Nobutsugu Fujino

Quality analysis of CSMA/CA communications in inter-vehicle communication services

Recently, inter-vehicle communication services which support safe driving have been attracting significant. CSMA/CA is a representative communication method in inter-vehicle communications. It is necessary to clarify the quality characteristics of inter-vehicle communication in order to achieve driving support. Although there are conventional models for CSMA/CA which are derived using an ideal environment, they are not consistent with behavior in actual inter-vehicle communication. This paper proposes a mathematical model that can analyze communication quality between the specific vehicles by dealing with the discrepancies between conventional theory and practice. Furthermore, we analyze communication performance between vehicles in specific accidents using the proposed model.

An indoor bidirectional message paging system with a pocket-size terminal using a direct-conversion FSK modem

The authors describe an indoor bidirectional message paging system which has good frequency utilization and serviceability. The trial system adopts microcells (with a zone radius of 50 to 100 m) and half-duplex communication using the carrier-sense multiple-access with collision detection access method in the 420 MHz band with an occupied bandwidth of 12.5 kHz and a transmission power of 10 mW, according to the Japanese RCR STD-3 standard. Messages of up to 64 alphanumeric or 32 Japanese (Kanji) characters can be transmitted from a pocket-sized mobile terminal using a direct-conversion FSK (frequency-shift keying) modem. The modem enables the size of the mobile terminal to be the same as that of the conventional message pager. The basic concept of this system can also be applied to future microcell public message communication systems.<<ETX>>