JP5848147B2 - Communication method and communication system - Google Patents

Description

  The present invention relates to a communication method and a communication system for transmitting data from a base station to a plurality of mobile stations and transmitting data from the mobile station to the base station.

  An example of a communication system is described in Patent Document 1. The communication system of Patent Literature 1 includes a radio base station having a plurality of radio communication units that perform radio communication using different communication channels, and a radio communication unit that can change the communication channel. Further, the communication system of Patent Document 1 includes a wireless terminal that wirelessly communicates with a wireless base station by a wireless communication unit and receives a service via the wireless base station.

JP 2010-226271 A

  In the ITS field, on-vehicle devices based on WAVE (Wireless Access in Vehicular Environments) communication standards that are intended to be used in common for various traffic-related services including road billing are road-to-vehicle, vehicle-to-vehicle. There is a communication system that performs communication.

  As shown in FIG. 6, such a communication system 100 charges a road by receiving information transmitted from a vehicle 102 traveling on the road 101 by a charging device 103 installed on the road 101.

  As shown in FIG. 7, the communication system 100 is an application example of vehicle-to-vehicle communication. When there is an approach 104 "or when an emergency vehicle approaches, a notice 105 of" Beware of the vehicle ahead "is sent.

  As shown in FIG. 8, such a communication system 100 divides a communication frequency band to be used into a plurality of communication channels 110 in a time division manner in order to realize different types of services according to the purpose. The communication channel 110 is divided into a control channel CC and a service channel SC. The control channel CC is shared by all the communication terminals 1, 2, and 3, and indicates the next service channel SC among them. Establish communication. On the other hand, in the service channel SC, information is transmitted and received, and different control services are realized in parallel by time division by alternately repeating the control channel CC and the service channel SC.

  Here, it is necessary for the communication channel 110 to synchronize the period, interval, and start timing between the transmission side and the reception side. As a synchronization method of the communication channel 110, one of the following methods is usually employed. A first synchronization method is to use UTC (Universal Time, Coordinated) absolute time included in a GPS (Global Positioning System) signal. The second synchronization method is to make the start timing of the communication message from the base station positive and to match it.

  However, as shown in FIG. 9, when the communication system 100 is in a place where GPS radio waves such as a valley of a building and a tunnel cannot be stably received and the state continues for a long time, there is an interval for accurate time correction by GPS. It will be. Therefore, in the meantime, errors accumulate to maintain the time with the built-in clock. Therefore, in the communication between the vehicles 120, 130, and 140, it is necessary to match the start timing with each other. Therefore, when the accumulated error exceeds the guard interval, a communication collision / failure occurs.

  On the other hand, even if the data for each of a plurality of services is received in parallel, Patent Document 1 completely receives each service data and can flexibly receive the data in response to a user request. However, Patent Document 1 uses time synchronization in accordance with the absolute time included in the GPS signal or the communication message from the base station in a communication system that needs to synchronize the timing of communication time slots. Therefore, in Patent Document 1, a GPS function and a base station are essential, and when there is an interval for accurate time correction by GPS, errors are accumulated and accumulated in order to maintain the time with a built-in clock. The error may exceed the guard interval. Therefore, Patent Document 1 sometimes causes a communication collision / failure.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a communication method and a communication system capable of maintaining accurate timing of communication when the GPS cannot be stably received for a long time. There is.

  In order to solve the above-described problem, according to the first aspect of the present invention, data is transmitted from a base station to a plurality of mobile stations through a downlink channel, and a base station is selected from a plurality of mobile stations selected from a plurality of base stations through an uplink channel. A communication method for transmitting data to a station, in which a mobile station receives a GPS signal, a step of determining the quality of the received GPS signal, and a time obtained from the GPS when the quality of the GPS signal is equal to or higher than a predetermined value. The position of the mobile station, referring to the GPS time accuracy reduced location database according to the position of the mobile station, determining whether or not it is in the accuracy reduced position, and the quality of the GPS signal is below a predetermined value, or Applying the time of the mobile station when the mobile station is present at the position of reduced accuracy in the GPS time accuracy reduced location database.

  If the quality of the GPS signal is lower than a predetermined value and the time quality of the mobile station is lower than the predetermined value, a step of applying a wireless LAN time may be further provided.

  According to the second aspect of the present invention, the WAVE communication function unit that performs communication in synchronization with roadside equipment or other vehicles by WAVE communication, and the absolute time is generated based on the signal received from the GPS for WAVE communication. A GPS time output function unit that outputs the GPS time used as a reference for the synchronization signal and outputs the GPS radio wave reception quality, and an absolute time based on the signal received from the mobile phone base station, and a synchronization signal for WAVE communication A mobile phone time output function unit that outputs mobile phone radio wave reception quality as well as a mobile phone time to be used as a reference, and obtains position information from GPS, and corrects it to a position on the road by road map data. Is output as self-location information, and the position information is output with a reliability indicating how reliable the estimation result is. A position estimation function unit, and a synchronization signal output function unit that corrects the built-in clock using the mobile phone time, GPS time, position information, and reliability, and outputs a synchronization signal necessary for WAVE communication based on the time of the built-in clock; A road map database having road information used by the position estimation function, and a GPS time accuracy reduced location database in which accuracy is measured in advance and a place where GPS time accuracy reduction is likely to be placed is databased Prepare.

  A wireless LAN time output function unit that generates absolute time based on a signal received from a wireless LAN access point, outputs the absolute time as a synchronization signal for WAVE communication, and outputs reception quality of the wireless LAN access point radio wave, and mobile phone time A synchronization signal output function for switching between output, GPS time output, wireless LAN time output, and built-in clock and outputting a synchronization signal necessary for WAVE communication may be further provided.

  According to the communication system of the present invention, there is an effect that the accurate timing of communication can be maintained when the GPS cannot be received stably for a long time.

It is a functional block diagram of the communication system of 1st Embodiment which concerns on this invention. It is a flowchart explaining the control operation of the communication system of 1st Embodiment which concerns on this invention. It is a functional block diagram of the communication system of 2nd Embodiment which concerns on this invention. It is area explanatory drawing of the communication system of 2nd Embodiment which concerns on this invention. It is a flowchart explaining the control operation of the communication system of 2nd Embodiment which concerns on this invention. It is the schematic of a related communication system. It is the schematic of the application example of the vehicle-vehicle communication in a related communication system. It is a schematic diagram of the time channel in the related communication system. It is explanatory drawing of the error in a related communication system.

  Hereinafter, communication systems according to a plurality of embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, a communication system 10 according to the first embodiment of the present invention is mounted on an in-vehicle device 11, and includes a WAVE communication function unit 12, a GPS time output function unit 13, and a mobile phone time output function. Unit 14 and a position estimation function unit 15. In addition, the communication system 10 includes a synchronization signal output function unit 16, a road map database 17, and a GPS time accuracy reduced place database 18.

  The WAVE communication function unit 12 performs communication in synchronization with the road side equipment (or other vehicle) 19 by WAVE communication. The GPS time output function unit 13 generates an absolute time based on a signal received from the GPS 20, outputs it as a GPS time used as a reference for a synchronization signal for WAVE communication, and outputs GPS radio wave reception quality. The cellular phone time output function unit 14 generates an absolute time based on the signal received from the cellular phone base station 22 and outputs the absolute time as a cellular phone time used as a reference for a synchronization signal for WAVE communication. Output.

  The position estimation function unit 15 obtains position information from the GPS 20, corrects it to a position on the road by road map data, estimates its own position, outputs the position information as self-position information, and the position information indicates an estimation result. Output with the reliability indicating whether it is reliable to some extent. The synchronization signal output function unit 16 corrects the internal clock using the mobile phone time, GPS time, position information, and reliability, and outputs a synchronization signal necessary for WAVE communication based on the internal clock time. The road map database 17 stores road information used by the position estimation function unit 15. The GPS time accuracy reduced place database 18 measures the accuracy in advance, and stores a place where there is a high possibility that the GPS time precision may be lowered.

  Next, the control operation of the communication system 10 will be described. Here, an outline of processing in which the synchronization signal output function unit 16 corrects the built-in clock using the mobile phone time, GPS time, position information, and reliability is shown. As shown in FIG. 2, when the control is started, the GPS time output function unit 13 receives the latest information on the GPS radio wave reception quality and the GPS time (S101). Next, the position estimation function unit 15 receives the latest information on position information and reliability (S102).

  Subsequently, when it is determined that the received GPS radio wave reception quality is equal to or higher than a predetermined threshold, the current position is referred to in the GPS time accuracy reduced place database 18 (S103 → S104). If the position information and reliability of the position estimation function unit 15 are further used to determine that the reliability is equal to or higher than a certain level and is within the location existing in the GPS time accuracy reduced place database 18, the GPS time will be It is determined that it can no longer be used, and the process proceeds to the correction determination based on the mobile phone time (S105 → S106).

  At this time, if it is determined that the reliability is not more than a certain level or is not within the place existing in the GPS time accuracy lowered place database 18, the internal clock is corrected with the GPS time (S105 → S107). Then, a synchronization signal is output to the WAVE communication function unit 12 based on the built-in clock time (S110). At this time, if it is determined from the GPS radio wave reception quality that the radio waves of the GPS 20 cannot be stably received, the mobile phone time output function unit 14 receives the latest information on the mobile phone radio wave reception quality and the mobile phone time (S106).

  If it is determined that the radio wave reception quality of the mobile phone is equal to or higher than a predetermined threshold, the internal clock is corrected with the mobile phone time (S108 → S109). At this time, if the reception quality of the mobile phone radio wave is not equal to or higher than a predetermined threshold value, the WAVE communication is performed by outputting the synchronization signal using the internal clock without correcting the internal clock at the mobile phone time (S108 → S110). Then, a synchronization signal is output to the WAVE communication function unit 12 based on the built-in clock time (S110).

  As described above, according to the communication system 10 of the first embodiment of the present invention, when the GPS 20 cannot be stably received for a long time, the accurate timing of communication can be maintained according to the mobile phone time.

  Further, according to the communication system 10, even when the GPS 20 can be stably received, when the GPS 20 is in a location where accuracy is known in advance, the GPS time and the mobile phone time are frequently calculated by applying the mobile phone time. Unstable operation due to reference switching can be avoided.

  Next, a communication system according to a second embodiment of the present invention will be described. Note that, in the following second embodiment, components that are the same as those in the first embodiment described above or components that are functionally similar are denoted by the same or corresponding reference numerals in the drawings, or the description is simplified. Omitted.

  As shown in FIG. 3, the communication system 30 according to the second embodiment of the present invention is mounted on the vehicle-mounted device 31, and includes a WAVE communication function unit 32, a GPS time output function unit 33, and a mobile phone time output function. Unit 34 and a position estimation function unit 35. Further, the communication system 30 includes a synchronization signal output function unit 36, a road map database 37, a GPS time accuracy reduced place database 38, and a wireless LAN time output function unit 39.

  The WAVE communication function unit 32 performs communication in synchronization with the road-side facility (or other vehicle) 19 by WAVE communication. The GPS time output function unit 33 creates an absolute time based on the signal received from the GPS 20, outputs it as a GPS time used as a reference for a synchronization signal for WAVE communication, and outputs GPS radio wave reception quality. The mobile phone time output function unit 34 creates an absolute time based on the signal received from the mobile phone base station 22 and outputs it as a mobile phone time used as a reference for a synchronization signal for WAVE communication, and the mobile phone radio wave reception quality. Output.

  The position estimation function unit 35 obtains position information from the GPS 20, corrects it to a position on the road by road map data, estimates its own position, outputs the position information as self-position information, and determines which position information has an estimation result. Output with the reliability indicating whether it is reliable to some extent. The synchronization signal output function unit 36 switches between the cellular phone time output, GPS time output, wireless LAN time output, and built-in clock, and outputs a synchronization signal necessary for WAVE communication. The road map database 37 stores road information used by the position estimation function unit 35. The GPS time accuracy reduced place database 38 measures the accuracy in advance, and stores a place where there is a high possibility that the GPS time precision may be lowered. Then, the wireless LAN time output function unit 39 generates an absolute time based on the signal received from the wireless LAN access point 40 and outputs it as a synchronization signal for WAVE communication. The reception quality of the wireless LAN access point radio wave is output.

  As shown in FIG. 4, the communication system 30 is a beacon signal periodically transmitted by the wireless LAN from a plurality of wireless LAN access points 40 installed in advance in a place where neither the GPS 20 nor the mobile phone base station 22 can be used. Use to correct the internal clock.

  Next, the control operation of the communication system 30 will be described. As shown in FIG. 5, when the control is started, the GPS time output function unit 33 receives the latest information on the GPS radio wave reception quality and the GPS time (S201). Next, the position estimation function unit 35 receives the latest position information and reliability information (S202).

  Subsequently, when it is determined that the received GPS radio wave reception quality is equal to or higher than a predetermined threshold, the current position is referred to in the GPS time accuracy reduced place database 38 (S203 → S204). If the position information and reliability of the position estimation function unit 35 are further used to determine that the reliability is equal to or higher than a certain level and is within a location existing in the GPS time accuracy location database 38, the GPS time is It is determined that it can no longer be used, and the process proceeds to the correction determination based on the mobile phone time (S205 → S206).

  At this time, if it is determined that the reliability is not more than a certain level or is not within the location existing in the GPS time accuracy lowered location database 38, the internal clock is corrected with the GPS time (S205 → S207). If it is determined that the GPS radio wave cannot be stably received from the GPS radio wave reception quality, the mobile phone time output function unit 34 receives the latest information on the mobile phone radio wave reception quality and the mobile phone time (S206).

  If it is determined that the reception quality of the cellular phone radio wave is not equal to or higher than a predetermined threshold, the wireless LAN time output function unit 39 receives the radio LAN access point radio wave reception quality and the wireless LAN time (S208 → S209). At this time, if it is determined that the reception quality of the mobile phone radio wave is equal to or higher than a predetermined threshold, the internal clock is corrected with the mobile phone time (S208 → S210).

  When it is determined that the received wireless LAN access point radio wave reception quality and the wireless LAN access point radio wave reception quality at the wireless LAN time are equal to or higher than a predetermined threshold, the built-in clock time is corrected with the wireless LAN access point time (S211 → S212). ). If it is determined that the received wireless LAN access point radio wave reception quality and the wireless LAN access point radio wave reception quality at the wireless LAN time are not equal to or greater than a predetermined threshold, a synchronization signal is output to the WAVE communication function unit 32 based on the built-in clock time. (S213).

  According to the communication system 30 of the second embodiment, when the GPS 20 cannot be stably received for a long time and the mobile phone radio wave reception quality cannot be stably received, the communication timing can be reliably acquired from the wireless LAN time information.

  Further, according to the communication system 30, the internal clock is corrected using beacon signals periodically transmitted by the wireless LANs of the plurality of wireless LAN access points 40 at locations where neither the GPS 20 nor the mobile phone base station 22 can be used. it can.

  Note that the communication system of the present invention is not limited to the above-described embodiments, and appropriate modifications and improvements can be made.

  As described above, according to the communication system of the present invention, accurate timing of communication can be maintained when GPS cannot be received stably for a long time. As a result, the product can be stabilized to improve quality, and the industrial applicability of the present invention can be said to be great.

DESCRIPTION OF SYMBOLS 10,30 Communication system 11,31 Onboard equipment 12,32 WAVE communication function part 13,33 GPS time output function part 14,34 Cell-phone time output function part 15,35 Location estimation function part 16,36 Synchronization signal output function part 17 , 37 Road map database 18, 38 GPS time accuracy reduced location database 22 Mobile phone base station 39 Wireless LAN time output function unit

Claims (4)

A communication method for transmitting data from a base station to a plurality of mobile stations through a downlink channel, and transmitting data from a mobile station alternatively selected from the plurality to a base station through an uplink channel,
The mobile station receiving a GPS signal;
Determining the quality of the received GPS signal;
Setting the time obtained from GPS when the quality of the GPS signal is equal to or higher than a predetermined value to the mobile station;
Determining whether or not the mobile station is in a position with reduced accuracy by referring to a GPS time precision lowered location database according to the position of the mobile station;
A method of applying the time of the mobile station when the quality of the GPS signal is equal to or lower than a predetermined value, or when the mobile station exists at a position of reduced accuracy in the GPS time accuracy reduced location database. The communication method according to claim 1, further comprising: applying a wireless LAN time when the quality of the GPS signal is lower than a predetermined value and the time quality of the mobile station is lower than a predetermined value. A WAVE communication function unit that performs communication in synchronization with roadside equipment or other vehicles by WAVE communication;
A GPS time output function unit that creates absolute time based on a signal received from GPS, outputs it as GPS time used as a reference for a synchronization signal for WAVE communication, and outputs GPS radio wave reception quality;
A cellular phone time output function unit that creates an absolute time based on a signal received from a cellular phone base station, outputs the absolute time as a cellular phone time used as a reference for a synchronization signal for the WAVE communication, and outputs cellular phone radio wave reception quality ,
Obtaining position information from the GPS, correcting to a position on the road by road map data, estimating its own position, outputting it as self-position information, and how reliable the estimation result is to the position information A position estimation function unit that outputs the reliability shown together;
A synchronization signal output function unit that corrects the internal clock using the mobile phone time, the GPS time, the position information, and the reliability, and outputs a synchronization signal necessary for the WAVE communication based on the time of the internal clock;
A road map database having road information used by the position estimation function;
A communication system comprising: a GPS time accuracy reduced location database in which accuracy is measured in advance and a place where the GPS time accuracy reduction is likely to be placed is databased. Based on the signal received from the wireless LAN access point, a wireless LAN time output function unit that creates an absolute time, outputs the absolute time as a synchronization signal for the WAVE communication, and outputs the reception quality of the wireless LAN access point radio wave;
4. A synchronization signal output function for switching a mobile phone time output, the GPS time output, the wireless LAN time output, or the built-in clock to output a synchronization signal required for the WAVE communication. The communication system according to 1.

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