Patent Publication Number: US-2011053629-A1

Title: Base station apparatus, antenna device, terminal device, communication system, and communication method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-201520, filed on Sep. 1, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a base station apparatus, an antenna device, a terminal device, a communication system, and a communication method that perform wireless communication. 
     BACKGROUND 
     In cellular mobile communication in which a base station communicates with a terminal, the base station determines the state of the uplink propagation path by using a reference signal sent from the terminal. The base station collects information indicative of the state of downlink propagation paths for each terminal by receiving downlink propagation path information measured and fed back by the terminal. The base station has a scheduling function of allocating uplink and downlink wireless resources based on such information. 
     During the cellular mobile communication, the propagation path state fluctuates drastically and communication quality changes significantly with the movement of the terminal. In particular, when the terminal is hidden behind an obstacle such as a building or when the terminal enters a tunnel, the propagation path state deteriorates significantly and consequently, the transmission speed is reduced or the communication is suspended. Therefore, a technology is under study that forecasts fluctuations caused by shadowing, such as by a building or entrance into the tunnel, and sets the communication method according to the forecast fluctuations. 
     For example, a technology has been disclosed that forecasts time transition of radio wave blocking, based on electronic map data or destination information possessed by a mobile object and performs scheduling, etc., according to results of the forecast (see, e.g., Japanese Laid-Open Patent Publication No. 2003-188802). A technology has been disclosed that measures field strength using an antenna provided at a forward aspect of the mobile object and performs communication using an antenna provided at a rear aspect of the mobile object, based on results of the measurement (see, e.g., Japanese Laid-Open Patent Publication No. H7-154856). 
     The conventional technologies, however, have a problem of being incapable of accurately forecasting fluctuations in the propagation quality at the terminal on the mobile object and incapable of enhancing the quality of communication between the base station and the mobile terminal. For example, the invention described in Japanese Laid-Open Patent Publication No. 2003-188802 has a problem in that use of electronic map data to forecast the radio wave blocking state involves processing an enormous amount of data and does not necessarily guarantee the accuracy of the forecast. The invention described in Japanese Laid-Open Patent Publication No. H7-154856 has a problem of being incapable of forecasting the fluctuation of the propagation quality at the mobile terminal in the mobile object and incapable of enhancing the quality of communication between the base station and the mobile terminal. 
     SUMMARY 
     According to an aspect of an embodiment, a base station apparatus that communicates with a terminal device includes an acquiring unit that acquires propagation quality between the base station apparatus and the terminal device and propagation quality between the base station apparatus and an antenna device provided forward of the terminal device; and a scheduler unit that allocates wireless resources for communication with the terminal device, based on the propagation qualities acquired by the acquiring unit. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram depicting a configuration of a communication system according to a first embodiment. 
         FIG. 2  is a sequence diagram of one example of operation of the communication system according to the first embodiment. 
         FIG. 3  is a flowchart of one example of scheduling operation of a base station apparatus according to the first embodiment. 
         FIG. 4  is a diagram depicting one example of a configuration of an antenna device according to the first embodiment. 
         FIG. 5  is a diagram depicting one example of the base station apparatus according to the first embodiment. 
         FIG. 6  is a diagram depicting a configuration of a terminal device according to the first embodiment. 
         FIG. 7  is a sequence diagram of one example of operation of the communication system according to the second embodiment. 
         FIG. 8  is a diagram depicting one example of a configuration of the antenna device according to the second embodiment. 
         FIG. 9  is a diagram depicting one example of a configuration of the base station apparatus according to the second embodiment. 
         FIG. 10  is a diagram depicting one example of a configuration of the base station apparatus according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will be explained with reference to the accompanying drawings. 
       FIG. 1  depicts a configuration of a communication system according to a first embodiment. As depicted in  FIG. 1 , a communication system  100  includes a base station apparatus  110 , a mobile object  120 , an antenna device  130 , and terminal devices  141  to  143 . The base station apparatus  110  communicates with the terminal devices  141  to  143  in the mobile object  120 . The base station apparatus  110  is equipped with an antenna  111  and uses the antenna  111  to wirelessly communicate with the antenna device  130  and the terminal devices  141  to  143 . 
     The mobile object  120  is a mobile object such as a train or a bus. A traveling direction  121  indicates the direction of movement of the mobile object  120 . The antenna device  130  is provided forward (with respect to the traveling direction  121 ) of the terminal devices  141  to  143  in the mobile object  120 . The mobile object  120  has an open space  122  capable of accommodating the terminal devices  141  to  143  behind (with respect to the traveling direction  121 ) the antenna device  130 . 
     The antenna device  130  is equipped with a forecast-use antenna  131  and a terminal-use antenna  132 . The antenna device  130  uses the forecast-use antenna to recursively transmit a reference signal to the base station apparatus  110 . The antenna device  130  uses the terminal-use antenna  132  to distribute (broadcast) to the open space  122 , identification information (e.g., reference number) indicative of the reference signal transmitted from the forecast-use antenna  131 . 
     The terminal devices  141  to  143  are communication terminals capable of mobile communication such as a cellular phone and a portable information terminal. The terminal devices  141  to  143  are located in the open space  122  of the mobile object  120 . The terminal devices  141  to  143  receive the identification information distributed from the antenna device  130  and transmit (signal) the received identification information to the base station apparatus  110 . Each of the terminal devices  141  to  143  recursively transmits the reference signal to the base station apparatus  110 . 
     The base station apparatus  110  measures the propagation quality (e.g., field strength) between the base station apparatus  110  and the antenna device  130 , based on the reference signal transmitted from the antenna device  130 . The base station apparatus  110  recognizes that the mobile object  120  carrying the terminal devices  141  to  143  is equipped with the antenna device  130 , based on the identification information transmitted from the terminal devices  141  to  143 . The base station apparatus  110  identifies the reference signal transmitted from the antenna device  130 , among various reference signals transmitted from other sources in the vicinity, based on the identification information transmitted from the terminal devices  141  to  143 . 
     The base station apparatus  110  measures the propagation quality between the base station  110  and the terminal devices  141  to  143  by receiving the reference signals transmitted from the terminal devices  141  to  143 . The base station apparatus  110  compares the propagation quality for the antenna device  130  and the propagation quality for the terminal devices  141  to  143  thus measured and performs scheduling of the terminal devices  141  to  143 , based on results of the comparison. 
     The reference signals to be transmitted and received between the base station apparatus  110 , antenna device  130 , and the terminal devices  141  to  143  are signals multiplexed by time, frequency, or code, etc. With different reference numbers respectively allocated for the antenna device  130  and the terminal devices  141  to  143 , the reference signals may be multiplexed for transmission and reception between the base station apparatus  110 , the antenna device  130 , and the terminal devices  141  to  143 . 
       FIG. 2  is a sequence diagram of one example of operation of the communication system according to the first embodiment. Although  FIG. 2  describes the operation of the terminal device  141  among the terminal devices  141  to  143 , operation of the terminal devices  142  and  143  is substantially identical. Firstly, the base station apparatus  110  transmits a sync signal for the terminal device  141  and the antenna device  130  to synchronize (step S 201 ). The antenna device  130  receiving the sync signal transmitted at step S 201 , adjusts the timing of reception and transmission and recognizes basic information (cell number, transmission bandwidth, transmission strength, etc.) of the base station apparatus  110 . 
     Then, the antenna device  130  requests the base station apparatus  110  to allocate a reference signal (step S 202 ). The request for allocation of a reference signal at step S 202  is made, for example, using an uplink random access channel, etc. Then, in response to the request for allocation at step S 202 , the base station apparatus  110  allocates a reference signal to the antenna device  130  (step S 203 ). 
     Subsequently, the antenna device  130  starts transmission of the reference signal allocated at step S 203  (step S 204 ). Then, the terminal device  141  establishes a link with the base station apparatus  110  by an initial access or a handover, etc. (step S 205 ). Through the operation at step S 205 , the terminal device  141  is allocated an uplink reference signal by the base station apparatus  110 . 
     Then, the terminal device  141  starts transmission of the reference signal allocated by the base station apparatus  110  (step S 206 ). Subsequently, the antenna device  130  distributes the identification information of the reference signal that the antenna device  130  has started to transmit at step S 204  (step S 207 ). The identification information distributed at step S 207  is received by the terminal device  141  located in the open space  122  of the mobile object  120 . 
     Then, the terminal device  141  transmits the identification information distributed at step S 207  to the base station apparatus  110  (step S 208 ). The base station apparatus  110  performs scheduling based on the reference signals whose transmission was started at step S 204  and step S 206  and notifies the terminal device  141  of results of the scheduling (step S 209 ), ending a sequence of operations. 
     At step S 209 , by receiving the reference signal indicated by the identification information transmitted at step S 208 , the base station apparatus  110  receives the reference signal from the antenna device  130 . These steps enable the base station apparatus  110  to perform the scheduling (allocation of wireless resources) for the terminal device  141 , based on the propagation quality between the base station apparatus  110  and the antenna device  130  and the propagation quality between the base station apparatus  110  and the terminal device  141 . 
     Although an example has been described where the base station apparatus  110  allocates the number of the reference signal to be transmitted by the antenna device  130 , the number of the reference signal used by the antenna device  130  may be preliminarily determined, in which case, there is no need for the allocation of the number of the reference signal by the base station apparatus  110 . 
       FIG. 3  is a flowchart of one example of scheduling operation of the base station apparatus according to the first embodiment. The base station apparatus  110  firstly measures the propagation quality based on the reference signal received from each terminal device to communicate with the base station apparatus  110  and determines the order of priority of the terminal devices, based on the measured propagation quality (step S 301 ). For example, the base station apparatus  110  may determine that a terminal device of a higher propagation quality will be given a higher priority. 
     Then, the base station apparatus  110  selects, from among the terminal devices, a subject terminal that is to be subject to priority rank adjustment (step S 302 ). The base station apparatus  110  determines whether the identification information, indicative of the reference signal of the antenna device  130 , has been received from the subject terminal selected at step S 302  (step S 303 ), whereby the base station apparatus  110  is able to determine whether the subject terminal is located on the mobile object  120  on which the antenna device  130  is provided. If the identification information has not been received from the subject terminal (step S 303 : NO), then the flow proceeds to step S 308 , without performing the priority rank adjustment. 
     At step S 303 , if the identification information has been received from the subject terminal (step S 303 : YES), the base station apparatus  110  determines whether the propagation quality for the antenna device  130  is lower than that for the subject terminal (step S 304 ), whereby the base station apparatus  110  is able to determine whether the propagation quality at the subject terminal is deteriorating. If the propagation quality for the antenna device  130  is lower than that for the subject terminal (step S 304 : YES), the base station apparatus  110  raises the priority rank of the subject terminal (step S 305 ) and the flow proceeds to step S 308 . 
     At step S 304 , if the propagation quality for the antenna device  130  is not lower than that for the subject terminal (step S 304 : NO), the base station apparatus  110  determines whether the propagation quality for the antenna device  130  is higher than that for the subject terminal (step S 306 ), whereby the base station is able to determine whether the propagation quality at the subject terminal is improving. If the propagation quality for the antenna device  130  is higher than that for the subject terminal (step S 306 : YES), the base station apparatus  110  lowers the priority rank of the subject terminal (step S 307 ) and the flow proceeds to step S 308 . 
     At step S 306 , if the propagation quality for the antenna device  130  is not higher than that for the subject terminal (step S 306 : NO), the base station apparatus  110  determines whether each of the terminal devices that is to communicate with the base station apparatus  110  has been selected at step S 302  (step S 308 ). If each of the terminal devices has not been selected (step S 308 : NO), the flow returns to step S 302 , where the base station apparatus  110  selects a terminal device not yet selected as the subject terminal, from among the remaining terminal devices. 
     At step S 308 , if all the terminal devices have been selected (step S 308 : YES), the base station apparatus  110  allocates the resources to terminal devices in the order of priority (step S 309 ), thereby ending a sequence of scheduling operations. These operations make it possible to raise the priority of a terminal device having a deteriorating propagation quality and to lower the priority of a terminal device having an improving propagation quality, relative to the terminal devices  141  to  143  in the mobile object. 
     The priority of a terminal device having a deteriorating propagation quality is raised so that wireless resources can be allocated and communication can be performed before the propagation quality deteriorates beyond that enabling communication. The priority of a terminal device having an improving propagation quality is lowered so that wireless resources can be allocated and communication can be performed after improvement of the propagation quality. Thus, the base station apparatus  110  is able to communicate with the terminal devices  141  to  143  under a state of better propagation quality and with improved throughput. 
       FIG. 4  depicts one example of a configuration of the antenna device according to the first embodiment. In  FIG. 4 , components identical those depicted in  FIG. 1  are given the same reference numerals used in  FIG. 1  and description thereof is omitted. As depicted in  FIG. 4 , the antenna device  130  is equipped with the forecast-use antenna  131 , the terminal-use antenna  132 , a duplexer  401 , a receiver  402 , a synchronization processor unit  403 , a signaling receiver unit  404 , a control unit  405 , a reference transmitter unit  406 , a signaling transmitter unit  407 , a transmitter  408 , an identification information transmitter unit  409 , and a transmitter  410 . 
     The forecast-use antenna  131  is an antenna for performing the wireless communication with the base station apparatus  110 . For example, the forecast-use antenna  131  receives a signal transmitted from the base station apparatus  110  and outputs the received signal to the duplexer  401 . The forecast-use antenna  131  outputs to the base station apparatus  110 , a signal from the duplexer  401 . While the forecast-use antenna  131  is an antenna having functions of a transmitting antenna and a receiving antenna, a transmitting antenna and a receiving antenna may separately be provided in place of the forecast-use antenna  131 . 
     The duplexer  401  outputs to the receiver  402 , the signal from the forecast-use antenna  131 . Further, the duplexer  401  outputs to the forecast-use antenna  131 , the signal from the transmitter  408 . If the transmitting antenna and the receiving antenna are separately provided in place of the forecast-use antenna  131 , the duplexer  401  may be omitted. 
     The receiver  402  down-converts the signal (radio-frequency signal (RF)) output from the duplexer  401  to a baseband signal and then converts the baseband signal to a digital signal. The receiver  402  outputs the digital signal to the synchronization processor unit  403  and the signaling receiver unit  404 . 
     The synchronization processor unit  403  receives a sync signal transmitted by the base station apparatus  110 , among the signals output from the receiver  402 . The synchronization processor unit  403  uses the received sync signal in processing of synchronizing time and frequency and in receiving basic information (cell number, transmission bandwidth, transmission strength, etc.) of the base station apparatus  110  to which connection is made. The synchronization processor unit  403  outputs to the control unit  405 , results of the synchronization processing and the basic information of the base station apparatus  110 . 
     The signaling receiver unit  404  receives a signaling signal transmitted by the base station apparatus  110 , among the signals output from the receiver  402 . The signaling signal includes the number of the reference signal allocated by the base station apparatus  110 . The signaling receiver unit  404  outputs to the control unit  405 , the number of the reference signal. 
     The control unit  405  performs communication control of the antenna device  130 . For example, the control unit  405  outputs the number of the reference signal output from the signaling receiver unit  404  to the reference transmitter unit  406 . The control unit  405  controls the signaling transmitter unit  407  so that the signaling signal to be transmitted to the base station apparatus  110  is generated based on the basic information output from the synchronization processor unit  403 . The control unit  405  outputs to the identification information transmitter unit  409 , the number of the reference signal output from the signaling receiver unit  404 . 
     The reference transmitter unit  406 , the transmitter  408 , and the forecast-use antenna  131  make up a transmitter unit that transmits the reference signal to the base station apparatus  110 . For example, the reference transmitter unit  406  generates the reference signal to be transmitted to the base station apparatus  110 , based on the number of the reference signal output from the control unit  405 . The reference transmitter unit  406  outputs the generated reference signal to the transmitter  408 . 
     Under the control of the control unit  405 , the signaling transmitter unit  407  generates a signaling signal to be transmitted to the base station apparatus  110 . The signaling signal generated by the signaling transmitter unit  407  is, for example, a signal requesting the base station apparatus  110  for an allocation of a reference signal. The signaling transmitter unit  407  outputs the generated signaling signal to the transmitter  408 . 
     The transmitter  408  converts the reference signal output from the reference transmitter unit  406  and the signaling signal output from the signaling transmitter unit  407 , to an analog signal. The transmitter  408  up-converts the analog signal (baseband signal) to an RF signal and outputs the RF signal to the duplexer  401 . 
     The identification information transmitter unit  409 , the transmitter  410 , and the terminal-use antenna  132  make up a distributor unit that distributes the identification information of the reference signal to be transmitted by the antenna device  130 . For example, the identification information transmitter unit  409  generates the identification information indicative of the reference signal allocated to the antenna device  130 . For example, the identification information transmitter unit  409  generates the identification information inclusive of the number of the reference signal output from the control unit  405 . The identification information transmitter unit  409  outputs the generated identification information to the transmitter  410 . 
     The transmitter  410  converts the identification information output from the identification information transmitter unit  409 , to an analog signal, up-converts the analog signal (baseband signal) to an RF signal, and outputs the RF signal to the terminal-use antenna  132 . The identification information output to the terminal-use antenna  132  from the transmitter  410  is wirelessly distributed to the terminal devices  141  to  143  by the terminal-use antenna  132 . 
     The synchronization processor unit  403 , the signaling receiver unit  404 , the control unit  405 , the reference transmitter unit  406 , the signaling transmitter unit  407 , and the identification information transmitter unit  409  may be implemented, for example, by an arithmetic device such as a digital signal processor (DSP). 
       FIG. 5  depicts one example of the base station apparatus according to the first embodiment. As depicted in  FIG. 5 , the base station apparatus  110  is equipped with the antenna  111 , a duplexer  501 , a receiver  502 , a data receiver unit  503 , a receiving buffer  504 , an external output unit  505 , a signaling receiver unit  506 , an identification information extractor unit  507 , a feedback receiver unit  508 , a propagation quality measurement unit  509 , a fluctuation analysis unit  510 , a control unit  511 , a scheduler unit  512 , a synch signal transmitter unit  513 , a signaling transmitter unit  514 , an external input unit  515 , a transmitting buffer  516 , a data transmitter unit  517 , and a transmitter  518 . 
     The antenna  111  is an antenna that performs the wireless communication with the antenna device  130  and the terminal devices  141  to  143 . The antenna  111  receives the signals transmitted from the antenna device  130  and the terminal devices  141  to  143  and outputs the received signals to the duplexer  501 . The antenna  111  transmits to the antenna device  130  and the terminal devices  141  to  143 , the signal from the duplexer  501 . While the antenna  111  is an antenna having functions of a transmitting antenna and a receiving antenna, a transmitting antenna and a receiving antenna may separately be provided in place of the antenna  111 . 
     The duplexer  501  outputs to the receiver  502 , the signal from the antenna  111 . The duplexer  501  outputs to the antenna  111 , the signal from the transmitter  518 . If the transmitting antenna and the receiving antenna are separately provided in place of the antenna  111 , the duplexer  501  may be omitted. 
     The receiver  502  down-converts the signal (RF: radio-frequency signal) output from the duplexer  501  to a baseband signal and then converts the baseband signal to a digital signal. The receiver  502  outputs the digital signal to the data receiver unit  503 , the signaling receiver unit  506 , the feedback receiver unit  508 , and the propagation quality measurement unit  509 . 
     Under the control of the control unit  511 , the data receiver unit  503  receives data (user data) transmitted by the terminal devices  141  to  143 , among the signals output from the receiver  502 . The data receiver unit  503  outputs the received data to the receiving buffer  504 . The receiving buffer  504  stores the data output from the data receiver unit  503 . The external output unit  505  reads out the data stored to the receiving buffer  504  and transmits the data to an external core network. 
     The signaling receiver unit  506  receives the signaling signal transmitted by the antenna device  130  and the terminal devices  141  to  143 , among the signals output from the receiver  502 . The signaling signal from the antenna device  130  and the terminal devices  141  to  143  includes a request for allocation of a reference signal. The signaling receiver unit  506  outputs to the control unit  511 , the received request for the allocation of a reference signal. 
     The signaling receiver unit  506  outputs to the identification information extractor unit  507 , the signaling signal transmitted by the terminal devices  141  to  143 . The identification information extractor unit  507  extracts the identification information included in the signaling signal output from the signaling receiver unit  506  and outputs the extracted identification information to the fluctuation analysis unit  510 . 
     The feedback receiver unit  508  receives downlink feedback information transmitted by the antenna device  130  and the terminal devices  141  to  143 , among the signals output from the receiver  502 . The feedback information indicates the propagation quality measured by the antenna device  130  and the terminal devices  141  to  143 , based on the reference signal from the base station apparatus  110 . The feedback receiver unit  508  outputs the received feedback information to the control unit  511 . 
     The propagation quality measurement unit  509  is an acquiring unit that acquires the propagation quality between the base station  110  apparatus and the terminal devices  141  to  143  and the propagation quality between the base station apparatus  110  and the antenna device  130 . For example, the propagation quality measurement unit  509  receives the reference signals transmitted by the antenna device  130  and the terminal devices  141  to  143 , among the signals output from the receiver  502  and measures uplink propagation quality based on the received reference signals. The propagation quality measurement unit  509  notifies the fluctuation analysis unit  510  and the control unit  511  of the measured propagation quality. 
     The fluctuation analysis unit  510  is a comparing device that compares the propagation quality for the terminal devices  141  to  143  and the propagation quality for the antenna device  130 . For example, the fluctuation analysis unit  510  compares the propagation quality between the antenna device  130  and the base station apparatus  110  and the propagation quality between the base station apparatus  110  and each of the terminal devices  141  to  143  using the propagation quality reported by the propagation quality measurement unit  509 . 
     The fluctuation analysis unit  510  outputs results of the comparison to the control unit  511 . The fluctuation analysis unit  510  is capable of identifying the propagation quality between the antenna device  130  and the base station apparatus  110 , among the propagation qualities reported by the propagation quality measurement unit  509 , based on the identification information output from the identification information extractor unit  507 . 
     The control unit  511  performs the communication control of the base station apparatus  110 . For example, the control unit  511  controls the sync signal transmitter unit  513  so as to generate the sync signal. The control unit  511  allocates reference signals (e.g., reference number) to the antenna device  130  and the terminal devices  141  to  143 , based on the request for the allocation of a reference signal output from the signaling receiver unit  506 . The control unit  511  notifies the signaling transmitter unit  514  of the results of the allocation. 
     The control unit  511  is equipped with the scheduler unit  512 . The scheduler unit  512  performs scheduling of plural communication terminals that communicate with the base station apparatus  110 . The communication terminals that communicate with the base station apparatus  110  may include, besides the terminal devices  141  to  143 , other terminal devices that are external to the mobile object  120 . 
     For example, the scheduler unit  512  allocates wireless resources to downlink communication with the terminal devices  141  to  143 , based on downlink propagation quality indicated by the feedback information output from the feedback receiver unit  508 . The scheduler unit  512  further allocates wireless resources to uplink communication with the terminal devices  141  to  143 , based on uplink propagation quality reported by the propagation quality measurement unit  509 . 
     The scheduler unit  512  establishes the order of priority for the communication terminals and allocates wireless resources to the communication terminals in descending order of priority. Therefore, a communication terminal with a higher priority as established by the scheduler unit  512  receives allocation of wireless resources to communicate with the base station apparatus  110  before a communication terminal with a relatively lower priority. 
     The scheduler unit  512  adjusts the priority rank of the terminal devices  141  to  143 , based on the comparison results output from the fluctuation analysis unit  510 . For example, the scheduler unit  512 , treating each of the terminal devices  141  to  143  as a subject terminal, raises the priority rank of a subject terminal if the propagation quality between the base station apparatus  110  and the antenna device  130  is relatively lower than the propagation quality between the base station apparatus  110  and the subject terminal, thereby enhancing the possibility that a subject terminal having a deteriorating propagation quality will be given allocation of the wireless resources before other communication terminals, shortening the period of time before communication is started. Thus, communication with the subject terminal can be performed before the propagation quality for the subject terminal is deteriorated beyond that enabling communication. 
     The scheduler unit  512 , treating each of the terminal devices  141  to  143  as a subject terminal, lowers the priority rank of a subject terminal if the propagation quality between the base station apparatus  110  and the antenna device  130  is relatively higher than the propagation quality between the base station apparatus  110  and the subject terminal, thereby enhancing the possibility that a subject terminal having an improving propagation quality will be given allocation of the wireless resources after other communication terminals, extending the period of time before the subject terminal having an improving propagation quality starts to communicate. Thus, communication with the subject terminal may be performed after the propagation quality for the subject terminal has improved. 
     The control unit  511  controls reception of the data at the data receiver unit  503 , based on results of the scheduling by the scheduler unit  512 . The control unit  511  controls transmission of the data at the data transmitter unit  517 , based on the results of the scheduling by the scheduler unit  512 . The control unit  511  outputs the results of the scheduling by the scheduler unit  512  to the data transmitter unit  517 . 
     Under the control of the control unit  511 , the sync signal transmitter unit  513  generates the sync signal for the antenna device  130  and the terminal devices  141  to  143  to synchronize with the base station apparatus  110 . The sync signal generated by the sync signal transmitter unit  513  is further used as the reference signal for measuring the downlink propagation quality, in the antenna device  130  and the terminal devices  141  to  143 . The sync signal transmitter unit  513  outputs the generated sync signal to the transmitter  518 . 
     The signaling transmitter unit  514  generates the signaling signal to be transmitted to the antenna device  130  and the terminal devices  141  to  143  and outputs the generated signaling signal to the transmitter  518 . The signaling signal generated by the signaling transmitter unit  514  includes the results of the allocation of the reference signal reported by the control unit  511  and the results of the scheduling output from the control unit  511 . 
     The external input unit  515  receives input of data (user data) transmitted from the external core network. The external input unit  515  outputs the received data to the transmitting buffer  516 . The transmitting buffer  516  stores the data output from the external input unit  515 . Under the control of the control unit  511 , the data transmitter unit  517  reads out the data stored to the transmitting buffer  516  and generates data to be transmitted to the terminal devices  141  to  143 . The data transmitter unit  517  outputs the generated data to the transmitter  518 . 
     The transmitter  518  converts the sync signal from the sync signal transmitter unit  513 , the signaling signal from the signaling transmitter unit  514 , and the data from the data transmitter unit  517  to an analog signal. The transmitter  518  up-converts the analog signal (baseband signal) to an RF signal and outputs the RF signal to the duplexer  501 . 
     The data receiver unit  503 , the signaling receiver unit  506 , the identification information extractor unit  507 , the feedback receiver unit  508 , the propagation quality measurement unit  509 , the fluctuation analysis unit  510 , the control unit  511 , the scheduler unit  512 , the sync signal transmitter unit  513 , the signaling transmitter unit  514 , and the data transmitter unit  517  may be implemented, for example, by an arithmetic device such as a DSP. 
       FIG. 6  depicts a configuration of the terminal device according to the first embodiment. Although  FIG. 6  describes a configuration of the terminal device  141 , among the terminal devices  141  to  143 , the terminal devices  142  and  143  have a substantially identical configuration. As depicted in  FIG. 6 , the terminal device  141  is equipped with an antenna  601 , a duplexer  602 , a receiver  603 , a data receiver unit  604 , a receiving buffer  605 , a data input/output unit  606 , a signaling receiver unit  607 , a propagation quality measurement unit  608 , an identification information detector unit  609 , a control unit  610 , a reference signal transmitter unit  611 , a feedback transmitter unit  612 , a signaling transmitter unit  613 , a transmitting buffer  614 , a data transmitter unit  615 , and a transmitter  616 . 
     The antenna  601  is an antenna for performing the wireless communication with the base station apparatus  110  and the antenna device  130 . The antenna  601  receives signals transmitted from the base station apparatus  110  or the antenna device  130  and outputs each received signal to the duplexer  602 . The antenna  601  transmits to the base station apparatus  110 , the signal output from the duplexer  602 . While the antenna  601  is an antenna having functions of a transmitting antenna and a receiving antenna, a transmitting antenna and a receiving antenna may separately be provided in place of the antenna  601 . 
     The duplexer  602  outputs to the receiver  603 , the signal from the antenna  601 . The duplexer  602  outputs to the antenna  601 , the signal from the transmitter  616 . If the transmitting antenna and the receiving antenna are separately provided in place of the antenna  601 , the duplexer  602  may be omitted. 
     The receiver  603  down-converts the signal (RF signal) output from the duplexer  602  to a baseband signal and then converts the baseband signal to a digital signal. The receiver  603  outputs the digital signal to the data receiver unit  604 , the signaling receiver unit  607 , the propagation quality measurement unit  608 , and the identification information detector unit  609 . 
     Under the control of the control unit  610 , the data receiver unit  604  receives the data (user data) transmitted by the base station apparatus  110 , among the signals output from the receiver  603 . The data receiver unit  604  outputs the received data to the receiving buffer  605 . The receiving buffer  605  stores the data output from the data receiver unit  604 . 
     The data input/output unit  606  is connected to a user interface, such as a display, a speaker, a keyboard, a microphone, etc., provided in the terminal device  141 . The data input/output unit  606  reads out the data stored to the receiving buffer  605  and outputs the read-out data to the user by way of the user interface. The data input/output unit  606  outputs to the transmitting buffer  614 , the data input by way of the user interface. 
     The signaling receiver unit  607  receives the signaling signal transmitted by the base station apparatus  110 , among the signals output from the receiver  603 . The signaling signal includes the number of the reference signal allocated to the terminal device  141  by the base station apparatus  110 . The signaling receiver unit  607  outputs the received number of the reference signal to the control unit  610 . The signaling signal includes the results of the scheduling of the terminal device  141  performed by the base station apparatus  110 . The signaling receiver unit  607  outputs the received results of the scheduling to the control unit  610 . 
     The propagation quality measurement unit  608  receives the reference signal transmitted by the base station apparatus  110 , among the signals output from the receiver  603 . The propagation quality measurement unit  608  measures the downlink propagation quality, based on the received reference signal. The propagation quality measurement unit  608  notifies the control unit  610  of the measured propagation quality. 
     The identification information detector unit  609  detects the identification information transmitted by the antenna device  130 , among the signals output from the receiver  603 . The identification information detector unit  609  outputs the detected identification information to the control unit  610 . The identification information from the antenna device  130  is broadcast inside the open space  122  of the mobile object  120  and the terminal device  141  receives the identification information by, for example, suspending reception of the signal from the base station apparatus  110 . Since it is sufficient for the identification information to be received at least once, the terminal device  141  may receive the identification information intermittently, over a long cycle. 
     The control unit  610  performs the communication control of the terminal device  141 . For example, the control unit  610  controls the reception of the data in the data receiver unit  604 , based on the results of the scheduling output from the signaling receiver unit  607 . The control unit  610  outputs to the reference signal transmitter unit  611 , the number of the reference signal output from the signaling receiver unit  607 . The control unit  610  notifies the feedback transmitter unit  612  of the propagation quality reported by the propagation quality measurement unit  608 . 
     The control unit  610  outputs to the signaling transmitter unit  613 , the identification information from the identification information detector unit  609 . The control unit  610  controls the signaling transmitter unit  613  so as to generate a signaling signal inclusive of a request to the base station apparatus  110  for the allocation of a reference signal. The control unit  610  controls the transmission of the data in the data transmitter unit  615 , based on the results of the scheduling output from the signaling receiver unit  607 . 
     The reference signal transmitter unit  611  generates a reference signal, based on the number of the reference signal output from the control unit  610  and outputs the generated reference signal to the transmitter  616 . The feedback transmitter unit  612  generates feedback information indicative of the propagation quality reported by the control unit  610  and outputs the generated feedback information to the transmitter  616 . 
     The signaling transmitter unit  613  generates a signaling signal inclusive of the identification information output from the control unit  610 . Under the control of the control unit  610 , the signaling transmitter unit  613  generates a signaling signal inclusive of a request for allocation of a reference signal. The signaling transmitter unit  613  outputs the generated signaling signal to the transmitter  616 . 
     The transmitting buffer  614  stores the data output from the data input/output unit  606 . Under the control of the control unit  610 , the data transmitter unit  615  reads out the data stored to the transmitting buffer  614  and generates data to be transmitted to the base station apparatus  110 . The data transmitter unit  615  outputs the generated data to the transmitter  616 . 
     The transmitter  616  converts the reference signal from the reference signal transmitter unit  611 , the feedback information from the feedback transmitter unit  612 , the signaling signal from the signaling transmitter unit  613 , and the data from the data transmitter unit  615  to an analog signal. The transmitter  616  up-converts the analog signal (baseband signal) to an RF signal and outputs the RF signal to the duplexer  602 . 
     The data receiver unit  604 , the receiving buffer  605 , the signaling receiver unit  607 , the propagation quality measurement unit  608 , the identification information detector unit  609 , the control unit  610 , the reference signal transmitter unit  611 , the feedback transmitter unit  612 , the signaling transmitter unit  613 , and the data transmitter unit  615  may be implemented, for example, by an arithmetic device such as a DSP. 
     In this way, in the communication system  100  according to the first embodiment, the use of the antenna device  130  provided at a forward aspect of the mobile object  120  enable forecast of the fluctuation of the propagation quality at the terminal devices  141  to  143  in the mobile object  120 . The scheduling performed based on the results of the forecast of the propagation quality fluctuation enhances the communication quality (throughput) between the base station apparatus  110  and the terminal devices  141  to  143 . 
     For example, the communication is performed with the wireless resources allocated to the terminal devices  141  to  143  under a better state of propagation quality, by adjusting the priority rank of the terminal devices  141  to  143 , based on the results of the forecast of the propagation quality fluctuation. This communication system may be implemented without using the propagation environment information, etc., correlated with the map information for the forecast of the propagation quality. This communication system may be implemented without making a major specification change, for example, to the terminal devices  141  to  143 . 
     A basic configuration of the communication system  100  according to a second embodiment is substantially identical to the configuration depicted in  FIG. 1 , with the exception that the antenna device  130  receives the reference signal from the base station apparatus  110  by the forecast-use antenna  131  and that the antenna device  130  measures the propagation quality, based on the received reference signal and transmits the feedback information indicative of the measured propagation quality to the base station apparatus  110  by the forecast-use antenna  131 . 
     The antenna device  130 , using the terminal-use antenna  132 , distributes to the terminal devices  141  to  143 , the identification information (e.g., feedback channel) indicative of the feedback information to be transmitted from the forecast-use antenna  131 . The terminal devices  141  to  143  receive the reference signal from the base station apparatus  110 , measure the propagation quality based on the received reference signal, and transmit feedback information indicative of the measured propagation quality to the base station apparatus  110 . The configuration of the terminal devices  141  to  143  according to the second embodiment is substantially identical to the configuration depicted in  FIG. 6 . 
     The base station apparatus  110  compares the propagation quality indicated by the feedback information from the antenna device  130  and the propagation quality indicated by the feedback information from the terminal devices  141  to  143  and performs the scheduling based on the results of the comparison. The base station apparatus  110  identifies the feedback information transmitted from the antenna device  130 , from among feedback information transmitted from other sources in the vicinity, based on the identification information transmitted from the terminal devices  141  to  143 . 
     The feedback information to be transmitted to the base station apparatus  110  from the antenna device  130  and the terminal devices  141  to  143  is signals multiplexed by time, frequency, or code etc. With different feedback channels allocated for the antenna device  130  and the terminal devices  141  to  143 , the feedback information from the antenna device  130  and the terminal devices  141  to  143  may be multiplexed for transmission to the base station apparatus  110 . 
       FIG. 7  is a sequence diagram of one example of operation of the communication system according to the second embodiment. Although  FIG. 7  describes the operation of the terminal device  141 , among the terminal devices  141  to  143 , the operation of the terminal devices  142  and  143  is substantially identical. The operation at step S 701  is substantially identical to that at step S 201  depicted in  FIG. 2 . After step S 701 , the antenna device  130  requests the base station apparatus  110  for allocation of a feedback channel (step S 702 ). The request for the allocation of the feedback channel at step S 702  is made using, for example, an uplink random access channel, etc. 
     In response to the request for the allocation at step S 702 , the base station apparatus  110  allocates a feedback channel to the antenna device  130  (step S 703 ). Subsequently, the antenna device  130 , using the feedback channel allocated at step S 703 , starts to transmit feedback information indicative of the propagation quality for the base station apparatus  110  (step S 704 ). 
     Then, the terminal device  141  in the mobile object  120  establishes a link, by initial access or handover, etc., with the base station apparatus  110  (step S 705 ). With the link established at step S 705 , the terminal device  141  is allocated a feedback channel by the base station apparatus  110 . 
     Then, the terminal device  141 , using the feedback channel allocated by the base station apparatus  110 , starts to transmit feedback information indicative of the propagation quality with the base station apparatus  110  (step S 706 ). 
     Then, the antenna device  130  distributes the identification information of the feedback information that the antenna device  130  has started to transmit at step S 704  (step S 707 ). The identification information distributed at step S 707  is received by the terminal device  141  located in the open space  122  of the mobile object  120 . The terminal device  141  transmits the identification information distributed at step S 707  to the base station apparatus  110  (step S 708 ). 
     Subsequently, the base station apparatus  110  performs the scheduling based on the feedback information, the transmission of which commencing at step S 704  and step S 706 , and notifies the terminal device  141  of results of the scheduling (step S 709 ), ending a sequence of operations. 
     These steps enable the base station apparatus  110  to perform the scheduling of the terminal device  141 , based on the propagation quality between the base station apparatus  110  and the antenna device  130  and the propagation quality between the base station apparatus  110  and the terminal device  141 . Although an example has been described of the base station apparatus  110  allocating the feedback channel by which the antenna device  130  transmits, the feedback channel used by the antenna device  130  may be preliminarily determined. In this case, there is no need for the allocation of the feedback channel by the base station apparatus  110 . 
       FIG. 8  depicts one example of a configuration of the antenna device according to the second embodiment. In  FIG. 8 , components identical to those depicted in  FIG. 4  are given same reference numerals used in  FIG. 4  and description thereof is omitted. As depicted in  FIG. 8 , the antenna device  130  according to the second embodiment is equipped with a propagation quality measurement unit  801  and a feedback transmitter unit  802  in addition to the configuration depicted in  FIG. 4 . The signaling receiver unit  404  receives the number of the feedback channel allocated by the base station apparatus  110 , among the signals output from the receiver  402 . The signaling receiver unit  404  outputs the received number of the feedback channel to the control unit  405 . 
     The propagation quality measurement unit  801  receives the reference signal transmitted from the base station apparatus  110 , among the signals output from the receiver  402 . The propagation quality measurement unit  801  measures the propagation quality between the antenna device  130  and the base station apparatus  110 , based on the received reference signal and notifies the control unit  405  of the measured propagation quality. 
     The control unit  405  controls the signaling transmitter unit  404  so as to generate, based on the basic information output from the synchronization processor unit  403 , a signaling signal requesting the base station apparatus  110  for a feedback channel. The control unit  405  notifies the feedback transmitter unit  802  of the number of the feedback channel output from the signaling receiver unit  404  and the propagation quality reported by the propagation quality measurement unit  801 . 
     Under the control of the control unit  405 , the signaling transmitter unit  407  generates the signaling signal requesting the base station apparatus  110  for a feedback channel. The signaling transmitter unit  407  outputs the generated signaling signal to the transmitter  408 . The feedback transmitter unit  802  generates feedback information indicative of the propagation quality reported by the control unit  405 , based on the number of the feedback channel reported by the control unit  405 . The feedback transmitter unit  802  outputs the generated feedback information to the transmitter  408 . 
     The transmitter  408  converts the feedback information output from the feedback transmitter unit  802  to an analog signal, up-converts the analog signal (baseband signal) to an RF signal, and outputs the RF signal to the duplexer  401 . Thus, the antenna device  130  is able to measure the propagation quality, based on the reference signal from the base station apparatus  110  and transmit feedback information indicative of the measured propagation quality to the base station apparatus  110 . 
       FIG. 9  depicts one example of a configuration of the base station apparatus according to the second embodiment. In  FIG. 9 , components substantially identical to those depicted in  FIG. 5  are given the same reference numerals used in  FIG. 5  and description thereof is omitted. As depicted in  FIG. 9 , the feedback receiver unit  508  of the base station apparatus  110  according to the second embodiment outputs the received feedback information to the fluctuation analysis unit  510  and the control unit  511 . In the base station apparatus  110  according to the second embodiment, the propagation quality measurement unit  509  needs not notify the fluctuation analysis unit  510  of the measured propagation quality. 
     The fluctuation analysis unit  510  compares the propagation quality between the antenna device  130  and the base station apparatus  110  and the propagation quality between the base station apparatus  110  and the terminal devices  141  to  143  by means of the propagation quality indicated by the feedback information output from the feedback receiver unit  508 . The fluctuation analysis unit  510  is capable of identifying the feedback information from the antenna device  130  from among feedback information reported by the feedback receiver unit  508 , based on the identification information output from the identification information extractor unit  507 . 
     Thus, in the communication system  100  according to the second embodiment, the use of the feedback information from the antenna device  130  and the terminal devices  141  to  143  makes it possible to forecast at the base station apparatus  110 , the fluctuation of the propagation quality at the terminal devices  141  to  143 . Consequently, the second embodiment achieves the same effect as that of the first embodiment. 
       FIG. 10  depicts one example of a configuration of the base station apparatus according to a third embodiment. In  FIG. 10 , components substantially identical to those depicted in  FIG. 5  are given same reference numerals and description thereof is omitted. As depicted in  FIG. 10 , the control unit  511  of the base station apparatus  110  according to the third embodiment is equipped with a computation unit  1001  in addition to the scheduler unit  512  depicted in  FIG. 5 . The computation unit  1001  acquires the propagation quality reported by the propagation quality measurement unit  509 . 
     The computation unit  1001  computes the time lag between the fluctuation of the propagation quality between the antenna device  130  and the base station apparatus  110  and the fluctuation of the propagation quality between the base station apparatus  110  and the terminal devices  141  to  143 , based on the acquired propagation quality. That is to say, the time lag computed by the computation unit  1001  is the time from a change in the propagation quality between the antenna device  130  and the base station apparatus  110  until a subsequent change in the propagation quality between the base station apparatus  110  and the terminal devices  141  to  143 . 
     Here, one example will be described of a method of calculating the time lag by the computation unit  1001 . The propagation quality (here, considered as field strength) of the antenna device  130  at time t i  is given as Po(t i ) and the field strength of the terminal devices  141  to  143  at time t i  is given as Pm(t i ). In this case, the correlation coefficient Δ of the field strength of antenna device  130  and the field strength of the terminal devices  141  to  143  at time lag τ may be computed, for example, by equation (1). 
     
       
         
           
             
               
                 
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     In equation (1), &lt; &gt; represents an averaging calculation. Equation (1) indicates that the smaller the correlation coefficient Δ is, the higher the fluctuation correlation of the field strength of the antenna device  130  and the field strength of the terminal devices  141  to  143  is. Equation (1) allows the computation unit  1001  to compute the time lag τ at which the correlation of these field strengths is highest, by calculating the correlation coefficient Δ while varying the time lag τ to obtain the time lag τ at which the correlation coefficient Δ is smallest. The computation unit  1001  notifies the scheduler unit  512  of the computed time lag. 
     The scheduler unit  512  changes the amount of adjustment in priority rank, based on the fluctuation forecast (see, e.g., steps S 305  and S 307  of  FIG. 3 ) according to the time lag reported by the computation unit  1001 . For example, the scheduler unit  512  has a threshold pre-established. The scheduler unit  512  compares the time lag reported by the computation unit  1001  and the threshold with respect to each of the terminal devices  141  to  143  and makes the amount of adjustment in priority rank greater for a terminal device having a time lag below the threshold as compared with a terminal device having a time lag at or above the threshold. 
     Here, it is assumed, for example, that the terminal device  141  is located close to the antenna device  130  (at the forward aspect of the mobile object  120 ) and that the terminal device  143  is located far from the antenna device  130  (at the rear aspect of the mobile object  120 ). It is also assumed that the time lag reported by the computation unit  1001  is below the threshold with respect to the terminal device  141  and that the time lag reported by the computation unit  1001  is at or above the threshold with respect to the terminal device  143 . In this case, the amount of adjustment in priority rank for the terminal device  141  is greater than the amount of adjustment of the priority rank for the terminal device  143 . 
     The scheduler unit  512  may, with respect to the terminal devices  141  to  143 , make the amount of adjustment greater for a terminal device having a smaller time lag reported by the computation unit  1001 . Here, it is assumed that the terminal device  141  is located close to the antenna device  130  and that the terminal device  143  is located far from the antenna device  130 . In this case as well, since the time lag of the terminal device  141  is smaller than that of the terminal device  143 , the amount of adjustment in priority rank for the terminal device  141  is greater than the amount of adjustment for the terminal device  143 . 
     Therefore, for example, at the time of the mobile object  120  entering a tunnel, if the propagation quality for the terminal devices  141  to  143  is deteriorating, the priority rank of the terminal device  141  becomes higher, with a greater amount of adjustment, than that of the terminal device  143  (see, e.g., steps S 305  and S 307  of  FIG. 3 ). This makes the priority rank of the terminal device  141  prone to be higher than that of the terminal device  143 . For this reason, the wireless resources may be allocated preferentially to the terminal device  141  whose propagation quality deteriorates before that of the terminal device  143 . The computation unit  1001  may be implemented, for example, by an arithmetic device such as a DSP. 
     Thus, the communication system  100  according to the third embodiment is capable of compensating for differences in the timing of the propagation quality fluctuations consequent to the position of the terminal devices  141  to  143  in the mobile object  120  by changing the amount of adjustment in priority rank according to the time lag computed by the computation unit  1001 . Therefore, the third embodiment has the same effect as that of the first embodiment and is capable of performing unbiased scheduling irrespective of the position of the terminal devices  141  to  143  in the mobile object  120 . 
     Here, an example has been described of achieving the third embodiment by providing the computation unit  1001  in the scheduler unit  512  (see  FIG. 5 ) of the base station apparatus  110  according to the first embodiment. By contrast, configuration may be so as to achieve the third embodiment by providing the computation unit  1001  in the scheduler unit  512  (see  FIG. 9 ) of the base station apparatus  110  according to the second embodiment. 
     As described above, according to the base station apparatus, the antenna device, the terminal device, the communication system, and the communication method, the use of the antenna device provided at the forward aspect of the mobile object makes it possible to accurately forecast fluctuations in the propagation quality for the terminal device in the mobile object, thereby enhancing communication quality. 
     In the embodiments described above, although the example has been described of using the field strength as the propagation quality, the propagation quality is not limited to field strength and may be Signal to Interference and Noise Ratio (SIRN) or error rate. 
     The disclosed base station apparatus, antenna device, terminal device, communication system, and communication method enhance communication quality. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.