JP2010081179A - Communication apparatus, communication method and communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of improving the accuracy of channel estimation without complicating calculation processing on a receiver side. <P>SOLUTION: There is provided a communication apparatus 10, mounted on a mobile body, including: a vehicle speed detecting section 12 for detecting a moving speed of the communication apparatus 10; a transmission frame generating section 14 for determining a frame length as the length of a frame in accordance with the vehicle speed detected by the vehicle speed detecting section 12, and generating a transmission frame having the frame length of the length of the entire frame; and a transmission section 17 for transmitting the transmission frame generated by the transmission frame generating section 14. The transmission frame generating section 14 stores frame length determining information in which the moving speed and the frame length are associated with each other, and determines the frame length by acquiring the frame length associated with the moving speed detected by the vehicle speed detecting section 12 from the frame length determining information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for setting a transmission frame length in an inter-vehicle communication system in which vehicles directly communicate with each other.

  Conventionally, the inter-vehicle communication system provides a safe driving support service and entertainment information during travel by directly communicating with each other without intervening infrastructure such as roadside devices by wireless communication technology using autonomous distributed control. The purpose is to realize services.

  Since the inter-vehicle communication system performs communication while each vehicle moves in the communication, the characteristics may be deteriorated due to the influence of the communication path. Specifically, the wireless signal transmitted from the inter-vehicle communication device is subjected to Doppler frequency fluctuations according to the vehicle speed, so that the communication quality is deteriorated. The effect is more strongly affected as the vehicle speed increases. This is shown in FIG. The vehicle 901 communicates with the vehicles 902 and 903, respectively. However, the vehicle 902 travels in the same direction as the vehicle 901, whereas the vehicle 903 travels in a direction facing the vehicle 901. Is different. In this case, the communication characteristics between the vehicle 901 and the vehicle 903 are deteriorated as compared with the communication between the vehicle 901 and the vehicle 902.

  As the above countermeasure, as the preamble portion 91 (see FIG. 8) at the beginning of the frame to be transmitted, a part (known signal part) that has already been transmitted to the reception side and is known on the reception side is provided. A method (channel estimation) for grasping the channel state of the preamble portion 91 (see FIG. 8), which is a known signal portion, is generally used. Accordingly, correction (channel compensation) can be performed on the data unit 93 (see FIG. 8) following the preamble unit 91 (see FIG. 8) based on the estimated channel estimation value. Here, the channel is the phase of the complex symbol rotated due to the frequency shift of the reference frequency signal in the mobile station. Further, this phase shift phenomenon is called channel fluctuation, and this phase shift is called channel fluctuation amount. In channel estimation, the channel fluctuation amount is estimated.

On the other hand, the state of channel fluctuation greatly depends on the moving speed of the vehicle. A parameter representing this is the maximum Doppler frequency of the channel. The maximum Doppler frequency f _D of the channel is expressed as follows using the carrier frequency f _c and the vehicle speed v.

f _D = v / (c / f _c ) (1)

  As is clear from the above equation (1), as the vehicle speed increases, the maximum Doppler frequency increases and the state of channel fluctuation becomes severe. When channel fluctuations are severe, channel estimation and channel compensation based on the preamble section 91 (see FIG. 8) may not work well. That is, when the vehicle speed is high, the channel estimation value obtained by channel estimation based on the preamble portion 91 (see FIG. 8), which is a known signal portion, and the channel fluctuation that actually occurs in the data portion 93 (see FIG. 8). The difference between the amount is greater. This situation is shown in FIG. The upper part of FIG. 8 shows the structure of the frame. The frame is composed of a header part 92 including a preamble part 91, a data part 93, and the like. Further, the lower part shows the relationship between the channel estimation value calculated based on the preamble section 91 and the actual channel fluctuation amount for each time t, and FIG. 8A shows a low vehicle speed. FIG. 8B shows a case where the vehicle speed is high.

  In FIG. 8A, since the vehicle speed is small, the error between the channel estimation value estimated based on the preamble section 91 and the channel fluctuation amount in the data section 93 is small. For this reason, channel estimation and channel compensation operate relatively well. However, as shown in FIG. 8B, when the vehicle speed is high, the channel estimation value estimated based on the preamble section 91 (see FIG. 8) and the channel fluctuation amount generated in the data section 93 Since the error between the two increases, channel estimation and channel compensation do not work well.

  In view of this problem, for example, Patent Document 1 discloses a technique for correcting a channel state estimated on the receiving side.

International Publication No. WO2006 / 075547 Pamphlet

  However, the technique disclosed in Patent Document 1 has a problem that the arithmetic processing for correcting the channel state estimated on the receiving side is complicated.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of improving the accuracy of channel estimation without complicating the arithmetic processing on the receiving side. It is to provide.

  In order to solve the above problem, according to a certain aspect of the present invention, a communication device mounted on a mobile body, which is detected by a movement speed detection unit that detects a movement speed of the communication device, and a movement speed detection unit A frame length that is a frame length is determined according to the moving speed, a transmission frame generation unit that generates a transmission frame having the frame length as the entire frame length, and a transmission that transmits the transmission frame generated by the transmission frame generation unit A communication device is provided.

  The transmission frame generation unit described above holds frame length determination information in which the moving speed and the frame length are associated with each other, and the frame length associated with the moving speed detected by the moving speed detection unit from the frame length determination information. It is also possible to determine the frame length by acquiring.

  The transmission frame generation unit described above may determine the frame length by obtaining the frame length using a calculation formula capable of calculating the frame length from the moving speed.

  As described above, according to the present invention, it is possible to provide a technique capable of improving the accuracy of channel estimation without complicating arithmetic processing on the receiving side.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol. The description will be given in the following order.

1. 1. Configuration of communication system according to this embodiment 2. Configuration of communication apparatus according to this embodiment 3. Data structure of frame length determination information according to this embodiment 4. Data structure of frame according to this embodiment 5. Operation at the time of frame transmission by the communication apparatus according to the present embodiment 6. Operation at the time of frame reception by the communication apparatus according to the present embodiment Effect by this embodiment 8. Modification of this embodiment

[1. Configuration of communication system according to the embodiment]
FIG. 1 is a diagram illustrating a configuration of a communication system according to the present embodiment. With reference to FIG. 1, the configuration of the communication system according to the present embodiment will be described.

  As illustrated in FIG. 1, the communication system 1 includes a communication device 10 (10A to 10C). The communication device 10 (10A to 10C) is mounted on each of the vehicles C (C1 to C3). In the present embodiment, there are three vehicles C, vehicles C1 to C3, but the number of vehicles C is not particularly limited as long as there are a plurality of vehicles C. Therefore, the communication system 1 includes a plurality of communication devices 10. In the present embodiment, the communication device 10 is mounted on the vehicle C. However, the communication device 10 may be mounted on some mobile body, and the mobile body on which the communication device 10 is mounted is not particularly limited.

  Further, in the present embodiment, each of the communication devices 10 includes both a function of transmitting a radio signal and a function of receiving a radio signal, but the configuration is not limited to such a configuration. The communication system 1 may be configured to include, for example, a transmission device that transmits a radio signal and a reception device that receives a radio signal transmitted from the transmission device.

[2. Configuration of Communication Device According to Embodiment]
FIG. 2 is a diagram illustrating a configuration of the communication apparatus according to the present embodiment. With reference to FIG. 2 (refer to FIG. 1 as appropriate), the configuration of the communication apparatus according to the present embodiment will be described. In addition, the communication apparatus here is provided with both the function as an above-described receiving apparatus and the function as a transmission apparatus.

  The communication device 10 includes a control unit 11, a vehicle speed detection unit 12, a reception frame processing unit 13, a transmission frame generation unit 14, a modulation unit 15, a demodulation unit 16, a transmission unit 17, and a reception unit 18. It is prepared for. The vehicle speed detection unit 12, the transmission frame generation unit 14, the modulation unit 15, and the transmission unit 17 are configured to function as a transmission device. The reception frame processing unit 13, the demodulation unit 16, the reception unit 18, and the like. Is a configuration that functions as a receiving device.

  The control unit 11 has a function of generating transmission data and outputting it to the transmission frame generation unit 14. Further, the control unit 11 has a function of performing processing based on information output from the reception frame processing unit 13.

  The vehicle speed detector 12 has a function of detecting the traveling speed (vehicle speed) of the vehicle C (or the communication device 10). As described above, the communication device 10 may be mounted on a moving body other than the vehicle C. In that case, the vehicle speed detection unit 12 functions as a moving speed detection unit that detects the moving speed of the moving body. To do.

  The reception frame processing unit 13 has a function of decoding the signal demodulated and output by the demodulation unit 16 and calculating a channel estimation value based on a part of the reception data obtained by decoding. The reception frame processing unit 13 has a function of performing channel compensation on the remaining part of the reception frame based on the calculated channel estimation value.

  The transmission frame generation unit 14 has a function of determining a frame length that is a frame length according to the vehicle speed detected by the vehicle speed detection unit 12. The transmission frame generation unit 14 has a function of generating a transmission frame with the determined frame length as the entire frame length. The transmission frame generation unit 14 encodes the generated transmission frame and outputs the encoded transmission frame to the modulation unit 15.

  The transmission frame generation unit 14 holds the frame length determination information 140 (see FIG. 3) in which the vehicle speed 141 (see FIG. 3) as the moving speed of the vehicle and the frame length 142 (see FIG. 3) are associated with each other. Also good. In that case, the transmission frame generation unit 14 determines the frame length by obtaining the frame length 142 associated with the vehicle speed detected by the vehicle speed detection unit 12 from the frame length determination information 140 (see FIG. 3). What should I do? Further, the transmission frame generation unit 14 may determine the frame length by obtaining the frame length using a calculation formula capable of calculating the frame length from the vehicle speed.

  The modulation unit 15 has a function of modulating the transmission frame encoded by the transmission frame generation unit 14 and transmitting the modulated transmission frame via the transmission unit 17.

  The demodulating unit 16 has a function of demodulating the signal received by the receiving unit 18 and outputting the demodulated signal to the received frame processing unit 13.

  The transmission unit 17 is configured by an antenna or the like, and has a function of transmitting a signal output from the modulation unit 15 as a radio signal.

  The receiving unit 18 includes an antenna or the like and has a function of receiving a radio signal. The receiving unit 18 has a function of outputting the received radio signal to the demodulating unit 16.

[3. Data structure of frame length determination information according to this embodiment]

  FIG. 3 is a diagram illustrating a data configuration of frame length determination information according to the present embodiment. With reference to FIG. 3, the data structure of the frame length determination information according to the present embodiment will be described.

  As shown in FIG. 3, the frame length determination information 140 is configured by associating a vehicle speed 141 with a frame length 142. In the example shown in FIG. 3, the vehicle speed 141 is set in n stages, and the frame length 142 is assigned to each of the vehicle speeds 141 divided in the n stages. n may be any number as long as it indicates a plurality. The values set in the items of the frame length determination information 140 are, for example, those obtained by calculating the optimal frame length according to the vehicle speed by simulation, propagation measurement, or the like.

[4. Data structure of frame according to this embodiment]

  FIG. 4 is a diagram showing a data structure of a frame according to the present embodiment. With reference to FIG. 4, the data structure of the frame according to the present embodiment will be described.

  As shown in FIG. 4, the frame includes a header part 22 and a data part 23. The header portion 22 may be set with values such as a preamble (not shown) and a data type (not shown). The header portion 22 also describes a value indicating the frame length.

[5. Operation during frame transmission by communication apparatus according to this embodiment]

  FIG. 5 is a diagram illustrating an operation at the time of frame transmission by the communication apparatus according to the present embodiment. With reference to FIG. 5 (refer to other figures as appropriate), the operation at the time of frame transmission by the communication apparatus according to the present embodiment will be described.

  The vehicle information generated by the control unit 11 is generated in the form of a frame in the transmission frame generation unit 14. On the other hand, the vehicle speed detector 12 always detects the vehicle speed of the vehicle. When generating a frame, the transmission frame generation unit 14 determines the vehicle speed of the vehicle at the time of generation, and determines the frame length according to the vehicle speed (step S101). When the vehicle speed is vx (where v2 ≦ vx <v3), the transmission frame generation unit 14 knows from the frame length determination information 140 that the corresponding frame length 142 is LF3. A frame is generated as LF3 (step S102).

  When the frame length determined as described above is LF3, the frame length is described in the header section 22, and the transmission frame generation section 14 generates a frame so that the entire frame length is LF3. . Thereafter, the generated frame is modulated into a radio signal by the modulation unit 15 and then transmitted via the transmission unit 17 (step S103).

[6. Operation when receiving a frame by the communication apparatus according to the present embodiment]

  FIG. 6 is a diagram illustrating an operation at the time of frame reception by the communication apparatus according to the present embodiment. With reference to FIG. 6 (refer to other figures as appropriate), the operation at the time of frame reception by the communication apparatus according to the present embodiment will be described.

  The receiving unit 18 receives a frame using a radio signal (step S201). The radio signal received by the reception unit 18 is demodulated by the demodulation unit 16 and output to the reception frame processing unit 13. The reception frame processing unit 13 processes the reception frame output from the demodulation unit 16. In performing this process, the reception frame processing unit 13 calculates a channel estimation value based on a part of the reception frame (step S202), and performs channel compensation on the remaining part of the reception frame based on the channel estimation value. (Step S203). At this time, a portion describing the frame length (frame length 21) may be set in the header 22 in the received frame, and the received frame processing unit 13 reads the described frame length 21. Thus, the length of the data unit 23 can be grasped and the vehicle information can be extracted from the reception frame.

[7. Effects of this embodiment]
According to this embodiment, the following effects can be obtained.

  By making the frame length variable according to the vehicle speed, the influence of the Doppler frequency depending on the vehicle speed can be reduced. Specifically, the frame length is shortened when the vehicle speed is high, and the frame length is lengthened when the vehicle speed is slow. When channel estimation is performed based on a preamble portion in which a known signal is set by shortening the frame length, the time when the preamble portion that is the basis of channel estimation is received and the channel compensation target The time when the data part is received is made close, and the error between the channel estimation value and the actual channel fluctuation amount of the data part can be reduced. Therefore, improvement in channel estimation accuracy can be expected.

  The only function that the inter-vehicle communication device on the receiving side should have is the function of processing the data part following the header part based on the frame length included in the header part, as represented by the adaptive modulation method and the like. There is no overhead such as exchange of modulation schemes between the transceivers. Therefore, channel estimation can be improved with a simple configuration.

[8. Modification of this embodiment]
In the above, preferred embodiments of the present invention have been described with reference to the accompanying drawings. However, it goes without saying that the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the present embodiment, in relation to the vehicle speed and the frame length, the frame length is determined by referring to a table calculated in advance by simulation or the like. For example, a calculation formula for calculating the frame length from the vehicle speed is as follows. It is also possible to prepare in advance and make the frame length variable in smaller units.

  In this embodiment, in order to specify a frame length for realizing a variable-length frame, a method for providing a part for specifying the frame length in the header part and performing processing based on the frame length on the receiving side has been described. The frame length information may be transmitted to the receiving side by other methods. For example, the present invention can be applied to a system using a control channel and a data channel (represented by a mobile phone).

  The present embodiment can also be applied to a system in which a modulation parameter is made variable such as adaptive modulation.

  In this embodiment, the channel estimation value is calculated using the known signal in the preamble part, but the channel estimation value calculation method is not limited. The present embodiment can be applied to any system that obtains channel estimation using a part of a transmission frame and performs channel compensation using the remaining part.

It is a figure which shows the structure of the communication system which concerns on this embodiment. It is a figure which shows the structure of the communication apparatus which concerns on this embodiment. It is a figure which shows the data structure of the frame length determination information which concerns on this embodiment. It is a figure which shows the data structure of the frame which concerns on this embodiment. It is a figure which shows the operation | movement at the time of the frame transmission by the communication apparatus which concerns on this embodiment. It is a figure which shows the operation | movement at the time of the frame reception by the communication apparatus which concerns on this embodiment. It is a figure explaining the relationship between Doppler frequency fluctuation | variation and vehicle speed. It is a figure which shows the error of a channel estimated value and a channel fluctuation amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Communication system 10 Communication apparatus 11 Control part 12 Vehicle speed detection part 13 Reception frame process part 14 Transmission frame generation part 15 Modulation part 16 Demodulation part 17 Transmission part 18 Reception part 21 Frame length 22 Header part 23 Data part 140 Frame length determination information 141 Vehicle speed 142 frame length

Claims (7)

A communication device mounted on a mobile body,
A moving speed detector for detecting the moving speed of the communication device;
A transmission frame generation unit that determines a frame length that is a frame length according to the movement speed detected by the movement speed detection unit, and generates a transmission frame having the frame length as the entire frame length;
A transmission unit for transmitting the transmission frame generated by the transmission frame generation unit;
A communication apparatus comprising: The transmission frame generation unit
By holding the frame length determination information in which the moving speed and the frame length are associated with each other, by acquiring the frame length associated with the moving speed detected by the moving speed detection unit from the frame length determination information The communication apparatus according to claim 1, wherein the frame length is determined. The transmission frame generation unit
The communication apparatus according to claim 1, wherein the frame length is determined by acquiring the frame length using a calculation formula capable of calculating the frame length from a moving speed. A communication method that is mounted on a mobile body and includes a moving speed detector, a transmission frame generator, and a transmitter.
The moving speed detecting unit detecting a moving speed of the communication device;
The transmission frame generating unit determining a frame length that is a frame length according to the moving speed detected by the moving speed detecting unit;
The transmission frame generation unit generating a transmission frame having the frame length as the length of the entire frame;
The transmitting unit transmitting the transmission frame generated by the transmission frame generating unit;
A communication method comprising: The transmission frame generation unit
By holding the frame length determination information in which the moving speed and the frame length are associated with each other, by acquiring the frame length associated with the moving speed detected by the moving speed detection unit from the frame length determination information The communication method according to claim 4, wherein the frame length is determined. The transmission frame generation unit
The communication method according to claim 4, wherein the frame length is determined by acquiring the frame length using a calculation formula capable of calculating the frame length from the moving speed. A communication system including a transmission device and a reception device mounted on a mobile body,
The transmitter is
A moving speed detector for detecting the moving speed of the transmitting device;
A transmission frame generation unit that determines a frame length that is a frame length according to the movement speed detected by the movement speed detection unit, and generates a transmission frame having the frame length as the entire frame length;
A transmission unit for transmitting the transmission frame generated by the transmission frame generation unit;
Have
The receiving device is:
A receiving unit that receives the transmission frame transmitted by the transmission device as a reception frame;
A reception frame processing unit that calculates a channel estimation value based on a part of the reception frame received by the reception unit, and that performs channel compensation on the remaining part of the reception frame based on the channel estimation value;
A communication system comprising:

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