Power distribution optimization method of D2D cooperative NOMA system

Abstract

The invention provides a power distribution optimization method of a D2D cooperative NOMA (Non-Orthogonal Multiple Access) system, which comprises the following steps of: firstly, constructing a D2D-assisted cooperative NOMA system model for two-time slot transmission, and calculating to obtain a system user average error probability and a system average effective throughput under a short packet communication constraint condition; and then solving an optimal power distribution strategy by using an iterative algorithm by maximizing the average effective throughput of the system. The method has the advantages that D2D communication is used under the short packet communication constraint condition, the pressure of the base station can be relieved, and the transmission delay is reduced. Compared with an existing cooperative NOMA system, the user transmission rate is improved, and the average effective throughput of the system is increased.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and specifically to a power allocation optimization method for a D2D cooperative NOMA system in a short packet communication scenario. Background Technology

[0002] Short packet communication, as a key technology in 5G and subsequent communication systems, is widely used in scenarios with stringent requirements for transmission latency and reliability, such as vehicle-to-everything (V2X) and industrial IoT. In these scenarios, data block lengths are relatively short, rendering traditional long packet communication theory based on Shannon channel capacity inapplicable. Therefore, it is necessary to combine finite block length communication theory with these technologies to analyze system performance.

[0003] NOMA technology differentiates between different users in the power domain, enabling multiple users to share the same time-frequency resources, effectively improving spectrum utilization and system capacity. Meanwhile, D2D communication allows neighboring users to transmit data directly without base station forwarding, alleviating base station transmission pressure and reducing end-to-end latency. Combining D2D communication with NOMA technology to build a D2D-assisted cooperative NOMA system can further optimize system performance in short packet communication scenarios.

[0004] Existing power allocation strategies in cooperative NOMA systems are mostly based on the assumption of long packet communication, failing to fully consider the finite block length characteristics of short packet communication. This results in insufficient average effective throughput in low-latency, short-packet transmission scenarios, making it difficult to meet user transmission rate demands. Therefore, there is an urgent need for a power allocation optimization method adapted to the constraints of short-packet communication, maximizing the system's average effective throughput and improving communication performance. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a power allocation optimization method for D2D cooperative NOMA systems, maximizing the system's average effective throughput. The technical solution provided by this invention is as follows:

[0006] A power allocation optimization method for a D2D cooperative NOMA system is proposed for a short-packet communication-based D2D cooperative NOMA downlink system, wherein the system includes one base station U and one relay node with D2D communication capability. and 2 user nodes and All nodes are configured with a single antenna and operate in half-duplex mode. The relay nodes use a decoding and forwarding protocol. Each node supports perfect continuous interference cancellation. All links undergo independent Rayleigh fading and use short data packet transmission, including the following steps.

[0007] Step 1: Based on the system's preset two-timeslot transmission mechanism, channel characteristics, and power allocation coefficient constraints, derive the data from the first timeslot base station to the user node. 1. Base station to relay node, 2. Second time slot relay node to user node Relay node to user node Substitute the instantaneous signal-to-noise ratio (SNR) expressions for each link into the channel fading gain and transmission SNR parameters to calculate the instantaneous SNR of each link;

[0008] Step 2: Based on the finite block length communication theory, and using the instantaneous signal-to-noise ratio of each link obtained in Step 1 as a basis, establish an instantaneous error probability model. Combined with the probability density function of the Rayleigh fading channel, derive the closed-form expression for the average block error probability of each link. Then, based on the two-slot transmission mechanism and the definition of the average effective throughput of users, integrate to obtain the total average effective throughput of the system.

[0009] Step 3: Employ an adaptive step-size one-dimensional search iterative algorithm to determine the power allocation coefficient in the second time slot. An iterative search within the feasible region is performed to find the optimal power allocation coefficient that maximizes the average effective throughput of the system. The algorithm is implemented by "coarse search to locate the optimal interval + fine search to solve accurately", which balances optimization accuracy and computational efficiency.

[0010] Preferably, the system's preset two-timeslot transmission mechanism specifically involves: the first timeslot base station transmitting data to the user node... The NOMA signal is superimposed on the relay node broadcast, and the signal expression is: ,in This represents the total transmission power of the base station. , Signals , The power allocation factor, and satisfying , User node Direct Decoding The relay node first decodes by eliminating continuous interference. And obtain after elimination The second time slot relay node superimposes and forwards signals in NOMA mode. With its own D2D signal The signal expression is ,in This refers to the relay node's transmit power. , Signals , The power allocation factor, and satisfying , User node decoding User node Decoding by eliminating continuous interference And obtain the signal after elimination .

[0011] Preferably, the parameters in step 1 are: For nodes With nodes Channel fading gain between ,in The node spacing, This is the path loss index. It exhibits small-scale fading and follows a cyclic symmetric complex Gaussian distribution with a mean of 0 and a variance of 1; For the transmission signal-to-noise ratio, where For signal power, This represents the noise power spectral density.

[0012] Preferably, the derivation process of the closed-form expression for the average block error probability of each link is as follows: the instantaneous error probability of short packet transmission is approximately: ,in For Shannon capacity, For channel dispersion, For signal-to-noise ratio, It is a Gaussian Q-function. The number of bits of signal data. Given the data packet block length; combining the characteristics of Rayleigh fading channels, integrating the instantaneous error probability, we obtain a closed-form expression for the average block error probability of each link. Key expressions include:

[0013] First time slot: ;

[0014] Second time slot: , ;in , For the achievable signal rate, This represents the average channel gain.

[0015] Preferably, the total average effective throughput of the system is: .

[0016] Preferably, the specific process of the adaptive step-size one-dimensional search iterative algorithm in step 3 is as follows:

[0017] Step 3.1: Initialize parameters, input system fixed parameters, and set the power distribution coefficient. Initial large step size Detailed search with small steps ;

[0018] Step 3.2: Use coarse search to locate the optimal candidate interval, traverse the feasible region with a large step size, calculate the average effective throughput corresponding to each position, update the historical best value and the optimal candidate interval, until all feasible points have been traversed.

[0019] Step 3.3: Fine-grained search for precise solution. Traverse the optimal candidate interval with small step sizes, calculate the average effective throughput corresponding to each position, and stop when the search reaches the right endpoint of the optimal interval, and update the optimal value.

[0020] Compared with the prior art, the beneficial effects achieved by this invention are as follows: This invention performs mathematical modeling of a D2D cooperative NOMA system based on finite block length communication, calculates the average error probability of each node in the system, and gives the average effective throughput of the system based on the average error probability of each node. The expression that maximizes As the ultimate optimization objective, an adaptive step-size one-dimensional search iterative algorithm is used for optimization. This dynamic adaptation logic, which combines "quickly locking the target range with fine-search for accurate solution," balances efficiency and accuracy, and is the core manifestation of the proposed algorithm's "adaptive" nature. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 This is a schematic diagram of the system model of D2D cooperative NOMA communication based on short packet communication according to the present invention;

[0023] Figure 2 This is a flowchart of the method of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objectives, features and effects of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1: This method is applicable to a D2D cooperative NOMA downlink system based on short packet communication. The system includes one base station, one relay node (user 3) with D2D communication capabilities, and two user equipment units. All nodes are configured with a single antenna and operate in half-duplex mode. The relay node uses a decoding-forwarding protocol. Each node supports perfect continuous interference cancellation. All links undergo independent Rayleigh fading and use short data packet transmission. The two-timeslot transmission mechanism of the system is as follows: In the first time slot, the base station broadcasts a superimposed NOMA signal to user 1 and the relay node. The signal expression is: ,in This represents the total transmission power of the base station. , Signals , The power allocation factor, and satisfying , User 1 directly decodes The relay node first decodes by eliminating continuous interference. And obtain after elimination The second time slot relay node superimposes and forwards signals in NOMA mode. With its own D2D signal The signal expression is ,in This refers to the relay node's transmit power. , Signals , The power allocation factor, and satisfying , User 1 Decoding User 2 decodes by eliminating continuous interference. And obtain the signal after elimination This method includes the following steps:

[0027] Step 1: Based on the system's preset two-timeslot transmission mechanism, channel characteristics, and power allocation coefficient constraints, derive the instantaneous signal-to-noise ratio (SNR) expressions for each link in the first timeslot from the base station to user 1, from the base station to the relay node, and from the relay node to user 1 and from the relay node to user 2 in the second timeslot. Substitute parameters such as channel fading gain and transmission SNR to complete the calculation of the instantaneous SNR for each link.

[0028] Step 2: Based on the finite block length communication theory, and using the instantaneous signal-to-noise ratio of each link obtained in Step 1 as a basis, establish an instantaneous error probability model. Combine the probability density function of the Rayleigh fading channel to derive the closed-form expression of the average block error probability of each link. Then, based on the two-timeslot transmission mechanism and the definition of the average effective throughput of users, integrate to obtain the total average effective throughput of the system.

[0029] Step 3: Employ an adaptive step-size one-dimensional search iterative algorithm to determine the power allocation coefficient in the second time slot. An iterative search within the feasible region is performed to find the optimal power allocation coefficient that maximizes the average effective throughput of the system. The algorithm is implemented by "coarse search to locate the optimal interval + fine search to solve accurately", which balances optimization accuracy and computational efficiency.

[0030] In step 1, the system typically uses a Rayleigh fading channel, and the key parameters are defined as follows: For nodes With nodes Channel fading gain between ,in The node spacing, This is the path loss index. It exhibits small-scale fading and follows a cyclic symmetric complex Gaussian distribution with a mean of 0 and a variance of 1; For the transmission signal-to-noise ratio, where For signal power, This represents the noise power spectral density.

[0031] In step 2, based on the finite block length communication theory, the instantaneous error probability of short packet transmission is approximately: ,in For Shannon capacity, For channel dispersion, For signal-to-noise ratio, It is a Gaussian Q-function. The number of bits of signal data. Given the data packet block length; combining the characteristics of Rayleigh fading channels, integrating the instantaneous error probability, we obtain a closed-form expression for the average block error probability of each link. Key expressions include:

[0032] First time slot: ;

[0033] Second time slot: , ;

[0034] in , For the achievable signal rate, The average effective throughput of the system can be derived from the expression for the average error probability of each link, which represents the average channel gain. :

[0035] .

[0036] The specific process for obtaining the system's optimal power allocation coefficient and maximum average effective throughput using the adaptive step-size one-dimensional search iterative algorithm in step 3 is as follows:

[0037] Step 3.1: Initialize parameters, input system fixed parameters, and set the power distribution coefficient. Initial large step size Detailed search with small steps ;

[0038] Step 3.2: Use coarse search to locate the optimal candidate interval, traverse the feasible region with a large step size, calculate the average effective throughput corresponding to each position, update the historical best value and the optimal candidate interval, until all feasible points have been traversed.

[0039] Step 3.3: Fine-grained search for precise solution. Traverse the optimal candidate interval with small step sizes, calculate the average effective throughput corresponding to each position, and stop when the search reaches the right endpoint of the optimal interval, and update the optimal value.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1.A method for power allocation optimization in a D2D cooperative NOMA system, characterized in that, A D2D cooperative NOMA downlink system based on short packet communication, the system includes 1 base station U, 1 relay node with D2D communication function And 2 user nodes And All nodes are configured with a single antenna and work in half duplex mode, the relay node adopts decode and forward protocol, each node supports perfect successive interference cancellation, all links experience independent Rayleigh fading and adopt short data packet transmission, including the following steps; Step 1, based on the system preset two time slot transmission mechanism, channel characteristics and power allocation coefficient constraint, deduce the first time slot base station to user node , base station to relay node, second time slot relay node to user node , relay node to user node The expression of each link instantaneous signal-to-noise ratio, substitute the channel fading gain, transmission signal-to-noise ratio parameter, calculate the instantaneous signal-to-noise ratio of each link; Step 2, based on the theory of finite block length communication, the instantaneous error probability model is established based on the instantaneous SNR of each link obtained in step 1, and the closed-form expression of the average block error probability of each link is derived by combining the probability density function of Rayleigh fading channel; then the total average effective throughput of the system is integrated according to the two-time slot transmission mechanism and the definition of user average effective throughput; Step 3, using an adaptive step one-dimensional search iterative algorithm to search iteratively in the feasible region of the second time slot power allocation coefficient , to solve the optimal power allocation coefficient that maximizes the system average effective throughput, which is realized by "coarse search positioning optimal interval + fine search accurate solution", and takes into account optimization accuracy and computational efficiency. 2.The power allocation optimization method for D2D cooperative NOMA system according to claim 1, characterized in that, The two time slot transmission mechanism preset by the system is specifically: the first time slot base station broadcasts superimposed NOMA signals to user nodes and relay nodes, and the signal expression is , wherein is the total transmission power of the base station, , are power allocation coefficients of the signals , , and satisfy , ; the user nodes directly decode , and the relay nodes acquire by first decoding through successive interference cancellation and then canceling Second time slot relay node superimposes forwarding signal in NOMA mode With self D2D signal , signal expression is Wherein is the relay node transmission power, , is the power allocation coefficient of signal , respectively, and satisfies , ; user node decodes , user node decodes through successive interference cancellation and obtains signal after cancellation. 3.The power allocation optimization method for D2D cooperative NOMA system of claim 2, wherein, The parameters in step 1 are: the channel fading gain between the node and the node , where is the distance between the nodes, is the path loss exponent, is the small scale fading and is a circularly symmetric complex Gaussian distribution with mean 0 and variance 1; is the transmission signal to noise ratio, where is the power of the signal , is the noise power spectral density. 4.The method of Claim 2, wherein, The derivation process of the closed-form expression of the average block error probability of each link is as follows: the instantaneous error probability of short packet transmission is approximated as wherein is the Shannon capacity, is the channel dispersion, is the signal-to-noise ratio, is the Gaussian Q function, is the number of signal data bits, is the data packet block length; Combined with the characteristics of Rayleigh fading channel, the instantaneous error probability is integrated to obtain the closed-form expression of the average block error probability of each link, and the key expressions include: First time slot: ; Second time slot: , ; wherein , is the signal attainable rate, is the average channel gain. 5.The power allocation optimization method for D2D cooperative NOMA system of claim 4, wherein, The system total average effective throughput is: . 6.The power allocation optimization method for D2D cooperative NOMA system of claim 1, wherein, The specific process of the adaptive step one-dimensional search iterative algorithm in step 3 is as follows: Step 3.1, initialize parameters, input system fixed parameters, set power distribution coefficient , initial large step size , fine search small step size ; Step 3.2, coarse search to locate the optimal candidate interval, traverse the feasible region with large step size, calculate the average effective throughput corresponding to each position, update the historical optimal value and the optimal candidate interval, until the search is completed to traverse all feasible points; Step 3.3, fine search for accurate solution, traverse with small step size in the optimal candidate interval, calculate the average effective throughput corresponding to each position, until the search is completed to the right endpoint of the optimal selected interval, update the optimal value.

Images