JP2006197032A - Data transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission system which reduces a packet collision and can attain an increase in the efficiency of a data transmission. <P>SOLUTION: The data transmission system includes a data transmitter which divides data into a plurality of splitting data and transmits the splitting data (310), and a data receiver which receives the splitting data transmitted from the data transmitter; transmits an ACK packet to the data transmitter; receives the predetermined number of the splitting data group; then decodes the splitting data groups to the data and starts the processing of the data (320). The transmission of the above both devices is assured with the control signal of an RTS packet and a CTS packet. When a remaining period exists in a transmitting permission period (TXOP) after the above data transmitter receives the ACK packet, the above data transmitter does not transmit the data to any communication terminal within the remaining period of the transmitting permission period. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a data transmission system.

  As an example of a standard regarding a wireless network, the Institute of Electronic Engineers of the United States (IEEE) (The Institute of Electrical and Engineering Engineers) 802.11, HiperLAN / 2, IEEE 302.15.3, Bluetooth, and the like can be given. There are various wireless communication protocols such as the IEEE802.11a standard, the IEEE802.11b standard, and the IEEE802.11e standard in the IEEE802.11 standard depending on the wireless communication method and the frequency band to be used.

  In such a known wireless communication protocol, a data string is divided into divided data corresponding to packets or the like on the data transmission side, and data transmission is performed using the divided data as a transmission unit. In order to recognize whether the above communication is performed normally, the data reception side transmits a reception completion signal (ACK) to the transmission side in response to reception of the divided data, and the transmission side receives the response and divides the data. It is confirmed that the data has been transmitted reliably. If the reception completion signal (ACK) is not confirmed, the data transmission side assumes that the divided data has not been transmitted correctly and retransmits the divided data.

  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. In such ad hoc communication, each communication terminal can directly and asynchronously perform wireless communication. On the other hand, when communication is performed between certain communication terminals, the communication terminal can communicate with one communication terminal but the other communication terminal. There is a problem of a third communication terminal that cannot communicate with the so-called hidden terminal.

  In order to avoid such collision of communication data due to hidden terminals, communication terminals that perform communication output control signals of RTS (Request To Send) packets and CTS (Clear To Send) packets in advance. A technique is known in which when at least one of the RTS or CTS packets is received, transmission from the own station is stopped for a certain period of time as a transmission prohibition period (NAV).

  On the other hand, RTS / CTS packets are exchanged with each other (RTS / CTS handshake), communication is established with the communication partner, and after the communication terminal (CTS terminal) serving as the communication partner transmits the DATA packet, In many cases, the CTS terminal can transmit the DATA packet to a communication terminal other than the communication terminal (RTS terminal) that has transmitted the RTS packet.

  For example, even in the case of the IEEE 802.11e or the like, the CTS terminal as described above can transmit a DATA packet to a communication terminal other than the RTS terminal. However, in such a conventional technique, in the environment of a hidden terminal, packet collision occurs between communication terminals, and the bandwidth utilization efficiency of the entire system is reduced.

  On the other hand, the NAV tends to become longer as the amount of divided data transmitted at a time increases. As a result, when the third communication terminal that is a hidden terminal receives a packet addressed to itself during the NAV period in the environment of the hidden terminal, the third communication terminal transmits an ACK packet for the packet. As a result, packet transmission / reception between the RTS terminal and the CTS terminal is hindered, and there is a problem in that packet collision occurs and bandwidth utilization efficiency decreases (for example, Non-Patent Document 1).

The Institute of Electronic Engineers IEEE (The Institute of Electrical and Electronics Engineers) 802.11e D10.0 9.9.2.2.2.1

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce packet collisions caused by the presence of hidden terminals and the like, and to improve the efficiency of data transmission. It is to provide a new and improved data transmission system.

  In order to solve the above problems, according to a first aspect of the present invention, data is divided into a plurality of divided data, a data transmitting apparatus that transmits the divided data, and a divided data transmitted from the data transmitting apparatus are received. A data receiving device that transmits an ACK packet to the data transmitting device and receives a predetermined number of divided data groups, then decodes the divided data groups into data and starts processing the data. Is provided with a data transmission system secured by control signals of the RTS packet and the CTS packet. The data transmission device in the data transmission system transmits data to any communication terminal within the remaining period of the transmission permission period when a remaining period exists in the transmission permission period after receiving the ACK packet. It is characterized by not.

  According to the present invention, the data transmitting apparatus does not transmit data to other communication terminals no matter how soon the divided data is completely transmitted to the data receiving apparatus. With such a configuration, when at least the other communication terminal performs data transmission / reception processing between the other communication terminals at almost the same time as the data transmission apparatus and receives the data, the data from the data transmission apparatus The risk of packet collision with data between the other communication terminals can be avoided, and throughput can be improved.

  After the ACK packet is received by the data transmitting apparatus, the data that is not transmitted to any communication terminal within the remaining period of the transmission permission period is configured to be at least one of the RTS packet and the divided data. May be.

  In order to solve the above problems, according to another aspect of the present invention, data is divided into a plurality of divided data, a data transmitting apparatus that transmits the divided data, and a divided data transmitted from the data transmitting apparatus are received. A data receiving device that transmits an ACK packet to the data transmitting device and receives a predetermined number of divided data groups, then decodes the divided data groups into data and starts processing the data. Is provided with a data transmission system secured by control signals of the RTS packet and the CTS packet. In the data transmission system, if there is a remaining period in the transmission permission period after receiving the ACK packet, the data transmission apparatus transmits data to the data receiving apparatus of the communication partner only within the remaining period of the transmission permission period. It is characterized by doing.

  In order to solve the above-described problem, according to another aspect of the present invention, data is divided into a plurality of divided data, a data transmitting apparatus that transmits the divided data, and a divided data transmitted from the data transmitting apparatus are received. An ACK packet is transmitted to the data transmitting apparatus, and after receiving a predetermined number of divided data groups, the data transmitting apparatus comprises a data receiving apparatus that decodes the divided data groups into data and starts processing the data. A data transmission system secured by control signals of RTS packets and CTS packets is provided. A communication terminal that has set a transmission prohibition period (NAV) at least in its own device by receiving an RTS packet or a CTS packet in the data transmission system does not transmit data.

  According to the present invention, a communication terminal that sets a transmission prohibition period does not transmit data even when data is received from a data transmission device or a data reception device. With this configuration, at least the communication terminal that sets the transmission prohibition period is configured to set the transmission prohibition period when data transmission / reception processing is performed between the other communication terminals and communication with the other communication terminal is possible. Therefore, it is possible to avoid the risk that the data to be transmitted causes a packet collision with the data transmitted and received between the other communication terminals, and the throughput can be improved.

  The communication terminal set with the transmission prohibition period may be configured not to transmit data even if it receives divided data within the transmission prohibition period, and the data is configured to be an ACK packet. May be.

  In order to solve the above problem, according to another aspect of the present invention, data is divided into a plurality of divided data, and the divided data transmitted from the data transmitting apparatus is transmitted to the data transmitting apparatus that transmits the divided data. And receiving an ACK packet to the data transmitting device, receiving a predetermined number of divided data groups, and then decoding the divided data groups into data and starting the processing of the data, A data transmission method is provided in which communication between both apparatuses is ensured by control signals of RTS packets and CTS packets. In the data transmission method, the data transmitting apparatus receives data from any communication terminal within the remaining period of the transmission permission period when the remaining period exists in the transmission permission period after receiving the ACK packet. It is characterized by not transmitting.

  In order to solve the above problems, according to another aspect of the present invention, data is divided into a plurality of divided data, a data transmitting apparatus that transmits the divided data, and a divided data transmitted from the data transmitting apparatus are received. An ACK packet is transmitted to the data transmission device, and after receiving a predetermined number of the divided data groups, the data transmission device decodes the divided data groups into data and starts processing the data, A data transmission method is provided in which the communication of the apparatus is secured by the control signals of the RTS packet and the CTS packet. In the above data transmission method, if there is a remaining period in the transmission permission period after receiving the ACK packet, the data transmitting apparatus transmits data to the communication partner data receiving apparatus only within the remaining period of the transmission permission period. It is characterized by doing.

  In order to solve the above-described problem, according to another aspect of the present invention, data is divided into a plurality of divided data, a data transmitting apparatus that transmits the divided data, and a divided data transmitted from the data transmitting apparatus are received. An ACK packet is transmitted to the data transmitting apparatus, and after receiving a predetermined number of divided data groups, the data transmitting apparatus comprises a data receiving apparatus that decodes the divided data groups into data and starts processing the data. A data transmission method secured by control signals of RTS packets and CTS packets is provided. In the data transmission method, a communication terminal that has set a transmission prohibition period by receiving an RTS packet or a CTS packet does not transmit data.

  As described above, according to the present invention, it is possible to avoid packet collision caused by the presence of a hidden terminal or the like and improve throughput.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description is omitted.

(Ad hoc communication)
Before describing the data transmission system according to the present embodiment, ad hoc communication as a premise thereof will be described in detail.

  By using a LAN (Local Area Network) by wireless communication, a wired cable or the like in a work space such as an office can be omitted, and the space can be effectively used. Therefore, the user can move a communication terminal such as a personal computer relatively easily. In recent years, the demand for wireless LAN systems using such wireless devices has increased significantly as the speed and price of wireless LAN systems have increased. Particularly in the near future, introduction of a PAN (Personal Area Network) for conducting information communication by constructing a small-scale wireless network between a plurality of electronic devices existing around the person is being studied. For example, different radio communication systems and radio communication apparatuses are defined using frequency bands such as 2.4 GHz band and 5 GHz band.

  As a standard regarding a wireless network, IEEE (The Institute of Electrical and Electronics Engineers) 802.11, HiperLAN / 2, IEEE 302.15.3, Bluetooth communication, and the like can be given. Regarding the IEEE 802.11 standard, various wireless communication systems such as the IEEE 802.11a standard, the IEEE 802.11b standard, and the IEEE 802.11e standard exist depending on the wireless communication system and the frequency band to be used.

  Conventionally, when configuring a LAN, a radio control station called an access point or coordinator is provided in the LAN area, and a network is formed under the overall control of the radio control station.

  In a wireless network in which the access point is arranged, when information transmission is attempted from a certain communication terminal, a bandwidth necessary for the information transmission is first reserved in the access point, and collision with information transmission in other communication terminals does not occur. So as to secure the transmission path. An access control method based on such bandwidth reservation is widely adopted. Therefore, in the wireless network in which the access point is arranged, communication terminals in the wireless network are synchronized with each other.

  In a wireless communication system using such an access point, the communication terminal must always go through the access point, and data cannot be transmitted directly to the wireless terminal to be communicated. Therefore, the transmission line utilization efficiency is drastically reduced.

  As one means for solving the above problem, ad-hoc communication in which communication terminals directly and asynchronously perform wireless communication is devised. In particular, in a small-scale wireless network composed of a relatively small number of communication terminals within a predetermined range, any communication terminal directly performs asynchronous wireless communication without using a specific access point, that is, ad hoc communication. Is considered appropriate. For example, in an IEEE802.11 wireless LAN system, an ad hoc mode that operates in a peer-to-peer manner in a distributed manner without providing a control station is prepared.

  On the other hand, it is known that a hidden terminal problem occurs in a wireless LAN network in an ad hoc environment. The hidden terminal is 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. Since it is not possible to negotiate with each other, transmission operations at each terminal may collide.

  As a method of solving such a hidden terminal problem, CSMA / CA (Carrier Sense Multiple Access with Collision Avidance) by RTS / CTS procedure is known.

  Here, CSMA / CA is a connection method for performing multiple access based on carrier detection. In wireless communication, it is difficult to receive a signal transmitted by itself, so a CSMA / CA (Collision Avidance) method is used instead of CSMA / CD (Collision Detection). In this method, collisions with other communication terminals are avoided by confirming that there is no information transmission of other communication terminals and then starting the transmission of information by itself.

  In the RTS / CTS procedure, first, the data transmission source communication terminal transmits an RTS (Request To Send) packet, and the data transmission destination communication terminal transmits a CTS (Clear To Send: confirmation notification) packet. Data is transmitted to the data transmission destination communication terminal based on the process of receiving. At this time, when the hidden terminal receives at least one of the RTS packet and the CTS packet and recognizes that the communication target is not its own terminal, a period during which the communication terminals performing communication are expected to perform data transmission, Stop transmitting information on your station. In this way, wireless communication collisions can be avoided.

  Here, the wireless network will be described using IEEE 802.11a, which is an extension standard of IEEE 802.11, as an example.

  First, the frame format in IEEE 802.11a will be briefly described. A preamble for indicating the existence of a packet is added to the head of each packet. The preamble has a known symbol pattern defined by the standard. The receiving terminal can determine whether or not the received signal deserves a preamble based on this known pattern.

  Following the preamble, a signal field is defined. The signal field stores information necessary for decoding the data field of the divided data.

  Information necessary for decoding the divided data is called a PLCP (Physical Layer Convergence Protocol) header. The PLCP header includes a RATE field indicating the transmission rate of the data field, a LENGTH field indicating the length of the information section, and a parity. -Bits and encoder tail bits are included. A receiver (or a data receiving apparatus or the like) performs decoding based on the decoding result of the RATE field and LENGTH field of the PLCP header.

  In IEEE 802.11, several frame types are defined. Here, only four types of packets, which are RTS, CTS, DATA, and ACK packets necessary for the description of the present embodiment, will be described.

  In each packet, a Frame Control field and a Duration field are defined in common. In the Frame Control field, information indicating the type and usage of the frame is stored. The Duration field stores information related to NAV (Network Allocation Vector), which will be described later, and includes a time until the transaction of the divided data ends.

  In addition to the above, the DATA packet includes an address field for identifying a transmission source communication terminal, a destination communication terminal, a sequence field (SEQ), and a checksum FCS (Frame Check Sequence). include. Note that the DATA packet according to the present embodiment may be a case where one piece of divided data is included in one packet, or a case where a plurality of pieces of divided data are included in one packet.

  The RTS frame includes a Receiver Address (RA) indicating the destination of the partner communication terminal, a Transmitter Address (TA) indicating the own communication terminal that is the transmission source, and an FCS that is a checksum.

  The CTS frame and the ACK frame include RA indicating the destination of the partner communication terminal, FCS that is a checksum, and the like.

  A CSMA / CA wireless communication network based on the RTS / CTS procedure is performed using such a frame.

  In IEEE 802.11, CSMA is adopted as a basic media access procedure. Therefore, before the transmitting terminal transmits information, the backoff timer is operated for a random time while monitoring other media states, and the transmission right is granted only when there is no transmission signal during this period. .

  Next, a specific procedure of RTS / CTS in IEEE 802.11 will be described.

  FIG. 1 is a schematic diagram schematically showing an operation example of RTS / CTS. FIG. 1 shows an example in which an arbitrary DATA packet is transmitted from the data transmission device 310 to the data reception device 320. In a wireless LAN network in an ad hoc environment, a hidden terminal problem generally occurs. As a method for reducing many of these problems, CSMA / CA by RTS / CTS procedure is performed. In addition, although the transmission example shown in FIG. 1 shall be IEEE802.11a, for example, it is not limited to this example.

  Prior to transmission of data (divided data) that is the content to be actually transmitted, the data transmission device 310 (RTS terminal) is directed to the data reception device 320 (CTS terminal) that is a communication partner according to the CSMA procedure. Send. In response to receiving the RTS packet 250, the data receiving device 320 returns a CTS packet 252 that feedbacks that the RTS packet has been received, to the data transmitting device 310.

  When receiving the CTS packet 252, the data transmission device 310, which is a transmission terminal, determines that the medium is clear, and immediately starts transmission of the DATA packet 254. Then, when receiving the DATA packet 254, the data receiving device 320 serving as a receiving terminal returns an ACK packet 256 to the data transmitting device 310. In this way, the transmission / reception transaction for one divided data is completed. Note that TXOP (Transmission Opportunity: transmission permission period) is a time allocated to a transmission / reception transaction between the RTS terminal and the CTS terminal.

  Next, for example, an operation example of RTS / CTS in the case of IEEE802.11e will be described with reference to FIG.

  Prior to transmission of data (divided data) that is the content to be actually transmitted, the data transmission device 310 transmits an RTS packet 250 to the data reception device 320 that is a communication partner according to the CSMA procedure. In response to receiving the RTS packet 250, the data receiving device 320 returns a CTS packet 252 that feedbacks that the RTS packet has been received, to the data transmitting device 310.

  When receiving the CTS packet 252, the data transmission apparatus 310 as a transmission terminal determines that the medium is clear, and immediately one or more DATA packets 254 (254-1, 254-2, ..., 254-64) exist. ). Note that the maximum number of DATA packets 254 that can be transmitted at one time is 64, for example. When transmitting 64 or more DATA packets 254, after receiving a BA (Block Acknowledgment) packet, the remaining DATA packets 254 are sent continuously.

  When the data transmission device 310 transmits all the DATA packets 254 (254-1, 254-2,..., 254-64), the data transmission device 310 transmits the BAR packet 257 to the data reception device 320.

  Next, when the data receiving device 320 as a receiving terminal finishes receiving the DATA packet 254 and further receives the BAR packet 257, it returns a BA packet 255 to the data transmitting device 310. In this way, a plurality of divided data can be processed by one transmission / reception transaction.

  FIG. 3 is a schematic diagram showing an example of the arrangement of communication terminals in such a wireless communication network. In this data transmission system, there is no specific control station as a communication station, and each communication terminal operates in an autonomous distributed manner to form an ad hoc network. Here, five communication terminals are shown, and each communication terminal (310, 315, 320) performs wireless communication with another communication terminal within its own communicable range 258.

  For example, as shown in FIG. 3, communication terminals such as a data transmission device 310a, a data reception device 320a, and a hidden terminal 315 that exist within the communicable range 258-1 can perform wireless communication. Note that the communication terminal in the communicable range 258 in FIG. 3 will be described by taking as an example the case where data is transmitted from the data transmission device 310 to the data reception device 320, but is not limited to such an example. For example, the data transmission device 310 is provided with a data reception function, and the data reception device 320 is provided with a data transmission function, so that the present invention can be implemented even when data is transmitted from the data reception device 320 to the data transmission device 310.

  Since the hidden terminal 315 belongs to both the communicable range 258-1 and the communicable range 258-2, the data transmitted in both communicable ranges 258 can be received. Therefore, the hidden terminal 315 solves problems such as packet collision by setting the NAV described later to itself. The present embodiment is not limited to the autonomous distributed wireless communication described above, and can be applied to wireless communication having a control station and wired communication.

  For example, when the data transmission device 310a attempts to transmit data (divided data) to the data reception device 320b, a communication terminal (hidden terminal) 315 exists in the vicinity. As described above, the hidden terminal 315 is a communication terminal that can communicate with one communication terminal but cannot communicate with the other communication terminal.

  Since the data transmission apparatus 310 describes the time until the transaction of the data transmission processing based on the RTS / CTS procedure ends in the RTS packet, it is necessary to determine the end time of the transaction at the time of transmitting the RTS packet. There is. That is, the data transmission device 310 that is the transmission source needs to determine all transmission rates including CTS packets, DATA packets, and ACK packets that are subsequently transmitted and received in the transaction at the time of transmitting the RTS packet. Further, the transmission rate determined here is related to the entire transaction, and it is not allowed to set the transmission rate individually for each divided data transmission within the transaction.

  As described above, the data transmission device 310 determines the transmission rate for the entire transaction at the time of transmitting the RTS packet 250. That is, the end time of the transaction, that is, the transmission permission time (TXOP) is estimated based on information held by the data transmission device 310, for example, the communication data amount and transmission rate in the entire transaction. Thereafter, the transmission rate in each of the CTS, DATA, and ACK packets that are transmitted and received basically follows the rate applied in the RTS packet.

  As described above, in IEEE 802.11n, the data reception device 320 can determine the transmission rate. Further, the transmission rate is a fixed value in IEEE 802.11e.

  In addition, when the distance between the communication terminals is short or the antenna directivity is narrowed to further reduce multipath, the data transmission device 310 can perform high-quality data transmission in such a data transmission system. Therefore, it is possible to switch to a higher transmission rate (for example, 100 Mbps to 200 Mbps).

  In addition, the transmission rate of the CTS packet 252 must be the same as that of the RTS packet 250. In the CTS packet, a time until the transaction ends, that is, a transmission permission time (TXOP), and a recognition ID (such as a MAC address) of the data transmission device 310 are described.

  The CTS packet 252 is also received by the hidden terminal 315 located in the vicinity, like the data transmission device 310 that is the transmission destination. The hidden terminal 315 receives data in the same procedure as the data receiving device 320, and recognizes that the communication terminal in the vicinity plans to receive the divided data during the transmission permission time (TXOP). As a result, the hidden terminal 315 stops the transmission by setting the NAV until the transaction is completed so as not to prevent the reception request of the data transmission device 310. The NAV is valid over the transmission permission time and is in a transmission non-permission state during the transmission permission time.

(First embodiment: data transmission system)
In the present embodiment, a data transmission system is provided in which data is transmitted by a plurality of communication terminals capable of exchanging data using various communication paths. Among such communication paths, communication is exchanged between a plurality of communication terminals, particularly assuming communication via a wireless transmission path. Each communication terminal has a communication station for wireless communication. Each communication station performs radio communication using a transmission medium composed of a single channel or a plurality of frequency channels (multi-channel). Furthermore, the data transmission system according to the present embodiment also avoids the problem caused by the hidden terminal 315 described above.

  FIG. 4 is a block diagram showing individual device configurations of the data transmission system. As shown in FIG. 4, the data transmission system includes a data transmission device 310 that transmits data, and a data reception device 320 that receives data transmitted from the data transmission device 310.

  In the data transmission system according to the present embodiment, a case where data is transmitted from the data transmission device 310 to the data reception device 320 will be described as an example. However, the present invention is not limited to this example. For example, the data transmission device 310 It is also possible to have a function of receiving data and a function of transmitting data to the data receiving device 320. By providing each of these functions, data can be transmitted and received regardless of the data transmission device 310 and the data reception device 320.

  Here, in order to facilitate understanding, the data transmission device 310 and the data reception device 320 shown in FIG. 4 will be taken and described in detail. The hidden terminal 315 that is a communication terminal as well as the data transmitting device 310 and the data receiving device 320 will be described in detail later.

(Data transmission device 310)
FIG. 5 is a block diagram illustrating a configuration of the data transmission device 310. The data transmission device 310 includes a data transmission control unit 350, a sequence assignment unit 352, an RTS transmission unit 354, a DATA transmission unit 356, and an antenna unit 360.

  The data transmission control unit 350 centrally manages and controls a series of processes in the data transmission device 310 by a control device including a central processing unit (CPU).

  The sequence assigning unit 352 divides the data to be transmitted in the data transmitting apparatus 310 into a plurality of divided data represented by a predetermined frame, arranges the plurality of divided data in the order of transmission, A unique sequence number represented by a number is assigned.

  The data receiving device 320 arranges the divided data received in the order of the sequence numbers as a predetermined number of divided data groups and decodes the data. Therefore, even if the order of the packets received by the data receiving device 320 changes, it can be reliably restored to data by rearranging the sequence numbers in ascending or descending order. The sequence number has a function of grasping the transmission order of the divided data by the data receiving device 320 and a function of restricting the number of divided data to be transmitted and received by the mutual communication terminals. The sequence number is incremented by one, for example, and is counted from 0 again when a predetermined number (upper limit) is exceeded.

  The RTS transmission unit 354 transmits an RTS packet including the number of divided data to be transmitted to the data reception device 320 via the antenna unit 360. The RTS packet can include the length (length) of the divided data to be transmitted, the sequence number, and the like.

  The number of the divided data refers to the number of DATA packets that the data transmitting apparatus 310 intends to transmit in one data transmission (a series of transactions including RTS packets and CTS packets). As described above, in IEEE 802.11e, the maximum number of DATA packets is 64 at a time.

  When the DATA transmission unit 356 receives a CTS packet that is a response from the data reception device 320 to the RTS packet transmitted by the RTS transmission unit 354, the DATA transmission unit 356 sets the transmission rate described in the CTS packet, a predetermined transmission rate, or the like. Based on this, a channel or the like is set, and a DATA packet including one or more of the divided data arranged in sequence number order is transmitted to the data receiving device 320 via the antenna unit 360.

  Note that the transmission rate according to the present embodiment is, for example, a fixed value in IEEE802.11e and a variable value that can be determined on the CTS terminal side in IEEE802.11n. The CTS packet transmitted by the data receiving device 320 is set.

  As shown in FIG. 2, after receiving the CTS packet, the DATA transmission unit 356 allocates one DATA packet to each of the divided data or one DATA packet for each of the plurality of divided data, and in order of the sequence number. The one or more DATA packets can be transmitted continuously.

  The antenna unit 360 wirelessly transmits an electromagnetic wave signal to the data receiving device 320 on a predetermined frequency channel, and receives a CTS packet and an ACK packet sent from the data receiving device 320. Also, other divided data, beacons and the like can be transmitted.

(Data receiver)
FIG. 6 is a block diagram showing a configuration of the data receiving device 320. The data receiving device 320 includes a data reception control unit 380, an RTS packet storage unit 382, a CTS transmission unit 384, an ACK transmission unit 386, a data processing unit 388, and an antenna unit 390.

  The data reception control unit 380 centrally manages and controls a series of processes in the data reception device 320 by a control device including a central processing unit (CPU).

  The RTS packet storage unit 382 stores the recognition ID corresponding to the MAC address of the data transmission device 310 in the RTS packet from the data transmission device 310, and the DATA packet length or the divided data length.

  The CTS transmitter 384 transmits the CTS packet to the data transmitter 310 via the antenna unit 390 based on the RTS packet from the data transmitter 310. The value of the transmission rate may be set in the CTS packet.

  By transmitting / receiving the RTS / CTS packet, the data transmission device 310 and the data reception device 320 can negotiate (handshake) to communicate with the communication partner before actually transmitting data.

  The ACK transmission unit 386 transmits an ACK packet to the data transmission device 310. If the sequence number of the actually received divided data is discontinuous, the ACK transmission unit 386 may request to retransmit the divided data after the missing data.

  The data processing unit 388 arranges the received divided data in the order of sequence numbers, decodes the divided data group into data when a predetermined number of divided data groups are received, and performs processing on the decoded data. Start.

  The antenna unit 390 wirelessly transmits an electromagnetic wave signal to the data transmission device 310 on a predetermined frequency channel, and receives an RTS packet and a DATA packet transmitted from the data transmission device 310. Also, other divided data, beacons and the like can be transmitted.

(Hidden terminal)
FIG. 7 is a block diagram illustrating a configuration of the hidden terminal 315. The hidden terminal 315 has the same basic configuration as the data transmission device 310 or the data reception device 320. The hidden terminal 315 includes a data reception control unit 380, an RTS packet storage unit 382, a CTS transmission unit 384, An ACK transmission unit 386, a data processing unit 388, a NAV setting unit 389, a data transmission control unit 391, and an antenna unit 392 are included.

  The data reception control unit 380 centrally manages and controls a series of processing mainly related to data reception processing in the hidden terminal 315 by a control device including a central processing unit (CPU).

  If the NAV setting unit 389 receives the RTS packet from the data transmission device 310 and is not the RTS packet addressed to itself, the NAV setting unit 389 sets the NAV that does not permit data transmission during the transmission permission time (TXOP) set in the RTS packet. Set. The set NAV value may be stored in storage means such as the RTS packet storage unit 382, for example.

  The data transmission control unit 391 centrally manages and controls a series of processing mainly related to data transmission processing in the hidden terminal 315 by a control device including a central processing unit (CPU).

  Next, a series of processes of the data transmission method according to the first embodiment will be described with reference to FIG. FIG. 8 is a sequence diagram illustrating an outline of a series of processes of the data transmission method according to the first embodiment.

  Note that communication terminals A to E (data transmission device 310, hidden terminal 315, and data reception device 320) shown in FIG. 8 correspond to the communication environment shown in FIG. It is assumed that communication is possible only with, but the present invention is not limited to such an example.

  Further, as shown in FIG. 8, a case where data is transmitted from the data transmitting apparatus 310a to the data receiving apparatus 320a and data is transmitted from the data transmitting apparatus 310b to the data receiving apparatus 320b will be described as an example.

  As shown in FIG. 8, first, prior to the process of transmitting the DATA packet, the data transmission device 310a transmits an RTS packet (transmission request packet) with the data transmission destination set as the data reception device 320a (S801).

  The data transmission apparatus 310a sets a transmission permission time (TXOP) indicating how long transmission is possible at the same time as or after transmission of the RTS packet to the data transmission apparatus 310a. As shown in FIG. 8, a bar indicated by gray hatching in the data transmission device 310 a (B) is a TXOP indicating a time zone during which transmission is possible. Note that the hatching means, for example, filling the inside of a closed region surrounded by a rectangle with an arbitrary color / pattern.

  Next, when the data receiving device 320a receives the RTS packet, the corresponding CTS packet (transmission permission packet) is transmitted to the data transmitting device 310a (S803). By transmitting such a CTS packet, both devices are handshaked and communication is established.

  The RTS packet and the CTS packet describe the time required for data transmission / reception processing (transmission permission time (TXOP)).

  The data receiving device 320a also sets TXOP to its own device in the same manner as TXOP is set on the data transmitting device 310a side. As shown in FIG. 8, bars displayed in gray hatching in the data receiving device 320a (A) are TXOPs indicating a time zone during which transmission is possible.

  When the hidden terminal 315 that is neither the data transmission device 310a nor the data reception device 320a receives an RTS packet from the data transmission device 310a, for example, the hidden terminal 315 sets the TXOP as a transmission prohibition period (NAV: Network Allocation Vector) in its own device, Meanwhile, no DATA packet is transmitted. As shown in FIG. 8, a bar displayed in gray on the hidden terminal 315 (C) is a NAV indicating a time zone in which packet transmission is prohibited.

  After the RTS / CTS procedure, the data transmitting apparatus 310a that has set TXOP transmits one or more DATA packets (or divided data) to the data receiving apparatus 320a (S805).

  When the reception of the DATA packet is completed, the data reception device 320a transmits an ACK packet to the data transmission device 310a that is the communication partner (S807). This completes a series of transactions related to DATA packet transmission.

  Note that the above-described transaction for transmitting the RTS / CTS packet and transmitting the DATA packet is also performed between the data transmission device 310b and the data reception device 320b belonging to the communicable range 258-2 shown in FIG. S809 to S815).

  In particular, in a data transmission system or the like to which IEEE802.11n is applied, when a series of transactions for transmitting a DATA packet is completed earlier than planned, that is, when there is a remaining period (Leftover term) in the TXOP, the data transmission device 310a Further, it is possible to transmit a DATA packet to the communication terminal.

  As shown in FIG. 8, an ACK packet is transmitted (S807). Immediately after receiving the ACK packet, the data transmitting apparatus 310a has a remaining period of TXOP. Here, if it is a data transmission system to which IEEE802.11n is applied, the data transmitting apparatus 310a transmits a DATA packet to the hidden terminal 315 (S817).

  The hidden terminal 315 belonging to both communicable ranges 258 (258-1, 258-2) tries to receive the DATA packet transmitted by the data transmitting apparatus 310a (S817), but the data transmission is performed at almost the same timing. Since the device 310b transmits the DATA packet to the data receiving device 320b (S813), a packet collision or the like is caused and the DATA packet from the data transmitting device 310a cannot be normally received.

  Therefore, the hidden terminal 315 cannot transmit the ACK packet to the data transmission device 310a (S819). That is, even if the data transmission device 310a transmits the DATA packet, it becomes useless processing, and the processing becomes inefficient. Further, the wireless communication bandwidth is wasted.

  Therefore, in order to solve the serious problem as described above, in the data transmission system according to the present embodiment, when such a TXOP remaining period exists, the DATA packet transmission process (S817) of the data transmission apparatus 310a shown in FIG. ) Is prohibited. Accordingly, the subsequent ACK packet transmission processing (S819) does not occur, and unnecessary processing does not occur, so that data transmission efficiency can be maintained.

  In the data transmission system according to the present embodiment, when there is a TXOP remaining period, the data transmitting apparatus 310 that is an RTS terminal prohibits DATA packet transmission during the remaining period as an example. However, the present invention is not limited to this example. For example, the present invention can be implemented even when only the data receiving device 320 that is a CTS terminal is permitted to transmit the DATA packet.

  In the case of a method such as IEEE802.11e or IEEE802.11n as shown in FIG. 2 where TXOPs for a plurality of DATA packets that can be transmitted are secured, the problem becomes even more serious.

(Second embodiment: data transmission system)
Next, a data transmission system according to the second embodiment will be described with reference to FIG. Note that detailed description of a configuration substantially similar to that of the first embodiment is omitted. FIG. 9 is a sequence diagram illustrating an outline of a series of processes of the data transmission method according to the second embodiment.

  Note that the communication terminal A to the communication terminal E (data transmission device 310, hidden terminal 315, data reception device 320) shown in FIG. 9 are the communication environment shown in FIG. 3 and the communication terminal D are the data reception device 320b. The communication terminal E is different in that it is the data transmission device 310b, and other than that, it is assumed that the communication terminal E can communicate only with adjacent communication terminals.

  Further, as shown in FIG. 9, a case where data is transmitted from the data transmission device 310a to the data reception device 320a and data is transmitted from the data transmission device 310b to the data reception device 320b will be described as an example.

  As shown in FIG. 9, before the data transmission device 310a (B) transmits a DATA packet addressed to the data reception device 320a (A), the data transmission device 310a transmits an RTS packet to the data reception device 320a (S901). . As in the first embodiment, TXOP is set in the own apparatus.

  When receiving the RTS packet from the data transmitting device 310a, the data receiving device 320a transmits the CTS packet to the data transmitting device 310a and sets TXOP in the own device (S903).

  A handshake is performed between the data transmission device 310a and the data reception device 320a by the transmission / reception of the RTS packet / CTS packet.

  On the other hand, the hidden terminal 315 (C) sets the NAV (transmission prohibited period) in its own device by the RTS packet from the data transmission device 310 a. At this time, the hidden terminal 315 records the identification ID (for example, MAC address) of the RTS packet transmission source data receiving apparatus 310a, and displays information indicating that the NAV is set by receiving the RTS packet from the data transmitting apparatus 310a. It is stored in storage means (RAM, HDD, etc.). It is assumed that the recognition ID is described in the RTS packet.

  As shown in FIG. 9, it can be seen that the hidden terminal 315 has a bar displayed in gray hatching. This indicates that the hidden terminal 315 has received the RTS packet from the data transmitting device 310a and has set the NAV in the own device based on the TXOP described in the RTS packet.

  When handshaking is performed between the communication terminals, one or more DATA packets (or divided data) are transmitted from the data transmission device 310a to the data reception device 320a to the data reception device 320a (S905).

  When the reception of the DATA packet is completed, the data reception device 320a transmits an ACK packet to the data transmission device 310a that is the communication partner (S907).

  On the other hand, it is assumed that a DATA packet is transmitted from the data transmission device 310b to the data reception device 320b within the NAV period set by the hidden terminal 315 that has received the RTS packet from the data transmission device 310a.

  In order to transmit data from the data transmitting apparatus 310b to the data receiving apparatus 320b, first, the data transmitting apparatus 310b transmits an RTS packet to the data receiving apparatus 320b (S909). It should be noted that TXOP is set in its own device in the same manner as the data transmission device 310a.

  When receiving the RTS packet from the data transmission device 310b, the data reception device 320b transmits the CTS packet to the data transmission device 310b and sets TXOP in the own device (S911).

  A handshake is performed between the data transmission device 310b and the data reception device 320b by the transmission / reception of the RTS / CTS packet.

  As shown in FIG. 9, the CTS packet transmitted from the data receiving device 320b in S911 is also received by the hidden terminal 315. However, since the TXOP (or Duration) described in the CTS packet from the data receiving device 320b is shorter than the time that the hidden terminal 315 has already set as the NAV, the hidden terminal 315 discards the CTS packet as it is.

  The hidden terminal 315 discards the CTS packet from the data receiving terminal 320b because the already set NAV period is longer than the TXOP period described in the subsequently received CTS packet. Discarding the CTS packet does not invalidate the set NAV. In other words, the NAV of the hidden terminal 315 is valid until the period ends, and data transmission processing or the like is prohibited during the NAV.

  On the other hand, when the data transmission apparatus 310a confirms that the data transmission (S905) to the data reception apparatus 320a is completed early and the remaining period of TXOP exists, the data transmission apparatus 310a uses the remaining period of TXOP to address the hidden terminal 315. Attempt to send a DATA packet.

  Prior to data transmission from the data transmission terminal 310a to the hidden terminal 315, an RTS packet is transmitted from the data transmission apparatus 310a to the hidden terminal 315 (S913). The hidden terminal 315 that has received it refers to the information indicating that the NAV has been set by the reception of the RTS packet from the previously stored data transmission device 310, and this is the source of the RTS packet received this time (the data transmission device 310 a ).

  When the hidden terminal 315 confirms that the transmission source of the RTS packet matches, the hidden terminal 315 cancels (or clears or initializes) the NAV already set in the own device, and transmits the CTS packet to the data transmission device 310a (S915). ).

  However, when the hidden terminal 315 transmits the CTS packet (S915), the transmission of the DATA packet from the data transmitting device 310b to the data receiving device 320b (S917) is almost the same as the transmission of the CTS packet (S915). It is hindered by packet collisions. That is, the hidden terminal 315 ignores the NAV and transmits the CTS packet to the data receiving device 320b even though the NAV is set to be valid for the device itself and within the period.

  When receiving the DATA packet from the data transmission device 310b, the data reception device 320b transmits an ACK packet to the data transmission device 310b (S919).

  In the data transmission system according to the present embodiment, in order to solve such a problem, the data transmission apparatus 310 uses the RTS / CTS packet even if it confirms that the TXOP remaining period exists in its own apparatus. Data should be transmitted only to the communication partner (data receiving device 320) on which the handshake is performed, and data transmission is prohibited to all other communication terminals including the hidden terminal 315.

  More specifically, as shown in FIG. 9, the data transmitting apparatus 310a has confirmed that the TXOP remaining period exists when the ACK packet is received from the data receiving apparatus 320a (S907). Even in such a case, it is prohibited to transmit the RTS packet to the hidden terminal 315 in order to transmit data to the hidden terminal 315 (S913). This is the end of the description of the series of operations of the data transmission system according to the second embodiment.

(Third embodiment: data transmission system)
Next, a data transmission system according to the third embodiment will be described with reference to FIGS. Note that a detailed description of a configuration substantially the same as that of the first embodiment or the second embodiment is omitted. FIG. 10 is a schematic diagram illustrating an arrangement example of each communication terminal in the wireless communication network according to the third embodiment. FIG. 11 illustrates a series of processes of the data transmission method according to the third embodiment. It is a sequence diagram which shows an outline.

  As illustrated in FIG. 10, the communication terminal A, the communication terminal B, and the communication terminal E are data transmission devices 310, the communication terminal C is a so-called hidden terminal 315, and the communication terminal D is a data reception device 320. Further, it is assumed that the communication terminals A to E can communicate only with adjacent communication terminals.

  Further, as shown in FIG. 10, a case where data is transmitted from the data transmission device 310a to the data reception device 320a will be described as an example.

  In the data transmission system according to the third embodiment, before the data transmission device 310a (E) transmits the DATA packet to the data reception device 320a (D), first, as shown in FIG. 11, the data transmission device 310a. Transmits an RTS packet to the data receiving device 320a (S1101). Note that the data transmission device 310a sets TXOP in its own device as in the first embodiment.

  When receiving the RTS packet from the data transmitting device 310a, the data receiving device 320a transmits the CTS packet to the data transmitting device 310a and sets TXOP in the own device (S1103).

  A handshake is performed between the data transmission device 310a and the data reception device 320a by the transmission / reception of the RTS packet / CTS packet.

  On the other hand, since the hidden terminal 315 (C) can receive the CTS packet from the data transmission device 320 a, the hidden terminal 315 sets the NAV (transmission prohibited period) in its own device by the CTS packet. .

  When handshaking is performed between the communication terminals, one or more DATA packets (or divided data) are transmitted from the data transmission device 310a to the data reception device 320a to the data reception device 320a (S1105).

  When the reception of the DATA packet is completed, the data reception device 320a transmits an ACK packet to the data transmission device 310a that is the communication partner (S1107).

  On the other hand, the data existing in the communicable range 258-1 overlaps with the period in which the data transmitting apparatus 310a transmits the DATA packet within the NAV period set in the self apparatus by the CTS packet from the data receiving apparatus 320a. The transmission device 310b may transmit a DATA packet to the hidden terminal 315 (S1109). This is because the data transmission device 310b cannot recognize the presence of the data transmission device 310a.

  However, in the data transmission system according to the third embodiment, the hidden terminal 315 transmits an ACK packet to the data transmission device 310b even when a DATA packet is transmitted from the data transmission device 310b. No (S1111).

  For example, in a conventional data transmission system simply applying IEEE 802.11e or the like, when the DATA packet is transmitted from the data transmission device 310b (S1109), the hidden terminal 315 returns an ACK packet (S1111). . The transmission of the ACK packet (S1111) collided with the DATA packet of the data transmission device 310a in S1105, and the data reception device 320a could not receive the DATA packet accurately, and the data transmission efficiency was significantly deteriorated.

  Therefore, in the data transmission system according to the third embodiment, even if the DATA packet is transmitted from the data transmission apparatus 310b under the above situation, the hidden terminal 315 does not transmit the ACK packet, thereby solving the problem. is doing. This is the end of the description of the series of operations of the data transmission system according to the third embodiment.

  Next, the series of processes described above can be performed by dedicated hardware or software. When a series of processing is performed by software, it can be implemented by installing a program constituting the software in a general-purpose computer or a microcomputer.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to this example. It is obvious for a person skilled in the art that various changes or modifications can be envisaged within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  In the above embodiment, the processing steps described or illustrated do not necessarily have to be processed in chronological order in the order described as a flowchart or a sequence diagram, but are executed in parallel or individually (for example, parallel processing) Or processing by an object).

  The present invention is applicable to a data transmission system.

It is the schematic diagram which showed typically the operation example of RTS / CTS. It is the schematic diagram which showed typically the operation example of RTS / CTS. It is the schematic which showed the example of arrangement | positioning of each communication terminal in a data transmission system. It is a block diagram which shows each apparatus structure of a data transmission system. It is a block diagram which shows an example of a schematic structure of a data transmitter. It is a block diagram which shows an example of a schematic structure of a data receiver. It is a block diagram which shows an example of a schematic structure of a hidden terminal. It is a sequence diagram which shows the outline of a series of processes of the data transmission method concerning 1st Embodiment. It is a sequence diagram which shows the outline of a series of processes of the data transmission method concerning 2nd Embodiment. It is the schematic which showed the example of arrangement | positioning of each communication terminal in the data transmission system concerning 3rd Embodiment. It is a sequence diagram which shows the outline of a series of processes of the data transmission method concerning 3rd Embodiment.

Explanation of symbols

310 data transmission device 315 hidden terminal 320 data reception device

Claims (9)

Data is divided into a plurality of divided data, a data transmission device that transmits the divided data, and the divided data transmitted from the data transmission device is received and an ACK packet is transmitted to the data transmission device, and a predetermined number of After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between the two devices is ensured by control signals of the RTS packet and the CTS packet. A data transmission system that:
The data transmitting apparatus is characterized in that, after receiving an ACK packet, if there is a remaining period in the transmission permission period, data is not transmitted to any communication terminal within the remaining period of the transmission permission period. A data transmission system. After the ACK packet is received by the data transmission device, the data that is not transmitted to any communication terminal within the remaining period of the transmission permission period is at least one of the RTS packet and the divided data. The data transmission system according to claim 1, wherein: Data is divided into a plurality of divided data, a data transmission device that transmits the divided data, and the divided data transmitted from the data transmission device is received and an ACK packet is transmitted to the data transmission device, and a predetermined number of After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between the two devices is ensured by control signals of the RTS packet and the CTS packet. A data transmission system that:
If there is a remaining period in the transmission permission period after receiving the ACK packet, the data transmission apparatus transmits data to the data receiving apparatus of the communication partner only within the remaining period of the transmission permission period. Characteristic data transmission system. Data is divided into a plurality of divided data, a data transmitting device that transmits the divided data, and the divided data transmitted from the data transmitting device is received and an ACK packet is transmitted to the data transmitting device, and a predetermined number of the data After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between both devices is ensured by control signals of the RTS packet and the CTS packet. A data transmission system:
A data transmission system, wherein a communication terminal that sets a transmission prohibition period by receiving the RTS packet or the CTS packet does not transmit data. 5. The data transmission system according to claim 4, wherein the communication terminal does not transmit the data even if the divided data is received within the transmission prohibition period. The data transmission system according to claim 4, wherein the data is the ACK packet. Data is divided into a plurality of divided data, a data transmission device that transmits the divided data, and the divided data transmitted from the data transmission device is received and an ACK packet is transmitted to the data transmission device, and a predetermined number of After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between the two devices is ensured by control signals of the RTS packet and the CTS packet. The data transmission method is:
The data transmitting apparatus is characterized in that, after receiving an ACK packet, if there is a remaining period in the transmission permission period, data is not transmitted to any communication terminal within the remaining period of the transmission permission period. Data transmission method. Data is divided into a plurality of divided data, a data transmission device that transmits the divided data, and the divided data transmitted from the data transmission device is received and an ACK packet is transmitted to the data transmission device, and a predetermined number of After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between the two devices is ensured by control signals of the RTS packet and the CTS packet. The data transmission method is:
If there is a remaining period in the transmission permission period after receiving the ACK packet, the data transmission apparatus transmits data to the data receiving apparatus of the communication partner only within the remaining period of the transmission permission period. Characteristic data transmission method. Data is divided into a plurality of divided data, a data transmitting device that transmits the divided data, and the divided data transmitted from the data transmitting device is received and an ACK packet is transmitted to the data transmitting device, and a predetermined number of the data After receiving the divided data group, it comprises a data receiving device that decodes the divided data group into data and starts processing the data, and communication between both devices is ensured by control signals of the RTS packet and the CTS packet. Data transmission method:
A data transmission method, wherein a communication terminal that sets a transmission prohibition period by receiving the RTS packet or the CTS packet does not transmit data.

Images