Communication system, base station, and control method

Abstract

To provide a communication system capable of satisfying specifications of a communication standard while improving communication quality when performing radio communication by broadcast or multicast.SOLUTION: The station 6 has a communication part 12 for transmitting a plurality of packets respectively including sequence numbers to each of the plurality of communication terminals 8a and 8b by broadcast or multicast in the order of the sequence numbers. Each of the plurality of communication terminals 8a and 8b includes a communication unit 18 for receiving packets transmitted from the base stations 6, and a re-transmission request unit 22 for requesting the base stations 6 to re-transmit one or more unreceived packets when there is a missing number in one or more sequence numbers included in one or more received packets. The determination unit 16 determines whether or not the one or more unreceived packets can be retransmitted based on the transmission time required to retransmit the one or more unreceived packets when the re-transmission request is received from the communication station 8a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a communication system, a base station, and a control method. [Background technology]

[0002] There is known a communication system that performs wireless communication in accordance with a communication standard (applied to, for example, the Radio Act of Japan) that limits the transmission time per unit time (see, for example, Patent Document 1). One such communication standard is known as IEEE802.11ah.

[0003] Generally, broadcast or multicast is used as a communication method between a base station and each of a plurality of communication terminals. By performing broadcast or multicast in the wireless communication conforming to the above-mentioned IEEE802.11ah, the base station can simultaneously transmit packets to each of a plurality of communication terminals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-188927 Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to its specifications, the wireless layer of the above-mentioned IEEE802.11ah has a problem in that even if a packet transmitted by broadcast or multicast from a base station is not received by a specific communication terminal and is lost, the packet is not retransmitted by broadcast or multicast.

[0006] Furthermore, if retransmission control is implemented at a higher layer (software side) to partially solve these problems, the retransmission process performed to prevent packet loss may suddenly exhaust the available transmission time in communications where the transmission time per unit time is limited (e.g., IEEE802.11ah), which could result in a new problem of not being able to maintain sufficient communication quality.

[0007] The present invention has been made in view of such problems, and its purpose is to provide a communication system, base station, and control method that can improve communication quality when conducting wireless communication by broadcast or multicast in a communication system using a communication standard in which the transmission time per unit time is limited, while satisfying the specifications of the communication standard. [Means for solving the problem]

[0008] (Technology 1) The present invention comprises a base station and a plurality of communication terminals that perform wireless communication between the base station and the base station in accordance with a communication standard in which the transmission time per unit time is limited, wherein the base station has a first communication unit that transmits a plurality of packets each including a sequence number to each of the plurality of communication terminals by broadcast or multicast in the order of the sequence numbers, and each of the plurality of communication terminals has a second communication unit that receives the packets transmitted from the base station, and a second communication unit that, when there is a missing number in one or more sequence numbers included in one or more received packets received by the second communication unit, a retransmission request unit that requests the base station to retransmit one or more unreceived packets that have not been received, when the base station receives a retransmission request from a specific communication terminal among the plurality of communication terminals, the base station further has a determination unit that determines whether or not retransmission of the one or more unreceived packets is possible based on a transmission time required to retransmit the one or more unreceived packets or a data size of the one or more unreceived packets to be retransmitted, and when the determination unit determines that retransmission of the one or more unreceived packets is possible, the first communication unit retransmits the one or more unreceived packets to the specific communication terminal.

[0009] According to Technology 1, when a retransmission request is received from a specific communication terminal, a determination unit of a base station determines whether retransmission of one or more unreceived packets is possible based on the transmission time required to retransmit the one or more unreceived packets or the data size of the one or more unreceived packets to be retransmitted. Then, when the determination unit determines that retransmission of the one or more unreceived packets is possible, a first communication unit of the base station retransmits the one or more unreceived packets to the specific communication terminal. This makes it possible to prevent packets transmitted from the base station by broadcast or multicast from being lost due to not being received by the specific communication terminal. As a result, in a communication system using a communication standard in which the transmission time per unit time is limited, it is possible to improve communication quality when performing wireless communication by broadcast or multicast while satisfying the specifications of the communication standard.

[0010] (Technology 2) The communication system described in Technology 1, wherein the determination unit determines that the one or more unreceived packets can be retransmitted if the remaining transmittable time specified by the communication standard is equal to or longer than the transmission time required to retransmit the one or more unreceived packets.

[0011] According to Technique 2, one or more unreceived packets can be retransmitted within the remaining transmittable time defined by a communication standard that limits the transmission time per unit time.

[0012] (Technology 3) The determination unit further (i) when receiving a retransmission request from the specific communication terminal among the plurality of communication terminals, determines whether to prioritize retransmission of the one or more unreceived packets or transmission of the one or more untransmitted packets that have not yet been transmitted from the base station, and (ii) when it has determined that transmission of the one or more untransmitted packets is prioritized, determines whether or not transmission of the one or more untransmitted packets is possible prior to retransmission of the one or more unreceived packets based on a transmission time required for transmission of the one or more untransmitted packets or a data size of the one or more untransmitted packets to be transmitted, and when it has determined by the determination unit that transmission of the one or more untransmitted packets is possible, the first communication unit transmits the one or more untransmitted packets to each of the plurality of communication terminals by broadcast or multicast prior to retransmission of the one or more unreceived packets.

[0013] According to Technique 3, one or more unsent packets can be transmitted within the remaining transmittable time defined by a communication standard that limits the transmission time per unit time.

[0014] (Technology 4) The communication system described in Technology 3, wherein the determination unit determines that the one or more untransmitted packets can be transmitted if the remaining transmittable time defined by the communication standard is equal to or longer than the transmission time required to transmit the one or more untransmitted packets.

[0015] According to the fourth technique, it is possible to easily determine whether or not one or more unsent packets can be transmitted, based on the transmission time required to transmit the one or more unsent packets.

[0016] (Technology 5) The communication system described in Technology 3, wherein the determination unit determines that the one or more untransmitted packets can be transmitted when the remaining transmittable data size calculated from the remaining communication time defined by the communication standard is equal to or larger than the data size of the one or more untransmitted packets.

[0017] According to Technique 5, it is possible to easily determine whether or not the one or more unsent packets can be transmitted, based on the data size of the one or more unsent packets to be transmitted.

[0018] (Technology 6) The communication system according to any one of techniques 1 to 5, wherein each of the plurality of communication terminals further has a buffer memory that temporarily stores the one or more received packets received by the second communication unit, and the second communication unit transfers the one or more received packets to an external device when there are no missing numbers in the one or more sequence numbers included in each of the one or more received packets stored in the buffer memory and the number of the one or more received packets reaches a predetermined number.

[0019] According to Technique 6, even if a packet transmitted by broadcast or multicast from a base station is lost without being received by a specific communication terminal, one or more unreceived packets can be retransmitted to the specific communication terminal, and then a predetermined number of one or more received packets can be transferred to an external device.

[0020] (Technology 7) a communication unit that transmits a plurality of packets, each including a sequence number, to each of the plurality of communication terminals in order of the sequence numbers by broadcast or multicast; and a determination unit that, when a retransmission request is received from a specific communication terminal among the plurality of communication terminals because one or more sequence numbers included in one or more received packets received by the specific communication terminal are missing, determines whether or not retransmission of the one or more unreceived packets is possible based on the transmission time required to retransmit the one or more unreceived packets that have not been received by the specific communication terminal or the data size of the one or more unreceived packets to be retransmitted; and when the determination unit determines that retransmission of the one or more unreceived packets is possible, the communication unit retransmits the one or more unreceived packets to the specific communication terminal.

[0021] According to Technology 7, it is possible to prevent packets transmitted by broadcast or multicast from a base station from being lost due to not being received by a specific communication terminal. As a result, when a communication standard that limits the transmission time per unit time is used, it is possible to improve communication quality when performing wireless communication by broadcast or multicast while satisfying the specifications of the communication standard.

[0022] (Technology 8) A control method for a communication system including a base station and a plurality of communication terminals that perform wireless communication between the base station and the base station in accordance with a communication standard in which the transmission time per unit time is limited, the method comprising: (a) a step in which the base station transmits a plurality of packets, each including a sequence number, to each of the plurality of communication terminals by broadcast or multicast in order of the sequence numbers; (b) a step in which each of the plurality of communication terminals receives the packets transmitted from the base station; and (c) a step in which, based on one or more sequence numbers included in one or more received packets received by a specific communication terminal among the plurality of communication terminals, the plurality of communication terminals transmits a packet by broadcast or multicast in order of the sequence numbers. A control method comprising: (a) a step in which, when there is a missing number, the specific communication terminal requests the base station to retransmit one or more unreceived packets that it has not received; (d) a step in which, when the base station receives a retransmission request from the specific communication terminal, the base station determines whether or not it is possible to retransmit the one or more unreceived packets based on the transmission time required to retransmit the one or more unreceived packets or the data size of the one or more unreceived packets to be retransmitted; and (e) a step in which, when the base station determines in (d) that it is possible to retransmit the one or more unreceived packets, the base station retransmits the one or more unreceived packets to the specific communication terminal.

[0023] According to Technology 8, it is possible to prevent packets transmitted by broadcast or multicast from a base station from being lost due to not being received by a specific communication terminal. As a result, in a communication system using a communication standard that limits the transmission time per unit time, it is possible to improve communication quality when performing wireless communication by broadcast or multicast while satisfying the specifications of the communication standard. [Effects of the Invention]

[0024] According to a communication system, etc. relating to one aspect of the present invention, in a communication system using a communication standard in which the transmission time per unit time is limited, it is possible to improve communication quality when performing wireless communication via broadcast or multicast while satisfying the specifications of the communication standard. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating a configuration of a communication system according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing a functional configuration of a base station according to an embodiment. [Figure 3] FIG. 2 is a block diagram showing a functional configuration of a communication terminal according to an embodiment. [Figure 4] 10 is a sequence diagram showing the flow of operations of the communication system according to the embodiment when a determination unit of the base station determines that retransmission of an unreceived packet is possible in retransmission priority mode. FIG. [Figure 5] 10 is a sequence diagram showing the flow of operations of the communication system according to the embodiment when a determination unit of the base station determines that retransmission of an unreceived packet is not possible in retransmission priority mode. FIG. [Figure 6] 10 is a flowchart illustrating a flow of operations of the communication terminal according to the embodiment. [Figure 7] 10 is a flowchart illustrating a flow of operations of a base station according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, steps, step order, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0027] (Embodiment) [1. Communication system configuration] First, the configuration of a communication system 2 will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the configuration of a communication system 2 according to an embodiment.

[0028] 1, communication system 2 includes camera 4, base station 6, multiple communication terminals 8a and 8b, and multiple displays 10a and 10b (examples of external devices). In this embodiment, communication system 2 is applied to a video distribution system for synchronously displaying video captured by camera 4 on multiple displays 10a and 10b. In this specification, "video" includes not only still images but also moving images.

[0029] In this embodiment, the communication system 2 is described as having two communication terminals 8a and 8b, but is not limited to this, and may have three or more communication terminals.

[0030] The camera 4 is, for example, a video camera for capturing an image of the projection target. The camera 4 is connected to the base station 6 by wire so as to be able to communicate with the base station 6, and transmits to the base station 6 image data representing the captured image of the projection target.

[0031] The base station 6 is connected to the camera 4 via a wired connection so as to be able to communicate with the camera 4, and receives the video data transmitted from the camera 4.

[0032] The base station 6 is also wirelessly connected to each of the multiple communication terminals 8a and 8b so that they can communicate with each other. More specifically, the base station 6 performs wireless communication with each of the multiple communication terminals 8a and 8b in accordance with a communication standard that limits the transmission time per unit time. An example of a communication standard that is subject to such legal restrictions (e.g., Japan's Radio Law) is IEEE802.11ah, which limits the transmission time per hour (3600 seconds) to six minutes (360 seconds). The base station 6 divides the video data from the camera 4 into multiple packets, each of which includes multiple sequence numbers. That is, each of the multiple packets includes a single sequence number. The base station 6 then simultaneously transmits the divided packets to each of the multiple communication terminals 8a and 8b by broadcast or multicast in the order of the sequence numbers.

[0033] The multiple sequence numbers are consecutive numbers starting from, for example, "1" (i.e., consecutive integer numbers such as "1," "2," "3," ...), and are assigned to multiple packets as sequence number information. In this case, first, the base station 6 transmits a packet including sequence number "1" to each of the multiple communication terminals 8a and 8b by broadcast or multicast. Next, the base station 6 transmits a packet including sequence number "2" to each of the multiple communication terminals 8a and 8b by broadcast or multicast. Thereafter, the base station 6 similarly transmits packets including sequence numbers "3" and subsequent sequence numbers to each of the multiple communication terminals 8a and 8b by broadcast or multicast.

[0034] Each of the multiple communication terminals 8a, 8b is, for example, a personal computer, a smartphone, or a tablet terminal, and is wirelessly connected to the base station 6 so as to be able to communicate with the base station 6. As described above, each of the multiple communication terminals 8a, 8b performs wireless communication with the base station 6 in accordance with a communication standard that limits the transmission time per unit time. Each of the multiple communication terminals 8a, 8b receives packets transmitted by broadcast or multicast from the base station 6 in the order of sequence numbers (i.e., in the order of consecutive numbers "1", "2", "3", ...).

[0035] Furthermore, the plurality of communication terminals 8a, 8b are each connected by wire to the plurality of displays 10a, 10b so as to be able to communicate with each other. When the sequence number included in a packet received from the base station 6 is a multiple of a predetermined number (for example, "5"), each of the plurality of communication terminals 8a, 8b transfers a predetermined number of packets (for example, a total of five packets each including sequence numbers "1" to "5") in a batch to the plurality of displays 10a, 10b. Note that in this embodiment, an example will be described in which a predetermined number of packets are transferred in a batch in multiples of "5", but the number of packets to be transferred in a batch is not limited to this and may be determined arbitrarily.

[0036] Each of the multiple displays 10a, 10b is, for example, a liquid crystal display. Each of the multiple displays 10a, 10b displays video for a certain period of time indicated by a predetermined number (for example, five) of packets transferred from the multiple communication terminals 8a, 8b. This allows each of the multiple displays 10a, 10b to display the video captured by the camera 4 in a synchronized manner between the displays 10a, 10b.

[0037] [2. Base station functional configuration] Next, the functional configuration of the base station 6 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the functional configuration of the base station 6 according to the embodiment.

[0038] As shown in FIG. 2, the base station 6 includes a communication unit 12 (an example of a first communication unit), a storage unit 14, and a determination unit 16.

[0039] The communication unit 12 is connected to the camera 4 (see FIG. 1) via a wire so as to be able to communicate with the camera 4. The communication unit 12 receives video data from the camera 4.

[0040] Furthermore, communication unit 12 is wirelessly connected to each of multiple communication terminals 8a and 8b (see FIG. 1) so as to be able to communicate with them. Communication unit 12 divides the video data from camera 4 into multiple packets, each of which includes multiple sequence numbers. Communication unit 12 then transmits the divided packets to each of the multiple communication terminals 8a and 8b in order of the sequence numbers by broadcast or multicast.

[0041] The storage unit 14 is a buffer memory and temporarily (for a predetermined period) stores the plurality of packets divided by the communication unit 12. The plurality of packets stored in the storage unit 14 are deleted from the storage unit 14 after being transmitted by the communication unit 12 to each of the plurality of communication terminals 8a, 8b, or after a predetermined period has elapsed.

[0042] When a retransmission request (described later) is received from a specific communication terminal (e.g., communication terminal 8a) among the multiple communication terminals 8a and 8b, the determination unit 16 determines whether or not it is possible to retransmit one or more unreceived packets based on the transmission time required to retransmit the one or more unreceived packets. In this specification, an "unreceived packet" refers to a packet that the base station 6 transmitted to each of the multiple communication terminals 8a and 8b by broadcast or multicast but that was not received by a specific communication terminal among the multiple communication terminals 8a and 8b and was therefore lost. A specific determination method by the determination unit 16 will be described later.

[0043] Furthermore, the determination unit 16 determines whether the mode related to packet transmission is the retransmission priority mode or the distribution priority mode. The mode related to packet transmission is set to either the retransmission priority mode or the distribution priority mode by the administrator of the base station 6. The retransmission priority mode is a mode in which the base station 6 retransmits one or more unreceived packets within the remaining transmittable time specified by legal regulations, and prioritizes reliable transmission without packet dropout (achieving synchronous playback between all displays 10a, 10b). On the other hand, the distribution priority mode is a mode in which the base station 6 transmits (distributes) all of the one or more untransmitted packets within the remaining transmittable time specified by legal regulations, and prioritizes real-time playback (suppressing playback delays).

[0044] In this specification, "untransmitted packets" refers to packets that have not yet been transmitted by the communication unit 12 to each of the multiple communication terminals 8a and 8b by broadcast or multicast (i.e., packets waiting to be transmitted in the storage unit 14). Also, in this specification, "remaining transmission time" refers to the remaining transmission time per unit time defined by legal regulations.

[0045] Furthermore, when the determination unit 16 determines that retransmission of one or more unreceived packets is possible, the communication unit 12 reads the one or more unreceived packets from the storage unit 14 and retransmits the read one or more unreceived packets to the specific communication terminal. On the other hand, when the determination unit 16 determines that retransmission of one or more unreceived packets is impossible, the communication unit 12 does not retransmit the one or more unreceived packets to the specific communication terminal. Furthermore, the communication unit 12 notifies each of the multiple communication terminals 8a, 8b whether the mode related to the transmission of the above-mentioned packets is the retransmission priority mode or the delivery priority mode. Of course, the base station 6 and each of the multiple communication terminals 8a, 8b may set the same mode before operation.

[0046] [3. Functional configuration of communication terminal] Next, the functional configuration of the communication terminal 8a will be described with reference to Fig. 3. Since the functional configurations of the communication terminals 8a and 8b are the same, only the functional configuration of the communication terminal 8a will be described below. Fig. 3 is a block diagram showing the functional configuration of the communication terminal 8a (8b) according to the embodiment.

[0047] As shown in FIG. 3, the communication terminal 8a includes a communication unit 18 (an example of a second communication unit), a storage unit 20, and a retransmission request unit 22.

[0048] The communication unit 18 is wirelessly connected to the base station 6 (see FIG. 1) so as to be able to communicate with it. The communication unit 18 receives packets transmitted by broadcast or multicast from the base station 6. These packets also include a packet notifying the mode of the base station 6, i.e., whether the mode is retransmission priority mode or delivery priority mode. The mode notified from the base station 6 is stored in the storage unit 20.

[0049] Furthermore, communication unit 18 is communicatively connected by wire to display 10a (see FIG. 1). When the sequence number included in a packet received from base station 6 is a multiple of a pre-specified number (e.g., "5"), communication unit 18 transfers a predetermined number of packets (e.g., a total of five packets each including sequence numbers "1" to "5") temporarily stored in storage unit 20 all at once to display 10a. In this way, by transmitting the received packets all at once to display 10a based on the number of packets with pre-specified sequence numbers having been received, smooth video playback can be performed on display 10a.

[0050] The storage unit 20 is a buffer memory, and temporarily (for a predetermined period of time) stores a plurality of packets received by the communication unit 18. The plurality of packets stored in the storage unit 20 are deleted from the storage unit 20 after being transferred to the display 10a by the communication unit 18.

[0051] Each time the communication unit 18 receives a packet, the retransmission request unit 22 refers to the memory unit 20 to determine whether there are any missing numbers in one or more sequence numbers contained in each of the one or more received packets received by the communication unit 18.

[0052] In this specification, a "received packet" refers to a packet received by the communication unit 18. In addition, in this specification, "one or more sequence numbers are missing" refers to, for example, (i) a case where the sequence number included in one received packet first received by the communication unit 18 is other than "1," or (ii) a case where two or more sequence numbers included in two or more received packets sequentially received by the communication unit 18 are not consecutive numbers.

[0053] When there are missing numbers in one or more sequence numbers included in one or more received packets received by communication unit 18, retransmission request unit 22 requests base station 6 via communication unit 18 to retransmit one or more unreceived packets that have not been received by communication unit 18. More specifically, retransmission request unit 22 transmits a retransmission request signal to base station 6 via communication unit 18 to request base station 6 to retransmit one or more unreceived packets.

[0054] [4. Operation of communication system] The operation of the communication system 2 when the determination unit 16 of the base station 6 determines that retransmission of an unreceived packet is possible in the retransmission priority mode will be described with reference to Fig. 4. Fig. 4 is a sequence diagram showing the flow of the operation of the communication system 2 according to the embodiment when the determination unit 16 of the base station 6 determines that retransmission of an unreceived packet is possible in the retransmission priority mode.

[0055] As shown in FIG. 4, first, the communication unit 12 of the base station 6 transmits a packet including a sequence number "1" to each of the plurality of communication terminals 8a and 8b by broadcast or multicast (S101, S102).

[0056] The communication unit 18 of the communication terminal 8a receives a packet including the sequence number "1" transmitted from the base station 6. At this time, the retransmission request unit 22 of the communication terminal 8a determines that there are no missing sequence numbers because the sequence number included in the single received packet that was first received by the communication unit 18 of the communication terminal 8a is "1".

[0057] Furthermore, communication unit 18 of communication terminal 8b receives a packet including sequence number "1" transmitted from base station 6. At this time, retransmission request unit 22 of communication terminal 8b determines that there are no missing sequence numbers because the sequence number included in the single received packet that was first received by communication unit 18 of communication terminal 8b is "1".

[0058] Next, the communication unit 12 of the base station 6 transmits the packet including the sequence number "2" to each of the plurality of communication terminals 8a and 8b by broadcast or multicast (S103, S104).

[0059] It is assumed that communication unit 18 of communication terminal 8a cannot receive a packet including sequence number "2" transmitted from base station 6. At this time, retransmission request unit 22 of communication terminal 8a does not determine whether there is a missing number in the sequence number because communication unit 18 of communication terminal 8a does not receive the packet.

[0060] Meanwhile, the communication unit 18 of the communication terminal 8b receives the packet containing the sequence number "2" transmitted from the base station 6. At this time, the retransmission request unit 22 of the communication terminal 8b determines that there are no missing sequence numbers because the two sequence numbers "1" and "2" contained in the two received packets received in succession by the communication unit 18 of the communication terminal 8b are consecutive numbers.

[0061] Next, the communication unit 12 of the base station 6 transmits the packet including the sequence number "3" to each of the plurality of communication terminals 8a and 8b by broadcast or multicast (S105, S106).

[0062] It is assumed that communication unit 18 of communication terminal 8a cannot receive a packet including sequence number "3" transmitted from base station 6. At this time, retransmission request unit 22 of communication terminal 8a does not determine whether there is a missing number in the sequence number because communication unit 18 of communication terminal 8a does not receive the packet.

[0063] Meanwhile, the communication unit 18 of communication terminal 8b receives the packet containing the sequence number "3" transmitted from the base station 6. At this time, the retransmission request unit 22 of communication terminal 8b determines that there are no missing sequence numbers because the three sequence numbers "1," "2," and "3" contained in the three received packets sequentially received by the communication unit 18 of communication terminal 8b are consecutive numbers.

[0064] Next, the communication unit 12 of the base station 6 transmits the packet including the sequence number "4" to each of the plurality of communication terminals 8a and 8b by broadcast or multicast (S107, S108).

[0065] The communication unit 18 of the communication terminal 8a receives a packet including the sequence number "4" transmitted from the base station 6. At this time, the retransmission request unit 22 of the communication terminal 8a determines that there is a missing sequence number (S109) because the two sequence numbers "1" and "4" included in the two already-received packets received in succession by the communication unit 18 of the communication terminal 8b (see S101 and S107) are not consecutive numbers.

[0066] Next, the retransmission request unit 22 of the communication terminal 8a requests the base station 6 to retransmit two unreceived packets containing the two sequence numbers "2" and "3" that have not been received by the communication unit 18 of the communication terminal 8a (S110).

[0067] Meanwhile, the communication unit 18 of communication terminal 8b receives the packet containing the sequence number "4" transmitted from the base station 6. At this time, the retransmission request unit 22 of communication terminal 8b determines that there are no missing sequence numbers because the four sequence numbers "1," "2," "3," and "4" contained in the four received packets sequentially received by the communication unit 18 of communication terminal 8b are consecutive numbers.

[0068] Next, upon receiving a retransmission request from communication terminal 8a (specific communication terminal), the judgment unit 16 of base station 6 judges that it is possible to retransmit the two unreceived packets, which respectively contain the two sequence numbers "2" and "3", based on the transmission time required to retransmit the two unreceived packets (S111).

[0069] Next, the communication unit 12 of the base station 6 transmits two unreceived packets containing the two sequence numbers "2" and "3" respectively to the communication terminal 8a by unicast (S112, S113). As a result, the communication unit 18 of the communication terminal 8a receives the two unreceived packets containing the sequence numbers "2" and "3" respectively transmitted from the base station 6. Note that the four received packets are rearranged in the order of sequence numbers "1", "2", "3", and "4" in the storage unit 20 of the communication terminal 8a. At this time, the retransmission request unit 22 of the communication terminal 8a determines that there are no missing sequence numbers because the four sequence numbers "1", "2", "3", and "4" contained in the four received packets sequentially received by the communication unit 18 of the communication terminal 8a are consecutive numbers.

[0070] The communication unit 12 of the base station 6 may transmit two packets, each containing the two sequence numbers "2" and "3," to each of the communication terminals 8a and 8b by broadcast or multicast. In this case, the communication unit 18 of the communication terminal 8b has already received the two packets, and therefore discards the two packets after receiving them.

[0071] Next, the determination unit 16 of the base station 6 determines whether or not the unsent packet (sequence number "5") can be transmitted, and determines that it can in this embodiment (S114). As a result, the communication unit 12 of the base station 6 transmits the packet including the sequence number "5" to each of the multiple communication terminals 8a and 8b by broadcast or multicast (S115, S116).

[0072] The communication unit 18 of the communication terminal 8a receives the packet containing the sequence number "5" transmitted from the base station 6. At this time, the retransmission request unit 22 of the communication terminal 8a determines that there are no missing sequence numbers because the five sequence numbers "1," "2," "3," "4," and "5" contained in the five received packets sequentially received by the communication unit 18 of the communication terminal 8a are consecutive numbers.

[0073] Meanwhile, communication unit 18 of communication terminal 8b receives a packet containing sequence number "5" transmitted from base station 6. At this time, retransmission request unit 22 of communication terminal 8b determines that there are no missing sequence numbers because the five sequence numbers "1," "2," "3," "4," and "5" contained in the five received packets sequentially received by communication unit 18 of communication terminal 8b are consecutive numbers.

[0074] Next, since the sequence number included in the packet last received from the base station 6 is the pre-specified number "5" (i.e., a multiple of "5"), the communication unit 18 of the communication terminal 8a transfers all five received packets including the five sequence numbers "1," "2," "3," "4," and "5" stored in the memory unit 20 of the communication terminal 8a to the display 10a (S117).

[0075] Furthermore, since the sequence number included in the last packet received from the base station 6 is "5," the communication unit 18 of the communication terminal 8b transfers all five received packets including the five sequence numbers "1," "2," "3," "4," and "5" stored in the memory unit 20 of the communication terminal 8b to the display 10b (S118).

[0076] Thereafter, although not shown in the figure, the communication unit 12 of the base station 6 transmits a packet including the sequence number "6" to each of the multiple communication terminals 8a, 8b by broadcast or multicast, and thereafter the same processing as described above is executed.

[0077] As described above, Fig. 4 shows a sequence diagram illustrating the flow of operation of the communication system 2 in the retransmission priority mode. In contrast to this, in the delivery priority mode, the determination unit 16 of the base station 6 first determines that the untransmitted packet (sequence number "5") can be transmitted, and then transmits the packet with sequence number "5". Next, the determination unit 16 determines whether or not the unreceived packets (sequence numbers "2" and "3") related to the retransmission request can be retransmitted, and if it determines that retransmission is possible, transmits the unreceived packets. Details will be explained below using Figs. 6 and 7.

[0078] Next, the operation of the communication system 2 when the determination unit 16 of the base station 6 determines that retransmission of an unreceived packet is not possible in the retransmission priority mode will be described with reference to Fig. 5. Fig. 5 is a sequence diagram showing the flow of the operation of the communication system 2 according to the embodiment when the determination unit 16 of the base station 6 determines that retransmission of an unreceived packet is not possible in the retransmission priority mode.

[0079] In the sequence diagram of FIG. 5, the same processes as those in the sequence diagram of FIG. 4 are assigned the same step numbers, and the description thereof will be omitted.

[0080] As shown in FIG. 5, steps S101 to S110 are executed in the same manner as in the sequence diagram of FIG.

[0081] After step S110, upon receiving a retransmission request from communication terminal 8a (specific communication terminal), determination unit 16 of base station 6 determines that retransmission of the two unreceived packets containing the two sequence numbers "2" and "3" is impossible based on the transmission time required to retransmit the two unreceived packets (S201). In this case, communication unit 12 of base station 6 does not retransmit the two unreceived packets to communication terminal 8a based on the determination result of determination unit 16.

[0082] Next, the determination unit 16 of the base station 6 determines whether or not the unsent packet (sequence number "5") can be transmitted, and determines that it can in this embodiment (S202). Next, steps S115 and S116 are executed, similarly to the sequence diagram of FIG.

[0083] After step S116, retransmission request unit 22 of communication terminal 8a executes a timeout process for the retransmission request (S203). Next, because the sequence number included in the packet last received from base station 6 is "5", communication unit 18 of communication terminal 8a transfers all three received packets including the three sequence numbers "1", "4", and "5" stored in storage unit 20 of communication terminal 8a to display 10a (S204).

[0084] Meanwhile, since the sequence number included in the last packet received from the base station 6 is "5," the communication unit 18 of the communication terminal 8b transfers all five received packets including the five sequence numbers "1," "2," "3," "4," and "5" stored in the memory unit 20 of the communication terminal 8b to the display 10b (S118).

[0085] 5 shows a sequence diagram illustrating the flow of operation of communication system 2 when it is determined that retransmission of an unreceived packet is impossible in retransmission priority mode. On the other hand, in distribution priority mode, determination unit 16 of base station 6 first determines that transmission of the untransmitted packet (sequence number "5") is impossible, and then determines whether retransmission of the unreceived packets (sequence numbers "2" and "3") related to the retransmission request is possible. Furthermore, in the distribution priority mode, since it becomes clear that communication terminal 8a is unable to receive five packets due to timeout processing, communication unit 18 determines that transfer to displays 10a and 10b is possible even when the number of received packets has not reached the predetermined number (five).

[0086] [5. Operation of communication terminal] Next, the operation of the communication terminal 8a will be described with reference to Fig. 6. Since the operations of the multiple communication terminals 8a and 8b are the same, only the operation of the communication terminal 8a will be described below. Fig. 6 is a flowchart showing the flow of the operation of the communication terminal 8a according to the embodiment.

[0087] As shown in FIG. 6, first, the communication unit 18 receives a packet transmitted from the base station 6 (S301).

[0088] Next, the communication unit 18 determines whether or not a received packet including the same sequence number as the packet received in step S301 is stored in the storage unit 20 (S302).

[0089] If a received packet including the same sequence number as the packet received in step S301 is not stored in storage unit 20 (NO in S302), communication unit 18 stores the packet received in step S301 as a received packet in storage unit 20 (S303), and then proceeds to step S304.

[0090] On the other hand, if a received packet containing the same sequence number as the packet received in step S301 is stored in the memory unit 20 (YES in S302), the communication unit 18 does not store the packet received in step S301 as a received packet in the memory unit 20, and proceeds to step S304.

[0091] In step S304, it is determined whether the timeout period has elapsed. If the timeout period has not elapsed (NO in S304), the communication unit 18 first determines whether the mode of the base station 6 stored in the storage unit 20 is the retransmission priority mode or the delivery priority mode (S305).

[0092] If the mode is retransmission priority mode ("retransmission priority mode" in S305), next, the playback request unit 22 determines whether or not there is a missing number in the sequence numbers included in the packets received in step S301 (S306).

[0093] If there is a missing sequence number (YES in S306), retransmission request unit 22 requests base station 6 via communication unit 18 to retransmit one or more packets that have not been received by communication unit 18 (S312). Then, the process returns to step S301 described above.

[0094] On the other hand, if there are no missing sequence numbers (NO in S306), the communication unit 18 determines whether the sequence number included in the packet received in step S301 is a predetermined number (for example, "5") (S307). If the number is not a predetermined number (NO in S307), the process returns to step S301 and waits for the next packet to be received.

[0095] In step S307, if the sequence number included in the packet received in step S301 is a pre-specified value (for example, "5") (YES in S307), communication unit 18 transfers one or more received packets stored in storage unit 20 to display 10a all at once (S308). Next, communication unit 18 initializes storage unit 20 by deleting one or more received packets stored in storage unit 20 from storage unit 20 (S313). Thereafter, the processing of the flowchart in FIG. 6 ends.

[0096] Returning to step S305, if the mode of the base station 6 stored in the storage unit 20 is the delivery priority mode ("delivery priority mode" in S305), the communication unit 18 first determines whether or not the sequence number included in the packet received in step S301 is a pre-specified value (e.g., "5") (S309). This is because, unlike the retransmission priority mode, reception of an untransmitted packet is given priority over a retransmission request for an unreceived packet. If the sequence number is not a pre-specified value (e.g., "5") (NO in S309), the process returns to step S301 to receive an untransmitted packet. On the other hand, if the sequence number is a pre-specified value (e.g., "5") (YES in S309), the retransmission request unit 22 then determines whether or not there is a missing number in the sequence number included in the packet received in step S301 (S311).

[0097] In step S311, if there are missing numbers in the sequence numbers (YES in S311), retransmission request unit 22 requests base station 6 via communication unit 18 to retransmit one or more unreceived packets that have not been received (S312). Then, the process returns to step S301 described above. In step S311, if there are no missing numbers in the sequence numbers (YES in S311), communication unit 18 transfers one or more received packets stored in storage unit 20 all at once to display 10a (S308). Then, the process proceeds to step S313.

[0098] Returning to step S304, if the timeout period has elapsed (YES in S304), retransmission request unit 22 executes a timeout process for the retransmission request (S310). Thereafter, communication unit 18 transmits packets that are stored in storage unit 20 and that have not yet been transmitted to display 10a, and proceeds to step S313 to initialize storage unit 20.

[0099] [6. Base Station Operation] Next, the operation of the base station 6 will be described with reference to Fig. 7. Fig. 7 is a flowchart showing the flow of the operation of the base station 6 according to the embodiment.

[0100] 7 shows a situation in which communication unit 12 sequentially divides video data from camera 4 into a plurality of packets each including a plurality of sequence numbers, and transmits the divided packets to each of a plurality of communication terminals 8a and 8b by broadcast or multicast in the order of the sequence numbers. Also, in FIG. 7, the explanation is based on the assumption that a specific communication terminal has already transmitted a retransmission request to base station 6, and that one or more untransmitted packets to be transmitted to the specific communication terminal are waiting in storage unit 14 at base station 6. Note that, as described above, "untransmitted packets" refer to packets that communication unit 12 has not yet transmitted to each of the multiple communication terminals 8a and 8b by broadcast or multicast, and that are waiting to be transmitted in storage unit 14.

[0101] As shown in FIG. 7, the communication unit 12 receives a retransmission request from a specific communication terminal (for example, communication terminal 8a) (S401).

[0102] Next, the decision unit 16 calculates a transmission time T1 required to retransmit one or more unreceived packets based on one or more sequence numbers included in the retransmission request from the specific communication terminal (S402).

[0103] Next, the decision unit 16 refers to the storage unit 14 to calculate a transmission time T2 required to transmit one or more untransmitted packets (S403).

[0104] Next, the determination unit 16 determines whether the mode set by the user is the retransmission priority mode or the delivery priority mode (S404). As described above, the retransmission priority mode is a mode that prioritizes retransmission of unreceived packets, and the delivery priority mode is a mode that prioritizes transmission (delivery) of all untransmitted packets.

[0105] If the retransmission priority mode is set ("retransmission priority mode" in S404), the decision unit 16 calculates the remaining transmission time regulated by law and the transmission time T1, and compares them (S405).

[0106] The determination unit 16 may calculate various transmission times (transmission times T1, T2) based on the following conditions: (a) communication standard: IEEE802.11ah, (b) data rate: MCS0, number of streams: 1, (c) transmission period: 3600 seconds per period, (d) channel width: 1 MHz, (e) guard interval: short, and (f) data size of the packet to be transmitted: 10 Kbytes.

[0107] If the remaining transmission time is equal to or greater than the transmission time T1 (YES in S405), the determination unit 16 determines that one or more unreceived packets can be retransmitted. In this case, the communication unit 12 reads one or more unreceived packets from the storage unit 14 based on one or more sequence numbers included in the retransmission request from the specific communication terminal, and retransmits the read one or more unreceived packets (S406). Needless to say, the retransmission of one or more unreceived packets reduces the remaining transmission time (S407).

[0108] Thereafter, the determination unit 16 calculates the remaining transmission time and the transmission time T2 of the unsent packet, and compares them (S408). If the remaining transmission time is equal to or greater than the transmission time T2 (YES in S408), the determination unit 16 determines that one or more unsent packets can be transmitted. In this case, the communication unit 12 transmits one or more unsent packets (S409). Next, the remaining transmission time is decremented by the transmission of the one or more unsent packets (S410). Thereafter, the processing of the flowchart in FIG. 7 ends.

[0109] 7, in the retransmission priority mode, as a result of comparing the remaining transmission time with the transmission time T1, if the remaining transmission time is shorter (NO in S405), retransmission of one or more unreceived packets is skipped. After that, the processing of the flowchart in FIG. 7 is terminated.

[0110] In the retransmission priority mode, if the remaining transmission time is shorter than the transmission time T2 (NO in S408), the transmission of one or more unsent packets is skipped. After that, the process of the flowchart in FIG. 7 ends.

[0111] In this way, in the retransmission priority mode shown in Fig. 7, even if an untransmitted packet can be delivered, the untransmitted packet is not delivered and the system waits for the remaining transmittable time to be restored until one or more unreceived packets can be retransmitted. In this embodiment, the processing in the retransmission priority mode has been described as shown in Fig. 7, but unlike Fig. 7, if an untransmitted packet can be delivered (i.e., if the remaining transmittable time is equal to or greater than the transmission time T2), the untransmitted packet may be delivered without waiting for the remaining transmittable time to be restored.

[0112] Returning to step S404, if the delivery priority mode is set ("Delivery priority mode" in S404), the judgment unit 16 first calculates the remaining transmittable time specified by the communication standard and the transmission time T2 of the unsent packet, and compares the two (S411).

[0113] If the remaining transmission time is equal to or greater than the transmission time T2 (YES in S411), the determination unit 16 determines that one or more unsent packets can be transmitted. In this case, the communication unit 12 first transmits one or more unsent packets (S412). Naturally, the transmission of these one or more unsent packets decrements the remaining transmission time (S413).

[0114] Thereafter, the determination unit 16 calculates the remaining transmission time and the retransmission time T1 of the unreceived packets, and compares them (S414). If the remaining transmission time is equal to or greater than the transmission time T1 (YES in S414), the determination unit 16 determines that one or more unreceived packets can be retransmitted. In this case, the communication unit 12 reads one or more unreceived packets from the storage unit 14 based on one or more sequence numbers included in the retransmission request from the specific communication terminal, and retransmits the read one or more unreceived packets (S415). Next, the remaining transmission time is decremented by the retransmission of the one or more unreceived packets (S416). Thereafter, the processing of the flowchart in FIG. 7 ends.

[0115] 7, in the delivery priority mode, as in the retransmission priority mode described above, if the remaining transmittable time is shorter than the transmission time T2 as a result of comparing the remaining transmittable time with the transmission time T2 (NO in S411), the transmission of one or more unsent packets is skipped. After that, the processing of the flowchart in FIG. 7 is terminated.

[0116] In the delivery priority mode, if the remaining transmittable time is shorter than the transmission time T1 (NO in S414), the retransmission of one or more unreceived packets is skipped. After that, the process in the flowchart of FIG. 7 ends.

[0117] In this way, in the delivery priority mode shown in Fig. 7, even if an unreceived packet can be retransmitted, the delivery priority mode waits for recovery of the remaining transmittable time without retransmitting the unreceived packet until one or more untransmitted packets can be transmitted, just like the retransmission priority mode. In this embodiment, the processing in the delivery priority mode has been described as shown in Fig. 7, but unlike Fig. 7, if an unreceived packet can be retransmitted (i.e., if the remaining transmittable time is equal to or greater than the transmission time T1), the unreceived packet may be retransmitted without waiting for recovery of the remaining transmittable time.

[0118] In this embodiment, in the delivery priority mode, the judgment unit 16 judges that one or more unreceived packets can be retransmitted when the remaining transmittable time is equal to or greater than the transmission time T1, but this is not limited to this, and the judgment unit 16 may also judge that one or more unreceived packets can be retransmitted when the remaining transmittable data size calculated from the remaining communication time is equal to or greater than the data size of one or more unreceived packets.

[0119] Furthermore, in this embodiment, in the delivery priority mode, the judgment unit 16 judges that one or more unsent packets can be transmitted when the remaining transmittable time is equal to or greater than the transmission time T2, but this is not limited to this, and the judgment unit 16 may also judge that one or more unsent packets can be transmitted when the remaining transmittable data size calculated from the remaining communication time is equal to or greater than the data size of one or more unsent packets.

[0120] [7. Effects] In this embodiment, when a retransmission request is received from a specific communication terminal, determination unit 16 of base station 6 determines whether or not retransmission of one or more unreceived packets is possible based on the transmission time required to retransmit the one or more unreceived packets. Then, when determination unit 16 determines that retransmission of one or more unreceived packets is possible, communication unit 12 of base station 6 retransmits the one or more unreceived packets to the specific communication terminal.

[0121] This makes it possible to prevent packets transmitted by broadcast or multicast from the base station 6 from being lost due to not being received by a particular communication terminal. As a result, in the communication system 2 using a communication standard that limits the transmission time per unit time, it is possible to improve the communication quality when performing wireless communication by broadcast or multicast while satisfying the specifications of the communication standard.

[0122] (Other variations, etc.) Although the communication system of the present invention has been described above based on the above embodiment, the present invention is not limited to the above embodiment. The present invention also includes modifications that can be made to the above embodiment by those skilled in the art, and other modifications that can be realized by arbitrarily combining the components of the above embodiment.

[0123] In the above embodiment, when a retransmission request is received from a specific communication terminal, the determination unit 16 of the base station 6 determines whether or not it is possible to retransmit one or more unreceived packets based on the transmission time required to retransmit the one or more unreceived packets. However, this is not limited to this. When a retransmission request is received from a specific communication terminal, the determination unit 16 of the base station 6 may determine whether or not it is possible to retransmit one or more unreceived packets based on the data size of the one or more unreceived packets to be retransmitted. In this case, the determination unit 16 determines that it is possible to retransmit one or more unreceived packets when the remaining transmittable data size calculated from the remaining available communication time specified by the communication standard is equal to or greater than the data size of the one or more unreceived packets.

[0124] In the above embodiment, the communication system 2 is applied to a video distribution system, but the present invention is not limited to this and may be applied to, for example, a video distribution system, a music distribution system, or the like.

[0125] In the above-described embodiments, each component may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may also be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory. [Industrial Applicability]

[0126] The present invention can be applied to, for example, a communication system in which a packet from a base station is transmitted to each of a plurality of communication terminals by broadcast or multicast. [Explanation of symbols]

[0127] 2. Communication Systems 4. Camera 6 base station 8a, 8b Communication terminal 10a, 10b Display 12,18 Communications Department 14,20 Storage part 16 Judgment section 22 Retransmission request section

Claims

1. A base station; a plurality of communication terminals that perform wireless communication with the base station in accordance with a communication standard in which a transmission time per unit time is limited; the base station has a first communication unit that transmits a plurality of packets, each including a sequence number, to each of the plurality of communication terminals by broadcast or multicast in order of the sequence numbers; Each of the plurality of communication terminals a second communication unit that receives packets transmitted from the base station; a retransmission request unit that requests the base station to retransmit one or more unreceived packets that have not been received by the second communication unit when one or more sequence numbers included in each of the one or more received packets received by the second communication unit are missing, the base station further comprises a determination unit that, when receiving a retransmission request from a specific communication terminal among the plurality of communication terminals, determines whether or not retransmission of the one or more unreceived packets is possible based on a transmission time required for retransmitting the one or more unreceived packets or a data size of the one or more unreceived packets to be retransmitted; The first communication unit retransmits the one or more unreceived packets to the specific communication terminal when the determination unit determines that retransmission of the one or more unreceived packets is possible. Communication system.

2. The determination unit determines that retransmission of the one or more unreceived packets is possible when a remaining transmission time defined by the communication standard is equal to or longer than a transmission time required to retransmit the one or more unreceived packets. The communication system of claim 1 .

3. The determination unit further (i) determines, when receiving a retransmission request from the specific communication terminal among the plurality of communication terminals, whether to prioritize retransmission of the one or more unreceived packets or transmission of one or more untransmitted packets that have not yet been transmitted from the base station, and (ii) when it determines that transmission of the one or more untransmitted packets is prioritized, determines, prior to retransmission of the one or more unreceived packets, whether or not transmission of the one or more untransmitted packets is possible based on a transmission time required to transmit the one or more untransmitted packets or a data size of the one or more untransmitted packets to be transmitted; When the determination unit determines that the one or more untransmitted packets can be transmitted, the first communication unit transmits the one or more untransmitted packets to each of the plurality of communication terminals by broadcast or multicast before retransmitting the one or more unreceived packets. The communication system of claim 1 .

4. The determination unit determines that the one or more untransmitted packets can be transmitted when a remaining transmittable time defined by the communication standard is equal to or longer than a transmission time required to transmit the one or more untransmitted packets. The communication system according to claim 3 .

5. The determination unit determines that the one or more untransmitted packets can be transmitted when a transmittable remaining data size calculated from a remaining communication time defined by the communication standard is equal to or larger than a data size of the one or more untransmitted packets. The communication system according to claim 3 .

6. each of the plurality of communication terminals further includes a buffer memory that temporarily stores the one or more received packets received by the second communication unit; The second communication unit transfers the one or more received packets to an external device when there are no missing numbers in the one or more sequence numbers included in each of the one or more received packets stored in the buffer memory and the number of the one or more received packets reaches a predetermined number. A communication system according to any one of claims 1 to 5.

7. A base station that performs wireless communication with a plurality of communication terminals in accordance with a communication standard in which the transmission time per unit time is limited, a communication unit that transmits a plurality of packets, each including a sequence number, to each of the plurality of communication terminals by broadcast or multicast in order of the sequence numbers; a determination unit that, when a retransmission request is received from a specific communication terminal among the plurality of communication terminals due to a missing number in one or more sequence numbers included in one or more received packets received by the specific communication terminal, determines whether or not retransmission of the one or more unreceived packets is possible based on a transmission time required to retransmit the one or more unreceived packets that have not been received by the specific communication terminal or a data size of the one or more unreceived packets to be retransmitted, The communication unit retransmits the one or more unreceived packets to the specific communication terminal when the determination unit determines that retransmission of the one or more unreceived packets is possible. Base station.

8. A control method in a communication system including a base station and a plurality of communication terminals that perform wireless communication between the base station in accordance with a communication standard in which a transmission time per unit time is limited, comprising: (a) transmitting, by the base station, a plurality of packets each including a sequence number to each of the plurality of communication terminals in order of the sequence numbers by broadcast or multicast; (b) each of the plurality of communication terminals receiving a packet transmitted from the base station; (c) when there is a missing number in one or more sequence numbers included in one or more received packets received by a specific communication terminal among the plurality of communication terminals, the specific communication terminal requests the base station to retransmit one or more unreceived packets that it has not received; (d) when the base station receives a retransmission request from the specific communication terminal, determining whether or not retransmission of the one or more unreceived packets is possible based on a transmission time required for retransmitting the one or more unreceived packets or a data size of the one or more unreceived packets to be retransmitted; (e) when the base station determines in (d) that retransmission of the one or more unreceived packets is possible, retransmitting the one or more unreceived packets to the specific communication terminal. Control method.

Images