KR20100003527A - Method for broadcasting in wireless ad hoc networks - Google Patents

Abstract

PURPOSE: A broadcasting method of a wireless ad-hoc network for minimizing the number of rebroadcasting packets is provided to improve the arrival rate of packets and prevent the collision of the packets by minimizing the number of rebroadcasting packets. CONSTITUTION: A receiving wireless node receives a message packet(201). It confirms whether the received packet was received to duplication(203). The initial value of a hop count is instituted(207). The reception wireless node establishes a rebroadcasting timer having delay time. The rebroadcasting timer acts. The reception wireless node decides whether the fixed delay time is.

Description

Method for Broadcasting in Wireless Ad Hoc Networks

The present invention relates to a broadcast method of a wireless network, and more particularly, to a broadcast method of a wireless ad hoc network capable of minimizing packet redundancy while maximizing the arrival rate of a packet.

A mobile ad hoc network (MANET) is a self-organizing and dynamically changing multi-hop network. All wireless nodes that make up an ad hoc network are connected to an existing communication infrastructure (e.g., base station or access). Or communicate with each other without going through a central point).

Accordingly, the wireless ad hoc network may be used for temporary construction networks, military networks such as disaster / disaster recovery or rescue and battlefields due to earthquakes, typhoons, terrorism, etc., and Bluetooth, HomeRF, etc. in a LAN (Local Area Network) environment.

Broadcasting in wireless ad hoc networks is widely used to perform route searching, address setting or various application tasks. In MANET, each wireless node has a limited transmission area and thus acts as a router for transmitting information to the destination.

The simplest broadcasting method among the broadcasting methods of the wireless ad hoc network is the floating method.

The floating method rebroadcasts a broadcast packet first received by each wireless node, stores the packet for later reference, and then discards the received packet when it is determined that the received packet is a rebroadcast packet.

In the floating method, since all radio nodes rebroadcast arbitrary packets once, if the network is not divided, the total number of rebroadcast packets is N-1 (N is the number of radio nodes in the wireless ad hoc network). However, the floating method has a disadvantage in that a lot of rebroadcast packets are duplicated, which wastes channel bandwidth.

Due to the operation characteristics as described above, the floating method has excessive packet redundancy, channel contention, and packet / channel collisions, which are called broadcast storm problems unless the rebroadcast limit technique is applied to each radio node. (collision) is generated.

Here, redundancy means a case where one wireless node receives the same packet from two or more neighboring wireless nodes. Channel contention is a problem that occurs when multiple radio nodes simultaneously rebroadcast a received packet, resulting in an increase in the collision rate of packets / channels.

In order to solve the above problems, various methods for determining whether rebroadcast operation is performed in each wireless node receiving a packet have been proposed.

In addition to the above-described floating method, the conventional broadcasting method includes a probabilistic method, a counter-based method, a distance-based method, a location-based method, and a neighboring knowledge base. classified as a neighbor-knowledge-based method.

The probabilistic method re-broadcasts the received packet according to a predetermined probability p of all wireless nodes that receive the broadcast packet. Therefore, the total number of rebroadcast packets is p × N. However, the probabilistic method has a disadvantage in that it is difficult to find an appropriate probability p.

The counter-based method determines whether to rebroadcast by counting the number of identical packets received by the wireless node during a random assessment delay (RAD). That is, if one wireless node receives more identical packets than a predetermined threshold, the wireless node does not rebroadcast the packets. In this case, RAD means a time from when a packet is received to a wireless node to rebroadcast.

The distance-based method rebroadcasts packets only to receiving wireless nodes remote from the transmitting wireless node. Here, the distance information is obtained by measuring the signal strength or using an additional device such as a global positioning system (GPS).

The distance-based method has the disadvantage that packets may not reach due to the dynamic topology of the network, and that wireless nodes that are out of a transmission range in a low node density network are difficult to receive broadcast packets.

The location-based method rebroadcasts a packet only when the new area covered by the receiving wireless node is larger than a predetermined threshold. Since the location-based method requires the location information of each wireless node, a separate location information providing apparatus is required like the distance-based method. For this reason, distance-based and location-based methods are sometimes referred to as area-based methods.

The neighbor knowledge-based method determines rebroadcasting of packets based on accurate neighbor radio node information. Here, each radio node periodically exchanges a HELLO message between neighbors to collect neighbor radio node information to create a neighbor list, and attaches a neighbor list to all broadcast packets. When a packet is delivered to neighboring wireless nodes of a predetermined wireless node, each neighboring wireless node compares its neighbor list with the neighboring list attached to the packet, and all its neighboring wireless nodes are included in the list attached to the packet. If there is, we do not rebroadcast.

The neighbor knowledge-based method can almost optimize the number of rebroadcast packets, but the HELLO message itself occupies channel bandwidth, and because the HELLO message transmission is transmitted over the air, the probability of collision increases and this results in a decrease in overall performance. have.

An object of the present invention for overcoming the above disadvantages is to provide a broadcast method of a wireless ad hoc network that can minimize the number of re-broadcast packets while reducing the packet transmission delay time and increase the arrival rate.

In accordance with an aspect of the present invention, there is provided a method for broadcasting a wireless ad hoc network. The method may further include determining whether a received packet is duplicated and determining that the received packet is a duplicated packet. And determining whether to rebroadcast the received packet based on hop count information of the received packet and distance information with the wireless node that transmitted the packet. The determining of whether the received packet is rebroadcasted includes the hop count information of the received packet being larger than an initial value of a hop count, and the wireless node receiving the packet includes a distance from the wireless node transmitting the packet. If it is smaller than the radius of the rebroadcast area, the rebroadcast of the received packet may be cancelled. The determining of whether the received packet is duplicated may include: information including at least one of source address information, destination address information, and sequence number information included in the header of the received packet in the header of the prestored packet; Compared with, it is possible to determine whether the duplicate reception. In the broadcasting method of the wireless ad hoc network, if it is determined that the received packet is not a duplicated packet, setting a rebroadcast timer having a predetermined delay time and receiving the delayed time when the rebroadcast timer ends and the delay time arrives. The method may further include rebroadcasting the packet. The rebroadcast timer having the predetermined delay time may include setting the predetermined delay time based on a preset maximum delay time, a distance between a transmitting wireless node and a receiving wireless node, a transmission range of the wireless node, and radius information of a rebroadcasting area. You can decide.

According to the broadcast method of the wireless ad hoc network as described above, if a predetermined wireless node that receives the broadcast packet determines whether to receive the duplicate packet through header information of the received packet, and determines that the received packet is a duplicate packet It determines whether to rebroadcast the received broadcast based on the hop count information of the received packet and the distance between the transmitting radio node.

Accordingly, by minimizing the number of re-broadcast packets, packet collisions can be prevented, thereby improving the arrival rate. In addition, as the arrival rate of the packet is improved as described above, the delivery delay time of the packet is reduced.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

1 is a conceptual diagram illustrating a broadcast method of a wireless ad hoc network according to an embodiment of the present invention.

Referring to FIG. 1, an ad hoc network includes a first wireless node 11 serving as a source for broadcasting a broadcast packet, a transmission range 10 of the first wireless node 11, and a first wireless node. Second to sixth wireless nodes 21 to 29 serving as neighboring nodes that receive the broadcasted packet from (11).

Here, the transmission range of the first wireless node 11 refers to a range in which the packet broadcasted by the first wireless node 11 can be normally received.

In the ad hoc network shown in FIG. 1, since the second wireless node 21, the third wireless node 23 and the fourth wireless node 25 are located in close proximity to each other, the transmission range of each wireless node is mostly overlapped. It exists in the re-broadcasting area (RA) 20.

Therefore, in the broadcast method of the wireless ad hoc network according to an embodiment of the present invention, when the second radio node 21 rebroadcasts a packet broadcast from the first radio node 11, the third radio node 23 and The fourth radio node 25 reduces collision of broadcast packets by not rebroadcasting packets broadcast from the first radio node 11.

In addition, in the wireless ad hoc network illustrated in FIG. 1, the fifth wireless node 27 and the sixth wireless node 29 are located far from the first wireless node 11 as the source wireless node. 11) Receive a broadcasted packet from the broadcaster and rebroadcast it.

That is, in the method of broadcasting a wireless ad hoc network according to an embodiment of the present invention, when any one of the wireless nodes included in the rebroadcast area rebroadcasts, the other wireless nodes in the rebroadcast area receive the rebroadcast packet. Suppress rebroadcast. In addition, in order to increase the reach of rebroadcast packets, a receiving radio node located far from a source radio node broadcasting a packet provides more rebroadcast opportunities.

2 is a flowchart illustrating a broadcast process of a wireless ad hoc network according to an embodiment of the present invention, and FIG. 3 shows a pseudo code for the broadcast method of the wireless ad hoc network shown in FIG. 4 is a conceptual diagram illustrating a wireless ad hoc network according to an embodiment of the present invention.

2 to 4, a receiving wireless node first receives a broadcasted packet from an arbitrary transmitting wireless node (step 201), and checks whether the received packet is duplicated based on header information of the received packet. (Step 203).

Here, the receiving wireless node may store the source address, the destination address, and / or the sequence number of the information included in the header of the received packet in the header of the prestored packet. Compared with, it is possible to determine whether the packet is duplicated.

That is, since a wireless node receiving and rebroadcasting a broadcast packet receives and rebroadcasts a predetermined packet and stores the received packet, when a new packet is received, whether a duplicate packet is received by comparing a previously stored packet with header information. Can be determined.

The receiving wireless node determines whether or not the received packet is duplicated (step 205), and if it is determined that the received packet is the first received packet rather than the duplicated packet, sets the initial value of the hop count HC0 (step 207). ). Here, the receiving wireless node may set the hop count information included in the header of the routing control packet (when using a protocol such as Dynamic Source Routing or AODV) or the TTL (Time To Live) information of the packet header (when using the Internet Protocol) to HC0. have.

Thereafter, the receiving wireless node sets a rebroadcast timer having a delay time t as shown in Equation 1 (step 209).

Here, the delay time t means the elapsed time from the time when a wireless node receives a predetermined packet to rebroadcasting the received packet.

In Equation 1, d represents a distance between a wireless node receiving a packet and a wireless node transmitting a packet, d _th represents a radius of a rebroadcast area, r represents a transmission range of a wireless node, and T _max represents a maximum delay time. In addition, T _upper represents the upper limit of the delay time, and T _lower represents the lower limit of the delay time.

The distance d between the receiving wireless node and the transmitting wireless node can be obtained by measuring the strength of the signal received at the receiving wireless node (e.g., the electric field strength), and T _max is determined based on the bandwidth of the wireless node. It can have a fixed value, for example 30 ms.

As described in Equation 1, the delay time t is determined based on the distance between the wireless node receiving the packet and the wireless node transmitting the packet, and the farther away the receiving wireless node is from the transmitting wireless node, the better the rebroadcast opportunity. Have more.

If the rebroadcast timer with delay time t is set in step 209, the receiving wireless node operates the rebroadcast timer with delay time t (step 211).

Thereafter, the receiving wireless node determines whether the set delay time arrives (step 213), and when the set delay time reaches, re-broadcasts the packet received from the transmitting wireless node (step 215).

In step 205, if it is determined that the received packet is a duplicately received packet, the receiving wireless node compares the hop count value of the received packet with HC0, which is the initial value of the hop count (step 217), and receives the received packet. It is determined whether the hop count value of has a value greater than HC0 (step 219).

Here, the hop count information may be obtained from a header of a routing control packet in protocols such as Dynamic Source Routing (DSR) and Ad hoc On-demand Distance Vector (AODV), and in a packet header in the case of IP (Internet Protocol). It can be obtained from the TTL (Time To Live) information.

The receiving wireless node also compares the distance d with the transmitting wireless node and the radius d _th of the rebroadcast area (step 221).

If the hop count value is larger than HC0 in step 219 and the distance d with the transmitting node is smaller than the radius d _th of the rebroadcast area in step 221, the rebroadcast of the received packet is canceled (step 223). ).

That is, the receiving radio node determines that the packet is rebroadcasted within the given rebroadcasting area when the hop count value of the received packet is greater than HC0 and the distance to the transmitting radio node is shorter than the radius d _th of the rebroadcasting area. It does not rebroadcast the received broadcast packet.

Here, the radius of the rebroadcast area d _th directly affects the packet redundancy and arrival rate. That is, the smaller the radius d _th of the rebroadcast area, the higher the redundancy and arrival rate. On the contrary, the larger the radius d _th of the rebroadcast area, the lower the redundancy and arrival rate.

Therefore, it is necessary to determine the radius d _th of the rebroadcast area to reduce packet redundancy and increase arrival rate. The optimal value of the radius of the rebroadcast area (d _th ) is influenced by the transmission range (r) of the radio node, and as a result of repeated experiments, the radius of the rebroadcast area (d _th ) is 0.4 to 0.6 of the transmission range of the radio node. The best performance was obtained when the embryo (ie 0.4 × r to 0.6 × r).

5 through 7 illustrate performance of a conventional method of broadcasting a wireless ad hoc network in accordance with a floating, stochastic method (PB), counter based method (CB), and distance based method. These graphs show the results compared with (DB).

Performance evaluation of the broadcast method of the wireless ad hoc network according to an embodiment of the present invention, was performed using the NS2 simulator, the network model is 40 to 120 in the 1.0km × 1.0km area to investigate the node density effect Configured as a wireless node. The initial positions of the wireless nodes were randomly selected, and a pair of wireless nodes transmitting and receiving packets were also randomly selected to generate constant bit rate / user datagram protocol (CBR / UDP) traffic. The channel bandwidth was set at 2 Mbps.

Each wireless node uses the IEEE 802.11 MAC protocol, and the channel model uses a wireless channel / wireless physical transmission model. Two ray ground model was used as radio transmission model, and transmission range and interference range of wireless node were set to 250m and 550m, respectively. The traffic source is CBR, five radio nodes are randomly selected for broadcast packets, and UDP packets are set to 64 bytes.

In each performance evaluation experiment, the simulation time was set to 200 seconds, and 10 simulations were performed under the same configuration conditions to avoid the occurrence of biased random numbers.

In addition, the rebroadcast probability of the probabilistic method PB is 0.6, the counter threshold of the counter-based method CB is 3, and the radius of the re-broadcasting area in the distance-based method DB and the broadcasting method according to an embodiment of the present invention. d _th ) was set at 167 m (0.67 x transmission range).

5 is a graph illustrating a result of comparing arrival rates of a broadcasting method and a conventional broadcasting method according to an embodiment of the present invention.

5, the arrival rate is the number of wireless node receives a broadcast packet (N _r) the number of the broadcast radio node packets are directly or possibly indirectly arrive (N _a) the ratio (i.e., arrival rate = N _r / N _a of ) Was obtained by calculating.

Referring to FIG. 5, when the number of wireless nodes is 40, it can be seen that the arrival rate of the distance-based method DB is the lowest, because the wireless nodes within the distance threshold have prevented rebroadcasting of packets. Thus, the distance based method (DB) is difficult for broadcast packets to be delivered to all wireless nodes in a network with low node density.

When the number of wireless nodes is 60 to 80, all broadcasting methods including the broadcasting method of the present invention showed the best arrival rate. When the number of wireless nodes exceeds 100, the arrival rate is reduced due to the high collision rate. That is, since many radio nodes keep trying to rebroadcast on the same packet, the collision rate is increased, and as a result, many packets are lost as shown in FIG.

As shown in FIG. 5, the broadcast method according to the embodiment of the present invention can reduce the packet collision rate because the wireless node that receives the packet determines the rebroadcast of the received packet based on the hop count and the distance. As a result, it is possible to obtain a high arrival rate compared to other conventional broadcasting methods.

FIG. 6 is a graph illustrating a result of comparing a rebroadcast rate of a broadcast method and a conventional broadcast method according to an embodiment of the present invention, and FIG. 7 is a broadcast method and a conventional broadcast according to an embodiment of the present invention. A graph showing the result of comparing the number of lost packets for the method.

The saved re-broadcast rate (SRB) in FIG. 6 was calculated by Equation 2 below.

In Equation 2, N _r denotes the number of radio nodes that have received the broadcast packet, and N _t denotes the number of radio nodes that substantially rebroadcast the packet.

6 and 7, the floating method shows 0% in all experimental conditions because the number of wireless nodes that have received the broadcast packet and the number of wireless nodes that substantially rebroadcast the packet are the same. In addition, as shown in FIG. 7, the floating method re-broadcasts all the wireless nodes that have received the packet, and thus many collisions occur. As the number of wireless nodes increases, the number of lost packets increases.

In the broadcast method according to an embodiment of the present invention, when the density of the radio nodes is low (for example, when the number of radio nodes is 40), the number of rebroadcast packets increases because the number of nodes in the rebroadcast area is small, thereby saving the rebroadcast rate. It is lower than the probabilistic method (PB) and the distance-based method (DB).

However, the broadcast method according to an embodiment of the present invention adjusts the number of rebroadcast packets according to the density of the wireless node, so that as the number of wireless nodes increases, the rebroadcast ratio saved is higher than that of the conventional broadcast methods. In addition, as shown in FIG. 7, in the broadcast method according to an embodiment of the present invention, as the number of wireless nodes increases, the number of lost packets decreases as compared with the conventional broadcast method.

As shown in FIGS. 5 to 7, the broadcasting method of the wireless ad hoc network according to the exemplary embodiment of the present invention has improved overall performance and efficiency by 20 to 30% over the conventional broadcasting methods.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

1 is a conceptual diagram illustrating a broadcast method of a wireless ad hoc network according to an embodiment of the present invention.

2 is a flowchart illustrating a broadcast process of a wireless ad hoc network according to an embodiment of the present invention.

FIG. 3 shows a pseudo code for a broadcast method of the wireless ad hoc network shown in FIG. 2.

4 is a conceptual diagram illustrating a wireless ad hoc network according to an embodiment of the present invention.

FIG. 5 is a graph illustrating a result of comparing arrival rates of a broadcast method of a wireless ad hoc network and a conventional broadcast method according to an embodiment of the present invention.

FIG. 6 is a graph illustrating a result of comparing a reduced rebroadcast rate for a broadcast method of a wireless ad hoc network and a conventional broadcast method according to an embodiment of the present invention.

7 is a graph illustrating a result of comparing the number of lost packets for the broadcast method of the wireless ad hoc network and the conventional broadcast method according to an embodiment of the present invention.

Claims (5)

In the broadcast method of a wireless ad hoc network, Determining whether a received packet is duplicated; And Determining whether the received packet is rebroadcast based on hop count information of the received packet and distance information with a wireless node that has transmitted the packet, if it is determined that the received packet is a duplicated received packet. Broadcast method of wireless ad hoc network. The method of claim 1, wherein the determining of whether to rebroadcast the received packet comprises: If the hop count information of the received packet is larger than an initial value of a hop count, and the distance from the wireless node that has transmitted the packet is smaller than the radius of the rebroadcast area including the wireless node that has received the packet, A broadcast method of a wireless ad hoc network, characterized in that to cancel the re-broadcast. The method of claim 1, wherein the determining of whether the received packet is duplicated comprises: And determining whether or not a duplicate reception is received by comparing at least one of the source address information, the destination address information, and the sequence number information included in the header of the received packet with information included in the header of the prestored packet. Broadcast method of ad hoc network. The method of claim 1, wherein the broadcast method of the wireless ad hoc network, If it is determined that the received packet is not a duplicated packet, Setting a rebroadcast timer having a predetermined delay time; And And rebroadcasting the received packet when the rebroadcast timer expires and the delay time arrives. The method of claim 4, wherein the setting of the rebroadcast timer having the predetermined delay time comprises: And determining the predetermined delay time based on a predetermined maximum delay time, a distance between a transmitting wireless node and a receiving wireless node, a transmission range of the wireless node, and radius information of a re-broadcasting area.

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