JPH0591555A - Channel switching control system for mobile communication - Google Patents

Abstract

PURPOSE:To reduce the forced disconnection of communication at the time of switching channels by previously reserving a channel in a cell whose channel switching is supposed prior to the execution of channel switching operation. CONSTITUTION:A mobile communication network is provided with base stations 131 to 133 for forming respective radio zones 121 to 123 and a control station 14 for controlling the base stations 131 to 133 and a mobile station 11 executes communication while switching communication channels with the base stations 131 to 133. In this case, channels are reserved in communication channel tables included in the base stations 131 to 133, and at the time of switching a certain channel based upon the detection of deterioration in communication quality, the current channel is switched to one of the reserved channels. Namely each of the base stations 131 to 133 refers to its own communication channel table at the time of receiving a channel reserving request from the control station, executes channel reservation when an idle channel exists, or when there is no idle channel, writes a mobile station identification number in a reservation queuing table to wait until a channel is made free.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel switching control system for cellular mobile communication in which a wireless zone is divided into a plurality of cells and the same frequency is repeatedly used.

[0002]

2. Description of the Related Art In a mobile communication system, a cellular system is used in which the same frequency is geographically repeatedly used within a service area in order to effectively use a radio frequency in response to an increase in demand. In the cellular system, the zone radius is made small in order to improve the frequency utilization rate. However, the smaller the zone radius, the more frequently the channels are switched due to the movement of mobile stations. Channel switching is performed by monitoring the uplink and downlink channels between the base station and mobile station, and when communication quality cannot be maintained, or when there is a base station with a high reception level by performing strong electric field measurement, etc. This is done by securing an empty channel in the station.

[0003]

As described above, in the method of searching for a vacant channel when the communication quality cannot be maintained, the communication may be forcibly terminated because there is no vacant channel. In addition, the communication may be forcibly disconnected before the channel switching procedure is established due to the rapid deterioration of the level. Such forced termination of communication adversely affects the service provision due to the loss of calls that are not connected when making or receiving a call.

It is an object of the present invention to reduce the occurrence of such forced termination of communication by reserving a switching channel and switching to the reserved channel.

[0005]

The present invention is a mobile communication system in which a plurality of base stations are arranged in a service area, and the base stations communicate with mobile stations in a zone through a plurality of radio channels. In the mobile communication system in which the station includes means for performing channel switching control with the mobile station, the base station includes means for performing channel switching reservation for an idle channel of the communication channel and access to the reserved channel. And means for performing channel switching control.

The control station for controlling the base station or a plurality of base stations is provided with means for predicting a cell in which channel switching is expected and means for requesting channel reservation to the base station of the predicted cell. You can

[0007]

In the base station, a channel reservation table is provided for empty communication channels, and mobile stations predicted for channel switching are registered. When the deterioration of communication quality between the base station and the mobile station or the strong electric field channel is detected, the channel is switched to the reserved channel. This can reduce the probability of forced disconnection of communication due to channel switching failure or the like.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows the configuration of a mobile communication network to which the embodiment of the present invention is applied. The mobile communication network, the base station _{131-134 3} forming each of the radio zones 12 ₁ to 12 ₃
And a control station 14 for controlling the base stations 13 _{1 to} 13 ₃ . The mobile station 11 uses the base stations 13 _{1 to} 13
Communication is performed while switching the communication channel with ₃ .

FIG. 2 shows a communication channel table provided in these base stations 13. In the communication channel table shown in FIG. 2, f _{1 to} f _n are frequencies (channels) for communication, and the base station has n communication channels. The types of channels include in-communication channels, reserved channels, unusable channels, and empty channels. The reserved channel has information for identifying to which mobile station the reservation is made. The unusable channel is a channel that is being communicated with or reserved by another base station.

FIG. 3 shows an example of a reservation waiting table held by the base station. When the base station tries to make a channel reservation for the mobile station, if there is no free channel in the communication channel table shown in FIG. 2, the mobile station identification number is registered in the reservation waiting table as shown in FIG. Wait for an empty channel to be created in the communication channel table. This reservation waiting table is for making reservations in order from the mobile stations input in the reservation waiting table first. First-in first-out FIFO
It has the same function as memory.

A feature of the present invention is that when a channel is reserved in the communication channel table provided in the base station and the channel is switched by detecting deterioration of communication quality, the channel is switched to the reserved channel. is there.

The reservation registration operation will be described with reference to the flowchart of the reservation procedure in the base station in FIG. First, when the base station receives a channel reservation request from the control station (step S4
1), the base station refers to the communication channel table (step S42), and if there is an empty channel, reserves the channel (step S43). If there is no free channel, the mobile station identification number is written in the reservation waiting table and the channel is waited for (step S44).

Next, the operation of the first embodiment will be described separately for a reservation operation when a communication connection request is made and an operation when a channel switching is needed. FIG. 5 is a flow chart showing an operation regarding reservation when a communication connection request is made. In this figure, a base station 1 is a base station which a mobile station makes a call and communicates with first, base stations 2 and 3 are base stations adjacent to the base station 1, and a control station controls these base stations. It is something to do. The mobile station makes a call (step S51), and the communication connection request is transmitted to the control station via the base station 1. The control station allocates a communication channel between the base station 1 and the mobile station (step S52). The mobile station and the base station 1 start communication on this assigned channel (step S53). Next, the control station makes a reservation request for the communication channel for the mobile station to the base stations 1 to 3 which are the base stations of the cell to which the channel is assigned and the cells adjacent to the cell (step S5).
4). Receiving the reservation request, each of the base stations 1 to 3 performs a reservation procedure (step S55). For this reservation, as shown in FIG. 4, if there is an empty channel in the communication channel table, the mobile station identification number is registered to make the reservation. If there is no empty channel, it is registered in the reservation waiting table. Every
Make a reservation in the communication channel table as soon as an empty channel occurs.

Next, FIG. 6 shows the relationship of the wireless cells which make a channel reservation when a communication connection request is made. In this example,
Reference numeral 61 denotes a mobile station which originates a call, reference numeral 62 is a cell for the communication connection with the mobile station, reference numeral 63 _{1-63 6} cells 6
2 shows a cell adjacent to 2. When the mobile station has a call in the cell 62, the control station performs RR to the base station of all the cells 63 ₁ to 63 ₆ adjacent to the cell 62 and cell 62. Receiving the reservation request, each of the base stations 1 to 3 makes a channel reservation according to the flowchart of FIG.

Next, the channel switching operation based on the channel reservation when the channel switching request is generated will be described with reference to the flowchart of FIG. In FIG. 7, the base station 1 is a base station that communicates with a mobile station before switching channels,
The base station 2 is a base station of the channel switching destination, the base station 3 is a base station which is not adjacent to the cell of the channel switching destination, and the base station 4 is a base station of a cell which is newly adjacent to the cell of the channel switching destination. When a channel switching request is generated during communication between the mobile station and the base station 1, the channel switching request is sent to the control station (step S71). The control station determines the cell to which the channel is switched by detecting the reception level and notifies the base station 2 of the cell (step S72). The base station 2 of the cell to which the channel is switched refers to the communication channel table (step S
73), when the reserved channel for the mobile station moving to the cell is not held, the control station determines another communicable cell (step S72). When the cell to which the channel is switched has the reserved channel for the mobile station,
The channel is switched to the reserved channel and communication is started (step S74). Here, the control station sends a reservation cancellation request to the base station 3 of the cell that is no longer adjacent to the cell for which the channel is switched (step S75), and the base station 3 that has received the reservation cancellation request performs the reservation cancellation procedure (step S75). Step S
76). Subsequently, the control station sends a reservation request to the base station 2 of the cell to which the channel is switched and the base station 4 of the cell to be newly adjacent (step S77). Each base station receiving the reservation request performs a reservation procedure (step S7).
8).

The cell for canceling the reservation and the cell for newly making the reservation differ depending on whether channel switching is performed within the same cell or when channel switching is performed on an adjacent cell.

An example of FIG. 8 shows a cell that reserves a channel when switching channels in the same cell. In FIG. 8, reference numeral 81 is a mobile station and reference numeral 82 is a cell. The mobile station 81 performs channel switching within the same cell in the cell 82. When channel switching is performed within the same cell, cells adjacent to the cell with which communication is performed do not change before and after channel switching. Therefore, only the cell that has performed channel switching needs to make channel reservation. Also, it is not necessary to cancel the channel reservation.

The relationship between the cell that reserves a channel and the cell that cancels the reserve when the channel is switched to an adjacent cell will be described with reference to the example of FIG. In FIG. 9, reference numeral 91 is a mobile station, and reference numerals 92, 93, 94 _{1 to} 94 ₃ and 95 _{1 to} 9 are used.
Reference numerals 5 ₃ denote cells, respectively. The cell 92 is a cell that is currently performing communication and performs channel switching, and the cell 93 is a cell that is a channel switching destination, and the mobile station performs channel switching from the cell 92 to the cell 93. After the channel switching, the cells 95 _{1 to} 95 ₃ are no longer adjacent to the destination cell 93, so that the cells 95 _{1 to} 9 3
The base station of 5 ₃ refers to the channel table for communication,
If there is a reserved channel for this mobile station, that channel is set as an empty channel. If there is no reserved channel in the communication channel table, the reservation number is referred to and the identification number of this mobile station is deleted. Also, a reservation request is made to the cell 93 of the channel switching destination and the base stations of the cells 94 _{1 to} 94 ₃ which are newly adjacent to the cell 93.

In the first embodiment, the channel reservation is made for the cell in which the mobile station exists and all cells adjacent to the cell. However, it is possible to detect the moving direction of the mobile station and move. There is a method of reserving the channel only for cells with high reliability. Further, in the above-described first embodiment, the reservation operation starts at the time when a communication connection request occurs and channel allocation is performed or when channel switching is performed, but the reservation is performed when communication quality deteriorates to some extent. There is a way to get into action. These methods are superior in frequency utilization efficiency to the first embodiment described above. Although these methods are independent of each other, an embodiment incorporating these two methods will be described as a second embodiment.

The channel reservation procedure in the base station is the same as in the first embodiment. FIG. 10 is a diagram for explaining a cell for explaining the second embodiment. Reference numeral 101 is a mobile station, reference numeral 102 is a cell in which the mobile station is located, 103 ₁ to
103 ₂ indicates a cell to be high channel reservation possibility that the mobile station moves.

The channel reservation operation will be described with reference to the flow chart of the operation relating to the channel reservation in FIG. Mobile station 1
01 is in the cell 102, and the mobile station 101 and the cell 102 are
The communication quality between the base stations is constantly monitored. When the communication quality becomes lower than a certain level (step S111),
The control station selects two cells to which the mobile station 101 is likely to move (cell 103 ₁ and cell 103 _{2 in} the example of FIG. 10),
A reservation request is sent to the base stations of those cells (steps S112 and S113). Regarding the method of predicting the cell to which the mobile station moves, for example, the applicant has filed Japanese Patent Application 1
The method of predicting the traveling direction of the mobile station based on the positional relationship of the neighboring base stations and the received level fluctuation disclosed in 181328 is used.

Next, the operation when channel switching is performed will be described with reference to the flowchart of FIG. When the channel switching request is generated (step S121), the channel switching destination cell is determined (step S122). The base station channel switching destination cell refers to the communication channel table (step S123), when not possess reservation channel of the mobile station 101 comes to move to the cell (cell 103 ₁ to 103 ₂ other than When performing channel switching to a cell), normal channel switching control is performed (step S
124). When the channel switching destination cell owns the reservation channel for the mobile station (cell 103 ₁ to the cell 10
3 ₂ When the channel switching) performs channel switching to the reservation channel (step S125). After switching the channels, all reserved channels for the mobile station 101 are released (step S126).

In the first and second embodiments described above, when channels are reserved for all mobile stations, the proportion of reserved channels in the communication channels of the base station increases, Frequency utilization efficiency deteriorates. Therefore, it is preferable to rank mobile stations and perform the reservation operation shown in the embodiment only for specific mobile stations. Moreover, the present invention becomes more effective by using a method in which one reserved channel is shared and used by a plurality of mobile stations.

In the above embodiment, the channel reservation request is described as being performed by the control station. However, the base station in communication predicts the destination cell of the mobile station and the base station moves to the destination via the control station. It is also possible to make a channel reservation request to the base station of the cell predicted to be.

[0026]

As described above, according to the present invention, a channel is reserved in advance in a cell where channel switching is expected before the channel switching operation is performed, so that communication is forced at the time of channel switching. It is possible to reduce disconnection and improve service.
Further, if the present invention is applied to a specific mobile station, the forced disconnection of communication when the mobile station switches the channel can be almost eliminated. Especially in the mobile communication of the micro cell system, such a channel reservation system brings about a great improvement in service because the number of times of channel switching increases and the level changes rapidly.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a mobile communication network in which the present invention is implemented.

FIG. 2 is a diagram showing an example of a communication channel table of a base station.

FIG. 3 is a diagram showing an example of a reservation waiting table of a base station.

FIG. 4 is a flowchart showing a reservation procedure in a base station.

FIG. 5 is a diagram illustrating an operation related to reservation when a communication connection request is generated in the first embodiment.

FIG. 6 is a diagram for explaining channel reservation when the mobile station of the first embodiment requests a communication connection.

FIG. 7 is a diagram illustrating an operation related to reservation when a channel switching request is generated according to the first embodiment.

FIG. 8 is a diagram for explaining channel reservation when channel switching is performed within the same cell according to the first embodiment.

FIG. 9 is a diagram for explaining channel reservation when performing channel switching to another cell according to the first embodiment.

FIG. 10 is a diagram for explaining the second embodiment.

FIG. 11 is a flowchart showing an operation regarding reservation according to the second embodiment.

FIG. 12 is a flowchart showing an operation when channel switching is performed in the second embodiment.

[Explanation of symbols]

11,61,81,91,101 the mobile station 2 ₁ to 2 _3, 62, 63 ₁ to 63 _6, 82,92,9
₃ , 94 _{1 to} 94 ₃ , 95 _{1 to} 95 ₃ , 102, 103
_{1 to} 103 ₂ cells 13 _{1 to} 13 ₃ base station 14 control station f _{1 to} f _n frequencies for communication

Claims (2)

[Claims] 1. A plurality of base stations are arranged in a service area, the base station is a mobile communication system that communicates with a mobile station in a zone through a plurality of wireless channels, and the base station communicates with the mobile station. In the mobile communication system including means for performing channel switching control, the base station includes means for making a channel switching reservation for an empty channel for communication and means for making a channel switching control to the reserved channel. A mobile communication channel switching control method characterized by being provided. 2. A base station or a control station for controlling a plurality of base stations comprises means for predicting a cell in which channel switching is expected and means for making a channel reservation request to the base station of the predicted cell. Item 1. A mobile communication channel switching control method according to Item 1.