KR101042007B1 - Routing method for extending lifetime of sensor networks - Google Patents

Abstract

A time synchronization method for extending the life of a sensor network is provided. The time synchronization method for extending the life of the sensor network according to the present invention comprises the steps of: the reference node and the reference node to synchronize the time information through handshaking (hand-shaking); Broadcasting, by the reference node, a first time synchronization signal including time information synchronized with the reference node; Synchronizing, by a receiving node receiving the first time synchronization signal, its own time information based on time information included in the first time synchronization signal; The reference node broadcasting a second time synchronization signal including time information synchronized with the reference node; And receiving, by the receiving node receiving the second time synchronization signal, its own time information synchronized based on the first broadcasting signal based on the second time synchronization signal.

Wireless Sensor Networks, AODV, LOAD, Energy Efficiency, Routing Protocols

Description

Routing method for extending lifetime of sensor networks

The present invention relates to a time synchronization method of a sensor network. More specifically, in a time synchronization method between sensor nodes required for data transmission of a sensor network, particularly data transmission by a time division multiple access (TDMA) scheme, each node minimizes power consumption, The present invention relates to a method for visual synchronization of a sensor network that can extend its life.

With the development of digital circuit design and micro electro-mechanical systems (MEMS) technology, low-power, small-scale, low-cost sensor nodes are being developed through system on chip (SoC) of wireless communication devices and computational processing devices. These sensor nodes, consisting of sensing, data processing, and communication components, together with a reference station acting as a gateway or data central station, form a sensor network, a kind of ad-hoc network.

Vision synchronization technology is required to accurately respond to various events occurring in a wireless sensor network. In existing distributed systems, time synchronization is performed using NTP (Network Time Protocol). However, the time synchronization technology used in existing distributed systems is not suitable for application on sensor networks with limited processing power and power due to the large amount of computation and high power consumption. In order to solve these problems, visual synchronization techniques applicable to sensor networks have recently been proposed.

One of the proposed time synchronization techniques is RBS (Reference Broadcast Synchronization) technology. The RBS technology is described in 'DJ. Elson, L. Girod, D. Estrin, “Fine-grained network time synchronization using reference broadcasts,” ACM Operating Systems Review, 36 (SI): 147-163, 2002. ' It is disclosed in detail in the literature.

According to the RBS technology, in order to reduce the error due to the transmission time and the access time, the receiver-receiver time synchronization is performed using the time stamp at the time when each sensor node transmits the packet to the network. That is, when a reference sender (transmitter) transmits a reference packet to a neighboring node (receiver), each node receiving the packet calculates a deviation rate by exchanging and comparing the received time with each other, thereby synchronizing the time. The advantage of this technique is that the broadcast time can be synchronized to reduce access and transmission time on small networks. However, as the number of nodes increases, a lot of broadcast message exchanges occur, which consumes a lot of power. In addition, since each sensor node must have information of all neighboring nodes, there is a problem that a storage space is required accordingly.

The other one of the proposed time synchronization techniques is the TPSN (Timing-sync Protocol for Sensor Network) technology. The TPSN technology is' S. Ganeriwal, R. Kumar, M.B. Srivastava, “Timing-sync protocol for sensor networks,” Proceedings of the 1st International Conference on Embedded Networked Sensor Systems, pp. 138-149, 2003. ' It is disclosed in detail in the literature.

The TPSN technique is divided into a level search step of determining the level of sensor nodes to generate a hierarchical structure, and a time synchronization step of synchronizing time in a manner similar to the Simple Network Time Protocol (SNTP). The purpose of the first step is to assign a level to each node in the network to form a hierarchical topology. That is, a tree structure is formed around one root node corresponding to level zero. In the second stage, lower level nodes perform time synchronization with higher level nodes. At the end of the synchronization phase, all nodes are synchronized to the root node, which results in a complete visual synchronization of the network. This method shows a double performance improvement in terms of speed compared to the RBS technology, but there is a problem in that there is no processing capability in case of a topology change caused by the addition or removal of nodes.

Another one of the proposed time synchronization techniques is the Floating Time Synchronization Protocol (FTSP) technique. The FTSP technology is' M. Marooti, B. Kusy, B. Simon, AA. Leedeczi, “The flooding time synchronization protocol” Proceedings of the 2nd International Conference on Embedded Networked Sensor Systems, pp.39-49, 2004. ' It is disclosed in detail in the literature.

The FTSP technology broadcasts the global reference time and the nodes receiving the duplicated broadcast messages reduce the clock error through linear operation, thereby synchronizing with the root node. In addition, this technique supports dynamic topologies that can dynamically respond to topology changes due to node failure and communication failure through flooding of periodic synchronization messages. However, the FTSP technology has a problem that synchronization is performed through a linear operation, so that the receiving nodes cannot calculate until a predetermined number of reference messages are received, so synchronization is not performed.

The technical problem to be solved by the present invention is to focus on the fact that the most influential factors in the energy consumption in each node of the sensor network to perform the time synchronization operation, the deviation rate calculation and the message transmission and reception, reducing the deviation rate calculation amount or It provides a sensor network routing method that reduces the number of message transmission and reception and extends the life of the sensor network to reduce energy consumption of sensor nodes during time synchronization.

The technical problems of the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a time synchronization method for extending the life of a sensor network, comprising: synchronizing visual information through a handshaking between a reference node and a reference node; Broadcasting, by the reference node, a first time synchronization signal including time information synchronized with the reference node; Synchronizing, by a receiving node receiving the first time synchronization signal, its own time information based on time information included in the first time synchronization signal; The reference node broadcasting a second time synchronization signal including time information synchronized with the reference node; And receiving, by the receiving node receiving the second time synchronization signal, correcting its own time information synchronized based on the first broadcasting signal based on the second time synchronization signal.

The first broadcast and the second broadcasted time synchronization signal may be propagated by only one hop.

In addition, it is preferable that all nodes except the reference node and the reference node among the nodes included in the sensor network receive the first time synchronization signal and the second time synchronization signal. In that case, all receiving nodes can correct the error according to the first time synchronization signal by receiving two time synchronization signals.

The receiving node may remove an error element by performing time stamping on the MAC layer.

According to the present invention as described above, each sensor node of the sensor network has the effect of extending the life of the entire network by minimizing the energy consumption required to perform the time synchronization.

Advantages and features of the present invention, and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms. The embodiments of the present invention make the posting of the present invention complete and the general knowledge in the technical field to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, the present invention will be described with reference to a block diagram for explaining a time synchronization method for extending the lifespan of a sensor network or drawings of a processing flowchart. At this point, it will be understood that each block of the flowchart illustrations and combinations of flowchart illustrations may be performed by computer program instructions. Since these computer program instructions may be mounted on a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, those instructions executed through the processor of the computer or other programmable data processing equipment may be described in flow chart block (s). It creates a means to perform the functions. These computer program instructions may be stored in a computer usable or computer readable memory that can be directed to a computer or other programmable data processing equipment to implement functionality in a particular manner, and thus the computer usable or computer readable memory. It is also possible for the instructions stored in to produce an article of manufacture containing instruction means for performing the functions described in the flowchart block (s). Computer program instructions may also be mounted on a computer or other programmable data processing equipment, such that a series of operating steps are performed on the computer or other programmable data processing equipment to create a computer-implemented process to generate a computer or other programmable data. Instructions for performing the processing equipment may also provide steps for performing the functions described in the flowchart block (s).

In addition, each block may represent a portion of a module, segment, or code that includes one or more executable instructions for executing a specified logical function (s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of order. For example, the two blocks shown in succession may in fact be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the corresponding function.

Hereinafter, a time synchronization method for extending the life of a sensor network according to an embodiment of the present invention will be described with reference to FIGS.

First, a node selected as a reference node and a reference node perform time synchronization through a handshake (S100). The time synchronization operation through the handshake (S100) may be understood as an operation of matching the visual information included in each of the reference node and the reference node, and may be synchronized with the visual information before any one of the reference node and the reference node. It may be synchronized to third time information different from the time information before synchronization of the reference node and the reference node. In addition, it is apparent that the time synchronization S100 through the handshake may be performed by a unicast communication method.

The reference node may be two or more selected nodes among the receiving nodes. The reference node is preferably selected so that the entire sensor network node can be covered by a broadcasting signal propagated by only one hop from the reference node.

Next, the reference node broadcasts a time stamped time synchronization message to synchronize time information of receiving nodes in a single hop (S102).

Next, the selected reference node broadcasts the time synchronization message once more, thereby synchronizing the time information of the receiving nodes in a single hop (S104). The receiving nodes receiving the time synchronization message broadcast by the reference node may once again correct the time information synchronized by the time synchronization message broadcast by the reference node.

FIG. 2 is a diagram illustrating when a time stamp of each node occurs.

First, when a base station (BS) timestamps the global time T1BS and performs a broadcast, the receiving node N records the reception time in its local time and synchronizes it with the T1BS. The broadcasting and synchronization may be repeated once more. That is, when a base station (BS) timestamps the global time T3BS and performs a broadcast, the receiving node N records the reception time in its local time and synchronizes it with the T3BS.

The time stamping may be performed at the MAC layer.

Equation 1: T5RN = T6N-T5ER

Equation 2: T7RN = T6N-T6ER

Reference node (RN) performs the same process as the reference node, but calculates an error value through the equations shown in Equations 1 and 2 and proceeds with the synchronization process.

Equation 3: T3BS + T3ER-T1BS = T4N-T2N + T1ER

The time synchronization calculation process is as shown in Equation 3. Equation 3 may be interpreted as follows. Adding the error T3ER to T3BS equals the global time of node N. However, considering the four components (transmission time, access time, transmission time, and reception time) that cause errors in time synchronization, the T1ER and T3ER appear to be in error.

In order to solve the error, the reference node and the reference node broadcast a time synchronization signal including their own time information. In addition, accurate time synchronization may be performed by calculating the errors T5ER and T6ER based on the reception time of the node N synchronized with the reference node and applying the mean time difference values of the two errors to the synchronization.

Existing RBS performs time synchronization through broadcast like the technique proposed in this section. However, after the broadcast at the reference node, the receiving nodes exchange messages to synchronize their local clocks, resulting in significant network usage. As a result, a lot of energy is consumed. In addition, the TPSN of the pairwise technique consumes an initial selection time and generates a large amount of messages depending on the number of nodes, thereby increasing network usage and energy consumption. However, in the case of the time synchronization scheme of the present invention, since the synchronization is performed through only a minimum of broadcasts, the amount of energy generated by the node can be greatly reduced by reducing the amount of messages generated.

3 is a view showing the effect of the time synchronization method according to the present embodiment. When the time synchronization method according to the present embodiment is applied, the number of messages transmitted and received for time synchronization is significantly reduced compared to the conventional TPSN technology.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a signal flow diagram of a time synchronization method for extending the life of a sensor network according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a time stamp generation time for each node according to a time synchronization method for extending the life of a sensor network according to an embodiment of the present invention.

3 is a view comparing the effect of the time synchronization method for extending the life of the sensor network according to an embodiment of the present invention and the TPSN technology.

Claims (6)

Synchronizing the visual information through the handshaking between the reference node and the reference node; Broadcasting, by the reference node, a first time synchronization signal including time information synchronized with the reference node; Synchronizing, by a receiving node receiving the first time synchronization signal, its own time information based on time information included in the first time synchronization signal; The reference node broadcasting a second time synchronization signal including time information synchronized with the reference node; And The receiving node receiving the second time synchronization signal corrects its own time information synchronized based on the first broadcasting signal based on the second time synchronization signal. Visual synchronization method. The method of claim 1, And the first broadcast and the second broadcast time synchronization signal are propagated by only one hop. The method of claim 1, The reference node is a time synchronization method for extending the life of the sensor network of the two or more selected nodes of the receiving node. The method of claim 1, The reference node is a time synchronization method for extending the life of the sensor network is selected so that the entire sensor network node can be covered by the broadcast signal propagated only one hop from the reference node. The method of claim 1, And all nodes except the reference node and the reference node among the nodes included in the sensor network receive the first time synchronization signal and the second time synchronization signal. The method of claim 1, The receiving node, A time synchronization method for extending the life of a sensor network that performs time stamping on the MAC layer.

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