JP2939115B2 - Mobile communication handover method, mobile station apparatus and base station apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a code division multiple access (hereinafter abbreviated as CDMA) using a spread spectrum code.
TECHNICAL FIELD The present invention relates to a mobile communication handover method, a mobile station apparatus, and a base station apparatus in a mobile communication system of a mobile communication system.

[0002]

2. Description of the Related Art In a CDMA mobile communication system using spread spectrum codes, a service area is divided into a plurality of unit areas, cells, and one base station is provided in each cell. A mobile station existing in a certain cell communicates with a base station of the cell via a radio line, and communicates with another mobile station or a telephone or the like from the base station via another radio line or a communication line. It has become.

In a CDMA mobile communication system, the base stations of each cell are assigned different unique spreading codes of the same frequency, spread with the spreading codes, and stop at a fixed transmission power without performing transmission power control. The tree channel is constantly transmitted. For example, as shown in FIG. 5, a plurality of cells 1, 1 provided in a service area
2, 3,... Respectively have base stations B1, B2, B3,
Are provided, and each base station B1, B2, B3,.
Have different spreading codes C1, C2, C3,.
Is assigned. Then, the base station of each cell always transmits the perch channel spread with the assigned spreading code.

As shown in FIG. 5, a mobile station M1 communicating with its base station B1 via a radio line 91 in a cell 1 moves in the direction shown by an arrow 92, and In the case of moving within 2 or 3, the mobile station M1
Since the communication level with the base station B1 during communication gradually decreases, the mobile station M1 performs communication with the base station B1 in cell 2
It is necessary to switch to communication with the base station B2 of the cell 3, the base station B3 of the cell 3, and the like.

Therefore, in order to perform such switching, that is, handover, in a conventional system,
The mobile station receives the spreading code of the neighboring cell from the communicating base station, sequentially scans the reception level of the pilot channel or the perch channel spread with the spreading code,
A cell whose reception level is equal to or higher than a predetermined threshold is selected, a communication channel of the selected cell is newly connected, and a simultaneous communication mode is established with the base station of the cell,
The reception level from the cell currently communicating is measured, and when the reception level falls below a predetermined low threshold value, an operation of disconnecting the communication line with the cell is performed.

[0006]

By the way, in the mobile communication system of the CDMA system, the frequency is the same in all cells, and the frequency divided by a spreading code is used as a carrier. Then, each cell is modulated at the same frequency, spread with a unique spreading code assigned differently, and constantly transmits a perch channel having a fixed transmission power without performing transmission power control, and this perch channel is referred to as a cell. In addition to being used for determination, ordinary communication channels and the like also use spreading codes in the same way.Each spreading code is not independent of each other but has a cross-correlation, which adds to the reception level as noise. Have been.

[0007] The noise added to the reception level as described above is, specifically, noise due to cross-correlation from other spreading codes, and the spreading codes are all different within one service area including a plurality of cells. Since it is repeatedly used outside the service area, the repeated use of its own spreading code includes noise and thermal noise.

FIG. 6 shows the characteristics when, for example, the correlation is applied to a certain spread code C1 in an attempt to synchronize, the reception level of the spread code C1 is indicated by oblique lines as shown in FIG. The noise shown above, that is, the spreading code C1, is raised and raised by noise due to mutual interference from other spreading codes C2, C3,...

Therefore, as shown in FIG. 6B, even if the reception level is measured in the same way, the noise indicated by the oblique line is added to the reception level shown on the right side considerably more than the reception level on the left side. Therefore, the communication quality of the line on which this reception level is selected is considerably deteriorated even though the reception level is the same.

That is, in the above-described conventional method, a reception level including noise such as an interference level is measured, and a cell to be communicated only at the reception level is selected.
Since the noise due to cross-correlation and the like is ignored, even if a cell with a high reception level is selected, noise such as a considerably large interference level is actually added to the reception level. If only a cell is selected, there is a problem that communication quality is considerably deteriorated.

Further, in the above-mentioned conventional method, a cell whose reception level is simply higher than a predetermined threshold value is selected from neighboring cells. In some cases, a cell that requires channel transmission power is selected, and performing communication with a cell that requires such a relatively large communication channel transmission power causes a problem of interfering with communication with other cells. .

Further, in a process of connecting cells having a reception level equal to or higher than a predetermined threshold value and disconnecting the cells when the reception level drops below a predetermined low threshold value, many cells overlap each other. In an area where cell connection and disconnection, that is, handover flutter occurs relatively frequently, control for this becomes difficult,
There is a problem that the load on the control device increases.

The present invention has been made in view of the above,
The purpose is not only to improve the communication quality by selecting a cell having a good carrier-to-noise ratio, but also to reduce the influence of interference on other cells, thereby reducing the subscriber capacity. It is an object of the present invention to provide a mobile communication handover method, a mobile station apparatus, and a base station apparatus, which can increase the number of mobile stations and can further reduce the load on control by suppressing handover flutter.

[0014]

In order to achieve the above object, a mobile communication handover method according to the present invention provides a base station in each of a plurality of cells, each base station being modulated at the same frequency and different from each other. A mobile communication handover method in a code division multiple access mobile communication system which constantly transmits a perch channel having a constant transmission power which is spread with an assigned unique spreading code and does not perform transmission power control, comprising: Measures the reception level of each perch channel of the neighboring cells during communication, and measures the carrier-to-noise ratio at a reception level exceeding a first predetermined reception level among the reception levels. Is greater than a first predetermined carrier-to-noise ratio, and
A cell in which the level difference between the reception level exceeding the reception level exceeding the maximum reception level and the maximum reception level is smaller than the first predetermined level difference is newly connected to the mobile station to enter the simultaneous communication mode. Is smaller than a second predetermined carrier-to-noise ratio that is smaller than the first predetermined carrier-to-noise ratio, or the reception level during simultaneous communication is the first level. When the second reception level is lower than the second predetermined reception level that is lower than the predetermined reception level, or when the level difference between the reception level during simultaneous communication and the maximum reception level is larger than the first predetermined level difference, In this case, when the level difference becomes larger than the predetermined level difference, the line for the cell is disconnected.

Further, in the mobile communication handover method of the present invention, in the step of measuring the reception level, a spreading code of a neighboring cell is notified from a base station which is currently communicating, and the neighboring cell is notified using the notified spreading code. The point is to measure the reception level of each perch channel.

Further, in the mobile station apparatus according to the present invention, a base station is provided in each of a plurality of cells, each base station is modulated at the same frequency, spread with a unique spreading code assigned differently, and transmitted. A mobile station device in a mobile communication system of a code division multiple access system that constantly transmits a perch channel having a constant transmission power without performing power control,
Measuring means for measuring the reception level of each perch channel of the peripheral cell during communication, and measuring a carrier-to-noise ratio at a reception level exceeding a first predetermined reception level among the reception levels measured by the measurement means The carrier-to-noise ratio is larger than a first predetermined carrier-to-noise ratio, and a level difference between a reception level exceeding the first reception level and a maximum reception level is larger than a first predetermined level difference. First detecting means for detecting a small cell, and a second predetermined carrier-to-noise ratio wherein the carrier-to-noise ratio of the reception level of the plurality of cells during simultaneous communication is smaller than the first predetermined carrier-to-noise ratio Cell, or a cell whose reception level during simultaneous communication is smaller than a second predetermined reception level that is smaller than the first predetermined reception level, or a cell whose simultaneous reception is lower than a second predetermined reception level. A second detecting means for detecting a cell in which a level difference between the signal level and the maximum reception level is larger than a second predetermined level difference which is larger than the first predetermined level difference. I do.

In the mobile station apparatus according to the present invention, as the measuring means, a spreading code of a neighboring cell is notified from a base station with which communication is currently being performed, and using the notified spreading code, a perch channel of each of the neighboring cells is used. The gist of the invention is to have means for measuring the reception level.

Further, the mobile station apparatus of the present invention further comprises simultaneous communication means for newly connecting a cell detected by the first detection means to enter a simultaneous communication mode with the cell.

Further, the mobile station apparatus of the present invention further comprises a notifying means for notifying the cell detected by the first detecting means to the base station, and the base station receiving the notification newly adds the cell. The gist of the present invention is to perform control to connect to a mobile station and enter a simultaneous communication mode with the cell.

Further, the mobile station device of the present invention further comprises a disconnecting means for disconnecting a line for the cell detected by the second detecting means.

Further, the mobile station apparatus of the present invention further comprises a notifying means for notifying a cell detected by the second detecting means to the base station, and the base station receiving the notification changes a line for the cell. The gist is to cut.

In the base station apparatus of the present invention, a base station is provided in each of a plurality of cells, each base station is modulated at the same frequency, spread with a unique spreading code assigned differently, and transmitted power control is performed. A base station apparatus in a code division multiple access mobile communication system that constantly transmits a fixed perch channel having a constant transmission power, and receives each perch channel of a neighboring cell during communication with the mobile station. A first receiving means for causing the mobile station to measure the level, transmitting the measurement result, and receiving the transmitted measurement result; and a first predetermined level among the reception levels received by the first receiving means. The mobile station measures the carrier-to-noise ratio for a reception level exceeding the reception level of the mobile station, transmits the measured carrier-to-noise ratio, and receives the transmitted carrier-to-noise ratio. And A-to-noise ratio receiving unit, a carrier-to-noise ratio received by the carrier-to-noise ratio receiving means first
Detecting a cell which is larger than a predetermined carrier-to-noise ratio and has a level difference between a reception level exceeding the first predetermined reception level and a maximum reception level smaller than the first predetermined level difference. Means, a second receiving means for causing the mobile station to measure a carrier-to-noise ratio of a reception level of a plurality of cells performing simultaneous communication, transmitting the measurement result, and receiving the transmitted measurement result; A cell in which the carrier-to-noise ratio of the reception level of the plurality of cells in simultaneous communication received by the second receiving means is smaller than a second carrier-to-noise ratio smaller than the first predetermined carrier-to-noise ratio, or A cell in which the reception level during simultaneous communication is lower than the second predetermined reception level that is lower than the first predetermined reception level, or the level difference between the reception level during simultaneous communication and the maximum reception level is earlier. Further comprising a second detection means for detecting a cell becomes greater than a second predetermined level difference greater than the first predetermined level difference and gist.

Further, the base station apparatus of the present invention, as the first receiving means, notifies a mobile station of a spreading code of a neighboring cell, and the mobile station uses each of the notified spreading codes to notify each of the neighboring cells. The gist of the present invention is to have a measuring means for measuring the reception level of the perch channel.

Further, the gist of the present invention is that the base station apparatus of the present invention further comprises simultaneous communication means for newly connecting a cell detected by the first detection means to the mobile station and entering a simultaneous communication mode. .

The base station apparatus according to the present invention further comprises a notifying means for notifying the mobile station of the cell detected by the first detecting means, and the mobile station receiving the notification newly connects the cell. The point is to control to enter the simultaneous communication mode with the cell.

Further, the gist of the invention is that the base station apparatus of the present invention further comprises a disconnecting means for disconnecting the line to the cell detected by the second detecting means.

[0027] The base station apparatus of the present invention further comprises a notifying means for notifying the mobile station of the cell detected by the second detecting means, and the mobile station receiving the notification disconnects the line for the cell. That is the gist.

[0028]

In the mobile communication handover method according to the present invention, the mobile station measures the carrier-to-noise ratio at a reception level exceeding a first predetermined reception level among the reception levels of the perch channels of the neighboring cells measured during communication. And said carrier to noise ratio is greater than a first predetermined carrier to noise ratio;
And a cell in which the level difference between the reception level exceeding the first reception level and the maximum reception level is smaller than the first predetermined level difference is newly connected to the mobile station to enter the simultaneous communication mode,
When the carrier-to-noise ratio of the reception levels of the plurality of cells during simultaneous communication is smaller than a second predetermined carrier-to-noise ratio that is smaller than the first predetermined carrier-to-noise ratio, or the reception level during simultaneous communication is When the reception level is lower than the second predetermined reception level which is lower than the first predetermined reception level, or the level difference between the reception level during simultaneous communication and the maximum reception level is larger than the first predetermined level difference. When the difference becomes larger than the second predetermined level difference, the line for the cell is disconnected.

Further, in the mobile communication handover method of the present invention, in the above, the spreading code of the neighboring cell is notified from the communicating base station, and the received level of the perch channel of the neighboring cell is measured using the spreading code. .

Further, the mobile station apparatus of the present invention measures a carrier-to-noise ratio at a reception level exceeding a first predetermined reception level among the reception levels of the perch channels of the neighboring cells measured during communication, A cell whose carrier-to-noise ratio is larger than a first predetermined carrier-to-noise ratio and whose level difference between the reception level exceeding the first reception level and the maximum reception level is smaller than the first predetermined level difference A cell in which the carrier-to-noise ratio of the detected levels of the plurality of cells during simultaneous communication is smaller than a second predetermined carrier-to-noise ratio that is smaller than the first predetermined carrier-to-noise ratio;
Alternatively, a cell whose reception level during simultaneous communication is lower than a second predetermined reception level that is lower than the first predetermined reception level, or a level difference between the reception level during simultaneous communication and the maximum reception level is the first level The cell which has become larger than the second predetermined level difference larger than the second predetermined level difference is detected.

In the mobile station apparatus according to the present invention,
The spreading code of the neighboring cell is notified from the base station in communication, and the received level of the perch channel of the neighboring cell is measured using the spreading code.

Further, in the mobile station device of the present invention, the first
The cell newly detected by the detecting means is newly connected to enter the simultaneous communication mode with the cell.

Further, in the mobile station device of the present invention, the first station
Notify the cell detected by the detecting means of the base station,
The base station that has received the notification controls the cell so as to newly connect the cell to the mobile station and enter the simultaneous communication mode with the cell.

In the mobile station apparatus according to the present invention, the second station
The line for the cell detected by the detecting means is disconnected.

Further, in the mobile station apparatus of the present invention, the second station
The cell detected by the detecting means is notified to the base station, and the base station receiving the notification disconnects the line for the cell.

In the base station apparatus of the present invention, the mobile station measures the reception level of the perch channel of the neighboring cell during communication with the mobile station, and the reception level exceeding the first predetermined reception level among the reception levels. Causing the mobile station to measure the carrier-to-noise ratio for the level, wherein the carrier-to-noise ratio is greater than a first predetermined carrier-to-noise ratio and exceeds a first predetermined reception level; Detecting cells whose difference is less than a first predetermined level difference;
The mobile station measures the carrier-to-noise ratio of the reception level of a plurality of cells during simultaneous communication, and the carrier-to-noise ratio becomes smaller than a second carrier-to-noise ratio smaller than a first predetermined carrier-to-noise ratio. Cell, or a cell whose reception level during simultaneous communication is smaller than a second predetermined reception level that is smaller than the first predetermined reception level, or a level difference between the reception level during simultaneous communication and the maximum reception level Is the first
The cell which has become larger than the second predetermined level difference larger than the second predetermined level difference is detected.

Further, in the base station apparatus of the present invention, in the above, the spreading code of the neighboring cell is notified to the mobile station, and the mobile station uses the notified spreading code to adjust the reception level of the perch channel of the neighboring cell. Measure.

Further, in the base station apparatus according to the present invention, the first station
The cell detected by the detecting means is newly connected to the mobile station to enter the simultaneous communication mode.

In the base station apparatus according to the present invention, the cell detected by the first detecting means is notified to the mobile station, and the mobile station receiving the notification newly connects the cell and performs simultaneous communication with the cell. Control to enter the mode.

Further, in the base station apparatus according to the present invention, the second station
The line for the cell detected by the detecting means is disconnected.

In the base station apparatus of the present invention, the cell detected by the second detecting means is notified to the mobile station, and the mobile station receiving the notification disconnects the line for the cell.

[0042]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a processing procedure of a mobile communication handover method according to one embodiment of the present invention. The mobile communication handover method shown in FIG. 1 performs a handover process required when a mobile station moves from a currently communicating cell to another cell in a CDMA mobile communication system using a spread spectrum code. .

In the mobile communication handover method of the present embodiment, to select a cell to communicate with, a perch channel constantly transmitted by the base station of each cell, that is, modulated by the same frequency, and assigned differently. The reception level of a perch channel that is spread with a unique spreading code and that does not perform transmission power control and has a constant transmission power is measured, and under the condition that this reception level is higher than a first predetermined reception level R1, As described with reference to FIG. 6, the reception level of the perch channel received from each cell has increased due to noise due to mutual interference and the like. Noise due to cross-correlation from other spreading codes, noise due to repeated use of its own spreading code, and thermal noise. Etc. Considering Noise including the ratio of the noise and the carrier, or carrier-to-noise ratio (hereinafter,
CNR), and selects a cell whose CNR is larger than a first predetermined CNR1 and whose level difference is smaller than a predetermined level difference D1, and enters a simultaneous communication mode with this cell. Further, under a predetermined condition, the line with the cell under communication is disconnected first, and a handover is performed.

As described above, in consideration of the CNR in addition to the reception level, for example, as shown in FIG. 6B, even the left and right signals having the same reception level have little noise due to mutual interference indicated by oblique lines. Will be selected. That is, in FIG. 6B, the C on the left side signal with small noise due to mutual interference and the like indicated by the hatched portion is shown.
Since the NR is larger than the CNR of the right signal having a large noise, the cell of the left signal is selected.

FIG. 2 is a block diagram showing the configurations of the mobile station transmitting / receiving section 10 and the base station 20 that implement the mobile communication handover method of FIG. The mobile station transmitting / receiving unit 10 includes an antenna 11 for communicating with the base station 20,
1, a transmission circuit unit 13 and a reception circuit unit 14 connected via a transmission / reception switch 12, a control unit 15 connected to the transmission circuit unit 13 and the reception circuit unit 14, and a reception circuit unit 1.
4 has a reception level / interference level detection unit 16 for measuring the reception level of the perch channel received in step 4 and an interference level included in the reception level and corresponding to noise due to the above-described mutual interference. The control unit 15 controls the reception level
The CNR and the level difference D are calculated based on the reception level and the interference level detected by the interference level detection unit 16.

The reception level / interference level detector 16 comprises a correlation detector 17, a level detector 18, and an interference detector 19.
In the interference level detector 16, the perch channel from the base station of each cell is transmitted to the antenna 11 and the duplexer 1
The output signal received by the receiving circuit unit 14 via the second circuit 2 is supplied to the correlation detector 17. The correlation detector 17 includes a controller 15
The correlation detection with the level monitoring spreading code of the perch channel designated by the above is sequentially performed, and the output signal of the receiving circuit unit 14 is despread with the corresponding level monitoring spreading code at the timing obtained by the correlation detector 17. The power spectrum obtained by this despreading is supplied to a level detector 18 and an interference detector 19, where the measurement of the reception level and the measurement of the interference level are performed. The obtained reception level and interference level are supplied to the control unit 15, and the control unit 15 calculates a carrier-to-noise ratio, that is, a CNR and a level difference D from the reception level and the interference level. This CNR is used in the processing of the flowchart shown in FIG. 1 described later, and an optimal cell is selected based on the CNR.

In the base station 20 shown in FIG.
The base station amplifier 26 to which the antenna 21 for communicating with the mobile station transmitting / receiving unit 10 is connected is connected to a modulation / demodulation device 27, which is connected to a spreading device 28. The modulation / demodulation device 27 has a control bus control 3
0, a supervisory control device 31, a 2M / 1.5M interface device 32, a base station control device 33, and a timing supply device 34.

The transmission data for the perch channel generated in the base station 20 constructed as described above is spread by a spreading code for level monitoring in a spreading device 28, and further added to a carrier signal by a modulation / demodulation device 27. The modulation output signal of the modem 27 is transmitted to the base station amplifier 26.
And transmitted as a radio wave from the antenna 21. In FIG. 2, the base station 20 shows only the circuit configuration of the transmission system and does not show the circuit configuration of the reception system. However, since the circuit configuration of the reception system is an ordinary well-known one, it is not shown. .

Next, the processing procedure of the mobile communication handover method will be described with reference to the flowchart shown in FIG.

In FIG. 1, a mobile station is notified of a spreading code of a neighboring cell from a communicating base station, sequentially receives a perch channel of a neighboring cell using the spreading code, and measures a reception level R thereof ( Step 110). Specifically, the spreading code of the perch channel from the base station is despread with the spreading code, and the reception level R is measured.

Then, of the measured reception levels R, the reception level R exceeding the first predetermined reception level R1
And the CNR 'is calculated, and the level difference D' between the reception level R exceeding the first predetermined reception level R1 and the maximum reception level during communication is calculated (step 120).

Then, a cell whose measured CNR 'is larger than the first predetermined CNR1 and whose calculated level difference D' is smaller than the first predetermined level difference D1 is newly connected, and the simultaneous communication mode is set. Enter (step 130).

The above relationship will be described with reference to FIG. 3 (a), (b), (c) and (d) show the positional relationship between the cell and the mobile station when the mobile station MS moves from the cell A to the cell B, the reception level, the CNR, and It is explanatory drawing which shows a level difference. As shown in FIG. 3A, a mobile station M existing in one cell A of two adjacent cells A and B having base stations BSa and BSb, respectively.
If S is moving right from cell A to cell B along dotted line 93 as shown by arrow 91, mobile station M
As S moves, the reception level R of the perch channel received from the base stations BSa and BSb changes as shown in FIG. That is, FIG. 3B shows the reception level R on the vertical axis and the mobile station MS along the dotted line 93 on the horizontal axis.
In FIG. 3B, Ra is the mobile station MS.
Indicates the reception level of the perch channel received from the base station BSa, and this reception level Ra becomes maximum when the mobile station MS comes closest to the base station BSa, and the base station BS
It becomes smaller as it moves away from a. Rb similarly indicates the reception level of the perch channel received by the mobile station MS from the base station BSb.

First, when the mobile station MS existing in the cell A and communicating with the base station BSa moves along the dotted line 93 as indicated by an arrow 91, the mobile station MS is notified from the base station BSa. It is constantly searching to receive a perch channel constantly transmitted from the base station BSb of the cell B which is a neighboring cell. When the mobile station MS is near the center of the cell A, the mobile station MS cannot yet receive the perch channel from the base station BSb, but the mobile station MS is located near the periphery away from the center of the cell A. At P10, as indicated by Rb in FIG.
The perch channel from b can be received. However, the reception level Rb at this position P10 is
In (b), the reception level is equal to or lower than the first predetermined reception level R1 indicated by a dotted line. When the mobile station MS further moves closer to the cell B and reaches the position P11, the reception level Rb of the cell B from the base station BSb becomes equal to or higher than the first predetermined reception level R1.

The mobile station MS has a first predetermined reception level R
When one or more reception levels Rb are detected, the CNR ′ of this reception level Rb is measured, and the reception level Rb is measured.
The level difference D ′ between b and the reception level currently being communicated, that is, the reception level Ra from the base station BSa of the cell A in FIG. 3, is calculated. Then, the measured CNR ′ is a first predetermined CNR as shown in FIG.
3 is greater than NR1 and the level difference D '
If the level difference is smaller than the first level difference D1 as shown in (d), the mobile station MS newly connects the base station BSb of the cell B having a large CNR 'and a small level difference D', and The simultaneous communication mode with the base station BSb is entered.

Returning to FIG. 1, the mobile station that has entered the simultaneous communication mode as described above receives Cs of a plurality of cells performing simultaneous communication.
NR "is constantly measured, and it is determined whether or not the CNR" is smaller than the second predetermined CNR2 which is smaller than the first predetermined CNR1 (step 140). As a result, C
If NR "becomes smaller than the second predetermined CNR2, the communication line for the cell having this CNR" is disconnected (step 160).

More specifically, referring to FIG. 3, when the base station BSb of the cell B is newly connected at the position P11 in FIG. B in the simultaneous communication mode with the base station BSb of each cell A and the CN of each reception level of the cell A and the cell B.
R "is constantly monitored. If the mobile station MS moves further in this state, the reception level Rb from the cell B gradually increases as shown in FIG. 3B, while its CNR" increases. , The reception level Ra from the cell A gradually decreases,
As a result, when the mobile station MS moves to the position P12, the CNR of the reception level Ra from the cell A becomes smaller than the second predetermined CNR2 as shown in FIG. Becomes smaller, the communication line for the cell having the CNR ", that is, the cell A, is disconnected.

Returning to FIG. 1, if the result of the determination in step 140 is that CNR "is not smaller than the second predetermined CNR2, the operation proceeds to step 150, where the reception level of the cell during simultaneous communication is determined. It is determined whether R is lower than a second predetermined reception level R2 that is lower than the first predetermined reception level R1.If the reception level R is lower than the second predetermined reception level R2, Then, the line for the cell is disconnected (step 170) Note that the determination using the second reception level R2 is mainly performed for the one having a low reception level.

Further, as a result of the determination in step 150, if the reception level R of the cell performing simultaneous communication is not lower than the second predetermined reception level R2, the process proceeds to step 160, in which a plurality of cells performing simultaneous communication are transmitted. The reception level R of the cell is measured, and a level difference D ″ between each of these reception levels R and the maximum reception level among the reception levels R is calculated, and this level difference D ″ is the first predetermined level. It is determined whether the level difference is larger than a second predetermined level difference D2 shown in FIG. 3D which is larger than the level difference D1 (step 160). As a result, when the level difference D "becomes larger than the second predetermined level difference D2, the communication line for the cell having this level difference D" is disconnected (step 160).

More specifically, referring to FIG. 3, when the mobile station MS moves further in the simultaneous communication state, the reception level Ra from the cell A gradually decreases as shown in FIG. 3 (b). In contrast, the reception level Rb from the cell B gradually increases, and the level difference D ″ between the two reception levels also gradually increases. As a result, when the mobile station MS moves to the position P13, the level difference Assuming that D ″ becomes larger than the second predetermined level difference D2 as shown in FIG. 3D, the communication line for the cell having this level difference D ″, that is, the cell A, is disconnected, and the maximum reception level of the cell A is cut off. Cell B, which is a cell, remains.

Returning to FIG. 1, as a result of the determination in step 160, the level difference D ″ is equal to the second predetermined level difference D2.
If not greater, the process returns to step 140 and the same processing is repeated.

Next, with reference to a flowchart shown in FIG. 4, a processing procedure of a base station which executes a mobile communication handover method according to another embodiment of the present invention will be described.

In FIG. 4, the base station notifies the mobile station in communication of the spreading code of the neighboring cell, and causes the mobile station to sequentially receive the perch channels of the neighboring cell using the spreading code. R is measured (step 21)
0). Then, the reception level R measured by the mobile station is transmitted and received by the base station (step 220).

The base station, among the received reception levels R, receives the C of the reception level R higher than the first predetermined reception level R1.
NR 'is measured by the mobile station, and a level difference D' between the reception level R exceeding the first predetermined reception level R1 and the maximum reception level during communication is calculated (step 23).
0).

The base station causes the mobile station to transmit the CNR 'measured in step 230, and receives it at the base station (step 240). Then, a cell in which the received CNR ′ is larger than the first predetermined CNR1 and the level difference D ′ calculated in step 230 is smaller than the first predetermined level difference D1 is newly connected to the mobile station, The simultaneous communication mode is entered (step 250).

The base station causes the mobile station to measure the reception level CNR "of the cell during simultaneous communication, causes the mobile station to transmit the measurement result, and receives the measurement result at the base station (step 260). It is determined whether CNR "is smaller than the second predetermined CNR2 (step 270). As a result, if the CNR "is smaller than the second predetermined CNR2, the communication line for the cell having the CNR" is disconnected (step 310).

In the determination of step 270, C
If NR "is not smaller than the second predetermined CNR2, the process proceeds to step 280, where the mobile station measures the reception level R of the cell performing simultaneous communication, and the reception level R is set to the first level.
Is determined to be lower than a second predetermined reception level R2 which is lower than the predetermined reception level R1 (step 2).
90). If the reception level R is lower than the second predetermined reception level R2, the line for the cell is disconnected (step 310).
Proceeding to step 300, it is determined whether or not the level difference D "between each of the reception levels R during simultaneous communication and the maximum reception level among the reception levels R is larger than the second predetermined level difference D2. As a result, if the level difference D "is larger than the second predetermined level difference D2, the line for the cell is disconnected (step 310), but if not, the process returns to step 260 and the same. Is repeated.

[0068]

As described above, according to the present invention,
The mobile station measures a carrier-to-noise ratio at a reception level exceeding a first predetermined reception level among the reception levels of the perch channels of the neighboring cells measured during communication, and the carrier-to-noise ratio is determined to be the first predetermined level. A cell having a carrier-to-noise ratio greater than the first reception level and a level difference between a reception level exceeding the first reception level and a maximum reception level being smaller than a first predetermined level difference is newly connected to the mobile station, and the simultaneous communication mode is set. And the carrier-to-noise ratio of the reception level of the plurality of cells during simultaneous communication is smaller than the first predetermined carrier-to-noise ratio.
Or the level difference between the reception level during simultaneous communication and the maximum reception level becomes larger than a second predetermined level difference that is larger than the first predetermined level difference. In this case, the line for the cell is disconnected, so that a cell requiring a large communication channel transmission power near the base station is not selected and connected for handover, and other cells can be connected with a large transmission power. Interference is less likely to occur in the communication, and the subscriber capacity can be increased. In addition, even though the interference level is large and the reception level appears to be large, a cell with poor communication quality is not selected, and the communication quality is good. The cell can be selected at the time of handover, and the handover can be prevented from fluttering.

Also, according to the present invention, the mobile station measures the reception level of the perch channel of the neighboring cell during communication with the mobile station under the control of the base station. The mobile station measures the carrier-to-noise ratio for a reception level that exceeds the predetermined reception level, the carrier-to-noise ratio being greater than a first predetermined carrier-to-noise ratio;
In addition, a cell in which the level difference between the reception level exceeding the first reception level and the maximum reception level is smaller than the first predetermined level difference is newly connected to the mobile station to enter the simultaneous communication mode. Causing the mobile station to measure the carrier-to-noise ratio of the reception level of the plurality of cells, wherein the carrier-to-noise ratio is smaller than a second predetermined carrier-to-noise ratio that is smaller than a first predetermined carrier-to-noise ratio, or A cell in which the level difference between the reception level during simultaneous communication and the maximum reception level is larger than a second predetermined level difference that is larger than the first predetermined level difference is detected. This eliminates the need to select and connect a cell that requires communication channel transmission power for handover, makes it difficult to interfere with communication of other cells with large transmission power, and increases subscriber capacity. It is possible to select a cell with good communication quality without selecting a cell with poor communication quality despite the fact that the interference level is large and the reception level looks high, and it is possible to suppress handover flutter. In addition, since the handover is performed under the control of the base station, the base station can perform common processing such as control, determination, and storage in the mobile station, thereby simplifying the configuration and processing of the mobile station. Can be

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of a mobile communication handover method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a mobile station and a base station that implement the mobile communication handover method of FIG.

FIG. 3 is an explanatory diagram showing a positional relationship between a cell and a mobile station, a reception level, a CNR, and a level difference when the mobile station moves from a cell A to a cell B.

FIG. 4 is a flowchart showing a processing procedure of a base station implementing a mobile communication handover method according to another embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between a plurality of cells constituting a service area of a CDMA mobile communication system and a mobile station moving in the plurality of cells.

FIG. 6 is an explanatory diagram illustrating noise such as an interference level included in a reception level.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 mobile station transmission / reception unit 12 transmission / reception switch 13 transmission circuit unit 14 reception circuit unit 15 control unit 16 reception level / interference level detection unit 17 correlation detector 18 level detector 19 interference detector 20 base station 21 antenna 26 base amplifier 27 Modulation / demodulation device 28 Spreading device 30 Control bus control 31 Monitoring / control device 32 2M / 1.5M interface device 33 Base station control device 34 Timing supply device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 7/26-7/26 113 H04Q 7/04-7/38 H04J 13/00-13/06

Claims (14)

(57) [Claims] 1. A base station is provided in each of a plurality of cells,
Each base station is modulated with the same frequency, spread with a unique spreading code assigned differently, and constantly transmits a perch channel with a constant transmission power without performing transmission power control. A mobile communication handover method in a communication system, wherein a mobile station measures a reception level of each perch channel of a peripheral cell during communication, and detects a reception level exceeding a first predetermined reception level among the reception levels. Measuring a carrier-to-noise ratio, wherein the carrier-to-noise ratio is greater than a first predetermined carrier-to-noise ratio and a level difference between a reception level exceeding the first reception level and a maximum reception level is a first predetermined level; A cell smaller than the level difference between the cells is newly connected to the mobile station and the mobile station enters the simultaneous communication mode. If the carrier-to-noise ratio is smaller than a second predetermined carrier-to-noise ratio that is smaller than the first predetermined carrier-to-noise ratio, or the reception level during simultaneous communication is lower than the first predetermined reception level. When the reception level becomes smaller than the second predetermined reception level, or when the level difference between the reception level during simultaneous communication and the maximum reception level is larger than the second predetermined level difference larger than the first predetermined level difference, A mobile communication handover method characterized by disconnecting a line for the cell when the value of the cell also becomes large. 2. The step of measuring the reception level,
2. The mobile station according to claim 1, wherein a spreading code of a neighboring cell is notified from a base station that is currently communicating, and a reception level of each perch channel of the surrounding cell is measured using the notified spreading code. Communication handover method. 3. A base station is provided in each of the plurality of cells,
Each base station is modulated with the same frequency, spread with a unique spreading code assigned differently, and constantly transmits a perch channel with a constant transmission power without performing transmission power control. A mobile station device in a communication system, comprising: measuring means for measuring a reception level of each perch channel of a peripheral cell during communication; and a first predetermined reception level among the reception levels measured by the measurement means. Measuring a carrier-to-noise ratio at a reception level exceeding the first reception level, wherein the carrier-to-noise ratio is greater than a first predetermined carrier-to-noise ratio, and a level difference between the reception level exceeding the first reception level and a maximum reception level; Is the first
First detecting means for detecting a cell smaller than the predetermined level difference, and a second detecting means for controlling the carrier-to-noise ratio of the reception level of the plurality of cells during simultaneous communication smaller than the first predetermined carrier-to-noise ratio. Cells that are smaller than a predetermined carrier-to-noise ratio of
Alternatively, the cell whose reception level during simultaneous communication is smaller than the second predetermined reception level that is smaller than the first predetermined reception level, or the level difference between the reception level during simultaneous communication and the maximum reception level is the aforementioned A mobile station apparatus comprising: a second detection unit configured to detect a cell that has become larger than a second predetermined level difference that is larger than the first predetermined level difference. 4. The measuring means is notified of a spreading code of a neighboring cell from a base station currently in communication, and measures the reception level of each perch channel of the neighboring cell using the notified spreading code. The mobile station device according to claim 3, comprising: 5. The mobile station apparatus according to claim 3, further comprising a simultaneous communication unit for newly connecting a cell detected by said first detection unit and entering a simultaneous communication mode with the cell. 6. A notifying unit for notifying a cell detected by the first detecting unit to a base station, and the base station receiving the notification newly connects the cell to a mobile station, and connects the cell to the mobile station. 4. The mobile station apparatus according to claim 3, wherein the mobile station apparatus is controlled to enter a simultaneous communication mode. 7. The mobile station apparatus according to claim 3, further comprising a disconnection unit that disconnects a line for the cell detected by said second detection unit. 8. The system according to claim 1, further comprising a notifying unit for notifying the cell detected by said second detecting unit to the base station, wherein the base station receiving the notification disconnects the line for the cell. Item 3. The mobile station device according to item 3. 9. A base station is provided in each of the plurality of cells,
Each base station is modulated with the same frequency, spread with a unique spreading code assigned differently, and constantly transmits a perch channel with a constant transmission power without performing transmission power control. A base station apparatus in a communication system, comprising: causing a mobile station to measure a reception level of each perch channel of a neighboring cell in communication with the mobile station; transmitting the measurement result; and transmitting the transmitted measurement result. First receiving means for receiving, and among the reception levels received by the first receiving means, the mobile station measures the carrier-to-noise ratio for a reception level exceeding a first predetermined reception level. Carrier-to-noise ratio receiving means for transmitting a carrier-to-noise ratio and receiving the transmitted carrier-to-noise ratio; and a carrier received by the carrier-to-noise ratio receiving means. A cell having a noise ratio larger than a first predetermined carrier-to-noise ratio and having a level difference between a reception level exceeding the first predetermined reception level and a maximum reception level smaller than the first predetermined level difference is detected. First detecting means for causing a mobile station to measure the carrier-to-noise ratio of the reception level of a plurality of cells in simultaneous communication, transmitting the measurement result, and receiving the transmitted measurement result. Means, wherein the carrier-to-noise ratio of the reception level of the plurality of cells in simultaneous communication received by the second receiving means is smaller than a second carrier-to-noise ratio smaller than the first predetermined carrier-to-noise ratio. Cell, or a cell whose reception level during simultaneous communication is lower than a second predetermined reception level that is smaller than the first predetermined reception level, or a reception level during simultaneous communication and a maximum reception level. And a second detecting means for detecting a cell whose level difference is larger than a second predetermined level difference that is larger than the first predetermined level difference. 10. The first receiving means notifies a spreading code of a neighboring cell to a mobile station, and the mobile station measures a reception level of each perch channel of the surrounding cell using the notified spreading code. The base station apparatus according to claim 7, further comprising a measuring unit that performs measurement. 11. The base station apparatus according to claim 9, further comprising simultaneous communication means for newly connecting a cell detected by said first detection means to a mobile station to enter a simultaneous communication mode. . 12. The mobile station further includes a notifying unit for notifying a mobile station of a cell detected by the first detecting unit, and the mobile station receiving the notification newly connects the cell and performs simultaneous communication with the cell. 10. A control to enter a mode.
The base station device as described in the above. 13. The base station apparatus according to claim 9, further comprising a disconnecting means for disconnecting a line for the cell detected by said second detecting means. 14. The mobile station further comprising a notifying unit for notifying a mobile station of a cell detected by the second detecting unit, and the mobile station receiving the notification disconnects a line for the cell. Item 10. The base station device according to item 9.