Power setting method of RIS auxiliary transmission system in NOMA network

Abstract

The invention discloses a power setting method of an RIS auxiliary transmission system in an NOMA network. The method is applied to a wireless communication system comprising a base station, a plurality of RISs and a plurality of users. According to the method, two RIS auxiliary transmission strategies, namely an exhaustive RIS auxiliary scheme and an opportunity RIS auxiliary scheme, are provided to optimize the transmitting power setting of the RIS auxiliary transmission system in the NOMA network, and the ERA scheme finds the optimal transmitting power through exhaustive search, so that the outage probability of all users reaches a target value for the first time, the optimal performance is provided, but the calculation complexity is relatively high. According to the ORA scheme, an opportunity selection mechanism is adopted, the transmitting power is adjusted with low calculation expenditure, and the system resource consumption is reduced while the user requirements are met. Through the two schemes, the system can adaptively regulate and control the transmitting power in different environments, resource waste caused by fixed power configuration is avoided, and efficient and reliable communication is achieved under the limited power condition.

Description

Technical Field

[0001] The present invention relates to a power setting method of a RIS-assisted transmission system in a NOMA network, which is characterized in that the system can dynamically adjust the transmission power of a base station according to the needs of each user. Background Art

[0002] With the continuous development of wireless communication technology, non-orthogonal multiple access (NOMA) as an effective multi-user access technology has broad application prospects in 5G and future 6G networks. NOMA technology greatly improves the efficiency of spectrum utilization by overlapping the signals of multiple users on the same frequency band, thereby improving the capacity and throughput of the network. However, in practical applications, the NOMA system faces problems such as signal interference, transmission distance and power limitation, which limits its performance in large-scale networks.

[0003] In order to optimize the propagation path of wireless signals and improve communication quality, intelligent reflection surface (IRS), also known as reconfigurable intelligent surface (RIS), has attracted widespread attention as an emerging technology. RIS can effectively improve the transmission conditions of signals and increase the coverage and data rate of communication systems by intelligently adjusting the phase, amplitude and other parameters of the reflection unit. The introduction of RIS has brought significant performance improvements to NOMA networks, especially in complex wireless propagation environments. RIS can improve the overall performance of the system by optimizing the signal reflection path, reducing signal attenuation and interference.

[0004] However, the deployment and operation of RIS requires a certain amount of system power consumption. Especially in large-scale networks, how to effectively utilize limited power resources becomes a major challenge. Most of the existing technologies focus on selecting RIS and scheduling its working state, but less consideration is given to the dynamic changes of user needs in adjusting the system transmission power. Therefore, the present invention proposes a power setting method for a RIS-assisted transmission system in a NOMA network, which dynamically adjusts the transmission power of the base station based on changes in user needs to optimize the resource allocation and communication quality of the system. Summary of the invention

[0005] The purpose of the present invention is to provide a power setting method for a RIS-assisted transmission system in a NOMA network, which solves the problem of how to perform power setting to improve the communication quality of the NOMA network and reduce system power consumption while meeting user needs (interruption probability requirements).

[0006] In this invention, two RIS-assisted transmission strategies, the exhaustive RIS-assisted scheme and the opportunistic RIS-assisted scheme, are proposed to optimize the transmission power setting of the RIS-assisted transmission system in the NOMA network. The ERA scheme finds the optimal transmission power through exhaustive search, so that the interruption probability of all users reaches the target value for the first time, thereby providing the best performance, but the computational complexity is high. The ORA scheme adopts an opportunistic selection mechanism to adjust the transmission power with lower computational overhead, reducing system resource consumption while meeting user needs. Through these two schemes, the system can adaptively adjust the transmission power in different environments, avoid the waste of resources caused by fixed power configuration, and achieve efficient and reliable communication under limited power conditions.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A power setting method for a RIS-assisted transmission system in a NOMA network is applied to a wireless communication system including a base station (BS), N RISs and K users (User), wherein the N RISs are named RIS1 to RIS N, and the nth RIS is equipped with L n reflection units, where n∈{1,2,...,N}, N≥2, K≥2. All RISs are deployed at different locations between the base station and the user. Both the base station and the user are single-antenna devices. There are two communication links from the BS to the User, one of which is direct communication between the BS and the User, and the other is communication between the BS and the User assisted by multiple RISs.

[0009] The power setting method of the RIS-assisted transmission system in the NOMA network specifically includes the following steps:

[0010] Step 1: The base station, N RISs, and K users perform channel estimation. First, the channel conditions between the base station and the user are estimated. Then, the channel conditions between the base station and the RIS, and between the RIS and the user are estimated, that is, the channel from the BS to each reflection unit on the N RISs, and the channel from each reflection unit on the N RISs to the kth user.

[0011] Step 2: The controller determines the reflection matrix of N RIS in the communication system according to the channel state information determined in step 1, notifies the N RIS and K users, and then determines the interruption probability requirements of the users. Set the transmit power of the base station.

[0012] Step 3: The base station sends a signal, and all RISs process the incident signal accordingly and reflect it to each user according to the working state and reflection matrix set by the controller.

[0013] Step 4: The user receives the transmitted signal from the base station and the reflected signal from the RIS. The user processes the received signal appropriately based on the RIS working state and the corresponding reflection matrix notified by the controller to ensure optimized signal transmission. Specifically, based on the RIS working state and the corresponding reflection matrix notified by the controller, the user first decodes the signal of the high-power user and eliminates its interference through the serial interference cancellation (SIC) technology, and then combines the RIS reflection matrix information to phase align and coherently combine the multipath signals from the base station and the activated RIS to maximize the effective signal strength and suppress interference, and finally achieve optimized demodulation of its own signal.

[0014] In step 2, when the transmission quality requirement indicator of all users is that the interruption probability must reach When the base station transmit power is set, the method is as follows:

[0015] Solution 1: Exhaustive RIS-aided (ERA) solution is adopted. All RIS participate in auxiliary communication. At this time, the optimal transmission power is for:

[0016]

[0017] Among them, the transmission power threshold at the kth user is Should meet:

[0018]

[0019] in, is the interruption probability threshold of the communication system, γ(·,·) is the lower incomplete Gamma function, and Z k The first-order moment and second-order moment of the channel coefficient of the kth user are expressed as is the variance of the Gaussian white noise generated by the kth user, γ th For a given interruption threshold, a i is the power allocation coefficient allocated to the i-th user, satisfying and a 1 >… >a k >… >a K , k ≥ q, Γ(·) is the Gamma function.

[0020] Solution 2: Opportunistic RIS-aided (ORA) solution is adopted to select the RIS with the best channel conditions from all RIS to participate in auxiliary communication. At this time, the optimal transmission power

[0021] The transmission power threshold of the kth user Should meet:

[0022]

[0023] in, is the interruption probability threshold of the communication system, and They are the channel coefficients h 0,k and M V,k The probability distribution function of , M is the approximate order, m∈{1,2,...,M}, is the variance of the Gaussian white noise generated by the kth user, γ th For a given interruption threshold, a i is the power allocation coefficient allocated to the i-th user, satisfying and a 1 >… >a k >… >a K , k≥q.

[0024] Compared with the prior art, the present invention can dynamically set the transmission power of the base station according to the needs of the user, so as to make full use of the limited power resources and maximize the performance of the communication system. This method can not only improve the communication quality, but also meet the user's transmission interruption probability requirements while ensuring low energy consumption, thus providing an efficient and energy-saving solution for RIS deployment in NOMA networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic diagram of the structure of a wireless communication system.

[0026] Figure 2 The figure is a flow chart of a method for setting power of a RIS-assisted transmission system in a NOMA network of the present invention.

[0027] Figure 3 The figure is a schematic diagram of the location distribution of BS, RIS and User in the present invention.

[0028] Figure 4 and Figure 5 The interruption probability change curves of User 1, User 2 and User 3 under the ERA scheme and the ORA scheme are shown respectively. And according to the method proposed by the present invention, the optimal transmission power has been calculated. DETAILED DESCRIPTION

[0029] The following is a further description with reference to the accompanying drawings and specific examples.

[0030] like Figure 1As shown, a power setting method for a RIS-assisted transmission system in a NOMA network is applied to a wireless communication system including a base station, N RISs (N≥2) and K users (K≥2), wherein the N RISs are named RIS1 to RIS N, and the nth RIS is equipped with L n reflection units, where n∈{1,2,...,N}. All RIS are deployed at different locations between the base station and the user. Both the base station and the user are single-antenna devices. In order to provide a more general system model and a more comprehensive performance analysis, the present invention assumes that a direct communication link from the BS to the User is available. Therefore, there are two communication links here, one of which is that there is no obstacle between the BS and the User, and direct communication can be carried out, and the other communication link is multiple RIS assisted communication.

[0031] The present invention proposes two purpose-oriented RIS-aided schemes, namely, an exhaustive RIS-aided (ERA) scheme and an opportunistic RIS-aided (ORA) scheme. The following is a specific analysis of the received signal expression, signal-to-interference-noise ratio expression and outage probability expression of the ERA scheme and the ORA scheme.

[0032] When the ERA scheme is adopted, all RIS participate in auxiliary communication, and the received signal expression at the kth user is:

[0033]

[0034] When the ORA scheme is adopted, the RIS with the best channel conditions participates in auxiliary communication. The following is the expression of the received signal at the kth user when the nth RIS assists communication:

[0035]

[0036] In the above received signal expression, the right side of the equation represents the expected signal and additive white Gaussian noise, k∈{1,2,...,K}, l∈{1,2,...,L n}, x i is the signal transmitted by the base station to the i-th user, P S is the average transmission power of the base station, a i is the power allocation coefficient allocated to the i-th user, satisfying and a 1 >… >a k >… >a K , w k is the Gaussian white noise generated by the kth user, with a mean of 0 and a variance of The average transmission signal-to-noise ratio is set to The channel coefficients of BS→User k (kth user), BS→RIS and RIS→User k can be expressed as Where j is the imaginary unit, h 0,k ,h nl , g nl,k is the amplitude of the channel coefficient, that is φ 0,k ,φ nl , ψ nl,k The channel coefficients are The phase of 0,k ,φ nl ,ψ nl,k}∈[0,2π), all channels obey independent Nakagami-m distribution.

[0037] Assume that the reflection phase matrix of the nth RIS assisting the kth user communication is where κ nl,k ∈(0,1] and θ nl,k ∈[0,2π) represent the amplitude and phase of the lth reflection unit of the nth RIS respectively. Assuming that each RIS has a high phase shift resolution and perfect channel state information, the nth RIS can produce an ideal phase shift when assisting the kth user communication. The phase error δ nl,k Can be zero, that is Ideal phase shift but:

[0038]

[0039] For the simplicity of symbols, according to the above analysis, we set Therefore, when using the ERA scheme, the channel coefficient expression of the kth user is When using the ORA scheme, the nth RIS with the best channel condition participates in auxiliary communication, and the channel coefficient expression of the kth user is

[0040] In NOMA technology, the base station communicates with all users at the same time. User k receives information from K users. User k needs to correctly decode the first k-1 users in the decoding order from high-power users to low-power users before it can decode its own information.

[0041] When the ERA scheme is adopted, based on the received signal expression at the user, according to the NOMA principle, the received signal-to-interference-noise ratio expression when the kth user decodes the qth user information (k≥q) is:

[0042]

[0043] Simplifying the above formula, we get:

[0044]

[0045] When the ORA scheme is adopted, based on the received signal expression at the user, according to the NOMA principle, when the nth RIS assists communication, the received signal-to-interference-noise ratio expression when the kth user decodes the qth user information (k≥q) is:

[0046]

[0047] The optimal nth RIS index can be expressed as:

[0048]

[0049] Therefore, argmax represents the value of the independent variable when the function takes the maximum value, and the channel coefficient R of the ORA scheme is k Can be simplified to Then the signal-to-interference-to-noise ratio expression of the ORA scheme is:

[0050]

[0051] Among them, h n*l , g n*l,k They represent the amplitudes of the channel coefficients from BS to the nth RIS with the best channel condition and from the nth RIS with the best channel condition to User k, κ n*l,k Indicates the amplitude of the lth reflection unit of the nth RIS with the best channel conditions.

[0052] Z k The true distribution of can be approximated by Gamma distribution, mainly using and Two parameters are used to represent it, namely in and The estimates are as follows:

[0053]

[0054] in, and Z k The first and second moments of in and They are h 0,k The first and second moments of and T kThe first and second order moments of .

[0055] Z k The approximate cumulative density function CDF is It can be expressed by the following formula:

[0056]

[0057] Among them, Γ(·) is the Gamma function, γ(·,·) is the lower incomplete Gamma function, and z is the variable of the probability distribution function.

[0058] R k The cumulative density function CDF approximate closed expression is as follows:

[0059]

[0060] in, and They are the channel coefficients h 0,k and M V,k The probability distribution function of M is the approximate order, m∈{1,2,...,M}, and x is the function variables.

[0061] The outage probability in a wireless communication system is defined as the instantaneous received signal-to-interference-to-noise ratio γ of the system is less than a given outage threshold γ th The probability that when γ<γ th The wireless communication system can be considered to be in an interrupted state. If any process of user k is interrupted during decoding of information from user 1 to user k, the communication system is interrupted. Therefore, the interruption probability of the communication system is equal to 1 minus the probability that the first k users can successfully decode, and the probability that the first k users can successfully decode is equal to the probability that the first to k users can successfully decode multiplied. Suppose the interruption probability threshold of the entire communication system is The following is a method for setting the optimal transmission power under the ERA scheme and the ORA scheme.

[0062] When using the ERA scheme, if the kth user cannot successfully decode the information of the qth user, an interruption occurs and this event is recorded as:

[0063]

[0064] Then the interruption probability of the kth user decoding the qth user information is:

[0065]

[0066] in, To satisfy The conditional probability, and Otherwise the user will remain interrupted.

[0067] Therefore, when the ERA scheme is adopted, if any process of user k is interrupted during the decoding process from user 1 to user k, the communication system is interrupted. Then the interruption probability of the kth user decoding its own information is equal to 1 minus the probability that the first k users can successfully decode, which is:

[0068]

[0069] Therefore, the transmit power threshold of each user using the ERA scheme is Should meet:

[0070]

[0071] Only K users have interruption probabilities that are less than or equal to the interruption probability threshold at the same time When In order to meet the needs of the entire communication system. Therefore, the transmission power of the base station must be greater than or equal to the transmission power threshold of K users. The largest one can meet the needs of the entire communication system, and the optimal transmission power using the ERA solution can be obtained. for:

[0072]

[0073] When using the ORA scheme, if the kth user cannot successfully detect the information of the qth user, an interruption occurs and this event is recorded as:

[0074]

[0075] Then the interruption probability of the kth user decoding the qth user information is:

[0076]

[0077] in, Otherwise the user will remain interrupted.

[0078] Therefore, when the ERA scheme is adopted, the interruption probability when the kth user decodes its own information is:

[0079]

[0080] Therefore, the transmit power threshold of each user using the ORA scheme is Should meet:

[0081]

[0082] Only K users have interruption probabilities that are less than or equal to the interruption probability threshold at the same time When In order to meet the needs of the entire communication system. Therefore, the transmission power of the base station must be greater than or equal to the transmission power threshold of K users. The largest one can meet the needs of the entire communication system, and the optimal transmission power using the ORA solution can be obtained. for:

[0083]

[0084] Figure 4 and Figure 5 The interruption probability change curves of User 1, User 2 and User 3 under the ERA scheme and the ORA scheme are shown respectively, and two target interruption probabilities are marked in the figure. Based on the method proposed in the present invention, the optimal transmission power of the entire communication system under the two conditions has been calculated respectively. Figure 4 and Figure 5 Further analysis shows that the ERA and ORA schemes are significantly better than the randomly selected RIS-assisted scheme in terms of outage probability performance. From the perspective of the transmission power requirement corresponding to the target outage probability, the two schemes proposed in the present invention require significantly lower power, which indicates that the scheme proposed in the present invention can meet strict reliability requirements with lower energy consumption, while the random selection scheme needs to significantly increase power to compensate for the performance loss caused by the unoptimized channel.

[0085] From the changing trends of these curves, it can be observed that as the transmission power gradually increases, the interruption probability of each user continues to decrease. This trend shows that a reasonable increase in the transmission power can effectively reduce the interruption probability, thereby improving the communication reliability and overall transmission performance of the system. However, the setting of the optimal transmission power is not simply to increase the power to achieve the lowest interruption probability, but to select based on precise power control criteria. Specifically, the condition for determining the optimal transmission power is that the interruption probability of all users meets or is lower than the preset target interruption probability for the first time. Only when the system as a whole meets this constraint condition is the transmission power value considered to be optimal. Figure 4 and Figure 5 This relationship is presented intuitively, and the optimal transmission power corresponds to the intersection point where the interruption probability of all users reaches the target value. At this point, the system achieves effective setting of transmission power while ensuring the quality of user communication, thereby avoiding energy waste caused by excessive power allocation.

[0086] The power setting method proposed in the present invention does not rely on a complex power allocation mechanism, but achieves optimal communication performance under power-constrained conditions by reasonably setting the transmission power. This method can flexibly adapt to user needs in different network environments and ensure that the RIS-assisted transmission system in the NOMA network maintains efficient and stable communication under a limited power budget. Its advantage is that by dynamically adjusting the transmission power, it can effectively balance the relationship between power consumption and communication reliability, thereby providing an efficient and low-energy power management solution, which has important theoretical significance and practical application value.

Claims

1. A power setting method for a RIS-assisted transmission system in a NOMA network, characterized in that: The method is applied to a wireless communication system including a base station, N RISs and K users. The N RISs are named RIS1 to RIS N respectively. The nth RIS is equipped with L n reflection units, where n∈{1,2,...,N}, N≥2, K≥2, all RIS are deployed at different locations between the base station and the user, the base station and the user are single-antenna devices, there are two communication links from the base station to the user, one is the direct communication between the base station and the user, the other is the communication between the base station and the user through multiple RISs; When the transmission quality requirement indicator of all users is that the interruption probability must reach When the transmission power of the base station is set, the method is: adopt the exhaustive RIS auxiliary scheme, all RIS participate in auxiliary communication, at this time, the optimal transmission power for: Among them, the transmission power threshold at the kth user is Should meet: in, is the interruption probability threshold of the communication system, γ(·,·) is the lower incomplete Gamma function, and Z k The first-order moment and second-order moment of the channel coefficient of the kth user are expressed as h 0,k ,h nl , g nl,k are the amplitudes of the channel coefficients from BS→user k, BS→RIS, and RIS→user k, respectively, nl,k ∈(0,1] represents the amplitude of the lth reflection unit of the nth RIS, k∈{1,2,...,K}, l∈{1,2,...,L n }, is the variance of the Gaussian white noise generated by the kth user, γ th For a given interruption threshold, a i is the power allocation coefficient allocated to the i-th user, satisfying and a1>…>a k >… >a K , k ≥ q, Γ(·) is the Gamma function.

2. A power setting method for a RIS-assisted transmission system in a NOMA network, characterized in that: The method is applied to a wireless communication system including a base station, N RISs and K users. The N RISs are named RIS1 to RIS N respectively. The nth RIS is equipped with L n reflection units, where n∈{1,2,...,N}, N≥2, K≥2, all RIS are deployed at different locations between the base station and the user, the base station and the user are single-antenna devices, there are two communication links from the base station to the user, one is the direct communication between the base station and the user, the other is the communication between the base station and the user through multiple RISs; When the transmission quality requirement indicator of all users is that the interruption probability must reach When the base station transmit power is set, the method is as follows: Adopt the opportunistic RIS auxiliary scheme, select the RIS with the best channel conditions from all RIS to participate in auxiliary communication, and the optimal transmission power is Among them, the transmission power threshold at the kth user is Should meet: in, is the interruption probability threshold of the communication system, and They are the channel coefficients h 0,k and M V,k The probability distribution function of M is the approximate order, m∈{1,2,...,M}, is the variance of the Gaussian white noise generated by the kth user, γ th For a given interruption threshold, a i is the power allocation coefficient allocated to the i-th user, satisfying and a1>...>a k >… >a K , k≥q.

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