Multi-cast communication system and method, and data communication unit and data communication method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a data communication technique for transmitting data between data terminals, and more particularly to a multicast type data communication technique for transmitting data to a plurality of specific data terminals at a time.

【0002】

More specifically, the present invention relates to a data communication technique for performing retransmission control that guarantees the quality and reliability of transmitted data during multicast system data communication, and particularly, retransmission without redundancy during multicast system data communication. Related to data communication technology for control.

【0003】

[Conventional technology]

Research and development related to "data communication" in which data is exchanged between two or more data terminals (DTEs) has been actively carried out. The main significance of such data communication is to share each computer resource and to smoothly share, distribute, distribute, and exchange information.

【0004】

Communication media for connecting data terminals include local areas such as LAN (Local Area Network), WANs (Wide Area Network) composed of LANs connected by dedicated lines, and the general public. There are various types, such as a wide area network (PSTN), and even the "Internet", which has become a huge network worldwide as a result of interconnection between servers. Recently, mobile communications such as PDC (Personal Digital Cellular), PHS (Personal Handyphone SYstem), and MMAC (Multimedia Mobile Access Communication system), and wireless data communications limited to short distances such as blouetooth have also appeared. It is beginning to spread.

【0005】

The data transmitted on the communication medium is usually divided into predetermined data sizes called "frames" or "packets". This is also to prevent the transmission path from being monopolized during data exchange between a specific data terminal (that is, the communication line is shared by a large number of data terminals) by making the transmission data intermittent. Packets are roughly classified into "data packets" for data transmission and "control packets" for the purpose of transmitting only control information.

【0006】

Further, in data communication, frame error inspection and retransmission control are performed to guarantee the quality and reliability of transmitted data. Of these, retransmission control is generally realized by performing an acknowledgment using a sequence number. The sequence number is initialized, for example, when a connection is established between the data transmission / reception terminals. On the data transmission side, frames are assigned a sequence number and transmitted in sequence. On the other hand, the data receiving side returns a response frame with a sequence number of the frame for which transmission is requested next. When the transmission frame can be received without error, the value obtained by incrementing the sequence number of the frame by 1 becomes the acknowledgment sequence number. The sequence number assigned by the data transmitting side is called FFI (Frame Forward Identification), and the sequence number assigned by the data receiving side is called FBI (Frame Backward Identification). On the data transmission side, it is possible to determine whether or not the frame is a retransmission request based on whether or not the FBI in the reply frame is FFI + 1.

【0007】

According to the retransmission control using the sequence number, the transmission data is divided and sequentially transmitted on the data transmitting side, and the error frame is automatically retransmitted by returning the sequence number of the frame in which the error occurred on the data receiving side. Error-free data transmission can be performed. This is also called the SR-ARQ (Selective Repeat type Automatic Repeat reQuest) method.

【0008】

Figure 1 conceptually shows the procedure for data transmission using the stop-and-weight ARQ method.

【0009】

In the example shown in the figure, in response to the data receiving side receiving frame # 1 with FFI = 1, a confirmation response with FBI = 2 (= FFI + 1) is returned, or confirmation by simple ACK / NACK is performed. Reply the reply. On the other hand, on the data transmission side, after sending FFI = 1, it continues to send frame # 2 with FFI = 1, and in response to receiving the confirmation response with FBI = 2, the next FFI = 2 Start sending frame # 3.

【0010】

However, when performing stop-and-weight retransmission control, even if a data transmission error does not occur, the data transmission side sends an FFI frame and then confirms it with the FBI (=). FFI + 1) to receive until that can not start the transmission of the next frame. As shown in Fig. 1, if the number of round trip frames (RTFs) required to confirm delivery from the data receiving side requires 3 frames, an extra (that is, redundant) frame must be transmitted by 2 frames. It disappears and wastes transmission time slots.

【0011】

That is, in the case of the stop-and-weight method, transmission and response are repeated on a frame-by-frame basis, so that data transmission is redundant and throughput is extremely low.

【0012】

As a retransmission control that eliminates such redundancy, for example, an SR-ARQ (Selective Repeat type Automatic Repeat reQuest) method can be mentioned. The SR-ARQ method has the redundancy that transmission and transmission confirmation are sequentially performed in frame units by providing a "modulo buffer" in which both the data transmission side and the reception side can temporarily store a plurality of frames. It is the one that solved.

【0013】

Figure 2 conceptually shows the procedure for data transmission using the SR-ARQ method. As shown in the figure, since the transmission frame is temporarily stored in the modulo buffer on the data transmission side, the next frame can be transmitted without waiting for the transmission confirmation from the data reception side.

【0014】

Further, as shown in the figure, when the data receiving side fails to receive the frame # 5, for example, the data receiving side makes a retransmission request with FBI = 5 until the frame # 5 is retransmitted and successfully received. Although it continues to reply, the data transmitting side can continue to unilaterally send the next frames # 6 and # 7 even during the retransmission request (that is, receiving FBI = 5). Therefore, the transmission time slot is not wasted. Also, on the data receiving side, the frames # 6 and # 7 to be received before the frame # 5 is retransmitted are temporarily stored in the modulo buffer, and the frames are aligned according to the sequence number in the modulo buffer. Therefore, the transmission order of frames can be guaranteed. When the retransmission of frame # 5 is completed, the data receiving side instructs the untransmitted first frame, that is, FBI = 8, so that the data transmitting side can resume the transmitting work from the untransmitted frame # 8, and successfully. There is no need to resend frame # 6 or frame # 7 delivered.

【0015】

Further, in FIG. 2, the data receiving side also requests retransmission of FFI = 10, that is, frame # 10, but the retransmission request is handled by the same processing procedure as described above.

【0016】

The modulo buffer is managed by the sequence number of the frame for window control, and more preferably it is composed of a continuous buffer area like a ring buffer.

【0017】

Note that frame retransmission control is usually performed in the transport layer (for example, TCP (Transport Control Protocol)) of the OSI (Open Systems Interconnection) basic reference model and the protocol layer corresponding to the link layer.

【0018】

By the way, recently, a "multicast" communication technology in which one frame or packet is transmitted to a plurality of specific data terminals at the same time has begun to spread. In one-to-one unicast, if there are multiple destinations, it is necessary to send frames with the same content to each other. Multicast, on the other hand, requires only one frame transmission, saving time and communication traffic. Also, unlike broadcast, multicast can only be sent to specific terminal groups.

【0019】

Of course, the multicast communication method can also be applied to direct communication by short-range wireless data communication such as bluetooth.

【0020】

For example, in an environment where each participant brings a data terminal such as a notebook PC in a conference room, data files such as presentation materials stored on the notebook PC of a participant can be stored at a short distance. By multicast transmission using wireless data communication, it can be distributed cordlessly and collectively to all notebook PCs (see Fig. 3).

【0021】

Even in such multicast communication, retransmission control is naturally required to guarantee the reliability and quality of the transmitted data.

【0022】

For example, a retransmission control method using ARQ for multicast communication on a wireless transmission line has been conventionally performed, but there is no SR-ARQ method of multicast communication. In addition, the conventional SR-ARQ method for multicast communication is implemented by a transport layer protocol such as TCP, and cannot be controlled by the link layer (for example, PIAFS (PHS Internet Access Forum Standard)). It means that it cannot be implemented by a protocol equivalent to the link layer such as.).

【0023】

Further, in a communication system such as mobile communication in which transmission quality is not guaranteed, one-to-one, that is, unicast communication is repeated in order to deliver the same data (frame) to a plurality of receiving terminals. -There is also a method of transmitting in the "relay" format (see Fig. 4). In this case, the SR-ARQ method of retransmission control can be applied to each unicast communication, but it goes without saying that the communication system as a whole is inefficient. In the case of the bucket brigade method, sufficient frequency resources are required to improve the transmission efficiency.

【0024】

The SR-ARQ method of retransmission control is possible for large-capacity communication lines using satellites and communication modes whose transmission quality is not as poor as that of mobile communication environments. For example, as a terminal on the data receiving side, assuming a stationary type, that is, a relatively large device, the SR-ARQ method should be applied to multicast communication by securing a sufficient buffer for retransmission control. Is possible.

【0025】

However, in the case of mobile communication, significant restrictions are imposed on the data terminal such as size and cost. Further, unlike other communication methods, there is no margin in transmission speed, so it is necessary to perform retransmission control more efficiently with as little information as possible.

【0026】

On the other hand, the conventional retransmission control method is not premised on a communication system in which the delay time until the transmission confirmation is obtained is relatively small as in the case of direct communication. Therefore, in terms of buffer size and the like, there is a redundant part to apply directly to the communication system.

【0027】

[Problems to be Solved by the Invention]

An object of the present invention is to provide an excellent multicast data communication technique capable of transmitting data to a plurality of specific data terminals at a time.

【0028】

A further object of the present invention is to provide an excellent data communication technique capable of performing retransmission control for guaranteeing the quality and reliability of transmitted data at the time of data communication of a multicast method.

【0029】

A further object of the present invention is to provide a data communication technique capable of transmitting data with high throughput by performing retransmission control without redundancy during data communication of a multicast method.

【0030】

A further object of the present invention is to retransmit without redundancy even when performing multicast communication by direct communication in which the delay time until confirmation of transmission is relatively small or when applied to a system. The purpose is to provide an excellent data communication technology that can be controlled and achieve high throughput.

【0031】

A further object of the present invention is to provide an excellent data communication technique capable of eliminating redundancy and realizing high throughput by applying SR-ARQ method retransmission control to multicast communication.

【0032】

[Means for solving problems]

The present invention has been made in consideration of the above problems, and the first aspect thereof is a multicast communication system in which a data transmitting terminal transmits data to a plurality of specific data receiving terminals at a time, and the data is described above. The transmitting terminal transmits a frame with the sequence number FFI (Frame Forward Identification) of the data frame, whereas each of the data receiving terminals transmits the sequence number FBI (Frame Backward Identification) of the data frame to be requested next. In addition to returning the response frame containing, the data transmitting terminal determines the FFI of the next data frame based on the received FBI without waiting for the response frame to be returned from all the data receiving terminals. It is a multicast communication system characterized by performing frame transmission.

【0033】

In the multicast communication system according to the first aspect of the present invention, the data transmission terminal can prioritize the unprocessed FBIs in chronological order to determine the next FFI. As a result, it is possible to improve the throughput of data transfer by performing retransmission control without redundancy while maintaining the reliability of data transfer.

【0034】

Further, the conventional SR-ARQ type communication mechanism can be applied as it is to the data receiving terminal side. That is, the value obtained by incrementing the FFI that could receive the frame correctly by 1 may be confirmed and responded as the FBI, and the FFI that could not receive the frame correctly may be used as the FBI to make a retransmission request.

【0035】

In the multicast communication method, a predetermined number of data receiving terminals may be treated as one receiving group, and response frames may be received from all receiving terminals in the receiving group in one reception time slot. The data transmitting terminal according to the present invention receives only the response frame from a single reception group in one reception time slot, and does not repeat the transmission of the same frame in the next transmission time slot (also). The FFI of the next transmission frame can be determined sequentially without waiting for a response from another receiving group.

【0036】

Further, in order to apply the retransmission control of the SR-ARQ method to the multicast communication according to the present invention, each of the data transmitting terminal and the data receiving terminal temporarily stores a plurality of frames while maintaining the transmission order. It is more preferable to have a buffer, that is, a modular buffer.

【0037】

The multicast communication method according to the present invention can be applied to direct communication using wireless such as ad hoc communication of bluetooth or MMAC (Multimedia Mobile Access Communication system).

【0038】

A second aspect of the present invention is a multicast communication method in which a data transmitting terminal transmits data to a plurality of specific data receiving terminals at a time, and (a) the data transmitting terminal is a sequence of data frames. A step of transmitting a frame with a number FFI (Frame Forward Identification), and (b) a response frame including the sequence number FBI (Frame Backward Identification) of the data frame to be requested to be transmitted next by each of the data receiving terminals. A step of replying, and (c) a step of determining the FFI of the next data frame based on the received FBI without waiting for the data transmitting terminal to return a response frame from all the data receiving terminals. It is a multicast communication method characterized by having.

【0039】

In the multicast communication method according to the second aspect of the present invention, in the step (c), the data transmitting terminal can prioritize the unprocessed FBIs in chronological order to determine the next FFI.

【0040】

Further, in the step (b), the data receiving terminal confirms and responds as an FBI with the value obtained by incrementing the FFI for which the frame can be correctly received by 1 as an FBI, and makes a retransmission request for the FFI for which the frame cannot be received correctly as the FBI. You can do it like this.

【0041】

Further, when a predetermined number of data receiving terminals are treated as one receiving group, in the step (c), the data transmitting terminal receives only response frames from a single receiving group in one reception time slot. It can be received and the FFI of the next transmission frame can be determined.

【0042】

A third aspect of the present invention is a data communication device or method that performs multicast communication that transmits data to a plurality of specific data receiving terminals at one time, and is a data frame sequence number FFI (Frame Forward Identification). Based on the transmitting means or step of transmitting the frame with, the receiving means or step of receiving the response frame including the sequence number FBI (Frame Backward Identification) of the data frame requested to be transmitted next, and the received FBI. It is equipped with a data processing means or step for determining FFI and generating a transmission frame, and is characterized in that the next data frame is transmitted without waiting for a response frame to be returned from all data receiving terminals. A data communication device or method to be used.

【0043】

In the data communication device or method according to the third aspect of the present invention, the data processing means or step may prioritize the unprocessed FBIs in chronological order to determine the next FFI.

【0044】

In addition, the data receiving terminal confirms and responds as an FBI by incrementing the FFI that was able to receive the frame correctly by 1 according to the conventional SR-ARQ method, and makes a retransmission request as it is as the FFI that could not receive the frame correctly. You just have to do it.

【0045】

Further, when treating a predetermined number of data receiving terminals as one receiving group, the receiving means or step receives only the response frame from a single receiving group in one reception time slot, and then receives the next. The FFI of the transmission frame of can be determined.

【0046】

[Action]

The present invention is an SR-ARQ method retransmission control applicable to multicast communication in which data is transmitted to a plurality of specific data terminals at one time.

【0047】

The data transmitting terminal side transmits the next data frame without waiting until the reply frame is received from all the data receiving terminals.

【0048】

Also, the FBI included in the current reply frame and the current unprocessed FBI are listed in chronological order, and the retransmission request is prioritized to determine the next FFI. Since retransmission control is performed without redundancy, high throughput can be achieved.

【0049】

The present invention is particularly effective in direct communication in which the delay time until the transmission confirmation is obtained is relatively small.

【0050】

Further, the retransmission control method according to the present invention can be realized only by adding a predetermined processing function to the data communication terminal equipped with the conventional SR-ARQ method. In many cases, this processing function can be provided in the form of program code, which makes it easy to modify the system. Further, according to the present invention, a multicast communication application can be easily provided even in a device such as a mobile terminal, which is required to be miniaturized, have low power consumption, and have a low price.

【0051】

Further, the communication method according to the present invention can also be applied to a communication system composed of a combination of a notebook computer and a mobile terminal. For example, it can be effectively applied when digital data such as presentation materials are distributed to each attendee in a situation where each terminal is located at a distance where each terminal can directly communicate at a meeting or the like. In addition, a specific data terminal is positioned as a "master unit" and other data terminals are positioned as a "slave unit", and information on all participants is obtained based on the information acquired during connection negotiation between the master unit and each slave unit. Centralized management by the master unit can facilitate the management of multicast destinations.

【0052】

When the data communication method according to the present invention is applied to the distribution of digital data at a conference or the like, paper resources can be saved as compared with the case of distributing materials by copying a conventional manuscript. That is, the present invention can contribute to resource saving and reduce the material distribution time and the material copy work time.

【0053】

Further, according to the communication method according to the present invention, the modulo buffer, which had conventionally been prepared in both terminals for transmitting and receiving data, can be saved in a single common buffer, so that the product cost can be reduced. Can be done.

【0054】

Still other objects, features and advantages of the present invention will be clarified by more detailed description based on the examples of the present invention described later and the accompanying drawings.

【0055】

BEST MODE FOR CARRYING OUT THE INVENTION

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

【0056】

FIG. 5 schematically shows the configuration of the communication system 100 used for the realization of the present invention. In the communication system 100 shown in the figure, there are five wireless data communication terminals indicated by reference numbers 10 to 14, and among the terminals, there are close proximity such as bluetooth and MMAC (Multimedia Mobile Access Communication system). It is assumed that multicast data communication (in other words, direct communication in which the delay time until confirmation of transmission is relatively small) is performed by distance radio data communication.

【0057】

In the example shown in FIG. 5, for convenience, the data communication terminal 10 is the master, that is, the transmitting side of the multicast communication, and the other data communication terminals 11, 12 ... Are the slaves, that is, the receiving side of the multicast communication. It is explained as. However, the Master-Slave relationship in multicast communication does not have to be fixed, and any data communication terminal may be a data transmitting side and a data receiving side at any time.

【0058】

In the multicast communication system 100 according to the present embodiment, the SR-ARQ (Selective Repeat type Automatic Repeat reQuest) method of retransmission control is performed. The SR-ARQ method has the redundancy that transmission and transmission confirmation are sequentially performed in frame units by providing a "modulo buffer" in which both the data transmission side and the reception side can temporarily store a plurality of frames. Is solved (mentioned above).

【0059】

That is, in the multicast communication system 100 according to the present embodiment, the master, that is, the data communication terminal 10 on the transmitting side receives confirmation responses from all the data communication terminals 11, 12 ... On the receiving side for each frame transmission. The transmission of the next frame can be started without waiting for.

【0060】

FIG. 6 illustrates a data communication sequence in the multicast communication system 100 according to this embodiment. However, in the example shown in the figure, the communication protocol allows up to two acknowledgment frames to be received in one receive time slot, but only one per receive frame or three per receive frame. It should be understood that the present invention works similarly even if it allows the reception of more than one acknowledgment frame.

【0061】

In this embodiment, the Master side transmits the next data frame without waiting for the acknowledgments to be received from all Slave. In addition, Master handles multiple Slave in several groups, maximizing the number of frames that can be received in one reception time slot. In the example shown in FIG. 6, Slave # 1 and # 2 are set as the first receiving group, and the remaining Slave # 3 and # 4 are set as the second receiving group.

【0062】

The Master sends data frame # 1 in the first transmit time slot, and all Slave receive this transmit frame (although it may contain receive errors). In the subsequent receive time slot, the data transmitting terminal receives only the reply frames from the first receive group, namely Slave # 1 and # 2, and ignores the reply frames from the second receive group. The send frame contains FFI (Frame Forward Identification), and the reply frame contains FBI (Frame Backward Identification) (described above).

【0063】

At this point, the Master can check which data frames were received based on the FBI returned by each Slave in the first receive group. When a reception error is detected in the first reception group, the frame is retransmitted according to the SR-ARQ method. On the other hand, the reception check is intentionally ignored for the second reception group.

【0064】

In the next transmission frame, data frame # 2 containing FFI is transmitted, and all Slave receive this transmission frame (however, it may contain a reception error). In the subsequent receive time slot, the data transmitting terminal receives only the reply frames from the second receive group, namely Slave # 3 and # 4, and does not receive the reply frames from the first receive group.

【0065】

At this point, the Master can check which data frames were received based on the FBI returned by each Slave in the second receive group. When a reception error is detected in the second reception group, the frame is retransmitted according to the SR-ARQ method. On the other hand, the reception check is intentionally ignored for the first reception group.

【0066】

From then on, in the same way, one receive time slot receives only reply frames from one receive group, and the next send time slot sends the next data frame (ie, repeats the same data frame). Do not send). In addition, retransmission control is performed based only on the reception error that occurred in the reception group that received the reply frame.

【0067】

Let's compare such a send / receive operation with a conventional data transmission operation in which the next data frame is transmitted only after the reply frames have been received from all Slave.

【0068】

In the case of such a conventional method, since reply frames from all data receiving terminals cannot be received in one reception time slot, the next transmission time slot is also spent for transmitting the same data frame as the previous one. Will be done.

【0069】

FIG. 7 schematically shows a data transmission / reception operation in the conventional method. The Master transmits data frame # 1 containing the FFI in the first transmit time slot. On the other hand, all Slave receive this (however, it may include a reception error) and return the reply frame including the FBI to the Master side. In the subsequent receive time slot, the Master can only receive reply frames from the first receive group, Slave # 1 and # 2. That is, since the reply from the second receiving group has not been received yet, the Master transmits the same data frame # 1 in the next transmission frame. In the next receive time slot, the Master can receive reply frames from the other receive group, Slave # 3 and # 4, so that the next transmit slot can determine the next data frame.

【0070】

As can be seen by comparing FIGS. 6 and 7, according to the conventional method shown in FIG. 7, only about half of the data frames shown in FIG. 6 are transmitted at the same number of transmission / reception time slots. (However, assuming that the error rate is the same). In other words, the send / receive operation is redundant and unnecessarily increases the network load.

【0071】

FIG. 8 shows a functional block diagram schematically showing the configuration of the data transmission terminal 10 according to this embodiment. As shown in the figure, the data transmission terminal 10 includes an RF reception / demodulation unit 51, an FBI processing unit 52, an SR-ARQ method FFI determination unit 53, and a framing modulation / RF transmission unit 54.

【0072】

When the RF reception and demodulation unit 51 receives the reply frame with FBI sent from the data receiving terminal side, it demodulates and deframes it, and outputs it to the FBI processing unit 52.

【0073】

One receive time slot can receive one or more reply frames (two in the example shown in Figure 6). The FBI processing unit 52 determines the value of the FBI to be applied to the retransmission control from among the plurality of FBIs. However, the details of this FBI decision processing procedure will be described later.

【0074】

The SR-ARQ method FFI determination unit 53 determines the data frame to be transmitted next, that is, the FFI, based on the FBI value determined by the FBI processing unit, and constructs data for transmission. When the FBI indicates that it is a retransmission request, error correction and retransmission control are performed by the SR-ARQ method. In addition, the transmission frame is temporarily stored in a modulo buffer (not shown).

【0075】

The framing modulation and RF transmission unit 54 framing the data for transmission together with other information (for example, control information such as a header), further modulates the data, and wirelessly transmits the data at the transmission timing specified in the communication protocol.

【0076】

Further, FIG. 9 shows a functional block diagram schematically showing the configuration of the data receiving terminal 11 according to the present embodiment. It should be understood that the other data receiving terminals 12 ... have the same configuration. As shown in the figure, the data receiving terminal 12 includes an RF receiving and demodulating unit 56, an SR-ARQ method FBI determining unit 57, and a framing modulation and RF transmitting unit 58.

【0077】

When the RF reception / demodulation unit 56 receives the reply frame with FFI sent from the data transmission terminal 10 side, it demodulates and deframes the reply frame and outputs it to the SR-ARQ method FBI determination unit 57.

【0078】

The SR-ARQ method FBI determination unit 57 performs retransmission request frame information, that is, FBI determination processing by the SR-ARQ method. That is, an FBI that is obtained by incrementing the FFI of a frame that can be received without error is generated by 1, or the FFI of a frame in which an error is found is used as it is as an FBI and a retransmission request is made. Also, the received data is taken into a modulo buffer (not shown).

【0079】

The framing modulation and RF transmission unit 58 frames the FBI determined by the FBI determination unit 57 as a reply frame, further modulates it, and wirelessly transmits it at the transmission timing specified in the communication protocol.

【0080】

In general, a data communication terminal is equipped with both data transmission and reception functions. It should be understood that such a data communication terminal has a configuration including all the functional modules shown in FIGS. 8 and 9.

【0081】

The data receiving terminal 11 may have substantially the same configuration as the conventional data receiving terminal that performs the SR-ARQ method retransmission control in unicast communication.

【0082】

FIG. 10 illustrates the FBI value determination processing procedure performed by the FBI processing unit 52 in the form of a flowchart. Hereinafter, each step of this flowchart will be described.

【0083】

The process shown in the flowchart starts when the data transmission terminal 10 ends receiving a reply frame including the FBI from each reception terminal in the reception group in a certain reception time slot.

【0084】

First, step S1 checks the value of one of the FBIs received in the current receive time slot.

【0085】

If this FBI is a value incremented by 1 from the FFI of the data frame sent in the previous transmit time slot (ie, a modulo value of FFI = 1), then the data frame was successfully received within the current receive group. It will be (step S2). In this case, the process proceeds to step S3 to determine whether or not there is an unprocessed FBI in the current reception group, and if the unprocessed FBI remains, the process returns to step S1 and the same processing as above is performed. repeat.

【0086】

On the other hand, if the FBI determines in step S1 that the FFI of the data frame sent in the previous transmit time slot is not incremented by 1, the data frame is successfully received within the current receive group. It will not be (step S4). In this case, the sequence number indicated by the FBI is set as the priority frame in the retransmission request (step S5). If unprocessed FBI remains, the process returns to step S1 and the same processing as above is repeated.

【0087】

When the determination process in the current receiving group is completed, then in step S6, the FBI in the other receiving group is included in the listing. The FBI processing unit 52 preferably has a mechanism for holding the FBI in which the retransmission request has not been processed.

【0088】

Then, in step S7, the unprocessed FBIs are relisted in chronological order to prioritize the FBIs, or retransmission request frames.

【0089】

Then, the FBI having the highest priority is selected and output to the subsequent SR-ARQ method FFI determination unit 53 (step S8), and the entire processing procedure is completed. The FBI for which the retransmission request remains unprocessed is continuously held in the data transmission terminal 10 (for example, the FBI processing unit 52).

【0090】

[Supplement] The present invention has been described in detail with reference to specific examples. However, it is self-evident that a person skilled in the art can modify or substitute the embodiment without departing from the gist of the present invention. That is, the present invention has been disclosed in the form of an example, and should not be construed in a limited manner. In order to judge the gist of the present invention, the column of claims described at the beginning should be taken into consideration.

【0091】

[Effect of the invention]

As described in detail above, according to the present invention, it is possible to provide an excellent multicast data communication technique capable of transmitting data to a plurality of specific data terminals at a time.

【0092】

Further, according to the present invention, it is possible to provide an excellent data communication technique capable of performing retransmission control for guaranteeing the quality and reliability of transmitted data at the time of data communication of a multicast method.

【0093】

Further, according to the present invention, it is possible to provide a data communication technique capable of eliminating redundancy and performing retransmission control with high throughput during data communication of a multicast method.

【0094】

Further, according to the present invention, even when multicast communication is performed by direct communication in which the delay time until confirmation of transmission is relatively small, or when applied to a system, retransmission without redundancy is performed. As a result of the control, it is possible to provide an excellent data communication technique capable of achieving high throughput.

【0095】

Further, according to the present invention, by applying the SR-ARQ method retransmission control to multicast communication, it is possible to provide an excellent data communication technique capable of eliminating redundancy and realizing high throughput.

【0096】

According to the retransmission control method according to the present invention, it is possible to improve the data transmission efficiency when performing multicast transmission by direct communication using wireless communication.

【0097】

Further, the retransmission control method according to the present invention can be realized only by adding a predetermined processing function to the data communication terminal equipped with the conventional SR-ARQ method. In many cases, this processing function can be provided in the form of program code, which makes it easy to modify the system. Further, according to the present invention, a multicast communication application can be easily provided even in a device such as a mobile terminal, which is required to be miniaturized, have low power consumption, and have a low price.

【0098】

Further, the communication method according to the present invention can also be applied to a communication system composed of a combination of a notebook computer and a mobile terminal. For example, it can be effectively applied when digital data such as presentation materials are distributed to each attendee in a situation where each terminal is located at a distance where each terminal can directly communicate at a meeting or the like. In addition, a specific data terminal is positioned as a "master unit" and other data terminals are positioned as a "slave unit", and information on all participants is obtained based on the information acquired during connection negotiation between the master unit and each slave unit. It can be centrally managed by the master unit, and the management of multicast destinations can be facilitated.

【0099】

When the data communication method according to the present invention is applied to the distribution of digital data at a conference or the like, paper resources can be saved as compared with the case of distributing materials by copying a conventional manuscript. That is, the present invention can contribute to resource saving and reduce the material distribution time and the material copy work time.

【0100】

Further, according to the communication method according to the present invention, the modulo buffer, which had conventionally been prepared in both terminals for transmitting and receiving data, can be saved in a single common buffer, so that the product cost can be reduced. Can be done.

[Simple explanation of drawings]

[Figure 1]

It is a chart diagram (conventional example) conceptually showing the procedure of data transmission by the stop-and-weight ARQ method.

[Figure 2]

It is a chart diagram (conventional example) conceptually showing the procedure of data transmission by the SR-ARQ method.

[Fig. 3]

It is a figure which described the state of multicast transmission between a plurality of notebook PCs using short-range wireless data communication.

[Fig. 4]

It is a figure which described the state of delivering the same data (frame) to a plurality of receiving terminals in a bucket relay format.

[Fig. 5]

It is a figure which showed typically the structure of the multicast communication system 100 used for the realization of this invention.

[Fig. 6]

It is a chart which showed the data communication sequence in the multicast communication system 100 which concerns on this Example.

[Fig. 7]

It is a chart which showed the data communication sequence in the multicast communication system 100 which concerns on the conventional method.

[Fig. 8]

It is a functional block diagram which schematically represented the structure of the data transmission terminal 10 which concerns on this Example.

[Fig. 9]

It is a functional block diagram which schematically represented the structure of the data receiving terminal 11 which concerns on this Example.

[Fig. 10]

It is a flowchart which showed the determination processing procedure of the FBI value performed by the FBI processing unit 52.

[Explanation of symbols]

10 ~ 14 ... Data communication terminal 51 ... RF receiver and demodulator 52 ... FBI Processing Department 53 ... SR-ARQ method FFI decision unit 54 ... Framing modulation and RF transmitter 56 ... RF receiver and demodulator 57 ... SR-ARQ method FBI determination unit 58 ... Framing modulation and RF transmitter