Disclosure of Invention
The technical problem to be solved by the invention is as follows: the existing multi-cell large-scale DAS only considers single-cell single-parameter research energy efficiency.
In order to solve the above technical problem, a technical solution of the present invention is to provide an energy efficiency optimization method based on a RAU and a user distance relationship in a multi-cell large-scale DAS, which is characterized by comprising the following steps:
step 1, obtaining a k cell user MS of a multi-cell large-scale DAS cellkEnergy efficiency analysis formula xi of downlinkEE:
In the formula, N represents the number of antennas of each user, PFIXRepresenting static power consumption partsM denotes the number of antennas arranged for each RAU, L denotes the number of RAUs, PRAURepresenting the dynamic power requirement, P, of each RAU antennatDenotes the total transmission power required by the user, tau denotes the power amplification factor, PBHDenotes power consumption of a backhaul link, γ denotes a signal-to-noise ratio, K denotes a total number of cells, α denotes a path loss factor, λ denotes a constant satisfying λ ═ 1n (10)/10, and σ denotesshRepresents the standard deviation;
step 2, solving energy efficiency analytic expression xi within the RAU number rangeEEComprises the following steps:
step 201, initializing RAU number l to 1, xiEE(L) 0, and the number of radio frequency chains is SL;
Step 202, if l is less than SLIf l' ═ l +1, xi is calculatedEE(L ═ L'), proceed to step 203; if l is greater than or equal to SLTerminating the algorithm;
step 203, judge xiEE(L=l′)≤ξEE(L ═ L) is established, and if so, L and ξ at that timeEE(L ═ L) is an optimum value, and is directly output, and if it is not true, L ═ L' is updated, and ξ is calculatedEE(L ═ L), return to step 202;
step 3, solving energy efficiency analytic expression xi within the range of the number of the user antennasEEComprises the following steps:
step 301, initializing the number n of user antennas to 1, ξEE(N-0) and the maximum number of user antennas is SN;
Step 302, if n is less than SNIf n' is n +1, xi is calculatedEE(N ═ N'), proceed to step 203; if n is greater than or equal to SNTerminating the algorithm;
step 303, judge xiEE(N=n′)≤ξEEWhether (N ═ N) is true or not, and if true, N and ξ at that timeEE(N ═ N) is an optimum value, and is directly output, and if not, N ═ N' is updated, and ξ is calculatedEE(N), return to step 302;
step 4, solving energy efficiency analytic expression xi in the range of emission powerEEIncluding the optimal solution ofThe following steps:
step 401, initializing the transmission power p to 1, ξ
EE(P
tSetting the threshold value of the maximum transmission power of the system as p) to 0
And step length lambda;
step 402, if
P' ═ p + λ, and ξ is calculated
EE(P
tP'), go to step 203; if it is
The algorithm is terminated;
step 403, judge ξEE(Pt=p′)≤ξEE(PtP), if true, p and xi at that timeEE(PtP) is the optimum value, and is directly output, if not, p is updated, and p is p', and xi is calculatedEE(PtP), return to step 402.
According to the invention, an analytic expression of system throughput is deduced according to the distance between the RAU and the user. And then establishing an optimization model of the system downlink energy efficiency according to the relation between a composite channel with the characteristics of path loss, shadow fading and multipath fading and a plurality of actual power consumption parameters. Finally, the change relation between the system energy efficiency and the number of the cell RAUs, the number of the user antennas and the transmitting power is deduced on the basis, and the theoretical value of the optimal system energy efficiency is obtained through the proposed algorithm.
The invention considers various factors (the number of user antennas, the number of cell RAUs, the maximum transmitting power and the like) influencing the energy efficiency of the multi-cell large-scale DAS at the same time, and optimizes the system energy efficiency under an actual channel model and a power consumption model containing a plurality of actual power consumption parameters, so that the invention has the advantages of obtaining the optimal system energy efficiency with less iteration times and being easy to realize.
Aiming at the communication scene of the multi-cell large-scale DAS, the mathematical analytic expression of the multi-cell large-scale DAS throughput is obtained based on the distance between the user and the RAUs, and the mathematical model of the system energy efficiency is established on the basis of considering the real channel and the actual power consumption model. Then, the fact that the energy efficiency of the multi-cell large-scale DAS system has the optimal solution in the value ranges of the number of RAUs, the number of user antennas, the transmitting power and the like is verified, and the optimal solution of the energy efficiency in the value ranges of the factors is solved through a low-complexity algorithm.
The invention has the advantages of low complexity and easy realization.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The invention provides an energy efficiency optimization method based on the RAU and user distance relationship in a multi-cell large-scale DAS, which is based on the following argument:
establishing a multi-cell large-scale DAS model based on the distance between the RAU and the user:
in the formula (1), YkA received signal representing a k cell user; k represents the total number of cells;HikIndicating all RAUs to MSs in cell ikOf the channel response matrix, MSkRepresents a k cell user; dikIndicating all RAUs to MSs in cell ikA distance vector of (d); xiIndicates all RAUs in cell ilkFor cell user MSkThe transmission signal of (1); n represents additive white gaussian noise.
During downlink communication, the l-th RAU in cell i is relative to the k-th cell user MSkA distance d betweenlikComprises the following steps:
when i ═ k:
when i ≠ k:
in the formulae (2), (3) and (4), (a)lik,θlik) Indicates the first RAU in the cell i relative to the k cell user MSkIn polar coordinate form; (rho, theta) is the k cell user MSkIn polar coordinate form; p (rho) and p (theta) are k cell users MSkA probability density function of the polar coordinates (p, θ) with respect to the center of the coverage area; r represents a cell radius; l represents the number of RAUs deployed per cell.
Kth cell user MSkAverage information amount of IkComprises the following steps:
in formula (5):
I
Man identity matrix representing the M dimensions; gamma represents the signal-to-noise ratio; n represents eachNumber of antennas of individual users, H
WRepresenting a small-scale fading matrix; i is
NAn identity matrix representing N dimensions;
represents an intermediate variable, wherein:
in the above formula, R ═ R; d ═ 2R; sLikRepresents logarithmic shadow fading; α represents a path loss factor.
In the above formula, HW,LDenotes an intermediate variable, HW,LikL-th to k-th cell user MS representing ith cellkThe small-scale fading matrix.
To IkK cell user MS obtained by averagingkAverage information amount C ofkComprises the following steps:
Ck=E[Ik] (6)。
according to the definition of energy efficiency, the user MS of the kth cell of the large-scale DAS system with multiple cells can be realizedkEnergy efficiency analysis formula xi of downlinkEE:
In the formula, N represents the number of user antennas, PFIXDenotes a static power consumption part, M denotes the number of antennas per RAU configuration, L denotes the number of RAUs, and P denotesRAURepresenting the dynamic power requirement, P, of each RAU antennatDenotes the total transmission power required by the user, tau denotes the power amplification factor, PBHDenotes power consumption of a backhaul link, γ denotes a signal-to-noise ratio, K denotes a total number of cells, α denotes a path loss factor, λ denotes a constant satisfying λ ═ 1n (10)/10,σshthe standard deviation is indicated.
Energy efficiency analytic formula xiEEThe optimal solution exists in the respective value ranges of the number of RAUs, the number of user antennas, the transmitting power and the like:
(1) energy efficiency analytic expression xi in the value range of RAU number LEEThere is an optimal solution.
Energy efficiency analysis formula xiEEThen, there are:
in the formula (7), PtotalRepresents the total power consumption of the system, CkIndicates the k cell user MSkAverage information amount of (2).
Since the denominator of the formula (7) is a positive number, the positive and negative of the formula (7) are completely determined by numerator. Order to
And taking a derivative of ζ (L) can result in:
this indicates that the zeta (L) value decreases with increasing L and satisfies
That is, there is l ∈ [0, ∞) ] so that ζ (l) becomes 0. At the same time satisfy
In [0, l]Greater than zero, and less than zero in [ l, ∞). So xi
EEIn [0, l]Increment, decrement at [ l, ∞). Presence of an appropriate l on [0, ∞) ] makes ξ
EEAnd max.
(2) Energy efficiency analytic expression xi in value range of user antenna number NEEThere is an optimal solution.
Paxi xi
EEDerived with respect to N
t represents an intermediate variable in the form of an integral of the gamma function.
Order to
Then there is
Visible energy efficiency analytical formula xi
EEIs a convex function with respect to N. So that there must be one n at [0, ∞) so that
Namely, it is
Greater than zero at [0, n) and less than zero at [ n, ∞). So xi
EEN is gradually increased at [0, N) and gradually decreased at [ N, ∞), and N is energy efficiency analysis formula xi
EEThe number of antennas at the optimum time.
(3) Energy efficiency analytic formula xiEEAt a transmission power PtThere is an optimal solution within the value range of (a).
Passing through xi
EEIn respect of P
tIs derived by
Order to
To P
tThe derivation can be:
visible Ψ (P)
t) With respect to variable P
tDecrease progressively and satisfy
I.e. the presence of a p at [0, ∞)
tSuch that Ψ (p)
t) Is equal to 0, and
at [0, p
t]Is greater than zero at [ p ]
tAnd ∞) is less than zero. Visible emission power of p
t(0≤p
t≤P
t) Time-energy efficiency analytic formula xi
EEAnd taking an optimal value.
Specifically, the method comprises the following steps:
in this example, considering a large-scale DAS including K uncooperative cells, L RAUs uniformly distributed along a circular optical fiber backhaul are deployed in each circular cell with a radius R, where the first RAU of the K-th cell is denoted as RAUlkL ∈ {1, 2., L }, K ∈ {1, 2., K }, each RAUlkAnd configuring M antennas. Each cell has only one user (MS) uniformly distributed in the cell, N antennas are configured, and a plurality of RAUs can be received simultaneouslylkIs transmitted. Considering the RAU of a non-own cellli(i ≠ k) for MSkIn case of interference of (3), L RAUsli(i ≠ k) in a circle of radius 2R (in MS)kThe center of the cell is the center of the circle). The parameter settings are shown in table 1 below:
TABLE 1
The energy efficiency is optimized by the embodiment, and the algorithm uses the condition energy efficiency analytic expression xiEEThe condition that the optimal solution exists in the respective value ranges of the RAU number, the user antenna number, the transmitting power and the like is met, and the evidence is obtained. Therefore, the following three algorithms can be set to respectively solve the optimal values of energy efficiency in the ranges of the number of RAUs, the number of user antennas, the transmission power and the like.
Algorithm 1: and solving the optimal value of the energy efficiency within the RAU number range. Since the number of RAUs cannot exceed the number of available radio frequency chains, the number of radio frequency chains can be used as a termination condition for seeking the number of RAUs. Meanwhile, since the number of RAUs can only be an integer, the step size can be set to 1 when the iterative step size is set.
Step 201, initializing the RAU number lIs 1, xiEE(L) 0, and the number of radio frequency chains is SL;
Step 202, if l is less than SLIf l' ═ l +1, xi is calculatedEE(L ═ L'), proceed to step 203; if l is greater than or equal to SLTerminating the algorithm;
step 203, judge xiEE(L=l′)≤ξEE(L ═ L) is established, and if so, L and ξ at that timeEE(L ═ L) is an optimum value, and is directly output, and if it is not true, L ═ L' is updated, and ξ is calculatedEE(L ═ L), return to step 202.
And 2, algorithm: and solving the optimal value of the energy efficiency within the range of the number of the user antennas. The maximum number of subscriber antennas to which the system can connect is taken as a termination condition and the step size is set to 1.
Step 301, initializing the number n of user antennas to 1, ξEE(N-0) and the maximum number of user antennas is SN;
Step 302, if n is less than SNIf n' is n +1, xi is calculatedEE(N ═ N'), proceed to step 203; if n is greater than or equal to SNTerminating the algorithm;
step 303, judge xiEE(N=n′)≤ξEEWhether (N ═ N) is true or not, and if true, N and ξ at that timeEE(N ═ N) is an optimum value, and is directly output, and if not, N ═ N' is updated, and ξ is calculatedEE(N), return to step 302.
Algorithm 3: and solving the optimal value of the energy efficiency in the transmission power range. The transmission power is set to be too large, which not only can not improve the system energy efficiency, but also causes resource waste, resulting in worse system performance, so the system usually sets a threshold of the maximum transmission power, and can use the threshold as an energy efficiency analytic expression xiEEWhen the optimal transmission power is optimal, seeking an optimal transmission power termination condition, setting a proper step length, and specifically implementing the following steps:
step 401, initializing the transmission power p to 1, ξ
EE(P
tSetting the threshold value of the maximum transmission power of the system as p) to 0
And step length lambda;
step 402, if
P' ═ p + λ, and ξ is calculated
EE(P
tP'), go to step 203; if it is
The algorithm is terminated;
step 403, judge ξEE(Pt=p′)≤ξEE(PtP), if true, p and xi at that timeEE(PtP) is the optimum value, and is directly output, if not, p is updated, and p is p', and xi is calculatedEE(PtP), return to step 402.
As shown in fig. 2, the energy efficiency EE is a value for different RAUs. As can be seen from fig. 2, in the present invention, the energy efficiency EE increases gradually and then decreases gradually as the number L of RAUs increases, that is, the energy efficiency EE has an optimal solution within the value range of the number L of RAUs. It can also be seen from the figure that: firstly, when the RAU antenna number L and the user antenna number N are determined, the energy efficiency EE is gradually increased along with the increase of the cell number K; and secondly, when the number L of the RAU antennas is constant with the number K of the cells, the energy efficiency EE is improved along with the increase of the number N of the user antennas.
As shown in fig. 3, energy efficiency EE is a value for the number of different user antennas. As can be seen from the legend 3, in the present invention, the energy efficiency EE increases and then decreases along with the overall variation trend of the user antenna number N, that is, the energy efficiency EE has an optimal solution within the value range of the user antenna number N. It can also be seen from the figure that: when the number of cells K and the transmission power PtWhen the number of RAUs is determined, the energy efficiency EE is increased along with the increase of the number L of the RAUs.
As shown in fig. 4, energy efficiency EE is a value at different transmission power. As can be seen from legend 4, in the present invention, the energy efficiency EE is a function of the transmitted power PtIncreasing and then decreasing, i.e. energy efficiency EE at transmission power PtThere is an optimal solution within the value range of (a). It can also be seen from the figure that: when the number of RAUs is fixed (L is 6), the energy efficiency EE is increased along with the increment of the number N of the user antennas; when the user is on dayWhen the number of lines is constant (N is 4), the energy efficiency EE decreases as the number L of RAUs increases.
As shown in fig. 5, the energy efficiency EE is a value when the transmission power and the RAU number are different. As can be seen from the figure, the energy efficiency is maximized when the number of RAUs is 4 and the transmission power is 6. As can be seen from the graph, energy efficiency can be optimized by simultaneously and appropriately setting the values of a plurality of parameters.
In the above embodiment, the step length is set to 1 in the algorithms (1) and (2), and the number of RAUs and the number of user antennas are not infinitely increased, so the algorithms (1) and (2) can find the optimal result with a small number of iterations. The algorithm (3) can also find the optimal solution quickly by reasonably setting the step length lambda. Therefore, the algorithm does not additionally increase excessive overhead in practical application and is easy to implement.
In conclusion, the method can obtain the optimal energy efficiency value with lower iteration times and is easy to realize in practice.