JP2000312371A - Radio communication terminal, base station and handover method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radio communication terminal and a base station that conduct hand-over by which a communication stop time can be reduced and to obtain its hand-over method. SOLUTION: A changeover destination object table (S3) where peripheral base stations corresponding to a plurality of control signals received by an intermittent open search in high-speed hand-over are arranged in the order of higher reception levels and the results are stored, and a changeover destination recommendation table where information of base stations being an object of a changeover destination included in each control signal is collected and the peripheral base stations are arranged in the order of frequency of incidences as the object and the results are stored are provided (S4), high-speed hand-over is continuously applied to a base station that transmits a control signal with a reception level over a specific threshold or over (S6), the presence of a base station that is at the outside of the object of the changeover destination base station from each table through open search is estimated when there is a base station with a specific threshold or over (S7), and interruption hand-over is applied to the base station by a prescribed procedure (S12).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TDMA (Time D
The present invention relates to a wireless communication terminal and a base station that perform communication according to an ivision Multiple Access (time division multiple access) method. In particular, the present invention relates to switching of a base station while continuing communication between terminals based on information from a communicating base station. It relates to a handover method to be performed.

[0002]

2. Description of the Related Art A conventional handover method will be described below. Generally, in a wireless communication system based on the TDMA system, a wireless communication terminal (hereinafter simply referred to as a terminal)
For example, when the deterioration of the wireless state is detected, after the connection with the base station currently in communication is stopped, the base station is switched while continuing the call, that is, handover (channel switching during communication) is performed. The communication that has been performed through the switching destination base station is restarted. Such a general handover in which the communication is interrupted once and the switching process is performed is hereinafter referred to as an interrupted handover. In the interrupted handover, the time required for the handover, that is, the communication is interrupted from when the connection with the communicating base station is stopped to when the communication with the switching base station is resumed. Becomes

As a technique for reducing the time required for the interrupted handover, that is, the time during which communication is interrupted, for example, processing required for handover in a slot other than the time slot of the TDMA system used by the terminal for communication (described later) (Eg, searching for a base station, acquiring a base station, establishing a communication channel, etc.) to perform communication and handover in parallel. Note that the handover in which the communication and the processing required for the handover are performed in parallel is hereinafter referred to as a high-speed handover.

[0004] The above-mentioned documents relating to high-speed handover include, for example, JP-A-9-327056 "Mobile communication method", JP-A-4-207643 "Handover method of mobile communication system" and JP-T-7-503593.
"Method of measuring adjacent base station and TDMA wireless system in TDMA wireless system".

Hereinafter, a conventional high-speed handover in a wireless communication system will be described. FIG. 14 is a diagram schematically showing the timing of the high-speed handover. FIG.
4. In the high-speed handover, during communication, a control signal of a base station existing in the vicinity is received on a physical control channel (hereinafter referred to as an open search), and an optimum base station from which a communication channel is to be established is set. Select a “base station search”, selectively receive only the control signal transmitted by the selected base station, and capture the timing at that base station. Performs a communication channel establishment request, establishes a communication channel in a TDMA time slot on the physical communication channel specified by the instruction of the base station, and establishes a "communication channel." The communication path “waiting for communication” is waited for switching from the base station with which the communication path has been communicating up to the present to the base station selected as the switching destination. Note that this procedure is the same for interrupted handover as shown, but all procedures are performed after communication is stopped.

FIG. 15 is a timing chart showing the operation of the open search in high-speed handover. Here, for example, as in PHS (personal handy-phone System) shown in the second edition of the second generation cordless telephone system standard (RCR-STD28), TDMA-TDD (Time Division Duplex) with four multiplexes is used.
lex) shows the timing when the terminal is communicating with the base station.

[0007] In FIG. 15, for example, TDMA time slot 0 is allocated to a reception slot of a terminal (base station transmits), and TDMA time slot 4 is allocated to a transmission slot of the terminal (base station receives). . During communication, synchronization is maintained in the TDMA slot allocated between the base station and the terminal, and transmission and reception are performed on the physical communication channel to maintain the communication channel.

Further, even during communication, slots 1 to 3
In addition, the times indicated by slots 5 to 7 are idle times during which the terminal does not perform transmission / reception. Therefore, the radio frequency switching of the radio carrier receiving unit mounted on the terminal is performed by T
If it can be performed sufficiently fast compared to the guard time set between the DMA slots, open search is performed intermittently at the timing indicated by the shaded area in the figure.
It becomes possible to receive a control signal transmitted on the physical control channel. Note that c (101) to c (10)
3) shows a control signal transmitted from a base station existing around the terminal.

Here, c (101) transmitted during the open search can be received by this terminal. However, it is transmitted at the same timing as the TDMA time slot used for communication (c10
3) and c (102) transmitted at a timing that partially overlaps the TDMA time slot used in communication are invalid because the terminal cannot receive the entire control signal. As described above, in the high-speed handover, of the control signals transmitted on the physical control channel, for example, only the control signal received in the intermittent (shaded portion) open search is “base station search” and “ The process of “base station capture” is performed.

[0010] The terminal establishes a communication channel while continuing communication with the base station with which it is currently communicating, then stops communication with the base station, and changes the communication path on the fixed network side to the switching destination. Wait for switching to the base station.

FIG. 16 is a flowchart showing a conventional high-speed handover process. Hereinafter, the operation of the terminal and the base station in the wireless communication system in the high-speed handover will be described with reference to FIG. First, upon detecting a state degradation during communication (step S101), the terminal starts a base station search by intermittent open search which is a process associated with high-speed handover (step S102). Then, when a base station capable of handover is found by base station search in high-speed handover (step S10)
In (3, Yes), the high-speed handover is continued according to the procedure shown in FIG. 14, and thereafter, a call is made to the switching destination base station (step S104).

On the other hand, if no base station capable of handover is found in the base station search (step S103,
In No), it is determined that there is no base station capable of handover around the terminal. At this time, when the terminal and the communicating base station determine that the communication can be maintained (step S105, Yes), the terminal maintains the communication (step S106), and determines that the communication cannot be maintained. At (Step S105, No), the communication is disconnected at that time (Step S107).

In addition to the above-described radio communication system for performing normal high-speed handover, for example, a list of neighboring base stations is received from a base station in communication, and a base station search is performed for the base station indicated by the information. A system for performing this is being studied. Documents relating to this system include, for example, Japanese Patent Application Laid-Open No. H6-77888, “Cellular Wireless Telephone System”. According to this method, at the time of handover,
A plurality of base stations existing around the communicating base station can be grasped by the terminal.

FIG. 17 is a diagram showing an operation environment of a terminal in the above system for performing a handover by receiving a list of peripheral base stations. In FIG. 17, for example, 101 to
Reference numeral 105 denotes a base station (corresponding to the CS shown in the figure);
Reference numerals 105a to 105a denote wireless zones formed by the base stations 101 to 105, respectively, and 100 denotes a mobile terminal (PS shown in the drawing) existing near the base stations 101 to 105.
). Each of the base stations 101 to 105 stores a list of base stations adjacent to its own base station. Specifically, for example, the base station 101 stores the adjacent base stations 102 to 105 in the adjacent base station list.

Also, terminal 100 receives, for example, a list of adjacent base stations from base station 101 when communicating with base station 101, and then receives the received adjacent base station list when performing handover. The base station search processing is performed on the base stations 102 to 105 included in the list. As a result, the power consumption for searching for a base station can be significantly reduced as compared to a handover that does not use the adjacent base station list.

[0016]

SUMMARY OF THE INVENTION However,
In the conventional high-speed handover (see FIG. 15), in an intermittent open search, the presence of a base station that has not been able to receive a control signal and has been excluded from base station search (for example, c
(102) and c (103)) cannot be recognized by the terminal. That is, the transmission timing of the control signal of the peripheral base station is determined by the TDM used by the communicating terminal.
When a collision occurs with the A time slot, the base station cannot be recognized at the time of high-speed handover execution. Therefore, there is a problem that the terminal determines that execution of high-speed handover is impossible even though a base station capable of handover exists near the terminal.

On the other hand, in a wireless communication system, a method of transmitting and receiving a list of base stations existing around the base station from a communicating base station and grasping a handover capable base station based on the list has been studied. ing. However, for example, even in the same wireless zone, such as an urban area, in an environment where the radio wave condition varies greatly, a large wireless zone configured by a high-power base station and a small wireless zone configured by a low-power base station are included. Are mixed, the list of adjacent base stations from the base station and the handover destination candidate of the terminal often do not match. Therefore, in the terminal, there is a problem that the base station is not included in the list despite the fact that there is a base station that can actually perform handover, or conversely, the base station included in the list However, there is a problem that handover to the base station cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and it is an object of the present invention to ascertain the existence of a base station that has been excluded from high-speed handover in a base station search and to determine whether a handover to that base station is possible. It is an object of the present invention to obtain a wireless communication terminal and a base station that perform a handover automatically and that can shorten the communication stop time by performing the estimation and the estimation of the base station, and to obtain the handover method.

[0019]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, in a wireless communication terminal according to the present invention, peripheral base stations corresponding to a plurality of control signals received by intermittent open search in high-speed handover are arranged and stored in descending order of reception level. Switching destination candidate storage means (corresponding to a candidate base station table of an embodiment described later), and information on base stations which are candidate switching destinations included in the control signals are totaled, and are sorted in descending order of the number of appearances. Means for storing the neighboring base stations side by side (corresponding to a recommended base station table), wherein the switching destination candidate storage means and the appearance number storage means are created in accordance with the deterioration of the communication state, and the switching is performed. In the first candidate storage means,
If there is a base station that has transmitted a control signal at a reception level equal to or higher than a certain threshold, high-speed handover is performed continuously for that base station, and if there is no base station, both storage units are compared. By doing so, it is possible to estimate the presence of a base station that has been excluded from the switching destination base station in the open search, and determine the number of appearances of the newly estimated base station as the number of occurrences of the base station included in both storage units. If more than that, recommend the base station as a switching destination, after stopping the communication with the base station currently communicating, the reception level of the control signal from the recommended base station to be received by continuous open search, If the value is equal to or more than the threshold value, interrupted handover is performed for the base station.

According to the present invention, when the communication state deteriorates and the necessity of handover arises, intermittent open search in high-speed handover is first performed, and there is a reception level of a control signal from a peripheral base station. A high-speed handover is continued with a base station having a specific threshold or more as a switching destination base station. On the other hand, as a result of the intermittent open search, even when there is no base station capable of high-speed handover, the presence or absence of the existence of the base station that has been excluded from the base station search is estimated, and it is determined that the existence is present. Then, it is determined whether or not interrupted handover is possible for the base station. As a result, when it is determined that it is possible, the base station is switched by the intermediate handover. As a result, even for a base station that has once been excluded from the base station search, the normal interrupted handover can be automatically continued, so that even if a base station capable of handover exists near the terminal. Regardless, it is determined that execution of handover is impossible ", which is a problem in high-speed handover.

[0021] In the wireless communication terminal according to the next invention, the continuous open search is immediately terminated when a control signal from the recommended base station is received, and thereafter, the communication channel of the communication channel is immediately transmitted to the recommended base station. It is characterized by establishing.

According to the present invention, the communication interruption time of the terminal is from the time when the communication with the communicating base station is stopped to the time when the interruption handover to the switching destination base station is completed.
However, among them, the time for searching for the base station is reduced, and the time for capturing the base station is omitted, so that the communication disconnection time can be reduced as a whole as compared with the conventional interrupted handover. Further, since the communication disconnection time can be reduced, the convenience of the terminal can be improved.

In the wireless communication terminal according to the next invention, intermittent open search is performed constantly irrespective of the communication state with the currently communicating base station, and the switching destination candidate storage is performed each time. The means and the appearance number storage means are updated.

According to the present invention, the base station to be switched to at the time of high-speed handover and interrupted handover can be estimated in advance by open search in parallel with communication. In other words, even for a base station that has been excluded from high-speed handover, the base station can be estimated by comparing the tables in advance. Thus, when the deterioration of the communication state is detected, a high-speed handover or a suspended handover can be immediately started based on the information, and the time required from the detection of the deterioration of the communication state to the completion of the handover can be reduced. , Can be greatly reduced. Further, by greatly shortening the time, the convenience of the terminal can be improved.

In the wireless communication terminal according to the next invention, the plurality of control signals received by the intermittent open search include a control signal which does not include information on a base station which is a switching destination candidate. In the case, the associated control channel is established with the base station currently communicating, and the control signal is transmitted via the associated control channel, the base station in communication, and the fixed network connecting the base stations. The information of the base station which is the candidate of the switching destination is received from the base station.

According to the present invention, a candidate base station as a switching destination at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. And transmits and receives information on the base station, and estimates a base station capable of handover. As a result, it is possible to estimate whether or not a handover is possible for a base station that has been excluded from the base station search in the intermittent open search without lowering the accuracy. Further, it is not possible to specify a base station to which handover can be performed due to a low estimation accuracy of the base station, so that the convenience of the terminal can be greatly improved.

[0027] In the base station according to the next invention, information on a base station present in the vicinity of the base station which can be a candidate for a switching destination is included in an empty field of a control signal, and the control signal is transmitted. It is characterized by the following.

According to the present invention, information on a base station which is a candidate for a switching destination existing around the own base station is transmitted while being included in an empty field of a control signal.
The wireless communication terminal can estimate the switching destination base station based on this information, and can perform highly accurate handover.

In the base station according to the next invention, a plurality of control signals received by the currently communicating wireless communication terminal in an intermittent open search are used as base station candidates for the switching destination. If there is a control signal that does not contain the information of, the associated control channel is established by a request from the wireless communication terminal, via a fixed network connecting base stations, from the base station that transmitted the control signal, Receiving information on the base station which is a candidate for the switching destination, and transmitting the information to the wireless communication terminal via the established associated control channel.

According to the present invention, a candidate base station to be switched to at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. Send information about As a result, the wireless communication terminal can estimate whether or not a handover to a base station that has been excluded from the base station search by the intermittent open search is possible without lowering the accuracy. Further, it is not possible to specify a base station to which handover can be performed due to a low estimation accuracy of the base station, so that the convenience of the terminal can be greatly improved.

In the handover method according to the next invention, after detecting deterioration of the communication state in the communicating radio communication terminal (step S1 of the embodiment described later), intermittent open search in high-speed handover is performed. A switching destination candidate storing step (corresponding to step S3) of storing the neighboring base stations corresponding to the plurality of control signals to be received in order of increasing reception level (corresponding to step S3); and a switching destination candidate base included in each of the control signals. The information of the stations is totaled, and the number of appearances storing step (corresponding to step S4) in which peripheral base stations are arranged and stored in descending order of the number of appearances, If there is a base station that has transmitted a control signal at a reception level above a certain threshold, high-speed handover is continued for that base station. The first base station switching step (corresponding to step S5 and step S6) is compared with the base station stored in both storage steps when there is no base station. The estimation step (corresponding to step S7) of estimating the presence of a base station that has been excluded from the above and the number of appearances of the newly estimated base station are calculated based on the number of appearances of the base station stored in both storage steps. A recommendation step (corresponding to step S8) of recommending the base station as a switching destination when the number is large;
After stopping the communication with the base station currently communicating, if the reception level of the control signal from the recommended base station received by continuous open search is equal to or higher than the threshold value, the base station is interrupted. And a second base station switching step for performing handover (corresponding to step 9 to step S12).

According to the present invention, when the communication state deteriorates and the necessity of a handover arises, first, an intermittent open search in a high-speed handover is performed, and there is a reception level of a control signal from a peripheral base station. A high-speed handover is continued with a base station having a specific threshold or more as a switching destination base station. On the other hand, as a result of the intermittent open search, even when there is no base station capable of high-speed handover, the presence or absence of the existence of the base station that has been excluded from the base station search is estimated, and it is determined that the existence is present. Then, it is determined whether or not interrupted handover is possible for the base station. As a result, when it is determined that it is possible, the base station is switched by the intermediate handover. As a result, even for a base station that has once been excluded from the base station search, the normal interrupted handover can be automatically continued, so that even if a base station capable of handover exists near the terminal. Regardless, it is determined that execution of handover is impossible ", which is a problem in high-speed handover.

[0033] In the handover method according to the next invention, in the second base station switching step, the continuous open search is immediately terminated when a control signal from the recommended base station is received, and immediately thereafter. A communication channel is established for a recommended base station.

According to the present invention, the communication interruption time of the terminal is from the time when the communication with the communicating base station is stopped to the time when the interruption handover to the switching destination base station is completed.
However, among them, the time for searching for the base station is reduced, and the time for capturing the base station is omitted, so that the communication disconnection time can be reduced as a whole as compared with the conventional interrupted handover. Further, since the communication disconnection time can be reduced, the convenience of the terminal can be improved.

In the handover method according to the next invention, the switching destination candidate storing step and the number of appearances storing step are replaced by a constant intermittently irrespective of the communication state with the currently communicating base station. Open search is performed (corresponding to step S21 of the embodiment described later), and each time the base stations corresponding to the plurality of control signals to be received are arranged and stored in descending order of the reception level, and further, each control signal is stored. , The information of base stations that are candidates for switching destinations included in the base station is totaled, and neighboring base stations are arranged and stored in descending order of the number of appearances.

According to the present invention, it is possible to preliminarily estimate a switching destination base station at the time of high-speed handover and at the time of interrupted handover by open search in parallel with communication. In other words, even for a base station that has been excluded from high-speed handover, the base station can be estimated by comparing the tables in advance. Thus, when the deterioration of the communication state is detected, a high-speed handover or a suspended handover can be immediately started based on the information, and the time required from the detection of the deterioration of the communication state to the completion of the handover can be reduced. , Can be greatly reduced. Further, by greatly shortening the time, the convenience of the terminal can be improved.

[0037] In the handover method according to the next invention, the plurality of control signals received by the intermittent open search include a control signal that does not include information on a base station that is a switching destination candidate. A base station that has established an associated control channel with a currently communicating base station, and transmitted the control signal via the associated control channel, the communicating base station, and a fixed network connecting the base stations. Receiving information on a base station which is a candidate for the switching destination from a station.

According to the present invention, a candidate base station to be switched to at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. And transmits and receives information on the base station, and estimates a base station capable of handover. As a result, it is possible to estimate whether or not a handover is possible for a base station that has been excluded from the base station search in the intermittent open search without lowering the accuracy. Further, it is not possible to specify a base station to which handover can be performed due to a low estimation accuracy of the base station, so that the convenience of the terminal can be greatly improved.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a radio communication terminal, a base station and a handover method according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited by the embodiment.

Embodiment 1 FIG. 1 is an operating environment of a wireless communication system according to the present invention, that is, a first embodiment of a wireless communication terminal (hereinafter simply referred to as a terminal) and a base station.
FIG. 3 is a diagram showing an operation environment of the system. In FIG. 1, reference numerals 1 to 8 denote base stations (corresponding to the CS shown in the drawing), reference numerals 1a to 8a denote radio zones formed by the base stations 1 to 8, respectively.
Are mobile terminals (corresponding to the PS shown in the figure) which are present near the base stations 1 to 8. In FIG. 1, the terminal 9 according to the present invention enables communication with the base stations 1 to 8 in a wireless communication system employing the TDMA scheme.

In FIG. 1, each base station has
Are assigned, and the base station identification codes are inserted into control signals transmitted by these base stations. FIG. 2 shows, among the transmitted / received base station identification codes, for example, a PHS (Personal Handy-Phone System) shown in the second edition of the second generation cordless telephone system standard (RCR-STD28). FIG. 4 is a diagram showing a specific example of a base station identification code.

As shown in FIG. 2, base station identification codes include:
For example, a carrier identification code (9b
It), information such as a paging area number (16 bits) specifying the paging area to which the base station belongs, an additional ID (17 bits) specifying the base station for each station, and the like. Therefore, a terminal that receives such information specifies each base station based on the base station identification code.

In the wireless communication system configured as described above, each base station grasps a plurality of base stations existing around the base station, and uses these base stations as candidates for switching destination at the time of handover. I remember. That is, in FIG. 1, the base station 1 switches the adjacent base station 2, base station 3, base station 4, base station 8, base station 5, and base station 7 to candidates for switching at the time of handover (the adjacent base station shown in the drawing). (Equivalent to a list). And the terminal 9 in communication
When a handover is performed, the control signal transmitted from the base station includes information on a candidate for a handover destination existing around the base station, that is, information on the base station stored in the adjacent base station list. . The information of the base station at the time of handover is transmitted / received using, for example, the additional ID of the base station identification code in FIG.

More specifically, in the PHS, the control signal transmitted by the base station on the physical control channel includes, for example, a BCCH (Broadcasting Control) for notifying broadcast information.
ol Channel: broadcast channel), PCH (Paging Channel: paging channel) for notifying a terminal of an incoming call,
SCCH (Signaling Control Channel) used to transfer information required for call connection between specific terminals and base stations
l: common bidirectional control channel), but base station information that is a candidate for a switching destination at the time of handover is inserted into an empty field of these channels and transmitted from the base station.

FIG. 3 shows an example of the field format when the information of the base station of the switching destination is inserted into the PCH. In the PHS, when there is no incoming call information to be notified to the terminal, the idle PCH is transmitted with the incoming call information field being empty. Therefore, here, additional IDs of three base stations, which are information of the base station to be switched, are inserted into the idle PCH as “adjacent base station information”.

FIG. 4 shows an example of the field format when the information of the base station to be switched is inserted into the SCCH. In the PHS, when there is no information necessary for a call connection with a terminal, the idle SCCH is transmitted with an information field on the call connection being empty. Therefore,
Here, base station 1 which is information of a base station to be switched to is included in this idle SCCH as “adjacent base station information”.
The additional ID for the station is inserted. Although not shown, an additional ID of an adjacent base station, which is information on a base station to be a switching destination, may be inserted into an empty field of the BCCH.

Next, a description will be given of a handover process in a terminal and a base station which constitute the above radio communication system. FIG. 5 is a flowchart of the first embodiment showing processing at the time of handover of a terminal according to the present invention.
Hereinafter, the processing at the time of handover of the terminal 9 shown in FIG. 1 will be described in detail with reference to FIG.

When the terminal 9 is communicating with the base station 1 at, for example, a point indicated by Point (1), the communication state between the terminal 9 and the base station 1 is as follows. It deteriorates because it is outside the wireless zone 1a. At this time, when the terminal 9 detects the deterioration of the communication state (step S1), the terminal 9 starts a high-speed handover while maintaining the communication with the base station 1.

First, the terminal 9 performs an intermittent open search and performs a base station search process (step S2). Here, the above-described open search accompanying the handover will be described. FIG. 6 is a timing chart showing the operation of the open search accompanying the handover of the terminal 9.
When the terminal 9 detects the deterioration of the communication state,
The open search is performed intermittently using the idle time of the time slot, and the control signal of the peripheral base station is received.
In FIG. 6, c (1) to c (8) indicate control signals transmitted by the base stations 1 to 8, respectively.

At this time, the terminal 9 performs the open search only during the period shown by the shaded portion in FIG.
In the example shown in FIG. 6, among the control signals c (1) to c (8), c (1) to c (3) and c (5) to c (7) can be received. Regarding (4) and c (8), as described in the related art, no reception was possible. Therefore, CS4 and CS8 outside the shaded portions are excluded from the base station search here.

Next, the terminal 9 that has received the control signals of the peripheral base stations by the intermittent open search creates a candidate base station table and a recommended base station table based on these control signals (step S3). Step S
4). For example, FIG. 7 is a graph showing a control signal reception level. L (1) to L (8) in the drawing indicate the reception levels of c (1) to c (8) in Point (1), respectively. As described above, in the terminal 9, c (1) to c (3), c
The reception level is measured only for (5) to c (6), the candidate base stations are rearranged according to this reception level, and the result is stored as a candidate base station table (step S3).

FIG. 8 is an example of the candidate base station table. As described above, the base station 4 and the base station 8 for which the control signal could not be received by the intermittent open search are not included in the candidate base station table. Further, in the present embodiment, among the base stations stored in the candidate base station table, only when the reception level of the control signal is equal to or higher than a certain threshold, the handover is targeted for high-speed handover. Therefore,
In this example, since only c (1) exceeds the threshold value, if the terminal 9 excludes the base station 1 currently in communication, there is no candidate base station to be switched to at the time of handover.

FIG. 9 is a diagram showing a method for creating a recommended base station table. Here, the terminal 9
All information on the candidate base stations to be switched included in the control signal received in the intermittent open search is totaled, and a candidate base station table is created based on the totaling result (step S4). . Specifically,
For example, the terminal 9 receives a plurality of control signals (corresponding to c (1) to c (3) and c (5) to c (7) shown) in intermittent open search in high-speed handover.

Since these control signals include information on the base station which is a switching destination candidate (for example, c (1) includes base station 2, base station 2 as shown in FIG. 9). 4 and the information of the base station 8),
The terminal 9 aggregates these pieces of information, associates the base station with the number of appearances of the base station, further sorts the candidate base stations according to the number of appearances, and places it in the recommended base station table. To memorize.

A base station with a large number of appearances in the recommended base station table exists near the terminal 9 and is likely to be a strong candidate as a switching destination base station at the time of handover. Therefore, in the example shown in FIG.
.. Can be estimated to be near the terminal 9 in the order of the base station 1, the base station 4, the base station 2,. Conversely, it can be determined that the base station 5 having a low number of appearances is unlikely to be present near the terminal 9.

Next, the terminal 9 determines whether there is a base station that can be handed over based on the contents of the above-mentioned candidate base station table (step S5). For example, if there is a base station capable of handover (step S
(5, YES), the high-speed handover is continued, for example, the communication with the communicating base station is stopped in the procedure of FIG. 14 described above, and then the communication with the switching destination base station is restarted ( Step S6).

On the other hand, if there is no handover capable base station in the candidate base station table (step S5), it is determined that high-speed handover cannot be performed, and the contents of the recommended base station table and the candidate base station table are compared. Thus, as a result of the intermittent open search, it is confirmed whether or not there is any base station that has been excluded from the base station search (step S7). Specifically, for example, FIGS.
In the example, since the base station 4 and the base station 8 that are not stored in the candidate base station table are present in the recommended base station table, it can be recognized that these base stations have been excluded from the base station search. .

As a result, if there is no base station excluded from the base station search (step S8, No), the terminal 9
Determines whether communication with the base station currently communicating can be maintained (step S13). If communication cannot be maintained (step S13, No), the communication is stopped (step S15). That is, a call cannot be made. On the other hand, when communication can be maintained (step S13, Yes)
Then, the communication with the base station with which communication is currently being performed is continued (step S14).

More specifically, for example, as shown in FIG. 10, when the communication state deteriorates at point (2), the terminal 9 performs a handover on the candidate base station table described above. The control signals of the base stations 1 and 2 which are the peripheral base stations are stored in the order of the reception level. In this example, it can be seen that the reception level of the base station 1 is the highest. On the other hand, it is assumed that, for example, only the base station 1 and the base station 2 are stored in the recommended base station table. However, in such a case, the terminal 9 determines that there is no base station capable of handover around (Step S8, No), and continues the communication with the base station 1 as it is (Step S14). Alternatively, the communication with the base station 1 is stopped (step S15).

In the process of step S7, there is a base station that has been excluded from the search for a base station, but there is no recommendation of a base station capable of handover (step S8,
No), the terminal 9 determines whether or not the communication with the base station currently in communication can be maintained in the same manner as described above (step S1).
3) If communication cannot be maintained (step S13, N
o), the communication is stopped (step S15). That is, a call cannot be made. On the other hand, when communication can be maintained (step S13, Yes), communication with the base station with which communication is currently being performed is continued (step S1).
4).

In the process of step S7, when it is determined that there is a base station that has been excluded from the search for a base station, and there is a recommendation of a base station to which handover is possible (step S8, Yes), The terminal 9 stops communication with the base station that is currently communicating (step S9), and then performs a base station search by a continuous open search (step S10). The determination as to whether or not there is a recommendation of a base station that can perform handover is performed based on the recommended base station table described above.

Specifically, for example, when each table is as shown in FIGS. 8 and 9, first, the number of appearances of the base station 8 in the recommended base station table, and both the recommended base station table and the candidate base station table are set. The number of appearances of the included base stations (base station 1, base station 2, base station 7, etc.) is compared. In this example, it can be seen that the number of appearances of the base station 8 is greater than the number of appearances of the base station 1, the base station 2, and the base station 7. Thereby, among the base stations included in the recommended base station table, the base station 8 is highly likely to be present near the terminal 9, and the control signal of the base station 8 is temporarily received by the intermittent open search. If so, it can be estimated that the reception level was sufficient as the switching destination at the time of handover. Therefore, in this example, the base station 8
Can be recommended as a strong candidate for a handover destination.

Next, in the terminal 9, the number of appearances of the base station 4 in the recommended base station table, and the base stations (base station 1, base station 2) included in both the recommended base station table and the candidate base station table. , Base station 7 etc.). In this example, it can be seen that the number of appearances of the base station 4 is the same as that of the base station 2 whose reception level is not sufficient for handover. Thereby, the base station 4 is unlikely to be present near the terminal 9, and even if the control signal of the base station 4 is received by intermittent open search, It can be estimated that the reception level is not sufficient. So, in this example,
The base station 4 cannot be recommended as a strong candidate for a handover destination.

Next, the base station search by the continuous open search is performed by the processing of step S10, and when it is determined that these base stations are not handover-capable base stations (step S11, No), the terminal 9 It is determined whether communication with the base station currently communicating can be maintained (step S13). If communication cannot be maintained (step S13, No), the communication is stopped (step S13).
15). That is, a call cannot be made. On the other hand, if communication can be maintained (step S13, Yes), communication with the base station with which communication is currently being performed is continued (step S14).

On the other hand, if it is determined that those base stations are handover-capable base stations (step S11,
Yes), the terminal 9 continues the interrupted handover, and resumes communication with the switching destination base station by, for example, the procedure of FIG. 14 described above (step S12).

As described above, according to the present invention, when the communication state deteriorates and a handover becomes necessary, first, an intermittent open search in a high-speed handover is performed to receive a control signal from a peripheral base station. The base station having the highest level (more than a certain threshold) is set as the base station to be switched to, and the high-speed handover is continued. On the other hand, as a result of the intermittent open search, even if there is no base station capable of high-speed handover, the presence or absence of the base station that has been excluded from the base station search is estimated, and when it is determined that the base station exists, Further determines whether or not interrupted handover is possible for the base station. As a result, if it is determined to be possible, the base station can be switched by an intermediate handover.

As a result, the terminal can automatically continue the normal interrupted handover even for the base station once excluded from the target of the base station search. However, even though there is a base station that can perform handover, it is determined that execution of handover is not possible. "

Embodiment 2 FIG. 11 is a timing chart of an embodiment 2 showing an operation of an open search accompanying a handover of a terminal according to the present invention. The terminal and the base station use the operating environment of the first embodiment described above with reference to FIG.

Here, it is determined by intermittent open search that there is no base station capable of high-speed handover.
In the subsequent base station search by the continuous open search, the continuous open search is stopped when the switching destination base station at the time of handover is detected, and the base station is immediately captured by the base station. Continue the interrupted handover process.

In FIG. 11, c (1) to c (1) to c
(8) shows control signals of base stations 1 to 8 existing around the terminal. In addition, T in FIG. 11 indicates, for example, a transmission interval time of a control signal from the base station, which is defined by a system to which the terminal and the base station belong.

Normally, in the base station search accompanying the interrupted handover, a continuous open search is performed over the transmission interval time T, and all control signals transmitted on the physical control channel are received. As a result, the terminal can perform a base station search for all base stations present in the vicinity.

Therefore, in Embodiment 1, for example, as shown in FIG. 5, when a base station capable of handover cannot be detected by high-speed handover, terminal 9 estimates base station from information in each table. Perform (Step S
7) If it is estimated that there is a base station capable of handover (step S8, Yes), the communication with the base station that is currently communicating is stopped (step S9), and all the base stations are successively searched by open search. A base station search is performed for the peripheral base station (step S10).

Hereinafter, a case will be described as Embodiment 2 where terminal 9 estimates base station 4 as a handover destination base station. As shown in FIG. 11, in high-speed handover, control signals c (4) and c (8), which are control signals of base station 4 and base station 8, are not received, and at this time, it is determined that there is no base station to which handover is possible. When done
In step S7 of FIG. 5, the terminal 9 estimates the base station and estimates the existence of the base station 4 and the base station 8 which may be the switching destination base stations at the time of the interrupted handover.

After that, in step S8, if the base station 4 is recommended as the switching destination at the time of the interrupted handover, the terminal 9 stops the communication with the base station with which communication is currently being performed in step S9. In S10, a continuous open search is started to receive the control signal c (4) of the base station 4. However, at this time, the terminal 9 has a time shorter than the transmission interval time T of the control signal,
That is, c (4) can be received before the search of all the neighboring base stations is completed. Therefore, when the continuous open search is forcibly terminated here, the time of the open search required for the base station 4 to capture the base station is reduced.

Further, the terminal 9 can specify the transmission timing of the control signal of the base station 4 at the time of receiving c (4) in the continuous open search. Acquisition will be completed immediately. That is, the acquisition of the base station can be completed simultaneously with the search for the base station with respect to the base station 4, and the time required for the acquisition of the base station can be omitted. The subsequent processes are the same as those in the flowchart of FIG.

As described above, according to the second embodiment, the time period during which the communication of the terminal 9 is interrupted is between the time when the communication with the communicating base station is stopped and the time when the interrupted handover to the base station 4 is completed, as described above. However, among them, the time for searching for the base station is reduced, and the time for capturing the base station is omitted, so that the communication disconnection time can be reduced as a whole as compared with the interrupted handover by the procedure described above.

As described above, according to the present invention, when it is determined that there is no base station to be switched to at the time of high-speed handover and base station to be switched at intermediate handover is estimated by subsequent base station estimation, It is possible to shorten the communication interruption time in the interrupted handover performed by the user, and accordingly, the convenience of the terminal can be improved.

Embodiment 3 FIG. 12 is a flowchart of the second embodiment illustrating processing at the time of handover of a terminal according to the present invention. Hereinafter, the processing at the time of handover of the terminal 9 shown in FIG. 1 will be described in detail with reference to FIG. In FIG. 12, the same steps as those in the flowchart of FIG. 5 described above are denoted by the same reference numerals, and description thereof will be omitted. The terminal and the base station use the operating environment of the first embodiment described above with reference to FIG.

Normally, the handover performed by the terminal 9 is performed when the deterioration of the communication state is detected (step S5 in FIG. 5).
(Corresponding to 1). However, in high-speed handover, since open search can be performed intermittently in parallel with communication, the terminal 9 during communication constantly searches for a base station before detecting deterioration of the communication state. Then, it is possible to always select the handover destination base station.

Therefore, in the present embodiment, deterioration of the communication state is detected in a state where it is determined that there is no base station capable of high-speed handover in the base station search that the communicating terminal 9 constantly performs. In this case, the interrupted handover is immediately started for the base station estimated in the base station search.

Hereinafter, the above operation will be described in detail. First,
The communicating terminal 9 constantly and intermittently performs an open search to search for a base station in an idle time other than the TDMA time slot used for communication (step S2).
1). Then, every time this base station search is performed, the information on the neighboring base stations is stored in the candidate base station table and the recommended base station table described above (steps S3 and S4).

As a result, the terminal 9 can always grasp the candidate of the high-speed handover destination even if the deterioration of the communication state is detected during the communication (step S22). By comparing the station table with the recommended base station table, it is possible to estimate the presence of a base station that has been excluded from the base station search even when there is no base station to which fast handover is switched. (Step S22), and the processing time here can be greatly reduced.

Therefore, for example, when the deterioration of the communication state is detected (step S23, Yes), the terminal 9 first determines whether or not there is a handover-capable base station by referring to the candidate base station table (step S5). ), When there is a base station capable of handover (step S5, Ye)
In s), the high-speed handover is continued for the base station (step S6). On the other hand, when there is no base station capable of handover (Step S5, No), if there is a base station that has been estimated in advance (Step S8, Yes), the method of Embodiment 1 or 2 described above is used. Perform an interrupted handover. If there is no base station estimated in advance (step S8, No), the subsequent processing is performed by the method of the first embodiment described above.

As described above, in the present embodiment, the base station to be switched between during high-speed handover and during interrupted handover can be estimated in advance in base station search in parallel with communication. In other words, even for a base station that has been excluded from handover in the base station search, it is possible for the terminal to estimate the base station by comparing the tables in advance. Therefore, when the terminal detects the deterioration of the communication state, based on the information, it can immediately start a high-speed handover or a suspended handover to the estimated base station by stopping communication, The time required from the detection of the deterioration of the communication state to the completion of the handover can be greatly reduced.

As described above, according to the present embodiment, it is possible to perform the handover process with a quick response to the deterioration of the communication state, and accordingly, it is possible to improve the convenience.

Embodiment 4 FIG. 13 is a diagram illustrating an operation environment of the fourth embodiment of the wireless communication terminal and the base station according to the present invention.

In the first embodiment, a terminal receives information on a candidate base station to be switched to at the time of handover inserted into an empty field of a control signal, and estimates a base station to be switched based on the information. Was explained. However, the base station may not be able to report this information, for example, because there is not enough empty field in the control signal. Therefore, in this embodiment, in such a case, an associated control channel is established between the terminal and the communicating base station, and information on the candidate base station to be switched to during handover is transmitted and received using this. By doing so, the estimation accuracy of the base station capable of handover is ensured.

Hereinafter, the above operation will be described in detail. Embodiment 4 will be described below with reference to the drawings. FIG.
, 11 to 13 are base stations (corresponding to the CS shown in the figure), and 11a to 13a are base stations 11 to 11 respectively.
3 is a wireless zone configured, and 14 and 15 are base stations 1
1 to mobile terminals existing in the vicinity of the base station 13 (corresponding to the illustrated PS).

The base stations 11 to 13 are connected to each other via a fixed network. In FIG. 13,
The terminal 14 is communicating with the base station 11 at Point (3), starts an intermittent open search during communication, and receives control signals c (12) and c (13) of the base stations 12 and 13. It is further assumed that the base station 13 has notified the terminal 15 of the incoming call at that time.

In this state, first, at the terminal 14, c (1
Since 2) and c (13) have been received, the information of the base stations 12 and 13 is stored in the above-mentioned candidate base station table. At this time, c (12) includes information on the base station 11 and the base station 13 as information on the candidate base station of the handover destination. On the other hand, since the base station 13 notifies the terminal 15 of the incoming call, c (13)
Has no empty fields. That is, c (13) does not include information on the candidate base station of the handover destination.

Here, in the terminal 14, since the information on the base stations 12 and 13 is included in the candidate base station table, if the information on the candidate base station to be switched at the time of handover can be received from the base station 13, In addition, the system for estimating the base station to be switched to can be improved.

Therefore, in the present embodiment, in such a case, terminal 14 establishes an associated control channel with base station 11 in communication and establishes base station 13 with base station 13.
Inquire about the information about the candidate base station to be switched to at the time of handover. Then, the base station 11 that has received the inquiry requests the base station 13 via the fixed network for information on the candidate base station to be switched to at the time of handover.

At the base station 13 receiving the information request,
The information is transmitted to the base station 11 via the fixed network, and the base station 11 notifies the terminal 14 of the information from the base station 13 using the previously established associated control channel. . Thereafter, the terminal 14 processes the information received from the base station 11 in the same manner as the case where the information is provided to the control signal from the base station 3, and estimates a base station that can be switched at the time of handover. Handover is performed by the method 2 or 3.

As described above, in the present embodiment, the handover at the time of handover is performed using the two-way associated control channel established between the terminal and the base station in communication with the vacant field of the control signal. And transmits and receives information on the candidate base station of the switching destination, and estimates a base station to which the terminal can perform handover. As a result, it is possible to estimate whether or not a handover is possible for a base station that has been excluded from the base station search in the intermittent open search without lowering the accuracy.

Further, according to the present embodiment, it is not impossible to specify a handover capable base station due to low estimation accuracy of the base station, so that the convenience of the terminal can be greatly improved. it can.

[0096]

As described above, according to the present invention, when the communication state is degraded and a handover is required, first, the base station having a control signal reception level equal to or higher than a specific threshold value is used. If a base station is set as a switching destination and high-speed handover is continued, and there is no base station capable of high-speed handover, interrupted handover can be performed for a base station that has been excluded from base station search. As a result, even for a base station that has once been excluded from the base station search, the normal interrupted handover can be automatically continued, so that even if a base station capable of handover exists near the terminal. Regardless, it is determined that execution of handover is impossible ", which is a problem in high-speed handover.

[0097] According to the next invention, the communication interruption time of the terminal is from the time when the communication with the communicating base station is stopped to the time when the interrupted handover to the switching destination base station is completed.
However, among them, the time for searching for the base station is reduced, and the time for capturing the base station is omitted, so that the communication interruption time can be reduced as compared with the conventional interrupted handover as a whole. Play. In addition, since the communication disconnection time can be reduced, there is an effect that the convenience of the terminal can be improved.

According to the next invention, it is possible to preliminarily estimate the switching destination base station at the time of the high-speed handover and the interrupted handover by the open search parallel to the communication.
In other words, even for a base station that has been excluded from high-speed handover, the base station can be estimated by comparing the tables in advance. This allows
When the deterioration of the communication state is detected, high-speed handover or interrupted handover can be started immediately based on the information, and the time required from the detection of the deterioration of the communication state to the completion of the handover is greatly reduced. This has the effect of being able to be shortened. In addition, by greatly shortening the time, it is possible to improve the convenience of the terminal,
This has the effect.

According to the next invention, a candidate base station to be switched to at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. Send and receive information about the station,
Estimate a handover-capable base station. As a result, it is possible to estimate whether or not handover is possible for a base station that has been excluded from base station search by intermittent open search without lowering the accuracy. Also,
It is not possible to specify a handover-capable base station due to low estimation accuracy of the base station, and it is possible to greatly improve the convenience of the terminal,
This has the effect.

According to the next invention, information on a base station which is a candidate for a switching destination existing around the own base station is transmitted in a state where it is included in an empty field of a control signal. Based on this information, it is possible to estimate the base station to be switched to, and it is possible to perform highly accurate handover.

According to the next invention, a candidate base station to be switched to at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. Send information about the station.
As a result, the wireless communication terminal has an effect that it is possible to estimate whether or not a handover is possible for a base station that has been excluded from the base station search in the intermittent open search without lowering the accuracy. In addition, it is not possible to specify a handover-capable base station due to a low estimation accuracy of the base station, and it is possible to greatly improve the convenience of the terminal.

According to the next invention, the communication state deteriorates,
If the need for handover arises, first, when the reception level of the control signal is a base station having a certain threshold or more, the high-speed handover is continued, and when there is no base station capable of high-speed handover, An interrupted handover can be performed for a base station that has been excluded from the base station search. As a result, even for a base station that has once been excluded from the base station search, the normal interrupted handover can be automatically continued, so that even if a base station capable of handover exists near the terminal. Regardless, it is determined that execution of handover is impossible ", which is a problem in high-speed handover.

According to the next invention, the communication interruption time of the terminal is set between the time when the communication with the communicating base station is stopped and the time when the interrupted handover to the switching destination base station is completed.
However, among them, the time for searching for the base station is reduced, and the time for capturing the base station is omitted, so that the communication interruption time can be reduced as compared with the conventional interrupted handover as a whole. Play. In addition, since the communication disconnection time can be reduced, there is an effect that the convenience of the terminal can be improved.

According to the next invention, the base station to be switched to at the time of high-speed handover or interrupted handover can be estimated in advance by open search in parallel with communication.
In other words, even for a base station that has been excluded from high-speed handover, the base station can be estimated by comparing the tables in advance. This allows
When the deterioration of the communication state is detected, high-speed handover or interrupted handover can be started immediately based on the information, and the time required from the detection of the deterioration of the communication state to the completion of the handover is greatly reduced. This has the effect of being able to be shortened. In addition, by greatly shortening the time, it is possible to improve the convenience of the terminal,
This has the effect.

According to the next invention, a candidate base station to be switched at the time of handover is utilized by utilizing an empty field of a control signal and a bidirectional associated control channel established between a terminal and a communicating base station. Send and receive information about the station,
Estimate a handover-capable base station. As a result, it is possible to estimate whether or not handover is possible for a base station that has been excluded from base station search by intermittent open search without lowering the accuracy. Also,
It is not possible to specify a handover-capable base station due to low estimation accuracy of the base station, and it is possible to greatly improve the convenience of the terminal,
This has the effect.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an operation environment of a wireless communication terminal and a base station according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a base station identification code transmitted and received by a PHS.

FIG. 3 is an example of a field format when information of a base station to be switched is inserted into a PCH.

FIG. 4 is an example of a field format when information of a base station to be switched is inserted into the SCCH.

FIG. 5 is a flowchart of a first embodiment showing a process at the time of handover of a terminal according to the present invention.

FIG. 6 is a timing chart showing an open search operation accompanying a handover of a terminal according to the present invention.

FIG. 7 is a graph showing a reception level of a control signal.

FIG. 8 is an example of a candidate base station table.

FIG. 9 is a diagram showing a method for creating a recommended base station table.

FIG. 10 is a diagram showing an operation environment of a terminal 9 according to the present invention.

FIG. 11 is a timing chart of an embodiment 2 showing an operation of an open search accompanying a handover of a terminal according to the present invention.

FIG. 12 is a flowchart of a third embodiment illustrating a process at the time of handover of a terminal according to the present invention.

FIG. 13 is a diagram illustrating an operation environment of a wireless communication terminal and a base station according to a fourth embodiment of the present invention.

FIG. 14 is a diagram schematically showing the timing of a high-speed handover.

FIG. 15 is a timing chart showing an open search operation in high-speed handover.

FIG. 16 is a flowchart showing a conventional handover process.

FIG. 17 is a diagram illustrating an operation environment of a terminal that performs a handover by receiving a peripheral base station list.

[Explanation of symbols]

1,2,3,4,5,6,7,8,11,12,13
Base stations, 1a, 2a, 3a, 4a, 5a, 6a, 7a,
8a, 11a, 12a, 13a Wireless zone, 9, 1
4,15 Wireless communication terminal.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K067 AA15 AA34 BB04 CC04 DD19 DD23 EE02 EE10 EE24 FF16 GG09 GG11 HH01 HH23 JJ03 JJ17 JJ37 JJ72 LL01

Claims (10)

[Claims] A wireless communication terminal that performs high-speed handover to a switchable base station in accordance with deterioration of a communication state with a communicating base station and continues the communication at a switching destination base station, Switching destination candidate storage means for storing a plurality of peripheral base stations corresponding to a plurality of control signals received by intermittent open search in the high-speed handover, arranged in descending order of reception level, and a switching destination included in each of the control signals. Aggregation of information on candidate base stations, appearance frequency storage means for storing the peripheral base stations arranged in descending order of the appearance frequency, and, with the deterioration of the communication state, the switching destination candidate storage means and Create an appearance count storage means, if the switch destination candidate storage means, there is a base station that has transmitted a control signal at a reception level above a certain threshold,
The high-speed handover is continuously performed on the base station, and when the base station does not exist, by comparing both the storage units, the presence of the base station which has been excluded from the switching destination base station in the open search is determined. If the estimated number of occurrences of the newly estimated base station is greater than the number of occurrences of the base station included in both storage means, the base station is recommended as a switching destination, and the base station currently communicating with the base station is After the communication is stopped, if the reception level of the control signal from the recommended base station to be received in the continuous open search is equal to or higher than the threshold value, the interrupted handover is performed to the base station. Wireless terminal device. 2. The continuous open search ends immediately upon receiving a control signal from the recommended base station,
The wireless terminal device according to claim 1, wherein a communication channel is established with a recommended base station immediately thereafter. 3. An intermittent open search is performed constantly irrespective of a communication state with a base station with which communication is currently being performed, and each time the switching destination candidate storage means and the appearance count storage means are updated. The wireless terminal device according to claim 1, wherein: 4. When a plurality of control signals received by the intermittent open search include a control signal that does not include information on a base station that is a candidate for a switching destination, a communication between the control signal and a base station that is currently communicating is performed. Establish the associated control channel at, via the associated control channel, the communicating base station, and the fixed network connecting the base stations, from the base station that transmitted the control signal, become the candidate for the switching destination 4. The wireless terminal device according to claim 1, wherein the wireless terminal device receives information of a base station. 5. A base station characterized in that information of a base station which is a candidate for a switching destination existing around its own base station is included in an empty field of a control signal and the control signal is transmitted. 6. An intermittent open search by a currently communicating wireless communication terminal, wherein a plurality of control signals received by the terminal include a control signal that does not include information on the base station to be a switching destination candidate. In some cases, the associated control channel is established by a request from the wireless communication terminal, and the base station that transmitted the control signal is transmitted from the base station that transmitted the control signal to the base station that is a candidate for the switching destination via a fixed network connecting the base stations. The base station according to claim 5, wherein the base station receives information and transmits the information to the wireless communication terminal via the established associated control channel. 7. A peripheral base station corresponding to a plurality of control signals received by intermittent open search in high-speed handover after detecting deterioration of a communication state in a communicating radio communication terminal,
A switching destination candidate storing step of arranging and storing in descending order of reception level, information of base stations which are candidate switching destinations included in the control signals are totaled, and neighboring base stations are arranged and stored in descending order of the number of appearances In the number of appearances storing step and among the base stations stored in the switching destination candidate storing step, if there is a base station that has transmitted a control signal at a reception level equal to or higher than a specific threshold, the base station A first base station switching step of continuously performing high-speed handover, and, if the base station does not exist, by comparing the base stations stored in both storage steps, the base station to be switched in the open search The estimation step of estimating the existence of a base station that has been excluded from the target and the number of appearances of the newly estimated base station If more than the number,
A recommendation step of recommending the base station as a switching destination; and a reception level of a control signal from the recommended base station, which is received by continuous open search after stopping communication with the base station currently communicating, is equal to the threshold. If the value is equal to or greater than the value, a second base station switching step of performing an interrupted handover to the base station is provided. 8. In the second base station switching step, the continuous open search is immediately terminated when a control signal from the recommended base station is received, and immediately thereafter, communication with the recommended base station is performed. The handover method according to claim 7, wherein a channel is established. 9. A continuous intermittent open search is performed in place of the switching destination candidate storing step and the occurrence count storing step regardless of a communication state with a base station with which communication is currently being performed. The neighboring base stations corresponding to the plurality of control signals to be received are arranged and stored in descending order of the reception level, and further, information on the base station which is a candidate for the switching destination included in each control signal is totaled, and the number of appearances 9. The handover method according to claim 7, wherein peripheral base stations are arranged and stored in descending order. 10. When a plurality of control signals received by the intermittent open search include a control signal that does not include information on a base station that is a candidate for a switching destination, a communication with a base station that is currently communicating is performed. Establish the associated control channel at, via the associated control channel, the communicating base station, and the fixed network connecting the base stations, from the base station that transmitted the control signal, become the candidate for the switching destination The handover method according to claim 7, 8 or 9, wherein the information of the base station is received.