Safety-Message Broadcast in Vehicular Ad Hoc Networks Based on Protocol Sequences

In vehicular collision avoidance systems, safety messages are broadcast by mobile users periodically on the highway to all of their neighbors within hearing range. These safety messages are time sensitive and have stringent delay requirements. Conventional carrier-sense multiple access, where users must content with channel access, is not suitable for this kind of application. In this paper, we propose using protocol sequences to broadcast safety messages. Protocol sequences are deterministic 0-1 sequences. Each user reads out the 0's and 1's of the assigned protocol sequence periodically and transmits a packet in a time slot if and only if the sequence value is equal to 1. It requires no time synchronization among the users. We compare the delay performance with an ALOHA-type random access scheme and show that the delay can, in fact, be reduced by employing protocol sequences instead.