Source: https://patents.google.com/patent/JP2009060213A/en
Timestamp: 2019-12-15 03:26:55
Document Index: 738916741

Matched Legal Cases: ['art 106', 'art 108', 'art 110', 'art 112', 'art 114', 'art 116']

JP2009060213A - Wireless communication device, wireless communication system, wireless communication method and program - Google Patents
JP2009060213A
JP2009060213A JP2007223747A JP2007223747A JP2009060213A JP 2009060213 A JP2009060213 A JP 2009060213A JP 2007223747 A JP2007223747 A JP 2007223747A JP 2007223747 A JP2007223747 A JP 2007223747A JP 2009060213 A JP2009060213 A JP 2009060213A
JP2007223747A
2007-08-30 Application filed by Sony Corp, ソニー株式会社 filed Critical Sony Corp
2007-08-30 Priority to JP2007223747A priority Critical patent/JP2009060213A/en
2009-03-19 Publication of JP2009060213A publication Critical patent/JP2009060213A/en
<P>PROBLEM TO BE SOLVED: To assign opportunities of transmission equally to terminals in a network by assuring a minimum necessary media at a transmission side. <P>SOLUTION: A band reservation type wireless communication device performing communication with a destination terminal connected through a wireless communication network comprises an RD traffic calculation section for estimating the amount of traffic when reply data are received from the destination terminal, and a section 100 for reserving media based on the amount of traffic. <P>COPYRIGHT: (C)2009,JPO&INPIT
In the CSMA / CS (carrier sense multiple access with collision detection) system represented by IEEE 802.11 of wireless local area network (WLAN), the free state detection of the media (Media; wireless transmission path), the media with other terminals Data transmission / reception is performed by repeating the procedures of contention for use rights, media reservation (reservation), data transmission, and retransmission request detection.
FIG. 15 is a timing chart showing how data is transmitted and received in the CSMA / CS system. First, the transmitting terminal (STA-A) transmits a signal RTS (request to send) notifying that the communication is ready and the receiving terminal (STA-B) indicates a signal CTS (clear to send). Thereby, the media is secured. Thereafter, data (Data to B) is sent from STA-A to STA-B, and ACK (acknowledge) is returned from STA-B to STA-A in order to notify that the data has been correctly received.
After that, STA-B senses the channel, sends RTS to STA-A, and receives the CTS response to secure the media. Then, data (Data to A) is transmitted from STA-B to STA-A, and an ACK response is received from STA-A.
While the above method can simply control data transmission / reception, there is a problem that throughput is deteriorated due to the following factors.
-The overhead of the time required for media availability detection and media usage right equalization processing with other terminals is large. For this reason, transmission is performed from a plurality of terminals to the same terminal, and packet collision occurs due to incomplete structure.
・ The protocol overhead required to secure media is large.
-Since the transmitter cannot recognize the transmission capability of the media, it cannot select the optimum data packet transmission rate.
Under such circumstances, IEEE 802.11n includes a reverse direction protocol (Reverse Protocol) that reduces the overhead and packet collision probability when performing bidirectional data communication between terminals.
Direction Protocol) is specified.
However, the method based on the reverse direction protocol has a problem that STA-A cannot grasp the media resources (the presence / absence of data, the amount of data, the transmittable rate) required by STA-B. Since it is impossible to determine how much media should be secured when securing the media, it is necessary to temporarily secure more resources than the amount of media actually used. Even if the media is reserved more than necessary, no penalty is imposed, so the media reservation itself is a factor for reducing the transmission opportunity of other terminals.
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a transmission opportunity to a terminal in a network by securing a minimum necessary medium on the transmission side. It is an object of the present invention to provide a new and improved wireless communication apparatus, wireless communication system, wireless communication method, and program that can be allocated equally.
In order to solve the above problems, according to an aspect of the present invention, there is provided a bandwidth reservation type wireless communication apparatus for performing communication with a communication destination terminal connected via a wireless communication network, the communication destination There is provided a wireless communication apparatus including a traffic amount estimation unit that estimates a traffic amount when receiving reply data from a terminal, and a media reservation unit that reserves media based on the traffic amount.
According to the above configuration, the traffic volume when receiving reply data from the communication destination terminal is estimated, and the media is reserved based on the traffic volume. Therefore, it is possible to secure the minimum necessary media according to the reply data from the communication destination terminal, and it is possible to suppress the securing of media exceeding the necessary amount of media actually, and transmission from other terminals It is possible to reliably prevent the opportunity from decreasing.
A transmission data amount calculation unit that calculates a transmission data amount to be transmitted to the communication destination terminal; an average transmission rate calculation unit that calculates an average transmission rate at the time of transmission; the traffic amount, the transmission data amount, and the average A media calculation unit for calculating a media reservation time based on a transmission rate, wherein the media reservation unit reserves a medium based on the media reservation time calculated by the media calculation unit. . According to this configuration, the media reservation time is calculated based on the traffic amount when receiving the reply data, the transmission data amount to be transmitted to the communication destination terminal, and the average transmission rate at the time of transmission, and the media reservation time is calculated based on the media reservation time. Is reserved. Therefore, it is possible to reserve the medium in consideration of the medium at the time of data transmission together with the traffic amount when receiving the reply data.
Moreover, the reply data from the communication destination terminal may be received together with the ACK returned for the data transmission to the communication destination terminal. According to such a configuration, it is possible to estimate the amount of traffic when receiving reply data in an apparatus that receives reply data together with ACK such as a reverse direction protocol in IEEE 801.11n.
The traffic volume estimation unit may estimate the traffic volume based on a request value transmitted by the communication destination terminal. According to such a configuration, it is possible to reserve media based on the request value transmitted by the communication destination terminal.
The traffic amount estimation unit may estimate the traffic amount based on information notified from an application higher than the MAC layer. According to this configuration, it is possible to accurately estimate the traffic volume based on information notified from an application higher than the MAC layer.
The upper application may be a TCP layer, and the traffic amount estimation unit may estimate the traffic amount based on a remaining amount of a TCP buffer of the communication destination terminal. According to such a configuration, when the remaining amount of the TCP buffer of the communication destination terminal is small, it can be predicted that data will be returned from the communication destination terminal. Therefore, the traffic amount is estimated based on the remaining amount of the TCP buffer. Is possible.
Further, the traffic amount estimation unit determines the TCP buffer from the difference between the window size of the TCP buffer of the communication destination terminal and the transmission data amount that has been transmitted to the communication destination terminal and has not been returned with an ACK. The remaining amount may be calculated. According to such a configuration, the remaining amount of the TCP buffer is calculated from the difference between the window size of the TCP buffer of the communication destination terminal and the amount of transmission data that has been transmitted to the communication destination terminal and has not been returned with an ACK. Therefore, the traffic volume can be estimated based on this.
Further, the traffic amount estimation unit may estimate the traffic amount according to a transmission data amount to be transmitted to the communication destination terminal and a communication application type recognized by the upper application. . According to this configuration, it is possible to estimate the traffic amount according to the amount of transmission data transmitted to the communication destination terminal and the type of communication application recognized by the higher-level application.
The traffic amount estimation unit may calculate the traffic amount by multiplying a transmission data amount transmitted to the communication destination terminal by a coefficient set according to a type of the communication application. According to this configuration, it is possible to calculate the traffic amount according to the coefficient set according to the type of communication application.
In addition, the media reservation unit includes a media use time management unit that manages a media use time after starting use of the media, and the media use time management unit calculates the media use time and the media reservation time. The media usage time may be updated by addition, and the addition amount of the media reservation time may be adjusted according to the load state of the wireless communication network. According to such a configuration, the media usage time and the media reservation time are added to update the media usage time, and the addition amount of the media reservation time is adjusted according to the load state of the wireless communication network. Therefore, it is possible to adjust the media usage time according to the load state of the wireless communication network and the media reservation time, and it is possible to suppress the transmission trigger for the wireless communication device having a long media securing time.
The media usage time management unit may increase the addition amount of the media reservation time as the load state of the wireless communication network is larger. According to such a configuration, in a system that suppresses transmission when the media usage time becomes large, the amount of media reservation time increases as the load state of the wireless communication network increases, so that the media is reserved excessively. It is possible to suppress the transmission trigger for the wireless communication device that has been used.
The media usage time management unit may update the media usage time by adding a value obtained by subtracting the media usage time used by the communication destination terminal from the media reservation time. According to such a configuration, it is possible to accurately determine the media usage time of the own device by subtracting the media usage time used by the communication destination terminal.
In addition, a transmission trigger suppression control unit that suppresses a transmission trigger when the media usage time exceeds a predetermined threshold value may be provided. According to such a configuration, since the transmission trigger is suppressed when the media usage time exceeds a predetermined threshold, it is possible to equally apply the transmission trigger to the devices in the network.
In order to solve the above-described problem, according to another aspect of the present invention, a bandwidth reservation type wireless communication system in which a transmission device and a reception device are connected via a wireless communication network, the transmission device Provides a wireless communication system including a traffic amount estimation unit that estimates a traffic amount when receiving reply data from the receiving device, and a media reservation unit that reserves media based on the traffic amount.
According to the above configuration, in the bandwidth reservation type wireless communication system in which the transmission device and the reception device are connected via the wireless communication network, the transmission device has a traffic amount when receiving reply data from the communication destination terminal. Estimated and media reserved based on traffic volume. Therefore, it is possible to secure the minimum necessary media according to the reply data from the communication destination terminal, and it is possible to suppress the securing of media exceeding the necessary amount of media actually, and transmission from other terminals It is possible to reliably prevent the opportunity from decreasing.
In order to solve the above problems, according to another aspect of the present invention, a wireless communication method in a bandwidth reservation type wireless communication apparatus that performs communication with a communication destination terminal connected via a wireless communication network And the wireless communication method provided with the step which estimates the traffic amount at the time of receiving the reply data from the said communication destination terminal, and the step which reserves a medium based on the said traffic amount is provided.
According to the above configuration, in the wireless communication method in the bandwidth reservation type wireless communication device that performs communication with the communication destination terminal connected via the wireless communication network, when the reply data from the communication destination terminal is received. The traffic volume is estimated and media is reserved based on the traffic volume. Therefore, it is possible to secure the minimum necessary media according to the reply data from the communication destination terminal, and it is possible to suppress the securing of media exceeding the necessary amount of media actually, and transmission from other terminals It is possible to reliably prevent the opportunity from decreasing.
In order to solve the above problem, according to another aspect of the present invention, there is provided a program in a bandwidth reservation type wireless communication apparatus that performs communication with a communication destination terminal connected via a wireless communication network. Thus, there is provided a program for causing a computer to function as means for estimating a traffic amount when receiving reply data from the communication destination terminal, and means for reserving media based on the traffic amount.
According to the above configuration, in the program in the bandwidth reservation type wireless communication apparatus that performs communication with the communication destination terminal connected via the wireless communication network, the traffic amount when receiving the reply data from the communication destination terminal And media is reserved based on traffic volume. Therefore, it is possible to secure the minimum necessary media according to the reply data from the communication destination terminal, and it is possible to suppress the securing of media exceeding the necessary amount of media actually, and transmission from other terminals It is possible to reliably prevent the opportunity from decreasing.
According to the present invention, it is possible to evenly allocate transmission triggers to terminals in a network by securing the minimum necessary media on the transmission side.
[Reverse Direction Protocol]
First, as a premise of the present embodiment, the reverse direction protocol in IEEE 801.11n will be described in detail. When bidirectional data transfer is performed, each terminal needs to independently execute the processing sequence described in FIG. In contrast, IEEE
The reverse direction protocol specified in 802.11n provides a mechanism for the sender to encourage the other party to send data for the purpose of reducing the protocol overhead required to secure the media and the probability of packet collision. ing.
FIG. 1 is a schematic diagram showing transmission / reception of packet data by a reverse direction protocol. First, an initiator (Initiator; STA-A) transmits an RTS to a responder (Responder; STA-B) and receives a CTS to secure a medium. Next, STA-A transmits a data packet (Data to B) to STA-B. At this time, the header of the data packet includes a flag indicating that STA-B is allowed to transmit. In order to allow transmission of STA-B, it is necessary that sufficient media remain at the time of RTS / CTS transmission / reception.
Next, STA-B receives the data packet, detects a transmission permission flag included in the header, and transmits an ACK for the reception of the data packet and a data packet (Data to A) to STA-A. In addition, the data packet transmitted here may be called RD data (reverse direction data; RD Data). Next, STA-A transmits an ACK for the reception of the data packet from STA-B. Next, STA-A transmits a broadcast packet (end packet (END)) for releasing the secured media.
In the reverse direction protocol, a flag (RD) indicating that data transmission from STA-B to STA-A is permitted is included in the header in the transmission data (Data to B) from STA-A to STA-B. 1 bit inside. STA-B transmits transmission data (Data to A) to STA-A together with ACK when the transmission data (Data to B) from STA-A includes a flag indicating that transmission is permitted. . Compared to FIG. 15, in the reverse direction protocol, it is not necessary to transmit / receive RTS and CTS when transmitting from STA-B to STA-A, so it is possible to reduce the overhead and the probability of packet collision. is there.
FIG. 2 is a schematic diagram showing a processing block in the case of performing processing by the reverse direction protocol. The processing block shown in FIG. 2 indicates a control path indicating the order of control, and mainly indicates control performed by the MAC (Media Access Control) of the terminal. The configuration shown in FIG. 2 is common to an initiator (Initiator; STA-A) that is a transmitting terminal and a responder (Responder; STA-B) that is a receiving terminal. As shown in FIG. 2, the processing block includes a media reservation unit (media reservation) 100, a transmission data processing unit (Forward Direction Data) 102, a reception data processing unit (Reverse Direction Data) 104, a release unit (Exchange Termination) 106, A transmission trigger suppression control unit (Admission Control) 108 is included.
The media reservation unit 100 performs processing for reserving media by transmitting and receiving RTS and CTS. The transmission data processing unit 102 is a block that performs transmission / reception processing of data to be transmitted from STA-A to STA-B. On the STA-A side, transmission processing of data to be transmitted from STA-A to STA-B is performed. On the STA-B side, reception processing of data received from STA-A is performed.
The reception data processing unit 104 is a block that performs transmission / reception processing of data to be transmitted from STA-B to STA-A. On the STA-A side, reception processing of data received from STA-B is performed. On the STA-B side, transmission processing of data to be sent from STA-B to STA-A is performed.
The canceling unit 106 is a block that performs processing of sending an end packet (END Packet) when transmission / reception of data is completed. The transmission opportunity suppression control unit 108 is a block that determines whether or not the medium can be used by comparing the reserved media reservation time and the time when the medium is used.
FIG. 3 is a flowchart showing processing of the initiator (STA-A) by the reverse direction protocol. In FIG. 3, each step and processing by each block in FIG. 2 are shown in association with each other.
In the processing of FIG. 3, first, in steps S1 and S2, processing by the media reservation unit 100 of FIG. 2 is performed. In step S1, RTS is transmitted from STA-A to STA-B, and STA-A receives CTS from STA-B, thereby securing media by RTS / CTS transmission / reception. In the next step S2, processing for accumulating the media reserved time secured by RTS / CTS transmission / reception to the media used time (Used Time) up to the present is performed. At this time, the media reservation time needs to be long enough to perform the subsequent processing.
Next, in steps S3 to S9, processing by the transmission data processing unit 102 in FIG. 2 is performed. Here, processing for transmitting a data packet (Data to B) from STA-A to STA-B is performed. At this time, the header of the data packet (Data to B) includes a flag (RD) indicating whether or not to allow STA-B to transmit. In order to permit transmission of STA-B, it is necessary that sufficient media remain at the time when RTS / CTS is transmitted / received (step S1).
Specifically, in step S3, it is determined whether or not the remaining amount of media for sending the data packet remains. If there is a remaining medium, the process proceeds to step S4. If there is no remaining medium, the process is terminated (RETURN).
In step S4, it is determined whether or not the data packet to be transmitted is the last data. If the data packet is not the last data, the process proceeds to step S5, and the data packet (Data to B) is transmitted to STA-B (Data TX ; “TX” indicates transmission.) At this time, since the data packet is not the last data, it is necessary to continuously transmit data, and the responder (STA-B) cannot be permitted to transmit. Accordingly, the flag RD is set to 0 (RD = 0), and transmission from STA-B is not permitted. In the next step S6, ACK is received from STA-B. Thereafter, the process returns to step S3, and the above processing is repeated. On the other hand, if the data packet transmitted in step S4 is the last data, the process proceeds to step S7 in order to permit the responder (STA-B) to transmit. In step S7, it is determined whether or not there is a remaining medium when permitting the responder (STA-B) to transmit.
If there is remaining media in step S7, the process proceeds to step S8, and the last data packet is transmitted from STA-A to STA-B (Data TX). At this time, in order to permit transmission to STA-B, the flag RD in the header of the data packet is set to 1 (RD = 1). In the next step S9, ACK is received from STA-B (Rx Ack; “RX” represents reception). If there is no remaining medium in step S7, the process proceeds to step S5. In this case, after the last data is transmitted in step S5, since there is no remaining medium in step S3, the process is terminated (RETURN).
Next, in steps S10 to S12, processing by the reception data processing unit 104 in FIG. 2 is performed. Here, STA-A receives data packet (RD data) sent from STA-B. In step S10, the data packet sent from STA-B is received (Data RX), and in the next step S11, ACK is transmitted to STA-B (ACK TX).
In the next step S12, a process of subtracting the reception time (RD time) of the RD data in steps S10 and S11 from the current media use time (Used Time) is performed (Used Time- = RD Time). This is because the data packet reception time in step S10 and the ACK transmission time in step S11 are STA-B media usage times.
Next, in steps S13 to S15, processing for canceling the media reservation is performed by the canceling unit 106 of FIG. First, in step S13, it is determined whether or not there is a remaining amount of media reservation time at present. If there is a remaining amount, an end packet is transmitted in step S14 (Tx END Packet), and the remaining resources are released. . The reserved media is released by the transmission of the end packet. On the other hand, if there is no remaining media reservation time in step S13, the process ends without sending an end packet (RETURN). In step S15, the time canceled by the transmission of the end packet is subtracted from the current media use time (Used Time- = canceled Time). After step S15, the process ends (RETURN).
After updating the media usage time by adding the media reservation time to the media usage time in step S2, the resource usage time of STA-B is subtracted in step S12, and the canceled time is subtracted in step S15 and released. Minutes are returned. As a result, in the initiator process, the processing time in steps S3 to S9 is added to the media usage time before the media reservation time is added in step S2, and the media usage time is updated.
FIG. 3 shows the processing by the transmission trigger suppression control unit 108 together with the above processing. First, in step S16, it is determined whether or not the current media usage time is greater than a predetermined threshold value Th. If the media usage time is greater than the threshold value Th, control for suppressing transmission in step S17 is performed. Do. Thereby, it is possible to suppress transmission to a station that uses a large amount of media.
In addition, the transmission opportunity suppression control unit 108 performs processing for resetting the media usage time. Here, a timer is operated to measure a certain observation time, and in step S18, it is determined whether or not the value of the timer exceeds an observer period (observe_period) that triggers resetting. If the timer value exceeds the observable period, the process proceeds to step S19 to reset the media usage time. On the other hand, if the timer value is less than or equal to the observable period, the process waits in step S18.
After step S19, the process proceeds to step S20, and the transmission suppression set in step S17 is released. In the next step S21, the timer time is reset and a new timer is operated.
FIG. 4 is a flowchart showing a responder (STA-B) process according to the reverse direction protocol, in which each step and each block in FIG. 2 are associated with each other. In the STA-B process, the state transition from the idle state (step S31) is determined (steps S32, S33, S34). The state transition is determined by determining whether an RTS has been received (step S32), whether a data packet has been received (step S33), and whether an end packet has been received (step S34). If it is determined in step S32 that RTS has been received from STA-A, CTS is returned in step S35, and the media reservation unit 100 of the initiator secures the media.
After securing the media in step S35, the process proceeds to step S36. If it is determined in step S33 that a data packet has been received from STA-A, the process proceeds to step S36.
In steps S36 to S38, processing by the transmission data processing unit 102 in FIG. 2 is performed. Here, first, in step S36, processing for receiving a data packet sent from STA-A is performed (Data RX). In the next step S37, processing for transmitting ACK to STA-A is performed (TX ACK). In the next step S38, it is determined whether or not the state of the flag RD included in the header of the data packet sent from the STA-A is 1.
If the flag RD is 1 in step S38, the responder is permitted to transmit, and the process proceeds to step S39. In steps S39 to S43, processing by the reception data processing unit 104 in FIG. 2 is performed. In step S39, it is determined whether there is a remaining amount of media reservation time. If there is a remaining amount of media reservation time, a data packet is transmitted in the next step S40 (Data TX). In the next step S41, an ACK for the packet data transmitted in step S40 is received from STA-A. In the next step S42, since the media is used for the RD time in the processing of steps S39 to S41, the RD time (RD Time) is added to the responder's media usage time (Used Time), and the media usage time is updated (Used Time + = RD Time). In the next step S43, it is determined whether or not the state of the flag RD is 1. If the state of the flag RD is 1 in step S43, since transmission by STA-B is permitted, the process returns to step S39 and the subsequent processing is performed again.
If it is determined in step S34 that an end packet has been received from STA-A, the process proceeds to step S44. In step S44, processing for receiving an end packet is performed (RX END Packet). The processing in step S44 is performed by the canceling unit 106 in FIG. After steps S38, S43, and S44, the state returns to the idle state.
In the reverse direction protocol as described above, the RTS / CTS is not sent or received when the responder sends data, so the media resources required by the responder (STA-B) (the presence of data, the amount of data) There is an implementation problem that the initiator (STA-A) side cannot grasp the transmission possible rate). For this reason, it is impossible to determine how much media should be secured when securing media on the initiator side. Since the amount of media to be secured cannot be estimated, as described above, a situation occurs in which more resources than the amount of media actually used are temporarily secured.
In addition, there is a problem that the data rate that the initiator (STA-A) transmits to the responder (STA-B) cannot be set freely. In securing the media, the initiator (STA-A) needs to estimate the time required for packet transmission performed by itself, and in order to transmit all packets, at the time of securing the media (RTS / CTS transmission / reception) It is necessary to transmit using the assumed transmission rate. However, considering the factors that increase the amount of required media, such as when it is necessary to lower the transmission rate due to fluctuations in the transmission path, or when retransmission is required due to an error in the transmission path, the amount of media actually used There will be a situation where more media is secured.
For this reason, at the time of securing the medium in step S1 of FIG. 3 (step S35 of FIG. 4), the securing of the medium is performed to the maximum by the maximum time that can be secured or a predetermined fixed time. Then, when there is a surplus of media after the communication, a method of transmitting the end packet and releasing the secured media is performed. However, in this method, there is a problem that not only media is secured more than necessary, but also a hidden terminal that cannot receive an end packet occurs. A terminal that can receive an end packet in the network recognizes that the medium has been released and can newly secure the medium. On the other hand, a hidden terminal that cannot receive an end packet cannot recognize that the use of media has ended, and therefore cannot participate in media reservation and cannot ensure fairness of media reservation. Considering such a case where there is a hidden terminal that cannot receive a media release packet, it is desirable to secure a medium that is as close as possible to the amount of media that is actually used at the RTS / CTS transmission / reception stage.
Also, the WLAN specification has a mechanism for limiting the amount of media used per time, called Used Media Time, in order to control the amount of media used by each terminal (Admission Control). This is to prevent the terminal from accessing the media again using a certain amount of media (steps S16 to S21 in FIG. 3), thereby maintaining the fairness of the media usage of the terminals in the BSS. It is. In this specification, monitoring of only the amount of media actually used is defined. However, as described above, the release of reserved media is not complete, and excessive media reservation itself is a trigger for transmission of other terminals. It becomes a factor to reduce. For this reason, management of the media usage time actually used is not enough to maintain fairness, and a protocol that gives a penalty when there is a difference between the reserved resource and the actually used resource. It is desirable to provide it.
FIG. 5 is a schematic diagram showing a configuration of a wireless communication network according to an embodiment of the present invention. The wireless communication network includes a terminal 10, a terminal 12, and a terminal 14. Here, each of the terminals 10, 12, and 14 has a function of performing media reservation (reservation), data transmission, and data reception. Also, a terminal that has reserved a medium is defined as an initiator, and a terminal that is a communication partner of the initiator is defined as a responder.
FIG. 6 is a schematic diagram showing processing blocks of the wireless communication device (initiator, responder) according to the present embodiment. The wireless communication apparatus according to the present embodiment performs processing based on the above-described reverse direction protocol. The wireless communication apparatus of the present embodiment includes a MAC layer and a TCP / IP layer that is an upper layer application of the MAC layer. Similar to the configuration illustrated in FIG. 2, FIG. 6 schematically illustrates processing blocks of control mainly performed by the MAC. As shown in FIG. 6, the processing blocks of the initiator and the responder are a media reservation unit (Media reservation) 100, a transmission data processing unit (Forward Direction Data) 102, a reception data processing unit (Reverse Direction Data) 104, and a release unit ( Exchange Termination) 106, transmission trigger suppression control unit (Admission Control) 108, rate control unit (Rate Control) 110, buffer management unit (Buffer statistics) 112, RD traffic amount calculation unit (RD traffic estimate) 114, media calculation unit ( Media estimate) 116 and buffer management unit 118 (Buffer statistics) 118.
6 is compared with FIG. 2, in the configuration of the present embodiment illustrated in FIG. 6, the rate control unit 110, the buffer management unit 112, the RD traffic amount calculation unit 114, the media calculation unit 116, and the configuration of FIG. The configuration of the buffer management unit 118 is added.
In the present embodiment, the rate control unit 110 is a block that controls the transmission rate when securing media, and calculates an average value (average transmission rate) of transmission rates to terminals (responders) that are transmission targets. . As the average transmission rate, for example, an average value of transmission rates measured over a relatively long period can be adopted.
The buffer management unit 112 is a functional block that manages the buffer on the initiator side, and manages statistics indicating how much data to be transmitted to the responder is held. The buffer management unit 112 outputs the amount of data to be transmitted to the responder and the number of packets (buffer amount). The buffer management unit 118 is a functional block that manages the buffer on the responder side, and has a function of calculating its own data amount and the number of packets (buffer amount) when the responder transmits data to the initiator. The initiator buffer amount calculated by the buffer management unit 118 is notified to the initiator. Further, the RD traffic amount calculation unit 114 outputs a traffic amount (RD traffic amount; RD Traffic) when receiving the reverse direction data (RD Data).
The media calculation unit 116 uses the transmission rate information for media reservation output from the rate control unit 110, the buffer amount output from the buffer management unit 112, and the RD traffic amount output from the RD traffic amount calculation unit 114. Thus, the required amount of media to be secured when transmitting / receiving RTS / CTS is calculated. Then, the RTS / CTS sequence is executed with the determined media amount.
The transmission data processing unit 102 performs data transfer processing from the initiator to the responder, as in the system of FIG. The transmission data rate or retransmission method used at this time is not particularly limited, and a rate suitable for a transmission path state derived by an independent separate algorithm or retransmission means can be used.
The reception data processing unit 104 processes data (RD Data) transmitted from the responder to the initiator, as in the system of FIG. Furthermore, in order to perform reverse direction most efficiently, the responder has a function of notifying the initiator of the amount of data that can be transmitted. For example, when operating in the IEEE 802.11 frame format, the notification of the data amount can be realized by using a reserve bit (RESERVE BIT) of the MAC header.
Moreover, the cancellation | release part 106 performs the process similar to the system of FIG. In this embodiment, when a medium reserved using an end packet is released, the released resource is not returned as it is, but only the amount corrected by the coefficient alpha is returned. This coefficient alpha (0 <alpha <1.0) is adjusted according to the media usage (medium occupancy) and bandwidth usage. The central management function such as access point (AP) is used by the number of users and channel occupancy. The value of the coefficient alpha is controlled from the above and notified to the terminals 10, 12, and 14 in the network. Further, one of the terminals 10, 12, and 14 in the network may control the value of the coefficient alpha from the number of users, the channel occupancy rate, and the like. In FIG. 5, it is assumed that the terminal 10 grasps the usage status of the media and controls the coefficient alpha. In the control of the coefficient alpha, a mechanism is adopted in which the coefficient alpha is brought closer to 0 as the media usage status and bandwidth usage status become congested.
In the system of the present embodiment configured as described above, the RD traffic amount calculation unit 114 performs processing for calculating the RD traffic amount. The RD traffic volume is an index representing the weight of the media, and indicates the traffic volume when RD data is transmitted from the responder. The larger the amount of RD traffic, the more media is given to the responder. This makes it possible to optimally secure media according to the communication status when communicating with the responder. Here, the amount of RD traffic can be expressed by a value (fact) indicating a ratio of a time (RD time) at the time of RD data transmission and a received data amount to a transmission data amount of the terminal itself.
The calculation of the RD traffic amount by the RD traffic amount calculation unit 114 is roughly divided into two methods. The first method is a method of determining the output value of the RD traffic amount based on the report value (RD request) from the responder. In this case, the initiator outputs the RD traffic amount according to the RD request value extracted from the reverse direction data in step S94 of FIG .
The second method is a method of calculating the RD traffic amount using auxiliary information of the application. Here, a method of calculating the RD traffic amount based on the application type and a method of deriving the RD traffic amount when using the TCP / IP protocol are assumed.
In the method of deriving the RD traffic amount from the application type, the data amount sent from the responder is calculated with respect to the data amount sent from the initiator according to the application type. For example, in an interactive application such as a videophone or VoIP, the transmission data amount and reception data amount of the terminal itself are almost equal. On the other hand, in other application types, the reception amount can be expressed by multiplying the transmission data amount by a predetermined coefficient. For this reason, the RD traffic amount calculation unit 114 outputs the ratio of the reception data amount to the transmission data amount of the terminal itself according to the application type. The application type can be acquired from the TCP / IP layer, which is an upper layer of the MAC layer.
In the method of deriving the traffic amount when using the TCP / IP protocol, TCP_ACK for transmission data is predicted and assigned. The prediction of TCP_ACK can be estimated from the state of the TCP buffer (TCP Buffer), and the amount of resources to be allocated is made variable according to the remaining amount of the TCP buffer of the counterpart terminal.
Specifically, the initiator side monitors the remaining amount of the responder's TCP buffer, and performs media reservation and media allocation to the partner terminal. The operation of the TCP buffer is defined in RFC (request for comments) 793.
FIG. 7 is a schematic diagram showing the state of the TCP buffer of the initiator. In FIG. 7, the packet data in the area A indicates a packet area that has been transmitted to the responder and ACK is returned from the responder. The packet data in the area B indicates a packet area that has been transmitted to the responder and has not yet returned an ACK from the partner. The area C indicates a packet area that can be transmitted from now on. D indicates a packet area that cannot be transmitted by the protocol. When the initiator itself transmits a packet or when the initiator receives a new ACK from the responder, the TCP buffer state update process shown in FIG. 7 is performed.
In FIG. 7, the total capacity of the area B and the area C is the TCP buffer window size (TCP Window Size). Here, the packet data in the area C is a packet area that can be transmitted from now on, and can be defined as the remaining buffer capacity of the responder. Specifically, the remaining buffer capacity of the responder can be the difference between the buffer size of the TCP buffer and the B area that is the transmitted packet in FIG. 7, and can be expressed by the following equation (1). .
In equation (1), the buffer size (buffsize [i]) corresponds to the window size of the TCP buffer reported from the responder that is the transmission partner, and is updated when an ACK is received from the responder. Further, the term represented by Σ is an integrated value of the packet size (packet_size) from packet #n to packet #m in FIG. 7, and indicates the capacity of packet data in region B in FIG.
Note that the variable i indicates that the buffer size (buffsize [i]) and rsize [i] vary with time because the buffer size is updated each time an ACK is returned. Although the above formula shows an example in which the sizes of already transmitted packets are integrated, the calculation may be performed including the packet scheduled to be transmitted next.
Here, in order to reduce the overhead of ACK, the responder side transmits ACK when the remaining buffer capacity is low. Therefore, it can be determined that the smaller the remaining buffer capacity, the higher the possibility that a data packet is sent from the responder together with the ACK. Since rsize [i] calculated by the above equation corresponds to the remaining TCP buffer capacity of the responder, the probability that ACK will be transmitted as the remaining TCP buffer capacity of the responder decreases and the value of rsize [i] decreases. It becomes clear that the amount of RD traffic increases. For this reason, in the present embodiment, the smaller the value of rsize [i], the more media is secured during RD data transmission, and the process of securing reverse direction resources is performed.
FIG. 8 shows processing for updating the output of the RD traffic amount calculation unit 114 in accordance with the value of rsize [i] calculated from the above equation. First, in step S51, it is determined whether or not rsize [i] calculated from equation (1) exceeds a predetermined threshold (thresh), and rsize [i] exceeds a predetermined threshold. If so, the output of the media calculation unit 116 is set to 0 in Step S52 (Normal Frame Exchange). In this case, since the value of rsize is relatively large, it can be determined that an ACK has not been returned from the responder for a while, and it can be determined that the amount of RD traffic is small. Therefore, normal frames (Normal
Frame) is set, and the RD time is set to 0.
On the other hand, if rsize [i] is equal to or smaller than the predetermined threshold (thresh) in step S51, the process proceeds to step S53, and the output of the RD time from the RD traffic amount calculation unit 114 is set to x [ms]. As a result, more media are provided for the response of the RD data by the responder.
As described above, according to the processing of FIG. 8, the output of the RD traffic amount calculation unit 114 is updated according to the value of rsize [i], so that it is possible to secure media according to the traffic amount. .
FIG. 9 is a flowchart showing processing including the above-described first and second methods when the RD traffic amount calculation unit 114 calculates the RD traffic amount. Here, the processing of steps S61 and S62 is processing for determining the output value of the RD traffic amount based on the report value from the responder by the first method described above. Further, the processes in steps S63 to S68 are processes for calculating the RD traffic amount based on the application type by the above-described second method. Further, the processes in steps S69 to S72 are processes for deriving the RD traffic amount when using the TCP / IP protocol.
First, in step S61, it is determined whether there is an RD request. If there is an RD request, the process proceeds to step S62, the RD time is set to the request time (RD_req) according to the RD request, and a value (fact) representing the ratio of the reception amount to the transmission data amount of the own terminal is set to 1.0. Set to.
If there is no RD request in step S61, the process proceeds to step S63 to determine whether or not the application type is TV / VoIP, and if it is TV / VoIP, the process proceeds to step S64. In step S64, the RD time is set to 0 and fact is set to 2.
If it is not TV / VoIP in step S63, the process proceeds to step S65 to determine whether it is another application type (App # 1). If it is App # 1, the process proceeds to step S66. In step S66, the value of the RD time is set to 0, and fact is set to a value (= 1.5) corresponding to the application type (App # 1).
If it is not another application type (App # 1) in step S65, the process proceeds to step S67. In step S67, it is further determined whether the type is another application type (App # 2). If it is App # 2, the process proceeds to step S68. In step S68, the RD time is set to 0, and the ratio (fact) is set to a value (= 1.25) corresponding to the application type (App # 2).
Similarly, after setting the RD time and the fact value for various conditions, in step S69, it is determined whether or not it is TCP / IP, and in the case of TCP / IP, the process proceeds to step S70. In step S70, the remaining buffer capacity rsize [i] is calculated, and the process proceeds to step S71. The processing after step S71 is the same as the processing described in FIG.
In step S71, it is determined whether or not the remaining amount rsize [i] of the buffer is larger than a predetermined threshold value (thresh). If the remaining amount is larger than the threshold value, the process proceeds to step S72. In step S72, the value of RD time is set to 0, and fact is set to 1.0. On the other hand, when the remaining amount of the buffer is equal to or smaller than the threshold value, the process proceeds to step S13, the RD time is set to x [ms], and the fact is set to 1.0.
When the RD traffic amount calculation unit 114 outputs the RD time and the value (fact) as described above, the media calculation unit 116 sets the transmission prohibition period (NAV) based on the RD time and the value (fact). Is reserved. Processing by the system of this embodiment including this media reservation processing will be described with reference to FIG. The processing in FIG. 10 shows processing by the initiator, and is performed in the same manner as part of the processing in FIG.
In the process of FIG. 10, the media amount to be reserved is calculated by the media calculation unit 116 in steps S81 to S83. At this time, the RD traffic amount calculated by the RD traffic amount calculation unit 114, the transmission data amount calculated by the buffer management unit 112, and the average transmission rate calculated by the rate control unit 110 are used.
In the media calculation by the media calculation unit 116, first, in step S81, the value of the transmission time Fd by the initiator is calculated. Here, the transmission time Fd is calculated from the following equation.
Fd = transmission data amount / average transmission rate + response time (Response) + IFS
In the above equation, the response time is the time required for the response at the time of transmission. IFS is a frame interval time of a packet.
In the next step S82, the transmission time Rd by the responder is calculated from the following equation.
Rd = RD time (Time) + (fact-1.0) * Fd
Here, the values of the RD time and the fact are set by the processes of FIGS. 8 and 9 as described above.
As described with reference to FIG. 9, in the case of the first method, the RD time is set to a request value (RD_req) from the responder. In this case, since fact = 1, the second term of the above equation for calculating the transmission time Rd is zero. Accordingly, the transmission time Rd is set to a request value from the responder.
Further, when the RD time is determined according to the application type by the second method, the RD time is 0, so the first term of the above equation is 0. In this case, since the ratio (fact) is set to a value such as 2, 1.5, or 1.25, the value of the transmission time Rd is determined by the second term of the above equation. For example, when the application type is a videophone, the transmission data amount and the reception data amount of the terminal itself are almost equal, so fact is set to 2 in step S64 of FIG. Therefore, the transmission time Fd of the initiator and the transmission time Rd of the responder are set to be the same by the second term of the above equation.
In the next step S83, the transmission prohibition period (Nav) is calculated from the following equation.
Nav = Fd + Rd
In steps S84 and S85, processing by the media reservation unit 100 is performed. The basic processing is the same as the processing in steps S1 and S2 in FIG. 3, but the media reservation time is set to the transmission prohibition period (Nav) calculated in step S3. As a result, the media reservation time can be set according to the media usage estimated from the RD traffic.
In the next steps S86 to S92, processing by the transmission data processing unit 102 is performed. The processing here is basically the same as the processing in steps S3 to S9 in FIG.
In the next steps S93 to S96, processing by the reception data processing unit 104 is performed. Here, the processes of steps S93, S95, and S96 are the same as the processes of steps S10, S11, and S12 of FIG. In the process of FIG. 10, in step S94, a process of extracting an RD request to the RD traffic amount calculation unit 114 from the data packet received from the responder is performed. The extracted RD request is sent to the RD traffic amount calculation unit 114.
Next, in steps S97 to S99, processing by the canceling unit 106 is performed. Here, the processes in steps S97 and S98 are the same as the processes in steps S13 and S14 in FIG. In the process of FIG. 10, in step S99, the value obtained by multiplying the cancellation time (Canceled Time) by the coefficient alpha is subtracted from the media usage time (Used Time- = alpha * Canceled Time).
As described above, the coefficient alpha is reported from the access point (AP) or a terminal in the network, and the value of the coefficient alpha approaches 0 as the media usage status and bandwidth usage status become congested. Therefore, as the media usage status is congested, the amount of subtraction from the media usage time decreases, and the media usage time is set to a larger value.
In FIG. 10, the processing of steps S101 to S106 by the transmission trigger suppression control unit 108 is the same as the processing of steps S16 to S21 of FIG. Here, if the media is canceled by the processing of step S99 when the usage status of the media is congested, the media usage time is set to a larger value. Therefore, in this case, it is easy to start transmission suppression in step S102, and a penalty due to transmission suppression can be imposed on a terminal that has canceled the media when the usage status of the media is congested.
FIG. 11 is a flowchart showing the responder process according to the present embodiment. In FIG. 11, the processes of steps S111 to S119 are the same as the processes of steps S31 to S39 of FIG. In the processing of FIG. 11, in the media securing in step S115, the necessary media amount is secured in consideration of the amount of RD traffic by the above-described processing on the initiator side.
In the process of FIG. 11, the process by the responder-side buffer management unit 118 is performed in steps S126 to S128. First, the buffer amount is calculated in step S126, and the average transmission rate is calculated in step S127. In the next step S127, a media time (RD request) required for transmission from the responder is calculated from the buffer amount and the average transmission rate.
In step S120, an RD request is inserted into the packet data in order to make a media request to the initiator based on the media time calculated in step S127. In the next step S121, the packet data in which the RD request is inserted is transmitted to the initiator. The subsequent steps S122 to S125 are the same as the steps S41 to S44 in FIG.
FIG. 12 is a schematic diagram illustrating an implementation method using the reserve bit of the Mac header when the responder notifies the initiator of an RD request as the amount of data that can be transmitted when operating in the IEEE 802.11 frame format. . As shown in FIG. 12, the ACK transmitted from the responder includes a header reserve bit. For this reason, the presence / absence of data to be transmitted to the initiator and the amount of data can be notified to the initiator by the header reserve bit. In FIG. 12, data is not added to the first ACK among the two ACKs transmitted from the responder. Therefore, information indicating that there is no transmission data is included in the header reserved bits of this ACK. Further, since data is added to the ACK transmitted next, information indicating that there is transmission data and data amount information are included in the header reserve bits of this ACK.
FIG. 13 is a schematic diagram illustrating an example of a data format. Specifically, for example, by defining the HT-Control Field defined in the MAC header of IEEE 802.11n as shown in FIG. 13, the responder (or initiator) 's own buffer amount (= RD request) is notified. Can do.
FIG. 14 shows data transmission / reception between the TCP / IP layer of the initiator (STA-A) and the MAC layer, wireless data transmission / reception between the MAC layer of the initiator and the MAC layer of the responder (STA-B), and the responder. It is a schematic diagram which shows transmission / reception of the data between a MAC layer and a TCP / IP layer.
First, in step S131 of FIG. 14, data is transmitted from the TCP / IP layer of the initiator to the MAC layer, and in step S132, data is transmitted wirelessly from the MAC layer of the initiator to the MAC layer of the responder. At this time, in the TCP / IP layer of the initiator, the flag RD in the data is not set to 0 until the remaining amount of the buffer is reduced.
On the responder side, in step S133, the data received from the MAC layer of the initiator is sent from the MAC layer of the responder to the TCP / IP layer. When receiving the data, the TCP / IP layer transmits TCP_ACK to the MAC layer (step S134).
The responder's MAC layer cannot send an ACK to the responder before the data flag RD from the initiator is set to 1, so the TCP_ACK sent from the responder's TCP / IP layer to the MAC layer It is stored in the MAC layer.
On the initiator side, when the TCP buffer remaining amount is reduced by data transmission, in step S135, the flag RD in the data to be sent to the responder is set to 1 and the data is sent to the responder. In response to the data transmission of the flag RD = 1, the responder transmits the TCP_ACK stored in the MAC layer to the initiator in step S136.
When the initiator MAC layer receives TCP_ACK, the TCP / IP layer does not recognize TCP_ACK, and in step S137, data transmission to the responder is performed with RD = 1. When the TCP / IP layer recognizes TCP_ACK, the flag RD is set to 0, and data transmission to the responder is performed as in step S131 (S138).
Note that, as shown in step S139, even when the flag RD of the data received by the responder is 0, TCP_ACK may be returned to the initiator depending on the condition.
It is a schematic diagram which shows transmission / reception of the packet data by a reverse direction protocol. It is a schematic diagram which shows the process block in the case of performing the process by a reverse direction protocol. It is a flowchart which shows the process of an initiator (STA-A) by a reverse direction protocol. It is a flowchart which shows the process of the responder (STA-B) by a reverse direction protocol. It is a schematic diagram which shows the structure of the radio | wireless communication network which concerns on one Embodiment of this invention. It is a schematic diagram which shows the processing block of the initiator and responder which concern on one Embodiment of this invention. It is a schematic diagram which shows the state of the TCP buffer of an initiator. It is a flowchart which shows the process which updates the output of a media calculation part according to the value of rsize [i]. It is a flowchart which shows the process including the 1st and 2nd method in the case of calculation of the RD traffic amount by the RD traffic amount calculation part. It is a flowchart which shows the process of the initiator by one Embodiment of this invention. It is a flowchart which shows the process of the responder by one Embodiment of this invention. When operating in the IEEE802.11 frame format, when the responder notifies an RD request as the amount of data that can be transmitted to the initiator, it is a schematic diagram showing an implementation method using reserved bits of the Mac header. It is a schematic diagram which shows an example of a data format. It is a schematic diagram showing data transmission / reception between the TCP / IP layer and the MAC layer of the initiator, data transmission / reception between the initiator and the responder, and data transmission / reception between the responder's MAC layer and the TCP / IP layer. . It is a timing chart which shows a mode that transmission / reception of data is performed by a CSMA / CS system.
DESCRIPTION OF SYMBOLS 100 Media reservation part 108 Transmission opportunity suppression control part 110 Rate control part 112 Buffer management part 114 RD traffic amount calculation part 116 Media calculation part
A bandwidth reservation type wireless communication device that performs communication with a communication destination terminal connected via a wireless communication network,
A traffic amount estimation unit for estimating a traffic amount when receiving reply data from the communication destination terminal;
A media reservation unit that reserves media based on the traffic volume;
A transmission data amount calculation unit for calculating a transmission data amount to be transmitted to the communication destination terminal;
An average transmission rate calculator for calculating an average transmission rate at the time of transmission;
A media calculation unit that calculates a media reservation time based on the traffic amount, the transmission data amount, and the average transmission rate;
The wireless communication apparatus according to claim 1, wherein the media reservation unit reserves media based on the media reservation time calculated by the media calculation unit.
The wireless communication apparatus according to claim 1, wherein reply data from the communication destination terminal is received together with ACK returned for data transmission to the communication destination terminal.
The wireless communication apparatus according to claim 1, wherein the traffic amount estimation unit estimates the traffic amount based on a request value transmitted by the communication destination terminal.
The wireless communication apparatus according to claim 1, wherein the traffic amount estimation unit estimates the traffic amount based on information notified from an application higher than a MAC layer.
The wireless communication according to claim 5, wherein the upper application is a TCP layer, and the traffic amount estimation unit estimates the traffic amount based on a remaining amount of a TCP buffer of the communication destination terminal. apparatus.
The traffic amount estimation unit determines the remaining amount of the TCP buffer from the difference between the window size of the TCP buffer of the communication destination terminal and the transmission data amount that has been transmitted to the communication destination terminal and has not been returned with an ACK. The wireless communication apparatus according to claim 6, wherein:
The traffic amount estimation unit estimates the traffic amount according to a transmission data amount to be transmitted to the communication destination terminal and a communication application type recognized by the higher-order application. 5. The wireless communication device according to 5.
The traffic amount estimation unit calculates the traffic amount by multiplying a transmission data amount to be transmitted to the communication destination terminal by a coefficient set according to a type of the communication application. The wireless communication device described.
The media reservation unit includes a media usage time management unit that manages media usage time after starting to use media,
The media usage time management unit
Update the media usage time by adding the media usage time and the media reservation time,
The wireless communication apparatus according to claim 2, wherein an addition amount of the media reservation time is adjusted according to a load state of the wireless communication network.
The wireless communication apparatus according to claim 10, wherein the media usage time management unit increases the amount of addition of the media reservation time as the load state of the wireless communication network is larger.
The wireless communication apparatus according to claim 10, wherein the media usage time is updated by adding a value obtained by subtracting the media usage time used by the communication destination terminal from the media reservation time.
The wireless communication apparatus according to claim 10, further comprising a transmission trigger suppression control unit that suppresses a transmission trigger when the media usage time exceeds a predetermined threshold.
A bandwidth reservation type wireless communication system in which a transmission device and a reception device are connected via a wireless communication network,
A traffic amount estimating unit for estimating a traffic amount when receiving reply data from the receiving device;
A wireless communication method in a bandwidth reservation type wireless communication device that performs communication with a communication destination terminal connected via a wireless communication network,
Estimating the amount of traffic when receiving reply data from the communication destination terminal;
Reserving media based on the traffic volume;
A program in a bandwidth reservation type wireless communication device that performs communication with a communication destination terminal connected via a wireless communication network,
Means for estimating a traffic amount when receiving reply data from the communication destination terminal;
Means for reserving media based on the traffic volume;
JP2007223747A 2007-08-30 2007-08-30 Wireless communication device, wireless communication system, wireless communication method and program Pending JP2009060213A (en)
JP2007223747A JP2009060213A (en) 2007-08-30 2007-08-30 Wireless communication device, wireless communication system, wireless communication method and program
US12/201,813 US20090059792A1 (en) 2007-08-30 2008-08-29 Wireless Communication Device, Wireless Communication System, Wireless Communication Method, and Program
JP2009060213A true JP2009060213A (en) 2009-03-19
ID=40407295
JP2007223747A Pending JP2009060213A (en) 2007-08-30 2007-08-30 Wireless communication device, wireless communication system, wireless communication method and program
US (1) US20090059792A1 (en)
JP (1) JP2009060213A (en)
JP2003218981A (en) * 2002-01-25 2003-07-31 Toshiba Corp Data transmission apparatus and data transmission method
JP2006166114A (en) * 2004-12-08 2006-06-22 Oki Electric Ind Co Ltd Qos control method of radio lan base station unit
JP2006352844A (en) * 2006-04-28 2006-12-28 Toshiba Corp Wireless communication apparatus
2007-08-30 JP JP2007223747A patent/JP2009060213A/en active Pending
2008-08-29 US US12/201,813 patent/US20090059792A1/en not_active Abandoned
US8605631B2 (en) 2009-07-22 2013-12-10 Panasonic Corporation Communication method
US20090059792A1 (en) 2009-03-05