Radio communication handover processing method, portable electronic device, and radio communication handover system

The present invention relates to a wireless communication handover processing method, a portable electronic device, and a wireless communication handover system.

Patent Document 1 discloses a wireless LAN terminal device capable of handover from a wireless LAN (Local Area Network) base station to which it currently belongs to another wireless LAN base station. The wireless LAN terminal device disclosed in Patent Document 1 is a peripheral wireless device according to the strength of the received signal level when the received signal level of the signal received from the currently belonging wireless LAN base station is weak. Determine the search time for searching for LAN base stations. A peripheral base station is searched based on a predetermined search time, and the magnitude of the received signal level between the detected peripheral base station and the currently belonging base station is compared. If the received signal level of the peripheral base station is higher, the wireless LAN terminal device is handed over to the wireless LAN base station.<patcit num="1"><text>Japanese Patent Application Laid-Open No. 2005-175932</text></patcit>

<p> The wireless LAN terminal device of Patent Document 1 targets all channels stored in the storage unit when searching for peripheral base stations. Therefore, even if a base station that has a sufficiently high received signal level and can communicate well is searched for in the middle of the channel before the base station search is completed, the base station search process cannot be completed. As a result, the wireless LAN terminal device of Patent Document 1 cannot shorten the base station search time, and eventually prolongs the interruption time of communication with the base station to which it currently belongs.</p><p> The same problem is common not only to wireless LAN communication but also to various portable electronic devices that communicate with a base station by wireless communication.</p><p> The present invention has been made in view of the above circumstances, and when searching for a base station to be a handover destination, a wireless communication handover processing method in which the target of the base station search is not fixed to all channels stored in the storage unit is provided. The purpose is to provide.</p><p> A further object of the present invention is to provide a portable electronic device provided with an attribution means for executing the wireless communication handover processing method. Another object of the present invention is to provide a wireless communication handover system having a handover function for executing the wireless communication handover processing method.</p>

<p> In order to solve the above problems, in the wireless communication handover processing method of the present invention, a portable electronic device provided with a wireless communication means for transmitting and receiving a wireless signal transmits a wireless communication base station to which the first base station belongs. It is a wireless communication handover processing method for switching to the second base station, based on the information acquisition step of acquiring the base station information of the first base station and the base station information of the first acquired base station. , The first determination step for determining whether or not it is necessary to search for a second base station other than the first base station, and the first determination step for searching for the second base station. When it is determined that it is necessary, according to a selection step of selecting a part or all of a plurality of pre-stored base station search conditions based on a predetermined criterion and the selected base station search conditions. Whether or not to execute the handover process based on the base station search step for searching the base station, the base station information of the base station detected in the base station search step, and the base station information of the first base station. The second discrimination step to discriminate and When it is determined that the handover process needs to be executed in the second determination step, the second base station is determined from the base stations detected in the base station search step, and the portable electronic device is used. It is characterized in that it is composed of an attribution step of switching the attribution destination so as to attribute the device to the defined second base station.</p><p> Further, in order to solve the above problems, the portable electronic device of the present invention is characterized in that it includes an attribution means for executing the handover of the attribution base station in accordance with the wireless communication handover processing method.</p><p> Further, in order to solve the above problems, the wireless communication handover system in the present invention includes a portable electronic device provided with an attribution means for executing the handover of the attribution base station according to the wireless communication handover processing method, and the portable electronic device. It is characterized by being composed of a first base station that belongs before the base station that belongs by the attribution means is changed, and a second base station that belongs after the base station is changed by the attribution means. To do.</p>

<p> According to the handover processing method of the present invention, when searching for a base station as a handover destination, communication is interrupted by selecting a part of all channels stored in the storage unit in advance as the target of the base station search. You can save time. Further, according to the handover processing method of the present invention, when the received signal level of the signal received from the base station is sufficiently high, the number of unnecessary base station search executions can be reduced.</p>

(Embodiment) Hereinafter, the wireless communication handover processing method according to the embodiment of the present invention will be described with reference to FIGS. 1 to 7. In this embodiment, a wireless LAN (Local Area Network) terminal device 1 is applied as a portable electronic device. The wireless LAN terminal device 1 has a function of executing a handover of a base station according to the wireless communication handover processing method of the present invention. In this embodiment, the wireless LAN terminal device 1 is used to change the base station to which it belongs from the base station to which it currently belongs to another base station.

As shown in FIG. 1, the wireless communication handover system HS of the present embodiment includes a wireless LAN terminal device 1, a first base station 2, a second base station 3, and a network 4. The wireless LAN terminal device 1 belongs to the first base station 2, and transmits data to the electronic device of the other party connected to the network through the network 4.

The wireless LAN terminal device 1 includes a control unit 11, a storage unit 12, a communication unit 13, a display unit 14, an operation unit 15, and a bus 16 as shown in the circuit configuration shown in FIG.

The control unit 11 is composed of a CPU (Central Processing Unit), and controls the overall operation of the wireless LAN terminal device 1 according to the program PG stored in the storage unit 12. For example, the control unit 11 performs the handover of the base station to which the control station belongs according to the program for executing the wireless communication handover processing method of the present embodiment. Further, the control unit 11 includes a timer unit 11A, a first base station information acquisition unit 11B, a received signal level determination unit 11C, a search condition determination unit 11D, a communication interruption unit 11E, a base station search unit 11F, and a handover execution determination unit 11G. The handover unit 11H is provided. Details of each of these components will be described later.

The storage unit 12 is composed of a non-volatile memory such as a flash memory, RAM (Random Access Memory), and the like, and also functions as a work memory of the control unit 11. The storage unit 12 has a program storage area 121, a first base station information storage area 122, a base station search condition storage area 123, a base station detection result storage area 124, and a timer value storage area 125.

In the program storage area 121, a program PG for causing the control unit 11 to execute a process according to the wireless communication handover processing method of the present embodiment shown in the flowchart of FIG. 4 is stored.

The first base station information storage area 122 stores the first base station information acquired from the first base station by the first base station information acquisition unit 11B. The first base station information includes the received signal strength of the signal received from the first base station received by the communication unit 13.

The base station search condition storage area 123 stores base station search conditions that can be selected when the base station search unit 11F searches for a base station that can be a candidate for the second base station 3 as the handover destination. There is.

The base station detection result storage area 124 stores the base station detection result in which the base station search unit 11F searches for the base station. The base station detection result is the base station information of the base station detected when the base station search unit 11F detects the base station, and is information indicating that the base station was not detected when the base station is not detected. is there.

The timer value storage area 125 stores a predetermined reference time (hereinafter, referred to as timer value TM) when the timer unit 11A measures the time. For example, the timer value TM is used to measure the elapsed time since the base station search unit 11F searches for the base station, or to measure the elapsed time after receiving the beacon signal. The timer value TM may have a plurality of reference times, and may have different values from each other. For example, a timer value TM (hereinafter referred to as beacon signal reception interval) that determines an interval for receiving a beacon signal and a timer value TM (hereinafter referred to as handover determination interval) that determines an interval for determining the necessity of handover execution. And may be different.

The communication unit 13 is composed of a network interface card or the like based on a standard such as IEEE 802.11, and connects the wireless LAN terminal device 1 to the network 4 via the antenna 13A. For example, the communication unit 13 enables reception of a signal from the first base station 2.

The display unit 14 is composed of a dot matrix type LCD (liquid crystal display) panel, a driver circuit, and the like, and displays an arbitrary image. For example, the display unit 14 displays the wireless channel selected by the operation unit 15 on the screen.

The operation unit 15 includes various keys or buttons for the user to input instructions and data, and inputs various instructions and data to the control unit 11. For example, it is possible to select a wireless channel when performing wireless communication. The bus 16 transmits data to each other between the control unit 11, the storage unit 12, the display unit 14, and the operation unit 15.

The first base station 2 is a base station to which the wireless LAN terminal device 1 currently belongs, and periodically sends a beacon signal for notifying the wireless LAN terminal device 1 of the existence of the first base station 2 itself. Send to. The second base station 3 periodically transmits a beacon signal for notifying the surrounding wireless communication terminal devices of the existence of the second base station 3 itself.

Next, each component in the control unit 11 will be described in detail with reference to FIG.

The timer unit 11A measures the elapsed time from a certain time with reference to the timer value TM stored in the timer value storage area 125 . For example, the base station search unit 11F measures the elapsed time from the start of the base station search. In the present embodiment, it is assumed that predetermined fixed values are set as the beacon signal reception interval and the handover determination interval, which are determined by the timer value TM. The beacon signal reception interval and the handover determination interval may be set to have different values. By changing the timer value TM, for example, an effect such as shortening the interruption time of communication with the first base station 2 when searching for a base station can be obtained. Details of these modifications will be described later.

The first base station information acquisition unit 11B acquires the first base station information including the received signal strength received from the first base station and stores it in the first base station information storage area 122. The timing for acquiring the first base station information is each timer value TM measured by the timer unit 11A.

When the timer value TM has elapsed, the received signal level determination unit 11C acquires the received signal strength P5 shown in FIG. 3, compares the magnitude of the received signal strength P5 with the threshold values TH1 and TH2, and determines whether or not handover is necessary. To determine. Both the threshold values TH1 and TH2 are the reference strengths of the signals received from the first base station 2 to which the wireless LAN terminal device 1 currently belongs. When the received signal strength P5 is equal to or higher than the threshold value TH1, it indicates that the reception state is good, and when the received signal strength P5 is equal to or lower than the threshold value TH2, it indicates that the reception state is poor. If the acquired received signal strength P5 is larger than the threshold value TH1 or equal to the threshold value TH1, the received signal level determination unit 11C determines that the reception state is good and it is not necessary to execute the handover process. When the acquired received signal strength P5 is less than the threshold value TH1 and larger than the threshold value TH2, it is considered that the reception state of the signal from the first base station 2 to which it currently belongs is deteriorating, and the handover reconnection destination Search for new candidate base stations. Note that the acquisition of the received signal strength P5 may be executed after the data transmission / reception is completed, regardless of the passage of the timer value TM, as long as the communication unit 13 is transmitting / receiving data.

The search condition determination unit 11D determines the search conditions for the base station, and reads only the corresponding base station search conditions from the base station search condition storage area 123. For example, the search condition determination unit 11D sets base station search conditions so as to search for a base station for some channels in the channels stored in the base station search condition storage area 123, or bases for all channels. It is possible to set base station search conditions to search for stations. Although a method of specifying a channel as a base station search condition will be described below as an example, the base station search condition is not necessarily limited to this. By targeting a part of the channels stored in the base station search condition storage area 123 as the target of the base station search, the search time of the base station is shortened as compared with the case of searching the base station for all the stored channels. , It is possible to shorten the communication interruption time with the base station to which it currently belongs.

The search condition determination unit 11D determines the base station search condition according to the priority given to the channel. The method of assigning priority to channels is predetermined in the present embodiment, and higher priorities are assigned to channels starting from 1 in ascending order. The channel next to the channel on which the base station search unit 11F has searched for the base station is given the highest priority for the next base station search target.

Further, the search condition determination unit 11D extracts the number of channels to be searched for the base station from the channels to which the priority is given. The number of channels to be extracted as the target of the base station search is also determined in advance in the present embodiment, and the number of channels is read by 3 channels for each base station search operation. That is, the search condition determination unit 11D determines the base station search conditions so that the base station search unit 11F starts from one channel to which the highest priority is given and searches for three base stations in ascending order. The search condition is read from the base station search condition storage area 123. A predetermined value is used for the maximum base station search time, which indicates the maximum time spent executing the base station search for each channel.

By changing the method of assigning the priority of the channels and the method of determining the number of channels, it is possible to shorten the search time when searching for the base station which is the handover reconnection destination. Details of the modification of the method of assigning the priority of channels and the modification of the method of determining the number of channels will be described later.

The communication interruption unit 11E controls the operation of the communication unit 13 so as to temporarily suspend communication with the first base station to which the base station search unit 11F currently belongs so that the base station search unit 11F can start searching for the base station.

The base station search unit 11F searches for a new base station and stores the detected base station detection result of the base station in the base station detection result storage area 124. When the base station search unit 11F detects a base station, the base station information of the detected base station is stored, and when the base station is not detected, information indicating that the base station is not detected is stored. As a base station search method when searching for a base station and acquiring base station information, for example, a scan process specified by IEEE 802.11 may be applied. In this case, when shortening the time required for the scan process, an active scan is applied in which the probe request is transmitted from the wireless LAN terminal device 1 and the probe response is received from the base station, and when the power consumption is kept low, the wireless LAN is used. A passive scan that receives a beacon from the base station without transmitting a signal from the terminal device 1 may be applied.

The handover execution determination unit 11G determines the necessity of handover based on the determination result of the received signal level determination unit 11C and the base station detection result detected by the base station search unit 11F, and determines whether or not there is a handover reconnection destination. To do. When the handover execution determination unit 11G determines that the handover is necessary, the handover unit 11H executes the handover from the currently belonging first base station 2 to the handover destination second base station 3.

The data structure of the base station detection result detected by the base station search unit 11F and stored in the base station detection result storage area 124 will be described with reference to the example of FIG. One record of the base station detection result is one line when scanned horizontally in the table of Fig. 3, that is, wireless LAN type P1, channel P2, network identifier (BSSID; Basic Service Set Identifier) P3, network logical name ( SSID; Service Set Identifier) P4, Received Signal Strength Indicator (RSSI) P5, Elapsed time after base station search P6.

The wireless LAN type P1 is information indicating which type of wireless LAN system, for example, 11a, 11b, 11g, etc., is scanned by the wireless LAN terminal device 1 in the IEEE 802.11 standard. Therefore, it indicates which frequency band the record is the scan result of.

Channel P2 represents the channel on which the wireless LAN terminal device 1 has searched for a base station. The frequency at which the base station search unit 11F searches for the base station is specified from the wireless LAN type P1 and the channel P2. Channel P2 is prioritized by the search condition determination unit 11D. In the present embodiment, the scanning order of 14 channels is ascending from 1 to 14, and the base station search is performed for each of 3 channels.

The network identifier (BSSID; Basic Service Set Identifier) P3 is an identifier for identifying the base station detected on the channel scanned by the base station search unit 11F. In this embodiment, it is the same as the MAC (Medium Access Control) address of the base station.

The network logical name (SSID; Service Set Identifier) P4 is a logical name of the network added for convenience to identify the network to which each base station belongs. The wireless LAN terminal device 1 communicates only with the base station whose network logical name P4 and the network logical name stored in the storage unit 12 match.

Received Signal Strength Indicator (RSSI) P5 is information indicating the latest received signal strength received from the base station detected by the base station search unit 11F.

The elapsed time P6 after the base station search represents the elapsed time after receiving the signal having the received signal strength indicated by the received signal strength P5.

When the base station is not detected even if the base station search unit 11F scans a certain channel, as shown in the record on the 8th line from the top of Fig. 3, the wireless LAN type P1, channel P2, and the elapsed time after the base station search Memorize only P6. The record in which a predetermined time has elapsed since it was stored in the base station detection result storage area 124 may be deleted by the control unit 11.

Next, the operation of the wireless LAN terminal device 1 handing over from the first base station 2 to the second base station 3 will be described with reference to the flowchart of FIG. As a premise, it is assumed that the wireless LAN terminal device 1 belongs to the first base station 2 and normally receives the beacon signal on a regular basis. When the wireless LAN terminal device 1 normally receives the beacon signal normally, the association processing specified in IEEE (Institute of Electrical and Electronic Engineers) 802.11 between the wireless LAN terminal device 1 and the first base station 2 , The authentication process has been completed.

The timer unit 11A determines whether or not the elapsed time from acquiring the first base station information related to the first base station 2 reaches the timer value TM in order to determine whether or not handover is necessary. (Step A1). If the timer value TM has not elapsed (step A1; No), the elapsed time is continued to be clocked until the timer value TM has elapsed.

When the timer value TM is reached (step A1; Yes), the first base station information acquisition unit 11B controls the communication unit 13 to receive the signal from the first base station 2 and starts from the first base station 2. The first base station information including the received signal strength P5 is acquired and stored in the first base station information storage area 122, and the received signal level determination unit 11C acquires the received signal strength P5 (step A2). The magnitude of the received signal strength P5 and the predetermined thresholds TH1 and TH2 (TH1&gt; TH2) is discriminated (steps A3 and A4).

The received signal level determination unit 11C first determines whether or not the received signal strength P5 is larger than the threshold value TH1 or equal to the threshold value TH1 (step A3). If the received signal strength P5 is equal to or higher than the threshold value TH1 (step A3; Yes), the received signal level determination unit 11C determines that the handover process is unnecessary, returns the process to step A1, and returns under the first base station. Continue to work with.

If the received signal strength P5 is less than the threshold TH1 (step A3; No), the received signal level determination unit 11C determines whether the received signal strength P5 is in the range between the threshold TH1 and the threshold TH2 (step A3; No). Step A4). When the received signal strength P5 is smaller than the threshold value TH2 (step A4; No), the control unit 11 shifts the processing to steps A10 to A15. Details of the processing contents of steps A10 to A15 will be described later.

When the received signal strength P5 is less than the threshold value TH1 and larger than the threshold value TH2 (step A4; Yes), the search condition determination unit 11D determines the base station search condition for searching for a new base station, and the corresponding base station. Only the search condition is read from the base station search condition storage area 123 (step A5). The communication interruption unit 11E temporarily suspends communication with the first base station 2 (step A6), and the base station search unit 11F attempts to search for a new base station (step A7). When the base station search unit 11F completes the base station search process based on the base station search conditions selected in step A5, the base station detection result is stored in the base station detection result storage area 124 (step A8).

The handover execution determination unit 11G determines whether or not the base station search unit 11F has detected the base station by referring to the base station detection result (step A9). If no base station is detected (step A9; No), the control unit 11 returns the process to step A1 and continues the operation under the first base station 2. When a base station is detected (step A9; Yes), the handover unit 11H executes attribution processing (association processing) for the base station selected as the reconnection destination (step A16), and wireless LAN terminal device 1 Operates under the second base station 3 of the handover destination.

On the other hand, if the received signal strength P5 is smaller than the threshold value TH2 in step A4 (step A4; No), the handover execution determination unit 11G refers to the base station information stored in the base station detection result storage area 124 and performs the handover. Determine if there is a reconnection destination for (step A10). If there is a handover reconnection destination (step A10; Yes), the handover unit 11H executes attribution processing (association processing) for the base station selected as the handover reconnection destination (step A16).

If there is no handover reconnection destination (step A10; No), the search condition determination unit 11D reads out all the base station search conditions stored in the base station search condition storage area 123 (step A11). The communication interruption unit 11E temporarily suspends communication with the first base station (step A12), and the base station search unit 11F attempts to search for a new base station for all channels (step A13). When the base station search unit 11F completes the base station search process based on all the base station search conditions selected in step A11, the base station detection result is stored in the base station detection result storage area 124 (step A14).

The handover execution determination unit 11G determines whether or not the base station search unit 11F has detected the base station by referring to the base station detection result (step A15). When the base station is not detected (step A15; No), the control unit 11 returns the process to step A1 and continues the operation under the first base station 2. When a base station is detected (step A15; Yes), the handover unit 11H executes attribution processing (association processing) for the base station selected as the reconnection destination (step A16), and wireless LAN terminal device 1 Operates under the second base station 3 of the handover destination. In step A16, when the attribution process to the second base station 3 is not completed normally, the base station search process is executed again according to the search conditions for all the base stations that can be used by the wireless LAN terminal device 1. You just have to search for the base station of.

When the received signal strength P5 is deteriorating due to the discrimination processing in steps A3 and A4 (threshold TH1&gt; received signal strength P5&gt; threshold TH2), the wireless LAN terminal device 1 searches for a base station for a part of all channels. When the received signal strength P5 is significantly deteriorated (threshold TH2 received signal strength P5), the base station search is performed. As a result, the number of channels for base station search can be changed according to the degree of deterioration of the received signal strength P5, and the base station search can be executed.

When the received signal strength P5 is significantly deteriorated (threshold value TH2 received signal strength P5), the handover is executed after determining whether or not there is a handover destination by the determination process in step A10. As a result, the handover can be executed in a short time. Further, when the handover destination cannot be detected in the determination process of step A10, the search for base stations is executed based on the search conditions for all base stations according to the processes of steps A11 to A15. This increases the possibility of detecting a base station that is a candidate for the handover destination.

Next, with reference to FIG. 5, a flow from the first base station 2 to the second base station 3 to which the wireless LAN terminal device 1 of the present embodiment currently belongs will be described.

In FIG. 5, the flow from the first base station 2 to the second base station 3 to which the wireless LAN terminal device 1 of the present embodiment currently belongs is shown with the horizontal axis as the elapsed time and the vertical axis as the channel. It is a representation. Steps S1, S3, and S5 are states in which the beacon signal from the first base station 2 is periodically received, the data frame is transmitted / received to / from the first base station 2, and the like. In steps S21 to S23, the base station search process to be the handover reconnection destination is executed by changing the wireless LAN channel in the base station search conditions to channels 1 to 3. Here, the processing time of the base station search from steps S21 to S23 is the communication interruption time with the first base station 2. If the number of channels for base station search is increased or the base station search time per channel is lengthened, the communication interruption time becomes longer, but the possibility of detecting the base station to be the handover reconnection destination increases.

In steps S41 to S43, as in steps S21 to S23, the search process for the base station to be the handover destination is executed while changing the channel for which the base station is searched according to the base station search conditions. However, the channels for searching for the base station in steps S41 to S43 are channels 4 to 6. By periodically repeating the base station search operation, the search process under all base station search conditions can be completed.

The transition from step S5 to step S6 represents a handover from the first base station 2 to the second base station 3. While executing the process of step S5, the received signal level determining unit 11C detects that the received signal strength P5 of the signal received from the first base station 2 is significantly deteriorated, and executes the handover. The discriminating unit 11G refers to the base station detection results detected in steps S21 to S23 and S41 to S43. The technical meaning that the beacon reception process in step S6 is located at the same level as step S42 on the vertical axis (channel) is that the second base detected by the handover execution determination unit 11G in the base station search process executed in step S42. It is determined that the received signal strength P5 of the signal received from the station 3 is the best, and it indicates that the second base station 3 is handed over.

By changing the embodiment of each process described in the flowchart of FIG. 4, various modifications having different effects can be considered. In the following, i) modification of the process of changing the timer value in step A1, ii) modification of the process of selecting the base station search condition in step A5, iii) modification of the process of determining the necessity of handover execution in step A9, iv) A modification of the process of determining the presence / absence of the handover destination in step A10 will be described.

First, the effect of changing the timer value TM, which is a reference when measuring the elapsed time from a certain time in the timer unit 11A in step A1, will be described.

As the first modification, if the received signal strength P5 of the base station to which it currently belongs is large, the handover discrimination interval is increased, and if the received signal strength P5 is small, the handover discrimination interval is decreased. The timer value TM that determines the handover determination interval is changed. As a result, when the reception state of the signal from the first base station is good, the number of executions of the base station search process can be reduced and the processing time can be shortened.

As a second modification, if the base station detection result detected by the base station search unit 11F in step A7 includes a base station having a received signal strength P5 larger than the threshold value, the handover determination interval is increased, and in other cases, the handover determination interval is increased. The timer value TM that determines the handover determination interval is changed according to the base station detection result so that the handover determination interval is reduced. As a result, the number of executions of the base station search process is increased when the candidate of the handover destination is not detected, and the probability of detecting the candidate of the handover destination is improved.

As a third modification, when more than a predetermined number of base stations with a received signal strength higher than the received signal strength P5 of the currently belonging base station are detected, the handover discrimination interval is increased, and at other times, the handover discrimination interval is increased. The timer value TM that determines the handover determination interval is changed so that the handover determination interval is reduced. As a result, the number of times the scan process is executed can be increased when the candidate for the handover destination is not detected, and the probability that the handover process fails can be reduced.

Next, as a method of selecting the base station search condition in step A5 of FIG. 4, a method of selecting a channel to be searched for the base station will be described. In step A5, only a part of all the channels available to the wireless LAN terminal device 1 is selected. In selecting this channel, the channels are first prioritized.

The first modification of the method of giving priority to channels is to give priority in a predetermined order, as applied in this embodiment. That is, the order of base station search for the channels included in channel P2 is ascending order from 1 to 14, descending order from 14 to 1, 1 6 11 14 2 7 12 . Priority is given according to a random order such as. The channel having the next priority of the channel on which the base station search was performed last time is set as the highest priority for the next base station search target.

The second modification of the method of assigning priority to the channel is to assign the highest priority in order from the base station information with the oldest date and time in the base station detection results stored in step A9. For example, in the case of the base station detection result shown in FIG. 3, the channel 6 having the longest elapsed time (7) after executing the base station search is given the highest priority, and the runner-up channels 11 and 40 are given the second priority. According to the second variant, by updating in order from the oldest record, a relatively new record always remains as a scan result, and the base station detection result stored in the base station detection result storage area 124 and the base for all channels are used. The difference in content from the base station detection result obtained by performing the station search becomes small. Therefore, it is possible to detect an appropriate handover destination in a shorter time than the method of searching for a base station for all channels. Note that there are records in the base station detection result in Fig. 3, such as channels that have never been searched for base stations, channels whose corresponding records have been deleted because a predetermined time has passed since the search for base stations was performed, and so on. The non-existent channel may be given the highest priority for the base station search target. Also at this time, an appropriate handover destination can be detected in a shorter time than searching for a base station for all channels.

The third modification of the method of giving priority to the channel is to give priority in order from the base station having the highest received signal strength P5 of the base station detection result stored in step A8. For example, in the base station detection result of FIG. 3, channels 1 and 6 having the highest received signal strength P5 (-65) are given the highest priority, and channels 11 and 36 having the second highest received signal strength P5 (-70) are given the highest priority. The second priority is given. In the third modification, a base station having a high received signal strength P5 contained in another channel cannot be detected, but the latest information can always be retained for a base station having a relatively high received signal strength P5. As a result, it is possible to detect an appropriate handover destination candidate in a shorter time than when searching for a base station for all channels. A threshold value TH3, which is a reference signal strength for excluding a base station having a weak reception signal strength, is set in advance, and the base station detection results include a base station having a reception signal strength P5 higher than the threshold value TH3. Priority may be given to the channels in descending order of received signal strength P5. As a result, it is possible to detect a handover destination with a better reception state without performing a base station search for a channel including a base station having a poor reception state with a reception signal strength P5 of the threshold value TH3 or less.

The fourth variant of the method of prioritizing channels is a combination of the first to third variants. For example, among the base station detection results, the channel used by the base station having the highest received signal strength P5 and larger than the threshold value TH3 (the channel determined according to the third modification) is given the highest priority, and after the base station search is completed. The channel of the record with the longest elapsed time (the channel determined according to the second transformation) is given the second priority, and the channel that is the runner-up in the predetermined order (the channel determined according to the first transformation) is given the third priority. To do. Any two of the first to third variants may be combined. In either modification, an appropriate handover destination can be detected in a shorter time than when searching for a base station for all channels.

Further, a modification of the method of determining the number of channels for base station search when the search condition determination unit 11D determines the base station search condition in step A5 will be described.

The first example of the method for determining the number of channels is a method in which the number of channels is predetermined. As applied in this embodiment, the method of setting 3 channels for each base station search, and the number of channels for each base station search operation such as 4 channels, 4 channels, 3 channels, and 3 channels are The pattern may be different but periodically fixed.

Further, the number of channels for searching the base station may be reduced during the period during which the data frame is transmitted / received as compared with the period during which the beacon signal is periodically received. As a result, the base station search time during data transmission / reception can be shortened, and the communication interruption time can be shortened. Further, when the base station search by the passive scan is performed, a waiting time for receiving the beacon signal from the base station is required, which may require a longer processing time than the base station search by the active scan. Therefore, when searching for a base station by passive scanning, the number of target channels may be reduced in one base station search operation. This reduces the communication interruption time due to the base station search. On the other hand, in the base station search by active scan, when the maximum base station search time is set short, the time required for the base station search can be shortened. Further, the maximum base station search time may be set to be different for each channel.

As the second modification of the channel number determination method, the total maximum base station search time and the maximum base station search time for each channel are determined, and the maximum number of channels that can be searched for base stations within the total maximum base station search time is determined. There is a way to calculate. At this time, the maximum base station search time for each channel is set to a predetermined value. In base station search by active scan, the total maximum base station search time is shortened by shortening the maximum base station search time for each channel. As a result, even if the number of channels targeted for one base station search process is increased, the interruption time of communication with the base station is shortened. Further, if the total maximum base station search time is made smaller than the reception interval for periodically receiving the beacon signal, the base station search process is performed without interrupting the beacon signal reception from the first base station 2 to which the beacon signal currently belongs. It is also possible to complete. Further, by making the total of the maximum base station search time during transmission / reception of the data frame shorter than the total of the maximum base station search time during the periodic reception of the beacon signal, the communication interruption time during transmission / reception of the data frame can be shortened. ..

From the channel priority information that associates the channels with the priorities assigned to the channels and the search channel number information indicating the number of channels to be searched when the base station search unit 11F performs the process of searching for the second base station 3. The base station search conditions in this embodiment are determined. The base station search unit 11F searches for a base station according to the base station search condition defined by the search condition determination unit 11D and read from the base station search condition storage area 123. The channel priority information and the search channel number information may be changed by the user. As a result, for example, the user changes the wireless LAN terminal device 1 so as to increase the number of channels for searching the base station when it is determined that the received signal strength from the base station to which the wireless LAN terminal device 1 currently belongs has weakened. It is possible to increase the possibility that 1 will detect the base station that is the handover destination.

Next, the three modifications of the process of determining the necessity of the handover execution in step A9 of FIG. 4 will be described in detail with reference to the flowcharts shown in FIGS. 6A, B, and C.

The first modification of the handover execution determination process is the key to the handover based on the magnitude comparison between the extracted received signal strength P5 and the received signal strength P5 of the currently assigned base station, as shown in the flowchart shown in FIG. 6A. It determines whether or not. From the base station detection result stored in the base station detection result storage area 124, a record in which the elapsed time P6 after the base station search is shorter than the predetermined time T is extracted (step B1). Here, the predetermined time T is a reference time for history management of the record of the base station detection result, and it is assumed that the control unit 11 deletes the record in which the elapsed time P6 after the base station search is larger than the predetermined time T. .. When the predetermined time T is set to "0", only the latest base station detection result is used when determining the handover execution.

The handover execution determination unit 11G extracts the record corresponding to the base station having the maximum received signal strength P5 from the extracted records (step B2). The base station corresponding to the record extracted in step B2 is a candidate for the handover destination. The reception signal strength P5 from the candidate base station of the handover destination is compared with the reception signal strength P5 of the first base station 2 to which it currently belongs (step B3). If the received signal strength P5 of the base station extracted from the base station detection result is larger, it is determined that the handover for that base station needs to be executed (step B3; Yes), and the process is performed in step A16 of FIG. Perform transfer handover. If the received signal strength P5 of the base station to which it currently belongs is greater (step B3; No), it is determined that the handover execution is not necessary, the process is moved to step A1 in FIG. 4, and the first base station 2 Continue to work under. As a result, the time required for handover can be shortened, and the interruption time of communication with the base station to which the current attribution belongs can be shortened.

The second modification of the handover execution determination process is a modification of step B3 in FIG. 6A to step C3 as shown in the flowchart shown in FIG. 6B. Of the processes shown in FIG. 6B, the same processes as those shown in FIG. 6A are designated by the same reference numerals as those shown in FIG. 6A. In step C3, the received signal strength P5 of the base station acquired in step B2 is compared with the signal strength obtained by adding a predetermined threshold value TH4 to the received signal strength P5 of the first base station 2 to which it currently belongs. If the received signal strength P5 of the base station extracted from the base station detection result is larger (step C3; Yes), it is determined that the handover execution is necessary, and the process is moved to step A16 of FIG. 4 to perform the handover. If the signal strength obtained by adding the predetermined threshold value TH4 to the received signal strength P5 of the first base station 2 is larger (step C3; No), it is determined that handover is unnecessary, and the operation under the first base station 2 is performed. To continue. As a result, the interruption time of communication with the first base station 2 to which the current attribution belongs is shortened, and the base station in which the reception signal strength P5 of the signal from the base station is sufficiently high and the reception state is good is reconnected. Handover is possible.

The third modification of the handover execution determination process is that the determination process step D0 is added to the previous stage of step B1 in FIG. 6A as shown in the flowchart shown in FIG. 6C. The processes in FIG. 6C are also designated by the same reference numerals as those in FIG. 6A for the same processes as those in FIG. 6A. In step D0 of FIG. 6C, the received signal strength P5 of the first base station 2 to which it currently belongs is compared with the predetermined threshold value TH5. If the received signal strength P5 of the first base station 2 is larger (step D0; Yes), it is determined that the handover is unnecessary, and the operation under the first base station 2 is continued. If the threshold value TH5 is larger (step D0; No), the handover determination processing of steps B1 to B3 is executed in the same manner as in FIG. 6A. As a result, it is possible to shorten the interruption time of communication with the first base station 2 to which the current attribution belongs when performing the handover determination process. Further, if the received signal strength P5 from the first base station 2 to which the current attribution belongs is sufficiently large, the handover is not executed, so that the execution of unnecessary handover can be reduced.

As a modification of the process for determining the necessity of handover execution, FIGS. 6B and 6C may be combined. In this case, it is possible to shorten the interruption time of communication with the first base station 2 to which it currently belongs, perform a handover with a base station in a good reception state as the reconnection destination, and further execute unnecessary handover. Can also be reduced.

Finally, a modification of the process of determining the presence or absence of the handover destination in step A10 of FIG. 4 will be described with reference to FIG. 7. Of the processes shown in FIG. 7, the same processes as those in FIG. 6A are designated by the same reference numerals as those in FIG. 6A. Step A10 is a determination process executed when it is determined in step A4 that the received signal strength P5 is smaller than the threshold value TH2. When the flow processing of FIG. 7 is activated, first, as in steps B1 and B2 of FIGS. 6A to 6, the elapsed time from the completion of the base station search among the base station detection results of the base station detection result storage area 124. Extracts records shorter than a predetermined time (step B1), and extracts the record with the maximum received signal strength P5 (step B2). The handover execution determination unit 11G compares the received signal strength P5 of the base station indicated by the record extracted in step B2 with the threshold value TH6 (step E3). If the received signal strength P5 of the base station is higher (step E3; Yes), this base station is determined to be the reconnection destination of the handover, and the process is shifted to step A16 of FIG. 4 to execute the handover. If the threshold value TH6 is larger (step E3; No), it is determined that there is no handover reconnection destination, and base station search based on all base station search conditions is executed according to the processes of steps A11 to A15. In step A15, when a base station whose received signal strength P5 is larger than a predetermined threshold value is detected before the base station search process under all the base station search conditions selected by the search condition determination unit 11D is completed, The base station search process may be terminated. As a result, the effect of shortening the base station search time is further enhanced.

The concept of the present invention can be widely applied to electronic devices having a wireless communication function, for example, mobile phone devices, PDAs, electronic cameras, electronic wristwatches, music players, and the like.

<figref num="1">It is a figure which shows the whole structure of the wireless communication handover system of embodiment of this invention.</figref><figref num="2">It is a block diagram which shows the circuit structure of the wireless LAN terminal apparatus of embodiment of this invention.</figref><figref num="3">It is a figure which shows the image of the data structure of the base station detection result stored in the base station detection result storage area of the wireless LAN terminal apparatus of this invention.</figref><figref num="4">It is a flowchart for demonstrating the operation which the wireless LAN terminal apparatus of embodiment of this invention hands over the base station to which it belongs.</figref><figref num="5">It is a figure which shows the chart which represented the flow from the 1st base station to the 2nd base station to which the wireless LAN terminal apparatus of this embodiment currently belongs, with the horizontal axis as the elapsed time.</figref><figref num="6A">It is a flowchart which concerns on the 1st modification in the determination process of the base station search condition of FIG.</figref><figref num="6B">It is a flowchart which concerns on the 2nd modification in the determination process of the base station search condition of FIG.</figref><figref num="6C">It is a flowchart which concerns on the 3rd modification in the determination process of the base station search condition of FIG.</figref><figref num="7">FIG. 5 is a flowchart relating to the first modification in the process of determining the presence / absence of the handover destination in FIG.</figref>

Code description

1 ... Wireless LAN terminal device, 11 ... Control unit, 11A ... Timer unit, 11B ... 1st base station information acquisition unit, 11C ... Received signal level determination unit, 11D ... Search Condition determination unit, 11E Communication interruption unit, 11F Base station search unit, 11G handover execution determination unit, 11H handover unit, 12 Storage unit, 121 Program storage Area, 122: 1st base station information storage area, 123: base station search condition storage area, 124: base station detection result storage area, 125: timer value storage area, 13: communication Department, 14 ... Display, 15 ... Operation, 16 ... Bus, 2 ... 1st base station, 3 ... 2nd base station, 4 ... Network, PG ... Program, P1 Wireless LAN type, P2 Channel, P3 Network identifier, P4 Network logical name, P5 Received signal strength, P6 Elapsed time after base station search