VLC / RF heterogeneous network resource optimization method based on cooperative NOMA

Abstract

The invention discloses a VLC / RF heterogeneous network resource optimization method based on cooperative NOMA, and relates to the field of resource allocation in a heterogeneous network, and the method comprises the steps: S1, building a mathematical model according to the scene of an indoor double-hop VLC / RF heterogeneous network system; s2, establishing a joint optimization problem of multivariable coupled mixed integer nonlinear programming MINLP according to the mathematical model obtained in the step S1; and S3, solving the optimization problem in the step S2. According to the VLC / RF heterogeneous network resource optimization method based on the cooperative NOMA, the total transmission rate is maximized under the limitation of the user connectivity, the transmitting power and the user QoS, so that a strong-weak user pair, a service link of each weak user and the transmission power of each user are jointly determined, and the transmission efficiency of the VLC / RF heterogeneous network resource optimization method based on the cooperative NOMA is improved. The problems of limited spectrum resources and non-uniform QoS distribution in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the field of resource allocation in heterogeneous networks, and in particular to a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA. Background Art

[0002] Although VLC's high data rate characteristics are promising, the VLC channel deteriorates significantly with increasing distance, and communication via light is easily blocked by intermediate obstacles, resulting in a large difference in the quality of service received by users, resulting in an uneven QoS distribution problem. Some users (hereafter referred to as strong users) will be well covered, while marginal users (hereafter referred to as weak users) will be poorly covered. In addition, the user's field of view (FOV) also plays a key role in the experience of a single user, because increasing the user's FOV will increase the probability of LoS availability but attenuate the received power, while reducing the FOV will have the opposite effect.

[0003] Therefore, it is necessary to provide a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, which maximizes the total transmission rate under the constraints of user connectivity, transmission power and user QoS, thereby jointly determining the strong-weak user pairs, the service link of each weak user and the transmission power of each user, and solving the existing problems of limited spectrum resources and uneven QoS distribution.

[0005] To achieve the above object, the present invention provides a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, comprising the following steps:

[0006] S1: Establish a mathematical model based on the scenario of indoor dual-hop VLC / RF heterogeneous network system;

[0007] S2: Establishing a joint optimization problem of multivariable coupled mixed integer nonlinear programming MINLP according to the mathematical model obtained in step S1; specifically comprising the following steps:

[0008] S21: Establishing a transmission rate expression between the access point AP and the user;

[0009] S22: Establishing an optimization objective function expression;

[0010] S23: Establishing optimization problem constraint expressions;

[0011] S24: Under the constraints in step S23, a joint optimization problem is established with the goal of maximizing the expression of the objective function in step S22;

[0012] S3: Solve the optimization problem in step S2.

[0013] Preferably, in step S1, based on the characteristics that VLC provides high throughput and low-cost data communication, highly relies on line-of-sight LoS channels and has limited coverage, and RF provides wide coverage, the VLC and RF networks are heterogeneous, and a mathematical model is established for the total transmission rate of the heterogeneous networks under the constraints of user connectivity, transmission power and user QoS.

[0014] Preferably, in step S21, the dual-hop VLC / RF heterogeneous network system model consists of a VLC-AP and N u =2K multiple users, where K is the number of user pairs. Users are divided into two groups: strong users and weak users. Strong users are composed of K users. s , is a user with a strong VLC channel, and the weak users are composed of K weak users U w , for users with weak VLC channels;

[0015] In an indoor environment, the RF channel gain between the jth strong user and the ith weak user is expressed as:

[0016]

[0017] in, is the RF multipath propagation channel, L(d i,j ) is the path loss between the jth strong user and the ith weak user, where d i,j is the distance between the i-th user and the j-th user, and the VLC channel h between the AP and the j-th user j The calculation formula is:

[0018]

[0019] Where m represents the Lambert order, which is expressed as m = -ln2 / ln(cosθ 12 ), θ 12 is the half-power angle of the LED, A p is the effective detection area of ​​the receiving PD, d j represents the distance between the AP and the jth user, φ is the radiation angle of the LED, and g of and f(θ) are the optical filter gain and optical concentrator gain, respectively;

[0020] When the transmission scheme is VLC direct transmission:

[0021] According to the NOMA principle, weak user i is paired with strong user j, and the expression of the signal sent from the AP to users i and j is:

[0022]

[0023] in and Assigned to x j and x i The power of the strong and weak users of the message, b is the DC current that must be added to ensure a non-negative transmission signal, and v is the scaling factor for the electro-optical power conversion;

[0024] The received signals of the i-th weak user and the j-th strong user are:

[0025]

[0026] in and are the channels of the jth strong user and the ith weak user, respectively, ρ is the detector responsivity, n i and n j is the noise component, the average additive Gaussian white noise variable with variance σ 2 =N v B v , where N v is the noise power spectral density, B v is the modulation bandwidth;

[0027] The strong user detects the weak user's message x i Then delete it or direct it to the weak user; the weak user passes the strong user's signal x j Considered as interference decoding signal x i ;

[0028] Therefore, the upper limit of the achievable data rate for a strong user signal is:

[0029]

[0030] The data rate achieved by weak user data decoded by strong users is upper bounded by:

[0031]

[0032] The upper limit of the achievable data rate received by the weak user from the VLC direct link is:

[0033]

[0034] in, e is the Euler number, L H The derived input current maximum limit for the LED is, but

[0035] When the transmission scheme is RF relay link:

[0036] The achievable data rate provided by strong user j to weak users through the RF link is:

[0037]

[0038] Among them B f,i is the RF modulation bandwidth at user j, N RF is the PSD of the RF signal;

[0039] If the number of weak users served by the relay VLC / RF link exceeds 1, the RF bandwidth must be divided among the weak users. If the number of weak users served by the RF link is N f , the total modulation bandwidth available for RF transmission is B f , then the modulation bandwidth at user j is:

[0040] Then the data rate that the weak user can achieve through the hybrid relay link RL is expressed as:

[0041]

[0042] Preferably, in step S22, the number of weak users connected via the RF link is

[0043] The sum of the achievable data rates for the i-th weak user and the j-th strong user is expressed as:

[0044]

[0045] The total transmission rate of system users, i.e. the optimization objective function expression, is:

[0046]

[0047] Preferably, in step S23, a K×K matrix Z of user pairings is defined, where Z is defined as follows:

[0048]

[0049] The link selection index vector X is defined as follows:

[0050]

[0051] To ensure eye safety and hardware limitations while maintaining illumination levels, the maximum transmitted optical power is limited to There are the following power constraints:

[0052]

[0053] To ensure the QoS required by users, the following constraints apply:

[0054]

[0055] The power constraints imposed on continuous interference cancellation in NOMA systems are:

[0056]

[0057] Maximize the achievable data transmission rate under the constraints of user connectivity, transmit power and user QoS.

[0058] Preferably, in step S24, the joint optimization problem expression is:

[0059]

[0060] in represents the set of optimization variables, Constraints C1-C3 ensure that each strong user is paired with only one weak user, and constraint C4 forces the weak user to receive information from either a direct VLC link or from a relayed hybrid VLC / RF link.

[0061] Preferably, in step S3, solving the optimization problem specifically includes the following steps:

[0062] From the constraints C1 and C2, we can see that constraint C5 can be equivalently transformed into:

[0063]

[0064] The optimization variables involved in the optimization problem P1 include both 0-1 integer variables and continuous variables, and the constraints C6 and C7 contain nonlinear functions of variable coupling, which are solved using the BARON solver.

[0065] Therefore, the present invention adopts the above-mentioned VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, establishes a mathematical model of an indoor dual-hop VLC / RF heterogeneous network system scenario, and establishes a joint optimization problem of multivariable coupled mixed integer nonlinear programming (MINLP) according to the above mathematical model to maximize the total transmission rate under the constraints of user connectivity, transmission power and user QoS, thereby jointly determining the strong-weak user pairs, the service link (direct VLC or VLC / RF hybrid link) of each weak user, and the transmission power of each user.

[0066] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a flow chart of a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA of the present invention;

[0068] Figure 2 The present invention is a dual-hop VLC / RF heterogeneous network system model diagram. DETAILED DESCRIPTION

[0069] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0070] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0071] The words "include" or "comprises" and the like used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms "inside", "outside", "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly specified and limited, the terms "attachment" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0072] Example

[0073] like Figure 1 As shown, the present invention provides a VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, comprising the following steps:

[0074] S1: Establish a mathematical model based on the scenario of indoor dual-hop VLC / RF heterogeneous network system;

[0075] In step S1, according to the characteristics that VLC provides high throughput and low-cost data communication, highly relies on line-of-sight LoS channels and has limited coverage, and RF provides wide coverage, the VLC and RF networks are heterogeneous, and a mathematical model is established for the total transmission rate of the heterogeneous networks under the constraints of user connectivity, transmission power and user QoS.

[0076] S2: Establishing a joint optimization problem of multivariable coupled mixed integer nonlinear programming MINLP according to the mathematical model obtained in step S1; specifically comprising the following steps:

[0077] S21: Establishing a transmission rate expression between the access point AP and the user;

[0078] In step S21, the dual-hop VLC / RF heterogeneous network system model consists of a VLC-AP and N u =2K multiple users, where K is the number of user pairs. Users are divided into two groups: strong users and weak users. Strong users are composed of K users. s , is a user with a strong VLC channel, and the weak users are composed of K weak users U w , for users with weak VLC channels;

[0079] In an indoor environment, the RF channel gain between the jth strong user and the ith weak user is expressed as:

[0080]

[0081] in, is the RF multipath propagation channel, L(d i,j ) is the path loss between the jth strong user and the ith weak user, where d i,j is the distance between the i-th user and the j-th user, and the VLC channel h between the AP and the j-th user j The calculation formula is:

[0082]

[0083] Where m represents the Lambert order, which is expressed as m = -ln2 / ln(cosθ 12 ), θ 12 is the half-power angle of the LED, A p is the effective detection area of ​​the receiving PD, d j represents the distance between the AP and the jth user, φ is the radiation angle of the LED, and g of and f(θ) are the optical filter gain and optical concentrator gain, respectively;

[0084] When the transmission scheme is VLC direct transmission:

[0085] According to the NOMA principle, weak user i is paired with strong user j, and the expression of the signal sent from the AP to users i and j is:

[0086]

[0087] in and Assigned to xj and x i The power of the strong and weak users of the message, b is the DC current that must be added to ensure a non-negative transmission signal, and v is the scaling factor for the electro-optical power conversion;

[0088] The received signals of the i-th weak user and the j-th strong user are:

[0089]

[0090] in and are the channels of the jth strong user and the ith weak user, respectively, ρ is the detector responsivity, n i and n j is the noise component, the average additive Gaussian white noise variable with variance σ 2 =N v B v , where N v is the noise power spectral density, B v is the modulation bandwidth;

[0091] The strong user detects the weak user's message x i Then delete it or direct it to the weak user; the weak user passes the strong user's signal x j Considered as interference decoding signal x i ;

[0092] Therefore, the upper limit of the achievable data rate for a strong user signal is:

[0093]

[0094] The data rate achieved by weak user data decoded by strong users is upper bounded by:

[0095]

[0096] The upper limit of the achievable data rate received by the weak user from the VLC direct link is:

[0097]

[0098] in, e is the Euler number, L H The derived input current maximum limit for the LED is, but

[0099] When the transmission scheme is RF relay link:

[0100] The achievable data rate provided by strong user j to weak users through the RF link is:

[0101]

[0102] Among them B f,i is the RF modulation bandwidth at user j, N RF is the PSD of the RF signal;

[0103] If the number of weak users served by the relay VLC / RF link exceeds 1, the RF bandwidth must be divided among the weak users. If the number of weak users served by the RF link is N f , the total modulation bandwidth available for RF transmission is B f , then the modulation bandwidth at user j is:

[0104] Then the data rate that the weak user can achieve through the hybrid relay link RL is expressed as:

[0105]

[0106] S22: Establishing an optimization objective function expression;

[0107] In step S22, the number of weak users connected via the RF link is

[0108] The sum of the achievable data rates for the i-th weak user and the j-th strong user is expressed as:

[0109]

[0110] The total transmission rate of system users, i.e. the optimization objective function expression, is:

[0111]

[0112] S23: Establish an optimization objective function expression; In step S23, define a user pairing K×K matrix Z, where Z is defined as follows:

[0113]

[0114] The link selection index vector X is defined as follows:

[0115]

[0116] To ensure eye safety and hardware limitations while maintaining illumination levels, the maximum transmitted optical power is limited to There are the following power constraints:

[0117]

[0118] To ensure the QoS required by users, the following constraints apply:

[0119]

[0120] The power constraints imposed on continuous interference cancellation in NOMA systems are:

[0121]

[0122] Maximize the achievable data transmission rate under the constraints of user connectivity, transmit power and user QoS.

[0123] S24: Under the constraints in step S23, a joint optimization problem is established with the goal of maximizing the expression of the objective function in step S22;

[0124] In step S24, the joint optimization problem expression is:

[0125]

[0126] in represents the set of optimization variables, Constraints C1-C3 ensure that each strong user is paired with only one weak user, and constraint C4 forces the weak user to receive information from either a direct VLC link or from a relayed hybrid VLC / RF link.

[0127] S3: Solving the optimization problem in step S2. Preferably, in step S3, solving the optimization problem specifically includes the following steps:

[0128] From the constraints C1 and C2, we can see that constraint C5 can be equivalently transformed into:

[0129]

[0130] The optimization variables involved in the optimization problem P1 include both 0-1 integer variables and continuous variables, and the constraints C6 and C7 contain nonlinear functions of variable coupling, which are solved using the BARON solver.

[0131] Therefore, the present invention adopts the above-mentioned VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, establishes a mathematical model of an indoor dual-hop VLC / RF heterogeneous network system scenario, and establishes a joint optimization problem of multivariable coupled mixed integer nonlinear programming (MINLP) according to the above mathematical model to maximize the total transmission rate under the constraints of user connectivity, transmission power and user QoS, thereby jointly determining the strong-weak user pairs, the service link of each weak user, and the transmission power of each user.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA, characterized by: The following steps are involved: S1: Establish a mathematical model based on the scenario of indoor dual-hop VLC / RF heterogeneous network system; S2: Establishing a joint optimization problem of multivariable coupled mixed integer nonlinear programming MINLP according to the mathematical model obtained in step S1; specifically comprising the following steps: S21: Establishing a transmission rate expression between the access point AP and the user; S22: Establishing an optimization objective function expression; S23: Establishing optimization problem constraint expressions; S24: Under the constraints in step S23, a joint optimization problem is established with the goal of maximizing the expression of the objective function in step S22; S3: Solve the optimization problem in step S2.

2. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 1, characterized in that: In step S1, according to the characteristics that VLC provides high throughput and low-cost data communication, highly relies on line-of-sight LoS channels and has limited coverage, and RF provides wide coverage, the VLC and RF networks are heterogeneous, and a mathematical model is established for the total transmission rate of the heterogeneous networks under the constraints of user connectivity, transmission power and user QoS.

3. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 2, characterized in that: In step S21, the dual-hop VLC / RF heterogeneous network system model consists of a VLC-AP and N u =2K multiple users, where K is the number of user pairs. Users are divided into two groups: strong users and weak users. Strong users are composed of K users. s , is a user with a strong VLC channel, and the weak users are composed of K weak users U w , for users with weak VLC channels; In an indoor environment, the RF channel gain between the jth strong user and the ith weak user is expressed as: in, is the RF multipath propagation channel, L(d i,j ) is the path loss between the jth strong user and the ith weak user, where d i,j is the distance between the i-th user and the j-th user, and the VLC channel h between the AP and the j-th user j The calculation formula is: Where m represents the Lambert order, which is expressed as m = -ln2 / ln(cosθ 12 ), θ 12 is the half-power angle of the LED, A p is the effective detection area of ​​the receiving PD, d j represents the distance between the AP and the jth user, φ is the radiation angle of the LED, and g of and f(θ) are the optical filter gain and optical concentrator gain, respectively; When the transmission scheme is VLC direct transmission: According to the NOMA principle, weak user i is paired with strong user j, and the expression of the signal sent from the AP to users i and j is: in and Assigned to x j and x i The power of the strong and weak users of the message, b is the DC current that must be added to ensure a non-negative transmission signal, and v is the scaling factor for the electro-optical power conversion; The received signals of the i-th weak user and the j-th strong user are: in and are the channels of the jth strong user and the ith weak user, respectively, ρ is the detector responsivity, n i and n j is the noise component, the average additive Gaussian white noise variable with variance σ 2 =N v B v , where N v is the noise power spectral density, B v is the modulation bandwidth; The strong user detects the weak user's message x i Then delete it or direct it to the weak user; the weak user passes the strong user's signal x j Considered as interference decoding signal x i ; Therefore, the upper limit of the achievable data rate for a strong user signal is: The data rate achieved by weak user data decoded by strong users is upper bounded by: The upper limit of the achievable data rate received by the weak user from the VLC direct link is: in, e is the Euler number, L H The derived input current maximum limit for the LED is, but When the transmission scheme is RF relay link: The achievable data rate provided by strong user j to weak users through the RF link is: Among them B f,i is the RF modulation bandwidth at user j, N RF is the PSD of the RF signal; If the number of weak users served by the relay VLC / RF link exceeds 1, the RF bandwidth must be divided among the weak users. If the number of weak users served by the RF link is N f , the total modulation bandwidth available for RF transmission is B f , then the modulation bandwidth at user j is: Then the data rate that the weak user can achieve through the hybrid relay link RL is expressed as:

4. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 3, characterized in that: In step S22, the number of weak users connected via the RF link is The sum of the achievable data rates for the i-th weak user and the j-th strong user is expressed as: The total transmission rate of system users, i.e. the optimization objective function expression, is:

5. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 4, characterized in that: In step S23, a K×K matrix Z of user pairs is defined, where Z is defined as follows: The link selection index vector X is defined as follows: To ensure eye safety and hardware limitations while maintaining illumination levels, the maximum transmitted optical power is limited to There are the following power constraints: To ensure the QoS required by users, the following constraints apply: The power constraints imposed on continuous interference cancellation in NOMA systems are: Maximize the achievable data transmission rate under the constraints of user connectivity, transmit power and user QoS.

6. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 5, characterized in that: In step S24, the joint optimization problem expression is: st in represents the set of optimization variables, Constraints C1-C3 ensure that each strong user is paired with only one weak user, and constraint C4 forces the weak user to receive information from either a direct VLC link or from a relayed hybrid VLC / RF link.

7. A VLC / RF heterogeneous network resource optimization method based on collaborative NOMA according to claim 6, characterized in that: In step S3, solving the optimization problem specifically includes the following steps: From the constraints C1 and C2, we can see that constraint C5 can be equivalently transformed into: The optimization variables involved in the optimization problem P1 include both 0-1 integer variables and continuous variables, and the constraints C6 and C7 contain nonlinear functions of variable coupling, which are solved using the BARON solver.

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