JP4777401B2 - Radio base station and radio communication method - Google Patents

Description

  The present invention relates to a radio base station provided with an adaptive array antenna, and a radio communication method for the radio base station.

In a radio communication system composed of an adaptive array radio base station having a plurality of antenna elements and a mobile communication terminal, throughput is reduced during reception depending on the state of the user of the terminal that performs radio communication with the radio base station. The problem arises. For example, when the user is using the terminal while moving at 80 km / h or more, high-speed fading fluctuation occurs in the received signal, and the throughput decreases.
For this reason, a radio communication apparatus has been proposed that selects transmission using an adaptive array antenna or transmission using MIMO from reception quality information acquired from a counterpart communication terminal so as to obtain better throughput (see Patent Document 1). ).
Japanese Patent Laid-Open No. 2007-128569

However, in the wireless communication device described in Patent Document 1 described above, when performing wireless communication using the selected transmission method, an appropriate throughput may be obtained depending on the interval at which the antenna elements used for wireless communication are arranged. There are cases where it is not possible.
This is because the antenna correlation (fading correlation) increases when the interval between the antenna elements is small, while the antenna correlation decreases when the interval between the antenna elements is large. This is because the communication quality may not be maintained because the antenna element suitable for the selected transmission method is not selected depending on the antenna interval.
Therefore, there is a problem that it is not possible to obtain the optimum throughput by the selected transmission method with respect to the change of the propagation environment according to the user's usage situation only by switching the wireless signal transmission method.

  The present invention has been made in view of such problems, and the object of the present invention is to maintain communication quality even when a radio signal transmission method is selected according to changes in the propagation environment. An object of the present invention is to provide a radio base station and a radio communication method capable of obtaining a high throughput.

In order to achieve the above object, a radio base station of the present invention has a plurality of antennas, and obtains reception quality information of each antenna for the plurality of antennas in a radio base station that performs radio communication with a communication destination device. An acquisition unit that performs acquisition, a grasping unit that grasps a fluctuation trend of a value related to reception quality of each antenna acquired by the acquisition unit, and a change trend of a value related to reception quality of each antenna that is grasped by the grasping unit Determining a transmission method in the wireless communication and selecting at least two or more antennas to be used in the determined transmission method from the plurality of antennas; A transmission unit configured to transmit information related to a transmission method to the communication destination device.

  The radio base station of the present invention further includes a determination unit that determines a degree of correlation between the antennas based on a tendency of variation in a value related to reception quality at each antenna, which is grasped by the grasping unit, Preferably, the selection unit selects an antenna to be used for the wireless communication according to a degree of correlation between the antennas determined by the determination unit.

  In the variation tendency of the value related to the reception quality at each of the antennas grasped by the grasping unit, the determination unit is equal to or more than a first predetermined value compared to the value related to the reception quality acquired immediately before the value related to the reception quality. It is preferable to detect the time point when the correlation is lowered and to determine the degree of correlation according to the time difference between the detected time points between the antennas.

  Further, in the radio base station of the present invention, the plurality of antennas are array antennas, and the selection unit selects one of radio communication by directivity control and radio communication by MIMO as a transmission method in the radio communication. It is preferable to determine.

  The radio base station of the present invention further includes a calculation unit that calculates a weight of each antenna in the plurality of antennas, and the selection unit includes a time interval for calculating a weight in the calculation unit, and the determination unit It is preferable to determine a transmission method to be used for the wireless communication based on the cycle in which the time point determined in step 1 occurs.

In addition, the wireless communication method of the present invention is a wireless base station wireless communication method having a plurality of antennas and performing wireless communication with a communication destination device, and for each of the plurality of antennas, obtains reception quality information of each antenna. According to the obtaining step, the grasping step for grasping the fluctuation tendency of the value related to the reception quality of each antenna obtained in the obtaining step, and the fluctuation tendency of the value relating to the reception quality at each antenna obtained in the grasping step, A step of determining a transmission method in wireless communication and selecting at least two or more antennas to be used for wireless communication from the plurality of antennas; and information on the transmission method determined in the selection step, And a transmission step of transmitting to the communication destination device.

  The radio base station according to the present invention selects the transmission method according to the propagation environment from the fluctuation tendency of the value related to the reception quality of each antenna, and selects the antenna element suitable for the selected transmission method, thereby improving the communication quality. It is possible to obtain the optimum throughput.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of a configuration example of a radio base station according to the present invention. A radio base station 20 shown in FIG. 1 includes a plurality of antenna elements 1 that are array antennas, and a plurality of radio (RF) units that are provided for each of the plurality of antennas and up / down convert radio signals from a counterpart communication device. 2, a transmission control unit 3, and a reception control unit 4. The transmission control unit 3 includes a transmission processing unit 5. The reception control unit 4 acquires a weight calculation unit (calculation unit) 11 that calculates the weight of each antenna in a plurality of antennas and reception quality information indicating reception quality of each antenna for each of the plurality of antennas at predetermined intervals. A reception quality information acquisition unit (acquisition unit) 12, a reception quality fluctuation trend grasping unit (grasping unit) 13 for grasping a fluctuation tendency of a value related to reception quality of each antenna acquired by the reception quality information acquisition unit 12, and a reception quality A correlation determination unit (determination unit) 14 that determines the degree of correlation between the antennas based on the variation tendency of the value regarding the reception quality at each antenna, which is grasped by the variation tendency grasping unit 13, and the correlation determination unit 14 determine The transmission method for wireless communication is determined according to the degree of correlation between each antenna, and the antenna to be used for wireless communication is selected from multiple antennas. Comprising-option antenna selecting section (selecting section) 7, and a reception processing unit 8 to perform processing for forming a beam emitted from the selected antenna. In this embodiment, the weight calculation unit 11, the reception quality information acquisition unit 12, the reception quality fluctuation tendency grasping unit 13, and the correlation determination unit 14 are provided in the reception control unit 4. However, the present invention is not limited to this. It may be configured independently.

  The reception quality information acquisition unit 12 acquires reception quality information of a reception radio signal from a communication destination device that is a communication partner. As a value related to reception quality in the reception quality information, a value indicating reception power measured at each antenna of a plurality of antennas and a value indicating reception quality such as SINR are acquired. The reception quality fluctuation tendency grasping unit 13 grasps the fluctuation tendency of the value related to the reception quality of each acquired antenna.

  The correlation determination unit 14 determines the degree of correlation based on the variation tendency of the value related to reception quality at each antenna, which is grasped by the reception quality variation tendency grasping unit 13.

  The antenna selection unit 7 performs wireless communication by directivity control using an adaptive array antenna as a transmission method in wireless communication from among a plurality of antennas according to the degree of correlation between the antennas determined by the correlation determination unit 14. And any one of MIMO wireless communication is determined. Further, the antenna selection unit 7 selects at least two or more antenna elements used for wireless communication. The antenna selected by the antenna selection unit 7 is used for receiving a radio signal from the communication destination device and used for transmitting a radio signal to the communication destination device.

  The transmission processing unit (transmission unit) 5 transmits information on the transmission method determined by the antenna selection unit 7 to the communication destination device in order to appropriately perform wireless communication with the communication destination device.

  Next, a transmission method selection and antenna selection method by the antenna selection unit 7 based on the correlation degree between the antennas determined by the correlation determination unit 14 will be described with reference to the flowchart of FIG. The plurality of antennas are configured by array antennas, and the weight calculation unit 11 calculates the weight of each antenna in the plurality of array antennas.

  When the reception control unit 4 of the radio base station starts communication with the communication destination device (step 101), the reception quality information acquisition unit 12 acquires the reception quality information of the reception radio signal of each antenna, and the reception quality fluctuation tendency The grasping unit 13 grasps the fluctuation tendency of the value related to the reception quality in the received reception quality information of each antenna (step 102). Correlation determination unit 14 determines the degree of correlation between the antennas according to the variation tendency of each antenna grasped by reception quality variation tendency grasping unit 13 (step 103) (details regarding the determination of the correlation degree will be described later). . Then, the antenna selection unit 7 uses the information regarding the fluctuation tendency of the value related to the reception quality determined by the correlation determination unit 14 to determine a transmission method in wireless communication and at least two or more antennas used for wireless communication Is selected (steps 104 to 112).

  In the flowchart of FIG. 2, as the transmission method determination and antenna selection method in the antenna selection unit 7, the antenna selection unit 7 uses the weight update time interval calculated by the weight calculation unit 11 and the correlation determination unit 14. Information on the fluctuation tendency of the value related to the determined reception quality is used. First, the antenna selection unit 7 compares the weight update time interval with a cycle (falling time interval) in which a time point (timing) at which a value related to reception quality becomes a predetermined value or less in a variation tendency of each antenna (step 104). ). As a result of the comparison, when the drop time interval is larger than the weight update time interval (in the case of Yes), the correlation of each antenna element of an arbitrary antenna element group (first antenna element group) that seems to have a high correlation degree The degree is investigated (step 105), and it is determined whether or not the antenna element group has a truly high degree of correlation (step 106). When the antenna selection unit 7 determines that the antenna element group has a high degree of correlation (in the case of Yes), the antenna selection unit 7 performs wireless communication by directivity control in order to keep the communication quality following the change in the propagation environment. Then, at least two or more antenna elements used for wireless communication are selected from the first antenna element group (step 107). In this case, if an antenna element having a low antenna correlation is added, there is a high possibility that the communication quality is deteriorated. Therefore, it is necessary to perform control by selecting only an antenna element having a high antenna correlation.

  In step 106, when the antenna selection unit 7 determines that the antenna element group has a low degree of correlation (in the case of No), the antenna selection unit 7 investigates the degree of correlation of each antenna element of another arbitrary antenna element group and finds the highest correlation. The antenna element group having a high degree is selected, wireless communication by directivity control is selected, and at least two or more antenna elements used for the wireless communication are selected from the antenna element group having the highest degree of correlation ( Step 108).

  In step 104, when the drop time interval is smaller than the weight update time interval (in the case of No), the antenna selection unit 7 selects another arbitrary antenna element group (second antenna element) that is considered to have a low degree of correlation. The degree of correlation of each antenna element in the group) is examined (step 109), and it is determined whether or not the antenna element group has a truly low degree of correlation (step 110). When it is determined that the antenna element group has a low correlation degree (in the case of Yes), the antenna selection unit 7 selects to perform wireless communication by MIMO that can increase the communication capacity as the correlation degree is lower, and further to the second At least two or more antenna elements used for wireless communication are selected from the antenna element group (step 111).

  In Step 110, when the antenna selection unit 7 determines that the antenna element group has a high degree of correlation (in the case of No), the antenna selection unit 7 selects the antenna element group with the lowest degree of correlation and selects to perform wireless communication by MIMO. Then, at least two or more antenna elements used for wireless communication are selected from the antenna element group having the lowest correlation (step 112).

  Then, the reception processing unit 8 generates a weight, and transmits / receives a radio signal to / from a communication apparatus serving as a communication partner using the generated weight by using the antenna selected by the antenna selection unit 7.

  Next, the correlation determination unit 14 uses the fluctuation tendency of the value related to the reception quality at each antenna grasped by the reception quality fluctuation tendency grasping unit 13 to determine the degree of correlation between the antennas (in FIG. 2). Step 103) in the flowchart will be described.

(Method 1 for determining the degree of correlation between antennas)
Correlation determining unit 14 compares the value indicating the reception power with the value indicating the reception power acquired immediately before the value indicating the reception quality at each antenna, as determined by reception quality variation tendency determination unit 13. A point of time when the value drops below the value is detected, and the degree of correlation is determined according to the time difference between the detected points of time between the antennas. At this time, when a time point lower than a predetermined value (first predetermined value) is detected immediately after the time point detected at a certain antenna, the degree of correlation is high if the time difference is small. If the time difference from the time point when the other antennas are lower than the predetermined value is large, the degree of correlation is low.

(Method 2 for determining correlation between antennas)
Correlation determining unit 14 determines a time point when the value indicating the received power is equal to or less than a predetermined value (second predetermined value) in the variation tendency of the value related to reception quality at each antenna, as grasped by reception quality variation tendency grasping unit 13. The degree of correlation may be determined according to the frequency of detection and the frequency at the time of detection, that is, the number of times that the value indicating the received power becomes a predetermined value or less per time.

(Method 3 for determining correlation between antennas)
The correlation determination unit 14 may determine the degree of correlation according to a time average obtained by performing complex multiplication (multiplication with a complex conjugate) between the reception signals of the two antennas. If the degree of correlation is high, the time average is high, and if the degree of correlation is low, the time average is a numerical value close to zero.

(Method 4 for determining correlation between antennas)
Correlation determining unit 14 determines a weighting factor to be given to each value indicating the received power related to the reception quality of each antenna, according to the fluctuation tendency that the value related to the reception quality of each antenna varies with time. The degree of correlation between the antennas may be determined or estimated based on an estimated received power value calculated by adding a weighting factor to a value indicating the received power.

Below, the case where the correlation degree between each antenna is determined based on an estimated received power value is demonstrated.
The fluctuation tendency of the value indicating the received power is configured by combining three kinds of trends A, B, and C. The tendencies A, B, and C will be described with reference to FIG. FIG. 3 schematically shows how the reception quality information (value regarding reception quality) X varies from X1 to any one of X2 to X5 as time (one frame period) elapses.
The tendency A indicates that the reception quality information has changed within a predetermined threshold value α as in the case where the reception quality information changes from X1 to X2 and from X1 to X3. Here, the predetermined threshold α is set to a range in which the reception quality can be determined to be stable (about the fluctuation width due to the noise of the reception quality). The tendency B indicates that the reception quality information has changed in a direction in which the reception quality increases by exceeding a predetermined threshold value α, as in the case where the reception quality information changes from X1 to X4. The tendency C indicates that the reception quality information has changed below the predetermined threshold value α, and the reception quality has decreased in a direction that the reception quality decreases, as in the case where the reception quality information changes from X1 to X5.

  The correlation determination unit 14 determines a variation tendency by a combination of the trends A, B, and C. FIG. 4A is an example of a graph showing the variation of the reception quality information X over time. In FIG. 4A, new reception quality information is plotted as time elapses from time t1 to t6. FIG. 4B is a table for explaining a method for determining a weighting factor.

Since the change from X11 to X12 is a change within a predetermined threshold value α, as shown in FIG. Further, since the change from X12 to X13 is a change in the direction in which the reception quality increases exceeding the predetermined threshold value α, it is indicated as a trend B as shown in FIG. Similarly, each of the three variations from X13 to X16 is shown as a trend B of 3 times.
The correlation determination unit 14 determines that the variation tendency is an improved variation tendency based on a combination of one trend A and four trends B (ABBBB), and a weighting coefficient D1 to be assigned to each of X11 to X16. ˜D6 is increased with time to satisfy D1 <D2 <D3 <D4 <D5 <D6.

Further, the correlation determination unit 14 determines that the fluctuation tendency is a decreasing fluctuation tendency when the fluctuation tendency is, for example, a combination of the tendency A twice and the tendency C three times (ACACC). The coefficients D1 to D6 are increased with time to satisfy D1 <D2 <D3 <D4 <D5 <D6.
Further, when the fluctuation tendency is, for example, a combination of five tendency A (AAAAAA), the correlation determination unit 14 determines that the fluctuation tendency is a stable fluctuation tendency, and uniformizes the weighting factors D1 to D6. In other words, D1 = D2 = D3 = D4 = D5 = D6 ≠ 0.

  Correlation determining section 14 multiplies reception quality information X11-X16 and weighting coefficients D1-D6 corresponding to X11-X16, respectively, and calculates an average value of the multiplication values, thereby calculating an estimated reception power value. Then, the correlation determination unit 14 estimates a fluctuation tendency based on the calculated estimated received power value, and determines the degree of correlation between the antennas based on the estimated fluctuation tendency.

  As described above, in the flowchart shown in FIG. 2, the transmission method is determined as either directivity control wireless communication or MIMO wireless communication, and at least two or more antennas are selected for wireless communication. did. However, depending on the radio conditions between the radio base station and the counterpart communication device, communication quality may not be maintained regardless of which transmission method is used. Therefore, in consideration of such cases, not only the above-described directivity control wireless communication and MIMO wireless communication, but also the selection diversity is selected when a transmission method is selected, and one antenna is used. The wireless communication may be executed. At the time of these selections, as described above, using the weight update time interval at which the weight calculation unit 11 calculates the weight and the information regarding the fluctuation tendency of the value regarding the reception quality determined by the correlation determination unit 14, What is necessary is just to determine the transmission system and the antenna to be used.

  As described above, according to the present invention, the communication quality is improved by selecting a transmission method according to the propagation environment and selecting an antenna suitable for the selected transmission method from the fluctuation tendency of the value regarding the reception quality of each antenna. The optimum throughput can be obtained by holding.

It is a block diagram which shows an example of a structure of the wireless base station of this invention. It is a flowchart explaining the method of selection of the transmission system and antenna selection by an antenna selection part based on the correlation degree between each antenna determined in the correlation determination part. It is a figure which shows typically a mode that the reception quality information X fluctuates with progress of time. It is a figure explaining the tendency which the reception quality information X fluctuates with progress of time, and the determination method of a weighting coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna element 2 Radio | wireless (RF) part 3 Transmission control part 4 Reception control part 5 Transmission processing part 7 Antenna selection part 8 Reception processing part 11 Weight calculation part 12 Reception quality information acquisition part 13 Reception quality fluctuation tendency grasp part 14 Correlation determination part 20 radio base stations

Claims (6)

In a wireless base station having a plurality of antennas and performing wireless communication with a communication destination device,
For the plurality of antennas, an acquisition unit that acquires reception quality information of each antenna;
A grasping unit for grasping a variation tendency of a value related to reception quality of each antenna obtained in the obtaining unit;
The transmission method in the wireless communication is determined according to the variation tendency of the value regarding the reception quality at each antenna, which is grasped by the grasping unit, and the determined transmission method is selected from the plurality of antennas. A selector for selecting at least two antennas to be used;
A transmission unit for transmitting information on the transmission method determined in the selection unit to the communication destination device;
A radio base station comprising: A determination unit that determines the degree of correlation between the antennas based on a variation tendency of a value related to reception quality at each antenna, which is grasped by the grasping unit;
The selection unit includes:
According to the degree of correlation between the antennas determined by the determination unit, an antenna to be used for the wireless communication is selected.
The radio base station according to claim 1. The determination unit
In the fluctuation tendency of the value related to the reception quality at each of the antennas grasped by the grasping unit, the value related to the reception quality is lower than the first predetermined value as compared with the value related to the reception quality acquired immediately before. Detecting a time point, and determining the degree of correlation according to the time difference between the detected time points between the antennas,
The radio base station according to claim 2. The plurality of antennas are array antennas;
The selection unit includes:
As a transmission method in the wireless communication, determine one of wireless communication by directivity control and wireless communication by MIMO,
The radio base station according to claim 1, wherein the radio base station is a radio base station. A calculation unit for calculating a weight of each antenna in the plurality of antennas,
The selection unit includes:
Determining a transmission method to be used for the wireless communication based on a time interval for calculating a weight in the calculation unit and a cycle in which the time point determined by the determination unit occurs;
The radio base station according to claim 3. In a radio communication method of a radio base station having a plurality of antennas and performing radio communication with a communication destination device,
An obtaining step of obtaining reception quality information of each antenna for the plurality of antennas;
A grasping step for grasping a fluctuation tendency of a value related to reception quality of each antenna obtained in the obtaining step;
At least two or more of the plurality of antennas used for wireless communication are determined in accordance with the fluctuation tendency of the value related to the reception quality at each of the antennas grasped in the grasping step, and used for the wireless communication from the plurality of antennas A selection step of selecting an antenna of
A transmission step of transmitting information related to the transmission method determined in the selection step to the communication destination device;
A wireless communication method for a wireless base station, comprising:

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