JP2006129041A - Data transfer system, transmission terminal, reception terminal, data transmission method, and data reception method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transfer system capable of efficiently using communication time between a plurality of communication terminals. <P>SOLUTION: The data transfer system comprises a transmission terminal 450 for transmitting data, and one or more reception terminals 500 for directly receiving data from the transmission terminal by wireless communication. A multicast period setting part 478 of the transmission terminal sets multicast transmission period, and the unicast period setting part 508 of the reception device sets a unicast reception period to itself for the multicast transmission period. The transmission terminal sets the unicast transmission period to reception terminals for the first time during the multicast transmission time, and performs unicast communication with the reception terminals within the multicast transmission period. So, the unicast communication can be defined at the time of actually transmitting data, allowing efficient use of communication time between a plurality of communication terminals. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a data transmission system, a transmission terminal, a reception terminal, a data transmission method, and a data reception method that enable direct wireless communication between a plurality of communication terminals.

  As an example of a standard regarding a wireless network, the Institute of Electronic Engineers (IEEE) (Electrical and Electronics Engineers) 802.11, HiperLAN / 2, IEEE 802.15.3, Bluetooth, and the like can be given. The IEEE802.11 standard includes various wireless communication protocols such as the IEEE802.11a standard and the IEEE802.11b standard depending on the wireless communication method and the frequency band to be used.

  In such a wireless communication protocol that has been conventionally known, when communication is attempted between arbitrary communication terminals, it is necessary to use a coordinator called a PNC (piconet coordinator). For example, in IEEE 802.15.3, the time allocated to each communication terminal is strictly managed by the PNC, and data can be transmitted and received only at the timing specified by the PNC.

  As an application of such wireless communication, ad-hoc communication that allows direct communication between communication terminals without using an access point has been devised. While such ad hoc communication allows each communication terminal to directly and asynchronously communicate wirelessly, communication between different terminals may overlap, making it difficult to transmit or receive, or may cause a period of no communication at all. .

  In order to avoid such communication collision between terminals, the time for performing data communication is negotiated in advance, and while the terminals set there are performing unicast communication, other communication terminals stop communication. Are known. In such a technique, it is not possible to know when data is transmitted from communication terminals existing in the surrounding area, and thus it is necessary to always maintain the reception state.

  Therefore, each communication terminal transmits a beacon signal (management information) to each other, notifies each other of the time for unicast communication between the respective communication terminals, and performs a reception operation only at the notified time (for example, Technical literature 1) was also devised. However, in the above technique, once a unicast communication period is set at the time of exchanging beacon signals, use of other communication terminals is not permitted during the communication time. Therefore, it is necessary to determine the data transmission amount in the unicast communication between the communication terminals at the time of transmitting the beacon signal. Also, in multicast communication in which the same information is unilaterally transmitted from one communication terminal to a plurality of communication terminals, it is necessary to secure a communication time when transmitting a beacon signal.

JP 2003-229869 A

  The present invention has been made in view of the above-described problems of conventional wireless communication systems, and an object of the present invention is to determine a unicast communication period at the time of actually transmitting data, not when transmitting a beacon signal. It is possible to provide a new and improved data transmission system, transmitting terminal, receiving terminal, data transmitting method, and data receiving method capable of efficiently using communication time between a plurality of communication terminals .

  In order to solve the above problems, according to an aspect of the present invention, a data transmission system including a transmitting terminal that transmits data and one or more receiving terminals that directly receive data from the transmitting terminal by wireless communication. In the transmitting terminal, a multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets; and each receiving terminal of the receiving terminal group A command transmission unit that transmits a command including information on the multicast transmission period during the command reception period; a data transmission unit that transmits data in a time division manner to each of the receiving terminals of the receiving terminal group during the multicast transmission period; The receiving terminal includes a command period setting unit that sets a command receiving period exclusive to other communication terminals; A unicast period setting unit configured to set a unicast reception period to itself according to the multicast transmission period when the multicast transmission period information is received during the command reception period; And a data receiving unit for receiving data from the transmitting terminal. A data transmission system is provided.

  The communication terminals including the transmission terminal and the reception terminal may be a personal computer, a PDA (Personal Digital Assistant), a mobile phone, or a video conference system capable of wireless communication.

  In the present invention, each receiving terminal secures a command receiving period, and when the transmitting terminal designates the receiving terminal and transmits data, the transmitting terminal receives each command according to the command receiving period set for each receiving terminal. Identify the device. In addition, the transmitting terminal temporarily secures a necessary minimum communication period to be transmitted as a multicast transmission period, and then sets a unicast transmission period to each receiving terminal for the first time in the multicast transmission time, and within the multicast transmission period. In unicast communication with each communication terminal. With this configuration, it is possible to reserve a data transmission period in a short time without complicated reservation processing at the time of beacon signal transmission, and to improve the efficiency of data transmission, which can be applied to best effort type data communication. A period-reserved wireless communication protocol.

  In addition, with the configuration in which the command reception period is set, the transmission destination can be easily specified only by processing in which surrounding communication terminals transmit some data during the command reception period of the target communication terminal. Therefore, there is no need to specify the receiving terminal using a separate identifier or the like. Further, the receiving terminal only needs to be activated only during the command reception period and the unicast reception period when data transmission to itself is requested during the command reception period, and power consumption is reduced. When there is no data to be transmitted to another communication terminal, the receiving terminal sets only such command reception period.

  In addition, the transmission terminal can specify a specific transmission destination (reception terminal) separately by setting only the multicast transmission period and transmitting a command during the command reception period of the transmission destination (reception terminal).

  The receiving terminal can grasp that there is data transmission to itself by the command received during the command receiving period. However, when receiving the command, it is not necessary to set a specific unicast reception period to itself, and a unicast reception period equal to the multicast transmission period included in the command may be set.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, a transmitting terminal that directly transmits data to a receiving terminal by wireless communication: receiving a plurality of receiving terminals selected as transmission targets A multicast period setting unit for setting a multicast transmission period as a period for transmitting data to the terminal group; a command transmission for transmitting a command including information on the multicast transmission period in each command reception period of the receiving terminal of the receiving terminal group And a data transmission unit for transmitting data to each reception terminal of the reception terminal group in a time division manner during the multicast transmission period.

  With this configuration, the same effect as the data transmission system can be obtained.

  The multicast period setting unit may set the multicast transmission period according to the amount of data to be transmitted in one multicast transmission and the buffering situation. Here, the total amount of data unicast transmitted to each receiving terminal is estimated. Therefore, it is not necessary to determine the amount of individual data that is actually unicast transmitted to each communication terminal at this point.

  The data transmission unit may complete unicast communication with the receiving terminal by an ACK control signal from the receiving terminal. In conventional multicast communication, since one-way data communication is performed between one transmitting terminal and a plurality of receiving terminals, there is no means for confirming whether the receiving terminal has received correctly. Since the present invention is unicast communication using the multicast communication area, reception completion in each unicast communication can be confirmed.

  The data transmission unit may specify a receiving terminal that performs unicast communication from the receiving terminal group by an RTS / CTS control signal. With such a configuration, even when a plurality of receiving terminals are designated by multicast communication, it is possible to perform unicast communication for individual receiving terminals.

  Further, a third communication terminal that can communicate with one communication terminal but cannot communicate with the other communication terminal when performing communication between specific communication terminals by the RTS / CTS control signal, so-called hidden. The terminal can be notified that the data transmission system is occupied and used, and transmission from the hidden terminal can be stopped.

  A transmission amount setting unit that sets the amount of data to be transmitted to each receiving terminal according to the total data amount of each receiving terminal to be transmitted or the priority of the data at the time of multicast transmission may be further provided. With such a configuration, the unicast transmission period to each receiving terminal can be freely allocated in the reserved multicast transmission period. The setting of the amount of data is determined according to the total amount of data to be transmitted to each communication terminal and the priority order of the data.

  The multicast period setting unit may set the multicast transmission period so as not to overlap with the command reception period in all receiving terminals of the data transmission system. The command reception period set exclusively for each communication terminal is the minimum necessary period to be secured for communication between the communication terminals. Therefore, communication efficiency can be improved by setting the multicast transmission period over the entire period other than the command reception period.

  First, the command period setting unit of each receiving terminal sets a command receiving period, and the set command receiving period is transmitted to surrounding communication terminals through a beacon signal. The multicast period setting unit secures a time other than the command reception period and determines an area in which multicast transmission is immediately performed. It is also possible to preferentially set the multicast transmission period in the vicinity of the command reception period.

  The multicast period setting unit may set its own multicast transmission period so as not to overlap with the multicast transmission period in all transmitting terminals of the data transmission system. If the multicast transmission periods overlap, transmission data collision occurs. Therefore, in addition to the command reception period, the multicast transmission period of other transmitting terminals is also avoided and the own multicast transmission period is set.

  The multicast period setting unit may use a beacon signal that synchronizes the plurality of communication terminals so that the multicast transmission period of the multicast period setting unit does not overlap with the multicast transmission periods of other transmission terminals. At this time, the receiving terminal group can be notified of the multicast transmission period set by the beacon signal.

  First, the multicast period setting unit of each transmitting terminal sets a multicast transmission period, and the set multicast transmission period is transmitted to surrounding communication terminals through a beacon signal. The multicast period setting unit secures a time other than the multicast transmission period at the other transmitting terminal, and determines an area for immediate multicast transmission.

  The multicast period setting unit can also specify one or two or more receiving terminals as multicast transmission destinations using a beacon signal for synchronizing the plurality of communication terminals.

  In order to solve the above-described problem, according to another aspect of the present invention, a receiving terminal that directly receives data from a transmitting terminal by wireless communication: a command that sets a command receiving period exclusive to another communication terminal A period setting unit; when information on a multicast transmission period as a period during which the transmitting terminal transmits data to a receiving terminal group including itself is received during the command receiving period of its own, A receiving terminal comprising: a unicast period setting unit that sets a unicast receiving period; and a data receiving unit that receives data from the transmitting terminal in the unicast receiving period.

  With this configuration, the same effect as the data transmission system can be obtained.

  The command period setting unit may use a beacon signal that synchronizes the plurality of communication terminals so that the command reception period does not overlap with other receiving terminals. By using the beacon signal, setting information of other communication terminals in the data transmission system can be obtained, and a command reception period can be set so as not to overlap with other communication terminals. In addition, it is possible to know the command reception period of other communication terminals. In addition, by setting the command reception period exclusively, it is possible to prevent the transmission terminal from designating a plurality of reception terminals.

  In addition, the receiving terminal receives the transmission request command from the transmitting terminal during the command receiving period, so that it can grasp that it is subject to multicast transmission and data may be transmitted. It can be carried out.

  In order to solve the above problems, according to another aspect of the present invention, a data transmission including a transmitting terminal that transmits data and one or more receiving terminals that directly receive data from the transmitting terminal through wireless communication. In the system: the transmitting terminal includes a multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets; A beacon transmitter for transmitting a beacon signal that synchronizes between the plurality of communication terminals, including information and information of the receiver terminal group; and time-division to each receiver terminal of the receiver terminal group during the multicast transmission period A data transmission unit for transmitting data at the receiving terminal, the beacon receiving unit for receiving the beacon signal; A unicast period setting unit for setting a unicast reception period to the beacon signal according to a multicast transmission period of the beacon signal when the receiving terminal is designated as a transmission target in the beacon signal; And a data receiving unit for receiving data from the transmitting terminal during the period. A data transmission system is provided.

  In the present invention, when a transmitting terminal designates a receiving terminal and transmits data, a multicast transmission period is transmitted to the receiving apparatus using a beacon signal. Except for not using the command reception period, the same effect as the data transmission system described above can be obtained.

  In addition, a transmission terminal and a reception terminal are provided, and a program for causing a computer to function as the transmission terminal and the reception terminal is also provided. Also provided are a data transmission method and a data reception method for transmitting and receiving data like the transmitting terminal and the receiving terminal.

  The transmission terminal and the reception terminal may be integrally formed. In this case, transmission / reception by wireless communication can be performed randomly and in full duplex.

  As described above, according to the present invention, a unicast communication period with each receiving terminal can be determined at the time of actually transmitting data, not at the time of transmitting a beacon signal for synchronization between communication terminals. It is possible to efficiently use communication time between communication terminals.

  In addition, by ensuring that the receiving terminal has an exclusive command receiving period, it is only necessary to communicate that there is data to be transmitted during the command receiving period without having to separately specify the destination by an identifier or the like. Unicast communication period can be set, and stable communication without errors is possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  In order to easily understand the configuration of this embodiment, first, an outline of wireless communication will be described.

  In recent years, standardization specifications for high-speed wireless PAN (Personal Area Network) in IEEE802.15.3 have been determined. According to this specification, a coordinator called a PNC (piconet coordinator) is selected for an arbitrary communication terminal to perform wireless communication with another communication terminal, and data is transmitted and received under the control of the PNC. In IEEE 802.15.3, the time used for communication by the PNC is strictly managed, and communication terminals forming such a wireless communication network can perform transmission / reception only at the timing specified by the PNC.

  In other words, when data is transmitted from a specific communication terminal (transmission terminal) to a specific communication terminal (reception terminal), first, the transmission terminal makes a request for acquiring a channel time necessary for data communication to the communication device serving as the PNC. , PNC beacon signal specifies the available channel time timing.

  According to the IEEE 802.15.3 specification, in communication between communication terminals, first, the PNC needs to secure a communication time, and the PNC must allocate a communication time each time according to the request. Necessitated a simple procedure. In such a wireless communication system that performs control using a PNC or an access point, there is a problem that it takes a long time to actually start communication.

  As an application of such wireless communication, ad-hoc communication that allows direct communication between communication terminals without using an access point has been devised. Such ad hoc communication does not require a control device such as an access point or a coordinator, and each communication terminal can be autonomously distributed to perform asynchronous wireless communication.

  In general ad hoc communication, since it is not known when data is transmitted to itself from surrounding communication terminals, each communication terminal must always be in a receiving state so that it can immediately respond to the transmission of the data. For this reason, it has been difficult to reduce power consumption.

  As a countermeasure for such a problem, as described in Japanese Patent Application Laid-Open No. 2003-229869 by the present applicant, each communication terminal transmits a beacon signal to other communication terminals existing in the vicinity, and each communicates with each other. The desired time is notified to ensure a mutual communication period.

  According to such wireless communication using beacon signals, when performing unicast communication in which communication terminals communicate with each other on a one-to-one basis, the time for performing data communication with a receiving terminal as a communication destination is negotiated in advance. , Wireless communication was performed by setting the unicast communication period exclusively. For this reason, other communication terminals cannot communicate during the unicast communication period.

  Also, in multicast communication in which the same information is transmitted from one communication terminal to multiple communication terminals, a multicast communication period is set, and the same data is transmitted to multiple communication terminals during that period, as in the case of unicast communication. I do. The target of multicast communication is performed by setting address information of a receiving terminal that receives such data in a multicast frame each time, and complicated processing is required.

  In addition, in the control method based on the random access of the carrier detection multiple access / collision avoidance (CSMA / CA) method, the wireless transmission path does not become idle for a predetermined time, so that time for its own communication is secured. This caused a delay in data transmission, which hindered real-time data transmission.

  Further, even in the invention for intermittent communication described in Japanese Patent Application Laid-Open No. 2003-229869, even if data is transmitted when the receiving terminal as the communication destination is not activated, the data does not reach correctly There was a problem. In addition, during intermittent communication, if a communication terminal that is in a dormant state is requested to start up and waits until the communication terminal is in an active state, a time loss has occurred.

  Furthermore, in conventional unicast communication, if the amount of data to be transmitted regularly is not constant, the data transmission may be terminated before the set time, and even in this case, communication is performed. Since terminals other than existing communication terminals are not allowed to perform communication, useless time during which communication is not performed occurs, and compatibility with best-effort communication is poor.

(First embodiment: data transmission system)
In view of the above problems, a data transmission system capable of efficiently using communication time between a plurality of communication terminals is proposed below. Hereinafter, unless otherwise specified, the transmitting terminal indicates a communication terminal that transmits data, and the receiving terminal indicates a communication terminal that receives data. In addition, when represented as a communication terminal, it has both transmission and reception functions.

  FIG. 1 is a configuration diagram for explaining an ad hoc network in which the data transmission system is implemented. In the ad hoc network, there is no specific control station as a communication station, and each communication terminal operates in an autonomous distributed manner. Here, five communication terminals 100, 102, 104, 106, 108 are shown, and each communication terminal 100, 102, 104, 106, 108 is connected to another communication terminal 100, within its own communicable range 110, respectively. Wireless communication is performed with 102, 104, 106, and 108.

  For example, the communication terminal 100 is the communication terminal 102, the communication terminal 102 is the communication terminals 100 and 104, the communication terminal 104 is the communication terminals 102 and 106, the communication terminal 106 is the communication terminals 104 and 108, and the communication terminal 108 is the communication terminal. 106 and a wireless communication transmission path are formed. Here, each communication terminal 100, 102, 104, 106, 108 is recognized as a communication terminal capable of communicating with a communication terminal within the communicable range 110 or as a communication terminal that may interfere with its own communication data. To do. The present embodiment is not limited to the above-described autonomous distributed wireless communication, but can also be applied to wireless communication having a control station and wired communication.

  When communication terminal 102 attempts to transmit data to communication terminal 104, communication terminals 100 and 106 exist in the vicinity, and communication terminal 100 and communication terminal 106 can communicate with one communication terminal. However, it is a so-called hidden terminal that cannot communicate with the other communication terminal. In order to avoid the data communication being hindered by such a hidden terminal, the communication terminal 102 and the communication terminal 104 specify the transmission terminal and the reception terminal using the RTS / CTS control signal.

  FIG. 2 is a timing chart showing normal communication in an ad hoc network. In the timing chart, a super frame 120 is defined, and the super frame 120 is repeated at a constant period. The super frame 120 can be further divided into a management area 122 and a data transmission area 124. Here, Beacon indicates a beacon signal, Tx and Rx indicate transmission and reception, and CTA (Channel Time Allocation) indicates time (area) allocated to each communication terminal.

  In the management area 122, a beacon signal is issued from each communication terminal constituting the ad hoc network. Based on the beacon signal, other communication terminals existing in the vicinity can be grasped or used with surrounding communication terminals. Adjust the data transmission period. The data transmission area 124 performs data communication according to the communication time of each communication terminal allocated through the beacon signal. For example, since the communication terminal 102 shown in FIG. 2 has a large amount of data to be communicated with other communication terminals, a long communication time is set accordingly, whereas a communication terminal 106 with a small amount of data has a short communication time. Is set.

  In addition, since transmission 130 from communication terminal 102 to communication terminal 100 designates one communication terminal as a receiving terminal, transmission 132 from communication terminal 102 to communication terminal 100 and communication terminal 104 corresponds to unicast communication. Since two communication terminals are designated as receiving terminals, this corresponds to multicast communication for unilateral transmission to a plurality of communication terminals.

  The present embodiment is characterized in that such multicast communication is used and unicast communication is performed within the multicast communication period. In order to easily grasp this configuration, the following will be explained step by step.

  Broadcast communication is a communication method similar to multicast communication. In multicast communication, a communication terminal is specified as a destination by a beacon signal, etc., whereas in broadcast communication, reception is possible without specifying a destination. The difference is that all the receiving terminals need to receive data.

  FIG. 3 is a timing chart showing data movement in the conventional multicast communication. Here, during the multicast transmission period 150, the communication terminal 104 performs data communication by multicast communication with the communication terminal 102 and the communication terminal 106 that exist in the vicinity. In the multicast communication, the communication terminal 104 designates the communication terminal 102 and the communication terminal 106 as multicast transmission destinations, and the same data is repeatedly transmitted from the communication terminal 104 a plurality of times, and the communication terminal 102 and the communication terminal 106 are transmitted. It is only necessary to receive any one of the plurality of data. In this case, the reception completion signal (ACK) is not transmitted, and data transmission is unidirectional in a sense.

  FIG. 4 is a timing chart showing unicast communication in multicast communication in the present embodiment. Here, a case is shown in which the communication terminal 104 performs unicast transmission to the communication terminal 102 and the communication terminal 106 existing in the vicinity within the multicast communication period 150. In this embodiment, an ACK control signal is returned for each unicast communication. The communication terminal 104 confirms that the communication terminal 102 and the communication terminal 106 have correctly received the data based on the ACK control signal. By this data transmission completion notification, even when a plurality of communication terminals are targeted, it is possible to continuously transmit data to each communication terminal without leaving a useless time interval.

  Further, at the time of the above transmission, the unicast communication is configured according to the total amount of data to be transmitted to each communication terminal or the priority of the data, so that the unicast to each receiving terminal can be performed during the secured multicast transmission period. The transmission period can be allocated freely. The setting of the amount of data is determined according to, for example, the total amount of buffered data and the priority order of the data. Since it is not necessary to ensure such a unicast communication period, transmission control with a high degree of freedom can be performed as a whole system.

  Further, in the multicast communication in FIG. 3, during the multicast transmission period 150, the communication of the hidden terminals other than the communication terminals 102, 104, 106, for example, the communication terminals 100, 108 must be stopped. It is necessary to notify 108 that the multicast transmission period 150 is set in advance. Such a problem is solved as follows.

  FIG. 5 is a timing chart showing unicast communication in multicast communication in this embodiment. Here, a case where the communication terminal 104 performs unicast transmission to the communication terminal 102 and the communication terminal 106 existing in the vicinity in the multicast communication period 150 is shown. In this embodiment, the RTS / CTS control signal is exchanged for each unicast communication. With this configuration, even when a plurality of communication terminals are designated by multicast communication, it becomes possible to perform unicast communication to individual communication terminals.

  In addition, the RTS / CTS control signal can notify the communication terminals 100 and 108 that are hidden terminals that the data transmission system is occupied and used, and the communication terminals 100 and 108 can be stopped. . For example, communication of the communication terminal 100 as a hidden terminal can be stopped by the CTS control signal 170, and communication of the communication terminal 108 can be stopped by the CTS control signal 172.

  Furthermore, even if the communication terminal 102 is in an unreceivable state because it is not activated or the like, the state can be grasped by the RTS control signal of the communication terminal 104. Communication can be performed. Therefore, the multicast communication period 150 can be used effectively.

  FIG. 6 is a timing chart showing an application example of multicast communication in the present embodiment. Here, a case where the communication terminal 104 performs unicast transmission to the communication terminal 102 and the communication terminal 106 existing in the vicinity in the multicast communication period 150 is shown. The difference from the case of FIG. 5 described above is that the communication terminal 104 does not transmit independent data to the communication terminals 102 and 106, but transmits one shared data. The CTS control signal is being used. First, the communication terminal 104 confirms that the communication terminal 102 and the communication terminal 106 can communicate with each other using an RTS / CTS control signal, and then performs multicast transmission. Finally, it is confirmed by the ACK control signal that the communication terminals 102 and 106 have completed reception, and the multicast communication is terminated. In this way, stable multicast communication is possible.

  As described above, the minimum necessary communication period to be transmitted in advance is ensured as the multicast transmission period by unicast communication using multicast communication or improved multicast communication. It is possible to set a unicast transmission period to the communication terminal and perform unicast communication with each communication terminal within the multicast transmission period. Therefore, a data transmission time can be reserved in a short time without complicated reservation processing at the time of transmitting a beacon signal, and a period reservation type wireless communication protocol that can be applied to best effort type data communication is realized.

  In the present embodiment, in addition to the above configuration, a command reception period for designating itself as a transmission destination from another communication terminal can be set. This command reception period is set exclusively with the command reception period of other terminals, and other communication terminals send commands during the command reception period without specifying their own reception terminals using identifiers, etc. The receiving terminal is specified only by such processing. The command reception period will be described below.

  FIG. 7 is a timing chart showing the arrangement of command reception periods in the data transmission system of this embodiment. The communication terminal shown in FIG. 7 sets only such a command reception period when there is no data to be transmitted to another communication terminal and no transmission request is received from another communication terminal. Therefore, when there is no data to be transmitted / received between the communication terminals, a beacon signal is set in the management area 122 and only a command reception period is set in the data transmission area 124 as shown in FIG.

  The command reception period is set exclusively for each communication terminal. In FIG. 7, the data is evenly distributed at regular intervals within the data transmission area 124 of the super frame 120. Here, for example, when the communication terminal 104 makes a request for unicast communication or multicast communication to the communication terminal 102, first, the command reception period of the communication terminal 102 set by using the beacon signal is acquired, and the communication terminal actually When the command reception period 200 of 102 arrives, a command or the like is transmitted during that period. During this period, since no other communication terminals in the data transmission system are receiving data, only the communication terminal 102 can grasp that there is a data transmission request to itself.

  FIG. 8 is a timing chart showing data transmission in the data transmission system of this embodiment. Here, as shown in FIG. 7, the communication terminal 104 makes a data transmission request during the command reception period 200 of the communication terminal 102.

  As described in FIG. 7, when data to be transmitted is accumulated in the buffer of the communication terminal 104, a multicast communication request (command) to the communication terminal 102 is transmitted during the command reception period 200 of the communication terminal 102. In response to this, the communication terminal 102 prepares for data reception from the communication terminal 104. The data transmission timing is synchronized between the terminals 102 and 104 by the command transmitted during the command reception period 200. Here, the period immediately after the command reception period 202 of the communication terminal 104 is set to the communication period, that is, the multicast transmission period (MTx) 204.

  In this multicast transmission period 204, the communication terminal 104 performs unicast communication in the multicast communication with respect to the communication terminal 102. The communication terminal 102 leaves the non-operating state during this multicast transmission period 204, and the communication terminal 104 Receive data.

  The reason why the multicast communication period of the communication terminal 104 is set to be different from the command reception period in the above is that if the command reception period is deleted due to the setting of the multicast communication period, a data transmission request to the communication terminal 104 cannot be received. . The reason why the multicast communication period is set immediately after the command reception period is that each communication terminal knows the command reception period based on the beacon signal and saves time and effort for changing the timing. In this way, each communication terminal can accept a data transmission request to itself while performing data transmission processing.

  In this way, when there is data to be transmitted in its own communication terminal, the transmission timing of the data is set after its own command reception period.

  FIG. 9 is an explanatory diagram showing the timing of data transmission to other communication terminals. As shown in FIG. 9, the communication terminal sets a multicast communication period for transmitting data following the command reception period to itself. The multicast communication period is adjusted according to the amount of data to be transmitted. For example, when there is no transmission data, only the RxCTA that is the command reception period is provided, and when there is transmission data, the occupation period of the communication terminal is increased by the multicast transmission period MulticastTxCTA according to the amount of the data. This is also applicable when the amount of data stored in the buffer of the sending terminal changes from moment to moment, and when the amount of buffered data exceeds a predetermined amount, the multicast transmission period is gradually increased, When the amount of data decreases, the multicast transmission period can be gradually reduced. When there is finally no data to be transmitted, only RxCTA remains.

  The order of setting RxCTA and MulticastTxCTA may be in the above order or vice versa.

  FIG. 10 is an explanatory diagram showing data transmission timing when the order of RxCTA and MulticastTxCTA is changed. With this configuration, the transmitting terminal originally starts multicast transmission from the time when it is in its own command receiving period, and the receiving terminal that has received a transmission request from the transmitting terminal is originally at the time when it is in the command receiving period of the transmitting terminal. Can be received from.

  FIG. 11 is a timing chart showing the same data transmission as in FIG. 8 by changing the order of the RxCTA and MulticastTxCTA. When data to be transmitted is accumulated in the buffer of the communication terminal 104, a multicast communication request (command) to the communication terminal 102 is transmitted during the command reception period 200 of the communication terminal 102. In response to this, the communication terminal 102 prepares for data reception from the communication terminal 104. Unlike the case of FIG. 8, such data transmission timing is the reception timing of the communication terminal 102 when the communication terminal 104 should originally be in the command reception period 202. The communication terminal 104 shifts the command reception period 202 backward and sets a multicast transmission period 204.

  As in FIG. 8, during this multicast transmission period 204, the communication terminal 104 performs unicast communication within the multicast communication to the communication terminal 102, and the communication terminal 102 is in an inactive state during this multicast transmission period 204. And the data of the communication terminal 104 is received. Also in the case of FIG. 11, the command reception period 202 of the communication terminal 104 is ensured, so that each communication terminal can accept a data transmission request to itself while performing a data transmission process. Thus, even if the order of RxCTA and MulticastTxCTA is changed, this embodiment can be implemented.

  FIG. 12 is a timing chart showing data transmission in the data transmission system of this embodiment. Here, communication terminal 104 performs multicast transmission to communication terminal 102 and communication terminal 106.

  When new transmission data is buffered, the communication terminal 104 issues a transmission request to the communication terminal 106 as well as the communication terminal 102 to be transmitted. This transmission request is a transmission request for multicast communication. In the transmission request, unicast communication is transmitted to each of the communication terminals 102 and 106, or notification that multicast communication is to be performed to both terminals.

  In FIG. 12, since the command reception period 210 of the communication terminal 106 is after the multicast communication period 212, it appears that the transmission request cannot be transmitted to the communication terminal 106 before the communication terminal 104 starts the multicast communication. However, there is no problem because the actual transmission request is transmitted during the command reception period 210 of the previous superframe 120. The communication terminal 102 and the communication terminal 106 that have received the transmission request from the communication terminal 104 set a unicast reception period immediately after the command reception period 202 of the communication terminal 104, and receive data during that period.

  In the following, in order to facilitate understanding of the data transmission described in FIGS. 8 and 12, a more detailed description will be given.

  FIG. 13 is a flowchart showing in detail data transmission in the data transmission system of this embodiment. In FIG. 13, each communication terminal 100, 102, 104, 106, 108 is represented vertically, and the passage of time is represented in the downward direction of the drawing. The communication terminals 100, 102, 104, 106, and 108 are provided adjacent to each other as described above, and the adjacent communication terminals in FIG. 13 are at a distance at which data can be exchanged. Here, the communication terminal 104 performs multicast communication with the communication terminal 102 and the communication terminal 106. The upper superframe in FIG. 13 shows the state of FIG. 8, and the lower superframe shows the state of FIG.

  First, each communication terminal 100, 102, 104, 106, 108 sets a command reception period via a beacon signal. The command reception period is set exclusively with other communication terminals. For example, the communication terminal 102 is arranged as Rx200, the communication terminal 104 is arranged as Rx202, and the communication terminal 106 is arranged as Rx210.

  When the data to be transmitted to the communication terminal 102 and the data to be transmitted to the communication terminal 106 are stored in its own data buffer, the communication terminal 104 sets the multicast transmission period 204 after its own command reception period (S250). . Here, since the transmission request can be made only to the communication terminal 102 before the multicast transmission of the communication terminal 104, the multicast transmission period 204 is limited to the data transmission to the communication terminal 102.

  Subsequently, the communication terminal 104 transmits a transmission request command during the command reception period 200 of the communication terminal 102 to be transmitted, and designates it as a multicast transmission destination (S252). Upon receiving this command, the communication terminal 102 returns a reception completion (ACK) control signal (S254), and sets its own unicast reception period 206 in the multicast transmission period 204 of the communication terminal 104 (S256).

  Next, the communication terminal 104 performs multicast transmission or unicast transmission in the set multicast transmission period 204 (S260). Here, since the transmission target is only the communication terminal 102, unicast communication with the communication terminal 102 is performed. In response to the transmission of this data, the communication terminal 102 returns an ACK control signal to the communication terminal 104 (S262). The period during which unicast communication is actually performed is determined at or just before the start of the multicast transmission period.

  Since data for the communication terminal 106 is also stored in the buffer of the communication terminal 104, the communication terminal 104 receives the command reception period 210 of the communication terminal 106 when the command reception period 210 of the communication terminal 106 arrives. A transmission request command is transmitted to and designated as a multicast transmission destination (S270). Upon receiving this command, the communication terminal 106 returns a reception completion (ACK) control signal (S272), and sets its own unicast reception period as the multicast transmission period of the communication terminal 104 (S274). In addition, the communication terminal 104 adds data for transmission to the communication terminal 106 during the multicast transmission period (S276).

  When the super frame ends and the next super frame starts, each communication terminal 100, 102, 104, 106, 108 sets a command reception period via a beacon signal. By exchanging the beacon signal, the communication terminal 104 can notify the peripheral communication terminal 102 and the communication terminal 106 that its own multicast transmission period has been extended.

  Since the communication terminal 104 has already made a transmission request to the communication terminal 102 and the communication terminal 106, it is not necessary to make a transmission request in the superframe. The communication terminal 102 and the communication terminal 106 add a unicast reception period as the multicast transmission period is extended, and the communication terminal 104 transmits the accumulated data during its own multicast transmission period 212. As shown in FIG. 13, in this multicast transmission period 212, individual unicast transmission to the communication terminal 102 and the communication terminal 106 is performed. Further, once receiving a transmission request, the communication terminals 102 and 106 may continue to set a unicast reception period until a transmission end command is received or until no data is received for a predetermined time.

  As described above, the communication terminal 104 can perform unicast communication with the communication terminal 102 and the communication terminal 106 using the multicast transmission period.

  FIG. 14 is a timing chart illustrating a case where each communication terminal sets the multicast transmission period described above. Here, all communication terminals in the data transmission system set a multicast communication period, and other communication terminals receiving the transmission request set a unicast reception period for the multicast transmission period as appropriate. To do.

  In this embodiment, as shown in FIG. 14, since the multicast transmission period is set to avoid the command reception period, each communication terminal always has a time to receive a transmission request from another during the superframe. Can be secured.

  FIG. 15 is a timing chart for explaining a case where the multicast transmission period of FIG. 14 is extended to the maximum. Here, all the communication terminals in the data transmission system set the multicast communication period fairly, and the other communication terminals receiving the transmission request appropriately set the unicast reception period for the multicast transmission period. Set. At this time, the multicast transmission period and the command reception period do not overlap.

  As in the case of FIG. 14, since the multicast transmission period is set avoiding the command reception period, each communication terminal can always secure a time for receiving a transmission request once during the superframe.

  FIG. 16 is a timing chart for explaining a case where multicast communication according to this embodiment is distributed in the data transmission area 124. Here, a large amount of data is buffered in the communication terminal 104, and a multicast transmission period is set using a transmission area of another communication terminal. Even in this case, the multicast transmission period and the command reception period do not overlap.

  Here, the communication terminal 104 has a large amount of data to be transmitted to the communication terminal 102 and the communication terminal 106, and attempts to perform data communication as much as possible during the period in which the communication terminals 102 and 106 can receive. Therefore, it is an area other than the command reception period 200 and the multicast transmission period 290 in which data cannot be received in the communication terminal 102 and the command reception period 210 and the multicast transmission period 292 in which data cannot be received in the communication terminal 106. In addition, the multicast transmission period of the communication terminal 104 is set during a period when transmission from the communication terminal 100 and the communication terminal 108 corresponding to the hidden terminal is not performed. In this way, whether or not the transmission area of another communication terminal can be used may be determined based on the priority order of the communication terminal or communication data.

  FIG. 17 is a timing chart for explaining a case where a specific communication terminal performs reception over the entire section of the data transmission area 124. Here, the communication terminal 104 sets all the areas of the data transmission area 124 excluding the multicast transmission period from itself as the reception period to itself. Therefore, data transmission to the communication terminal 104 can be performed at an arbitrary timing. Thereby, data communication with the communication terminal 104 is processed in a short time.

  FIG. 18 is a timing chart illustrating a case where all communication terminals perform reception over the entire section of the data transmission area 124. This is an application of the embodiment shown in FIG. 17. Here, all communication terminals set all the areas of the data transmission area 124 excluding the multicast transmission period from the data transmission area 124 as the reception period to itself. ing. Therefore, data transmission to all communication terminals can be performed at an arbitrary timing. Thereby, data communication is processed in a shorter time.

  As described above, in the data transmission system of this embodiment, efficient data transmission can be performed by appropriately allocating the command reception period and the multicast transmission period in the data transmission area 124. Hereinafter, commands or data transmitted in such a data transmission system will be described in detail.

  FIG. 19 is an explanatory diagram showing a configuration example of the beacon signal. The beacon signal includes MAC header information 300, HCS (Header Check Sequence) 302, beacon payload information 304, and FCS (Frame Check Sequence) 306.

  The MAC header information 300 includes a frame type indicating that the signal is a beacon frame, a group identifier for specifying a network group for communication, an address indicating a destination (broadcast is specified in the case of a beacon signal), a transmission It consists of an address indicating its origin (own address) and control information. The HCS 302 is a checksum for detecting an error in the header portion.

  The beacon payload information 304 is composed of network synchronization information, unique information elements such as device attributes and capabilities, CTA elements describing time information used for communication by itself, and a reserved area. The FCS 306 is a checksum for detecting an error in the payload portion. The CTA element is composed of a CTA block in which an element ID, its length, time information actually used, and the like are described. In this CTA block, the setting of the multicast transmission period and the setting of the unicast reception period according to the present embodiment are sequentially described.

  FIG. 20 is an explanatory diagram showing a configuration example of a multicast group request command. Similar to the beacon signal, such a multicast group request command also includes MAC header information 310, HCS 312, command payload information 314, and FCS 316.

  The MAC header information 310 includes a frame type indicating that the signal is a beacon frame, a group identifier for specifying a network group for communication, an address indicating a destination (address of a communication terminal requesting reception), a source Address (self address) and control information. The HCS 312 is a checksum for detecting an error in the header portion.

  The command payload information 314 includes a CTA element in which multicast communication time is described. The FCS 316 is a checksum for detecting an error in the payload portion. Such a CTA element is provided with at least one CTA block, and the setting of the multicast transmission period is sequentially described.

  FIG. 21 is an explanatory view showing a parameter description example of the CTA block in the multicast transmission period. Here, a multicast ID is designated as the reception destination ID (Dest. ID), and its own ID is set as the transmission source ID (Src. ID). Furthermore, an index set for each CTA block setting is set in the stream index (Stream Index), a CTA transmission start time is set in CTA Location, and a transmission end time is set in CTA Duration.

  FIG. 22 is an explanatory diagram showing a parameter description example of the CTA block in the unicast reception period. Here, its own ID is designated as the reception destination ID (Dest. ID), and the multicast ID is set as the transmission source ID (Src. ID). Furthermore, an index set for each CTA block setting is set in the stream index (Stream Index), a CTA transmission start time is set in CTA Location, and a transmission end time is set in CTA Duration.

(Second embodiment: data transmission system)
In the present embodiment, a more specific data transmission system incorporating the concept of hardware based on the data transmission system as described above will be described. The data transmission system includes a transmitting terminal that transmits data and one or more receiving terminals that directly receive data from the transmitting terminal through wireless communication. Here, a hardware configuration common to the transmitting terminal and the receiving terminal will be described with reference to a communication terminal.

  FIG. 23 is a block diagram schematically showing a hardware configuration of the communication terminal 400 according to the present embodiment. As illustrated in FIG. 23, the communication terminal 400 includes a CPU 402, a memory 404, an input unit 406, a display unit 408, a communication driver 410, and an antenna 412.

  The CPU 402 functions as an arithmetic processing unit and a control unit, and controls processing of each unit in the communication terminal 400.

  The memory 404 includes, for example, a RAM, a ROM, a cache memory, a hard disk drive, a flash memory, and the like, and stores various data related to the processing of the CPU 402, a software program, and the like. The memory 404 may store an OS (Operation System), a BIOS (Basic Input / Output System), and other drivers.

  The input unit 406 includes, for example, operation means such as a mouse, a keyboard, a touch panel, a button, a switch, and a lever, and an input control circuit that generates an input signal and outputs it to the CPU 402. The user of the communication terminal 400 can input various data or instruct processing operations by operating the input unit 406.

  The display unit 408 includes, for example, a CRT display device, a liquid crystal display (LCD) device, a display device such as a lamp, and an audio output device such as a speaker.

  The communication driver 410 performs bidirectional communication with other communication terminals in the data transmission system via the antenna 412.

  The communication terminal 400 including such hardware specifically has the following components. Such components may be implemented by the CPU 402 and expressed in the form of modules. Here, a specific configuration of the transmission terminal and the reception terminal in the data transmission system will be described. In the above example, the communication terminal 400 is described in which both terminals are integrally provided. However, here, description will be given separately for a transmission terminal and a reception terminal.

(Sending terminal)
FIG. 24 is a block diagram illustrating a schematic configuration of the transmission terminal 450. The transmission terminal 450 includes an access control unit 460, a wireless reception unit 462, a wireless transmission unit 464, an antenna 466, a beacon analysis unit 468, a CTA control unit 470, a beacon generation unit 472, an interface 474, data A buffer 476, a multicast period setting unit 478, a central control unit 480, a command transmission unit 482, a buffering data amount determination unit 484, a transmission amount setting unit 486, and a data transmission unit 488 are configured. .

  The access control unit 460 controls wireless access of the wireless reception unit 462 and the wireless transmission unit 464. For example, when the management area 122 of the superframe 120 arrives, that is, when a beacon signal is exchanged, the access control unit 460 operates the wireless reception unit 462. Then, the wireless reception unit 462 receives the beacon signal via the antenna 466 and transfers the beacon signal to the beacon analysis unit 468.

  The beacon analysis unit 468 analyzes the beacon signal and supplies the CTA control unit 470 with information such as the beacon signal reception period and the CTA usage status.

  The CTA control unit 470 changes its own CTA setting based on information such as the beacon signal reception period and CTA usage status, and transmits the changed setting to the beacon generation unit 472. In this way, self information to be added to the beacon signal is constructed.

  When the own beacon signal transmission timing arrives, the access control unit 460 operates the wireless transmission unit 464 and the data of the beacon generation unit 472 is transmitted via the antenna 466. A command reception period is set in each communication terminal by exchanging beacon signals.

  When a data transmission request is received from an application connected through the interface 474, the data is stored in the data buffer 476. Thereafter, the multicast period setting unit 478 sets, via the central control unit 480, a reception terminal group that is a plurality of reception terminals selected as transmission targets, and a multicast transmission period as a period for transmitting data, This is provided to the command transmission unit 482.

  The command transmission unit 482 includes a transmission request command including information on the multicast transmission period via the wireless transmission unit 464 and the antenna 466 in the command reception period of each receiving terminal to be transmitted provided from the multicast period setting unit 478. Send.

  Further, when the multicast transmission period as a data transmission period approaches, information on the data amount stored in the data buffer 476 is provided to the buffering data amount determination unit 484. When the multicast transmission period arrives, the transmission amount setting unit 486 sends to each receiving terminal that is transmitted in one multicast transmission based on the data amount that is the determination result of the buffering data amount determination unit 484 and its priority order. Set the amount of data. The set data amount is provided to the data transmission unit 488. Here, the transmission amount setting unit 486 may include the function of the buffering data amount determination unit 484.

  The data transmission unit 488 transmits data in a time division manner to each receiving terminal via the wireless transmission unit 464 and the antenna 466 during the multicast transmission period. The data transmission unit in the present invention is not limited to such a data transmission unit 488, and is assumed to have at least a function for transmitting data.

  In addition, a computer program that functions as the transmission terminal 450 is also provided.

(Receiving terminal)
FIG. 25 is a block diagram illustrating a schematic configuration of the receiving terminal 500. The receiving terminal 500 includes an access control unit 460, a wireless reception unit 462, a wireless transmission unit 464, an antenna 466, a beacon analysis unit 468, a CTA control unit 470, a beacon generation unit 472, an interface 474, data A buffer 476, a central control unit 480, a command period setting unit 502, a data analysis unit 504, a request command analysis unit 506, a unicast period setting unit 508, and a data reception unit 510 are configured.

  The access control unit 460 controls wireless access of the wireless reception unit 462 and the wireless transmission unit 464. Similar to the case of FIG. 24, the access control unit 460 operates the wireless reception unit 462 when the management area 122 of the superframe 120 arrives, that is, when a beacon signal is exchanged. The wireless reception unit 462 receives the beacon signal via the antenna 466 and transfers the beacon signal to the beacon analysis unit 468.

  The beacon analysis unit 468 analyzes the beacon signal and supplies the CTA control unit 470 with information such as the beacon signal reception period and the CTA usage status.

  The CTA control unit 470 changes its own CTA setting based on information such as the beacon signal reception period and CTA usage status, and transmits the changed setting to the beacon generation unit 472. Also, the command period setting unit 502 sets a command reception period exclusive to other communication terminals via the central control unit 480, and sends information on the command reception period to the CTA control unit 470 and the beacon generation unit 472. Send. In this way, self information to be added to the beacon signal is constructed.

  When the own beacon signal transmission timing arrives, the access control unit 460 operates the wireless transmission unit 464 and the data of the beacon generation unit 472 is transmitted via the antenna 466. A command reception period is set in each communication terminal by exchanging beacon signals. When there is no transmission request in the previous superframe, the access control unit 460 temporarily stops the operation of the wireless reception unit 462 and shifts to the sleep state.

  When the command reception period set by the command period setting unit 502 arrives, the access control unit 460 operates the wireless reception unit 462 again and transmits the data received via the antenna 466 to the data analysis unit 504.

  The data analysis unit 504 analyzes the reception data transmitted from the wireless reception unit 462, and if the data is a transmission request command to itself, transfers the transmission request command to the request command analysis unit 506. If the received data is transmission data to itself, it is transferred to the data receiving unit 510. The request command analysis unit 506 analyzes the transmission request command and provides the multicast transmission period information to the unicast period setting unit 508.

  The unicast period setting unit 508 sets the unicast reception period to itself according to the multicast transmission period extracted from the transmission request command. The set unicast reception period is supplied to the CTA control unit 470, and data is received at that timing. The data receiving unit 510 transmits the received data to the data buffer 476. Such data is stored in the data buffer 476 and then provided to an application connected via the interface 474. The data receiving unit in the present invention is not limited to the data receiving unit 510, and has at least a function for receiving data.

  In addition, a computer program that functions as the receiving terminal 500 is also provided.

  FIG. 26 is a block diagram showing a communication terminal 400 in which the transmission terminal 450 and the reception terminal 500 described above are integrated. The communication terminal 400 has both a data transmission function and a reception function. The constituent elements already described in the description of FIGS. 24 and 25 have substantially the same functions as the constituent elements of the communication terminal in FIG.

(Third embodiment: data transmission method)
A data transmission method for realizing the data transmission system as described above will be described below. Here, a communication terminal having both a data transmission function and a reception function is assumed.

  FIG. 27 is a flowchart showing the flow of the data transmission method in this embodiment. First, a communication terminal having both functions of the transmitting terminal 450 and the receiving terminal 500 continuously receives a predetermined superframe at a predetermined cycle immediately after power-on, and checks whether there are other communication terminals around it. . A beacon signal is set to grasp the presence or absence of the communication terminal (S600).

  When the setting of the beacon signal is completed, a normal sequence is entered and the above-described super frame is repeated. For example, in this embodiment, processes such as beacon signal exchange, data reception, and data transmission are repeated. In the beacon signal exchange, when the beacon signal transmission time arrives (S602), the beacon signal is transmitted (S604), and when the beacon signal reception time arrives (S606), the beacon signal is received. (S608). A command reception period is set when the beacon signal is exchanged. In the data reception, command reception is performed during the command reception period (S610) (S612), and unicast reception is performed during the unicast reception period (S614) (S616). In the data transmission, when there is transmission data (S618), transmission data is set (S620), and when a command transmission time, that is, a command reception period to be transmitted has arrived (S622), transmission of a transmission request command is performed. (S624), and multicast transmission is performed during the multicast transmission period (S626) (S628). In the following, the detailed operation of each process described above will be described.

  FIG. 28 is a flowchart showing in detail the setting of the beacon signal (S600). Here, when a beacon signal is detected and reception of a beacon signal is confirmed (S650), an empty beacon slot (beacon signal transmission timing) is searched (S652), and when no beacon signal is received, If there is no slot available, a beacon slot is set by itself (S654). The beacon signal transmission position is determined by referring to the thus secured beacon slot (S656).

  FIG. 29 is a flowchart showing in detail the transmission of the beacon signal (S604). When the transmission time of the beacon signal has arrived (S602), CTA information that is the usage information of its own data transmission area 124 is acquired (S660), and transmission is performed as a beacon signal (S662). At this time, its own command reception period exclusive to other communication terminals is also set.

  FIG. 30 is a flowchart showing in detail the reception of the beacon signal (S608). When the reception time of the beacon signal has arrived (S606), a beacon signal reception operation is performed. When a beacon signal is received (S670), parameters such as the CTA information of the communication terminal are acquired and stored (S672), and the CTA setting status of the communication terminal in the vicinity is additionally set based on the information (S672). S674). This beacon signal reception operation may be repeated when the beacon signal reception time is reached.

  FIG. 31 is a flowchart showing in detail the reception of the command (S612). When the own command reception period (S610) comes, the communication terminal that issued the transmission request command is set as the unicast communication destination (S680), and this unicast communication period is set as the own unicast reception period (S682). ).

  FIG. 32 is a flowchart showing in detail the unicast reception (S616). When the self-unicast reception period (S614) set above is reached, the presence or absence of data addressed to the self-communication terminal is confirmed from the communication terminal serving as the transmission source (S690). Store in the buffer (S692). When output is possible via the interface (S694), data is supplied to the application (S696).

  FIG. 33 is a flowchart showing in detail the transmission data setting (S620). When there is data to be transmitted from the application via the interface (S618), it is determined whether or not the beacon signal of the communication terminal that is the transmission destination is received (S700), and it is confirmed that the communication terminal exists in the surroundings. Then, the receiving terminal is registered as a multicast transmission destination (S702), a multicast transmission period is set (S704), and a transmission request command to the reception destination communication terminal is set (S706). This transmission request command is transmitted to the transmission target communication terminal after confirming that no other communication is performed after performing predetermined access control in the above-described transmission of command (S624). Here, if the amount of buffered data increases and it is necessary to add a multicast transmission period (S708), the multicast transmission period in its own communication terminal is extended (S710).

  FIG. 34 is a flowchart showing in detail the multicast transmission (S628). When the multicast transmission period (S626) arrives, first, the presence / absence of data to be transmitted is confirmed (S720). If there is data, the unicast transmission destination (receiving terminal) within the multicast transmission period and each receiving terminal are confirmed. The amount of data to be transmitted is determined based on the total amount of data to be transmitted to each receiving terminal and the priority order (S722), and it is confirmed whether the receiving terminal as the receiving destination is activated (S724). Data is transmitted to the communication terminal (S726). This process is repeated as long as the multicast transmission period continues. When the amount of data to be transmitted decreases, it is determined whether the multicast transmission period can be reduced (S728). The time of the multicast transmission period is reduced (S730).

  Here, the data transmission amount determination step (S722) will be described in detail.

  FIG. 35 is an explanatory diagram showing the data transmission order when data to be transmitted is stored in the data buffer 476 of the communication terminal 104. Here, the adjacent communication terminal 104 has data to be transmitted to the communication terminal 102 and the communication terminal 106, and the priority order is set for the data to be transmitted to each of the communication terminals 102 and 106.

  Referring to FIG. 35, the data buffer 476 of the communication terminal 104 stores 5 units of general data to be transmitted to the communication terminal 102 and 2 units of data to be transmitted with priority, and the general data to be transmitted to the communication terminal 106. 1 unit of data is stored, and 3 units of data to be preferentially transmitted are stored. Further, the communication terminal 106 is set to transmit with priority to the communication terminal 102.

  Therefore, first, three units with high priority are transmitted to the communication terminal 106, and one unit with high priority is transmitted to the communication terminal 102 in consideration of the total amount of data to be transmitted. Three units of general data are transmitted. This time, it is assumed that general data to the communication terminal 106 is not transmitted. Thus, the actual transmission data amount to each communication terminal is determined in consideration of the balance between the priority order and the data amount at the time of transmission. Here, the distribution of the data amount may be performed by transmitting a small amount of data each time, or may be performed by transmitting the data once every several times. Further, the priority order may be set according to the type of data such as voice, image, and text.

  With this configuration, the amount of data to each communication terminal can be adjusted arbitrarily at the time of multicast transmission, so the transmission path is used more effectively than when unicast communication is performed by specifying a unicast communication destination in advance. be able to.

  In addition, according to each of the above-described embodiments, the receiving terminal secures an exclusive command reception period, thereby transmitting that there is data to be transmitted in the command reception period without separately specifying a destination by an identifier or the like. Therefore, a unicast communication period with the receiving terminal can be set, and stable communication without error is possible.

(Fourth embodiment: data transmission system)
Further, it is possible to adopt a configuration in which a multicast transmission period is set using a periodic beacon signal without providing the command reception period.

  Such a data transmission system includes a beacon transmission unit and a beacon reception unit instead of the command transmission unit and the command period setting unit. Since the components already described in the above embodiment have substantially the same functions, the redundant description will be omitted, and only components having different configurations will be described here.

  The beacon transmission unit includes at least information on the multicast transmission period set by the multicast period setting unit 478 and information on one or more receiving terminals to be transmitted, and synchronizes the plurality of communication terminals. Take a beacon signal. This beacon transmission unit can be implemented by the beacon generation unit 472 and the wireless transmission unit 464 shown in FIG.

  The beacon receiving unit receives the beacon signal as described above. When the receiving terminal of the received beacon signal is designated as the transmission target, the unicast period setting unit sets the unicast reception period to itself according to the multicast transmission period of the beacon signal. This beacon receiving unit can be implemented by the wireless receiving unit 462 and the beacon analyzing unit 468 shown in FIG.

  In this embodiment, the command reception period is omitted, and data communication information including the multicast transmission period is exchanged using a beacon signal.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are of course within the technical scope of the present invention. Understood.

  Note that the steps in the data transmission method of this specification do not necessarily have to be processed in chronological order according to the order described in the flowchart, but are performed in parallel or individually (for example, parallel processing or object-based processing). Processing).

  The present invention can be applied to a data transmission system, a transmission terminal, a reception terminal, a data transmission method, and a data reception method capable of direct wireless communication between a plurality of communication terminals.

It is a block diagram for demonstrating the ad hoc network with which a data transmission system is implemented. 3 is a timing chart showing normal communication in an ad hoc network. It is the timing chart which showed the movement of the data in the conventional multicast communication. It is the timing chart which showed the unicast communication in multicast communication. It is the timing chart which showed the unicast communication in multicast communication. 5 is a timing chart showing an application example of multicast communication. It is the timing chart which showed arrangement | positioning of the command reception period in a data transmission system. It is the timing chart which showed the data transmission in the data transmission system. It is explanatory drawing which showed the data transmission timing to another communication terminal. It is explanatory drawing which showed the data transmission timing. It is the timing chart which showed the data transmission in the data transmission system. It is the timing chart which showed the data transmission in the data transmission system. It is a flowchart showing in detail data transmission in the data transmission system. It is a timing chart explaining the case where each communication terminal sets a multicast transmission period. It is a timing chart explaining the case where the multicast transmission period of FIG. 14 is extended to the maximum. 6 is a timing chart illustrating a case where multicast communication is distributed within a data transmission area 124. It is a timing chart explaining the case where a specific communication terminal performs reception over all the sections of a data transmission area. It is a timing chart explaining the case where all the communication terminals receive over all the sections of a data transmission area. It is explanatory drawing which showed the structural example of the said beacon signal. It is explanatory drawing which showed the structural example of the multicast group request command. It is explanatory drawing which showed the parameter description example of the CTA block in a multicast transmission period. It is explanatory drawing which showed the parameter description example of the CTA block in a unicast reception period. It is a block diagram which shows roughly the hardware constitutions of a communication terminal. It is a block diagram which shows the schematic structure of a transmission terminal. It is a block diagram which shows the schematic structure of a receiving terminal. It is the block diagram which showed the communication terminal which integrated the transmission terminal and the receiving terminal. It is the flowchart which showed the flow of the data transmission method. It is the flowchart which showed the setting of the beacon signal in detail. It is the flowchart which showed the transmission of the beacon signal in detail. It is the flowchart which showed reception of the beacon signal in detail. It is the flowchart which showed reception of the command in detail It is the flowchart which showed the unicast reception in detail. It is the flowchart which showed the setting of transmission data in detail. It is the flowchart which showed the multicast transmission in detail. It is explanatory drawing which showed the data transmission order when the data transmitted to the data buffer of a communication terminal are accumulate | stored.

Explanation of symbols

450 Transmission terminal 478 Multicast period setting unit 482 Command transmission unit 486 Transmission amount setting unit 488 Data transmission unit 500 Reception terminal 502 Command period setting unit 508 Unicast period setting unit 510 Data reception unit

Claims (17)

In a data transmission system including a transmitting terminal that transmits data and one or more receiving terminals that directly receive data from the transmitting terminal by wireless communication:
The transmitting terminal is
A multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets;
A command transmission unit that transmits a command including information on the multicast transmission period in a command reception period of each of the reception terminals of the reception terminal group;
A data transmission unit that transmits data in a time-sharing manner to each of the receiving terminals of the receiving terminal group during the multicast transmission period;
With
The receiving terminal is
A command period setting unit for setting a command reception period exclusive to other communication terminals;
A unicast period setting unit configured to set a unicast reception period to itself according to the multicast transmission period when information on the multicast transmission period is received during the command reception period of its own;
A data receiving unit for receiving data from the transmitting terminal during the unicast receiving period;
A data transmission system comprising: A transmitting terminal that transmits data directly to a receiving terminal by wireless communication:
A multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets;
A command transmission unit that transmits a command including information on the multicast transmission period in a command reception period of each of the reception terminals of the reception terminal group;
A data transmission unit that transmits data in a time division manner to each of the receiving terminals of the receiving terminal group during the multicast transmission period;
A transmitting terminal comprising:   The transmission terminal according to claim 2, wherein the multicast period setting unit sets a multicast transmission period according to a data amount to be transmitted in one multicast transmission.   The transmitting terminal according to claim 2, wherein the data transmitting unit completes unicast communication with the receiving terminal by an ACK control signal from the receiving terminal.   The transmission terminal according to claim 2, wherein the data transmission unit specifies a reception terminal that performs unicast communication by an RTS / CTS control signal from the reception terminal group.   And a transmission amount setting unit for setting an amount of data to be transmitted to each receiving terminal according to a total data amount of each receiving terminal to be transmitted or a priority order of the data at the time of multicast transmission. Item 3. The transmission terminal according to Item 2.   The transmission terminal according to claim 2, wherein the multicast period setting unit sets a multicast transmission period so as not to overlap with the command reception period in all reception terminals of the data transmission system.   The transmission terminal according to claim 2, wherein the multicast period setting unit sets its own multicast transmission period so as not to overlap with the multicast transmission period in all transmission terminals of the data transmission system.   The multicast period setting unit uses a beacon signal that synchronizes between the plurality of communication terminals, and sets the multicast transmission period so that it does not overlap with the multicast transmission period of other transmitting terminals, The receiving terminal according to claim 7 or 8.   3. The reception according to claim 2, wherein the multicast period setting unit specifies one or more receiving terminals of the multicast transmission destination using a beacon signal for synchronizing the plurality of communication terminals. Terminal. A program for transmitting data directly to a receiving terminal by wireless communication:
Computer
A multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets;
A command transmission unit that transmits a command including information on the multicast transmission period in a command reception period of each of the reception terminals of the reception terminal group;
A data transmission unit that transmits data in a time-sharing manner to each of the receiving terminals of the receiving terminal group during the multicast transmission period;
Program to make it function. A data transmission method for transmitting data directly to a receiving terminal by wireless communication:
A multicast period setting step of setting a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets;
A command transmission step of transmitting a command including information of the multicast transmission period in a command reception period of each of the receiving terminals of the receiving terminal group;
A data transmission step of transmitting data in a time division manner to each receiving terminal of the receiving terminal group during the multicast transmission period;
A data transmission method comprising: A receiving terminal that receives data directly from a transmitting terminal by wireless communication:
A command period setting unit for setting a command reception period exclusive to other communication terminals;
When information on a multicast transmission period as a period during which the transmitting terminal transmits data to a receiving terminal group including itself is received during its own command reception period, a unicast reception period to itself according to the multicast transmission period A unicast period setting unit for setting;
A data receiving unit for receiving data from the transmitting terminal during the unicast receiving period;
A receiving terminal comprising:   The command period setting unit uses a beacon signal that synchronizes the plurality of communication terminals to set a command reception period so as not to overlap with other reception terminals. Receiving terminal. A program for receiving data directly from a sending terminal by wireless communication:
Computer
A command period setting unit for setting a command reception period exclusive to other communication terminals;
When information on a multicast transmission period as a period during which the transmitting terminal transmits data to a receiving terminal group including itself is received during its own command reception period, a unicast reception period to itself according to the multicast transmission period A unicast period setting unit for setting;
A data receiving unit for receiving data from the transmitting terminal during the unicast receiving period;
Program to make it function. A data receiving method for receiving data directly from a transmitting terminal by wireless communication:
A command period setting step for setting a command reception period exclusive to other communication terminals;
When information on a multicast transmission period as a period during which the transmitting terminal transmits data to a receiving terminal group including itself is received during its own command reception period, a unicast reception period to itself according to the multicast transmission period A unicast period setting step for setting
A data receiving step of receiving data from the transmitting terminal during the unicast receiving period;
A method for receiving data, comprising: In a data transmission system including a transmitting terminal that transmits data and one or more receiving terminals that directly receive data from the transmitting terminal by wireless communication:
The transmitting terminal is
A multicast period setting unit that sets a multicast transmission period as a period for transmitting data to a receiving terminal group that is a plurality of receiving terminals selected as transmission targets;
A beacon transmitter that includes at least information of the multicast transmission period and information of the receiving terminal group, and transmits a beacon signal for synchronizing the plurality of communication terminals;
A data transmission unit that transmits data in a time-sharing manner to each of the receiving terminals of the receiving terminal group during the multicast transmission period;
With
The receiving terminal is
A beacon receiving unit for receiving the beacon signal;
A unicast period setting unit configured to set a unicast reception period to itself according to a multicast transmission period of the beacon signal when the receiving terminal of the beacon signal is designated as a transmission target;
A data receiving unit for receiving data from the transmitting terminal during the unicast receiving period;
A data transmission system comprising:

Images