CN117956479A - Satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation - Google Patents
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Abstract
A satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation belongs to the field of satellite-ground integrated network spectrum sharing. The method solves the problems of serious co-channel interference during satellite-to-ground spectrum sharing and high calculation complexity of the existing spectrum sharing method. The method specifically comprises the following steps: step one, constructing a satellite-ground integrated network spectrum sharing model; step two, constructing a satellite-ground integrated network resource optimization allocation problem based on the constructed satellite-ground integrated network spectrum sharing model; step three, decoupling the problem constructed in the step two into a power allocation sub-problem and a frequency resource scheduling sub-problem; on the interference coordination unit, calculating a power distribution result according to the power distribution sub-problem and returning the power distribution result to the base station; and the base station calculates the number of the resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem to obtain the resource block allocation result. The method can be applied to satellite-ground integrated network spectrum sharing.
Description
Technical Field
The invention belongs to the field of satellite-ground integrated network spectrum sharing, and particularly relates to a satellite-ground integrated network spectrum sharing method.
Background
Satellites can be used alone, and L, S and C bands that achieve global coverage are almost completely allocated. The frequency bands of Ku, ka and Q/V are difficult to be used for the satellite direct connection mobile phone due to the limitation of the terminal antenna, the link budget and the international telecommunication union rule, and the frequency bands of 2GHz and below can support the satellite direct connection mobile phone. However, L and S bands have only a small amount of spectrum resources available for satellite systems, most of which are allocated to terrestrial mobile communications. The current satellite mobile communication and ground mobile communication allocate frequency bands in an exclusive mode, and to realize satellite direct-connection mobile phone broadband communication, the existing rule needs to be broken through, namely, the ground network is allowed to be deployed in the satellite frequency band, and the satellite system is allowed to be deployed in the ground mobile communication frequency band. The 6G needs more medium and low frequency bands to improve the deployed capacity and coverage area with low cost, and the problem of resource shortage can be relieved by sharing the frequency spectrum with the ground network in consideration of the characteristics of wide satellite coverage area and low frequency spectrum utilization rate.
Satellite networks can supplement the performance of terrestrial networks and provide an access environment anywhere and anytime, but have limited communication resources and explosive growth of data traffic for user equipment puts pressure on quality of service. As satellite-to-ground fusion continues to deepen, co-channel interference caused by satellite-to-ground spectrum sharing becomes a serious problem. Although the interference can be reduced by increasing the guard area, limiting the number of terminals and the transmission power, etc., increasing the guard area reduces the available frequency resources of the network, and limiting the number of terminals or the transmission power also affects the capacity thereof. The satellite-ground integrated network needs to perform joint management of frequency, time, space and other resources so as to meet the service quality requirements of various users and flows. Furthermore, the ground network typically performs a resource allocation algorithm for one or several base stations in a small area. However, the radius of coverage of satellites is from tens to thousands of kilometers, and joint resource management for a large number of base stations and satellites is extremely complex. In a star-to-ground integrated network, the distributed resource management policies are more efficient than the centralized resource management of the entire network.
The star-ground integrated network can more fully utilize power and spectrum resources through joint resource allocation, and achieves higher capacity and high-efficiency bandwidth utilization. Research on related spectrum sharing solutions has been carried out at home and abroad, and joint optimization is carried out by constructing a target optimization model with the aim of maximizing throughput of users and with the quality of service of the users as a constraint condition. The time-frequency resource allocation algorithm is adopted in the satellite-ground integrated network, so that the requirements of the number of users and timeliness which change dynamically can be met. However, the existing spectrum sharing method has higher computation complexity, the star-ground integrated network needs more flexible spectrum sharing, and research on resource allocation strategies with low computation complexity is needed.
Disclosure of Invention
The invention aims to solve the problems of serious co-channel interference during satellite-to-ground spectrum sharing and high calculation complexity of the existing spectrum sharing method, and provides a satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation specifically comprises the following steps:
Step one, constructing a satellite-ground integrated network spectrum sharing model, wherein the model comprises a satellite, a satellite terminal, a base station, a ground user and an interference coordination unit, and the uplink of the ground user shares frequency with the downlink of the satellite;
Step two, constructing a satellite-ground integrated network resource optimization allocation problem based on the satellite-ground integrated network spectrum sharing model constructed in the step one;
step three, decoupling the problem constructed in the step two into a power allocation sub-problem and a frequency resource scheduling sub-problem;
On the interference coordination unit, calculating a power distribution result according to the power distribution sub-problem and returning the power distribution result to the base station;
And the base station calculates the number of the resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem to obtain the resource block allocation result.
The beneficial effects of the invention are as follows:
The invention designs a joint power and frequency resource allocation algorithm considering interference protection constraint aiming at the problems of low channel uncertainty and low frequency utilization rate of an interference link in a satellite-ground integrated spectrum sharing network, and a base station controls the transmitting power and frequency resource of a ground user in order to meet the interference protection requirement of a satellite terminal. The optimization problem aims at maximizing the throughput of the ground network, the interference protection of the satellite terminal and the service quality of the ground user are used as constraints, the optimization problem is decomposed into power allocation and frequency resource scheduling sub-problems, in the power allocation sub-problems, the channel uncertainty is considered by adopting a power allocation algorithm based on the interference probability constraint, and the sub-optimal solution of the power allocation is obtained by an iterative optimization method. In the frequency resource scheduling sub-problem, the non-convexity of the problem is processed by improving a heuristic algorithm, and the time complexity of the algorithm is reduced.
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Fig. 1 is a schematic diagram of a satellite-ground integrated network spectrum sharing model in an embodiment of the present invention;
Fig. 2 is a schematic diagram of a resource management architecture of a star-to-ground integrated network according to an embodiment of the present invention;
FIG. 3 is a graph showing the relationship between the maximum transmission power of a ground user and the channel gain ratio at different distances between a base station and a satellite terminal in an embodiment of the present invention;
FIG. 4 is a graph showing the relationship between the received interference power and the channel gain ratio of a satellite terminal at different distances between a base station and the satellite terminal according to an embodiment of the present invention;
FIG. 5 is a graph showing the relationship between the maximum transmitting power of the ground user and the channel gain ratio under different power allocation algorithms according to the embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the interference power received by a satellite terminal and the channel gain ratio under different power distribution algorithms according to an embodiment of the present invention;
FIG. 7 is a graph of terrestrial network throughput versus number of users in a cell in an embodiment of the invention;
In the figure, under the number of each ground user, the corresponding four bar graphs are an interior point method, a power distribution algorithm based on interference probability constraint (namely the method of the invention), a power distribution algorithm based on compact restriction constraint and a frequency exclusive access algorithm in turn from left to right;
FIG. 8 is a graph of ground network throughput versus base station and satellite terminal distance in an embodiment of the invention;
In the figure, under each distance, the corresponding four bar graphs are an interior point method, a power distribution algorithm based on interference probability constraint (namely the method of the invention), a power distribution algorithm based on compact restriction constraint and a frequency exclusive access algorithm in sequence from left to right.
Detailed Description
The application will be described in further detail below with reference to the drawings by means of specific embodiments. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the application. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without making any inventive effort are within the scope of the present application.
The first embodiment of the present invention is a satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation, the method specifically comprising the following steps:
Step one, constructing a satellite-ground integrated network spectrum sharing model, wherein the model comprises a satellite, a satellite terminal, a base station, a ground user and an interference coordination unit, and the uplink of the ground user shares frequency with the downlink of the satellite;
Step two, constructing a satellite-ground integrated network resource optimization allocation problem based on the satellite-ground integrated network spectrum sharing model constructed in the step one;
step three, decoupling the problem constructed in the step two into a power allocation sub-problem and a frequency resource scheduling sub-problem;
On the interference coordination unit, calculating a power distribution result according to the power distribution sub-problem and returning the power distribution result to the base station;
And the base station calculates the number of the resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem to obtain the resource block allocation result.
The method comprises the step of maximizing the throughput of a ground network on the premise of ensuring the service quality of ground users by considering the uncertainty of the interference protection constraint of a satellite terminal and the channel state information of a ground interference link. Unlike the existing method which only considers the resource allocation with perfect channel state information, the probability model of the aggregation interference is introduced for analysis so as to ensure the stable operation of the satellite terminal.
The second embodiment is as follows: the difference between the present embodiment and the specific embodiment is that n bs base stations with shared frequencies are disposed around the satellite terminal, and the number of ground users in the jth base station isJ=1, 2, …, n bs, and the base station is configured to allocate a time-frequency resource block to a ground user.
Other steps and parameters are the same as in the first embodiment.
And a third specific embodiment: this embodiment differs from the first or second embodiments in that the satellite downlink uses orthogonal frequency division multiple access and the terrestrial user uplink uses single carrier frequency division multiple access.
Other steps and parameters are the same as in the first or second embodiment.
The specific embodiment IV is as follows: the difference between the present embodiment and one of the first to third embodiments is that the specific process of the second step is:
Step two, the transmitting power of the ground user is as follows:
Wherein P i m represents the maximum transmission power allowed by the ith ground user in the shared frequency band, P i max represents the maximum transmission power of the ith ground user, P 0 represents the nominal receiving power of the base station, M i represents the number of resource blocks allocated to the ith ground user, alpha represents a path loss compensation factor, 0 < alpha is less than or equal to 1, Representing the channel gain of the ith terrestrial user to base station (where base station is the base station associated with user i)/> Representing the antenna gain of the ith terrestrial user to the base station,/>Representing the path loss of the ith terrestrial user to the base station, delta i representing the modulation compensation factor of the ith terrestrial user;
Step two, the aggregate interference power constraint of the uplink of the ground user on the satellite terminal is as follows:
Where n r denotes a set of resource blocks overlapping with the guard bandwidth, n ue denotes the total number of terrestrial users, P i denotes the transmission power of the ith terrestrial user, Representing the channel gain on resource block k from the ith terrestrial user to the satellite terminal, Representing the gain of the receiving antenna of the ith terrestrial user to the satellite terminal,/>Indicating the path loss from the ith ground user to the satellite terminal, Z ik indicating the channel fading variable of the ith ground user on the resource block k, and Z ik obeying a lognormal distribution with a mean value of m z and a standard deviation of sigma z (the mean value of m z is equal to 0dB and the standard deviation of sigma z is equal to 10 dB), delta ik indicating the resource block indicating variable, delta ik indicating that the resource block k is allocated to the ith ground user when delta ik is equal to 0, indicating that the resource block k is not allocated to the ith ground user, epsilon s indicating the interference protection threshold of the satellite terminal;
Step two, the constraint of step two is expressed as a probability constraint that the aggregate interference needs to meet by using a statistical model because the random variable Z ik cannot be directly measured:
where ρ s represents the probability threshold for aggregate interference, Representation calculationProbability of (2);
step two, the resource optimization allocation problem is constructed by taking the maximum throughput of the uplink of the ground user as a target, wherein the resource optimization allocation problem is constructed by the following steps:
s.t.δijk∈{0,1}；
where U ij represents the system utility function (similar to the functional form of equation (6)), n bs represents the total number of base stations, and the value of U ij depends on the power allocation matrix And resource block allocation matrix/>P ijk is the power level of the kth resource block used by the jth base station to the jth ground user, delta ijk is equal to 1, which indicates that the resource block k is allocated to the ith ground user of the jth base station, delta ijk is equal to 0, which indicates that the resource block k is not allocated to the ith ground user of the jth base station, n ue indicates the total number of ground users of the ground network, i.e. the/> Is the total number of the ground users in the jth base station, M ij represents the number of resource blocks allocated to the ith ground user by the jth base station,/>Representing the channel gain of the ith terrestrial user of the jth base station to the satellite terminal over resource block k, and Z ijk represents the channel fading variation of the ith terrestrial user of the jth base station over resource block k.
Constraint 1-3 in equation (4) indicates that each user is allocated a resource block in a continuous manner, constraint 2 indicates that a resource block can be allocated to only one user, and constraint 3 indicates that resource blocks allocated to a particular user must be adjacent. Constraint 4 represents limiting the user transmit power to a viable range. The optimization problem couples the frequency scheduling problems of a plurality of base stations through interference protection constraint, so that the computational complexity is greatly increased.
Other steps and parameters are the same as in one to three embodiments.
Fifth embodiment: this embodiment differs from one to four embodiments in that the power distribution sub-problem is:
Wherein U (P) represents an objective function of the power allocation sub-problem, Representing the channel gain of the ith terrestrial user to the satellite terminal, Z i represents the channel fading variable of the ith terrestrial user;
The objective function U (P) is:
Where N represents the noise power at the base station receiver.
Other steps and parameters are the same as in one to four embodiments.
To clarify the relationship between power allocation and path loss, the transmit power of a user is correlated with path loss, and assuming that uncertainty in channel state is not considered, the power allocation can be expressed as a deterministic problem:
and solving by using Karush-Kuhn-Tucker conditions to obtain the transmission power of the user i to satisfy the following conditions:
wherein μ represents a multiplier, and the upper corner "+" represents: if it is Positive value, then/>If/>Negative value, then/>
The first term of the minimization problem of equation (8) is regarded as the solution of the water-filling algorithm, the second term limits the user's transmit power, and defines the channel gain ratio of user i asThe base station is deployed at a position far away from the satellite terminal, and the path loss satisfies/>Indicating that user i has a large channel gain ratio. According to equation (8), users with large channel gain ratios are assigned power levels that tend to be equal.
According to the relation between the transmitting power and the channel gain ratio, a power allocation algorithm based on interference probability constraint in the sixth embodiment is provided. Assuming that the interference power caused by the user with higher transmission power tends to be a fixed value, the interference power is approximated to be equal using a step function.
Specific embodiment six: the difference between the present embodiment and one to fifth embodiments is that, in the interference coordination unit, a power allocation result is calculated according to a power allocation sub-problem and returned to the base station; the method comprises the following steps:
Step 1, initializing the number n=1 of ground users allocated with non-zero transmission power, initializing the throughput u 1 =0 of the ground users, and initializing the saved maximum throughput u 2 =0;
step 2, the channel gain ratio of the ith ground user is recorded as According to/>The method comprises the steps of performing descending order arrangement on all ground users;
If u 2≥u1 and n is less than n ue, calculating interference power level xi (n) of the ground users arranged in the first n bits, and continuing to execute the step 3;
Otherwise, taking the transmitting power of each ground user obtained in the last iteration as a final power distribution result;
Step 3, calculating the transmitting power of each ground user according to the interference power level xi (n):
P1,i＝0,i＝n+1,n+2,…,nue
And 4, updating the throughput of the ground users according to the transmitting power of each ground user, wherein the updated throughput of the ground users is as follows:
Step 5, judging whether the throughput of the updated ground user is larger than u 2;
If the updated ground user throughput is greater than u 2, let u 2 equal to the updated ground user throughput, let n=n+1, and return to execute step 2 by using updated u 1 and u 2;
If the updated terrestrial user throughput is equal to or less than u 2, n=n+1 is returned to step 2 by using u 1 after updating (at this time, u 2 is not updated, and step 2 is performed by using u 2 after the last updating).
Other steps and parameters are the same as in one of the first to fifth embodiments.
Seventh embodiment: this embodiment differs from one to six of the embodiments in that the channel gain ratioThe method comprises the following steps:
Other steps and parameters are the same as in one of the first to sixth embodiments.
Eighth embodiment: this embodiment differs from one of the first to seventh embodiments in that the calculating the interference power level ζ (n) of the top n-bit terrestrial users is specifically:
converting the constraint in equation (5) to:
From the Fenton-Wilkinson (FW) approximation, we obtain E is the base of the natural logarithm, and the variable x i obeys the mean value as/>Variance is/>Normal distribution of (i.e./>) Variable y obeys mean m y, variance/>Normal distribution of (a), i.emyβ2lnw1-lnw2/2，/> R ij denotes the correlation coefficient, then the mean m y and the varianceThe method comprises the following steps of: /(I)
The probability constraint of equation (9) is translated into:
Wherein Q is a right tail function of a standard normal distribution; the base of log here is 10;
The expression for obtaining the interference power level ζ (n) is:
Wherein, the upper subscript "-1" represents the reciprocal.
Other steps and parameters are the same as those of one of the first to seventh embodiments.
Detailed description nine: the difference between this embodiment and one to eight embodiments is that the frequency resource scheduling sub-problem is:
the following frequency resource scheduling sub-problems are respectively established for each base station, and the j-th base station is taken as an example:
Wherein U i(Pik,δik) is an objective function of the frequency resource scheduling sub-problem (similar to the functional form of equation (6), Is the number of users in base station j, P ik is the power level of the kth resource block used by the ith terrestrial user, and P i lim is the power allocation result returned by the base station to the ith terrestrial user.
Other steps and parameters are the same as in one to eight of the embodiments.
Detailed description ten: the difference between this embodiment and one of the first to ninth embodiments is that the base station calculates the number of resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem, specifically:
Step (1), definition For a measure of the amount of information transmitted by user i on resource block k,B is the bandwidth of the resource block, i=1, 2, …, n ue,k＝1,2,…,nr;
Step (2), connecting As the kth column of the metric matrix Λ, k=1, 2, …, n r, the metric matrix Λ is obtained;
Initializing c=1;
step (3), judging whether the unallocated resource block set R is an empty set (the set R is a set containing all resource blocks during initialization);
if the unallocated resource block set R is not an empty set, executing step (4);
if the unallocated resource block set R is an empty set, completing resource block allocation;
Step (4) of selecting a resource block k having a c-th largest metric value from the unallocated resource block set R according to the metric matrix Λ, and expressing the c-th largest metric value as
Step (5), let Γ be the set of resource blocks already allocated to user i;
If k is adjacent to a resource block in Γ or Distributing the resource block k with the c-th largest metric value to the user i, removing the metric value related to the resource block k from the metric matrix to obtain an updated metric matrix, deleting the resource block k from the unassigned resource block set R to obtain an updated unassigned resource block set; let c=1, and return to step (3);
Otherwise, let c=c+1, return to step (3).
Other steps and parameters are the same as in one of the first to ninth embodiments.
Examples
The embodiment of the invention provides a satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation, which specifically comprises the following steps:
Step 1: based on the satellite, the satellite terminal, the base station, the ground user and the interference coordination unit, the uplink of the ground user and the downlink of the satellite share the frequency, and a satellite-ground integrated network spectrum sharing model is constructed;
In step 1, the satellite downlink employs orthogonal frequency division multiple access, and the terrestrial uplink employs single carrier frequency division multiple access. And the base stations sharing the frequency are deployed around the satellite terminal, so that the interference of the ground user to the satellite terminal is reduced, as shown in fig. 1. Assuming that the number and location of base stations and terrestrial users are known, the base stations allocate time-frequency resource blocks to the relevant users at the time of scheduling.
Step 2: on the basis of the satellite-ground integrated network spectrum sharing model constructed in the step 1, the base station adjusts the transmitting power level of the ground user according to the channel condition of the ground user, ensures that the aggregate interference power of the uplink of the ground user to the satellite terminal meets the interference protection constraint on probability, and constructs the satellite-ground integrated network resource optimization allocation problem;
Specifically, the transmission power of the ground user and the potential interference power level to the satellite terminal depend on the distance from the user to the base station, and the transmission power of the ground user is:
Where P i max denotes the maximum transmit power of the user, P 0 denotes the nominal receive power of the base station, M i denotes the number of resource blocks allocated to user i, alpha denotes the path loss compensation factor (0 < alpha.ltoreq.1), Representing the channel gain of a user to a base station,/>Representing the user antenna gain,/>Representing the path loss, delta i represents the modulation compensation factor.
In the embodiment of the invention, the interference link is modeled by adopting a double-ray ground reflection model, and the channel uncertainty is simulated by introducing the space uncorrelated lognormal fading. Thus, it is necessary to ensure that the aggregate interference power of the user uplink to the satellite terminals is below the interference protection threshold:
Where n r denotes the set of resource blocks overlapping with the guard bandwidth, n ue denotes the number of terrestrial users, P i denotes the transmit power of user i, Representing the channel gain of a user to a satellite terminal over resource block k,/>Representing satellite terminal receiving antenna gain,/>Representing path loss, Z ik represents a channel fading variable subject to a lognormal distribution, the mean value of the lognormal distribution is m z, the standard deviation is sigma z,δik, delta ik is equal to 1 and 0, respectively, represents allocation and non-allocation of resource blocks k to users i, and epsilon s represents an interference protection threshold of a satellite terminal. Based on the location information of the terrestrial users and the satellite terminals, the channel gain can be estimated using the path loss model, but the random variable Z ik cannot be measured directly.
Thus, to approximate aggregate interference and ensure that the interference constraints are met with probability, the statistical model used is:
Where ρ s represents the probability threshold for aggregate interference, i.e. the aggregate interference is allowed to exceed the protection threshold for a fraction of the time ρ s. In the embodiment of the invention, the satellite-ground integrated network considers optimizing the resource allocation of the ground users to improve the frequency spectrum utilization rate and simultaneously ensures the communication performance of the satellite terminal. The resource management architecture of a satellite-to-ground integrated network is shown in fig. 2, where the interference coordination unit has an interface to communicate with all base stations in the vicinity of the satellite terminal. The user returns channel state information of the communication and interference links to the interference coordination unit through the base station. In addition, the interference coordination unit is provided with an interface for communicating with a satellite, and the satellite terminal feeds back the channel state information of a satellite downlink to the interference coordination unit to update an interference protection threshold. Finally, the base station serves the users in its coverage area through power control and resource block scheduling to maximize the throughput of the user uplink, and constructs the resource allocation problem as:
s.t.δijk∈{0,1}； (4a)
Wherein the system utility function depends on the power distribution matrix And resource block allocation matrixThe number of users of the ground network is related to the number of users served by each base station, i.e. the requirement is satisfiedWherein/>Is the number of users in base station j and n bs is the number of base stations. Constraints (4 a) - (4 c) indicate that each user is allocated resource blocks in a sequential manner, constraint (4 b) indicates that resource blocks can only be allocated to one user, and constraint (4 c) indicates that resource blocks allocated to a particular user must be contiguous. Constraint (4 d) represents limiting the user transmit power to a viable range, where M ij is the number of resource blocks allocated to user i by base station j. The optimization problem couples the frequency scheduling problems of a plurality of base stations through interference protection constraint, so that the computational complexity is greatly increased.
Step 3: the resource allocation problem constructed based on step 2 is non-convex and highly complex, considering decoupling the optimization problem into power allocation and frequency resource scheduling sub-problems to find sub-optimal solutions. The power allocation algorithm is hosted in the interference coordination unit for centralized calculation, and the power allocation result is returned to the corresponding base station. The base station modifies the measurement value of the available resource blocks of each user according to the returned maximum transmitting power, and calculates the number of the resource blocks allocated to each user by using a frequency resource scheduling algorithm;
In embodiments of the present invention, the power control sub-problem only considers users sharing the spectrum and determines the power allocation to maximize the throughput of the users. Therefore, the corresponding superscripts and subscripts in the optimization problem can be removed without considering the association of the user with the base station or the resource block, and the power allocation problem is expressed as:
Where U (P) denotes that the objective function depends on the power allocation, and P i denotes the total transmit power of user i in the protected band. If the optimization problem is a convex instance, a concave objective function is required and the constraint describes a convex set. Thus, a concave sum rate function is used as the objective function:
Wherein, Representing the channel gain from user i to the associated base station, and N represents the noise power at the base station receiver.
Step 4: the power allocation sub-problem according to step 3 considers only the surface users sharing the spectrum and determines the power allocation to maximize the throughput of the surface network. Based on the relation between the user transmitting power and the channel gain ratio, a power distribution algorithm based on interference probability constraint is provided, and the maximum allowable transmitting power of the user is obtained through iterative solution;
specifically, to determine the relationship between the power allocation and the path loss, the transmit power of the user is associated with the path loss, and assuming that the uncertainty of the channel state is not considered, the power allocation may be expressed as a deterministic problem:
and solving by using Karush-Kuhn-Tucker conditions to obtain the transmission power of the user i to satisfy the following conditions:
Where μ represents a multiplier. The first term to minimize the problem is considered as a solution to the water-filling algorithm, the second term limits the user's transmit power, defining the channel gain ratio for user i as
In the embodiment of the invention, the base station is arranged at a position far away from the satellite terminal, and the path loss satisfies the following conditionsIndicating that user i has a large channel gain ratio. From equation (8), users with larger channel gain ratios are assigned power levels that tend to be equal. Since equation (5) does not resolve, an interior point method is used for solving. In the simulation, the ground network adopts 3 base stations, the distances between the ground network and the satellite terminal are respectively 8km, 12km and 16km, 30 users which are uniformly distributed exist in the coverage area of each base station, and the simulation parameter values are shown in table 1.
TABLE 1
As shown in fig. 3, users with low channel gain ratio are allocated lower transmit power and have lower interference levels to the satellite terminals. By adjusting the transmit power, the throughput of users with high channel gain ratio can be improved. The relationship between the channel gain ratio and the interference level shown in fig. 4 is consistent with the conclusion of equation (8), and the user with high channel gain ratio has an average effect on the interference of the satellite terminal, so that the probability of the interference deviating from the average value can be reduced. The scheduling period of the resource block in the ground network is 1ms, and the time complexity of the interior point method isEpsilon is the target precision. Therefore, the interior point method has high time complexity, and is difficult to be applied to the power distribution problem.
And according to the relation between the transmitting power and the channel gain ratio, a power distribution algorithm based on interference probability constraint is provided. Assuming that the interference power caused by the user with higher transmission power tends to be a fixed value, the interference power is approximated to be equal using a step function. The algorithm flow is as follows:
Firstly, according to the channel gain ratio of users, arranging according to descending order, adopting approximate method of interference probability constraint and step function to determine the number of users allocated with non-zero transmitting power and interference power level Finally, the transmit power of the user is determined based on the interference power level. Thus, the interference protection constraint of equation (5) is converted into:
/>
From the Fenton-Wilkinson (FW) approximation, we obtain Variables x i and y obey normal distribution,/>By FW approximation, the mean and variance of the variable y are m y＝2lnu1-lnu2/2 and/>, respectivelyWherein the method comprises the steps ofR ij represents the correlation coefficient, and the mean and variance of y are obtained as/>, respectivelyAnd
Thus, the probability constraint of aggregate interference is translated into:
The upper bound of probability constraint is adopted, and a closed expression of interference power level xi (n) is obtained by using a right tail function of standard normal distribution:
Algorithm 1 in table 2 is a pseudo code of a power allocation algorithm based on an interference probability constraint, u 1 represents a user-implemented throughput, and P 1 represents a power allocation array of n ue users. The goal of algorithm 1 is to allocate transmit power to users whose interference power levels tend to be equal, looking for the number of users with the greatest throughput in each round of operation. O (n ue) operations are needed for computing u 1 and ζ (n), O (n ue) operations are needed for loop iteration, and the time complexity of the obtained algorithm is
TABLE 2
Step 5: and (3) according to the frequency resource scheduling sub-problem obtained in the step (3), limiting the resource blocks to be allocated to a single user by adopting single carrier frequency division multiple access, wherein all the resource blocks allocated to the same user are adjacent. Obtaining a resource allocation scheme by using a recursive maximum expansion algorithm according to the user transmitting power obtained in the step 4 as a constraint condition of the satellite terminal;
In the embodiment of the invention, the base station modifies the measurement of the corresponding resource block according to the maximum transmitting power of the user, then calculates the quantity of the resource blocks allocated to the user by using a frequency resource scheduling algorithm, and updates the resource block allocation in each time slot to adapt to the dynamic communication requirement. However, the power allocation algorithm need not run every slot, but should be sufficient to account for the time dependence of the channel state information. The returned power is taken as the maximum transmitting power P i lim of the user to meet the protection threshold of the satellite terminal, namely Thus, decoupling equation (4) into the frequency resource scheduling problem of a single base station: /(I)
The problem of single base station frequency domain resource scheduling with continuous resource block constraint is a mixed integer nonlinear programming problem, and is usually solved by adopting a heuristic approximation algorithm. The frequency resource scheduling problem of equation (12) is solved using a recursive maximum expansion algorithm with the pseudocode of the recursive maximum expansion algorithm being algorithm 2 in table 3 by appropriately modifying the constraint of the user transmit power. Definition of the definitionFor user i's metric over resource block c,/>And modifying the measurement of the resource blocks in the shared frequency band according to the power distribution result, if the transmission power distributed to the user is zero, setting the measurement of the resource blocks in the shared frequency band to be zero, ensuring that the algorithm does not distribute the resource blocks in the shared frequency band to the user, but the algorithm can distribute the resource blocks which are not in the shared frequency band to any user.
TABLE 3 Table 3
/>
Step 6: and (5) adjusting a resource block allocation strategy according to the resource allocation scheme obtained in the step (5), and maximizing the frequency spectrum utilization rate while meeting the interference protection requirement of the satellite terminal.
In step 6, simulation analysis is performed on the satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation, and simulation parameter values are shown in table 1. The performance of the power allocation algorithm in terms of user transmit power and interference level is analyzed in fig. 5 and 6. When the channel gain ratio is high, the transmission power of the power allocation algorithm based on the interference probability constraint is close to the interior point method. When the channel gain ratio is low, the transmission power distributed by the interior point method is non-zero, the transmission power of a power distribution algorithm based on interference probability constraint and compact restriction constraint is zero, and users distributed with non-zero transmission power have larger power distribution space. The power allocation algorithm based on the compact constraint reduces the feasible area of power by the compact constraint, and the transmitting power and the interference level of the user are low. Therefore, the performance of the power allocation algorithm based on the interference probability constraint is closer to that of the interior point method, and the time complexity is lower.
In fig. 7, the throughput achieved by the joint power and frequency allocation algorithm is analyzed as a function of the number of users, the base station being 10km from the satellite terminal. Compared with the frequency exclusive access algorithm, the method performs power distribution through an interior point method, performs frequency scheduling through a recursive maximum expansion algorithm, and does not share frequency spectrum between satellites and a ground network. When the number of users in a cell is small, all resource blocks cannot be fully utilized, and the throughput achieved by the network is low. The interior point method and the power allocation algorithm based on the interference probability constraint achieve the same throughput. In fig. 8, the effect of the distance of the base station and the satellite terminal on throughput is analyzed, and the terrestrial cell has 16 users. The farther the base station is from the satellite terminal, the lower the interference level of the user and the higher the throughput achieved. The number of users and resource blocks in the network is fixed, and the throughput realized by the frequency exclusive access algorithm does not change with distance. Therefore, the star-ground integrated network can realize low time complexity and full utilization of spectrum resources by using an algorithm based on joint power and frequency allocation.
Those of ordinary skill in the art will appreciate that all or a portion of the steps in the various methods of the above embodiments may be implemented by hardware associated with program instructions, where the program may be stored on a computer readable storage medium, where the storage medium may include: ROM, RAM, magnetic or optical disks, etc.
The above examples of the present invention are only for describing the calculation model and calculation flow of the present invention in detail, and are not limiting of the embodiments of the present invention. Other variations and modifications of the above description will be apparent to those of ordinary skill in the art, and it is not intended to be exhaustive of all embodiments, all of which are within the scope of the invention.
Claims (10)
1. A satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation is characterized by comprising the following steps:
Step one, constructing a satellite-ground integrated network spectrum sharing model, wherein the model comprises a satellite, a satellite terminal, a base station, a ground user and an interference coordination unit, and the uplink of the ground user shares frequency with the downlink of the satellite;
Step two, constructing a satellite-ground integrated network resource optimization allocation problem based on the satellite-ground integrated network spectrum sharing model constructed in the step one;
step three, decoupling the problem constructed in the step two into a power allocation sub-problem and a frequency resource scheduling sub-problem;
On the interference coordination unit, calculating a power distribution result according to the power distribution sub-problem and returning the power distribution result to the base station;
And the base station calculates the number of the resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem to obtain the resource block allocation result.
2. The satellite-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 1, wherein n bs base stations sharing frequencies are deployed around the satellite terminal, and the number of ground users in the jth base station isThe base station is used for distributing time-frequency resource blocks to the ground users.
3. The method for spectrum sharing of a satellite-to-ground integrated network based on joint power and frequency allocation according to claim 2, wherein the satellite downlink employs orthogonal frequency division multiple access and the terrestrial user uplink employs single carrier frequency division multiple access.
4. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 3, wherein the specific process of the step two is as follows:
Step two, the transmitting power of the ground user is as follows:
Wherein, Representing the maximum transmit power allowed by the ith terrestrial user in the shared frequency band,/>Represents the maximum transmit power of the ith terrestrial user, P 0 represents the nominal receive power of the base station, M i represents the number of resource blocks allocated to the ith terrestrial user, α represents the pathloss compensation factor,/>Representing the channel gain of the ith terrestrial user to the base station,/> Representing the antenna gain of the ith terrestrial user to the base station,/>Representing the path loss of the ith terrestrial user to the base station, delta i representing the modulation compensation factor of the ith terrestrial user;
Step two, the aggregate interference power constraint of the uplink of the ground user on the satellite terminal is as follows:
Where n r denotes a set of resource blocks overlapping with the guard bandwidth, n ue denotes the total number of terrestrial users, P i denotes the transmission power of the ith terrestrial user, Representing the channel gain on resource block k from the ith terrestrial user to the satellite terminal, Representing the gain of the receiving antenna of the ith terrestrial user to the satellite terminal,/>Representing the path loss from the ith ground user to the satellite terminal, Z ik represents the channel fading variable of the ith ground user on a resource block k, Z ik obeys the logarithmic normal distribution with the mean value of m z and the standard deviation of sigma z, delta ik represents the resource block indicating variable, delta ik is equal to 1, when delta ik is equal to 0, the resource block k is allocated to the ith ground user, and epsilon s represents the interference protection threshold of the satellite terminal;
And step two, representing the constraint of the step two as a probability constraint which needs to be met by the aggregation interference:
where ρ s represents the probability threshold for aggregate interference, Representation of/>Probability of (2);
step two, the resource optimization allocation problem is constructed by taking the maximum throughput of the uplink of the ground user as a target, wherein the resource optimization allocation problem is constructed by the following steps:
s.t.δijk∈{0,1}；
where U ij represents the system utility function, n bs represents the total number of base stations, and the value of U ij depends on the power allocation matrix And resource block allocation matrix/>P ijk is the power level of the kth resource block used by the jth base station to the jth ground user, delta ijk is equal to 1, which indicates that the resource block k is allocated to the ith ground user of the jth base station, delta ijk is equal to 0, which indicates that the resource block k is not allocated to the ith ground user of the jth base station, n ue indicates the total number of ground users of the ground network, i.e. the/> Is the total number of the ground users in the jth base station, M ij represents the number of resource blocks allocated to the ith ground user by the jth base station,/>Representing the channel gain of the ith terrestrial user of the jth base station to the satellite terminal over resource block k, and Z ijk represents the channel fading variation of the ith terrestrial user of the jth base station over resource block k.
5. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation of claim 4, wherein the power allocation sub-problem is:
Wherein U (P) represents an objective function of the power allocation sub-problem, Representing the channel gain of the ith terrestrial user to the satellite terminal, Z i represents the channel fading variable of the ith terrestrial user;
The objective function U (P) is:
Where N represents the noise power at the base station receiver.
6. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 5, wherein the interference coordination unit calculates a power allocation result according to a power allocation sub-problem and returns the power allocation result to the base station; the method comprises the following steps:
Step 1, initializing the number n=1 of ground users allocated with non-zero transmission power, initializing the throughput u 1 =0 of the ground users, and initializing u 2 =0;
step 2, the channel gain ratio of the ith ground user is recorded as According to/>The method comprises the steps of performing descending order arrangement on all ground users;
If u 2≥u1 and n is less than n ue, calculating interference power level xi (n) of the ground users arranged in the first n bits, and continuing to execute the step 3;
Otherwise, taking the transmitting power of each ground user obtained in the last iteration as a final power distribution result;
Step 3, calculating the transmitting power of each ground user according to the interference power level xi (n):
P1,i＝0,i＝n+1,n+2,…,nue
And 4, updating the throughput of the ground users according to the transmitting power of each ground user, wherein the updated throughput of the ground users is as follows:
Step 5, judging whether the throughput of the updated ground user is larger than u 2;
If the updated ground user throughput is greater than u 2, let u 2 equal to the updated ground user throughput, let n=n+1, and return to execute step 2 by using updated u 1 and u 2;
if the updated ground user throughput is less than or equal to u 2, let n=n+1, and return to execute step 2 by using the updated u 1.
7. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation of claim 6, wherein the channel gain ratio isThe method comprises the following steps:
8. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 7, wherein the calculating the interference power level ζ (n) of the top n-bit ground users is specifically:
converting the constraint in equation (5) to:
e is the base of the natural logarithm, and the variable x i obeys the mean value as/> Variance is/>Normal distribution of (i.e./>)
The probability constraint of equation (9) is translated into:
Wherein Q is a right tail function of a standard normal distribution;
The expression for obtaining the interference power level ζ (n) is:
Wherein, the upper subscript "-1" represents the reciprocal.
9. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 8, wherein the frequency resource scheduling sub-problem is:
wherein U i(Pik,δik) is an objective function of the frequency resource scheduling sub-problem, Is the number of users in base station j, P ik is the power level of the kth resource block used by the ith terrestrial user,/>The power distribution result returned by the base station to the ith ground user.
10. The satellite-to-ground integrated network spectrum sharing method based on joint power and frequency allocation according to claim 9, wherein the base station calculates the number of resource blocks allocated to each ground user according to the returned power allocation result and the frequency resource scheduling sub-problem, specifically:
Step (1), definition For a measure of the amount of information transmitted by user i on resource block k,B is the bandwidth of the resource block, i=1, 2, …, n ue,k＝1,2,…,nr;
Step (2), connecting As the kth column of the metric matrix Λ, k=1, 2, …, n r, the metric matrix Λ is obtained;
Initializing c=1;
Step (3), judging whether the unallocated resource block set R is an empty set;
if the unallocated resource block set R is not an empty set, executing step (4);
if the unallocated resource block set R is an empty set, completing resource block allocation;
Step (4) of selecting a resource block k having a c-th largest metric value from the unallocated resource block set R according to the metric matrix Λ, and expressing the c-th largest metric value as
Step (5), let Γ be the set of resource blocks already allocated to user i;
If k is adjacent to a resource block in Γ or Distributing the resource block k with the c-th largest metric value to the user i, removing the metric value related to the resource block k from the metric matrix to obtain an updated metric matrix, deleting the resource block k from the unassigned resource block set R to obtain an updated unassigned resource block set; let c=1, and return to step (3);
Otherwise, let c=c+1, return to step (3).
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