JP5246409B2 - Mobile communication device and communication control method - Google Patents

Description

  The present invention relates to a mobile communication device and a communication control method.

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, advanced road traffic systems that improve the safety of vehicles by receiving information from infrastructure devices installed on the road and utilizing this information have been studied. (For example, refer to Patent Document 1).
This traffic system is mainly composed of a plurality of roadside communication devices that are wireless communication devices on the infrastructure side, and in-vehicle communication devices (mobile communication devices) that are wireless communication devices mounted on each vehicle.

In this case, a combination of communication performed between communication subjects includes road-to-road communication between road-side communication devices, road-to-vehicle (or vehicle-road) communication between road-side communication devices and vehicle-mounted communication devices, and vehicle-mounted communication. Vehicle-to-vehicle communication performed between aircraft.
Japanese Patent No. 2806801

In the above-described intelligent road traffic system, in order to coexist each communication such as inter-vehicle communication, road-to-vehicle communication, and road-to-road communication, it becomes a problem how to perform communication control using the frequency band effectively. Therefore, it has been studied that multiple access is used to perform communication between roads, road vehicles, and vehicles within a limited band.
As this multi-access method, there are frequency division multiplexing (FDMA) and code division multiple access (CDMA), but only in-vehicle communication devices in areas where roadside communication devices are not installed. For example, an autonomous random access method typified by CSMA (Carrier Sense Multiple Access) is preferably adopted as the multi-access method as the inter-vehicle communication that is assumed to be performed.

  Here, in general, when providing blind spot information such as right-straight / left-turn insertion, road-to-vehicle communication is superior to vehicle-to-vehicle communication in terms of restrictions on installation location and equipment capacity. Information can be provided. Therefore, road-to-vehicle communication should be given priority over vehicle-to-vehicle communication.

In order to prioritize road-to-vehicle communication, it is conceivable to allocate a time zone for roadside communication devices that can be transmitted only by roadside communication devices, and prohibit vehicle-to-vehicle communication within the time zone.
In this case, the inter-vehicle communication is performed in a time zone other than the time zone for the roadside communication device.
However, the in-vehicle communication device needs to acquire information on the time zone for the roadside communication device so that the inter-vehicle communication is not performed in the time zone for the roadside communication device.

By the way, as described above, in vehicle-to-vehicle communication, a carrier sense communication method such as CSMA is preferable, but due to the presence of a “hidden terminal”, vehicle-to-vehicle communication interferes with road-to-vehicle communication to be prioritized. there is a possibility.
A “hidden terminal” is a terminal (vehicle communication device) that does not know the time zone for a roadside communication device in an area where road-to-vehicle communication can be performed. For example, a vehicle (in-vehicle communication device) that exists in a suburb where no roadside communication device is installed and performs only vehicle-to-vehicle communication enters a busy street where roadside communication devices are lined up, or a vehicle (in-vehicle When a communicator enters a main street where radio waves from a roadside communication device reach from a narrow street where radio waves from the roadside communication device do not reach, a hidden terminal occurs.

  When a hidden terminal occurs, the hidden terminal does not know the time zone for the roadside communication device, so it transmits a signal even in the time zone for the roadside communication device, and the signal interferes with the road-vehicle communication. There is a possibility.

Therefore, in order to prevent interference with road-to-vehicle communication, it is necessary to inform the in-vehicle communication device that does not know the time zone for the roadside communication device of the time zone for the roadside communication device as soon as possible. .
Therefore, an object of the present invention is to make it easier for an in-vehicle communication device (mobile communication device) that does not know the time zone for roadside communication devices to know the time zone for roadside communication devices, and to suppress the presence of hidden terminals. To do.

  (1) The present invention is a mobile communication device that performs wireless communication by a carrier sense method, and includes a transmitter for transmitting a radio signal, and a radio signal in a propagation path for acquiring a transmission opportunity by the transmitter A carrier sense control unit for detecting the roadside slot, an acquisition unit for acquiring roadside slot information indicating a time zone for a roadside communication device assigned to the roadside communication device, and acquiring the roadside slot information, In order to transfer to the mobile communication device, when the radio signal including the roadside slot information is transmitted from the transmitter, the information transfer unit and the roadside slot information are acquired, than when the roadside slot information is not acquired, The communication conditions are adjusted so that the radio signal transmitted by the transmitter is received by another mobile communication device that has not acquired the roadside slot information. That it comprises a, an adjustment unit for performing a mobile communication device according to claim.

According to the present invention, when the mobile communication device acquires the roadside slot information indicating the time zone for the roadside communication device, the slot information is transferred to another mobile communication device, so that the mobile communication device cannot communicate directly with the roadside communication device. Even a mobile communication device can acquire roadside slot information.
Moreover, when the mobile communication device acquires the roadside slot information, the radio signal transmitted by the transmission unit of the mobile communication device is improved so that the opportunity to be received by the mobile communication device that has not acquired the roadside slot information is improved. Since the communication conditions of the mobile communication device are adjusted, a mobile communication device that has not acquired roadside slot information can acquire roadside slot information more reliably.

(2) When the adjustment unit acquires the roadside slot information, the wireless signal transmitted by the transmission unit is detected by carrier sense performed by the other mobile communication device, compared to when the roadside slot information is not acquired. It is preferable to adjust the communication conditions so that the probability of being increased. In this case, since the probability that the radio signal transmitted by the transmitter is detected by carrier sense performed by another mobile communication device increases, the radio signal transmitted by the transmitter is received by the other mobile communication device. Opportunities to improve.

(3) It is preferable that the adjustment of the communication condition performed by the adjustment unit is a shortening of a transmission opportunity acquisition time interval. In this case, the transmission opportunity by a transmission part increases, and the opportunity that the radio signal which the transmission part transmitted is received by another mobile communication apparatus improves. In order to shorten the transmission opportunity acquisition time interval, the transmission waiting time (transmission cycle) is shortened, or the back-off time in the CAMA system (the time from when no signal is detected by carrier sense until actual transmission starts). ) Should be shortened.

(4) It is preferable that the adjustment of the communication condition performed by the adjustment unit is an increase in transmission power of the transmission unit. In this case, when the transmission power is increased, the radio signal transmitted by the transmission unit is easily received by another mobile communication device, and the reception opportunity at the other mobile communication device is improved.

(5) When the adjusting unit acquires the roadside slot information, the probability that the carrier sense control unit detects a radio signal transmitted by the other mobile communication device, compared to when the roadside slot information is not acquired. It is preferable to reduce the carrier sense sensitivity in the carrier sense control unit so as to decrease.
In this case, since the carrier sense sensitivity of the mobile communication device that acquired the roadside slot information decreases, even if the mobile communication device that acquired the roadside slot information performs carrier sense, it detects the radio signal transmitted by another mobile communication device. It becomes difficult to do. Therefore, transmission opportunities by the mobile communication device that has acquired the roadside slot information are increased, and as a result, reception opportunities at other mobile communication devices are improved.

(6) It is preferable that the said adjustment part returns the said communication conditions to the value before adjustment, when the said road side slot information is acquired and predetermined time passes. By acquiring the roadside slot information and returning the communication condition after a predetermined time has elapsed, it is possible to prevent the communication condition from being adjusted even after leaving the roadside communication device.

(7) When the roadside slot is not acquired, communication in which the radio signal transmitted by the roadside communication device is received by other mobile communication devices more frequently than the radio signal transmitted by the transmission unit. It is preferable to transmit a radio signal under conditions. Since the mobile communication device that has not acquired the roadside slot does not know the time zone that the roadside communication device transmits, it transmits in the time zone that the roadside communication device transmits. May interfere with reception of the signal. However, as described above, the wireless signal transmitted by the roadside communication device transmits the wireless signal under a communication condition that increases the chance of being received by the other mobile communication device. The possibility of obstructing reception of signals from the roadside communication device is reduced. For this purpose, for example, a mobile communication device that has not acquired roadside slot information transmits with a transmission power sufficiently smaller than the transmission power of the roadside communication device, or a mobile communication device that has not acquired roadside slot information can perform roadside communication. What is necessary is just to detect the electric power of the signal received from an apparatus and to transmit with power smaller than the received power.

(8) According to another aspect of the present invention, when the mobile communication device acquires the roadside slot information indicating the time zone for the roadside communication device assigned to the roadside communication device, the mobile communication device from the time when the roadside timing information is not acquired. Also, adjusting the communication conditions of the mobile communication device so that the chance that the radio signal transmitted by the mobile communication device is received by another mobile communication device that has not acquired the roadside slot information is improved, The communication control method is characterized in that the roadside slot information is transmitted to the other mobile communication device.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a mobile communication apparatus in the state which cannot communicate directly with a roadside communication apparatus, it becomes easy to acquire roadside slot information.

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS).
As shown in FIG. 1, the intelligent traffic system includes a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, and an in-vehicle communication device (mobile communication device) 3. Including vehicles 5 and the like.

Each traffic signal 1 is installed at each of a plurality of intersections Ci (i = 1 to 12 in the figure), and is connected to a router 8 via a communication line 7 such as a telephone line. This router 8 is connected to the central device 4 in the traffic control center.
The central device 4 constitutes a LAN (Local Area Network) with the traffic signal device 1 and the roadside communication device 2 of each intersection Ci included in the monitoring area under its control. Therefore, the central device 4 can perform bidirectional communication with each traffic signal 1 and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

  In FIG. 1 and FIG. 2, for simplification of illustration, only one signal lamp is depicted at each intersection Ci, but at each actual intersection Ci, at least 4 for ascending and descending roads intersecting each other. There are two signal lights.

[Wireless communication systems, etc.]
FIG. 2 is a road plan view showing a part of the monitoring area of the intelligent road traffic system.
In FIG. 2, each of two roads intersecting each other is illustrated as one lane on one side in the up and down directions, but the road structure is not limited to this.
As shown also in FIG. 2, the traffic system of this embodiment includes a plurality of roadside communication devices 2 capable of wireless communication with the in-vehicle communication device 3, and other communication devices using a carrier sense method (CSMA / CA). 2 and 3 and an in-vehicle communication device 3 that is a kind of mobile wireless transceiver that performs wireless communication.

The plurality of roadside communication devices 2 are installed at each roadside intersection, and are attached to the pillars of the traffic signal device 2 in the examples of FIGS. 1 and 2. On the other hand, the in-vehicle communication device 3 is mounted on each vehicle 5 traveling on the road.
Each roadside communication device 2 has a communication area A of a predetermined range extending around the roadside communication device 2 and can communicate with the in-vehicle communication device 3 of each vehicle 5 traveling in the communication area A. The communication area A is an area where the roadside communication device 2 is transmitting radio waves, and the in-vehicle communication device 3 is an area where the radio waves can be received.

  In the traffic system (communication system) of the present embodiment, wireless communication is used between the roadside communication devices 2 (communication between roadways), and between the roadside communication device 2 and the in-vehicle communication device 3 (from the “road”). Wireless communication is also used for both the vehicle-to-vehicle communication to “car” and the vehicle-to-vehicle communication from “car” to “road”. . The same communication band is used for these communications.

In the communication system of this embodiment, since the transmission of the roadside communication device 2 is prioritized over the transmission of the in-vehicle communication device 3, a time (slot) for the roadside communication device 2 to transmit is secured. A time division multiplexing (TDMA) system is used for slot allocation to a plurality of roadside communication devices 2 within this time.
During the time other than the time for the roadside communication device 2 to communicate, the in-vehicle communication device 3 is used for inter-vehicle communication by the CSMA method. That is, the in-vehicle communication device 3 performs wireless communication with another in-vehicle communication device 3 around the roadside communication device 2 by the carrier sense method.
Each roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing.

In addition, the above description presupposes the downtown area where there are many intersections and many roadside communication devices 2 are installed. In the city center, in addition to vehicle-to-vehicle communication, road-to-vehicle communication and road-to-road communication are performed, and since the number of vehicles 5 is large, the limited communication band is in a tight situation.
On the other hand, in the suburbs where there are few intersections where signals are installed and the number of roadside communication devices 2 is small or not set, only vehicle-to-vehicle communication is mainly performed. In the suburbs, road-to-vehicle communication and road-to-road communication are hardly performed, and the number of vehicles 5 is small, so that there is a margin in the communication band compared to the city center.

[Roadside communication devices and in-vehicle communication devices]
FIG. 3 is a block diagram showing internal configurations of the roadside communication device 2 and the in-vehicle communication device 3.
The roadside communication device 2 includes a wireless transmission / reception unit (wireless communication unit) 21 connected to an antenna 20 for wireless communication, a wired transmission / reception unit (wired communication unit) 22 that performs bidirectional communication with the central device 4, and these communications A control unit 23 including a processor (CPU: Central Processing Unit) that performs control and a storage unit 24 including a storage device such as a ROM and a RAM connected to the control unit 23 are provided.
The wireless communication unit 21 can be configured to be normally used for wireless communication, and includes an oscillator, a modulator, a demodulator, an amplifier, and the like.
The storage unit 24 stores a computer program for communication control executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 23 of the roadside communication device 2 causes the wireless communication unit 22 to perform wireless communication between roads and roads and between roads by a time division multiplexing method. For this reason, the control unit 23, as a functional unit achieved by the execution of the computer program, a first time slot T1 for wireless transmission by the roadside communication device 2 itself and a second time for allowing wireless transmission of the in-vehicle communication device 3 An allocation unit 23A that allocates the slot T2 in a time-sharing manner at regular intervals is provided.
The allocation of the first time slot T1 and the second time slot T2 does not need to be determined periodically, and the roadside communication device 2 or a device (such as a central control device) that controls the roadside communication device 2 is mainly used. It may be the allocation determined in the above.

FIG. 4 shows an example of the first time slot and the second time slot. In principle, the first time slot T1 is a period in which only the roadside communication device 2 has the authority to transmit, and transmission (vehicle-to-vehicle communication) by the in-vehicle communication device 3 is prohibited. In the first time slot T1, road-to-vehicle communication is mainly performed, but road-to-road communication may be performed. Further, the slot T1 may be assigned to a specific vehicle permitted by the roadside communication device 2 in advance, and the vehicle may be used for inter-vehicle communication.
Note that each first time slot T1 may be used by only one roadside communication device 2 or may be shared by a plurality of roadside communication devices 2 by time division. Also, the number of roadside slots corresponding to the first time slot T1 is not limited to one in one cycle, and may be plural.

  The second time slot T2 is a time other than the first time slot T1, and in this time zone, a plurality of in-vehicle communication devices 3 acquire a transmission opportunity by the CSMA / CA method, and the inter-vehicle communication and the inter-road communication Communicate. In the second time slot T2, the roadside communication device 2 may perform communication (such as road-to-vehicle communication) by the CSMA / CA method. Furthermore, the roadside communication device 2 may have a function of securing a transmission period in a system that presupposes the CSMA / CA scheme, such as HCCA in IEEE 802.11e.

  The allocation unit 23A indicates a time zone (roadside communication device time zone) assigned to the in-vehicle communication device 3 for the roadside communication device 2 in order to prohibit inter-vehicle communication in the first time slot T1. A process of transmitting roadside slot information is performed. The slot information is transmitted (broadcast transmission) to the in-vehicle communication device 3 by the wireless transmission / reception unit 21.

The control unit 23 of the roadside communication device 2 further includes a data transfer unit 23B.
The data transfer unit 23 </ b> B temporarily stores traffic information such as traffic jam information of the central device 4 received by the wired transmission / reception unit 22 in the storage unit 24, and transmits the traffic information to the in-vehicle communication device 2 via the wireless transmission / reception unit 21. Broadcast transmission.
At this time, the roadside slot information indicating the time zone for the roadside communication device described above may be broadcasted together with the traffic information.

The in-vehicle communication device 3 includes a transmission / reception unit (wireless communication unit) 31 connected to an antenna 30 for wireless communication, a control unit 32 including a processor that performs communication control on the transmission / reception unit 31, and the control unit 32. And a storage unit 33 including a storage device such as a ROM or a RAM connected to the storage.
The transmitter / receiver 31 can be configured to be normally used for wireless communication, and functions as a transmitter (transmitter) and a receiver (receiver) of radio signals. Equipment, amplifier, etc.
The storage unit 33 stores a computer program for communication control executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 32 of the in-vehicle communication device 3 causes the communication unit 31 to perform wireless communication using a carrier sense method (CSMA / CA method) for vehicle-to-vehicle communication. For this purpose, the carrier sense control unit 35 of the control unit 32 detects whether a radio signal having a predetermined carrier frequency exists in the radio signal propagation path, and if the radio signal does not exist, after the back-off time has elapsed. Acquire a transmission opportunity and control the transmission.
When determining whether or not a radio signal having a predetermined carrier frequency exists in the radio signal propagation path, if the reception level received by the transmission / reception unit 31 is equal to or higher than a predetermined threshold (carrier sense level) It is determined that there is a radio signal having a predetermined carrier frequency, and if it is less than the threshold (carrier sense level), it is determined that there is no radio signal having a predetermined carrier frequency.

  The control unit 32 of the in-vehicle communication device 3 wirelessly transmits the current position information, speed information, and the like of the vehicle 5 from the transmission / reception unit 31 to the outside. For this reason, in the other vehicle 5 or the roadside communication device 2 that has received the position information, the speed information, and the like, for example, safe driving support control for avoiding a right-handed collision or a head-on collision can be performed.

[Other functions of the control unit of the in-vehicle communication device]
In addition to the carrier sense control unit 35, the control unit 32 of the in-vehicle communication device 3 performs information acquisition unit 36, information transfer unit 37, and information invalidation unit 38 as functional units executed by the computer program stored in the storage unit 33. , And an adjustment unit 38.

The information acquisition unit 36 performs processing for acquiring road-side slot information transmitted from the in-vehicle communication device 3 or another in-vehicle communication device 3. When the information acquisition unit 36 acquires the road side slot information, the road side slot information is stored in the storage unit 33.
In the state where the roadside slot information is acquired, the control unit 32 prohibits transmission in the time zone indicated by the roadside slot information. That is, in the time slot indicated by the roadside slot information, transmission is limited so that a transmission opportunity is not obtained even if a radio signal does not exist in the propagation path. As a result, in the time zone allocated for the roadside communication device 2, vehicle-to-vehicle communication does not occur, and interference with road-to-vehicle communication is prevented.

However, in a state where the roadside slot information is not acquired (including the case where the acquired roadside slot information is invalidated by the information invalidation unit 39), transmission is not prohibited for the roadside communication device 2, and in-vehicle communication The time zone in which the machine 3 can acquire the transmission opportunity is all the time zones. Therefore, in the suburbs where the roadside communication device 2 does not exist, there is no time zone in which transmission is prohibited, and vehicle-to-vehicle communication can be performed efficiently.
The roadside slot information does not need to be acquired from the roadside communication device 2, and may be acquired by an optical beacon, for example.

  The information transfer unit 37 is for performing a process of transferring (wireless transmission) the acquired roadside slot information to another in-vehicle communication device 3. This roadside slot information is transmitted (broadcast transmission) in addition to a packet for transmitting position information, speed information, etc. of the vehicle 5, for example.

  When the vehicle-mounted communication device 3 acquires the road-side slot information, the road-side slot information cannot be directly acquired from the road-side communication device 2 by transferring the acquired road-side slot information to other vehicle-mounted communication devices 3 ( For example, roadside slot information can be acquired even for an in-vehicle communication device 3 in the vicinity of the outer edge of the communication area of the roadside communication device 2 or a narrow street in the communication area.

  As a result, before the vehicle-mounted communication device 3 comes to a position where there is a possibility of interfering with road-to-vehicle communication, road-side slot information is acquired by the vehicle-mounted communication device 3, and in the time zone allocated for the road-side communication device 2. Transmission of the in-vehicle communication device 3 can be prohibited. As a result, it is easy to prevent the in-vehicle communication device 3 from becoming a hidden terminal, and interference with road-to-vehicle communication that occurs when the roadside slot information is delayed can be suppressed.

The information invalidation unit 38 invalidates the acquired roadside slot information when the in-vehicle communication device 3 goes out of the communication area of the roadside communication device 2, and the in-vehicle communication device 3 does not acquire the roadside slot information. It is for making a state. Specifically, the information invalidation unit 38 deletes (resets) the roadside slot information stored in the storage unit 33 if the roadside slot information is not newly acquired for a certain period after the information acquisition unit 36 acquires the information. ), And the vehicle-mounted communication device 3 is in a state where the roadside slot information is not acquired.
When invalidating the road side slot information, various values (communication conditions) adjusted by the adjustment unit 39 are returned to the original values (initial values) before adjustment.

  When the information acquisition unit 36 acquires the roadside slot information, the adjustment unit 39 adjusts the communication conditions. When the information invalidation unit 38 enters the roadside slot information non-acquisition state, the adjustment unit 39 returns the communication conditions to the original values before adjustment. Is.

In the present embodiment, the communication conditions adjusted by the adjustment unit 39 are backoff time, carrier sense level (carrier sense sensitivity), modulation degree, and transmission power in the CSMA scheme. The transmission waiting time (transmission cycle) may be adjusted.
Among these communication conditions, the back-off time, the carrier sense level, and the transmission power are parameters that affect the probability that a radio signal transmitted by the in-vehicle communication device 3 is received by another in-vehicle communication device 3.

That is, if the back-off time is shortened, transmission opportunities are obtained more frequently than when the back-off time is long. For this reason, there are many cases where a radio signal of the in-vehicle communication device 3 with a short back-off time exists in the propagation path, and the radio signal of the in-vehicle communication device 3 with a long back-off time decreases. That is, the in-vehicle communication device 3 having a long back-off time waits for a longer time for transmission, but the opportunity to receive a radio signal from another communication device increases accordingly.
Therefore, when the in-vehicle communication device 3 shortens the back-off time, the probability that the radio signal transmitted by the in-vehicle communication device 3 is received (detected by carrier sense) by another in-vehicle communication device 3 having a long back-off time. Becomes higher.

Further, when the in-vehicle communication device 3 increases the carrier sense level, the carrier sense sensitivity decreases, and even if a radio signal having a reception level lower than the level exists in the propagation path, the in-vehicle communication device 3 The probability of detecting the presence of a signal is reduced.
Therefore, the vehicle-mounted communication device 3 with a high carrier sense level has a higher probability of acquiring a transmission opportunity than when the carrier sense level is low.
Therefore, when the vehicle-mounted communication device 3 increases its carrier sense level, the wireless signal transmitted by the vehicle-mounted communication device 3 is another vehicle-mounted communication device 3 with a low carrier sense level (vehicle-mounted communication that does not grasp roadside slot information). The probability of receiving (detected by carrier sense) by a machine (having roadside slot information but including in-vehicle communication equipment whose information is older than the regulation) increases.

Further, when the transmission power is increased, the radio wave is likely to reach far away, so that it is easily received by the other in-vehicle communication device 3.
Further, when there are a plurality of in-vehicle communication devices 3 (including in-vehicle communication devices having road side slot information but whose information is older than the standard) from which roadside slot information has not been acquired, that is, the transmission power is increased. In the case where there are a plurality of in-vehicle communication devices 3, when such in-vehicle communication devices 3 are “in-vehicle communication device 3 </ b> A” and “in-vehicle communication device 3 </ b> B”, the in-vehicle communication device 3 </ b> C with increased transmission power and the in-vehicle communication When the distance between the machine 3A and the distance between the in-vehicle communication device 3B and the in-vehicle communication device 3A are equal and the in-vehicle communication device 3C and the in-vehicle communication device 3B transmit at the same time, the in-vehicle communication device 3A transmits A signal from the in-vehicle communication device 3C having high power is easily received.
Therefore, when the in-vehicle communication device 3 increases its transmission power, the probability that the radio signal transmitted by the in-vehicle communication device 3 is received (detected by carrier sense) by the other in-vehicle communication device 3 increases. Moreover, by increasing the transmission power while changing the modulation degree to a high value, it is possible to maintain the transmittable range in the inter-vehicle communication even if the modulation degree is high. In this case, since the degree of modulation is high, the use period of the communication band can be shortened and the communication band can be effectively used.

[Communication control method to prioritize road-to-vehicle communication]
FIG. 5 shows a communication control method performed in the in-vehicle communication device 3 in order to give priority to road-to-vehicle communication over vehicle-to-vehicle communication in the traffic system (communication system).
First, initial setting is performed at the beginning of the process (step S1). In the initial setting, the transmission timer and the information invalid timer are set to zero. The transmission timer is used for the in-vehicle communication device 3 to determine a transmission interval (transmission waiting time). The information invalid timer is used to determine the time until the acquired road side slot information is invalidated.

  Further, at the time of initial setting, the in-vehicle communication device 3 is in a state where roadside slot information has not been acquired. Therefore, there is no time zone T1 during which vehicle-to-vehicle communication is prohibited for road-to-vehicle communication.

  Further, at the time of initial setting, the values of “back-off time”, “carrier sense level”, “modulation method”, and “transmission power” that can be adjusted by the adjustment unit 39 are initial values (before adjustment). ing. The initial value of each value is, for example, average backoff time = 34 μsec, carrier sense level = −85 [dBm], modulation scheme = “BPSK”, and transmission power = 10 [dBm].

After the initial setting, a process of counting up (+1) the transmission timer is performed (step S1), and it is further determined whether or not the road slot information has been acquired by the information acquisition unit 36 (step S3).
Although the roadside slot information has not been acquired in the past, if the roadside slot information is newly acquired by the information acquisition unit 26 (step S4), the adjustment unit 39 adjusts the communication conditions (step S5). This adjustment is for improving the chance that the radio signal transmitted by the transmission / reception unit 31 is received by the other in-vehicle communication device 3.

In the adjustment by the adjustment unit 39, the back-off time is shorter than the initial value, the carrier sense level is increased, the modulation scheme is increased, and the transmission power is increased.
Note that the transmission power is increased to such an extent that it can be demodulated at the same distance as the communicable distance that can be demodulated by the modulation scheme before adjustment (the modulation scheme at the initial value) even if the modulation scheme is set to a high value. The adjusted values are, for example, average back-off time = 25 μsec, carrier sense level = −80 [dBm], modulation scheme = “16 QAM”, and transmission power = 20 [dBm].

  In step S4, when the information acquisition unit 26 acquires the roadside slot information, the control unit 32 prohibits wireless signal transmission in the time zone (time for roadside communication devices) indicated by the roadside slot information. This prevents the inter-vehicle communication from interfering with the road-to-vehicle communication.

  On the other hand, if it is determined in step S4 that roadside slot information has not been acquired, it is determined whether or not the transmission timer has passed a transmission waiting time (predetermined transmission cycle; for example, 100 msec) (step S6). When the transmission timer has passed the transmission waiting time and a transmission opportunity is obtained, a radio signal for vehicle-to-vehicle communication is transmitted from the transmission / reception unit 31 (step S7). When roadside slot information has not been acquired, there is no time zone during which transmission is prohibited, so efficient communication can be performed.

  When transmission is completed, the transmission timer is reset to 0 (step S8), the process returns to step S2, and processing for the next transmission is continued.

On the other hand, if it is determined in step S3 that roadside slot information has been acquired in the past, or if it is determined in step S4 that roadside slot information is newly acquired this time, the in-vehicle communication device 3 While the conditions are adjusted, communication in the time zone indicated by the roadside slot information is prohibited.
In this case, the information invalid timer is counted up (+1) (step S9).

  When the information invalid timer is less than the set value, it has not passed so much time since the in-vehicle communication device 3 acquired the road side slot information, and the in-vehicle communication device 3 is in the communication area of the road side communication device 2 or the like. Is located and is considered to have the potential to interfere with road-to-vehicle communications. In this case, a radio signal for vehicle-to-vehicle communication is transmitted via the transmission waiting time determination in step S6 (step S7). The acquired road side slot information is added to the transmission packet at the time of transmission. The other in-vehicle communication device 3 can acquire the road side slot information. Further, since this transmission is performed in a state where the communication conditions are adjusted, the road side slot information is easily received by the other in-vehicle communication device 3. Details of this point will be described later.

  On the other hand, when the information invalid timer exceeds the set value in step S10, it means that the time of the set value has elapsed since the in-vehicle communication device 3 acquired the road side slot information. In this case, it is considered that the in-vehicle communication device 3 (vehicle 5) is sufficiently out of the communication area of the roadside communication device 2.

When the vehicle is sufficiently out of the communication area of the roadside communication device 2, there is no possibility that the inter-vehicle communication interferes with the road-vehicle communication. Therefore, the control unit 32 cancels the prohibition of inter-vehicle communication at the time indicated by the roadside slot information. Along with the cancellation of the prohibition, the adjustment unit 39 returns each value of the communication condition to the initial value before the adjustment (step S11). Furthermore, the information invalidation part 38 also deletes the road side slot information preserve | saved at the memory | storage part 33 (step S11). Also, the information invalid timer is reset to zero (step S12).
By deleting the road side slot information, the in-vehicle communication device 3 is in a state where the road side slot information is not acquired.

  In step S12, when the road side slot information is deleted and the road side slot information is not acquired, a radio signal for inter-vehicle communication is transmitted via the transmission waiting time determination of step S6 (step S6). S7). If the roadside slot information has not been acquired, there is no time zone during which transmission is prohibited, and efficient communication can be performed. Moreover, since transmission power is suppressed, it contributes to power saving.

[Adjust communication conditions]
6 to 8 are explanatory diagrams when the adjustment unit 39 adjusts the communication conditions (backoff time, carrier sense level, modulation method, transmission power) of the in-vehicle communication device.
First, FIG. 6 shows preconditions, and the radio signal transmitted by the roadside communication device 2 and the vehicle-mounted communication device 3B before communication condition adjustment (roadside slot information not acquired) is between the two and 3B. The received power intensity in the case of being received by the in-vehicle communication device 3A located in FIG.

In the present embodiment, the roadside communication device 2 has higher transmission power (= 20 [dBm]) and a higher modulation scheme (= 16 QAM) than the in-vehicle communication device 3B before the communication condition adjustment. For this reason, if the in-vehicle communication device 3A is located between the two and 3B, the reception power of the radio signal from the roadside communication device 2 is larger than the reception power of the radio signal from the in-vehicle communication device 3B. (Power difference = P1).
Therefore, even if the radio signal of the vehicle-to-vehicle communication by the in-vehicle communication device 3B that does not know the road-side slot information collides with the road-to-vehicle communication of the road-side communication device 2, the in-vehicle communication device 3A It becomes easier to receive the signal, and the opportunity to receive from the roadside communication device 2 is higher.
As a result, the in-vehicle communication device 3A can more surely acquire the roadside slot information transmitted from the roadside communication device 2.

  Even if the in-vehicle communication device 3B detects the received power of the signal from the roadside communication device 2 and transmits a radio signal with a power smaller than the received power, the signal from the roadside communication device 2 in the in-vehicle communication device 3A Can increase the receiving opportunity.

  The roadside communication device 2 may transmit the roadside slot information by the CSMA / CA method (carrier sense method) using the time zone T2 assigned to the inter-vehicle communication. In this case, the in-vehicle communication device 3A is transmitted from the road-side communication device 2 by shortening the back-off time of the road-side communication device 2 and increasing the carrier sense level as compared with the in-vehicle communication device 3B before the communication condition adjustment. Roadside slot information can be acquired more reliably. In this case, the average backoff time of the roadside communication device 2 can be set to 16 [μsec], for example, and the carrier sense level can be set to −80 [dBm], for example.

When the in-vehicle communication device 3A acquires the roadside slot information, the in-vehicle communication device 3A adjusts the communication condition. FIG. 7 shows a state in which the communication power is adjusted in the in-vehicle communication device 3A, and the transmission power is larger than that in the in-vehicle communication device 3B that has not acquired the roadside slot information. In the in-vehicle communication device 3A, the modulation scheme is changed to a higher value (16QAM) as the transmission power increases.
In the in-vehicle communication device 3A, the carrier sense level is changed to a higher value (L2). On the other hand, in the in-vehicle communication device 3B from which roadside slot information has not been acquired, the carrier sense level remains at a lower value (L1: initial value).

In the state shown in FIG. 7, the power level of the radio signal from the in-vehicle communication device 3A when reaching the in-vehicle communication device 3B is equal to or higher than the carrier sense level L1. Therefore, the radio signal from the in-vehicle communication device 3A is received (detected by carrier sense) by the in-vehicle communication device 3B.
On the other hand, the power level of the wireless signal from the in-vehicle communication device 3B when reaching the in-vehicle communication device 3A is less than the carrier sense level L2. Therefore, the radio signal from the in-vehicle communication device 3B is not received (detected) by the in-vehicle communication device 3A.

For this reason, since the in-vehicle communication device 3A has more transmission opportunities and the in-vehicle communication device 3B has more reception opportunities, the road side slot information transmitted from the in-vehicle communication device 3A is easily transmitted to the in-vehicle communication device 3B.
In addition, the transmission waiting time of the in-vehicle communication device 3A is further increased by reducing the transmission waiting time in the in-vehicle communication device 3A.
Furthermore, in the in-vehicle communication device 3A, since the modulation method is changed to a high value while increasing the transmission power, high-speed transmission is possible, the communication band usage time is shortened, and the band can be effectively used.

  When the in-vehicle communication device 3B also acquires the roadside slot information, the in-vehicle communication device 3B also adjusts the communication conditions. FIG. 8 shows a state in which the communication conditions are adjusted in both the in-vehicle communication device 3A and the in-vehicle communication device 3B, and the transmission power of both the 3A and 3B is increased.

  In the in-vehicle communication devices 3A and 3B shown in FIG. 8, since the transmission power is large, for example, the in-vehicle communication device 3B transfers road side slot information to another in-vehicle communication device (not shown). If an attempt is made, if the carrier sense level remains at a low value (L1), the in-vehicle communication device 3B detects the presence of a radio signal from the in-vehicle communication device 3A and acquires a transmission opportunity. The time interval until is increased, and the transmission opportunity is reduced. However, if the carrier sense level of the in-vehicle communication device 3B is changed to a high value (L2), the radio signal from the in-vehicle communication device 3A is not detected, and the time interval until the transmission opportunity is acquired can be reduced. There are many opportunities.

As described above, according to the present embodiment, in the city center where the roadside communication device 1 exists, the vehicle-to-vehicle communication is performed while suppressing the interference with the roadside vehicle communication by the in-vehicle communication device 3 that has not acquired the roadside slot information. Can be performed without any problem and the communication band can be utilized effectively.
On the other hand, in the suburbs where the roadside communication device 1 is small, the vehicle-to-vehicle communication between the vehicle-mounted communication devices 3 in which the roadside slot information is not acquired is mainly used, but even if the modulation degree is low and the backoff time is long, Since the number of vehicles is smaller than in the city center, there is less bandwidth and there are fewer problems, and power can be saved.

In addition, with respect to the present invention, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not meant to be described above, but is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.
For example, in the present embodiment, all values related to the exemplified communication conditions are adjusted, but any one of “transmission waiting time”, “backoff time”, “carrier sense level”, and “transmission power (and modulation scheme)” Only one may be adjusted. Moreover, you may adjust only any two.
Moreover, although this embodiment demonstrated as the vehicle-mounted communication apparatus 3 (mobile communication apparatus for vehicles mounted in the vehicle 5), you may mount the mobile communication apparatus of this invention in addition to a vehicle, and a mobile telephone terminal You may have.

It is a schematic perspective view which shows the whole structure of an intelligent road traffic system. It is a top view which shows a part of intelligent traffic system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a time chart which shows the slot of road-to-vehicle communication and vehicle-to-vehicle communication. It is a flowchart which shows the communication control method of a vehicle-mounted communication apparatus. It is a figure which shows the received power intensity | strength of the radio signal from a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a figure which shows the received-power intensity | strength of the radio signal from the vehicle-mounted communication apparatus which has acquired roadside slot information, and the vehicle-mounted communication apparatus which has not acquired roadside slot information. It is a figure which shows the received power intensity | strength of the radio signal from each of two vehicle-mounted communication apparatuses which are acquiring road side slot information.

Explanation of symbols

1 traffic signal 2 roadside communication device 3 in-vehicle communication device (mobile communication device)
5 Vehicle 30 Antenna 31 Wireless Communication Unit 32 Control Unit 33 Storage Unit 35 Carrier Sense Control Unit 36 Information Acquisition Unit 37 Information Transfer Unit 38 Information Invalidation Unit 39 Adjustment Unit

Claims (8)

A mobile communication device that performs wireless communication using a carrier sense method,
A transmitter for transmitting a radio signal;
A carrier sense control unit that detects a radio signal in a propagation path in order to acquire a transmission opportunity by the transmission unit;
An acquisition unit for acquiring roadside slot information indicating a time zone for a roadside communication device assigned to the roadside communication device;
Upon obtaining the roadside slot information, an information transfer unit that causes the transmitter to transmit a radio signal including the roadside slot information in order to transfer the roadside slot information to another mobile communication device;
When the roadside slot information is acquired, an adjustment unit that adjusts communication conditions;
With
When the adjustment unit acquires the roadside slot information, the wireless signal transmitted by the transmission unit has acquired the roadside slot information more than when the roadside slot information has not been acquired. to enhance the chance of being received by the mobile communication device, characterized in that intends line adjustment of the communication conditions.   When the adjustment unit acquires the roadside slot information, the probability that the radio signal transmitted by the transmission unit is detected by carrier sense performed by the other mobile communication device, compared to when the roadside slot information is not acquired. The mobile communication device according to claim 1, wherein the communication condition is adjusted so that the value increases.   The mobile communication device according to claim 2, wherein the adjustment of the communication condition performed by the adjustment unit is a shortening of a transmission opportunity acquisition time interval.   The mobile communication device according to claim 2, wherein the adjustment of the communication condition performed by the adjustment unit is an increase in transmission power of the transmission unit.   When the adjusting unit acquires the roadside slot information, the probability that the radio signal transmitted by the other mobile communication device is detected by the carrier sense control unit is lower than when the roadside slot information is not acquired. The mobile communication device according to claim 1, wherein the carrier sense sensitivity in the carrier sense control unit is reduced.   The mobile communication device according to any one of claims 1 to 5, wherein the adjustment unit returns the communication condition to a value before adjustment when the roadside slot information is acquired and a predetermined time elapses. When the roadside slot information is not acquired, the wireless signal transmitted by the roadside communication device is more likely to be received by another mobile communication device than the wireless signal transmitted by the transmission unit. The mobile communication device according to claim 1, which transmits a radio signal. In a communication system in which a roadside communication device time zone is assigned to a roadside communication device, a communication control method for a mobile communication device that performs wireless communication by a carrier sense method,
When the mobile communication device acquires the roadside slot information indicating the time zone for the roadside communication device assigned to the roadside communication device, the radio signal transmitted by the mobile communication device is more than when the roadside slot information is not acquired. The communication conditions of the mobile communication device are adjusted so that the chance that the road side slot information is received by another mobile communication device that has not yet acquired is improved, and the road side slot information is transferred to the other mobile communication device . A communication control method characterized by transmitting.

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