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abling collection of bus location data sent from the com-munication devices installed in Seika Kururin buses when the buses are traveling along their service routes. is in-formation was used to make bus location notication service available to the public.We describe below the characteristics of the D2D com-munication system we developed, the structure of test terminals installed in the testbeds, testbed operations and the demonstration experiments we conducted. We explain these mainly using the D2D communication testbeds in their forms as of July 2017.2Concept and characteristics of D2D communicatione concept of the D2D communication system we developed is illustrated in Fig. 1. We developed various types of test terminals, including signage terminals, rooop terminals and sensor terminals. ey are composed of communication devices for data transmission and recep-tion, peripheral devices and interfaces such as displays that meet the purposes of each test terminal. From a network conguration standpoint, we developed systems that are not centrally controlled by any terminal or device, and in which all communication devices perform the same func-tions. When a communication device transmits informa-tion, it does so using a predetermined time slot and a broadcasting mode specied in the communication proto-col mentioned below. Other communication devices within range receive the broadcasted information.A communication device set in a signage terminal in-stalled in a bus repeatedly transmits and receives data while it is travelling to/from other test terminals installed along the bus routes. is communication method enables travel-ling buses to repeatedly update and provide various types of community-related information such as local govern-ment information, event information and advertisements, within the local community. e eectiveness of the method depends on the bus service area size and bus service frequency.e D2D communication system is not centrally con-trolled and autonomously establishes a network between communication devices existing within communication range. erefore, additional communication facilities, such as base stations, are unnecessary. In addition, the system is resistant to natural disasters because failure of some com-munication devices in the network only slightly aects the entire network. Moreover, the D2D communication system has the following additional characteristics.(1) Autonomous communication protocol and GPS-based synchronizationCommunication protocols must be determined in ad-vance so that the devices within communication range can autonomously communicate with each other. We rst de-cided that all devices would use the same frequency chan-nel so they can quickly detect signals transmitted from each other. When the number of communication devices exceeds FiF1　Conceptual illustration of the D2D communication networkInformation collected from sensor terminalsServerBus routeDisplaying government and event informationInformation sharing among different groupsLocal government, etc.Portable terminalRooftop terminalSensor terminalSignage terminal (in a facility)Bus location notificationBus in operation collects, carries and distributes informationSignage terminal (in a bus)Expansion of the communication areaDistributing government information and advertisements2 Terrestrial Communication Technology Research and Development44　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)