JP2011250053A - Terminal device and radio equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for controlling a parameter which should be set in decision feedback according to communication condition.SOLUTION: An FFT section 110 receives packet signal during a first period or second period. A reception weight deriving section 118 derives an instantaneous value of weight. A reception weight updating section 120 and a reception weight averaging section 122 performs updating in time direction and averaging in frequency direction based on the instantaneous value of the weight, for deriving a weight. An equalizing section 112 subjects a received packet signal to decision feedback equalizing using the derived weight. The reception weight updating section 120 and the reception weight averaging section 122 adjust a parameter value for updating in time direction as well as a parameter value for averaging in frequency direction, depending on whether the packet signal was received during the first period or it was received during the second period.

Description

  The present invention relates to communication technology, and more particularly, to a terminal device and a wireless device that transmit and receive a signal including predetermined information.

  Road-to-vehicle communication is being studied to prevent collisions at intersections. In the road-to-vehicle communication, information on the situation of the intersection is communicated between the roadside device and the vehicle-mounted device. Road-to-vehicle communication requires the installation of roadside equipment, which increases labor and cost. On the other hand, if it is the form which communicates information between vehicle-to-vehicle communication, ie, vehicle equipment, installation of a roadside machine will become unnecessary. In that case, for example, the current position information is detected in real time by GPS (Global Positioning System), etc., and the position information is exchanged between the vehicle-mounted devices so that the own vehicle and the other vehicle enter the intersection respectively. (See, for example, Patent Document 1).

  In addition, when packet communication is performed in a high-speed moving environment such as vehicle-to-vehicle communication or road-to-vehicle communication, transmission path characteristics, that is, amplitude phase fluctuation is adaptively estimated in order to improve reception characteristics (for example, Patent Document 2). Further, in order to avoid an excessive traffic state due to simultaneous access in vehicle-to-vehicle communication, road-to-vehicle communication and vehicle-to-vehicle communication are controlled by time division (see, for example, Patent Document 3).

JP 2005-202913 A JP 2002-271293 A JP 2009-021790 A

  In a wireless LAN (Local Area Network) compliant with a standard such as IEEE 802.11, an access control function called CSMA / CA (Carrier Sense Multiple Access Collision Aviation) is used. Therefore, in the wireless LAN, the same wireless channel is shared by a plurality of terminal devices. In such CSMA / CA, due to the distance between terminal devices and the influence of obstacles that attenuate radio waves, a situation occurs in which radio signals do not reach each other, that is, a situation where carrier sense does not function. When carrier sense does not function, packet signals transmitted from a plurality of terminal devices collide.

  On the other hand, when a wireless LAN is applied to vehicle-to-vehicle communication, it is necessary to transmit information to an unspecified number of terminal devices, so it is desirable that the signal be transmitted by broadcast. However, at an intersection or the like, an increase in the number of vehicles, that is, an increase in the number of terminal devices increases traffic, and therefore, an increase in packet signal collision is assumed. As a result, data included in the packet signal is not transmitted to other terminal devices. If such a situation occurs in vehicle-to-vehicle communication, the objective of preventing a collision accident at the intersection encounter will not be achieved. Furthermore, if the road-to-vehicle communication is executed in addition to the vehicle-to-vehicle communication, the communication forms are various. In that case, reduction of the mutual influence between vehicle-to-vehicle communication and road-to-vehicle communication is requested | required.

  In addition, when performing packet communication in a high-speed moving environment, it is important to accurately estimate the distortion of the transmission path characteristics and correct the distortion. As a technique for compensating for the distortion of the transmission path characteristic, for example, decision feedback equalization as in Patent Document 2 can be cited. In such decision feedback equalization, optimum values of parameters to be set in decision feedback differ depending on channel conditions (AWGN, Rayleigh, Rice, etc.) and packet length. The parameters to be set in the determination feedback are, for example, a forgetting coefficient for determination feedback and a filter coefficient used for smoothing transmission path characteristics. In Patent Document 2, the estimated value of the transmission path characteristic is compensated in order to follow a sudden change in the transmission path characteristic. For example, depending on communication conditions such as road-to-vehicle communication and inter-vehicle communication, parameters There is no control. Moreover, in patent document 3, although the traffic excessive state at the time of vehicle-to-vehicle communication is avoided using the time information of a roadside machine, the setting for reception is controlled according to road-to-vehicle communication and vehicle-to-vehicle communication. Absent.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for controlling a parameter to be set in determination feedback in accordance with communication conditions.

  In order to solve the above-described problem, a terminal apparatus according to an aspect of the present invention has a first period for the base station apparatus to broadcast the packet signal and a second period for the terminal apparatus to broadcast the packet signal. Multiplexed, receiving unit that receives the packet signal in the first period or the second period, a first deriving unit that derives an instantaneous value of the weight of the packet signal received in the receiving unit, and derived in the first deriving unit Based on the instantaneous value of the weight, by performing update in the time direction and averaging in the frequency direction, the second derivation unit for deriving the weight and the weight derived by the second derivation unit received by the reception unit And an equalization unit that performs decision feedback equalization on the packet signal. The second deriving unit determines a parameter value for performing update in the time direction according to whether the receiving unit receives the packet signal in the first period or whether the receiving unit receives the packet signal in the second period. And adjust the value of the parameter to perform frequency direction averaging.

  Another aspect of the present invention is a wireless device. The apparatus includes a receiving unit that receives a variable-length packet signal, a first deriving unit that derives an instantaneous value of the weight of the packet signal received by the receiving unit, and an instantaneous value of the weight that is derived by the first deriving unit. In addition, by performing update in the time direction and averaging in the frequency direction, the second derivation unit for deriving the weight, and the packet signal received in the reception unit by the weight derived in the second derivation unit, determination feedback, etc. And an equalization unit. The second deriving unit adjusts the value of the parameter for executing the update in the time direction and the value of the parameter for executing the averaging in the frequency direction according to the length of the packet signal received by the receiving unit.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to control parameters to be set in determination feedback according to communication conditions.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the structure of the base station apparatus of FIG. FIGS. 3A to 3D are diagrams showing frame formats defined in the communication system of FIG. FIG. 4 is a diagram illustrating a configuration of a subframe in FIG. 3. FIGS. 5A to 5B are diagrams showing a format of a packet signal defined in the communication system of FIG. FIGS. 6A and 6B are diagrams showing the format of the MAC frame stored in the packet signal defined in the communication system of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. It is a figure which shows the structure of the modem part of FIG. FIGS. 9A to 9C are diagrams for explaining an outline of processing in the reception weight averaging unit in FIG. It is a flowchart which shows the reception procedure in the terminal device of FIG. It is a flowchart which shows the reception procedure in the terminal device which concerns on the modification of this invention.

  Before describing the present invention in detail, an outline will be described. Embodiments of the present invention relate to a communication system that performs vehicle-to-vehicle communication between terminal devices mounted on a vehicle, and also executes road-to-vehicle communication from a base station device installed at an intersection or the like to a terminal device. As inter-vehicle communication, the terminal device broadcasts and transmits a packet signal storing information such as the speed and position of the vehicle (hereinafter referred to as “data”). Further, the other terminal device receives the packet signal and recognizes the approach of the vehicle based on the data. Further, as road-to-vehicle communication, the base station apparatus repeatedly defines a frame including a plurality of subframes. The base station apparatus selects any one of the plurality of subframes, and broadcasts a packet signal in which control information and the like are stored in the period of the head portion of the selected subframe.

  The control information includes information related to a period for the base station apparatus to broadcast the packet signal (hereinafter referred to as “road vehicle transmission period”). The terminal device specifies a road and vehicle transmission period based on the control information, and transmits a packet signal in a period other than the road and vehicle transmission period. Thus, since the road-to-vehicle communication and the vehicle-to-vehicle communication are time-division multiplexed, the collision probability of packet signals between them is reduced. That is, when the terminal device recognizes the content of the control information, interference between road-vehicle communication and vehicle-to-vehicle communication is reduced. In addition, the area where the terminal device performing inter-vehicle communication is mainly classified into three types.

  One is an area formed around the base station apparatus (hereinafter referred to as “first area”), and the other is an area formed outside the first area (hereinafter referred to as “second area”). Another one is an area formed outside the second area (hereinafter referred to as “outside the second area”). Here, in the first area and the second area, the terminal device can receive the packet signal from the base station apparatus with a certain quality, whereas outside the second area, the packet signal from the base station apparatus is received. The terminal device cannot receive with a certain quality. The first area is formed closer to the center of the intersection than the second area. Since the vehicle existing in the first area is a vehicle existing near the intersection, the packet signal from the terminal device mounted on the vehicle can be said to be important information from the viewpoint of suppressing collision accidents.

  Corresponding to such area regulations, a period for vehicle-to-vehicle communication (hereinafter referred to as “vehicle transmission period”) is formed by time division multiplexing of a priority period and a general period. The priority period is a period for use by a terminal apparatus existing in the first area, and the terminal apparatus transmits a packet signal in any of a plurality of slots forming the priority period. The general period is a period for use by a terminal apparatus existing in the second area, and the terminal apparatus transmits a packet signal by the CSMA method in the general period. In addition, the terminal device existing outside the second area transmits a packet signal by the CSMA method regardless of the frame configuration. Here, it is determined in which area the terminal device mounted on the vehicle is present.

  Since the packet signal notified from the base station apparatus in road-to-vehicle communication includes information on a plurality of vehicles, the information amount of such a packet signal is the information of the packet signal notified from the terminal apparatus in vehicle-to-vehicle communication. Generally more than. Therefore, the length of the packet signal in road-to-vehicle communication tends to be longer than the length of the packet signal in vehicle-to-vehicle communication. A preamble is added to the head portion of the packet signal, and the terminal apparatus equalizes the subsequent data signal with the transmission path characteristic value estimated based on the preamble. In such a case, when the length of the packet signal is increased, the phase rotation amount of the constellation increases in the latter half of the packet signal due to the influence of fading or the like. As a result, the accuracy of the transmission path specific value deteriorates.

  In order to cope with this, the transmission path estimation value is sequentially updated for each data symbol by decision feedback equalization. The decision feedback equalization is particularly effective for road-to-vehicle communication, but of course is also effective for vehicle-to-vehicle communication. However, when the packet signal lengths are different as in road-to-vehicle communication and vehicle-to-vehicle communication, the optimum values of parameters to be set in decision feedback equalization are different. For example, set values such as a forgetting coefficient in feedback and a filter coefficient h used for smoothing transmission path characteristics are different. Therefore, in the present embodiment, the communication period of road-to-vehicle communication and vehicle-to-vehicle communication is determined based on time information from the base station apparatus, and parameters set by determination feedback equalization are appropriately switched.

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. This corresponds to a case where one intersection is viewed from above. The communication system 100 includes a base station device 10, a first vehicle 12a, a second vehicle 12b, a third vehicle 12c, a fourth vehicle 12d, a fifth vehicle 12e, a sixth vehicle 12f, and a seventh vehicle 12g, collectively referred to as a vehicle 12. , The eighth vehicle 12h, and the network 202. Each vehicle 12 is equipped with a terminal device (not shown). The first area 210 is formed around the base station apparatus 10, the second area 212 is formed outside the first area 210, and the second outside area 214 is formed outside the second area 212. ing.

  As shown in the drawing, the road that goes in the horizontal direction of the drawing, that is, the left and right direction, intersects the vertical direction of the drawing, that is, the road that goes in the up and down direction, at the central portion. Here, the upper side of the drawing corresponds to the direction “north”, the left side corresponds to the direction “west”, the lower side corresponds to the direction “south”, and the right side corresponds to the direction “east”. The intersection of the two roads is an “intersection”. The first vehicle 12a and the second vehicle 12b are traveling from left to right, and the third vehicle 12c and the fourth vehicle 12d are traveling from right to left. Further, the fifth vehicle 12e and the sixth vehicle 12f are traveling from the top to the bottom, and the seventh vehicle 12g and the eighth vehicle 12h are traveling from the bottom to the top.

  The communication system 100 arranges the base station device 10 at an intersection. The base station device 10 controls communication between terminal devices. The base station device 10 repeatedly generates a frame including a plurality of subframes based on a signal received from a GPS satellite (not shown) and a frame formed by another base station device 10 (not shown). Here, the road vehicle transmission period can be set at the head of each subframe. The base station apparatus 10 selects a subframe in which the road and vehicle transmission period is not set by another base station apparatus 10 from among the plurality of subframes. The base station apparatus 10 sets a road and vehicle transmission period at the beginning of the selected subframe. The base station apparatus 10 stores control information including information on a road and vehicle transmission period in a packet signal. The base station apparatus 10 also stores predetermined data in the packet signal. The base station apparatus 10 notifies the packet signal in the set road and vehicle transmission period.

  A first area 210 and a second area 212 are formed around the base station apparatus 10 according to the reception situation when the terminal apparatus receives a packet signal from the base station apparatus 10. As shown in the figure, a first area 210 is formed in the vicinity of the base station apparatus 10 as an area having a relatively good reception status. It can be said that the first area 210 is formed near the central portion of the intersection. On the other hand, the second area 212 is formed outside the first area 210 as a region where the reception situation is worse than that of the first area 210. Further, outside the second area 212, an area outside the second area 214 is formed as an area where the reception status is worse than that in the second area 212. Note that the packet signal error rate and received power are used as the reception status.

  The plurality of terminal apparatuses receive the packet signal broadcasted by the base station apparatus 10 and, based on the reception status of the received packet signal, in any of the first area 210, the second area 212, and the second outside area 214 Estimate if it exists. When it is estimated that the data exists in the first area 210 or the second area 212, the terminal device generates a frame based on the control information included in the received packet signal. As a result, the frame generated in each of the plurality of terminal devices is synchronized with the frame generated in the base station device 10. Further, the terminal device recognizes the road and vehicle transmission period set by each base station device 10 and specifies the vehicle and vehicle transmission period for transmission of the packet signal. Specifically, when it exists in the first area 210, the priority period is specified, and when it exists in the second area 212, the general period is specified. Further, the terminal apparatus broadcasts a packet signal in the inter-terminal communication by executing TDMA in the priority period and executing CSMA / CA in the general period.

  Note that the terminal apparatus also selects subframes having the same relative timing in the next frame. In particular, in the priority period, the terminal device selects slots having the same relative timing in the next frame. Here, the terminal device acquires data and stores the data in a packet signal. The data includes, for example, information related to the location. The terminal device also stores control information in the packet signal. That is, the control information transmitted from the base station device 10 is transferred by the terminal device. On the other hand, when the terminal device is estimated to exist outside the second area 214, the terminal device transmits a packet signal by executing CSMA / CA regardless of the frame configuration.

  As described above, the terminal device recognizes the road and vehicle transmission period and the vehicle transmission period in the frame based on the information included in the packet signal from the base station device 10. Here, the packet signal includes information on the road and vehicle transmission period. The terminal device appropriately changes the parameter in the decision feedback equalization according to whether it is the road-vehicle transmission period or the vehicle-vehicle transmission period. As a result, parameters can be set according to the length of the packet signal, and communication quality can be improved.

  FIG. 2 shows the configuration of the base station apparatus 10. The base station apparatus 10 includes an antenna 20, an RF unit 22, a modem unit 24, a processing unit 26, a control unit 30, and a network communication unit 80. The RF unit 22 receives a packet signal from a terminal device (not shown) or another base station device 10 by the antenna 20 as a reception process. The RF unit 22 performs frequency conversion on the received radio frequency packet signal to generate a baseband packet signal. Further, the RF unit 22 outputs a baseband packet signal to the modem unit 24. In general, baseband packet signals are formed by in-phase and quadrature components, so two signal lines should be shown, but here only one signal line is shown for clarity. Shall be shown. The RF unit 22 includes an LNA (Low Noise Amplifier), a mixer, an AGC, and an A / D conversion unit.

  As a transmission process, the RF unit 22 performs frequency conversion on the baseband packet signal input from the modem unit 24 to generate a radio frequency packet signal. Further, the RF unit 22 transmits a radio frequency packet signal from the antenna 20 during the road-vehicle transmission period. The RF unit 22 also includes a PA (Power Amplifier), a mixer, and a D / A conversion unit.

  The modem unit 24 demodulates the baseband packet signal from the RF unit 22 as a reception process. Further, the modem unit 24 outputs the demodulated result to the processing unit 26. The modem unit 24 also modulates the data from the processing unit 26 as a transmission process. Further, the modem unit 24 outputs the modulated result to the RF unit 22 as a baseband packet signal. Here, since the communication system 100 corresponds to an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, the modem unit 24 also performs FFT (Fast Fourier Transform) as reception processing and IFFT (Inverse Fast Forward) as transmission processing. Also execute.

  The processing unit 26 receives a signal from a GPS satellite (not shown), and acquires time information based on the received signal. In addition, since a well-known technique should just be used for acquisition of the information of time, description is abbreviate | omitted here. The processing unit 26 generates a plurality of frames based on the time information. For example, the processing unit 26 generates 10 frames of “100 msec” by dividing the period of “1 sec” into 10 on the basis of the timing indicated by the time information. By repeating such processing, the frame is defined to be repeated. Note that the processing unit 26 may detect control information from the demodulation result and generate a frame based on the detected control information. Such processing corresponds to generating a frame synchronized with the timing of the frame formed by another base station apparatus 10.

  3A to 3D show frame formats defined in the communication system 100. FIG. FIG. 3A shows the structure of the frame. The frame is formed of N subframes indicated as the first subframe to the Nth subframe. For example, when the frame length is 100 msec and N is 10, a subframe having a length of 10 msec is defined. FIG. 3B shows a configuration of a frame generated by the first base station apparatus 10a. The first base station apparatus 10a sets a road and vehicle transmission period at the beginning of the first subframe. Moreover, the 1st base station apparatus 10a sets a vehicle transmission period following the road and vehicle transmission period in a 1st sub-frame. The vehicle transmission period is a period during which the terminal device can notify the packet signal. That is, in the road and vehicle transmission period which is the head period of the first subframe, the first base station apparatus 10a can notify the packet signal, and in the frame, the terminal apparatus transmits in the vehicle and vehicle transmission period other than the road and vehicle transmission period. It is defined that the packet signal can be broadcast. Furthermore, the first base station apparatus 10a sets only the vehicle transmission period from the second subframe to the Nth subframe.

  FIG. 3C shows a configuration of a frame generated by the second base station apparatus 10b. The second base station apparatus 10b sets a road and vehicle transmission period at the beginning of the second subframe. Also, the second base station apparatus 10b sets the vehicle transmission period from the first stage of the road and vehicle transmission period in the second subframe, from the first subframe and the third subframe to the Nth subframe. FIG. 3D shows a configuration of a frame generated by the third base station apparatus 10c. The third base station apparatus 10c sets a road and vehicle transmission period at the beginning of the third subframe. In addition, the third base station apparatus 10c sets the vehicle transmission period from the first stage of the road and vehicle transmission period in the third subframe, the first subframe, the second subframe, and the fourth subframe to the Nth subframe. As described above, the plurality of base station apparatuses 10 select different subframes, and set the road and vehicle transmission period at the head portion of the selected subframe.

  FIG. 4 shows the structure of a subframe. As illustrated, one subframe is configured in the order of a road and vehicle transmission period, a priority period, and a general period. The priority period and the general period correspond to the vehicle transmission period shown in FIG. When the road and vehicle transmission period is not included in the subframe, the subframe is configured in the order of the priority period and the general period. In the priority period, a plurality of slots are time-division multiplexed. With such a configuration, a frame including at least a plurality of slots is repeated.

  FIGS. 5A and 5B show packet signal formats defined in the communication system 100. FIG. FIG. 5A shows a packet signal that is broadcast from the base station apparatus 10 and corresponds to a packet signal used in road-to-vehicle communication. In the packet signal, STF (Short Training Field), LTF (Long Training Field), SIG (Signal), and data are arranged in order from the head. The format of this packet signal conforms to the IEEE 802.11 standard. Here, the STF is used for detecting a packet signal on the receiving side, for automatic gain control (AGC) on the receiving side, for coarse adjustment of carrier frequency synchronization, and for detecting symbol timing. Is done.

  The LTF is used for channel estimation for fine adjustment of carrier frequency synchronization on the receiving side. The SIG includes information on the transmission rate and information on the data length. The data includes, for example, 1000 bytes of information. FIG. 5B shows a packet signal that is broadcast from the terminal device, and corresponds to a packet signal used in inter-vehicle communication. The configuration of the packet signal is the same as that in FIG. 5A, but the data amount is smaller than that in FIG. The data includes, for example, 100 bytes of information. Returning to FIG.

  The processing unit 26 inputs a demodulation result from another base station device 10 or a terminal device (not shown) via the RF unit 22 and the modem unit 24. Here, the configuration of the MAC frame stored in the packet signal will be described as a demodulation result. The MAC frame input to the processing unit 26 and the MAC frame output from the processing unit 26 have the same configuration. FIGS. 6A and 6B show a format of a MAC frame stored in a packet signal defined in the communication system 100. FIG. FIG. 6A shows the format of the MAC frame. In the MAC frame, “MAC header”, “RSU control header”, “application data”, and “CRC” are arranged in order from the top. The RSU control header corresponds to the control information described above. The application data stores data to be notified to the terminal device such as accident information.

  FIG. 6B shows the format of the RSU control header. The RSU control header includes “basic information”, “timer value”, “transfer count”, “subframe number”, “frame period”, “used subframe number”, “start timing & time length” in order from the top. Deploy. Note that the configuration of the RSU control header is not limited to that shown in FIG. 6B, and some elements may be excluded or other elements may be included. The number of times of transfer indicates the number of times that the control information transmitted from the base station apparatus 10, particularly the content of the RSU control header, has been transferred by a terminal device (not shown). Here, the base station device 10 corresponds to the base station device 10 for the MAC frame output from the processing unit 26, and the base station device 10 corresponds to the MAC frame input to the processing unit 26. Corresponds to another base station apparatus 10. This is common in the following description.

  The MAC frame output from the processing unit 26 has the transfer count set to “0”. In addition, the number of transfers for the MAC frame input to the processing unit 26 is set to “0” or more. The number of subframes indicates the number of subframes forming one frame. The frame period indicates the period of the frame, and is set to, for example, “100 msec” as described above. The used subframe number is a number of a subframe in which the base station device 10 sets a vehicle transmission period. As shown in FIG. 3A, the subframe number is set to “1” at the head of the frame. In the start timing & time length, the start timing of the road and vehicle transmission period at the beginning of the subframe and the time length of the road and vehicle transmission period are indicated. Returning to FIG.

  Here, a procedure for selecting a subframe in which a road and vehicle transmission period is to be set will be described. This corresponds to the processing unit 26 generating a frame synchronized with the timing of the frame formed by the other base station apparatus 10. The processing unit 26 extracts a MAC frame whose transfer count is set to “0” from the MAC frames. This corresponds to a packet signal directly transmitted from another base station apparatus 10. The processing unit 26 specifies the value of the used subframe number among the extracted MAC frames. This corresponds to specifying a subframe used by another base station apparatus 10. The processing unit 26 measures the received power of the packet signal arranged at the head of the already identified subframe. This corresponds to measuring the reception power of the packet signal from the other base station apparatus 10.

  The processing unit 26 extracts a MAC frame whose transfer count is set to “1” or more from the MAC frames. This corresponds to a packet signal transmitted from the other base station apparatus 10 and then transferred by the terminal apparatus. The processing unit 26 specifies the value of the used subframe number among the extracted MAC frames. This corresponds to specifying a subframe used by another base station apparatus 10. The terminal device transfers the subframe number when the terminal device receives a packet signal from another base station device 10.

  The processing unit 26 also measures the received power of these packet signals. Further, the processing unit 26 estimates that the acquired received signal is the received power of the packet signal from the other base station apparatus 10 to which the control information is transferred by the packet signal. The processing unit 26 identifies a subframe in which a road and vehicle transmission period is to be set. Specifically, the processing unit 26 checks whether there is an “unused” subframe. If present, the processing unit 26 selects one of the “unused” subframes. Here, when a plurality of subframes are unused, the processing unit 26 selects one subframe at random. When there is no unused subframe, that is, when each of the plurality of subframes is used, the processing unit 26 preferentially specifies a subframe with low reception power.

  The processing unit 26 sets a road and vehicle transmission period at the beginning of the subframe having the specified subframe number. The processing unit 26 generates a MAC frame to be stored in the packet signal. At that time, the processing unit 26 determines the value of the RSU control header of the MAC frame according to the setting of the road and vehicle transmission period. This corresponds to control information related to the frame configuration. The processing unit 26 acquires predetermined information via the network communication unit 80 and includes the predetermined information in the application data. Here, the network communication unit 80 is connected to a network 202 (not shown). As described above, the amount of information included in the packet signal generated by the processing unit 26 is 1000 bytes. The processing unit 26 broadcasts the packet signal to the modem unit 24 and the RF unit 22 during the road and vehicle transmission period. Here, the packet signal includes control information and identification information for identifying the base station apparatus 10. Identification information for identifying the base station apparatus 10 is included in the MAC header of FIG. The control unit 30 controls processing of the entire base station apparatus 10.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  FIG. 7 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 50, an RF unit 52, a modem unit 54, a processing unit 56, and a control unit 58. The processing unit 56 includes a generation unit 64, a timing identification unit 60, a transfer determination unit 90, and a notification unit 70. The timing specifying unit 60 includes an extraction unit 66, a selection unit 92, and a carrier sense unit 94. The antenna 50, the RF unit 52, and the modem unit 54 execute the same processing as the antenna 20, the RF unit 22, and the modem unit 24 in FIG. Therefore, here, the difference will be mainly described.

  The modem unit 54 and the processing unit 56 receive packet signals from other terminal devices 14 and the base station device 10 (not shown). As described above, a subframe in which the priority period and the general period are time-multiplexed is defined, and the road and vehicle transmission period may be time-multiplexed in the subframe. The road and vehicle transmission period is a period during which a packet signal can be notified from the base station apparatus 10. Here, the modem unit 54 and the processing unit 56 receive the packet signal from the base station apparatus 10 in the road and vehicle transmission period. The packet signal includes identification information for identifying the base station apparatus 10 that is a notification source of the packet signal. The priority period is a period that the terminal apparatus 14 existing in the first area 210 formed around the base station apparatus 10 should use for broadcasting the packet signal. Multiple slots are included in the priority period. The general period is a period that the terminal device 14 existing in the second area formed outside the first area 210 should use for broadcasting the packet signal. Also, a frame in which a plurality of subframes are time-multiplexed is defined.

  The extraction unit 66 measures the received power of the packet signal from the base station device 10. Based on the measured received power, the extraction unit 66 estimates whether it exists in the first area 210, the second area 212, or outside the second area 214. For example, the extraction unit 66 stores a first threshold for area determination and a second threshold for area determination. Here, the first threshold for area determination is defined to be larger than the second threshold for area determination. If the received power is greater than the first threshold value for area determination, the extraction unit 66 determines that it exists in the first area 210. If the received power is equal to or smaller than the first threshold for area determination and is larger than the second threshold for area determination, the extraction unit 66 determines that the second area 212 exists. If the received power is equal to or smaller than the second threshold for area determination, the extraction unit 66 determines that the power is present outside the second area 212. Note that the extraction unit 66 may use an error rate instead of the received power, or may use a combination of the received power and the error rate.

  Based on the estimation result, the extraction unit 66 determines any one of the priority period, the general period, and the timing unrelated to the frame configuration as the transmission period. More specifically, when it is estimated that the extraction unit 66 exists outside the second area 214, the extraction unit 66 selects a timing unrelated to the frame configuration. When it is estimated that the extraction unit 66 exists in the second area 212, the extraction unit 66 selects the general period. When it is estimated that the extraction unit 66 exists in the first area 210, the extraction unit 66 selects a priority period.

  When the demodulation result from the modem unit 54 is a packet signal from the base station apparatus 10 (not shown), the extraction unit 66 specifies the timing of the subframe in which the road-vehicle transmission period is arranged. Further, the extraction unit 66 generates a frame based on the subframe timing and the content of the RSU control header. Note that the generation of the frame may be performed in the same manner as the processing unit 26 described above, and thus the description thereof is omitted here. As a result, the extraction unit 66 generates a frame synchronized with the frame formed in the base station apparatus 10. Moreover, the extraction part 66 specifies a road and vehicle transmission period based on the content of the RSU control header.

  When selecting the priority period, the extraction unit 66 outputs information on the priority period to the selection unit 92. When the general period is selected, the extraction unit 66 outputs information on the frame and subframe timing and the vehicle transmission period to the carrier sense unit 94. When selecting the timing irrelevant to the frame configuration, the extraction unit 66 instructs the carrier sense unit 94 to execute carrier sense. The selection unit 92 receives information on the priority period from the extraction unit 66. In addition, the selection unit 92 selects any slot from the plurality of slots included in the priority period, and determines the selected slot as the transmission timing. Here, received power may be used to select a slot. For example, a slot with a small reception power is selected. The selection unit 92 notifies the generation unit 64 of the determined transmission timing.

  The carrier sense unit 94 receives information about the timing of frames and subframes and the vehicle transmission period from the extraction unit 66. The carrier sense unit 94 measures the interference power by performing carrier sense in the general period. Further, the carrier sense unit 94 determines the transmission timing in the general period based on the interference power. More specifically, the carrier sense unit 94 stores a predetermined threshold value in advance, and compares the interference power with the threshold value. If the interference power is smaller than the threshold value, the carrier sense unit 94 determines the transmission timing. When receiving the carrier sense execution instruction from the extraction unit 66, the carrier sense unit 94 determines the transmission timing by executing the CSMA without considering the frame configuration. The carrier sense unit 94 notifies the generation unit 64 of the determined transmission timing.

  The generation unit 64 includes a GPS receiver (not shown), a gyroscope, a vehicle speed sensor, and the like. Based on data supplied from these, the location of the vehicle 12 (not shown), that is, the position of the vehicle 12 on which the terminal device 14 is mounted, travel Get direction, speed, etc. The existence position is indicated by latitude and longitude. Since a known technique may be used for these acquisitions, description thereof is omitted here. The generation unit 64 uses the MAC frame shown in FIGS. 6A to 6B and stores the presence position in the application data. The generation unit 64 generates a packet signal including a MAC frame, and generates the packet signal via the modulation / demodulation unit 54, the RF unit 52, and the antenna 50 at the transmission timing determined by the selection unit 92 or the carrier sense unit 94. Broadcast packet signals. As described above, the amount of information included in the packet signal generated by the generation unit 64 is 100 bytes. The transmission timing is included in the vehicle transmission period.

  The transfer determination unit 90 controls transfer of the RSU control header. The extraction unit 66 extracts an RSU control header from a packet signal for which the base station device 10 is an information source. As described above, when the packet signal is directly transmitted from the base station apparatus 10, the number of transfers is set to “0”, but when the packet signal is transmitted from another terminal apparatus 14. The number of transfers is set to a value of “1 or more”. Here, since the used subframe number is not changed when transferred by the terminal apparatus 14, the subframe used in the base station apparatus 10 serving as the information source is specified by referring to the used subframe number. The

  The transfer determination unit 90 acquires information on the number of transfers for each base station apparatus 10 that is an information source. More specifically, the transfer determining unit 90 sequentially acquires the number of transfers corresponding to the subframe number “1”, and then executes the same processing for the number of transfers corresponding to other subframe numbers. . Further, the transfer determination unit 90 acquires, for each base station device 10 serving as an information source, the smaller transfer number, for example, the value of the minimum transfer number, from the information related to the transfer number related to the base station device 10. To do. That is, the transfer determination unit 90 obtains the minimum value of the number of transfers corresponding to the subframe number “1”, the minimum value of the number of transfers corresponding to the subframe number “2”, and the like.

  The transfer determination unit 90 measures the RSU control header, that is, the number of extractions of control information, for each base station apparatus 10 that is an information source. Moreover, the transfer determination part 90 selects the frequency | count of extraction of the control information containing the value of the frequency | count of transfer acquired in the transfer determination part 90 for every base station apparatus 10 used as an information source. More specifically, the transfer determination unit 90 measures the number of times control information is extracted for each transfer number for one subframe number. As a result, for example, for the subframe number “1”, the number of times control information is extracted is “0”, and the number of times control information is extracted is “4”. ", And the number of times control information is extracted is" 6 "times. If the acquired transfer count is “1”, the transfer determination unit 90 selects the control information extraction count “4” including the transfer count.

  The transfer determination unit 90 stores the subframe number, the transfer count, and the extraction count in association with each other. In addition, the transfer determination unit 90 updates the stored content when the number of transfers and the number of extractions are updated. The transfer determination unit 90 acquires the number of transfers and the number of extractions for each base station device 10. The transfer determination unit 90 selects control information corresponding to at least one base station apparatus 10 as control information to be transferred based on the number of transfers and the number of extractions. More specifically, the transfer determination unit 90 compares the number of transfers with the plurality of base station devices 10 and then compares the number of extractions. That is, after selecting the control information with the smaller number of transfers, for example, the control information with the minimum number of transfers, the control information with the larger number of extractions and the maximum number of extractions are selected from the selected control information. Selected control information is selected.

  In this way, control information having the minimum number of transfers and control information having the maximum number of extractions corresponding to the number of transfers is selected by the transfer determination unit 90. It can be said that control information is received near the base station apparatus 10 which becomes an information source, so that the frequency | count of transfer is small. In addition, it can be said that the control information is received in a situation where the variation in the wireless environment is smaller as the number of extractions is larger. Therefore, it can be said that the terminal device 14 has selected the control information from the base station apparatus 10 installed as close as possible by selecting the control information that satisfies the above-described situation.

  The transfer determination unit 90 instructs the generation unit 64 to generate an RSU control header based on the selected control information. The transfer determination unit 90 increases the number of transfers in the information related to the number of transfers when storing the control information in the RSU control header. In response to such an instruction, the generation unit 64 generates an RSU control header based on the control information selected by the transfer determination unit 90 and increases the number of transfers at that time.

  The notification unit 70 acquires a packet signal from the base station device 10 (not shown) in the road and vehicle transmission period, and acquires a packet signal from another terminal device 14 (not shown) in the vehicle and vehicle transmission period. As a process for the acquired packet signal, the notification unit 70 notifies the driver of the approach of another vehicle 12 (not shown) or the like via a monitor or a speaker in accordance with the content of data stored in the packet signal. The control unit 58 controls the operation of the entire terminal device 14.

  FIG. 8 shows the configuration of the modem unit 54. The modem unit 54 includes an FFT unit 110, an equalization unit 112, a phase tracking unit 114, a determination unit 116, a reception weight derivation unit 118, a reception weight update unit 120, and a reception weight averaging unit 122. FIG. 8 shows only the demodulation function, particularly the decision feedback process, of the modem unit 54.

  The FFT unit 110 receives a baseband packet signal from the RF unit 52 (not shown). As described above, the road or vehicle transmission period and the vehicle transmission period are time-multiplexed in the frame or subframe, and the packet signal is received in the road or vehicle transmission period or vehicle transmission period. The FFT unit 110 converts the time domain signal into a frequency domain signal by performing FFT on the received packet signal. Hereinafter, the packet signal in the frequency domain is also simply referred to as “packet signal”. The packet signal is indicated as R (m, n). Here, m is a symbol number, where m = 0 is LTF, m = 1 is SIG, and m = 2 or more is data. N is a subcarrier number. FFT section 110 outputs the packet signal to equalization section 112 and reception weight derivation section 118.

The equalization unit 112 receives the packet signal from the FFT unit 110 and derives the reception weight from the reception weight averaging unit 122. Although details of the reception weight derived by the reception weight averaging unit 122 will be described later, the reception weight is indicated as WA (m−1, n). The equalization unit 112 performs decision feedback equalization on the packet signal based on the reception weight. Specifically, the same subcarriers are associated with each other and multiplied by R (m, n) and WA (m-1, n) components. The packet signal equalized by the reception weight averaging unit 122 has D (m, n) as follows.
D (m, n) = R (m, n) .WA (m-1, n) (1)
The reception weight averaging unit 122 outputs the equalized packet signal to the phase tracking unit 114.

  The phase tracking unit 114 receives the equalized packet signal from the reception weight averaging unit 122. The phase follower 114 corrects the rotation due to the phase noise for the packet signal. For the rotation correction, for example, a pilot signal included in the packet signal may be used. Since a known technique may be used for this, description thereof is omitted here. The packet signal with the phase noise corrected is denoted as DA (m, n). The phase tracking unit 114 outputs the packet signal corrected for the phase noise to the determination unit 116 and also outputs it to a deinterleaver and error correction decoding unit (not shown).

  The determination unit 116 receives the packet signal with the phase noise corrected from the phase tracking unit 114. The determination unit 116 determines a signal for each subcarrier. For example, when the modulation method is QPSK, the determination unit 116 extracts a signal of one subcarrier from the packet signal whose phase noise is corrected, and is closest to the extracted signal among the four signal points of QPSK. Selected signal points. The determination unit 116 outputs a signal corresponding to the selected signal point. The above processing is performed for all subcarriers, and the signal determined by the determination unit 116 is indicated as A (m−1, n). Determination unit 116 outputs the determined signal to reception weight deriving unit 118.

The reception weight deriving unit 118 receives the packet signal from the FFT unit 110 and also the signal determined by the determination unit 116. The reception weight deriving unit 118 derives an instantaneous value of the reception weight based on these signals. The instantaneous value W (m-1, n) of the reception weight is derived as follows.
W (m-1, n) = A (m-1, n) / R (m, n) (2)
The reception weight deriving unit 118 outputs the instantaneous value of the reception weight to the reception weight update unit 120.

The reception weight update unit 120 receives the instantaneous value of the reception weight from the reception weight deriving unit 118. The reception weight update unit 120 performs time direction update on the instantaneous value of the reception weight. Specifically, the update result WB (m-1, n) in the time direction of the reception weight is derived as follows using the past update result WB (m-2, n).
WB (m−1, n) = αWB (m−2, n) + (1−α) W (m−1, n) (3)
Here, α is a forgetting factor and determines the speed of time update of the reception weight. α indicates how much the past update result is reflected in the update result of the reception weight in the time direction. The larger α is, the greater the influence of the past update result on the update result of the reception weight in the time direction. As described above, in order to execute the update in the time direction, the reception weight update unit 120 uses the forgetting factor for the instantaneous value of the reception weight.

  The optimum value of the forgetting factor varies depending on channel conditions (AWGN, Rayleigh, Rice, etc.) and the length of the packet signal. Here, the forgetting factor (hereinafter referred to as “first forgetting factor”) when a packet signal is received during the road-to-vehicle transmission period, and the forgetting factor (hereinafter referred to as “first forgetting factor”) when the packet signal is received during the vehicle-to-vehicle transmission period. , “Second forgetting factor”). Note that the length of the packet signal to be received in the road and vehicle transmission period is longer than the length of the packet signal to be received in the vehicle and vehicle transmission period. Here, this reason will be described. In decision feedback equalization, an instantaneous value of the reception weight is generated at the current time, and smoothing in the time direction is performed using the reception weight obtained from the previous symbol.

  For this reason, once an error occurs in the process of generating the reception weight at the current time, the error affects the final symbol of the packet signal. In particular, in a long packet signal used in road-to-vehicle communication, the influence of error propagation of the reception weight is increased, and there is a possibility that the reception characteristics are deteriorated. Therefore, in road-to-vehicle communication, it is necessary to reduce the error propagation of the reception weight. In order to cope with this, regarding the speed of time update in road-to-vehicle communication, a large weight is given to the reception weight of the previous symbol, and a forgetting factor is set so as to follow slowly over time. This is equivalent to increasing one item on the right side of Equation (3).

  On the other hand, since the length of the packet signal to be received during the vehicle-to-vehicle transmission period is shorter than the length of the packet signal to be received during the road-to-vehicle transmission period, the influence of reception weight error propagation is reduced. For this reason, the second forgetting factor in the vehicle transmission period is set to a value smaller than the first forgetting factor. In addition, by reducing the forgetting factor, the followability to fluctuations in transmission path characteristics is enhanced.

  The reception weight update unit 120 is notified of a road-vehicle transmission period or a vehicle-vehicle transmission period from a control unit 58 (not shown). The reception weight update unit 120 sets the first forgetting factor in the road and vehicle transmission period, and sets the second forgetting factor in the vehicle and vehicle transmission period. In other words, the reception weight updating unit 120 adjusts the value of the forgetting factor according to whether the packet signal is received during the road-to-vehicle transmission period or whether the packet signal is received during the vehicle-to-vehicle transmission period. Here, the reception weight updating unit 120 holds the first forgetting coefficient and the second forgetting coefficient in advance as an information table, and the first forgetting coefficient or the second forgetting coefficient is determined according to the road-to-vehicle transmission period or the vehicle-to-vehicle transmission period. Select and set the coefficient. Alternatively, the packet signal from the base station apparatus 10 includes the first forgetting factor and the second forgetting factor, and the reception weight updating unit 120 may use these. The reception weight update unit 120 outputs the reception weight update result in the time direction to the reception weight averaging unit 122.

The reception weight averaging unit 122 receives the update result of the reception weight in the time direction from the reception weight update unit 120. The reception weight averaging unit 122 derives a reception weight by performing averaging in the frequency direction on the update result of the reception weight in the time direction. More specifically, the reception weight WA (m−1, n) after averaging is derived as follows.
WA (m-1, n) = h (n-4) .WB (m-1, n-4)
+ H (n-3) .WB (m-1, n-3)
+ H (n-2) .WB (m-1, n-2)
+ H (n-1) .WB (m-1, n-1)
+ H (n) · WB (m-1, n)
+ H (n + 1) · WB (m−1, n + 1)
+ H (n + 2) .WB (m-1, n + 2)
+ H (n + 3) .WB (m-1, n + 3)
+ H (n + 4) .WB (m-1, n + 4) (4)
Here, for simplification of explanation, n is assumed to be from −4 to +4, and h is a filter coefficient. The cut-off width of the filter is determined according to the value of h. Thus, the reception weight averaging unit 122 uses a filter in order to perform averaging in the frequency direction.

  The reception weight averaging unit 122 receives the cut-off width (hereinafter referred to as “first cut-off width”) when the packet signal is received during the road-vehicle transmission period, and receives the packet signal during the vehicle-vehicle transmission period. Is made narrower than the cutoff width (hereinafter referred to as “second cutoff width”). That is, by using the first cut-off width, the reception weight becomes smoother in the frequency direction than when the second cut-off width is used. The filter coefficient for realizing the first cut-off width is referred to as “first filter coefficient”, and the filter coefficient for realizing the second cut-off width is referred to as “second filter coefficient”. FIGS. 9A to 9C are diagrams for explaining an outline of processing in the reception weight averaging unit 122. FIG. FIG. 9A shows a reception weight before the reception weight averaging unit 122 executes averaging. The horizontal axis indicates the frequency, and the vertical axis indicates the size of the reception weight. FIG. 9B shows the result of averaging the reception weight of FIG. 9A with the first filter coefficient. FIG. 9C shows the result of averaging the reception weight of FIG. 9A with the second filter coefficient. Returning to FIG.

  In decision feedback equalization, the determination unit 116 generates a reference transmission line estimation value, and the reception weight deriving unit 118 divides the reference transmission line estimation value by the input signal after the FFT, thereby instantaneously receiving the reception weight. Generate a value. In a reception environment where the influence of noise is large, that is, in an environment where the CNR is low, an error may occur in the reference transmission path estimation value. As a result, an error occurs in the process of generating the instantaneous value of the reception weight, and this error affects the final symbol of the packet signal. In particular, in a long packet signal used in road-to-vehicle communication, the influence of error propagation of the reception weight is increased, and there is a possibility that the reception characteristics are deteriorated. Therefore, in road-to-vehicle communication, it is necessary to reduce the error propagation of the reception weight. In order to cope with this, in road-to-vehicle communication, a filter coefficient is set so as to smooth the thermal noise and reduce the influence of the noise. On the other hand, since the length of the packet signal to be received during the vehicle-to-vehicle transmission period is shorter than the length of the packet signal to be received during the road-to-vehicle transmission period, the influence of reception weight error propagation is reduced. Therefore, the second cutoff width in the vehicle transmission period is set to a value that is wider than the first cutoff width.

  The reception weight averaging unit 122 is notified of a road and vehicle transmission period or a vehicle and vehicle transmission period from a control unit 58 (not shown). The reception weight averaging unit 122 sets the first filter coefficient in the road and vehicle transmission period, and sets the second filter coefficient in the vehicle and vehicle transmission period. That is, the reception weight averaging unit 122 adjusts the value of the filter coefficient depending on whether the packet signal is received during the road-to-vehicle transmission period or whether the packet signal is received during the vehicle-to-vehicle transmission period. Here, the reception weight averaging unit 122 holds the first filter coefficient and the second filter coefficient in advance as an information table, and the first filter coefficient or the second filter coefficient is determined according to the road-vehicle transmission period or the vehicle-vehicle transmission period. Select and set the filter coefficient. Alternatively, the packet signal from the base station device 10 includes the first filter coefficient and the second filter coefficient, and the reception weight averaging unit 122 may use these. The reception weight averaging unit 122 outputs the reception weight to the equalization unit 112.

  The operation of the communication system 100 configured as above will be described. FIG. 10 is a flowchart showing a reception procedure in the terminal device 14. When the packet signal is received during the road and vehicle transmission period (Y in S10), the reception weight updating unit 120 uses the first forgetting factor, and the reception weight averaging unit 122 corresponds to the first cutoff width. The first filter coefficient is used (S12). On the other hand, when the packet signal is not received during the road and vehicle transmission period (N in S10), the reception weight update unit 120 uses the second forgetting factor, and the reception weight averaging unit 122 sets the second cutoff width. The corresponding second filter coefficient is used (S14).

  Next, a modification of the present invention will be described. The modification also relates to a communication system similar to the embodiment, and particularly relates to a terminal device that performs decision feedback equalization. The terminal device according to the embodiment sets a parameter for decision feedback equalization according to whether it is a road-vehicle transmission period or a vehicle-vehicle transmission period. On the other hand, the terminal device according to the modification sets parameters for decision feedback equalization according to the length of the received packet signal. The communication system 100 according to the modification is of the same type as that of FIG. 1, the base station device 10 is of the same type as that of FIG. 2, the terminal device 14 is of the same type as that of FIG. Is the same type as in FIG. Here, the difference will be mainly described.

  In the modem unit 54 of FIG. 8, the reception weight deriving unit 118 derives an instantaneous value of the reception weight. The reception weight updating unit 120 performs time-direction updating on the instantaneous value of the reception weight, and outputs a reception weight update result in the time direction. The reception weight averaging unit 122 derives a reception weight by performing averaging in the frequency direction on the update result of the reception weight in the time direction. Reception weight updating section 120 selects and uses either the first forgetting coefficient or the second forgetting coefficient as the forgetting coefficient, and reception weight averaging section 122 uses the first filter coefficient as the filter coefficient. And the second filter coefficient is selected and used.

  Here, the packet signal input to the modem unit 54 has the format shown in FIGS. The SIG part includes information on the transmission rate and information on the data length. Reception weight updating section 120 and reception weight averaging section 122 set a predetermined forgetting factor and a predetermined filter coefficient for STF, LTF, and SIG of the packet signal, and execute update processing and average processing. The predetermined forgetting factor may be a different value from the first forgetting factor or the second forgetting factor, or may be either the first forgetting factor or the second forgetting factor. The same applies to the predetermined filter coefficient.

  The processing unit 56 or the control unit 58 (not shown) acquires the SIG demodulated by the modem unit 54. The processing unit 56 or the control unit 58 extracts information regarding the data length included in the SIG, and compares the data length with a threshold value. When the data length is greater than or equal to the threshold value, the processing unit 56 or the control unit 58 instructs the reception weight update unit 120 to use the first forgetting factor, and the reception weight averaging unit 122 uses the first filter. Directs the use of coefficients. On the other hand, when the data length is shorter than the threshold value, the processing unit 56 or the control unit 58 instructs the reception weight update unit 120 to use the second forgetting factor, and the reception weight averaging unit 122 Indicates the use of two filter coefficients.

  The reception weight update unit 120 selects a forgetting factor to be used for the data in accordance with an instruction from the processing unit 56 or the control unit 58. The reception weight averaging unit 122 selects a filter coefficient to be used for the data in accordance with an instruction from the processing unit 56 or the control unit 58. That is, as the packet signal becomes longer, the reception weight update unit 120 increases the forgetting factor, and the reception weight averaging unit 122 decreases the filter cutoff width.

  FIG. 11 is a flowchart showing a reception procedure in the terminal device 14 according to the modification of the present invention. When the length of the packet signal is equal to or greater than the threshold (Y in S20), the reception weight updating unit 120 uses the first forgetting factor, and the reception weight averaging unit 122 uses the first cutoff frequency corresponding to the first cutoff width. The filter coefficient is used (S22). On the other hand, when the length of the packet signal is not equal to or greater than the threshold value (N in S20), the reception weight update unit 120 uses the second forgetting factor, and the reception weight averaging unit 122 sets the second weight corresponding to the second cutoff width. Two filter coefficients are used (S24).

  According to the embodiment of the present invention, the forgetting factor and the filter cut-off width are adjusted in the road and vehicle transmission period and the vehicle and vehicle transmission period, so that the communication quality of road-to-vehicle communication and vehicle-to-vehicle communication can be improved. In addition, since the forgetting factor is set larger in the road and vehicle transmission period than in the vehicle and vehicle transmission period, the influence of error propagation can be reduced. In addition, since the influence of error propagation is reduced, deterioration of communication quality can be suppressed even if the length of the packet signal is increased. In addition, since the forgetting factor is made smaller in the vehicle transmission period than in the road vehicle transmission period, it is possible to follow fluctuations in transmission path characteristics. Further, since the filter cutoff width is narrowed in the road and vehicle transmission period as compared with the vehicle and vehicle transmission period, the influence of noise can be reduced. In addition, since the influence of noise is reduced, the influence of error propagation can be reduced.

  In addition, since the road and vehicle transmission period is separated from the road and vehicle transmission period based on the information on the time length of the road and vehicle transmission period included in the packet signal notified from the base station apparatus, the road and vehicle transmission period and the vehicle The transmission period can be accurately determined. In addition, since a plurality of forgetting coefficients and a plurality of filter coefficients are held in advance and any one of the forgetting coefficients or one of the filter coefficients is selected and set, the processing can be simplified. In addition, a plurality of forgetting coefficients and a plurality of filter coefficients are received from the base station apparatus, and one of the forgetting coefficients and one of the filter coefficients is selected and set, so that the plurality of forgetting coefficients and the plurality of filter coefficients can be easily set. Can change. Further, since the forgetting factor and the filter cutoff width are adjusted according to the length of the packet signal, the communication quality of road-to-vehicle communication and vehicle-to-vehicle communication can be improved.

  Since received power is used to distinguish between the first area and the second area, a range in which the propagation loss is within a predetermined level can be defined as the first area. In addition, since the range in which the propagation loss is within a predetermined level is defined in the first area, the vicinity of the center of the intersection can be used as the first area. In addition, since the time division multiplexing by slots is executed in the priority period, the error rate can be reduced. Moreover, since CSMA / CA is performed in a general period, the number of terminal devices can be adjusted flexibly.

  Also, since the subframe used by the other base station apparatus is specified based on the packet signal received from the terminal apparatus as well as the packet signal directly received from the other base station apparatus, The frame identification accuracy can be improved. In addition, since the accuracy of identifying subframes in use is improved, the probability of collision between packet signals transmitted from the base station apparatus can be reduced. Moreover, since the collision probability between packet signals transmitted from the base station apparatus is reduced, the terminal apparatus can accurately recognize the control information. Further, since the control information is accurately recognized, the road and vehicle transmission period can be accurately recognized. Further, since the road and vehicle transmission period is accurately recognized, the collision probability of the packet signal can be reduced.

  In addition, since a subframe other than the currently used subframe is used preferentially, it is possible to reduce the possibility of transmitting a packet signal at a timing overlapping with packet signals from other base station apparatuses. Further, when any subframe is used by another base station apparatus, a subframe with low received power is selected, so that the influence of packet signal interference can be suppressed. Further, since the received power of the terminal device is used as the received power from another base station device that is the transmission source of the control information relayed by the terminal device, the received power estimation process can be simplified.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the modulation / demodulation unit 54 of the terminal device 14 executes the determination feedback process. However, the present invention is not limited to this. For example, the modem unit 24 of the base station apparatus 10 may execute the determination feedback process. For the determination feedback process, the modem unit 24 includes the configuration of FIG. According to this modification, also in the base station apparatus 10, the communication quality of road-to-vehicle communication and vehicle-to-vehicle communication can be improved.

  In the embodiment of the present invention, the reception weight updating unit 120 uses two types of forgetting coefficients, and the reception weight averaging unit 122 uses two types of filter coefficients. However, the present invention is not limited to this. For example, the reception weight updating unit 120 and the reception weight averaging unit 122, or any one of them, may use three or more types of forgetting coefficients and filter coefficients. More specifically, the reception weight update unit 120 and the reception weight averaging unit 122 select a forgetting coefficient and a filter coefficient according to the length of the packet signal. According to this modification, the forgetting factor and the filter factor can be set in detail according to the length of the packet signal.

  According to the embodiment of the present invention, the reception weight updating unit 120 adjusts the forgetting factor according to whether it is a road-vehicle transmission period or a vehicle-vehicle transmission period, that is, according to the length of the packet signal. Yes. However, the present invention is not limited to this. For example, the reception weight update unit 120 may adjust the forgetting factor according to another parameter. One of the other parameters is the moving speed of the vehicle 12. The moving speed may be received from a speed sensor mounted on the vehicle 12. Alternatively, the Doppler frequency may be measured from the received packet signal, and the moving speed may be estimated from the Doppler frequency. The reception weight updating unit 120 decreases the forgetting factor as the moving speed increases even for the same packet signal length. For this reason, the reception weight updating unit 120 uses a plurality of forgetting factors for the length of one packet signal. According to this modification, the forgetting factor can be set in detail.

  In the embodiment of the present invention, the reception weight averaging unit 122 adjusts the cut-off width of the filter according to whether it is a road-vehicle transmission period or a vehicle-vehicle transmission period, that is, according to the length of the packet signal. is doing. However, the present invention is not limited to this. For example, the reception weight averaging unit 122 may adjust the cutoff width in accordance with another parameter. Another parameter is the delay characteristic of the transmission line. This may be a delay spread. Since a known technique may be used for measuring the delay spread, the description thereof is omitted here. The reception weight averaging unit 122 widens the cut-off width as the delay spread increases even for the same packet signal length. Therefore, the reception weight averaging unit 122 uses a plurality of cutoff widths for the length of one packet signal. According to this modification, the cut-off width can be set in detail.

  10 base station devices, 12 vehicles, 14 terminal devices, 20 antennas, 22 RF units, 24 modulation / demodulation units, 26 processing units, 30 control units, 50 antennas, 52 RF units, 54 modulation / demodulation units, 56 processing units, 58 control units, 60 timing identification unit, 64 generation unit, 66 extraction unit, 70 notification unit, 80 network communication unit, 90 transfer determination unit, 92 selection unit, 94 carrier sense unit, 100 communication system, 110 FFT unit, 112 equalization unit, 114 A phase tracking unit, 116 determination unit, 118 reception weight deriving unit, 120 reception weight update unit, 122 reception weight averaging unit, 202 network.

Claims (4)

A first period for the base station apparatus to broadcast the packet signal and a second period for the terminal apparatus to broadcast the packet signal are time-multiplexed, and the packet signal is received in the first period or the second period. A receiver,
A first derivation unit for deriving an instantaneous value of the weight of the packet signal received by the reception unit;
A second derivation unit for deriving a weight by executing update in the time direction and averaging in the frequency direction based on the instantaneous value of the weight derived in the first derivation unit;
An equalization unit that performs decision feedback equalization on the packet signal received at the reception unit by the weight derived at the second deriving unit;
The second derivation unit is configured to perform a time direction update depending on whether the reception unit receives a packet signal in a first period or whether the reception unit receives a packet signal in a second period. A terminal device that adjusts parameter values and parameter values for performing averaging in the frequency direction.   The second derivation unit uses a forgetting factor with respect to the instantaneous value of the weight to perform update in the time direction, and uses a filter to perform averaging in the frequency direction. When the reception unit receives the packet signal in the first period, the forgetting factor is increased and the filter cutoff width is narrowed compared to the case where the reception unit receives the packet signal in the second period. The terminal device according to claim 1. A receiver for receiving a variable-length packet signal;
A first derivation unit for deriving an instantaneous value of the weight of the packet signal received by the reception unit;
A second derivation unit for deriving a weight by executing update in the time direction and averaging in the frequency direction based on the instantaneous value of the weight derived in the first derivation unit;
An equalization unit that performs decision feedback equalization on the packet signal received at the reception unit by the weight derived at the second deriving unit;
The second deriving unit adjusts a parameter value for performing time direction updating and a parameter value for performing frequency direction averaging according to the length of the packet signal received by the receiving unit. A wireless device.   The second derivation unit uses a forgetting factor with respect to the instantaneous value of the weight to perform update in the time direction, and uses a filter to perform averaging in the frequency direction. 4. The radio apparatus according to claim 3, wherein the longer the packet signal received by the unit, the larger the forgetting factor and the narrower the filter cutoff width.

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