JP2698233B2 - Handover method in mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handover method in a mobile communication system for performing a handover between base stations in accordance with the movement of a mobile station in the mobile communication system.

[0002]

2. Description of the Related Art FIG. 16 is a block diagram showing a conventional mobile communication system to which the handover method of the present invention is applied. In the figure, reference numeral 1 denotes an exchange according to a stored program control system, and 2 denotes a fixed terminal such as a telephone connected to the exchange 1. Reference numerals 3a to 3d denote a plurality of base stations connected to the exchange 1, respectively, and reference numerals 4a to 4d denote communication lines connecting these base stations 3a to 3d to the exchange 1.

[0003] Reference numerals 5a to 5d denote communication zones in which the base stations 3a to 3d perform wireless communication, respectively.
Is a crossover zone in which the communication zones 5a to 5d overlap. Reference numeral 7 denotes a communication area of the mobile communication system formed by a set of communication zones 5a to 5b.

The communication zones 8a and 8b move within the communication area 7 beyond the communication zones 5a to 5d, and
These are a plurality of mobile stations that communicate with the base stations 3a to 3d that cover the mobile stations 5a to 5d via a set wireless channel.

Next, the operation will be described. Here, FIG.
FIG. 7 is a sequence flow diagram showing a flow of processing of a handover method in a conventional mobile communication system. Hereinafter, the case where the mobile station 8a moves from the communication zone 5a to the communication zone 5b will be described with reference to FIG.

The mobile station 8a constantly monitors the S / N ratio from the base station 3a by a built-in S / N ratio measurement circuit during a call on the communication channel. The mobile station 8a is connected to the communication zone 5a.
As we move closer to crossover zone 6, SN
The ratio measurements degrade. When the S / N ratio falls below the specified value,
The control circuit of the mobile station 8a detects this, immediately stops the call on the communication channel, shifts to communication on the control channel, and sends a call continuation request signal for requesting continuation of the call.

This signal is received by each of the base stations 3a to 3d, and the SN ratio is measured by an SN ratio measurement circuit built in each of the base stations 3a to 3d. In each of the base stations 3a to 3d, the control circuit processes the S / N ratio and notifies the exchange 1 of a continuation reception signal including the obtained S / N ratio information.

The exchange 1 analyzes and compares the continuation reception signals received from the base stations 3a to 3d, selects a base station having a value satisfying the standard value, for example, the base station 3b, and selects the base station 3b. Send a signal. On the other hand, the restoration signal is transmitted to the base station 3a, 3c, 3d which is not selected, and the exchange 1 waits for the reception of the restoration reception signal from the base station 3a, 3c, 3d which has transmitted the restoration signal, and the exchange 1 repeats the sequence. finish.

The base station 3b selected as a handover destination from the exchange 1 transmits a mobile paging signal including information such as the frequency of the transfer communication channel selected by the base station 3b itself or the exchange 1 on the control channel. Is transmitted, and thereafter, the processing shifts to communication on the communication channel.

The mobile station 8a receiving the mobile paging signal
Shifts to communication on the specified communication channel, and sends a connection confirmation signal to the base station 3. The base station 3b that has received the connection confirmation signal sends a connection confirmation response signal to the mobile station 8a, and also sends a call path setting request signal to the exchange 1, and enters a state of talking with the mobile station 8a. The exchange 1 that has completed the above series of processing restores the base station 3a.

As a document describing a technique related to a handover method in such a conventional mobile communication system, there is Japanese Patent Application No. 2-43718 , for example.

[0012]

Since the conventional handover system in the mobile communication system is configured as described above, the mobile station 8 is not included in the handover process.
If a (8b) stops the communication on the communication channel and shifts to the communication on the control channel, a problem occurs that the voice communication is interrupted during the communication on the control channel, and the mobile station 8a (8b) And the base station 3a (up to 3
Even in the case where d) adopts the method of not shifting to the control channel, disconnection of the call for several hundred milliseconds from transmission of the connection confirmation signal of the mobile station 8a (8b) to switching of the communication path by the exchange 1 cannot be avoided. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a handover method in a mobile communication system in which a call is not practically disconnected during a voice call. I do.

[0014]

Handover method in a mobile communication system according to the problem-solving means for the this invention comprises a function of performing the inter-base-station handover due to movement of the mobile station, the mobile at the start handover sequence source base station, the mobile Destination
The voice and data information from the base station and the communication partner terminal are added / subtracted, and each base station or terminal is added to the other two.
Using a switch equipped with a conference trunk function that sends out information obtained by adding information from the user, the base station detects that a radio link between the mobile station and the base station has been established or disconnected, and sends the information to its own control circuit. Line establishment detecting means for notifying, voice to the exchange, voice mute means for inserting a silence signal into the data signal, and with the establishment of the wireless line, invalidating the voice mute means, voice and data to the exchange A means for transmitting information from the mobile station to the signal, enabling the voice mute means in accordance with the disconnection of the radio line, and a means for stopping the transmission of information from the mobile station to the voice and data signals to the exchange. Things.

[0015]

According to the handover method of the present invention, when a mute means inserts a silent signal into a signal on a line to an exchange, and two base stations and a communication partner terminal enter a three-party conference state, Prevents noise received by the base station whose mobile station and the line are not established from being transmitted to the two parties during the call, and establishes a wireless line between the mobile station and the base station by the line establishment detecting means.
The disconnection is detected, the voice mute means at the time of establishment of the wireless line is disabled, and voice and data signals from the mobile station are sent to the line to the exchange. By stopping the transmission of voice and data signals from the office to the exchange, it is possible to connect the communication path after handover without control from the exchange, and the time during which the call is interrupted during the handover process can be practically used. A mobile communication system that can be eliminated is realized.

[0016]

【Example】

Embodiment 1 FIG. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a base station 3a used in one embodiment of a handover method in a mobile communication system according to the present invention.
It is a block diagram which shows the structure of 3d. Note that this embodiment is also applied to a mobile communication system equivalent to the conventional case shown in FIG.

In FIG. 1, reference numeral 11 denotes a control circuit which includes a processor, storage means, base station control information transmission / reception SIO, etc., and realizes functions of controlling the base stations 3a to 3d and transmitting / receiving information to / from the exchange 1.

Reference numeral 12 denotes a line transceiver for transmitting and receiving voice, data signals and control signals to and from the exchange 1. In this embodiment, the exchange 1 and each base station 3
The voice, data signal, and control signal between a to 3d are transmitted and received at line speeds of 64 Kbps and 16 Kbps, respectively.

Reference numeral 13 designates 64 Kbps voice and data signals as 3
In addition to the 2Kbps compression function,
An audio mute / pulse code modulation encoding / decoding means (hereinafter referred to as audio mute / PCM CODEC) as an audio mute means having an audio mute function of inserting an audio signal into a data signal and a control signal.

Reference numeral 14 denotes base stations 3a to 3d and mobile stations 8a and 8
A wireless transmission / reception unit that sets up a wireless line between b and transmits / receives various information, and 15 is a wireless system control unit that controls the wireless transmission / reception unit 14. Reference numeral 16 denotes a control signal interface for transmitting and receiving information between the radio system control means 15 and the control circuit 11.

The control circuit 11 detects the establishment and disconnection of synchronization between the mobile stations 8a and 8b and the base stations 3a to 3d and the presence or absence of a radio signal based on the signal from the radio transmission / reception means 14, and sends it to the control circuit 11. This is a line establishment detecting means for notifying.

Next, the operation will be described. FIG. 2 is a sequence flow chart showing a flow of processing of a handover method in the mobile communication system of this embodiment.
FIGS. 3 to 5 are flowcharts showing the processing flow of the source base station, the destination base station and the exchange. Less than,
The case where the mobile station 8a moves from the communication zone 5a to the communication zone 5b will be described with reference to FIGS.

Here, the mobile station 8a which has detected the deterioration of the electric field strength during the call transmits a call continuation request signal to the base station 3a during the call on the control information transmission / reception channel on the call radio line.

FIG. 6 shows the connection between the fixed terminal 2 and the mobile station 8a at that time. At this point, switch 1
Is in a normal two-party communication state. In FIG. 2, reference numeral 21 denotes a base station 3a, 3b for adding and subtracting voice and data signals from the source and destination base stations 3a, 3b and the other party's fixed terminal 2. This is a conference trunk for transmitting information obtained by adding information from the two parties described above, and the other corresponds to those given the same reference numerals in FIG.

In this embodiment, the radio line is a digital time division multiplexing circuit, and the frame format of the line information is shown in FIG. In the figure, GR is the guard time, CR
Is carrier lock reproduction.

The voice and data signals are represented by DATA in the figure.
When the information is transmitted and received at # (N) and the information includes a voice signal, when the signal is received from the mobile station 8a (8b), the base station 3
Only this part inside a (.about.3d) is input to an ADPCM (adaptive quantization difference PCM) decoder and is decoded into 64 Kbps PCM.

On the other hand, when transmitting a signal to the mobile station 8a (8b), the 64 Kbps PCM voice signal is transmitted to the base station 3a (.about.).
The data is ADPCMC-coded by the ADPCM coder inside 3d) and transmitted on DATA # (N) in FIG. If the transmitted and received signals are a set of data, ADPC
The M coder / decoder is disabled and passed through without processing the signal.

SACCH # (N) in FIG. 7 is a frame for sending control information corresponding to a time slot of a radio channel.

The base station 3 receiving the call continuation request signal
a sends a call continuation request reception signal to the exchange 1. Information included in this signal includes, as shown in FIG.
Signal type, additional information length, mobile station ID, destination exchange ID,
There are a source base station ID, an end identifier, and the like.

The exchange 1, which has received the call continuation request reception signal, transmits an interference measurement call signal to the base station 3b adjacent to the base station 3a, and determines the radio wave intensity of the radio line used by the mobile station 8a and the base station. The base station 3b measures the radio wave interference situation of the vacant channel of the station 3b. In this case, only one of the measurements may be performed.

As shown in FIG. 9, the information included in the interference measurement notification signal includes a signal type, an additional information length, an exchange ID, a destination base station ID, a destination mobile station ID, a source exchange ID, an end identifier, and the like. There is.

The base station 3b that has completed the measurement notifies the exchange 1 of the measurement result by an interference measurement notification response signal. As shown in FIG. 10, the information included in the interference measurement notification response signal includes a signal type, an additional information length, a destination exchange ID, a source base station ID, an interference measurement result, an end identifier, and the like.

The measurement of the radio wave intensity and the interference is performed by the base station 3.
b, the convergence time of the phase-locked loop (PLL) used for the local oscillation circuit in the wireless transmission / reception means 14 is shortened.
It is assumed that the two wireless transmission / reception means 14 can measure different frequencies in time slots other than during a call and during communication.

Upon receiving the measurement result, the exchange 1 selects an optimum destination base station (in this case, the base station 3b) and notifies the base station 3a of information on the destination wireless line of the destination base station 3b. . Further, the base station 3b notifies the mobile station 8a of the information of the destination wireless channel by using the above-mentioned on-line control signal by using the empty slot notification signal.

As shown in FIG. 11, the information included in the empty slot notification signal includes a signal type, additional information length, a destination base station ID, a destination mobile station ID, a source exchange ID, empty slot information, and an end identifier. and so on.

Mobile station 8a receiving an empty slot communication signal
Performs interference measurement of the destination wireless line in the mobile station, and sends a switching preparation signal to the base station 3a if the criterion is satisfied. As shown in FIG. 12, information included in this signal includes a signal type, additional information length, a destination base station ID, a destination exchange ID, a source mobile station ID, an end identifier, and the like.

Further, the switching preparation signal is also sent from the base station 3a to the exchange 1. Along with this, the exchange 1 sets a communication path also in the base station 3b, and enters a so-called three-party conference state. FIG. 13 shows a connection state between the other party's fixed terminal 2 and the mobile station 8a in this case. As shown, the audio mute is disabled in the base station 3a, and is enabled in the base station 3b.

Here, when the audio mute function is enabled, in the case of voice communication, a 64 Kbps PCM output from an ADPCM decoder is used instead of a signal in the ADPCM encoding method used. In the case of data communication, a signal indicating silence, and in data communication, "0" is set for all bits, respectively.
To be sent.

In the case of voice communication, the conference trunk 21 implements its function by temporarily converting a 64 Kbps PCM signal into voice, and adding / subtracting the signal in an analog manner. However, after converting the PCM of 64 Kbps (usually non-linear coding method is used) in a linear coding PCM signal, it may perform processing of digitally addition / subtraction.

The exchange 1 having received the switching preparation signal sends a switching communication signal to the base stations 3a and 3b. The base station 3a that has received the switching notification signal monitors the disconnection of the wireless line, and the base station 3b monitors the establishment of the wireless line by the respective line establishment detecting means 17.

When a wireless channel is established between the mobile station 8a and the base station 3b and the wireless channel between the mobile station 8a and the base station 3a is disconnected, the audio mute is disabled in the base station 3b and the audio mute is disabled in the base station 3a. To enable. FIG. 14 shows a state of connection between the other party's fixed terminal 2 and the mobile station 8a at that time. Note that switching between valid / invalid of the audio mute is performed based on a signal from the control circuit 11 based on the audio mute / PCM CODEC 13.
Done by

The base station 3b, which has detected the establishment of the wireless line by the line establishment detecting means 17, notifies the exchange 1 of a connection completion signal. The exchange 1 receiving this restores the base station 3a. FIG. 15 shows a state of connection between the other party's fixed terminal 2 and the mobile station 8a at this time.

[0043]

As described above, according to the present invention, an exchange having a so-called conference trunk function is used, and a base station is provided with a line establishment detecting means and a voice mute means.
When a handover occurs, the source base station, the destination base station, and the terminal of the communication partner are temporarily set in a three-party conference state. Disable mute means,
Since the voice and data signals from the mobile station are transmitted to the exchange, and when the disconnection of the wireless line is detected, the voice mute means is enabled and a silent signal is inserted into the voice and data signals to be transmitted to the exchange. Enable audio mute /
In an environment where the processing of the exchange is not required for invalidation and sufficient electric field strength can be obtained, the call disconnection time is the time difference between the disconnection of the radio line of the source base station and the establishment of the radio line of the destination base station. (Usually less than several tens of milliseconds), which is a very short time, which is about the sum of the processing time of at most dozens of steps by the processor, and a mobile communication system that can perform handover without disconnection in a voice call in practical use. In this case, there is an effect that a handover method can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a base station used for a handover method in a mobile communication system according to one embodiment of the present invention.

FIG. 2 is a sequence flow chart showing a flow of a handover process in the embodiment.

FIG. 3 is a flowchart showing a flow of processing of a source base station in the embodiment.

FIG. 4 is a flowchart showing a flow of processing of a destination base station in the embodiment.

FIG. 5 is a flowchart showing a flow of processing of the exchange in the embodiment.

FIG. 6 is an explanatory diagram showing a state of connection between a partner terminal and a mobile station at the time of starting handover in the embodiment.

FIG. 7 is an explanatory diagram showing a frame format of line information in the embodiment.

FIG. 8 is an explanatory diagram showing a configuration of a call continuation request acceptance signal in the embodiment.

FIG. 9 is an explanatory diagram showing a configuration of an interference measurement notification signal in the embodiment.

FIG. 10 is an explanatory diagram showing a configuration of an interference measurement notification response signal in the embodiment.

FIG. 11 is an explanatory diagram showing a configuration of an empty slot notification signal in the embodiment.

FIG. 12 is an explanatory diagram showing a configuration of a switching preparation signal in the embodiment.

FIG. 13 is an explanatory diagram showing a state of connection between a partner terminal and a mobile station when a communication path is initially set to a destination base station in the embodiment.

FIG. 14 is an explanatory diagram showing a state of connection between a partner terminal and a mobile station immediately after a wireless link between the target base station and the mobile station is established in the embodiment.

FIG. 15 is an explanatory diagram showing a state of connection between a partner terminal and a mobile station at the end of handover in the embodiment.

FIG. 16 is a configuration diagram showing a conventional mobile communication system to which a handover method according to the present invention is applied.

FIG. 17 is a sequence flow chart showing a flow of processing of a handover method in a conventional mobile communication system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Switch 3a-3d Base station 5a-5d Communication zone 7 Communication area 8a, 8b Mobile station 11 Control circuit 13 Voice mute / PCM CODEC (voice mute means) 17 Line establishment detection means 21 Conference trunk

Claims (1)

(57) [Claims] A plurality of base stations each having a communication zone in which a wireless communication is performed and a communication area of the system being formed by a set of communication zones; A plurality of mobile stations that communicate with a base station and transmit and receive voice, data communication, control information of the mobile station, and dial information; and the base stations are connected to each of the base stations and move with the mobile stations. In a handover method in a mobile communication system including a switch having a function of performing a handover between the mobile stations, a function of managing the position of the mobile station, and a function of a conference trunk for adding / subtracting three or more voice signals, In the base station,
A line establishment detecting means for detecting the establishment of a wireless line with the mobile station and notifying the control circuit for realizing functions such as control of the base station and transmission and reception of information with the exchange; and When the mobile station moves from a zone of one base station to a zone of another base station, the signal on the line to the exchange is controlled by a circuit, and a signal on the line to the exchange is sent to indicate a silent state. Before the wireless link between the source base station and the mobile station is cut off, the destination base station starts transmission and reception on the wireless channel to which the mobile station transitions, and the source and destination voices and data The signal is added / subtracted by using the function of the conference trunk, and voice and data signals to each of the base stations and the mobile station are added with information of the other two parties, and transmitted. The station communicates with the mobile station Until the connection is established, sends a signal indicating silence on the voice and data signals, stops sending a signal indicating silence to the switch after the radio line with the mobile station is established, and The base station of the movement source transmits a signal from the mobile station to the exchange while a wireless line with the mobile station is established, and transmits the signal from the mobile station to the exchange. A mobile communication system characterized by transmitting a signal indicating silence after a line is cut off, and the exchange recovers the line with the source base station after the series of tracking exchange processes is completed. Handover method.