagrams shown in (d) are used as the basis of the thinking constellation diagram, and the fourth dimension F and -F are added to their coordinates, thereby obtaining a 16-point four-dimensional constellation diagram model, and the coordinates of the constellation points in the four-dimensional constellation diagram model are: (4) Wherein, r represents the radius of the sphere of the three-dimensional spherical constellation diagram; Represents the rotation angle of the four-dimensional constellation point; F represents the fourth dimension.

[0040] From (4), it can be concluded that the distance from each constellation point to the origin in the designed 16-point four-dimensional constellation model is In order to simplify the optimization process, the distance from each constellation point to the origin is normalized, so =1, the coordinates of the constellation points under the maximum CFM of the four-dimensional constellation model are found by numerical simulation and gradient descent method. The calculation expression of the coordinates of the constellation points of the four-dimensional constellation model is: (5) Constraints: (6) in, Indicates the minimum value of the gain index of the four-dimensional constellation diagram; represents the i-th constellation point; represents the nth constellation point; i represents the sequence number of the selected constellation point; n represents the sequence number of the selected constellation point.

[0041] See also Figure 3 In the embodiment of the present invention, Perform numerical simulations, such as Figure 3 (a) and 3(c), The function graph of is approximately a convex function in the domain, and is calculated using the gradient descent method. The maximum value of, in order to meet the requirements of the objective function in formula (6), Perform numerical simulations, such as Figure 3 (b) and 3(d), by calculation, when and , -CFM 4D The minimum value is -1.1716, which is CFM 4D The maximum value is 1.1716.

[0042] In order to make the above-designed four-dimensional constellation diagram widely used in short-distance optical communications, the present invention designs a DD-OCDM optical transmission mechanism based on four-dimensional constellation diagram mapping. At the transmitting end, the modulated four-dimensional constellation point signal sequence is first divided into two different branch signals, namely the first branch signal and the second branch signal, and then the first branch signal and the second branch signal are OCDM modulated respectively, and finally the power allocation technology in non-orthogonal multiple access (NOMA) is used to allocate power to the four-dimensional constellation point in each branch, and the power is superimposed and sent into the channel. At the receiving end, the transmission signal sent by the transmitting end is received, and after OCDM demodulation of the transmitted signal, the SIC technology is used to restore the constellation point signals of the two branches to eliminate or reduce interference between multiple users, and the restored constellation point signal is mapped by the four-dimensional constellation diagram to restore the original signal bit stream.

[0043] Further, see Figure 4 , dividing the modulated four-dimensional constellation point signal sequence, specifically including the following steps: Step S41, arbitrarily combining four real numbers in the constellation point coordinates in the four-dimensional constellation point signal sequence into two complex numbers to form a new constellation point signal sequence with a sequence length of 2N; like Figure 4 As shown in (a), is the four-dimensional constellation point after being mapped by the four-dimensional constellation diagram. Each point is represented by four real coordinates. In order to make the four-dimensional constellation point meet the transmission requirements of OCDM, the four real numbers in each point are combined into Figure 4 (b) in the form of.

[0044] In order to make the average energy of the divided first branch signal and the second branch signal similar before power distribution, the method of step S42 is used to perform cross-over superposition.

[0045] Step S42: divide the new constellation point signal sequence at a sequence length of N, wherein the first half at N is the first branch signal, and the second half at N is the second branch signal, and a training sequence and a zero sequence are added to the first branch signal and the second branch signal.

[0046] The combined four-dimensional constellation points are Figure 4 (c) and 4 (d) are cross-superimposed. At this time, the length of the entire constellation point sequence is 2N, and it is divided at the length N, as shown in Figure 4 As shown in (e), the first half of the constellation point sequence is the first branch signal, and the second half is the second branch signal. In addition, training sequences (TS1 and TS2) and zero sequences are added at the front and back ends of each branch signal to provide reference signals and reduce errors during OCDM modulation and demodulation.

[0047] It should be noted that, in order to facilitate OCDM modulation and demodulation, we set the length of the training sequence and the zero sequence to the length of an OCDM symbol (the length N of the entire signal constellation point sequence is an integer multiple of the length of the OCDM symbol).

[0048] Secondly, in Figure 4 In the first branch and the second branch shown in (e), the training sequence and the zero sequence are added at different positions, so that after the two branch signals are power-divided and superimposed, the OCDM symbols and training sequence of one branch will not cause crosstalk to the training sequence of the other branch.

[0049] Taking into account the spectral efficiency of transmitting four-dimensional constellation point signals, since PDM multiplexes the first branch and the second branch in the power domain, the two branches occupy the same frequency band, and transmitting two-dimensional constellation point signals with the same number of points is equivalent to using one of the branches for transmission. It can be found that the bandwidth used to transmit four-dimensional constellation point signals and two-dimensional constellation point signals is the same, and their spectral efficiency is equal at the same transmission rate.

[0050] After dividing the four-dimensional constellation point signal sequence, OCDM modulation is performed on the two branches respectively. In the digital communication system, DFnT is used to realize OCDM digital modulation and demodulation. The discrete Fresnel DFnT matrix can be expressed as: (7) Wherein, M represents the number of chirp subcarriers; represents the DFnT matrix; j represents the imaginary unit; m represents the mth row of the DFnT matrix; n represents the nth column of the DFnT matrix.

[0051] Furthermore, the DFnT matrix can be decomposed into ,in, The expressions are: (8) (9) in, Represents the four-dimensional constellation point of the first branch, that is, the first branch signal; Represents the four-dimensional constellation point of the second branch, that is, the second branch signal.

[0052] Furthermore, the expression for OCDM modulation of the four-dimensional constellation points of the two branches is: (10) in, represents the modulated OCDM signal of the first branch; represents the modulated OCDM signal of the second branch; represents the discrete inverse Fresnel transform matrix; Indicates the constellation point signal of the first branch; A constellation point signal representing the second branch; Indicates that the signal of the first branch is converted into serial-to-parallel according to the number of OCDM subcarriers and the number of symbols; It indicates that the signal of the second branch is converted into serial-to-parallel according to the number of OCDM subcarriers and the number of symbols; F indicates the fourth dimension; represents the first additional phase matrix; represents the second additional phase matrix.

[0053] It should be noted that The existence of makes DFnT no longer have the complex conjugate symmetry property of discrete Fourier transform (DFT).

[0054] Furthermore, after OCDM modulation, the time domain transmission signal sequence is sequentially subjected to parallel-to-serial conversion and digital up-conversion operations, and the power allocation technology in NDMA is used to perform power allocation on the time domain transmission signal sequence subjected to parallel-to-serial conversion and digital up-conversion to form multiple PDM signals, and the expression of the PDM signal is: (11) in, Indicates the PDM signal sent; represents the weight assigned to the first branch; represents the weight assigned to the second branch; Represents the OCDM signal of the first branch after parallel-to-serial conversion and digital up-conversion; Represents the OCDM signal of the second branch after parallel-to-serial conversion and digital up-conversion; The multiple PDM signals are superimposed to form a final transmission signal.

[0055] Furthermore, the weight of power allocation satisfies the following conditions: (12) Without loss of generality, we assume p1>p2. Considering the impact of fiber channel characteristics on PDM signal transmission, at the receiving end, the time domain received signal includes the signal and noise of the two branch four-dimensional constellation points, and the formula can be expressed as: (13) in, represents the received signal in the time domain; represents additive white Gaussian noise in time domain; represents the circular convolution symbol; represents the time domain channel of the first branch; Represents the time domain channel of the second branch.

[0056] Furthermore, the transmitted signal (time domain received signal) received from the channel is subjected to digital down conversion (DDC) and OCDM demodulation to obtain a frequency domain received signal. , the expression of the frequency domain received signal is: (14) in, Represents the received OCDM signal multiplexed in the power domain; It represents the noisy constellation point signal of the two branches superimposed after OCDM demodulation; Represents the OCDM signal multiplexed in the power domain after serial-to-parallel conversion.

[0057] The frequency domain received signal After parallel-to-serial conversion, the converted frequency domain signal is obtained ; The frequency domain signal expression after the conversion is: (15) in, represents a frequency domain signal; represents the frequency domain channel relative to the first branch; represents the frequency domain channel relative to the second branch; represents the demodulated four-dimensional constellation point signal in the first branch; represents the demodulated four-dimensional constellation point signal in the second branch; represents additive white Gaussian noise in the time domain.

[0058] Further, and It can be expressed as: (16) Further, see Figure 5 , using serial interference cancellation technology to Demodulation is performed again to restore the constellation point signals in the two branches, which specifically includes the following steps: Step S81: considering the constellation point signal in the second branch as noise, and demodulating the constellation point signal in the first branch; Step S82: performing channel equalization on the constellation point signal in the first branch by using the training sequence TS1, and demapping the constellation point signal by using the maximum likelihood criterion to restore the bit stream signal of the first branch; Step S83: Map the bit stream signal of the first branch to the four-dimensional constellation model again to obtain a corresponding constellation point signal, and multiply the constellation point signal by the channel response to restore the original constellation point signal of the first branch; Step S84: using the frequency domain signal Subtracting the constellation point signal of the first branch to obtain the constellation point signal of the second branch; Step S85: Use the training sequence TS2 to equalize the constellation point signal in the second branch, and use the maximum likelihood criterion to demap the constellation point signal to restore the bit stream signal of the second branch. Example

[0059] System sender: A data acquisition and conversion module, used to acquire the data to be transmitted and convert the data to be transmitted into an original signal bit stream, and the module also includes a digital-to-analog conversion unit, used to convert the digital signal modulated by the OCDM into an analog electrical signal; A constellation mapping and allocation module, used to map the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and divide the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; An OCDM modulation module, used to perform OCDM modulation on the first branch signal and the second branch signal respectively to generate a first time domain transmission signal sequence and a second time domain transmission signal sequence; A power allocation and superposition module, used to allocate power to and superpose the first time domain transmission signal sequence and the second time domain transmission signal sequence to form a final transmission signal, thereby ensuring effective spectrum utilization of the signal during transmission; The data acquisition and conversion module also includes a digital-to-analog conversion unit for converting the OCDM modulated digital signal into an analog electrical signal. The OCDM modulation module includes a Mach-Zehnder modulator for converting the analog electrical signal into an optical signal for transmission through an optical fiber.

[0060] System receiving end: The received optical signal is firstly power-amplified by a pre-amplifier, and then the noise and unnecessary frequency components are filtered out by an optical bandpass filter. The photodetector is responsible for converting the filtered optical signal into an electrical signal, and the analog-to-digital conversion unit then converts these electrical signals into digital signals in preparation for subsequent digital signal processing. The OCDM demodulation and interference elimination module is used to receive the transmission signal from the channel, perform OCDM demodulation on the transmission signal, and use serial interference elimination technology to recover the constellation point signals in the two branches; The demapping module is used to demap the constellation point signals in the two branches through the four-dimensional constellation diagram model to obtain the original signal bit stream.

[0061] In one embodiment of the present invention, see Figure 6 ,The input code element (data) is first modulated in the high-dimensional constellation mapping unit, and then processed by the OCDM modulation unit to generate an OCDM signal multiplexed in the power domain, such as Figure 7 These signals are transmitted to the receiving end through the optical fiber. After passing through the optical fiber channel, the power spectrum of the received signal is as follows: Figure 8As shown, the received optical signal is first power amplified by a pre-amplifier and then filtered using an optical bandpass filter to eliminate noise and unwanted frequency components. After that, the photodetector converts the filtered optical signal into an electrical signal. Next, the analog-to-digital conversion unit converts the electrical signal into a digital signal to prepare for subsequent digital signal processing. Finally, the OCDM demodulation unit demaps the high-dimensional constellation diagram to demodulate and recover the original symbol data. These data represent the digital form of the original transmitted information, thus completing the complete transmission and recovery process of the signal.

[0062] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method, characterized in that: include: Acquire data to be transmitted, and convert the data to be transmitted into an original signal bit stream; Mapping the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and dividing the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; Performing OCDM modulation on the first branch signal and the second branch signal respectively to generate a first time domain transmit signal sequence and a second time domain transmit signal sequence; The first time domain transmission signal sequence and the second time domain transmission signal sequence are power allocated and superimposed to form a final transmission signal.

2. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method according to claim 1, characterized in that: The preset four-dimensional constellation diagram model includes: Selecting multiple points evenly distributed on a circle with a radius of r in a two-dimensional plane, and extending the multiple points to a three-dimensional spherical surface with a radius of r, to obtain a first three-dimensional constellation diagram; Rotate multiple points evenly distributed on a circle with a radius of r in the two-dimensional plane clockwise by a predetermined angle to form a new two-dimensional constellation diagram, and expand the new two-dimensional constellation diagram to a three-dimensional spherical surface with a radius of r to obtain a second three-dimensional constellation diagram; The first three-dimensional constellation diagram and the second three-dimensional constellation diagram are used as a basis, and a fourth dimension is added to the three-dimensional constellation diagram to obtain a four-dimensional constellation diagram model.

3. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method according to claim 2, characterized in that: The expression of the four-dimensional constellation model is: ； Constraints: ； in, Indicates the minimum value of the gain index of the four-dimensional constellation diagram; represents the i-th constellation point; represents the nth constellation point; i represents the selected constellation point number; n represents the selected constellation point number; r represents the spherical radius of the three-dimensional spherical constellation diagram; Indicates the rotation angle of the 4D constellation point.

4. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method according to claim 1, characterized in that: Dividing the four-dimensional constellation point signal sequence includes: Arbitrarily combining four real numbers in the constellation point coordinates in the four-dimensional constellation point signal sequence into two complex numbers to form a new constellation point signal sequence with a sequence length of 2N; The new constellation point signal sequence is divided at a sequence length of N, the first half at N is the first branch signal, the second half at N is the second branch signal, and a training sequence TS1 and a zero sequence are added to the first branch signal, and a training sequence TS2 and a zero sequence are added to the second branch signal.

5. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method according to claim 1, characterized in that: The expression of the OCDM modulation is: ； in, represents a modulated first branch signal; represents a modulated second branch signal; represents the discrete inverse Fresnel transform matrix; Indicates the first branch signal; Indicates the second branch signal; Indicates that the first branch signal is serial-to-parallel converted according to the number of OCDM subcarriers and the number of symbols; Indicates that the second branch signal is serial-to-parallel converted according to the number of OCDM subcarriers and the number of symbols; represents the first additional phase matrix; represents the second additional phase matrix; F represents the fourth dimension.

6. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission sending method according to claim 1, characterized in that: The first time domain transmit signal sequence and the second time domain transmit signal sequence are power-allocated and superimposed, including: The first time domain transmission signal sequence and the second time domain transmission signal sequence are respectively subjected to parallel-to-serial conversion and digital up-conversion operations in sequence, and the power allocation technology in NDMA is used to allocate power to the first time domain transmission signal sequence and the second time domain transmission signal sequence that have undergone parallel-to-serial conversion and digital up-conversion, so as to form a plurality of PDM signals, and the expression of the PDM signal is: ； in, represents the weight assigned to the first branch; represents the weight assigned to the second branch; represents the first branch signal after parallel-to-serial conversion and digital up-conversion; represents the second branch signal after parallel-to-serial conversion and digital up-conversion; Indicates PDM signal; The multiple PDM signals are superimposed to form a final transmission signal.

7. Receive a transmission signal from the channel, perform OCDM demodulation on the transmission signal, and use serial interference cancellation technology to recover the constellation point signals in the two branches; The constellation point signals in the two branches are demapped through the four-dimensional constellation model to obtain an original signal bit stream.

8. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission and receiving method according to claim 7, characterized in that: The recovering of constellation point signals in two branches comprises: The transmitted signal received from the channel is digitally down-converted and OCDM demodulated to obtain the frequency domain received signal ; The frequency domain received signal After parallel-to-serial conversion, the frequency domain signal is obtained ; The frequency domain signal is processed by serial interference cancellation technology Demodulate again to recover the constellation point signals in the two branches; The expression of the frequency domain signal is: ； in, represents a frequency domain signal; represents the frequency domain channel relative to the first branch; represents the frequency domain channel relative to the second branch; represents the demodulated constellation point signal in the first branch; represents the demodulated constellation point signal in the second branch; Represents additive white Gaussian noise in the time domain.

9. The multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission and receiving method according to claim 8, characterized in that: The serial interference cancellation technique is used to eliminate the frequency domain signal Demodulate again, including: treating the constellation point signal in the second branch as noise, and demodulating the constellation point signal in the first branch; Performing channel equalization on the constellation point signal in the first branch by using the training sequence TS1, and demapping the constellation point signal by using the maximum likelihood criterion to restore the bit stream signal of the first branch; Mapping the bit stream signal of the first branch into the four-dimensional constellation model again to obtain a corresponding constellation point signal, and multiplying the constellation point signal by the channel response to restore the original constellation point signal in the first branch; Using the frequency domain signal Subtracting the constellation point signal in the first branch to obtain the constellation point signal of the second branch; The constellation point signal in the second branch is equalized by using the training sequence TS2, and the constellation point signal is demapped by using the maximum likelihood criterion to restore the bit stream signal of the second branch.

10. A multi-dimensional constellation mapping enhanced orthogonal chirp multiplexing optical transmission system, characterized in that: include: System sender: A data acquisition and conversion module, used to acquire data to be transmitted and convert the data to be transmitted into an original signal bit stream; A constellation mapping and allocation module, used to map the original signal bit stream through a preset four-dimensional constellation diagram model to generate a four-dimensional constellation point signal sequence, and divide the four-dimensional constellation point signal sequence into a first branch signal and a second branch signal; An OCDM modulation module, configured to perform OCDM modulation on the first branch signal and the second branch signal to generate a first time domain transmission signal sequence and a second time domain transmission signal sequence; A power allocation and superposition module, used to allocate power to and superpose the first time domain transmission signal sequence and the second domain transmission signal sequence to form a final transmission signal; System receiving end: An OCDM demodulation and interference cancellation module, used to receive the transmission signal from the channel, perform OCDM demodulation on the transmission signal, and use serial interference cancellation technology to restore the constellation point signals in the two branches; The demapping module is used to demap the constellation point signals in the two branches through the four-dimensional constellation diagram model to obtain the original signal bit stream.

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