JP3110202B2 - Frequency reuse method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a frequency reuse how in the mobile communication system.

[0002]

2. Description of the Related Art A frequency reuse technology conventionally applied to a cellular mobile communication system will be described.

FIG. 4 is a system configuration diagram of an example of a general cellular mobile communication system.

As shown in FIG. 1, in the mobile communication system of this example, a plurality of radio base stations 2,...
Is connected to the general public network. And the radio base station 4
The mobile terminal 9 exists in the service area.

In such a mobile communication system,
Frequency reuse is to use a frequency used for a communication channel in a certain radio base station (for example, the radio base station 3) in another radio base station (for example, the radio base station 6) that is far away.

FIG. 5 is a diagram for explaining a conventional frequency reuse technique. In FIG. 5, it is assumed that frequency reuse is performed in the radio base station A10 and the radio base station B20.

[0007] As indicated by broken lines and chain lines, the radio wave levels 12 and 22 emitted from the radio base stations A10 and B20 decrease as the distance from the radio base stations A10 and B20 increases.

In FIG. 5, the service area boundary of the radio base station A10 closest to the radio base station B20 is defined as SA,
When the radio wave level from the radio base station A10 to the service area SA is LA and the radio wave level from the radio base station B20 is LB, the ratio of the radio wave levels LA and LB is defined as the worst C / I ratio. I do. Here, C means a desired wave, that is, a radio wave level from the radio base station A10, and I means an interference wave, that is, a radio wave level from the radio base station B20.

If the C / I ratio is reduced, the communication quality is degraded due to interference or a call loss is caused by the failure of the radio wave connection confirmation signal. Therefore, the communication service quality limit for each system, that is, the worst limit value of the worst C / I ratio Is determined, and as a result of frequency reuse, frequency reuse is performed so that the worst C / I ratio does not fall below an allowable limit.

In FIG. 5, the arrival radio wave level LA is inversely proportional to the radius R of the service area 11 of the radio base station A10, and the arrival radio wave level LB is inversely proportional to the distance D between the radio base station A10 and the radio base station B20. ing. For this reason,
In order to keep the worst C / I ratio below the permissible limit,
The frequency reuse distance when performing frequency reuse between wireless base stations having a large service area radius is long, and the frequency reuse distance when performing frequency reuse between wireless base stations having a small service area radius is shortened.

FIGS. 6A and 6B are diagrams showing an example of the configuration of a single service area, random traffic channel device in a conventional mobile communication system.

In FIG. 6A, the radio base station service area 90 is a single service area. In addition, as shown in FIG.
, 4n are connected to the antenna 40.

Here, when the number of subscribers increases and a large number of communication channels are required in the system, it becomes necessary to improve the frequency reuse efficiency. One method for improving the frequency reuse efficiency is to reduce the frequency reuse distance, that is, to reduce the service area of the wireless base station.

When the service area of a radio base station is reduced in order to improve the frequency reuse efficiency, conventionally, the radio base station uses physical information such as the transmission output of a radio, antenna mounting height, mounting angle and antenna directivity. It was coped with by proper adjustment.

[0015]

The miniaturization of the radio base station service area by the conventional physical adjustment requires not only the time required for the adjustment work but also the necessity of stopping the communication service during the adjustment work. There were problems such as an increase in equipment costs.

Further, if the radio base station service area is excessively miniaturized, there is a problem that the system construction cost increases due to the increase in the radio base station equipment cost.

[0017]

According to the present invention, a radio base station having a control channel device for controlling establishment of a mobile terminal call and a plurality of communication channel devices for providing a communication service to the mobile terminal. And a mobile telephone exchange to which a plurality of the radio base stations are connected, wherein a service area of the radio base station is set to a concentric inner area and an outer field in accordance with an expected call volume. The radio base station is divided into two groups, a communication channel device group for the inside area and a communication channel device group for the outside area.
The mobile telephone, comprising a group of two communication channel devices, measuring a received electric field level when receiving a call signal or an incoming response signal from the mobile terminal, and including a measurement result in the call signal or the incoming response signal. Report to the switching center that the received electric field level from the mobile terminal is less than a predetermined inner area / outer area boundary level threshold while the inner area communication channel is providing a call service. When this happens, a first channel switching request from the inside area communication channel to the outside area communication channel is made to the mobile telephone exchange, and while the outside area communication channel is providing a communication service. When the electric field level received from the mobile terminal is less than a predetermined boundary level threshold of the service area of the external area / neighboring radio base station. The neighbor radio base from the communication channel for outside area to the mobile telephone exchange when the
A second channel switching request is made to a station, and a level of a received electric field from the mobile terminal is changed to a predetermined boundary level between the external area / internal area while providing the external area communication service. When the threshold value is exceeded, the mobile telephone exchange issues a third channel switching request from the external area communication channel to the internal area communication channel, and the mobile telephone exchange sends The received electric field level in the call signal or the incoming call response signal is compared with an internal area / external area location determination threshold predetermined for each of the radio base stations, and the received electric field level is compared with the internal area / external area location. If it is equal to or greater than the determination threshold, from the inside area communication channel group existing in the radio base station where the call signal or the termination response signal is reported. A first assignment is performed in which a desired unused call channel is assigned to a call of the mobile terminal that has transmitted the calling signal or the incoming call response signal, and the reception electric field level is determined to be an inner area / outer area. If the threshold value is less than the threshold value, a second assignment for allocating any one unused communication channel from the outside area communication channel group existing in the radio base station to the communication of the mobile terminal is performed, and Performing a first handoff with the external area communication channel device as a channel switching destination when a channel switching request from the external communication channel to the external area communication channel is received from the radio base station; When receiving a channel switching request from the wireless base station to the neighboring wireless base station communication channel from the wireless base station, A second handoff is performed by selecting an optimal communication channel as a channel switching destination candidate using the communication channel device of the base station, and a request for channel switching from the external area communication channel to the internal area communication channel is issued to the radio base station. There is provided a frequency reuse method characterized in that a third handoff is performed with the outside area communication channel device as a channel switching destination when received from a station.

[0018]

[0019]

EXAMPLES Next, will be described with reference to the drawings frequency reuse how the present invention.

FIGS. 2A and 2B are diagrams showing an example of the configuration of a radio base station service area and a communication channel device according to the present invention.

In the present invention, as shown in FIG. 2A, the radio base station service area 30 is obtained by changing the size of the radio base station service area 90 (FIG. 6A) which has conventionally been a single configuration. Instead, it is divided into a double concentric inner area 32 and an outer area 31.

Accordingly, as shown in FIG. 2B, a group of communication channel devices (communication channel devices 41,..., 4n).
4n (see FIG. 6)
Without changing the radio characteristics such as the transmission characteristics and the reception characteristics of (b)), they are divided into two groups, that is, the internal area communication channel device group 50 and the external area communication channel device group 51, and are managed.

This grouping is logically performed by a communication channel assignment control and a handoff control described later. In this grouping, each communication channel device group 5
The number of communication channel devices 0 and 51 is determined according to the expected traffic volume in each of the internal area and the external area.

On the other hand, with respect to a control channel device for performing call establishment control, the configuration of a conventional control channel device (not shown) is also implemented in the present invention.

Next, call connection control of the mobile telephone exchange and the radio base station in the radio base station service area and the communication channel device configuration will be described.

(A) Communication channel device allocation control The mobile telephone exchange station is caused to previously hold area grouping identification information indicating whether the communication channel device is for the inside area or the outside area for each communication channel device.

[0027] Also, when a mobile terminal transmits a signal on an uplink control channel to a mobile telephone exchange at a boundary area between an inner world area and an outer world area, it is predicted that the radio base station will receive the signal. The radio wave level threshold is held for each radio base station. This radio wave level threshold is
This is referred to as an external area location determination threshold.

The radio base station measures the received radio wave level when a transmission signal or an incoming response signal is received from the mobile terminal, and when the transmission signal or the incoming response signal is relayed to the mobile telephone exchange, the measurement result is obtained. Report including

When the mobile telephone exchange receives an outgoing signal or an incoming response signal from the radio base station, the mobile telephone exchange station receives the measured value of the received level of the outgoing signal or the incoming response signal and the internal area / area corresponding to the radio base station of the signal transmission source. The threshold value is compared with an external area location determination threshold value.

As a result, the mobile telephone exchange determines that the location of the mobile terminal is in the internal area if the received radio wave level measurement value ≧ the threshold for determining the location of the internal area / external area. If the measured radio wave level <the threshold value for determining the location of the inside area / outside area, it is determined that the location of the mobile terminal is in the outside area.

As a result of the area location determination, the mobile switching center selects any one unused communication channel device from the group of communication channel devices for the area where the mobile terminal will exist, and selects the mobile terminal and the mobile terminal. A communication channel assignment process is performed on the wireless base station device.

When the mobile telephone exchange performs the above-mentioned communication channel device assignment, the mobile terminal having a high received radio wave level from the radio base station, that is, a mobile terminal located near the radio base station, makes a call for the internal area. A channel device is allocated, and the reception radio wave level from the radio base station is not so strong. That is, a communication channel device for an outside area is allocated to a mobile terminal located far from the radio base station, and the provision of a communication service is started. You.

(B) Handoff control from the inner world area to the outer world area Handoff when the mobile terminal existing in the inner world area at the start of the call moves to the outer world area during a call is performed as follows. .

Each communication channel device is made to hold in advance group attribute information indicating which group of the inside area / outside area.

Thus, each communication channel device determines whether it should operate as a communication channel for the inside area or a communication channel for the outside area while providing the communication service.

Also, when the mobile terminal transmits a radio wave to the internal communication area uplink traffic channel at the boundary between the internal area and the external area, the radio wave level predicted to be received by the radio base station is set. The threshold value is determined in advance and held in each of the internal area communication channel devices. This radio wave level threshold is referred to as a boundary threshold level of the inside area / outside area.

The communication channel device constantly measures the level of the radio wave received from the mobile terminal during the provision of the communication service. When the result of the received radio wave level measurement on the internal area communication channel falls below the boundary threshold level between the internal area / external area, the internal area communication channel apparatus transmits an external communication signal to the mobile telephone exchange. A channel switching request signal is transmitted to the area communication channel device.

Upon receiving the channel switching request signal from the internal area communication channel device to the external area communication channel device, the mobile telephone exchange exchanges a call in the external area paired with the signaled internal area. An arbitrary unused communication channel device is selected as a channel switching destination from the channel device group, and handoff is performed.

(C) Handoff control from the outside world area to a nearby radio base station When a mobile terminal existing in the outside world area at the start of a call moves to a nearby radio base station service area during a call, the following handoff is performed. It is carried out as follows.

When a mobile terminal transmits a radio wave on the uplink communication channel for the external world area at a boundary area between the external area and the neighboring radio base station service area, the radio wave level predicted to be received by the radio base station is determined. The threshold value is determined in advance and held in each of the internal area communication channel devices. This radio wave level threshold is referred to as a boundary threshold level of the service area of the external area / neighboring radio base station.

If the measured result of the received radio wave level in the outside area communication channel is less than the boundary threshold level of the service area of the outside area / neighboring radio base station, the outside area communication channel device is switched to the mobile telephone. A channel switching request signal to a communication channel device of a nearby radio base station is transmitted to the station.

The mobile telephone exchange, which has received the channel switching request signal from the outside area communication channel device to the communication channel device of the neighboring radio base station, transmits the signal to the outside radio area and the service area adjacent to each other. The base station is set as a channel switching destination candidate, and each candidate radio base station is caused to measure a radio wave level received from the corresponding mobile terminal.

The mobile switching center further determines the most suitable channel switching destination radio base station by summing up the measurement results performed by each candidate radio base station, and determines the most suitable channel switching destination radio base station among the communication channel devices existing in the optimum radio base station. , An arbitrary unused communication channel device is selected as a channel switching destination, and handoff is executed.

(D) Handoff control from the outside area to the inside area When the mobile terminal that was present in the outside area at the time of starting the call moves to the inside area during the call, the handoff is performed as follows. .

When the mobile terminal transmits a radio wave to the external area uplink traffic channel at the boundary area between the internal area and the external area, the radio level threshold value that is predicted to be received by the radio base station is set to It is determined in advance and stored in each external area communication channel device. This radio wave level threshold is referred to as a boundary threshold level between the outside area and the inside area.

If the measured result of the received radio wave level in the outside area communication channel is equal to or higher than the above-mentioned outside area / inside area boundary threshold level, the outside area communication channel apparatus sends a signal to the mobile telephone exchange. A channel switching request signal is transmitted to the internal area communication channel device.

Upon receiving the channel switching request signal from the external area communication channel device to the internal area communication channel device, the mobile telephone exchange exchanges a call in the internal area paired with the external area for which the signal was reported. An arbitrary unused communication channel device is selected as a channel switching destination from the channel device group, and handoff is performed.

The above-described mobile telephone exchange and the call connection control and the handoff control by the radio base station can limit the service area of the inner bounds areas for call channel group, described next frequency reuse how Can be implemented.

[0049] Figure 1 is a diagram for explaining an example of frequency reuse how the present invention.

In FIG. 1, the service areas of the radio base station A60, the radio base station B70 and the radio base station C80 are divided into double concentric inner areas 61, 71, 81 and outer areas 62, 72, 82. Has been split.

Here, it is assumed that the external area radius is the smallest radius that can be achieved by the conventional frequency reuse technology. Also, between the radio base station A60 and the radio base station B70,
Conventional frequency reuse is performed, and worst case C /
The I ratio is the worst C / I ratio (L
A, LB).

Assuming that the radio wave level 63 reached by the radio base station A60 at the boundary between the inside area 61 and the outside area 62 of the radio base station A60 is LA (S), only the communication channel apparatus group for the inside area is used. Frequency reuse can be performed with the worst C / I ratio where the arrival wave level LA (S) is set to a desired wave level.

The arriving radio wave level LA (S) becomes higher than the level LA by an amount closer to the radio base station A60, and the interference wave level becomes higher by the higher the desired wave level.
That is, frequency reuse can be performed at a wireless base station closer to the wireless base station A60 than the wireless base station B70.

For example, a radio base station C80 exists between a radio base station A60 and a radio base station B70, for which frequency reuse has been performed by the conventional technique, and an inner area 61 and an outer area 62 of the radio base station A60. Base station C to the boundary area of
Assuming that the arrival radio wave level of 80 is LC, the worst C / I ratio (LA (S), LC) is the worst C / I ratio (LA,
LB) or more, the internal area communication channel group of the radio base station A60 performs frequency reuse with any of the internal area 81 and the external area 82 communication channel group of the radio base station C80. be able to.

[0055] Thus, as can be seen from FIG. 3 showing an example of the result of applying the frequency reuse how the present invention, according to the present invention, the frequency reuse efficiency is significantly improved.

In FIG. 3, the hatched portions are the outside area communication channels that have a frequency reuse relationship, and the lattice hatched portions are the inside area communication channels that have a frequency reuse relationship. is there.

[0057]

As described above, according to the present invention, the service area of the radio base station can be logically changed according to the expected traffic without increasing the number of radio base stations and without increasing the number of facilities of the radio base station. By dividing into the inner world area and the outer world area, the frequency reuse efficiency can be improved.

Further, since no additional equipment is required, the present invention can improve the frequency reuse efficiency at lower cost and without any construction time as compared with the conventional technology.

[Brief description of the drawings]

It is a diagram for explaining an example of frequency reuse how of the present invention; FIG.

FIGS. 2A and 2B are diagrams showing an example of the configuration of a radio base station service area and a communication channel device according to the present invention.

3 is a diagram showing an example of a result of applying the frequency reuse how the present invention.

FIG. 4 is a system configuration diagram of an example of a general cellular mobile communication system.

FIG. 5 is a diagram for explaining a conventional frequency reuse technique.

FIGS. 6A and 6B are diagrams showing an example of a configuration of a single service area, random traffic channel device in a conventional mobile communication system.

[Explanation of symbols]

Reference Signs List 1 mobile telephone exchange 2, ..., 8 radio base station 9 mobile terminal 10, 60 radio base station A 11, 21, 30, 90 service area 12, 22, 63, 73, 83 radio level 20, 70 radio base Station B 31, 62, 72, 82 External area 32, 61, 71, 81 Internal area 40 Antenna 41, 42, 43, ..., 4 (n-1), 4n Communication channel device 50 Communication channel device for internal area Group 51 Communication channel device group for outside area 80 Radio base station C

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04Q ^7/ 00-7/36

Claims (1)

(57) [Claims] 1. A wireless base station having a control channel device for establishing a mobile terminal call and a plurality of traffic channel devices for providing a speech service to the mobile terminal, and a plurality of the radio base stations are connected. In a mobile communication system comprising a mobile telephone exchange to be performed, the service area of the radio base station is logically divided into a concentric inner area and an outer area in accordance with an expected traffic, The radio base station includes two communication channel device groups, a communication channel device group for the inner world area and a communication channel device group for the outer world area,
When receiving a call signal or an incoming call response signal from the mobile terminal, measure a reception electric field level and report the call signal or the incoming call response signal including the measurement result to the mobile telephone switching center, The mobile telephone exchange is performed when an electric field level received from the mobile terminal becomes less than a predetermined threshold value of a boundary level between the inside area and the outside area while the area communication channel is providing the communication service. Making a first channel switching request from the inside area communication channel to the outside area communication channel to the station, and receiving the electric field from the mobile terminal while the outside area communication channel provides a communication service. When the level falls below a predetermined threshold value of the boundary between the outside area and the service area of the neighboring radio base station, the mobile telephone exchange is performed. Communication channel for outside area for the
Makes a second channel switching request to the neighboring radio base station from the outside area / inside field where the level of the received electric field from the mobile terminal is predetermined while providing the outside area call service. When the area boundary level threshold value or more, a third channel switching request from the external area communication channel to the internal area communication channel to the mobile telephone exchange,
The mobile telephone exchange compares the received electric field level in the outgoing call signal or the incoming call response signal with an internal area / external area location determination threshold predetermined for each of the radio base stations. Is greater than or equal to the inside area / outside area location determination threshold, any one of the inside area communication channel groups existing in the radio base station for which the call signal or the termination response signal has been reported. Assigning an unused call channel to a call of the mobile terminal that has transmitted the call signal or the call response signal;
If the received electric field level is less than the threshold value for determining the location of the inside area / outside area, any one unused communication channel is selected from the outside area communication channel group existing in the radio base station. Performing a second assignment to be allocated to a call of the mobile terminal, and receiving a channel switching request from the internal area communication channel to the external area communication channel from the radio base station; Performing a first handoff with the device as a channel switching destination, and receiving a channel switching request from the outside area communication channel to the neighboring wireless base station communication channel from the wireless base station when the communication channel of the nearby wireless base station is received. A second handoff is performed by selecting an optimal communication channel with the device as a channel switching destination candidate; When receiving a channel switching request from the rear communication channel to the internal area communication channel from the radio base station, a third handoff is performed using the external area communication channel device as a channel switching destination. Frequency reuse method.