JP2000222683A - On-vehicle communication equipment provided with frequency selection function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely judge a radio frequency which a base station operates in short time by recognizing that control information and the setting of a reception part are matched on the signal of the base station whose reception level is constant. SOLUTION: A channel received by the control of a frequency control part is set to an outgoing channel A. When the reception of FCMC is waited and plural FCM are received within a prescribed time, FCMC whose reception level is the largest is preserved (S601 and 602). When the detected reception level is not less than a value which is previously set, the operation radio frequency mode of a base station, which is contained in transmission channel control information (SIG) in received FCMC, is compared with the received channel which an on-vehicle device sets (S604). When they match, the received channel which is set at present is decided (S605) and the decision processing of a frequency is terminated. Then, a link request signal (ACTC) is transmitted to the base station of an identification number FID contained in FCMC when the frequency is decided and a link is requested.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road-to-vehicle communication system for performing wireless communication between a base station set at a fixed location and a vehicle-mounted communication device installed in a moving vehicle. The present invention relates to an in-vehicle communication device of a road-to-vehicle communication system using a communication method for performing communication using different radio frequencies.

[0002]

2. Description of the Related Art In order to realize services aimed at improving safety, transportation efficiency, and comfort, an intelligent transportation system (ITS: Intelligent Transport) that integrates a road and a vehicle.
t Systems) is under development. In this system, these services are to be realized by road-to-vehicle communication performed between a base station installed on a road and a mobile station mounted on a vehicle, and vehicle-to-vehicle communication performed between mobile stations.

As an example of a communication system in this intelligent transportation system, there is a standard "A toll road automatic toll collection system standard A" defined by the Association of Radio Industries and Businesses.
RIB STD-T55 Version 1.0 "(established on November 27, 1997) is known.

The above-mentioned standard defines a road-vehicle communication system using spot communication with a limited communication area, and includes communication from a base station to a mobile station (hereinafter referred to as downlink communication) and communication from a mobile station to a base station (hereinafter referred to as a base station). In the following, a different frequency is used for uplink communication, and a slotted Aloha system, which is a synchronous time-division communication system in which a communication frame is time-divided into fixed-length sections called slots, is adopted.

Further, in order to use different frequencies for uplink communication and downlink communication, and to prevent interference between adjacent base stations, two different frequencies are used as radio frequencies for uplink and downlink communication, respectively. It is specified that four frequencies be used. FIG. 2 shows the assignment of each frequency. The frequencies f1 and f2 are used for downlink communication,
f4 is used for uplink communication, and the frequencies f1 and f3 are paired,
The frequencies f2 and f4 are used in combination in pairs. That is, in the communication range of a certain base station, the frequency f1 is used for downlink communication.
(Hereinafter, downlink channel A), frequency f3 (hereinafter, uplink channel A) is used for uplink communication (hereinafter, mode A). Other base stations adjacent to the base station operating in mode A use frequency f2 (hereinafter, downlink channel B) for downlink communication and frequency f4 (hereinafter, uplink channel B) for uplink communication (hereinafter, mode B).

The communication frame of the slotted Aloha system is
The communication slot is roughly divided into a communication slot and a control slot. The communication slot is a message data slot (M) for performing data exchange between road and vehicle so that communication with a plurality of mobile stations is possible.
A plurality of DSs (Message Data Slots) are arranged. The control slot includes a frame control message slot (F) storing configuration information of a communication frame transmitted by the base station, a usage state of the communication slot, and the like.
CMS: Frame Control Message
e Slot) and an activation slot (AC) for the mobile station to request the base station to allocate a communication slot.
TS: Activation Slot). F
The CM is also a reference signal for a slot period, and is a signal that is constantly transmitted periodically even when communication with the mobile station is not performed.

FIG. 3 shows an example of operation according to the above technique.
In the figure, 301 is a road, 302 is a gantry installed on the road, 303 and 304 are base station antennas mounted on the gantry, 305 is a communication area of the antenna 303, 306 is a communication area of the antenna 304, and 307 is a communication area of the antenna 304. A base station device 308 is installed on the ground, 308 is a vehicle, and 309 is a vehicle-mounted communication device mounted on the vehicle. Since the antennas 303 and 304 are installed adjacent to each other, they are operated at different radio frequencies to prevent mutual interference. In this case, the antenna 303 is operated in mode A and the antenna 304 is operated in mode B.

[0008] The vehicle 308 is connected to the communication area 3 of the antenna 303.
Prior to communication, the in-vehicle communication device 309 needs to detect that it has entered the communication area of the base station and to know the mode of the radio frequency operated by the base station before entering the network.

The entry into the communication area 305 of the base station can be detected by receiving the FCM signal transmitted from the base station. However, as shown in FIG.
Even if the communication area is set not to overlap for each lane, due to the influence of reflection of other passing vehicles, etc.,
In some cases, the signal of the antenna 304 in the next lane may be received.

In order to avoid such a situation, a system is provided which comprises a plurality of receiving means, measures the level (reception level) of the received electric field for each radio frequency, and responds to the antenna of the radio frequency having the highest reception level. Has been devised. An example of such an apparatus is disclosed in JP-A-7-3
No. 25996, and the like.

[0011]

According to the above prior art, a plurality of receiving means are required according to the number of operating frequencies. However, considering the cost of the communication device, it is desirable not to have more wireless circuits than necessary.

However, when only a single receiving means is used, not only the FCM of the adjacent base station is received as described above, but also the base station antenna which is installed independently without the adjacent antenna. However, if the radio wave transmitted by the antenna is very strong, even if the onboard communication device is set to receive a frequency different from the transmission frequency of the base station to detect the frequency, May be received too strongly. As a result, there is a problem that an incorrect frequency is determined. This is because, in a large vehicle or the like, the installation location of the vehicle-mounted communication device may be too close to the antenna of the base station.

When only a single receiving means is used, even for a radio frequency which has not been transmitted, it waits once in the receiving state and tries to detect the FCM, so that the time for selecting the frequency becomes longer, and during that time, When the vehicle travels a considerable distance, the speed at which the vehicle travels at high speed reduces the time spent in the communication area, and the vehicle may move out of the communication area before communication with the base station is completed. Occurs.

An object of the present invention is to provide an in-vehicle communication device capable of correctly determining a radio frequency operated by a base station without increasing costs. It is still another object of the present invention to provide an in-vehicle communication device that can reduce the time required to determine a radio frequency.

[0015]

According to the first aspect of the present invention, an in-vehicle communication device of the present invention receives an FCMC while switching a radio frequency to be received, and receives the received FCMC.
Is above a certain level, it is detected that it has entered the communication area of the base station.
When the operation information of the radio frequency included in C and the setting of the reception frequency of the receiving unit of the on-vehicle device match, the radio frequency set by the receiving unit is determined to be the operating frequency of the base station. Further, at the time of a link request to the base station, a link request signal is transmitted by designating the identification number of the base station included in the FCMC at the time of determining the radio frequency. Therefore, it is possible to reliably communicate with the selected base station without selecting an incorrect frequency.

According to the second aspect of the present invention, the in-vehicle communication device of the present invention detects that the received FCMC has entered a communication area of the base station when the received FCMC is above a certain level, and further detects the received FCMC. The operation frequency of the base station is determined based on the operation information of the radio frequency included in the information. Further, at the time of a link request to the base station, the identification number of the base station included in the FCMC at the time of determining the radio frequency is designated,
Send a link request signal. Therefore, it is possible to reliably communicate with the selected base station without selecting an incorrect frequency. Further, since reception is possible over a plurality of downlink channels, there is no need to receive FCMC while switching the reception frequency, and it is possible to select a frequency in a shorter time.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the inter-vehicle communication system of the present invention will be described below with reference to the drawings. First, a communication format for communication between the vehicle-mounted communication device and the roadside device of the present invention will be described in advance.

FIG. 4 is a diagram showing a format of communication between a road and a vehicle. FIG. 1 shows an example in which communication between a road and a vehicle is made up of three slots in one frame. In the case of the configuration shown in the figure, the downlink channel of slot 1 is used for a frame control slot (FCMS), the uplink channel of slot 3 is used for a link request slot (ACTS), and slot 2 is used for data exchange. Communication slot (MDS)
It is used for

A mobile station that performs road-to-vehicle communication using this communication frame needs to synchronize with a communication frame transmitted by the base station in order to determine the position of the communication slot allocated to the mobile station. Therefore, in the road-vehicle communication method,
Frame control signal FCMC (F
Frame Control Message Cha
nnel) is a signal MDC arranged in another slot.
(Message Data Channel), AC
KC (Acknowledgment Channel), A
A synchronization signal pattern different from that of CTC (Activation Channel) is multiplexed so that the position of a frame control slot can be identified as a time reference of a communication frame. Also, the frame control signal FCMC includes:
Since frame configuration information such as a radio channel operated by the base station, a frame period, and a slot position assigned to the own station are multiplexed, the mobile station can reproduce a communication frame.

FIG. 5 is a diagram showing details of the FCM shown in FIG. In the figure, 501 is a preamble (PR),
502, a unique word (UW) which is a bit pattern unique to the FCM; 503, transmission channel control information (SIG) including control information of the FCM channel; 504, an identification number (FID) for identifying a base station; Denotes frame configuration information (FSI) including frame configuration information;
Reference numeral 6 denotes release timer information (RLT) for the base station to limit the link request of the in-vehicle device, 507 denotes service application information (SC) including service information provided by the base station, and 508 denotes allocation information (SC) of each slot.
I) and 509 are codes (CRC) for error detection.

By detecting the unique word 502, the mobile station can know that the received content is FCMC. Further, the transmission channel control information 503 includes mode information of a radio frequency operated by the base station that has transmitted the FCMC, and determines whether the radio frequency operated by the base station is mode A or mode B. Is possible.

FIG. 1 shows an embodiment of the in-vehicle communication device according to the present invention, taking as an example a case in which the above-mentioned wireless communication format is followed. In the figure, 101 and 102 are antennas, 103 is a radio receiving unit, 104 is a demodulation unit of a received signal, 105 is a reception level detection unit that detects the electric field level of a received signal, 106 is an oscillator, and 107 controls an oscillator. A frequency control unit, 108 is a modulation unit for modulating transmission data, 109 is a wireless transmission unit, and 110 is a communication control unit.

The frequency control unit 107 controls the oscillation frequency of the oscillator 106 to switch the reception channel of the reception unit 103 and the transmission channel of the transmission unit 109.
A radio signal from the base station is received by the antenna 101, and a signal of a desired channel is extracted by the receiving unit 103. Further, the data is converted into digital data by the demodulation unit 104 and input to the signal processing unit 110 as reception data. at the same time,
The electric field strength of the signal received by the reception level detection unit 105 is measured, and is similarly input to the signal processing unit 110. The transmission data is modulated by the modulator 108 and transmitted from the transmitter 109 at the radio frequency of the transmission channel.

Next, the frequency selection operation of the communication control unit in the on-vehicle communication device of FIG. 1 will be described with reference to FIG.
First, prior to the selection operation, the receiving channel is set to the downlink channel A under the control of the frequency control unit 107 (process 601). While the receiving channel is set to the downlink channel A, the reception of the FCMC is waited. When the FCM is received, the received FCMC and the reception level at the time of reception are stored. If the FCM cannot be received after waiting for a predetermined time, it is determined that there is no reception level, and the next process is performed. When a plurality of FCMs are received within a predetermined time, the FCMC with the highest reception level is stored (step 60).
2).

At this time, the length of time to wait for reception of FCMC is at least longer than the transmission cycle of FCMC.
If is sent, be sure to set a time that can be received. In this embodiment, for example, the time is set to twice the FCMC transmission cycle. When the reception level detected in the process 602 is equal to or higher than a preset value, the process branches to a process 604, and when the reception level is equal to or lower than the specified level, the process branches to a process 606 (process 603).
The process also branches to process 606 if no FCMC has been received. When the process branches to step 606, the receiving channel is switched. If the current setting is the downlink channel A, the downlink channel B is set. If the current setting is the downlink channel B, the downlink channel A is set. After setting the reception channel, the same processing is performed again from processing 602.

When the in-vehicle communication device is out of the communication area of the base station, there is no reception of FCMC.
Will continue to wait for reception.

When the vehicle enters the communication area, a case where the signal is received at a certain level or higher occurs in the branching process of the process 603, and the process branches to the process 604. When the process branches to the process 604, the transmission channel control information (SI
The operation radio frequency mode of the base station included in G) is compared with the reception channel set by the in-vehicle device, and if they match, the process branches to step 605 to determine the currently set reception channel and determine the frequency. The processing ends. If they do not match, the process branches to process 606, switches the receiving channel, and performs the same process again from process 602.

After the frequency determination processing is completed, a link request signal (ACTC) is transmitted to the base station of the identification number FID included in the FCMC at the time of determining the frequency to make a link request. Since the ACTC transmitted by the in-vehicle communication device includes the identification number FID of the partner base station requesting the link, even if the adjacent base station receives the ACTC, communication is not performed erroneously.

In the above-mentioned processing 603, the reason why the reception is performed again when the received level is equal to or less than the specified value is that, although there is a case where the reception can be performed temporarily near the boundary of the communication area, the communication is started from that position. This is because communication is performed while frequent communication errors occur. The vehicle is moving toward the communication area of the base station, and the reception level gradually increases as the vehicle enters the communication area. If communication is started at that point, stable communication is possible.

Another reason is to eliminate signals from adjacent base stations. That is, when the base stations are arranged adjacent to each other, the signal from the base station in the communication area to which the vehicle is about to enter from the adjacent base station is
Even if the signal can be received, the reception level is relatively small because the distance to the vehicle is large. Therefore, when the reception level is low, the signal from the adjacent base station can be eliminated by receiving the signal again.

In the process 604, the operation radio frequency mode of the base station is compared with the reception channel set by the on-vehicle device because signals of a channel different from the reception channel set by the on-vehicle communication device are interfering. However, even if a signal with interference is received, the received radio frequency information in the FCMC does not match the reception channel being set in the in-vehicle device, so that malfunction can be prevented. Such a situation may occur when the vehicle-mounted communication device is too close to the antenna of the base station, for example, when the position of the driver's seat is high, such as in a large vehicle, and therefore, the position of the vehicle-mounted communication device is easily approached to the antenna.

In the above-described embodiment, since the receiving channel is awaited for the FCMC while alternately switching the receiving channel between the downlink channel A and the downlink channel B, the receivers are provided as many as the number of the radio frequencies and the signal of each radio frequency is provided. And the same operation as that of receiving is possible.

As described above, according to the present embodiment, the radio frequency operated by the base station can be correctly determined without requiring more devices than those required for communication, and interference from different channels may occur. In this case, the FCM received by the interference is not erroneously selected. Further, since the link request signal is transmitted based on the FID included in the FCMC when the frequency is selected, communication with the correct base station can be performed.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing a configuration of the receiving unit 103 of the in-vehicle communication device in FIG. In the figure, 701 and 704 are amplifiers, 702 is a frequency converter, and 703 is a bandpass filter.

When a signal transmitted from a base station is received by a vehicle-mounted device, a signal received by an antenna is amplified by an amplifier 701 and then converted to an intermediate frequency by a frequency converter 702. From the converted signal, only necessary frequency components are extracted by a band-pass filter 703, amplified by an amplifier 704, and sent to a demodulation unit or a reception level detection unit.

Here, the characteristics of the band-pass filter 703 are set as shown in FIG. That is, the band of the band-pass filter is set to the downlink channel A and the downlink channel B
It is set to cover both. for that reason,
Even if the received signal is the downlink channel A or the downlink channel B, reception is possible. Next, the frequency selection operation of the in-vehicle communication device including the receiving unit shown in FIG. 7 will be described with reference to FIG. First, the reception of the FCMC is waited for a predetermined time, and when the FCM is received, the received FCMC and the reception level at the time of reception are stored. After waiting for a predetermined time,
If the CM cannot be received, it is determined that there is no reception level, and the process proceeds to the next process. Multiple FCMs within a given time
Is received, the FCMC with the highest reception level is stored (process 901). If the reception level detected in step 901 is equal to or higher than a preset value, step 903
If the level is equal to or lower than the specified level, the process returns to step 901 and waits for reception of the FCMC again (step 902). The process also returns to step 901 if no FCMC has been received. If the reception level is equal to or higher than the predetermined value, the operation radio frequency mode of the base station included in the transmission channel control information (SIG) in the received FCMC is detected, and the selection of the frequency is terminated. After completion of the frequency selection processing, the transmission frequency is switched to a channel operated by the base station for communication with the base station. Also, F
The base station to be communicated with is identified by the identification number FID of the base station included in the CMC, and when a link request is made, a link request signal (ACTC) is transmitted to the base station of the FID at the time when the frequency is determined above. .

Waiting for the reception of the FCM for a predetermined time in the process 901 is performed in the vicinity of the boundary between a plurality of base stations when the FCM from a different base station can be received. This is for selecting a station, that is, a base station closest to the vehicle. Also, the time to wait for the FCM should be at least longer than the FCMC transmission cycle.
If the MC has been transmitted, the time must be set so that it can be received.

In the embodiment described above, since it is not necessary to wait for the FCMC while switching the standby channel of the receiving unit for a plurality of radio frequencies, the time until the radio frequency is determined can be reduced.

In the above embodiment, the case where only one kind of bandpass filter is used has been described. However, a bandpass filter having a narrow band is also provided, and once the frequency selection is completed, the bandpass filter is used. If the reception operation is switched to a narrow band, interference from adjacent channels can be reduced.

[0040]

As described above, according to the present invention,
For a certain level of reception level when receiving a signal from the base station, it is possible to correctly determine the radio frequency operated by the base station to confirm that the control information and the setting of the receiving unit of the in-vehicle communication device match. Thus, an in-vehicle communication device can be realized.

Further, by setting the receiving unit so as to be able to receive over a plurality of wireless channels, it is not necessary to switch the receiving wireless channel, so that the time required to determine the wireless frequency can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an in-vehicle communication device of the present invention.

FIG. 2 is a characteristic diagram showing a radio frequency used in the road-vehicle communication system.

FIG. 3 is a diagram showing an operation example of road-vehicle communication.

FIG. 4 is a diagram showing a communication format of road-vehicle communication.

FIG. 5 is a detailed diagram of a frame control message.

FIG. 6 is a flowchart of the operation of the in-vehicle communication device according to the present invention.

FIG. 7 is a configuration diagram of a receiving unit of the in-vehicle communication device according to the present invention.

FIG. 8 is a characteristic diagram showing characteristics of a band-pass filter of a receiving unit.

FIG. 9 is a flowchart of the operation of the in-vehicle communication device of the present invention.

[Explanation of symbols]

101, 102: antenna, 103: receiving unit, 104:
Demodulation unit, 105: reception level detection unit, 106: oscillator,
107: frequency control unit, 108: modulation unit, 109: transmission unit, 701, 704: amplifier, 702: frequency converter,
703 ... Band pass filter.

Continuing on the front page (72) Inventor Koji Abe 2520 Odaiba, Hitachinaka-shi, Ibaraki F-term in the Automotive Equipment Division of Hitachi, Ltd. (Reference) 5H180 AA01 BB04 FF12 FF13 5K067 BB21 CC02 DD19 EE02 EE10 EE63 EE71 GG03 JJ13 JJ14 JJ31

Claims (2)

[Claims] 1. A communication frame having a format in which a frame control slot including control information necessary for road-to-vehicle communication is arranged, and at least a communication slot for data exchange is arranged after the frame control slot. Transmission and data transmission from the base station installed on the road in the communication slot to the mobile station mounted on the vehicle using the radio frequency allocated for downlink communication, and from the mobile station to the base station in the communication slot. Data transmission is performed using a radio frequency assigned for uplink communication, the radio frequency for the downlink communication, has a plurality of combinations of radio frequencies for the uplink communication, among the plurality of sets of radio frequencies In a road-to-vehicle communication system that performs communication between a base station and a mobile station using one set, the radio frequency to be received can be switched and transmitted from the base station. Receiving means for demodulating the communication control signal in the frame control slot to be sent to the communication control unit, detecting the electric field strength of the received radio wave, and receiving level detection means for notifying the detected level to the communication control unit, The communication control unit waits for the reception of the communication control signal while switching the reception frequency of the reception unit at regular intervals, and receives the communication control signal received when the base station enters the communication area, and the received communication control signal. Based on the operation mode information of the radio frequency included in the signal and the setting state of the reception frequency of the in-vehicle communication device, the reception frequency of the reception unit is determined, and the base station included in the communication control signal when the reception frequency is determined An in-vehicle communication device having a frequency selection function for transmitting a link request signal based on the identification number of a vehicle. 2. A control frame in which a frame control slot including control information necessary for road-to-vehicle communication is arranged, and at least a communication slot for data exchange is arranged after the frame control slot. Data transmission from the base station installed on the road in the communication slot to the mobile station mounted on the vehicle using the radio frequency assigned for downlink communication, and the data from the mobile station to the base station in the communication slot. Transmission is performed using a radio frequency assigned for uplink communication, and a plurality of combinations of the radio frequency for downlink communication and the radio frequency for uplink communication are provided. In a road-to-vehicle communication system that performs communication between a base station and a mobile station using A receiving unit that demodulates a communication control signal transmitted from the base station and sends the demodulated communication control signal to the communication control unit; and a reception level detection unit that detects an electric field strength of a received radio wave and notifies the communication control unit of the detected level. The communication control means, when entering the communication area of the base station, based on the reception level of the received communication control signal and the operation mode information of the radio frequency included in the communication control signal, the communication frequency with the base station And transmitting a link request signal based on the identification number of the base station contained in the received communication control signal.