JP2008270940A - Base station apparatus and common control signal transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise a ratio in which a common control signal is transmitted to a direction in which traffic is high. <P>SOLUTION: In a base station 12 with an adaptive array antenna 20 which is composed of a plurality of antenna elements, the apparatus includes a traffic distribution creation unit 32 which creates a traffic distribution showing a relation of direction specifying information which specifies a direction and an amount of communication with a mobile station which stays in the direction; and a transmission weight control unit 34 which controls the weight of the respective antenna elements used for transmission of the common control signal based on the traffic distribution created by the traffic distribution creation unit 32 so as to raise a ratio of common control signal transmission to the direction in which traffic is high. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base station apparatus and a common control signal transmission method, and more particularly, to a technique for transmitting a common control signal while switching a plurality of directivity patterns using an adaptive array antenna including a plurality of antenna elements.

  In a conventional mobile communication system, a common control signal is transmitted so that radio waves reach evenly in all directions. For example, a base station equipped with an adaptive array antenna transmits a common control signal evenly in the cover area while sequentially switching a plurality of directivity patterns that complement each other with null points.

Patent Document 1 discloses a wireless communication system that intermittently scans the main beam of an antenna in all directions and fixes the direction of the main beam used for subsequent communication in the direction in which the strongest electric field strength is received. It is disclosed.
JP-A-7-87011

  In general, there is a bias in the call volume distribution (traffic distribution) within the coverage area. That is, even within the same cover area, there are areas with a large call volume and areas with a small call volume. However, in the above-described conventional mobile communication system, the common control signal is transmitted so that the radio wave can reach the radio coverage area evenly regardless of the uneven call distribution. For this reason, even in a mobile station located in an area with a large amount of call, a common control signal can be received only with the same frequency as a mobile station located in an area with a small amount of call. There was a problem of not being optimized.

  The present invention has been made in view of the above-described conventional problems, and provides a base station apparatus and a common control signal transmission method capable of increasing the rate at which a common control signal is transmitted in a direction with a large call volume. Objective.

  In order to solve the above problems, a base station apparatus according to the present invention includes an adaptive array antenna including a plurality of antenna elements, and a common control signal while switching a plurality of directivity patterns formed by the adaptive array antenna. A call volume distribution generating means for generating a call volume distribution indicating a relationship between direction specifying information for specifying a direction and an amount of communication with a mobile station apparatus located in the direction; Based on the call volume distribution generated by the call volume distribution generating means, the weight of each antenna element used for transmission of the common control signal is increased so that the ratio of transmitting the common control signal in the direction with a large call volume increases. Transmission weight control means for controlling.

  In the present invention, a call volume distribution (traffic distribution) indicating a relationship between direction specifying information for specifying a direction and an amount actually communicated with a mobile station apparatus located in the direction based on past communication results with the mobile station apparatus. ) Is generated. The generated call volume distribution indicates a direction in which the call volume is large and a direction in which the call volume is small as viewed from the base station apparatus. According to the present invention, the weight of each antenna element used for transmission of the common control signal is controlled so that the ratio of transmitting the common control signal in the direction with the larger call volume estimated based on the call volume distribution increases. For this reason, the user tolerance of a mobile communication system can be expanded.

  Further, according to one aspect of the present invention, it further includes mobile station direction storage means for storing the direction specifying information for specifying the location direction of the mobile station apparatus that communicated at the time in association with the time, and generating the call volume distribution generation The means generates the call volume distribution according to time based on the time and direction specifying information stored in the mobile station direction storage means, and the transmission weight control means generates the call volume distribution and the current time. Based on this, the weight of each antenna element used for transmission of the common control signal is controlled. According to this aspect, since the transmission ratio of the common control signal in each direction is suitably controlled according to the change in call volume distribution with time, the user capacity of the mobile communication system can be constantly maintained at a high level. .

  Moreover, in one aspect of the present invention, the direction specifying information is directivity pattern identification information that identifies a directivity pattern used for transmission of a common control signal for which there was a response from the mobile station apparatus. According to this aspect, for example, the relationship between the directivity pattern used for transmission of the common control signal including a call (incoming call notification) and the number of responses to the call is generated as a call volume distribution. For this reason, it becomes possible to estimate a directivity pattern having a high response probability from the mobile station apparatus, that is, a directivity pattern covering a direction with a large call volume, based on the call volume distribution.

  In one aspect of the present invention, the direction specifying information includes a main beam direction indicating a main beam direction of a directivity pattern calculated from a weight of each antenna element used for receiving a communication signal from the mobile station apparatus. Information. According to this aspect, it is estimated that the main beam direction is the location method of the mobile station apparatus, and a detailed call volume distribution indicating the relationship between the main beam direction indicating the location of the mobile station apparatus and the communication volume is generated. . For this reason, it becomes possible to accurately estimate a direction with a large call volume.

  In this aspect, the antenna element further includes reception signal power variation detection means for detecting variation in reception signal power in each antenna element, and the direction specifying information includes the received signal power detected by the reception signal power variation detection means. The main beam direction information when the magnitude of variation is equal to or less than a predetermined value may be used. By so doing, communication when the main beam direction does not coincide with the location of the mobile station apparatus due to the influence of multipath or the like is excluded from the call volume distribution, so that a more accurate call volume distribution can be generated. For this reason, a direction with a large call volume can be estimated with higher accuracy.

  Further, in one aspect of the present invention, the transmission weight control means, based on the call volume distribution, further transmits the common control signal using a directivity pattern having directivity in a direction with a large call volume. The weight of each antenna element used for transmission of the common control signal is controlled. According to this aspect, it is possible to increase the rate at which the common control signal is transmitted in the direction with a large call volume.

  In one aspect of the present invention, the transmission weight control means determines an application frequency of a directivity pattern used for transmission of the common control signal based on the call volume distribution, and transmits the common control signal according to the determination. The weight of each antenna element used for the control is controlled. According to this aspect, it is possible to increase the frequency at which the common control signal is transmitted using the directivity pattern that covers the direction with a large call volume.

  A common control signal transmission method according to the present invention is a common control signal transmission method for transmitting a common control signal while switching a plurality of directivity patterns using an adaptive array antenna including a plurality of antenna elements. A call volume distribution generating step for generating a call volume distribution indicating a relationship between direction specifying information for specifying a direction and an amount of communication with a mobile station apparatus located in the direction, and the common control in a direction with a large call volume. A transmission weight control step for controlling the weight of each antenna element used for transmission of the common control signal based on the call amount distribution generated in the call amount distribution generation step so that the ratio of signal transmission increases. It is characterized by including.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a mobile communication system 10 according to an embodiment of the present invention. As shown in the figure, the mobile communication system 10 includes a base station 12 and a plurality of mobile stations 14A to 14G (here, seven). In general, the cover area 16 of the base station 12 includes an area in which the mobile stations 14 are likely to be crowded and the call volume (traffic) is relatively large (here, the area where 14A to 14D are located) and a small area. That is, there are many cases in which the call volume distribution in the cover area 16 is biased.

  The base station 12 is provided with an adaptive array antenna composed of a plurality of antenna elements as will be described later. While switching the directivity pattern formed by the adaptive array antenna, other common for calling (incoming call notification) Control signals are transmitted throughout the cover area 16. In particular, in the mobile communication system 10 according to the present embodiment, the base station 12 generates a call volume distribution in the cover area from the communication history with each mobile station 14 in the past, and the direction in which the call volume is large as viewed from the base station 12. The weight of each antenna element is controlled so that the ratio at which the common control signal is transmitted increases. In this way, the user capacity of the mobile communication system 10 is increased.

  Below, the structure with which the base station 12 is provided in order to implement | achieve the said process is demonstrated in detail.

  FIG. 2 is a functional block diagram of the base station 12. As shown in the figure, the base station 12 includes an adaptive array antenna 20, a receiving unit 22, a demodulating unit 24, a received signal power variation detecting unit 26, a mobile station direction estimating unit 28, a mobile station direction specifying information storage unit 30, a call A quantity distribution generation unit 32, a transmission weight control unit 34, a modulation unit 36, and a transmission unit 38 are included.

  The adaptive array antenna 20 is an array of a plurality of antenna elements, radiates a signal supplied from the transmission unit 38 from each antenna element, and receives a signal transmitted from each mobile station 14 by each antenna element. The signal is output to the receiving unit 22. This transmission and reception are switched in a time division manner.

  The reception unit 22 down-converts a radio signal from the mobile station 14 received by each antenna element of the adaptive array antenna 20 into a baseband signal and outputs the baseband signal to the demodulation unit 24.

  The demodulator 24 decodes data received from the mobile station 14 from the baseband signal input from the receiver 22. The reception data decoded by the demodulator 24 is output to a higher-level device (not shown).

  The received signal power variation detector 26 detects variations in received signal power at each antenna element based on the baseband signal input from the receiver 22. Specifically, if the received signal power difference between the antenna elements exceeds a predetermined value, it is determined that the variation is large, and if it is equal to or less than the predetermined value, it is determined that the variation is small.

  The mobile station direction estimation unit 28 calculates the weight of each antenna element used for communication with each mobile station 14 based on the baseband signal input from the reception unit 22 and the known reference signal. Specifically, the adaptive array antenna 20 forms a main beam in the arrival direction of the reference signal corresponding to each mobile station 14 and directs null in the arrival direction of a signal (interference signal) having a low correlation with the reference signal. The weights of the antenna elements constituting the are converged.

Then, the mobile station direction estimation unit 28 calculates the main beam direction of the directivity pattern of the adaptive array antenna 20 formed by the weight based on the weight of each antenna element thus obtained. It is presumed that each mobile station 14 is located (the direction of arrival of a signal transmitted from each mobile station 14). The carrier wave frequency of the desired wave is f, the propagation speed (light velocity) is c, and the position of the k-th antenna element measured from the reference point (an arbitrary fixed point different from the position of any antenna element) is d _k. When the weight w _{k of the} antenna element is expressed by w _k = A _k exp (jδ _k ) (A _k and δ _k are the amplitude and the amount of phase shift applied to the k-th antenna element, respectively), the adaptive array antenna 20 The main beam direction (angle θ with respect to the adaptive array antenna 20) is given by the following equation (1).

  Further, the mobile station direction estimation unit 28 specifies the main beam direction (angle θ) calculated by the equation (1) every time a signal is received or every predetermined time (for example, every 5 minutes). The information is stored in the information storage unit 30. However, the case where the received signal power variation detection unit 26 determines that the received signal power difference between the antenna elements exceeds a predetermined value is excluded.

  FIG. 3 is a diagram showing (a) the case where the main beam direction coincides with the direction in which the mobile station 14 is located, and (b) the case where they do not coincide. As shown in FIG. 2A, when the transmission wave from the mobile station 14 arrives at the base station 12 without widening the angle, the base station 12 directs the main beam in the direction of the mobile station 14 (= arrival wave direction). . On the other hand, as shown in FIG. 5B, when the transmission wave from the mobile station 14 has an angular spread due to the influence of multipath or the like, the base station 12 transmits the main beam in a direction different from the direction in which the mobile station 14 is located. Turn. In this case, the main beam direction (angle θ) calculated by the equation (1) does not indicate the location direction of the mobile station 14.

  In general, when the incoming wave from the mobile station 14 has an angular spread, the variation in received signal power between the antenna elements in the base station 12 tends to increase. This is because when the signal transmitted from the mobile station 14 arrives at the base station 12 through two or more different paths, the degree of phase shift of the incoming wave differs depending on the position of the antenna element. That is, signals received in the same phase (substantially the same phase) are emphasized in a certain antenna element, and signals received in an opposite phase (substantially opposite phase) are canceled out in each antenna element. The received signal power in the element tends to vary.

  Therefore, the mobile station direction estimating unit 28 determines that the main beam direction is the location of the mobile station 14 when the received signal power variation detecting unit 26 determines that the received signal power difference between the antenna elements exceeds a predetermined value. Since there is a high possibility that the direction does not coincide with the direction, the main beam direction (angle θ) obtained by Expression (1) is discarded without being stored in the mobile station direction specifying information storage unit 30. Thus, the mobile station direction estimation unit 28 stores the main beam direction (angle θ) obtained by the equation (1) in the mobile station direction specifying information storage unit 30 only when the location direction of the mobile station 14 can be correctly estimated. Like to do.

  The mobile station direction estimation unit 28 may obtain an average value of the angle θ at a predetermined cycle (for example, at a cycle of 10 minutes) and store the average value as the representative main beam direction.

  The mobile station direction specifying information storage unit 30 is configured to include a memory, and stores direction specifying information for specifying the location direction of the mobile station 14 that communicated at that time in association with the time for each predetermined time. Is.

  FIG. 4 is a diagram illustrating an example of the mobile station direction specifying information storage unit 30. As shown in the figure, the mobile station direction specifying information storage unit 30 stores the main beam direction (angle θ) calculated by the mobile station direction estimation unit 28 using the equation (1) every minute here. Yes.

  The call volume distribution generation unit 32 generates a call volume distribution indicating the relationship between the direction specifying information and the amount communicated with the mobile station 14 located in the direction specified by the direction specifying information. Specifically, based on the time stored in the mobile station direction specifying information storage unit 30 and the main beam direction, the call volume distribution is generated by totaling the call volume by time and direction.

  FIG. 5 is a diagram illustrating an example of call volume distribution generated by the call volume distribution generation unit 32. As shown in the figure, in this embodiment, since the relationship between the direction seen from the base station 12 and the call volume in that direction is counted every 30 minutes, the call volume in which direction is large in which time zone. It is possible to grasp in detail the time change of the call volume distribution. Note that the call volume may be aggregated by assigning a large weight to the direction of the main beam with a new time and assigning a small weight to the direction of the main beam with an old time. In this way, the call volume distribution generated by the call volume distribution generation unit 32 takes into account the temporal reproducibility more.

  The transmission weight control unit 34 stores a plurality of basic weight sets that form a plurality of directivity patterns (hereinafter referred to as “basic directivity patterns”) conventionally used for transmission of common control signals. Based on the call volume distribution generated by the call volume distribution generation unit 32 and the current time so that the ratio of transmitting the common control signal in the direction in which it is estimated that the call volume is large, each used for transmission of the common control signal It controls the weight of the antenna element. Specifically, in addition to the conventional basic directivity pattern, the weight of each antenna element is set so that a common control signal is transmitted by further using a directivity pattern having directivity in the direction where the call volume is estimated to be large at the present time. To control. Further, among the conventional basic directivity patterns, the weight of each antenna element may be controlled so that the application frequency of the directivity pattern that covers the direction in which the call volume is estimated to be large at the present time is increased. As a result, the transmission ratio of the common control signal in each direction is appropriately changed according to the time variation of the call volume distribution, so that the user capacity of the mobile communication system 10 can always be kept high. .

  The modulator 36 converts transmission data to each mobile station 14 input from a higher-level device (not shown) into a baseband signal and inputs it to the transmitter 38.

  The transmission unit 38 sets the weight of each antenna element constituting the adaptive array antenna 20 according to the instruction of the transmission weight control unit 34. Then, the baseband signal input from the modulation unit 36 is upconverted to a radio signal, amplified to a transmission output level, and supplied to each antenna element.

  Here, the operation of the base station 12 will be described with reference to FIGS.

  FIG. 6 is a flowchart showing the storage processing of the direction specifying information for specifying the location direction of the mobile station 14. This process is executed every time a signal transmitted from each mobile station 14 is received or every predetermined time (for example, every 5 minutes).

  As shown in the figure, when the signal transmitted from the mobile station 14 is received by the adaptive array antenna 20, the mobile station direction estimating unit 28 receives the baseband signal input from the receiving unit 22, the known reference signal, Based on the above, the weight of each antenna element used for communication with each mobile station 14 is calculated (S100). Based on the weight of each antenna element obtained in S100, the main beam direction of the directivity pattern formed by the weight is calculated (S102). Further, the received signal power variation detector 26 detects variations in received signal power in each antenna element based on the baseband signal input from the receiver 22 (S104). Then, it is determined whether or not the detected variation in received signal power is equal to or less than a predetermined value (S106).

  If it is determined in S106 that the magnitude of the variation in the received signal power is equal to or less than the predetermined value, the mobile station direction estimation unit 28 uses the main beam direction calculated in S102 as information for specifying the location direction of the mobile station 14. The mobile station direction specifying information storage unit 30 stores the calculated time together with the calculated time (S108). On the other hand, if it is determined in S106 that the magnitude of the variation in the received signal power is equal to or less than the predetermined value, the main beam direction calculated in S102 is discarded without being stored in the mobile station direction specifying information storage unit 30. .

  Next, FIG. 7 is a flowchart showing a common control signal transmission process by the base station 12. This process is executed when the base station 12 transmits a common control signal to the cover area.

  As shown in the figure, first, the call volume distribution generation unit 32, for each time (for example, every 30 minutes) and for each direction, based on the time and main beam direction stored in the mobile station direction specifying information storage unit 30. By collecting the call volume, a call volume distribution by time is generated (S200). Next, the transmission weight control unit 34 estimates the direction in which the call volume is large at the present time based on the call volume distribution by time generated in S200 and the current time (S202). Then, the weight of each antenna element is controlled so that the directivity pattern has directivity in the direction estimated in S202, and a common control signal is transmitted (S204). Thereafter, a common control signal is transmitted throughout the cover area 16 while switching the conventional basic directivity pattern (S206). Note that the order of S204 and S206 may be reversed, and the process of S204 may be executed one or more times while switching the basic directivity pattern in S206.

  According to the base station 12 described above, it is used for transmission of the common control signal based on the call volume distribution indicating the relationship between the direction specifying information for specifying the direction and the amount of communication with the mobile station 14 located in the direction. The weight of each antenna element is controlled. For this reason, the ratio by which a common control signal is transmitted to the direction with much call volume can be raised, and the user tolerance of the mobile communication system 10 can be expanded.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible. For example, in the above embodiment, the main beam direction of the directivity pattern calculated based on the weight of each antenna element is used as the direction specifying information for specifying the location direction of the mobile station 14, but instead of the main beam direction. The weight of each antenna element itself may be used, or a basic directivity pattern ID for identifying the basic directivity pattern of the common control signal may be used.

  Hereinafter, an embodiment in which the basic directivity pattern ID is used as direction specifying information for specifying the location of the mobile station 14 will be described. In the present embodiment, the mobile station direction estimating unit 28 uses the ID of the basic directivity pattern used for transmission of a common control signal (for example, an incoming call notification) for which there is a response from the mobile station 14 as the location of the mobile station 14. Estimated direction. The basic directivity pattern ID is stored in the mobile station direction specifying information storage unit 30 together with the time when the base station 12 receives the response (see FIG. 8). In this case, the call volume distribution generation unit 32, based on the time and the basic directivity pattern ID stored in the mobile station direction specifying information storage unit 30, the basic directivity pattern ID used for transmission of the common control signal and the relevant A call volume distribution indicating the relationship with the number of responses from the mobile station 14 to the common control signal is generated. According to the call volume distribution obtained in this way, when a common control signal is transmitted, it is possible to grasp a basic directivity pattern with a high probability that a response from the mobile station 14 is obtained and a basic directivity pattern with a small probability. Based on the call volume distribution, the transmission weight control unit 34 transmits a common control signal using more basic directivity patterns with a high probability of obtaining a response from the mobile station 14. For this reason, the ratio by which a common control signal is transmitted to the direction with much call volume can be raised, and the user tolerance of the mobile communication system 10 can be expanded.

1 is an overall configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a functional block diagram of the base station which concerns on embodiment of this invention. It is a figure which shows the case where a main beam direction and a movement local presence direction correspond, and the case where it does not correspond. It is a figure which shows an example of a mobile station direction specific information storage part. It is a figure which shows an example of the call volume distribution produced | generated by the call volume distribution production | generation part. It is a flowchart which shows the memory | storage process of the direction specific information which specifies the location direction of a mobile station. It is a flowchart which shows the transmission process of a common control signal. It is a figure which shows an example of a mobile station direction specific information storage part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Mobile communication system, 12 Base station, 14 Mobile station, 16 Cover area, 20 Adaptive array antenna, 22 Receiver, 24 Demodulator, 26 Received signal power variation detector, 28 Mobile station direction estimation part, 30 Mobile station direction specification Information storage unit, 32 call volume distribution generation unit, 34 transmission weight control unit, 36 modulation unit, 38 transmission unit.

Claims (8)

A base station apparatus comprising an adaptive array antenna composed of a plurality of antenna elements, and transmitting a common control signal while switching a plurality of directivity patterns formed by the adaptive array antenna,
Call volume distribution generating means for generating a call volume distribution indicating a relationship between direction specifying information for specifying a direction and an amount of communication with a mobile station apparatus located in the direction;
Based on the call volume distribution generated by the call volume distribution generating means, the weight of each antenna element used for transmission of the common control signal is increased so that the ratio of transmitting the common control signal in the direction with a large call volume increases. Transmission weight control means for controlling;
A base station apparatus comprising: The base station apparatus according to claim 1,
The mobile station direction specifying information storage means for storing the direction specifying information for specifying the location direction of the mobile station apparatus communicated at the time in association with the time,
The call volume distribution generating means generates the call volume distribution by time based on the time and direction specifying information stored in the mobile station direction specifying information storage means,
The transmission weight control means controls the weight of each antenna element used for transmitting the common control signal based on the call volume distribution and the current time.
A base station apparatus. In the base station apparatus according to claim 1 or 2,
The direction specifying information is directivity pattern identification information for identifying a directivity pattern used for transmission of a common control signal in response from the mobile station device.
A base station apparatus. In the base station apparatus according to claim 1 or 2,
The direction specifying information is main beam direction information indicating a main beam direction of a directivity pattern calculated from a weight of each antenna element used for receiving a communication signal from the mobile station device.
A base station apparatus. In the base station apparatus according to claim 4,
A reception signal power variation detecting means for detecting a variation in received signal power in each antenna element;
The direction specifying information is the main beam direction information when the received signal power variation detected by the received signal power variation detecting means is less than or equal to a predetermined value.
A base station apparatus. In the base station apparatus according to claim 4 or 5,
The transmission weight control means is used for transmitting the common control signal based on the call volume distribution so as to further transmit the common control signal using a directivity pattern having directivity in a direction with a large call volume. Control the weight of each antenna element,
A base station apparatus. In the base station apparatus in any one of Claim 1 to 5,
The transmission weight control means determines an application frequency of a directivity pattern used for transmission of the common control signal based on the call volume distribution, and determines a weight of each antenna element used for transmission of the common control signal according to the determination. Control,
A base station apparatus. A common control signal transmission method for transmitting a common control signal while switching a plurality of directivity patterns using an adaptive array antenna composed of a plurality of antenna elements,
A call volume distribution generating step for generating a call volume distribution indicating a relationship between direction specifying information for specifying a direction and an amount of communication with a mobile station apparatus located in the direction;
Based on the call volume distribution generated in the call volume distribution generation step, the weight of each antenna element used for transmission of the common control signal is increased so that the ratio of transmitting the common control signal in a direction with a large call volume increases. A transmission weight control step to control;
The common control signal transmission method characterized by including.

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