Abstract:
A wireless base station, includes: a wireless transceiver configured to transmit to a wireless terminal a downlink frame including a downlink control information, the wireless downlink control information includes information representing a specified offset, wherein the wireless transceiver is further configured to receive an uplink frame from the wireless terminal; and a processor circuit coupled to the wireless transceiver and configured to determine uplink control information from the uplink frame, the uplink control information being offset by at least the specified offset from a location in the uplink frame that is the same as a location where the downlink control information was located in the downlink frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. application Ser. No. 14/487,664, filed Sep. 16, 2014, which is a continuation application of International Application No. PCT/JP2012/001907, filed on Mar. 19, 2012, the entire contents of each are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates to a wireless communication system, a wireless terminal, a wireless base station, and a wireless communication method. 
       BACKGROUND 
       [0003]    In recent years, in an attempt to further increase speed and capacity of wireless communication in a wireless communication system, such as a mobile phone system (cellular system), discussions are held on wireless communication technology for the next generation. For example, in the 3GPP (3rd generation partnership project), which is a standards organization, a communication standard called as LTE (long term evolution) and a communication standard called as LTE-A (LTE-advanced) based on the wireless communication technique of LTE are suggested. 
         [0004]    The latest communication standard completed in the 3GPP is Release 10 compatible with LTE-A, in which Releases 8 and 9 compatible with LTE are greatly functionally enhanced. Currently, discussions are held for completion of Release 11, in which Release 10 is further enhanced. In the descriptions below, “LTE” includes, in addition to LTE and LTE-A, other wireless communication systems that are made by enhancing LTE unless otherwise noted. 
         [0005]    In Release 11 of the 3GPP, coordinated multiple point (CoMP) is one of the techniques that are discussed actively in particular. Simply put, CoMP is a technique to coordinate sending and receiving to a wireless terminal (UE: user equipment) between different wireless base stations (eNB: evolved node B). In the following descriptions, a wireless link in a direction from a wireless terminal to a wireless base station is called as an uplink (UL) and a wireless link in a direction from a wireless base station to a wireless terminal is called as a downlink (DL). 
         [0006]    There are several forms of CoMP, and a scenario is known in which a wireless terminal carries out communication with different wireless base stations for UL and DL. In a regular case, a wireless terminal carries out communication with an identical wireless base station for UL and DL. That is, it is common that a wireless terminal carries out communication with a connected wireless base station (serving cell). As an example, a wireless terminal receives UL scheduling information from a connected wireless base station on a DL and sends data to the connected wireless base station on a UL based on the received UL scheduling information. As another example, a wireless terminal receives data from a connected wireless base station on a DL and sends a response signal (ACK signal or NACK signal) to the received data to the connected wireless base station on a UL. 
         [0007]    However, there is sometimes another wireless base station whose communication quality of UL for the wireless terminal is higher than the connected wireless base station. Even when certain communication quality of DL (receiving quality, propagation delay, and the like) is secured, in such a case that a wireless terminal is located at a cell edge, the communication quality of UL may not be good. When there is another wireless base station whose communication quality of DL is higher than the connected wireless base station, the connected wireless base station of the wireless terminal is switched by handover, so that this is out of the problem. 
         [0008]    Such problem easily occurs as well in a so-called heterogeneous network, for example, where macrocells, which are regular base stations, and picocells and the like (also microcells, femtocells, and the like), which are small base stations, are mixed. In a heterogeneous network, a picocell is desired to suppress the DL cell size (suppress the sending power) in order to inhibit interference in a macrocell. That is, a macrocell and a picocell greatly differ in DL cell size (sending power). Therefore, a situation may occur that, for a wireless terminal located at a cell edge of the connected macrocell, the DL quality is better with a macrocell while the UL quality is better with a picocell. 
         [0009]    In the 3GPP, in view of such problems, a scenario is under review in which a wireless terminal carries out communication with different wireless base stations for UL and DL as described above. In this scenario, when there is another wireless base station whose communication quality of UL for a wireless terminal is higher than the connected wireless base station, the wireless terminal carries out UL communication with the base station different from the connected wireless base station. As an example, it is possible that the wireless terminal receives UL scheduling information from the connected wireless base station on a DL and sends data to a base station different from the connected wireless base station on a UL based on the received UL scheduling information. As another example, it is possible that a wireless terminal receives data from the connected wireless base station on a DL and sends a response signal to the received data to a base station different from the connected wireless base station on a UL. In such a manner, it becomes possible to secure the UL wireless communication quality to a wireless terminal that has poor UL wireless quality with the connected wireless base station. Then, as a result, an effect of improving transmission efficiency of the entire system is expected. 
         [0010]    Non Patent Literatures 3GPP TS36.211 V10.4.0 (2011 December), 3GPP TS36.213 V10.4.0 (2011 December), 3GPP TR36.814 V9.0.0 (2010 March), 3GPP TR36.819 V11.0.0 (2011 September), 3GPP R1-114324 “On Reference Signal Enhancements for UL CoMP” (2011 November) are examples of the related art. 
       SUMMARY 
       [0011]    According to an aspect of the invention, a wireless communication system includes a wireless base station, and a wireless terminal configured to receive from the wireless base station a downlink frame including data and a downlink control signal for decoding the data, the downlink control signal being mapped to a first downlink control resource element of downlink control resource elements that are resource units used for transmissions of downlink control signals in the downlink frame, and to transmit an uplink frame including an uplink control signal for acknowledging a decoding result of the data, the uplink control signal being mapped to a first uplink control resource element of uplink control resource elements that are resource units used for transmissions of uplink control signals in the uplink frame, the first uplink control resource element being determined by shifting a second uplink control resource element of the uplink control resource elements by an offset number whose unit is one of the uplink control resource elements, the second uplink control resource element being determined based on a location of the first downlink control resource element in the downlink frame, the offset number being determined based on a first offset information included in the downlink control signal. 
         [0012]    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. 
         [0013]    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 
         [0014]      FIG. 1  is a diagram illustrating problems in conventional techniques. 
           [0015]      FIG. 2  is a diagram illustrating one example of a network configuration of a wireless communication system in a first embodiment. 
           [0016]      FIG. 3  is one example of a process sequence diagram of the wireless communication system in the first embodiment. 
           [0017]      FIG. 4  is a diagram illustrating one example of a DCI format in the wireless communication system of the first embodiment. 
           [0018]      FIG. 5  is one example of a functional configuration diagram of a wireless base station in the wireless communication system of the first embodiment. 
           [0019]      FIG. 6  is one example of a functional configuration diagram of a wireless terminal in the wireless communication system of the first embodiment. 
           [0020]      FIG. 7  is one example of a hardware configuration diagram of the wireless base station in the wireless communication system of the first embodiment. 
           [0021]      FIG. 8  is one example of a hardware configuration diagram of the wireless terminal in the wireless communication system of the first embodiment. 
           [0022]      FIG. 9  is one example of a process sequence diagram of a wireless communication system in a second embodiment. 
           [0023]      FIG. 10  is a diagram illustrating one example of a DCI format in the wireless communication system of the second embodiment. 
           [0024]      FIG. 11  is one example of a process sequence diagram of a wireless communication system in a third embodiment. 
           [0025]      FIG. 12  is one example of a process sequence diagram of a wireless communication system in a fourth embodiment. 
           [0026]      FIG. 13  is one example of a process sequence diagram of a wireless communication system in a fifth embodiment. 
           [0027]      FIG. 14  is one example of a process sequence diagram of a wireless communication system in a sixth embodiment. 
           [0028]      FIG. 15A  is a diagram illustrating one example of a DCI format in a wireless communication system of a seventh embodiment. 
           [0029]      FIG. 15B  is a diagram illustrating one example of a DCI format in a wireless communication system of a seventh embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    When a wireless terminal and a wireless base station carry out communication, with some exceptions, scheduling of a wireless resource (hereinafter, may be referred to simply as scheduling) is carried out. Scheduling of a wireless resource is to determine a wireless resource that is used for sending and receiving of a wireless signal (to assign a wireless resource or to determine allocation of a wireless resource is synonymous). For example, a wireless resource is defined by a time component and a frequency component. Scheduling of a wireless resource is carried out by a connected wireless base station to a subordinate wireless terminal. The connected wireless base station notifies a connected wireless terminal of scheduling information related to the determined scheduling on a DL, and the connected wireless terminal and the wireless base station carry out sending and receiving of a wireless signal based on the scheduling information. 
         [0031]    Consideration is given to the above described scheduling in the scenario where a wireless terminal carries out communication with different wireless base stations for UL and DL. Now, it is assumed that a wireless terminal is intended to send data on a UL. At this time, the wireless terminal sends a signal that requests UL scheduling to the connected wireless base station. Next, it is assumed that the connected wireless base station that has received the signal that requests UL scheduling determines to cause another wireless base station to receive UL data of the wireless terminal based on receiving quality of the wireless signal from the wireless terminal and the like. 
         [0032]    At this time, the connected wireless base station sends UL scheduling information to the wireless terminal on a DL. The wireless terminal sends a wireless signal including UL data using a UL wireless resource that is specified by the received UL scheduling information. 
         [0033]    Meanwhile, in parallel with the above, the connected wireless base station sends the UL scheduling information also to another wireless base station via a backhaul network (network that links between wireless base stations and a wireless base station with a core network). The other wireless base station receives a wireless signal including UL data from the wireless terminal using the wireless resource that is specified by the received UL scheduling information. 
         [0034]    According to the above consideration, in the scenario where a wireless terminal carries out communication with different wireless base stations for UL and DL, it may also be considered that scheduling is carried out without a problem and the other wireless base station is capable of receiving data from the wireless terminal. However, in such scenario, a phenomenon is confirmed in which another wireless base station different from the connected base station is sometimes not capable of receiving data from the wireless terminal. 
         [0035]    The disclosed technique has made in view of the above, and it is an object thereof to provide a wireless communication system, a wireless terminal, a wireless base station, and a wireless communication method that allow, when a wireless terminal carries out communication with different wireless base stations for UL and DL, another wireless base station different from the connected base station to receive data from the wireless terminal. 
         [0036]    Descriptions are given below to embodiments of a wireless communication system, a wireless terminal, a wireless base station, and a wireless communication method of the disclosure, with reference to the drawings. Although descriptions are given as separate embodiments for convenience, it is of course possible to also obtain effects of combination by combining respective embodiments and further enhance the usability. 
       [a] Identification of Problem 
       [0037]    As described above, in the scenario where a wireless terminal carries out communication with different wireless base stations for UL and DL, a phenomenon is confirmed in which another wireless base station different from the connected base station is sometimes not capable of receiving data from the wireless terminal. Keenly reviewing this phenomenon, the inventor has found that there are problems of wireless resource scheduling in the scenario. Here, before describing the respective embodiments, descriptions are given to identification of the problems that the inventor has found. 
         [0038]    As described above, a wireless terminal sends a wireless signal including UL data (called as a first wireless signal) using a wireless resource that is specified by UL scheduling information received from the connected wireless base station. In contrast, another wireless base station receives a wireless signal including UL data from the wireless terminal based on scheduling information received from the connected wireless base station (that is, based on a wireless resource defined by the connected wireless base station). However, at this time, there is a possibility that the other wireless base station has already sent the scheduling information specifying the wireless resource to another wireless terminal connected thereto. This is because it is not possible for the other wireless base station to predict a UL reception request from the connected wireless base station in advance. 
         [0039]    In such a case, the other wireless terminal sends a wireless signal including data (called as a second wireless signal) to the other wireless base station using the wireless resource specified by the UL scheduling information received from the other wireless base station. Thus, the wireless terminal and the other wireless terminal turn out to carry out UL sending using same wireless resources (sending time, sending frequency). In other words, the first wireless signal and the second wireless signal are sent on same wireless resources. As a result, conflict occurs in a UL wireless resource. Since the first wireless signal and the second wireless signal include different data and interfere with each other, it becomes difficult for the other wireless base station to decode any data. Accordingly, in such a case, the other wireless base station turns out not to be capable of receiving data without an error from the wireless terminal.  FIG. 1  illustrates an outline of this problem. 
         [0040]    To sum up above, in the scenario where a wireless terminal carries out communication with different wireless base stations for UL and DL, conflict of a wireless resource may occur in UL sending. Then, when conflict of a wireless resource occurs in UL sending, it is not possible that another wireless base station different from the connected base station receives data without an error from the wireless terminal. Accordingly, in the scenario where a wireless terminal carries out communication with different wireless base stations for UL and DL, there is a problem that the other wireless base station is sometimes not capable of receiving data from the wireless terminal. 
         [0041]    In addition, when the other wireless base station is not capable of receiving data without an error (not capable of decoding data), the wireless terminal and the other wireless terminal turn out to carry out resending of data in response to reception of a NACK signal or a timeout of a response signal. Resending of data leads to a waste of wireless resources and thus is not preferred. 
         [0042]    The technique of the disclosure has been embodied based on the findings of the above problems by the inventor. 
       [b] First Embodiment 
       [0043]      FIG. 2  illustrates a network configuration of a wireless communication system in the first embodiment. The present embodiment is an embodiment of a wireless communication system compliant with LTE. Therefore, some of LTE specific terms and concepts appear. However, the present embodiment is merely one example and it is noted that it is applicable to a wireless communication system compliant with a communication standard other than LTE. 
         [0044]    The wireless communication system illustrated in  FIG. 2  is provided with a plurality of wireless base stations (eNB: evolved node B)  1   a ,  1   b ,  1   c , wireless terminals (UE: user equipment)  2   a ,  2   b , and the like. In the descriptions below, the plurality of wireless base stations  1   a ,  1   b ,  1   c  may be represented collectively as wireless base stations  1 . In addition, the plurality of wireless terminals  2   a ,  2   b  may be represented collectively as wireless terminals  2 . 
         [0045]    Wireless networks between the wireless base stations and the wireless terminals are called as wireless access networks. The wireless base stations  1  are connected with a wired or wireless network (transmission network) called as a backhaul network. A backhaul network is a network that links between the wireless base stations  1  and the wireless base stations  1  with a core network. The wireless base stations  1  are capable of carrying out communication with a device connected to the core network via the backhaul network. To the core network, an MME (mobility management entity), an SAE-GW (system architecture evolution gateway), and the like that are not illustrated are connected. An LTE network may also be called as an EPS (evolved packet system). The EPS includes a eUTRAN (evolved universal terrestrial radio network), which is a wireless access network, and an EPC (evolved packet core), which is a core network. The core network may also be called as an SAE (system architecture evolution). 
         [0046]    The wireless base stations  1  (may also be called simply as base stations) in  FIG. 2  is a device that carries out wireless communication with the wireless terminals  2  via the wireless access network and also is connected to the backhaul network. The wireless base station  1   a  carries out sending and receiving of data with the subordinate wireless terminal  2   a  (may be referred to as a connected wireless terminal) and also carries out a variety of control over the wireless terminal  2   a  by exchanging various types of control information with the subordinate wireless terminal  2   a . In addition, the wireless base station  1   a  carries out relay of data with the other wireless base stations  1   b ,  1   c , each other, via the backhaul network and also is capable of cooperation by exchanging various types of control information with the other wireless base stations  1   b ,  1   c.    
         [0047]    The wireless base stations  1  carries out exchange of a variety of control information with a control device, such as an MME connected to the core network beyond the backhaul network, via the backhaul network. In addition, the wireless base station  1   a  relays the data received from the subordinate wireless terminal  2   a  to a relay device, such as an SAE-GW connected to the core network, and also relays the data received from the relay device, such as an SAE-GW, to the subordinate wireless terminal  2   a.    
         [0048]    The wireless base stations  1  may be connected with the backhaul network by wire and may also be connected wirelessly. In addition, the wireless base stations  1  may also have a communication function with the wireless access network as an extended RRH, which is a separate device, and connect by wire therewith. 
         [0049]    Although a “cell” is a range that the wireless base stations  1  covers in order that the wireless terminals  2  sends and receives a wireless signal (strictly, there are UL cells and DL cells), the wireless base stations  1  and the cell are almost corresponding concepts, so that it does not matter if the “cell” and the “wireless base station” are read interchangeably as appropriate in the descriptions below. 
         [0050]    Meanwhile, the wireless terminals  2  (may also be called simply as terminals; may also be called as user devices, subscriber stations, mobile stations, and the like) in  FIG. 2  are devices that carry out wireless communication with the wireless base stations  1  via the wireless access network. The wireless terminal  2   a  is connected to one wireless base station  1   a , and as a change occurs in a wireless state by transfer and the like, the wireless base station  1  to be connected is switched by handover. Here, while “connection” indicates that a wireless terminal is registered in (attached to) a wireless base station, it may also be interpreted to simply mean in communication. The wireless base station  1   a  connected by the wireless terminal  2   a  is called as a connected wireless base station or a serving cell. The wireless terminal  2   a  carries out sending and receiving of data by wireless communication with the connected wireless base station  1   a  and also is subject to a variety of control by exchanging various types of control information by wireless communication with the connected wireless base station  1   a.    
         [0051]    The wireless terminal  2   a  in the present embodiment receives a DL wireless signal from the connected wireless base station  1   a . The wireless terminal  2   a  in the present embodiment is capable of sending a UL wireless signal to the connected wireless base station  1   a  or the other wireless base stations  1   b ,  1   c . Accordingly, the wireless terminal  2   a  in the present embodiment is capable of carrying out communication with wireless base stations  1  different for DL and UL. Details are described later. 
         [0052]    The wireless communication system in the present embodiment is configured with, as well as a DL wireless signal and a UL wireless signal, a wireless frame (may also be referred to simply as a frame) having a predetermined length (for example, 10 milliseconds). Further, one wireless frame is respectively configured with a predetermined number (for example, 10) of wireless subframes (may also be referred to simply as subframes) having a predetermined length (for example, 1 millisecond). Then, each subframe is further divided into each physical channel, which is a physical communication path. Since a “frame” and a “subframe” are merely terms that indicate processing units of a wireless signal, these terms may also be read interchangeably as appropriate in the following. 
         [0053]    As a DL physical channel, there are a downlink shared channel (PDSCH: physical downlink shared channel) that is used for transmission of a DL data signal and the like, a downlink control channel (PDCCH: physical downlink control channel) that is used for transmission of a DL control signal, and the like. In a PDSCH, as well as a DL data signal, a DL reference signal for various types of measurement and the like are also mapped. Meanwhile, as a UL physical channel, there are an uplink shared channel (PUSCH: physical uplink shared channel) that is used for transmission of a UL data signal and the like, an uplink control channel (PUCCH: physical uplink control channel) that is used for transmission of a UL control signal, and the like. In PUSCH, as well as a UL data signal, a UL reference signal for various types of measurement and the like are also mapped. 
         [0054]    Next, based on  FIG. 3 , descriptions are given to a process sequence of the wireless communication system in the first embodiment.  FIG. 3  is a process sequence when sending data (UL data) to the connected wireless base station  1   a  occurs in the wireless terminal  2   a . As described before, the wireless terminal  2   a  in the present embodiment is capable of receiving a DL wireless signal from the connected wireless base station  1   a  and also sending a UL wireless signal to the connected wireless base station  1   a  or the other wireless base station  1   b , which is another wireless base station. That is, the wireless terminal  2   a  is capable of carrying out communication with wireless base stations  1  different for DL and UL.  FIG. 3  is one example of such asymmetric wireless communication. 
         [0055]    In S 101  in  FIG. 3 , UL data occurs in the wireless terminal  2   a . For example, UL data occurs when an audio signal, data, and the like are sent from the wireless terminal  2   a  to the other wireless terminal  2   b , when an application on the wireless terminal  2   a  sends data to a server on the Internet, and the like. As the UL data occurs, in S 102 , the wireless terminal  2   a  sends UL schedule requesting information, which is information to request a UL wireless resource in order to send the UL data, to the connected wireless base station  1   a  on a UL wireless signal. In the UL schedule requesting information, information indicating a UL wireless resource amount to be used (UL wireless resource amount information) is stored. 
         [0056]    As receiving the UL schedule requesting information, the connected wireless base station  1   a  starts scheduling of a UL wireless resource to the wireless terminal  2   a . The connected wireless base station  1   a  firstly obtains, for example, UL receiving quality from the wireless terminal  2   a . It is possible to obtain the UL receiving quality based on a sound reference signal (SRS) included in the UL wireless signal. Then, the connected wireless base station  1   a  decides whether the obtained UL receiving quality satisfies a predetermined criterion. Based on this decision, in S 103 , the connected wireless base station  1   a  determines whether or not to set a base station to receive UL data as a local station (connected wireless base station  1   a ). When the receiving quality satisfies the predetermined criterion, the connected wireless base station  1   a  determines the base station to receive UL data as the local station (connected wireless base station  1   a ). In contrast, when the receiving quality does not satisfy a predetermined criterion, the connected wireless base station  1   a  determines the base station to receive UL data as any of the other wireless base stations  1   b ,  1   c  other than the local station (at this time point, the other wireless base stations  1   b ,  1   c  do not have to be determined into one). This is because, when the UL receiving quality from the wireless terminal  2   a  in the connected wireless base station  1   a  is poor, it is possible to secure communication efficiency of the entire system more by causing the UL data from the wireless terminal  2   a  to be received by the other wireless base stations  1   b ,  1   c.    
         [0057]    Although the connected wireless base station  1   a  in this example carries out determination of whether or not to receive at a local station in S 103  based on the UL receiving quality, instead of or in addition to this, the determination may also be carried out based on another index. For example, when the UL wireless resource use amount or activity rate of the local station is not less than the predetermination (when there are less space in the UL wireless resource), it is possible that the connected wireless base station  1   a  determines the base station to receive UL data as other than the local station. 
         [0058]    Back to the description of  FIG. 3 , in this example, it is assumed that the connected wireless base station  1   a  determines, in S 103 , the base station to receive UL data as other than the local station (connected wireless base station  1   a ). At this time, in S 104 , the connected wireless base station  1   a  sends wireless resource requesting information, which is information to request a UL wireless resource to the other wireless base stations  1   b ,  1   c  via the transmission network. Here, the connected wireless base station  1   a  is capable of carrying out selection of a sending destination of the wireless resource requesting information based on, for example, DL receiving quality of each wireless base station stored in a measurement report, not illustrated, that is successively received from the wireless terminal  2   a . The other wireless base stations  1   b ,  1   c  to be the sending destination of wireless resource requesting information may be one or a plurality, and in the example of  FIG. 3 , it is assumed that two other wireless base stations  1   b ,  1   c  are selected as the sending destination. 
         [0059]    In S 105  in  FIG. 3 , as receiving the wireless resource requesting information respectively, the other wireless base stations  1   b ,  1   c  obtain unused wireless resources. Here, for example, an unused wireless resource in the other wireless base station  1   b  is a UL wireless resource that the other wireless base station  1   b  does not cause any subordinate wireless terminal  2   b  to use for UL sending (not to be scheduled for UL sending). In other words, even when the wireless terminal  2   a  subordinate to the connected wireless base station  1   a  carries out UL sending using an unused wireless resource to the other wireless base station  1   b , resource conflict turns out not to occur. Since the other wireless base station  1   b  controls and manages schedules of all subordinate wireless terminals  2   b , it is possible to obtain the unused wireless resources easily. In S 106 , the other wireless base stations  1   b ,  1   c  respectively send other station wireless resource information including unused wireless resources information that indicates the obtained unused wireless resources to the connected wireless base station  1   a  via the transmission network. 
         [0060]    The connected wireless base station  1   a  receives the other station wireless resource information including the unused wireless resources information respectively from the other wireless base stations  1   b ,  1   c . Then, in S 107 , the connected wireless base station  1   a  determines a UL wireless resource (referred to as a determined wireless resource) that is used for UL sending from the subordinate wireless terminal  2   a  and the other wireless base station (referred to as a determined wireless base station) to be a sending destination of the UL sending based on the received unused wireless resources information. Here, it is assumed that the magnitude of the determined wireless resources is not less than the UL wireless resource amount requested in the UL schedule requesting information from the wireless terminal  2   a . In S 107 , the connected wireless base station  1   a  is capable of determining the determined wireless resource and the determined wireless base station by an arbitrary criterion based on the unused wireless resources indicated by the unused wireless resources information. For example, it is possible that the connected wireless base station  1   a  selects arbitrary one from the unused wireless resources capable of securing the requested UL wireless resource amount to determine the determined wireless resource therefrom. Then, the connected wireless base station  1   a  is capable of setting the other wireless base station  1   b  that has sent the selected unused wireless resource (information) as the determined wireless base station. Here, it is assumed that the connected wireless base station  1   a  determines the determined wireless resource from the unused wireless resources that the other wireless base station  1   b  has sent and determines the other wireless base station  1   b  as the determined wireless base station. 
         [0061]    In S 108 , the connected wireless base station  1   a  sends information indicating the determined wireless resource determined in S 107  (referred to as determined wireless resource information) to the subordinate wireless terminal  2   a  on a DL wireless signal. Here, this DL wireless signal includes DCI (data control information), which is a DL control signal defined by LTE. DCI is a DL control signal including control information, such as information related to data scheduling, used by the wireless terminal  2   a  for sending and receiving of data. There are several formats in DCI, and a control object is different depending on the format. For example, format 0 in DCI is to control over the PUSCH, that is, UL data. Formats 1A, 1B, 1C, 1, 2 are respectively to control over the PDSCH, that is, DL data. 
         [0062]      FIG. 4  illustrates one example of a DCI format in the first embodiment. The DCI illustrated in  FIG. 4  is defined by LTE, and it is used as is in the first embodiment. The DCI in  FIG. 4  includes an RNTI (radio network temporary identifier), which is an identifier of a DCI destination (wireless terminal  2   a ), RB assignment (resource block assignment), which is information indicating the wireless resource having data allocated thereto (to which resource block (RB) on the wireless frame data is assigned), and MCS (modulation and coding scheme), which indicates modulation and coding scheme of data. Although DCI includes, as well as these, parameters, such as an RV (redundancy version), an NDI (new data indicator), a HARQ (hybrid automatic repeat request) processing number, and PUCCH power control, details are omitted. 
         [0063]    In the present embodiment, the determined wireless resource information corresponds to the RB assignment of DCI. That is, in S 108 , the connected wireless base station  1   a  in the present embodiment sends the determined wireless resource information to the subordinate wireless terminal  2   a  by sending the DCI on a DL wireless signal. In contrast, in S 108 , the wireless terminal  2   a  receives the DL wireless signal including the DCI that includes the determined wireless resource information (RB assignment). At this time, the wireless terminal  2   a  recognizes (detects) the DCI towards itself based on the RNTI included in the DCI. In addition, the wireless terminal  2   a  recognizes (detects) that the DCI targets the UL data based on the DCI format. 
         [0064]    In S 109  in  FIG. 3 , the connected wireless base station  1   a  sends the determined wireless resource information to the other wireless base station  1   b , which is the determined wireless base station determined in S 107  via the transmission network. The connected wireless base station  1   a  in the present embodiment sends the determined wireless resource information to the other wireless base station  1   b , which is the determined wireless base station, by sending the DCI in S 109 . Here, S 108  and S 109  may also be simultaneous or opposite in order. This completes scheduling of UL wireless sending from the subordinate wireless terminal  2   a  to the other wireless base station  1   b  by the connected wireless base station  1   a . When the connected wireless base station  1   a  determines the base station to receive UL data as the local station in S 103 , regular UL wireless resource scheduling may be carried out, so that the description is omitted. 
         [0065]    Subsequently, in S 110  in  FIG. 3 , the wireless terminal  2   a  sends a UL wireless signal including the UL data using the UL wireless resource indicated by the received determined wireless resource information (RB assignment of DCI). At this time, the wireless terminal  2   a  carries out coding and modulation of the UL data based on an MCS included in the DCI received in S 108 . In contrast, in S 110 , the other wireless base station  1   b  receives the UL wireless signal sent by the wireless terminal  2   a  using the UL wireless resource indicated by the received determined wireless resource information. At this time, the other wireless base station  1   b  carries out demodulation and decoding of the UL data based on the MCS included in the DCI received in S 109 . Lastly, in S 111 , the other wireless base station  1   b  sends (transfers) the UL data included in the received UL wireless signal to the connected wireless base station  1   a  via the transmission network. This completes reception of the UL data in S 112 . 
         [0066]    As described above, in the wireless communication system of the first embodiment, the connected wireless base station  1   a  receives the other station wireless resource information including the unused wireless resources information, which is information indicating UL wireless resources not used by the other wireless base station  1   b , from the other wireless base station  1   b . Then, the connected wireless base station  1   a  schedules the UL wireless resource used for UL sending from the subordinate wireless terminal  2   a  to the other wireless base station  1   b  based on the received unused wireless resources information. Thus, it is possible to avoid conflict in the UL wireless resource between the UL sending from the wireless terminal  2   a  subordinate to the connected wireless base station  1   a  to the other wireless base station  1   b  and the UL sending from another wireless terminal  2   a  subordinate to the other wireless base station  1   b  to the other wireless base station  1   b . Accordingly, according to the wireless communication system in the first embodiment, when the wireless terminal  2   a  carries out communication with different wireless base stations for UL and DL, it is possible that the other wireless base station different from the connected base station receives data from the wireless terminal. In addition, as a result, it is possible to achieve efficient utilization of wireless resources. 
         [0067]    Next, based on  FIG. 5  and  FIG. 6 , descriptions are given to functional configuration of each device in the first embodiment in order. 
         [0068]      FIG. 5  is a diagram illustrating one example of functional configuration of the wireless base station  1  in the first embodiment. The wireless base station  1  is provided with, for example, a UL wireless receiving unit  101 , a UL frame analysis unit  102 , a UL reference signal processing unit  103 , a UL control signal demodulation and decoding unit  104 , a UL data signal demodulation and decoding unit  105 , a scheduler unit  106 , a DL data signal generation unit  107 , a DL data signal coding and modulation unit  108 , a DL control signal generation unit  109 , a DL control signal coding and modulation unit  110 , a DL reference signal generation unit  111 , a DL frame generation unit  112 , a DL wireless sending unit  113 , a transmission network sending unit  114 , and a transmission network receiving unit  115 . 
         [0069]    Firstly, descriptions are given to each of these functions in the connected wireless base station  1   a  of the first embodiment. 
         [0070]    The UL wireless receiving unit  101  receives a UL wireless signal, downconverts the received wireless signal by frequency conversion and the like for conversion to a baseband signal corresponding to a UL frame, and outputs it to the UL frame analysis unit  102 . The UL frame analysis unit  102  extracts a UL data signal, a UL control signal, and a UL reference signal from the baseband signal corresponding to the UL frame. At this time, the UL frame analysis unit  102  carries out extraction of each signal based on UL scheduling information (information equivalent to RB assignment of DCI) inputted from the scheduler unit  106 . Then, the UL frame analysis unit  102  outputs the UL reference signal to the UL reference signal processing unit  103 , outputs the UL control signal to the UL control signal demodulation and decoding unit  104 , and outputs the UL data signal to the UL data signal demodulation and decoding unit  105 . 
         [0071]    The UL reference signal processing unit  103  obtains UL channel characteristics based on a demodulation reference signal (DM-RS) among the UL reference signal and inputs them to the UL control signal demodulation and decoding unit  104  and the UL data signal demodulation and decoding unit  105 . In addition, the UL reference signal processing unit  103  obtains UL receiving quality based on a sounding reference signal (SRS), which is a reference signal for scheduling, among the UL reference signal and inputs it to the scheduler unit  106 . 
         [0072]    The UL control signal demodulation and decoding unit  104  demodulates the UL control signal to carry out error correction and decoding. The UL control signal demodulation and decoding unit  104  carries out demodulation and decoding of the UL control signal using the UL channel characteristics inputted from a UL reference signal generation unit  212  and predetermined modulation scheme and error correction and coding scheme. The UL control signal demodulation and decoding unit  104  inputs the demodulated and decoded UL control signal to the scheduler unit  106 . As examples of the UL control signal, there are UL schedule requesting information, a UL response signal (ACK/NACK signal) to DL data, and the like. 
         [0073]    The UL data signal demodulation and decoding unit  105  demodulates the UL data signal to carry out error correction and decoding. The UL data signal demodulation and decoding unit  105  carries out demodulation and decoding of the UL data signal using the UL channel characteristics inputted from the UL reference signal generation unit  212  and the modulation scheme and the error correction and coding scheme inputted from the scheduler unit  106 . The UL data signal demodulation and decoding unit  105  inputs the demodulated and decoded UL data signal to the scheduler unit  106 . 
         [0074]    Descriptions are given to the scheduler unit  106  in the present embodiment. The scheduler unit  106  carries out scheduling of a wireless resource used for wireless communication and also carries out a variety of control associated with the scheduling of a wireless resource. The scheduler unit  106  schedules respective UL and DL wireless resources. As a first example, when UL schedule requesting information, which is one item of the UL control information sent by the wireless terminal  2   a , is inputted from the UL control signal demodulation and decoding unit  104 , the scheduler unit  106  schedules a UL wireless resource to the wireless terminal  2   a . As a second example, in such a case that a DL schedule requisition is inputted from an upper layer unit  206  (a case that data has to be sent to the wireless terminal  2   a  on a DL), the scheduler unit  106  schedules a DL wireless resource. 
         [0075]    Here, when scheduling a UL wireless resource to the wireless terminal  2   a , the scheduler unit  106  in the present embodiment selectively determines the wireless base station  1  to be a UL sending destination. In other words, the scheduler unit  106  in the present embodiment is capable of selecting the other wireless base stations  1   b ,  1   c  other than the local station (wireless base station  1   a ) as the UL sending destination. Of course, it goes without saying that the scheduler unit  106  may also select the local station (wireless base station  1   a ) as the UL sending destination. The scheduler unit  106  may employ a variety of methods in determination of the wireless base station  1  to be the UL sending destination of the wireless terminal  2   a  and determination of the UL wireless resource to be assigned to the wireless terminal  2   a . The scheduler unit  106  may also carry out these determinations collectively and may also carry out them in order. 
         [0076]    Descriptions are given to scheduling of a UL wireless resource when the scheduler unit  106  in the present embodiment selects the other wireless base station  1   b  as the UL sending destination from the wireless terminal  2   a . In this case, the scheduler unit  106  has to avoid the conflict in a UL wireless resource described above. With that, when selecting the other wireless base station  1   b  as the UL sending destination, the scheduler unit  106  obtains information related to the UL wireless resource used by the wireless terminal  2   a  subordinate to the other wireless base station  1   b  (hereinafter, may also be referred to as other station wireless resource information). This point is one of the processes that conventional techniques do not perform, so that detailed descriptions are given below. 
         [0077]    Descriptions are given to contents of the other station wireless resource information in the present embodiment. The contents of the other station wireless resource information may be, as an example, information indicating a UL wireless resource not used by the other wireless base station  1   b  (referred to as unused wireless resources information). The unused wireless resources information is, so to speak, information indicating a wireless resource where resource conflict does not occur even when being used by the wireless base station  1   a  (even when being scheduled as the UL wireless resource used in UL sending from the wireless terminal  2   a  subordinate to the wireless base station is to the other wireless base station  1   b ). It becomes possible to avoid UL resource conflict by that the scheduler unit  106  of the connected wireless base station  1   a  selectively determines the UL wireless resource to be assigned to the subordinate wireless terminal  2   a  from the unused wireless resources information received from the other wireless base station  1   b.    
         [0078]    The unused wireless resources information is merely one example of the other station wireless resource information. As another example of the other station wireless resource information, information indicating a UL wireless resource used by the other wireless base station  1   b  (referred to as used wireless resource information) is also available. The used wireless resource information is, so to speak, information indicating a wireless resource where resource conflict occurs when being used by the wireless base station  1   a  (when being scheduled as the UL wireless resource used in the UL sending from the wireless terminal  2   a  subordinate to the wireless base station to the other wireless base station  1   b ). It becomes possible to avoid UL resource conflict by that the scheduler unit  106  of the wireless base station  1   a  selectively determines the UL wireless resource to be assigned to the subordinate wireless terminal  2   a  from the UL wireless resource other than the used wireless resource information received from the other wireless base station  1   b.    
         [0079]    Descriptions are given to a procedure where the connected wireless base station  1   a  of the present embodiment obtains the other station wireless resource information from the other wireless base stations  1   b ,  1   c . In the procedure where the wireless base station obtains the other station wireless resource information, the scheduler unit  106  carries out, for example, sending of requesting information (referred to as wireless resource requesting information) that requests other station wireless resource information to the other wireless base stations  1   b ,  1   c . Specifically, it goes as follows, for example. Firstly, when the UL receiving quality inputted from the UL reference signal unit is lower than a predetermined value, the scheduler unit  106  determines to send wireless resource requesting information. Next, the scheduler unit  106  sends wireless resource requesting information to the other wireless base stations  1   b ,  1   c  (adjacent wireless base or peripheral wireless base station). The other wireless base stations  1   b ,  1   c  to be the sending destination may be one or may also be a plurality. In addition, it is possible to carry out the selection of the other wireless base stations  1   b ,  1   c  to be the sending destination based on, for example, DL receiving quality information for each wireless base station that is stored in a measurement report received from the wireless terminal  2   a . As receiving the wireless resource requesting information, the other wireless base stations  1   b ,  1   c  send other station information including the other station wireless resource information to the connected wireless base station  1   a  in response to the wireless resource requesting information. Thus, the scheduler unit  106  of the wireless base station  1   a  is capable of obtaining the other station wireless resource information from the other wireless base stations  1   b ,  1   c . There are other examples considered as the procedure where the connected wireless base station  1   a  obtains other station wireless resource information from the other wireless base stations  1   b ,  1   c , and they are described later (described in a fourth embodiment through a sixth embodiment). 
         [0080]    As receiving the other station wireless resource information from the other wireless base stations  1   b ,  1   c  as described above, the scheduler unit  106  carries out UL scheduling to the subordinate wireless terminal  2   a  based on the other station wireless resource information. Specifically, the scheduler unit  106  determines the determined wireless resource, which is the UL wireless resource used for the UL sending from the subordinate wireless terminal  2   a , and the determined wireless base station, which is the other wireless base station  1   b  to be the sending destination of the UL sending, based on the unused wireless resources information included in the received other station wireless resource information. Here, it is assumed that the magnitude of the determined wireless resources is not less than the UL wireless resource amount requested in the UL schedule requesting information from the wireless terminal  2   a . The scheduler unit  106  is capable of determining the determined wireless resource and the determined wireless base station by an arbitrary criterion based on the unused wireless resources indicated by the unused wireless resources information. For example, it is possible that the scheduler unit  106  selects arbitrary one from the unused wireless resources capable of securing the requested UL wireless resource amount to determine the determined wireless resource therefrom. Then, the scheduler unit  106  is capable of setting the other wireless base station  1   b  that has sent the selected unused wireless resource (information) as the determined wireless base station. 
         [0081]    As described above, the scheduler unit  106  carries out scheduling of the UL wireless resource to the wireless base station  1   b  from the wireless terminal  2   a  when the other wireless base station  1   b  is selected as the UL sending destination from the wireless terminal  2   a . After that, in order to generate a DCI, the scheduler unit  106  inputs the UL scheduling result to the DL control signal generation unit  109 . The UL scheduling result is information including a wireless resource for UL sending (the above determined wireless resource), an identifier of the wireless terminals  2   a , a coding and modulation scheme of a signal, and the like. In addition, when selecting the other wireless base station  1   b , the scheduler unit  106  also inputs the UL scheduling result to the transmission network sending unit  114 . Further in this case, the scheduler unit  106  inputs base station identification information indicating the UL receiving other wireless base station  1   b  (corresponding to the determined wireless base station) to the transmission network sending unit  114 . 
         [0082]    In contrast, when selecting the local station as the UL sending destination from the wireless terminal  2   a , the scheduler unit  106  carries out general UL scheduling (the description is omitted). Then, in order to generate a DCI, the scheduler unit  106  inputs the UL scheduling result to the DL control signal generation unit  109 . For the preparation of UL reception at the local station, the scheduler unit  106  inputs the UL scheduling result to the UL frame analysis unit  102 . 
         [0083]    Meanwhile, when DL data occurs, the scheduler unit  106  schedules DL sending. In this case, the scheduler unit  106  carries out general DL scheduling (the description is omitted). In order to generate a DCI, the scheduler unit  106  inputs the DL scheduling result to the DL control signal generation unit  109 . The DL scheduling result is information including a wireless resource for DL sending, an identifier of the wireless terminal  2   a , a coding and modulation scheme of a signal, and the like. In addition, the scheduler unit  106  inputs DL data to the DL data signal generation unit  107 . 
         [0084]    Back to the descriptions in  FIG. 5 , as the DL data is inputted from the scheduler unit  106 , the DL data signal generation unit  107  generates a DL data signal and inputs it to a DL data coding and modulation unit. The DL data coding and modulation unit codes and modulates the DL data signal based on the coding scheme and the modulation scheme inputted from the scheduler unit  106  and inputs it to the DL frame generation unit  112 . 
         [0085]    A DL control information generation unit generates DL control information based on the scheduling result inputted from the scheduler unit  106  and inputs it to the DL control signal coding and modulation unit  110 . As an example, the DL control signal generation unit  109  generates the DCI described before based on the inputted scheduling result. The DL control signal generation unit  109  sets an RB assignment value of the DCI based on the determined wireless resource included in the scheduling result inputted from the scheduler unit  106 . In addition, the DL control signal generation unit  109  sets the wireless terminal identifier inputted from the scheduler as an RNTI value and sets the modulation scheme and the coding scheme as an MCS value. The DL control signal generation unit  109  inputs the generated DL control signal to the DL control signal coding and modulation unit  110 . 
         [0086]    The DL control signal coding and modulation unit  110  codes and modulates the DL control signal based on the predetermined modulation scheme and coding scheme and inputs it to the DL frame generation unit  112 . The DL reference signal generation unit  111  generates the DL reference signal and inputs it to the DL frame generation unit  112 . 
         [0087]    The DL frame generation unit  112  places (also called as maps) the DL data signal, the DL control signal, and the DL reference signal after coding and modulation in a DL frame and generates a DL frame. The DL frame generation unit  112  carries out mapping of each DL signal using the DL scheduling result inputted from the scheduler unit  106 . That is, the DL frame generation unit  112  carries out mapping of each signal to the wireless resource (RB) defined in the DL scheduling result inputted from the scheduler unit  106 . The DL frame generation unit  112  inputs the baseband signal corresponding to the generated DL frame to the DL wireless sending unit  113 . 
         [0088]    The DL wireless sending unit  113  upconverts the baseband signal corresponding to the inputted DL frame to a wireless signal by frequency conversion and the like and wirelessly sends the wireless signal to the wireless terminal  2   a.    
         [0089]    The transmission network sending unit  114  sends a data signal and a control signal to the other wireless base stations  1   b ,  1   c , other control devices, relay devices, and the like via the backhaul network. As an example, when the scheduler unit  106  selects other than the local station as the UL sending destination, the transmission network sending unit  114  sends the wireless resource requesting information described above to the other wireless base stations  1   b ,  1   c . The sending of the wireless resource requesting information is carried out by accepting an input of base station identifiers indicating the other wireless base stations  1   b ,  1   c  from the scheduler unit  106 . As an example, when the scheduler unit  106  selects the other wireless base station  1   b  as the UL sending destination, the transmission network sending unit  114  sends the determined wireless resource information described above to the other wireless base station  1   b . The sending of the determined wireless resource information is carried out by accepting an input of the UL scheduling result and the base station identifier from the scheduler unit  106 . 
         [0090]    The transmission network receiving unit  115  receives a data signal and a control signal from the other wireless base stations  1   b ,  1   c , other control devices, relay devices, and the like via the backhaul network. For example, when the scheduler unit  106  selects other than the local station as the UL sending destination, the transmission network receiving unit  115  receives the other station wireless resource information described before from the other wireless base stations  1   b ,  1   c . The transmission network receiving unit  115  inputs the received other station wireless resource information to the scheduler unit  106 . 
         [0091]    Next, descriptions are given to the other wireless base station  1   b  in the first embodiment (the other wireless base station  1   c  is similar). 
         [0092]    Although the other wireless base station  1   b  also has a functional configuration same as  FIG. 5 , different process is carried out in a part of the functions. It goes without saying that the respective wireless base stations  1  may be provided with both a function provided in the connected wireless base station  1   a  and a function provided in the other wireless base station  1   b . In other words, the respective wireless base stations are capable of behaving as the connected wireless base station to a certain wireless terminal and behaving as another wireless base station to another wireless terminal. 
         [0093]    The transmission network receiving unit  115  of the other wireless base station  1   b  receives a data signal and a control signal from the connected wireless base station  1   a , other control devices, relay devices, and the like connected to the backhaul network. As an example, when the connected wireless base station  1   a  selects other than the local station (connected wireless base station  1   a ) as the UL sending destination from the subordinate wireless terminal  2   a , the transmission network receiving unit  115  receives the wireless resource requesting information described before from the connected wireless base station  1   a . The transmission network receiving unit  115  inputs the received wireless resource requesting information to the scheduler unit  106 . As another example, the transmission network receiving unit  115  receives the determined wireless resource information described before from the connected wireless base station  1   a . The transmission network receiving unit  115  inputs the received determined wireless resource assignment information to the scheduler unit  106 . 
         [0094]    The scheduler unit  106  of the other wireless base station  1   b  generates other station wireless resource information based on the inputted wireless resource requesting information. In the present embodiment, as described before, the other station wireless resource information includes the unused wireless resources information, which is information indicating UL resources not used by the other wireless base station  1   b . The scheduler unit  106  generates the unused wireless resources information as follows. 
         [0095]    The scheduler unit  106  of the other wireless base station  1   b  subjectively and also fully determines scheduling of each wireless terminal  2   b  subordinate to the other wireless base station  1   b . Therefore, the scheduler unit  106  recognizes fixed scheduling (wireless resource to be used) in the present and future of each subordinate wireless terminal  2   b . In addition, the scheduler unit  106  is also capable of controlling not to use a certain wireless resource in the future (not to use a certain frequency range in a certain period). Accordingly, the scheduler unit  106  of the other wireless base station  1   b  is capable of recognizing a wireless resource not used by the local station (other wireless base station  1   b ), in other words, a wireless resource not to be scheduled for the subordinate wireless terminal  2   b  by the local station. With that, the scheduler unit  106  of the other wireless base station  1   b  selects a part or all of the wireless resources not used by the local station to set information indicating the selected wireless resource as the unused wireless resources information. Then, the scheduler unit  106  generates other station wireless resource information including the unused wireless resources information. The scheduler unit  106  inputs the generated other station wireless resource information to the transmission network sending unit  114 . 
         [0096]    In addition, the scheduler unit  106  of the other wireless base station  1   b  carries out scheduling to accept the UL sending from the wireless terminal  2   a  subordinate to the connected wireless base station  1   a  based on the determined wireless resource information received from the connected wireless base station  1   a . The determined wireless resource information is determined by the connected wireless base station  1   a  based on the unused wireless resources information sent earlier, and is information indicating a part or all of the UL wireless resource indicated by the unused wireless resources information. The scheduler unit  106  inputs the UL scheduling result that reflects the received UL resource assignment information to the UL frame analysis unit  102 . The UL frame analysis unit  102  extracts respective information from the UL frame based on the UL scheduling result. Thus, it becomes possible that the other wireless base station  1   b  receives data on a UL from the wireless terminal  2   a  subordinate to the connected wireless base station  1   a.    
         [0097]    When the connected wireless base station  1   a  selects the other wireless base station  1   b  as the UL sending destination, the transmission network sending unit  114  of the other wireless base station  1   b  in the present embodiment sends the other station wireless resource information including the unused wireless resources information to the connected wireless base station  1   a . The sending is carried out by accepting an input of the other station wireless resource information from the scheduler unit  106 . 
         [0098]    Next, descriptions are given to the wireless terminal  2   a  in the first embodiment. 
         [0099]      FIG. 6  is a diagram illustrating one example of a functional configuration of the wireless terminals  2   a  in the first embodiment. The wireless terminal  2   a  is provided with, for example, a DL wireless receiving unit  201 , a DL frame analysis unit  202 , a DL reference signal processing unit  203 , a DL control signal demodulation and decoding unit  204 , a DL data signal demodulation and decoding unit  205 , an upper layer unit  206 , a UL schedule management unit  207 , a UL data signal generation unit  208 , a UL data signal coding and modulation unit  209 , a UL control signal generation unit  210 , a UL control signal coding and modulation unit  211 , a UL reference signal generation unit  212 , a UL frame generation unit  213 , and a UL wireless sending unit  214 . 
         [0100]    The DL wireless receiving unit  201  receives a DL wireless signal, downconverts the received wireless signal by frequency conversion and the like to convert it to a baseband signal corresponding to the DL frame, and outputs it to the DL frame analysis unit  202 . The DL frame analysis unit  202  extracts a DL data signal, a DL control signal, and a DL reference signal from the baseband signal corresponding to the DL frame. Then, the DL frame analysis unit  202  outputs the DL reference signal to the DL reference signal processing unit  203 , outputs the DL control signal to the DL control signal demodulation and decoding unit  204 , and outputs the DL data signal to the DL data signal demodulation and decoding unit  205 . 
         [0101]    The DL reference signal processing unit  203  of the wireless terminal  2   a  estimates DL channel characteristics based on the DL reference signal and outputs the DL channel characteristics respectively to the DL control signal demodulation and decoding unit  204  and the DL data signal demodulation and decoding unit  205 . 
         [0102]    The DL control signal demodulation and decoding unit  204  demodulates the DL control signal and extracts DL control information by carrying out error correction and decoding. The DL control signal demodulation and decoding unit  204  carries out demodulation and decoding of the DL control signal using the DL channel characteristics and predetermined demodulation scheme and error correction and decoding scheme. As obtaining the DCI, which is the DL control information, by demodulation and decoding, the DL control signal demodulation and decoding unit  204  recognizes (detects) a DCI towards itself based on the RNTI included therein. The DL control signal demodulation and decoding unit  204  recognizes (detects) whether the scope of DCI application is UL data (PUSCH) or DL data (PDSCH) based on the DCI format. Regarding the DCI towards itself that targets the DL data, the DL control signal demodulation and decoding unit  204  inputs the RB assignment and the MCS included in the DCI to the DL data signal demodulation and decoding unit  205 . Regarding the DCI towards itself that targets the UL data, the DL control signal demodulation and decoding unit  204  inputs the RB assignment and the MCS included in the DCI to the UL schedule management unit  207 . 
         [0103]    The DL data signal demodulation and decoding unit  205  demodulates the DL data signal and extracts DL data information by carrying out error correction and decoding. In the DL data signal, one or more items of data information to the wireless terminal  2   a  are multiplexed. The DL data signal demodulation and decoding unit  205  carries out extraction of a DL data signal towards itself using the RB assignment inputted from the DL control signal demodulation and decoding unit  204 . After that, the DL data signal demodulation and decoding unit  205  carries out demodulation and decoding of the DL data signal based on the DL channel characteristics and the MCS inputted from the DL control signal demodulation and decoding unit  204 . The DL data signal demodulation and decoding unit  205  inputs the obtained DL data to the upper layer unit  206 . 
         [0104]    The upper layer unit  206  processes the inputted DL data to provide various functions in the wireless terminal  2   a . Although there are, for example, a voice call, a web browser, a mailer, and the like as the functions provided by the upper layer unit  206 , there may also be other arbitrary functions. The upper layer unit  206  generates UL data (information) based on the functions to be provided and inputs them to the UL schedule management unit  207 . 
         [0105]    The UL schedule management unit  207  carries out management of the UL schedule when UL data occurs. This is carried out as follows. As UL data is inputted from the upper layer unit  206 , the UL schedule management unit  207  inputs an instruction signal that is to send UL wireless resource requesting information, which is one of the UL control signal, to the connected wireless base station  1   a  to the UL control signal generation unit  210  for the purpose of securing the UL wireless resource in a resource amount to be used for the UL data. With respect to the UL wireless resource requesting information, the connected wireless base station  1   a  notifies the wireless terminal  2   a  of the UL wireless resource by the DCI, which is a DL control signal. After that, as described before, regarding the DCI towards itself that targets the UL data, the DL control signal demodulation and decoding unit  204  inputs the RB assignment and the MCS included in the DCI to the UL schedule management unit  207 . As they are inputted, the UL schedule management unit  207  inputs the UL data inputted earlier to the UL data signal generation unit  208  for the purpose of carrying out UL data sending. Further, the UL schedule management unit  207  inputs the inputted MCS to the data signal coding and modulation unit and also inputs the RB assignment to the UL frame generation unit  213 . 
         [0106]    The UL data signal generation unit  208  generates a UL data signal based on the inputted UL data information and inputs it to the UL data signal coding and modulation unit  209 . The UL data signal coding and modulation unit  209  makes error correction and coding and modulation of the inputted UL data signal based on the MCS inputted from the UL schedule management unit  207  and inputs it to the UL frame generation unit  213 . 
         [0107]    The UL control information generation unit generates UL control information based on the instruction signal inputted from the UL schedule management unit  207  and the like and inputs it to the UL control signal coding and modulation unit  211 . As examples of the UL control signal, there are UL schedule requesting information to request a UL wireless resource to the connected wireless base station  1   a  when UL data occurs, a response signal (ACK/NACK signal) to DL data, and the like. The UL control signal coding and modulation unit  211  makes error correction and coding and modulation of the UL control signal inputted from the UL control signal generation unit  210  based on a predetermined modulation scheme and a coding scheme and inputs it to the UL frame generation unit  213 . 
         [0108]    The UL reference information generation unit generates UL reference information based on the instruction from the UL schedule management unit  207  and inputs it to the UL frame generation unit  213 . UL reference signals include, as described before, a DM-RS (demodulation reference signal) and a SRS (surrounding reference signal). 
         [0109]    The UL frame generation unit  213  places (maps) the UL data signal, the UL control signal, and the UL reference signal in a UL frame and generates a UL frame. The UL frame generation unit  213  carries out mapping of each signal using the RB assignment inputted from the UL schedule management unit  207 . The UL frame generation unit  213  inputs a baseband signal corresponding to the generated UL frame to a wireless sending unit. The wireless sending unit upconverts the baseband signal corresponding to the inputted UL frame by frequency conversion and the like to a wireless signal for wireless sending of the wireless signal to the wireless base station  1 . 
         [0110]    Next, based on  FIGS. 7 and 8 , descriptions are given to a hardware configuration of each device in the wireless communication system of the first embodiment. 
         [0111]      FIG. 7  illustrates one example of a hardware configuration of the wireless base station  1  in the present embodiment. Each function of the wireless base stations  1  described before are achieved by a part or all of the hardware components below. The wireless base station  1  in an embodiment is provided with a wireless IF (interface)  11 , an analog circuit  12 , a digital circuit  13 , a processor  14 , a memory  15 , a transmission network IF  16 , and the like. 
         [0112]    The wireless IF  11  is an interface device to carry out wireless communication with the wireless terminals  2  and is, for example, an antenna. The analog circuit  12  is a circuit to process an analog signal and may be roughly categorized into those carrying out receiving process, those carrying out sending process, and those carrying out other process. The analog circuit that carries out receiving process includes, for example, a low noise amplifier (LNA), a band pass filter (BPF), a mixer, a low pass filter (LPF), an automatic gain control amplifier (AGC: automatic gain controller), an analog-to-digital converter (ADC), a phase locked loop (PLL), and the like. The analog circuit that carries out sending process includes, for example, a power amplifier (PA), a BPF, a mixer, an LPF, a digital-to-analog converter (DAC), a PLL, and the like. The analog circuit that carries out other process includes a duplexer and the like. The digital circuit  13  is a circuit to process a digital signal and includes, for example, an LSI (large scale integration), an FPGA (field-programming gate array), an ASIC (application specific integrated circuit), and the like. The processor  14  is a device to process data and includes, for example, a CPU (central processing unit), a DSP (digital signal processor), and the like. The memory  15  is a device to memorize data and includes, for example, a ROM (read only memory), a RAM (random access memory), and the like. The transmission network IF  16  is an interface device to be connected to the backhaul network of the wireless communication system by a wired link or a wireless link and to carry out wired communication or wireless communication with a device on a transmission network side including another wireless base station  1  connected to the backhaul network or the core network. 
         [0113]    Descriptions are given to correspondence relationship of the functional configuration and the hardware configuration of the wireless base station  1 . 
         [0114]    The UL wireless receiving unit  101  is achieved by, for example, the wireless IF  11  and the analog circuit  12  (those carrying out receiving process). That is, the wireless IF  11  receives a UL wireless signal from the wireless terminal  2   a , and the analog circuit  12  downconverts the received wireless signal by frequency conversion and the like to convert it to a baseband signal corresponding to a UL frame. The UL frame analysis unit  102  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and extracts a UL data signal, a UL control signal, and a UL reference signal from the baseband signal corresponding to the UL frame. In addition, the digital circuit  13  may also extract a UL data signal, a UL control signal, and a UL reference signal from the baseband signal corresponding to the UL frame. 
         [0115]    The UL reference signal processing unit  103  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, obtains the UL channel characteristics based on the DM-RS, and obtains the UL receiving quality based on the SRS. In addition, the digital circuit  13  may also obtain the UL channel characteristics based on the DM-RS and obtain the UL receiving quality based on the SRS. 
         [0116]    The UL control signal demodulation and decoding unit  104  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, demodulates a UL control signal, and carries out error correction and decoding. In addition, the digital circuit  13  may also demodulate a UL control signal and carry out error correction and decoding. The UL data signal demodulation and decoding unit  105  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, demodulates a UL data signal, and carries out error correction and decoding. In addition, the digital circuit  13  may also demodulate a UL data signal and carry out error correction and decoding. 
         [0117]    The scheduler unit  106  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and carries out scheduling of the wireless resource used for wireless communication, and also carries out a variety of control associated with the scheduling of the wireless resource. In addition, the digital circuit  13  may also carry out scheduling of the wireless resource used for wireless communication and also carry out a variety of control associated with the scheduling of the wireless resource. 
         [0118]    The DL data signal generation unit  107  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and generates a DL data signal. In addition, the digital circuit  13  may also generate a DL data signal. The DL data coding and modulation unit is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and codes and modulates a DL data signal. In addition, the digital circuit  13  may also code and modulate a DL data signal. The DL control information generation unit is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and generates DL control information. In addition, the digital circuit  13  may also generate DL control information. The DL data coding and modulation unit is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and codes and modulates a DL control signal. In addition, the digital circuit  13  may also code and modulate a DL control signal. The DL reference signal generation unit  111  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and generates a DL reference signal. In addition, the digital circuit  13  may also generate a DL reference signal. The DL frame generation unit  112  is achieved by, for example, the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, places the DL data signal, the DL control signal, and the DL reference signal after coding and modulation in a DL frame, and generates a DL frame. In addition, the digital circuit  13  may also place the DL data signal, the DL control signal, and the DL reference signal after coding and modulation in a DL frame and generate a DL frame. 
         [0119]    The DL wireless sending unit  113  is achieved by, for example, the wireless IF  11  and the analog circuit  12  (those carrying out sending process). That is, the analog circuit  12  upconverts a baseband signal corresponding to the inputted DL frame by frequency conversion and the like to a wireless signal, and the wireless IF  11  wirelessly sends the wireless signal to the wireless terminals  2 . While the DL wireless sending unit  113  and the UL wireless receiving unit  101  may be achieved by different wireless IFs  11  (antennas), they may also share one wireless IF  11  by using a duplexer, which is the analog circuit  12 . 
         [0120]    The transmission network sending unit  114  is achieved by, for example, the transmission network IF  16 , the analog circuit  12 , the processor  14 , the memory  15 , and the digital circuit  13 . That is, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and converts a data signal and a control signal to be sent to a digital baseband signal. In addition, the analog circuit  12  converts the digital baseband signal to a wired signal or a wireless signal, and the transmission network IF  16  sends the wired signal or the wireless signal. The transmission network receiving unit  115  is achieved by, for example, the transmission network IF  16 , the analog circuit  12 , the processor  14 , the memory  15 , and the digital circuit  13 . That is, the transmission network IF  16  receives the wired signal or the wireless signal, and the analog circuit  12  converts the wired signal or the wireless signal to a digital baseband signal. In addition, the processor  14  controls the memory  15  as occasion calls, cooperates with the digital circuit  13  as occasion calls, and converts a digital baseband signal to a data signal and a control signal. 
         [0121]      FIG. 8  illustrates one example of a hardware configuration of the wireless terminal  2  in the first embodiment. Each function of the wireless terminals  2  described before is achieved by a part or all of the hardware components below. The wireless terminal  2  in the above embodiment is provided with a wireless IF  21 , an analog circuit  22 , a digital circuit  23 , a processor  24 , a memory  25 , an input IF  26 , an output IF  27 , and the like. 
         [0122]    The wireless IF  21  is an interface device to carry out wireless communication with the wireless base stations  1  and is, for example, an antenna. The analog circuit  22  is a circuit to process an analog signal and may be roughly categorized into those carrying out receiving process, those carrying out sending process, and those carrying out other process. The analog circuit that carries out receiving process includes, for example, an LNA, a BPF, a mixer, an LPF, an AGC, an ADC, a PLL, and the like. The analog circuit that carries out sending process includes, for example, a PA, a BPF, a mixer, an LPF, a DAC, a PLL, and the like. The analog circuit that carries out other process includes a duplexer and the like. The digital circuit  23  includes, for example, an LSI, an FPGA, an ASIC, and the like. The processor  24  is a device to process data and includes, for example, a CPU, a DSP, and the like. The memory  25  is a device to memorize data and includes, for example, a ROM, a RAM, and the like. The input IF  26  is a device to carry out an input and includes, for example, an operation button, a microphone, and the like. The output IF  27  is a device to carry out an output and includes, for example, a display, a speaker, and the like. 
         [0123]    Descriptions are given to correspondence relationship of the functional configuration and the hardware configuration of the wireless terminal  2 . 
         [0124]    The DL wireless receiving unit  201  is achieved by, for example, the wireless IF  21  and the analog circuit  22  (those carrying out receiving process). That is, the wireless IF  21  receives a DL wireless signal from the wireless base station  1 , and the analog circuit  22  downconverts the received wireless signal by frequency conversion and the like to convert it to a baseband signal corresponding to a DL frame. The DL frame analysis unit  202  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and extracts a DL data signal, a DL control signal, and a DL reference signal from the baseband signal corresponding to the DL frame. In addition, the digital circuit  23  may also extract a DL data signal, a DL control signal, and a DL reference signal from the baseband signal corresponding to the DL frame. 
         [0125]    The DL reference signal processing unit  203  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and obtains the DL channel characteristics based on the DL reference signal. In addition, the digital circuit  23  may also obtain the DL channel characteristics based on the DL reference signal. 
         [0126]    The DL control signal demodulation and decoding unit  204  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, demodulates a DL control signal, and carries out error correction and decoding. In addition, the digital circuit  23  may also demodulate a DL control signal and carry out error correction and decoding. The DL data signal demodulation and decoding unit  205  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, demodulates a DL data signal, and carries out error correction and decoding. In addition, the digital circuit  23  may also demodulate a DL data signal and carry out error correction and decoding. 
         [0127]    The upper layer unit  206  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, processes the inputted DL data, provides various functions in the wireless terminal  2   a , and also generates UL data (information) based on the provided functions. In addition, the digital circuit  23  may also process the inputted DL data, provide various functions in the wireless terminal  2   a , and also generate UL data (information) based on the provided functions. The UL schedule management unit  207  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and carries out management of a UL schedule when UL data occurs. In addition, the digital circuit  23  may also carry out management of a UL schedule when UL data occurs. 
         [0128]    The UL data signal generation unit  208  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and generates a UL data signal. In addition, the digital circuit  23  may also generate a UL data signal. The UL data coding and modulation unit is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and codes and modulates a UL data signal. In addition, the digital circuit  23  may also code and modulate a UL data signal. The UL control information generation unit is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and generates UL control information. In addition, the digital circuit  23  may also generate UL control information. The UL data coding and modulation unit is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and codes and modulates a UL control signal. In addition, the digital circuit  23  may also code and modulate a UL control signal. The UL reference signal generation unit  212  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, and generates a UL reference signal. In addition, the digital circuit  23  may also generate a UL reference signal. The UL frame generation unit  213  is achieved by, for example, the processor  24 , the memory  25 , and the digital circuit  23 . That is, the processor  24  controls the memory  25  as occasion calls, cooperates with the digital circuit  23  as occasion calls, places the UL data signal, the UL control signal, and the UL reference signal after coding and modulation in a UL frame, and generates a UL frame. In addition, the digital circuit  23  may also place the UL data signal, the UL control signal, and the UL reference signal after coding and modulation in a UL frame and generate a UL frame. 
         [0129]    The UL wireless sending unit  214  is achieved by, for example, the wireless IF  21  and the analog circuit  22  (those carrying out sending process). That is, the analog circuit  22  upconverts a baseband signal corresponding to the inputted UL frame by frequency conversion and the like to a wireless signal, and the wireless IF  21  wirelessly sends the wireless signal to the wireless terminals  2 . While the UL wireless sending unit  214  and the DL wireless receiving unit  201  may be achieved by different wireless IFs  21  (antennas), they may also share one wireless IF  21  by using a duplexer, which is the analog circuit  22 . 
         [0130]    As have been described based on  FIGS. 2 through 8 , in the wireless communication system in the first embodiment, the connected wireless base station  1   a  receives other station wireless resource information including unused wireless resources information, which is information indicating a UL wireless resource not used by the other wireless base station  1   b  from the other wireless base station  1   b . Then, the connected wireless base station  1   a  schedules a UL wireless resource used for UL sending from the subordinate wireless terminal  2   a  to the other wireless base station  1   b  based on the received unused wireless resources information. Thus, it is possible to avoid conflict in a UL wireless resource between UL sending from the wireless terminal  2   a  subordinate to the connected wireless base station  1   a  to the other wireless base station  1   b  and UL sending from another wireless terminal  2   a  subordinate to the other wireless base station  1   b  to the other wireless base station  1   b . Accordingly, according to the wireless communication system in the first embodiment, when the wireless terminal  2   a  carries out communication with different wireless base stations for UL and DL, it is possible that the other wireless base station  1   b  different from the connected base station  1   a  receives data from the wireless terminal  2   a . In addition, as a result, it is possible to achieve efficient utilization of a wireless resource. 
       [c] Second Embodiment 
       [0131]    In the second embodiment, descriptions are given to an example other than the first embodiment when the wireless terminal  2   a  carries out communication with wireless base stations  1  different for DL and UL. In the second embodiment, descriptions are given to a case where sending data (DL data) to the subordinate wireless terminal  2   a  occurs in the wireless base station  1   a.    
         [0132]    In the second embodiment, there are many points in common with the first embodiment. In the following descriptions, descriptions are given mainly to the points different from the first embodiment in the second embodiment. 
         [0133]    Based on  FIG. 9 , descriptions are given to a process sequence in the second embodiment.  FIG. 9  corresponds to process, as described before, where sending data (DL data) to the subordinate wireless terminal  2   a  occurs in the wireless base station  1   a.    
         [0134]    In S 201  in  FIG. 9 , firstly, DL data occurs in the connected wireless base station  1   a . For example, DL data occurs when an audio signal, data, and the like are sent from the other wireless terminal  2   b  to the subordinate wireless terminal  2   a , a server on the Internet sends data to the wireless terminal  2   a , and the like. 
         [0135]    In S 202 , as DL data occurs, the connected wireless base station  1   a  schedules a DL wireless resource to send the DL data to the wireless terminal  2   a . Here, the scheduling of a DL wireless resource may use a general technique, so that the descriptions are omitted here. 
         [0136]    Next, the connected wireless base station  1   a  schedules a UL wireless resource to receive a response signal (ACK/NACK signal) from the wireless terminal  2   a  that have received the DL data. This is carried out as below. The connected wireless base station  1   a  obtains the UL receiving quality from the wireless terminal  2   a  and determines whether or not to set a reception destination of the response signal as the local station based on the UL receiving quality in S 203 . In S 204 , as determining the base station to receive the UL data as any of the wireless base stations  1  other than the local station, the connected wireless base station  1   a  sends wireless resource requesting information to the other wireless base stations  1   b ,  1   c  via the transmission network. In contrast, the other wireless base stations  1   b ,  1   c  respectively obtain unused wireless resources in S 205 , and send other station wireless resource information including the unused wireless resources information to the connected wireless base station  1   a  via the transmission network in S 206 . Then, it is assumed that, in S 207 , the connected wireless base station  1   a  determines a UL wireless resource for the response signal and the other wireless base station  1   b  to be the UL sending destination. S 203  through S 207  are similar to S 103  through S 107 , so that the details are omitted. 
         [0137]    In S 208  in  FIG. 9 , next, the connected wireless base station  1   a  sends determined wireless resource information, which is information indicating the selected UL wireless resource, to the subordinate wireless terminal  2   a  on a DL wireless signal. At this time, the connected wireless base station  1   a  in the second embodiment sends, in addition to the determined wireless resource information, DL data on a DL wireless signal as well. 
         [0138]    Here, once leaving from  FIG. 9 , which is a process sequence of the second embodiment, descriptions are given to process when the connected wireless base station  1   a  sends DL data in a conventional LTE system. As scheduling a DL wireless resource to be assigned to DL data, the connected wireless base station  1   a  places (maps) the DL data in the DL wireless resource (resource block) on the DL frame. Together with this, the connected wireless base station  1   a  places a DCI (refer to  FIG. 4 ), which is DL control information, in a predetermined region of the DL frame same as the DL data. As illustrated in  FIG. 4 , the DCI includes RB assignment, which is information indicating the DL wireless resource assigned to the DL data. Then, the connected wireless base station  1   a  sends a DL wireless signal including the DL frame to the wireless terminal  2   a.    
         [0139]    The descriptions for the conventional LTE system are continued. The wireless terminal  2   a  receives a DL wireless signal including the DL frame. The wireless terminal  2   a  recognizes (detects) the presence of DL data towards itself based on the RNTI included in the DCI in the DL frame, and recognizes (detects) that the scope of DCI application is the DL data (PDSCH) based on the DCI format. Further, the wireless terminal  2   a  extracts the DL data based on the RB assignment included in the DCI and carries out demodulation and decoding of the DL data based on the MCS included in the DCI. The wireless terminal  2   a  sends a response signal (an ACK signal indicating decoding success or a NACK signal indicating decoding failure) to the connected wireless base station  1   a  on a UL frame in accordance with the decoding result. 
         [0140]    At this time, the wireless terminal  2   a  places the response signal in the UL frame corresponding to the placement of the DCI itself in the DL frame received earlier (note that it is not the placement indicated by the RB assignment in the DCI). Thus, the connected wireless base station  1   a  is capable of easily linking the sent DL data with the received response signal. 
         [0141]    Specifically, the following specifications are defined in the LTE. Resource specification in the PUCCH (logical channel for a UL control signal) is carried out by a CCE (control channel element) number of the PDCCH (logical channel for a DL control signal) represented by a formula (1). In other words, specification of the UL wireless resource for ACK/NACK is carried out by placement of the DCI resource represented by a formula (1). 
         [0000]      [Math 1] 
         [0000]        n   PUCCH   (1,{tilde over (p)}     0     )   =n   CCE   +N   PUCCH   (1)   (1)
 
         [0142]    Here, P 0  is an antenna port, n CCE  is a minimum CCE number used for sending of the corresponding DCI (for example, minimum CCE number upon configuring the PDCCH), and N PUCCH   (1)  is a parameter notified by an upper layer. Although a CCE is a wireless resource unit that a RB is divided further, details are omitted. 
         [0143]    Accordingly, in the conventional LTE system, the DL control information (DCI) related to the DL data and the UL control information (ACK/NACK) are only capable of using a mutually corresponding wireless resource. Accordingly, regarding control information related to the DL data, when the other wireless base station  1   b  uses a certain UL wireless resource R 1 , for example, the connected wireless base station  1   a  is not only incapable of using the UL wireless resource R 1  (to avoid resource conflict) but also incapable of using a DL wireless resource R 1 . Even in a situation where the DL resources do not interfere with each other, the connected wireless base station  1   a  in this example has no option but to use a UL wireless resource R 2  (≠R 1 ) and a DL wireless resource R 2 . Accordingly, in the conventional LTE system, scheduling for control information related to the DL data may be considered to be poor in flexibility. 
         [0144]    With that, in the present embodiment, it is made possible to separate the correspondence relationship of the DL control information (DCI) related to DL data and the UL control information (ACK/NACK) and to allow assignment of a wireless resource that does not correspond mutually. Therefore, in the DCI, which is the DL control information, a region to store an offset in the placement (mapping) from the corresponding UL control information (referred to as a resource offset) is provided. Then, the wireless terminal  2   a  having received the DL data as well as the DCI places a response signal to the DL data in a wireless resource that is shifted by the resource offset stored in the DCI from the corresponding wireless resource of the DCI. 
         [0145]      FIG. 10  illustrates one example of a DCI format according to the second embodiment. The DCI format in  FIG. 10  includes the resource offset. The resource specification using the resource offset may be represented as a formula (2). 
         [0000]      [Math 2] 
         [0000]        n   PUCCH   (1,{tilde over (p)}     0     )   =n   CCE   +N   PUCCH   (1)   +n   PUCCH   _   offset   (1)
 
         [0146]    Here, n PUCCH   _   offset  is a resource offset of the PUCCH, and the unit is a CCE. 
         [0147]    In such a manner, in the wireless communication system in the second embodiment, it is possible to assign a non-corresponding wireless resource to the DL control information (DCI) related to the DL data and the UL control information (ACK/NACK). For example, when the other wireless base station  1   b  uses a certain UL wireless resource R 1  and a DL wireless resource R 1 , the connected wireless base station  1   a  is capable of using a UL wireless resource R 2  (=R 1 +resource offset) and the DL wireless resource R 1 . Accordingly, in the wireless communication system in the present embodiment, it becomes possible to carry out flexible scheduling for the control information related to the DL data. 
         [0148]    Back to the descriptions of  FIG. 9 , in S 208 , the connected wireless base station  1   a  sends the DCI, which is DL control information, and the DL frame including the DL data to the wireless terminal  2   a . The DCI includes, in addition to the resource offset described before, the RNTI, the RB assignment related to the DL data, the MCS, and the like. Here, this resource offset corresponds to the determined wireless resource information (UL wireless resource for UL sending from the wireless terminal  2   a  to other wireless base station  1   b ). 
         [0149]    In contrast, in S 208 , the wireless terminal  2   a  receives the DL frame sent by the connected wireless base station  1   a . The wireless terminal  2   a  recognizes (detects) the presence of the DL data towards itself based on the RNTI included in the DCI in the DL frame, and recognizes (detects) that the scope of DCI application is the DL data (PDSCH) based on the DCI format. Further, the wireless terminal  2   a  extracts DL data based on RB assignment included in the DCI, and carries out demodulation and decoding of the DL data based on the MCS included in the DCI. Thus, in S 209 , the reception of DL data is completed. The resource offset included in the DCI is to be used when sending a UL control signal (ACK/NACK) and is not used here. 
         [0150]    In S 210  in  FIG. 9 , the connected wireless base station  1   a  sends determined wireless resource information to the other wireless base station  1   b , which is a sending source of the unused wireless resource to be the origin of the determined wireless resource via the transmission network. Here, the determined wireless resource information sent by the connected wireless base station  1   a  corresponds to information indicating placement of adding the resource offset included in the DCI to the placement of the DCI included in the DL frame sent by the connected wireless base station  1   a . S 208  and S 210  may be simultaneous or in the reverse order. 
         [0151]    This completes the scheduling of the UL wireless resource to the wireless terminal  2   a  by the connected wireless base station  1   a . In S 203 , when the connected wireless base station  1   a  determines the local station as the base station to receive UL data, regular UL wireless resource scheduling may be carried out (details are omitted). 
         [0152]    In S 211  in  FIG. 9 , in response to the decoding result of S 208 , the wireless terminal  2   a  sends a UL wireless signal including the UL frame where a response signal (ACK signal indicating decoding success or NACK signal indicating decoding failure), which is a UL control signal, is placed. At this time, the wireless terminal  2   a  of the present embodiment places a response signal in a UL frame using the resource offset included in the DCI as described before. Specifically, the wireless terminal  2   a  has placement of the response signal in the UL frame as placement where the resource offset included in the DCI is added to the placement of the DCI itself in the DL frame received earlier. 
         [0153]    In contrast, in S 211 , the other wireless base station  1   b  receives a response signal, which is a UL control signal placed in the UL frame included in the UL wireless signal sent by the wireless terminal  2   a . At this time, in S 210 , the other wireless base station  1   b  receives a response signal using the UL wireless resource indicated by the determined wireless resource information received from the connected wireless base station  1   a . As described before, the determined wireless resource information received from the connected wireless base station  1   a  is the information indicating placement where the resource offset included in the DCI is added to the placement of the DCI included in the DL frame sent by the connected wireless base station  1   a.    
         [0154]    Lastly, in S 212 , the other wireless base station  1   b  sends (transfers) the response signal included in the received UL wireless signal to the connected wireless base station  1   a  via the transmission network. This completes the reception of a response signal (ACK/NACK) in the connected wireless base station  1   a  in S 213 . 
         [0155]    As described above based on  FIGS. 9 and 10 , in the wireless communication system of the second embodiment, correspondence relationship related to the placement of the DL control information (DCI) related to the DL data and the UL control information (ACK/NACK) is separated and sends the information related to the placement of the corresponding UL control information in the DL control information. Thus, the wireless communication system in the second embodiment exhibits, in addition to the effect obtained in the wireless communication system in the first embodiment, an effect of allowing flexible scheduling to the control information related to the DL data. 
         [0156]    The functional configuration and the hardware configuration of the respective device in the second embodiment follow those in the first embodiment, so that the description is omitted. 
       [d] Third Embodiment 
       [0157]    The third embodiment is a modification that is applicable to the first embodiment or the second embodiment, and the connected wireless base station  1   a  selects the other wireless base station  1   b , which is a UL sending destination, based on the UL receiving quality notified in advance from the other wireless base stations  1   b.    
         [0158]    In the following descriptions, descriptions are given to a modification where the third embodiment is applied to the first embodiment. Since this modification has many points in common with the first embodiment, descriptions are given mainly to the points different from the first embodiment in the following descriptions. As described before, although the third embodiment may be modified by applying to the second embodiment, it may be applied similarly to that to the first embodiment and the details are omitted. 
         [0159]    Based on  FIG. 11 , descriptions are given to a process sequence of a modification where the third embodiment is applied to the first embodiment. Since S 301  through S 303  in  FIG. 11  are similar to S 101  through S 103  in  FIG. 3 , the description is omitted. In S 304 , the connected wireless base station  1   a  sends, in addition to wireless resource requesting information (similar to S 104  in  FIG. 3 ), SRS resource information to the other wireless base stations  1   b ,  1   c . Here, the SRS resource information indicates resource information to be used for reception of an SRS, which is a UL reference signal for UL receiving quality measurement generated by the wireless terminal  2   a . The SRS resource information includes, for example, an RB to which an SRS is assigned, data series information of an SRS, and the like. Since the generated SRS is different for each wireless terminal  2 , only the connected wireless base station  1   a  that regularly recognizes the SRS resource information is capable of receiving it. By obtaining the SRS resource information, the other wireless base stations  1   b ,  1   c  become capable of receiving an SRS. 
         [0160]    In S 305  in  FIG. 11 , the other wireless base stations  1   b ,  1   c  confirm a used wireless resource (similar to S 105  in  FIG. 3 ). Next, in S 306 , the other wireless base stations  1   b ,  1   c  receive an SRS from the wireless terminal  2   a  using the SRS resource information and measures the UL receiving quality. Then, in S 307 , the other wireless base stations  1   b ,  1   c  send, in addition to the other station wireless resource information (similar to S 106  in  FIG. 3 ), the UL receiving quality information measured in S 306  to the connected wireless base station  1   a.    
         [0161]    In S 308  in  FIG. 11 , the connected wireless base station  1   a  is capable of using the received UL receiving quality information in the determination of UL reception destination and UL resource. As an example, the connected wireless base station  1   a  is capable of determining, among the other wireless base stations  1   b ,  1   c  capable of securing the UL wireless resource in the amount requested in the UL schedule requesting information (this is obtained by the other station wireless resource information), that having best receiving quality indicated by the received UL receiving quality information as the UL reception destination. Since S 309  through S 313  in  FIG. 11  are similar to S 108  through S 112  in  FIG. 3 , the description is omitted. 
         [0162]    As descriptions are given above based on  FIG. 11 , in the wireless communication system of the third embodiment, the connected wireless base station  1   a  selects the other wireless base station  1   b , which is the UL sending destination, based on the UL receiving quality notified in advance from the other wireless base stations  1   b ,  1   c . In addition, therefore, the connected wireless base station  1   a  sends the SRS resource information to the other wireless base stations  1   b ,  1   c  in advance. Thus, the wireless communication system in the third embodiment exhibits, in addition to an effect obtained by the wireless communication system in the first embodiment, an effect of allowing selection of the other wireless base stations  1   b ,  1   c  having good UL receiving quality as the UL sending destination. 
         [0163]    The functional configuration and the hardware configuration of the respective device in the third embodiment follow those in the first embodiment, so that the description is omitted. 
       [e] Fourth Embodiment 
       [0164]    The fourth embodiment is a modification that is applicable to as any of the first embodiment through the third embodiment, and the connected wireless base station  1   a  notifies the other wireless base stations  1   b ,  1   c  in advance of a wireless resource amount to be used for the UL sending of the wireless terminal  2   a.    
         [0165]    In the following descriptions, descriptions are given to a modification where the fourth embodiment is applied to the first embodiment. Since this modification has many points in common with the first embodiment, descriptions are given mainly to the points different from the first embodiment in the following descriptions. As described before, although the fourth embodiment may be modified by applying to the second embodiment or the third embodiment, it may be applied similarly to that to the first embodiment and the details are omitted. 
         [0166]    Based on  FIG. 12 , descriptions are given to a process sequence of a modification where the fourth embodiment is applied to the first embodiment. 
         [0167]    Since S 401  through S 403  in  FIG. 12  are similar to S 101  through S 103  in  FIG. 3 , the description is omitted. In S 404  in  FIG. 12 , the connected wireless base station  1   a  sends wireless resource requesting information, which is information to request a UL wireless resource, to the other wireless base stations  1   b ,  1   c  via the transmission network. At this time, the connected wireless base station  1   a  in the present embodiment stores requested amount information of the UL wireless resource included in the UL schedule requesting information received in S 402  in the wireless resource requesting information for sending. 
         [0168]    In S 405  in  FIG. 12 , as receiving wireless resource requesting information respectively, the other wireless base stations  1   b ,  1   c  obtain unused wireless resources. At this time, the other wireless base stations  1   b ,  1   c  in the present embodiment obtain the unused wireless resources of the requested amount based on the UL wireless resource amount information included in the received wireless resource requesting information. In S 406 , the other wireless base stations  1   b ,  1   c  send other station wireless resource information including unused wireless resources information indicating the obtained unused wireless resources to the connected wireless base station  1   a  via the transmission network, respectively. The other station wireless resource information sent in S 406  satisfies the requested amount (of the UL wireless resource) included in the wireless resource requesting information received in S 404 . 
         [0169]    In S 406 , the connected wireless base station  1   a  receives other station wireless resource information including the unused wireless resources information respectively from the other wireless base stations  1   b ,  1   c . Then, in S 407 , the connected wireless base station  1   a  selects the UL wireless resource that is used for UL data sending from the wireless terminal  2   a  based on the received unused wireless resources information. Here, the connected wireless base station  1   a  in the first embodiment arbitrarily selects unused wireless resources of the requested wireless resource amount based on the received unused wireless resources information in S 107  in  FIG. 3 . In contrast, the unused wireless resources information received by the connected wireless base station  1   a  of the present embodiment indicates unused wireless resources of the requested wireless resource amount. Therefore, the connected wireless base station  1   a  in the present embodiment may select one item of the unused wireless resources information received respectively from the other wireless base stations  1   b ,  1   c  in S 407 . That is, in the connected wireless base station  1   a  of the present embodiment, selection of the UL wireless resource based on the unused wireless resources and selection of the other wireless base station  1   b  to be a sending destination of UL sending are equivalent. Here, it is assumed that the connected wireless base station  1   a  selects the unused wireless resources of the other wireless base station  1   b  as the UL wireless resource. 
         [0170]    In S 408  in  FIG. 12 , the connected wireless base station  1   a  sends the determined wireless resource information to the wireless terminal  2   a  (similar to S 108  in  FIG. 3 ). In S 409 , the connected wireless base station  1   a  sends response information indicating to be selected as the other wireless base station  1   b  to be a sending destination of UL sending to the other wireless base station  1   b  to be the sending destination of the UL sending. Here, the connected wireless base station  1   a  in the present embodiment, different from the connected wireless base station  1   a  in the first embodiment, does not have to notify the other wireless base station  1   b  of information indicating the selected unused wireless resources. This is because the other wireless base station  1   b  recognizes the selected unused wireless resources. Since S 410  through S 412  in  FIG. 12  are same as S 110  through S 112  in  FIG. 3 , the description is omitted. 
         [0171]    In the fourth embodiment, compared with the first embodiment, although a size of wireless resource requesting information is slightly greater for including the UL wireless resource amount information, the other station wireless resource information (unused wireless resources information) may be same or smaller. In addition, the connected wireless base station  1   a  may send, instead of the determined wireless resource information, the response information. Accordingly, according to the fourth embodiment, compared with the first embodiment, an effect of suppressing the information amount sent and received between the wireless base stations  1  is expected. 
         [0172]    The functional configuration and the hardware configuration of the respective device in the fourth embodiment follow those in the first embodiment, so that the description is omitted. 
       [f] Fifth Embodiment 
       [0173]    The fifth embodiment is a modification that is applicable to any of the first embodiment through the third embodiment, and the connected wireless base station  1   a  notifies of, without obtaining other station wireless resource information from the other wireless base stations  1   b ,  1   c , a UL wireless resource used for the UL sending from the wireless terminal  2   a . In other words, the connected wireless base station  1   a  notifies the other wireless base stations  1   b ,  1   a  one-sidedly of the UL wireless resource used for the UL sending from the wireless terminal  2   a.    
         [0174]    In the following descriptions, descriptions are given to a modification where the fifth embodiment is applied to the first embodiment. Since this modification has many points in common with the first embodiment, descriptions are given mainly to the points different from the first embodiment in the following descriptions. As described before, although the fifth embodiment may be modified by applying to the second embodiment or the third embodiment, it may be applied similarly to that to the first embodiment and the details are omitted. 
         [0175]    Based on  FIG. 13 , descriptions are given to a process sequence of a modification where the fifth embodiment is applied to the first embodiment. 
         [0176]    Since S 501  through S 503  in  FIG. 13  is similar to S 101  through S 103  in  FIG. 3 , the description is omitted. When the UL reception destination is determined as other than the local station in S 503 , the connected wireless base station  1   a  further determines a UL wireless resource and a UL reception destination used for the UL reception in S 504 . The connected wireless base station  1   a  is capable of determining the UL wireless resource and the UL reception destination used for the UL reception in an arbitrary method. 
         [0177]    In S 505 , the connected wireless base station  1   a  sends the determined UL wireless resource to the wireless terminal  2   a  (similar to S 108  in  FIG. 3 ). Then, in S 506 , the connected wireless base station  1   a  sends wireless resource requesting information, which is the information to request the determined UL wireless resource, to the other wireless base station  1   b , which is the determined UL sending destination, via the transmission network. Since S 507  through S 509  in  FIG. 13  are similar to S 110  through S 112  in  FIG. 3 , the description is omitted. 
         [0178]    In the fifth embodiment, compared with the first embodiment, the other station wireless resource information (unused wireless resources information) becomes not requested and the information sent from the connected wireless base station  1   a  to the other wireless base station  1   b  is also reduced. Accordingly, according to the fifth embodiment, compared with the first embodiment, an effect of suppressing the information amount sent and received between the wireless base stations  1  is expected. 
         [0179]    The functional configuration and the hardware configuration of the respective device in the fifth embodiment follow those in the first embodiment, so that the description is omitted. 
       [g] Sixth Embodiment 
       [0180]    The sixth embodiment is a modification that is applicable to as any of the first embodiment through the third embodiment, and the other wireless base stations  1   b ,  1   c  sense an event to be an opportunity, thereby sending other station wireless resource information to the connected wireless base station  1   a . In other words, without sending wireless resource requesting information from the connected wireless base station  1   a  to the other station wireless base stations  1   b ,  1   c , the other station wireless base stations  1   b ,  1   c  send other station wireless resource information to the connected wireless base station  1   a.    
         [0181]    In the following descriptions, descriptions are given to a modification where the sixth embodiment is applied to the first embodiment. Since this modification has many points in common with the first embodiment, descriptions are given mainly to the points different from the first embodiment in the following descriptions. As described before, although the sixth embodiment may be modified by applying to the second embodiment or the third embodiment, it may be applied similarly to that to the first embodiment and the details are omitted. 
         [0182]    Based on  FIG. 14 , descriptions are given to a process sequence of a modification where the sixth embodiment is applied to the first embodiment. 
         [0183]    In S 601  in  FIG. 14 , the other wireless base stations  1   b ,  1   c  sense a predetermined event to be a trigger (opportunity) to send other station wireless resource information. This event may be an arbitrary event and may be, as an example, a lapse of predetermined time from the last sending of the other station wireless resource information. As another example, it may be the UL wireless used resource amount in the other wireless base stations  1   b ,  1   c  at a predetermined value or less. Then, in S 602  and S 603 , the other station wireless base stations  1   b ,  1   c  confirm the used wireless resource and send the other station wireless resource information (similar to S 105  and S 106  in  FIG. 3 ). 
         [0184]    In addition, in S 604  through S 606  in  FIG. 14 , UL data occurs in the wireless terminal  2   a , and the wireless terminal  2   a  sends UL schedule requesting information and the connected wireless base station  1   a  determines whether or not to set the UL reception destination as the local station (similar to S 101  through S 103  in  FIG. 3 ). Then, when the UL reception destination is determined as other than the local station in S 606 , the connected wireless base station  1   a  determines, in S 607 , a UL wireless resource and a UL reception destination based on the other station wireless resource information received in S 603 . Since S 607  through S 612  in  FIG. 14  are similar to S 107  through S 112  in  FIG. 3 , the description is omitted. Although S 601  through S 603  in  FIG. 14  are carried out at a timing before S 605 , they do not have to be so and S 601  through S 603  may be at any timing as long as before S 607 . 
         [0185]    In the sixth embodiment, compared with the first embodiment, the wireless resource requesting information becomes not requested. Accordingly, according to the sixth embodiment, compared with the first embodiment, an effect of suppressing information amount sent and received between the wireless base stations  1  is expected. 
         [0186]    The functional configuration and the hardware configuration of the respective device in the sixth embodiment follow those in the first embodiment, so that the description is omitted. 
       [h] Seventh Embodiment 
       [0187]    In the seventh embodiment, the wireless terminal  2   a  generates and sends a DM-RS, which is one of the UL reference signals, in accordance with the other wireless base station  1   b , which is a UL sending destination. It is possible to combine the seventh embodiment with the first embodiment or the second embodiment, and there are many points in common with them. In the following descriptions, descriptions are given mainly to the points in the seventh embodiment different from the first embodiment in the following descriptions. 
         [0188]    In a conventional LTE system and the wireless communication system of the first embodiment, when sending a UL wireless frame, the wireless terminal  2   a  generates a DM-RS, which is one of the UL reference signal, and maps it in a UL wireless frame for sending. The connected wireless base station  1   a  that has received the UL wireless frame demodulates the UL control signal and the data signal using channel characteristics to estimate the channel characteristics based on the DM-RS. 
         [0189]    Here, the DM-RS is information (pattern) different for each wireless base station  1 . Specifically, the DM-RS is generated based on a base station identifier. In a regular LTE system, the wireless terminal  2   a  generates a DM-RS for the connected wireless base station  1   a  using the identifier of the connected wireless base station  1   a  and sends it in a UL wireless frame. Then, the connected wireless base station  1   a  carries out channel estimation by analyzing the DM-RS in the received UL wireless frame using the identifier of the connected wireless base station  1   a . Thus, the connected wireless base station  1   a  is capable of appropriately receiving the DM-RS and capable of estimating the channel characteristics with high precision, so that decoding errors are suppressed. 
         [0190]    However, a problem occurs in the first embodiment and the second embodiment when the UL sending destination of the wireless terminal  2   a  becomes the other wireless base station  1   b . Even when the wireless terminal  2   a  sends the DM-RS towards the connected wireless base station  1   a , the other wireless base station  1   b  receives the DM-RS and utilizes it for demodulation. Since the DM-RS towards the other wireless base station  1   b  is generally different from the DM-RS towards the connected wireless base station  1   a , the other wireless base station  1   b  is not capable of appropriately estimating the channel characteristics based on the DM-RS. In this case, it turns out to increase decoding errors and thus not preferred. 
         [0191]    In order to solve this problem, in the seventh embodiment, when the UL sending destination of the subordinate wireless terminal  2   a  is the other wireless base station  1   b , the connected wireless base station  1   a  stores an identifier of the other wireless base station  1   b  in the DL control information (DCI) for sending. Then, the wireless terminal  2   a  having received the DL wireless frame, when sending the UL wireless frame, generates the DM-RS using the identifier of the other wireless base station  1   b  and maps the DM-RS in the UL wireless frame for sending. 
         [0192]      FIG. 15  illustrates a DCI format in the seventh embodiment.  FIG. 15  (A) is a DCI format of a modification where the seventh embodiment is applied to the first embodiment.  FIG. 15  (B) is a DCI format of a modification where the seventh embodiment is applied to the second embodiment. The DCI formats in  FIG. 15  both have a region to store a UL sending destination identifier, which is an identifier of the other wireless base station  1   b.    
         [0193]    According to the seventh embodiment, the wireless terminal  2   a  is capable of generating and sending the DM-RS towards the other wireless base station  1   b , so that an effect of suppressing decoding errors in the other wireless base station  1   b  is obtained. 
         [0194]    The functional configuration and the hardware configuration of the respective device in the seventh embodiment follow those in the first embodiment, so that the description is omitted. 
       [i] Eighth Embodiment 
       [0195]    The eighth embodiment is also to solve the problem same as the seventh embodiment, and it is possible to combine with the first embodiment or the second embodiment. Since the eighth embodiment has many points in common with the seventh embodiment, descriptions are given mainly to the points in the eighth embodiment different from the seventh embodiment in the following descriptions. 
         [0196]    In the eighth embodiment, it does not have to store an identifier of the other wireless base station  1   b  in the DCI as in the seventh embodiment. Instead, in the eighth embodiment, the other wireless base station  1   b  analyzes the DM-RS in the received UL wireless frame using the identifier of the connected wireless base station  1   a  (not the identifier of itself) and carries out channel estimation. The other wireless base station  1   b  is capable of learning the identifier of the connected wireless base station  1   a  in a message sent and received with the connected wireless base station  1   a.    
         [0197]    According to the eighth embodiment, the other wireless base station  1   b  is capable of appropriately receiving the DM-RS towards the connected wireless base station  1   a  and capable of estimating the channel characteristics with high precision, so that an effect of suppressing decoding errors is obtained. Comparing the seventh embodiment with the eighth embodiment, the former has to use a function compatible with both the wireless base stations  1  and the wireless terminals  2 , while the latter has to use a function compatible only with the wireless base stations  1 , so that the latter is considered to be easier for introduction. 
         [0198]    The functional configuration and the hardware configuration of the respective device in the eighth embodiment follow those in the first embodiment, so that the description is omitted. 
       [j] Ninth Embodiment 
       [0199]    The ninth embodiment is also to solve the problem same as the seventh embodiment and the eighth embodiment, and it is possible to combine with the first embodiment or the second embodiment. The ninth embodiment is equivalent to an embodiment in which the seventh embodiment and the eighth embodiment are combined. 
         [0200]    When an identifier of the other wireless base station  1   b  is stored in the DCI in the received DL wireless frame, the wireless terminal  2   a  in the present embodiment generates the DM-RS using the identifier of the other wireless base station  1   b . At this time, the other wireless base station  1   b  analyzes the DM-RS in the UL wireless frame received as regularly using the identifier of itself and carries out channel estimation. 
         [0201]    In contrast, when the identifier of the other wireless base station  1   b  is not stored in the DCI, the wireless terminal  2   a  generates the DM-RS using an identifier of the connected wireless base station  1   a . At this time, the other wireless base station  1   b  analyzes the DM-RS in the received UL wireless frame using the identifier of the connected wireless terminal  2   a  and carries out channel estimation. 
         [0202]    The other wireless base station  1   b  is regularly not capable of learning whether or not an identifier of the other wireless base station  1   b  is stored in the DCI. Therefore, the other wireless base station  1   b  has to be notified of whether or not the identifier of the other wireless base station  1   b  is stored in the DCI from the connected wireless base station  1   a  in advance. 
         [0203]    By the ninth embodiment as well, similar to the seventh and eighth embodiments, an effect of suppressing decoding errors in the other wireless base station  1   b  is obtained. 
         [0204]    The functional configuration and the hardware configuration of the respective device in the ninth embodiment follow those in the first embodiment, so that the description is omitted. 
       [k] Other Embodiments 
       [0205]    In the first through ninth embodiments described above, when the wireless terminal  2   a  is UL sent to the other wireless base station  1   b , the connected wireless base station  1   a  carries out determination of the other wireless base station  1   b  to be the destination (determined wireless base station) and the UL wireless resource to be used (determined wireless resource). However, the subject of such determination is not limited to the connected wireless base station  1   a.    
         [0206]    For example, an upper station (upper device) connected to the core network and the like may also determine the determined wireless base station and the determined wireless resource. In addition, the other wireless base station  1   b  different from the connected wireless base station  1   a  may also determine the determined wireless base station and the determined wireless resource. Further, the wireless terminal  2   a  may also determine the determined wireless base station and the determined wireless resource. 
         [0207]    Further, an upper station (upper device), the other wireless base station  1   b , the wireless terminal  2   a , and the like may also receive other station wireless resource information from the other wireless base stations  1   b ,  1   c  in a procedure similar to that carried out by the connected wireless base station  1   a  in the first through ninth embodiments described above. Then, the upper station (upper device), the other wireless base station  1   b , wireless terminal  2   a , and the like may also determine the determined wireless base station and the determined wireless resource based on the received other station wireless resource information. 
         [0208]    By the way, in this application, for example, “connected to” is able to be replaced with “coupled to”. Moreover, for example, when an element is referred to as being “connected to” or “coupled to” another element, it can be not only directly but also indirectly connected or coupled to the other element (namely, intervening elements may be present). So do “connecting to”, “coupling to”, “connection to”, “coupling to” and so on. 
         [0209]    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.