CN109743087B - Distributed antenna transmission mode selection and power optimization method in high-speed rail scene - Google Patents
Distributed antenna transmission mode selection and power optimization method in high-speed rail scene Download PDFInfo
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Abstract
The invention discloses a method for selecting a transmission mode and optimizing power of a distributed antenna in a high-speed rail scene, which comprises the following steps: s1, initializing a transmitting end power distribution strategy; s2, acquiring channel information by using the train position information; s3, carrying out selective operation according to the judgment condition, and optimizing the system energy efficiency if and only if the judgment condition is met; s4, solving an optimization problem according to a Lagrange multiplier method, and obtaining the relation between the system transmitting power and the Lagrange multiplier under various transmission modes at each moment; and S5, determining the transmission mode at each moment and maximizing the energy efficiency of the system. The invention not only meets the limitation of the system transmitting power and the time delay constraint, but also ensures the minimum speed requirement of the train at each moment, maximizes the system energy efficiency and has very high use and popularization values.
Description
Technical Field
The invention relates to a high-speed rail wireless mobile communication technical method, in particular to a distributed antenna transmission mode selection and power optimization method for improving system energy efficiency based on position information in a high-speed rail scene, and belongs to the technical field of wireless communication.
Background
In recent years, the technology of high-speed railways in China is rapidly developed. With the rapid popularization of the number of mobile users and the intelligent terminals, the wireless data service requirements of passengers are greatly increased, so that the current high-speed rail communication network is exposed to the problem of low energy efficiency. Under such a large background, how to improve the energy efficiency of the communication network becomes a problem to be solved urgently in order to research the new generation of railway wireless communication.
The distributed Antenna system is that a plurality of Remote Antenna Units (RAUs) are dispersedly deployed at a certain distance in a cell, and the RAUs serve users at the same time, so that good system coverage is formed, communication dead angles in the cell are solved, and communication service quality is improved. As a promising technology, a Distributed Antenna System (DAS) can be used to improve mobile communication service performance. In this case, the problem of maximizing system energy efficiency in a high-speed rail scenario can be solved by jointly optimizing distributed antenna transmission mode selection and time domain power allocation.
A search of prior art documents found that Hui Li et al published a text entitled "Energy Efficiency of Large Multi-Antenna Systems with Transmit Antenna Selection" in IEEE Transactions on Communications, Volume 62, Issue 2, Feb 2014, pp.638-647 (journal of the institute of Electrical and electronics Engineers, 2014 2, vol.62, 2 nd, pp.638-647). The article mainly proposes to improve the energy efficiency of the system through an antenna selection scheme at a transmitting end, however, the article does not consider a high-speed rail scene and does not realize power optimization. Jianxun Lu et al published a text entitled "Differential Service in HSR Communication Systems: Power Allocation and Antenna Selection in high-speed railway Communication Systems" in 201723 rd Asia-Pacific Conference on Communications (APCC),11-12Dec.2017 (23 rd Atai Communication Conference on 12.12.12.2017). The article reduces the power consumed by the system by jointly optimizing dynamic time domain power allocation and antenna selection, but the article does not realize the optimization of the energy efficiency of the system. Chuang Zhang et al published a text entitled "Optimal Power Allocation With Delay Constraint From Train to Base station for Signal Transmissions From Moving Train to Base Stations" in IEEE Transactions on Vehicular Technology Jan.2015, pp.5775-5788 (periodic published by the institute of Electrical and electronics Engineers, pp.5775-5788 in 2015.1). This article minimizes transmit power by matching data arrival rate at the access point to the wireless transmission rate, but does not achieve optimal system energy efficiency under the limitation of maximizing average power currently available.
It is found that Tao Li et al published a sentence entitled "Service-Oriented Power Allocation for High-Speed radio Wireless Communications" in IEEE Access May 2017, pp.8343-8356 (the society of Electrical and electronic Engineers, 5.2017, pages 8343-8356). This paper studies a quality of service based differentiated time domain power allocation algorithm to achieve the maximum achievable rate region for delay sensitive and delay insensitive flows. The disadvantage is that the time fairness problem is not considered. Yuhui Dong et al published a document entitled "A Dynamic Antenna Selection strategy based on the average channel gain of a Distributed Antenna System" in 20135 th IEEE International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications (the 5th IEEE International research conference on Microwave, Antenna, Propagation and EMC Technologies 2013). The article proposes a dynamic antenna selection strategy in a distributed antenna system, which can reduce the power of an antenna array and ensure the communication quality, but the article considers a static scene and has no great reference value for the technical realization in the dynamic scene.
In addition to the above literature, chinese patent publication No. CN103796294A was found in the search to introduce a method for increasing the channel capacity of DAS systems for DAS systems with frequency selective fading and shadow fading, but it does not consider optimizing the system energy efficiency through antenna selection. Chinese patent publication No. CN101459954 proposes a multi-antenna coordinated power allocation method suitable for a distributed antenna system, which can save the transmission power of a base station. But again, it suffers from the disadvantage of not optimizing system energy efficiency.
In summary, the prior art has many imperfections, and how to provide a new method related to the high-speed rail wireless mobile communication technology based on the prior art, so as to further improve the transmission efficiency and optimize the system energy efficiency, becomes a problem to be solved by researchers in the industry at present.
Disclosure of Invention
In view of the above-mentioned drawbacks in the prior art, an object of the present invention is to provide a method for selecting a transmission mode and optimizing power of a distributed antenna in a high-speed rail scenario, which includes the following steps:
s1, initializing a transmitting end power distribution strategy;
s2, acquiring channel information by using the train position information;
s3, carrying out selective operation according to the judgment condition, and optimizing the system energy efficiency if and only if the judgment condition is met;
s4, solving an optimization problem according to a Lagrange multiplier method, and obtaining the relation between the system transmitting power and the Lagrange multiplier under various transmission modes at each moment;
and S5, determining the transmission mode at each moment and maximizing the energy efficiency of the system.
Preferably, the plurality of transmission modes include a SIMO transmission mode and a MIMO transmission mode.
Preferably, S1 specifically includes the following steps:
the maximum power which can be provided by the transmitting terminal at each moment is Pmax, P (t) is the actual transmitting power of the system at the moment t,
when only one RAU is selected to provide service, namely in an SIMO transmission mode, wherein Ps (t) is P (t), and P (t) is less than or equal to Pmax, and Ps (t) is the actual transmission power of the system in the SIMO transmission mode at the time t;
when two RAUs are selected to provide service, namely in a MIMO transmission mode, Pm (t) is equal to P (t), and P (t) is less than or equal to Pmax, each RAU is allocated with power of Pm (t)/2, and Pm (t) is actual transmission power of a system in the MIMO transmission mode at the time t.
Preferably, S2 specifically includes the following steps:
the transmitting terminal obtains the real-time position information d of the train through the feedback of the GPS positioning sensor along the railway tracki，j(t)(i＝1、2，j＝1、2)，
Wherein j represents the jth RAU of the transmitting terminal, i represents the ith receiving relay on the train, and di，j(t) represents the distance from the jth RAU to the ith receiving relay, dr is the distance between adjacent RAUs, dh is the vertical distance from the RAU to the train track, dm is the distance between two mobile relays, and v is the running speed of the train;
then according to the formula
Calculating the channels from the jth RAU to the ith receiving relay at time t, wherein alpha is an element of [2, 5 ]]Representing the path loss factor.
Preferably, the judgment conditions in S3 include three conditions, which are:
a)P(t)≤Pmax，
b)C(t)≥Rmin(t)，
c)μs(t)＝λs(t)+1/τmax，
the condition a limits the total transmitting power which can be provided by a transmitting terminal of the train at each moment when the train passes through the RAUs coverage area;
condition b takes into account that the receiving rate of the train at each moment must meet its minimum rate requirement Rmin(t)，Rmin(t)＝BLμs(t), where B is the bandwidth, L is the average packet length, μs(t) is the service rate at time t;
condition c considers a delay constraint, where μs(t) denotes the service rate at time t, λs(t) data arrival rate at time t, τmaxIndicating the maximum delay allowed.
Preferably, S4 specifically includes the following steps:
solving the optimization problem according to the Lagrange multiplier method to obtain the power Ps(t) and Pm(t) and Lagrange multiplier λ1(t)、λ2(t) and the energy efficiency factor η (t) are in the following relationship,
Ps(t)＝B(1+λ2(t))/((η(t)+λ1(t))ln2)；
let X be (B (1+ lambda))2(t))(α1(t)α2(t)-β(t)2)-ln2N0(α1(t)+α2(t))(η(t)+λ1(t))，
Z＝(α1(t)α2(t)-β(t)2)ln2(η(t)+λ1(t))，
Then, Pm(t)＝(X+Y)/Z；
Wherein T belongs to [0, T/2], B is transmission bandwidth, N0 is Gaussian white noise power,
α1(t)＝h1，1(t)2+h2，1(t)2,α2(t)＝h1，2(t)2+h2，2(t)2，
β(t)＝h1，1(t)h1，2(t)+h2，1(t)h2，2(t)，
wherein λ is1(t) for constraining the system power at each instant to meet the maximum transmit power limit, λ, of the system2And (t) is used for restricting the receiving rate of the system at each moment to meet the requirement of the minimum rate of the train, and eta (t) is an energy efficiency factor for representing whether the system achieves the maximum energy efficiency.
Preferably, S5 specifically includes the following steps:
s51, initializing a group of Lagrange multipliers lambda1(t)、λ2(t) and η (t) are substituted into the formula of S4 to calculate P at that times(t) and Pm(t)；
S52, calculating the receiving rate in SIMO transmission mode and MIMO transmission mode respectively,
the calculation formula of the reception rate in the SIMO transmission mode is as follows,
Cs(t)＝Blog2(1+α2(t)Ps(t)/NO)；
the calculation formula of the reception rate in the MIMO transmission mode is as follows,
s53, respectively calculating the system energy efficiency under the SIMO transmission mode and the MIMO transmission mode,
the calculation formula of the system energy efficiency in the SIMO transmission mode is as follows,
Es(t)＝Cs(t)/(Ps(t)+Pc)；
the calculation formula of the system energy efficiency in the MIMO transmission mode is as follows,
Em(t)＝Cm(t)/(Pm(t)+Pc)；
where Pc represents the electric power consumed by the transmitting end;
s54, comparison Es(t) and Em(t) the size of the (t),
if Es(t)≥Em(t), the SIMO transmission mode is selected at that time, i.e., E (t) is Es(t)，C(t)＝Cs(t)，P(t)＝Ps(t)，
Otherwise, the MIMO transmission mode is selected at that moment, i.e. E (t) ═ Em(t)，C(t)＝Cm(t)，P(t)＝Pm(t)，
P (t), C (t) and E (t) represent the actual transmitting power, the actual receiving rate and the actual energy efficiency of the system at the moment t;
s55, comparing C (t) with Rmin(t) the size of the (t),
if C (t) is not less than Rmin(t), the next step is continued,
otherwise, updating lambda by a secondary gradient method2(t), return to S51 until updated λ2(t) satisfies the condition that C (t) ≥ Rmin(t), followed by the next step;
s56, comparing P (t) with PmaxThe size of (a) is (b),
if P (t) is less than or equal to PmaxThen, the next step is continued,
otherwise, updating lambda by a secondary gradient method1(t), go back to S51 until the updated Lagrangian multiplier satisfies C (t) ≧ Rmin(t) and P (t) is less than or equal to PmaxThen continuing to the next step;
s57, setting an optimal energy efficiency error threshold value, and judging whether | C (t) - η (t) (P (t) + Pc) | is in an error range, wherein | | is an absolute value sign,
if | C (t) - η (t) (P (t) + Pc) | <, the current energy efficiency value is the optimal energy efficiency,
otherwise, returning to S51 by updating eta (t) until | C (t) -eta (t) (P (t) + Pc) | <ismet, so that the system energy efficiency reaches the maximum value;
and S58, selecting the transmission mode and optimizing the power at the next moment, and returning to S51 until the transmission mode selection and the power optimization at each moment in [0, T/2] meet the conditions, and each moment of the system reaches the maximum energy value.
Compared with the prior art, the invention has the advantages that:
the distributed antenna transmission mode selection and power optimization method in the high-speed rail scene meets the limitation of system transmission power and time delay constraint, ensures the minimum speed requirement of a train at each moment, maximizes the system energy efficiency, remarkably improves the energy efficiency of a high-speed rail communication network, and has high use and popularization values.
In addition, the invention also provides reference for other related problems in the same field, can be expanded and extended on the basis of the reference, is applied to other related technical schemes of wireless mobile communication in the same field, and has very wide application prospect.
The following detailed description of the embodiments of the present invention is provided in connection with the accompanying drawings for the purpose of facilitating understanding and understanding of the technical solutions of the present invention.
Drawings
Fig. 1 is a model diagram of an antenna selection system in a high-speed rail scenario according to the present invention;
FIG. 2 is a graph comparing energy efficiency of the system at each instant of power control and no power control;
FIG. 3 is a graph of electrical power consumed versus average energy efficiency of the system in three different transmission modes;
FIG. 4 is a graph of the minimum train rate requirement versus the average energy efficiency of the system in three different transmission modes;
fig. 5 is a flowchart of the antenna selection and power optimization scheme for each time instant according to the present invention.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings, and the present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection authority of the present invention is not limited to the following embodiments.
In order to avoid large penetration loss, a two-hop transmission structure adopted by a high-speed rail communication system is shown in fig. 1, wherein transmitting ends RAUs are distributed at equal intervals, a train has 8 carriages in total, and a Mobile Relay (MR) is arranged at a head carriage and a tail carriage. Because the relative mobility of the mobile relay and the users in the carriage is very low in the running process of the train, and the communication transmission quality is high, the invention only discusses the transmission performance of the communication link from the base station to the mobile relay. After the train enters the RAUs coverage area, the position information can be fed back to the base station through the railway track line GPS positioning sensor, and since the invention only considers the time period of [0, T/2] (the position of the train when T is 0 and T is T/2 is drawn in fig. 1), the train can be regarded as running at a constant speed in the process.
Specifically, the method for selecting a transmission mode and optimizing power of a distributed antenna in a high-speed rail scene comprises the following steps:
and S1, initializing a transmitting end power allocation strategy.
And S2, acquiring channel information by using the train position information.
And S3, selectively operating according to the judgment condition, and optimizing the energy efficiency of the system if and only if the judgment condition is met.
And S4, solving the optimization problem according to the Lagrange multiplier method, and obtaining the relation between the system transmitting power and the Lagrange multiplier under various transmission modes at each moment.
And S5, determining the transmission mode at each moment and maximizing the energy efficiency of the system.
The multiple transmission modes in the technical scheme of the invention comprise a SIMO transmission mode and a MIMO transmission mode.
S1 specifically includes the following steps:
the maximum power which can be provided by the transmitting terminal at each moment is Pmax, P (t) is the actual transmitting power of the system at the moment t,
when only one RAU is selected to provide service, namely in the SIMO transmission mode, Ps (t) is P (t), and P (t) is less than or equal to Pmax, and Ps (t) is the actual transmission power of the system in the SIMO transmission mode at the time t.
When two RAUs are selected to provide service, namely in a MIMO transmission mode, Pm (t) is equal to P (t), and P (t) is less than or equal to Pmax, each RAU is allocated with power of Pm (t)/2, and Pm (t) is actual transmission power of a system in the MIMO transmission mode at the time t.
S2 specifically includes the following steps:
the transmitting terminal obtains the real-time position information d of the train through the feedback of the GPS positioning sensor along the railway tracki，j(t)(i＝1、2，j＝1、2)，
Wherein j represents the jth RAU of the transmitting terminal, i represents the ith receiving relay on the train, and di，j(t) represents the distance from the jth RAU to the ith receiving relay, dr is the distance between adjacent RAUs, dh is the vertical distance from the RAU to the train track, dm is the distance between two mobile relays, and v is the running speed of the train.
Then according to the formula
Calculating the channels from the jth RAU to the ith receiving relay at time t, wherein alpha is an element of [2, 5 ]]Representing the path loss factor.
The judgment conditions in S3 include three conditions, which are:
a)P(t)≤Pmax，
b)C(t)≥Rmin(t)，
c)μs(t)＝λs(t)+1/τmax，
the condition a limits the total transmitting power that can be provided by the transmitting end of the train at each moment when the train passes through the RAUs coverage area.
Condition b takes into account that the receiving rate of the train at each moment must meet its minimum rate requirement Rmin(t)，Rmin(t)＝BLμs(t), where B is the bandwidth, L is the average packet length, μsAnd (t) is the service rate at time t.
Condition c considers a delay constraint, where μs(t) represents tService rate of the moment, lambdas(t) data arrival rate at time t, τmaxIndicating the maximum delay allowed.
S4 specifically includes the following steps:
solving the optimization problem according to the Lagrange multiplier method to obtain the power Ps(t) and Pm(t) and Lagrange multiplier λ1(t)、λ2(t) and the energy efficiency factor η (t) are in the following relationship,
Ps(t)＝B(1+λ2(t))/((η(t)+λ1(t))ln2)。
let X be (B (1+ lambda))2(t))(α1(t)α2(t)-β(t)2)-ln2N0(α1(t)+α2(t))(η(t)+λ1(t))，
Z＝(α1(t)α2(t)-β(t)2)ln2(η(t)+λ1(t))，
Then, Pm(t)＝(X+Y)/Z。
Wherein T belongs to [0, T/2], B is transmission bandwidth, N0 is Gaussian white noise power,
α1(t)＝h1，1(t)2+h2，1(t)2,α2(t)＝h1，2(t)2+h2，2(t)2，
β(t)＝h1，1(t)h1，2(t)+h2，1(t)h2，2(t)，
wherein λ is1(t) for constraining the system power at each instant to meet the maximum transmit power limit, λ, of the system2And (t) is used for restricting the receiving rate of the system at each moment to meet the requirement of the minimum rate of the train, and eta (t) is an energy efficiency factor for representing whether the system achieves the maximum energy efficiency.
S5 specifically includes the following steps:
s51, initializing a group of Lagrange multipliers lambda1(t)、λ2(t) and η (t) into the formula of S4Calculating P in the equations(t) and Pm(t)。
S52, calculating the receiving rate in SIMO transmission mode and MIMO transmission mode respectively,
the calculation formula of the reception rate in the SIMO transmission mode is as follows,
Cs(t)＝Blog2(1+α2(t)Ps(t)/NO)。
the calculation formula of the reception rate in the MIMO transmission mode is as follows,
s53, respectively calculating the system energy efficiency under the SIMO transmission mode and the MIMO transmission mode,
the calculation formula of the system energy efficiency in the SIMO transmission mode is as follows,
Es(t)＝Cs(t)/(Ps(t)+Pc)。
the calculation formula of the system energy efficiency in the MIMO transmission mode is as follows,
Em(t)＝Cm(t)/(Pm(t)+Pc)。
where Pc denotes the electric power consumed by the transmitting end.
S54, comparison Es(t) and Em(t) the size of the (t),
if Es(t)≥Em(t), the SIMO transmission mode is selected at that time, i.e., E (t) is Es(t)，C(t)＝Cs(t)，P(t)＝Ps(t)，
Otherwise, the MIMO transmission mode is selected at that moment, i.e. E (t) ═ Em(t)，C(t)＝Cm(t)，P(t)＝Pm(t)，
Wherein, P (t), C (t) and E (t) represent the actual transmitting power, the actual receiving rate and the actual energy efficiency of the system at the time t.
S55, comparing C (t) with Rmin(t) the size of the (t),
if C (t) is not less than Rmin(t), the next step is continued,
otherwise, go toUpdating lambda by passing through gradient method2(t), return to S51 until updated λ2(t) satisfies the condition that C (t) ≥ Rmin(t), and then the next step is continued.
S56, comparing P (t) with PmaxThe size of (a) is (b),
if P (t) is less than or equal to PmaxThen, the next step is continued,
otherwise, updating lambda by a secondary gradient method1(t), go back to S51 until the updated Lagrangian multiplier satisfies C (t) ≧ Rmin(t) and P (t) is less than or equal to PmaxAnd then proceeds to the next step.
S57, setting an optimal energy efficiency error threshold value, and judging whether | C (t) - η (t) (P (t) + Pc) | is in an error range, wherein | | is an absolute value sign,
if | C (t) - η (t) (P (t) + Pc) | <, the current energy efficiency value is the optimal energy efficiency,
otherwise, by updating eta (t) and returning to S51 until | C (t) -eta (t) (P (t) + Pc) | <issatisfied, the system energy efficiency is maximized.
And S58, selecting the transmission mode and optimizing the power at the next moment, and returning to S51 until the transmission mode selection and the power optimization at each moment in [0, T/2] meet the conditions, and each moment of the system reaches the maximum energy value.
In this embodiment, the RAUs obtain the minimum speed requirement of the train from the feedback of the access point inside the car, and the packets sent by the RAUs are first transmitted to the mobile relays, and then each relay transmits the information to all users of the car through the access point inside the car. According to the scheme for selecting the transmission mode and optimizing the power of the distributed antenna, the transmission mode with higher energy efficiency is selected at each moment, then power optimization is carried out, the energy efficiency of the system at each moment is maximized, and therefore the total system energy efficiency of a train in [0, T/2] is maximized.
The simulation parameters are shown in the following table:
TABLE I simulation scenario principal parameters
| Parameter(s) | Definition of | Value taking |
| dr | The separation distance between two adjacent RAUs | 1000m |
| dm | Distance separating two relays | 400m |
| dh | Perpendicular distance of RAU to track | 50m |
| P | Total power of transmitting base station | 40w |
| σ2 | Noise power | 2×10-11w |
| α | Path loss factor | 3.8 |
| υ | Speed of train | 139m/s |
| B | Bandwidth of | 1Hz |
| L | Average packet length | 0.01bit/Hz |
| τmax | Maximum allowed delay | 10ms |
As shown in fig. 2, the energy efficiency of the system obtained by the scheme proposed by the present invention is greater at each time than when the power is not constrained, and since it is considered that the channel condition is first better and then worse in the process of moving the train from the central position of two RAUs to the next RAU, it can be seen that the maximum energy efficiency of the system is also greater at the time when the channel condition is better.
As shown in fig. 3, as the electric power consumed by the transmitting end increases, the average maximum energy efficiency of the system obtained by the SIMO transmission mode, the MIMO transmission mode and the scheme proposed by the other invention decreases gradually in a period of time, and decreases rapidly first and then slowly.
As shown in fig. 4, as the minimum speed requirement of the train increases, the average maximum energy efficiency of the system obtained by the SIMO transmission mode, the MIMO transmission mode and the scheme proposed by the present invention in a period of time gradually decreases, and decreases slowly first and then decreases quickly.
In the distributed antenna transmission mode selection and power optimization method in the high-speed rail scene, during specific operation, after a transmitting terminal RAUs obtains position information fed back by a GPS positioning sensor along a railway track, channel information of different transmission modes at each moment is calculated; and solving the optimization problem by a Lagrange multiplier method to obtain the relation between the emission power of two transmission mode (SIMO and MIMO) systems and the Lagrange multiplier at each moment. Initializing a group of Lagrange multipliers and energy efficiency factors to be substituted into a power expression to obtain corresponding receiving rate and system energy efficiency, then comparing energy efficiency values obtained by different transmission modes calculated at each moment, and selecting a transmission mode with higher energy efficiency as a transmission mode of the current system; and the system meets the constraint of the transmitting power and the receiving rate by updating the Lagrange multiplier, and the maximum energy efficiency value of the system at the moment is obtained by updating the energy efficiency factor. The scheme not only meets the limitation of the transmitting power and the time delay constraint of the system, but also ensures the minimum speed requirement of the train at each moment, maximizes the energy efficiency of the system, obviously improves the energy efficiency of a high-speed rail communication network, and has very high use and popularization values.
In addition, the invention also provides reference for other related problems in the same field, can be expanded and extended on the basis of the reference, is applied to other related technical schemes of wireless mobile communication in the same field, and has very wide application prospect.
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, and any reference signs in the claims are not intended to 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 selecting a transmission mode and optimizing power of a distributed antenna in a high-speed rail scene is characterized by comprising the following steps:
s1, initializing a transmitting end power distribution strategy;
s2, acquiring channel information by using the train position information;
s3, carrying out selective operation according to the judgment condition, and optimizing the system energy efficiency if and only if the judgment condition is met;
s4, solving an optimization problem according to a Lagrange multiplier method, and obtaining the relation between the system transmitting power and the Lagrange multiplier under various transmission modes at each moment;
s5, determining a transmission mode at each moment and maximizing system energy efficiency;
s1 specifically includes the following steps:
the maximum power which can be provided by the transmitting terminal at each moment is Pmax, P (t) is the actual transmitting power of the system at the moment t,
when only one RAU is selected to provide service, namely in an SIMO transmission mode, wherein Ps (t) is P (t), and P (t) is less than or equal to Pmax, and Ps (t) is the actual transmission power of the system in the SIMO transmission mode at the time t;
when two RAUs are selected to provide service, namely in a MIMO transmission mode, wherein Pm (t) is equal to P (t), and P (t) is less than or equal to Pmax, each RAU is allocated with power of Pm (t)/2, and Pm (t) is actual transmission power of a system in the MIMO transmission mode at time t;
s2 specifically includes the following steps:
the transmitting terminal obtains the real-time position information d of the train through the feedback of the GPS positioning sensor along the railway tracki，j(t)(i＝1、2，j＝1、2)，
Wherein j represents the jth RAU of the transmitting terminal, i represents the ith receiving relay on the train, and di，j(t) represents the distance from the jth RAU to the ith receiving relay, dr is the distance between adjacent RAUs, dh is the vertical distance from the RAU to the train track, dm is the distance between two mobile relays, and v is the running speed of the train;
then according to the formula
Calculating the channels from the jth RAU to the ith receiving relay at time t, wherein alpha is an element of [2, 5 ]]Representing the path loss factor.
2. The method of claim 1, wherein the method for distributed antenna transmission mode selection and power optimization in a high-speed rail scene comprises: the plurality of transmission modes include a SIMO transmission mode and a MIMO transmission mode.
3. The method according to claim 1, wherein the determination condition in S3 includes three conditions, which are respectively:
a)P(t)≤Pmax，
b)C(t)≥Rmin(t)，
c)μs(t)＝λs(t)+1/τmax，
the condition a limits the total transmitting power which can be provided by a transmitting terminal of the train at each moment when the train passes through the RAUs coverage area;
condition b takes into account that the receiving rate of the train at each moment must meet its minimum rate requirement Rmin(t)，Rmin(t)＝BLμs(t), where B is the bandwidth, L is the average packet length, μs(t) is the service rate at time t;
condition c considers a delay constraint, where μs(t) denotes the service rate at time t, λs(t) data arrival rate at time t, τmaxIndicating the maximum delay allowed.
4. The method for selecting the transmission mode and optimizing the power of the distributed antenna in the high-speed rail scene according to claim 3, wherein S4 specifically includes the following steps:
solving the optimization problem according to the Lagrange multiplier method to obtain the power Ps(t) and Pm(t) and Lagrange multiplier λ1(t)、λ2(t) and the energy efficiency factor η (t) are in the following relationship,
Ps(t)＝B(1+λ2(t))/((η(t)+λ1(t))ln2)；
let X be (B (1+ lambda))2(t))(α1(t)α2(t)-β(t)2)-ln2N0(α1(t)+α2(t))(η(t)+λ1(t))，
Z＝(α1(t)α2(t)-β(t)2)ln2(η(t)+λ1(t))，
Then, Pm(t)＝(X+Y)/Z；
Wherein T belongs to [0, T/2], B is transmission bandwidth, N0 is Gaussian white noise power,
α1(t)＝h1，1(t)2+h2，1(t)2，α2(t)＝h1，2(t)2+h2，2(t)2，β(t)＝h1，1(t)h1，2(t)+h2，1(t)h2，2(t)，
wherein λ is1(t) for constraining the system power at each instant to meet the maximum transmit power limit, λ, of the system2And (t) is used for restricting the receiving rate of the system at each moment to meet the requirement of the minimum rate of the train, and eta (t) is an energy efficiency factor for representing whether the system achieves the maximum energy efficiency.
5. The method for distributed antenna transmission mode selection and power optimization in a high-speed rail scene according to claim 4, wherein S5 specifically includes the following steps:
s51, initializing a group of Lagrange multipliers lambda1(t)、λ2(t) and η (t) are substituted into the formula of S4 to calculate P at that times(t) and Pm(t)；
S52, calculating the receiving rate in SIMO transmission mode and MIMO transmission mode respectively,
the calculation formula of the reception rate in the SIMO transmission mode is as follows,
Cs(t)＝Blog2(1+α2(t)Ps(t)/N0)；
the calculation formula of the reception rate in the MIMO transmission mode is as follows,
s53, calculating the system energy efficiency in the SIMO transmission mode and the MIMO transmission mode, respectively, wherein the calculation formula of the system energy efficiency in the SIMO transmission mode is as follows,
Es(t)＝Cs(t)/(Ps(t)+Pc)；
the calculation formula of the system energy efficiency in the MIMO transmission mode is as follows,
Em(t)＝Cm(t)/(Pm(t)+Pc)；
where Pc represents the electric power consumed by the transmitting end;
s54, comparison Es(t) and Em(t) the size of the (t),
if Es(t)≥Em(t), the SIMO transmission mode is selected at that time, i.e., E (t) is Es(t)，C(t)＝Cs(t)，P(t)＝Ps(t)，
Otherwise, the MIMO transmission mode is selected at that moment, i.e. E (t) ═ Em(t)，C(t)＝Cm(t)，P(t)＝Pm(t)，
P (t), C (t) and E (t) represent the actual transmitting power, the actual receiving rate and the actual energy efficiency of the system at the moment t;
s55, comparing C (t) with Rmin(t) the size of the (t),
if C (t) is not less than Rmin(t), the next step is continued,
otherwise, updating lambda by a secondary gradient method2(t), return to S51 until updated λ2(t) satisfies the condition that C (t) ≥ Rmin(t), followed by the next step;
s56, comparing P (t) with PmaxThe size of (a) is (b),
if P: (t)≤PmaxThen, the next step is continued,
otherwise, updating lambda by a secondary gradient method1(t), go back to S51 until the updated Lagrangian multiplier satisfies C (t) ≧ Rmin(t) and P (t) is less than or equal to PmaxThen continuing to the next step;
s57, setting an optimal energy efficiency error threshold value, and judging whether | C (t) - η (t) (P (t) + Pc) | is in an error range, wherein | | is an absolute value sign,
if | C (t) - η (t) (P (t) + Pc) | <, the current energy efficiency value is the optimal energy efficiency,
otherwise, returning to S51 by updating eta (t) until | C (t) -eta (t) (P (t) + Pc) | <ismet, so that the system energy efficiency reaches the maximum value;
and S58, selecting the transmission mode and optimizing the power at the next moment, and returning to S51 until the transmission mode selection and the power optimization at each moment in [0, T/2] meet the condition, and each moment of the system reaches the maximum energy value, wherein T represents a moment limit.
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