JP4708293B2 - COMMUNICATION DEVICE, COMMUNICATION METHOD, COMMUNICATION PROGRAM, AND RECORDING MEDIUM CONTAINING COMMUNICATION PROGRAM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a telecommunication apparatus capable of performing more exact time synchronization of a clock means in each telecommunication apparatus in the telecommunication apparatus constituting a telecommunication system which performs a transmission in a plurality of telecommunication devices. <P>SOLUTION: When the reception of a frame (TF) is recognized at the moment of multicast being carried out from a first telecommunication device 1 by a TF acknowledgement portion 30, a sampler 40 samples the time at that time, and this is set to tTX. A framer 50 creates the synchronous frame (SF) containing the sampled tTX, and transmits to a tertiary telecommunication device 3. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a communication device, a communication method, a program, and a computer-readable recording medium on which a program is recorded, for communicating frames that require synchronization.

  Conventionally, a communication network including a plurality of terminal devices is known. FIG. 12 is a diagram showing an example of such a communication network. In the figure, the communication network 70 includes a terminal device 71, a terminal device 72, and a terminal device 73. The terminal device 71 includes a communication device 81, the terminal device 72 includes a communication device 82, and the terminal device 73 includes a communication device 83.

  A situation will be considered below in which the terminal device 71 transmits to the terminal devices 72 and 73 stream data such as video data and audio data that is required to be guaranteed in real time. Each of the communication devices 81 to 83 has a clock which becomes a reference when reproducing video data and audio data, and the clock usually swings within the accuracy range of the crystal oscillator. If the progress of the clock when the oscillation frequency of the crystal oscillator has the nominal value is called a standard clock, as shown in FIG. 13, the actual clock progress of the communication device is the progress of the standard clock. It is faster or slower than the degree. Further, the degree of advancement of the timepiece of the communication device is usually different for each communication device 81-83. Therefore, as shown in FIG. 14, the time differs between the communication devices.

  However, for example, taking a situation where video data is transmitted to the communication device 82 and audio data is transmitted to the communication device 83 in real time, the communication device 82 and the communication device 83 are synchronized with each other with high accuracy. Obviously there is a need to do that. Specific methods for realizing this include synchronizing both the communication device 82 and the communication device 83 with the communication device 81, synchronizing the communication device 83 with the communication device 82, and communicating with the communication device 82. A method of synchronizing with the device 83 is conceivable. In the following description, the “clock of the terminal device” indicates the clock of the communication device in the terminal device.

  There are proposals of Non-Patent Document 2 and Patent Document 1 as a method in which upper layers synchronize with each other on a wireless LAN (Local Area Network) in accordance with the standard of IEEE 802.11 (Non-Patent Document 1).

  Each upper layer has an upper layer level clock, and one communication device serves as a clock master at the upper layer level as means for synchronizing them with each other. As shown in FIG. 15, the clock master periodically samples its own clock, puts the sampled time in a multicast frame for synchronization (frame identifier information is denoted as n), and transmits it to a communication device that wants to share the clock. To do. The clock master can know the timing of the instant when the local station transmits or receives the tail of the multicast frame for synchronization, and records the time of the upper layer clock (denoted as tTX [n]) at that moment.

  Further, the non-clock master communication device can know the timing of the moment when the last part of the frame is received, and records the time of the upper layer clock (denoted as tRX [n]) at that moment. The timing at which the last part of the frame is transmitted or received needs to be designed so that the wireless LAN layer can accurately notify the upper layer.

  The clock master puts the synchronization multicast frame identifier information n and tTX [n] sent by itself in the next synchronization multicast frame (the frame identifier information is n + 1) to the non-clock master communication device. Send to. When the non-clock master communication device receives the synchronization multicast frame with the identifier (n + 1), the information of tTX [n] embedded therein and the tRX [ n] can be compared to compare the clock values of the upper layers of both stations at the moment when both stations received the synchronization multicast frame having the identifier n.

Since multicast frames are transmitted using a method that does not involve acknowledgment (ACK), it can be assumed that the time when both stations received the same frame is almost the same. It is possible to know whether it is early or late with respect to the clock master, and based on that, it is possible to adjust the clock of the local station to the clock of the clock master.
IEEE Std 802.11 (January 1999) IEEE Std 802.11e Draft 13 (January 2005) US Patent Application 200301172179 (release date: September 11, 2003)

  However, when one synchronization multicast frame (n-th) is not received correctly, both the previous (n−1) tTX [n−1] information included therein and tRX [n] The value cannot be known, and as a result, the clock is adjusted twice (tTX [n-1] and tRX [n-1] and tTX [n] and tRX [n]) continuously. There was a problem of being unable to.

  For example, FIG. 16 shows a case where the clock of a non-clock master is adjusted using a PLL. The horizontal axis in the figure is time, and the vertical axis is the difference between the clock master and the non-clock master clock. In the figure, (1) is able to adjust the clock (PLL) without any problems at all timings, (2) is not able to adjust once at the timing of T3, (3) Shows the case where the adjustment cannot be made at the timing of T3 and T4 twice, and the figure shows how much the difference between the clocks of both stations is affected in each case Yes. As can be seen from the figure, the time difference between the clock master and the non-clock master increases with the number of adjustments that cannot be made.

  Further, when the synchronization method of Patent Document 1 is used for IEEE802.11e, a communication device that can transmit a multicast frame in the wireless LAN layer is limited to an AP (Access Point) that is a central station. For this reason, when the clock master is not an AP, the clock master first transmits a multicast frame for synchronization to the AP, and the AP needs to multicast the received frame to all stations again. That is, multicast communication is performed in two steps, and there is a problem that a bandwidth for that is wasted.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to further synchronize time of clock means in each communication device in a communication device constituting a communication system in which a plurality of communication devices communicate. An object of the present invention is to provide a communication device, a communication method, a communication program, and a recording medium recording the communication program that can be accurately performed.

  In order to solve the above problem, a communication device according to the present invention is a communication device that constitutes a communication system in which a plurality of communication devices are connected to each other via a communication network, and includes a clock unit that indicates time, A first frame recognizing means for detecting reception or transmission of a specific first frame transmitted without requiring delivery confirmation to a plurality of communication devices in a communication network; and the first frame on the transmitting side. Time detecting means for determining the first frame detection time when the reception or transmission of the first frame is detected by the recognition means based on the time indicated by the clock means; and a second including the first frame detection time information Second frame transmission means for transmitting a frame to an external communication device via the communication network in a state requiring delivery confirmation.

  The communication method according to the present invention is a communication method of a communication apparatus constituting a communication system in which a plurality of communication apparatuses are connected for communication via a communication network. The transmission side first frame recognition step for detecting the reception or transmission of the specific first frame transmitted and the transmission side first frame recognition step and the first frame reception time when the reception or transmission of the first frame is detected. A time detection step for determining one frame detection time based on a time indicated by a clock means included in the communication device, and a second frame including the first frame detection time information via an external communication device via the communication network A second frame transmission step of transmitting to the second frame.

  According to the above configuration or method, first, a specific first frame is transmitted to a plurality of communication devices. Here, the first frame may be transmitted by the communication apparatus or may be transmitted by another communication apparatus. Then, the second frame including the first frame detection time information at which the reception or transmission of the first frame is detected is transmitted to the external communication device. That is, the first frame is a frame for determining the timing for adjusting the time of the clock means in each communication device, and the second frame is a frame for exchanging the timing information.

  Conventionally, the multicast frame for synchronization has the above two roles, that is, the function of specifying the reference time point for sampling the clock almost simultaneously and the function of transmitting the time of the sampled clock. Therefore, when the reception of the multicast frame for synchronization fails, there is a problem that the clock cannot be set twice, as described above, and the time difference between the clocks in each communication device becomes large.

  On the other hand, according to the above configuration or method, even if the transmission / reception of the first frame fails, the transmission / reception of the second frame is almost certainly performed by confirming the delivery. You don't have to do it once. Therefore, since it is possible to increase the possibility that the clock is set correctly, it is possible to provide a communication system in which the clocks in each communication device are more accurately synchronized.

  The communication device according to the present invention is a communication device that constitutes a communication system in which a plurality of communication devices are communicably connected via a communication network, and includes a clock means for indicating time and a plurality of communication devices in the communication network. Reception or transmission of the first frame is detected by the transmission side first frame recognition means for detecting reception or transmission of a specific first frame transmitted to the apparatus and the transmission side first frame recognition means. Time detection means for determining the first frame detection time based on the time indicated by the clock means and a second frame including the first frame detection time information to an external communication device via the communication network. And a second frame transmitting means for transmitting.

  According to the above configuration, when the first frame or the second frame is lost, the clock of the second communication device need not be adjusted only once. Therefore, as shown in FIG. 16 (details will be described later), the configuration of the present invention can provide a communication system in which time synchronization in each communication device is performed more accurately than the conventional configuration.

  The communication device according to the present invention may be configured such that, in the above configuration, the second frame is transmitted to an external communication device via the communication network in a state where delivery confirmation is required.

  According to the above configuration, when the second frame is lost, the second frame can be retransmitted, and the transmission of the second frame can be performed almost certainly. Therefore, since it is possible to increase the possibility that the clock is set correctly, it is possible to provide a communication system in which the clocks in each communication device are more accurately synchronized.

  The communication device according to the present invention may be configured such that, in the above configuration, the first frame is transmitted to a plurality of communication devices in a state that does not require delivery confirmation in the communication network. .

  According to the above configuration, for example, a broadcast or multicast frame can be used as the first frame.

  The communication device according to the present invention is a communication device that constitutes a communication system in which a plurality of communication devices are communicably connected via a communication network, and includes a clock means for indicating time and a plurality of communication devices in the communication network. The reception side first frame recognition means for detecting the reception or transmission of a specific first frame transmitted without requiring delivery confirmation to the device, and the reception side first frame recognition means Time detection means for determining the first frame detection time when reception or transmission of a frame is detected based on the time indicated by the clock means; and the second frame from the communication device according to the invention. Second frame receiving means for receiving via the network; first frame detection time information included in the second frame; and the first frame on the receiving side. Based on the first frame detection time detected by the recognizing means is configured to include an adjusting means for adjusting the time of the clock means.

  The communication device according to the present invention is a communication device that constitutes a communication system in which a plurality of communication devices are communicably connected via a communication network, and includes a clock means for indicating time and a plurality of communication devices in the communication network. Reception or transmission of the first frame is detected by the reception side first frame recognition means for detecting reception or transmission of the specific first frame transmitted to the apparatus and the reception side first frame recognition means. Time detection means for determining the first frame detection time at the time based on the time indicated by the clock means, and second time for receiving the second frame from the communication device according to the present invention via the communication network. Detected by the frame receiving means, the first frame detection time information included in the second frame, and the receiving-side first frame recognition means On the basis of the frame sensing time, which is configured to include an adjusting means for adjusting the time of the clock means.

  The communication method according to the present invention is a communication method of a communication apparatus constituting a communication system in which a plurality of communication apparatuses are connected for communication via a communication network. The reception side first frame recognition step for detecting the reception or transmission of the specific first frame transmitted and the reception side first frame recognition step and the first frame reception time when the reception or transmission of the first frame is detected. A time detection step for determining one frame detection time based on a time indicated by a clock means included in the communication device; and a second detection step for receiving the second frame from the communication device according to the present invention via the communication network. A two-frame receiving step, first frame detection time information included in the second frame, and the receiving-side first frame recognition Based on the first frame detection time detected by step, a method having an adjusting step of adjusting the time of the clock means.

  According to the above configuration or method, the timing for adjusting the time of the clock means is determined by the first frame, and it is possible to recognize how much the clock means should be adjusted by receiving the second frame. It becomes possible. Therefore, it is possible to accurately synchronize with the time of the clock means in the communication apparatus that has transmitted the second frame.

  The communication device according to the present invention may be configured such that, in the above configuration, the first frame is transmitted to a plurality of communication devices in a state that does not require delivery confirmation in the communication network. .

  According to the above configuration, for example, a broadcast or multicast frame can be used as the first frame.

  Further, the communication device according to the present invention may be configured such that, in the above configuration, the adjusting unit adjusts a parameter for setting a time of the clock unit and / or a parameter for adjusting a speed at which the clock of the clock unit advances. Good.

  According to the above configuration, when the clock means in the communication apparatus that has transmitted the second frame is out of synchronization with the clock means included in the own apparatus, the estimated value of the current time of the clock means in the own apparatus is directly By writing, time synchronization can be performed quickly. In addition, when the time of the clock means in the communication device that has transmitted the second frame is synchronized with the time of the clock means provided in the own device, the speed at which the clock of the clock means provided in the own device is advanced is finely adjusted. Can be kept in sync.

  The communication apparatus according to the present invention may be configured such that, in the above configuration, the transmission-side first frame recognition means detects reception or transmission of a specific portion of the first frame.

  The communication apparatus according to the present invention may be configured such that, in the above configuration, the receiving-side first frame recognition means detects reception or transmission of a specific portion of the first frame.

  According to the above configuration, synchronization can be performed using a specific portion of the first frame as a reference point. Therefore, the synchronization accuracy can be improved.

  In the communication apparatus according to the present invention, in the above configuration, the adjustment unit includes a buffer, and the buffer stores the first frame detection time up to the latest n (n ≧ 1). Also good.

  According to the above configuration, by using the buffer, it is possible to store up to n latest frame detection times (integers where n ≧ 1) that can be transmitted or received. For example, if the transmission of the second frame takes too long, the next first frame may be transmitted before the transmission of the second frame is completed. In this case, if n = 1, there is an option of deleting the previous first frame detection time or not recording a new first frame detection time, but in any case, the clock cannot be adjusted once. . On the other hand, if n ≧ 2, both the previous first frame detection time and the new first frame detection time can be recorded, and the clock can be adjusted for both. Therefore, the accuracy of synchronization can be prevented from deteriorating by setting n to the maximum delay of the second frame.

  In the communication device according to the present invention, in the configuration described above, the first frame includes an identifier for identifying the first frame, and the second frame transmission unit includes the second frame in the second frame. It may be configured to include the identifier of the first frame corresponding to the first frame detection time information included in the second frame.

  In the communication device according to the present invention, in the configuration described above, the first frame includes an identifier for identifying the first frame, and the second frame reception unit includes the first frame detection time information. The second frame including the identifier of the corresponding first frame is received, and the buffer stores the first n frame detection times and the combination of the identifiers up to the latest n (n ≧ 1). Good.

  According to the above configuration, by using the identifier, for example, when the first frame or the second frame is lost, the identifier of the first frame received by the device itself and the first frame detection included in the second frame are detected. By comparing the identifier corresponding to the time information, it is possible to easily recognize the association between the two.

  In the communication apparatus according to the present invention, in the above configuration, the adjustment unit searches the buffer for the same identifier as the identifier included in the received second frame, and when the same identifier exists in the buffer, the identifier (1) This time is initial When the second frame identifier is found in the buffer for the first time after conversion, or (2) ABS (tTX0-tRX0)> TH (ABS is an absolute value) (TH is a constant), the time of the clock means is set to (current Time-tRX0 + tTX0 + K (K is a constant)), and if the above condition (1) or (2) is not satisfied, Based on the RX0, may be configured to adjust the speed of travel of said clock means.

  According to the above configuration, the time of each clock means is set when the clock of the initial stage is set, when the second frame is continuously lost over a long period of time, or when the time of the clock means in each communication device is excessively shifted. Can be approached at once.

  Further, the communication device according to the present invention may be configured such that, in the above configuration, the adjustment unit stores a synchronized flag indicating whether or not the clock unit of the own device is synchronized.

  According to the above configuration, by using the synchronized flag indicating whether or not synchronization is achieved, the adjustment unit can perform a response suitable for the synchronization state, and can perform more accurate adjustment.

  The communication apparatus according to the present invention may be configured such that, in the above configuration, the synchronized flag is initialized to false at the time of reset.

  According to said structure, since it is a state which cannot synchronize in an initial state, this state can be represented at the time of reset.

  Further, in the communication apparatus according to the present invention, in the above configuration, the adjustment unit includes first frame detection time information included in the received second frame and all first frame detection times stored in the buffer. The first frame detection time with the smallest absolute value is selected, the selected first frame detection time is tRX0, the previous tRX0 is tRX1, and the first frame detection time information of the received second frame is tTX0. (1) When the absolute value of the difference is smaller than or equal to TH (TH is a constant), the speed at which the timepiece advances is adjusted based on tTX0 and tRX0 and the synchronization is completed. Set the flag to true and the condition (1) above is not met and the synchronized flag is false, or the condition (1) above is met And the synchronized flag is true and ABS (tTX0-tRX1)> TH1 (ABS is an absolute value) (TH1 is a constant), or the condition (1) is not satisfied and If the synchronized flag is true and ABS (tTX0−tTX1)> TH1, the time of the clock means is set to (current time of clock means−tRX0 + tTX0 + K (K is a constant)), and The synchronized flag may be set to false.

  According to the above configuration, since the identifier is not used, the LAN layer only needs to inform the upper layer of the moment when the first frame is transmitted or received. When the LAN layer and the upper layer are different chips, It is possible to reduce the implementation price of information to be exchanged between each other. The reasons why the price is cheap are as follows. When the identifier is used, it is necessary to notify the identifier from the LAN layer to the upper layer. Although it is possible to notify the identifier to the host using a normal PCI interface, the PCI interface cannot be used for advanced synchronization because various delays and jitters occur in the PCI interface. For this reason, it is necessary to prepare an interface having real-time characteristics separately. Since the upper layer chip and the wireless LAN chip are usually different chips, the number of pins of the chip increases and the design of the board becomes complicated. Usually, it is not desirable to increase the number of pins of a chip, and it is important to make an effort to reduce the price of the chip by reducing it as much as possible. In the case of a method that does not use an identifier, the signal line between the LAN layer chip and the upper layer chip, for example, rises for a certain time at the timing of transmitting or receiving the first frame, or the voltage level changes 1 All necessary information exchange can be achieved with only the signal lines of the book.

  The communication device according to the present invention may be configured such that, in the above configuration, the adjusting unit uses a PLL (Phase Locked Loop) for adjusting the clock unit.

  According to the above configuration, more accurate synchronization can be achieved by using the PLL.

  Moreover, the communication apparatus according to the present invention may be configured to support a wireless LAN (Local Area Network) or a PLC (Power Line Communication) in the above configuration.

  According to the above configuration, high-accuracy synchronization can be achieved even in a wireless LAN or PLC network environment.

  In the communication apparatus according to the present invention, the first frame may be a wireless LAN beacon frame.

  According to the above configuration, the second frame can be directly transmitted from the first communication device to the second communication device even when IEEE 802.11e is used as the transmission method. On the other hand, when the synchronization method of Patent Document 1 is used for IEEE802.11e and the clock master is not an AP, the multicast frame for synchronization needs to be transmitted in two steps. Therefore, under the above conditions, the transmission method of the present invention can perform synchronization using a smaller band. When IEEE802.11e is used, the first frame of the present invention can be a beacon frame, and both the present invention and Patent Document 1 need to transmit beacon frames periodically. The band used by the frame (beacon frame) is not an additional band.

  Further, the communication device according to the present invention corresponds to a wireless LAN (Local Area Network) in the above configuration, the first frame is a beacon frame of the wireless LAN, and the identifier is a TSF included in the beacon frame. (Timing Synchronization Function) A time stamp or sequence number of a timer may be used.

  According to the configuration described above, by using the identifier as the time stamp or sequence number of the TSF timer included in the beacon frame, it is possible to use the existing information standardized without defining a new frame as the identifier.

  The communication device may be realized by a computer. In this case, a communication program for causing the communication device to be realized by the computer by causing the computer to operate as the above-described means, and a computer-readable program that records the communication program. Various recording media are also within the scope of the present invention.

  The communication device according to the present invention, as described above, receives the clock means that indicates the time and the reception of the specific first frame transmitted in a state that does not require delivery confirmation to the plurality of communication devices in the communication network, Alternatively, the clock means indicates the first frame detection time when reception or transmission of the first frame is detected by the transmission side first frame recognition means for detecting transmission and the transmission side first frame recognition means. And second frame transmission means for transmitting a second frame including the first frame detection time information to an external communication device via the communication network in a state requiring delivery confirmation. It is the structure provided with.

  As a result, it is possible to increase the possibility that the clock is set correctly, and thus it is possible to provide a communication system in which the clocks in each communication device are more accurately synchronized.

  An embodiment of the present invention is described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of a communication system according to the present embodiment. As shown in the figure, the communication system includes a first communication device 1, a second communication device 2, and a third communication device 3. The first to third communication devices 1 to 3 are connected to each other via a network 210. FIG. 2 shows a communication sequence in the communication system.

  The first communication device 1 is a communication device that periodically transmits an instantaneous frame (TF: first frame) in a form without delivery confirmation. However, examples of transmission formats that do not accompany delivery confirmation include broadcast frames, multicast frames, and unicast frames that do not use ACK frames. Note that the instantaneous frame may be in a form with delivery confirmation.

  The TF is transmitted from the first communication device 1 at time T1, passes through the network 210, arrives at the third communication device 3 at T2, and arrives at the second communication device 2 at T3.

  Assuming, for example, a wireless LAN as a network, T2-T1 is a time until the radio wave reaches the third communication device 3 from the first communication device 1, and T3-T1 is a radio wave from the first communication device 1 to the second communication device. It is the time to reach 2. The radio wave normally moves about 30 cm in 1 ns.

  The second communication device 2 includes a TF recognition unit (transmission-side first frame recognition means) 30, a clock (clock means) 20, a sampler (time detection means) 40, and a framer (second frame transmission means) 50. It has become.

  In the second communication device 2, when the TF is received, the TF is recognized by the TF recognition unit 30, and the TF recognition unit 30 uses the specific part of the frame as a reference point, for example, at the beginning or the end of the frame, and the reference The sampler 40 is recognized and notified to the sampler 40, and the sampler 40 samples the time of the clock 20 as tTX at this moment. The framer 50 creates a synchronization frame (SF: second frame) including the sampled tTX, and the second communication device 2 transmits the SF to the third communication device 3 at time T6. The period from T3 to T5 is a fixed processing time required for the TF recognition unit.

  The SF arrives at the third communication device 3 through the network 210 at T7.

  The third communication device 3 includes a TF recognition unit (reception-side first frame recognition unit) 130, a clock (clock unit) 120, a sampler (time detection unit) 140, a framer (second frame reception unit) 150, and an adjustment unit ( (Adjustment means) 160 is provided.

  The third communication device 3 receives the same TF almost at the same time that the second communication device 2 receives the TF. The TF is recognized by the TF recognition unit 130 of the third communication device 3, and the TF recognition unit 130 recognizes the reference instant (T4) using a specific part of the frame as a reference point, for example, at the beginning or end of the frame. The sampler 140 samples the timepiece 120 as tRX at this moment, and tRX is passed to the adjustment unit 160. The period from T2 to T4 is a fixed processing time required for the TF recognition unit.

  Next, the SF transmitted by the second communication device 2 arrives at the third communication device 3 at T7. Here, the SF is passed to the framer 150, and the framer 150 extracts at least the value of tTX in the SF and passes it to the adjustment unit 160. Next, when the adjustment unit 160 receives at least information on tTX, the adjustment unit 160 performs an adjustment process for adjusting the parameters of the timepiece 120. Specific processing contents of the adjustment processing will be described later.

In the description so far, it is assumed that the clock master (second communication device 2) that receives the instantaneous frame transmits the synchronization frame immediately after that, and therefore, the non-clock master transmits the synchronization frame immediately after receiving the instantaneous frame. Although it is assumed that it is received, the timing at which the instantaneous frame / synchronization frame is actually transmitted is considered to change due to the following reasons.
(1) When the non-real-time OS (Operating System) is processing the second communication device 2 or the third communication device 3, and the processing time varies greatly.
(2) When the network is congested.
(3) When an error occurs in the transmission of the synchronization frame and it takes time to retransmit.

  Therefore, there may be a case where it is difficult to understand which instantaneous frame corresponds to a certain synchronization frame. However, this problem can be solved by storing a plurality of tRX values.

  For example, even if the transmission of a synchronization frame takes a long time and the next instantaneous frame is transmitted before the arrival of the synchronization frame corresponding to a certain instantaneous frame, the tTX value included in the synchronization frame that arrives late If the tRX value corresponding to is still in the buffer, the clock 120 can be adjusted without any problem.

  As described above, the adjustment unit 160 may use a buffer that can store the latest n (n ≧ 1 integer) TF data. The data includes at least tRX of the clock 120 sampled at the moment when the third communication device 3 transmits or receives TF.

  However, both stations have sufficiently accurate crystal oscillators, and it can be assumed that the corresponding tTX value and tRX value are very close to each other. At the same time as the tTX value, the master notifies the non-clock master of information on the identifier of the corresponding instantaneous frame, and it is assumed that the non-clock master stores the tRX value and the information of the identifier of the corresponding instantaneous frame. May be.

  If the buffer is full when data is stored, it is possible to refer to a newer sample result by deleting the oldest data in order to store the latest data.

  A specific example of this is shown in FIG. Here, TF1 of an instantaneous frame is first transmitted by the first communication device 1, and tTX1 and tRX1, which are sample values of the clock at the time when the TF1 is received by the second communication device 2 and the third communication device 3, respectively, are sampled. . In the third communication device 3, tRX1 is further stored in the buffer. Next, the second communication device 2 transmits SF1 for TF1, but it takes time to transmit this, and TF2 of the next instantaneous frame is transmitted by the first communication device 1 before SF1 arrives at the third communication device 3. Consider the case.

  In this case, tTX2 and tRX2, which are sample values of the clock at the time when TF2 is received by the second communication device 2 and the third communication device 3, are sampled, and tRX2 is stored in the buffer in the third communication device 3. After that, SF1 arrives at the third communication device 3 with a delay.

  In this case, tTX1 and tRX1 are required for the third communication device 3 to adjust the timepiece 120. If n = 1, tRX1 is deleted from the buffer when tRX2 is stored in the buffer, so this adjustment cannot be made and the synchronization accuracy of the clock deteriorates. However, if n = 2, the value of tRX1 is Since it is still in the buffer, the above adjustment can be performed. As is apparent from the above description, it is important that the value of n representing the size of the buffer be a value that can cover the degree of variation in the transmission delay of the synchronization frame. A method for searching for the corresponding tRX from the buffer when the SF is received will be described later.

  The second communication device 2 corresponds to the first communication device, and the third communication device 3 corresponds to the second communication device. In this embodiment, the TF recognition units 30 and 130 and the framers 50 and 150 correspond to communication means.

  The first communication device 1 and the second communication device 2 may be the same. In this case, the second communication device 2 does not receive the TF but transmits the TF, and the TF recognition unit 30 uses the specific part of the frame as a reference, for example, at the beginning or end of the frame, and The sampler 40 samples the moment of the reference point and samples the time of the clock 20 as tTX.

  Further, the first communication device 1 and the third communication device 3 may be the same. In this case, the third communication device 3 transmits TF instead of receiving TF, and the TF recognition unit 130 uses a specific part of the frame as a reference, for example, at the beginning or end of the frame, The sampler 140 samples the moment of the reference point and uses the time of the clock 120 as tRX.

  Note that there may be a plurality of communication devices (third communication device 3A, third communication device 3B,...) That align the clock with the second communication device 2. In this case, the second communication device 2 transmits TF to all these communication devices at the same time in a form without delivery confirmation, and then sends SF to each of these communication devices individually in a form with delivery confirmation. To transmit. The operations of the third communication device 3A, the third communication device 3B,... Are the same as those of the third communication device 3. Here, the second communication device 2 may simultaneously transmit TF to all these communication devices by broadcast or multicast. In addition, the SF may be a unicast frame with confirmation of delivery or a format without confirmation of delivery.

  In the same network, a subnetwork composed of a group of communication devices that synchronize the clock with the clock 20A of the second communication device 2A, and another subgroup composed of a communication device group that synchronizes the clock with the clock 20B of the second communication device 2B. A plurality of second communication devices 2 (a plurality of sub-networks) such as a network may exist.

  A PLL may be used to adjust the clock. By using the PLL, the shift of the timepiece 120 with respect to the timepiece 20 can be reduced.

  Note that the communication means of the first to third communication apparatuses 1, 2, and 3 may be, for example, an IEEE 802.11 wireless LAN or PLC. In this case, the first communication device 1 may be an AP and the TF may be a beacon frame.

(Embodiment 1)
One embodiment of the present invention will be described below. In the present embodiment, synchronization is performed using an identifier, and the third communication device 3 simply samples tTX and tRX at the same moment by comparing the identifier of the instantaneous frame with the identifier of the synchronous frame. It can be confirmed that it is the time. Note that the description of this embodiment is limited to the portion related to the identifier.

  First, it is assumed that an identifier such as a sequence number is included in the instantaneous frame (TF).

  When receiving the TF, the second communication device 2 reads the identifier from the TF. Next, a synchronization frame (SF) including the tTX value of the clock 20 sampled at the moment when TF is transmitted or received and the identifier is generated and transmitted to the third communication device 3.

  It is assumed that the adjustment unit 160 of the third communication device 3 has a buffer that can store a set of up to n (n ≧ 1 integers) latest tRX values and identifiers.

  When the third communication device 3 receives the TF, the tRX value and the identifier of the watch 120 sampled at the moment of receiving the TF are stored in the buffer. Next, when the third communication device 3 receives the SF, the tTX and the identifier are read from the SF, and the adjustment unit 160 searches the buffer for the same identifier as the SF identifier. If the SF identifier is found in the buffer, the adjustment unit 160 performs the following processing.

  First, the tRX value corresponding to the found identifier is stored in the register tRX0. Further, the tTX value included in the received SF is stored in the register tTX0, and the previous value of the register tTX0 is moved to the register tTX1. Next, if the SF identifier is found in the buffer for the first time after initialization, it is considered that the clocks of the second communication device 2 and the third communication device 3 are greatly deviated from each other. It is considered appropriate to perform control to write the estimated value of the current time of the clock 20 at the same time. Specifically, the time of the clock 120 is set to (current time of the clock 120−tRX0 + tTX0 + K (K is a constant)). Note that K is a constant representing the processing time from sampling the current time of the clock 120, performing the above calculation, and setting a value in the clock 120. When a PLL is used, it is preferable to initialize the PLL parameters under these conditions.

  In addition, even after the synchronization is established once, at least one of the second communication device 2 and the third communication device 3 cannot receive the instantaneous frame for a long time, or the third communication device 3 is synchronized for a long time. If the frame cannot be received, it may be desirable to perform control similar to the above to write the estimated value of the current time of the clock 20 to the clock 120 at once. The above determination can be made, for example, as ABS (tTX0-tRX0)> TH. However, ABS represents an absolute value.

  TH is a threshold value for confirming whether the clock 20 and the clock 120 are synchronized when SF is received. Guidelines for determining this threshold value are as follows.

  First, every time TF is transmitted, the time of the clock 20 and the clock 120 is sampled as tTX and tRX almost simultaneously, but tTX and tRX are not completely the same value. The reason for this is that the clock 20 and the clock 120 are not completely synchronized to indicate the same time, and the transmission time of the TF differs depending on the multipath phenomenon occurring in the propagation path and the transmission distance between the stations. (The radio wave moves about 30 cm in 1 ns). Therefore, when the clock 20 and the clock 120 are synchronized within a certain range, it is considered that the absolute value of the difference between tTX and tRX sampled for the same TF also falls within a certain error. For example, when the clock 20 and the clock 120 are synchronized within a range of 100 ns, TH may be set to about 1 μs with a margin. In this case, if the difference absolute value of (tTX−tRX) is equal to or less than TH, it can be determined that tTX and tRX are sampled by the same TF.

  Once synchronization is established, the clock 20 and the clock 120 are considered to be sufficiently close to each other. In this state, it is desirable to adjust the clock according to the policy of finely adjusting the speed of advance of the clock 120 from the information of tTX0 and tRX0, rather than writing the estimated value of the current time of the clock 20 to the clock 120. In this way, fluctuations in individual sample times are smoothed, and a smoother clock adjustment can be performed.

  Note that the communication means of the first to third communication devices 1, 2, and 3 is, for example, an IEEE 802.11 system, the first communication device 1 is an AP, and TF is a beacon frame, it is included in the beacon frame. The time stamp or sequence number of the TSF timer may be used as the identifier.

(Embodiment 2)
Another embodiment of the present invention is described below. This embodiment is a case where synchronization is performed without using an identifier as used in the first embodiment. In this case, since the identifier is not used, the third communication device 3 needs to search for tRX corresponding to tTX included in the synchronization frame received from the data stored in the buffer. The method is as follows.

  The adjustment unit 160 includes the following registers for synchronized flag (Sync), tTX0, tTX1, tRX0, tRX1 and tRX2. Sync is a register indicating whether or not the clock 120 is synchronized, and means that the absolute difference between the time of the clock 20 and the time of the clock 120 is within a certain error. tTX0 is a register that holds a tTX value included in the received SF. tTX1 is a register that holds the tTX value included in the SF received last time. tRX0 is a register that holds a tRX value corresponding to the tTX value included in the received SF. tRX1 is a register that holds tRX corresponding to the tTX value included in the previously received SF. FIG. 4 shows an algorithm of the adjustment unit 160 that adjusts the clock. Although the processing of TF is not shown in the chart of FIG. 4, the timepiece 120 is sampled at the moment of receiving TF, and the value of tRX of the sample result is passed to the adjustment unit 160, and the adjustment unit 160 The value of is stored in the buffer.

  First, after reset (S10), the process proceeds to S20 first. In S20, Sync is set to false. Next, it waits for SF to be received in S30. When the SF is received, the process proceeds to S40. In S40, tTX included in the SF is stored in tTX0.

  Next, the one having the smallest absolute difference from tTX0 is selected from all the tRX values stored in the buffer of adjustment unit 160 and stored in register tRX0. Next, the process proceeds to S50, where it is confirmed whether or not the absolute value of the difference between tTX0 and tRX0 is less than TH (TH is a constant). If this is true, the clock indicates a synchronized state, and the process proceeds to S90. If it is false, it means that the clocks are not synchronized, or tTX0 and tRX0 are not sample values corresponding to the same SF, and in this case, the process proceeds to S60. Whether or not synchronization is actually lost can be confirmed by checking the value of Sync (S60).

  If Sync is false, it indicates that the clock is out of synchronization, and the process proceeds to S70. If Sync is true, it means that the clock is synchronized, and the process proceeds to S120. In S70, the time of the clock 120 is set to (current time of the clock 120−tRX0 + tTX0 + K), and the process returns to S20. In S90, the state is synchronized. First, Sync is set to true, and the speed at which the timepiece 120 advances is finely adjusted based on tTX0 and tRX0, and the process proceeds to S100. In S100, tRX1 is set to tRX0, the process proceeds to S110, tTX1 is set to tTX0, and the process returns to S30 to wait for the next SF. In S120, ((tTX0-tRX1)> TH1)) OR ((tTX0-tTX1)> TH1)) is compared. However, TH1 indicates a sufficiently long time compared to the interval at which TF is transmitted.

  The former inequality holds when the third communication device 3 cannot receive the TF for a long time, and the latter inequality holds when the second communication device 2 cannot receive the TF for a long time. Show the case. Therefore, if either of these holds, it indicates that there is a high possibility that the clock 20 and the clock 120 are out of synchronization.

  If this is false, it means that there is a high possibility that the clock is still synchronized. In S110, tTX1 = tTX0 is set, and the flow returns to S30 to wait for the next SF. If true, it means that the clock is out of synchronization, and the process proceeds to S70.

  Next, a case where the processing of this embodiment is performed will be shown. In these cases, TH1 = 1050, TH2 = 10, K = 0, and buffer n = 3.

  FIG. 5 shows a case where the synchronization can be smoothly achieved from the initial state. First, after reset, the timepiece 20 and the timepiece 120 are not synchronized (Sync = false). When TF1 is transmitted for the first time, tTX is sampled as 1000 in the second communication device 2, and tRX is sampled as 6500 in the third communication device 3 and stored in the buffer. Next, SF1 is transmitted from the second communication device 2 to the third communication device 3, and the third communication device 3 performs the process of adjusting the timepiece of FIG. 4 based on SF1, and the details are as follows.

  In S40, tTX0 = 1000 and tRX0 = 6500. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S70. In S70, tRX2 = 6560, and in S80, the time of the clock 120 is set to (6560-6500 + 1000 + 0) = 1060. At this time, the clock 20 indicates 1059, and thus synchronization is achieved.

  Next, TF2 is transmitted, and tTX is sampled as 1100 and tRX as 1101. After SF2 is transmitted, the third communication apparatus 3 starts the time adjustment process. First, tTX0 = 1100 and tRX0 = 1101 are set in S40, S50 becomes true, and the process proceeds to S90. In S90, Sync = true is set, indicating a synchronized state. Further, the speed at which the timepiece 120 advances is adjusted based on tTX0 and tRX0. Finally, tRX1 is set to 1101 in S100, tTX1 is set to 1100 in S110, and the process returns to S30.

  FIG. 6 shows a case where the first TF from the initial state fails in the second communication device 2. First, after reset, the timepiece 20 and the timepiece 120 are not synchronized (Sync = false). When TF1 is transmitted for the first time, tTX is sampled as 1000 in the second communication device 2, and the third communication device 3 does not receive TF1, and therefore does nothing. Next, SF1 is transmitted from the second communication device 2 to the third communication device 3, and the third communication device 3 performs the process of adjusting the timepiece of FIG. 4 based on SF1, and the details are as follows.

  In S40, tTX0 = 1000 and tRX0 = undecided value. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S70. In S70, tRX2 = 6560, and in S80, the time of the clock 120 is set to (6560−undecided value + 1000 + 0) = undecided value, and the clock 120 is not yet synchronized. Next, TF2 is transmitted, and tTX is sampled as 1100, and tRX is sampled as XX (undecided value). After SF2 is transmitted, the third communication apparatus 3 starts the time adjustment process. First, in S40, tTX0 = 1100 and tRX0 = XX. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S70. In S70, tRX2 = XX + 79, and in S80, the time of the clock 120 is set to (XX + 79−XX + 1100 + 0) = 1079. At this time, the clock 20 indicates 1080, and thus synchronization is achieved. The next TF3 and SF3 are transmitted smoothly and are the same as described with reference to FIG. 5, and Sync is set to true in the process of adjusting the clock with respect to SF3 and represents a synchronized state.

  FIG. 7 shows a case where the first TF is lost in the third communication device 3 and the next TF is lost in the third communication device 3 from the initial state. First, after reset, the timepiece 20 and the timepiece 120 are not synchronized (Sync = false). When TF1 is transmitted for the first time, TF1 fails in the second communication device 2, the second communication device 2 does not process TF1, and the third communication device 3 samples tRX as 6500 and stores it in the buffer. The Next, TF2 is transmitted, tTX is sampled as 1100 in the second communication apparatus 2, and the third communication apparatus 3 does not receive TF2, and therefore does nothing. Next, SF2 is transmitted from the second communication device 2 to the third communication device 3, and the third communication device 3 performs the time adjustment processing of FIG. 4 based on SF2, and details are as follows.

  In S40, tTX0 = 1100 and tRX0 = 6500. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S70. In S70, tRX2 = 6683, and in S80, the time of the clock 120 is set to (6683-6500 + 1100 + 0) = 1283, and the clock 120 is not yet synchronized. Next, TF3 is transmitted, tTX is sampled as 1200, and tRX is sampled as 1302. After SF3 is transmitted, the third communication device 3 starts the time adjustment process. First, in S40, tTX0 = 1200 and tRX0 = 1302. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S70. In S70, tRX2 = 1350 is set, and in S80, the time of the clock 120 is set to (1350-1302 + 1200 + 0) = 1248. At this time, the clock 20 indicates 1250, and thus synchronization is achieved. When the next TF4 and SF4 are transmitted smoothly, the description is the same as the description of FIG.

  FIG. 8 shows a case where the second communication apparatus 2 cannot receive TF from the state where the clock 120 is synchronized (Sync = true). At first, synchronization is established, and transmission of TF1 and SF1 with respect to TF1 is transmitted without any problem. Therefore, when SF3 is received by the third communication device 3, in order of S30, S40, S50, S90, S100, and S110. Process. Next, when TF2 is transmitted, TF2 fails in the second communication device 2, the second communication device 2 does not process TF2, and in the third communication device 3, tRX is sampled as 1101 and stored in the buffer. The Next, TF3 is transmitted, and TF3 and SF3 are transmitted smoothly. Since the error between the clock 20 and the clock 120 is within TH2, the process proceeds smoothly. Therefore, in this case, since the second communication device 2 could not receive TF2, the adjustment processing of the clock 120 with respect to SF2 is not performed. However, even if only one TF is lost, the clock deviation does not change greatly, and Processing proceeds smoothly at TF3.

  FIG. 9 shows a case where the third communication device 3 cannot receive TF from the state where the clock 120 is synchronized (Sync = true). At first, synchronization is established, and the transmission of TF1 and SF1 to TF1 is also transmitted without any problem. Therefore, when SF3 is received by the third communication device 3, the order of S30, S40, S50, S90, S100, and S110 is smoothly performed. In step S100, tRX1 is set to 1000, and in step S110, tTX1 is set to 1000. Next, TF2 is transmitted, tTX0 is sampled as 1100 in the second communication device 2, and the third communication device 3 does not receive TF2, and therefore does nothing. Next, SF2 is transmitted from the second communication device 2 to the third communication device 3, and the third communication device 3 performs the time adjustment processing of FIG. 4 based on SF2, and details are as follows.

  In S40, tTX0 = 1100 and tRX0 = 1000. Next, since TH2 = 10 and 1100−1000 = 100, S50 becomes false. Next, the process goes from S60 to S120. In S120, since tTX0 = 1100, tRX1 = 1000, tTX1 = 1000, and TH1 = 1050, S120 becomes true, and in S110, tTX1 = 1100 is set and the process returns to S30. Next, TF3 is transmitted, and TF3 and SF3 are transmitted smoothly. Since the error between the clock 20 and the clock 120 is within TH2, the process proceeds smoothly. Therefore, in this example, since the third communication device 3 could not receive TF2, adjustment of the clock of the clock 120 with respect to SF2 is not performed, but even if only one TF is lost, the clock deviation does not change greatly, and Processing proceeds smoothly at TF3.

  FIG. 10 shows an example of a state in which the third communication device 3 cannot receive TF continuously for a long time from a state where the clock 120 is synchronized (Sync = true). The processing of TF1 and TF2 is the same as the case of FIG. 9, and tRX1 is set to 1000 at the end of the processing of adjusting the timepiece of SF1. After TF2, the TF cannot be received by the third communication apparatus 3 for a long time. Since the process for SF is from SF2 to SF11, the difference between tTX0 and tRX1 is smaller than TH1 = 1000. Therefore, the clock adjustment process is the same as SF2. It becomes processing. In the processing of TF12, tTX0 is about 2100 and tRX1 is 1000, so this difference is larger than TH1 = 1050, the state proceeds from S120 to S70, and finally S20 is Sync = false, that is, no synchronization is achieved. It becomes a situation. This situation continues until T23 when TF and SF can be transmitted smoothly, and the processing after TF23 is the same as that in FIG.

  FIG. 11 shows a case where the second communication device 2 cannot receive TF continuously for a long time from the state where the clock 120 is synchronized (Sync = true). The processing of TF1 and TF2 is the same as the case of FIG. At first, synchronization is established, and the transmission of TF1 and SF1 to TF1 is also transmitted without any problem. Therefore, when SF3 is received by the third communication device 3, the order of S30, S40, S50, S90, S100, and S110 is smoothly performed. Processing is performed, and tTX1 is set to 1000 in S110. From TF2 to TF82, the state where TF cannot be received by the second communication device 2 continues, and SF is not transmitted, and the third communication device 3 updates the buffer by sampling the time of the clock 120. Not performed. With the transmission of TF83, the TF can be received by the second communication devices 2 and 2, and the second communication device 2 samples tTX as 9200, and the third communication device 3 samples tRX as 9230 and stores it in the buffer. . Since the timepiece 120 is not adjusted from TF2 to TF82, the difference between the timepiece 20 and the timepiece 120 is 9230-9200 = 30> TH2 (10), and the state is out of synchronization. Next, SF 83 is transmitted from the second communication device 2 to the third communication device 3, and the third communication device 3 performs the time adjustment processing of FIG. 4 based on the SF 83, and details are as follows.

  In S40, tTX0 = 9200 and tRX0 = 9230. Next, since TH2 = 10, S50 becomes false. Next, the process goes from S60 to S110 and transitions to S70 because tTX0-tTX1 = 9200-1000 = 8000> TH1 (1000). The watch 120 is set to 9251 in S70 and S80, and Sync = false in S20. When the next TF 94 and SF 94 are transmitted smoothly, Sync = true, and the state returns to the synchronized state.

  As described above, the communication device according to the present embodiment is the first communication device, and includes the communication unit, the timepiece 1, and the sampling unit that samples the timepiece 1, and the communication unit performs delivery confirmation. The sampling means is notified of the moment when a specific frame (instantaneous frame) is transmitted or received, and the sampling means samples the time of the clock 1 as tTX at the instant, and the communication means includes a synchronization frame including the tTX. It is good also as a structure which transmits and transmits to a 2nd communication apparatus by the method with delivery confirmation. The instantaneous frame may be in a form accompanied with delivery confirmation, or may be a broadcast or unicast frame. Further, the synchronization frame may be in a format that does not accompany delivery confirmation, or may be a unicast frame that accompanies synchronization delivery confirmation.

  The communication apparatus according to the present embodiment is a second communication apparatus, and includes a communication unit, a timepiece 2, a sampling unit that samples the timepiece 2, and an adjustment unit that adjusts the timepiece 2. The communication means informs the sampling means of the moment when the instantaneous frame is transmitted or received, the sampling means samples the time of the clock 2 as tRX at the instant and passes it to the adjustment means, and the communication means A frame is received from the first communication device, and at least the tTX is extracted from the synchronization frame and transferred to the adjusting means. When the adjusting means receives at least the tTX from the communication means, the timepiece 1 receives its own clock 2 It is good also as a structure which performs operation which matches.

  According to the configuration of the first and second communication devices described above, the present invention uses the instantaneous frame as a reference time point for sampling the clocks of the first and second communication devices almost simultaneously, and another frame that is not the instantaneous frame. The tTX of the clock 1 sampled by the first communication device using (synchronization frame) is transmitted from the first communication device to the second communication device.

  On the other hand, in Patent Document 1, the multicast frame for synchronization transmits the above two roles, that is, the reference time point for sampling the clock almost simultaneously and the time of the sampled clock. In Patent Document 1, when the synchronization multicast frame is lost, the clock cannot be adjusted twice in succession. However, according to the above configuration, even if the instantaneous frame is lost, the second communication device The clock need not be adjusted once. Therefore, as shown in FIG. 16, it is possible to obtain a higher synchronization accuracy than that of Patent Document 1 according to the present invention. Since the synchronization frame used in the present invention is transmitted by a method of confirming delivery, it can be retransmitted at the wireless LAN layer level. Therefore, the probability of losing a synchronization frame can be considered to be negligibly small compared to the probability of losing an instantaneous frame.

  Further, in the second communication device, the adjustment unit may include a process of setting a time of the timepiece 2 or adjusting a speed at which the timepiece is advanced.

  According to the above configuration, when the timepiece 2 and the timepiece 1 are out of synchronization, an estimated value of the current time of the timepiece 1 is directly written into the timepiece 2 to thereby set the time of the timepiece 2. The time of the timepiece 1 can be quickly approached. When the time of the timepiece 2 and the timepiece 1 is synchronized, the speed at which the timepiece of the timepiece 2 advances can be finely adjusted to keep the synchronization.

  Further, the first or second communication device may be configured such that a specific part of the frame is used as a reference point at the moment of transmission or reception, for example, at the beginning or end of the frame.

  According to the above configuration, by using a specific portion of the instantaneous frame as a reference point, the instants at which the first and second communication devices sample the clock 1 and the clock 2 can be made to coincide with each other, and synchronization accuracy can be improved. Can be improved.

  In the second communication device, the adjustment unit includes a buffer, and the buffer can store data of the latest n frames (n ≧ 1 integer) that can be transmitted or received. The data may include at least the tRX.

According to the above configuration, by using the buffer, at least tRX of the latest n frames (n ≧ 1 integer) that can be transmitted or received can be stored. For example, it may take too much time to transmit the synchronization frame, and the next instantaneous frame may be transmitted before the transmission of the synchronization frame is completed. In this case, if n = 1, there is an option to erase the previous tRX for the instantaneous frame or not record a new tRX, but in any case the clock cannot be adjusted once. If n = 2, both the previous tRX and the new tRX can be recorded and the clock can be adjusted for both. Therefore, the accuracy of synchronization can be prevented from deteriorating by setting n to the maximum delay of the synchronization frame.

  Further, in the first communication device, the synchronization frame created by the communication unit of the first communication device includes an identifier for identifying the synchronization frame, and the identifier is included in the tTX included in the synchronization frame. It is good also as a structure copied from the said instantaneous frame corresponding to.

  In addition, the second communication device receives a synchronization frame transmitted by the first communication device, and the data stored in the buffer includes at least the tRX and a set of identifiers included in the instantaneous frame corresponding to the tRX. May be included.

  According to the above configuration, when the identifier is used, for example, when the instantaneous frame or the synchronization frame is lost, the second communication apparatus supports the identifier of the instantaneous frame received by the local station in the past and tTX included in the synchronization frame. It is possible to easily confirm whether or not tTX and tRX are sampling results corresponding to the same synchronization frame.

  Further, in the second communication device, the adjustment unit searches the buffer for the same identifier as the identifier of the received synchronization frame, and when the same identifier exists in the buffer, tRX corresponding to the identifier is set to tRX0, The previous tRX0 is set to tRX1, the tTX of the received synchronization frame is set to tTX0, and the previous tTX0 is set to tTX1. If (tTX0−tRX0)> TH (ABS is an absolute value) (TH is a constant), the parameter is set so that the time of the clock 2 is set to (the current time of the clock 2−tRX0 + tTX0 + K (K is a constant)). (2) If the condition of (1) is not met, adjust the parameter based on tTX0 and tRX0. It may be configured to adjust the speed of travel of the clock 2 and.

  According to the above configuration, when the timepiece setting of the initial stage, the synchronization frame is lost continuously over a long period of time, or the timepiece 2 is too far from the timepiece 1, the time of the timepiece 2 is set again. You can get closer to the time.

  Further, in the second communication device, the adjustment unit may include a synchronized flag.

  Further, the second communication device may be configured such that the synchronized flag is initialized to false at the time of resetting.

  Further, in the second communication apparatus, the adjustment unit selects the tTX, the total tRX stored in the buffer, and the tRX having the smallest difference absolute value with respect to the tTX included in the received synchronization frame. If the selected tRX is tRX0, the previous tRX0 is tRX1, the tTX of the received synchronization frame is tTX0, and the previous tTX0 is tTX1, (1) If the difference absolute value is smaller than TH (TH is a constant) Alternatively, if they are equal, the parameter is adjusted based on tTX0 and tRX0 to adjust the speed of advance of the timepiece 2 and the synchronized flag is set to true. (2) If the condition of (1) is satisfied And the synchronized flag is false, or the condition (1) is not satisfied and the synchronized flag is true and ABS ( TX0-tRX1)> TH1 (ABS is an absolute value) (TH1 is a constant), or the condition (1) is not satisfied and the synchronized flag is true and ABS (tTX0-tTX1)> TH1 In this case, the parameter may be adjusted to set the time of the timepiece 2 to (the time of the current timepiece 2−tRX0 + tTX0 + K (K is a constant)), and the synchronized flag may be set to false. .

  In the above configuration, since the identifier is not used, the LAN layer only needs to inform the upper layer of the timing at which the instantaneous frame is transmitted or received, and should be exchanged when the LAN layer and the upper layer are different chips. The information implementation price can be kept low. The reasons why the price is cheap are as follows. When the identifier is used, it is necessary to notify the identifier from the LAN layer to the upper layer. Although it is possible to notify the identifier to the host using a normal PCI interface, the PCI interface cannot be used for advanced synchronization because various delays and jitters occur in the PCI interface. For this reason, it is necessary to prepare a separate real-time interface. Since the upper layer chip and the wireless LAN chip are usually different chips, the number of pins of the chip increases and the board design becomes complicated. . Usually, it is not desirable to increase the number of pins of a chip, and it is important to make an effort to reduce the price of the chip by reducing it as much as possible. In the case of a method that does not use an identifier, for example, one signal line between the LAN layer chip and the upper layer chip that rises for a certain time at the timing of transmitting or receiving an instantaneous frame or the voltage level changes. All necessary information can be exchanged using only the signal line.

  Further, the second communication device may be configured to use a PLL (Phase Locked Loop) for clock adjustment.

  According to said structure, since PLL is used for the 2nd communication apparatus, synchronization with higher precision can be achieved.

  Further, in the first or second communication apparatus, the communication unit may be configured to support a wireless LAN (Local Area Network) or a PLC (Power Line Communication).

  Moreover, it is a 1st or 2nd communication apparatus, Comprising: The said instantaneous frame with which a communication apparatus communicates is good also as a structure which is a beacon frame of wireless LAN.

  According to the above configuration, high-accuracy synchronization can be achieved even in a wireless LAN or PLC network environment.

  Further, according to the above configuration, the synchronization frame can be directly transmitted from the first communication device to the second communication device even when IEEE 802.11e is used as the transmission method. On the other hand, when the synchronization method of Patent Document 3 is used for IEEE802.11e and the clock master is not an AP, the multicast frame for synchronization needs to be transmitted in two steps. Therefore, under the above conditions, the transmission method of the present invention can perform synchronization using a smaller band. In addition, when using IEEE802.11e, the instantaneous frame of the present invention can be a beacon frame, and both the present invention and Patent Document 3 need to transmit beacon frames periodically. The band used by the beacon frame is not an additional band.

  The identifier may be a first or second communication device that uses the identifier, and the identifier may be a time stamp or a sequence number of a TSF (Timing Synchronization Function) timer included in the beacon frame.

  According to the above configuration, by using the identifier as the time stamp or sequence number of the TSF timer included in the beacon frame, it is possible to use the existing information standardized without defining a new frame as the identifier.

  Finally, each block of the second communication device 2 and the third communication device 3 may be configured by hardware logic, or may be realized by software using a CPU as follows.

  That is, the second communication device 2 and the third communication device 3 expand a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and the program. A random access memory (RAM), and a storage device (recording medium) such as a memory for storing the program and various data. The object of the present invention is to read the program code (execution format program, intermediate code program, source program) of the control program of the second communication device 2 and the third communication device 3 which is software that realizes the above-described functions with a computer. The recording medium recorded as possible is supplied to the second communication device 2 and the third communication device 3, and the computer (or CPU or MPU) reads and executes the program code recorded on the recording medium. Achievable.

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The second communication device 2 and the third communication device 3 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  Since the time signal transmission jitter can be reduced, the present invention can be applied to various communication devices such as a communication device that needs to perform data communication requiring a small jitter and a terminal device including the communication device.

It is a block diagram which shows schematic structure of the communication system which concerns on one Embodiment of this invention. It is a figure which shows the communication sequence in the said communication system. It is the figure which showed the example where the next instantaneous frame is transmitted before transmission of a synchronous frame is complete | finished. It is a flowchart which synchronizes a clock, when not using the information of an identifier using tTX and tRX information. It is a figure which shows a communication sequence in case a timepiece is synchronized smoothly from an initial state. It is a figure which shows a communication sequence when the first TF from an initial state fails in a 2nd communication apparatus. It is a figure which shows a communication sequence in case the first TF is failed by the 2nd communication apparatus from an initial state, and the next TF is lost by the 3rd communication apparatus. It is a figure which shows a communication sequence when TF cannot be received in the 2nd communication apparatus from the state (Sync = true) where the clock is synchronized. It is a figure which shows a communication sequence when TF cannot be received in the 3rd communication apparatus from the state (Sync = true) where the clock is synchronized. It is a figure which shows a communication sequence when TF cannot be continuously received for a long time by the 3rd communication apparatus from the state (Sync = true) in which the clock is taken. It is a figure which shows a communication sequence when TF cannot be continuously received for a long time by the 2nd communication apparatus from the state (Sync = true) in which the clock is synchronized. It is the figure which showed the communication network which consists of a terminal device provided with the communication apparatus. It is the figure which showed the relationship between the advance degree of the time of the clock contained in a communication apparatus, and the advance degree of standard time. It is the figure which showed the exchange of time information performed between the said communication apparatuses. It is a figure regarding a prior art, Comprising: It is a figure which synchronizes using the multicast frame for a synchronization. It is the figure which showed the shift | offset | difference of the clock when the adjustment of PLL is performed smoothly, the case where adjustment is not performed once, and the case where adjustment is not performed twice continuously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st communication apparatus 2 2nd communication apparatus 3 3rd communication apparatus 20 Clock (timepiece means)
30 TF recognition unit (transmission side first frame recognition means)
40 Sampler (time detection means)
50 framer (second frame transmission means)
120 Clock (clock means)
130 TF recognition unit (reception side first frame recognition means)
140 Sampler (time detection means)
150 framer (second frame receiving means)
160 Adjustment unit (adjustment means)
210 network

Claims (23)

A communication device constituting a communication system in which a plurality of communication devices are connected for communication via a communication network,
Clock means for indicating time;
Receiving a specific first frame transmitted to a plurality of communication devices in the communication network, or transmitting first frame recognition means for detecting transmission;
A time detection means for determining a first frame detection time when reception or transmission of the first frame is detected by the transmission side first frame recognition means based on a time indicated by the clock means;
A communication apparatus comprising: a second frame transmission unit configured to transmit a second frame including the first frame detection time information to an external communication apparatus via the communication network.   The communication apparatus according to claim 1, wherein the second frame is transmitted to an external communication apparatus via the communication network in a state where delivery confirmation is required.   3. The communication apparatus according to claim 1, wherein the first frame is transmitted to a plurality of communication apparatuses in a state where delivery confirmation is not required in the communication network. A communication device constituting a communication system in which a plurality of communication devices are connected for communication via a communication network,
Clock means for indicating time;
Receiving a specific first frame transmitted to a plurality of communication devices in the communication network, or receiving side first frame recognition means for detecting transmission;
Time detection means for determining a first frame detection time when reception or transmission of the first frame is detected by the reception side first frame recognition means based on a time indicated by the clock means;
A second frame receiving means for receiving the second frame from the communication device according to claim 1 via the communication network;
Adjusting means for adjusting the time of the clock means based on the first frame detection time information included in the second frame and the first frame detection time detected by the receiving-side first frame recognition means; A communication apparatus comprising:   5. The communication apparatus according to claim 4, wherein the first frame is transmitted to a plurality of communication apparatuses in a state where delivery confirmation is not required in the communication network.   6. The communication apparatus according to claim 4, wherein the adjusting means adjusts a parameter for setting a time of the timepiece means and / or a parameter for adjusting a speed at which the timepiece of the timepiece means is advanced.   2. The communication apparatus according to claim 1, wherein the transmission-side first frame recognition means detects reception or transmission of a specific portion of the first frame.   6. The communication apparatus according to claim 4, wherein the receiving-side first frame recognizing unit detects reception or transmission of a specific portion of the first frame. The adjusting means comprises a buffer;
6. The communication apparatus according to claim 4, wherein the buffer stores the first n frame detection times up to the latest n (n ≧ 1). The first frame includes an identifier for identifying the first frame,
2. The communication apparatus according to claim 1, wherein the second frame transmitting means includes an identifier of the first frame corresponding to the first frame detection time information included in the second frame in the second frame. The first frame includes an identifier for identifying the first frame,
The second frame receiving means receives a second frame including an identifier of the first frame corresponding to the first frame detection time information;
10. The communication apparatus according to claim 9, wherein the buffer stores combinations of the first frame detection time and the identifier up to the latest n (n ≧ 1). The adjusting means searches the buffer for the same identifier as that included in the received second frame, and when the same identifier exists in the buffer, the first frame detection time corresponding to this identifier is set to tRX0, and the previous tRX0 Is tRX1,
The first frame detection time information included in the received second frame is tTX0, and the previous tTX0 is tTX1.
(1) If the second frame identifier is found in the buffer for the first time after initialization, or
(2) When ABS (tTX0-tRX0)> TH (ABS is an absolute value) (TH is a constant),
The time of the clock means is set to (current time of clock means−tRX0 + tTX0 + K (K is a constant)),
12. The communication apparatus according to claim 11, wherein when the condition (1) or (2) is not satisfied, the speed of the clock means is adjusted based on tTX0 and tRX0.   10. The communication apparatus according to claim 9, wherein the adjustment means stores a synchronized flag indicating whether or not the clock means of the own apparatus is synchronized.   14. The communication apparatus according to claim 13, wherein the synchronized flag is initialized to false when resetting. The adjustment means selects the first frame detection time having the smallest difference absolute value between the first frame detection time information included in the received second frame and all the first frame detection times stored in the buffer. And
The selected first frame detection time is tRX0, the previous tRX0 is tRX1,
The first frame detection time information of the received second frame is set to tTX0, and the previous tTX0 is set to tTX1.
(1) When the absolute value of the difference is smaller than or equal to TH (TH is a constant),
Based on tTX0 and tRX0, the speed of the clock means is adjusted and the synchronized flag is set to true,
The condition (1) is not satisfied and the synchronized flag is false, or the condition (1) is not satisfied and the synchronized flag is true, and
ABS (tTX0-tRX1)> TH1 (ABS is an absolute value) (TH1 is a constant), or
The condition (1) above is not satisfied and the synchronized flag is true, and
If ABS (tTX0-tTX1)> TH1,
14. The communication apparatus according to claim 13, wherein the time of said clock means is set to (current time of clock means-tRX0 + tTX0 + K (K is a constant)), and said synchronized flag is set to false.   6. The communication apparatus according to claim 4, wherein the adjusting means uses a PLL (Phase Locked Loop) for adjusting the timepiece means.   6. The communication device according to claim 1, wherein the communication device is compatible with a wireless LAN (Local Area Network) or a PLC (Power Line Communication).   18. The communication apparatus according to claim 17, wherein the first frame is a wireless LAN beacon frame. It supports wireless LAN (Local Area Network),
The first frame is a wireless LAN beacon frame,
12. The communication apparatus according to claim 10, wherein the identifier is a time stamp or a sequence number of a TSF (Timing Synchronization Function) timer included in the beacon frame. A communication method of a communication device that constitutes a communication system in which a plurality of communication devices are connected for communication via a communication network,
Receiving a specific first frame transmitted to a plurality of communication devices in the communication network, or transmitting side first frame recognition step for detecting transmission;
A time detection step of determining a first frame detection time when reception or transmission of the first frame is detected by the transmission side first frame recognition step based on a time indicated by a clock means included in the communication device;
And a second frame transmission step of transmitting a second frame including the first frame detection time information to an external communication device via the communication network. A communication method of a communication device that constitutes a communication system in which a plurality of communication devices are connected for communication via a communication network,
Receiving a specific first frame transmitted to a plurality of communication devices in the communication network, or receiving side first frame recognition step for detecting transmission;
A time detection step of determining a first frame detection time when reception or transmission of the first frame is detected by the reception side first frame recognition step based on a time indicated by a clock means included in the communication device;
A second frame receiving step for receiving the second frame from the communication device according to claim 1 via the communication network;
An adjusting step for adjusting the time of the clock means based on the first frame detection time information included in the second frame and the first frame detection time detected by the receiving-side first frame recognition step; A communication method characterized by comprising:   A communication program for operating the communication device according to any one of claims 1 to 19, wherein the communication program causes a computer to function as each of the above means.   A computer-readable recording medium on which the communication program according to claim 22 is recorded.

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