1. Introduction More than 100 years have already passed since Carl Benz invented the gasoline automobiles. Automobiles have become an essential part of our dairy lives today. However, serious problems such as humans’ death due to traffic accidents, loss of time due to traffic con- gestion and environmental pollution due to CO 2 emis- sion, essentially remain unsolved. Inter-vehicle communications that promptly exchan- ges status information such as on the vehicle location, speed, sudden braking etc. are expected to reduce the traffic accidents such as collisions among vehicles, and to reduce humans’ death. For inter-vehicle communications, much research [1-8] has been carried out and standardizations are now in process. Especially, IEEE is now going to stan- dardize as 802.11p. Also in Japan, ITS Info-communi- cations Forum, under the Ministry of Internal Affair and Communications of Japan, is now in the process to standardize specifications of inter-vehicle communica- tion focusing on safe driving [9]. Communication schemes adopted in the most of the researches and the standardization on inter-vehicle com- munications, are based on the conventional media ac- cess control (MAC), i.e. carrier sense multiple access/ collision avoidance (CSMA/CA) [10], which is popular- ly used in wireless LANs. However, CSMA/CA has a limit in transmission de- lay and packet delivery ratio, due to its control scheme based on the carrier sensing. For satisfying challeng- ing requirements on supporting safe driving, we have proposed a new scheme called “Multi-carrier Multi- code Spread ALOHA (MM-SA)”, which is based on code division multiple access (CDMA) [11] technology. This scheme significantly reduces the transmission laten- cy to millisecond order and improves the packet deliv- ery ratio among vehicles [12-17]. It also has inherent robustness to the increase of vehicle density as well as to the hidden terminal problem [18]. This paper introduces our research on novel com- munication technologies for safe driving, using wire- less ad hoc network, that promptly exchanges the sta- tus information on the vehicles such as on the vehicle location, speed, sudden braking etc. The later parts of this paper consist of the following sections: Section 2 introduces the communication scheme of MM-SA; Sec- tion 3 shows the performance evaluation by computer simulation; Section 4 refers to the prototyping to eval- uate the performance in actual environment. Finally, we summarize future studies. Figure 1. Example of Communication Channel Structure in MM-SA VOLUME LXV. • 2010/I 3 Keywords: ITS, Inter-vehicle Communications, Safe Driving, Media Access Control (MAC), CSMA, CDMA Safe driving support is one of the most attractive and important applications of an inter-vehicle communication systems. Real-time and reliable exchange of status information on such as vehicle location, speed, sudden braking etc., among vehicles, is a key to offering prompt warnings to drivers in order to avoid fatal traffic accidents. We have proposed a novel media access control (MAC) scheme based on code division multiple access (CDMA) technology, which offers fast response and high packet delivery ratio to meet the above requirements. This scheme is inherently robust to the hidden terminal problem and significantly outperforms the conventional MAC scheme, CSMA/CA, in the environment with high vehicle density. This paper introduces the proposed scheme, performance evaluation by simulation, and prototyping for field experiment. It also mentions future studies.  INVITED PAPER Fast-response inter-vehicle communications SADAO OBANA, RYU MIURA, HIROYUKI YOMO, OYUNCHIMEG SHAGDAR, T AKASHI OHYAMA, HIDEO TSUTSUI, MICHIO MIYAMOTO, EIJI T AKIMOTO, YOSHIHISA KONDO, JUN HASEGAWA, SUHUA T ANG Adaptive Communications Research Laboratories, Advanced Telecommunications Research Institute International (ATR), Kyoto, Japan obana@atr.jp