JPH04117822A - Method for discriminating in-zone cell in mobile communication - Google Patents

Abstract

PURPOSE:To make discrimination of an in-zone cell by a mobile equipment accurate at all times by correcting a reception level from a base station measured by the mobile equipment used for discriminating an in-zone cell based on a correction value of the reception level informed from the base station to the mobile equipment. CONSTITUTION:When a mobile equipment 27 stays in a location 27, the equipment receives a low reception level of any cell. A cell 20 is selected based on the discrimination of a level 29 resulting from correcting a reception level 28. Suppose that a minimum required level in signal transmission is 30, a sufficient level in the signal transmission is not secured by the selected cell 20. Thus, when the reception level before the correction of cells does not satisfy the predetermined level required for the signal transmission, cells are discriminated again at a level not corrected and the result is used as the final discrimination. Thus, the cell 15 is selected and an event that the selection of a cell at a lower reception level resulting from the correction regardless of the presence of a cell able to be received clearly at a higher level is avoided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention reduces the amount of interference such as co-channel interference by rationally selecting the cell in which a mobile device is located in a mobile communication system with a cellular configuration. The present invention relates to a method for determining the serving cell that can be used.

[Conventional technology]

As an example of a conventional technique, a method for determining the cell in which a mobile device is located in a large-capacity car telephone system will be described.

In large-capacity car telephone systems, radio channels are divided into three types: communication channels, outgoing control channels, and incoming call control channels, each of which is used to make calls, control when a mobile device makes an outgoing call, and control when a mobile device receives a call. Ru. Among these, the so-called multi-station simultaneous/sequential transmission system using the same frequency is adopted for the incoming call control wholesale channel.

This will be explained based on FIG. 11. In the figure, 1 represents a central control station, 2 to 4 are base stations, 5 to 7 are cell boundaries covered by these base stations, and 8 to 10 are signals transmitted from each base station. Each base station 2 to 4 is synchronized, and the transmission signals from the base stations are transmitted at the same time, in which all base stations transmit the same signal at the same time, and in sequential transmission, in which each base station individually transmits signals sequentially. It consists of timing.

At the simultaneous transmission timing, cell common information such as system common information C and incoming call signal P for the mobile device is transmitted. At the sequential transmission timing, base station individual information such as the transmission control channel number used by each base station is transmitted.

The mobile device in standby sequentially measures the reception level of the transmission timing portion of the radio waves from each base station.

Among these reception levels, the base station corresponding to the signal received at the maximum level is the base station in which the mobile device is located.

However, the propagation conditions of radio waves within a cell are not uniform; for example, radio waves are attenuated greatly in areas with dense buildings or in lowlands. Generally, when there are places where it is difficult for radio waves to reach, the design is done by increasing the transmission power so that radio waves can be received at a sufficient level even in such places.

When a cell (referred to as cell A) with higher transmission power than surrounding cells coexists in this way, the amount of interference increases in the following two ways.

The first reason is that the transmission power itself is large. In other words, in cell B, which repeatedly uses the same frequency as cell A, or in cell C, which uses a frequency that is interleaved with the frequency to the cell,
The level of interference waves from cell A increases by the amount that the transmission power is increased, and therefore the interference increases.

The second reason is that as a result of increasing the transmission power, the cell radius becomes larger than expected in other locations within the cell that are not in densely built areas or low-lying areas. In other words, a mobile device in cell A can be located closer to cell B or cell C by the increased cell radius.
Interference increases as the distance approaches.

Among these, the first reason, that is, increased interference due to high transmission power, can be improved to some extent by employing transmission power control. For example, the transmission power of the mobile device is controlled by feedback control so that the reception level at the base station is the minimum necessary. This is because, in areas where radio waves can easily reach, radio waves are not transmitted at a level below the required level. However, even in this case, since the radius of the cell is larger than the surrounding cells, mobile devices near the cell will still transmit at a high level commensurate with the increased cell radius.) That is, even if transmission power control is adopted, it is not possible to reduce the increase in interference due to the increase in the cell radius (due to the second reason).

Next, the second reason, that is, the interference degradation due to an increase in the cell radius will be explained in detail with reference to FIG. 1
1 to 14 are cell boundaries. FIG. 12(a) is an example in which the radius of cells repeating the same frequency is the same, and the repeat use distance is as follows: (D /R-1)-△. α is a constant determined by the propagation path conditions and is 3
The value is about 4. The above is described in detail, for example, in the literature (edited by Masaaki Shindo, "Mobile Communication", July 30, 1989, published by Maruzen Co., Ltd.) from page 34, line 21 to page 35, line 5.

If you increase the transmission power because there are areas within the cell where radio waves are difficult to reach, the cell boundaries in the direction where radio waves are difficult to reach will be closer to the intended ones, but the radio waves will not be as normal in other directions. In the direction of reach, the cell boundaries will be wider than expected. In other words, the cell radius has become larger.

The radius of one cell is R to R as shown in Figure 12(b).
', the same frequency can only be repeated at a distance D' that satisfies (D'/R'-1)-8.

On the other hand, if the repetition is repeated at a distance of D as in FIG. 12(a), the interference will increase.

[Problem to be solved by the invention]

As explained above, in the conventional cell determination method, if the transmission power of a base station is increased for a part of the cell where radio waves are difficult to reach, it will be Because the radio waves fly too much, the cell radius becomes larger, resulting in increased co-frequency interference and interleaved channel interference.To avoid this, it is necessary to increase the frequency repetition distance, thus reducing the frequency utilization rate. There was a drawback of letting it happen.

The present invention was made to solve these problems, and by transmitting a signal from a base station that can control the size of the cell, it suppresses the increase in cell radius in places where radio waves easily travel. The purpose of this invention is to provide a mobile communication cell determination method that allows radio waves to be received at a high level in places where radio waves are difficult to reach.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention corrects the reception level from the base station measured by the mobile device used for determining the cell in which it is located, by the correction value of the reception level notified from the base station to the mobile device. It is possible to accurately determine the cell in which the mobile device is located without being influenced by bias in transmission power due to individual factors of the cell. Furthermore, if the mobile device is located in a place where it is difficult for radio waves to reach and the reception level is not at a sufficient level for signal transmission, it is possible to determine the serving cell based on the reception level itself without performing the above correction. It is a characteristic.

[For production]

In the present invention, there are a plurality of base stations that transmit broadcast signals, and a mobile device that has a function of receiving broadcast signals from the plurality of base stations and a function of measuring reception levels, and moves the reception levels of the plurality of base stations. In a cellular mobile communication system configured to allow comparison between base stations, each base station first notifies the mobile station of a correction value for the reception level, and the mobile station measures the reception level of each base station. The mobile device corrects the reception level using the correction value broadcasted from the base station, selects the maximum of the corrected reception levels, and determines the cell corresponding to this as the cell in which it is located.

If it is necessary to avoid determining cells with reception level (g) that do not meet the required level by correction, the selection operation is further performed as follows.In other words, the selection operation is performed as follows. If the reception level value of the corrected cell before correction is less than a predetermined value, the mobile device re-determines the serving cell based on the uncorrected reception level and makes this the final determination. do.

With such a configuration, even if there are areas within the cell where radio waves are difficult to reach, and therefore it is necessary to increase the transmission power of that base station, the cell radius can be increased in areas where radio waves are easily reachable. Since there is no radio wave, it is possible to determine the serving cell regardless of the magnitude of the transmission power, and in places where radio waves are difficult to reach, it is possible to determine as the serving cell a cell that can secure a sufficient reception level.

By using the method described below, the cell boundaries can be set as designed regardless of the size of the transmission power.
The second reason mentioned in the prior art above, that is, the increase in interference caused by the mobile station approaching an interfering cell can be avoided.

Note that in the above method, the first reason, that is, the influence of increased interference due to high transmission power, is not solved by the above techniques. In order to solve this problem, the base station and the mobile device may use transmit power control together. The first specific method of transmit power control is to reduce the transmit power of the mobile device or base station so that when the reception level at the base station (or mobile device) exceeds a certain value, the increased transmit power is canceled. This is a way to reduce the

The second method is to control the transmission power of the mobile device or base station by feedback control so that the reception level at the base station (or mobile device) becomes the minimum necessary value. Note that even if transmission power control is performed in a place where radio waves are difficult to reach, transmission will be performed at the maximum power allowed for that cell, and interference reduction by the above-mentioned transmission power control cannot be expected. However, in places where it is difficult for radio waves to reach, the level of interference waves is generally low, and in this case, the desired wave to interference wave level ratio does not deteriorate, so this is not a big problem.

As described above, according to the present invention, cell determination can be performed accurately as designed, and the increase in interference due to increased transmission power can be reduced by transmission power control.As a result, the amount of interference is reduced, and the frequency without reducing utilization rate,
It is possible to eliminate areas with low reception levels.

〔Example〕

Hereinafter, embodiments of the present invention will be explained based on the drawings. Ru.

FIG. 1 is a diagram showing the area of influence of each cell when there are places where radio waves are difficult to reach, where 15 to 26 are cells and 27 is a place where radio waves are difficult to reach. The area of influence of a certain cell is a collection of locations where the radio waves of that cell are received more strongly than the radio waves of any other cell. It is assumed that the transmission power of cells 15 and 16 is, for example, 5 dB higher than the transmission power of the other cells in order to ensure a sufficient reception level even for location 27. For this reason, the range of influence of cells 15 and 16 is expanded by narrowing the range of influence of the other cells 17 to 24, as shown by the solid line in FIG.

Note that the power diagram when the transmission power is the same in all cells should be as shown by the broken line in FIG. The base station (not shown) is at the center of the sphere of influence shown by the dashed line, which is different from the center of the sphere of influence shown by the solid line due to differences in transmit power.

Even if the transmission power is increased, if the cell boundaries can be shaped as shown by the broken lines, the cell radius will not expand, and therefore no interference problem will occur.

FIG. 2(a) shows the correction value to be added to the reception level of each cell, and FIG. 2(b) shows the reception level 28 of each cell and the reception level 29 after correction.

An example of reception when the mobile device is located at a location intermediate between the base stations of cells 15, 16, and 20 and close to the base station of cell 20, for example, point A in FIG. 1, is shown in (b) of FIG. .

Since cells 15 and 16 are transmitting with a transmission power 5 dB higher than the normal value, these base stations broadcast that the correction value is 5 dB, and the other base stations do not broadcast the correction value. The radio waves from the base stations of cells 15, 16, 20, and 21 that are not available (or that the correction value is OdB) are 28 and 2 shown in FIG. 2 (b), respectively.
It is being received at a level of 8.2929. The mobile device determines the cell in which it is located based on 29, 29, 29.29, which is the correction value added to this. In this case, as shown in the figure, since the corrected reception level is highest in cell 20, it is determined that the mobile device is in the cell 20 area.

That is, when not correcting as in the conventional case, cell 15
Since the level is the highest, it is determined that the cell is in the cell 15 area, but as a result of correction, it is determined that the cell is in the cell 20.

FIG. 3 shows an example of the reception level when the mobile station is at 27 locations, and the reception level of every cell is low. If the cell is determined based on the received level 29 with correction added to the reception level 28, the cell 20 will be selected. Now, if the minimum value of the required level for signal transmission is set to 30, a sufficient level for signal transmission cannot be secured in the selected cell 20.

Therefore, in the present invention, if the reception level before correction of the cell determined by the reception level after correction is less than the level required for predetermined signal transmission, the cell is set to the level without correction. will be re-judged and this will be the final judgment. In the example of FIG. 3, cell 15 is therefore selected, and it is possible to avoid selecting a cell with a low reception level as a result of correction even though there is a cell that can clearly receive reception at a higher level.

In order to carry out the present invention, it is necessary to receive not only radio waves from the serving cell but also radio waves from neighboring cells. An example of this method will be described below.

FIG. 4 is a diagram illustrating an example in which the present invention is applied during reception on a control channel, in which a different frequency is assigned to each cell, and all mobile terminals are
,,G2. It is divided into three groups like G3. Control for mobile stations residing in a certain cell is transmitted and received using the control channel frequency assigned to that cell, but control signals for mobile stations in each group are transmitted and received within the timing assigned to each group. only. In the example shown, cell 15 has fl, cell 16 has f2. A frequency of 13 is assigned to cell 20 and a frequency of f4 is assigned to cell 21, and the control signal transmission timing in each cell for the mobile terminal group of GL is G ll + G 21 + G: l ++ 041,
The control signal transmission timing in each cell for the mobile terminal group of G2 is G1□l 02□G3°+04□, G3
The control signal transmission timing in each cell for the mobile station group is 0131 G23Gll+G43. The mobile devices of the G1 group located in the cell 15 need to receive radio waves from the base station at timing G11, but do not need to receive radio waves from the base station at other timings G I 2CI3. Therefore, at the timings C, 2, C, 3, the mobile device receives the frequency f2 of the control channel of the adjacent cell.
f3. F4 is sequentially switched to measure the reception level, and at the same time, the reception level correction value broadcasted on the control channel is received.

FIG. 5 shows a flowchart showing control 411 of the base station and mobile device in the cell determination method according to claim 1. Further, FIG. 6 is a flowchart showing control of a base station and a mobile device in the cell determination method according to claim 2. In either case, by determining the control<MU channel for which the reception level or the reception level after correction is the maximum, the cell corresponding to this control channel can be indirectly determined.

FIG. 7 is a diagram illustrating an example in which the present invention is applied when a mobile device determines the cell in which it is located in order to switch channels during communication, and the communication channel between the mobile device and the base station is 6-channel multiplexed. TDMA is adopted. In transmission time slot T, base station transmission, mobile device reception, and reception time slot l
In -R, the mobile device is transmitting and receiving from the base station, but at other timings (indicated by 1), the mobile device is not transmitting or receiving. Therefore, during this timing, the frequency of the control channel or communication channel of other cells is sequentially switched to receive these channels, the reception level is measured, and a correction value that is not broadcast is received.

Next, an example of transmission of correction values and the like will be explained.

FIG. 8 is an example of a signal configuration in the control channel shown in FIG. 4, where 3L38 is a code representing a group number, 32.39
does not represent a correction value; 3340 is a cell identification code; 34
, 35, 36, 41. .

42' and 43 are mobile station calling codes or communication channel designation codes for the mobile station. 31 to 36 are the signals 37 transmitted at the timing for the first group, and 38 to 43 are the signals 37 to be transmitted at the timing for the second group.
A signal 44 is configured to be transmitted at group timing. 3
The same numerical value as a correction value is transmitted to 2 and 39, and the same code as a cell identification code is transmitted to 33 and 40.

FIG. 9 shows a second signal configuration example of the control channel shown in FIG. 4, in which a multi-station simultaneous/sequential transmission system is adopted. In other words, the control channel uses the same frequency at multiple base stations, and there are two types of timing: simultaneous transmission timing in which the same signals are transmitted from these multiple base stations at the same time, and simultaneous transmission timing in which multiple base stations transmit individual signals in sequence. It consists of individual transmission timing. 49 is system common information, 50-5
3. 55 to 58 are incoming call information for the mobile device, 54 is base station information, the numbers other than 54 are multi-station simultaneous transmission, and 54 is multi-station sequential transmission. The base station repeatedly transmits these signals at appropriate intervals. The incoming call information is divided into timings corresponding to groups of mobile devices, and each mobile device receives the incoming call information at a timing corresponding to its own group. If these timings are 50 and 51, the mobile device is at 49,50°5.
1, and 54, which is the base station information of the cell in which the cell is located. The base station information of other cells is transmitted at a timing between 51 and 52, a timing between 56 and 57, or the like. By receiving the signals at these timings, measuring their reception levels, and decoding the signals, the mobile device can learn the level of radio waves from neighboring cells and the correction value in that cell.

In the case of receiving a control channel in an empty time slot in FIG. 7 and measuring its level, etc., the method of transmitting the correction value etc. in FIG. 8 can be applied as is. When receiving a communication channel of a neighboring cell in an empty time slot, it is necessary to provide the communication channel signal with a function of transmitting a cell identification code, a correction value, etc. FIG. 10 is a diagram illustrating an example of a signal configuration of a communication channel applied in this case.
5 is a cell identification code, 46 is a correction value, 47 is a communication signal, 4
8 is a base station transmission time slot T.

〔Effect of the invention〕

As explained above, according to the present invention, even if there is a part of a cell where it is difficult for radio waves to reach and the transmission power of that cell is increased for this location, the transmission power is not increased, but the radio waves are Since it is possible to determine the cell in which the mobile device is located based on the level determined by the transmission power if there were no hard-to-reach places, there is an advantage that it is possible to avoid an increase in interference due to an increase in the cell radius.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the range of influence of each cell when there are places where radio waves are difficult to reach, Figure 2 is a diagram explaining the reception level and the reception level with corrections added to it, and Figure 3 is a diagram showing the range of influence of each cell when there are places where radio waves are difficult to reach. Figure 4 is a diagram illustrating an example in which the present invention is applied to the control channel while standby is being received at the base station. and a flowchart showing the control of the mobile device, FIG. 7 is a diagram explaining an example in which the present invention is applied when the mobile device determines the serving cell for channel switching during communication, and FIGS. 8 and 9. is a diagram showing an example of the signal groove configuration of the control channel,
FIG. 10 is a diagram illustrating an example of a signal configuration of a communication channel;
Figure 11 is a diagram explaining the multi-station simultaneous/sequential transmission system in the conventional large-capacity car telephone system, and Figure 12 is a diagram explaining the repeating distance between stations when the same frequency is repeatedly used between cells with different radii. It is a diagram. ■...Central control station, 2-4...Base station, 5-7...
- Cell boundaries covered by the base station, 8 to 10... Signals transmitted from the base station, 11 to 14... Cell boundaries, 15
~26...Cell, 27...Places where radio waves are difficult to reach,
28...Reception level, 29...Reception level after correction, 30...Minimum level necessary for signal transmission, 31.38
... Code representing group number, 32.39... Code representing correction value, 33.40... Cell identification code, 34,35
゜36.41, 42.43... Call code of the mobile device or communication channel designation code to the mobile device, 37... Signal transmitted at the timing for the first group, 44... Second
Signal transmitted at group timing, 45... Cell identification code, 46... Correction value, 47... Communication signal, 48
. . . Base station transmission time slot, 49 . . . System common information, 50 to 53 55 to 58 . . . Call information for mobile equipment, 54 . . . Base station information.

Claims (1)

[Claims] 1. A mobile communication system in which a service area is composed of a plurality of base stations and a plurality of cells covered by these base stations, and in which base stations separated by a certain distance or more repeatedly use channels of the same frequency. In this step, the transmission power of the base station covering the cell is increased or decreased according to the radio wave propagation conditions within the cell, and the base station broadcasts a correction value corresponding to the increase or decrease in the transmission power to the mobile device, and the mobile device Measure the reception level of radio waves from each base station and receive the broadcasted correction value. Based on the magnitude of the reception level as a result of correcting the reception level of radio waves from each base station with the correction value, 1. A method for determining a serving cell in mobile communication, the method comprising determining a cell in which a cell is located. 2. The mobile communication system according to claim 1, wherein when the reception level of radio waves from the base station selected as a candidate does not satisfy a predetermined value, the cell in which the cell is located is determined based on the magnitude of the reception level before correction. A method for determining the cell in which the cell is located.