JP2005269369A - Time synchronizing method in frequency hopping data communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform time synchronization in frequency hopping data communication from a master station over wide range beyond the communication range of the master station, without installing a plurality of master stations. <P>SOLUTION: In this time synchronization in the frequency hopping data communication, the master station comprises the steps of periodically transmitting frequency-hopping time information to each node; updating a self-timer for frequency hopping to the time information, when each node receives the time information; transmitting the received frequency hopping time as each relay transmission node, when each node receives the time information; updating its own timer for frequency hopping to the time information, when each node outside the communication range of the master receives the time information from each relay transmission node; and transmitting the received frequency-hopping time as each relay transmission node, when each node outside the communication range of the master receives the time information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a time synchronization method in frequency hopping data communication, and has a relay function provided to at least one access point (hereinafter referred to as a master station) within and outside the communication range of the master station. The present invention relates to a time synchronization method in relation to a communication device (hereinafter referred to as a node).

  The frequency hopping time synchronization method is used in the wireless LAN (IEEE 802.11) method. When performing data communication, it is necessary to install at least one master station within the data communication range.

A standard frequency hopping time synchronization method will be briefly described with reference to FIG.
The beacon B from the master station includes time information for frequency hopping. Based on the time information in the beacon, the process moves to the next frequency (f2), (f3). Data communication with the master station is performed only at the same frequency. The master station transmits NT1, and in response, node 1 returns NR1. The master station transmits data NT3 to node 3, and in response, node 3 returns NR3. These steps perform data communication within the same frequency time (T). After time T, the frequency is changed all at once and the data is moved to the frequency (f2) to perform data communication. After the frequency shift, the beacon B is always transmitted from the master station and the time until the next frequency shift is set.
IEEE Std 802.11, 1999 Edition for Information Technology-Telecommunications and Information Exchange between Systems-Local and Metropolitan Area Network-Specific Requirements-Part 11: Wireless Lan Medium Access Control (MAC) and Physical Layer (PHY) Specifications P156-P167

In FIG. 6, when data communication is performed outside the communication area of the master station A, the node 1 cannot receive the beacon B1 from the master station A. It searches for all available frequencies set in advance until a beacon B2 from a further master station 2 is found. When the node 1 finds a new master station 2, it matches the frequency hopping timer value included in the beacon B2 of the master station. Thereafter, the node 1 can perform data communication with the master station 2.
IEEE Std 802.11, 1999 Edition for Information Technology-Telecommunications and Information Exchange between Systems-Local and Metropolitan Area Network-Specific Requirements-Part 11: Wireless Lan Medium Access Control (MAC) and Physical Layer (PHY) Specifications P125-P130

Further, in FIG. 7, the master station 1 and the master station 2 are electrically connected by Ethernet (registered trademark) or the like. The master station 1 can communicate data with the node 1 in the area 1, and the master station 2 can communicate data with the node 2 in the area 2. When data communication from the node 1 to the node 2 is necessary, data is transmitted from the node 1 to the master station 1 and then to the node 2 through the master station 2.
Here, in the data communication between the nodes, the master station grasps the ID of the node within a range where data communication is possible.
JP 2000-151467 A

In the frequency hopping method as shown in FIG. 8, the distance between the master stations can be brought close to some extent by mapping the used frequency channel with the orthogonal code.
IEEE Std 802.11, 1999 Edition for Information Technology-Telecommunications and Information Exchange between Systems-Local and Metropolitan Area Network-Specific Requirements-Part 11: Wireless Lan Medium Access Control (MAC) and Physical Layer (PHY) Specifications P178-P181

  The problem to be solved is that when performing time synchronization using the frequency hopping method between the master station and the node, a node must exist within the range of the master station to perform time synchronization. In order to cover the communication range, it was necessary to install many master stations.

  In addition, if the master stations are close to each other, an interference problem will occur within the time when the same frequency is used. Therefore, the installation cost of the master station and its communication range becomes expensive in consideration of the interference problem. It was a point.

  Further, in the frequency hopping method, since the number of predetermined use frequencies is large, it takes a long time for the node to search for a new master station.

  Furthermore, when performing data communication between the master station and the node, since the data communication between the nodes is performed via the master station, even if the data communication between the nodes is possible, it is outside the data communication range of the master station. The more complex data communication through the station has to be provided.

  The main feature of the present invention is that time synchronization in frequency hopping data communication is performed over a wide range from nodes provided within and outside the communication range of the master station without installing a plurality of master stations. .

  According to the time synchronization method in the data communication of the frequency hopping method of the present invention, frequency hopping is performed in a wide area by periodically transmitting one time synchronization information to each node, and each node relaying the time synchronization information. System synchronization can be taken. Therefore, there is an advantage that it can be installed freely without being aware of the location of the access point such as a normal wireless LAN. Furthermore, there is also an advantage that a multi-hop system using the frequency hopping method can be easily performed by inserting the self node ID when transmitting the time synchronization information of the frequency hopping method.

  In the frequency hopping synchronization method according to the present invention, a master station periodically transmits frequency hopping time information to each node, and each node sets a self-timer for frequency hopping when receiving the time information. A step of updating to time information, a step of transmitting the received frequency hopping time as each relay transmission node at the time of reception by each of the nodes, and a time information from each relay transmission node of each node outside the communication range of the master station Updating the self-timer for frequency hopping to the time information when receiving the signal, and transmitting each received frequency hopping time as each relay transmitting node when each node outside the communication range of the master station receives, The object was realized by comprising.

  The master station periodically transmits the frequency hopping time information to each node if the transmitting node transmits its own frequency hopping timer value in the data and transmits it by broadcast or by one-to-one data communication. Good.

Further, when each node transmits as a relay node, the own node ID is embedded in the data, and the relay transmission node can automatically determine whether to perform relay transmission by checking the own node ID in the received data. .
Note that the relay node may use the relay ID in the received data as a routing table.

According to the above means, the following operation can be obtained. That is,
1. The master station periodically transmits frequency hopping time information to each node. All the nodes that have received the time information have the same time information, and further relay the time information, so that the time information can be easily time synchronized with the outside of the data communication range of one node.
2. Since the self ID is included in the data when relaying the time information, the route to the node that sent the frequency hopping time information can be easily detected.
3. The route can be stored in a memory and used for data communication to a time information transmission base.
4). Since route information is periodically sent along with time information, a change in the relay route to the time information transmission source is recognized by comparing with the stored information as described above, so it can easily cope with dynamic changes. .
5). Since the relay of the time information is not performed when the self ID is included in the relay data, it is possible to easily avoid an infinite loop when relay data is transmitted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a time synchronization method in frequency-hopping data communication as Embodiment 1 of the present invention.
The master station (node ID 0) periodically transmits time information of the frequency hopping method and the used frequency currently used in data communication by simultaneous broadcast. In FIG. 1, transmission is performed by simultaneous broadcast to predetermined frequencies, for example, all frequencies of F1, F2, F3, F4, and F5. The residence time of each frequency F1, F2, F3, F4, and F5 used in the broadcast communication is set sufficiently shorter than the transition time to the next frequency used in data communication.
The data communication possible range from the master station (node ID 0) is node ID 1 and node ID 2.
Node ID 1 and node ID 2 are in a state where data communication is possible at a frequency of F1. Node ID 11 and node ID 2 receive time information from the master station (node ID 0). This time information means a transition time to a predetermined frequency pattern. Node IDs 1 and 2 update the value of the self-timer and the current data communication use frequency with the received broadcast data.
In FIG. 1, the frequency for data communication is changed after the broadcast communication.
The time information of the frequency hopping method is simultaneously broadcast again using the node ID 1 and node ID 2. At this time, the self-node ID is put in the broadcast data and transmitted.
It is confirmed that the self node ID is not included in the received broadcast, and if the self node ID is included, the broadcast is not transmitted. Thereby, loop detection is performed.
Node ID 2 broadcasts simultaneously to all the used frequencies of F 1, F 2, F 3, F 4, and F 5 in the same manner as the master station (node ID 0).
Node ID 2 switches to a predetermined frequency (here, frequency F 1) from the broadcast data after sending the broadcast to all the used frequencies.
Since the node ID 3 can perform data communication at the frequency F2, the node ID 2 receives the time information for the frequency hopping method when performing the simultaneous broadcast communication at the frequency F2. The broadcast data includes time information and use frequency information. Node ID 3 updates the self-timer value using time information, and performs loop broadcast after adding loop detection and self-node ID to the data, similar to node ID 2. After the broadcast communication, the frequency F1 included in the broadcast communication is switched.
Since the node ID 4 is capable of data communication at the frequency F2, the node ID 3 receives the time information for the frequency hopping method when performing the broadcast communication at the frequency F2. Node ID 4 updates the self-timer value using time information, and performs loop broadcast after adding loop detection and self-node ID to the data in the same manner as other nodes. After performing simultaneous broadcast communication, the frequency is switched to F1.
Since node ID 5 is capable of data communication at frequency F 5, node ID 4 receives time information for the frequency hopping method when broadcast communication is performed at frequency F 5. The node ID 5 updates the self-timer value using the time information, and performs loop broadcast after adding the loop detection and the self-node ID to the data in the same manner as other nodes. After performing simultaneous broadcast communication, the frequency is switched to F1.
As described above, the node ID1, ID2, ID3, ID4, and ID5 can have time information of the same frequency hopping method.

As described above, each node that receives the broadcast from the master station stores the route information included in the broadcast data in the node memory. FIG. 2 shows a route table stored in each node.
In FIG. 2, since the master station (node ID 0) is the node that sent the simultaneous broadcast, nothing is stored. In the node ID 1 table, two routes are stored by the table created at the time of direct broadcast reception directly from the master station (node ID 0) and the broadcast received from the node ID 2.
In the node ID 2 table, two routes are stored by the table created at the time of simultaneous broadcast reception directly from the master station (node ID 0) and the broadcast received from the node ID 1.
The node ID3 table stores the route table of the node ID2-parent station (node ID0) included in the simultaneous broadcast received from the node ID2.
The node ID4 table stores a route table of node ID3-node ID2-master station (node ID0) included in the broadcast received from node ID3.
The node ID5 table stores a route table of node ID4-node ID3-node ID2-parent station (node ID0) included in the broadcast received from node ID4.

The route table does not transmit more than an appropriate length so that extremely long information does not circulate.
In order to confirm the route table, each node transmits data to the master station (node ID 0). When a response (ACK) is returned from the master station (node ID 0), the route table is used for data communication.
For confirmation of the route table, another route table possessed by each node may be used. If no response (ACK) is returned from the master station (node ID 0), the next simultaneous broadcast may be awaited.
Since the route information is included in the data from each node that has reached the master station (node ID 0), a response (ACK) addressed to each node is issued and at the same time, each node appears in the route table of the master station (node ID 0). Save the route to.
Maintenance of the route table of each node including the master station (node ID 0) is performed based on information that the route information is different from each node with respect to the time information of the periodic frequency hopping method.
Each node has route information to a plurality of master stations (node ID 0) on the route table.
The master station (node ID 0) has route information to all nodes capable of data communication in the route table by route confirmation from each node.

FIG. 3 illustrates an operation for performing fine adjustment of time synchronization of inter-node frequency hopping.
When performing data communication from the node ID 5 to the master station (node ID 0), the route table information shown in FIG. 2 is included in the data and data communication is performed. At this time, the data includes data such as frequency hopping time information, path information, packet ID, and the like.
Node ID 4 receives data from node ID 5 and sets its own timer. The node ID 4 confirms that the self ID is included in the route information in the received data and transmits the data.
Node ID 3 receives data from node ID 4 and sets its own timer. Confirm that the self ID is included in the route information in the received data and transmit the data.
Similarly, node ID2 receives data from node ID3 and sets its own timer. Confirm that the self ID is included in the route information in the received data and transmit the data.
The master station (node ID 0) receives data from node ID 2 and sets its own timer.
In such data communication, the time information of the frequency hopping method is finely adjusted while relaying.

An example of when a retransmission occurs using route table of FIG. 2, as a second embodiment will be described with reference to FIG.
When node ID3 tries to perform data communication with the master station (node ID0), the master station (node ID0) is selected through route table ID1. The route information is put into the data from the node ID3 and is transmitted to the node ID1 (NT1). However, if the response (ACK) from the node ID 1 is not returned, the node ID 3 tries to transmit data using another route table if there is no response after several retransmission attempts.
In the case of FIG. 4, the data is transmitted from the node ID 3 to the node ID 2 (NT2). If there is no error in the received data, the node ID2 returns a response (ACK3) to the node ID3. The node ID 2 transmits data to the master station (node ID 0) by the route information in the data. If there is no error in the received data, the master station (node ID 0) returns a response (ACK 2) to node ID 2.

Using this method, the present invention can be applied even when a combination with the direct spreading method (DS) or OFDM method, the DS-FH method or the OF-DM-FH method is used.
Since the DS method and OFDM method are used in wireless LAN and terrestrial digital broadcasting, detailed description thereof is omitted.
That is, regardless of signal processing such as DS spread code or OFDM Fourier transform, it is possible to maintain a time synchronization relationship with one node by combining frequency hopping methods.

As described above, according to the time synchronization method in the frequency hopping data communication of the present invention, one time synchronization information is periodically transmitted to each node, and each node relays the time synchronization information. Thus, frequency hopping synchronization can be achieved over a wide area.
Therefore, it can be installed freely without being aware of the location of an access point such as a normal wireless LAN.
Furthermore, a multi-hop system using the frequency hopping method can be easily performed by inserting the self-node ID when transmitting the time synchronization information of the frequency hopping method.

  According to the present invention, data can be communicated using the relay function outside the communication range of the master station, and the route can be automatically changed by using the route information. For this reason, it is used for data communication in a large factory where reliability is required, particularly for transmission of sensor information. Similarly, the present invention can be applied to power monitoring at sea or mountain sightseeing spots, water spraying at golf courses, power monitoring, or the like.

It is a figure for demonstrating the time synchronization method in the data communication of the frequency hopping system of Example 1 of this invention. It is a figure for demonstrating the route table of the time synchronization method in the data communication of the frequency hopping system of Example 1 of this invention. It is a figure for demonstrating exchange of the synchronization time fine adjustment of the time synchronization method in the data communication of the frequency hopping system of Example 1 of this invention. A transmission interval of transmission data from each node in the case of transmitting time critical data in the centralized control method of retransmission operation of the time synchronization method in frequency hopping data communication according to the second embodiment of the present invention will be described. FIG. It is a figure for demonstrating the time synchronization method of the conventional frequency hopping system. It is a figure for demonstrating the mode of communication between the main | base station of a conventional frequency hopping system, and a node. It is a figure for demonstrating the general network structure of the conventional several master station and a node. It is a figure for demonstrating the installation form of the main station when the conventional frequency hopping system is used.

Claims (4)

A time synchronization method in frequency hopping data communication, the method comprising:
The master station periodically transmits frequency hopping time information to each node;
When each node receives the time information, updates a self-timer for frequency hopping to the time information;
Transmitting each received frequency hopping time as a relay transmission node when each of the nodes receives,
When each node outside the communication range of the master station receives time information from each relay transmission node, updating a self-timer for frequency hopping to the time information,
When each node outside the communication range of the master station receives, sending the received frequency hopping time as each relay transmission node;
A time synchronization method in frequency hopping data communication.   2. The time synchronization method in frequency hopping data communication according to claim 1, wherein the step in which one predetermined node periodically transmits the frequency hopping time information to each node comprises A time synchronization method in frequency hopping data communication, wherein a frequency hopping timer value is inserted into data and transmitted by broadcast or by one-to-one data communication.   3. The time synchronization method in frequency hopping data communication according to claim 2, wherein each node embeds its own node ID in the data when transmitting as a relay node, and the relay transmission node A time synchronization method in frequency hopping data communication, wherein node ID is confirmed and whether or not relay transmission is performed is automatically determined.   4. The frequency hopping communication apparatus according to claim 3, wherein the relay node uses a relay ID in the received data as a routing table.

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