Indoor VLC-RF downlink cooperative transmission time-frequency resource allocation method based on interference pattern

Abstract

The invention relates to a time-frequency resource allocation method for downlink cooperative transmission of an indoor VLC-RF heterogeneous network, and belongs to the field of optical wireless communication. The time-frequency resource allocation method for multi-VLC AP cooperative transmission, which meets user service requirements, is provided for the problem of VLC inter-cell interference in an indoor VLC-RF heterogeneous network. The method comprises the following steps: firstly, creating a VLC AP cluster by adopting a weighted undirected interference graph method according to the condition of an interference cell; secondly, according to a user signal-to-noise ratio value and a service request rate, determining a user scheduling duration user accessed to the VLC AP cluster or the RF AP by adopting a user-centered time resource allocation algorithm; and then, executing a multi-cell resource allocation algorithm based on interference management according to the service rate requirements of the candidate users, and determining subcarriers of the VLC AP cluster or the RF AP associated with the users. According to the method provided by the invention, the throughput of a multi-VLC AP cooperative transmission system is improved and the inter-cell interference is reduced by optimizing the duration of accessing the VLC AP cluster or the RF AP by the user and the subcarrier resource allocation.

Description

Technical Field

[0001] The invention belongs to the field of optical wireless communications and relates to a time-frequency resource allocation method for indoor VLC-RF downlink collaborative transmission based on an interference graph. Background Art

[0002] In the research and exploration of realizing the future 6G (6th Generation Mobile Communication Technology) mobile communication needs, VLC-RF (Visible Light Communication-Radio Frequency) networking technology is considered to be one of the most important key technologies. However, in the scenario of multiple visible light (Visible Light Communication) communication cells, due to the overlapping coverage between cells, users in the overlapping coverage area can receive signals from multiple access points (APs), resulting in serious interference problems, affecting the service performance and resource utilization of VLC-RF heterogeneous networks. In order to cope with the challenges of inter-cell interference and reduced resource utilization in indoor VLC-RF heterogeneous networks, it is necessary to implement a flexible multi-cell resource allocation strategy based on effective interference management to balance the resource competition problem between different users. The interference in the overlapping coverage area of ​​multiple VLC APs is divided into two categories: inter-cell interference and intra-cell interference. Inter-cell interference occurs when different access points transmit data for different users on the same frequency, while intra-cell interference is caused by the same access point transmitting data for different users on the same frequency. Using frequency division multiple access technology to allocate subcarriers to different users in a cell is considered to be an effective technology to alleviate interference within a cell; however, inter-cell interference caused by the deployment of multiple VLC APs with dense indoor coverage is still an important challenge affecting system performance and resource utilization.

[0003] For indoor VLC-RF heterogeneous networks, the dense distribution of VLC APs will lead to serious inter-cell interference, which will reduce the user's QoE (Quality of Experience) and the communication performance of the network. In particular, for users at the edge of the cell, they can simultaneously receive weaker optical signals emitted by multiple VLC APs within their communication coverage. The signal-to-noise ratio (SNR) of the signal received by the receiving device is small. Under the interference of other VLC AP signals, it is more difficult to extract valuable information from the received signal, which leads to a decrease in signal quality, thereby affecting the transmission efficiency of the entire network. Therefore, how to enhance the received signal strength in the edge area of ​​the VLC AP and reduce interference is one of the effective ways to improve the QoE and system performance of users in the edge area of ​​the VLC AP. The present application considers the downlink data transmission situation in the coverage area of ​​multiple VLC APs, and adopts a conflict-free interference graph method to optimize the scheduling time of users accessing multiple VLC APs, and a method for allocating subcarrier resources for collaborative transmission of multiple VLC APs. This method further enhances the throughput performance of the VLC-RF heterogeneous network while reducing inter-cell interference. Summary of the invention

[0004] In view of this, the core of the present invention is to provide a time-frequency resource allocation method for indoor VLC-RF downlink cooperative transmission based on interference graph, reduce inter-cell interference, and improve the total user rate and average user satisfaction.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for allocating time-frequency resources for indoor VLC-RF downlink cooperative transmission based on an interference graph, characterized in that the method comprises the following steps:

[0007] S1: Input user set M, VLC AP set N, 1 RF AP, and each VLC AP transmission power P V and unit carrier bandwidth, the RF AP transmit power is P R and unit carrier bandwidth, the VLC AP subcarrier set is C s , RF subcarrier set, input the general rate value, minimum rate value and maximum rate value of the user's requested service, and set the minimum number of VLC AP clusters K min and the maximum number of clusters K max , the satisfaction threshold of the VLC system; according to the Lambertian radiation model of VLC, the channel gain value from each user to each VLC AP is calculated; according to the Rayleigh fading channel model, the channel gain from each user to the RF AP is calculated;

[0008] Among them, the formula for calculating the line-of-sight channel gain from VLC AP n to the receiver of user m based on the Lambertian radiation model is:

[0009]

[0010] In the formula, A PD Indicates the light receiving area; D m,n is the straight-line distance between user m and VLC AP n; is the VLC AP emission angle; f represents the Lambertian radiation order, and is the half-power angle of the VLC AP; ψ is the incident angle of the optical receiver; ψ c is the field of view of the optical receiver; T(ψ) and g(ψ) are the optical filter gain and optical concentrator gain of the optical receiver, respectively; if 0≤ψ≤ψ c , then the concentrator g(ψ)=c 2 / sin 2 (ψ c ), where the refractive index c = 1.5; if ψ>ψ c , then g(ψ)=0;

[0011] According to the Rayleigh fading model, the channel gain between the RF AP and user m is calculated as follows:

[0012]

[0013] Where L (dB) represents the path loss of the RF channel in dB, which is calculated as follows:

[0014]

[0015] In the above formula, d mn is the length of the communication link from RF AP n to user m; f c is the center carrier frequency in GHz; X σ is the shadow fading represented by a zero-mean Gaussian random variable with a standard deviation of 3 dB; d BP is a reference distance of 10 m; the free space path loss L(d mn )=20log 10 (f c d mn )-147.5;

[0016] S2: Execute the user-centric time resource allocation algorithm, the specific process is: construct a VLC AP weighted undirected interference graph, determine the clustering set of VLC APs in the interference graph according to the sum of the maximum achievable rates obtained by the user accessing the VLC AP cluster and the minimum average satisfaction value of the VLC system; determine the scheduling duration of each VLC AP cluster serving the user service transmission according to the rate value of the user request service;

[0017] S3: executing a multi-cell resource allocation algorithm based on interference management, wherein the specific process is: calculating in turn the positive impact of the idle carrier of the user accessing the VLC AP cluster and the negative impact caused by other users competing for the subcarrier resources, determining the priority factor value of the user selecting the idle subcarrier of the VLC AP cluster, executing the multi-cell resource allocation algorithm based on interference management, and obtaining the visible light subcarrier association information of the user accessing the VLC AP cluster and the subcarrier association information of the user accessing the RF AP.

[0018] The specific method of S2 is:

[0019] S201: According to the user positions and the field of view of the receiving device, the VLC AP positions and the transmission angles of the indoor VLC-RF heterogeneous network, the communication coverage overlap range between the VLC AP cells and the user set in the overlap area are determined, and a weighted undirected interference graph G(V, E) reflecting the degree of line of sight transmission interference between the VLC APs is constructed, where the node set V = {1, ..., |N|} of the interference graph corresponds to the VLC AP set, and the edge set of the interference graph is E = {e r,j |r,j∈N I},N I is a set of VLC APs with users in the overlapping coverage area;

[0020] The interference graph shows that there is an interference edge e between VLC AP r and VLC AP j. r,j The weight value is:

[0021]

[0022] In the formula, ζ j is the interfering user set of VLC AP j, which consists of users in the overlapping area of ​​VLC AP r and VLC AP j but not connected to VLC AP j, h m,r is the line-of-sight channel gain between VLC AP r and user m; r is the interfering user set of VLC AP r, which consists of users in the overlapping area of ​​VLC AP r and VLC AP j but not connected to VLC AP r, h m,j is the line-of-sight channel gain between VLC AP j and user m; in the graph G(V, E), W(er,j )=W(e j,r );

[0023] S202: Calculate the interference strength value of each VLC AP, determine the weight of each node in the interference graph G(V, E), and let K C =K min , K min is the minimum number of cluster heads for the set VLC AP clustering;

[0024] The weight of node j in G(V, E) is the interference intensity value of the jth VLC AP, and its calculation formula is:

[0025]

[0026] S203: Add the VLC AP corresponding to the node with the largest weight in G(V, E) to the GL set as the cluster head node of the GL set. If the number of cluster head nodes in the GL set is equal to K C , add all nodes in G(V, E) that are not added to the GL set to the GM set, and go to step S204; otherwise, delete the nodes added to the GL set from G(V, E), and return to step S203;

[0027] S204: If the GM set is an empty set, go to step S206, otherwise, go to step S205;

[0028] S205: Compare the interference edges between the GM set nodes and the GL set nodes, select the GM set node corresponding to the edge with the smallest interference edge weight, and mark it as j. If there is an edge with the smallest weight, add node j to the cluster head set of GL, delete node j from the GM set, and go to step S204;

[0029] S206: adding all VLC APs as clusters with only cluster heads to the GL set, solving the cluster head set where users in non-multi-VLC AP overlapping areas or overlapping areas with large interference only receive communication services from one VLC AP, and obtaining a VLC AP cluster set GL for multi-VLC AP services and single VLCAP services;

[0030] S207: Access the users in the VLC AP coverage area to the VLC AP cluster in the GL with the largest channel gain. If there is only one node in the VLC AP cluster, the user accepts the VLC AP information transmission service; if there are multiple nodes in the VLC AP cluster, the user accepts the cooperative transmission service of the VLC AP cluster, calculates the maximum achievable rate value of each user, calculates the minimum average satisfaction value of the VLC system, and if the minimum average satisfaction value is greater than or equal to the satisfaction threshold of the VLC system, go to step S207; otherwise, if K C <K max , let KC =K C +1, go to step S203; if K C =K max , go to step S208;

[0031] The calculation formula for the maximum achievable rate of the kth VLC AP cluster cooperatively serving user m is:

[0032]

[0033] In the above formula, C k represents the VLC AP set in the kth VLC AP cluster, B0 is the bandwidth of the VLC AP unit subcarrier; SNR m,n It represents the signal-to-noise ratio of user m accessing VLC AP n. Its calculation formula is:

[0034]

[0035] In the above formula, P V represents the optical transmission power of the VLC AP; γ is the optical / electrical conversion coefficient of the user receiving end; N 0 is the power spectral density of AWGN (Additive White Gaussian Noise); B V is the total system bandwidth of the VLC AP;

[0036] The minimum average satisfaction of the system is the ratio of the system throughput to the minimum total rate required by the user request, and its calculation formula is:

[0037]

[0038] In the above formula, is the minimum rate value required by user m to request the service; GL is the VLC AP divided into K C The cluster set of clusters, C k is the VLC AP set of the kth cluster;

[0039] S207: If the minimum average satisfaction value of the VLC system is less than 1, go to step S208; otherwise, set the scheduling duration of each user to 1 time scheduling cycle, go to step S209;

[0040] S208: Calculate the scheduling time of each VLC AP cluster serving the user according to the request rate requirement of each user, and then go to step S209;

[0041] Among them, user m accesses VLC AP cluster C k Scheduling time The calculation formula is:

[0042]

[0043] Where U m is the normal rate requirement value of the service requested by user m, T is the unit duration of a scheduling cycle, Indicates rounding up to an integer;

[0044] S209: Connect users that are not in the coverage area of ​​the VLC AP to the RF AP, calculate their scheduling duration, and then go to step S210;

[0045] Among them, the scheduling time for user m to access the RF AP is The calculation formula is:

[0046]

[0047] In the formula, is the maximum achievable rate of user m accessing the RF AP. According to the Shannon formula, the value is calculated as follows:

[0048]

[0049] In the above formula, B R is the bandwidth of the RF AP unit carrier; R Indicates the transmit power of the RF AP; B R is the total system bandwidth of the RF AP;

[0050] S210: Output the GL set of the VLC AP cluster, the duration of each user accessing the VLC AP cluster and the scheduling duration in the cluster, and the scheduling duration of users accessing the RF AP.

[0051] The S3 specific method is:

[0052] S301: According to the scheduling duration of the user being associated with the VLC AP cluster or the VLC AP, count the users associated with the VLC AP cluster and save them in the set M A In the RF AP, the user is associated with the RF AP and saved in the M R Calculate M in sequence A The positive impact of a carrier of a VLC AP cluster associated with a user on other users;

[0053] Among them, user m accesses VLC AP cluster C k The calculation formula of the positive influence of the carrier L is:

[0054]

[0055] In the above formula, C s is the total carrier set of the VLC AP; is the maximum achievable rate of carrier L of user m accessing VLC AP n, which is calculated as follows:

[0056]

[0057] In the above formula, Access VLC AP cluster C for user m k The scheduling duration, Indicates that user m accesses VLC AP cluster C k The signal-to-interference ratio of carrier L of VLC AP n is calculated as follows:

[0058]

[0059] In the above formula, ζ n is the interfering user set of VLC AP n, which is composed of users in the overlapping area of ​​VLC AP r and VLC AP n. The number of users who use carrier L but do not access VLC AP n during the scheduling period; t is a Boolean variable. When users in overlapping coverage areas of VLC APs of different clusters use the same carrier L in the tth scheduling duration unit time, λ t =1; otherwise, λ t =0;

[0060] S302: Calculate M in sequence A The negative impact and total weighted negative impact caused by a carrier of a VLC AP cluster associated with a user on other users in the coverage area of ​​the VLC AP cluster;

[0061] Among them, user m is associated with VLC AP cluster C k The positive influence of the carrier L on q m The calculation formula for the total negative impact on the weight of other users in the cluster is:

[0062]

[0063] In the above formula, Y m Associate VLC AP cluster C with user m k The set of users affected by carrier L; Associate VLC AP cluster C for user m k The negative impact value of carrier L on other users m′ in the coverage area of ​​the cluster is calculated as follows:

[0064]

[0065] Where U max is the maximum required rate of all users in the system, U minis the minimum required rate of all users in the system, U m' is the normal data rate requirement value of user m'; L' and L are the subcarrier numbers used;

[0066] Where, user m is associated with VLC AP cluster C k The user set Y affected by carrier L m The method to determine is: H j Cluster C k The set of users in the coverage area of ​​VLC AP j;

[0067] S303: Calculate M in sequence A The priority factor for users to select VLC AP clusters;

[0068] The calculation formula of the priority factor value of the subcarrier selected by user m in the VLC AP cluster is:

[0069]

[0070] S304: According to M A The user priority factor values ​​are arranged in descending order from high to low. A Users in the collection;

[0071] S305: Select M A The first user whose VLC AP subcarrier allocation is not checked in the set is selected, and the AP cluster where the VLC AP with the largest channel gain is located is selected for the user. If there is one, go to step S306; otherwise, add the user to the set M. R and from M A Delete the user from the set and go to step S307;

[0072] S306: Allocate idle subcarriers with the same sequence number of each VLC AP in the VLC AP cluster to the user, update the subcarrier association matrix, and go to step S307;

[0073] S307: If the set M A If all users in the VLC AP subcarrier allocation are checked, go to step S308; otherwise, go to step S305;

[0074] S308: If the set M R If it is an empty set, go to step S309; ​​otherwise, it is the set M R The user selects an idle subcarrier of RF. If RF has no idle subcarrier resources, the blocking set M R If the service request of the user to which the subcarrier is not allocated is received, the process goes to step S309;

[0075] S309: Output the scheduling duration information of all users associated with the VLC AP or RF AP, and the users obtain the subcarrier sequence number information of the VLC AP or RF AP. A and the set of users accessing the RF AP M R .

[0076] The beneficial effects of the present invention are as follows: the present invention relates to a method for allocating time-frequency resources for indoor VLC-RF downlink cooperative transmission based on an interference graph. First, the interference situation between VLC APs is modeled as a weighted undirected interference graph; second, the number of cooperative VLC AP groups is dynamically adjusted according to the user signal-to-noise ratio value to determine the cooperative VLC AP set and the user group they serve; then, the service user scheduling duration of each VLC AP is adjusted according to the rate requirements of the grouped users; finally, the priority of user subcarrier resource allocation is determined according to the SNR and user rate requirements and the impact of the connection between the user and the VLC AP on other users, and the subcarriers of the VLC AP and the RF AP are allocated to the user according to the priority. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the following drawings, in which:

[0078] Attached Figure 1 Indoor VLC-RF multi-cell heterogeneous network model;

[0079] Attached Figure 2 Schematic diagram of constructing a weighted undirected interference graph of VLC AP;

[0080] Attached Figure 3 Flowchart of the time-frequency resource allocation algorithm for downlink cooperative transmission in indoor VLC-RF heterogeneous networks;

[0081] Attached Figure 4 Flowchart of user-centric time resource allocation algorithm;

[0082] Attached Figure 5 Flowchart of multi-cell resource allocation algorithm based on interference management. DETAILED DESCRIPTION

[0083] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents described in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0084] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0085] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0086] Attached Figure 1 It is an indoor VLC-RF multi-cell heterogeneous network model, which consists of N VLC APs distributed on the indoor roof in a uniform rectangular manner and 1 RF AP located at the center of the roof. They provide communication services for M UEs (User Equipments) randomly distributed indoors. In the edge area where multiple VLC APs overlap, there are multiple VLC APs cooperating to serve users, called Coordinated Multi-point (CoMP) UEs. Multiple CoMP UEs in the overlapping area constitute a CoMP cluster. Correspondingly, UEs served by a single VLC AP are called non-CoMP UEs. Each VLC AP is equipped with an LED (Lighting Emitting Diode), and each UE is equipped with a photodetector. The VLC APs are connected to the indoor CCU (Central Control Unit) through power lines. The CCU is responsible for obtaining user location, demand, and status information of each VLC AP and RF AP, and executing resource allocation algorithms to allocate VLC-RF resources to users. According to user requests, it coordinates user connections with the Internet.

[0087] Attached Figure 2 (a) and Figure 2 (b) shows the user location and VLC AP coverage area plan view and the constructed VLCAP weighted undirected interference graph instance. Figure 2In (a), N=6, M=10, and the signal strength coverage area of ​​each VLC AP is represented by a dotted circle. UE 1, UE 4, UE 6, and UE10 can only receive one VLC AP signal, and there is no interference. The blue five stars represent users, and the black solid line represents the line of sight transmission line connected to the VLC AP; UE 2, UE 3, UE 5, UE 6, UE7, UE 8, and UE 9 may receive signals from multiple VLC APs at the same time, resulting in inter-cell interference; users are represented by red five stars. In the absence of cooperative transmission, the UE in the overlapping area only receives one VLC AP signal as a useful signal, and the other VLC AP signals received are regarded as interference signals. The interference signal transmission line is represented by a red dotted line, thus obtaining Figure 2 (b) The interference graph. Figure 2 In (b), the interference edge is represented by a solid line, such as e i,j , indicating that there is a user in the overlapping coverage area of ​​VLC AP i and VLC AP j. The user can receive signals from VLC AP i and VLC AP j at the same time, which will cause interference when cooperative transmission is not adopted. The numbers on the edge represent weights. According to formula (4), we can get Figure 2 (b) The weight of the interference edge, such as: W(e i,j ) represents the interference edge e i,j The nodes at both ends of the edge represent the VLC APs with interference, and the numbers next to the nodes represent the interference intensity values ​​received by the nodes, which are calculated by formula (5): Figure 2 (b) The interference strength value of each VLC AP node, such as: W(i) represents the sum of the interference edge weights affected by VLC AP i, that is, the interference strength value of VLC AP i.

[0088] Attached Figure 3 This is a flow chart of the time-frequency resource allocation algorithm for downlink cooperative transmission of indoor VLC-RF heterogeneous networks, which will be described in detail below:

[0089] Input: Input user set M, VLC AP set N, and each VLC AP transmission power P V and unit carrier bandwidth, the transmission power of one RF AP is P R and unit carrier bandwidth, the VLC AP subcarrier set is C s , RF AP subcarrier set, input the general rate value, minimum rate value and maximum rate value of the user request service, set the minimum number of VLC AP clusters K min and the maximum number of clusters K max ;

[0090] Output: The scheduling duration of each user's association with the VLC AP cluster, VLC AP or RF AP, and the allocated carrier resource information.

[0091] Step 1: According to formula (1), the line-of-sight channel gain h from each VLC AP to the user receiver is calculated using the Lambertian radiation model. m,n , m∈M,n∈N;

[0092] Step 2: Calculate the channel gain from the RF AP to each user using formula (2):

[0093] Step 3: If there are users in the VLC AP cell overlap area, the VLC AP is abstracted as a node of a weighted undirected interference graph G(V, E), and interference edges are added between the VLC AP nodes with users in the VLC AP cell overlap area. The weight of each interference edge is determined by formula (4); after all interference edges are determined, the interference strength value of each node in the interference graph is calculated by formula (5);

[0094] Step 4: In the interference graph, perform the following Figure 4 The user-centric time resource allocation algorithm shown determines the cooperative transmission VLC AP cluster and scheduling duration of users in the overlapping area and the duration of users in the non-overlapping area accessing a certain VLC AP or RF AP;

[0095] Step 5: Execute the attached Figure 5 The multi-cell resource allocation algorithm based on interference management shown in the figure determines VLC

[0096] The carrier resources allocated to each user by an AP cluster or RF AP;

[0097] Step 6: Output the scheduling duration and carrier information of the VLC AP cluster, VLC AP or RF AP accessed by each user in the set M.

[0098] Attached Figure 4 This is a flowchart of the user-centric time resource allocation algorithm, which will be described in detail below:

[0099] Input: Input user set M, VLC AP set N, and each VLC AP transmission power P V and unit carrier bandwidth, the transmission power of one RF AP is P R and unit carrier bandwidth, input the weighted undirected interference graph G(V, E) of the users covered by the VLC AP; input the general rate value, minimum rate value and maximum rate value of the user's requested service, and set the minimum number of VLC AP clusters K min and the maximum number of clusters K max , the satisfaction threshold of the VLC system, let K C =0,

[0100] Output: Status information and scheduling duration of each user-associated VLC AP cluster, VLC AP or RF AP, and the set of users M accessing the VLC AP set A The set of users accessing the RF AP is M. R .

[0101] Step 1: Let K C =K min ;

[0102] Step 2: Add the VLC AP corresponding to the node with the largest weight in G(V, E) to the GL set as the cluster head node of the GL set. If the number of cluster head nodes in the GL set is equal to K C , add all nodes in G(V, E) that are not added to the GL set to the GM set, and go to step S3; otherwise, delete the nodes added to the GL set from G(V, E), and return to step 2;

[0103] Step 3: If the GM set is an empty set, go to step 5, otherwise, go to step 4;

[0104] Step 4: Compare the interference edges between the GM set nodes and the GL set nodes, select the GM set node corresponding to the edge with the smallest interference edge weight, marked as j, if there is an edge with the smallest weight, then add node j to the GL cluster head set, delete node j from the GM set, and go to step 3;

[0105] Step 5: Add all VLC APs as clusters with only cluster heads to the GL set, solve the cluster head set where users in non-multi-VLC AP overlapping areas or overlapping areas with large interference only receive communication services from one VLC AP, and obtain the VLC AP cluster set GL for multi-VLC AP services and single VLCAP services, and go to step 6;

[0106] Step 6: Save the users in the VLC AP coverage area in M A In the above example, A For the user in the VLC AP cluster, the user is allowed to access the VLC AP cluster in GL with the largest channel gain. If there is only one node in the VLC AP cluster, the user accepts the information transmission service of the VLC AP; if there are multiple nodes in the VLC AP cluster, the user accepts the cooperative transmission service of the VLC AP cluster. According to formula (6), the maximum achievable rate value of each user is calculated; according to formula (8), the minimum average satisfaction value of the VLC system is calculated. If the minimum average satisfaction value is greater than or equal to the VLC system satisfaction threshold, go to step 6. Otherwise, if K C <K max , let K C =K C+1, go to step 4; if K C =K max , go to step 7;

[0107] Step 6: If the minimum average satisfaction value of the VLC system is less than 1, go to step 7; otherwise, set the scheduling duration of each user to 1 time scheduling cycle, and go to step 8;

[0108] Step 7: According to the request rate requirement of each user, the scheduling time of each VLC AP cluster serving the user is calculated by formula (9), and then go to step 8;

[0109] Step 8: Connect users who are not in the coverage area of ​​the VLC AP to the RF AP, and save the users who are connected to the RF AP in the set M. R According to formula (10), the scheduling time required for the user to access the RF AP is calculated, and then go to step 9;

[0110] Step 9: Output the GL set of VLC AP clusters and the user set M A and M R , the duration of each user accessing the VLC AP cluster and being scheduled in the cluster, and the duration of the user accessing the RF AP.

[0111] Attached Figure 5 This is a flow chart of the multi-cell resource allocation algorithm based on interference management, which will be described in detail below:

[0112] Input: Input user set M, VLC AP set N, and each VLC AP transmission power P V and unit carrier bandwidth, unit carrier bandwidth of RF AP, VLC AP clustering and subcarrier set C s , RF AP subcarrier set, input the general rate value, minimum rate value and maximum rate value of the user request service, set the minimum number of VLC AP clusters K min and the maximum number of clusters K max ;

[0113] Output: The scheduling duration information of all users associated with the VLC AP or RF AP, and the carrier sequence number information of the users accessing the VLC AP or RFAP.

[0114] Step 1: Count the users associated with the VLC AP cluster and save them in set M A The user set associated with the RF AP is stored in M R In the example, let m = 1;

[0115] Step 2: According to formula (12), calculate M in sequence A The positive impact of a carrier of a VLC AP cluster associated with a user in the set on other users;

[0116] Step 3: According to formula (15), calculate M in sequence A The negative impact and total weighted negative impact caused by a carrier of a VLC AP cluster associated with a user in the set on other users in the coverage area of ​​the VLC AP cluster;

[0117] Step 4: Calculate M in turn using formula (17): A The priority factor value of the VLC AP cluster selected by the user in the set;

[0118] Step 5: Follow the M A The user priority factor values ​​in the set are arranged in descending order from high to low. A Users in the collection;

[0119] Step 6: Select M A For the first user in the set that does not check the VLC AP subcarrier allocation, select the AP cluster where the VLC AP with the largest channel gain is located for the user, and determine whether there are available subcarriers in the cluster. If so, go to step 7; otherwise, add the user to the set M. R and from the set M A Delete the user and go to step 8;

[0120] Step 7: Allocate the idle subcarriers with the same sequence number of each VLC AP in the VLC AP cluster to the user, update the subcarrier association matrix, and go to step 8;

[0121] Step 8: If the set M A After all users have been checked, go to step 9; otherwise, go to step 6;

[0122] Step 9: If the set M R After checking the RF AP carrier allocation of the user in, go to step 10; otherwise, the set M R The user selects an idle subcarrier of RF. If RF has no idle subcarrier resources, the blocking set M R If the service request of the user to which the subcarrier is not allocated is received, go to step 10;

[0123] Step 10: Output the user set M that accesses the VLC AP cluster A and the set of users accessing the RF AP M R , the user obtains the subcarrier sequence number information of the access VLC AP or RF AP.

[0124] 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 the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for allocating time-frequency resources for downlink collaborative transmission in indoor VLC-RF heterogeneous networks, characterized by: The method comprises the following steps: S1: Input user set M, VLC (Visible Light Communication) access point (AP) set N, 1 RF (Radio Frequency) AP, and the transmission power of each VLC AP is P V and unit carrier bandwidth, the RF AP transmit power is P R and unit carrier bandwidth, the VLC AP subcarrier set is C s , RF subcarrier set, input the general rate value, minimum rate value and maximum rate value of the user's requested service, and set the minimum number of VLC AP clusters K min and the maximum number of clusters K max , the satisfaction threshold of the VLC system; according to the Lambertian radiation model of VLC, the channel gain value from each user to each VLC AP is calculated; according to the Rayleigh fading channel model, the channel gain from each user to the RF AP is calculated; Among them, the formula for calculating the line-of-sight channel gain from VLC AP n to the receiver of user m based on the Lambertian radiation model is: In the formula, A PD Indicates the light receiving area; D m,n is the straight-line distance between user m and VLC AP n; is the VLC AP emission angle; f represents the Lambertian radiation order, and is the half-power angle of the VLC AP; ψ is the incident angle of the optical receiver; ψ c is the field of view of the optical receiver; T(ψ) and g(ψ) are the optical filter gain and optical concentrator gain of the optical receiver, respectively; if 0≤ψ≤ψ c , then the concentrator g(ψ)=c 2 / sin 2 (ψ c ), where the refractive index c = 1.5; if ψ>ψ c , then g(ψ)=0; According to the Rayleigh fading model, the channel gain between the RF AP and user m is calculated as follows: Where L (dB) represents the path loss of the RF channel in dB, which is calculated as follows: In the above formula, d mn is the length of the communication link from RF AP n to user m; f c is the center carrier frequency in GHz; X σ is the shadow fading represented by a zero-mean Gaussian random variable with a standard deviation of 3 dB; d BP is a reference distance of 10 m; the free space path loss L(d mn )=20log 10 (f c d mn )-147.5; S2: adopt the method described in claim 2 to execute the user-centric time resource allocation algorithm, the specific process is: construct a VLC AP weighted undirected interference graph, and determine the clustering set of VLC APs in the interference graph according to the sum of the maximum achievable rates obtained by the user accessing the VLC AP cluster and the minimum average satisfaction value of the VLC system by using the Shannon formula; determine the scheduling duration of each VLC AP cluster serving the user service transmission according to the rate value of the user request service; S3: The method described in claim 3 is adopted to execute a multi-cell resource allocation algorithm based on interference management. The specific process is: the positive impact of the idle carrier of the user accessing the VLC AP cluster and the negative impact caused by other users competing for the subcarrier resources are calculated in turn, the priority factor value of the user selecting the idle carrier of the VLC AP cluster is determined, and the multi-cell resource allocation algorithm based on interference management is executed to obtain the visible light subcarrier association information of the user accessing the VLC AP cluster and the subcarrier association information of the user accessing the RF AP.

2. The method for allocating time-frequency resources for downlink collaborative transmission of indoor VLC-RF heterogeneous networks according to claim 1, characterized in that: The specific method of S2 is: S201: According to the user position and the field of view of the receiving device, the position and the transmission angle of the VLC AP in the indoor VLC-RF heterogeneous network, the communication coverage overlap range between the VLC AP cells and the user set in the overlap area are determined, and a weighted undirected interference graph G(V, E) reflecting the degree of line of sight transmission interference between the VLC APs is constructed, where the node set V = {1, ..., |N|} of the interference graph corresponds to the VLCAP set, and the edge set of the interference graph is E = {e r,j |r,j∈N I },N I is a set of VLC APs with users in the overlapping coverage area; The interference graph shows that there is an interference edge e between VLC APr and VLC AP j. r,j The weight value is: In the formula, ζ j is the interfering user set of VLC AP j, which consists of users in the overlapping area of ​​VLC APr and VLC AP j but not connected to VLC AP j, h m,r is the line-of-sight channel gain between VLC APr and user m; r is the interfering user set of VLC APr, which consists of users in the overlapping area of ​​VLC APr and VLC AP j but not connected to VLC APr, h m,j is the line-of-sight channel gain between VLC APj and user m; in the graph G(V, E), W(e r,j )=W(e j,r ); S202: Calculate the interference strength value of each VLC AP, determine the weight of each node in the interference graph G(V, E), and let K C =K min , K min is the minimum number of cluster heads for the set VLC AP clustering; The weight of node j in G(V, E) is the interference intensity value of the jth VLC AP, and its calculation formula is: S203: Add the VLC AP corresponding to the node with the largest weight in G(V, E) to the GL set as the cluster head node of the GL set. If the number of cluster head nodes in the GL set is equal to K C , add all nodes in G(V, E) that are not added to the GL set to the GM set, and go to step S204; otherwise, delete the nodes added to the GL set from G(V, E), and return to step S203; S204: If the GM set is an empty set, go to step S206, otherwise, go to step S205; S205: Compare the interference edges between the GM set nodes and the GL set nodes, select the GM set node corresponding to the edge with the smallest interference edge weight, and mark it as j. If there is an edge with the smallest weight, add node j to the cluster head set of GL, delete node j from the GM set, and go to step S204; S206: adding all VLC APs as cluster heads to the GL set to obtain a VLCAP cluster set GL for multi-VLC AP services and a single VLC AP service; S207: Access the users in the VLC AP coverage area to the VLC AP cluster in the GL with the largest channel gain. If there is only one node in the VLC AP cluster, the user accepts the VLC AP information transmission service; if there are multiple nodes in the VLC AP cluster, the user accepts the cooperative transmission service of the VLC AP cluster, calculates the maximum achievable rate value of each user, calculates the minimum average satisfaction value of the VLC system, and if the minimum average satisfaction value is greater than or equal to the satisfaction threshold of the VLC system, go to step S207; otherwise, if K C <K max , let K C =K C +1, go to step S203; if K C =K max , go to step S208; The calculation formula for the maximum achievable rate of the kth VLC AP cluster cooperatively serving user m is: In the above formula, C k represents the VLC AP set in the kth VLC AP cluster, B0 is the bandwidth of the VLC AP unit carrier; SNR m,n It represents the signal-to-noise ratio of user m accessing VLC AP n. Its calculation formula is: In the above formula, P V represents the optical transmission power of the VLC AP; γ is the optical / electrical conversion coefficient of the user receiving end; N 0 is the power spectral density of AWGN (Additive White Gaussian Noise); B V is the total system bandwidth of the VLC AP; The minimum average satisfaction of the system is the ratio of the system throughput to the minimum total rate required by the user request, and its calculation formula is: In the above formula, is the minimum rate value required by user m to request the service; GL is the VLC AP divided into K C The cluster set of clusters, C k is the VLC AP set of the kth cluster; S207: If the minimum average satisfaction value of the VLC system is less than 1, go to step S208; otherwise, set the scheduling duration of each user to 1 time scheduling cycle, go to step S209; S208: Calculate the scheduling time of each VLC AP cluster serving the user according to the request rate requirement of each user, and then go to step S209; Among them, user m accesses VLC AP cluster C k Scheduling time The calculation formula is: Where U m is the normal rate requirement value of the service requested by user m, T is the unit duration of a scheduling cycle, Indicates rounding up to an integer; S209: Connect users that are not in the coverage area of ​​the VLC AP to the RF AP, calculate their scheduling duration, and then go to step S210; Among them, the scheduling time for user m to access the RF AP is The calculation formula is: In the formula, is the maximum achievable rate of user m accessing the RF AP. According to the Shannon formula, the value is calculated as follows: In the above formula, B R is the bandwidth of the RF AP unit carrier; R Indicates the transmit power of the RF AP; B R is the total system bandwidth of the RF AP; S210: Output the GL set of the VLC AP cluster, the time each user accesses the VLC AP cluster and is scheduled in the cluster, and the time each user accesses the RFAP.

3. The method for allocating time-frequency resources for downlink collaborative transmission of indoor VLC-RF heterogeneous networks according to claim 1, characterized in that: The S3 specific method is: S301: According to the scheduling duration of the user being associated with the VLC AP cluster or the VLC AP, count the users associated with the VLC AP cluster and save them in the set M A In the RF AP, the user is associated with the RF AP and saved in the M R Calculate M in sequence A The positive impact of a carrier of a VLC AP cluster associated with a user on other users; Among them, user m accesses VLC AP cluster C k The calculation formula of the positive influence of the carrier L is: In the above formula, C s is the total carrier set of the VLC AP; is the maximum achievable rate of carrier L of user m accessing VLC AP n, which is calculated as follows: In the above formula, Access VLC AP cluster C for user m k The scheduling duration, Indicates that user m accesses VLC AP cluster C k The signal-to-interference ratio of carrier L of VLC AP n is calculated as follows: In the above formula, ζ n is the interfering user set of VLC AP n, which is composed of users in the overlapping area of ​​VLC APr and VLC AP n. The number of users who use carrier L but do not access VLC AP n during the scheduling period; t is a Boolean variable. When users in the overlapping coverage area of ​​VLCAPs of different clusters use the same carrier L in the tth scheduling duration unit time, λ t =1; otherwise, λ t =0; S302: Calculate M in sequence A The negative impact and total weighted negative impact caused by a carrier of a VLC AP cluster associated with a user on other users in the coverage area of ​​the VLC AP cluster; Among them, user m is associated with VLC AP cluster C k The positive influence of the carrier L on q m The calculation formula for the total negative impact on the weight of other users in the cluster is: In the above formula, Y m Associate VLC AP cluster C with user m k The set of users affected by carrier L; Associate VLC AP cluster C for user m k The negative impact value of carrier L on other users m′ in the coverage area of ​​the cluster is calculated as follows: Where U max is the maximum required rate of all users in the system, U min is the minimum required rate of all users in the system, U m' is the normal data rate requirement value of user m'; L' and L are the subcarrier numbers used; Where, user m is associated with VLC AP cluster C k The user set Y affected by carrier L m The method for determining is: H j Cluster C k The set of users in the coverage area of ​​VLC AP j; S303: Calculate M in sequence A The priority factor for users to select VLC AP clusters; The calculation formula of the priority factor value of the carrier selected by user m in the VLC AP cluster is: S304: Sort the user priority factors in descending order. A Users in the collection; S305: Select M A The first user whose VLC AP subcarrier allocation is not checked in the set is selected, and the AP cluster where the VLC AP with the largest channel gain is located is selected for the user. If there is one, go to step S306; otherwise, add the user to the set M. R and from M A Delete the user from the set and go to step S307; S306: Allocate idle subcarriers with the same sequence number of each VLC AP in the VLC AP cluster to the user, update the subcarrier association matrix, and go to step S307; S307: If the set M A If all users in the VLC AP subcarrier allocation are checked, go to step S308; otherwise, go to step S305; S308: If the set M R If it is an empty set, go to step S309; ​​otherwise, it is the set M R The user selects an idle subcarrier of RF. If RF has no idle subcarrier resources, the blocking set M R If the service request of the user to which the subcarrier is not allocated is received, the process goes to step S309; S309: Output the scheduling duration information of all users associated with the VLC AP or RF AP, and the users obtain the subcarrier sequence number information of the accessed VLC AP or RFAP. A and the set of users accessing the RF AP M R .

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