WO2016023513A1 - 轨道交通中的无线局域网切换方法及装置 - Google Patents

轨道交通中的无线局域网切换方法及装置 Download PDF

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Publication number
WO2016023513A1
WO2016023513A1 PCT/CN2015/086914 CN2015086914W WO2016023513A1 WO 2016023513 A1 WO2016023513 A1 WO 2016023513A1 CN 2015086914 W CN2015086914 W CN 2015086914W WO 2016023513 A1 WO2016023513 A1 WO 2016023513A1
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access point
sequence
sequence identifier
trackside
type
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PCT/CN2015/086914
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English (en)
French (fr)
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白小飞
阮卫
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华为技术有限公司
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Publication of WO2016023513A1 publication Critical patent/WO2016023513A1/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
    • H04W36/083—Reselecting an access point wherein at least one of the access points is a moving node

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  • the present disclosure relates to the field of wireless network technologies, and in particular, to a wireless local area network switching method and apparatus in rail transit.
  • the vehicle-to-ground communication system uses a wireless local area network (English: wireless local area network, abbreviated as WLAN) technology.
  • the vehicle-to-vehicle communication system includes: an in-vehicle access point 1, a track-side access point 2, and a switch 3.
  • the trackside access point 2 is connected to the switch 3.
  • the trackside access point 2 is an access point (English: access point, abbreviated as AP) disposed next to the track, usually beside the track.
  • AP access point
  • a plurality of trackside access points 2 are disposed, and the distance between the two trackside access points 2 is generally 50 meters to 200 meters, and the vehicle access point 1 is an AP disposed on the vehicle, and the vehicle access is performed.
  • Point 1 establishes a link with the trackside access point 2 and transmits wireless data to the trackside access point 2 that establishes the link, so that the wireless network covers the vehicle and meets the passenger's Internet access requirements.
  • the vehicle access point 1 acquires the received signal strength indicator (English: received signal strength indicator, abbreviation: RSSI).
  • RSSI received signal strength indicator
  • the RSSI of the trackside access point establishing a link with the in-vehicle access point is too small or close to saturation, or the RSSI of other trackside access points is compared to the track of the in-vehicle access point
  • the in-vehicle access point needs to perform a wireless local area network (English: wireless local area network, abbreviation: WLAN) switching operation, and the WLAN switching can meet the requirements of other RSSIs through the WLAN switching.
  • the trackside access points establish links to ensure channel quality.
  • the stability of the wireless environment is poor, and the RSSI of the trackside access point will randomly fluctuate, especially in a space with a narrow space (such as when the vehicle passes through the tunnel), and the RSSI random fluctuation of each track access point is more obvious. If the traditional WLAN switching mode is adopted, the random fluctuation of the RSSI may cause the switching to be too frequent, and the switching may become an invalid switching.
  • the embodiment of the invention provides a method and a device for switching a wireless local area network in rail transit, to solve to some extent, in the conventional technology, when switching the wireless local area network in the rail transit, the switching may occur too frequently, or the switching becomes invalid. Switching problems.
  • a wireless local area network switching method in rail transit wherein a vehicle carrying an in-vehicle access point runs on a fixed track, and a plurality of track side access points are placed along the fixed track, the method include:
  • the in-vehicle access point acquires a first sequence identifier, where the first sequence identifier is a first type of sequence identifier, and the first type of sequence identifier is a trackside access point that currently establishes a link with the in-vehicle access point.
  • Sequence identifier is a first type of sequence identifier, and the first type of sequence identifier is a trackside access point that currently establishes a link with the in-vehicle access point.
  • the in-vehicle access point acquires a plurality of second-class sequence identifiers, and the second-type sequence identifier is a sequence identifier of a track-side access point that does not establish a link between the current in-vehicle access point;
  • the second sequence identifier Determining, by the in-vehicle access point, the second sequence identifier according to the sequence direction, if the sequence direction is from small to large, the second sequence identifier is greater than the first sequence identifier in the plurality of second type sequence identifiers
  • the second type of sequence identifier, the smallest second type of sequence identifier, if the sequence direction is from large to small, the second sequence identifier is the first sequence of the plurality of second type sequence identifiers Identifying the smallest sequence identifier of the second type of sequence identifier;
  • the in-vehicle access point establishes a link with the target track-side access point, and the sequence identifier of the target track-side access point is the second sequence identifier.
  • the in-vehicle access point acquires multiple second-type sequence identifiers, including:
  • the in-vehicle access point acquires the RSSI of all the track-side access points, and selects a plurality of track-side access points in which all the track-side access points have an RSSI greater than a preset threshold;
  • the in-vehicle access point acquires sequence identifiers of the plurality of track-side access points as the plurality of second-class sequence identifiers.
  • the sequence identifier is a location number of the trackside access point along the fixed
  • the position numbers of the plurality of trackside access points placed in the track are strictly increased or strictly reduced according to the direction of the fixed track.
  • the sequence identifier is a MAC address of the trackside access point along the fixed
  • the value of the MAC address of the plurality of trackside access points on which the track is placed is strictly increased or strictly decremented according to the direction of the fixed track.
  • the sequence identifier is a MAC address of the trackside access point
  • the vehicle access The point is pre-stored with a full-order set including the MAC addresses of all track-side access points placed along the fixed track, and in the full-order set, placed along the fixed track
  • the MAC addresses of the plurality of trackside access points are strictly increased or strictly decremented according to the direction of the fixed track.
  • the second aspect provides a wireless local area network switching device in a rail transit, wherein the vehicle carrying the vehicle access point runs on a fixed track, and the plurality of track side access points are placed along the fixed track, including:
  • a first acquiring module configured to acquire a first sequence identifier, where the first sequence identifier is a first type of sequence identifier, and the first type of sequence identifier is a trackside access that currently establishes a link with the in-vehicle access point The sequence identifier of the point;
  • a second acquiring module configured to acquire a plurality of second type sequence identifiers, where the second type sequence identifier is a sequence identifier of a trackside access point that is not currently connected with the in-vehicle access point;
  • a determining module configured to determine a second sequence identifier according to the sequence direction, if the sequence direction is from small to large, the second sequence identifier is greater than the first sequence identifier in the plurality of second type sequence identifiers
  • the second type of sequence identifier, the smallest second type of sequence identifier, if the sequence direction is from large to small, the second sequence identifier is the first sequence identifier of the plurality of second type sequence identifiers
  • a link establishing module configured to establish a link with the target trackside access point, where the sequence identifier of the target trackside access point is the second sequence identifier.
  • the second acquiring module includes:
  • a first acquiring unit configured to acquire RSSIs of all trackside access points, and select a plurality of trackside access points in the trackside access points that have an RSSI greater than a preset threshold;
  • a second acquiring unit configured to acquire sequence identifiers of the plurality of trackside access points, and use the same as the multiple second type sequence identifiers.
  • the sequence identifier is a location number of the trackside access point along the fixed
  • the position numbers of the plurality of trackside access points placed in the track are strictly increased or strictly reduced according to the direction of the fixed track.
  • the sequence identifier is a MAC address of the trackside access point along the fixed
  • the value of the MAC address of the plurality of trackside access points on which the track is placed is strictly increased or strictly decremented according to the direction of the fixed track.
  • the sequence identifier is a MAC address of the trackside access point
  • the wireless local area network switching device in the rail transit further includes:
  • a storage module configured to pre-store a full-order set, where the full-sequence set includes MAC addresses of all track-side access points placed along the fixed track, and, in the full-order set, along the The MAC addresses of the plurality of trackside access points on which the fixed track is placed are strictly increased or strictly decremented according to the direction of the fixed track.
  • an access point in a third aspect, includes: a processor, a memory, a bus, and a wireless interface, where
  • the processor is connected to the memory through a bus
  • the wireless interface is connected to the processor through the bus;
  • the memory configured to store a program code of a wireless local area network switch in the rail transit;
  • the processor is configured to acquire program code stored in the memory, and perform the following operations according to the program code:
  • the second sequence identifier Determining, according to the sequence direction, the second sequence identifier, if the sequence direction is from small to large, the second sequence identifier is a second type of sequence identifier of the plurality of second type sequence identifiers that is larger than the first sequence identifier The smallest second type of sequence identifier. If the sequence direction is from large to small, the second sequence identifier is a second class of the plurality of second type sequence identifiers that is smaller than the first sequence identifier. The largest sequence identifier in the sequence identifier;
  • the sequence identifier of the target trackside access point being the second sequence identifier.
  • the trackside access point that establishes a link with the vehicle access point is referred to as a target trackside access point, and the target trackside access point is located in the moving direction of the vehicle, and
  • the target trackside access point is a trackside access point that establishes a link with the vehicle access point before switching from the WLAN, and the closest to the car access point among the plurality of trackside access points along the moving direction of the vehicle Trackside access point.
  • the target trackside access point is less affected by the fluctuation than the other trackside access points, and the vehicle access point and the target trackside access point can be guaranteed. Inter-channel quality to avoid invalid mis-switching.
  • the solution avoids invalid mis-handover, it can also reduce the service loss caused by frequent handover.
  • FIG. 1 is a schematic diagram of a network structure of a wireless local area network based on rail transit;
  • FIG. 2 is a flowchart of an embodiment of a method for switching a wireless local area network in rail transit according to the present disclosure
  • FIG. 3 is a schematic structural diagram of a wireless local area network switching apparatus in rail transit according to the present disclosure
  • FIG. 4 is a schematic structural diagram of an access point according to the present disclosure.
  • the embodiment of the present invention provides a method and a device for switching a wireless local area network in a rail transit, so as to solve the problem that the switching may occur too frequently or switch to an invalid handover when performing the WLAN switching based on the rail transit in the conventional technology.
  • a wireless local area network switching method in rail transit is disclosed, which is applied to an in-vehicle access point, wherein a vehicle carrying an in-vehicle access point runs on a fixed track, and multiple tracksides
  • the access point is placed along the fixed track, and the sequence identification of the plurality of trackside access points placed along the fixed track is strictly increased or strictly reduced according to the direction of the fixed track.
  • 2 is a flow chart of the method, as shown in FIG. 2, the method includes the following steps:
  • Step S11 The in-vehicle access point acquires a first sequence identifier, where the first sequence identifier is a first type of sequence identifier, and the first type of sequence identifier is a trackside that currently establishes a link with the in-vehicle access point.
  • the sequence identifier of the access point is a first type of sequence identifier, and the first type of sequence identifier is a trackside that currently establishes a link with the in-vehicle access point.
  • Step S12 The in-vehicle access point acquires a plurality of second-class sequence identifiers, and the second-type sequence identifier is a sequence identifier of a trackside access point that does not establish a link between the current in-vehicle access point.
  • the second type of sequence identifier may be a sequence identifier of all trackside access points except the first type of sequence identifier that can be obtained by the vehicle access point through the wireless medium, or may be an onboard access point according to one or more conditions. All available Some of the sequence identifiers of all trackside access points except the first type of sequence identifier are selected from the second type of sequence identifiers that satisfy the above conditions.
  • Step S13 The in-vehicle access point determines a second sequence identifier according to the sequence direction. If the sequence direction is from small to large, the second sequence identifier is the first one of the plurality of second type sequence identifiers. The second type of sequence identifier of the second type of sequence identifier having a large sequence identifier, if the sequence direction is from large to small, the second sequence identifier is the plurality of second type sequence identifiers The first sequence identifies the smallest sequence identifier of the second type of sequence identifier.
  • sequence direction is determined according to the direction in which the vehicle carrying the onboard access point runs on the fixed track. Sequence directions range from small to large, and from large to small. If the sequence direction is from small to large, the second sequence identifier is one of the plurality of second type sequence identifiers that is larger than the first sequence identifier, and the smallest second type of sequence identifier . If only one second type of sequence identifier is larger than the first sequence identifier, then the second type of sequence identifier is the second sequence identifier. If the sequence direction is from large to small, the second sequence identifier is one of the plurality of second type sequence identifiers that is smaller than the first sequence identifier, and the largest one Sequence identification. If only one second type of sequence identifier is smaller than the first sequence identifier, then the second type of sequence identifier is the second sequence identifier.
  • the sequence direction can characterize the trend of the sequence identification of the trackside access points that establish a link with the vehicle access point in sequence during the operation of the vehicle.
  • the sequence direction can be pre-specified or it can be obtained in real time. For example, there are five track-side access points placed on the fixed track side in the east-west direction.
  • the sequence identification of the five track-side access points is from 1 to 5 from east to west. If the sequence direction is specified in advance, the sequence direction is designated as small to large when the vehicle moves from east to west, and the sequence direction is designated from large to small when the vehicle moves from west to east. If the sequence direction is obtained in real time, when the vehicle moves from east to west, the vehicle access point first uses the traditional wireless LAN switching method to determine the trackside access point with which the link is established.
  • the vehicle access point Or other devices used to calculate the direction of the sequence find that the sequence identifier of the trackside access point that establishes a link with the in-vehicle access point is larger and larger, and the sequence direction is determined to be from small to large, after which the car access point is converted to the use of the present.
  • the wireless local area network switching method of the embodiment of the invention determines the second sequence identifier from small to large according to the sequence direction. For example, after using the traditional wireless LAN switching method for a period of time, if the number of positions of the P times of the recorded N times of WLAN switching is increased, the sequence direction is obtained from small to large, if the recorded N times are switched.
  • the sequence direction is obtained from large to small, wherein P is a value greater than 0.5N.
  • the sequence direction can also be obtained in other real-time ways.
  • an imaging device is disposed on the vehicle, and during the running of the vehicle, the imaging device takes a picture at a preset time, and the picture includes surrounding scenes such as a stop sign and the like when the vehicle passes.
  • Car set in the vehicle Carrying an access point, or other device for calculating a sequence direction, processing the picture, determining each location passing through the vehicle according to the surrounding scene in the picture, and according to the pre-stored route and each of the paths
  • the location, the direction in which the vehicle is operating on the fixed track can be determined, and then the sequence direction can be determined by the direction of the run.
  • the trackside access point identified by the second sequence identifier obtained by the above step is located in a moving direction of the vehicle, and the track side access point corresponding to the second sequence identifier is a plurality of second type sequence
  • the trackside access point identified by the identification is the starting point of the trackside access point from which the vehicle access point currently establishes the link, and is closest to the trackside access point of the vehicle access point along the direction of motion of the vehicle.
  • Step S14 The in-vehicle access point establishes a link with the target trackside access point, and the sequence identifier of the target trackside access point is the second sequence identifier.
  • the operation of the wireless LAN switching is performed to establish a link with the track-side access point identified by the second sequence identifier, that is, the target track-side access point.
  • the process of establishing a link between the in-vehicle access point and the target track-side access point is a process of completing the WLAN handover.
  • step S11 and step S12 there is no strict sequence between step S11 and step S12, and step S11 and step S12 can be performed in parallel.
  • a wireless local area network switching method in rail transit is disclosed by steps S11 to S14.
  • the trackside access point that establishes a link with the in-vehicle access point is referred to as a target trackside access point, and the target trackside access point is located in a moving direction of the vehicle, and the The target trackside access point is a trackside access point that establishes a link with the car access point before the WLAN switch, and the closest to the car access point among the plurality of trackside access points along the moving direction of the vehicle Trackside access point.
  • the target trackside access point When a random fluctuation of the RSSI occurs, the target trackside access point is less affected by the fluctuation than the other trackside access points, and the vehicle access point and the target trackside access point can be guaranteed. Inter-channel quality to avoid invalid mis-switching. Moreover, since the solution avoids invalid mis-handover, it can also reduce the service loss caused by frequent handover.
  • the wireless local area network switching method in the rail transit disclosed in the present application is applicable to various forms of wireless networks, such as a wireless mesh network and a wireless distributed system (English: wireless distribution system, abbreviation: WDS) network. .
  • WDS wireless distribution system
  • the wireless local area network WLAN network used in the vehicle-to-vehicle communication system is a mesh network
  • the primary link and the backup link may exist in the mesh network.
  • the standby link is considered as an unbuilt link. .
  • the plurality of second type sequence identifiers in step S12 of the foregoing embodiment may be sequence identifiers of all trackside access points except the first type of sequence identifier that can be obtained by the in-vehicle access point through the wireless medium, or may be based on one Or multiple bars
  • a second type of sequence identifier that satisfies the above conditions is selected among all the sequence identifiers of all trackside access points that can be obtained except the first type of sequence identifier.
  • the size of the RSSI of the wireless signal of the trackside access point can be used as the above condition.
  • the method for the vehicle access point to acquire the plurality of second type sequence identifiers includes: first, the vehicle access point acquires all the trackside access points. And obtaining a plurality of trackside access points in the trackside access points that have an RSSI greater than a preset threshold; and then acquiring sequence identifiers of the plurality of trackside access points as the plurality of The second type of sequence identifier.
  • the preset threshold may be preset according to network requirements.
  • All of the above-mentioned trackside access points refer to the respective trackside access points where the in-vehicle access point can acquire wireless signals.
  • a remote or malfunctioning distance from the onboard access point may result in the wireless signal of the trackside access point being unavailable to the in-vehicle access point.
  • the RSSI of each track-side access point marked by the plurality of second-class sequence identifiers obtained by the foregoing steps is greater than a preset threshold, so that the network requirement of the in-vehicle access point can be satisfied.
  • the wireless local area network switching method in the rail transit disclosed in the present application determines the target trackside access point by using the sequence identifier of the trackside access point, and the sequence identifier can be in various forms, and only needs to be secured along the fixed
  • the sequence identification of the plurality of trackside access points placed by the track may be strictly increased or strictly reduced according to the direction of the fixed track.
  • the sequence identifier may be a location number of a trackside access point or a media access control (abbreviation: MAC) address of a trackside access point.
  • the sequence identifier is a position number of the trackside access point, and a position number of the plurality of trackside access points placed along the fixed track is in accordance with a direction of the fixed track Strictly increasing or strictly decreasing.
  • the position number can be a number, other characters, or a combination of numbers and other characters, as long as the order between any two different elements in the set of position numbers that can be set can be determined according to the position number.
  • each trackside access point is preset with a position number.
  • the trackside access point may carry a preset position number of the trackside access point in a WLAN management frame (such as a beacon frame and a probe response frame).
  • a WLAN management frame such as a beacon frame and a probe response frame.
  • a reserved field for the extension of the device manufacturer is set, that is, a “Vendor Specific” field, and the trackside access point can set the position number of the trackside access point in the field. in.
  • the vehicle access point receives the WLAN management frame and acquires the location number in the WLAN management frame.
  • the sequence identifier is a MAC address of the trackside access point, and a value of a MAC address of the plurality of trackside access points placed along the fixed track is fixed according to the fixed The direction of the track is strictly increasing or strictly decreasing.
  • the MAC address of each trackside access point needs to be modified, so that the modified MAC address values of the plurality of trackside access points are in accordance with the The direction of the fixed track is strictly increasing or strictly decreasing.
  • the in-vehicle access point receives the WLAN frame sent by the trackside access point, and obtains the sender address (English: transmitter address, abbreviation: TA) in the WLAN frame, which is the MAC address of the trackside access point.
  • the sender address (English: transmitter address, abbreviation: TA) in the WLAN frame, which is the MAC address of the trackside access point.
  • the basic service set identifier (English: basic service set identifier, BSSID) is the MAC address of the trackside access point
  • BSSID basic service set identifier
  • the sequence identifier is a MAC address of the trackside access point
  • the full sequence set is saved at the in-vehicle access point before the vehicle is running, or is saved and capable of being in-vehicle access
  • the full sequence set includes MAC addresses of all trackside access points placed along the fixed track, and, in the full sequence set, is placed along the fixed track
  • the MAC addresses of the plurality of trackside access points are strictly increased or strictly decremented according to the direction of the fixed track. That is, the order between the MAC addresses of the trackside access points that are identified by the sequence does not depend on the value of the MAC address, but rather on the order in which the MAC addresses are discharged in the full sequence set.
  • the MAC addresses of all track-side access points placed beside the fixed track are arranged in the order of the fixed track along each track-side access point to obtain the full
  • the sequence set is such that the MAC address of the trackside access point in the full sequence set is strictly increased or strictly decremented according to the direction of the fixed track.
  • all of the trackside access points refer to all trackside access points that need to pass during the operation of the vehicle along a fixed orbit.
  • the in-vehicle access point can also determine whether WLAN switching is required.
  • the in-vehicle access point may determine whether a WLAN handover is currently required according to one or more of the following parameters: RSSI of a trackside access point of a current wireless connection, RSSI of an adjacent trackside access point, current wireless connection The throughput of the trackside access point.
  • the adjacent track-side access point refers to a second type in which each of the track-side access points that are not connected to the in-vehicle access point has a gap with the first sequence identifier within a preset range.
  • the track identifies the trackside access point that is marked.
  • the method for the car access point to determine whether it needs to perform WLAN switching includes:
  • the in-vehicle access point determines that the RSSI of the trackside access point for performing wireless data transmission with itself is smaller than the first RSSI threshold, and the RSSI of the adjacent trackside access point is greater than the second RSSI threshold, and When the throughput of the trackside access point for wireless data transmission is less than the first throughput threshold, it is determined that it needs to perform WLAN handover.
  • the present application also discloses a wireless local area network switching device in rail transit, which is applied to an in-vehicle access point, wherein a vehicle carrying an in-vehicle access point runs on a fixed track, and multiple track-side accesses are used. The points are placed along the fixed track.
  • the wireless local area network switching apparatus in the rail transit includes: a first acquisition module 100, a second acquisition module 200, a determination module 300, and a chain.
  • the road establishment module 400 is included in the wireless local area network switching apparatus in the rail transit.
  • the first obtaining module 100 is configured to obtain a first sequence identifier, where the first sequence identifier is a first type of sequence identifier, and the first type of sequence identifier is a current link with the in-vehicle access point. Sequence identification of the trackside access point;
  • the second obtaining module 200 is configured to obtain a plurality of second type sequence identifiers, where the second type sequence identifier is a sequence identifier of a trackside access point that does not establish a link between the current in-vehicle access point;
  • the determining module 300 is configured to determine, according to a sequence direction, a second sequence identifier, where the sequence direction is from small to large, and the second sequence identifier is the first sequence of the plurality of second type sequence identifiers The smallest second type of sequence identifier of the second type of sequence identifier, if the sequence direction is from large to small, the second sequence identifier is the number of the second type of sequence identifiers The largest sequence identifier of the second type of sequence identifier with a small sequence identifier;
  • the link establishing module 400 is configured to establish a link with a target trackside access point, where the sequence identifier of the target trackside access point is the second sequence identifier.
  • the second obtaining module 200 includes: a first acquiring unit, configured to acquire a received signal strength indication RSSI of all trackside access points, and select an RSSI of the all trackside access points that is greater than a preset threshold. Multiple trackside access points;
  • a second acquiring unit configured to acquire sequence identifiers of the plurality of trackside access points, and use the same as the multiple second type sequence identifiers.
  • the sequence identification can be implemented in various ways.
  • the sequence identifier is a position number of the trackside access point, and a position number of the plurality of trackside access points placed along the fixed track is in accordance with the fixed track.
  • the direction is strictly increasing or strictly decreasing.
  • the sequence identifier is a medium access control MAC address of the trackside access point, and a value of a MAC address of the plurality of trackside access points placed along the fixed track is The direction of the fixed track is strictly increasing or strictly decreasing.
  • the sequence identification is a medium access control MAC address of the trackside access point.
  • the wireless LAN switching device in the rail transit further includes: a storage module, the storage module is configured to pre-store a full-order set, and the full-order set includes the along the fixed track. MAC addresses of all trackside access points, and in the full sequence set, the MAC addresses of the plurality of trackside access points placed along the fixed track are strictly incremented according to the direction of the fixed track Or strictly decreasing.
  • the trackside access point that establishes a link with the vehicle access point is referred to as a target trackside access point, and the target trackside access point is located at the vehicle.
  • the target trackside access point is a trackside access point that establishes a link with the in-vehicle access point before switching from the WLAN, and a plurality of trackside access points along the direction of motion of the vehicle.
  • the trackside access point closest to the car access point When a random fluctuation of the RSSI occurs, the target trackside access point is less affected by the fluctuation than the other trackside access points, and the vehicle access point and the target trackside access point can be guaranteed. Inter-channel quality to avoid invalid mis-switching. Moreover, since the solution avoids invalid mis-handover, it can also reduce the service loss caused by frequent handover.
  • the application also discloses an access point.
  • the access point is an in-vehicle access point.
  • the access point 500 includes a processor 501, a memory 502, a bus 503, and a wireless interface 504, where
  • the processor 501 is connected to the memory 502 via a bus 503;
  • the wireless interface 504 is connected to the processor 501 through the bus 503;
  • the memory 502 is configured to store a program code of a wireless local area network switch in the rail transit;
  • the processor 501 is configured to acquire program code stored in the memory, and perform the following operations according to the program code:
  • the second sequence identifier Determining, according to the sequence direction, the second sequence identifier, if the sequence direction is from small to large, the second sequence identifier is a second type of sequence identifier of the plurality of second type sequence identifiers that is larger than the first sequence identifier The smallest second type of sequence identifier. If the sequence direction is from large to small, the second sequence identifier is a second class of the plurality of second type sequence identifiers that is smaller than the first sequence identifier. The largest sequence identifier in the sequence identifier;
  • the sequence identifier of the target trackside access point being the second sequence identifier.
  • sequence identification can be implemented in a variety of ways.
  • the sequence identifier is a position number of the trackside access point, and a position number of the plurality of trackside access points placed along the fixed track is in accordance with the fixed track.
  • the direction is strictly increasing or strictly decreasing.
  • the sequence identifier is a medium access control MAC address of the trackside access point, and a value of a MAC address of the plurality of trackside access points placed along the fixed track is The direction of the fixed track is strictly increasing or strictly decreasing.
  • the sequence identifier is a media access control MAC address of the trackside access point
  • the access point is pre-stored with a full sequence set, where the full sequence set includes the fixed a MAC address of all trackside access points that are placed in the track, and in the full sequence set, the MAC addresses of the plurality of trackside access points placed along the fixed track are in accordance with the fixed track
  • the direction is strictly increasing or strictly decreasing.
  • the access point disclosed in the present application is typically used as an in-vehicle access point, the vehicle carrying the in-vehicle access point is operated on a fixed track, and a plurality of trackside access points are placed along the fixed track.
  • the in-vehicle access point implements WLAN switching according to the wireless local area network switching procedure in the above-mentioned rail transit, which can ensure channel quality between the in-vehicle access point and the track-side access point, and avoid invalid mis-handover, thereby improving channel quality.
  • the techniques in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform.
  • the technical solution in the embodiment of the present invention may be embodied in the form of a software product, and the computer software product may be stored in a storage medium, such as a read-only memory (English: read-only memory, abbreviation: ROM).
  • ROM read-only memory
  • a random access memory (English: random-access memory, RAM), a magnetic disk, an optical disk, etc., includes a number of instructions for causing a processor to perform the methods described in certain embodiments of the present invention or embodiments.

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Abstract

本申请公开一种轨道交通中的无线局域网切换方法及装置，利用该方案实现WLAN切换后，与车载接入点建立链路的轨旁接入点称为目标轨旁接入点，所述目标轨旁接入点位于车辆的运动方向上，并且，所述目标轨旁接入点为从WLAN切换前与车载接入点建立链路的轨旁接入点为起点，沿着车辆的运动方向的多个轨旁接入点里最接近车载接入点的轨旁接入点。在发生RSSI的随机波动时，相对于其他轨旁接入点来说，所述目标轨旁接入点受到波动的影响比较小，能够保障车载接入点与所述目标轨旁接入点之间的信道质量，避免无效误切换。并且，由于本方案避免了无效误切换，还能够减少频繁切换带来的业务损失。

Description

轨道交通中的无线局域网切换方法及装置
本申请要求于2014年8月14日提交中国专利局、申请号为201410401408.X、发明名称为“轨道交通中的无线局域网切换方法及装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本公开涉及无线网络技术领域，尤其涉及一种轨道交通中的无线局域网切换方法及装置。
背景技术
为满足轨道交通车辆中乘客的上网需求，目前为轨道交通车辆设置有车地通信***，所述车地通信***采用无线局域网(英文：wireless local area network，缩写：WLAN)技术。参见图1，所述车地通信***包括：车载接入点1、轨旁接入点2和交换机3。其中，所述轨旁接入点2与所述交换机3相连接，所述轨旁接入点2为设置在轨道旁的接入点(英文：access point，缩写：AP)，通常在轨道旁布设多个轨旁接入点2，两个轨旁接入点2之间的距离一般为50米至200米，所述车载接入点1为设置在车辆上的AP，所述车载接入点1与轨旁接入点2建立链路，并与建立链路的轨旁接入点2进行无线数据的传输，从而使无线网络覆盖至车辆，满足乘客的上网需求。
在车辆行驶过程中，车载接入点1会获取轨旁接入点2的接收的信号强度指示(英文：receive signal strength indicator，缩写：RSSI)。当与所述车载接入点建立链路的轨旁接入点的RSSI过小或趋近饱和，或者其他轨旁接入点的RSSI相比与所述车载接入点建立链路的轨旁接入点的RSSI较大时，则所述车载接入点需要执行无线局域网(英文：wireless local area network，缩写：WLAN)切换的操作，通过WLAN切换，车载接入点能够与其他RSSI符合需求的轨旁接入点建立链路，以保证信道质量。
但是，无线环境的稳定性差，轨旁接入点的RSSI会发生随机波动，特别是在空间狭窄的环境中(如车辆通过隧道时)，各轨旁接入点的RSSI随机波动更明显。如果采用传统的WLAN切换方式，受到RSSI随机波动的影响，可能导致切换过于频繁，也可能导致切换成为无效切换。
发明内容
本发明实施例提供了一种轨道交通中的无线局域网切换方法及装置，以一定程度上解决传统技术中，在进行轨道交通中的无线局域网切换时，会出现的切换过于频繁，或者切换成为无效切换的问题。
为了解决上述技术问题，本发明实施例公开了如下技术方案：
第一方面，提供一种轨道交通中的无线局域网切换方法，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，所述方法包括：
所述车载接入点获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
所述车载接入点获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
所述车载接入点根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
所述车载接入点与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
结合第一方面，在第一方面第一种可能的实现中，所述车载接入点获取多个第二类序列标识，包括：
所述车载接入点获取所有轨旁接入点的RSSI，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；
所述车载接入点获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
结合第一方面，或者结合第一方面第一种可能的实现，在第一方面第二种可能的实现中，所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
结合第一方面，或者结合第一方面第一种可能的实现，在第一方面第三种可能的实现中，所述序列标识为所述轨旁接入点的MAC地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
结合第一方面，或者结合第一方面第一种可能的实现，在第一方面第四种可能的实现中，所述序列标识为所述轨旁接入点的MAC地址，所述车载接入点预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
第二方面，提供一种轨道交通中的无线局域网切换装置，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，包括：
第一获取模块，用于获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
第二获取模块，用于获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
确定模块，用于根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
链路建立模块，用于与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
结合第二方面，在第二方面第一种可能的实现中，所述第二获取模块包括：
第一获取单元，用于获取所有轨旁接入点的RSSI，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；
第二获取单元，用于获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
结合第二方面，或者结合第二方面第一种可能的实现，在第二方面第二种可能的实现中，所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
结合第二方面，或者结合第二方面第一种可能的实现，在第二方面第三种可能的实现中，所述序列标识为所述轨旁接入点的MAC地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
结合第二方面，或者结合第二方面第一种可能的实现，在第二方面第四种可能的实现中，所述序列标识为所述轨旁接入点的MAC地址；
所述轨道交通中的无线局域网切换装置还包括：
存储模块，用于预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
第三方面，提供一种接入点，所述接入点包括：处理器、存储器、总线和无线接口，其中，
所述处理器通过总线与所述存储器相连接；
所述无线接口通过所述总线与所述处理器相连接；
所述存储器，用于存储所述轨道交通中的无线局域网切换的程序代码；
所述处理器，用于获取所述存储器中存储的程序代码，并根据所述程序代码执行以下操作：
通过所述无线接口获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
通过所述无线接口获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
通过所述无线接口与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
通过本方案完成WLAN切换后，将与车载接入点建立链路的轨旁接入点称为目标轨旁接入点，所述目标轨旁接入点位于车辆的运动方向上，并且，所述目标轨旁接入点为从WLAN切换前与车载接入点建立链路的轨旁接入点为起点，沿着车辆的运动方向的多个轨旁接入点里最接近车载接入点的轨旁接入点。在发生RSSI的随机波动时，相对于其他轨旁接入点来说，所述目标轨旁接入点受到波动的影响比较小，能够保障车载接入点与所述目标轨旁接入点之间的信道质量，避免无效误切换。并且，由于本方案避免了无效误切换，还能够减少频繁切换带来的业务损失。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其它的附图。
图1为基于轨道交通的无线局域网的网络结构示意图；
图2为本发明公开的一种轨道交通中的无线局域网切换方法的实施例流程图；
图3为本发明公开的一种轨道交通中的无线局域网切换装置的结构示意图；
图4为本发明公开的一种接入点的结构示意图。
具体实施方式
本申请实施例提供一种轨道交通中的无线局域网切换方法及装置，以解决传统技术中，在进行基于轨道交通的WLAN切换时，会出现的切换过于频繁，或者切换为无效切换的问题。
为了使本领域的技术人员更好地理解本发明实施例中的技术方案，并使本发明实施例的上述目的、特征和优点能够更加明显易懂，下面结合附图对本发明实施例中技术方案作进一步详细的说明。
本申请一示例性实施例中，公开一种轨道交通中的无线局域网切换方法，该方法应用于车载接入点，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，沿所述固定的轨道安放的所述多个轨旁接入点的序列标识按照所述固定的轨道的方向严格递增或严格递减。图2为所述方法的流程图，如图2所示，该方法包括以下步骤：
步骤S11、所述车载接入点获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识。
步骤S12、所述车载接入点获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识。
第二类序列标识可以是车载接入点通过无线介质能获得的除第一类序列标识外的所有轨旁接入点的序列标识，也可以是车载接入点根据一个或多个条件，在所有能获得 的除第一类序列标识外的所有轨旁接入点的序列标识中选取的一些满足上述条件的第二类序列标识。
步骤S13、所述车载接入点根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识。
其中，序列方向根据携带所述车载接入点的车辆在所述固定的轨道上运行的方向确定。序列方向包括从小到大，以及从大到小两种形式。如果序列方向为从小到大，第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的一个或多个第二类序列标识中，最小的第二类序列标识。如果只有一个第二类序列标识比第一序列标识大，则这个第二类序列标识就是第二序列标识。如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的一个或多个第二类序列标识中，最大的序列标识。如果只有一个第二类序列标识比第一序列标识小，则这个第二类序列标识就是第二序列标识。
序列方向能够表征车辆在运行过程中，依次与所述车载接入点建立链路的轨旁接入点的序列标识的变化趋势。序列方向可以是预先指定的，也可以是实时得到的。例如，在东西方向的固定轨道边安放有5个轨旁接入点，这5个轨旁接入点的序列标识从东向西依次为1至5。如果预先指定序列方向，则当车辆从东向西运动时，序列方向被指定为从小到大，当车辆从西向东运动时，序列方向被指定为从大到小。如果用实时的方式得到序列方向，当车辆从东向西运动时，车载接入点先使用传统的无线局域网切换方法确定与其建立链路的轨旁接入点，一段时间后，车载接入点或者用于计算序列方向的其他设备发现与车载接入点建立链路的轨旁接入点的序列标识越来越大，则判定序列方向为从小到大，此后车载接入点转为使用本发明实施例的无线局域网切换方法，并按照序列方向为从小到大确定第二序列标识。例如，采用传统的无线局域网切换方法一段时间后，若记录的N次WLAN切换中，有P次的位置序号都是增加的，则得到所述序列方向为从小到大，若记录的N次切换中，有P次的位置序号都是减小的，则得到所述序列方向为从大到小，其中，P为大于0.5N的数值。可替换的，还可以用其他实时的方式得到序列方向。例如，在车辆上设置摄像装置，在车辆运行的过程中，所述摄像装置每隔预设时间拍摄一张图片，所述图片中包含车辆经过时的周边景物，如站牌标识等。设置在车辆中的车 载接入点，或者用于计算序列方向的其他设备，对所述图片进行处理，根据图片中的周边景物确定车辆运行过程中途经的各个地点，并根据预先存储的路线和所述途经的各个地点，能够确定车辆在所述固定的轨道上运行的方向，然后通过所述运行的方向即可确定所述序列方向。
通过上述步骤获取到的所述第二序列标识所标识的轨旁接入点，位于车辆的运动方向上，并且，所述第二序列标识对应的轨旁接入点为多个第二类序列标识所标识的轨旁接入点里，从车载接入点当前建立链路的轨旁接入点为起点，沿着车辆的运动方向，最接近车载接入点的轨旁接入点。
步骤S14、所述车载接入点与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
车载接入点需要切换与其建立链路的轨旁接入点时，执行无线局域网切换的操作，以和第二序列标识所标识的轨旁接入点，即目标轨旁接入点建立链路。所述车载接入点与目标轨旁接入点建立链路的过程，即为完成WLAN切换的过程。
另外，上述实施例中，步骤S11和步骤S12之间并无严格的先后顺序，可以并行的执行步骤S11和步骤S12。
上述实施例中，通过步骤S11至步骤S14公开了一种轨道交通中的无线局域网切换方法。通过该方法实现WLAN切换后，将与车载接入点建立链路的轨旁接入点称为目标轨旁接入点，所述目标轨旁接入点位于车辆的运动方向上，并且所述目标轨旁接入点为以WLAN切换前与车载接入点建立链路的轨旁接入点为起点，沿着车辆的运动方向的多个轨旁接入点里最接近车载接入点的轨旁接入点。在发生RSSI的随机波动时，相对于其他轨旁接入点来说，所述目标轨旁接入点受到波动的影响比较小，能够保障车载接入点与所述目标轨旁接入点之间的信道质量，避免无效误切换。并且，由于本方案避免了无效误切换，还能够减少频繁切换带来的业务损失。
本申请所公开的轨道交通中的无线局域网切换方法适用于多种形式的无线网络，如无线网格(英文：mesh)网络网络和无线分布式***(英文：wireless distribution system，缩写：WDS)网络。
如果在车地通信***中采用的无线局域网WLAN网络为mesh网络，所述mesh网络中可能会同时存在主链路和备用链路，这种情况下，所述备用链路作为未建链路考虑。
在上述实施例的步骤S12中的多个第二类序列标识可以是车载接入点通过无线介质能获得的除第一类序列标识外的所有轨旁接入点的序列标识，也可以根据一个或多个条 件，在所有能获得的除第一类序列标识外的所有轨旁接入点的序列标识中选取一些满足上述条件的第二类序列标识。例如，可以用轨旁接入点的无线信号的RSSI的大小作为上述条件。
当用轨旁接入点的无线信号的RSSI的大小作为上述条件时，车载接入点获取多个第二类序列标识的方法包括：首先，所述车载接入点获取所有轨旁接入点的RSSI，并获取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；然后，获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
其中，所述预设阈值可以根据网络需求被预先设定。
上述的所有轨旁接入点，指的是车载接入点能够获取无线信号的各个轨旁接入点。距离所述车载接入点较远或发生故障可能导致轨旁接入点的无线信号无法被车载接入点获取。
通过上述步骤获取的所述多个第二类序列标识所标记的各轨旁接入点的RSSI均大于预设阈值，从而能够满足车载接入点的网络需求。
另外，本申请所公开的轨道交通中的无线局域网切换方法，利用轨旁接入点的序列标识确定目标轨旁接入点，所述序列标识可以为多种形式，只需保证沿所述固定的轨道安放的所述多个轨旁接入点的序列标识按照所述固定的轨道的方向严格递增或严格递减即可。例如，序列标识可以为轨旁接入点的位置序号或者轨旁接入点的介质访问控制(英文：media access control，缩写：MAC)地址。
在一种实现中，所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。位置序号可以是数字，其他字符，或者数字和其他字符的组合，只要根据位置序号能够确定可被设置的位置序号的集合中任意两个不同的元素间的顺序即可。
当所述序列标识为所述轨旁接入点的位置序号时，各个轨旁接入点被预先设置位置序号。
轨旁接入点可以在WLAN管理帧(如信标(英文：beacon)帧和探测响应(英文：probe response)帧)中携带该轨旁接入点被预先设置的位置序号。在beacon帧和probe response帧的帧结构中，均设置有供设备厂商扩展使用的保留字段，即“Vendor Specific”字段，轨旁接入点可将轨旁接入点的位置序号设置在该字段中。车载接入点接收到WLAN管理帧，获取该WLAN管理帧中的位置序号。
在另一种实现中，所述序列标识为所述轨旁接入点的MAC地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
在该实现中，轨旁接入点安放在固定的轨道旁之后，需要修改各个轨旁接入点的MAC地址，使得修改后的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
车载接入点接收到轨旁接入点发送的WLAN帧，获取该WLAN帧中的发送方地址(英文：transmitter address，缩写：TA),即为轨旁接入点的MAC地址。或者在基本服务集标识(英文：basic service set identifier，缩写：BSSID)为轨旁接入点的MAC地址的情况下，车载接入点获取接收到轨旁接入点发送的WLAN帧中的BSSID即为轨旁接入点的MAC地址。
在又一种实现中，所述序列标识为所述轨旁接入点的MAC地址，在车辆运行前，全序集合被保存在车载接入点，或者被保存在与能够与该车载接入点通信的车载设备中，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。也就是说，作为序列标识的轨旁接入点的MAC地址间的顺序不依赖于MAC地址的值，而是取决于该MAC地址在所述全序集合中的排放顺序。在轨旁接入点安放在固定的轨道旁之后，安放在固定的轨道旁的所有轨旁接入点的MAC地址被按照各个轨旁接入点沿固定的轨道的顺序排列以得到所述全序集合，使得所述全序集合中的轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
其中，所述所有轨旁接入点指的是车辆沿固定的轨道运行过程中，需要经过的所有轨旁接入点。
另外，在本申请公开的轨道交通中的无线局域网切换方法中，车载接入点还可以判断是否需要进行WLAN切换。所述车载接入点可根据以下参数中的一个或多个判断当前是否需要进行WLAN切换：当前无线连接的轨旁接入点的RSSI，相邻的轨旁接入点的RSSI，当前无线连接的轨旁接入点的吞吐量。
其中，所述相邻的轨旁接入点，指的是未与车载接入点建立链路的各个轨旁接入点中，与第一序列标识的差距在预设范围内的第二类序列标识所标记的轨旁接入点。
在判断当前是否需要进行WLAN切换时，可以只根据上述任一参数，或者任意两个参数进行判断。为了提高判断精度，还可以同时结合上述三个参数共同判断是否需要进行 WLAN切换。当同时结合上述三个参数时，所述车载接入点判断自身是否需要进行WLAN切换的方法包括：
当所述车载接入点确定与自身进行无线数据传输的轨旁接入点的RSSI小于第一RSSI阈值，并且，相邻的轨旁接入点的RSSI大于第二RSSI阈值，并且，与自身进行无线数据传输的轨旁接入点的吞吐量小于第一吞吐量阈值时，确定自身需要进行WLAN切换。
结合所述三个参数进行判断的方案，综合考虑了各个参数对WLAN网络的影响，能够提高判断精度。
相应的，本申请还公开了一种轨道交通中的无线局域网切换装置，该装置应用于车载接入点，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放。在本申请公开的一示例性实施例中，参见图3所示的结构示意图，所述轨道交通中的无线局域网切换装置包括：第一获取模块100、第二获取模块200、确定模块300和链路建立模块400。
其中，所述第一获取模块100，用于获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
所述第二获取模块200，用于获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
所述确定模块300，用于根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
所述链路建立模块400，用于与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
其中，所述第二获取模块200包括：第一获取单元，用于获取所有轨旁接入点的接收的信号强度指示RSSI，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；
第二获取单元，用于获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
在本申请所公开的轨道交通中的无线局域网切换装置中，所述序列标识能够以多种方式实现。
在其中一种实现中，所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
在另一种实现中，所述序列标识为所述轨旁接入点的介质访问控制MAC地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
在另一种实现中，所述序列标识为所述轨旁接入点的介质访问控制MAC地址。这种情况下，所述轨道交通中的无线局域网切换装置还包括：存储模块，所述存储模块，用于预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
利用上述轨道交通中的无线局域网切换装置实现WLAN切换后，将与车载接入点建立链路的轨旁接入点称为目标轨旁接入点，所述目标轨旁接入点位于车辆的运动方向上，并且所述目标轨旁接入点为从WLAN切换前与车载接入点建立链路的轨旁接入点为起点，沿着车辆的运动方向的多个轨旁接入点里最接近车载接入点的轨旁接入点。在发生RSSI的随机波动时，相对于其他轨旁接入点来说，所述目标轨旁接入点受到波动的影响比较小，能够保障车载接入点与所述目标轨旁接入点之间的信道质量，避免无效误切换。并且，由于本方案避免了无效误切换，还能够减少频繁切换带来的业务损失。
进一步的，本申请还公开了一种接入点。该接入点为车载接入点。参见图4，所述接入点500包括：处理器501、存储器502、总线503和无线接口504，其中，
所述处理器501通过总线503与所述存储器502相连接；
所述无线接口504通过所述总线503与所述处理器501相连接；
所述存储器502，用于存储所述轨道交通中的无线局域网切换的程序代码；
所述处理器501，用于获取所述存储器中存储的程序代码，并根据所述程序代码执行以下操作：
通过所述无线接口获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
通过所述无线接口获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
通过所述无线接口与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
另外，所述处理器501执行的操作中，所述序列标识能够以多种方式实现。
在其中一种实现中，所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
在另一种实现中，所述序列标识为所述轨旁接入点的介质访问控制MAC地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
在另一种实现中，所述序列标识为所述轨旁接入点的介质访问控制MAC地址，所述接入点预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
本申请所公开的接入点通常用作车载接入点，携带所述车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放。所述车载接入点按照上述公开的轨道交通中的无线局域网切换程序实现WLAN切换，能够保障车载接入点与轨旁接入点之间的信道质量，避免无效误切换，从而提高信道质量。另外，还能够减少频繁切换带来的业务损失。
本领域的技术人员可以清楚地了解到本发明实施例中的技术可借助软件加必需的通用硬件平台的方式来实现。基于这样的理解，本发明实施例中的技术方案可以以软件产品的形式体现出来，该计算机软件产品可以存储在存储介质中，如只读存储器(英文：read-only memory，缩写：ROM)、随机存取存储器(英文：random-access memory，缩写：RAM)、磁碟、光盘等，包括若干指令用以使得处理器执行本发明实施例或者实施例的某些部分所述的方法。
本说明书中的各个实施例均采用递进的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其它实施例的不同之处。尤其，对于***实施例而言，由于其基本相似于方法实施例，所以描述的比较简单，相关之处参见方法实施例的部分说明即可。
应当理解的是，本发明并不局限于上面已经描述并在附图中示出的精确结构，并且可以在不脱离其范围进行各种修改和改变。本发明的范围仅由所附的权利要求来限制。

Claims (15)

  1. 一种轨道交通中的无线局域网切换方法，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，其特征在于，包括：
    所述车载接入点获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
    所述车载接入点获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
    所述车载接入点根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
    所述车载接入点与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
  2. 根据权利要求1所述的方法，其特征在于，所述车载接入点获取多个第二类序列标识，包括：
    所述车载接入点获取所有轨旁接入点的接收的信号强度指示(RSSI)，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；
    所述车载接入点获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
  3. 根据权利要求1或2所述的方法，其特征在于，
    所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
  4. 根据权利要求1或2所述的方法，其特征在于，
    所述序列标识为所述轨旁接入点的介质访问控制(MAC)地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
  5. 根据权利要求1或2所述的方法，其特征在于，
    所述序列标识为所述轨旁接入点的MAC地址，所述车载接入点预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
  6. 一种轨道交通中的无线局域网切换装置，其中，携带车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，其特征在于，包括：
    第一获取模块，用于获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
    第二获取模块，用于获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
    确定模块，用于根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
    链路建立模块，用于与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
  7. 根据权利要求6所述的装置，其特征在于，所述第二获取模块包括：
    第一获取单元，用于获取所有轨旁接入点的接收的信号强度指示(RSSI)，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点；
    第二获取单元，用于获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
  8. 根据权利要求6或7所述的装置，其特征在于，
    所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
  9. 根据权利要求6或7所述的装置，其特征在于，
    所述序列标识为所述轨旁接入点的介质访问控制(MAC)地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
  10. 根据权利要求6或7所述的装置，其特征在于，
    所述序列标识为所述轨旁接入点的MAC地址；
    所述轨道交通中的无线局域网切换装置还包括：
    存储模块，用于预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
  11. 一种接入点，所述接入点为车载接入点，携带所述车载接入点的车辆运行在固定的轨道上，多个轨旁接入点沿所述固定的轨道安放，所述接入点包括：处理器、存储器、总线和无线接口，其中，
    所述处理器通过总线与所述存储器相连接；
    所述无线接口通过所述总线与所述处理器相连接；
    所述处理器，用于通过所述无线接口获取第一序列标识，所述第一序列标识为第一类序列标识，所述第一类序列标识为当前与所述车载接入点建立链路的轨旁接入点的序列标识；
    所述处理器，还用于通过所述无线接口获取多个第二类序列标识，所述第二类序列标识为当前与所述车载接入点间未建立链路的轨旁接入点的序列标识；
    所述处理器，还用于根据序列方向确定第二序列标识，如果所述序列方向为从小到大，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识大的第二类序列标识中，最小的第二类序列标识，如果所述序列方向为从大到小，所述第二序列标识为所述多个第二类序列标识中比所述第一序列标识小的第二类序列标识中，最大的序列标识；
    所述处理器，还用于通过所述无线接口与目标轨旁接入点建立链路，所述目标轨旁接入点的序列标识为所述第二序列标识。
  12. 根据权利要求11所述的接入点，其特征在于，所述处理器通过所述无线接口获取多个第二类序列标识，包括：
    所述处理器，用于获取所有轨旁接入点的接收的信号强度指示(RSSI)，并选取所述所有轨旁接入点中RSSI大于预设阈值的多个轨旁接入点，获取所述多个轨旁接入点的序列标识，将其作为所述多个第二类序列标识。
  13. 根据权利要求11或12所述的接入点，其特征在于，
    所述序列标识为所述轨旁接入点的位置序号，沿所述固定的轨道安放的所述多个轨旁接入点的位置序号按照所述固定的轨道的方向严格递增或严格递减。
  14. 根据权利要求11或12所述的接入点，其特征在于，
    所述序列标识为所述轨旁接入点的介质访问控制(MAC)地址，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址的值按照所述固定的轨道的方向严格递增或严格递减。
  15. 根据权利要求11或12所述的接入点，其特征在于，
    所述序列标识为所述轨旁接入点的MAC地址，所述存储器预先存储有全序集合，所述全序集合中包括沿所述固定的轨道安放的所有轨旁接入点的MAC地址，并且，在所述全序集合中，沿所述固定的轨道安放的所述多个轨旁接入点的MAC地址按照所述固定的轨道的方向严格递增或严格递减。
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