JP2018074534A - Base station and radio device - Google Patents

Abstract

An object of the present invention is to make the transmission / reception frequency of a synchronization packet between wireless devices appropriate. A base station 10 performs packet transmission / reception processing with synchronization wireless devices 14-1 to 14-n. The packet transmission / reception process includes a synchronization packet transmission process for broadcasting a synchronization packet to each synchronization radio apparatus, and a request reception process for receiving each information request packet transmitted from each synchronization radio apparatus in response to the synchronization packet. Including. The request reception process includes a process for obtaining an information request reception time indicating a time when the information request packet is received. The base station 10 adjusts the transmission cycle for executing the synchronization packet transmission process based on the synchronization status information included in each information request packet. The synchronization status information is information indicating a synchronization state between the local clock included in the synchronization wireless device and the base station clock included in the base station 10. [Selection] Figure 1

Description

  The present invention relates to a base station, a radio apparatus, and a radio communication system, and more particularly, to a synchronization process by packet transmission / reception.

  Wireless LAN (Local Area Network) is widely used. Some wireless LANs are provided with a plurality of access points connected to a communication network such as the Internet. An information terminal such as a personal computer or a smart phone performs packet communication using a radio signal with an access point, and is connected to a communication network via the access point.

  Each access point forms a service area in which wireless communication with an information terminal is possible. Each access point performs time-division communication with the information terminal to construct a plurality of communication lines. When the information terminal moves from one service area to another service area, the information terminal performs uninterrupted communication by the handover process. Thus, in order for each access point to perform time division communication and a plurality of access points operate in cooperation, the packet transmission / reception timing of each access point needs to be synchronized.

  Therefore, each access point acquires time information for synchronization processing from a signal transmitted from, for example, 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 a GPS satellite, and generates a time packet for synchronizing the time. The master broadcasts (broadcasts) time packets to a plurality of slaves via the wireless LAN. Non-Patent Document 2 describes a wireless LAN in which wireless communication is performed between a plurality of measurement nodes. Each measurement node includes a device that measures 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 timings based on communication between the plurality of measurement nodes.

JP 2009-111654 A

Masayuki Hiyama et al., “Examination and experiment of high-accuracy time synchronization method in wireless LAN”, IEICE Technical Report, vol. 108, no. 460, IA2008-79, pp. 73-78, March 2009. , SITE2008-56, IA2008-79.

  Some wireless communication standards require a transmission suspension for a predetermined time or more after transmitting a wireless signal. When a plurality of wireless devices execute the synchronization processing under such a standard, each wireless device needs to execute the synchronization processing under the limitation of the transmission time of the wireless signal. Under such a time limit, it is necessary for each wireless device to execute synchronization processing quickly. However, when a plurality of wireless devices attempt to execute synchronization processing quickly, packets for synchronization processing are frequently transmitted and received between wireless devices, resulting in communication congestion.

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

  The present invention provides a base station comprising: 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. A transmission / reception process including a synchronization packet transmission process for broadcasting to a wireless device and a request reception process for receiving each information request packet transmitted from each wireless device in response to the synchronization packet is repeated together with the wireless unit. The control unit further executes synchronization indicating synchronization status information included in each of the information request packets and indicating a synchronization state between a local clock included in each wireless device and a base station clock included in the base station The transmission cycle for executing the synchronous packet transmission process is adjusted based on status information.

  Preferably, the synchronization state includes a lock 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, a time indicated by the local clock, and the base station clock There is a non-locking state in which the difference from the indicated time is outside a predetermined range, and the control unit includes the number of non-locking devices of the non-locking state among the plurality of wireless devices included in each of the information request packets Obtained based on the synchronization status information, and adjust the transmission cycle based on the number of non-locks.

  Preferably, the control unit shortens the transmission cycle when the number of non-locks is 1 or more than when the number of non-locks is zero.

  Preferably, the request reception process includes a process of obtaining an information request reception time indicating a time when the information request packet is received, and the control unit indicates a time when the synchronization packet is transmitted in the previous transmission / reception process. The synchronization packet transmission time and the information request reception time obtained corresponding to each wireless device in the previous transmission / reception process are included in the synchronization packet transmitted in the next transmission / reception process.

  Preferably, the request reception process includes a process of obtaining an information request reception time indicating a time at which the information request packet is received, and the control unit is obtained corresponding to each of the wireless devices in the previous transmission / reception process. The information request reception time and a synchronization packet transmission time indicating a time at which the synchronization packet is transmitted in the next transmission / reception process are included in the synchronization packet transmitted in the next transmission / reception process.

  Further, the present invention provides a radio apparatus comprising a radio unit that transmits and receives packets to and from a base station, and a control unit that controls the radio unit, wherein the control unit is transmitted from the base station, and has a timing A synchronization packet reception process for receiving a specified 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; a time when the information request packet is transmitted And a transmission / reception process including a synchronization process for synchronizing a local clock included in the wireless device and a base station clock included in the base station based on synchronization information included in the synchronization packet together with the wireless unit 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 includes a process of including the synchronization status information to the information request packet, it is characterized.

  Preferably, the synchronization status information includes a locked state where 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 an unlocked state where the difference is outside the predetermined range. Contains information indicating either.

  Preferably, the information for synchronization includes the time at which another synchronization packet is transmitted prior to the synchronization packet, or information indicating the time at which the synchronization packet is transmitted, and the information request in the previous transmission / reception process. Information indicating the time when the packet was received at the base station.

  ADVANTAGE OF THE INVENTION According to this invention, the transmission / reception frequency of the packet for a synchronization between radio | wireless apparatuses can be made appropriate.

It is a figure which shows the structure of the communication system which concerns on embodiment of this invention. It is a sequence chart of repeated synchronous 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 a synchronization.

(1) Configuration of Communication System FIG. 1 shows a 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 and constitutes 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 performs wireless communication with an access point that forms a service area in which the information terminal 20 exists, and is connected to the Internet 18.

  The base station 10 includes a base station clock for defining operation timing. The base station 10 receives the reference time information from the GPS satellite, and adjusts the time (base station time) generated 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 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 executes synchronization processing together with the synchronization wireless device 14-j. The synchronization wireless device 14-j adjusts the time generated by its own local clock to the base station time by executing the synchronization process. The local clock gives the time matched to the base station time to the wireless LAN node 16-j. The wireless LAN node 16-j operates at a timing according to the time given from the local clock. As a result, the operations of the wireless LAN nodes 16-1 to 16-3 are synchronized.

(2) Repetitive Synchronization Processing (2-1) Packet Transmission / 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 a synchronization packet to each synchronization wireless device at a predetermined transmission cycle ST, and each synchronization wireless device that has received the synchronization packet transmits an information request packet to the base station 10. It is processing. The base station 10 includes the information obtained according to the information request packet in the synchronization packet to be transmitted next. Thus, in the repeated synchronization process, the synchronization process by the transmission of the synchronization packet by the base station 10 and the transmission of the information request packet by each synchronization wireless device (packet transmission / reception process) is repeated. In the repeated synchronization processing, the base station 10 adjusts the transmission cycle ST and adjusts the frequency of packet transmission / reception according to whether or not the local clock of each synchronization wireless device is synchronized with the base station clock.

  The base station 10 transmits a synchronization packet destined for the synchronization wireless devices 14-1 to 14-3 at time t0 (S101). The synchronization packet is a packet to be transmitted to each synchronization wireless device in order to define the timing for executing the synchronization process. When transmitting the synchronization packet, the base station 10 includes the broadcast address commonly assigned to the synchronization wireless devices 14-1 to 14-3 in the synchronization packet. In addition, 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 radio apparatuses 14-1 to 14-3 with the base station clock, and will be described in detail later. The base station 10 further obtains an initial time t0 (synchronization packet transmission time) at which the synchronization packet is transmitted from its own base station clock, and stores the initial time t0. Each radio apparatus for synchronization executes processing according to the synchronization packet by recognizing that the broadcast address is included in the received synchronization packet.

  Specifically, the synchronization wireless device 14-1 receives the synchronization packet at time t11 after time Δ1 from time t0. The synchronization wireless device 14-2 receives the synchronization packet at time t12 after time Δ2 from time t0. Synchronization wireless device 14-3 receives the synchronization packet at time t13, which is after time Δ3 from time t0. Each radio apparatus for synchronization obtains the synchronization packet reception time when the synchronization packet is received by using a local clock included in the synchronization apparatus, and stores the synchronization packet reception time. That is, the synchronization wireless devices 14-1 to 14-3 store the synchronization packet reception times t11 to t13, respectively.

  Each synchronization wireless device transmits an information request packet when a predetermined response delay time elapses after receiving the synchronization packet (S102). In the example shown in FIG. 2, response delay times d1 to d3 are defined for the synchronization wireless devices 14-1 to 14-3, respectively. When transmitting the information request packet, each synchronization wireless device obtains an information request transmission time for transmitting the information request packet by using a local clock provided therein, 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 wireless device includes synchronization status information described later in the information request packet. The synchronization status information indicates the synchronization state 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 a locked state or an unlocked state. The 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 is within a predetermined range for a predetermined time or longer, for example, a predetermined time for a predetermined time or longer. It is a state that is below the threshold value. The non-locked state is a state in which the difference between the time indicated by the local clock provided in the synchronization wireless device and the time indicated by the base station clock provided in the base station 10 is outside a predetermined range, for example, a state exceeding a predetermined threshold. Say.

  Further, the non-lock state includes a standby state and a holdover state. The standby state refers to a state from when the synchronization wireless device is activated until the local clock is locked by the synchronization process. The holdover state is a state where the local clock is once locked, but communication of the synchronization packet or information request packet becomes impossible due to deterioration of the communication state, etc., and the local clock is no longer locked, or that state Until the local clock is locked by the synchronization process.

  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 information request reception times t31, t32, and t33 at which each information request packet has been received from the base station clock. Further, the base station 10 stores the synchronization status information included in each information request packet. As will be described later, the base station 10 adjusts the transmission cycle 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 radio apparatus is determined so that a plurality of information request packets transmitted from a plurality of synchronization radio apparatuses are not received by the base station 10 in a time zone. . 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, receives a synchronization packet after a time Δi from the initial time t0. Then, it is assumed that the other synchronization wireless device 14-j receives the synchronization packet after the time Δj from the 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 wireless device 14-j is Δj. .

  When 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, when 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 at the base station 10 with overlapping time zones, the response is made so 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 destined for 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 about 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 with the transmission of the synchronization packet (S101) and the reception of the information request packet (S102) executed within the previous transmission cycle ST. The reception time information is information in which the address of the source synchronization wireless device is associated with the reception time (information request reception time) of the information request packet transmitted from the synchronization wireless device. If the addresses of the synchronization wireless devices 14-1 to 14-3 are AD1 to AD3, respectively, the reception time information in which the address AD1 is associated with the information request reception time t31, and the address AD2 and the information request reception time t32 are represented. The associated reception time information and the reception time information in which the address AD3 and the information request reception time t33 are associated are included in the synchronization packet.

  FIG. 3 shows the structure of the synchronization packet. The synchronization packet includes a head part 22 and a payload part 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 portion 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 accumulated value of elapsed time from a certain time, or may be a value representing GMT (Greenwich Mean Time). The error correction code 40 is used by the synchronization wireless device to perform error detection and error correction for the codes representing the preamble 24, the communication data 26, the destination address 28, the initial time 36, and the reception time information 38-1 to 38-n. This is a code for execution.

  Returning to FIG. 2, the repeated synchronization process will be described. Each radio apparatus for synchronization executes processing according to the synchronization packet by recognizing that the broadcast address is included in the received 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 Δ2 from time t4. The synchronization wireless device 14-3 receives the synchronization packet at time t53 after time Δ3 from time t4.

  Each synchronization wireless device extracts the initial time t0 from the synchronization packet and stores it. Also, the reception time information corresponding to itself is extracted from the synchronization packet, and the information request reception time is acquired from the reception time information and stored. 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.

  As described above, the synchronization wireless device 14-1 receives the synchronization packet, transmits the information request packet, and further receives the next synchronization packet, whereby the initial time t0, the synchronization packet reception time t11, and the information request transmission. 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 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 has been described. The number is arbitrary.

(2-2) Calculation of offset time for adjustment and time adjustment processing Synchronization wireless device 14-k, which is one of n synchronization wireless devices 14-1 to 14-n, performs packet transmission / reception processing. Assume that the initial time t0, the synchronization packet reception time t1k, the information request transmission time t2k, and the information request reception time t3k are stored. The synchronization radio apparatus 14-k obtains the propagation time Dk between the synchronization radio apparatus 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 determined by the base station clock included in the base station 10, and the synchronization packet reception time t1k and the information request transmission time t2k are local clocks included in the synchronization wireless device 14-k. Is the time determined by Assuming that the local clock is advanced by the offset time To with respect to the base station clock, the propagation time Ds of the synchronization packet and the propagation time Dd of the information request packet are expressed as (Equation 2) and (Equation 3), respectively. Is done.

(Expression 2) Ds = t1k−t0−To
(Equation 3) Dd = t3k−t2k + To

  Since propagation time Ds and propagation time Dd are equal to Dk, (Equation 1) is obtained by adding both sides of (Equation 2) and (Equation 3) and dividing by 2.

  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 = (t1k-t0) -Dk

  Note that 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

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

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

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

  Σ means to add and sum q = 0 to M−1. To (q) indicates the offset time To obtained in the past packet transmission / reception process q times. g (q) is a weighting coefficient for the offset time obtained in the past packet transmission / reception process q times. For example, by increasing g (q) as q is smaller, the contribution to the adjustment offset time Ta increases as the offset time To becomes a newly obtained value. All of g (0) to g (M-1) may be 1. When the number of executions of packet transmission / reception processing is less than M times, such as at startup, the synchronization wireless device 14-k obtains a weighted moving average value for the offset time To obtained by the number of executions, An adjustment offset time Ta is obtained.

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

  Other synchronization wireless devices other than the synchronization wireless device 14-k perform the same processing. That is, a time adjustment process is performed in which each local time is brought close to or coincident 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 the wireless LAN node attached thereto.

  In the repeated synchronization process, the packet transmission / reception process is repeated, and each synchronization wireless device repeatedly executes the time adjustment process. As a result, the local time of each synchronization wireless device approaches or matches 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 equal to or less than a predetermined threshold, and by repeating the time adjustment process, The local time of each synchronization wireless device converges to the base station time. As a result, the local clock is changed from the unlocked state to the locked state.

  Each time the time adjustment process is executed, the synchronization wireless device 14-k (k = 1 to n) generates synchronization status information. That is, the synchronization radio apparatus 14-k obtains an adjustment offset time indicating a difference between the base station time and the local time, and when the adjustment offset time is equal to or shorter than a predetermined threshold over a predetermined time. The local clock of the synchronization wireless device 14-k is determined to be locked. On the other hand, when the adjustment offset time exceeds a predetermined threshold, it is determined that the local clock of the synchronization wireless device 14-k is in an unlocked state. The synchronization wireless device 14-k generates synchronization status information indicating whether its own local clock is locked or unlocked, and transmits an information request packet to the base station 10 every time a synchronization packet is received. Include synchronization status information. The synchronization status information is acquired by the base station 10 that has received the information request packet. As will be 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.

  Through such processing, each wireless LAN node acquires a 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. As a result, the operations of the plurality of wireless LAN nodes are synchronized.

  Further, according to the processing executed in the communication system, a synchronization packet is broadcast by using a plurality of synchronization wireless devices as destinations. As a result, information related to the synchronization process is quickly given to each synchronization wireless device.

  In IEEE 1588, which is a standard related to 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 wireless device). 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 the synchronization processing. Accordingly, since two types of packets may be used, the processing becomes simpler than that according to IEEE 1588, and the synchronization processing is performed quickly.

  In the above description, the embodiment has been described in which the initial time t0 for 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 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 time at which this synchronization packet is transmitted is described in the initial time 36 of the payload section 32 shown in FIG. When the base station 10 transmits a 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 wireless device 14-k that has received the first synchronization packet obtains 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 it. To do. Each of the synchronization wireless devices 14-k is based on the information request reception time t3k extracted from the second synchronization packet in addition to the previously stored initial time t0, synchronization packet reception time t1k, and information request transmission time t2k. To obtain the offset time To.

(3) Transmission period adjustment process Next, the process in which the base station 10 adjusts the transmission period of a synchronous packet is demonstrated. When the local clock included in each of the synchronization wireless devices 14-1 to 14-n is in the locked state, the transmission cycle may be longer than that in the unlocked state. This is because once the local clock is locked, the oscillation frequency of the oscillator included in the local clock and the phase of the clock signal generated by the oscillator may be stabilized, and the frequency of the time adjustment process may be reduced. Therefore, the base station 10 executes the following transmission cycle adjustment process every time each synchronization wireless apparatus executes the time adjustment process.

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

  The base station 10 sets the transmission cycle to the first transmission cycle when the number of non-locks is 1 or more. On the other hand, when the number of non-locks 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 longer after transmitting a wireless signal. When designing a communication system according to this standard, the first transmission cycle and the second transmission cycle are set to a length equal to or 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 a newly set transmission cycle has elapsed since the time when the synchronization packet was transmitted first.

  According to such a process, every time the information request packet transmitted from each of the synchronization wireless devices 14-1 to 14-n is received in the packet transmission / reception process, the base station 10 executes the transmission cycle adjustment process, The transmission cycle from the transmission of the synchronization packet to the next transmission of the synchronization packet is set. As a result, the transmission cycle when the number of non-locks is 1 or more is shorter than the transmission cycle when the number of non-locks is 0, and the time interval at which the time adjustment process is executed is shortened. Therefore, the local clock in the non-locked 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 there is at least one synchronization wireless device in which the local clock is in the unlocked state. The cycle becomes longer. As a result, the number of packets transmitted / received between the base station 10 and each synchronization wireless device within a predetermined time is reduced, 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-locks is 1 or more, and the transmission cycle is set to the second transmission cycle when the number of non-locks is 0. The process of changing the cycle in two stages has been described. In addition to such processing, the base station 10 may execute processing for changing the transmission cycle in three or more stages according to the number of unlocked devices. For example, you may perform the process which shortens a transmission period, so that the number of non-locks increases.

(4) System provided with relay station FIG. 4 shows a configuration of a communication system according to an application embodiment. In this communication system, a relay station 42 is provided with respect to the communication system shown in FIG. The relay station 42 includes a relay radio device 44 and a relay base station 46. The relay wireless device 44 has the same configuration as that of the synchronization wireless devices 14-1 and 14-2, and executes the same processing as that of the synchronization wireless devices 14-1 and 14-2. The relay base station 46 has the same configuration as that of the base station 10 and executes the same processing as that of the base station 10.

  The relay radio device 44 executes a synchronization process with the base station 10 and adjusts the time of the local clock to the base station time. The relay radio device 44 gives the time of the local clock to the relay base station 46. The relay base station 46 adjusts the time of the base station clock included in the relay base station 46 to the time given from the relay wireless device 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 executing 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.

  Through such processing, each wireless LAN node 16-j acquires time synchronized with the base station time of the relay base station 46 and further synchronized with the base station time of the base station 10. Each wireless LAN node 16-j operates at a timing according to the time given from the synchronization wireless device 14-j, so that the operations of a plurality of access points are synchronized. 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 executes synchronization processing with the relay station 42, and the relay station 42 executes synchronization processing with the base station 10. Therefore, the distance between the base station 10 and each access point 12-j may be increased as compared with the communication system shown in FIG.

  The synchronization wireless device and the wireless LAN node may constitute an ad hoc wireless device as well as a wireless LAN access point. The plurality of ad hoc wireless devices transmit packets from the source ad hoc wireless device to the destination ad hoc wireless device by multi-hop communication. Multi-hop communication is communication in which a packet transmitted from a source ad hoc wireless device is directly transmitted to a destination ad hoc wireless device by relay transmission by one or more other ad hoc wireless devices depending on the communication status. Refers to the form.

(5) Ad Hoc Communication System FIG. 5 shows the configuration of an ad hoc communication system. The ad hoc wireless device 48-j (j = 1 to 3) includes a synchronization wireless device 14-j and a wireless LAN node 16-j. The synchronization wireless device 14-j performs synchronization processing with the base station 10 and generates a time synchronized with the reference time. The synchronization wireless device 14-j gives the time synchronized with the reference time to the wireless LAN node 16-j. The wireless LAN node 16-j operates according to the time given from the synchronization wireless device 14-j. As a result, the operation timings of the wireless LAN nodes 16-1 to 16-3 are synchronized. 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) Base Station Hardware FIG. 6 shows an example of the base station 10 hardware. 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 the reference time information from the GPS satellite 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 adjust the base station time to the reference time.

  The wireless unit 54 receives the packet and outputs it to the control unit 52. In addition, 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 using a pre-read program or a pre-written program. The control unit 52 repeatedly executes packet transmission / reception processing together with the wireless unit 54.

  The packet transmission / reception processing includes (i) a synchronization packet transmission process for broadcasting a 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 for obtaining an information request reception time indicating a time when the information request packet is received. The control unit 52 obtains the synchronization packet transmission time indicating the time when the synchronization packet was transmitted in the previous packet transmission / reception process, and the information request reception time obtained for each synchronization wireless device in the previous packet transmission / reception process. And included in the synchronous packet transmitted in the next packet transmission / reception process. The synchronization packet transmission time may be the time at which the synchronization packet itself is transmitted, not the time at which the synchronization packet was transmitted in the previous packet transmission / reception process.

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

(7) Hardware of Synchronization Radio Device FIG. 7 shows an example of hardware of the synchronization radio 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 or 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 radio unit 60 receives the packet and outputs it to the control unit 56. Further, the radio unit 60 transmits the packet output from the control unit 56.

  The control unit 56 is configured by, for example, a processor that performs arithmetic processing using a pre-read program or a pre-written program. The control unit 56 repeatedly executes packet transmission / reception processing together with the wireless unit 60.

  The packet transmission / reception processing includes (i) a synchronization packet reception processing for receiving 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 reception of the synchronization packet. Based on the request transmission processing for transmitting the request packet, and (iii) 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, It includes a synchronization process for synchronizing the local clock provided with the base station clock provided in the base station 10. The synchronization process includes a process of generating synchronization status information indicating the synchronization state between 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. And reception time. The synchronization packet reception process includes a process for obtaining a synchronization packet reception time indicating a time when the synchronization packet is received. The request transmission process includes a process for obtaining an information request transmission time indicating a time at which the information request packet is transmitted. The synchronization packet transmission time may be the time when the synchronization packet itself is transmitted from the base station 10 instead of the time when the base station 10 transmits the synchronization packet in the previous packet transmission / reception process. Different response delay times may be set 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 adjusts the time emitted by the local clock 57 to the base station time.

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

  10 base station, 12-1 to 12-3 access point, 14-1 to 14-3 synchronization wireless device, 16-1 to 16-3 wireless LAN node, 18 Internet, 20 information terminal, 22 head unit, 24 preamble , 26 Communication data, 28 Destination address, 32 Payload part, 36 Initial time, 38-1 to 38-n Reception time information, 40 Error correction code, 42 Relay station, 44 Relay radio equipment, 46 Relay base station, 48- 1-48-3 Ad hoc wireless device, 50 GPS receiver, 51 base station clock, 52,56 control unit, 54,60 radio unit, 57 local clock, 58 interface.

Claims (8)

A wireless unit that transmits and receives packets to and from a plurality of wireless devices;
In a base station comprising a control unit that controls the radio unit,
The controller is
A synchronization packet transmission process that broadcasts to each wireless device a synchronization packet that defines timing; and
A request reception process for receiving each information request packet transmitted from each wireless device in response to the synchronization packet;
Repeatedly performing the transmission / reception process including the wireless unit,
The control unit further includes:
Transmission of the synchronization packet based on synchronization status information included in each of the information request packets, the synchronization status information indicating a synchronization state between a local clock included in each of the wireless devices and a base station clock included in the base station A base station characterized by adjusting a transmission cycle for executing processing. In the base station according to claim 1,
The synchronization state includes a lock 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, a time indicated by the local clock, and a time indicated by the base station clock. There is a non-locking state where the difference of is outside the predetermined range,
The controller is
Obtaining the number of unlocked ones of the plurality of wireless devices in the unlocked state based on the synchronization status information included in each of the information request packets, and adjusting the transmission cycle based on the number of unlocked devices, A base station characterized by that. In the base station according to claim 2,
The controller is
The base station characterized in that when the number of non-locks is 1 or more, the transmission cycle is made shorter than when the number of non-locks is 0. In the base station according to any one of claims 1 to 3,
The request reception process includes:
A process for obtaining an information request reception time indicating a time at which the information request packet is received;
The controller is
The synchronization packet transmission time indicating the time at which the synchronization packet was transmitted in the previous transmission / reception process, and the information request reception time determined corresponding to each wireless device in the previous transmission / reception process, A base station, which is included in the synchronization packet transmitted by transmission / reception processing. In the base station according to any one of claims 1 to 3,
The request reception process includes:
A process for obtaining an information request reception time indicating a time at which the information request packet is received;
The controller is
The information request reception time obtained corresponding to each wireless device in the previous transmission / reception process, and a synchronization packet transmission time indicating a time at which the synchronization packet is transmitted in the next transmission / reception process, The base station is included in the synchronization packet transmitted in the transmission / reception process. A wireless unit that transmits and receives packets to and from the base station;
A wireless device comprising: a control unit that controls the wireless unit;
The controller is
A synchronization packet reception process for receiving a synchronization 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;
Based on the time when the synchronization packet was received, the time when the information request packet was transmitted, and the synchronization information included in the synchronization packet, the local clock included in the wireless device and the base station included in the base station Synchronization processing to synchronize with the watch,
Repeatedly performing the transmission / reception process including the wireless unit,
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 wireless transmission apparatus, wherein the request transmission process includes a process of including the synchronization status information in the information request packet. The wireless device according to claim 6, wherein
The synchronization status information indicates either a locked 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, or an unlocked state where the difference is outside the predetermined range. A wireless device comprising information to indicate. The radio apparatus according to claim 6 or 7,
The information for synchronization is
The time at which another synchronization packet was transmitted prior to the synchronization packet, or information indicating the time at which the synchronization packet was transmitted;
Information indicating the time at which the information request packet was received at the base station in the previous transmission / reception process;
A wireless device comprising:

Images