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Today I would like to introduce our research on radio wave propagation for vehicle-to-vehicle communication technology, which will prove useful for reducing traffic accidents. Road-curve mirrors are convenient items with which we can see other vehicles that normally would not come into our field of view. We named the technology "Radio Curve Mirror" since we can achieve the same function as a traditional road-curve mirror using radio waves.
A decade ago, the number of annual fatalities resulting from road traffic accidents was over 10,000. The number of fatalities has been declining due to some measures such as air-bag systems; however, we should continue to make this number even smaller. Moreover, the number of traffic accidents themselves and injuries has actually been increasing, and thus we want to cut this number in half. It is said that about 70% of the causes of traffic accidents are due to human errors, so if we can successfully work on the issues, it will be possible to reduce traffic accidents. If drivers could detect other cars in advance, even at intersections without a traditional curved mirror or traffic signal, more than likely there would be a reduction in the number of accidents. With "Radio Curve Mirrors," using vehicle-to-vehicle communication technology, drivers will be able to do just that.
Vehicle-to-vehicle communication is a system in which vehicles autonomously communicate with each other. However, there is a big gap between "what the system actually can do" and "what the system should be able to do." It is not just a matter of vehicles being able to send messages to each other. If our final goal is to accurately alert the driver of oncoming danger using this system, there are still many differences between that ideal and reality. Some of the technical studies include transmission technology, that is, how to send the signals, the creation of high-reliability links (since lives are on the line), and network technology to get location information. Although it will be possible to obtain each other's location information by studying these technologies, this is not the end of our challenge. We will still need to study vehicle-to-vehicle communication technology, including ergonomics, that has the ability to select the information of only the dangerous oncoming vehicles for the driver.
On the most basic level, vehicle-to-vehicle communication is one vehicle transmitting its information to another vehicle. There are many types of information, and among them, we are currently examining how one vehicle can inform other vehicles of its location using a GPS system. We can see other vehicles that we could not see before by mutually letting each other know where we are currently located. We are carrying out studies on radio wave propagation for this purpose, and I would like to introduce two studies in this field.
The first one is research being done in Germany. One of the simulating methods you can use for research on radio wave propagation is ray tracing. Comparison between the simulation results and the results actually measured on the road at night usually show a rough correspondence with a little discrepancy in the details. We can say that ray tracing is a useful method for getting to know the general outline.
We also have the research results obtained by Doshisha University using a different kind of ray tracing. What these radio wave propagation models tell us, of course, is that the lower the frequency, the farther the wave can reach. Should radio waves travel as far as possible? Not necessarily. Waves that travel too far could be a cause of interference, and thus we need to establish service areas with the propagation characteristics of waves in mind.
We need to carefully observe their ray tracing results. For example, the results could change if there are many vehicles or roadside trees. However, these are not the only elements that affect the results, so further examination is necessary.
One of the more effective technology for transmitting information securely is array antenna technology. This technology, when used for receiving only, is called "diversity," while the other type for both sending and receiving is called "MIMO." MIMO has two main features, increased transmittable data volume and reliable links. Since we don't have to handle a large volume of data in ITS, it will be better to aim for building unbreakable links. For example, two antennas can help each other receive data when one of them has bad reception. Another challenge for this system is how to deal with the fact that both antennas need to receive quickly fading waves during vehicle-to-vehicle communication. Although some measures have been proposed, we will need further examination into this issue.
So far, I have discussed the subject of how one vehicle can securely exchange information with another. However, vehicle-to-vehicle communication has to deal with information among many vehicles so that any vehicle can recognize any other vehicle. We are also studying the possibility of using terrestrial digital broadcasting waves to synchronize many vehicles.
Since no one vehicle acts as a reference station of a group of vehicles, it will be important to synchronize the timing of sending and receiving packets. If we use some external system for synchronization, it would be a good idea to use the terrestrial digital broadcasting waves even though the 1PPS signal of the GPS system is accurate as well. The reason why synchronization is so important is that packet loss will be considerably greater among vehicles without a reference for the system since packets could interfere with each other, as compared with the completely synchronized transmission and reception of packets.
Even if your group was synchronized, when your group interacts with other groups, it would be very difficult to re-synchronize the new, larger group. So we have been studying a system that can provide a 1PPS synchronizing pulse using the terrestrial digital broadcasting system. The results of our experiments show that we can use this system even under circumstances where so much noise exists you could not watch TV. Sending packets in synch with this pulse will at least reduce the interference due to packet collisions caused by timing errors.
This vehicle-to-vehicle communication technology can reduce traffic accidents. The development of infrastructures is definitely required for road-to-vehicle communication. However, since many traffic accidents tend to occur on small streets, establishing vehicle-to-vehicle communication technology should have priority. Road-to-vehicle communication is also important as well as the relationship between human and vehicle. A unified road-to-vehicle, vehicle-to-vehicle, and man-to-vehicle system would be the accomplishment of our goals. Research is being conducted on building a system that does not just feed us all of the information, but can filter through all the information to warns us of potential dangers.