STAR-RIS assisted downlink NOMA system based on index enabling

Abstract

The invention relates to the technical field of wireless communication, and discloses an index enabling-based STAR-RIS auxiliary downlink NOMA system, which comprises a base station, an STAR-RIS and a plurality of pieces of user equipment. The base station selects a power distribution coefficient from a predefined power distribution matrix and performs rotation processing, and constructs a superposed signal by using the rotated coefficient; the STAR-RIS transmits and reflects signals to user equipment on different sides at the same time under a mode switching protocol; the far-end user equipment acquires additional information bits by jointly detecting the power level index and the modulation symbol, and the near-end user equipment sequentially detects far-end and own signals through a successive interference elimination process. According to the method, index modulation is introduced into the power domain, so that the information transmission dimension is expanded on the premise that the transmitting power and the modulation order are not increased, the spectrum efficiency of the system is remarkably improved, meanwhile, the communication reliability of edge users is improved, and the contradiction between the spectrum efficiency and the communication quality in a traditional STAR-RIS-NOMA system is effectively solved.

Description

Technical Field

[0001] This application relates to the field of wireless communication technology, specifically a STAR-RIS-assisted downlink NOMA system based on index empowerment. Background Technology

[0002] In the field of wireless communication technology, particularly for the high spectral efficiency and massive connectivity requirements of sixth-generation (6G) networks, the integration of reconfigurable intelligent surfaces (RIS) and non-orthogonal multiple access (NOMA) technologies is considered a key development direction. Among these, the simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) overcome the limitation of traditional RIS, which can only serve one side of the user base. STAR-RIS can dynamically adjust the wireless propagation environment, effectively expanding network coverage. Meanwhile, power-domain NOMA technology significantly improves the system's spectral efficiency and user access capacity by superimposing multiple user signals on the same resource block and supplementing it with successive interference cancellation (SIC) technology. To further explore the spectrum's potential, index modulation (IM) technology has been introduced into this system. It carries additional information bits by activating the index of a specific transmission entity (such as an antenna or sub-surface) without increasing power overhead. Existing research has explored various schemes for applying spatial domain indexed modulation in STAR-RIS-NOMA systems, such as embedding index information by selecting receiving antennas or dividing service sub-surfaces. These schemes have improved the spectral efficiency of the system to some extent.

[0003] However, current methods for integrating indexed modulation techniques into STAR-RIS-NOMA systems primarily focus on the utilization of resources in the spatial dimension, failing to fully explore the dimensions and degrees of freedom existing in the power domain. Specifically, after power allocation, the power factor in existing STAR-RIS-NOMA systems is typically fixed or adaptively adjusted based on channel conditions to differentiate users, but it is not further utilized as an effective information-carrying dimension. This limits the system's ability to transmit additional information, and further improvements in spectral efficiency face bottlenecks. Furthermore, to maintain specific spectral efficiency targets under traditional architectures, remote users are often forced to adopt higher-order modulation schemes, which, given their typically poor channel conditions, directly leads to a decrease in their reception reliability (e.g., bit error rate performance). Therefore, existing technologies present an inherent contradiction and technical challenge in how to improve system spectral efficiency while ensuring the quality of service for multiple users, especially remote users. Summary of the Invention

[0004] The purpose of this application is to provide an index-enabled STAR-RIS-assisted downlink NOMA system to solve the technical problems mentioned in the background art, and to achieve a synergistic improvement in spectral efficiency and transmission reliability in a downlink assisted by a smart metasurface that can simultaneously transmit and reflect.

[0005] To achieve the above objectives, this application discloses the following technical solution: an index-enabled STAR-RIS assisted downlink NOMA system, including a base station, STAR-RIS, and multiple user equipment; The base station is configured to: select a set of power allocation coefficients from a predefined power allocation matrix, the power allocation matrix including multiple sets of power allocation factors, rotate the selected set of power allocation coefficients, and construct a superimposed signal using the rotated power allocation coefficients and broadcast it to the STAR-RIS; The STAR-RIS is configured to operate under a mode switching protocol, simultaneously transmitting and reflecting the received superimposed signal to user equipment located on different sides of it; The user equipment includes a near-end user equipment located in the STAR-RIS reflection zone and a far-end user equipment located in the STAR-RIS transmission zone; the far-end user equipment is configured to simultaneously detect the power level index and modulation symbol from the received signal; the near-end user equipment is configured to perform a successive interference cancellation process, first detecting the signal of the far-end user equipment and then detecting its own signal; wherein, additional information bits generated by power level selection are allocated to the far-end user equipment.

[0006] Optionally, the STAR-RIS includes A passive component, The passive components are divided into Each sub-surface includes There are elements, among which , and All are positive integers, and each of the sub-surfaces is assigned to a user equipment.

[0007] Optionally, the power allocation matrix have Group power allocation factor, , It is a positive integer. Each power allocation factor includes power allocation coefficients for each user equipment, and for any power allocation factor, the sum of the power allocation coefficients of each user equipment it contains is 1.

[0008] Optionally, the rotation process is performed using a rotation matrix. To achieve the rotation matrix It is a diagonal matrix, and its diagonal elements are The rotated power distribution coefficient matrix Through formula Calculated.

[0009] Optionally, the superimposed signal is obtained through the formula Construction, in which Indicates the first Power distribution coefficient after rotation of each user equipment Indicates the first Modulation symbols for each user equipment This indicates the base station's transmit power. Indicates the index of the selected power allocation factor group. .

[0010] Optionally, the remote user equipment minimizes the objective function. Detection power level index and its own modulation symbol ,in This indicates the received signal of the remote user equipment. This indicates the cascaded channel response from the base station to the remote user equipment. This represents the power distribution coefficient of the remote user equipment after rotation.

[0011] Optionally, the successive interference cancellation process performed by the near-end user equipment includes: By minimizing the objective function Detect the power level index of the remote user equipment and modulation symbols ,in This indicates the received signal of the near-end user equipment. This represents the power distribution coefficient of the remote user equipment after rotation; From the received signal Subtract the detected signal component of the remote user equipment from the middle; By minimizing the objective function Detect its own modulation symbols ,in This represents the received signal after subtracting the signal component from the remote user equipment. This represents the power distribution coefficient of the near-end user equipment after rotation.

[0012] Optionally, the channel from the base station to the STAR-RIS and the channel from the STAR-RIS to each of the user equipments are both modeled as Rayleigh fading channels.

[0013] Optionally, the modulation symbols of the user equipment use pulse amplitude modulation.

[0014] Optionally, the number of additional information bits generated by the power level selection is: .

[0015] Beneficial Effects: The STAR-RIS-assisted downlink NOMA system based on index empowerment proposed in this application utilizes the selection and rotation of power allocation coefficients to carry additional information bits and allocate them to remote users, thereby synergistically improving spectral efficiency and transmission reliability at the system level. Compared with existing technologies, this scheme allows remote users to increase data transmission rates without relying on higher-order modulation formats, while also achieving better anti-interference capabilities due to the fact that its symbols can use low-order modulation; the rotation operation increases the distinguishability between different power combinations, enhancing the robustness of system detection; and ultimately, it effectively resolves the inherent contradiction in traditional schemes where the pursuit of spectral efficiency sacrifices the reliability of remote users, achieving a higher signal-to-noise ratio gain for users under the same bit error rate requirements. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a system block diagram of an index-enabled STAR-RIS-assisted downlink NOMA system provided in an embodiment of this application. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application. Secondly, in this document, the term "comprising" is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0019] Existing STAR-RIS-NOMA systems primarily achieve multi-user access through fixed or adaptive power allocation, but they fail to fully utilize the information carrying capacity of the power domain, resulting in limited spectral efficiency. Simultaneously, for remote users, poor channel conditions mean that using higher-order modulation to increase data rate significantly reduces reliability, creating an inherent conflict between spectral efficiency and communication quality. Therefore, a new information transmission mechanism is needed to expand the information dimension and improve the user experience at the edge without increasing energy consumption.

[0020] Therefore, this embodiment provides a method such as Figure 1 The STAR-RIS-assisted downlink NOMA system shown includes a base station, STAR-RIS, and multiple user equipment. The base station communicates with the multiple user equipment via STAR-RIS.

[0021] The base station is configured to: select a set of power allocation coefficients from a predefined power allocation matrix, the power allocation matrix including multiple sets of power allocation factors, rotate the selected set of power allocation coefficients, and construct a superimposed signal using the rotated power allocation coefficients and broadcast it to the STAR-RIS; The STAR-RIS is configured to operate under a mode switching protocol, simultaneously transmitting and reflecting the received superimposed signal to user equipment located on different sides of it; the user equipment includes a near-end user equipment located in the STAR-RIS reflection zone and a far-end user equipment located in the STAR-RIS transmission zone; the far-end user equipment is configured to simultaneously detect the power level index and modulation symbol from the received signal; the near-end user equipment is configured to perform a successive interference cancellation process, first detecting the signal of the far-end user equipment, and then detecting its own signal; wherein, additional information bits generated by power level selection are allocated to the far-end user equipment.

[0022] In this embodiment, the system consists of a single-antenna base station (BS) and a unit containing... The system consists of one passive unit STAR-RIS and two user equipment units, denoted as follows: (Near-end users) and (Remote users), both are equipped with a single receiving antenna. Assume the direct link from the BS to the user is blocked by an obstacle, and communication relies on STAR-RIS assistance. STAR-RIS is deployed between the BS and the user, supporting simultaneous transmission and reflection, and operates on a mode switching (MS) protocol, meaning each unit can be in either full transmission or full reflection state at any given time. Power allocation matrix. Include Possible power allocation combinations for the group ( Each group corresponds to a set of normalized power factors. ,satisfy ,and Indicates the first The base station uses the index of the group combination based on the data to be transmitted. The bit index information selects the corresponding row as the power allocation strategy for the current frame.

[0023] Subsequently, the coefficients are subjected to complex phase rotation to obtain the rotated matrix. ,in For the first The user in the first Rotational power coefficients within the group. The base station uses these coefficients to construct the superimposed signal: in For unit transmission power, For the first The modulation symbols for each user, by Pulse Amplitude Modulation (PAM) generation, satisfying The signal is amplified by the radio frequency front end and then sent to STAR-RIS. STAR-RIS divides it into... Each sub-surface serves one user and optimizes the phase of each unit based on channel state information. To maximize the cascaded channel gain. For the receiver, the remote user Due to its lower path loss, it enjoys a higher effective gain. Maximum likelihood detection is used to directly and jointly estimate the power index. and its own symbol Near-end users Decoding is required first. The signal is processed and interference is removed by SIC before decoding its own information. All channel state information is assumed to be known at the receiver and can be obtained through pilot training. In practical applications, the base station can use the general software radio platform USRP X310 in conjunction with MATLAB to implement baseband signal processing; this application does not limit this.

[0024] The system operates by encoding some information bits into the power allocation mode selection process to achieve Power Selection Index Modulation (PS-IM). The base station not only transmits information through modulation symbols but also implicitly conveys additional information by selecting which power allocation mode to use. STAR-RIS enhances the equivalent channel quality for users on both sides by directionally modulating electromagnetic waves. Far-end users directly detect composite signals using their higher received power, while near-end users use the SIC mechanism to filter out strong interference signals. The entire process enables multi-dimensional information fusion and transmission within the same resource block.

[0025] By adopting the above implementation method, the effective data rate and spectral efficiency of the system can be significantly improved without increasing the transmit power and modulation order. Since the index bits are allocated to remote users with poor channel conditions, throughput can be increased without employing high-order modulation, thus balancing spectral efficiency and transmission reliability. Theoretical analysis and simulation verification show that this scheme achieves a lower bit error rate compared to the traditional STAR-RIS-NOMA system. At this time, a signal-to-noise ratio gain of approximately 4dB or more can be obtained.

[0026] STAR-RIS includes A passive component, The passive components are divided into Each sub-surface includes There are elements, among which , and All are positive integers. This also refers to the number of user devices, and each of the sub-surfaces is assigned to one user device.

[0027] STAR-RIS is by Composed of several passive metamaterial units, arranged in a rectangular array (8×8 structure), the overall size is approximately .this Each unit is logically divided into Each sub-surface contains 1 sub-surface. Units.

[0028] The partitioning method is a physically contiguous partition: the first 32 units constitute sub-surface 1, serving near-end users in the reflective zone. The last 32 units constitute sub-surface 2, serving the distant users in the transmission zone. The reflection / transmission phase of each sub-surface is determined by a uniform diagonal phase matrix. Control, its diagonal elements Indicates the first The complex gain of each unit (amplitude 1, phase adjustable). The phase value is determined based on channel state information. and The design aims to minimize phase mismatch and enable the synthetic channel. Phase alignment is achieved to maximize the signal-to-noise ratio. In practical applications, the array can also employ staggered partitioning or other topologies, which are not limited in the embodiments of this application.

[0029] The purpose of this partitioning mechanism is to achieve user-level beamforming and resource isolation. Each sub-surface independently serves one user, avoiding cross-user interference, and facilitating the establishment of a clear cascaded channel model at the receiver, supporting subsequent SiC and joint detection.

[0030] This implementation enhances STAR-RIS's spatial multiplexing capability, ensuring optimal equivalent channel gain for each user, thereby improving overall system rate and fairness. Furthermore, the modular design reduces control complexity, facilitating engineering implementation.

[0031] The power allocation matrix has Group power allocation factor, , It is a positive integer. Each power allocation factor includes power allocation coefficients for each user equipment, and for any power allocation factor, the sum of the power allocation coefficients of each user equipment it contains is 1.

[0032] Power allocation matrix It is A real matrix of dimension, where This indicates the total number of available power combinations. A positive integer, determining the number of index bits that can be transmitted. For example, when hour, It can transmit 1 bit of index information; when hour, It can transmit 2 bits. Each row in the matrix represents a specific power allocation scheme, the first row being... The line represents the first Groups, in the form of:

[0033] in Indicates the first Group assigned to the first users ( The power ratio satisfies the following constraints: In a typical design, remote users Allocated higher power (i.e.) This ensures basic communication needs are met. All combinations are pre-stored in the base station's lookup table, and the baseband processor determines the combinations based on the input data stream. Bits select the corresponding row. For example, when At that time, the two groups can be set as follows:

[0034] In practical applications, The value of can be flexibly adjusted according to system requirements, and this application embodiment does not limit it.

[0035] The purpose of this matrix is ​​to construct a discrete power index space, so that each combination can not only distinguish users but also carry additional information. It is the fundamental structure for implementing PS-IM.

[0036] This implementation effectively expands the dimensions of information transmission and increases system throughput without increasing the symbol modulation order. Furthermore, by rationally designing the power ratios of each group, a balance can be achieved between performance and robustness.

[0037] Rotation processing is performed using a rotation matrix. To achieve the rotation matrix It is a diagonal matrix, and its diagonal elements are The rotated power distribution coefficient matrix Through formula Calculated.

[0038] Rotation matrix Defined as: That is, the first The diagonal elements are This matrix acts on the original power allocation matrix. Above, generate the rotated complex matrix: Among them, the first Behavior: here It is the first The user in the first The rotational power coefficient under the group is a complex number that includes both the original power amplitude and introduces a unique phase shift. This operation is performed in the base station's digital baseband processing unit, with complex multiplication operations executed by an FPGA or DSP chip. For example, when At that time, the four phases are respectively In practical applications, this phase sequence can also be replaced with other orthogonalization designs (such as the Walsh-Hadamard extension), and this application does not limit this.

[0039] The core function of this rotation mechanism is to enhance the Euclidean distance between different power combinations. Especially when the power ratios are similar, combinations that were originally difficult to distinguish become easier to identify due to phase differences, thereby reducing the probability of false detection.

[0040] This implementation method can significantly improve the detection accuracy of power index at the receiver, especially in low signal-to-noise ratio or multipath environments, and helps to reduce the overall bit error rate.

[0041] Superimposed signals are obtained through the formula Construction, in which Indicates the first Power distribution coefficient after rotation of each user equipment Indicates the first Modulation symbols for each user equipment This indicates the base station's transmit power. Indicates the index of the selected power allocation factor group. .

[0042] In this embodiment, the base station first determines based on Bit index information determines the currently used combined index. Then from the pre-stored rotation matrix Read the first OK Next, the modulation symbols of the two users are acquired. They come from -PAM and -PAM constellation set, for example (BPSK equivalent) Or 4. Set the transmit power (Normalization processing), constructing superimposed signals: The signal is a complex baseband signal, which is fed into a DAC to be converted into an analog signal, then up-converted to the millimeter-wave band (e.g., 28 GHz) and transmitted through a single antenna. The entire process is implemented in discrete time within the baseband processor, with a sampling rate set to 1 GS / s. In practical applications, the modulator can use the AD9361 transceiver chip from Analog Devices, which has the advantages of high integration and low power consumption; however, this application does not limit the specific implementation of this chip.

[0043] The function of this signal construction method is to transfer index information (through...) ) and content information (through Multidimensional modulation is achieved by integrating transmission within the same resource block.

[0044] By adopting this implementation method, constellation symbols and index bits can be transmitted simultaneously in a single signal, significantly improving spectral efficiency without increasing bandwidth or power overhead.

[0045] Remote user equipment minimizes the objective function Detection power level index and its own modulation symbol ,in This indicates the received signal of the remote user equipment. This indicates the cascaded channel response from the base station to the remote user equipment. This represents the power distribution coefficient of the remote user equipment after rotation.

[0046] remote users The received signal model is: in To from BS via STAR-RIS subsurface 2 to Cascaded channel response, This is the sum of noise and interference. Because... Will This is considered additive interference. The detection process involves traversing all possible... Combine and calculate the Euclidean distance:

[0047] and known locally and The decision is made based on statistical characteristics. This algorithm is executed by the user-side baseband processor and implemented using parallel comparison circuits or a Viterbi-like search. In practical applications, suboptimal detection algorithms (such as MMSE-SIC) can also be used to reduce complexity; this application does not limit the implementation in this regard.

[0048] The working principle of this detection mechanism is to make full use of the high power advantage and channel knowledge of the remote user, bypass the SIC process to directly obtain its own information and index bits, simplify the receiving process and improve anti-interference capability.

[0049] This implementation method can significantly reduce the decoding latency and error rate of remote users, and is particularly robust in high-load scenarios where SIC is prone to errors.

[0050] The successive interference cancellation process performed by the near-end user equipment includes: 1) By minimizing the objective function Detect the power level index of the remote user equipment and modulation symbols ,in This indicates the received signal of the near-end user equipment. This indicates the cascaded channel response from the base station to the near-end user equipment. This represents the power distribution coefficient of the remote user equipment after rotation; 2) From the received signal Subtract the detected signal component of the remote user equipment from the middle; 3) By minimizing the objective function Detect its own modulation symbols ,in This represents the received signal after subtracting the signal component from the remote user equipment. This represents the power distribution coefficient of the near-end user equipment after rotation.

[0051] Near-end users The received signal is: in , The SIC process is as follows: The first step is to iterate through all... Combinations, calculations: Find the most likely ; The second step is to reconstruct the interference items. and from Subtracting from the middle, we get the purification signal: The third step is to... Under the premise of demodulating its own symbols: The entire process relies on accurate channel estimation and power index identification. In practical applications, if SIC fails, a retransmission mechanism or soft combining strategy can be enabled; this application does not limit this approach.

[0052] The purpose of this SIC process is to retain the basic NOMA mechanism while incorporating joint detection capabilities for power index, ensuring that near-end users can correctly strip away strong interference signals.

[0053] This implementation method can effectively improve the decoding accuracy of near-end users, and can significantly reduce the risk of error propagation, especially when the power difference is moderate.

[0054] The channels from the base station to the STAR-RIS and from the STAR-RIS to each of the user equipment are both modeled as Rayleigh fading channels.

[0055] From BS to STAR-RIS The channel vector of each sub-surface is denoted as , its first The channel coefficients of each element are: in For path gain, For path loss per unit distance, The distance from BS to STAR-RIS This is the path loss index. and These represent the channel amplitude and phase, respectively, and both follow a Rayleigh distribution. Similarly, STAR-RIS to the user... The Channel vector of each sub-surface , its first The elements are: in , From B / S to user The distance, such as , All channels are independently and identically distributed, exhibiting frequency-flat slow fading. In practical applications, this model is suitable for non-line-of-sight (NLOS) urban microcell environments, but this application does not limit it to this specific scenario.

[0056] The purpose of this channel modeling method is to accurately reflect the wireless propagation characteristics and support subsequent performance analysis and simulation verification.

[0057] By adopting this implementation method, a theoretical basis that conforms to the actual scenario can be provided for system design, thereby enhancing the practicality and credibility of the solution.

[0058] The modulation symbols for user equipment use pulse amplitude modulation.

[0059] user and modulation symbols and Each by -PAM and -PAM modulation generation. For example, when At that time, the constellation point was ;when At that time, the constellation point was ,in Modulation is performed in the baseband, where a digital signal processor performs a lookup operation to generate a symbol stream. In practical applications, this modulator can be implemented using a Xilinx Zynq series SoC, offering both flexibility and real-time performance; however, this application does not limit the implementation in this regard.

[0060] The purpose of this modulation scheme is to match the channel quality of different users, so that users with high signal-to-noise ratio can use high-order modulation to improve the data rate, while users with low signal-to-noise ratio can use low-order modulation to ensure reliability.

[0061] By adopting this implementation method, dynamic resource adaptation can be achieved, improving spectrum utilization and system robustness.

[0062] The number of additional information bits generated by power level selection is .

[0063] Because the power allocation matrix contains Each group has a unique index, representing a different combination. Therefore, it can represent Bit information. For example, when When, 1 bit is transmitted; when At that time, 2 bits are transmitted. These bits are considered additional information and are specifically allocated to the remote user. This is considered part of its data stream. At the transmitting end, this... The bits come from the segmentation field of the higher-layer data packet; at the receiving end, Demodulation The information can then be restored. In practical applications, this number of bits can be dynamically configured according to business needs, and this application embodiment does not limit this.

[0064] The purpose of this design is to quantify information gain and clarify the extent of system capacity improvement.

[0065] By adopting this implementation method, the system throughput can be improved without increasing physical resources, and the gain increases with... It increases linearly.

[0066] In the embodiments provided in this application, it should be understood that the embodiments described herein can be implemented in hardware, software, firmware, middleware, code, or any suitable combination thereof. For hardware implementation, the processor may be implemented in one or more of the following: application-specific integrated circuits (ASICs), digital signal processors, digital signal processing devices, programmable logic devices, field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to implement the functions described herein, or combinations thereof. For software implementation, some or all of the processes of the embodiments may be performed by a computer program instructing the associated hardware. During implementation, the program may be stored in a computer-readable storage medium or transmitted as one or more instructions or code on a computer-readable storage medium. Computer-readable storage media include computer storage media and communication media, wherein communication media include any medium that facilitates the transfer of a computer program from one place to another. Storage media may be any available medium accessible to a computer. Computer-readable storage media may include, but are not limited to, random access memory, solid-state memory, electrically erasable programmable read-only memory, read-only optical disk storage or other optical disk storage, magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible to a computer.

[0067] Finally, it should be noted that the above description is only a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A STAR-RIS-assisted downlink NOMA system based on index empowerment, characterized in that, This includes base stations, STAR-RIS, and multiple user equipment. The base station is configured to: select a set of power allocation coefficients from a predefined power allocation matrix, the power allocation matrix including multiple sets of power allocation factors, rotate the selected set of power allocation coefficients, and construct a superimposed signal using the rotated power allocation coefficients and broadcast it to the STAR-RIS; The STAR-RIS is configured to operate under a mode switching protocol, simultaneously transmitting and reflecting the received superimposed signal to user equipment located on different sides of it; The user equipment includes a near-end user equipment located in the STAR-RIS reflection zone and a far-end user equipment located in the STAR-RIS transmission zone; the far-end user equipment is configured to simultaneously detect the power level index and modulation symbol from the received signal; the near-end user equipment is configured to perform a successive interference cancellation process, first detecting the signal of the far-end user equipment and then detecting its own signal; wherein, additional information bits generated by power level selection are allocated to the far-end user equipment.

2. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 1, characterized in that, The STAR-RIS includes A passive component, The passive components are divided into Each sub-surface includes There are elements, among which , and All are positive integers, and each of the sub-surfaces is assigned to a user equipment.

3. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 2, characterized in that, The power allocation matrix have Group power allocation factor, , It is a positive integer. Each power allocation factor includes power allocation coefficients for each user equipment, and for any power allocation factor, the sum of the power allocation coefficients of each user equipment it contains is 1.

4. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 3, characterized in that, The rotation process is performed through a rotation matrix. To achieve the rotation matrix It is a diagonal matrix, and its diagonal elements are The rotated power distribution coefficient matrix Through formula Calculated.

5. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 4, characterized in that, The superimposed signal is obtained through the formula Construction, in which Indicates the first Power distribution coefficient after rotation of each user equipment Indicates the first Modulation symbols for each user equipment This indicates the base station's transmit power. Indicates the index of the selected power allocation factor group. .

6. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 5, characterized in that, The remote user equipment minimizes the objective function. Detection power level index and its own modulation symbol ,in This indicates the received signal of the remote user equipment. This indicates the cascaded channel response from the base station to the remote user equipment. This represents the power distribution coefficient of the remote user equipment after rotation.

7. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 5, characterized in that, The successive interference cancellation process performed by the near-end user equipment includes: By minimizing the objective function Detect the power level index of the remote user equipment and modulation symbols ,in This indicates the received signal of the near-end user equipment. This indicates the cascaded channel response from the base station to the near-end user equipment. This represents the power distribution coefficient of the remote user equipment after rotation; From the received signal Subtract the detected signal component of the remote user equipment from the middle; By minimizing the objective function Detect its own modulation symbols ,in This represents the received signal after subtracting the signal component from the remote user equipment. This represents the power distribution coefficient of the near-end user equipment after rotation.

8. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 1, characterized in that, The channels from the base station to the STAR-RIS and from the STAR-RIS to each of the user equipment are both modeled as Rayleigh fading channels.

9. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 1, characterized in that, The modulation symbols of the user equipment use pulse amplitude modulation.

10. The STAR-RIS-assisted downlink NOMA system based on index empowerment according to claim 3, characterized in that, The number of additional information bits generated by power level selection is: .

Images