Patent Application
20100067393
The present invention relates to a method of measuring a packet Round Trip Time (referred to as an RTT hereinafter), and a wireless communication system using the method. In particular, the present invention relates to a method of measuring, for example, an RTT between a source device and a sink device of audiovisual devices (referred to as AV devices hereinafter) in a wireless communication system for transmitting content data to be copyrighted, in a form of packet data, and a communication system using the method.
Digital infrastructures (network infrastructures) have been constructed by using digital broadcasting, high-speed Internet and the like. At the same time, large-capacity recording media such as a DVD and a BD have become widespread. Therefore, anyone can easily obtain digital contents without any deterioration via the network. In this situation, copyright protection method is quite important. The application range of DTCP (Digital Transmission Content Protection) standard for protecting copyright of contents on the network has been particularly enlarged to IEEE1394, USB (Universal Serial Bus), MOST (Media Oriented Systems Transport), Bluetooth, and Internet Protocols (IP), and the number of products compliant with the DTCP has already increased.
In DTCP-IP (See Non-Patent Document 1), any connection between an in-house network and an external network via a router is not permitted, and a range of connection between a source device transmitting content data and a sink device receiving the content data is restricted. Namely, a packet round trip time RTT between the source device and the sink device is measured, and only when the RTT is ranged within a restricted time period (7 milliseconds, for example), the source device authenticates the sink device and can transmit data to the sink device. In the Non-Patent Document 1, there is defined a method of determining a device to be connected and a method of key exchange based on an Authentication and Key Exchange (referred to as an AKE hereinafter).
Patent Document 1 discloses a packet round trip time measuring program according to a prior art.
Patent Document 1: Japanese patent laid-open publication No. JP-2006-270248-A.
Non-Patent Document 1: DTCP Volume 1, Supplement E, Mapping DTCP to IP, (Information Version), Hitachi, Ltd. et al., Revision 1.1, Feb. 28, 2005.
In the packet round trip time measuring program according to the prior art, it is assumed that the RTT is measured in a communication system which uses a communication protocol compliant with the IEEE802.11 standard for wireless LANs (Local Area Networks). The source device 201 of
However, in a wireless communication system for transmitting uncompressed video content data in a form of packet data, when the high-definition data of 1080/60i system is transmitted, the data transfer rate reaches about 1.5 Gbps, and when video data of 1080/60p system is transmitted, the transfer rate reaches about 3 Gbps. Accordingly, during the RTT measurement in the wireless communication system, problems will occur which will be described below with reference to
Referring to
With reference to
The wireless communication system of
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Further, in
The wireless signal transmitted from the receiver station 405 is received by the antenna 409, and thereafter, inputted to the uncompressed video wireless transmission module unit 403. After demodulating the wireless signal into a digital signal, the uncompressed video wireless transmission module unit 403 extracts the accepted response from the digital signal. The uncompressed video wireless transmission module unit 403 transmits the extracted accepted response command to the RTT measurement unit 402 via the transmission line 404. In this case, transmission of the accepted response command is delayed by delay time 507 caused by the transmission line 404 and the interface process performed by the communication interface.
It is to be noted that a packet of the RTT test command stores higher 80 bits of a hash value of a Kauth (authentication key) previously shared between the transmitter station 401 of a source device and the receiver station 405 of a sink device derived using SHA (Secure Hash Algorithm)-1. In this case, the hash value is a hash value of a sum of MK and a trial number N of the RTT measurement derived using the SHA. In addition, lower 80 bits of the hash value are stored in a packet of the accepted response. Namely, a data length of each of the RTT test command and the accepted response command is equal to 10 bytes.
In this case, in the DTCP, the RTT to be measured is defined as a time period from a timing when the source device transmits the RTT test command to the sink device to a timing when the source device receives an accepted response command from the sink device, which transmits the accepted response command to the source device after receiving the RTT test command (See
Referring to
It is an object of the present invention to provide a method of measuring the RTT and a wireless communication system using the same, each capable of solving the above-mentioned problems and measuring an RTT between a source device and a sink device surely and accurately as compared with the prior art.
According to a first aspect view of the invention, there is provided a method of measuring a packet round trip time RTT for a wireless communication system for wirelessly transmitting content data from a source device to a sink device in a form of packets. The wireless communication system includes band management means for performing band management for wireless transmission of the packets. The source device includes first controller means for controlling wireless communication with the sink device. When the first controller means measures a packet round trip time RTT to the sink device, the first controller transmits a band width request command signal for requesting allocation of bands for round trip packets to the band management means. In response to the band width request command signal, within a predetermined frame period, the band management means allocates a first reservation period for transmitting a first packet from the source device to the sink device and a second reservation period for sending back a second packet from the sink device to the source device, and notifies the first controller means of the first reservation period and the second reservation period. The first controller means transmits the first packet and starts measuring the packet round trip time RTT at a first timing, which is a start timing of the first reservation period, finishes measuring the packet round trip time RTT at a second timing when the first controller receives the second packet, and calculates the packet round trip time RTT based on a time difference between the first timing and the second timing.
In the above-mentioned method of measuring the packet round trip time RTT, the band management means preferably allocates a third reservation period and a fourth reservation period for transmitting the content data within the frame period, and allocates the first reservation period and the second reservation period between the third reservation period and the fourth reservation period so that the second reservation period is subsequent to the first reservation period.
In addition, in the above-mentioned method of measuring the packet round trip time RTT the band management means preferably previously retains a predetermined time period for allocating the first reservation period and the second reservation period therein within the frame period, and allocates the first reservation period and the second reservation period into the predetermined time period so that the second reservation period is subsequent to the first reservation period.
Further, in the above-mentioned method of measuring the packet round trip time RTT the band management means preferably allocates a third reservation period and a fourth reservation period for transmitting the content data before and after the predetermined time period, respectively.
Still further, in the above-mentioned method of measuring the packet round trip time RTT, after finishing measuring the packet round trip time RTT, the first controller means preferably transmits a band release request command signal for requesting release of the first reservation period and the second reservation period to the band management means, and, in response to the band release request command signal, the band management means releases the first reservation period and the second reservation period, and retains the released first and second reservation periods for measurement of a packet round trip time RTT between the other devices in the wireless communication system.
In addition, in the above-mentioned method of measuring the packet round trip time RTT as claimed, the sink device preferably includes second controller means for controlling the wireless communication with the source device, and, in response to the first packet from the source device, the second controller means transmits the second packet to the first controller means.
Further, in the above-mentioned method of measuring the packet round trip time RTT the second controller means preferably generates the second packet before the sink device receives the first packet from the source device.
Still further, in the method of above-mentioned measuring the packet round trip time RTT the source device preferably further includes third controller means for performing a predetermined copyright protection process on the content data, the third controller means transmits an RTT measurement request command signal for requesting start of measurement of the packet round trip time RTT to the sink device to the first controller means, and, in response to the RTT measurement request command signal, the first controller means transmits the bandwidth request command signal to the band management means.
In addition, in the above-mentioned method of measuring the packet round trip time RTT the sink device preferably further includes fourth controller means for performing a predetermined copyright protection process on the content data, the fourth controller means transmits an RTT response setting request command signal for requesting generation of the second packet to the second controller means, and, in response to the RTT response setting request command signal, the second controller means generates the second packet.
According to a second aspect view of the present invention, there is provided a wireless communication system for wirelessly transmitting content data from a source device to a sink device in a form of packets. The wireless communication system includes band management means for performing band management for the wireless transmission of the packets. The source device includes first controller means for controlling wireless communication with the sink device. When the first controller means measures a packet round trip time RTT to the sink device, the first controller transmits a band width request command signal for requesting allocation of bands for round trip packets to the band management means. In response to the band width request command signal, within a predetermined frame period, the band management means allocates a first reservation period for transmitting a first packet from the source device to the sink device and a second reservation period for sending back a second packet from the sink device to the source device, and notifies the first controller means of the first reservation period and the second reservation period. The first controller means transmits the first packet and starts measuring the packet round trip time RTT at a first timing, which is a start timing of the first reservation period, finishes measuring the packet round trip time RTT at a second timing when the first controller receives the second packet, and calculates the packet round trip time RTT based on a time difference between the first timing and the second timing.
In the above-mentioned wireless communication system, the band management means preferably allocates a third reservation period and a fourth reservation period for transmitting the content data within the frame period, and allocates the first reservation period and the second reservation period between the third reservation period and the fourth reservation period so that the second reservation period is subsequent to the first reservation period.
In addition, in the above-mentioned wireless communication system, the band management means preferably previously retains a predetermined time period for allocating the first reservation period and the second reservation period therein within the frame period, and allocates the first reservation period and the second reservation period into the predetermined time period so that the second reservation period is subsequent to the first reservation period.
Further, in the above-mentioned wireless communication system, the band management means preferably allocates a third reservation period and a fourth reservation period for transmitting the content data before and after the predetermined time period, respectively.
Still further, in the above-mentioned wireless communication system, after finishing measuring the packet round trip time RTT, the first controller means preferably transmits a band release request command signal for requesting release of the first reservation period and the second reservation period to the band management means, in response to the band release request command signal, the band management means releases the first reservation period and the second reservation period, and retains the released first and second reservation periods for measurement of a packet round trip time RTT between the other devices in the wireless communication system.
In addition, in the above-mentioned wireless communication system, the sink device preferably includes second controller means for controlling the wireless communication with the source device, and, in response to the first packet from the source device, the second controller means transmits the second packet to the first controller means.
Further, in the above-mentioned wireless communication system, the second controller means preferably generates the second packet before the sink device receives the first packet from the source device.
Still further, in the above-mentioned wireless communication system, the source device preferably further includes third controller means for performing a predetermined copyright protection process on the content data, the third controller means transmits an RTT measurement request command signal for requesting start of measurement of the packet round trip time RTT to the sink device to the first controller means, and, in response to the RTT measurement request command signal, the first controller means transmits the bandwidth request command signal to the band management means.
In addition, in the wireless communication system, the sink device preferably further includes fourth controller means for performing a predetermined copyright protection process on the content data, the fourth controller means transmits an RTT response setting request command signal for requesting generation of the second packet to the second controller means, and, in response to the RTT response setting request command signal, the second controller means generates the second packet.
According to the method of measuring the RTT and the wireless communication system using the same according to the present invention, the source device includes first controller means for controlling a wireless communication with the sink device, and when the first controller means measures a packet round trip time RTT to the sink device, the first controller transmits a band width request command signal for requesting allocation of bands for round trip packets to the band management means. In response to this, within a predetermined frame period, the band management means allocates a first reservation period for transmitting a first packet from the source device to the sink device and a second reservation period for sending back a second packet from the sink device to the source device, and notifies the first controller means of the first reservation period and the second reservation period. The first controller means transmits the first packet and starts measuring the packet round trip time RTT at a first timing, which is a start timing of the first reservation period, finishes measuring the packet round trip time RTT at a second timing when the first controller receives the second packet, and calculates the packet round trip time RTT based on a time difference between the first timing and the second timing. Therefore, as compared with the prior art, it is possible to measure the packet round trip time RTT accurately and surely.
Embodiments of the present invention will be described hereinafter with reference to the drawings. In the embodiments, components similar to each other are denoted by the same reference numerals.
The method of measuring the packet round trip time RTT and the wireless communication system using the same according to the first embodiment are characterized as follows. A source device 10 includes a controller 13 for controlling wireless communication with a sink device 20. When the controller 13 measures the packet round trip time RTT to the sink device 20, the controller 13 transmits a bandwidth request command signal for requesting allocation of bands for round trip packets to a band management unit 28. In response to this, within a super frame period, the band management unit 28 allocates a reservation period CTBt for transmitting a packet including the RTT test command from the source device 10 to the sink device 20 and a reservation period CTBr for transmitting back a packet including the RTT response command from the sink device 20 to the source device 10, and notifies the controller 13 of the reservation periods CTBt and CTBr. The controller 13 transmits the packet including the RTT test command and starts measuring the packet round trip time RTT at a first timing which is a start timing of the reservation period CTBt, finishes measuring the packet round trip time RTT at a second timing when the controller 13 receives the packet including the RTT response command, and calculates the packet round trip time RTT based on a time difference between the first and second timings.
First of all, there will be described below configurations of the source device 10 and the sink device 20 connected to each other via a wireless communication line of a wireless communication network of a wireless video area network (referred to as a WVAN hereinafter), and operations of the source device 10 and the sink device 20.
Referring to
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In addition, in
In this case, the array antenna apparatus 17 includes a plurality of antenna elements, a duplexer for separating transmitted and received signals, a plurality of phase shifters each shifting a phase of each of the received wireless signal and the wireless signal to be transmitted by a predetermined phase shifting amount, a signal combiner for combining a plurality of phase-shifted wireless signals, and a signal divider for dividing the wireless signal to be transmitted into a plurality of wireless signals. The array antenna apparatus 17 has a low-rate physical layer (referred to as an LRP hereinafter) mode of performing wireless communication using a 60 GHz-band. An index (identifier) of transmission mode of the LRP mode is 0. The LRP mode includes (a) an omni-directional transmission LRP mode (referred to as an omni LRP mode or an LRP omni-directional mode hereinafter), and (b) a directional transmission LRP mode (referred to as an LRP directional mode hereinafter). In the LRP omni-directional mode, the controller 13 transmits a wireless signal with controlling the respective phase shifters so as to direct a main beam of the array antenna apparatus 17 to eight predetermined directions sequentially. On the other hand, in the LRP directional mode, the controller 13 transmits a wireless signal with controlling the respective phase shifters so as to direct the main beam of the array antenna apparatus 17 to one predetermined direction.
Referring to
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Referring to
Referring to
Next, referring to
In a packet communication in the wireless communication network of
In the frame format of
Next, a method of reserving the reservation periods CTBt and CTBr will be described. First of all, in the contention period RATB, the controller 13 of the source device 10 generates a bandwidth request command and transmits the bandwidth request command to the band management unit 28 in the controller 21 of the sink device 20 (referred to as a band management unit 28 hereinafter) so as to request allocation of the reservation periods CTBt and CTBr and to reserve the reservation periods CTBt and CTBr. As shown in
Packets formed in the LRP mode are normally used for the RTT measurement. Referring to
Referring to
It is to be noted that the band management unit 28 may allocate the reservation periods TBav1 and TBav2 for transmitting the AV data, and allocate the reservation periods CTBt and CTBr between the reservation periods TBav1 and TBav2 so that the reservation period CTBr is subsequent to the reservation period CTBt. With this configuration, the buffer capacities of the buffer memory 15m of the source device 10 and the buffer memory 26m of the sink device 20 can be minimized, and it is possible to decrease the probability of overflow and underflow of video and audio data, as compared with the prior art.
Next, referring to
Referring to
d=8×N/2.542(microseconds) [Equation 1]
In this case, N denotes a data amount of the packet body 45. For example, if the data amount N of the packet body 45 is 20 octets (which is a typical length of the packet body 45 including an MAC command header, a content protection header, and a payload), the time length d of the packet body 45 becomes 62.9 microseconds. Therefore, each of the time length required for the packet of the RTT test command and the time length required for the packet of the RTT response command packet becomes 163.6 microseconds (=42.4+7.9+25.2+12.6+62.9+12.6). Therefore, in the parameters included in the bandwidth request command (See
Next, referring to
On the other hand, in the sink device 20 of the RTT acceptor, the controller 23 of the content protection entity transmits an RTT response setting request command (RTT_REPLY_SET.req) for requesting the controller 21 to generate the RTT response command to the controller 22. In response to this, the controller 22 transmits an RTT response setting request command (MLME_SET_RTT_REPLY.req) for requesting the controller 21 to generate the RTT response command to the controller 21. In response to this, the controller 21 previously generates the RTT response command before the controller 21 receives the RTT test command from the source device 10. Thereafter, upon receiving the RTT test command at a timing t21, the controller 21 wirelessly transmits the generated RTT response command to the source device 10 at a timing t22 in the allocated reservation period CTBr. Further, the controller 21 transmits an RTT response setting confirmation command (MLME_SET_RTT_REPLY.cfm) for notifying the controller 23 that the RTT response command has been transmitted to the source device 10 to the controller 22. In response to this, the controller 22 transmits an RTT response setting confirmation command (RTT_REPLY_SET.cfm) for notifying the controller 23 that the RTT response command has been transmitted to the source device 10 to the controller 23.
Referring to
On the other hand, after finishing measuring the RTT at the timing t13, the controller 13 wirelessly transmits a band release request command for requesting release of the reservation periods CTBt and CTBr to the controller 21 of the sink device 20 in the contention period RATB. In response to this, the band management unit 28 of the controller 21 performs a predetermined band release process for releasing the reservation periods CTBt and CTBr for RTT measurement performed by the other devices in the WVAN, and wirelessly transmits a band release notification response command notifying the source device 10 of the release of the reservation periods CTBt and CTBr to the source device 10. Further, the band management unit 28 notifies the release of the reservation periods CTBt and CTBr using the beacon signal. The band management unit 28 retains the reservation periods CTBt and CTBr for measurement of RTT between the other devices in the WVAN, and for measurement of RTT by the source device 10 for a device other than the sink device 20 in the WVAN. In this case, the band management unit 28 does not allocate reservation periods (the reservation periods for the AV data, for example) other than the reservation periods CTBt and CTBr within the retained period. Therefore, as compared with the prior art, it is possible to measure the RTT surely.
As mentioned above, the controller 13 starts measuring the RTT by activating the timer circuit 13t at the timing t11 (substantially corresponding to the start timing of the reservation period CTBt) just before the start timing of the reservation period CTBt allocated to the source device 10. Further, the controller 13 finishes measuring the RTT by stopping the timer circuit 13t at the timing t13 when the controller 13 receives the RTT response command. Further, the controller 13 calculates the RU based on the time difference between the timing t13 and the timing t11. Therefore, MAC access delay time, which is the transmission delay time 501 and 507 included in the time RTT measured by the RTT measurement unit 402 according to the prior art of
In addition, in the measurement of the RTT, the RTT acceptor needs to transmit the RTT response command to the RTT initiator as soon as possible after the RTT test command has arrived to the RTT acceptor to meet a processing time constraint (for example, several milliseconds or less) of the RTT acceptor specified in a content protection specification such as the DTCP. According to the present embodiment, the reservation period CTBr in which the sink device 20 of the RTT acceptor transmits the RTT response is allocated to be adjacent to and after the reservation period CTBt in which the source device of the RTT initiator transmits the RTT test command as shown in
Further, the controller 23 of the content protection entity of the sink device 20 requests the controller 21 via the controller 22 to generate the RTT response command before receiving of the RTT test command. In response to this, the controller 21 generates the RTT response command before receiving of the RTT test command. Therefore, upon receiving the RTT test command, the controller 21 can promptly transmit the RTT response command as compared with the prior art. In addition, the RTT measured by the method of measuring the RTT according to the present embodiment substantially does not include the transmission delay time 503 and 505, and the processing time 504 included in the time RTTm measured by the RTT measurement unit 402 according to the prior art of
In the present embodiment, after releasing the reservation periods CTBt and CTBr, the band management unit 28 retains the reservation periods CTBt and CTBr for measurement of RTT between the other devices in the WVAN, and for measurement of RTT by the source device 10 for a device other than the sink device 20 in the WVAN. However, the present invention is not limited to this, and, after releasing the reservation periods CTBt and CTBr, the band management unit 28 may retain the predetermined time period Tpre for measurement of RTT between the other devices in the WVAN, and for measurement of RTT by the source device 10 for a device other than the sink device 20 in the WVAN. In addition, the predetermined time period Tpre may be used to transmit the audio and video data. In this case, in such a case where a device in the WVAN performs the RTT measurement, a time period other than the predetermined time period Tpre may be reserved for the RTT measurement, or the predetermined time period Tpre which is used for transmission of the audio and video data may be released for the RTT measurement.
Referring to
According to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to measure the RTT surely and accurately as compared with the prior art, in a manner similar to that of the method of measuring the RTT and the wireless communication system according to the first embodiment.
As compared with the wireless communication system of
According to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to measure the RTT surely and accurately as compared with the prior art, in a manner similar to that of the method of measuring the RTT and the wireless communication system according to the first embodiment.
Referring to
Next, a method of reserving the reservation periods CTBt and CTBr will be described. First of all, the controller 13 of the source device 10 generates the bandwidth request command, and transmits the bandwidth request command to the band management unit 28 provided in the controller 31 of the coordinator device 30 within the contention period RATB, so as to request allocation of the reservation periods CTBt and CTBr and to reserve the reservation periods CTBt and CTBr, in a manner similar to that of the controller 13 of
According to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to measure the RTT surely and accurately as compared with the prior art, in a manner similar to that of the method of measuring the RTT and the wireless communication system according to the first embodiment.
In the first to fourth embodiments, an antenna apparatus, directivity of which can be changed, such as an ESPAR can be used in stead of each of the array antenna apparatuses 17, 24, and 33.
Referring to
The wireless communication system according to the present embodiment is characterized by providing the RTT measurement unit 604 of the transmitter station 601 in the uncompressed video transmission wireless module unit 603 of the transmitter station 601, and by providing the RTT response transmitter unit 614 of the receiver station 611 in the uncompressed video transmission wireless module unit 613 in a manner similar to that of the RTT measurement unit 604. Therefore, since the RTT measurement unit 604 is provided in the uncompressed video module unit 603, the RTT measurement unit 604 can transmit an RTT test command (RTT_TEST.CMD) and start measuring the RTT at a timing the same as a start timing of the contention time period 303 (shown in
Next, referring to
Referring to
In response to the RTT_TEST.CMD 114, the RTT response transmitter unit 614 performs a predetermined process requiring a processing time 115, and transmits the ACCEPTED.RSP 116 to the transmitter station 601 without transferring the received RTT_TEST.CMD 114 to the DTCP command transceiver unit 612. Upon receiving the ACCEPTED.RSP 116, the RTT measurement unit 604 stops the timer circuit, and transmits a command including an MT measurement completion notification 117 which includes a timer value measured by the timer circuit to the DTCP command transceiver unit 602.
The DTCP command transceiver unit 602 calculates the RTT based on the timer value included in the received RTT measurement completion notification 117, and determines whether or not the RTT is equal to or less than 7 milliseconds. As a result, when the RTT is equal to or less than 7 milliseconds, the DTCP command transceiver unit 602 determines that the receiver station 611 is a device satisfying a condition required for the packet round trip time RTT according to the DTCP, and the process goes to a next step of an authentication process of authenticating the receiver station 611.
When the RTT is greater than 7 milliseconds, the RTT is measured again. When the WIT value is not equal to or less than 7 milliseconds even when the RTT is measured 1024 times, the DTCP command transceiver unit 602 determines that the receiver station 611 is a device that does not satisfy the condition required for the RTT according to the DTCP, the authentication process is finished, and the process does not go to the next step of the authentication process.
In this case, the time RTT measured by the method of measuring the RTT according to the prior art of
According to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to measure the RTT that does not include the communication time 501, 503, 505, and 507 spent in the transmitter station 601 and the receiver station 611, since the RTT measurement unit 604 is provided in the uncompressed transmission wireless module unit 603, and the RTT response transmitter unit 614 is provided in the uncompressed video transmission wireless module unit 613. In addition, since the uncompressed video transmission wireless module unit 603 holding information on the start timing of the contention time period 303, it is possible to measure the RTT that does not include the waiting time 502 and 506 for waiting the contention time period. Namely, since the waiting time 113 in which the transmitter station 601 waits the contention time period 303 is not substantially included in the measured RTT, it is possible to greatly remove the transmission delay time added to the RTT and accurately measure the RTT as compared with the prior art. Further, by inserting a packet including the RTT_TEST.CMD 114 and a packet including the ACCEPTED.RSP 116 into one contention time period 303, the delay time added to the RTT can be removed therefrom. Therefore, according to the method of measuring the RTT according to the present embodiment, it is possible to measure the RTT accurately as compared with the prior art. Accordingly, it is possible to measure the accurate RTT value equal to or less than 7 milliseconds to, for example, the device erroneously determined as the device to which the RTT is greater than 7 milliseconds by the method of measuring the RTT according to the prior art.
In addition, according to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to reduce the communication time in the receiver station 611 since the RTT response transmitter unit 614 of the receiver station 611 does not need to transmit the received RTT_TEST.CMD 114 to the DTCP command transceiver unit 612. In addition, the RTT response transmitter unit 614 can send back the ACCEPTED.RSP 116 immediately in the contention time period 303 in which the RTT_TEST.CMD 114 is transmitted to the RTT response transmitter unit 614. It is to be noted that this contention time period 303 may be either retained only at the time of the RTT measurement or always set.
Four methods of reducing a time length of the contention time period 303 used for the RTT measurement will next be described.
The first method includes setting the packet including the RTT_TEST.CMD 114 and the packet including the ACCEPTED.RSP 116 to packets which do not require a receipt acknowledgement. Therefore, the receiver station 611 or transmitter station 601 receiving the above-mentioned packets can transmit a next packet without transmitting a receipt acknowledgement packet. Accordingly, it is possible to reduce time spent transmit the receipt acknowledgement packet in the contention time period 303.
The second method includes, in the receiver station 611 which receives the RTT_TEST.CMD 114, transmitting a receipt acknowledgement packet in response to the RTT_TEST.CMD 114 which includes information on the ACCEPTED.RSP 611. Generally speaking, although the receipt acknowledgement packet does not include any data, this method can be realized by providing a data portion in the receipt acknowledgement packet. In this case, it is also possible to reduce a back-off period and an SIFS period required until the receiver station 611 transmits the receipt acknowledgement packet in the contention time period 303.
The third method includes transmitting the RTT_TEST.CMD 114 and the ACCEPTED.RSP 116 using beam packets. In the wireless communication system according to the present embodiment, it is possible to use a directional packet (a beam-formed packet) and an omni-directional packet (an omni packet), and preamble lengths of the both packets are different from each other. Since the preamble length of the beam formed packet is shorter than that of the short omni packet, it is possible to reduce the time length of the contention time period 303 used for the RTT measurement.
The fourth method includes removing back-off waiting time generated when the RTT_TEST.CMD 114 and the ACCEPTED.RSP 116 are transmitted. Generally speaking, when a packet is transmitted in the contention time period 303, transmission waiting time (back-off period) is set. This transmission waiting time is provided for collision avoidance according to CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol. It is designed to avoid such a case as much as possible where a plurality of stations transmit packets simultaneously and the packets collide with each other by setting this waiting time. However, by giving priorities to packets to be transmitted, this back-off period can be removed. Concretely speaking, for example, priorities of 1 to 3 are given to packets, respectively, the packet having the priority 1 is assumed as a highest priority packet, the packet having the priority 3 is assumed as a lowest priority packet, and the packet having the priority 2 is assumed as a packet having an intermediate priority between the highest and lowest priorities. Further, priorities of the packet including the RTT_TEST.CMD 114 and the packet including the ACCEPTED.RSP 116 are set to the highest priority 1. In this case, by designing the MAC so that a packet having the priority 1 can be transmitted without any back-off period, the RTT_TEST.CMD 114 and the ACCEPTED.RSP 116 can be transmitted without any back-off periods, and the time length of the contention time period 303 used for the RTT measurement can be reduced.
As mentioned above, the time length of the contention time period 303 used for the RTT measurement can be reduced, and the RTT can be measured accurately as compared with the prior art without unnecessarily extending the contention time period 303.
According to the method of measuring the RTT and the wireless communication system according to the present embodiment, it is possible to measure the RTT accurately when content data including video data copyrighted by the DTCP are transmitted using the uncompressed video transmission wireless system. Accordingly, as compared with the prior art, it is possible to accurately detect devices which meet a requirement that the packet round trip time RTT between a source device and a sink device is equal to or less than 7 milliseconds. In this case, the above-mentioned requirement is a constraint for transmitting content data including the contents of moving images copyrighted by the DTCP. Therefore, the method of measuring the RTT and the wireless communication system according to the present embodiment are useful for transmitting content data copyrighted using the DTCP in the uncompressed video transmission wireless system.
In the present embodiment, communication packets related to the RTT measurement are transmitted and received in the contention time period 303. Alternatively, a non-contention time period may be reserved and used for RTT communication packets (corresponding to the packets including the RTT_TEST.CMD 114 and the packet including the ACCEPTED.RSP 116). Concretely speaking, before starting the AKE operation according to the DTCP or before measuring the RTT, the transmitter station 601 reserves a part of the non-contention time period for RTT communication packets, and transmits the RTT communication packets in the reserved non-contention time period. After finishing the measurement of the RTT or after finishing the AKE operation, the transmitter station 601 requests the coordinator device for performing the band management for the wireless communication system to release the reserved non-contention time period.
As described above in detail, according to the method of measuring the RTT and the wireless communication system using the same according to the present invention, the source device includes first controller means for controlling a wireless communication with the sink device, and when the first controller means measures a packet round trip time RTT to the sink device, the first controller transmits a band width request command signal for requesting allocation of bands for round trip packets to the band management means. In response to this, within a predetermined frame period, the band management means allocates a first reservation period for transmitting a first packet from the source device to the sink device and a second reservation period for sending back a second packet from the sink device to the source device, and notifies the first controller means of the first reservation period and the second reservation period. The first controller means transmits the first packet and starts measuring the packet round trip time RTT at a first timing, which is a start timing of the first reservation period, finishes measuring the packet round trip time RTT at a second timing when the first controller receives the second packet, and calculates the packet round trip time RTT based on a time difference between the first timing and the second timing. Therefore, as compared with the prior art, it is possible to measure the packet round trip time RTT accurately and surely. In particular, the present invention is applicable to RTT measurement for transmission of content data to be copyrighted in a wireless communication system compliant with the wireless communication standard such as a WirelessHD (Wireless High-Definition).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-014851 | Jan 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/051088 | 1/25/2008 | WO | 00 | 7/24/2009 |
