CN108809371B - Beam width optimization method and switching method in large-scale antenna system - Google Patents

Beam width optimization method and switching method in large-scale antenna system Download PDF

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CN108809371B
CN108809371B CN201810588248.2A CN201810588248A CN108809371B CN 108809371 B CN108809371 B CN 108809371B CN 201810588248 A CN201810588248 A CN 201810588248A CN 108809371 B CN108809371 B CN 108809371B
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beam width
user terminal
switching
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theta
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CN108809371A (en
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张天魁
耿立茹
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Beijing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0408—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas using two or more beams, i.e. beam diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
    • H04B7/0695—Hybrid systems, i.e. switching and simultaneous transmission using beam selection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0802—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection
    • H04B7/0834—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using antenna selection based on external parameters, e.g. subscriber speed or location
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0868—Hybrid systems, i.e. switching and combining
    • H04B7/088—Hybrid systems, i.e. switching and combining using beam selection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data

Abstract

The application relates to the technical field of wireless communication, in particular to a beam width optimization method and a switching method in a large-scale antenna system, which comprises the following steps: obtaining the data rate c and the effective beam width theta of the base station BSBSObtaining the angular difference delta α between the position of the user terminal UE and the position of the base station BS, determining the beam switching probability p according to the angular difference delta αswitchAnd a switching overhead m; constructing an objective function according to the data rate c and the switching cost m
Figure DDA0001689913570000011
Solving the objective function according to the constraint condition of the objective function to obtain the effective beam width theta of the next momentBSThe optimum value of (c). According to the method and the device, the influence of the movement speed of the mobile terminal UE on the beam switching overhead under a mobile scene is considered, the user data rate and the beam switching overhead are considered in a balanced manner, the ratio of the user data rate to the beam switching overhead is used as an optimization function, the effective beam width is obtained through maximum solution, the optimal beam width is realized, the switching times are reduced, and the compromise between the performance and the overhead is achieved.

Description

Beam width optimization method and switching method in large-scale antenna system
Technical Field
The invention relates to the technical field of wireless communication, in particular to a beam width optimization method and a switching method in a large-scale antenna system.
Background
In recent years, with the widespread use of smart phones and tablet computers, the traffic volume of various applications has increased dramatically, and mobile data applications have increased at an accelerated rate, which makes mobile communication systems cellular networks face significant challenges. However, the microwave band below 6GHz, which is widely used at present, cannot provide sufficient spectrum resources, and the system capacity limit cannot further meet the requirement of high-speed services, so the millimeter wave band of 30-300GHz is widely regarded. Although it implies rich available spectrum resources, it can relieve the pressure of scarcity of spectrum resources, and the millimeter wave band also has some inherent defects. The path loss of the millimeter wave is high and the penetration capability to obstacles is poor, so that the cell coverage is reduced. But this can be overcome by applying multi-antenna technology, and the high gain obtained by using beamforming technology can increase the area coverage, expand the system capacity and reduce the interference. Meanwhile, the short wavelength of the millimeter wave band is more beneficial to the deployment of large-scale antennas. In summary, a millimeter wave large-scale antenna (Massive MIMO) system is one of the key technologies for the next generation of mobile communication.
Because the path loss of the millimeter wave system is very large, both the transmitting and receiving sides need to use the beam forming technology, and the loss of the wireless link transmission is compensated by the high gain caused by the high-directivity beam alignment. However, in practice, the user may move anytime and anywhere. When a user terminal (UE) rotates or moves, the UE position and orientation may change, and the current serving beam is no longer aligned, so that the transmission quality is degraded, and even a link may be interrupted, which affects the system throughput and user experience. In order to reduce the loss caused by the movement of the UE, the conventional scheme mostly needs to perform periodic monitoring of the received signal, and when the detected amount is lower than a certain threshold, the appropriate receiving and transmitting beam pair is searched again, and the switching is performed before the current beam pair completely fails. Considering that the signal propagation distance of the millimeter wave system is short and the beam width is small, a slight movement of the UE may cause frequent handover, which may reduce the system capacity, increase the time delay, increase the overhead, and also affect the communication process.
Therefore, how to reduce the number of handovers on the basis of ensuring the system performance, achieve the optimal beam width, and achieve the compromise between performance and overhead is a technical problem that needs to be solved by those skilled in the art at present.
Disclosure of Invention
The application provides a beam width optimization method and a switching method in a large-scale antenna system, so that the switching times are reduced, the optimal beam width is realized, and compromise between performance and cost is achieved.
In order to solve the technical problem, the application provides the following technical scheme:
a method for optimizing beam width in a large-scale antenna system comprises the following steps: obtaining the data rate c and the effective beam width theta of the base station BSBSObtaining the angular difference delta α between the position of the user terminal UE and the position of the base station BS, determining the beam switching probability p according to the angular difference delta αswitchAnd handoverAn overhead m; constructing an objective function according to the data rate c and the switching cost m
Figure BDA0001689913550000021
Solving the objective function according to the constraint condition of the objective function to obtain the effective beam width theta of the next momentBSThe optimum value of (c).
The method for optimizing the beam width in the large-scale antenna system as described above, wherein it is preferable to obtain the data rate c and the effective beam width θ of the base station BSBSThe relation of (1) comprises the following steps: defining a half-power beamwidth as an effective beamwidth θBS(ii) a The beam width theta of a user terminal UEUEFix, the effective beam width theta of the base station BSBSAs a variable, and the transmission power PtAnd noise N is a constant value, the path loss P L is related to the distance between the user terminal UE and the base station BS, the path loss P L is regarded as a constant value under low-speed movement, and gamma in the simplified beam codebook model is regarded asdB＝Pt+Gt(θBS)+Gr(θUE) -P L-N reduced to γdB(θBS) (ii) a According to the absolute form of the signal-to-noise ratio gamma and the decibel form of the signal-to-noise ratio gammadBIs a relation of (a)dB10log γ, yielding γ (θ)BS) (ii) a According to data rate c log2(1+ γ) results in a data rate c log2(1+γ(θBS) ); wherein G istFor the beam gain of the base station BS, Gt(θBS) Represents GtIs at θBSAs a function of the argument; grFor the beam gain of the user terminal UE, Gr(θUE) Represents GrIs at θUEAs a function of the argument; gamma raydB(θBS) Represents gammadBIs at θBSAs a function of the argument; gamma (theta)BS) The representation of gamma is thetaBSAs a function of the argument.
The method for optimizing the beam width in the large-scale antenna system as described above, wherein preferably obtaining the angular difference Δ α between the positions of the user terminal UE and the base station BS at the previous and subsequent times comprises obtaining the distance between the user terminal UE and the base station BS at the previous timestObtaining the moving speed v of the user terminal UE, the included angle β between the moving direction of the user terminal UE and the horizontal outward extension designated direction of the base station BS at the previous moment, and the included angle α between the position of the user terminal UE and the base station BS at the previous moment in the designated directiont(ii) a Obtaining the distance between the user terminal UE and the base station BS at the later moment
Figure BDA0001689913550000022
Obtaining the included angle between the position of the user terminal UE and the position of the base station BS in the appointed direction at the later moment
Figure BDA0001689913550000023
The angular difference Δ α between the location of the UE and the location of the BS is αt+1-αt(ii) a According to the distance st+1Only the moving speed v of the user terminal UE, the included angle αt+1The obtained angle difference Δ α is a function of v as the argument, i.e., Δ α (v), where t is the designated time of the movement of the user terminal UE.
The beam width optimization method in a large-scale antenna system as described above, wherein the beam switching probability p is preferably determined according to the angle difference Δ αswitchAnd the switching overhead m comprises the step of if the angle difference a α is greater than the effective beam width θBSThen switching is carried out and the beam switching probability p is determinedswitchIs 1, if the angle difference delta α is less than the effective beam width thetaBSThen probability p of beam switchingswitchProportional to the angular difference Δ α, and the effective beam width θBSIn inverse proportion, determining the probability of beam switching
Figure BDA0001689913550000031
Obtaining the switching cost m proportional to the beam switching probability p according to the fact that the switching cost m required for executing one switching operation is a fixed valueswitchI.e. m (theta)BS,v)∝pswitch(θBSV); wherein p isswitch(θBSV) represents pswitchIs at θBSAnd v is a function of the argument, m (θ)BSV) m is θBSAnd v is a function of the argument.
The method for optimizing the beam width in the large-scale antenna system as described above, preferably, before constructing the objective function, further includes the following steps: set an optimization objective to
Figure BDA0001689913550000032
Determining constraint conditions s.t. gamma is more than or equal to TH and vt is less than d; wherein TH is the lowest threshold satisfying the link quality, d is the coverage of the base station BS.
The method for optimizing the beam width in the large-scale antenna system as described above, wherein preferably, the objective function is constructed according to the data rate c and the handover overhead m, and particularly, the optimization function is constructed according to the optimization objective
Figure BDA0001689913550000033
Is that
Figure BDA0001689913550000034
Figure BDA0001689913550000035
The method for optimizing the beam width in a large-scale antenna system as described above, wherein preferably solving the objective function according to the constraint condition comprises the steps of solving the objective function according to Δ α > θBSThe switching is performed with a constant switching overhead m, resulting in only the effective beam width θBSInfluence optimization function f (theta)BSV); then the effective beam width theta obtained when the signal-to-noise ratio gamma meets the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the later timeBSThe optimum value of (c).
The method for optimizing the beam width in the large-scale antenna system, as described above, wherein preferably solving the objective function according to the constraint condition comprises the following steps:
Δα＜θBStime, optimization function
Figure BDA0001689913550000036
Signal-to-noise ratio gamma in decibel formdBThe signal-to-noise ratio gamma of the alternative absolute form is obtained as an optimization function
Figure BDA0001689913550000037
According to
Figure BDA0001689913550000038
And gammadBObtained as 10log gamma
Figure BDA0001689913550000039
Will be provided with
Figure BDA00016899135500000310
Defined as a, will
Figure BDA00016899135500000311
Defined as b, and simplified by substituting the optimization function
Figure BDA00016899135500000312
Figure BDA00016899135500000313
According to the switching overhead m and the beam switching probability pswitchThe ratio k of (A) is a constant value; according to angle of vertical direction of beam
Figure BDA00016899135500000314
B is a constant value if the value is a constant value; according to thetaUEFixed, then Gr(θUE) Is constant and is according to PtN, P L is constant, then a is constant, get
Figure BDA00016899135500000315
Is a convex function;
solving according to the convex function to obtain the effective beam width theta of the later momentBSThe optimum value of (c).
A method for optimizing and switching beam width in a large-scale antenna system comprises the following steps: receiving motion data of a user terminal UE at the current moment; according toCalculating the position of the user terminal UE, the moving speed v and the moving direction of the current moment according to the motion data of the current moment, determining the signal-to-noise ratio of the beam at the position of the user terminal UE at the next moment according to the position of the user terminal UE, the moving speed v and the moving direction of the current moment, judging the angle difference delta α between the position of the user terminal UE at the previous moment and the position of the base station BS if the signal-to-noise ratio of the beam at the position of the next moment is less than a hard threshold, and judging the angle difference delta α if the angle difference delta α is less than the effectiveBSAccording to a convex function
Figure BDA0001689913550000041
Solving to obtain the effective beam width theta of the next momentBSWhere Δ α (v) is a function of the angular difference Δ α with respect to the argument v, and k is the switching overhead m and the beam switching probability pswitchThe ratio of (A) to (B) is a constant value;
Figure BDA0001689913550000042
wherein the beam width θ of the user terminal UEUEFixed, is a constant value, then Gr(θUE) Is constant, and the transmission power PtNoise N and path loss P L are constant values, then a is constant value;
Figure BDA0001689913550000043
in which the angle of the beam in the vertical direction
Figure BDA0001689913550000044
If it is constant, if pi is constant, then b is constant.
The method for optimizing and switching beam width in a large-scale antenna system as described above preferably further comprises the step of determining whether the angle difference Δ α is greater than the effective beam width θBSThen, the effective beam width theta obtained when the signal-to-noise ratio gamma meets the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the next timeBSThe optimum value of (c).
In contrast to the background art, the method for optimizing the beam width in the large-scale antenna system of the present invention includes: obtaining a data rate c and an effective beam width of a base station BSDegree thetaBSObtaining the angular difference delta α between the position of the user terminal UE and the position of the base station BS, determining the beam switching probability p according to the angular difference delta αswitchAnd a switching overhead m; constructing an objective function according to the data rate c and the switching cost m
Figure BDA0001689913550000045
Solving the objective function according to the constraint condition of the objective function to obtain the effective beam width theta of the next momentBSThe optimum value of (c). The beam width optimization method and the switching method in the large-scale antenna system are applied to the information center network, the influence of the movement speed of the mobile terminal UE on the beam switching overhead under a mobile scene is considered, and the relation between the beam width optimization method and the beam switching overhead is intuitively deduced; the user data rate and the beam switching cost are considered in a balance mode, the ratio of the user data rate to the beam switching cost is used as an optimization function, the optimal beam width is achieved through the effective beam width obtained through maximum solution, the switching times are reduced, and the compromise between the performance and the cost is achieved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings can be obtained by those skilled in the art according to the drawings.
Fig. 1 is a flowchart of a method for optimizing a beam width in a large-scale antenna system according to an embodiment of the present application;
fig. 2 is a schematic diagram of a beam model provided in an embodiment of the present application;
fig. 3 is a schematic diagram of a mobile scenario of a user equipment UE and a base station BS according to an embodiment of the present application;
fig. 4 is a schematic diagram of a mobile model of a UE and a BS according to an embodiment of the present disclosure;
fig. 5 is a flowchart of a method for beam width optimized handover in a large-scale antenna system according to an embodiment of the present application.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative only and should not be construed as limiting the invention.
As shown in fig. 1, the present application provides a method for optimizing a beam width in a large-scale antenna system, which includes the following steps:
step S110, obtaining the data rate c and the effective beam width theta of the base station BSBSThe relational expression of (1);
as shown in fig. 2, first, a beam is modeled. Regarding the range covered by the half-power beam width of the directional beam as the effective coverage range of the beam, regarding the effective coverage range of the beam as a sector, and regarding the angle of each sector as the effective beam width thetaBSAnd can cover all radiation ranges of the antenna, neglecting interference caused by overlapping of adjacent beams. The half-power beam width is 3dB beam width, half-power angle, and is a parameter for identifying a beam.
Then, solving the data rate c and the effective beam width theta through a beam modelBSThe relational expression (c) of (c). Please continue to refer to fig. 2, which is as follows:
in a single-user millimeter wave Massive MIMO system, the user data rate c is only related to the signal-to-noise ratio γ in the absolute form of reception, that is, the formula: c log2(1+γ) (1)；
Signal-to-noise ratio gamma in decibels in a simplified beam codebook modeldBCan be expressed as:
γdB＝Pt+Gt(θBS)+Gr(θUE)-PL-N (2)；
wherein, PtIs the transmission power of the base station BS; gtFor the beam gain of the base station BS, Gt(θBS) Represents GtIs at θBSAs a function of the argument; grFor the beam gain of the user terminal UE, Gr(θUE) Represents GrIs at θUEAs a function of the argument, P L the path loss, and N the noise.
Since the embodiment of the present application is a beam width optimization method provided based on optimizing the beam width on the BS side of the base station, the effective beam width θ on the BS side of the base station is obtainedBSAs a variable, the beam width on the user terminal UE side is regarded as constant, i.e., the beam width θ of the fixed user terminal UEUEThen, the beam width θ of the user terminal UE is usedUEAs a function of the argument Gr(θUEAlso constant.
Also, since the path loss P L is related to the distance between the user terminal UE and the base station BS, the distance between the user terminal UE and the base station BS at the current time and the distance between the user terminal UE and the base station BS at the next time may be considered unchanged under low-speed (based on the moving speed of the user terminal UE with respect to the transmission speed of the millimeter wave), i.e., the path loss P L is considered to be constant.
In conclusion, due to Gr(θUE) For the fixed value, the path loss P L is fixed value, and also due to the transmission power P of the base station BStAnd the noise N is also constant, the formula (2) is simplified to gammadBIs at θBSAs a function of the argument, i.e.: gamma raydB(θBS)。
According to the absolute form of the signal-to-noise ratio gamma and the decibel form of the signal-to-noise ratio gammadBIs a relation of (a)dBThe signal-to-noise ratio γ obtained in absolute form is also θ, 10log γBSAs a function of the argument, i.e. gamma (theta)BS) (ii) a According to data rate c log2(1+ gamma) obtaining the data rate c and the effective beam width theta of the base station BSBSThe relation of (A) is as follows:
c＝log2(1+γ(θBS)) (3)
referring to fig. 1, the method for optimizing the beam width in the large-scale antenna system further includes:
step S120, obtaining an angle difference delta α between the position of the user terminal UE at the previous moment and the position of the base station BS;
in a single-user millimeter wave Massive MIMO system, a base station BS is usually fixed, and a user terminal UE is mobile. And establishing a moving model according to the current time and the next time of the UE. Fig. 3 shows the current time and the next time of the UE, where the index i of the serving beam at the current time is known, and the index of the target beam at the next time is j, which can be derived by predicting the UE position at the next time, where i and j only play a role of identification. FIG. 4 illustrates a built movement model; abstracting a base station BS and a user terminal UE into a two-dimensional coordinate system; the base station BS is positioned at the origin O and is fixed in position; the user terminal UE is in a moving state, the point A is the position of the user terminal UE at the current moment, and the point B is the position of the user terminal UE at the next moment.
The position of the UE at the next time may be calculated from the distance between the UE and the BS at the current time, the moving direction of the UE, and the velocity of the UE. The distance between the user terminal UE and the base station BS, the moving direction of the user terminal UE and the speed of the user terminal UE at the current moment can be measured by sensors such as an accelerometer and a magnetic sensor built in the user terminal UE (such as a smart phone).
As shown in FIG. 4, first, the distance s between the UE and the BS at the current time is obtainedtI.e. stOA. As an example, the distance between the user terminal UE and the base station BS may be calculated by the round trip propagation time of the signal transmission. Compared with the 2.4/5GHz frequency band widely used in the traditional mobile communication, the millimeter wave frequency band is less likely to be diffracted by obstacles, so that the calculation result is more accurate.
Continuing to refer to FIG. 4, the moving speed v of the UE, the angle β between the moving direction of the UE and the horizontal outward-extending designated direction of the BS at the current moment, i.e. the angle between AB and the x-axis, and the angle between the position of the UE and the BS at the current momentDirectional included angle αtI.e. the angle between AO and the x-axis direction. As an example, the moving direction of the user terminal UE may be measured by a built-in sensor. The measurement results are typically composed of three dimensional parameters (X, Y, Z), where X is the angle of movement of the device relative to the north pole of the magnetic field, Y is the angle to the ground (Y is 90 degrees, indicating vertical), and Z represents the angular change of the device relative to its own coordinates (Z changes when the UE is rotated). Assuming that a user holds a user terminal UE (e.g. a smartphone) in hand while moving, the moving direction can be predicted by the X value. Even if the position of a user terminal UE (such as a smart phone) changes in the moving process of a user (such as the user puts the phone into a bag from the hand), angle calibration can be carried out through equipment such as a gyroscope, an accelerometer and the like. Finally, the measurement of the UE velocity can be directly obtained by the accelerometer.
Then, the distance s between the UE and the BS at the next time is obtainedt+1I.e. st+1BO. Point C is the intersection of line AB with the x-axis, and points D and E are the perpendicular point from point B to the x-axis and the perpendicular point from point O to line AB, respectively. Calculating to obtain DO ═ stsin(β-αt) And BD ═ vt-cos (β - α)t) And the distance between the UE and the BS at the next moment is as follows:
Figure BDA0001689913550000071
according to BE ═ BCsin β ═ vtsin β -stsinαtAnd obtaining an included angle between the position of the user terminal UE and the position of the base station BS in the appointed direction at the next moment, namely the included angle between the user terminal UE and the x axis at the next moment is as follows:
Figure BDA0001689913550000072
α according to the included angle between the current time position of the user terminal UE and the position of the base station BS in the designated directiontAnd the angle α between the UE position and the BS position in the specified direction at the next time pointt+1The angular difference between the position of the user terminal UE before and after the time and the position of the base station BS is obtained, wherein delta α is αt+1-αt(6)；
According to the distance st+1Only the moving speed v of the user terminal UE, the included angle αt+1The obtained angle difference Δ α is a function of v as the argument, i.e., Δ α (v), where t is a specified time of the movement of the user terminal UE and is a specified value introduced for research convenience, and the time value may be a predetermined value according to the requirement, for example, 1ms, 1s, 2s, and so on.
Continuing with fig. 1, step S130 determines the beam switching probability p according to the angle difference Δ αswitchAnd a switching overhead m. For example, first, a beam switching probability p is performedswitchAs a derivation of the effective beam width θBSIf the angle difference Δ α is greater, there is a possibility that the beam switching is not necessary, and the beam switching probability p is setswitchProportional to the angular difference Δ α, and the effective beam width θBSIn inverse proportion, determining the probability of beam switching
Figure BDA0001689913550000073
When the effective beam width is less than delta α and beam switching must be performed, the beam switching probability p is determinedswitchIs 1; the beam switching probability thus solved is:
Figure BDA0001689913550000074
obtaining the switching cost m proportional to the beam switching probability p according to the fact that the switching cost m required for executing one switching operation is a fixed valueswitchI.e. m (theta)BS,v)∝pswitch(θBS,v)；
Wherein p isswitch(θBSV) represents pswitchIs at θBSAnd v is a function of the argument, m (θ)BSV) m is θBSAnd v is a function of the argument.
Continuing with FIG. 1, step S140 constructs an objective function based on the data rate c and the handover cost m
Figure BDA0001689913550000081
In order to achieve compromise between user data rate c and switching overhead m, an optimization target is also set before an objective function is constructed, and the maximum value of the ratio of the data rate c to the switching overhead m is the optimization target, namely:
Figure BDA0001689913550000082
the constraint conditions s.t. gamma are more than or equal to TH and vt is less than d; (8)
the first constraint condition for the optimization target is that the signal-to-noise ratio gamma is greater than the lowest threshold TH meeting the link quality, namely gamma is greater than or equal to TH; and the second constraint condition is to ensure that the current time and the next time of the user terminal UE are in the coverage range of the same base station BS, namely vt is less than d, and d is the coverage range of the base station BS.
The embodiment of the application considers the moving speed v and the effective beam width theta of the user terminal UEBSTrade-off consideration of user data rate c and handover overhead m, objective function
Figure BDA0001689913550000083
Can be expressed as
Figure BDA0001689913550000084
Referring to fig. 1, in step S150, the objective function is solved according to the constraint condition of the objective function to obtain the effective beam width θ at the next timeBSThe optimum value of (c).
Due to the probability of handover pswitchIs a piecewise function, i.e. the switching cost m is a piecewise function, so the objective function is solved from the following two aspects:
(1) the angular difference delta α (v) between the position of the user terminal UE at the time before and after the time and the position of the base station BS is greater than the effective wave velocity width thetaBSWhen Δ α > θBSBeam switching operations must be performed, since the switching overhead m is constant, only the effective beam width θBSInfluence optimization function f (theta)BSV), i.e. the objective function is determined only by the transmission rate c, is only related to the signal-to-noise ratio γ, and requiresAnd the constraint condition is satisfied. Due to the effective beam width θBSThe smaller the user transmission rate c, the larger the user transmission rate c, and therefore, in this case, the constraint condition is satisfied, that is, the effective beam width θ obtained when the signal-to-noise ratio γ satisfies the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the next timeBSThe optimum value of (c).
(2) The angular difference Δ α (v) between the mobile terminal UE front and rear time position and the base station BS position is smaller than the effective beam width θBSWhen, namely, Delta α < thetaBSIn this case, the handover probability is less than 1, and the objective function is complex:
probability of handover pswitchThe direct ratio relation with the switching overhead m, namely the formula (7) is substituted into the formula (9) to obtain:
Figure BDA0001689913550000085
signal-to-noise ratio gamma in decibel formdBReplacing the signal-to-noise ratio γ in absolute form yields:
Figure BDA0001689913550000086
according to
Figure BDA0001689913550000087
And
Figure BDA0001689913550000088
obtaining a formula:
Figure BDA0001689913550000091
also according to gammadBThe formula is obtained by taking 10log γ and formula (12):
Figure BDA0001689913550000092
Figure BDA0001689913550000093
will be provided with
Figure BDA0001689913550000094
Defined as a, will
Figure BDA0001689913550000095
Defined as b, and is simplified by substituting into the objective function
Figure BDA0001689913550000096
Figure BDA0001689913550000097
According to the switching overhead m and the beam switching probability pswitchThe ratio k of (A) is a constant value; according to angle of vertical direction of beam
Figure BDA0001689913550000098
B is a constant value if the value is a constant value; according to thetaUEFixed, then Gr(θUE) Is constant and is according to PtN, P L is constant, then a is constant, get
Figure BDA0001689913550000099
Is a convex function; the objective function f (theta) can also be usedBSV) satisfaction of the entry into the convex function
Figure BDA00016899135500000910
Using independent variable theta simultaneouslyBSV replacement of the convex function satisfies the arguments x and y in the condition, further proving that the objective function f (θ)BSAnd v) is a convex function.
Since at Δ α < θBSTime, objective function f (theta)BSV) is a convex function, then the effective beam width theta at the next moment can be obtained by solving according to the convex functionBSThe optimal value of (2) can be specifically obtained by solving the optimal solution of the convex function according to the KKT condition, specifically by transforming the formula (8):
Figure BDA00016899135500000911
constraint s.t.h (a) ═ γ (θ)BS)-TH≥0
n(A)＝d-vt≥0 (15)
Wherein A is an independent variable thetaBSAnd v, h (A) and n (A) are constraints;
the lagrange function L under the inequality constraint is expressed as:
L(A，λ，μ)＝f(A)+λh(A)+μm(A) (16)
both λ and μ are constraint coefficients. The conditions to be satisfied are:
Figure BDA00016899135500000912
λ≥0
μ≥0
μn(A*)＝0
λh(A*)＝0
n(A)≥0 (17)
wherein A is*The value of a is given when h (a) ═ 0 and n (a) ═ 0.
As shown in fig. 5, the present application further provides a method for optimizing and switching beam width in a large-scale antenna system, which includes the following steps:
when the received signal-to-noise ratio is lower than the soft threshold, the user terminal UE collects the motion data of the user terminal UE at the current time, and can measure the motion data (the moving speed v, the moving direction and the like at the current time) of the user terminal UE according to a sensor (an accelerometer, a magnetic sensor and the like) built in the user terminal UE and report the measured motion data to the base station BS;
the base station BS receives the current moment motion data of the user terminal UE, and calculates the position of the user terminal UE at the current moment, the distance between the user terminal UE and the base station BS and the like according to the current moment motion data;
predicting the position of the user terminal UE at the next moment according to the position of the user terminal UE at the current moment, the moving speed v and the moving direction at the current moment, and then determining the signal-to-noise ratio of a beam at the position of the user terminal UE at the next moment;
if the signal-to-noise ratio of the beam of the user terminal UE at the position at the next moment is between the soft threshold and the hard threshold, the beam is not switched for the moment; if the signal-to-noise ratio of the beam at the position where the user terminal UE is located at the next moment is smaller than the hard threshold, a beam set to be switched can be generated firstly according to the predicted position, so that a proper beam is selected from the beam set to be switched according to the effective beam width calculated subsequently, and the technical effect of reducing the switching time is achieved; and sending the generated beam set to be switched and the information to be predicted to the user terminal UE.
Then, the user terminal UE calculates the angle difference delta α between the time position before and after the user terminal UE and the base station BS position, sends the calculated angle difference delta α to the base station BS, the base station BS judges the angle difference delta α between the time position before and after the user terminal UE and the base station BS position, and if the angle difference delta α is smaller than the effective beam width thetaBSAccording to a convex function
Figure BDA0001689913550000101
Solving to obtain the effective beam width theta of the next momentBSWhere Δ α (v) is a function of the angular difference Δ α with respect to the argument v, and k is the switching overhead m and the beam switching probability pswitchThe ratio of (A) to (B) is a constant value;
Figure BDA0001689913550000102
wherein theta isUEIs a constant value, Gr(θUE) Is a constant value, and PtN, P L is constant, then a is constant;
Figure BDA0001689913550000103
in which the angle of the beam in the vertical direction
Figure BDA0001689913550000104
If it is constant, b is constant.
On the basis of the above, if the angle difference Δ α is larger than the effective beam width θBSThen, the effective beam width theta obtained when the signal-to-noise ratio gamma meets the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the next timeBSThe optimum value of (c).
Calculating to obtain the effective beam width theta of the next momentBSAfter the optimum value of (c), can be based on the nextEffective beam width theta at timeBSThe optimal value of the beam switching value is to select a proper beam from the set of beams to be switched, execute the flow of beam switching, and finally end the operation.
The beam width optimization method and the switching method in the large-scale antenna system provided by the invention are applied to the information center network and have the following advantages:
1. the influence of the movement speed of the mobile terminal UE on the beam switching overhead under a mobile scene is considered, and a relational expression between the movement speed of the mobile terminal UE and the beam switching overhead is intuitively deduced;
2. the user data rate and the beam switching cost are considered in a balance mode, the ratio of the user data rate to the beam switching cost is used as an optimization function, the optimal beam width is achieved through the effective beam width obtained through maximum solution, the switching times are reduced, and the compromise between the performance and the cost is achieved.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims (5)

1. A method for optimizing beam width in a large-scale antenna system is characterized by comprising the following steps:
obtaining data rate c and baseEffective beamwidth θ of station BSBSIs log2(1+γ(θBS) Where γ (θ)BS) The representation of gamma is thetaBSAs a function of the argument;
obtaining an angle difference delta α between the time position before and after the user terminal UE and the position of the base station BS, wherein delta α is αt+1-αt，
Wherein, αt+1For the angle between the UE position and the BS position in the designated direction at the next moment,
Figure FDA0002492497820000011
Figure FDA0002492497820000012
αtthe included angle between the position of the user terminal UE and the position of the base station BS in the specified direction at the previous moment,
v is the moving speed of the user terminal UE, t is the designated time of the user terminal UE, β is the included angle between the moving direction of the user terminal UE and the designated direction extending horizontally outwards from the base station BS at the previous moment, stIs the distance, s, between the UE and the BS at the previous momentt+1For the distance between the user terminal UE and the base station BS at a later moment,
Figure FDA0002492497820000013
Figure FDA0002492497820000014
determining the beam switching probability p according to the angle difference delta αswitchAnd a switching overhead m of the network, and,
Figure FDA0002492497820000015
obtaining the switching cost m proportional to the beam switching probability p according to the fact that the switching cost m required for executing one switching operation is a fixed valueswitchI.e. m (theta)BS,v)∝pswitch(θBSV) wherein pswitch(θBsV) represents pswitchIs at θBSAnd vAs a function of the argument, m (θ)BSV) m is θBSAnd v is a function of the argument, Δ α (v) is a function of the angle difference Δ α with v as the argument;
set an optimization objective to
Figure FDA0002492497820000016
Determining constraint conditions s.t. gamma is more than or equal to TH and vt is less than d;
wherein, TH is the lowest threshold value which meets the link quality, d is the coverage of the base station BS; constructing an objective function according to the data rate c and the switching cost m
Figure FDA0002492497820000017
Is that
Figure FDA0002492497820000018
Solving the objective function according to the constraint condition of the objective function to obtain the effective beam width theta of the next momentBSIs determined to be the optimum value of (c),
Δα＜θBStime, optimization function
Figure FDA0002492497820000019
Signal-to-noise ratio gamma in decibel formdBThe signal-to-noise ratio gamma of the alternative absolute form is obtained as an optimization function
Figure FDA00024924978200000110
Figure FDA00024924978200000111
According to
Figure FDA00024924978200000112
And gammadBObtained as 10log gamma
Figure FDA00024924978200000113
Wherein, PtFor transmit power, N is noise, PtAnd N is a constant value, P L is a path loss, P L is related to the distance between the user terminal UE and the base station BS, and the path loss P L is considered as a constant value under low-speed movement, GtFor the beam gain of the base station BS, Gt(θBS) Represents GtIs at θBSAs a function of the argument; grFor the beam gain of the user terminal UE, Gr(θUE) Represents GrIs at θUEAs a function of the argument;
will be provided with
Figure FDA0002492497820000021
Defined as a, will
Figure FDA0002492497820000022
Defined as b, and simplified by substituting the optimization function
Figure FDA0002492497820000023
Figure FDA0002492497820000024
According to the switching overhead m and the beam switching probability pswitchThe ratio k of (A) is a constant value; according to angle of vertical direction of beam
Figure FDA0002492497820000025
B is a constant value if the value is a constant value; according to thetaUEFixed, then Gr(θUE) Is constant and is according to PtN, P L is constant, then a is constant, get
Figure FDA0002492497820000026
Is a convex function;
solving according to the convex function to obtain the effective beam width theta of the later momentBSThe optimum value of (c).
2. In the large-scale antenna system according to claim 1The method for optimizing the beam width is characterized in that the data rate c and the effective beam width theta of the base station BS are obtainedBSIs log2(1+γ(θBS) Comprises the following steps:
defining a half-power beamwidth as an effective beamwidth θBS；
The beam width theta of a user terminal UEUEFix, the effective beam width theta of the base station BSBSAs a variable, gamma in the simplified beam codebook modeldB＝Pt+Gt(θBS)+Gr(θUE) -P L-N reduced to γdB(θBS)；
According to the absolute form of the signal-to-noise ratio gamma and the decibel form of the signal-to-noise ratio gammadBIs a relation of (a)dB10log γ, yielding γ (θ)BS)；
According to data rate c log2(1+ γ) results in a data rate c log2(1+γ(θBS))；
Wherein, γdB(θBS) Represents gammadBIs at θBSAs a function of the argument.
3. The method for optimizing the beam width in the large-scale antenna system according to claim 1 or 2, wherein solving the objective function according to the constraint condition comprises the following steps:
according to Δ α > θBSThe switching is performed with a constant switching overhead m, resulting in only the effective beam width θBSInfluence optimization function f (theta)BS，v)；
Then the effective beam width theta obtained when the signal-to-noise ratio gamma meets the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the later timeBSThe optimum value of (c).
4. A method for optimizing and switching beam width in a large-scale antenna system is characterized by comprising the following steps:
receiving motion data of a user terminal UE at the current moment;
calculating the position of the user terminal UE, the moving speed v and the moving direction at the current moment according to the motion data at the current moment;
determining the signal-to-noise ratio of a beam at the position of the user terminal UE at the next moment according to the position of the user terminal UE at the current moment, the moving speed v and the moving direction at the current moment;
if the signal-to-noise ratio of the wave beam at the position of the next moment is less than the hard threshold, judging the angle difference delta α between the positions of the user terminal UE and the base station BS at the front and back moments;
if the angular difference Δ α is less than the effective beam width θBSAccording to a convex function
Figure FDA0002492497820000031
Solving to obtain the effective beam width theta of the next momentBSThe optimum value of (d);
wherein Δ α (v) is a function of the angular difference Δ α with respect to the argument v, and k is the switching overhead m and the beam switching probability pswttchThe ratio of (A) to (B) is a constant value;
Figure FDA0002492497820000032
wherein the beam width θ of the user terminal UEUEFixed, is a constant value, then Gr(θUE) Is a constant value, GrFor the beam gain of the user terminal UE, Gr(θUE) Represents GrIs at θUEAs a function of the argument, and the transmission power PtNoise N and path loss P L are constant values, then a is constant value;
Figure FDA0002492497820000033
in which the angle of the beam in the vertical direction
Figure FDA0002492497820000034
If it is constant, if pi is constant, then b is constant.
5. The method for beam width optimized handover in a massive antenna system according to claim 4, further comprising the steps of:
corner angleThe degree difference Δ α is greater than the effective beam width θBSThen, the effective beam width theta obtained when the signal-to-noise ratio gamma meets the minimum threshold TH of the link quality is solvedBSEffective beam width theta for the next timeBSThe optimum value of (c).
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