CN109922487B - Resource allocation method under downlink MIMO-NOMA network - Google Patents
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Abstract
The invention discloses a resource allocation method under a downlink MIMO-NOMA network, which is characterized in that user clustering is carried out on the basis of channel state information analysis of users, multidimensional resources such as space, frequency spectrum and power are comprehensively considered by taking multidimensional resource allocation research under the downlink MIMO-NOMA network as a main line, network performance is measured by effective capacity, a multidimensional resource allocation model under the downlink MIMO-NOMA network is established, and optimal multidimensional resource allocation is rapidly realized by using the characteristics of convergence and low complexity of an alternating iteration optimization theory. The invention fully considers the characteristics of beam directivity, service diversity and the like, meets the beam directivity by user clustering, meets the service diversity by effective capacity, and realizes the multi-dimensional resource allocation under the downlink MIMO-NOMA network.
Description
Technical Field
The invention relates to a multi-dimensional resource allocation method based on user clustering in a downlink MIMO-NOMA network, belonging to the technical field of network resource allocation.
Background
The 5G is a new generation mobile communication system developed for the demand of mobile communication after 2020, and according to the development rule of mobile communication, the 5G needs to have higher spectrum efficiency and network capacity to meet the exponentially increasing user demand. Non-orthogonal multiple access (NOMA) is an alternative multiple access technology of 5G, and can effectively improve the spectrum efficiency. Different from the conventional Orthogonal Multiple Access (OMA), NOMA enables multiple users to share the same time-frequency resource through power domain multiplexing, and meanwhile, a Serial Interference Cancellation (SIC) technology is adopted at a receiving end to decode step by step to obtain signals so as to eliminate simultaneous same-frequency interference.
In the Multiple-input Multiple-output (MIMO) technology, spatial multiplexing is realized by using multi-antenna transmission at a transmitting end and a receiving end, and network capacity is improved on the premise of not increasing frequency spectrum resources and transmitting power. In order to further improve the performance of NOMA, MIMO technology is applied to NOMA to form a MIMO-NOMA network. Compared with the traditional LTE network, the network increases the resource reuse of a space domain and a power domain, and can remarkably improve the spectrum efficiency and the network capacity through a resource allocation algorithm with excellent performance. But the resources in the MIMO-NOMA network include multidimensional resources such as space, spectrum and power, and the resource allocation faces a serious challenge.
The method comprises the steps of clustering users based on channel state information analysis of the users, taking multidimensional resource allocation research under a downlink MIMO-NOMA network as a main line, comprehensively considering multidimensional resources such as space, frequency spectrum and power, measuring network performance by Effective Capacity (EC), establishing a multidimensional resource allocation model under the downlink MIMO-NOMA network, and having great practical significance for realizing the multidimensional resource allocation under the optimal downlink MIMO-NOMA network.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides a resource allocation method under a downlink MIMO-NOMA network, which is characterized in that the method is used for clustering users on the basis of channel state information analysis of the users, takes multidimensional resource allocation research under the downlink MIMO-NOMA network as a main line, comprehensively considers multidimensional resources such as space, frequency spectrum, power and the like, measures network performance by EC, establishes a multidimensional resource allocation model under the downlink MIMO-NOMA network, and quickly realizes optimal multidimensional resource allocation by utilizing the characteristics of convergence and low complexity of an alternating iteration optimization theory.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the technical scheme that:
a resource allocation method under a downlink MIMO-NOMA network comprises the following steps:
step 1), clustering users: acquiring channel state information and cell information of users, and performing user clustering on each cell by combining the channel state information of the users, so that the users in the clusters occupy the same wave beam, share the same time-frequency resource, and determine the optimal user clustering;
step 2), beam allocation: analyzing the beam forming process, and determining the optimal beam distribution quantity by utilizing the zero forcing beam forming theory as the user clustering distribution beam direction obtained in the step 1);
step 3), problem formation: introducing EC as an index for measuring network performance, and establishing an optimization problem by taking the EC of the maximized user as a target;
step 4), channel allocation: under the given condition of power distribution, converting the optimization problem obtained in the step 3) into an equivalent maximum weighted bipartite graph matching problem, and solving by using the Hungarian algorithm to obtain the optimal channel distribution
Step 5), power distribution: under the condition of assuming given channel allocation, converting the optimization problem obtained in the step 3) into an equivalent Lagrange dual problem, and solving by utilizing a sub-gradient algorithm to obtain optimal transmission power allocation;
step 6), alternately and iteratively optimizing: and alternately iterating the step 4) and the step 5) until the effective capacity of the user tends to converge, so as to obtain the optimal channel allocation and power allocation.
The specific steps of the step 1) are as follows:
step 11), dividing users of the cell n into G groups based on the average channel gain of the users, and recording the G groups as the G groupsWhereinIs the set of users in the G-th group in cell n, G ═ 1, 2.Inner userThe channel gain vector on subcarrier u is noted asWherein the content of the first and second substances,is the user in antenna mChannel gain, M, over subcarrier unRepresents the number of antennas in cell n; user' sIs expressed as the average channel gain vectorDefining usersAnd the userThe average channel gain correlation coefficient between is:
wherein the content of the first and second substances,andare respectively average channel gain vectorsAndthe evaluation index of whether the user can be divided into a cluster is defined as the minimum correlation coefficient rho whenThen the userAnd the userCan be divided into one cluster;
Step 13), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionTurning to the step 12), otherwise, turning to the step 13 from g';
step 14), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionGo to step 12), otherwise go to step 13);
step 15), dividing the users obtained by traversing into a cluster, deleting the users from the G group, and repeating the steps 11) -13) until all the users are divided; the users who get cell n are divided into LnA cluster ofWherein C isnlIs the user set of the ith cluster in the cell n and is recorded as|CnlIs | CnlThe number of users.
The specific steps of the step 2) are as follows:
step 21), the users of the cell n obtained according to step 1 are divided into LnAn individual clusterWherein C isnlIs the user set of the l-th cluster in the cell nCell recordingn is the vector of the transmitted signal on channel uWhereinIs CnlThe superposition coded signal transmitted on channel u,is allocated on channel uPower ratio of (A) to (B) Is thatA transmit signal on channel u; the beamforming matrix for cell n on channel u isWhereinIs CnlA beam vector on channel u; the transmitted signal of cell n on channel u is:
step 22), mixingIs shown asWhereinFor eliminating CnlInter-cluster interference experienced by the inner user on channel u,for determining C on channel unlAllocated power, defining usersThe channel gain vector on channel u isAssuming that the number of transmitting antennas is greater than or equal to the number of receiving antennas, the inter-cluster interference is completely eliminated, CnlInter-cluster interference experienced by an inner user on channel u is divided by C in cell nnlUser generation, definition of other clustersIs dividing C in cell nnlChannel gain matrix on channel u for users in other clusters, whereinIs CnlA channel gain matrix for the inner user on channel u;
step 23), forSingular value decomposition to obtainWhereinIs thatFront K ofn-|CnlL left singular vectors, correspondingA non-zero singular value of;is thatRear M ofn-Kn+|CnlL left singular vectors, correspondingAnd zero singular value ofOrder toIs equal toSum of medium anisotropyBy usingElimination of CnlInter-cluster interference experienced by the inner user on channel u,is formed byIs used to form a matrix of singular values of,is thatRight singular matrix of (a).
The specific steps of the step 3) are as follows:
step 31) utilizingElimination of CnlAfter inter-cluster interference experienced by the inner user on channel u,the received signal of the terminal on channel u is:
wherein the first term isThe second term is intra-cluster interference, the third term is inter-zone interference,is noise that follows a complex gaussian distribution;
step 32), because the users in the cluster occupy the same wave beam and share the same time-frequency resource, the SIC technology is utilized to decode the user signals step by step according to the sequence of increasing the channel gain; hypothesis CnlThe channel gain vector of the inner user on the channel u satisfiesThe decoding order of SIC is The terminal decodes the user by SIC technologyAfter the signal of (2), the userThe signal to interference plus noise ratio on channel u is:
wherein the content of the first and second substances,is a userQoS index of (E [. cndot.)]Represents expectation in view ofTime of flightThe above equation is therefore Taylor expanded at 1 as:
ignoring the higher order terms of the above, the simplified EC expression is:
whereinIs the sub-carrier indicator, if CnlOccupying sub-carrier u thenOtherwise, the reverse is carried outWill be provided withSubstituting the expression to obtain:
Step 35) of jointly optimizing the subcarrier indication factorsInter-cluster power allocationAnd between users in the clusterPower distribution ratioObtaining an optimization problem aiming at maximizing EC of users in a downlink multi-cell MIMO-NOMA network:
wherein the content of the first and second substances,is a userMinimum EC requirements of (a);is the maximum transmit power of cell n; defining variablesUsing variablesReplacing variablesAnda simplified optimization problem P2 is obtained:
the specific steps of the step 4) are as follows:
step 41) assuming that the transmission power is evenly distributed to the users, the optimization problem P2 is simplified as follows:
construct weighted bipartite graph F ═ VC×VSE), in which VCAnd VSSet of vertices, V, representing clusters and subcarriers, respectivelyCVertex v in (1)C(n, l) represents Cnl,VSVertex v in (1)S(u) denotes the subcarrier u, E denotes the connection VCAnd VSE (n, l, u) in E represents a connecting vertex vC(n, l) and vertex vS(u) the weight defining the edge e (n, l, u) isA match definition for graph F is a set of pairs of non-adjacent edges, i.e., any two edges in a match cannot share the same vertex, and according to the definition, the optimization problem P3 is transformed into a maximum weighted bipartite graph matching problem, i.e., a match E is found in graph F*So that E*The sum of the weights of the middle edges is maximum, the classical Hungarian algorithm is utilized to directly solve,
step 42), construct weighted bipartite graph F ═ VC×VSE), in which VCSet of vertices, V, representing all clustersSVertex set representing all subcarriers, E represents connection VCAnd VSUsing Hungarian algorithm to solve to obtain a matching E*;
Step 43), judging whether P3 is satisfied (C1), and if not, reconstructing a weighted bipartite graph F '((V)'C×V'SAnd E '), wherein V'CRepresents a set of vertices, V ', of clusters that do not satisfy P3 (C1)'SRepresents a vertex set of unmatched subcarriers, E 'represents a connection V'CAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E'*Repeating step 42) until P3(C1) is satisfied;
step (ii) of44) Judging whether unmatched subcarriers exist or not, and if the unmatched subcarriers exist, reconstructing a weighted bipartite graph F ″ (V)C×V'SE') in which VCSet of vertices, V ', representing all clusters'SVertex set representing unmatched subcarriers, E' representing connection VCAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E'*And repeating the step 43) until the sub-carriers are allocated.
The specific steps of the step 5) are as follows:
step 51), after the sub-carriers are allocated according to the step 4), the optimization problem P2 is simplified into:
step 52), obtaining the Lagrangian function of the optimization problem P4 according to the Lagrangian theory as follows:
where μ and v are lagrange multiplier vectors introduced according to the optimization problems P4(C1) and P4(C2), respectively,and vnElements in μ and v, respectively, whose dual function is
Wherein sup {. is a supremum, and the lagrangian dual problem from which the optimization problem P4 is derived is:
s.t.C1:μ≥0,v≥0
step 53), updating simultaneously with a sub-gradient algorithmAnd vnTo minimize L (μ, v). L (. mu.v) about variablesAnd vnThe sub-gradients of (a) are:
where s is the number of iterations, phi(s)Andthe update step sizes of mu and v in the s-th iteration process, {. cndot. }+=max{·,0};
Step 54), assumeIs the optimal solution of the optimization problem P4, and obtains mu by iteration of a sub-gradient algorithm*And v*After-utilization ofTo pairIs equal to 0 to obtain
The specific steps of the step 6) are as follows:
step 61) obtaining the optimal channel allocation under the fixed transmitting power according to the step 4);
step 62) obtaining the optimal transmission power distribution under the fixed channel according to the step 5);
step 63) repeats steps 61) and 62) until the effective capacity of the user tends to converge.
Preferably: the use of a decreasing step update scheme ensures that the algorithm converges quickly:
Compared with the prior art, the invention has the following beneficial effects:
the invention carries out user clustering based on the analysis of the channel state information of the user, takes multidimensional resource allocation research under the downlink MIMO-NOMA network as a main line, comprehensively considers multidimensional resources such as space, frequency spectrum and power, and the like, measures the network performance by effective capacity, establishes a multidimensional resource allocation model under the downlink MIMO-NOMA network, and quickly realizes optimal multidimensional resource allocation by using the characteristics of convergence and low complexity of the alternating iterative optimization theory. The invention fully considers the characteristics of beam directivity, service diversity and the like, meets the beam directivity by user clustering, meets the service diversity by effective capacity, and realizes the multi-dimensional resource allocation under the downlink MIMO-NOMA network.
Drawings
Fig. 1 is a multi-dimensional resource allocation diagram based on user clustering in a downlink MIMO-NOMA network.
Fig. 2 is a schematic diagram of user clustering in a downlink MIMO-NOMA network.
Detailed Description
The present invention is further illustrated by the following description in conjunction with the accompanying drawings and the specific embodiments, it is to be understood that these examples are given solely for the purpose of illustration and are not intended as a definition of the limits of the invention, since various equivalent modifications will occur to those skilled in the art upon reading the present invention and fall within the limits of the appended claims.
A resource allocation method under a downlink MIMO-NOMA network is characterized in that user clustering is carried out on the basis of channel state information analysis of users, multidimensional resources such as space, frequency spectrum and power are comprehensively considered as a main line for multidimensional resource allocation research under the downlink MIMO-NOMA network, network performance is measured by effective capacity, a multidimensional resource allocation model under the downlink MIMO-NOMA network is established, and optimal multidimensional resource allocation is rapidly realized by using the characteristics of convergence and low complexity of an alternative iteration optimization theory.
The method specifically comprises the following steps:
1) clustering users: acquiring channel state information and cell information of users, and performing user clustering on each cell by combining the channel state information of the users, so that the users in the cluster can occupy the same wave beam, share the same time-frequency resource, and determine the optimal user clustering.
Step 11) as shown in fig. 2, the users in cell n are divided into G groups based on the average channel gain of the users, and the G groups are recorded asWhereinIs the set of users in the g-th group in the cell n;inner userThe channel gain vector on subcarrier u is noted asWhereinIs the user in antenna mChannel gain on subcarrier u; user' sIs expressed as the average channel gain vectorDefining usersAnd the userThe average channel gain correlation coefficient between is:
whereinAndare respectively average channel gain vectorsAndof (1). The evaluation index of whether the user can be divided into one cluster is defined as the minimum correlation coefficient rho whenGreater than rho then userAnd the userMay be divided into a cluster.
Step 12), introducing a variable G as an index for traversing the G group, wherein the initial value of G is 1; fromIn randomly selecting a user
Step 13), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionTurning to the step 12), otherwise, turning to the step 13 from g';
step 14), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionGo to step 12), otherwise go to step 13);
and 15) dividing the users obtained by traversing into a cluster, deleting the users from the G group, and repeating the steps 11) to 13) until all the users are divided.
2) Beam allocation: analyzing the beam forming process, and obtaining the optimal cluster distribution beam vector by using a zero-forcing beam forming theory as the step 1).
Step 21) assume that users of cell n are divided into LnA cluster ofWherein C isnlIs the user set of the ith cluster in the cell n and is recorded as|CnlIs | CnlThe number of users. The transmitted signal vector of cell n on channel u isWhereinIs CnlThe superposition coded signal transmitted on channel u,is allocated on channel uPower ratio of (A) to (B) Is thatThe signal is transmitted on channel u. The beamforming matrix for cell n on channel u isWhereinIs CnlA beam vector on channel u. The transmitted signal of cell n on channel u is:
step 22) Beam vectorThe functions of (1) are as follows: 1) eliminating inter-cluster interference; 2) determine the power allocation between clusters and thereforeIs shown asWhereinFor eliminating CnlInter-cluster interference experienced by the inner user on channel u,for determining C on channel unlThe allocated power. Defining usersThe channel gain vector on channel u isThe number of transmitting antennas is assumed to be greater than or equal to the number of receiving antennas, so that inter-cluster interference can be completely eliminated. CnlInter-cluster interference experienced by an inner user on channel u is divided by C in cell nnlUser generation, definition of other clustersIs dividing C in cell nnlChannel gain matrix on channel u for users in other clusters, whereinIs CnlA channel gain matrix for the inner user on channel u;
step 23) pairSingular value decomposition to obtainWhereinIs thatFront K ofn-|CnlL left singular vectors, correspondingA non-zero singular value of;is thatRear M ofn-Kn+|CnlL left singular vectors, correspondingAnd zero singular value ofOrder toIs equal toSum of medium anisotropyBy usingCan eliminate CnlInter-cluster interference experienced by the inner user on channel u.
3) Problems are formed: and introducing EC as an index for measuring network performance, and establishing an optimization problem by taking the EC of the maximized user as a target.
Step 31) utilizingElimination of CnlAfter inter-cluster interference experienced by the inner user on channel u,the received signal of the terminal on channel u is:
wherein the first term isThe second term is intra-cluster interference, the third term is inter-zone interference,is noise that follows a complex gaussian distribution;
step 32), because the users in the cluster occupy the same wave beam and share the same time-frequency resource, the SIC technology is utilized to decode the user signals step by step according to the ascending sequence of the channel gain. Hypothesis CnlThe channel gain vector of the inner user on the channel u satisfiesThe decoding order of SIC is The terminal decodes the user by SIC technologyAfter the signal of (2), the userThe signal to interference plus noise ratio on channel u is:
step 34) because the 5G service has different requirements for bandwidth, delay and packet loss rate, and the network capacity can only reflect the requirements for bandwidth, EC is introduced as an index for measuring network performance.EC of (a) may be expressed as:
whereinIs a userQoS index of (E [. cndot.)]Representing the expectation. In view ofTime of flightThe above equation is therefore Taylor expanded at 1 as:
ignoring the higher order terms of the above, the simplified EC expression is:
whereinIs the sub-carrier indicator, if CnlOccupying sub-carrier u thenOtherwise, the reverse is carried outWill be provided withSubstituting the expression to obtain:
Step 35) indicating factor by joint optimization of subcarriersInter-cluster power allocationPower distribution ratio between users in clusterObtaining an optimization problem aiming at maximizing EC of users in a downlink multi-cell MIMO-NOMA network:
wherein C1 ensures that the different requirements of the user on bandwidth, delay and packet loss rate are met,is a userMinimum EC requirements of (a); equations C2 and C3 ensure that the sum of the transmit powers allocated by the cell to the users does not exceed the maximum transmit power of the cell,is the maximum transmit power of cell n; equation C4 ensuresIs a binary variable; equation C5 ensures that one subcarrier corresponds to one cluster. Variables in the objective function due to the optimization problem P1Andall occur as products, thus defining variablesUsing variablesReplacing variablesAnda simplified optimization problem P2 is obtained:
4) channel allocation: under the condition of given transmitting power, the optimization problem P2 is converted into an equivalent maximum weighted bipartite matching problem, and the optimal channel allocation is obtained by utilizing the Hungarian algorithm to solve.
Step 41) assuming that the transmit power is evenly distributed to the users, the optimization problem P2 can be simplified as:
construct weighted bipartite graph G ═ VC×VSE), in which VCAnd VSSet of vertices, V, representing clusters and subcarriers, respectivelyCVertex v in (1)C(n, l) represents Cnl,VSVertex v in (1)SAnd (u) represents a subcarrier u. E represents a connection VCAnd VSE (n, l, u) in E represents a connecting vertex vC(n, l) and vertex vS(u) the weight defining the edge e (n, l, u) isA match of graph G is defined as a set of pairs of non-adjacent edges, i.e., any two edges in a match cannot share the same vertex. According to the above definition, the optimization problem P3 can be converted into a maximum weighted bipartite graph matching problem, i.e. finding a match E in graph G*So that E*The sum of the weights of the middle edges is the largest, and the classical Hungarian algorithm can be used for directly solving.
Step 42) construct weighted bipartite graph G ═ VC×VSE), in which VCSet of vertices, V, representing all clustersSVertex set representing all subcarriers, E represents connection VCAnd VSUsing Hungarian algorithm to solve to obtain a matching E*;
Step 43) determines whether P3 is satisfied (C1), and if not, reconstructs weighted bipartite graph G '═ V'C×V'SAnd E '), wherein V'CRepresents a set of vertices, V ', of clusters that do not satisfy P3 (C1)'SRepresents a vertex set of unmatched subcarriers, E 'represents a connection V'CAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E'*. Repeating step 42) until P3(C1) is satisfied;
step 44) judging whether unmatched subcarriers exist or not, and if the unmatched subcarriers exist, reconstructing a weighted bipartite graph G ″ (V)C×V'SE') in which VCSet of vertices, V ', representing all clusters'SVertex set representing unmatched subcarriers, E' representing connection VCAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E'*. Repeating step 43) until the sub-carriers are allocated.
5) Power distribution: under the condition of channel allocation, converting the optimization problem P2 into an equivalent Lagrangian dual problem, and solving by using a sub-gradient algorithm to obtain optimal transmission power allocation.
Step 51) after allocating the sub-carriers according to step 4), the optimization problem P2 can be simplified as:
step 52) obtaining the lagrangian function of the optimization problem P4 according to the lagrangian theory is:
where μ and v are lagrange multiplier vectors introduced according to the optimization problems P4(C1) and P4(C2), respectively,and vnAre the elements in μ and v, respectively. Its dual function is
Where sup {. is the supremum, the lagrange dual problem from which the optimization problem P4 is derived is:
s.t.C1:μ≥0,v≥0
step 53) Simultaneous update with a sub-gradient AlgorithmAnd vnTo minimize L (μ, v). L (. mu.v) about variablesAnd vnThe sub-gradients of (a) are:
where s is the number of iterations, phi(s)Andthe update step sizes of mu and v in the s-th iteration process, {. cndot. }+=max{·,0}。φ(s)Andthe choice of (b) influences the convergence of the sub-gradient algorithm, if phi(s)Andif the choice is too large, the algorithm may fail to converge, if φ(s)Andif chosen too small, the algorithm may converge too slowly. The use of a decreasing step update scheme therefore ensures that the algorithm can converge quickly:
step 54) supposeIs the optimal solution of the optimization problem P4, and obtains mu by iteration of a sub-gradient algorithm*And v*After-utilization ofTo pairIs equal to 0 to obtain
6) Alternate iterative optimization: and alternately iterating the step 4) and the step 5) until the effective capacity of the user tends to converge.
Step 61) obtaining the optimal channel allocation under the fixed transmitting power according to the step 4);
step 62) obtaining the optimal transmission power distribution under the fixed channel according to the step 5);
step 63) repeats steps 61) and 62) until the effective capacity of the user tends to converge.
The invention carries out user clustering based on the analysis of the channel state information of the user, takes multidimensional resource allocation research under the downlink MIMO-NOMA network as a main line, comprehensively considers multidimensional resources such as space, frequency spectrum and power, and the like, measures the network performance by effective capacity, establishes a multidimensional resource allocation model under the downlink MIMO-NOMA network, and quickly realizes optimal multidimensional resource allocation by using the characteristics of convergence and low complexity of the alternating iterative optimization theory. The invention fully considers the characteristics of beam directivity, service diversity and the like, meets the beam directivity by user clustering, meets the service diversity by effective capacity, and realizes the multi-dimensional resource allocation under the downlink MIMO-NOMA network.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (3)
1. A resource allocation method under a downlink MIMO-NOMA network is characterized by comprising the following steps:
step 1), clustering users: acquiring channel state information and cell information of users, and performing user clustering on each cell by combining the channel state information of the users, so that the users in the clusters occupy the same wave beam, share the same time-frequency resource, and determine the optimal user clustering;
the specific steps of the step 1) are as follows:
step 11), dividing users of the cell n into G groups based on the average channel gain of the users, and recording the G groups as the G groupsWhereinIs the set of users in the G-th group in cell n, G ═ 1, 2.Inner userThe channel gain vector on subcarrier u is noted asWherein the content of the first and second substances,is the user in antenna mChannel gain, M, over subcarrier unRepresents the number of antennas in cell n; user' sIs expressed as the average channel gain vectorDefining usersAnd the userThe average channel gain correlation coefficient between is:
wherein the content of the first and second substances,andare respectively average channel gain vectorsAndthe evaluation index of whether the user can be divided into a cluster is defined as the minimum correlation coefficient rho whenThen the userAnd the userDividing the data into a cluster;
step 12), introducing a variable G as an index for traversing the G group, wherein the initial value of G is 1; fromIn randomly selecting a user
Step 13), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionTurning to the step 12), otherwise, turning to the step 13 from g';
step 14), g is g + 1; if G > G, go to step 14), otherwise go fromIs selected so thatMaximum and satisfyTo a userIf there are users who satisfy the conditionGo to step 12), otherwise go to step 13);
step 15), dividing the users obtained by traversing into a cluster, deleting the users from the G group, and repeating the steps 11) to 13) until all the users are dividedFinishing; the users who get cell n are divided into LnCluster, denoted as Cn1,Cn2,...,CnLnIn which C isnlIs the user set of the ith cluster in the cell n and is recorded as|CnlIs | CnlThe number of users;
step 2), beam allocation: analyzing the beam forming process, and determining the optimal beam distribution quantity by utilizing the zero forcing beam forming theory as the user clustering distribution beam direction obtained in the step 1);
the specific steps of the step 2) are as follows:
step 21), the users of the cell n obtained according to step 1 are divided into LnAn individual cluster Cn1,Cn2,...,CnLnIn which C isnlIs the user set of the l-th cluster in the cell nLet the vector of the transmitted signal of cell n on channel u beWhereinIs CnlThe superposition coded signal transmitted on channel u,is allocated on channel uPower ratio of (A) to (B) Is thatA transmit signal on channel u; the beamforming matrix for cell n on channel u isWhereinIs CnlA beam vector on channel u; the transmitted signal of cell n on channel u is:
step 22), mixingIs shown asWhereinFor eliminating CnlInter-cluster interference experienced by the inner user on channel u,for determining C on channel unlAllocated power, defining usersThe channel gain vector on channel u isAssuming that the number of transmitting antennas is greater than or equal to the number of receiving antennas, the inter-cluster interference is completely eliminated, CnlCluster of inner users experienced on channel uInter-interference by dividing C within cell nnlUser generation, definition of other clustersIs dividing C in cell nnlChannel gain matrix on channel u for users in other clusters, whereinIs CnlA channel gain matrix for the inner user on channel u;
step 23), forSingular value decomposition to obtainWhereinIs thatFront K ofn-|CnlL left singular vectors, correspondingA non-zero singular value of;is thatRear M ofn-Kn+|CnlL left singular vectors, correspondingAnd zero singular value ofOrder toIs equal toSum of medium anisotropyBy usingElimination of CnlInter-cluster interference experienced by the inner user on channel u,is formed byIs used to form a matrix of singular values of,is thatRight singular matrix of (d);
step 3), problem formation: introducing EC as an index for measuring network performance, and establishing an optimization problem by taking the EC of the maximized user as a target;
the specific steps of the step 3) are as follows:
step 31) utilizingElimination of CnlAfter inter-cluster interference experienced by the inner user on channel u,is received by the terminal on channel uThe numbers are:
wherein the first term isThe second term is intra-cluster interference, the third term is inter-zone interference,is noise that follows a complex gaussian distribution;
step 32), because the users in the cluster occupy the same wave beam and share the same time-frequency resource, the SIC technology is utilized to decode the user signals step by step according to the sequence of increasing the channel gain; hypothesis CnlThe channel gain vector of the inner user on the channel u satisfiesThe decoding order of SIC is The terminal decodes the user by SIC technologyAfter the signal of (2), the userThe signal to interference plus noise ratio on channel u is:
wherein the content of the first and second substances,is a userQoS index of (E [. cndot.)]Represents expectation in view ofTime of flightThe above equation is therefore Taylor expanded at 1 as:
ignoring the higher order terms of the above, the simplified EC expression is:
whereinIs the sub-carrier indicator, if CnlOccupying sub-carrier u thenOtherwise, the reverse is carried outWill be provided withSubstituting the expression to obtain:
Step 35) of jointly optimizing the subcarrier indication factorsInter-cluster power allocationPower distribution ratio between users in clusterObtaining an optimization problem aiming at maximizing EC of users in a downlink multi-cell MIMO-NOMA network:
wherein the content of the first and second substances,is a userMinimum EC requirements of (a);is the maximum transmit power of cell n; defining variablesUsing variablesReplacing variablesAnda simplified optimization problem P2 is obtained:
step 4), channel allocation: under the given condition of power distribution, converting the optimization problem obtained in the step 3) into an equivalent maximum weighted bipartite graph matching problem, and solving by using a Hungarian algorithm to obtain optimal channel distribution;
the specific steps of the step 4) are as follows:
step 41) assuming that the transmission power is evenly distributed to the users, the optimization problem P2 is simplified as follows:
construct weighted bipartite graph F ═ VC×VSE), in which VCAnd VSSet of vertices, V, representing clusters and subcarriers, respectivelyCVertex v in (1)C(n, l) represents Cnl,VSVertex v in (1)S(u) denotes the subcarrier u, E denotes the connection VCAnd VSE (n, l, u) in E represents a connecting vertex vC(n, l) and vertex vS(u) the weight defining the edge e (n, l, u) isA match definition for graph F is a set of pairs of non-adjacent edges, i.e., any two edges in a match cannot share the same vertex, and according to the definition, the optimization problem P3 is transformed into a maximum weighted bipartite graph matching problem, i.e., a match E is found in graph F*So that E*The sum of the weights of the middle edges is maximum, the classical Hungarian algorithm is utilized to directly solve,
step 42), construct weighted bipartite graph F ═ VC×VSE), in which VCSet of vertices, V, representing all clustersSVertex set representing all subcarriers, E represents connection VCAnd VSUsing Hungarian algorithm to solve to obtain a matching E*;
Step 43), judging whether P3 is satisfied (C1), and if not, reconstructing a weighted bipartite graph F '((V)'C×V′SAnd E '), wherein V'CRepresents a set of vertices, V ', of clusters that do not satisfy P3 (C1)'SRepresents a vertex set of unmatched subcarriers, E 'represents a connection V'CAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E'*Repeating step 42) until P3(C1) is satisfied;
step 44), judging whether unmatched subcarriers exist or not, and if the unmatched subcarriers exist, reconstructing a weighted bipartite graph F ″ (V)C×V′SE "), wherein VCSet of vertices, V ', representing all clusters'SVertex set representing unmatched subcarriers, E' representing connection VCAnd V'SThe edge set is solved by using Hungarian algorithm to obtain a matching E ″)*Repeating the step 43) until the sub-carriers are distributed;
step 5), power distribution: under the condition of assuming given channel allocation, converting the optimization problem obtained in the step 3) into an equivalent Lagrange dual problem, and solving by utilizing a sub-gradient algorithm to obtain optimal transmission power allocation;
the specific steps of the step 5) are as follows:
step 51), after the sub-carriers are allocated according to the step 4), the optimization problem P2 is simplified into:
step 52), obtaining the Lagrangian function of the optimization problem P4 according to the Lagrangian theory as follows:
where μ and v are lagrange multiplier vectors introduced according to the optimization problems P4(C1) and P4(C2), respectively,and vnElements in μ and v, respectively, whose dual function is
Wherein sup {. is a supremum, and the lagrangian dual problem from which the optimization problem P4 is derived is:
s.t.C1:μ≥0,v≥0
step 53), updating simultaneously with a sub-gradient algorithmAnd vnTo minimize L (μ, v); l (. mu.v) about variablesAnd vnThe sub-gradients of (a) are:
where s is the number of iterations, phi(s)Andthe update step sizes of mu and v in the s-th iteration process, {. cndot. }+=max{·,0};
Step 54), assumeIs the optimal solution of the optimization problem P4, and obtains mu by iteration of a sub-gradient algorithm*And v*After-utilization ofTo pairIs equal to 0 to obtain
Step 6), alternately and iteratively optimizing: and alternately iterating the step 4) and the step 5) until the effective capacity of the user tends to converge, so as to obtain the optimal channel allocation and power allocation.
2. The method for allocating resources in a downlink MIMO-NOMA network according to claim 1, wherein: the specific steps of the step 6) are as follows:
step 61) obtaining the optimal channel allocation under the fixed transmitting power according to the step 4);
step 62) obtaining the optimal transmission power distribution under the fixed channel according to the step 5);
step 63) repeats steps 61) and 62) until the effective capacity of the user tends to converge.
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