JP2789987B2 - Microcell mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to a service area where the number of subscribers is large and communication demand is large, such as in a central area.
Using a micro-cell mobile communication system that provides cordless telephone services for users moving at low speeds, it is possible to provide mobile communication services for mobile terminals moving at high speed, and to maintain battery life of mobile terminals. The present invention relates to a cell configuration method, a radio channel assignment method, and a radio channel switching method of a mobile communication system that improve the time and further increase the number of subscribers capable of simultaneous communication by reducing the same radio channel interference amount.

[0002]

2. Description of the Related Art At present, a land mobile communication system can be roughly divided into a cell configuration composed of macro cells, a cellular car telephone system for users moving at high speed, and a cell configuration composed of micro cells, Are provided on two independent networks of cordless telephone systems intended for users traveling to the United States. Therefore, the user had to have two different mobile terminals when using these systems.

In a conventional cellular land mobile communication system composed of macro cells, the radius of a cell is equal to 0.
The communication between the mobile terminal and the serving macrocell base station is several hundred meters.
This is performed via a wireless line with a transmission output of about W to several W. As described above, since the transmission power from the mobile terminal is large, the power consumption of the mobile terminal is also large, and the duration of the battery is currently limited to about one day. Further, since the cell radius is large, it is necessary to increase the frequency reuse distance, and the number of simultaneous call subscribers is inferior to the micro cell system described below. However, since the cell radius is large, radio line switching that occurs when moving between cells is reduced, which is an advantageous system for mobile terminals that move at high speed.

On the other hand, a cordless telephone system is constituted by microcells having a cell radius of several tens to hundreds of meters. Therefore, the reuse distance of the frequency can be reduced, and the number of simultaneous call subscribers can be increased as compared with the macro cell method described above. Also,
Since the cell radius is small, the mobile terminal can communicate with the serving microcell base station via a wireless line with a low transmission power of about several mW, and the battery life of the mobile terminal can be reduced to one week. Degree. However, since the cell radius is small, radio line switching frequently occurs for a mobile terminal moving at high speed, and the control for this is very complicated. Is intended for pedestrians.

[0005]

As described above, the cellular mobile communication system composed of macro cells and the cordless telephone system composed of micro cells differ in the moving speed of the mobile terminal handled by each system. Are configured by different systems. Therefore, in order to access these systems, it is necessary to use dedicated mobile terminals, which is inconvenient for the user.

A cordless telephone system composed of microcells is superior to a cellular car telephone system composed of macrocells in terms of effective use of frequency and battery life of a mobile terminal. Since the radius is small, there is a disadvantage that only a user moving at a low speed with a small number of handover occurrences can be handled.

On the other hand, a cellular automobile system composed of macro cells has a large cell radius.
It has the advantage of being able to handle users moving at high speed, but on the other hand, it is inferior to microsystems in terms of effective use of frequency due to the large cell radius and the battery life of mobile terminals. Has disadvantages.

The present invention utilizes a microcell system for a cordless telephone system that moves at a low speed, enables one mobile terminal to provide a communication service for a mobile terminal that moves at a high speed, and enables simultaneous communication. An object of the present invention is to propose a microcell mobile communication system aiming at improving the number of subscribers, saving power of mobile terminals, and achieving high quality of wireless channel switching.

[0009]

SUMMARY OF THE INVENTION The present invention provides a communication service to a mobile terminal moving at a high speed using an infrastructure of a micro cell system.
In realizing the present invention, it is necessary to solve a radio channel control method capable of realizing efficient radio channel switching for a mobile terminal moving at a high speed in a micro cell configuration and effectively utilizing a frequency.

In the present invention, a plurality of microcells covering one area, a mobile terminal moving in the microcell at a first speed about a walking speed, and a mobile terminal existing in the microcell are provided. In a mobile communication system having a microcell base station that outputs transmission power that can perform radio channel control, one area covered by a plurality of microcells is regarded as one area covered by one virtual macrocell. Perform radio channel control of multiple microcell base stations to handle 1
The virtual macro cell control means has two virtual macro cell control means, and the virtual macro cell control means performs radio channel control of the mobile terminal moving at a second speed higher than the first speed.

[0011] The power saving of a mobile terminal moving at the speed of a running car is realized by the mobile terminal communicating with a microcell base station constituting a virtual macrocell with a low transmission output of about several mW. Is done.

In realizing the virtual macrocell according to the present invention, it is necessary to solve a radio channel control method which can realize efficient radio channel switching for a mobile terminal moving at a high speed in a microcell configuration and can use frequency effectively. There is.

In the present invention, the wireless channel switching is realized by performing the wireless channel control of the mobile terminal for each virtual macro cell composed of a plurality of micro cells. In addition, since the connection between the mobile terminal and the terrestrial network is performed via the base station installed in each microcell, the mobile terminal moving at high speed needs to switch the base station at high speed. For this, see the document "IEEE Vehicular Techn.
ology Society 42nd VTS Conference, May 1992, Hirofum
i ICHIKAWA etc., 'DYNAMIC CHANNEL ASSIGNMENT USING
SUB-CARRIER MULTIPLEXING TECHNIQUES IN MICROCELLU
LAR SYSTEMS ', p. 645-p. 648, can be realized by using the subcarrier transmission scheme proposed. Uplink radio channel signals from a mobile terminal moving at high speed are received by a plurality of microcell base stations constituting a virtual macrocell, and the received signals are received by E / O converters (wireless / The optical signal is converted to an optical signal by an optical signal converter, and the optical signal is concentrated to a virtual macrocell control unit using an optical fiber. Next, each signal collected using an optical fiber from each microcell base station is converted into a radio signal by an O / E converter (optical / wireless signal converter),
By comparing the reception quality of these radio signals, a microcell base station having the best reception quality is selected, and transmission / reception communication between the terrestrial network and the mobile terminal is performed through the selected base station. Even if a mobile terminal moves between microcells, a high-quality and stable communication service can be realized.

With respect to a radio channel control method that enables effective use of frequency, virtual macrocells are repeatedly arranged for each required radio channel repetition distance, so that frequency reuse can be performed with a shorter radio channel repetition distance than the conventional macrocell configuration method. Can be realized. This is because the virtual macro cell is realized by a plurality of micro cells, and the required wireless channel repetition distance is determined in units of micro cells. In addition, further improvement in frequency utilization efficiency
This can be realized by an n-layer virtual macrocell configuration method in which virtual macrocells that are repeatedly arranged are treated as layers and the layers are multilayered so as to cover the service area without gaps.

[0015] Regarding the high quality of wireless channel switching, when the mobile terminal moves out of the virtual macro cell under the n-layer virtual macro cell layer configuration, the position of the mobile terminal after the movement is the center of the destination virtual macro cell. By performing a handover in which a layer including a virtual macro cell that is in the vicinity is selected as a switching destination layer, a flapping phenomenon that has been a problem at the time of wireless line switching in the conventional cell configuration is improved.

The radio channel allocation method in the n-layer virtual macro cell configuration is realized by a virtual macro cell fixed allocation method or a virtual macro cell dynamic allocation method. In the virtual macrocell fixed allocation method, a radio channel is fixedly allocated to each of n layers in advance, and each radio channel allocated for each layer is repeatedly reused in all virtual macrocells in the layer. At the time of wireless channel setting, first, the mobile terminal determines a layer and a virtual macro cell in a relationship located closest to the center, and then selects an empty wireless channel from the wireless channels assigned to the virtual macro cell and transmits the selected wireless channel to the mobile terminal. assign. In the virtual macrocell dynamic allocation method, a layer and a virtual macrocell are determined in the same manner, and an available free radio channel is selected from all the radio channels and allocated to the mobile terminal.

[0017]

[Embodiment 1] This embodiment corresponds to the first aspect of the present invention.

FIG. 1 is a diagram for explaining the configuration of a virtual macrocell according to the present invention.

In the figure, 1 is a microcell, 2 is a virtual macrocell composed of a plurality of microcells, 3 is a microcell base station, 4 is a microcell base station E / O (wireless /
Optical signal), O / E (optical / wireless signal) converter, 5 is a virtual macrocell control unit, 6 is an optical fiber group for concentrating / distributing transmission / reception signals of the microcell base station in the virtual macrocell to the virtual macrocell control unit, 7 Is an E / O and O / E converter of the virtual macro cell control unit, 8 is a group of level measuring instruments for measuring the reception level of the radio line collected from each micro cell, and 9 is selected based on the level measurement result. A cross-connect switch for connecting a signal transmitted / received from the base station to a modulator / demodulator group, 10 is a modulator / demodulator group composed of a plurality of modulators and demodulators, and 11 is a This is a virtual macro cell controller that controls the cross connect switch 9. Reference numeral 12 denotes a virtual macro cell radio channel control unit that controls radio channels over a plurality of virtual macro cells when performing radio channel switching and virtual macro cell dynamic allocation. Reference numeral 13 denotes a microcell controller that controls a wireless channel of a mobile terminal that moves at a low speed. Reference numeral 14 denotes a mobile terminal.

During communication between the mobile terminal 14 and the terrestrial network, a plurality of microcell base stations 3 constituting the virtual macrocell 2 receive the uplink radio channel transmitted from the mobile terminal 14. In each microcell base station 3, an E / O converter 4 converts an uplink radio channel received signal from the mobile terminal 14 into an optical signal. These optical signals are collected to a virtual macrocell control unit 5 via an optical fiber group 6. The virtual macrocell control unit 5 converts an optical signal collected from the microcell base station 3 via the optical fiber group 6 into an electric signal using the O / E converter 7. The level of the converted electric signal is measured by the level measuring device group 8, and the measurement result is sent to the virtual macrocell controller 11. The virtual macrocell controller 11 selects a microcell base station having the best reception quality based on the level measurement result, selects only signals from the base station by the cross-connect switch 9, and connects to the modem group 10. . On the other hand, communication from the ground network to the mobile terminal 14 is performed via the base station selected above.

As described above, when the mobile terminal 14 moves between the microcells 1, the radio channel switching is performed by switching the microcell base station 3 connected to the modem using the cross connect switch 9. Regardless of the movement of the terminal 14 between the microcells 1, the virtual macrocell control unit 5 can continuously use the same modem. Therefore, as long as the mobile terminal 14 does not move out of the virtual macrocell 2, the mobile terminal 14 can continue to use the same wireless channel without being aware of the wireless channel switching, and the base station side wireless communication can be performed. The instantaneous interruption time of line switching is only the switching time in the cross-connect switch 9,
It is possible to provide a high quality communication service to the mobile terminal 14 moving at high speed.

The mobile terminal 14 that moves at high speed is managed in units of two virtual macrocells by the above configuration.
Wireless channel assignment and wireless channel switching when the mobile terminal 14 moves at a low speed are managed in units of microcells.
Only the serving microcell base station 3 receives the uplink radio channel transmitted from the mobile terminal 14 moving at a low speed. The reception signal of the uplink radio line from the mobile terminal 14 is converted into an optical signal by the E / O converter 4 of the serving microcell base station 3 and then sent to the virtual macrocell control unit 5 via the optical fiber group 6. . In the virtual macrocell control unit 5, the optical signal sent from the serving microcell base station 3 via the optical fiber group 6 is converted into an electric signal by the O / E converter 7. The converted electric signal is connected to a modulator / demodulator group 10 via a cross-connect switch 9. The microcell controller 13 manages the assignment status of the radio channel to all mobile terminals moving in the virtual macrocell 2 moving at a low speed. When the mobile terminal 14 moving at a low speed moves out of the serving microcell 1, handover between microcells accompanied by radio line switching occurs. At this time, the wireless channel being used is used by the destination microcell by using the allocation status of the wireless channel of the microcell around the destination microcell managed by the microcell controller 13 and the level measuring device group 8. The microcell controller 13 determines whether or not it can be used continuously. If the wireless channel cannot be used continuously, a different wireless channel is assigned to the mobile terminal 14 in the destination microcell. on the other hand,
When the wireless line can be continuously used, by switching the cross-connect switch 9 from the source microcell base station to the destination microcell base station, the mobile terminal moving at high speed can move in the same manner as the mobile terminal moves in the virtual macrocell. High quality wireless line switching is also possible for mobile terminals that move at a low speed.

The mobile terminal performs communication by switching between a radio channel managed by the virtual macrocell controller 11 in the virtual macrocell control unit 5 and a radio channel managed by the microcell controller 13 in accordance with the moving speed. Therefore, a function for determining the moving speed of the mobile terminal is required. This determination is made by autonomous determination by the mobile terminal. Immediately after the power is turned on, the mobile terminal autonomously judges the moving speed, and reports the judgment result to the virtual macrocell control unit 5. After that, the mobile terminal in standby repeats the estimation of the moving speed at regular intervals, and when a change in the moving speed is detected from the high speed to the low speed or from the low speed to the high speed, the moving speed is transmitted to the virtual macrocell control unit 5. Report changes. When a mobile terminal makes or receives a call, a wireless channel is allocated according to the moving speed of the mobile terminal. A terminal moving at a high speed is assigned a radio channel managed by the virtual macrocell controller 11 in units of virtual macrocells 2, and a mobile terminal moving at a low speed is assigned a radio channel managed by the microcell controller 13 in units of one microcell. Assigned.
The mobile terminal repeatedly estimates the moving speed even during communication. When the moving speed changes from a high speed to a low speed or from a low speed to a high speed, a radio line switching from a radio line managed by two virtual macrocells to a radio line managed by one microcell is performed. Wireless line switching is performed from a wireless line managed by one unit to a wireless line managed by two virtual macrocells. Next, an autonomous moving speed estimation method of the mobile terminal will be described. The microcell base station 3 transmits a time-division control signal so that the frequency and the slot do not overlap each other. A mobile terminal located in the microcell 1 repeatedly receives a time-division control signal on a predetermined frequency and slot in synchronization with time-division control signals of a plurality of receivable microcell base stations. The moving speed of the mobile terminal is estimated from the speed at which the reception level fluctuates.

[0024]

Embodiment 2 This embodiment relates to the second aspect of the present invention.

FIG. 2 shows a cell configuration of a virtual macrocell system having three frequency repetitions according to the present invention. 21a is a virtual macro cell using the wireless channel group a, 21b is a virtual macro cell using the wireless channel group b, and 21c is a virtual macro cell using the wireless channel group c. As described above, the wireless channel groups a, b, and c are repeatedly reused in another virtual macro cell. Each virtual macrocell is composed of 27 microcells 1, and the service area covered by the microcell 1 is covered without gaps by the virtual macrocell 2 as shown in FIG. FIG. 6 shows an example of a cell configuration of a conventional macro cell system having seven frequency repetitions. Reference numerals 61a to 61g denote seven types of wireless line groups.

In the present invention, as shown in FIG. 2, a plurality of microcells 1 constitute a macrocell. Here, the mobile terminal located in a certain virtual macro cell switches the base station in each micro cell 1 according to the movement of the mobile terminal by the method described in the first embodiment. However, in the virtual macro cell, the same wireless channel is used, and handover with wireless channel switching is performed only when the mobile terminal crosses the virtual macro cell. Since the communication between the mobile terminal and the terrestrial network is performed between the base station of each microcell, by adopting the configuration shown in FIG. Handover with radio line switching is performed, and for a terminal moving at high speed, handover with radio line switching is performed in virtual macro cell units, so that the frequency of handover can be reduced, In addition, the effective use of frequency can be improved as compared with the conventional macro cell system.

[0027]

[Embodiment 3] FIG. 3 illustrates an n-layer virtual macro cell configuration according to claim 3, and shows an embodiment in the case where n = 3. 2 in the figure indicates a virtual macro cell, and 3
1a is a virtual macrocell layer a using a radio channel group a,
31b is a virtual macro cell layer b using the wireless channel group b, and 31c is a virtual macro cell layer c using the wireless channel group c. Reference numeral 31 denotes a virtual macro cell configuration when 31a, 31b, and 31c are superimposed.

In the n-layer virtual macrocell configuration, there are areas covered by only one virtual macrocell layer and areas covered by a plurality of virtual macrocell layers. If the location of the mobile terminal is an area covered by a plurality of virtual macro cell layers, before performing wireless channel assignment at the time of wireless channel setting or wireless channel switching for the mobile terminal,
It is necessary to determine a virtual macrocell base station and a virtual macrocell layer that manage a mobile terminal. In this case, the virtual macro cell in which the location of the mobile terminal is closest to the center and the virtual macro cell layer including the virtual macro cell are selected. By this selection, the mobile terminal is always located at the center of the virtual macro cell when setting the wireless channel, and the flapping phenomenon described later is suppressed. From the above,
After the virtual macrocell base station and the virtual macrocell layer to be managed by the mobile terminal are determined, the mobile terminal is assigned a radio channel.

In the virtual macrocell fixed allocation method according to the present invention, a radio channel is fixedly allocated to each virtual macrocell layer in advance, and a mobile terminal is provided with an unused unused virtual macrocell at that time. Assigned wireless line. In the virtual macrocell dynamic allocation method according to the fourth aspect, all virtual macrocell layers share all radio channels. Therefore, by allocating a wireless channel to a mobile terminal, another mobile terminal using the same wireless channel located near the mobile terminal can perform wireless channel switching even though the mobile terminal has not moved out of the virtual macro cell. There is a possibility. To avoid such a situation,
The virtual macrocell radio channel control unit 12 in FIG. 1 adjusts and manages radio channel allocation across a plurality of virtual macrocells. In addition, the virtual macrocell radio channel control unit 12 determines a switching destination layer when radio channels are switched due to the mobile terminal moving out of the virtual macrocell, and transfers information between the switching destination and the switching source virtual macrocell. It also manages.

FIG. 5 illustrates the configuration of a conventional macrocell base station. 51 is a macro cell base station, 52 is a radio controller for controlling a radio channel, and 53 is a macro cell. When a request for wireless channel setting is issued from the mobile terminal 14, the wireless controller 52 assigns a wireless channel to the mobile terminal 14. When the mobile terminal 14 moves to another macro cell 2, the wireless channel switching is performed by communication between the wireless controllers 52 of the adjacent macro cell base stations 51.

FIG. 7 illustrates handover in a conventional macro cell system. Reference numeral 71 denotes a switching source macro cell, and reference numeral 72 denotes a switching destination macro cell. In the conventional macro cell configuration, when the mobile terminal 14 moves on the boundary between macro cells, the mobile terminal 14 and the switching source macro cell 71
Since the distance between the switching target macrocell 72 and the distance between the switching destination macrocells 72 are substantially equal to each other, the switching from the switching destination macrocell 72 to the switching source macrocell 71 is continued until the communication with the switching destination macrocell 72 is stabilized. A flapping phenomenon accompanied by excessive switching, ie, re-switching to 72, occurs.

In the virtual macro cell configuration according to the present invention, when the mobile terminal 14 moves out of the virtual macro cell as shown in FIG. 4, the position of the mobile terminal 14 after the movement is close to the center of the destination virtual macro cell. By selecting the virtual macro cell having the following relationship as the switching destination macro cell, sufficient communication quality is secured between the switching destination macro cell and the mobile terminal 14 immediately after switching, and the occurrence of the flapping phenomenon is suppressed.

20 × 20 = 400 as service area
A comparison is made between the three-layer virtual macrocell configuration and the conventional macrocell configuration in a region covered by three microcells. However, the calculation of traffic volume is infinite
It is calculated by Erlang's loss formula, which represents the relationship of the number of outgoing lines n / the added traffic volume a / the blocking rate B. Further, as a configuration of the proposed system, the number of layers is three, and the number of wireless lines is fixedly allocated to the number of wireless lines equal to three layers (corresponding to claim 4).
It is assumed that one virtual macro cell is composed of 27 micro cells. In the conventional macro cell system, the size of the macro cell is assumed to be the same as that of the virtual macro cell, and the frequency repetition is assumed to be 7. FIG. 6 shows a conventional macro cell system. 61a, 61b, 61
c, 61d, 61e, and 61f indicate macro cells to which different wireless channel groups are respectively assigned.

The above-mentioned assumption and the traffic volume Y that can be processed in the service area of the three-layer virtual macro cell configuration shown in FIG.
It can be obtained by the following equation.

F (N ÷ L ′, B) × M ′ × L ′ = Y N: total number of radio lines available in the service area L ′: number of virtual macro cells in the virtual macro cell layer / service area B: regulation F (N ÷ L ', B): 1 traffic volume that can be processed in a virtual macrocell [Erlang] M': Number of multilayer layers Y: Total traffic volume that can be processed in a service area [Erlang]

On the other hand, the conventional frequency repetition 7 shown in FIG.
Of traffic that can be processed in the service area of the macro cell configuration X
Is obtained by the following equation.

F (N ÷ L, B) × M × L = X N: the total number of radio lines available in the service area L: the number of macro cells used by each frequency group / the service area B: the prescribed call blocking rate f ( N ÷ L, B): Traffic volume that can be processed in one macro cell [Erlang] M: Number of repeated reuses of macro cell radio lines X: Total traffic volume that can be processed in a service area [Erlang]

Here, N = 120, B = 0.01, M '
In the case of = 3, L = 8.5 (three-layer average value), and the total call volume that can be processed is X = 740 [erlang].

On the other hand, in the case of the conventional method, assuming N = 120 and B = 0.01, which are the same conditions as above, when M = 7, L = 2.1 (average value of 7 macro cells), and processing is possible. The total call volume is X = 142 [Erlang].

As described above, the processable traffic volume of the three-layer virtual macro cell configuration is 5.2 times that of the conventional macro cell configuration with frequency repetition of 7, and the number of subscribers who can talk simultaneously is greatly improved. Recognize.

[0041]

According to the present invention, a microcell mobile communication system for providing a cordless telephone service for a user moving at a low speed in a service area where the number of subscribers is large and communication demand is large, such as in a city center. To provide mobile communication services for mobile terminals that move at high speed, improve the battery life of mobile terminals, and perform wireless line switching with less flutter at the time of handover. This has the effect of improving the number of subscribers who can talk at the same time by reducing the amount of interference.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a virtual macro cell system according to the present invention.

FIG. 2 is a diagram illustrating a cell configuration of a virtual macro cell system according to the present invention.

FIG. 3 is a diagram illustrating a cell configuration of a three-layer virtual macro cell system according to the present invention.

FIG. 4 is a diagram illustrating a handover in a three-layer virtual macrocell configuration according to the present invention;

FIG. 5 is a diagram illustrating a cell configuration of a conventional macrocell base station.

FIG. 6 is a cell configuration diagram of a conventional macro cell system.

FIG. 7 is a diagram illustrating a handover in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microcell 2 Virtual macrocell 3 Microcell base station 4 E / O converter 5 Virtual macrocell control unit 6 Optical fiber group 7 O / E and E / O converter 8 Modulator / demodulator group 9 Level measuring instrument group 10 Cross-connect switch 11 Virtual macrocell controller 12 Virtual macrocell radio channel controller 13 Microcell controller 14 Mobile terminal 21a Virtual macrocell using radio channel group a 21b Virtual macrocell using radio channel group b 21c Virtual macrocell using radio channel group c 31a Radio channel group virtual macrocell layer 1 31b using a a virtual macrocell layer 2 31c using a radio channel group a virtual macrocell layer 3 using a radio channel group a 51 macrocell base station 52 radio controller 53 macrocell 61a macrocell 61b using a radio channel group a radio channel 61b Macro cell using group b 61c Macro cell using radio channel group c 61d Macro cell using radio channel group d 61e Macro cell using radio channel group e 61f Macro cell using radio channel group f 61g Macro cell using radio channel group g 71 Switching source macro cell 72 Switching destination macro cell

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/26

Claims (4)

(57) [Claims] 1. A plurality of microcells covering one area, a mobile terminal moving in the microcell at a first speed about a walking speed, and a radio link for the mobile terminal existing in the microcell. And a microcell base station that outputs a transmission power to the extent that control can be performed. In the mobile communication system, the one area covered by the plurality of microcells is one area covered by one virtual macrocell. A single virtual macrocell control means for controlling the radio channels of the plurality of microcell base stations, and the radio channel control of the mobile terminal moving at a second speed higher than the first speed. Is performed by the virtual macro cell control means. 2. The microcell mobile communication system according to claim 1, wherein the virtual macrocell is arranged repeatedly. 3. An area covered by repeatedly arranging the virtual macro cells using the same radio channel is treated as one layer, and the layer is a layer of the virtual micro cell different from the layer. When the mobile terminal moves out of the virtual macrocell, the position of the mobile terminal after movement is near the center of the destination virtual macrocell when the mobile terminal moves out of the virtual macrocell. 3. The microcell according to claim 2, wherein a handover accompanied by wireless channel switching is performed so that a layer including a virtual macrocell having a relationship as follows is selected as a switching destination layer. 4. Mobile communication system. 4. A fixed division of all radio channels into n layers each having n layers, so that when a radio channel is set for a mobile terminal, the radio channel is fixedly allocated to a layer where the mobile terminal is located. A fixed allocation method for allocating an idle wireless line to the mobile terminal from the wireless line that has been established, or an n-layered n layers that share all the wireless lines, 4. The microcell mobile communication system according to claim 3, wherein a wireless channel is set by a dynamic allocation method in which an available wireless channel is selected from the channels and assigned to the mobile terminal.