JP3448650B2 - Road-to-vehicle communication method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road that enables mobile communication with a vehicle-mounted device by arranging a road antenna near a road and forming an area on the road. The present invention relates to an inter-vehicle communication method. 2. Description of the Related Art FIGS. 6 and 7 show an example of a road-to-vehicle communication system that provides a service for providing information in adjacent areas (eg, intersections) according to the prior art.
Shown in In order to prevent radio wave interference between adjacent areas while transmitting radio waves in each area, it is necessary to make carrier frequencies of radio waves transmitted from base stations provided in each area different. [0004] For example, each intersection A shown in FIG.
In B, C, and D, radio waves are transmitted using directional antennas directed along four roads extending from the intersection. At this time, in order to make the carrier frequency of the radio wave from the intersection different for each road connecting the intersections, the carrier frequency f1 is applied to the road facing left from the intersection in FIG. The frequency f2 is assigned to the upward road, and the carrier frequency f3 is assigned to the downward road, and the carrier frequency f4 is assigned to the downward road. When a radio wave is transmitted from the directional antenna with a frequency assigned in this manner, for example, a road connecting the intersections A and B receives a radio wave of the carrier frequency f2 from the left and a radio wave of the carrier frequency f1 from the right. Then, the carrier frequency f
Since 1 and f2 are different, both radio waves do not cause interference on this road. In addition, corresponding to the road in each direction, the base stations 1-1 to 1-4 provided at the intersection A are:
The centralized base stations 2-1 to 2-2 control the entire system. FIG. 7 shows the relationship between the services provided at each of the intersections A, B, C, and D and the allocation of carrier frequencies. In this case, for convenience of explanation, the services provided at the respective intersections A, B, C, and D are a,
It is indicated by the symbols b, c and d. Since the intersection A provides the service a, the information of the service a is transmitted on each of the carrier frequencies f1, f2, f3, and f4 assigned to the road in each direction at the intersection A, and the radio wave is transmitted. Similarly, since the service b is provided at the intersection B, the carrier frequencies f1, f2, f3 and f3 assigned to the roads in each direction at the intersection B are provided.
The radio wave is transmitted with the information of the service b on each of the f4s. Further, the same applies to the assignment of the service to the carrier frequency at the intersections C and D. A case will be described below wherein a service is allocated to a carrier frequency at each intersection and a radio wave is received by a receiver mounted on a vehicle. Conventional receivers can only receive one carrier frequency at a time. For example, when tuning to the carrier frequency f1, only the carrier frequency f1 at any one of the intersections A, B, C, and D can be received as shown by the solid line in FIG. On the other hand, considering the case where the vehicle passes through the intersections A and B from left to right in FIG. 6, the carrier frequency f1 is received until the vehicle passes through the intersection A, and the carrier frequency is switched to the carrier frequency f2 immediately after passing through the intersection A. When the vehicle approaches the intersection B, it receives the carrier frequency f1 again. Immediately after passing through the intersection B, it is necessary to switch to the carrier frequency f2 for reception. [0007] In such a conventional road-vehicle communication system, since the radio frequency is different when the radio area is switched, it is necessary to switch the radio frequency on the receiver side. Frequency search means and frequency switching means were required. In particular, when receiving a service in a complicated place such as an intersection, a receiver that moves at a high speed such as a car frequently switches the reception frequency. However, since it is difficult to switch the receiving frequency instantaneously, there is a problem that the service cannot be received because the frequency switching is not in time. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a road-vehicle communication method capable of performing mobile communication with a vehicle-mounted device without having to switch a radio frequency on a receiver side. I do. [0009] According to an aspect of the present invention, such eye
In order to achieve the target, the invention according to claim 1 inputs information to be sent to adjacent areas, modulates a subcarrier in an orthogonal frequency division multiplexing system with the information, and provides the information in each area. The modulated signals are transmitted at the same carrier frequency from an antenna. [0010] A is as described above, the invention according to claim 1 inputs information to be sent respectively adjacent area, the sub-carriers in the OFDM classified corresponding to each area, each group Are modulated with the information, and the respective modulated signals are transmitted at the same carrier frequency from antennas provided in each area. An embodiment of the present invention will be described below with reference to the drawings shown in FIGS. In the illustrated embodiment according to the present invention, portions having the same configuration as the conventional road-vehicle communication system shown in FIGS. 6 and 7 will be described using the same reference numerals. FIGS. 1 and 2 show a first embodiment of the present invention. In the first embodiment, as shown in FIG. 1, at each of the intersections A, B, C, and D, radio waves are transmitted using directional antennas directed along four roads extending from the intersections. In the first embodiment, since the OFDM modulation method is used, there is no problem even if radio waves from a plurality of base stations 1-1 to 1-4 are mixed and received. Therefore, it is only necessary to transmit radio waves at the same carrier frequency F0 from each directional antenna. In this embodiment, on the transmitter side, different groups of subcarriers f are assigned one by one to adjacent areas. In other words, each service at each intersection
It is transmitted in association with the carrier group. This transmission state is shown in FIG. For example, at the intersection A that provides the service a, the four base stations 1-1 to 1-4 that supply radio waves to the directional antennas transmit the information of the service a transmitted from the base central station 2 to the carrier frequency F0. On one subcarrier group of the OFDM signal is transmitted as indicated by the solid line. Similarly, at the intersection B, the information of the service "b" sent from the base station is loaded on one subcarrier group of the OFDM signal of the frequency F0 and transmitted as shown by the solid line. Similarly, at the intersections C and D, different subcarrier groups of the OFDM signal of the frequency F0 are allocated and transmitted as indicated by the solid lines corresponding to the respective services c and d. According to this embodiment, on the receiver side, decoding is performed in each area using only one subcarrier group corresponding to the area. That is, the frequency F0
, The service can be received by collectively receiving the OFDM signals and extracting only the subcarrier group on which necessary information is carried. For example, assuming that the vehicle passes through the intersections A and B from left to right in FIG. 1, the receiver mounted on the car always receives the OFDM signal of the carrier frequency F0 and selects the subcarrier group. And decode it. Specifically, a subcarrier group corresponding to the service a of the intersection A is selected and decoded until the vehicle approaches the middle of the intersection A and the intersection B, and passes through the vicinity of the middle of the intersection A and the intersection B. After that, the subcarrier group corresponding to the service b at the intersection B may be selected and decoded. Then, services a and b corresponding to the respective intersections A and B can be received. As described above, according to this embodiment, since the carrier frequency of the OFDM signal received by the receiver is always F0, there is no need to switch the reception frequency as required in the prior art. It should be noted that the subcarrier group to be decoded needs to be switched every time the reception area is moved, but it is not as frequent as the reception frequency switching process required in the related art, and after receiving the carrier. Therefore, the processing time is not required as much as the reception frequency switching processing. In each intersection, it is more preferable to transmit not only the service of the own intersection but also the service of an adjacent or nearby intersection at the same time. Specifically, at the intersection A, as shown by the solid line in FIG.
At the same time as loading on one subcarrier group, the services b, c, and d of the intersections B, C, and D located next to or near each other are loaded on different subcarrier groups and transmitted as shown by the broken line in FIG. That is, at intersection A, services a,
Send b, c, d. Similarly, intersections B, C, and D also transmit services a, b, c, and d, respectively. Needless to say, the subcarrier group corresponding to service a is unified at each intersection. The subcarrier groups corresponding to the services b, c, and d are similarly unified at each intersection.
In this way, the contents transmitted at each intersection are all the same after all, so that there is an advantage that preparation of transmission data is simplified. As described above, in the receiver, at each of the intersections A, B, C, and D, one subcarrier group corresponding to the intersection may be selected and decoded. When traveling from the intersection A to the intersection B, near the middle of the two intersections, the subcarrier groups corresponding to the service a and the service b are included from both the backward intersection A and the forward intersection B. Radio waves arrive. For this reason, even if a large car is running immediately before or after the own vehicle and the front or rear side is in the shadow of radio waves, radio waves can be received from the opposite side, so the possibility of radio waves being interrupted Can be reduced. In addition, service a and service b
, The point at which the subcarrier group to be decoded is switched from the subcarrier group corresponding to the service a at the intersection A to the subcarrier group corresponding to the service b at the intersection B is shifted back and forth. No problem. In the above description, it has been described that the receiver selects one subcarrier group and decodes it.
Embodiments are also possible in which all the subcarrier groups are decoded to select a desired service or services. As apparent from the above description, it is not necessary to change the carrier frequency to be transmitted at each intersection according to the direction of the road. Therefore, the same radio wave can be transmitted to roads in all directions. FIG. 3 shows a second embodiment of the present invention. In FIG. 3, the same radio wave is transmitted to roads in four directions by one omnidirectional antenna. As can be seen from the comparison with the first embodiment, the configurations of the base station and the antenna are simplified as compared with the case where four directional antennas provided for each road are used. Next, FIGS. 4 and 5 show a third embodiment in which there are a large number of grid-shaped intersections A to T. FIG.
As shown in (1), when there are a large number of grid-shaped intersections A to T, there are adjacent intersections at the top, bottom, left, and right of a certain intersection. Focusing on this point, five subcarrier groups are prepared, and different subcarrier groups are assigned to adjacent intersections as shown in FIG. For example, focusing on the intersection G in FIG. 4, the intersections adjacent to this intersection are the intersections H, L, B, and F. Then, as shown in the subcarrier group of the intersection G in FIG. 5, the service g of the intersection G, the service h of the intersection H,
Different subcarrier groups may be assigned to the service 1 at the intersection L, the service b at the intersection B, and the service f at the intersection F. On the other hand, focusing on the intersection H in FIG. 4, the intersections adjacent to this intersection are the intersections G, I, M, and C. Compared with the case of focusing on the intersection G, the intersections L,
B and F are no longer adjacent, but instead are adjacent to intersections I, M and C. Then, as shown in the subcarrier group at the intersection H in FIG.
Services i, m, and c may be reassigned to the subcarrier groups assigned to b and f. Needless to say, since the intersection G and the intersection H are adjacent to each other, the subcarrier groups assigned to the service g and the service h are the same. Further, in the same manner, in the intersections I, L, M, and N, the same subcarrier group is allocated to each service, and the same subcarrier group is reallocated to services in non-adjacent intersections. Is shown in FIG. Although illustration is omitted, cross-shaped intersections are similarly spread outside the intersections shown in FIG. 4, and subcarrier groups are similarly allocated even when a service is provided at each intersection. be able to. In the third embodiment, five subcarrier groups are prepared for the base station provided at the grid-like intersection, and one different group is assigned to the adjacent area.
Although the case of assigning one by one has been described as an example, needless to say, an embodiment in which six or more subcarrier groups are prepared and different groups are assigned one by one to adjacent areas is also possible. In this case, it is possible to increase the interval between areas to be allocated to the same subcarrier group. In the above-described embodiment, an example in which the transmitting antenna of the base station is provided at the intersection has been described. However, if the height of the transmitting antenna is relatively lower than the height of the building, It is preferred to provide a transmitting antenna at the intersection at a point of view. However, in consideration of the case where the height of the building is low or the case where transmission is possible even when radio waves are reflected by the building, it goes without saying that the installation location of the transmitting antenna is not necessarily limited to the intersection. As described above , according to the road-to-vehicle communication method according to the first aspect, since there is no need to perform frequency switching, a frequency search and a frequency switching protocol become unnecessary, and the vehicle moves at high speed. However , in addition to the effect that the service can be provided, it is not necessary to transmit the same information on a different frequency, so that the frequency can be effectively used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing a first embodiment of the present invention. FIG. 2 is an explanatory diagram showing a carrier frequency allocation state according to the first embodiment; FIG. 3 is an explanatory diagram showing a second embodiment of the present invention. FIG. 4 is an explanatory diagram showing a third embodiment of the present invention. FIG. 5 is an explanatory diagram showing a carrier frequency allocation state of the above. FIG. 6 is an explanatory diagram showing an example of a conventional road-vehicle communication system. FIG. 7 is an explanatory diagram showing a carrier frequency allocation state of the above. [Description of Code] 1-1 to 1-4 Base Stations 2-1 to 2-2 Base Concentration Stations A, B, C, D, F, H, I, L, M Intersections a, b, c, d, f, h, i, l, m Service f1 to f4 Carrier frequency

──────────────────────────────────────────────────続 き Continued on the front page (58) Investigated field (Int.Cl. ⁷ , DB name) Reaction

Claims (1)

(57) [Claims] [Claim 1] Information to be sent to adjacent areas is input, and subcarriers in a road-vehicle communication system of an orthogonal frequency division multiplexing method are classified according to each area. And a method of modulating subcarriers of each group with the information, and transmitting the respective modulated signals at the same carrier frequency from antennas provided in each area.