Construction of hierarchical optical broadcasting systems for intelligent transport system

The local broadcast systems, that transmit both the wide-area information and the local-area information, are proposed. A nearby user, which is near to the broadcasting station, demodulates together the wide-area information and local-area information. Even if a distant user, which is far to the station, does not receive the local-area information, it is expected that he receives wide-area information only. In the proposed systems, the broadcast information is hierarchized by combining the two modulation scheme. In particular, the two proposed systems are described; the ASK-CSK system which combines amplitude-shift-keying(ASK) with code-shift-keying(CSK) and the CNK-CSK system which combines code-number-keying(CNK) with CSK. The CNK-CSK system is superior to the ASK-CSK system.