Patent Application
20120236841
1. Field of the Invention
The present invention relates to communication technology, and in particular, relates to abase station apparatus that transmits or receives a signal including predetermined information.
2. Description of the Related Art
To prevent an intersection collision, road-to-vehicle communication has been discussed. In road-to-vehicle communication, information about circumstances of an intersection is communicated between a road-side apparatus and an on-vehicle apparatus. It is necessary to install a road-side apparatus for road-to-vehicle communication, leading to increased labor and costs.
In inter-vehicle communication, that is, in a form in which information is communicated between on-vehicle apparatuses, by contrast, there is no need to install a road-side apparatus. In that case, the current position information is detected in real time by, for example, GPS (Global Positioning System) and the position information is exchanged between on-vehicle apparatuses to judge on which road leading to the intersection the own vehicle and other vehicle are each positioned.
In wireless LAN (Local Area Network) conforming to standards such as IEEE802.11, an access control function called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used. Therefore, the same radio channel is shared by a plurality of terminal apparatuses in the wireless LAN. In CSMA/CA, a packet signal is transmitted after making sure that no other packet signal is transmitted by a carrier sense.
When, like ITS (Intelligent Transport Systems), wireless LAN is applied to inter-vehicle communication, on the other hand, it is necessary to transmit information to an unspecified many terminal apparatuses and thus, it is desirable to transmit a signal by broadcasting. However, with an increasing number of vehicles, that is, with an increasing number of terminal apparatuses, an increase in collision of packet signals is assumed due to increased traffic. As a result, data contained in packet signals is not transmitted to other terminal apparatuses. If such a situation arises in inter-vehicle communication, an object of preventing intersection collisions will not be achieved.
The shape of intersection and the traffic volume vary and there are some intersections for which a packet signal should be transmitted immediately before entering the intersection and a packet signal should be transmitted in advance some distance apart from the intersection for others. In the former case, the importance of a packet signal transmitted from a terminal apparatus close to an intersection is higher than the importance of a packet signal transmitted from a terminal apparatus apart from an intersection. In the latter case, on the other hand, the importance of a packet signal transmitted from a terminal apparatus apart from an intersection is higher than the importance of a packet signal transmitted from a terminal apparatus close to an intersection. Thus, setting priorities in accordance with the position from which a packet signal should be transmitted is required. Incidentally, there are some intersections where the number of terminal apparatuses does not increase enormously and simple communication control is desired for such intersections rather than reducing the probability of packet signal collisions. Therefore, implementation of highly flexible inter-vehicle communication is desired. Further, if road-to-vehicle communication is performed in addition to inter-vehicle communication, the communication forms will be diversified. In such a case, the reduction of mutual influence between inter-vehicle communication and road-to-vehicle communication is required.
The present invention is made in view of such circumstances and an object thereof is to provide a technology that realizes highly flexible inter-terminal communication.
To solve the above problems, abase station apparatus in an aspect of the present invention is abase station apparatus controlling inter-terminal communication, including a generation unit configured to generate a packet signal containing an identifier to identify that basic information of the basic information and extended information is contained in the packet signal or the basic information and the extended information are contained in the packet signal, wherein the basic information contains information about a first period and the extended information contains the information about a second period and a third period, and a broadcasting unit configured to broadcast the packet signal containing the identifier generated by the generation unit.
Meanwhile, optional combination of the above-described components and those obtained by converting representation of the present invention among a method, an apparatus, a system, a recording medium, and a computer program also are effective as an aspect of the present invention.
Embodiments will now be described, byway of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.
Before specifically describing the present invention, an overview will be provided. An embodiment of the present invention relates to a communication system that performs inter-vehicle communication between terminal apparatuses mounted on vehicles and also performs road-to-vehicle communication from a base station apparatus installed at an intersection or the like to a terminal apparatus. In the inter-vehicle communication, a terminal apparatus transmits a packet signal in which information such as the speed and position of a vehicle (hereinafter, called “data”) is stored by broadcasting. Other terminal apparatuses receive the packet signal and recognize an approaching vehicle or the like based on the data. The base station apparatus defines a frame containing a plurality of subframes repeatedly. The base station apparatus selects one of the plurality of subframes for road-to-vehicle communication and transmits a packet signal in which control information or the like is stored in a period of the leading portion of the selected subframe by broadcasting.
The control information contains information about a period (hereinafter, called a “road-to-vehicle transmission period”) in which the base station apparatus transmits a packet signal by broadcasting. The terminal apparatus identifies the road-to-vehicle transmission period based on the control information and transmits a packet signal in a period other than the road-to-vehicle transmission period. Thus, road-to-vehicle communication and inter-vehicle communication are time-division multiplexed and so the probability of collision of packet signals of both types of communication is reduced. That is, interference between road-to-vehicle communication and inter-vehicle communication is reduced by content of control information being recognized by the terminal apparatus. The area in which the terminal apparatus performing inter-vehicle communication is present can roughly be divided into three types of area.
One type of area is an area formed around a base station apparatus (hereinafter, called a “first area”), another type of area is an area (hereinafter, called a “second area”) formed outside the first area, and still another type of area is an area (hereinafter, called “outside the second area”) formed outside the second area. While a packet signal from the base station apparatus can be received by a terminal apparatus in a certain level of quality in the first area and the second area, a packet signal from the base station apparatus cannot be received by a terminal apparatus in a certain level of quality outside the second area. The first area is formed closer to the center of an intersection than the second area. The following two situations can be assumed depending on the shape of an intersection. The first situation is a case when a vehicle present in the second area is approaching the intersection and a packet signal from the terminal apparatus mounted on the vehicle is important information from the viewpoint of suppressing a collision. The second situation is a case when a vehicle present in the first area is present close to an intersection and a packet signal from the terminal apparatus mounted on the vehicle is important information from the viewpoint of suppressing a collision.
Corresponding to such area definitions, a period (hereinafter, called a “inter-vehicle transmission period”) for inter-vehicle communication is formed by time-division multiplexing of a priority period and a general period. The priority period is formed from a plurality of slots and the terminal apparatus broadcasts a packet signal in one of the plurality of slots. The general period has a predetermined period and the terminal apparatus broadcasts a packet signal by the CSMA method in the general period. A terminal apparatus present outside the second area transmits a packet signal by the CSMA method regardless of the frame configuration. In the first situation described above, a terminal apparatus present in the second area is allowed to use a priority period and a terminal apparatus present in the first area is allowed to use a general period. In the second situation described above, a terminal apparatus present in the first area is allowed to use a priority period and a terminal apparatus present in the second area is allowed to use a general period. Here, in which area the terminal apparatus mounted on a vehicle is present is determined. Incidentally, some base station apparatuses have no first area formed therearound. In such a case, the inter-vehicle transmission period contains no priority period and is formed of general periods only.
As shown in
In the communication system 100, the base station apparatus 10 is arranged at an intersection. The base station apparatus 10 controls communication between terminal apparatuses. The base station apparatus 10 repeatedly generates a frame containing a plurality of subframes based on a signal received from a GPS satellite (not shown) or frames generated by the other base station apparatuses 10. A road-to-vehicle transmission period is allowed to be set to the leading portion of each subframe. The base station apparatus 10 selects a subframe to which no road-to-vehicle period is set by another base station apparatus 10 from the plurality of subframes. The base station apparatus 10 sets a road-to-vehicle transmission period to the leading portion of the selected subframe. The base station apparatus 10 broadcasts a packet signal in the set road-to-vehicle transmission period.
A plurality of types of data can be assumed as data to be contained in a packet signal. One type of data is data such as traffic j am information and construction information and another type of data is data on each slot contained in the priority period. The latter contains slots (hereinafter, called “vacant slots”) used by none of terminal apparatuses, slots (hereinafter, called “used slots”) used by one terminal apparatus, and slots (hereinafter, called “collision slots”) used by a plurality of terminal apparatuses. A packet signal (hereinafter, called an “RSU packet signal”) containing data such as traffic jam information and construction information and a packet signal (hereinafter, called a “control packet signal”) containing data on each slot are generated separately. The RSU packet signal and the control packet signal are generically called a “packet signal”.
The first area 210 and the second area 212 are formed around the communication system 100 in accordance with receiving conditions when a terminal apparatus receives a packet signal from the base station apparatus 10. As shown in
Two types of control information are contained in a packet signal from the base station apparatus 10. One type is information (hereinafter, called a “basic part”) about the set road-to-vehicle transmission period and the other type is information (hereinafter, called an “extension part”) about the set priority period. The terminal apparatus generates a frame based on the basic part contained in a received packet signal. As a result, a frame generated by each of the plurality of terminal apparatuses is synchronized with a frame generated by the base station apparatus 10. The terminal apparatus receives a packet signal broadcasted by the base station apparatus 10 and estimates in which of the first area 210, the second area 212, and the area outside second area 214 the terminal apparatus is present based on receiving conditions of the received packet signal and the extension part.
Further, the extension part contained in the packet signal from the base station apparatus 10 contains information (hereinafter, called a “priority area identifier”) indicating the correspondence between the area and the inter-vehicle transmission period. The information indicating the correspondence between the area and the inter-vehicle transmission period can be said to be information indicating in which of the first area 210 and the second area 212 the priority period should be used. A first arrangement and a second arrangement are defined and the general period is used in the first area 210 and the priority period is used in the second area 212 in the first arrangement. On the other hand, the priority period is used in the first area 210 and the general period is used in the second area 212 in the second arrangement. When the priority area identifier indicates the first arrangement, the terminal apparatus broadcasts a packet signal by a carrier sense in a general period if the terminal apparatus is present in the first area 210 and broadcasts a packet signal in one of slots contained in a priority period if the terminal apparatus is present in the second area 212. When the priority area identifier indicates the second arrangement, the terminal apparatus broadcasts a packet signal in one of slots contained in a priority period if the terminal apparatus is present in the first area 210 and broadcasts a packet signal by a carrier sense in a general period if the terminal apparatus is present in the second area 212.
As a result, TDMA is executed in the priority period and CSMA/CA is executed in the general period. The terminal apparatus selects a subframe of the same relative timing also in the next frame. Particularly in the priority period, the terminal apparatus selects a slot of the same relative timing in the next frame. The terminal apparatus acquires data and stores the data in a packet signal. The data includes information about the position of presence. The terminal apparatus also stores control information in a packet signal. That is, control information transmitted from the base station apparatus 10 is transferred by the terminal apparatus. If the terminal apparatus estimates to be present in the area outside second area 214, the terminal apparatus broadcasts a packet signal by executing CSMA/CA regardless of the frame configuration.
The RF unit 22 generates a packet signal at radio frequency by making a frequency conversion of a baseband packet signal input from the modem unit 24 as transmission processing. Further, the RF unit 22 transmits a packet signal at radio frequency from the antenna 20 in a road-to-vehicle transmission period. The RF unit 22 also includes a PA (Power Amplifier), mixer, and A/D conversion unit.
The modem unit 24 performs demodulation of a baseband packet signal from the RF unit 22 as receiving processing. Further, the modem unit 24 outputs a demodulation result to the processing unit 26. The modem unit 24 also performs demodulation of data from the processing unit 26 as transmission processing. Further, the modem unit 24 outputs the demodulation result to the RF unit 22 as a baseband packet signal. The communication system 100 supports the OFDM (Orthogonal Frequency Division Multiplexing) modulation method and thus, the modem unit 24 also performs FFT (Fast Fourier Transform) as receiving processing and also performs IFFT (Inverse Fast Fourier Transform) as transmission processing.
The frame defining unit 40 receives a signal from a GPS satellite (not shown) and acquires time information based on the received signal. A publicly known technology may be used to acquire time information, so that the description thereof is herein omitted. The frame defining unit 40 generates a plurality of frames based on time information. For example, the frame defining unit 40 generates 10 frames of “100 msec” by dividing a “1 sec” period into 10 frames relative to the timing indicated by time information. Frames are defined to be repeated by repeating the above processing. The frame defining unit 40 may generate frames based on control information detected from a demodulation result. Such processing corresponds to generation of frames synchronized with the timing of frames generated by the other base station apparatus 10.
The selection unit 42 selects a subframe to which a road-to-vehicle transmission period should be set from a plurality of subframes contained in the frame. More specifically, the selection unit 42 receives a frame defined by the frame defining unit 40. The selection unit 42 has a demodulation result from the other base station apparatuses 10 or terminal apparatuses (not shown) input thereinto via the RF unit 22 and the modem unit 24. The selection unit 42 extracts a demodulation result from the base station apparatus 10 from among the input demodulation results. The extraction method will be described later. The selection unit 42 identifies subframes from which no demodulation result is received by identifying subframes from which demodulation results have been received. This corresponds to identification of subframes to which no road-to-vehicle transmission period by the other base station apparatus 10 is set, that is, unused subframes. If a plurality of unused subframes is present, the selection unit 42 randomly selects one subframe. If no unused subframe is present, that is, each of the plurality of subframes is used, the selection unit 42 acquires received power corresponding to the demodulation result and selects a subframe of small received power preferentially.
The setting unit 48 has an interface to receive instructions from an operator and receives setting instructions of parameters via the interface. For example, the interface is a button and the setting unit 48 receives setting instructions of parameters through input to the button. The interface may also be a connection terminal to the network communication unit 80 described later. At this point, the setting unit 48 receives setting instructions of parameters via the network communication unit 80, the network 202 (not shown), and a PC. Setting instructions of parameters concern whether to use the first arrangement or the second arrangement. The setting unit 48 outputs the received setting instructions to the generation unit 46.
The detection unit 44 identifies whether each of a plurality of slots contained in the priority period is unused, in use, or collided. Before describing processing by the detection unit 44, the configuration of a subframe will be described.
The detection unit 44 measures received power for each slot and also measures the error rate for each slot. An example of the error rate is BER (Bit Error Rate). If received power is smaller than a received power threshold, the detection unit 44 judges that the slot is unused (hereinafter, such a slot will be called a “vacant slot”). On the other hand, if received power is equal to or larger than the received power threshold and the error rate is smaller than an error rate threshold, the detection unit 44 judges that the slot is in use (hereinafter, such a slot will be called a “used slot”). If received power is equal to or larger than the received power threshold and the error rate is equal to or larger than the error rate threshold, the detection unit 44 judges that a collision has occurred in the slot (hereinafter, such a slot will be called a “collided slot”). The detection unit 44 performs such processing on all slots and outputs results thereof (hereinafter, called “detection results”) to the generation unit 46.
The generation unit 46 receives setting instructions from the setting unit 48, the subframe number from the selection unit 42, and detection results from the detection unit 44. The generation unit 46 sets a road-to-vehicle transmission period to the subframe of the received subframe number and generates control packet signals and RSU packet signals to be broadcasted in the road-to-vehicle transmission period.
Here, the configurations of a control packet signal and an RSU packet signal will be described.
The protocol version shows the version of the corresponding protocol. The transmitting node type shows the transmission source of a packet signal containing the MAC frame. For example, “0” indicates a terminal apparatus and “1” indicates the base station apparatus 10. If the selection unit 42 extracts demodulation results of the other base station apparatuses 10 from input demodulation results, the selection unit 42 uses the value of the transmitting node type. The reuse count shows an indicator of validity when the message header is transferred to terminal apparatuses and the TSF timer shows the transmission time. The RSU transmission period length shows the length of a road-to-vehicle transmission period and is information relating to the road-to-vehicle transmission period.
The inter-vehicle slot size shows the size of a slot contained in the priority period, the priority/general ratio shows the ratio of the priority period to the general period, and the priority/general threshold is a threshold to cause the terminal apparatus 14 to select the use of the priority period or the use of the general period and also a threshold for received power. The priority area identifier is an identifier to indicate the use of the first arrangement or the second arrangement. If the first arrangement is used, that is, the arrangement in
The processing unit 26 causes the modem unit 24 and the RF unit 22 to transmit packet signals by broadcasting in the road-to-vehicle transmission period. That is, the processing unit 26 broadcasts control packet signals and RSU packet signals containing the basic part and the extension part in base station broadcasting period. The control unit 30 controls processing of the whole base station apparatus 10.
Although this configuration may be realized by a CPU, memory, and another LSI of an optional computer in a hardware aspect and is realized by a program loaded on the memory and the like in a software aspect, a functional block realized by combining these aspects is herein described. Therefore, one skilled in the art may comprehend that these functional blocks may be realized in various modes only by hardware, or only by software, or combination thereof.
The modem unit 54 and the processing unit 56 receive packet signals from the other terminal apparatuses 14 and the base station apparatus 10 (not shown). As described above, the modem unit 54 and the processing unit 56 receive packet signals from the base station apparatus 10 in the road-to-vehicle transmission period. As described above, the modem unit 54 and the processing unit 56 receive packet signals from the other terminal apparatuses 14 in the priority period and general period.
If a demodulation result from the modem unit 54 is a packet signal from the base station apparatus 10 (not shown), the extraction unit 66 identifies the timing of the subframe in which the road-to-vehicle transmission period is arranged. The extraction unit 66 generates a frame based on the subframe timing and content of the basic part in the message header of the packet signal, more specifically, content of the RSU transmission period length. The frame may be generated in the same manner as the frame defining unit 40, so that the description thereof is herein omitted. As a result, the extraction unit 66 generates a frame synchronized with a frame generated by the base station apparatus 10.
The extraction unit 66 measures received power of a packet signal from the base station apparatus 10. Based on the measured received power, the extraction unit 66 estimates to be present in the first area 210, the second area 212, or the area outside second area 214. For example, the extraction unit 66 stores an area judgment threshold. The area judgment threshold corresponds to the above priority/general threshold. If the received power is larger than the area judgment threshold, the extraction unit 66 decides to be present in the first area 210. If the received power is equal to or smaller than the area judgment threshold, the extraction unit 66 decides to be present in the second area 212. If no packet signal from the base station apparatus 10 is received, the extraction unit 66 decides to be present outside the second area 212. Instead of the received power, the extraction unit 66 may use the error rate or a combination of the received power and the error rate.
The extraction unit 66 decides whether the area in which the extraction unit 66 is present is a priority area or a general area based on an estimation result and the priority area identifier. When the priority area identifier is “1”, the extraction unit 66 selects the priority area if present in the first area 210 and the general area if present in the second area 212. When the priority area identifier is “0”, on the other hand, the extraction unit 66 selects the general area if present in the first area 210 and the priority area if present in the second area 212.
Further, if the extraction unit 66 estimates to be in the area outside second area 214, the extraction unit 66 selects timing independent of the frame configuration. If the extraction unit 66 selects a general area, the extraction unit 66 selects a general period. If the extraction unit 66 selects a priority area, the extraction unit 66 selects a priority period. If the extraction unit 66 selects a priority area, the extraction unit 66 outputs detection results contained in the payload of a control packet signal to the selection unit 92. If the extraction unit 66 selects a general area, the extraction unit 66 outputs the timing of the frame and subframes and information about the inter-vehicle transmission period to the carrier sense unit 94. If the extraction unit 66 selects timing independent of the frame configuration, the extraction unit 66 instructs the carrier sense unit 94 to perform a carrier sense.
The selection unit 92 receives detection results from the extraction unit 66. Detection results show, as described above, whether each of a plurality of slots contained in the priority period is a vacant slot, used slot, or collided slot. The selection unit 92 selects one of vacant slots. If a slot is already selected and the slot is a used slot, the selection unit 92 uses the same slot as before. On the other hand, if a slot is already selected and the slot is a collided slot, the selection unit 92 newly selects a vacant slot. The selection unit 92 notifies the generation unit 64 of information about the selected slot as transmission timing.
The carrier sense unit 94 receives the timing of the frame and subframes and information about the inter-vehicle transmission period from the extraction unit 66. The carrier sense unit 94 measures interference power by performing a carrier sense in a general period. The carrier sense unit 94 also decides transmission timing in the general period based on interference power. More specifically, the carrier sense unit 94 stores a predetermined threshold in advance and compared the interference power with the threshold. If the interference power is smaller than the threshold, the carrier sense unit 94 decides the transmission timing. If the carrier sense unit 94 is instructed by the extraction unit 66 to perform a carrier sense, the carrier sense unit 94 decides the transmission timing by executing CSMA without consideration of the frame configuration. The carrier sense unit 94 notifies the generation unit 64 of the decided transmission timing.
The acquisition unit 72 includes a GPS receiver, gyroscope, speed sensor (not shown) and the like and the position of presence, traveling direction, traveling speed and the like (hereinafter, generically called “position information”) of the vehicle 12 (not shown), that is, the vehicle 12 on which the terminal apparatus 14 is mounted are acquired from data supplied from the above components included in the acquisition unit 72. Incidentally, the position of presence is indicated by latitude and longitude. The well-known technology may be used to acquire them, so that the description thereof is herein omitted. The acquisition unit 72 outputs position information to the generation unit 64.
The transfer decision unit 90 controls transfer of the message header. The transfer decision unit 90 extracts the message header from a packet signal. If a packet signal is directly transmitted from the base station apparatus 10, the reuse count is set to “0”, but if a packet signal is transmitted from the other terminal apparatus 14, the reuse count is set to a value of “1 or greater”. The transfer decision unit 90 selects the message header to be transferred from extracted message headers. For example, the message header of the smallest reuse count is selected. The transfer decision unit 90 may also generate a new message header by combining content contained in a plurality of message headers. The transfer decision unit 90 outputs the message header to be selected to the generation unit 64. At this point, the transfer decision unit 90 increments the reuse count by “1”.
The generation unit 64 receives position information from the acquisition unit 72 and a message header from the transfer decision unit 90. The generation unit 64 stores the position information in the payload by using the MAC frame shown in
The notification unit 70 acquires a packet signal from the base station apparatus 10 (not shown) in a road-to-vehicle transmission period and also acquires packet signals from the other terminal apparatuses 14 (not shown) in an inter-vehicle transmission period. As processing on the acquired packet signal, the notification unit 70 notifies the driver of the approaching vehicle 12 (not shown) in accordance with content of data stored in the packet signal via a monitor or speaker. The control unit 58 controls the operation of the whole terminal apparatus 14.
The operation of the communication system 100 in the above configuration will be described.
A modification of the present invention will be described. In the modification of the present invention, a vehicle present in the first area is a vehicle present close to an intersection and thus, a packet signal from the terminal apparatus of the vehicle is important information from the viewpoint of suppressing a collision. Corresponding to such area definitions, a period (hereinafter, called a “inter-vehicle transmission period”) for inter-vehicle communication is formed by time-division multiplexing of a priority period and a general period. The priority period is a period to be used by a terminal apparatus present in the first area and the terminal apparatus transmits a packet signal in one of a plurality of slots forming the priority period. The general period is a period to be used by a terminal apparatus present in the second area and the terminal apparatus transmits a packet signal by the CSMA method in the general period. A terminal apparatus present outside the second area transmits a packet signal by the CSMA method regardless of the frame configuration. Here, in which area the terminal apparatus mounted on a vehicle is present is determined. Incidentally, some base station apparatuses have no first area formed therearound. In such a case, the inter-vehicle transmission period contains no priority period and is formed of general periods only.
That is, two types of frame configuration are defined. The base station apparatus notifies terminal apparatuses of information about the frame in use by a packet signal broadcasted in a road-to-vehicle transmission period. Because a frame containing no priority period (hereinafter, called a “first frame”) has a simpler frame configuration than a frame containing a priority period (hereinafter, called a “second frame”), reducing the information amount of control information. To simplify the configuration of control information, the base station apparatus according to the present modification includes information about the road-to-vehicle transmission period in a packet signal when the first frame is used and includes, in addition to information about the road-to-vehicle transmission period, information about the priority period in a packet signal when the second frame is used.
The setting unit 1048 has an interface to receive instructions from an operator and receives setting instructions of parameters via the interface. For example, the interface is a button and the setting unit 1048 receives setting instructions of parameters through input to the button. The interface may also be a connection terminal to the network communication unit 1080 described later. At this point, the setting unit 1048 receives setting instructions of parameters via the network communication unit 1080, the network 1202 (not shown), and a PC. Setting instructions of parameters concern whether to use the first frame or the second frame. The setting unit 1048 outputs the received setting instructions to the detection unit 1044 and the generation unit 1046.
The detection unit 1044 receives setting instructions from the setting unit 1048. If setting instructions concern the use of the first frame, no processing will be performed. If setting instructions concern the use of the second frame, the detection unit 1044 identifies whether each of a plurality of slots contained in the priority period is unused, in use, or collided. Before describing processing by the detection unit 1044, the configuration of a subframe in the second frame will be described.
The protocol version shows the version of the corresponding protocol and also contains identification that only the basic part is contained in the message header or the basic part and the extension part are contained in the message header. The former corresponds to
The reuse count shows an indicator of validity when the message header is transferred to terminal apparatuses and the TSF timer shows the transmission time. The RSU transmission period length shows the length of a road-to-vehicle transmission period and is information relating to the road-to-vehicle transmission period. The inter-vehicle slot size shows the size of a slot contained in the priority period, the priority/general ratio shows the ratio of the priority period to the general period, and the priority/general threshold is a threshold to cause the terminal apparatus 1014 to select the use of the priority period or the use of the general period and also a threshold for received power. That is, the extension part corresponds to information relating to the priority period and the general period.
Next, a case when setting instructions concern the use of the first frame will be described. The generation unit 1046 sets a road-to-vehicle transmission period to the subframe of the received subframe number and generates RSU packet signals to be broadcasted in the road-to-vehicle transmission period. No control packet signal is generated.
The processing unit 1026 causes the modem unit 1024 and the RF unit 1022 to transmit packet signals by broadcasting in the road-to-vehicle transmission period. That is, the processing unit 1026 causes transmission of RSU packet signals containing the basic part by broadcasting in the base station broadcasting period when the first frame is used and broadcasts control packet signals and RSU packet signals containing the basic part and the extension part in the base station broadcasting period when the second frame is used. The control unit 1030 controls processing of the whole base station apparatus 1010.
The modem unit 1054 and the processing unit 1056 receive packet signals from the other terminal apparatuses 1014 and the base station apparatus 1010 (not shown). As described above, the modem unit 1054 and the processing unit 1056 receive packet signals from the base station apparatus 1010 in the road-to-vehicle transmission period. As described above, the modem unit 1054 and the processing unit 1056 receive packet signals from the other terminal apparatuses 1014 in the general period when the first frame is used and receive packet signals from the other terminal apparatuses 1014 in the priority period and the general period when the second frame is used.
If a demodulation result from the modem unit 1054 is a packet signal from the base station apparatus 1010 (not shown), the extraction unit 1066 identifies the timing of the subframe in which the road-to-vehicle transmission period is arranged. The extraction unit 1066 generates a frame based on the subframe timing and content of the basic part in the message header of the packet signal, more specifically, content of the RSU transmission period length. The frame may be generated in the same manner as the frame defining unit 1040, so that the description thereof is herein omitted. As a result, the extraction unit 1066 generates a frame synchronized with a frame generated by the base station apparatus 1010.
The extraction unit 1066 recognizes the use of the second frame when reception of control packet signals and RSU packet signals in the road-to-vehicle transmission period or inclusion of the basic part and the extension part in the message header of the received packet signal is detected. On the other hand, the extraction unit 1066 recognizes the use of the first frame when reception of only RSU packet signals in the road-to-vehicle transmission period or inclusion of only the basic part in the message header of the received packet signal is detected.
If the use of the second frame is recognized, the extraction unit 1066 measures received power of a packet signal from the base station apparatus 1010. Based on the measured received power, the extraction unit 1066 estimates to be present in the first area 1210, the second area 1212, or the area outside second area 1214. For example, the extraction unit 1066 stores an area judgment threshold. The area judgment threshold corresponds to the above priority/general threshold. If the received power is larger than the area judgment threshold, the extraction unit 1066 decides to be present in the first area 1210. If the received power is equal to or smaller than the area judgment threshold, the extraction unit 1066 decides to be present in the second area 1212. If no packet signal from the base station apparatus 1010 is received, the extraction unit 1066 decides to be present the area outside second area 1214. Instead of the received power, the extraction unit 1066 may use the error rate or a combination of the received power and the error rate.
Based on the estimation result, the extraction unit 1066 decides in favor of one of the priority period, general period, and timing independent of the frame configuration as the transmission time. More specifically, if the extraction unit 1066 estimates to be in the area outside second area 1214, the extraction unit 1066 selects timing independent of the frame configuration. If the extraction unit 1066 estimates to be in the second area 1212 or detects the use of the first frame, the extraction unit 1066 selects a general period. If the extraction unit 1066 estimates to be in the first area 1210, the extraction unit 1066 selects a priority period. If the extraction unit 1066 selects a priority area, the extraction unit 1066 outputs detection results contained in the payload of a control packet signal to the selection unit 1092. If the extraction unit 1066 selects a general area, the extraction unit 1066 outputs the timing of the frame and subframes and information about the inter-vehicle transmission period to the carrier sense unit 1094. If the extraction unit 1066 selects timing independent of the frame configuration, the extraction unit 1066 instructs the carrier sense unit 1094 to perform a carrier sense.
The selection unit 1092, the carrier sense unit 1094, the acquisition unit 1072, the transfer decision unit 1090, the generation unit 1064, the notification unit 1070, and the control unit 1058 corresponds to the selection unit 92, the carrier sense unit 94, the acquisition unit 72, the transfer decision unit 90, the generation unit 64 in
The operation of the communication system 1100 in the above configuration will be described.
Next, another modification of the present invention will be described. Like the modification, the other modification also relates to a communication system used in ITS. In the modification, the message header formed of the basic part is stored in RSU packet signals when the first frame is used and the message header formed of the basic part and the extension part is stored in control packet signals and RSU packet signals when the second frame is used. The other modification seeks to improve transmission efficiency when the second frame is used. In the other modification, the message header formed of the basic part and the extension part is stored only in control packet signals when the second frame is used. The communication system according to the other modification is the same type as shown in
The generation unit 1046 generates RSU packet signals to be broadcasted in the base station broadcasting period when the first frame is used and control packet signals and RSU packet signals to be broadcasted in the base station broadcasting period when the second frame is used. The generation unit 1046 includes the basic part in the message header of RSU packet signals to be broadcasted when the first frame is used and the basic part and the extension part in the message header of control packet signals to be broadcasted when the second frame is used. The generation unit 1046 does not include any message header in RSU packet signals to be broadcasted when the second frame is used. Incidentally, the generation unit 1046 may include only the basic part in the message header of RSU packet signals to be broadcasted when the second frame is used.
Next, still another modification of the present invention will be described. The frame defining unit 1040 in
Corresponding to these definitions, whether to use the first frame, the second frame, or the third frame is input into the setting unit 1048 in
According to an embodiment of the present invention, a terminal apparatus present in the first area around the base station apparatus can broadcast a packet signal in a general period and a terminal apparatus present in the second area surrounding the first area can broadcast a packet signal in a priority period and thus, a higher priority can be attached to communication in the second area. If a higher priority can be attached to communication in the second area, the probability of a packet signal broadcasted from a terminal apparatus present in the second area being received can be increased. Moreover, because the probability of a packet signal broadcasted from a terminal apparatus present in the second area being received is increased, important data can preferentially be transmitted. The first arrangement and the second arrangement can be switched and thus, attaching a higher priority to communication in the first area and attaching a higher priority to communication in the second area can be switched. Because attaching a higher priority to communication in the first area and attaching a higher priority to communication in the second area is switched, an area to be prioritized can be selected in accordance with the intersection. Moreover, the selection of the first arrangement or the second arrangement is indicated by the priority area identifier and thus, processing can be made simpler.
Because received power is used to distinguish between the first area and the second area, the range in which the transmission loss is within certain limits can be defined as the first area. Because the range in which the transmission loss is within certain limits can be defined as the first area, a central portion of an intersection can be used as the first area. Moreover, the priority period is time-division multiplexed by slots and thus, the error rate can be reduced. In addition, CSMA/CA is executed in a general period and thus, the number of terminal apparatuses can flexibly be adjusted.
Because subframes used by other base station apparatuses are identified based on not only packet signals directly received from the other base station apparatuses, but also packet signals received from other terminal apparatuses, the precision with which subframes being used are identified can be improved. Because the precision with which subframes being used are identified is improved, the probability of collisions between packet signals transmitted from the base station apparatuses can be reduced. Because the probability of collisions between packet signals transmitted from the base station apparatuses is reduced, the terminal apparatus can recognize control information correctly. Because control information is recognized correctly, the road-to-vehicle transmission period can be recognized correctly. Because the road-to-vehicle transmission period is recognized correctly, the probability of collision of packet signals can be reduced.
Because subframes excluding subframes in use are preferentially used, the possibility of transmitting a packet signal in overlapping timing with a packet from another base station apparatus can be reduced. Because a subframe with lower received power is selected when all subframes are used by other base station apparatuses, an influence of interference of packet signals can be limited. Because received power of a terminal apparatus is used as received power from another base station apparatus to be the source of control information relayed by the terminal apparatus, estimation processing of the received power can be simplified.
Because the basic part is generated when the first frame is used and the basic part and the extension part are generated when the second frame is used, the message header in accordance with the frame configuration can be generated. Because the message header in accordance with the frame configuration is generated, highly flexible vehicle-vehicle communication can be realized. Because highly flexible vehicle-vehicle communication is realized, a highly flexible terminal apparatus can be realized. Because the basic part is generated and the extension part is not generated when the first frame is used, transmission efficiency can be improved. Because the basic part and the extension part are generated when the second frame is used, necessary information can be notified. Processing can be simplified because it is only necessary to change whether to generate the extension part depending on which of the first frame and the second frame to use. Processing can be simplified because the basic part is generated regardless of whether the first frame is used or the second frame is used.
Because a packet signal contains an identifier to distinguish between inclusion of only the basic part in the packet signal and inclusion of the basic part and the extension part in the packet signal, whether the extension part is included can reliably be notified. Also because a packet signal contains an identifier to distinguish between inclusion of only the basic part in the packet signal and inclusion of the basic part and the extension part in the packet signal, the inclusion of the extension part can easily be notified. Because the extension part can include the size of a slot contained in the priority period, the ratio of the priority period to the general period, and a threshold to cause a terminal apparatus to select the use of the priority period or the use of the general period, information necessary for operation can be notified.
Because the basic part and the extension part are included in control packet signals and RSU packet signals, the receiving probability of the basic part and the extension part can be improved. Because the probability of receiving the basic part and the extension part is improved, processing by a terminal apparatus can be made correct. Because the basic part is included in RSU packet signals broadcasted when the first frame is used and the basic part and the extension part are included in control packet signals and RSU packet signals broadcasted when the second frame is used, the receiving probability can be improved while degradation in transmission efficiency being limited. Because the basic part is contained in RSU packet signals broadcasted when the first frame is used and the basic part and the extension part are contained in control packet signals broadcasted when the second frame is used, the receiving probability can be improved while transmission efficiency being improved. Because frames of a plurality of types of formats can be used, various communication conditions can be tackled. Because the length of the priority period can be adjusted, various communication conditions can be tackled.
Because received power is used to distinguish between the first area and the second area, the range in which the transmission loss is within certain limits can be defined as the first area. Because the range in which the transmission loss is within certain limits can be defined as the first area, a central portion of an intersection can be used as the first area. Moreover, the priority period is time-division multiplexed by slots and thus, the error rate can be reduced. In addition, CSMA/CA is executed in a general period and thus, the number of terminal apparatuses can flexibly be adjusted.
Because subframes used by other base station apparatuses are identified based on not only packet signals directly received from the other base station apparatuses, but also packet signals received from other terminal apparatuses, the precision with which subframes being used are identified can be improved. Because the precision with which subframes being used are identified is improved, the probability of collisions between packet signals transmitted from the base station apparatuses can be reduced. Because the probability of collisions between packet signals transmitted from the base station apparatuses is reduced, the terminal apparatus can recognize control information correctly. Because control information is recognized correctly, the road-to-vehicle transmission period can be recognized correctly. Because the road-to-vehicle transmission period is recognized correctly, the probability of collision of packet signals can be reduced.
Because subframes excluding subframes in use are preferentially used, the possibility of transmitting a packet signal in overlapping timing with a packet from another base station apparatus can be reduced. Because a subframe with lower received power is selected when all subframes are used by other base station apparatuses, an influence of interference of packet signals can be limited. Because received power of a terminal apparatus is used as received power from another base station apparatus to be the source of control information relayed by the terminal apparatus, estimation processing of the received power can be simplified.
The present invention has been described above based on an embodiment. The embodiment is illustrative only and one skilled in the art may comprehend that various modifications of combination of the components and the processes are possible and such modifications are also included within the scope of the present invention.
The present embodiment may be characterized by the following items:
A base station apparatus controlling inter-terminal communication, including a generation unit configured to generate information about a frame in which a first period, a second period, and a third period are time-multiplexed and a broadcasting unit configured to broadcast a packet signal containing the information generated by the generation unit in the first period, wherein a terminal apparatus present in a first area around the base station apparatus can broadcast the packet signal in the third period indicated by the information generated by the generation unit and the terminal apparatus present in a second area surrounding the first area can broadcast the packet signal in the second period.
According to the item, importance can be set in accordance with the position from which a packet signal should be transmitted.
The base station apparatus according to item 1, wherein the generation unit includes an identifier in the information and uses one of a first arrangement in which the terminal apparatus present in the first area around the base station apparatus can broadcast the packet signal in the third period and the terminal apparatus present in the second area surrounding the first area can broadcast the packet signal in the second period and a second arrangement in which the terminal apparatus present in the first area around the base station apparatus can broadcast the packet signal in the second period and the terminal apparatus present in the second area surrounding the first area can broadcast the packet signal in the third period based on the identifier.
A terminal apparatus controlling inter-terminal communication, including a communication unit configured to receive information about a frame in which a first period, a second period, and a third period are time-multiplexed in the first period from a base station apparatus and an instruction unit configured to select use of the second period or the use of the third period based on the information received by the communication unit and notifies the communication unit of broadcasting of a packet signal in the selected period, wherein the instruction unit selects the use of the third period when present in a first area around the base station apparatus and the use of the second period when present in a second area surrounding the first area.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-114717 | May 2010 | JP | national |
| 2010-114718 | May 2010 | JP | national |
| 2010-116772 | May 2010 | JP | national |
| 2010-124950 | May 2010 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2011/002775 | May 2011 | US |
| Child | 13425146 | US |
