Optimal selection method of RIS in NOMA network under power limited condition

Abstract

The invention discloses an optimal selection method of an RIS (Radio Information System) in an NOMA (Non-Orthogonal Multiple Access) network under a power limited condition, which is applied to a wireless communication system consisting of three parts, namely a base station (BS), a plurality of RISs and a plurality of users (Users). When the power provided for the whole communication system is relatively high, all RISs work at the same time and can participate in auxiliary communication. When the power provided for the whole communication system is not enough to support all RISs to work at the same time, the previous RIS with the best transmission effect works, and other RISs sleep. When the power provided for the whole communication system is low, all RISs sleep, no RIS participates in auxiliary communication, and only direct communication between the BS and the User is carried out. According to the invention, the working state of each RIS can be dynamically adjusted according to the power provided for the whole communication system, and the communication quality of the communication system is improved under the condition of lower energy consumption.

Description

Technical Field

[0001] The present invention relates to an optimal selection method of RIS in a NOMA network under power-constrained conditions, and the method is characterized in that the system can dynamically adjust the working states of all RIS according to power. Background Art

[0002] With the continuous development of wireless communication technology, NOMA (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 utilization efficiency of the spectrum 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 received 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 consumes a certain amount of system power, especially in large-scale networks. How to effectively utilize limited power resources has become a major challenge. In the existing technology, most RIS selection and scheduling methods do not fully consider the power limitation situation. When power resources are insufficient, they often cannot effectively select a suitable RIS for assistance, thus affecting the communication quality.

[0005] Therefore, the present invention proposes an optimal selection method for RIS in NOMA network under power-constrained conditions, which can dynamically adjust the working state of each RIS according to the power provided to the entire communication system to make full use of 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, thereby providing an efficient and energy-saving solution for RIS deployment in NOMA network. Summary of the invention

[0006] The purpose of the present invention is to provide an optimal selection method for RIS in a NOMA network under limited power resource conditions, so as to improve the communication quality of the NOMA network (such as reducing the interruption probability) and reduce system power consumption.

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

[0008] An optimal selection method for RIS in a NOMA network under power-constrained conditions is applied to a wireless communication system including a base station (BS), N RISs and K users, where all RISs are 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. The first is direct communication between the BS and the User, and the second is communication between the BS and the User assisted by multiple RISs.

[0009] The optimal selection method of RIS in the NOMA network under the power-limited condition specifically includes the following steps:

[0010] Step 1: The base station, N RISs, and K users perform channel estimation. First, the channel between the base station and the user is estimated. Then, the channel between the base station and the RIS, and the channel 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 working states and reflection matrices of N RISs in the communication system according to the channel state information determined in step 1 and the power provided to the entire communication system, and notifies the N RISs and K users;

[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: According to the working states of the N RISs determined in step 2, the user receives the transmission signal from the base station and the reflected signal of the RIS in normal working state, and the user processes the received signal appropriately according to the working state of the RIS notified by the controller and the corresponding reflection matrix to ensure the optimized transmission of the signal. The appropriate processing of the received signal specifically refers to first decoding the signal of the high-power user and eliminating its interference through the serial interference cancellation (SIC) technology, and then combining 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 the optimized demodulation of the own signal.

[0014] In step 2, the working status of N RIS is analyzed as follows:

[0015] if Then all RIS participate in auxiliary communication;

[0016] if Then, according to the power that the current system can provide to the RIS, the first s RIS with the best channel conditions are selected to assist in communication;

[0017] if Then all RIS cannot work normally, and only direct communication between the base station and the user can be carried out.

[0018] Among them, P tol is the power provided to the entire communication system, P S is the base station transmit power, is the circuit dissipation power of the lth reflector unit on the nth RIS, P RIS is the power consumed by the RIS in normal working condition, s is the number of RIS in normal working state, s∈{1,2,...,N}, is the circuit dissipation power of the base station, is the circuit dissipation power per user.

[0019] In step 2, the reflection matrix of N RIS is determined as follows:

[0020] 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.

[0021] In step 1, all channels obey independent Nakagami-m distributions. The channel coefficients from BS to the kth user, from BS to each reflection unit on the Nth RIS, and from each reflection unit on the N RIS to the kth user can be expressed as where h 0,k ,h nl , g nl,k is the size of the channel coefficient, φ 0,k ,φ nl , ψ nl,k The channel coefficients are The phase of 0,k ,φ nl ,ψ nl,k}∈[0,2π).

[0022] Compared with the prior art, the present invention makes full use of the power provided and can dynamically adjust the working state of each RIS according to the power provided to the entire communication system, so as to make full use of 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, thereby providing an efficient and energy-saving solution for RIS deployment in NOMA networks. Compared with the traditional method of using all RIS to work at the same time or relying on a single RIS for transmission, the method of the present invention can intelligently select the RIS with the best transmission effect for assistance when power is insufficient, thereby significantly reducing energy consumption and improving the overall performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the wireless communication system of the present invention.

[0024] Figure 2 The figure is a flow chart of the optimal selection method of RIS in NOMA network under power-constrained conditions according to the present invention.

[0025] Figure 3 The figure is a schematic diagram of the location distribution of BS, RIS and User in the present invention.

[0026] Figure 4 , Figure 5 and Figure 6 The following are the interruption probability variation curves of the system when different transmission schemes are used, depending on the power provided to the entire communication system when User 1, User 2 and User 3 have different transmission powers.

[0027] Figure 7 The energy consumption curves of different transmission schemes are shown in Figure 2 when the transmit power is different. DETAILED DESCRIPTION

[0028] The following is a further description with reference to the accompanying drawings and specific examples.

[0029] like Figure 1 As shown in FIG. 1 , an optimal selection method for RIS in a NOMA network under power-constrained conditions is applied to a wireless communication system consisting of a base station, N RISs (N ≥ 2) and K users (K ≥ 2). 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. The base station and the user are both 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 base station and the user, and direct communication can be carried out, and the other communication link is multiple RIS assisted communication.

[0030] Assume that the power provided to the entire communication system is P tol , including the base station transmission power and the circuit dissipation power (CDP) of each component. The base station transmission power is defined as P S , is the CDP on the lth reflector unit on the nth RIS, P RIS is the power consumed by all RIS in normal working condition, s is the number of RIS in normal working state, l∈{1,2,...,L n}, is the CDP of the base station, is the CDP of each user, and the power consumed by the entire communication system is defined as The power supplied by the system to RIS is equal to

[0031] The following is a detailed analysis of the received signal expression and signal-to-interference-noise ratio expression under different power conditions:

[0032] Case 1: If Then all RIS participate in the auxiliary communication. This transmission scheme is named Exhaustive RIS-aided (ERA) scheme. The received signal expression at the kth user is:

[0033]

[0034] 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:

[0035]

[0036] Case 2: If According to the power that the current system can provide to RIS, the first s RIS with the best channel conditions are selected to assist in communication. This transmission scheme is named Opportunistic RIS-aided (ORA) scheme. The received signal expression at the kth user is:

[0037]

[0038] Among them, sort t (·) means the tth element after sorting the sequence in descending order of modulus value.

[0039] 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:

[0040]

[0041] Case 3: If Then all RIS cannot work properly, and only direct communication between the base station and the user can be carried out. This transmission scheme is named non-RIS, and the received signal expression at the kth user is:

[0042]

[0043] 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:

[0044]

[0045] In the above received signal expression, the right side of the equation represents the expected signal and additive white Gaussian noise, respectively. 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 a1>…>a k >… >a K , w kis the Gaussian white noise generated by the kth user. The channel coefficients of BS→User k, BS→RIS and RIS→User k can be expressed as Where j is the imaginary unit, k∈{1,2,...,K}, h 0,k ,h nl , g nl,k is the size 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.

[0046] For the simplicity of symbols, according to the above analysis, the expression of the channel coefficient of the ERA scheme is:

[0047]

[0048] The channel coefficient expression of the ORA scheme is:

[0049]

[0050] 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 Therefore, the channel coefficient Z k Can be simplified to Channel coefficient R k Can be simplified to but and Simplified to:

[0051]

[0052] The outage probability in a wireless communication system is defined as the instantaneous 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 thThe wireless communication system can be considered to be in an interrupted state. Therefore, the interruption probability at the kth user is:

[0053]

[0054] in, To satisfy The conditional probability, is the interruption threshold of the qth user.

[0055] Figure 4 , Figure 5 , Figure 6 The relationship between the interruption probability and the transmission power of User 1, User 2 and User 3 when using different transmission schemes is shown in the figure. It can be seen from the figure that if the power provided to the entire communication system is low, then all RISs are dormant, no RIS participates in auxiliary communication, and the non-RIS scheme is adopted. At this time, the interruption probability of the system is high. If the power provided to the system is high, then all RISs participate in auxiliary communication, that is, the ERA scheme is adopted, and the interruption power of the system is low. If the power provided only supports the normal operation of some RISs, the ORA scheme is adopted, and s RISs with the best channel conditions are selected for auxiliary communication. Compared with randomly selecting s RISs for auxiliary communication, the interruption probability of the scheme proposed by the present invention is lower. As the transmission power increases, the interruption probability suddenly increases because the power provided by the system is insufficient to support the original number of RISs for auxiliary communication, and the normal working RIS is reduced by one, resulting in an increase in the interruption probability.

[0056] Figure 7 The figure shows the energy consumption when using different transmission schemes. It can be seen from the figure that when the non-RIS scheme is used, there is no RIS to assist in communication, and the power consumption of the system is particularly low. When the ERA scheme is used, all RIS participate in assisting communication, and the power consumption of the system is particularly high. If the power provided only supports the normal operation of some RIS, the ORA scheme is used at this time. The power consumption of selecting s RIS with the best channel conditions is the same as that of randomly selecting s RIS to assist in communication. Figure 4 , Figure 5 , Figure 6 It can be seen from the interruption probability curve in that, compared with randomly selecting s RIS to assist in communication, the scheme proposed in the present invention has a lower interruption probability while consuming the same power.

Claims

1. An optimal selection method for RIS in a NOMA network under power-constrained conditions, characterized in that: The method is applied to a wireless communication system including a base station, N RISs and K users, wherein 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, both the base station and the user are single-antenna devices, there are two communication links from the base station to the user, the first is direct communication between the base station and the user, the second is communication between the base station and the user through multiple RISs; The optimal selection method of RIS in NOMA network is as follows: if Then all RIS participate in auxiliary communication; if Then, according to the power that the current system can provide to the RIS, the first s RIS with the best channel conditions are selected to assist in communication; if Then all RIS cannot work normally, and only direct communication between the base station and the user can be carried out. Among them, P tol is the power provided to the entire communication system, P S is the base station transmit power, is the circuit dissipation power of the lth reflector unit on the nth RIS, P RIS is the power consumed by the RIS in normal working condition, s is the number of RIS in normal working state, s∈{1,2,...,N}, is the circuit dissipation power of the base station, is the circuit dissipation power of each user, and the power consumed by the entire communication system is

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