WO2019007134A1 - 无线接入点的切换方法、装置以及列车 - Google Patents

无线接入点的切换方法、装置以及列车 Download PDF

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Publication number
WO2019007134A1
WO2019007134A1 PCT/CN2018/083537 CN2018083537W WO2019007134A1 WO 2019007134 A1 WO2019007134 A1 WO 2019007134A1 CN 2018083537 W CN2018083537 W CN 2018083537W WO 2019007134 A1 WO2019007134 A1 WO 2019007134A1
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Prior art keywords
wireless access
access point
time window
wireless
window factor
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PCT/CN2018/083537
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English (en)
French (fr)
Inventor
王文松
王发平
周全
吕姝慧
李波波
周清
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比亚迪股份有限公司
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Publication of WO2019007134A1 publication Critical patent/WO2019007134A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/08—Reselecting an access point

Definitions

  • the present invention relates to the field of wireless communications, and in particular, to a method, an apparatus, and a train for switching a wireless access point.
  • Vehicle-to-ground wireless communication in urban rail transit signals and communication systems usually uses a communication system such as WLAN (Wireless Local Area Network) or LTE (Long Term Evolution) to establish a series of wireless APs along the track.
  • WLAN Wireless Local Area Network
  • LTE Long Term Evolution
  • each wireless AP next to the track constitutes a ground communication network through a communication cable
  • an in-vehicle wireless AP is set as a mobile terminal on the train, and the train passes the AP and the AP at the track in the running process.
  • Wireless communication is established to realize the function of wireless communication of the vehicle.
  • the process of switching between the wireless access points in the wireless communication of the vehicle is generally as follows: the vehicle AP detects the network information of the plurality of wireless APs that are closer to the trackside and judges Whether the signal strength of the first AP currently associated with the network site is lower than the network signal strength threshold, and if so, searching for the MAC of each AP of the multiple APs in a MAC (Media Access Control) address mapping table Corresponding geographical location information, and determining, according to the geographic location information corresponding to each AP, a plurality of second APs whose in-vehicle APs are close to each other in the mobile process, and switching the network sites from the first AP to the plurality of second The second AP with the strongest network signal strength in the AP.
  • MAC Media Access Control
  • the current problem is that there are more and more corners on the ground part of the rail transit, and more and more buildings are added near the track after the line is running.
  • the point threshold or the dynamic point threshold is used as the basis for the switching.
  • the ping-pong effect of the switching is likely to occur, resulting in Repeated switching reduces the stability of the handover and increases the latency and error probability of wireless communication.
  • the object of the present invention is to solve at least one of the above technical problems to some extent.
  • a first object of the present invention is to propose a method of switching a wireless access point.
  • the method can effectively avoid the ping-pong effect problem of the wireless AP switching of the vehicle after the line AP signal coverage is enhanced, which greatly shortens the switching time and improves the reliability of the signal link.
  • a second object of the present invention is to provide a switching device for a wireless access point.
  • a third object of the invention is to propose a train.
  • a method for switching a wireless access point includes: detecting a plurality of wireless access points to be connected located around a vehicle-mounted wireless access point; determining current wireless connection with the vehicle Entering a link-connected wireless AP with a communication connection at the in-point; acquiring a first signal strength value of each to-be-connected wireless access point within a preset time, and acquiring the currently-built link wireless connection within the preset time a second signal strength value of the ingress point; calculating, according to the first signal strength value of each of the to-be-connected wireless access points, the first time window factor of each of the to-be-connected wireless access points; The second signal strength value calculates a second time window factor of the currently-established linked wireless access point; and according to the second time window factor and the first time window factor of each of the to-be-connected wireless access points, Determining, from the plurality of to-be-connected wireless access points, a target wireless access point to be connected; and
  • the method further includes: determining whether there is currently a communication connection with the in-vehicle wireless access point a wireless access point; if yes, determining the first wireless access point as the currently-established linked wireless access point; if not, acquiring each to-be-connected wireless access in the preset time
  • the first signal strength value of the point; the first time window factor of each of the to-be-connected wireless access points is separately calculated according to the first signal strength value of each wireless access point to be connected within the preset time;
  • the first time window factor selects a to-be-connected wireless access point having a maximum first time window factor from the plurality of to-be-connected wireless access points; and the to-be-connected wireless access having the largest first time window factor
  • the point is the wireless access point to be connected as the target.
  • a first time window factor of each of the to-be-connected wireless access points including: for each wireless connection to be connected Pointing, using a preset time window function, fitting the first signal intensity value in the preset time time to a first line equation; calculating a first slope of the first line equation, and the first The slope is taken as the first time window factor.
  • the calculating, according to the second signal strength value, the second time window factor of the currently-built link wireless access point comprising: fitting the second signal strength value in the preset time by using a preset time window function Forming a second straight line equation; calculating a second slope of the second straight line equation and using the second slope as the second time window factor.
  • the preset time window function is expressed as follows:
  • y is the signal strength value within the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • Determining, according to the second time window factor and the first time window factor of each of the to-be-connected wireless access points, the target to be connected to the wireless access point comprising: determining whether the second time window factor is a negative value; If the second time window factor is a negative value, further determining whether an absolute value of the second time window factor is smaller than an average value of the first time window factor of each of the to-be-connected wireless access points; if yes, Selecting a wireless access point to be connected with the largest first time window factor among the plurality of to-be-connected wireless access points; and connecting the wireless access point to be connected with the largest first time window factor as the target to be connected Wireless access point.
  • the method for filtering the time window factor can solve the problem that the loop straddle monorail can be reliably switched under a small turning radius, thereby effectively avoiding the wireless AP signal coverage enhancement.
  • the ping-pong effect of the car's wireless AP switching in the clubhouse greatly shortens the switching time and improves the reliability of the signal link.
  • a switching device for a wireless access point includes: a detecting module, configured to detect a plurality of wireless access points to be connected located around an in-vehicle wireless access point; a module, configured to determine a currently-established link wireless access point that is currently in communication connection with the in-vehicle wireless access point; and an acquiring module, configured to acquire a first signal strength of each to-be-connected wireless access point within a preset time And obtaining a second signal strength value of the currently-established link wireless access point in the preset time; the first calculating module is configured to: each wireless access point to be connected according to the preset time a first signal strength value, respectively calculating a first time window factor of each of the to-be-connected wireless access points; and a second calculating module, configured to calculate the currently-built link wireless access according to the second signal strength value a second time window factor of the point; the second determining module is configured to use the plurality of to-be-connected
  • the switching device of the wireless access point further includes: a determining module, configured to determine whether there is currently a first wireless access point that has a communication connection with the in-vehicle wireless access point; the first determining module is further used to When the determining module determines that there is a first wireless access point that has a communication connection with the in-vehicle wireless access point, determining the first wireless access point as the currently-established linked wireless access point.
  • the second determining module is further configured to: when the determining module determines that there is no first wireless access point that has a communication connection with the in-vehicle wireless access point, according to the first time of each of the to-be-connected wireless access points a window factor, selecting, from the plurality of to-be-connected wireless access points, a wireless access point to be connected having a maximum first time window factor as the target wireless access point to be connected.
  • the first calculating module is specifically configured to: for each wireless access point to be connected, use a preset time window function to fit the first signal strength value in the preset time period to a first linear equation; a first slope of the first line equation and the first slope as the first time window factor.
  • the second calculating module is specifically configured to: fit a second signal strength value in the preset time to a second linear equation by using a preset time window function; calculate a second slope of the second linear equation, And using the second slope as the second time window factor.
  • the preset time window function is expressed as follows:
  • y is the signal strength value in the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • the second determining module includes: a first determining unit, configured to determine whether the second time window factor is a negative value; and a second determining unit, configured to further determine when the second time window factor is a negative value Whether the absolute value of the second time window factor is smaller than an average value of the first time window factor of each of the to-be-connected wireless access points; and the selecting unit is configured to: the absolute value of the second time window factor is less than the When the average value of the first time window factor of each wireless access point to be connected is selected, the wireless access point to be connected having the largest first time window factor is selected from the plurality of to-be-connected wireless access points; The wireless AP to be connected having the largest first time window factor is used as the target wireless access point to be connected.
  • the method for filtering the time window factor can solve the problem that the loop straddle monorail can be reliably switched under a small turning radius, thereby effectively avoiding the wireless AP signal coverage enhancement.
  • the ping-pong effect of the car's wireless AP switching in the clubhouse greatly shortens the switching time and improves the reliability of the signal link.
  • At least one in-vehicle wireless access point is provided on the train, and the in-vehicle wireless access point is used to perform the first embodiment of the present invention. How to switch wireless access points.
  • FIG. 1 is a flowchart of a method for handover of a wireless access point according to an embodiment of the present invention
  • FIG. 2 is a diagram showing an example of a time window factor model of a trackside to-be-connected wireless AP, in accordance with an embodiment of the present invention
  • FIG. 3 is a diagram showing an example of a time window factor model of a link-side wireless AP currently being built in a trackside according to an embodiment of the present invention
  • FIG. 4 is a flowchart of a method for switching a wireless access point according to another embodiment of the present invention.
  • FIG. 5 is a diagram showing an example of a vehicle-ground wireless AP link according to an embodiment of the present invention.
  • FIG. 6 is a schematic structural diagram of a switching apparatus of a wireless access point according to an embodiment of the present invention.
  • FIG. 7 is a schematic structural diagram of a switching apparatus of a wireless access point according to another embodiment of the present invention.
  • the method for switching a wireless access point in the embodiment of the present invention is applicable to the switching device of the wireless access point in the embodiment of the present invention.
  • the switching device can be configured in the train.
  • the switching device can be an in-vehicle line access point disposed in the train.
  • the method for switching the wireless access point of the embodiment of the present invention can be described from the side of the in-vehicle line access point.
  • the method for switching the wireless access point may include:
  • the broadcast information can be transmitted to the in-vehicle wireless AP by means of broadcast, and the wireless AP located around the in-vehicle wireless AP can feed back the corresponding information when receiving the broadcast information, and the feedback information can be It is known which wireless APs currently located around the in-vehicle wireless AP can be connected.
  • the wireless AP can be determined whether there is currently a wireless AP connected to the in-vehicle wireless AP, and if so, the wireless AP is used as the currently-connected wireless AP.
  • the RSSI (Received Signal Strength Indication) value of each of the to-be-connected wireless APs in the preset time is obtained, and the RSSI value of the currently-established linked wireless AP in the preset time is obtained.
  • the preset time may be determined according to actual application requirements, for example, the preset time may be 50 milliseconds.
  • S140 Calculate, according to the first signal strength value of each to-be-connected wireless AP in a preset time, a first time window factor of each to-be-connected wireless AP.
  • a preset time window function may be used to fit the first signal strength value in the preset time period to the first line equation, and A first slope K F of the first line equation is calculated, and a first slope K F is taken as the first time window factor.
  • the preset time window function may be expressed as follows:
  • y is the signal strength value within the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • multiple time instants may be selected for the preset time period, wherein the duration between each time is the same, and then the signal strength value corresponding to each time is determined and utilized.
  • a preset time window function using the plurality of times as the abscissa and the signal intensity value corresponding to the plurality of times as the ordinate, performing linear fitting to obtain a corresponding line equation, and then obtaining the line equation
  • the slope is, and the slope is the first time window factor of the wireless AP to be connected.
  • the train is driving into a certain area
  • the wireless AP located in the area should be the wireless AP to be connected
  • the wireless APs to be connected are about to establish a connection with the in-vehicle AP in the train, that is, the preset time period
  • the signal strength values of the wireless APs to be connected should be gradually increased. Therefore, the time window factor of the wireless AP to be connected should be calculated as a positive number. For example, as shown in FIG. 2, for the time window factor model of the wireless AP to be connected to the track, it can be seen that the signal strength value of the wireless AP to be connected in the preset time period is gradually increased, so the calculated
  • the time window factor (ie, the slope K F as shown in FIG. 2 ) to be connected to the wireless AP is a positive number.
  • the second signal strength value in the preset time may be fitted to the second linear equation by using a preset time window function, and the second slope of the second linear equation is calculated. And using the second slope as the second time window factor.
  • the preset time window function may be expressed as follows:
  • y is the signal strength value within the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • the preset time period may be selected by using a plurality of moments, wherein the durations between the moments are the same, and then determining the signal strength value corresponding to each moment, and using a preset time window function, The plurality of times are used as the abscissa and the signal intensity values corresponding to the plurality of times are used as the ordinate, and linear fitting is performed to obtain a corresponding straight line equation. Then, the slope K B of the line equation can be obtained, and the slope is obtained. K B can be the second time window factor of the currently linked wireless AP.
  • the wireless AP currently connected to the vehicle AP in the train may be the wireless AP of the previous area, and when the train enters the next area, the current link with the vehicle Ap exists.
  • the signal strength value of the built-in wireless AP will gradually become smaller. Therefore, the time window factor of the currently-built link wireless AP is generally calculated to be a negative number.
  • the time window factor model of the currently linked wireless AP in the trackside it can be seen that the signal strength value of the currently-built link wireless AP in the preset time period is gradually smaller. Therefore, the calculated time window factor (i.e., the slope K B as shown in FIG. 3) of the currently-built link wireless AP is a negative number.
  • S160 Determine, according to the second time window factor and the first time window factor of each to-be-connected wireless AP, the target to-be-connected wireless AP from the plurality of to-be-connected wireless APs.
  • the satisfying the switching condition of the wireless access point may include: the second time window factor is a negative value; and the absolute value of the second time window factor is smaller than the first time of each wireless AP to be connected The average of the window factors.
  • the wireless AP serves as a target to be connected to the wireless AP.
  • the second time factor is not a negative value or the absolute value of the second time window factor is greater than or equal to an average of the first time window factors of the respective wireless access points to be connected, maintaining the current connection without The handover is performed, that is, in this case, the currently-established link wireless AP is the target wireless AP to be connected.
  • the network station of the in-vehicle wireless AP may be switched from the currently-established linked wireless AP to the target to-be-connected wireless AP, The process of wireless access point switching in vehicle-to-ground wireless communication.
  • the method for switching the access point may further include:
  • step S420 If yes, the first wireless AP is determined to be the currently-established linked wireless AP, and step S130 is continued.
  • the to-be-connected wireless AP having the largest first time window factor is used as the target to be connected to the wireless AP.
  • a time window factor selecting, from the plurality of to-be-connected wireless APs, the to-be-connected wireless AP having the largest first time window factor according to the first time window factor, and using the to-be-connected wireless AP having the largest first time window factor as The target to be connected to the wireless AP, that is, directly determining the target wireless AP to be connected from the plurality of to-be-connected wireless APs, and then switching the in-vehicle wireless AP to the target wireless AP to be connected, so as to implement wireless AP switching in the vehicle-to-ground wireless communication. process.
  • the method for switching a wireless access point is applied to a signal system of a rail transit, wherein a vehicle-mounted wireless AP is disposed at a front and a rear of the train, and a rail is disposed on one side or both sides of the track line.
  • Side wireless AP network During the movement of the train, the in-vehicle wireless AP generally detects 3 or 4 trackside wireless APs, as shown in the vehicle wireless AP link in Figure 5.
  • the vehicle wireless AP and the trackside wireless AP1 have Establishing a link
  • the in-vehicle wireless AP uses the time window function and the second signal strength value of the currently-built link wireless AP in the preset time to calculate the second time window factor K B of the currently-built link wireless AP in real time, and simultaneously utilizes
  • the time window function, and the first signal strength value of each wireless AP to be connected within a preset time calculate the first time window factors of the wireless AP2, the wireless AP3, and the wireless AP4 in real time, that is, K F2 , K F3 , and K F4 .
  • the wireless AP3 and the wireless AP4 ie, K F2 , K F3 , K F4 .
  • the wireless AP with the largest time window factor value can be found from the wireless AP2, the wireless AP3, and the wireless AP4, and the wireless AP is used as the target wireless AP to be connected, and the in-vehicle wireless AP is switched to the The target is to be connected to the wireless AP.
  • the wireless AP of the track may change in a hopping manner, and the embodiment of the present invention may establish the time window factor pair.
  • the connected trackside wireless AP performs a filtering process to avoid the ping-pong effect when connecting, and enhances the effectiveness of switching the AP.
  • the purpose of the present invention is to integrate the actual requirements of wireless communication in the current urban rail transit, especially for the actual demand of the loop straddle monorail, and propose a method for switching the wireless access point based on the time window factor. .
  • the method for switching a wireless access point according to the embodiment of the present invention can solve the problem that the loop straddle monorail can be reliably switched at a small turning radius by using the time window factor filtering method, thereby effectively avoiding the wireless AP signal coverage enhancement.
  • the ping-pong effect problem of wireless AP switching in the vehicle ground has greatly shortened the switching time and improved the reliability of the signal link.
  • an embodiment of the present invention further provides a switching device for a wireless access point, which is provided by the wireless access point according to the embodiment of the present invention.
  • the apparatus corresponds to the method for switching the wireless access point provided by the foregoing embodiments. Therefore, the implementation manner of the foregoing method for switching the wireless access point is also applicable to the switching apparatus of the wireless access point provided in this embodiment. It will not be described in detail in the embodiment.
  • FIG. 6 is a schematic structural diagram of a switching apparatus of a wireless access point according to an embodiment of the present invention. As shown in FIG.
  • the switching device of the wireless access point may include: a detecting module 610, a first determining module 620, an obtaining module 630, a first calculating module 640, a second calculating module 650, a second determining module 660, and switching. Module 670.
  • the detecting module 610 is configured to detect a plurality of wireless access points to be connected located around the in-vehicle wireless access point.
  • the first determining module 620 is configured to determine a currently-built link wireless access point that currently has a communication connection with the in-vehicle wireless access point.
  • the obtaining module 630 is configured to obtain a first signal strength value of each to-be-connected wireless access point in a preset time, and obtain a second signal strength value of the currently-built link wireless access point in the preset time.
  • the first calculating module 640 is configured to separately calculate a first time window factor of each wireless access point to be connected according to the first signal strength value of each wireless access point to be connected within a preset time. Specifically, in an embodiment of the present invention, the first calculating module 640, for each wireless access point to be connected, uses a preset time window function to fit the first signal strength value in the preset time to the first A straight line equation calculates the first slope of the first line equation and the first slope as the first time window factor.
  • the preset time window function is expressed as follows:
  • y is the signal strength value within the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • the second calculating module 650 is configured to calculate a second time window factor of the currently-established linked wireless access point according to the second signal strength value. Specifically, in an embodiment of the present invention, the second calculating module 650 may use a preset time window function to fit the second signal strength value in the preset time to the second line equation, and calculate the second line. The second slope of the equation and the second slope as the second time window factor. Wherein, in the embodiment of the present invention, the preset time window function is expressed as follows:
  • y is the signal strength value within the preset time
  • ⁇ t is the preset time
  • x is the current time
  • k is the slope
  • b is the intercept of the time window function on the y-axis.
  • the second determining module 660 is configured to determine, according to the second time window factor and the first time window factor of each to-be-connected wireless access point, the target wireless access point to be connected from the plurality of to-be-connected wireless APs.
  • the switching device of the wireless access point may include: a determining module, configured to determine whether there is currently a first wireless access point that has a communication connection with the in-vehicle wireless access point.
  • the first determining module 620 is further configured to: when the determining module determines that there is a first wireless access point that has a communication connection with the in-vehicle wireless access point, determine the first wireless access point as the The link to the wireless access point is currently under construction.
  • the second determining module 660 is further configured to: when the determining module determines that there is no first wireless access point that has a communication connection with the in-vehicle wireless access point, according to the first wireless access point to be connected a time window factor, selecting, from the plurality of to-be-connected wireless access points, a wireless access point to be connected having a maximum first time window factor as the target wireless access point to be connected.
  • the second determining module 660 may include: a first determining unit 661 , a second determining unit 662 , a selecting unit 663 , and a determining unit 664 .
  • the first determining unit 661 is configured to determine whether the second time window factor is a negative value.
  • the second determining unit 662 is configured to further determine, when the second time window factor is a negative value, whether an absolute value of the second time window factor is smaller than an average value of the first time window factors of the wireless access points to be connected.
  • the selecting unit 663 is configured to select, when the absolute value of the second time window factor is smaller than the average value of the first time window factors of the wireless access points to be connected, the maximum first time window from the plurality of to-be-connected wireless access points Factor of the wireless access point to be connected.
  • the determining unit 664 is configured to use the wireless access point to be connected with the largest first time window factor as the target wireless access point to be connected.
  • the determining unit 664 is further configured to: when the second time factor is not a negative value or the absolute value of the second time window factor is greater than or equal to the first time of each of the to-be-connected wireless access points When the average of the window factors is determined, the currently established link wireless access point is determined as the target wireless access point to be connected.
  • the switching module 670 is configured to switch the in-vehicle wireless access point access point to the target wireless access point to be connected.
  • the switching device of the wireless access point can solve the problem that the loop straddle monorail can be reliably switched under a small turning radius, thereby effectively avoiding the wireless AP switching of the vehicle after the wireless AP signal coverage is enhanced.
  • the ping-pong effect problem greatly shortens the switching time and improves the reliability of the signal link.
  • the present invention also provides a train on which at least one in-vehicle wireless access point AP can be disposed, wherein the in-vehicle wireless access point AP is used to perform any of the above embodiments of the present invention.
  • the method for switching the wireless access point is not limited to, but not limited to, but not limited to, but not limited to, but not limited to, but not limited to, but not limited to, but not limited to, but not limited to perform any of the above embodiments of the present invention.
  • first and second are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated.
  • features defining “first” and “second” may include at least one of the features, either explicitly or implicitly.
  • the meaning of "a plurality" is at least two, such as two, three, etc., unless specifically defined otherwise.
  • the terms “installation”, “connected”, “connected”, “fixed” and the like shall be understood broadly, and may be either a fixed connection or a detachable connection, unless explicitly stated and defined otherwise. , or integrated; can be mechanical or electrical connection; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction of two elements, unless otherwise specified Limited.
  • the specific meanings of the above terms in the present invention can be understood on a case-by-case basis.
  • a "computer-readable medium” can be any apparatus that can contain, store, communicate, propagate, or transport a program for use in an instruction execution system, apparatus, or device, or in conjunction with the instruction execution system, apparatus, or device.
  • computer readable media include the following: electrical connections (electronic devices) having one or more wires, portable computer disk cartridges (magnetic devices), random access memory (RAM), Read only memory (ROM), erasable editable read only memory (EPROM or flash memory), fiber optic devices, and portable compact disk read only memory (CDROM).
  • the computer readable medium may even be a paper or other suitable medium on which the program can be printed, as it may be optically scanned, for example by paper or other medium, followed by editing, interpretation or, if appropriate, other suitable The method is processed to obtain the program electronically and then stored in computer memory.
  • portions of the invention may be implemented in hardware, software, firmware or a combination thereof.
  • multiple steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system.
  • a suitable instruction execution system For example, if implemented in hardware, as in another embodiment, it can be implemented by any one or combination of the following techniques well known in the art: having logic gates for implementing logic functions on data signals. Discrete logic circuits, application specific integrated circuits with suitable combinational logic gates, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.
  • each functional unit in each embodiment of the present invention may be integrated into one processing module, or each unit may exist physically separately, or two or more units may be integrated into one module.
  • the above integrated modules can be implemented in the form of hardware or in the form of software functional modules.
  • the integrated modules, if implemented in the form of software functional modules and sold or used as stand-alone products, may also be stored in a computer readable storage medium.
  • the above mentioned storage medium may be a read only memory, a magnetic disk or an optical disk or the like.

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Abstract

本发明公开了一种无线接入点的切换方法、装置及列车。其中方法包括：检测位于车载AP周围的多个待连接无线AP；确定当前与车载AP存在通信连接的当前在建链接无线AP；获取预设时间内的各个待连接无线AP的第一信号强度值，并获取预设时间内的当前在建链接无线AP的第二信号强度值；根据该第一信号强度值分别计算各个待连接无线AP的第一时间窗因子；根据第二信号强度值计算当前在建链接无线AP的第二时间窗因子；根据第二时间窗因子和各个待连接无线AP的第一时间窗因子，从多个待连接无线AP中确定出目标待连接无线AP；将车载AP切换至目标待连接无线AP中。该方法可以有效的避免线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题。

Description

无线接入点的切换方法、装置以及列车
相关申请的交叉引用
本申请基于申请号为201710537047.5，申请日为2017年7月4日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此引入本申请作为参考。
技术领域
本发明涉及无线通信领域，尤其涉及一种无线接入点的切换方法、装置以及列车。
背景技术
城市轨道交通信号和通信系统中的车地无线通信，通常是利用WLAN(Wireless Local Area Network，无线局域网)或LTE(Long Term Evolution，长期演进)等通信制式，在轨旁建立一系列的无线AP(Access Point，接入点)，轨旁的各个无线AP通过通信光缆组成地面通信网络，同时在列车上设置车载无线AP作为移动终端，列车在运行过程中通过车载的AP和轨旁的AP之间建立无线通信，从而实现车地无线通信的功能。
相关技术中，列车在移动过程中，车地无线通信中的无线接入点之间的切换的实现过程通常如下：车载AP通过检测轨旁距离较近的多个无线AP的网络信息，并判断当前与网络站点关联的第一AP的信号强度是否低于网络信号强度阈值，若是，则在MAC(Media Access Control，媒体访问控制)地址映射表中查找多个AP中每个AP的所述MAC地址对应的地理位置信息，并根据每个AP对应的地理位置信息确定车载AP在移动过程中与其地理位置相互接近的多个第二AP，并将网络站点从第一AP切换到多个第二AP中网络信号强度最强的第二AP。
但是目前存在的问题是，目前轨道交通地面部分的弯道越来越多，线路运行后轨道附近增加的建筑物也越来越多，在利用传统的无线接入点切换方法切换AP过程中，由于车载运行线路周围环境的复杂性和外界干扰信号的不确定性，利用点阈值或动态点阈值来做切换的依据条件，在信号强度的出现跳跃的情况下，容易出现切换的乒乓效应，造成反复切换，降低了切换的稳定性和增加了无线通信的延时和出错的几率。
发明内容
本发明的目的旨在至少在一定程度上解决上述的技术问题之一。
为此，本发明的第一个目的在于提出一种无线接入点的切换方法。该方法可以有效的避免线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题，大大缩短了切换的 时间，并提升了信号链路的可靠性。
本发明的第二个目的在于提出一种无线接入点的切换装置。
本发明的第三个目的在于提出一种列车。
为了实现上述目的，本发明第一方面实施例提出的无线接入点的切换方法，包括：检测位于车载无线接入点周围的多个待连接无线接入点；确定当前与所述车载无线接入点存在通信连接的当前在建链接无线AP；获取预设时间内的各个待连接无线接入点的第一信号强度值，并获取所述预设时间内的所述当前在建链接无线接入点的第二信号强度值；根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；根据所述第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子；根据所述第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中确定出目标待连接无线接入点；将所述车载无线接入点切换至所述目标待连接无线接入点中。
在所述确定当前与所述车载无线接入点存在通信连接的当前在建链接无线接入点之前，所述方法还包括：判断当前是否有与所述车载无线接入点存在通信连接的第一无线接入点；若是，则将所述第一无线接入点确定为所述当前在建链接无线接入点；若否，则分别获取所述预设时间内的各个待连接无线接入点的第一信号强度值；根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；根据所述第一时间窗因子从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；将所述具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
所述根据预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子，包括：针对每个待连接无线接入点，利用预设的时间窗函数将所述预设时间内的第一信号强度值拟合成第一直线方程；计算所述第一直线方程的第一斜率，并将所述第一斜率作为所述第一时间窗因子。
所述根据第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子，包括：利用预设的时间窗函数将所述预设时间内的第二信号强度值拟合成第二直线方程；计算所述第二直线方程的第二斜率，并将所述第二斜率作为所述第二时间窗因子。
所述预设的时间窗函数表示如下：
Figure PCTCN2018083537-appb-000001
其中，y为所述预设时间内的信号强度值，Δt为所述预设时间，x为当前时刻，k为 斜率，b为所述时间窗函数在y轴上的截距。
所述根据第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，确定出目标待连接无线接入点，包括：判断所述第二时间窗因子是否为负值；如果所述第二时间窗因子为负值，则进一步判断所述第二时间窗因子的绝对值是否小于所述各个待连接无线接入点的第一时间窗因子的平均值；若是，则从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；将所述具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
根据本发明实施例的无线接入点的切换方法，利用时间窗因子滤波的方法，可以解决环线跨坐式单轨在较小的转弯半径下可靠地切换，有效的避免了无线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题，大大缩短了切换的时间，并提升了信号链路的可靠性。
为了实现上述目的，本发明第二方面实施例提出的无线接入点的切换装置，包括：检测模块，用于检测位于车载无线接入点周围的多个待连接无线接入点；第一确定模块，用于确定当前与所述车载无线接入点存在通信连接的当前在建链接无线接入点；获取模块，用于获取预设时间内的各个待连接无线接入点的第一信号强度值，并获取所述预设时间内的所述当前在建链接无线接入点的第二信号强度值；第一计算模块，用于根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；第二计算模块，用于根据所述第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子；第二确定模块，用于根据所述第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中确定出目标待连接无线接入点；切换模块，用于将所述车载无线接入点切换至所述目标待连接无线接入点中。
所述的无线接入点的切换装置还包括：判断模块，用于判断当前是否有与所述车载无线接入点存在通信连接的第一无线接入点；所述第一确定模块进一步用于在所述判断模块确定有与所述车载无线接入点存在通信连接的第一无线接入点时，将所述第一无线接入点确定为所述当前在建链接无线接入点。
所述第二确定模块还用于在所述判断模块确定没有与所述车载无线接入点存在通信连接的第一无线接入点时，根据所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
所述第一计算模块具体用于：针对每个待连接无线接入点，利用预设的时间窗函数将所述预设时间内的第一信号强度值拟合成第一直线方程；计算所述第一直线方程的第一斜率，并将所述第一斜率作为所述第一时间窗因子。
所述第二计算模块具体用于：利用预设的时间窗函数将所述预设时间内的第二信号强度值拟合成第二直线方程；计算所述第二直线方程的第二斜率，并将所述第二斜率作为所述第二时间窗因子。
所述预设的时间窗函数表示如下：
Figure PCTCN2018083537-appb-000002
其中，y为所述预设时间内的信号强度值，Δt为所述预设时间，x为当前时刻，k为斜率，b为所述时间窗函数在y轴上的截距。
所述第二确定模块包括：第一判断单元，用于判断所述第二时间窗因子是否为负值；第二判断单元，用于在所述第二时间窗因子为负值时，进一步判断所述第二时间窗因子的绝对值是否小于所述各个待连接无线接入点的第一时间窗因子的平均值；选取单元，用于在所述第二时间窗因子的绝对值小于所述各个待连接无线接入点的第一时间窗因子的平均值时，从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；确定单元，用于将所述具有最大第一时间窗因子的待连接无线AP作为所述目标待连接无线接入点。
根据本发明实施例的无线接入点的切换装置，利用时间窗因子滤波的方法，可以解决环线跨坐式单轨在较小的转弯半径下可靠地切换，有效的避免了无线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题，大大缩短了切换的时间，并提升了信号链路的可靠性。
为了实现上述目的，本发明第三方面实施例提出的列车，所述列车上设置有至少一个车载无线接入点，所述车载无线接入点用于执行本发明第一方面实施例所述的无线接入点的切换方法。
本发明附加的方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本发明的实践了解到。
附图说明
本发明上述的和/或附加的方面和优点从下面结合附图对实施例的描述中将变得明显和容易理解，其中：
图1是根据本发明一个实施例的无线接入点的切换方法的流程图；
图2是根据本发明实施例的轨旁待连接无线AP的时间窗因子模型的示例图；
图3是根据本发明实施例的轨旁当前在建链接无线AP的时间窗因子模型的示例图；
图4是根据本发明另一个实施例的无线接入点的切换方法的流程图；
图5是根据本发明实施例的车地无线AP链路的示例图；
图6是根据本发明一个实施例的无线接入点的切换装置的结构示意图；
图7是根据本发明另一个实施例的无线接入点的切换装置的结构示意图。
具体实施方式
下面详细描述本发明的实施例，所述实施例的示例在附图中示出，其中自始至终相同或类似的标号表示相同或类似的元件或具有相同或类似功能的元件。下面通过参考附图描述的实施例是示例性的，旨在用于解释本发明，而不能理解为对本发明的限制。
下面参考附图描述本发明实施例的无线接入点的切换方法、装置以及列车。
图1是根据本发明一个实施例的无线接入点的切换方法的流程图。需要说明的是，本发明实施例的无线接入点的切换方法可应用于本发明实施例的无线接入点的切换装置。其中，该切换装置可被配置于列车中。例如，该切换装置可为设置于列车中的车载线接入点。换言之，本发明的实施例无线接入点的切换方法可从车载线接入点侧进行描述。
如图1所示，该无线接入点的切换方法可以包括：
S110，检测位于车载无线AP周围的多个待连接无线AP。
具体地，在列车移动过程中，可通过广播的方式向车载无线AP周围发送广播信息，位于车载无线AP周围的无线AP在接收到该广播信息时可反馈相应信息，通过该反馈的信息即可获知当前位于车载无线AP周围有哪些无线AP可进行连接。
S120，确定当前与车载无线AP存在通信连接的当前在建链接无线AP。
具体地，可确定当前是否有与车载无线AP存在通信连接无线AP，若有，则将该无线AP作为当前在建链接无线AP。
S130，获取预设时间内的各个待连接无线AP的第一信号强度值，并获取预设时间内的当前在建链接无线AP的第二信号强度值。
具体地，可分别获取预设时间内的各个待连接无线AP的RSSI(Received Signal Strength Indication，接收的信号强度指示)值，并获取预设时间内的当前在建链接无线AP的RSSI值。其中，在本发明的实施例中，该预设时间可以是根据实际应用需要所决定的，例如，该预设时间可为50毫秒。
S140，根据预设时间内的各个待连接无线AP的第一信号强度值，分别计算各个待连接无线AP的第一时间窗因子。
具体而言，在本发明的一个实施例中，针对每个待连接无线AP，可利用预设的时间窗 函数将预设时间内的第一信号强度值拟合成第一直线方程，并计算第一直线方程的第一斜率K F，以及将第一斜率K F作为第一时间窗因子。其中，在本发明的实施例中，上述预设的时间窗函数可表示如下：
Figure PCTCN2018083537-appb-000003
其中，y为预设时间内的信号强度值，Δt为预设时间，x为当前时刻，k为斜率，b为时间窗函数在y轴上的截距。
更具体地，针对每个待连接无线AP，可将该预设时间段选取多个时刻，其中，每个时刻之间的时长相同，然后，确定每个时刻所对应的信号强度值，并利用预设的时间窗函数，将该多个时刻作为横坐标、该多个时刻所对应的信号强度值作为纵坐标，进行线性拟合，得到相应的直线方程，之后，可求出该直线方程的斜率，并将该斜率即可为该待连接无线AP的第一时间窗因子。
可以理解，列车在驶入某个区域中，位于该区域中的无线AP应为待连接无线AP，而由于这些待连接无线AP是即将与列车中的车载AP建立连接的，即预设时间段内的这些待连接无线AP的信号强度值应是逐渐增大的，所以，计算出该待连接无线AP的时间窗因子应为正数。例如，如图2所示，为轨旁待连接无线AP的时间窗因子模型，可以看出，该预设时间段内的待连接无线AP的信号强度值是逐渐增大的，所以计算出的待连接无线AP的时间窗因子(即如图2中所示的斜率K F)为正数。
S150，根据第二信号强度值计算当前在建链接无线AP的第二时间窗因子。
具体而言，在本发明的一个实施例中，可利用预设的时间窗函数将预设时间内的第二信号强度值拟合成第二直线方程，并计算第二直线方程的第二斜率，以及将第二斜率作为第二时间窗因子。其中，在本发明的实施例中，上述预设的时间窗函数可表示如下：
Figure PCTCN2018083537-appb-000004
其中，y为预设时间内的信号强度值，Δt为预设时间，x为当前时刻，k为斜率，b为时间窗函数在y轴上的截距。
更具体地，可将该预设时间段选取多个时刻，其中，每个时刻之间的时长相同，然后，确定每个时刻所对应的信号强度值，并利用预设的时间窗函数，将该多个时刻作为横坐标、 该多个时刻所对应的信号强度值作为纵坐标，进行线性拟合，得到相应的直线方程，之后，可求出该直线方程的斜率K B，并将该斜率K B即可为该当前在建链接无线AP的第二时间窗因子。
可以理解，列车在移动的过程中，列车中的车载AP当前连接的无线AP可能会是上一个区域的无线AP，则此时列车驶入下一个区域中时，与车载Ap存在链接的当前在建链接无线AP的信号强度值会逐渐变小，所以，计算出该当前在建链接无线AP的时间窗因子一般为负数。例如，如图3所示，为轨旁当前在建链接无线AP的时间窗因子模型，可以看出，该预设时间段内的当前在建链接无线AP的信号强度值是逐渐变小的，所以计算出的当前在建链接无线AP的时间窗因子(即如图3中所示的斜率K B)为负数。
S160，根据第二时间窗因子和各个待连接无线AP的第一时间窗因子，从多个待连接无线AP中确定出目标待连接无线AP。
具体地，可根据各个待连接无线AP的第一时间窗因子判断该第二时间窗因子是否满足无线接入点的切换条件，若满足，则从多个待连接无线AP中确定出目标待连接无线AP。其中，在本发明的实施例中，该满足无线接入点的切换条件可包括：第二时间窗因子为负值；以及第二时间窗因子的绝对值小于各个待连接无线AP的第一时间窗因子的平均值。
具体而言，在本发明的一个实施例中，可判断第二时间窗因子是否为负值，如果第二时间窗因子为负值，则进一步判断第二时间窗因子的绝对值是否小于各个待连接无线AP的第一时间窗因子的平均值，若是，则从多个待连接无线AP中选取具有最大第一时间窗因子的待连接无线AP，并将具有最大第一时间窗因子的待连接无线AP作为目标待连接无线AP。
若所述第二时间因子不为负值或所述第二时间窗因子的绝对值大于或等于所述各个待连接无线接入点的第一时间窗因子的平均值，则维持当前连接而无需进行切换，即在此情况下，当前在建链接无线AP即为目标待连接无线AP。
S170，将车载无线AP切换至目标待连接无线AP中。
具体地，在从多个待连接无线AP中确定出目标待连接无线AP之后，可将车载无线AP的网络站点从所述当前在建链接的无线AP切换到该目标待连接无线AP中，实现了车地无线通信中的无线接入点切换的过程。
可以理解，当网络很差，或者车载无线AP周围没有无线AP时，可能会导致车载无线AP当前没有与轨旁的任何无线AP进行连接，因此，还需考虑这种特殊情况下，如何实现无线AP的切换。可选地，在本发明的一个实施例中，在确定当前与车载无线AP存在通信连接的当前在建链接无线AP之前，如图4所示，在如图1所示的基础上，该无线接入点的切换方法还可包括：
S410，判断当前是否有与车载无线AP存在通信连接的第一无线AP。
S420，若是，则将第一无线AP确定为当前在建链接无线AP，并继续执行步骤S130。
S430，若否，则分别获取预设时间内的各个待连接无线AP的第一信号强度值。
S440，根据预设时间内的各个待连接无线AP的第一信号强度值，分别计算各个待连接无线AP的第一时间窗因子。
S450，根据第一时间窗因子从多个待连接无线AP中选取具有最大第一时间窗因子的待连接无线AP。
S460，将具有最大第一时间窗因子的待连接无线AP作为目标待连接无线AP。
也就是说，在判断当前没有与车载无线AP存在通信连接的无线AP时，无需考虑当前在建连接的无线AP的信号强度的问题，而是可以直接计算所述多个待连接无线AP的第一时间窗因子，并根据第一时间窗因子从多个待连接无线AP中选取具有最大第一时间窗因子的待连接无线AP，并将该具有最大第一时间窗因子的待连接无线AP作为目标待连接无线AP，即直接从该多个待连接无线AP确定出目标待连接无线AP，进而将车载无线AP切换至目标待连接无线AP中，以实现车地无线通信中的无线AP切换的过程。
举例而言，假设本发明实施例的无线接入点的切换方法应用于轨道交通的信号系统中，其中，列车的车头和车尾设置车载无线AP，在轨道线路的单侧或两侧设置轨旁无线AP网络。在列车的移动过程中，车载无线AP一般探测到3或4个轨旁无线AP，如图5中车地无线AP链路所示，列车在行驶过程中，车载无线AP和轨旁无线AP1已经建立链接，车载无线AP利用时间窗函数、和预设时间内的当前在建链接无线AP的第二信号强度值，实时计算当前在建链接无线AP的第二时间窗因子K B，同时，利用时间窗函数、和预设时间内的各个待连接无线AP的第一信号强度值，实时计算无线AP2、无线AP3、无线AP4的第一时间窗因子，即K F2、K F3、K F4。
然后，判断第二时间窗因子K B为负值，且第二时间窗因子K B的绝对值小于无线AP2、无线AP3、无线AP4的各个时间窗因子(即K F2、K F3、K F4)的平均值，此时，可从无线AP2、无线AP3、无线AP4中找出时间窗因子值最大的那个无线AP，并将该无线AP作为目标待连接无线AP，并将车载无线AP切换至该目标待连接无线AP中。由此，在车辆行驶的环境有较强的同频干扰或车辆正在通过较小的弯道时，轨旁的无线AP会出现跳跃式的变化，本发明实施例可通过时间窗因子对即将建立连接的轨旁无线AP进行一次滤波处理，避免了连接时的乒乓效应，增强了切换AP的有效性。
综上，本发明的目的是综合当前城市轨道交通中车地无线通信的实际需求，特别是针 对环线跨座式单轨的实际需求，提出了一种基于时间窗因子的无线接入点的切换方法。本发明实施例的无线接入点的切换方法，利用时间窗因子滤波的方法，可以解决环线跨坐式单轨在较小的转弯半径下可靠地切换，有效的避免了无线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题，大大缩短了切换的时间，并提升了信号链路的可靠性。
与上述几种实施例提供的无线接入点的切换方法相对应，本发明的一种实施例还提供一种无线接入点的切换装置，由于本发明实施例提供的无线接入点的切换装置与上述几种实施例提供的无线接入点的切换方法相对应，因此在前述无线接入点的切换方法的实施方式也适用于本实施例提供的无线接入点的切换装置，在本实施例中不再详细描述。图6是根据本发明一个实施例的无线接入点的切换装置的结构示意图。如图6所示，该无线接入点的切换装置可以包括：检测模块610、第一确定模块620、获取模块630、第一计算模块640、第二计算模块650、第二确定模块660和切换模块670。
具体地，检测模块610用于检测位于车载无线接入点周围的多个待连接无线接入点。
第一确定模块620用于确定当前与车载无线接入点存在通信连接的当前在建链接无线接入点。
获取模块630用于获取预设时间内的各个待连接无线接入点的第一信号强度值，并获取预设时间内的当前在建链接无线接入点的第二信号强度值。
第一计算模块640用于根据预设时间内的各个待连接无线接入点的第一信号强度值，分别计算各个待连接无线接入点的第一时间窗因子。具体而言，在本发明的一个实施例中，第一计算模块640针对每个待连接无线接入点，利用预设的时间窗函数将预设时间内的第一信号强度值拟合成第一直线方程，并计算第一直线方程的第一斜率，以及将第一斜率作为第一时间窗因子。其中，在本发明的实施例中，上述预设的时间窗函数表示如下：
Figure PCTCN2018083537-appb-000005
其中，y为预设时间内的信号强度值，Δt为预设时间，x为当前时刻，k为斜率，b为时间窗函数在y轴上的截距。
第二计算模块650用于根据第二信号强度值计算当前在建链接无线接入点的第二时间窗因子。具体而言，在本发明的一个实施例中，第二计算模块650可利用预设的时间窗函数将预设时间内的第二信号强度值拟合成第二直线方程，并计算第二直线方程的第二斜率，以及将第二斜率作为第二时间窗因子。其中，在本发明的实施例中，上述预设的时间窗函数表示如下：
Figure PCTCN2018083537-appb-000006
其中，y为预设时间内的信号强度值，Δt为预设时间，x为当前时刻，k为斜率，b为时间窗函数在y轴上的截距。
第二确定模块660用于根据第二时间窗因子和各个待连接无线接入点的第一时间窗因子，从多个待连接无线AP中确定出目标待连接无线接入点。
作为一种示例，该无线接入点的切换装置可以包括：判断模块，用于判断当前是否有与所述车载无线接入点存在通信连接的第一无线接入点。所述第一确定模块620进一步用于在所述判断模块确定有与所述车载无线接入点存在通信连接的第一无线接入点时，将所述第一无线接入点确定为所述当前在建链接无线接入点。所述第二确定模块660还用于：在所述判断模块确定没有与所述车载无线接入点存在通信连接的第一无线接入点时，根据所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
作为一种示例，如图7所示，该第二确定模块660可以包括：第一判断单元661、第二判断单元662、选取单元663和确定单元664。
其中，第一判断单元661用于判断第二时间窗因子是否为负值。第二判断单元662用于在第二时间窗因子为负值时，进一步判断第二时间窗因子的绝对值是否小于各个待连接无线接入点的第一时间窗因子的平均值。选取单元663用于在第二时间窗因子的绝对值小于各个待连接无线接入点的第一时间窗因子的平均值时，从多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点。确定单元664用于将具有最大第一时间窗因子的待连接无线接入点作为目标待连接无线接入点。作为一种示例，该定单元664还用于在所述第二时间因子不为负值或所述第二时间窗因子的绝对值大于或等于所述各个待连接无线接入点的第一时间窗因子的平均值时，确定当前在建链接无线接入点作为目标待连接无线接入点。
切换模块670用于将车载无线接入点接入点切换至目标待连接无线接入点中。
根据本发明实施例的无线接入点的切换装置，可以解决环线跨坐式单轨在较小的转弯半径下可靠地切换，有效的避免了无线AP信号覆盖增强后会所出现车地无线AP切换的乒乓效应问题，大大缩短了切换的时间，并提升了信号链路的可靠性。
为了实现上述实施例，本发明还提出了一种列车，该列车上可设置有至少一个车载无线接入点AP，其中，该车载无线接入点AP用于执行本发明上述任一个实施例所述的无线 接入点的切换方法。
在本发明的描述中，需要理解的是，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括至少一个该特征。在本发明的描述中，“多个”的含义是至少两个，例如两个，三个等，除非另有明确具体的限定。
在本发明中，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或成一体；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通或两个元件的相互作用关系，除非另有明确的限定。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本发明中的具体含义。
在本说明书的描述中，参考术语“一个实施例”、“一些实施例”、“示例”、“具体示例”、或“一些示例”等的描述意指结合该实施例或示例描述的具体特征、结构、材料或者特点包含于本发明的至少一个实施例或示例中。在本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
流程图中或在此以其他方式描述的任何过程或方法描述可以被理解为，表示包括一个或更多个用于实现特定逻辑功能或过程的步骤的可执行指令的代码的模块、片段或部分，并且本发明的优选实施方式的范围包括另外的实现，其中可以不按所示出或讨论的顺序，包括根据所涉及的功能按基本同时的方式或按相反的顺序，来执行功能，这应被本发明的实施例所属技术领域的技术人员所理解。
在流程图中表示或在此以其他方式描述的逻辑和/或步骤，例如，可以被认为是用于实现逻辑功能的可执行指令的定序列表，可以具体实现在任何计算机可读介质中，以供指令执行系统、装置或设备(如基于计算机的系统、包括处理器的系统或其他可以从指令执行系统、装置或设备取指令并执行指令的系统)使用，或结合这些指令执行系统、装置或设备而使用。就本说明书而言，"计算机可读介质"可以是任何可以包含、存储、通信、传播或传输程序以供指令执行系统、装置或设备或结合这些指令执行系统、装置或设备而使用的装置。计算机可读介质的更具体的示例(非穷尽性列表)包括以下：具有一个或多个布线的电连接部(电子装置)，便携式计算机盘盒(磁装置)，随机存取存储器(RAM)，只读存储器(ROM)，可擦除可编辑只读存储器(EPROM或闪速存储器)，光纤装置，以及便携式光盘只读存储器(CDROM)。另外，计算机可读介质甚至可以是可在其上打印所述程序的纸 或其他合适的介质，因为可以例如通过对纸或其他介质进行光学扫描，接着进行编辑、解译或必要时以其他合适方式进行处理来以电子方式获得所述程序，然后将其存储在计算机存储器中。
应当理解，本发明的各部分可以用硬件、软件、固件或它们的组合来实现。在上述实施方式中，多个步骤或方法可以用存储在存储器中且由合适的指令执行系统执行的软件或固件来实现。例如，如果用硬件来实现，和在另一实施方式中一样，可用本领域公知的下列技术中的任一项或他们的组合来实现：具有用于对数据信号实现逻辑功能的逻辑门电路的离散逻辑电路，具有合适的组合逻辑门电路的专用集成电路，可编程门阵列(PGA)，现场可编程门阵列(FPGA)等。
本技术领域的普通技术人员可以理解实现上述实施例方法携带的全部或部分步骤是可以通过程序来指令相关的硬件完成，所述的程序可以存储于一种计算机可读存储介质中，该程序在执行时，包括方法实施例的步骤之一或其组合。
此外，在本发明各个实施例中的各功能单元可以集成在一个处理模块中，也可以是各个单元单独物理存在，也可以两个或两个以上单元集成在一个模块中。上述集成的模块既可以采用硬件的形式实现，也可以采用软件功能模块的形式实现。所述集成的模块如果以软件功能模块的形式实现并作为独立的产品销售或使用时，也可以存储在一个计算机可读取存储介质中。
上述提到的存储介质可以是只读存储器，磁盘或光盘等。尽管上面已经示出和描述了本发明的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本发明的限制，本领域的普通技术人员在本发明的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (13)

  1. 一种无线接入点的切换方法，其特征在于，包括以下步骤：
    检测位于车载无线接入点周围的多个待连接无线接入点；
    确定当前与所述车载无线接入点存在通信连接的当前在建链接无线接入点；
    获取预设时间内的各个待连接无线接入点的第一信号强度值，并获取所述预设时间内的所述当前在建链接无线接入点的第二信号强度值；
    根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；
    根据所述第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子；
    根据所述第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，确定出目标待连接无线接入点；
    将所述车载无线接入点切换至所述目标待连接无线接入点中。
  2. 如权利要求1所述的无线接入点的切换方法，其特征在于，在所述确定当前与所述车载无线接入点存在通信连接的当前在建链接无线接入点之前，所述方法还包括：
    判断当前是否有与所述车载无线接入点存在通信连接的第一无线接入点；
    若是，则将所述第一无线接入点确定为所述当前在建链接无线接入点；
    若否，则分别获取所述预设时间内的各个待连接无线接入点的第一信号强度值；
    根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；
    根据所述第一时间窗因子从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；
    将所述具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
  3. 如权利要求1或2所述的无线接入点的切换方法，其特征在于，所述根据预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子，包括：
    针对每个待连接无线接入点，利用预设的时间窗函数将所述预设时间内的第一信号强度值拟合成第一直线方程；
    计算所述第一直线方程的第一斜率，并将所述第一斜率作为所述第一时间窗因子。
  4. 如权利要求1-3任意一项所述的无线接入点的切换方法，其特征在于，所述根据第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子，包括：
    利用预设的时间窗函数将所述预设时间内的第二信号强度值拟合成第二直线方程；
    计算所述第二直线方程的第二斜率，并将所述第二斜率作为所述第二时间窗因子。
  5. 如权利要求3或4所述的无线接入点的切换方法，其特征在于，所述预设的时间窗函数表示如下：
    Figure PCTCN2018083537-appb-100001
    其中，y为所述预设时间内的信号强度值，Δt为所述预设时间，x为当前时刻，k为斜率，b为所述时间窗函数在y轴上的截距。
  6. 如权利要求1-5任意一项所述的无线接入点的切换方法，其特征在于，所述根据第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，确定出目标待连接无线接入点，包括：
    判断所述第二时间窗因子是否为负值；
    如果所述第二时间窗因子为负值，则进一步判断所述第二时间窗因子的绝对值是否小于所述各个待连接无线接入点的第一时间窗因子的平均值；
    若是，则从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；将所述具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
  7. 一种无线接入点的切换装置，其特征在于，包括：
    检测模块，用于检测位于车载无线接入点周围的多个待连接无线接入点；
    第一确定模块，用于确定当前与所述车载无线接入点存在通信连接的当前在建链接无线接入点；
    获取模块，用于获取预设时间内的各个待连接无线接入点的第一信号强度值，并获取所述预设时间内的所述当前在建链接无线接入点的第二信号强度值；
    第一计算模块，用于根据所述预设时间内的各个待连接无线接入点的第一信号强度值，分别计算所述各个待连接无线接入点的第一时间窗因子；
    第二计算模块，用于根据所述第二信号强度值计算所述当前在建链接无线接入点的第二时间窗因子；
    第二确定模块，用于根据所述第二时间窗因子和所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中确定出目标待连接无线接入点；
    切换模块，用于将所述车载无线接入点切换至所述目标待连接无线接入点中。
  8. 如权利要求7所述的无线接入点的切换装置，其特征在于，还包括：
    判断模块，用于判断当前是否有与所述车载无线接入点存在通信连接的第一无线接入点；
    所述第一确定模块进一步用于在所述判断模块确定有与所述车载无线接入点存在通信连接的第一无线接入点时，将所述第一无线接入点确定为所述当前在建链接无线接入点。
    所述第二确定模块还用于在所述判断模块确定没有与所述车载无线接入点存在通信连接的第一无线接入点时，根据所述各个待连接无线接入点的第一时间窗因子，从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点作为所述目标待连接无线接入点。
  9. 如权利要求7或8所述的无线接入点的切换装置，其特征在于，所述第一计算模块具体用于：
    针对每个待连接无线接入点，利用预设的时间窗函数将所述预设时间内的第一信号强度值拟合成第一直线方程；
    计算所述第一直线方程的第一斜率，并将所述第一斜率作为所述第一时间窗因子。
  10. 如权利要求7-9任意一项所述的无线接入点的切换装置，其特征在于，所述第二计算模块具体用于：
    利用预设的时间窗函数将所述预设时间内的第二信号强度值拟合成第二直线方程；
    计算所述第二直线方程的第二斜率，并将所述第二斜率作为所述第二时间窗因子。
  11. 如权利要求9或10所述的无线接入点的切换装置，其特征在于，所述预设的时间窗函数表示如下：
    Figure PCTCN2018083537-appb-100002
    其中，y为所述预设时间内的信号强度值，Δt为所述预设时间，x为当前时刻，k为斜率，b为所述时间窗函数在y轴上的截距。
  12. 如权利要求7-11任意一项所述的无线接入点的切换装置，其特征在于，所述第二确定模块包括：
    第一判断单元，用于判断所述第二时间窗因子是否为负值；
    第二判断单元，用于在所述第二时间窗因子为负值时，进一步判断所述第二时间窗因子的绝对值是否小于所述各个待连接无线接入点的第一时间窗因子的平均值；
    选取单元，用于在所述第二时间窗因子的绝对值小于所述各个待连接无线接入点的第 一时间窗因子的平均值时，从所述多个待连接无线接入点中选取具有最大第一时间窗因子的待连接无线接入点；
    确定单元，用于将所述具有最大第一时间窗因子的待连接无线AP作为所述目标待连接无线接入点。
  13. 一种列车，所述列车上设置有至少一个车载无线接入点，其特征在于，所述车载无线接入点用于执行如权利要求1至6中任一项所述的无线接入点的切换方法。
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