JP2007006395A - Mobile terminal and transmission power control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide techniques capable of performing a communication with appropriate transmission power even in an environment where a relative distance between mobile terminals varies. <P>SOLUTION: The mobile terminal, which performs a wireless communication, comprises: a wireless communication means; a prediction means for predicting a relative distance between a present node and a communicating party node after the lapse of a predetermined time; and a communication control means for controlling transmission power of the wireless communication means based on the predicted relative distance. A location information acquisition means is further provided for acquiring current locations and moving speeds of the present node and of the communicating party node and it is preferable that, based on said information, the prediction means predicts the relative distance between the present node and the communicating party node after the lapse of the predetermined time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for controlling transmission power of a mobile terminal.

  When all the terminals communicate with the maximum transmission power when performing wireless communication, a large number of radio wave interference occurs as shown in FIG. There is transmission power control as a technique for reducing radio wave interference and optimizing the communication environment.

In the conventional technique, transmission power is optimized based on the reception strength of each other. That is, a technique is known in which when the signal strength of the received signal is lower than a predetermined threshold, the transmission power is increased stepwise, and when the signal strength of the received signal exceeds the threshold, the increase in transmission power is stopped. (Patent Document 1).
Japanese Patent Laid-Open No. 2004-260753

  However, the prior art as described above is not suitable for a mobile terminal having a large relative speed between terminals such as an in-vehicle terminal. When the relative speed between the terminals is large, the distance between the terminals greatly changes in a short time, and the reception intensity varies greatly accordingly. In the method of controlling the transmission power based on the intensity of the received radio wave as in the prior art, since there is a time lag between reception and transmission power control, it is not possible to follow the situation where the reception intensity changes greatly in a short time. is there.

  As shown in FIG. 9, when the distance between the terminals becomes large, the transmission power of the terminal A optimized at a certain time causes a problem that the radio wave does not reach the communication partner terminal B at the next time. . Conversely, when the distance between the terminals becomes small, communication is performed with more transmission power than necessary at the next time point, and the use efficiency of radio waves decreases.

  These problems are particularly serious when the terminal moves at high speed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of performing communication with appropriate transmission power even in an environment where the relative distance between mobile terminals changes. It is in.

  In order to achieve the above object, in the present invention, transmission power is controlled in a mobile terminal by the following means or processing.

  The mobile terminal according to the present invention controls the transmission power of the radio communication means based on the radio communication means, the prediction means for predicting the relative distance after a predetermined time between the own node and the communication partner node, and the predicted relative distance. Communication control means.

  Here, the mobile terminal means that the terminal device itself can be carried around, such as a notebook computer, PDA, mobile phone, etc., and the terminal device itself is fixedly installed in an automobile etc. like an in-vehicle terminal. However, an object in which an installed object (such as an automobile) is a moving object is also included.

The communication partner node is a node with which the transmission node communicates directly. When the transmitting node communicates directly with the receiving node, the receiving node becomes the communication partner node. In an ad hoc wireless communication system in which a transmission node and a reception node communicate with each other via a relay node, the relay node that performs the first relay is a communication partner node.

  The relative distance after a predetermined time between the own node and the communication partner node is obtained by the position information acquisition means acquiring the position and movement speed of the own node and the position and movement speed of the communication partner node, and the information acquired by the prediction means. It is preferable to predict based on The moving speed includes the moving speed and the moving direction. For example, the position of the own node is acquired by GPS, the speed of movement is acquired by a speed sensor, and the direction of movement is acquired by a gyro. The speed and direction of movement may be estimated using GPS.

  Moreover, it is preferable to acquire the position and moving speed of a communicating party node by radars, such as a millimeter wave radar and a laser radar, autonomous sensors, such as an ultrasonic sensor and an image sensor. In addition to this method, the base station may acquire the position and moving speed using a radar or the like as described above, and the mobile terminal may acquire such information from the base station through communication. Further, the communication partner node itself may acquire the position and the moving speed, and the mobile terminal may acquire these information from the communication partner node by communication.

  If the current position and the moving speed of the own node and the communication partner node can be acquired, the prediction means can predict the relative distance between the own node and the communication partner node after a predetermined time based on these information. Note that the predetermined time is preferably the time until the next node performs transmission. And it is preferable that a communication control means calculates transmission power using the function which makes the estimated relative distance a variable. It is also preferable to divide the relative distance into levels and use transmission power according to the level of the relative distance.

  In addition to the method of directly calculating the appropriate transmission power as described above, the transmission power may be controlled step by step using the relative distance between the own node and the communication partner node. That is, the communication control means increases the transmission power by a predetermined level when the relative distance between the own node and the communication partner node increases, and decreases the transmission power by a predetermined level when the relative distance decreases. . In this case, it is also preferable not to focus only on the change in the relative distance but to control the transmission power in consideration of the current relative distance. That is, even when the relative distance is small, control such as maintaining the transmission power without decreasing depending on the current relative distance may be performed.

  Thus, in order to predict the relative distance after a predetermined time between the own node and the transmission partner node, and determine the output intensity of the transmission radio wave based on the predicted relative distance, the relative speed between the own node and the transmission partner node is Even if it is large, it is possible to perform communication with appropriate transmission power. In other words, transmission power is determined based on the relative distance between nodes at the time of radio wave transmission, not based on past information such as the radio wave intensity of the received radio wave. Communication can be performed with a sufficient transmission power.

  When the relative distance between the own node and the transmission partner node increases, communication between both nodes is ensured by increasing the transmission power. On the other hand, if the relative distance between the local node and the destination node is small, by reducing the transmission power, it is not necessary to use transmission power that is higher than necessary, and radio wave interference can be suppressed. Become. That is, according to the present invention, it is possible to perform wireless communication between mobile terminals moving at high speed without interruption of communication and with transmission power with good radio wave utilization efficiency.

The mobile terminal according to the present invention acquires a radio wave condition that includes at least one of the number of nodes existing around the own node, the noise level around the own node, and the radio wave intensity of the radio wave received from the communication partner node. It is preferable that the communication control unit includes an acquisition unit and controls the transmission power in consideration of the acquired radio wave condition.

  The number of nodes existing around the own terminal may be obtained by receiving position information from the neighboring nodes. If the mobile terminal is an in-vehicle terminal, traffic congestion information is obtained from a traffic information distribution system such as VICS (Vehicle Information and Communication System), and the number of surrounding nodes (in-vehicle terminals) is estimated based on this information. good. In addition, traffic information (for example, crowded in the morning and evening, but free in the daytime, but busy on the weekend but free on weekdays) is stored in the in-vehicle terminal. The number of surrounding nodes may be estimated based on the map information stored in advance. When there are many other nodes in the vicinity, it is preferable that the communication control unit performs control so as to reduce the transmission power in order to avoid radio wave interference.

  When the noise level around the own node is high, the communication control means preferably controls to increase the transmission power. For example, when the transmission power calculated based on the relative distance is smaller than the noise level, the transmission power larger than the noise level is used. Thus, when calculating the appropriate transmission power, it is possible to determine the appropriate transmission power by considering not only the relative distance to the communication partner node but also the noise level.

  In addition, when the received radio wave intensity of the radio wave received from the communication partner node is high, it is preferable that the communication control unit performs control so as to reduce the transmission power.

  In this way, in addition to the relative distance to the communication partner node, the transmission power is determined in consideration of the radio wave conditions such as the number of surrounding nodes, noise level, and received radio wave intensity, so that communication with appropriate transmission power can be performed. Can be done. Therefore, radio wave interference can be reduced, and communication with high radio wave utilization efficiency can be performed.

  The present invention can be understood as a mobile terminal having at least a part of the above means. Further, the present invention can be understood as a transmission power control method including at least a part of the above processing or a program for realizing such a method. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  For example, in the transmission power control method as one aspect of the present invention, a mobile terminal that performs wireless communication predicts a relative distance after a predetermined time between its own node and a communication partner node, and transmits power based on the predicted relative distance. To control.

  The program as one aspect of the present invention causes a mobile terminal that performs wireless communication to predict a relative distance after a predetermined time between this node and a communication partner node, and controls transmission power based on the predicted relative distance. .

  Moreover, the vehicle as 1 aspect of this invention is a vehicle provided with said mobile terminal.

  According to the present invention, communication can be performed with appropriate transmission power even in an environment where the relative distance between mobile terminals changes.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

(First embodiment)
In the first embodiment of the present invention, an in-vehicle terminal (mobile terminal) performs inter-vehicle communication using an ad hoc wireless communication method. In ad hoc wireless communication, communication is performed with a target node via one or more relay nodes. In this embodiment, the relay node is a node adjacent to the transmission source node. However, a node separated by a predetermined distance can be used as a relay node.

  FIG. 1 is a block diagram showing a configuration of the in-vehicle terminal 1 in the present embodiment. The in-vehicle terminal 1 includes a communication unit 2, a position information acquisition unit 3, a radio wave status acquisition unit 4, a distance prediction unit 5, and a communication control unit 6.

  The communication unit 2 transmits and receives radio waves. The position information acquisition unit 3 includes a host vehicle position information acquisition unit 31 and another vehicle position information acquisition unit 32. The own vehicle position information acquisition unit 31 includes a GPS, a gyro, and a vehicle speed sensor. The own vehicle position information acquisition unit 31 acquires the position of the own vehicle from the GPS, acquires the moving direction of the own vehicle from the gyro, and acquires the speed of movement of the own vehicle from the vehicle speed sensor. The moving direction may be acquired using an electronic compass other than the gyro. As long as the vehicle speed can be measured, any technique such as a magnetic type or a mechanical type may be used for the vehicle speed sensor.

  The other vehicle position information acquisition unit 32 acquires the position and travel speed of the communication partner node (relay node). In the present embodiment, the information distributed from the roadside device is acquired by the communication unit 2 receiving the information. That is, each in-vehicle terminal transmits the position and traveling speed acquired by the own vehicle position information acquisition unit 31 to the roadside device, and the roadside device distributes the position and traveling speed information to surrounding in-vehicle terminals.

  The other vehicle position information acquisition unit 32 is configured to have a radar such as a millimeter wave radar or a laser radar, an autonomous sensor such as an ultrasonic sensor, an image sensor, and the like so as to acquire the position and traveling speed of the communication partner node. Anyway. Further, any configuration may be used as long as the location and traveling speed of the communication partner node can be acquired.

  The radio wave status acquisition unit 4 detects the noise level from the radio wave received by the communication unit 2.

  The distance prediction unit 5 predicts the positions of the host vehicle and the other vehicle after a predetermined time from the current positions and travel speeds of the host vehicle and the other vehicle acquired by the position information acquisition unit 3, and predicts the relative distance. Here, the predetermined time may be a time until the next data transmission time, or may be a longer time.

  The communication control unit 6 calculates an appropriate transmission power based on the noise level detected by the radio wave condition acquisition unit 4 and the relative distance predicted by the distance prediction unit 5. Then, radio waves are transmitted from the communication unit 2 using the calculated transmission power.

  FIG. 2 is a flowchart showing a flow of transmission power control processing performed by the in-vehicle terminal 1. First, in step S101, it is determined whether communication is performed. If communication is not performed, the process ends. In the case of performing communication, the process proceeds to step S102, and a communication partner is searched (scanned). In step S103, it is determined whether there is a communication partner. If there is no communication partner, the process returns to step S101 to search for the communication partner again. If there is a communication partner, the process proceeds to step S104 to perform processing for calculating appropriate transmission power.

  In step S104, the other vehicle position information acquisition unit 32 acquires the position and traveling speed of the communication partner. In step S105, the vehicle position information acquisition unit 31 acquires the position and travel speed of the vehicle. In step S106, the radio wave condition acquisition unit 4 acquires a surrounding noise level.

  In step S107, the distance prediction unit 5 predicts the position of the host vehicle and the communication partner terminal after a predetermined time (for example, 20 milliseconds later) from the current position and the traveling speed, and the host vehicle and the communication partner from each predicted position. Predict the relative distance to the terminal.

In step S108, the communication control unit 6 obtains transmission power from the predicted relative distance. Reach of the radio waves is proportional to the cube root to 1 / 4th power of the transmission power, suitable transmission power P is obtained as P = aL ^n. Here, L is a distance between nodes, n is a coefficient of propagation loss, and a is a constant. The propagation loss coefficient n takes a value of 3-4. The propagation loss coefficient n may be a predetermined value, for example. In addition, the vehicle-mounted terminal 1 may be configured to hold the value determined for each road that is running along with the map information, and the coefficient of propagation loss on the road that is running may be used based on the position information of the vehicle. Moreover, you may comprise so that the coefficient of the propagation loss for every road may be delivered from a roadside machine, without storing in the vehicle-mounted terminal 1. FIG.

  In step S109, it is determined whether the transmission power calculated above is equal to or higher than the ambient noise level. When the calculated transmission power is equal to or smaller than the noise level, the process proceeds to step S110, and the power exceeding the noise level is used as the transmission power. In step S111, radio waves are transmitted using the calculated transmission power or the transmission power set to be equal to or higher than the noise level.

  Note that the transmission power control processing in steps S108 to S111 does not have to be performed every time data is transmitted, and the processing may be executed at predetermined time intervals.

  When the relative speed between the own node and the communication partner node is large because the relative distance between the own node and the communication partner node at the time of transmitting the radio wave is predicted and the transmission power is calculated based on this relative distance. Even so, it is possible to perform communication with appropriate transmission power. As shown in FIG. 3, even when the speed difference between the vehicle A and the vehicle B is large and the relative distance increases, the vehicle A predicts that the relative distance will increase and increases the transmission power. Therefore, communication between the vehicle A and the vehicle B will not be interrupted. Conversely, when the relative distance between the vehicle A and the vehicle B becomes small, the vehicle A can reduce the transmission power and perform communication to suppress radio wave interference.

  Since each vehicle performs communication using appropriate transmission power in this way, the influence of radio wave interference is reduced as shown in FIG. 4 compared to the case where each vehicle performs communication with maximum power (FIG. 8). It becomes possible to suppress. Therefore, it is possible to realize communication with high radio wave utilization efficiency.

(Second Embodiment)
In the second embodiment of the present invention, control is performed to change the transmission power stepwise based on the predicted relative distance.

  The configuration of the in-vehicle terminal in the present embodiment is the same as that of the first embodiment and is as shown in FIG. In addition, the radio wave condition acquisition unit 4 in the present embodiment acquires the number of in-vehicle terminals existing around the terminal from the roadside device, and also acquires the noise level of the surroundings.

  The transmission power control process in this embodiment will be described using the flowchart of FIG. In steps S201 to S203, as in the case of the first embodiment, it is confirmed whether communication is performed and whether there is a communication partner.

In step S204, the other vehicle position information acquisition unit 32 acquires the position and traveling speed of the communication partner node. In step S205, the own vehicle position information acquisition unit 31 acquires the position and travel speed of the own vehicle.

  In step S206, the radio wave condition acquisition unit 4 acquires a surrounding noise level. In step S207, the radio wave condition acquisition unit 4 acquires the number of surrounding nodes.

  In step S208, the distance prediction unit 5 calculates the current relative position between the own node and the communication partner node and the relative position after a predetermined time. In step S209, the communication control unit 6 adjusts transmission power stepwise based on a matrix (table) in consideration of the relative position, the displacement of the relative position, the number of peripheral terminals, and noise.

  FIG. 6 is an example of a matrix used in this embodiment. In the matrix of FIG. 6, a matrix is used in which the current relative distance to the communication partner node and the displacement of the relative distance, the number of peripheral terminals, and noise are input. The relative distance is divided into two types, near or far, with a predetermined threshold as a reference. The displacement of the relative distance is divided into two types: approaching or leaving. The number of surrounding nodes is divided into two types, that is, whether the number is large or small with reference to a predetermined threshold, and the noise is also divided into two types, which are large or small with reference to the predetermined threshold. By controlling transmission power according to such a matrix, communication with appropriate transmission power is possible.

  An example of controlling transmission power according to a matrix will be described with reference to FIG. The upper graph in FIG. 7 is a graph showing transmission power control with the vertical axis representing transmission power and the horizontal axis representing time. The lower side of FIG. 7 is a table showing the relative distance to the communication partner node at each time point t1 to t5, the displacement of the relative distance, the number of surrounding nodes, and the noise level.

  At time t1, the relative distance to the communication partner node is long, the displacement of the relative distance is approaching, the number of surrounding nodes is small, and the noise is small. When the transmission power control in this state is read from the matrix of FIG. 6, it can be seen that the transmission power is lowered. Therefore, the communication control unit 6 performs control to lower the transmission power at time t1. Hereinafter, similarly at each time from t2 to t5, the communication control unit 6 controls the transmission power as specified in the matrix of FIG. 6 according to the surrounding situation.

  In FIG. 6, for example, the relative distance is classified into two types, near and far, but may be classified more finely according to the distance. Similarly, the displacement of the relative distance, the number of surrounding nodes, and the noise level can be finely classified. Also, the amount of adjustment for transmission power control may be changed according to conditions, without always adjusting a certain range.

  In addition to the relative distance, the displacement of the relative distance, the number of surrounding nodes, and the noise, a matrix that takes into account the reception intensity of the radio wave received from the communication partner can be created, and the transmission power can be controlled based on the matrix.

  In the present embodiment, the transmission power can be determined by a simple process by using a matrix.

It is a figure showing the functional block of the vehicle-mounted terminal in 1st Embodiment. It is a flowchart which shows the transmission power control process in 1st Embodiment. It is a figure explaining the transmission power control process in 1st Embodiment. It is a figure explaining the transmission power control process in 1st Embodiment. It is a flowchart which shows the transmission power control process in 2nd Embodiment. It is a figure explaining the transmission power control method in 2nd Embodiment. It is a figure which shows the example of the transmission power control in 2nd Embodiment. It is a figure which shows the electromagnetic wave condition at the time of using the conventional transmission power control. It is a figure which shows the electromagnetic wave condition at the time of using the conventional transmission power control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 In-vehicle terminal 2 Communication part 3 Position information acquisition part 4 Radio wave condition acquisition part 5 Distance prediction part 6 Communication control part 31 Own vehicle position information acquisition part 32 Other vehicle position information acquisition part A, B vehicle

Claims (6)

Wireless communication means;
A prediction means for predicting a relative distance after a predetermined time between the own node and the communication partner node;
Communication control means for controlling transmission power of the wireless communication means based on the predicted relative distance;
A mobile terminal. Having position information acquisition means for acquiring the position and movement speed of the own node and the position and movement speed of the communication partner node;
The mobile terminal according to claim 1, wherein the prediction unit predicts the relative distance based on information acquired by the position information acquisition unit. Radio wave condition acquisition means for acquiring a radio wave condition including at least one of the number of nodes existing around the own node, the noise level around the own node, and the radio wave intensity of the radio wave received from the communication partner node;
The mobile terminal according to claim 1 or 2, wherein the communication control unit controls transmission power in consideration of an acquired radio wave condition.   A vehicle comprising the mobile terminal according to claim 1. A mobile terminal that performs wireless communication
Predict the relative distance after a predetermined time between the own node and the communication partner node,
A transmission power control method for controlling transmission power based on the predicted relative distance. To mobile terminals that perform wireless communication,
Predicting the relative distance between the node and the correspondent node after a predetermined time;
A program that controls transmission power based on the predicted relative distance.

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