This application claims the benefit of Korean Patent Application No. 10-2007-0123644, filed on Nov. 30, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a network system including wireless sensor nodes, and more particularly, to a wireless sensor network system in which each node calculates and updates a relay probability for message transmission to dynamically route a message and a method of controlling the wireless sensor network system.
The present invention is derived from a research project supported by the Information Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) and the Institute for Information Technology Advancement (IITA) [2005-S-038-03, Development of UHF RF-ID and Ubiquitous Networking Technology]
2. Description of the Related Art
A wireless sensor network includes a number of cooperating sensor nodes. Each sensor node is driven by a battery and includes a small-capacity memory and a processing device. Therefore, it is necessary to consider energy consumption, memory, and an operational efficiency for designing a communications protocol in the sensor network. Particularly, a routing protocol has to be light-weight and simple. In addition, since a node in the sensor network may disappear or brake down, self-configurability is required. When a fixed path includes a broken node, transmission fails and energy efficiency significantly decreases due to re-transmission through the broken path.
In order to deliver a message in the aforementioned wireless network, a multi-hop routing method is required. A representative routing method applicable to the wireless network is an ad hoc on-demand distance vector (AODV) algorithm based on a carrier sensing mechanism.
However, there are problems in that the conventional message routing method needs an additional media access controller (MAC) layer, and when a wireless node moves, throughput per node decreases.
The present invention provides a network system in which each sensor node calculates a relay probability, periodically updates the relay probability, and dynamically determines a node for relaying a message on the basis of the relay probability, so that throughput per node is improved and a media access control (MAC) layer is not needed.
The present invention also provides a wireless sensor network in which loads are distributed and decreased.
The objects and advantages of the present invention will be explained in the following description, which includes exemplary embodiments of the present invention. In addition, it can be easily understood that the objects and advantages of the present invention can be implemented with means disclosed in the appended claims and combinations thereof.
According to an aspect of the present invention, there is provided a wireless sensor network including: a destination node broadcasting a beacon signal to nodes in a network; a transmission node transmitting a request-to-send message to neighboring nodes to select a relay node that relays a message to be transmitted to the destination node, receiving acknowledgement messages from the neighboring nodes which determine whether to transmit the acknowledgement messages on the basis of relay probabilities, and selecting the relay node on the basis of the acknowledgement messages; and a relay node receiving a beacon signal, measuring a strength of the beacon signal, transmitting an acknowledgement message including the strength of the beacon signal to the transmission node, and receiving the message from the transmission node.
According to another aspect of the present invention, there is provided a method of controlling a wireless sensor network including: a transmission node transmitting a request-to-send message to neighboring nodes in the network; each of the neighboring nodes determining whether or not to transmit an acknowledgement message on the basis of its own reliability and transmitting the acknowledgement message to the transmission node; the transmission node determining a node that is to relay data to be transmitted to the destination node from among the neighboring nodes that transmit the acknowledgement messages; the transmission node counting the number of the acknowledgement messages and determining a decrease or increase in the number of nodes in the network; and each of the transmission node and the neighboring nodes updating its own relay probability on the basis of the decrease or increase in the number of the nodes.
According to another aspect of the present invention, there is provided a computer-readable medium having embodied thereon a computer program for the method of controlling a wireless sensor network.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. Like reference numerals in the drawings denote like elements. In the description of the present invention, if it is determined that a detailed description of commonly-used technologies or structures related to the invention may unnecessarily obscure the subject matter of the invention, the detailed description will be omitted.
In addition, when a part “comprises” a component, it means that the part may further comprise other components but does not exclude other components unless specifically described.
According to the present invention, terms such as data, a packet, a data packet, a message, and a signal carry the same general meaning and are exchangeable.
Message routing through relay nodes according to the present invention employs a basketball routing algorithm. A random basketball routing (BR) is per-hop-based multi-hop routing for integrating mobility of a simple node with a routing design. In BR, a mobile node can receive and transmit the same packet many times. The BR has self-configurability in that a next transmitter (referred to as a relay node) is adaptively (or opportunistically) determined without knowing the entire network topology. The BR integrates a MAC with routing in a cross-layer optimized manner and therefore can be appropriately used for the sensor network.
Referring to
During the transmission, the node transmits its packet to a relay node or directly transmits the packet to a destination node in consideration of a distance and the like. By simply controlling the relay probability, routing in addition to the MAC in the network can be controlled. For example, if p=0, there is no packet relay, and routing is single-hop transmission in which all nodes simultaneously perform transmission. As the relay probability increases, the number of relay nodes around a transmission node increases (that is, the number of the transmission nodes decreases), and an average transmission distance and a delay due to re-transmission decrease. However, the transmission probability (1-p) of the node is also decreased, and the number of transmission opportunities decreases. As another example, if p=1, since there is no transmission node, an optimal relay probability exists, and a maximum network throughput can be obtained.
Referring to
First, the destination node D periodically broadcasts a beacon signal.
Each of the nodes that receive the beacon signal, that is, the source node S and the nodes i and j, measures and stores strength of the beacon signal, so that all nodes in the wireless network perceive a position of the destination node. In addition, each node calculates and determines its relay probability p.
When the source node S is to transmit a message, the source node S transmits a request-to-send (RTS) signal to the neighboring nodes i and j in a radio range. An RTS frame header includes an identification ID of the source node S that transmits the RTS signal.
Each of the neighboring nodes i and j that receive the RTS signal determines whether or not to transmit an acknowledgement (ACK) on the basis of the relay probability p and transmits an ACK signal after waiting for a short random backoff time slots to avoid a collision. An ACK packet header includes the measured strength of the received beacon signal and an ID.
The source node S receives the ACK signals from the neighboring nodes i and j, compares the strengths of the beacon signal included in the ACK signals, and determines a node that transmits the strongest beacon signal as the relay node. The source node S transmits a data packet to the selected relay node j and terminates transmission after receiving the ACK signal from the relay node j.
If the relay node j that receives the data packet is not a destination node, the relay node j repeats operations performed by the aforementioned source node S.
As described above, transmitting a message through the relay nodes is referred to as multi-hop routing, and in this case, a probability of a message transmission success and the number of needed hops can be calculated by using the relay probability.
Referring to
When the source node S does not receive ACK signals from the neighboring nodes i and j that have received an RTS signal transmitted from the source node S, the source node S directly transmits a packet to be transmitted to the destination node D.
Here, the source node S does not expect the packet to be transmitted to the destination node D without fail, and only when receiving an ACK signal from the destination node D, the source node S terminates transmission.
In this case, a probability of the message transmission success may be calculated by using a relay probability.
In order for the source node S to succeed in transmitting the packet to a relay node or the destination node, a reception signal-to-interference ratio (SIR) at a reception node (the relay node or the destination node) has to be a target SIR or higher.
Referring to
The source node S terminates the transmission after receiving the ACK.
Referring to
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Each of the RTS message and the location informing message includes identification information broadcastNodeID on a broadcast node. The ACK message for the RTS message includes identification information on a broadcast node (broadcastNodeID), identification information on a response node (responseNodeID), and a message of a destination node (RSSI dstRSSI). The data message includes identification information on a transmission node (sourceNodeID), identification information on a destination node (destNodeID), identification information on a current relay node (sendNodeID), identification information on a next relay node (recvNodeID), and a hopcount. The ACK message for the data includes identification information on a response node (responseNodeID).
For example, when power is supplied to a sensor node, node listens to channels to receive a packet. A destination node periodically broadcasts a TYPE_DSTBCAST message to inform other nodes of a position of the destination node. Each node that receives the TYPE_DSTBCAST message measures and stores an RSSI as a dstRSSI. A source node broadcasts a TYPE_SRCBCAST message in order to select a next relay node. Each of neighboring nodes determines whether or not to transmit a TYPE_RESPONSE message on the basis of its relay probability after receiving the TYPE_SRCBCAST message. Next, the transmission node compares its dstRSSI with a dstRSSI contained in the received TYPE_SRCBCAST message. When the dstRSSI of the source node is largest, the source node directly transmits a TYPE_ROUTING message to the destination node. Otherwise, the source node transmits a TYPE_ROUTING message by using a node having the largest dstRSSI value as the relay node. The relay node that receives the TYPE_ROUTING message transmits a TYPE ACK message to the source node and checks whether or not a destNodeID is the same as a local address of the relay node. If the destNodeID is the same as the local address, routing is terminated, and otherwise, the relay node broadcasts a TYPE_SRCBCAST message and the aforementioned operations are repeated.
In a case where a message is transmitted through relay nodes or directly transmitted to a destination node, if a transmission node does not receive an ACK signal, it means that message transmission is not complete, so that the message or data can be re-transmitted through the BEB scheme.
Referring to
In order to prevent the message loop, according to the present invention, the hopcount representing the number of hops through which a message is transmitted is used.
In order to prevent a case where a message is transmitted only between specific nodes and cannot be transmitted to a destination node, a loop-free mechanism is used. In the loop free mechanism, a loop threshold is set in advance, and if hop count exceeds the loop threshold at a current relay node, a relay node does not transmit a received message to a node that has transmitted the same message to the relay node. By applying the loop-free mechanism, the message can be transmitted to the destination node.
Referring to
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Since the sensor network system according to the present invention supports mobility of a sensor node, sensor nodes may come into the network system to be included therein or move out of the network system to be excluded therefrom. In this case, by updating a relay probability of each node, a message transmission performance of the sensor network can be dynamically optimized.
Referring to
The number of ACK messages (Rik+1) is compared with the number of previous ACK messages (Rik), and it is determined whether or not the numbers are equal (operation S1030).
When the numbers are different, it is determined that decrease or increase in the number of sensor nodes in the network occurs, and each of the sensor nodes updates a relay probability of the sensor node by using the following equation (operation S1050). When the relay probability is updated, a kth value is substituted by a (k+1)th value, and operations S1010 to S1030 are periodically repeated. A relay probability updated at a node i is calculated by using a ratio of the number of previous sensor nodes to the number of current sensor nodes (that is, a ratio of numbers of ACK messages received before and after the updating).
Referring to
According to the current embodiment, five to fifteen nodes are disposed in a space of 2.05M×14M, a source node and a destination node are disposed at both ends, and relay nodes are disposed therebetween. A transmission coverage of each node is set to 6M, an optimal relay probability p is set to 0.83, a response wait time RESPONSE_WAIT_TIME is set to 5 s, an ACK wait time ACK WAIT TIME is set to 2 s, a request-to-send message transmission time BCAST_TIME is set to 10 s, and a loop threshold is set to 10 hop.
As shown in the graphs, when the present invention is applied, the number of hops required is smaller than that in the AODV routing, and it can be seen that a performance according to the present invention is improved as compared with the AODV routing as the number of nodes in the network is increased.
For example, as illustrated in
Referring to
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According to the present invention, a message routing method based on relay probability is applied. Therefore, throughput per node can be improved, and a wireless network in which a message can be transmitted without a MAC layer can be configured.
In addition, message transmission loads can be distributed and decreased in the wireless network according to the present invention.
The invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.
Number | Date | Country | Kind |
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10-2007-0123644 | Nov 2007 | KR | national |