Takashi Ohyama

Message Dissemination in Inter-Vehicle CDMA Networks for Safety Driving Support

Although the near-far effect has been considered to be the major issue preventing CDMA from being used in ad-hoc networks, in this paper, we show that the near-far effect is not a severe issue in inter-vehicle networks for safety driving support, where packet transmissions are performed in the broadcast manner. Indeed, the near-far effect provides extremely reliable transmissions between near nodes, regardless of node density, which can not be achieved by CSMA/CA. However, CDMA can not be directly applied in realistic traffic accident scenarios, where highly reliable transmissions are required between far nodes as well. This paper proposes to apply packet forwarding and transmission scheduling methods that try to expand the area, where reliable transmissions are achievable. Simulation results show that the proposed scheme achieves approximately 100% of delivery ratio and 4 milliseconds of delay in a realistic traffic accident scenario, where CSMA/CA achieves approximately 60% of delivery ratio and 80 milliseconds of delay.

Safety Driving Support Using CDMA Inter-Vehicle Communications

Although the near-far effect has been considered to be the major issue preventing CDMA from being used in ad-hoc networks, in this paper, we show that the near-far effect is not a severe issue in inter-vehicle networks for safety driving support, where packet transmissions are generally performed in the broadcast manner. Indeed, the near-far effect provides extremely reliable transmissions between near nodes, regardless of node density, which cannot be achieved by CSMA/CA. However, CDMA cannot be directly applied in realistic traffic accident scenarios, where highly reliable transmissions are required between far nodes as well. This paper proposes to apply packet forwarding and transmission scheduling methods that try to expand the area, where reliable transmissions are achievable. Simulation results show that the proposed scheme significantly excels a CSMA/CA-based scheme in terms of delivery ratio and delay under realistic traffic accident scenarios. Specifically, the proposed scheme achieves approximately 90% of delivery ratio and 4 milliseconds of end-to-end delay in a scenario, where the CSMA/CA scheme achieves 60% of delivery ratio and 80 milliseconds of delay.

Development of a CDMA intervehicle communications system for driving safety support

Driving safety support is one of the most attractive applications of an intervehicle communications system. Real-time and reliable packet exchange among vehicles is key to offering timely warnings to drivers in order to avoid fatal accidents. In this article we introduce multicarrier multicode spread Aloha (MM-SA) system, an intervehicle communications system developed to satisfy challenging requirements for supporting driving safety. MM-SA is based on code-division multiple access technology, and has inherent robustness to the increase of node density as well as the hidden terminal problem. We present an overview of MM-SA system including protocol design and prototyping as well as the GUI tool, which are all developed for avoiding intersection collisions. We also present performance comparison between the MM-SA system and a CSMA-based system under a realistic accident scenario. Our evaluation results show that the MM-SA system has superior performance to the CSMA-based system, and achieves the communication performance required for driving safety support.

Supporting Safety Driving with Inter-Vehicle CDMA Networks Under Realistic Accident Scenarios

In this paper, we investigate inter-vehicle networks offering an application of safety driving support. For appropriately evaluating the efficiency of inter-vehicle communication systems to support such an application, it is of paramount importance to make extensive evaluations under realistic accident model. In this paper, assuming realistic intersection collisions scenarios, we provide simulation results of an inter-vehicle network based on an experimental guide-line defined for inter- vehicle communications system in Japan. Besides the guideline system, we also present our newly developed inter-vehicle communication system based on code division multiple access (CDMA) scheme. Our numerical results show that the proposed CDMA based system can effectively combat hidden-terminal problem as well as high level of congestion around an intersection, and is the only system to satisfy the requirements set by the application for safety driving support.

Transmission scheduling in multi-carrier multi-code spread aloha inter-vehicle communications system

Intelligent Transportation System (ITS) sets its target at a quite high level such as zero fatalities, to which safety driving support with inter-vehicle communications can largely contribute. Because code division multiple access (CDMA) technology provides delay-free channel access, we developed a CDMA-based inter-vehicle communications system, called a multi-carrier multi-code spread aloha (MM-SA) system, to meet challenging requirements on supporting safety driving. This paper introduces a transmission scheduling method that is a key function of MM-SA to provide highly reliable communications between vehicles. The performances of MM-SA are evaluated under realistic traffic accident scenarios. Our evaluation results show that MM-SA system is a promising solution to offering safety driving support.

MM-SA: Inter-vehicle communications system based on CDMA technology

Safety driving support is one of the most attractive applications of an inter-vehicle communications system. Real-time and reliable packet exchange among vehicles is a key to offering timely warnings to drivers in order to avoid fatal accidents. In this paper, we introduce the multi-carrier multi-code spread aloha (MM-SA) system, an inter-vehicle communications system developed for satisfying challenging requirements on supporting safety driving. MM-SA is based on code division multiple access (CDMA) technology, and has inherent robustness to the increase of node density as well as the hidden terminal problem. This paper presents an overview of MM-SA system including protocol design and prototyping as well as graphical user interface (GUI) tool, which are all developed for avoiding intersection collisions.