JPH0937327A - Method for controlling handover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of service by measuring the level of a received input or the quality of communication, detecting its variation inclination and performing a handover to a prescrubed radio zone based upon each detected result. SOLUTION: It is supposed that the radio zones 22, 23 of radio base stations 12, 13 are superposed to the end of the radio zone 21 of a mobile station 1 where a receiving level or communication quality from a radio base station 11 is less than a prescribed value. When a receiving level or communication quality from the station 12 is in falling and that from the station 13 is rising, communication is performed by handover from the zone 21 to the zone 23. When the receiving level or communication quality from both the stations 12, 13 is rising but that from the station 13 is lower and when the receiving level or communication quality from both the stations 12, 13 is falling but that from the station 13 is higher, communication is performed by handover from the zone 21 to the zone 23 in both the cases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handover control method in a mobile communication system, in which when a mobile station in communication moves to another wireless zone, the communication channel of the wireless zone of the moving destination is captured and communication is continued. Regarding

[0002]

2. Description of the Related Art FIG. 4 shows an outline of handover control in a mobile communication system. In the figure, a radio base station 1
When moving from the wireless zone 21 of the mobile station 1 to the wireless zone 22 of the adjacent wireless base station 12, the mobile station 1 communicates with the mobile station 1 by handing over at the zone end of the wireless zone 21 to continue communication. The call channel of the base station 12 needs to be acquired.

FIG. 5 shows an example of conventional handover control. As shown in FIG. 5 (1), when there are a plurality of radio base stations in the traveling direction of the mobile station 1 and a plurality of radio zones 22 and 23 overlap at the zone edge of the radio zone 21, the mobile station 1 Select a handover destination. As shown in Fig. 5 (2), the procedure is to measure the received input level or communication quality (bit error rate, frame error rate, etc.) from the wireless base station 11 during communication, and at least one of them is below a predetermined value. Then, the reception input level or communication quality of the control signal transmitted from the other radio base stations 12 and 13 is measured. In the conventional handover control, of the reception input levels or communication qualities from a plurality of radio base stations, the radio base station having the highest reception input level or communication quality (here, 12) is selected, and is selected as the communication channel of the radio zone. It was supposed to switch and continue communication.

[0004]

By the way, radio base stations are often arranged in high density in an urban area, and a plurality of radio zones may overlap at the zone edge. In the conventional handover control method, when a mobile station in communication moves to another radio zone, a radio base station having the highest control signal reception input level or communication quality is selected. Therefore, as shown in FIG. 5, the handover operation is activated one after another, and the quality of service may be deteriorated due to a momentary interruption (a silent or noise state for a short time) that occurs during the handover.

FIG. 6 shows the relationship between the moving distance from the base point to the measurement point and the average deterioration rate according to the conventional handover control method. Here, the wireless zone arrangement shown in FIG. 5 (1) is used as a model, the radius R of each wireless zone is 250 m, and the distances d12 and d23 between the zones are 200 m. The mobile speed of the mobile station is 80
m / min, and instantaneous interruption time due to handover is 2 seconds / time. Further, it is assumed that the handover is performed to the wireless zone having the highest reception input level, and the base point is the center of the wireless zone 21.

As shown in the figure, when the handover is performed at the zone edge of the wireless zone 21, the service quality is temporarily deteriorated and then the service quality is recovered. However, the service quality is greatly deteriorated again at the next handover. However, the average deterioration rate with respect to the movement history of the mobile station increases. This average deterioration rate Fa is in the case of a linear zone.

[0007]

[Equation 1]

[0008] Where F is the deterioration rate around the zone,

[0009]

[Equation 2]

It is represented by However, mr indicates the required CNR margin at the point of interest around the zone, and σ indicates the standard deviation (σ ₀ = 10σ loge [dB]). Further, in the conventional handover control method, since the handover operation is frequently activated, there is a problem that the traffic of the control signal also increases at the same time. It is an object of the present invention to provide a handover control method that can reduce the number of handovers as much as possible and can suppress deterioration of service quality and increase of control signal traffic.

[0011]

According to the handover control method of the present invention, when there are a plurality of wireless zones to be handed over, the reception input level or communication quality from each wireless base station tends to change (there is an increasing tendency). Or if the handover destination is determined accordingly.

That is, when there are a plurality of wireless zones as handover targets, (1) handover to a wireless zone of a wireless base station whose reception input level or communication quality tends to increase, and (2) wireless which tends to increase. If there are multiple base station wireless zones, handover to the lowest wireless zone where the reception input level or communication quality is at or above a specified value, and (3) if there is no rising wireless base station wireless zone, Handover is performed to a wireless zone having the highest reception level or communication quality.

[0013]

1 shows an embodiment of a handover control method of the present invention. Here, at the zone edge of the wireless zone 21 in which the mobile station 1 receives the input level from the radio base station 11 or the communication quality is below a predetermined value, the radio base station 1 whose receive input level or communication quality exceeds the predetermined value.
It is assumed that the wireless zones 22 and 23 of 2 and 13 overlap.

In the case shown in (1), the reception input level from the radio base station 12 or the communication quality tends to decrease,
The reception input level or communication quality from the wireless base station 13 tends to increase. In this case, the wireless zone 21 is handed over to the wireless zone 23. In the case shown in (2), the reception input level from the radio base stations 12 and 13 or the communication quality tends to increase, but the reception input level from the radio base station 13 or the communication quality is low. In this case, the wireless zone 21 is handed over to the wireless zone 23.

In the case shown in (3), the radio base station 12,
The reception input level or communication quality from the wireless base station 13 tends to decrease, but the reception input level or communication quality from the wireless base station 13 is high. In this case, the wireless zone 21 is handed over to the wireless zone 23.

[0016]

FIG. 2 shows an operation flow of the handover control method of the present invention. In the figure, the reception input level or communication quality from the wireless base station during communication is measured, and it is detected that at least one of them is below a predetermined value. In other words, when the mobile station detects that the zone edge is approaching, it measures the reception input level or communication quality of the control signal sent from another radio base station, and the radio base station indicates that it is above a predetermined value. Detecting the fluctuation tendency of the reception input level or the communication quality. Next, a radio base station whose reception input level or communication quality fluctuation tendency tends to increase is selected, and if there is one radio base station, handover is performed to that radio zone. Further, if there are a plurality of radio base stations that are on the rise, handover is performed to the radio zone where the reception input level or communication quality is equal to or higher than a predetermined value and is lowest. If there is no rising radio base station, handover to the radio zone with the highest reception level or communication quality is performed.

FIG. 3 shows the relationship between the moving distance from the base point to the measurement point and the average deterioration rate according to the handover control method of the present invention. Here, it is assumed that the same simulation conditions as shown in FIG. 6 are set, and the handover is performed to the wireless zone of the wireless base station in which the reception input level tends to increase. As shown in the figure, it can be seen that the average deterioration rate with respect to the movement history of the mobile station is greatly reduced by reducing the number of handovers.

[0018]

As described above, according to the handover control method of the present invention, when there are a plurality of wireless zones to be handed over, the reception input level or communication quality from each wireless base station tends to increase. The wireless zone of the base station determines the handover destination. As a result, the distance that can be moved within the same radio zone is increased and the number of handovers is reduced, so that it is possible to improve quality of service and prevent an increase in traffic of control signals.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a handover control method of the present invention.

FIG. 2 is a diagram showing an operation flow of a handover control method of the present invention.

FIG. 3 is a diagram showing a relationship between a moving distance from a base point to a measurement point and an average deterioration rate according to the method of the present invention.

FIG. 4 is a diagram showing an outline of handover control in a mobile communication system.

FIG. 5 is a diagram showing an example of conventional handover control.

FIG. 6 is a diagram showing a relationship between a moving distance from a base point to a measurement point and an average deterioration rate according to a conventional method.

[Explanation of symbols]

 1 Mobile station 11, 12, 13 Radio base station 21, 22, 23 Radio zone

Claims (1)

[Claims] 1. A mobile station communicating with a radio base station moves to a zone end of the radio zone, and at least one of a reception input level and communication quality from the radio base station becomes a predetermined value or less, In a handover control method for continuing communication by switching to a communication channel of another radio zone, when at least one of a reception input level and a communication quality from the radio base station with which the mobile station is in communication becomes a predetermined value or less, The reception input level or communication quality from another radio base station is measured to detect its fluctuation tendency, and the radio zone of the radio base station in which the fluctuation tendency of the reception input level or communication quality tends to increase is selected and increased. If there is only one radio zone for a radio base station that has a tendency, handover to that radio zone is performed, and if there are multiple radio zones for a radio base station that has an upward trend Handover to the wireless zone having the lowest received input level or communication quality at a predetermined value or higher, and to the wireless zone having the highest received level or communication quality when there is no wireless zone of an upwardly increasing wireless base station. And a handover control method.