COMMUNICATION SYSTEM, RECEIVING STATION, COMMUNICATION METHOD, AND COMPUTER PROGRAM

Abstract

To provide a receiving station which can determine which communication channel can be used when a plurality of communication channels between a transmitting station and the receiving station are used, to provide a communication system and a communication method in each of which, it can be determined which communication channel can be used when a plurality of communication channels between a transmitting station and the receiving station are used, and to provide a computer program.SOLUTION: A transmitting station comprises: a first transmission section performing transmission of video data using a first communication channel between the transmitting station and a receiving station; and a second transmission section performing transmission of video data using a second communication channel between the transmitting station and the receiving station. The video data is data obtained by compressing a moving image. The receiving station comprises: a first reception section receiving video data using the first communication channel; a second reception section receiving video data using the second communication channel; and a channel selection section that on the basis of whether or not decoding of a first frame holding all information of a frame included in reception data of the first communication channel is successful, selects which communication channel of the first communication channel and the second communication channel is to be used as a reception channel receiving the video data from the transmitting station.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication system, a receiving station, a communication method, and a computer program. [Background technology]

[0002] Remote monitoring of autonomous vehicles is often performed using video transmitted from on-board cameras installed in the autonomous vehicles. For this reason, it is important to create an environment where on-board camera video can be received and displayed without interruption. There is known a communication system that has a working system and a backup system to ensure communication connectivity, and when communication becomes impossible with the working system, switches to the backup system to continue communication. For example, the opposing devices of the working system and the backup system feed back the data reception status, and switches the line depending on the feedback status (see, for example, Patent Document 1). For example, by configuring a transmitter and a receiver redundantly and sending the same data to both transmission paths, even if an abnormality occurs in the transmission path of the working system, the receiving side can receive video without interruption by adopting data from the transmission path of the backup system (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-147055 A [Patent Document 2] JP 2009-017508 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described above switches lines only after the communication situation has deteriorated, which often results in situations where communication is not possible. For this reason, if this technology is applied to a remote monitoring system, it is expected that situations will arise where video cannot be received and monitoring cannot be continued. The technology described above transmits the same video data to the active and standby systems, and a buffer is provided in the receiving section to time-synchronize the received data between the active and standby systems. This causes a delay before the video is displayed. An object of the present invention is to provide a communication system, a receiving station, a communication method, and a computer program that enable the receiving station to determine which communication line to use when multiple communication lines are used between a transmitting station and a receiving station. [Means for solving the problem]

[0005] (1) One aspect of the present invention is a communication system including a transmitting station and a receiving station, the transmitting station including a first transmitting unit that transmits video data using a first communication line between the transmitting station and the receiving station, and a second transmitting unit that transmits video data using a second communication line between the transmitting station and the receiving station, the video data transmitted by the first transmitting unit being video-compressed data, the transmitting station transmits the video data via both the first communication line and the second communication line; The receiving station includes a first receiving unit that receives video data using the first communication line, a second receiving unit that receives video data using the second communication line, and a first receiving unit that receives the video data from the first communication line. The video data a line selection unit that selects, based on whether a first frame that holds all information of the frame has been successfully decoded, which of the first communication line and the second communication line is to be used as a receiving line for receiving video data from the transmitting station; a control unit that displays video data received using one of the first communication line and the second communication line selected by the line selection unit; and The present invention relates to a communication system. (2) In one aspect of the present invention, in the communication system described in (1) above, the line selection unit transitions between a first state in which decoding of the first frame included in the received data of the first communication line is successful, a second state in which decoding of the first frame included in the received data of the first communication line is unsuccessful, and a third state in which a stop of the video stream is detected, and selects which of the first communication line or the second communication line to use as a receiving line for receiving video data from the transmitting station based on whether the receiving station is in the first state, the second state, or the third state. (3) In one aspect of the present invention, in the communication system described in (2) above, the first state is a state in which both the first frame included in the received data of the first communication line of the first receiving unit and a second frame that can be decoded by referring to the first frame are successfully decoded without detecting a path loss, and the second state is a state in which a path loss is detected or decoding of either or both of the first frame and the second frame included in the received data of the first communication line of the first receiving unit fails. (4) In one aspect of the present invention, in the communication system described in (2) or (3) above, the line selection unit transitions to the first state when, in the second state, the first frame included in the received data of the first communication line is successfully decoded, and transitions to the first state when, in the third state, the resumption of the video stream is detected. ( 5) One aspect of the present invention is that in the communication system described in (1) above, the line selection unit selects which of the first communication line and the second communication line to use as a receiving line for receiving video data from the transmitting station, based on whether or not decoding of a second frame that can be decoded by referring to the first frame is successful. ( 6 ) One aspect of the present invention is the above (1) or the above ( 5 In the communication system according to the above, the line selection unit The above A reception line for receiving video data from the transmitting station is selected based on whether or not a packet including the first frame in its payload has been received, or based on the cumulative number of receptions of the packet. ( 7 ) One aspect of the present invention is the above (1) to the above ( 5 In the communication system described in any one of claims 1 to 4, the line selection unit selects a receiving line for receiving video data from the transmitting station based on whether or not a packet loss has been detected or on the cumulative number of packet losses. ( 8 ) One aspect of the present invention is the above (1) to the above ( 7 In the communication system according to any one of claims 1 to 5, The above A receiving line for receiving video data from the transmitting station is selected based on whether the decoding of the first frame has been completed or the cumulative number of first frames for which decoding has been completed. ( 9 ) One aspect of the present invention is the above (1) to the above ( 8 ), the first transmission unit transmits first video data using the first communication line, and the second transmission unit transmits second video data different from the first video data using the second communication line.

[0006] ( 10 One aspect of the present invention is a method for receiving video data by using a first communication line, a second communication line, and a first receiving unit that receives video data by using a second communication line. The video dataa line selection unit that selects, based on whether a first frame that holds all information of the frame has been successfully decoded, which of the first communication line and the second communication line is to be used as a receiving line for receiving video data from a transmitting station; a control unit that displays video data received using one of the first communication line and the second communication line selected by the line selection unit; and the video data received by the first receiving unit is video-compressed data. The video data is transmitted via both the first communication line and the second communication line. It is a receiving station.

[0007] ( 11 One aspect of the present invention is a communication method for a communication system including a transmitting station and a receiving station, the transmitting station providing a first communication line between the transmitting station and the receiving station. and the second communication line Use to transmit video data. Send Communication step and ,before A first receiving step in which the receiving station receives video data using the first communication line, a second receiving step in which the receiving station receives video data using the second communication line, and the receiving station receives the video data included in the received data of the first communication line. The video data a line selection step of selecting, based on whether a first frame holding all information of the frame has been successfully decoded, which of the first communication line and the second communication line is to be used as a receiving line for receiving video data from the transmitting station; a display step of displaying the video data received using one of the first communication line and the second communication line selected in the line selection step; and Send In the communication method, the video data transmitted in the transmitting step is compressed video data.

[0008] ( 12 One aspect of the present invention includes a first receiving step of receiving video data using a first communication line, a second receiving step of receiving video data using a second communication line, and a step of receiving a video data included in the received data of the first communication line. The video data a line selection step of selecting, based on whether a first frame holding all information of the frame has been successfully decoded, which of the first communication line and the second communication line is to be used as a receiving line for receiving video data from a transmitting station; a display step of displaying the video data received using either the first communication line or the second communication line selected in the line selection step; the video data received in the first receiving step is compressed video data. The video data is transmitted via both the first communication line and the second communication line.A communication method implemented by a receiving station.

[0009] ( 13 In one aspect of the present invention, a computer program for a receiving station includes a first receiving step of receiving video data using a first communication line, a second receiving step of receiving video data using a second communication line, and a step of detecting a video signal included in the received data of the first communication line. The video data a line selection step of selecting, based on whether a first frame holding all information of the frame has been successfully decoded, which of the first communication line and the second communication line is to be used as a receiving line for receiving video data from a transmitting station; a display step of displaying the video data received using either the first communication line or the second communication line selected in the line selection step; the video data received in the first receiving step is compressed video data. The video data is transmitted via both the first communication line and the second communication line. It is a computer program. Effect of the Invention

[0010] According to the present invention, when a plurality of communication lines are used between a transmitting station and a receiving station, the receiving station can determine which communication line to use. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing an example of the configuration of a communication system according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a state transition model applied to a fixed station according to the embodiment. [Diagram 3] FIG. 4 is a diagram showing an example of a transmission process on the transmitting side (transmitting station) according to the present embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a reception process on the receiving side (receiving station) according to the embodiment. [Diagram 5] FIG. 11 is a block diagram showing an example of the configuration of a communication system according to a second embodiment. [Figure 6] FIG. 13 is a block diagram showing an example of the configuration of a communication system according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Next, a communication system, a receiving station, a communication method, and a computer program according to the present embodiment will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment. In all the drawings for explaining the embodiment, the same reference numerals are used for parts having the same functions, and repeated explanations will be omitted.

[0013] (First embodiment) 1 is a block diagram showing an example of the configuration of a communication system according to the first embodiment. In the communication system 1 according to the first embodiment, communication is performed between a mobile station 100 and a base station 200. In the communication system 1, there are cases where the mobile station 100 serves as a transmitting station and transmits data to the base station 200 (receiving station), and cases where the mobile station 100 serves as a receiving station and receives data from the base station 200 (transmitting station). The communication system 1 is, for example, a system in which a mobile station 100, which is an autonomous vehicle, and a fixed station 200, which is a remote monitoring console, communicate with each other, and is for remotely monitoring the autonomous vehicle using the remote monitoring console. Since the behavior of the autonomous vehicle is constantly monitored in this remote monitoring, stable communication between the mobile station 100 and the fixed station 200 is required. The mobile station 100 includes a first communication terminal 101, a second communication terminal 102, and a control unit 103. The base station 200 includes a first communication terminal 201, a second communication terminal 202, a control unit 203, a line selection unit 204, and a video display unit 205.

[0014] (Mobile station) The first communication terminal 101 performs communication using the first wireless communication network NW1. The first communication terminal 101 connects to a base station of the first wireless communication network NW1 and performs wireless communication with the base station. The first communication terminal 101 of the mobile station 100 establishes a communication line L1 with the first communication terminal 201 of the fixed station 200. The communication line L1 corresponds to the first communication line. The second communication terminal 102 performs communication using the second wireless communication network NW2. The second communication terminal 102 connects to a base station of the second wireless communication network NW2 and performs wireless communication with the base station. The second communication terminal 102 of the mobile station 100 establishes a communication line L2 with the second communication terminal 202 of the fixed station 200. The communication line L2 corresponds to the second communication line.

[0015] The communication line L1 is a communication line that is primarily used. The communication line L2 is a communication line that is used as a backup. The first wireless communication network NW1 used for the communication line L1 is, for example, a wireless communication network that is excellent in terms of communication performance and cost. On the other hand, since the communication line L2 is used as a backup, it is preferable that the second wireless communication network NW2 used for the communication line L2 has communication stability equal to or greater than that of the first wireless communication network NW1. It is preferable that the second wireless communication network NW2 has, for example, a wider communication area for mobile communication than the first wireless communication network NW1 and is less susceptible to communication interruptions than the first wireless communication network NW1. For example, when the first wireless communication network NW1 is a 5G (fifth generation mobile communication system) with excellent communication performance, the second wireless communication network NW2 is an LTE (Long Term Evolution) system with excellent communication stability. For example, when the first wireless communication network NW1 is a WiMAX system with excellent cost, the second wireless communication network NW2 is an LTE system with excellent communication stability. For example, when used at sea, when the first wireless communication network NW1 is an LTE system with excellent cost, the second wireless communication network NW2 is a satellite line system with excellent communication stability.

[0016] The control unit 103 controls the mobile station 100. The control unit 103 controls the start and end of communication of the mobile station 100 according to instructions to start and end communication from an operator of the mobile station 100, the mobile station side system 10, etc. An example of the mobile station side system 10 is an automatic driving control system for an automatic driving vehicle. The automatic driving control system transmits information about a monitored vehicle to the control unit 103. Examples of the information about the vehicle include an on-board camera image, vehicle position information, driving route information, etc. The control unit 103 transmits the transmission data received from the mobile station side system 10 to the base station 200 via at least one of the communication lines L1 and L2. The communication line L1 is mainly used as the transmission line for transmitting data to the base station 200. An example of the transmission data is video data. The following continues the explanation of the case where the transmission data is video. The control unit 103 encodes the video. For example, the control unit 103 uses a video compression technique to encode the video into video data including an I frame (intra-coded frame) and a P frame (predicted frame). An I frame is a frame that holds all frame information. A receiving station can decode an I frame without referring to other frames. A P frame is a frame that holds information of a difference between a previously transmitted I frame or a previously transmitted P frame. A receiving station can decode a P frame by referring to a previously transmitted I frame or a previously transmitted P frame. An example of the video compression technique is one that complies with a video compression standard such as H.264 Baseline Profile. The control unit 103 transmits the video data to the fixed station 200 through at least one of the communication lines L1 and L2.

[0017] The control unit 103 transmits the reception data received from the base station 200 to the mobile station side system 10. The communication line L1 is mainly used as the reception line for receiving data from the base station 200. When data is normally received from only one of the communication lines L1 and L2 from the base station 200, the control unit 103 determines the communication line for normal reception as the reception line for receiving data from the base station 200. The control unit 103 may have a function of adjusting the amount of transmission data by changing the transmission bit rate, etc., depending on the performance of the first communication terminal 101 and the second communication terminal 102 when the mobile station 100 transmits data to the base station 200.

[0018] (Fixed station) The first communication terminal 201 and the second communication terminal 202 communicate using a communication network NW3. The communication network NW3 may be a wireless communication network or a wired communication network. Since the fixed station 200 does not communicate while moving, even if the communication network NW3 is a wireless communication network, the wireless communication quality is stable and good. In this embodiment, the first communication terminal 201 and the second communication terminal 202 use the same communication network NW3, but the first communication terminal 201 and the second communication terminal 202 may use different communication networks. The first communication terminal 201 of the base station 200 establishes a communication line L1 with the first communication terminal 101 of the mobile station 100. The second communication terminal 202 of the base station 200 establishes a communication line L2 with the second communication terminal 102 of the mobile station 100. The first communication terminal 201 measures the reception data quality (status) of data received from the first communication terminal 101 of the mobile station 100 via the communication line L1. The reception data quality (status) is, for example, the number of packet losses, the number of packets received that contain an I frame in the payload, the number of I frames that have been decoded, the bit rate of the video elementary stream, etc. The second communication terminal 202 judges whether data has arrived from the second communication terminal 102 of the mobile station 100 via the communication line L2.

[0019] The control unit 203 controls the base station 200. The control unit 203 controls the start and end of communication of the base station 200 according to instructions to start and end communication from an operator of the base station 200, the base station side system 20, etc. The base station side system 20 is, for example, a remote monitoring system for remotely monitoring an autonomous vehicle. The control unit 203 transmits the transmission data received from the fixed station side system 20 to the mobile station 100 through at least one of the communication lines L1 and L2. The communication line L1 is the communication line that is mainly used as the transmission line for transmitting data to the mobile station 100. The control unit 203 transmits the reception data received from the mobile station 100 to the fixed station side system 20. The communication line L1 is the communication line that is mainly used as the reception line for receiving data from the mobile station 100. The control unit 203 acquires the reception data quality (status) from the first communication terminal 201. The control unit 203 transmits the acquired reception data quality (status) to the line selection unit 204. When the control unit 203 receives a reception line selection result from the line selection unit 204, it determines the reception line for receiving data from the mobile station 100 from the communication lines L1 and L2 based on the reception line selection result. Based on the determined receiving line, the control unit 203 selects one of the video data from each of the communication lines L1 and L2, and outputs the selected video data to the video display unit 205. Note that when the control unit 203 normally receives data from the mobile station 100 only from one of the communication lines L1 and L2, the control unit 203 outputs the video data from the communication line that is normally received to the video display unit 205, regardless of the receiving line selection result of the line selection unit 204.

[0020] The control unit 203 may have a function of adjusting the amount of transmission data by changing the transmission bit rate, etc., depending on the performance of the first communication terminal 201 and the second communication terminal 202 when the base station 200 transmits data to the mobile station 100. The line selection unit 204 has a receiving line selection function. The line selection unit 204 receives the reception data quality (status) transmitted by the control unit 203. The line selection unit 204 selects a receiving line for receiving data from the mobile station 100 from the communication lines L1 and L2 based on the received reception data quality (status). An example of a process in which the line selection unit 204 selects a receiving line for receiving data from the mobile station 100 will be described. In video transmission using image compression codecs such as H264, H265, and VP9, ​​if the decoding of an I frame or P frame fails, the video has a tendency to be distorted until the decoding of the next I frame is successful, regardless of the reception status thereafter. For this reason, a state transition model is constructed in which the state of the fixed station 200 transitions depending on the failure of decoding either one or both of the I frame and the P frame and the success of the decoding of the I frame with respect to the video data received by the first communication terminal 201.

[0021] 2 is a diagram showing an example of a state transition model applied to the base station according to this embodiment. The base station 200 transitions to one of a normal state S01, a continuous disturbance state S02, and a temporary disturbance state S03. The normal state S01 is a state in which the base station 200 does not detect a path loss and the first communication terminal 201 successfully decodes both an I frame and a P frame for the video data received. The continuous disturbance state S02 is a state in which the base station 200 detects a path loss, or the first communication terminal 201 fails to decode either an I frame or a P frame, or both, for the video data received. The temporary disturbance occurrence state S03 is a state in which the base station 200 detects a stop of the video stream due to jitter generation or rendering delay in the communication line. The stop of the video stream may occur successively depending on the state of the communication line, and the range of influence is limited to the period during which the video stream is stopped. Therefore, independently of the transition between the normal state S01 and the continuous disturbance occurrence state S02, when the base station 200 detects a stop of the video stream, it determines that the video has stopped, and transitions to the temporary disturbance occurrence state S03. For example, the base station 200 determines that it has detected a stop of the video stream when the bit rate of the video stream is 0 (zero), the number of received packets does not increase, or the number of decoded frames does not increase. The base station 200 determines that it has detected a start (restart) of the video stream when the bit rate of the video stream is not 0 (zero), the number of received packets increases, or the number of decoded frames increases.

[0022] With reference to FIG. 2, a process of the base station 200 transitioning between the normal state S01, the continuous disturbance occurrence state S02, and the temporary disturbance occurrence state S03 will be described. The line selection unit 204 determines whether or not a packet including an I frame in the payload is received immediately after starting communication with the mobile station 100, and transitions the base station 200 to the normal state S01 when it is determined that a packet including an I frame in the payload is received. For example, the line selection unit 204 transitions the base station 200 to the normal state S01 when it detects reception of a packet including an I frame in the payload based on the number of packets including an I frame in the payload included in the reception data quality, or when the cumulative number of packets including an I frame in the payload is increased to a predetermined threshold or more. For example, the first communication terminal 201 determines whether or not an I frame is included in the payload based on a flag indicating a frame type included in the payload. In the case of the H.264 codec, it is determined based on the AVC NAL unit type included at the beginning of the payload. The line selection unit 204 judges whether the decoding of either or both of the I frame and the P frame has failed in the normal state S01, and when it is judged that the decoding of either or both of the I frame and the P frame has failed, it transitions the base station 200 from the normal state S01 to the disturbance continuing occurrence state S02 (T01). For example, when the line selection unit 204 detects the reception of a packet loss based on the number of packet losses included in the reception data quality, or when the cumulative number of packets judged to be packet losses increases to a predetermined threshold or more, it determines that the decoding of either or both of the I frame and the P frame has failed, and transitions the base station 200 from the normal state S01 to the disturbance continuing occurrence state S02.

[0023] The line selection unit 204 judges whether the decoding of the I frame is completed in the disturbance continuation state S02, and when it judges that the decoding of the I frame is completed, transitions the base station 200 from the disturbance continuation state S02 to the normal state S01 (T02). For example, the line selection unit 204 transitions the base station 200 from the disturbance continuation state S02 to the normal state S01 when it detects the completion of the decoding of the I frame based on the number of I frames whose decoding is completed, which are included in the reception data quality, or when the cumulative number of received I frames whose decoding is completed increases to a predetermined threshold or more. The line selection unit 204 judges whether the stop of the video stream is detected in the normal state S01, and when it detects the stop of the video stream, transitions the base station 200 from the normal state S01 to the disturbance temporary occurrence state S03 (T03). For example, when the line selection unit 204 detects a stop of the video stream based on the bit rate of the video elementary stream included in the received data quality, the line selection unit 204 transitions the base station 200 from the normal state S01 to the temporary disturbance occurring state S03. The line selection unit 204 determines whether or not restart of the video stream is detected in the disturbance temporary occurrence state S03, and when restart of the video stream is detected, transitions the base station 200 from the disturbance temporary occurrence state S03 to the normal state S01 (T04). For example, when the line selection unit 204 detects restart of the video stream based on the bit rate of the video elementary stream included in the received data quality, transitions the base station 200 from the disturbance temporary occurrence state S03 to the normal state S01.

[0024] The line selection unit 204 judges whether the decoding of either or both of the I frame and the P frame has failed in the disturbance temporary occurrence state S03, and when it is judged that the decoding of either or both of the I frame and the P frame has failed, it transitions the fixed station 200 from the disturbance temporary occurrence state S03 to the disturbance continuing occurrence state S02 (T05). For example, when the line selection unit 204 detects the reception of a packet loss based on the number of packet losses included in the reception data quality, or when the cumulative number of packets judged to be packet losses increases to a predetermined threshold or more, it judges that the decoding of either or both of the I frame and the P frame has failed, and transitions the fixed station 200 from the disturbance temporary occurrence state S03 to the disturbance continuing occurrence state S02. Returning to FIG. 1, the explanation will be continued.

[0025] The line selection unit 204 creates a receiving line selection result including information specifying the communication line L1 when in the normal state S01, and outputs the created receiving line selection result to the control unit 203. The line selection unit 204 creates a receiving line selection result including information specifying the communication line L2 when in the continuous disturbance occurrence state S02 or the temporary disturbance occurrence state S03, and outputs the created receiving line selection result to the control unit 203. Based on the receiving line selection result from the line selection unit 204, if the information specifying the communication line L1 is included, the control unit 203 selects video data from the communication line L1 and outputs the selected video data to the video display unit 205. Based on the receiving line selection result from the line selection unit 204, if the information specifying the communication line L2 is included, the control unit 203 selects video data from the communication line L2 and outputs the selected video data to the video display unit 205. The video display unit 205 is, for example, configured by a display device, and displays the video transmitted from the control unit 203.

[0026] (Transmission process on the sending side (transmitting station)) 3 is a diagram showing an example of transmission processing on the transmitting side (transmitting station) according to this embodiment. Here, a mobile station 100 is taken as an example of the transmitting side (transmitting station) for explanation. The mobile station 100 starts communication with the base station 200 in response to an instruction to start communication from an operator of the mobile station 100, the mobile station side system 10, etc. The mobile station 100 transmits transmission data received from the mobile station side system 10 to the base station 200. (Step S1-1) The control unit 103 uses a video compression technique to encode video into video data including I frames and P frames. (Step S2-1) The control unit 103 outputs video data to the first communication terminal 101 (first transmission unit). The first communication terminal 101 acquires the video data output by the control unit 103, and transmits the acquired video data to the base station 200 using the communication line L1 (first communication line). (Step S3-1) The control unit 103 outputs the video data to the second communication terminal 102 (second transmission unit). The second communication terminal 102 acquires the video data output by the control unit 103, and transmits the acquired video data to the base station 200 using the communication line L2 (second communication line). Then, the process returns to step S1-1. When the mobile station 100 receives an instruction to end communication from the operator of the mobile station 100, the mobile station side system 10, or the like, the mobile station 100 ends the transmission process in FIG. In the above explanation of the transmission process, the mobile station 100 is taken as an example of the transmitting side (transmitting station), but the transmission process of FIG. 3 may also be applied to the base station 200 as the transmitting station.

[0027] (Reception processing at the receiving side (receiving station)) 4 is a diagram showing an example of reception processing on the receiving side (receiving station) according to this embodiment. Here, the base station 200 is taken as an example of the receiving side (receiving station) for explanation. The base station 200 starts communication with the mobile station 100 in response to an instruction to start communication from an operator of the base station 200, the base station side system 20, or the like. The base station 200 transmits the reception data received from the mobile station 100 to the base station side system 20. (Step S1-2) The first communication terminal 201 (first receiving unit) receives data from the mobile station 100 using the communication line L1 (first communication line). The first communication terminal 201 measures the reception data quality (status) of the received data. The control unit 203 acquires the reception data quality (status) from the first communication terminal 201. The control unit 203 transmits the acquired reception data quality (status) to the line selection unit 204. The line selection unit 204 receives the reception data quality (status) transmitted by the control unit 203. The line selection unit 204 determines whether or not a packet including an I frame in its payload is being received. (Step S2-2) When it is determined that a packet including an I-frame in its payload has been received, the line selection unit 204 determines, based on the number of packet losses included in the received data quality, whether or not a packet loss has been detected, or whether or not the cumulative number of packets determined to have been packet losses has increased to or above a predetermined threshold. (Step S3-2) When the line selection unit 204 detects reception of a packet loss, or when the cumulative number of packets determined to be packet losses increases to or exceeds a predetermined threshold, the line selection unit 204 transitions the fixed station 200 to the disruption continuing occurrence state S02. (Step S4-2) When in the disturbance continuing occurrence state S02, the line selection unit 204 creates a receiving line selection result including information for identifying the communication line L2, and outputs the created receiving line selection result to the control unit 203. Since the receiving line selection result from the line selection unit 204 includes information for identifying the communication line L2, the control unit 203 selects the video data from the communication line L2 based on the receiving line selection result from the line selection unit 204, and outputs the selected video data to the video display unit 205. Then, the process returns to step S1-2.

[0028] (Step S5-2) When the line selection unit 204 determines that a packet including an I frame in its payload has not been received, the line selection unit 204 determines whether or not a packet loss has been detected, or whether or not the cumulative number of packets determined to be packet losses has increased to or above a predetermined threshold, based on the number of packet losses included in the received data quality. When the line selection unit 204 determines that a packet loss has not been detected, or that the cumulative number of packets determined to be packet losses is less than the predetermined threshold, the process returns to step S1-2. (Step S6-2) When the line selection unit 204 detects reception of a packet loss or determines that the cumulative number of packets determined to be packet loss has increased to or exceeds a predetermined threshold, it transitions the fixed station 200 to the disruption continuing occurrence state S02. (Step S7-2) If it is determined that no packet loss has occurred, the line selection unit 204 determines whether or not the decoding of the I frame has been completed. If the decoding of the I frame has not been completed, the process returns to step S2-2. (Step S8-2) If it is determined that the decoding of the I frame is completed, the line selection unit 204 causes the base station 200 to transition to the normal state S01. (Step S9-2) When in normal state S01, line selection unit 204 creates a receiving line selection result including information specifying communication line L1, and outputs the created receiving line selection result to control unit 203. Based on the receiving line selection result from line selection unit 204, control unit 203 selects video data from communication line L1 because the receiving line selection result includes information specifying communication line L1, and outputs the selected video data to video display unit 205. Thereafter, the process returns to step S1-2. When the base station 200 receives an instruction to end communication from the operator of the base station 200 or the base station side system 20, the base station 200 ends the reception process in FIG. In the above explanation of the reception processing, the fixed station 200 is taken as an example of the receiving side (receiving station), but the reception processing of the mobile station 100 as a receiving station is also similar.

[0029] According to the first embodiment described above, the communication system 1 includes a mobile station 100 as a transmitting station and a fixed station 200 as a receiving station. The transmitting station includes a first transmitting unit as a first communication terminal 101 that transmits video data using a first communication line between the transmitting station and the receiving station, and a second transmitting unit as a second communication terminal 102 that transmits video data using a second communication line between the transmitting station and the receiving station. The video data transmitted by the first transmitting unit is video-compressed data. The receiving station includes a first receiving unit as a first communication terminal 201 that receives video data using the first communication line, a second receiving unit as a second communication terminal 202 that receives video data using the second communication line, and a line selecting unit 204 that selects which of the first and second communication lines to use as a receiving line for receiving video data from the transmitting station, based on whether the first receiving unit has successfully decoded a first frame that holds all information of a frame included in the received data of the first communication line. With this configuration, the receiving station can determine which of the video data from the vehicle-mounted camera or the like transmitted from the multiple communication lines to use (display). Therefore, even if it is necessary to frequently switch the video data to be used between the multiple communication lines, the receiving station can switch the displayed video without delay. The receiving station can determine whether or not there is a disturbance in the received video based on the success of decoding the first frame as an intraframe, and can grasp the start time and duration of the disturbance in the video, so that it is possible to maximize the time for remote monitoring using the video from the vehicle-mounted camera on the side that is to be used, while building an environment in which monitoring can be continued using the video from the second communication line (sub-line) when a disturbance occurs. The receiving station selects which of the first and second communication lines to use as the receiving line for receiving the video data from the transmitting station based on whether or not the decoding of the first frame included in the received data from the first communication line of the first receiving unit is successful, so that there is no need to buffer the video from the vehicle-mounted camera, and therefore the delay time until the video is displayed can be shortened.

[0030] In the communication system 1, the line selection unit 204 selects which of the first and second communication lines to use as the receiving line for receiving video data from the transmitting station, based on whether the second frame, which can be decoded by referring to the first frame, has been successfully decoded. With this configuration, the receiving station can determine whether there is any disturbance in the received video based on the success or failure of the decoding of the second frame, and can grasp the start time and duration of the disturbance in the video, thereby creating an environment in which the time for remote monitoring using the video from the vehicle-mounted camera on the desired side can be maximized, while monitoring can be continued using the video from the second communication line (sub-line) when a disturbance occurs. In the communication system 1, the line selection unit 204 selects a receiving line for receiving video data from the transmitting station based on whether or not a packet including the first frame in its payload has been received, or on the basis of the cumulative number of received packets. With this configuration, the receiving station can determine which of the video data from an in-vehicle camera or the like transmitted from a plurality of communication lines to use (display), after receiving a packet including the first frame in its payload, or after the cumulative number of received packets has increased. In the communication system 1, the line selection unit 204 selects a receiving line for receiving video data from a transmitting station based on whether a packet loss has been detected or the accumulated number of packet losses. With this configuration, the receiving station can determine which of the video data from an in-vehicle camera or the like transmitted from a plurality of communication lines to use (display) based on whether a packet loss has been detected or the accumulated number of packet losses has increased.

[0031] In the communication system 1, the line selection unit 204 selects a receiving line for receiving video data from a transmitting station based on whether or not the decoding of the first frame is completed, or on the cumulative number of first frames for which decoding has been completed. With this configuration, the receiving station can determine which of the video data from an in-vehicle camera or the like transmitted from a plurality of communication lines to use (display), based on whether or not the decoding of the first frame is completed, or on the cumulative number of first frames for which decoding has been completed, has increased. In the communication system 1, the first transmission unit transmits the first video data using the first communication line, and the second transmission unit transmits the second video data different from the first video data using the second communication line. By configuring in this way, the transmitting station can transmit the second video data with a smaller capacity than the first video data, so that the vehicle-mounted camera video can be transmitted according to the bandwidth of the communication line.

[0032] [Second embodiment] Fig. 5 is a block diagram showing a configuration example of a communication system according to the second embodiment. In the communication system 1 according to the first embodiment described above, the base station 200 shown in Fig. 1 includes a first communication terminal 201 that establishes a communication line L1 and a second communication terminal 202 that establishes a communication line L2, but in the communication system 1a according to the second embodiment, the base station 200a shown in Fig. 5 establishes the communication line L1 and the communication line L2 with the mobile station 100 by one communication terminal 201a. Other than this point, the system is the same as the first embodiment described above.

[0033] [Third embodiment] 6 is a block diagram showing a configuration example of a communication system according to the third embodiment. In the communication system 1b according to the third embodiment, a mobile station 100b and a base station 200b communicate with each other. In the communication system 1b, there are two cases: the mobile station 100b becomes a transmitting station and transmits data to the base station 200b (receiving station), and the mobile station 100b becomes a receiving station and receives data from the base station 200b (transmitting station). The mobile station 100b includes a first communication terminal 101, a second communication terminal 102, a control unit 103b, a line selection unit 104b, and a communication quality prediction unit 110b. The base station 200b includes a first communication terminal 201, a second communication terminal 202, a control unit 203b, a line selection unit 204b, and a video display unit 205.

[0034] (Mobile station) The first communication terminal 101 measures the quality of wireless communication when communicating using the first wireless communication network NW1. The wireless communication quality is, for example, RSRP (Reference Signal Received Power), SINR (Signal to Interference and Noise power Ratio), throughput, etc. Furthermore, the first communication terminal 101 acquires a base station identifier (base station ID) that identifies a base station of the first wireless communication network NW1 to which the terminal itself is connected, and the current location (latitude and longitude) of the terminal itself. Furthermore, the first communication terminal 101 measures the reception data quality of data received from the first communication terminal 201 of the fixed station 200 via the communication line L1. The reception data quality is, for example, whether data is normally received, a packet loss rate, jitter, an image quality evaluation value of image data, etc. The second communication terminal 102 judges whether or not data has arrived from the second communication terminal 202 of the base station 200 via the communication line L2. The control unit 103b can apply the control unit 103. However, when the control unit 103b receives a transmission line selection result from the line selection unit 104b, the control unit 103b determines a transmission line for transmitting data such as video data to the fixed station 200 from the communication lines L1 and L2 based on the transmission line selection result. The control unit 103b transmits the transmission line selection result received from the line selection unit 104b to the fixed station 200 through at least one of the communication lines L1 and L2. When the control unit 103b receives a reception line selection result from the line selection unit 104b, the control unit 103b determines a reception line for receiving data from the fixed station 200 from the communication lines L1 and L2 based on the reception line selection result. Note that, when data is normally received from the fixed station 200 only from one of the communication lines L1 and L2, the control unit 103b determines the communication line for normal reception as the reception line for receiving data from the fixed station 200 regardless of the reception line selection result of the line selection unit 104b.

[0035] The communication quality prediction unit 110b predicts the wireless communication quality of the communication line L1 between the mobile station 100b and the base station 200. In predicting the wireless communication quality, it is predicted whether the wireless communication quality of the communication line L1 will deteriorate or improve in the future. Below, several examples of the wireless communication quality prediction method will be described. (Example 1 of wireless communication quality prediction method) The communication quality prediction unit 110b predicts the wireless communication quality of the communication line L1 based on the measurement result of the wireless communication quality measured by the first communication terminal 101. The measurement result of the wireless communication quality of the first communication terminal 101 is a measurement result of the wireless communication quality when the first communication terminal 101 communicates using the first wireless communication network NW1, and corresponds to a wireless quality measurement value of the communication line L1. The measurement result of the wireless communication quality of the first communication terminal 101 is notified to the communication quality prediction unit 110b from the first communication terminal 101 via the control unit 103b. The wireless communication quality is, for example, RSRP, SINR, throughput, etc. The communication quality prediction unit 110b calculates a score (evaluation value) of the wireless communication quality from each measurement result of, for example, RSRP and SINR by a predetermined score calculation method. In this score calculation, weighting may be applied to RSRP and SINR, respectively. The communication quality prediction unit 110b predicts that the wireless communication quality of the communication line L1 will deteriorate in the future when the score of the wireless communication quality does not satisfy a predetermined score threshold (wireless communication quality evaluation standard). For example, if the wireless communication quality score changes from a good state in which the wireless communication quality score is above a predetermined score threshold for a certain period of time or more to a state in which the wireless communication quality score is below the predetermined score threshold for a certain period of time or more, it may be predicted that the wireless communication quality of the communication line L1 will deteriorate in the future. On the other hand, the communication quality prediction unit 110b predicts that the future wireless communication quality of the communication line L1 will be good if the score of the wireless communication quality satisfies a predetermined score threshold. For example, if the score of the wireless communication quality exceeds a predetermined score threshold for a certain period of time or more, the communication quality prediction unit 110b may predict that the future wireless communication quality of the communication line L1 will be good.

[0036] (Example 2 of wireless communication quality prediction method) The communication quality prediction unit 110b predicts the wireless communication quality of the communication line L1 based on the distance between the first communication terminal 101 and a base station of the first wireless communication network NW1 to which the first communication terminal 101 is connected. The communication quality prediction unit 110b acquires the position (latitude and longitude) of the base station of the first wireless communication network NW1 to which the first communication terminal 101 is connected based on the base station ID of the base station. The base station ID of the base station of the first wireless communication network NW1 to which the first communication terminal 101 is connected is notified to the communication quality prediction unit 110b from the first communication terminal 101 via the control unit 103b. In addition, the current position (latitude and longitude) of the first communication terminal 101 is notified to the communication quality prediction unit 110b from the first communication terminal 101 via the control unit 103b. The communication quality prediction unit 110b calculates the distance (terminal-base station distance) between the base station of the first wireless communication network NW1 to which the first communication terminal 101 is connected and the first communication terminal 101 based on the position (latitude and longitude) of the base station and the current position (latitude and longitude) of the first communication terminal 101. The communication quality prediction unit 110b predicts that the wireless communication quality of the future communication line L1 will deteriorate when the terminal-base station distance does not satisfy a predetermined terminal-base station distance threshold (wireless communication quality evaluation criterion). For example, it may be predicted that the wireless communication quality of the future communication line L1 will deteriorate when the terminal-base station distance changes from a good state in which the terminal-base station distance is below the predetermined terminal-base station distance threshold for a certain period of time or more to a state in which the terminal-base station distance exceeds the predetermined terminal-base station distance threshold for a certain period of time or more. On the other hand, the communication quality prediction unit 110b predicts that the wireless communication quality of the future communication line L1 will be good when the terminal-base station distance satisfies the predetermined terminal-base station distance threshold. For example, if the distance between the terminal and the base station is below a predetermined threshold value for the distance between the terminal and the base station for a certain period of time or more, it may be predicted that the wireless communication quality of the communication line L1 will be good in the future.

[0037] (Example 3 of wireless communication quality prediction method) The communication quality prediction unit 110b predicts the wireless communication quality of the communication line L1 based on a record of past wireless communication quality on a route (planned travel route) along which the mobile station 100b is scheduled to travel. The communication quality prediction unit 110b calculates a distance (a judgment target distance) between the current position of the mobile station 100b (for example, the current position (latitude and longitude) of the first communication terminal 101) and a point on the planned travel route of the mobile station 100b that does not satisfy a predetermined wireless communication quality evaluation standard based on a communication quality map in which past wireless communication quality for the first wireless communication network NW1 used for the communication line L1 is recorded for each point, and based on planned travel route information of the mobile station 100b. The planned travel route of the mobile station 100b is set in advance in the control unit 103b. For example, communication quality map data of an area including the planned travel route of the mobile station 100b is downloaded in advance from a communication quality map storage server (not shown) to the mobile station 100b as the communication quality map. The communication quality prediction unit 110b predicts that the wireless communication quality of the communication line L1 will deteriorate in the future when the determination target distance does not satisfy a predetermined determination target distance threshold (wireless communication quality evaluation criterion). For example, it may predict that the wireless communication quality of the communication line L1 will deteriorate in the future when the determination target distance changes from a good state (a state away from a point that does not satisfy the wireless communication quality evaluation criterion) in which the determination target distance exceeds a predetermined determination target distance threshold to a state in which the determination target distance falls below the predetermined determination target distance threshold (a state approaching a point that does not satisfy the wireless communication quality evaluation criterion). On the other hand, the communication quality prediction unit 110b predicts that the wireless communication quality of the future communication line L1 is good when the determination target distance satisfies a predetermined determination target distance threshold. For example, when the determination target distance exceeds a predetermined determination target distance threshold, the communication quality prediction unit 110b may predict that the wireless communication quality of the future communication line L1 is good. If there is no point on the planned travel route of the mobile station 100b that does not satisfy a predetermined wireless communication quality evaluation standard, the determination target distance is set to infinity "∞", so that the determination target distance exceeds the predetermined determination target distance threshold, resulting in a prediction that the wireless communication quality of the future communication line L1 is good. The control unit 103b may acquire information such as the current position (latitude and longitude) and planned travel route of the mobile station 100b from the mobile station side system 10.

[0038] The line selection unit 104b has a transmission line selection function and a reception line selection function. The transmission line selection function of the line selection unit 104b selects whether or not to perform data transmission using the communication line L2 by the second communication terminal 102 based on the prediction result of the wireless communication quality of the communication line L1 of the mobile station 100b. The prediction result of the wireless communication quality of the communication line L1 of the mobile station 100b is notified to the line selection unit 104b from the communication quality prediction unit 110b via the control unit 103b. When the prediction result of the wireless communication quality of the communication line L1 is deteriorated, the transmission line selection function of the line selection unit 104b notifies the control unit 103b of the transmission line selection result "start transmission on the communication line L2", and causes the control unit 103b to start data transmission using the communication line L2 in addition to data transmission on the communication line L1. On the other hand, when the predicted wireless communication quality of the communication line L1 is good, the line selection unit 104b notifies the control unit 103b of the transmission line selection result "end of transmission on communication line L2" and causes the control unit 103b to stop data transmission using the communication line L2.

[0039] When the transmission line selection function of the line selection unit 104b is requested by the fixed station 200b to start data transmission using the communication line L2, the transmission line selection result "Start transmission using the communication line L2" is notified to the control unit 103b, and the control unit 103b starts data transmission using the communication line L2. A communication start request to start data transmission using the communication line L2 is received from the fixed station 200b by either the communication line L1 or L2, and notified to the line selection unit 104b via the control unit 103b. The reception line selection function of the line selection unit 104b selects which of the communication lines L1 and L2 is to be used as a reception line for receiving data from the fixed station 200b, based on the reception data quality of the communication line L1 of the first communication terminal 101. The reception data quality is, for example, whether data is normally received, a packet loss rate, a jitter, an image quality evaluation value of image data, etc. The received data quality is notified from the first communication terminal 101 to the line selection unit 104b via the control unit 103b. The receiving line selection function of the line selection unit 104b determines that the receiving data quality of the communication line L1 is good when the receiving data quality of the communication line L1 meets a predetermined receiving data quality standard. When the receiving data quality of the communication line L1 is good, the receiving line selection function of the line selection unit 104b selects the communication line L1 as the receiving line for receiving data from the fixed station 200b. On the other hand, when the receiving data quality of the communication line L1 does not meet a predetermined receiving data quality standard, the receiving line selection function of the line selection unit 104b determines that the receiving data quality of the communication line L1 is not good. When the receiving data quality of the communication line L1 is not good, the receiving line selection function of the line selection unit 104b selects the communication line L2 as the receiving line for receiving data from the fixed station 200b.

[0040] In addition, the receiving line selection function of the line selection unit 104b requests the base station 200 to start data transmission using the communication line L2 when the quality of received data on the communication line L1 is not good and data is not received from the base station 200b via the communication line L2. Whether data is received from the base station 200 via the communication line L2 is notified from the second communication terminal 102 to the line selection unit 104b via the control unit 103b. A communication start request to start data transmission using the communication line L2 is transmitted from the line selection unit 104b to the base station 200b via either the communication line L1 or L2, based on the receiving line selection result of the line selection unit 104b. The control unit 103b transmits the reception data received from the base station 200b via the reception line to the mobile station side system 10. When the reception line selection result of the line selection unit 104b is the communication line L1, the control unit 103b determines the reception line for receiving data from the fixed station 200 to be the communication line L1. When the reception line selection result of the line selection unit 104b is the communication line L2, and data has arrived from the fixed station 200b via the communication line L2, the control unit 103b determines the reception line for receiving data from the fixed station 200b to be the communication line L2. On the other hand, when the reception line selection result of the line selection unit 104b is the communication line L2, and data has not arrived from the fixed station 200 via the communication line L2, the control unit 103b sets the communication line L1 as the reception line for receiving data from the fixed station 200b. When the receiving line selection result of the line selection unit 104b is the communication line L2, when the state changes from one in which data is not received from the fixed station 200b via the communication line L2 to one in which data is received, the control unit 103b determines that the receiving line for receiving data from the fixed station 200b is the communication line L2.

[0041] (Fixed station) The first communication terminal 201 measures the reception data quality (status) of data received from the first communication terminal 101 of the mobile station 100b via the communication line L1. The reception data quality (status) is, for example, the number of packet losses, the number of received packets containing an I-frame in the payload, the number of I-frames that have been decoded, the bit rate of the video elementary stream, whether data has been received normally, the packet loss rate, jitter, and the image quality evaluation value of the image data. The control unit 203b can apply the control unit 203. However, when the control unit 203b receives a transmission line selection result from the mobile station 100b, the control unit 203b determines the transmission line for transmitting data to the mobile station 100b from the communication lines L1 and L2 based on the transmission line selection result. Note that when data is normally received from the mobile station 100b only from one of the communication lines L1 and L2, the control unit 203b determines the communication line for normal reception as the reception line for receiving data from the mobile station 100b, regardless of the reception line selection result of the line selection unit 204b.

[0042] In the third embodiment, the line selection unit 104b of the mobile station 100b has a transmission line selection function, the mobile station 100b notifies the base station 200b of the transmission line selection result, and the control unit 203b of the base station 200b determines a transmission line for transmitting data to the mobile station 100b from the communication lines L1 and L2 based on the transmission line selection result notified from the mobile station 100b. Note that the line selection unit 204 of the base station 200b may also have a transmission line selection function, the mobile station 100b may notify the base station 200b of the prediction result of the wireless communication quality of the communication line L1 by the communication quality prediction unit 110b, and the transmission line selection function of the line selection unit 204 of the base station 200b may select whether or not to perform data transmission using the communication line L2 based on the prediction result of the wireless communication quality of the communication line L1. In this case, the control unit 203b of the base station 200b determines, based on the transmission line selection result of the line selection unit 204, the transmission line for transmitting data to the mobile station 100b from the communication lines L1 and L2.

[0043] The receiving line selection function of the line selection unit 204 selects which of the communication lines L1 and L2 is to be used as a receiving line for receiving data from the mobile station 100b, based on the reception data quality of the communication line L1 of the first communication terminal 201. The reception data quality is, for example, whether data is normally received, a packet loss rate, jitter, or an image quality evaluation value of image data. The reception data quality is notified to the line selection unit 204 from the first communication terminal 201 via the control unit 203b. The receiving line selection function of the line selection unit 204 determines that the reception data quality of the communication line L1 is good when the reception data quality of the communication line L1 satisfies a predetermined reception data quality standard. When the reception data quality of the communication line L1 is good, the receiving line selection function of the line selection unit 204 selects the communication line L1 as a receiving line for receiving data from the mobile station 100b. On the other hand, the receiving line selection function of the line selection unit 204 determines that the receiving data quality of the communication line L1 is not good when the receiving data quality of the communication line L1 does not satisfy a predetermined receiving data quality standard. When the receiving data quality of the communication line L1 is not good, the receiving line selection function of the line selection unit 204 selects the communication line L2 as the receiving line for receiving data from the mobile station 100b.

[0044] Furthermore, when the received data quality of the communication line L1 is not good and no data is received from the mobile station 100b via the communication line L2, the receiving line selection function of the line selection unit 204 requests the mobile station 100b to start data transmission using the communication line L2. Whether or not data is received from the mobile station 100b via the communication line L2 is notified to the line selection unit 204 from the second communication terminal 202 via the control unit 203b. A communication start request requesting the start of data transmission using the communication line L2 is transmitted from the line selection unit 204 via the control unit 203b to the mobile station 100b via either the communication line L1 or L2. The control unit 203b determines whether the reception line for receiving data from the mobile station 100b should be the communication line L1 or the communication line L2, based on the reception line selection result of the line selection unit 204. The control unit 203b transmits the reception data received from the mobile station 100b via the reception line to the fixed station side system 20. When the reception line selection result of the line selection unit 204 is the communication line L1, the control unit 203b determines the reception line for receiving data from the mobile station 100b to be the communication line L1. When the reception line selection result of the line selection unit 204 is the communication line L2, and data has arrived from the mobile station 100b via the communication line L2, the control unit 203b determines the reception line for receiving data from the mobile station 100b to be the communication line L2.

[0045] On the other hand, when the reception line selection result of the line selection unit 204 is the communication line L2, and data is not received from the mobile station 100b via the communication line L2, the control unit 203b sets the communication line L1 as the reception line for receiving data from the mobile station 100b. When the reception line selection result of the line selection unit 204 is the communication line L2, and the state changes from a state in which data is not received from the mobile station 100b via the communication line L2 to a state in which data is received, the control unit 203b determines the reception line for receiving data from the mobile station 100b to be the communication line L2. According to each of the above-described embodiments, in a communication system in which at least one of a transmitting station and a receiving station is a mobile station, when multiple communication lines are used between the transmitting station and the receiving station, it is possible to adapt to local fluctuations or deterioration in wireless communication quality in the mobile station, and to improve communication quality while minimizing communication interruptions as much as possible.

[0046] Although the embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes within the scope of the present invention are also included. In addition, a computer program for realizing the functions of each of the above-mentioned devices may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed. Note that the "computer system" referred to here may include hardware such as an OS and peripheral devices. In addition, the term "computer-readable recording medium" refers to writable non-volatile memory such as a flexible disk, an optical magnetic disk, a ROM, or a flash memory, a portable medium such as a DVD (Digital Versatile Disc), or a storage device such as a hard disk built into a computer system. Furthermore, the term "computer-readable recording medium" includes a memory that holds a program for a certain period of time, such as a volatile memory (e.g., DRAM (Dynamic Random Access Memory)) inside a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. The above-mentioned program may be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium, or by a transmission wave in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The above-mentioned program may be a program for realizing part of the above-mentioned functions. Furthermore, the above-mentioned function may be realized in combination with a program already recorded in the computer system, that is, a so-called difference file (difference program). The communication systems, mobile stations, and fixed stations of the above-described embodiments are expected to improve traffic safety and enable all people to have access to safe, affordable, easy-to-use and sustainable transportation systems, which will contribute to Goal 11 of the United Nations Sustainable Development Goals (SDGs), "Sustainable cities and communities."

[0047] Although the embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes within the scope of the present invention are also included. For example, a computer program for implementing the functions of each of the above-mentioned devices may be recorded on a computer-readable recording medium, and the computer program recorded on the recording medium may be read into a computer system and executed. The "computer system" referred to here may include hardware such as an OS and peripheral devices. Furthermore, the "computer-readable recording medium" refers to a storage device such as a flexible disk, a magneto-optical disk, a ROM, a writable non-volatile memory such as a flash memory, a portable medium such as a DVD, or a hard disk built into a computer system. Furthermore, the "computer-readable recording medium" refers to a storage device that holds a program for a certain period of time, such as a volatile memory (e.g., a dynamic random access memory (DRAM)) inside a computer system that becomes a server or a client when a computer program is transmitted via a network such as the Internet or a communication line such as a telephone line. The above program may be transmitted from a computer system in which the program is stored in a storage device or the like to another computer system via a transmission medium, or by transmission waves in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The above program may also be one that realizes part of the above-mentioned functions. Furthermore, it may be a so-called difference file (difference program) that can realize the above-mentioned functions in combination with a program already recorded in the computer system. [Explanation of symbols]

[0048] Reference Signs List 1, 1a, 1b...communication system, 10...mobile station side system, 20...fixed station side system, 100, 100b...mobile station, 101...first communication terminal, 102...second communication terminal, 103, 103b...control unit, 104b...line selection unit, 110b...communication quality prediction unit, 200, 200a, 200b...fixed station, 201...first communication terminal, 201a...communication terminal, 202...second communication terminal, 203, 203b...control unit, 204, 204b...line selection unit, 205...video display unit

Claims

1. In a communication system including a transmitting station and a receiving station, The transmitting station, a first transmission unit that transmits video data using a first communication line between the transmitting station and the receiving station; a second transmission unit that transmits video data using a second communication line between the transmitting station and the receiving station; Equipped with the video data transmitted by the first transmission unit is compressed video data, the transmitting station transmits the video data via both the first communication line and the second communication line; The receiving station, a first receiving unit that receives video data using the first communication line; a second receiving unit that receives video data using the second communication line; a line selection unit that selects, based on whether a first frame, which holds all information of the frame of video data included in the received data on the first communication line of the first receiving unit, is successfully decoded, from the first communication line to the second communication line to be used as a receiving line for receiving the video data from the transmitting station; a control unit that displays video data received using one of the first communication line and the second communication line selected by the line selection unit; and Equipped with Communication systems.

2. The communication system described in claim 1, wherein the line selection unit transitions between a first state in which decoding of the first frame included in the received data of the first communication line is successful, a second state in which decoding of the first frame included in the received data of the first communication line is unsuccessful, and a third state in which a stop of the video stream is detected, and selects which of the first communication line and the second communication line to use as a receiving line for receiving video data from the transmitting station based on whether the receiving station is in the first state, the second state, or the third state.

3. The first state is a state in which both the first frame included in the received data of the first communication line of the first receiving unit and a second frame that can be decoded by referring to the first frame are successfully decoded without detecting a path loss, 3. The communication system according to claim 2, wherein the second state is a state in which a path loss is detected or decoding of either or both of the first frame and the second frame contained in the received data of the first communication line of the first receiving unit has failed.

4. A communication system as described in claim 2 or claim 3, wherein the line selection unit transitions to the first state when, in the second state, the first frame contained in the received data of the first communication line is successfully decoded, and transitions to the first state when, in the third state, the resumption of the video stream is detected.

5. 2. The communication system according to claim 1, wherein the line selection unit selects which of the first communication line and the second communication line to use as a receiving line for receiving video data from the transmitting station, based on whether decoding of a second frame that can be decoded by referring to the first frame is successful or not.

6. 6. The communication system according to claim 1, wherein the line selection unit selects a receiving line for receiving video data from the transmitting station based on whether or not a packet including the first frame in its payload has been received, or based on a cumulative number of received packets.

7. 6. The communication system according to claim 1, wherein the line selection unit selects a receiving line for receiving video data from the transmitting station based on whether or not a packet loss has been detected, or on a cumulative number of packet losses.

8. 8. The communication system according to claim 1, wherein the line selection unit selects a receiving line for receiving video data from the transmitting station based on whether or not decoding of the first frame has been completed, or based on a cumulative number of first frames for which decoding has been completed.

9. The first transmission unit transmits first video data using the first communication line; The communication system according to claim 1 , wherein the second transmission unit transmits second video data different from the first video data using the second communication line.

10. a first receiving unit that receives video data using a first communication line; a second receiving unit that receives video data using a second communication line; a line selection unit that selects, based on whether a first frame that holds all information of the frame of video data included in the received data on the first communication line of the first receiving unit has been successfully decoded, either the first communication line or the second communication line to be used as a receiving line for receiving video data from a transmitting station; a control unit that displays video data received using one of the first communication line and the second communication line selected by the line selection unit; and Equipped with the video data received by the first receiving unit is compressed video data, A receiving station, wherein the video data is transmitted via both the first communication line and the second communication line.

11. A communication method for a communication system including a transmitting station and a receiving station, comprising: a transmitting step in which the transmitting station transmits video data using both a first communication line and a second communication line between the transmitting station and the receiving station; a first receiving step in which the receiving station receives video data using the first communication line; a second receiving step in which the receiving station receives video data using the second communication line; a line selection step in which the receiving station selects, based on whether a first frame, which holds all information of the frame of video data included in the received data of the first communication line, is successfully decoded, the receiving station selects which of the first communication line and the second communication line is to be used as a receiving line for receiving the video data from the transmitting station; a display step of displaying the video data received using one of the first communication line and the second communication line selected in the line selection step; having The video data transmitted in the transmitting step is compressed video data. Communication methods.

12. a first receiving step of receiving video data using a first communication line; a second receiving step of receiving the video data using a second communication line; a line selection step of selecting, based on whether a first frame, which holds all information of the frame of video data included in the received data of the first communication line, is successfully decoded, the first communication line or the second communication line to be used as a receiving line for receiving video data from a transmitting station; a display step of displaying the video data received using one of the first communication line and the second communication line selected in the line selection step; having the video data received in the first receiving step is compressed video data, A communication method executed by a receiving station, wherein the video data is transmitted via both the first communication line and the second communication line.

13. The receiving station's computer program a first receiving step of receiving video data using a first communication line; a second receiving step of receiving the video data using a second communication line; a line selection step of selecting, based on whether a first frame, which holds all information of the frame of video data included in the received data of the first communication line, is successfully decoded, the first communication line or the second communication line to be used as a receiving line for receiving video data from a transmitting station; a display step of displaying the video data received using either the first communication line or the second communication line selected in the line selection step; Run the command, the video data received in the first receiving step is compressed video data, The video data is transmitted via both the first communication line and the second communication line.

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