Abstract:
A radio transmission apparatus and a radio transmission method for readily controlling retransmission timing presets a frame cycle for retransmission, and transmits only packets for which no acknowledgement of receipt has been received within the frame cycle as a reply from a receiving apparatus to a transmitting apparatus. Thus, timing for retransmission can be readily determined. Also, the retransmission timing is determined based on when a packet is actually transmitted. Therefore, multiple acknowledgements of receipt can be returned as a combined reply.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a radio transmission apparatus and a radio transmission method for transmitting various information by a radio signal, for example, between a plurality of communication terminals. 
   As a conventional method of retransmission control in radio transmission, a method has been used which starts a timer after transmitting information, and retransmits the information whose receipt acknowledging information has not been transmitted from an information receiver before time-out of the timer. 
   Also, consideration has recently been given to a method which packetizes information to be transmitted by an information transmitter into predetermined size and transmits resulting packets by radio, and reconstructs the original information by collecting the packets at an information receiver. 
   The method has been considered for use in conjunction with a selective retransmission type automatic retransmission control method (SR-ARG system), which transmits information that the information receiver has successfully received a packet to the information transmitter as receipt acknowledging information, and selects and retransmits only an unreceived packet from the information transmitter. 
   In addition, as a conventional method of packet transmission, a retransmission method capable of dealing with a burst error in a transmission line has been realized which, in retransmission control, waits for a reply of receipt acknowledging information from the information receiver over a certain long period of time, and then retransmits a packet whose receipt acknowledging information has not been received. 
   Furthermore, as a conventional technique, a method has been proposed which prevents unlimited retransmissions of packets by setting a finite number of retransmissions. 
   By setting such a limit on the number of retransmissions, it is possible to use the same sequence number repeatedly, and thus make efficient transmission. 
   Furthermore, when using the conventional selective retransmission type automatic retransmission control method, by returning a certain amount of receipt acknowledging information in one transmission, it is possible to reduce packets, which represent the number of pieces of information flowing in a radio transmission line, and thus reduce information traffic. 
   Such conventional retransmission control methods need to start a timer every time information is transmitted. Therefore, when information is packetized for transmission, a timer needs to be started for each packet. 
   Also, with a method of retransmission after waiting for a certain long period of time, when a time for retransmission is to be controlled by software, it is difficult for the software to determine that an access right on a transmission line has been obtained. Therefore, there occurs a time difference between a time when a timer is started and a time when a packet is actually transmitted, and thus the time when a timer is started cannot be used for precise retransmission control. 
   In addition, the conventional retransmission method using a timer needs to handle a time of a retransmitted packet. Therefore, a timer needs to be started for each packet so as to handle its time. 
   Moreover, in addition to control of a time for retransmission, it is necessary to handle a time for discarding a packet whose receipt acknowledging information has not been received after repeated retransmissions. 
   Furthermore, when using the conventional selective retransmission type automatic retransmission control method and returning a certain amount of receipt acknowledging information in one transmission, it is necessary to define a time for integrating the receipt acknowledging information. This reduces a degree of freedom in designing transmission apparatus, and makes it impossible to secure compatibility between apparatus of different manufacturers. 
   Furthermore, even if the time for integrating the receipt acknowledging information is defined, the receipt acknowledging information cannot be returned unless an access control right is obtained. Therefore, a time required obtaining the access control right needs to be set as a redundant time, and thus the time for integrating the receipt acknowledging information needs to be reduced in effect. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above, and it is accordingly an object of the present invention to provide a radio transmission apparatus and a radio transmission method that can readily control retransmission timing. 
   According to a first aspect of the invention, there is provided a radio transmission method for transmitting a packet from a radio transmission apparatus serving as an information transmitter to a radio transmission apparatus serving as an information receiver, returning receipt acknowledging information of a received packet from the radio transmission apparatus serving as the information receiver to the radio transmission apparatus serving as the information transmitter after transmission of information, and retransmitting an unreceived packet from the radio transmission apparatus serving as the information transmitter to the radio transmission apparatus serving as the information receiver in a wireless network, the wireless network being formed with a plurality of transmission apparatus serving as communication stations, the radio transmission method including the steps of: 
   on a side of the radio transmission apparatus serving as the information transmitter, 
   setting a predetermined transmission frame cycle; 
   presetting a frame cycle for retransmission; and 
   automatically retransmitting only a packet whose receipt acknowledging information has not been received on arrival of the frame cycle for retransmission. 
   With this configuration, the radio transmission method according to the present invention predetermines a frame cycle for retransmission, and retransmits only a packet whose receipt acknowledging information has not been received on arrival of the frame cycle. The radio transmission method according to the present invention thereby eliminates the need for starting a timer after transmitting information and controlling the timer for each packet as in the conventional method. Therefore, it is possible to readily determine timing for retransmission. In addition, the retransmission timing is determined on the basis of timing in which a packet is actually transmitted. Therefore, the radio transmission method according to the present invention provides a most desirable radio transmission method allowing pieces of receipt acknowledging information to be combined into one reply. 
   According to a second aspect of the invention, there is provided a radio transmission method for transmitting a packet from a radio transmission apparatus serving as an information transmitter to a radio transmission apparatus serving as an information receiver, returning receipt acknowledging information of a received packet from the radio transmission apparatus serving as the information receiver to the radio transmission apparatus serving as the information transmitter after transmission of information, and retransmitting an unreceived packet from the radio transmission apparatus serving as the information transmitter to the radio transmission apparatus serving as the information receiver in a wireless network, the wireless network being formed with a plurality of transmission apparatus serving as communication stations, the radio transmission method including the steps of: 
   on a side of the radio transmission apparatus serving as the information transmitter, 
   setting a predetermined transmission frame cycle; 
   entering a sequence number of a last packet transmitted in the frame cycle as a transmission pointer value of the frame; and 
   referring to the transmission pointer value of a frame cycle for retransmission in each the frame cycle and automatically retransmitting only a packet whose receipt acknowledging information has not been received. 
   With this configuration, the radio transmission method according to the present invention enters a sequence number of a last packet transmitted in the frame cycle as a transmission pointer value of the frame, refers to a transmission pointer value of a frame cycle for retransmission in each frame cycle, and automatically retransmits only a packet whose receipt acknowledging information has not been received. Thus, it is possible to readily determine timing for retransmission. 
   Preferably, in a radio transmission method according to a first aspect of the invention, the frame cycle for retransmission is preset to an arbitrary frame cycle depending on size of an asynchronous transmission area available for asynchronous transmission in a radio transmission line allowing band-reserved transmission or band-secured transmission. 
   With this configuration, the radio transmission method according to the present invention can set a retransmission cycle arbitrarily. Therefore, it is possible to change retransmission timing freely according to traffic of the transmission line, and thus make retransmission efficiently according to a condition of the transmission line. 
   Preferably, in a radio transmission method according to a first aspect of the invention, the predetermined number of retransmissions are set, and then retransmission is made the number of retransmissions. 
   With this configuration, the radio transmission method according to the present invention can set the number of retransmissions arbitrarily. Therefore, it is possible to set the number of retransmissions arbitrarily according to packets to be transmitted and traffic of the transmission line, and thus make retransmission efficiently. 
   Preferably, in a radio transmission method according to a first aspect of the invention, a frame cycle for discarding unreceived packets is preset, and a packet whose receipt acknowledging information has not been returned until the frame cycle is discarded. 
   With this configuration, the radio transmission method according to the present invention presets a frame cycle for discarding unreceived packets, and discards a packet whose receipt acknowledging information has not been returned until the frame cycle. Therefore, it is possible to prevent unnecessary retransmission. In addition, by repeatedly using a buffer area for storing packets for retransmission and a sequence number, it is possible to reduce processing. 
   Preferably, in a radio transmission method according to a second aspect of the invention, the sequence number of the last packet transmitted in the frame cycle is entered as the transmission pointer value of the frame; and the transmission pointer value of a frame cycle for discarding packets is referred to in each the frame cycle and a packet whose receipt acknowledging information has not been received is discarded. 
   With this configuration, the radio transmission method according to the present invention enters a sequence number of a last packet transmitted in the frame cycle as a transmission pointer value of the frame, and discards a packet whose receipt acknowledging information has not been received by referring to a transmission pointer value of a frame cycle to discard the packet in each frame cycle. In addition, by repeatedly using a buffer area for storing packets for retransmission and a sequence number, it is possible to reduce processing. 
   According to a third aspect of the invention, there is provided a radio transmission apparatus for transmitting information in a wireless network, the wireless network being formed with a plurality of communication apparatus serving as communication stations, the radio transmission apparatus including: 
   packetizing means for packetizing asynchronous information into packets as predetermined information units on the wireless network; 
   transmitting means for transmitting the packets under predetermined access control; 
   receiving means for receiving receipt acknowledging information from a radio transmission apparatus serving as an information receiver; 
   frame cycle setting means for setting a predetermined transmission frame cycle; 
   timing means for timing the frame cycle; 
   retransmission frame cycle setting means for presetting a frame cycle for retransmission; and 
   retransmitting means for automatically retransmitting only a packet whose receipt acknowledging information has not been received on arrival of the frame cycle for retransmission. 
   With this configuration, the radio transmission apparatus according to the present invention has a function of setting a predetermined frame cycle and presetting a frame cycle for retransmission, and has a function of retransmitting only a packet whose receipt acknowledging information has not been received on arrival of the frame cycle. Therefore, it is possible to realize a radio transmission apparatus capable of simple retransmission control. 
   According to a fourth aspect of the invention, there is provided a radio transmission apparatus for transmitting information in a wireless network, the wireless network being formed with a plurality of communication apparatus serving as communication stations, the radio transmission apparatus including: 
   packetizing means for packetizing asynchronous information into packets as predetermined information units on the wireless network; 
   transmitting means for transmitting the packets under predetermined access control; 
   receiving means for receiving receipt acknowledging information from a radio transmission apparatus serving as an information receiver; 
   frame cycle setting means for setting a predetermined transmission frame cycle; 
   transmission pointer recording means for recording a sequence number of a last packet transmitted in the frame cycle as a transmission pointer value of the frame; 
   timing means for timing the frame cycle; 
   retransmission frame cycle setting means for presetting a frame cycle for retransmission; and 
   retransmitting means for referring to the transmission pointer value of the frame cycle for retransmission in each the frame cycle and automatically retransmitting only a packet whose receipt acknowledging information has not been received. 
   With this configuration, the radio transmission apparatus according to the present invention has a function of setting a predetermined frame cycle and recording a sequence number of a last packet transmitted in the frame cycle as a transmission pointer value of the frame, and has a function of automatically retransmitting only a packet whose receipt acknowledging information has not been received from a transmitter of the information by referring to the transmission pointer value of the frame cycle for retransmission in each frame cycle. Therefore, it is possible to realize a radio transmission apparatus capable of simple retransmission control. 
   According to a fifth aspect of the invention, there is provided a radio transmission apparatus for transmitting information in a wireless network, the wireless network being formed with a plurality of communication apparatus serving as communication stations, the radio transmission apparatus including: 
   packetizing means for packetizing asynchronous information into packets as predetermined information units on the wireless network; 
   transmitting means for transmitting the packets under predetermined access control; 
   receiving means for receiving receipt acknowledging information from a radio transmission apparatus serving as an information receiver; 
   frame cycle setting means for setting a predetermined transmission frame cycle; 
   timing means for timing the frame cycle; 
   discarding frame cycle setting means for presetting a frame cycle for discarding packets; and 
   discarding means for discarding a packet whose receipt acknowledging information has not been received on arrival of the frame cycle for discarding packets. 
   With this configuration, the radio transmission apparatus according to the present invention has a function of setting a predetermined frame cycle and presetting a frame cycle for discarding unreceived packets, and discards a packet whose receipt acknowledging information has not been received on arrival of the frame cycle. In addition, by repeatedly using a buffer area for storing packets to be discarded and a sequence number, it is possible to reduce processing. 
   The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing a configuration of a wireless network applied to an embodiment of the present invention; 
       FIG. 2  is a block diagram showing a configuration of a radio transmission apparatus; 
       FIG. 3  is a diagram showing a configuration of a radio transmission frame; 
       FIG. 4  is a diagram showing a sequence of transmission of asynchronous information; 
       FIG. 5  is a diagram showing an arrangement of a transmission pointer control table; 
       FIG. 6  is a flowchart of asynchronous transmission; 
       FIG. 7  is a flowchart of packet transmission processing; 
       FIG. 8  is a flowchart of processing at an end of a frame; 
       FIG. 9  is a flowchart of processing for receiving receipt acknowledging (ACK) information; 
       FIG. 10  is a flowchart of packet retransmission processing; 
       FIG. 11  is a flowchart of processing for discarding a packet; and 
       FIG. 12  is a flowchart of processing for receiving a packet. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will hereinafter be described. 
   A radio transmission method according to the present embodiment as a method for control of automatic retransmission of packets provides a transmission frame cycle, sets a frame cycle for retransmission in advance, handles a sequence number of a last packet transmitted in the frame cycle as a transmission pointer, and retransmits only a packet whose receipt acknowledging information has not been received on arrival of a retransmission frame cycle. 
   The present embodiment will hereinafter be described.  FIG. 1  is a diagram showing a configuration of a network system to which the radio transmission method according to the present embodiment is applied. 
   As shown in  FIG. 1 , for example, a radio transmission apparatus  11  is wired to a personal computer  1  and a printer output apparatus  2  via a cable or the like. Similarly, a radio transmission apparatus  12  is wired to a VTR  3  via a cable or the like. Similarly, a radio transmission apparatus  13  is wired to a set top box  4  and a telephone apparatus  5  via a cable or the like. Similarly, a radio transmission apparatus  14  is wired to a television receiver  6  and a game apparatus  7  via a cable or the like. 
   Thus, the apparatus are connected to their respective radio transmission apparatus, and the radio transmission apparatus form a network  10 . 
   In this case, the radio transmission apparatus  11  to  14  are associated with each other as communication stations # 1  to # 4 , respectively, thus forming a wireless network. 
   The radio transmission apparatus  14  can be present at a center of the network  10  to be thereby capable of communication with all of the other communication apparatus. Accordingly, for convenience, the radio transmission apparatus  14  serves as a control station of the network  10  to define a frame cycle, send a predetermined access control signal, and handle band reserving information. The other radio transmission apparatus  11  to  13  serve as communication stations. 
     FIG. 2  shows a configuration of the radio transmission apparatus  11  to  14  forming the communication stations. 
   In this case, the radio transmission apparatus  11  to  14  basically have a common configuration. The radio transmission apparatus  11  to  14  each have an antenna  21  for transmission and reception, and a radio transmission processing unit  22  connected to the antenna  21  for performing radio transmission processing and radio reception processing. Thereby the radio transmission apparatus  11  to  14  can each make radio transmission with the other transmission apparatus. 
   In this case, a transmission method using a multicarrier signal referred to as an OFDM (Orthogonal Frequency Division Multiplex) method, for example, is used as a transmission method for transmission and reception by the radio transmission processing unit  22  in this example. A very high frequency band (for example a 5-GHz band) is used as frequencies for transmission and reception. 
   In this case, a relatively weak output is set as transmission output; for indoor use, for example, the output is set so as to enable radio transmission for a relatively short distance of a few meters to a few tens of meters. The output may be adjusted as required. 
   The radio transmission processing unit  22  has a function of detecting a specific frequency carrier on a radio transmission line and a function of detecting a synchronizing signal. When the radio transmission processing unit  22  has received the synchronizing signal, the radio transmission processing unit  22  receives an information portion succeeding the synchronizing signal. 
   The radio transmission apparatus further includes: a reception control processing unit  23 C for reception and decoding of various transmission information of a signal received by the radio transmission processing unit  22 ; a buffer memory  23 A for storing packet information required to be transmitted by the radio transmission processing unit  22 ; and a transmission buffer  23 B for storing a packet that may be transmitted after an access control right is obtained. 
   The radio transmission apparatus further includes an information conversion processing unit  24  for carrying out data conversion of a packet information signal of the signal received by the reception control processing unit  23 C, and also making data conversion into packet information to be stored in the buffer memory  23 A for transmission by the radio transmission processing unit  22 . 
   Furthermore, the data converted by the information conversion processing unit  24  is supplied to a connected apparatus  29  via an interface unit  25 , and data supplied from the connected apparatus  29  is supplied to the information conversion processing unit  24  via the interface unit  25  to be subjected to conversion processing. 
   In this case, an external interface of the interface unit  25  of the radio transmission apparatus is configured to be able to transmit and receive audio and video information, or various data information to and from the connected apparatus  29  via a high-speed serial bus  28  in IEEE1394 format, for example. 
   Alternatively, the radio transmission apparatus may be incorporated within the body of the connected apparatus  29 . 
   Each part within each of the radio transmission apparatus is configured to perform processing under control of a control unit  26  formed by a microcomputer or the like. 
   Information captured by the information conversion processing unit  24  via the interface unit  25  which information is required to be transmitted asynchronously is packetized into predetermined fragment size, and packets of up to a receipt acknowledging (ACK) reception pointer value −1 to be described later are stored in the buffer memory  23 A as packet information. 
   Packet information from a transmission pointer value to sequence window size, which information can be transmitted by an access control right to be described later, is stored from the buffer memory  23 A into the transmission buffer  23 B. 
   When the signal decoded by the reception control processing unit  23 C of the transmission apparatus is packet information directed to the transmission apparatus itself, the packet information is stored in the information conversion processing unit  24 . Also, the control unit  26  makes determination, constructs receipt acknowledging (ACK) information, and stores the receipt acknowledging (ACK) information as a packet in the transmission buffer  23 B. 
   When the signal decoded by the reception control processing unit  23 C of the transmission apparatus is receipt acknowledging (ACK) information, the receipt acknowledging (ACK) information is stored in the control unit  26 . The control unit  26  enters the packet including the received receipt acknowledging (ACK) information by the resetting of a transmitted bit map in a control information memory  27 . 
   The transmission apparatus  14  serving as the control station constructs an access control signal (transmission permitting signal) for setting a right to transmission from each of the transmission apparatus in an asynchronous transmission area, and then supplies the access control signal from the control unit  26  to the radio transmission processing unit  22  for radio transmission. 
   When a signal received by the radio transmission apparatus  11 ,  12 , or  13  other than the control station is an access control signal (transmission permitting signal), the radio transmission apparatus supplies the signal from the reception control processing unit  23 C to the control unit  26 , and then the control unit  26  analyzes the access control signal (transmission permitting signal). When the transmission apparatus obtains the transmission right, the transmission apparatus performs processing for transmitting information from the transmission buffer  23 B. At this point, a sequence number of a transmitted packet is set in the transmitted bit map in the control information memory  27 . 
   When the signal decoded by the reception control processing unit  23 C is information in a control information transmitting area, the control unit  26  sets each part to a state indicated by the information of the received control signal. 
   The control unit  26  is connected with the control information memory  27 . The control information memory  27  is configured to temporarily store data necessary for communication control, information on the number of communication stations forming the network and a method of using a transmission line and the like. 
   In addition, the radio transmission apparatus  14  serving as the control station supplies a synchronizing signal of outbound control information (FS) to be sent to the transmission apparatus  11 ,  12 , and  13  other than the control station from the control unit  26  to the radio transmission processing unit  22  for radio transmission. 
   When a signal received by the transmission apparatus  11 ,  12 , or  13  other than the control station is a synchronizing signal of outbound control information (FS), the control unit  26  determines timing of receiving the synchronizing signal, and sets a frame cycle based on the synchronizing signal to perform communication control processing in the frame cycle. 
   When the frame cycle is ended, each of the transmission apparatus stores a transmission pointer value to be described later in the control information memory  27  as last transmission pointer information in the frame. 
   On arrival of a preset frame cycle in which retransmission is to be made, the control unit  26  makes determination to select from the buffer memory  23 A a packet whose receipt acknowledging (ACK) information has not been received, by referring to the transmitted bit map in the control information memory  27 , and then stores the packet in the transmission buffer  23 B for automatic retransmission. 
     FIG. 3  is a diagram showing an arrangement of a radio transmission frame according to the present embodiment. While the figure shows the frame defined for convenience, the frame does not necessarily need to have such a frame structure.  FIG. 3  shows the defined transmission frame arriving in each given transmission frame cycle  31  in a radio transmission line  30 , which frame includes a control information transmitting area  32  and an information transmitting area  33 . 
   An outbound control information transmitting section  34  (FS: Frame Start) for frame synchronization and sending common network information is disposed at the head of the frame, followed by a temporal information correction transmitting section  35  (CR: Cycle Report) disposed as required, and further a station synchronizing signal transmitting and receiving section  36  (SS: Station Sync). 
   The outbound control information transmitting section (FS) is used to transmit necessary information shared in the network from the control station, and is formed by a fixed length area and a variable length area. 
   The fixed length area specifies the number of communication stations for transmission in the station synchronizing signal transmitting and receiving section (SS) and specifies the number of band reservation transmitting areas (RSV) to determine length of the variable length area, and the variable length area specifies the communication stations for transmission in the station synchronizing signal transmitting and receiving section (SS) and specifies the band reservation transmitting areas (RSV). 
   The station synchronizing signal transmitting and receiving section (SS) has a predetermined length and is configured to allot a transmitting communication station to each of the communication stations forming the network with a certain cycle by the outbound control information. 
   For example, by receiving all portions of the station synchronizing signal transmitting and receiving section (SS) other than a portion transmitted by a station, the station can grasp a state of a connection link with a communication station present around the station. 
   Furthermore, when a next station reports a state of a connection link in information transmitted in the station synchronizing signal transmitting and receiving section (SS), each of the communication stations can grasp a connection state of the network. 
   The information transmitting area  33  is formed by a band reservation transmitting area (RSV: Reserve)  37  set as required, an asynchronous transmission area (ASY: Asynchronous)  38  under centralized transmission control of the control station, and an unused area (NUA: Not Using Area)  39  that is not under transmission control of the control station and is allowed to be used by another radio system or the like. 
   Hence, when the band reservation transmitting area (RSV) and the unused area (NUA) are not required, all of the information transmitting area  33  can be transmitted as the asynchronous transmission area (ASY)  38  under centralized control. 
   It is preferable that with such a frame structure, isochronous transmission defined by IEEE1394 format, for example, is made in the band reservation transmitting area (RSV)  37 , and asynchronous transmission is made in the asynchronous transmission area (ASY)  38 . 
   Operation of the thus formed radio transmission apparatus according to the present embodiment will be described in the following. 
     FIG. 4  is a diagram showing a sequence of transmission of asynchronous transmission packets according to the present embodiment. The figure shows that a retransmission frame cycle is predetermined before transmitting a packet, and a packet whose receipt acknowledging (ACK) information has not been received by the frame cycle is retransmitted. 
   Suppose that as shown in a packet transmission  43  in  FIG. 4 , transmissions  401  to  407  of pieces of packet information A to F are made from a transmitting apparatus  41  to a receiving apparatus  42  under predetermined access control. 
   In this case, suppose that the pieces of packet information C 403 , D 404 , and F 407  did not reach the receiving apparatus  42  correctly. 
   Next, an ACK information reply  405  denoted by  46  for notifying reception of the pieces of packet information A 401  and B 402  is made from the receiving apparatus  42  to the transmitting apparatus  41 . 
   When the transmitting apparatus  41  has received the ACK information reply  405 , the transmitting apparatus  41  stores the packets received by the receiving apparatus  42 . 
   In addition,  FIG. 4  shows a state in which an ACK information reply  408  denoted by  47  for notifying reception of the piece of packet information E 406  was made from the receiving apparatus  42  to the transmitting apparatus  41 , but the transmitting apparatus  41  was unable to receive the information. 
   On arrival of a predetermined retransmission frame cycle T, the transmitting apparatus  41  determines whether there are packets not received by the receiving apparatus  42 , and then retransmits unreceived packet information. 
   In  FIG. 4 , a retransmission  44  of unreceived packets indicated by black solid circles denotes the retransmission frame cycle T. While a black solid circle A in the unreceived packet retransmission  44  denotes the packet information A 401  in the retransmission frame cycle T, and a black solid circle B in the unreceived packet retransmission  44  denotes the packet information B 402  in the retransmission frame cycle T, the black solid circles A and B indicate that the transmitting apparatus  41  has already received the ACK information reply  405  for the packets, and therefore the packets will not be retransmitted. 
   A black solid circle C in the unreceived packet retransmission  44  denotes the packet information C 403  in the retransmission frame cycle T. The transmitting apparatus  41  has not received ACK information for the packet information C 403 , and therefore makes a packet information retransmission C 409  in the unreceived packet retransmission  44 . 
   A black solid circle D in the unreceived packet retransmission  44  denotes the packet information D 404  in the retransmission frame cycle T. The transmitting apparatus  41  has not received ACK information for the packet information D 404 , and therefore makes a packet information retransmission D 410  in the unreceived packet retransmission  44 . 
   A black solid circle E in the unreceived packet retransmission  44  denotes the packet information E 406  in the retransmission frame cycle T. The transmitting apparatus  41  has not received ACK information for the packet information E 406 , and therefore makes a packet information retransmission E 411  in the unreceived packet retransmission  44 . 
   A black solid circle F in the unreceived packet retransmission  44  denotes the packet information F 407  in the retransmission frame cycle T. The transmitting apparatus  41  has not received ACK information for the packet information F 407 , and therefore makes a packet information retransmission F 412  in the unreceived packet retransmission  44 . 
   Then, an ACK information reply  413  denoted by  48  for the pieces of packet information D 404  and E 406  is made from the receiving apparatus  42  to the transmitting apparatus  41 . 
   Also on arrival of a re-retransmission frame cycle T denoting a predetermined packet re-retransmission  45 , the transmitting apparatus  41  determines whether there are packets not received by the receiving apparatus  42 , and then makes a re-retransmission  45  of unreceived packet information. 
   On arrival of the re-retransmission frame cycle T for the packet re-retransmission  45 , the information transmitting apparatus  41  makes a re-retransmission  414  of packet information C whose ACK information has not been received. 
   Then, an ACK information reply  415  denoted by  49  in response to the retransmission  412  of the arrived packet information F and the re-retransmission  414  of the arrived packet information C is made from the receiving apparatus  42  to the transmitting apparatus  41 . 
   The transmitting apparatus  41  receives the ACK information, whereby the transmitting apparatus  41  receives the ACK information for all of the pieces of packet information A to F, and the series of asynchronous information transmissions is completed. 
     FIG. 5  is a diagram illustrating a retransmission control method using a transmission pointer value at the end of a frame according to the present embodiment. 
   At an absolute frame number # 71  in  FIG. 5 , both a transmission pointer and an ACK reception pointer indicate a value 100, meaning that there is no ACK-unreceived packet at this point. 
   Then, in a frame cycle of a frame number # 72 , one packet is transmitted and thereby the transmission pointer indicates  101 ; in a frame cycle of a frame number # 73 , four packets are transmitted and thereby the transmission pointer indicates  105 ; and in a frame cycle of a frame number # 74 , one packet is transmitted. 
   In a frame cycle of a frame number # 75 , no packet is transmitted, and therefore the transmission pointer continues to indicate  106 . 
   In this cycle, because the packet  101  indicated by  55  was transmitted in a period from the frame # 71  of four frames back to the frame # 72  of three frames back indicated by  51 , arrival of ACK information for the packet  101  is checked, and when the ACK information has not been received, the packet  101  is retransmitted. 
   Also in a frame cycle of a frame number # 76 , no packet is transmitted, and therefore the transmission pointer continues to indicate  106 . 
   In this cycle, because the four packets  102  to  105  indicated by  55  were transmitted in a period from the frame # 72  of four frames back to the frame # 73  of three frames back indicated by  51 , arrival of ACK information for the packets  102  to  105  is checked, and when the ACK information has not been received, only the corresponding packets are retransmitted. 
   Then, in a frame cycle of a frame number # 77 , two packets are transmitted and thereby the transmission pointer indicates  108 . In this cycle, because the packet  106  indicated by  55  was transmitted in a period from the frame # 73  of four frames back to the frame # 74  of three frames back indicated by  51 , arrival of ACK information for the packet  106  is checked, and when the ACK information has not been received, the packet  106  is retransmitted. 
   In a frame cycle of a frame number # 78 , no packet is transmitted, and therefore the transmission pointer continues to indicate  108 . In this cycle, because no packet was transmitted in a period from the frame # 74  of four frames back to the frame # 75  of three frames back indicated by  51 , no packet is retransmitted. 
   Also in a frame cycle of a frame number # 79 , no packet is transmitted, and therefore the transmission pointer continues to indicate  108 . In this cycle, because the packet  101  indicated by  55  was retransmitted in a period from the frame # 75  of four frames back to the frame # 76  of three frames back indicated by  51 , arrival of ACK information for the packet  101  is checked, and when the ACK information has not been received, the packet  101  indicated by  56  is re-retransmitted. 
   Then, in a frame cycle of a frame number # 80 , two packets are transmitted and thereby the transmission pointer indicates  110 . In this cycle, because the packets  107  and  108  indicated by  55  were transmitted in a period from the frame # 76  of four frames back to the frame # 77  of three frames back indicated by  51 , arrival of ACK information for the packets  107  and  108  is checked, and when the ACK information has not been received, the packets  107  and  108  are retransmitted. 
   In addition, because the four packets  102  to  105  indicated by  56  were transmitted in a period from the frame # 72  of eight frames back to the frame # 73  of seven frames back indicated by  52 , arrival of ACK information for the packets  102  to  105  is checked, and when the ACK information has not been received, the packets  102  to  105  indicated by  56  are re-retransmitted. 
   Also in subsequent frame cycles of a frame number # 81  to a frame number # 88 , according to the above rules, the packets indicated by  55  transmitted in a period from a frame number of four frames back to a frame number of three frames back indicated by  51  are retransmitted; the packets indicated by  56  transmitted in a period from a frame number of eight frames back to a frame number of seven frames back indicated by  52  are re-retransmitted; and the packets indicated by  57  transmitted in a period from a frame number of twelve frames back to a frame number of eleven frames back indicated by  53  are re-re-retransmitted. 
   Also, an example will be shown in which a packet whose ACK information has not been received after three retransmissions in the past 16 frames is discarded on arrival of a frame number # 87 . 
   In this case, the packet  100  indicated by  57  was re-re-retransmitted in the frame number # 83  of four frames back indicated by  53 , the packet  100  indicated by  56  was re-retransmitted in the frame number # 79  of eight frames back indicated by  52 , and the packet  100  indicated by  55  was retransmitted in the frame number # 75  of twelve frames back indicated by  51 . However, because ACK information of the packet  100  of sixteen frames back indicated by  54  has not been received yet, the packet  100  indicated by  58  is deleted on arrival of the frame number # 87 , and an upper layer that has made a request for the transmission of the packet is notified that the transmission of the packet is not possible. 
   Similarly, when a frame number # 88  arrives, three retransmissions have been made during the past 16 frames; that is, the packet  101  indicated by  57  was re-re-retransmitted in the frame number # 84  of four frames back indicated by  53 , the packet  101  indicated by  56  was re-retransmitted in the frame number # 80  of eight frames back indicated by  52 , and the packet  101  indicated by  55  was retransmitted in the frame number # 76  of twelve frames back indicated by  51 . However, because ACK information of the packet  101  of sixteen frames back indicated by  54  has not been received yet, the packet  101  indicated by  59  is deleted on arrival of the frame number # 88 , and the upper layer that has made a request for the transmission of the packet is notified that the transmission of the packet is not possible. 
   It is to be noted that while an example of operation performed in each frame cycle is taken to describe a concrete example of the present embodiment, the present invention is not limited to the handling of transmission pointer information in each frame cycle; a method of handling the transmission pointer information in a cycle of a few milliseconds, for example, may be used as a method for applying the present invention to a radio transmission line with no frame cycle. 
     FIG. 6  is a flowchart of an asynchronous transmission method. 
   At a step S 61  in  FIG. 6 , whether a request for transmission of asynchronous information is received by the interface unit  25  shown in  FIG. 2  is determined. 
   When the request for transmission of asynchronous information is not received at the step S 61 , processing from a branch of NO is omitted. When the request for transmission of asynchronous information is received, the information conversion processing unit  24  shown in  FIG. 2  packetizes the asynchronous information into predetermined fragment units at a step S 62  from a branch of YES. At a step S 63 , the information conversion processing unit  24  shown in  FIG. 2  adds a sequence number to each of the packets. At a step S 64 , the control unit  26  shown in  FIG. 2  sets a frame cycle for retransmission of the packets. At a step S 65 , the control unit  26  sets the number of retransmissions. At a step S 66 , packets transmissible by one access control are stored in the transmission buffer  23 B shown in  FIG. 2 . 
   It is to be noted that the present embodiment can set these parameters as arbitrary values. Specifically, the present embodiment can set retransmission frame cycles such as a first retransmission frame cycle, a second retransmission frame cycle, a third retransmission frame cycle, and so on arbitrarily. 
     FIG. 7  is a flowchart of a packet transmission processing method. 
   At a step S 71  in  FIG. 7 , whether an access control right of a radio transmission line is received by the apparatus of the radio transmission processing unit  22  shown in  FIG. 2  is determined. 
   When the access control right is not received at the step S 71 , processing from a branch of NO is omitted. When the access control right is received, whether there are transmission packets is determined at a step S 72  from a branch of YES. 
   When there are no transmission packets at the step S 72 , processing from a branch of NO is omitted. When there are transmission packets, the packets stored in the transmission buffer  23 B shown in  FIG. 2  are transmitted at a step S 73  from a branch of YES. 
   At a step S 74 , transmission pointer information is updated, and the transmission pointer information is stored in the control information memory  27  shown in  FIG. 2 , whereby the packet transmission processing is ended. 
     FIG. 8  is a flowchart of processing at an end of a frame. 
   At a step S 81  in  FIG. 8 , the control unit  26  shown in  FIG. 2  determines whether an end of a predetermined frame cycle is detected. When the frame cycle is ended, last transmission pointer information in the frame cycle is entered in the control information memory  27  shown in  FIG. 2  at a step S 82 . 
     FIG. 9  is a flowchart of processing at the time of receiving ACK information. 
   At a step S 91  in  FIG. 9 , the control unit  26  shown in  FIG. 2  determines whether reception of ACK information directed to its station is detected. When the ACK information is received, ACK sequence number information of a packet entered in the ACK information is entered as ACK reception information at a step S 92 . 
     FIG. 10  is a flowchart of packet retransmission processing. 
   At a step S 101  in  FIG. 10 , the control unit  26  shown in  FIG. 2  determines whether an end of a predetermined frame cycle is detected. When the frame cycle is ended, a fourth frame cycle, an eighth frame cycle, and a twelfth frame cycle, for example, are obtained as retransmission frame cycle setting information at a step S 102 . At a step S 103 , transmission pointer information in the retransmission frame cycle is obtained from the control information memory  27  shown in  FIG. 2 . At a step S 104 , set information of a frame immediately preceding the retransmission frame cycle is obtained. 
   At a step S 105 , a difference between these pieces of information is obtained to determine whether there are packets that need to be retransmitted. When there are such packets, ACK information is obtained from the control information memory  27  shown in  FIG. 2  at a step S 106 . At a step S 107 , the control unit  26  shown in  FIG. 2  determines whether there are packets whose ACK information has not been received. When there are packets whose ACK information has not been received, only the packets whose ACK information has not been received are stored from the buffer memory  23 A into the transmission buffer  23 B shown in  FIG. 2 , and then retransmitted at a step S 108 . 
   Then, at a step S 109 , whether processing for another retransmission frame cycle, for example the eighth frame cycle or the twelfth frame cycle is to be performed is determined. When retransmission processing is necessary, the processing returns to the step S 102  to perform packet retransmission processing. When retransmission processing for all the frame cycles, that is, the fourth frame cycle, the eighth frame cycle, and the twelfth frame cycle has been performed, the series of processing steps is ended. 
     FIG. 11  is a flowchart of processing for discarding a packet. 
   At a step S 111  in  FIG. 11 , the control unit  26  shown in  FIG. 2  determines whether an end of a predetermined frame cycle is detected. When the frame cycle is ended, a sixteenth frame cycle, for example, is obtained as discarding frame cycle setting information at a step S 112 . At a step S 113 , transmission pointer information in the discarding frame cycle is obtained from the control information memory  27  shown in  FIG. 2 . At a step S 114 , set information of a frame immediately preceding the discarding frame cycle is obtained. At a step S 115 , ACK reception information is obtained. 
   At a step S 116 , the control unit  26  shown in  FIG. 2  determines whether there are packets whose ACK information has not been received. When there are packets whose ACK information has not been received, packets whose ACK information has not been received are discarded from the buffer memory  23 A shown in  FIG. 2  at a step S 117 . 
   At a step S 118 , the ACK information is reset. At a step S 119 , the interface unit  25  shown in  FIG. 2  is notified that the asynchronous information has not been received, whereby the series of processing steps is ended. 
     FIG. 12  is a flowchart illustrating packet reception processing by a transmission apparatus serving as an information receiver. 
   In this case, it is supposed that a plurality of pieces of ACK information are combined into one ACK packet as an ACK information reply within a time period that does not exceed a retransmission frame cycle, and the packet is returned to an information transmitter. However, the present invention is not limited to this method; an ACK information reply may be made for each packet received. 
   At a step S 121  in  FIG. 12 , whether a packet directed to the station of the information receiver is received is determined. When a packet directed to the station of the information receiver is received, ACK information is constructed at a step S 122 . When no packet directed to the station of the information receiver is received at the step S 121 , the processing proceeds to a step S 123 . At the step S 123 , whether a time for combining ACK information has passed is determined. 
   In this case, ACK information may be combined regularly in each cycle of two frames, for example. When the time has not passed at the step S 123 , the processing returns from a branch of NO to the step S 121  to detect reception of packets directed to the station. When the time has passed, ACK information that has been stored is returned to the information transmitter at a step S 124  from a branch of YES. 
   While the present embodiment has been described above by taking a concrete example of setting retransmission timing such as the fourth frame cycle, the eighth frame cycle, and the twelfth frame cycle, and setting discarding timing such as the sixteenth frame cycle, the present invention is not limited to this example, and other timing may be set. 
   While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.