Patent Application
20140293855
The present invention relates to a wireless communication system and a wireless router and, in particular, to a wireless communication system and a wireless router in an ad-hoc network whose components become active intermittently.
In industrial fields, there is a growing demand for wireless communication in terms of easiness of installation, low cost, easiness of operation, and expandability. In particular, a multi-hop communication is regarded as promising as a means for exceeding one-to-one communication distance limits attributed to power consumption and legal restrictions. To implement long-term operation of such a wireless communication system, it is necessary that terminals and routers that make up the system can operate at low power consumption. In this regard, the IEEE802.15.4e standard proposes a communication method in which a communication session starts upon receiving an activation notice from a receiving end. A receiving end (router) becomes active intermittently, broadcasts an activation notice toward its surroundings, and waits for a response. A transmitting end (terminal), if it has information to transmit, waits for an active notification from its surroundings and transmits information to a router that transmitted the active notification to the terminal. In this way, time during which routers are active is reduced and their power consumption is lowered.
Generally, in an ad-hoc network, depending on how routers are deployed, communication traffic may concentrate on some of the routers, which results in variance in the routers' battery consumptions. If the battery of a router on which communication traffic has concentrated runs out, it will have an impact on the entire system. An invention of patent literature 1 addresses this situation as follows: in a multi-hop wireless communication system in which a plurality of wireless terminals relay and transmit a transmission packet to one another based on routing information that is transmitted to and received from one another, each terminal changes an interval of transmitting routing information to its surrounding terminals depending on the remaining amount of its battery and the surrounding terminals judge the reliability of that terminal from the changed interval. That is, when transmitting routing information stored in a routing information table, each terminal determines an interval of transmitting the routing information to its surrounding terminals based on the remaining amount of its battery obtained from its battery remaining amount detecting unit and the setting in a transmission interval table. Based on that, the system changes routing, thereby smoothing the terminals' power consumptions.
In an invention of patent literature 2, a wireless terminal measures its power consumption after communicating for a given period with another wireless terminal which becomes active intermittently and changes its intermittent activation interval based on the measurement result. That is, based on the power consumptions of the terminals in the network, the intermittent activation cycle periods of the terminals are controlled. Thereby, terminals with less power consumption are preferentially selected as those through which a communication route is set up and thus the terminals' power consumptions are smoothed.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2005-295310
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2010-28168
As noted previously, in an ad-hoc network, generally, depending on how routers are deployed, communication traffic may concentrate on some of the routers, which results in variance in the routers' battery consumptions.
The invention of patent literature 1 seeks to smooth the battery power consumptions of the terminals that make up the multi-hop wireless communication system in such a way that each terminal changes the interval of transmitting routing information depending on the remaining amount of its battery. However, a plurality of terminals transmit routing information to one another in a non-intermittent mode; that is, they are always active. Consequently, there is a difficulty in reducing the power consumptions of all terminals across the multi-hop wireless communication system and attempting long-term operation of the system.
In the invention of patent literature 2, each terminal needs to communicate with another terminal for a certain period in order to make an analysis for acquiring routing information. Therefore, the intermittent activation interval and communication environment of a communication partner and which terminal is selected as the one with which to communicate, among others, have an influence on power consumption measurement and there is a possibility of setting up an inefficient route.
Meanwhile, a large difference in the easiness to replace the batteries of routers may arise depending on the positions where the routers are installed. In this situation, it can be considered that maintenance becomes easier by concentrating communication traffic on a router whose battery is easy to replace, rather than evenly consuming the batteries of all routers configured in the system. Moreover, if there is a router having a method of power feeding by itself such as a solar battery panel or power supply, it can be considered that a total of battery consumption across the system is suppressed by concentrating communication traffic on such a router.
However, in the heretofore known techniques regarding an ad-hoc network based on intermittent activation, a way of smoothing a disparity in the remaining amounts of the batteries of the routers was not adaptable to the routers' communication environments such as a characteristic specific to a router and installation condition. For example, if there occurred a disparity in the remaining amounts of the batteries of wireless routers, each wireless router were unable to change a communication route by itself. Therefore, even if there was a router having a larger remaining amount of battery, a router whose battery is easy to replace, or a router having means for power feeding by itself such as a solar battery panel, it was impossible to exploit such a router preferentially.
An object of the present invention is to solve the problems of the foregoing heretofore known techniques and provide a multi-hop wireless communication system and a wireless router in which a wireless router changes a communication route by itself and long-term operation of the system is enabled.
An example of a typical implementation of the present invention is as follows: a wireless communication system for multi-hop communication through an ad-hoc network, the wireless communication system comprising a plurality of wireless routers and at least one terminal, characterized in that: each wireless router includes a battery, a detection means for detecting the battery state, a table providing information on its own intermittent operation interval of the wireless router, and a control device that controls communication; the intermittent operation interval in the table is set so that, depending on communication environment of the wireless router, including the station's battery state, the intermittent operation interval should be set shorter for a wireless router having a better communication environment; and each wireless router sets or changes its intermittent operation interval, based on its communication environment and information in the table, and forwards communication information from the terminal during the intermittent operation.
According to the present invention, long-term operation of the system becomes feasible.
According to a typical embodiment of the present invention, in a multi-hop wireless network for communication via a plurality of routers, each wireless router operating intermittently changes its intermittent operation interval depending on its communication environment including its battery state by its own judgment.
Embodiments which will be described hereinafter are assumed to be implemented in a wireless communication system for ad-hoc communication in an asynchronous and intermittent activation manner, based on the IEEE802.15.4e standard which is anticipated to be standardized as a wireless connection scheme for use in an ad-hoc network.
In an ad-hoc network, a purpose-built base station is not used and making a terminal-to-terminal connection among many terminals is performed using a relay function that each terminal device itself has and by a “multi-hop communication” technique without intervention of a base station. That is, in the multi-hop communication, the network configures a group of terminals that are interconnected temporarily and the communication area is expanded, while transmissions are relayed through other terminals even without a base station. Thus, the multi-hop communication is suitable for a wireless system that covers a wide range with low power consumption.
According to a typical embodiment of the present invention, in a wireless communication system using a multi-hop communication scheme, including a plurality of routers operating intermittently and at least one terminal that performs data transmission upon receiving an activation notice signal from any router, each router that operates intermittently (becomes active intermittently) changes an interval of intermittent operation depending on its communication environment condition by its own judgment. The interval of intermittent operation should be set shorter for a wireless router having a better communication environment. Thereby, each wireless router is able to change a communication route by itself and long-term operation of the system becomes feasible. That is, the following are made possible: battery consumptions depending on communication environment such as a characteristic specific to a router and installation condition; and long-term operation of the system. Besides, because each router can judge by itself if an activation interval has changed; it is possible to make a route selection to allow for lengthening the system lifetime without being influenced by the intermittent activation interval and communication environment of a communication partner and which terminal is selected as the one with which to communicate, among others.
In the following, embodiments of the present invention will be described with the aid of the drawings. In the following description, it is assumed that a router forwards communication information transmitted by a terminal to an access point (AP).
A first embodiment of the present invention with regard to a multi-hop wireless communication system in ad-hoc network is described with reference to
The multi-hop wireless communication system of the present invention includes a plurality of wireless routers 10 (A, B) operating intermittently, a plurality of terminals 100 (A, B, C) that perform data transmission upon receiving an activation notice signal from any router, and an access point 1 (AP) that is a destination of communication information transmitted by each terminal. The terminals 100 (A, B, C) have a function of acquiring new communication information specific to the terminal by a sensor or the like and are capable of transmitting the communication information. The routers 10 (A, B) become active intermittently and have a function capable of changing their activation cycle period and a function of transmitting and receiving communication information. For the sake of simplifying description, the system presented here configures three terminals, two routers, and one access point (AP) (1). It goes without saying that there is no limitation in the number of these respective types of devices making up the wireless communication system. An example of
The control device of each router has a function of by itself creating ad-hoc network routing to route a transmission via any other router serially to the access point (AP) during inactivity according to a routing protocol for multi-hop wireless communication. This routing information is retained in a routing table (omitted from depiction) and updated periodically. As the routing protocol, an optimal scheme which may be, e.g., proactive or reactive may be adopted according to the scale and density of routers configured in the multi-hop wireless communication system and a high or low degree of mobility of the routers, among others. In other words, a router 10 is configured with a computer and includes a ROM having stored therein a control program that controls the control device (microprocessor) 302 and causes it to perform various control operations for multi-hop wireless communication and a RAM storing therein various kinds of information in table form or the like, such as intermittent operation interval information and routing information, which are accessed by the control device 302.
When a value measured by the timer becomes equal to the intermittent operation interval T, i.e., the time to go into reactivation, the router 10 becomes active (becomes active intermittently). Once having become active intermittently, the router 10 first turns the battery sensor 304 on and detects the remaining amount of its battery (S501). It determines whether or not the remaining amount of the battery is less than a predetermined value (Tlim) (S502). That is, it is determined whether or not the remaining amount of the battery is less than (Tlim) based on the value in the table 306 retained in the RAM. Here, according to the example of
Otherwise, if the remaining amount of the battery is more than or equal to 10(%), the router sets its intermittent operation interval T depending on the remaining amount of the battery (S504). Then, the router broadcasts an activation notice, goes into a wait state for reception, and awaits reception (S505). When the router receives a requirement for communication in a reception ready state (S506), it performs a process of forwarding communication information (S507) and, upon completing the process, becomes awaiting reception. When a given period of time (an active period of the router 10) L has elapsed (S508), the router performs sleep processing (509) and returns to the sleep state.
The active period L of the router 10 is set quite shorter than the intermittent operation interval T, i.e., the sleep state period (L<T). By way of example, in a state when the remaining amount of the battery is 100(%), the given active period L is set at one tenth or below of the sleep state period T. Of course, if it takes time to complete a process of forwarding communication information, L/T may become larger, e.g., 0.3 to 0.5. Overall, L should shrink considerably than T (L<T). By reducing the active period of each router depending on the remaining amount of the battery, it is possible to reduce a total of power consumption across the wireless communication system, while maintaining required communication environments. That is, each router operates intermittently and the intermittent operation interval should be set shorter for a wireless router having a better communication environment. Thereby, it is possible to reduce a total of power consumption across the multi-hop wireless communication system, while maintaining required communication environments.
A transmitting-end terminal 100N, when communication information is generated in it, waits for activation of a router (202) in order to receive an activation notice (200) from each router 10. From the router 10N, once having received an activation notice, a second activation notice-2 (200) in this example, the terminal transmits communication information (203) to the router 10N that transmitted the second activation notice-2 (200) to the terminal. In this way, in the IEEE802.15.4e communication protocol, a communication session starts upon receiving an activation notice from a receiving end. When the router 10N receives the communication information (203) during a wait for reception (201), the router goes into a wait for activation of a router (202) and awaits a requirement for communication (204) from an access point AP1 or an activation notice (200) from a next router.
The access point AP1 broadcasts a requirement for communication (204) to each relation station 10 and each terminal 100 at an arbitrary interval and goes into a wait for reception (201).
When the router 10N or the terminal 100N receives the requirement for communication (204) from the access point AP1, it transmits communication information (203) to the access point AP1 and then goes into a wait for a requirement for communication (205).
If the router 10N has not received communication information (203) for a given period (active period L) or longer during the wait for reception or the wait for a requirement for communication (205), it goes into the sleep state. After the intermittent operation interval T that has been set, it becomes active again and repeats the foregoing operations.
In a case where the terminal 100N has determined that it needs to transmit communication information, e.g., when its sensor connected to it has detected an abnormal value or when a given period has elapsed after the previous transmission of communication information, the terminal waits for activation of a relation station (202). In other words, the activation interval of the terminal 100N is not defined. In this state, once the terminal 100N has received an activation notice (200) or a requirement for communication (204), it transmits communication information (203) to the router or the AP that is the notification or request transmitter. At this time, before transmitting communication information (203), the terminal 100N may transmit an advance notice of transmission of communication information to the notification or request transmitter (router or AP) and establish a link; after that, the terminal may transmit the communication information (203). Even in a case where this method is used, the present invention can be applied.
Thereby, for a router for which the remaining amount of the battery is larger, the number of times it operates per unit time increases and it is more probable for the router to relay communication information 203 from a terminal 100. On the other hand, for a router for which the remaining amount of the battery is smaller, its intermittent operation interval T (sleep state) becomes longer and it is less probable for the router to relay communication information. That is, there is a higher probability that a router for which the remaining amount of the battery is larger relays communication information even without an ad-hoc route setup in advance. Consequently, a router for which the remaining amount of the battery is larger forwards communication information more often and it is possible to smooth a disparity in the remaining amounts of the batteries of the routers within the multi-hop wireless system. Thus, long-term operation of the system is enabled.
Assuming a case where a plurality of routers exist in the surroundings of a terminal,
According to the present embodiment, the following are made possible: battery consumptions depending on communication environment specific to a router; and long-term operation of the system. Besides, because a router can judge by itself if an activation interval has changed; it is possible to make a route selection to allow for lengthening the system lifetime without being influenced by the intermittent activation interval and communication environment of a communication partner and which terminal is selected as the one with which to communicate, among others.
Next, a second embodiment of the present invention is described.
In the present embodiment, intermittent operation intervals T are quantized per router in consideration of difficulty D of battery replacement from, inter alia, environments where routers are installed. In an example of
Accordingly, the following are made possible: battery consumptions depending on communication environment such as a characteristic specific to a router and installation condition; and long-term operation of the system. Besides, because a router can judge by itself if an activation interval has changed; it is possible to make a route selection to allow for lengthening the system lifetime without being influenced by the intermittent activation interval and communication environment of a communication partner and which terminal is selected as the one with which to communicate, among others.
Next, a third embodiment of the present invention is described.
Thereby, a router provided with the power feeding means as a communication environment becomes active frequently and the number of times other routers transmit and receive information is reduced and their power consumptions are suppressed. Because a router provided with the power feeding means is able to charge its battery with the power feeding means, a total of battery consumption across the system is reduced and the system lifetime can be lengthened.
Next, a fourth embodiment of the present invention is described.
The terminal also serving as a router 110 configures a sensor interface (I/F) 104 for connecting a sensor 105 that measures sensed data to the terminal, a built-in battery 103 and a battery sensor 107 that measures the remaining amount of the battery B, a control device 112 that controls the sensor 105 and the battery sensor 107 and controls communication, and a transceiver 111 for transmitting communication information under command of the control device 112 and receiving communication information.
In the present embodiment, the terminal also serving as a router 110 becomes active intermittently to forward communication information from another terminal as the router, in addition to transmitting communication information by it. Details of the terminal and router functions of the terminal also serving as a router 110 are the same as described in the first through third embodiments.
Even in the present embodiment, the intermittent operation interval should be set shorter for a terminal also serving as a router having a better communication environment. Thereby, the following are made possible: battery consumptions depending on communication environment such as a characteristic specific to a terminal also serving as a router and installation condition; and long-term operation of the system. Besides, because a terminal also serving as a router can judge by itself if an activation interval has changed; it is possible to make a route selection to allow for lengthening the system lifetime without being influenced by the intermittent activation interval and communication environment of a communication partner and which terminal also serving as a router (or which router) is selected as the one with which to communicate, among others.
Next, a fifth embodiment of the present invention is described. The multi-hop communication system through an ad-hoc network of the present invention can widely be applied to wireless systems covering a wide range with low power (low power consumption), such as AMI (Advanced Metering Infrastructure) and in-house wireless networks. The invented system is suitable for, for example, installing a terminal with a sensor or a terminal also serving as a router in each home of condominiums and single-family homes, acquiring communication information comprising data such as electric energy, gas quantity, water service consumption, fire detection, and monitored data related to energy saving of electric equipment or the like acquired from each home, and making collection and management of such communication information. In the case of a high-rise condominium, it is possible to forward communication information from terminals or terminals serving as a router installed at the top story via routers or terminals serving as a router installed at lower stories in turn to an access point AP located at the ground floor or in some other place and further collect such information to a higher-order server system. Thereby, with regard to each home of the high-rise condominium, it is possible to seek to improve a variety of tasks and improve customer services, not only a simple meter reading task, by making good use of collected data. The communication environment of each router or each terminal also serving as a router which operates intermittently differs depending on the overall structure of the high-rise condominium, the positions in which the terminals also serving as a router for each customer are installed, whether or not these terminals or routers are provided with a power feeding means, etc. According to the present embodiment, each router or each terminal also serving as a router sets or changes its intermittent operation interval based on its communication environment and information in the table. Thus, it is possible to reduce a total of power consumption across the multi-hop wireless communication system and long-term operation of the system becomes feasible.
Even for an in-house wireless network, each router or each terminal also serving as a router operating intermittently may expediently set or change its intermittent operation interval based on communication environment such as the amount of its battery consumption, the position where it is installed in the house, and whether or not it is provided with a power feeding means. Thereby, it is possible to reduce a total of power consumption across the multi-hop wireless communication system and long-term operation of the system becomes feasible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-164017 | Jul 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/065827 | 5/21/2012 | WO | 00 | 3/27/2014 |
