Abstract:
A wireless communication apparatus is disclosed. A transmitting device transmits a first aggregation frame in which first transmission data frames are aggregated. A measuring device measures a number value of retransmission of each of the first transmission data frames. A storage stores a limiting value of the number value of retransmission. A determination device determines whether the number value of retransmission of each of the first transmission data frames exceeds the limiting value. A transmission buffer buffers the first transmission data frames for which it is determined that the number value of retransmission does not exceed the limiting value, and discards the first transmission data frames for which it is determined that the number value of retransmission exceeds the limiting value, of the first transmission data frames. A retransmitting device retransmits the first aggregation frame in which the first transmission data frames buffered in the transmission buffer are aggregated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a Continuation Application of PCT Application No. PCT/JP2006/318803, filed Sep. 15, 2006, which was published under PCT Article 21(2) in English. 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-285324, filed Sep. 29, 2005, the entire contents of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a wireless communication apparatus suitable for a cell phone or wireless LAN apparatus. 
   2. Description of the Related Art 
   In a CSMA/CA type wireless communication system represented by wireless LAN communication defined by IEEE 802.11 in conventional wireless communication systems, if an acknowledgement frame (Ack frame) for transmission data cannot be received, the transmission data is retransmitted. In this case, on the basis of the retry count and lifetime unique to each transmission data, retransmission is limited by using the retry count and transmittable time of the transmission data. 
   In the QoS (Quality of Service)-extended wireless LAN standard IEEE 802.11e, communication is separately performed in two periods, i.e., a contention-based period during which each terminal station performs distributed access by using a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) method, and a contention-free period during which a base station performs centralized control. The latter access control method using centralized control is called an HCCA (HCF Controlled Channel Access) method, and the former access control method using distributed control is called an EDCA (Enhanced Distributed Channel Access) method. A wireless LAN terminal is able to access a medium by using one of these access control methods, acquire TXOP (transmission opportunity) representing a period during which a plurality of data can be transmitted, and communicate data during the TXOP period (see IEEE 802.11e Draft 13.0, IEEE P802.11e/D13.0, January 2005 below). 
   In IEEE 802.11n aiming at high-speed transmission has proposed a method in which a terminal having acquired a TXOP period gives a part of this TXOP period to the data receiving terminal, and bi-directional communication is performed by a piggy back method in the TXOP period, thereby increasing the transmission efficiency. This method is called a bi-directional data flow or reverse direction. 
   In IEEE 802.11n, unlike in the existing IEEE 802.11 standard, an aggregation frame is formed by collecting (i.e., aggregating) a plurality of data into one data frame, and transmitted as one data frame, thereby reducing the overhead existing between individual data frames (when they are not aggregated). 
   To acquire a TXOP period for transmitting an aggregation frame in the EDCA method, the transmitting terminal (initiator) transmits an IAC frame, and the receiving terminal (responder) returns an RAC frame when SIFS has elapsed after that, thereby performing IAC-RAC frame exchange. Alternatively, RTS-CTS frame exchange defined by IEEE 802.11 may also be used instead of IAC-RAC frame exchange. 
   When IAC-RAC frame exchange is to be performed in the bi-directional data flow, the data receiving terminal notifies a data frame length and transmission data rate, which the terminal can transmit when given a part of a TXOP period, by writing the data in an RAC frame. 
   On the basis of the values written in the RAC frame, the transmitting terminal determines that part (RDG duration: reverse direction communication permission period) of the TXOP period, which is to be given after an aggregation frame is transmitted. The transmitting terminal writes the determined RDG duration in an IAC frame, attaches the IAC frame to the head of the aggregation frame, and transmits the aggregation frame when SIFS has elapsed after the RAC frame is received. The receiving terminal having received the aggregation frame having the IAC frame attached to the head must notify the reception status by a Block Ack (block acknowledgement) frame when SIFS has elapsed after the aggregation frame is received from the transmitting terminal. When the bi-directional data flow is used, the receiving terminal transmits the Block Ack frame when SIFS has elapsed by using the piggy back method by which several data frames are transmitted as they are aggregated in the Block Ack frame, thereby simultaneously transmitting the data and Block Ack frame. In this case, the transmission time of the aggregation frame formed by aggregating several data frames in the Block Ack frame cannot exceed the time of the RDG duration written in the IAC frame. 
   In this manner, a part of the TXOP period acquired by the transmitting terminal can be given to the receiving terminal. 
   If the receiving terminal further requests an RDG duration when transmitting an aggregation frame by the piggy back method, the receiving terminal can further request an RDG duration by writing, in an RAC frame, a data frame length and transmission data rate prepared for transmission, and returning the RAC frame by attaching it to the head of the aggregation frame to be transmitted by the piggy back method (see TGn Sync Proposal Technical Specification, IEEE 802.11-04/889r4, March 2005). 
   Also, JP-A 2003-60562 (KOKAI) below describes that retransmission is controlled by adjusting the signal length of a burst signal in burst communication by radio. 
   The following problem arises if the retransmission limiting method for each transmission data defined in the existing IEEE 802.11 is applied to the retransmission limiting method for burst transmission such as the Block Ack method defined in the conventional IEEE 802.11e. That is, if data in which error has occurred by burst transmission is transmitted simultaneously with new transmission data, burst data transmissions are excessively concentrated to the same terminal. 
   Also, when the transmission opportunities of data having a plurality of priority degrees are grouped in accordance with the priority degrees as defined in the conventional IEEE 802.11e, the transmission opportunities are excessively given to the same priority degree. 
   The above problem similarly arises in the aggregation method by which a plurality of transmission data are aggregated into one frame as burst data. The problem also similarly arises in the bi-directional data flow method by piggy back in which a part of the acquired TXOP period is given to the receiving terminal. 
   Furthermore, a new problem of the bi-directional data flow method is that although data are transmitted from both the transmitting side and receiving side in the bi-directional data flow method, if no transmission error occurs in the data transmitted from the transmitting side and an error occurs in only the data transmitted from the receiving side, the transmitting side need not retransmit the data. Therefore, no retransmission band is allocated to the receiving side, so the data in which the error has occurred is not retransmitted unless the receiving terminal reacquires the transmission right. 
   In addition, when data transmission is performed from a terminal station to a base station in the HCCA method of IEEE 802.11e, a QoS Cf-poll frame is transmitted to give the terminal station the transmission right of a TXOP period, and the terminal having acquired the transmission right transmits data during this TXOP period. If a transmission error or the like occurs in the TXOP period and TXOP reallocation is immediately performed, TXOP allocations may be concentrated to the same terminal. 
   BRIEF SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a wireless communication apparatus used in a system which allows a plurality of terminals or a plurality of priority degrees to equally secure bands by preventing excess concentration of transmissions by the same terminal or the same priority degree when burst transmission and retransmission are performed. 
   According to one aspect of the present invention, a wireless communication apparatus includes a transmitting device which transmits a first aggregation frame in which first transmission data frames are aggregated; a measuring device which measures a number value of retransmission of each of the first transmission data frames; a storage to store a limiting value of the number value of retransmission; a determination device which determines whether the number value of retransmission of each of the first transmission data frames exceeds the limiting value; a transmission buffer which buffers the first transmission data frames for which it is determined that the number value of retransmission does not exceed the limiting value, and discards the first transmission data frames for which it is determined that the number value of retransmission exceeds the limiting value, of the first transmission data frames; and a retransmitting device which retransmits the first aggregation frame in which the first transmission data frames buffered in the transmission buffer are aggregated. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is block diagram showing a wireless communication apparatus according to an embodiment; 
       FIG. 2  is a view for explaining a burst transmission method performed by the bi-directional data flow method; 
       FIG. 3  is a view for explaining a conventional retransmission method in burst transmission; 
       FIG. 4  is a view for explaining a retransmission limiting method using the lifetime for each frame exchange sequence of burst data when retransmission is performed in burst transmission; 
       FIG. 5  is a view for explaining the bi-directional data flow method which is a piggy back type bi-directional communication method using a QoS Cf-Poll frame; 
       FIG. 6  is a view for explaining a retransmission limiting method according to the second embodiment, using the retry count for each frame exchange sequence of burst data; 
       FIG. 7  is a view for explaining a retransmission limiting method according to the third embodiment; and 
       FIG. 8  is another view for explaining a retransmission limiting method according to the third embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   First Embodiment 
   An embodiment will be explained below by taking IEEE 802.11 of wireless LAN communication as one of communication methods using a wireless communication system. However, this wireless LAN communication method of IEEE 802.11 is regarded as one of wireless communication methods from which the effects of the present embodiment can be expected, so the present embodiment is applicable not only to IEEE 802.11 but also to general wireless communication methods. Also, the embodiment will be explained by taking, as an example, a case in which the piggy back type bi-directional data flow method proposed in IEEE 802.11n is applied as one of burst transmission communication methods. Note that a burst transmission communication method to which the present embodiment is applicable is not limited to the bi-directional data flow method. For example, the present embodiment is applicable to a method which uses a poll type frame instead of a band allocation method for a responder terminal in the bi-directional data flow method. 
   As is well known, in wireless communication by CSMA/CA, a wireless communication terminal which intends to transmit data packet by packet performs carrier sense before transmission of each data, thereby avoiding collision with packets from other terminals. In burst transmission in which a plurality of transmission data are successively transmitted, carrier sense is performed for only the first packet (transmission data) of burst data, and the other packets of the burst data are transmitted without performing any carrier sense. 
   In a burst transmission method using an aggregation method, a plurality of transmission data are aggregated into one frame and the frame is transmitted by burst transmission. In this case, various aggregation methods are possible. Examples are a method in which a plurality of MAC frames are aggregated into one PHY frame and a preamble is attached to only the head of the frame, and a method which increases the error estimation accuracy by inserting a mid preamble in the middle of one PHY frame. The present embodiment is not limited to any specific aggregation method, and applicable to general communication methods which perform burst-like transmission. In addition, the present embodiment is applicable not only to transmission using aggregation frames, but also to a communication method which performs burst transmission in which data frames are spaced by SIFS periods or RIFS periods in a usable communication period. 
   As shown in  FIG. 1 , a wireless communication apparatus  101  according to this embodiment comprises a transmission data manager  102  which has a transmission queue for buffering transmission data and performs a retransmission limitation unique to each transmission data, an access controller  103  which determines a data transmitting/receiving method, performs access control in processes of transmitting, receiving, and retransmitting data frames and acknowledgement frames, and, when a plurality of transmission data are to be transmitted by burst transmission, performs a retransmission limitation for each frame exchange sequence of burst data, which is different from the retransmission limitation unique to each transmission data performed by the transmission data manager  102 , a transmission processor  104  which performs a data transmitting process, and a reception processor  105  which performs a received frame identification process and a receiving process by which, e.g., a bitmap of acknowledgement is formed. 
   The transmission data manager  102  comprises a transmission queue manager  106  which has a transmission queue for buffering transmission data, a packet transmissibility determination unit  107  which performs a retransmission limitation unique to each transmission data, and a backoff processor  108  which performs backoff processing based on CSMA/CA. 
   The transmission queue manager  106  includes a counter for counting the retry count of each transmission data. 
   The packet transmissibility determination unit  107  stores the limit of the lifetime for each frame exchange sequence of each transmission data. The packet transmissibility determination unit  107  compares the stored lifetime limit or retry limit with the retry count of each transmission data obtained by the transmission queue manager  106  by using the counter or the lifetime of each transmission data obtained by a transmission/reception state manager  110  (to be described later) by using a timer, thereby determining whether to retransmit each packet. 
   The access controller  103  comprises a data transmitting/receiving method determination unit  109  which determines, e.g., a data transmitting method to be used in data transmission such as an aggregation method or bi-directional data flow method, the length of TXOP, and a retransmission limiting method according to the present embodiment which is performed for each frame exchange sequence of burst data, the transmission/reception state manager  110  which manages the timings of data transmission/reception performed by the transmitting/receiving method determined by the data transmitting/receiving method determination unit  109 , performs access control in a retransmission process and the like, and, when a plurality of transmission data are to be transmitted by burst transmission, performs a retransmission limitation for each frame exchange sequence of burst data separately from the retransmission limitation unique to each transmission data which is performed by the transmission data manager  102 , a frame formation/transmission processor  111  which forms and transmits various control frames and aggregation frames, and a carrier sense unit  112  which manages carrier sense information required in the backoff processor  108 . 
   The transmission/reception state manager  110  includes a timer for measuring the lifetime for each frame exchange sequence of burst data. 
   The reception processor  105  comprises a frame information identification unit  113  which identifies the success or failure of the reception of a received frame and control information in the received frame, and a bitmap formation unit  114  which, when burst data is received, forms a bitmap of acknowledgement to be placed in an acknowledgement frame from the success or failure of the reception of each frame in the burst data. 
   First, a burst transmission method performed by the bi-directional data flow method will be explained with reference to  FIG. 2 . In the bi-directional data flow method, a terminal A  201  having acquired the data transmission right describes the use of the bi-directional data flow method in an IAC (Indicator Aggregation Control) frame  203 , and transmits it to a terminal B  202 . The terminal B  202  having received the IAC frame  203  describes, in an RAC (Responder Aggregation Control) frame  204 , a transmission rate and frame length to be transmitted when the transmission right is given by the bi-directional data flow, and returns the RAC frame  204 . The terminal A 201  having received the RAC frame  204  forms an aggregation frame by aggregating a plurality of transmission data and attaching the IAC frame  205  to the head of the data, and transmits the aggregation frame. In this case, a transmission period  206 , which is determined on the basis of, e.g., the information described in the RAC frame  204 , to be given to the terminal B  202  is described in the IAC frame  205 . When receiving the aggregation frame having the IAC frame  205  attached to the head, the terminal B  202  forms a Block Ack frame  207  containing the reception status of each data. Then, the terminal B  202  forms an aggregation frame by adding an RAC frame  208  before the Block Ack frame  207  and aggregating a plurality of transmission data to be transmitted to the terminal A  201  after the Block Ack frame  207 , and returns the aggregation frame. Note that the transmission period of the aggregation frame returned by the terminal B  202  does not exceed the transmission period  206  given from the terminal A  201  to the terminal B  202 . Note also that it is not always necessary to use the RAC frame  208 . After that, the terminal A  201  returns a Block Ack frame  209  as the reception status of the data from the terminal B  202 . Communication is performed by the flow as described above. Although the aggregation frames make one round trip in  FIG. 2 , they may also be transmitted and received a plurality of number of times. The operation of the bi-directional data flow method is described in detail in TGn Sync Proposal Technical Specification, IEEE 802.11-04/889r4, March 2005 described earlier. 
   In a conventional retransmission method shown in  FIG. 3 , after frame exchange between an IAC frame and RAC frame is completed, a terminal A  301  calculates an RDG duration as a transmission period to be allocated to a terminal B  302 , writes the RDG duration in the IAC frame, forms an aggregation frame together with a plurality of transmission data Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A from the terminal A  301 , and transmits the aggregation frame. The terminal B  302  having received the plurality of transmission data Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A transmitted by the terminal A  301  forms a Block Ack frame  303  describing the reception statuses of the plurality of transmission data. The terminal B  302  forms an aggregation frame which falls within the range of the RDG duration as the transmission period given from the terminal A  301 , by aggregating the Block Ack frame  303 , the RAC frame, and the plurality of data Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B to be transmitted to the terminal A  301 , and returns this aggregation frame to the terminal A  301 . This sequence is a first burst data frame exchange sequence  304  performed by the bi-directional data flow method. 
   In the first burst data frame exchange sequence  304  performed by the bi-directional data flow method, if Data  3 -A and Data  4 -A transmitted by the terminal A  301  are transmission errors, the terminal A  301  detects from the reception statuses described in the Block Ack frame  303  that Data  3 -A and Date  4 -A must be retransmitted. Therefore, when returning a Block Ack frame  305  describing the reception statuses of a plurality of transmission data Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B transmitted by the terminal B  302 , the terminal A  301  does not return only the Block Ack Frame  209  as shown in  FIG. 2 , but forms an aggregation frame by aggregating the Block Ack frame  305 , an IAC frame  306 , Data  3 -A and Data  4 -A as the retransmission data, and Data  5 -A as new data, and transmits this aggregation frame. The terminal A  301  detects that Data  2 -B and Data  3 -B transmitted by the terminal B  302  are transmission errors when forming the Block Ack frame  305 , so the terminal A  301  describes in the IAC frame  306  a period during which the terminal B  302  can retransmit Data  2 -B and Data  3 -B. Then, the terminal B  302  having received the aggregation frame containing the Block Ack frame  305  and IAC frame  306  and given the transmission period described in the IAC frame  306  describes in a Block Ack frame  307  the reception statuses of Data  3 -A and Data  4 -A retransmitted from the terminal A  301  and Data  5 -A as the new data, forms an aggregation frame which falls within the range of the RDG duration as the transmission period given from the terminal A  301 , by aggregating an RAC frame, the Block Ack frame  307 , Data  2 -B and Data  3 -B as the retransmission data from the terminal B  302 , and Data  5 -B as new data, and returns this aggregation frame to the terminal A  301 . 
   If a transmission error occurs in the data transmitted by a frame exchange sequence  308  for the first retransmission of the burst data, an aggregation frame as burst data is retransmitted again. Referring to  FIG. 3 , in a frame exchange sequence  309  for the second retransmission of the burst data, Data  5 -A from the terminal A  301  and Data  3 -B from the terminal B  302  are retransmission data, and an aggregation frame formed by further aggregating new data after these retransmission data is transmitted and received. If transmission errors keep occurring in some data transmitted from the terminal A  301  or terminal B  302  as described above, the problem that data transmission/reception is kept performed by the bi-directional data flow method arises. Note that the transmission interval between individual data shown in the transmitting/receiving methods of  FIGS. 2 and 3  is an SIFS period. 
   A retransmission limiting method according to the present embodiment which solves the above problem by using the lifetime for each frame exchange sequence of burst data when the burst data is retransmitted by the bi-directional data flow method will be explained below with reference to  FIGS. 1 and 4 . 
   When data is stored in the transmission queue in the transmission queue manager  106  of the transmission data manager  102  of the wireless communication apparatus  101  of a terminal A  401 , the transmission queue manager  106  instructs the backoff processor  108  to perform backoff processing. The backoff processor  108  instructed to perform backoff processing inquires about the use state of a radio space managed by the carrier sense unit  112 . If the use state is IDLE, the backoff processor  108  performs a countdown process of backoff. After completing this backoff countdown, the backoff processor  108  notifies the transmission queue manager  106  of the completion of backoff. By this backoff completion, the terminal A  401  acquires the transmission right. 
   The transmission queue manager  106  notified of the backoff completion transmits the number of data stored in the transmission queue and the transmission data to the packet transmissibility determination unit  107 . The packet transmissibility determination unit  107  confirms that the transmission time of each transmission has not exceeded the lifetime uniquely managed for the transmission data, and the retry count of each transmission data has not exceeded the retry limit (retransmission limitation) of the transmission data. After confirming the lifetime and retry count of each transmission data, the packet transmissibility determination unit  107  transmits the number of data stored in the transmission queue and the transmission data to the transmission/reception state manager  110  in the access controller  103 . The transmission/reception state manager  110  notifies the transmitting/receiving method determination unit  109  of the number of data stored in the transmission queue to determine whether to use the bi-directional data flow method, and whether to perform IAC-RAC frame exchange before the transmission of an aggregation frame. In this embodiment, it is determined that the bi-directional data flow method is used and IAC-RAC frame exchange is performed. At this time, the transmission/reception state manager  110  notified of the determined data transmitting/receiving method from the data transmitting/receiving method determination unit  109  sets (starts) the timer of lifetime  403  for each frame exchange sequence of burst data. After that, the transmission/reception state manager  110  instructs the frame formation/transmission processor  111  to transmit an IAC frame. The frame formation/transmission processor  111  having received this IAC frame transmission instruction forms an IAC frame describing the use of the bi-directional data flow method, and transmits the formed IAC frame to the transmission processor  104 . As shown in  FIG. 4 , the transmission processor  104  having received the IAC frame transmits it as an IAC frame  404  for starting the bi-directional data flow method from the terminal A  401  to a terminal B  402 . 
   In the terminal B  402  having received the IAC frame  404 , the frame information identification unit  113  of the reception processor  105  identifies the IAC frame describing the start of the bi-directional data flow method, and transmits to the transmission/reception state manager  110  a request signal which requests transmission of an RAC frame describing a transmission rate and frame length to be transmitted when the transmission right is given by the bi-directional data flow. The transmission/reception state manager  110 , which has received this RAC frame transmission request, of the terminal B  402  refers to the data amount in the transmission queue of the transmission queue manager  106 , and determines the transmission rate and frame length to be transmitted when the transmission right is given by the bi-directional data flow. The transmission/reception state manager  110  then transmits to the frame formation/transmission processor  111  an instruction to transmit the transmission rate and frame length to be transmitted when the transmission right is given by the bi-directional data flow and an RAC frame when SIFS has elapsed after the IAC frame  404  is received. The frame formation/transmission processor  111  forms an RAC frame and transmits it from the transmission processor  104 . 
   The terminal A  401  receives from the terminal B  402  the RAC frame which responds to the IAC frame  404 , and starts a first burst data frame exchange sequence  405  by the bi-directional data flow method when SIFS has elapsed after frame exchange between the IAC frame and RAC frame is completed. When the RAC frame is received by the terminal A  401 , the frame information identification unit  113  of the reception processor  105  of the terminal A  401  identifies the received RAC frame. As a result of the identification of the RAC frame, the frame information identification unit  113  extracts the transmission rate and frame length, which are described in the RAC frame, to be transmitted when the terminal B  402  is given the transmission right by the bi-directional data flow, and notifies the transmission/reception state manager  110  of the data. The transmission/reception state manager  110  notifies the data transmitting/receiving method determination unit  109  of the amount of transmission queues stored in the transmission queue, and the transmission rate and frame length, which are notified by the RAC frame, to be transmitted when the terminal B  402  is given the transmission right by the bi-directional data flow. By using the values notified from the transmission/reception state manager  110 , the data transmitting/receiving method determination unit  109  determines the number of data or a data frame length to be transmitted from the terminal A  401  and the value (RDG duration) of a part of a TXOP period to be given to the terminal B  402 . The transmission/reception state manager  110  requests the transmission queue manager  106  to extract, from the transmission queue, transmission data necessary to perform data transmission by the number of data or the data frame length, which is determined by the data transmitting/receiving method determination unit  109 , to be transmitted from the terminal A  401 . The packet transmissibility determination unit  107  confirms that the transmission time of each of the transmission data extracted by the transmission queue manager  106  has not exceeded the lifetime uniquely managed for the transmission data, and that the retry count of each transmission data has not exceeded the retry limit of the transmission data, and transmits the data to the transmission/reception state manager  110 . The transmission/reception state manager  110  transmits to the frame formation/transmission processor  111  the value of RDG duration determined by the data transmitting/receiving method determination unit  109 , and four data frames Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A to be transmitted by the first burst data frame exchange sequence  405  performed by the bi-directional data flow method. The frame formation/transmission processor  111  forms an IAC frame  406  by using the value of RDG duration determined by the data transmitting/receiving method determination unit  109 , forms an aggregation frame by aggregating a total of five MAC frames, i.e., the IAC frame  406  and four data frames Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A, and transmits the aggregation frame. 
   The terminal B  402  having received the aggregation frame formed by aggregating a total of five MAC frames, i.e., the IAC frame  406  and four data frames Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A returns an aggregation frame when SIFS has elapsed after the aggregation frame from the terminal A  401  is received. The frame information identification unit  113  in the reception processor  105  of the terminal B  402  identifies each frame in the aggregation frame received from the terminal A  401 . The frame information identification unit  113  extracts the value of RDG duration in the IAC frame  406  at the head of the aggregation frame, and notifies the transmission/reception state manager  110  of the extracted value. Then, the frame information identification unit  113  confirms the reception statuses of the plurality of data frames in the aggregation frame, and the bitmap formation unit  114  forms a bitmap of the reception statuses of the plurality of data frames and notifies the transmission/reception state manager  110  of the bitmap. The transmission/reception state manager  110  notified of the value of RDG duration in the IAC frame  406  and the bitmap of the reception statuses of the plurality of data frames extracts four transmission data Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B from the transmission queue manager  106 , in order to form an aggregation frame which can be transmitted by the value of RDG duration in the IAC frame  406 . When four transmission data Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B are extracted from the transmission queue manager  106 , the packet transmissibility determination unit  107  confirms that the transmission time of each transmission data has not exceeded the lifetime uniquely managed for the transmission data, and that the retry count of each transmission data has not exceeded the retry limit of the transmission data, and transmits the four transmission data to the transmission/reception state manager  110 . The transmission/reception state manager  110  transmits to the frame formation/transmission processor  111  that bitmap of the reception statuses of the plurality of data frames, which is formed by the bitmap formation unit  114 , and four transmission data Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B. The frame formation/transmission processor  111  forms an RAC frame, forms a Block Ack frame  407  by using that bitmap of the reception statuses of the plurality of data frames, which is formed by the bitmap formation unit  114 , forms an aggregation frame by aggregating a total of six MAC frames, i.e., the RAC frame, the Block Ack frame  407 , and four data frames Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B, and returns this aggregation frame. Note that the value of RDG duration described in the IAC frame  406  cannot be exceeded. 
   When the aggregation frame returned from the terminal B  402  is received, the frame information identification unit  113  of the reception processor  105  of the terminal A  401  detects by the bitmap of the reception statuses described in the Block Ack frame  407  transmitted from the terminal B  402  that Data  3 -A and Data  4 -A transmitted by the terminal A  401  are not normally received. Subsequently, when a bitmap of the reception statuses of the plurality of data frames aggregated after the Block Ack frame  407  is formed by using the frame information identification unit  113  and bitmap formation unit  114 , it is detected that Data  2 -B and Data  3 -B transmitted by the terminal B  402  are not normally received. The transmission/reception manager  110 , which has collected these pieces of information indicating the abnormal receptions, of the terminal A  401  determines that retransmission is necessary. The transmission/reception manager  110 , which has determined that retransmission is necessary, of the terminal A  401  notifies the packet transmissibility determination unit  107  that retransmission is to be performed, and the packet transmissibility determination unit  107  counts up the retry counts of Data  3 -A and Data  4 -A as the retransmission data from the terminal A  401 , and confirms that each counted-up retry count has not reached the upper limit of the retry count of the data, and that the lifetime unique to each data has not expired. After confirming that the retry count has not reached the upper limit of the retry count and the lifetime unique to each data has not expired, the packet transmissibility determination unit  107  notifies the data transmitting/receiving method determination unit  109  of the frame length of a retransmission frame and the length of a new frame existing in the transmission queue, via the transmission/reception manager  110 , and the data transmitting/receiving method determination unit  109  determines that period of a frame exchange sequence  408  for the first retransmission of the burst data, which is necessary when data is retransmitted. The transmission/reception manager  110  having received that period of the frame exchange sequence  408  for the first retransmission of the burst data, which is determined by the data transmitting/receiving method determination unit  109  and necessary when data is retransmitted, determines whether the frame exchange sequence  408 , which is the period necessary when data is retransmitted, for the first retransmission of the burst data can be transmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data. If the frame exchange sequence  408  for the first retransmission of the burst data can be transmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data, the first retransmission of the burst data is performed. 
   In the frame exchange sequence  408  for the first retransmission of the burst data, the data transmitting/receiving method determination unit  109  has already confirmed that Data  3 -A and Data  4 -A as the retransmission data from the terminal A  401  have not reached the upper limits of the retry counts and the lifetime unique to each data has not expired, so the packet transmissibility determination unit  107  sets retry bits of Data  3 -A and Data  4 -A, extracts Data  5 -A as new transmission data from the transmission queue manager  106 , confirms that the upper limit of the retry count is not reached and the lifetime unique to the data has not expired in the same manner as for Data  3 -A and Data  4 -A as the retransmission data, and transmits Data  3 -A and Data  4 -A as the retransmission data and Data  5 -A as the new transmission data to the transmission/reception manager  110 . The transmission/reception manager  110  transmits, to the frame formation/transmission processor  111 , that transmission period for retransmission to be given to the terminal B  402 , which is determined by the data transmitting/receiving method determination unit  109 , Data  3 -A and Data  4 -A as the retransmission data, Data  5 -A as the new transmission data, and that bitmap of the statuses of the plurality of data frames aggregated after the Block Ack frame  407 , which is formed by the bitmap formation unit  114 . The frame formation/transmission processor  111  transmits, as the frame exchange sequence  408  for the first retransmission of the burst data, an aggregation frame formed by aggregating an IAC frame describing the transmission period for retransmission to be given to the terminal B  402 , a Block Ack frame which returns the reception statuses to the terminal B  402 , Data  3 -A and Data  4 -A as the retransmission data, and Data  5 -A as the new transmission data, when SIFS has elapsed after the first burst data frame exchange sequence  405  performed by the bi-directional data flow method. After that, when transmitting data in the given transmission period for retransmission, the terminal B  402  checks the retry count and lifetime of each of Data  2 -B and Data  3 -B as retransmission data, as in the terminal A  401 . After confirming that the upper limit of the retry count is not reached and the lifetime has not expired for both Data  2 -B and Data  3 -B, the terminal B  402  forms an aggregation frame by aggregating Data  2 -B and Data  3 -B as the retransmission data after an RAC frame and Block Ack frame while setting retry bits of Data  2 -B and Data  3 -B, and aggregating Data  5  as new data, and returns the aggregation frame when SIFS has elapsed, thereby performing the frame exchange sequence  408  for the first retransmission of the burst data. 
   When the aggregation frame returned from the terminal B  402  is received by the terminal A  401  in the frame exchange sequence  408  for the first retransmission of the burst data, the frame information identification unit  113  of the reception processor  105  of the terminal A  401  analyzes the bitmap of the reception statuses described in a Block Ack frame  409  transmitted from the terminal B  402 , and detects that Data  5 -A newly transmitted by the terminal A  401  in the frame exchange sequence  408  for the first retransmission of the burst data is not normally received. Then, when a bitmap of the reception statuses of the plurality of data frames aggregated after the Block Ack frame  409  is formed by using the frame information identification unit  113  and bitmap formation unit  114 , it is detected that Data  3 -B retransmitted by the terminal B  402  in the frame exchange sequence  408  for the first retransmission of the burst data is not normally received. The transmission/reception manager  110 , which has collected these pieces of information indicating the abnormal receptions, of the terminal A  401  determines that retransmission is necessary. The transmission/reception manager  110 , which has determined that retransmission is necessary, of the terminal A  401  notifies the packet transmissibility determination unit  107  that retransmission is to be performed, and the packet transmissibility determination unit  107  counts up the retry count of Data  5 -A as the retransmission data from the terminal A  401 , and confirms that the counted-up retry count has not reached the upper limit of the retry count of the data, and that the lifetime unique to the data has not expired. Since Data  5 -A whose retry count and lifetime are confirmed is data newly transmitted in the frame exchange sequence  408  for the first retransmission of the burst data, the upper limit of the retry count is of course not reached, and the lifetime has of course not expired. Accordingly, it is determined that retransmission is necessary. Then, the packet transmissibility determination unit  107  notifies the data transmitting/receiving method determination unit  109  of the frame length of a retransmission frame and the length of a new frame existing in the transmission queue, via the transmission/reception manager  110 , and the data transmitting/receiving method determination unit  109  determines that period of a frame exchange sequence  410  for the second retransmission of the burst data, which is necessary when data is retransmitted. The data transmitting/receiving method determination unit  109  notifies the transmission/reception manager  110  of the determined period of the frame exchange sequence  410  for the second retransmission of the burst data. The transmission/reception manager  110  determines whether the frame exchange sequence  410 , which is notified by the data transmitting/receiving method determination unit  109  and serves as a necessary period when data is retransmitted, for the second retransmission of the burst data can be transmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data. As shown in  FIG. 4 , if the frame exchange sequence  410  for the second retransmission of the burst data cannot be transmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data, the transmission/reception manager  110  interrupts the retransmission process, interrupts the burst data transmission/reception process by transmitting a Block Ack frame  411  when SIFS has elapsed after the frame exchange sequence  408  for the first retransmission of the burst data, and advances to a burst data frame exchange sequence  412  performed for another terminal by the bi-directional data flow method. In this case, it is already confirmed for Data  5 -A as an object of retransmission in the terminal A  401  that the retry count has not reached the upper limit of the retry count of the data and the lifetime unique to the data has not expired, so Data  5 -A is returned to the transmission queue in the transmission queue manager  106 . 
   The operation after the retransmission of the burst data is interrupted is not limited to the burst data transmission/reception process performed for another terminal by the aggregation method, and it is also possible to advance to, e.g., burst data transmission performed for another priority degree in the same terminal by the aggregation method, burst data transmission performed for another terminal by a method other than the aggregation method, burst data transmission performed for another priority degree in the same terminal by a method other than the aggregation method, QoS Cf-Poll frame transmission which initiates downlink TXOP transmission performed from a base station to a terminal by the HCCA method of IEEE 802.11e or uplink TXOP transmission performed by the HCCA method of IEEE 802.11e, or data transmission performed by an access method using CSMA/CA such as the DCF method of IEEE 802.11 or the EDCA method of IEEE 802.11e. Referring to  FIG. 4 , the interval between the Block Ack frame  411  and the burst data frame exchange sequence  412  performed for another terminal by the bi-directional data flow method is short. However, if the burst data frame exchange sequence  412  performed for another terminal by the aggregation method is the HCCA method, this interval can be an interval for performing PIFS carrier sense. If the burst data frame exchange sequence  412  performed for another terminal by the aggregation method is the EDCA method, this interval can be an interval for performing AIFS carrier sense and backoff processing. 
   Also, when the transmission/reception state manager  110  in the access controller  103  of the terminal A  401  determines whether the frame exchange sequence  410  for the second retransmission of the burst data can be transmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data, if the whole frame exchange sequence  410  for the second retransmission of the burst data cannot be transmitted but there is a time for transmitting and receiving only Data  5 -A to be retransmitted from the terminal A  401  and Data  3 -A to be retransmitted from the terminal B  402 , which are the data unsuccessfully transmitted in the frame exchange sequence  408  for the first retransmission of the burst data, retransmission is performed by using only the retransmission data without attaching any new data. If there is a time for transmitting only Data  5 -A as the retransmission data and Data  6 -A as new data from the terminal A  401 , only the data from the terminal A  401  is transmitted without using the bi-directional data flow method. That is, data transmission/reception can be performed within a transmissible range in accordance with the remaining time of the timer of the lifetime  403  for each frame exchange sequence of the burst data. 
   In this embodiment, as the method of selective retransmission, the Implicit Block Ack Request method proposed in IEEE 802.11n is used as a method of increasing the efficiency of the Block Ack method standardized by IEEE 802.11e. This is the method which omits a Block Ack Request frame which is necessary to receive a Block Ack frame indicating the reception status of transmission data from terminal B in the Block Ack method of IEEE 802.11e. Since the retransmission limiting method according to the present embodiment can be used regardless of the method of selective retransmission, it is unnecessary to use the Implicit Block Ack Request method as in this embodiment, and the existing Block Ack method of IEEE 802.11e may also be used. Also, in this embodiment, the number of data to be aggregated is  4  for both terminals A and B in the first frame exchange sequence, and  3  for the both in the first retransmission. However, the number of data to be aggregated does not limit the form of use of this embodiment, so the number of data to be aggregated can be variable or need not be the same for terminals A and B. 
   Although an IAC frame and RAC frame are exchanged at the start of data transmission in this embodiment, it is also possible to use a method in which an RTS frame and CTS frame are exchanged instead of an IAC frame and RAC frame or terminal A transmits a CTS-self frame, or to start aggregation frame transmission immediately after the data transmission right is acquired without performing any frame exchange using the IAC frame and the like. In addition, an IAC frame is used as a method by which terminal A gives a transmission period to terminal B, but another frame such as a QoS Cf-Poll frame may also be used as will be described later in the second embodiment, or the transmission period may also be described in a data frame without using any other frame. If no IAC frame is used at the head of each aggregation frame, no RAC frame is used at the head of an aggregation frame transmitted from terminal B, either. 
   As described above, for each transmission data which cannot be retransmitted within the remaining time of the timer of the lifetime  403  for each frame exchange sequence of burst data, the packet transmissibility determination unit  107  of the transmission data manager  102  of the wireless communication apparatus  101  determines whether to discard the transmission data by using the retry count and lifetime uniquely managed for the transmission data. The transmission data is returned to the transmission queue in the transmission queue manager  106 , if the timer of the lifetime  403  for each frame exchange sequence of burst data has expired, but the retry count uniquely managed for the transmission data has not reached the upper limit of the retry count, and the lifetime uniquely managed for the transmission data has not expired. If the retry count uniquely managed for the transmission data has exceeded the upper limit of the retry count or the lifetime uniquely managed for the transmission data has expired, the data is not returned to the transmission queue but discarded. 
   In this embodiment as described above, the retransmission of burst data in burst transmission can be limited for each frame exchange sequence of the burst data, so scheduling calculations can be performed by taking account of the retransmission of the burst data. It is also possible to secure necessary bands for different QoS requests from a plurality of terminals or a plurality of applications. 
   Second Embodiment 
   This embodiment is basically the same as the first embodiment except that the retry count for each frame exchange sequence of burst data is used instead of using the lifetime  403  for each frame exchange sequence of burst data to limit the retransmission of the burst data as explained in the first embodiment, and that a QoS Cf-Poll frame is used instead of an IAC frame and RAC frame by the bi-directional data flow method which is a piggy back type bi-directional communication method, so the differences from the first embodiment will be mainly explained below. 
   First, a communication method conforming to the bi-directional data flow method which is a piggy back type bi-directional communication method using a QoS Cf-Poll frame will be explained with reference to  FIG. 5 . Before data transmission, a terminal A  501  having acquired the transmission right after AIFS carrier sense and backoff processing or after PIFS carrier sense notifies a terminal B  502  that data transmission is to be performed by transmitting an RTS frame  503  to the terminal B  502 . The terminal B  502  returns a CTS frame  504  to the terminal A  501 , and confirms that the RTS frame  503  is received. After that, the terminal A  501  determines a period  506  to be given to the terminal B  502  by the bi-directional data flow method, and forms a QoS Cf-Poll frame  505  describing the period  506  to be given to the terminal B  502 . The terminal A  501  forms an aggregation frame by aggregating the QoS Cf-Poll frame  505  and Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A as data to be transmitted to the terminal B  502 , and transmits the aggregation frame to the terminal B  502 . The terminal B  502  having received the aggregation frame having the QoS Cf-Poll frame  505  attached to the head detects the period  506  to be given to the terminal B  502  from the QoS Cf-Poll frame  505 . The terminal B  502  forms a Block Ack frame  507  for returning the reception statuses of Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A as the received data, forms an aggregation frame by aggregating, after the Block Ack frame  507 , Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B as data to be transmitted to the terminal A  501 , and transmits the aggregation frame. In this case, the terminal B  502  forms an aggregation frame which does not exceed the period  506  to be given to the terminal B  502  by the QoS Cf-Poll frame  505 , as the aggregation frame to be returned. The terminal A  501  having received the aggregation frame returned from the terminal B  502  and having the Block Ack frame  507  attached to the head returns a Block Ack frame  508  containing the reception statuses of Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B transmitted from the terminal B  502 . When the terminal A  501  returns the Block Ack frame  508 , if both the data transmitted from the terminal A  501  and the data transmitted from the terminal B  502  are normally transmitted and no more data is transmitted from the terminal A  501 , the transmission process from the terminal A  501  can be completed by the transmission of the Block Ack frame  508 . Also, if an NAV (Network Allocation Vector) for performing virtual carrier sense to avoid transmission from other terminals is formed more than the transmission end time of the Block Ack frame  508  by the RTS frame  503  and CTS frame  504 , it is possible to use a method of clearing the NAV by transmitting a Cf-end frame when SIFS has elapsed after the transmission of the Block Ack frame  508 , in order to clear the NAV. 
   A case in which the retry count for each frame exchange sequence of burst data is used as the retransmission limiting method according to the present embodiment when retransmission in burst transmission is performed by the bi-directional data flow method as a piggy back type bi-directional communication method using a QoS CF-Poll frame will be explained below with reference to  FIGS. 1 and 6 . 
   In this embodiment, the retry count for each frame exchange sequence of burst data is used as the limitation on retransmission in burst transmission performed by the bi-directional data flow method as a piggy back type bi-directional communication method using a QoS Cf-Poll frame, instead of the lifetime  403  for each frame exchange sequence of burst data used in the first embodiment, and the upper limit of the retry count for each frame exchange sequence of burst data is 2. That is, burst data is retransmitted only once. However, the upper limit of the retry count for each frame exchange sequence of burst data is not limited to 2, and can be adjusted in accordance with the form of use. 
   When data is stored in a transmission queue in a transmission queue manager  106  of a transmission data manager  102  of a wireless communication apparatus  101  of a terminal A  601 , the transmission right is acquired by performing AIFS carrier sense and backoff processing or PIFS carrier sense by using a carrier sense unit  112  and backoff processor  108  in the same manner as in the first embodiment. After the transmission right is acquired, the transmission queue manager  106  transmits the number of data stored in the transmission queue and the transmission data to a packet transmissibility determination unit  107 . The packet transmissibility determination unit  107  confirms that the transmission time of each transmission data has not exceeded the lifetime uniquely managed for the transmission data, and that the retry count of each transmission data has not exceeded the retry limit for the transmission data. After confirming the lifetime and retry count of each transmission data, the packet transmissibility determination unit  107  transmits the number of data stored in the transmission queue and the transmission data to a transmission/reception state manager  110  in an access controller  103 . The transmission/reception state manager  110  notifies a data transmitting/receiving method determination unit  109  of the number of data stored in the transmission queue, and determines, e.g., whether to use the bi-directional data flow method, and whether to perform RTS-CTS frame exchange before transmission of an aggregation frame. In this embodiment, it is determined that the bi-directional data flow method is used and RTS-CTS frame exchange is performed. The transmission/reception state manager  110  notified of the determined data transmitting/receiving method by the data transmitting/receiving method determination unit  109  initializes the retry count for each frame exchange sequence of burst data (initializes the retry count to 0). After that, the transmission/reception state manager  110  instructs a frame formation/transmission processor  111  to transmit an RTS frame. The frame formation/transmission processor  111  having received the RTS frame transmission instruction forms an RTS frame, and transmits the formed RTS frame to a transmission processor  104 . The transmission processor  104  having received the RTS frame transmits it as an RTS frame  603  for initiating the bi-directional data flow method from the terminal A  601  to a terminal B  602 . 
   The terminal B  602  having received the RTS frame  603  returns a CTS frame  604  when SIFS has elapsed after the RTS frame  603  is received. As the frame formats of the RTS frame  603  and CTS frame  604 , normal frame formats standardized by IEEE 802.11 are used. Then, the transmission/reception state manager  110  of the terminal A  601  having received the CTS frame  604  is notified of the reception of the CTS frame  604  from a frame information identification unit  113  of a reception processor  105 . When starting a first burst data frame exchange sequence  605  by the bi-directional data flow method, the transmission/reception state manager  110  notifies the data transmitting/receiving method determination unit  109  of a data length to be transmitted. The data transmitting/receiving method determination unit  109  determines a transmission period to be given to the terminal B  602  when the bi-directional data flow method is used, and notifies the transmission/reception state manager  110  of the determined transmission period. The transmission/reception state manager  110  transmits, to the frame formation/transmission processor  111 , Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A as transmission data, and that transmission period to be given to the terminal B  602  when the bi-directional data flow method is used, which is determined by the data transmitting/receiving method determination unit  109 . The frame formation/transmission processor  111  forms a QoS Cf-Poll frame  606  describing the transmission period to be given to the terminal B  602  when the bi-directional data flow method is used, forms an aggregation frame by aggregating the QoS Cf-Poll frame  606  and Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A as the transmission data, and transmits the aggregation frame to the terminal B  602  by using the transmission processor  104 . As in the first embodiment, the terminal B  602  forms a Block Ack frame  607  describing the reception statuses of Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A, forms an aggregation frame by aggregating the Block Ack frame  607  and Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B as data to be transmitted to the terminal A  601 , and returns the aggregation frame to the terminal A  601 . In this case, the terminal B  602  forms a frame which does not exceed that transmission period to be given to the terminal B  602  when the bi-directional data flow method is used, which is described in the QoS Cf-Poll frame  606 , as the aggregation frame having the Block Ack frame  607  attached to the head. 
   In the first burst data frame exchange sequence  605  performed by the bi-directional data flow method, the terminal A  601  having received the aggregation frame formed by aggregating the Block Ack frame  607  and Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B from the terminal B  602  detects that Data  3 -A and Data  4 -A transmitted by the terminal A  601  and Data  2 -B and Data  3 -B transmitted by the terminal B  602  are transmission errors and must be retransmitted, as in the first embodiment. In this case, as in the first embodiment, the transmission/reception state manager  110  determines whether the first retransmission of the burst data is possible. The transmission/reception state manager  110  counts up the retry count for each frame exchange sequence of the burst data from 0 to 1, and checks whether the retry count has exceeded 2 as the upper limit of the retry count for each frame exchange sequence of the burst data. Since the retry count for each frame exchange sequence of the burst data has not exceeded 2 as the upper limit of the retry count, the first retransmission of the burst data is performed. 
   In a frame exchange sequence  608  for the first retransmission of the burst data, as in the first embodiment, the packet transmissibility determination unit  107  of the terminal A  601  checks the retry count and lifetime of each of Data  3 -A and Data  4 -A as the retransmission data and Data  5 -A as new transmission data, and transmits an aggregation frame formed by aggregating a Block Ack  609  describing the reception statuses of Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B received from the terminal B  602 , a QoS Cf-Poll frame  610  describing a period to be given to the terminal B  602  again, Data  3 -A and Data  4 -A as the retransmission data, and Data  5 -A as the new transmission data. The terminal B  602  having received the aggregation frame transmitted from the terminal A  601  in the frame exchange sequence  608  for the first retransmission of the burst data returns an aggregation frame formed by aggregating a Block Ack frame, Data  2 -B and Data  3 -B as the retransmission data, and Data  5 -B as new transmission data as in the first embodiment, thereby performing the frame exchange sequence  608  for the first retransmission of the burst data. 
   Then, after frame exchange is completed in the frame exchange sequence  608  for the first retransmission of the burst data, the transmission/reception state manager  110  of the terminal A  601  confirms transmission errors of Data  5 -A transmitted by the terminal A  601  and Data  5 -B transmitted by the terminal B  602 . If an access controller  12  of a wireless communication apparatus  15  determines that the second retransmission is necessary, the transmission/reception state manager  110  determines whether the second retransmission of the burst data is possible. 
   The transmission/reception state manager  110  counts up the retry count for each frame exchange sequence of the burst data from 1 to 2, and checks whether the retry count has exceeded 2 as the upper limit of the retry count for each frame exchange sequence of the burst data. Since the retry count for each frame exchange sequence of the burst data is equal to 2 as the upper limit of the retry count, the burst data retransmission process is interrupted. In this case, the terminal A  601  interrupts the burst data transmission/reception process by transmitting a Block Ack frame  612 , instead of a frame exchange sequence  611  for the second retransmission of the burst data, when SIFS has elapsed after the frame exchange sequence  608  for the first retransmission of the burst data, and advances to a burst data frame exchange sequence  613  performed for another terminal by the bi-directional data flow method using a QoS Cf-Poll frame. Since it is already confirmed for Data  5 -A as an object of retransmission in the terminal A  601  that the retry count has not reached the upper limit of the retry count and the lifetime unique to the data has not expired, Data  5 -A is returned to the transmission queue in the transmission queue manager  106 . 
   The operation after the retransmission of the burst data is interrupted is not limited to the burst data transmission/reception process performed for another terminal by the bi-directional data flow method using a QoS Cf-Poll frame, and it is also possible to advance to, e.g., burst data transmission performed for another priority degree in the same terminal by the aggregation method, burst data transmission performed for another terminal by a method other than the aggregation method, burst data transmission performed for another priority degree in the same terminal by a method other than the aggregation method, QoS Cf-Poll frame transmission which initiates downlink TXOP transmission performed from a base station to a terminal by the HCCA method of IEEE 802.11e or uplink TXOP transmission performed by the HCCA method of IEEE 802.11e, or data transmission performed by an access method using CSMA/CA such as the DCF method of IEEE 802.11 or the EDCA method of IEEE 802.11e. 
   In this embodiment, as the method of selective retransmission, the Implicit Block Ack Request method proposed in IEEE 802.11n is used as a method of increasing the efficiency of the Block Ack method standardized by IEEE 802.11e. This is the method which omits a Block Ack Request frame which is necessary to receive a Block Ack frame indicating the reception status of transmission data from terminal B in the Block Ack method of IEEE 802.11e. Since the retransmission limiting method according to the present embodiment can be used regardless of the method of selective retransmission, it is unnecessary to use the Implicit Block Ack Request method as in this embodiment, and the existing Block Ack method of IEEE 802.11e may also be used. Also, in this embodiment, the number of data to be aggregated is 4 for both terminals A and B in the first frame exchange sequence, and 3 for the both in the first retransmission. However, the number of data to be aggregated does not limit the form of use of this embodiment, so the number of data to be aggregated can be variable or need not be the same for terminals A and B. 
   Although an RTS frame and CTS frame are exchanged at the start of data transmission in this embodiment, it is also possible to use a method in which an IAC frame and RAC frame are exchanged instead of an RTS frame and CTS frame or terminal A transmits a CTS-self frame, or to start aggregation frame transmission immediately after the data transmission right is acquired without performing any frame exchange using the RTS frame and the like. In addition, a QoS Cf-Poll frame is used as a method by which terminal A gives a transmission period to terminal B, but it is also possible to use an IAC frame as in the first embodiment, or describe the type of the first data frame of an aggregation frame as a Poll+ Data type frame without aggregating any other frame. 
   Also, although the method of exchanging one aggregation frame in turn between terminals A and B is explained in this embodiment, it is also possible to give a transmission period to terminal B after a plurality of aggregation frames are transmitted from terminal A by burst transmission with an SIFS interval or an interval shorter than that, and transmit a plurality of aggregation frames from terminal B given the transmission period by burst transmission which falls within the range of the given transmission period. In this case, however, terminal A aggregates a QoS Cf-Poll frame which gives the transmission period to the last aggregation frame of the plurality of aggregation frames to be transmitted by burst transmission, or places information which gives terminal B the transmission period in the last aggregation frame. 
   Alternatively, it is also possible to separate a control frame such as an acknowledgement frame from the aggregation frame, and transmit an aggregation frame formed by aggregating a plurality of data frames and the control frame by burst transmission. 
   As described above, for each transmission data which cannot be retransmitted because the data has exceeded the upper limit of the retry count for each frame exchange sequence of burst data, the packet transmissibility determination unit  107  of the transmission data manager  102  of the wireless communication apparatus  101  determines whether to discard the transmission data by using the retry count and lifetime uniquely managed for the transmission data. The transmission data is returned to the transmission queue in the transmission queue manager  106 , if the data has exceeded the upper limit of the retry count for each frame exchange sequence of the burst data, but the retry count uniquely managed for the transmission data has not exceeded the upper limit of the retry count, and the lifetime uniquely managed for the transmission data has not expired. If the retry count uniquely managed for the transmission data has exceeded the upper limit of the retry count or the lifetime uniquely managed for the transmission data has expired, the data is not returned to the transmission queue but discarded. 
   In this embodiment as described above, the retransmission of burst data in burst transmission can be limited for each frame exchange sequence of the burst data, so scheduling calculations can be performed by taking account of the retransmission of the burst data. It is also possible to secure necessary bands for different QoS requests from a plurality of terminals or a plurality of applications. 
   Third Embodiment 
   In this embodiment, a retransmission process and retransmission limiting method in a case in which no transmission error occurs in data transmitted by terminal A, and a transmission error occurs in only data transmitted by terminal B, when it is determined whether to perform burst data retransmission by the bi-directional data flow method using a QoS Cf-Poll frame explained in the second embodiment, will be described below. 
   In this embodiment, a method of limiting retransmission by using the retry count for each frame exchange sequence of burst data as in the second embodiment will be explained. Note that although the retry count for each frame exchange sequence of burst data is used in the retransmission limiting method of this embodiment, it is also possible to use the lifetime instead of the retry count as in the first embodiment. 
   When this embodiment is compared with the second embodiment, transmission errors occur in data transmitted by terminal A in the second embodiment, but no such error occurs in this embodiment. Therefore, this embodiment differs from the second embodiment in the part of processing which determines whether to perform retransmission. However, the rest is basically the same as the second embodiment, so the difference from the second embodiment will be mainly explained. The basic configuration of a wireless communication apparatus is the same as shown in  FIG. 1 . The embodiment will be described below with reference to  FIGS. 1 ,  7 , and  8 . 
     FIG. 7  is a view for explaining a retransmission limiting method using the retry count for each frame exchange sequence of burst data in a case in which if no error occurs in transmission data from a terminal A  701  and transmission data from terminal B is generated in burst transmission performed by the bi-directional data flow method using a QoS Cf-Poll frame, new data is transmitted from terminal A and the data is retransmitted from terminal B.  FIG. 8  is a view for explaining a retransmission limiting method using the retry count for each frame exchange sequence of burst data in a case in which if no error occurs in transmission data from terminal A and transmission data from terminal B is generated in burst transmission performed by the bi-directional data flow method using a QoS Cf-Poll frame, no new data is transmitted from terminal A and the data is retransmitted from terminal B. 
   In this embodiment, the upper limit of the retry count for each frame sequence of burst data is  2 , and burst data is retransmitted only once, as in the second embodiment. However, the upper limit of the retry count for each frame exchange sequence of burst data is not limited to  2 , and can be adjusted in accordance with the form of use. 
   As shown in  FIG. 7 , when a first burst data frame exchange sequence  703  performed by the bi-directional data flow method using a QoS Cf-Poll frame starts, a transmission/reception state manager  110  of an access controller  103  of the terminal A  701  initializes the retry count for each frame exchange sequence of burst data (initializes the retry count to 0). If all data transmitted by the terminal A  701  are normally received by a terminal B  702  in the first burst data frame exchange sequence  703  performed by the bi-directional data flow method, a Block Ack frame  704  formed by the terminal B  702  indicates that Data  1 -A, Data  2 -A, Data  3 -A, and Data  4 -A transmitted by the terminal A  701  are normally received. The transmission/reception state manager  110  of the terminal A  701  having received an aggregation frame returned by the terminal B  702  in the first burst data frame exchange sequence  703  detects from the Block Ack frame  704  that all the data transmitted by the terminal A  701  are normally received and no retransmission is necessary. However, if Data  2 -B and Data  3 -B of Data  1 -B, Data  2 -B, Data  3 -B, and Data  4 -B transmitted by the terminal B  702  are not received, the transmission/reception state manager  110  of the terminal A  701  detects from a reception status bitmap formed by a bitmap formation unit  114  in a reception processor  105  of the terminal A  701  that it is necessary to retransmit Data  2 -B and Data  3 -B to be returned to the terminal B  702 . Accordingly, the transmission/reception state manager  110  of the terminal A  701  determines that the first retransmission of the burst data is necessary in order for the terminal B  702  to perform a retransmission process, and determines whether the first retransmission of the burst data is possible as in the second embodiment. 
   The transmission/reception state manager  110  counts up the retry count for each frame exchange sequence of the burst data from 0 to 1, and checks whether the retry count has exceeded 2 as the upper limit of the retry count for each frame exchange sequence of the burst data. Since the retry count for each frame exchange sequence of the burst data has not exceeded 2 as the upper limit of the retry count, the first retransmission of the burst data is performed. 
   In a frame exchange sequence  705  for the first retransmission of the burst data, a data transmitting/receiving method determination unit  109  of the terminal A  701  determines a transmission period to be allocated to the terminal B  702 . A frame formation/transmission processor  111  notified of that transmission period to be allocated to the terminal B  702 , which is determined by the data transmitting/receiving method determination unit  109 , forms a QoS Cf-Poll frame, aggregates, after this QoS Cf-Poll frame, a Block Ack  706  describing the reception statuses of the data transmitted from the terminal B  702  in the first burst data frame exchange sequence  703 , forms an aggregation frame by further aggregating new data Data  5 -A, Data  6 -A, and Data  7 -A to be transmitted to the terminal B  702 , and transmits the aggregation frame. The terminal B  702  which is given the transmission period for retransmission in the frame exchange sequence  705  for the first retransmission of the burst data checks the retry count and lifetime of each retransmission data as in the second embodiment, aggregates, after a Block Ack frame, Data  2 -B and Data  3 -B for each of which it is confirmed that the upper limit of the retry count is not reached and the lifetime has not expired, forms an aggregation frame by further aggregating new data Data  5 -B, and transmits the aggregation frame to the terminal A  701 . 
   Then, after frame exchange is completed in the frame exchange sequence  705  for the first retransmission of the burst data, if the transmission/reception state manager  110  of the terminal A  701  determines that the data transmitted by the terminal A  701  are normally received, transmission errors occur in the data transmitted by the terminal B  702 , and the second retransmission is necessary, as before the start of the frame exchange sequence  705  for the first retransmission of the burst data, the transmission/reception state manager  110  determines whether the second retransmission of the burst data is possible. 
   The transmission/reception state manager  110  counts up the retry count for each frame exchange sequence of the burst data from 1 to 2, and checks whether the retry limit has exceeded 2 as the upper limit of the retry count for each frame exchange sequence of the burst data. Since the retry count for each frame exchange sequence of the burst data is equal to 2 as the upper limit of the retry count, the transmission/reception state manager  110  interrupts the burst data retransmission process, interrupts the burst data transmission/reception process by transmitting a Block Ack frame  708  when SIFS has elapsed after the frame exchange sequence  705  for the first retransmission of the burst data, and advances to a burst data frame exchange sequence  709  performed for another terminal by the bi-directional data flow using a QoS Cf-Poll frame. The operation after the retransmission of the burst data is interrupted is not limited to the burst data transmission/reception process performed for another terminal by the bi-directional data flow method using a QoS Cf-Poll frame, and it is also possible to advance to, e.g., burst data transmission performed for another priority degree in the same terminal by the aggregation method, burst data transmission performed for another terminal by a method other than the aggregation method, burst data transmission performed for another priority degree in the same terminal by a method other than the aggregation method, QoS Cf-Poll frame transmission which initiates downlink TXOP transmission performed from a base station to a terminal by the HCCA method of IEEE 802.11e or uplink TXOP transmission performed by the HCCA method of IEEE 802.11e, or data transmission performed by an access method using CSMA/CA such as the DCF method of IEEE 802.11 or the EDCA method of IEEE 802.11e. 
   Also, as shown in  FIG. 8 , in a case in which if no error occurs in transmission data of a terminal A  801  which has initiated burst data transmission by the bi-direction data flow method using a QoS Cf-Poll frame, errors occur in only transmission data of a terminal B  802 , and there is no new transmission data from the terminal A  801 , a retransmission process is performed to give a transmission period to the terminal B  802  in order to retransmit the data which is transmitted from the terminal B  802  but is not received, this band allocation for retransmission may also be performed by the retransmission limiting method using the retry count for each frame exchange sequence of the burst data in the same manner as in  FIG. 7 . 
   After a first burst data frame exchange sequence  803  performed by the bi-directional data flow method using a QoS Cf-Poll frame, if no error occurs in data transmitted from the terminal A  801  and Data  2 -B and Data  3 -B transmitted from the terminal B  802  are transmission errors, a transmission/reception state manager  110  of the terminal A  801  determines whether to perform a retransmission process for giving the terminal B  802  a transmission period for retransmission. If no new transmission data exists in the terminal A  801  when the burst data retransmission process is to be performed, after the first burst data frame exchange sequence  803  performed by the bi-directional data flow method using a QoS Cf-Poll frame is completed, the terminal A  801  transmits an aggregation frame formed by aggregating a Block Ack frame  804  and a QoS Cf-Poll frame  805  describing the transmission period to be allocated to the terminal B  802 , and the terminal B  802  returns an aggregation frame formed by aggregating Data  2 -B and Data  3 -B as the retransmission data and Data  5 -B as new data, thereby performing a frame exchange sequence  806  for the first retransmission of the burst data. As explained with reference to  FIG. 7 , the transmission/reception state manager  110  of the terminal A  801  can limit the retransmission by using the retry count for each frame exchange sequence of the burst data in the retransmission limiting method in this case as well. After the frame exchange sequence  806  for the first retransmission of the burst data, therefore, the transmission/reception state manager  110  interrupts the burst data transmission/reception process by transmitting a Block Ack frame  808  when SIFS has elapsed after the frame exchange sequence  806  for the first retransmission of the burst data, without performing a frame exchange sequence  807  for the second retransmission of the burst data, and advances to a burst data frame exchange sequence  809  performed for another terminal by the bi-directional data flow method using a QoS Cf-Poll frame. The operation after the retransmission of the burst data is interrupted is not limited to the burst data transmission/reception process performed for another terminal by the bi-directional data flow method using a QoS Cf-Poll frame, and it is also possible to advance to, e.g., burst data transmission performed for another priority degree in the same terminal by the aggregation method, burst data transmission performed for another terminal by a method other than the aggregation method, burst data transmission performed for another priority degree in the same terminal by a method other than the aggregation method, QoS Cf-Poll frame transmission which initiates downlink TXOP transmission performed from a base station to a terminal by the HCCA method of IEEE 802.11e or uplink TXOP transmission performed by the HCCA method of IEEE 802.11e, or data transmission performed by an access method using CSMA/CA such as the DCF method of IEEE 802.11 or the EDCA method of IEEE 802.11e. 
   Although a method of limiting retransmission by using the retry count for each frame exchange sequence of burst data is explained in this embodiment, it is also possible to use the lifetime for each frame exchange sequence of burst data as in the first embodiment. When this lifetime is used, if the remaining period of the lifetime for each frame exchange sequence of burst data is short, it is also possible to use, when a retransmission process is performed, a method by which an aggregation frame formed by aggregating only the Block Ack frame  804  and QoS Cf-Poll frame  805  is transmitted without transmitting any new data from terminal A as shown in  FIG. 8 , only a period during which data having a reception error and required to be retransmitted can be transmitted is given as the transmission period to be allocated to the terminal B  802 , and an aggregation frame formed by aggregating only the retransmission data is returned. 
   In this embodiment, as the method of selective retransmission, the Implicit Block Ack Request method proposed in IEEE 802.11n is used as a method of increasing the efficiency of the Block Ack method standardized by IEEE 802.11e. This is the method which omits a Block Ack Request frame which is necessary to receive a Block Ack frame indicating the reception status of transmission data from terminal B in the Block Ack method of IEEE 802.11e. Since the retransmission limiting method according to the present embodiment can be used regardless of the method of selective retransmission, it is unnecessary to use the Implicit Block Ack Request method as in this embodiment, and the existing Block Ack method of IEEE 802.11e may also be used. Also, in this embodiment, the number of data to be aggregated is 4 for both terminals A and B in the first frame exchange sequence, and 3 for the both in the first retransmission. However, the number of data to be aggregated does not limit the form of use of this embodiment, so the number of data to be aggregated can be variable or need not be the same for terminals A and B. 
   Although an RTS frame and CTS frame are exchanged at the start of data transmission in this embodiment, it is also possible to use a method in which an IAC frame and RAC frame are exchanged instead of an RTS frame and CTS frame or terminal A transmits a CTS-self frame, or to start aggregation frame transmission immediately after the data transmission right is acquired without performing any frame exchange using the RTS frame and the like. In addition, a QoS Cf-Poll frame is used as a method by which terminal A gives a transmission period to terminal B, but it is also possible to use an IAC frame as in the first embodiment, or describe data by using a duration/ID field of a Block Ack frame without aggregating any other frame. 
   In this embodiment as described above, even when no error occurs in transmission data of terminal A and an error occurs in only transmission data of terminal B in data transmission/reception performed by the bi-directional data flow method, a retransmission band can be allocated to terminal B, thereby reducing the process by which terminal B reacquires the transmission right for retransmission. 
   Also, the retransmission of burst data in burst transmission can be limited for each frame exchange sequence of the burst data, so scheduling calculations can be performed by taking account of the retransmission of the burst data. It is also possible to secure necessary bands for different QoS requests from a plurality of terminals or a plurality of applications. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.