Polarization code cooperation method in free space optical communication system

Abstract

The invention provides a polarization code cooperation method in a free space optical communication system, which comprises the following steps that: each user performs polarization coding on a first data block of the user and broadcasts the first data block, a base station receives the first data block of each user, and each user receives the first data block of a partner user; each user decodes the received first data block of the partner user, and performs XOR operation on the decoded data block of the partner user and a second data block of the partner user to generate a joint data block; each user performs polarization coding on the joint data block and sends the joint data block to a base station; and the base station constructs a joint log-likelihood ratio sequence by using the nested structure characteristic of the polarization code based on the data blocks received in the two stages, and obtains the data information of each user through decoding of a joint decoder.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communications technology, and specifically relates to a polarization code collaboration method in a free-space optical communication system. In particular, it relates to a polarization-based Joint Polar Coded Cooperation (JPCC) scheme in a free-space optical (FSO) communication scenario. Background Art

[0002] Free-space optics (FSO), a high-bandwidth, low-cost wireless transmission technology, has demonstrated significant advantages in metropolitan area access networks, enterprise dedicated lines, and emergency communications. It utilizes laser beams to transmit data in free space, offering inherent electromagnetic compatibility and physical layer security, making it particularly suitable for use in scenarios with restricted radio frequencies or complex spectrum licensing. However, atmospheric channel instability remains a core challenge limiting system reliability. Atmospheric turbulence, caused by temperature gradients and pressure inhomogeneities, results in random fluctuations in the refractive index along the beam propagation path, leading to intensity flicker and phase distortion at the receiving end. This time-varying signal fading is particularly pronounced over long-distance transmission, making it difficult for traditional modulation methods to maintain stable bit error rate performance. Furthermore, meteorological conditions such as rain and fog can induce Mie scattering, resulting in additional optical power attenuation. In poor weather conditions with low visibility, communication links can be completely disrupted.

[0003] To combat channel fading, cooperative diversity technology has been introduced into FSO systems. Its basic principle is to construct spatially diverse paths through cooperative transmission between multiple user nodes to improve system robustness. In a typical two-user cooperative model, users first broadcast their own data and then forward their partner's information to each other, allowing the base station to obtain multiple independent copies of the same data. While this model can improve the probability of outage, it also introduces new technical contradictions. On the one hand, the inter-user channel is easily affected by building obstruction or mobile terminal displacement, resulting in a high outage rate for the cooperative link. On the other hand, the repeated transmission mechanism sacrifices spectral efficiency, creating a bottleneck in data rate-sensitive scenarios. Although existing dynamic cooperative schemes attempt to adaptively switch transmission modes based on channel status, their reliance on real-time channel measurements makes it difficult to operate stably in rapidly changing turbulent environments.

[0004] At the coding scheme level, polar codes have become the standard for communication systems such as 5G due to their ability to approach the Shannon limit and their low encoding and decoding complexity. Recent research has attempted to apply them to FSO collaborative systems, but compatibility challenges remain. The frozen bit design of standard polar codes primarily targets static channel characteristics, whereas time-varying fading caused by atmospheric turbulence requires dynamic reconstruction capabilities. Furthermore, multi-user collaborative scenarios require integrating distributed node data into a joint codeword structure. Traditional concatenated coding schemes, lacking in-depth utilization of the recursive nature of polar codes, result in a surge in decoding complexity with the number of users. Experimental studies have shown that existing collaborative polar code schemes exhibit a significant error plateau effect under strong turbulence conditions, and decoding latency is an increasingly prominent issue in real-time services. Developing a polar code joint encoding and decoding architecture that adapts to the dynamic FSO channel is a key breakthrough in improving system performance. Summary of the Invention

[0005] To address existing shortcomings in free-space optical (FSO) communications, such as severe signal fading caused by atmospheric turbulence, weak inter-user data correlation, and high joint decoding complexity in traditional collaborative coding schemes, this paper proposes a polarization-based FSO coding collaboration method. By deeply integrating the characteristics of polarization codes with a collaborative mechanism, this method significantly improves system fading resistance and decoding efficiency. Through an innovative joint coding architecture and dynamic collaborative mechanism, this method effectively combats channel fading caused by atmospheric turbulence.

[0006] This method constructs a collaborative framework of "two-stage transmission and joint decoding": In the first stage, each user polarize-encodes and broadcasts its first data block, which is received by the base station and the partner user separately. After decoding the partner data, the user adds it to its second data block through an XOR operation to generate a joint data block. In the second stage, the user broadcasts this joint data block to the base station. Based on the data received in the two stages, the base station uses the nested structure of polar codes to establish the internal connection between the data blocks, construct a joint log-likelihood ratio (LLR) value, and directly recover each user's data through a low-complexity decoder.

[0007] To address practical scenarios where inter-user channels are imperfect, this method further designs a dynamic collaboration mode: flexibly switching between full collaboration (mutual data transmission), partial collaboration (single-user forwarding), or non-collaborative (independent retransmission) modes based on inter-user channel interruptions. At the same time, the method dynamically allocates transmission power based on the distance between the user and the base station (for example, higher power is allocated in the second phase for distant users), balancing transmission reliability and energy efficiency.

[0008] Its core innovation lies in:

[0009] Joint data generation mechanism: User data is fused through an XOR operation, and the Plotkin structure of the recursive polar code is combined to generate nested joint codewords to reduce redundant transmission;

[0010] Dynamic channel adaptation strategy: switches between fully cooperative, partially cooperative, and non-cooperative modes in real time based on the probability of channel outage between users, and allocates differentiated power based on the distance between the user and the base station (long-distance users receive higher power in the second phase);

[0011] Efficient joint decoding design: The received signal constellation distribution is mapped into four layers of log-likelihood ratio components (XOR value, bit combination, independent data probability ratio), which are then recombined into a long sequence according to the polar code nesting rules and input into the decoder.

[0012] Performance verification system: Verify the decoding convergence speed through the mapping relationship between prior mutual information and output mutual information.

[0013] Compared with traditional solutions, the present invention enhances user data correlation through the structural characteristics of polar codes, avoiding error accumulation in successive interference cancellation (SIC); reduces the complexity of multi-user decoding through the collaborative design of XOR superposition and joint decoding; and enhances the system's adaptability to complex turbulent environments through the dynamic collaboration mode and power allocation strategy, effectively improving the anti-fading performance and practical application stability of FSO communications.

[0014] The technical solution specifically adopted by the present invention to solve the technical problem is:

[0015] A polarization code cooperation method in a free-space optical communication system:

[0016] Each user performs polarization encoding on its own first data block and broadcasts it. The base station receives the first data block of each user, and at the same time, each user receives the first data block of its partner user.

[0017] Each user decodes the received first data block of the partner user, and performs an XOR operation on the decoded partner user data block and its own second data block to generate a joint data block;

[0018] Each user performs polarization encoding on the joint data block and sends the result to the base station;

[0019] Based on the data blocks received in two stages, the base station uses the nested structure of polar codes to construct a joint log-likelihood ratio sequence, and decodes it through a joint decoder to obtain the data information of each user.

[0020] Furthermore, the joint log-likelihood ratio sequence is obtained by calculating a joint constellation distribution of two-stage received signals, and the joint constellation distribution includes a joint probability mapping of four groups of original data (u1-u4) of two users.

[0021] Furthermore, the joint log-likelihood ratio sequence includes:

[0022] First component: Log-likelihood ratio of the XOR values ​​of the original data of the two users in the two phases (corresponding to the operation of u1-u4, that is, the log-likelihood of the global XOR check value of the original data of the two users in the first and second phases);

[0023] Second component: Joint log-likelihood ratio of some bits of user second-stage data; (corresponding to the operation of u2 and u4, that is, the cross-user combined log-likelihood ratio of user U2's first-stage data and user U1's second-stage data)

[0024] The third component: the cross-user combination log-likelihood ratio of the user in the second stage (corresponding to the operation of u3 and u4, that is, the cross-user combination log-likelihood ratio of the second stage data of user U2 and the second stage data of user U1);

[0025] Fourth component: the log-likelihood ratio of the user's second-stage independent data (corresponding to the operation of u4, that is, the independent log-likelihood ratio of the user U1's second-stage data);

[0026] Among them, u1-u4 represent the first-stage original data of user U1, the first-stage original data of user U2, the second-stage original data of user U2, and the second-stage original data of user U1, respectively; u1 and u2 can be obtained by decoding the received signal in the first stage, and u3 and u4 can be obtained by decoding the received signal in the second stage combined with the first stage.

[0027] Each component is mapped to a different segment of the joint LLR sequence according to the nested structure of the polar code.

[0028] Furthermore, the polar coding adopts a recursive generator matrix structure, and the generator matrix satisfies the Plotkin construction;

[0029] The joint data block is generated by XORing the partner user's decoded data with its own second data block (user U1 uses its second-stage data u4 for XORing, and user U2 uses its second-stage data u3 for XORing).

[0030] Furthermore, the two user data are integrated through a joint coding matrix, where the joint coding matrix includes a recursive polar code sub-matrix and a zero matrix block, forming a block diagonal structure.

[0031] Furthermore, the cooperation mode is dynamically selected according to the probability of channel interruption between users, including:

[0032] Fully collaborative mode: two users decode and forward each other's data;

[0033] Partial collaboration mode: only one user forwards the other party's data;

[0034] Non-collaborative mode: Users retransmit their own data independently.

[0035] Furthermore, the transmission power is dynamically allocated based on the channel gain from the user to the base station. For users whose channel gain is lower than a preset threshold, higher power is allocated in the second stage.

[0036] The preset threshold is determined based on a path loss between the user and the base station.

[0037] Furthermore, the joint decoder verifies the decoding convergence speed through a mapping relationship between the prior mutual information and the output mutual information.

[0038] Furthermore, the joint decoder adopts a successive-cancellation (SC) decoding algorithm.

[0039] And, a coded cooperation system for free-space optical communication, comprising:

[0040] A plurality of user devices are configured to perform:

[0041] Polarization-encode the first data block and broadcast it;

[0042] receiving a first data block from a partner user and decoding the data;

[0043] Performing an XOR operation on the decoded partner user data block and its own second data block to generate a joint data block;

[0044] performing polarization encoding on the joint data block and sending the resultant data block;

[0045] The base station device is configured to perform:

[0046] receiving a first data block broadcast by each user equipment;

[0047] receiving a joint data block sent by each user equipment;

[0048] Based on the data blocks received in two stages, the nested structure of polar codes is used to construct a joint log-likelihood ratio sequence, which is then decoded by a joint decoder to obtain the data information of each user.

[0049] And, a computer device includes a memory, a processor and a computer program stored in the memory, and the processor implements the above method when executing the computer program.

[0050] A non-transitory computer-readable storage medium stores a computer program, which implements the method described above when executed by a processor.

[0051] Compared with the prior art, the present invention and its preferred embodiments have at least the following beneficial effects:

[0052] 1. Significantly improve spectrum efficiency and fading resistance: By fusing user data through an XOR operation and utilizing the Plotkin recursive structure of polar codes to generate joint codewords, redundant transmissions are reduced while maintaining the same diversity gain, effectively overcoming deep fading caused by atmospheric turbulence.

[0053] 2. Enhanced system robustness: Dynamically switches between cooperative modes (full / partial / non-cooperative) based on the probability of channel interruption between users, adaptively adapting to complex channel environments and significantly reducing the risk of cooperative link failure.

[0054] 3. Optimizing decoding performance: The two-stage received signals are mapped into a layered log-likelihood ratio sequence (including components such as XOR values ​​and bit combinations). This is combined with the nested nature of polar codes to construct a joint decoding input, significantly improving decoding reliability and accelerating convergence.

[0055] 4. Realize refined resource management and control: Dynamically allocate power based on user distance (long-distance users receive higher power in the second phase), balance node energy consumption and link quality, and extend network lifecycle;

[0056] 5. Provide verifiable performance guarantee: Verify the decoding convergence speed through the mutual information transfer model to ensure that the system stably reaches the theoretical performance boundary in turbulent channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0058] Figure 1 This is a diagram of a coding collaboration system implementation model according to an embodiment of the present invention;

[0059] Figure 2 This is a comparison chart of outage probability curves of the JPCC solution and the SIC solution in an embodiment of the present invention;

[0060] Figure 3 This is a comparison chart of the EXIT curves of the JPCC solution and the APCC solution in an embodiment of the present invention;

[0061] Figure 4 This is a comparison chart of bit error rate curves of the JPCC scheme and the APCC scheme under different atmospheric turbulence intensities according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] In order to make the features and advantages of the present invention more clearly understood, the following embodiments are given for detailed description:

[0063] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this application belongs.

[0064] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0065] To overcome the effects of atmospheric turbulence on free-space optical communication systems, this paper employs coded cooperative communication technology and proposes a two-user joint polarimetric coding (JPCC) scheme based on polarization effects. Taking into account the imperfect nature of the inter-user channel, JPCC is carefully designed using a multi-level structure of polar codes. To reduce the probability of outage and improve the coding gain at the destination, the information set is jointly optimized using the concept of nested coding. The newly constructed joint codeword significantly improves the system's decoding performance.

[0066] This scheme, designed for FSO communication systems, aims to utilize polar coding cooperation to combat atmospheric turbulence attenuation. The scheme first studies the structural characteristics of polar coding and derives a combined codeword structure. By constructing new codewords, nested codewords based on information XOR are implemented to enhance the channel polarization effect. At the receiver, the LLR values ​​used for the joint decoder can be calculated using the XOR mapping rules of the nested codewords. Furthermore, based on the coded cooperation system, outage probability expressions for each user and system are derived, and an EXIT diagram is used to verify that the system has greater output mutual information, reflecting faster convergence and stronger bit error rate performance. Simulation results show that the proposed JPCC scheme significantly outperforms the baseline scheme in FSO communication systems, with decoding performance reaching 2.8 dB.

[0067] like Figure 1 As shown, the embodiment of the present invention provides a design and implementation process of the coding cooperation system based on polarization effect, including the following steps:

[0068] Step S1: In the FSO scenario, in the first stage, each user encodes and broadcasts its first block of data. , the base station receives the data blocks broadcast by each user, and the partner users receive the data blocks transmitted by the users respectively;

[0069] Step S2: The user decodes the data blocks of its partner users and adds the first block of data of each partner user and its own second block of data together using an XOR operation as the joint data block for the second stage transmission. ; The user thereby realizes joint network and channel coding of its own data and that of its partner users;

[0070] Step S3: Each user forwards the joint data block in the second phase; the base station receives the data block of each user in the first phase and receives the joint data block forwarded by each user in the second phase;

[0071] In step S4, the base station utilizes the inherent connection between the user data blocks received in steps S2 and S3 and performs joint decoding on these received data blocks based on the structural characteristics of the polar code. At the receiving end, LLR values ​​twice the length of the single-user code are obtained and substituted into the decoder for decoding to directly obtain the data block information of each user.

[0072] Step S5: The scheme is theoretically analyzed. The external information transfer curve verifies that the scheme can achieve faster convergence speed and stronger bit error rate performance. The outage probability of the scheme is derived, and the scheme (JPCC) is compared with the existing dynamic polar coding cooperation scheme (APCC).

[0073] The present invention is aimed at free-space optical (FSO) communication scenarios and innovatively utilizes the coding structure characteristics of polarization codes to combine the data information of two users, effectively realizing coding collaboration between users. A joint decoding method is adopted at the receiving end to directly obtain the data information of each user. Compared with the traditional SIC scheme, better decoding performance can be achieved. Compared with the existing APCC scheme, the system has a lower interruption probability and a higher amount of mutual information.

[0074] As a preferred solution of this embodiment, step S1 includes the following steps:

[0075] Step S11: In the FSO scenario, the linear coding characteristics of the polar code are used to ,user Information Encode each one first , .

[0076] Step S12, Plotkin construction is a distributed polar code construction method that is very suitable for multi-point coded cooperative systems. This method can generate two short polar codes from a long polar code. Assume that the index sets of information bits and frozen bits are marked as and ,according to It is worth noting that the generator matrix of the polar code, as shown in formula (1), naturally satisfies the Plotkin structure as shown in formula (2). and , then the polarization codeword can be obtained by generate.

[0077] (1)

[0078] (2)

[0079] in, Represents two short code words and v are connected to form a In the JPCC scheme proposed in this embodiment, each user Put it bit message encoded into the first data block In the first phase, the partner user (For example, ) is received and decoded. In the next stage, the user First, add the extra The information bits are encoded into Then, the decoded information of the partner user is combined with the Plotkin structure to construct a new data block. .

[0080] Step S13: Using the joint coding matrix The codewords of the two users in the two phases are jointly encoded. It can be observed that the Plotkin codeword structure is formed in the first and second phases of the user sending the codeword. Since the architecture of the two phases is similar, this embodiment derives the codeword structure at the two user nodes for illustration. Assuming that the total length is The polar code of , for the bit sequence Encode, where the encoding process is shown in formula (3). The coded codeword information is , the codeword information actually sent after encoding is After modulation, the signal is obtained , and distribute power , then the first block of data Broadcast transmission out.

[0081] (3)

[0082] Step S14: Through the atmospheric turbulence channel in the FSO scenario, the base station receives the superimposed data blocks from each user after the channel is attenuated, and the user end receives the data blocks from the partner user after the channel is attenuated.

[0083] As a preferred solution of this embodiment, step S2 includes the following steps:

[0084] Step S21: In the FSO scenario, in the joint polarization coding cooperation (JPCC) system based on polarization effect, at stage , the signal received by the base station or partner user can be expressed as:

[0085] (4)

[0086] in, Indicates the user sending data , Indicates the receiving end, if , it means the base station receives the information, otherwise it means the user end receives the information.

[0087] Step S22: After receiving the data information from the partner user, the user decodes it. The decoded information is re-encoded and network-coded with the second block of data information of the user, that is, the two blocks of information are XORed. Operation, get the joint coding data block transmitted by the user in the second phase .

[0088] As a preferred solution of this embodiment, step S3 includes the following steps:

[0089] Step S31: In the second stage, each user puts the joint data block The base station receives the jointly coded data block sent by each user in the second phase. The signal received by the base station in the second phase can be rewritten as:

[0090] (5)

[0091] Step S32: In the atmospheric turbulence channel, the weakened signals received by the base station in the two phases contain all the information of the two users, so the data block information of each user can be directly obtained by constructing a new joint decoder.

[0092] As a preferred solution of this embodiment, step S4 includes the following steps:

[0093] In step S41, the weakened signal received by the base station in step S2 and step S3 contains all the information of the two users. According to the coding structure characteristics of the polarization code, the intrinsic connection between the data blocks can be found. As shown in formula (4), in the FSO system, the signals received in the JPCC transmission scheme are naturally superimposed, which enables the receiving end to implement network coding. Specifically, the initial LLR value of the XOR codeword is obtained by adopting network coding mapping at the receiving end of the base station, and the base station focuses on the decoding in the first and second stages. Since the signals received by the two users are similar in the first stage, this embodiment uses the first user as the first LLR value. Take as an example to explain the network coding mapping rules of this scheme.

[0094] In the FSO system, the symbol set of the modulated signal is defined as Without considering the signal repetition, a superposition signal with equal probability of occurrence and total probability of 1 will be formed, and the received signal constellation is defined as The constellation of the base station receiving signal is defined as In the first stage, assume that each element exist There are equal prior probabilities in , In the known Under the conditions of The received value The probability can be expressed as:

[0095] (6)

[0096] Step S42: In the second phase, the constellation distribution remains similar. Therefore, the signal constellations received in the two phases can be combined into 16 combinations. Denotes the XOR codeword of the data blocks sent by two users in the first phase. Define L1 and L2 as codeword blocks respectively. 、 、 and Middle The initial LLR values ​​of the bits can be calculated using formula (7):

[0097] (7)

[0098] Step S43: Considering the codeword structure of the polar code series, constructing an initial LLR value of a joint two-user data block decoder should also conform to the joint codeword block series structure, that is, , the expanded formula is shown in (8):

[0099] (8)

[0100] because and are two sub-codewords in a polar code, so the LLR values ​​obtained above can be used for joint decoding of two users. It is input into a cyclic redundancy check-assisted SCL (CA-SCL) decoder to recover the information of each user.

[0101] As a preferred solution of this embodiment, step S5 includes the following steps:

[0102] Step S51: Next, assume The average received signal strength is higher than The goal of this project is to find Probability of system outage experienced at the base station , that is, the destination cannot restore the user The probability of the data.

[0103] The interruption performance of the destination depends in part on whether the inter-user channel is interrupted. For users The instantaneous signal-to-interference-plus-noise ratio (SINR) at , the interruption probability of the inter-user channel can be expressed as:

[0104] (9)

[0105] Step S52: For an imperfect inter-user channel, this solution has four cooperative diversity modes based on the transmission conditions in the second phase. When the inter-user channel is interrupted, the two users will resend information data blocks, which may cause the destination to receive duplicate data blocks, thus affecting the perfect cooperation between the users. Mode 1 represents a scenario where the two users fully cooperate, while Mode 4 represents a return to a non-cooperative state. In Mode 2, Unable to decode correctly In the first phase the data blocks are transferred, so In the second phase, only its own information block is sent. In contrast, in mode 3, Can be decoded correctly In the first phase the data blocks are transmitted, while Unable to decode correctly The data blocks transmitted in the first phase.

[0106] Assumptions Indicates that in stage ( ), where Indicates the index of the transmitter, Represents the index of the receiving end. Then, the user Total probability of experiencing a disruption at the destination They can be calculated as:

[0107] : (10) and (11)

[0108] : (12) and (13)

[0109] : (14) and (15)

[0110] : (16) and (17)

[0111] Step S53: Analyze the mutual information transferred between decoders through the external information transfer curve (EXIT graph) to predict the convergence characteristics of iterative decoding.

[0112] In the atmospheric turbulence channel, the prior log-likelihood ratio (LLR) value used as input to the decoder , which can be compared with the known transmission symbol Combined, through the Gaussian random variable To model:

[0113] (18)

[0114] in, is a Gaussian random variable. is also a Gaussian random variable with mean satisfy , and the variance ,in is the noise variance in the actual channel. Assume yes The observed value of The conditional probability density function (PDF) is:

[0115] (19)

[0116] According to the existing consistency conditions and proof conditions, The PDF satisfies:

[0117] (20)

[0118] Therefore, according to formula (19), Mutual information is defined as:

[0119] (twenty one)

[0120] The mutual information in formula (21) and standard deviation The functional relationship between them can be defined as:

[0121] (twenty two)

[0122] Because the function is a monotonically increasing continuous function, so its inverse function exists, which is recorded as:

[0123] (twenty three)

[0124] Will As the input LLR of the decoder, at the end of the iteration, the output LLR of the decoder is recorded as The corresponding mutual information It can be calculated by the following formula:

[0125] (twenty four)

[0126] Usually, in formula (24) The probability distribution of Can be measured by the histogram method. In order to facilitate the calculation, and They are all Gaussian distributions, and the geometric mean can be used to replace the statistical mean. Equations (21) and (24) can be approximated as:

[0127] (25)

[0128] (26)

[0129] in, It is transmission symbols The input prior LLR, is The corresponding output LLR. Equations (21) and (24) show that and The value range is limited to . And for a given , the decoder can calculate the corresponding Therefore, it can be seen that and The change from the mutual information of the prior likelihood ratio to the LLR value of the output external information reveals the external information transfer characteristics of the polar code decoder. , which is reflected as the EXIT curve, which is recorded as:

[0130] (27)

[0131] Step S54: To draw the EXIT curve of the polar code decoder, the prior mutual information As the independent variable, it starts from 0 and gradually increases to 1 in small steps. Then the corresponding standard deviation It can be calculated by the inverse function of formula (23).

[0132] Usually an approximate calculation is used to For the boundary Divided into two parts on the number axis, its approximate formula is the following piecewise expression:

[0133] (28)

[0134] The parameters are

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[0136] Sure back, The mean According to formula (18), the corresponding LLR value can be generated . Use it as the input prior LLR of the decoder, that is, initialize the elements of the last column in the left information matrix After the decoder iteration, the decoder output LLR is obtained:

[0137] (29)

[0138] Substitute it into formula (26) to calculate At this time, for a given , its corresponding Once it is determined, the EXIT curve can be drawn.

[0139] Compared with the existing technology, the embodiments of the present invention utilize the characteristics of the polar code encoding structure to combine user information. The transmitter first performs independent encoding, and then the receiver jointly decodes the received information using a joint coding matrix. When decoding the first user, the received superimposed information is XOR-mapped to directly obtain the LLR value of that user's codeword. For the remaining users, the LLR values ​​of the remaining users are obtained based on the characteristics of the polar code decoding structure. The obtained jointly decoded LLR values ​​are input into the decoder to directly obtain estimated information for each user. This is equivalent to constructing a corresponding long polar code, which not only improves the system's polarization effect but also enhances user decoding performance. In addition, by deriving the system's outage probability, simulations have verified that this system has a lower outage probability than existing traditional systems. EXIT diagrams also verify that the system has a higher output mutual information, demonstrating that the present invention has faster convergence speed and stronger bit error rate performance.

[0140] The following is a specific test example to verify the effect of the above solution of this embodiment:

[0141] This example simulates the performance of a two-user uplink coding cooperative system in an FSO communication system. The distances between the two users and the base station are , . Use code length , bit rate To ensure user fairness, the polarization code is used as follows: .

[0142] Figure 2 The outage probabilities of the JPCC solution and the SIC solution are compared. The figure compares the outage probability curves for User 1, User 2, and the system as a whole. The figure shows that the JPCC solution has a lower overall system outage probability than both the traditional SIC solution and the improved SIC solution.

[0143] Figure 3 The comparison of the EXIT curves of the JPCC scheme and the APCC scheme is shown in the figure. The gradual increase, It shows a monotonically increasing trend and eventually reaches a maximum value The blue curve of the JPCC decoder in the figure is closer to the upper left of the coordinate axis than the red curve of the APCC decoder, indicating that it can Higher output mutual information , and reach the upper bound faster , reflecting faster convergence speed and stronger bit error rate performance.

[0144] Figure 4 The figure compares the bit error rate curves of the JPCC scheme and the APCC scheme under different atmospheric turbulence intensities. The figure compares the decoding performance under different atmospheric turbulence intensities, where the atmospheric refractive index structure constants are , , As can be seen from the figure, the bit error rate of the JPCC scheme is Compared with the APCC scheme, the performance gains are 2 dB, 2.2 dB, and 2.8 dB respectively.

[0145] Based on the same inventive concept, the present invention also provides a computer device, which includes: one or more processors and a memory for storing one or more computer programs; the program includes program instructions, and the processor is used to execute the program instructions stored in the memory. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is used to implement one or more instructions, specifically for loading and executing one or more instructions in a computer storage medium to implement the above method.

[0146] It should be further explained that, based on the same inventive concept, the present invention also provides a computer storage medium having a computer program stored thereon, which, when executed by a processor, performs the above-described method. The storage medium may be any combination of one or more computer-readable media. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection having one or more conductors, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In the present invention, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0147] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0148] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

[0149] The present invention is not limited to the above-described preferred embodiment. Based on the teachings of the present invention, anyone can derive various other forms of a polarization code cooperation method in a free-space optical communication system. All equivalent changes and modifications made within the scope of the patent application of the present invention are intended to fall within the scope of the present invention.

Claims

1. A polarization code cooperation method in a free-space optical communication system, characterized by: Each user performs polarization encoding on its own first data block and broadcasts it. The base station receives the first data block of each user, and at the same time, each user receives the first data block of its partner user. Each user decodes the received first data block of the partner user, and performs an XOR operation on the decoded partner user data block and its own second data block to generate a joint data block; Each user performs polarization encoding on the joint data block and sends the result to the base station; Based on the data blocks received in two stages, the base station uses the nested structure of polar codes to construct a joint log-likelihood ratio sequence, and decodes it through a joint decoder to obtain the data information of each user.

2. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: The joint log-likelihood ratio sequence is obtained by calculating a joint constellation distribution of two-stage received signals, where the joint constellation distribution includes a joint probability mapping of four groups of original data of two users.

3. The polarization code cooperation method in a free-space optical communication system according to claim 2, wherein: The joint log-likelihood ratio sequence includes: The first component: the log-likelihood ratio of the XOR values ​​of the original data of two users in two stages; Second component: Joint log-likelihood ratio of the user's second-stage data bits; The third component: the log-likelihood ratio of the user's cross-user combination in the second stage; The fourth component: the log-likelihood ratio of the user's second-stage independent data; Each component is mapped to a different segment of the joint LLR sequence according to the nested structure of the polar code.

4. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: The polar coding adopts a recursive generator matrix structure, and the generator matrix satisfies the Plotkin construction; The joint data block is generated by XORing the partner user's decoded data and its own second data block.

5. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: The two user data are integrated through a joint coding matrix, which includes a recursive polar code sub-matrix and a zero matrix block, forming a block diagonal structure.

6. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: Dynamically select the cooperation mode based on the probability of channel interruption between users, including: Fully collaborative mode: two users decode and forward each other's data; Partial collaboration mode: only one user forwards the other party's data; Non-collaborative mode: Users retransmit their own data independently.

7. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: Dynamically allocate transmission power based on the channel gain from the user to the base station. For users whose channel gain is below a preset threshold, higher power is allocated in the second stage. The preset threshold is determined based on a path loss between the user and the base station.

8. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: The joint decoder verifies the decoding convergence speed through the mapping relationship between the prior mutual information and the output mutual information.

9. The polarization code cooperation method in a free-space optical communication system according to claim 1, wherein: The joint decoder adopts a serial cancellation decoding algorithm.

10. A coded cooperative system for free space optical communication, characterized in that: include: A plurality of user devices are configured to perform: Polarization-encode the first data block and broadcast it; receiving a first data block from a partner user and decoding the data; Performing an XOR operation on the decoded partner user data block and its own second data block to generate a joint data block; performing polarization encoding on the joint data block and sending the resultant data block; The base station device is configured to perform: receiving a first data block broadcast by each user equipment; receiving a joint data block sent by each user equipment; Based on the data blocks received in two stages, the nested structure of polar codes is used to construct a joint log-likelihood ratio sequence, which is then decoded by a joint decoder to obtain the data information of each user.

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