JP3889923B2 - Terminal device for wireless communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mobile terminal device for a wireless communication system including a plurality of base stations each having a communication area and using a plurality of slots, and more particularly to a handover function thereof.
[0002]
[Prior art]
A wireless communication system including a plurality of base stations each having a communication area, for example, a personal handy phone system (hereinafter referred to as “PHS”) (registered trademark) has a small range that can communicate with one base station because of a small zone system. When moving during a call, communication is taken over by another adjacent base station (handover). For handover, when a handover is requested from the base station to the PHS terminal apparatus, the reception level at which the PHS terminal apparatus is communicating is measured, and the reception level specified by the base station (recall type handover holding level). ) There are two ways to perform the handover process by judging that the following has occurred, both of which measure the neighboring base stations at the start of the handover and hand over to the base station with the highest reception level from among the received base stations However, in the case of communication using a plurality of slots (hereinafter referred to as “multi-slot”), the handover destination base station also needs to be compatible with multi-slots. If all base stations in the call area are not multi-slot compatible, There is a possibility to select a multi-slot non-compliant base station Te. Whether a base station is compatible with multi-slots cannot be determined unless the control channel of the base station is received for 4.8 seconds or longer. However, since the RCR-SDT 28 has a maximum handover time of 6 seconds, it is difficult to establish synchronization with the handover destination base station in the remaining 1.2 seconds.
[0003]
[Problems to be solved by the invention]
In the handover process defined in the conventional RCR-STD 28, the neighboring base stations are measured after the handover is started, and the handover destination is determined only by the result. In an actual public network, there are base stations that do not support multi-slots, and thus there is a problem that the selected base station may not be handed over.
[0004]
In addition, in the conventional PHS terminal apparatus, a multi-slot compatible base station is selected by performing a search for 4.8 seconds at the time of a handover search, but since the handover time is a maximum of 6 seconds from RCR-SDT28. However, it is difficult to establish synchronization with the handover destination base station in the remaining 1.2 seconds.
[0005]
For the problem of long handover processing time, in order to solve this problem, the reception level from another base station is detected using a slot different from the call slot during a call, and the reception level is the threshold level. In the case of exceeding, the identification information (CS-ID) of the base station that is transmitting the reception level signal is stored in the memory together with the radio reception level. After that, when a transition to the handover process is instructed from the base station in a call, the terminal device refers to the CS-ID in the memory and performs the handover process on the corresponding base station.
[0006]
In this case, there is Japanese Patent Laid-Open No. 10-98756 characterized in that if it is not stored in the memory, a connection switchback process is performed on the original base station, but this is a communication that does not select a base station such as voice communication. In this case, when searching for a multi-slot compatible base station during communication, there is a problem that the call time is reduced due to an increase in power consumption.
[0007]
Further, it detects a downlink control channel signal transmitted from a neighboring base station while maintaining communication during communication, selects a base station having the best reception level among the neighboring base stations, and selects the best base station Japanese Patent Laid-Open No. 11-4470 is characterized by maintaining synchronization with downlink control channel signals. However, this limits the base stations to be handed over, so it is optimal for handover when the PHS terminal device is moving. It was difficult to say that selecting a suitable base station.
[0008]
Therefore, the problem of the present invention is that the base station can reliably perform handover even while moving even in an area that does not support multi-slot, and has little influence on the call time, and further performs handover to an optimal base station. It is an object of the present invention to provide a movable terminal device for a multi-slot wireless communication system that can perform the above-mentioned.
[0009]
[Means for Solving the Problems]
The above-described problem is a wireless communication system including a plurality of base stations each having a communication area and using a plurality of slots, wherein the radio includes a mixed area of multislot-compatible base stations and non-multislot-compatible base stations. in the mobile terminal device capable for use in a communication system, comprising: means for receiving level in communication is judged that a predetermined value or less, if the reception level of the base station in communication is below a predetermined value, a predetermined time interval Base station measurement using a slot not used for communication, base station information of a predetermined reception level or higher as a result of the base station measurement, and the multi-slot compatible base station previously performed by the terminal device found on the basis of search means and the multi-slot information is a communicable base station information of the corresponding base station that is held in the terminal device to determine either by matching When a base station that matches the communicable base station information held by the terminal device cannot be measured, a neighboring base station is searched using an unused slot that is not used for communication without interrupting the current communication. Means for storing the base station capable of handover among the multi-slot compatible base stations received in the communicable base station information, and the reception of each base station when the reception level during communication is further deteriorated and the handover function is activated. Wireless communication, comprising: means for detecting a level and performing a handover to a base station having the highest reception level among the multi-slot compatible base stations that match the base station information communicable with the detected base station. It is solved by the system terminal device.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The basic concept and preferred embodiments of the present invention will be described below with reference to the drawings.
[0011]
FIG. 1 shows a conceptual diagram of the present invention when a PHS is used as a wireless communication system including a plurality of base stations each having a communication area and using a plurality of slots. When base stations 1 to 4 (CS1 to CS4) are arranged as shown in FIG. 1 (the base station is installed at the center of the circle and the circumference is close to the center of the circle at the point where the handover needs to be performed) Also, the reception level is higher, and only CS2 is a non-multislot-capable base station.), And the PHS terminal device that is talking with multislot-compatible base station 1 (CS1) in state A moves in the direction of the arrow. Suppose that In addition, it is assumed that two base stations CS1 and CS3, which are multi-slot compatible base stations, are stored in the communicable base station information possessed by the PHS terminal apparatus.
[0012]
In the state A, since the reception level is high, the same operation as the communication of the conventional PHS terminal apparatus is performed without measuring the neighboring base stations, so that the same call time as the conventional one can be secured. It is assumed that when the PHS terminal device reaches the point A, the reception level is lowered to a level at which measurement described later is started. Therefore, when the PHS terminal device moves and crosses the point A, the neighboring base stations are measured using the empty slots without interrupting communication periodically, and reception exceeding a predetermined reception level, for example, the handover selection level. A base station having a level is measured with a base station that matches the above-described communicable base station information (that is, CS1 is CS3 because CS1 is currently talking). In state B, since it is possible to receive the multi-slot compatible base station CS3, a search for a new multi-slot compatible base station is not performed. For this reason, the search time can be kept to a minimum. If the PHS terminal device further moves and crosses the point B, the multi-slot compatible base station CS3 cannot be received in the measurement of the base station that matches the communicable base station information during communication. As a result, the multi-slot compatible base station CS1 that is currently in communication is the only multi-slot compatible base station that can be received in the communicable base station information possessed by the PHS terminal apparatus. Is performed once to find the multi-slot compatible base station CS4, and the information of the multi-slot compatible base station CS4 is newly stored in the communicable base station information. In state C, since the multi-slot compatible base station CS4 is already registered in the communicable base station information, the multi-slot compatible base station measurement is not performed again, so that the search time can be minimized. When the PHS terminal device further moves and crosses point C, it becomes difficult to maintain communication with the multi-slot compatible base station CS1, and handover is started. In the handover search at the point C, the base station CS2 has the highest reception level, but since it is unclear whether multi-slot support is available in the search during communication, it is the most reception level registered in the communicable base station information. A handover process is performed for the multi-slot compatible base station CS4 having a high value. That is, the handover search at this point C is the same as the conventional one, and the reception level of each base station is detected. In the case shown in FIG. 1, CS2 has the highest reception level and CS4 is the next highest, but CS2 is not a base station registered in the communicable base station information and cannot be a handover target base station. However, it is unclear whether CS2 is compatible with multi-slots at this stage. Similar to the conventional handover process, the base station with the highest reception level is selected from the plurality of base stations registered in the communicable base station information, and the handover process is performed. In the case shown in FIG. 1, since only the base station CS4 is registered, the handover process is performed for the multi-slot compatible base station CS4 as the base station with the highest reception level. Since CS4 is known to be a multi-slot compatible base station, handover can be successful if the base station is in a communicable state.
[0013]
Next, a preferred embodiment in which the above basic concept of the present invention is applied to PHS will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of a PHS terminal device to which the present invention is applied. The PHS terminal device is housed in a housing 13, and a wireless unit 2 is connected to an antenna 1 and has a function of demodulating and modulating. The circuit of the system is shown. The voice processing unit 3 is a circuit that performs control related to sound such as band limitation.
[0014]
The A / D converter 4 converts the reception level value input from the wireless unit 2 into a digital signal that can be processed by the control unit 5. The control unit 5 controls the radio unit 2, the A / D converter 4, the audio processing unit 3, the speaker (ie, ear receiver) 8, the microphone 9, the external 1 / F 11 and the PIAFS 10 according to the operation state of the PHS terminal device. Processes the input information. The controller 5 operates based on the program stored in the ROM 6 and stores communicable base station information in the RAM 7. During data communication, the external 1 / F 11 or the PIAFS 10 processes transmission / reception data with the wireless unit 2. The output information is configured by the display unit 12.
[0015]
FIG. 3 is a flowchart showing control contents during a call of the PHS terminal device configured as described above.
It is assumed that the PHS terminal device is communicating. It is determined whether the communication state is a multi-slot communication state or a single slot communication state (step f1). If this determination is NO, that is, if the communication state of a single slot, proceed to return, and repeat the slot f1 after a predetermined time. On the other hand, if this determination is YES (for example, corresponding to state A in FIG. 1), it is determined whether or not the reception level has deteriorated below a predetermined level during this multi-slot call (step f2). If this determination is NO, that is, if the reception level has not deteriorated below the predetermined level, the process proceeds to return, and the slot f1 is repeated after a predetermined time. On the other hand, if this determination is YES (for example, corresponding to point A in FIG. 1), it is determined whether a base station search is not performed during the current communication, that is, whether a search is being performed during the current communication. (Step f3). If this determination is YES, that is, if a search is being executed during the current communication, the process proceeds to return, and the slot f1 is repeated after a predetermined time. On the other hand, if this determination is NO, it is determined whether or not start of search during communication is permitted (step f4). If this determination is NO, the process proceeds to return, and the slot f1 is repeated after a predetermined time. On the other hand, if this determination is YES, that is, if the start of the search during communication is permitted, the temporary search prohibit timer is started to operate (step f5). Next, without interrupting the current communication in preparation for handover, the surrounding base station search is performed for a certain time of 310 msec using an empty slot not used for communication, and a predetermined reception level, here, the handover selection level or higher The received base station information (CS_ID) is the base station having the reception level (step f6). After the search, it is determined whether or not there is a base station that matches the communicable base station information (LISTCS) stored in the PHS in the received base station information (CS_ID) (step f7). When there is a base station that matches the communicable base station information (LISTCS) stored in the PHS terminal device in the received base station information (CS_ID) (“match” in the flowchart) (for example, the state of FIG. 1 B), since the handover is possible with the current communicable base station information, the communication search operation is terminated and the normal communication operation is resumed. On the other hand, when the received base station information does not match any communicable base station information ("mismatch" in the flowchart) (for example, corresponding to point B in FIG. 1), the current communication is not interrupted. A search for surrounding base stations is performed for 4.8 seconds using unused unused slots to search for multislot-compatible base stations (step f8). After this search is completed, it is determined whether or not a multi-slot compatible base station has been found (step f9). If this determination is NO, that is, if a multi-slot compatible base station is not found, the process proceeds to return, and the slot f1 is repeated after a predetermined time. On the other hand, if this determination is YES, that is, if one or a plurality of multi-slot compatible base stations are found, the base station information with a high reception level is preferentially stored in the communicable base station information (step f10). . At this time, if there is no available storage location for communicable base station information, the base station information with the oldest storage time is exchanged with the latest base station information. After this, if the reception level during communication further deteriorates and falls below the handover selection level (for example, point C in FIG. 1), the handover is started and the handover target base station is determined by a handover search similar to the conventional one. In this case, handover is performed from the received base stations to the base station with the highest reception level among the base stations that match the communicable base station information stored in the PHS terminal device. Specifically, in the flow of the flowchart of FIG. 3, after returning from step f10, this flow is exited, the reception level of each base station is detected, and the detected base station is stored in the communicable base station information. A base station (all multi-slot compatible) is collated with the highest received level and handed over to the first multi-slot compatible base station. This enables successful handover in a short time by storing the existence of multi-slot compatible base stations and communicable base station information during communication before starting handover even in locations where multi-slot communication is compatible / non-compatible It becomes possible to make it. Further, when the information is stored as communicable base station information, the search time during communication can be shortened, so that power consumption can be reduced and the reduction in communication time can be minimized. That is, it is possible to minimize the measurement time of the communicable base station and the handover time during communication, minimize the shortening of the call time, and perform the handover to the optimal base station capable of communication.
[0016]
Next, a modification of the embodiment shown in FIG. 2 will be described. When the movement of the PHS terminal device is fast, the reception level of the same base station is different between the point to be searched in step f6 and the point to be handed over in FIG. 3, and the latter may have a lower reception level than the former. . This modified form is suitable for such a case, and in the search for whether or not a base station that matches the communicable base station information can be received during communication in step f6 in FIG. When the value is smaller than the value obtained by adding the correction value A to the handover selection level, a function for discarding received data is added. The correction value A is an operational value. When the reception level of the base station information of the communicable base station information held by the PHS terminal device is low, a base station that can be handed over is stored in the communicable base station information among the base stations that have been searched for and received from the neighboring base stations . As a result, even if the base station stored in the communicable base station information exists, if the received level of the stored base station is low, a communication is performed by newly searching a peripheral multi-slot compatible base station. Since the possible base station information can be updated, it is possible to perform handover to a more optimal base station at a point to be handed over.
[0017]
Next, another modification of the embodiment shown in FIG. 2 will be described. When the movement of the PHS terminal device is fast, the reception level of the same base station at the search point of the multi-slot compatible base station in step f8 in FIG. 3 and the point to be handed over are different, and the latter has a higher reception level than the former. May be. This modified form is suitable for such a case, and a search for a multi-slot compatible base station is performed in which a search for surrounding base stations is performed for 4.8 seconds using an empty slot not used for communication in step f8 of FIG. In this case, when the reception level of the base station is higher than the handover holding level at the time of reception, it is validated. Handover is performed to a base station at a handover selection level or higher, but in searching for a multi-slot compatible base station during communication, a PHS terminal apparatus is communicating while moving by searching for a base station at a holding level lower than the selection level. This is effective when a multi-slot-compatible base station is searched even if the electric field is weak even if it is above the selected level during handover. This is particularly effective when there are a plurality of base stations at that location and the percentage of multi-slot compatible base stations is small.
[0018]
The case where the present invention is applied to the PHS has been described as a preferred embodiment of the present invention, but the present invention is not limited to the PHS, and includes a plurality of base stations each having a communication area and wireless communication using a plurality of slots. It includes all mobile terminal devices used in any system that needs to be handed over.
[0019]
【The invention's effect】
As described above, according to the present invention, in multi-slot communication, a base station can reliably perform handover while moving even in an area that does not support multi-slots, and minimizes the effect on call time. Thus, handover to the optimal base station can be performed.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a handover operation according to the present invention.
FIG. 2 is a configuration diagram of a PHS terminal device to which the present invention is applied.
FIG. 3 is a flowchart showing control contents during a call of the PHS terminal device shown in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna 2 Radio | wireless part 3 Audio | voice processing part 4 A / D converter 5 Control part 6 ROM
7 RAM
8 Speaker (ear receiver)
9 Microphone 10 PIAFS 11 External 1 / F
12 Display 13 Case

Claims (3)

A wireless communication system including a plurality of base stations each having a communication area and using a plurality of slots, wherein the wireless communication system includes an area where a multi-slot compatible base station and a multi-slot non-compatible base station exist. In a mobile terminal device,
Means for determining that the reception level during communication is below a certain value;
When the reception level with the base station in communication is below a certain value, the base station measurement is performed using a slot not used for communication every predetermined time , and the result of the base station measurement is equal to or higher than the predetermined reception level. Base station information and communicable base station information which is information of a multi-slot compatible base station which is discovered based on a search for a multi-slot compatible base station previously performed by the terminal device and is held in the terminal device. and means for determining a match to Luke,
When a base station that matches the communicable base station information held by the terminal device cannot be measured, a neighboring base station is searched using an unused slot that is not used for communication without interrupting the current communication. Means for storing in the communicable base station information a base station that can be handed over among the multi-slot compatible base stations received,
When the reception level during communication further deteriorates and the handover function is activated, the reception level of each base station is detected, and among the base stations corresponding to the multi-slots that match the communicable base station information at the detected base station And a means for performing handover to a base station having the highest reception level. Means for determining whether the matching, according to claim 1, characterized in that it comprises a means for discarding the received data when the reception level of the received base station is less than a value obtained by adding the correction value to the handover selection level radio A communication system terminal device.   The means for storing stores base stations that can be handed over in base station information that can be handed over among base stations received by searching for a neighboring base station at a handover holding level different from a handover search condition with respect to a reception level. The terminal device for a wireless communication system according to claim 1.

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