Self-adaptive non-orthogonal multiple access relay transmission method and system based on space-time coding in large-scale network

Abstract

The invention relates to a space-time coding-based adaptive non-orthogonal multiple access relay transmission method and system in a large-scale network, and the method comprises the steps: assisting two remote users to transmit data to a base station by two relay nodes in each cellular cell; the whole transmission process comprises a plurality of continuous equal-length time blocks, and each time block is divided into two stages: in the first stage, two far-end users occupy the same frequency band at the same time to broadcast respective data, and two relay nodes demodulate the data of the two far-end users from received mixed signals by using an SIC technology; and in the second stage, the two relay nodes adaptively select different transmission modes according to own demodulation conditions, and forward the demodulated data of the two far-end users to the base station, and the base station demodulates the data of the two far-end users by adopting maximum ratio merging and SIC technologies. According to the method, the uncertainty of a channel can be better dealt with, the robustness and efficiency of data transmission are improved, and services with higher quality are provided for users.

Description

Technical Field

[0001] The present invention relates to an adaptive non - orthogonal multiple access relay transmission method and system based on space - time coding in a large - scale network, belonging to the field of wireless communication technology. Background Art

[0002] In a traditional orthogonal multiple access (OMA) communication system, multiple users occupy mutually orthogonal physical resources to transmit signals. It is relatively easy for the receiver to distinguish the data of different users. However, this access method fails to fully utilize the spectrum resources and limits the number of accessible users. Non - orthogonal multiple access (NOMA) uses superposition coding technology to simultaneously transmit the information of multiple users on the same physical resources, effectively improving the spectral efficiency (SE) of the system and the network user capacity. NOMA schemes are generally divided into power - domain NOMA and code - domain NOMA. In power - domain NOMA, the transmitter superimposes the data of different users according to a certain power ratio to form a composite signal and performs wireless broadcasting. The receiver uses successive interference cancelation (SIC) technology to demodulate the required data from the received mixed signal. Alamouti coding is a space - time coding technology that can orthogonalize the channel matrix without the transmitter knowing the channel state information. By obtaining spatial diversity gain, it can effectively combat the influence of multipath fading and co - channel interference and improve the signal transmission quality and efficiency. In a multi - user wireless communication system, by introducing relay nodes, the long communication link can be divided into multiple hops, reducing the path loss of each hop, lowering the transmission power, reducing link interference, and improving the reliability and data throughput of communication. Cooperative relay is a way to assist in communication with the help of relay nodes. Without increasing the number of antennas of a single node, it can obtain spatial diversity effects and effectively combat adverse factors such as deep channel fading, obstacle blocking, and path loss.

[0003] Power-domain NOMA effectively improves spectral efficiency and network user capacity through superposition coding technology. However, it relies on successive interference cancellation (SIC) technology, which is difficult to effectively distinguish user signals with similar signal strengths and rates, and is prone to error propagation in multi-user scenarios. Traditional relay transmission methods can reduce path loss in multi-hop communication, but relay node selection and resource allocation strategies often lack adaptability and are difficult to cope with dynamic network environments and user requirements. Although existing space-time coding technologies can provide spatial diversity gain, their coding efficiency and decoding complexity still need to be optimized in complex scenarios with multiple users and multiple relays. Moreover, the impact of full frequency reuse in large-scale networks on NOMA, optimal relay node selection, and space-time coding is not clear. Therefore, there is an urgent need to design an adaptive non-orthogonal multiple access relay transmission method based on space-time coding for large-scale networks to improve communication reliability and data throughput while ensuring high spectral efficiency and user capacity. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology and to meet the data transmission requirements of remote users in the cell with high quality and significantly improve the spectral efficiency and robustness of wireless communication, the present invention proposes an adaptive NOMA relay transmission method based on Alamouti space-time coding in a large-scale network.

[0005] To enhance the robustness of data transmission and make full use of existing spectral resources, the present invention proposes an adaptive NOMA relay transmission method based on Alamouti coding for large-scale networks. The present invention models the random position distribution of base stations in large-scale cellular networks using stochastic geometry theory, constructs an aggregate interference model under full frequency reuse, analyzes the average success probability and throughput of base stations receiving data, and jointly optimizes time and power allocation to maximize system throughput.

[0006] The present invention studies the impact of key parameters on system performance through a large number of simulations. Compared with the benchmark transmission strategy, the present invention can significantly improve the system average throughput. The research results help guide the design of efficient transmission mechanisms for large-scale networks, guide the implementation of NOMA relay transmission of multiple users' data using Alamouti space-time coding technology, contribute to the realization of spectrum-efficient and green sustainable communication, and have important theoretical significance and application value.

[0007] The present invention also proposes an adaptive non-orthogonal multiple access relay transmission system based on space-time coding in a large-scale network.

[0008] Term Explanation:

[0009] 1. Large-scale network: It refers to a network that covers the entire two-dimensional plane. The network contains a large number of base stations and mobile users. Due to the influence of population distribution, geographical environment, etc., the location distribution of base stations has a certain randomness, and the location distribution of mobile users is random. In order to improve the spectral efficiency in the network, full frequency reuse technology is adopted between different cells.

[0010] 2. SIC technology: Successive Interference Cancellation. Successive interference cancellation technology is a signal processing technology used in wireless communication systems, mainly for multi-user environments. The receiver gradually demodulates the signals of target users by successively decoding and canceling stronger interference signals. SIC technology can significantly improve the spectral efficiency and user capacity of the system.

[0011] 3. MRC method: Maximum Ratio Combining. Maximum ratio combining is a signal combining technology used in multi-antenna receiving systems. Based on knowing the channel state information, the receiver weights and combines the signals from different antennas to maximize the signal-to-noise ratio, thereby improving the quality of the received signal.

[0012] 4. Cellular cell: It is the basic geographical coverage unit of a mobile communication network. Each cellular cell is responsible for providing wireless signal coverage by a base station. Its name comes from the honeycomb-like network layout design. By dividing the service area into multiple hexagonal cells, frequency reuse and efficient coverage are achieved.

[0013] The technical solution of the present invention is as follows:

[0014] An adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network, including:

[0015] In each cellular cell, two relay nodes assist two remote users in transmitting data to the base station. The relay nodes adaptively adjust the transmission mode according to their own demodulation situations, so as to realize the communication between the two remote users and the base station; the entire transmission process includes multiple consecutive and equal-length time blocks (Time Block), and each time block is divided into two stages:

[0016] In the first stage, the two remote users simultaneously occupy the same frequency band to broadcast their respective data, and the two relay nodes use SIC technology to demodulate the data of the two remote users from the received mixed signals.

[0017] In the second stage, the two relay nodes adaptively select different transmission modes according to their own demodulation situations, and forward the demodulated data of the two remote users to the base station. The base station uses maximum ratio combining (Maximal Ratio Combining, MRC) and SIC technology to demodulate the data of the two remote users.

[0018] Preferably according to the present invention, two remote users U 1 and U 2 transmit data to the base station BS with the help of relay nodes R 1 and R 2 ; the duration of each time block is normalized to 1 second; each time block is divided into a first stage and a second stage by using a time allocation factor β, 0 < β < 1, and the durations are β and 1 - β respectively;

[0019] In the first stage, the two relay nodes use SIC technology to demodulate the data of the two remote users from the received mixed signal; including: first demodulating the data of remote user U 1 's data, at this time regarding the data of remote user U 2 as interference, after demodulating the data of remote user U 1 's data, deleting the data of remote user U 1 from the mixed signal, and then demodulating the data of remote user U 2 's data;

[0020] In the second stage, 7 transmission modes are set, and the two relay nodes adaptively select the best transmission mode to forward the data of the remote users to the base station BS;

[0021] If the base station BS receives the data of the two remote users, it uses SIC technology to demodulate the data of the two remote users; the SIC demodulation method is: first demodulating the data of remote user U 1 's data, at this time regarding the data of remote user U 2 as interference, after demodulating the data of remote user U 1 's data, deleting the data of remote user U 1 from the mixed signal, and then demodulating the data of remote user U 2 's data;

[0022] If BS receives the data of a single remote user, it uses the MRC method to demodulate the user data.

[0023] Preferably according to the present invention, in the first stage, after R 1 receives the mixed signal from the two users, it first tries to demodulate the data of U 1 , and the signal to interference plus noise ratio (SINR) of the data of U 1 is denoted as Expressed as:

[0024]

[0025] Wherein, and Denote the distances of U associated with the typical base station x 0 and U 1 to the typical cell R 2 and R 1 as; 2 the distance; and respectively denote the small-scale power fading of the channels between U 1 and U 2 and R 1 ; σ 2 is the power of additive white Gaussian noise (AWGN). Two remote users U 1 and U 2 occupy the same frequency band and transmit signals simultaneously, with powers of and

[0026] The total interference caused by other users to R 1 is:

[0027]

[0028] wherein, and represent the distances of U b and U 0 associated with BSx ∈ Φ 1 and U 2 to R 1 and R 2 in the typical cell, and represent the large-scale path loss between them; and respectively denote the small-scale power fading of U b and U 0 associated with BSx ∈ Φ 1 and U 2 to R 2 in the typical cell; Y x represents the distance from BSx ∈ Φ b / {x 0} to the typical base station x 0 ; Since the base stations are sparsely distributed in the two-dimensional plane and the average distance between different base stations is much larger than the communication distance within each cell, it is assumed that

[0029] If R 1 successfully demodulates and cancels the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as Expressed as:

[0030]

[0031] and respectively represent the small-scale power fading of U 1 and U 2 to R 2 in this typical cell; R 2 first attempts to demodulate the data of U 1 At this time, the SINR is denoted as Expressed as:

[0032]

[0033] where the total interference caused by other users to R 2 is:

[0034]

[0035] and represent the small-scale power fading between U b / {x 0} associated with BS x∈Φ 1 and U 2 to the typical cell R 2 ; If R 2 successfully demodulates and eliminates the data of U 1 then the SINR for demodulating the data of U 2 is denoted as Expressed as:

[0036]

[0037] According to the preferred embodiment of the present invention, in the second stage, 7 transmission modes are set, and two relay nodes adaptively select the best transmission mode to forward the data of the remote user to the base station BS; including:

[0038] The first case: When R 1 successfully demodulates the data of U 1 and U 2 and R 2 successfully demodulates the data of U 1 the two relay nodes use the NOMA method based on Alamouti coding to send signals to BS;

[0039] After BS receives the mixed signal, it first attempts to demodulate the data of U 1 After successful demodulation, the data of U 1 is deleted from the mixed signal, and then U2 Data; Each relay node is assigned the same power P r to forward user data; R 1 and R 2 perform Alamouti coding on the data of U 1 Meanwhile, R 1 superimposes the data of U 2 onto the Alamouti-coded signal to obtain a composite signal, and sends the composite signal to BS; R 1 The power of the signal sent by U 1 is ρP r , 0 < ρ < 1, R 1 The power of the signal sent by U 2 is (1 - ρ)P r Meanwhile, R 2 uses the power P r to send the signal of U 1 ;

[0040] In two consecutive time slots, map the two symbols 1 in U onto the transmit antennas and assume that the small-scale channel powers of the two relays fading to BS are and n 1 and n 2 are the interference and noise powers in the two time slots respectively; The signals received by BS are denoted as r 1 and r 2 , then:

[0041]

[0042] BS first attempts to demodulate the data of U 1 At this time, regarding the data of U 2 as interference, the SINR is denoted as which is expressed as:

[0043]

[0044] where and represent the small-scale power fades between R 1 and R 2 to the typical base station x 0 in a typical cell, Y r represents the distance from R 1 and R 2 to the typical base station x 0 in a typical cell;

[0045] The total interference caused by other users to the BS is:

[0046]

[0047] Among them, and represent the events of data forwarding by R b / {x 0} associated with BSx∈Φ 1 and R 2 ; and represent the small-scale power fading between R b / {x 0} associated with BSx∈Φ 1 and R 2 to the typical base station x 0 ; Y x(r) is the distance between R b / {x 0} associated with BSx∈Φ 1 and R 2 to the typical base station x 0 ; Since the base stations are sparsely distributed in the two-dimensional plane and the average distance between different base stations is much larger than the communication distance within each cell, it is assumed that Y x(r) ≈Y x ;

[0048] If the BS successfully demodulates and cancels the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as and expressed as:

[0049]

[0050] The second case: When R 1 only successfully demodulates the data of U 1 , and R 2 successfully demodulates the data of U 1 and U 2 , R 1 and R 2 perform Alamouti coding on the data of U 1 , and at the same time R 2 superimposes the data of U 2 onto the signal after Alamouti coding to obtain a composite signal, and sends this composite signal to the BS; R 1 and R 2 send the data of U 1 using Alamouti coding, where R 1 uses the power of P r to send the data of U1 The data of R 2 Use ρP r To transmit U with the power of 1 The data of R 2 Use (1 - ρ)P r To superimpose the data of U with the power of 2 Onto the encoded data of U 1 At this time, the BS demodulates U 1 The SINR of the data is denoted as Expressed as:

[0051]

[0052] If the BS successfully demodulates and eliminates the data of U 1 Then the SINR of the data of U 2 Is denoted as Expressed as:

[0053]

[0054] The third case: When R 1 Successfully demodulates the data of U 1 And U 2 The data of R 2 When the user data is not successfully demodulated by R 1 R adopts the NOMA method to superimpose the data of U 1 And U 2 Into a composite signal and send it to the BS; Among them, R 1 Uses ρP r To transmit the data of U with the power of 1 Uses (1 - ρ)P r To transmit the data of U with the power of 2 At this time, the BS demodulates U 1 The SINR of the data is denoted as Expressed as:

[0055]

[0056] If the BS successfully demodulates and eliminates the data of U 1 Then the SINR of the data of U 2 Is denoted as Expressed as:

[0057]

[0058] The fourth case: When R 2 Successfully demodulates the data of U 1 And U 2 The data of R 1 When the user data is not successfully demodulated by R 2Using the NOMA method, the data of U 1 and U 2 are superimposed into a composite signal and sent to the BS; R 2 uses the power of ρP r to send the data of U 1 and uses the power of (1 - ρ)P r to send the data of U 2 ; At this time, the SINR of the BS demodulating the data of U 1 is denoted as and is expressed as:

[0059]

[0060] If the BS successfully demodulates and cancels the data of U 1 , then the SINR of the BS demodulating the data of U 2 is denoted as and is expressed as:

[0061]

[0062] The fifth case: When both R 1 and R 2 only successfully demodulate the data of U 1 , at this time, according to the states of the transmission channels of the two relay nodes fed back by the BS, the relay node with the best channel to the BS is selected to send the data of U1 with the power of P r ; The SINR of the BS demodulating the data of U 1 is denoted as When is better than , is the same as and is Conversely, is the same as and is

[0063] The sixth case: If R 1 only successfully demodulates the data of U 1 , and R 2 does not successfully demodulate the user data, then R 1 uses the power of P r to send the data of U 1 ; At this time, the SINR of the BS demodulating the data of U 1 is denoted as and is expressed as:

[0064]

[0065] The seventh case: If R 2 only successfully demodulates the data of U 1 ​1 When the user data is not successfully demodulated, R 2 Use P r to transmit the data of U 1 ; At this time, the BS demodulates the U 1 The SINR of the data is denoted as Expressed as:

[0066]

[0067] A computer device includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the steps of an adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network are implemented.

[0068] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the steps of an adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network are implemented.

[0069] An adaptive non-orthogonal multiple access relay transmission system based on space-time coding in a large-scale network. In each cellular cell, two relay nodes assist two remote users in transmitting data to the base station. The relay nodes adaptively adjust the transmission mode according to their own demodulation conditions, so as to realize the communication between the two remote users and the base station; including:

[0070] The first stage module is configured to: two remote users simultaneously occupy the same frequency band to broadcast their respective data, and two relay nodes use the SIC technology to demodulate the data of the two remote users from the received mixed signal;

[0071] The second stage module is configured to: two relay nodes adaptively select different transmission modes according to their own demodulation conditions, forward the demodulated data of the two remote users to the base station, and the base station uses the maximal ratio combining (MRC) and SIC technologies to demodulate the data of the two remote users.

[0072] The beneficial effects of the present invention are:

[0073] 1. The present invention proposes to introduce the Alamouti coding method in NOMA transmission. The specific implementation is: when two relay nodes successfully demodulate the data of two users, the distributed Alamouti coding method is used to transmit the U 1 data to the BS, and at the same time, a single relay node uses the superposition coding method to transmit the U 2The data is loaded onto the signal after space-time coding; two relay nodes simultaneously broadcast the coded signal to the base station, and the base station demodulates the data of the two users using the successive interference cancellation method. Alamouti coding can obtain spatial diversity gain, effectively improve the signal strength received by the base station, enable the base station to better perform interference cancellation demodulation, and enhance the robustness of relay transmission. By introducing Alamouti coding, the present invention can better cope with the uncertainty of the channel, improve the robustness and efficiency of data transmission, and provide higher-quality services for users.

[0074] 2. For large-scale networks, the present invention proposes an adaptive NOMA relay transmission mechanism based on Alamouti coding. Different from the traditional demodulation and transmission methods, the present invention analyzes various situations of two relay nodes demodulating the data of different users and designs seven different transmission methods, specifically: (1) The first situation: R 1 successfully demodulates the data of U 1 and U 2 . R 2 successfully demodulates the data of U 1 . At this time, the data of U 1 is transmitted using the distributed Alamouti coding method, and the data of U 2 is superimposed onto the signal after space-time coding on the antenna of R 1 ; (2) The second situation: R 1 only successfully demodulates the data of U 1 . R 2 successfully demodulates the data of U 1 and U 2 . At this time, the data of U 1 is transmitted using the distributed Alamouti coding method, and the data of U 2 is superimposed onto the signal after space-time coding on the antenna of R 2 ; (3) The third situation: R 1 successfully demodulates the data of U 1 and U 2 . R 2 does not successfully demodulate the user data. At this time, R 1 transmits the data of U 1 and U 2 using the NOMA method; (4) The fourth situation: R 2 successfully demodulates the data of U 1 and U 2 . R 1 does not successfully demodulate the user data. At this time, R 2 transmits the data of U 1 and U 2 using the NOMA method; (5) The fifth situation: R 1 and R 1All successfully demodulated only U 1 's data. At this time, select the relay node with the best BS channel state to transmit U 1 's data; (6) The sixth case: R 1 only successfully demodulated U 1 's data, and R 2 did not successfully demodulate the user data. At this time, R 1 transmits U 1 's data; (7) The seventh case: R 2 only successfully demodulated U 1 's data, and R 1 did not successfully demodulate the user data. At this time, R 2 transmits U 1 's data. This adaptive mechanism enables the relay node to flexibly select the most suitable transmission strategy based on the demodulation situation of the user data, more fully improve the spectral efficiency, and better meet the transmission requirements of remote users.

[0075] 3. The present invention jointly optimizes the time allocation factor β, and the power allocation factor ρ during the transmission process, and conducts computer simulations of large-scale networks to verify, revealing the important impact of time and power allocation parameters on system performance. The simulation results show that the proposed scheme of the present invention can significantly improve the system throughput compared with the benchmark scheme. The experimental results reveal the impact of resource allocation strategies with different system parameter configurations on system performance, which helps to guide the planning and deployment of large-scale systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 is a schematic diagram of an adaptive NOMA relay transmission system model based on Alamouti space-time coding;

[0077] Figure 2 is a schematic diagram of the process of adaptive NOMA relay transmission based on Alamouti space-time coding;

[0078] Figure 3 is a schematic diagram of the data transmission process of the benchmark scheme;

[0079] Figure 4 is a schematic diagram of the change of system throughput with the time allocation factor;

[0080] Figure 5 is a schematic diagram of the change of system throughput with the power allocation factor;

[0081] Figure 6 is a schematic diagram of the change of system throughput with the data transmission rate v 1 ;

[0082] Figure 7The system throughput increases with the data transmission rate v 2 Schematic diagram of the changes;

[0083] Figure 8 Schematic diagram of the change of throughput with distance allocation factor. DETAILED DESCRIPTION

[0084] The present invention will be further defined below in conjunction with the accompanying drawings and embodiments, but is not limited thereto.

[0085] Example 1

[0086] An adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network, comprising:

[0087] In each cellular cell, two relay nodes assist two remote users in transmitting data to the base station. The relay nodes adaptively adjust the transmission mode according to their own demodulation conditions, thereby realizing communication between the two remote users and the base station. The entire transmission process includes multiple consecutive time blocks of equal length, and each time block is divided into two stages:

[0088] In the first stage, two remote users simultaneously occupy the same frequency band to broadcast their respective data, and the two relay nodes use SIC technology to demodulate the data of the two remote users from the received mixed signal;

[0089] In the second stage, the two relay nodes adaptively select different transmission modes according to their own demodulation conditions and forward the demodulated data of the two remote users to the base station. The base station demodulates the data of the two remote users using Maximum Ratio Combining (MRC) and SIC technology.

[0090] Example 2

[0091] Adaptive non-orthogonal multiple access relay transmission method based on space-time coding in large-scale networks,

[0092] The present invention considers Figure 1 The adaptive relay transmission system shown in the figure has two remote users U 1 and U 2 It needs to transmit data to the associated base station (BS). Due to the long signal transmission distance, severe path loss, and the influence of obstacles and channel deep fading, as well as strong co-channel interference from other cells, U 1 , U 2 There is no direct link between the two remote users U 1 and U 2 With the help of relay node R 1 and R2 Transmit data to the base station BS; the entire transmission process consists of multiple consecutive equal-time blocks, and the duration of each time block is normalized to 1 second; the time allocation factor β is used to divide each time block into a first stage and a second stage, where 0 < β < 1, and the durations are β and 1 - β respectively;

[0093] In the first stage, two relay nodes use SIC technology to demodulate the data of two remote users from the received mixed signal; including: first demodulate the data of remote user U 1 At this time, regard the data of remote user U 2 As interference, after demodulating the data of remote user U 1 Delete the data of remote user U 1 From the mixed signal, and then demodulate the data of remote user U 2 Data;

[0094] In the second stage, considering the situation of two relay nodes demodulating the data of two remote users, set 7 transmission modes, and the two relay nodes adaptively select the best transmission mode to forward the data of the remote users to the base station BS;

[0095] If the base station BS receives the data of two remote users, then use SIC technology to demodulate the data of the two remote users; the SIC demodulation method is: first demodulate the data of remote user U 1 At this time, regard the data of remote user U 2 As interference, after demodulating the data of remote user U 1 Delete the data of remote user U 1 From the mixed signal, and then demodulate the data of remote user U 2 Data;

[0096] If BS receives the data of a single remote user, then use the MRC method to demodulate the user data.

[0097] The present invention jointly optimizes the power allocation factor ρ (0 < ρ < 1) of NOMA transmission and the time allocation factor β of the two stages by maximizing the system throughput. Numerical results show that in most cases, compared with the benchmark transmission scheme that only includes one relay node, the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed by the present invention can significantly improve the system throughput.

[0098] Assume that the typical base station x 0 Is located at the origin, and the cell covered by the typical base station is called the typical cell. Taking the typical cell as an example, analyze the specific communication process. Two remote users U 1 And U 2 Occupy the same frequency band and send signals simultaneously, with powers of And Benefiting from the broadcast characteristics of wireless channels, R 1 and R 2 The mixed signals from two users are received at the same time, R 1 and R 2 Know U 1 and U 2 The channel state information between them all performs SIC demodulation: first try to demodulate U 1 data, then U 2 The data is considered as interference. If U 1 The data is removed from the received mixed signal and then demodulated U 2 Otherwise, if U is demodulated incorrectly 1 If the two users' data are not transmitted, the interference cannot be eliminated and the demodulation of the two users' data fails.

[0099] The wireless transmission process of the signal experiences small-scale channel block fading and large-scale path loss. The channel block fading varies independently on different links and time blocks; small-scale fading is generally modeled as Rayleigh distribution. Since the distance between the two relay nodes is very close, the distance between a single user and the two relay nodes is roughly the same. In the first stage, R 1 After receiving the mixed signal from two users, we first try to demodulate U 1 Data, U 1 The signal to interference plus noise ratio (SINR) of the data is recorded as It is expressed as:

[0100]

[0101] in, and Represents the typical base station x 0 Associated U 1 and U 2 To the typical community R 1 and R 2 distance; and Respectively represent U 1 and U 2 With R 1 The small-scale power fading of the channel between 2 is the power of Additive White Gaussian Noise (AWGN), and the two remote users U 1 and U 2 Occupying the same frequency band and sending signals at the same time, the power is and

[0102] The total interference caused by other users to R 1 is:

[0103]

[0104] wherein, and represent the distances between U b / {x 0} associated with BSx∈Φ 1 and U 2 to R 1 and R 2 in a typical cell, and represent the large-scale path loss between them; and respectively represent the small-scale power fades of U b / {x 0} associated with BSx∈Φ 1 and U 2 to R 1 in a typical cell; Y x represents the distance from BSx∈Φ b / {x 0} to the typical base station x 0 ; Since the BSs are sparsely distributed in the two-dimensional plane and the average distance between different base stations is much larger than the communication distance within each cell, it is assumed that

[0105] If R 1 successfully demodulates and eliminates the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as and is expressed as:

[0106]

[0107] Similarly, and respectively represent the small-scale power fades of U 1 and U 2 to R 2 in this typical cell; R 2 first attempts to demodulate the data of U 1 , and at this time the SINR is denoted as and is expressed as:

[0108]

[0109] wherein, the total interference caused by other users to R2 The total interference caused is:

[0110]

[0111] and represents the U associated with BS x∈Φ b / {x 0} related U 1 and U 2 to the small-scale power fading between the typical cell R 2 ; if R 2 successfully demodulates and eliminates the data of U 1 then the SINR for demodulating the data of U 2 is denoted as Expressed as:

[0112]

[0113] In the second stage, 7 transmission modes are set, and two relay nodes adaptively select the best transmission mode to forward the data of the remote user to the base station BS, including:

[0114] In the first stage, R 1 and R 2 There are multiple different situations for demodulating the data of two users. Therefore, in the second stage, the ways for the relay nodes to transmit signals to BS are also different. These situations will be discussed separately below.

[0115] The first situation: When R 1 successfully demodulates the data of U 1 and U 2 's data, and R 1 successfully demodulates the data of U 1 's data, the two relay nodes use the NOMA method based on Alamouti coding to send signals to BS; use the distributed Alamouti coding method to transmit the data of U 1 's data, and superimpose the data of U 2 onto the signal after space-time coding and send the signal to BS; 1

[0116] After BS receives the mixed signal, it first tries to demodulate the data of U 1 . After successful demodulation, it deletes the data of U 1 from the mixed signal, and then demodulates the data of U 2 ; Since the uplink channel state information from the relay node to the base station is unknown, and the distances between the antennas of the two relay nodes and BS are basically the same, the channel fades from the two antennas to BS can be considered to be independent and identically distributed. Each relay node is allocated the same power P rForward user data; R 1 and R 2 Perform Alamouti coding on the data for U 1 , and at the same time, R 1 Overlay the data of U 2 onto the Alamouti-coded signal to obtain a composite signal, and send this composite signal to BS; R 1 Send the U 1 signal with power ρP r , 0 < ρ < 1, R 1 Send the U 2 signal with power (1 - ρ)P r , and at the same time, R 2 Transmit the signal of U r using power P 1 ;

[0117] The second stage can be regarded as a series of time slots, and every two consecutive time slots can be paired to transmit the data of two users. In two consecutive time slots, map the two symbols 1 in U onto the transmit antennas and Assume that the small-scale channel powers of the two relays fading to BS are and n 1 and n 2 are the interference and noise powers of the two time slots respectively; The signals received by BS are denoted as r 1 and r 2 , then:

[0118]

[0119] BS first attempts to demodulate the data of U 1 , and at this time, regard the data of U 2 as interference, then this SINR is denoted as and is expressed as:

[0120]

[0121] Among them, and represent the small-scale power fades between R 1 and R 2 in a typical cell to the typical BSx 0 , Y r represents the distance from R 1 and R 2 in a typical cell to the typical base station x 0 ;

[0122] The total interference caused by other users to BS is:

[0123]

[0124] Among them, and represent the event of data forwarding by R b / {x 0} associated with BSx∈Φ 1 and R 2 ; and represent the small-scale power fading between R b / {x 0} associated with BSx∈Φ 1 and R 2 to the typical base station x 0 ; Y x(r) is the distance between R b / {x 0} associated with BSx∈Φ 1 and R 2 to the typical base station x 0 ; Since BSs are sparsely distributed in the two-dimensional plane and the average distance between different base stations is much larger than the communication distance within each cell, the present invention assumes that Y x(r) ≈Y x ;

[0125] If BS successfully demodulates and cancels the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as Expressed as:

[0126]

[0127] The second case: When R 1 only successfully demodulates the data of U 1 , and R 2 successfully demodulates the data of U 1 and U 2 , R 1 and R 2 perform Alamouti coding on the data of U 1 . Meanwhile, R 2 superimposes the data of U 2 onto the Alamouti-coded signal to obtain a composite signal, and sends the composite signal to BS; R 1 and R 2 send the data of U 1 using Alamouti coding. Among them, R 1 uses the power of P r to send the data of U 1The data, R 2 Use ρP r To transmit U with the power of 1 The data, R 2 Use (1 - ρ)P r The power to superimpose the data of U 2 Onto the encoded data of U 1 At this time, the BS demodulates U 1 The SINR of the data is denoted as Expressed as:

[0128]

[0129] If the BS successfully demodulates and eliminates the data of U 1 Then the SINR of the data of U 2 Is denoted as Expressed as:

[0130]

[0131] The third case: When R 1 Successfully demodulates the data of U 1 And U 2 The data, R 2 Fails to successfully demodulate the user data, R 1 Adopts the NOMA method to superimpose the data of U 1 And U 2 Into a composite signal and sends it to the BS; Among them, R 1 Uses ρP r The power to transmit the data of U 1 Uses (1 - ρ)P r The power to transmit the data of U 2 At this time, the BS demodulates U 1 The SINR of the data is denoted as Expressed as:

[0132]

[0133] If the BS successfully demodulates and eliminates the data of U 1 Then the SINR of the data of U 2 Is denoted as Expressed as:

[0134]

[0135] The fourth case: When R 2 Successfully demodulates the data of U 1 And U 2 The data, R 1 Fails to successfully demodulate the user data, R 2 Adopts the NOMA method to superimpose the data of U1 and U 2 The data is superimposed with U to form a composite signal and sent to the BS; R 2 Uses ρP r to send the data of U 1 Uses (1 - ρ)P r to send the data of U 2 At this time, the BS demodulates the SINR of the data of U 1 and is denoted as Expressed as:

[0136]

[0137] If the BS successfully demodulates and eliminates the data of U 1 then the SINR of the data of U 2 demodulated by the BS is denoted as Expressed as:

[0138]

[0139] The fifth case: When R 1 and R 2 both only successfully demodulate the data of U 1 At this time, according to the states of the transmission channels of the two relay nodes fed back by the BS, the relay node with the best channel to the BS is selected to send the data of U r with the power of P 1 The BS demodulates the SINR of the data of U 1 and is denoted as When is better than then is the same as and is Conversely is the same as and is

[0140] The sixth case: If R 1 only successfully demodulates the data of U 1 and R 2 does not successfully demodulate the user data, then R 1 uses the power of P r to send the data of U 1 At this time, the BS demodulates the SINR of the data of U 1 and is denoted as Expressed as:

[0141]

[0142] The seventh case: If R 2 only successfully demodulates the data of U 1 and R1 When the user data is not successfully demodulated, R 2 uses the power of P r to transmit the data of U 1 ; at this time, the BS demodulates the SINR of the U 1 data and records it as Expressed as:

[0143]

[0144] The performance analysis is as follows:

[0145] Two relay nodes R 1 and R 2 transmit the user data in an adaptive manner, which is summarized into 7 ways as Figure 2 shown. Assume that the data transmission rates of U 1 and U 2 are fixed at v 1 and v 2 respectively. When the channel achievable rate is greater than the data transmission rate, that is, when the SINR or SNR is greater than a certain threshold, the data transmission is considered successful. The system throughput of the adaptive NOMA relay transmission mechanism based on Alamouti coding is expressed as:

[0146] θ = θ 1 + θ 2 + θ 3 + θ 4 + θ 5 + θ 6 + θ 7 (19);

[0147] Among them, θ 1 、θ 2 、θ 3 、θ 4 、θ 5 、θ 6 and θ 7 represent the throughput of the first case to the seventh case respectively.

[0148] The rate of transmitting the data of U 1 is fixed at v 1 , then in the first stage, the SINR / SNR threshold for judging whether the transmission of the data of U 1 and R 2 to R 1 is successful is recorded as The SINR / SNR threshold for judging whether the transmission of the data of U 1 and R 2 to R 2 is successful is recorded as In the second stage, judge whether to transmit U 1The SINR / SNR threshold for whether the data is successful is denoted as Transmit U to the BS 2 The SINR / SNR threshold for whether the data is successful is denoted as To calculate the total system throughput θ, it is necessary to first calculate θ 1 Up to θ 7 value.

[0149] The first case: R 1 Successfully demodulate U 1 and U 2 data, R 2 Successfully demodulate U 1 data;

[0150] θ 1 Is the system throughput in the first case, that is, R 1 Successfully demodulate U 1 and U 2 data, and R 2 Successfully demodulate U 1 data. At this time, there are three cases of "BS successfully demodulates U 1 and U 2 data", "BS only successfully demodulates U 1 data" and "BS fails to successfully demodulate any data", then θ 1 should be the sum of the joint probabilities in different cases multiplied by the corresponding data transmission rates, expressed as:

[0151]

[0152] Among them, the first probability in formula (20) represents that R 1 Successfully demodulate U 1 and U 2 data, R 2 Successfully demodulate U 1 data, and the joint probability that BS can successfully demodulate U 1 and U 2 data is denoted as P C1-1 , and further derived to the success probability as:

[0153]

[0154] Among them, 1{...} is an indicator random variable. When the condition in the parentheses holds, this indicator random variable is 1, otherwise it is 0.

[0155] The first probability calculation formula in formula (21) is denoted as P C1-1-1 , and the derivation is:

[0156]

[0157] Among them, C = (η 1 + 1)(1 - ρ), and

[0158] For the convenience of expression, let:

[0159]

[0160] The expected transformation of interference is:

[0161]

[0162] Among them is the probability that event occurs, which is

[0163]

[0164] is the probability that event occurs and the activation probability is the same as , which is

[0165] The second probability calculation formula in formula (21) is denoted as P C1-1-2 , and the derivation is:

[0166]

[0167] The third probability calculation formula in formula (21) is denoted as P C1-1-3 , and the derivation is:

[0168]

[0169] Among them,

[0170] R 1 successfully demodulates U 1 and U 2 data, R 2 successfully demodulates U 1 data, and the joint probability that the BS only successfully demodulates U 1 data is denoted as P C1-2 , and the success probability is further derived as:

[0171]

[0172] Among them,

[0173] The second case: R 1Only successfully demodulated U 1 's data, R 2 successfully demodulated U 1 and U 2 's data;

[0174] θ 2 is the system throughput in the second case, that is, R 2 successfully demodulated U 1 and U 2 's data, and R 1 successfully demodulated U 1 's data. At this time, there are three situations: "BS successfully demodulated U 1 and U 2 's data", "BS only successfully demodulated U 1 's data" and "BS did not successfully demodulate any data", then

[0175]

[0176] The derivation method is similar to the first case.

[0177] The third case: R 1 successfully demodulated U 1 and U 2 's data, R 2 did not successfully demodulate the user data;

[0178] θ 3 is the system throughput in the third case, that is, R 1 successfully demodulated U 1 and U 2 's data, R 2 did not successfully demodulate the user data. At this time, there are three situations: "BS successfully demodulated U 1 and U 2 's data", "BS only successfully demodulated U 1 's data" and "BS did not successfully demodulate any data", then

[0179]

[0180] The derivation method is similar to the first case.

[0181] The fourth case: R 2 successfully demodulated U 1 and U 2 's data, R 1 did not successfully demodulate the user data

[0182] θ 4 is the system throughput in the fourth case, that is, R 2 successfully demodulated U 1 and U 2Data, R 1 Failed to successfully demodulate the user data. At this time, there are three situations: "BS successfully demodulated the data of U 1 and U 2 ", "BS only successfully demodulated the data of U 1 ", and "BS failed to successfully demodulate any data". Then

[0183]

[0184] The derivation method is similar to that of the first case.

[0185] Fifth case: When R 1 and R 2 both only successfully demodulated the data of U 1 ;

[0186] θ 5 is the system throughput in the fifth case, that is, R 1 and R 2 both only successfully demodulated the data of U 1 . At this time, select the relay node with the best BS channel state to transmit the data of U r with the power of P 1 . At this time, there are two situations: "BS successfully demodulated the data of U 1 " and "BS failed to successfully demodulate any data". Then

[0187]

[0188] The derivation method is similar to that of the first case.

[0189] Sixth case: If R 1 only successfully demodulated the data of U 1 , R 2 failed to successfully demodulate the user data;

[0190] θ 6 is the system throughput in the sixth case, that is, R 1 only successfully demodulated the data of U 1 , R 2 failed to successfully demodulate the user data, and R 1 used the power of P r to transmit the data of U 1 . At this time, there are two situations: "BS successfully demodulated the data of U 1 " and "BS failed to successfully demodulate any data". Then

[0191]

[0192] The derivation method is similar to that of the first case.

[0193] The seventh case: If R 2 only successfully demodulates the data of U 1 and R 1 does not successfully demodulate the user data;

[0194] θ 7 is the system throughput in the seventh case, that is, R 2 only successfully demodulates the data of U 1 and R 1 does not successfully demodulate the user data. R 2 uses the power of P r to transmit the data of U 1 At this time, there are two situations: "the BS successfully demodulates the data of U 1 " and "the BS does not successfully demodulate any data", then

[0195]

[0196] The derivation method is similar to the first case.

[0197] For performance comparison, the present invention proposes a benchmark scheme. The model includes a relay node R for NOMA transmission. The transmission time is divided into equal-length time blocks, and the duration of each time block is normalized to 1 second. The time allocation factor is used to divide each time block into a first stage and a second stage, and the durations are respectively and In the first stage, two remote users U 1 and U 2 occupy the same frequency band to simultaneously transmit their respective data, and the powers are respectively and After R receives the mixed signal, it uses SIC technology to demodulate the user information. The demodulation method is as follows: First, demodulate the data of U 1 , and at this time, regard the data of U 2 as interference. When the data of U 1 is successfully demodulated, delete the data from the mixed signal, and then demodulate the data of U 2 . In the second stage, R selects a suitable transmission method according to the demodulation situation to send the user data to the BS. If R successfully demodulates the data of both users, it uses the NOMA method to send the user data. At this time, the BS uses SIC technology to demodulate the user information. The demodulation method is as follows: First, demodulate the data of U 1 , and at this time, regard the data of U 2 as interference. When the data of U 1 is successfully demodulated, delete the data from the mixed signal and then demodulate the data of U 2 . If R only successfully demodulates the data of U 1If the data of the user is received, only the user data is forwarded. At this time, the BS demodulates the user data using the MRC method. If R demodulates the data of U incorrectly 1 the interference cannot be eliminated, resulting in the inability to demodulate the data of the two remote users. In the benchmark model, the distances from U 1 and U 2 to R, and the distance from R to the BS are the same as those in the aforementioned system model, denoted as and Y r .

[0198] The first stage of the transmission process:

[0199] In the first stage, after R receives the mixed signal sent by the user, it first attempts to demodulate the data of U 1 . The SINR is denoted as and is expressed as:

[0200]

[0201] where the total interference received by the relay R is:

[0202]

[0203] and represent the large-scale path loss from U b / {x 0} associated with the BS x ∈ Φ 1 and U 2 to the typical cell R. and represent the small-scale power fading in this process. denotes the large-scale path loss from the BS x ∈ Φ b / {x 0} to the typical base station x 0 . Since the BSs are sparsely distributed in the two-dimensional plane and the distances between different base stations are much larger than the communication distances within each cell, it is assumed that

[0204] If R successfully demodulates and eliminates the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as and is expressed as:

[0205]

[0206] The second stage of the transmission process:

[0207] If R successfully receives the mixed signal and successfully demodulates U 1 and U 2For the data, in the second stage, R will superimpose the signals of the two remote users and send the composite signal to the BS. The transmit power of R is P r , where, with power to send U 1 data, power to send U 2 data.

[0208] G r represents the small-scale channel power fading from R of a typical cell to the typical base station x 0 . Y r is the distance from R of a typical cell to the typical base station x 0 . After receiving the composite signal from R, the BS first attempts to demodulate the data of U 1 , and denote the SINR as expressed as:

[0209]

[0210] where the total interference received by the BS is:

[0211]

[0212] where, represents the event of data forwarding by R associated with BS x∈Φ b / {x 0}. G x(r) represents the small-scale power fading from R associated with BSx∈Φ b / {x 0} to the typical base station x 0 . Y x(r) is the distance from R associated with BSx∈Φ b / {x 0} to the typical base station x 0 . Since the BSs are sparsely distributed in the two-dimensional plane and the average distance between base stations is much larger than the communication distance within the cell, the present invention assumes that Y x(r) ≈Y x .

[0213] If the BS successfully demodulates and cancels the data of U 1 , then the SINR for demodulating the data of U 2 is denoted as expressed as:

[0214]

[0215] When R only successfully demodulates x 1 , it will only use all its power to send U 1Forward the data of U to the BS. In this case, the BS demodulates U 1 The SINR of the data is denoted as Expressed as:

[0216]

[0217] Performance analysis:

[0218] Assume that the data transmission rates of U 1 and U 2 are fixed at v 1 and v 2 respectively. When the channel achievable rate is greater than the data transmission rate, that is, when the SINR or SNR is greater than a certain threshold, the data transmission is considered successful. The system throughput of the benchmark scheme is where represents the system throughput when R successfully demodulates the data of U 1 and U 2 The system throughput when R only successfully demodulates the data of U represents the system throughput when R only successfully demodulates the data of U 1 The system throughput when R only successfully demodulates the data of U

[0219] In the first stage, the SINR / SNR threshold for determining whether the transmission of U 1 data to R is successful is denoted as The SINR / SNR threshold for determining whether the transmission of U 2 data to R is successful is denoted as In the second stage, the SINR / SNR threshold for determining whether the transmission of U 1 data to the BS is successful is denoted as The SINR / SNR threshold for determining whether the transmission of U 2 data to the BS is successful is denoted as Calculate the total system throughput It is necessary to calculate to value.

[0220] When R successfully demodulates the data of U 1 and U 2 R forwards the composite signal in the NOMA mode. At this time, there are three cases: "BS successfully demodulates the data of U 1 and U 2 ", "BS only successfully demodulates the data of U 1 " and "BS does not successfully demodulate any data". Then is

[0221]

[0222] The derivation method is similar to the first case in the second stage of the present invention.

[0223] Based on the above analysis process, the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed by the present invention Figure 3 is the system transmission flow chart of the benchmark scheme. It includes the following steps:

[0224] Step 1: Users U 1 and U 2 occupy the same spectrum and simultaneously send their respective data, and the transmission powers are and R 1 and R 2 simultaneously receive the mixed signals from U 1 and U 2 . The SIC technology is used to demodulate the user data, and the demodulation method is to first demodulate the data of U 1 , regard the data of U 2 as interference. When R 1 successfully demodulates the data of U 1 , delete this data from the mixed signal and then demodulate the data of U 2 . Broadcast the demodulated user data adaptively according to the situation of demodulating the user data.

[0225] Step 2: When the BS receives the information of two users forwarded by the relay node, the SIC technology is used to demodulate the user data, and the demodulation method is to first demodulate the data of U 1 , regard the data of U 2 as interference. But after the BS successfully demodulates the data of U 1 , delete this data from the received mixed signal, and then demodulate the data of U 2 . When the BS receives the information of a single user sent by the relay node, the MRC method is used to demodulate the user data.

[0226] Step 3: Use the stochastic geometry theory to model the base station location distribution and co-channel cumulative interference in the network, calculate the system throughput of the adaptive NOMA relay transmission mechanism based on Alamouti space-time coding, and jointly optimize the time allocation factor β and the power allocation factor ρ to maximize the system throughput.

[0227] When performing computer simulation, the number of Monte Carlo iterations is 10 5 times. Unless otherwise specified, the parameters of the system are set as the path loss exponent α = 3, the power of AWGN σ 2 = -90dBm, the transmission power 1 of U is -5dBm, the transmission power 2 of U is -10dBm, and the transmission power P of the relay node ris 40 dBm, BS density λ b = 10 -6 angle distance time allocation factor power allocation factor target transmission rate v 1 = 0.3 bits / s / Hz, v 2 = 0.5 bits / s / Hz.

[0228] The adaptive NOMA relay transmission mechanism based on Alamouti coding proposed in the present invention is labeled with "NOMA with Alamouti coding", the benchmark scheme is represented by "NOMA", the theoretical results are labeled with "Theoretical", and the simulation results are labeled with "Simulation".

[0229] Figure 4 Shows the relationship between the system throughput of the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed in the present invention and the time allocation factor β. Among them, ρ is set to 0.5 and 0.6 respectively. Figure 4 Also shows the throughput of the benchmark scheme and the time factor relationship, and will be set to 0.5 and 0.6 respectively. The theoretical analysis results are in good agreement with the simulation results, verifying the correctness of the theoretical analysis, indicating that the scheme proposed in the present invention is superior to the benchmark scheme in terms of performance. As the time parameter increases, the system throughput shows a trend of first increasing and then decreasing, and there is a time parameter that maximizes the system throughput value. When β and are small, the relay node does not have enough time to demodulate the user data, resulting in a low system throughput; while when β and are large, the base station also faces the problem of insufficient demodulation time, thus reducing the system throughput. Among them, the benchmark scheme drops steeply when is about 0.75, while the system scheme of the present invention has a smaller decline under the same conditions, and the overall performance is better than the benchmark network.

[0230] Figure 5 Shows the relationship between the system throughput of the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed in the present invention and the power allocation factor ρ. β is set to 0.5 and 0.7 respectively. Figure 5 Also shows the throughput of the benchmark scheme and the time factor relationship, and will They are set to 0.5 and 0.7 respectively. As the power allocation factor increases, the system throughput first rises and then falls, indicating that there is a power allocation factor that maximizes the system throughput value. When ρ and are small, the power allocated by the relay node to transmit U 1 is insufficient, resulting in the BS being unable to successfully demodulate the data of U 1 , thus reducing the system throughput; when ρ and are large, the power allocated by the relay node to transmit U 2 is insufficient, resulting in the BS being unable to successfully demodulate the data of U 2 , thus reducing the system throughput. As can be seen from Figure 5 , the reference scheme can achieve better system throughput only when a certain amount of power is allocated to the data of U 1 . When the power allocated to U 1 is insufficient, the system throughput is very small. The scheme proposed in the present invention is significantly superior to the reference scheme under the same conditions.

[0231] As can be seen from Figure 4 and Figure 5 , in the system scheme and the reference scheme proposed in the present invention, there is a set of time allocation parameters and power allocation parameters that maximize the system throughput value respectively. Therefore, these four parameters need to be optimized to maximize the system throughput. The following analysis is obtained under the optimal time allocation factor and power allocation factor.

[0232] Figure 6 shows the comparison of the system throughput between the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed in the present invention and the reference scheme under the change of the data transmission rate v 1 . When v 1 reaches the optimal value under the current conditions, the system throughput of the present invention is significantly higher than that of the reference scheme. Since the system throughput is the product of the occurrence probability and the data transmission rate, as v 1 increases, the system throughput first gradually rises until it reaches the system throughput peak. When v 1 further increases, due to the excessive data transmission rate, the SINR threshold related to v 1 increases, reducing the probability of successfully demodulating the user information, thus reducing the system throughput.

[0233] Figure 7 shows the comparison of the system throughput between the adaptive NOMA relay transmission mechanism based on Alamouti coding proposed in the present invention and the reference scheme under the change of the data transmission rate v 2 . When v 2 increases, the system throughput first shows an upward trend. However, when v 2When it further increases, the SINR threshold related to v 2 increases, reducing the probability of successfully demodulating user information, thus causing the system throughput to decrease.

[0234] Figure 8 shows the comparison of the system throughput between the adaptive NOMA relay transmission mechanism system based on Alamouti coding proposed in the present invention and the system throughput of the reference scheme under the condition of distance change. In order to comprehensively consider the distance from the user to the relay and and the distance Y from the relay to the BS r on the system throughput, the present invention introduces the parameter τ (0 < τ < 1). Assuming that the total distance from the midpoint between the two users to the BS is Y ub , then the distance from the user to the relay station is The distance from the relay station to the base station is (1 - τ)Y ub . The influence of the change of τ on the system throughput is as Figure 8 shown. The system throughput shows a trend of first increasing and then decreasing as τ increases. This is because when the transmission distance in a certain stage is too large, the path loss in this stage becomes larger, resulting in a decrease in the probability of successful demodulation, and then the system throughput decreases. From Figure 8 it can also be seen that when the total distance Y ub becomes larger, the overall system throughput decreases. This is because the farther the distance, the greater the path loss, but the scheme proposed in the present invention is still significantly better than the reference scheme.

[0235] Embodiment 3

[0236] A computer device includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, it implements the steps of the adaptive non-orthogonal multiple access relay transmission method based on space-time coding in the large-scale network described in Embodiment 1 or 2.

[0237] Embodiment 4

[0238] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, it implements the steps of the adaptive non-orthogonal multiple access relay transmission method based on space-time coding in the large-scale network described in Embodiment 1 or 2.

[0239] Embodiment 5

[0240] In the large-scale network, an adaptive non-orthogonal multiple access relay transmission system based on space-time coding. In each cellular cell, two relay nodes assist two remote users in transmitting data to the base station. The relay nodes adaptively adjust the transmission mode according to their own demodulation conditions, so as to realize the communication between the two remote users and the base station; including:

[0241] The first-stage module is configured to: two remote users simultaneously occupy the same frequency band to broadcast their respective data, and two relay nodes use the SIC technology to demodulate the data of the two remote users from the received mixed signal;

[0242] The second-stage module is configured to: two relay nodes adaptively select different transmission modes according to their own demodulation situations, forward the demodulated data of the two remote users to the base station, and the base station uses the Maximal Ratio Combining (MRC) and SIC technologies to demodulate the data of the two remote users.

Claims

1. An adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network, characterized in that: include: In each cellular cell, two relay nodes assist two remote users in transmitting data to the base station. The relay nodes adaptively adjust the transmission mode according to their own demodulation conditions, thereby achieving communication between the two remote users and the base station. The entire transmission process consists of multiple consecutive time blocks of equal length, each of which is divided into two stages: In the first stage, two remote users simultaneously occupy the same frequency band to broadcast their respective data, and the two relay nodes use SIC technology to demodulate the data of the two remote users from the received mixed signal; In the second stage, the two relay nodes adaptively select different transmission modes according to their own demodulation conditions and forward the demodulated data of the two remote users to the base station. The base station uses maximum ratio combining and SIC technology to demodulate the data of the two remote users.

2. The adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network according to claim 1, characterized in that: Assume that two remote users U1 and U2 transmit data to the base station BS via relay nodes R1 and R2; the duration of each time block is normalized to 1 second; each time block is divided into the first stage and the second stage using the time allocation factor β, 0<β<1, and the durations are β and 1-β respectively; In the first stage, the two relay nodes use the SIC technology to demodulate the data of the two remote users from the received mixed signal, including: first demodulating the data of the remote user U1, at which time the data of the remote user U2 is regarded as interference, after demodulating the data of the remote user U1, deleting the data of the remote user U1 from the mixed signal, and then demodulating the data of the remote user U2; In the second stage, seven transmission modes are set, and the two relay nodes adaptively select the best transmission mode to forward the remote user's data to the base station BS; If the base station BS receives data from two remote users, it uses the SIC technology to demodulate the data of the two remote users. The SIC demodulation method is: first demodulate the data of the remote user U1, then treat the data of the remote user U2 as interference, and after demodulating the data of the remote user U1, delete the data of the remote user U1 from the mixed signal, and then demodulate the data of the remote user U2. If the BS receives data from a single remote user, it demodulates the user data using the MRC method.

3. The adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network according to claim 2, characterized in that: In the first stage, after R1 receives the mixed signals from two users, it first tries to demodulate U1's data. The signal-to-interference ratio of U1's data is recorded as It is expressed as: in, and represents the distances from U1 and U2 associated with the typical base station x0 to the typical cells R1 and R2; and Respectively represent the small-scale power fading of the channel between U1 and U2 and R1; σ 2 is the power of additive white Gaussian noise. Two remote users U1 and U2 occupy the same frequency band and send signals at the same time. The powers are and The total interference caused by other users to R1 is: in, and Represents the same as BS x∈Φ b / {x0} The distance between U1 and U2 associated with a typical cell and R1 and R2, and represents the large-scale path loss between them; and Respectively represent and BS x∈Φ b / {x0} related small-scale power fading from U1 and U2 to R1 in a typical cell; Y x Represents from BSx∈Φ b / {x0} is the distance from the typical base station x0; since the BSs are sparsely distributed on the two-dimensional plane, the average distance between different base stations is much larger than the communication distance within each cell, so it is assumed that If R1 successfully demodulates and eliminates the data of U1, then the SINR of the demodulated data of U2 is recorded as It is expressed as: and They represent the small-scale power fading from U1 and U2 in a typical cell to R2 in the typical cell. R2 first tries to demodulate the data of U1, and the SINR is recorded as It is expressed as: Among them, the total interference caused by other users to R2 is: and Represents and BS x∈Φ b / Small-scale power fading between U1 and U2 associated with {x0} to the typical cell R2; If R2 successfully demodulates and eliminates the data of U1, then the SINR of the demodulated U2 data is recorded as It is expressed as:

4. The adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network according to claim 2, characterized in that: In the second stage, seven transmission modes are set, and the two relay nodes adaptively select the best transmission mode to forward the remote user's data to the base station BS; include: Case 1: When R1 successfully demodulates the data of U1 and U2, and R2 successfully demodulates the data of U1, the two relay nodes send signals to the BS using the NOMA method based on Alamouti coding; After receiving the mixed signal, the BS first tries to demodulate the data of U1. After the demodulation is successful, it removes the data of U1 from the mixed signal and then demodulates the data of U2. Each relay node is allocated the same power P r To forward user data; R1 and R2 perform Alamouti coding on U1’s data. At the same time, R1 superimposes U2’s data on the Alamaouti coded signal to obtain a composite signal, and sends the composite signal to the BS; the power of R1 sending U1 signal is ρP r , 0<ρ<1, the power of R1 sending U2 signal is (1-ρ)P r At the same time, R2 uses power P r Send U1 signal; In two consecutive time slots, the two symbols in U1 are Mapped onto the transmit antenna and Assume that the small-scale channel powers of the two relays fading to the BS are and n1 and n2 are the interference and noise power of the two time slots respectively; the signals received by the BS are represented by r1 and r2, then: The BS first attempts to demodulate the data of U1, and then regards the data of U2 as interference. The SINR is marked as It is expressed as: in, and represents the small-scale power fading between R1 and R2 in a typical cell and the typical base station x0, Y r represents the distance from R1 and R2 in a typical cell to the typical base station x0; The total interference caused by other users to the BS is: in, and Represents BS x∈φ b / {x0} is an event in which R1 and R2 associated with each other forward data. and Represents BS x∈φ b / {x0} associated with small-scale power fading between R1 and R2 to the typical base station x0; Y x(r) is related to BS x∈φ b / {x0} is the distance between R1 and R2 associated with the typical base station x0; since the BSs are sparsely distributed on the two-dimensional plane, the average distance between different base stations is much larger than the communication distance within each cell, so it is assumed that Y x(r) ≈Y x ; If the BS successfully demodulates and eliminates the data of U1, the SINR of the demodulated data of U2 is recorded as It is expressed as: The second case: When R1 successfully demodulates only the data of U1, and R2 successfully demodulates the data of U1 and U2, R1 and R2 perform Alamouti coding on the data of U1, and R2 superimposes the data of U2 on the Alamouti coded signal to obtain a composite signal, and sends the composite signal to the BS; R1 and R2 use Alamouti coding to send the data of U1, where R1 uses P r The power used to send U1 data is ρP. r The power used to send U1’s data is (1-ρ)P r The power of U2 is superimposed on the coded data of U1; at this time, the SINR of BS demodulating U1 data is recorded as It is expressed as: If the BS successfully demodulates and eliminates the data of U1, the SINR of the demodulated data of U2 is recorded as It is expressed as: Case 3: When R1 successfully demodulates the data of U1 and U2, but R2 fails to demodulate the user data, R1 uses NOMA to superimpose the data of U1 and U2 into a composite signal and sends it to BS. R1 uses ρP r The power used to send the data of U1 is (1-ρ)P r The power of U2 is used to send the data of U2. At this time, the SINR of BS demodulating the data of U1 is recorded as It is expressed as: If the BS successfully demodulates and eliminates the data of U1, the SINR of the demodulated data of U2 is recorded as It is expressed as: The fourth case: When R2 successfully demodulates the data of U1 and U2, but R1 fails to demodulate the user data, R2 uses NOMA to superimpose the data of U1 and U2 into a composite signal and sends it to BS; R2 uses ρP r The power used to send the data of U1 is (1-ρ)P r The power of U2 is used to send the data of U2. At this time, the SINR of BS demodulating the data of U1 is recorded as It is expressed as: If the BS successfully demodulates and eliminates the data of U1, the SINR of the demodulated data of U2 is recorded as It is expressed as: The fifth case: When R1 and R2 only successfully demodulate the data of U1, at this time, according to the state of the transmission channels of the two relay nodes fed back by the BS, the relay node with the best BS channel is selected to use P r The power of U1 is used to send the data of U1; the SINR of BS demodulating the data of U1 is recorded as when Better than hour, and Same, for on the contrary, and Same, for Case 6: If R1 only successfully demodulates U1's data and R2 fails to demodulate the user data, R1 uses P r The power of BS is used to send the data of U1. At this time, the SINR of BS demodulating the data of U1 is recorded as It is expressed as: Case 7: If R2 only successfully demodulates U1's data and R1 fails to successfully demodulate user data, R2 uses P r The power of BS is used to send the data of U1. At this time, the SINR of BS demodulating the data of U1 is recorded as It is expressed as:

5. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network are implemented in any one of claims 1-4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the adaptive non-orthogonal multiple access relay transmission method based on space-time coding in a large-scale network according to any one of claims 1 to 4 are implemented.

7. An adaptive non-orthogonal multiple access relay transmission system based on space-time coding in a large-scale network, in which in each cellular cell, two relay nodes assist two remote users in transmitting data to a base station, and the relay nodes adaptively adjust the transmission mode according to their own demodulation conditions, thereby realizing communication between the two remote users and the base station; characterized in that, include: The first stage module is configured as follows: two remote users simultaneously occupy the same frequency band to broadcast their respective data, and two relay nodes use SIC technology to demodulate the data of the two remote users from the received mixed signal; The second stage module is configured as follows: the two relay nodes adaptively select different transmission modes according to their own demodulation conditions, and forward the demodulated data of the two remote users to the base station. The base station uses maximum ratio combining and SIC technology to demodulate the data of the two remote users.

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