Disclosure of Invention
The invention aims to provide a design method of key parameters of a downlink in an energy-efficient large-scale antenna system, aiming at the problems that a user distribution model is not practical enough and the energy efficiency of the system is low in the current situation.
The design method of the key parameters of the downlink in the high-energy-efficiency large-scale antenna system comprises the following steps: counting distance information between users and a base station in a coverage area of the base station to obtain an actual user distribution model; calculating key parameters of the corresponding user distribution model; deriving an energy efficiency expression EE ═ f (M, K, P) for a large-scale antenna system downlinkT) (ii) a According to the resource allocation condition of the system, analyzing to obtain several different conditions and further obtaining the optimal parameters under each condition
The actual user distribution model comprises:
(1) if the users are distributed in the center of the cell in a centralized way, a user distribution model in the center is adopted, and the probability density function of the user distribution adopts the following formula
Wherein R represents a cell radius, R0Representing the minimum distance of the user from the base station, a and b are key parameters related to a user distribution model;
(2) if the users are distributed in the edge of the cell in a concentrated way, the user distribution model in the edge concentration is adopted, and the probability density function of the user distribution adopts the following formula
Wherein R represents a cell radius, R0Representing the minimum distance of a user from the base station, a and b are key parameters related to the user distribution model.
The calculation of the key parameters a and b comprises the following steps:
(1) if the model is a user distribution model with centralized center, a controls the degree of the users approaching the center of the cell, the larger a indicates that more users are distributed in the central area of the cell, and vice versa, when a is 0, the users are subjected to uniform distribution, b is a normalization constant of a probability density function, and the normalization constant can be obtained through calculation
The user distribution model of the central set is a large-scale shopping mall and a street;
(2) if the model is a user distribution model with concentrated edges, a controls the degree of the users approaching the edge of the cell, the larger a indicates that more users are distributed in the edge area of the cell, and vice versa, when a is 0, the users are subjected to uniform distribution, b is a normalization constant of a probability density function, and the normalization constant can be obtained through calculation
The resource allocation condition of the system comprises given (M, K, P)T) Any two parameters, any one parameter and zero parameters, thereby creating three different optimization methods: the method comprises a single-variable optimization method, a double-variable joint optimization method and a three-variable joint optimization method.
The univariate optimization method comprises the following steps: given (M, K, P)T) Any two of these three parameters, the other one, for the individual optimization of the number of base station antennas M and the total base station transmitted power PTIn both cases, by closed form solution of MoptAnddirectly, and for the case of individually optimizing the number of users K, it is necessary to obtain the optimal value K by maximizing the energy efficiency of the system in a limited spaceopt。
The bivariable joint optimization method comprises the following steps: given (M, K, P)T) Any one of these three parameters, two other parameters are optimized, including:
(1) given the number of users K, jointly optimizing the number M of base station antennas and the base station transmitting power PT;
S100, when the algorithm starts to operate, setting initial base station transmitting power PT>0;
S101, updating the number M of base station antennas to be Mopt;
S102, updating the transmitting power PTIs composed of
S103, circularly executing the steps S101 and S102 until the algorithm is converged, and obtaining the optimal number M of the base station antennasoptAnd base station transmit power
Wherein the judgment condition of algorithm convergence is that the integer M is not changed any more;
(2) given the number M of base station antennas, jointly optimizing the number K of users and the transmission power P of the base stationT;
S110, when the algorithm starts to run, setting initial base station transmitting power PT>0;
S111, updating the transmitting power PTIs composed of
S112, optimizing the number K of users to be Kopt;
S113, circularly executing the steps S111 and S112 until the algorithm converges, and obtaining the optimal user number KoptAnd base station transmit power
Wherein the judgment condition of algorithm convergence is that the integer K is not changed any more;
(3) given the number of base station antennas PTJointly optimizing the number K of users and the transmitting power M of the base station;
s120, setting the initial user number K to be 1 when the algorithm starts to run;
s121, updating the number M of the base station antennas to beMopt;
S122, for MoptRounding off, and optimizing the number of users K to Kopt;
S123, circularly executing the steps S121 and S122 until the algorithm converges, and obtaining the optimal user number KoptAnd base station transmission power Mopt;
The judgment condition of algorithm convergence is that the integers K and M are not changed any more.
The three-variable joint optimization method comprises the following steps: to (M, K, P)T) Performing joint optimization on the three parameters;
s20, when the algorithm starts to run, setting the initial base station transmitting power PTThe number K of users is more than 0, the number M of base station antennas is more than 3;
s21, updating the number K of users to Kopt;
S22, updating the number M of base station antennas to Mopt;
S23, updating the transmitting power PTIs composed of
S24, circularly executing the steps S21 to S23 until the algorithm converges and obtaining the optimal three important system parameters
The judgment condition of algorithm convergence is that the integers K and M are not changed any more.
The invention has the beneficial effects that:
(1) the invention considers that the user distribution is limited by physical environment and is influenced by crowd aggregation, establishes a more practical user distribution model, comprises two modes of central concentration and edge concentration, and can adjust the relevant parameters of the model to adapt to different user distribution scenes. Avoiding the impracticality of the conventional uniformly distributed model.
(2) The invention optimizes (M, K, P) according to different system requirementsT) The three important system parameters enable the system to have the highest energy efficiency, and compared with the traditional power control or beam forming method, the method has the advantage of low algorithm complexity. By means of the optimization design, partial resources and expenses are saved, the system energy efficiency is improved to the maximum extent, and the green communication concept is met.
Detailed Description
The method for designing the key parameters of the downlink in the high-energy-efficiency large-scale antenna system comprises the following steps:
counting distance information between users and a base station in a coverage area of the base station to obtain an actual user distribution model; calculating key parameters of the corresponding user distribution model; deriving an energy efficiency expression EE-f (M, K, P) for a large-scale antenna system downlinkT) (ii) a According to the resource allocation condition of the system, analyzing to obtain several different conditions and further obtaining the optimal parameters under each condition
The actual user distribution model comprises:
(1) if the users are distributed in the center of the cell in a centralized way, a user distribution model in the center is adopted, and the probability density function of the user distribution adopts the following formula
Wherein R represents a cell radius, R0Representing the minimum distance of the user from the base station, a and b are key parameters related to a user distribution model;
(2) if the users are distributed in the edge of the cell in a concentrated way, the user distribution model in the edge concentration is adopted, and the probability density function of the user distribution adopts the following formula
Wherein R represents a cell radius, R0Representing the minimum distance of a user from the base station, a and b are key parameters related to the user distribution model.
The calculation of the key parameters a and b comprises the following steps:
(1) if the model is a user distribution model with centralized center, a controls the degree of the users approaching the center of the cell, the larger a indicates that more users are distributed in the central area of the cell, and vice versa, when a is 0, the users are subjected to uniform distribution, b is a normalization constant of a probability density function, and the normalization constant can be obtained through calculation
The user distribution model of the central set is a large-scale shopping mall and a street;
(2) if the model is a user distribution model with concentrated edges, a controls the degree of the users approaching the edge of the cell, the larger a indicates that more users are distributed in the edge area of the cell, and vice versa, when a is 0, the users are subjected to uniform distribution, b is a normalization constant of a probability density function, and the normalization constant can be obtained through calculation
The resource allocation condition of the system comprises given (M, K, P)T) Any two parameters, any one parameter and zero parameters, thereby creating three different optimization methods: the method comprises a single-variable optimization method, a double-variable joint optimization method and a three-variable joint optimization method.
The univariate optimization method comprises the following steps: given (M, K, P)T) Any two of these three parameters, the other one, for the individual optimization of the number of base station antennas M and the total base station transmitted power PTIn both cases, by closed form solution of MoptAnddirectly, and for the case of individually optimizing the number of users K, it is necessary to obtain the optimal value K by maximizing the energy efficiency of the system in a limited spaceopt。
The bivariable joint optimization method comprises the following steps: given (M, K, P)T) Any one of these three parameters, two other parameters are optimized, including:
(1) given the number of users K, jointly optimizing the number M of base station antennas and the base station transmitting power PT;
S100, when the algorithm starts to operate, setting initial base station transmitting power PT>0;
S101Updating the number M of base station antennas to Mopt;
S102, updating the transmitting power PTIs composed of
S103, circularly executing the steps S101 and S102 until the algorithm is converged, and obtaining the optimal number M of the base station antennasoptAnd base station transmit power
Wherein the judgment condition of algorithm convergence is that the integer M is not changed any more;
(2) given the number M of base station antennas, jointly optimizing the number K of users and the transmission power P of the base stationT;
S110, when the algorithm starts to run, setting initial base station transmitting power PT>0;
S111, updating the transmitting power PTIs composed of
S112, optimizing the number K of users to be Kopt;
S113, circularly executing the steps S111 and S112 until the algorithm converges, and obtaining the optimal user number KoptAnd base station transmit power
Wherein the judgment condition of algorithm convergence is that the integer K is not changed any more;
(3) given the number of base station antennas PTJointly optimizing the number K of users and the transmitting power M of the base station;
s120, setting the initial user number K to be 1 when the algorithm starts to run;
s121, updating the number M of the base station antennas to be Mopt;
S122, for MoptRounding off, and optimizing the number of users K to Kopt;
S123, circularly executing the steps S121 and S122 until the algorithm converges, and obtaining the optimal user number KoptAnd base station transmission power Mopt;
The judgment condition of algorithm convergence is that the integers K and M are not changed any more.
The three-variable joint optimization method comprises the following steps: to (M, K, P)T) Performing joint optimization on the three parameters;
s20, when the algorithm starts to run, setting the initial base station transmitting power PTThe number K of users is more than 0, the number M of base station antennas is more than 3;
s21, updating the number K of users to Kopt;
S22, updating the number M of base station antennas to Mopt;
S23, updating the transmitting power PTIs composed of
S24, circularly executing the steps S21 to S23 until the algorithm converges and obtaining the optimal three important system parameters
The judgment condition of algorithm convergence is that the integers K and M are not changed any more.
The invention is further described with reference to the following figures and specific embodiments.
The method for designing the key parameters of the downlink in the high-energy-efficiency large-scale antenna system is suitable for a Multi-user Multi-antenna (Multi-user MIMO) system of a single cell. The method specifically comprises the following steps:
a base station is positioned in the center of a circular cell, M antennas are configured on the base station, users of K single antennas are randomly distributed in the cell, the noise power is-114 dbm, shadow fading follows lognormal distribution, the mean value is 0, and the variance is 8 dB. Defining the energy efficiency of the system asWherein R isdlIs the sum rate (bits/channel use), P, of all users in the systemtotalRepresenting the total energy loss (Joule/channel use) of the system.
The energy loss of the single-cell system comprises three parts:
(1) energy loss P of power amplifierPA。
Wherein, PTRepresenting the total transmit power of the base station, 0 < η ≦ 1 is the energy efficiency of the amplifier, determined by the performance of the amplifier.
(2) Energy loss P of circuitC。
The circuit energy loss is an important component of the total energy consumption of the system, and the hardware facilities of each antenna of the base station comprise a digital-to-analog converter, a mixer, a filter and the like, and the energy loss is PBSThe hardware facilities of each user include low noise amplifier, direct frequency amplifier, filter and analog-digital converter, etc., and the energy loss is PUE。PsynFor the energy loss of the frequency synthesizer, P0Including energy losses in refrigeration systems and the like. The energy loss of this part can be expressed as:
PC=MPBS+2Psyn+KPUE+P0
(3) letterNumber processing energy consumption PSP。
As the number of antennas increases, the power consumption of signal processing cannot be ignored, and before analyzing the power consumption of signal processing, a quantity L (flops/Watt) characterizing the efficiency of calculating signal processing is defined and the channel state is considered to be constant in the T period. According to the sequence of signal processing, first, the base station encodes and modulates the K information sequences sent to the user, consuming KP each time using the channelcodThe energy of the joule. Secondly, the base station performs precoding once in each coherence time T, where zero forcing precoding method with low complexity is selected, so it costs each time the channel is utilizedThe energy of the joule. Then, in the signal transmission stage, the precoding matrix needs to be multiplied by the information sequence, which consumesThe energy of the joule. Finally, the user end decodes the received signal and consumes KPdecThe energy of the joule. So PSPCan be expressed as:
since the zero-forcing precoding algorithm is used at the base station end in the present embodiment, K < M. The flow chart is shown in fig. 1.
S30, in the coverage area of the base station, counting the distance information between the user and the base station in the coverage area of the base station to obtain an actual user distribution model;
s31, calculating key parameters a and b;
s32, calculating to obtain an energy efficiency expression EE ═ f (M, K, P) of the large-scale antenna systemT)
Wherein,representing the signal-to-noise ratio, PTThe total transmit power of the base station is obtained β based on the user distribution, and for the user distribution model in the central set,for a user distribution model that is edge-concentrated,α is a large scale fading factor.
S33, resource demand analysis and corresponding algorithm. The method comprises the following steps:
s330, setting key parameters (M, K, P) according to the requirements of the systemT) The number of (2) is divided into three cases.
Case 1: given (M, K, P)T) Any two parameters of (1), optimizing the remaining one parameter;
case 2: given (M, K, P)T) Jointly optimizing the remaining two parameters according to any one parameter of the two parameters;
case 3: given (M, K, P)T) Zero parameters of (2), jointly optimizing the three parameters;
s331, algorithm of case 1.
If the situation is 1, executing a univariate optimization method, comprising the following steps:
(1) given (M, K, P)T) Of these three parameters, (M, K), P is optimizedT;
In the case of this kind of situation,can be directly obtained by closed-type solution
(2) Given (M, K, P)T) Of these three parameters (M, P)T) Optimizing K;
for this case, K needs to be obtained by maximizing the energy efficiency of the system in a limited spaceopt。
(3) Given (M, K, P)T) Of these three parameters (K, P)T) Optimizing M;
for this case, MoptCan be directly obtained by closed-type solution
S332, algorithm of the 2 nd case.
If the situation is 2, executing a bivariate joint optimization method, comprising the following steps:
(1) given the number of users K, jointly optimizing the number M of base station antennas and the base station transmitting power PT;
Executing steps S100-S103;
(2) given the number M of base station antennas, jointly optimizing the number K of users and the transmission power P of the base stationT;
Executing steps S110-S113;
(3) given the number of base station antennas PTJointly optimizing the number K of users and the transmitting power M of the base station;
executing steps S120-S123;
s333, algorithm of case 3.
If the case 3 is true, the three-variable joint optimization method is executed, i.e., the steps S20-S24 are executed.
The principle of the method and the achieved technical effect can be as follows:
the invention provides a method with guiding significance for the design of key parameters of a down link in a high-energy-efficiency large-scale antenna system, namely, a user distribution model is actually and accurately obtained according to the number M of base station antennas, the number K of cell users and transmitting power PTThe three key parameters are used as entry points, and (M, K, P) is optimized according to different system requirementsT) These three key system parameters make the system energy efficient. Compared with the traditional power control or beam forming method, the method has the advantage of low algorithm complexity, saves partial resources and expenses, improves the energy efficiency of the system to the maximum extent, and accords with the concept of green communication.
Fig. 2(a) is a central user distribution model in this embodiment, where a is set to 1, and 1000 users are randomly generated in (R, R)0) In a cell of (600,50) m, the dots in blue represent users.
Fig. 2(b) shows a distribution model of users with edge concentration in this embodiment, where a is set to 1, and 1000 users are randomly generated in (R, R)0) In a cell of (600,50) m, the dots in blue represent users.
FIG. 3 is a diagram illustrating the setting of the total transmission power P of the base station for different user models in this embodimentTWhen the number of base station antennas is 0.001W, the system energy efficiency varies with the number of users in the cell. It can be seen that the larger the conventional number M of base station antennas, the higher the system energy efficiency is, and it does not apply here, but there is an optimum value for the number of base station antennas. In addition, the impact of user distribution on system energy efficiency can also be seen by fig. 3.
Fig. 4 shows the optimal number M of base station antennas obtained by performing the bivariate joint optimization method under the condition that the radius of the cell is 600M and different user numbers K are given in this embodimentoptAnd base station transmit powerThe above sub-diagram describes the optimal number of base station antennas M corresponding to different numbers of users KoptThe following sub-diagram describes the optimal base station transmit power for different numbers of users KFor convenience of expression, the ordinate represents the optimum base station transmission powerCorresponding maximum signal-to-noise ratio ρopt。
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be covered by the present invention.