CN110166987B - D2D communication energy efficiency optimization method for guaranteeing QoS of cellular mobile communication system - Google Patents

D2D communication energy efficiency optimization method for guaranteeing QoS of cellular mobile communication system Download PDF

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CN110166987B
CN110166987B CN201910353537.9A CN201910353537A CN110166987B CN 110166987 B CN110166987 B CN 110166987B CN 201910353537 A CN201910353537 A CN 201910353537A CN 110166987 B CN110166987 B CN 110166987B
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base station
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cellular user
user
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CN110166987A (en
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史锋峰
陈瑞璐
赵春明
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Southeast University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/06—TPC algorithms
    • H04W52/14—Separate analysis of uplink or downlink
    • H04W52/143—Downlink power control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
    • H04W52/243—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account interferences
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
    • H04W52/265—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the quality of service QoS
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/30—TPC using constraints in the total amount of available transmission power
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/38—TPC being performed in particular situations

Abstract

The invention discloses a D2D communication energy efficiency optimization method for guaranteeing QoS of a cellular mobile communication system, which comprises the following steps: the base station selects downlink frequency band resources of cellular users in the cell to share for the selected D2D users through scheduling to carry out device-to-device communication; a base station acquires real-time channel state information of a downlink transmission link and an interference link; the base station preferentially meets the service quality requirement of the cellular user according to the channel state information and determines a power distribution scheme; the base station sends the power allocation scheme to the D2D transmitting terminal, and the base station and the D2D transmitting terminal complete data transmission according to the power allocation scheme. The method can be effectively applied to the power distribution scenes of a downlink cellular layer and a D2D layer of an actual mobile communication network, ensures the communication quality of cellular users, simultaneously ensures that the energy efficiency of a D2D system is expected to be optimal, improves the spectrum efficiency of the system, reduces the energy consumption and interference of the whole network, and accords with the concept of green communication of a 5G system.

Description

D2D communication energy efficiency optimization method for guaranteeing QoS of cellular mobile communication system
Technical Field
The invention belongs to the field of wireless resource management of a cellular mobile communication D2D system, and particularly relates to a D2D communication energy efficiency optimization method for guaranteeing QoS of a cellular mobile communication system.
Background
With the popularity of smart phones and smart terminals, the use of telecommunications will reach new heights in the coming years, the download traffic of cellular phones is expected to increase more than eight times per month, and new mobile users worldwide each year continue to rise in millions. At the same time, 5G networks put higher and faster demands on system capacity and rate requirements. In this context, D2D (Device-to-Device) communication technology has gained general attention, and the technology mainly performs direct communication between users by selectively multiplexing frequency band resources in a cell or using orthogonal idle resources, so as to reduce the transmission power of a terminal Device, reduce transmission delay, improve the frequency spectrum resources of the cell, improve the throughput of the system, and alleviate the problem of insufficient frequency spectrum resources of a wireless communication system to a certain extent. Meanwhile, compared with other similar technologies, such as WLAN, bluetooth, etc., the D2D technology uses the authorized frequency band of the telecom operator, and has the advantages of controllable interference, etc.
Besides, one of the main problems in the design of wireless communication systems is the continuous consumption of energy, green communication is the inevitable trend of the upcoming 5G networks, and the optimization of energy efficiency as the target of system design is somewhat responsive to the concept of green communication, but at present, there is less research on the optimization of D2D energy efficiency as the target. Of course, the introduction of D2D users inevitably increases interference to Cellular User Equipment (CUE) in a cell, and how to perform effective radio resource management, that is, while maximizing system capacity or energy efficiency, the interference to the CUE from D2D devices is controlled within a tolerable range, which is a serious issue in the D2D technology.
Currently, D2D radio resource management methods are classified into two types, centralized control and distributed control. In the centralized control method, the base station controls the connection and maintenance of the D2D device, collects the real-time channel state information of all links, makes a power allocation scheme, and downloads the power allocation scheme to each user, and the control scheme undoubtedly increases the signaling consumption in the cell; in the distributed control method, the D2D users can autonomously perform connection and maintenance of the D2D, and it is easier to collect channel state information among the D2D users than centralized control, but the complexity of the D2D equipment is disadvantageously increased.
The interference problem of the D2D user to the cellular cell system can be solved by proper and effective power control, and the frequency spectrum efficiency can be maximized and the throughput of the cell can be improved on the premise of not influencing the communication quality of the cellular user equipment of the original cell. Currently, there are two common power control schemes, static power control and dynamic power control. The static power control scheme means that the base station cannot acquire real-time channel state information of the D2D user, and when a D2D session is initiated, a fixed power allocation scheme is determined, and until the session is ended, the power control scheme does not increase the signaling consumption of a cell, but cannot ensure the system performance in a complex and variable wireless fading environment, because when the spectrum resources of the cell are multiplexed, the interference of the D2D user to the original cell is related to not only the channel condition between the base station and the D2D user, but also the channel condition between the D2D user and the cellular user, and the channel condition between the D2D user. The fixed power allocation scheme also introduces a power increase factor of the cellular user while ensuring that the signal-to-noise ratio of the D2D user reaches the minimum SINR, and ensures the target SINR of the cellular user by increasing the power of the cellular user, but this may cause too many users inside the cell to transmit with larger power, which may aggravate the interference inside the cell. In the dynamic power control scheme, the base station can acquire real-time channel state information among users and perform power distribution according to the real-time channel state information. Compared with static power control, although dynamic power control increases certain signaling consumption, the performance of the system in the aspects of throughput, energy efficiency and the like is greatly improved,
in addition, in a cell, frequency band resources of one cell user are generally scheduled to be reused by a pair of D2D users, because if there are more D2D links, interference is large and complex, and it is difficult to perform effective power control. Therefore, the power allocation method which is universal, effective and capable of ensuring the communication quality of the cellular user and enabling the D2D communication energy efficiency to be expected to be optimal has good practical significance.
Disclosure of Invention
The purpose of the invention is as follows: the 5G era is coming, and in order to meet the requirements of a 5G system on higher and faster spectrum efficiency, system throughput, user rate and the like, and to respond to the concept of green communication, the invention provides a downlink power allocation method which can be effectively applied to the D2D scene of actual cellular mobile communication, a D2D user is allowed to reuse cell frequency band resources in a cellular cell, and a base station adopts a resource management mode of centralized control and dynamic power allocation, can acquire real-time channel state information of users in the cellular cell, and allocates appropriate power to cellular users and D2D users according to the channel state information. The method can ensure that the statistical energy efficiency expectation of the D2D system is optimal on the premise of ensuring the communication quality of cellular users.
The technical scheme is as follows: in order to achieve the purpose of the present invention, the technical scheme adopted by the present invention is a downlink power allocation method for ensuring optimized D2D communication energy efficiency of a cellular mobile communication system QoS, which specifically comprises the following steps:
(1) the base station with the D2D detection and mode selection functions schedules and selects downlink frequency band resources of one cellular user in a cell to be shared to a proper D2D user for direct device-to-device communication;
specifically, in the cell, the base station uses a radio resource management method of centralized control to schedule the cellular users by using a common scheduling algorithm in the existing communication system, and shares the downlink frequency band resources of the cellular users to an appropriate D2D link for device-to-device communication.
Specifically, the "suitable D2D users" are scheduled so that the base station and the cellular users' communications and the D2D linked communications interfere with each other as little as possible, and the respective QoS requirements can be guaranteed on the premise of resource sharing. Taking distance as an example, the distance between the D2D link and the base station and the distance between the D2D link and the cellular user sharing the frequency band resource are all suitable, and it is generally required that the distance between the scheduled D2D link and the base station is greater than the distance between the cellular user and the base station, and the distance between the D2D link and the cellular user sharing the frequency band resource is also a certain distance, which can be set according to actual needs.
(2) A base station acquires real-time channel state information of a downlink transmission link and an interference link;
specifically, the transmission links include channels between base stations to cellular users and channels between D2D users; the interfering link includes channels from D2D users to cellular users and channels from the base station to D2D, see fig. 1 of the specification.
Specifically, the base station sends a control signal to each user in the cell, the cell user is linked according to the cell user selected by the base station in the step (1) and the corresponding D2D, firstly, the cell user carries out channel estimation to obtain the channel state information of a transmission link between the cell user and the base station, and simultaneously obtains the channel state information of an interference link between the cell user and a D2D transmitting terminal through the channel estimation, and then, the channel information is quantized according to a codebook which is commonly known with the base station, and the quantized channel information is fed back to the base station; meanwhile, the D2D user firstly performs channel estimation to obtain the channel state information of the transmission link between the D2D, and simultaneously obtains the channel state information of the interference link between the D2D receiving end and the base station through the channel estimation, and then quantizes the channel information according to the codebook known by the user and the base station, and feeds back the quantized channel information to the base station.
Specifically, according to the method described in the previous paragraph, the base station may obtain real-time channel state information of each link, based on which the base station may obtain the real-time rate of the cellular users in the cell. In order to satisfy the communication quality of the cellular user k, the base station performs power control, and the transmission power satisfies the constraint condition
Figure BDA0002044695330000031
Then, the cellular user can reach the rate R under the power allocation schemekGreater than the minimum rate R required to guarantee its QoSCNamely:
Figure BDA0002044695330000032
wherein:
RCrepresents the minimum rate requirement to guarantee the communication quality of the cellular user;
v represents the fading state of the real-time channel;
Figure BDA0002044695330000033
representing a transmit power threshold of the base station to the cellular user;
Figure BDA0002044695330000034
represents the transmit power threshold of the D2D link;
pk(v) representing the transmission power of the base station to the cellular user k in the fading state v;
Figure BDA0002044695330000035
channel state information representing the transmission link between a base station and a cellular user k in a fading condition v
Figure BDA0002044695330000041
Wherein lkRepresenting the path loss, h, of the transmission link between the base station and the cellular subscriber kk(v) Represents the normalized channel gain, delta, of the transmission link between cellular user k and base station in fading condition vkRepresenting the variance of white gaussian noise in the communication link between the base station and the cellular user k;
pj(v) representing the transmitting power of the transmitting end of the D2D link j under the fading state v;
Figure BDA0002044695330000042
representing the interfering link channel state information of D2D link j to cellular user k in fading state v,
Figure BDA0002044695330000043
wherein ljkRepresents the path loss, g, of the interfering link of D2D link j to cellular user kjk(v) Represents the normalized channel gain, δ, of the D2D link j to the interfering link of cellular user k under the fading condition vjkRepresenting the variance of D2D link j to gaussian white noise in the interfering link for cellular user k.
(3) And the base station preferentially meets the service quality requirement of the cellular user according to the acquired real-time channel state information and determines a power distribution scheme.
Base station ensuring cellular user to reach its minimum rate requirement RCTo optimize the statistical energy efficiency η of the D2D userTarget, power allocation, the expression for energy efficiency is as follows:
Figure BDA0002044695330000044
wherein:
e { } represents a statistical average over different channel states v;
pj(v) representing the transmitting power of the transmitting end of the D2D link j in the fading state v;
ζ represents the power amplification factor at the transmit end of the D2D link,
Figure BDA0002044695330000045
representing D2D link circuit power consumption;
Figure BDA0002044695330000046
channel state information representing the transmission link of D2D link j in fading condition v
Figure BDA0002044695330000047
Wherein ljRepresents the path loss, h, of the transmission link of D2D Link jj(v) Represents the normalized channel gain, δ, of the D2D link j transmission link in the fading state vjRepresenting the variance of Gaussian white noise of the transmission link j of the D2D link;
pk(v) represents the transmission power allocated to a cellular user k by the base station in a fading state v;
Figure BDA0002044695330000051
channel state information representing an interfering link between a base station and a receiver of a D2D link j in a fading state v
Figure BDA0002044695330000052
Wherein lkjRepresents the path loss, g, of the interfering link between the base station and the receiver of the D2D link jkj(v) Representing the return of an interference link between a base station and a D2D link j receiving end under a fading state vNormalized channel gain, deltakjRepresenting the variance of the white gaussian noise of the base station to the D2D link interfering link.
According to classical fractional programming theory, an energy-optimized objective function eta (p)j(v) From fractional programming) can be translated into a nonlinear programming problem of the following formula:
Figure BDA0002044695330000053
considering also the requirement of minimum rate for cellular users, so:
Figure BDA0002044695330000054
objective function f (p)j(v) Eta) and pk(v) Is inversely proportional, therefore
Figure BDA0002044695330000055
Time-energy efficiency is maximized, while the base station assigns a power expectation E { p to the cellular userk(v) Should be controlled not to exceed a threshold
Figure BDA0002044695330000056
Namely:
Figure BDA0002044695330000057
wherein the content of the first and second substances,
Figure BDA0002044695330000058
will be provided with
Figure BDA0002044695330000059
Substituting into the objective function, which can be proved to be a concave function, and solving by Lagrange multiplier method.
Considering the power expectation E p of the base station to allocate to the cellular usersk(v) Should be controlled not to exceed a threshold
Figure BDA00020446953300000510
And the power expectations E p that the base station allocates to D2D usersj(v) Should be controlled not to exceed a threshold
Figure BDA00020446953300000511
The two constraints, introducing Lagrangian factors lambda and mu, are used for transforming the target function f (p)j(v) η) to:
Figure BDA0002044695330000061
wherein:
Figure BDA0002044695330000062
as can be seen from the above equation, the objective function L (p)j(v) λ, μ) can be converted to the solution E { G' (v) }.
Since G' (v) has the same structure for each of the different fading states v, v in the expression is truncated, and the objective function L (p) is the same as V in the following formula for the sake of brevityj(v) λ, μ) can be converted into:
Figure BDA0002044695330000063
when it is satisfied with
Figure BDA0002044695330000064
Conditional, power distribution scheme
Figure BDA0002044695330000065
Achieving an energy efficiency optimization goal η*The superscripts are shown as optimization results.
η*Iterative solution can be found based on the Dinkelbach method: setting eta as 0, calculating power distribution result p at the momentj，pkAnd corresponding lagrange factors lambda and mu, when optimizedAs a result, the objective function f (p)j(v) η) should be zero and the end condition of the loop iteration is that the target function reaches the set accuracy requirement | f (p)j(v),η)|≤εfWhen the precision condition is not met, eta is updated according to the cycle distribution result of the current round, the Dinkelbach method is high in convergence speed, and the iteration frequency is usually within 10 times under the simulation condition. Regarding the accuracy requirements: due to inevitable accuracy problems in optimization operations and computer operation, it is often impossible for the objective function to reach exactly zero, and therefore the accuracy requirement epsilon is set for itfE.g. epsilonf＝10-4And when the absolute value of the difference value of the target function and 0 is smaller than the precision requirement, the convergence condition is considered to be satisfied.
At eta*In each iteration cycle, corresponding lagrangian factors λ and μ introduced in the optimization process need to be searched, and the two factors can be iteratively solved by a gradient method: firstly setting initial values of lambda and mu (for example, setting them as 0) and adjusting step length (for example, setting them as 0.1), when the optimum result is reached, the constraint conditions of lambda and mu are required to meet the set accuracy requirement, before the accuracy requirement is not reached, regulating lambda and mu according to the set step length along the gradient direction until the accuracy requirement is reached, in order to accelerate convergence speed, the selection of initial values and step length can be regulated according to the actual conditions. The initial values of λ and μ and the adjustment step length can be set according to actual needs, and specific data are used as examples.
η*The iterative solution process for the three quantities λ and μ is shown in the method flow diagram of fig. 2.
Specifically, the power allocated to D2D and cellular users, respectively, is (superscript @, shown as the algorithm output result):
Figure BDA0002044695330000071
Figure BDA0002044695330000072
wherein the content of the first and second substances,
Figure BDA0002044695330000073
three intermediate variables A introduced for concise formula descriptionj,k，Bj,k，Cj,kIs defined as:
Figure BDA0002044695330000074
Figure BDA0002044695330000075
Figure BDA0002044695330000076
(4) and (4) the base station sends the power allocation scheme to the transmitting terminal of the D2D, and the base station and the transmitting terminal of the D2D complete data transmission according to the power allocation scheme in the step (3).
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
(1) the downlink power allocation scheme provided by the invention takes the optimal D2D communication energy efficiency as a target, not only considers the maximum power consumption of a D2D link, but also considers the communication quality of a cellular user and the power threshold sent by a base station to the cellular user, so that on the premise of ensuring the communication quality of the cellular user, the spectrum efficiency and the energy efficiency of a cell are improved, the transmission power of terminal equipment is reduced, the endurance time of the terminal equipment can be prolonged, and meanwhile, the concept of green communication of a 5G system is met.
(2) The invention considers the time-varying channel in the real communication scene, introduces the fading state factor v of the real-time channel gain, and the provided downlink power distribution method not only can adapt to different fading states, but also can ensure that the energy efficiency expectation of D2D communication is optimal, thereby being more in line with the application scene of the real system.
(3) The invention provides a downlink power allocation method which can be effectively applied to the actual D2D scene of cellular mobile communication, and the optimal power allocation scheme can be quickly obtained according to the provided power closed solution only by the base station acquiring the real-time channel state information of all transmission links and interference links in the cell and the minimum speed requirement of the selected cellular user, thereby improving the processing timeliness of the base station and reducing the transmission delay of the transmitting end.
Drawings
Fig. 1 is a diagram of a cellular mobile communication system model supporting D2D communication according to the present invention;
FIG. 2 is a flow chart of a method of the present invention;
FIG. 3 is a graph of D2D communication energy efficiency versus cellular user minimum rate requirement when determining distances between D2D users;
FIG. 4 is a graph of D2D communication energy efficiency versus distance between D2D users when a cellular user minimum rate requirement is determined;
FIG. 5 is a graph of D2D traversal capacity, cellular user traversal capacity, and total cell traversal capacity versus cellular user minimum rate requirements for determining distances between D2D users;
fig. 6 is a graph of D2D traversal capacity, cellular user traversal capacity, and total cell traversal capacity versus distance between D2D users when a cellular user minimum rate requirement is determined.
Detailed Description
The present invention will be further described with reference to the accompanying drawings. As shown in the flowchart of the method in fig. 1, in the cell, the D2D users are allowed to reuse the cell band resources, and the base station can acquire the real-time channel state information of the users in the cell by using a resource management manner of centralized control and dynamic power allocation, and allocate the appropriate power to the cellular users and the D2D users according to the channel state information. The method can ensure that the energy efficiency of the D2D system is expected to be optimal on the premise of ensuring the communication quality of cellular users.
Power expectation E { p of cellular users in simulationk(v) Threshold value
Figure BDA0002044695330000091
Set to 46dBm, power expectation E { p for D2D userj(v) Threshold value
Figure BDA0002044695330000092
Set to 20 dBm. The power amplification coefficient zeta of the transmitting end of the D2D link is set to be 0.2, and the power consumption of the D2D link circuit is set to be 0.2
Figure BDA0002044695330000093
50mW was set.
Assuming that the base station is located at the center of the cell and a centrally controlled radio resource management method is employed, the downlink frequency band resources of the cellular users are scheduled to be shared to the appropriate D2D users for device-to-device communication. In the simulation, the radius R of the cell is set to be 500m, when the base station schedules, the distance from the D2D link to the base station is larger than the distance from the cellular user to the base station, and the distance from the D2D link to the cellular user sharing the frequency band resource is also a certain distance, so that the interference of the base station to the D2D link and the interference of the D2D link to the cellular user are reduced as much as possible. In the simulation, the distance range between the cellular user and the base station 120m, the distance between the D2D link and the base station 300m, the distance between the D2D link and the cellular user sharing the frequency resource 300m, and the distance between the D2D user are controlled within 50 m. Path loss model using path loss factor alphalWeighted free space loss model L32.45 +20lg (f)c)+20αllg (d), wherein the carrier is in GHz and the distance is in m. Carrier frequency fcSet to 2GHz, the path loss factor alpha of all transmission links and interfering linkslAre set to 1.75 and the shadow fading is set to-4 dBm.
Communication channel h between base station and cellular subscriberkOf an interference channel gkj，gjkBy adopting a Rayleigh fading model, the direct path existence probability of the D2D link is high, so that the channel h of the D2D link is highjFour scenes of rayleigh fading and rice fading (rice coefficients K are respectively 3dBm,0dBm and-3 dBm) are considered. At the same time, the white Gaussian noise in all links is set to-120 dBm.
FIG. 3 is
Figure BDA0002044695330000094
The relationship between the energy efficiency of D2D communication and the minimum rate requirement of the cellular user is plotted when the monte carlo number num is 100000 and the distance between D2D users is 50 m. Comparing the power allocation methods provided in the present invention, the performance of the two power allocation schemes is not considered to optimize the equal power allocation method (denoted by (eq) in the figure) that only satisfies the minimum rate requirement of the cell and two power thresholds, and it can be seen from the figure that the power allocation scheme of the present invention is superior to the power allocation scheme that only satisfies the constraint without considering the optimization, and even if the minimum rate requirement of the cell user is increased to 12bps/Hz, the energy efficiency of the present invention is still superior to the power allocation scheme that only satisfies the constraint without considering the optimization. Meanwhile, as can be seen from the figure, the case where the rice coefficient K is 3dBm is better than the case where K is 0dBm is better than the case where K is-3 dBm, the energy efficiency of the rayleigh channel is the lowest, and the power distribution scheme of the present invention maintains its advantages not only for the rayleigh channel but also for the rice channel whose rice coefficient K is 3dBm,0dBm, and-3 dBm, respectively.
FIG. 4 is
Figure BDA0002044695330000095
The Monte Carlo number num is 100000, and the D2D communication energy efficiency is plotted against the distance between D2D users under the condition that the minimum speed requirement of the cellular users is 10 bps/Hz. The power allocation methods provided in the present invention are compared, and the performance of the two power allocation schemes is not considered for optimizing the equal power allocation method (denoted by (eq) in the figure) that only satisfies the cellular minimum rate requirement and the two power thresholds. As can be seen from the figure, as the distance between D2D users increases, the energy efficiency of D2D communication decreases, since the increase in distance causes the channel of the D2D link to deteriorate, but the power allocation scheme of the present invention is always superior to the power allocation scheme that satisfies only the constraint without regard to optimization.
FIG. 5 is
Figure BDA0002044695330000101
When the monte carlo number num is 100000 and the distance between D2D users is 50m, the power score of the present inventionD2D traversal capacity, cellular user traversal capacity, and total cell traversal capacity versus cellular user minimum rate requirement for the allocation method. As can be seen from the figure, under the power allocation method of the present invention, the cellular users reach their minimum rate requirements, and as the minimum rate requirements of the cellular users increase, the actual rate reached by the D2D users decreases, because the minimum rate requirements of the cellular users would cause the power allocated to them by the base station to become larger, but this would cause the interference to the communications of the D2D users to become larger. Meanwhile, it can be seen that, by adding D2D users in a cell, the total traversal capacity (and rate) of the whole cell is greatly increased, and the spectrum efficiency of the cell is improved, especially when the minimum rate requirement of cellular users is low, the effect is more obvious.
FIG. 6 is
Figure BDA0002044695330000102
When the monte carlo number num is 100000 and the minimum rate requirement of the cellular user is 10bps/Hz, the relationship between the D2D traversal capacity, the cellular user traversal capacity and the total cell traversal capacity of the power allocation method of the present invention and the distance between the D2D users is plotted. When the minimum rate requirement of the cellular user is 10bps/Hz, the cellular user reaches the minimum rate requirement under the condition of different distances of D2D users, and the total traversal capacity (and rate) of the whole cell is greatly improved. As the distance between D2D users increases, the energy efficiency of D2D communications decreases, but as D2D users get closer together, the actual rate of D2D users even exceeds the actual rate of cellular users. The frequency spectrum efficiency of the cell is greatly improved while the communication quality of the cellular user is ensured.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims (4)

1. A D2D communication energy efficiency optimization method for guaranteeing QoS of a cellular mobile communication system, comprising the steps of:
(1) the base station with the D2D detection and mode selection functions schedules and selects downlink frequency band resources of one cellular user in a cell to be shared to a proper D2D user for direct device-to-device communication;
(2) a base station acquires real-time channel state information of a downlink transmission link and an interference link;
(3) the base station preferentially meets the service quality requirement of a cellular user according to the acquired real-time channel state information, and determines a power allocation scheme;
(4) the base station sends the power allocation scheme to the transmitting terminal of D2D, and the base station and the transmitting terminal of D2D complete data transmission according to the power allocation scheme in the step (3); the specific method for determining the power allocation scheme in the step (3) is as follows:
(3.1) to satisfy the communication quality of cellular user k, the base station performs power control when the transmission power satisfies the constraint condition
Figure FDA0003293478680000011
Then, the cellular user can reach the rate R under the power allocation schemekGreater than the minimum rate R required to guarantee its QoSCNamely:
Figure FDA0003293478680000012
wherein:
RCrepresents the minimum rate requirement to guarantee the communication quality of the cellular user;
v represents the fading state of the real-time channel;
Figure FDA0003293478680000013
representing a transmit power threshold of the base station to the cellular user;
Figure FDA0003293478680000014
represents the transmit power threshold of the D2D link;
pk(v) representing the transmission power of the base station to the cellular user k in the fading state v;
Figure FDA0003293478680000015
channel state information representing the transmission link between a base station and a cellular user k in a fading condition v
Figure FDA0003293478680000016
Wherein lkRepresenting the path loss, h, of the transmission link between the base station and the cellular subscriber kk(v) Represents the normalized channel gain, delta, of the transmission link between cellular user k and base station in fading condition vkRepresenting the variance of white gaussian noise in the communication link between the base station and the cellular user k;
pj(v) representing the transmitting power of the transmitting end of the D2D link j under the fading state v;
Figure FDA0003293478680000021
representing the interfering link channel state information of D2D link j to cellular user k in fading state v,
Figure FDA0003293478680000022
wherein ljkRepresents the path loss, g, of the interfering link of D2D link j to cellular user kjk(v) Represents the normalized channel gain, δ, of the D2D link j to the interfering link of cellular user k under the fading condition vjkRepresents the variance of the white gaussian noise in the interference link of the D2D link j to the cellular user k;
(3.2) the base station is ensuring that the cellular user reaches its minimum rate requirement RCOn the premise that the statistical energy efficiency eta of the D2D user is optimized, power distribution is carried out, and the expression of the energy efficiency is as follows:
Figure FDA0003293478680000023
wherein:
e { } represents a statistical average over different channel states v;
pj(v) representing the transmitting power of the transmitting end of the D2D link j in the fading state v;
ζ represents the power amplification factor at the transmit end of the D2D link,
Figure FDA0003293478680000024
representing D2D link circuit power consumption;
Figure FDA0003293478680000025
channel state information representing the transmission link of D2D link j in fading condition v
Figure FDA0003293478680000026
Wherein ljRepresents the path loss, h, of the transmission link of D2D Link jj(v) Represents the normalized channel gain, δ, of the D2D link j transmission link in the fading state vjRepresenting the variance of Gaussian white noise of the transmission link j of the D2D link;
pk(v) represents the transmission power allocated to a cellular user k by the base station in a fading state v;
Figure FDA0003293478680000027
channel state information representing an interfering link between a base station and a receiver of a D2D link j in a fading state v
Figure FDA0003293478680000028
Wherein lkjRepresents the path loss, g, of the interfering link between the base station and the receiver of the D2D link jkj(v) Represents the normalized channel gain, delta, of the interference link between the base station and the receiving end of the D2D link j under the fading state vkjRepresenting the variance of white gaussian noise of the base station to the D2D link interference link;
(3.3) energy-optimized objective function η (p)j(v) A nonlinear programming problem that translates to the following formula:
Figure FDA0003293478680000031
considering also the requirement of minimum rate for cellular users, so:
Figure FDA0003293478680000032
objective function f (p)j(v) Eta) and pk(v) Is inversely proportional, therefore
Figure FDA0003293478680000033
Time-energy efficiency is maximized, while the base station assigns a power expectation E { p to the cellular userk(v) Should be controlled not to exceed a threshold
Figure FDA0003293478680000034
Namely:
Figure FDA0003293478680000035
wherein the content of the first and second substances,
Figure FDA0003293478680000036
will be provided with
Figure FDA0003293478680000037
Substituting into the objective function, which can be proved to be a concave function, and solving by a Lagrange multiplier method;
(3.4) Power expectation E p assigned to cellular user by base station in view ofk(v) Should be controlled not to exceed a threshold
Figure FDA0003293478680000038
And the power expectations E p that the base station allocates to D2D usersj(v) Should be controlled not to exceed a threshold
Figure FDA0003293478680000039
The two constraints, introducing Lagrangian factors lambda and mu, are used for transforming the target function f (p)j(v) η) to:
Figure FDA00032934786800000310
Figure FDA0003293478680000041
wherein:
Figure FDA0003293478680000042
(3.5) As can be seen from the above formula, the objective function L (p)j(v) λ, μ) can be converted to the solution E { G' (v) };
since G' (v) has the same structure for each different fading state v, v in the expression is truncated, the objective function L (p)j(v) λ, μ) can be converted into:
Figure FDA0003293478680000043
when it is satisfied with
Figure FDA0003293478680000044
Conditional, power distribution scheme
Figure FDA0003293478680000045
Achieving an energy efficiency optimization goal η*；
(3.6) the power allocated to D2D users and cellular users is:
Figure FDA0003293478680000046
Figure FDA0003293478680000047
wherein the content of the first and second substances,
Figure FDA0003293478680000048
wherein A isj,k，Bj,k，Cj,kIs defined as:
Figure FDA0003293478680000049
Figure FDA00032934786800000410
Figure FDA0003293478680000051
2. the method of claim 1, wherein the step (1) is that in the cell of the cellular user, the base station uses a centralized radio resource management method to schedule and select a cellular user, and shares the frequency band resource of the cellular user to an appropriate D2D user pair for device-to-device communication.
3. The method for optimizing D2D communication energy efficiency for guaranteeing QoS in a cellular mobile communication system according to claim 1 or 2, wherein the D2D user is selected according to the following principles: it is required that the distance of the scheduled D2D link from the base station is larger than the distance of the cellular user from the base station, and there is also a certain distance between the D2D link and the cellular user sharing its frequency band resource.
4. The method as claimed in claim 3, wherein the D2D communication energy efficiency optimizing method for guaranteeing QoS of the cellular mobile communication system, in step (2), the base station obtains the real-time channel status information of the downlink link and the interfering link, and the method comprises: according to the cellular user selected by the base station in the step (1) and the corresponding D2D link, firstly, the cellular user carries out channel estimation to obtain the channel state information of a transmission link between the cellular user and the base station, and simultaneously obtains the channel state information of an interference link between the cellular user and a D2D transmitting end through the channel estimation, and then the channel information is quantized according to a codebook which is known by the cellular user and the base station, and the quantized channel information is fed back to the base station; meanwhile, the D2D user firstly performs channel estimation to obtain the channel state information of the transmission link between the D2D, and simultaneously obtains the channel state information of the interference link between the D2D receiving end and the base station through the channel estimation, and then quantizes the channel information according to the codebook known by the user and the base station, and feeds back the quantized channel information to the base station.
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