Wireless communication system, wireless communication system control method, and buffer management method

Abstract

To provide a wireless communication system configured to receive voice data without fail even when a radio base station is switched.SOLUTION: A buffer management unit 24 of a radio base station 20 includes a buffer 240 including ring buffers for each of radio terminals including a first radio terminal connected to the base station and a second radio terminal not connected to the base station. The buffer management unit 24 updates, for each transmission period, a read index for designating an area where voice data is read from a first ring buffer of the first radio terminal, and updates a read index for designating an area where voice data is read from a second ring buffer of the second radio terminal. The buffer management unit 24 clears a sequence number in the area designated by the read index of the second ring buffer, to an invalid value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a wireless communication system, a control method for a wireless communication system, and a buffer management method. [Background technology]

[0002] As described in Patent Document 1, a wireless communication system called an intercom system is used in stores and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-165378 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, a wireless communication system may be constructed using a wireless LAN communication standard (such as IEEE802.11). In a wireless communication system that performs data communication using a specific communication standard, not limited to wireless LAN, it is required to be able to receive voice data without any problems even if the wireless base station to which the wireless terminal is connected is switched.

[0005] The present invention aims to provide a wireless communication system, a control method for a wireless communication system, and a buffer management method that enable voice data to be received without any problems even if a wireless base station to which a wireless terminal is connected is switched. [Means for solving the problem]

[0006] The present invention provides a wireless communication system comprising a center device, a plurality of wireless base stations connected to the center device via a wired network, and one or more wireless terminals wirelessly connected to each of the plurality of wireless base stations.

[0007] The center device multicasts a multicast voice packet to all of the multiple wireless base stations, the multicast packet including multiple pairs of voice data and a sequence number indicating the order in which the voice data is transmitted for each wireless terminal to which the voice data is transmitted.

[0008] Each wireless base station has ring buffers provided corresponding to each wireless terminal including a first wireless terminal connected to the wireless base station and a second wireless terminal not connected to the wireless base station, a write index for each ring buffer specifying an area into which voice data and a sequence number are written in each ring buffer, and a read index for each ring buffer specifying an area into which the voice data written in each ring buffer is read, and has a buffer management unit that writes the voice data included in a received multicast voice packet to an area specified by the write index in a ring buffer provided corresponding to a destination wireless terminal to which the voice data is to be transmitted, and reads the voice data written in the area specified by the read index in a first ring buffer provided corresponding to the first wireless terminal, a transmission cycle management unit that manages a transmission cycle so that all wireless base stations transmit the voice packets including the voice data read from the first ring buffer to the first wireless terminal at the same timing, and a transmission unit that transmits the voice packets including the voice data read from the first ring buffer to the first wireless terminal.

[0009] Each ring buffer has an area for writing audio data, which includes areas for writing audio data from the latest transmission cycle through audio data from a predetermined cycle ago.

[0010] The buffer management unit updates a read index that specifies an area from which voice data is read from the first ring buffer for each transmission period, and after updating a read index that specifies an area from which voice data is read from a second ring buffer provided corresponding to the second wireless terminal, clears the sequence number written in the area specified by the read index of the second ring buffer to an invalid value.

[0011] The present invention provides a control method for a wireless communication system as follows: A center device transmits, by multicast, a multicast audio packet including a plurality of pairs of audio data and a sequence number indicating the order of the audio data to be transmitted for each destination wireless terminal to which the audio data is transmitted, to all of a plurality of wireless base stations connected to the center device via a wired network. Each wireless base station is provided with a ring buffer corresponding to each wireless terminal including a first wireless terminal connected to the center device and a second wireless terminal not connected to the center device, and each ring buffer has an area for writing audio data, in which audio data from the latest transmission period to a predetermined period before is written.

[0012] Each wireless base station manages a write index for each ring buffer that specifies an area in each ring buffer into which voice data and sequence numbers are written, and a read index for each ring buffer that specifies an area from which the voice data written in each ring buffer is read.

[0013] Each wireless base station writes the audio data contained in the received multicast audio packet to an area specified by the write index of a ring buffer provided corresponding to a wireless terminal to which the audio data is to be transmitted, and reads out the audio data written in an area specified by the read index of a first ring buffer provided corresponding to the first wireless terminal.

[0014] Each wireless base station manages a transmission cycle so that all wireless base stations transmit voice packets including the voice data read from the first ring buffer to the first wireless terminal at the same timing. Each wireless base station transmits voice packets including the voice data read from the first ring buffer to the first wireless terminal, updates a read index specifying an area from which the voice data is read from the first ring buffer for each transmission cycle, and updates a read index specifying an area from which the voice data is read from a second ring buffer provided corresponding to the second wireless terminal, and then clears a sequence number written in an area specified by the read index of the second ring buffer to an invalid value.

[0015] The present invention provides a buffer management method in which a buffer management unit provided in each wireless base station in a wireless communication system including a center device, a plurality of wireless base stations connected to the center device via a wired network, and one or more wireless terminals wirelessly connected to each of the plurality of wireless base stations manages ring buffers provided in each wireless base station corresponding to each wireless terminal, including a first wireless terminal connected to the wireless base station and a second wireless terminal not connected to the wireless base station.

[0016] The buffer management method manages a write index for each ring buffer that specifies an area in which audio data and a sequence number indicating the order of the audio data are written in each ring buffer, and a read index for each ring buffer that specifies an area from which the audio data written in each ring buffer is read.

[0017] The buffer management method writes audio data contained in a multicast audio packet received by each wireless base station to an area specified by the write index of a ring buffer provided corresponding to a wireless terminal to which the audio data is to be transmitted, and reads out the audio data written in an area specified by the read index of a first ring buffer provided corresponding to the first wireless terminal.

[0018] The buffer management method updates a read index specifying an area from which the voice data is read from the first ring buffer for each transmission period in which all wireless base stations transmit voice packets containing voice data read from the first ring buffer to the first wireless terminal at the same timing, and updates a read index specifying an area from which the voice data is read from a second ring buffer provided corresponding to the second wireless terminal, and then clears a sequence number written in the area specified by the read index of the second ring buffer to an invalid value. Effect of the Invention

[0019] According to the wireless communication system, the control method for the wireless communication system, and the buffer management method of the present invention, even if the wireless base station to which the wireless terminal is connected is switched, it is possible to receive voice data without any problems. [Brief description of the drawings]

[0020] [Figure 1] 1 is a block diagram showing an example of the overall configuration of a wireless communication system according to an embodiment; [Diagram 2] 2 is a block diagram showing an example of the configuration of a center device in the wireless communication system of the embodiment; [Diagram 3] 1 is a block diagram showing an example of the configuration of a wireless base station in a wireless communication system according to an embodiment; [Figure 4] 1 is a block diagram showing an example of the configuration of a wireless terminal in a wireless communication system according to an embodiment; [Diagram 5] 1 is a conceptual diagram showing a base station management table managed by a base station management unit of a center device. [Figure 6] 11 is a conceptual diagram showing a terminal information table managed by a wireless terminal management unit of the center device. FIG. [Figure 7] 10 is a sequence diagram showing a communication sequence when a wireless terminal connects to a wireless base station and a center device registers the wireless terminal. FIG. [Figure 8]11 is a conceptual diagram showing a wireless terminal registration request transmitted from a wireless terminal to a center device. FIG. [Figure 9] 1 is a conceptual diagram showing terminal information of a wireless terminal that a center device transmits to a wireless base station. [Figure 10] 1 is a conceptual diagram showing a wireless terminal information table managed by a wireless terminal management unit of a wireless base station. [Figure 11] FIG. 11 is a sequence diagram showing a registration process executed between a center device and a wireless base station. [Figure 12] FIG. 13 is a conceptual diagram showing a radio base station registration response that the center device transmits to the radio base station. [Figure 13] 10 is a sequence diagram showing an example of a voice data transmission / reception process executed between a center device, a wireless base station, and a wireless terminal; FIG. [Figure 14] 1 is a conceptual diagram showing an example of the structure of a multicast voice packet transmitted from a center device to a wireless base station; [Figure 15] 15 is a conceptual diagram showing an example of the configuration of terminal audio data of one wireless terminal included in aggregated audio data of the multicast audio packet shown in FIG. 14. FIG. [Figure 16] 1 is a conceptual diagram illustrating a ring buffer included in a buffer management unit of a wireless base station. [Figure 17] 1 is a conceptual diagram showing an example of the structure of a voice packet transmitted from a wireless base station to a wireless terminal; [Figure 18] 18 is a diagram showing an example of the configuration of a flag included in the voice packet shown in FIG. 17. [Figure 19] 18 is a diagram showing a specific example of the voice packet shown in FIG. 17. [Figure 20] FIG. 2 is a diagram showing reference timings at which a center device, a wireless base station, and a wireless terminal transmit voice packets. [Figure 21] 13 is a flowchart showing a transmission and reception process in a wireless base station. [Figure 22] 22 is a flow chart showing a receiving process of a multicast audio packet transmitted from a center device, out of the transmitting / receiving process in step S212 shown in FIG. [Diagram 23]23 is a flowchart showing detailed processing of step S222 shown in FIG. 22. [Figure 24] 22 is a flowchart showing a receiving process of a voice packet transmitted from a wireless terminal, out of the transmitting and receiving process in step S212 shown in FIG. [Diagram 25] 22 is a flowchart showing a transmission process for transmitting voice packets to a center device and a wireless terminal, out of the transmission and reception process in step S212 shown in FIG. 21. [Figure 26] 26 is a flowchart showing a transmission process for transmitting a voice packet to the center device in step S252 shown in FIG. [Figure 27A] 26 is a partial flowchart showing a transmission process in which the wireless base station transmits a voice packet to the wireless terminal in step S252 shown in FIG. 25. [Figure 27B] 27B is a partial flowchart subsequent to FIG. 27A, showing the transmission process in which the wireless base station transmits a voice packet to the wireless terminal in step S252 shown in FIG. [Figure 27C] 27B is a partial flowchart subsequent to FIG. 27A, showing the transmission process in which the wireless base station transmits a voice packet to the wireless terminal in step S252 shown in FIG. [Figure 28] 10 is a flowchart showing a method by which a wireless terminal that has switched a wireless base station to which it is connected due to roaming acquires an IP address of the newly connected wireless base station. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, a wireless communication system, a control method for the wireless communication system, and a buffer management method according to an embodiment will be described with reference to the accompanying drawings. As shown in Fig. 1, the wireless communication system includes a center device 10, wireless base stations 20A, 20B, and 20C, and wireless terminals 30A, 30B, 30C, and 30D. Any of the wireless base stations 20A to 20C will not be specified, and any of the wireless base stations including other wireless base stations not shown will be referred to as a wireless base station 20. Any of the wireless terminals 30A to 30D will not be specified, and other wireless terminals not shown will be referred to as a wireless terminal 30.

[0022] The numbers of wireless base stations 20 and wireless terminals 30 shown in FIG. 1 are merely examples, and the numbers of wireless base stations 20 and wireless terminals 30 are not limited.

[0023] The center device 10 and the wireless base stations 20A to 20C are connected via a wired network 15N. The wireless base station 20 may be directly connected to the center device 10, or may be connected to the center device 10 via another wireless base station 20. The method of connection between the center device 10 and the wireless base stations 20 is not limited. The center device 10 manages the wireless base stations 20A to 20C and the wireless terminals 30A to 30D. The center device 10 mixes the voice data received from the wireless terminals 30A to 30D via the wireless base stations 20A to 20C to create voice data for group calls.

[0024] Wireless communication ranges 40A, 40B, and 40C indicate ranges in which the wireless terminal 30 can connect to and communicate with the wireless base stations 20A, 20B, and 20C, respectively. In FIG. 1, the wireless terminal 30A is located within the wireless communication range 40A and is connected to the wireless base station 20A. The wireless terminal 30B is located within the wireless communication range 40B and is connected to the wireless base station 20B. The wireless terminals 30C and 30D are located within the wireless communication range 40C and are connected to the wireless base station 20C. The wireless communication ranges 40A, 40B, and 40C form a wireless network.

[0025] The wireless communications between the wireless base stations 20A to 20C and the wireless terminals 30A to 30D comply with IEEE802.11, which is a wireless LAN communication standard.

[0026] 2, the center device 10 includes a receiving unit 11, a received data processing unit 12, a base station management unit 13, a voice data processing unit 14, a wireless terminal management unit 15, a transmission cycle management unit 16, a transmission data creation unit 17, and a transmitting unit 18. The solid arrows to the receiving unit 11 and the solid arrows from the transmitting unit 18 correspond to a wired network 15N connected to a wireless base station 20. The base station management unit 13 manages a base station management table 130, and the wireless terminal management unit 15 manages a terminal information table 150.

[0027] 3, the wireless base station 20 includes a receiver 21, a received data processor 22, a synchronization manager 23, a buffer manager 24, a wireless terminal manager 25, a transmission cycle manager 26, a transmission data generator 27, and a transmitter 28. The solid arrow to the receiver 21 and the solid arrow from the transmitter 28 correspond to a wired network 15N connected to the wireless base station 20. The dashed-dotted arrow to the receiver 21 and the dashed-dotted arrow from the transmitter 28 correspond to a wireless network with the wireless terminal 30. The buffer manager 24 has a buffer 240. The wireless terminal manager 25 manages a wireless terminal information table 250.

[0028] 4, the wireless terminal 30 includes a receiving unit 31, a received data processing unit 32, a synchronization management unit 33, a buffer management unit 34, a transmission cycle management unit 35, a transmission data creation unit 36, and a transmitting unit 37. The dashed dotted arrow line to the receiving unit 31 and the dashed dotted arrow line from the transmitting unit 37 correspond to a wireless network with the wireless base station 20. The buffer management unit 34 has a playback buffer 340.

[0029] The general operations of the center device 10, the wireless base station 20, and the wireless terminal 30 will be described. In Fig. 2, the receiver 11 receives data from the wired network 15N. The received data processing unit 12 processes the data received by the receiver 11. When the receiver 11 receives a wireless base station registration request (described later) from the wireless base station 20, the base station management unit 13 receives the wireless base station registration request from the received data processing unit 12. The base station management unit 13 assigns a base station ID to the IP address of the wireless base station 20. As shown in Fig. 5, the base station management unit 13 stores the base station ID and the IP address in a pair in the base station management table 130.

[0030] When the receiver 11 receives a wireless terminal registration request, described later, from the wireless base station 20, the wireless terminal management unit 15 receives the wireless terminal registration request from the received data processing unit 12. The wireless terminal management unit 15 assigns a terminal ID to the IP address of the wireless terminal 30. As shown in Fig. 6, the wireless terminal management unit 15 stores a set of the terminal ID, IP address, MAC address of the wireless terminal 30, and the buffer size of the playback buffer 340 in the terminal information table 150. The wireless terminal management unit 15 manages a sequence number indicating the order of the audio data, described later, for each wireless terminal 30 to which the audio data is to be transmitted.

[0031] The audio data processing unit 14 processes the audio data received by the receiving unit 11 and supplies it to the transmission data creation unit 17. The transmission cycle management unit 16 manages the transmission timing of multicast audio packets, which will be described later. The transmission data creation unit 17 creates transmission data based on the audio data supplied from the audio data processing unit 14. The transmission data creation unit 17 may synthesize audio data transmitted from multiple wireless terminals 30 to create a multicast audio packet. The transmitting unit 18 transmits the multicast audio packet to the wired network 15N.

[0032] The following shows an example of a multicast audio packet created by the audio data processing unit 14. As an example, it is assumed that there are six wireless terminals 30, 30A to 30F, and among the wireless terminals 30A to 30F, the wireless terminals 30A to 30C belong to a call group of group 1, and the wireless terminals 30D to 30F belong to a call group of group 2.

[0033] The voice data processing unit 14 mixes the voice data received from the wireless terminals 30B and 30C to create voice data addressed to the wireless terminal 30A. This voice data becomes the voice data included in FIG. 15, which will be described later. The voice data processing unit 14 mixes the voice data received from the wireless terminals 30A and 30C to create voice data addressed to the wireless terminal 30B. The voice data processing unit 14 mixes the voice data received from the wireless terminals 30A and 30B to create voice data addressed to the wireless terminal 30C.

[0034] When the aggregated voice data in FIG. 14 described later includes voice data addressed to wireless terminal 30A, wireless terminal 30B, and wireless terminal 30C, the aggregated voice data includes three sets of terminal ID, sequence number, and voice data in FIG.

[0035] The transmission data creation unit 17 creates a multicast audio packet as shown in Fig. 14 using the audio data addressed to each wireless terminal 30 sent from the audio data processing unit 14. The multicast audio packet does not depend on the group, and audio data addressed to, for example, wireless terminal 30C and wireless terminal 30D belonging to different groups may be included in one multicast audio packet.

[0036] 3, the receiving unit 21 receives multicast audio packets from the wired network 15N. The receiving unit 21 receives audio packets from a wireless network. The received data processing unit 22 processes the data received by the receiving unit 21. As described later, the received data processing unit 22 may analyze or judge the data received by the receiving unit 21. The synchronization management unit 23 generates a reference timing for the transmitting unit 28 to transmit audio packets, and supplies the reference timing to the transmission cycle management unit 26.

[0037] The buffer management unit 24 stores voice data in the buffer 240, reads voice data from the buffer 240, and manages various types of data described later. The wireless terminal management unit 25 stores information about the wireless terminal 30 transmitted from the center device 10 and information about the wireless terminal 30 connected to its own station in a wireless terminal information table 250, and manages the wireless terminal 30.

[0038] The transmission cycle management unit 26 manages a transmission timer, which will be described later, and generates a transmission trigger, which will be described later. The transmission data creation unit 27 creates transmission data and supplies it to the transmission unit 28. The transmission unit 28 transmits the data to the wired network 15N or the wireless network.

[0039] In FIG. 4, the receiving unit 31 receives data from the wireless network. The received data processing unit 32 processes the data received by the receiving unit 31. The synchronization management unit 33 generates a reference timing for the transmitting unit 37 to transmit audio packets and supplies it to the transmission cycle management unit 35. The buffer management unit 34 manages a playback buffer 340 that stores audio data. The transmission cycle management unit 35 manages the transmission timing of the audio packets. The transmission data creation unit 36 ​​creates transmission data. The transmitting unit 37 transmits the transmission data created by the transmission data creation unit 36 ​​to the wireless network.

[0040] 7 shows a communication sequence when the wireless terminal 30A connects to the wireless base station 20A and the center device 10 registers the wireless terminal 30A. In step S71, the wireless terminal 30A transmits a connection request to the wireless base station 20A, and in step S72, the wireless base station 20A transmits a connection response to the wireless terminal 30A. As a result, the wireless terminal 30A connects to the wireless base station 20A. Steps S71 and S72 are connection processing executed between the wireless base station 20A and the wireless terminal 30A.

[0041] In step S73, the wireless terminal 30A transmits a wireless terminal registration request R73 to the center device 10. As shown in Fig. 8, the wireless terminal registration request R73 transmitted by the wireless terminal 30A to the center device 10 in step S73 includes the MAC address of the wireless terminal 30A and the buffer size of the playback buffer 340 provided in the wireless terminal 30A. In step S74, the center device 10, which has received the wireless terminal registration request R73, transmits a wireless terminal registration response to the wireless terminal 30A via the wireless base station 20A. At this time, the center device 10 assigns a terminal ID to the wireless terminal 30A. As a result, the center device 10 registers the wireless terminal 30A.

[0042] Steps S73 and S74 are wireless terminal registration processing executed by the center device 10 and the wireless terminal 30A.

[0043] In steps S75, S76, and S77, the center device 10 transmits terminal information I30A of the wireless terminal 30A to the wireless base stations 20A, 20B, and 20C, respectively. As shown in Fig. 9, the terminal information I30A includes the terminal ID of the wireless terminal 30A assigned by the center device 10, the IP address, MAC address, and buffer size of the wireless terminal 30A. The MAC address and buffer size of the wireless terminal 30A are included in the received wireless terminal registration request R73. The IP address of the wireless terminal 30A can be obtained when the center device 10 receives the wireless terminal registration request R73.

[0044] Fig. 10 shows a wireless terminal information table 250 managed by the wireless terminal management unit 25 of the wireless base station 20. When the receiving unit 21 of the wireless base stations 20A to 20C receives the terminal information I30A shown in Fig. 9, the received data processing unit 22 supplies the terminal information I30A to the wireless terminal management unit 25, and the wireless terminal management unit 25 stores the terminal ID, IP address, MAC address, buffer size, and reception time of the wireless terminal 30A in the wireless terminal information table 250. If the receiving unit 21 of the wireless base stations 20A to 20C similarly receives the terminal information I30 of other wireless terminals 30, the terminal IDs, IP addresses, MAC addresses, buffer sizes, and reception times of the multiple wireless terminals 30 are stored in the wireless terminal information table 250.

[0045] Fig. 11 shows a registration process executed between the center device 10 and the wireless base station 20A. In step S111, the wireless base station 20A transmits a wireless base station registration request R111 to the center device 10. As described above, when the receiving unit 11 of the center device 10 receives the wireless base station registration request R111, the base station management unit 13 stores the base station ID and IP address as a pair in the base station management table 130 shown in Fig. 5. In step S112, the transmitting unit 18 of the center device 10 transmits a wireless base station registration response R112 to the wireless base station 20A.

[0046] 12, the wireless base station registration response R112 includes a base station ID assigned to the wireless base station 20, a connected terminal count which is the number of wireless terminals 30 connected to the center device 10 via the wireless base station 20, and connected terminal information which is terminal information I30 of the connected wireless terminals 30. It is assumed that wireless terminals 30A, 30B, and one or more other wireless terminals 30 are connected to the center device 10. In this case, the connected terminal information includes terminal information I30A of the wireless terminal 30A, terminal information I30B of the wireless terminal 30B, and terminal information I30 of the other one or more wireless terminals 30.

[0047] 13, an example of a transmission and reception process of audio data executed between the center device 10, the wireless base station 20, and the wireless terminal 30 will be described. In step S1301, the center device 10 transmits a multicast audio packet including audio data addressed to the wireless terminal 30A and the wireless terminal 30B to the wireless base stations 20A to 20C by multicast.

[0048] In step S1302, the center device 10 transmits, by multicast, a multicast voice packet including voice data addressed to the wireless terminal 30C and the wireless terminal 30D to the wireless base stations 20A to 20C.

[0049] In this manner, audio data addressed to a plurality of wireless terminals 30 is transmitted to each wireless base station 20 by multicast.

[0050] In step S1303, the wireless base station 20A transmits the voice data received from the wireless terminal 30A and buffered as a voice packet to the center device 10. In step S1304, the wireless base station 20A transmits the voice data addressed to the wireless terminal 30A, which was received from the center device 10 in step S1301 and buffered, as a voice packet to the wireless terminal 30A.

[0051] At step S1305, which is simultaneous with step S1304, the wireless base station 20B transmits the voice data addressed to the wireless terminal 30B, which has been received and buffered from the center device 10 at step S1301, as a voice packet to the wireless terminal 30B.

[0052] In step S1306, the wireless base station 20B transmits the voice data received from the wireless terminal 30B and buffered as a voice packet to the center device 10. In steps S1307 and S1308, the wireless base station 20C transmits the voice data received from the wireless terminals 30C and 30D and buffered as a voice packet to the center device 10.

[0053] In step S1309, the wireless terminal 30A transmits the voice data as voice packets to the wireless base station 20A. In step S1310, the wireless terminal 30B transmits the voice data as voice packets to the wireless base station 20B.

[0054] The center device 10, the wireless base stations 20A and 20B, and the wireless terminals 30A and 30B execute steps S1311 to S1320 which are similar to steps S1301 to S1310.

[0055] 14 shows an example of the configuration of a multicast audio packet transmitted to wireless base stations 20A to 20C in steps S1301, S1302, S1311, and S1312. The multicast audio packet includes a synchronization flag indicating that the packet is used as a reference for transmission timing by wireless base station 20, a terminal number indicating the number of terminal audio data included in the packet, and aggregated audio data consisting of audio data addressed to multiple wireless terminals 30. The aggregated audio data includes audio data for the number of wireless terminals 30 indicated by the terminal number. If the number of terminals is 0, the multicast audio packet does not include aggregated audio data.

[0056] 15 shows an example of the configuration of terminal audio data for one wireless terminal 30 included in the aggregated audio data. The terminal audio data is composed of the terminal ID of the wireless terminal 30 that is the destination of the audio data included in the aggregated audio data, a sequence number indicating the order of the audio data managed for each wireless terminal 30, and one period of audio data. The number of terminal audio data to be included in one multicast audio packet may be limited to a size that does not cause fragmentation in IP communication.

[0057] As shown in Fig. 16, the buffer 240 has a ring buffer 240R. Although only one ring buffer 240R is shown in Fig. 16, the buffer 240 has a ring buffer 240R for each wireless terminal 30. The ring buffer 240R has four areas that can be selected by buffer indexes 0 to 3, and can store four sets of sequence numbers and voice data. The four areas of the ring buffer 240R are areas for writing voice data from the latest transmission cycle to the predetermined cycle ago (here, three cycles ago).

[0058] The buffer management unit 24 can specify an area to write sequence numbers and audio data by cyclically specifying buffer indexes 0 to 3 using a write index. The buffer management unit 24 can specify an area to read sequence numbers and audio data by cyclically specifying buffer indexes 0 to 3 using a read index. The buffer management unit 24 manages updates of the write index and read index. Note that the write index and read index are not synchronized.

[0059] When the wireless base station 20 receives a multicast audio packet from the center device 10, the buffer management unit 24 selects the ring buffer 240R corresponding to the terminal ID of the wireless terminal 30 shown in Fig. 15, and stores the sequence number and audio data. Since the write index is 2 in Fig. 16, the buffer management unit 24 writes the sequence number and audio data in the area of ​​the buffer index 2.

[0060] The wireless terminal manager 25 stores the time when the multicast audio packet with the synchronization flag set as shown in FIG. 14 was received as the reception time corresponding to the terminal ID in the wireless terminal information table 250 shown in FIG.

[0061] In FIG. 16, since the read index is 1, when the wireless base station 20 transmits voice data stored in the ring buffer 240R to the wireless terminal 30, the buffer management unit 24 reads the sequence number and voice data from the area of ​​the buffer index 1.

[0062] FIG. 17 shows an example of the configuration of voice packets that the wireless base station 20A transmits to the wireless terminal 30A in steps S1304 and S1314, and that the wireless base station 20B transmits to the wireless terminal 30B in steps S1305 and S1315.

[0063] The voice packet includes a communication ID assigned to the wireless terminal 30 by the wireless base station 20, and a sequence number stored in an area specified by the buffer index indicated by the read index. The voice packet includes a delay time, which is a value obtained by subtracting the reception time corresponding to the terminal ID in the wireless terminal information table 250 shown in Fig. 10 from the time when the wireless base station 20 starts transmitting the voice packet, and a flag indicating information on the voice data included. The voice packet also includes multiplexed voice data including the voice data stored in an area specified by the buffer index indicated by the read index. The multiplexed voice data can include multiple pieces of voice data.

[0064] Fig. 18 shows an example of the configuration of the flag included in the audio packet shown in Fig. 17. As shown in Fig. 18, the flag consists of 8 bits of data. The bit marked N is the least significant bit, and the bit marked N-7 is the most significant bit. The least significant bit indicates whether or not the audio data of the sequence number included in the audio packet (audio data of buffer index 1 in Fig. 16) is included in the multiplexed audio data in the audio packet. The second bit marked N-1 indicates whether or not the audio data of the sequence number one cycle before the sequence number included in the audio packet is included in the multiplexed audio data.

[0065] Similarly, the 3rd to 7th bits, represented as N-2 to N-6, respectively indicate whether or not audio data with sequence numbers 2 to 6 periods earlier is included in the multiplexed audio data. The most significant bit indicates whether or not audio data with a sequence number 7 periods earlier is included in the multiplexed audio data. If audio data is included in the multiplexed audio data, the value of each bit is "1", and if audio data is not included in the multiplexed audio data, the value of each bit is "0".

[0066] As an example, if the flag is "11110111", this means that the audio data having the sequence number three periods ago is not included in the multiplexed audio data, and audio data having other sequence numbers is included in the multiplexed audio data.

[0067] The multiplexed audio data included in the audio packet shown in Fig. 17 is obtained by concatenating the audio data indicated by the flags in reverse chronological order. The flag is not limited to 8 bits and may be of another size.

[0068] Fig. 19 shows a specific example of the audio packet shown in Fig. 17. As shown in Fig. 19, the communication ID is 10, the sequence number is 3000, the delay time is 5, and the flag is 00000101. Since the flag is 00000101, the multiplexed audio data includes audio data with sequence number 3000 and audio data with sequence number 2998, which is the sequence two cycles earlier. The audio packet shown in Fig. 19 includes multiplexed audio data in which the audio data with sequence number 3000 and the audio data with sequence number 2998 are concatenated in this order.

[0069] 20 shows the reference timings at which the center device 10, the wireless base station 20, and the wireless terminal 30 transmit voice packets. The center device 10 starts transmitting multicast voice packets to the wireless base station 20 at the first reference timings CT1, CT2, ... of the transmission period P1. When the first reference timings CT1, CT2, ... arrive, the center device 10 sets a synchronization flag at the beginning as shown in FIG. 14, and transmits aggregated voice data by multicast addressed to all wireless terminals 30, the number of which is indicated by the number of terminals.

[0070] The wireless base station 20 transmits voice packets to the center device 10 and the wireless terminals 30 based on the second reference times AT1, AT2, ... of the transmission period P1. The wireless base station 20 sets the second reference times AT1, AT2, ... to the time points when an offset time d1 has elapsed since the wireless base station 20 received a multicast voice packet with a synchronization flag set.

[0071] In detail, the wireless base station 20 transmits a voice packet to the center device 10 at a time obtained by adding the base station ID to the second reference timing AT1, AT2, .... This makes it possible to shift the timing at which each wireless base station 20 transmits a voice packet to the center device 10. A different value other than the base station ID may be added to the second reference timing AT1, AT2, ... for each wireless base station 20 to shift the timing at which the voice packet is transmitted to the center device 10.

[0072] By staggering the timing at which the multiple wireless base stations 20 transmit voice packets to the center device 10, collisions of voice packets in the wired network 15N can be avoided, and data loss of voice data hardly occurs.

[0073] The wireless base station 20 starts transmitting voice packets to the wireless terminal 30 at the second reference times AT1, AT2, .... That is, all the wireless base stations 20 transmit voice packets to the wireless terminal 30 at the same timing.

[0074] The wireless terminal 30 starts transmitting voice packets to the wireless base station 20 at third reference times ST1, ST2, ... of the transmission period P1. The third reference times ST1, ST2, ... are times when an offset time d2 has elapsed from the second reference times AT1, AT2, .... The wireless terminal 30 subtracts the delay time included in the voice packet shown in Fig. 17 from the reception time of the voice packet transmitted from the wireless base station 20 and adds the offset times d1 and d2 to the time, and sets the time as the third reference times ST1, ST2, ....

[0075] Next, a method for the wireless terminal 30 to always receive the latest voice data even when switching the wireless base station 20 and a method for reducing voice interruptions during roaming will be described. The wireless base stations 20A to 20C connected to the center device 10 receive multicast voice packets transmitted by the center device 10.

[0076] Each wireless base station 20 stores voice data addressed to a wireless terminal 30 (first wireless terminal) connected to the own station in a ring buffer 240R (first ring buffer) provided corresponding to the wireless terminal 30 connected to the own station. Each wireless base station 20 stores voice data addressed to a wireless terminal 30 (second wireless terminal) not connected to the own station in a ring buffer 240R (second ring buffer) provided corresponding to the wireless terminal 30 not connected to the own station.

[0077] The wireless base station 20 transmits the voice data stored in the ring buffer 240R as voice packets to the wireless terminal 30 connected to the wireless base station at a transmission period P1, and therefore updates the read index of the ring buffer 240R provided corresponding to the wireless terminal 30 connected to the wireless base station at each transmission period P1. Since the wireless base station 20 does not need to transmit voice packets to wireless terminals 30 that are not connected to the wireless base station, it is considered that the wireless base station 20 does not update the read index of the ring buffer 240R provided corresponding to the wireless terminal 30 that is not connected to the wireless base station.

[0078] However, in this case, when the wireless terminal 30 switches the wireless base station 20 from another wireless base station 20 (other station) to the wireless terminal 30 due to roaming, the latest voice data cannot be transmitted to the wireless terminal 30.

[0079] Therefore, the buffer management unit 24 of each wireless base station 20 not only updates the read index of the ring buffer 240R provided corresponding to the wireless terminal 30 connected to the wireless base station for each transmission period P1, but also updates the read index of the ring buffer 240R provided corresponding to the wireless terminal 30 not connected to the wireless base station (connected to another station) for each transmission period P1.

[0080] After updating the read index of the ring buffer 240R, the buffer management unit 24 clears the sequence number indicated by the read index of the ring buffer 240R provided in correspondence with the wireless terminal 30 not connected to the own station.

[0081] Clearing the sequence number means invalidating the sequence number by setting it to "-1," which is an example of an invalid value. The read index indicates the buffer index of the ring buffer 240R that contains the audio data to be transmitted in the next transmission cycle P1.

[0082] In this manner, each wireless base station 20 can transmit the latest voice data to the wireless terminal 30 when the wireless terminal 30 switches from another wireless base station 20 to its own station due to roaming.

[0083] Also, the arrival of voice data transmitted from the center device 10 to the wireless base station 20 may be delayed, and the voice data may not be written in the buffer index area pointed to by the read index. By clearing the sequence number, it is possible to determine whether the voice data is written in the buffer index area pointed to by the read index.

[0084] The second reference timings AT1, AT2, ..., which are the reference for the timing at which the wireless base station 20 transmits voice packets, are the same for all the wireless base stations 20. Therefore, by updating the read index of the ring buffer 240R provided for each wireless terminal 30 for each transmission period P1, it is possible to synchronize the voice data to be transmitted to the wireless terminals 30 between the wireless base stations 20.

[0085] 21 shows a flow chart illustrating a transmission / reception process in the wireless base station 20. When the process starts, the wireless base station 20 executes a timing synchronization process in step S211, executes a transmission / reception process in step S212, and then ends the process.

[0086] Specifically, when the receiving unit 21 receives a multicast voice packet with a synchronization flag set and transmitted from the center device 10, in step S211, the received data processing unit 22 analyzes the received data, and the synchronization management unit 23 generates second reference timings AT1, AT2 ... and supplies them to the transmission cycle management unit 26. The transmission cycle management unit 26 starts a transmission timer. The transmission timer is a timer that expires every transmission cycle P1. In step S212, the receiving unit 21 and the transmitting unit 28 receive the multicast voice packet transmitted from the center device 10, receive the voice packet transmitted from the wireless terminal 30, and transmit the voice packet to the center device 10 and the wireless terminal 30.

[0087] The flowchart shown in Fig. 22 shows the receiving process of a multicast audio packet transmitted from the center device 10, among the transmitting / receiving process in step S212 shown in Fig. 21. When the process starts, in step S221, the receiving unit 21 receives a multicast audio packet transmitted from the center device 10. In step S222, the buffer management unit 24 stores the audio data of the received multicast audio packet in the buffer 240.

[0088] The flowchart shown in Fig. 23 shows detailed processing of step S222 shown in Fig. 22. When processing starts, the received data processing unit 22 determines in step S231 whether the amount of unprocessed voice data is 1 or more. If processing of all voice data for the number of wireless terminals 30 indicated by the number of terminals has not been completed, the amount of unprocessed voice data is 1 or more. If the amount of unprocessed voice data is 1 or more (YES), the buffer management unit 24 selects a ring buffer 240R corresponding to the terminal ID of the wireless terminal 30 in step S232.

[0089] In step S233, the buffer management unit 24 stores the voice data in the selected ring buffer 240R. In step S234, the buffer management unit 24 stores the sequence number in the ring buffer 240R. In step S235, the buffer management unit 24 updates the number of untransmitted data stored in the ring buffer 240R and not yet transmitted to the wireless terminal 30 by incrementing it by 1. In step S236, the received data processing unit 22 updates the number of unprocessed voice data by decrementing it by 1, and returns the process to step S231.

[0090] If the number of unprocessed voice data items is not 1 or more in step S231 (NO), this means that processing of all voice data items for the number of wireless terminals 30 indicated by the number of terminals has been completed, and the wireless base station 20 ends the processing.

[0091] The flowchart shown in Fig. 24 shows the reception process of a voice packet transmitted from the wireless terminal 30, which is part of the transmission and reception process in step S212 shown in Fig. 21. When the process starts, the receiver 21 receives a voice packet transmitted from the wireless terminal 30 in step S241. The buffer manager 24 stores the voice data of the received voice packet in the ring buffer 240R in step S242. The received data processor 22 updates the number of data yet to be transmitted to the center device 10 by incrementing it by 1 in step S243, and ends the process.

[0092] The flowchart shown in Fig. 25 shows the transmission process of transmitting voice packets to the center device 10 and the wireless terminal 30 from the transmission and reception process of step S212 shown in Fig. 21. When the process is started, the transmission cycle management unit 26 receives a reference timing from the synchronization management unit 23, and in step S251 starts a transmission timer and generates a transmission trigger when the transmission timer expires. When the transmission timer expires, a transmission trigger is generated. In step S252, the transmission unit 28 transmits voice packets to the center device 10 and the wireless terminal 30 and ends the process.

[0093] The flowchart shown in Fig. 26 shows the transmission process of transmitting a voice packet to the center device 10 in step S252 shown in Fig. 25. When the process starts, the buffer management unit 24 determines in step S261 whether the number of pieces of untransmitted data is 1 or more. If the number of pieces of untransmitted data is 1 or more (YES), the transmission data creation unit 27 creates a voice packet to be transmitted in step S262. The transmission unit 28 transmits the created voice packet to the center device 10 in step S263. The buffer management unit 24 updates the number of pieces of untransmitted data to increment by 1 in step S264, and returns the process to step S261.

[0094] If the number of untransmitted data items is not equal to or greater than 1 in step S261 (NO), the wireless base station 20 ends the process.

[0095] Through the transmission process shown in FIG. 26, the wireless base station 20 transmits the voice data received from each wireless terminal 30 and buffered in the buffer 240 to the center device 10.

[0096] The flowcharts shown in FIGS. 27A to 27C show the transmission process in which the wireless base station 20 transmits a voice packet to the wireless terminal 30 in step S252 shown in FIG.

[0097] 27A, when processing starts, the buffer management unit 24 determines in step S2701 whether the number of untransmitted wireless terminals 30 (hereinafter, untransmitted terminals) is 1 or more. If the number of untransmitted terminals is 1 or more (YES), the buffer management unit 24 selects a wireless terminal 30 (transmitting terminal) to transmit a voice packet in step S2702. The buffer management unit 24 determines in step S2703 whether the number of untransmitted data addressed to the wireless terminal 30 selected in step S2702 is 1 or more.

[0098] If the number of untransmitted data pieces is 1 or more in step S2703 (YES), the buffer management unit 24 determines in step S2704 whether or not this is the first transmission after the wireless terminal 30 is connected. That is, the buffer management unit 24 determines whether or not the voice packet to be transmitted is the first voice packet that the wireless base station 20 transmits to the wireless terminal 30 after the wireless terminal 30 is connected to the wireless base station 20.

[0099] If it is the first transmission in step S2704 (YES), the transmission data creation unit 27 creates a voice packet including the voice data of the latest sequence number pointed to by the read index stored in the ring buffer 240R and the voice data of the sequence number before the latest one in step S2705. After step S2705, the wireless base station 20 shifts the process to step S2707.

[0100] However, if the size of the audio data of the sequence number before the latest is larger than the buffer size of playback buffer 340 of wireless terminal 30, it is not possible to play back the part of the audio data that exceeds the buffer size of playback buffer 340. Therefore, if the size of the audio data of the sequence number before the latest is equal to or smaller than the buffer size of playback buffer 340 of wireless terminal 30, transmission data creation unit 27 creates an audio packet including all of the audio data of the sequence numbers before the latest.

[0101] If the size of the voice data of an older sequence number than the latest one exceeds the buffer size of playback buffer 340 of wireless terminal 30, transmission data creation unit 27 creates a voice packet including voice data equal to or smaller than the buffer size of playback buffer 340. In this case, transmission data creation unit 27 selects voice data of a newer sequence number and creates a voice packet equal to or smaller than the buffer size of playback buffer 340.

[0102] By executing the process of step S2705 by the transmission data creation unit 27, it is possible to reduce voice interruptions during roaming. A wireless terminal 30 (third wireless terminal) connected to any wireless base station 20 (first wireless base station) can receive at least a part of the voice data written in a ring buffer 240R (third ring buffer) provided corresponding to the third wireless terminal. The third wireless terminal can receive the voice data that could not be received during the process of switching to another wireless base station 20 (second wireless base station) as valid voice data within the buffer size of the reproduction buffer 340.

[0103] If it is not the first transmission in step S2704 (NO), the transmission data creation unit 27 creates a voice packet including the voice data of the latest sequence number pointed to by the read index stored in the ring buffer 240R in step S2706. After step S2706, the wireless base station 20 shifts the process to step S2707.

[0104] In step S2707, the transmitting unit 28 transmits the voice packets generated in step S2705 or S2706 to the wireless terminal 30, and moves the process to step S2708 in FIG. 27B.

[0105] On the other hand, if the number of untransmitted data items is not 1 or more in step S2703 (NO), this means that there is no untransmitted voice data, and the wireless base station 20 transitions the process to step S2708 in FIG. 27B.

[0106] 27B, the buffer management unit 24 updates the value of the read index in step S2708. In step S2709, the buffer management unit 24 decrements the number of pieces of untransmitted data by 1 to update the number of pieces of untransmitted data.

[0107] In step S2710, the buffer management unit 24 determines whether the number of unsent data is 0 or less. If the number of unsent data is 0 or less (YES), in step S2711, the buffer management unit 24 clears the sequence number of the ring buffer 240R pointed to by the read index, and moves the process to step S2712. If the number of unsent data is not 0 or less (NO), the buffer management unit 24 moves the process to step S2712. In step S2712, the buffer management unit 24 decrements the number of unsent terminals by 1 to update the number of unsent terminals, and returns the process to step S2701 in FIG. 27A.

[0108] In this way, the buffer management unit 24 updates the read index and the number of pieces of untransmitted data and clears the sequence number when the number of pieces of untransmitted data is not 1 or more in step S2703. This makes it possible to synchronize the data transmitted by the wireless base station 20 to the wireless terminal 30 with the data transmitted by other wireless base stations 20 to the wireless terminal 30 even if the wireless base station 20 loses a multicast audio packet transmitted from the center device 10.

[0109] 27A (NO), the buffer management unit 24 determines whether the number of unconnected terminals is 1 or more in step S2713 of Fig. 27C. The number of unconnected terminals is the number of wireless terminals 30 that are not connected to the wireless base station 20.

[0110] If the number of unconnected terminals is 1 or more in step S2713 (YES), the buffer management unit 24 selects an unconnected terminal in step S2714, and then updates the value of the read index of the ring buffer of the selected unconnected terminal in step S2715. The buffer management unit 24 decrements the number of untransmitted data by 1 to update the number of untransmitted data in step S2716.

[0111] In step S2717, the buffer management unit 24 determines whether the number of untransmitted data is 0 or less. If the number of untransmitted data is 0 or less (YES), in step S2718, the buffer management unit 24 clears the sequence number of the ring buffer 240R pointed to by the read index, and proceeds to step S2719. If the number of untransmitted data is not 0 or less (NO), the buffer management unit 24 proceeds to step S2719. In step S2719, the buffer management unit 24 decrements the number of unconnected terminals by 1 to update the number of unconnected terminals, and returns the process to step S2713.

[0112] When the number of unconnected terminals is 1 or more in step S2713, the buffer management unit 24 updates the read index and the number of unsent data, and clears the sequence number. This makes it possible to synchronize the data transmitted from the wireless base station 20 to the wireless terminal 30 with the data transmitted from another wireless base station 20 to the wireless terminal 30 connected to the other wireless base station 20.

[0113] If the number of unconnected terminals is not 1 or more in step S2713 (NO), the buffer management unit 24 ends the process.

[0114] Using the sequence diagram shown in Fig. 28, a method will be described in which a wireless terminal 30 that has switched the wireless base station 20 to which it is connected by roaming acquires an IP address of the newly connected wireless base station 20. Fig. 28 shows a sequence diagram when the wireless base station 20 to which a wireless terminal 30A is connected is switched from the wireless base station 20A to the wireless base station 20B.

[0115] The wireless base stations 20A and 20B transmit voice packets to the center device 10 and the wireless terminal 30 at second reference timings AT281, AT282, AT283, .... The wireless base station 20A transmits voice data to the wireless terminal 30A in step S281. The wireless terminal 30A transmits the voice data to the wireless base station 20A in step S282. The wireless terminal 30A disconnects from the wireless base station 20A by a disconnection process in step S283.

[0116] The wireless terminal 30A connects to the wireless base station 20B by the connection process in step S284. The wireless base station 20B transmits voice data to the wireless terminal 30A in step S285. The wireless terminal 30A receives the voice data transmitted from the wireless base station 20B, thereby acquiring the IP address, communication ID, and delay time of the wireless base station 20B. The IP address can be acquired from the IP header of the IP packet.

[0117] The wireless terminal 30A uses the acquired IP address, communication ID, and delay time of the wireless base station 20B to transmit the voice data to the wireless base station 20B at step S286, which is the transmission timing assigned to the wireless terminal 30A.

[0118] As described above, the wireless communication system of this embodiment is configured using the wireless LAN communication standard, and can receive voice data without any problems even if the wireless base station to which the wireless terminal is connected is switched.

[0119] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0120] 10 Center device 20,20A,20B,20C Wireless base station 30, 30A, 30B, 30C, 30D Wireless terminal 11,21,31 Receiver 12,22 Received data processing section 13 Base station management department 14 Audio data processing section 15,25 Wireless Terminal Management Department 16,26,35 Transmission cycle management section 17, 27, 36 Transmission data creation section 18,28,37 Transmitter 23,33 Synchronization management section 24,34 Buffer Management Unit 130 Base Station Management Table 150 Terminal Information Table 240 buffers 240R Ring Buffer 250 Wireless terminal information table 340 Playback Buffer

Claims

1. A center device; a plurality of wireless base stations connected to the center device via a wired network; one or more wireless terminals wirelessly connected to each of the plurality of wireless base stations; Equipped with the center device transmits, by multicast, to all of the plurality of wireless base stations, a multicast voice packet including a plurality of pairs of voice data and a sequence number indicating an order of the voice data to be transmitted for each of the wireless terminals to which the voice data is to be transmitted; Each wireless base station a ring buffer provided for each wireless terminal including a first wireless terminal connected to the own station and a second wireless terminal not connected to the own station; a buffer management unit which manages a write index for each ring buffer which designates an area in which audio data and sequence numbers are to be written in each ring buffer and a read index for each ring buffer which designates an area from which the audio data written in each ring buffer is to be read, writes the audio data included in a received multicast audio packet to an area designated by the write index in a ring buffer provided corresponding to a destination wireless terminal to which the audio data is to be transmitted, and reads the audio data written in the area designated by the read index in a first ring buffer provided corresponding to the first wireless terminal; a transmission cycle management unit that manages a transmission cycle so that all wireless base stations transmit voice packets including the voice data read from the first ring buffer to the first wireless terminal at the same timing; a transmitter that transmits a voice packet including the voice data read from the first ring buffer to the first wireless terminal; having Each ring buffer has an area for writing audio data, and an area for writing audio data from the latest transmission cycle to a predetermined cycle before, The buffer management unit A read index designating an area from which voice data is read from the first ring buffer is updated for each transmission period, and after updating a read index designating an area from which voice data is read from a second ring buffer provided corresponding to the second wireless terminal, a sequence number written in the area of ​​the second ring buffer designated by the read index is cleared to an invalid value. Wireless communication system.

2. When a third wireless terminal connected to a first wireless base station is disconnected from the first wireless base station and connected to a second wireless base station, The second wireless base station transmits, in a first transmission period after the third wireless terminal is connected, to the third wireless terminal, a voice packet including voice data that is equal to or smaller than a buffer size of a playback buffer of the third wireless terminal, among the voice data written in a third ring buffer provided corresponding to the third wireless terminal.

2. The wireless communication system according to claim 1.

3. A center device transmits, by multicast, a multicast voice packet including a plurality of pairs of voice data and a sequence number indicating an order of the voice data to be transmitted for each destination wireless terminal to which the voice data is transmitted, to all of a plurality of wireless base stations connected to the center device by a wired network; Each wireless base station is provided with a ring buffer corresponding to each wireless terminal including a first wireless terminal connected to the wireless base station and a second wireless terminal not connected to the wireless base station, and each ring buffer has an area for writing voice data, the area including voice data from the latest transmission period to a predetermined period before the latest transmission period; Each wireless base station managing a write index for each ring buffer that designates an area in which the voice data and the sequence number are to be written in each ring buffer and a read index for each ring buffer that designates an area from which the voice data written in each ring buffer is to be read; writing the audio data included in the received multicast audio packet into an area designated by the write index of a ring buffer provided corresponding to a destination wireless terminal to which the audio data is to be transmitted; reading out voice data written in an area designated by the read index of a first ring buffer provided corresponding to the first wireless terminal; managing a transmission cycle so that all wireless base stations transmit voice packets including the voice data read from the first ring buffer to the first wireless terminal at the same timing; transmitting a voice packet including the voice data read from the first ring buffer to the first wireless terminal; A read index designating an area from which voice data is read from the first ring buffer is updated for each transmission period, and after updating a read index designating an area from which voice data is read from a second ring buffer provided corresponding to the second wireless terminal, a sequence number written in the area of ​​the second ring buffer designated by the read index is cleared to an invalid value. A method for controlling a wireless communication system.

4. A buffer management method for a wireless communication system including a center device, a plurality of wireless base stations connected to the center device via a wired network, and one or more wireless terminals wirelessly connected to each of the plurality of wireless base stations, the buffer management unit of each wireless base station managing ring buffers provided in each wireless base station corresponding to each of the wireless terminals, the ring buffers including a first wireless terminal connected to the wireless base station and a second wireless terminal not connected to the wireless base station, managing a write index for each ring buffer that designates an area in which audio data and a sequence number indicating the order of the audio data are written in each ring buffer, and a read index for each ring buffer that designates an area from which the audio data written in each ring buffer is read; writing voice data included in a multicast voice packet received by each wireless base station into an area designated by the write index of a ring buffer provided corresponding to a destination wireless terminal to which the voice data is to be transmitted, and reading out the voice data written into an area designated by the read index of a first ring buffer provided corresponding to the first wireless terminal; A read index designating an area from which the voice data is read from the first ring buffer is updated for each transmission period in which all wireless base stations transmit voice packets including the voice data read from the first ring buffer to the first wireless terminal at the same timing, and after updating a read index designating an area from which the voice data is read from a second ring buffer provided corresponding to the second wireless terminal, a sequence number written in the area designated by the read index of the second ring buffer is cleared to an invalid value. Buffer management methods.

Images