JP4138769B2 - Wireless communication terminal, wireless communication method, and wireless communication system - Google Patents

Description

  The present invention relates to a technical field of wireless communication, and more particularly, to a wireless communication terminal, a wireless communication method, and a wireless communication system having a system handover function corresponding to a plurality of wireless communication systems.

  In recent years, wireless communication composite terminals (hereinafter referred to as “multi-mode terminals”) having functions of a plurality of wireless communication methods such as PDC (Personal Digital Cellular), W-CDMA (Wideband-Code Division Multiple Access) and wireless LAN have been developed. It is going to be put to practical use. In such a multi-mode terminal, the wireless communication method and communication protocol can be changed by switching hardware or replacing software. Therefore, in multi-mode terminals, it is possible to perform system handover to other wireless communication system systems by switching hardware or software, and multiple systems can be used to realize ubiquitous services. Switching can be performed seamlessly (see, for example, Patent Document 1).

When performing system handover, if a system with a high priority determined based on transmission rates, billing charges, etc. is preferentially selected and connected from among multiple wireless communication systems, a ping-pong phenomenon that repeats unnecessary system handover may occur. May occur. Repeating unnecessary system handovers consumes a lot of power and leads to a decrease in throughput. Therefore, in order to prevent this ping-pong phenomenon, a method of performing system handover using GPS (Global Positioning System) or the like and taking position information into consideration has been proposed (for example, see Patent Document 2).
JP 2002-291011 A JP 2002-199428 A

  However, in the method of performing system handover using position information in this way, it is necessary to incorporate GPS in order to calculate position information, and the position of each base station using a predetermined wireless communication method is determined. It is necessary to grasp using some method.

  The present invention has been made in consideration of the above-described circumstances, and is capable of preventing unnecessary system handover without using position information and capable of performing communication in a system with as high a priority as possible. An object is to provide a terminal, a wireless communication method, and a wireless communication system.

  In order to solve the above-described problems, a wireless communication terminal of the present invention is a wireless communication terminal that communicates with a plurality of wireless base stations that use different wireless communication methods, and each has a communication quality with each wireless base station. Measurement means for measuring, storage means for storing each communication quality, calculation means for calculating a variation value of each communication quality with reference to the storage means, and information unique to each radio base station Reference means for determining the priority of each radio base station indicating the degree of priority for communication, and when performing handover processing between systems based on each of the fluctuation values and each of the priorities Changing means for changing each threshold set corresponding to each radio base station; first determining means for determining whether or not a handover process needs to be performed based on communication quality; and 1 judgment means A second determination unit that determines whether or not there is a radio base station that performs a handover process by comparing each of the threshold values with each of the communication qualities when it is determined that a handover process needs to be performed; When the determination unit of 2 determines that there is a radio base station performing the handover process, the handover process is performed with the radio base station having the highest priority among the radio base stations determined by the second determination unit. And executing means for performing.

  The radio communication method of the present invention is a radio communication method for communicating with a plurality of radio base stations that use different radio communication schemes, respectively, measuring communication quality with each radio base station, and measuring each of the communication qualities. Each wireless unit that prepares a storage unit to store, calculates a variation value of each communication quality with reference to the storage unit, and indicates a priority level for performing communication based on information unique to each wireless base station Each priority set for each radio base station, which is referred to when performing a handover process between systems based on each of the variation values and each of the priorities, determines the priority of the base station The threshold value is changed, it is determined whether or not the handover process needs to be performed based on the communication quality, and when it is determined that the handover process needs to be performed, the threshold values and the communication quality are compared. , Handover processing It is determined whether or not there is a radio base station to perform, and when it is determined that there is a radio base station performing handover processing, between the determined radio base stations and the radio base station with the highest priority A handover process is performed.

A wireless communication system of the present invention is a wireless communication system comprising a plurality of wireless base stations and a wireless communication terminal that communicates with the wireless base station,
The plurality of radio base stations respectively use different radio communication schemes,
The radio communication terminal calculates a communication value with each radio base station, a storage unit that stores the communication quality, and a variation value of each communication quality with reference to the storage unit A calculating means; a determining means for determining a priority of each radio base station indicating a priority level for performing communication based on information unique to each radio base station; each variation value; and each priority. The change means for changing each threshold value set corresponding to each radio base station, which is referred to when performing a handover process between systems based on the above, and the handover process needs to be performed based on the communication quality When the first determination unit that determines whether or not the first determination unit determines that the handover process needs to be performed, the threshold value is compared with the communication quality, and the handover process is performed. Wireless base to perform A second determination unit that determines whether or not there is a station; and a radio base that is determined by the second determination unit when the second determination unit determines that there is a radio base station that performs a handover process. And executing means for performing a handover process with a radio base station having the highest priority among the stations.

  According to the wireless communication terminal, the wireless communication method, and the wireless communication system of the present invention, it is possible to prevent unnecessary system handover without using location information and to perform communication in a system with as high a priority as possible.

Hereinafter, a wireless communication terminal, a wireless communication method, and a wireless communication system according to embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
In this embodiment, as shown in FIG. 1, handover between base stations (also referred to as inter-system handover) is possible across a plurality of wireless communication base stations that provide a plurality of wireless communication services. It is assumed that the communication network is controlled. In FIG. 1, for simplicity, a W-CDMA system, a PDC system, and a wireless LAN system are shown, but there may actually be a system that uses other wireless communication systems. In the example of FIG. 1, the W-CDMA base station 104 provides the service area 101 in the W-CDMA system, the PDC base station 105 provides the service area 102 in the PDC system, and the W-LAN base station 106 in the wireless LAN system. Provides a service area 103.
The wireless communication terminal 107 is a multi-mode terminal capable of communicating with a plurality of systems using a certain wireless communication method (hereinafter simply referred to as a system).

Next, the wireless communication terminal 107 in FIG. 1 will be described with reference to FIG.
The wireless communication terminal 107 includes at least a multiband antenna 201, a wireless control unit 202, and a control unit 218.
The multiband antenna 201 is for performing communication with a plurality of base stations having a plurality of systems. The radio control unit 202 controls transmission / reception with a plurality of base stations having a system using a radio communication scheme. The control unit 218 performs control for performing system handover.

  The radio control unit 202 includes system radio control units 203, 204, and 205 corresponding to each system. Each system radio control unit 203, 204, 205 includes transmitters 206, 208, 210 and receivers 207, 209, 211, respectively, and performs transmission / reception corresponding to the system. Here, each system radio control unit 203, 204, 205 is configured by hardware, and even if the corresponding system can be changed by switching with a switch, the corresponding system can be changed by rewriting software. It does not matter if it can be changed. In addition, a plurality of systems may be operated simultaneously without changing or the like.

The control unit 218 includes at least a communication quality measurement unit 212, a communication quality variation calculation unit 213, a system priority determination unit 214, a system handover threshold change unit 215, a system handover necessity determination unit 216, and a system handover execution unit 217. I have.
Based on the information received by each receiver 207, 209, 211 at regular intervals or at certain timings in each system, the communication quality measuring unit 212, the wireless communication terminal 107, which is its own terminal, and each wireless communication base station 104, Measurement of communication quality (for example, values based on reception conditions of received electric field strength (RSSI) and signal-to-noise power ratio (SNR)) is performed. The communication quality measuring unit 212 stores the measured communication quality. At that time, the communication quality measurement performed by the communication quality measuring unit 212 may use the instantaneous communication quality, or the reception quality from each of the receivers 207, 209, and 211 is averaged twice or more. May be calculated.
When the communication quality measurement performed by the communication quality measurement unit 212 is obtained by averaging the reception information from each receiver 207, 209, 211 twice or more, the communication quality measurement unit 212 includes the receiver 207, Averaging may be performed using a forgetting factor so that new received information obtained from 209 and 211 is more weighted. The communication quality of each system measured by the communication quality measuring unit 212 is output to the communication quality fluctuation calculating unit 213.

  The communication quality variation calculation unit 213 calculates a variation value between the communication quality of each system input from the communication quality measurement unit 212 and the communication quality of each system input last time, and uses this variation value as a system handover threshold change unit. Output to 215.

  The system priority determination unit 214 determines the order of priority of each system for communication in a plurality of systems that can communicate with the wireless communication terminal 107. When determining the priority order, the system priority determination unit 214 sets parameters specific to each system such as a transmission rate, a charging fee, a channel capacity, etc., or a time such as a received electric field strength or an SNR, depending on usage. The priority of each system is determined using information specific to the radio base station, including parameters related to the radio propagation environment, which may be fluctuated depending on, or both. Apart from these, the user can also directly prioritize each wireless communication system. Therefore, the priority order of the system may change each time.

  The system handover threshold changing unit 215 performs system handover to each system according to the communication quality variation value of each system obtained from the communication quality variation calculating unit 213 and the system priority order determined by the system priority determining unit 214. The threshold value referred to when determining whether or not to perform is changed for each system. The threshold is set for each system.

  The system handover necessity determination unit 216 determines whether handover to another system is possible based on the system handover threshold changed by the system handover threshold change unit 215.

  The system handover execution unit 217 performs system handover processing when the system handover necessity determination unit 216 determines that system handover is possible or system handover is necessary. Further, the system handover execution unit 217 resets the threshold of the system handover threshold change unit 215.

  Next, a system handover switching operation performed by the wireless communication terminal 107 in FIG. 1 will be described with reference to FIG. Note that the operation of the wireless communication terminal 107 shown in FIG. 3 is based on the control of the control unit 218 unless otherwise specified. For simplicity of explanation, it is assumed that the wireless communication terminal 107 can communicate with four systems: system A, system B, system C, and system D. Further, the system priority determination unit 214 determines that the priority of each system is highest in the system A, and lower in the order of the system B, the system C, and the system D (that is, the priority level is symbolically set). , It is assumed that system A> system B> system C> system D) is determined. It is assumed that the wireless communication terminal 107 has selected the system C as the currently communicating system.

  As shown in FIG. 3, first, the communication quality measurement unit 212 measures the communication quality of each system periodically or at a preset timing (step S301). The communication quality measurement unit 212 determines whether or not the system measured in step S301 is a currently communicating system (step S302). If the system is currently in communication, the process returns to step S301. If the communication quality is in a system other than the currently communicating system, the process proceeds to step S303.

  In step S303, the communication quality fluctuation calculation unit 213 calculates a fluctuation value with respect to the previous communication quality, and outputs the fluctuation value to the system handover threshold change unit 215. In step S303, for example, when the communication quality in the system A is -70 dBm at the previous measurement and -67 dBm at the current measurement, the communication quality fluctuation calculation unit 213 sets the communication quality fluctuation value of the system A to +3 dB and vice versa. In addition, if it is -70 dBm at the previous measurement and -72 dBm at the current measurement, it is notified to the system handover threshold changing unit 215 as a variation value of -2 dB. Here, for example, RSSI is used as the communication quality.

  The system handover threshold changing unit 215 changes the threshold for system handover based on the notified communication quality fluctuation value and system priority order (step S304). Note that a threshold value for system handover exists for each system, and the handover threshold value for system A is used in determining to perform system handover from system C to system A. Therefore, when the system measured in step S301 is system A, the handover threshold for system A is changed, and each system is changed each time according to the communication quality measurement of each system in step S301. The handover threshold for is changed. Here, the threshold for system handover will be described. Basically, when the communication quality fluctuation value notified by the communication quality fluctuation calculation unit 213 in step S303 is a positive value (that is, when the communication quality is generally improving), the system of the corresponding system. If the threshold value for handover (that is, the threshold value corresponding to the system that is not currently communicating) is lowered and the notified communication quality fluctuation value is negative (that is, the communication quality is generally in the direction of deterioration), Raise the threshold for system handover of the corresponding system. Furthermore, the system handover threshold change unit 215 increases the fluctuation range of the threshold for system handover to be changed as the notified communication quality fluctuation value is larger regardless of whether it is positive or negative.

  By doing in this way, when the communication quality is drastically improved, the handover threshold is greatly lowered to facilitate system handover, and conversely, when the communication quality is rapidly deteriorated, the handover threshold is set. It can be greatly increased to make system handover difficult.

  Further, when determining the threshold fluctuation range for system handover performed by the system handover threshold changing unit 215, the priority of the corresponding system determined by the system priority determining unit 214 is also taken into consideration. The system handover threshold changing unit 215 includes a storage unit (not shown) in which a threshold fluctuation range reference value for system handover is determined for each system priority order in advance for each system. The reference value is the threshold fluctuation range when a certain communication quality fluctuation value is notified. The higher the priority of the corresponding system, the larger the reference value, and conversely the system priority. The lower the value, the smaller the reference value. That is, even if the communication quality fluctuation value notified from the communication quality fluctuation calculation unit 213 is the same, the fluctuation range of the threshold value to be changed is different between the case where the priority order of the system is higher and the case where it is lower. Will be different. Details of this will be described later with reference to FIG.

  In step S305, the system handover necessity determination unit 216 determines whether or not the system C currently in communication is out of the communication range or system handover is necessary due to communication quality degradation. If it is determined that the currently communicating system C is out of the communication range or that system handover is required due to communication quality degradation, the process proceeds to step S306, while the currently communicating system C is not out of the communication range or the communication quality If it is determined that system handover is not necessary due to deterioration, the process returns to step S301.

In step S306, the system handover necessity determination unit 216 compares the system handover threshold determined by the system handover threshold change unit 215 with the communication quality of each system, and determines whether the system handover is necessary. Next, the system handover necessity determination unit 216 determines whether or not there is a system whose communication quality exceeds the corresponding system handover threshold (step S307). If there is no system exceeding the system handover threshold and system handover cannot be performed, the process proceeds to step S310. If there is a system exceeding the system handover threshold, the process proceeds to step S308. In step S310, communication in the current system is maintained or disconnected. In step S308, the system handover execution unit 217 performs system handover processing and switches the systems to be communicated. Thereafter, the system handover execution unit 217 instructs the system handover threshold change unit 215 to reset all the system handover thresholds.
Here, it is assumed that the system handover necessity determination is performed from a radio communication system with a high priority order. That is, the determination is performed in the order of system A, system B, and system D.

Next, when determining the fluctuation range of the threshold for system handover performed by the system handover threshold changing unit 215, the priority of the corresponding system determined by the system priority determining unit 214 is also considered. This will be described with reference to FIG. FIG. 4 shows a transition example of the system handover threshold change.
As a specific example, as shown in FIG. 4, in system A, the reference value in the case of the highest priority is a threshold fluctuation width of 1 dB with respect to the communication quality fluctuation of 1 dB, or the second priority. Is determined to be a threshold fluctuation range of 0.4 dB with respect to 1 dB of communication quality fluctuation. In this situation, when the communication quality fluctuation value of system A calculated by the communication quality fluctuation calculation unit 213 in step S303 and notified to the system handover threshold change unit 215 is +4 dB, the system handover threshold change unit 215 In the case where the priority of the system A is the highest priority and the second priority, a process of lowering the system handover threshold by 4 dB and 1.6 dB is performed.

  On the contrary, when the communication quality fluctuation value of the system A notified by the system handover threshold changing unit 215 in step S303 is −2 dB, the system handover threshold changing unit 215 determines that the priority of the system A is the highest priority. In the second case, the system handover threshold is increased by 2 dB and 0.8 dB, respectively. In addition, when the communication quality fluctuation value is negative (that is, the communication quality is in the deterioration direction), as described above, when the priority is taken into consideration when the threshold is increased, the threshold for the higher priority is increased. This is likely to make handover difficult. In order to avoid this, when the communication quality is in the deterioration direction, a difference may not be provided in the threshold change width according to the priority of the system. In other words, when the communication quality deteriorates and the threshold value is raised, the priority order of the system is not related, and it may be made to depend only on the fluctuation range of the communication quality. Further, an upper limit and a lower limit are provided for the handover threshold, and the handover threshold is changed within the range. Further, an initial threshold value is determined for each system handover threshold value. When a system handover is executed, all the handover threshold values are all reset to the initial threshold value.

  As described above, the higher the priority ranking or the higher the priority system, the greater the fluctuation range of the threshold value to be changed, thereby facilitating handover to the system. Further, by providing a restriction on the threshold value, it is possible to prevent handover in a situation where communication is originally impossible due to the threshold value being too low, or that handover cannot be performed at all due to the threshold value being too high.

(Second Embodiment)
In the first embodiment, the system handover is performed only when the system C becomes incapable of communication. However, in the second embodiment, the system C communicates not only when the system C becomes incapable of communication. Even if possible, if a system having a higher priority than system C exceeds the system handover threshold, system handover is positively performed. The wireless communication terminal 107 is the same as in the first embodiment, but the operation is slightly different. The operation of the wireless communication terminal 107 of this embodiment will be described with reference to FIG. Of the steps shown in FIG. 5, the same steps as those described with reference to FIG.

  In step S501, the system handover necessity determination unit 216 determines whether the system C currently in communication is out of the communication range or whether system handover is necessary due to communication quality degradation. If it is determined that the currently communicating system C is out of the communication range or that system handover is required due to communication quality degradation, the process proceeds to step S306, while the currently communicating system C is not out of the communication range or the communication quality If it is determined that system handover is not necessary due to deterioration, the process proceeds to step S502.

  In step S502, the system handover necessity determination unit 216 determines whether a system handover is possible for a system having a higher priority than the system C. If there is no system whose communication quality exceeds the system handover threshold value and there is no system capable of system handover, the process returns to step S301 to continue communication in the system C, while a system whose communication quality exceeds the system handover threshold value. If it exists, the process proceeds to step S308, and the system handover execution unit 217 performs system handover processing to switch the system.

  In step S502, it is assumed that only a system having a higher priority than the currently communicating system C is determined, and a system having a lower priority than the system C is not determined. Also, step S502 is different from step S306, considering that the system C is in a communicable state. In the system handover necessity determination in step S502, the system handover determined in step S303 to prevent unnecessary system handover. A margin α may be added to the threshold value, the condition for system handover may be made stricter than in step S306, and it may be determined whether or not system handover is possible.

  According to the embodiment described above, since the threshold value for system handover is changed according to fluctuations in communication quality, it is possible to prevent unnecessary system handover when communication quality is severely deteriorated, and at the same time, communication quality. When the improvement is significant, the system handover can be facilitated.

  Further, since the threshold value for system handover is changed according to the priority of the system, system handover to a system with higher priority is possible, and communication in a system with higher priority can be performed.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which shows the radio | wireless communications system which concerns on embodiment of this invention. The block diagram of the radio | wireless communication terminal which concerns on embodiment of this invention. 3 is a flowchart showing the operation of the wireless communication terminal according to the first embodiment of the present invention. The figure which shows an example of the transition which changes the threshold value of a system handover which the system handover threshold value change part of FIG. 2 performs. The flowchart which shows operation | movement of the radio | wireless communication terminal which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... W-CDMA system service area, 102 ... PDC system service area, 103 ... Wireless LAN system service area, 104 ... W-CDMA base station, 105 ... PDC base station, 106 ... Wireless LAN base station, 107 ... Wireless communication terminal , 201, multiband antenna, 202, wireless controller, 203, 204, 205, system wireless controller, 206, 208, 210, transmitter, 207, 209, 211, receiver, 212, communication quality measuring unit, 213 ... Communication quality fluctuation calculation unit, 214 ... System priority determination unit, 215 ... System handover threshold change unit, 216 ... System handover necessity determination unit, 217 ... System handover execution unit, 218 ... Control unit.

Claims (11)

A wireless communication terminal that communicates with a plurality of wireless base stations that use different wireless communication methods,
Measuring means for measuring the communication quality with each radio base station,
Storage means for storing each of the communication qualities;
Calculating means for calculating a variation value of each communication quality with reference to the storage means;
Determining means for determining the priority of each radio base station, indicating the priority of communication based on information unique to each radio base station;
Based on each of the fluctuation values and each of the priorities, changing means for changing each threshold set corresponding to each of the radio base stations, which is referred to when performing a handover process between systems,
First determination means for determining whether or not a handover process needs to be performed based on communication quality;
When the first determination means determines that it is necessary to perform a handover process, the second threshold value is compared with each communication quality to determine whether there is a radio base station that performs the handover process. Determining means,
When the second determination unit determines that there is a radio base station that performs the handover process, the radio base station having the highest priority among the radio base stations determined by the second determination unit An execution means for performing a handover process.   2. The radio communication terminal according to claim 1, wherein the measurement means calculates a communication quality by averaging values based on a reception status of a signal from the radio base station at least twice.   3. The wireless communication terminal according to claim 2, wherein the measuring means averages the communication quality using a forgetting factor.   The changing means lowers the threshold corresponding to the communication quality when the communication quality measured by the measuring means fluctuates in the improvement direction, and when the communication quality measured by the measuring means fluctuates in the deterioration direction. The wireless communication terminal according to any one of claims 1 to 3, wherein a threshold value corresponding to the communication quality is increased.   2. The change unit according to claim 1, wherein the change unit determines a change range of each threshold value set corresponding to each radio base station based on each variation value and each priority. Item 5. The wireless communication terminal according to any one of Item 4.   The said execution means resets each said threshold value to the initial threshold value decided for every radio | wireless base station, when performing a handover process, The any one of Claims 1-5 characterized by the above-mentioned. Wireless communication terminal.   The said change means changes a threshold value into the value between the upper limit and lower limit of each threshold value set for every wireless base station, The one of Claims 1-6 characterized by the above-mentioned. Wireless communication terminal.   8. The wireless communication terminal according to claim 1, wherein the change unit increases a change range of a corresponding threshold value as the priority determined by the determination unit is higher. .   9. The wireless communication terminal according to claim 1, wherein the change unit increases a change range of a corresponding threshold value as the variation value calculated by the calculation unit increases. . A wireless communication method for communicating with a plurality of wireless base stations respectively using different wireless communication methods,
Measure the communication quality with each radio base station,
A storage means for storing each communication quality is prepared,
Calculating a variation value of each communication quality with reference to the storage means;
Based on the information unique to each radio base station, determine the priority of each radio base station, indicating the priority of communication,
Based on each of the fluctuation values and each of the priorities, each threshold set corresponding to each of the radio base stations is referred to when performing a handover process between systems,
Determine whether it is necessary to perform handover processing based on communication quality,
When it is determined that a handover process needs to be performed, the threshold values and the communication qualities are compared to determine whether there is a radio base station that performs the handover process,
A wireless communication method characterized in that, when it is determined that there is a radio base station performing handover processing, handover processing is performed with a radio base station having the highest priority among the determined radio base stations. A wireless communication system comprising a plurality of wireless base stations and a wireless communication terminal that communicates with the wireless base station,
The plurality of radio base stations respectively use different radio communication schemes,
The wireless communication terminal is
Measuring means for measuring the communication quality with each radio base station,
Storage means for storing each of the communication qualities;
Calculating means for calculating a variation value of each communication quality with reference to the storage means;
Determining means for determining the priority of each radio base station, indicating the priority of communication based on information unique to each radio base station;
Based on each of the fluctuation values and each of the priorities, changing means for changing each threshold set corresponding to each of the radio base stations, which is referred to when performing a handover process between systems,
First determination means for determining whether or not a handover process needs to be performed based on communication quality;
When the first determination means determines that it is necessary to perform a handover process, the second threshold value is compared with each communication quality to determine whether there is a radio base station that performs the handover process. Determining means,
When the second determination unit determines that there is a radio base station that performs the handover process, the radio base station having the highest priority among the radio base stations determined by the second determination unit A wireless communication system comprising: execution means for performing a handover process.

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