Intelligent roaming method applied in automatic guidance vehicle

Intelligent roaming method applied to automatic guided vehicles

<p>100. . . Local area network</p><p>101. . . Basic service group</p><p>102. . . Basic service group</p><p>103. . . workstation</p><p>104. . . File server</p><p>301. . . Idle state</p><p>302. . . set up</p><p>303. . . Identification signal box</p><p>304. . . Jump sequence</p><p>305. . . confirm</p><p>306. . . During the connection phase</p><p>307. . . Exchange signal box</p>

Figure 1: Illustrates the typical hardware architecture of a wireless local area network system.

Figure 2: According to wireless local area network standards(IEEE 802.11), The frequency hopping bandwidth of the radio signal _， In the U.S. and Canada79Of channels, are between2.04GHZ-2.50GHZbetween.

Figure 3: Illustrates the traditional media capture control for a wireless local area network mobile station from finding to registering with a wireless base station and a wireless base station(medium access control MAC)Second level(sub-layer)Management structure.

Figure 4: Illustrates the detection procedure of the present invention.

Figure 5: Schematic description of the Ethernet identification signal of the present invention(ETHE-BEACON).

Figure 6: Illustrates the geographic location of adjacent base stations of the present invention.

Figure 7: Illustrates the coverage of the base station of the present invention.

[Technical field]

The invention field of the present invention is related to wireless local area network(WirelessLocal Area Network,WLAN)Roaming algorithm. Especially the action station(mobile Station)Connection method with radio local area network base station for application in automatic guided vehicles(automatic guidancevbhicle,AGV).

Background of the invention[Prior art]

According to wireless local area network standards(IEEE802.11), A wireless local area network mobile station needs to be connected to a wireless base station to exchange information with the file server of the network system or other mobile stations. This radio base station is connected to a distributed system(distribute systems)And a set of basic service groups(basic Service areas). After a wireless base station has established a connection, a mobile station in a wireless local area network can communicate with a mobile station in another radio local area network at a longer distance through this radio base station. In addition, a radio base station also provides a mobile station in the wireless local area network, through which the radio base station retrieves network resources in the distributed system.

picture1It is a typical hardware architecture of a wireless local area network system. As shown1As shown, aether(Ethernet)Local area network100There are two basic service groups(basic service sets)101(Bss1)with102(Bss2), A workstation(workstation)103And a file server(fileserver)104. Each basic service group includes a wireless base station and two wireless mobile stations. Basic service groupBSSIIncluding wireless base stationAP1And two wireless mobile stationsSTA1withSTA2. Basic service groupBSS2Including wireless base stationAP2And two wireless mobile stationsSTA3withsTA4. Each wireless mobile station itself must be connected to a wireless base station before it can be connected to the Ethernet LAN100File server104Or workstation103communication. When a wireless local area network mobile station is turned on, the mobile station first looks for a wireless base station. After finding a wireless base station, the mobile station will register with the wireless base station(registration). After completing the registration procedures, the mobile station can synchronize with the wireless base station. After that, the mobile station can send and receive data through the wireless base station.

According to wireless local area network standards(1EEE 802.11), The bandwidth of the working frequency of the radio network, in the United States and Canada79Of channels, are between2.40GHZand2.50GHZBetween, as shown in the figure2Shown. The radio base station will be the master of time(time master)To perform the time synchronization function(timing Synchronization function,TSF)In order to maintain the benchmark, and synchronize with all wireless local area network mobile stations in the same basic service group based on this benchmark. In order to synchronize with all wireless local area network mobile stations in the basic service group, for each channel, the wireless base station will periodically transmit the identification signal frame(beacon), Each identification signal box contains the parameters of the time synchronization timer of the wireless base station and the sequence of frequency hopping(hopping sequence). The radio base station will transmit an identification signal frame in a fixed time interval, and this fixed time interval is called an identification signal frame interval(beaconinterval).

The wireless local area network mobile station that receives the identification signal frame will always use the identification signal frame contained in the wireless base station.`Time information, this wireless base station serves the basic service group of this mobile station. If the time synchronization function timer of the wireless local area network mobile station is different from the time mark in the received identification signal box(time stamp), The wireless local area network mobile station that has received the identification signal frame will transfer its internal(local)The timer is set to the received time mark value.

Traditionally, when a wireless base station in the basic service group is turned on, the wireless base station will periodically send an identification signal frame to all wireless local area network mobile stations in the basic service group. The identification signal frame contains the information synchronized with the wireless base station, and this information will be referenced by the wireless local area network mobile station that is looking for the wireless base station. Because the identification signal frame interval used by traditional technology is long (100Milliseconds), which may cause the wireless LAN mobile station to search for the wireless base station for too long.

Before a wireless local area network mobile station can communicate with a wireless base station, it must first register. according toIEEE 802.11Standard, registration consists of two stages. The first stage is confirmation(authentication). This program is used to identify whether the mobile station has legal rights and capture control via a medium(medium access contral,MAC)Floor(layer)To capture this wireless local area network. After the confirmation is passed, the mobile station needs to connect with the wireless base station by sending a connection request signal box to the wireless base station(connectionlink), And then wait to receive a response box from the radio station, which informs the connection status.

For a wireless local area network mobile station, from the search to the traditional media capture control that is registered with a wireless base station(Sub-layer)Management structure, as shown in the figure3Shown. According to the picture3The design of a wireless local area network mobile station will perform three phases: search(Scan)Stage, confirmation(authentication)Phase, and connection(association)stage. During the search phase, allIEEE 802.11Wireless local area network mobile station, starting at "idle(IDLE)"Status (step301). The channel hopping work of the radio network is set by the hardware (step302). In order to find the wireless base station, the wireless local area network mobile station will search in each channel and search the identification signal frame sent from the wireless base station (step303). Once the identification signal frame on the channel and the radio base station is found, the search phase is complete. Otherwise, the wireless LAN mobile station will search for the next channel and go back to step302. Set the skip channel of the next radio network.

After receiving the identification signal frame of the wireless base station, the wireless local area network mobile station sets its own channel hopping time and channel hopping sequence according to the parameters contained in the identification signal frame of the wireless base station (step304) To synchronize with the wireless base station. The remaining steps continue with the confirmation phase and the connection phase.

In the confirmation phase,IEEE802.11Usually a two-way confirmation is required. In steps305In the wireless local area network mobile station and the wireless base station exchange certain signal frames to confirm. This stage can include three more steps: identity declaration(assertion of identity), Identity verification(challengeof assertion)And verify response(response to challenge). In the connection phase (step306), the wireless local area network mobile station exchanges certain connection signal frames with the wireless base station to complete the registration of the wireless base station. The communication link between the wireless local area network mobile station and the wireless base station is thus established. After that, the wireless local area network mobile station can start to exchange information frames with the wireless base station (step307).

Because the wireless local area network is in2.40GHzwith2.50GHzFrequency hopping work between, if according to the Federal Communications Commission(Federal CommunicationsCommissions,FCC)Requirements, the wireless local area network mobile station may be79In each channel, it takes a while to search for wireless base stations that may work on any channel.

Each box used for confirmation and connection must be802.11standard(CarrierSense Multiple Access With Collision AVoidanceCsMA/CA)Was sent out. For a wireless local area network mobile station, the time it takes to complete all the processes of confirmation and connection varies greatly and is unpredictable, especially when the information traffic of the wireless channel is busy. So, for followIEEE802.11For standard wireless local area network mobile stations, the time from finding a wireless base station to completing registration is unpredictable.

From the above-mentioned conventional techniques, we can see the shortcomings of the traditional capture technology, which is insufficient for the efficiency of the connection between the wireless local area network mobile station and the wireless base station. Therefore, for wireless local area network mobile stations, there is an urgent need for more rapid connection technology to quickly capture a wireless local area network through a wireless base station.

Problem description of this creation

Generally speaking, wireless local area networks are used in work areas. A vehicle passes through multiple basic service groups along a pre-designed path(BSS).NDCExisting roaming algorithms in China cannot support this application, switching from the current base station to the next base station, similar to mobile phone applications, without any delay. As automated guided vehicles(Automatic Guidance Vehicle)Mobility, this delay is the key to factory applications. For example, the scan time of each channel is200How seconds(mini seconds), So if there is80A hopping channel, for an automated guided vehicle, it takes on average8It takes only a few seconds to establish a connection with the base station in the basic service group. This is a long time delay. Usually in this time interval, the automated guided vehicle has moved a long distance. As a result, there are many messages that cannot be communicated between the automatic guided vehicle and other control units. Automated guided vehicles will lose their guidance, causing industrial safety problems in the factory.

Therefore, a smart roaming algorithm is needed to solve this problem. According to this roaming algorithm, it is hoped that the search time for jumping from one basic service group to another basic service group can be greatly reduced.

[Summary of the invention]

The purpose of the present invention is to be used in automatic guided vehicles(automaticguidance vehicle,AGV)Provides an intelligent roaming algorithm to support the processing of base stations in wireless local area network systems, in which automatic guided vehicles can roam in a predetermined path. To achieve the purpose of fast roaming, the key is to reduce the time for the mobile station to search for the next base station to roam to. To achieve the purpose of reducing the search time, each base station will be set in advance with neighboring base stations. When connecting, the mobile station can obtain information about its neighboring base stations from the base station currently connected to. In this way, the mobile station can continue to monitor the signal strength of its neighboring base stations. During roaming, the mobile station can choose the best base station connection without searching all channels.

[Implementation]

Detailed description of the best embodiment:1.Introduction: First explain the wireless local area network(wireless Local AreaNetwork)Intelligent roaming algorithm of the system. After the detailed description of the preferred embodiment, the system settings will be explained.

Those who are familiar with the technology should be able to understand that the description in the text can only be used as an embodiment, and understand the present invention based on the description in the text. In addition, those skilled in the art can modify this embodiment within the scope and spirit of the present invention defined by the scope of the patent application.

2.Purpose: In traditional systems, a mobile station must search every channel (in the Federal Communications Commission(FCC)The largest in the adjustment area79Channels), find a base station most suitable for connection with the mobile station during roaming. For some time-critical applications, too long search time is not allowed. Therefore, an algorithm for reducing roaming time has been developed to meet the needs of this critical application.

In addition to fast roaming, the design of the present invention allows a roaming mobile station to move freely in any direction when it leaves the coverage of the connected base station. This design makes the system more flexible in application.

In addition to roaming, the implementation of the present invention also improves the search algorithm after the mobile station is turned on. By applying the modified algorithm of the present invention, the mobile station can always find the best base station and connect with it after starting up.

3.Algorithm: This section will briefly describe the intelligent roaming algorithm that can shorten the search time. The key to achieving fast roaming is to reduce the time for the mobile station to search for the next base station to roam to. In order to reduce the search time, each base station will be set in advance with neighboring base stations. During the connection period, the mobile station can obtain the information of the neighboring base station from the base station currently connected to the mobile station. In this way, the mobile station can continuously monitor the signal strength of the base station adjacent to it. During roaming, the mobile station can choose the best base station connection without searching all channels.

The intelligent roaming algorithm consists of five parts, which are explained as follows:3.1Synchronize(Synchronization)This section explains how these base stations are combined with smart roaming functions and how the base stations can connect to the Ethernet(Ethernet)Time synchronization function(Timing Synchronization Function,TSF).Synchronize with other base stations. In addition, the present invention also includes a backup(back Up)Algorithm to solve the time master(timing master)Disconnection problem.

(1)To achieve these functions must be managed by the network management system(networkmanagement network System, NMS)Set up a base station in advance as the time synchronization function(TSF)Time master(timing master). With the master of time, this master base station will be through the Ethernet network(Ethernet network)Periodic transmission time synchronization function(TSF)Time, and allow other base stations to update the time of the time synchronization function with the master base station(master access point)Stay in sync.

(2)All other base stations, we call them slave base stations(slaveaccess point), Until it receives the time synchronization function from the master base station(TSF)time. When selecting the same time synchronization function as the master base station(TSF)After that time, the subordinate base station can start their basic service group. After that, when the slave base station receives the synchronization function from the master control base station(TSF)Time, the slave base station needs to dynamically(dynamically)Adjust their internal timers(local timer)To maintain synchronization with the master base station. With this method, all base stations and mobile stations can synchronize their time(TSF)Time synchronization(Synchronization). Its worth noting that according to the wireless local area network standard802.11(IEEE802.11), The base station and the connected base station can periodically mark the signal frame through wireless(Beacon frame)Make time synchronization function(TSF)Time synchronization.

(3)In addition to the master base station, from now on we call it the first master(primary-master)The base station can also be managed through the network management system(network management system,NMS)Set the second master(Secondary-maSter)Base station. If the first main control base station is disconnected after the second main control base station has been set, the second main control base station will take over from the first main control base station and act as the main control base station, and it must periodically transmit its time synchronization Function(TSF)Time, so that the time of the entire system can be synchronized.

3.2Adjacent base station(Neighboring APs)This section describes the algorithm, which includes how each base station collects information from its neighboring base stations and how the mobile station obtains this information.

(1)Manage the system through the network(NetWOrk Management SyStem,NMS), Each base station and neighboring base stations must be set in advance(2)All exist in the same subnet(SUb-net)All base stations must know the frequency hopping type of other base stations(hOpping pattern)And frequency hopping collection(hOpping Set). In order to achieve this, each base station must periodically send its own frequency hopping information to the Ethernet network(Ethernet)superior.

(3)After opening and synchronizing, the base station will receive the frequency hopping information of neighboring base stations through the above(2)The described receiving and sending box, and then storing the received information in their database(database). In this way, by exchanging information through the Ethernet, each base station will have the same secondary network as itself(Subnet)And the frequency hopping information of neighboring base stations.

(4)In terms of connection, the mobile station will first request the currently connected base station to provide the frequency hopping information of the adjacent base station. At any time, as long as the base station receives the connection request issued by the mobile station(Association-request), The base station must place the frequency hopping information of the adjacent base station in the link response box(association-response frame)Respond to the action station. Therefore, after the connection is completed, the mobile station will know the frequency hopping information of the base station adjacent to the current base station.

3.3Detect the identification signal of adjacent base stations(Sniffing theBeacon of neighboring APS)Referring to Figure 4, after connecting with the base station, the mobile station has obtained the frequency hopping information of the adjacent base station. Then the base station can continuously detect the identification signal of the base station adjacent to itself. The mobile station will also convert the collected identification signals into received signal strength indicators(Received Signal Strength indicator,RSSI)The value is stored in its own database, and when the mobile station is roaming, the information will be referenced. It is worth noting that the received signal strength index converted from the received identification signal(RSSI)The value can be regarded as the relative distance index value between the mobile station and the adjacent base station. If the received signal strength index value is large, it means that the distance between the mobile station and the base station is short. Therefore, when roaming, the mobile station always chooses to have the best received signal strength index(RSSI)Value base station and connect with it. The detection(Sniff)The method is explained in detail.

(1)If frequency hopping stays(hopping dWell)The time is set to identify the signal frame interval(Beacon interval)When it is a multiple of, the base station will transmit its identification signal frame at the beginning of each frequency hopping camp. Because each base station and mobile station have been synchronized and the mobile station has received frequency hopping information after connecting with the neighboring base station, the mobile station can directly jump to the base station channel adjacent to the mobile station and stay for a short period of time To listen to the identification signal from the neighboring base station. If an identification signal is received during this period _， The received signal strength index in the identification signal(RSSI)The value will be stored in the database of the mobile station. Figure 4 shows the start of detection at each frequency hopping dwell(Sniff)When identifying the signal, how does the mobile station jump between the currently connected base station and the base station adjacent to itself.

(2)During the detection period, the base station and each connected mobile station cannot transmit data packets(packets). Only the identification signal frame transmitted by the base station can be received in space during this period.

(3)At the beginning of each hop channel, the mobile station will continue to detect the identification signal of the base station adjacent to it(Beacon). In addition, the detection(Sniff)The sequence will be executed successively between adjacent base stations. For example, if there are multiple adjacent base stations (base stations1, Base station2And base station3), its detection(Sniff)The order will be the base station1Base station2Base station3And then go back to the original sequence base station1Continue to execute.

(4)For each adjacent base station, the mobile station will save the last four received signal strengths collected by the identification signal(RSSI)value. When the mobile station is roaming, the received signal strength(RSSI)The value will be used by reference. This means that the mobile station can obtain the signal strength of the neighboring base station at the moment of roaming.

3.4roaming(Roaming)This section explains how the mobile station in the base station adjacent to its own base station decides to roam to the best mobile station. In addition, it also describes the algorithm used when the mobile station cannot be connected to all adjacent base stations. _‥

(1)As with the algorithm described in the previous section, the mobile station will retain the received signal strength indicators of the last four detections(RSSI)result. When roaming starts (that is, the quality of the received identification signal is lower than the roaming threshold), the mobile station will first average the received signal strength identification of the last second detection identification signal of each adjacent base station(RSSI)value. If the detected identification signal is not received even in the last second attempt, the mobile station will refer to the received signal strength of the last third and fourth detected identification signal(RSSI)Value, and average the received signal strength value. This is designed for the situation where the standard signal frame may be lost due to interference. The mobile station averages the received signal strength values of all neighboring base stations, and the mobile station will arrange the average values in descending order and connect with them in order. It is worth noting that if it fails to receive any identification signal frames for the last four detection attempts, the mobile station will consider that the adjacent base station does not exist and will not continue to connect.

(2)If the mobile station cannot connect to all the adjacent base stations, including the example of missing the identification signal frame of the last four detections, the mobile station will start scanning all channels to find the best connected base station.

(3)Because there is no need to scan the base station, the delay in roaming is only for confirmation(authentication),coupling(association)as well ass/w overheadNote: The purpose of the smart roaming algorithm is to shorten the roaming time. There is no guarantee that data packets can be received during roaming.

3.5The section Searching for the base station at startup describes how the mobile station is activated(booted UP)When finding the best connection base station.

(1)When activated, the mobile station will start to detect all hopping channels. This behavior is in the wireless local area network standard802.11Active scan(active scan). If there is a base station in the channel and a detection request is received, the base station will immediately return a detection response box to the mobile station(response frame). Therefore, after detecting all channels, compare the received signal strength indicators of the detection response(RSSI)Value, the mobile station can select the best received signal strength(RSSI)Value and connect with this base station.

(2)Therefore, when the mobile station detects, the base station may jump nearby. The mobile station needs to scan all channels four times to make sure that all base stations can be completely searched in this area.

4.Base station synchronization time4.1Ethernet logo signal box(ETHE-BEACON frame)like3.lAs mentioned in the section, through the Ethernet, the master base station needs to periodically transmit its time synchronization function(TSF)time. So a multi-cast box is defined to transmit the time synchronization function of the master base station(TSF)time. In addition, this multi-transmission box will be referred to as the Ethernet identification signal from now on(ETHE-BEACON), It can be used to transmit the jump information of the base station, this part will be3.2Section mentioned. Basic service group(BSS)After that, each base station will continuously transmit the Ethernet identification signal(ETHE-BEACON)To the Ethernet.

Figure 5 shows the Ethernet network identification signal(ETHE-BEACON)Format. In this format, the Ethernet identification signal(ETHE-BEACON)Destination address of the frame(Destination, Address, DA)Set to"03:00:00:00:00:07", And roaming notification box(roaming notificationframe)The settings are the same. Original address(SourceAddress, SA)It is the Ethernet media capture control of the transmission base station(MAC)Address. The length of the Ethernet identification signal frame is one byte(byte)And its value is fixed72. Type is used to distinguish media access control on the network(MAC)The shape of the frame is similar to other frames. Select the value of the appropriate Ethernet identification signal (in16Carry is1234) To avoid access control with other media(MAC)The box repeats. Users can manage the system through the network(NMS)The setting to specify the alias of the base station as a logical name. Wireless LAN domain name(ESSID), Wireless network base station name(BSSID), Jump group(Hopping Set)And jump mode(Hopping Pattern)It is the parameters of wireless hop information. In order to achieve the purpose of connection, the mobile station that is roaming will refer to these parameters. If the Ethernet identification signal(ETHE- BEACON)Is sent by the master base station, time synchronization function(TSF)Will include the time stamp of the time synchronization function of the master base station(time Stamp). Otherwise, the Ethernet identification signal sent by the slave base station(ETHE-BEACON)Time synchronization function(TSF)Value will be0.

4.2Send Ethernet identification signal(Send ETHE-BEACON)When the master base station is activated, it will first immediately send an Ethernet identification signal frame to the Ethernet. After that, the master base station will10Send an Ethernet identification signal in seconds(ETHE-BEACON)frame. Once the slave base station receives the Ethernet identification signal from the master base station, the slave base station will delay for a random time and then start to transmit its Ethernet identification signal to the Ethernet network. Just like the action of the master base station, when the slave base station sends out the first Ethernet identification signal(ETHE-BEACON)Later, the slave base station will also be10Transmission of Ethernet identification signal within seconds(ETHE-BEACON)To the Ethernet.

4.3Filter wireless LAN domain names and neighboring base stations(ESSID filtering and neighboring APS)When the base station receives the Ethernet identification signal(ETHE-BEACON)Box, to filter out the domain name of your own wireless local area network(ESSID)Different identification signal boxes. If the wireless local area network domain name(ESSID)If they are the same, the content of the Ethernet identification signal frame will be stored in the database. In the current design, the database of a base station can store up to20Pen jump information.

Whenever the mobile station requests connection, the base station should filter out the base stations close to itself from the database and respond this data to the mobile station. In the current design, a base station can be set up to4A neighboring base station.

4.4Time control timer and backup master base station(Agingtimerand back upmaster)A time-controlled timer for each member in the database, its time is initially set to60Second. When the base station receives the Ethernet identification signal(ETHE-BEACON)Time, the time-controlled timer will be reset. If the Ethernet identification signal has not been received before the timer expires(ETHE-BEACON), The member in the database will be deleted.

If the first main control base station fails, the second main control base station will take the initiative to assume the role of the main control base station and continue to use the Ethernet identification signal(ETHE-BEACON)Box transfers its time synchronization function(TSF)time. If the first master and the second master base station fail at the same time, the mobile station in the minimum jump mode will take the initiative to assume the role of the master base station and begin to transmit its time synchronization function(TSF)Time to maintain the synchronization of the time synchronization function.

When the base station starts, if the first master base station is disconnected, no more Ethernet identification signal is sent(ETHE-BEACON), The second master base station will be15After seconds begin to transmit the Ethernet identification signal(ETHE-BEACON)And add its own time synchronization function(TSF).

5.system program(System Configuration)When the installed system has the function of intelligent roaming, this section points out the points that must be paid attention to.

5.1Set the base station and roaming mobile station to have the same wireless LAN domain name(Set APS and roaming STAS to theSame ESSID)The system administrator must set the same wireless area network domain name (wireless area name) for all base stations so that roaming mobile stations can connect with them. The intelligent roaming base station will filter the value of different wireless local area network domain names in the Ethernet identification signal box. If the wireless local area network domain names of the mobile station and the base station are different, the mobile station cannot receive the frequency hopping information of the neighboring base stations.

5.2Assign a unique alias and frequency hopping sequence to each base station. Before setting the neighbors of the base station, each base station must be managed by the network management system(NMS)Set a unique alias. After the alias is set, the system administrator can start to set the neighbors of the base station. In addition, each base station needs to set a different frequency hopping sequence to avoid cases where more than one basic service group may have partial overlap of hopping channels. Similarly, through the setting of the network management system, the setting of the frequency hopping sequence can be better.

5.3Set neighboring base stations based on geographic location because roaming mobile stations must be based on received signal strength indicators(RSSI)To select a base station means that the relative distance between the roaming mobile station and the neighboring base station must be set according to the geographic location of the application environment.

As shown in Figure 6, there are four base stations (base station1Base station2Base station3Base station4), on the base station0The surrounding area is installed, part of the coverage area signal overlaps, the base station0(AP0)Can move the base(AP1)Base station2(AP2)Base station3(AP3)Base station4(AP4)Set as the base station close to you. In this way, when the base station0When the mobile station leaves the covered area, these neighboring base stations will be referenced by the roaming mobile station.

5.4To designate the master control base station for synchronization, the system administrator must be in the wireless local area network domain(ESS)Designate a base station as the first master base station. In addition, in addition to the first main control base station, the system administrator must also select another base station as the second main control base station to serve as the backup of the first main control base station.

5.5Connect the base station to the same Ethernet subnet(Connect APSto the Same Ethernet Subnet)Since the Ethernet identification signal(ETHE-BEACON)Multi-send frame(multicast frame)To the Ethernet network, the smart roaming base station should be able to connect with the Ethernet cable(Cable)Connect and correctly receive from the same local network domain(ESSdomain)Of multiple transmission boxes.

5.6Set each base station to have the same frequency hopping dwell time, identification signal period and carrier settings(Carrier Set)The dwell time of wireless frequency hopping information, identification signal period, and frequency band settings are not included in the Ethernet identification signal box. Therefore, each base station sets these data in the same wireless local area network domain(ESS domain)Among them, the purpose is to make sure that the settings of these parameter values are the same. These parameter values are the same at the initial setting.

In addition, in order to detect the identification signal of the adjacent base station at the beginning of each frequency hopping dwell time, the frequency hopping dwell time must be set to the identification signal interval(beacon intervals)Multiples of. For example, the frequency hopping dwell time and the time of the identification signal frame interval are respectively set as200Hao seconds and100How many seconds. With these values, the mobile station can successfully detect the identification signal of the base station adjacent to it.

5.7The mobile station must be opened after the relevant information of the base station is established(Start APS in ahead of STAS)When the system starts, all base stations must be turned on before all mobile stations can be activated (note that before the start of the mobile station30Second). This is because the base station needs time to do hardware self-testing(Self-test), Time synchronization function(TSF)Sync and collect information from neighboring base stations. After completing these actions, the mobile station can start and then connect with the best base station and receive frequency hopping information from neighboring base stations.5.8The coverage of the base station In order to provide the network connection of the roaming mobile station, the neighboring base stations must be installed to overlap the coverage.

The quality of the received identification signal (meaning the percentage value of the signal quality between the base station and the mobile station) and the roaming threshold (parameters can be set) will determine the roaming coverage and roaming time. For example, if the identification signal quality of a roaming mobile station drops below the critical value, the mobile station will start to roam to the next base station. Therefore, if a higher threshold is set, the coverage of the base station will be smaller, and the mobile station will switch to the base station more frequently. Therefore, after the mobile station is connected to the base station,4Within seconds, the identification signal quality of adjacent base stations can be correctly calculated. Therefore, the system administrator can install a base station within the signal coverage area, which can support roaming mobile stations at least4The movement distance in seconds. picture7Illustrates this situation.

6.Algorithm to cover the algorithm of the present invention will be briefly described below.

6.1)Each base station must first set the relative position of the base station adjacent to it. E.g. base station2For reference, its setting is West as the base station3, Dongfang is the base station1, The north is the base station4And the south is the base station5. When the base station is activated, in addition to its own frequency hopping information, it also needs to transmit an Ethernet identification signal that includes information about its proximity(ETHE-BEACON)frame.

6.2)When the mobile station is connected to the base station, the mobile station will download the frequency hopping information of the neighboring base station from the currently connected base station.

6.3)In other cases, the mobile station must scan the neighboring base stations and find the best base station and connect with it. The best connection to the base station is determined by the signal strength indicator(RSSI)The value is determined, and the signal strength index value is collected by the base station identification signal frame. Since the mobile station already knows the frequency hopping information of the neighboring base station after connection, it will be shorter than the scanning time required for the mobile station to directly synchronize with the neighboring base station and listen to the identification signal frame. For example, if the signal interval is identified(Beacon interval)Set to listen10millisecond(ms), Then scan4The time spent by a neighboring base station is approximately45-50millisecond. This arrangement is ideal for mobile stations that can roam in any direction.

6.4)When activated, the mobile station needs to scan all hopping channels to receive the identification signal frames of all base stations (negative scanning). According to the received identification signal(Beacon)Compare received signal strength indicators(RSSI)The mobile station can select the base station with the best received signal strength index value and connect with it. If the signal interval is marked(Beacon Interval)Set to10millisecond(ms), The action station will spend2400millisecond(80Channel scan3Make sure that all base stations have been found) to find the best base station. Guided vehicles in motion(Automatic Guidance Vehicle,AGV)In the example, the automated guided vehicle may be activated at any position in the path. If this method is used, the mobile station can calculate the best base station and connect to it.

6.5)After the connection, the mobile station will download the frequency hopping information of the next adjacent base station as the connected base station. When all adjacent base stations are disconnected, the roaming mobile station will use6.4)The proposed method selects an optimal base station to connect.

Schematic description

Figure 1: Illustrates the typical hardware architecture of a wireless local area network system.

Figure 2: According to wireless local area network standards(IEEE 802.11), The frequency hopping bandwidth of the radio signal _， In the U.S. and Canada79Of channels, are between2.04GHZ-2.50GHZbetween.

Figure 3: Illustrates the traditional media capture control for a wireless local area network mobile station from finding to registering with a wireless base station and a wireless base station(medium access control MAC)Second level(sub-layer)Management structure.

Figure 4: Illustrates the detection procedure of the present invention.

Figure 5: Schematic description of the Ethernet identification signal of the present invention(ETHE-BEACON).

Figure 6: Illustrates the geographic location of adjacent base stations of the present invention.

Figure 7: Illustrates the coverage of the base station of the present invention.

Symbol description of main components

100. . . Local area network

101. . . Basic service group

102. . . Basic service group

103. . . workstation

104. . . File server

301. . . Idle state

302. . . set up

303. . . Identification signal box

304. . . Jump sequence

305. . . confirm

306. . . During the connection phase

307. . . Exchange signal box