Combination multiple access method and system based on discrete affine fourier transform domain

Abstract

The present application relates to the technical field of wireless communication, and particularly relates to a combination multiple access method and system based on a discrete affine Fourier transform domain, the method comprising: adopting a base station and a plurality of users to set a downlink transmission scene, and dividing the users into a plurality of user groups; designing a hybrid multiple access structure based on the user groups, inputting a transmission signal of the base station into the hybrid multiple access structure, combining affine Fourier domain modulation DAFT domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access, and outputting a time domain signal; performing double-selectivity channel modeling on time domain signal transmission of any user in the user groups, and determining a corresponding time domain signal of a receiving end; obtaining a DAFT domain receiving signal of the time domain signal of the receiving end through DAFT transformation, and performing channel detection to obtain a result index corresponding to the transmission signal. The problems of limited OMA resource utilization and insufficient NOMA reliability in the affine Fourier domain system are effectively solved, and the AFDM downlink transmission in a high Doppler multi-user scene is balanced.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and specifically to a combined multiple access method and system based on the discrete affine Fourier transform domain. Background Technology

[0002] With the development of mobile communication technology, Orthogonal Frequency Division Multiplexing (OFDM) has become the main transmission method for 4G and 5G wireless systems. It utilizes Discrete Fourier Transform (DFT) to divide the spectrum into multiple orthogonal subcarriers, improving spectrum utilization. However, in high-speed mobile scenarios, OFDM is susceptible to the Doppler effect, resulting in inter-carrier interference (ICI), which degrades system performance. Furthermore, it requires strict orthogonality in the frequency domain, limiting its adaptability in high-frequency bands, large-scale access, and high-dynamic scenarios.

[0003] Against this backdrop, Affine Fourier Division Multiplexing (AFDM) emerged. It utilizes the Discrete Affine Fourier Transform (DAFT) domain to achieve signal modulation. A one-dimensional transformation can achieve Doppler resistance similar to OTFS (Orthogonal Time-Frequency Space Modulation), while also being compatible with OFDM, significantly reducing complexity. Therefore, AFDM is considered a promising air interface waveform for 6G and future wireless communication systems.

[0004] Furthermore, future mobile communication systems not only need to withstand high-speed mobility but also meet the demands of large-scale user access. Traditional orthogonal multiple access methods (such as OFDMA) rely on strict orthogonal resource allocation, which leads to a decrease in spectral efficiency in large-scale access scenarios. Non-orthogonal multiple access (NOMA), as a new type of multiple access technology, effectively improves system capacity by multiplexing multiple user signals on the same time-frequency resources. Depending on the multiplexing method, NOMA is mainly divided into power domain NOMA and code domain NOMA. Power domain NOMA allows different users to share the same resource block by layering the power domain and uses successive interference cancellation (SIC) for detection at the receiver. Code domain NOMA, on the other hand, distinguishes users through sparse codes or spreading codes.

[0005] Existing research indicates that combining NOMA with novel modulation schemes can further improve the spectral efficiency and anti-interference performance of a system; however, the combination of AFDM and NOMA, especially in power domain NOMA, remains a gap. In AFDM systems, the choice of multi-user access methods faces a significant trade-off between spectral efficiency and communication reliability. On the one hand, Orthogonal Multiple Access (OMA) effectively suppresses multi-user interference and ensures stable bit error rate performance by allocating non-overlapping resources to different users in the transform domain and setting guard bands; however, this method dedicates resources to each user, and the presence of guard bands results in low system spectral utilization, making it difficult to meet the transmission requirements of high-density user scenarios. On the other hand, Power-Domain Non-Orthogonal Multiple Access (NOMA) effectively improves spectral efficiency by superimposing multiple user signals on the same resource; however, in high-dimensional modulation systems like AFDM, due to the banded and cyclic characteristics of the equivalent channel in the DAFT domain, multi-user interference is easily spread, and the reliability of the continuous interference cancellation (SIC) process decreases significantly, especially with an increase in the number of users or a large Doppler spread, leading to a severe degradation in system bit error rate performance. Summary of the Invention

[0006] To address the technical problem in existing AFDM systems where the selection of access methods for multiple users cannot simultaneously balance spectral efficiency and communication reliability, this invention aims to provide a combined multiple access method based on the discrete affine Fourier transform domain. The specific technical solution adopted is as follows:

[0007] The downlink transmission scenario is deployed using base stations and several users, and the users are divided into multiple user groups;

[0008] Based on the user group design, a hybrid multiple access structure is designed. The base station's transmit signal is input into the hybrid multiple access structure, which combines affine Fourier domain modulation DAFT domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access to output a time domain signal.

[0009] Perform dual-selective channel modeling on the time-domain signal transmission of any user in the user group to determine the corresponding receiver time-domain signal;

[0010] The received signal in the DAFT domain is obtained by performing DAFT transformation on the time-domain signal at the receiving end, and channel detection is performed to obtain the result index corresponding to the transmitted signal.

[0011] Preferably, a downlink transmission scenario is deployed using a base station and several users, and the users are divided into multiple user groups, including:

[0012] The base station is defined as the transmitter and the user as the receiver, and the transmitter and receiver are integrated to form a downlink transmission scenario;

[0013] Design a user grouping algorithm based on Doppler sorting to divide users into multiple user groups.

[0014] Preferably, a user grouping algorithm based on Doppler sorting is designed to divide users into multiple user groups, including:

[0015] Integrate all users to create a user set, and collect the input parameters of each user;

[0016] Users are divided into two groups based on the number of users: the first user group and the ungrouped users.

[0017] Initial user pairs are formed based on ungrouped users. The input parameters of users in the initial user pairs are analyzed to obtain the weighted distance. Preset constraints are applied, and the weighted distance is combined with the analysis to construct the second user group.

[0018] The first user group and the second user group are integrated to form a user group set. The input parameters corresponding to each user group in the user group set are analyzed to identify weak channel users and strong channel users in the user group respectively, and the DAFT domain data range and guard band range of each user group are determined.

[0019] Preferably, the input parameters include the user's maximum Doppler frequency shift, the user's average channel gain, the total dimension of the DAFT domain, and the weighting coefficients.

[0020] Preferably, a hybrid multiple access structure is designed based on user groups. The base station's transmit signal is input into the hybrid multiple access structure, which combines affine Fourier domain modulation (DAFT) domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access to output a time-domain signal, including:

[0021] Output the set of resource indexes and corresponding constraints allocated to the user group in the DAFT domain based on the DAFT domain data range of the user group;

[0022] Based on the input parameters, the corresponding power allocation is performed on the weak channel users and strong channel users within the user group to obtain the superimposed signal of the user group in the DAFT domain;

[0023] By analyzing the superimposed signals, a DAFT matrix is ​​established through affine Fourier domain modulation, mapping the superimposed signals into time-domain signals.

[0024] Preferably, bi-selective channel modeling is performed on the time-domain signal transmission of any user in the user group to determine the corresponding receiver time-domain signal, including:

[0025] Perform biselective channel modeling on the time-domain signal transmission of any user in the user group to determine the discrete-time-delay channel impulse response of the corresponding user.

[0026] Based on the discrete-time-delay channel impulse response, the integer time delay is used to evaluate the noise interference on the time-domain signal. The effective CPP matrix and the user's channel gain matrix are obtained in sequence, and the corresponding receiver time-domain signal is determined by combining the time-domain signal.

[0027] Preferably, the received time-domain signal is transformed by DAFT to obtain the received signal in the DAFT domain, and channel detection is performed to obtain the result index corresponding to the transmitted signal, including:

[0028] The DAFT matrix is ​​obtained from the time-domain signal, and the DAFT transform is performed on the time-domain signal at the receiving end based on the DAFT matrix to obtain the received signal in the DAFT domain.

[0029] For the user corresponding to the received signal in the DAFT domain, construct the LMMSE detection matrix, and perform channel detection in combination with the SIC criterion to obtain the equivalent received signal of the user in the user group;

[0030] The SIC criterion is used to evaluate spectrum utilization for both weak-channel and strong-channel users.

[0031] Preferably, the SIC criterion is used to evaluate spectrum utilization for both weak-channel and strong-channel users, including:

[0032] Users with weak channels do not perform SIC, while users with strong channels perform SIC, which determines the reachable rate of the corresponding users.

[0033] Obtain the number of resource dimensions occupied by user groups in the DAFT domain and the corresponding guard band width, determine the proportion of effective available DAFT dimensions, and combine this with the user's reachable rate to obtain the spectrum utilization rate.

[0034] To address the aforementioned problems, this invention also provides a combined multiple access system based on the discrete affine Fourier transform domain. The system includes a processor, a communication interface, a memory, and a communication bus. The processor, communication interface, and memory communicate with each other via the communication bus. The processor calls logical instructions from the memory to execute the combined multiple access method based on the discrete affine Fourier transform domain described in any of the preceding claims.

[0035] The present invention has the following beneficial effects:

[0036] 1. For multi-user access methods of transmitted signals, a hybrid DAFT domain orthogonal and power domain NOMA multi-user access scheme is proposed. This scheme combines affine Fourier domain modulation DAFT domain orthogonal multiple access with intra-group power domain non-orthogonal multiple access. By grouping users in the transform domain and using orthogonal resource allocation, cross-group interference is suppressed. At the same time, power domain NOMA is introduced within the group to improve resource utilization. This achieves higher spectral efficiency while ensuring the reliability of affine Fourier domain modulation. This access method combines the characteristics of orthogonal and non-orthogonal multiple access and effectively solves the problem of limited resource utilization of pure OMA in affine Fourier domain (AFDM) systems by combining user group division. It provides a feasible compromise solution for AFDM downlink transmission in high Doppler multi-user scenarios.

[0037] 2. The combined multiple access system based on the discrete affine Fourier transform domain provided by this invention has the same beneficial effects as the combined multiple access method based on the discrete affine Fourier transform domain provided by this invention, and will not be elaborated here. Attached Figure Description

[0038] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart illustrating the steps of a combined multiple access method based on the discrete affine Fourier transform domain, provided in an embodiment of the present invention.

[0040] Figure 2 This invention provides a multi-user system framework with a hybrid multiple access structure based on a combined multiple access method in the discrete affine Fourier transform domain, as an embodiment of the present invention.

[0041] Figure 3 This is a schematic diagram of a user packet resource placement scheme corresponding to a user packet algorithm based on Doppler sorting, which is a combined multiple access method based on the discrete affine Fourier transform domain, provided in an embodiment of the present invention.

[0042] Figure 4 A schematic diagram showing a comparison between a user grouping algorithm based on Doppler sorting and existing algorithms provided in an embodiment of the present invention for a combined multiple access method based on the discrete affine Fourier transform domain;

[0043] Figure 5An example diagram illustrating the transmission of four user signals in a combined multiple access method based on the discrete affine Fourier transform domain, provided as an embodiment of the present invention;

[0044] Figure 6 This is a schematic diagram of a resource placement scheme for four users in a combined multiple access method based on the discrete affine Fourier transform domain, provided in an embodiment of the present invention.

[0045] Figure 7 A comparative simulation of four users using different methods in a combined multiple access method based on the discrete affine Fourier transform domain provided in one embodiment of the present invention. Figure 1 ;

[0046] Figure 8 A comparative simulation of four users using different methods in a combined multiple access method based on the discrete affine Fourier transform domain provided in one embodiment of the present invention. Figure 2 . Detailed Implementation

[0047] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a combined multiple access method and system based on the discrete affine Fourier transform domain proposed in accordance with the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0049] The following description, in conjunction with the accompanying drawings, details the specific scheme of the combined multiple access method and system based on the discrete affine Fourier transform domain provided by this invention.

[0050] Please combine Figure 1 and Figure 2 The first embodiment of the present invention provides a combined multiple access method based on the discrete affine Fourier transform domain, the method comprising:

[0051] Step S1: Deploy downlink transmission scenarios using base stations and several users, and divide users into multiple user groups;

[0052] Step S2: Design a hybrid multiple access structure based on user groups. Input the base station's transmit signal into the hybrid multiple access structure, combine affine Fourier domain modulation DAFT domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access, and output a time domain signal.

[0053] Step S3: Perform dual-selective channel modeling for the time-domain signal transmission of any user in the user group to determine the corresponding receiver time-domain signal;

[0054] Step S4: The received signal in the DAFT domain is obtained by DAFT transformation of the time domain signal at the receiving end, and channel detection is performed to obtain the result index corresponding to the transmitted signal.

[0055] To better illustrate, the Discrete Affine Fourier Transform Domain (DAFT) is a mathematical transformation framework used in signal processing. It combines affine transformation and discrete Fourier transform, expanding the analytical capabilities of traditional Fourier transform by introducing affine parameters corresponding to geometric operations such as translation, scaling, and rotation. This allows for better handling of non-stationary signals or signals with geometric deformations, and provides a more flexible frequency-space representation, enhancing adaptability to complex data and analytical accuracy. Multiple access methods, through specific signal processing and resource allocation mechanisms, allow multiple users to communicate simultaneously on the same channel or in the same spectrum, avoiding or reducing interference between them. Combining these two technologies optimizes resource allocation and signal separation between users, achieving efficient and reliable multi-user access.

[0056] Further, step S1 includes:

[0057] Step S11: Define the base station as the transmitter and the user as the receiver, and integrate the transmitter and receiver to form a downlink transmission scenario; that is, one base station transmits signals to several users at the same time to form a one-to-many communication architecture, so as to reflect the application mode of the downlink in the actual network.

[0058] Step S12: Design a user grouping algorithm based on Doppler sorting to divide users into multiple user groups.

[0059] It is explained that grouping users can achieve a trade-off between suppressing multi-user interference and improving resource reuse efficiency; that is, by grouping users, mutual interference between users can be reduced, signal transmission quality can be improved, and reasonable grouping can enable multiple users to share the same resource block, improve spectrum utilization efficiency, and optimize overall performance.

[0060] Please see Figure 3 Furthermore, step S12 includes:

[0061] Step S121: Integrate all users to establish a user set and collect the input parameters of each user.

[0062] As explained, in step S1, several users are defined as Create a user set, denoted as . Input parameters are collected for each user in the user set.

[0063] Furthermore, the input parameters include the user's maximum Doppler frequency shift, the user's average channel gain, the total dimension of the DAFT domain, and the weighting coefficients.

[0064] It can be noted that the maximum Doppler frequency shift for each user is denoted as . , indicating the first The maximum Doppler frequency shift per user, i.e., the maximum frequency shift caused by the Doppler effect when a user moves relative to the base station, is used to measure the impact of user mobility on communication quality; the average channel gain per user is denoted as... , indicating the first The average channel gain per user, i.e., the average signal enhancement allocated to each user in a transmission environment, measures the average increase in signal power after passing through the channel during signal transmission from the transmitter to the receiver; the total dimension of the DAFT domain is denoted as... This refers to the sum of all dimensions involved in a comprehensive evaluation of the signal; the weighting coefficient refers to the relevant parameters for subsequent user calculation of the weighted distance.

[0065] Step S122: Divide users according to the number of users to obtain the first user group and ungrouped users.

[0066] Specifically, based on the input parameters, the corresponding data is initialized, and the base station classifies users according to Channel State Information (CSI). There are multiple user groups, which correspond to multiple first user groups. Each group contains two users, denoted as... , indicating the first The first user group , They represent the first The first and second users in the first user group are identified; then, ungrouped users are determined based on the number of users. This is because, due to factors such as user mobility, multipath effects, and interference fluctuations, the channel state of some users may be at the boundary conditions of group division, making it difficult to strictly match the preset group criteria; all users not included in any first user group are integrated to form an ungrouped user set, denoted as . , This represents a set of users.

[0067] Step S123: Based on the ungrouped users, form initial user pairs, analyze the input parameters of the users in the initial user pairs to obtain the weighted distance, preset constraints, combine the weighted distance for analysis, and construct the second user group.

[0068] Specifically, based on the ungrouped user set obtained in step S122 above. In reality, when Then, the corresponding analysis is carried out, that is, arbitrarily selecting two ungrouped users from the ungrouped user set to form an initial user pair, denoted as . , Based on the weighting coefficients in the input parameters, the maximum Doppler frequency shift and average channel gain between each pair of users are analyzed to obtain the weighted distance. The corresponding calculation formula is as follows:

[0069]

[0070] in, Indicates the first The and the first Weighted distance between ungrouped users; , All represent weighting coefficients; , They represent the first The and the first Maximum Doppler shift for ungrouped users; , They represent the first The and the first Average channel gain for ungrouped users.

[0071] Next, set the constraints, that is... The initial user pairs that satisfy the constraints are denoted as one of the corresponding second user groups, and are referred to as... and never grouped user sets Remove two users from the initial user pair, according to the first... The and the first Similarly, ungrouped users are divided into sets of ungrouped users. For all users in the group, construct a second user group.

[0072] Step S124: Integrate the first user group and the second user group to form a user group set, analyze the input parameters corresponding to each user group in the user group set, identify weak channel users and strong channel users in the user group respectively, and determine the DAFT domain data range and guard band range of each user group.

[0073] As explained, the user group set formed by integrating the first user group and the second user group will be denoted as... , Represents the user group index; Indicates the number of user groups.

[0074] As an optional implementation, in this embodiment, to better describe the relevant users involved in the user group, a description method of the first user group is adopted, namely... Furthermore, each user group in the user group set is described using this parameter.

[0075] Specifically, based on user groups The two users in the user group are ranked according to the average channel gain, that is... Therefore For users with weak channels; For strong channel users; then, when using power-domain NOMA within a user group, to ensure the feasibility and stability of Successive Interference Cancellation (SIC), users within the group should have a certain average channel gain difference to enhance separability in the power domain; simultaneously, the guard band size between different user groups is related to the maximum Doppler shift of users within the group, based on the current... Each user group is described, and the corresponding guardrail width is obtained. The corresponding calculation formula is:

[0076]

[0077]

[0078] in, Indicates the first The width of the protection band for each user group; Indicates the maximum number of Doppler taps; ,

[0079] They represent the first The maximum Doppler shift of the first and second users in a user group; Indicates the fractional Doppler protection interval; This indicates the maximum number of delay taps.

[0080] Preferably, the fractional Doppler guard interval refers to a protection mechanism used to address the effects of Doppler frequency shift. By rationally designing the signal interval, the impact of frequency shift caused by relative motion on communication quality can be effectively reduced. In this embodiment, It can be configured according to the actual situation.

[0081] Next, in order to correctly separate interference between user groups, take If in order to improve the effect of SIC, Assigning two users with significant differences to the same group would lead to a waste of protection zone resources. Therefore, a user grouping algorithm based on Doppler sorting was designed.

[0082] Then, the DAFT domain is uniformly divided into Given a series of contiguous resource blocks, determine the length of each resource block. , Indicates the first The length of the resource block corresponding to each user group; Indicates the total dimension of the DAFT domain; Indicates the number of user groups; the first Each user group was assigned to a DAFT domain data range. The valid data range is: The corresponding protection zone range is .

[0083] Understandably, an analysis is conducted on user groups to establish a hybrid multiple access structure, namely AFDM-NOMA, which combines DAFT domain OMA and power domain NOMA within user groups. Among user groups, different user groups occupy non-overlapping resource blocks in the DAFT domain and achieve approximate orthogonality through guard bands. Within user groups, each user group uses power domain NOMA, and users are distinguished by power allocation and SIC.

[0084] Please see Figure 4 To better illustrate this point and verify the reliability of the designed user grouping algorithm based on Doppler sorting, it was compared with the exhaustive algorithm and random grouping algorithm in the prior art. It can be seen that the exhaustive algorithm gives an upper bound on the performance of spectral efficiency under constraints; the user grouping algorithm based on Doppler sorting approaches this upper bound with low complexity; while the random grouping algorithm suffers significant performance degradation because it cannot control guard overhead.

[0085] Further, step S2 includes:

[0086] Step S21: Output the set of resource indexes and corresponding constraints allocated to the user group in the DAFT domain based on the user group's DAFT domain data range; still based on the first step... This section describes a user group, assuming that the set of resource indexes allocated to this user group in the DAFT domain is as follows: The corresponding constraints are: This facilitates the subsequent overlay of DAFT fields in the feedback.

[0087] Step S22: Based on the input parameters, perform corresponding power allocation for weak channel users and strong channel users within the user group to obtain the superimposed signal of the user group in the DAFT domain.

[0088] Specifically, no. In each user group The modulation symbol vectors of the two users are respectively as follows: The base station allocates power to users within a user group based on the average channel gain, that is, it allocates power accordingly to users with weak channels and users with strong channels, satisfying the requirements of the base station. , , These represent the power allocation coefficients for the first and second users in the user group, respectively; thus, the power allocation coefficients for the first and second users in the user group are determined. The superimposed signals of each user group in the DAFT domain are calculated using the following formula:

[0089]

[0090] in, Indicates the first Superimposed signals of user groups in the DAFT domain; This indicates the total power of the signal transmitted by the base station.

[0091] Step S23: Analyze the superimposed signal, establish a DAFT matrix through affine Fourier domain modulation, and map the superimposed signal into a time domain signal.

[0092] Specifically, according to the first Similarly, the superimposed signals of all user groups in the DAFT domain are obtained, and the superimposed signals of all user groups are concatenated to form a signal of length [length missing]. The DAFT domain signal sequence, i.e. Construct the DAFT matrix, that is , , This indicates an adjustable parameter, therefore , These represent two adjustable parameters of AFDM; Represents a DFT matrix, with elements of , Represents the frequency domain index of the signal. Represents the time-domain index of the signal, meaning that the signals corresponding to both are from... These correspond to the row and column indices for time and frequency, respectively; additionally, in multi-user AFDM, adjustable parameters... The path separation requirements of the most demanding users must be met, i.e. The transmitter maps the DAFT domain signal to the time domain signal using AFDM modulation. The corresponding calculation formula is as follows:

[0093]

[0094] in, Represents a time-domain signal; Represents the DAFT matrix; This represents the DAFT domain signal.

[0095] Furthermore, step S3 includes:

[0096] Step S31: Perform biselective channel modeling on the time-domain signal transmission of any user in the user group to determine the discrete-time-delay channel impulse response of the corresponding user.

[0097] Specifically, let the user group's first The channel for each user is configured with a channel response time of [time value missing]. The time delay is of The path consists of several paths, which in turn determine the first path. The formula for calculating the discrete-time-delay channel impulse response for an individual user is as follows:

[0098]

[0099] in, Represents the discrete-time-delay channel impulse response; This represents the path index corresponding to the user; Indicates the number of paths; Indicates the first The first user's Channel gain of each path; Indicated by An exponential function with base 0; Indicates the first The first user's Doppler frequency shift along the path; Represents the impulse function; Indicates the first The first user's Integer delay for each path.

[0100] It can be explained that, That is, the first The Doppler frequency shift of the path is normalized with respect to the subcarrier spacing, and is expressed as: ,in, Indicates Doppler frequency shift The integer part, , Represents the largest integer Doppler; Indicates Doppler frequency shift The fractional part, .

[0101] Step S32: Output integer time delay based on discrete-time-delay channel impulse response, evaluate the noise interference on the time-domain signal through integer time delay, obtain the effective CPP matrix and the user's channel gain matrix in sequence, and determine the corresponding receiver time-domain signal in combination with the time-domain signal.

[0102] Specifically, integer delay, i.e. To evaluate the noise interference experienced by the time-domain signal, denoted as... First, an effective CPP (Channel Pulse Power) matrix is ​​established to accurately reflect the time delay characteristics and energy distribution of the signal along the propagation path, effectively filtering out incoherent components introduced by multipath effects and noise. The corresponding calculation formula is as follows:

[0103]

[0104] in, This represents the effective CPP matrix.

[0105] Next, based on the first The channel gain matrix is ​​established for each user, and the corresponding calculation formula is:

[0106]

[0107]

[0108]

[0109] in, Indicates the first Channel gain matrix for each user; This indicates the difference in Doppler frequency shift along the path; This represents the forward cyclic shift matrix.

[0110] Finally, determine the number The calculation formula for the time-domain signal of the receiver corresponding to each user is as follows:

[0111]

[0112] in, Indicates the first The receiving end time domain signal corresponding to each user; Represents a time-domain signal; This indicates the noise interference received.

[0113] Further, step S4 includes:

[0114] Step S41: Obtain the DAFT matrix from the time-domain signal, and perform DAFT transformation on the time-domain signal at the receiving end based on the DAFT matrix to obtain the received signal in the DAFT domain.

[0115] Specifically, the DAFT matrix is ​​obtained based on the aforementioned steps. And still based on the first The analysis is performed on the 1st user, and the receiver performs AFDM demodulation, i.e., DAFT transformation, to obtain the 1st user. The calculation formula for the received signal in the DAFT domain of an individual user is as follows:

[0116]

[0117]

[0118] in, Indicates the first Received signals in the DAFT domain of each user; This indicates that noise is also affected by the product of the demodulation matrix.

[0119] Understandably, in the proposed AFDM-NOMA, different user groups adopt orthogonal resource allocation within the DAFT domain, and a guard band is introduced between adjacent resource blocks. Therefore, under ideal conditions, the equivalent channel coupling term between different user groups is... It can be approximated as zero, and inter-group interference can be ignored; for two users within the same user group and Since they share the same DAFT domain resource blocks, the main source of interference is the non-orthogonal superposition of power domain signals from another user in the group, i.e., power domain NOMA interference. In addition, the received signal also contains additive white Gaussian noise (AWGN) and residual interference noise introduced by DAFT domain energy leakage under limited guard band conditions; therefore, in the AFDM-NOMA system under consideration, the main source of interference for each user can be attributed to the sum of the superposition of power domain signals and noise terms from users in the same group.

[0120] Step S42: Construct the LMMSE detection matrix for the user corresponding to the received signal in the DAFT domain, and perform channel detection in combination with the SIC criterion to obtain the equivalent received signal of the user in the user group.

[0121] The LMMSE (Linear Minimum Mean Square Error) detection matrix effectively suppresses noise and interference in the received signal by minimizing the mean square value of the estimation error, thereby improving the accuracy of signal detection and the overall performance of the system.

[0122] Specifically, based on the first The LMMSE detection matrix is ​​constructed for each user, and the corresponding calculation formula is as follows:

[0123]

[0124] in, Indicates the first LMMSE detection matrix for each user; Indicates the first Channel gain matrix for each user; Indicates the noise variance; Represents the identity matrix.

[0125] Next, according to the SIC criterion, the decoding order is for users with higher previously allocated power (i.e., users with lower channel gain). Layer-by-layer ideal SIC is used to eliminate interference from NOMA users. Based on the aforementioned steps, the power coefficient allocated to users within the same user group is... The decoding order is as follows: the first user is decoded, and the interference and noise from the other users are treated as interference; the remaining users first decode the signal decoded by the high-power user, and then decode their own signal; thus, the SIC sequence is followed by the user group... and The equivalent received signal is

[0126]

[0127]

[0128] in, , Representing users respectively and The equivalent received signal.

[0129] Step S43: Use the SIC criterion to evaluate spectrum utilization for weak channel users and strong channel users.

[0130] To clarify, spectrum utilization refers to the achievable sum of data rates for all users within a unit bandwidth, and its corresponding definition is:

[0131]

[0132] in, Indicates spectrum utilization rate; This indicates the total bandwidth occupied by the hybrid multiple access architecture AFDM-NOMA; Indicates the first The achievable rate for each user; Indicates the user index; Indicates the number of users.

[0133] It should be added that, in AFDM systems, since DAFT domain resources correspond one-to-one with time domain symbols, spectral efficiency can also be equivalently expressed as the normalized sum and rate across all DAFT dimensions.

[0134] Further, step S43 includes:

[0135] Step S431: Weak channel users do not perform SIC, strong channel users perform SIC, and the reachable rate of the corresponding users is determined.

[0136] Specifically, based on the first To explain for each user group, as can be seen from the preceding steps, For users with weak channels; For strong channel users, SIC is not performed; for weak channel users, the corresponding achievable rate is:

[0137]

[0138] Strong channel users perform SIC, which means that weak channel user signals are detected and eliminated through SIC. The corresponding achievable rate is:

[0139]

[0140] in, Indicates the user's reachable rate; Indicates the user's power allocation factor; This indicates the total power of the signal transmitted by the base station; Indicates the noise variance; Indicates user Equivalent channel gain on the corresponding allocated DAFT resource block.

[0141] Step S432: Obtain the number of resource dimensions occupied by the user group in the DAFT domain and the corresponding guard band width, determine the proportion of effective available DAFT dimensions, and obtain the spectrum utilization rate by combining the user's reachable rate.

[0142] Specifically, based on the aforementioned steps, the first... The number of resource dimensions occupied by each user group in the DAFT domain, i.e., the resource block length determined above. The corresponding protective strip width is The effective and usable DAFT dimension ratio is determined by the following formula:

[0143]

[0144] in, This indicates the proportion of valid and available DAFT dimensions.

[0145] Finally, based on the definition of spectral efficiency, the effective spectral efficiency of AFDM-NOMA is determined, and the corresponding calculation formula is as follows:

[0146]

[0147] in, This indicates the spectrum utilization rate.

[0148] Understandably, for multi-user access methods of transmitted signals, a hybrid DAFT domain orthogonal and power domain NOMA multi-user access scheme is proposed. This scheme combines affine Fourier domain modulation DAFT domain orthogonal multiple access with intra-group power domain non-orthogonal multiple access. By grouping users in the transform domain and using orthogonal resource allocation, cross-group interference is suppressed. At the same time, power domain NOMA is introduced within the group to improve resource utilization. This achieves higher spectral efficiency while ensuring the reliability of the affine Fourier domain modulation method. This access method combines the characteristics of orthogonal and non-orthogonal multiple access and effectively solves the problem of limited resource utilization of pure OMA in affine Fourier domain (AFDM) systems by combining user group division. It provides a feasible compromise solution for AFDM downlink transmission in high Doppler multi-user scenarios.

[0149] Please see Figure 5 To better illustrate this, a four-user system example is presented based on the combined multiple access method in the discrete affine Fourier transform domain proposed in this application. This system includes one base station (BS) and four user equipments (UE1, UE2, UE3, and UE4), where the channel gain between the user equipments and the base station is denoted as... Furthermore, users 1 and 3 are closer to the base station, while users 2 and 4 are farther away from the base station.

[0150] Specifically, the base station performs channel coding on the data from the four users separately. For example, it uses Low Density Parity Check (LDPC) coding, which improves data transmission reliability by introducing sparse parity checks into the information bits. The encoded bit sequence is then mapped to modulation symbol vectors, corresponding to... , , and The user equipment is grouped using a Doppler sorting-based user grouping algorithm: Group 1 includes users 1 and 2; Group 2 includes users 3 and 4. Following the power domain NOMA allocation strategy, different power allocation coefficients are assigned to the two groups, ensuring that the power allocation coefficients for two users within a group add up to 1. The modulation symbol vectors are then weighted and superimposed to obtain:

[0151]

[0152]

[0153]

[0154] A protective strip is placed between the two groups of resources, and the relevant parameters are determined, as shown in Table 1, the simulation parameter setting table.

[0155] Table 1 Simulation Parameter Settings

[0156]

[0157] Please see Figure 6 First, based on the parameters, through the formula Calculate the normalized Doppler frequency shift, where, Indicates user speed; Represents the speed of light; Indicates Doppler frequency shift; Represents the carrier frequency; according to the formula To obtain the maximum number of Doppler taps, This indicates the sampling period of the signal, and ;in, Indicates the maximum number of Doppler taps; Indicate the number of AFDM symbols; then, according to Determine the protection bandwidth for each user in the user group, i.e. , , and .

[0158] It should be noted that the grouping algorithm proposed in this solution will have better results when there are more users and more groups. For the sake of simplicity, the simulation only simulates the case of four users.

[0159] Then, the superimposed signal obtained above After AFDM modulation, it is mapped to the corresponding time-domain signal. After transmission through a dual-selective wireless channel, the receiver is affected by multipath fading, delay spread, and Doppler shift. This determines the user's corresponding receiver time-domain signal. At the receiving end, the time-domain signal is demodulated, that is, mapped from the time domain to the DAFT domain. Based on the grouping of the four users, the corresponding DAFT domain resources are extracted, i.e., the first half of the resources are extracted for group 1, and the second half of the resources are extracted for group 2. An LMMSE detection matrix is ​​then constructed for each user. Subsequently, intra-group SIC detection is performed for users within each group to remove intra-group interference. Taking users 1 and 2 in group 1 as an example, it is assumed that user 2 has low channel gain and high allocated power, so direct detection is performed. If User 1 has a high channel gain and low allocated power, then User 1 should be decoded first and the power should be canceled out. Then, it checks its own data to complete the overall operation of AFDM-NOMA.

[0160] Please see Figure 7Comparative tests were conducted using four users with different access methods. The PD-NOMA scheme, due to the complete power superposition of the four users on the same resource, experienced rapid accumulation of inter-user interference with Doppler spread under dual-selection channel conditions. Even at higher signal-to-noise ratios, the bit error rate remained at a high level, demonstrating a clear lower limit for bit errors. While the OMA scheme exhibited better bit error performance at low signal-to-noise ratios, its performance improvement came at the cost of sacrificing significant spectrum resources.

[0161] Please see Figure 8 The NOMA scheme combined with grouping in this application achieves a better trade-off between reliability and resource utilization, and its spectral efficiency is between that of the PD-NOMA scheme and the OMA scheme. Its advantage is that while ensuring that the bit error rate performance is significantly better than that of PD-NOMA, it avoids the overly conservative resource isolation method in the OMA scheme, so as to achieve higher effective spectral efficiency in the dual-selection channel environment. Therefore, the hybrid multiple access structure proposed in this application can achieve a more reasonable trade-off between reliability and spectral efficiency.

[0162] It can be seen from various simulation results that the AFDM-NOMA scheme can effectively achieve a trade-off between multi-user throughput and bit error rate in multi-user scenarios, and significantly improves the total throughput through the power domain multiplexing mechanism; at the same time, it effectively reduces the bit error rate and complexity in multi-user scenarios; therefore, it realizes a multi-user access scheme that balances spectrum efficiency and bit error rate in high-speed mobile scenarios.

[0163] The second embodiment of the present invention provides a combined multiple access system based on the discrete affine Fourier transform domain. The system includes a processor, a communication interface, a memory, and a communication bus. The processor, the communication interface, and the memory communicate with each other through the communication bus. The processor calls logical instructions in the memory to execute the combined multiple access method based on the discrete affine Fourier transform domain described in any embodiment of the present invention.

[0164] When it operates, it needs to use a combined multiple access method based on the discrete affine Fourier transform domain. Therefore, whether the system and program data are integrated or different hardware is configured to produce functions with similar effects to those achieved by this invention, they all fall within the protection scope of this invention. This system has the same beneficial effects as the combined multiple access method based on the discrete affine Fourier transform domain provided above, and will not be elaborated here.

[0165] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0166] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A combined multiple access method based on the discrete affine Fourier transform domain, characterized in that, The method includes: The downlink transmission scenario is deployed using base stations and several users, and the users are divided into multiple user groups; Based on the user group design, a hybrid multiple access structure is designed. The base station's transmit signal is input into the hybrid multiple access structure, which combines affine Fourier domain modulation DAFT domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access to output a time domain signal. Perform dual-selective channel modeling on the time-domain signal transmission of any user in the user group to determine the corresponding receiver time-domain signal; The received signal in the DAFT domain is obtained by performing DAFT transformation on the time-domain signal at the receiving end, and channel detection is performed to obtain the result index corresponding to the transmitted signal.

2. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 1, characterized in that, The downlink transmission scenario employs a base station and several users, and the users are divided into multiple user groups, including: The base station is defined as the transmitter and the user as the receiver, and the transmitter and receiver are integrated to form a downlink transmission scenario; Design a user grouping algorithm based on Doppler sorting to divide users into multiple user groups.

3. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 2, characterized in that, Design a user grouping algorithm based on Doppler sorting to divide users into multiple user groups, including: Integrate all users to create a user set, and collect the input parameters of each user; Users are divided into two groups based on the number of users: the first user group and the ungrouped users. Initial user pairs are formed based on ungrouped users. The input parameters of users in the initial user pairs are analyzed to obtain the weighted distance. Preset constraints are applied, and the weighted distance is combined with the analysis to construct the second user group. The first user group and the second user group are integrated to form a user group set. The input parameters corresponding to each user group in the user group set are analyzed to identify weak channel users and strong channel users in the user group respectively, and the DAFT domain data range and guard band range of each user group are determined.

4. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 3, characterized in that, The input parameters include the user's maximum Doppler frequency shift, the user's average channel gain, the total dimension of the DAFT domain, and the weighting coefficients.

5. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 3, characterized in that, Based on a user group-based hybrid multiple access structure, the base station's transmit signal is input into the hybrid multiple access structure, combining affine Fourier domain modulation (DAFT) domain orthogonal multiple access and intra-group power domain non-orthogonal multiple access to output a time-domain signal, including: Output the set of resource indexes and corresponding constraints allocated to the user group in the DAFT domain based on the DAFT domain data range of the user group; Based on the input parameters, the corresponding power allocation is performed on the weak channel users and strong channel users within the user group to obtain the superimposed signal of the user group in the DAFT domain; By analyzing the superimposed signals, a DAFT matrix is ​​established through affine Fourier domain modulation, mapping the superimposed signals into time-domain signals.

6. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 3, characterized in that, Perform biselective channel modeling on the time-domain signal transmission of any user in the user group to determine the corresponding receiver time-domain signal, including: Perform biselective channel modeling on the time-domain signal transmission of any user in the user group to determine the discrete-time-delay channel impulse response of the corresponding user. Based on the discrete-time-delay channel impulse response, the integer time delay is used to evaluate the noise interference on the time-domain signal. The effective CPP matrix and the user's channel gain matrix are obtained in sequence, and the corresponding receiver time-domain signal is determined by combining the time-domain signal.

7. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 6, characterized in that, The received time-domain signal is transformed using DAFT to obtain the received signal in the DAFT domain, and channel detection is performed to obtain the result indicators corresponding to the transmitted signal, including: The DAFT matrix is ​​obtained from the time-domain signal, and the DAFT transform is performed on the time-domain signal at the receiving end based on the DAFT matrix to obtain the received signal in the DAFT domain. For the user corresponding to the received signal in the DAFT domain, construct the LMMSE detection matrix, and perform channel detection in combination with the SIC criterion to obtain the equivalent received signal of the user in the user group; The SIC criterion is used to evaluate spectrum utilization for both weak-channel and strong-channel users.

8. The combined multiple access method based on the discrete affine Fourier transform domain according to claim 7, characterized in that, The SIC criterion is used to evaluate spectrum utilization for both weak-channel and strong-channel users, including: Users with weak channels do not perform SIC, while users with strong channels perform SIC, which determines the reachable rate of the corresponding users. Obtain the number of resource dimensions occupied by user groups in the DAFT domain and the corresponding guard band width, determine the proportion of effective available DAFT dimensions, and combine this with the user's reachable rate to obtain the spectrum utilization rate.

9. A combined multiple access system based on the discrete affine Fourier transform domain, characterized in that, The system includes a processor, a communication interface, a memory, and a communication bus. The processor, the communication interface, and the memory communicate with each other through the communication bus. The processor calls logical instructions in the memory to execute the combined multiple access method based on the discrete affine Fourier transform domain as described in any one of claims 1 to 8.

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