JP5606964B2 - Wireless communication device, transmission power determination method, program, and transmission power calculation device - Google Patents

Description

  The present invention relates to a wireless communication device or a method for determining transmission power of a wireless communication device.

  In inter-vehicle communication in next-generation ITS (Intelligent Transport Systems), services such as avoiding collisions at intersections by wirelessly broadcasting vehicle location information and allowing each vehicle to recognize each other's location information Is being considered.

  In addition, when wireless communication is performed, a workaround for the hidden terminal problem is important. As a workaround for the hidden terminal problem, an RTS (Request to Send) / CTS (Clear to Send) method is effective for one-to-one communication. However, the RTS / CTS method cannot be adopted in the above-mentioned inter-vehicle communication that requires broadcast communication between a plurality of unspecified vehicles. This is because, since the transmission destinations are a plurality of unspecified vehicles, it cannot be determined from which vehicle the communication is possible.

  Further, in Patent Document 1 below, an AP (access point: base station) obtains interference level information in a mobile terminal from the mobile terminal, thereby causing a hidden terminal (interference target terminal that becomes a noise source of the mobile terminal). The hidden terminal problem is solved by estimating the influence of the transmission and controlling the transmission power.

JP 2003-258719 A

  However, the technique described in Patent Document 1 above is a measure that is established in the relationship between an AP (base station) and a mobile terminal in a cellular system, and is based on vehicle-to-vehicle communication that does not use an AP as in the next-generation ITS. The technique described in Patent Document 1 cannot be applied to a wireless communication environment. This is because the technique described in Patent Document 1 focuses on only the communication quality between a specific mobile terminal and an AP.

  In inter-vehicle communication in next-generation ITS, the communication devices of each vehicle are in an equal position, and when the transmission power of a certain device is increased, the device may be a hidden terminal and adversely affect the communication of other communication devices. . Therefore, in the inter-vehicle communication in the next-generation ITS, the technique described in Patent Document 1 does not provide a countermeasure for the hidden terminal problem in the entire area where a plurality of vehicles exist.

  That is, in the technique described in Patent Document 1, a method for calculating the transmission power of the wireless device in consideration of the packet collision probability by the hidden terminal has not been established, and the hidden terminal from which CSMA (Carrier Sense Multiple Access) control does not work. Packet errors occur in communication packets due to interference with other transmission packets.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a vehicle-to-vehicle communication in which a base station does not exist. It is to reduce the influence on the communication of the wireless communication device.

In order to solve the above problems, the present invention is a wireless communication device that is mounted on a vehicle and wirelessly communicates with another wireless communication device mounted on another vehicle, for example,
Parameters of reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length T _h , frequency f, and allowable packet collision probability R _th Input information receiving means for receiving input; and
Input information holding means for holding each parameter received by the input information receiving means;
Region calculation means for calculating an area S of a region where a hidden terminal may exist using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit; ,
A hidden terminal number calculating means for calculating the number of hidden terminals N _c using the vehicle density ρ held by the input information holding means and the area S calculated by the area calculating means;
The input information holding means the held communication data amount B, the communication speed r, the frame length T _f, and by using the header length T _h, packet collisions when two wireless communication device sends a packet to a random A communication packet collision probability calculating means for calculating the probability R _p ;
The packet collision probability R attributed to the hidden terminal is calculated using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating means and the packet collision probability R _p calculated by the packet collision probability calculating means. A hidden terminal collision probability calculating means;
Transmission power for determining a transmission power P _{t at} which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating means is less than or equal to the allowable packet collision probability R _th held by the input information holding means. A determination means;
A wireless communication device is provided, comprising: a transmission unit that wirelessly transmits a packet with the transmission power determined by the transmission power determination unit.

  According to the present invention, in vehicle-to-vehicle communication in which no base station exists, it is possible to reduce the influence of radio waves transmitted by the wireless communication devices of the respective vehicles on the communication of the wireless communication devices of other vehicles as hidden terminals. .

1 is a system configuration diagram illustrating an example of a configuration of a vehicle-to-vehicle communication system 10 according to an embodiment of the present invention. 2 is a block diagram illustrating an example of a functional configuration of a wireless communication device 20 mounted on each vehicle 11. FIG. It is a figure which shows the example of calculation of vehicle density (rho). It is a conceptual diagram for demonstrating the calculation model of a hidden terminal. It is a figure which shows the example of calculation of the packet collision probability R resulting from a hidden terminal. It is a figure which shows the example of calculation of the packet collision probability R resulting from a hidden terminal. 5 is a flowchart illustrating an example of the operation of the wireless communication device 20. 2 is a diagram illustrating an example of a hardware configuration of a wireless communication device 20. FIG. 3 is a block diagram illustrating an example of a functional configuration of a transmission power calculation device 40. FIG. 3 is a diagram illustrating an example of a hardware configuration of a transmission power calculation device 40. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a system configuration diagram showing an example of a configuration of a vehicle-to-vehicle communication system 10 according to an embodiment of the present invention. The inter-vehicle communication system 10 includes a plurality of vehicles 11 on which wireless communication devices 20 are mounted.

  The wireless communication device 20 installed in each vehicle 11 follows the method of standardization work, for example, IEEE802.11p based on the wireless LAN technology, and the location information of the vehicle and the traffic information around the vehicle. Etc. are wirelessly transmitted to another wireless communication device 20. At that time, each wireless communication device 20 wirelessly transmits the information at a power level that can suppress the adverse effect on the communication of the other wireless communication device 20 as a hidden terminal.

  FIG. 2 is a block diagram illustrating an example of a functional configuration of the wireless communication device 20 mounted on each vehicle 11. The wireless communication device 20 includes an input information receiving unit 200, an input information holding unit 201, a first collision probability calculating unit 202, an area calculating unit 203, a hidden terminal number calculating unit 204, a second collision probability calculating unit 205, transmission power. A determination unit 206, a wireless communication unit 207, a reception data processing unit 208, and a transmission data processing unit 209 are provided.

  The wireless communication unit 207 modulates radio waves based on the transmission data generated by the transmission data processing unit 209, and transmits the modulated radio waves to other power via the antenna 210 with the transmission power determined by the transmission power determination unit 206. Transmit to the wireless communication device 20. In addition, the wireless communication unit 207 demodulates radio waves received via the antenna 210 to restore received data, and sends the restored received data to the received data processing unit 208.

The input information receiving unit 200 receives input information from a user of the wireless communication device 20 and causes the input information holding unit 201 to hold the received input information. In the present embodiment, the input information received by the input information receiving unit 200 includes reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length. T _h , frequency f, and allowable packet collision probability R _th are included.

Here, the reception sensitivity _Pr is, for example, the minimum reception power (dBm) for the wireless communication device 20 to obtain a desired communication quality. Further, the desired wave-to-interference wave ratio β is, for example, D / U (Desired to Undesired Signal ratio) (dB). The communication data amount B is, for example, the number of payload bits included in one packet. The communication speed r is, for example, the number of bits (bps) transmitted per unit time. The frame length _Tf is a certain period (second) for performing communication. Also, the header length T _h, a transmission time of the header included in a packet (s).

Here, the transmission time T _p of one packet is expressed by, for example, the following calculation formula (1) using the header length T _h , the communication data amount B, and the communication speed r.

Further, the frequency f is a frequency of a radio wave transmitted by the wireless communication device 20 (for example, 5.8 GHz). The allowable packet collision probability R _th is a packet collision probability allowed for the inter-vehicle communication system 10 and is, for example, 5% in the present embodiment. When each wireless communication device 20 increases the transmission power, the packet collision probability increases. However, each wireless communication device 20 in the present embodiment increases the transmission power within a range in which the packet collision probability can satisfy the _Rth or less. decide.

Further, the vehicle density ρ (car / km ² ) is calculated using, for example, the following calculation formula using the inter-vehicle distance W (m), the number of routes X (lines), the road interval Y (m), and the contribution rate Z (%). Calculated by (2).

In the present embodiment, as the vehicle density ρ (vehicles / km ² ), as shown in FIG. 3, three types of urban (U), sub-urban (SU), and rural (L) are assumed as an example. Note that the calculation method of the vehicle density ρ (units / km ² ) is not limited to the calculation formula (2), and is preferably optimized as appropriate according to the characteristics of the area where the wireless communication device 20 is used.

The area calculation unit 203 reads the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f from the input information holding unit 201, and uses these read data to set the light speed to c (km / s) and transmission. Assuming that the power is P _t (dBm), the area S (km ² ) of the region where the hidden terminal may exist is calculated by the following calculation formula (3), for example.

Here, for example, as shown in FIG. 4, if the distance to the farthest wireless communication device 20 with which the wireless communication device 20 located at the point P can communicate is defined as L ₁ , the wireless communication device 20 located at the point P. The amount of attenuation α at which the radio wave transmitted from the antenna attenuates to the lowest level of power that can be received in free space is determined by the light speed c (km / s), transmission power P _t (dBm), reception sensitivity P _r , and frequency f. It can be expressed as a function of the distance L ₁ (km) as shown in the following calculation formula (4).

When the calculation formula (4) is modified, the following calculation formula (5) is obtained.

For example, as shown in FIG. 4, when the wireless communication device 20 located at the point P is communicating with another wireless communication device 20, the farthest hidden terminal in which a packet error occurs due to the influence of the hidden terminal. Is defined as L ₂ (km), the distance L ₂ includes the speed of light c (km / s), transmission power P _t (dBm), reception sensitivity P _r , frequency f, and desired wave to interference ratio β. For example, it can be expressed as the following calculation formula (6).

Further, for example, since the area 30 indicated by the oblique lines in FIG. 4 is an area where there is a possibility that a hidden terminal exists, the area S (km ² ) of the area is calculated by, for example, the following calculation formula (7). The

To the equation (7), the above equation and L ₁ (5) and substituting the L ₂ of the above equation (6), can be obtained the above equation (3).

The hidden terminal number calculation unit 204 reads the vehicle density ρ from the input information holding unit 201, and uses the read vehicle density ρ and the area S calculated by the region calculation unit 203, for example, the following calculation formula (8) Thus, the number N _{c of} hidden terminals is calculated.

First collision probability calculating unit 202, a communication data amount B reads the communication rate r, a frame length T _f, and the header length T _h from the input data storing unit 201, the read using these data, the calculation of the above The packet collision probability R _p when two wireless communication devices transmit packets at random is calculated by the equation (1) and the following equation (9).

The second collision probability calculation unit 205 uses the number of hidden terminals N _c calculated by the hidden terminal number calculation unit 204 and the packet collision probability R _p calculated by the first collision probability calculation unit 202, For example, the packet collision probability R caused by the hidden terminal is calculated by the following calculation formula (10).

The transmission power determining unit 206 reads the allowable packet collision probability R _th from the input information holding unit 201, and the packet collision probability R caused by the hidden terminal calculated by the second collision probability calculating unit 205 is the input information holding unit 201. For example, the transmission power P _t satisfying the following calculation formula (11) is determined so as to be equal to or less than the permissible packet collision probability R _th read from.

The transmission power determining section 206, from the viewpoint of transmitting the information to the wireless communication device 20 of the vehicle 11 located wider range, for example, the largest of the transmit power P _t that satisfies the above equation (11) It is preferable to determine the power as the transmission power P _t .

5 and 6 are diagrams illustrating calculation examples of the packet collision probability R caused by the hidden terminal. In the calculation examples shown in FIGS. 5 and 6, the reception sensitivity P _r , the desired wave to interference ratio β, the communication data amount B, the frame length T _f , the header length T _h , and the frequency f are fixed values, and the communication speed r For some combinations of transmission power P _t and vehicle density ρ, packet collision probability R due to the hidden terminal is calculated.

In the calculation examples shown in FIGS. 5 and 6, the transmission speed r is three ways of 54 Mbps, 12 Mbps, and 6 Mbps, the transmission power P _t is four ways of 0 dBm, 10 dBm, 20 dBm, and 30 dBm, and the vehicle density ρ is 267. Three values are used: (unit / km ² ) (urban), 120 (unit / km ² ) (sub-urban), and 50 (unit / km ² ) (rural).

Further, in the calculation examples shown in FIGS. 5 and 6, the desired wave to jamming wave ratio β is 6 (dB), the communication data amount B is 1000 (bits), the frame length T _f is 100 (milliseconds), and the header length T _h is fixed at 24 (μ seconds) and the frequency f is fixed at 5.8 (GHz). Also, the receiver sensitivity P _r, -89 dBm because it depends on the communication speed r, -74 dBm if the communication speed r is 54 Mbps, -80 dBm if the communication speed r is 12Mbps, when the communication speed r is 6Mbps It is fixed to.

In the packet collision probability R due to the hidden terminal in FIGS. 5 and 6, the allowable packet collision probability R _th (see FIG. 5) at any vehicle density ρ of Urban (U), Sub Urban (SU), and Rural (L). for the combination of 5%) or less and comprising transmitting a communication speed r power P _t is in the 5 and 6 example are denoted by the ○ labeled on the rightmost column of the table of Figure 5 and 6.

As can be seen from the calculation results of FIGS. 5 and 6, when the communication speed r is 54 Mbps, the transmission power P _{t is set} to 0 (dBm) or 10 (dBm), so that the urban (U) and the sub-urban (SU) , And in the vehicle density ρ of the rural (L), it is possible to perform communication with a communication quality in which the packet collision probability R caused by the hidden terminal is lower than the allowable packet collision probability R _th . Further, if the communication speed r is 12 Mbps, the transmission power P _{t is set} to 0 (dBm), so that the vehicle density ρ of any of Urban (U), Sub Urban (SU), and Rural (L) can be obtained. Communication can be performed with a communication quality in which the packet collision probability R caused by the hidden terminal is lower than the allowable packet collision probability R _th . Such transmission power P _t satisfies the above-described calculation formula (11).

As described above, the wireless communication device 20 determines the transmission power P _t that satisfies the above-described calculation formula (11), thereby performing communication in which the packet collision probability R caused by the hidden terminal is equal to or less than the allowable packet collision probability R _th. Can be realized.

  FIG. 7 is a flowchart illustrating an example of the operation of the wireless communication device 20. For example, at a predetermined timing such as when the input information in the input information holding unit 201 is updated, the wireless communication device 20 starts the operation illustrated in this flowchart.

First, the area calculation unit 203 reads out the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f from the input information holding unit 201, and uses these read out data according to the above-described calculation formula (3). Then, the area S of the area where the hidden terminal may exist is calculated (S100).

Next, the hidden terminal number calculation unit 204 reads the vehicle density ρ from the input information holding unit 201, and uses the read vehicle density ρ and the area S calculated in step S100, the above-described calculation formula (8). Thus, the number N _{c of} hidden terminals is calculated (S101).

Next, the first collision probability calculating unit 202, a communication data amount B reads the communication rate r, a frame length T _f, and the header length T _h from the input data storing unit 201, the read using these data, The packet collision probability R _p when two wireless communication devices transmit packets at random is calculated by the above-described calculation formula (9) (S102).

Next, the second collision probability calculation unit 205 uses the number N _{c of} hidden terminals calculated in step S101 and the packet collision probability R _p calculated in step S102 to calculate the above equation (10). Thus, the packet collision probability R caused by the hidden terminal is calculated (S103).

Next, the transmission power determination unit 206 reads the allowable packet collision probability R _th from the input information holding unit 201, and the packet collision probability R caused by the hidden terminal calculated by the second collision probability calculation unit 205 is determined based on the input information. The transmission power P _t that satisfies the above-described calculation formula (11) is determined so as to be equal to or less than the allowable packet collision probability R _th read from the holding unit 201 (S104).

The wireless communication unit 207 starts the transmission of the radio wave at the transmission power P _t determined in step 104 (S105).

  FIG. 8 is a diagram illustrating an example of a hardware configuration of the wireless communication device 20. The wireless communication device 20 includes a central processing unit (CPU) 21, a random access memory (RAM) 22, a read only memory (ROM) 23, a wireless device 24, and an input interface (I / F) 25.

  The CPU 21 operates based on a program stored in the ROM 23 and controls each part. The ROM 23 is a rewritable flash ROM, for example, and stores a program executed by the CPU 21 when the wireless communication device 20 is activated, a boot program depending on the hardware of the wireless communication device 20, and the like.

  The radio 24 receives and demodulates radio waves from the other radio communication devices 20 via the antenna 210, reproduces data contained in the radio waves, and sends it to the CPU 21. The wireless device 24 modulates the radio wave based on the data generated by the CPU 21 and transmits the modulated radio wave to the other radio communication device 20 via the antenna 210 with the transmission power instructed by the CPU 21. The input interface 25 acquires data from the outside and sends the acquired data to the CPU 21.

  The CPU 21 of the wireless communication device 20 executes the program loaded on the RAM 22, thereby executing the input information receiving unit 200, the first collision probability calculating unit 202, the region calculating unit 203, the hidden terminal number calculating unit 204, the second The functions of the collision probability calculation unit 205, the transmission power determination unit 206, the wireless communication unit 207, the reception data processing unit 208, and the transmission data processing unit 209 are realized. The ROM 23 stores data in the input information holding unit 201.

  The CPU 21 of the wireless communication device 20 obtains these programs from the outside via the input interface 25, stores them in the ROM 23, reads them from the ROM 23, and executes them. As another example, these programs are obtained by wireless communication or the like. You may acquire from another apparatus.

  The embodiment of the present invention has been described above.

  As is clear from the above description, according to the inter-vehicle communication system 10 of the present embodiment, in the inter-vehicle communication in which no base station exists, the radio wave transmitted by the wireless communication device 20 of each vehicle 11 is another hidden terminal. The influence on the communication of the wireless communication device 20 of the vehicle 11 can be reduced, and wireless data communication with higher quality can be realized.

  In addition, this invention is not limited to above-described embodiment, Many deformation | transformation are possible within the range of the summary.

For example, in the above-described embodiment, the area calculation unit 203 calculates the area S of the area where the hidden terminal may exist using the illustrated calculation formula (3), and the hidden terminal number calculation unit 204 The number N _{c of} hidden terminals is calculated using the calculated formula (8), and the first collision probability calculating unit 202 uses the calculated formula (9) to allow the two wireless communication devices to randomly transmit packets. The packet collision probability R _p in the case of transmission is calculated, and the second collision probability calculation unit 205 calculates the packet collision probability R caused by the hidden terminal using the illustrated calculation formula (10), and the transmission power determination unit 206 determines the transmission power P _t using the illustrated calculation formula (11), but the present invention is not limited to this, and each functional unit calculates or determines each value using another calculation formula. You may do it. Other formulas other than free space loss include formulas that consider building density (Okumura / Hagi) and formulas that consider antenna height.

  In the above-described embodiment, the input information receiving unit 200 receives input information from the user and holds the input information in the input information holding unit 201. However, the present invention is not limited to this. For example, an input information generation device that collects information such as the location of the wireless communication device 20 and surrounding radio wave conditions from various sensors and generates part or all of the input information using the collected information is provided in the vehicle 11. The input information receiving unit 200 may receive the input information generated by the input information generation device and cause the input information holding unit 201 to hold the input information. Then, the first collision probability calculation unit 202, the region calculation unit 203, the hidden terminal number calculation unit 204, the second collision probability calculation unit 205, and the transmission power determination unit 206 are configured so that the input information in the input information holding unit 201 is Each time it is updated, each process may be executed to determine the transmission power.

  Also, in the input information holding unit 201, a plurality of values are prepared in advance as respective input information, and the first collision probability calculation unit 202, the region calculation unit 203, the hidden terminal number calculation unit 204, the second collision probability. The calculation unit 205 and the transmission power determination unit 206 determine which values are used as input information as needed according to input signals from various sensors, and determine transmission power each time using the determined values. You may do it. For example, the vehicle density ρ may be associated with each region on the map in advance, and the vehicle density ρ of the region where the vehicle 11 is located may be used based on the GPS signal.

  In the above-described embodiment, the wireless communication device 20 mounted on each vehicle 11 calculates and determines transmission power that can reduce the influence on the communication of the wireless communication device 20 of the other vehicle 11 as a hidden terminal. However, the present invention is not limited to this. For example, a device that calculates transmission power that can reduce the influence on communication of the wireless communication device 20 of another vehicle 11 as a hidden terminal, and a wireless communication device 20 that transmits radio waves with the transmission power calculated by the device. And may be configured separately.

  For example, as shown in FIG. 9, an input information receiving unit 200, an input information holding unit, and a device for calculating transmission power that can reduce the influence on the communication of the wireless communication device 20 of another vehicle 11 as a hidden terminal. A transmission power calculation apparatus 40 including 201, a first collision probability calculation unit 202, a region calculation unit 203, a hidden terminal number calculation unit 204, a second collision probability calculation unit 205, and a transmission power determination unit 206 is conceivable.

  Since the functional units included in the transmission power calculation device 40 illustrated in FIG. 9 have the same functions as the functional units denoted by the same reference numerals in FIG. 2 except for the points described below, description thereof will be omitted. The input information receiving unit 200 receives input information via an input device such as a keyboard or a mouse, and causes the input information holding unit 201 to hold the received input information.

The transmission power determining unit 206 reads the allowable packet collision probability R _th from the input information holding unit 201, and the packet collision probability R caused by the hidden terminal calculated by the second collision probability calculating unit 205 is the input information holding unit 201. The transmission power P _t satisfying the above-described calculation formula (11) is determined so that the allowable packet collision probability R _th read from the data is less than or equal to, and information indicating the determined transmission power P _t is output to an output device such as a monitor or a printer Output to.

The transmission power calculation device 40 illustrated in FIG. 9 is configured so that the user can change the input information such as the reception sensitivity P _r , the desired wave-to-jamming wave ratio β, and the vehicle density ρ to various values while changing the optimum transmission power P It can be used as a simulator for determining _t . Then, the wireless communication device 20 transmits radio waves with the transmission power calculated by the transmission power calculation device 40. In this case, the wireless communication device 20 includes an input information receiving unit 200, an input information holding unit 201, a first collision probability calculating unit 202, an area calculating unit 203, a hidden terminal number calculating unit 204, and a second collision probability calculating unit. 205 and the transmission power determination unit 206 do not need to be provided, a memory for storing the transmission power calculated by the transmission power calculation device 40 is provided in the wireless communication device 20, and the wireless communication unit 207 is stored in the memory. It may be configured to transmit radio waves with the transmission power that is present.

  Such a transmission power calculation device 40 is configured by hardware as shown in FIG. 10, for example. The transmission power calculation device 40 includes a CPU 41, a RAM 42, a ROM 43, an HDD 44, an input interface 45, an output interface 46, and a media interface 47.

  The CPU 41 operates based on a program stored in the ROM 43 or the HDD 44 and controls each part. The ROM 43 stores a boot program executed by the CPU 41 when the transmission power calculation device 40 is activated, a program depending on the hardware of the transmission power calculation device 40, and the like.

  The HDD 44 stores a program executed by the CPU 41, data used by the program, and the like. The CPU 41 controls an input device such as a keyboard and a mouse via the input interface 45 and acquires data from the input device via the input interface 45. The CPU 41 controls an output device such as a display or a printer via the output interface 46 and outputs the generated data to the output device via the output interface 46.

  The media interface 47 reads a program or data stored in the recording medium 48 and provides it to the CPU 41 via the RAM 42. The CPU 41 loads the program from the recording medium 48 onto the RAM 42 via the media interface 47 and executes the loaded program. The recording medium 48 is, for example, an optical recording medium such as a DVD (Digital Versatile Disk) or PD (Phase change rewritable disk), a magneto-optical recording medium such as an MO (Magneto-Optical disk), a tape medium, a magnetic recording medium, or a semiconductor memory. Etc.

  The CPU 41 of the transmission power calculation device 40 executes a program loaded on the RAM 42 to thereby execute an input information reception unit 200, a first collision probability calculation unit 202, an area calculation unit 203, a hidden terminal number calculation unit 204, a first 2 functions of the collision probability calculation unit 205 and the transmission power determination unit 206 are realized. The ROM 43 or the HDD 44 stores data in the input information holding unit 201.

  The CPU 41 of the transmission power calculation device 40 reads these programs from the recording medium 48 and executes them, but as another example, these programs may be acquired from other devices via a communication line.

DESCRIPTION OF SYMBOLS 10 ... Inter-vehicle communication system, 11 ... Vehicle, 20 ... Wireless communication device, 200 ... Input information reception part, 201 ... Input information holding part, 202 ... First collision probability Calculation unit, 203 ... area calculation unit, 204 ... hidden terminal number calculation unit, 205 ... second collision probability calculation unit, 206 ... transmission power determination unit, 207 ... wireless communication unit, 208: reception data processing unit, 209: transmission data processing unit, 210 ... antenna, 30 ... area, 40 ... transmission power calculation device

Claims (10)

A wireless communication device mounted on a vehicle and wirelessly communicating with another wireless communication device mounted on another vehicle,
Parameters of reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length T _h , frequency f, and allowable packet collision probability R _th Input information receiving means for receiving input; and
Input information holding means for holding each parameter received by the input information receiving means;
Region calculation means for calculating an area S of a region where a hidden terminal may exist using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit; ,
A hidden terminal number calculating means for calculating the number of hidden terminals N _c using the vehicle density ρ held by the input information holding means and the area S calculated by the area calculating means;
The input information holding means the held communication data amount B, the communication speed r, the frame length T _f, and by using the header length T _h, packet collisions when two wireless communication device sends a packet to a random A communication packet collision probability calculating means for calculating the probability R _p ;
The packet collision probability R attributed to the hidden terminal is calculated using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating means and the packet collision probability R _p calculated by the packet collision probability calculating means. A hidden terminal collision probability calculating means;
Transmission power for determining a transmission power P _{t at} which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating means is less than or equal to the allowable packet collision probability R _th held by the input information holding means. A determination means;
A wireless communication device comprising: transmission means for wirelessly transmitting a packet with the transmission power determined by the transmission power determination means. The wireless communication device according to claim 1,
The area calculating means includes
The light speed is c, the transmission power is P _t, and using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit, the following calculation formula (1): Calculate the area S of the area where the hidden terminal may exist,

The hidden terminal number calculating means is:
Using the vehicle density ρ held by the input information holding unit and the area S calculated by the region calculation unit, the number N _{c of} hidden terminals is calculated by the following calculation formula (2):

The communication packet collision probability calculating means includes:
Using the communication data amount B, the communication speed r, the frame length T _f , and the header length T _h held by the input information holding means, two wireless communication devices are randomly selected according to the following calculation formula (3). Packet collision probability R _p when a packet is transmitted to

The hidden terminal collision probability calculating means is
Using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating means and the packet collision probability R _p calculated by the packet collision probability calculating means, the hidden terminal is determined by the following calculation formula (4). Calculate the resulting packet collision probability R,

The transmission power determination means includes
The following equation (5) is satisfied, in which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating unit is equal to or less than the allowable packet collision probability R _th held by the input information holding unit. wireless communication device and determining a transmit power P _t.

The wireless communication device according to claim 2,
The transmission power determination means includes
A wireless communication device characterized in that the maximum transmission power among the transmission powers satisfying the calculation formula (5) is determined as the transmission power at which the transmission means wirelessly transmits a packet.   A vehicle-to-vehicle communication system comprising a plurality of vehicles provided with the wireless communication device according to any one of claims 1 to 3. A transmission power determination method in a transmission power calculation device that calculates transmission power of a wireless communication device that is mounted on a vehicle and wirelessly communicates with another wireless communication device mounted on another vehicle,
The transmission power calculation device
Parameters of reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length T _h , frequency f, and allowable packet collision probability R _th An input information receiving step for receiving input and holding each received parameter in the input information holding means;
A region calculation step of calculating an area S of a region where a hidden terminal may exist using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit; ,
A hidden terminal number calculating step of calculating the number of hidden terminals N _c using the vehicle density ρ held by the input information holding means and the area S calculated in the region calculating step;
The input information holding means the held communication data amount B, the communication speed r, the frame length T _f, and by using the header length T _h, packet collisions when two wireless communication device sends a packet to a random A communication packet collision probability calculating step for calculating the probability R _p ;
A hidden terminal that calculates a packet collision probability R attributed to a hidden terminal using the number N _{c of} hidden terminals calculated in the hidden terminal number calculation step and the packet collision probability R _p calculated in the packet collision probability calculation step A collision probability calculation step;
Transmission power determination for determining a transmission power P _{t at} which the packet collision probability R caused by the hidden terminal calculated in the hidden terminal collision probability calculating step is equal to or less than the allowable packet collision probability R _th held by the input information holding means. Steps,
And a step of outputting information indicating the transmission power determined in the transmission power determination step. The transmission power determination method according to claim 5,
The transmission power calculation device
In the region calculation step, the following calculation is performed using c as the speed of light and P _{t as} the transmission power, and using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding means. Using the equation (1), the area S of the area where the hidden terminal may exist is calculated,

In the hidden terminal number calculating step, using the vehicle density ρ held by the input information holding means and the area S calculated in the region calculating step, the number N _{c of} hidden terminals is calculated by the following formula (2). To calculate

In the communication packet collision probability calculating step, the input information holding means holding the communication data amount has B, communication speed r, using a frame length T _f, and the header length T _h, by the following calculation equation (3) Calculate the packet collision probability R _p when two wireless communication devices randomly transmit packets,

In the hidden terminal collision probability calculating step, using the number N _{c of} hidden terminals calculated in the hidden terminal number calculating step and the packet collision probability R _p calculated in the packet collision probability calculating step, the following calculation formula ( 4) to calculate the packet collision probability R caused by the hidden terminal,

In the transmission power determination step, the following calculation in which the packet collision probability R caused by the hidden terminal calculated in the hidden terminal collision probability calculation step is equal to or less than the allowable packet collision probability R _th held by the input information holding unit. A transmission power determination method characterized by determining a transmission power P _t satisfying equation (5).

A program that causes a computer to operate as a transmission power calculation device that calculates transmission power of a wireless communication device that is mounted on a vehicle and wirelessly communicates with another wireless communication device that is mounted on another vehicle,
In the computer,
Parameters of reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length T _h , frequency f, and allowable packet collision probability R _th An input information reception function that accepts input and holds each received parameter in the database;
A region calculation function for calculating an area S of a region where a hidden terminal may exist, using the reception sensitivity P _r , the desired wave to interference ratio β, and the frequency f held in the database;
A hidden terminal number calculating function for calculating the number N _{c of} hidden terminals using the vehicle density ρ held in the database and the area S calculated by the area calculating function;
Packet collision probability R _p when two wireless communication devices randomly transmit packets using communication data amount B, communication speed r, frame length T _f , and header length T _h held in the database. A communication packet collision probability calculation function for calculating
The packet collision probability R caused by the hidden terminal is calculated using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating function and the packet collision probability R _p calculated by the packet collision probability calculating function. Hidden terminal collision probability calculation function,
Transmission power for determining the transmission power P _t that causes the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculation function to be less than or equal to the allowable packet collision probability R _th held by the input information holding means. A decision function;
A program for realizing an output function for outputting information indicating transmission power determined by the transmission power determination function. The program according to claim 7,
The area calculation function is:
Using the reception speed P _r , desired signal to interference ratio β, and frequency f stored in the database, the light speed is c, the transmission power is P _t , and the hidden terminal is calculated by the following calculation formula (1). Calculate the area S of the region where

The hidden terminal number calculation function is:
Using the vehicle density ρ held in the database and the area S calculated by the region calculation function, the number N _{c of} hidden terminals is calculated by the following calculation formula (2),

The communication packet collision probability calculation function is
Using the communication data amount B, the communication speed r, the frame length T _f , and the header length _Th that the database holds, the two wireless communication devices randomly transmit packets by the following calculation formula (3). Calculate the packet collision probability R _p when transmitted,

The hidden terminal collision probability calculation function is
A number N _c of hidden terminals calculated by the hidden terminal number calculation function, using said packet collision probability calculation function packet collision probability is calculated by R _p, the following calculation equation (4), the hidden terminal Calculate the resulting packet collision probability R,

The transmission power determination function is
The following equation (5) is satisfied, in which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating function is equal to or less than the allowable packet collision probability R _th held by the input information holding unit. program and determines the transmit power P _t.

A transmission power calculation device that calculates transmission power of a wireless communication device that is mounted on a vehicle and wirelessly communicates with another wireless communication device that is mounted on another vehicle,
Parameters of reception sensitivity P _r , desired wave to jamming ratio β, vehicle density ρ, communication data amount B, communication speed r, frame length T _f , header length T _h , frequency f, and allowable packet collision probability R _th Input information receiving means for receiving input; and
Input information holding means for holding each parameter received by the input information receiving means;
Region calculation means for calculating an area S of a region where a hidden terminal may exist using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit; ,
A hidden terminal number calculating means for calculating the number of hidden terminals N _c using the vehicle density ρ held by the input information holding means and the area S calculated by the area calculating means;
The input information holding means the held communication data amount B, the communication speed r, the frame length T _f, and by using the header length T _h, packet collisions when two wireless communication device sends a packet to a random A communication packet collision probability calculating means for calculating the probability R _p ;
The packet collision probability R attributed to the hidden terminal is calculated using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating means and the packet collision probability R _p calculated by the packet collision probability calculating means. A hidden terminal collision probability calculating means;
Transmission power for determining a transmission power P _{t at} which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating means is less than or equal to the allowable packet collision probability R _th held by the input information holding means. A transmission power calculation apparatus comprising: a determination unit; and an output unit that outputs information indicating the transmission power determined by the transmission power determination unit. The transmission power calculation apparatus according to claim 9, wherein
The region calculation means includes
The light speed is c, the transmission power is P _t, and using the reception sensitivity P _r , the desired wave-to-interference wave ratio β, and the frequency f held by the input information holding unit, the following calculation formula (1): Calculate the area S of the area where the hidden terminal may exist,

The hidden terminal number calculating means is:
Using the vehicle density ρ held by the input information holding unit and the area S calculated by the region calculation unit, the number N _{c of} hidden terminals is calculated by the following calculation formula (2):

The communication packet collision probability calculating means includes:
Using the communication data amount B, the communication speed r, the frame length T _f , and the header length T _h held by the input information holding means, two wireless communication devices are randomly selected according to the following calculation formula (3). Packet collision probability R _p when a packet is transmitted to

The hidden terminal collision probability calculating means is
Using the number N _{c of} hidden terminals calculated by the hidden terminal number calculating means and the packet collision probability R _p calculated by the packet collision probability calculating means, the hidden terminal is determined by the following calculation formula (4). Calculate the resulting packet collision probability R,

The transmission power determination means includes
The following equation (5) is satisfied, in which the packet collision probability R caused by the hidden terminal calculated by the hidden terminal collision probability calculating unit is equal to or less than the allowable packet collision probability R _th held by the input information holding unit. transmission power calculating unit and determines a transmit power P _t.

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