JPH08186857A - Base station selection method - Google Patents

Abstract

PURPOSE: To improve the reception quality, to reduce the transmission power and interference quantity and to increase a subscriber capacity or the like by selecting a base station offering best quality after synthesis in the case of starting simultaneous connection. CONSTITUTION: The base station selection method is a method for a radio communication system having plural base stations 1 connecting to a communication network and mobile stations 7 simultaneously connected to the plural base stations 1 by radio channels. The mobile station 7 receives a prescribed signal sent respectively by a prescribed power from the plural base stations 1 and the signals are synthesized and the communication quality after synthesis in the radio channel with each of base stations connected simultaneously is estimated and the connection with the base station 1 is controlled based on the estimated result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base station selection method in a radio communication system in which a mobile station is simultaneously connected to a plurality of base stations.

[0002]

2. Description of the Related Art Conventionally known wireless communication systems use one mobile station 7 and a plurality of base stations when communicating via a wireless line between a mobile station 7 and a base station 1 as shown in FIG. 1
, are connected to a plurality of radio lines Ca, Cb, ..., And a plurality of signals arriving from different propagation paths are simultaneously received and combined by a higher station such as a switching center 3 to obtain signals. There is a technology called site diversity that improves the quality of.

In this site diversity, instantaneous fluctuations in each radio line, that is, Rayleigh fluctuations are uncorrelated, and when these signals are simultaneously received and combined, the signal quality is greatly improved. Further, the smaller the difference between the average levels of the signals, the greater the effect of combining.

Therefore, when a base station to be newly connected is selected, the propagation loss between the mobile station 7 and the base station 1a currently in communication and between the mobile station 7 and the newly connected base station 1b are determined. A common method is to compare the propagation losses and start the connection when the difference is within a certain range. As means for comparing the propagation losses, there is a method in which the mobile station 7 receives a signal having a constant transmission power, which is constantly transmitted by each base station 1a, 1b, ... It is taken.

[0005]

If the level fluctuation in the radio channel is the Rayleigh fluctuation only, there is no problem in the conventional base station selection method. However, in reality, there is shadowing that occurs when radio waves are blocked by the building A or the like. When a wireless line is connected between a certain mobile station 7 and a plurality of base stations 1a, 1b, 1c, shadowing between the mobile station 7 and each wireless line Ca, Cb, Cc has a correlation. Generally, the correlation between the wireless channel Cb and the wireless channel Cc of the base station 1b and the base station 1c, which are in the same direction as the mobile station 7, is large.
The correlation between the wireless line Ca and the wireless line Cb and the wireless line Ca and the wireless line Cc in which the base station is in the opposite direction is small (FIG. 9).

Similarly to Rayleigh fluctuations, the smaller the correlation between shadowing fluctuations, the higher the signal quality after combination. However, in the conventional method, cell selection in consideration of the shadowing correlation is not performed, and therefore, there is a drawback in that base station selection that maximizes reception quality is not necessarily performed. Further, in the system for controlling the transmission power, there is a drawback that the transmission power becomes unnecessarily large and the interference given to others also becomes large. Further, in an interference limited system such as a CDMA system, there is a drawback that the subscriber capacity is reduced due to an increase in the amount of interference.

The present invention has been made in view of the above problems, and considers the correlation of shadowing between the mobile station and each base station when starting the simultaneous connection, so that the quality after combination is the best. By selecting a base station that improves, it is possible to provide a base station selection method that can achieve significant effects such as improved reception quality, reduced transmission power, reduced interference, and increased subscriber capacity. To aim.

[0008]

In order to achieve the above object, the first invention of the present application is to provide a plurality of base stations connected to a communication network and a mobile station which can be simultaneously connected to the plurality of base stations via a wireless line. A method of selecting a base station in a wireless communication system including a station, wherein the mobile station receives predetermined signals transmitted from the plurality of base stations with predetermined power, respectively, and combines the signals. According to the above, the post-combination communication quality is estimated in the wireless channel between each of the simultaneously connected base stations, and the control relating to the connection with the base station is performed based on the estimation result.

The second invention of the present application comprises a plurality of base stations connected to a communication network and a mobile station connected to the base stations via a wireless line, and each mobile station comprises a plurality of base stations. A method of selecting a base station in a wireless communication system capable of simultaneous connection, wherein the mobile station sequentially receives, in a time division manner, a predetermined channel transmitted from each of the plurality of base stations with a predetermined power, and different base stations. By combining the reception results with the smallest time difference among the reception results from, the quality after combining when the communication channels are combined is estimated, and the control related to the connection with the base station is performed based on the estimation result. The point is to do.

Further, the third invention of the present application is that the control relating to the connection with the base station according to claims 1 and 2 is for determining the simultaneous connection start and selecting the simultaneously connected base station. And

[0011]

According to the base station selection method of the first invention of the present application, the mobile station receives signals of constant transmission power transmitted from the respective base stations, combines the received signals, and combines them when the communication channels are simultaneously connected. Estimate quality. Based on this estimation result, simultaneous connection start determination and simultaneous connection base station selection are performed. In this estimation, since the influence of the correlation of shadowing is also included, it is possible to accurately estimate the quality improvement amount of the combined communication channel as compared with the case where the reception levels are simply compared. That is, it is possible to select a base station that gives the best combined quality. Therefore, compared with the conventional base station selection method, it is possible to obtain effects such as improved reception quality, reduced transmission power, reduced interference, and increased subscriber capacity.

Further, in the base station selection method of the second invention of the present application, if the mobile station sequentially receives in time division the channels which are constantly transmitted by each base station with constant power, the receiver is minimized. Also, the power consumption of the mobile station is reduced. Further, by combining the reception results with the smallest time difference among the reception results from different base stations, the estimation accuracy of the quality improvement amount when the communication channels are simultaneously connected can be kept high.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wireless communication system to which the base station selection method of the present invention is applied will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a wireless communication system according to the present invention. Referring to FIG. 1, a large number of base stations 1a, 1b, 1c, ... Are arranged at appropriate intervals (only three of them are shown in FIG. 1). These first base station 1a, second base station 1b, and third base station 1c are
It is connected to the exchange 3, and the exchange 3 is further connected to the communication network 5.

The mobile station 7 is also connected to the first base station 1
a, the second base station 1b, and the third base station 1c are to be moved in the communicable area. In FIG. 1, the mobile station 7 is the second
Is located in an area where simultaneous connection with the base station 1b and the third base station 1c is possible, and the second base station 1b is connected for communication. The first base station 1a, the second base station 1b, and the third base station 1c constantly transmit the base station selection signals Sa, Sb, Sc with constant transmission power. The mobile station 7 receives these base station selection signals Sa, Sb, Sc and determines the simultaneous connection start.

Next, the configuration of the base station 1 shown in FIG. 1 will be described with reference to FIG. Since the first base station 1a, the second base station 1b, and the third base station 1c have almost the same configuration, the internal configuration of the first base station 1a will be described here as an example. . The first base station 1a includes an antenna duplexer 11 connected to an antenna, a transmitter 13, and a plurality of receivers 1
5 (15a, 15b, ...) And a plurality of transmitters 17 (17
a), 17b, ...) And a baseband processing unit 19. Further, the exchange 3 includes a combining unit 33, a distributing unit 37, and switching circuits 31 and 39.

In FIG. 2, the transmitter 13 of the first base station 1a constantly transmits the base station selection signal Sa at a constant transmission power via the antenna duplexer 11 and the antenna. Here, when the mobile station 7 does not perform simultaneous connection and is connected only to the first base station 1a, the transmission signal of the mobile station 7 is transmitted to any one of the plurality of receivers 15a, 15b ,. The received signal is received by the receiver and the baseband processing unit 19
Output to. In the baseband processing unit 19, after the baseband processing is performed, the baseband processing unit 19 transmits the baseband processing to the switching center 3 and passes through the combining unit 33 to the communication network 5. Here, the switching circuit 31 has a function of forming an arbitrary set (combination) of all the channels of each base station and sending it to the synthesizing unit 33, and the switching circuit 39 is the distributing unit 37.
It has a function of transmitting a set of signals distributed by the above method to an arbitrary channel.

On the contrary, the signal from the other party sent from the communication network 5 passes through the distributor 37 of the exchange 3 and then,
The data is transmitted to the base station 1, subjected to baseband processing, and transmitted from any one of the plurality of transmitters 17a, 17b, ....

On the other hand, in the case of simultaneous connection, the signals respectively received by the plurality of base stations 1a, 1b, ... Are transmitted to the exchange 3 and are combined by the combining unit 33 before being connected to the communication network 5.
Sent to. Further, the signal from the other party sent from the communication network 5 is distributed by the distribution unit 37 of the exchange 3 and transmitted to each base station 1, and thereafter, the baseband processing unit 19 performs the baseband processing. It is transmitted from one of the transmitters 17.

Next, the configuration of the mobile station will be described with reference to FIG. The mobile station 7 includes an antenna duplexer 71 connected to an antenna, a receiver 73, and a plurality of receivers 75 (75
a, 75b, ...) And a plurality of transmitters 77 (77a, 77a).
b), a baseband processing unit 79, a base station selection unit 81, and a terminal processing unit 83.

The receiver 73 is for receiving the base station selection signal S output from the base station 1, and includes a first base station 1a, a second base station 1b, and a third base station 1c. It is for sequentially receiving the base station selection signal S transmitted from. The base station selection unit 81 determines whether to start the simultaneous connection and selects a base station to be simultaneously connected from the plurality of base stations 1a, 1b, ... And the base station 1 in communication through the baseband processing unit 79. Report to. First receiver 75a, second receiver 75b and first transmitter 77
a, the second transmitter 77b is used to perform information transmission with the base station 1 via the wireless line C. When the simultaneous connection is not performed, only the first receiver 75a and the first transmitter 77a are used. In this case, the synthesis unit and the distribution unit are through paths.

Since the mobile station 7 shown in FIG. 3 is provided with two sets of the receiver 75 and the transmitter 77, it has the capability of simultaneously connecting with a maximum of two base stations 1. Further, when performing simultaneous connection, the two base stations 1a and 1b are connected.
Respectively, the respective transmitted signals are received by the first receiver 75a and the second receiver 75b, and the respective signals are combined by the baseband processing unit 79 and sent to the terminal device 83. Further, after the signal sent from the terminal device 83 is subjected to the baseband processing in the baseband processing unit 79, the first transmitter 77a and the second transmitter 77 are provided.
It is transmitted from b to the two base stations 1a and 1b. Regarding the transmission, for example, only one transmitter 77a is used for transmission, and the same signal having a different propagation path is used for the two base stations 1.
It can also be received by a and 1b.

Next, the processing in the base station selection unit 81, which is the main part of this embodiment, will be described. The receiver 73 is shown in FIG.
And as shown in FIG. 5, the base station selection signal S from the first base station 1a, the second base station 1b, and the third base station 1c.
Are sequentially received every 10 msec, for example, and the reception level is sent to the base station selection unit 81. In this embodiment, the mobile station 7 is in connection with the second base station 1b. Therefore, the base stations that may be newly connected are the first base station 1a and the third base station 1c. In the base station selection unit 81,
(a) reception quality when connecting only to the second base station 1b,
(b) receiving by the second base station 1b and the first base station 1a,
Reception quality when combined, (c) second base station 1b and third base station
The reception qualities when they are received by the base station 1c and are combined, are estimated and compared. The estimation method differs depending on the combination method used for simultaneous connection. Here, a case of selective combination and a case of maximum ratio combination will be described.

First, the case of selective combining will be described.

(1) Reception quality when connecting to only the second base station 1b The results of reception of the base station selection signal S from the second base station 1b, that is, only the reception level BS2 is averaged. (Fig. 4 (a)) (2) Reception quality when received and combined by the second base station 1b and the first base station 1a Signal for base station selection from the second base station 1b in the same frame The reception result of S (reception level BS2) and the reception result of the base station selection signal S from the first base station 1a (reception level BS1) are compared, and the larger one is selected. This selection is performed every frame and averaged. (FIG. 4 (b)) (3) Reception quality when received and combined by the second base station 1b and the third base station 1c Base station selection signal from the second base station 1b in the same frame The reception result of S (reception level BS2) and the reception result of the base station selection signal S from the third base station 1c (reception level BS3) are compared, and the larger one is selected. This selection is performed every frame and averaged. (FIG. 4C) Next, the case of maximum ratio combination will be described. (4) Reception quality when connecting to only the second base station 1b Only the reception result (reception level BS2) of the base station selection signal S from the second base station 1b is averaged. (Fig. 5
(A)) (5) Reception quality when received and combined by the second base station 1b and the first base station 1a Reception of the base station selection signal S from the second base station 1b in the same frame The result (reception level BS2) and the reception result (reception level BS1) of the base station selection signal S from the first base station 1a are added. This calculation is performed for each frame and the results of addition are averaged. In reality, perfect combining is impossible, and therefore the reception quality when realistic combining is performed can also be obtained. (FIG. 5 (b)) (6) Reception quality when received and combined by the second base station 1b and the third base station 1c Base station selection signal from the second base station 1b in the same frame The reception result of S (reception level BS2) and the reception result of the base station selection signal S from the third base station 1c (reception level BS3) are added. This calculation is performed for each frame and the results of addition are averaged. In reality, perfect combining is impossible, and therefore the reception quality when realistic combining is performed can also be obtained. (FIG. 5C) As described above, the communication quality after combining can be estimated from the average results of (1) to (6).

Further, according to the present embodiment, besides the above, it is possible to easily estimate the post-synthesis quality according to the synthesis method.

By the way, in the above (1) to (6), an example in which a plurality of signals in the same frame are combined is shown. However, since signals at the same time are combined when they are simultaneously connected and combined, it is desirable to combine signals for selecting base stations at the same time in order to accurately estimate the reception quality after combination. For example, by using a plurality of receivers, it is possible to receive signals at the same time and with a constant level transmitted by each base station, and combine the signals at the same time. Further, in the case of using one receiver for time division for power saving etc., if signals with a time difference sufficiently shorter than the fluctuation cycle of shadowing are combined, they are combined at the same time. It is possible to obtain the same effect as the case.

On the other hand, as described above, in order to combine the signals having the smallest time difference with each other, when the signals of the adjacent frames are closer in time than the signals of the same frame, the signals of the adjacent frames are combined. Good to do.

For example, when the first frame is composed of three time slots T11, T12 and T13 as shown in FIG. 4, the time slot T of the first frame is
When 11 and time slot T13 are combined in the same frame, the time difference between time slot T11 and time slot T13 is 20 msec. However, time slot T13 of this first frame and the next second frame If the time slot T21 is combined with the time slot T21, the time difference between the time slot T13 and the time slot T21 is 10 msec. In the figure, the time slot T11 of the first frame,
T12 and T13 are respectively a first base station, a second base station,
BS1 is set to correspond to the first base station
The reception level of the signal for selecting the base station from the base station of
Reference numeral 2 represents the reception level of the base station selection signal from the second base station, and BS3 represents the reception level of the base station selection signal from the third base station.

The base station selection unit 81 also determines the start of simultaneous connection and selects the base station 1 to be newly connected. Examples of these methods are shown in FIGS. 6 and 7. Normally, as shown in FIG. 6, the quality when connecting with only the second base station 1b is compared with the quality when simultaneously connecting with other base stations 1a and 1c, and the quality increases when performing simultaneous connection. If the amount is equal to or larger than the reference increase amount, simultaneous connection is started.

However, as shown in FIG. 7, when the deterioration of the communication quality is large, the simultaneous connection is started even if the quality increase amount in the simultaneous connection is less than the reference increase amount. Of course, the base station with the larger increase in reception quality is selected.

As described above, according to the base station selection method of the present embodiment, simultaneous connection start determination and selection of simultaneous connection base station are performed in consideration of the shadowing correlation between the mobile station and each base station. be able to. That is, when the correlation is small, the communication quality after combining is estimated to be higher than when the correlation is large. Further, the relative increase amount of the combined quality with respect to the current communication quality can be estimated fairly accurately, and the base station selection becomes more accurate.

[0032]

As described above, according to the base station selection method of the present invention, simultaneous connection start determination and selection of simultaneous connection base station can be performed in consideration of the influence of shadowing correlation. Compared to a case where the reception levels are simply compared, the quality improvement amount of the combined communication channel can be estimated more accurately. That is, it is possible to select a base station that gives the best combined quality. Therefore, compared with the conventional base station selection method, it is possible to obtain effects such as improved reception quality, reduced transmission power, reduced interference, and increased subscriber capacity.

Further, in the mobile station, if the channels which are constantly transmitted by the base stations with constant power are sequentially received in a time division manner, the receiver is minimized and the power consumption of the mobile station is reduced. Further, by combining the reception results with the smallest time difference among the reception results from different base stations, the estimation accuracy of the quality improvement amount when the communication channels are simultaneously connected can be kept high. In this case, the mobile station configuration is almost the same as the conventional system and can be dealt with only by changing the software.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a wireless communication system to which a base station selection method according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a base station.

FIG. 3 is a block diagram showing a configuration of a mobile station.

FIG. 4 is a diagram illustrating a method of estimating quality after selective combining.

FIG. 5 is a diagram illustrating a method of estimating quality after maximum ratio combination.

FIG. 6 is a diagram illustrating simultaneous connection start determination and simultaneous connection base station selection.

FIG. 7 is a diagram illustrating simultaneous connection start determination and simultaneous connection base station selection.

FIG. 8 is a block diagram illustrating site diversity.

FIG. 9 is a block diagram illustrating the correlation of shadowing.

[Explanation of symbols]

 1 Base Station 3 Switching Station 5 Communication Network 7 Mobile Station 11,71 Antenna Duplexer 13,17,77 Transmitter 15,73,75 Receiver 19,79 Baseband Processing Unit 31,39 Switching Circuit 33 Combining Unit 37 Distribution Unit 81 base station selection unit 83 terminal processing unit C wireless line S base station selection signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04Q 7/04 K

Claims (3)

[Claims] 1. A method of selecting a base station in a wireless communication system having a plurality of base stations connected to a communication network and a mobile station that can be simultaneously connected to the plurality of base stations via a wireless line, the method comprising: The mobile station receives a predetermined signal transmitted from each of the plurality of base stations with a predetermined power, and combines the signals to combine them in a wireless link with each of the simultaneously connected base stations. A base station selection method, characterized in that the subsequent communication quality is estimated, and control relating to connection with the base station is performed based on the estimation result. 2. A base station selection method in a wireless communication system having a plurality of base stations connected to a communication network and a mobile station that can be simultaneously connected to the plurality of base stations via a wireless line, the method comprising: The mobile station sequentially receives a predetermined channel transmitted from each of the plurality of base stations at a predetermined power in a time division manner, and combines reception results with the smallest time difference among reception results from different base stations. According to the method, the quality after combining when the communication channels are combined is estimated, and the control relating to the connection with the base station is performed based on the estimation result. 3. The base station selection method according to claim 1, wherein the control relating to the connection with the base station is for determining a simultaneous connection start and selecting a simultaneous connection base station.