JPH05252098A - Mobile communication system - Google Patents

Abstract

PURPOSE:To allow the mobile communication system to cover entirely a town and a premises with large traffic and a suburb and a thinly populated area with small traffic, to use the frequency utilizing efficiency efficiently and to suppress increase in the traffic due to hand-off. CONSTITUTION:In the mobile communication system 10 comprising plural cells each of which has at least one radio base station (1-1-1-N) in which mobile stations 2-1-2-M moves in an area covered by the cells, the plural cells are made up of cells having various radii from a minimum cell to a maximum cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system composed of a plurality of cells, having at least one radio base station in each cell, and allowing a mobile station to move within an area covered by these cells. ..

[0002]

2. Description of the Related Art In the future, a microcell type mobile communication system is about to be put into practical use as a mobile communication system targeting a narrow area with a large traffic volume such as an urban area or a premises. This micro-cell type mobile communication system is composed of cells having a minimized radius (for example, several tens of meters), and a certain area is divided into small parts, and each mobile station bears a radio base station. This is a system that enables efficient use of frequency utilization efficiency by reducing the number of.

For wide area communication, a macrocell type mobile communication system having cells with a large radius (for example, several kilometers) such as those used in car telephones is used. Since this macro cell type mobile communication system has a large cell radius, it cannot efficiently use the frequency utilization efficiency and can be normally used only in a place where the traffic volume is small, but the number of handoffs of the mobile station is small. It can be suppressed.

[0004]

However, in such a conventional mobile communication system, when a microcell type mobile communication system is used, it is impossible to cover a wide range (for example, all over Japan) with a very small cell. Besides, there is a problem that the number of handoffs increases unnecessarily.

In addition, although the macrocell type mobile communication system enables communication over a wide range, on the other hand, since the frequency utilization efficiency decreases, it cannot be used normally in urban areas where the traffic volume is large. There is a problem called. Furthermore, it is very difficult to provide compatibility between these microcell type mobile communication systems and systems having a large cell radius such as car phones.

The present invention was devised in view of the above problems, and it is possible to collectively cover a large traffic area such as an urban area or a premises to a small traffic area such as a suburb or a sparsely populated area. An object of the present invention is to provide a mobile communication system capable of efficiently using the usage efficiency and suppressing an increase in traffic volume due to handoff.

[0007]

FIG. 1 is a diagram for explaining the principle of the present invention. In FIG. 1, reference numeral 10 denotes a mobile communication system, which is composed of a plurality of cells and at least One radio base station 1-i for each cell
(I = 1 to N; N is an integer of 2 or more), and the mobile station 2-
1-2-M (M is an integer of 2 or more) can move within the area covered by these cells.

The plurality of cells have various cell radii from the smallest to the largest (claim 1). Then, the minimum cell is configured as a cell having a cell radius of several tens of meters, and the maximum cell is configured as a cell having a cell radius of several hundred meters to tens of kilometers (claim 2). ..

The mobile stations 2-1 to 2-M have the functions of varying the transmission power according to the size of the cell and keeping the average reception power constant (claim 3).
4). Further, the mobile communication system 10 has a double cell structure by providing a maximum cell capable of covering the area with one radio base station 1'in an area where a minimum number of cells are gathered. 5) In this case, when the number of handoffs exceeds a predetermined value when the mobile stations 2-1 to 2-M move in the extremely small cell, the mobile station 2-1.
The communication destination from ~ 2-M is switched to the radio base station 1'for the maximum cell that covers the area where the minimum cells are gathered (claim 6).

[0010]

In the above-described mobile communication system of the present invention, as shown in FIG. 1, the mobile stations 2-1 to 2-M have a minimum cell (a cell having a cell radius of several tens of meters) and a maximum cell (a cell having a radius of several tens of meters). It moves within an area covered by a cell having a cell radius of several hundred meters to several tens of kilometers (claim 1,
2).

The transmission power of the mobile stations 2-1 to 2-M is made variable according to the size of the cell, and
Further, the average reception power of the mobile stations 2-1 to 2-M is kept constant (claims 3 and 4). Further, when the mobile stations 2-1 to 2-M move in an area where extremely small cells are gathered and the number of handoffs exceeds a predetermined value, the communication destinations from the mobile stations 2-1 to 2-M are extremely small. The area in which the cells are gathered is covered with one and switched to the radio base station 1'for the maximum cell having the double cell structure (claims 5 and 6).

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 2 is a block diagram showing an embodiment of the present invention. In FIG. 2, 10 is a mobile communication system, and the mobile communication system 10 is composed of a plurality of cells. It has various cell radii from the maximum to the maximum.

The minimum cell is used in an area with a large traffic volume (for example, an urban area) as shown by the broken line in FIG. 2, and it is minimized in order to improve the frequency utilization efficiency in this area. It has a cell radius of several tens of meters. Also, the maximum cell is
It is used in areas with a small amount of traffic outside the dashed line (for example, in the suburbs or in the mountains), and has a maximized cell radius of several hundred meters to several tens of kilometers to cover a wide area. It was constructed by.

Further, in an area in which extremely small cells are gathered, that is, in an extremely small cell area where the number of handoffs is large, FIG.
As shown by a thick solid line, a maximum cell capable of covering this area with one radio base station is provided in a stacked manner in order to reduce the number of handoffs, and has a double cell structure. Then, FIG. 3 shows these cells in detail by enlarging them, but as shown in this figure, these cells have at least one radio base station 1-i for each cell.
(I = 1 to N; N is an integer of 2 or more), and the maximum cell covering the minimum cell area has a radio base station 1'dedicated to this area. In the area covered by these cells, the mobile stations 2-1 to 2-1
2-M can move.

Here, the radio base stations 1-1 to 1-N form cells in charge based on the range in which radio waves can be transmitted and received,
Transmission / reception is performed with each mobile station 2-1 to 2-M in the cell, and the transmission / reception signal is relayed to a predetermined mobile station 2-1 to 2-M or a terminal. In addition, the radio base stations 1-1 to 1-N are mobile stations 2-j (j = 1 to M; M).
Is an integer greater than or equal to 2), the control of the mobile stations 2-1 to 2-M is switched by the handoff control between the stations newly accepting the mobile stations 2-1 to 2-M. You can do it.

Further, the radio base stations 1-1 to 1-N use the information such as the cell size of their own station or the designation of the transmission power as control information of the transmission power in the cell of their own station by the control channel or the like. It is also designed to be transmitted to certain mobile stations 2-1 to 2-M. The wireless base station 1'is the wireless base station 1
Mobile stations 2-1 to 2-M having the same configuration as that of -1 to 1-N, but further moving in an area having a dual cell configuration.
Monitors the number of times each time handoff control is performed,
The mobile stations 2-1 to 2-M are added with a function of starting a connection with themselves at the time of connection for the third time, for example.

The handoff control for switching from the minimum cell to the maximum cell is performed by the same control as a normal (for example, between minimum cells) handoff. That is, the radio base station 1'is the same as the normal one except that it monitors the number of handoffs in the extremely small cell area and issues a command for handoff control.

The mobile stations 2-1 to 2-M are radio base stations 1-
It transmits and receives to and from each terminal via 1 to 1-N, and further has a function of varying the transmission power according to the size of the cell and keeping the average reception power constant. Because, if the mobile stations 2-1 to 2-M are designed for extremely small cells, if they are moved near the radio base stations 1-1 to 1-N of the largest cells, the mobile stations Two
This is because the receiving units of -1 to 2-M are saturated and do not operate normally.

In order to satisfy the above conditions, the mobile station 2-1
2 to M are antenna 21, transmitter 20, hybrid circuit 25, receiver 40, and control device 3 as shown in FIG.
4, voice codec 35, speaker 36A, microphone 3
It has 6B. Here, the hybrid circuit 25
Is for outputting a reception signal from the antenna 21 to the receiving unit 40 and outputting a transmission signal from the transmitting unit 20 to the antenna 21.

The transmission section 20 is configured so that the transmission power can be varied, and for this reason, the variable amplifier 22, the bandpass filter (BPF) 23, and the modulator (MOD) 2 are used.
It is composed of four. Here, the modulator 24 modulates the transmission signal, and the bandpass filter 23
The modulated signal from the modulator 24 passes a desired frequency signal, and the variable amplifier 22 further increases or decreases the amplitude of the signal from the bandpass filter 23 according to the control signal to change the transmission power. .. That is, it is possible to cope with the transmission power from the minimum cell to the maximum cell, and when the mobile stations 2-1 to 2-M are in the minimum cell, in order to reduce the power consumption of itself, and, In order not to cause interference to other cells, according to the control signals from the radio base stations 1-1 to 1-N of its own cell,
It is possible to increase or decrease the transmission power suitable for this cell.

The signal from the control device 33 is transmitted to the antenna 2 by the transmitting section 20 having such a configuration.
1, the transmission power is increased or decreased according to the signals from the radio base stations 1-1 to 1-N for the cells covering the mobile stations 2-1 to 2-M. Further, the receiving unit 40 is configured to be able to vary the received power, and for this reason, the amplifier 26, the variable amplifier 27, the AG
It comprises a C circuit (automatic gain control circuit) 28, a detector 29, a mixer 30, a local oscillator 31, and a demodulator (DEM) 32.

Here, the amplifier 26 is for amplifying the received signal coming through the antenna 21, and the variable amplifier 2
Reference numeral 7 adjusts and outputs the signal input from the amplifier 26 in accordance with the control signal from the AGC circuit 28 so that the received average power becomes constant. The AGC circuit 28 is
The receiving unit 40 of each of the mobile stations 2-1 to 2-M keeps the average received power constant. That is, the level difference between the received powers of the radio base stations 1-1 to 1-N, which have variations, detected by the detector 29 and the reference received average power is absorbed, and which cell is used after the AGC amplifier. It operates so that the average power becomes constant no matter where the position is.

It should be noted that, regardless of the radius of the cell, the difference between the vicinity of the radio base stations 1-1 to 1-N and the average received power on the cell boundary is several tens of dB, but the AGC circuit 28 , It does not contribute to this received power difference. The mixer 30 is a circuit that combines the input received signal and the signal from the local oscillator 31 to down-convert the signal frequency to an intermediate frequency, and the demodulator 32 further demodulates the signal from the mixer 30. It is something to give.

The receiving unit 40 having such a configuration performs the receiving process including the demodulating process while varying the received power. Further, the control device 34 controls signals between the transmitting unit 20, the receiving unit 40, and the voice codec 35. The voice codec 35 decodes the signal from the control device 34 and outputs it to the speaker 36A, and also encodes the output from the microphone 36B and outputs it to the control device 34.

It should be noted that the mobile stations 2-1 to 2-M each operate independently of the AGC of their own regardless of the information about the cell size of the radio base stations 1-1 to 1-N or the control channel such as designation of transmission power.
Since the circuit 28 can recognize the change in the average received power, it is possible to control the transmission power based on the information. Further, as shown by the chain line part of the receiving section 40 in FIG. 4, even if the IF system detector 33 is used instead of the detector 29 and the detection information after the mixer 30 is obtained, the AGC circuit 28
Can be controlled by.

With the above-mentioned configuration, the extremely small cells are used in an area having a large traffic amount such as an urban area to efficiently use the frequency, and a large area is covered in an area having a small traffic amount such as a suburb. It Further, the mobile stations 2-1 to 2-M perform communication within cells having various cell radii by moving themselves, and at that time, depending on the size of the cell radii, the radio base stations 1-1 to 1-1. 1
Since the transmission power of −N is different, the mobile stations 2-1 to 2-M are required to increase the dynamic range of the average power.

That is, the radio base stations 1-1 to 1-N forming a cell for communication output the size information of the cell or the designation of the transmission power by the control channel or the like as the control information of the transmission power. Is done. Now, the transmission power of the radio base stations 1-1 to 1-N of the extremely small cells is 10 milliwatt (mW), and the radio base stations 1-1 to 1-N of the very large cell are
When the transmission power of 5W is 5W, when moving from one to the other,
A 30 dB output difference occurs.

Therefore, the receivers 40 of the mobile stations 2-1 to 2-M use the AGC circuit 28 to send the control information from the radio base stations 1-1 to 1-N so that the average reception power becomes constant. Originally, the level difference of the received power from the received average power is absorbed, and after the AGC amplifier, the average power is constant at any position in any cell. In this way, the AGC circuit 2
8 absorbs the level difference of the received average power of 30 dB and apparently cancels the output power difference of the radio base stations 1-1 to 1-N.

Next, the transmission power of the mobile stations 2-1 to 2-M in this case will be described. The transmission power of the mobile stations 2-1 to 2-M is according to the control information of the radio base stations 1-1 to 1-N.
When in a very small cell, in order to reduce the power consumption of the mobile stations 2-1 to 2-M themselves, and to prevent interference in other cells, the transmission power is reduced to that suitable for that cell. .. When in the maximum cell, the wireless base station 1
-1 to 1-N according to the control information, the radio base station 1-
It is amplified to a suitable transmission power considering the distance from 1 to 1-N. In this way, the transmission power of the mobile stations 2-1 to 2-M is made variable according to the size of the cell.

Further, FIG. 5 schematically shows a state of a mobile station passing through a plurality of micro cells in the dual cell structure. In this way, the mobile station 2-j frequently performs handoff. When repeating, the following control is performed by the maximum cell. That is, when the mobile station 2-j is communicating in a very small cell, the number of handoffs is 3 within a specific time (not necessarily 3 but any appropriate number depending on the location).
Radio base stations 1-1 to 1 which have recognized this
-N changes the communication destination of the mobile station 2-j to the radio base stations 1-1 to 1-N of the maximum cell.

FIG. 6 is a signal sequence diagram showing the above situation, and shows a case where the mobile station 2-j moves through the minimum cells A to D. Mobile station 2
-J performs handoff three times until reaching the minimum cells A to D, and reaches the minimum cell D (see FIG. 6).
During this time, the radio base station 1-i for the maximum cell that covers the area where the minimum cells that monitor the number of handoffs are gathered
Monitors the number of times handoff control is performed.

Then, when the mobile station 2-j is connected to the radio base station 1-i of the minimum cell D, that is, when the number of handoffs reaches three, the mobile station 2-j switches to its own station and connects to itself. To start communication (see FIG. 6). As shown in FIG. 7, in a very small cell area where the number of handoffs can be sufficiently suppressed to an appropriate number with only the very small cell, it is possible to perform appropriate communication without using the double cell configuration.

As described above, in the mobile communication system 10 including a plurality of cells and having the radio base stations 1-1 to 1-N in each cell, several hundred meters from a very small cell having a cell radius of several tens of meters. -Because it is composed of multiple cells with various cell radii up to a maximum cell with a cell radius of more than a dozen kilometers, with the advantage that one system can cover a wide service area in an area with a small traffic volume, In an area with a large amount of traffic, it is possible to obtain the advantage that the frequency utilization efficiency can be increased together. As a result, the service area of the entire mobile communication system can be expanded and the efficiency can be improved.

Further, the mobile stations 2-1 to 2-M have a function of varying the transmission power according to the size of the cell, so that the radio waves are transmitted with appropriate transmission power regardless of the size of the cell radius. can do. As a result, it is possible to perform transmission without using more transmission power than necessary in a very small cell or in the vicinity of the radio base stations 1-1 to 1-N where sufficient transmission power is sufficient. It is possible to eliminate waste of power of -1 to 2-M and efficiently transmit high-quality radio waves.

Further, the mobile stations 2-1 to 2-M make the reception average power constant by the AGC circuit 28 provided in the reception system thereof, so that the radio base stations 1-1 to 1-1 depending on the size of the cell radius. The transmission power of 1-N is changed, and the mobile station 2-
Even if the dynamic range of the average power of 1 to 2-M becomes large, normal reception can be performed regardless of the size of the cell radius without expanding the dynamic range of itself.

In addition, in the area where the minimum cells are gathered, the maximum cells are provided to form the double cell structure, and the number of handoffs is performed when the mobile stations 2-1 to 2-M move the minimum cells. Exceeds a predetermined value, the number of handoffs can be reduced by switching the communication destination to the radio base station for this maximum cell. The mobile station 2-
Each mobile station 2-1 to 2-M or the like may independently provide a means for monitoring the number of handoffs of 1 to 2-M and controlling the handoff from the minimum cell to the maximum cell.

[0037]

As described in detail above, according to the mobile communication system of the present invention, the mobile communication system is composed of a plurality of cells, at least one radio base station is provided in each cell, and the mobile station is covered by these cells. In a mobile communication system capable of moving within a certain area, a plurality of cells are composed of cells having various cell radii from a minimum cell to a maximum cell, and these minimum cells are several tens of meters. In addition to being configured as a cell having a cell radius of 100 μm and a maximum cell configured as a cell having a cell radius of several hundred meters to several tens of kilometers, one system can cover a wide service area, and In an area with a large traffic volume, there is an advantage that the frequency utilization efficiency can be used high (claims 1 and 2).

Since the mobile station is provided with means for varying the transmission power according to the size of the cell, there is an advantage that radio waves of high quality can be efficiently transmitted regardless of the size of the cell radius. There is (claim 3). In addition, the mobile station
By providing the means for keeping the received average power constant, there is an advantage that it can operate normally regardless of the change in the dynamic range of the average received power depending on the size of the cell radius (claim 4).

In addition, by providing a maximum cell capable of covering the area with one radio base station in the area where the minimum cells are gathered, a dual cell structure is provided, and the minimum cells are mobile stations. As they move,
When the number of handoffs exceeds a predetermined value, the advantage of enabling the number of handoffs to be reduced by switching the communication destination from the mobile station to the radio base station for the largest cell that covers the area where the smallest cells gather. Yes (Claim 5,
6).

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram showing a structure of a maximum / minimum cell and a dual cell which constitute a mobile communication system according to an embodiment of the present invention.

FIG. 3 is a diagram showing details of each cell in one embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a mobile station according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation of handoff control of a dual cell according to an embodiment of the present invention.

FIG. 6 is a signal sequence diagram illustrating the operation of dual cell handoff control according to an embodiment of the present invention.

FIG. 7 is a diagram showing maximum / minimum cells configuring a mobile communication system as a modified example of one embodiment of the present invention.

[Explanation of symbols]

 1-1 to 1-N, 1'Radio base station 2-1 to 2-M Mobile station 10 Mobile communication system 20 Transmitter 21 Antenna 22 Variable amplifier 23 Bandpass filter 24 Modulator 25 Hybrid circuit 26 Amplifier 27 Variable amplifier 28 AGC circuit 29 Detector 30 Mixer 31 Local oscillator 32 Demodulator 33 IF system detector 34 Controller 35 Voice codec 36A Speaker 36B Microphone 40 Receiver

Claims (6)

[Claims] 1. A plurality of cells, each cell having at least one radio base station (1-1 to 1-N), and mobile stations (2-1 to 2-M) covering these cells. In a mobile communication system (10) capable of moving within a specified area, the plurality of cells are composed of cells having various cell radii from a minimum cell to a maximum cell.
Mobile communication system. 2. The minimum cell is configured as a cell having a cell radius of several tens of meters, and the maximum cell is configured as a cell having a cell radius of several hundred meters to tens of kilometers. The mobile communication system according to claim 1. 3. The mobile communication according to claim 1, wherein the mobile station (2-1 to 2-M) has means for varying transmission power according to the size of the cell. system. 4. The mobile communication system according to claim 1, wherein said mobile stations (2-1 to 2-M) are provided with means for keeping the average received power constant. 5. A double cell structure is provided by providing a maximum cell capable of covering the area with one radio base station (1-1 to 1-N) in an area where the minimum cells are gathered. The mobile communication system according to claim 1, wherein: 6. The mobile station (2-1 to 2-
When the number of handoffs exceeds a predetermined value when M) moves, the communication destination from the mobile station (2-1 to 2-M) is the maximum cell covering the area where the minimum cells are gathered. The mobile communication system according to claim 5, wherein the mobile communication system is switched to a wireless base station (1-1 to 1-N) for use.