JP2013026651A - Wireless communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce communication traffic at route search.SOLUTION: A discovery packet P is transmitted from a transmission source node N0 by broadcast at a transmission power PWL lower than a transmission power PWN at normal transmission. In a similar way, at relay nodes, the discovery packet P is transferred by broadcast at the transmission power PWL lower than the transmission power PWN at the normal transmission.

Description

  The present invention relates to a wireless communication system having a mesh network structure.

  In recent years, systems that perform environmental measurement, monitoring, control, and the like using wireless communication are increasing. In a wireless communication system that performs environmental measurement, monitoring, control, and the like, there are many cases where the target area is relatively wide or there are many obstacles for wireless communication in the target area. In such a case, in order to cover the target area, even if it is not possible to communicate directly depending on the environment such as the installation position of the receiver and the transmitter and the radio wave condition, it is possible to perform communication by relaying other devices. It is advantageous to use a communication network.

  As this type of wireless communication network, a mesh network such as a wireless communication network using a Zigbee (registered trademark) protocol has been proposed. In this mesh network, a large number of communication nodes (devices) are arranged in a mesh shape, and bidirectional communication between the communication nodes is performed by directly relaying other communication nodes in the communication area. Even if communication is disabled due to the influence of multipath fading, it is a technique that can continue communication by searching for another communication path. Multipath fading refers to a phenomenon in which a received radio wave is canceled due to a phase difference generated between a plurality of communication radio wave reflection paths, and reception becomes impossible.

  Here, a technique for searching for another communication path (relay path) and continuing communication is referred to as route search. In this route search, a transmission packet (route search transmission source node) is a communication packet called a discovery packet ( The route search packet) is broadcasted directly to other communication nodes in the communication area, and the other communication node (relay node) that receives this discovery packet receives information about the route between them (route information (self identifier and communication quality). )) Is written in the discovery packet, and the discovery packet in which this route information is written is broadcasted and directly transferred to other communication nodes in the communication area, thereby repeating the discovery via a plurality of routes in the mesh network. Packet to destination node (route search destination node And finally to reach the. The destination node determines an optimal relay route between the transmission source node and the destination node based on the route information written in the reached discovery packet (see, for example, Patent Document 1).

JP 2006-20221 A

  However, in the route search in the mesh network described above, since each node relays discovery packets by broadcast, there is a problem that communication traffic becomes high and congestion occurs in some cases. In particular, when a network is activated, a route search may be performed at the same time in each node, so that it may take a considerable time for the network to complete activation.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a wireless communication system capable of reducing communication traffic during route search.

  In order to achieve such an object, the present invention relays a route search source device, a route search destination device, and a route search packet transmitted by broadcast from the route search source device to the route search destination device. A plurality of relay devices, and after the communication route is determined using the route search packet between the route search source device and the route search destination device, communication between the devices is performed according to the determined communication route. In a wireless communication system that performs transmission power at the time of normal transmission determined in advance, a route search transmission source device is provided with means for transmitting a route search packet by broadcast at a transmission power lower than the transmission power at the time of normal transmission, Transmitting route search packets lower than the transmission power during normal transmission to relay devices It is provided with a means for transferring broadcast by force.

  According to the present invention, the route search source device broadcasts a route search packet with a transmission power lower than the transmission power during normal transmission, and the relay device transmits a route with a transmission power lower than the transmission power during normal transmission. Since the search packet is forwarded by broadcast, the number of relay devices that receive the route search packet is reduced, and the communication traffic during route search is reduced. Thereby, it is possible to suppress the occurrence of congestion at the time of route search and to shorten the time until the network is completely started up.

It is a block diagram which shows the outline of one Embodiment of the radio | wireless communications system which concerns on this invention. It is a flowchart which shows the transmission process of the discovery packet in the transmission origin node in Embodiment 1 of this radio | wireless communications system. It is a flowchart which shows the transfer process of the discovery packet in the relay node in Embodiment 1 of this radio | wireless communications system. It is a flowchart which shows the reception process of the discovery packet in the destination node in Embodiment 1 of this radio | wireless communications system. It is a flowchart which shows the transmission process of the discovery packet in the transmission origin node in Embodiment 2 of this radio | wireless communications system. It is a flowchart which shows the transfer process of the discovery packet in the relay node in Embodiment 2 of this radio | wireless communications system. It is a functional block diagram at the time of making a communication node function as a transmission source node. It is a functional block diagram at the time of making a communication node function as a relay node.

Hereinafter, the present invention will be described in detail based on embodiments.
[Embodiment 1]
FIG. 1 is a block diagram showing an outline of an embodiment of a radio communication system according to the present invention. In the figure, N0 to N4 are communication nodes, and a mesh network is configured by these communication nodes N0 to N4.

  In this mesh network, the communication nodes N0 to N4 are realized by hardware including a processor and a storage device, and a program that realizes various functions in cooperation with these hardware. It has a route search function.

  Hereinafter, with the communication node N0 as a transmission source node (route search transmission source node), the communication node N1 as a destination node (route search destination node), and the communication nodes N2 to N4 as relay nodes, a route search is performed while combining the functions of each communication node. The operation at the time will be described.

  Note that the communication nodes N0 to N4 have all the functions as a route search source node, a relay node, and a route search destination node, and these functions are combined with the route search function described above. Say about the function.

  The communication nodes N0 to N4 perform communication according to the determined communication route after the communication route is determined using the above-described route search function. In this case, communication between each communication node is performed with transmission power at the time of normal transmission determined in advance. In the present embodiment, the transmission power during normal transmission between the communication nodes is PWN.

[Discovery packet transmission]
When instructed to start route search (FIG. 2: YES in step S101), the transmission source node N0 sets the transmission power to a transmission power PWL that is lower than the transmission power PWN during normal transmission (step S102).

  Then, with the transmission power PWL lower than that during normal transmission, the self-identifier is attached as route information, the communication node N1 is designated as the destination node, and the discovery packet P is directly transmitted to other communication nodes within the communication area. The broadcast is transmitted (step S103).

  In this embodiment, the discovery packet P is transmitted from the transmission source node N0 with a transmission power PWL lower than that during normal transmission. In this case, the transmission power PWL is transmitted with the transmission power PWN during normal transmission. The margin for judging the communication quality at the receiving side node assuming that the transmission has been assumed is expected, and the transmission power PWN at the time of normal transmission is reduced by the margin.

  The above margin will be described. Even if there is a node that can receive the discovery packet P at the time of route search, it is unclear whether it can be adopted as a stable communication route because it can be received only once because the radio wave quality is accompanied by time change. is there. Therefore, when transmitting the discovery packet P with the transmission power PWN, normally, at the receiving side node, a certain margin is added to the threshold value of the received electric field strength, and the threshold value obtained by adding this margin is compared with the received electric field strength. Thus, the reception status is judged as good or bad.

  As described above, normally, a certain margin is added to the threshold value of the received electric field strength at the reception-side node. However, in this embodiment, the transmission power PWN at the time of normal transmission is reduced by the margin, and this The reduced transmission power is set as the transmission power PWL at the time of route search, and no margin is added to the threshold value at the node on the receiving side.

[Reception packet reception]
In this embodiment, the communication nodes N2 and N3 are in the direct communication area with the transmission power PWN at the normal transmission of the transmission source node N0, and only the communication node N2 of the communication nodes N2 and N3 is the transmission source node N0. It is assumed that the user is in a direct communication range with a transmission power PWL lower than that during normal transmission.

  In this case, the discovery packet P transmitted by broadcast from the transmission source node N0 is received only by the communication node N2. That is, when the discovery packet P is transmitted from the transmission source node N0 with the transmission power PWN at the normal transmission time, the discovery packet P is received by both the communication nodes N2 and N3. Since discovery packet P is transmitted with lower transmission power PWL than during communication, discovery packet P is received only at communication node N2.

  When the communication node (relay node) N2 receives the discovery packet P from the transmission source node N0 (FIG. 3: YES in step S201), the communication node (relay node) N2 sends a response (ACK) indicating that the discovery packet P has been received to the transmission source node N0. Return (step S202).

  When the transmission source node N0 receives the ACK from the relay node N2 within a predetermined time after transmitting the discovery packet P (FIG. 2: YES in step S104), the transmission processing of the discovery packet P is terminated.

[Discovery packet transfer]
After returning the ACK to the transmission source node N0, the relay node N2 sets the transmission power to a transmission power PWL lower than the transmission power PWN during normal transmission in the same manner as the transmission source node N0 (step S203).

  Then, with the transmission power PWL lower than that during normal communication, the own identifier and communication quality (reception state of the discovery packet P) are attached as route information, and the discovery packet P is broadcast directly to other communication nodes within the communication area. (Step S204).

  In this case, the discovery packet P from the transmission source node N0 is expected to have a margin for determining the communication quality at the receiving node when it is assumed that the transmission packet is transmitted with the transmission power PWN at the time of normal transmission. Since transmission is performed with transmission power PWL obtained by reducing transmission power PWN during normal transmission, the fact that discovery packet P can be received by relay node N2 itself indicates that the reception state is good.

[Reception packet reception]
In this embodiment, the communication nodes N3 and N4 are in the direct communication area with the transmission power PWN at the normal transmission time of the relay node N2, and only the communication node N3 of the communication nodes N3 and N4 is the normal communication of the relay node N2. It is assumed that the user is in a direct communication range with a transmission power PWL lower than the time.

  In this case, the discovery packet P transferred by broadcast from the relay node N2 is received only by the communication node N3. That is, when the discovery packet P is transferred from the relay node N2 with the transmission power PWN during normal transmission, the discovery packet P is received by both the communication nodes N3 and N4, but from the relay node N2 during normal communication Since the discovery packet P is transferred with a lower transmission power PWL, the discovery packet P is received only at the communication node N3.

  Upon receiving the discovery packet P from the relay node N2 (FIG. 3: YES in step S201), the communication node (relay node) N3 returns a response (ACK) indicating that the discovery packet P has been received to the relay node N2. (Step S202).

  When the relay node N2 receives the ACK from the relay node N3 within a predetermined time after the transfer of the discovery packet P (YES in step S205), the relay node N2 ends the discovery packet P transfer process.

[Discovery packet transfer]
After returning the ACK to the relay node N2, the relay node N3 sets the transmission power to a transmission power PWL lower than the transmission power PWN during normal transmission in the same manner as the relay node N2 (step S203).

  Then, with the transmission power PWL lower than that during normal communication, the own identifier and communication quality (reception state of the discovery packet P) are attached as route information, and the discovery packet P is broadcast directly to other communication nodes within the communication area. (Step S204).

  In this case, the discovery packet P from the relay node N2 is expected to have a margin for judging the communication quality at the receiving side node when it is assumed that the packet is transmitted with the transmission power PWN at the time of normal transmission. Since transmission is performed with transmission power PWL obtained by reducing transmission power PWN at the time of transmission, reception of discovery packet P at relay node N3 itself indicates that the reception state is good.

  Similarly, the discovery packet P is relayed also in other communication nodes.

[Destination node]
For example, when receiving the discovery packet P from the relay node N4 (FIG. 4: YES in step S301), the destination node N1 returns a response (ACK) indicating that the discovery packet P has been received to the relay node N4 (step S302). ).

  The destination node N1 receives the discovery packet P sent via another route in the same manner as the discovery packet P from the relay node N4. When the reception of all the discovery packets P is completed (YES in step S303), the optimum connection between the transmission source node N0 and the destination node N1 is performed based on the path information written in each received discovery packet P. A relay route is determined (step S304), and the determined optimum relay route is returned to the transmission source node N0 (step S305).

  As described above, in the mesh network of the present embodiment, the transmission source node N0 broadcasts the discovery packet P with the transmission power PWL lower than the transmission power PWN at the time of normal transmission, and the relay nodes N2, N3, and N4 normally Since discovery packet P is transmitted by broadcast with transmission power PWL lower than transmission power PWN at the time of transmission, the number of relay nodes that receive discovery packet P is reduced, and communication traffic at the time of route search is reduced. As a result, the occurrence of congestion at the time of route search can be suppressed, and the time until the network is completely started can be shortened.

[Retransmission of discovery packet from the source node]
In the above description, it is assumed that only the communication node N2 is located in the direct communication area with the transmission power PWL lower than that in the normal communication of the transmission source node N0. There may be no. In this case, after the discovery packet P is transmitted, no response (ACK) indicating that the discovery packet P has been received is returned to the transmission source node N0.

  If no ACK is returned after transmission of the discovery packet P (FIG. 2: NO in step S104), the transmission source node N0 increases the transmission power PWL at that time by a predetermined amount ΔP (step S105, PWL = PWL + ΔP), the discovery packet P is retransmitted (step S103).

  The transmission source node N0 repeats this retransmission of the discovery packet P while increasing the transmission power PWL by ΔP until ACK is returned. Note that the upper limit of the transmission power PWL in this case does not exceed the transmission power PWN during normal transmission. As a result, it is possible to avoid a situation where there is no communication node that can transmit the discovery packet P from the transmission source node N0.

[Retransmission of discovery packet from relay node]
In the above description, it is assumed that only the communication node N3 is located in the direct communication area with the transmission power PWL lower than that in the normal communication of the relay node N2, but there is no other communication node in this direct communication area. In some cases. In this case, after transmitting the discovery packet P, no response (ACK) indicating that the discovery packet P has been received is returned to the relay node N2.

  If no ACK is returned after transmission of the discovery packet P (FIG. 3: NO in step S205), the relay node N2 increases the transmission power PWL at that time by a predetermined amount ΔP (step S206, PWL = PWL + ΔP). ) And retransmit the discovery packet P (step S206).

  The relay node N2 repeats this retransmission of the discovery packet P while increasing the transmission power PWL by ΔP until ACK is returned. Note that the upper limit of the transmission power PWL in this case does not exceed the transmission power PWN during normal transmission. As a result, it is possible to avoid a situation where there is no communication node that can transfer the discovery packet P from the relay node N2. The same operation is performed at the relay nodes N3 and N4.

[Embodiment 2]
In the first embodiment, for example, when a plurality of ACKs are returned in response to the transmission of the discovery packet P from the transmission source node N0 (YES in step S104), the transmission process of the discovery packet P is terminated as it is. The same applies to the relay node N2, and when a plurality of ACKs are returned for the transfer of the discovery packet P from the relay node N2 (YES in step S205), the transfer process of the discovery packet P is terminated as it is. In this case, the number of relay nodes that receive the discovery packet P increases, and communication traffic during route search increases.

  Therefore, in the second embodiment, the number of relay nodes that receive the discovery packet P is reduced as much as possible to reduce communication traffic during route search. FIG. 5 shows a flowchart of discovery packet transmission processing at the transmission source node in the second embodiment. FIG. 6 is a flowchart of the discovery packet transfer process in the relay node according to the second embodiment.

[Source node]
In the second embodiment, the transmission source node N0 transmits a discovery packet P with a transmission power PWL lower than that during normal communication (step S403), and if an ACK is returned within a predetermined time (YES in step S404). ), The number of ACKs returned within the predetermined time is checked (step S405).

  If the number of ACKs is one (YES in step S405), the discovery packet P transmission process ends. If the number of ACKs is plural (NO in step S405), the transmission power PWL at that time is decreased by a predetermined amount ΔP (step S406, PWL = PWL−ΔP), and the discovery packet P is retransmitted (step S403).

  If the number of ACKs returned within a predetermined time is one by the retransmission of the discovery packet P (YES in step S405), the discovery packet P transmission process is terminated. If the number of ACKs returned within the predetermined time is still plural (NO in step S405), the transmission power PWL at that time is further decreased by a predetermined amount ΔP (step S406, PWL = PWL−ΔP), and the discovery packet P is retransmitted (step S403).

  If no ACK is returned due to retransmission of the discovery packet P (NO in step S404), it is confirmed that there were a plurality of previous ACKs (YES in step S407), and transmission at that time The power PWL is increased by a predetermined amount ΔP (step S409, PWL = PWL + ΔP), the discovery packet P is retransmitted (step S410), and the discovery packet P is transmitted by designating the communication node that has returned the ACK earliest. (Step S411).

[Relay node]
In the second embodiment, when receiving the discovery packet P from the transmission source node N0 (YES in step S501), the relay node N2 returns an ACK to the transmission source node N0 (step S502). Then, the timing of the predetermined waiting time T1 is started (step S503). The waiting time T1 is a predetermined time exceeding the time T0 when the time required from the transmission of the discovery packet P to the retransmission at the transmission source node N0 is T0.

  When the relay node N2 receives the same discovery packet P as the previous time from the transmission source node N0 while measuring the waiting time T1 (YES in step S505), the relay node N2 returns an ACK to the transmission source node N0 (step S502), and wait time T1. Is restarted (step S503).

  The relay node N2 does not receive the same discovery packet P as the previous one from the transmission source node N0, and when the waiting time T1 is up (YES in step S504), or the discovery packet P addressed to itself is measured during the waiting time T1 timing. Is received (YES in step S506), the transmission power is set to a transmission power PWL lower than the transmission power PWN during normal transmission (step S507).

  Then, with the transmission power PWL lower than that during normal transmission, the identifier and communication quality (reception state of the discovery packet P) are attached as route information, and the discovery packet P is directly broadcast to other communication nodes within the communication area. (Step S508).

  If the ACK is returned within a predetermined time after the transfer of the discovery packet P (YES in Step S509), the relay node N2 checks the number of ACKs returned within the predetermined time (Step S510). .

  If the number of ACKs is one (YES in step S510), the discovery packet P transmission process is terminated. If the number of ACKs is plural (NO in step S510), the transmission power PWL at that time is decreased by a predetermined amount ΔP (step S406, PWL = PWL−ΔP), and the discovery packet P is retransmitted (step S508).

  If the number of ACKs returned within a predetermined time is one by retransfer of the discovery packet P (YES in step S510), the transfer process of the discovery packet P is terminated. If the number of ACKs returned within the predetermined time is still plural (NO in step S510), the transmission power PWL at that time is further decreased by a predetermined amount ΔP (step S511, PWL = PWL−ΔP), and the discovery packet P is retransferred (step S508).

  If no ACK is returned due to the re-transfer of the discovery packet P (NO in step S509), it is confirmed that there were a plurality of previous ACKs (YES in step S512), and transmission at that time The power PWL is increased by a predetermined amount ΔP (step S514, PWL = PWL + ΔP), the discovery packet P is retransmitted (step S515), and the discovery packet P is transferred by specifying the communication node that has returned the ACK earliest. (Step S516).

[Function block of the source node]
FIG. 7 shows a functional block diagram when the communication node functions as a transmission source node. In FIG. 7, the source node is indicated by the symbol NA in order to distinguish it from the relay node and the destination node.

  Upon receiving an instruction to start route search, the transmission source node NA broadcasts and transmits a discovery packet P directly to other communication nodes in the communication area with a transmission power PWL lower than the transmission power PWN during normal transmission. 1, an ACK receiving unit 2 that receives a response (ACK) from another communication node indicating that the discovery packet P has been received from the discovery packet transmitting unit 1, and a discovery packet P from the discovery packet transmitting unit 1 If no ACK is received by the ACK receiving unit 2 after transmission, the transmission power PWL at that time is increased by a predetermined amount ΔP and the discovery packet transmitting unit 1 retransmits the discovery packet P. A first discovery packet retransmission unit 3 and a discovery packet; When a plurality of ACKs are received by the ACK receiving unit 2 after the discovery packet P is transmitted from the transmitting unit 1, the transmission power PWL at that time is decreased by a predetermined amount ΔP to the discovery packet transmitting unit 1. And a second discovery packet retransmission unit 4 that performs retransmission of the discovery packet P.

[Function block of relay node]
FIG. 8 shows a functional block diagram when the communication node functions as a relay node. In FIG. 8, the relay node is denoted by reference numeral NB in order to distinguish it from the transmission source node and the destination node.

  The relay node NB includes a discovery packet receiving unit 5 that receives the discovery packet P from the transmission source node and other relay nodes, and the discovery packet P received by the discovery packet receiving unit 5 is more than the transmission power PWN at the time of normal transmission. Discovery packet transfer unit 6 that broadcasts and transfers to other communication nodes directly within the communication area with low transmission power PWL, and a response (ACK) from other communication nodes indicating that discovery packet P from discovery packet transfer unit 6 has been received ) And the transmission power PWL at that time when no ACK is received in the ACK receiver 7 even after a predetermined time has elapsed after the discovery packet P is transferred from the discovery packet transfer unit 6. Discovery packet transfer is increased by a predetermined amount ΔP The first discovery packet retransmission unit 8 that causes the unit 6 to retransmit the discovery packet P and the ACK reception unit 7 during the predetermined time after the discovery packet P is transferred from the discovery packet transfer unit 6 Is received, a second discovery packet re-forwarding unit 9 is provided that causes the discovery packet transfer unit 6 to re-transmit the discovery packet P by reducing the transmission power PWL at that time by a predetermined amount ΔP.

  The wireless communication system of the present invention can be used in various fields such as a medium-scale and large-scale monitoring control system having a mesh structure in which a communication trunk line is wireless. Specifically, it can be applied to a room air conditioning system by VAV (variable air volume adjustment).

  N0 to N4 ... communication node, P ... discovery packet, NA ... transmission source node, NB ... relay node, 1 ... discovery packet transmission unit, 2 ... ACK reception unit, 3 ... first discovery packet retransmission unit, 4 ... first 2 discovery packet retransmission unit, 5... Discovery packet reception unit, 6... Discovery packet transfer unit, 7... ACK reception unit, 8... First discovery packet retransmission unit, 9.

Claims (3)

A route search source device; a route search destination device; and a plurality of relay devices that relay a route search packet transmitted from the route search source device to the route search destination device by broadcast. After the communication route using the route search packet between the search source device and the route search destination device is determined, normal transmission in which communication between the devices is determined in advance according to the determined communication route In a wireless communication system that performs with the transmission power at the time,
The route search source device is:
Means for broadcasting the route search packet with a transmission power lower than the transmission power at the time of normal transmission;
The relay device is
A wireless communication system comprising: means for transferring the route search packet by broadcast at a transmission power lower than the transmission power at the time of normal transmission. The wireless communication system according to claim 1, wherein
The route search source device is:
If no response is returned indicating that the route search packet has been received even after a predetermined time has elapsed after transmission of the route search packet, the transmission power is increased to reduce the route search packet. With means to retransmit,
The relay device is
If no response indicating that the route search packet has been received is returned even after a predetermined time has elapsed after the transfer of the route search packet, the transmission power is increased to increase the route search packet. A wireless communication system comprising means for retransfer. The wireless communication system according to claim 1, wherein
The route search source device is:
After a plurality of responses indicating that the route search packet has been received after transmission of the route search packet, the device includes means for reducing the transmission power and retransmitting the route search packet,
The relay device is
A means for reducing the transmission power and retransmitting the route search packet when a plurality of responses indicating that the route search packet has been received are returned after the route search packet is transferred. A wireless communication system.

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