JP6539249B2 - Base station and wireless device - Google Patents

Description

  The present invention relates to a base station, a wireless device and a wireless communication system, and more particularly to synchronization processing by packet transmission and reception.

  Wireless LANs (Local Area Networks) are widely used. Some wireless LANs are provided with a plurality of access points communicatively connected to a communication network such as the Internet. An information terminal such as a personal computer or a smartphone performs packet communication with the access point by a wireless signal, and establishes communication connection with a communication network through the access point.

  Each access point forms a service area in which wireless communication can be performed with the information terminal. Further, each access point performs time division communication with the information terminal to establish a plurality of communication lines. When moving from one service area to another service area, the information terminal performs uninterrupted communication by handover processing. As described above, in order for each access point to perform time division communication and a plurality of access points operate in cooperation, packet transmission / reception timing of each access point needs to be synchronized.

  Therefore, each access point acquires time information for synchronization processing from, for example, a signal transmitted from a GPS (Global Positioning System). There is also a wireless LAN in which each access point acquires time information from the Internet using NTP (Network Time Protocol).

  Patent Document 1 below describes a time synchronization processing system using GPS. In this system, the master receives reference time information transmitted from GPS satellites, and generates a time packet for performing time synchronization. The master broadcasts (or broadcasts) time packets to a plurality of slaves via a wireless LAN. Further, Non-Patent Document 2 describes a wireless LAN in which wireless communication is performed between a plurality of measurement nodes. Each measurement node includes an apparatus for measuring a physical quantity to be measured, and transmits and receives a packet including a measurement value. One of the plurality of measurement nodes receives time information from the GPS satellite, and the plurality of measurement nodes synchronize operation timing based on communication between the plurality of measurement nodes.

JP, 2009-111654, A

Hiyama Masayuki et al., "Examination and Experiment of High Precision Time Synchronization Method in Wireless LAN," IEICE Tech. Res. Inst. Vol. 108, no. 460, IA2008-79, pp. 73-78, March 2009. , SITE 2008-56, IA 2008-79.

  Among the standards of wireless communication, there are those which require transmission pause for a predetermined time or more after transmission of a wireless signal. When a plurality of wireless devices execute synchronization processing under such a standard, each wireless device needs to execute synchronization processing under the limitation of transmission time of wireless signals. Under such time restrictions, each wireless device needs to execute synchronization processing quickly. However, when a plurality of wireless devices try to execute the synchronization process quickly, packets for the synchronization process may be frequently transmitted and received between the wireless devices, resulting in communication congestion.

  An object of the present invention is to make the transmission and reception frequency of synchronization packets appropriate between wireless devices.

In the base station according to the present invention, in a base station including a radio unit that transmits and receives packets to and from a plurality of radio devices, and a control unit that controls the radio unit, the control unit determines synchronization packets for defining timing. Transmission and reception processing including the synchronous packet transmission processing for multicasting to the wireless device and the request reception processing for receiving each information request packet transmitted from each wireless device in response to the synchronous packet is repeated with the wireless unit The control unit is a synchronization status information further included in each of the information request packets, the synchronization indicating a synchronization state between a local clock provided in each of the wireless devices and a base station clock provided in the base station based on the status information, said adjusting the transmission period for performing synchronization packet transmitting process, the synchronization status, the a time indicated by the local clock, the group There is a locked state in which the difference between the time indicated by the local clock is within a predetermined range, and the non-locked state in which the difference between the time indicated by the local clock and the time indicated by the base station clock is outside the predetermined range. The unit obtains the number of non-locked ones among the plurality of wireless devices in the non-locked state based on the synchronization status information included in each information request packet, and the transmission cycle based on the number of non-locked ones. It is characterized by adjusting.

  Preferably, when the number of unlocked units is one or more, the control unit makes the transmission cycle shorter than when the number of unlocked units is zero.

Further, according to the present invention, in a base station including a wireless unit that transmits and receives packets to and from a plurality of wireless devices, and a control unit that controls the wireless unit, the control unit determines a synchronization packet that defines timing. The wireless unit includes transmission / reception processing including synchronous packet transmission processing for multicasting to each of the wireless devices, and request reception processing for receiving each information request packet transmitted from each of the wireless devices in response to the synchronous packets. The control unit further executes synchronization status information included in each of the information request packets, the synchronization status between a local clock included in each of the wireless devices and a base station clock included in the base station. based on the synchronization status information indicating, by adjusting the transmission period for executing the synchronization packet transmission processing, the request receiving process receives the information request packet The control unit includes a process for obtaining an information request reception time indicating a time, and the control unit transmits a synchronization packet transmission time indicating a time when the synchronization packet is transmitted in the transmission and reception process, and the wireless devices in the transmission and reception process. and said information request reception time determined in response to, and characterized in that included in the synchronization packets transmitted following the transmission and reception processing.

Further, according to the present invention, in a base station including a wireless unit that transmits and receives packets to and from a plurality of wireless devices, and a control unit that controls the wireless unit, the control unit determines a synchronization packet that defines timing. The wireless unit includes transmission / reception processing including synchronous packet transmission processing for multicasting to each of the wireless devices, and request reception processing for receiving each information request packet transmitted from each of the wireless devices in response to the synchronous packets. The control unit further executes synchronization status information included in each of the information request packets, the synchronization status between a local clock included in each of the wireless devices and a base station clock included in the base station. based on the synchronization status information indicating, by adjusting the transmission period for executing the synchronization packet transmission processing, the request receiving process receives the information request packet The control unit determines the information request reception time indicating the time, and the control unit determines the information request reception time determined for the wireless device in the transmission / reception process and the synchronization process in the next transmission / reception process. and a synchronous packet transmission time indicating the time the packet is transmitted, characterized in that included in the synchronization packets transmitted in the following the transmission and reception processing.

Further, according to the present invention, in a wireless apparatus including: a wireless unit that transmits and receives a packet to and from a base station; and a control unit that controls the wireless unit, the control unit transmits from the base station A synchronization packet reception process for receiving a synchronization packet, a request transmission process for transmitting an information request packet after the synchronization packet is received, a time when the synchronization packet is received, and a time when the information request packet is transmitted Transmitting and receiving processing including synchronization processing for synchronizing a local clock included in the wireless device with a base station clock included in the base station based on information for synchronization included in the synchronization packet and the wireless unit The process is repeatedly executed, and the synchronization process includes a process of generating synchronization status information indicating a synchronization state between the local clock and the base station clock. The request transmission process, see contains the process to include the synchronization status information to the information request packet, information for the synchronization, the time other synchronization packets earlier than the synchronization packet is transmitted, or the synchronization packet There characterized that you includes information indicating the time sent, and information indicating a time at which the information request packet in the transmission and reception processing of previously received by the base station.

  Preferably, the synchronization status information may be in a locked state in which a difference between a time indicated by the local clock and a time indicated by the base station clock is within a predetermined range, or in a non-locked state in which the difference is outside the predetermined range. It contains information indicating one of them.

  According to the present invention, the frequency of transmission and reception of synchronization packets between wireless devices can be made appropriate.

It is a figure showing the composition of the communication system concerning the embodiment of the present invention. It is a sequence chart of repetition synchronization processing. It is a figure which shows the structure of a synchronous packet. It is a figure which shows the structure of the communication system which concerns on application embodiment. It is a figure which shows the structure of an ad hoc communication system. It is a figure which shows the example of the hardware of a base station. It is a figure which shows the example of the hardware of the radio | wireless apparatus for synchronization.

(1) Configuration of Communication System FIG. 1 shows the configuration of a communication system according to an embodiment of the present invention. The communication system includes a base station 10, access points 12-1 to 12-3, and an information terminal 20. Here, an example in which three access points 12-1 to 12-3 are provided is shown, but the number of access points is arbitrary.

  Each access point 12-j (j = 1 to 3) is connected to the Internet 18 to configure a wireless LAN. The information terminal 20 is, for example, a personal computer or a mobile phone.

  Each access point 12-j forms a service area where wireless communication with the information terminal 20 is possible. The information terminal 20 wirelessly communicates with an access point that forms a service area in which the information terminal 20 exists, and communicatively connects to the Internet 18.

  The base station 10 includes a base station clock for defining operation timing. The base station 10 receives reference time information from GPS satellites, and adjusts the time (base station time) emitted by the base station clock to the reference time represented by the reference time information.

  The access point 12-j includes a synchronization wireless device 14-j and a wireless LAN node 16-j. The synchronization wireless device 14-j includes a local clock that outputs the time to the wireless LAN node 16-j. The base station 10 communicates with the synchronization wireless device 14-j included in the access point 12-j, and performs synchronization processing with the synchronization wireless device 14-j. The synchronization wireless device 14-j synchronizes the time when its local clock emits with the base station time by executing synchronization processing. The local clock provides the wireless LAN node 16-j with the time adjusted to the base station time. The wireless LAN node 16-j operates at timing according to the time given by the local clock. By this, the operations of the wireless LAN nodes 16-1 to 16-3 are synchronized.

(2) Repeated Synchronization Processing (2-1) Packet Transmission and Reception Processing FIG. 2 shows a sequence chart of repeated synchronization processing executed in the communication system. In the repetitive synchronization processing, the base station 10 repeatedly transmits the synchronization packet to each synchronization wireless device at a predetermined transmission cycle ST, and each synchronization wireless device having received the synchronization packet transmits an information request packet to the base station 10 It is a process. The base station 10 includes information obtained in response to the information request packet in the synchronization packet to be transmitted next. As described above, in the repetitive synchronization processing, synchronization processing by transmission of synchronization packets by the base station 10 and transmission of information request packets by each synchronization wireless device (packet transmission / reception processing) is repeated. Further, in the repetitive synchronization processing, the base station 10 adjusts the transmission cycle ST and adjusts the frequency of transmission and reception of packets depending on whether or not the local clock of each synchronization wireless device is synchronized with the base station clock.

  At time t0, the base station 10 transmits a synchronization packet addressed to the synchronization wireless devices 14-1 to 14-3 (S101). The synchronization packet is a packet to be transmitted to each synchronization wireless device in order to define the timing of executing the synchronization process. When transmitting the synchronization packet, the base station 10 includes, in the synchronization packet, a broadcast address commonly assigned to the synchronization wireless devices 14-1 to 14-3. Further, the base station 10 includes information obtained according to the immediately preceding packet transmission / reception process in the synchronization packet. This information is information for synchronizing the local clocks of the synchronization wireless devices 14-1 to 14-3 with the base station clock, and the details will be described later. The base station 10 further obtains an initial time t0 (synchronization packet transmission time) at which the synchronization packet has been transmitted by using its own base station clock, and stores the initial time t0. Each of the synchronization wireless devices recognizes that the received synchronization packet includes a broadcast address, and executes processing according to the synchronization packet.

  Specifically, the synchronization wireless device 14-1 receives the synchronization packet at time t11 after time Δ0 from time t0. The synchronization wireless device 14-2 receives the synchronization packet at time t12 after time Δ0 from time t0. The synchronization wireless device 14-3 receives the synchronization packet at time t <b> 13 after time Δ <b> 3 from time t <b> 0. Each synchronization wireless device determines the synchronization packet reception time at which the synchronization packet has been received, using a local clock provided for each device, and stores the synchronization packet reception time. That is, the synchronization wireless devices 14-1 to 14-3 store synchronization packet reception times t11 to t13, respectively.

  Each synchronization wireless device transmits an information request packet when a predetermined response delay time has elapsed since the reception of the synchronization packet (S102). In the example illustrated in FIG. 2, response delay times d1 to d3 are determined for the synchronization wireless devices 14-1 to 14-3, respectively. When transmitting the information request packet, each synchronization wireless device obtains the information request transmission time for transmitting the information request packet by using a local clock provided for each of them, and stores the information request transmission time. That is, the synchronization wireless devices 14-1 to 14-3 store information request transmission times t21 to t23, respectively.

  Each synchronization radio apparatus includes synchronization status information described later in the information request packet. The synchronization status information indicates the synchronization status between the local clock and the base station clock. Specifically, it indicates whether the local clock of the synchronization wireless device that transmits the information request packet is in the locked state or in the unlocked state. The lock state is a state in which the difference between the time indicated by the local clock of the synchronization wireless device and the time indicated by the base station clock is within a predetermined range over a predetermined time, for example, predetermined over a predetermined time It is a state below the threshold of The non-locked state is a state in which the difference between the time indicated by the local clock of the synchronization wireless device and the time indicated by the base station clock of the base station 10 is out of a predetermined range, for example, a state exceeding a predetermined threshold. Say.

  Furthermore, the non-locking state includes a standby state and a holdover state. The standby state is a state until the synchronization wireless device is activated and the local clock is locked by synchronization processing. In the holdover state, although the local clock has once been in the locked state, communication of the synchronization packet or information request packet has become impossible due to deterioration of the communication state, etc. and the local clock has become out of lock state or State until the local clock is locked by synchronization processing.

  The base station 10 receives each information request packet transmitted from each of the synchronization wireless devices 14-1 to 14-3. The base station 10 obtains and stores the information request reception times t31, t32 and t33 at which the information request packets have been received using the base station clock. The base station 10 also stores synchronization status information included in each information request packet. As described later, the base station 10 adjusts the transmission period ST of the synchronization packet based on the synchronization status information acquired from each synchronization wireless device.

  The response delay time determined for each synchronization wireless device is determined so that the plurality of information request packets transmitted from the plurality of synchronization wireless devices are not received by the base station 10 in overlapping time zones. . For example, it is assumed that the synchronization wireless device 14-i which is one of the synchronization wireless devices 14-1 to 14-3 is known to receive the synchronization packet after a time Δi from the initial time t0. Then, it is assumed that another synchronization wireless device 14-j receives a synchronization packet after a time Δj from an initial time t0. In this case, the propagation time of the packet between the base station 10 and the synchronization wireless device 14-i is Δi, and the propagation time of the packet between the base station 10 and the synchronization radio device 14-j is Δj. .

  Assuming that the response delay time of the synchronization wireless device 14-i is di, the base station 10 receives the information request packet transmitted from the synchronization wireless device 14-i at time t0 + di + 2Δi. Similarly, assuming that the response delay time of the synchronization wireless device 14-j is dj, the base station 10 receives the information request packet transmitted from the synchronization wireless device 14-j at time t0 + dj + 2Δj. In order to prevent the information request packet transmitted from the synchronization wireless device 14-i and the synchronization wireless device 14-j from being received by the base station 10 with overlapping time zones, responses such that t0 + di + 2Δi and t0 + dj + 2Δj are different The delay times di and dj may be set. For example, the absolute value of the difference between the response delay time di and the response delay time dj may be set to be sufficiently larger than the absolute value of the difference between the propagation time Δi and the propagation time Δj.

  At time t4 when the transmission cycle ST has elapsed since the base station 10 transmitted the synchronization packet, the base station 10 transmits the next synchronization packet addressed to the synchronization wireless devices 14-1 to 14-3 (S103). ).

  When transmitting the synchronization packet, the base station 10 includes the broadcast address, the initial time t0, and the reception time information for each synchronization wireless device in the synchronization packet. The initial time t0 and the reception time information are information acquired by the base station 10 along with the transmission of the synchronization packet (S101) performed within the previous transmission cycle ST and the reception of the information request packet (S102). The reception time information is information in which the address of the synchronization radio apparatus of the transmission source is associated with the reception time of the information request packet (information request reception time) transmitted from the synchronization radio apparatus. Assuming that the addresses of wireless devices 14-1 to 14-3 for synchronization are AD1 to AD3, respectively, reception time information in which address AD1 and information request reception time t31 are associated, address AD2 and information request reception time t32 The reception time information associated with each other and the reception time information associated with the address AD3 and the information request reception time t33 are included in the synchronization packet.

  The structure of the synchronization packet is shown in FIG. The synchronization packet includes a head unit 22 and a payload unit 32. The head unit 22 includes a preamble 24, communication data 26 and a destination address 28. The preamble 24 includes a code for the synchronization wireless device to identify that the synchronization packet has been received. The communication data 26 includes, for example, information for reading a code included in the synchronization packet. A broadcast address is described in the destination address 28.

  The payload section 32 includes an initial time 36, reception time information 38-1 to 38-n and an error correction code 40. The reception time information 38-1 to 38-n is information addressed to the synchronization wireless devices 14-1 to 14-n, respectively. The information request reception time included in each reception time information may be a value representing an integrated value of elapsed time from a certain time, or may be a value representing Greenwich Mean Time (GMT). The error correction code 40 includes the preamble 24, the communication data 26, the destination address 28, the initial time 36, and the error detection and error correction for the code representing the reception time information 38-1 to 38-n by the synchronization radio device. It is a code to execute.

  Returning to FIG. 2, the repetitive synchronization processing will be described continuously. Each of the synchronization wireless devices recognizes that the received synchronization packet includes a broadcast address, and executes processing according to the synchronization packet.

  Specifically, the synchronization wireless device 14-1 receives the synchronization packet at time t51 after time Δ1 from time t4. The synchronization wireless device 14-2 receives the synchronization packet at time t52 after time Δ4 from time t4. The synchronization wireless device 14-3 receives the synchronization packet at time t53 after time Δ4 from time t4.

  Each synchronization wireless device extracts and stores an initial time t0 from the synchronization packet. Also, it extracts reception time information corresponding to itself from the synchronization packet, and further acquires and stores an information request reception time from the reception time information. That is, the synchronization wireless device 14-1 acquires and stores the initial time t0 and the information request reception time t31. The synchronization wireless device 14-2 acquires and stores the initial time t0 and the information request reception time t32. The synchronization wireless device 14-3 acquires and stores the initial time t0 and the information request reception time t33.

  Thus, the synchronization wireless device 14-1 receives the synchronization packet, transmits the information request packet, and further receives the next synchronization packet, thereby transmitting the initial time t0, the synchronization packet reception time t11, and the information request. The time t21 and the information request reception time t31 are stored. Similarly, the synchronization wireless device 14-2 stores an initial time t0, a synchronization packet reception time t12, an information request transmission time t22, and an information request reception time t32. The synchronization wireless device 14-3 stores an initial time t0, a synchronization packet reception time t13, an information request transmission time t23, and an information request reception time t33.

  Here, an example has been described in which there are three access points 12-1 to 12-3, and each access point 12-j (j = 1 to 3) includes the synchronization wireless device 14-j. The number is arbitrary.

(2-2) Calculation of Adjustment Offset Time and Time Adjustment Process The synchronization wireless device 14-k, which is one of the n synchronization wireless devices 14-1 to 14-n, performs packet transmission / reception processing. It is assumed that an initial time t0, a synchronization packet reception time t1k, an information request transmission time t2k, and an information request reception time t3k are stored. The synchronization wireless device 14-k obtains the propagation time Dk between the synchronization wireless device 14-k and the base station 10 according to the following (Equation 1).

  (Equation 1) Dk = [(t1k−t0) + (t3k−t2k)] / 2

  (Equation 1) is derived as follows. The initial time t0 and the information request reception time t3k are times obtained by the base station clock provided in the base station 10, and the synchronization packet reception time t1k and the information request transmission time t2k are local clocks provided in the synchronization wireless device 14-k. Is the time determined by Assuming that the local clock has advanced by the offset time To relative to the base station clock, the propagation time Ds of the synchronization packet and the propagation time Dd of the information request packet are respectively represented by Eqs. (2) and (3). Be done.

(Equation 2) Ds = t1 k-t0-To
(Equation 3) Dd = t3k−t2k + To

  Since the propagation time Ds and the propagation time Dd are equal to Dk, the equation (1) can be obtained by adding both sides of the equations (2) and (3) and dividing by two.

  The synchronization wireless device 14-k obtains the offset time To according to the following (Equation 4). This equation is obtained by solving equation (2) for the offset time To, and replacing Ds representing the same propagation time with Dk.

  (Equation 4) To = (t1 k-t0)-Dk

  The synchronization wireless device 14-k may obtain the offset time To based on the following (Equation 5) instead of (Equation 4).

  (Equation 5) To = [(t1k−t0) − (t3k−t2k)] / 2

  The equation (5) is an equation obtained by solving the equations (2) and (3) for the offset time To. Further, (Equation 5) can also be obtained by substituting Dk of (Equation 1) into Dk of (Equation 4).

  In the repetitive synchronization process, the transmission of the synchronization packet by the base station 10 and the transmission of the information request packet by each of the synchronization wireless devices 14-1 to 14-n (packet transmission / reception process) are repeated. Each time the packet transmission / reception process is performed, the synchronization radio device 14-k obtains the offset time To. The synchronization wireless device 14-k obtains a weighted moving average value for M offset times To obtained by the packet transmission and reception process performed for a plurality of M times retroactively including the latest packet transmission and reception process. The adjustment offset time Ta is obtained. For example, the adjustment offset time Ta can be obtained based on (Equation 6).

  (Equation 6) Ta = (1 / M) · Σ [g (q) · To (q)]

  Σ means adding up for q = 0 to M-1. To (q) indicates the offset time To obtained in the packet transmission / reception process in the past by q times. g (q) is a weighting factor for the offset time obtained in the packet transmission / reception process in the past by q times. For example, by increasing g (q) as q becomes smaller, contribution to the adjustment offset time Ta becomes larger as the offset time To is a newly obtained value. All g (0) to g (M-1) may be 1. When the number of executions of the packet transmission and reception process does not reach M times, such as at startup, the synchronization wireless device 14-k obtains a weighted moving average value for the offset time To determined by the number of times of execution. The adjustment offset time Ta is obtained.

  The synchronization wireless device 14-k executes time adjustment processing to make the local time closer to or coincide with the base station time obtained by subtracting the adjustment offset time Ta from the time (local time) of its own local clock. The synchronization wireless device 14-k outputs its local time to the wireless LAN node 16-k.

  The other synchronization radio devices other than the synchronization radio device 14-k execute the same processing. That is, time adjustment processing is performed to make each local time approach or coincide with the base station time obtained by subtracting the adjustment offset time from each local time. Each synchronization wireless device outputs its own local time to a wireless LAN node attached to it.

  In the repeat synchronization process, the packet transmission / reception process is repeated, and each synchronization wireless device repeatedly executes the time adjustment process. Thereby, the local time of each synchronization wireless device approaches or coincides with the base station time. That is, in one time adjustment process, the difference between the local time of each synchronization wireless device and the base station time (adjustment offset time Ta) may not be less than or equal to a predetermined threshold, and repetition of the time adjustment process may cause The local time of each synchronization radio unit converges to the base station time. This causes the local clock to go from unlocked to locked.

  Each time the time adjustment process is performed, the synchronization wireless device 14-k (k = 1 to n) generates synchronization status information. That is, the synchronization radio device 14-k obtains an adjustment offset time indicating the difference between the base station time and the local time, and when the adjustment offset time is less than or equal to a predetermined threshold over a predetermined time. It is determined that the local clock of the synchronization wireless device 14-k is in a locked state. On the other hand, when the adjustment offset time exceeds the predetermined threshold value, it is determined that the local clock of the synchronization wireless device 14-k is in the unlocked state. The synchronization wireless device 14-k generates synchronization status information indicating whether its local clock is locked or unlocked, and sends an information request packet to the base station 10 each time a synchronization packet is received. Includes synchronization status information. The synchronization status information is acquired by the base station 10 having received the information request packet, and as described later, the base station 10 determines the transmission cycle ST of the synchronization packet based on the synchronization status information acquired from each synchronization wireless device. adjust.

  By such processing, each wireless LAN node acquires time synchronized with the base station time. Since the base station time is synchronized with the reference time transmitted from the GPS satellite, the time recognized by each wireless LAN node is synchronized with the reference time. This synchronizes the operation of each of the plurality of wireless LAN nodes.

  Also, according to the process executed by the communication system, synchronization packets are broadcasted to a plurality of synchronization wireless devices as destinations. As a result, information on the synchronization process is quickly given to each synchronization wireless device.

  In IEEE 1588, which is a standard for packet communication, a Sync message, a Follow-up message, and a Delay-Response message are defined as packets transmitted from a master (base station) to a slave (synchronization radio apparatus). Also, a Delay-Request message is defined as a packet transmitted from the slave to the master. In the communication system according to the present invention, only the synchronization packet corresponding to the Sync message and the information request packet corresponding to the Delay-Request message are repeatedly used for synchronization processing. Therefore, since two types of packets may be used, the processing is simplified as compared with the case in accordance with IEEE 1588, and the synchronization processing is performed quickly.

  In the above, the embodiment has been described in which the initial time t0 of the synchronization packet transmitted from the base station 10 is transmitted from the base station 10 to each synchronization wireless device by the synchronization packet to be transmitted next. The initial time t0 may be transmitted from the base station 10 to each synchronization wireless device by the synchronization packet itself transmitted at the initial time t0. In this case, the initial time 36 of the payload section 32 shown in FIG. 3 describes the time at which this synchronization packet is transmitted. When transmitting the synchronization packet (first synchronization packet), the base station 10 obtains an initial time t0 at which the first synchronization packet is transmitted, and includes the initial time t0 in the first synchronization packet.

  Each synchronization radio device 14-k that has received the first synchronization packet determines and stores the synchronization packet reception time t1k, and extracts and stores the initial time t0 from the first synchronization packet. Then, the information request packet is transmitted, and the information request transmission time t2k is obtained and stored. Each synchronization wireless device 14-k receives the synchronization packet (second synchronization packet) transmitted from the base station 10 in the next transmission cycle, extracts the information request reception time t3k from the second synchronization packet, and stores the same. Do. In addition to the initial time t0, the synchronization packet reception time t1k, and the information request transmission time t2k stored in advance, each synchronization wireless device 14-k is based on the information request reception time t3k extracted from the second synchronization packet. To determine the offset time To.

(3) Transmission Cycle Adjustment Process Next, a process in which the base station 10 adjusts the transmission cycle of the synchronization packet will be described. When the local clock provided in each of the synchronization wireless devices 14-1 to 14-n is in the locked state, the transmission cycle may be longer than in the non-locked state. This is because, once the local watch is locked, the oscillation frequency of the oscillator included in the local watch and the phase of the clock signal generated by the oscillator become stable, and the frequency of the time adjustment process may be lowered. Therefore, the base station 10 performs the following transmission cycle adjustment process each time the synchronization radio devices execute the time adjustment process.

  After receiving the information request packet transmitted from each synchronization radio device, the base station 10 executes transmission cycle adjustment processing in a time zone until transmission of the next synchronization packet (S105). The base station 10 determines, based on the synchronization status information acquired from each synchronization wireless device, whether the local clock included in each synchronization wireless device is in the locked state or in the unlocked state. Then, the number of unlocked devices, which is the number of synchronization wireless devices in which the local clock is unlocked, is determined.

  The base station 10 sets the transmission cycle to the first transmission cycle when the number of unlocked units is one or more. On the other hand, when the number of unlocked units is 0, the transmission cycle is set to the second transmission cycle. Here, the first transmission cycle is defined as a time shorter than the second transmission cycle. As described above, some wireless communication standards require transmission suspension for a predetermined time or more after transmission of a wireless signal. When designing a communication system according to this standard, the first transmission cycle and the second transmission cycle are set to be longer than the transmission pause time defined in the standard. For example, the first transmission cycle is 125 milliseconds, and the second transmission cycle is 1 second. The base station 10 transmits the next synchronization packet when the newly set transmission cycle has elapsed from the time of transmitting the synchronization packet first.

  According to such a process, the base station 10 executes the transmission cycle adjustment process each time the information request packet transmitted by each of the synchronization radio apparatuses 14-1 to 14-n is received in the packet transmission / reception process. The transmission cycle from transmission of the synchronization packet to transmission of the next synchronization packet is set. As a result, the transmission cycle when the number of unlocked units is 1 or more is shorter than the transmission cycle when the number of unlocked units is 0, and the time interval at which the time adjustment process is performed is shortened. Therefore, the local clock in the unlocked state (standby state or holdover state) is locked in a short time, and the local clock of each synchronization wireless device is quickly synchronized with the base station clock.

  On the other hand, when the local clocks of all the synchronization wireless devices 14-1 to 14-n are in the locked state, transmission is performed as compared with the case where even one synchronization wireless device has the local clock in the unlocked state. The cycle becomes longer. As a result, the number of packets transmitted / received in a fixed time between the base station 10 and each synchronization wireless device decreases, communication traffic is suppressed, and communication congestion hardly occurs.

  In the above, the transmission cycle is set to the first transmission cycle when the number of non-lockings is 1 or more, and the transmission cycle is set to the second transmission cycle when the number of non-lockings is 0. The process of changing the cycle in two steps has been described. Other than such processing, the base station 10 may execute processing of changing the transmission cycle in three or more stages according to the number of non-locks. For example, processing may be performed to shorten the transmission cycle as the number of unlocked units increases.

(4) System in which Relay Station is Provided FIG. 4 shows the configuration of a communication system according to an applied embodiment. This communication system is provided with a relay station 42 in the communication system shown in FIG. The relay station 42 comprises a relay radio apparatus 44 and a relay base station 46. Relay radio apparatus 44 has the same configuration as synchronization radio apparatuses 14-1 and 14-2, and executes the same processing as synchronization radio apparatuses 14-1 and 14-2. The relay base station 46 has the same configuration as the base station 10 and executes the same processing as the base station 10.

  The relay radio unit 44 executes synchronization processing with the base station 10, and adjusts the time of the local clock to the base station time. The relay radio apparatus 44 gives the time of the local clock to the relay base station 46. The relay base station 46 synchronizes the time of its own base station clock with the time given by the relay radio apparatus 44.

  The relay base station 46 performs synchronization processing with the synchronization wireless device 14-j included in each access point 12-j (j = 1 or 2). While performing the synchronization process, the synchronization wireless device 14-j gives the time of the local clock to the wireless LAN node 16-j attached thereto.

  By such processing, each wireless LAN node 16-j synchronizes with the base station time of the relay base station 46, and further acquires the time synchronized with the base station time of the base station 10. The operations of the plurality of access points are synchronized by operating each wireless LAN node 16-j at timing according to the time given by the synchronization wireless device 14-j. Further, since the base station time of the base station 10 is synchronized with the reference time transmitted from the GPS satellite, the time recognized by each access point is synchronized with the reference time.

  In this communication system, each access point 12-j performs synchronization processing with the relay station 42, and the relay station 42 performs synchronization processing with the base station 10. Therefore, the distance between the base station 10 and each access point 12-j may be increased compared to the communication system shown in FIG.

  The synchronization wireless device and the wireless LAN node may configure an ad hoc wireless device in addition to configuring an access point of a wireless LAN. A plurality of ad hoc wireless devices transmit packets from a source ad hoc wireless device to a destination ad hoc wireless device by multi-hop communication. In multi-hop communication, a packet transmitted from a source ad hoc wireless device is transmitted to a destination ad hoc wireless device directly depending on the communication status by relay transmission by one or more other ad hoc wireless devices. It says a form.

(5) Ad hoc communication system FIG. 5 shows the configuration of the ad hoc communication system. The ad hoc wireless device 48-j (j = 1 to 3) includes the synchronization wireless device 14-j and the wireless LAN node 16-j. The synchronization wireless device 14-j executes synchronization processing with the base station 10 and generates a time synchronized with the reference time. The synchronization wireless device 14-j gives the wireless LAN node 16-j a time synchronized with the reference time. The wireless LAN node 16-j operates according to the time given by the synchronization wireless device 14-j. This synchronizes the operation timings of the wireless LAN nodes 16-1 to 16-3. The wireless LAN nodes 16-1 to 16-3 perform multi-hop communication in a state where the operation timing is synchronized.

  An information terminal 20-j is connected to the wireless LAN node 16-j. The information terminal 20-j performs packet communication with the destination information terminal by causing the wireless LAN node 16-j to perform multi-hop communication.

(6) Hardware of Base Station An example of the hardware of the base station 10 is shown in FIG. The base station 10 includes a GPS receiving unit 50, a base station clock 51, a control unit 52, and a radio unit 54. The GPS receiving unit 50 receives reference time information from GPS satellites, and outputs the reference time to the control unit 52. The base station clock 51 outputs the base station time to the control unit 52. The control unit 52 controls the base station clock 51 to set the base station time to the reference time.

  The wireless unit 54 receives the packet and outputs the packet to the control unit 52. Also, the wireless unit 54 transmits the packet output from the control unit 52.

  The control unit 52 is configured by, for example, a processor that executes arithmetic processing according to a previously read program or a previously written program. The control unit 52 repeatedly executes packet transmission / reception processing with the wireless unit 54.

  The packet transmission / reception process includes (i) synchronization packet transmission processing for broadcasting the synchronization packet to each synchronization wireless device, and (ii) each information request packet transmitted from each synchronization wireless device in response to the synchronization packet. Includes request reception processing to receive.

  The request reception process includes a process of obtaining an information request reception time indicating a time when the information request packet is received. The control unit 52 transmits a synchronization packet transmission time indicating the time at which the synchronization packet was transmitted in the previous packet transmission / reception process, and an information request reception time obtained corresponding to each synchronization wireless device in the previous packet transmission / reception process. , And included in the synchronization packet transmitted in the next packet transmission / reception process. The synchronization packet transmission time may not be the time when the synchronization packet was transmitted in the previous packet transmission / reception process, but may be the time when the synchronization packet itself is transmitted.

  The control unit 52 performs the transmission cycle adjustment process together with the wireless unit 54. That is, the control unit 52 adjusts the transmission cycle for executing synchronous packet transmission processing based on the synchronization status information included in each information request packet. The synchronization status information indicates the synchronization status between the local clock and the base station clock provided in each synchronization wireless device.

(7) Hardware of Synchronization Wireless Device FIG. 7 shows an example of hardware of the synchronization wireless device 14. The synchronization wireless device 14 includes a control unit 56, a local clock 57, an interface 58, and a wireless unit 60. The interface 58 is connected to an information processing apparatus such as the above-described wireless LAN node and an information terminal. The local clock 57 generates a time that defines the operation timing of the information processing apparatus connected to the interface 58 and outputs the time to the control unit 56.

  The wireless unit 60 receives the packet and outputs the packet to the control unit 56. Also, the wireless unit 60 transmits the packet output from the control unit 56.

  The control unit 56 is configured by, for example, a processor that executes arithmetic processing according to a previously read program or a previously written program. The control unit 56 repeatedly executes the packet transmission and reception process together with the wireless unit 60.

  The packet transmission / reception process includes (i) synchronization packet reception processing for transmitting a synchronization packet that is transmitted from the base station 10 and defines timing, and (ii) information when a predetermined response delay time has elapsed since the synchronization packet is received. Based on request transmission processing for transmitting a request packet, and (iii) the time when the synchronization packet is received, the time when the information request packet is sent, and the synchronization information included in the synchronization packet, The synchronization process which synchronizes a provided local clock and the base station clock with which base station 10 is provided is included. Also, the synchronization process includes a process of generating synchronization status information indicating the synchronization state of the local clock and the base station clock, and the request transmission process includes a process of including the synchronization status information in the information request packet.

  The synchronization packet includes a synchronization packet transmission time indicating the time when the base station 10 transmitted the synchronization packet in the previous packet transmission / reception process, and an information request indicating the time when the base station 10 received the information request packet in the previous packet transmission / reception process The reception time is included. The synchronous packet reception process includes a process of obtaining a synchronous packet reception time indicating a time when the synchronous packet is received. The request transmission process includes a process of obtaining an information request transmission time indicating a time at which the information request packet was transmitted. The synchronization packet transmission time may not be the time when the base station 10 transmits the synchronization packet in the previous packet transmission / reception process, but may be the time when the synchronization packet itself is transmitted from the base station 10. Different response delay times may be defined for each of the plurality of synchronization wireless devices.

  The control unit 56 controls the local clock 57 based on the initial time, the synchronization packet reception time, the information request transmission time, and the information request reception time, and synchronizes the time generated by the local clock 57 with the base station time.

  The control unit 56 outputs the time when the local clock 57 emits to the information processing apparatus connected to the interface 58.

  DESCRIPTION OF SYMBOLS 10 base station, 12-1 to 12-3 access point, 14-1 to 14-3 radio | wireless apparatus for synchronization, 16-1 to 16-3 wireless LAN node, 18 internet, 20 information terminal, 22 head part, 24 preamble , 26 communication data, 28 destination address, 32 payload section, 36 initial time, 38-1 to 38-n reception time information, 40 error correction code, 42 relay stations, 44 relay radios, 46 relay base stations, 48- 1 to 48-3 ad hoc wireless devices, 50 GPS receivers, 51 base station clocks, 52, 56 controllers, 54, 60 wireless units, 57 local clocks, 58 interfaces.

Claims (6)

A wireless unit that transmits and receives packets to and from a plurality of wireless devices;
A control unit configured to control the wireless unit;
The control unit
Synchronous packet transmission processing for broadcasting a synchronous packet defining timing to each of the wireless devices;
Request reception processing for receiving each information request packet transmitted from each wireless device in response to the synchronization packet;
Repeatedly performing transmission and reception processing including the
The control unit is further configured to:
The synchronization packet transmission based on synchronization status information included in each of the information request packets, the synchronization status information indicating a synchronization status between a local clock included in each wireless device and a base station clock included in the base station. Adjust the transmission cycle to execute the process,
The synchronization state includes a lock state where the difference between the time indicated by the local clock and the time indicated by the base station clock is within a predetermined range, the time indicated by the local clock, and the time indicated by the base station clock. There is a non-locking condition where the difference between
The control unit
The unlocked number of those in the non-locked state of the plurality of the wireless device, determined based on the synchronization status information included in each of said information request packet, you adjust the transmission cycle based on the unlocked number said base station and a child. In the base station according to claim 1 ,
The control unit
Wherein when unlocked number is 1 or more, said base station and shorten to Turkey the transmission cycle than the unlocked number is zero. A wireless unit that transmits and receives packets to and from a plurality of wireless devices;
A control unit configured to control the wireless unit;
The control unit
Synchronous packet transmission processing for broadcasting a synchronous packet defining timing to each of the wireless devices;
Request reception processing for receiving each information request packet transmitted from each wireless device in response to the synchronization packet;
Repeatedly performing transmission and reception processing including the
The control unit is further configured to:
The synchronization packet transmission based on synchronization status information included in each of the information request packets, the synchronization status information indicating a synchronization status between a local clock included in each wireless device and a base station clock included in the base station. Adjust the transmission cycle to execute the process,
The request reception process is
Including processing for determining an information request reception time indicating a time when the information request packet is received,
The control unit
A synchronization packet transmission time indicating a time when the synchronization packet is transmitted in the transmission / reception process described above, and an information request reception time determined corresponding to each wireless device in the transmission / reception process in advance A base station characterized by being included in the synchronization packet transmitted in transmission / reception processing. A wireless unit that transmits and receives packets to and from a plurality of wireless devices;
A control unit configured to control the wireless unit;
The control unit
Synchronous packet transmission processing for broadcasting a synchronous packet defining timing to each of the wireless devices;
Request reception processing for receiving each information request packet transmitted from each wireless device in response to the synchronization packet;
Repeatedly performing transmission and reception processing including the
The control unit is further configured to:
The synchronization packet transmission based on synchronization status information included in each of the information request packets, the synchronization status information indicating a synchronization status between a local clock included in each wireless device and a base station clock included in the base station. Adjust the transmission cycle to execute the process,
The request reception process is
Including processing for determining an information request reception time indicating a time when the information request packet is received,
The control unit
The information request reception time determined for each wireless device in the transmission / reception process above and the synchronization packet transmission time indicating the time when the synchronization packet is transmitted in the next transmission / reception process A base station characterized by being included in the synchronization packet transmitted in the transmission / reception process. A radio unit that transmits and receives packets to and from a base station;
A control unit configured to control the wireless unit;
The control unit
Synchronous packet reception processing for receiving a synchronous packet transmitted from the base station and defining timing;
A request transmission process for transmitting an information request packet after the synchronization packet is received;
A local clock included in the wireless device based on the time when the synchronization packet is received, the time when the information request packet is transmitted, and the synchronization information included in the synchronization packet, and a base station included in the base station Synchronization process to synchronize with the clock,
Repeatedly performing transmission and reception processing including the
The synchronization process includes a process of generating synchronization status information indicating a synchronization state between the local clock and the base station clock.
The request transmission process, see contains the process to include the synchronization status information to the information request packet,
The information for synchronization is
Information indicating the time when another synchronization packet was sent prior to the synchronization packet, or the time when the synchronization packet was sent,
Wireless device according to claim it to contain information indicating the time at which the information request packet in the previous the transmission and reception processing is received at the base station. In the wireless device according to claim 5 ,
The synchronization status information is either a locked state in which a difference between a time indicated by the local clock and a time indicated by the base station clock is within a predetermined range, or a non-locked state in which the difference is outside the predetermined range. A wireless device characterized by including information to be shown.

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