JP2002027517A - Communication terminal and handover control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication terminal and a handover control method which can restrict an execution of an unrequired handover, thereby lessening the occurrence of a sound break. SOLUTION: Entering selection step (S3), a control part 18 confirms whether or not a base station selected in accordance with a sorting order in step S31 is a base station during a speech communication, and if not during the speech communication, the step proceeds to step S11, and on the other hand, if during the speech communication, the step proceeds to step S32. The control part 18 compares a field strength of a control channel of the base station during the speech communication with the field strength of the speech communication channel in step S32, and if the field strength of the control channel is greater, the step proceeds to step S11, but on the other hand, if during the speech communication, the step proceeds to step S33, and the sorting order selects the next base station to proceed to step S11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication terminal apparatus and a handover control method, and more particularly, to the field intensity of a control channel transmitted by a peripheral base station when communicating via a first base station. The present invention relates to a communication terminal apparatus and a handover control method for selecting a base station suitable for communication, performing handover by measuring the base station, and continuing communication.

[0002]

2. Description of the Related Art In recent years, PHS (Personal Handy phone Sy
stem) and PDC (Personal Digital Cellular telecommuni)
2. Description of the Related Art Mobile communication devices such as cation systems have become widespread due to reductions in size and weight, improvement in communication quality, and reduction in main unit prices and telephone charges.

[0003] In PHS or PDC, communication between a mobile communication device and a base station uses a communication channel (traffic channel: hereinafter also abbreviated as "TCH") and a control channel (contr).
ol channel: Hereinafter also abbreviated as “CCH”. ).

[0004] Here, TCH is a channel used for communication with another mobile communication device or telephone via a base station, and CCH is used when a call is made or received in a standby state.
H is a channel used to control the transition to H.

FIG. 1 shows a base station selection process in a conventional mobile communication device (personal station: PS in the figure) in the PHS system, and a description of a mobile communication device and a base station (cell statio).
FIG. 11 is a diagram showing a link establishment sequence at the time of transition from CCH to a communication channel with (n: CS in the figure).

In the base station selection process shown in FIG. 1, when the power of the mobile communication device is turned on, when searching for another base station at the time of handover, the base station is instructed to switch to another base station during a call. This is done in some cases.

[0007] First, the mobile communication device is connected to a plurality of base stations.
Monitor CH. In the case of PHS, a specific frequency is allocated for CCH, and a plurality of base stations are assigned respective CCHs.
Are time-division multiplexed. The mobile communication device sequentially receives a signal of a specific frequency, and when it is able to decode the identifier (CSID) of the base station from the signal of each CCH, sets the CSID and the reception field strength of the CCH as a set. (S1).

[0008] Further, the mobile communication device may store the stored CSI.
The set of received field strengths of D and CCH is sorted in the order of the received field strength (S2),
The base station of the CH is selected (S3). If this selection is made immediately after the power is turned on, the mobile communication device registers its location with the selected base station, and then enters a CCH standby reception state.

In FIG. 1, a link establishment sequence is performed when a call is made or received from a standby state, or when switching to a handover destination base station during a call.

In these cases, the mobile communication device transmits a link channel establishment request on the CCH to the base station selected by the base station selection process (S11), and transmits the request on the CCH from the base station in response. The assigned link channel assignment is received (S12), and the electric field strength of the assigned TCH U wave is measured (S153). Since the electric field strength of the U wave is the electric field strength of the TCH immediately after link channel allocation, that is, in a period in which neither the base station nor the mobile communication device uses the TCH yet, the U wave is an interference wave of the assigned TCH (ie, , Noise). If the reception level of the U wave is high, it is determined that the TCH is not suitable for the call, and the request is made again from the link channel establishment request.

When the level of the U wave is low, the mobile communication device and the base station establish synchronization of the TCH by sequentially transmitting a synchronization burst signal and a TCH idle burst signal on the TCH (S154 to S157). (S158). The link establishment sequence up to the establishment of the synchronization corresponds to the processing of the layer 1 (physical layer).

Further, it is confirmed that the mobile communication device and the base station can communicate with each other (S159 and S160). This corresponds to layer 2 (data link layer) processing, and thereafter, transmission and reception of a call connection message and a location registration message are performed. This corresponds to processing of layer 3 (network layer) or higher.

The above is the description of base station selection and CC in the case of PHS.
Although this is a link establishment sequence when transitioning from H to TCH, the same processing is performed in a system such as a PDC that uses CCH and TCH properly.

[0014]

However, recent PHs
In S, in order to solve the conventional problems such as disconnection of calls and interruption of sound during high-speed movement, H "(Edge: registered trademark), which is a PHS with improved handover performance, has been developed. Performance (data communication function and call quality)
Combined with its original strength, it is gradually recovering its share held by PDC.

A brief description of the handover method of the H "system PHS is that a base station of a transfer destination is searched for in advance during a call, the state is changed to a communicable state, and then the old base station is switched to a new base station. As compared with the conventional method of temporarily holding a call and then searching for and switching to a destination base station, the call performance in high-speed movement is remarkably improved. However, in order to improve the call performance, it tries to perform a handover as soon as possible to find a new base station to which the mobile station is to be migrated. Start processing. As a result, even if the call quality limit has not been reached, and even though the base station is in a call, it is unlikely that a higher quality TCH will be allocated than the current TCH, and unnecessary handover will occur. Since the process is executed, the sound of “puzzle” frequently occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a communication terminal apparatus and a handover control capable of suppressing unnecessary handovers and thereby reducing the occurrence of interruptions in sound. The aim is to provide a method.

[0017]

According to a first aspect of the present invention, there is provided a communication terminal apparatus which transmits data via a first base station when a peripheral base station transmits data via a first base station. By measuring the electric field strength of the control channel to be performed, a handover is performed by selecting a base station suitable for communication, and in the communication terminal apparatus which continues the communication, the second terminal station stores the electric field strength of the communication channel of the first base station. 1 storage means, second storage means for storing the electric field strength of the control channel of the base station suitable for the selected communication, and electric field strength of the communication channel stored in the first storage means and the second storage means Comparing means for comparing the magnitude with the electric field strength of the control channel to be performed;
Judging means for judging whether the base station suitable for the selected communication and the first base station are the same, and when the judging means judges that they are the same, the result of the comparison by the comparing means, When the electric field strength of the control channel is higher than the electric field strength of the communication channel, the control means performs a handover control with the first base station during communication.

According to a second aspect of the present invention, there is provided a communication terminal device comprising:
2. The communication terminal device according to claim 1, wherein the control unit performs a handover with the first base station during communication when an electric field intensity of the control channel is larger than an electric field intensity of the communication channel by a predetermined value or more. It is characterized by performing control.

The handover control method of the present invention according to claim 3 is suitable for communication by measuring the electric field strength of a control channel transmitted by a peripheral base station when communicating via the first base station. In the handover control method for a communication terminal apparatus which selects a suitable base station, performs handover, and continues communication, a first step of storing a field strength of a communication channel of the first base station; A second step of storing the electric field strength of the control channel of the base station; and a second step of comparing the magnitude of the electric field strength of the control channel stored in the first storage means with the electric field strength of the control channel stored in the second storage means. Three steps, a fourth step of determining whether a base station suitable for the selected communication and the first base station are the same, and determining that the fourth step is the same. In the case, as a result of the comparison in the third step, when the electric field strength of the control channel is larger than the electric field strength of the speech channel, a fifth step of performing handover control with the first base station during communication is performed. It is characterized by including.

According to a fourth aspect of the present invention, in the handover control method according to the third aspect, in the fifth step, the electric field strength of the control channel is higher than the electric field strength of the speech channel. A step of performing a handover control with the first base station during communication when the value is larger than a predetermined value.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of the communication terminal device according to the present invention.

The communication terminal device (also referred to as a mobile communication device) includes an antenna 10, a transmission / reception switching unit 11, and a radio unit 1.
2. Modem unit 13, TDMA / TDD (time division m
ultipleaccess / time division duplex:
Time-division bidirectional) unit 14, audio processing unit 15, microphone 16,
It comprises a speaker 17 and a control unit 18.

The control unit 18 includes a memory 181 and a CPU 18
2 and the program stored in the memory 181 is C
The execution of the PU 182 controls the entire communication terminal device.

When the control unit 18 shifts from the control channel to the communication channel, the control unit 18 assigns the T assigned from the base station.
Recieved signal strength Indic of CH
ator: Hereinafter referred to as RSSI. ) Is configured to request the base station or another base station to allocate a new TCH if insufficient.

Further, the control unit 18 measures the RSSIs of CCHs of a plurality of peripheral base stations during a call and stores them in the memory 181 together with the CSID in the order of the electric field strength, and the FER (frame error rate) of the received signal. Is started when the communication signal is degraded below a predetermined value or when the RSSI of the communication channel is weakened below a predetermined level. In particular, at the time of this handover process, when the base station having the strongest electric field strength is the same as the base station during a call, the control unit 18 compares the electric field strength of the communication channel and the electric field strength of the control channel, and When the electric field strength of the communication channel is larger than the electric field strength of the communication channel, the handover control with the base station in communication is started. The control unit 18
Is configured to start the handover control with the communicating base station only when the electric field strength of the control channel is larger than the electric field strength of the communication channel by a predetermined value or more.

In FIG. 1, an antenna 10, a transmission / reception switching unit 11, a radio unit 12, a modem unit 13, a TDMA /
A circuit portion including the TDD unit 14, the audio processing unit 15, the microphone 16, and the speaker 17 is a general configuration of a communication terminal device of the TDMA / TDD system, and is specified by, for example, the PHS standard “RCR STD-28”. TDMA
/ TDD wireless communication circuit. Therefore,
Although a detailed description thereof is omitted, only the TDMA / TDD scheme will be briefly described.

FIG. 3 is an explanatory diagram of the time division multiplexing method in the PHS.

In the TDMA / TDD method according to the present embodiment, 5 milliseconds is defined as one TDMA / TDD frame. One TDMA / TDD frame is divided into eight time slots. The first to fourth slots are slots for downlink (base station to communication terminal device) (hereinafter referred to as downlink slots), and the fifth to eighth slots are slots for uplink (communication terminal device to base station). (Hereinafter, referred to as uplink slot).

The TCH is a combination of an uplink slot and a downlink slot, for example, a combination of a first slot and a fifth slot, and a combination of a second slot and a sixth slot. Since a plurality of carrier frequencies for TCH are assigned, one TCH is
It is specified by a carrier frequency (carrier number) and uplink and downlink slot numbers.

The CCH is also a combination of an uplink slot and a downlink slot, but is assigned a specific carrier frequency (about one or two waves) and is intermittently transmitted and received. The intermittent transmission / reception is periodically transmitted / received at a rate of, for example, once every 100 milliseconds (20 frames). In this case, the carrier wave for CCH can perform time division multiplexing of intermittent transmission / reception signals of CCH by a maximum of 80 (20 frames × 4 divisions) base stations.

Next, the operation and the handover control method of the communication terminal device according to the present invention configured as described above will be described.

FIG. 4 is a flowchart showing a base station selection process and a link channel establishment sequence.

As described above with reference to FIG. 1, the base station selection process is performed when the mobile communication device is turned on, when searching for another base station at the time of handover, or when the base station changes from a base station to another base station during a call. This is performed when switching is instructed.

First, the control unit 18 of the mobile communication device monitors the CCHs of a plurality of base stations, and in the case of PHS, sequentially receives signals of a specific frequency. Then, when the base station identifier (CSID) can be decoded from the signal of each CCH, the CSID and the received field strength of the CCH are stored as a set (S1).

Further, the control unit 18 stores the stored CSID
And the received electric field strengths of the CCH are sorted in the order of the received electric field strength (S2). According to the sorting order, it is determined whether or not the base station satisfies a predetermined condition, and a base station that satisfies the condition is selected. (S3).

FIG. 5 is a flowchart showing details of the selection step (S3) during the base station selection process.

When the control unit 18 enters the selection step (S3), the control unit 18 checks whether the base station selected according to the sorting order in step S31 is a busy base station, and if not, proceeds to step S11. The process proceeds to step S32 if the call is in progress. Control unit 18
In step S32, the electric field strength of the control channel of the base station during communication and the electric field strength of the communication channel are compared, and if the electric field strength of the control channel is larger, the processing proceeds to step S11.
To step S3.
The process proceeds to step S3, where the next base station in the sorting order is selected, and the process proceeds to step S11. In step S32, by comparing the electric field strength of the control channel of the base station during communication and the electric field strength of the communication channel, it is determined whether or not the electric field strength of the control channel is larger than a predetermined value. Is also good.

By the selection process (S3), when the base station to be handed over is a busy base station, the electric field strength of the CCH and the electric field strength of the TCH are compared to assign a larger TCH. The possibility is determined, and when the possibility is low, the handover to the base station during the call is not executed, so that the occurrence of unnecessary sound interruption can be suppressed.

Returning to FIG. 4, the link establishment sequence is performed when switching to a handover destination base station during a call. As shown in FIG.
In the link establishment sequence for shifting from CCH to TCH, the TCH is transmitted through the CCH of the handover destination base station.
Is transmitted (S11), and when a TCH allocation is received from the base station as a response thereto (S1).
2) A synchronization burst signal (S1) which is a signal for link establishment transmitted from the base station through the allocated TCH.
6) acquiring the electric field strength from the RSSI detector 124,
It is determined whether or not the electric field strength is equal to or less than a threshold value (Th1) (S17). If it is determined that the electric field strength is equal to or less than the threshold value Th1, the link establishment is stopped and the CCH of the base station is stopped.
Control to retransmit the TCH allocation request through.

In the determination of the electric field strength of the TCH in S17, even if the difference from the electric field strength of the U wave (interfering wave) is equal to or smaller than the threshold value (three), the TCH allocation request is retransmitted. Control to do.

On the other hand, if the electric field strength of the TCH is larger than the threshold Th1 and the difference between the electric field strengths of the TCH and the U-wave (interfering wave) is larger than the threshold Th2, the controller 18 (Synchronization establishment signal) transmission / reception is continued to establish a link of the TCH (S18 to S2).
1).

Thus, when the electric field strength of the TCH allocated from the base station is insufficient, the present communication terminal apparatus retransmits another TCH allocation request, so that the actual communication (communication) can be performed. Before the transition, a TCH with an electric field strength that does not hinder communication is secured.

[0044]

As described above, according to the communication terminal apparatus and the handover control method according to the present invention, when the base station of the handover destination and the base station during a call are the same, the control channel is further increased. The handover is performed after comparing the electric field strength with the electric field strength of the communication channel to determine whether the reception level is large and the possibility of better allocation of the communication channel is performed. As a result, the number of unnecessary handovers performed is reduced. This can reduce the occurrence of sound interruption.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional base station selection process and a link channel establishment sequence.

FIG. 2 is a block diagram illustrating a configuration of a communication terminal device according to the present invention.

FIG. 3 is an explanatory diagram of a time division multiplexing method in PHS.

FIG. 4 is a flowchart showing a base station selection process and a link channel establishment sequence.

FIG. 5 is a flowchart illustrating details of a selection step (S3) during base station selection processing.

[Explanation of symbols]

 Reference Signs List 10 antenna 11 transmission / reception switching unit 12 radio unit 13 modem unit 14 TDMA / TDD unit 15 audio processing unit 16 microphone 17 speaker 18 control unit 181 memory 182 CPU

Claims (4)

[Claims] When performing communication via a first base station, an electric field strength of a control channel transmitted by a peripheral base station is measured to select a base station suitable for communication and perform handover. In a communication terminal device for continuing communication, a first terminal for storing an electric field strength of a communication channel of the first base station.
Storage means, second storage means for storing the electric field strength of the control channel of the base station suitable for the selected communication, and electric field strength of the communication channel stored in the first storage means and the second storage means The comparing means for comparing the magnitude with the electric field strength of the control channel, the judging means for judging whether the base station suitable for the selected communication and the first base station are the same, and the judging means are the same. If the control unit determines that the electric field strength of the control channel is larger than the electric field strength of the communication channel, the control unit performs a handover control with the first base station during communication. Means, and a communication terminal device comprising: 2. The communication terminal device according to claim 1, wherein
A communication terminal for performing handover control with the first base station during communication when the electric field strength of the control channel is larger than the electric field strength of the communication channel by a predetermined value or more. apparatus. 3. When performing communication via the first base station, by measuring the electric field strength of a control channel transmitted by a peripheral base station, a base station suitable for communication is selected and handover is performed. In the handover control method for a communication terminal apparatus that continues communication, a first step of storing a field strength of a communication channel of the first base station, and storing a field strength of a control channel of a base station suitable for the selected communication. Second
A step of comparing the electric field strength of the communication channel stored in the first storage means with the electric field strength of the control channel stored in the second storage means; and a base station suitable for the selected communication. And a fourth step of determining whether the first base station is the same as the first base station. If it is determined that the fourth step is the same, the result of the comparison of the third step indicates that the electric field strength of the control channel Is greater than the electric field strength of the communication channel, the first
A fifth step of performing handover control with the base station;
A handover control method comprising: 4. The handover control method according to claim 3, wherein the fifth step is performed when the electric field strength of the control channel is larger than the electric field strength of the communication channel by a predetermined value or more. A sixth step of performing handover control with one base station.