JP2009033340A - Communication system between vehicles, vehicle-mounted transmitter, and communicating method between vehicles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a communication system between vehicles which improves frequency using efficiency, offers a substantial service to receiving-side vehicles, and ensure the reception of high preference information by the receiving-side vehicles when a receiving C/N (Carrier to Noise ratio) is very inferior. <P>SOLUTION: A vehicle-mounted receiver is provided with: a C/N estimation unit 21 which calculates quality information of a signal transmitted from a vehicle-mounted transmitter; a modulation system switching unit 22 for demodulation which indicates a modulation system used for demodulation based on the quality information; a high hierarchy modulation system 231 which performs demodulation by a high hierarchy modulation system; and a low hierarchy modulation system demodulation unit 232 which performs demodulation by a low hierarchy modulation system. A vehicle-mounted transmitter is provided with: a preference discrimination unit 11 which classifies the vehicle information into high-preference information and low-preference information; a low hierarchy bitmapping unit 122 which assigns the high preference information to low hierarchy bits; and a high hierarchy bitmapping unit 121 which assigns the low preference information to high hierarchy bits; and modulates the mapped information by the high hierarchy modulation system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inter-vehicle communication system, an in-vehicle transmission device, and an inter-vehicle communication method for exchanging vehicle information.

  Reduction of traffic accident fatalities using ITS (Intelligent Transport Systems) has been sought as a national priority measure, and by exchanging information on each other's location information, speed, etc. directly between vehicles using wireless communication. Realization of an inter-vehicle communication system that prevents accidents is expected. Domestic inter-vehicle communication is currently being standardized at the ITS Forum. In this standardization work, the vehicle is equipped with a vehicle-to-vehicle communication vehicle-mounted device, and the vehicle's position information, speed information, brake information, blinker information, etc. are aggregated into one packet (packet length: fixed). A system that repeatedly transmits at a transmission cycle of is assumed. It is assumed that the vehicle that has received the packet analyzes the packet and performs an action to call attention or avoid danger when it is determined that a vehicle that threatens the safety of the vehicle exists in the vicinity. For example, it is assumed that a warning is displayed on the display of a car navigation system, or that intervention control (for example, forced braking) is performed as necessary.

  On the other hand, in order to avoid frontal collisions and encounter collisions between vehicles having a relatively large number of accidents by inter-vehicle communication, it is desirable that the inter-vehicle communication device covers a very wide communication area. For example, in the case of a frontal collision, assuming that each other is traveling at high speed, considering the reaction time until the human recognizes the information and starts to brake, system delay, etc., several hundred meters from the vehicle collision point It is necessary to realize communication from the front. As the communication area becomes wider, the number of vehicles accommodated per frequency band increases, so it is desirable that the inter-vehicle communication is a system that effectively uses limited frequency resources.

  From the viewpoint of effective use of frequency resources, it is desirable to use a modulation scheme with high transmission efficiency. If a large amount of information is transmitted by a modulation scheme with high transmission efficiency, a rich service can be provided to the vehicle driver on the receiving side. However, if the modulation scheme is fixed to a scheme with high transmission efficiency, a packet error occurs if the received C / N (Carrier to Noise ratio) is less than the required C / N of the modulation scheme, and the packet is discarded. I have to. In order to avoid such a problem, a hierarchical transmission scheme that transmits signals simultaneously by a plurality of modulation schemes having different required C / N is effective. In the hierarchical transmission scheme, for example, the transmitting side transmits signals simultaneously by the high-layer modulation scheme and the low-layer modulation scheme with different required C / N, and the reception side estimates the C / N of the received signal is the high-layer modulation. If it is worse than the required C / N of the scheme, the demodulation is switched to the low-layer modulation scheme with a lower required C / N. The hierarchical transmission scheme that switches to demodulation using the low-layer modulation scheme when the reception C / N is poor can reduce the packet discard rate and effectively use frequency resources. Furthermore, even when the reception C / N is poor, information with a high priority can be received at a minimum, which is effective for preventing accidents in inter-vehicle communication.

  Such a hierarchical transmission system is used in BS digital broadcasting. In BS digital broadcasting, demodulation is performed using an 8PSK modulation method with excellent transmission efficiency when the radio wave condition is good. On the other hand, when the radio wave condition is poor, the QPSK modulation method and the BPSK modulation method can be demodulated even with low C / N. By performing demodulation using, broadcast contents can be viewed with some satisfactory video and sound even when the radio wave condition is poor. With regard to such a hierarchical transmission scheme, for example, the receiver estimates the bit error rate or reception C / N of a received signal, and compares which estimation scheme is used with a preset threshold value to use which modulation scheme. Has been proposed (see, for example, Patent Document 1 below).

Japanese Patent Laid-Open No. 2003-24469

  However, according to the above-described conventional layered transmission technology for BS digital broadcasting, since it is specialized for image and sound transmission, transmission data using the high-layer modulation method and transmission data using the low-layer modulation method differ in image quality. Are transmitting the same content, and the information to be transmitted is not selected by priority. For this reason, when applied to inter-vehicle communication as it is, there is a problem that when the reception C / N is poor, there is a possibility that the receiving vehicle may not be able to correctly receive high priority information.

  The present invention has been made in view of the above, and improves frequency use efficiency in inter-vehicle communication, and provides a rich service to a receiving vehicle when reception C / N is good. It is an object of the present invention to obtain an inter-vehicle communication system, an in-vehicle transmission device, and an inter-vehicle communication method that allow a receiving vehicle to correctly receive high priority information when the reception C / N is poor.

  In order to solve the above-described problems and achieve the object, the present invention is an inter-vehicle communication system including an in-vehicle transmission device that transmits vehicle information and an in-vehicle reception device that receives the vehicle information, The in-vehicle receiving device includes: quality information calculating means for calculating quality information indicating the quality of the received signal transmitted from the in-vehicle transmitting device; a predetermined high-layer modulation scheme and a predetermined low-layer modulation scheme based on the quality information Modulation modulation switching means for instructing which modulation system to perform demodulation, high hierarchy modulation demodulation means for demodulating a received signal based on the higher hierarchy modulation scheme, and based on the lower hierarchy modulation scheme Low-level modulation system demodulating means for demodulating the received signal, and the in-vehicle transmission device prioritizes the vehicle information into high priority information and low priority information based on a predetermined priority determination criterion. A low-order bit that assigns the high-priority information to a predetermined low-level bit corresponding to the number of bits of one symbol of the low-level modulation method among transmission bits per symbol of the high-level modulation method Mapping means; and high hierarchy bit mapping means for assigning the low priority information to high hierarchy bits obtained by removing low hierarchy bits from the transmission bits, and mapping by the low hierarchy bit mapping means and the high hierarchy bit mapping means The received information is modulated by the high-layer modulation scheme and transmitted.

  According to the present invention, the hierarchical transmission method is applied to the inter-vehicle communication, and the transmission side determines the priority of the transmission information and modulates and transmits by the low-layer modulation method, thereby improving the frequency utilization efficiency. In addition, when the reception C / N is good, it provides a rich service to the receiving vehicle, and when the receiving C / N is poor, the receiving vehicle can correctly receive high priority information. There is an effect.

  Embodiments of an inter-vehicle communication system, an in-vehicle transmission device, and an inter-vehicle communication method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a functional configuration example of a main part of the in-vehicle transmission device according to the first embodiment of the present invention. As shown in FIG. 1, the in-vehicle transmission device according to the present embodiment includes an information priority determination unit 11 that classifies a bit sequence of transmission data into high priority information and low information, and an information priority determination unit 11 And a modulation unit 12 for modulating the bit sequence. In addition, the modulation unit 12 includes a high-layer bit mapping unit 121 that assigns a bit sequence classified as low-priority information by the information priority determination unit 11 to a high-layer bit described later on transmission mapping, and information priority determination And a low-layer bit mapping unit 122 that assigns a bit sequence classified as high-priority information to a low-layer bit described later on transmission mapping.

  In the inter-vehicle communication system of the present embodiment, communication is normally performed in a predetermined high-layer modulation scheme (for example, 16QAM (Quadrature Amplitude Modulation)), and the in-vehicle transmission device modulates information by the high-layer modulation scheme. Send. Further, a predetermined low layer modulation scheme (for example, QPSK (Quadrature Phase Shift Keying)) whose required C / N is lower than that of the high layer modulation scheme is defined. Then, one symbol transmission bit of the high layer modulation scheme is divided into low layer bits corresponding to the number of bits of one symbol of the low layer modulation scheme and high layer bits that are transmission bits other than the low layer bits, and are converted into low layer bits. Allocate high priority information. Then, in the case of a transmission path state that does not satisfy the required C / N of the high-layer modulation scheme, the receiving side demodulates with the low-layer modulation scheme and obtains information with high priority assigned to the low-layer bits.

  FIG. 2 is a diagram illustrating a functional configuration example of a main part of the in-vehicle receiving device of the present invention. As shown in FIG. 2, the in-vehicle reception device of the present embodiment includes a C / N estimation unit 21 that estimates C / N based on a received signal, and a C / N and a C / N estimated by the C / N estimation unit 21 are high. When the required C / N of the hierarchical modulation scheme is compared, and the estimated C / N is equal to or higher than the required C / N, the higher-layer modulation scheme is indicated, and the estimated C / N is lower than the required C / N Includes a demodulation modulation scheme switching unit 22 instructed by a low-layer modulation scheme, and a demodulation unit 23 that performs demodulation by a low-layer modulation scheme or a high-layer modulation scheme based on an instruction from the demodulation modulation scheme switching unit 22. . The demodulator 23 also instructs the high-layer modulation scheme demodulator 231 that performs demodulation using the high-layer modulation scheme, the low-layer modulation scheme demodulator 232 that performs demodulation using the low-layer modulation scheme, and the demodulation modulation scheme switching unit 22. The switching unit 233 is configured to switch the output destination of the received signal input based on the high-level modulation modulation demodulator 231 and the low-layer modulation modulation demodulator 232.

  Here, transmission information and priority according to the present embodiment will be described. For example, there are items such as GPS position data, GPS time, vehicle speed, vehicle traveling direction, vehicle type, reserve bit, greeting message, and the like as broadcast information currently being studied in the standardization of the inter-vehicle communication system. These can be classified into high priority information and low information to prevent accidents between vehicles. In the present embodiment, transmission information is set as broadcast information, GPS position data, GPS time, vehicle speed, and vehicle traveling direction are assumed as high priority information, and other information (vehicle type) is assumed as low priority information. , Reserve bits, greeting messages, etc.). Note that the items of transmission information and the classification method of high priority information and low priority information are not limited to this, and items suitable for the inter-vehicle communication system may be set.

  It continues and demonstrates operation | movement of the vehicle-mounted transmission apparatus of this Embodiment. First, the information priority determination unit 11 classifies the bit sequence of transmission data into information with high priority and information with low priority in order to prevent accidents between vehicles. Then, the information priority determination unit 11 outputs the bit sequence classified as low priority information to the high layer bit mapping unit 121, and outputs the bit sequence classified as high priority information to the low layer bit mapping unit 122. To do. The higher layer bit mapping unit 121 assigns the input bit sequence to the higher layer bits on the transmission mapping. The lower layer bit mapping unit 122 assigns the input bit sequence to the lower layer bits on the transmission mapping.

  FIGS. 3A and 3B are diagrams for explaining the high layer bits and the low layer bits of the present embodiment when the high layer modulation scheme is 16QAM. FIG. 3A is a diagram illustrating 16QAM symbol mapping. In the present embodiment, when 4 bits of 16QAM transmission are changed from bit 0 to bit 3 in order from the left, bit 1 and bit 3 are set as high hierarchy bits, and bit 0 and bit 2 are set as low hierarchy bits. FIG. 3B is a diagram illustrating symbol mapping obtained by extracting only the lower hierarchy bits. As shown in FIG. 3B, when only the lower layer bits are extracted, they are mapped as QPSK symbols having a required C / N lower than 16QAM. Thus, by mapping information with high priority as a QPSK symbol, information with high priority can be obtained when performing demodulation by QPSK.

  In the present embodiment, as described above, the symbol mapping corresponding to the high-layer modulation scheme is divided into high-layer bits and low-layer bits, and information with high priority is converted into low-layer bits with low priority information. Performs hierarchical mapping (hereinafter referred to as hierarchical encoding). By performing such hierarchical coding, all transmission information is obtained when the receiving side demodulates with a high-layer modulation scheme (in this case, 16QAM), and demodulates with a low-layer modulation scheme (in this case, QPSK). In this case, only transmission information with high priority is obtained.

  It is to be noted that which of the transmission bits of one symbol of the high layer modulation method is used as a low layer bit (the number of low layer bits and the bit position (bit number)) depends on the high layer modulation method and the low layer modulation method used. Therefore, it is determined based on the number of transmission bits per symbol and the signal point arrangement in each of the high layer modulation scheme and the low layer modulation scheme. Specifically, the number of bits of the lower layer bits is the number of transmission bits of one symbol of the lower layer modulation scheme. The bit position of the low layer bit is such that the distance between the signal points on the IQ plane is maximized when the low layer bit is extracted from the signal point of the high layer modulation system (so that the signal points are farthest from each other). What is necessary is just to determine the bit position extracted as a low hierarchy bit.

  FIG. 4 is a diagram illustrating an example of a packet format according to the present embodiment. As shown in FIG. 4, the packet format of this embodiment is composed of a preamble (PR), a unique word (UW), and data. This hierarchy coding is not performed for the preamble and unique word that are located at the beginning of the packet and are used for time synchronization, frequency synchronization, and the like.

  It continues and demonstrates operation | movement of the vehicle-mounted receiving apparatus of this Embodiment. First, the C / N estimation unit 21 estimates the reception C / N based on the reception signal. Then, the demodulation modulation scheme switching unit 22 compares the estimated received C / N with the required C / N of the higher layer modulation scheme (for example, 16QAM), and when the received C / N is equal to or greater than the required C / N. Instructs the switching unit 233 of the demodulator 23 to perform demodulation using the high-layer modulation scheme, and instructs the switching unit 233 of the demodulation unit 23 to perform demodulation using the low-layer modulation scheme when the received C / N is lower than the required C / N. The switching unit 233 of the demodulator 23 receives the received signal from the high layer modulation system demodulator 231 when the demodulation by the high layer modulation system is instructed, and when the demodulation by the low layer modulation system is instructed by the low layer The data is output to the modulation scheme demodulator 232. Then, the high layer modulation scheme demodulator 231 or the low layer modulation scheme demodulator 232 to which the received signal is input performs demodulation according to each modulation scheme.

  In general, an in-vehicle communication device mounted on a vehicle has both a transmission function and a reception function. In this case, in order to apply the present invention, the in-vehicle communication device may include the above-described in-vehicle transmission device as a transmission unit and the above-described in-vehicle reception device as a reception unit.

  As described above, in this embodiment, two types of hierarchized transmission of a high-layer modulation scheme and a low-layer modulation scheme are performed, and transmission bits of the high-layer modulation scheme are divided into high-layer bits and low-layer bits. In order to prevent an accident between vehicles, the transmission apparatus maps information with high priority to low-order bits and maps information with low priority to high-order bits. When the estimated value of the received C / N exceeds the required C / N of the higher layer modulation scheme, the in-vehicle receiving device demodulates with the higher layer modulation scheme, and the received C / N estimate is higher than the higher layer modulation scheme. When the required C / N is lower than the required value, demodulation is performed using a low-layer modulation method. For this reason, the frequency utilization efficiency is improved, and a rich service is provided to the receiving vehicle when the receiving C / N is good, and the receiving vehicle is given priority when the receiving C / N is poor. Highly accurate information can be received correctly. As a result, even when the reception C / N is poor, the minimum information can be obtained, and the accident rate between vehicles can be reduced.

  In the present embodiment, the explanation is limited to the case where the modulation scheme for performing hierarchical coding is 16QAM and QPSK, which are absolute phase-locked detection modulation schemes. However, the present invention is not limited to this, and 8PSK, BPSK, etc. Other absolute phase synchronous detection type modulation methods may be used. Further, a differential demodulation type modulation method such as 16 DAPSK (Differential Amplitude and Phase Shift Keying) or DQPSK (Differential Quadrature Phase Shift Keying) may be used. FIGS. 5A and 5B are diagrams illustrating an example of symbol mapping when 16 DAPSK is used as a high-layer modulation scheme and DQPSK is used as a low-layer modulation scheme. FIG. 5A illustrates symbol mapping of 16 DAPSK, and FIG. 5B illustrates an example of symbol mapping of DQPSK. For example, out of 4 bits of 16 DAPSK, 1 bit and 3 bits are set as low hierarchy bits, and 0 bit and 2 bits are set as high hierarchy bits, and the same operation as this embodiment can be performed. Furthermore, instead of performing hierarchical encoding using two modulation schemes, a format in which hierarchical encoding is performed by multiplexing three or more modulation schemes (for example, 16QAM, QPSK, and BPSK) may be used.

Embodiment 2. FIG.
FIG. 6 is a diagram illustrating a functional configuration example of a main part of the in-vehicle receiver according to the second embodiment of the present invention. As shown in FIG. 6, the in-vehicle receiver of this embodiment includes a C / N estimator 21 and a demodulation modulation scheme switching unit 22 of the in-vehicle receiver of Embodiment 1, respectively, a bit error rate calculator 31 and a demodulator. The present embodiment is the same as the in-vehicle receiving apparatus according to the first embodiment except that the modulation system switching unit 22a is used. Components having the same functions as those in the first embodiment are given the same reference numerals and description thereof is omitted.

  The in-vehicle transmission device according to the present embodiment is the same as the in-vehicle transmission device according to the first embodiment. The operation of the in-vehicle transmission device of the present embodiment is the same as that of the first embodiment, and the packet format is the same as that of the first embodiment. Hereinafter, description of the same parts as those in the first embodiment will be omitted, and parts different from those in the first embodiment will be described.

  The in-vehicle receiving device of this embodiment will be described. First, the bit error rate calculation unit 31 calculates the bit error rate based on the known information (unique word, preamble, etc.) of the header portion of the received signal. The demodulating modulation scheme switching unit 32 compares the bit error rate calculated by the bit error rate calculating unit 31 with a predetermined threshold value. When the bit error rate is less than the threshold value, the demodulation unit 23 performs demodulation using the higher-layer modulation scheme. When the bit error rate is equal to or greater than the threshold value, the demodulation unit 23 is instructed to perform demodulation using the low-layer modulation scheme. Subsequent operations of the demodulator 23 are the same as the operations of the in-vehicle receiver of the first embodiment.

  As described above, in this embodiment, two types of hierarchized transmission of a high-layer modulation scheme and a low-layer modulation scheme are performed, and transmission bits of the high-layer modulation scheme are divided into high-layer bits and low-layer bits. In order to prevent an accident between vehicles, the transmission apparatus maps information with high priority to low-order bits and maps information with low priority to high-order bits. The in-vehicle receiving device demodulates with a high-level modulation method when the bit error rate of the received signal falls below a predetermined threshold, and decreases when the bit error rate of the received signal exceeds the predetermined threshold. Demodulated by hierarchical modulation. For this reason, as in the first embodiment, the frequency utilization efficiency is improved, and when the reception C / N is good, a rich service is provided to the vehicle on the reception side, and the reception C / N is poor. In this case, the receiving vehicle can correctly receive high priority information. As a result, even when the reception C / N is poor, the minimum information can be obtained, and the accident rate between vehicles can be reduced.

Embodiment 3 FIG.
FIG. 7 is a diagram illustrating a functional configuration example of a main part of the in-vehicle receiving device according to the third embodiment of the present invention. As shown in FIG. 7, the in-vehicle receiver of the present embodiment includes a CRC (Cyclic Redundancy Check) check unit for the C / N estimation unit 21 and the demodulation modulation method switching unit 22 of the in-vehicle receiver of the first embodiment. 41, except for changing to the demodulation modulation switching unit 22b, is the same as the in-vehicle receiving apparatus of the first embodiment. In addition, the CRC check unit 41 according to the present embodiment includes a high layer modulation scheme CRC check unit 411 and a low layer modulation scheme CRC check unit. Components having the same functions as those in the first embodiment are given the same reference numerals and description thereof is omitted.

  The in-vehicle transmission device according to the present embodiment is the same as the in-vehicle transmission device according to the first embodiment. In the in-vehicle transmission device according to the present embodiment, high layer bit mapping section 121 calculates a CRC code of a bit sequence to be allocated to high layer bits, and low layer bit mapping section 122 calculates a CRC code of the bit sequence to be allocated to low layer bits. Although it differs from Embodiment 1 in that the calculated CRC code is included in the packet and transmitted, the other operations are the same as the operation of the in-vehicle transmission device of Embodiment 1. Hereinafter, description of the same parts as those in the first embodiment will be omitted, and parts different from those in the first embodiment will be described.

  Here, although the high layer bit mapping unit 121 and the low layer bit mapping unit 122 calculate the CRC code, the CRC calculation for calculating the CRC code of each bit sequence allocated to the high layer bit and the low layer bit is described. You may make it provide a part separately. FIG. 8 is a diagram illustrating an example of a packet format according to the present embodiment. As shown in FIG. 8, in the packet format of the present embodiment, in addition to the preamble, unique word, and data, a CRC for a high layer bit (a CRC code of a bit sequence used for high layer modulation), a CRC for a low layer bit ( Bit sequence CRC code used for low-layer modulation).

  The operation of the in-vehicle receiving device of this embodiment will be described. First, the high layer modulation scheme CRC check unit 411 of the CRC check unit 41 performs CRC check of the bit sequence assigned to the high layer bits based on the CRC for the high layer bits included in the received signal and the data of the received signal, The check result is output to the demodulation modulation method switching unit 22b. The CRC check unit 412 of the CRC check unit 41 performs CRC check on the bit sequence assigned to the low layer bits based on the CRC for the low layer bits included in the received signal and the received signal. Is output to the modulation method switching unit 22b for demodulation.

  When the modulation modulation switching unit 22b detects that the CRC check result output from the higher layer modulation CRC checker 411 is normal, it instructs the demodulation unit 23 to perform demodulation using the higher layer modulation method. Is detected, the demodulation unit 23 is instructed to perform demodulation using the low-layer modulation method. The subsequent operation of the demodulator 23 is the same as that of the first embodiment. Note that the low layer modulation scheme CRC check unit 412 is not used to determine whether the demodulation unit 23 switches between the high layer modulation scheme and the low layer modulation scheme, but the check result of the low layer modulation scheme CRC check unit 412 is abnormal. In this case, predetermined error processing is performed.

  As described above, in the present embodiment, the in-vehicle transmission device has a bit sequence assigned to high-order bits (transmission information with low priority) and a bit sequence assigned to low-order bits (transmission information with high priority). A CRC code is calculated for each and the calculation result is included in the transmitted packet. Then, the in-vehicle receiver performs a CRC check on the bit sequence (transmission information with low priority) assigned to the high layer bit, and performs a demodulation by the high layer modulation method when the check result is normal, which is abnormal. In some cases, demodulation by a high-level modulation method was not performed. For this reason, it is possible to extract information with high priority even in an environment where the transmission path in which the low priority information assigned to the high layer bits cannot be demodulated is reduced, and the accident rate between vehicles is reduced. It becomes possible to do.

Embodiment 4 FIG.
FIG. 9 is a diagram illustrating a functional configuration example of a main part of the in-vehicle receiver according to the fourth embodiment of the present invention. As shown in FIG. 9, the in-vehicle receiver of this embodiment includes a C / N estimator 21 and a demodulation modulation scheme switching unit 22 of the in-vehicle receiver of Embodiment 1 as a unique word demodulator 51 and a demodulator, respectively. Except for the change to the modulation system switching unit 22c, the present embodiment is the same as the in-vehicle reception device of the first embodiment. Further, the unique word demodulation unit 51 of the present embodiment includes a high layer modulation scheme demodulation unit 511 and a low layer modulation scheme demodulation unit 512. Components having the same functions as those in the first embodiment are given the same reference numerals and description thereof is omitted.

  The in-vehicle transmission device according to the present embodiment is the same as the in-vehicle transmission device according to the first embodiment. In the in-vehicle transmission device according to the present embodiment, the unique word is hierarchically encoded in the same manner as data, but the other operations are the same as those of the in-vehicle transmission device according to the first embodiment. Hereinafter, description of the same parts as those in the first embodiment will be omitted, and parts different from those in the first embodiment will be described.

  The operation of the in-vehicle receiving device of this embodiment will be described. First, the high layer modulation system demodulator 511 and the low layer modulation system demodulator 512 of the unique word demodulator 51 demodulate the unique word using the high layer modulation system and the low layer modulation system, respectively. Then, the high-layer modulation scheme demodulator 511 and the low-layer modulation scheme demodulator 122 each output information indicating whether or not demodulation has been performed to the demodulation modulation scheme switching section 22c as a unique word demodulation result. When the unique word demodulation result indicates that the unique word can be demodulated by the high layer modulation method, the demodulation modulation method switching unit 22c demodulates the data portion so that the data portion is also demodulated by the high layer modulation method. And indicates that the demodulator 23 is demodulated using the low-layer modulation method for the data portion. The subsequent operation of the demodulator 23 is the same as that of the first embodiment.

  As described above, in the present embodiment, when the in-vehicle transmission device performs hierarchical encoding on a unique word, and the in-vehicle reception device demodulates the unique word using a high-level modulation scheme, and can demodulate the unique word. In this case, the data portion is demodulated by the high-layer modulation method, and when the unique word cannot be demodulated by the high-layer modulation method, the data portion is demodulated by the low-layer modulation method. For this reason, it is possible to extract information with high priority even in an environment where the transmission path in which high-layer modulation cannot be performed is poor, and it is possible to reduce the accident occurrence rate between vehicles.

Embodiment 5 FIG.
FIG. 10 is a diagram illustrating a functional configuration example of a main part of the in-vehicle transmission device according to the fifth embodiment of the present invention. As shown in FIG. 10, the in-vehicle transmission device according to the present embodiment includes an information priority determination unit 11, a modulation scheme attribute determination unit 61, and a modulation unit 12a. The modulation unit 12 a includes a switching unit 123, an absolute phase synchronous detection type modulation scheme modulation unit 62, and a differential demodulation type modulation scheme modulation unit 63. The absolute phase synchronous detection type modulation method modulation unit 62 is further configured by a high layer bit mapping unit 621 and a low layer bit mapping unit 622. The differential demodulation type modulation method modulation unit 63 is further configured by a high layer bit mapping unit 631. , And a low layer bit mapping unit 632.

  It continues and demonstrates operation | movement of the vehicle-mounted transmission apparatus of this Embodiment. Since the operation of the information priority determination unit 11 of the present embodiment is the same as that of the information priority determination unit 11 of the first embodiment, the description thereof is omitted. The modulation method attribute determining unit 61 is, for example, a moving speed of the own vehicle, a relative speed with a vehicle traveling on the opposite lane by Doppler radar, DSRC (Dedicated Short Range Communication), an optical beacon, an FM (Frequency Modulation) beacon, an RFID (Radio Frequency Identification) or other information such as the court speed limit of the vehicle traveling area received by road-to-vehicle communication, or use the absolute phase-locked detection type modulation method when generating packets or the differential demodulation type modulation method Is used, and the determination result is instructed to the switching unit 123 of the modulation unit 12a.

  The switching unit 123 switches the output destination of the transmission information between the absolute phase synchronous detection type modulation scheme modulation unit 62 and the differential demodulation type modulation scheme modulation unit 63 based on the instructed determination result. In addition, the switching unit 123 further switches the output destination of the transmission information based on the priority classified by the information priority determination unit 11. Specifically, when receiving an instruction to use an absolute phase synchronous detection type modulation scheme, the switching unit 123 converts low priority information into a higher layer bit mapping unit of the absolute phase synchronous detection type modulation scheme modulation unit 62. The information is output to 621, and the high priority information is output to the lower layer bit mapping unit 622 of the absolute phase synchronous detection modulation type modulation unit 62. In addition, when receiving an instruction to use the differential demodulation type modulation scheme, the switching unit 123 outputs low priority information to the higher layer bit mapping unit 631 of the differential demodulation type modulation scheme modulation unit 63, Information with high priority is output to the lower layer bit mapping unit 632 of the differential demodulation type modulation scheme modulation unit 63.

  The absolute phase synchronous detection type modulation system of this embodiment is the same as that of Embodiment 1, and for example, 16QAM is used as the high-layer modulation system and QPSK is used as the low-layer modulation system. As a differential demodulation type modulation system, for example, 16 DAPSK is used as a high layer modulation system, and DQPSK is used as a low layer modulation system.

  FIG. 11A is a diagram illustrating an example of a packet format according to the present embodiment. The packet format of the present embodiment is obtained by adding a detection method notification bit indicating information on whether the modulation is performed by the absolute phase synchronous detection modulation method or the differential demodulation modulation method to the packet format of the first embodiment. Other than that, the packet format is the same as that of the first embodiment. Further, as in the second embodiment, the CRC codes of the high layer bits and the low layer bits may be calculated and included in the packet format. FIG. 11B is a diagram illustrating an example of a packet format in which CRC codes of higher layer bits and lower layer bits are added in addition to the detection method notification bits. Further, in addition to the detection method notification bit in the packet format, similarly to the third embodiment, the unique word may be subjected to the same hierarchical encoding as the data.

  In general, when compared with the same multi-value number, the transmission characteristics of the absolute phase-locked detection type is higher than that of the differential demodulation type when it is assumed that the communication devices are stationary and the propagation path does not fluctuate dynamically. Becomes better. On the other hand, it is known that the differential demodulation type has better transmission characteristics than the absolute phase synchronous detection type as the moving speed increases. Therefore, in an environment such as inter-vehicle communication in which the traveling speed of each vehicle is dynamically changed, it is desirable to switch between the absolute phase synchronous detection type and the differential demodulation type modulation method according to the moving speed of the vehicle. In particular, assuming a frontal collision prevention application, Doppler fluctuations increase because two vehicles approach each other at high speed. In this case, if hierarchical encoding is performed using only the absolute phase synchronous detection type modulation method, even if packet demodulation is performed using a modulation method with a low required C / N such as BPSK, it cannot follow high-speed Doppler fluctuations and can be used forever. There is a risk that the packet cannot be received and the frontal collision accident cannot be avoided.

  Therefore, in this embodiment, the traveling speed of the host vehicle, the relative speed with the vehicle traveling in the opposite lane by Doppler radar, etc., and the traveling of the host vehicle received by road-to-vehicle communication such as DSRC, optical beacon, FM beacon, RFID, etc. Based on information such as the area court speed limit, it is determined whether modulation is to be performed using the absolute phase-locked detection modulation method or the differential demodulation modulation method, and the packet is transmitted. Then, by including a detection method notification bit indicating which method is used for modulation in the transmission packet, the in-vehicle receiver can determine the modulation method.

  As a specific judgment material when adopting the differential demodulation type instead of the absolute phase synchronous detection type at the time of packet transmission, for example, when the moving speed of the vehicle is higher than a predetermined speed, or running on the opposite lane by Doppler radar etc. The case where it detects that the relative speed with a vehicle is large etc. can be considered. In addition, for example, when the speed limit of the host vehicle traveling area is notified by road-to-vehicle communication such as DSRC, optical beacon, FM beacon, and RFID, and if the speed limit is high, all surrounding vehicles are moving at high speed. Therefore, it is possible to adopt a differential demodulation type.

  At this time, since it is assumed that the detection method notification bits are not in error, the detection method notification bits are modulated by a differential demodulation type modulation method that can be reliably demodulated even during high-speed movement, and error correction also has a coding rate. It is desirable to ensure demodulation by applying a high and powerful error correction code.

  FIG. 12 is a diagram illustrating a functional configuration example of a main part of the in-vehicle reception device according to the present embodiment. As shown in FIG. 12, the in-vehicle receiving apparatus of the present embodiment is based on a C / N estimation unit 21, a demodulation modulation scheme switching unit 22d, a demodulation unit 23a, and a detection scheme notification bit included in a packet. And a method detecting unit 71 that detects a modulation method of received data. Further, the demodulator 23a includes an absolute phase synchronous detection modulation scheme demodulator 72, a differential demodulation modulation scheme demodulator 73, and a switching unit 233a. The absolute phase synchronous detection type modulation scheme demodulator 72 further comprises a high layer modulation scheme demodulator 721 and a low layer modulation scheme demodulator 722. The differential demodulation type modulation scheme demodulator 73 further comprises a high layer modulation scheme demodulator 73. A hierarchical modulation scheme demodulator 731 and a low hierarchy modulation scheme demodulator 732 are included.

  The operation of the in-vehicle receiving device of this embodiment will be described. The operation of C / N estimation unit 21 is the same as the operation of C / N estimation unit 21 of the first embodiment. The method detector 71 demodulates the detection method notification bit included in the received signal, and performs modulation using the absolute phase-locked detection modulation method or modulation using the differential demodulation modulation method based on the demodulated bit value. And the determination result is notified to the switching unit 233a and the demodulation modulation scheme switching unit 22d. The demodulation modulation scheme switching unit 22d performs the same operation as that of the demodulation modulation scheme switching unit 22 of the first embodiment, but based on the detection result of the scheme detection unit 71, the corresponding modulation scheme (absolute phase synchronous detection type). The required C / N and the received C / N of the high-level modulation method of the modulation method or the high-level modulation method of the differential demodulation type modulation method are compared, and either the high-level modulation method or the low-level modulation method is selected. It is determined whether to instruct modulation.

  Based on the notified determination result, the switching unit 233a switches the output destination of the transmission information between the absolute phase synchronous detection type modulation method demodulation unit 72 and the differential demodulation type modulation method demodulation unit 73. Further, based on the instruction from the demodulation modulation method switching unit 22d, the switching unit 233a further outputs the higher-layer modulation method demodulation unit 721 and the lower-layer modulation method demodulation unit 722 in the case of the absolute phase synchronous detection modulation method. To switch between. In the case of the differential demodulation type modulation method, the switching unit 233a further switches the output destination between the high layer modulation method demodulation unit 731 and the low layer modulation method demodulation unit 732. When a received signal is input, the high layer modulation system demodulator 721, the low layer modulation system demodulator 722, the high layer modulation system demodulator 731, and the low layer modulation system demodulator 732 demodulate the received signal according to each modulation system. Do.

  In the present embodiment, the required C / N is used to determine whether to perform demodulation in the high-layer modulation scheme or the low-layer modulation scheme, but the bit error rate is the same as in the second embodiment. May be compared with a predetermined threshold value to determine whether to perform demodulation in the high layer modulation method or the low layer modulation method. In addition, as shown in FIG. 11-2, the packet format includes a CRC of a high hierarchy bit and a CRC of a low hierarchy bit, and the determination is made based on the CRC check result of the high hierarchy bit as in the third embodiment. You may make it do. Similarly to the fourth embodiment, the in-vehicle transmission device also performs hierarchical encoding for the unique word in the same manner as the data portion, and the in-vehicle reception device demodulates the unique word and makes a determination based on the demodulation result. It may be.

  As described above, in this embodiment, the in-vehicle transmission device switches between the absolute phase synchronous detection type and the differential demodulation type modulation method according to the moving speed of the own vehicle, and the packet indicates which method is used for modulation. Included as a detection method notification bit. For this reason, even in an environment where both a stationary environment and a dynamic environment such as inter-vehicle communication are mixed, a modulation method with good transmission characteristics can be selected appropriately, and transmission errors are reduced compared to the first embodiment, and the vehicle It is possible to reduce the accident rate during that time.

  As described above, the inter-vehicle communication system, the in-vehicle transmission device, and the inter-vehicle communication method according to the present invention are useful for an inter-vehicle communication system for exchanging vehicle information, and are particularly suitable for an inter-vehicle communication system with limited frequency resources. ing.

It is a figure which shows the function structural example of the principal part of Embodiment 1 of the vehicle-mounted transmission apparatus concerning this invention. It is a figure which shows the function structural example of the principal part of the vehicle-mounted receiving apparatus of Embodiment 1 of this invention. It is a figure which shows the symbol mapping of 16QAM. It is a figure which shows the symbol mapping which extracted only the low hierarchy bit. 6 is a diagram illustrating an example of a packet format according to Embodiment 1. FIG. It is a figure which shows the symbol mapping of 16DAPSK. It is a figure which shows an example of the symbol mapping of DQPSK. 6 is a diagram illustrating a functional configuration example of a main part of the in-vehicle reception device according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a functional configuration example of a main part of the in-vehicle receiving device according to the third embodiment. FIG. 10 is a diagram illustrating an example of a packet format according to the third embodiment. FIG. 10 is a diagram illustrating a functional configuration example of a main part of an in-vehicle receiving device according to a fourth embodiment. FIG. 10 is a diagram illustrating a functional configuration example of a main part of an in-vehicle transmission device according to a fifth embodiment. FIG. 20 is a diagram illustrating an example of a packet format according to the fifth embodiment. FIG. 20 is a diagram illustrating another example of a packet format according to the fifth embodiment. FIG. 10 is a diagram illustrating a functional configuration example of a main part of an in-vehicle reception device according to a fifth embodiment.

Explanation of symbols

11 Information priority determination unit 12, 12a Modulation unit 21 C / N estimation unit 22, 22a, 22b, 22c, 22d Demodulation modulation mode switching unit 23, 23a Demodulation unit 31 Bit error rate calculation unit 41 CRC check unit 51 Unique word Demodulator 61 Modulation method attribute determination unit 62 Absolute phase synchronous detection type modulation method modulation unit 63 Differential demodulation type modulation method modulation unit 71 Method detection unit 72 Absolute phase synchronous detection type modulation method demodulation unit 73 Differential demodulation type modulation method demodulation unit 121,621,631 High layer bit mapping unit 122,622,632 Low layer bit mapping unit 123,233,233a Switching unit 231,511,721,731 High layer modulation system demodulation unit 232,512,722,732 Low layer modulation System demodulation unit 411 High layer modulation method CRC check unit 412 Low layer modulation method C C check unit

Claims (17)

A vehicle-to-vehicle communication system including an in-vehicle transmission device that transmits vehicle information and an in-vehicle reception device that receives the vehicle information,
The in-vehicle receiver is
Quality information calculating means for calculating quality information indicating the quality of the received signal transmitted from the in-vehicle transmission device;
A demodulation modulation mode switching means for instructing whether to perform demodulation based on a modulation scheme of a predetermined high-layer modulation scheme or a predetermined low-layer modulation scheme based on the quality information;
High-layer modulation scheme demodulation means for demodulating a received signal based on the high-layer modulation scheme;
Low-layer modulation scheme demodulation means for demodulating a received signal based on the low-layer modulation scheme;
With
The in-vehicle transmission device is
Priority determination means for classifying the vehicle information into high priority information and low priority information based on a predetermined priority determination criterion;
Low layer bit mapping means for allocating the high priority information to predetermined low layer bits corresponding to the number of bits of one symbol of the low layer modulation method among transmission bits per symbol of the high layer modulation method;
High layer bit mapping means for assigning the low priority information to high layer bits obtained by removing low layer bits from the transmission bits;
With
An inter-vehicle communication system, wherein information mapped by the low layer bit mapping means and the high layer bit mapping means is modulated by the high layer modulation system and transmitted. The quality is an estimated value of received C / N based on the received signal,
The demodulation modulation method switching means instructs demodulation by the higher layer modulation method when the received C / N is equal to or higher than the required C / N of the higher layer modulation method, and the received C / N is the higher layer 2. The inter-vehicle communication system according to claim 1, wherein demodulation is instructed by the low-layer modulation method when the required C / N of the modulation method is not satisfied. The quality is a bit error rate based on a received signal,
The demodulation modulation scheme switching means instructs demodulation by the higher layer modulation scheme when the bit error rate is less than a predetermined threshold, and the lower layer modulation when the bit error rate is equal to or greater than a predetermined threshold. The inter-vehicle communication system according to claim 1, wherein demodulation is instructed by a system. The in-vehicle transmission device transmits the high layer bit CRC code and the low layer bit CRC code included in transmission information,
The quality is a CRC check result based on the CRC code of the higher layer bits and the received signal,
The demodulation modulation method switching means instructs the demodulation by the higher layer modulation method when the check result is normal, and instructs the demodulation by the lower layer modulation method when the check result is abnormal. The inter-vehicle communication system according to claim 1, wherein The in-vehicle transmission device distributes a known sequence included in a header of transmission information to the high layer bit and the low layer bit, modulates the high layer modulation method, and transmits the modulated signal.
The quality information calculating means demodulates the known sequence by the high-layer modulation method, and determines whether the known sequence has been correctly demodulated as the quality information,
The demodulation modulation mode switching means instructs demodulation by the higher layer modulation method when the known sequence can be demodulated correctly, and instructs demodulation by the lower layer modulation method when the known sequence cannot be demodulated correctly. The inter-vehicle communication system according to claim 1.   The inter-vehicle communication system according to any one of claims 1 to 5, wherein the high-layer modulation scheme and the low-layer modulation scheme are absolute phase-locked detection modulation schemes.   The inter-vehicle communication system according to any one of claims 1 to 5, wherein the high hierarchy modulation scheme and the low hierarchy modulation scheme are differential demodulation modulation schemes. The in-vehicle transmission device is
Method selection means for selecting either an absolute phase synchronous detection type modulation method or a differential demodulation type modulation method based on a moving speed of a vehicle on which the device is mounted or a relative speed with a vehicle that receives the vehicle information;
Further comprising
The high layer bit mapping means and the low layer bit mapping means are configured to be compatible with each of the absolute phase synchronous detection modulation method and the differential demodulation modulation method,
A scheme identifier indicating the selected scheme by modulating the information mapped by the higher hierarchy bit mapping means and the lower hierarchy bit mapping means corresponding to the selected scheme with the higher hierarchy modulation scheme of the selected scheme Included in the transmission signal,
on the other hand,
The in-vehicle receiver is
A method detecting means for detecting a modulation method used for demodulation based on the method identifier;
Further comprising
The high-layer modulation scheme demodulation means and the low-layer modulation scheme demodulation means are configured to be compatible with the absolute phase synchronous detection modulation scheme and the differential demodulation modulation scheme,
2. The inter-vehicle communication system according to claim 1, wherein the higher layer modulation method demodulation unit and the lower layer modulation method demodulation unit corresponding to the detected method perform demodulation. The quality is an estimated value of received C / N based on the received signal,
The demodulation modulation method switching means instructs demodulation by the higher layer modulation method when the received C / N is equal to or higher than the required C / N of the higher layer modulation method, and the received C / N is the higher layer 9. The inter-vehicle communication system according to claim 8, wherein when the required C / N of the modulation method is not satisfied, demodulation by the low-layer modulation method is instructed. The quality is a bit error rate based on a received signal,
The demodulation modulation scheme switching means instructs demodulation by the higher layer modulation scheme when the bit error rate is less than a predetermined threshold, and the lower layer modulation when the bit error rate is equal to or greater than a predetermined threshold. The inter-vehicle communication system according to claim 8, wherein demodulation according to a system is instructed. The in-vehicle transmission device transmits the high layer bit CRC code and the low layer bit CRC code included in transmission information,
The quality is a CRC check result based on the CRC code of the higher layer bits and the received signal,
The demodulation modulation method switching means instructs the demodulation by the higher layer modulation method when the check result is normal, and instructs the demodulation by the lower layer modulation method when the check result is abnormal. The inter-vehicle communication system according to claim 8, The in-vehicle transmission device distributes a known sequence included in a header of transmission information to the high layer bit and the low layer bit, modulates the high layer modulation method, and transmits the modulated signal.
The quality information calculating means demodulates the known sequence by the high-layer modulation method, and determines whether the known sequence has been correctly demodulated as the quality information,
The demodulation modulation mode switching means instructs demodulation by the higher layer modulation method when the known sequence can be demodulated correctly, and instructs demodulation by the lower layer modulation method when the known sequence cannot be demodulated correctly. The inter-vehicle communication system according to claim 8.   13. The predetermined low layer bit is determined so as to maximize the distance between signal points on an IQ plane based on the signal point arrangement of the low layer modulation system. Vehicle-to-vehicle communication system described in 1. A vehicle-to-vehicle communication system including an in-vehicle transmission device that transmits vehicle information and an in-vehicle reception device that receives the vehicle information,
The in-vehicle transmission device is
Priority determination means for determining the priority of the vehicle information based on a predetermined priority determination criterion, and classifying the vehicle information for each priority;
A bit mapping means for allocating the vehicle information classified into the priority corresponding to the assigned bit to the assigned bit based on the correspondence between the predetermined priority and the assigned bit, and the classification result;
With
The allocation bit corresponds to each signal point arrangement of a predetermined hierarchical modulation scheme having the same number of layers as the number of priority classifications,
The information mapped by the bit mapping means is modulated and transmitted by a predetermined modulation method,
on the other hand,
The in-vehicle receiver is
Quality information calculating means for calculating quality information indicating the quality of the received signal transmitted from the in-vehicle transmission device;
A demodulating modulation scheme switching means for instructing which of the predetermined hierarchical modulation schemes to perform demodulation based on the quality information;
High-layer modulation scheme demodulation means for performing demodulation based on the modulation scheme of each layer for each layer;
A vehicle-to-vehicle communication system comprising: An in-vehicle transmission device that configures a communication system between vehicles together with an in-vehicle receiving device that receives vehicle information, and transmits the vehicle information,
Priority determination means for classifying the vehicle information into high priority information and low priority information based on a predetermined priority determination criterion;
Low-layer bit mapping means for allocating the high-priority information to predetermined low-layer bits corresponding to the number of bits of one symbol of the predetermined low-layer modulation system among transmission bits per symbol of the predetermined high-layer modulation system When,
High layer bit mapping means for assigning the low priority information to high layer bits obtained by removing low layer bits from the transmission bits;
With
An in-vehicle transmission device characterized in that the information mapped by the low layer bit mapping means and the high layer bit mapping means is modulated by the high layer modulation system and transmitted. Method selection means for selecting either an absolute phase synchronous detection type modulation method or a differential demodulation type modulation method based on a moving speed of a vehicle on which the device is mounted or a relative speed with a vehicle that receives the vehicle information;
Further comprising
The high layer bit mapping means and the low layer bit mapping means are configured to be compatible with each of the absolute phase synchronous detection modulation method and the differential demodulation modulation method,
A scheme identifier indicating the selected scheme by modulating the information mapped by the higher hierarchy bit mapping means and the lower hierarchy bit mapping means corresponding to the selected scheme with the higher hierarchy modulation scheme of the selected scheme The in-vehicle transmission device according to claim 15, wherein the transmission signal is transmitted by being included. A vehicle-to-vehicle communication method in a vehicle-to-vehicle communication system that includes a vehicle-mounted transmission device that transmits vehicle information and a vehicle-mounted reception device that receives the vehicle information,
A priority determination step for classifying the vehicle information into high priority information and low priority information based on a predetermined priority determination criterion;
The in-vehicle transmission device transmits the high priority information to predetermined low layer bits corresponding to the number of bits of one symbol of a predetermined low layer modulation method among transmission bits per symbol of a predetermined high layer modulation method. A low-level bit mapping step to assign;
The in-vehicle transmission device assigns the low priority information to a high layer bit obtained by removing a low layer bit from the transmission bit, and a high layer bit mapping step,
The in-vehicle transmission device transmits the information mapped by the low layer bit mapping means and the high layer bit mapping means by modulating the information by the high layer modulation scheme,
A quality information calculating step in which the in-vehicle receiving device calculates quality information indicating the quality of the received signal transmitted from the in-vehicle transmitting device;
A modulation modulation switching step for demodulation instructing whether the in-vehicle receiving apparatus performs demodulation based on which of the high-layer modulation method and the low-layer modulation method based on the quality information;
When the in-vehicle receiver is instructed to the high layer modulation method, a high layer modulation method demodulation step for demodulating a received signal based on the high layer modulation method;
When the in-vehicle receiver is instructed by the low layer modulation method, the low layer modulation method demodulation step for demodulating the received signal based on the low layer modulation method;
A vehicle-to-vehicle communication method comprising:

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