Patent Application
20150271817
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-056962, filed on Mar. 19, 2014; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a communication device, a wireless communication system, a communication method, and a computer program product.
In related art, for building an autonomous distributed network in a wireless communication environment, any of a plurality of communication stations belonging to a network is put into a state in which the communication station can receive a beacon from a communication station (hereinafter may be referred to as a “new communication station”) attempting to newly join the network, and the new communication station can be added to the network when the beacon from the new communication station is received by the communication station.
Furthermore, in recent years, lower power consumption is important particularly for mobile devices, and methods for reducing power used for wireless modules as much as possible have been devised. For example, a method of exchanging information indicating timings (active timings) at which communication stations that recognize each other can transmit/receive information between the communication stations to reduce power used for wireless modules when power is not required has been proposed.
In the related art, since any of a plurality of communication stations already joining a network always needs to be put in a state in which the communication station can receive a beacon from a new communication station attempting to join the network, there is a disadvantage that power consumption cannot be sufficiently reduced.
According to an embodiment, a communication device for dynamically building a network includes a first receiver and a first transmitter. When the communication device attempts to newly join the network, the first receiver waits for reception of a first beacon containing information for joining the network from another communication device already joining the network for a predetermined first period. When the communication device is already joining the network, the first transmitter determines a schedule indicating timings at which a plurality of communication devices already joining the network transmit first beacons so that intervals at which the communication devices transmit the first beacons in the network as a whole do not exceed the first period and transmit the first beacon according to the schedule.
Embodiments will be described in detail below with reference to the accompanying drawings.
The communication station N includes a first receiver 10 and a first transmitter 20. In the present embodiment, the communication station N has a hardware configuration including a CPU (central processing unit), a ROM, a RAM, a communication interface (I/F), etc. The functions of the respective components (the first receiver 10, the first transmitter 20) of the communication station N are implemented by expanding and executing programs stored in the ROM into the RAM by the CPU. Alternatively, at least some of the functions of the respective components (the first receiver 10, the first transmitter 20) of the communication station N may be implemented by dedicated hardware circuits (such as semiconductor integrated circuits)
When the communication station N attempts to newly join a network, the first receiver 10 waits for a beacon (corresponding to a “first beacon” in the claims) containing information for joining the network from another communication station N joining the network for a predetermined first period. As will be described later, in this example, a beacon transmitted by each communication station N also contains a signal (an identifier to be described later) for indicating the presence of the communication station N and thus serves as both of a “first beacon” in the claims and a “second beacon” in the claims, but the beacon is not limited thereto. For example, a first beacon containing information for joining a network and a second beacon containing a signal for indicating the presence of the communication station N may be different signals. Note that the information for joining a network is information required for allowing communication with any of communication stations N already joining the network by using predetermined procedures.
When the communication station N is already joining the network, the first transmitter 20 thereof determines a schedule indicating the timings at which the communication stations N each transmit a beacon (corresponding to the “first beacon” in the claims) so that the intervals at which the communication stations N already joining the network transmit beacons (corresponding to the “first beacon” in the claims) in the network as a whole will not exceed the first period, and transmits a beacon according to the schedule. Specifically, when the communication station N is already joining the network, the first transmitter 20 thereof determines a schedule indicating the timings at which the communication stations N already joining the network each transmit a beacon (corresponding to the “first beacon” in the claims) so that the interval between transmission of a beacon by one of the communication stations N and transmission of a beacon by another communication station N in the network as a whole will not exceed the first period, and transmits a beacon according to the schedule. More specifically, the configuration is as follows.
The first transmitter 20 has an arbitration phase representing a state of arbitrating between the communication station N and other communication stations N to determine a schedule, and a beacon transmission phase representing a state of sending (transmitting) a beacon of the communication station N according to the determined schedule. For determining a schedule, the first transmitter 20 transmits a beacon (corresponding to the “second beacon” in the claims) containing a signal for indicating the presence of the communication station N on the basis of the information for joining the network (in this example, information indicating a timing of a next arbitration phase as will be described later), and the first receiver 10 receives beacons (corresponding to the “second beacon” in the claims) from other communication stations N and determines the schedule on the basis of the signal (a signal for indicating the presence of the communication station N) contained in the beacon of the communication station N and the beacon of another communication station N. In this example, the first transmitter 20 of each of all the communication stations N already joining the network transmits a beacon to other communication stations N within a predetermined time period (1 second, for example) in the arbitration phase. Each of the communication stations N receives beacons from the other communication stations, and determines a schedule on the basis of the beacon of the communication station N and the beacons from the other communication stations N. In this example, a beacon contains an identifier representing a number for identifying the communication station N that transmits the beacon. In this example, the identifier corresponds to the signal for indicating the presence of the communication station N. The first transmitter 20 of each communication station N determines an order in which the identifier contained in the beacon (corresponding to the “second beacon” in the claims) of the communication station N and the identifiers contained in the beacons (corresponding to the “second beacons” in the claims) of the other communication stations N are arranged according to a predetermined rule to be the order in which the communication stations N transmit beacons (corresponding to the “first beacons” in the claims). Subsequently, the transmission phase is entered, and the first transmitter 20 of each communication station N transmits the beacon of the communication station N according to the schedule determined in the arbitration phase.
In this example, in the transmission phase, a beacon is transmitted according to the schedule each time the time period Ta (four seconds in this example, but not limited thereto) corresponding to the first period elapses, and the arbitration phase is entered again at the time point when a predetermined time period (three seconds in this example, but not limited thereto) has elapsed from the time point when transmission of beacons from all the communication stations N was completed.
In this example, a communication station N identified by an identifier represented by “x” will be represented by “Nx”. For example, as illustrated in
When attention is focused on the communication station N3, in the arbitration phase, the first transmitter 20 of the communication station N3 transmits a beacon of the communication station N3, and the first receiver 10 of the communication station N3 receives beacons from the other communication stations N1, N10, and N15. The first transmitter 20 of the communication station N3 determines the order (in this example, the order in ascending order of the numbers) in which the identifier (the identifier represented by “3”) contained in the beacon of the communication station N3 and the identifiers contained in the beacons of the other communication stations N1, N10, and N15 are arranged according to a predetermined rule to be the order in which the communication stations N transmit beacons. In this example, the first transmitter 20 of the communication station N3 determines the communication station N3 to be the second communication station to transmit its beacon. Furthermore, since the first transmitter 20 of the communication station N3 can detect that there are three other communication stations N (N1, N10 and N15) already joining the network, the first transmitter 20 deems that four communication stations N including the communication station N3 build up the network and determines the next arbitration phase to take place 4 seconds×4=16 seconds later. Similarly, the first transmitters 20 of the other communication stations N can determine the order in which the beacons of the communication stations N are transmitted and the timing of the next arbitration phase.
In this example, a beacon transmitted by each communication station N also contains information for joining the network in addition to the identifier of the communication station N, but the beacon is not limited thereto. If the time period from transmission of a beacon from a certain communication station N until transmission of a beacon from a next communication station N is determined in advance, the timing of the next arbitration phase can be derived from the beacon of the communication station N and the beacons received from the other communication stations N. Thus, a beacon containing information for joining the network may be a beacon itself serving as information for joining the network. Herein, the information indicating the timing of the next arbitration phase can be regarded as corresponding to the “information for joining the network”. Alternatively, the configuration may be such that communication with the communication stations N already joining the network is allowed as a result of transmitting a beacon within n second from immediately after receiving a beacon, and participation in the network is allowed as a result of the communication.
In the example of
The first transmitter 20 of each communication station N enters the arbitration phase again at time 16 that is three seconds after time 13 when transmission of beacons from all the communication stations N (N1, N3, N10, and N15) is completed, and determines the order of transmitting beacons to be the communication station N1→the communication station N3→the communication station N10→the communication station N15 similarly to the arbitration phase at time 0, and determines the timing of the next arbitration phase to be time 32 that is 16 seconds after time 16. The transmission phase is then entered, the first transmitter 20 of the communication station N1 sends a beacon at time 17, the first transmitter 20 of the communication station N3 sends a beacon at time 21 that is four seconds after time 17, the first transmitter 20 of the communication station N10 sends a beacon at time 25 that is four seconds after time 21,and the first transmitter 20 of the communication station N15 sends a beacon at time 29 that is four seconds after time 25.
The first transmitter 20 of each communication station N enters the arbitration phase again at time 32 that is three seconds after time 29 when transmission of beacons from all the communication stations N (N1, N3, N10, and N15) is completed, and determines the order of transmitting beacons to be the communication station N1→the communication station N3→the communication station N10→the communication station N15 similarly to the arbitration phases at time 0 and time 16, and determines the timing of the next arbitration phase to be time 48 that is 16 seconds after time 32. In this manner, beacons of the communication stations N are transmitted at intervals of four seconds (in four-second periods).
Here, as illustrated in
Furthermore, when a communication station N disconnects from the network, the communication station N preferably sends its beacon before disconnection. This can ensure transmission of beacons from the communication stations N at four-second intervals.
According to the above, if each of the communication stations N puts a communication module for carrying out radio communication into a state capable of transmitting a beacon only twice during 20 seconds from time 48 to immediately before time 68, for example, it is possible to ensure that a communication station attempting to newly join the network only needs to wait for a beacon for four seconds to join the network and to reduce power consumption of the communication modules of the communication stations N already joining the network. Furthermore, if a beacon is not received within four seconds, the communication station N attempting to newly join the network can confirm the absence of the network and thus need not further consume power at the communication module for waiting for a beacon.
Furthermore, according to the present embodiment, it is not necessary to always put any one of a plurality of communication stations N building a network into a state capable of receiving a beacon from a communication station N attempting to newly join the network but it is only necessary to intermittently put the communication module of each communication station N into a state capable of transmitting a beacon, which can achieve an advantageous effect that power consumption can be sufficiently reduced as compared to the configuration of the related art.
Next, a second embodiment will be described. Description of parts that are the same as those in the first embodiment described above will not be repeated as appropriate.
The newly joining function 100 is a function for newly joining a network, and includes a first receiver 10 and a second transmitter 11. As described above, when the communication station N attempts to newly join a network, the first receiver 10 thereof waits for a beacon (corresponding to the “first beacon” in the claims) from another communication station N joining the network for the predetermined first period. If the first receiver 10 receives a beacon within the first period, the communication station N joins the network and enters a network maintenance mode to maintain the network.
If the first receiver 10 receives no beacon within the first period, the second transmitter 11 transmits a beacon (corresponding to a “third beacon” in the claims) of the communication station N in a predetermined pattern P. This beacon is a beacon containing information for another communication station N to communicate with the communication station N. Since the communication station N has not joined the network yet, this beacon does not contain information for joining the network. In this example, in the pattern P, the communication station N transmits the beacon each time the time period Ta (four seconds in this example) corresponding to the first period elapses. Note that the pattern P is not limited to defining of a constant period, but may be a pattern using a pseudorandom number sequence, for example. When a response to the beacon transmitted in the pattern P is returned, the communication station N can join the network with the signal of the response and the state of the communication station N enters the network maintenance mode.
The network maintaining function 110 is a function for maintaining the network, and includes the first transmitter 20 and a monitor 21. The functions of the first transmitter 20 are the same as those in the first embodiment described above. When the communication station N is already joining the network, the monitor 21 monitors whether or not another communication station N to be monitored transmit a beacon according to the schedule determined in the arbitration phase. In this example, the communication stations N to be monitored by each of a plurality of communication stations N building the network are determined in advance, but the communication stations N to be monitored are not limited thereto and may be determined through arbitration similarly to scheduling of the timings at which beacons are to be transmitted, for example. In the example of
In the present embodiment, if the communication station N to be monitored does not transmit a beacon according to the schedule, the monitor 21 also has a function of monitoring whether or not a communication station N to be monitored by the communication station N to be monitored transmits a beacon according to the schedule. As illustrated in
The description is continued referring back to
The new communication station checking function 120 is a function for checking the presence of a communication station attempting to newly join the network, and includes an estimator 121 and a second receiver 122. If no beacon is transmitted for a second period longer than the first period described above as a result of monitoring by the monitor 21, the estimator 121 assumes that a new communication station N waiting for a beacon (corresponding to the “first beacon” in the claims) to join the network is present in the second period and estimates a third period representing a time period during which the new communication station N may have started to wait for a beacon.
In
The estimator 121 estimates the second period Tb on the basis of information indicating the schedule and information indicating a beacon that could not be confirmed from the monitor 21. The estimator 121 then estimates the third period representing the time period during which the new communication station N started to wait for a beacon on the basis of the estimated second period Tb and the predetermined first period Ta. As illustrated in
The description is continued referring back to
For example, when it is confirmed that the communication station N to be monitored does not transmit a beacon according to the schedule, each of the communication stations N building the network can transmit a beacon in place of the communication station N to be monitored. As illustrated in
As illustrated in
As illustrated in
As illustrated in
The embodiments described above can be combined as appropriate. Moreover, although the arbitration phase for carrying out arbitration in a determined time for scheduling is provided in the embodiments, etc. described above, the embodiments are not limited thereto.
Programs to be executed by the communication stations N described above may be stored on a computer system connected to a network such as the Internet, and provided by being downloaded via the network. Alternatively, the programs to be executed by the communication stations N described above may be provided or distributed through a network such as the Internet. Still alternatively, the programs to be executed by the communication stations N described above may be embedded on a nonvolatile storage medium such as a ROM in advance and provided therefrom.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-056962 | Mar 2014 | JP | national |
