This application claims the priority of Japanese Patent Application No. JP 2012-202214, filed Sep. 14, 2012, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a wireless communication device, a wireless communication system, and a wireless communication control method.
2. Background Art
In recent years, with a rise in awareness of environmental problems and institutionalization, there is an increasing technical need for energy management. On the side of consumers who consume energy, an energy management system (EMS), such as a home energy management system (HEMS) in which energy management is performed at home, a building energy management system (BEMS) in which energy management is performed at an apartment house or a building, or a city energy management system (CEMS) in which energy management is performed in an area of a community, is expected. On the side of electric power companies which generate energy, a smart meter or an advanced metering infrastructure (AMI) in which automatic reading of a power meter is performed, or a smart grid for stabilizing a power distribution/transmission system is required. There is also a study on the concept of a smart city in which these techniques are collectively applied in a city area.
In order to realize an energy-related management system, it becomes essential to secure the infrastructure of communication means. As the communication means, there are various options, such as wireless communication, wired communication, optical communication, and power line communication, and optimum means is selected depending on an environment which is constructed as the infrastructure. Of these, wireless communication is excellent from the viewpoint of ease of installation and maintenance, low-cost devices, ease of expansion, and the like, and is highly expected.
When wireless communication is used as the communication infrastructure means, an installation environment should also be taken into consideration and optimization is required depending on the purposes. For example, in regard to the smart meter in the AMI, there is a need for allowing multiple wireless terminals to perform communication regularly (every 30 minutes or the like) in a comparatively close area within several 100 m or 1 km. In the smart grid, when emergency communication is required, it is necessary to perform communication at a high speed (low latency or short time) over a long distance of about 10 km. Examples of emergency communication include short-circuiting due to electric wire breakage, an emergency stop instruction of power distribution, and the like.
Of the background, in the related art, as disclosed in the following patent literatures, wireless techniques for optimally realizing an AMI wireless network have been developed, and multiple demonstration experiments have been carried out. Practically, however, read data from the AMI wireless network should be transmitted to the electric power company through the smart grid wireless network, and control information or an emergency instruction from the electric power company should be transmitted through the smart grid wireless network and the AMI wireless network. For this reason, a wireless communication scheme which can integrate a plurality of wireless networks having different requested specifications or features, such as the smart grid wireless network and the AMI wireless network, in a single wireless network is required.
JP-A-2012-015897 discloses a technique which constructs an optimum communication root on the basis of link metric information between wireless nodes in a mesh network centering on a wireless gateway.
JP-A-2009-188469 discloses a technique which performs transmission/reception only for a given period of time in a given cycle in an ad-hoc network and a mesh network to enable a network with low power consumption in an asynchronized communication scheme.
An object of the invention is to enable wireless communication between a plurality of independent ad-hoc wireless networks and multi-hop wireless networks in a wireless communication network.
In the related art, in one ad-hoc or multi-hop wireless network, a technique for optimizing communication reliability, power consumption, the number of connected transceivers, low cost, and the like depending on the purposes has been studied and developed. However, when there is a plurality of ad-hoc or multi-hop wireless networks, and communication should be performed between the wireless networks, since there is no common communication protocol between the wireless networks, it is not possible to realize wireless communication between the wireless networks.
That is, the invention has been accomplished in consideration of the problems in the related art, and an object of the invention is to provide a wireless communication device, a wireless communication system, and a wireless communication control method which enable the realization of a plurality of ad-hoc/multi-hop networks (sub-networks) in a wireless communication network and an ad-hoc/multi-hop network (main network) connecting the sub-networks using a single wireless protocol. Another object of the invention is to prevent wireless communication of sub-networks from affecting communication quality of other main networks and sub-networks in realizing the above-described object.
A wireless communication device, a wireless communication system, and a wireless communication control method of the invention for solving the above-described problems have the following means.
The features of the invention are as follows.
An access point (AP) is arranged in at least one of wireless communication devices in each sub-network, and a main network is configured between the APs to realize communication between a plurality of sub-networks. Since the main network is a main system, and there is a high probability that high-priority communication is occurred, a communication opportunity between the APs is preferentially secured in accordance with a wireless application specification. Besides, each AP allocates the time other than the communication opportunity between the main networks to the communication time between the sub-networks to which the AP belongs.
When the AP performs communication between the main networks, the start time of carrier sense (a structure in which radio power strength around the wireless device is measured to determine the presence/absence of a transmission radio wave, and if there is a transmission radio wave, radio wave transmission is delayed to avoid packet collision) immediately before radio wave transmission is set to be smaller than the start time of carrier sense of the wireless communication devices in the sub-network, thereby placing priority on communication between the main networks by the AP.
According to the invention, it is possible to provide a wireless communication device, a wireless communication system, and a wireless communication control method which enable the realization of a plurality of ad-hoc/multi-hop networks (sub-networks) in a wireless communication network and an ad-hoc/multi-hop network (main network) connecting the sub-networks using a single wireless protocol. It is also possible to provide a wireless communication network system which enables wireless communication in which main network communication by the AP is placed priority and prevents wireless communication of one sub-network from affecting communication quality of other main networks and sub-networks.
Hereinafter, a wireless communication device, a wireless communication system, and a wireless communication control method according to the invention will be described in detail referring to an embodiment shown in the drawings.
The network configuration example shown in
The server 100 installed in a substation or the like is connected to the higher level of the main network 1, and in the server 100, power read information from each sub-network is collected through the AP installed in an electric pole, and signals, such as a power control signal and an emergency instruction, according to the read information are transmitted to a controlled device, such as a switch, through the AP. The ND assumes a smart meter, and a sub-network covers a close distance (about 100 m to 1 km) at a communication interval of 30 minutes as an AMI wireless network. The power read information is collected from the smart meter to the AP and the server by the ad-hoc/mesh network, and the AP preferentially transmits control information from the server to a controlled device, such as a household electrical appliance.
Hereinafter, a communication procedure by a career sense multiple access (CSMA) scheme and a communication procedure by a time division multiple access (TDMA) scheme which are commonly used in Examples will be described. In general, since the CSMA scheme is a simple protocol, while functional mounting is eased, packet collision is likely to occur. While the TDMA scheme is complicated and requires the number of man-hour for functional mounting, packet management can be performed, thereby avoiding packet collision.
In the CSMA scheme, carrier sense is performed immediately before data transmission, and radio power strength is measured to check whether or not the other wireless device is transmitting data. If no radio wave of the other wireless device is detected, data is transmitted as scheduled.
If a radio wave of the other wireless device is detected, scheduled data transmission is cancelled, and retransmission is performed in the next transmission opportunity. Accordingly, it is possible to avoid packet collision due to the matching of the data transmission timing.
In the CSMA scheme, the period in which carrier sense is performed is set to be random in each transmission opportunity.
For this reason, the transmitter 200b avoids scheduled data transmission (206), stands by the completion of data transmission of the transceiver 200c, performs carrier sense (207), and then perform data transmission again (209). Since the receiver 200a is in the reception standby state (201), data transmission (209) of the transmitter can be received. The transmitter 200b is changed to a reception standby state (212) in a short time after data transmission (209) and stands by a response (Ack. This means an acknowledge signal. The same applies to the following) from the receiver 200a. If data reception (210) is completed, the receiver 200a immediately transmits Ack (211), the transmitter 200b receives Ack (212), and communication is completed.
In the CSMA mode, during a period other than carrier sense, data transmission, Ack transmission, and the data transmission avoidance period, reception standby is performed to prepare for data reception.
In the TDMA scheme, transmission/reception of a packet for synchronization (Adv: Advertise) between the transmitter and the receiver is preformed regularly to perform time synchronization between the transmitter and the receiver, and communication is performed while matching the communication timing.
For this reason, as in the CSMA scheme, there is an advantage in that packet collision or transmission delay due to a transmission radio wave of the other transceiver in the host system does not occur.
The receiver performs reception standby for a given time in the timeslots 317 and 318 ((301), (308)), when there is no data reception (301), is changed to the next timeslot directly, and when there is data reception (308), transmits Ack at the end of the timeslot (314).
If transmitting data is generated (302), for example, the transmitter 300b performs carrier sense over a given period in the timeslots 317 and 318 ((303), (309)), when no radio wave is detected (311), performs data transmission (310), and when a radio wave is detected (305), avoids scheduled data transmission (306).
Reception standby is performed in a short time at the end of the timeslot ((307), (316)), and Ack is received from the receiver 300a. In the example shown in
A repetition cycle of communication having a plurality of timeslots is referred to as a superframe.
Hereinafter, Examples will be described in detail referring to the drawings. While the carrier sense time immediately before data transmission is not shown unless particularly required, in Examples, it is assumed that carrier sense immediately before data transmission is performed.
This example illustrates an example of the invention when transmission/reception of a packet for time synchronization (Adv) is performed between the server 100 and the AP 101, 102, or 103 in the main network of
In
In the main network communication period (509), the packet for time synchronization (Adv) is transmitted to the AP 102 to perform time synchronization. Communication by the CSMA scheme is performed using an unoccupied time between the main network communication periods (501, 508, and 509) as a sub-network 11 communication period.
For the server 100, the AP 102, and the AP 103, similarly, communication with an AP is performed in the main network 1 communication period. For the AP 102 and the AP 103, the unoccupied time between the main network communication periods is allocated to the communication periods of the sub-networks 12 and 13.
While
In the polling scheme, the data request (Req.) is transmitted to an ND, and only the ND which receives Req. can transmit data. The AP 101 transmits Req. to the next ND first when data reception from the ND is completed. Description will be provided on the basis of the example of
Thereafter, the procedure is changed to a loop of communication processing, and it is confirmed whether or not the main network communication timing is reached (705) referring to the main network communication time and destination AP list 406 which is referenced to by the communication control unit 403. If the main network communication timing is reached, data transmission/reception with the AP in the main network is performed in accordance with the list 406, and if the main network communication timing is not reached, the Req. packet is transmitted to the ND of the sub-network 11, 12, or 13 (707).
If the reception of data from the ND of the sub-network 11, 12, or 13 is completed, the procedure is changed again to main network communication timing determination (705).
In this example, a case where communication in the sub-network 11, 12, or 13 in Example 1 is performed by the TDMA scheme will be described.
In this example, since the sub-network uses the TDMA scheme, communication of the sub-network 11 does not affect communication of the main network 1. For this reason,
The ND 111 transmits data (111d) to the AP 101 in the timeslot No. 3, receives data (121d) from the ND 121 in the timeslot No. 4, and transfers data (121d) to the AP 101 in the timeslot No. 5. Data (122d) of the ND 122 is received by the ND 111 in the timeslot No. 6, and is transferred to the AP 101 in the timeslot No. 7.
The packet for time synchronization (Adv) is broadcasted from the AP 101 to the ND in the timeslots No. 14 and 15. The superframe configuration, the communication timing, and the transmission/reception ND of
If the power is turned on (1101), the AP is changed to reception standby (1102) and receives the packet for synchronization (Adv) (1103). If the packet for synchronization (Adv) is received, the superframe table 806 is confirmed (1105), and a communication schedule is determined. Thereafter, it is confirmed whether or not the present time is the main network communication timing described in the superframe table 806 (1106), when the main network communication timing is reached, signal transmission/reception with the AP in the main network is performed (1107), and when the main network communication timing is not reached, communication with the ND in the sub-network is performed as described in the superframe table 806.
In this example, a method which, when transmitting emergency data or a device control command from the server 100 of
The other transceiver (1200) may be the ND in the same sub-network 11 as the ND 111, or may be the AP or the ND in the other sub-network. In this case, both the AP 101 and the other transceiver 1200 avoid data communication (1204) and (1214) with carrier sense (1202) and (1212), and enter a retransmission process simultaneously after data transmission of the ND 111 ends.
While carrier sense is performed immediately before data transmission in the retransmission process, the carrier sense time is set to be random so as to give the same transmission probability to all transceivers.
Accordingly, as shown in
Accordingly, in
In this example, a method which, when transmitting priority data, such as emergency data or a device control command, from the server 100 of
There is a case in which communication between the AP 102 and the AP 103 is delayed due to radio wave interference from the ND in the sub-network 11 during communication between the AP 102 and the AP 103 in
Specifically, when the AP 102 transmits priority data to the AP 103 in a communication allocation period (903) (timeslot No. 4) of the main network 1 of the AP 102 of the
The ND 121 and the AP 102 perform carrier sense (1403) and (1409) immediately before transmission when executing the generation of transmitting data (1402) and priority transmitting data (1408) in the timeslot (1401).
In the TDMA scheme, since the carrier sense time (1404) and (1403) is constant, both the ND 121 and the AP 102 determine that no radio wave is detected (1405) in carrier sense, and thus transmit data simultaneously (1406) and (1411). For this reason, packet collision (1414) occurs.
Accordingly, when performing communication between the AP 102 and the AP 103, as shown in
For this reason, it is possible to reduce transmission delay of the main network due to interference of a communication radio wave of the sub-network.
This example illustrates an example of the invention when time synchronization by the transmission/reception of the packet for time synchronization (Adv) is not established between the server 100 and the AP 101, 102, or 103 in the main network of
In this example, since the sub-network 11 and the sub-network 12 independently uses the TDMA scheme, the time between the sub-network 11 and the sub-network 12 is asynchronous, and the superframe length is different.
For this reason, it is not possible to configure the main network by connecting the sub-networks together.
Accordingly, the sub-network 11 and the sub-network 12 are connected together by means shown in
Besides, for example, when transmitting data addressed to the AP 102 is generated (1701) in the AP 101, the communication control unit 803 rewrites the superframe table 806 so as to transmit (S) (1702, 1703) data to the AP 102 successively after the next timeslot (1702).
When this happens, data transmitted to the AP 102 in the timeslot (1702) undergoes communication failure because the AP 102 is not in the reception (R) mode of data from the AP 101. Meanwhile, in regard to transmitting data which is transmitted to the AP 102 in the timeslot (1703), since the AP 102 is in the reception (R) mode, transmission/reception is established.
Accordingly, communication through the main network can also be performed between the sub-networks which independently configure a wireless network by the TDMA scheme.
However, similarly to the timeslot (1702), when a timeslot allocated to data reception from the ND 111 is written to transmission (S), the AP 101 performs carrier sense for a radio wave of data (111d), and there is a possibility that transmission to the AP 101 in the same timeslot is cancelled. For this reason, the shortest carrier sense time (1509) in
If the power is turned on (1401), the AP confirms the superframe table (1402). Next, the carrier sense time is set to be shortest (1403), and the procedure is changed to a communication mode. In the communication mode, the presence/absence of a communication request for the main network (AP) is confirmed (1404). When there is a communication request, the superframe table 806 is rewritten by the communication control unit 803, and successive transmission to the main network (AP) is performed (1406) until Ack is receivable. When there is no communication request for the main network (AP), transmission/reception with the ND of the sub-network is performed (1407) in accordance with the superframe table 806.
This example illustrates an example of the invention when time synchronization by transmission/reception of the packet for time synchronization (Adv) is not established between the server 100 and the AP 101, the AP 102, or the AP 103 in the main network of
The superframe configuration in
In this example, main network communication timeslots (1902 to 1908) are arranged cyclically in the superframes of the AP 101 and the AP 102. In the example of
If transmitting data addressed to the AP 102 is generated (1901), while the AP 101 transmits data to the AP 102 in the timeslot (1902), since the AP 102 is not allocated to the main network communication timeslot in this timeslot, communication failure (1909) occurs.
However, if the AP 101 retransmits the same data in the timeslot (1903) (1910), the AP 102 is also allocated to the main network communication timeslot (1907) in this timeslot, whereby communication can be successful.
This example illustrates an example of the invention when time synchronization by transmission/reception of the packet for time synchronization (Adv) is not established between the server 100 and the AP 101, 102, or 103 in the main network of
In the example of
While the AP 101 transmit data addressed to the AP 102 immediately after carrier sense is performed in carrier sense (2004), if data (111d) of the ND (111) is detected in carrier sense (2004), data transmission addressed to the AP 102 is put off until the transmission of data (111d) of the ND 111 is completed, and retransmission is attempted.
In the retransmission (2005), since no transmission radio wave is detected by carrier sense (2006), transmission of data (101d) addressed to the AP 102 is performed, and Ack (102) is received from the AP 102.
In this example, data communication of the main network or means for transmitting high-priority data, such as emergency information or control information, while giving priority over normal power monitoring information main network will be described in association with Example 6.
In the example of the
Accordingly, in this example, as shown in
When there is no high-priority communication request in (2202), the presence/absence of a normal priority communication request is confirmed (2207). If there is no normal priority communication request, reception standby is performed.
If there is a normal priority communication request, first, the carrier sense time is set to be random (2208), it stands by the end of transmission of the other wireless device (2209), carrier sense is performed, and if no radio wave is detected, data is transmitted (2211).
(1) An example where the main network 1 and the sub-networks 12, 13, and 14 in all of Examples perform communication by different communication frequency channels to avoid mutual interference and to realize wireless communication with low latency is included in Examples.
(2) An example where a synchronized scheme/asynchronized scheme is switched depending on a system utilization location and traffic of wireless communication such that a synchronized scheme is used at a location, such as a city area or a residential area, where the density of wireless communication devices is high, and an asynchronized scheme is used at a location, such as a mountain area, where the density of wireless communication devices is low is included in Examples.
Number | Date | Country | Kind |
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2012-202214 | Sep 2012 | JP | national |