Sharing perceptual data with other vehicles enhances the traffic safety of autonomous vehicles because it helps vehicles locate other vehicles and pedestrians in their blind spots. Such safety applications require high throughput and short delay, which cannot be achieved by conventional microwave vehicular communication systems. Therefore, millimeter-wave (mmWave) communications are considered to be a key technology for sharing perceptual data because of their wide bandwidth. One of the challenges of data sharing in mmWave communications is broadcasting because narrow-beam directional antennas are used to obtain high gain. Because many vehicles should share their perceptual data to others within a short time frame in order to enlarge the areas that can be perceived based on shared perceptual data, an efficient scheduling for concurrent transmission that improves spatial reuse is required for perceptual data sharing. This paper proposes a data sharing algorithm that employs a graph-based concurrent transmission scheduling. The proposed algorithm realizes concurrent transmission to improve spatial reuse by designing a rule that is utilized to determine if the two pairs of transmitters and receivers interfere with each other by considering the radio propagation characteristics of narrow-beam antennas. A prioritization method that considers the geographical information in perceptual data is also designed to enlarge perceivable areas in situations where data sharing time is limited and not all data can be shared. Simulation results demonstrate that the proposed algorithm doubles the area of the cooperatively perceivable region compared with a conventional algorithm that does not consider mmWave communications because the proposed algorithm achieves high-throughput transmission by improving spatial reuse. The prioritization also enlarges the perceivable region by a maximum of 20 .
Dissemination algorithms for local information were proposed in @cite_2 @cite_14 @cite_6 . In @cite_2 , a scalable dissemination protocol, called segment-oriented data abstraction and dissemination (SODAD), and its application, self-organizing traffic-information system (SOTIS), were proposed. SOTIS is a mechanism for gathering traffic information sensed by vehicles. It aggregates the received traffic information from road segments and sends only up-to-date information to vehicles. In @cite_14 , Zone Flooding and Zone Diffusion were proposed to suppress redundant data broadcasting. In Zone Flooding, only vehicles in a flooding zone forward received packets. Zone Diffusion is a data aggregation method considering geographical information, where vehicles merge road environment data as it is received and broadcast only merged data. @cite_6 proposed controlling the frequency of information broadcasting and selecting the data to send to reduce communication traffic. Although these studies considered the geographical information in each datum, they did not focus on concurrent transmission.
@cite_14 @cite_6 @cite_2
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Vehicular ad-hoc networks is an emerging research area focussing on communication infrastructures that support vehicles and road-signs in distributing road-state data such as information about hazardous road conditions ahead, approaching emergency vehicles, and traffic delays. Vehicular ad-hoc networks combine the areas of sensor networks (data acquisition) with mobile ad-hoc networks (highly dynamic topology and lack of pre-existing infrastructure). One of the main challenges of vehicular ad-hoc networks is the data dissemination protocols capable of distributing road-state information among vehicles. This paper presents two candidates for dissemination protocols: a zone flooding protocol and a zone diffusion protocol. The two protocols combine ideas from sensor networks and geocasting to ensure that data is aggregated and distributed only in a bounded geographical area. We present a comparative simulation study of the two protocols evaluating their relative performance using conventional metrics (such as network load) as well as application-specific metrics (such as awareness). The simulation study has been conducted using the network simulator 2 (NS-2) and has highlighted key properties of the two protocols that can be used as a basis for selecting the most appropriate protocol. When we drive a car, we often want to know the situation of roads near our destination. Ishihara et. al. proposed a VANET based information sharing system named Real-Time Visual Car Navigation System, in which a driver can obtain Location-Dependent Information (LDI), such as pictures or videos of his her Point of Interest (POI) by telling the automotive equipment, e.g. car navigation device, the POI. The simplest way to provide LDI to vehicles is flooding the LDI to all vehicles in the VANET, but unneeded LDI may be disseminated, and network resources may be wasted. We have proposed a data dissemination scheme based on Demand map for effectively disseminating LDI to multiple vehicles that need it. In this scheme, each vehicle has Demand map (Dmap), a data set representing the geographical distribution of the strength of demands for LDI. Each vehicle exchanges a subset of data constituting a Dmap (Dmap Information: DMI) with other vehicles. According to the information in the Dmap, each vehicle preferentially sends new LDI or forwarded LDI strongly demanded to the area containing many vehicles that demand the LDI. In this paper, we propose strategies for controlling the frequency of sending DMI and strategies for selecting DMI to be sent for reducing the communication traffic without loss of the accuracy of information in Dmaps. Simulation results show that one of the proposed strategies, LTZ strategy, achieves high accuracy of Dmaps with a small amount of communication traffic. Intervehicle communication (IVC) is an emerging topic in research and application that is getting increasing attention from all major car manufacturers. In this paper, a novel method for scalable information dissemination in highly mobile ad hoc networks is proposed: segment-oriented data abstraction and dissemination (SODAD). With SODAD, information can be distributed in an information range multiple orders of magnitude larger than the transmission range of the air interface, even if only 1 -3 of all vehicles are equipped with an IVC system, e.g., during market introduction. By restricting the method to the dissemination of map position-based data, scalability is achieved. In the second half of this paper, an example application for the SODAD method is presented: a self-organizing traffic-information system (SOTIS). In SOTIS, a car is equipped with a satellite navigation receiver, an IVC system, and a digital map. Each individual vehicle collects traffic information for its local area. Using the digital map, the traffic information is analyzed based on road segments. By distributing the information in the ad hoc intervehicle network using the SODAD method, a decentralized traffic information system is created. The performance of the proposed methods is evaluated using network simulation with vehicular mobility models. Simulation results for typical scenarios are presented. Furthermore, a prototype implementation based on commercially available standard hardware demonstrates the feasibility of the proposed approach.