Patent Application
20100195569
The present invention relates to a communication terminal device and a communication method that use a power line as a communication channel.
In the field of wireless communication, a moving terminal detects, when receiving a beacon transmitted from a base station, that the moving terminal is in a range which allows communication with the base station. A beacon in the field of wireless communication is modulated by using a modulation method having the lowest communication speed among a plurality of modulation methods that can be used by the base station. This is because modulation by using the modulation method having the lowest communication speed expands to the maximum extent possible the range which allows communication with the base station. In the case of wireless communication, it is assumed that a moving terminal moves, and thus it is highly possible for the moving terminal to come out of the range which allows communication with the base station. In the communication using a base station, all the communication to be performed by the moving terminals that have received beacons needs to be relayed by the base station. Accordingly, if a moving terminal comes out of the range which allows communication with the base station, the moving terminal can no longer perform communication. Therefore, the base station modulates a beacon, using the modulation method having the lowest communication speed, and expands to the maximum extent possible the range which allows communication with the base station, thereby reducing the probability that the moving terminal comes, due to the movement thereof, out of the range which allows communication with the base station.
Further, in a wireless network, there also is an ad hoc wireless network in which terminals function as relay terminals, thereby enabling, without using a base station, other terminals existing in a specific range from the relay terminals to perform data communication with the relay terminals. In the ad hoc wireless network, terminals perform relays with each other, thereby realizing a wider range of communication, compared with the case where one base station is used. However, in the ad hoc wireless network, different from the communication using a base station, the terminals functioning as relay terminals are not specified. Accordingly, in order to perform data communication between two terminals, it is necessary to specify, as a relay terminal, a terminal which is appropriate to relay the data to all the other terminals existing within a specific range from the relay terminal.
Methods for exchanging control information for specifying a relay terminal are classified into two methods: a proactive method that periodically exchanges control information (for example, see Non-Patent Literatures 1 and 2) and a reactive method that exchanges control information at the time of initiation of data communication (for example, see Non-Patent Literatures 3 and 4). Generally, it is said that the proactive method is effective when a terminal is moving at a low speed and the reactive method is effective when a terminal is moving at a high speed.
Non-Patent Literature 1: REQUEST FOR COMMENT 3626: Optimized Link State Routing Protocol (OLSR)
Non-Patent Literature 2: REQUEST FOR COMMENT 3684: Topology Dissemination Based on Reverse-Path Forwarding (TBRPF)
Non-Patent Literature 3: REQUEST FOR COMMENT 3561: Ad hoc On-Demand Distance Vector (AODV) Routing
Non-Patent Literature 4: REQUEST FOR COMMENT 4728: The Dynamic Source Routing (DSR) Protocol for Mobile Ad Hoc Networks for IPv4
However, when the above-described conventional art is applied to power line communication that uses a power line as a communication channel, the following problem arises.
Since it is assumed that the conventional art is used in wireless communication, a beacon is transmitted from a relay terminal by using a modulation method having a lowest communication speed, as in the case of the beacon in the communication using a base station. This is performed in order to prevent a terminal from becoming unable to communicate due to the movement thereof. However, a PLC (Power Line Communication) terminal using a power line as a communication channel is a terminal which does not move. Accordingly, a control packet to be transmitted to a slave device by a relay device existing in a network of power line communication need not, in order to expand to the maximum extent possible the range which allows communication with the relay device, to be modulated by using a modulation method having the lowest communication speed among a plurality of modulation methods that can be used by the relay device. Rather, there is a problem that since an ad hoc network includes a plurality of relay devices that output control packets, if control packets each modulated by using a modulation method having a lowest communication speed are transmitted, more bands are consumed, in the whole network, for transmitting the control packets, thereby reducing the bands that can be used for transmitting data that is intended to be transmitted.
Therefore, in view of the problem described above, an object of the present invention is to provide a communication terminal device and a communication method that allow, in an ad hoc network using a power line, a great reduction of the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication, and to ensure the transmission of data intended to be transmitted.
In order to solve the problem described above, a communication terminal device of an embodiment of the present invention modulates, when not receiving from the network for a predetermined period of time a request packet for requesting a control packet to be used for setting a communication path to a terminal on a network of power line communication, a request packet for the control packet, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network, and transmits the modulated request packet to the network.
A communication terminal device according to a first embodiment includes: a communication section connected to a network of power line communication; and a control section that modulates, in a case where a control packet to be used for setting a communication path to a terminal on the network is not received from the network for a predetermined period of time, a request packet for the control packet, using a modulation method having a lowest communication speed among a plurality of modulation methods that can be used in the network, and transmits the modulated request packet to the network.
According to the present embodiment, in a case where a control packet to be used for setting a communication path to a terminal on the network is not received from the network for a predetermined period of time, a request packet for the control packet is modulated by using a modulation method having a lowest communication speed among a plurality of modulation methods that can be used in the network, and the modulated request packet is transmitted to the network. Accordingly, even in a case where the communication terminal device comes, due to a change of the state of a communication channel, out of the range that allows communication with a terminal on the network, if a request packet is modulated by using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the request packet. As a result, the request packet reaches one of the terminals on the network, thereby enabling a restart of communication with the terminal.
In a communication terminal device according to a second embodiment based on the above embodiment, the case where the control packet is not received from the network for a predetermined period of time includes a time of a startup. According to the present embodiment, the control section transmits a request packet at the time of a startup. Accordingly, even in a case where a communication terminal device is newly included in the network, if a request packet is modulated by using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the request packet. As a result, the request packet reaches one of the terminals on the network, thereby enabling a start of communication with the terminal.
In a communication terminal device according to a third embodiment based on the above embodiment, the control section receives, from a first terminal that has responded to the request packet, a control packet that has been modulated by using a modulation method having a highest communication speed that can be used between the communication terminal device and the first terminal.
According to the present embodiment, between the communication terminal device and the first terminal which the request packet has reached, by receiving the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, it is possible to reduce to the maximum extent possible the range, which allows communication, of the first terminal. Accordingly, it is possible to minimize the overlapping portion between the range, which allows communication, of the first terminal and the range, which allows communication, of another terminal, and therefore, to minimize the range in which a control packet is transmitted from the first terminal. As a result, it is possible to reduce the probability that control packets overlap with each other in the whole network, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In a communication terminal device according to a fourth embodiment based on the above embodiment, in a case where, during a time period when the control packet is received from the first terminal, a control packet that has been modulated by using a modulation method having a different communication speed than the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, is received from a second terminal, the control section switches a transmission source of the control packet, from the first terminal to the second terminal.
According to the present embodiment, in a case where, during a time period when the control packet is received from the first terminal, a control packet that has been modulated by using a modulation method having a different communication speed than the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, is received from a second terminal, the control section switches a transmission source of the control packet, from the first terminal to the second terminal. Accordingly, in a case where there exists a second terminal that modulates a control packet by using a modulation method having a lower communication speed, the communication range of the second terminal is larger than the communication range of the first terminal. This enables more terminals to receive a control packet from the second terminal, and if the second terminal being the transmission source of the control packet to be received by the more terminals is selected, it is possible to reduce the number of transmission bodies of control packets. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
Further, in a case where there exists a second terminal that modulates a control packet by using a modulation method having a lower communication speed, the communication range of the control packet transmitted from the second terminal is smaller than the communication range of the control packet transmitted from the first terminal. Accordingly, if the second terminal having the smaller communication range of the control packet is selected, it is possible to reduce the number of transmission bodies of control packets and to reduce the communication ranges of beacons in the whole network. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In a communication terminal device according to a fifth embodiment based on the above embodiment, when switching the transmission source of the control packet, from the first terminal to the second terminal, the control section notifies the first terminal of the switching of the transmission source of the control packet. According to the present embodiment, when switching the transmission source of the control packet, from the first terminal to the second terminal, the control section notifies the first terminal of the switching of the transmission source of the control packet, whereby the first terminal being the transmission source of the control packet can perform processing such as stopping the transmission of the control packet in accordance with the notification. Accordingly, it is possible to reduce the number of transmission bodies of control packets, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In a communication terminal device according to a sixth embodiment based on the above embodiment, in a case where the first terminal is notified of the switching of the transmission source of the control packet and has another terminal being a transmission destination of the control packet, the first terminal modulates the control packet, using a modulation method having a highest communication speed that can be used between the first terminal and the other terminal, and transmits the modulated control packet to the other terminal.
According to the present embodiment, in a case where the first terminal is notified of the switching of the transmission source of the control packet and has another terminal being a transmission destination of the control packet, the first terminal modulates the control packet, using a modulation method having a highest communication speed that can be used between the first terminal and the other terminal, and transmits the modulated control packet to the other terminal. Accordingly, it is possible to reduce the communication range of the first terminal to the minimum range that can include the other terminal. Therefore, it is possible to minimize the overlapping portion between the communication range of the first terminal and the communication range of the second terminal, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
In a communication terminal device according to a seventh embodiment based on the above embodiment, in a case where the first terminal is notified of the switching of the transmission source of the control packet and has no other terminal being a transmission destination of the control packet, the first terminal stops transmitting the control packet.
According to the present embodiment, in a case where the first terminal is notified of the switching of the transmission source of the control packet and has no other terminal being a transmission destination of the control packet, the first terminal stops transmitting the control packet. Accordingly, the communication range of the control packet provided by the first terminal disappears, and thus the overlapping portion between the communication range of the first terminal and the communication range of the second terminal disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
In a communication terminal device according to an eighth embodiment based on the above embodiment, in a case where after the control packet is received from the second terminal, a control packet is not received for a predetermined period of time, the control section modulates a request packet, using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, and transmits the modulated request packet to the network.
According to the present embodiment, in a case where after the control packet is received from the second terminal, a control packet is not received for a predetermined period of time, the control section modulates a request packet, using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, and transmits the modulated request packet to the network. Accordingly, in a case where a control packet from the second terminal, with which communication has been performed, is not received due to a change of the state of a communication channel, a request packet is modulated by using the modulation method having the lowest communication speed among a plurality of modulation methods that can be used in the network, and therefore, it is possible to expand to the maximum extent possible the range which allows communication of the request packet. As a result, the request packet reaches one of the terminals on the network, thereby enabling a restart of communication with the terminal and reincorporation of, into the network, the communication terminal device whose communication with the second terminal has been stopped.
In a communication terminal device according to a ninth embodiment based on the above embodiment, information about the communication path to the terminal on the network includes at least one of: information indicating a relay device; path information indicating which path via the relay device allows a connection to a master device; and path information indicating which path via the relay device allows a connection to another terminal on the network.
In a communication terminal device according to a tenth embodiment based on the above embodiment, the control packet that has been modulated by using the modulation method having the lowest communication speed among the modulation methods that can be used in the network is a broadcast packet, and the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal is a unicast packet.
According to the present embodiment, the control packet that has been modulated by using the modulation method having the lowest communication speed is transmitted as a broadcast packet. On the other hand, the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal is transmitted as a unicast packet. Accordingly, broadcast packets are modulated by using a modulation method having the lowest communication speed among the modulation methods that can be used in the network, and thus it is possible to substantially increase the communication speed of a control packet even in a system that does not allow an increase of the communication speed. As a result, it is possible to reduce, to the maximum extent possible, the range in which the control packet is transmitted from the first terminal to the terminal that is currently communicating with the first terminal.
In a communication terminal device according to an eleventh embodiment based on the above embodiment, the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal is a broadcast packet, and the control packet that has been modulated by using the modulation method having the lower communication speed than the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, the control packet being received from the second terminal, is a broadcast packet.
According to the present embodiment, even in a case where a broadcast packet is used as a control packet, the broadcast packet is not modulated by using a modulation method having the lowest communication speed. Instead, the communication speed of the control packet to be transmitted from the first terminal and the communication speed of the control packet to be transmitted from the second terminal are changed. Accordingly, it is possible to reduce to the maximum extent possible, relative to the second terminal, the range in which the control packet is transmitted from the first terminal.
In a communication terminal device according to a twelfth embodiment based on the above embodiment, the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal is a unicast packet; and the control packet that has been modulated by using the modulation method having the lower communication speed than the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, the control packet being received from the second terminal, is a broadcast packet.
According to the present embodiment, the control packet that has been modulated by using the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal is a unicast packet. On the other hand, the control packet that has been modulated by using a modulation method having a lower communication speed than the modulation method having the highest communication speed that can be used between the communication terminal device and the first terminal, the control packet being received from the second terminal, is a broadcast packet. Accordingly, broadcast packets are modulated by using a modulation method having the lowest communication speed among the modulation methods that can be used in the network. Therefore, even in a system that does not allow an increase of the communication speed, the communication speed of the control packet to be transmitted from the first terminal can be higher than the communication speed of the control packet to be transmitted from the second terminal. As a result, it is possible to reduce to the maximum extent possible, relative to the second terminal, the range in which the control packet is transmitted from the first terminal.
A communication terminal device of a thirteenth embodiment includes: a communication section that transmits, to a terminal connected to a network of power line communication, a control packet to be used for setting a communication path to the terminal; and a control section that modulates, in a case where a response to the control packet is not received from the terminal for a predetermined period of time, the control packet, using a modulation method having a lowest communication speed among a plurality of modulation methods that can be used in the network, and transmits the modulated control packet to the terminal.
According to the present embodiment, in a case where a response to the control packet is not received from the terminal for a predetermined period of time, the control packet is modulated by using a modulation method having the lowest communication speed among a plurality of modulation methods that can be used in the network, and the modulated control packet is transmitted to the terminal. Accordingly, the transmission terminal of the control packet determines that the reception terminal cannot currently receive the control packet, expands the range which allows communication of the control packet, and retransmits a control packet in such a manner that the reception terminal can receive the control packet. Thus, the control packet reaches the reception terminal, whereby communication with the reception terminal can be resumed.
In a communication terminal device according to a fourteenth embodiment based on the above embodiment, the communication section transmits, by unicast, the control packet to the terminal; and in a case where the response to the control packet is not received from the terminal for a predetermined period of time, the control section modulates the control packet, using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, and transmits, by broadcast, the modulated control packet to the terminal.
According to the present embodiment, the communication section transmits, by unicast, the control packet to the terminal; and in a case where a response to the control packet is not received from the terminal for a predetermined period of time, the control section transmits, by broadcast, the control packet, using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network. This expands the range which allows communication of the control packet, and thus, the control packet reaches the reception terminal, whereby communication with the reception terminal can be resumed.
In a communication terminal device according to a fifteenth embodiment based on the above embodiment, the case where the response to the control packet is not received from the terminal for a predetermined period of time includes a case where the control section does not receive, from the terminal, a response to the control packet a predetermined number of times. According to the present embodiment, the communication terminal device can also be applied to a case where a response to a control packet is not received from a terminal a predetermined number of times.
A communication method of a sixteenth embodiment includes modulating, in a case where a control packet to be used for setting a communication path to a terminal connected to a network of power line communication is not received from the network for a predetermined period of time, a request packet for the control packet, using a modulation method having a lowest communication speed among a plurality of modulation methods that can be used in the network; and transmitting the modulated request packet to the network.
According to the present embodiment, even in a case where the communication terminal device comes, due to a change of the state of a communication channel, out of the range that allows communication with a terminal on the network, if a request packet is modulated by using the modulation method having the lowest communication speed among the plurality of modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the request packet. As a result, the request packet reaches one of the terminals on the network, thereby enabling a start or a restart of communication with the terminal.
According to the communication terminal device in the embodiments described above, it is possible, in an ad hoc network using a power line, to greatly reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication, and to ensure the transmission of data intended to be transmitted.
Each of the terminals including reception terminals 108 to 110 refers to the destination address 306 and the relay destination address 308, and starts reception processing of the payload 303 if the destination address 306 or the relay destination address 308 coincides with or includes the address of its own terminal. Note that, if the modulation method is the one that allows the terminal to perform reception, the terminal may perform reception irrespective of the addresses. In the path information packet according to the present embodiment, although ff:ff:ff:ff:ff:ff is set as the relay destination address 308 so as to allow all the terminals to perform reception, the modulation method is adapted to a particular terminal.
The modulation method determination section 402 determines, based on information obtained from the utilization efficiency determination section 403, a modulation method for the packet to be relayed. In the present embodiment, described is a case that employs a modulation method having a communication speed other than the lowest communication speed, for a path information packet (hereinafter referred to as a “beacon”) that includes data such as path information and that is periodically transmitted to all the terminals, different from a beacon in the field of wireless communication. Use of a modulation method having a communication speed other than the lowest communication speed allows a great reduction of the bands consumed by the beacon.
The utilization efficiency determination section 403 stores information indicating to which terminal each of the relay terminals 103 to 107 is transmitting a beacon and which terminal can receive the beacon transmitted from its own terminal, and determines a modulation method and a relay terminal that optimize the utilization efficiency of the ad hoc network. For example, the utilization efficiency determination section 403 requests, when it is better to change the modulation method for the beacon being transmitted from its own terminal, the modulation method determination section 402 to change the modulation method to the optimum modulation method. The utilization efficiency determination section 403 requests, when it is better to stop transmitting the beacon being transmitted from its own terminal, a transmission processing section 405 to stop the transmission. The utilization efficiency determination section 403 requests, when it is better to change the relay terminal from which its own terminal is receiving a beacon, the control packet transmission section 404 to change the relay terminal.
The control packet transmission section 404 transmits various kinds of control packets in accordance with a request from the reception processing section 401 or the utilization efficiency determination section 403. For example, the control packet transmission section 404 transmits a beacon request packet or a beacon response packet, in accordance with a request from the reception processing section 401. Further, for example, the control packet transmission section 404 transmits a determination packet or a registration information update packet, in accordance with a request from the utilization efficiency determination section 403. Each of the beacon request packet, the beacon response packet, the determination packet, and the registration information update packet is described below.
The transmission processing section 405 transmits various kinds of control packets provided by the control packet transmission section 404 and a beacon packet. The transmission processing section 405 also transmits general data.
Hereinafter, with reference to
In
As described above, between the terminal C503 and the terminal E505, communicated is a beacon modulated by using a modulation method having the highest communication speed that can be used between the terminals. Accordingly, it is possible to reduce to the maximum extent possible the cover area 508, which allows communication, of the terminal C503. Accordingly, it is possible to minimize the overlapping portion between the cover area 508 of the terminal C503 and the cover area 507, which allows communication, of the terminal B502, so as to minimize the range in which a beacon is transmitted from the terminal C503. As a result, it is possible to reduce the probability that beacons overlap with each other in the whole network, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Accordingly, even in a case where the terminal F701 exists outside the cover area which allows the terminal F701 to communicate with other terminals on the network, if the terminal F701 transmits a beacon request packet, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the beacon request packet. As a result, the beacon request packet reaches one of the terminals on the network, thereby enabling the terminal F701 to start communication with the terminal.
Accordingly, in a case of an existence of the terminal C503 that modulates a beacon by using a modulation method having a higher communication speed, the beacon communication range of the terminal C503 is smaller. Therefore, if the terminal C503 that has the smaller beacon communication range is selected, it is possible to reduce the number of the beacon transmission bodies, and to reduce the beacon communication ranges in the whole network. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Further, when the beacon transmission source is switched from the terminal B502 to the terminal C503, the control packet transmission section 404 of the terminal D504 notifies the terminal B502 of the switching of the beacon transmission source. In a case where the terminal B502 has been notified of the switching of the beacon transmission source and has no other beacon transmission destination than the terminal D504, the terminal B502 stops transmitting a beacon (see
In this manner, in a case where the beacon transmission source is switched from the terminal B502 to the terminal C503, when the terminal B502 is notified of the switching of the beacon transmission source, the terminal B502, which has been the beacon transmission source, may stop transmitting a beacon in accordance with the notification. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
In addition, in a case where the terminal B502 has been notified of the switching of the beacon transmission source and has no other beacon transmission destination than the terminal D504, the terminal B502 stops transmitting a beacon, whereby the beacon communication range provided by the terminal B502 (that is, the cover area 507) disappears. Accordingly, the overlapping portion between the cover area 507 of the terminal B502 and the communication range of the terminal C503 (that is, the cover area 901) disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
Having received the beacon request 1304, the terminal C503 transmits to the terminal F701 a CE (CHANNEL ESTIMATION) request 1305, and receives, from the terminal F701, a CE response 1306 as a response to the CE request 1305. Thereby, the terminal C503 estimates a modulation method having the highest communication speed among the modulation methods that allow communication with the terminal F701. Once the modulation method having the highest communication speed is known, the control packet transmission section 404 in the terminal C503 returns a beacon response 1307, using the modulation method, via the transmission processing section 405, to the terminal F701.
Having received the beacon response, the terminal F701 makes a determination of the terminal C503 as the relay terminal for relaying a beacon, and the control packet transmission section 404 in the terminal F701 transmits, via the transmission processing section 405, to the terminal C503, a determination response 1308 for having the terminal C503 relay a beacon. Here, since the terminal C503 is already communicating with the terminal E505 (see
As described above, the terminal F701 transmits a beacon request packet, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network. Accordingly, even in a case where the terminal F701 exists outside the cover area which allows the terminal F701 to communicate with other terminals on the network, if the terminal F701 transmits a beacon request packet, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the beacon request packet. As a result, the beacon request packet reaches one of the terminals on the network, thereby enabling the terminal F701 to start communication with the one of the terminals.
Since the beacon 1302 from the terminal C503 is now transmitted by using a lower speed modulation method, the terminal D504 can receive both of the beacon 1302 from the terminal B502 and the beacon 1302 from the terminal C503. Now, the terminal D504 switches the relay source to a terminal that can perform a higher speed communication. It is assumed that, different from a beacon in the field of wireless communication, information about to which terminal a high speed communication is possible is stored, as path information, in a beacon. When a reception terminal no longer needs a relay from a relay source, the relay source may stop relaying a beacon. Since the present embodiment allows transmission by using a modulation method having a higher communication speed, a beacon relay from the terminal B502, which has been the relay source, is stopped, and a beacon relay from the terminal C503, which is a new relay source, is started. After the terminal B502 has stopped the relay to the terminal D504, the terminal B502 may stop relaying a beacon since there is no other terminal to which the terminal B502 should relay a beacon.
As described above, in the present first embodiment, in a case where, during the time period when the terminal D504 receives a beacon from the terminal B502, the terminal D504 receives, from the terminal C503, a beacon modulated by using a modulation method having a higher communication speed than the communication speed used between the terminal D504 and the terminal B502, the terminal D504 switches the beacon transmission source, from the terminal B502 to the terminal C503. In a case of an existence of the terminal C503 that modulates a beacon, using a higher communication speed, the beacon communication range of the terminal C503 is smaller. Therefore, if the terminal C503 that has the smaller beacon communication range is selected, it is possible to reduce the number of the beacon transmission bodies and to reduce the beacon communication ranges in the whole network. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
The control packet transmission section 404 in the terminal D504 transmits, via the transmission processing section 405, to the terminal B502, a registration information update packet 1309 so as to request the terminal B502 to stop the relay, and transmits to the terminal C503 a registration information update packet 1310 so as to request the terminal C503 to start a relay. As a result, a beacon 1303 is transmitted from the terminal C503 to both of the terminal D504 and the terminal F701. Note that, beacons from the terminal C503, as having been transmitted by broadcast, have already reached the terminal D504. The reason why the terminal D504 transmits to the terminal C503 the registration information update packet 1310 and requests the terminal C503 to start a relay is to notify the terminal C503 that the terminal D504 is now a terminal receiving beacons from the terminal C503.
In this manner, in a case where the beacon transmission source is switched from the terminal B502 to the terminal C503, the control packet transmission section 404 of the terminal D504 transmits a registration information update packet 1309 to the terminal B502, so as to switch the beacon transmission source. In a case where the terminal B502 has been notified of the switching of the beacon transmission source, the terminal B502 stops transmitting a beacon since there is no other terminal, than the terminal D504, to which the terminal B502 should transmit a beacon.
In a case where the beacon transmission source is switched from the terminal B502 to the terminal C503, when the terminal B502 is notified of the switching of the beacon transmission source, the terminal B502, which has been the beacon transmission source, may stop transmitting a beacon in accordance with the registration information update packet 1309. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Further, when the terminal B502 stops transmitting a beacon, the beacon cover area 507 provided by the terminal B502 disappears. Accordingly, the overlapping portion between the cover area 507 of the terminal B502 and the cover area 901 of the terminal C503 disappears (see
Accordingly, even in a case where a terminal exists outside the cover areas of other terminals on the network, if the terminal transmits a beacon request packet, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network, it is possible to expand to the maximum extent possible the range which allows communication of the beacon request packet. As a result, the beacon request packet reaches one of the terminals on the network, thereby enabling the terminal to restart or start communication with the one of the terminals on the network.
On the other hand, when having received a beacon (step S1511), the terminal checks whether or not the terminal itself can accept the modulation method and receive the payload (step S1512). When the terminal cannot receive the payload, the processing returns to step S1501. When the terminal can receive the payload, if the beacon transmission source coincides with the current relay terminal, the processing returns to the ordinary beacon reception processing. When the beacon transmission source does not coincide with the current relay terminal (step S1513), it is determined which of the current relay terminal and the terminal being the beacon transmission source consumes fewer bands in total (step S1514).
Specifically, when the communication speed used by the terminal being the beacon transmission source is compared with the communication speed used by the current relay terminal, and if the communication speed used by the terminal being the beacon transmission source is higher than the communication speed used by the current relay terminal, the beacon communication range provided by the terminal being the beacon transmission source is smaller. In such a case, if the terminal being the beacon transmission source is selected instead of the current relay terminal, it is possible to reduce the number of the beacon transmission bodies and to reduce the beacon communication ranges in the whole network. In this case, since it is determined that a relay performed by the terminal being the beacon transmission source consumes fewer bands in total than a relay performed by the current relay terminal, a registration information update packet is transmitted to the current relay terminal so as to request the current relay terminal to stop the relay (step S1515). Concurrently, a registration information update packet is transmitted to the terminal being the beacon transmission source so as to request the terminal being the beacon transmission source to become a new relay terminal and start a relay (step S1516). As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. Note that, the above determination may be made based on path information included in a beacon.
When a registration information update packet that includes an instruction to start a relay is received (step S1611), the reception terminal information is updated (step S1612), and based on the updated reception terminal information, a modulation method having the highest communication speed among the modulation methods that allow all the terminals to perform reception is selected as the optimum modulation method (step S1613). Thereafter, beacon relay processing is started (step S1614).
When a registration information update packet that includes an instruction to stop the relay is received (step S1621), the reception terminal information is updated (step S1622), and then made is a determination of the number of terminals to which a beacon is to be transmitted, excluding the terminal that has transmitted the instruction to stop the relay (step S1623). When the number of the terminals is zero, beacon relay processing is stopped (step S1625). Accordingly, the beacon communication range provided by the present terminal disappears. Accordingly, it is possible to reduce the number of the beacon transmission bodies and to eliminate the overlapping portion between the communication range of the present terminal and that of the other terminal. As a result, it is possible to prevent needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication, and to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted. On the other hand, when other reception terminals remain, the optimum modulation method is selected based on the registered reception terminal information, and beacon relay processing is continued (step S1624).
In the first embodiment, description is given on operations to be performed in a case where a new terminal has entered the network. In a PLC network, where terminals are not moved, a change of a state of the network may occur in a case where a PLC terminal is newly connected to the PLC network, or a PLC terminal is removed from the PLC network; and also, in a case where a noise source is generated when an electrical household appliance, such as a cleaner, has just been connected to the PLC network, or when an electrical household appliance, such as a microwave oven, which has been connected to the PLC network is turned ON/OFF. In the present second embodiment, description is given on operations to be performed in a case where a noise source is generated when an electrical household appliance is connected or the like.
In the present second embodiment, since the terminal F1706 has not received a beacon from the network for a predetermined period of time, the terminal F1706 transmits, using a modulation method having the lowest communication speed among the modulation methods that can be used between the terminal F1706 and the terminal B1702, a beacon request packet to the terminal B1702 that has been transmitting beacons. Accordingly, even in a case where the terminal F1706 exists in the cover area 1708 of the terminal B1702 but cannot receive a beacon from the terminal B1702, if the terminal F1706 transmits a beacon request packet, using a modulation method having the lowest communication speed among the modulation methods that can be used between the terminal F1706 and the terminal B1702, it is possible to expand to the maximum extent possible the range which allows communication of the beacon request packet. As a result, the beacon request packet reaches the terminal B1702, thereby enabling the terminal F1706 to restart communication with the terminal B1702.
As described above, use of a modulation method having a lower communication speed reduces the area in which a packet loss is generated. As a result, the terminal B1702 is able to include the terminal F1706 in the cover area 2101, thereby enabling the terminal F1706 to receive a beacon from the terminal B1702. The state of the beacon tree in
That is, since the terminal B1702 has the expanded cover area 2101, the terminal E1705 now belongs to both of the cover areas 2101 and 1709 of the terminal B1702 and the terminal C1703, respectively. Accordingly, the terminal E1705 receives beacons from both of the terminal B1702 and the terminal C1703. Here, if the terminal C1703 stops relaying the beacon to the terminal E1705, it is possible to suppress the band consumption in total. Therefore, in the present second embodiment, in a case where, during the time period when the terminal E1705 receives a beacon from the terminal C1703, the terminal E1705 receives, from the terminal B1702, a beacon modulated by using a modulation method having a lower communication speed than the communication speed used between the terminal E1705 and the terminal C1703, the terminal E1705 switches the beacon transmission source, from the terminal C1703 to the terminal B1702.
In a case of an existence of the terminal B1702 that modulates a beacon by using a modulation method having a lower communication speed, the cover area 2101 of the terminal B1702 is larger than the cover area 1709 of the terminal C1703. This allows many terminals to receive a beacon from the terminal B1702, and therefore, if the terminal B1702, which is the transmission source of a beacon that is to be received by more terminals, is selected, it is possible to reduce the number of the beacon transmission bodies. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, the control packet transmission section 404 in the terminal E1705 notifies the terminal C1703 of the switching of the beacon transmission source. In a case where the terminal C1703 has been notified of the switching of the beacon transmission source and has no other beacon transmission destination than the terminal E1705, the terminal C1703 stops transmitting a beacon.
As described above, in a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, when the terminal C1703 is notified of the switching of the beacon transmission source, the terminal C1703, which has been the beacon transmission source, may stop transmitting a beacon in accordance with the notification. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Further, when the terminal C1703 stops transmitting a beacon, the beacon cover area 1709 provided by the terminal C1703 disappears. Accordingly, the overlapping portion between the cover area 1709 of the terminal C1703 and the cover area 2101 of the terminal B1702 disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
Having received the beacon request 2511, the terminal B1702 transmits a CE request 2512 to the terminal F1706, receives, as a response, a CE response 2513 from the terminal F1706, and selects the optimum modulation method in the presence of the noise source. The terminal B1702 returns a beacon response 2514, using the optimum modulation method. When having received the beacon response 2514, the terminal F1706 returns a determination response 2515. Here, since the terminal B1702 is already communicating with the terminal D1704 (see
Note that, the operations after the beacon response may be omitted and the modulation method for the beacon itself may be changed. In that case, if a beacon is lost, another beacon request is transmitted.
A beacon transmitted from the terminal B1702 by using the changed modulation method reaches the terminal F1706, without being lost. In this case, the terminal E1705 receives a beacon 2503 from each of the terminal B1702 and the terminal C1703. In the present second embodiment, in a case where, during the time period when the terminal E1705 receives a beacon from the terminal C1703, the terminal E1705 receives, from the terminal B1702, a beacon modulated by using a modulation method having a lower communication speed than the communication speed used between the terminal E1705 and the terminal C1703, the terminal E1705 switches the beacon transmission source, from the terminal C1703 to the terminal B1702.
In a case of an existence of the terminal B1702 that modulates a beacon, using a modulation method having a lower communication speed, the cover area 2101 of the terminal B1702 is larger than the cover area 1709 of the terminal C1703. This allows many terminals to receive a beacon from the terminal B1702, and therefore, if the terminal B1702, which is the transmission source of a beacon that is to be received by more terminals, is selected, it is possible to reduce the number of the beacon transmission bodies. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In order to select the terminal B1702, the terminal E1705 transmits a registration information update packet 2516 toward the terminal C1703 so as to request the terminal C1703 to stop relaying a beacon. In a case where the terminal C1703 has received the update packet 2516 and has no other beacon transmission destination than the terminal E1705, the terminal C1703 stops transmitting a beacon. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. Further, when the terminal C1703 stops transmitting a beacon, the beacon cover area 1709 provided by the terminal C1703 disappears. Accordingly, the overlapping portion between the cover area 1709 of the terminal C1703 and the cover area 2101 of the terminal B1702 disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
The terminal E1705 transmits a registration information update packet 2517 toward the terminal B1702 so as to request the terminal C1702 to start relaying a beacon. Accordingly, the terminal E1705 receives the beacon 2504 only from the terminal B1702. Note that, beacons from the terminal B1702, as having been transmitted by broadcast, have already reached the terminal E1705. The reason why the terminal E1705 transmits to the terminal B1702 the registration information update packet 2517 so as to request the terminal B1702 to start a relay, is to notify the terminal B1702 that the terminal E1705 is now a terminal receiving beacons from the terminal B1702.
With reference to
On the other hand, when having received a beacon (step S2711), the terminal checks whether or not the terminal itself can accept the modulation method and receive the payload (step S2712). When the terminal cannot receive the payload, the processing returns to step S2701. When the terminal can receive the payload, if the beacon transmission source coincides with the current relay terminal, the processing returns to the ordinary beacon reception processing. When the beacon transmission source does not coincide with the current relay terminal (step S2713), it is determined which of the current relay terminal and the terminal being the beacon transmission source consumes fewer bands in total (step S2714).
When the communication speed used by the terminal being the transmission source of a beacon is compared with the communication speed used by the current relay terminal, and if the communication speed used by the terminal being the beacon transmission source is higher than the communication speed used by the current relay terminal, the beacon communication range provided by the terminal being the beacon transmission source is smaller. In such a case, if the terminal being the beacon transmission source is selected instead of the current relay terminal, it is possible to reduce the number of the beacon transmission bodies and to reduce the beacon communication ranges in the whole network. In this case, since it is determined that a relay performed by the terminal being the beacon transmission source consumes fewer bands in total than a relay performed by the current relay terminal, a registration information update packet is transmitted to the current relay terminal so as to request the current relay terminal to stop the relay (step S2715). Concurrently, a registration information update packet is transmitted to the terminal being the beacon transmission source so as to request the terminal being the beacon transmission source to become a new relay terminal and start a relay (step S2716). As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. Note that, the above determination may be made based on path information included in a beacon.
Further, the beacon reception processing performed at each terminal in the second embodiment may include operations shown in
With reference to
In the first and second embodiments described above, description has been given on the cases where ff:ff:ff:ff:ff:ff is set as the relay destination address and the modulation method is adapted to a particular terminal. This method is effective in a case where modulation methods are divided into several levels, from low communication speed to high communication speed, and where a terminal can accept all the modulation methods that have a lower communication speed than the communication speed that allows the terminal itself to perform reception. However, when an adaptive modulation method (such as a modulation method, in OFDM, which is changed for each subcarrier) is used, the modulation method is adapted to two specific terminals, thereby enabling very high speed communication. Accordingly, the modulation method that is adapted to two specific terminals may consume fewer bands than a modulation method that allows communication among a plurality of terminals which are not specified.
Therefore, in the present third embodiment, description is given on operations to be performed in a case where reduction of the band consumption is achieved by combining two modulation methods: a transmission method in which ff:ff:ff:ff:ff:ff is set as the relay destination address and a modulation method having a lowest communication speed is used (hereinafter referred to as “broadcast”), and a transmission method in which the address of a specific terminal is set as the relay destination address and a modulation method having a highest communication speed is used between the relay source and the relay destination (hereinafter referred to as “unicast”). Note that, in unicast, a reception terminal returns to a transmission terminal an acknowledgment (hereinafter referred to as “ACK”) that notifies the transmission terminal that data has normally been received, and therefore, when an ACK is not returned irrespective of repeated retransmissions, an occurrence of a packet loss is known.
In the present third embodiment, in a case where no ACK is returned irrespective of a plurality of unicast transmissions that have been performed, the optimum modulating speed is redetermined based on a CE request and a CE response. However, the present invention is not limited thereto, the above redetermination may be made in a case where an ACK in response to a beacon transmitted by unicast has not been returned for a predetermined period of time. Further, the same processing may also be performed when there is an entry of a new terminal. That is, the same processing may be performed in a case where fewer bands are consumed when a beacon is transmitted, by broadcast, by the terminal B1702 to three terminals of the terminal D1704, the terminal F1706 and a new terminal, than by unicast.
In this manner, in a case where the terminal B1702 transmits a beacon to the terminal F1706 by unicast, and does not receive, from the terminal F1706 a predetermined number of times or for a predetermined period of time, an ACK in response to the beacon, the terminal B1702 transmits a beacon to the terminal F1706 by broadcast, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network. Thus, the beacon transmission terminal B1702 determines that the reception terminal F1706 cannot currently receive the beacon, expands the range which allows communication of the beacon, and retransmits a beacon in such a manner that the reception terminal F1706 can receive the beacon. Accordingly, the beacon reaches the reception terminal F1706, enabling the terminal B1702 to resume communication with the reception terminal F1706.
In a case of an existence of the terminal B1702 that transmits a beacon by broadcast, using a modulation method having a lower communication speed, the cover area 3101 of the terminal B1702 is larger than the cover area 2903 of the terminal C1703. This allows many terminals to receive a beacon from the terminal B1702, and therefore, if the terminal B1702, which is the transmission source of a beacon that is received by more terminals, is selected, it is possible to reduce the number of the beacon transmission bodies. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
In a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, the control packet transmission section 404 in the terminal E1705 notifies the terminal C1703 of the switching of the beacon transmission source. In a case where the terminal C1703 has been notified of the switching of the beacon transmission source and has no other beacon transmission destination than the terminal E1705, the terminal C1703 stops transmitting a beacon.
In this manner, in a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, when the terminal C1703 is notified of the switching of the beacon transmission source, the terminal C1703, which has been the beacon transmission source, may stop transmitting a beacon in accordance with the notification. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Further, when the terminal C1703 stops the unicast transmission of a beacon, the beacon cover area 2903 provided by the terminal C1703 disappears. Accordingly, the overlapping portion between the cover area 2903 of the terminal C1703 and the cover area 3101 of the terminal B1702 disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
Note that, this processing is the same as that of the second embodiment.
Next, a beacon 3302 is transmitted, by unicast, from the terminal B1702 to the terminal D1704 and the terminal F1706, and is transmitted, by unicast, from the terminal C1703 to the terminal E1705. Here, to a packet 3315 and a packet 3353, an ACK 3316 and an ACK 3354 have been returned, respectively, and the transmission has been completed normally. However, to a packet 3317, an ACK has not been returned. Accordingly, a packet 3318 and a packet 3319 are retransmitted. When an ACK packet still cannot be received, the terminal B1702 determines that a packet cannot be communicated by using the modulation method.
In the present third embodiment, the noise source 1901 is generated. When having detected a change in the network, the terminal B1702 transmits a CE request 3320 to the terminal F1706 and receives a CE response 3321 from the terminal F1706, and researches a modulation method having the highest communication speed that allows communication in that state. Using the result, the terminal B1702 determines which is better, to transmit a beacon by using a plurality of unicasts or to transmit a beacon by broadcast. When having determined that it is better to transmit a beacon by broadcast, the terminal B1702 transmits a beacon 3303 by broadcast. Note that, the beacon 3302 has been transmitted, by unicast, from the terminal C1703 to the terminal E1705, by using a packet 3353. In contrast, an ACK packet 3354 has been returned from the terminal E1705 to the terminal C1703.
Next, a packet 3322 of the beacon 3303 transmitted by broadcast from the terminal B1702 is received not only by the terminal D1704 and the terminal F1706 but also by the terminal E1705. The terminal E1705 also receives a packet 3355 of the beacon 3303 transmitted by unicast from the terminal C1703. The terminal E1705 switches, using the same method as that in the second embodiment, the terminal from which the terminal E1705 receives a beacon, to the terminal B1702. That is, in a case where, during the time period when the terminal E1705 receives, by unicast, the packet 3355 of the beacon 3303 from the terminal C1703 and returns an ACK packet 3356 to the terminal C1703, the terminal E1705 receives, for example, by broadcast, from the terminal B1702, the packet 3322 of the beacon 3303 modulated by using a modulation method having a lower communication speed than the communication speed used between the terminal E1705 and the terminal C1703, the terminal E1705 switches the beacon transmission source, from the terminal C1703 to the terminal B1702.
In a case of an existence of the terminal B1702 that modulates the packet 3322 of the beacon 3303 by using a modulation method having a lower communication speed, the cover area 3101 of the terminal B1702 is larger than the cover area 2903 of the terminal C1703. Accordingly, since there are many terminals that can receive the packet 3322 of the beacon 3303 from the terminal B1702, if the terminal B1702, which is the transmission source of the packet 3322 of the beacon 3303 that is received by more terminals, is selected, it is possible to reduce the number of the beacon transmission bodies. As a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication.
The terminal E1705 transmits a registration information update packet 3358 toward the terminal C1703, and requests the terminal C1703 to start relaying a beacon. Accordingly, the terminal E1705 receives a packet 3323 of a beacon 3304, and a packet 3324 of a beacon 3305, only from the terminal B1702. Note that, beacons from the terminal B1702, as having been transmitted by broadcast, have already reached the terminal E1705. The reason why the terminal E1705 transmits to the terminal B1702 a registration information update packet 3358 and requests the terminal B1702 to start a relay is to notify the terminal B1702 that the terminal E1705 is now a terminal receiving beacons from the terminal B1702.
In a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, the control packet transmission section 404 in the terminal E1705 notifies the terminal C1703 of the switching of the beacon transmission source, using a registration information update packet 3357. In a case where the terminal C1703 has been notified of the switching of the beacon transmission source and has no other beacon transmission destination than the terminal E1705, the terminal C1703 stops transmitting the beacon 3303.
Subsequently, the packet 3323 of the beacon 3304 and the packet 3324 of the beacon 3305 that are transmitted, by broadcast, from the terminal B1702 reach the terminal D1704, the terminal E1705, and the terminal F1706.
In this manner, in a case where the beacon transmission source is switched from the terminal C1703 to the terminal B1702, when the terminal C1703 is notified of the switching of the beacon transmission source, the terminal C1703, which has been the beacon transmission source, may stop transmitting a beacon in accordance with the notification. Accordingly, it is possible to reduce the number of the beacon transmission bodies, and as a result, it is possible to effectively reduce the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication.
Further, when the terminal C1703 stops transmitting a beacon, the beacon cover area 2903 provided by the terminal C1703 disappears. Accordingly, the overlapping portion between the cover area 2903 of the terminal C1703 and the cover area 3101 of the terminal B1702 disappears, thereby enabling prevention of needless increase in the percentage of the bands consumed for transmission of beacons in the bands consumed for all the communication. As a result, it is possible to effectively secure the bands that are to be consumed for transmitting data intended to be transmitted.
First, a relay terminal is transmitting, by unicast, a beacon to a reception terminal. When having failed in receiving, a predetermined number of times or for a predetermined period of time, an ACK in response to the beacon, the relay terminal determines that the beacon cannot be relayed by using the current modulation method (step S3501). Next, the relay terminal researches the optimum modulation method for the beacon transmission destination, using a CE request and a CE response (step S3502). Based on the research result, the relay terminal determines which one, unicast or broadcast, achieves the least band consumption in total (step S3503). In accordance with the determination result, the relay terminal starts relaying a beacon (step S3504).
In this manner, in a case where the relay terminal transmits a beacon to the reception terminal by unicast, and does not receive, from the reception terminal a predetermined number of times or for a predetermined period of time, an ACK in response to the beacon, the relay terminal transmits a beacon to the reception terminal, using a modulation method having the lowest communication speed among the modulation methods that can be used in the network. In this manner, the relay terminal that transmits a beacon determines that the reception terminal cannot currently receive the beacon, expands the range that allows communication of the beacon, and retransmits a beacon in such a manner that the reception terminal can receive the beacon. As a result, the beacon reaches the reception terminal, enabling the relay terminal to resume communication with the reception terminal.
According to the present invention, it is possible to provide a communication terminal device, a communication method, and the like that are able to greatly reduce, in an ad hoc network using a power line, the percentage of the bands consumed for transmission of control packets in the bands consumed for all the communication and are able to ensure the transmission of data intended to be transmitted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-115684 | Apr 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/001861 | 4/23/2009 | WO | 00 | 1/13/2010 |
