KR101085421B1 - Communication station, communication method, computer readable storage medium, and communication system - Google Patents

Abstract

A communication station receives data from a transmitting station, transmits a reception response indicating a reception status of data, and among those other communication stations, a communication station that does not normally receive data from the transmitting station based on a reception response from other communication stations exists. Determine whether or not. When data is normally received from the transmitting station, when there is a communication station that does not normally receive data from the transmitting station, the communication station transmits the data received from the transmitting station to a communication station that does not normally receive the data. At the time of the transmission, based on a predetermined priority, it is determined whether or not to perform the transmission to a communication station that does not normally receive the data.

Communication station, sending station, receiving station, storage medium, communication system

Description

COMMUNICATION STATION, COMMUNICATION METHOD, COMPUTER READABLE STORAGE MEDIUM, AND COMMUNICATION SYSTEM}

The present invention relates to a technique for relaying received data between communication stations.

For efficient data communication between a transmitting station and a plurality of receiving stations, a method of multicasting one packet containing data to each receiving station is known. The method of improving the efficiency of a reception response is also examined (Japanese Patent Laid-Open No. 2007-502564).

In the case of multicast communication, a technique for causing the sending station to send data again when the receiving station cannot receive data directly from the transmitting station has been studied. Moreover, the technique which transmits data to a relay station is also examined (Japanese Patent Laid-Open No. 11-252114).

However, in multicast communication, a communication station designated as a relay station normally receives data from a transmitting station due to a change in a communication link caused by interference (for example, a static obstacle such as a wall or a dynamic obstacle such as a person). It may not be possible. When the communication link is changed by a static obstacle such as a wall, communication is enabled by transmission by a predetermined relay station. On the other hand, when the communication link changes due to a dynamic obstacle, the relay station cannot be determined in advance. For this reason, it is impossible to accurately transmit data to a communication station that cannot directly receive data from the transmitting station.

In a system that can receive data from a plurality of relay stations using a mesh topology, even if the communication link is changed by dynamic obstacles, there is a high possibility that data transmission is surely performed. However, even if one station has already successfully received data, the same station repeatedly receives the same data many times. This operation increases power consumption.

In addition, transmitting data to a communication station that has already correctly received data is a waste of the band of the wireless medium. As a result, power consumption of each terminal increases, and interference to other communication systems also increases.

The present invention can provide a communication station, a communication method, a computer readable storage medium, and a communication system capable of improving the reliability of data communication and suppressing redundant data communication.

According to a first aspect of the present invention, a communication station includes: receiving means for receiving data from a transmitting station, response means for transmitting a reception response indicating a reception status of data by the receiving means, and reception responses from other communication stations. Determining means for determining whether a communication station which does not normally receive data from the transmitting station is present among the other communication stations, and if the receiving means normally receives data from the transmitting station, When it is determined that there is a communication station that does not normally receive data from the transmitting station, the communication means which transmits the data received by the receiving means is provided to a communication station that does not receive the data normally. Based on the set priorities, the data is normally It is determined whether or not to perform the transmission for a communication station that has not received.

The communication method of a communication station according to the second aspect of the present invention is characterized in that the data is normally sent from the transmitting station based on the transmission of a reception response indicating the reception status of the data from the transmission station and the reception response from other communication stations. Determining whether or not a communication station which has not been received exists among the other communication stations, and when it is determined that there is a communication station that has not normally received data from the transmitting station when the data is normally received from the transmitting station, A communication station that has not received the data normally, on the basis of a predetermined priority when transmitting the data received from the transmitting station, to the communication station that has not normally received the data. To do the transfer for Determines whether or not.

According to a third aspect of the present invention, there is provided a computer-readable storage medium storing a computer program, the computer program comprising: receiving means for receiving data from a transmitting station and a computer built in a communication station; Based on the response means for transmitting the reception response indicating the reception status of the data and the reception response from the other communication stations, determining whether there is a communication station among the other communication stations that did not normally receive data from the transmitting station. When the determining means and the receiving means normally receive data from the transmitting station, when the determining means determines that there is a communication station that does not normally receive data from the transmitting station, To a communication station that does not And functions as a transmitting means for transmitting data, the transmitting means, and determines whether or not on the basis of a predetermined priority, whether to perform the transport with respect to the communication station does not receive the data properly.

According to a fourth aspect of the present invention, there is provided a communication system including a transmitting station for transmitting data and a plurality of communication stations for receiving data from the transmitting station, wherein each communication station receives data from the transmitting station. On the basis of the receiving means for receiving, the response means for transmitting the reception response indicating the reception status of the data by the receiving means, and the communication station that has not normally received data from the transmitting station based on the reception response from other communication stations, Judging means for determining whether any of the other communication stations exist, and if the receiving means normally receives data from the transmitting station, there is a communication station for which the judging means has not normally received data from the transmitting station. When determining, to a communication station that does not receive the data normally. And transmission means for transmitting the data received by the reception means, and the transmission means determines whether or not to perform the transmission to a communication station that has not normally received the data based on a predetermined priority.

Other features of the present invention will become apparent from the following exemplary embodiments with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the components, numerical expressions, and numerical values in these embodiments do not limit the scope of the present invention.

(First embodiment)

1 is a diagram showing an example of the overall configuration of a communication system according to an embodiment of the present invention.

Reference numeral 101 denotes a communication station on the transmitting side (hereinafter referred to as a transmitting station), and reference numerals 111 to 114 denote communication stations on the receiving side (hereinafter referred to as a receiving station) that receive data from the transmitting station 101. The interferer 120 interferes with the radio signal. In this case, the interferer 120 interferes with the radio signal transmission from the transmitting station 101 to the receiving station 111.

A computer is built in each of the transmitting station 101 and the receiving stations 111 to 114. The computer includes, for example, a main control unit such as a CPU, a storage unit such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The computer also includes an input / output unit such as a display or touch panel and a communication unit such as a wireless network card. These components are connected via a bus and controlled by executing the program stored in the storage unit to the main control unit.

FIG. 2 is a diagram illustrating an example of an outline of communication in the communication system shown in FIG. 1.

Communication of each communication station is separated by predetermined time intervals (time slots). Reference numeral 200 denotes a transmission timeslot of the transmitting station 101, reference numerals 210, 220, and 230 denote relay timeslots of the receiving stations 111-114, and reference numerals 201 to 204, 211, 213, 214, and 222 to 224. , 231, 232, and 234 are reception responses of respective receiving stations. A reference number ending in 1 indicates a reception response from the receiving station 111. Reference numerals ending in 2 indicate a reception response of the receiving station 112. That is, in Fig. 2, the last digit of the reference number in the reception response indicates the correspondence with the receiving stations 111 to 114.

In the transmission timeslot 200, in response to the data transmitted from the transmitting station 101, each of the receiving stations 112 and 113 sends the normal received signal Ack back to multicast within a predetermined time. Each of the receiving stations 111 and 114 returns the abnormal reception signal Nack.

In the relay timeslot 210 executed after the transmission timeslot, the receiving station 111 has the transmission right having the highest priority. However, the receiving station 111 does not normally receive data from the transmitting station 101. Therefore, the receiving station 112 with the second highest priority transmits data (hereinafter also referred to as relay transmission). Since the receiving station 112 received the multicast Nack from the receiving station 111, it recognizes that the receiving station 111 did not receive data normally. In the relay timeslot 210, even if data is relayed and transmitted by the receiving station 112, the receiving station 114 returns Nack 214. That is, the receiving station 114 cannot receive data normally.

In the relay timeslot 220, since the receiving station 111 received the data normally, the receiving station 111 having the highest transmission priority relays the data in the relay timeslot 220. In this relay transmission, the receiving station 114, which has not yet received the data, receives data normally. In other words, all receiving stations succeeded in receiving data. Therefore, after the reception response 224, no receiving station transmits or receives data until the transmitting station 101 transmits the next data.

In the above, the outline | summary of the data communication from the transmitting station 101 to the receiving station 111-114 was demonstrated. In the above description, after the relay station 112 performs relay transmission in the relay timeslot 210, it is excluded from the list of transmission priority of subsequent relay timeslots. Instead of excluding the recipient from the list, its priority may be lowered. In the above description, the reception station 101 does not cause any reception response to the communication station (hereinafter referred to as a relay station) that performs relay transmission. However, in order to simplify the time slot management of the reception response, the reception response time slot of the relay station may be left. If each receiving station has a unit that knows the time of the next transmission time slot, the timeslot of the reception response of the receiving station that has already transmitted the Ack may be omitted.

With reference to FIG. 3, an example of the functional structure of the receiving station shown in FIG. 1 is demonstrated. Here, the functional configuration will be described using the receiving station 111 as a representative example. Receiving stations 112 to 114 also adopt the same configuration.

The receiving station 111 includes a transmitting antenna 301, a receiving antenna 302, a transmitting unit 303, and a receiving unit 304. The priority holding unit 305 holds the transmission priority of the receiving station in each relay time slot. The priority held by the priority holding unit 305 is changed for each relay timeslot.

The transmission right determination unit 306 determines the acquisition of the transmission right in each relay time slot. The time controller 307 manages each transmission time slot. The time controller 307 controls, for example, the reception timing of data from the transmitting station 101 or another receiving station and the reception timing of the reception response from each receiving station. The receiving station 111 adjusts the time of the time controller 307 based on the received data and synchronizes with the transmitting station or another receiving station. The reception determination unit 308 determines whether or not data has been normally received. The receiver has been described above.

4 and 5 are flowcharts showing an example of the sequence of processing in the receiving stations 111 to 114.

First, with reference to FIG. 4, the sequence of the process of receiving data from the transmitting station 101, and the process in the reception response time of the receiving station of interest after data reception are demonstrated.

The receiving station knows in advance the transmission timeslot of the transmitting station 101. When the reception station reaches the transmission time of the transmission station 101 (YES in step S401), the reception station starts reception (step S402).

In the reception response time of the interested reception station (YES in step S403), the reception station transmits a reception response in accordance with the reception status of the data from the transmission station 101. If data reception is normally performed (YES in step S404), the receiving station terminates the process after multicasting the normal reception response Ack (step S405).

If data reception cannot be performed normally (NO in step S404), the receiving station multicasts an abnormal reception response Nack (step S406). After the Nack transmission, the receiving station waits until the next relay time slot (YES in step S407, then NO in step S408). Even after all relay timeslots for one transmission data (NO in step S407), if the data is still not normally received, the receiving station gives up acquiring the data. In this case, the receiving station waits until the next transmission time slot of the transmitting station 101 to acquire the next transmission data.

Next, with reference to FIG. 5, the process in the reception response time of another receiving station is demonstrated.

This process is started when the response time of any other receiving station (other than the receiving station of interest) is reached (YES in step S501). When this processing is started, the receiving station determines whether data is normally received. If data is not normally received (NO in step S502), this processing ends. This is because relay transmission is impossible if data is not normally received.

If data is normally received (YES in step S502), the receiving station checks whether the reception response from the remaining receiving station contains a Nack. If no Nack is received even after the reception response time of the other station (NO in step S503, then YES in step S504), the receiving station terminates this processing and waits until the next transmission time slot of the transmitting station.

When Nack is detected from the reception response received from another receiving station (YES in step S503), the receiving station determines the transmission right in the next relay time slot. In the relay time slot, the transmission priority of each terminal is predetermined. The receiving station which has already received the data from the transmitting station 101 acquires the transmission right in the next relay time slot if no other receiving station having a higher transmission priority than the receiving station of interest has received the data normally. do.

When the transmission right is acquired (YES in step S505), the receiving station waits until the next relay time slot. When the next relay time slot is started (YES in step S506, and then YES in step S507), the receiving station performs the relay transmission to another receiving station that has not normally received data (step S508). Quit. If all relay timeslots have ended and there are no further relay timeslots (NO in step S506), this processing ends.

(Second embodiment)

Next, a second embodiment will be described. Since the overall configuration of the second embodiment is the same as that of Fig. 1 of the first embodiment, the description thereof will not be repeated.

6 is a diagram illustrating an example of a summary of communication in the communication system according to the second embodiment.

Communication of each communication station is divided into predetermined time intervals (time slots). Reference numeral 600 is a transmission timeslot of the transmitting station 101, reference numerals 610, 620, and 630 are relay timeslots of the receiving station, and reference numerals 601 to 604, 611, 613, 614, 623, 624, and 634 is a reception response of the receiving station. Like the first embodiment, the reference number ending in 1 indicates a reception response of the receiving station 111. Reference numerals ending in 2 indicate a reception response of the receiving station 112. That is, in Fig. 6, the last digit of the reference number in the reception response indicates the correspondence with the receiving station.

In the second embodiment, each receiving station communicates by carrier sense multiple access (CSMA). Each receiving station performs back-off time management and carrier sense in the relay time slot to dynamically control the transmitting station 101.

In the transmission timeslot 600, in response to the data transmitted from the transmitting station 101, the receiving stations 112 and 113 return the normal received signal Ack. Each of the receiving stations 111 and 114 returns the abnormal reception signal Nack.

In the relay timeslot 610 executed after the transmission timeslot, the receiving station 111 has a transmission right having the highest priority. In the relay timeslot 610, the receiving station 111 has a right to transmit without a backoff time. However, since the receiving station 111 did not normally receive data from the transmitting station 101, the receiving station 111 does not transmit in the relay time slot 610. In this case, the second highest priority receiving station 112 performs a carrier sense after waiting for the (eg shortest) backoff time. The receiving station 112 checks the transmission status of the other receiving station (in this case, the receiving station 111) according to the carrier sense, confirms that there is no data transmission by the other receiving station (in this case, the receiving station 111), and then performs the relay transmission. Do it. The receiving station 113 must wait for a backoff time longer than the receiving station 112. This aims to shift the transmission start time in the relay timeslot. The reception station 113 performs carrier sense after waiting for the backoff time. At this time, the receiving station 113 detects the carrier of the receiving station 112 and loses the transmission right. Even when data is relayed and transmitted by the receiving station 112, the receiving station 114 returns the Nack 614. That is, the receiving station 114 cannot receive data normally.

The receiving station 112 with the highest transmission priority has already relayed. For this reason, in the relay time slot 620, the receiving station 113 acquires a transmission right and performs relay transmission without waiting for the backoff time. In this case, even if data is relayed and transmitted by the receiving station 113, the receiving station 114 still returns the Nack 624. That is, the receiving station 114 cannot receive data normally.

In the relay timeslot 630, the receiving station 113 having the highest transmission priority has been removed from the list of relay stations since the relay transmission has already been performed. In the relay timeslot 630, the receiving station 114 with the second highest priority has transmission rights. However, the receiving station 114 does not perform relay transmission because it failed to receive data normally. In this case, after the receiving station 111 waits for the backoff time, the relay station transmits after performing the carrier sense of the receiving station 114.

In the above, the outline | summary of the data communication from the transmitting station 101 to the receiving station which concerns on 2nd Example was demonstrated. In the above description, receiving stations (for example, receiving stations 112 and 113) that have performed relay transmission are excluded from the list of transmission priorities of subsequent relay timeslots. Instead of excluding recipients from the list, their priorities may be lowered. In the above description, the transmitting station 101 and the relay station do not return any reception response. However, in order to simplify the time slot management of the reception response, the time slot of the reception response of the relay station may be left. If each receiving station has a unit that knows the time of the next transmission timeslot, the timeslot of the reception response of the receiving station which has already transmitted the Ack may be omitted.

7, an example of a functional configuration of a receiving station according to the second embodiment will be described. Here, the functional configuration described above will be described using the receiving station 111 as a representative example. The receiving stations 112 to 114 adopt the same configuration. In FIG. 7, since the same reference numerals as those in FIG. 3 of the first embodiment represent the same parts, only different points in FIGS. 7 and 3 will be described.

The carrier detector 309 performs carrier sense after waiting for the backoff time controlled by the time controller 307.

The time controller 307 determines the backoff time of the receiving station in the relay time slot based on the transmission priority. The transmission right determination unit 306 determines the presence or absence of a transmission right based on the carrier detection result (the presence or absence of a carrier of another receiving station) of the carrier detection unit 309.

The receiving station according to the second embodiment has been described above. Since the sequence of the processing in each receiving station 111-114 is the same as that of FIG. 4 and FIG. 5 of a 1st Example, it abbreviate | omits about detailed description. The second embodiment is somewhat different from the first embodiment in the transmission right determination processing in S505 of FIG. In the second embodiment, transmission right acquisition is determined by setting the backoff time based on CSMA and transmission priority.

(Third Embodiment)

Next, a third embodiment will be described.

8 is a diagram showing an example of the entire configuration of a communication system according to the third embodiment.

Reference numeral 101 is a transmitting station, and reference numerals 111 to 114 are receiving stations that receive data from the transmitting station 101. The interferer 120 interferes with the radio signal. The transmitting station 101 of the third embodiment has two transmitting antennas 9011 and 9012.

9 is a diagram showing an example of an outline of communication in the communication system according to the third embodiment.

The transmission station 101 performs transmission diversity in transmission timeslots 8001 and 8002. The reception station 111 avoids transmission disturbance by the interferer 120 due to this transmission diversity. Even if the transmitting station 101 performs transmit diversity, the receiving station 114 cannot receive data normally. When the receiving station 111 performs relay transmission in the relay timeslot 820, the receiving station 114 can normally receive data.

10 is a diagram showing an example of a functional configuration of a transmitting station according to the third embodiment.

The transmitting station 101 includes a transmitting antenna 9011 and 9012, a receiving antenna 902, a data transmitting unit 903, and an Ack / Nack receiving unit 904 for receiving reception acknowledgments (Ack, Nack) from each receiving station. It includes. The time controller 907 manages each time slot. The time controller 907 controls the timing of data transmission, the switching timing between the transmission antennas 9011 and 9012, and the reception timing of the reception response from each receiving station. The transmission data acquisition unit 909 acquires data transmitted to each receiving station.

The transmitting station according to the third embodiment has been described above. The configuration and the sequence of the processing in each receiving station are the same as those of the first and second embodiments described above, and thus the description thereof will not be repeated.

As described above, according to the first to third embodiments, the receiving station that has normally received data relays to another receiving station that has failed to receive the data. This increases the reliability of data communication. Data transmission is not performed for a receiving station that has already received data normally. As a result, redundant data transmission and reception are eliminated, power consumption is reduced, and traffic is controlled. Without redundant data transmission and reception, for example, interference noise can be reduced in a space where other systems overlap.

In the first to third embodiments, the operation in the multicast communication has been described. If the number of communication stations is known, it is possible to perform approximately the same operation in broadcast communication. The receiving station may not send back Ack but only Nack. On the contrary, the receiving station may send back Ack instead of Nack.

In the first to third embodiments, description has been made using the expressions "transmitting station" and "receiving station". However, all communication stations may function as transmission stations. It is not necessary that the transmitting station and the receiving station always have a relationship between the master station and the slave station.

In the above, a representative embodiment of the present invention has been described. The present invention is not limited to the embodiments shown in the above and the drawings, and various modifications and changes can be appropriately made within the spirit and scope of the present invention.

The present invention may take the form of a system, apparatus, method, program or recording medium, for example. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to a device consisting of one device.

The present invention also includes a case where a program of software is directly or remotely supplied to a system or apparatus, and a computer embedded in the system or apparatus reads and executes the supplied program code to achieve the functions of the present embodiment. In this case, the supplied program is a computer program corresponding to the flowchart shown in the embodiment.

Therefore, in order to realize the functional processing of the present invention by a computer, the program code itself installed in the computer also implements the present invention. That is, the present invention also includes the computer program itself for realizing the functional processing of the present invention. In that case, if the function of the program can be obtained, the program can take the form of an object code, a program executed by an interpreter, script data supplied to an operating system (OS), and the like.

Computer-readable recording media for supplying computer programs include floppy disks, hard disks, optical disks, magneto-optical disks, MOs, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and nonvolatile memory cards. , ROM, DVD (DVD-ROM, DVD-R).

As another program supplying method, a client computer connects to a homepage on the Internet using a browser and downloads the computer program of the present invention to a recording medium such as a hard disk from the homepage. In this case, the downloaded program may be a compressed file including an automatic installation function. The program code included in the program of the present invention may be divided into a plurality of files, and each file may be downloaded from another home page. That is, the present invention also includes a WWW server for downloading a program file for realizing the functional processing of the present invention to a plurality of users.

The program of the present invention can be encrypted, stored in a recording medium such as a CD-ROM, and distributed to users. A user who satisfies a predetermined condition can download key information for decrypting a password from a homepage via the Internet, execute an encrypted program using the key information, and install the program on a computer.

When the computer executes the read program, not only the function of the above-described embodiment is realized but also the function of the embodiment may be realized in cooperation with an OS or the like running on the computer based on the instruction of the program. In this case, the function of the above-described embodiment is realized by the OS or the like performing part or all of the actual processing.

In addition, the program read from the recording medium may be recorded in a memory of a function expansion board inserted into a computer or a function expansion unit connected to a computer to realize some or all of the functions of the above-described embodiments. In this case, after the program is recorded on the function expansion board or the function expansion unit, the function expansion board or the CPU (Central Processing Unit) of the function expansion unit or the like may perform some or all of the actual processing based on the instruction of the program. Run

According to the present invention, reliability of data communication can be improved and redundant data communication can be suppressed.

Although the present invention has been described with reference to exemplary embodiments, it is not limited to this exemplary embodiment of the present invention. The following claims are to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.

1 is a diagram showing an example of the overall configuration of a communication system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of an outline of communication in the communication system shown in FIG. 1.

FIG. 3 is a block diagram showing an example of a functional configuration of the receiving station shown in FIG.

FIG. 4 is a first flowchart showing an example of a sequence of processing in each receiving station shown in FIG. 1.

FIG. 5 is a second flowchart showing an example of the sequence of processing in each receiving station shown in FIG. 1.

6 is a diagram illustrating an example of a summary of communication in the communication system according to the second embodiment.

7 is a diagram showing an example of a functional configuration of a receiving station according to the second embodiment.

8 is a diagram showing an example of the entire configuration of a communication system according to the third embodiment.

9 is a diagram showing an example of an outline of communication in the communication system according to the third embodiment.

10 is a diagram showing an example of a functional configuration of a transmitting station according to the third embodiment.

Claims (9)

Receiving means for receiving data from a transmitting station; Response means for transmitting a reception response indicating a reception status of data by the reception means; Determining means for determining whether a communication station not receiving data from the transmitting station exists among the other communication stations, based on a reception response from other communication stations; When the receiving means receives data from the transmitting station, when the determining means determines that there is another communication station that has not received data from the transmitting station, the transmitting station is sent from the transmitting station to another communication station that has not received the data. A transmission means for transmitting the received data, The transmission means, On the basis of the priorities predetermined for each communication station, it is determined whether or not to perform the transmission for a communication station that has not received the data, The receiving means, And when data from the transmitting station has not been received, receives data from another communication station that has received data from the transmitting station. The method of claim 1, And said transmission means performs said transmission based on the transmission priority of each communication station in a relay time slot for relaying data transmitted from said transmitting station. The method of claim 2, And the transmitting means shifts the start time of the transmission in the relay time slot based on the transmission priority of each communication station. The method of claim 2, And a transmission priority of each communication station is changed for each of the relay timeslots. The method of claim 1, The transmission of the reception response by the response means is performed after a time slot of one of a transmission timeslot for transmitting data by the transmitting station and a relay timeslot for relaying data received from the transmitting station. . The method of claim 1, And said transmission means checks the data transmission status of said other communication stations at the time of transmission, and performs said transmission if at least one of said other communication stations is not performing data transmission. As a communication method of a communication station, Transmitting a reception response indicating a reception status of data from a transmitting station; Based on a reception response from other communication stations, determining whether a communication station not receiving data from the transmitting station exists among the other communication stations, When data is received from the transmitting station, when it is determined that there is another communication station that has not received data from the transmitting station, it is preferable to transmit data received from the transmitting station to another communication station that has not received the data. Including, When transmitting the data received from the transmitting station, it is determined whether or not to perform the transmission to a communication station that has not received the data, based on a priority given to each communication station in advance. And when data from the transmitting station is not received, receiving data from another communication station that has received data from the transmitting station. A computer readable storage medium storing a computer program, the computer program comprising: a computer built in a communication station; Receiving means for receiving data from a transmitting station; Response means for transmitting a reception response indicating a reception status of data by the reception means; Determining means for determining whether a communication station not receiving data from the transmitting station exists among the other communication stations, based on a reception response from other communication stations; When the receiving means receives data from the transmitting station, when the judging means determines that there is another communication station that has not received data from the transmitting station, the transmitting station is sent to the other communication station that has not received the data. Function as a transmission means for transmitting the received data, The transmission means, On the basis of the priorities predetermined for each communication station, it is determined whether or not to perform the transmission to a communication station that does not receive the data, The receiving means, And when data from the transmitting station has not been received, receive data from another communication station that has received the data from the transmitting station. A communication system comprising a transmitting station for transmitting data and a plurality of communication stations for receiving data from the transmitting station, Each communication station, Receiving means for receiving data from the transmitting station; Response means for transmitting a reception response indicating a reception status of data by the reception means; Determining means for determining whether a communication station not receiving data from the transmitting station exists among the other communication stations, based on a reception response from other communication stations; When the receiving means receives data from the transmitting station, when the judging means determines that there is another communication station that has not received data from the transmitting station, the transmitting station is sent to the other communication station that has not received the data. A transmission means for transmitting the received data, The transmission means, On the basis of the priorities predetermined for each communication station, it is determined whether or not to perform the transmission for a communication station that has not received the data, The receiving means, And when data from the transmitting station is not received, receive data from another communication station that has received data from the transmitting station.

Images