JP3078193B2 - Base station selection method and base station selection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting a base station 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, when performing communication via a radio line between a mobile station 7 and a base station 1 as shown in FIG. 1
a, 1b,..., a plurality of radio circuits Ca, Cb,... are connected, a plurality of signals arriving from different propagation paths are simultaneously received, and the signals are synthesized by a higher-level station such as the exchange 3. There is a technique called site diversity, which improves the quality of products.

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

Therefore, when selecting a base station to be newly connected, the propagation loss between the mobile station 7 and the base station 1a currently in communication and the transmission loss between the mobile station 7 and the newly connected base station 1b are determined. A general method is to compare the propagation loss and start the connection when the difference is within a certain value. As a means for comparing the propagation loss, a method in which the mobile station 7 receives a signal having a constant transmission power constantly transmitted by each of the base stations 1a, 1b,..., Averages the signals received for a certain period of time, and compares the values. Has been taken.

[0005]

If the level fluctuation in the radio channel is only Rayleigh fluctuation, there is no problem with the conventional base station selection method. However, in reality, there is shadowing that occurs when a radio wave is 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 of the wireless lines Ca, Cb, Cc has a correlation. Generally, the correlation between the radio channel Cb and the radio channel Cc of the base station 1b and the base station 1c in the same direction as viewed from the mobile station 7 is large, and the mobile station 7
The correlation between the radio channel Ca and the radio channel Cb and the correlation between the radio channel Ca and the radio channel Cc in which the base stations are in opposite directions are small (FIG. 9).

[0006] Similarly to the Rayleigh fluctuation, the smaller the correlation between the shadowing fluctuations, the higher the signal quality after the synthesis. However, in the conventional method, since cell selection taking into account the correlation of shadowing is not performed, there is a drawback that a base station that maximizes reception quality is not necessarily selected. Further, in a system that performs transmission power control, there is a drawback that transmission power becomes unnecessarily large and interference with others is also increased. Further, in an interference-limited system such as the CDMA system, there is a disadvantage that the subscriber capacity is reduced due to an increase in the amount of interference.

[0007] The present invention has been made in view of the above-mentioned problems, and when starting simultaneous connection, the quality after combining is the best considering the correlation of shadowing between the mobile station and each base station. It is an object of the present invention to provide a base station selection method capable of obtaining a remarkable effect such as improvement of reception quality, reduction of transmission power, reduction of interference amount, increase of subscriber capacity, and the like by selecting a base station that improves. Aim.

[0008]

In order to achieve the above object, the present invention comprises 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 radio line. A method of selecting a base station in a wireless communication system having the mobile station, wherein the mobile station receives predetermined signals transmitted at predetermined power from the plurality of base stations, and synthesizes those signals to simultaneously The gist of the present invention is to estimate the communication quality of a radio link after being combined with each connected base station, and to perform control related to connection with the base station based on the estimation result.

Further, the present invention comprises a plurality of base stations connected to a communication network, and mobile stations connected to the base stations via radio lines. Each mobile station is connected to the plurality of base stations simultaneously. A method for selecting a base station in a wireless communication system, comprising:
The mobile station sequentially receives a predetermined channel transmitted at a predetermined power from each of the plurality of base stations in a time-division manner, and combines reception results with the smallest time difference among reception results from different base stations. Accordingly, the gist is to estimate the quality after combining when the communication channels are combined, and to perform control related to connection with the base station based on the estimation result. It should be noted that the control relating to the connection with the base station may be a determination of simultaneous connection start and selection of a simultaneously connected base station, and the combining of the received signals may be any one of selective combining or maximum ratio combining. It may be performed by a method.

[0010] The present invention is also a base station selecting apparatus in a wireless communication system having 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. And receiving means comprising a plurality of receivers each receiving a predetermined signal transmitted at a predetermined power from each of the plurality of base stations,
Combining means for combining predetermined signals received by the plurality of receivers, and estimating the communication quality of the combined radio line between the base stations connected at the same time based on the result of the combining performed by the combining means. The gist of the present invention is to include base station selecting means for performing control related to connection with the base station based on the estimation result. Further, the present invention is a base station selecting apparatus in a wireless communication system having a plurality of base stations connected to a communication network and a mobile station capable of being connected to the plurality of base stations substantially simultaneously via a wireless line. Receiving means for sequentially receiving a predetermined channel transmitted at predetermined power from each of the plurality of base stations in a time-division manner, and receiving results from different base stations sequentially received in a time-division manner. A combining means for combining signals having the smallest time difference in reception time among them, and estimating quality after combining when a communication channel is combined by the combining result in the combining means, and the base station and the base station based on the estimation result. And a base station selecting means for performing control related to the connection.

[0011]

According to the present invention, the mobile station receives a signal having a constant transmission power transmitted from each base station, combines the received signals, and estimates the combined quality when the communication channels are simultaneously connected.
Based on the estimation result, the simultaneous connection start determination and the selection of the simultaneous connection base station are performed. Since the estimation includes the influence of the correlation of shadowing, the quality improvement amount of the communication channel after the combination can be estimated more accurately than when the reception levels are simply compared. That is, it is possible to select a base station having the best combined quality. Therefore, compared with the conventional base station selection method, it is possible to obtain effects such as improvement of reception quality, reduction of transmission power, reduction of the amount of interference, and increase of subscriber capacity.

Further, according to the present invention, the mobile station sequentially receives, in a time-division manner, the channel that each base station constantly transmits at a constant power, so that the number of receivers is minimized and the consumption of the mobile station is minimized. The power is also reduced. Also, 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 radio communication system to which the base station selecting 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 stations are shown in FIG. 1). These first base station 1a, second base station 1b, and third base station 1c
The exchange 3 is connected to the exchange 3, and the exchange 3 is connected to the communication network 5.

Further, the mobile station 7 is connected to the first base station 1
a, it is assumed that it moves in an area where it can communicate with the second base station 1b and the third base station 1c. In FIG. 1, the mobile station 7 is
The base station 1b and the third base station 1c are located in an area where simultaneous connection is possible, and are connected to the second base station 1b 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 at a constant transmission power. The mobile station 7 receives these base station selection signals Sa, Sb, Sc and determines the start of simultaneous connection.

Next, the configuration of the base station 1 shown in FIG. 1 will be described with reference to FIG. Note that the first base station 1a, the second base station 1b, and the third base station 1c have substantially the same configuration, and therefore the internal configuration of the first base station 1a will be described here as an example. . The first base station 1 a 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. The switching center 3 includes a combining unit 33, a distribution unit 37, and switching circuits 31, 39.

In FIG. 2, the transmitter 13 of the first base station 1a constantly transmits the base station selection signal Sa via the antenna duplexer 11 and the antenna at a constant transmission power. 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 one of the plurality of receivers 15a, 15b,. Of the baseband processing unit 19
Output to In the baseband processing unit 19, after performing the baseband processing, it is transmitted to the exchange 3, passed through the combining unit 33 and sent to the communication network 5. Here, the switching circuit 31 has a function of creating an arbitrary set (combination) of all the channels of each base station and transmitting the set to the combining unit 33, and the switching circuit 39 includes a distributing unit 37.
Has a function of transmitting a set of signals distributed by the above to an arbitrary channel.

Conversely, the signal from the other party sent from the communication network 5 passes through the distribution unit 37 of the exchange 3 and then passes through the distribution unit 37.
It is transmitted to the base station 1, performs baseband processing, and is transmitted from any one of the plurality of transmitters 17a, 17b,.

On the other hand, in the case of simultaneous connection, the signals received by the plurality of base stations 1a, 1b,... Are transmitted to the exchange 3 and combined by the combining unit 33.
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 then the baseband processing unit 19 performs 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, 77b).
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. For sequentially receiving the base station selection signal S transmitted from. The base station selection unit 81 determines whether or not to start simultaneous connection, and selects a base station to be simultaneously connected from the plurality of base stations 1a, 1b,... Report to First receiver 75a, second receiver 75b, and first transmitter 77
a, The second transmitter 77b is used to transmit information to and from the base station 1 via the radio 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 combining unit and the distributing unit are through paths.

Since the mobile station 7 shown in FIG. 3 has two sets of the receiver 75 and the transmitter 77, the mobile station 7 has the ability to connect with up to two base stations 1 at the same time. When performing simultaneous connection, two base stations 1a, 1b
, The first and second receivers 75a and 75b respectively receive the transmitted signals, combine the respective signals in the baseband processing unit 79, and send them to the terminal device 83. After the baseband processing unit 79 performs baseband processing on the signal transmitted from the terminal device 83, the first transmitter 77 a and the second transmitter 77
b to the two base stations 1a and 1b. Regarding transmission, for example, transmission is performed using only one transmitter 77a, and the same signal having only a different propagation path is transmitted to two base stations 1
a, 1b.

Next, the processing in the base station selecting section 81 which is a main part of the present embodiment will be described. The receiver 73 is shown in FIG.
As shown in FIG. 5 and FIG. 5, base station selection signals S from the first base station 1a, the second base station 1b, and the third base station 1c.
Are sequentially received, for example, every 10 msec, and the reception level is transmitted to the base station selecting unit 81. In this embodiment, the mobile station 7 is being connected to 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 connected only to the second base station 1b,
(b) received by the second base station 1b and the first base station 1a,
(C) Second base station 1b and third base station 1b
, And the reception quality when the signals are combined with each other is estimated and compared. The estimation method differs depending on the combination method at the time of simultaneous connection. Here, the case of selective combining and the case of maximum ratio combining will be described.

First, the case of selective combining will be described.

(1) Reception quality when connected only to second base station 1b The reception result of base station selection signal S from second base station 1b, that is, only reception level BS2 is averaged. (FIG. 4 (a)) (2) Reception quality when receiving and combining at second base station 1b and first base station 1a Signal for base station selection from second base station 1b in the same frame The reception result of S (reception level BS2) is compared with the reception result of the base station selection signal S from the first base station 1a (reception level BS1), and the larger one is selected. This selection is made every frame and averaged. (FIG. 4 (b)) (3) Reception quality when receiving and combining at second base station 1b and third base station 1c Signal for base station selection from second base station 1b in the same frame The reception result of S (reception level BS2) is compared with the reception result of the base station selection signal S from the third base station 1c (reception level BS3), and the larger one is selected. This selection is made every frame and averaged. (FIG. 4C) Next, the case of the maximum ratio combination will be described. (4) Reception quality when connected only to second base station 1b Only the reception result (reception level BS2) of base station selection signal S from second base station 1b is averaged. (FIG. 5
(A)) (5) Reception quality when receiving and combining by second base station 1b and first base station 1a Receiving base station selection signal S from 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 every frame, and the result of addition is averaged. In reality, complete combining is impossible, so that it is possible to obtain the reception quality when realistic combining is performed. (FIG. 5 (b)) (6) Reception quality when receiving and combining at second base station 1b and third base station 1c Signal for base station selection from 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 every frame, and the result of addition is averaged. In reality, complete combining is impossible, so that it is possible to obtain the reception quality when realistic combining is performed. (FIG. 5 (c)) As described above, the communication quality after combining can be estimated from the average results of (1) to (6).

Further, according to this embodiment, it is possible to easily estimate the post-synthesis quality according to the synthesis method other than the above.

By the way, in the above-mentioned (1) to (6), examples in which a plurality of signals in the same frame are synthesized are shown. However, since signals at the same time are combined in simultaneous connection and combining, it is desirable to combine base station selection signals at the same time in order to accurately estimate the combined reception quality. For example, by using a plurality of receivers, it is possible to receive the same-level constant signal transmitted from each base station at the same time and combine the signals at the same time. Also, when time-division reception is performed using one receiver for power saving or the like, if signals with a time difference sufficiently shorter than the fluctuation period of shadowing are synthesized, the signals are synthesized at the same time. The same effect as in the case can be obtained.

On the other hand, as described above, in order to combine signals having a time difference as small as possible, when a signal in an adjacent frame is temporally closer than a signal in the same frame, the signal and the signal in the adjacent frame 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.
When the time slot T13 and the time slot T13 are combined, when the time slot T11 and the time slot T13 are combined in the same frame, the time difference between the time slot T11 and the time slot T13 is 20 msec. 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 slots T11, T11 of the first frame are shown.
T12 and T13 are a first base station, a second base station,
BS1 is set to correspond to the third base station, and BS1
The reception level of the base station selection signal from the base station of
2 indicates the reception level of the base station selection signal from the second base station, and BS3 indicates the reception level of the base station selection signal from the third base station.

The base station selection section 81 also determines the start of simultaneous connection and selects a base station 1 to be newly connected. One example of these methods is shown in FIGS. Normally, as shown in FIG. 6, the quality when connected only to the second base station 1b is compared with the quality when connected simultaneously to the other base stations 1a and 1c, and the quality increases when simultaneous connection is performed. If the amount is equal to or greater 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 when the amount of increase in the quality of the simultaneous connection is less than the reference increase. Note that, of course, the base station with the larger increase in the 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 simultaneously connected base stations are performed in consideration of the correlation of shadowing between the mobile station and each base station. be able to. That is, when the correlation is small, the communication quality after the combination is estimated to be higher than when the correlation is large. Also, the amount of increase in the combined quality relative 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, it is possible to determine the simultaneous connection start in consideration of the influence of the shadowing correlation and to select the simultaneous connection base station. Compared to a case where reception levels are simply compared, it is possible to accurately estimate the quality improvement amount of the communication channel after the combination. That is, it is possible to select a base station having the best combined quality. Therefore, compared with the conventional base station selection method, it is possible to obtain effects such as improvement of reception quality, reduction of transmission power, reduction of the amount of interference, and increase of subscriber capacity.

Further, if the mobile station successively receives, in a time-division manner, channels that are constantly transmitted by each base station at a constant power, the number of receivers is minimized, and the power consumption of the mobile station is reduced. Also, 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 the 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 illustrating a configuration of a base station.

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

FIG. 4 is a diagram for explaining a method of estimating quality after selective synthesis.

FIG. 5 is a diagram for explaining a method of estimating the maximum ratio combined quality.

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 a correlation of shadowing.

[Explanation of symbols]

 Reference Signs List 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 section 31, 39 switching circuit 33 synthesis section 37 distribution section 81 base station selection unit 83 terminal processing unit C wireless line S base station selection signal

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-222124 (JP, A) JP-A-4-167720 (JP, A) JP-A-6-45,991 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 102 H04Q ^7/ 00-7/38

Claims (6)

(57) [Claims] 1. A method for selecting a base station in a wireless communication system having a plurality of base stations connected to a communication network and a mobile station capable of simultaneously connecting to the plurality of base stations via a wireless line, The mobile station receives a predetermined signal transmitted at a predetermined power from each of the plurality of base stations, and combines the signals to thereby combine the signals in the radio link between the base stations and the base stations connected simultaneously. A base station selection method comprising: estimating communication quality to be performed later; and performing control related to connection with the base station based on the estimation result. 2. A method for selecting a base station in a wireless communication system having a plurality of base stations connected to a communication network and a mobile station capable of being connected to the plurality of base stations substantially simultaneously via a wireless line, The mobile station sequentially receives a predetermined channel transmitted at a predetermined power from each of the plurality of base stations in a time-division manner, and combines reception results with the smallest time difference among reception results from different base stations. A base station selecting method for estimating quality after combining when communication channels are combined, and performing control relating to connection with the base station 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 includes performing a simultaneous connection start determination and selecting a simultaneously connected base station. 4. The base station selecting method according to claim 1, wherein the combining of the received signals is performed by one of a combining method of a selective combining and a maximum ratio combining. 5. A base station selecting apparatus in a wireless communication system, comprising: a plurality of base stations connected to a communication network; and a mobile station capable of simultaneously connecting to the plurality of base stations via a wireless line, The mobile station includes: a receiving unit including a plurality of receivers each receiving a predetermined signal transmitted at a predetermined power from each of the plurality of base stations; and combining the predetermined signals received by the plurality of receivers. Estimating the communication quality of the radio channel between the base station and the base station connected simultaneously by the synthesis result of the synthesis means, and controlling the connection with the base station based on the estimation result. And a base station selecting means for performing the following. 6. A base station selection device in a wireless communication system having a plurality of base stations connected to a communication network, and a mobile station capable of being connected to the plurality of base stations substantially simultaneously via a wireless line, The mobile station is a receiving unit that sequentially receives a predetermined channel transmitted at a predetermined power from each of the plurality of base stations in a time-division manner, and includes a reception result from a different base station sequentially received in a time-division manner. Combining means for combining signals having the smallest time difference in reception time, and estimating quality after combining when a communication channel is combined based on the combining result of the combining means, and based on the estimation result, A base station selecting apparatus, comprising: a base station selecting means for performing control related to connection.