JP2006295442A - Communication method and wireless terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for executing efficient and sure communication on an ad-hoc wireless network. <P>SOLUTION: The communication method is executed on the ad-hoc wireless network. The wireless terminal receiving a packet detects received radio field intensity, calculates a relay latency time corresponding to the detected received radio field intensity, and relays the received packet when not receiving the same packet as the received packet in the relay latency time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for performing wireless communication between wireless terminals via relaying by one or a plurality of wireless terminals.

  In a so-called ad hoc wireless communication network in which a wireless terminal can communicate with other wireless terminals directly or via one or more wireless terminals, route information may not be used. In this case, a relay method is required to deliver the packet to the target wireless terminal without using the route information.

  As the simplest method, there is a method in which all wireless terminals that have received a communication packet relay the packet to neighboring wireless terminals. By repeating the relay in this way, information can be distributed to all wireless terminals in the network.

  However, this method is inefficient when the distribution density of wireless terminals is high and there are a large number of wireless terminals within the communicable range. FIG. 8 is a diagram when a black circle wireless terminal transmits a packet and a white circle wireless terminal relays the packet. Since a large number of wireless terminals perform relaying, a communication band is consumed. In addition, since many of these wireless terminals perform relay simultaneously, a lot of radio wave interference occurs and congestion occurs.

In order to perform efficient relaying, a wireless terminal at the end of the communicable range may perform relaying. In order to realize this, a method is known in which a wireless terminal that receives a packet detects the received electric field strength and relays the received packet only when the received electric field strength is below a reference level (patent) Reference 1).
JP 2003-8591 A

  The above-described method is effective in a situation where there is always a wireless terminal that receives a packet with a relatively high distribution density of wireless terminals, that is, a reception electric field strength that is lower than a reference level. In such a case, the wireless terminal at the end of the communicable range relays, and efficient packet relaying can be realized.

  However, when the distribution density of the wireless terminals is low, there are wireless terminals near the transmitting terminal, but there may be no wireless terminals that receive the received electric field intensity below the reference level. In this case, the relay is interrupted, causing a problem that information cannot be distributed to all wireless terminals in the network.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for performing efficient and effective communication regardless of the distribution density of wireless terminals.

  In order to solve the above problem, when one or a plurality of wireless terminals perform communication between wireless terminals by relaying a packet, the packet is relayed by the following method. That is, the wireless terminal that receives the packet detects the received electric field strength, calculates the relay waiting time according to the detected received electric field strength, and does not receive the same packet as the packet received within the relay waiting time, Relay received packets.

  Regarding the relationship between the received electric field strength and the distance between the transmitting and receiving terminals, the distance between the transmitting and receiving terminals is longer as the received electric field strength is lower. In the present invention, the relay waiting time is set shorter as the received electric field strength is weaker. Therefore, the farther the receiving terminal is from the transmitting terminal, the shorter the relay waiting time. In this way, the receiving terminal located far from the transmitting terminal preferentially relays transmission, and the terminal that receives the same packet within the relay waiting time stops relaying, so that efficient packet relaying can be performed.

  Even when the distribution density of the wireless terminals is low, the receiving terminal located near the transmitting terminal also transmits after the relay waiting time elapses, so that information can be distributed to all wireless terminals in the network.

  Note that the relay waiting time is preferably calculated as a step-like function that increases in accordance with the received electric field strength. Thereby, the influence of a measurement error etc. can be excluded.

  According to the present invention, efficient and effective communication can be performed regardless of the distribution density of wireless terminals.

  Exemplary embodiments of the present invention will be described below in detail with reference to the drawings. In the present embodiment, an example in which broadcast communication is performed in an ad hoc wireless communication network including mobile terminals will be described.

  FIG. 2 is a diagram illustrating a packet structure used in the present embodiment. The packet 10 includes a transmission source terminal ID 11 and data 12. The source terminal ID 11 stores an identifier of a terminal that transmits a broadcast packet. Data 12 stores data to be distributed.

  Next, processing of the terminal that has received the broadcast packet will be described with reference to the flowchart of FIG. The process in FIG. 3 is executed by the CPU of the terminal according to the program.

  In step S101, the receiving terminal detects the electric field strength of the received radio wave. As shown in FIG. 1, the received electric field strength is a downward convex function asymptotically approaching “0”. Psrc is the intensity of the radio wave output from the transmitting terminal. Pmin is a lower limit value of the received electric field strength that enables stable data communication.

  Returning to the flowchart of FIG. In step S102, it is determined whether the received packet is a packet that has been received so far. If the packet has already been received, the process proceeds to step S108, the packet is discarded, and the process is terminated. If it is the first packet to be received, the process proceeds to step S103 and the data 12 is processed.

  In step S104, the relay waiting time corresponding to the received electric field strength detected in step S101 is calculated. The relationship between the received electric field strength and the relay waiting time will be described with reference to FIG. Pmin in FIG. 4 is the same as Pmin in FIG. 1, and is the lower limit value of the received electric field strength capable of data communication. Ideally, the relay waiting time may be a function proportional to the received electric field strength as indicated by the dotted line graph. Actually, since fluctuation of the received electric field strength and measurement error are included, it is preferable to calculate as a step-like function as shown by a solid line graph.

Returning to the flowchart of FIG. In step S105, the apparatus waits for the relay waiting time calculated in step S104.

  In step S106, it is determined whether the same packet as the received broadcast packet is received during standby. The determination of whether or not the packets are the same may be made by comparing the data 12 or by comparing the hash values of the data 12. Receiving the same broadcast packet within the relay waiting time means that a terminal having a shorter waiting time than the own terminal, that is, a terminal farther away from the transmitting terminal is relaying, and therefore does not relay. End the process.

  If the same packet is not received during standby, this packet is relayed and transmitted in step S107.

  By performing broadcast communication by the above method, the wireless terminal at the end of the communicable range preferentially performs relay transmission, and efficient broadcasting can be realized. As shown in FIG. 5, only the terminal a at the end of the terminal (white circle) that receives the broadcast from the transmitting terminal (black circle) relays. Terminals b and c do not relay since they receive packets from terminal a during standby. Compared with the conventional method (FIG. 8), since the number of terminals to be relayed can be reduced, the consumption of the communication band can be suppressed. In addition, since the number of terminals relayed simultaneously is reduced, radio wave interference is reduced, and thus congestion can be suppressed.

  Further, even when there is no wireless terminal at the end of the communicable range, the relay is not interrupted because a nearby terminal relays after the relay waiting time elapses. FIG. 6 is a diagram for explaining this. There is no wireless terminal at the end of the communicable range of the transmitting terminal (black circle). However, since the terminal b relays after the relay waiting time elapses, broadcast communication can be performed for all wireless terminals in the network.

  The present invention is particularly effective when used for inter-vehicle ad hoc communication. This will be described with reference to FIG. Circles (white circles and black circles) in the figure are vehicles. The vehicle has a feature that it is distributed one-dimensionally (on a line) along the road and the distribution density changes abruptly. Since it is distributed one-dimensionally, only a small number of terminals (black circles) can relay and realize efficient broadcasting. For example, the density changes suddenly at the end of a traffic jam. Also in this case, according to the present invention, it is possible to distribute information to the entire network without interruption.

It is a figure which shows the relationship between the distance between terminals, and receiving electric field strength. It is a figure which shows a packet structure. It is a flowchart which shows the process of the terminal which received the broadcast packet. It is a figure which shows the relationship between receiving electric field strength and relay waiting time. It is a figure which shows the example of relay at the time of performing broadcast communication in this embodiment. It is a figure which shows the example of relay at the time of performing broadcast communication in this embodiment. It is a figure which shows the example of a relay at the time of performing broadcast communication in a vehicle-to-vehicle ad hoc network. It is a figure which shows the example of relay at the time of broadcasting by the conventional method.

Explanation of symbols

10 packet 11 source terminal ID
12 data

Claims (5)

A communication method in which one or a plurality of wireless terminals communicate between wireless terminals by relaying a packet,
The wireless terminal that received the packet
Detect received field strength,
Calculate the relay waiting time according to the detected received field strength,
If the same packet as the received packet is not received within the relay waiting time, relay the received packet;
A communication method characterized by the above. The relay waiting time is calculated as a step-like function that increases according to the received electric field strength.
The communication method according to claim 1.   A wireless terminal that relays packets by the communication method according to claim 1.   A vehicle comprising the wireless terminal according to claim 3.   A program for executing the communication method according to claim 1.

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