JPH04336790A - Handover system for moving body communication system - Google Patents

Abstract

PURPOSE:To obtain a moving body communication system not permitting a call to be actually interrupted, in a handover. CONSTITUTION:A switchboard provided with a so-called conference trunk function is used and base stations 3a and 3a are provided with a line establishment detection means and a sound muting means. When the handover takes place, the terminals of a moving source base station, a moving destination base station and the communication opponent are temporarily brought into a three-party conference state. In the respective stations, when the line establishment detection means detects the establishment of a radio line, the sound muting means is invalidated. When it detects the disconnection of the radio line, the sound muting means is validated and inserts a silence signal in the sound and data signal to be transmitted to the switchboard. Thus, the processing by the switchboard is not required for validating/invalidating the sound muting, the disconnection time can be reduced to extremely short time when enough electric field intensity is available, and the moving body communication system capable of handover without disconnection of a sound call can be obtained in practice.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handover system in a mobile communication system, which performs handover between base stations as a mobile station moves.

0002

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

[0003] Reference numerals 5a to 5d are communication zones in which each of the base stations 3a to 3d performs wireless communication;
is a crossover zone where the communication zones 5a to 5d overlap. 7 is a communication area of the mobile communication system formed by a set of communication zones 5a to 5b.

[0004] 8a and 8b move within the communication area 7 beyond each communication zone 5a to 5d, and
These are a plurality of mobile stations that communicate with base stations 3a to 3d covering 5d through established wireless lines.

Next, the operation will be explained. Here, Figure 1
7 is a sequence flow diagram showing the process flow of a handover method in a conventional mobile communication system. The case where the mobile station 8a moves from the communication zone 5a to the communication zone 5b will be described below using FIG. 17.

[0006] While the mobile station 8a is talking on the communication channel, it constantly monitors the SN ratio from the base station 3a using a built-in SN ratio measuring circuit. The mobile station 8a is in the communication zone 5a
As you move closer to crossover zone 6, the SN
The ratio measurements deteriorate. When the SN ratio is 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 out a call continuation request signal requesting continuation of the call.

[0007] This signal is received by each base station 3a to 3d, and the SN ratio is measured by an SN ratio measuring circuit built in each base station 3a to 3d. In each base station 3a to 3d, a control circuit processes the SN ratio and notifies the exchange 1 of a continuation acceptance signal containing the obtained SN ratio information.

The exchange 1 analyzes and compares the continuation acceptance signals received from each base station 3a to 3d, selects a base station having a value that satisfies the standard value, for example, base station 3b, and selects the base station 3b as the base station. Send a signal. On the other hand, the exchange 1 sends a recovery signal to the base stations 3a, 3c, and 3d that were not selected, and waits for the reception of a recovery acceptance signal from the base stations 3a, 3c, and 3d that sent the recovery signal, and then executes the sequence. finish.

The base station 3b selected as a handover destination from the exchange 1 sends a mobile paging signal on the control channel containing information such as the frequency of the transfer destination communication channel selected by the base station 3b itself or by the exchange 1. , and then transitions to communication on the communication channel.

Mobile station 8a that received the mobile paging signal
The terminal shifts to communication on the designated communication channel and sends a connection confirmation signal to the base station 3. Upon receiving this connection confirmation signal, the base station 3b sends a connection confirmation response signal to the mobile station 8a, and also sends a communication path setting request signal to the exchange 1, thereby entering into a communication state with the mobile station 8a. After completing the above series of processes, the exchange 1 restores the base station 3a.

[0011] Documents describing techniques related to handover methods in such conventional mobile communication systems include, for example, Japanese Patent Laid-Open No. 2-43718.

0012

[Problems to be Solved by the Invention] Since the handover method in the conventional mobile communication system is configured as described above, in the process of handover processing, the mobile station 8
If mobile station a (8b) cancels communication on the call channel and shifts to communication on the control channel, there will be a problem that the voice call will be interrupted during the call on the control channel, and the mobile station 8a (8b) and base station 3a (~3d
) does not shift to the control channel, even if the mobile station 8a (8b) sends a connection confirmation signal to the exchange 1
There were problems such as the unavoidable disconnection of a call for several hundred milliseconds until the call was switched over.

[0013] This invention was made to solve the above-mentioned problems, and its purpose is to provide a handover method in a mobile communication system that practically does not cause call drop during voice calls. do.

[0014]

[Means for Solving the Problems] A handover method in a mobile communication system according to the present invention has a function of performing handover between base stations as the mobile station moves, and a function of performing handover between base stations as the mobile station moves, and The voice and data information from the destination mobile station and communication partner terminal are added/subtracted, and each base station or terminal is sent to the other two.
Using a switch equipped with a conference trunk function that sends out information by adding information from other parties, the base station detects when a wireless line between the mobile station and the base station is established or disconnected, and sends the information to its own control circuit. a line establishment detection means for notifying the exchange; a voice mute means for inserting a silence signal into the voice and data signals to the exchange; Information from the mobile station is sent to the signal, and when the wireless line is disconnected, the audio mute means is activated, and the audio and data signals to the exchange are provided with means to stop sending the information from the mobile station. It is something.

[0015]

[Operation] In the handover method of the present invention, a silent signal is inserted into the signal on the line to the exchange using the audio mute means, and when two base stations and the communication partner terminal enter a three-way conference state, Establishment of a wireless link between the mobile station and the base station by preventing the noise received by the base station, which has not established a line with the mobile station, from being transmitted to the two parties during the call, and using the line establishment detection means.
When disconnection is detected, the audio mute means is disabled when the wireless line is established, and voice and data signals from the mobile station are sent to the line to the exchange, while the audio mute means is enabled when the wireless line is disconnected, and the mobile station By stopping the sending of voice and data signals from the station to the exchange, it is possible to connect the call path after handover without control from the exchange, and this reduces the time that calls are interrupted during handover processing. To realize a mobile communication system that can eliminate

[0016]

【Example】

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

In the figure, reference numeral 11 denotes a control circuit that includes a processor, storage means, base station control information transmitting/receiving SIO, etc., and realizes functions such as controlling the base stations 3a to 3d and transmitting and receiving information with 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 3a
It is assumed that voice, data signals, and control signals between 3d and 3d are transmitted and received at line speeds of 64 Kbps and 16 Kbps, respectively.

13 is a voice muting means that has a function of compressing 64Kbps voice and data signals to 32Kbps and also has a voice mute function of inserting voice signals into the voice, data signals and control signals sent to the exchange 1. This is an audio mute/pulse code modulation encoding/decoding means (hereinafter referred to as audio mute/PCM CODEC).

Reference numeral 14 indicates base stations 3a to 3d and mobile stations 8a and 8.
15 is a wireless system control means for controlling the wireless transmitting and receiving means 14. FIG. Reference numeral 16 denotes a control signal interface for transmitting and receiving information between the wireless system control means 15 and the control circuit 11.

17 detects the establishment and disconnection of synchronization between the mobile stations 8a, 8b and the base stations 3a to 3d and the presence or absence of a radio signal based on the signal from the radio transmitting/receiving means 14, and sends the information to the control circuit 11. This is a line establishment detecting means to notify.

Next, the operation will be explained. Note that FIG. 2 is a sequence flow diagram showing the flow of handover method processing in the mobile communication system of this embodiment.
3 to 5 are flowcharts showing the processing flow of the source base station, destination base station, and exchange. below,
A case in which the mobile station 8a moves from the communication zone 5a to 5b will be described using FIGS. 2 to 5.

[0023] Here, the mobile station 8a, which detects a deterioration in the electric field strength during the call, sends a call continuation request signal to the base station 3a, which is currently in the call, via the control information transmission/reception channel on the call radio line.

FIG. 6 shows how the fixed terminal 2 and the mobile station 8a are connected at that time. At this point, switch 1
is in a normal two-party communication state. Here, in this FIG. 2, 21 adds/subtracts the voice and data signals from the source and destination base stations 3a, 3b and the partner fixed terminal 2, and sends them to each base station 3a, 3b or the partner terminal 2. This is a conference trunk that sends information obtained by adding information from two parties, and the other parts correspond to those with the same reference numerals in FIG. 16.

In this embodiment, the radio line is a digital time division multiplex circuit, and the frame format of the line information is shown in FIG. In the figure, GR is guard time, CR
is a career rock rebirth.

[0026] Also, voice and data signals are indicated by DATA in the figure.
# (N), and if the information here includes an audio signal, when receiving the signal from the mobile station 8a (8b), the base station 3
Only this part inside a (~3d) is input to the ADPCM (adaptive quantization differential PCM) decoder and is processed at 64Kbps.
is decoded into PCM.

Conversely, when transmitting a signal to the mobile station 8a (8b), the 64 Kbps PCM audio signal is sent to the base station 3a (8b).
~3d) internally by the ADPCM coder
It is encoded and transmitted on DATA#(N) in FIG. In addition, if the signal to be sent and received is a set of data, ADP
It is assumed that the CM coder/decoder is disabled and the signal is passed through without being processed.

Note that SACCH#(N) in FIG. 7 is a frame for transmitting control information corresponding to the time slot of the wireless line.

Base station 3 that received the call continuation request signal
a sends a call continuation request acceptance signal to the exchange 1. The information contained 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, etc.

[0030] Upon receiving the call continuation request acceptance signal, the exchange 1 sends an interference measurement call signal to the base station 3b adjacent to the base station 3a, and measures the radio wave intensity of the wireless line used by the mobile station 8a and the base station. The base station 3b is made to measure the radio wave interference situation of the vacant channel of the station 3b. Note that in this case, only one of the measurements may be performed.

As shown in FIG. 9, the information included in this interference measurement notification signal includes the signal type, additional information length, exchange I
D, destination base station ID, destination mobile station ID, source exchange I
D, termination identifier, etc.

After completing the measurement, the base station 3b notifies the exchange 1 of the measurement result using an interference measurement notification response signal. As shown in FIG. 10, the information included in this interference measurement notification response signal includes signal type, additional information length, destination exchange ID, source base station ID, interference measurement result, termination identifier, etc.

[0033] This radio field strength and interference measurement is performed at the base station 3.
1 by shortening the convergence time of the phase-locked loop (PLL) used in the local oscillation circuit in the wireless transmitting/receiving means 14.
The wireless transmitting/receiving means 14 of the stand is capable of measuring different frequencies in time slots during and outside of communication.

[0034] Having received the measurement results, the exchange 1 selects the optimum destination base station (in this case, 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 information on the destination radio channel using an empty slot notification signal using the above-mentioned communication line control signal.

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

Mobile station 8a receiving empty slot communication signal
The mobile station measures the interference of the destination radio line in the mobile station, and if the criteria are met, sends a switching preparation signal to the base station 3a. As shown in FIG. 12, the information included in this signal includes the signal type, additional information length, destination base station ID, destination exchange ID, source mobile station ID, termination identifier, etc.

Furthermore, the switching preparation signal is also sent to the exchange 1 from the base station 3a. Along with this, the exchange 1 also sets up a communication path to the base station 3b, creating a so-called three-party conference state. FIG. 13 shows how the partner fixed terminal 2 and the mobile station 8a are connected in this case. As shown in the figure, audio muting is disabled in the base station 3a, and enabled in the base station 3b.

[0038] If this audio mute function is enabled, during voice communication, the 64 Kbps PCM output from the ADPCM decoder is used instead of the signal in the ADPCM encoding method used. The line transceiver 1 transmits a signal that means silence, and when transmitting data, all bits are set to “0”.
2.

Furthermore, in the case of voice communication, the conference trunk 21 first converts the 64 Kbps PCM signal into voice, and
This function is achieved by adding/subtracting signals in an analog manner. However, 64Kbps PCM (normally non-linear encoding method is applied) is converted to linear encoding PCM.
After converting into a CM signal, addition/subtraction processing may be performed digitally.

[0040] Upon receiving the switching preparation signal, the exchange 1 sends a switching communication signal to the base stations 3a and 3b. Upon receiving this switching notification signal, the base station 3a monitors the disconnection of the wireless line, and the base station 3b monitors the establishment of the wireless line using their respective line establishment detection means 17.

[0041] When a wireless line is established between the mobile station 8a and the base station 3b, and the wireless line with the base station 3a is disconnected, the base station 3b disables the audio mute, and the base station 3a disables the audio mute. To enable. FIG. 14 shows how the partner fixed terminal 2 and the mobile station 8a are connected at that time. Note that the audio mute is enabled/disabled based on the signal from the control circuit 11.
3.

[0042] The base station 3b, which detects establishment of a wireless line by the line establishment detecting means 17, notifies the exchange 1 of a connection completion signal. The exchange 1 that receives this restores the base station 3a. FIG. 15 shows how the partner fixed terminal 2 and the mobile station 8a are connected at this time.

[0043]

As described above, according to the present invention, an exchange equipped with a so-called conference trunk function is used, and a base station is provided with a line establishment detection means and an audio mute means.
When a handover occurs, the source base station, destination base station, and communication partner terminal are temporarily placed in a three-way conference state, and when the line establishment detection means detects the establishment of a wireless line at each base station, the audio Disables the mute means and sends voice and data signals from the mobile station to the exchange, and when disconnection of the wireless line is detected, activates the voice mute means and inserts a silence signal into the voice and data signals sent to the exchange. Therefore, in an environment where sufficient electric field strength can be obtained, there is no need for exchange processing when enabling/disabling audio mute, and the call disconnection time is the same as that of the source base station's wireless line. The time difference between disconnection and the establishment of a wireless link at the destination base station (usually several tens of milliseconds or less) is extremely short, about the sum of the processing time of at most ten or more steps by the processor. This has the effect of providing a handover method in a mobile communication system that can perform handover by disconnection.

[Brief explanation of drawings]

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

FIG. 2 is a sequence flow diagram showing the flow of handover processing in the above embodiment.

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

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

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

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

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

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

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

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

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

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

FIG. 13 is an explanatory diagram showing the state of connection between a mobile station and a partner terminal at the beginning of setting a communication path to a destination base station in the above embodiment.

FIG. 14 is an explanatory diagram showing the state of connection between the destination base station and the mobile station immediately after the wireless link between the destination base station and the mobile station is established in the above embodiment;

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

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

FIG. 17 is a sequence flow diagram showing the process flow of a handover method in a conventional mobile communication system.

[Explanation of symbols]

1 Exchanges 3a to 3d Base stations 5a to 5d Communication zone 7 Communication areas 8a, 8b Mobile station 11 Control circuit 13 Audio mute/PCM CODEC (audio mute means) 17 Line establishment detection means 21 Conference trunk

Claims (1)

[Claims] 1. A plurality of base stations each having a communication zone for wireless communication, and a communication area of the system is formed by a collection of each communication zone; Each of the base stations is connected to a plurality of mobile stations that communicate with the base station and send and receive voice, data communications, and control information and dialing information for the mobile station, and the base station is connected to the base station as the mobile station moves. In a handover method in a mobile communication system comprising a switch having a function of performing handover between mobile stations, a function of managing the location of the mobile station, and a conference trunk function of adding/subtracting three or more audio signals, to the base station,
a line establishment detection means for detecting the establishment of a wireless line with the mobile station and notifying a control circuit that realizes functions such as controlling the base station and transmitting and receiving information with the exchange; and the control circuit. A sound muting means is controlled by a circuit and transmits a signal indicating a silent state to the signal on the line to the exchange, and when the mobile station moves from the zone of one base station to the zone of another base station. , before the radio rotation between the source base station and the mobile station is terminated, the base station at the destination of the mobile station starts transmitting and receiving on the wireless channel to which the mobile station is moving, and the voice of the source and destination is transmitted and received. The data signals are added/subtracted using the function of the conference trunk, and the voice and data signals to each of the base stations and the mobile station are sent with the information of the other two parties added. The base station transmits a signal indicating silence on the voice and data signals to the exchange until a wireless link with the mobile station is established, and transmits a signal indicating silence to the exchange after the wireless link with the mobile station is established. The source base station stops transmitting the signal indicating the mobile station and transmits the signal sent via the wireless link, and the source base station receives no signals from the mobile station while the wireless link with the mobile station is established. After the wireless line is disconnected, a signal indicating silence is sent to the exchange, and after the series of tracking exchanges are completed, the exchange disconnects the line with the source base station. A handover method in a mobile communication system characterized by restoration.